::::::::Removable armor plates are common. If the tank is disabled and just sitting there, you could rush up and start removing armor. Eventually, the guys inside will try to come out to stop you and it will be man vs. man instead of man vs. tank. -- [[User:Kainaw|<font color='#ff0000'>k</font><font color='#cc0033'>a</font><font color='#990066'>i</font><font color='#660099'>n</font><font color='#3300cc'>a</font><font color='#0000ff'>w</font>]][[User talk:Kainaw|™]] 17:33, 2 July 2008 (UTC)
::::::::Removable armor plates are common. If the tank is disabled and just sitting there, you could rush up and start removing armor. Eventually, the guys inside will try to come out to stop you and it will be man vs. man instead of man vs. tank. -- [[User:Kainaw|<font color='#ff0000'>k</font><font color='#cc0033'>a</font><font color='#990066'>i</font><font color='#660099'>n</font><font color='#3300cc'>a</font><font color='#0000ff'>w</font>]][[User talk:Kainaw|™]] 17:33, 2 July 2008 (UTC)
(EC)
::::::::What about MacGyver solutions? Take the gunpowder out, make a kind of bomb, could at least blow the tracks off.
Could destroy the main gun in a similar way. With no movement or firepower you could burn the people out...--[[User:Shniken1|Shniken1]] ([[User talk:Shniken1|talk]]) 17:37, 2 July 2008 (UTC)
== Evolution - Woman as Well? ==
== Evolution - Woman as Well? ==
Revision as of 17:37, 2 July 2008
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.
You are having a minor problem with the laws of physics: icarus-style wings will not work in earth gravity ant earth atmospheric pressure. Look a Gossamer Condor for the first human-powered flight. Look at paraglider if you are not an Olympic-class athelete. -Arch dude (talk) 01:31, 25 June 2008 (UTC)[reply]
is it dangerous to use a product like bouniful breast for breast growth ? supposedly this product is progesterone based.
i read the progesterone article and it seems that progesterone is beneficial in a lot of cases. —Preceding unsigned comment added by 75.69.26.8 (talk) 02:16, 25 June 2008 (UTC)[reply]
Wikipedia does not provide medical advice. Consult a doctor, pharmacist, or other medical professional. — Lomn04:30, 25 June 2008 (UTC)[reply]
All drugs are prescribed for different things, and "beneficial" may be good for something, but bad for another. Talk to your local pharmacist, if you're interested about a drug. Mac Davis (talk) 17:11, 25 June 2008 (UTC)[reply]
Relays and solenoids take a certain amount of electromagnetism to "pull in". This is usually stated in terms of ampere turns. That is, a given highly-sensitive relay may require (say) "10 ampere turns" to pull-in/pick-up. After that, it's all Ohm's law. For that hypothetical "10 ampere turn} relay mechanism, we could design a ten-turn coil and the relay will pick-up if you apply enough voltage to flow 1 Ampere through that ten turn coil. Or we could design a 1000 turn coil and the relay will pick-up if we apply enough voltage to flow 0.01 Amperes through that coil. Because this second coil is wound with many more turns of probably-finer gauge wire, it will have a lot more resistance than the first coil so it will probably require substantially more voltage than that first coil. But to pick-up the relay, both coils have to manage to produce the 10 ampere turns of electromagnetism that the basic mechanics of the relay require.
Pick-up takes more electromagnetic force than that required to hold the relay picked-up. (You need to overcome static friction and there's usually an air-gap in the magnetic circuit; this air-gap usually closes once the relay picks-up.) If the current is then reduced, you eventually reach a lower value (sometimes, much lower) value of electromagnetic force where the spring action in the relay finally causes the relay to drop-out.
Empty space still has volume and time and is governed by the laws of physics. The singularity that was present before the Big Bang had none of these properties; see Timeline of the Big Bang. Because the laws of physics were not applicable during the Augustinian era (just as dividing by zero yields no result), extrapolating to that time period is meaningless. --Bowlhover (talk) 05:49, 25 June 2008 (UTC)[reply]
You are making an assumption that can't be tested. Maybe the Big Bang is the start of time and space, and maybe it isn't. The simple fact of the matter is that nothing we can measure is able to tell us definitively about "before" the Big Bang. Models like the Big Bounce would suggest that things existed before the Bang, but we have no meaningful way to test those theories. Dragons flight (talk) 06:04, 25 June 2008 (UTC)[reply]
How does the Big Bounce theory work with regards to time? Is there a continuous flow of time from one universe to the next? If not, then you need quotes around the second use of "before" as well! --Tango (talk) 14:57, 25 June 2008 (UTC)[reply]
"There was nothing before the universe" just means that there wasn't a before the universe, not that pre-universe space was empty. Similarly, saying "I see nothing out of the back of my head" means that I can't see out of the back of my head, and is very different than saying "I see pitch black out of the back of my head". Another example is the difference between a computer that has no hard drive, which truly has nothing in its memory, and a computer with a blank hard drive, which has several gigabytes of zeros in its memory. I suppose the best way to describe it is that empty space means a medium in its default state, where nothing means no medium. — DanielLC18:16, 25 June 2008 (UTC)[reply]
I vaguely remember an author of one of my physics books lamenting over explaining this. His analogy was to ask "what's north of the North Pole?" It's not there is nothing, but there is no "north of the North pole" ie not even nothing. What was before the big bang is similar (according to these theories anyway). Kind of a Koan-type enlightenment thing going on there. --Bennybp (talk) 06:53, 26 June 2008 (UTC)[reply]
Nordic walking, also known as ski walking, pole walking or fitness walking
Does anyone know where and/or can point out to where I could get phthalate and bisphenol A free Nordic walking, ski walking, pole walking and/or fitness walking poles?68.148.164.166 (talk) 08:30, 25 June 2008 (UTC)[reply]
I wouldn't care about softeners in sports gear used outdoors, as they evaporate into the surrounding air and thus won't harm you. If you're perfectionist you would store them at home somewhere airy. Rather, I'd worry more about good nutrition. --Ayacop (talk) 09:05, 25 June 2008 (UTC)[reply]
(Actually, it looks like your intent was to move the question to a more appropriate desk. That's fine, but you should make it clear to people here that you've asked it elsewhere and received some responses, either by providing a link to the old question, or copying the responses you've gotten. That way, people won't waste time duplicating previous answers.) -- Coneslayer (talk) 14:58, 25 June 2008 (UTC)[reply]
Rhesus macaque with a tumor?
click here to get a full resolution version of this photo
I'm not questioning the fact that monkeys can have tumors. I have no medical experience so I want to get some independent opinions before I decide if I should insert "this monkey has a tumor" text into the description of this photo on Wikicommons. Mieciu K (talk) 10:18, 25 June 2008 (UTC)[reply]
You could say "this monkey appears to have a tumour, possibly a goitre." Since from the full resolution pic, it really does look like it, but we can never be totally sure. Fribbler (talk)
Should I be concerned about meeting with someone with hepatitis C?
I’m going to meet with someone in a very near future, and who is known to have hepatitis C. I can’t avoid this meeting any longer, is there anything I can do to protect myself? Or, is it dangerous to meet with this person? Chailai (talk) —Preceding comment was added at 11:49, 25 June 2008 (UTC)[reply]
(edit conflict) My advice? Buy a shotgun and binoculars TODAY. Scope them out, and when they start approaching just go into Zombie Attack mode. It's your LIFE on the line. Do what you gotta do. —Preceding unsigned comment added by 82.120.108.31 (talk) 12:14, 25 June 2008 (UTC)[reply]
Hepatitis C is spread through blood-to-blood contact and also unprotected sexual intercourse. Avoid those things and you're not at risk of catching the disease as it cannot be spread by saliva or any of the other germ-spreading mechanisms (e.g. coughing, sneezing etc) — CycloneNimrodtalk?contribs?12:12, 25 June 2008 (UTC)[reply]
Hence the binoculars. In light of the fact that the disease is spread thru blood it is very important to be out of splatter range. —Preceding unsigned comment added by 82.120.108.31 (talk) 12:17, 25 June 2008 (UTC)[reply]
Thank you kindly for your response. Like many, I like to help people but do not wish to get sick from doing that. Again, Thanks. Chailai (talk) 23:49, 25 June 2008 (UTC)[reply]
You could also ask that person about any precautions you should take, he or she might be more familiar. You can ask on phone, you probably can't be infected during that (or at least that's what the Golgafrinchans thought). – b_jonas12:42, 27 June 2008 (UTC)[reply]
Let's apply some common sense here. If a person were diagnosed with a condition that was (a) dangerous and (b) so contagious that it could be passed on by normal social contact, don't you think they would be quarantined by the appropriate authorities ? Gandalf61 (talk) 13:05, 27 June 2008 (UTC)[reply]
I live in the US and every now and then I see expose reports on local news programs about unliciensed medical practitioners who operated a private practice for years before it was revealed that their degrees were fraudulent. The fact that the medical profession is regulated does not necessarily prohibit folks from making false claims, though it makes it more difficult and provides a few consequences. --Shaggorama (talk) 19:31, 26 June 2008 (UTC)[reply]
Anyone can claim to be a "doctor" in the UK without legal recourse. When health minister, Gerald Malone said that the title "doctor" was largely defined by common usage, but that "physician, doctor of medicine, licentiate in medicine and surgery, bachelor of medicine, surgeon, general practitioner and apothecary" did have special protection in law. Therefore nothing is stopping you from adding the title "Dr." to your name at any time. However, you may not claim to be a registered medical practitioner or any variation thereof for financial gain, or attempt to offer medical services under a title (unless you are registered). If you do you can be prosecuted. Rockpocket05:35, 27 June 2008 (UTC)[reply]
I believe that is the same everywhere. Here in the U.S., we have PC Doctors, Rug Doctors, Tire Doctors... The name "doctor" has no clinical or legal meaning. Physician, surgeon, licensed are examples of terms that do have a clinical and legal meaning. -- kainaw™15:32, 27 June 2008 (UTC)[reply]
What distance is travelled on foot by an average person between birth and adulthood?
Well, how far do you think the "average person" travels on foot in one day? You don't have to be exact—that's the point of estimating. Do you think it's 10 miles (16 km)? No, that's surely too much for an average. How about 100 yards/metres? No, that's not enough. So you might decide that a reasonable daily average is a quarter mile, or a mile, or something like that. Now we have to multiply that by the number of days, but surely our average child isn't walking from birth, and even once they learn to walk, they won't walk very far. So maybe we say there's 12 good walking years between birth and adulthood, and get (12 yr)*(365 days/yr)*(0.5 miles/day) = 2190 miles. Call it 2,000 miles. If you make different assumptions, you might get 1,000 miles or 5,000 miles, and that's OK. Now, how could we do better? Well, it might help to pin down whether we're talking about a sedentary kid in the suburbs, an African villager 5 miles from the drinking well, or someone in between (say, a New Yorker who actually walks to get places). We could also try to find relevant statistics—a couple of years ago, there was a trend of wearing a pedometer to record the number of steps you took each day, with the intent of meeting some goal. I bet those came with statistics on the average number of steps people took. I hope you see that the idea of estimating is that it's OK to start with a crappy estimate. Get some idea of what the answer should be. Rule out insane answers, like walking 100 miles a day. Then try to do a little bit better from there. If you start out by worrying that you're going to be "wrong", then you may be paralyzed by fear and not get anywhere. Estimation is all about letting yourself be a little wrong, to get an answer that's good enough. See also Fermi problem. -- Coneslayer (talk) 14:14, 25 June 2008 (UTC)[reply]
Edit conflict, comment: It depends on how you define the average person. If you consider yourself as average then you could base the estimates on your personal experiences. The best way is to calculate a value per year. Babies don't walk so you can rule out year 1. I would say year 2-5 a child would walk 1-2 miles a week, including just general activity like toddling around the house. Years 5 - 10 I would say this would be more like 10 miles per week. When the child goes to school they might walk up to 1-2 miles per day. This model doesn't take into account long trips and assumes the same activity everyday, but I think the innaccuracies will cancel. So we have (2[miles]*52[weeks])+(10[miles]*52[weeks])+(2[miles]*7[days]*52[weeks]) = 1352 miles. The best way though to get really good estimate would be to conduct a survey across a number of different age groups. Jdrewitt (talk) 14:28, 25 June 2008 (UTC)[reply]
Interesting. There's a campaign in the UK to "take 1000 10000 steps a day". Let's say you do, and one step is say 0.5metres. The average age of death in the UK is about 80. You're probably fully-mobile for 70 of those; since 1000 10000 steps and 0.5 m are probably both on the above-average side, assume you walk no distance at all during the 10 less-mobile years. Then you walk 100010000*0.5*365*70 = 127,750,000 metres = 79,000 miles. Which (unlike my first draft...) is staggeringly different to your estimate. But you've not averaged that back to one year and then expanded to cover human life...if you do, then you predict about 31,000 miles-per-life, but then you didn't include any guesstimates of later-life years. Splash - tk15:24, 25 June 2008 (UTC)[reply]
Ah, the question was birth -> adulthood. Well, let's say that the average step-length increases linearly over the range 2-18 years, so is on average 0.25m over the time. Then in 16 years, 10000*0.25*365*16 = 14,600,000 metres = 9100 miles. Taking Jdrewitts estimates and using the number of years in the proposal, we get, if the 10miles/week holds for ages 5-18: (2[miles]*52[weeks]*3[years])+(10[miles]*52[weeks]*13[years])+(2[miles]*5[days]*35[weeks in a school year]*13[years]) = 11600 miles. Which is actually remarkably close to the 10000-steps estimate of 9100 miles. Since most people don't manage 10000 steps, both are probably over-estimates by a fairly large margin. As 10,000-steps is a target to aim for, probably the range is something like 4000-10000 steps in practise, so that a mid-point is 7000 steps a day, suggesting that both estimates are too much by 30-50%. So maybe something like 6000-7000 miles for a normal person up to adulthood. Splash - tk16:23, 25 June 2008 (UTC)[reply]
I would have to agree, average person depends largely on how you define 'average person' For example, if you are talking about the world, which we can presume based on the fact you just said average person not average person in the US/UK/developed world/whatever, then we have to consider that the vast majority of kids by far live in the developing world. Most kids in the developing world probably travel a lot on foot more then those in the developed world. Also by average do you mean median or mean? If you mean 'mean' then given that the is a resonable number of kids who travel very, very far, e.g. refugees, this is going to push your average up quite high. The number of kids who travel very little is going to help push it down, but there's probably not enough of them. The median IMHO is likely to be signficantly lower then the mean. Nil Einne (talk) 03:26, 26 June 2008 (UTC)[reply]
Natural In-Store Herbs that have the Similar Euphoric Effects of Dihydrocodeinone
Lots of drugs have euphoric effects. Consult a physician? Your best bet is probably to pick a Recreational drug use and then try to find something that has it in there. If you're dead set on trying something, please have a trip sitter and take other safety precautions. EagleFalconn (talk) 18:18, 25 June 2008 (UTC)[reply]
Frog on a lily pad (or ??)
I'm doing a reality check on a story for preschoolers that includes a variation on the classic image of a frog seated on a lily pad. I've read that frogs in the wild (i.e. not just a landscaper's lily pond) do live in swamps, but I'm not sure that water lilies do. So now I need to know what sort of vegetation would grow on swampwater's surface and support the weight of your local frog. "Floating leaf" might do, though I'd prefer something more specific. The bottom line is that such a plant and behavior would be within the realm of actuality, not merely an exercise of poetic license. -- Thanks, Deborahjay (talk) 15:28, 25 June 2008 (UTC)[reply]
See this for evidence of water lillies in the U.S. south - which is what I assume you mean by swamp areas. Both water lillies and frogs are found all around the world, so seeing a frog on a lilly pad is not something purely imaginary. See this for photos of frogs on lilly pads. -- kainaw™17:15, 25 June 2008 (UTC)[reply]
If you've ever seen large lily pads, you know they can hold weight very well. I don't see why the biggest frog couldn't sit on one. Mac Davis (talk) 17:24, 25 June 2008 (UTC)[reply]
My problem isn't the frog/lily pad juxtaposition, but the swamp (vs. pond). Most if not all the water lily photos and texts seem to avoid the "s"-word, and that's what the author prefers: Wetlands with characteristic muddy bottom. My tendency was to play it safe with pond but I decided against such sanitizing so as to retain the muddy bottom element. -- Deborahjay (talk) 17:29, 25 June 2008 (UTC)[reply]
In south-eastern australia I've never seen a live stationary frog in the open (and I've been looking). In dams and "wetlands" they hide in and around the water. I've heard that in the tropics things are different though.Polypipe Wrangler (talk) 22:09, 28 June 2008 (UTC)[reply]
Hypertension medication
I have heard from some doctors that the Pharmaceutical companies encourage doctors to prescribe drugs for lowering High Blood Pressure just to sell their products.The lower value of blood pressure which these doctors define as "high" is not 90 as they say but much more higher.Is it true ? —Preceding unsigned comment added by Amrahs (talk • contribs) 15:58, 25 June 2008 (UTC)[reply]
140/90mmHg is normal blood pressure so I don't really see how they've heightened it at all? Either way, I doubt it's true. Why would doctors do such a thing when there is no benefit to the doctor or the patient if they prescribe drugs for mild blood pressure. The only party is helps is the pharmaceutical company. The most efficient treatment (usually) in hypertensive patients consists of lifestyle changes. Medication is usually for more severe hypertension or hypertension which is not resolved by the lifestyle changes. — CycloneNimrodtalk?contribs?16:12, 25 June 2008 (UTC)[reply]
Absent any other complications, a physician will tend to recommend exercise and dietary changes before prescribing medications for mild hypertension. The first-line prescription medication for treatment of mild hypertension, meanwhile, is usually a thiazidediuretic; such diuretics have been around for ages, and are sold as inexpensive off-patent generics: only modestly profitable to a drug company.
I recommend reading The Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (link) to get some idea of the risks associated with, and recommended therapies for, hypertension. Interesting bits (supported by detailed studies):
"The relationship between BP and risk of cardiovascular disease (CVD) events is continuous, consistent, and independent of other risk factors. The higher the BP, the greater the chance of myocardial infarction, heart failure (HF), stroke, and kidney disease. For individuals aged 40 to 70 years, each increment of 20 mm Hg in systolic BP or 10 mm Hg in diastolic BP doubles the risk of CVD across the entire BP range from 115/75 to 185/115 mm Hg."
"In clinical trials, antihypertensive therapy has been associated with 35% to 40% mean reductions in stroke incidence; 20% to 25% in myocardial infarction; and more than 50% in HF. It is estimated that in patients with stage 1 hypertension (systolic BP, 140-159 mm Hg and/or diastolic BP, 90-99 mm Hg) and additional cardiovascular risk factors, achieving a sustained 12-mm Hg decrease in systolic BP for 10 years will prevent 1 death for every 11 patients treated."
