After Lasik surgery, a common complication is dry eyes, and a common cure is for an optometrist to put tiny plugs into the channel openings to prevent the tears from draining and keep the eye moist. What are these plugs made off and how do they stay in there so well? Thanks. [[User:Mac Davis|Mac Davis]] ([[User talk:Mac Davis|talk]]) 09:03, 2 May 2009 (UTC)
After Lasik surgery, a common complication is dry eyes, and a common cure is for an optometrist to put tiny plugs into the channel openings to prevent the tears from draining and keep the eye moist. What are these plugs made off and how do they stay in there so well? Thanks. [[User:Mac Davis|Mac Davis]] ([[User talk:Mac Davis|talk]]) 09:03, 2 May 2009 (UTC)
:Punctum or punctal plugs are made from a variety of materials, some temporary and others permanent[http://www.eyecaretrust.org.uk/view.php?item_id=274]. Temporary materials include animal [[collagen]], [[polygloconate]] (a fibre also used in sutures), gelling [[polysaccharide]], [[polycaprolactone]] (PCL, a degradable [[polyester]])[http://www.agingeye.net/dryeyes/plugsetc.php], while [[silicone]] is usual for permanent plugs[http://www.dryeyepain.com/StandardTreatments.htm#punctal-occlusion][http://www.dailymail.co.uk/health/article-81455/A-cure-dry-eye-misery.html].
== Speakers ==
== Speakers ==
Revision as of 17:19, 2 May 2009
Welcome to the science section of the Wikipedia reference desk.
The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.
Why do the children's toys that you dip into soapy water to blow bubbles with have all those vanes on them? How is this design better than just a plain plastic loop? Dismas|(talk)00:04, 24 April 2009 (UTC)[reply]
The vanes (those grooves along the edge is what I assume you are refering to) hold extra soap, which is fed into the bubble blowing area after you blow a bubble. With a plain plastic hoop, you'd only get one or two bubbles before having to reload; the vanes allow for more bubbles to be blown on a single dip. As a father of a three-year old, I have must first-hand knowledge in this field of study... --Jayron32.talk.contribs00:39, 24 April 2009 (UTC)[reply]
I couldn't find any information specifically about the function of the globose nucleus. From "Color Atlas of Neuroscience", Greenstein, p. 202: "The spinocerebellum exerts control over axial musculature through the efferent outputs from the vermian cortex and the fastigial nucleus. It controls limb movements through outputs to the globose and emboliform nuclei." Other texts provide similar information. Axl¤[Talk]08:40, 25 April 2009 (UTC)[reply]
Water consumption while dehydrated
From the dehydration article: "It is wise to slowly drink liquids when dehydrated." I've heard that advice all my life but never really understood why. Also, how come most poisonous product labels advise: "if ingested, do not induce vomiting." I figure vomiting would be a good idea and all if you just swallowed something poisonous? TravisAF (talk) 02:41, 24 April 2009 (UTC)[reply]
Once someone starts re-hydrating, the risk is in rapid fluid shifts (since the dehydration won't get any worse). So there's generally no rush to the re-hydration, but overdoing it can cause electrolyte imbalances. Regarding your second question, it's a bad idea to induce vomiting for caustic substances like drain cleaners, because they can cause significant damage on the way up - better to let a poison control center advise on how to treat. --Scray (talk) 03:05, 24 April 2009 (UTC)[reply]
Another concern about induced vomiting is the risk of aspiration of vomitus into the lungs. Some toxins will be absorbed much more rapidly from the lungs than they would from the stomach, other nasties – like the caustics Scray mentions – are apt to do much more severe damage to the delicate tissues of the lung (compared to the relatively tough lining of the stomach). Inflammation of the lungs or trachea (caused by even small amounts of aspirated vomitus) may close airways and make a bad situation much worse. TenOfAllTrades(talk) 03:30, 24 April 2009 (UTC)[reply]
For more on the electrolyte-imbalance thing, see water intoxication. It can kill. --Anonymous, 03:59 UTC, April 24, 2009.
Indeed, if you are drinking water, rather than specially designed re-hydration fluids, you could get into serious trouble. Anything more than very mild dehydration should be treated with proper salts, not plain water. (Rule of thumb: If you can drink the re-hydration stuff without it being so disgusting it makes you gag, then you need it.) --Tango (talk) 10:30, 24 April 2009 (UTC)[reply]
It might be worth pointing out that "dehydration" goes way beyond just being thirsty. I've frequently come back from a desert hike or bike ride and slugged down a half gallon of water or Gatorade without ill effect. You have to be gallons down before you get into really serious concerns about rehydrating in the right way. Looie496 (talk) 19:00, 24 April 2009 (UTC)[reply]
Indeed, half a gallon wouldn't generally be enough to cause a problem. I think not eating properly can increase the risk - it's all about the balance between water and salt, if you aren't getting enough salt in your diet (NB: the required amount of salt is very low - this is not an excuse to put loads of salt on your chips!), even a small amount of water could be too much. When you've been on these hikes, etc., you have probably been eating high energy food like chocolate - the milk chocolate wrapper I've just looked at says it has 200mg of sodium per 100g, the RDA (according to Wikipedia) being about 1500mg, this is a good example of how much salt there is in many of the foods we eat. --Tango (talk) 19:56, 24 April 2009 (UTC)[reply]
Lost in the woods
If i became lost in the woods, why would i not just eat grass and leaves until i found my way? It seems obvious to me to eat them if i was starving. EVAUNIT-66603:38, 24 April 2009 (UTC)[reply]
The question is why you can't survive on grass and any old leaves: after all, some animals are happy with that sort of diet (and there are some leaves we do eat, such as lettuce). The main difference is that humans can't digest cellulose, which tends to be a large constituent of various kinds of plant material. Also, some leaves may be toxic, as Scray points out. However, we do have a long list of plants with edible leaves, with some cautions at the top. --Anonymous, 04:04 UTC, April 24, 2009.
You won't be able to get much nutrition from grass as was explained above. Dehydration should be bigger concern anyways. Dauto (talk) 04:29, 24 April 2009 (UTC)[reply]
If you get lost in the woods, you may want to remember that an average adult should survive some hours without shelter, some days without water, and some weeks without food. (YMMV: weather and your starting physical condition will greatly affect these estimates. If you are in the snow or in the desert, adjust accordingly.) "OMG! I NEED TO EAT RIGHT NOW!!!" should not be your first concern, even when you start to feel a bit peckish. First worry about sleeping out of rain, wind, hot sunlight, and night frost. Later think about clean water. 88.114.222.252 (talk) 12:44, 24 April 2009 (UTC)[reply]
There we go again. What's up with that? That's the second time I see someone on these pages talking about people not being able to survive more than a few hours without shelter. That's only true on the most extreme conditions. I would worry first about water if I got lost in a forest. Dauto (talk) 17:44, 24 April 2009 (UTC)[reply]
What woods, when and where? As noted above the human digestive system is ill adapted to gain much nutrition from grass. However, most forests will provide nuts and berries which you could very well live on for a while. You'd have to know what grows where and when locally. Many plant buds and some flowers are also edible and contain more energy than leaves. The problem would also be that gathering all those would be taking time you might spend better on finding the next road or river. (Most flowing water ends up at/near human habitation downstream sooner or later.) 76.97.245.5 (talk) 15:55, 24 April 2009 (UTC)[reply]
If not in an extreme case (rainforest or taiga) you should just go downhill until you eventually reach a creek. Following it will lead you to inhabited area long before hunger could become an issue. --131.188.3.21 (talk) 13:32, 26 April 2009 (UTC)[reply]
To clarify, most fish can only survive in one environment or the other, but there are some, such as salmon, which can handle either fresh- or salt-water. StuRat (talk) 07:38, 24 April 2009 (UTC)[reply]
"exact" is a tough thing here...the earth isn't a billiard ballapparently, it is...see below! But the numbers from the Earth article that TravisAF quotes above are pretty reasonable. The standard for the shape of the earth that is most commonly used in exacting applications is called 'WGS-84' or World Geodetic System from the World Geophysical Survey of 1984. The values it gives are the best "mean sea level" description of the shape available - and I presume that the numbers above are from that definition. However, if you stretched a piece of string around the circumpherence of the planet then measured it - the answer would not be exactly that given above - and the result would vary depending on where you measured it - and probably on where the sun and moon were at the time because shape of the earth is affected by tides. It's probably also worth mentioning that the surface of the earth is like a fractal - so a precise measurement even at a particular moment in time and a particular direction over the planet is going to suffer from the Coastline paradox (see also: How Long Is the Coast of Britain? Statistical Self-Similarity and Fractional Dimension).
"The earth isn't a billiard ball". From the above figures the earth's circumference varies by only a few parts in a thousand. Are billiard balls that accurately spherical? And the bumps in the earth are less than one part in a thousand. Are billiard balls smoother than that? DJ Clayworth (talk) 15:09, 24 April 2009 (UTC)[reply]
From Earth: "Local topography deviates from this idealized spheroid, though on a global scale, these deviations are very small: Earth has a tolerance of about one part in about 584, or 0.17%, from the reference spheroid, which is less than the 0.22% tolerance allowed in billiard balls." Dragons flight (talk) 15:16, 24 April 2009 (UTC)[reply]
Wow! That's a cool observation. But - an 0.17% tolerance means that when we say the circumpherence is 40,041.47 km - we're overstating the precision by a couple of orders of magnitude! SteveBaker (talk) 19:39, 24 April 2009 (UTC)[reply]
Of course, the number is almost exactly 40,000 kilometers because that was the original definition of the kilometer; it was defined as 1/10000 the distance between the north pole and the equator along a meridian of longitude; which would be 1/4th of a circumference. But you all knew that... --Jayron32.talk.contribs21:27, 24 April 2009 (UTC)[reply]
This reminds me of a study that I think appeared in the Journal of Irreproducible Results, where the authors tried to determine whether Nebraska (or maybe it was Kansas?) was indeed "as flat as a pancake". The conclusion was that it was very much flatter than a pancake. If it were only as flat as a pancake, there would be miles-deep canyons all over the place. Or something like that. --Trovatore (talk) 21:32, 24 April 2009 (UTC)[reply]
The above discussion correctly notes that the Earth is smoother than a billiard ball, but it's not quite round enough. Discussion here. --Sean22:46, 24 April 2009 (UTC)[reply]
Yes - the poles are considerably squashed compared to the equator. The problem here is that we're presented with numbers that are accurate to 10 meters! Even with (proportionately) billiard-ball smoothness - that's way too much precision. Having just one mountain or valley along your chosen "circle" will throw off your measurement of the circumpherence by vastly more than 10 meters! That number can only be the result of a specification for the idealised shape of the earth - per WGS-84's ruling on the matter. SteveBaker (talk) 00:06, 25 April 2009 (UTC)[reply]
Smoothness and roundness are similar. The way I think about it is as a "power spectrum". Using a spherical harmonic breakdown (such as the set of WGS-84 coefficients), you can actually see how much "energy" is contained at each "frequency" (really, it's not energy, because it's a geometric description, but "frequency" is a moderately reasonable word - the spherical harmonics functions map well as spatial frequencies, albeit not sinusoidal frequency). And I'm sure you could find some way to represent mass-distribution as gravitational potential energy too, so "energy spectrum" is not really such a bad terminology after all). Anyway, the point is, Earth's deviation from perfect sphere is evident at the lower-order terms of the spherical harmonic decomposition, and its roughness is evident from the magnitudes of the higher-order terms. With sufficient number of terms, (impractical and unwieldy, but definitely possible), every topographic feature could also be described. The magnitudes of those coefficients would be REALLY small (in the same way that a band-limited radio-signal has zero spectral power at "infinitely high" frequencies). Nimur (talk) 14:47, 27 April 2009 (UTC)[reply]
Name
What's the name given to a situation when you hear something going on in a dream, then you wake up to hear it going on in the real world? 58.165.23.195 (talk) 07:14, 24 April 2009 (UTC)[reply]
You might be thinking of something paranormal, such as precognition or premonition. Or you might have fallen asleep with the television on.
Sounds more like he's asking about a real-world sound making it into a dream (very possible) and then waking up with the sound still there. Nothing paranormal about it. :) -- Aeluwas (talk) 08:49, 24 April 2009 (UTC)[reply]
Forgive me if I missed it, but I think I skimmed all the relevant pages on Wikipedia and didn't see anything. I've been wondering lately how the earliest links were drawn between proteins and genes. Many genetic mutations were connected to visible phenotypes long before the central dogma was developed. Was the connection with a particular protein made for any of these mutations? How were the chemical functions of the earliest studied proteins identified? Thank you. Someguy1221 (talk) 07:44, 24 April 2009 (UTC)[reply]
The current theory from my biology book is that RNA was a molecule which dabbled in several roles of the cell. It did things which we think of proteins doing--regulating the rates of reactions, and they were involved in metabolic pathways and they even stored "blueprints" for other RNA molecules (because remember, RNA can be transcribed off of another RNA strand--that is how RNA viruses do their thing, theey call it "the RNA directed synthesis of new RNA".
Also don't over hype the difference between RNA and DNA. The difference is only an oxygen on the sugar backbone. All that "difference" does is help the molecule be more stable. DNA can last several years, RNA can last only about 45 minutes on its own, without being sequestered from common reagent molecules.
The difference between RNA and protein, is well, that RNA is an acid. Both molecules owe their properties to organic chemistry. Both RNA (in the rna world) and current proteins had the same exact functional groups. However, proteins generally were more effecient, could fold better, and were recycleable.
In a way, your question could be answered that evolution took place and RNA simply became excinct because it is a fierce job market inside the cell, and well, RNA's job got sent overseas and only a few vestigial pathways still utilize RNA as a reactant in reactions today. Some even in your own cells!JameKelly (talk) 08:49, 24 April 2009 (UTC)[reply]
That answer seems a bit off topic to me... I certainly could be wrong, but the way I read the question, the OP is interested in the first example of a gene (i.e. the DNA sequence) being causally related to the protein it codes for. I think the answer you are looking for is found in the biochemistry article, which discusses the discovery and characterization of proteins. The first instance of a gene being linked to the enzyme it produces (from Biochemistry): "In 1958, George Beadle and Edward Tatum received the Nobel Prize for work in fungi showing that one gene produces one enzyme" (for research performed in the 1940's). The History of biochemistry article, which should be a good resource, is focused more on the 1800's and is surprisingly sparse on the advances of the 20th century. --- Medical geneticist (talk) 11:11, 24 April 2009 (UTC)[reply]
In addition (since the OP is interested in mutations & phenotypes) -- Archibald Garrod is widely acclaimed as the first to postulate that an inherited disorder could be due to deficiency of a particular enzyme, as in the case of alkaptonuria. However, although he made the connection in the early 1900's, the actual enzymatic deficiency was first demonstrated in 1958 and the gene mutations weren't described until 1996! In terms of the discovery of genetic mutations that cause disease, it's hard to ascribe a "first" for many things since many discoveries are made in parallel. There is a nice timeline at the National Human Genome Research Institute (http://www.genome.gov/25019887) that shows the progress from Beadle & Tatum's "one gene one enzyme" theory in 1941, the discovery of the double helix structure in 1953, discovery of the genetic code in the 1960's, development of DNA sequencing in the 1970's, to the first human disease gene Huntingtin being mapped in 1983 and cloned in 1993. Genes that are defective in chronic granulomatous disease, Duchenne muscular dystrophy, and retinoblastoma were all mapped and characterized in the 1980s-1990's, with many more following after that and still continuing today. --- Medical geneticist (talk) 13:12, 24 April 2009 (UTC)[reply]
Differential Capacitive sensors
Well i want to be very frank. I am a first year undergraduate Electrical Engg student. For joining one of my professors for a summer time project, he gave me a paper something to do with "Switched Capacitor Dual Slope Capacitance to Digital Converter For Differential Capacitive sensors". Unfortunately, being just a first year, i haven't the faintest inkling what these terms mean, except the term capacitor! I have tried searching on Google and wiki, but the sites only give highly technical information way above my head. However, i am determined to understand this topic. So can someone please explain me what the above mentioned terms are, in a down to earth, layman manner, so that a person with just basic electrical knowledge would catch the point ? Or perhaps suggest a link which does so? I am dearly in need of help !!Rkr1991 (talk) 10:13, 24 April 2009 (UTC)[reply]
Well, I'm no expert - but we can try to break up that turgid title into manageable bites:
Switched capacitor -- OK so we're going to use a switch to choose one of two or more capacitors.
Dual slope -- So the graph of some function is going to have two straight-line slopes. Probably because the slope changes when you switch from one capacitor to the other.
Capacitance to Digital convertor -- sounds like an analog to digital convertor that measures capacitance instead of voltage.
Differential Capacitive sensor -- well, whenever something is 'differential' you're either measuring the rate at which something changes or the difference between two things - this 'convertor' is clearly a 'sensor'.
So I guess (and I'm no expert either!) that this is a project to build a gizmo that measures some aspect of the capacitance of something using a computer. How it's gonna work is by somehow switching capacitors on and off. I think I'd start by searching on "Capacitance to Digital convertor" to understand how capacitance is measured digitally.
I agree that this does sound a little tough for a first year project - but that's the point of doing things like this with experts in the field. So talk to your professor. He's there to teach you - and if you don't understand what the heck this thing is - it's because (I presume) he has not yet taught you about it. That's his fault, not yours. So make every effort to read as much as you can - then go to him and ask for an explanation and a break-down of the project into bite-sized pieces.
Hopefully others here will be able to explain this in more detail.
(ec) A dual-slope analog to digital converter (ADC) is a specific type of ADC commonly used in digital multimeters. It is described in our article integrating ADC which is an alternative name for it. It is more accurate than a single-slope ADC because it lets through a greater number of clock pulses but is slower to update as a result. The "switched capacitor" bit of the title is probably referring to changes of range, which are achieved sometimes by switching the value of the integrating capacitor and sometimes by switching the value of an offset voltage or current. The "for differential capacitive sensors" is probably referring to the type of input that is being measured. Many transducers (eg displacement detector) are essentially capacitors and the quantity being measured physically moves one of the plates causing the capacitance to change. The requirement of the measuring system is thus to measure the capacitance, either absolute, or the difference between the transducer and a reference capacitor (hence differential). Of course, some of that is guesswork; for a more specific answer you will need to provide a link to the paper you are reading, or at least some of the details (author, exact title, journal, date etc) and hope someone here has access to it. SpinningSpark13:17, 24 April 2009 (UTC)[reply]
Learning something new requires juggling some number of unfamiliar concepts in short term memory. With time and effort, you can push concepts into your long term memory - once you have done that, you have "learned." When learning is difficult, that means you are encountering too many unfamiliar concepts at once to fit into your short term memory. This happens readily because short term memory is very limited - most people can only manipulate between four and seven "chunks" of information that way. Short term memory seems to work like a FIFO queue - if the unfamiliar chunks keep coming, they push earlier chunks out, and you lose them. Your emotional brain responds by generating emotions of anxiety and frustration. Long term memory, in contrast, is seemingly unlimited. As long as your brain continues to work, you can apparently just keep pushing more knowledge into your long term memory. The problem is that chunks can only move from short term memory into long term memory at a slow rate. Because short term memory is very limited, and long term memories can be slow to form, humans hit on a trick, thousands of years ago, to augment memory: writing. When you are trying to learn something that overwhelms your short term memory, you should immediately start writing. For example, read the paper you are trying to understand, but don't worry about understanding it right away. Instead, do this:
Make a list of all the terms in the paper you don't understand yet.
For each term, try searching the Web and so on, and write whatever you find that might relate to it.
Keep coming back each day, re-read the paper, review your list of terms, and see if you notice anything you missed before.
Look up all the references that the paper cites, read them, and see if any of them shed further light on your list of terms.
Identify your conceptual sticking points. You will figure out some terms sooner than others. When you figure something out, move it to the bottom of your notes. Keep the unknown items at the top.
Look for clues about the interrelatedness of terms. Probably every jargon term in the paper relates to the other jargon terms in various ways. The paper is not just a stream of consciousness list of random terms. You want to understand not only what each term means in isolation, but why the author used them all together. Sometimes you can understand the relationship between two items before you fully understand the items. See: ontology.
Show your notes to some experts, and ask them to comment. They may suggest introductory references you can read, or they may point out errors in your thinking. For example, you might have listed a particular concept more than once, because maybe the paper refers to it by synonyms. In that case, your problem got simpler, because instead of two concepts to learn, you find you only have to learn one.
I couldn't find the exact link on the net, but here are its details : Novel Switched-Capacitor Dual Slope Capacitance to Digital Converter for Differential Capacitive Sensors by, Boby George, Member, IEEE and V Jagadeesh Kumar, member, IEEE. I hope someone would be able to find the exact paper, and then explain what exactly is the problem being approached, and the principle used in this case. I would like to add that it is not my professor's fault for not teaching this. I, being free in the coming summer, approached him for doing some extra work, and he has offered to take me in his research team as an assistant, if i can tell him what i understood from this.(He is one of the authors of this paper.) Thanks in advance for all the help.Rkr1991 (talk) 06:33, 25 April 2009 (UTC)[reply]
I would also like to thank 2 particular users - SpinningSpark and SteveBaker, who have both helped me out on numerous questions. Thanks for your time guys ! And thanks to Teratornis too...Rkr1991 (talk) 07:13, 25 April 2009 (UTC)[reply]
No, I can't find it either, but I did find this and wonder if the paper you have is a pre-print of the published paper with a different title. Sorry, I don't have a current subscription to IEEE Explore so cannot read it, and it doesn't have an abstract. You might want to take a look at this book though, which you can preview in google books. SpinningSpark12:38, 25 April 2009 (UTC)[reply]
Eggplant is in the nightshade family which contains toxic substances. Hair loss may be an effect of poisoning from ingesting unripe/inedible parts of the plant or an allergic reaction. As our article notes aubergines are high in nicotine, which can cause hair loss through constriction of blood flow to the follicles and accelerated cell aging. That is for prolonged exposure and high quantities, though. I doubt the average person would regularly eat 9 kgs of eggplants. That would signify a highly deficient diet that would cause many other health effects. High doses of caffeine can also cause hair loss, while low doses actually stimulate hair growth. This page [[1]] recommends eggplant leaves as a remedy for hair loss, but I'd rate that one under "people will try anything". 76.97.245.5 (talk) 15:14, 24 April 2009 (UTC)[reply]
"Female" DNA
Google doesn't lie ... so there is "male DNA" and "female DNA" (the question for "male Cellulose" and "female proteins" (the shapely ones) comes later...). Question: When "female DNA" is found at a crime scene, does that mean that no Y-chromosome genes were found in this sample or was there another test done ? (because X-Chromosomes are found in males and females). Does "The blood in the car showed female DNA" actually mean "in the blood we found no Y-chromosome genes but lots of other genes and human markers, so it must be the blood of a woman/female" ? Thanks --83.141.221.231 (talk) 14:38, 24 April 2009 (UTC)[reply]
I don't know the answer but most likely the absence of Y specific markers would indicate "female". Of course if the woman had AIS then the test would be misleading. And any test that relies on the absence of a marker is prone to contamination from other sources. David D.(Talk)14:42, 24 April 2009 (UTC)[reply]
Another possible way to confirm a "female" sample would to look at a lot of polymorphic markers on the X chromosome. A male would have only one in every case (hemizygous for X) but a female would be heterozygous for many of the markers. David D.(Talk)14:48, 24 April 2009 (UTC)[reply]
What would you see in the latter case? Female: More bands than usual (male)? Could you conclude from the complexity of the pattern whether the blood was from 1, 2, more women? In the meantime, I found the (a) (SRY-F + SRY-R) and (b) (PABX-F + PABX-R) Primer-pair approach. A male should give 2 bands, a female one band, a mix (of blood) of 2 females should give 2 diff. (PABX-F + PABX-R) results. --83.141.221.231 (talk) 15:06, 24 April 2009 (UTC)[reply]
You could not detect such a difference with PCR. It could be done using antibody pulldown, probably directed at lysine methylation on histones. In males the X sequences would far less represented than in females. But to be pedantic, what if a male had Kleinfelter's Syndrome (XXY)? Such a male would have half his X sequences silenced. And besides, the sensitivity would be problematic at a forensic level. David D.(Talk)00:58, 26 April 2009 (UTC)[reply]
You're all overthinking this. "We found female DNA" = "We did a karyotype and the sex chromosomes were 'XX"". "We found male DNA" = "We did a karyotype and the sex chromosomes were "XY". Depending on the circumstances, it may not even be as complicated as that....e.g. we found male DNA in the sperm specimen. - Nunh-huh01:12, 26 April 2009 (UTC)[reply]
Looks like you can differentially label the X and Y, so don't need a full karyotype.[2] That would also solve rare genetic combinations and multiple contributors, since it seems to allow counting of the chromosomes in whole cells. In other ideas, there are non-genetic ways to identify the sex of a biological sample, so "high levels of PSA" would mean the sample's DNA is probably male (though surprising-to-me high rate of false-positive), whereas DNA from a sample that also has high levels of various pregnancy horomones is from a female. Going the other way, if the biological sample is sperm, I can guarantee it contains DNA from a male. DMacks (talk) 07:24, 26 April 2009 (UTC)[reply]
Canis lilliputia and canis brobdingnag
What happens when a female St. Bernard/Wolfhound/Great Dane is impregnated by a male Chihuahua/Yorkshire Terrier/Toy Poodle? And what happens in the reverse situation? I assume this never happens naturally but would have to be by insemination (please correct me if I'm wrong). I imagine a very smalle female dog would have more trouble than the reverse situation, but is such a pregnancy viable? Are there any examples of such dogs carrying to term? And for the reverse, I imagine this might either kill the tiny female or, as the pup grows too big, her body will reject through a miscarriage? Or does it work that a female can carry and the combination of genes still results in a very small dog despite the large male breed? I've always wondered about this.--70.19.69.27 (talk) 21:42, 24 April 2009 (UTC)[reply]
Thank you for that link Deor. Extremely unsatisfying answers based on sheer speculation but that may be because the answers are simply unknown.--70.19.69.27 (talk) 03:37, 25 April 2009 (UTC)[reply]
I'm gonna take a stab in the dark and guess that this has to do with sorbitol, a sweetener that's often used in chewing gum and the excessive consumption of which can cause extreme weight loss due to its laxative effect. How much counts as excessive is probably going to vary from person to person, but frankly, it's not that hard to tell when you've eaten too much of it, what with the diarrhea and all. -- Captain Disdain (talk) 01:51, 25 April 2009 (UTC)[reply]
With another stab in the dark, chewing gum provides pretty much no nutrients; therefore it isn't 'necessary'; therefore it is "excessive consumption". That's taking a very extreme view that "excessive" means anything more than is necessary for life. DJ Clayworth (talk) 14:16, 27 April 2009 (UTC)[reply]
In the true spirit of modern "psychobabble", it's only too much if it is negatively interfering with other areas of your lifestyle. This tautological statement doesn't convey a lot of information, but it's used to describe a lot of addiction-spectrum conditions without making normative claims, moral pronouncements, or legal advice. Nimur (talk) 14:52, 27 April 2009 (UTC)[reply]
Line spectrum question
Doubly ionized lithium Li2+ (Z = 3) and triply ionized beryllium Be3+ (Z = 4) each emit a line spectrum. For a certain series of lines in the lithium spectrum, the shortest wavelength is 365.1 nm. For the same series of lines in the beryllium spectrum, what is the shortest wavelength?
I'm not entirely sure, but since 365.1nm is in the visible light spectrum that means it's in the Balmer series? Therefore you have to use the equation, 1/wavelength=R(1/2^2-1/n^2), and then solve for n. But when I solve for n I get 55.79 which doesn't make sense since it should be an integer. Also when I solve for n, I'm not sure where to plug that in. I'm thinking I need the equation, 1/wavelength=1.097x10^7(Z^2)(1/nf^2-1/ni^2), but I'm not entirely sure. Also I don't know which n I solved for in the original equation. 69.69.75.22 (talk) 00:08, 25 April 2009 (UTC)[reply]
You used the equation for Hydrogen. The correct equation is 1/wavelength=R(Z^2/2^2-Z^2/n^2) for a balmer series line. See Rydberg formula. The Z=1 for hydrogen, which is where you went wrong. The more general equation is needed for all other elements. --Jayron32.talk.contribs00:38, 25 April 2009 (UTC)[reply]
Forget about ni and nf. get the Rydelberg equation for the Lithium and devide by the Rydelberg equation for the beryllium. The mistery factor cancels out. Dauto (talk) 03:21, 25 April 2009 (UTC)[reply]
I need clarification on this issue. I know for endothermic solution reactions, solubility increases with temperature. Conceptually this makes sense dH is positive therefore Energy in the form of higher temperature must be invested to make this reaction happen. Secondly, Le Chatelier's principle also supports this.
Now, for exothermic reactions, Le Chatelier's principle suggests that solubility decreases with temperature since "heat" is a product here so the system will shift to reduce heat/temperature. However from a thermodynamics standpoint (dG=dH - TdS) such a reaction will be very spontaneous since dH is negative and T increases therefore the "-TdS" term becomes more negative and the overall dG is negative. Intuitively, I am slightly leaning more towards the Thermodynamics implication thinking that this scenario might be a limitation in the scope of Le Chatelier's principle.
Please explain the apparent paradox assuming there's one. I understand physics without nearly as much effort as I have to spend on rectifying chemistry!
P.S. I will try to incorporate whatever feedback this question generates into the paragraph here since I imagine that is where the information is best suited, correct?
Le Chatelier's principle is correct. To use Gibbs free energy as you've done you must assume an isobaric and isothermic process. Since the reaction is exothermic, the only way the process can also be isothermic is if the excess heat is being absorbed by the surroundings. As heat leaves the system, the change in its entropy must be negative (dS<0) throughing a wrench in your reasoning. Dauto (talk) 04:08, 25 April 2009 (UTC)[reply]
Indeed, to explain a little more; the Gibbs equation is a state function; so all values are as measured at any instant in time. It's not dTdS, its TdS, which means that the entropy value is not dependent on changes of temperature; it is dependent on absolute temperature at any point. It has nothing to do with whether the solution is heating up or cooling down, only with what the temperature is at the point where you are measuring the values. --Jayron32.talk.contribs04:30, 25 April 2009 (UTC)[reply]
Thanks for the answers. I realized I was trying to derive one from the other, but I didn't realize what I was asking. I was so stuck thinking that I just didn't see something, but the straightforward answers I have received today were very helpful and rock solid; this enabled me to reevaluate what I was seeking to find, and in hindsight I was trying to derive one from the other, which I can't so I can rest easy now and move on to the next subject. Thank you again, JameKelly (talk) 12:11, 25 April 2009 (UTC)[reply]
will 1,3,5-trimethoxybenzene react with hydrochloric acid? (Or even base?!)
