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February 13

Einstein's theory was wrong

Last sentence of this article Spacetime in General relativity says Einstein's theory was wrong, which surprised me. According to me, this is wrong since this article doesn't contain any reference. What do you think about this? 27.62.78.249 (talk) 02:40, 13 February 2013 (UTC)[reply]

That was just a vandal, and he's been reverted. It's a terrible article though, in any event. Someguy1221 (talk) 02:41, 13 February 2013 (UTC)[reply]

Holy cow, you aren't exagerating... Snow (talk) 02:48, 13 February 2013 (UTC)[reply]

Human beings can believe in terrible ideas. It is no wonder some people believed Eistein's theory was wrong. --PlanetEditor (talk) 03:50, 13 February 2013 (UTC)[reply]

My favourite wacky website Conservapedia has a particular problem with Einstein, see E=mc²? Not on Conservapedia Dmcq (talk) 11:45, 13 February 2013 (UTC)[reply]

It's there under Einstein himself,[1] and has been since at May of 2007.[2] Maybe no one has bothered to write a separate article about it there yet. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:32, 13 February 2013 (UTC)[reply]

OMG! I see why that vandal "improved" our article.

That's incredible...evidently, in the Bible: John 4:46-54, it says that a man visited Jesus saying that his son was dying - Jesus tells him to go home and his son will be just fine. The guy goes back and his household staff tells him that his son got better at 1pm the previous day which was the exact same time he was talking to Jesus! Cool!! So we may conclude that it took zero amount of time for Jesus' cure to reach the child - which means that the cure travelled faster than the speed of light - which Einstein said was impossible! The bible must be right, ergo Einstein was wrong and presumably the Missouri House of Representatives can mandate that it shouldn't be taught in schools. I guess Newton is still OK though...(although he rejected trinitarianism, so you'd better get your kids to learn "f=ma" while they still can - I fear calculus is already a lost cause!)

From which I infer that millisecond (or better) clocks were in routine use in Jesus' time, and that some Christians don't really believe in miracles. —Tamfang (talk) 19:10, 3 December 2013 (UTC)[reply]

Then...if that's not enough...we are told that Obama used Einstein's Relativity to "prove" that abortion is OK. The truth of that turns out to be that about 20 years ago, some legal theorist wrote that just as Einstein showed that space-time is curved by gravity, so the landscape of our legal system is changed by the way people interpret the law. He then goes on to use the abortion debate as an example of that changing legal landscape. This paper was published in an obscure law journal that Obama was the editor of. Obama neither wrote nor endorsed the paper, he merely accepted it for publication - the paper made no mention of relativity having anything whatever to do with abortion or even advocated on either side of the abortion debate. But now Einstein is on the religious nut's shit-list right up there with Darwin.

Wow!...just Wow!

SteveBaker (talk) 15:01, 13 February 2013 (UTC)[reply]

Clearly you haven't read much ID literature :-). Einstein has always been on the shit list. One of the greatest difficulties for ID proponents is to explain why, if the world is only a few thousand years old, light from distant stars appears to have been traveling toward us for millions or billions of years. Unless you assume that the light was created "in transit" -- which seems absurd even to ID proponents -- there is no way to make things work without trashing relativity. Looie496 (talk) 16:00, 13 February 2013 (UTC)[reply]

But without a finite speed of light, explaining red-shift would be exceedingly difficult. Understanding why there is a lag in transatlantic telephone calls made via satellite gets tricky...well, all manner of very obvious facts about what we see in our daily lives would be exceedingly hard to explain. These computers we're typing on would be very different beasts if the speed of light were any different than it is. Argh...there is simply no point in chasing it down this particular rabbit-hole. Demolishing these arguments is like shooting fish in a barrel. SteveBaker (talk) 20:41, 13 February 2013 (UTC)[reply]

Devils advocate: If you really wanted, you could explain redshift and propagation delay without a finite speed of light by assuming luminiferous aether exists (with some adjustments of course, perhaps assuming that the aether flows under gravity). Ariel. (talk) 23:05, 13 February 2013 (UTC)[reply]

I see Conservapedia now have a E=Mc² article. It was set up with the comment 'E=mc2 is a meaningless statement in physics that purports to relate light to matter. In fact, no theory has successfully unified the laws governing mass (i.e., gravity) with the laws'. So perhaps to say that they cover it is about equivalent to saying we cover the government conspiracy over 9/11. Dmcq (talk) 20:48, 13 February 2013 (UTC)[reply]

Wait a minute... Conservapedia actually says that 9/11 was a government conspiracy?! 24.23.196.85 (talk) 02:05, 15 February 2013 (UTC)[reply]

No it doesn't either -- in fact, it REFUDIATES all such conspiracist bullshit! Here's their actual article about 9/11 24.23.196.85 (talk) 02:11, 15 February 2013 (UTC)[reply]

No I should have been clearer, someone above said that they did have E=Mc² but I was saying they have that in only in the same sense as we have 9/11 was a government conspiracy in Wikipedia. Sorry for confusing things. Dmcq (talk) 14:31, 15 February 2013 (UTC)[reply]

"Simply put, E=mc² is liberal claptrap." --PlanetEditor (talk) 02:26, 14 February 2013 (UTC)[reply]

How many times thicker is the dermis than the epidermis?

At the same spot. Sagittarian Milky Way (talk) 02:59, 13 February 2013 (UTC)[reply]

Well, the thickness of dermis and epidermis are not the same at every spot of your body; the thickness varies. The epidermis is 0.05 mm ( eyelids) to 1.5 mm (palms and soles) thick at different places. On the other hand, the dermis is 0.3 mm to 4 mm thick at different spots. As a rule of thumb, the dermis is 10 times thicker than epidermis at the same spot. But this thickness can go further in the range of 10 to 40 times at some places. --PlanetEditor (talk) 03:09, 13 February 2013 (UTC)[reply]

(edit conflict)

"The dermis is 10 to 40 times thicker than the epidermis.""^[3]

~:74.60.29.141 (talk) 03:13, 13 February 2013 (UTC)[reply]

But this "rule" does not apply uniformly. For example, according to the Wikipedia article Skin, the skin on the palms is 4 mm thick and the epidermis on the palms is 1.5 mm thick. So the dermis on the palms is 4 - 1.5 = 2.5 mm thick. So the dermis on the palms is 1.6 times thicker than the epidermis on the palms. How is it 10 times thicker? --PlanetEditor (talk) 03:41, 13 February 2013 (UTC)[reply]

Value chain of SLES (Sodium Lauryl Ether Sulfate)

Need to know the value chain of SLES (Sodium Lauryl Ether Sulfate) with all the respective % , sources, Process and cost indication details — Preceding unsigned comment added by 170.252.219.1 (talk) 04:24, 13 February 2013 (UTC)[reply]

Please do your own homework.

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know.--Jayron32 06:06, 13 February 2013 (UTC)[reply]

I'm not so sure it's homework, but I'd be curious how you answer this. I looked up value chain... I know the difference between sodium laureth sulfate and sodium laurel sulfate (the former has some ethanol units pasted between the twelve carbon chain and the sulfate), and from the article I know it is made by "ethoxylation of dodecyl alcohol. The resulting ethoxylate is converted to a half ester of sulfuric acid, which is neutralized by conversion to the sodium salt." The dodecyl alcohol apparently comes from reduction of coconut or palm oil. But how do you find out what companies do this, what their efficiency and profit margin is in modern practice (as opposed to probably ancient journal publications about efficiency of the synthesis in the lab)? Does a question like this go all the way back to the coconut plantation? It would be good to see this answered properly. Wnt (talk) 04:48, 15 February 2013 (UTC)[reply]

I'm not so sure that the coconut plantation has to be involved in the production process in any shape or form -- last I checked, they could also make sodium lauryl sulfate from ethylene by Ziegler-Natta polymerization (and I know these things -- petrochemicals are my area of expertise). 24.23.196.85 (talk) 06:17, 15 February 2013 (UTC)[reply]

Homo sapiens subspecies

I was just going through the article Elephas maximus and found the basis of their subspecies classification:

Elephas maximus maximus: shoulder height between 2 and 3.5 m, 19 pairs of ribs, skin color is darker than of indicus and of sumatranus
Elephas maximus indicus: shoulder height between 2 and 3.5 m, 19 pairs of ribs, skin color is lighter than of maximus with smaller patches of depigmentation, but darker than of sumatranus
Elephas maximus sumatranus: shoulder height between 2 and 3.2 m, 20 pairs of ribs, skin color is lighter than of maximus and indicus with least depigmentation

Then I read the article Subspecies. According to Subspecies#Criteria,

Members of one subspecies differ morphologically or by different coding sequences of DNA from members of other subspecies of the species. Subspecies are defined in relation to species.

This means a species may have two or more subspecies which are:

either morphologically different, or
genetically different, or
both.

Now I have a thought. If elephants can be divided into different subspecies based on morphological differences, why can't humans be classified into different subspecies given that humans have vast morphological as well as genetic differences. I'm not talking about the extinct Homo sapiens idaltu or the extinct Homo sapiens neanderthalensis, I'm talking about extant Homo sapiens. Also, it has nothing to do with scientific racism which is the scientific manifestation of the political belief of racial superiority. Differentiating humans into different subspecies should be scientific (just as in the case of Asian elephants) and does not claim one subspecies is superior to the other, it is just morphological and genetic differences. So I'm curious to know why humans have not been classified into subspecies. --PlanetEditor (talk) 09:20, 13 February 2013 (UTC)[reply]

In modern times with modern techniques, a new classification of subspecies would only be accepted if it had at least a hypothetical phylogenetic basis. And although you can classify people into groups based on genetic similarities, it's very difficult to form a monophyletic groups of humans that can be distinguished from other such groups by any significant, unique characteristics. You can certainly group people by race, and these groupings will have some genetic and morphological traits they share more often with eachother than with outgroups, but it will not be taxonomically valid. And that's not to even mention all the interbreeding that takes place. Read more at race and genetics. I know you didn't ask specifically about race, but that's the most on-topic article. Someguy1221 (talk) 09:33, 13 February 2013 (UTC)[reply]

Thanks for the explanation. --PlanetEditor (talk) 10:57, 13 February 2013 (UTC)[reply]

Homo sapiens sapiens, Homo sapiens neanderthalensis. μηδείς (talk) 18:02, 13 February 2013 (UTC)[reply]

Homo sapiens idaltu. RNealK (talk) 22:23, 13 February 2013 (UTC)[reply]

If you're interested in this, the starting point of your research should be Human mitochondrial DNA haplogroup and Early human migrations. There is a torrent of information in those articles, much of it quite recent, and I haven't kept up with all of it. But to cut to the chase, the best candidates for a subspecies would be the members of Haplogroup L0 (mtDNA), which our article says is 100% prevalent in the ǃKung people, renowned to us for their differences as Bushmen and "Hottentot Venus". Everyone not in L0 has mitochondria more related to one another than to the L0 members. That said, however, the various mitochondrial subtypes are very commonly mixed in a race; races with different haplotypes can look very similar and can look very different with the same haplotype; and even if populations are separate in matrilineal contributions that doesn't mean there hasn't been other gene flow, nor does it immediately rule out a more recent founder effect to explain the prevalence of one mitochondrial type. I recall that mainstream opinion, e.g. Stephen Jay Gould, was that the people of South Africa carry 99% of all human genetic variation among them, making the distinction in mitochondrial subtype quite an anomaly. One might try to present the !Kung are some rare remnant of an ancestral subspecies with much of Africa as a hybrid zone, but it would appear that nobody has made that case, to say the least. Now looking to see if anyone has tried to go down this path and claim enough genetic separation to make a subspecies a meaningful thing, I run into rather disturbing "European Culture" type websites that talk about "Khoisanids", formerly Capoids, but it has a very fringey feel to it. Hunting for the most interesting bit, the steatopygia and L0 (relating the mitochondrial marker to some visible sign would at least be a beginning) I came up with [4] which says that some southern Sandawe have steatopygia like the Khoisan, and it turns out that according to our article on Macro-haplogroup L (mtDNA) they have some L0d "indicating a connection to the Khoisan". So there's the absolute skeleton there of an argument that you could say that humans should "really" be counted as a polytypic species with big beautiful butts associated with this marker and smaller daintier butts with all the others, but, well, nobody has put in the research to prove it. Dunno why, it sounds like you could recruit volunteers to wield the tape measures pretty easily. :) Plus, you have the obvious flaw that the Onge (also listed in steatopygia) are in subgroup M (of L3, of L1-6, not L0) so the trait can arise in other populations, which rather undermines the idea of using it to define two independent taxons. In any case, it seems like too small and pedantic a character to really justify calling the humans two subspecies, and of course I wouldn't be surprised if some researchers are wisely steering clear of the point for fear that some idiot will try to use it for a racist argument, though not a particularly logical one. Wnt (talk) 23:17, 16 February 2013 (UTC)[reply]

What is the latest on olive oil and antioxidants? Are they supposed to be good or bad for you now?