Treating hypertension actually has pretty clear benefits from both financial and quality-of-life perspectives. While I agree that there are legitimate concerns about both over-medicalization and over-prescription, and that those problems are often driven by drug companies and their lobbyists, I don't think that hypertension is an area where this is a problem. TenOfAllTrades(talk) 16:53, 25 June 2008 (UTC)[reply]
I have spent the last five years providing data on well over two million patients to hypertension researchers. It is very clear that reducing BP below 140/90 (130/80 for diabetics) is critical for reduction of cardiovascular disease. How BP is reduced is a different topic. Most doctors push for diet and lifestyle changes along with medications. Of course, most people will refuse diet and lifestyle changes, so they are left with just medication. -- kainaw™17:09, 25 June 2008 (UTC)[reply]
a few years ago, people might have thought that 90 was normal. nowadays, more like 80. probably go down further in the future. what's "normal" for a middle-aged American turns out to be high for somebody who lives a "healthier lifestyle"; and turns out to have pretty clear risks. so we don't call it "normal" any more. Gzuckier (talk) 18:09, 25 June 2008 (UTC)[reply]
I can say that the average of the 2.6 million patients in my database is 132/75. That includes patients who are taking hypertension medication. Because this is my field of work, I think it is important to note that 140/90 is not "normal". It isn't even average. It is a cutoff determined by comparing blood pressure to cardiovascular and stroke risk. If you are interested, type "10 year risk score" into Google and you'll find many calculators for risk. If you know your blood pressure, cholesterol, weight, age, and so on, you can check your own risk. -- kainaw™22:54, 25 June 2008 (UTC)[reply]
Probably mentioned already, but I saw a couple of references to 140/90. No, it's not average, and no it's not normal. In fact, it's borderline hypertension. Basic clinical physiology. Wisdom89(T / C)01:44, 26 June 2008 (UTC)[reply]
Amine chirality
Tertiary amines with 3 different substituents (as well as secondary amines with 2 different substituent) are chiral at least in principle, but usually not at room temperature. At what temperature can the chirality be observed (let's assume the substituents are short-chained alkyls)? Icek (talk) 18:09, 25 June 2008 (UTC)[reply]
Before any (other) mean spirited person tells you to do your own homework (It really sounds like a homework problem by the way) allow me to point out that Amine#Chirality states
The energy barrier for the inversion of the stereocenter is relatively low, e.g., ~7 kcal/mol for a trialkylamine.
Now using that information can you work out at what temperature molecules have sufficient energy such that
a. a few molecules will have sufficient energy for inversion.
b. more than 1/2 the molecules will have sufficient energy for inversion.. etc
Hint you need to find out at what temperature only a very small percentage (or non of) of the molecules will have thermal energy more than 7kcal/mol
Unfortunately it seems you didn't properly understand my question. Both states are of equal energy (except for a very small difference due to the chirality of the weak interaction which is not relevant here). So in equilibrium at any temperature, half of the molecules are in either state. With about 30 kJ/mol barrier one arrives at a Boltzmann factor of exp(-(3608 K)/T) for the transition state and Boltzmann factors of 1 for each of the ground states, so as a low temperature approximation a fraction of exp(-(3608 K)/T)/2 of the molecules being in the transition state; but that is assuming that we may calculate as if there was only a single transition state which I'm not sure of. Anyways, that's still not what I want to know; more relevant is the conversion rate. Let's assume that at every collision of 2 molecules, the probability that one enantiomer is excited to the transition state is exp(-(3608 K)/T); we could approximate by taking the mean free path and the average velocity of particles (see Maxwell distribution). More accurately we should integrate over the Maxwell distribution and take into account the kinetic energy in the probability for a transition ... you see, it's not all that easy as computing the Boltzmann factors, and the results of a simplified computation could be quite far from the real conversion rate, and therefore I really wanted to ask at which temperature it becomes practical to actually observe chirality (e.g. by rotation of the plane of polarization of light). Icek (talk) 20:32, 25 June 2008 (UTC)[reply]
I thought I did.. Anyway it looks like you already have the answer to your question almost complete - but read on - I have an idea - there certainly already exist easy methods to calculate how often two molecules collide (assuming it's still a gas)..
However if a molecule has exactly the barrier energy (ignoring other energy 'nodes' eg simplifying and ignoring vibrational energy etc) then that molecule will be in the 'sp2' planar state that leads to racemisation/inversion. So if a molecule has that energy or greater then you can assume racemisation has probability 1/2
Here's a bit I think you missed - if you can calculate/estimate the vibrational energy going from one isomer to the other eg the 'umbrella inversion' vibration - then from the energy you can get the frequency of vibration - and hence it's speed... Does that sound useful?87.102.86.73 (talk) 21:08, 25 June 2008 (UTC)[reply]
From there it looks like simple maths to convert 'percentage of molecules with enough energy to racematise' and 'rate of molecule inversion with energy ~7kc/mol' into a 'half life' or similar for an enantiomeric mixture.
(Of course you probably could observe one enatiomer by selectively trapping one form with another optically active acid) - but that would be cheating - I don't believe that's what you intended.87.102.86.73 (talk) 21:15, 25 June 2008 (UTC)[reply]
Thanks for the help so far. I could calculate the fraction of molecules with a kinetic energy higher than the inversion energy from the Maxwell distribution, but assuming that all collisions will cause an inversion with probability 1/2 seems only reasonable in the gaseous state. An important question for me is (and to what I actually hoped to get an answer here): What are the experimental results? I'm sure someone has experimented with this. Icek (talk) 22:01, 25 June 2008 (UTC)[reply]
I spotted a possible problem - the rate of inversion of molecules which have sufficient vibrational energy to do so I estimate at 10^14Hz - that figure is meaningless in the absense of the collision rate - but I 'll assume that it's far faster..
The problem is the energy exchange - on collision, since the molecules have the same mass the energies should just be swapped.. and the cross sectional area is constant - so the collisional volume should be proportional the the velocity ie sqrt(energy). I bit more work should give a real figure.
But any given molecule can collide with any other - with a range of energies - causing the distribution of racemisation vs energy to change over time. At this point I have to take back my previous statement "From there it looks like simple maths".. It looks to me like difficult maths. Difficult differential equations that you could hope to get help from on the maths desk.
Actually I have never seen any work on how a boltzmann (or other) distribution will exchange energy with another (identical one) over time. It might have been done.(or not)
....between the enantiomers is very small (25 kJ mol-1)and hence they are rapidly interconverted by a process called nitrogen inversion or amine inversion. The rate of this inversion is very high (2.3x10*10sec-1) ...
might help - assuming this rate of reaction is for room temp - you could using the activiation energy work backwards using the any activation energy/rate of reaction equation you have to get the rate at low temp.. then pick a temperature at which you feel the 'half life' is long enough eg >1hr.. That really is all I can find - I big library might be able to help you out - I'd guess that n.m.r. experiments could be useful here - maybe chemical abstracts is online - and free? that might be a way to get the numbers.87.102.86.73 (talk) 23:03, 25 June 2008 (UTC)[reply]
I've got a feeling a saw figures in the textbook "Mechanism and Theory in Organic Chemistry By Thomas H. Lowry, Kathleen Schueller Richardson" , not 100% certain.87.102.86.73 (talk) 12:02, 26 June 2008 (UTC)[reply]
Use Tröger's base in which the conformation is frozen, and the interconversion is nearly zero!
Thanks to all of you. If the Arrhenius equation is valid over the wide temperature range in this case and the mean lifetime at room temperature, 4.3x10-11 s (multiplicative inverse of the number given by 87.102.86.73) is correct, the mean lifetime is about 1 s at 88 K with a 25 kJ/mol inversion barrier; 1 hour at 71 K; at the boiling point of nitrogen it's 114 seconds, and at the boiling point of neon it's far longer than the age of the universe (2.6x1033 s).
I suppose if I mixed the tertiary amine with a chiral acid - getting the stable chiral salt with one component enriched I could then add base - liberating the free amine, and at the same time observe the rate of reaction using a suitably fast technique; possibly nmr.. 87.102.86.73 (talk) 00:47, 27 June 2008 (UTC)[reply]
I took a good look through that book you mentioned; didn't see any numbers on this. It mentions it only in passing, then goes on to speculate on carbanion inversion. Any other books you can think of...I have a whole pile of orgo books available to me.
Shame - I remember more.. I was hoping it would be in the references.. - as I remember 'lowry and richardson' is pretty in depth for mechanism etc - so it looks like a search in chemical abstracts would be in order..87.102.86.73 (talk) 10:35, 28 June 2008 (UTC)[reply]
Youcould even use a non-resolved secondary amine with a nearby chiral center (i.e., the amine-inversion gives diastereomers). Look at 1H-NMR signal of the N-H at different temperatures. When you get two well-resolved signals, you know the inversion rate is "slow" compared to the NMR timescale. DMacks (talk) 04:19, 27 June 2008 (UTC)[reply]
Medical grades
What is the difference between the various medical grades in the UK? Clinical Fellow, Teaching Fellow, Clinical Assistant, Assosciate Specialist, Staff Grade, etc. Thanks. 92.4.53.191 (talk) 21:03, 25 June 2008 (UTC)[reply]
That page talks about the training grade levels, from FY1 up to Consultant, but the ones I asked about are in regards to the non-consultant non-training pathway. I know that Clinical Assistants are often GPs who work a few hours in another department, e.g. dermatology or A&E, but not sure about the others. The Fellows, etc. 92.4.53.191 (talk) 11:13, 26 June 2008 (UTC)[reply]
Crows already have a very well-developed society, they can learn and teach, they can make tools. And they've developed an air force. They might already be there for all we know. However, it seems that development of writing is essential to our definition of civilization. Franamax (talk) 01:31, 26 June 2008 (UTC)[reply]
Civilization is not a well defined term. See civilization for some of the various ways of defining it (eg, living in cities, farming, writing, "being civil", etc). That page also seems pretty clear in saying that the term is one that applies specifically to humans. Pfly (talk) 04:20, 26 June 2008 (UTC)[reply]
Franamax: you mind expounding on that little? Learning, teaching, and tool making are talents for sure, but i feel that a "well-developed society" implies a structured, organized cooperative that is sustained by its members through generations. Perhaps this could apply to a flock (or a murder I guess) but I don't know if there is enough structure or population in a flock of birds (at least crows) to qualify it as a society. I feel like maybe if there was evidence for some sort of "super-flock" maybe we could call that a society? I think penguins might be a good model. --Shaggorama (talk) 20:22, 26 June 2008 (UTC)[reply]
Crows work in large groups, with well-defined roles and leaders. Those groups roost together as well and I believe the membership stays stable. It's a lot of fun to watch a group of crows systematically go through a neighbourhood, spotting where the watch-crows are, listening to the calls as the working crows are warned and given permission to move around. They're definitely not just a mob. I'd call that a society, though others will differ. Franamax (talk) 22:26, 26 June 2008 (UTC)[reply]
June 26
Weird "grass circles".
In my apartment lawn, there are these semicircular, dark patches of grass. Does anyone know what they are? I'm convinced they are the work of aliens. Here are the pics. [2]. Thanks for any input 199.76.188.69 (talk) 01:14, 26 June 2008 (UTC)[reply]
That's very interesting. Is there anything interesting at the physical centres? Sprinkler outlet or anything?
I feel like this one is the most likely explanation. A sprinkler that disproportionately sprayed water at a specific radius would produce these effects. EagleFalconn (talk) 04:00, 26 June 2008 (UTC)[reply]
Maybe your best bet is to wait 'til you see the lawn maintenance people, then run out there and ask. Or maybe the building manager. Do post the answer here though. Oh and when you say aliens, do you mean there are immigrants taking care of the grounds? :) Franamax (talk) 01:28, 26 June 2008 (UTC)[reply]
I've found the answer! No, they aren't from ET aliens nor illegal aliens. They are fairy rings. They're caused by fairies and elves dancing, though the scientific explanation is that they're caused by fungal growth.
There may have been at one time a series of decorative walls in a semi-circle repeating pattern through the lawn. When the walls were removed, they landscaper planted grass seed that wasn't of the same variety as the rest of the lawn. So the different variety of grass is a different shade of green. Dismas|(talk)03:36, 26 June 2008 (UTC)[reply]
The "darkness" of the grass is often proportional to the amount of nitrogen-bearing fertilizer applied to the lawn; a broadcast spreader slings fertilizer out within a circle of a certain diameter (say five feet for a hand-pushed spreader). An accident with such a spreader could easily leave a dark, over-fertilized area of grass.
Consider a controllable, variable DC voltage source some distance away from a load. The load requires a constant voltage and a varying current (consider a house with various numbers of lamps lit); the amount of current required is a fixed function of time, and may be considered to be known in advance if it helps. We can achieve this by varying the source voltage, but as the required current increases, the amount of power dissipated in the lines to and from the load increases quadratically. It seems that a way to reduce this waste would be to install reservoir capacitors near the load, so that when more current is required it can be drawn from them and when less current is required they can be replenished, with appropriate adjustments to the voltage source to make this happen. The RMS current from the source should thus be reduced even though the absolute average current (dictated by the load's requirements) is the same. However, the obvious approach of simply putting a capacitor in parallel with the load fails completely because the load by definition has constant voltage, so the capacitor has constant charge and 0 current. (In the perhaps more realistic case where the voltage is allowed to change slightly, the capacitor is merely inefficient, as it stores much more charge than it ever may dispense before being recharged.)
What is the correct approach, then? A variable capacitor, perhaps? Ideally we'd have some sort of (ideal) rechargeable battery that can store energy but has no correlation between amount of charge and potential difference (except that obviously no energy implies no voltage). Furthermore, how might this approach be extended to support an AC source — not a rectifier, but a true AC source and load where a capacitor in parallel would fail to store any energy permanently? --Tardis (talk) 02:42, 26 June 2008 (UTC)[reply]
Isn't it enough to have everything in parallel? If the sole need for changing current is turning items on and off, they'll get the mains voltage regardless when they're in parallel. You can accomodate the increasing voltage across the mains wire by using a higher voltage than necessary, and placing a variable resistor before it branches to the parallel circuits. You said the voltage needed is constant, so that sounds about right. But practically speaking, the actual example you gave (a house with appliances) can tolerate the variations in voltage that would result. Someguy1221 (talk) 04:06, 26 June 2008 (UTC)[reply]
It's not so much the precise control over the voltage that's the problem, but the non-linear wasted power in the lines. To take an extreme example in the vein of the house analogy, consider some small constant load and then a thousand hair dryers that are all used together for less than a minute per day. The average required power (thus average current) is not very large, but the RMS power (to which the waste is proportional) is huge because of the spikes. As the number of dryers increases, the useful power increases linearly, but the wasted power increases quadratically, so eventually almost all of the power is being wasted in the lines. Drawing the average current over the lines at all times would be preferable, if there were a way to store the "hair dryer energy" locally until it was needed. (Of course, the house is just a good example of a variable load; any sort of pulsed power arrangement would have this problem.) Does that make the question clearer? --Tardis (talk) 13:43, 26 June 2008 (UTC)[reply]
Active electronics or an electromechanical regulator at the load (like a variable capacitor or storage batteries and controller) ) would not be free of cost. You need to balance the cost of a novel regulator system at the load with the cost of having larger feeders or of placing a source of power closer to the load. A battery bank near the load or rotating equipment at the load could also regulate voltage. Batteries might be more economical than capacitors, unless the load cycle was quite short. If a huge load of short duration is to be placed on a power system, flicker must be limited. The customer who creates the flicker (like a factory which uses a huge of current once an hour) is made to pay for the system reinforcement, or may be told to build his own generating plant. A compromise which has been used for a customer who needs to do 30,000 amp short duration fault tests a few times a day is to use utility power to spin up a flywheel on a customer generator, which is then disconnected from the utility and serves to supply the fault current as it spins down. Capacitors at the customer site could also be used to supply spikes of energy. In the early days of central station DC power in the 19th century, the mains could be quite large, to prevent excess voltage drop, and the generating stations might be located every couple of miles. Sensing conductors (non-load carrying) could be placed at various points in the close to the load to inform the generating plant of the user voltage, to supplement line drop compensation. Regulation of AC systems was later accomplished by placing AC substations closer together than the generating stations, which supplied higher transmission voltage. The substations transformed it down to distribution voltage and were a point of voltage regulation. AC capacitor banks along the line furnished additional regulation. Simply placing pole mounted or pad mounted transformers at closer spacings improves regulation, without tap changers, which are usually found only in substations. In summary, I would hesitate to pay to reinforce an entire distribution system either for delicate load which requires a constant voltage, or for demanding loads which impose huge infrequent brief loads. Another approach would be to run a dedicated line from a dedicated transformer to the high surge load, or to run a transmission line to it an give it its own transformer, with rectifiers if it is a DC load. Or a motor generator could be used to give it adequate voltage. It sounds like engineering questions which utilities and industrial customers face frequently. The questions are how bad is the load factor, and what is the cheapest way to prevent excess flicker. Edison (talk) 12:28, 27 June 2008 (UTC)[reply]
Soap is really like a surfactant that aids is removing germs from the skin. I'm not sure of how long, but bacteria and fungus can certainly live/grow on soap or in detergent. Wisdom89(T / C)03:54, 26 June 2008 (UTC)[reply]
Yes...the purpose of soaps and detergents are to remove undesired material from whatever you're washing, in this case yourself. They are not designed to actually destroy what they are washing away. If you're really concerned, you can go for antibacterial soap, but outside of disinfecting your hands before performing surgery, there is no evidence to my knowledge of an actual benefit to using it; Specifically with respect to a study on hand soap, I recall the quote (something like this, anyway), "It's getting the bacteria off your hands that's important, not killing them as they rinse down the drain." Although I'll admit I've thrown out a bottle of soap after it sat unused for years and took on a funny color...Someguy1221 (talk) 04:00, 26 June 2008 (UTC)[reply]
Soap is in fact primarily composed of a surfactant. What happens on your skin is that bacteria and dirt and such get stuck on the oil on your skin, or in the case of your hair in the sebum. This oil is non-water soluble, making it very difficult to get rid of a lot of this stuff. Soap decreases the surface tension between the water and the oil making the oil (and hence all the stuff in it) water soluble so it is possible to wash away. So you really don't have anything to worry about with the soap getting dirty. If you're really that concerned about it, a quick rinse (5 seconds) of the bar of soap at the end of your shower would be sufficient to eliminate anything stuck to the surface since the surfactant most commonly used is very water soluble. EagleFalconn (talk) 04:08, 26 June 2008 (UTC)[reply]
One of my favorite Pluggers cartoon panels showed a plugger coming in from working hard outside, maybe on his car; the caption was "A plugger has to wash the soap after he washes his hands." If you're concerned, take that advice and just clean off the soap a bit after you shower. ;-)
Antibacterial soap that contains antibiotics (bactericides, really) is a bad idea. It just helps breed superbugs. As for the OP, just wash off the surface of the soap in the stream of water before you start using it to clean your cavities, and you'll be fine. Also, harsh soaps are meant for ordinary skin, not mucous membranes. Be gentle with your mucous membranes. --arkuat(talk)07:37, 27 June 2008 (UTC)[reply]
optimum size when maximising star lifespan
What I consider interesting is that the largest stars have far larger quantities of fuel but their large size also increases the rate of reaction such that the lifespans of such stars become way shorter. Are there any methods of formulae to calculate what is the theoretical "optimum size" for stars to live the longest (with active fusion?). I assume if you start out with too little fuel (though with enough critical mass to start a reaction), your lifespan will also be cut short. John Riemann Soong (talk) 04:26, 26 June 2008 (UTC)[reply]
Though I think the original poster likely has a point. If you take a star just ever-so-barely this side of a non-fusing brown dwarf, it probably fuses for a shorter period than a star perhaps 10% larger. The reference you mention (at red dwarf the star, not Red Dwarf the BBC programme) isn't specific enough regarding dwarf stars to address this issue either way. — Lomn04:53, 26 June 2008 (UTC)[reply]
See main sequence, it has the answer. Basically, if the star has enough mass to ignite the hydrogen in its core, it would normally stay in this "steady state" for a very long time; the less massive is the star the longer, very possibly longer than the lifetime of the universe so far. So, the smaller the better. Lifetime-versus-mass table is here. Cheers, --Dr Dima (talk) 05:43, 26 June 2008 (UTC)[reply]
Actually, I'll follow up with more definite data to my previous answer -- this is not a trend that is indefinitely sustainable. Brown dwarf notes that those stars (less massive than red dwarfs) can cease fusion on a scale of millions of years. There is some point larger than "minimum size for fusion" at which "length of time fusing" maximizes. — Lomn12:59, 26 June 2008 (UTC)[reply]
Brown dwarfs are a special case: they're fusing deuterium rather than hydrogen, so they've got less usable fuel to begin with. "Star" is generally defined as any body capable of sustained fusion of hydrogen. --Carnildo (talk) 23:28, 26 June 2008 (UTC)[reply]
Electrolysis of Saline Solution
I was trying something i found in an old science book but since I'm only in high school i only know that much of chemistry so perhaps someone could explain it better.