I suspect it reacts with sulfuric acid, if I have my unknown correct. I didn't manage to complete an HCl or NaHCO3 reactivity test in lab however ... would the H+ attach to the ether oxygens, whereupon there is some weird nucleophilic substitution and the alkyl groups fall off (probably with some nucleophile at the end to stabilise the leaving group) and resonance stabilisation stabilises the former ether oxygen...? Or what? Why else would sulfuric acid attack 1,3,5-trimethoxybenzene? Surely it's not a strong enough electrophile (well, perhaps without the presence of SO3) to attack benzene bonds? John Riemann Soong (talk) 05:57, 25 April 2009 (UTC)[reply]
You may get some chlorine-for-methoxy substitution, but probably not in high yields, and you may also get a mixture of mono-, di-, and tri- chloro products. A low enough pH will protonate the oxygen, which will make methanol as a decent leaving group. The chlorine is likely just a good enough nucleophile to substitute here. --Jayron32.talk.contribs17:19, 25 April 2009 (UTC)[reply]
Yup, protonation of an ether oxygen is pretty good bet. But then I'd think more ikely to hydrolyze (I assume your "sulfuric acid" is a few-molar aqueous solution?). the Me-O side of this ether than the O-Ar side. Once you're at an oxonium, SN2 nucleophilic attack on the methyl seems easier than first going to an even less stable structure like aryl carbocation (SN1...can't do SN2 on an sp2 center). DMacks (talk) 07:01, 26 April 2009 (UTC)[reply]
I'm trying to find out why it would react with sulfuric acid (the bottle / lab manual said "concentrated"), but not 5% HCl ... I guess it was just the acidity of the solution? John Riemann Soong (talk) 08:00, 26 April 2009 (UTC)[reply]
Doesn't your textbook/lab-manual tell you what sorts of functional groups give a positive test for each of your qualitative analysis methods? Is conc. sulfuric a test for ethers or for aromatics? Your text (if it's any good) or other class materials would explain why/how each one behaves under the various test conditions. What exactly makes this test "positive" (something dissolves, precipitates, changes color, releases a gas, catches fire, ...)? DMacks (talk) 06:31, 27 April 2009 (UTC)[reply]
My lab manual only explains how to do the test. We're supposed to test for "solubility", but a reaction or color change counts as a positive for solubility. I thought ethers were fairly inert actually, and so were aromatic compounds, in the absence of metal catalysts. John Riemann Soong (talk) 18:12, 27 April 2009 (UTC)[reply]
If the remainder of the solution isn't very volatile, and you aren't concerned with keeping it sterile, you can just leave the solution exposed to the air until the water evaporates. This could be done, for example, to create sea salt from sea water. StuRat (talk) 20:43, 25 April 2009 (UTC)[reply]
The blast radius of a nuclear bomb is a few miles, so let's be generous and say that 100 square miles would be affected. The area of Antarctica is about 5,000,000 square miles. That's 50,000 bombs - more than the U.S. and Russia have combined. That's not taking into consideration the fact that the ice can be quite thick, so one bomb probably wouldn't melt all of it in its assigned sector. Clarityfiend (talk) 09:39, 25 April 2009 (UTC)[reply]
(After edit conflict; another big number) Well, a typical nuclear test can create a crater hundreds of metres across, but that is still very small compared to the size of a whole continent. So let's crunch some numbers. Antarctica article says area of Antartica is 14 million km2 and 98% of the continent is covered by ice with an average depth of 1.6 km. So that is about 22 million km3 of ice. That has a mass of about 22 x 1018 kg. For simplicity, let's assume this is all just on the point of melting (so we ignore the heat required to warn it up to 0oC). Water (data page) says latent heat of fusion of ice is about 6 kJ/mol. 1 mole of ice has a mass of about 18 grammes, so 22 x 1018 kg is about 1.2 x 1021 moles, which will require about 7.2 x 1024 J of heat to melt it. One megaton is 4.184 x 1015 J, so 7.2 x 1024 J is about 1.7 x 109 Mt. The most powerful hydrogen bomb ever tested had an energy yield of 50 Mt. So to melt all the ice covering Antarctica, you would need at least 35 million hydrogen bombs, even if all if the bombs' energy was released as heat energy and absorbed by the ice. Gandalf61 (talk) 09:47, 25 April 2009 (UTC)[reply]
Agreed. By an independent calculation based on very similar assumptions I got an estimate of 50 million bombs. You could probably achieve the same effect with much less energy by painting the ice black and letting the sun do the work. --Heron (talk) 11:44, 25 April 2009 (UTC)[reply]
The first few bombs might result in dark dust falling on the rest of the ice, so it might not be necessary to paint it all, just use a few nukes. --Tango (talk) 14:51, 25 April 2009 (UTC)[reply]
I don't see where the dark material would come from - you're mostly blowing up kilometers-thick ice - what's going to get chucked up into the air will be water-vapor. Even dark dust would get tossed into the upper atmosphere. That would tend to block the sun - making the continent colder - and reducing the amount of melting. That's been a notable effect of large volcanoes and such. It's hard to predict - so it's far from obvious which effect wins. SteveBaker (talk) 15:39, 25 April 2009 (UTC)[reply]
Drop the bomb on a bit with thinner ice so you expose the ground underneath. I seem to recall using bombs to spread dark dust over ice to make it melt being proposed in the context of terraforming Mars - perhaps it wouldn't work so well on Earth, with a thicker atmosphere to hold onto the dust. --Tango (talk) 16:22, 25 April 2009 (UTC)[reply]
Nuclear weapons are very powerful against human-sized targets. But not geographical-sized targets. You could easily make a large area uninhabitable for humans with exceptionally "dirty" hydrogen bombs. But melting, totally destroying it, no. No more than you could crack the planet in half with nukes. --98.217.14.211 (talk) 17:31, 25 April 2009 (UTC)[reply]
Nukes alone would not do it, but there might be another way. If we were to find a large asteroid (or more), we could use nuclear pulse propulsion on it, and direct it towards Antarctica. It wouldn't be very easy with our current technological level, but I think it can be done. 69.69.75.22 (talk) 17:50, 25 April 2009 (UTC)[reply]
Yes, that might work. Antarctica wouldn't be an easy target, though. Most asteroids are in the plane of the solar system so for them to hit Antarctica it would need to be a "glancing blow". There wouldn't be much margin for error (too much one way, you miss Antarctica and hit something else, too far the other way and you miss the Earth entirely) and it would have to travel through more atmosphere, so more of it would burn up before impact so you would need to start with a larger asteroid (which means more nukes, or whatever else you use, would be needed to propel it). --Tango (talk) 18:57, 25 April 2009 (UTC)[reply]
It would be easier if you pick an asteroid with more or less the right orbit to start with. You need an earth-crossing asteroid with a highly inclined orbit, preferably eccentric as well. 1866 Sisyphus fits the bill but might be a little too big - it would be the dinosaurs all over again. I recommend 2102 Tantalus as a candidate missile. SpinningSpark22:35, 25 April 2009 (UTC)[reply]
Exploding a nuke directly over Antarctica probably wouldn't melt the continent, but exploding a few in the most vulnerable areas to subglacial seepage (which would undermine parts of the ice shelf) might do the trick. For example, Pine Island Bay in West Antarctica, and the Totten and Cook glaciers/ice shelves in East Antarctica. ~AH1(TCU)01:33, 26 April 2009 (UTC)[reply]
What's more, Antarctica is a continent — a ton of explosions would melt the ice cap at a particular location, but you couldn't melt the continent any easier than you could melt land anywhere else. Nyttend (talk) 12:42, 26 April 2009 (UTC)[reply]
That's a good point. We interpreted the question as "melt the ice cap that covers Antarctica", but that isn't actually what the OP asked. --Tango (talk) 21:23, 26 April 2009 (UTC)[reply]
There is something I really don't understand. The North American Plate includes both continental and oceanic crust. Therefore, I imagine that the younger oceanic crust, which comes from the Mid-Atlantic Ridge, subducts under the older continental cruster (otherwhise, I guess there wouldn't be any old continental crust). But there is no convergent boundary within the North American Plate! Where is my mistake? Where is going the oceanic crust? Enherdhrin (talk) 10:48, 25 April 2009 (UTC)[reply]
PS : sorry for my english.
The oceanic crust in the Atlantic isn't subducting; it's just pushing North America farther westward as it's created at the Mid-Atlantic Ridge. The subduction is taking place on the other side of the continent, as the westward-moving continental crust overrides the Pacific Plate. Deor (talk) 13:15, 25 April 2009 (UTC)[reply]
The explanation above is correct. I'm curious about that statement: "I imagine that the younger oceanic crust, which comes from the Mid-Atlantic Ridge, subducts under the older continental cruster (otherwhise, I guess there wouldn't be any old continental crust)." I don't understand your logic. There is no subduction zone on the east side of the northamerican continental crust, And yet, the continental crust is much older than the oceanic crust right next to it. I don't understand why you would think that's a contradiction. I isn't. Dauto (talk) 14:01, 25 April 2009 (UTC)[reply]
New oceanic crust is always being created at the Mid-Atlantic ridge, so the North American Plate always gets bigger, but the land area stays the same. The crust near the ridge at a certain distance is always of a certain age, but the crust closer to the continental shelf gets older and older, as does the land itself (discounting any newer orogenies). The expansion of the plate does not present a contradiction because plates are always being subsided somewhere else. ~AH1(TCU)01:19, 26 April 2009 (UTC)[reply]
The North American Plate is growing; the "continental" portion of it stays about the same size, and the "oceanic" portion is being added to at the Mid Atlantic Ridge. This is not a problem, since other plates, especially the Pacific Plate, are actually shrinking as they are being subducted under several plates, including the North American Plate. Crust creation and subduction is a zero-sum game, but not per plate, only over the whole earth. The individual plates are shrinking and/or growing based on what is happening at the plate boundaries.--Jayron32.talk.contribs01:33, 26 April 2009 (UTC)[reply]
@Deor : thanks for your reply. @Dauto : AH1 and Jayron32 have perfectly analysed my mistake : I falsely assumed that the size of the North American was fixed. Thanks to all of you for your explanations.Enherdhrin (talk) 11:30, 26 April 2009 (UTC)[reply]
Male/female ratio
Seeing as both the birth and death rates are higher in males than in females, which gender is more prevalent in the world: male or female? 58.165.23.195 (talk) 13:42, 25 April 2009 (UTC)[reply]
All your questions are answered at human sex ratio. In short, more boys are born than girls (105:100), possibly an evolutionary method to balance out the ratio, although sex-selective abortion and female infanticide heavily skew the numbers in some countries. But demonstrating precisely what you said, the male:female ratio gets considerably skewed the other way in older and older populations. In some countries, the ratio amongst people over 65 is 70:100 or worse. Someguy1221 (talk) 13:54, 25 April 2009 (UTC)[reply]
I recall reading once that males are more likely to die in the womb but the ratio at birth was as you say, something like 105:100. This surprised me at the time and no explaination was offered. I presume most likely there's something going on earlier then is being detected here, e.g. females less likely to be implanted, male sperm more successful in fertilising ova (which entails a whole lot of possibile reasons), more male sperm etc. Alternatively sex selective abortion is more widespread then people realise. The book was a rather old sociology book so there may be more info available now. Nil Einne (talk) 19:48, 25 April 2009 (UTC)[reply]
Social Science/Sociological Question: What is the difference between Modernity and the Enlightenment?
Modernity and the Enlightenment are majoratively written about as two seperate entities, although they share similar features and are sometimes interlinked as one and the same. Please can someone identify what the features are that distinguish between the two? —Preceding unsigned comment added by Sheepdisease (talk • contribs) 14:42, 25 April 2009 (UTC)[reply]
The Enlightenment is a period; Modernity is a state of mind. Enlightenment leads to Modernity. Such is a very crude way to think about it but it mostly works. Both terms are rather vague (esp. modernity, which basically stands for whatever one wants it to). --98.217.14.211 (talk) 17:36, 25 April 2009 (UTC)[reply]
Storage of medicines
I've seen it many times that on the packaging of medicine it says "store at room temperature." I wonder why they don't say "store at a temperature below X °C/°F" instead. I think most medicines are not harmed by low temperature. (I can't imagine all over-the-counter medicines are transported in heated trucks during the winter months. Short-term exposure to low temperature must be OK for most of them.) What are some mechanisms by which medicines will go bad when stored at low temperature? (I can think of one: some components of a mixture crystallize out and settle at the bottom of the container, thereby changing the composition of the mixture.) --173.49.78.81 (talk) 15:40, 25 April 2009 (UTC)[reply]
They may just say that to clarify that they don't need to be refrigerated. If there was a maximum temperature (that wasn't so high as to be unnecessary to warn against) that they could be stored at, I think it would say so. --Tango (talk) 16:51, 25 April 2009 (UTC)[reply]
Also, need to target the lowest common denominator of consumer, who doesn't know what the actual numerical temperature is. So "room temp", "cool, dry place", "refrigerate" are clear and are good enough descriptions for safe and enough storage to have the expiration date be reasonable. Also, no reason to confuse people into storing stuff in the fridge "just to be sure I don't exceed this temperature" (people don't know how close they need to be or how long and how much too hot is bad...what the hell is a "degree"?). Yes, I have a jaded view of the typical consumer:( Some (and many more, more recently) do actually also specify a maximum temperature. One problem with fridge isn't the low temp, but that the low temp leads to condensation, and water can lead to pills losing structural integrity and also major chemical changes for things that need to be stored "dry" as well (a good Slow News Day evening news topic is how bad it is to store medicines in the cabinet next to a steamy hot shower). DMacks (talk) 18:59, 25 April 2009 (UTC)[reply]
In the case of dry meds, generally the colder they are stored the longer they will last. In the case of liquid meds, it may be important to avoid freezing, so the colder you can store them, without risking freezing, the better. As to why the manufacturers don't include such info; it simply wouldn't increase their profits to do so. First, they'd have to spend lots of money to determine how long their med lasts at various temps. Then they would also lose money if people are able to use old meds which otherwise would have been tossed out and replaced with new meds. So, they do the bare minimum and give some relatively short period for which they know the meds will last at room temps, and call it good enough. StuRat (talk) 20:34, 25 April 2009 (UTC)[reply]
I guess the next question is: Why don't countries impose laws on drugs companies requiring them to include such information? Probably because the benefit would be minimal and it isn't worth annoying people with extra red-tape. --Tango (talk) 23:40, 25 April 2009 (UTC)[reply]
From my past experience working within the Pharmacological Industry (*see disclaimer below) - Governments (via Regulatory Bodies like the FDA (US), MHRA (UK) etc) do expend considerable resources on determining and specifying exactly what information drugs companies should and must include on/in their products' packaging and information leaflets. Similarly, every drugs company expends considerable resources on complying:
Because if they don't they face potentially onerous penalties (even if no harm results - I know of one company forced into closure because it failed to properly maintain documentation proving its compliance with manufacturing regulations);
Because they don't want to hurt profits by actually harming their customers;
And because, believe it or not, most Pharma Industry people are decent human beings with consciences who genuinely want to provide the best and safest medications they can.
This leads me to conclude that such basic information as storage instructions, that has been scrutinised and worked on by both Regulators and Manufacturers, is likely to be about as appropriate as it can be. (Assuming a legitimate source - counterfeiting drugs and their packaging is a major global industry.)
(*Disclaimer: I was employed by a contracting company to administer facilities maintenance at a drug manufacturing/packaging/distribution site, but no longer have any connection with, or have any reason to doctor spin for, "Big Pharma.") 87.81.230.195 (talk) 19:45, 26 April 2009 (UTC)[reply]
I believe that the drug companies are complying with the regulations - and that this means that their storage instructions are safe. However, the US Army (who maintain LARGE supplies of drugs in storage in case of urgent need) tested a bunch of drugs and found that the "use-by" dates on almost all of the medication they had was too conservative by orders of magnitude. They had been tossing out expensive drugs by the truckload because they were past their expiry dates - when in fact, they would have been both safe and effective for years afterwards. It's possible that the drug companies are being deliberately over-cautious in order to avoid any risk whatever - but it's also possible that either they want to make money by giving their product an unnecessarily short shelf-life - or that they simply don't bother to test them for long enough to find out when they finally do start to degrade. There is also a fine line for them to tread if a drug would last longer if kept under ideal conditions but degrade rapidly at room temperature or whatever. Do they put the shorter room-temperature number on the label on the grounds that people are too stupid to keep the drugs properly cool/dry/whatever - or do they put a longer duration and hope that people pay attention to the storage instructions? SteveBaker (talk) 13:07, 29 April 2009 (UTC)[reply]
Expansion of the universe
Is it true that the universe is expanding at an increasing rate? Meaning it's expanding faster now than it did billions of years ago? Also this statement found on the article, Metric expansion of space confuses me. It says, "The metric expansion leads naturally to recession speeds which exceed the "speed of light" c". What does "recession speeds" mean? 69.69.75.22 (talk) 17:44, 25 April 2009 (UTC)[reply]
Yes, current observations support an accelerating expansion. Recession speed means the speed at which two objects are moving apart (usually with us as one of those objects). We observe distant galaxies which have redshifts corresponding to them moving away from us faster than the speed of light. For normal motion, that is impossible, but since it is the universe itself expanding, rather than just objects moving through space, that rule doesn't apply. --Tango (talk) 18:53, 25 April 2009 (UTC)[reply]
To clarify: Those galaxies were not receding from us faster than the speed of light when the light we now observe was emitted. And, as best as we currently can determine, the universe's expansion first slowed down, and then sped up again. So if you asked "billions of years ago", you have to be specific. Current thinking is that gravity pulls the universe together, but dark energy pushes it apart. When the universe was smaller, gravity was the dominant force, slowing the expansion down. However, the universe still grew past the threshold where dark energy overtook gravity as the most significant large-scale force. --Stephan Schulz (talk) 23:46, 25 April 2009 (UTC)[reply]
Actually most of them were receding faster than c when they emitted the light we now observe. Recession speeds have mostly been decreasing since the big bang, so if they're larger than c now they were even larger in the past when the light was emitted. (There has been a slight increase recently, but only slight—the predicted exponential expansion is still in the future.) In the diagram on the right, the red line is light emitted by the yellow object (a distant quasar) and detected 12–13 billion years later by the brown object (Earth). Cosmological time is measured vertically from the cone's apex to its base, and distance is measured circularly around the cone (as shown by the orange line). The "recession speed" is the change in that distance over time. It can increase faster than c = 300,000 km/sec, but there's no direct connection between that and the speed of light, which is a local limitation on the angle that these lines can be tilted from the vertical. It's kind of hard to see in this image (easier in the top-down view), but the distance between us and the light increased at first, which means that the distance between us and the quasar was increasing faster than c then (and still is—the speed is around 2c now and was around 3c then). -- BenRG (talk) 12:48, 26 April 2009 (UTC)[reply]
Just by the way, any observations of increased redshift in objects that already have an enormously large redshift would not indicate an accelerating expansion, because those objects are seen as they were farther in the past to begin with. Therefore, the acceleration would have to have been determined by other sources. ~AH1(TCU)01:04, 26 April 2009 (UTC)[reply]
The expansion affects the light in transit, so redshifts do contain information about the expansion after the light was emitted. Specifically what the redshift tells you is a(now)/a(then), and what you want to know is a''(t). If you measured the redshift of the cosmic microwave background for a long time (i.e. keeping "then" fixed while varying "now"), then an acceleration in the redshift would be direct evidence for accelerating expansion happening now. But we haven't been doing astronomy nearly long enough for that—the predicted rate of acceleration is about 0.3% per billion years per billion years. A better technique is to look at many objects at different redshifts, which amounts to varying "then" while keeping "now" fixed. The first actual evidence for accelerating expansion came from redshift measurements of type Ia supernovas out to z≈1, which is several billion years back, enough to see a (somewhat noisy) trend. -- BenRG (talk) 12:48, 26 April 2009 (UTC)[reply]
acid
I went to the store but they only had 5% vinegar for sale remainder is water. Does anyone know a simple way that I can concentrate the vinegar I get from to store to 25%? Wikivanda199 (talk) 18:27, 25 April 2009 (UTC)[reply]
Acetic acid (the key ingredient in vinegar) boils at a slightly higher temperature than water (118C) and the combination doesn't form an azeotrope, so distillation should work. Boil the vinegar and more water will evaporate than acetic acids so what you end up with should be a higher concentration of acetic acid than you started with. Keep boiling it until you reach the desired concentration. --Tango (talk) 18:50, 25 April 2009 (UTC)[reply]
Many chemical supply companies will sell "glacial" acetic acid, which is about as concentrated as you can get. You can order some of that and dilute it down to 25% also. --Jayron32.talk.contribs18:56, 25 April 2009 (UTC)[reply]
Check also gardening, cleaning-products, and photo-lab suppliers (not sure what concentration is sold for stop bath)--lots of strong (and reasonably priced) chemicals. Googling around, apparently there are some vinegars that are much higher acid concentration than normal. DMacks (talk) 19:15, 25 April 2009 (UTC)[reply]
I've never seen it elsewhere, but a local East Asian food shop sells 5x concentrated white vinegar. (Strangely, it's from Germany. I think it's called "Essig Essenz". There's a warning on the label in big, bold letters "DILUTE BEFORE USING".) You might be able to get it at a specialty shop, or order it online. -- 75.42.235.205 (talk) 19:49, 25 April 2009 (UTC)[reply]
"Essig-Essenz" is commonly available in German supermarkets. It's sold as a food item with other vinegars, but is used for both food and non-food applications, in particular cleaning of tiles, or anything that suffers from lime build-up and can stand acid. For consumption, it is very boring and without real flavor if diluted with water, but it can be diluted with other fluids, in particular wine, to make e.g. interesting salad dressings. --Stephan Schulz (talk) 08:41, 26 April 2009 (UTC)[reply]
Ebay.com has a number of suppliers under "acetic acid". You can also look under "vinegar", but there are so many things under that category you should limit the search to "everything else." (that would include food). —Preceding unsigned comment added by 98.21.107.30 (talk) 21:15, 25 April 2009 (UTC)[reply]
Well if you had 25% vinegar and wanted to get down to 5%, you would just add water. So what you want is to add negative water. What is negative water? Well, for one thing, it could be water owed. So maybe you could buy the appropriate amount of distilled water on your credit card or borrow it from a friend and so on with your slips. I haven't worked out all the specifics however mathematically I believe my reasoning is correct. Let us know the results. 79.122.60.88 (talk) 12:48, 26 April 2009 (UTC)[reply]
That sounds like something out of an adventure game. I remember one that had a packet of "Instant something-or-other" with the instructions "Just add nothing!", so you had to add the contents of an empty bottle to it. You idea is much the same, just taken to a greater extreme. --Tango (talk) 21:17, 26 April 2009 (UTC)[reply]
How about adding NaOH or KOH as you have acetic acid in your diluted vinegar, and then evaporate all the liquid...you'll have solid sodium (or potassium) acetate left. Add to it an equivalent amount of hydrochloric acid having (at least) the desired concentration of acetic acid you want. Now you've got acetic acid and salt at whatever concentration the acid was. Distill it if you don't want to have any salt present--don't have to worry about being careful to separate the acetic acid from the water (which is pretty hard unless you have a good still from what I hear). DMacks (talk) 21:46, 26 April 2009 (UTC)[reply]
The question you should be asked is 'why do you want 25% Acid'? if you say> there may be something all ready to do the job your trying to do>>unless it was just a question?Chromagnum (talk) 10:22, 30 April 2009 (UTC)[reply]
April 26
radical addition of alkynes
There are two (pencil and paper) subsyntheses I would like to make (well the reason I'm adding halogens is that I'm trying to attach the products onto an aryl group later, but that's not the issue). Can I check that the following ideas are valid:
first synthesis
First synthesis: I know alkene reactivity > alkyne reactivity, but would it be possible to use acid-catalysed hydration of just the alkene bond? If I set the temperature low enough, it would be possible to get a major product where I just added to the alkene bond but not the alkyne bond, right?
In addition, how would I design the reaction so I can "stop" at the alkene stage, and not do a double-hydrobromination? (My textbook says you can stop it for normal Marvkovnikov addition, without commentary on radical addition, such that you don't form geminal halides, but I have no idea how you would detect the optimal formation of your alkene product such that you could stop the reaction on time.)
In addition, does the overall idea of radical (anti-Markovnikov) addition of Br to an alkyne bond work? Are radical stability effects magnified such that the formation of 2-bromo product is limited? I assume that the radical addition for alkenes is much faster than the carbocation formation step, hence why the radical effect dominates, but is a radical on an sp-carbon going to be more unstable than say a radical on a secondary sp2 carbon? John Riemann Soong (talk) 08:34, 26 April 2009 (UTC)[reply]
second synthesis
Second synthesis: Assuming the validity of radical addition to an alkyne, this second synthesis seems to imply I would get a cis-product as well as a trans-product. I only want the trans-product. Is it possible to design a reaction that favours the formation of trans-product? (The formation of diastereomers isn't important for my first synthesis.) John Riemann Soong (talk) 08:34, 26 April 2009 (UTC)[reply]
Enhancement by implants
More and more often I would find a third arm or an implanted wlan interface to my computer very useful. Being in a hurry very often, I would greatly appreciate a way to put on my socks while continue to operate the keyboard, just as an example. Or to make a phone call, talking silently via some future-style nerve-reading interface while listening to some slow talking time-sucker on the normal phone.
I know this is far from practice, at least for otherwise healthy people (and thus this is not asking for medical advice), but what is the state of art for such enhancements? (Well, I know I could buy a headset for a start ...) 93.132.137.0 (talk) 11:45, 26 April 2009 (UTC)[reply]
Well - perhaps not as far as you think. If you'd be prepared to use your real hands for putting on your socks on, there is a guy who has demonstrated typing by thought alone ([3]). See Brain-computer interface for example. At present, it's rather slow (eight characters per minute!) - but it's getting there. There are plans to sell a starwars-themed toy that lets you control the motion of a ball moving up and down a tube by thought alone: [4]. So it's certainly possible. SteveBaker (talk) 14:54, 26 April 2009 (UTC)[reply]
The thing that has real prospects is "add-ons" to replace things that are missing, such as an amputated limb. The big problem with wholly new things like a third arm is that you don't have any brain circuitry to manage them. There are some tricks that potentially could be used to reconfigure brain circuitry that has other functions, but none of them are likely to come into play very soon. Looie496 (talk) 16:47, 26 April 2009 (UTC)[reply]
The strange thing is that when I try to put on my socks while brushing my teeth and wanting to do even more in parallel (but not attempting for certainty of failure) I really feel like I could handle a third or forth arm. After all, I frequently pick up things with my feet. (Maybe I was a spider in some previous life.) As for the links from Steve Baker (thanks!), they made me realize I won't need any extra limbs implanted when there is/would be the possibility to steer some detached actuators instead --- a kind of real-science telekinesis. 93.132.137.0 (talk) 22:04, 26 April 2009 (UTC)[reply]
Earthrise on the Moon
Earthrise, today's featured picture at Commons
Today's featured picture at Commons has the following caption: "Taken by Apollo 8 crewmember Bill Anders on December 24, 1968, showing the Earth seemingly rising above the lunar surface. Note that this phenomenon is only visible from someone in orbit around the Moon. Because of the Moon's synchronous rotation about the Earth (i.e., the same side of the Moon is always facing the Earth), no Earthrise can be visible from the surface of the Moon." I can understand this very well. However, would you always see the exact same scene? Would Earth appear to be basically a circle in the sky that doesn't move? Or would it move somewhat because the Moon isn't always precise-to-the-millimetre facing the same way? Just curious...Nyttend (talk) 12:55, 26 April 2009 (UTC)[reply]
It would appear as the Moon does from Earth, just larger -- that is, it would exhibit phases as well as size changes due to orbital eccentricities and the libration that allows us to see more than half the Moon. — Lomn12:59, 26 April 2009 (UTC)[reply]
From the perspective of someone standing on the surface of the moon, the earth would stay in more or less the exact same place in the sky, hour by hour, day by day, year by year (it would move a little because the moon 'librates' - see image at right) - but as the long lunar day progresses from dawn to dusk to night, the earth would go through phases - just as the moon appears to go through phases from earth. SteveBaker (talk) 14:45, 26 April 2009 (UTC)[reply]
I haven't seen anything written about this, but the Earth would almost certainly have to move slightly, because the Moon's orbit is slightly elliptical rather than circular, and in addition is perturbed by the Sun. Looie496 (talk) 16:37, 26 April 2009 (UTC)[reply]
Also of course you would see evolving cloud patterns on the surface and a complete rotation every ~25 hours. It would be a lot more dynamic than the view we have of the Moon. -- BenRG (talk) 18:46, 26 April 2009 (UTC)[reply]
Googling on "libration in longitude", I found a page at demonstrations.wolfram.com that says the extent of this libration is 6°. Since the Earth's visual diameter as soon from the Moon is about 2°, it follows that there are parts of the Moon -- ones that we see roughly edge-on from the Earth's surface -- where you could indeed see the Earth rise. It would never come very high above the horizon, and later it would turn around and set in practically the same place, the whole cycle taking about a month. --Anonymous, 21:25 UTC, April 26, 2009.
This "almost stationary" earth phenomenon was a critical element of Apollo's lunar surface S-band communications antennae, which where directional and set up to point to one spot in the sky (towards Earth). Nimur (talk) 15:09, 27 April 2009 (UTC)[reply]
Yes, but the Apollo missions each spent only a few days on the lunar surface. Given that the earth would make its apparent motion over an entire month, the amount of motion over a few days might well be little enough to make the assumption that it's stationary be a viable one. SteveBaker (talk) 12:41, 28 April 2009 (UTC)[reply]
A new article on an interesting supernova. I'm an astronomy amateur and would therefore appreciate review of the text by someone with a little more experience. Thanks, —Anonymous DissidentTalk13:32, 26 April 2009 (UTC)[reply]
One of the missing info would be, is it in the Milky Way, in what galaxy, what distance? How fast did it rise and dim, to what magnitude (visible for whom?). All that theoretic stuff that now is in the article would just be a chapter. --Ayacop (talk) 18:20, 26 April 2009 (UTC)[reply]
I'm fairly sure I know the answer to this - but I need some evidence. At my local car club, we restore a lot of rusty old wrecks. Getting rid of rust is obviously important - but what I want to know is whether rust spreads because the rusty metal traps water and salt better than smooth metal - or whether it's because the existing rust is acting chemically as some kind of catalyst for reaction. It's obvious that rust starts as a little spot and then grows - it's just a question of what that mechanism is. I'm pretty sure it's not a chemical effect - but there is a big argument about it that needs resolving.