What is the latest on olive oil and antioxidants? On balance of the best evidence available, are they supposed to be good or bad for your health? --173.49.81.79 (talk) 13:36, 13 February 2013 (UTC)[reply]

On the balance of what? Insofar as you use olive oil in stead of other oils, it is probably better for you than those other oils, but in general it is best to keep overall fat consumption low (not zero, but probably lower than the average western diet). So olive oil is both good (better than other, highly refined oils) and bad (too much fat in a diet of any sort can be problematic). And there are several "antioxidants"(which is a marketing term that has become almost meaningless due to its overuse) which are not only good, but are vital, such as Vitamin C. --Jayron32 13:46, 13 February 2013 (UTC)[reply]

Too much anything (fat, carbohydrates, protein, vitamins, mineral, water, oxygen) is bad for health. What is important is to check the daily total calorie consumption. A popular misconception exists about carbohydrates. Carbohydrates are not essential nutrients; although dietary fibers are important for health. Carbohydrates only provide energy, and processed carbohydrates (high glycemic load) and fruits (due to presence of fructose) do a lot of harm. --PlanetEditor (talk) 14:14, 13 February 2013 (UTC)[reply]

"Fruits (due to presence of fructose) do a lot of harm"?^{[citation needed]} From Fructose#Compared to sucrose:

Fructose is often recommended for diabetics because it does not trigger the production of insulin by pancreatic β cells, probably because β cells have low levels of GLUT5.[57][58][59] Fructose has a very low glycemic index of 19 ± 2, compared with 100 for glucose and 68 ± 5 for sucrose.[60] Fructose is also seventy-three percent sweeter than sucrose (see relative sweetness) at room temperature, so diabetics can use less of it. Studies show that fructose consumed before a meal may even lessen the glycemic response of the meal.[61]

And from Fruit#Nutritional value:

Fruits are generally high in fiber, water, vitamin C and sugars, although this latter varies widely from traces as in lime, to 61% of the fresh weight of the date.[31] Fruits also contain various phytochemicals that do not yet have an RDA/RDI listing under most nutritional factsheets, and which research indicates are required for proper long-term cellular health and disease prevention. Regular consumption of fruit is associated with reduced risks of cancer, cardiovascular disease (especially coronary heart disease), stroke, Alzheimer disease, cataracts, and some of the functional declines associated with aging.[32]

Diets that include a sufficient amount of potassium from fruits and vegetables also help reduce the chance of developing kidney stones and may help reduce the effects of bone-loss. Fruits are also low in calories which would help lower one's calorie intake as part of a weight-loss diet.[33]

Duoduoduo (talk) 16:08, 14 February 2013 (UTC)[reply]

Sorry I made mistake. Actually I should have said fruit juice instead of fruit. The main benefits of eating fruits are fiber, vitamins and minerals. Anyway here are two interesting pieces: [5] and [6]. --PlanetEditor (talk) 16:28, 14 February 2013 (UTC)[reply]

Still not right. From Fruit juice#Health effects:

For example, orange juice is rich in vitamin C, folic acid, potassium, is an excellent source of bioavailable antioxidant phytochemicals[9] and significantly improves blood lipid profiles in people affected with hypercholesterolemia.[10] Prune juice is associated with a digestive health benefit. Cranberry juice has long been known to help prevent or even treat bladder infections, and it is now known that a substance in cranberries prevents bacteria from binding to the bladder.[11]....fruit juices are actually known for their ability to raise serum antioxidant capacity and even offset the oxidative stress and inflammation normally caused by high-fat and high-sugar meals.[13]....fruit juice intake has been consistently associated with reduced risk of many cancer types,[15][16][17][18][19][20][21][22] might be protective against stroke[23] and delay the onset of Alzheimer's disease.[24]....

Duoduoduo (talk) 22:04, 14 February 2013 (UTC)[reply]

Olive oil is low in saturated fat (commonly called "bad fat" linked with coronary heart disease), high is MUFA (good fat), and moderate in PUFA (another fat which is both "good" and "bad"). A high PUFA consumption is detrimental to health, and there have been a lot of noise made about the effects of saturated fat. So olive oil is an ideal choice for cooking and salad dressing, it will give you the good fat MUFA, and limit your saturated fat consumption. Another oil that you can chose is canola oil. --PlanetEditor (talk) 13:54, 13 February 2013 (UTC)[reply]

Antioxidants are essential. But a study shows excess intake of vitamin c can reduce the benefits of exercise. However in that study the volunteers took 1000 mg vit. C per day, which is a very high dose and well above the RDI. --PlanetEditor (talk) 14:02, 13 February 2013 (UTC)[reply]

KWh problem

I have a problem where a fridge has a COP of 1.4. A 20W light in the fridge is switched on when the fridge door is open which is for 31,317,000 seconds of the year. I require the energy consumption of the fridge (for the light bulb only so ignoring energy consumption to power fridge itself) in KWh/year. I know from my calculations that the energy the bulb requires in a year is 20x31,317,000 which is 626340000J. The energy the fridge can supply is 20/1.4 which is 14.29J. This would be per second I think. I'm lost from here because of the KWh/yr. I don't understand this unit and I don't know how to get the energy consumption of the fridge for the bulb in KWh/yr. Clover345 (talk) 16:42, 13 February 2013 (UTC)[reply]

Are you sure about this setup? Your time value is equal to the full number of seconds in a year, so you are assuming that the door is open all the time. Is that really what you want to do? Regardless of the answer, converting to Joules here does not help you. Basically your problem is to convert from Watt-seconds to Kilowatt-hours -- the "/yr" part simply indicates that you should do this on a one-year basis. Looie496 (talk) 16:55, 13 February 2013 (UTC)[reply]

I couldn't find the TLA "COP" in Wikipedia (unless you meant Coefficient of performance which doesn't apply to the light bulb), so I'm not sure where the 1.4 comes in. I agree with Looie496 that the joule isn't the simplest unit to use here, but, if you insist, then 20W is 20 joules per second, and one kWh is: 1000 (joules per second) times 60 (seconds in a minute) times 60 (minutes in an hour) ~~times 24 (hours in a day)~~ joules. Alternatively, if you look at the Kilowatt hour article you will see that one kWh is equivalent to 3.6 million joules. Leaving the fridge door open for a full year with the fridge switched on will waste a lot more energy than that used by the light bulb. Dbfirs 17:29, 13 February 2013 (UTC)[reply]

Leave out Dbfirs' last "times 24" or you'll be dealing in "kilowatt days" Rojomoke (talk) 17:41, 13 February 2013 (UTC)[reply]

Oops! Brain slipped out of gear! Dbfirs 20:58, 13 February 2013 (UTC)[reply]

Don't forget that the bulb dumps waste heat into the refrigerator - which it then has to remove - so the actual amount of energy consumed if the light inside fails to turn off when you shut the door is going to be at least twice what the bulb consumes...probably much more. SteveBaker (talk) 20:36, 13 February 2013 (UTC)[reply]

Your estimate is far too high. Typically it takes %25 of the input energy to cool that amount. So a 40 watt light will consume 10 watt in order to cool it. Maybe slightly more because the fridge is cold, but certainly not "twice what the bulb consumes". Ariel. (talk) 01:07, 14 February 2013 (UTC)[reply]

I think I recall this problem from my 'Physics 101' exam. -Which doesn't necessarily mean that I recall the answer. ;) ~:74.60.29.141 (talk) 21:09, 13 February 2013 (UTC)[reply]

COP (coeficient of performance) is the ratio of heat removed to electrical energy consumed and applies to any form of refrigeration - airconditioners, fridges, thermo-electric beer cooler, etc. To get the electricity consumed in kW.hr due to the 20 W light, you need to multipy 20 watts by 1 plus 1/COP, and then multiply by the total door open time in hours. You need to add 1 because the light draws power directly, as well as causing the refigeration to draw more power. However, the COP given by the OP is way too low. Typical kitchen fridge COP's will be in the range 3 to 4. Some very small units can be as low as 2. Wickwack 124.178.132.174 (talk) 00:17, 14 February 2013 (UTC)[reply]

If the fridge has a faulty door switch (so that the 20w bulb is always on), then the power consumed by the lamp plus fridge motor just because of the faulty switch will be 20 watts times (1 + 1/COP) as explained by Wickwack, but if the door is left open in a warm room, then the power used might be even greater, and the interior temperature is unlikely to be maintained. Dbfirs 08:21, 14 February 2013 (UTC)[reply]

Where can I find real video of the moon orbiting the Earth from perspective outside Moon's orbit?

A few years ago, I remember watching a video of the Moon orbiting the Earth from a perspective outside the Moon's orbit, but I can't seem to find it. This is actual footage, not an animation. I don't remember all the details, but obviously there can't be too many videos of the Moon orbiting the Earth from this perspective. The video was short, maybe a minute or two, and time-elapsed. I'm guessing the video was taken from a satalite orbiting the Sun, but I could be mistaken on that. Can anyone help me out here? A Quest For Knowledge (talk) 16:49, 13 February 2013 (UTC)[reply]

Was it this 2008 video of the transit of the Moon in front of Earth, as seen by the Deep Impact probe? TenOfAllTrades(talk) 17:05, 13 February 2013 (UTC)[reply]

For bonus points, I'll also throw in this small collection of still images taken by other missions. The Voyager image at the bottom of the page was the very first of its kind. TenOfAllTrades(talk) 17:11, 13 February 2013 (UTC)[reply]

@TenOfAllTrades: Yep, I'm pretty sure that was it. Thanks! A Quest For Knowledge (talk) 17:21, 13 February 2013 (UTC)[reply]

Coefficient of Performance

Are my calculations here correct?

My air con unit has a temp of 5C in its coils, and the temp outside is 25C, the rate of heat transfer from the coil to the refrigerant is 5000kj/hour, and the power input required is 1250 kj/hour.

I've calculated the Coeffecient of Performance as 5000/1250 = 4 and the maximum coefficient of performance if the system were reversible as 1/(298/278)-1 = 13.9.

I've also calculated what it's Coefficient of performance would be as a heater if I reversed the unit as 1/1-(278/298) = 14.9. This is the max Coefficient of Performance as a heater so in reality it would be 4(from the Coefficient of performance as a air con) + 1 =5. 1 is from 14.9 -13.9. Clover345 (talk) 17:51, 13 February 2013 (UTC)[reply]

I see nothing wrong with your math, except I don't know where you got the 298/278 numbers. For heating COP you want: (5000+1250)/1250 = 5. BTW this is a pretty efficient A/C, I don't believe any units of this size, and still this efficient are available on the market. (This efficiency is usually only available for much larger sizes than this.) Ariel. (talk) 18:30, 13 February 2013 (UTC)[reply]

Also "the rate of heat transfer from the coil to the refrigerant" - for a system like this you actually want the rate from inside air to outside air. There are two heat transfers in this system, so don't just calculate one of them. Ariel. (talk) 18:31, 13 February 2013 (UTC)[reply]

The 298/278 are the temps in kelvin. And can you elaborate on the second system I should calculate? Thanks. Clover345 (talk) 19:06, 13 February 2013 (UTC)[reply]

Heat transfer from the room to the cold coils, and from the hot coils to the outside air. If you are using temperature to do your calculations you have to do it twice (you started your question by mentioning temperatures). If you just look at net flow then both will be the same of course, except that the hot side also deals with waste heat. Ariel. (talk) 23:09, 13 February 2013 (UTC)[reply]

basic theoretical question (no application)

Hi,

I have a basic theoretical question that has no application. Is a glider, like a sailboat, able to "glide" against wind (when looking at ground coordinates, I mean). What are the theoretical constraints? What I mean is, theoretically if you are at an altitude, A, and have a glider of mass m and wing area w that is willing to lose y meters of height in order to go straight into the direction from which wind is coming from at a velocity V - will that be possible? Or, normally, will a glider be unable to perform this overall action. If it can perform the action overall (including via crisscrossing) what is the average theoretical limit of the speed it can gain (wrt to ground) in directly same direction wind is coming from? This is a point of curiosity only and has no intended applications at present, but is intended to help me understand basic ralationships. Thanks. 178.48.114.143 (talk) 18:41, 13 February 2013 (UTC)[reply]

No. A glider can (for a while) steer into the wind and make progress by losing speed and/or altitude - or by maintaining altitude in a rising air stream...but it can't "tack" into the wind like a sailing ship. To do that the sailing ship is using the resistance of the water against the flow of the air. A land-yacht does is using friction against the ground with its' wheels. The glider doesn't have anything to push against, so it can't do that. A glider that could fly up-wind would be a perpetual motion machine - and those don't work! SteveBaker (talk) 20:32, 13 February 2013 (UTC)[reply]

Could you or someone specify what "for a while" is theoretically, for different wind speeds, altitude a, mass m, wing area w, and so forth. Am I supposed to just take the potential energy that the glider has due to its altitude, and convert that into forward motion directly (i.e. in newtons)? i.e. I can theoretically give a glider as much forward thrust as it loses in kinetic energy from losing energy? In that case would I simply subtract the speed of the wind from that to see if it can (even theoretically) move forward with respect to ground when faced with that wind, losing altitude to do so? My suspicion is there is a limiting rate, thus for any combination of the above there is a wind you cannot fight for any amount of time as you just can't convert altitude to forward motion fast enough. I'd like to know the equation I can use to calculate this, if possible. This is meant to increase my theoretical understanding only. Thanks for any help. 178.48.114.143 (talk) 21:36, 13 February 2013 (UTC)[reply]

It's far from possible to answer your question using just mass, wing area "and so forth". The shape of the glider is critical - and it requires wind tunnel testing to know for sure what the glide ratio, drag coefficient, angle-of-attack-versus-lift curves and so forth are like.

The easiest way to think about flight through wind is to ignore the wind and instead, pretend that the ground is moving in the opposite direction and the air is stationary. As far as the glider is concerned, the ground doesn't even exist past take-off and landing! So do your math in the coordinate system of the air and then add in the wind vector at the end. This works great when the wind speed is constant - or varying very slowly...but in gusty or turbulent air, things get much more complicated - especially for sailplanes that have very flexible wings.

The art of flying gliders over long distances (and the world record is something like 1800 miles!) is in finding sources of naturally upwelling air such as:

Thermals created by some weather systems
The upwelling air over a large tarmac parking lot or a cornfield on a sunny day
Slope lift caused by wind blowing up a steep hillside

By spiralling around to stay within one of these upwelling airflows, you can gain altitude. Once you get high enough (or the air ceases to move upwards) - then you must push the nose of the glider downwards and trade the height that you've gained for more forward speed so that you can glide away towards the next thermal. By doing that expertly, you can (in principle) keep the glider in the air indefinitely - and fly against the wind. The trick is to find those upwelling airflows from tens of miles away with sufficient confidence to make it worth flying there to get another altitude boost. The ability to spot those things reliably is what make a great long-distance glider pilot - they do things like watching birds, cloud formations or dust whipped up by the wind - and just knowing where the thermals are likely to be. Having found one, staying inside the thermal is another tricky matter...especially because there is often down-moving air right next to the up-moving air! SteveBaker (talk) 15:09, 14 February 2013 (UTC)[reply]

Have you read Polar curve (aviation)? --catslash (talk) 22:39, 13 February 2013 (UTC)[reply]

If you want to increase your theoretical understanding, please start by reading our article on gliding flight. Looie496 (talk) 22:46, 13 February 2013 (UTC)[reply]

Could any engineer devise a toilet operation contingency plan for cruise-ships?

Seen this? http://www.cnn.com/2013/02/13/travel/cruise-ship-fire/index.html

Whenever I get on my first cruise ship, I would like to be reassured that the ship's sanitary systems have some kind of contingency plan so that if the main source of power fails, there will be some way to keep the toilets running anyhow; a fail-safe.

I wouldn't mind if the toilets even opened a "contingency valve" that releases the waste directly to the waters (but ONLY during such emergencies like the Carnival Triumph's) as that emergency would make the waste-release the lesser of our concerns.

But what is preventing that from happening? And what would it take to invent a contingency system that will keep a cruise ship's toilets working anyhow during this kind of emergency? How hard is it to invent, what would the cost be, how much extra $ would that be passed on to passengers in terms of ticket prices, and how many years off do you suppose such inventions are?