We've tried something similar to this at school using a Hoffman voltameter but this more primitive setup worked just as well. Opposing poles of a 9 volt battery are attached to 2 graphite pencils partially submerged in the water/salt solution. The result should be the separation of the hydrogen and the oxygen no? that worked fine. Something like H2O -> H2 + O. (forget the sodium here)
Then i tried just putting the wire directly in. I didnt do this for long because i suspected it might produce chlorine. Anyway NaCl is ionic right so the ions should seperate in water? So its something like this perhaps NaCl + H20 -> Na + CL ?? . Im not sure what to do there. Anyway my question is was chlorine produced?
Also there were white solids floating in the water.
This could be salt but that means chlorine wasn't produced.
The inverse works that same way being they were seperate and it wasnt salt but something else.
So what was the solid?
Salt dissolves in water to give Na+ and Cl-, there is also a small amount of autoionisation of water itself to give H+ and OH- ions.
At the negative electrode hydrogen will be produced, (even if sodium were made it would react immediately with the water to give the same product hydrogen)
At the positive electron two reactions can occur:
2OH- turns into H2O + 0.5 O2 +2e-
2Cl- turns into Cl2 +2e-
The first reaction you already know, from the electrolysis of water, the second makes chlorine, and occurs in the presence of Cl- ions.
In fact the chlorine can often react with the water to give bleach
ANSWER If you run this cell - you'll get some chlorine give off (green gas), and some dissolves (making the solution bleachy). Small amounts aren't harmuful, large amounts are.87.102.86.73 (talk) 12:18, 26 June 2008 (UTC)[reply]
I was thinking of this reaction the other day and I was trying to think of some common substance that would provide the ions needed to charge the water but not get in the way of oxidizing the water to produce oxygen and I thought either sodium bicarbonate (baking soda) or acetic acid (vinegar) would work. Anyone tried this?72.219.143.150 (talk) 19:57, 26 June 2008 (UTC)[reply]
bicarb is a good choice, as is NaOH if you can get it (pearl caustic soda) - used for clearing drains - be careful - can burn you.. both will work - and you only need a small amount - enough to increase the ionic conductivity of the water.
acetic acid - not so sure - acetate should be relatively stable to oxidation - but that could depend on what your electrode is made of.87.102.86.73 (talk) 23:08, 26 June 2008 (UTC)[reply]
Is this picture for real? Why doesn't Arnold take just a LITTLE bit of care of himself, like a few minutes? Or is it just not possible given his age? If I don't want to look like that when I'm old, what can I do?
Firstly he is 60 - if you look anything like as toned as he does (even in that photo) at 60 you will be more than happy with yourself. Secondly - a single photograph designed specifically to show-off someone's flaws is always going to look much worse than if you were to see him in the flesh. The photographer will have had maybe 50 shots of him in that little segment and will have deliberately picked the one that made Arnie look worst. Finally the photo to the left is from a competition-event so it's a ridiculous comparison to make. In short Arnie looks great for 60, and I expect the reason is that he has kept himself physically fit for a long time in his life, he keeps his mind and body active (judging by the work he's undertaken in his life) and that helps too. I wouldn't be amazed if the shot was photoshopped a bit but then so will the competition shot. 194.221.133.226 (talk) 11:17, 26 June 2008 (UTC)[reply]
Not to mention he was posing in the first one in a way designed to show off the muscles, whereas in the second I wouldn't be surprised if the photographer did everything he could to catch Arnie in a non-posed moment designed to show off the flab. Confusing Manifestation(Say hi!) 00:06, 27 June 2008 (UTC)[reply]
how much walking until adulthood?
I asked this question above but didn't get the answer I was looking for. I'd like the answer in terms of number of roads, not total distance. —Preceding unsigned comment added by 82.120.107.22 (talk) 11:02, 26 June 2008 (UTC)[reply]
With all due respect, phrasing the question as "What distance..." probably wasn't the best way to get the answer you need. If you ask for a distance, that's what we'll give you. The new form of the question is rather vague. Are you only counting distinct roads, or do you count a road every time you walk on it? Is the shopping mall a "road"? The school building? A sidewalk through the middle of the park? Do you count a road when you merely cross it (after all, you're "on" it for 10+ metres)? For me personally, I would bet that 95% of my walking is not along a road. -- Coneslayer (talk) 11:21, 26 June 2008 (UTC)[reply]
What if you pace back and forth on the same road your entire life? Does that count as 1? I wonder how many responses are necessary to point out that "roads" is not a unit of measurement. This question is no different than asking "How many hedgehogs does a the average person walk?" -- kainaw™12:34, 26 June 2008 (UTC)[reply]
I'm not sure this response is from the OP since the IP adresses are different. Anyway, significant thought has gone into some of the original answers and I suggest you read them and use some ingenuity to apply these estimates to the actual solution you are looking for, whatever that may be. Jdrewitt (talk) 07:24, 28 June 2008 (UTC)[reply]
Since you haven't apparently clarified the original question, I'd have to answer very few since many children don't walk on roads most of the time, or at least what we commonly consider roads. As I mentioned in my response to the original question, most children live in the developing world (in particular a large number live in India and Africa and to a lesser extent, China) Nil Einne (talk) 06:48, 29 June 2008 (UTC)[reply]
More Importantly, Children not left in my care are taught to use Pavements (sidewalks to those of you somewhat illiterate) in the apparently none-developing (?) world. However, i'd say for the ones I encourage... about 1 road, then a car, of course technically they don't reach adulthood, so perhaps they don't count. Then of course, for those children that survive me, we have to take into account Adulthood, and how it is defined by the particular culture. In some ancient, but still existing cultures a 14 year old is considered an adult, while in Korea, children don't exist, they've all been replaced by MMORPG characters. Then in order to average it out you also have to factor in all children who ever lived and all who ever will. Ok, i'll just quickly add that up on my NP-complete machine... well i'll be damned Tango was right, precisely 42. - Jimmi Hugh (talk) 22:27, 2 July 2008 (UTC)[reply]
So, it got around to that time of the week again, where, precipicated by the reading of an article [4] about the continued accumulation of evidence for a fractal (non-homogenous) distribution of matter on cosmological scales, I was given cause to resume a habitual musing, to wit: What has GR ever done for me, anyway? Raising the question in various irc channels was, to say the least, unproductive, so I decided to bring up the matter here, where I expect a more reasoned, interesting, and informative response. To be as precise as possible, I will reformulate the question and append a precautionary note, so as to preclude the most obvious inanity from replies. Which, if any, technological advances have directly required the acceptance, or at least conception, of General Relativity Theory?
1. GPS does not require GR for its fundamental theoretical operation, and those correctional factors which it does employ are not predicted exclusively by GR, nor would have been in the remotest part difficult to ascertain empirically. —Preceding unsigned comment added by 153.1.253.80 (talk) 12:39, 26 June 2008 (UTC)[reply]
Well, the fact is that GR doesn't have a lot of human-scale benefits is not terribly surprising, given the scales it operates on. Waving away GPS is a bit cheap, IMO—other theories may incorporate the correctional factors but none of them have passed the many, many tests of all aspects of GR. (Which is not to say that GR is complete or final; it's likely it's not. There's that whole incompatibility with the standard model problem. But it does indicate that GR is probably substantially correct, and certainly a more reliable theory than anything else out there at the moment.) GPS is the only technology out there at the moment that incorporates GR. Saying that other theories "could" account for the same factors is not how science works—the question is about falsification, not verification.
But asking "What has GR done for me lately?" is sort of like asking "What has Jupiter done for me lately?" It's out there, it's big, it's useful for astronomers—but it doesn't affect things on a human scale much at all. --74.223.170.249 (talk) 13:01, 26 June 2008 (UTC)[reply]
You have, perhaps inadvertantly, hit upon the main kernel of frustration that mandates my original question: it is exactly this (supposed, and vociferously defended) nonapplicability of GR to the if-not-yet-then-quickly-becoming infamous "classical realm" which is the root of its objectability. Its cosy incubation within the comsological regieme -- where experimentation is all but off-limits, and observable data can be accounted for by multiple, conceptually-incompatable, theories -- enables it to dawdle merrily in the penumbra of falsifiability, metamorphosising ever more convincingly into an academic white elephant that devours great swarths of cognitive resource for diminishing returns, with the impunity accorded to its (de facto) religious sacredness. Were this vertible lightning-rod-for-inspiration not planted firmly in the fertile imaginative ground of our blossoming physicists, who knows what other paths of least potential credulity might be traversed by the bolts of intuition to which they are prone. Perhaps one might stumble upon a theory of cosmological evolution which entails consequences germane to that sphere in which we live, and have the liberty of active investigation through the controlled variation of parameters. Good lord, that might almost be considered progress... —Preceding unsigned comment added by 153.1.253.80 (talk) 14:10, 26 June 2008 (UTC)[reply]
the beauty of physical soapboxes, as stood-upon in public streets, was that the uninterested had the liberty of simply walking past. please feel free and welcome to act analogously. —Preceding unsigned comment added by 153.1.253.80 (talk) 14:53, 26 June 2008 (UTC)[reply]
If you're going to reject GPS as an answer, you'll probably reject everything else on similar grounds. You can always just measure the systematic error in your results and correct for it without knowing the cause. It's much nicer to know the cause, though! Other than GPS, I expect the effects of GR are limited to aerospace - I expect it had to be taken into account when planning communications with probes near the sun. --Tango (talk) 14:22, 26 June 2008 (UTC)[reply]
The distinction I intended to extend by discounting GPS as having required GR was that between enabling and facilitating theory as regards technological advance. Refinements in theoretical prediction of the involved variables will generally assist in the implimentation, precision, effectiveness or applicability of a particular invention. However, this facilitation is not on par with the enablement exhibited when a theoretical breakthrough makes concievable technology which, prior to its arrival, was speculative, if even imaginable. In this sense, I was asking whether GR has lead to any qualitative, rather than simply quantitative progression in our ability to harness the physical universe. —Preceding unsigned comment added by 153.1.253.80 (talk) 15:01, 26 June 2008 (UTC)[reply]
Perhaps you are underestimating the effect of GR on GPS. It's not just a matter of the results being a little imprecise, the error is very large. According to [5], the readings would drift by about 10km a day. GPS would be useless if it wasn't corrected for relativistic effects. I think trying to distinguish between qualitative and quantitative effects is a bad idea - Newtonian physics is a decent approximation of GR on every day scales, and it a rough approximation even at quite large scales. Most results of GR can be interpreted as simply corrections to Newtonian physics. The only things that can't are likely to be related to black holes (which are too far away to affect us) or gravity waves (which aren't even measurable with current technology, although we're getting close). --Tango (talk) 15:41, 26 June 2008 (UTC)[reply]
None that I'm aware of. GR also predicts the precession of planetary orbits (with applications to astrology, I guess ;-). Gravitational lensing allows us to see things otherwise invisible, including extrasolar planets. And of course there is a huge difference between technological application and falsifiability. --Stephan Schulz (talk) 23:21, 26 June 2008 (UTC)[reply]
I find it beautiful that a theory created decades ago now find a place in the cars of many a person who distrusts scientists. There are few moments that rival the confirmation of a long-predicted scientific result. Many a time the original scientists aren't there to observe it. Imagine Reason (talk) 04:29, 27 June 2008 (UTC)[reply]
You seem to be conflating the idea that because GR doesn't relate to human technologies it is somehow outside the range of experiment/experience. This is not true. GR has satisfied many experiments—over and over again it has managed to accord with very precise predictions and succeed where no other competing theory has be able to. You can test GR many different ways, without too much trouble (unlike String Theory). Most of those ways don't translate into human technologies. But that has no relation to its ontological status. That doesn't mean it's "correct" in an ultimate sense—it has to be "incomplete" on some level, because it is not compatible with quantum mechanics. But so far nothing else has come close to displacing it or being as experimentally rigorous. The other advantage of GR is that it is conceptually quite simple—once you re-define what "gravity" is then the rest of it falls into place rather easily, which is also to its credit (it is not ad hoc or based on purely mathematical tricks). --140.247.10.12 (talk) 10:52, 27 June 2008 (UTC)[reply]
Costly Projector Bulbs
How come the bulb in a projector is so expensive (perhaps a few hundred dollars)? Are they hard to manufacture? Do they have some particularly expensive material in them? Thanks. —Preceding unsigned comment added by 140.247.241.132 (talk) 14:15, 26 June 2008 (UTC)[reply]
Relatively few of any given type of projector lamp are produced so you don't get huge economies of scale in their production. But probably more importantly, like so many things in life, projector lamps are expensive simply because they can be and you'll still pay for them. Capitalism takes away at least as often as it gives. Meanwhile, you may enjoy our article about metal halide lamps.
The article on negative feedback amplifiers didn't seem to explain why they increase stability and linearity. Can anyone explain this to me? Thanks. —Preceding unsigned comment added by 140.247.241.132 (talk • contribs) 14:19, 26 June 2008
(note: please sign your posts.) I'll try, but I'll admit I'm no expert. When the signal goes through the amplifier's "output chain" (output tubes/transistors, wiring, _maybe_ output panel, part of speaker cable, speaker, etc.) the first time, all the components are going to have non-linear effects on the signal. If feedback were not used, these non-linear effects would add up and cause distortion (possibly audible and unpleasant). Feedback "feeds back" or adds a bit of the inverse ("negative") of the signal/distortion and this removes a bit of the non-linearity. It can be enough to get an amplifier with a good low THD (0.01%) from imperfect non-linear components, which are cheaper than completely linear ones. Flayked (talk) 22:28, 27 June 2008 (UTC)[reply]
If you look at the formula for the gain of the amplifier you will find that it depends on the feed back amount and the gain of the underlying non-ideal amplifier. But when this last gain is high, it has very little effect on what comes out. This means that the n egative feedback amplifier is very linear, and has very low distortion. To look at the instability, you will need to understand why an amplifier would be unstable, that is oscillate. If the output is added back to the input then the output can head off to infinity, with an unstable result. But if you subtract output from input, that will cancel any tendency to add, and make oscillation unlikely. In reality there will be time delays on going through the amplifier, but even so the input will be settled down by the feedback and oscillation is harder. Graeme Bartlett (talk) 22:46, 27 June 2008 (UTC)[reply]
Why should an amplifier without any feed back be unstable? I would venture that this is impossible!
As to linearity, any negative fb tends to compare the input with the output thus improving linearity, reducing distortion/noise etc. —Preceding unsigned comment added by 79.76.191.71 (talk) 23:58, 27 June 2008 (UTC)[reply]
Calculating the horizontal force exerted by a 60 ton vertical press on an aluminum extrusion
we have an aluminum extrusion and we want to be able to test the 4 welds on it, so we want to stick it in our 60 ton press and make sure that it will not break under a force of 36,000 psi.
knowns:
round extrusion
OD=7.00"
ID=3.18"
thickness=1.00"
60 ton press
do not want to exceed max force on ID = 36,000 psi
We plan on making cone shaped hardened tooling for each end of the press, also we will be making 2 half mooned hardened sleeves that will fit inside the aluminum extrusion to apply equal pressure across the whole inside diameter. Both ends of the sleeve will have a coned shaped groove to fit the tooling of the press. As the press is activated the press will drive the 2 half moons apart applying a force to the inside diameter of the aluminum extrusion to test the welds.
My question is how can I calculate the force on the inside of this aluminum extrusion? I'm guessing it will have some relationship to the downward force of the hydrualic press —Preceding unsigned comment added by Gbalamut (talk • contribs) 14:25, 26 June 2008 (UTC)[reply]
It will be related to the downward force of the press. You need to know the shape/size of the internal cavity. Then, you can assume the aluminum has a constant pressure across the surface of the internal cavity. Knowing that pressure, you can consider it to be hydrolic - surface size and pressure of the press compared to surface size and unknown pressure of the internal cavity. That will give you a good estimate. -- kainaw™14:48, 26 June 2008 (UTC)[reply]
QUERY From your description it sounds like you are using the press to get a force outwards from the inside of a (circular cross sectioned?) extrusion.. One problem I see here is that if you use 'half moon' inserts then the force will not be equal all around the edge - especially if the aluminium deforms before breaking - did that make sense?
An alternative might be using hydraulic pressure directly to apply this inner force which has the advantage of being equal all over - in this case you'll need to be able to form a pressure proof join between the hydraulics and extrusion - maybe the hydraulic method won't produce enough pressure.
ANSWER (possible) Assuming your conical inserts have angle A (A is half the angle at the cone tip), then the force outwards at the contact of the conical insert and half moon should be F/ tan(A) where F is the total hydraulic press force, then divide by the surface area of the contact between half moons and extrution to get the pressure.
The cone is acting as a Wedge (mechanical device) - the force is split between the two sides - for a more evenly distributed force use sections ie using a 6 segment splitter will result in force on outside of each splitter of F/6 tan(A)
The knowns above are the specifications on the aluminum extrusion. I agree that more segments in a splitter would be a better design, but for the moment I am just assuming that the pressure will be equal. cause my biggest concern is that the 4 welds hold.Gbalamut (talk) 19:49, 26 June 2008 (UTC)[reply]
Given that the 2 piece splitter gives most of its force along one axis (in opposed directions) I'd suggest trying the splitter in different orientations..
The angle on my conical surface is 30 degrees, max force on the inside of the extrusion is 36,000 psi, and the area is (PI X 3.18 X 1) so I believe what you are saying is.