I think iron rust spreads because it's flaky. It exposes the material below to further rusting. (This is from something that I read about why iron and steel rust but aluminum doesn't. Catalysis was not mentioned.) --173.49.78.81 (talk) 15:38, 26 April 2009 (UTC)[reply]
As I understand it (which may not be very far), rusting is an example of electrochemicalcorrosion and any initial defect in the protective paint layer forms an anode with a current formed through the water (which is why salt water is so destructive because of its high conductivity). This link has some further explanation [5] which you may find useful. BTW both chloride and sulphate commonly act as catalysts in rusting. Mikenorton (talk) 19:00, 26 April 2009 (UTC)[reply]
I agree - rust is electrochemical, so it will induce local static voltage in the electrically connected metal. Because the rust is a worse conductor than the "pure" iron (or steel/alloy), it has some resistivity and the voltage does not equalize; current flows; and this current encourages the further rusting. (Those electrons have to go somewhere - and they go to the oxidation reaction, encourage it, and move along to the next spot). You can weld on some extra metal like Zinc to preferentially absorb that current, but I've never heard of this being used on a land vehicle (I'm no auto-body expert though). Anyway, I think this is neither mechanical (flaking) nor catalytic because the existing rust is actively participating in the electrochemical reaction throughout the entire connected surface. Nimur (talk) 15:14, 27 April 2009 (UTC)[reply]
On high-speed tallow candles
The Dictionary of Misinformation(a trivia book dedicated to debunking common misconceptions), in a section about the claims that a botfly can fly at 800 mph, says that "a tallow candle will penetrate a board at such a velocity". Is this true? I recall the Mythbusters refuting a similar proposition about a straw penetrating through a tree trunk in a hurricane(about 300 mph wind speed), but 800 mph is more than twice that, so I'm not sure how to extrapolate from that to the presumably softer candle. 69.224.37.48 (talk) 18:38, 26 April 2009 (UTC)[reply]
The Botfly thing has been debunked over and over (Here, for example) - one good reason being that it would have to consume more than it's own weight in food every few minutes in order to be able to produce that much energy.
But I wouldn't be quite so quick to dismiss the idea of the candle going through a board at 800mph. It's not the hardness of the candle that matters so much as the mass. When any object hits any other object and is stopped - all of the kinetic energy that the moving object had has to go somewhere. A candle weighs...I dunno...0.1kg let's say. At 800mph - 350 ms-1 it's going about a third of the muzzle velocity of a 50cal bullet with about three times the mass. But kinetic energy is proporitional to the SQUARE of the velocity - so it's going to deliver only about a third of the 'punch' of a modern 50cal bullet. However, the target is a "board" - perhaps just a half inch of wood. I've seen karate people smash "boards" with their open hands. I think that an 800mph candle would go through a "board" like a knife through butter!
The Mythbusters did point out that a straw couldn't go through a tree trunk - but they did get them to penetrate a fair way into the trunk (a tree trunk is a lot thicker than a board) - and they found that a heavier projectile would do considerably more damage. A candle weighs maybe 50 times more than a straw, we're talking about it going almost three times faster - so perhaps 450 times more energy - and through a 1/2" board rather than an 8" tree...I think that's no problem at all!
It would probably be seriously deformed (unless you shaped it to be very aerodynamic), but it is very difficult to stop something that is moving that fast - unless it had to travel a long distance through the air, I'm pretty sure it would make it in some form or other and, as Steve says, all that really matters is the mass, what form that mass is in is pretty much irrelevant. --Tango (talk) 22:54, 26 April 2009 (UTC)[reply]
Besides - the original "thought experiment" didn't say there was air - we may therefore assume the whole thing happen in a vacuum. At any rate, it's pretty much specified that the candle hits the board at 800mph...who knows how? SteveBaker (talk) 02:49, 27 April 2009 (UTC)[reply]
The board is toast. Same as if the board moving 800 mph in vacuum hit a stationary candle. Same as if foam space shuttle insulation hit a carbon fiber wing surface at several hundred miles per hour. Edison (talk) 04:42, 27 April 2009 (UTC)[reply]
I'm confused - the tallow candle is propelled to high velocity by some external energy source? Is it possible that they are using the (archaic) usage of "candle" to mean "rocket"? (This seems unlikely since they call it a "tallow candle", but a modern hybrid fuel rocket can work on paraffin with pretty good combustion). Is the idea that at 800 mph, even something as soft as tallow can penetrate a solid object? I'm also thinking that the flame exit velocity of a regular candle could actually be close to 800 mph (transsonic at high temperatures) in a very local sense; but I don't see how this convective flow would penetrate a board at 800 mph (unless the board is not combusting but is acting as a rocket nozzle or venturi tube... in that case, the flame gases could easily exit at 800 mph if confined to a small hole. Nimur (talk) 15:28, 27 April 2009 (UTC)[reply]
Does it have to be recognizable as a candle after it hits the board? I think you would have a demolished board, and little bits of candle everywhere. —Preceding unsigned comment added by 65.121.141.34 (talk) 20:01, 27 April 2009 (UTC)[reply]
To clarify, all the book says on this subject is the clause I quoted above, with no indication of how you'd accelerate the candle to that speed. I get the impression that it's supposed to remain intact while cleanly punching a hole through the board, but everything shattering into bits seems more likely. 69.224.37.48 (talk) 23:57, 27 April 2009 (UTC)[reply]
If a candle were attached to a rocket fired in space and accelerated to 800 mph (357 meters/sec), then detached from the rocket and made to strike a board, the board would become splinters and the candle would probably liquify or vaporize, or at least be smashed to small fragments. If it were in a stable axial trajectory, it might just blast a circular hole throught the board about the diameter of the candle, like a jet airliner smashing into the Pentagon at several hundred miles per hour. If you tried firing a candle from a gun, it might turn to melted tallow. It is low in density, and would decelerate quickly in air. It might be possible to accelerate it to 800 mph with a discarding sabot and high pressure air in a long tube, such as Mythbusters used to accelerate frozen chickens to smash into airplane windshields. The board should then be fairly close to the muzzle. Definitely do not try this at home. (But if you do I would like to see the video.) Edison (talk) 00:45, 28 April 2009 (UTC)[reply]
I've seen a demonstration (real-life, not on TV) of a soft tallow candle fired through boards. I don't know at what speed but it was definitely subsonic. It was fired from a home-made rifle! Dbfirs16:24, 28 April 2009 (UTC)[reply]
I decided to so some spring cleaning this weekend and my project turned up a ton of alkaline batteries. I raed on my the website for my community waste disposal agency that batteries manufactuerd after 1996 don't have lead in them and can be disposed of safely with regular garbage. Thing is, I have no idea how old these batteries are: no dates! are there any indicators I can look for to indicate lead safety? Thanks --Shaggorama (talk) 20:38, 26 April 2009 (UTC)[reply]
I have no idea about procedures in MD, but in the EU every supermarket provides receptacles for spent batteries. They all (I believe) contain heavy metals which is bad for the ears, not to mention refuse dumps :) --Cookatoo.ergo.ZooM (talk) 22:19, 26 April 2009 (UTC)[reply]
You could buy a modern, non-lead battery and weigh it. Then weigh the old batteries. If any of the old batteries are heavier, they probably contain lead. This is not a certain test, of course. It would be best to dispose of all the old batteries as if they; contained lead. – GlowWorm. —Preceding unsigned comment added by 98.21.107.234 (talk) 18:08, 27 April 2009 (UTC)[reply]
If the batteries actually are labelled as "alkaline batteries" as you say, then they're pretty much guaranteed not to be lead-based - see alkaline battery. Lead-based batteries are, additionally, quite uncommon as small household batteries even pre-1996; and they generally are clearly labelled even going back into the 1980s. The danger of lead isn't a particularly new discovery. ~ mazcat|c13:14, 28 April 2009 (UTC)[reply]
Alkaline batteries usually contained cadmium -- not good for landfill. Large modern rechargeable torches often have sealed lead-acid batteries, again, not good for landfill. It would be good to try to find a recycling facility if possible. Dbfirs16:33, 28 April 2009 (UTC)[reply]
Indeed, Dbfirs does have a good general point though - even in the case of alkaline batteries, there's a possibility of mercury being used in small amounts, and that's no more pleasant than lead or cadmium. As a general rule it's always best to recycle batteries if practical - lead is not the only dangerous heavy metal involved. ~ mazcat|c19:31, 28 April 2009 (UTC)[reply]
Best is a matter of opinion. You must explain to use what you define as being "best" to get an answer there. As for most durable (and ignoring the astroturf answer), tall festuca is popular for high-traffic areas that require durable grass. There are many types, so it is usually possible to find a type that grows in most areas that have sunshine. -- kainaw™23:25, 26 April 2009 (UTC)[reply]
Hi. This is from a question that didn't really get answered last time, but hopefullt this is answerable. Let's say you have a depression in the land, and water is starting to fill it. I want a general formula that calculates the amount of time needed for water to completely fill the depression. I know parameters such as the average and maximum depth of the area, the elevation at which the water is coming, the area of land filled, the length that the water initially needs to travel in order to meet the lowest point, whether the depression is dry or already has water in it, etc. Would I need any other information such as the salinity of the water, the temperature, the curvature of the Earth, the density of the rock, the air pressure in the depression, the wind direction and speed, etc? Does the formula, d = t2(a/2) (where d is distance, t is time, and a is acceleration (9.98 m/s)) be related to this formula? Thanks. ~AH1(TCU)22:39, 26 April 2009 (UTC)[reply]
Surely all the information you need is the volume to be filled and the rate at which the water is flowing in? Divide one by the other and you have your answer. --Tango (talk) 22:49, 26 April 2009 (UTC)[reply]
Perhaps, but I need to calculate the rate at which the water is filling in, from parameters such as the depth of the depression using a type of formula. So, how do I do this? ~AH1(TCU)22:53, 26 April 2009 (UTC)[reply]
If the water is falling in from above the depression, then Tango is entirely correct: flow rate and volume are the only necessary parameters. If you add in drainage, you may need to move up to a differential equation, but even then, salinity and all that should be irrelevant. — Lomn01:14, 27 April 2009 (UTC)[reply]
The rate the water is filling it in is something you need to measure, you can't calculate it without far more information that it is reasonable to have (assuming you are talking about a real world situation, rather than some idealised one). You need to measure the cross sectional area of the river that is filling it in and how fast it is moving, multiply those together and you get the amount of water filling the depression per unit time. --Tango (talk) 12:17, 27 April 2009 (UTC)[reply]
If you want to know the depth of water as a function of time then you're going to need to learn some calculus. You need an equation describing the shape of the depression - then you're going to calculate the integral of that function - and this new function can then be evaluated to figure the rate of filling. SteveBaker (talk) 02:43, 27 April 2009 (UTC)[reply]
Don't ignore the flow of water through the soil into the aquifer. Newton-Raphson matrix methods might help in providing non-determinate solutions.Edison (talk) 04:39, 27 April 2009 (UTC)[reply]
Yes, if there is significant drainage then it gets more complicated. The drainage will depend on how filled it is already so you will, as Lomn says, need a differential equation. --Tango (talk) 12:17, 27 April 2009 (UTC)[reply]
The Earth's magnetic field is certainly strong enough to have a noticeable repulsion: all you have to do is point an opposing magnetic pole and you will be repelled. That's how a compass works: it's a lightweight magnet, and if you flip it around, you can notice it being repelled from the "wrong" way and attracted towards pointing North. Levitation is hard because most of us are on the "side" of the earth as considering it a bar magnet, so the field is relatively weak and is substantially parallel to the surface. At the poles, the field is stronger and pointed perpendicular to the surface. However, the field is still really weak (0.6 gauss according to the article) and a gauss is a pretty small field, so you'd need something pretty light to be able to levitate well. DMacks (talk) 07:28, 27 April 2009 (UTC)[reply]
As well as being quite weak, the Earth's magnetic field is approximately uniform over distances of the order of a few metres. The force that turns a compass needle is a torque, which is present even in a uniform magetic field, because the forces on the two poles of the compass needle are opposite in direction. However, to produce a net force on a magnetised object you need to have a non-uniform magnetic field, to make the forces on the two ends of the object also different in magnitude. The Earth's magnetic field is so close to uniform that the net force on any reasonably sized magnetised object will be minute.
You do get a net force on a current carrier moving through a uniform magnetic field. 0.6 gauss is 60 microteslas, so a wire that is perpendicular to this strength of field will experience a force of 6x10-5 N per metre per amp - so to get a measurable force you need either a very long wire and/or a very large current. However, stronger magnetic fields produce bigger effects - this NewScientist item says that a field of 17 teslas can levitate a frog ! Gandalf61 (talk) 12:24, 27 April 2009 (UTC)[reply]
Very small and charged items like electrons and some light ions do get trapped by Earth's magnetic fields, and can be "repelled", "trapped", "resonated", and a variety of other interesting magnetic-field related motions. Take a look at the Van Allen radiation belt article. Those electrons and ions, under gravity, would get pulled into the lower ionosphere; under thermal motion, they would blow into space pretty fast; but they get trapped in the magnetic field and pulled into an "equilibrium" distance, complete with fun bouncing helical orbits that look nothing like your classic Newtonian gravitational elliptic orbits! Nimur (talk) 15:34, 27 April 2009 (UTC)[reply]
Hi,
Can you tell me What is a steam table?.How to calculate the value of enthalpy,using steam table for a given value of pressure and temperature?.Please reply if you are having any idea about this, plz share with me.... —Preceding unsigned comment added by Smenonp (talk • contribs) 12:04, 27 April 2009 (UTC)[reply]
Steam table redirects to the Water data page steam table. If you don't understand enthalpy, there is an article on that also. Basically the idea is that the enthalpy of vaporization is not constant - it actually depends on the temperature of the source water. To really understand this, you have to realize that while the "boiling point" of water is the phase transition point, in reality there is an equilibrium reaction between water and its vapor at any temperature. The steam table will tell you the values you need to calculate the parameters of that vaporization reaction. Nimur (talk) 15:38, 27 April 2009 (UTC)[reply]
Chameleons Changing Colors As Camouflage?
I have a question regarding our article on List of common misconceptions, specifically whether or not chameleons change their color to match their surroundings as a form of camouflage. Our article currently states:
"Chameleons do not change color to match their surroundings. They are naturally camouflaged and, although they can change their skin color into a variety of different colors, these changes are caused by temperature or interaction with predators or other Chameleons.[1]".
Another editor is disputing this here [6]. The video [7] he cites appears to be legit to my eyes, but maybe this is a video of an anole and not a chameleon.
well, the video is not a legitimate source. it could easily be photoshopped (and probably is—doesn't look natural at all). by contrast, the source against it comes from a major university. Wikipedia has long guidelines about what is a reliable source, about how "original research" is not allowed, etc. --98.217.14.211 (talk) 14:08, 27 April 2009 (UTC)[reply]
Hmm, but the chameleon article itself states, with two (possibly less credible, but still) citations:
"Recent research indicates that they do not only change their color for reasons of camouflage, but also use colour changes as a method of communication, including to make themselves more attractive to potential mates." -- Aeluwas (talk) 14:22, 27 April 2009 (UTC)[reply]
The issue here is having good citations and reading what they actually say. If it can be cited effectively, great. If not, then no. In those cases, citation #1 is about communication, not camouflage ("Overall, our results suggest that the evolution of the ability to exhibit striking changes in colour evolved as a strategy to facilitate social signalling and not, as popularly believed, camouflage."). Citation #2 specifically says it is not about camouflage ("Chameleons can produce a wide range of colors and patterns on their skin, but they do this primarily to express mood, not to blend in with different environments."). So I'd say that the distillation of these sources that claims they are camouflage PLUS expression rather than expression and NOT camouflage is incorrect (certainly not what the sources say). --98.217.14.211 (talk) 14:28, 27 April 2009 (UTC)[reply]
I knew that was going to bite me in the ass. ;) I was very close to adding a "I haven't had time to check the citations" part, but I omitted it. -- Aeluwas (talk) 16:34, 27 April 2009 (UTC)[reply]
That video looks like it was intentionally made to show off a cool match moving technique. (The super-shaky camera is common in these sorts of clips. Subtly is apparently not the goal.) APL (talk) 16:30, 27 April 2009 (UTC)[reply]
The video is not a good source, but the statement in the list of misconceptions seems to be wrong according to sources that are good, such as this recent PLOS paper. It looks like a case of confusion. Apparently there are arguments that color changes are used for more than just camouflage, and that the other functions may have been most important in driving the evolution of the capability. But there doesn't seem to be any dispute about the claim that color changes do have a camouflage ("crypsis") function. Looie496 (talk) 16:53, 27 April 2009 (UTC)[reply]
This is OR: But when I lived in Kenya as a kid in the late 1960's, I caught a baby chameleon and kept it as a pet for several months before my parents made me let it go. They certainly do change color in an effort to match their surroundings - but it takes them maybe 30 seconds to complete the change (maybe adults are faster), the range of colors they can produce isn't all that great and they certainly can't reproduce patterns in the background. However, they certainly DO change through shades of green, brown, reddish brown and grey. Obviously, if you are a kid and have one of these things as a pet - you're going to try to make it do crazy color changes - and it really can't. If you sit it on a bright red sheet of paper, then after maybe half a minute, you have a reddish-brown chameleon because that's the closest it can come. If you put it on a sheet of yellow paper - you get a kind of greenish brown because mine couldn't turn yellow at all...but if you put it on a sheet of dark green paper, it'll make a reasonably good match for it. It's not going to completely vanish - but the match is good enough in 'real world' situations that the animal might encounter. Attempts to make it match spots and stripes produced a greyish-brown chameleon no matter what. It was cool to have this thing sit on your finger so you could carry it around the room looking for flies and watch that AMAZING tongue shoot out...that's by far the most impressive thing they do. SteveBaker (talk) 18:36, 27 April 2009 (UTC)[reply]
It sounds like the claim in the article that color change does not match background as camo is bogus and original research, rather than adding that some other factors in addition to background matching/camo produce color change as well. I have certainly watched a chamelion change color to match the background, and background matching is widely accepted as a survival mechanism. If it changes color to indicate temp, that would make it a great thermometer, but would be an implausible evolutionary way to enhance survival. As a reality check, what do other encyclopedias such as Britannica say? Wiki editors often go off on a crusade as True Believers in a viewpoint not widely shared in a particular field, hanging their prejudices on one reference and ignoring many others with other conclusions. Edison (talk) 15:09, 28 April 2009 (UTC)[reply]
I added a contrary ref: "Others state that chameleons can change their color in milliseconds for camouflage as well as social signalling.[2]National Geographic quotes an expert on chameleon color change, Christopher Raxworthy, associate curator of herpetology at the American Museum of Natural History, to the effect that they match the background to survive, but they also color change as a social signalling mechanism: ""Most of the time, chameleons are behaving as highly cryptic animals trying to avoid detection from predators." So the only "misconception" would be that they 'only color change for camouflage, and that's a pretty trivial one. If scientists disagree, then it should not be on a list of "common misconceptions" at all. — Preceding unsigned comment added by Edison (talk • contribs)
They change color in MILLISECONDS! I find that hard to swallow. The pet chameleon that I owned took a good 30 seconds to do it. Perhaps adult animals are faster - perhaps there are sub-species differences - but I strongly doubt it. There are animals out there that can change color that fast (cuttlefish for example) - but I never saw my chameleon do that. It's certainly possible that they could also change color to reflect mood or mating status or something - but most of the time it's certainly camoflage. These are slow-moving animals with plenty of enemies - this is their only defense! I strongly suspect that the nay-sayers are trying to make the poor critter do something it's unable to do - like match patterns or colors that it's simply unable to do...or perhaps they are buying into the "changing in milliseconds" idea and not waiting the 30 seconds that my chameleon took...or possibly they have been looking at some particular sub-species that doesn't do it. My chameleon came from a tree outside our apartment on the outskirts of Nairobi, Kenya...who knows what chameleons from other places do? I know for 100% sure that my chameleon could match reasonable backgrounds like tree bark or leaves or reddish dirt if given time. When you're an 12 year old kid with a pet chameleon - that's pretty much their only party trick (they don't obey "sit", "down" or "roll over" - and they have a whole different take on the game of "fetch"!) - so everyone who comes to your house gets to see it! Actually - I know my mother has this on video - but unfortunately, that's 8mm cine film and it's currently on the other side of the planet - so I can't easily produce it! SteveBaker (talk) 23:17, 28 April 2009 (UTC)[reply]
If they can really change color in milliseconds I suggest making computer monitors out of chameleon leather. APL (talk) 13:02, 29 April 2009 (UTC)[reply]
What's so special about swine flu?
There is something I don't quite understand about this current swine flu panic we are having right now. I'm not trying to be flippant, but I don't really get what the big deal is. Every year influenza kills hundreds of thousands of people, every year new varieties of flu start spreading. I don't get why this particular one is getting so much attention? Is it deadlier than all those other varieties? Is it much more contagious? Belisarius (talk) 14:59, 27 April 2009 (UTC)[reply]
This outbreak is getting attention because of the possibility that it could become a pandemic. See swine flu. The H1N1 strain of flu is a subtype of Influenza A that descended from the virus that caused the "Spanish" influenza pandemic of 1918-1919 that "infected one third of the world's population (or ≈500 million persons at that time) and caused ≈50 million deaths." Sounds pretty important to me. --- Medical geneticist (talk) 15:27, 27 April 2009 (UTC)[reply]
But, so, why? Why is this influenza so much more dangerous than the gazillion other types of influenza out there? You know, the diseases that hundreds of millions of people contract every year, the diseases that kill hundreds of thousands of people annually? Belisarius (talk) 15:51, 27 April 2009 (UTC)[reply]
I was going to ask the same question here. I would love to see statistics on how many people die of the flu each year in Mexico. I feel like the media just happen to be jumping on this one more than other years. -- MacAddct1984(talk • contribs)16:09, 27 April 2009 (UTC)[reply]
You are asserting that human influenza is a petty illness, and for a heathy adult it's almost always non-lethal. The problems start arising when you are dealing with a group of individuals with a weaker immune system, such as the young children, ill or elderly population. You'll notice that over 1000 cases of swine flu have been reported during this pandemic, but comparatively few deaths (about 1:10, maybe just over/under). When flu infects individuals with compromised immune systems, it can cause some serious, and potentially lethal, consequences (whether it is human, bird of swine flu). Regards, --—Cyclonenim | Chat 16:13, 27 April 2009 (UTC)[reply]
We weren't asserting that it was a petty illness, on the contrary, we were saying that it is a big deal, but did not seem any worse than any other year, when thousands die each year from influenza. But I guess the fact that it's a new illness is the problem and there is currently no easy vaccine. -- MacAddct1984(talk • contribs)16:40, 27 April 2009 (UTC)[reply]
Sorry, upon rereading (where I added the below comment) I realised I misunderstood the original question, but forgot to strike. Will do so now. Regards, --—Cyclonenim | Chat 16:45, 27 April 2009 (UTC)[reply]
I realised that I probably didn't answer the question. The reason that this has so much more attention is that it has the potential to go wildly out of control. With human influenza, we have flu jabs which we can provide to the immune-compromised individuals and hopefully keep them alive through tough times like winter. With a new strain of swine flu, one which we have essentially no vaccination for, all of those immune-compromised individuals are at risk of catching the disease, meaning it can spread much, much faster and therefore kill more people. See the Spanish flu, for example, which mutated and killed thousands and thousands of people because there was no vaccination. The same problem can occur now if we don't have a vaccination, although a vaccine may be created quicker than back then. Regards, --—Cyclonenim | Chat 16:17, 27 April 2009 (UTC)[reply]
There are two things special about this outbreak. First, the genetic structure of the strain is quite different from other flu variants. Secondly, there are reports from Mexico that many of the people most seriously affected are in the 25-45 age range, a group that normally is the least affected by flu. However, more recent reports make it unclear to what extent the original reports are correct. Looie496 (talk) 16:41, 27 April 2009 (UTC)[reply]
The picture to the right compares the death rates (per 100 000) of the spanish flu with the death rates of more common flus. Notice the 'bump' around 30 year old people. Dauto (talk) 18:05, 27 April 2009 (UTC)[reply]
It's of note that this is not the first Swine flu pandemic fear—there was one in 1976 as well that didn't turn into a pandemic. The fear is, as noted, that it is related to the 1918 strain, which was much more deadly than the normal ones floating around in "flu season." --98.217.14.211 (talk) 02:08, 28 April 2009 (UTC)[reply]
To embellish a bit upon what Looie said above: Any disease that can take a perfectly healthy adult and cripple and/or kill them is scary, and when that disease is transmitted via air with no known cure it is triply scary. Add to that the fact that, unlike with the SARS and Bird flu scares of recent years, this disease has manifested itself strongly in a large population center/transportation hub relatively early in the outbreak, leading to the cases now being reported on 3 continents. Add all that with today's Twitter-minded society (and resulting hysteria), and you get a big deal in the media.
It will probably end up being nothing bigger than SARS and the bird flu--already it seems that subsequent cases outside of Mexico are less virulent (although it might be a bit too early to draw that conclusion), and though it seems to have a death rate ~1%, there may be untold numbers more who never got sick enough to go to the hospital (and thus be counted as a suspected case). Also, lets not forget how much medical care has improved since 1918.-RunningOnBrains02:46, 28 April 2009 (UTC)[reply]
The 1918-1919 flu did not mostly kill the elderly or those with weak immune systems. It killed healthy 19 -25 year olds, since their robust immune systems overreacted and the consequences of that compromised lung function. Edison (talk) 15:05, 28 April 2009 (UTC)[reply]
I have a problem of drooling while I sleep. Usually when I wake up, I find my pillow wet from my saliva. At any normal time my mouth has excess saliva. Is there a cure for this? What basically is the problem? Thanks. —Preceding unsigned comment added by 116.71.46.207 (talk) 15:02, 27 April 2009 (UTC)[reply]
If it is really bad, you could consult your doctor on whether you have a mouth condition that might be causing excessive salivation. If it is only moderate, you could try a mild diuretic before going to sleep, such as drinking tea. Looie496 (talk) 16:37, 27 April 2009 (UTC)[reply]
[comment removed - suggesting a specific OTC drug (which I don't think it actually intended to reduce salivation but just does so as a side effect) is unquestionably medical advice and is inappropriate for the reference desk --Tango (talk) 18:22, 27 April 2009 (UTC)][reply]
Mouth breathing certainly isn't the only way you end up drooling in your sleep, but mouth breathers do tend to drool in their sleep more frequently. I'd guess everybody does it sometimes, whether they're aware of it or not. The explanation for it is pretty simple: when you're asleep, you don't swallow saliva as often as you do when you're awake, and your mouth tends to go slack. If your head is in a certain position, gravity takes care of the rest; in itself, this is a really common and everyday thing. The excessive saliva may or may not be another story; if that concerns you, OP, you should probably talk to a doctor. -- Captain Disdain (talk) 20:14, 27 April 2009 (UTC)[reply]
Try swallowing your spit during the day, and closing your mouth when you sleep. I find that by the time I'm hours into sleep my saliva tends to evaporate away anyway (leaving my mouth dry). Also, It's been found that napping causes more drooling than regular sleeping. ~AH1(TCU)00:04, 28 April 2009 (UTC)[reply]
Looking at this again, I see that I probably didn't get what you were asking. The arcuate fibers are a set of connections -- the set of nerve fibers connecting the two brain areas I mentioned. Looie496 (talk) 19:44, 27 April 2009 (UTC)[reply]
I think the original question was about the arcuate fibers, not arcuate fasciculus. Please do not confuse between the two. The original question refers to the fact that the arcuate fibers article, in its present form, contains little more than just links to the three following articles: Internal arcuate fibers, Anterior external arcuate fibers, and Posterior external arcuate fibers. Now, from what I've read, all these fibers are formed by axons of neurons in nucleus gracilis and nucleus cuneatus of medulla oblongata. While medulla oblongata is generally associated with basic autonomous functions, the two aforementioned nuclei are thought to be mainly somatosensory. Lesioning experiments in cats and rodents show mostly propioceptive and somatosensory deficits following lesions to nucleus gracilis and nucleus cuneatus. So, I would say that the overarching function is delivering somatosensory information to various brain areas. You will have to do more reading to know the details. You will also have to do some research to find out if arcuate fibers in humans are implicated in some additional functions; they very well may be. Hope this helps. --Dr Dima (talk) 19:50, 27 April 2009 (UTC)[reply]
Right Hand Rule and Help with Magnetism
I do not get how to use the right hand rule at all...is there a way to find direction of a field, direction of velocity of a charged particle, or direction of force without using it?
Or
Could someone help me with a sample problem so i can better understand it??
"If a negativley charged particle were moving downward along the right edge of this page, which way would the mangetic field be oriented so that the particle would initially be deflected to the left?"
and
"Three particeles are moving in a uniform magnetic field. Each initially have a velociety pointing to the right. One goes into a circle that is clockwise, two goes straight, three goes in a larger circle that is counterclockwise. One and three have the same velociety and magnitude of electric charge. What can be said about the charges and masses of these particles?"