Remember that necessity is the mother of invention! There's very much a necessity for this happening lately! Thank you. --70.179.161.230 (talk) 19:28, 13 February 2013 (UTC)[reply]

Ships use vacuum toilets to keep pipe size and weight down and to assure operation when the ship is in motion. Buildings, which don't move, operate entirely by gravity, but need bigger pipes and more-or-less direct runs to a drain or sump, and aren't suitable for seagoing use on a large scale. I'm not sure what the pertinent maritime law is, but I doubt that it allows for an emergency sewage system on large vessels: they must operate under all circumstances. It seems to me that backup power is needed to assure that the vacuum system works: it apparently wasn't a priority in this case, or it failed or was damaged in the fire. Acroterion (talk) 19:33, 13 February 2013 (UTC)[reply]

The "pertinent maritime law" is the International Convention for the Prevention of Pollution From Ships (know as MARPOL 73/78), specifically its Annex IV - Sewage. Our article doesn't go into the details, but this IMO page does, and it states that untreated sewage may be regularly discharged overboard when the vessel is more than 12 nautical miles from the nearest land, and that properly treated (comminuted and disinfected) sewage may be discharged when more than 3 nautical miles from the nearest land, both while outside designated special areas. Here is the complete annex. Even this has the exception that the regulation does not apply to the discharge of sewage from a ship necessary for the purpose of securing the safety of a ship and those on board or saving life at sea, or resulting from damage to a ship or its equipment if all reasonable precautions have been taken before and after the occurrence of the damage, for the purpose of preventing or minimizing the discharge. -- ToE 07:25, 15 February 2013 (UTC) To the OP: Hello Manhattan, Kansas![reply]

Buckets, gunwale, lots of wet wipes... passengers might raise a ruckus, but it's simple, it works and it is cheap. And for a short term emergency solution it's good enough. WegianWarrior (talk) 20:24, 13 February 2013 (UTC)[reply]

The solution is to make sure you don't totally lose power - and that requires generators and fuel for those generators to be stored someplace OTHER than where the main generators and their fuel is stored. If it hadn't been the toilets backing up - or the food running out - or the A/C not working, there would have been something else. A ship like this simply can't function without adequate power...and a design that allows it to lose all power from a single point of failure (like a fire in the engine room) is a poor design. They needed to spend the money to keep a couple of days of reserve power and not on some complicated solution for zero-powered toilets. That sounds tough to do though. SteveBaker (talk) 20:54, 13 February 2013 (UTC)[reply]

They could have a supply of Porta-John™ folding portable toilets: "Ideal for special events, emergencies, disaster relief and military use".^[9] (They can be shipped/stored 12 per pallet)^[10] ~E:[edit]74.60.29.141 (talk) 22:21, 13 February 2013 (UTC)[reply]

This is about the sixth total power outage on such a cruise ship in recent years. The owners seem to register the ships in countries which do not require publishing the results of root-cause investigations, so it is hard to find out why having two separate engine rooms does not provide the expected redundancy when one diesel generator catches fire. Surely a fire in one engine room does not lead to spraying water or foam in both rooms. If it spreads to the 6600 volt switchboard and knocks it out, that might be an explanation. Redundant switchboard design (ring buses) at increased cost might be an option. Complete loss of propulsion in a storm or with the wind driving the ship towards the rocks might doom the 4000 aboard in some future failure. If i somehow get the money for a cruise, I'll go somewhere and stay in nice hotels instead. Edison (talk) 01:01, 14 February 2013 (UTC)[reply]

The usual procedure while fishing is to squat over an empty bait bucket and toss it over the side, or just aim over the side if you're equipped for that. Unless a bucket's unsuitable for Hyacinth?— Preceding unsigned comment added by Medeis (talk • contribs) 18:06, 13 February 2013 (UTC)[reply]

If Hyacinth was put in charge of the bucket brigade she would perform... her duty, spectacularly I am sure, although she will be repeatedly wishing she could be providing fancier chamber pots for the more "prestigious" guests. :-) --Modocc (talk) 01:12, 14 February 2013 (UTC)[reply]

They don't seem to have much of an emergency plan, do they ? I can think of many ways to improve things:

1) Bring ships alongside and connect cables to provide electricity.

2) Offload passengers onto other ships.

3) Deliver many Port-a-Potties.

4) During construction, they could have covered the sides and top of the ship with solar panels, which should hopefully be enough to operate the toilets during daylight, at least. When everything is working, they could also supply extra power. StuRat (talk) 00:51, 14 February 2013 (UTC)[reply]

There isn't really a "top" available to cover - that's the deck, and people walk on it. The sides would get hit with saltwater which would destroy the solar panel in short order. Ariel. (talk) 01:31, 14 February 2013 (UTC)[reply]

Put a clear lacquer over them, both to protect from salt-water and footsteps. The panels would need to be cleaned regularly, but they clean those areas anyway. StuRat (talk) 01:39, 14 February 2013 (UTC)[reply]

I wonder how much ~~tidal power~~ wave energy a cruise ship could extract from waves lapping up against it (without spending too much on the backup system that is). Wnt (talk) 01:35, 14 February 2013 (UTC)[reply]

Good point! --70.179.161.230 (talk) 06:01, 14 February 2013 (UTC)[reply]

It's a customer problem, not an engineering problem. Any reasonably competent electrical engineer can design a redundant power system that makes a ship-wide power outage about as likely as the ship being hit by a meteor. The customers have not demanded that, but they have demanded lower ticket prices, and so they are getting what they want. --Guy Macon (talk) 01:36, 14 February 2013 (UTC)[reply]

I wonder if the customers can sue for pain and suffering ? Then again, if they were sailing to a third-world nation, how wonderful to have a taste of life in the third world for themselves: no food, no light, no electricity, no running water, and sewage everywhere ! StuRat (talk) 01:43, 14 February 2013 (UTC)[reply]

Well, remember that the cruise ship also flies the flag of some third-world nation or the like, so suing them requires a long stay in that country. Plus the Athens Convention limits liability to $80,000. [11] Wnt (talk) 15:42, 14 February 2013 (UTC)[reply]

I'm not sure I'd call Bahamas a third-world nation, given their per-capita GDP, literacy rate, life expectancy, and such. And it's not an unpleasant place to stay at all. (And just $250 or so round-trip from Miami.) --jpgordon^{::==( o )} 21:54, 14 February 2013 (UTC)[reply]

I don't see it as a customer problem. You can't expect tourists & holidaymakers, most of whom are probably making a one-time trip, to understand anything about what it takes to run a ship properly. I don't know anything about that particular ship and what happened to it. But as a professional Engineer who has investigated incidents elsewhere, and performed maintenance audits, I can say that these sorts of problems are almost NEVER due to deficiencies in design. It is sufficiently easy, and quite the norm, in ships, hospitals, and other large projects where life must be protected, to design and build in redundancy in power generation and electrical distribution. And, if the operating Engineers and maintenance staff are left alone to do their jobs, mostly they will maintain that designed in redundancy, becaue hey understand its' importance. The problem arises with non-technical management at the top - business managers, promoted matrons, and the like in hospitals, captains and admin officers in ships, who came up from the business or navigation career path (or, in one case I know about, the captain was a complete fool who passed exams and got promoted up out of the ship's security team!) Upon learning that a) the ship/hospital/whatever has a dual power distribution, and b) one of the duals has failed, but the ship/hospital can still function with only one, they tell the engineers "don't fix it yet - the budget is tight / we need to leave port / whatever.) And then the one remaining system fails. Ratbone 121.221.231.100 (talk) 02:24, 14 February 2013 (UTC)[reply]

That assumes that the managers in charge of running the ship are willing to sacrifice redundancy for increased profit but the managers in charge of building the ship are not. Do you have a theory as to why this might be so? We can test your theory; somewhere there is information about whether that ship had no redundant generators on the other end of the ship that were not maintained or whether they weren't built in the first place. I am betting on the latter. Let's check to see what our Carnival Triumph page says. Port of registry: Bahamas. That wasn't decided by operations managers. Let's see what Google has: http://www.usatoday.com/story/cruiselog/2013/02/12/carnival-triumph-cruise-ship-fire-stranding/1914191/ "By law, they do have emergency back-up systems, but only enough to operate critical functions" So clearly they could have built-in enough capacity to run the toilets, and maybe the refrigerators in the kitchens. But it would have cost money to build that in, money for the fuel to lug around the extra weight, and money would be lost by having fewer cabins. So they didn't. --Guy Macon (talk) 05:03, 14 February 2013 (UTC)[reply]

Your newspaper article has a limitation in that it doesn't define what "critical function" is. It has been stated (the Wiki article has this) that an onboard emergency generator was operational, but some other fault or deficiency meant that it could not run the sewage system for half the ship. You make a good point on builder managers vs operator managers. My theory, based on experience, is this: Builder/construction managers employ professional engineers with appropriate professional (university) qualifications and professional body accreditation. It is a very brave manager who overrules a professional engineer on safety or reliability. For me personally, every time I dug my heals in on safety and reliability, the manager has backed off. They weren't happy but they backed off. And such engineers are very mobile - when the thing's finished they move on. In contrast, operational guys are more dependent on their manager for a job, they don't have the same professional qualifications and acreditation. So while they DO know their job, they are more easily dictated to. Safety Of Life At Sea (SOLAS - see Wiki article) requirements are detailed and very high. Regardless of where a ship is registered, it will have to meet requirements for registration and it WILL have to meet requirements at commisioning or it cannot be insured. But once at sea, slack and dumb crew leadership can let all manner of things go downhill. Ratbone 120.145.48.96 (talk) 06:32, 14 February 2013 (UTC)[reply]

We have a hotel chain in the US which takes slack maintenance to the extreme, Econo Lodge. A new Econo Lodge link is perfectly fine, but, as things break, they don't bother repairing them. This seems to be the plan from the start, because it's not designed to permit maintenance, such as having pipes and wires inside solid concrete walls. They just close off non-functional rooms until so many become non-functional that they can't make a profit any more, then they tear the whole mess down and start over. They appear to have perfected the concept of the disposable motel. StuRat (talk) 06:48, 14 February 2013 (UTC) [reply]

This looks off topic, besides it sounds like a "cash flow problem" to me, but please, quit these hijinks. Wnt (talk) 04:36, 15 February 2013 (UTC)[reply]

That's the approach I'm using with my current car. -- Jack of Oz ^[Talk] 07:53, 14 February 2013 (UTC) [reply]

Err, StuRat! Having pipes and wires inside solid concrete walls has been the normal way in most if not all countries for 70+ years. With pipes, you can pretty much always unblock them with plummer's "snakes", as inspection/access ports are required by plumming codes. The ones that can't be unblocked with snakes, well, the plumber just gets his electric jackhammer out - a few minutes and he's exposed and unblocked it, just neeed to trowel over some new concrete. With wiring, if it is installed per code, fuses and circuit breakers will prevent the actual wiring from failing. Whatever ideas the management have for constrction standards, any construction will still have to comply with legally enforced standards - in the USA the National Electrical Code (NEC) and whatever plumbing standards you have. It is quite normal for hotels at all levels of rating to close & seal rooms from time to time. Easy meaintenance is done by the hotel's own staff if any; with the more involved maintenance, except in season when bookings are high, it is more economic to acuumulate rooms with faults and then get a contractor in and do one big job and fix the lot, rather than have them come and go all the time. Is this another one of your joke posts or off the cuff nonsense posts? Wickwack 121.221.85.179 (talk) 08:22, 14 February 2013 (UTC)[reply]

Let's see some sources proving that solid concrete interior walls are the normal construction method in the US, where this chain is located. Also, you seem to be neglecting the accumulation of scale in the pipes, meaning they eventually need to be replaced. And using a jackhammer in a motel with occupants is definitely out. StuRat (talk) 16:48, 14 February 2013 (UTC) [reply]

Please give a source for your claim. I'm not going to join the stupid edit war, but your comment naming a specific business is not appropriate unless you can actually back it up with some sources. --Onorem ♠Dil 01:10, 16 February 2013 (UTC)[reply]

I doubt if they would admit this strategy publicly. I suggest you stay in an old one, and see what condition it's in (failing that, check out the numerous one star reviews here, especially the one with pictures: [12]). Our article does say that the power can be cut off to each room individually, though, which does support the idea of them planning to shut down a good portion of the rooms, at some point. StuRat (talk) 01:21, 16 February 2013 (UTC) [reply]

A simple 'no' would've been fine. Please redact. --Onorem ♠Dil 01:39, 16 February 2013 (UTC)[reply]

Did you even bother to look at those pics ? No sign of maintenance being done there. StuRat (talk) 01:42, 16 February 2013 (UTC) [reply]

That still just adds up to a big pile of OR and doesn't belong here. There is no sign of maintenance in those pics, therefore "We have a hotel chain in the US which takes slack maintenance to the extreme, (Redacted) is perfectly fine, but, as things break, they don't bother repairing them...." and the rest of your unsourced and inappropriate commentary. It doesn't belong here. Please source your comment or remove the name of the business. --Onorem ♠Dil 01:48, 16 February 2013 (UTC)[reply]

It's just typical StuRat nonsense. The odd complaint from a few guests who might have had a shitty on or some agenda means nothing. He's again claimed that the ability to cut power to individual rooms is evidence of some sort of intent. But it is normal practice to have cicuit breakers or isolating switches for each room or suite in a hotel. Ratbone 124.178.182.98 (talk) 02:52, 16 February 2013 (UTC) [reply]

If it was typical, our article wouldn't have mentioned it, now would they ? That would be like saying "This motel chain has windows in every room." StuRat (talk) 17:35, 16 February 2013 (UTC) [reply]

Yes, it would be like saying every room has a window. It is like saying every room has a window. As to why the article mentioned it, who knows? Wikipedia articles vary in standard - this one is definitely not one of the best - it contains many statements not supported by any reference. It also says that management reduced maid workload by having box beds so the maids don't have to clean under the beds. Multitudes of motels, the cheaper hotels, and church-run youth hostels have done that for a very long time. The YMCA, where I used to live and work at, has done that at least 70 years. Wickwack 60.230.238.152 (talk) 02:45, 17 February 2013 (UTC) [reply]

As long as we're off-topic anyway — the business model suggested by Stu strikes me as very unlikely to be cost-effective, but I haven't actually run the numbers, so who knows. Assuming arguendo that it were cost-effective, I'm not sure what would be so terrible about it from a customer perspective; if they close the bad rooms as they fail, then you don't get stuck in one, unless you're the unlucky first customer on that day (which can happen to you in any hotel). --Trovatore (talk) 23:06, 17 February 2013 (UTC) [reply]

Yes, as we are off topic:- As is typical with Stu, he's not entirely wrong. Stu is a pretty smart guy, but he just loves to post without checking - possibly to see what we do about it (ie trolling). It is actually common practice in hotels to close rooms with problems rather than fix them right away. Most of the year, most hotels can't get full occupancy. Where he is most likely wrong is in assuming this particular chain, which I am not familiar with, never fixes anything ever. What some hotels do is just let the number of rooms closed due to faults accumulate, and then, often enough to satisfy occupancy rate needs, get them all fixed in one go. When I was a young lad, I worked for and lived at a 14-storey low cost but very nice hotel owned by the YMCA - they did the same thing, getting all crook rooms fixed up just before tourist season, when they needed all the rooms. Consider getting a plumber out to fix one blocked toilet (common in hotels as some guests use far too much paper and/or put tissues in the loo). In my city, a typical plummer charge is $180 callout plus $55 per 15 minutes on site. Unblocking a toilet might take him 10 minutes, and he'll use the remaining 5 to write up the paperwork, so total change is $235. Now, say the hotel has called a plummer to unblock 20 toilets. At least 6 or so will have pretty much come good anyway if just left for a few days and the paper & poo dissolves, and only need 2 minutes. The charge will be $180 + (14 x 10 minutes + 6 x 2 minutes + 5 minutes) x $55/15 = $711.67. If each toilet was fixed one by one when it failed, the total would have been $4700. The other aspects Stu mentioned, having wiring and pipes buried in the concrete or brick walls, and being able to isolate electrical service to each room, is standard practice in hotels as Ratbone said, and box beds not at all unusual. Wickwack 120.145.59.43 (talk) 23:59, 17 February 2013 (UTC) [reply]

Even if they added one, I'm not sure their emergency toilet will have a bidet, so will you be satisfied? Nil Einne (talk) 07:15, 14 February 2013 (UTC)[reply]

February 14

String vibration close to resonance.