F press = Tan 30 X 36000 psi X 9.990
doesn't seem to make sense? what about friction? doesn't that need to be taken into account. I would assume that the force from the press and the force exerted out vertically would be pretty close in value?? got any suggestions on websites were I could refresh my memory on all these formulas? its been about 15 years and i am quit rusty. —Preceding unsigned comment added by 147.154.235.53 (talk) 20:14, 27 June 2008 (UTC)[reply]
You need to look at Wedge (mechanical device) for an explanation - curiously friction does come into it in the static case - but stiction could cause some 'noise' in the force/distance moved by ram graph
I've just done my morning stroll to get some coffee and once again was serenaded by a mockingbird that lives nearby. Or perhaps he only works here and commutes from somewhere else, just like me. But that's not important right now. What has me curious is why does a mockingbird sing all those different songs? I can find plenty of sites that tell me how many songs might be in an average repertoire, and that some birds have imitated car alarms and dogs barking, and things like that, but there has to be some purpose to all that parroting (so to speak), other than making LarryMac smile. Our Northern mockingbird article says "The Northern Mockingbird's mimicry is likely to serve as a tool for increasing the size of its repertoire and thus its ability to attract females" which seems to beg the question. It learns songs so that it knows more songs, and that makes it a good catch? Any ornithologists out there? --LarryMac | Talk14:51, 26 June 2008 (UTC)[reply]
What I always heard was that knowing a large number of songs meant that the bird had a productive habitat (capable of supporting many species). I suppose it could also indicate that the bird had "been around a while", and hence had good genes for survival. (At an old apartment, the mockingbird liked to mimic "Garbage Truck Backing Up". I translated this into English as: "Hey, ladies! My habitat supports a garbage truck! Have you ever seen how much those things eat? This is a great spot!") -- Coneslayer (talk) 15:12, 26 June 2008 (UTC)[reply]
Could it also be possible that the birds use mimicry in order to locate other members of their local flock? I read somewhere[citation needed] that Budgerigars do this - copying other birds of their own/other species and local sounds in order that they might be identified as members of a particular 'clan' within a much larger gathering (the idea being that birds from a similar area will have similar learned vocalizations), making it easier for friendly birds to find each other. --Kurt Shaped Box (talk) 21:57, 26 June 2008 (UTC)[reply]
You're right, it does beg the question. The same question might be asked of peacocks and birds of paradise: Why have such elaborate feathering, which both hinders the bird's movement and attracts predators with bright colouring. Basically, females choose the best male singer. Their offspring, then, are hardwired for the same: the male offspring will be a good singer, and the female offspring will be attracted to good singers. Look up sexual selection for more. − Twas Now ( talk • contribs • e-mail ) 00:57, 27 June 2008 (UTC)[reply]
IANAO, but I had always heard that mockingbirds sang other birds' songs so as to claim a large amount of territory: the thrushes think that there's already a thrush eating the food over there, so they don't visit, and similarly for the robins, the jays, etc. The mockingbird then gets its pick from all the different kinds of food and nesting areas that the other species would otherwise divide. --Tardis (talk) 13:17, 27 June 2008 (UTC)[reply]
Flooding in the US midwest
I am wondering how the floods occurred. June 2008 Midwest floods it states that the levees were breached. Why were the Levees breached in the first place? Weren't they strong enough? Considering US has the latest civil engineering technology could they have prevented the flooding? My other question is that when the streets get flooded, there is a storm sewer every block or so, so why did the storm sewers did not work in this occasion? --64.228.196.97 (talk) 16:32, 26 June 2008 (UTC)[reply]
A cynic might suggest that we're too busy spending our borrowed money to blow shit up to have any left over to properly maintain and improve our national infrastructure.
There is no practicality to building levees tall enough to withstand flooding that has never occurred before. There's a kind of a viscious cycle going on near big rivers like the mississippi: They build levees to keep the floods out, but since this makes the river more confined, the waters rise higher, so that when they do fail the flooding is worse. I don't know too much about hydrometeorological engineering, but I would think that the cost of maintaining 4000 miles of 50-foot tall levees during a 500-year flood would require about, say 1000 engineers (on each side), each equipped with a construction team to fix any weak spots they may find. It's just not practical.
You could just say build the levees taller, and make them out of concrete so they can't leak, but this causes yet another problem: If you build a levee taller, this decreases the frequency of major floods, but makes the potential for more catastrophic flooding when the levees finally do get overtopped (or the soil fails underneath). Besides, the reason there's all this fertile land for growing crops out there is because of floods like this (see Floodplain#Ecology). I hope this helps.-RunningOnBrains17:59, 26 June 2008 (UTC)[reply]
Exactly. Current thinking is to build sacrificial flood-zones into the flood protection system. Towns and cities, and infrastructure like power plants and water works get protection, and the flood control scheme deliberately sends the water to low-value areas like farmland (and the farmer gets compensation for the loss of his crop). Its pragmatic - expensive flood control measures are used to protect only expensive things. This is a change from the "man conquers nature" mind-set that has prevailed (not just in the US, in many places). In a lot of ways this is an analogous shift to the changes in forest-fire management strategy, where thinking is shifting from total suppression to managed burns. Unfortunately the media (certainly not just in the US) has a "something must be done" mindset, and (faced with pictures of sad looking cows in flooded fields) it takes a strong-willed politician to say "we shouldn't be spending billions to keep some fields from getting wet". -- Finlay McWalter | Talk20:20, 26 June 2008 (UTC)[reply]
As to the storm sewer, that's dependent on the sewer having somewhere to drain. That's great when it rains and the water drops down to river level. It's useless when river level is above the drains. — Lomn18:24, 26 June 2008 (UTC)[reply]
In low-lying areas where there is not any convenient downhill location to shunt water to, storm sewers are often designed as dry well systems. This works fine for a few inches of rain, but it has only a finite capacity that will be totally overwhelmed during a riverine flood. Dragons flight (talk) 21:17, 26 June 2008 (UTC)[reply]
Depending on the extent of the fire, they may also be removed in the fire elevator. Wheelchair uses tend to choose low or ground floors for their residences; however, they may not have many choices in workplaces. I don't know of a fire warden who has been pre-selected for the job, but fire fighters are certainly trained for such carries. It is thus a wise wheelchair user who keeps his/her body weight as low as possible. ៛ Bielle (talk) 17:29, 26 June 2008 (UTC)[reply]
Some stairwells in Ireland have toboggan-like slides which are intended to allow anyone assist a disabled person down the stairs. They look outrageously dangerous, but I suppose it is better than the alternative PlasticupT/C18:18, 26 June 2008 (UTC)[reply]
My (seven-storey) building has 2 units per floor reserved for people with wheelchairs. When the fire alarm rings they just stay put. I think the fire department is supposed to help them out if necessary. —Preceding unsigned comment added by 64.231.11.47 (talk) 00:58, 27 June 2008 (UTC)[reply]
This is referred to as shelter in place, another term for which Wikipedia doesn't yet have an article. [7]
Having just watched The Godfather III on DVD again tonight, I find myself pondering one of the more famous scenes in the movie - i.e. where one of the villains of the piece is killed by having his own spectacles jammed into his throat, severing his carotid artery. Now, one of the 'making of' bits on the bonus discs (I gots me the new trilogy box set) has Francis Ford Coppola commenting that he has no idea if it's actually possible to kill someone with a pair of glasses (sounds like one of those things he gets asked by fans on a regular basis). So, I'd like to know if it would actually be possible, as seen on screen...
Looking at my own specs, I'd guess that I could probably give someone a few bloody gashes with them (were I so inclined), if I held them end-on in my fist and got a few good downward stabs in - but I doubt I'd be able to stick them deep enough into the flesh to cause a fatal wound. I think that they'd just bend/break. Thinking about it, you could probably fashion a shiv from a broken lens and the frame - but that's not what was done in the movie, so let's forget about that for now. --Kurt Shaped Box (talk) 21:41, 26 June 2008 (UTC)[reply]
I haven't seen the film, so I can't say whether they way they do it is possible. As for breaking the lenses and using the shards as a weapon - it's worth noting quite a lot of glasses are made out of plastic these days for safety reasons, so you would need to make sure your glasses are actually glass before relying on them for your killing needs! --Tango (talk) 22:03, 26 June 2008 (UTC)[reply]
But of course the movie is set in the early 80s. I suspect that glasses were more deadly back then. I mean, we even ate full-fat yoghurt back then, and that both ways up and against the wind! --Stephan Schulz (talk) 22:34, 26 June 2008 (UTC)[reply]
Yes, I remember whittling my first personal computer from a tree branch, back when the internet was stll being used to play volleyball. Those were good days... Franamax (talk) 22:51, 26 June 2008 (UTC)[reply]
Some plastics can have very sharp edges when broken too. Not sure about the particular plastic used in spectacle lenses (I think mine are polycarbonate) but I once saw a man stabbed in the gut with a shard from a plastic beer glass during a bar right. I believe that someone was once murdered after having his throat torn open with the handle from a plastic fork too. --Kurt Shaped Box (talk) 23:17, 26 June 2008 (UTC)[reply]
Are we talking lenses or frames here? Maybe it was not the specs but the technique of the hand that did – looking at the shiv article, there's one made of two tongue depressors so maybe not too far off in concept. Julia Rossi (talk) 13:35, 27 June 2008 (UTC)[reply]
The scene in the movie involves the victim's glasses being pulled off, folded and jammed end-on into his throat with a downward stabbing motion. Nothing to do with shivs or broken lenses at all. Just the frames with the lenses in them. --Kurt Shaped Box (talk) 15:25, 27 June 2008 (UTC)[reply]
Based on the very close proximity of the artery to the esophagus, and there being no obstructions, that leads me to think it is very possible as long as the glasses had an edge that could cut through a little of that tissue. Mac Davis (talk) 18:11, 27 June 2008 (UTC)[reply]
Usually two gamma rays (or maybe pions?), but sometimes other stuff. Theoretically it could make anything as long as energy, electric charge, and a bunch of other things are conserved. Hold on and I'll try to look it up in PDGLive. —Keenan Pepper01:27, 27 June 2008 (UTC)[reply]
Take a look at annihilation and electron-positron annihilation. As Keenan says, products could be almost anything, depending on energy of collision, as long as energy, charge, momentum etc. are conserved. Enough rest mass alone in a neutron pair to produce a small zoo of particles, and if they have significant kinetic energy then the possibilities increase. Electron-positron annihilation article says that W and Z bosons have been produced by banging just electrons and positrons together with enough energy. Gandalf61 (talk) 09:05, 27 June 2008 (UTC)[reply]
I'm asking about a low energy interaction. A low energy interaction between an electron and positron will yield two gamma ray photons. I want to know what a low energy interaction between a neutron and antineutron will yield. ScienceApe (talk) 14:58, 27 June 2008 (UTC)[reply]
Was there ever nose hair clippers before 1910? For people who had nose hair that was too long, what was the pattern and how long out of the nostril did it come out of? —Preceding unsigned comment added by 68.148.164.166 (talk) 04:28, 27 June 2008 (UTC)[reply]
Man has also been equipped with fists that enable him to punch himself in the testicles if he so wishes. That doesn't make it a good idea. :) --Kurt Shaped Box (talk) 23:24, 27 June 2008 (UTC)[reply]
what is this formula?
PVU = Δ x Δ p >= h / (4 п) = h/2
(not the best rendering, the second H is supposed to be an h with a line towards the top) but maybe someone recongises it? A different but related question, what is the best way to search for formulas? I tried searching for PVU and for h/4 but didn't get much... I think PVU isn't the right thing there though ++Lar: t/c04:37, 27 June 2008 (UTC)[reply]
Looking over the previous question, it appears the point is a case of understanding exactly what is meant by the rate of emission. Hawking radiation, as best I can tell, does not say that there is more radiation from a smaller black hole than a larger. Rather, the point is likely one of surface area to volume (if we consider volume to be defined by the event horizon, since that's where the radiation originates). Since volume is a radius-cubed function and surface area radius-squared, a small black hole will have a higher surface area to volume ratio than a large one. With volume being proportional to mass, and Hawking radiation proportional to surface area, that means a small black hole has a larger radiation to mass ratio than a large one. Thus, it evaporates "faster" taken as a unit (one black hole) even if it's evaporating less in a more absolute sense. — Lomn14:03, 27 June 2008 (UTC)[reply]
Tell me if I'm wrong, but assuming that the event horizon is proportional to (or indeed, defined by) the Schwarzschild radius, which in turn is defined by the mass of the black hole, does the square/cube ratio explanation still hold up? I guess what I'm saying is, does the changing mass affect the Schwarzschild radius in a linear way, or not? I can see the equation on the Schwarzschild radius page, but I'm not sure how to do it!
The event horizon is the sphere whose radius is the Schwarzchild radius. The event horizon is based on the density of a body (radius and mass), but the Schwarzchild radius is based on the mass. By multiplicity, there is a linear relationship (mass is multiplied by two constants). If you have a graphing calculator you can enter in y=(G*1/c^2)x and substitute the real values for G and c to see the graph of the function. For future reference, if the variable is squared, cubed, etc, that's what makes it a square/cube relationship, etc. Mac Davis (talk) 18:01, 27 June 2008 (UTC)[reply]
Removed reposted thread... the new addition is a description of the poster's symptoms, which is clearly a request for medical advice. -- Coneslayer (talk) 13:31, 27 June 2008 (UTC)[reply]
Options after completing MBBS
Usually, after completing MBBS, a person would choose courses like Scan reading (Radiology), Diabetis specialist or other things like Psychiatry or MD general medicine.
Is there any other options apart from those usual courses?
What should a person after completing MBBS should do to join companies like Pfizer to do research in that company? Or what are the options in biotechnology and bioinformatics?
If you're interested in research, you're going to want to get an MD/PhD. Short of that, you're pretty much limited to medical practice. To do something like biotech or bioinformatics you should really get a bachelors in a science and then go for a PhD in that science...at least those are the most common routes. Strictly speaking, you could probably wind up in almost any career based on any training. Also, to do research with most pharmaceutical companies you're going to want a PhD in chemistry or biology (unless you want to be a lab tech, in which case a bachelors in either of those will do). As above, there are lots of different paths to the same career. But in my experience not much else really gets hired.
Our article on harlequin type ichthyosis describes a few, rare examples where patients have survived into adolescence and adulthood. I was looking for a video on Youtube or elsewhere that shows an older survivor, but the only videos I can find are of babies. I also tried the links at the bottom of the Wikipedia article to no avail. I'm interested to know if they can move around, talk, etc.--The Fat Man Who Never Came Back (talk) 14:56, 27 June 2008 (UTC)[reply]
IIRC, adults with the condition don't actually look as bad as you might expect. I'd guess that the really horrific pics that people trick people into viewing on the internet are the more serious examples that are invariably weeded out by nature shortly after birth. --Kurt Shaped Box (talk) 23:18, 27 June 2008 (UTC)[reply]
Eating cancer cell
Do eating live cancer cells impose danger to human? I know gastric juice will digest incoming living cells.But, will some cells attach on the inner wall of oesophagus and try to invade adjacent tissues?
I would expect eating one's own cancer cells to be dangerous if they somehow survived the digestive system. But I think someone else's cancer cells ought to be recognized as foreign and attacked by the immune system. --Allen (talk) 19:50, 27 June 2008 (UTC)[reply]
Why do you think so? It wouldn't be more contagious than any other infection that is transmitted by body cells, i.e. much less contagious than super-light viral particles. Also, if you read the Tasman Devil disease article, the animals' immune system is compromised which wouldn't be the case with humans. --Ayacop (talk) 08:28, 28 June 2008 (UTC)[reply]
I was basing my opinion on the canine version. Well, we're a very sexually active species and cancer can erupt anytime. The animals are immunocompromised because they little biodiversity and this might also be the case in some isolated human culture/colony.--Lenticel(talk)06:54, 29 June 2008 (UTC)[reply]
What is this spider?
Hi, please see Image:Mystery OR jumping spider.jpg. I apologize for the poor quality of the pictures - my camera doesn't take close-ups very well and this spider is about 7mm from the tip of the antennae to the tail. I've never seen any of these until this week, but I've seen three different ones in about a five-mile area this week. Two were on the exterior walls of 2 different houses, and another was in my living room. They were all seen in extremely NW Oregon. I'm curious what species/classification you can narrow it down to. I think it's a jumping spider because I've seen two of them jump around. Flayked (talk) 21:32, 27 June 2008 (UTC)[reply]
Cool, thanks a lot to both of you. I think I've narrowed it down to Zebra spider - the stripe pattern on mine matches that on the photo 161.222.160.8 linked to. The color marking pattern on the Phidippus audax is very different from mine (no noticeable stripes on legs, and zebra/tiger-like stripes, not the dot and semi-circle). Thanks again. I think what threw me off was the eyes - the spider was too small for me to really notice the "large eyes" which are supposedly characteristic of jumping spiders. Flayked (talk) 22:06, 27 June 2008 (UTC)[reply]
Really? A watergun? :-P But back to the main point, if you're referring to a single shot, my guess is even if accurately aimed at the head (which would be rather difficult behind closed curtains/blinds) some sort of 'light' pistol with low calibre ammunition (sorry I know next to nothing about guns) may not be enough for death if your lucky [I wouldn't bet my life on it tho ;-) ]. But since the first shot is going to break the windows I would concur it's probably enough with multiple shots presuming the target doesn't run away. And as I've already mentioned, it's going to be rather difficult to aim accurately at the very least you may need some sort of infrared vision sensot Nil Einne (talk) 06:47, 28 June 2008 (UTC)[reply]
Infrared won't work behind double windows (I've even doubts as to single ones). Remember those heat pictures of houses where windows are undifferentiated rectangles/heat leaks. --Ayacop (talk) 08:19, 28 June 2008 (UTC)[reply]
Glass is pretty opaque to (far) infra-red, I believe (that's why greenhouses work), so thermal imaging through even a single window pane would be very difficult. --Tango (talk) 15:19, 28 June 2008 (UTC)[reply]
June 28
Why is spitting in someone's face considered to be particularly offensive?
Whilst hitting or insulting another person are taken as offensive acts, what is it about spitting on another person in particular that can drive the victim into an immediate murderous rage?
At least where I'm from, it seems to be the unwritten rule that 'a man should not spit on other man under any circumstances' and that to do so is completely disgusting, reprehensible and dishonourable. If you insult or punch another man during a disagreement, you may end up in a fight. If you spit in another man's face during a disagreement, you *will* end up in a serious fight.
Based on my personal observations of life and people falling out over various things in my homeland, my general perceived severity of various insults is so (going from least offensive to most offensive):
Yeah, I assume it's the general taboo about unwilling exchange of bodily fluids, which people instinctively dislike due to diseases being spread that way. Spitting simply falls into that category in the same way as someone intentionally coughing on you, urinating on you, ejaculating on you, whatever. ~ mazcat | c00:23, 28 June 2008 (UTC)[reply]
Because saliva is abject. Violence (perversely enough) is not. Most bodily fluids are in a special psychological category of grossness for (most) human beings that far outdoes any rational reason. --74.223.170.187 (talk) 02:10, 28 June 2008 (UTC)[reply]
In Ireland I remember old farmers sealing a deal by spitting on their hands before shaking (sealed with a spit, I guess) but spitting on another person would be deeply offensive there.Gaiatechnician (talk) 16:32, 1 July 2008 (UTC)[reply]
It's probably worth noting that this is likely to be a fairly culture-specific thing. I mean, you can say whatever you want about my mother, and unless you actually know my mother and are making a specific personal comment about her, it's not likely to mean anything to me other than make me aware of the fact that you're trying to offend me. Whether you tell me to go fuck myself or call my mother a whore, it's just noise, you know? It obviously won't make me happy, but that choice of subject matter won't make me any more angry. I think that generally speaking, this definitely goes for most of the people I know as well. I know that this definitely isn't the case in many other cultures. Likewise, if someone were to spit in my face, it would probably make me really, really angry simply because it's such a hostile thing to do, but I'd still strongly prefer it to a punch in the face. On the other hand, at least according to our article on spitting, the Maasai tribespeople spit on each other as a form of greeting and farewell. Personally, I think I'm gonna stick with shaking hands for the time being... -- Captain Disdain (talk) 13:03, 29 June 2008 (UTC)[reply]
That could explain something that I've wondered about. According to the Laws of the Game for soccer, "Spitting on someone" is specifically called out as an immediate sending-off offence (red card). I've wondered why that was necessary -- perhaps it's for the benefit of those for whom spitting is not an affront, to let them know that it is for many others?