These are obviously homework problems, but I have about 40 problems like these and help with these two would definatley help me grasp the concept that I am trying to learn. —Preceding unsigned comment added by 70.129.227.81 (talk) 18:05, 27 April 2009 (UTC)[reply]
There are two different right-hand rules in magnetism as you can see in those pictures. The first one is used to find the direction of the magnetic field produced by a current. The second one is used to find the direction of the magnetic force on a (positive) charge moving with velocity 'v' (revert direction for a negative charge). I hope these pictures help. Dauto (talk) 18:38, 27 April 2009 (UTC)[reply]
OK, for those problems you will make use of the second rule which relates the direction of three physical quantities -- Velocity, Magnetic Field and Force, as indicated on the picture. The problems always give you information about two of those directions and you use the picture to help you find the direction of the third quantity in order to answer the question. Your first problem, for instance, gives the direction of the velocity (downward the page) and the direction of the force (towards the left) and asks about the orientation of the magnetic field. Keep in mind that for a negative charge the direction of the force will be the opposite of the one shown in the picture. Put your open right hand in the air with the thumb away from the other fingers in such a way that your thumb points towards the direction of the velocity and the palm (for a positive charge) or the back of your hand (for a negative charge) points towards the direction of the force. Your mid finger will be pointing towards the direction of the magnetic field. Dauto (talk) 20:30, 27 April 2009 (UTC)[reply]
In physics or electrical engineering exams it is funny to see students moving their right hands around with orthogonal thumb and digits trying to line them up with the illustrations on the exam for particle movement and magnetic field. It looks sort of like they are throwing down Gang signal#Hand signs for the Latin Kings. The illustration attached to the response is unhelpful to the OP since it shows all the fingers held straight. See also the illustration from Right hand rule, which unfortunately also has problems. Edison (talk) 14:48, 28 April 2009 (UTC)[reply]
There seem to be many different right-hand rules. This one is closer to the rule I learned. (The hand shape is the same as in your image but the labels are permuted.) That straight-palm version is as good as any other; there are still three distinguishable axes, and it looks less silly in public. You can use a left-hand rule, for that matter, if you assign the labels appropriately. And here's yet another variation. Pick one that you like and learn it. But whatever you do, don't learn two. -- BenRG (talk) 21:32, 28 April 2009 (UTC)[reply]
That straight-palm version makes a lot of sense now that I look at it. Your fingers show the direction of the parallel field lines, your thumb shows the current in the wire, and the force is in the direction you would push with your hand. I endorse that one. -- BenRG (talk) 21:47, 28 April 2009 (UTC)[reply]
I used to have a cartoon for the magnetic field around a wire using a student reading aloud from a physics textbook: "as you face the direction of current flow (had a vector pointing forward along the spine), magnetic field moves through the book from the front front cover to the back cover" and a caption "Moral: you won't get physics if you don't look in your textbook." Well, you get the idea. I know, {{global}}. DMacks (talk) 21:41, 28 April 2009 (UTC)[reply]
Measuring the temp of the Sun
Reading through the Sun article reveals a lot of information about the temperatures of various parts of the Sun. How are these temps measured? How about measure the temp of the core of the earth? Are these considered actual measurements (no one has taken a thermometer to either) or are they just theoretical calculations? Thanks. Anythingapplied (talk) 19:50, 27 April 2009 (UTC)[reply]
They are theoretical calculations. I wouldn't use the word Just. Those models (specially the one for the sun core) are very solid and thrustworthy models, and have been confirmed by indirect observations. Dauto (talk) 20:34, 27 April 2009 (UTC)[reply]
(ec)These are not direct measurements. The usual approach involves either analytic or numerical models of the star or planet interior. The models are calibrated using seismology (Earth) / helioseismology (Sun) data and - in the case of the Sun at least - the light that the Sun emits at different wavelengths. Different wavelengths (different photon energies) can escape from different depths: more energetic photons usually come from deeper within the Sun as they usually have smaller absorption and scattering cross-sections; but be warned that this is by no means always the case. Matching observed spectra to the models makes it possible to infer temperature distributions with higher reliability. So these are indirect measurements. --Dr Dima (talk) 20:43, 27 April 2009 (UTC)[reply]
It is funny now to read analyses by 19th century scientists trying to account for the high temperature of the sun and the extreme age of the sun, in terms of chemical reactions (the reactants would have been used up by then) or cooling from an initial high temperature. Early measurements of the sun's tempereature did not equal todays. In 1876, astronomers determined the sun was at 1354 to 2000 degrees Centigrade(p18).By 1907, the estimate was up to "12,000 to 15,000 Fahrenheit(6600 to 8300 C) . By 1907 the best explanation seems to be not nuclear fusion, but that the sun was contracting 220 feet per year (supposedly adequate to account for its continued constant heat output for 24 million years), although presciently they referred to the relatively newly known power of radium to continue giving off heat for a very long time, at least a baby step toward the modern nuclear explanation. The 1907 estimate was actually a bit high, if it was supposed to be the surface, today estimated at 5778K (5504C) per the Sun article. Edison (talk) 00:25, 28 April 2009 (UTC
The sound that sports arena spotlights make when switched on
In movies when large spotlights are turned on (e.g. at a football sports arena) there is an accompanying sound, sort of like a shutter being closed. What is the cause of this? ----SeansPotato Business22:57, 27 April 2009 (UTC)[reply]
Flood lights involve a high power electrical arc. That heats the gas inside the light and will cause it to expand, creating a sound in exactly the same way thunder is produced. (The arc continues to exist after that, but since the gas is already hot there is no further sound.) I expect, but I'm not 100% sure (this is just personal deduction, rather than something I've read in a reliable source), that that is the characteristic sound of flood lights turning on. --Tango (talk) 23:19, 27 April 2009 (UTC)[reply]
It might also be enhanced for dramatic effect. In the actual site, the sound of lights being turned on would likely be drowned out by background noise such as air handling equipment, traffic on the street outside, and airplanes flying over. See Foley (filmmaking)Edison (talk) 00:19, 28 April 2009 (UTC)[reply]
There is also a loud sound when floodlights are turned on at a movie studio sound stage. Normally, the sound is not heard in the actual movie ("Lights, camera, action.") But it can be heard in a scene in the movie "Singing In the Rain" which shows the floodlights being turned on. It is the sound of heavy duty relays, called "contactors", actuating. The moving part of each relay slaps against the electromagnet. Contactors are used so that only light wiring is needed to connect the floodlights to a control panel. Heavy wiring for the floodlights themselves goes directly from the building electrical service entrance to the floodlights. This reduces long runs of heavy wiring and the need for heavy switches in the control panel. Big electrical machinery, such as at steel plants, also uses this method. Undoubtedly it is the same at sports stadiums. – GlowWorm. —Preceding unsigned comment added by 98.21.107.234 (talk) 02:57, 28 April 2009 (UTC)[reply]
In a movie, every sound you hear is intentionally placed on the soundtrack in post-production, unless it is a low budget documentary. In more modern stage lighting, the control is electronic and is not simply relays closing in full voltage. In vintage lighting, knife switches on a lighting board were used along with banks of rheostats as dimmers, again not always with noisy relays. Movies would have the luxury of turning on the lights without distracting the audience. In sports venues the clunking of relays would not be heard over the murmer of fans (of both sorts). Edison (talk) 14:40, 28 April 2009 (UTC)[reply]
April 28
Microgravity and Moon missions
Astronauts in orbit around the Earth experience microgravity because they are in free fall--there are lots of explanations of this phenomena out there. But what gravitational effects did the Apollo astronauts experience while they were in transit to the Moon, since they weren't in orbit anymore? 128.103.197.57 (talk) 00:11, 28 April 2009 (UTC)[reply]
In earth orbit, in moon orbit, or in a trajectory between the earth and moon or between the earth and another planet, for all the recent talk of "microgravity" the astronauts and everything in and near their craft are essentially weightless, in free fall. They are literally falling. Only when the craft is spinning or is accelerated by rockets are they other than weightless. Food or liquid released in midair stays there, affected only perhaps by air currents of static charges. Anyone can put on his/her pants two legs at a time with ease (as one astronaut demonstrated). There is no "up" or "down." Edison (talk) 00:17, 28 April 2009 (UTC)[reply]
Some astronauts vomit because of the weightlessness. How many of them undergo that? Wouldn't it be a good idea to use sailors as astronauts?—Preceding unsigned comment added by 98.21.107.234 (talk) 00:37, 28 April 2009 (UTC)[reply]
I suppose that's why astronauts undergo training, and those who manage not to vomit in training, or learn to control their reactions, are those that actually get a ticket to orbit. --Ouro (blah blah) 06:20, 28 April 2009 (UTC)[reply]
Apparently, about half of astronauts suffer from Space adaptation syndrome (space sickness), but it doesn't last too long so it is usually just accepted as part of life in space. I'm not sure if being used to dealing with motion sickness would actually help, our article doesn't say if any particular people are more susceptible than others. --Tango (talk) 12:13, 28 April 2009 (UTC)[reply]
Spaceships don't normally rock back and forth like boats (with one exception). Throw in the fact that the sailors would have to have a lot of advanced education and training, and it would seem to be an impractical idea. Clarityfiend (talk) 18:40, 28 April 2009 (UTC)[reply]
The Apollo astronauts did not follow a straight-line course to the moon. So I am pretty sure that you'll find that the answer is that the astronauts were in freefall any time they weren't accelerating.
Consider this thought experiment : If the Apollo capsule was stationary with its engines off halfway between the Earth and the Moon, would the astronauts feel Earth's gravity? No. Because the capsule would fall. With nothing holding it up the capsule would fall like a broken elevator. When you're falling you don't feel gravity. APL (talk) 14:07, 28 April 2009 (UTC)[reply]
It goes without saying that if their engines were not turned on and there is no air or ground or other form of drag or thrust forces on their spacecraft then there could only be free-fall. Since that was the case for most of the trip - they were in zero g most of the time. However, whenever they turned the engines on - there would be acceleration - and therefore some kind of pull that they would feel just like gravity. The term "free fall" is really better than "zero-g" - any time you're falling freely you're not going to feel the force of whatever gravity there is. It is a common misconception that the people on the International Space Station are "in zero g" just because they are out in space. But that's not the reason - it's because they are falling freely. If they tried to hover over one spot on the earth at their present altitude (which would require some seriously impressive engines) - they'd feel gravity almost as strongly as we do. SteveBaker (talk) 23:00, 28 April 2009 (UTC)[reply]
Often I'll talk with a dog owner who claims their particular breed of dog has "hair" instead of "fur". Is this a bunch of nonsense? Our fur article says that "fur" means "the hair of a nonhuman mammal". I think the distinction these dog owners are trying to make is that their dog's breed doesn't shed, or doesn't shed as much, as dog breeds that have "fur". Nonsense or truth? Tempshill (talk) 02:26, 28 April 2009 (UTC)[reply]
Well, the distinction between "hair" and "fur" is pretty arbitrary (making humans the special case has nothing to do with biology). What they probably mean is that the fur in question more resembles human hair than it does other dog furs. --98.217.14.211 (talk) 02:37, 28 April 2009 (UTC)[reply]
Hair IMHO refers collectively or individually to strands that are relatively long and can be directed (combed) individually. Fur is always a collective word for relatively short strands that trap air that can keep one warm. Cuddlyable3 (talk) 12:51, 28 April 2009 (UTC)[reply]
the sun's surface
Given that the sun consists of gas, I'd expect it to look like a density gradient rather than suddenly becoming opaque at a well-defined sphere. What changes at that level? —Tamfang (talk) 06:21, 28 April 2009 (UTC)[reply]
There is no level. As I said in a response to an earlier post today, photons of different energies escape, on average, from different depths. For any photon, the deeper within the Sun it was emitted, the lower is its probability of escape. For a photon of a given energy, there is formally a certain depth from which the probability of escape is exp(-1); probability of escape from deeper layers is smaller, and probability of escape from less deep layers is higher. That particular depth is the depth where the Sun becomes "opaque" for that particular energy of a photon. The important thing is that that depth is different for different photon energies. X-ray photons escape from deeper layers than visible-light photons, and photons at the centers of spectral lines usually escape from shallower layers than continuum photons. If you need more detail, please see Opacity (optics). --Dr Dima (talk) 07:53, 28 April 2009 (UTC)[reply]
You are correct, there is no well defined surface of the sun. The corona extends a long way out from what we would usually consider the surface, it just gets more and more tenuous. The same is true of the Earth's atmosphere, the exosphere doesn't have a well-defined top. --Tango (talk) 12:08, 28 April 2009 (UTC)[reply]
Skeptics are saying the homo floresiensis are homo sapiens ("us") with the serious disorder microcephaly. Given that microcephaly happens to us tragically often, could it be it is an "obsolete" and ancestral trait we share with homo floriensis, and it is blocked from appearing in humans unless the genes that now prevent it are disabled or missing, or (or perhaps the same thing)the genes that caused it are allowed to be expressed? Let me try to say what I mean again:The hobbits do have microcephaly, but it's not a disorder? For us, it's a disorder?Thanks, Rich (talk) 07:14, 28 April 2009 (UTC)[reply]
I think basically the question is unanswerable. How could anybody know if microcephaly would have been seen as an disorder in these hominids, if we don't know what was their "normal" state? It all depends on the basic question: Were these people Homo sapiens or where they something different? As long is this is not answered, you cannot derive anything about deviation from any "norm". TheMaster17 (talk) 08:48, 28 April 2009 (UTC)[reply]
I don't understand why whether they were homo sapiens or not is the basic question. It seems to me that whether they were diseased or not is at least as basic. After all, if they weren't homo sapiens, they might be a diseased form of some other hominid. In addition, if we find further remains, perhaps of a fetus, we might figure out if the small brains were normal to them. And in us, maybe geneticists will find a large ensemble of unused and perhaps degraded genes that code for the development of microcephalic but potentially "thrivable" offspring. Thank you for your comments.Rich (talk) 09:15, 28 April 2009 (UTC)[reply]
I think you misunderstood what I wanted to express: The presence of a disorder can only be stated if the normal state is known. So only when we know what kind of hominids these people were, can we say anything about disorders. There is no alternative to this approach I could think of, because every other method to infer "disorders" of some kind are just speculation and extrapolation from known hominids. And how would you, to mention your example, infer from a fetus what the "normal" state would be in an adult? Human fetusses are far from finished when you look at body proportions, and as long as you don't know what kind of hominids you are looking at, you cannot safely transfer any proportion of growth (even when you know the species, this may not be possible, as growth patterns have changed during hominid evolution). I think I didn't get your last point: What would an unexpressed gene in humans tell you about the unknown kind of hominid on Flores? (btw: There is no such thing as a degraded gene. Genes change all the time, and these changes are what enables evolution, allowing changes in the function of the geneproduct.) It is not possible to infer a function from a genomic sequence, just to make an educated guess at the parts that the product would have. So finding a gene (or the remnants of a once-active gene) would never tell you that it would cause microcephaly in humans. TheMaster17 (talk) 09:47, 28 April 2009 (UTC)[reply]
The Nova documentary I just finished watching on this very topic said (with convincing detail) that the microcephaly theory is busted and it's pretty clear now that they were indeed a separate species. Small bones in the Hobbit's hands are a close match for apes and are quite different from those in later hominids. Also, most of their anatomy is very close indeed to "Lucy" - another early hominid specimin. Conclusion was that the Hobbits were simply a parallel thread of evolution - an almost completely separate species (far more separate than, for example, the Neanderthals). Still around on their idyllic island until maybe 18,000 years ago - probably wiped out by a volcanic eruption. SteveBaker (talk) 02:30, 29 April 2009 (UTC)[reply]
Also, why is it so hard to get a proper high-resolution computer image of a *real* skew-T diagram? Isn't this supposed to be like, public domain information? John Riemann Soong (talk) 07:59, 28 April 2009 (UTC)[reply]
I'm guessing that while the information ON the diagram may be in the public domain, the weird triangular graph paper it's drawn onto belongs to some graph-paper printing company who's copyright you'd be violating if you posted a blank sheet of the stuff online and at useful resolutions. You can get free graph paper in PDF form here (A very useful site that should be in every working scientist's bookmark folder!) - but not with all of the shading and peripheral annotations in the JPEG image you linked to. Still, since it's an emergency - perhaps something there will suffice for your needs. SteveBaker (talk) 12:30, 28 April 2009 (UTC)[reply]
No. But if applied to a product as a novel part of its design (artistic or functional) then yes. The graph on a graph paper is not IMO novel. Cuddlyable3 (talk) 12:43, 28 April 2009 (UTC)[reply]
Cured??? Most viral illnesses are self-limited and don't need to be "cured". For the common viral illnesses everyone is familiar with (the "common cold", the "flu", "viral gastroenteritis" etc.) we treat the symptoms and let the immune system do the rest. There are very few modern medicines that directly kill a virus or interfere with the mechanisms of viral entry into the host cell, replication, or dissemination. Far fewer than 100. Probably 10-20 at best (at least in widespread use). The antiviral drug article has a useful summary of some of the approaches. --- Medical geneticist (talk) 13:52, 28 April 2009 (UTC)[reply]
(multiple ec) In the strictest sense: none. Medicine does not cure a disease, it only treats the disease so that the body itself can cope with it better. Another problem is in numbering virusses: They mutate very fast, so would you count every different strain as a new kind of virus? Or only broader groups, like influenza? So it depends on the perspective. Have a look at viral disease, but this list is far from complete, as stated. In what context do you want to know this "number"? Concerning the previous answer to this topic: what is "killing a virus"? It's as meaningful as "killing a shoe", because virusses are not considered to be living by most if not all current definitions. TheMaster17 (talk) 13:59, 28 April 2009 (UTC)[reply]
I can just judge from what I know: In my studies of biology, I never met any biologist who considered virusses to be lifeforms. Every definition of life I know excludes virusses, because they always lack central properties of life: homeostasis, response to stimuli, growth and/or undergoing cellular division, a metabolism of their own. For sure it is possible to speculate about some form of "non-cellular life", i.e. some other kind of physical system which shows all characteristics of life. But this only blurs the everyday meaning of the word life: life as we know it on earth. And in this sense, a virus is "just" a very complex transportation device for nucleic acids. Without the machinery of a living cell it is only sitting around, slowly degrading. TheMaster17 (talk) 14:44, 28 April 2009 (UTC)[reply]
Medical geneticist, I could guess that you meant it colloquial, but as the initial question had some rather blurry words and concepts, I wanted to make clear that a virus is not living, and that many other misconceptions follow from this original one. A blurry answer to a blurry question usually helps nobody ;-). TheMaster17 (talk) 14:50, 28 April 2009 (UTC)[reply]
Viruses are not individually living any more than toenail clippings are, but they are clearly part of life in a holistic sense. They certainly require other living beings to aid them in most of their life processes, but they aren't "non-living" either. So, are my toenail clippings living? Well, no. But are they entirely outside of the concept of "life". No on that either, since they would not exist without life. The convenience of classifying something as living or not is arbitrary; even deciding what constitutes an individual organism can be tricky (see Lichen). So the question is more Is a virus an organism No, it probably isn't. But it still part of "life". --Jayron32.talk.contribs01:43, 29 April 2009 (UTC)[reply]
Jayron, I don't agree with your definition of life, but I can understand that some people like the idea of "the entire earth constituting a living being", then that is what you are running into when you follow this line of thought. I'm perfectly fine with calling my toenail clippings dead and never living: Just because they were built by living cells, they are not anymore living than for example the skeleton that corals built or the slime that snails excrete. Whatever you do with your toenail clippings, they will never have a metabolism or be able to divide and grow on their own. But we are getting rather off-topic. TheMaster17 (talk) 06:54, 29 April 2009 (UTC)[reply]
Well, if what you said were my definition of life, i would disagree with it too. What I said was that Viruses were part of life in the sense that they are not part of geology. Granite is certainly not living. I never once said that the whole earth constituted a living being That bullshit never was typed by me, and I would appreciate it that if you were going to refute my arguements, it would be helpful if you actually refuted my arguements, and not arguements you decided I made. Seriously. Now, back to this issue. If we have to draw a bright line somewhere and say "this stuff is part of life and its processes" and "this stuff on the other side has nothing at all to do with life and its processes" then viruses clearly fall on the "life" side of the equation. They certainly are not part of geologic processes; the weather does not create them. They are here on earth, and they exist because of life, and are part of life. Look at it another way: If we take an earthlike planet that never had life on it at all, and never would ever produce life in the future, could you imagine viruses existing? --Jayron32.talk.contribs01:36, 30 April 2009 (UTC)[reply]
Viruses are much closer to living organisms than toenail clippings are. No matter where you put a toenail clipping, it will not cause another toenail clipping to be generated.
The distinction about whether viruses reproduce "on their own" is specious. Do we reproduce on our own? Viruses (some of them at least) have clearly functional machinery adapted to parasitizing cells and thereby reproducing themselves. They do need the cells to do it, but so what? The cells are prey. Lots of organisms can't reproduce without a specific parasitic host.
It's also not true that viruses (some of them at least) don't respond to stimuli — they attach to specific surface features of cells, and respond by inserting their genetic material.
The main distinction, which is true, is that they don't have a metabolism. If you think that makes them "not life", then fine, that's your definition and you're welcome to it. But I think you can see how others might reasonably disagree. --Trovatore (talk) 07:49, 29 April 2009 (UTC)[reply]
(unindent) I think we are really getting into a philosophical discussion here: What is "on its own" (so basically, what constitutes "self")? What is "reacting to stimuli" (Is a lock reacting to stimuli when it opens the door after I have turned the key? Basically this is the way that insertion mechanisms in virusses work.)? If you want, we can talk about this on my talk page, but for the starting question, this is off-topic. But you are totally right that I can see how others can reasonably disagree: This is really muddy water and many generations of very bright people have discussed this, and all depends on very personal definitions of cause and effect. TheMaster17 (talk) 08:31, 29 April 2009 (UTC)[reply]
The purpose and use are extremely important. You need to think about biological and chemical hazards, radiation safety, and protocols for any animal work - among a slew of other things. Wisdom89(T / C)19:32, 28 April 2009 (UTC)[reply]
An easy place to check for local regulations is your local City Hall, if such a thing exists where you live. There are permits needed for places that serve food, places that handle food ... there are possibly permits for places that handle such-and-such types of chemicals or animals or nuclear fusion reactors or whatever it is you're planning to conduct research on. Tempshill (talk) 00:50, 29 April 2009 (UTC)[reply]
Wearing Black on a hot day
People keep telling me to wear lighter colors when it's hot. None of them seem to know precisely why they think this is a good idea.
I don't think it is quite that simple. Light colours reflect heat better so they stop you getting warmed up, however they are worse at radiating heat, so they stop you cooling down. There are desert tribes that traditionally wear black, and they probably know what they're doing when it comes to staying cool. Dark colours can also help protect your eyes from the bright sunlight (I've seen it suggested that you wear black paint/soot/whatever under your eyes in bright sunlight if you don't have any sunglasses). I think it is more important to wear lose fitting clothing that covers most of your body (exposed skin is at risk of sunburn, etc.). An unbuttoned shirt worn over a t-shirt is supposed to work well. --Tango (talk) 19:31, 28 April 2009 (UTC)[reply]
As a long-time desert dweller, I can tell you from experience that in a hot sun, light is a lot better than dark -- the heat absorption of dark clothes is the dominant factor. If it's hot because you're in the jungle, it might not make much of a difference. Looie496 (talk) 20:09, 28 April 2009 (UTC)[reply]
As a camper, one of the luxery items you can buy are shower bags. They are entirely black, you fill them up with water and leave them in the sun and they warm up. Then you hang them from a tree and have a warm shower. If it weren't black it probably would get much hotter than the ground around it, but the can get quite warm. Anythingapplied (talk) 20:33, 28 April 2009 (UTC)[reply]
You need to read "Why Do Bedouins Wear Black Robes in Hot Deserts?" by Taylor, Finch, Shkolnik and Borut, Nature283, 373-375 (24 January 1980). That's a subscription-only link, but there's a summary in the Guardian here. To summarise, white garments let more radiation in while black ones absorb more, so the effects almost balance out. --Heron (talk) 21:08, 28 April 2009 (UTC)[reply]
The simple answer is that the color black absorbs light (that's why its black.), the energy from that absorbed light is transformed into heat. Therefore, on a sunny day, a black object will be noticeably warmer than a similar white object.
As mentioned above, the situation with clothing is complex because so many additional factors go into it, including how the clothes "breath", how much sun penetrates the cloth and hits your skin, etc.
If I had to theorize, I'd bet that a cloth that was black on the inside and white on the outside might keep you coolest, but that's just a wild guess. APL (talk) 21:25, 28 April 2009 (UTC)[reply]
The question is largely to do with whether the heat is conducted into your body (because the air temperature is above body heat) or radiated into your body (from the sun). If the heat is in the air itself - then no amount of light-colored clothing will help you to avoid that - and the light colored cloth reflects heat that your body is trying to radiate back in again - so black clothing would be cooler. However, if the heat is coming from the rays of the sun - then reflecting them away is a big win compared to the downside of a reduction in the amount of heat your body can radiate. Hence - (although I'm slightly hesitant of my conclusion) it ought to be better to wear dark clothing in the shade - and when the air temperature is above body heat - and you're better off with light clothing in sunlight and when the air temperature is below body heat.
Furthermore - let's examine the whole premise of this. Do Bedouins really wear black out in the desert? Sure, we're all leaping to that conclusion - but is it actually true? Let's take a look at the WikiCommons photos in Category:Bedouins [10] - and the first few pages of photos from a Google/Images search on "Bedouin" - a rough count says that about two thirds of those photos are of people wearing light colored clothing - with only a third or so in black or other dark colors (there are some judgment calls to be made on blue, green and striped clothing - also white headgear with black robes - so it's not a "Black and white" question!). Perhaps these people are aware of the kinds of distinctions I describe. If you're planning to spend the day in the shade of your tent on a hot day - wear black - if you're out on your camel doing whatever it is you do - wear white. If you're in your honking great SUV - crank up the A/C and wear a hawaiian shirt? SteveBaker (talk) 22:44, 28 April 2009 (UTC)[reply]
Well to be fair it was in Nature. Also if you look more carefully at the category, most of the black and white images show dark coloured clothing. These are likely I expect to be the older images (in general) so it's possible Bendouin clothing colour choice has changed over the past 100 years or so particularly since anyone there is obviously interacting enough with the outside community to be photographed. (It's also quite ORry.) None of this of course means the reason they choose black coloured clothing has anything to do with whether it keeps them cooler Nil Einne (talk) 02:20, 29 April 2009 (UTC)[reply]
That doesn't work - oxygen and air pressure are also minimal necessities and without them, starvation and dehydration are not a problem! SteveBaker (talk) 02:26, 29 April 2009 (UTC)[reply]
It may literally be hotter if you're taking fluid from the center of the cup instead of sipping at the surface. Do you still notice the effect if your stir the drink well right before you take your sip? APL (talk) 21:27, 28 April 2009 (UTC)[reply]
"Taste hotter"?
Anyway, another reason might be partial cooling of the liquid as it passes your lips on its way to the tongue, rather than being channeled straight to your tongue through a straw. ~Amatulić (talk) 22:04, 28 April 2009 (UTC)[reply]
Indeed and I would expect the initial contact (surface) area when your sipping to be larger then when you're drinking from a straw Nil Einne (talk) 02:25, 29 April 2009 (UTC)[reply]
You'd expect the straw to allow for extra cooling of the liquid - so my bet is with User:APL - try placing the end of the straw as close to the surface and as near to the edge of the container as possible. That's where you'd be sipping liquid from if you weren't using a straw - not the middle/bottom of the cup where it's undoubtedly hotter. SteveBaker (talk) 22:28, 28 April 2009 (UTC)[reply]
I don't see why it would though. The liquid doesn't stay in the straw for long. A straw has a low heat capacity and quickly heats up and is surrounded by an insulator (air). Your lips have a large heat capacity and are better conductors. Of course either way it may or may not be enough to make a significant difference Nil Einne (talk) 02:25, 29 April 2009 (UTC)[reply]
This is my theory, and it depends on how you drink from the cup. If you "slurp" from the edge of the cup like I think many people do, you may actually be drinking the hot liquid at a slow rate, and you're sucking quite a bit of air into the mouth in the process. The air flow causes both convective(?) and evaporative cooling of the hot liquid right before it gets into your mouth. Compare this with drinking through a straw, you may be drinking at a faster rate in the latter case. A plastic straw is not a good conductor of heat and there's little convective and no evaporative cooling as the hot liquid is sucked into your mouth. (There's another mechanism I can think of that contributes to the difference, which would be more significant if you're drinking from a relatively empty cup and/or if the cup is a good conductor of heat.) --98.114.146.142 (talk) 04:52, 29 April 2009 (UTC)[reply]
Is it possible to sniff blood from the nose into the eyes during a nosebleed?
In my experience, most medical people say it is impossible to bleed from the eyes. Many online posts from the general public on the subject though suggest that if fluid can drain from the eye into the nose, when you cry or with an allergy for example, surely it could also go the other way, resulting in the blood from the nose being secreted from the tear duct.
There is a duct or channel from the eye to the nasal cavity that allows for drainage of tears. After Lasik surgery, a common complication is dry eyes, and a common cure is for an optometrist to put tiny plugs into the channel openings to prevent the tears from draining and keep the eye moist.
Because that duct exists (and I have seen some people hold their nose and manage to force air up into them and out the eyelids), it would be possible to force a blood through those ducts, if you have a noseful of blood to start with. ~Amatulić (talk) 22:02, 28 April 2009 (UTC)[reply]
PCR is performed on a nasal swab to detect Influenza A (Swine flu falls within this category) or Influenza B. The turnaround time in a good clinical lab should be within 8-12 hours, or 24 hours at the longest. If positive, the lab should reflex to type the specimen. That probably takes another few days, but they wouldn't wait to initiate therapy if the PCR was positive. The PCR-based assays are very sensitive (95-99%) and specific (90-99%). With the second typing assay on all PCR positives you'd end up with very few false positives. The rapid antigen screens that are sometimes used would be less reliable and give significantly higher false positives. --- Medical geneticist (talk) 21:09, 28 April 2009 (UTC)[reply]
Agree, but would add that Electrospray ionization mass spectrometry is accurate, much faster than conventional analysis of PCR products, can provide results in under 3 hours, and the sample processing rate is about 1 specimen per minute (PMID 17534439). Amazing - though the hardware isn't available in many places at this point. --Scray (talk) 01:26, 29 April 2009 (UTC)[reply]
Sorry for the jargon. What I should have written was: If the PCR is positive for Influenza A, The "reflex response" from the lab should be to perform an additional test to determine the specific subtype. --- Medical geneticist (talk) 16:49, 29 April 2009 (UTC)[reply]
OK, thanks. Is there movement towards having a generic system wherein you could stick a swabbed sample into a machine, download H1N1.xml from www.cdc.gov, and have the machine say "match" or "no match"? --Sean14:37, 30 April 2009 (UTC)[reply]
Elastic Potential energy
If you apply stress pass the point where the potential energy growth is linear, will you get less energy back, or does it just mean you're applying less energy to store the energy? 99.227.94.24 (talk) 21:14, 28 April 2009 (UTC)[reply]
If you applied less energy than was stored, that would involve energy appearing from nowhere, so that can't be happening. When you go past the elastic limit of an object it permanently deforms, which uses up energy, that is why you get less back. --Tango (talk) 21:56, 28 April 2009 (UTC)[reply]
Sorry about that, I was referring to the growth in energy in graphs. Probably should have made that clearer. But that answers the question anyhow. 99.227.94.24 (talk) 23:16, 28 April 2009 (UTC)[reply]
Electrodynamic potential energy
How can electrodynamic potential energy be liberated? When a electric motor spins, is it turning electrodynamic potential energy in to mechanical energy? 99.227.94.24 (talk) 23:55, 28 April 2009 (UTC)[reply]
Electrodynamic potential energy is a term I am unfamiliar with, but it sounds like the energy stored by electrically charged particles which are in the presence of other electrically charged particles. If I have two electrons which are being held stationary near each other, the repulsive force between them implies that there is a potential energy generated by their proximity. Anything which causes these electrons to go from a stationary state into one of motion away from each other will convert that potential energy into kinetic energy. --Jayron32.talk.contribs01:31, 29 April 2009 (UTC)[reply]
Apparently, electrodynamic potential energy is the same as magnetic potential energy. The power supply to the motor creates a current in the motor windings. The entire circuit consisting of the power supply and the windings induces a magnetic field, which contains magnetic potential energy. The magnetic field exerts a force on the rotor. As the rotor moves, energy is transferred from the magnetic field to the rotor, which gains kinetic energy. So the answer to the question appears to be "yes". --Heron (talk) 09:35, 29 April 2009 (UTC)[reply]
But the whole setup is in a steady state: as long as the motor keeps getting power it will keep producing useful work, but the energy stored in the electromagnetic field won't change. The energy source that's ultimately being depleted in exchange for the work is probably chemical or nuclear or hydroelectric or wind or solar. Only if you powered the motor by a capacitor would you really be converting stored-up electromagnetic field energy into work. -- BenRG (talk) 18:55, 29 April 2009 (UTC)[reply]
I'm not saying you're wrong, BenRG, but there are two ways of looking at this. It's only a steady state if you think in the frequency domain and ignore the fact that the magnetic field in the motor is alternating or rotating. I was thinking in the time domain, where a non-steady state exists as the magnetic field alternates. As one half-cycle of the field builds up, the power supply feeds energy into the field, which pushes the rotor round a bit. As the field collapses, some of the energy returns to the source minus the energy that it took to push the rotor. Then the cycle begins again with the opposite polarity. In that sense, some of the magnetic energy of each half-cycle is being transformed into mechanical energy, isn't it? --Heron (talk) 18:39, 30 April 2009 (UTC)[reply]
I'm not sure if that's it. This is a popular children's toy. It's a flat sheet of plastic with ridges and an image on it. The viewing angle affects what is seen on the plastic. -- penubag (talk) 01:52, 29 April 2009 (UTC)[reply]
EC = edit conflict (though this'll get confusing if a bunch of us try answering at the same time, and then get a notice that someone else has saved an edited version of the content since it was loaded = edit conflict). --Scray (talk) 03:22, 29 April 2009 (UTC)[reply]
Usually someone will mention an edit conflict because they haven't bothered to read the new replies (or if they have, haven't modified their reply) which could already address what they are discussing or may help clarify some uncertainty or whatever. In this specific case I started to reply but couldn't quite remember the name so had to search. I also got distracted by something else. By the time I found what I was looking for, you had replied but I didn't bother to consider your latest reply and modify you post hence I mentioned an edit conflict (if I did I probably wouldn't have bothered to mention holograms since I was a bit uncertain from your first post but your reply sounds precisely like lenticular printing) Nil Einne (talk) 23:40, 29 April 2009 (UTC)[reply]
if a small legal (chemical)analytical lab got a "DEA number" for handling chemicals of concern,
would every one in the lab(exept for janitors,guards,etc.)also need a "DEA number" to handle the chemicals? —Preceding unsigned comment added by 66.237.50.35 (talk) 04:18, 29 April 2009 (UTC)[reply]
Youtube video: Take a bottle of Mountain Dew, pour out all but about one quarter inch, put a very small amount of baking soda in, pour a bit of hydrogen peroxide in and shake, and it glows brightly. What's going on here? Is this just fake? If not, how does it work? Does it have to be this soda? Or is it carbolic acid that's needed or soemthing else in soda?--70.19.69.27 (talk) 04:41, 29 April 2009 (UTC)[reply]
Well, 99% of YouTube 'science' videos are faked - but this one could just maybe be real. Our Hydrogen Peroxide article says:
"Hydrogen peroxide is used with phenyl oxalate ester and an appropriate dye in glow sticks as an oxidizing agent. It reacts with the ester to form an unstable CO2 dimer which excites the dye to an excited state; the dye emits a photon (light) when it spontaneously relaxes back to the ground state."