I have a long belt-driven machine - a software-controlled stepper motor drives a toothed pulley - there is an idler pulley several feet away and a loop of 1/4" toothed belt between them.

I want to determine the tension in the belt without resorting to expensive instruments, microphones...nothing.

I know that the resonant frequency of the belt is proportional to it's length and it's tension. The length is essentially fixed and known - so the tension is the only variable.

So the plan is to have the software step the motor rapidly back and forth at a frequency that sweeps gradually from less than twice the expected resonant frequency to more than twice - and have the operator watch to see when there is a null point at the center of the belt and hit a key on the keyboard...then the software can note the frequency that it's using at that instant, figure out the tension in the belt and display it for the operator.

The fundamental frequency at the design tension is around 50Hz and the motor is easily capable of hundreds of hertz motion.

Before I go off and write software, my question is whether the expected null point will be at a sharply defined frequency...what does this look like when we're close to the right frequency but not EXACTLY there? How precise could I expect the resulting effect to be?

(A "gut feel" answer is OK here...although math would be handy!)

TIA SteveBaker (talk) 03:53, 14 February 2013 (UTC)[reply]

Whack the belt with a big wooden mallet or paddle and see if you can make it ring. If it damps out in one or two cycles, your plan won't work. If it does, rig some sort of lever on the (unpowered) drive wheel and give it a whack to see if the system rings when the force is parallel to the belt instead of at right angles. Again, if it damps out in one or two cycles, your plan won't work. If you get a nice oscillation, loosen or tighten the belt by 5% and try again. That will give you a rough curve of resonant frequency vs. belt tension.

The longer it oscillates after a whack, the sharper the peak when you run your test.

If you trust your operator to hit a key at the right time, why not trust him to put a known weight on the belt and measure the deflection with a yardstick you have mounted in an appropriate position? --Guy Macon (talk) 05:17, 14 February 2013 (UTC)[reply]

The belt does vibrate quite a bit in normal use (it's driving the head of a laser cutter which is dancing around in all sorts of complicated ways) - when those vibrations get too big (because of resonance) and if the belt isn't tight enough, it can skip a tooth - which is "A Very Bad Thing" when you a hundred watts of laser energy bouncing off of a mirror that's now misaligned! So I know the belt can be vibrated by the motor and will resonate visibly.

Well, two of the three belts on this machine are mounted in such a way that you certainly can use a weight hung off of them to get a measurement of tension. In fact, my current advice to users is: "Take a 12oz can of soda and hang it from the belt by the ring-pull using a paper-clip. If the belt deflects by more than 2cm, then it's not tight enough"! But the belt that I'm more concerned about is mounted with the pulleys laid horizontally over a flat plate - so hanging anything off of it is impossible without resorting to more complicated mechanical contrivances. Whacking parts of the system for any reason whatever is strongly discouraged! Sure, there are all sorts of mechanical arrangements that might be used (someone else is using a guitar tuner - and another person is recording audio from the sound of the belt being twanged and analysing the recording using Audacity!) - but why do that if I can do it using only software and someones' eyes? At any rate, I want to know whether my approach will work - not whether there are other techniques that might work instead. SteveBaker (talk) 14:35, 14 February 2013 (UTC)[reply]

This field of study is called vibrations analysis. StuRat (talk) 07:22, 14 February 2013 (UTC)[reply]

Yes, I know - but there is nothing there that tells me what happens when we're close to hitting the resonant frequency. I don't imagine (for example) that I have to vibrate my 50Hz-resonance system at precisely 100.000000000 Hz to get that visible stationary point on the belt - I'm reasonably sure that I'd see it at 100.000000001 Hz also. So how wide is that margin? Is there a way to know how stationary the mid point of the belt will be when I vibrate it at 99Hz and 101Hz? This would give me some idea as to the precision I might expect to get from this test without having to go to the hassle of writing the software and actually doing it.

As I said, a "gut feel" answer is good enough here!

SteveBaker (talk) 14:35, 14 February 2013 (UTC)[reply]

I have absolutely no understanding of this (I don't understand why the speed of the motor affects resonance) but note that the article resonance does give the math for a "universal resonance curve" which is broader depending on how much damping is present. Wnt (talk) 15:36, 14 February 2013 (UTC)[reply]

The stepper motor causes resonance because it doesn't produce a continuous smooth motion - it's (more or less) a series of abrupt 'steps', controlled by computer software - the frequency of those steps can be anywhere between zero and a few thousand kilohertz - and at some movement speeds, it causes the belt to resonate enough to cause problems if the belt isn't tight enough. If the belt is too tight, it can cause premature wear on the motor bearings - so it's desirable to get the tension just right. SteveBaker (talk) 17:10, 14 February 2013 (UTC)[reply]

Hmmm - OK - so it looks like this "Q-factor" thing is what I need to consider. That's basically the ratio of the resonant frequency to the frequency range over which the belt will resonate. If the Q-factor is large, then the resonance will be over a smaller frequency range. Now all I need is an estimate of the Q-factor for my belt... SteveBaker (talk) 17:31, 14 February 2013 (UTC)[reply]

Consider using a strobe light set to the same frequency as the motor. Use the technique you described to find the resonance and then fine tune your measurement by turning the strobe light on and slowly varying the motor frequency. It becomes much easier to identify the exact spot of maximum resonance that way. Dauto (talk) 00:46, 15 February 2013 (UTC)[reply]

Again, I'm aware that there are other ways to do this - but I particularly want one that doesn't require any additional hardware whatever...so no strobe light. SteveBaker (talk) 18:17, 15 February 2013 (UTC)[reply]

Would it be possible move the idler or add an extra one nearer to the pulley that is having the problem? It seems like that would both limit the magnitude of the vibration and raise the resonant frequency, hopefully preventing the belt from slipping a tooth as easily. 38.111.64.107 (talk) 13:44, 15 February 2013 (UTC)[reply]

Well, some kind of gizmo of that nature might work - but adjusting the belt tension correctly is something we want people to do for other reasons. As I said, this is a laser cutter - and a sloppy belt results in hysteresis effects and other nastiness - while an over-tight one wears out bearings prematurely. So getting the thing properly adjusted is important - aside from the vibration issues. SteveBaker (talk) 18:17, 15 February 2013 (UTC)[reply]

Or you could just install a Tensioner. --Guy Macon (talk) 22:19, 15 February 2013 (UTC)[reply]

Egg whites and avidin

Egg whites contain avidin, a protein that binds biotin in the intestine and prevents it from being absorbed. According to Biotin_deficiency#Confirmed_causes, eating raw egg whites can cause biotin deficiency. My question is why is it raw egg white that cause biotin deficiency, what happens to avidin when egg white is heated (boiled or poached)? --PlanetEditor (talk) 06:20, 14 February 2013 (UTC)[reply]

It is denatured. Looie496 (talk) 07:09, 14 February 2013 (UTC)[reply]

One more question. If avidin, being a protein, loses its effectiveness by denaturation, does other protein (albumin for example) also lose its effectiveness due to denaturation? If this is the case, how do we get nutritionally useful protein from cooked food? --PlanetEditor (talk) 08:45, 14 February 2013 (UTC)[reply]

Even if it's called "nutritional protein", that name is a bit missleading. The proteins that you eat can only be taken up when they are split into their constituent amino acids (see, for example, Nutrition). So, all proteins that you digest are eventually disassembled into their building blocks, which are then taken up by your body to reassemble them into new proteins of your body. Cooked and uncooked can make a difference in this process, as the accessibility of the protein to your digestion can change (better or worse) according to its structure. --TheMaster17 (talk) 10:43, 14 February 2013 (UTC)[reply]

So what are you saying, denatured protein gives the same nutritional value as they provide the same amino acids? --PlanetEditor (talk) 11:16, 14 February 2013 (UTC)[reply]

Yes, as far as I know (I have never heard otherwise, and I studied digestive physiology during my undergraduate degree), I can't think of any good reason why not. I would imagine that most proteins (but not all) would be denatured by the acid environment of the stomach in any case, and most cooked foods have most of their protein denatured to some degree. Equisetum (talk | contributions) 11:29, 14 February 2013 (UTC)[reply]

According to this, denaturation of protein results in higher rate of protein absorption. Does it mean cooking increases bioavailability of protein? --PlanetEditor (talk) 12:33, 14 February 2013 (UTC)[reply]

This was something that mystified me long ago - thanks for reminding me. Why is it that egg white is not denatured in the intestine to release the biotin? Well, it turns out that (as suggested by a remarkably non-scientific source [13]) egg whites also contain a variety of trypsin inhibitors [14] (humans aren't even vulnerable to the one present at the highest level) and therefore of a raw egg white only 50% is digested. [15] So the egg seems to be making a fairly well-coordinated effort to kill habitual egg-eaters this way, which cooks circumvent. Wnt (talk) 15:29, 14 February 2013 (UTC)[reply]

Just a small Question?

It is said that both earth and the Newton's apple accelerate toward each other gravitationally but apple looks a lot to the earth due to its greater acceleration as compared to the earth toward apple which is so minuscule to be distinguished but would aforementioned apple and earth accelerate toward each other gravitationally if an apple is tossed/ accelerated in the absence of air with a force a-tad greater than gravitational, if yes then how?

Since, according to Newton's third law of motion, both earth and the Newton's apple accelerated AWAY from each other but apple would look a lot AWAY from earth due to its greater acceleration as compared to the earth AWAY from apple which is so tiny to be noticed, nonetheless, they both would experience gravitational force but lesser than the force with which apple was tossed at all-time and also gravity feebler at a distance.50.99.56.103 (talk) 07:18, 14 February 2013 (UTC)Eclectic Eccentric Khattak No.1[reply]

I can't understand your question. For example, what does "apple would look a lot AWAY from earth" mean ? The word "look" seems completely out of place. Also, use shorter sentences. If you are asking if the apple and Earth would fall towards each other more quickly in the absence of air, then the apple would, yes, but there would be no measurable difference in the Earth. StuRat (talk) 07:36, 14 February 2013 (UTC)[reply]

I struggle to understand exactly what is being asked, too. By Newton's Third Law, the throwing force that accelerates the apple upwards will be balanced by an equal and opposite downwards force on the earth, and this will give the earth a minuscule speed away from the apple. Air resistance will exert equal and opposite forces on both apple and earth, but this becomes significant only at higher speeds. Gravity is the main force (again equal and opposite) that brings the apple back to earth, and the earth back into its previous orbit. It would have to be an impossibly heavy apple to have a measurable effect on the earth. Dbfirs 08:03, 14 February 2013 (UTC)[reply]

The apple does not accelerate away from the Earth if it's tossed upwards. It moves away, but it immediately starts to slow down, which is effectively the same as accelerating toward the Earth. Rojomoke (talk) 13:45, 14 February 2013 (UTC)[reply]

Yes, I should have made that point more clearly. Once the apple leaves the hand (or whatever projected it upwards), gravity is the subsequent accelerating force back towards the earth, with air resistance helping gravity on the way up, but opposing gravity on the way down. (During the fraction of a second during which the apple is "being thrown" upwards, the apple experiences a large upwards acceleration, but this ceases once the apple leaves the hand. If the thrower was standing on a weighing scale, there would be an increase in the reading during the short "throwing" time.) Dbfirs 14:36, 14 February 2013 (UTC)[reply]

A mini rocket is attached to aforesaid apple which is responsible for the upward accealaration of an apple. The produced accelaration of an apple is always slightly greater than "g" of earth. — Preceding unsigned comment added by 162.139.255.35 (talk) 06:48, 16 February 2013 (UTC)[reply]

If your mini-rocket has unlimited fuel so that it can continue to provide an acceleration slightly greater than "g" away from the earth, then the speed of the apple will always increase and it will soon leave the earth's atmosphere, never to return. Dbfirs 13:10, 16 February 2013 (UTC)[reply]

What kind of monkey is this?

monkey! – Kerαunoςcopia^◁_galaxies 07:22, 14 February 2013 (UTC)[reply]

It looks like a Goeldi's marmoset (also known as Goeldi's monkey) (Callimico goeldii) to me. --Guy Macon (talk) 11:51, 14 February 2013 (UTC)[reply]

Our article: Goeldi's marmoset. -- ToE 06:50, 15 February 2013 (UTC)[reply]

I added it there :) – Kerαunoςcopia^◁_galaxies 01:28, 16 February 2013 (UTC)[reply]

Beautiful, thank you so much, Guy. – Kerαunoςcopia^◁_galaxies 20:05, 14 February 2013 (UTC)[reply]

Wow, cute monkey! --PlanetEditor (talk) 07:01, 15 February 2013 (UTC)[reply]

Why, thank you! I have always thought of myself as... Oh. Wait. You were talking about the Goeldi's marmoset, weren't you? --Guy Macon (talk) 00:47, 16 February 2013 (UTC)[reply]

looking for a closeup of an anglerfish lure

Hi - it's a reference for a drawing - there are plenty of anglerfish pics on the web, but none that I can find featuring the lure in hideous detail. Can anyone help please?