I have been trying to design a heliostat that is on equatorial mount with some sort of clock drive. And I think I have hit on a design that will eventually work. (It is on instructables.com).
(Clockwork being simpler and potentially cheaper than throwing computer power at everything).
I just got everything uploaded and then I was very surprised to find out that clock based heliostats are an old concept!
They were used for many years by early scientists.
and
http://www.earlytech.com/common/show_image.phtml?Id=491390987&Item_Name=Heliostat+by+Silbermann+1843 shows how the geometry works.
I confess that i do not understand it at all!
So, it is too late for me and I will continue with my little design. Mine goes at 15 degrees per hour, but I think these old ones go at a different rate, either twice as fast or twice as slow as the sun appears to travel around the earth.
So, anyone like to explain or just mention how the old scientific heliostats worked? On the heliostat page would be great.
Thank you 24.69.192.200 (talk) 03:00, 28 June 2008 (UTC)[reply]
First of all, please do not ask for knowledge questions to be answered on article talk pages. The article talk is for discussing improvements to the article, this desk is the right place to ask questions.
The heliostat in that link needs to rotate at half the speed of the sun because it is trying to keep the direction of reflection constant. If you are just trying to keep a telescope or camera pointing directly at the sun then you need to rotate at the same speed. So it depends what you are trying to do, if you want to redirect the sunlight to a fixed point where you can use it to do work then 15o/hr is going to be wrong.
Note that to track the stars (siderostat) it needs to rotate at a different speed to a clock because the earth is not rotating once every 24 hours with respect to the stars. The earth rotates in 24 hours with respect to the sun which is not quite the same thing. In one day, the earth has moved on 1/365th of its orbit around the sun and so needs to rotate a further 1/365th of a revolution in order to face the sun again. The siderostat therefore needs to run 1/365th parts per day slowfast (about 4 minutes) otherwise your photographs of the stars will be streaks instead of nice points. SpinningSpark13:08, 28 June 2008 (UTC)[reply]
I made my first model http://www.youtube.com/watch?v=WRTX1S7PD-U and the principles seem to work. In this case, the mirror does not turn at all, but 2 pointers decide its angle as it pivots round its centre. One is pointed at where the light will go and one is pointed at the sun. (That one turns on the equatorial mount axis).
I used 2 rubber bands to bisect the distance between the pointers and attached a post at the centre of the mirror to the bands.
This seems such a simple method but I do not see it documented anywhere.Gaiatechnician (talk) 16:40, 1 July 2008 (UTC)[reply]
AC Power - Generation, Voltage and Current
I know that this might seem very basic, but it does not seem to be answered by the existing Wiki sections on AC power. The questions stems from an argument that you don't get electrocuted if you (are grounded) and touch the negative side of an AC power point.
There is also no basic explanation that in an AC (Alternating Current) circuit it also has Alternating Voltage. Most graphs show AC voltage varying in a sine wave pattern, with a graph that that has its X axis at 0 and the voltage varying equally to the positive and negative side. It seems to mean that the voltage in the AC system fluctates from +240 to -240v (Australian voltages). This doesn't seem correct to me - I though it fluctuated and its average (RMS) was +240V.
Could someone please explain how the electrical generator at the power station, ends up at 240VAC at my power point. And what the actual voltage graph, and current, looks like at:
1 - the generator
2 - the transmission lines
3 - the transformers
4 - my domestic power point.
There is no "negative" side to A/C power. In the US, there are "neutral" and a "hot" wires feeding typical 120V outlets. The neutral side is usually tied to ground at the service entrance, while the hot wire carries the A/C voltage sine wave. So in this case, coming in contact with the neutral wire will not likely cause injury, although I wouldn't bet my life on it. -- Tcncv (talk) 04:43, 28 June 2008 (UTC)[reply]
To better answer your questions: Power is typically generated and distributed as three-phase electric power. Because power is equal to voltage times current (amperage) while power loss during electric power transmission due to electrical resistance is proportional to current and not voltage, it is more economical to step up voltage and reduce current using transformers when transmitting power over long distances. As the power nears the consumer, transformers are again used at several points (electrical substations and pole top transformers) to step down the voltage to consumer levels. Also, while three phase power is used in most industrial and many business users, for residential use, the power is typically converted to single-phase electric power or split-phase electric power. For single-phase electric power, only one voltage is available to the customer. For split-phase electric power, two opposing AC voltage feeds are provided plus a neutral. One voltage (such as 120V in the U.S.) is obtained by using one of the hot feeds together with the neutral, while another voltage (240V in the U.S.) by using the two opposing hot feeds. If you follow the links above, you should find more detailed answers to your questions. -- Tcncv (talk) 05:28, 28 June 2008 (UTC)[reply]
To bring it back to your Australian case (or in my case, South Africa), what you have in your house is a Live, Neutral and Earth wire. Typically a sinusoidal voltage is supplied between the live and neutral. The neutral wire is grounded (connected to the physical earth) at some point where it comes into your house. Thus typically touching the neutral wire while you are in contact with the ground should be less lethal because there will be almost zero voltage across your body. DO NOT try this! More on the neutral/ground issue further on, for the time being let's deal with amplitudes and that sine wave.
The voltage at the live terminal is quoted as 240 V AC. First off the 240 is not the amplitude, it is actually the RMS value, and equates to the amplitude/sqrt(2) for a sine wave. The actual amplitude is therefore 240*sqrt(2)=340 V. More on RMS in a couple of sentences, keep reading. The signal does indeed fluctuate between +340 V and -340 V, thus the average value of the voltage signal is in fact zero. This is obviously not a useful quantity when talking about AC voltages, so how do we actually quantity the "magnitude" of an AC signal?
This is where RMS comes in. (p.s. if you how to do integral calculus you can actually derive this yourself which will give you good insight). How do we quantify usefully the magnitude of an AC signal in order to equate it to a DC signal of "equivalent size"? Obviously using the amplitude will give an over-estimate (the signal is only briefly at max amplitude), and obviously the average is zero no matter how high the voltage. The concept that is thus used is that of "equal POWER": what amplitude of AC volts does it take to generate the same amount of power in a load as a steady 1 volt DC signal. The answer turns out to be sqrt(2). Thus the convention when talking about "1 volt AC" is that you're talking about a signal of amplitude sqrt(2), because this 1 V AC signal does the same amount of work as a 1 V steady DC signal.
Let's derive the sqrt(2): given a 1 V DC signal placed across a 1 ohm resistor, how much power generated? well, going by P=V²/R gives 1 Watt. Now let's take an AC signal of amplitude A. What size of A gives 1 Watt dissipated? Now your voltage is Asin(2Πf*t) where f is 50 Hz for Aus I assume (but that's immaterial because we are working out the average power over 1 cycle of the AC wave). P = V²/R = A²sin²(2Πf*t)/1. Now we calculate the average power dissipated over 1 cycle of the AC wave. The average of the sin² term is 0.5 (do some trig to derive this if you don't know it already). Thus we have 0.5*A²=P=1 Watt which gives A=sqrt(2).
As to why we use RMS rather than just the amplitudes: well one of the applications of AC is obviously electrical power generation and distribution, in which case you have to know how much power is being produced and absorbed. Using the RMS values instead of absolute amplitudes makes it easier to work things out (you don't carry factors of sqrt(2) everywhere in teh calculations) and thus has become the convention.
When wiring in a house breaks or is improperly installed, the neutral or ground wires can become energized at the supply voltage, and in such situations touching the neutral and ground wires could place the full supply voltage across your body, causing injury or electrocution. When everything is installed and working as designed, there may still be a few volts between ground and neutral at some points in the circuit, because of the voltage drop from load current in the neutral. A low resistance connection, such as a wire jumper from ground to neutral can carry very high current from this small voltage difference. Do not attempt the experiment. Edison (talk) 19:29, 28 June 2008 (UTC)[reply]
Evolution in Physics
In biology, evolution is presented as the major scientific cause of change in wildlife. But what about the other sciences ? I evolution was very significant, would't it be directly observable in nuclerar physics, astrononym, chemistry and the like ? 69.157.237.196 (talk) 09:20, 28 June 2008 (UTC)[reply]
Because, as you certainly know, living things consist of molecules, evolution is in fact a chemical phenomenon. It's just that people take the really complicated chemistry and call it biology. Also, as molecules behave to the laws of physics, in the same way evolution is also a physical phenomenon. On the other hand, the objects astronomy deals with aren't living things, and as evolution is a phenomenon of life, it won't apply to astronomical objects. --Ayacop (talk) 09:39, 28 June 2008 (UTC)[reply]
There is such a thing as evolution of stars etc but that is really a different subject.
I don't know why you'd think that something that pertains to one branch of nature would necessarily exist in others in any major way. There's no doubt that matter-antimatter annihilation exists in nuclear physics, but it doesn't exist anywhere else. There's no equivalent for special relativity in biology—I'm not sure what that would even look like. And there's no requirement that biological evolution exist outside of biology. --74.223.170.157 (talk) 13:09, 28 June 2008 (UTC)[reply]
Generally, all biology is complicated chemistry and all chemistry is complicated physics. Everything in biology or chemistry could, given the time, be linked to physics. However, not everything in physics can be linked to biology or chemistry. It only works one way. — CycloneNimrodtalk?contribs?15:03, 28 June 2008 (UTC)[reply]
Evolution in the sense of changes through time from initial conditions does indeed occur in the hard sciences: that is what cosmology is. The processes that dictate how the changes happen are, of course, different from biological evolution. In fact, when looking at the universe today, or looking at the geology of our own planet, the only way you can make sense of it is to be aware of the historic evolution that occurred.--Eriastrum (talk) 16:00, 28 June 2008 (UTC)[reply]
Medical diagnosis
Yes, I am looking for medical advice and treatment, but not here.
Here, I am asking a question about medical diagnosis.
I have been ill with the recurring symptoms of an infection for about three months now. It starts to endanger my job.
The doctor tells me I won't get antibiotics unless I have at least 39 C temperature. He did a thorough and costly physical examination and came up with the result that all examined organs were healthy but that I probably had some kind of infection. (What a surprise for that lot of money spent!)
He did nothing that could lead to a diagnosis of what kind of infection I have, whether it's viral or bacterial. He even neglected to ask me if I had been to foreign countries recently. And I had similar experiences with other doctors in the past with other cases of diseases. It looks like they won't do anything useful until a disease has already done damage to the organs. (And yes, I am angry.)
Now the question: are there really no methods to diagnose the kind of an infection? What would they be, are there any plausible reasons why they are not applied, and, finally where can I get them (note this is asking about medical advice, not for).
I know that situation, and it's a good question. There are ways, however, to have a good guess (besides a post-mortem), for example by exclusion: you can ascertain it's not disease X if you don't have its typical symptoms; it can't be in organ Y because all the numbers concerning that organ are fine; and so on. Secondly, the symptoms you encounter at the moment should be a hint. Thirdly, you could try to apply natural antibiotics---for example, garlic will temporarily kill any bacteria in the stomach and many bad boys in the upper intestine: if you feel better after that, then you know. Make yourself informed, do (harmless) experiments.
There may also be special diagnostic tools that just aren't applied by doctors because they aren't known well enough, take too much time, cost too much. For years I read about methods to recognize diseases from the breath, but where is that stuff? The teams probably show a prototype, but the pharma boss decides against it, probably. However, it is possible to get a lot of diagnostics privately from laboratories, if you know what you're looking for, and are willing to pay for it. --Ayacop (talk) 14:18, 28 June 2008 (UTC)[reply]
Really good general diagnosticians get busy pretty quickly. They also have to explore and process a lot of information, which is time-consuming (and poorly compensated relative to other activities that require similar amounts of training, intelligence, and time). I anticipate that some aspects of the task will be automated soon - software could elicit symptoms and ask some pretty standard questions (like recent travel, as you point out) that would help a good diagnostician do a more thorough job. Sorry to hear about your frustrations - I hope things improve soon. Scray (talk) 19:02, 28 June 2008 (UTC)[reply]
There are tests for all kinds of bacterial and viral infections. Nearly all known bacterial/viral infections can be detected. It appears that you are in a country with nationalized health care (or worse, HMO-controlled healthcare). There are many studies on nationalized health care that point out the weakness of doctors not being able to go "off script" for special cases. As the doctor pointed out, he is not allowed to treat you for a bacterial infection until you meet the guidelines necessary to qualify for bacterial infection treatment. As such, he was basically telling you what to do. You need to return and tell them that you had a fever of 39C but took a fever reducer and a cold bath to reduce it enough so you could show up at the doctor's office. Then, he can treat you. It is important to listen to what the doctor says. He cannot say "Go home and come back complaining of a 39C fever." He can only say "I cannot give you antibacterial treatment until you have a 39C fever." -- kainaw™23:26, 28 June 2008 (UTC)[reply]
Well it's a bit more complicated. He told me that unless I had 39C a blood culture would be too insensitive. I'm well aware of antibiotic-resistance and that there is a 1:1 chance that the infection is viral and for the other 50% there is a good chance that those bacteria will not respond to general broadband antibiotics, so I see the need to know what those little critters really are. I explicitly asked him about PCR and genetic detection and he honestly could not tell me why this is not used for diagnosis. He obviously didn't know about ELISA either, this seems not to be part of the education. As I understand, a blood culture would only be positive if the disease is caused by bacteria (or other microbes, not viruses or poisons) and only if they proliferate in the blood, so infections where the microbes grow is specialized tissue could only be detected when they are so numerous that they penetrate into the blood stream.
I live in Germany where another reason for reluctant prescription is that each doctor has a limited budget for all his patients and has to pay the excess amount from his own earnings. I don't know if it would be perfectly legal to go abroad for treatment, and more, I don't know which countries allow a better and more effective treatment. And as for pretending fever, yes, I think that would work but, that's why they are becoming us a bread of liars and cheaterlings. 77.3.168.22 (talk) 08:39, 29 June 2008 (UTC)[reply]
The typical reason that a doctor is reluctant to prescribe antibiotics is to prevent the evolution of antibiotic-resistant microbes. For a more specific diagnosis you could call the doctor and express your concerns to him directly, or you could ask a specialist (if you are in the United States, look for somebody who is board-certified in Infectious Disease Medicine) for a second opinion. I hope you feel better soon. 69.140.152.55 (talk) 03:34, 29 June 2008 (UTC)[reply]
This whole exchange illustrates why there is a policy against medical advice here. The original question contains at least 4 false assumptions, none of which were pointed out or explained by any of the responders. Second, the responses contain numerous irrelevant, and not a few erroneous "facts". Finally, no one has provided a direct and accurate answer to the two direct questions asked at the end of the initial account. This is no better than an impromptu conversation among 6 strangers on a train. The inquirer is a fool to rely on this information to make decisions about his health and should have asked his questions of the one person who heard his whole story, had the training to sort out the facts, could have answered his questions accurately, and could be held legally responsible for the answer. 159.14.240.230 (talk) 13:26, 1 July 2008 (UTC)[reply]
You are welcome to give an answer to the question as well as to explicitly point out what you think were false assumptions of mine. When I saw that the whole thing would boil down to legal questions I removed the entire section but it was restored. 77.3.134.249 (talk) 18:20, 1 July 2008 (UTC)[reply]
I don't think any explicit medical advice has been given here. The answers are attempting to explain the methodology of the practice of medical diagnoses itself, in line with the original question which clearly states medical advice is not being sought. A discussion is however in progress at Wikipedia talk:Reference_desk/Science. Jdrewitt (talk) 20:40, 1 July 2008 (UTC)[reply]
EMF Transmission Dangers
Is there significant scientific evidence to support claims of health dangers from living in close proximity to electric power stations?70.58.154.222 (talk) 18:35, 28 June 2008 (UTC)[reply]
There have been studies which found statistical association between exposure to electromagnetic radiation from power lines, and studies which found no such association where one might have been expected, such as among power system workers. Biological stidies have found some effects of powerline frequency EMF on cells and tissues. Overall, the association with cancer or other ailments is far less clear than for ionizing radiation, asbestos, smoking, exposure to sunlight or exposure to several other well known health hazards. Research continues. Edison (talk) 19:23, 28 June 2008 (UTC)[reply]
There are many different types of galaxies, see Galaxy morphological classification. Now, edge-on is simply a term describing the inclination of the galaxy with respect to an observer on earth. If a galaxy is inclined 90° relative to the earth then you will observe the galaxy directly from the side, or edge. Jdrewitt (talk) 09:59, 29 June 2008 (UTC)[reply]
Please note that the above pictures do not appear to be fully edge-on or fully face-on, although they are quite close. Perhaps the images below illustrate an edge-on galaxy and face-on galaxies with an inclination relative to the earth closer to 90° and 0° respectively.
An edge-on glaxy with an inclination of 90° relative to the earth.
A face-on galaxy with an inclination of 0° relative to the earth.
The "edge-on" picture shows lots of light coming from oval regions above and below the disc. A spinning disc shaped arrangement of stars could be reasonably stable, but why does light come from above and below the disc? Are there a significant number of stars in soupbowl shaped regions above and below the disc to create the apparent glowing clouds? If so, what keeps the gravity of the disc stars from pulling them into the disc? If the stars are in the disc and the light is being scattered, what is there to scatter the light in space? If dust, gasses, or small objects, then again why doesn't the gravity of the stars in the spinning discull in the surrounding matter? —Preceding unsigned comment added by Edison (talk • contribs) 11:57, 29 June, 2008 (UTC)
The region you are referring to is the galactic halo which exists around spiral galaxies. Its shine is due to the stars and star clusters that exist in that region, but at much lower density to the main disk region of the galaxy. There is a lack of new material in the galactic halo and so there is no new star formation. The stars that exist in the halo have much different orbits to stars lying in the plane of the galaxy, and halo stars may pass through the disk and nucleus of the galaxy. See Galactic spheroid. Jdrewitt (talk) 12:53, 29 June 2008 (UTC)[reply]
Actually - I think this person is referring to the galactic bulge, rather than the halo. But the article referred to by Jdrewitt is a good one to check out. PhySusie (talk) 00:40, 30 June 2008 (UTC)[reply]
Is this some kind of a riddle? It sounds to me that you already know the answer. Anyway, humans have no wings and are incapable of flight by themselves, but they still do a fair bit of flying by various means. -- Captain Disdain (talk) 12:48, 29 June 2008 (UTC)[reply]
It sounds like it may involve some kind of word play - in which case, original poster, are you sure you've got the exact wording of the question? If not, there could be a vital clue missing. Confusing Manifestation(Say hi!) 23:01, 29 June 2008 (UTC)[reply]
Medicine-Patella replacement.
Whilst looking at a page on the Patella, a sesamoid bone, I wondered whether replacing the Bone with something larger would be beneficial to jumpers or distance runners. The larger bone would create more leverage for the muscle which the primary functional role is knee extension. Obviously after healing and training, it may improve top speed for runners, like a high gear on a bicycle. Whereas jumpers, long or triple jumpers, might find it beneficial for their sport. However you look at it, controversial, cheating or whatever, do you think it possible?