Is there any "phenyl oxalate ester" in Mountain Dew? The amount of dubious chemicals they put in that stuff...anything is possible! But perhaps something else in the soda has a similar effect and is creating an artificial "glow stick"?
Another possibility (assuming the video is indeed a fake) is that I believe that Hydrogen Peroxide glows nicely in UV light - so perhaps they have a UV lamp illuminating the 'set' when they do the experiment. The baking soda makes it froth up nicely, the Hydrogen Peroxide makes it glow and the bright food coloring in the Mountain Dew gives it the vibrant color. That's a guess though.
There are a ton of youtube videos of this, all with lots of "it's a fake" comments. Either external light projected, which diffuses due to the cloudiness of the Dew or (more commonly suggested) another chemical is added (maybe glowstick material itself). DMacks (talk) 05:57, 29 April 2009 (UTC)[reply]
Yes - well, it wouldn't surprise me - as I said, there is this worrying trend that about 99% of so-called science videos on YouTube are faked. Most of the people who actually figure out the fake then go on to post fakes of their own instead of properly debunking the original video. Sad...very sad. I daren't ask how many kids are encouraged to play around with hydrogen peroxide in an effort to reproduce this. Anyway there are lots of videos where people try the exact same trick and it doesn't work - and just a couple which show someone adding contents of the inner tube from a glow-stick into the 'dew' and only then getting the same results. Since we know that hydrogen peroxide is one ingredient of a glow stick - then adding the 'missing' phenyl oxalate ester from a glow stick would indeed produce the effect we're seeing in the videos. So this is 'busted'. SteveBaker (talk) 12:51, 29 April 2009 (UTC)[reply]
Triboluminescence is a very dim light - and it requires physical force to be exerted. It happens when the candy breaks suddenly - there is a brief flash of light that you have to be in a totally dark room with dark-adapted eyes to see. What these videos proport to show is glowing that's visible in broad daylight - even after you stop shaking the bottle. Besides, explain how adding either baking soda or hydrogen peroxide would help that? No - it's not triboluminescence - it's an idiot with a video camera and too much time on his hands. SteveBaker (talk) 01:08, 30 April 2009 (UTC)[reply]
Hydrogen bonds
Chlorine is more electronegative than Nitrogen, so why doesn't it form hydrogen bonds? Is it because Cl has a larger atomic radius? Thanks. —Preceding unsigned comment added by 116.71.62.233 (talk) 07:43, 29 April 2009 (UTC)[reply]
Maybe I'm mis-understanding your question or the types of structures you're considering, but given that electronegativity means (casually) "holds its electrons tightly", it seems pretty intuitive that the more tightly an atom holds its valance electrons, the less likely/stable it would be to share them with an adjacent hydrogen atom. DMacks (talk) 07:49, 29 April 2009 (UTC)[reply]
And the answer from DMacks was: Because it is too electronegative to share an electron with a hydrogen. Have a look at electronegativity. The high electronegativity is one way to explain while certain elements "prefer" to make ionic bonds. TheMaster17 (talk) 08:47, 29 April 2009 (UTC)[reply]
I have to correct myself. I misunderstood what was a hydrogen bond in english. I thought it meant "covalent bond", but as a colleague of mine pointed out, it means the partially covalent binding that hydrogen can built to any electronegative atom (like the bond between the O in one water molecule to the H of another). I'm no chemist, but in my chemical training I was told that all partially negative atoms can form this kind of bound state with a hydrogen under the right conditions, so I would think that chlorine is perfectly fit to do so. Hmm, I'm suprised that DMacks as a chemist obviously also mixed up the terms. TheMaster17 (talk) 09:17, 29 April 2009 (UTC)[reply]
There are several inter-related effects involved, so depending on what you are comparing and unless you feel like really examining every detail, easiest to pick one that casually explains that one particular example. A more formal explanation (as always for (semi)covalent bonding) is whether your valence electrons are in n=2 or n>2, how many you have, and what your nuclear charge is, and these are observed as electronic effects such as polarizeability, electronegativity, bonding atomic-orbital overlap, atomic radius. They all correlate, but not really possible to pick any one as "the cause" of every example of any given effect. Electronegativity is a one of several good "rules of thumb" for patterns of hydrogen-bonding. Atomic radius as such is another that correlates with H-bonding, but seems poorer as a primary cause (per question as asked): electrons further out are less tightly held (further from the positive nucleus), so they should be more able to reach out and bond. It's virtually all really just back-rationalization of observations and the real reason is "because that's how it is", so we pick something that explains certain cases satisfactorily:( DMacks (talk) 13:36, 29 April 2009 (UTC)[reply]
Yes, but that's not what hydrogen bonding means - a hydrogen bond is (usually) a temporary intramolecular bond formed between polar molecules. Our hydrogen bond article says that hydrogen bonding occurs in compounds in which hydrogen is bonded to oxygen, nitrogen or fluorine. These elements have electronegativiies of 3.04, 3.44 and 3.98 respectively on the Pauling scale. The electronegativity of chlorine is 3.16, in between nitrogen and oxygen - so asking why hydrogen bonding does not occur in chlorine compounds such as HCl is a good question (and one to which I don't know the answer). Gandalf61 (talk) 13:30, 29 April 2009 (UTC)[reply]
N, O and F are all period-2 elements; Cl is in period-3, and is thus much more massive than the other three, which causes inter-molecular forces to be unstable because the tiny hydrogen nucleus cannot hold a Cl atom in place (note this is just my ad-hoc explanation which may or may not reflect reality, the real reason the bond is not stable could be determined by calculating the energies of the quantum-mechanical wavefunction). Truthforitsownsake (talk) 13:41, 29 April 2009 (UTC)[reply]
That doesn't make sense. A heavier atom moves more slowly making it easier to be bond to. That's the oposite of what you said. I think the mass of the atom plays no role here, but the size of the atom (clorine is about twice as big as a fluorine, for instance) may be important. Dauto (talk) 16:28, 29 April 2009 (UTC)[reply]
I think I still didn't get it: Chlorine is really unable to form hydrogen bonds, though it is strongly electronegative? What happens in organic compounds were chlorine sits at the border of the molecule, in contact to water as solvent? Doesn't it form even weak hydrogen bonds with the solvent molecules (as N,O and F would do in this situation)? This would be a fact to remember for me. TheMaster17 (talk) 14:12, 29 April 2009 (UTC)[reply]
I think I'll take a crack at it. Most of these are just educated guesses, but I think there are a few points to be made.
1.) The hydrogen itself must be bonded to an electronegative atom. This polarizes the H atom, giving it a partially negative charge. This partial negative charge helps create a temporary (transient) dipole-dipole moment with another electronegative atom.
2.) The chlorine (or whatever) atom itself is part of a molecule. Due to its electronegativity, it is polarized as well. In this case it's negative, however I believe it would not be as negative as a more electronegative element (like F) in the same position.
3.) In chemistry, there can be a lot of gray areas. Pretty much all molecular bonding is a mixture of covalent and ionic bonds, for example. The same can be true for hydrogen bonding. Indeed, the article lists a very large range of strengths (With molecular dynamics. I'm tempted to run some ab initio calculations of my own, although that would be OR). There is no hard line, and I imagine at the lower end, "slightly stronger van der Waals interactions" can be interpreted as hydrogen bonding, and vice versa.
4.) The hydrogen bonding article says that the H-bond has been shown to be partly covalent. If true, the better the overlap of orbitals, the stronger the covalent part of the bond. Hydrogen and fluorine overlap very well (1s-2p overlap). Hydrogen and chlorine overlap pretty well (1s-3p), but not as good as H-F (That's why HF is a "weak acid", but HCl is a strong acid - HF bond is so good, it doesn't want to dissociate). I think that this is a good explanation, but I'm lacking a bit of evidence at the moment.
So it all comes down to the point that HCl molecules should form hydrogen bonds but they dont. Why they dont form hydrogen bonds is a blur. Somebody contact the IUPAC. —Preceding unsigned comment added by 116.71.63.56 (talk) 07:28, 30 April 2009 (UTC)[reply]
Isn't this all related to whether HCl can "donate" hydrogen bonds or whether it can just receive them? Notice that HCl, HBr, HI, etc. all dissociate completely in solution and are all monoprotic acids. They all also interestingly, form gases at room temperature. H-F is a weak acid but is a liquid at room temperature. Sulfuric acid has two hydrogens, so still can donate hydrogen bonds after losing one, but are also weaker acids than the hydrogen halides (after H-F). Nitric acid boils at 83 C and has a pKa of -1.4, so maybe there's a trend here. I suppose the other idea is: how stable is an intermolecular HCl-HCl bond
I believe that's muddying the water a bit. It's not fair to compare carbon tetrafluoride to methylene fluoride, since methylene fluoride has a permanent dipole-dipole moment and carbon tetrafluoride does not. And methylene chloride/fluoride is not capable of having "hydrogen bonds" - the fact that the chloride has a higher BP can be explained by increased van der Waals forces (Cl is bigger and has more electrons).
When you ask how stable the intermolecular HCl-HCl bond is, that is exactly the point. This is not at all about 'true' (covalent or ionic) bonding, but about intermolecular forces where there exists 1.) A hydrogen bonded to N, O, or F. AND 2.) An N, O, or F on another molecule that is free to interact with the aforementioned hydrogen. And we've given it that distinction because they seem to be much stronger than other interactions.
So does the hydrogen in HCl interact with the Cl on another molecule? Yes. However, we've chosen not to call that a hydrogen bond since it would be relatively weak. The reasons I've outlined above are my best guesses as to why it would be so much weaker than say, HF, despite Cl still being fairly electronegative. It's obvious electronegativity is not the real explanation.
And just to point something out (and I believe SteveBaker likes to point this out sometimes): The concept of a hydrogen bond is a purely human concept. And in fact, especially in organic chemistry, all the explanations you hear are just rationalizations, and generally don't have any bearing on what actually happens (which is all governed by quantum mechanics). Nature doesn't care if our feeble minds can properly label everything and sort them neatly into boxes - it just does what it does. --Bennybp (talk) 23:47, 30 April 2009 (UTC)[reply]
(EC) This depends on your definition of "at risk". It seems the virus is able to be transmitted from human to human, so you can catch it without getting anywhere near pigs. But the prerequisite for this is that the other person is infected, and at the moment, the outbreaks are local and rather small in all countries except mexico (and the situation there is far from clear because a normal influenza is also circulating). TheMaster17 (talk) 08:54, 29 April 2009 (UTC)[reply]
Another important fact is that most people (outside of mexico at least) seem to get better rather quick. Why there seems to be such a contrast between mexico and the rest of the affected countries is a mystery, at least to me, at the moment. TheMaster17 (talk) 09:02, 29 April 2009 (UTC)[reply]
I don't find this puzzling at all. I have high confidence in the Mexican government's ability to count the bodies of the dead (that's the numerator). The denominator (the number of people in Mexico who've had this flu) is another matter entirely - Mexico city is absolutely huge, and the health care system is overwhelmed. As a result, one would expect an under-estimate of the denominator, giving a falsely high death rate. --Scray (talk) 11:22, 29 April 2009 (UTC)[reply]
And as the mexican administration had to correct even the number of deaths from the new H1N1 type A strain today, it seems they are unable to get any number correct. All calculations done so far are false. Now the new mystery (and also the real mystery in the past) to me is the complete naivness of the WHO. They have sparked significant panics all over the civilized world (you should hear what they are teaching here in germany at the schools: according to one teacher, the "new flu" is worse than the black death from medieval times...), because they obiously did not expect that the mass media would twist every word and number they release. But scientifically speaking, there is nothing near an EPIdemic ongoing at the moment, with the exception that the situation in mexico is unclear. So to use the word "possible PANdemic" in this connection is unfounded: Every year we have a "possible pandemic of flu", if the new yearly strains should acquire the required characteristics. TheMaster17 (talk) 12:04, 29 April 2009 (UTC)[reply]
There are really three versions of this kind of disease:
Swine Flu that only pigs get that can't be passed to humans - which has probably been around in various strains for millions of years - just like bird flu, cat flu and flu varieties for most other species on the planet.
Swine Flu that mutated so that humans could catch it from pigs but could not pass it on to other humans - perhaps it's been around for a while - it's hard to tell because people don't usually live in very close proximity to pigs, so not many people catch it.
Swine Flu that's mutated AGAIN so it can be passed between humans.
All of the concern with Bird Flu a few years ago was because that virus had just taken the step from (1) to (2) in countries where people habitually allow their chickens and ducks to wander through their houses. At stage (2), the disease is easily controlled - don't go near birds and you won't catch it - but the concern is that it's now only one mutation step away from the super-dangerous stage (3) when it can pass like wildfire from person to person.
So the huge concern is that Swine Flu appears to be in stage (3) right now. Worse still, many new diseases are much more lethal than older strains. That's because the virus cannot spread from a dead victim, hence, over time, diseases evolve to be less lethal so that they can spread more easily. A disease that's so mild that you don't even take a day off work spreads VERY easily. Hence there is significant evolutionary pressure on diseases that spread by coughs and sneezes to become gentler. Brand new diseases such as Swine Flu have not yet evolved that gentler nature - so for the first year or so, they can be very dangerous.
However, as others have pointed out - we know how many people have died (around 100 so far) - but we have no idea how many were infected and survived - possibly without any symptoms at all. If only 200 people were infected but 100 died - then with a 50% mortality rate, this would be a deeply scary disease. If a million people were infected but 100 died - then this is not much worse than a typical flu season and there is really no reason to panic. We still don't know where we are along that scale - so we're taking reasonable precautions until we know for sure.
This disease was certainly passed from a pig to a human sometime in the past when it was in stage (2) - but now that it's mutated into stage (3) - which must have happened inside a human - it's just a regular human disease and you're far more likely to catch it from another person than from a pig because the pigs can only have type (1) and (2) of the virus. To get type (3) they'd have to catch it from an infected human - and that's really unlikely! You need to be much more concerned about catching it from another person than catching it from a pig.
So in areas where the disease is rampant - avoid crowds - stay away from sick people - wash hands regularly, keep your hands away from your eyes, nose and mouth where possible (unless you've just washed them carefully). If you get flu-like symptoms, stay away from other people and call a doctor. However, those measures are far from 100% effective - the virus can hang around for quite a while on non-biological surfaces and people show no symptoms until they've had the disease in their bodies for many days...so these safety measures are only improving your odds.
No lower than for a person in a non-Muslim country that doesn't go near pigs. I would expect that cooking pork makes it safe to eat - it does with most diseases and I haven't seen any health warnings telling people not to eat pork. That this flu originally came from pigs is pretty much irrelevant at this point. It can pass from human to human - that's going to be by far the most common way people catch it from now on. --Tango (talk) 12:50, 29 April 2009 (UTC)[reply]
I think you've misunderstood. The disease came from pigs originally but now it's carried by humans.
For now any country that's not Mexico is pretty safe. However, it's entirely possible for someone infected to get on a plane and fly to any other country of the world and start a new outbreak. He would not have to bring a pig with him.
I'm not sure we can say how likely that is, we're not experts, and even the experts are still working on it. APL (talk) 12:53, 29 April 2009 (UTC)[reply]
Yes - that's well worth emphasizing - we have enough economic and societal problems as it is without people suddenly abandoning eating pork for absolutely no good reason! Flu is spread through respiratory processes - coughing and sneezing. Dead pigs do neither - they are perfectly safe. But as I said before - you're never going to catch THIS strain of swine flu from a pig anyway - even in the exceedingly unlikely event that it's coughing an sneezing all over you. The evolutionary step that enabled this disease to spread from human to human happened inside a human - not inside a pig. If a pig ever did catch this strain, they'd be getting it from the farmer! Really: right now, the only things to avoid is other people with symptoms - and (arguably) people who visited Mexico during the last couple of weeks. SteveBaker (talk) 13:17, 29 April 2009 (UTC)[reply]
Forget the "swine" part of it. Once it goes human-to-human the original vector does not matter. It's just "a flu", one that humans at the moment have no native resistance to. --140.247.251.93 (talk) 20:16, 29 April 2009 (UTC)[reply]
Of course they have "native resistance". While few people have had the opportunity to develop immunity, most human bodies are well equipped to fight (resist) such an illness. We can see this by the fact that the overwhelming majority of people who have had the illness have recovered. You may find it useful to read the World Health Organisation's FAQ, with particular note on the safety of pork products, and the fact that most infected people have merely displayed standrad flu symptoms and have recovered without medical treatment. Gwinva (talk) 22:33, 29 April 2009 (UTC)[reply]
What warning level does the WHO have to raise the alert to (already at 5 out of 6) for it not to appear rude to wear a mask when dealing with the public all day? Edison (talk) 23:24, 29 April 2009 (UTC)[reply]
Generally speaking, at level 5, i would think it's ok to wear a mask where ever u are in the world. I live in london and I am going to start wearing a mask in busy public places. —Preceding unsigned comment added by 80.47.226.203 (talk) 00:09, 30 April 2009 (UTC)[reply]
If you are not suffering from flu yourself, or are not actually caring for someone with flu then it's almost certainly pointless wearing a mask, and not particularly helpful. "The available scientific evidence does not suggest that this is an effective preventative measure". The influenza virus is not airborne, but passed by droplets (that is, from coughs, sneezes, runny noses) which requires contact. So, avoid direct contact with ill people and wash your hands frequently (along with other basic hygiene). Further info hereGwinva (talk) 01:05, 30 April 2009 (UTC)[reply]
Not all authorities seems to quite agree with that, for example the CDC [13] "You are well and do not expect to be in close contact with a sick person but need to be in a crowded place. Limit the amount of time you spend in these crowded places and wear a facemask while you are there." and [14]. It seems to me that after dealing with the public, if you wear a mask and carefully discard it each time (perhaps with gloves) and then wash your hands properly it may be somewhat effective if it's difficult to stop touching your face completely Nil Einne (talk) 12:18, 30 April 2009 (UTC)[reply]
IMHO, we would to well to follow current US government practices and call this the "2009 H1N1" flu - because calling it "Swine flu" is clearly confusing the general public - and since pigs and pork products are entirely unrelated to the problem - all we're doing is handing a bunch of farmers a problem they REALLY don't need right now! SteveBaker (talk) 13:32, 30 April 2009 (UTC)[reply]
Why in the world would we follow the US government? It's a worldwide issue, commonly known as Swine flu, it would be more confusing calling it "H1N1", no one has any associations to that name. It's not we who're causing problems, its not our problem that people are ignorant (and this they can't eat pork, because its widely reported that you can't get it from pork). Swine flu is the obvious Common name, I can only speak for the two languages I know and it's known as Swine flu (and translation) in both. chandler···13:40, 30 April 2009 (UTC)[reply]
I think Steve meant "we" as in people in general, rather than Wikipedia. Wikipedia's policies are clear - we use the most commonly used name. --Tango (talk) 14:21, 30 April 2009 (UTC)[reply]
firing an SCR
Hi, I am doing a project on controlled rectifiers. At some point, I have the output of an op-amp (+11v) to fire an scr. The gate current required to fire it is nearly 100uA. I believe the opamp isnt able to provide that much of current. Any idea what device to use to increase the opamp output current ? 218.248.80.114 (talk) 20:45, 29 April 2009 (UTC)[reply]
Calling all electronics design experts! Steve Baker? 100 microamps sounds like a minimal demand on an op amp. Most of the old ones I used could carry tens of milliamps. Which op amp? Which SCR? I have some in the basement if I could find them, but using data sheets is more of an approved "engineering" approach. [15] has a test circuit to make sure the device has not been accidentally fried (all too common in labs). Edison (talk) 23:16, 29 April 2009 (UTC)[reply]
You don't say whether you actually need the +11 V to fire the SCR, or whether a lower voltage would do. Assuming that you do need 11 V, you could use a CMOS device like the CD4050B. This device will output a voltage as high as the supply voltage that you give it, up to a maximum of 20 V, and it can source around 8 mA. The maximum input current is 1 uA, usually much less, so your puny op-amp could probably just about drive it. Like all CMOS-input devices, you have to be careful not to zap it with static. --Heron (talk)
1918 Spanish flu mortality
Can someone make sense of the following figures for me:
An estimated one third of the world's population (or ≈500 million persons) were infected and had clinically apparent illnesses during the 1918–1919 influenza pandemic. The disease was exceptionally severe. Case-fatality rates were >2.5%, compared to <0.1% in other influenza pandemics. Total deaths were estimated at ≈50 million and were arguably as high as 100 million.
Perhaps the numbers are including people killed by things like famine caused by the Spanish flu that might kill people who were not infected? 65.121.141.34 (talk) 20:54, 29 April 2009 (UTC)[reply]
which I read, suggests that it is not true. The 50-100 million figure does include deaths due to influenza, pneumonia, bronchitis, phthisis cased by the infection, but not secondary effects like famine etc. Anyone have easy access to the sources cited for the >2.5% estimate ? Abecedare (talk) 21:10, 29 April 2009 (UTC)[reply]
People surviving once and being re-infected again later - possibly mutiple times - before dying of it, may skew the results slightly. Vimescarrot (talk) 21:24, 29 April 2009 (UTC)[reply]
True, but each person would have to be infected 4-8 times, in order to make the numbers work. Seems unlikely, especially since infection by the (common) flu virus is supposed to provide temporary immunity. Abecedare (talk) 22:10, 29 April 2009 (UTC)[reply]
"had clinically apparent illnesses" - perhaps the mortality rate is computed using a figure for all infected, not just cases of "clinically apparent illness". But I don't know how they would estimate that. Rmhermen (talk) 21:58, 29 April 2009 (UTC)[reply]
The world population in 1918 was around 1.5Bn. So even assuming that everyone was "infected", 50-100million deaths would imply 3.3-6.7% mortality. Still significantly higher 2.5% ! Abecedare (talk) 22:10, 29 April 2009 (UTC)[reply]
our article indicates that morbidity and mortality rate estimates vary greatly. Not surprising, when there's mathematical disagreement within one source as quoted above! Gwinva (talk) 23:02, 29 April 2009 (UTC)[reply]
What is meant by the term "Case-fatality" in the OP's question? Might it mean that 2.5% of people who were under the care of a doctor (looking after their "case") died? Then it might not be surprising if 10% of the general population died if the vast majority could not get to a doctor. Perhaps the 2.5% refers to patients who were treated and their cases followed carefully. The remainder might be very hard to pin down to definite causes - hence the 10% to 20% uncertainty. But that's speculation. SteveBaker (talk) 01:01, 30 April 2009 (UTC)[reply]
I think the OP has identified a widely-quoted discrepancy that does need correction. The trick here is the ">2.5%". The "actual figures" are ten to twenty percent, which is indeed greater than two and a half percent. my guess is that basically all major countries has percentages greater than 2.5%, but some populous countries such as India and China had percentages that were MUCH greater than 2.5%. Our current knowledge of the 1918 epidemic is filtered through the perspective of the American and European reportage of the 1918 era, which focused primarily on American and European countries where the case fatality rates were closer to 2.5%. -Arch dude (talk) 08:15, 2 May 2009 (UTC)[reply]
effects of caffeine
Hopefully this question doesn't overstep the mark and creep into asking medical advice - which I know cannot be issued by wikipedians. If this question is unacceptable I am very sorry. The article on caffeine says its half life is approx 4.9 hrs in healthy adults. I am a healthy adult and my question is why don't the effects last that long? - as presumably you should still be feeling half of 'buzz' you originally got 4.9 hours after you ingested it. After a less than 2 hours I seem to be back to normal. This is the case for many other people I know as well. Is there any reason why people stop feeling the effects before the caffeine has even had a half life? I don't consume caffeine excessively, 2 cups of tea a day at most so I wouldn't say I have a high tolerance to caffeine. Many thanks and I hope someone can shed some light on the subject! —Preceding unsigned comment added by 92.16.11.107 (talk) 21:33, 29 April 2009 (UTC)[reply]
I would expect that the half-life is not necessarily a reliable indicator of the amount of time it will 'noticeably' have an affect on the body when asking a person. For instance many people will wake up the morning after a night of drinking and feel perfectly fine, but if tested they may well still be over the limit. What they 'feel' is 'normal' but what they are is still showing the effects of alcohol consumption. Hopefully someone will be able to clarify for you though, would be interesting to know ny156uk (talk) 22:36, 29 April 2009 (UTC)[reply]
The "half-life" probably refers to the detectable amount in your system. That isn't the same as the amount bound to receptors and due to weakening action potential that again doesn't equate the same effect. 76.97.245.5 (talk) 23:41, 29 April 2009 (UTC)[reply]
It's of note that my doctor told me that since I have sleep-related problems I should really stop drinking caffeine around 2pm, because otherwise there will still be appreciable amounts kicking around my body come 11pm, leading to some of the effects albeit in obviously weaker form. Enough to keep you from falling asleep? Maybe if you are sensitive to it. (I don't think I'm actually all that sensitive to it, and that my sleep issues are unrelated to it, but anyway, it makes some sense, and I have cut back.) --98.217.14.211 (talk) 02:09, 30 April 2009 (UTC)[reply]
Hello, I need help. I would like to know how to solve the following question, what Geometry/Physics you need to know for it.
A satellite is launched into a circular orbit around a planet with negligible radius in a direction tangent to the orbit at a distance R, and another satellite is launched with half the velocity of the first one. What is the minimum distance between the planet and the satellite during the orbit, in terms of R? —Preceding unsigned comment added by 173.66.142.5 (talk) 23:17, 29 April 2009 (UTC)[reply]
I haven't found this in our article, but what causes a tree/shrub to be suitable as a plant for a hedge. a} I had read before that trees that you trim the top off die. Why isn't that happening when I trim e.g. a birch to be a hedge. b) Would fig trees work and could you still get figs from them if it were trimmed to be a hedge? 76.97.245.5 (talk) 23:47, 29 April 2009 (UTC)[reply]
There are several factors that are involved when deciding how suitable a plant is to be a hedge. Of some importance would be the plants ability to be trimmed on a regular basis. most plants can survive this as long as it is started when the plant is relatively young. Some plants, for instance some pines, will not reshoot if cut back, especially if they are old plants. On the other hand there are many plants, lonicera, privet, hawthorn which will shoot back when trimmed severely, allowing radical shaping and control. Some plant will never look good as hedges, fig for instance with its large leaves and irregular stems is hard to imagine as an attractive fence (but there’s no accounting for taste). Finally it would be best if the plant did not sucker and spread like bamboo or some species of sumach a predictable, controllable hedge is probably preferable. Birch trees are really not dense enough nor vigorous enough to make a satisfactory hedge. A fig might work but my experience with figs is that to get reasonable fruit requires watering and this leads to excessive leafy growth unless the roots are restricted. That is why they are often grown in a large pot or tub.Richard Avery (talk) 08:07, 30 April 2009 (UTC)[reply]
When trimming becomes difficult and the hedge is getting too high, it is common practice to "lay" the hedge by partly cutting through stems and bending them to a horizontal position, thus stimulating new leafy growth at a lower level. It is still true that some trees are not suitable for this process because they do not readily produce new shoots from old trunks. Dbfirs08:20, 30 April 2009 (UTC)[reply]
The key to trimmability is whether apical meristem tissue remains in the untrimmed part. If you cut off the top of a mature tree, for most species it just stays that way. But some species have lots of meristem tissue staying quiescent (because auxin hormones tell them to) and when they realize they are now at the top/outside of the plant, they begin the process of tissue growth (sprouting). That's what makes a good hedge plant. Younger sprouts are good candidates for developing a hedge, because they have lots of meristem tissue - so if you clip off a very young branch, you will often get two more in its place. Good candidates for hedges (in cold climates anyway) are cedar and alpine currant, because they have that property of multiplying when trimmed. Franamax (talk) 19:54, 30 April 2009 (UTC)[reply]
Thanks. I'll see where I can get with the shrubs/trees we have available. (BTW. I meant beech instead of birch, keep mixing those up unfortunately.) I was thinking it would be silly to rip out the wild shoots that keep cropping up all over our yard and then going out spending oodles of money on plants for a hedge from a nursery. On the other hand I didn't want to invest all the work in digging just to have the things shrivel and die. The info on apical meristem tissue was what I was missing. (We're in Atlante and the general rule on gardening here seems to be that everything you don't want grows copiously whereas intentionally planted stuff gets crowded out and dies.;-) 76.97.245.5 (talk) 06:15, 1 May 2009 (UTC)[reply]
April 30
Envying the Chimps
You mean to tell me what with all of the lifting, the protein shakes, and the basically looking more badass—I will never be stronger than a CHIMP? How does this work? These things are eating berries and ants they poked out of mounds with twigs—and they certainly aren't going to the gym. Are their muscles simply more efficient?