Thanks Adambrowne666 (talk) 10:51, 14 February 2013 (UTC)[reply]

This is specifically about lure. This image also shows the lure. --PlanetEditor (talk) 12:05, 14 February 2013 (UTC)[reply]

Perfect, thank you, Planet! Adambrowne666 (talk) 13:39, 14 February 2013 (UTC)[reply]

Wow. I had no idea they came in so many shapes. --jpgordon^{::==( o )} 21:38, 14 February 2013 (UTC)[reply]

In reality, they probably come in a much vaster variety, given that, as with most deep-sea fauna, we've likely seen only the barest fraction of angler species. And shape is only one inconstant element; there's considerable variation in the bioluminescent properties as well. Looking foreward, I wouldn't be surprised if some species are found who employ the appendage in uses quite aside from a lure, such as social/mating interactions or misdirection/defense (if indeed such haven't been documented already). Snow (talk) 04:57, 15 February 2013 (UTC)[reply]

world-wide wind speed average and standard deviation

Hi, What is the average wind-speed (over the course of a year) world-wide, and what is its standard deviation? (With this information I could calculate that for a given wind speed, say, 253.5 mph whether it is within one, two, three, four, five, etc, standard deviations of worldwide average). If you have it I would like to look at a graph of the distribution as well, to see how closely it resembles a bell curve - but this might be too much to ask! My own research has consisted of the following searches:

https://www.google.com/search?q=average+worldwide+wind+speed

https://www.google.com/search?q=what+is+the+average+wind+speed+worldwide

https://www.google.com/search?q=average+wind+speed+over+a+year

https://www.google.com/search?q=wind+speed+standard+deviation

https://www.google.com/search?q=worldwide+wind+speed

I tried to look at the top twenty links on each of the above, but saw standard deviations only for specific regions or streams - not for worldwide wind speed. Does anyone know more or have references, or maybe can see something I missed? Thanks. 91.120.48.242 (talk) 10:57, 14 February 2013 (UTC)[reply]

253.5 mph ? That's like the wind speed within an F5 tornado. StuRat (talk) 16:40, 14 February 2013 (UTC)[reply]

Just for reference as to how fast that really is, the highest ever surface wind speed (i.e. at the ground) directly measured was 231 mph in 1934 at Mount Washington, New Hampshire, and was a straight-line wind, not a tornado. There have been wind speeds measured via doppler radar in tornadoes which get up to around 300 mph, but to be a verified record there needs to be a physical anemometer reading at ground level, and this was a doppler measurement from a distance, and was aloft and not at ground level. --Jayron32 23:21, 14 February 2013 (UTC)[reply]

Both the mean and the standard deviation will depend upon what measurements you choose to include. Wind speeds on the tops of mountains are often much higher than those nearer sea level, but less frequently measured. Most quoted figures are probably averages of the measurements taken at weather stations, with an uneven area distribution. Do you require an average and standard deviation over world land area, or do you include wind-speed at sea? The answers are going to be very different, and I don't think you are likely to get one reliable figure, just some estimates. Dbfirs 09:04, 15 February 2013 (UTC)[reply]

Hi (OP), estimates are fine. Actually I would like to know the mean and standard deviation of every wind-speed (with respect to ground) at every altitude throughout the whole world, over the course of a year. Very rough estimates are fine. So, it sound slike, for example, 231 mph might be 6-10 standard deviations from the average? BUt this is a wild guess on my part. Do you guys have any guesses at all for the standard deviation of the average windspeed as I just described it? You don't have to take "every altitude" quite literally, just the air space in use. I am trying to come up with theoretical calculations only, so don't read too much (anything) into the question, I would just like to have an idea of the variance of windspeed worldwide, with respect to ground, so I can further my understanding on my own. if you can't find references either, do you have some kind of crude guess? Thanks. 178.48.114.143 (talk) 09:10, 15 February 2013 (UTC)[reply]

I could make only the same estimates that you would make from the data you have found, though someone else might find some better data. One concern over standard deviation figures is that the distribution of wind speeds will not be a Normal distribution because there are large areas of the earth (such as the Intertropical Convergence Zone where the wind speed is often close to zero, so the distribution will be very skewed (see Skewness). I wonder if a Half-normal distribution would be appropriate? Dbfirs 13:29, 15 February 2013 (UTC)[reply]

Autosomal Chromosomes =

22 pairs, that's understandable. but, are the X's of the 23's pair (XX/XY), are they also autosomal? — Preceding unsigned comment added by 79.179.134.180 (talk) 16:38, 14 February 2013 (UTC)[reply]

No - see autosome. Sex chromosomes are called allosomes. Gandalf61 (talk) 16:42, 14 February 2013 (UTC)[reply]

See pseudoautosomal region, which is shared by X and Y. But even that is, well, "pseudo" autosomal, because of the way the definitions are set. Wnt (talk) 04:33, 15 February 2013 (UTC)[reply]

February 15

Lists of textbooks

The MAA has "a list of books recommended by the Association for purchase by college and university libraries". Where are the lists for topics other than math? I know many universities have lists of their course books online, but those aren't that comprehensive. --83.84.137.22 (talk) 00:43, 15 February 2013 (UTC)[reply]

Perthes disease

perthis diseases — Preceding unsigned comment added by 115.249.81.251 (talk) 01:41, 15 February 2013 (UTC)[reply]

See Perthes disease. Ariel. (talk) 02:09, 15 February 2013 (UTC)[reply]

Research access to data in the New England Journal of Medicine

I am not familiar with the usages that prevail in medical journals. When an article published in the New England Journal of Medicine reports conclusions of a statistical analysis of data, without explicitly giving the data itself, does the journal provide access, via the web or otherwise, to the actual data? Michael Hardy (talk) 12:10, 15 February 2013 (UTC)[reply]

Different journals have different standards and requirements. Within a particular journal, the specific requirements may depend on the type of data and type of analysis. NEJM makes specific demands for accessibility to raw clinical trial data and raw microarray data: NEJM manuscript submission requirements. Many medical journals, NEJM included, follow the ICMJE's Uniform Requirements for Manuscripts Submitted to Biomedical Journals. TenOfAllTrades(talk) 13:47, 15 February 2013 (UTC)[reply]

Interesting, but it only applies to studies with human subjects and to microarray data, and not necessarily to public health data, which is closer to what I'm looking for. Michael Hardy (talk) 02:02, 16 February 2013 (UTC)[reply]

Depending on the nature of the data that you're looking for, and the degree of 'raw'-ness, there may be issues with converting the data into a properly anonymized form that would be suitable for release (and permitted by ethics committee of the institution or organization that generated the data in the first place). TenOfAllTrades(talk) 15:55, 16 February 2013 (UTC)[reply]

It would be impossible for a journal to provide raw data -- the variability in formats would be impossible to handle in a reasonable way. Even if the journal requires the data to be available, you would have to contact the corresponding author of the paper to get it. Looie496 (talk) 22:04, 15 February 2013 (UTC)[reply]

Fluorine Swallowing

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.

TenOfAllTrades(talk) 13:29, 15 February 2013 (UTC)[reply]

Air pressure

Hi,
I would like to know why in different heights only the ears feel the pressure, and not some other organs.
Exx8 (talk) 12:19, 15 February 2013 (UTC)[reply]

The thin tympanic membrane bulges inward or outward. The eustacian tube is supposed to equalize pressure, but is easily blocked. The nerves in the area are quite sensitive, in order to protect the ear from damage (if you do something which would cause a hearing loss, you feel pain and hopefully stop). Most of the other organs aren't as sensitive to pressure, but the eyes might be the next most sensitive. However, people with rheumatism often report their pain varies with atmospheric pressure. StuRat (talk) 13:07, 15 February 2013 (UTC)[reply]

The bends can cause pain and injury elsewhere, but the pressure change involved is much greater. Ears are designed to sense pressure changes (sound), even vibrations on the scale of a single atomic diameter. Wnt (talk) 16:32, 15 February 2013 (UTC)[reply]

The difference between Fjord and Gulf?

Hi,
I would like to know what is the difference between a Fjord and a Gulf? Exx8 (talk) 12:23, 15 February 2013 (UTC)[reply]

A fjord is an inlet carved by a glacier. A gulf is just a general term for a large inlet. Dauto (talk) 14:32, 15 February 2013 (UTC)[reply]

To quote our own article, a fjord is "a long, narrow inlet with steep sides or cliffs, created in a valley carved by glacial activity". It isn't just any small inlet. Gulfs are arms or bays of oceans or seas. In fact the Gulf of Mexico is larger than most seas. (Aside, why can't I find a list of water bodies by size on Wikipedia?) Rmhermen (talk) 18:45, 15 February 2013 (UTC)[reply]

Wnt please go away from my sections. You are right buy you annoy me.I had a mistake okay, English IS NOT my mother tongue such as modesty is not your main attribute. Thanks for the rest who resisted their desire of making fun of spelling mistakes and for answering my answer.Exx8 (talk) 21:03, 15 February 2013 (UTC)[reply]

Hey man, don't let it get to you. Humor is a good thing. I though the jokes were OK. What's not OK is for you (or whoever did it) to erase other people's posts (even if they were just jokes.) Dauto (talk) 21:56, 15 February 2013 (UTC)[reply]

Here's a link to the deleted posts since none of this makes any sense otherwise: diff. μηδείς (talk) 02:41, 16 February 2013 (UTC)[reply]

It sounds like Exx8 got my statement backwards here - I was not making fun of him and indeed do not even regard saying "a Golf" as a mistake when you are speaking of a map of Sweden. Wnt (talk) 21:23, 16 February 2013 (UTC)[reply]

Note that the tern "fjord" is a technical term used by geographers, but in general speech specifically refers to these features in Scandinavia. In Scotland, they are generally called "sea lochs", an example is Loch Goil, and in the rest of the English speaking world (someone will correct me if I'm wrong about this) "inlet" is used, an example is Burrard Inlet in Canada. However, because these are general terms, they are sometimes applied to features that are not technically fjords. Alansplodge (talk) 11:42, 16 February 2013 (UTC)[reply]

The region of New Zealand where the inlets are very similar in both look and geology to those of Norway is "correctly" called Fiordland. However, the fjords themselves have names containing the word sound, e.g. Milford Sound./Coffeeshivers (talk) 15:12, 17 February 2013 (UTC)[reply]

The role of splitter plates in jet engine inlet geometry

I started the article Splitter plate (aircraft) thinking I knew I how they worked, otherwise I wouldn't have started the article, but looking for citations on the net has led me to doubt my understanding of the topic. I had thought that what the splitter plate did in supersonic flight was that in breaking up the boundary layer air, it tipped turbulent air into the stream of air entering the intakes creating an air dam that slowed the ingested air sufficiently that a simple pitot intake, without the need for intake ramps or inlet cones, was sufficient to insure air entering the engine was within its operational range. Am I very mistaken? One source I found stated that the purpose of the splitter plates was to prevent slow boundary layer air entering the intakes since the engine would work at their most efficient by maximising the intake of fast travellin free air. I know that these things are compromises and trade offs, are different effects at play at different speeds/altitudes --KTo288 (talk) 14:42, 15 February 2013 (UTC)[reply]

I don't fly jets, so I'm not very familiar with supersonic technology; but fast piston-powered aircraft use cowl flaps to control airflow for cooling and air-intake, at the expense of extra drag. Complex aircraft can open and close the cowl flaps as needed. Nimur (talk) 15:33, 15 February 2013 (UTC)[reply]

I don't design or fly jets either. I did carry out a quick Google search, however, using the term "boundary air control above mach 1" which resulted in this: Hughes, Donald L; Holztman, Jon K; Johnson, Harold J (1972). "Flight-Determined Characteristics of an Air Intake System of an F-111A Airplane" (PDF). Technical Note. D–6679. NASA. Retrieved 15 February 2013. It may be of help --Senra (talk) 19:55, 15 February 2013 (UTC)[reply]
Also Hünecke, Klaus (1997). Jet Engines. England: Airlife. pp. 76–79. ISBN 1853108340. ... the thickening of the boundary layer that develops at high angles-of-attack along the lower side of the fuselage forebody [in the F-16]. In order to prevent low-energy flow from entering the engine, the intake had to be offset from the fuselage to free it from the boundary layer, which uninterruptedly passes along the fuselage. The intake cowl [of the F-16] features a moderately blunt lower lip that transitions into a sharp leading-edge extension or splitter plate on the upper side (close to the fuselage). {{cite book}}: |access-date= requires |url= (help); Check date values in: |accessdate= (help) My bold-italic emphasis --Senra (talk) 20:32, 15 February 2013 (UTC)[reply]

Perhaps this will help: Diverterless supersonic inlet talks about diverting the boundary layer with some sexy grooves and bumps, and the photo in that article contrasts it with the F16's conventional intake. More explicitly, that article cites as a reference this Lockheed Martin article, which talks about different ways of dealing with boundary layer effects in supersonic jet intakes. That seems to be differentiating between a "diverter" and a "splitter plate". This says "Splitter plate not required with proper diverter design". So I'm not sure that what Splitter plate (aircraft) is talking about isn't really a diverter, of which a splitter plate is an optional element (rather than a synonym). But anyway, all of that differs from your "breaking up the boundary layer" idea, but rather at preventing the boundary layer air from entering the intake at all. -- Finlay McWalterჷTalk 21:27, 15 February 2013 (UTC)[reply]

Entropy

Is the following the correct equation to use to find the entropy generation when iron is quenched?