I think you´d be hard pressed to find a runner who would undergo a risky knee surgery like that. Replacing the bone would require disconnecting all sorts of tendons and ligaments, reattaching them, then a long rehab which may not necessarily return all function to the limb. I guess it´s possible that it could work, but I think ít´s about as likely as a runner having his legs removed completely and replaced with prosthetics (which apparently can have some advantages over actual legs). You´d probably find Oscar_Pistorius#Dispute_over_prosthetics interesting. --Shaggorama (talk) 01:13, 30 June 2008 (UTC)[reply]
Human and agricultural uses of antibiotics, and the development of drug-resistant bacteria
Is it known how great the contribution of non-judicious human use of antibiotics is to the development of drug-resistant bacteria, when compared with the contribution of antibiotics use in animal farming? —Preceding unsigned comment added by 71.162.249.44 (talk) 12:58, 29 June 2008 (UTC)[reply]
Not to me, at least. But I suspect nobody really knows, but the uppers fear it and do everything to reduce the use of antibiotics for humans so they will still work when the important people like soccer players, stock bulls or politicians fall ill. 77.3.168.22 (talk) 15:36, 29 June 2008 (UTC)[reply]
Heh... "Important people like soccer players"? You make it sound as if they're more worthy of healthcare than anyone else... -- Aeluwas (talk) 16:03, 29 June 2008 (UTC)[reply]
I think 77* was being sarcastic, though unfortunately so. Antibiotic resistance, it seems to me, will harm people with less money disproportionately. Rich people will be more likely to have access to the few remaining effective antibiotics. (And by the way, the article I linked to has a section on use in animals, though apparently it's under dispute.) --Allen (talk) 16:13, 29 June 2008 (UTC)[reply]
Hey, yes, I am sarcastic. But soccer players really do get better treatment, so that proves they effectively are more important, at least for those people that decide who gets the real medication and who only get the dopes so they don't feel so much ill any more.
But are there any serious alternatives to antibiotics? Washing hands won't get you healthy again once someone else has sneezed his bacteria into you. And phages are natural vectors for genes, including those for antibiotic resistance. Unlike antibiotics they mutate and have a potential to get out of control. 77.3.168.22 (talk) 18:01, 29 June 2008 (UTC)[reply]
Well, no, there aren't serious alternatives to antibiotics... that's the whole point of fighting antibiotic resistance by discouraging overuse, right? --Allen (talk) 03:59, 30 June 2008 (UTC)[reply]
Inseminating Mars
If humans sent spaceships to nuke Mars with bacteria, would new life develop and would this new life eventually generate itw own atmosphere, allowing people to breathe easily ? 69.157.237.196 (talk) 13:53, 29 June 2008 (UTC).[reply]
This is indeed an area of great interest to scientists, and is studied and theorized about frequently. We have a nice article about it: Terraforming of Mars. Apparently the biggest problem currently is that Mars is waaaaay cold, so we'd need to heat it up considerably. The good thing is that once you get the heating process started, Mars can help along, since there is considerable quantities of CO2 frozen at the poles. When it got warmer, that would be released into the atmosphere and help along the greenhouse effect. It's some sort of irony that the things that would make Mars more like earth is vast quantities of CFCs and CO2.
After that it is done, the article says gives essentially your plan for continuing:
After the heavy dust-storms subside, the warmer planet could conceivably be habitable to some forms of terrestrial life. Certain forms of algae and bacteria that are able to live in the Antarctic would be prime candidates. By filling a few of the rockets with algae spores and crashing them in the polar areas where there would still be water-ice, they could not only grow but even thrive in the no-competition, high-radiation, high CO2 environment.
(I assume that this is what you meant, and not literally nuking the surface of Mars. That would probably not be the greatest plan for allowing life to spread). The article is fascinating, I highly recommend you read it. 217.213.153.218 (talk) 14:08, 29 June 2008 (UTC)[reply]
Starting out with electronics...
(not sure if this is more computing than science, but here goes...)
After seeing a bunch of guides and how-tos on the internet about how to easily program microcontrollers to control LEDs or build robots or do whatever (you know, MAKE magazine stuff), I've sort-of become intersted in learning this stuff. I'm great at computers, and I can develop in a number of different languages (including C, which I suppose is the language you'd use to program microcontrollers), and I have a deep understand how computers work. The thing is, I've always concentrated on the software side, I don't think I've ever in my life held a soldering iron in my hand. I know some of the theory behind electronics and basically how it all works, but I don't really know about this stuff in practice (When do you need a power-supply capacitor? How big does it need to be? Where do you put it? How big a resistor do you need not to fry stuff? And how do you read those colorful bars? And how do you solder without burning yourself and your stuff? etc.) I'm betting that out there there's a book for me, called "I'm a pretty smart guy and I want to try to build stuff but don't really know how" or something. Or maybe a website? Can anyone make a recommendation? Like, a beginners crash-course. 217.213.153.218 (talk) 13:56, 29 June 2008 (UTC)[reply]
I had similar motivations once. I did some research and decided to buy The Art of Electronics. I kind of fizzled out after a couple chapters, but that was my fault. The book seemed excellent. Hopefully someone who's actually finished a book will also respond :-). --Allen (talk) 15:59, 29 June 2008 (UTC)[reply]
Allen, you beat me to it with your recommendation for Art of Electronics. Another good one is Electronic Circuits and Applications by Senturia and Wedlock. But I'm not sure either of these books will teach the more-practical aspects of electronics (such as which end of the soldering iron to hold; I'm not sure about reading color codes, but Wiki's article is probably enough there). In the old days, Heathkit, Eico, and Knightkit were the best answers for learning the more-practical skills, but they're gone, of course. You can still buy kits of parts with a PC board from a few electronics parts shops (such as "You-blew-it", err, "You-do-it" Electronics in Needham, Massachusetts[11]). They can also sell you a soldering iron, electronic test equipment, and the like. (Soldering is like any other skill; practice makes perfect.)
It's gotten a lot harder to learn anything about electronics as a hobbyist; the prevalence of VLSI, very-fine-pitch parts, and surface mount devices has made the bar to entry much, much higher than when I joined the trade.
This seems oddly fitting, since I learned many of my programming skills from The Art of Computer Programming (my dear parents gave me all three volumes my second year in high school; it is the best birthday present I've ever got). I can at least check them out from the library to see if they are what I want :) 83.250.202.36 (talk) 17:22, 29 June 2008 (UTC)[reply]
Someone in one of the electronics magazines a couple of years ago noted that electronics became a great hobby when the era arrived in the 1960's that you could build radios amplifiers and other gadgets using transistors and LEDs rather than vacuum tubes with high voltage power supplies. Breadboarding became cheap and easy. People built TVs, oscilloscopes, computers and even robots from Heathkit kits. Ham radio was a popular pursuit for tecchie. Then along came computers as a tecchie pursuit, with people programming them to do amazing things with BASIC programs. Large scale integration meant that there was not all that much soldering to do in building an electronic device. Websurfing seemed to replace ham radio to some extent. Then PCs arrived with less accesss to the lower level functioning and no BASIC. No more games to be typed into the computer from a monthly computer magazine and debugged so they actually worked. Just the running of applications and games. With the passing of the era of big chemistry sets, Heathkits, and other hands-on technology, there seems to be less interest and ability of those entering college today to understand the inner workings of the electronic and computer devices they use. So it is great to see someone interested in tinkering. You can approach electronics from a low technical level of perhaps experimenting with one of the larger Radio Shack electronic experimenter sets, and you can still buy lots of interesting kits from the electronics magazines. Community colleges offer some great courses in basic electronics that are less of a calculus fest than electrical engineering courses. Edison (talk) 19:15, 30 June 2008 (UTC)[reply]
Look for the evil genius series of books, like the title Electronic Gadgets for the Evil Genius or 53 High-Tech Pranks for the Evil Genius, Bionics for the Evil Genius (etc.) they all have introductions to electronics and stuff. While not exactly textbooks or courses in electronics, they make learning electronics an enjoyable activity. They have some really phenomenal projects, ranging in difficulty from absolute beginner to experienced. Ilikefood (talk) 01:37, 1 July 2008 (UTC)[reply]
SImple pendulum
1.If a simple pendulum with a period of 1 second is set in motion on the moon, determine the new period of this pendulum.
2. will a simple pendulum swing continuosly in air? explain why.
suggest the condition required for a pendulum to swing continuoslyMinjiun (talk) 14:21, 29 June 2008 (UTC)Lmj[reply]
For #1, see the article on pendulum; see also the article on the moon for value of lunar gravitational acceleration. For #2, see the articles on drag and damping.
(After edit conflict) 1. Not enough information - doesn't say where the pendulum has a period of 1 second. But let's assume that is on the surface of the Earth. Somewhere in your texbook there is an expression for the period of a simple pendulum in terms of its length and the local acceleration due to gravity (or g) - if you can't find it in your textbook, take a look at our pendulum article. Now, keep everything constant apart from g. Reduce g to 1/6th of its value on Earth (that is approximately correct for the surface of the Moon). What is the change in the period of the pendulum ?
You are assuming the question is badly phrased. It is likely verbatim to what the questioner's teacher said in class, drew a diagram of on the board, and explained would be in the homework - all while the questioner was busy texting his friends about much it sucks to repeat physics class in summer school. -- kainaw™00:27, 30 June 2008 (UTC)[reply]
There are places on the planet where the regular school year is still in session! —Preceding unsigned comment added by 62.145.19.66 (talk) 08:46, June 30, 2008 (UTC)
Please clarify what you mean by "life", "exist", "on", and "can". And because I'm feeling mean, "mars". (Translation: Could a human being, without any form of life support, survive for any meaningful length of time on Mars? No. Is it possible that just below the surface of Mars there is a habitat in which single-celled creatures similar to those found on Earth could possibly survive? Definitely. In between? Maybe.) Confusing Manifestation(Say hi!) 22:59, 29 June 2008 (UTC)[reply]
Is it true the amount of energy on earth is the same today as when the earth was formed? If so who is credited with the theory that the energy amount is the same only changed to a different form? I believe I remember in my study of Physics years ago that it was taught that if two boxcars were pushed together one was moving the other still that the energy of the moving one was transfer to the other and some energy went into heat and sound as the still boxcar would never begin moving as fast as the moving car.
The general idea you're looking for is the conservation of energy, with the conservation of momentum relating a little closer to the boxcar example. However, it is not true that the amount of energy on Earth is unchanging, because the Earth is not a closed system. Solar energy radiates in (at a changing rate) and heat energy radiates away (at a changing rate). An ice age, for instance, is a period where the Earth has less energy (though I've no idea what that difference would be in percentage terms -- likely very very small if you start talking about "the whole earth").
As for "who", no one man can be credited with fully formulating an explanation of the conservation of energy. The history section of that article should be illuminating. — Lomn14:40, 29 June 2008 (UTC)[reply]
Several energy factors are changing and I doubt it can simply be assumed that the total Earth energy is less during an ice age. Earth picks up more mass from the Solar system (meteors and such) than it looses. If the equivalent energy per mass–energy equivalence is included then it may be important. More heat energy radiates away than Solar energy radiates in. This once caused wrong estimates of the maximum age of the Earth because heat energy from radioactivity in the Earth was not discovered and included in the calculations. PrimeHunter (talk) 15:55, 29 June 2008 (UTC)[reply]
Excluding meteors (an excellent point, by the way), I think the ice age idea holds up pretty well. Air and surface temperatures decrease, and everything else holds. Insignificant in a grand e=mc2 mass-of-the-earth example, but a good practical one. — Lomn13:01, 30 June 2008 (UTC)[reply]
Because they produce fissile material from fertile material; that is, they produce more usable nuclear fuel than they consume. However, they're only liberating potential energy stored in the nuclei of (otherwise unusable as fuel) U-238 atoms. So they don't violate conservation of energy, but can easily be mistaken by a novice for doing so. --arkuat(talk)04:49, 1 July 2008 (UTC)[reply]
Oil doesn't sit in voids in the earth, it is usually in porous rocks. So when oil is extracted, the rocks remain. Following extraction of the oil, the pores in the rocks will either be filled with natural or atmospheric gases or the oil may be replaced by water, which is either used to force the oil out or naturally seeps into the rock from the natural water table. Jdrewitt (talk) 15:04, 29 June 2008 (UTC)[reply]
In some cases, the pore spaces contract when you remove the fluids they have been storing. In effect, the land in the regions settles, but in general the amount of such settling is not very noticable for practical volumes of oil/gas. Dragons flight (talk) 00:55, 30 June 2008 (UTC)[reply]
So, geologists take note, if you pump oil or natural gas out of a land area, you may expect that land area's water table to contract naturally as a result. Or am I reading the replies wrong? --arkuat(talk)08:28, 30 June 2008 (UTC)[reply]
That is possible, yes. But sometimes the way they get the oil out is by pumping water into the ground, the pressure of which pushes the oil up and out. I doubt that this method has an impact on the water table. PlasticupT/C12:44, 30 June 2008 (UTC)[reply]
There is an insect at my home in Kentucky. It looks like a cross between a bee and a humming bird or butterfly. Can you tell me what it is? And if it will sting me?
98.19.3.125 (talk) 20:41, 29 June 2008 (UTC)[reply]
You may also want to look at Carpenter bee. It doesn't match the description you gave as closely, but it can sting if you try to catch it; so you may see if that's not it. --Dr Dima (talk) 21:00, 29 June 2008 (UTC)[reply]
Check out the Sphingidae article for more extremely hummingbirdy bugs in the same family as Dr. Dima's suggestion. These bugs are not to be trusted! Look at this Gaudy Sphinx Caterpillar: [12]. --76.182.119.241 (talk) 23:29, 29 June 2008 (UTC)[reply]
Complexity and Self-organization in Thermodynamics
Consider computer simulations of dissipative (open) thermodynamical systems. Some examples include Cellular Automata grids, fluid motion, and autocatalytic sets. Have replicating "units" ever been observed emerging within such simulations, even in very simple ones? What about the so-called, effective dissipaters of gradients? paros (talk) 04:24, 30 June 2008 (UTC)[reply]
While looking in a plowed field I found a round 1 inch ball made of stone. Could this be a native american artifact and if so what was its purposeCuriouspatty (talk) 01:02, 30 June 2008 (UTC)[reply]
I am still very curious but I have to admit to being a computer novice and I don't know how to post a picture. I do know how to take the picture and put it on my computer. What would be the next step without giving my e-mail address? The ball is on tour through the family right now so it may take a couple of days.Curiouspatty (talk) 00:53, 1 July 2008 (UTC)[reply]
Why Mars after Earth (and the moon!)? Venus after Mercury?, Andremeda galaxy after our own solar system?, etc. You get the picture. Is there a particular reason, such as this group of rocks formed over there, that group of rocks gathered yonder why things in space are laid out the way they are? 5 dollars rides on this bet.THE WORLD'S MOST CURIOUS MAN (talk) 01:28, 30 June 2008 (UTC)[reply]
Hi. Have you read Formation and evolution of the solar system? Also, the Andromeda Galaxy after ours is because we live in our own galaxy. Also, is there any reason why they seemingly shouldn't be in that order? Earth, for example, wouldn't support much life were it as close to the sun as Venus or as far as Mars. One theory states that the planets are in that order partly because the rocks were heavier and settled closer to the sun, but this isn't usually true in other solar systems. Venus is hotter than Mercury because it has a heavy Carbon dioxide atmosphere. Hope this helps. Thanks. ~AH1(TCU)01:37, 30 June 2008 (UTC)[reply]
When the solar system was forming two big rock smashed together. Their combined gravity pulled in more rock. Eventually the was a planet. So in answer to your question: Completely random (Unless you believe in God) 4.159.183.112 (talk) 02:37, 30 June 2008 (UTC)[reply]
Venus can be so bright because it's close enough to the Sun, but not so close as the Mercury so it's still often visible on the sky. It's quite obvious that the planet at that position has to be named after the godess of beuty. —Preceding unsigned comment added by B jonas (talk • contribs) 13:37, June 30, 2008 (UTC)
I don't quite follow your logic, why should the 2nd planet obviously be named Venus simply because of its position (as opposed to it's magnitude and majestic qualities)? Unless you mean that the position of the planet gives it those qualities, although I would say it is more to do with the thick cover of cloud. Additionally, Mercury is certainly visible from Earth, see Observation, although its proximity to the sun does limit how often the planet is visible from earth. Jdrewitt (talk) 14:49, 30 June 2008 (UTC)[reply]
Take a look at List of oldest trees. Apparently the 9550yr figure for this Spruce is just the age of the clone. And since there are much older clones in the world (quaking aspen), I'd say there's a bit of unwarranted hype surrounding this Norway Spruce. --Allen (talk) 18:00, 30 June 2008 (UTC)[reply]
Identify this kelp?
What is it??
I took a picture of this while visiting tidepools at the Oregon coast, but for the life of me I cannot figure out what it is. I can't find any species of kelp that have so many small, ruffly leaves, which seem to grow out of long, thin strap. Nor can I find anything with air bladders that shape and size. It's not very long, just a few feet. Any ideas? --Masamage♫05:03, 30 June 2008 (UTC)[reply]
After some more hunting, I think it's Egregia menziesii. Here are some other pictures for comparison. Seems like a good match to me? --Masamage♫06:09, 30 June 2008 (UTC)[reply]
Volume percent
What's the usual abbreviation for volume percent in English? %vol or vol% or something else? Our article doesn't say. (I'm more interested in the use in general chemistry, not necessarily in alcohol content of drinks.) 62.145.19.66 (talk) 08:03, 30 June 2008 (UTC)[reply]
For chemistry, I use more explicit "% v/v" or "% w/v" (g/100 mL) to clarify if the solute was measured in volume or mass. A bare "volume percent" value is only unambiguous in meaning--regardless of how it's written--if it's unambiguous what kind of measurements one is using:) DMacks (talk) 08:10, 30 June 2008 (UTC)[reply]
I'm translating a document out of German. I think the context will be clear enough to the reader; the original uses "Vol%", but German allows both "Vol%" and "%Vol" as abbreviations. I'm pretty sure only one of the two is usual in English, I just can't remember which. 62.145.19.66 (talk) 08:17, 30 June 2008 (UTC)[reply]
The ACS Style Guide remains fairly silent on this subject. DMacks is correct as far as the ambiguity, but if you are just translating, there may not be a preferred way for the ambiguous case. I would typically prefer something such as "25% by volume," but that might be just a personal preference. (Note: The style guide does list "vol %" in its list of abbreviations, but I don't know if that can be used as a unit or not). --Bennybp (talk) 18:14, 30 June 2008 (UTC)[reply]
Excuse me, but I watched all the Neil Armstrong stuff on teevee when I was a child. Can someone please explain to me why primates aren't living and working on the Moon right now to help out all the primates and other species on Earth? I was brought up to believe that this would have happened by now, and I'm rather puzzled that it hasn't. Someone please explain this to me. --arkuat(talk)08:48, 30 June 2008 (UTC)[reply]
Establishing a colony for people or animals on the Moon would be incredibly expensive and I don't see how it would help us on Earth. Itsmejudith (talk) 09:50, 30 June 2008 (UTC)[reply]
Okay, that makes sense, but why do some people think it is more important to have primates on Mars before we establish primates on the Moon? I guess that's the part that I really don't understand yet. --arkuat(talk)11:04, 30 June 2008 (UTC)[reply]
Humans haven't been on Mars yet and many people want to go to new places. Mars is considered scientifically more interesting than the Moon, especially when looking for extraterrestrial life. In the really long run (and very hypothetical), Mars seems better suited for terraforming. PrimeHunter (talk) 11:59, 30 June 2008 (UTC)[reply]
I think that once America won the Space Race, the political point had been proven and there was insufficient imagination among our political leaders to understand why a sustained human presence on the moon would be useful for the long-term progress of our species. (Of course, this was before many folks realized how close we were to actually destroying the conditions on our planet that sustain life, leading to projects such as the Svalbard Global Seed Vault; nowadays, having a back-up planet or even moon might be viewed as handy.)