I'm sorry, this is going to be a lot of questions—clearly chimpanzees have been on my mind lately.
Is there any downside to this demonic strength?
Why haven't humans evolved this kind of strength? Even with all of the intelligence and what have you, a human could still be a real lady's man with that kind of virility. Did humans and chimps evolve from a shared beastly ancestor—and humans just lost it? Or did we just never evolve it in the first place?
And—are apes unique in this respect? Or are humans just the weaklings of the animal kingdom? I've never noticed, say, a dog, having a surprising amount of strength (not that they're weak, but it doesn't seem like they are deceptively strong).
In part, it's a matter of geometry - the shape of their bones and placement of muscles are different from ours. We have grace and dexterity plus endurance that a Chimp simply cannot match. We're simply engineered for a different job. SteveBaker (talk) 00:53, 30 April 2009 (UTC)[reply]
Perhaps because calories used for muscle could be better used for a large brain. A brain allows better development of tools and cooperative hunting, which is a much greater force multiplier than more muscle strength. Particularly when the strength becomes a moot point at some level. Domesticating plants and animals takes it to a whole other level.
You also ask about virility in comparison. That's always going to be a relative measure. In the past few generations, strength has been relatively unimportant, beyond a certain minimum. The fact that humans are less strong than chimps, gorillas, orangutans, etc. (but we are stronger than many other primates) suggests that for much of our evolution, other factors were more important than pure strength. This actually opens two questions that I don't know the answer to: 1) what's the average daily caloric intake of a chimp, and 2) are physically stronger chimps often the alphas, or is that a weak measure. An orangutan consumes between 4000 and 8000 calories a day (minus about a thousand to two-thousand for a female).
Maybe the real answer to why more men aren't more ripped is that 1) it's hard, and 2) it isn't as good at attracting women as one might assume. Shadowjams (talk) 05:57, 30 April 2009 (UTC)[reply]
Your body isn't fundumenltally incapable of making you look like a body-builder when you're actually a couch-potato. It just doesn't bother unless it thinks you need the extra muscle. — DanielLC14:55, 30 April 2009 (UTC)[reply]
That's true of strong humans too. I've see a picture (which I can't seem to find) comparing bodybuilders with olympic weightlifters. The latter just looked fat. — DanielLC14:55, 30 April 2009 (UTC)[reply]
Smoothing capacitor advice
Can I ask for some kindly advice on smoothing capacitors, please. The scenario is, the ancient gas heating system in my house causes four seconds or so of nasty RFI, affecting my BBC Radio 4 listening pleasure, each time the (presumably) thermostat decides to switch the system on or off. Changing the whole system is out of the question, sadly. Do you think I have any realistic options in terms of suppressing the RFI? Is this a scenario amenable to smoothing capacitors or some other sort of RFI suppression? If so, is it possible that such smoothing could be done at the AC source to the unit, or is it more likely that it would have to be done local to the thermostat? thanks. --Tagishsimon(talk)01:30, 30 April 2009 (UTC)[reply]
Have you determined where exactly the RFI originates? Does the furnace have a standing pilot or does it ignite the gas with an electric arc from a transformer? That would be a potent source of RFI. Is it a relay or contactor, which should not be creating RFI all that long. Is the RFI reaching your receiver through the electric supply lines or through the air? If you can herer it outside on a battery AM radio, it is likely through the air. There are ways to reduce if not eliminate RFI. Is an AM or FM station? The BBC Radio 4 article says they broadcast FM, AM and other modes, not to mention Internet streaming audio and satellite, which should be less affected by RFI. Capacitors and inductors of various sorts can be used as a filter to block the RFI from emanating from the source, or can be used to filter it from reaching a receiver. For FM (or AM) an external antenna might increase the signal strength and lessen the impact of the noise, as could re-orineting the antenna on the receiver (unless it is coming to the circuit through the mains). The BBC has RFI information at [16] and [17]. Note that if the BBC finds you are causing interference to neighbors, you may be compelled to get the source of interference fixed. Edison (talk) 02:47, 30 April 2009 (UTC)[reply]
The heating system is using A/C power - so nothing as simple as a capacitor is going to work. There are circuits you can buy to reduce power spikes coming from equipment like that - you very often find them sold by computer stores. If your radio is picking up the interference that way - then plug the radio into one of these gadgets and the problem should go away. However, as Edison points out - if this is radio interference - then it's a tougher problem. Sometimes you can screen out the interference by wrapping the source in some kind of shielding (see: Electromagnetic shielding, Faraday cage and mu metal depending on the frequency range). I've successfully shielded the motor on my freezer from producing RFI spikes (long story!) by wrapping it in a few layers of fine-meshed chicken wire and earthing that to the houses' earth wiring...but it's one of those 'black art' things - sometimes you get lucky - sometimes you don't. But the first step is definitely to try a battery powered radio and thereby discover whether this is a power supply spike or a radio-signal spike. SteveBaker (talk) 13:23, 30 April 2009 (UTC)[reply]
Steve, I would really like to have a tour of your house someday. By the time that happens, you will probably have whipped up a gravity-field generator so you don't get dirty footprints in the hall! :) Franamax (talk) 20:03, 30 April 2009 (UTC)[reply]
Have a look at Problems Thermostats Can Cause to Television and Radio Reception on the Radiocommunications Agency's website. Appropriately, the URL begins "www.ofcom.org.uk/static". It says that thermostats are supposed to be fitted with suppression devices, but perhaps yours is too old to have one. You will find more useful stuff if you Google "boiler intereference suppressor". --Heron (talk) 17:40, 30 April 2009 (UTC)[reply]
This depends on your definition of a fart and a burp. If you mean "expel gas from the anus", then a bird can (and does) fart. If you mean "make a loud fart noise from the anus", then a bird will not fart primarily because the bird's intestines are too short and the food passes through them too quick to get enough gas buildup to produce the expected fart noise. Basically, a bird expels a tiny bit of gas rather frequently instead of a lot of gas every now and then. As for burping, it depends on "allowing gas to escape from the stomach through the throat" or "making a burp noise". Birds do not have the biological structures to make a burp noise the same way that humans do. However, birds can (and do) vomit. When they vomit, excess gas is released. Because vomiting is something birds can do easily, they are able to release any excess gas with ease. Again, they are able to release a tiny bit of gas frequently instead of releasing a lot of built up gas every now and then. -- kainaw™03:33, 30 April 2009 (UTC)[reply]
Hello. If the volume of an ideal gas at absolute zero is nothing, then shouldn't the matter occupy some space? I realize that absolute zero is an unattainable limit and that no known substance has a boiling point less than 0 K. However, I am looking forward to a theoretical answer. Thanks in advance. --Mayfare (talk) 05:23, 30 April 2009 (UTC)[reply]
Well, you've just given a totally convincing proof that no real gas can behave like an ideal gas all the way down to absolute zero. An ideal gas is simply an approximation of reality. Looie496 (talk) 05:42, 30 April 2009 (UTC)[reply]
And of course all gasses except (I think) helium are solids well before you get down to absolute zero...and of course the laws of thermodynamics don't allow us to actually reach absolute zero. Nature is very good at covering up zeroes and infinities in our equations! SteveBaker (talk) 13:11, 30 April 2009 (UTC)[reply]
It depends on the pressure, but I think all gasses are at least liquids before they get to the zero-point, the smallest possible temperature which is slightly above absolute zero. — DanielLC14:44, 30 April 2009 (UTC)[reply]
As far as I know the zero point (ground state) is absolute zero by definition. It is a reachable state in principle in quantum mechanics because any (bound) system only has finitely many energy levels. It can take an insanely long time to reach the bottom (like 101000 years, to invent a number out of nowhere), but it's a finite time. It can also happen very quickly (like a lone hydrogen atom). I suppose the absolute-zero version of a gas would be a perfect Bose–Einstein condensate or fermionic condensate, not that I really know anything about this. -- BenRG (talk) 18:51, 1 May 2009 (UTC)[reply]
Everyone already jumped on this one, but to restate it: an "ideal gas" is a mathematical fiction. It is a heuristic idea based on the fact that "real gases" behave like "ideal gases" at most normal conditions. Only at very high pressures or very low temperatures do the difference start to show up. However, the assumptions one makes for an ideal gas are demonstratably false and even internally inconsistant. For example, the concept of an ideal gas assumes that individual molecules have zero volume. Even if a zero-volume particle was possible, how would it collide with other zero-volume particles? They would have no surfaces to bump, and yet Kinetic Molecular Theory demands that particles must collide and rebound off of each other. The concept of an ideal gas is useful because differences between the predicted behavior of an ideal gas, and the actual behavior of a real gas, are so small as to be practically unmeasurable under anything close to room conditions. See Van der Waals equation for the equation that applies to "real gases" as opposed to "ideal gases". --Jayron32.talk.contribs03:56, 1 May 2009 (UTC)[reply]
The ideal gas model doesn't demand that gas particles bounce off of each other, in fact it assumes that they don't. It does demand that they bounce off the walls, though. I assume the original poster is thinking of PV = nRT. When T = 0 that reduces to PV = 0, but that doesn't mean V is zero, it means P is zero regardless of V. The reason for that is simple: the particles aren't moving, so they don't bounce off of anything, so there's no pressure. That's not correct in quantum mechanics, though, where a particle in a box still pushes on the walls even in its lowest energy state (because of the uncertainty principle). -- BenRG (talk) 18:51, 1 May 2009 (UTC)[reply]
ALIENS
Ok i can all ready see people looking at the title and thinking OMG not again but bare with me...I would like to ask if we are looking for ET with boddies like [[19]] How do they think they will detect alien life? i understand the idea of looking for radio signals ECT...is there any thought on say how a non-carbon based life form may comunicate? what type of gas in the atmosphere would they give off meaning type of vegatation on a non carbon based world say if it was made of siliconm a common thought that i have heard of; what type of gas would it give off if burned do we look for the tell tail signs of these during the search or do we just look for the humanoid version of an Alien? —Preceding unsigned comment added by Chromagnum (talk • contribs) 09:02, 30 April 2009 (UTC)Chromagnum (talk) 09:03, 30 April 2009 (UTC)[reply]
Have you read the SETI article that you link to? It explains what they are looking for, what assumptions they are making. At the distances they are looking they cannot detect things like atmospheric gas on individual planets or anything like that. --98.217.14.211 (talk) 09:53, 30 April 2009 (UTC)[reply]
Actually, looking at the spectrum given off by a planet to see if there is oxygen in the atmosphere is something exoplanet hunters are either doing or planning to do in the near future (I'm not sure which). --Tango (talk) 10:01, 30 April 2009 (UTC)[reply]
Can they resolve extrasolar planets to that resolution? At the moment I have not seen any indication that they can, even with gas giants. --98.217.14.211 (talk) 10:08, 30 April 2009 (UTC)[reply]
You don't need any particularly high resolution to analyse a spectrum. The difficulty is getting the spectrum of the planet separate from the spectrum of the star, which is what they are currently working on. --Tango (talk) 10:22, 30 April 2009 (UTC)[reply]
There are just a few extrasolar planets that are sufficiently large, bright and far away from their parent star that we can image their light separately from the star and get their spectra directly...but those are few and far between - and they are such odd-ball planets that we're not likely to find life on them anyway. (No possibility of liquid water, etc). Fortunately, analysing the spectrum of a star is very easy - a routine matter for astronomers. So what they have to do is to watch how the star wobbles as the planet moves around it to figure out how fast the planet is moving and where it is in it's orbit - this is difficult - but we're getting the hang of it and we know the orbital periods of all 350 or so planets that we've found. Once you know that - you can (in principle) detect the subtle changes in the light reflected from the planet. When the planet is behind it's parent star, it's light is missing from the stars' spectrum. When the planet is in front of the star - its light is added to that of the star. By subtracting the spectrum when the planet is hidden from when it's in view you can theoretically eliminate the contribution of light from the star itself - so what you have left is just the spectrum of the planet. Then they can look for peaks or troughs in that spectrum to estimate the gasses present in the atmosphere. This is an exceedingly difficult thing to do - the amount of light from the planet is utterly dwarfed by that of the star - and not all extrasolar planets are 'eclipsed' by the star from our perspective (we could be looking the solar system from 'above' for example). So we can't do this for all extrasolar planets - and for those that are eclipsed, the measurements have to be taken over a long period of time and they have to be amazingly accurate - this may mean measuring the spectrum from the star for years in order to accumulate enough light to do this subtle calculation. For earthbound telescopes, where the light is first filtered by our own atmosphere, it would be easy to mistake changes in our atmosphere's absorption over time for changes from the star and its planets - and we'd end up merely measuring biologically active gasses in our own atmosphere changing from summer to winter or depending on the wind direction or whatever! Hence, we need big, expensive space telescopes to do this work. SteveBaker (talk) 12:12, 30 April 2009 (UTC)[reply]
I don't think the wobble method is much use for this. To get a noticeable wobble you need a large planet close in. For life you need a small planet far out. The transit method, detecting the drop in light from the star as the planet transits across is, is far more likely to find Earth-like planets (which is where we would expect to find human-like life, which is the only type of intelligent life we have any evidence to suggest exists). Subtracting the star's spectrum from itself at different points in the planet's orbit is certainly one way of getting the planet's spectrum. I believe another way is to use the Doppler effect - the planet is moving in relation to the star so its absorption lines will be shifted compared to those of the star. Since the radial (from the perspective of Earth) motion varies during the orbit, those lines will move around. If you see an oxygen line moving around in a star's spectrum, that's evidence for a planet with an oxygen atmosphere (especially if you already know there is a planet with that orbital period, which you presumably would otherwise you wouldn't be looking that closely at the star's spectrum). --Tango (talk) 14:20, 30 April 2009 (UTC)[reply]
So many questions! Let's take them one-by-one:
Ok i can all ready see people looking at the title and thinking OMG not again - Actually, we RD folks secretly love these kinds of question. So much better than "How makes babby?".
How do they think they will detect alien life? - Really there are three approaches:
Hoping that the aliens are capable of detecting us from our feeble communications or the signature of advanced civilisation in our atmosphere (oxygen plus steeply rising CO2 levels for example) and sending us unmistakable narrow-beam communications (either laser or radio). Since our civilisation is fairly young - the aliens would have to be pretty close. We've only had the kind of advanced technological society that they might be able to detect for perhaps 200 years. So they'd have to live within 100 lightyears of us for our existence to have been noticed and for the message from the aliens to have reached us. There really aren't that many stars as close as 100 lightyears away. If only 10% of those have planets (which seems likely from extrasolar planet hunting) and only 10% of those are able to support life - it's pretty unlikely that we're going to be hearing from one of these civilisations for a few hundred years yet. However, in another 200 years - aliens as far as 200 light years away will have hopefully noticed us - and that would be 8 times as many potentially habitable worlds...so the longer we wait - the more likely someone will try to talk to us. But who knows? Perhaps there is this vast galactic civilisation - which (like on StarTrek) have rules that forbid them to talk to us until we try to talk to them? We aren't making much of an effort to do that right now.
Imagining that the aliens have hugely powerful radio transmitters (much, MUCH more powerful than our own) and are broadcasting in all directions at once. Remember - if you took the most powerful radio transmitter humans have ever built - and put it on a planet orbitting the nearest star (just 4 lightyears away) - we'd be completely unable to detect it with the most sensitive radio telescopes we have. Since the strength of radio signals reduces as the square of the distance - at distances like 400 light years - we'd need the aliens to be broadcasting at more than 10,000 times the power of the best transmitter we can build! That's asking a lot. Recall how hard it is to measure the spectrum of light reflected from an extrasolar planet? Detecting their communications comes down to the same thing - we have to detect changes in the spectrum of all the electromagnetic radiation coming from their planet - against the background of this honking great star which is putting out billions of times as much. So for us to notice that - the amount of light their system is putting out has to be around the same as their entire planet reflects naturally. Put another way - if their 'transmitter' is able to produce that much energy - it would need a solar power station that covered their entire planet to make it work! This is a very hard thing to expect the aliens to do! Of course if they took the trouble to beam that energy directly at us - they'd need a lot less - but now were back to scenario (1) above - where they have to know where we are before they can talk to us.
Hoping to detect their chemical 'signatures' in the atmosphere of extrasolar planets (see my preceeding answer).
Sadly, two out of the three of those possibilities assume that these are aliens that are much more scientifically advanced than us - and who are interested in talking to us. The third option is actually much more promising because it detects life rather than intelligence - and would allow us to send narrow-beam messages to them.
...is there any thought on say how a non-carbon based life form may comunicate? - Well, for starters, it's really not clear that sufficiently complex molecules can exist based around non-carbon chemistry. The nature of carbon is such that it makes much more complicated molecules than any other element. So it seems highly likely that all 'natural' life will have carbon chemistry. However, we could imagine a carbon-based culture such as ours inventing sophisticated robotics and artificial intelligence - then dying out leaving the computers in charge. That would result in a non-carbon civilisation. But there is no reason to assume that life based around other kinds of chemistry would be communicating any differently than we imagine. There are really only just so many things you can do. All communication over those distances needs to be with light or radio waves - and those waves have to be sufficiently different from 'natural' source that the recipient could find them. So what SETI are looking for is not a very specific kind of signal - but ANY signal that doesn't have the characteristics of a natural source.
what type of gas in the atmosphere would they give off meaning type of vegatation on a non carbon based world say if it was made of silicon - As I said - I don't think non-carbon-based life is possible. However, a 'second generation' civilisation (life as in: computers/robots/AI) might exist in deep space - not on a planet at all - or it might exist somewhere like on our moon - where there is no atmosphere at all. So such a civilisation would be impossible to detect unless it WANTED to be detected. In that case, who knows what advanced technology it might use to change the atmosphere of a nearby 'junk planet' to say "LOOK! HERE WE ARE!" - but if they are doing it right - we'll know it when we see it.
what type of gas would it give off if burned do we look for the tell tail signs of these during the search or do we just look for the humanoid version of an Alien? - For "Life as we know it", we can look for oxygen. Oxygen is a chemically reactive gas. Without plants around to make more of the stuff - it would pretty soon get used up by (for example) rusting iron or burning carbon to CO2. If we find oxygen out there - that's a pretty strong sign. There are other signature gasses to look for - methane for one - but we've found that in the Martian atmosphere - and so far, no little green men have appeared to issue traffic violations to our mar rovers. The problem is that one has to be skeptical - and there are always complicated explanations other than life for phenomena we see in planetary atmospheres.
What's difficult here is that there are three kinds of possibilities: "Life as we know it" - carbon-based, needing liquid water and oxygen - and with something like DNA so it can reproduce and evolve. "Life as we don't know it" - things like robotic civilisations or beings floating in the cloud layers of gas giants or based on weird chemistry. But there is also the possibility of "Life as we don't know it AND CAN'T IMAGINE IT" - since we can't (by definition) imagine it - we can't say anything meaningful about it - we just have to hope that we'll know it when we see it.
Here is the question. Can anyone help me out with the answer and also give an explanation.
When dangerous chemicals are transported by road, vehicles must carry signs that indicate what measures should be taken in the even of a spillage of the chemical carried.
Which material must be used if there were a spillage of metallic sodium?
Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.
We're not allowed to give you the answers to homework questions - but we can give you ideas about where to look. In this case, it's pretty obvious: You can definitely find the answer in our article on sodium. SteveBaker (talk) 11:54, 30 April 2009 (UTC)[reply]
I would say the same arguments for homework apply to self study of this sort. Note even if it's not a past exam it could be self study from an example question book or whatever Nil Einne (talk) 12:31, 30 April 2009 (UTC)[reply]
How do we tell if a feature of a living creature is a violation of nested hierarchy predicted by common decent or from convergent evolution? —Preceding unsigned comment added by 121.241.167.100 (talk) 11:55, 30 April 2009 (UTC)[reply]
Imagine a creature with traits (and ideally, gene sequences) very similar to a wide variety of taxa. Provided you could rule out lateral gene transfer, a creature with some genes that are similar to those which evolved separately in different orders of mammals, for instance, would undermine an otherwise very well developed taxonomic tree rooted in evolution. The trick would be to show that each gene evolved subsequent to the divergence of the order. Suppose you found an animal with gene sequences from dogs, bats, and whales. If you could show that the common ancestor of each of these did not have the traits you found, but subsequent species from the various orders, you'd have shown our understanding of the evolution of mammals is very doubtful. This would be shown very well if you could examine neutral sequences (those not under selection) to rule out homoplasy as well.
There are many lines of evidence that point to evolution of which the tree is only one, but undermining such a tree would be enough to give anyone pause, perhaps enough to make people question evolution. Find such an animal and people will have to do some rethinking, to be sure. (You may be asking for a Popperian falsification, but those don't really exist anywhere in science, by the Duhem-Quine thesis; but through removal of supporting evidence, as described above, you can make something seem very unlikely.) --TeaDrinker (talk) 13:19, 30 April 2009 (UTC)[reply]
The ultimate way to tell is by looking at the genome. If a common feature results from common descent, the genes responsible for producing it are likely to be very similar. If it results from convergent evolution, they are likely to be quite different. There are other less certain approaches, but that's the ideal way to do it (short of tracing out the fully ancestry). Looie496 (talk) 15:39, 30 April 2009 (UTC)[reply]
Without genetics, it's really hard to tell in some cases. Consider eyes - for example. Eyes appear to have evolved quite independently in half a dozen different branches of the evolutionary tree. This is convergent evolution - vision is useful - and there are only just so many ways of capturing light and handing it off to the brain - but even so, the resulting eyes are fundamentally different from each other. However, you find differences even when divergent evolution is happening. The eyes of cats have slit-like pupils and dogs have circular pupils. Did cats and dogs evolve their eyes separately from each other? No...we can find fossil mammals that are the clear ancestors of both dogs and cats that clearly have eyeballs - so this must be divergent. But the common ancestors of (say) mammals and octupii or mammals and insects - were blind - so that must be convergent. You have to consider the whole organism and other features than the one you are looking specifically at. At the genetic level - one assumes that the genes for producing vision in octupii would be very different from those in cats and dogs - and we'd assume that the vision-related genes of cats and dogs would be almost identical. The odds of independent/convergent evolution of identical genes is a matter of statistics - it's very unlikely that convergence would produce identical genes since so many tiny variations on that gene work just as well. So if the same basic feature of two lifeforms have a totally different genetic basis - then we should assume convergence - if the genetic makeup is mostly identical - but with a few tiny differences - then divergence is more likely. SteveBaker (talk) 15:44, 30 April 2009 (UTC)[reply]
To give the context of my question, I asked it after I saw this [21] article.
A post here [22] described it as "Chromosomal sex determination in the platypus discovered to be a combination of mammal and bird systems. The resemblance to birds is now more than just superficial."
First, I am not sure if that's what the article is saying, are they saying that platypus chromosomal sex determination is similar to birds or different from both mammals and birds?
Second, does either scenario pose a problem for nested hierarchy?
Lastly, you said "...This would be shown very well if you could examine neutral sequences (those not under selection) to rule out homoplasy as well"
I am not sure I understood that, could you clarify with an example? Say the platypus' chromosomal sex determination is similar to birds, how would one go about showing they evolved the trait independently? How would neutral sequences show this? —Preceding unsigned comment added by 121.241.167.100 (talk) 16:08, 30 April 2009 (UTC)[reply]
It is almost certainly convergent evolution. The only proof of that would be to show that the most recent common ancestor lacked the feature, which isn't possible. The reason it seems almost certain is that the evolutionary distance between bird and platypus is huge -- their lineages diverged around 350 million years ago. Basically, all four-legged land animals except amphibians date back to that same divergence point (the split between synapsids and diapsids) -- so if birds and platypus have a common feature, but other land animals lack it, it is very likely to arise from convergent evolution. Looie496 (talk) 16:23, 30 April 2009 (UTC)[reply]
With reference to the blog that you linked to, perhaps you could clarify the question you have in mind. What "feature" or "trait" are you referring to? Sex determination? You might find some explanation of your questions here (http://www.ncbi.nlm.nih.gov/pubmed/18983263). In any event, the paper that is referenced in the blog (and the discussion of its implications) are getting a bit dated (2006!!!). They've recently published the Platypus genome sequence (http://www.ncbi.nlm.nih.gov/pubmed/18464734), which in comparison to other species is beginning to shed some light on this fascinating critter!
In regard to your most recent questions, 1) Platypus sex-determination is more similar to birds (which use the ZZ-male/ZW-female system) than primates/rodents/marsupials (which use the XX-female/XY-male system). Not the same as birds, mind you -- the platypus has a really funky chain of small chromosomes that were called X1, X2, X3, X4, X5, and Y1, Y2, Y3, Y4, Y5. The unfortunate use of the same letters to designate the chromosomes doesn't mean that there's any DNA homology between the Platypus X and Y and the X and Y of placental mammals. 2) I don't really see a problem for "nested hierarchy" here. I'm certainly not an expert in the field, but the genome evidence seems to support that the lineage leading to the modern-day platypus diverged somewhere after the reptile/avian branch and before the marsupial/eutherian branch. --- Medical geneticist (talk) 18:13, 30 April 2009 (UTC)[reply]
What are the products of the reaction of sodium with Sand
Hi, can anyone tell me what sodium produces on reaction with sand? I am so confused and I am skeptical whether they react at all.... —Preceding unsigned comment added by 123.49.43.236 (talk) 12:08, 30 April 2009 (UTC)[reply]
P.S. In case it wasn't obvious, this wasn't a genuine question, rather I was posing the question to the OP to help get them thinking how they can answer the question Nil Einne (talk) 18:26, 30 April 2009 (UTC)[reply]
As I explained in my answer to your previous question - you can definititely find the answer to your original question in our article on Sodium. The article speaks very specifically about how water reacts with sodium (short answer: KABOOOOMMMM!!!!) and in the section called "Precautions" it tells you precisely the answer to your original question - if you understand a little chemistry already - then there is a strong clue in the very first introductory paragraph. If you are going to learn - you have to study by reading articles and finding the information from them. If we spoon-feed it to you, then you learn NOTHING and will not be as successful in life as you otherwise would. We're doing you a favor by not answering this one! SteveBaker (talk) 15:30, 30 April 2009 (UTC)[reply]
Sand usually consists of silicon dioxide (there might be other types, but these are rarer). If there is also air, sodium at first will burn, producing sodium oxide. If there is no air, but there is elevated temperatures, there might form sodium silicate and sodium silicide). Similar process (using magnesium instead of sodium), seems have been used to produce silicon or silane (by reacting silicide with acid). Also, sodium oxide will react with silicon dioxide (not sure about temperature requirements) producing sodium silicate. -Yyy (talk) 16:56, 1 May 2009 (UTC)[reply]
(EC) I want to know how come some people can't use the search box to the left which also has its special page here; or use Google, Live Search, Yahoo or whatever to find out article on photon probably taking less time then it takes to write out "I want to know about the nature of Photon". Guess neither of us will ever know... (edit: or perhaps I was wrong about your case) Nil Einne (talk) 13:58, 30 April 2009 (UTC)[reply]
Hey, that's a little unfair. I've been reading about photons all my adult life and I still don't understand their nature. --Sean14:54, 30 April 2009 (UTC)[reply]
But that's the point though isn't it? The question is unfocused and suggests either 1) The person has read all there is to know but is so hopelessly they don't know what to ask OR 2) The person hasn't read much, probably not even our article hence they asked so an unfocused question and our article is a good starting point, a starting point they could have more easily found themselves say if they knew how to search (hence I taught them how even if in not quite the most civil way). or perhaps 3) The person just has poor English or otherwise doesn't know that if they ask a generic question, they get a generic answer. I know which one I'm betting on... Nil Einne (talk) 18:21, 30 April 2009 (UTC)[reply]
Sadly, yes - RTFA. Check out our article: photon - if there is anything you don't understand, follow links until you find something that explains what you don't understand. If you have a more specific question, we'll try to answer it. SteveBaker (talk) 15:23, 30 April 2009 (UTC)[reply]
Karrick Process
I have read the articles for Karrick Process and also for pyrolisis. From what I can tell, the two are the same thing. Could someone perhaps explain to me how they are different? 65.121.141.34 (talk) 16:19, 30 April 2009 (UTC)[reply]
Sure. Pyrolysis is the general term for any decomposition via heating. The Karrick process is a specific pyrolysis reaction applied to coal. The concept of pyrolysis is a huge idea, and covers lots of chemical processes. The Karrick process is a specific application of a specific pyrolysis reaction. The difference is that one is a general class of chemical reactions and the other is a specific reaction. --Jayron32.talk.contribs03:47, 1 May 2009 (UTC)[reply]
Central metal ions and EDTA
So I was wondering today about central metal ions and multidentate ligands, and EDTA comes to mind as a ligand which forms six bonds to its central metal ion. We studied in class about how it can displace unidentate ligands, but then I wondered, how could you displace a ligand which forms, say, six bonds to the central ion? Are there ways to strip EDTA off, say, an aluminum (III) ion? I'm studying at under university level, so forgive me if my idea isn't all that smart. It's bound to happen. Regards, --—Cyclonenim | Chat 19:30, 30 April 2009 (UTC)[reply]
My guess is that one could mess with the pH to protonate the EDTA4- and return it to its acid form, and thus change its ability to form ligand bonds to the metal ions. Our article on EDTA notes that the ligand is the EDTA4- form, and that the tetraprotonated form, H4EDTA is not an effective ligand. So, it would seem to me if you added acid, you could remove the EDTA from its bonded metal ions, returning the metal to a free-ion form. Just speculation on my part however. --Jayron32.talk.contribs
Swine flu (the 2009 A/H1N1 virus) is new on the scene and information is sketchy right now. Viruses in general evolve to not kill their hosts, since they can't spread if their host is dead. The virus presumably is a mix of avian, porcine and human virus DNA (at least I think it's a DNA virus) and presumably can still be resident in pigs. Like any virus, some percentage of the infected population will die. Pigs don't get on planes though, so the spread through the pig population will be more limited. I've not seen anything to indicate massive pig die-offs, so yes, we're talking about a virus spread through human-human contact at the moment. Don't know if that helps! Franamax (talk) 20:39, 30 April 2009 (UTC)[reply]
The flu virus is a RNA virus. As far as we know pigs might even be completely immune to that virus. We don't know. Dauto (talk) 22:53, 30 April 2009 (UTC)[reply]
The strain of "swine flu" that we humans are all worried about probably won't itself infect that many pigs, but don't be mistaken -- plenty of pigs are going to be affected by it. It is being reported that Egypt is slaughtering 300,000 pigs in a misguided attempt to prevent the outbreak. SO, you could say that more pigs have been killed by this outbreak than humans so far. --- Medical geneticist (talk) 21:30, 30 April 2009 (UTC)[reply]
The exact flu now appearing in humans has not been detected yet in swine; however; a very similar virus has been present in North America swine since 1998.[25]Rmhermen (talk) 23:11, 30 April 2009 (UTC)[reply]
Type of coffee
What is the name of the coffee that is fed to some kind of animal (possibly cats?) in bean form and then brewed from the feces? --Retracted (talk) 21:37, 30 April 2009 (UTC)[reply]
What goes up must come down. Where else would you have it stop? The cell ends as soon as the air becomes cold enough (by radiation) that the atmosphere would become unstable if the cell didn't end there. There's nothing magical about 30 degrees or three cells. Jupiter as you can see, seem to have about half a dozen cells per hemisphere. Dauto (talk) 23:34, 30 April 2009 (UTC)[reply]
They way I learned it was this: Imagine an idealized earth, or any planet, that is spinning slowly enough that the coriolis effect is negligible, but enough that the equator is equally heated. Since the air at the equator is hot, and since hot air rises, it will rise. Air from more polar latitudes will circulate in, while air at the poles is cold and sinks and so has a higher pressure. So a surface flow of air from the poles to the equator is formed. In the upper atmosphere however the hot air that rose above the equator flows towards the poles where it sinks, thus forming two giant cells, one on each hemisphere. Adding the coriolis effect changes things however: breaking it up into multiple cells. Cells behave in some sense like gears, adjacent cells must rotate in opposite directions, so only certain numbers of cells are possible: 2 (as above), 6 (like earth), 10, 14 (like Jupiter I believe) etc... The number of cells that it breaks up into depends on the strength of the coriolis effect which depends on how fast the planet is rotating about its axis. Here are some articles which also explain this (about 3/4 down) : [26] : (the section "3-Cell Theory") [27]. Jkasd06:29, 1 May 2009 (UTC)[reply]
Ooh, thanks! It makes so much sense now! Well, enough sense. I mean, I'm not seeing the equations go into this and physically I'd like a (non-obtuse) way to see how exactly the Coriolis force causes it to break up at such magic intervals.