S(water)= mclnT/T S(iron) = mclnT/T Total S generated = S(water) + S(Iron)

Thanks Clover345 (talk) 17:59, 15 February 2013 (UTC)[reply]

Entropy production

I know that dS=(Q/T)out - (Q/T)in + S(produced in the system). But how do you find dS so that you can find S(produced in system). For some reason my calculation works if I set dS to 0 but I don't know why. My system is a building wall and I calculated the entropy generated by it given the temps outside and inside, it's conductivity & convection heat transfer coefficients from wall to environment and wall to inside. Why is dS 0? Clover345 (talk) 19:04, 15 February 2013 (UTC)[reply]

Because no entropy is produced in the wall except for one related to heat transfer through the wall. Ruslik_Zero 19:21, 15 February 2013 (UTC)[reply]

isn't that contradictory? If entropy is produced by heat transfer through the wall, shouldn't dS be over 0? Clover345 (talk) 19:47, 15 February 2013 (UTC)[reply]

\Delta S=0

for the wall over any period during which the temperatures on the two sides are (taken to be) constant, because entropy is a state function and the wall's state is constant. The entropy changes from the heat transfer occur on the two sides: a negative change on the warm side and a (larger) positive side on the cold side. --Tardis (talk) 03:58, 16 February 2013 (UTC)[reply]

thanks but this confuses me. If dS=0, why is the entropy produced by the wall higher than 0. Clover345 (talk) 19:43, 16 February 2013 (UTC)[reply]

The entropy produced "by" the wall (that is, because the wall isn't a perfect insulator and heat is flowing through it) can be non-zero even though the entropy produced in the wall (that is, because of any change in the wall's state) is zero.

We can associate with any heat flux an entropy flux:

{\vec {s}}:={\frac {1}{T}}{\vec {q}}

(recall that we usually do not define division (as in

\Delta S={\frac {Q}{T}}

) for vectors), and in direct analogy to the first law, we may write

{\frac {\partial \rho _{S}}{\partial t}}=\rho _{\dot {S}}-{\vec {\nabla }}\cdot {\vec {s}}

(the change of entropy density is equal to the entropy (density) generation rate minus the divergence of the entropy flux). (The difference between the first and second laws is that

\rho _{\dot {Q}}

must be balanced by some change in the internal energy of the system, whereas

\rho _{\dot {S}}\geq 0

but is otherwise unrestricted.) For every point in the wall,

{\frac {\partial \rho _{S}}{\partial t}}=0

, so

\rho _{\dot {S}}={\vec {\nabla }}\cdot {\vec {s}}

. The only kind of process occurring is heat flow (no chemistry, work, compression, etc.), so this entropy production is entirely due to the heat flow.

Assuming a linear temperature profile in (say) x, as for a wall of uniform material and small temperature changes, this rate is

{\frac {\partial s_{x}}{\partial x}}={\frac {d}{dx}}{\frac {q}{T}}=q{\frac {-1}{T^{2}}}{\frac {dT}{dx}}={\frac {k}{T^{2}}}\left({\frac {dT}{dx}}\right)^{2}

(the thermal conductivity times the square of the logarithmic derivative of temperature over space). Letting the wall extend from 0 (where the temperature is

T_{1}

) to X (where the temperature is

T_{2}

), this is

{\frac {k}{(T_{1}/m+x)^{2}}}

, where

m={\frac {T_{2}-T_{1}}{X}}

is the thermal gradient. So the entropy is produced throughout the wall, most intensely at the colder side (

x=0

for

m>0

), but it is all emitted at that side and none is retained in the wall. (I won't claim to have proven this point, since I derived

\rho _{\dot {S}}

from the statement that

{\frac {\partial \rho _{S}}{\partial t}}=0

, but I hope that it's easier to accept given this context and explanation.) --Tardis (talk) 19:25, 17 February 2013 (UTC)[reply]

February 16

One Kidney Giving Out

If one of someone's kidneys gives out but the person's other kidney is still working, would the person need to remove the failed kidney from his body in order to continue to survive or how would that work? Also, one kidney can fail while another would continue to function properly, correct? Thank you very much and sorry if this is a stupid question. Futurist110 (talk) 00:11, 16 February 2013 (UTC)[reply]

It all depends on why one kidney failed; if it's cancer, then it should be removed (or irradiated or otherwise dealt with). If not, it may just atrophy without causing any further problems. And yes, one kidney can continue to function alone, although a diet and habits that take it easy on the remaining kidney would be a good idea. StuRat (talk) 00:30, 16 February 2013 (UTC)[reply]

StuRat's answer is, unfortunately, a typical StuRat off-the-cuff answer. He's right of course about a cancerous kidney - as cancer can spread. However, as with muscles and most other things in the body, kidneys grow to a size able to take the load. If you lose one kidney, the other one increases in size and there is more or less no permanent impact. There is no need for a special diet or habits. See http://www.kidney.org/atoz/content/onekidney.cfm. The main impact is that a urinary tract infection that impacts on the kidney will have a more serious impact, but such infections are fairly rare, especially in men. Sulpha antibiotics, which tend to cause scaring in the urinary tract, have a higher impact in people with only one kidney. No doubt StuRat will come back, he usually does, with some abuse and/or some website that almost but not quite supports that a special diet is indicated. Wickwack 58.164.228.62 (talk) 03:48, 16 February 2013 (UTC)[reply]

Yea, like this source: "You simply need to make healthy choices, including fruits, vegetables, grains, and low-fat dairy foods. Limit your daily salt (sodium) intake to 2,000 milligrams or less if you already have high blood pressure. Reading nutrition labels on packaged foods to learn how much sodium is in one serving and keeping a sodium diary can help. Limit alcohol and caffeine intake as well. Avoid high-protein diets. Protein breaks down into the waste materials that the kidneys must remove, so excessive protein puts an extra burden on the kidneys. Eating moderate amounts of protein is still important for proper nutrition. A dietitian can help you find the right amount of protein in your diet." [16]. Now for your abuse: You're the one who doesn't know what he's talking about, as usual. StuRat (talk) 04:18, 16 February 2013 (UTC)[reply]

You left out the first sentence in that section (Eating sensibly): "Having a single kidney does not mean you have to follow a special diet". And you didn't mention that the 2 grams of salt and the rest of it is just about standard advice given to every one these days, regardless of number of kidneys. Wickwack 124.182.162.210 (talk) 05:00, 16 February 2013 (UTC)[reply]

The moderating protein intake isn't a normal recommendation. Also, I didn't say a special diet was required, that was you. I just said "a diet and habits that take it easy on the remaining kidney would be a good idea". This is using "diet" to mean "what you eat", not "a crash weight loss plan" or any other meaning. StuRat (talk) 05:45, 16 February 2013 (UTC)[reply]

Consuming an excessive fraction of protein is not a particularly good idea for anyone, two kidneys or not, and is standard advice ever since the Swedish Govt devised the well-known "food pyramid" in 1974 (which advises protein consumption between 10 and 15% measured by calorific content), and was inherent dietry advice for the general population well before 1974 - I remember being taught at school 60 years ago to eat from a balance of 5 food groups (Most govts now advise on the basis of 7 groups). The essense of the advice from the various websites provided here by myself, yourself, and others can be summed up as follows: No special diet is needed, however a bad diet may carry greater risk for a person with only one kidney. If that's what you meant, why didn't you say so? You said "a diet and habits that take it easy on the the remaining kidney would be a good idea." Which means a special diet. Why didn't you say no special diet needed? Because you posted off-the-cuff without thinking or checking, as usual. Wickwack 121.221.31.66 (talk) 09:48, 17 February 2013 (UTC)[reply]

As our article Kidney transplantation says, when someone receives a new kidney his or her own kidneys are not removed. There seems to be no drawback to keeping the non-functional kidneys, and an increased risk by removing them. Also, as I understand it, sometimes their own kidneys still have some function and you want to keep that if possible. Sjö (talk) 08:21, 16 February 2013 (UTC)[reply]

Information about High protein, high fat, low carbohydrate (Atkins) diets and normal (dual) kidneys:

http://abcnews.go.com/blogs/health/2012/06/01/high-protein-low-carb-diet-safe-for-kidneys/

http://news.yahoo.com/atkins-type-diets-look-kidney-friendly-study-210610591.html

http://health.usnews.com/health-news/news/articles/2012/05/31/atkins-type-diets-look-kidney-friendly-study

We know that some sorts of kidney disease require a low protein diet, so the person with one kidney should ask his/her physician if whatever was wrong with the first one is also wrong with the second one.

We also know that obesity is bad for your kidneys, so if the diet helps you to lose weight that is a plus.

I cannot find any studies on high-protein diets and single kidneys. Some doctors advise avoiding a high-protein diets with a single kidney, but the question is whether this is backed up by studies or just being cautious. --Guy Macon (talk) 09:00, 16 February 2013 (UTC)[reply]

This is all pure OR. My father received a kick to one of his kidneys while playing rugby, which resulted in him missing 18 months schooling and the kidney itself failing completely. That was not known until 40 years later, when he was hospitalised for severe hypertension. His kidney function was assessed as 20% in the one remaining functional kidney. He didn't need any special diet, he was advised to moderate his salt intake (which he ignored) and was put on medication which he took for the remaining 30 years of his life. So the answer to the OP's questions are no, you don't need to have a non-functional kidney removed: in fact, you can live for many years without even knowing you have a non-functional kidney. I'll have a trawl of a website to confirm with references for you. --TammyMoet (talk) 13:17, 16 February 2013 (UTC) Here's a webpage that answers your questions. --TammyMoet (talk) 13:22, 16 February 2013 (UTC)[reply]

What do these terms mean?

On the Doctor Who Restoration Team website, there are repeated references to "tramline damage", "off-lock"s, and "phosphor hole"s. What do these terms mean? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 00:20, 16 February 2013 (UTC)[reply]

Tramline damage is simply long scrapes down the film or tape caused by something scratching the tape is it moves past. [17]
Video tape, and analog video signals in general, contains synchronisation information about the end of a line and the end of the whole screen (it's much more complicated than that, but that's the idea). A player uses that information to keep its own clock in line with the tape. If the tape is damaged or degraded, that synchronisation information can be corrupted. This causes the player to lose an accurate idea of where the video has got to; it has lost "lock". When this happens the picture rolls up or down or breaks up entirely. See Analog television#Synchronization
This posting (the bottom one) explains a phosphor hole.

-- Finlay McWalterჷTalk 01:04, 16 February 2013 (UTC)[reply]

So when it loses lock, the player simply scribbles lines across the screen in all the wrong places? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 02:28, 16 February 2013 (UTC)[reply]

Assuming you are familiar with that site, are they bringing back any lost episodes, or just restoring known ones? μηδείς (talk) 02:37, 16 February 2013 (UTC)[reply]

See Doctor Who missing episodes and Doctor Who Restoration Team. -- Finlay McWalterჷTalk 02:48, 16 February 2013 (UTC)[reply]

Thanks. I was familiar with the first article. It would be interesting to see one of the improved episodes. μηδείς (talk) 03:50, 16 February 2013 (UTC)[reply]

If you've watched any dvds of the first seven doctors' adventures, then you already have. 86.163.209.18 (talk) 09:33, 16 February 2013 (UTC)[reply]

If it loses vertical lock, the picture rolls up (or down) (with stuff that goes off one margin coming on at the other) - usually there's a wide blanking gap (a black strip) which sometimes contains flashing garbage. If you ever had to tune an old TV with a bad antenna you'd recognise this. Losing horizontal lock is worse; depending on the system, and the kind of degradation, the picture might slide sideways, go all sideways-diagonal-ish, or just turn into a horrible cascade of little horizontal slices of picture that jerk about on the screen. -- Finlay McWalterჷTalk 02:46, 16 February 2013 (UTC)[reply]

How many isomers does 1024-ane have(both including and excluding stereoisomers)?

Already checked the OEIS record, but that is still too complicated for me to understand. I just want to add this information to a humor page.--Inspector (talk) 01:37, 16 February 2013 (UTC)[reply]

It is too long ago, but I think I remember that only if you exlude ring systems which you obviously not do a solution with a relative easy algorythm is possible with ring systems they said it is very complicated.--Stone (talk) 10:24, 17 February 2013 (UTC)[reply]

Let's s say there is no ring system. What does the formula expanded look like?--Inspector (talk) 12:12, 17 February 2013 (UTC)[reply]

Conservation of energy

Consider a workman using a heavy implement such as an axe or sledgehammer to do irreversible work such as splitting a block of wood, breaking a rock or flattening an empty beverage can. The workman gives the implement a large amount of potential energy by raising it above his head. He then lets it fall and the potential energy is converted to kinetic energy. After the implement has struck the wood, rock or beverage can, all mechanical energy has disappeared. It is not possible to recover the lost mechanical energy by re-joining the block of wood, re-assembling the rock or stretching the flattened beverage can. Has energy been conserved? If so, to what form of energy has the mechanical energy been converted? How do we explain the validity of the law of conservation of energy in this situation? Dolphin (t) 03:17, 16 February 2013 (UTC)[reply]

Is this a homework question? Someguy1221 (talk) 03:27, 16 February 2013 (UTC)[reply]

No, it isn't a homework question. I know the answer ("Yes, energy is conserved") but I am asking it here to see how different Users go about explaining it. Our article Conservation of energy doesn't address the situation. Dolphin (t) 03:32, 16 February 2013 (UTC)[reply]

Wait a sec, you claim on your userpage to have a college degree in engineering...Someguy1221 (talk) 03:28, 16 February 2013 (UTC)[reply]

I would like to think that only someone with a college degree in physics or engineering would be able to formulate this question. I think it would be a good question in a physics exam. Dolphin (t) 03:41, 16 February 2013 (UTC)[reply]

Of course I can tell you where the energy is going, but I do not have the competence in physics to really explain why the energy cannot be got back without waving my hands rather furiously. I was hoping to build an explanation around conservative vs. non-conservative forces, but our article seems to go into no detail on the practical implications of a force being one or the other. Someguy1221 (talk) 03:49, 16 February 2013 (UTC)[reply]

Most literature, including Conservation of energy, focusses all attention on converting energy from one form to another. A small amount of literature also talks about doing reversible work such as dropping an object onto a spring so that the object rebounds to its original height. All the literature (that I am aware of) is silent on the subject of doing irreversible work. Dolphin (t) 03:54, 16 February 2013 (UTC)[reply]

(ec) Ignore the energy lost because a human is an inefficient chemically-driven thermodynamic machine. (That is easy to understand in a hand-waving way, but it's harder to explain specifically unless we want to dive into the depths of biochemistry and metabolism). Consider only the irreversible energy-transfer related to the cutting of a material. Plastic deformation is the opposite of elastic deformation, in that it is irreversible. In the microscopic case, if we really really really zoom in on the act of cutting a material, we see that the act of cutting performs work on the material, in the form of both elastic- and plastic- deformation. Both types of work on a material can result in temperature change; temperature change can mean that additional heat energy will be lost via conduction and radiation, and will not be recoverable (for the usual reasons). Now - why are some materials subject to plastic (irreversible) deformation; and others are not? Because the molecules are arranged differently. This is a game of statistics calculated among ensembles of particles. For some materials, there are lots and lots and lots of local minima in the energy for lots of arrangements of molecules, so by proverbially "shaking up the lattice" you might find a different mechanical layout that is stable. For other molecule arrangements, there is one clearly-lowest-energy arrangement, and if you deviate from that arrangement, the material's constituent particles all try to go back towards its optimal arrangement. The exact nature of these materials is well-studied; we can elaborate on different metallurgies and ductile deformations and brittle failures and so forth; but, you're an aeronautical engineer! This should have been covered ad nauseum in a materials engineering class! Nimur (talk) 03:58, 16 February 2013 (UTC)[reply]