Although Earth may be in worsening shape, it is still a much better environment for human life than any other planet or satellite in the solar system. Itsmejudith (talk) 14:56, 30 June 2008 (UTC)[reply]
Thanks to all of you for your many interesting responses, especially to PrimeHunter for posting the relevant link and to Carmildo for the interesting point, new to me, about fuel consumption. I will confess that I am interested in solar power satellites, which will probably require raw materials support from workers established on the Moon if they are to become economically feasible. --arkuat(talk)05:01, 1 July 2008 (UTC)[reply]
From the article : Historically, leap seconds have been inserted about every 18 months. However, because the Earth's rotation rate is unpredictable in the long term, it is not possible to predict the need for them more than six months in advance.
And from INTERNATIONAL EARTH ROTATION AND REFERENCE SYSTEMS SERVICE (IERS) NO positive leap second will be introduced at the end of June 2008.
Essentially, there isn't one currently scheduled. However, if the 18 months figure it true, we're overdue since the last one was December 2005, 18 months later would have been June 2007. APL (talk) 13:01, 30 June 2008 (UTC)[reply]
The 18 months figure is approximate, and based on past trends which have apparently changed. We really don't know when the next leap second will be needed; we just have to keep monitoring the rotation of the Earth and noticing each time it slows down a little or speeds up a little.
As for your question 2, I'm not sure, but it may have just been a side-effect of a decision to set UTC, at that time, to a particular offset from Ephemeris Time or TAI during the years shortly before the introduction of leap seconds. The Ephemeris Time article may have more info. --arkuat(talk)04:41, 1 July 2008 (UTC)[reply]
Relevance of "Space, Time, and Gravity" by Robert Wald
I'm about to read Robert Wald's "Space, Time, and Gravity: The Theory of the Big Bang and Black Holes," second edition (1992). Should I? I'm wondering if there is anything significant in there refuted by recent discoveries. I might also ask the same question about the Feynman lectures. Cannongrandee (talk) 13:52, 30 June 2008 (UTC)[reply]
I can tell you that the Feynman lectures are very unlikely to be refuted anytime soon. See our article, but basically it was intended for first year undergraduates. Consequently, much of the material in there was very well studied by that point. On a side note, they're an excellent text to learn from, good choice. EagleFalconn (talk) 18:41, 30 June 2008 (UTC)[reply]
(Relative) Quantification of Human Genetic Diversity
Someone on the innertubulars asked something along the lines of "Is it true [what I heard from someone in a philosophy discussion channel] that human genetic diversity is tiny, among the least diverse of all animals?". I was, of course, struck by an instant bout of premium-strength dubiosity regarding the source and reliability of the information. However, a brief attempt to remedy with a timely injection of actual scientific results was sadly unforthcoming. To which end, I wonder if anyone knows of any studies that have been conducted into the absolute or relative degree of genetic diversity in humans, or how best to go about finding such a study should one exist. It's possible, I'm aware, that the technology has only recently descended to the level of affordability to undertake such investigations, and as such relevant information may not yet be available, though I'd like to think that such a matter would have aroused scientific interest already. Appreciative regards 153.1.253.80 (talk) 15:26, 30 June 2008 (UTC)[reply]
I recall reading that humans came very close to going extinct relatively recently and that we are all descended from a very small group of survivors, so there is less genetic diversity than other, related species, such as chimps (see Population bottleneck). This article states that the "genetic diversity [of chimpanzees and bonobos] is much larger than that of our species", despite their much smaller numbers. This article concurs. Clarityfiend (talk) 16:47, 30 June 2008 (UTC)[reply]
I've read that as early as Darwin it was realized that diversity in Africa is greater than in any other place in the world, and that was the reason for Darwin's widely ridiculed out-of-Africa theory. Imagine Reason (talk) 11:34, 1 July 2008 (UTC)[reply]
Nemesis
I was just reading Nemesis (star) and the article says that "due to orbiting the Sun it would have a very low proper motion and would escape detection by proper motion surveys". Surely at 1–1½ light years away it would have a large proper motion compared with other stars. Am I missing something?--Shantavira|feed me17:48, 30 June 2008 (UTC)[reply]
In a bound orbit, the relative velocity of the two objects goes down as the orbit size increases. Hence, if Nemesis orbits the sun at such a great distance then relative to the sun it must be moving quite slowly. Much slower, in fact, than most of the stars we observe in the sky. Dragons flight (talk) 17:54, 30 June 2008 (UTC)[reply]
(ec) The trick is that both the Sun and Nemesis would be moving about a common center of gravity (the barycenter of the system), so the only contribution to proper motion would be from their very low orbital velocity about the barycenter of the system. If we assume that Nemesis has the mass of the Sun and orbits 1 light year out, we're looking at an orbital period of roughly two billion years (if I've plugged in numbers correctly...) which cooks down to a proper motion of something like 0.6 milli-arcseconds per year: very, very small. Of course, that doesn't say anything about improper motions. The parallax shift of such a near companion would be quite large, and would indeed stick out like a sore thumb if noticed. TenOfAllTrades(talk) 18:04, 30 June 2008 (UTC)[reply]
I think you're out by 5 orders of magnitude on the orbital period! At least, one of us is, and my 20 million figure matches the 26 million figure mentioned in the article as the average time between extinction events. --Tango (talk) 18:07, 30 June 2008 (UTC)[reply]
(ec) Nemesis is predicted to have an orbital period somewhere in the 20 million years range. 360 degrees, divided by 20 million years gives a proper motion of about 0.06 arcseconds per year. The star with the largest proper motion, Barnard's Star, has a proper motion of 10.3 arcseconds per year, so you can see that Nemesis wouldn't have a very large proper motion. --Tango (talk) 18:07, 30 June 2008 (UTC)[reply]
Yes, but we still don't have an all-sky survey of paralax extending down to red dwarfs. Nemesis (star)#Looking for Nemesis lists a couple planned projects that would either find or exclude Nemesis (as a red dwarf) by comprehensively measuring paralax through out the local region of space. Dragons flight (talk) 21:36, 30 June 2008 (UTC)[reply]
Yes, the theory says it could be a Red Dwarf, but in its hypothesized orbit it would have an apparent magnitude between 9 and 12. We are talking about an object brighter than Pluto. Amateur astronomers would be able to see it with their own telescopes. A 12 inch aperture would be more than sufficient. An object that big with such a massive parallax shift would have been spotted decades ago. PlasticupT/C12:14, 1 July 2008 (UTC)[reply]
It's nothing of any consequence but I've always wondered about this. Whenever I stroke/scratch my Hyacinth Macaw's head in a certain place, it makes her open her beak wide and stretch her neck, like she's yawning. It's always the same spot that triggers it off, just behind her beak on both sides. Any idea what causes this? It doesn't seem to actually bother her in any way. --84.66.131.165 (talk) 19:44, 30 June 2008 (UTC)[reply]
If you put your fingers to the back of your throat, you'll soon learn that reflexes can last a lifetime! (I don't actually recommend doing that, throwing up isn't nice, but the point stands) — CycloneNimrodtalk?contribs?20:43, 30 June 2008 (UTC)[reply]
Thinking about it, my budgies do that sometimes after scratching their cheek areas with their claws or rubbing their faces against the aviary mesh. I always figured that it was just some sort of expression of relief from an itch. Same thing, you think? --Kurt Shaped Box (talk) 02:10, 1 July 2008 (UTC)[reply]
Frozen heart
In the film Rat Race a heart is shown is a cooler box on transit to a patient waiting for it to be installed. The driver says "it's been locked in that cooler box for seven hours". Can this really be true? The heart was not beating and was just shown in a plastic bag on top of ice. Would it really work if it was put into someone? Plemis monter (talk) 20:19, 30 June 2008 (UTC)[reply]
I don't know if "seven hours" is accurate or not, but even though there's always a great deal of hurry to get the patient into surgery after an organ becomes available, it's certainly true that they can be kept on ice for several hours before they're actually put into the recipient's body. This article, for example, tells us that a kidney was "put aboard an AirNet jet less than an hour after it was picked up from a Miami hospital. After a 2,700-mile flight, it arrived in San Diego the next morning for transplant into the patient." That's going to spend several hours in transport, no matter how you slice it. Of course, maybe kidneys travel better than hearts, I don't know, but seven hours doesn't sound that crazy to me. -- Captain Disdain (talk) 21:19, 30 June 2008 (UTC)[reply]
My understanding is that while 4-6 hours is the gold standard, hearts can and do remain viable for longer periods. This abstract describes a successful transplant with an ischemic time (the heart was without circulating, oxygenated blood) of 13 hours, including 12 hours on ice. There are various experimental procedures for extending the cold shelf life of donor hearts out to 24 hours or more (see [14] for example). Regarding Captain Disdain's comment above, it is indeed correct that different organs tolerate cold ischemia to different degrees. TenOfAllTrades(talk) 21:24, 30 June 2008 (UTC)[reply]
What is the limiting factor? It would be nice if organs could be stored much longer (i.e. years). That way we wouldn't have to waste organs if a donor becomes available but there is no immediately matching recipient. I assume it has been tried with animals, but what goes wrong? Obviously sperm and other more limited cell cultures can be preserved in liquid nitrogen for long times. Dragons flight (talk) 21:43, 30 June 2008 (UTC)[reply]
I have to catch a train, so I'll just cover freezing for now. Have you seen what happens to the texture of a chicken breast when you freeze and then thaw it? Just like chicken breast, the heart is muscle tissue, and freezing it without causing harm is very challenging. Leaving out the biology for a moment, there are two purely mechanical difficulties in freezing living cells and tissues. First, when water freezes, it expands slightly, while it contracts as it thaws. If you've ever had a can of soda explode in your freezer, or watched an ice cube crack when you drop it into warmer liquid, you can see why plain old expansion and contraction over a full-sized organ has the potential for harm. The second mechanical issue arises on a smaller scale—water, when it freezes, has a nasty habit of forming crystals. These crystals are very pretty when they make snowflakes, but their pointy little ends are deadly to delicate cell membranes.
In cell cultures, we can often get around these problems fairly easily. By adding a glassifying agent like DMSO or glycerol to our freezing medium, we can prevent or restrict the formation of ice crystals. (As the cells are chilled, the formation of large, ordered crystals is discouraged; the frozen state is more like a glass.) Expansion is a bit less of a problem for single cells; you don't have the accumulation of stress over large distances, and individual cells can stretch a bit. As well, some water actually comes out of cells during freezing. (Solidification of water happens outside the cell first, drawing liquid out.) Timing is important during the freezing process—freeze too quickly and the cells end up with too much water (ice) inside and are stressed; freeze too slowly and the cells start to find the glassifying agents toxic. Different cell types prefer different freezing regimens: different glassifying agents and different cooling rates.
Now, try and freeze a whole organ. You've got a combination of different cell types that each prefer different freezing conditions. You have a thick lump of material, so you can't chill it uniformly throughout. As the blood vessels freeze, it's difficult to get water in and out of the entire organ. You can see why freezing a heart is a nontrivial challenge. TenOfAllTrades(talk) 22:02, 30 June 2008 (UTC)[reply]
An important point that no one seems ot have made explicitly although everyone's hinting at it is that there is a big difference between "on ice" and "frozen." Laying an organ on top of ice but not in direct contact with the ice will keep it cold but it won't freeze. --Shaggorama (talk) 16:53, 1 July 2008 (UTC)[reply]
Best to avoid buying them in the first place. Check your product carefully before you buy, and insist on a pure product. Buying this sort of stuff will just encourage more adulteration. What products are you having trouble with. Graeme Bartlett (talk) 01:57, 1 July 2008 (UTC)[reply]
By having an effective network of inspectors, checking for adulteration, and with the power to take action when it is found? (if I have understood the question correctly?)87.102.86.73 (talk) 09:58, 1 July 2008 (UTC)[reply]
This has been a problem for a long time, and it ebbs and flows with waves of government regulation and deregulation. The classical (fictionalized) work on this is Upton Sinclair's muckrakingnovelThe Jungle.
I was watching a documentary, Regulus - The First Nuclear Missile Submarines, after WW2, in that it states how they managed to make the missile from remote go up and down, right and left, and eventually land. More information: [15]. Anyways if can control a missile from remote, why has there been no unmanned aircraft yet? Like a remote control one? I mean with the GPS and satellite technology it is possible. Is the United States Forces holding back on something they have in secret? --69.156.94.136 (talk) 01:17, 1 July 2008 (UTC)[reply]
There are unmanned aircraft. They don't even need to be remote controlled, they can be controlled by computer AI. Unmanned combat aircraft are probably the future of air warfare. Bombers and attack aircraft will be first. Followed by fighter aircraft.ScienceApe (talk) 01:29, 1 July 2008 (UTC)[reply]
I wanted some input on freezing cheese. I'm taking a five hour flight and want to take a two pound block of cheese with me.
I know that many people say, cheese shouldn't be refrigerated because it inhibits the life, and flavor inside the cheese, But hey I'm an American. And I know that freezing turns the moisture inside items into sharp shards, basically perforating what ever your freezing from the inside. But is freezing cheese GOOD or BAD? —Preceding unsigned comment added by Semi-smart (talk • contribs) 03:34, 1 July 2008 (UTC)[reply]
Freezing cheddar is no good, it destroys the texture and it all goes crumbly. Parmesan powder freezes OK though. For a short flight like this, just pre cool it in the fridge, and then wrap it in something insulated like bubble wrap to keep it cool. Graeme Bartlett (talk) 07:13, 1 July 2008 (UTC)[reply]
But freezing cheddar is fine if you're going to use it in cooking, since the texture won't matter [16]. My Googling suggests that this is true of a lot of cheeses... in applications where texture doesn't matter, freezing is usually fine. --Allen (talk) 07:18, 1 July 2008 (UTC)[reply]
I agree with Graeme Bartlett that the best way to deal with this would be to just cool it and keep it cool by insulating it. A simple way to do this would be to buy a small cooler -- I've seen ones that are about the size of a small handbag -- and sticking a couple of ice packs in with the cheese. (The "ice pack" article appears to deal only with the medical ice packs, but what I mean is the thing that is also called a "freezer block" or "ice brick", a rigid plastic brick filled with water that you can freeze and then use to keep things cool, the mainstay of coolers all over the world. (Can it be that we really don't have an article for them, or am I just completely blanking on the terminology here?)) Depending on where you are and how paranoid they are about you using your cheese to destroy the plane in midair, taking that with you as carry-on might be problematic, but you could just stick it in your bag and check it.
That said, a cheaper and more low-tech approach would be simply wrapping the refrigerated cheese tightly in newspaper. It makes a pretty good insulator, and you could always stick in an ice pack with the cheese to make sure it stays cool, if you're worried about that, but the newspaper by itself will probably do the trick, if the cheese is cool to begin with. You can probably get some extra mileage out of the newspaper by sticking it in the fridge with the cheese so it's also cool. As long as the newspaper is dry (water conducts heat very well), it'll work just fine. -- Captain Disdain (talk) 11:02, 1 July 2008 (UTC)[reply]
Why don't you test it out? Try freezing a bit and seeing whether it survives. I would be interested in hearing your results. PlasticupT/C13:01, 1 July 2008 (UTC)~[reply]
I say screw it. The flight is only 5 hours pal, leaving cheese out of the fridge for that long probably won't be that bad for it. Moreover, if it's 2 pounds of cheese it should hold a temperature for a while. I'm all for captain disdain's strategy of insulating the cheese. But for the record, remember that if you're flight is international they're probably going to take the cheese at customs. --Shaggorama (talk) 16:46, 1 July 2008 (UTC)[reply]
When we returned from France, we brought back a variety of cheeses, probably mostly of the semi-dry styles. They were wrapped well in butcher paper at the cheese shop and we then closed the cheese shop's plastic bag as well as we could and chucked them in the middle of the clothes in our luggage. Between the insulation of the clothing and the likely cold baggage hold of the plane, they survived the ten-ish hour trip just fine. And even though the cheeses were from (gasp!) France, we declared them at American customs and were still allowed back into the country, cheeses and and all. (The preceding does not constitute legal advice; it just recounts Wikipedian's one anecdote.)
Hello to all
Please if some one can guide me about data rates of different catagerizes of QAM that is the data rate of 8-QAM, 16-QAM, 32-QAM, 64-QAM, 128-QAM, 256-QAM
The different rates will depend on what bandwidth in general you want. For particular applications such as digital television or ADSL the appropriate standard will specify the rates to select from. With 8-QAM you will get 3 bits per symbol, 16-QAM will give you 4 bits per symbol, and so on till 256-QAM with 8 bits per symbol. Graeme Bartlett (talk) 06:18, 1 July 2008 (UTC)[reply]
In my experience, a model is something that is fed into a simulation to give it the information needed to simulate, so to speak. Said in another way, the model is the abstraction and the simulator takes that abstraction and performs calculations on it to produce an expected result. The Monte Carlo method is a good example of this. The model is the input and the simulation is the action taken on it and the final result. In common parlance, they are often used interchangeably. An experiment is a totally different thing. It is an empirical study of something. Rather than having a known model, a series of observations are taken and analysed. In some cases, a model fit can be used to test a hypothesis. It is important to note that the experiment is totally based on observation. Simulation and modelling can be used to create a hypothesis, but experimentation is usually necessary to reject or not reject a hypothesis. Gjmulhol (talk) 12:06, 1 July 2008 (UTC)[reply]
I have just begun building a guitar pedal, but no have no electronics expereience, but a good deal of knowledge (theoretical knowledge) of the subject.
I have become stuck where the schematic tells me to connect to ground.
I am soldering to a sheet of stripboard, and it has a thin copper track running down both sides of the board, but with no holes in them; Is this where i should connect grounded connections to? And do i connect all grounded connections to the one place, or should i cut the track so as to separate them from one another?
If this is a standalone pedal (not powered by a wall outlet), it is very possible that you do not have ground inside the footpedal at all. In that case, I would assume that you are using a 1/4" plug from the guitar/amp and assume that the shielding of that connector is ground. So, attach there. If, instead, you are powering this from a wall outlet, ensure you are using a grounded plug (three prongs in the U.S.). Then, you will have ground where the power is soldered onto the board. Because this is an audio device, be wary of ground loops. If you ground your pedal and plug it into one outlet, then plug the guitar/amp into another outlet, it is possible that they do not share the same ground. You can easily get a hum or buzz on the speakers. So, inside the pedal, ensure you connect the ground from your power input to the ground on the shield of the cable from the guitar/amp. Then, you will joining the possible difference in grounds and eliminating the buzz. -- kainaw™12:54, 1 July 2008 (UTC)[reply]
Additional Help with Electronics
Thanks to kainaw for answering my previous question about grounding, but i still have some queries.