I mean, 2,6,10,14 -- don't those remind you of the number of electrons that can fit into a subshell? Probably pure coincidence. I mean, I suppose the coincidence comes from the "discrete" part -- you can't have 3 and a half circulating cells and maybe there's some deeper mathematical significance somewhere (or not). John Riemann Soong (talk) 07:14, 1 May 2009 (UTC)[reply]
The sequence 2,6,10,14 is simply twice the odd numbers, so I suspect it will turn up in thousands of theories about all sorts of different things. To see why a number like 4 won't work here, try to put 4 cells on a planet, given that air will rise at the equator and sink at the poles. Jkasd07:46, 1 May 2009 (UTC)[reply]
I guess my (actual) question is -- how does the Coriolis force cause a single cell to break up? Presumably, having a Coriolis force means you start to get longitudinal airstream velocity, but why does this cause convergence at the surface around the 30 N latitude, forming the Azores high and such? (Longitudinal airstreams ==> Divergence aloft?)
I don't really know much more than I've already explained, this all just all from my memory of a meteorology class I took once. The second article I linked to explains how the coriolis effect breaks up the cell. I think that the reason the cells break at 30 and 60 degrees is simply because that gives each cell equal spans of latitude, but I'm not sure. Jkasd07:46, 1 May 2009 (UTC)[reply]
I also note that while the Hadley cells definitely exist, my textbook tells me the Ferrel cells and the polar cells were more like idealisations. However, Wikipedia tells me the Polar cells and Hadley cells are more "real" while the Ferrel cells are just idealisations. Which is it? (Idealisation disrupted ==> because of presence of continents when the models assume 100% ocean?) John Riemann Soong (talk) 07:19, 1 May 2009 (UTC)[reply]
This whole explanation is just an idealization, but so is pretty much every explanation for anything, I'm sure the continents will alter it, and besides atmospheric circulation is largely chaotic. I tired to find some mathematical formula for this somewhere but the best I could find were the two articles I linked too. (Admittedly I didn't try very hard) I have no idea which cell is the most like the idealization, but I would suspect the Hadley cell and the Polar cell since the Ferrell cell is mostly the result of forming a "gear" in between the other two cells.
Are there any elements that we don't have an application for? It seems pretty much every element ever discovered can be used in some way I suppose. Just was curious. 69.69.75.22 (talk) 22:54, 30 April 2009 (UTC)[reply]
A bunch of them are too rare or too unstable to do much except be studied themselves. Which leads to "studying elements to learn about how to make them, what their structure is, how stable they are" as the major application. DMacks (talk) 23:47, 30 April 2009 (UTC)[reply]
There's an old Time/Life poster (maybe taken from their Matter book?, definitely a few decades old now!) in my department with a picture of every element that had been isolated. Or in one or two cases, just lab notebook data for the "only made a few atoms for a few microseconds" ones. There's also a quick sentence or two about uses, or at least potentially interesting properties. There's often an "Applications" section in the . I know some chemists keep a periodic table on which they check off each element they have personally used, separated by "at all in life" vs "as part of a science experiment" (yeah, we're usually the life of a party:). My latter one is over half-checked. DMacks (talk) 00:15, 1 May 2009 (UTC)[reply]
(e/c) Thanks for the question, it's always fascinated me! I'm not aware of any element that human ingenuity hasn't found a use for somewhere. Hopefully others can point out what I'm missing. Beryllium is quite toxic, but even it has some uses, as in emeralds. I'd love to see an answer, it's one of the the subjects that ever drew me to Wikipedia. :) Franamax (talk) 00:01, 1 May 2009 (UTC)[reply]
Beryllium is has a number of nuclear properties that make it very important for a lot of applications. It is a great neutron source (hit it with alpha particles and it gives you neutrons), and is a great neutron reflector, and as such is used in nuclear weapons for these two purposes. --98.217.14.211 (talk) 01:29, 1 May 2009 (UTC)[reply]
For many of the artificially created, high atomic number, very short-lived elements, their only function to date has been to provide intellectual stimulation for nuclear scientists and scholars, and income for textbook publishers, journal publishers, and physics teachers. Of course the same could have been said for several newly discovered elements in the early 1800's which are in everyday use today. "No application" today may turn to "must have it" tomorrow. Edison (talk) 18:42, 1 May 2009 (UTC)[reply]
Wikipedia has articles on each element, and all ofthe 111 articles are linked to from the Periodic table article. Each "element" article has a "use" section of some sort when the element has a use. You will need to decide whether or not to count the "use" of an element as part of a compound: some elements are almost never found in nature in elemental form. As stated above, many elements have no long-lived isotopes. Of the 111 elements, only 92 were known before about 1930. The periodic table in a high-school chemistry text from 1930 has 92 elements. -Arch dude (talk) 23:57, 1 May 2009 (UTC)[reply]
Are household bleach or disinfectant effective at killing viruses on hard surfaces?
Their articles mostly mention their anti-bacterial properties - not the same thing. I'm wondering if its worth paying far more for some fancy brand-name spray, instead of using just bleach or disinfectant diluted half and half with water. Would bleach or disinfectant be equally effective? 78.149.130.97 (talk) 22:56, 30 April 2009 (UTC)[reply]
Bleach and similar oxidizing agents are generally effective at destroying most viruses. Other types of disinfectants will vary in effectiveness depending on their method of action. Some common antimicrobial approaches, such as alcohol, tend to be relatively ineffective against viruses. It is also worth noting that soapy water followed by a thorough wipe with a dry cloth will generally remove, but not necessarily destroy, most viruses deposited on most hard surfaces via casual contact. Dragons flight (talk) 23:19, 30 April 2009 (UTC)[reply]
If we are talking about influenza in particular (and isn't everyone these days?) then I would note that according to the CDC it can be inactivated by alcohol. See here for a discussion of influenza cleaning methods. Dragons flight (talk) 23:29, 30 April 2009 (UTC)[reply]
The advice from that American government site is to "use a chlorine bleach solution made by adding 1 tablespoon of bleach to a quart (4 cups) of water" (with an American quart being 32 fluid ounces). This seems a very weak solution. Is American household bleach more concentrated than British household bleach? The label on my bottle of British household bleach says it contains "less than 5% chlorine based bleaching agent" and the rest must be water. 89.241.144.80 (talk)
I believe that standard "bleach" in the US is only 3% actual bleach. However, it's a very powerful chemical, even at that level of dilution, as anyone who has ever gotten any on their hands or clothes knows. So, diluting it further may be wise, especially since bleach fumes can be toxic in an enclosed area.
Two things I've noticed are how important time and air is with bleach. If I spray it on the toilet bowl, the vertical surfaces don't get cleaned, because the bleach runs right off. Also, under the waterline, where the bleach remains, but without much air, it doesn't work all that well. Right at the waterline it does a good job. So, making the bleach into a paste or foam seems quite important to get it to adhere to a surface long enough to do it's job, especially for vertical surfaces. StuRat (talk) 14:11, 1 May 2009 (UTC)[reply]
May 1
Elephants are good mimics?!?!
I was listening to NPR today - they had a piece about how Parrots can dance. They commented that parrots and elephants are the only species other than humans that can genuinely adapt their moves to the speed of the music and to more complex beat patterns. They went on to explain that the probable reason for that is that both parrots and elephants are good mimics!! The idea being that in order to be a good mimic, you have to be able to adapt to the rhythm of some other sounds in order to mimic them.
OK - but who ever heard of elephants being good mimics?! I can't imagine a talking elephant - what they heck would they mimic?
The thing is, there are actually elephants all around you—they are such good mimics though that you never notice. I know a number of people who later turned out to be elephants. I once had a car that was actually an elephant. --98.217.14.211 (talk) 01:30, 1 May 2009 (UTC)[reply]
Accounts by people who've worked with Asian elephants (I'm thinking in particular of the explorer Col. John Blashford-Snell, Hon. Life President of the CFZ to which I belong) suggest that elephants are routinely capable of learning to understand simple human speech (true speech, not merely a set of commands), as well as body language and even smells. Conversely, while elephants are obviously not physiologically well suited to reproduce human speech, humans are well able to learn elephant body language and human-audible sound signals, so mutual communication and even affections (or, sometimes, antipathies) readily arise, resulting in close elephant-mahout partnerships that may last decades. In such elephant-human co-operative contexts, there would be no pressing need for the elephant to learn to reproduce human speech, but doubtless they could if specifically tasked, and evidently can for their own amusement. (I second Steve Baker's "wow!")
Note that in one respect, the Asian elephant article is misleading. Modern working elephants (always female) are tamed but notdomesticated, which implies captive breeding and consequent physical and temperamental modification in the descendant captive population. Captive elephants rarely breed, and most working elephants are captured from the wild and tamed. (It's possible that one or more populations of truly domesticated elephants once existed.)
As Norwegian Blue suggests, intelligent social animals largely learn both physical and vocal skills by mimicking their elders and peers ("monkey see, monkey do" and so forth), and can apply this skill to other aspects of their environments, including their interactions with other intelligent species. Humbling, when you reflect on it. 87.81.230.195 (talk) 18:32, 1 May 2009 (UTC)[reply]
Does an early case of mild swine flu immunize one against a more severe case should this become a fully-fledged pandemic?
[response] People who are infected with swine influenza H1N1 will have immunity, or at least partial immunity, should there be a full-fledged pandemic.
But influenza viruses mutate constantly - they can become more or less severe.
If I understand this correctly, then shouldn't health officials take samples of the mild form of the virus, and prepare to give it to everyone, if ever a more virulent form of the virus appears? --Phenylalanine (talk) 02:09, 1 May 2009 (UTC)[reply]
This is essentially how vaccination works, using either a naturally weaker form of a virus (as when cowpox (hence "vaccination" from vache = cow) was first administered by innoculation to immunize against more serious smallpox), or an artificially weakened or dead version of the virulant form (accepting that "alive" and "dead" are contentious concepts where viruses are concerned).
As of now, governments and biotech firms worldwide will be striving to produce and breed an attenuated version of this particular new version of swine flu, but (a) it may take weeks to produce a suitable form (you have to minimize the risk of it mutating back to virulence, or being too strong to begin with), and (b) it will take months to breed enough of it and to manufacture the hundresds of millions of doses that, at minimum, may be needed (because the world don't have enough of the right equipment available). In the meantime you have to hope that the wild virus doesn't mutate again into a form still virulent, but sufficiently different that the immunization conferred by the tame virus vaccine doesn't work.
At the moment, we don't know why some cases of this virus are proving lethal while others are less so, so getting yourself infected with what you hope is a 'milder' form would be a very high risk strategy. 87.81.230.195 (talk) 02:40, 1 May 2009 (UTC)[reply]
Most influenza vaccines have been inactivated, only recently have live attenuated vaccines been widely used. For the 2009 A/H1N1 strain, it seems unlikely that they will attempt to perfect a live-attenuated strain in time for fall 2009; rather, an inactivated vaccine would be much simpler (more predictable in terms of safety and efficacy). --Scray (talk) 02:49, 1 May 2009 (UTC)[reply]
You've suggested immunizing everyone, just in case. Here are some reasons why we don't:
1) There is some risk with any vaccine (or any injection, really). Thus, the benefit needs to exceed this risk, for us to justify the vaccination.
2) Immunizing everyone has a high cost associated with it. This money may be better spent on actual, current threats to public health than on possible future threats.
3) If we get people to come in for vaccinations all the time when they don't really need them, they will get sick of being poked and not come in any more, even in cases where they really need to.
Therefore, the recommendations for flu shots are limited to people with reduced or suppressed immune systems, such as small children, the elderly, those with AIDS, those taking immuno-suppressants, etc. People who regularly come in contact with such individuals should also be immunized. StuRat (talk) 14:02, 1 May 2009 (UTC)[reply]
The problem here is that we don't know how virulent this disease really is. Taking the most extreme numbers from Mexico - we get 500 or so confirmed cases and 110 people suspected to have died from the disease which suggests a horrifying 20% mortality rate - very scary indeed. However, we don't know how many unreported cases there are where people got a mild dose of the flu and got over it without reporting it - and of those 110 dead, only 12 are confirmed as having died from the flu rather than from something else entirely. Taking the other extreme, we find that there have been 2000 reported-but-unconfirmed cases in Mexico and only 12 confirmed deaths - so the mortality rate could be as low as 0.5% - and there could easily be a million more people who have been infected who not only aren't dead and didn't report it to their doctors - but who aren't even showing symptoms - 12 deaths per million is a very mild strain of flu indeed! Remember that tens of thousands of people die from regular old-fashioned flu every year - and nobody panics about that.
Here in the US, we've got just one death from 200 or more confirmed cases - so the 0.5% looks reasonable - until you realise that that one solitary death was from a 2 year old child who had contracted the disease in Mexico...the fact that she subsequently travelled to the US is rather irrelevent. So of the people infected inside the US, there has not been a single fatality. The sample size is in no way statistically meaningful anyway.
Seen against a possible 0% fatality rate, doing ANYTHING to try to immunize people is a bad idea - simple, routine injection site infection might wind up doing more harm than good.
We simply don't have enough information yet. The prudent course is to prepare for large scale action but to actually DO nothing whatever (except, perhaps, to gag Joe Biden!). SteveBaker (talk) 16:39, 1 May 2009 (UTC)[reply]
I'm not sure why we would exclude a death from a patient who contracted the disease outside the US. That still means there isn't a zero percent death rate, unless we think that Mexico has a different strain than the US. (If so, it's nice of those germs to respects the border; that fence is really working. We should get more illegal immigrants to build another fence with Canada.) StuRat (talk) 22:51, 1 May 2009 (UTC)[reply]
Bad idea, this virus is dangerous now since, even if it only kills half of one percent of those it infects (I'm guessing from bad statistics) nobody has immunity to it. Even a half of one percent of the human population is three million deaths. Tim Vickers (talk) 19:54, 1 May 2009 (UTC)[reply]
Let's not forget the great 1976 swine flu vaccine debacle. US president Gerald Ford receiving his swine flu vaccination in 1976 A mild outbreak of H1N1 influenza caused great panic among government officials and fears of a pandemic like the 1918 flu led to mass immunization of the U.S. public. President Ford was immunized before TV cameras. 40 million people were given the vaccine. Skeptics said "Tell me when the corpse collectors are calling out "Bring out your dead!" like in Monty Python and the Holy Grail and I'll consider getting the jab." The actual flu only killed only one person. The vaccine killed 25 people. 178,000,000 in the U.S. survived the "pandemic" without getting vaccinated. See a CDC article on the debacle[28]. Edison (talk) 22:35, 1 May 2009 (UTC)[reply]
midlatitude cyclogenesis -- exactly how do low pressure systems deepen?
Can someone explain to me the whole process of deepening -- I did read the article, and I understand there is a surface level component and an upper atmosphere component involved. I just don't get how an initial turbulence developing around a minor disturbance in a stationary front triggers strengthening of a low pressure system. Winds will tend to circulate and spiral inwards into a low pressure system, but presumably, the low strengthens by convective updrafts. What reinforces the initial updraft? John Riemann Soong (talk) 05:25, 1 May 2009 (UTC)[reply]
As a general rule for weather systems the updrafts are reinforced by buoyancy due to latent heat released when water vapor condendes. Dauto (talk) 14:37, 1 May 2009 (UTC)[reply]
INVISABILITY CLOAK
I was reading an article on an invisability cloak [29] that has been created by smoothing light around the object like water flows around an object. This is at present very small; what are the difficulties of making this on a large scale? Could you not group together X number of small parts to make it bigger?Chromagnum (talk) 05:49, 1 May 2009 (UTC)[reply]
Note: This post continues the thread of question "What are the products of the reaction of sodium with Sand" April 29th, 2009. Plse don't start a new topic with a continuing thread. Thks.76.97.245.5 (talk) 06:43, 1 May 2009 (UTC)[reply]
Hey, no offence, but the fact is, YOU ARE NOT GETTING THE POINT.
Understand this, when sodium reacts with ethanol, sodium ethoxide is formed. If it reacts with water, it forms NaOH with hell lot of exothermic activity. Now, if sodium reacts with SAND, yes SAND, not WAAATTTEEERRR or ETHAAANOLLL, are there any products formed? If u are unable to answer and say it's SPOON FEEDING, you might as well change the definition of SPOON FEEDING.
When sodium reacts with ethanol hydrogen is formed, this is easily found by searching on Google, Live Search, Yahoo or some other search engine for 'ethanol hydrogen reaction' and may be mentioned somewhere in one of our articles too (I didn't see it but didn't look that hard). If you know sodium ethoxide is formed you should also be able to work this out when writing a balanced equation. Hydrogen is also highly combustible. As our article mentions, it is also a exothermic reaction albeit not as strongly as with water. I expect you should know this if you are doing A-level chemistry. You have already stated that sodium probably does not react with sand although you are not sure. So let's see we have
sodium + water =
KABOOM!!!!!
sodium + ethanol = KABOOM?!? (at least a fire hazard)
sodium + sand = nothing (probably)
Let's say there's a sodium spill, which one would I choose to try and prevent anything nasty happening?
If you are still unable to answer the question, I don't know if we can help you, you may need a tutor who can help you learn critical thinking since frankly this is very basic critical thinking and if you can't even answer this you don't have much hope in your A-level let alone with your dreams to study in an American university
If you are now able to answer the question, then why couldn't you answer it before? You appear to have already guessed or researched enough to know most of what I've said here, none of it is new. If you weren't sure you were right then you should have simply offered your reasoning as I have done (well without the need to be so fancy) and people would have helped confirm you answer. This is what Steve, me and many of the RD want people asking homework questioners to do. Don't be afraid to be wrong, people usually won't and shouldn't make fun of you, unless perhaps you have shown absolutely no evidence of having done even the most basic research and thinking. When you show evidence of having thought about it and looked in to it yourself and just need confirmation, people will generally be more then happy to help.
Guys, I think you're being too harsh. The main issue in reactivity I suspect, is that sand is solid, and so is sodium. EtOH and HOH isn't. Let's say you brought your reaction conditions down to -20 degrees Celsius, and you brought sodium and solid octanol together. Would they react? Probably very very slowly.
The other real issue of course, is whether sodium's electron prefers to be transferred to SiO3 (radical), or OH (radical). Because we know if it's the former, then the reaction is definitely exothermic and the main obstacle is reaction conditions. John Riemann Soong (talk) 06:47, 1 May 2009 (UTC)[reply]
The Silicon in SiO2 isn't really acidic. It's in fact, not hydrogen, so it would take some effort to pry off. (Presumably, Na giving its electron to oxygen is more favourable than giving it to less electronegative silicon.) In fact, silicon and oxygen are fairly well ionically bonded (with some partial covalent character), so your first issue is dissolving that Si-O bond. Melting it sounds like a good option. SiO2 also reacts with hot NaOH to yield sodium silicate. I'm not sure if the high heat is required for solubility, or for driving an endothermic reaction, but Na reacts exothermically with water to yield NaOH, so a reaction between sand and sodium isn't that all impossible. Your main barrier is that both of your reactants are solids. For a non high-temperature alternative, perhaps "dissolve" (or crush) the sodium in a non-reactive organic solvent and pass it through a sand column chromatography mixture, and collect the appropriate eluent? I don't know what the yield would be, but it sounds like a possible mechanism. John Riemann Soong (talk) 06:35, 1 May 2009 (UTC)[reply]
Also, what about adding sodium, sand and water? Sodium hydroxide would be formed as an intermediate, the reaction would be exothermic, the hydrogen would ignite, making the sodium hydroxide even hotter, so now you have adequate delta-H to complete the reaction (I think?). Add in sand and you get sodium silicate. (Theoretically.) John Riemann Soong (talk) 06:38, 1 May 2009 (UTC)[reply]
Maybe the questioner's obstacle to understanding is not knowing why sodium doesn't react with sand. (Yes, there are people like that, who know their chemistry but suck horribly at exam skills. What happened to WP:AGF?) I am curious though. I mean, suppose you tried to clean up the spill with n-decanol in subfreezing conditions. Would I get flame and burning? How do you clean up a spill with solid sand anyway? I would think some sort of (liquid) "nonreactive" organic solvent would be more effective. Is crown ether an option? John Riemann Soong (talk) 06:56, 1 May 2009 (UTC)[reply]
I think the idea is to use the sand to dilute the sodium so you can then sweep it up without dealing with highly reactive sodium (since the mixture would be much less reactive). The sand is also likely to absorb water and stop it reacting with the sodium. --Tango (talk) 08:09, 1 May 2009 (UTC)[reply]
I think we're over analysing the situation here. This isn't a question on how to clean up a sodium spill. It's a question on what a bystander should do if they come across a spill or the person carrying the sodium should do if it spills. The main thing is you need something accessible and easy to use. You just want to stop a fire or explosion before they get there. You are NOT supposed to be the one dealing with cleaning up a sodium spill. You let the people trained to do that deal with it. Nil Einne (talk) 08:45, 1 May 2009 (UTC)[reply]
The questioner gave no indication they wanted to know why sodium doesn't react with sand. They first stated they didn't think that sodium would react with sand. He/she then stated "if sodium reacts with SAND, yes SAND, not WAAATTTEEERRR or ETHAAANOLLL, are there any products formed". So I am AGF here. It appears the OPs problem is that they are not confident in their believe that sodium doesn't react with sand and therefore is unable to answer the question. It seems to me it is you that are not AGF since you are presuming that the OP's problem is that they have poor English or are otherwise unable to ask a simple question like "why doesn't sodium react with sand" when that is what they want to know and instead ask a lot of other stuff when they actually want to know something else. I prefer to accept an OP's question at face value particularly when they have given no indication they have trouble explaining what they want to know or have poor English. And I have made a good effort to explain the thinking which the OP needs to do to get the answer. As I have already stated, if the OP still can't get the answer, then they probably need further help from external sources. If the OP wants to know why sand doesn't react with sodium there's nothing wrong with that and they are welcome to ask, so far they have not. P.S. I should add that if the OP does have poor exams skills, your answers aren't exactly helping. When you are in an exam particularly an MCQ, you don't generally have time to analyse each answer carefully. Sometimes you have to rely on educated guesses if you aren't certain about something. In this case as I have already explained it appears to me the OP had sufficient info to be able to answer the question already. They may not be certain, and it's good practice to not only make sure you are right, but understand why you are right, in other words there's nothing wrong with the OP coming here to ask why sodium doesn't react with sand and the reference desk would welcome such questions. But there's no indication from the OP that they want to know that yet. Instead every indication is that the OP is still struggling with the question. In this case, distracting information like why sodium doesn't react with sand is unhelpful and unnecessary. If the OP to spends their time analysing each answer in this way, they're liable to run out of time and fail because that's not how you answer MCQs. Nil Einne (talk) 09:14, 1 May 2009 (UTC)[reply]
The Kaboom is energy! So you need to get energy from the reaction of
You get two mol of Na2O for every mol of SiO2 so yo double that number.
-911 is more negative than -828.4; this means that the SiO2 is energetically on a lower level and that it is more stable. You would not get energy from that reaction and without energy no KABOOM!!!!!.--Stone (talk) 08:12, 1 May 2009 (UTC)[reply]
Yes, but what are the kinetics of that reaction? If the half-life of the reaction is 1000 years, it doesn't matter much if it is that exothermic, its not going to happen to any appreciable level. Given that it's essentially a solid-state reaction, I imagine the kinetics to be quite slow. Plus, I suspect the Na + O2 reaction to be fast enough that functionally, you would be reacting Na2O with SiO2. --Jayron32.talk.contribs13:44, 1 May 2009 (UTC)[reply]
Well then add water as a catalyst. One concern I suppose is that excess water will drive the reaction in the other direction, so I suppose the key is to add only enough water to make concentrated NaOH. (The water gets recycled.) John Riemann Soong (talk) 14:12, 1 May 2009 (UTC)[reply]
OK, so the question NOW becomes, "does a concentrated solution of NaOH react appreciably with Silicon Dioxide" and the answer of which is demonstratably "NO". After all, glass is just amorphous sand, and you can store NaOH in glass safely for years with no problem. Given that, since a) the kinetics behind a Na - SiO2 reaction is likely prohibitively slow and b) Basic Na derivatives like Na2O and NaOH will not likely react at all the answer is STILL that sand and sodium should not react in any reasonable way. --Jayron32.talk.contribs18:08, 1 May 2009 (UTC)[reply]
Then why does the silicon dioxide article mention that it reacts with *hot* sodium hydroxide? It's the heat that matters, I think, for the activation energy. But that heat is readily supplied by the reaction of sodium with water. John Riemann Soong (talk) 06:43, 2 May 2009 (UTC)[reply]
The easy way to answer this question: This MSDS [30] for sodium says to cover a large spill with dry earth, sand or other non-combustible material. So if the sodium supplier says to cover it with sand if spilled, I think it is a safe bet that sodium doesn't react with sand. No chemistry required. anonymous649413:57, 1 May 2009 (UTC)[reply]
I really don't appreciate all of the large font text and bitching at me, personally. I first told our OP to look in Sodium for the answer. Then we got a follow-up question and it was evident that my first response did no good - I posted again to reveal the obvious fact that water is not the right choice (leaving us with a tougher choice between sand and ethanol). Then I suggested the 'Precautions' section of the Sodium article - which I will now quote:
"Because of the reaction scale problems discussed above, disposing of large quantities of sodium (more than 10 to 100 grams) must be done through a licensed hazardous materials disposer. Smaller quantities may be broken up and neutralized carefully with ethanol (which has a much slower reaction than water), or even methanol (where the reaction is more rapid than ethanol's but still less than in water), but care should nevertheless be taken, as the caustic products from the ethanol or methanol reaction are just as hazardous to eyes and skin as those from water."
Since we're told in the question that there is a truckload of the stuff involved here ("more than 10 to 100 grams") - that quote allows anyone who takes the time to actually read the article to eliminate ethanol as a means to safely neutralize this LARGE sodium spill. You don't need any chemistry skills whatever - just the ability to read what the article says. What remains from the list of choices is only sand - so that MUST be the correct answer. I maintain that anyone who took the time to read the article (as I directed them to on TWO separate occasions) would have been able to find that out - and anyone who does not read the article when directed to do so in a Ref.Desk answer is demanding to be told the actual answer - which is spoon-feeding a homework answer. That is most certainly not allowed per the Ref.Desk guidelines which the OP will find at the very top of this page - and which I had explained to the OP the first time around using the {{dyoh}} template.