(ec) Just about any undergrad uni physics textbook has this question or something just like it in the student exercises section (Mine has the workman driving a nail into wood), so I am a bit skeptical about the clained college degree too. The answer of course, it that the potential energy given to the hammer by the workman when he lifts it is conveted to kinetic energy, which, when the can is flattened / nail driven in / wood split or whatever, is converted via plastic deformation / friction / whatever, as respectively applicable, into heat. With a bit of "spherical cow" simplification and a value for specific heat of the can / nail /wood you can calculate the temperature rise in the can / nail/ wood. Wickwack 121.221.89.248 (talk) 04:00, 16 February 2013 (UTC)[reply]

A lot of the energy goes into producing sound and heat. The sound pretty soon turns into heat too. The heat can't be collected together again and put back into moving the axe because of the nature of entropy. SteveBaker (talk)

Not much will go into sound though. Almost all will go directly into heat. I can show why with some calcs, but doing so will reveal too much. I think this is a homework question (because in undergrad physics it is a common homework question), so I won't show the math, unless the OP comes back and shows he's made an honest go at it, and got stuck. You don't need to understand the concept of entropy to do this one. Wickwack 121.215.77.163 (talk) 09:58, 16 February 2013 (UTC)[reply]

I like SteveBaker's explanation, particularly his reminder that entropy is relevant in this situation. I agree with Wickwack that an understanding of conservation of energy comes before an understanding of entropy, but despite that, I think I will find some of the concepts from thermodynamics to be helpful. For example, when flattening an empty beverage can the work done on the beverage can will equal the increase in internal energy of the material comprising the can. It may all go to an increase in temperature of the material, or alternatively work hardening of the deformed metal may also represent an increase in internal energy, leading to less of an increase in temperature. I will think about it overnight.Dolphin (t) 12:10, 16 February 2013 (UTC)[reply]

About orbits of planets, electrons and other objects in dimensions higher than 3

Is is true that there can be no stable orbits for dimensions higher than 3, because the strength of gravitational and electrical field decreases more rapidly than in 3 dimensions, (e.g in 4 dimensional space the gravitational force is inversely proportional to the cube of distance)?--Inspector (talk) 14:56, 16 February 2013 (UTC)[reply]

The article Newton's theorem of revolving orbits has a short discussion of other central force laws like the inverse cubic. Actually magnets at some distance apart attract with an overall inverse cubic force so one could try this in space with a couple of magnets. Well actually they'd have to keep the same orientation, if one is rotating it goes down quite a bit faster. Dmcq (talk) 01:23, 17 February 2013 (UTC)[reply]

Next glacial period and survival of civilization

The earth is currently in an interglacial period (Holocene interglacial) since the last 12000 years. The next glacial period will start 50000 years later. I'm interested in knowing whether the global climate in a glacial period suitable for normal functioning of civilization (agriculture, public health, industry, transport etc). Will the next glacial period affect human activities in certain regions or all over the world (to the extent that human populations from one region have to migrate to other or die out)? --PlanetEditor (talk) 15:24, 16 February 2013 (UTC)[reply]

If what we've been told so far is true, natural cooling and warming cycles like this happen so slowly that we could "migrate" the necessary distance by each generation being born in a hospital ten miles further north or south (as necessary). My mathematics may be a little off, but you get the idea - if a climate change takes thousands of years, it's really not quick enough for human civilisation to really care.

Or, of course, we might be experts on anthropogenic climate change by then, and be able to stave off ice ages by increasing our CO2 output by some amount. --Demiurge1000 (talk) 15:33, 16 February 2013 (UTC)[reply]

Agreed. Our technology then will be so far advanced, that we shouldn't worry about it. For example, we may also have fusion reactors working then, providing the cheap energy needed for hydroponics. StuRat (talk) 17:29, 16 February 2013 (UTC)[reply]

First, there's no prediction that the next glacial period will begin in 50,000 years--the record is chaotic and there have been interglacials that have lasted less time than the one were'in. Second, there's evidence the change may be rather abrupt, on the order of a decade, not centuries. Migration on that scale would be rather traumatic. Third, there's absolutely no guarantee of progress, Rome fell and something like a luddite caliphate is always possible. But lastly, there's no reason to believe humanity wouldn't survive in the lower latitudes no matter what. μηδείς (talk) 20:17, 16 February 2013 (UTC)[reply]

There have been short-term, localized regions where technological progress stopped, or even reversed, but not worldwide, over a period of 50,000 years, during the era of modern humans. StuRat (talk) 20:43, 16 February 2013 (UTC)[reply]

Well, once again, there is no reliable source for the 50,000 year number--this could happen within the century--and global civilization could easily fall due to nuclear war or a plague, etc. The bottom line is, assuming there are people alive they will not go extinct because of an ice age itself. μηδείς (talk) 20:13, 17 February 2013 (UTC)[reply]

Unusually long interglacial, happens every 400,000 years I think. And also, due to anthropogenic greenhouse gasses, we are guaranteed at least 50,000 years of no glacial. Sagittarian Milky Way (talk) 21:12, 17 February 2013 (UTC)[reply]

was robert boyle an idiot.? or only had a partial understanding of the world.

i would like to ask if robert boyls was an idiot - or he had only a partial understanding of the world.

because he 'invented' the perpetual-motion machine, the "self-flowing flask" (visible in his wikipedia page if you search for 'self-flowing flask'). In fact, if he had actually built it, he would have seen that it does not work.

so was he an idiot? today every school child knows "boyle's law." So, while he was naive and wrong, still, did he advanced the state of understanding in the world which shows he was not idiot?

similar with a perpetual-motion machine: especially when there is a readily available source of energy, such as a heat differential (at different water depths), a current moving against the bottom of a river, wind moving against a surface, large amounts of light that can be harnessed via the photovoltaic effect, natural motions of the earth or moon, negative acceleration that is already in use to bring vehicles to a stand-still in traffic, and so forth. All of these are an actual source of energy input - ulike boyle's contraption.

so, if he was not idiot surely same devices with actual source of energy input is not worthy of calling idiot? or should i abandon exploration of such systems? 86.101.32.82 (talk) 15:32, 16 February 2013 (UTC)[reply]

Boyle died in 1691. The law of conservation of energy (which essentially forbids perpetual motion machines) wasn't truly formulated and accepted until 140 years later. So it was far from obvious to Boyle that perpetual motion is impossible. Like many perpetual motion machine inventors - the problem that they state is always that some small optimisation in performance will make this theoretical machine work - even though their current practical implementation doesn't quite work. For a classic example of this kind of failed reasoning, check out the "SMOT" (Simple Magnetic Overunity Toy) - which was "invented" three hundred years after Boyle and doesn't work (of course)...despite endless numbers of faked videos on YouTube. The web is full of people who think they could make this perpetual motion machine work, if only they could just reduce the friction a tiny bit more - or get a tiny bit stronger magnet - or if they could just adjust that ramp to exactly the right shape. Those people are indeed idiots because there is rock-solid science that says that they are all wasting their time.

In the case of the self-filling flask, you can easily be lead to believe that it might work because surface tension will indeed make the height of the liquid in the thin tube be a little higher than in the main bowl of the goblet. Surface tension was not studied methodically until Benjamin Franklin in the 1740's, so Boyle had no science available to him to allow him to understand that effect. His reasoning behind the failure of the practical machine might have been that he imagined that the precise taper of the glass tube (required for this idea to work) might have been incorrect or that the material that it was made of caused a problem...something like that. The state of science in the 1680's (when several people reported this idea) was actually rather primitive. Alchemy was still widely practiced. Isaac Newton (who was definitely not an idiot!) was still practicing alchemy some 40 years after Boyle died. At the time Boyle was working, calculus had not been invented and even the concept of negative numbers had not yet entered European mathematics!

You, on the other hand, have the benefit of three hundred years of solid scientific experimentation and theory. "The Scientific Method" is well-established now. You have access to all of the great ideas of science at your literal fingertips here at Wikipedia and elsewhere. Mathematics has advanced beyond recognition and even children at the age of 8 years old understand the usefulness of negative numbers and teenagers are taught calculus. So, if still you think you have a perpetual motion machine, then you will most likely (and justifiably) be called "an idiot". But a machine that operates with a bonafide source of energy and which doesn't violate any of the laws of thermodynamics is perhaps not impossible.

SteveBaker (talk) 16:20, 16 February 2013 (UTC)[reply]

Justified? Hardly, and not by anyone who knows the difference between scientific knowledge and the scientific method. -Modocc (talk) 17:13, 16 February 2013 (UTC)[reply]

(ec) Robert Boyle was certainly smarter than your average guy (not an idiot) and he had a partial understanding of the world (who doesn't?). He understood energy, but not the current paradigm of thermodynamics, in which perpetual-motion machines of any kind are considered impossible, came later. In addition, our science is supposed to fit reality, thus its important to keep a critical eye on the models because sometimes theorists unintentionally build sandcastles and strawmen instead. In other words, their models do not entirely accord with reality and therefore get knocked down. As to what you should do, that is entirely your decision. -Modocc (talk) 16:48, 16 February 2013 (UTC)[reply]

These links are fascinating, thanks to everyone. It's amazing that these obviously impossible devices (due to thermodynamics, as there is no source external power) gets so many youtube view. Check this: http://www.youtube.com/watch?v=zz-Lupbn7mc 86.101.32.82 (talk) 20:04, 16 February 2013 (UTC)[reply]

Since paradigms have changed since Boyle's day and can change again, you may also be interested in the article on Paradigm shift. Modocc (talk) 21:43, 16 February 2013 (UTC)[reply]

And you might be interested in Maxwells demon to see that all the business abot perpetual motion machines is not at all obvious. Dmcq (talk) 01:12, 17 February 2013 (UTC)[reply]

Russian meteor

Meteor/asteroid coincidence

According to 2013_Russian_meteor_event#Coinciding_asteroid_approach, those two events happening 16 hours apart are just a coincidence. I'm not convinced:

1) What are the odds of such major events happening within 16 hours, if independent ? (Use whatever assumptions you like.) Here are my thoughts:

The meteor appears to be the biggest since the 1908 Tunguska event, so we could use 1/((2013-1908)*365) or 1/38325 chance of it happening on a given day. If we allow for the events to happen in either order, that's a 32 hour window, so let's multiply by 32/24 to get a 1/28744 chance of it happening within 16 hours of this particular asteroid. However, there must have been other asteroids as significant as this one. Here I'm less sure of the numbers.

2) Have scientists considered all ways in which the two events might be related ? For example, could a piece have broken off the asteroid on the last pass by the Earth, traveled roughly parallel to the main piece, but slowly diverged, then have gone around the far side of the Moon, quite close to it, and been wildly deflected this time ? StuRat (talk) 16:54, 16 February 2013 (UTC)[reply]

Well it isn't a coincidence. It is a secret, but as I know you can keep it, I will tell you. The Proxies, the space aliens from Proxima Centauri will not tolerate any space-faring races in their proximity, so they decided to eliminate our spaceports. 2012 DA14 was sent to destroy Cape Canaveral Air Force Station. Being the Proxies first try, they sent a heavy asteroid that would work disaster even when it didn't hit the target exactly. Lucky for us, it missed completely. With advances in their technology, they again sent now a cheaper, smaller, but faster and more well aimed object to destroy Baikonur. It was orchestrated as a double blow, so we wouldn't have the time to take defensive measures. As our radio transmissions need some time to reach them, they don't know of other launch sites yet.

The two orbits were not related. If something were broken off and then widely altered in orbit - it also wouldn't arrive at the same time . Rmhermen (talk) 19:29, 16 February 2013 (UTC)[reply]

Wouldn't they, under the scenario I gave ? They only diverge slightly until one goes behind the Moon, just hours before hitting/passing. StuRat (talk) 19:31, 16 February 2013 (UTC)[reply]

They came from opposite directions. If you look up any specific meteor shower you will see that all the meteors from one shower will move in the same direction from one origin in the sky, the constellation out of which they come giving the name of the shower; e.g., the Perseids. If these tow bodies had been associated they'd have come from the same area of the sky and been moving in the same direction. μηδείς (talk) 19:58, 16 February 2013 (UTC)[reply]

Not if one had gone around the far side of the Moon and had it's direction changed by 180°, as I suggested. Can someone tell me if the Moon was in the proper position for this ? StuRat (talk) 20:01, 16 February 2013 (UTC)[reply]

My first thought was that it could be some satellite orbiting 2012 DA14. As I am plain lazy, and besides, it would violate wikipedia rule WP:OR, I did not look at celestial mechanics to calculate the hypothetical orbit of the object that hit the earth around 2012 DA14 by myself. From imagination, it could well be some moonlet on its way back (back relative to the trajectory of the main object). 95.112.182.106 (talk) 20:30, 16 February 2013 (UTC)[reply]

Nope. This isn't biology, so some things really are impossible. :) And one of those things is a satellite orbiting a really, really weak gravity source, but doing so with such speed that when the primary nearly strikes the earth at that tremendous speed, the satellite strikes us at something near a right angle to it.