When you say to connect to the ground from the guitar jack, do you mean the input or the output jack?
And does it matter whether i connect all the grounded connections directly to the ground terminal of the jack, or if i connect them all (Including the ground from the jack) to the copper track at the side of the stripboard?
"Ground" is often used in an imprecise way. The two most common usages are as "Ground"/"Earth" (yes I know this has reused "Ground") for the purpose of one or more of safety and screening/shielding and as 0V. Eventually Ground/Earthwants to get connected to a physical Ground - eg a copper rod stuck into the planet's soil. For this to work well as a safety connection, it wants to be well connected "in all directions". For it to work well as screening, you don't want current to flow through it, so only one connection to each bit of ground should be made, ideally in a star configuration but at worst as a tree configuration branching out from the trunk where the copper rod is. The other common usage informally means 0V. This has come about since often the 0V terminal of a PSU gets connected to ground to "stop it floating". This often creates loops and current flows in screening circuitry. With your pedals etc, you want all the 0V connected to each other once (no loops). A starter would be to see if, without your circuit in place the screen of the Inlet jack was connected somehow to the screen of the Outlet jack. If not, connect your ground signal to BOTH outers, otherwise choose one - the most convenient. There is an element of art rather than science about getting ground/0V/earth/screening right. -- SGBailey (talk) 13:52, 1 July 2008 (UTC)[reply]
To expand on SGBailey's point, "ground" in the context in which you're asking means "the reference voltage" (which we conventionally then call "0 volts"). All other signals in the circuit are measured "in reference" to this point, "the ground". For your guitar effects pedal, both the input and output jacks each have an outer terminal which should be connected to "the ground" (reference voltage) in your circuit.
Odds are that your guitar effects pedal should be designed to operate solely from battery power. Otherwise, any connection to mains/line power, even through a power supply/wall wart, is likely to cause a ground loop and that can induce your guitar amplifier to produce noise, hum, and other nasty stuff.
I can't find this anywhere. I would like to know if there is an image which shows the figure of the earth without the water on it. I.e. only the rock part of the earth. Does such an image exist? — Adriaan (T★C) 13:44, 1 July 2008 (UTC)[reply]
No, not what I'm looking for. I was wondering if there was a pic in true colour of the earth, just with the water edited out. Something like an artist's impression of what the earth would look like if all the water suddenly disappeared. Like a 3D pic of an object supposed to be the earth - but without water. — Adriaan (T★C) 15:52, 1 July 2008 (UTC)[reply]
In reading about the ancillary benefits of NASA's space program in articles like this and this, it strikes me that most the advances that are mentioned aren't dependent on the space travel part of the equation. Rather, they were inspired or triggered by space travel, but could just as easily have been developed for the same cost for a land-based application. For example, water filtration was (according to the NASA site above) developed in part for the Apollo program, but it's not as though it couldn't have been developed for non-space applications. Are there practical benefits to the space program, readily apparent to regular folks, that could only come with space travel? jeffjon (talk) 14:28, 1 July 2008 (UTC)[reply]
Define 'regularly apparent to regular folk'. There are thousands of experiments in space, many of which will have furthered our understanding of the world and how things react in given situations. Do you just want a list of products that use techniques based on the space program? Or do wooly benefits such as "improving the knowledge of mankind" and "continuing the exploration of the universe"? Personally I find that when people start to try to qualify the value of Nasa based on products/technological developments overlook the strongest argument for the space-program - that there's a universe out there that holds limitless possibilities and the more we go out there and the further we venture the more interesting things we will find. Of course this is from an exploratory enthusiast who supports the cause, certainly there are plenty of worthy groups vying for already scarce government funding. 194.221.133.226 (talk) 15:02, 1 July 2008 (UTC)[reply]
I'm with you; I think exploration for sake of pure discovery is motivation enough. My wife isn't convinced, so I was trying to come up with a more tangible benefit that she receives for that almost 1% of every dollar she pays in taxes, whether it's a product, a health benefit, a scientific advance with other implications, etc. jeffjon (talk) 15:10, 1 July 2008 (UTC)[reply]
IMHO the scientific benefits are good enough. But to counter the "they totally could've been developed anyway" argument, I guess the question is why. Why would any of that be built? Why would the US build a water filter when we've got good tapwater? Necessity is the mother of invention. We need a way to recycle water in space. It also happens to work really well on Earth? We should sell that to the third world and people who are superstitious about tap water! As the first source you cite mentions, if you look at a lot of the products, most of them are saying "NASA was doing this obscure scientific thing and it totally improved this product by leaps and bounds!" Thats pretty damn impressive, and I consider it a good testament to the power of a good R&D budget. EagleFalconn (talk) 15:24, 1 July 2008 (UTC)[reply]
I wouldn't expect R&D for space to be any more likely than anything else to have things that help in unexpected ways. If NASA didn't invent water filtration, maybe it wouldn't have occurred to anyone, but, by the same token, maybe there's something that hasn't occurred to us because we weren't spending that money on R&D for something of more obvious practical significance. Doing R&D for something practical has the added advantage of helping in expected ways. For those of you who think NASA does pull its weight, how much of your money do you donate to it? You don't think it's only worth it if it's money the government takes from you forcefully, do you? I'm currently saving up for college, but when I'm done with that, I plan on donating to a microcredit group, like Unitus. I think they have more practical significance than NASA. — DanielLC15:49, 1 July 2008 (UTC)[reply]
That's a bit of a red herring, isn't it? I don't make voluntary cash donations to my local water treatment plant or the city subway system, but I still think it's worthwhile for those projects to receive funding. If you want to talk about research, in the United States good solid research is carried out or funded by government agencies from the Department of Energy to the Department of Veterans Affairs; I don't make donations to those organizations either. TenOfAllTrades(talk) 17:26, 1 July 2008 (UTC)[reply]
Global Positioning System saves a lot of time and needless erring around. LINEAR is another point. And then, for people like me, it's simply interesting and sometimes even exciting to look at real pictures from space. And when I saw Neil Armstrong live on TV stepping on the moon that is something to remember. 77.3.134.249 (talk) 20:27, 1 July 2008 (UTC)[reply]
Though I am certainly no expert, I have read in the past that zero gravity experiments have been done on cultures of bacteria. These have shown unique characteristics. I also remember evidence of a super-bug, but I don't remember where that is from. Gravity is vital to life, it is important that we know how plants and animals react in such an environment. From a materials perspective (I am a materials scientist), some crystals and structures can only be formed in a zero-g environment. If extra-planetary colonization ever takes place, it would be good to know how to take advantage of these new, potentially revolutionary structures. Gjmulhol (talk) 11:55, 2 July 2008 (UTC)[reply]
physics
Question: When we throw a ball on the wall in a particular direction, then why does the ball comes back to us in some other direction ?'' —Preceding unsigned comment added by 61.2.190.79 (talk) 16:33, 1 July 2008 (UTC)[reply]
Start with Reflection (physics), but the most basic principle is that "the angle of incidence equals the angle of reflection". And remember, gravity is constantly working on the path of the ball.
Well, yes and no; it would just take a corner cube, but gravity is still affecting the track of the ball (which is probably what you were referring to in the need for "more energy").
Also, it is very difficult to throw a ball with zero spin. If you are familiar at all with the sport of tennis you will know that depending on the surface the ball is striking, the spin can change the direction dramatically. This is particularly evident if you use a hard rubber ball on a rough surface (e.g., a lacrosse ball on asphalt). The spin will alternate and dampen until the ball rolls flat. Thus, you see a low, long bounce followed by a short, high bounce, and on and on until the ball flies with negligible spin or it simply starts rolling. Gjmulhol (talk) 11:52, 2 July 2008 (UTC)[reply]
And where would you obtain the natural endorphins? You can't just buy it. And if you synthesized it, it would then be an artificial rather than "natural" substance. The closest analogue is morphine, which is routinely injected during childbirth and other painful periods. ~Amatulić (talk) 18:53, 1 July 2008 (UTC)[reply]
Also note that administering natural endorphins long-term would likely cause the same problems as other such drugs. A tolerance would develop, requiring more and more to get the same effect. And addiction would occur, so people would feel sick if the endorphin supplement was ever stopped. StuRat (talk) 15:42, 2 July 2008 (UTC)[reply]
Insulators for copper wiring
I'm wondering if there is any way to accuratly measure the resistivity of a substance...is there a way to get a quantitative value for resistivity in substances that could potentially be used to insulate basic copper wiring? 24.34.168.154 (talk) 18:43, 1 July 2008 (UTC)Fiziks[reply]
A megger is a good answer if you're interested in the performance of the insulator at relatively high voltages (~1KV), but at lower voltages, one would use a nanoammeter, a voltage source, and some careful experiment design including guarding. Keithley Instruments is a typical vendor of nanoammeters. And here's a good article from EDN about proper techniques: [18].
[This is really eight related questions, some of which may share answers.] Consider either (a) one or (b) eight soldiers armed with normal-caliber machine guns and an arbitrary amount of any kind(s) (armor piercing rounds?) of ammunition for them. They are free to walk the top of a tall concrete wall that is, say, 75m on a side. Trapped inside the wall on open ground is either (a) one unarmed enemy tank or (b) one enemy and one friendly tank, armed only with their main cannons. All tanks are modern main battle tanks; the unarmed tank may be considered to be repairing supposedly-minor damage to its anti-personnel weapons in (vain) hopes that it may return fire, and the armed tanks fire only at each other. How may the infantry in each of the four situations disable or destroy the enemy tank (a) in the least time or (b) using the least ammunition?
The purpose of the first bifurcation is to increase the infantry's effectiveness in the situation where there is a friendly tank, as well as to allow them to surround the enemy. The purpose of the second is to distinguish between an enemy that is fighting (albeit not against the infantry) and one that is doing nothing but trying to evade/weather fire. The purpose of the third is obvious, but in the case where there is a friendly tank present the "least ammunition" option should be taken to require some material contribution to the battle. I would also be interested in hearing about the mechanism by which (a large amount of) machine gun fire damages the high-grade armor against which it is not frequently used. Thanks for the myriad answers. --Tardis (talk) 01:11, 2 July 2008 (UTC)[reply]
Good luck. Modern tank armor (e.g. Chobham armor) is really, really tough. I'm no expert, but I doubt that anything fired from a machine gun would have a chance of doing any real damage. You're probably better off having these guys break out their shovels and cover the trapped tank with dirt. Clarityfiend (talk) 06:49, 2 July 2008 (UTC)[reply]
They could try and open the hatch and shoot the people inside. Trying to damage the armour would be in vain, I imagine. --Tango (talk) 14:04, 2 July 2008 (UTC)[reply]
Yeah- small arms fire against modern armor would be useless, no matter what ammo you're using. You'd need to get the hatch open somehow. Trap the tanks somehow, and wait for the people inside to get hungry? I don't know. Friday(talk)14:39, 2 July 2008 (UTC)[reply]
75m square? What sort of ground? Discharge five 40 tonne road tankers of diesel into the area (so 3cm deep without bothering to do the maths) and ignite it? The thermal conduction of armour is pretty high and baking the people in it cannot be too hard. --BozMotalk14:55, 2 July 2008 (UTC)[reply]
Even with an arbitrary amount (and duration; give the tanks infinite fuel if needed) of sustained fire? Surely something would happen to the armor, even if it shattered or reflected the bullets, and it wouldn't get stronger… --Tardis (talk) 15:02, 2 July 2008 (UTC)[reply]
I suppose if you had a billion rounds of machine-gun bullets, you could eventually wear a hole in the armor, but that's just getting a bit silly, the occupants of the tank would starve to death first. There may be a few weak spots, though, like the exhaust port, which might be more vulnerable to small arms fire. StuRat (talk) 15:38, 2 July 2008 (UTC)[reply]
Removable armor plates are common. If the tank is disabled and just sitting there, you could rush up and start removing armor. Eventually, the guys inside will try to come out to stop you and it will be man vs. man instead of man vs. tank. -- kainaw™17:33, 2 July 2008 (UTC)[reply]
(EC)
What about MacGyver solutions? Take the gunpowder out, make a kind of bomb, could at least blow the tracks off.
Today I was speaking to a Jehovah's Witness that came by my door. We got into talking about everyone's favorite topic, evolution. He brought up an objection to the theory that I had not heard before. I don't remember exactly what it was, but it was along the lines of "even if a man evolved into a human, what are the chances that a woman evolved too, at the same place, and the same time?". I'm sure there is an easy rebuttal to this, but I was wondering if this objection has a name and how I can rebut it in layman's terms. (In a somewhat related query, does anyone know where one can find very old (circa 1894) copies of the Watchtower magazine?) Thanks! Abeg92contribs03:56, 2 July 2008 (UTC)[reply]
Let me see if I understand the argument first. The idea is that if a male evolves from Species A to Species B, then there has to be a female that goes from Species A to Species B as well, otherwise there would be no-one to breed with? I can see what's wrong with the argument, but I'm finding it hard to put into words, except to point out that (a) evolution isn't sudden jumps, it's a gradual process (at least gradual in the sense that new species don't suddenly crop up in a single generation), (b) speciation occurs when an entire hereditary line becomes so genetically different to another that they cannot reliably interbreed, so it's actually the combination of a man and a woman who are, by necessity, genetically different, passing a particular combination of those different genes onto their offspring that leads to the creation of a new species. I'd try to explain it in terms of the historical development of language, but presumably the Witnesses believe that all happened when God struck down the Tower of Babel. I will leave the understandable explanation to someone with more experience in the subject matter. Confusing Manifestation(Say hi!) 04:56, 2 July 2008 (UTC)[reply]
Put another way, your Jehovah's Witness friend is mistaken in thinking that the process of speciation is something that occurs in an individual. Populations become species, individuals do not. - Nunh-huh05:06, 2 July 2008 (UTC)[reply]
The entire mechanism of reproduction involves males and females sharing their genomes again and again. The amount of genome that differentiates males and females is tiny. Your friend seems to think that males and females are terribly genetically different. They aren't. And again, all members of the species are products of their mating. So the genome isn't going to get out of sync between the two of them. --98.217.8.46 (talk) 13:53, 2 July 2008 (UTC)[reply]
If you want a more technical answer, consider how traits are distributed upon reproduction. Say I have a hypothetical gene for red hair. (Hair is a bit more complicated than one Mendelian trait but for our example it is concrete.) It sits somewhere on one of my chromosomes. I mate with a woman who had a gene for brown hair. It sits on one of her chromosomes. Inside the sperm, egg, etc., half of my genes are randomly thrown together with half of her genes. It's entirely possible that all of our male or female children could have my gene expressed, or half with her gene expressed. The resulting children are a mix-and-match of our two gene pools. It isn't that the "female gene pool" is separate from the "male gene pool" and has to "evolve" at the same time. They'll evolve together, as long as none of the evolutionary changes are great enough to make evolving with another human impossible. The gene pool of course allows for a certain amount of flexibility (if it didn't, even simple reproduction with genetically different members of the same species would be impossible). Beneficial mutations have a certain chance of being passed down to children of either sex. Males and females are, again, genetically (and developmentally, up to a certain point) almost identical—they are both humans, and it is the firing off of different hormones at different times that differentiate the two physically, mentally, etc. --98.217.8.46 (talk) 14:09, 2 July 2008 (UTC)[reply]
The number of chromosome is different in man and chimp, lets asume that the last comon ancestor had the same number than one of the two species. So sometime ago a chromosome split or paired with another to get to the different number. This happened in one single individuum not to the whole group.What I know from genetics this makes interbreeding very complicated what it is seen in donkey and horse. Has this problem of genetics been solved yet?---Stone (talk) 14:25, 2 July 2008 (UTC)[reply]
There are lots of theories as to how this can work. Needless to say, yes, it seems pretty clear that it can work. Even in individual humans you can do weird things like have too many chromosomes (e.g. XYY syndrome, trisomy 21). It is not usually positive in such cases though, but the point is, it can happen—it doesn't mean automatic death of the organism or inability to reproduce. --98.217.8.46 (talk) 15:24, 2 July 2008 (UTC)[reply]
There seems to be a false assumption that males and females evolve completely independently of one another. This is untrue. For the most part, only the X and Y chromosomes evolve independently, in humans. I can try to make this into a reasonable objection to evolution:
"Since, in humans, the X chromosome determines (or at least triggers) female characteristics and the Y chromosome male characteristics, the two must evolve in parallel so that any change in females matches a corresponding change in males. For example, the tendency in females towards nurturing, homemaking, and gathering required a corresponding change in males toward hunting, to ensure that all the child-rearing and food provision needs of the group were met, utilizing a division of labor."
I suppose this is true, but, in cases where both sexes developed noncomplimentary traits, like everyone going hunting and leaving the children unattended, those traits would not be likely to be passed down. StuRat (talk) 15:30, 2 July 2008 (UTC)[reply]
What is the process of decompossition of the human body?
consider a uniformly charged sphere with a cavity inside. the electric field inside the cavity is non zero and uniform... but if we draw a gaussian surface inside the cavity, the charge enclosed will be zero. so field zero on the surface... why the contradiction???? —Preceding unsigned comment added by 117.201.49.226 (talk) 07:46, 2 July 2008 (UTC)[reply]
Shell theory explains the field (works for any inverse square relation ship) both inside and outside hollow spheres..
Note at the centre of the cavity the field is zero. I've no idea what you mean by "but if we draw a gaussian surface inside the cavity..." if you wan't the field then shell theory has a mathematical method of how to get it.
One answer "... inside the cavity, the charge enclosed will be zero. so field zero on the surface.." - the surface is not inside the cavity - it's on the boundary - which is different..87.102.86.73 (talk) 15:10, 2 July 2008 (UTC)[reply]
Can I get fully solved IIT-JEE question papers in Physics (mechanics only) of past 10-20 years?
I want to know whether I can get fully solved Physics question papers of past 10-20 years of the IIT-JEE examination from you.
If you do this small favor for me,I'll be very very thankful to you.Please send them (if possible) as an attachment to your response mai
I posted this at Talk:Yeast but thought I should place it here too.
What defines a yeast? Do yeasts have some intrinsic trait that qualifies a particular species as being a "yeast" rather than just generically being a "fungus"? What is special about all (or most) of the species of yeast that qualifies them as yeasts? --Alecmconroy (talk) 15:07, 2 July 2008 (UTC)[reply]
How fast does the "wind" go when we blow on something?
Just lbew an ant off my book outside with a gust of wind, and it made me wonder - how fast does that "gust" blow that we creat when we blow?
I'm thikning, just from experimenting, maybe 50 MPH or so at first, but then of course air resistance will slow it down a lot. Plus, the amoung of saliva probably affects things. Holding my hand about a foot away from me (like when blowing out candles on a birthday cake) it still feels gusty, but not too much; maybe 20 MPH or so?209.244.30.221 (talk) 17:35, 2 July 2008 (UTC)[reply]
An edge-on glaxy with an inclination of 90° relative to the earth.
A face-on galaxy with an inclination of 0° relative to the earth.
![[12]](http://www.whatsthatbug.com/images/gaudy_sphinx_cat.jpg){kind=link}
![[17]](https://en.wikipedia.org/wiki/Image:AYool_topography_15min.png){kind=link}