I found it extremely confusing that people would AGF of someone who is clearly deliberately ignoring attempts to help them and just shouting at the attempted helper. I'm sorry if this isn't the done thing, but I have to say, I disapprove of the manner in which these people answered the OP's question - doing his homework, and then some. Steve gave the perfect answer days ago. Vimescarrot (talk) 19:55, 1 May 2009 (UTC)[reply]
geostrophic/gradient wind and equilibrium
Suppose the ideal condition of no friction, and a region of low pressure or high pressure. Wouldn't air slowly move across the isobars eventually? I'd suppose you have air parcels which once, having gotten into the system, would continue to blow parallel to the isobars. But the initial set up (non-equilibrium) required some displacement from high to low. So wouldn't there be slow but steady movement of air across the isobars? Just wondering. John Riemann Soong (talk) 08:07, 1 May 2009 (UTC)[reply]
The other thing I'm wondering about is the whole Coriolis Force and PGF balance. Why does the parcel keep its initial horizontal velocity component but not its velocity in the PGF direction. I assume when PGF = CF, there is no acceleration, but there is still velocity. Or is there sort of like an elastic spring motion? (Funnily, this is probably not related to the encouragement of troughs and wavelike motion, isn't it.) John Riemann Soong (talk) 08:07, 1 May 2009 (UTC)[reply]
The geostrophic equilibrium is a quasi-equilibrium between the pressure gradient force (PGF) and the coriolis force (CF). Assuming ideal conditions as you requested, we can make that an exact equilibrium in which case the two forces are equal and oposite. the CF is always perpendicular to the direction of motion, so for this idealised condition the PGF also must be perpendicular to the motion in which case the air motion would be exactly parallel to the isobars. All this is for an idealised condition. In the real world of course there is indeed some movement across isobars. I'm not sure I understand the second part of your question. Would you care to elaborate? Dauto (talk) 15:45, 1 May 2009 (UTC)[reply]
lifespan of dinosaurs
Anyone know what the longevity of a large dinosaur was likely to have been? Also, did they hatch from eggs? How long did they take to hatch? 207.241.239.70 (talk) 09:34, 1 May 2009 (UTC)[reply]
Our article Physiology of dinosaurs says: "It appears that individual dinosaurs were rather short-lived, e.g. the oldest (at death) Tyrannosaurus found so far was 28 and the oldest sauropod was 38. Predation was probably responsible for the high death rate of very young dinosaurs and sexual competition for the high death rate of sexually mature dinosaurs". Yes, they reproduced by laying eggs. I don't know how long their eggs took to hatch. Gandalf61 (talk) 09:51, 1 May 2009 (UTC)[reply]
How do we know it lived 28 years? (I don't have an account with Nature.com so I can't read the cited reference and the abstract doesn't provide enough information for me to understand.) A Quest For Knowledge (talk) 13:30, 1 May 2009 (UTC)[reply]
We might be able to come up with some guesstimates for how long the eggs took to hatch. Since this period tends to be longer for larger and more complex animals, we should probably start with the largest eggs we have now. Those are ostrich eggs, and take 35-45 days to hatch. (See Ostrich#Reproduction.) Dinosaurs weren't really any more complex. Some were smaller than ostriches, some were larger. So, for the smaller dinos maybe we could cut that period in half, while, for the larger dinos we could maybe double it. StuRat (talk) 13:01, 1 May 2009 (UTC)[reply]
Let's also look at existing reptiles. According to Gila_monster#Life_history, they have a 9 month incubation period. According to Komodo_Dragon#Reproduction, they have a 7-8 month incubation period. However, since the current theory is that dinos were warm-blooded, like birds, rather than cold-blooded, like reptiles, this likely means their incubation period would be more in line with birds, too. StuRat (talk) 13:30, 1 May 2009 (UTC)[reply]
It's not clear why a dinosaur large enough not to get eaten would not live a very long time, considering the extreme ages their cousins alligators(70 years) turtles(100 years+) or parrots(80 years+) can reach.Edison (talk) 18:27, 1 May 2009 (UTC)[reply]
In the case of reptiles with slow metabolic rates, especially turtles, that's reason enough to explain high life expectancies. Dinos are thought to be warm-blooded with higher metabolic rates, though, which would tend to mean shorter life expectancy. Parrots and people are a bit of an exception, though, which both have relatively long life expectancies despite being warm-blooded with higher metabolic rates. In the case of people, a long childhood and learning that extends well into adulthood means a long life is needed to fully benefit from this knowledge. Perhaps the same applies to parrots ? StuRat (talk) 22:39, 1 May 2009 (UTC)[reply]
Mobile phone radiation
Moved from Miscellaneous Desk
A widely circulated sms message says that a mobile handset's radiation is 100 times higher when the battery is low. Is there any basis for this? —Preceding unsigned comment added by Ramkinkar (talk • contribs) 09:47, 1 May 2009 (UTC)[reply]
I very much doubt it. A mobile phone chooses its output strength based on the signal strength between it and the cell tower, battery power shouldn't have anything to do with it. If it does, then it would be lower radiation when the battery is low in order to conserve power (but I don't think that's the case, I think the battery just goes flat quicker if the phone requires a high powered signal). It should also be noted that, to the best of my knowledge, no study has found any evidence of harm to adults from mobile phone usage (I think results vary for studies on children). --Tango (talk) 10:30, 1 May 2009 (UTC)[reply]
The only effect that's been observed so far is that one side of the head is slightly warmer right after cell phone usage. However, this likely has nothing to do with "radiation", unless you're talking about infrared radiation/heat from the phone and the hand holding the phone. StuRat (talk) 12:51, 1 May 2009 (UTC)[reply]
Yeah. In fact, one side of your head will also be slightly warmer than the other if you hold a slab of plastic the size of a cell phone against your ear for five minutes. That's thermodynamics in action. -- Captain Disdain (talk) 14:10, 1 May 2009 (UTC)[reply]
This whole business of radio waves and other forms of radiation from cellphones being harmful in any measurable way has been spectacularly well researched and busted, busted, busted. Don't worry about it. On the other hand - the number of car accidents and pedestrian accidents due to cellphones is off the charts...so if you need something to worry about - consider tripping and falling while texting! SteveBaker (talk) 14:49, 1 May 2009 (UTC)[reply]
I do not consider it busted at all. Lets see the effect on young people in a few decades after they spend hours with a celphone stuck next to their head. A test is whether lefties get left side brain tumors compared to righties with right side brain tumors. Similar data came from US locomotive cab crews, where the engineer had his right side exposed to sunlight and the fireman had his left side exposed to sunlight many hours a day for many years. The melanoma distribution was as one might expect. Edison (talk) 18:25, 1 May 2009 (UTC)[reply]
Both the above responses are reasonable approximations of the truth. As a rough rule of thumb, electromagnetic waves (including radio waves) tend to interact very weakly with objects significantly shorter than their wavelength — they just don't 'see' them. FM radio waves (frequency about 100 MHz) have a wavelength of about 3 meters (10 feet); AM radio waves (frequency about 1 MHz) have a wavelength of about 300 meters (1000 feet). A typical human being standing in the path of a radio wave is about a third of a meter thick, resulting in weak attenuation of FM radio and virtually negligible effect on AM radio broadcasts.
Mobile telephone networks operate at frequencies between about 400 and 2100 MHz, depending on the jurisdiction. Those have wavelengths between (roughly) 1 meter and 15 centimeters (3 feet to six inches). Consequently, those signals can be significantly attenuated by human-sized absorbers. TenOfAllTrades(talk) 14:10, 1 May 2009 (UTC)[reply]
Some OR: I use a mobile phone as a music player when running, with a bluetooth headset. When I carry the phone in a belt bag and the signal has to travel through my body, the signal gets slightly chopped up (misses out bits about every thirty seconds, enough to be quite annoying). When the phone is in a pocket, this never happens. --NorwegianBluetalk14:47, 1 May 2009 (UTC)[reply]
It is a common experience that where someone stands strongly affects FM radio reception (where the antenna is just a wire hanging from the radio) or TV (nondigital) reception from rabbit ears. I have not noticed an effect on AM reception (much longer wavelength). So clearly the FM and TV signal is absorbed by, polarized by, refracted by or reflected from humans. Edison (talk) 18:21, 1 May 2009 (UTC)[reply]
In the antenna nearfield it becomes much more complicated because you are effectively loading the antenna's radiating element with a dielectric material consisting of an air gap and tissue, bones and the like. A human standing in the nearfield will not be directly affecting the RF, they will actually be affecting the antenna itself by tuning its various resonances. Readro (talk) 22:28, 1 May 2009 (UTC)[reply]
I'm thinking of cases where the antenna is compact and the person is many feet away, say 13 feet, but when they walk between the FM radio and the transmitting antenna, it affects the sound pretty dramatically. Edison (talk) 23:59, 1 May 2009 (UTC)[reply]
Avoid the sun - causes skin damage and wrinkles. For similar reasons do not smoke, do not drink. Stay slim - avoid junk food and saturated fats, eat plenty of vegetables and fruit. 89.241.144.80 (talk) 13:43, 1 May 2009 (UTC)[reply]
thanks! This is exactly what I was looking for (to the point that I almost listed avoiding the sun as an example of what I was talking about). Any more answers along the same line are much appreciated. 94.27.137.4 (talk) 14:27, 1 May 2009 (UTC)[reply]
Take care of your skin, don't use overly powerful cleaning agents. Get plenty of sleep, eat lots of healthy foods and avoid greasy and fat stuff like deep fired.
I'm sure SteveBakers comment was meant as a joke and not to offend, as signified by the small text he used to show it wasn't a serious answer. However I agree it would maybe have been better if he'd not commented at all
I didn't see anything offensive in SteveBaker's joke. For one thing, he didn't menssion gender at all so that rules out sexism, in case that's what was bodering you. Dauto (talk) 15:29, 1 May 2009 (UTC)[reply]
removed own comment; u can remove ur replies to it too if u want
Good bone structure will take you through the menopause, assuming you're a woman. Also not being too thin, as your subcutaneous fat layer will ensure you don't get wrinkles while that lasts. A little embonpoint looks far more attractive than as if you've already gone through the embalming process IMNSHO! Do not smoke, ever: smoking is how they preserve ham and kippers! Eat plenty of fresh fruit and veg. Look in the mirror and tell yourself how lovely you are, for if you believe you are beautiful then other people will too! A positive mental attitude is both attractive and contagious. Oh and smile more often than you frown.--TammyMoet (talk) 17:33, 1 May 2009 (UTC)[reply]
I second avoiding the sun (and sunlamps, tanning beds, etc.). I get less sunlight than the average vampire, and don't have a wrinkle on my face, as a result. (Not bursting into flames and turning into dust is a secondary benefit, if you actually happen to be a vampire.) :-) StuRat (talk) 22:31, 1 May 2009 (UTC)[reply]
There is some information in the Oil paint#Carrier article. But sadly medium oil itself hasn't been written (should probably be set as a redirect for now, but I'm having trouble getting reliable WP response right now...hope this post gets through:( DMacks (talk) 15:41, 1 May 2009 (UTC)[reply]
I am just curious, and I do have a few theories as to how it could POSSIBLY be done(Still need to do a bit more research, though my resources for knowlege are a bit limited at the moment), but I would like to simply ask..
Do you believe it can be done? And if so, how do you think I could go upon doing so?
This question has also been posted on the Misc desk (here). I suggest all discussion take place there, to keep things in one place. --Tango (talk) 16:20, 1 May 2009 (UTC)[reply]
Instincts in Humans
Why do some people, particularly women, sometimes place their hand over their mouth when they witness a scene of horror? For an example see http://news.bbc.co.uk/2/low/europe/8028317.stm. (Mouse over the photo to see the caption.) That was an involuntary response and therefore instinctive. Also, women sometimes scream when they experience fear - that is an instinctive cry for help. But what purpose does the hand-over-mouth instinct serve? (Some sociologists say that the only instincts humans have is fear of falling and fear of loud noises. I think we are loaded with instincts. These are two of them.) - GlowWorm. —Preceding unsigned comment added by 98.17.33.211 (talk) 16:41, 1 May 2009 (UTC)[reply]
Er, well everything you've listed here applies to both men and women. Sure there must be a reason, but I doubt it only applies to one gender. Personally my instinct when I see a scene of horror is to get out my camera and take a picture. —Preceding unsigned comment added by 82.44.54.169 (talk) 16:45, 1 May 2009 (UTC)[reply]
I don't think this applies to fear but the fact that their mouth is open. I've also noticed people cover their mouth when yawning and burping. People even chew food with their mouth closed. -- penubag (talk) 17:56, 1 May 2009 (UTC)[reply]
Covering your mouth when yawning or burping is cultural, rather than instinctive. It's a social norm that has to be learnt. Parents will teach their children to cover their mouths when doing such things, they won't teach their children how to scream. I think covering your mouth when frightened is instinctive, rather than learnt, although I can't offer any real evidence for that. --Tango (talk) 18:12, 1 May 2009 (UTC)[reply]
An unlikely explanation: placing a hand in front of the mouth could stifle involuntary sounds in order to avoid alerting a threat. It sounds a little dumb to me (a simpler and more efficient instinct would be to simply shut up, after all), but I've heard it said. A more likely explanation: raising a hand up there protects the vulnerable face from a potential threat (and makes it easier to strike at an enemy, or block of an attack to the face), but leaving it a little low, at mouth level, doesn't obstruct the vision. Is that really the reason for the instinct? I don't know, but it sounds pretty reasonable.
Another, a little less primitive instinctual response could be to mask your emotions, either because open display of harsh emotions is something people are taught to avoid, or because spreading panic in a herd is not a good idea. This is, of course, pure speculation.
And as has already been stated, these instincts certainly don't apply only or even mostly to women. That's just silly: guys yell out when they're startled all the time, and the image in your example includes a guy doing the exact same thing as the woman. -- Captain Disdain (talk) 17:58, 1 May 2009 (UTC)[reply]
That's an interesting question. Screaming is a sensible reaction to something frightening, it's an alarm call that either warns other people of the danger or requests help from them. Plenty of animals have alarm calls. Why one would cover their mouth, though, I don't know... Thinking about it, covering the mouth is usually associated with a gasp rather than a scream, perhaps the hand is simply to prevent foreign objects from entering the mouth? (The gasp being an instinctive attempt to get air before doing whatever needs to be done - fight or flight, most likely.) I've never heard anyone say humans have only two instincts, but if somebody did then they are clearly wrong. There are all kinds of things humans do instinctively. Our major drives could all be considered instincts (sex, food, etc.). Our various reflex reactions (withdrawing a hand that comes into contact with something hot, for example). Even something like involuntary breathing could be considered an instinct. --Tango (talk) 18:12, 1 May 2009 (UTC)[reply]
Another human instinct that is hard to explain is being "petrified by fear". I used to think that was a figure of speech. But once when I was close to a caged wild animal it made the most terrifying snarl I have ever heard. I was so shocked I could not move or make a sound for about 3 seconds. That seems counter productive. If that animal had been free, it could have done me considerable harm while I could not move. Why do we become petrified by fear and unable to defend ourselves? It is an involuntary response, so I suppose it could be called instinctive. – GlowWorm.
As to the question by GlowWorm on "petrified by fear": I recently read about a Japanese study which indicates that "playing dead" (terms seem to be thanatosis and akinesis) are quite useful survival strategies amongst different species of prey. More often than not the predator charges after those who flee in panic and ignore any individuals who have been petrified. --Cookatoo.ergo.ZooM (talk) 20:24, 1 May 2009 (UTC)[reply]
It is far easier to spot movement than to spot a stationary object, so keeping very still, even when in the open, can be a good way of hiding. --Tango (talk) 21:08, 1 May 2009 (UTC)[reply]
This is a wild guess but I wonder if it (the hand in front of the mouth) is to prevent hyperventilation. When I imagine myself making that gesture, that's what it feels like I'm doing. I don't know why someone would do that rather than just slow their breathing, but people do hyperventilate, so who knows. -- BenRG (talk) 19:42, 1 May 2009 (UTC)[reply]
I'm not sure it would be very effective. You would have a significantly restrict the airflow, which I don't when I try and act it out (I restrict it a little, but I don't think enough to make a difference). --Tango (talk) 21:08, 1 May 2009 (UTC)[reply]
Some of the anthropoid species have fearsome-looking teeth which they show as a counter-threat when they feel fear. However, putting a paw in front of the mouth will hide the teeth. Perhaps that is an instinctive signal of non-aggressiveness. It counteracts the instinctive display of the teeth, and is thus an example of one instinct counteracting another instinct. A second thought, so to speak - or more precisely, a second instinct; it's not a matter of thought. Maybe that is why it seems to be done mainly by females – they tend to surrender rather than fight. This is far fetched, but I'll pass it along. – GlowWorm. —Preceding unsigned comment added by 98.17.33.211 (talk) 23:06, 1 May 2009 (UTC)[reply]
The scream reaction is demonstrated by every newborn baby. The next instinctual behaviour is to seek the comfort of pressing the mouth to mother's breast. These instinctive reactions re-emerge on occasions of stress. The hand pressed to the mouth substitutes for the breast in the same way as the thumb that a young child sucks or the cigarette that an adult sucks. Cuddlyable3 (talk) 13:19, 2 May 2009 (UTC)[reply]
Is that a guess or are you basing that on something? It sounds rather Freudian to me, and most of his theories have been debunked. --Tango (talk) 13:26, 2 May 2009 (UTC)[reply]
Materials science
Is it possible to make a small homemade model plane or glider out of readily available materials that can carry a mass which is over 300 grams? Clover345 (talk) 17:40, 1 May 2009 (UTC)[reply]
Define "carry." How far, how high? I made one and threw it out the 2nd floor window and it carried the load straight down to the ground. Hard landing. Maybe a bigger wingspan was needed. Edison (talk) 18:16, 1 May 2009 (UTC)[reply]
Carried across about 10 metres launched from the 2nd floor of a building. As you said, any attempt just seems to fall straight down. What material will actually do this? Thanks. Clover345 (talk) 18:29, 1 May 2009 (UTC)[reply]
define "small". not knowing anything about the subject, i'd think something along the line of a hang-glider, where you could have a fairly large wing without much weight. if a big one can carry a person, i'd think a small one could carry 300 grams. Gzuckier (talk) 19:13, 1 May 2009 (UTC)[reply]
It is probably possible. If the cargo weight is 1/2 of the total weight, and your wings are 15mm wide and meet the maximum dimensions, your wing loading will be about 1/3 that of a Piper Cub airplane, so your structure could be about 40% as strong. While the Piper Cub is not strictly a glider, it glides reasonably well in unpowered flight. Now as a practical matter, you are going to have a lot of difficulty with stability, especially if you are using household materials. For instance, how symmetrically can you make an airfoil shape with plastic wrap, glue and chopsticks? This seems like a project that can be done, but will take a lot of time to get right. 65.121.141.34 (talk) 20:13, 1 May 2009 (UTC)[reply]
Maybe something inherently stiff and lightweight for the wing, like a piece of foam insulation panel, which is made rigid by the foil on each side. Does the wing have to be airfoil or would flat work? The keel could be the same material. It is the sort of thing that I might find laying around as a leftover building material. Alternatively, perhaps cardboard. Ordinary drawing paper seems too weak to have large wings supporting a heavy weight. You could get fancy and have support cables from various points on a paper wing to the keel, with stiffeners across the wing. A bit like building a bridge. Edison (talk) 22:11, 1 May 2009 (UTC)[reply]
I may not be getting into the spirit of the thing, but if your aim is to get a reasonably soft landing 10m away from the building, I think throwing the object the 10m and making it a parachute might be more effective than a glider. --Tango (talk) 21:05, 1 May 2009 (UTC)[reply]
Placing the weight at the center of gravity of the plane is important. You should be able to balance the plane on your finger at the weight, if it's placed properly. You also need enough speed to start with, to provide adequate lift. Perhaps a slingshot mechanism could be used to launch the plane ? StuRat (talk) 22:21, 1 May 2009 (UTC)[reply]
For any given design, lift is proportional to the square of velocity, see airfoil. That means you can always keep something in the air by making it move fast enough. If you have enough wing area to make the required velocity less than the terminal velocity of the object, it will "glide" to some degree. The calculations are pretty complicated, but it looks to me like with a wing of that area, you need a velocity around 10 m/sec to get enough lift to counteract gravity. In other words, you have to come pretty close to hurling the thing across the space, even with optimal design. I'm not very confident of my arithmetic, though. Looie496 (talk) 02:00, 2 May 2009 (UTC)[reply]
I suspect keeping the plane from aiming straight down would be a problem. I'd suggest placing the weight on a rigid structure below the plane to balance it. Alternately, you could tilt the wing up in the back. — DanielLC15:13, 2 May 2009 (UTC)[reply]
Please help identify the correct species of this butterfly
Looks like the owl butterfly, Caligo sp. to me. Not sure about the species, could be Caligo memnon. I'll try to look up the species and post it later. A less likely candidate is Eryphanis sp., but I don't think that's it. --Dr Dima (talk) 22:20, 1 May 2009 (UTC)[reply]
Please help identify the correct species of this bird / duck / egret - what ever it is!
Alcohol (hand sanitizer, communion wine) and the flu
The Centers for Disease Control has said alcohol based hand sanitizers can prevent the spread of flu. The Alcohol rub article says they must be 60% alcohol to be effective. Is there some virus eliminating effect of alcohol in lower concentrations? For instance, if communicants at a church drink from a common chalice, and it is filled with Angelica communion wine(22% alcohol) does that in any way lessen the chances of a virus being transmitted from person to person compared to ordinary wine with 12% alcohol? This assumes that wiping the outside with a cloth does not eliminate virus transmission from contact of the mouth with the wine. (I would have said "killing the virus," but I have read on this page that scientists do not consider them to be "living.") Edison (talk) 21:54, 1 May 2009 (UTC)[reply]
The 60% is based on the level necessary to kill bacteria. The concentration needed to affect the virus will depend on the quirks of the virus. Some viruses are not affected by alcohol at all, but as noted in a previous section the CDC does say that alcohol inactivates influenza, though I've yet to see anything about the concentration necessary. I suspect though that most studies of this would have been done at bactericidal concentrations (>60% alcohol) so there may not be any studies of low concentrations like wine. As noted, the Roman Catholic church is temporary suspending use of the common chalice to prevent transmission. Dragons flight (talk) 00:33, 2 May 2009 (UTC)[reply]
May 2
Correspondence section of scientific journals
Some scientific journals appear to have a section of "correspondence", usually addressed "to the editor". They often look more or less like very small articles, complete with graphs etc. What is it all about? Is this what happens when there is not enough data for a full article? —Preceding unsigned comment added by 137.120.53.1 (talk) 01:25, 2 May 2009 (UTC)[reply]
Sometimes a Correspondence section is used for contributions that aren't substantial enough to make a full article, but more frequently they're used for letters that object to or otherwise comment on things that the journal has previously published. It varies a lot, there really aren't any solid rules about what can go there. Looie496 (talk) 01:31, 2 May 2009 (UTC)[reply]
They are also a way to rush a new discovery into print — typically the turn-around on such little things is a lot faster. (Probably because they aren't peer reviewed, just reviewed by the editor? Probably varies by journal). So there are quite a lot of famous discoveries that were first reported in this fashion ("holy smokes, I found something great! Article to follow.") --98.217.14.211 (talk) 12:37, 2 May 2009 (UTC)[reply]
With the lack of solid rules so-called Letters to the Editor can be exploited in various ways. They may be anonymous or signed by a pseudonym, and be concocted to stimulate interest or debate in the journal. A journal may use such a fictive letter to test the interest in an issue or to make editorial statements with subsequent deniability. An unethical example is to print a letter signed by a real person who never wrote it, in order to smear the person or to imply that the person endorses the journal. Such letters may also be used for early announcement of discoveries. Cuddlyable3 (talk) 12:54, 2 May 2009 (UTC)[reply]
Term for sounds or smells that trigger past memories
I though I remembered there being an article on this, but I don't know what the term is. When someone hears a song on the radio, or a specific sound, or a certain odor and it instantly triggers some memory. It's psychology-related. Is there a specific term for this? 71.252.216.16 (talk) 02:31, 2 May 2009 (UTC)[reply]
I don't think there is a specific term for it. The famous example is Proust's "madeleine" episode from In Search of Lost Time, but I'm not aware of a special word used to describe it. You might be thinking of deja vu, but that means something a bit different. In psychology it's just called a "cue" as far as I know. Looie496 (talk) 04:02, 2 May 2009 (UTC)[reply]
Agreed that Proust usually gets credit (though it is called into question at this blog). I was actually shocked that I couldn't find a "scientific-sounding" name for this phenomenon -- perhaps a term needs to be invented, like "osmnemia" ("osm" from the olfactory sense, as in anosmia, and "mnemia" from the Greek for memory) or parosmnemia (bringing in the idea of paresthesia as the feeling of something that isn't there)??? Anyways most of the papers I Googled use terms like "odor-evoked autobiographical memory" or "long-term odor memory", which are probably much better descriptive terms, but the Wikipedia articles that seem as though they should address this topic (autobiographical memory and episodic memory) don't address the odor-evoked memories at all, and the olfactory memory article focuses mainly on the mother-infant bond. For more information, you may be interested in this review article which discusses the psychology aspects. --- Medical geneticist (talk) 11:36, 2 May 2009 (UTC)[reply]
It certainly sounds like a good umbrella term for memories triggered by various stimuli, although that article also doesn't mention olfactory memory. It seems like someone with a psychology background is needed to help expand/unify these various articles... --- Medical geneticist (talk) 13:38, 2 May 2009 (UTC)[reply]
The concept of "involuntary memory" would be considered out-of-the-mainstream in modern cognitive psychology. Most psychologists nowadays think that memories are evoked, not by an effort of will, but by associations. Thus the only thing that distinguishes "voluntary" memory is that it is reached by thinking about related things until something is hit that triggers the memory. In other words, voluntary and involuntary are not different types of memory, they only differ in that one is triggered as a result of a strategy rather than accidentally. Looie496 (talk) 15:12, 2 May 2009 (UTC)[reply]
I am not familiar with the variety of squash known as "hairy squash". Generally speaking, squashes come in two variates. If it is a summer squash like, for example, zucchini, the skin is generally thin enough to be fully edible. If it is a winter squash, like for example pumpkin, the skins are generally thick and hard and entirely unpalatable. --Jayron32.talk.contribs12:18, 2 May 2009 (UTC)[reply]
More commonly known as "moqua" -- I'm surprised we don't have an article about it. I'm not sure whether it has to be peeled, but it wouldn't be very appetizing otherwise. A kiwi doesn't really have to be peeled, but almost everybody does. Looie496 (talk) 15:20, 2 May 2009 (UTC)[reply]
Tear duct plugs
After Lasik surgery, a common complication is dry eyes, and a common cure is for an optometrist to put tiny plugs into the channel openings to prevent the tears from draining and keep the eye moist. What are these plugs made off and how do they stay in there so well? Thanks. Mac Davis (talk) 09:03, 2 May 2009 (UTC)[reply]
I've got a pair of speakers for my computer. When I touch the headphone jack feedback occurs, at least I think that is what it is. However, today I had an aluminum MacBook with me. When I touched the MacBook with my right hand and touched the headphone jack with my left, the noise got much louder. In fact, as I rubbed my finger against the metal of the jack I could feel the electricity coursing through. I touched the jack to my face and was painfully shocked.
See mains hum which is a rough explanation of the effect. Basically, what you are describing as "feedback" is the result of the 60-Hz alternating current from the wall "bleeding through" into the speeker wires and coming out of the speaker as audible interference. The effect becomes more prounced when there is a complete circuit to the earth (which happens when you touch the wire with your hand) and the metal computer improves the conducatance through this circuit as well. --Jayron32.talk.contribs12:12, 2 May 2009 (UTC)[reply]
Thanks! Yep, that's definitely the 60 Hz hum. I do not understand what you mean about "current from the wall bleeding through," and I really don't understand the article very well either. The wall? What wall is that? Mac Davis (talk) 16:46, 2 May 2009 (UTC)[reply]
You probably have a bad headphone jack or plug. Those plugs aren't very robust, and bend or wear out easily. I don't think this can damage the speakers (speakers are pretty robust), but if you keep trying weird things, you could eventually damage your computer. If you can, you should try replacing the plug. (I'm not very confident about this, because I'm not sure I understand what you mean by "touch the headphone jack". It shouldn't be possible for you to touch the jack when something is plugged in to it -- the jack is the hole that the plug goes into.) Looie496 (talk) 15:34, 2 May 2009 (UTC)[reply]
Sorry, I was talking about the 3.5 mm TRS connector. It was not plugged into anything. Also, you said I could damage my computer? This is the normal casing of the computer, not the inside or anything. Do you still think so? Mac Davis (talk) 16:46, 2 May 2009 (UTC)[reply]
Why can we envision things from before we were born?
I have an idea, but I wanted to ask here, too.
When I've visited historic sites, I could almost see, for instance, Ty Cobb roaming the outfield in old Tiger Stadium when I was there, though he retired 40 years before I was born. Why is that possible?
My hunch is that it is imagination at work in semantic memory. Episodic memory deals with personal things - what I've seen and heard at baseball games I've been to. But, going to Tiger Stadium, Wrigley Field, etc., causes things I've experienced to merge with my daydreams, and with things I've read about players like Cobb. In other words, our minds don't just insert information to fill in gaps in our experiences later, there can be active filling of information at the time, in certain cases. So that - while a visitor to Independence Hall didn't see the Constitution being drafted, they can come away with a feeling of having been there. Even just from things they read on here.Somebody or his brother (talk) 12:55, 2 May 2009 (UTC)[reply]
We can envision things that never happened at all, why wouldn't we be able to envision things from before we were born? I think you're thinking too hard about this. Looie496 (talk) 15:36, 2 May 2009 (UTC)[reply]
Speed of Electricity Part II
Sorry, I'm just getting around to reading the last responses to this thread
[35]. I have a follow-up question but the thread is already in the archives. My understanding is that the electrons themselves flow relatively slowly. Using the garden hose and half-inch ball-bearings analogy, what about the very first time you turn on the water hose? There are no ball-bears in the water hose yet, so shouldn't it take a long time for the first ball-bearing to flow all the way through the hose and out the other side? A Quest For Knowledge (talk) 13:12, 2 May 2009 (UTC)[reply]
Your analogy is faulty: the wire is already full of electrons. As briefly explained at Copper#Electrical_properties, the electrons in good conductors form an "electron sea" in which virtually all of the valence electrons are potentially mobile. As a result, your garden hose is always full of ball bearings, whether or not you've turned on the tap. — Lomn13:16, 2 May 2009 (UTC)[reply]
A battery is not a source of electrons that dries up when it is out of electrons. It only moves the electrons already present in the circuit. Mac Davis (talk) 16:51, 2 May 2009 (UTC)[reply]
I've read on countless pages, most if not all unsources, that "stress depletes the body of B vitamins". Does anyone have a reliable source on this? It sounds plausible, but I haven't found any credible evidence to back it up, and after some (admittedly quick) looking through Wikipedia, I found nothing either confirming nor contradicting this, with the same results on google and pubmed. -- Aeluwas (talk) 15:08, 2 May 2009 (UTC)[reply]
Are all sexually reproducing animals genetically unique?
I'm not too sure on this one - I was wondering if anyone could assess my thought process. I thought clones aren't necessarily genetically unique because if you take the nucleus of a cell and put it into an egg cell (which had had its nucleus removed) taken from another organism, the resulting organism is not a clone and therefore not genetically unique because of the mitochondrial DNA in the egg cell which does not belong to the cell from which the nucleus was derived. (I think that was the process by which dolly the sheep was cloned.) But then I thought what if you took an egg cell from an organism, removed the haploid nucleus and then inserted a diploid nucleus from the same organism - would you then have a proper clone which is not genetically unique? If this is possible then is it incorrect to say that all sexually reproducing animals are genetically unique? Anyone else got any ideas? Thanks in advance for suggestions.
Science Channel Documentary and Quantum Uncertainty
I don't really know how to best phrase this question since I don't really understand quantum mechanics and some the terminology I use might be wrong. But I'll try my best. I was just watching a documentary on the atom on the Science Channel. At the end when explaining Shroedinger's Cat thought experiment, the narrator stated that atoms have no location until measured and that an atom is spread out. I believe he was referring to Heisenberg's uncertainty principle. I thought this uncertainty only applies to subatomic particles, specifically electrons, not to atoms as a whole. Can someone clear this up for me? Does this apply to atoms as a whole or just to subatomic particles? A Quest For Knowledge (talk) 16:53, 2 May 2009 (UTC)[reply]
Please do your own homework.
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