I'll go with the theory that friendly aliens moved the 150-foot meteoroid just enough so that it wouldn't hit us, but sent the other one at us to remind us that we ought to learn to do this for ourself. :) Wnt (talk) 21:16, 16 February 2013 (UTC)[reply]

Yes, the supposition is impossible. You are suggesting that two bodies travelling together with the same speed and trajectory and then closely passing by the moon (which was not predicted for DA14) were deflected so that one simply kept going (albeit much more slowly to explain the 16 hor time gap--although it arrived exactly when it had been predicted to do so for weeks), while the other one swang around the earth, but, instead of staying in orbit, then dropped down into the atmosphere from the entirely opposite direction. μηδείς (talk) 20:08, 17 February 2013 (UTC)[reply]

You don't seem to be understanding me at all. Here's a diagram:

          _                <-  . Little asteroid
         / \ Moon
   __    \_/
  /  \
 |    | Earth                                                                          
  \__/
                                                                   <-  * Big asteroid

      <-  .
         / \ Moon
   __    \_/
  /  \
 |    | Earth                                                                          
  \__/
                                              <-  *

          _
        ./ \ Moon
   __    \_/
  /  \
 |    | Earth                                                                          
  \__/
                                            <-  *

          _
         / \ Moon
   __  . \_/
  /  \
 |    | Earth                                                                          
  \__/
                                           <-  *

          _
         / \ Moon
   __    \_/
  /  \.
 |    | Earth                                                                          
  \__/
                                         <-  *

          _
         / \ Moon
   __    \_/
  /  \ 
 |   ( Earth                                                                          
  \__/
                                       <-  *

16 hours later:
          _
         / \ Moon
   __    \_/
  /  \ 
 |   ( Earth                                                                          
  \__/
<-  *

You see, they already would have broken apart years before approaching Earth (this time), and would have separated in space and/or time since then. StuRat (talk) 00:02, 18 February 2013 (UTC)[reply]

I see a new conspiration theory here. Honestly, wondering about coincidences after the facts is a waste of time at least. — Preceding unsigned comment added by 88.8.74.141 (talk) 20:29, 16 February 2013 (UTC)[reply]

A conspiracy requires conspirators. Or are you imagining a scenario where humans somehow caused this ? I believe looking at apparent coincidences after the fact has led to many scientific discoveries. StuRat (talk) 20:38, 16 February 2013 (UTC)[reply]

Well, moving a 10-ton rock is far from impossible, with even a small rocket. One might even explain the coincidence of dates as being because the nefarious party stupidly expected people to think it was a chunk of the famous meteor everyone was looking at. I imagine that the Russians will be looking over the wreckage of the meteor very carefully for signs of terrestrial rocket motors being attached, but then again ... a smart villain would have programmed his rocket to take off into space after it finished doing its job and long before impact. Wnt (talk) 22:18, 16 February 2013 (UTC)[reply]

To be clear the one that hit Earth was 10,000 tons, not 10 tons. Rmhermen (talk) 17:43, 17 February 2013 (UTC)[reply]

Impact crater

Something else which confuses me is that the meteor appeared to be going through the atmosphere at a shallow angle, yet the impact crater in a frozen-over lake is circular, not elliptical, as I would have thought: 2013_Russian_meteor_event#Impact. Why is this ? StuRat (talk) 17:00, 16 February 2013 (UTC)[reply]

That's quite a common question and [18] hopefully will answer it for you. Dmcq (talk) 18:22, 16 February 2013 (UTC)[reply]

Thanks. StuRat (talk) 20:46, 16 February 2013 (UTC)[reply]

Window glass

Excuse me for hijacking the original questions. On some pictures it looks like the windows were "old fashioned" double glass windows, the kind easily broken by a mislead ball by some playing kids, not the kind of glass that is used nowadays with high thermal insulation and nearly indestructible even when deliberately using a hammer. So I wonder if the extent of destruction also has to do with cheap, or old, buildings.

I also wonder if buildings specially designed to withstand earthquakes, as Japan, would have had less damage or it protection against on does not give protection against the other.

95.112.182.106 (talk) 18:56, 16 February 2013 (UTC)[reply]

Much of the construction under communism was quite shoddy, yes. And, even since then, there are pockets of poverty where new construction, if any, is likely to be just as bad. StuRat (talk) 19:13, 16 February 2013 (UTC)[reply]

Causes of raised pcp levels in the body

I would like to confirm what the causes for raised (Natural) PCP levels in the body are. I know that Pcp is a halucinogenic drug, I know there are natural levels of pcp in the body, I would like to identify what causes the natural levels to become elevated. & if Hyperthyroid could cause this. — Preceding unsigned comment added by 96.243.19.132 (talk) 17:41, 16 February 2013 (UTC)[reply]

Are you sure you mean PCP itself ? Piperidine is found in black pepper and also used in the production of PCP. StuRat (talk) 18:14, 16 February 2013 (UTC)[reply]

Did you confuse PCP with PTP (Protein tyrosine phosphatase)? PTPs are a class of hormones. I don't know what their connection to hyperthyroidism may be... --Jayron32 20:49, 16 February 2013 (UTC)[reply]

Hunting for endogenous phencyclidine I find a probably non-reliable source [19] which briefly describes a 1986 NIDA research monograph [20] (does anyone actually have access to these?) which postulated a PCP-like compound in schizophrenics. But so far as I know the mainstream thought runs toward PCP having a mix and match of effects on certain dopamine and glutamate receptors [21] which is dependent on the qualities of this exact chemical, which does not occur naturally in the body. As such, I would surmise that PCP-like states of mind might be assembled if these pathways are affected strangely enough in just the same proportion by natural or pathogenic physiological conditions, but there would be no particular mechanism to cause a mentally ill person to have that exact set of changes in these pathways as opposed to some other set that causes weird behavior but different weird behavior. But ... no promises that is true; this sort of biology is notorious for major do-overs. Wnt (talk) 21:12, 16 February 2013 (UTC)[reply]

It sounds like the OP has had a blood test and been told that they have elevated "PCP", which almost certainly won't be referring to phencyclidine (unless it was a drugs test). Maybe they misheard PCV. Either way, this is bordering on medical advice so until the OP asks a more specific question we can't answer it. Markr4 (talk) 13:33, 17 February 2013 (UTC)[reply]

what does it mean that relativity and qm are incompatible?

what does it mean that relativity and qm are incompatible? I've put this query into the google and read the first answer. it is from 2009 however and says : "Quantum Mechanics (QM) and relativity are both 100% accurate, so far as we have been able to measure (and our measurements are really, really good). The incompatibility shows up when both QM effects and relativistic effects are large enough to be detected and then disagree. This condition is strictly theoretical today, but in the next few years our observations of Sagittarius A*, and at CERN should bring the problems between QM and relativity into sharp focus."

since it is 2009 + 4 = 2013 can you elaborate thank you. 86.101.32.82 (talk) 22:07, 16 February 2013 (UTC)[reply]

General relativity is not incompatible with quantum mechanics, it is just that the theory is non-renormalizable, which means that the results of computations depend on exactly how you define the theory down to the smallest lengths scales. In case of renormalizable theories, what happens at some fixed lenght or energy scale in some experiment can be expressed in terms of a few other measuarable quantities to any accuracy that is desired. So, you can then eliminate the unknown physics at the very smallest length scales (or equivalently, the highest energy scales). Count Iblis (talk) 23:06, 16 February 2013 (UTC)[reply]

For the benefit of other readers, the answer you're talking about is here.

The extremely successful standard model of particle physics combines special relativity and quantum mechanics. Combining general relativity and quantum mechanics (into quantum gravity) has turned out to be amazingly difficult, but they are obviously not incompatible since they coexist in the real world.

There is a philosophical/foundational problem with combining even special relativity with quantum mechanics, which is that both special and general relativity treat time and space in essentially the same way, while in quantum mechanics they are totally different: This is called the problem of time, and Wikipedia should have an article on it but currently doesn't. It probably has something to do with the difficulty of making quantum gravity work, and it's surprising (to me, anyway) that it doesn't cause more trouble in the Standard Model as well.

I don't know why "The Physicist" thought that observations of Sagittarius A* (a black hole) or experiments at CERN (presumably meaning the LHC) would cast any light on quantum gravity. Sagittarius A* is very far away and we can only vaguely measure its properties. The LHC has a maximum design collision energy of 14 TeV, while quantum gravitational effects are expected to become significant at around 10,000,000,000,000,000 TeV (the Planck energy). Many particle physicists did hope that the LHC would find something new that would tell us something about quantum gravity, but it hasn't happened yet. -- BenRG (talk) 19:14, 17 February 2013 (UTC)[reply]

Regarding the article Homogenized Milk and Atherosclerosis

I have removed this discussion because we are not allowed to give medical advice. All a wikipedia article can give you is general information. For specific situations, you need to see a doctor. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:54, 17 February 2013 (UTC)[reply]

February 17

KEF-2013

This is being reported as the name of the Russian meteor, but the name doesn't seem to follow the patterns discussed in our Astronomical naming conventions article. What system are the Russians using here (and do we need to expand our article)? Rmhermen (talk) 00:40, 17 February 2013 (UTC)[reply]

If any astronomy convention applies, it would be Provisional designation in astronomy, not Astronomical naming conventions. That being said, I don't think that either of those apply to objects within the earth's atmosphere. The Meteoritical Society has some guidelines,[22] but if it is within Russian airspace, I am pretty sure that the Russian Federal Space Agency gets to name it. --Guy Macon (talk) 08:25, 17 February 2013 (UTC)[reply]

Our Astronomical naming conventions article covers provisional naming. But that would yield a name like 2013 C[x]_[x] and meteorite naming will involve the name Chelyabinsk probably. Our articles don't seem to mention national bodies making up their own naming system. Do we know any details? Rmhermen (talk) 14:00, 17 February 2013 (UTC)[reply]

The question is whether astronomical naming conventions apply to non-astronomical phenomena such as meteors and meteorites. What is the IAU designation for the Canyon Diablo meteorite? The Sutter's Mill meteorite? The Sikhote-Alin meteorite? The only meteor or meteorite that I know of that has an IAU designation is 2008 TC3, and that is because it was observed, tracked, and named prior to reaching Earth. --Guy Macon (talk) 14:55, 17 February 2013 (UTC)[reply]

Non-astronomical? Not really. But my question is what system yields a name KEF-2013 and why doesn't Wikipedia seem to know about this system? 17:35, 17 February 2013 (UTC)

I'm very sceptical that anyone really does call this KEF-2013. Our use of that name seem to come from this report, which says Speaking at the Krasnoyarsk Economic Forum, Mr Medvedev called the fallen meteorite in Chelyabinsk "KEF-2013," according to a translation obtained by Newsroom America. I'm suspicious if that site has mistaken the name for the meeting at which Medvedev was speaking - Krasnoyarsk Economic Forum (KEF-2013 / КЭФ-2013) [23] - for a name for the meteor. I note that the Russian Wikipedia article about the meteor does not call it KEF or КЭФ (except for where it parrots that questionable, unsure newsroomamerica ref, as we do). So TL;DR: I don't believe it is called KEF-2013, as I can find no reliable source that it is. -- Finlay McWalterჷTalk 18:49, 17 February 2013 (UTC)[reply]

I should say that I don't think there is anywhere in Russia called "Кзф" (except what I think is a North African restaurant in Yekaterinburg). There's a really minor geoname Кеф in northern Sakhalin, which is nowhere near the meteor's area. -- Finlay McWalterჷTalk 18:58, 17 February 2013 (UTC)[reply]

I have been editting the article, and when I had added the KEF name to the lead I went to look for better reliable science sources, of which there are apparently none in English or Russian. μηδείς (talk) 19:59, 17 February 2013 (UTC)[reply]

Quantum tunneling

What's the probability that Andy Roddick's fastest serve (155 mph) would tunnel through the net? Also, how fast must he serve in order for the ball to have a non-negligible tunneling probability? (Also, for the sake of the argument, how fast must he serve in order to physically make a hole in the net?) 24.23.196.85 (talk) 06:46, 17 February 2013 (UTC)[reply]

what makes you think there is a speed at which there is non-negligible tunnelling probability at such huge, macro scales? you do know there's a univeral speed limit.... 86.101.32.82 (talk) 08:53, 17 February 2013 (UTC)[reply]

What would happen as that speed limit was approached by a baseball or tennis ball is analyzed here. --Guy Macon (talk) 15:00, 17 February 2013 (UTC)[reply]

Interesting question! Answering the first question is a bit tricky, as the standard textbook estimates based on particles tunelling through a barrier will greatly overestimate the probability. What happens with the ball is that the constant interactions with the air molecules effectively leads to the state of the ball being measured very frequently, which greatly suppresses the tunneling probability. This is called the quantum zeno effect. Count Iblis (talk) 15:45, 17 February 2013 (UTC)[reply]

Reminds me of an exercise in my physics class where we had to calculate the probability of Santa Claus tunneling into a house. As far as I remember assuming a rectangular potential barrier was considered sufficient then (it was Christmas time so the examiners were kind...). bamse (talk) 20:56, 17 February 2013 (UTC)[reply]

Relevance of physics to microbiology.

What are the relevance of physics to biology? — Preceding unsigned comment added by 196.46.246.49 (talk) 12:31, 17 February 2013 (UTC)[reply]

You might want to start with gravity, acoustics, optics, thermodynamics, motion, aerodynamics, sound, sun, tides, and energy.--Shantavira|^{feed me} 13:55, 17 February 2013 (UTC)[reply]

Also you should know that you, your body is nothing but a combination of chemical elements held together by laws of physics. Your mind is nothing but a manifestation of chemical activities. Simply put, you are nothing but a complex combination of natural elements. There is no difference between you and a rock except that you have signaling and self-sustaining processes known as life. A rock lacks signaling and self-sustaining process. And this very thing called life would have never originated without the laws of physics. The laws of physics enabled you to write this question in the reference desk. --PlanetEditor (talk) 15:55, 17 February 2013 (UTC)[reply]

There's a whole discipline called biophysics. -- 67.40.213.4 (talk) 21:46, 17 February 2013 (UTC)[reply]

3d effect when watching TV while you look through a small hole with one eye

A long time ago when I got interested in 3D pictures I noticed you get a strange 3 D effect watching a normal t.v. program if one of the eyes is looking through a small hole. The effect is clearly visible when looking at moving objects on the screen. I guess what is going on is that by looing at the screen this way, you mess up the information about the parallax (which should be amost exactly the same for all objects on the screen) slightly, and then the brain uses other information like motion to "correct" the information about the parallax, usually leading to natural 3d effect. I'm not sure about this explanation, though. Count Iblis (talk) 15:39, 17 February 2013 (UTC)[reply]

This sounds like one of a few strange effects that depend on the fact that the response time of the retinal cells is dependent on light intensity. I assume you mean a hole small compared to your iris, in a card or something held close to the eye, thus "stopping down" the light entering the eye. Stronger light produces a faster response. You get an effect similar to what you describe if, if lighting conditions are right, you look at a TV with a sunglass lens (not polaroid type) in front of only one eye. A more surprising (to most people) is trying this with an analog TV tuned to a vacant channel, so that what's on the screen is just snow. The effect of reducing the light intensity to only one eye is a rotating barrel effect - some of the the snow seems to move to the right in front of or behind some of the snow moving in the opposite direction. If (say) your are looking at a scene with objects moveing to the right, and you stop down the right eye, then the right eye image is effectively delayed slightly, which means the object is displaced to the left, giving a false 3D effect. There was a university chap who researched this about 20 years ago. No promises, but if I can remember his name, I'll post some details. Wickwack 121.221.31.66 (talk) 16:08, 17 February 2013 (UTC)[reply]

Is this related to the Pinhole camera effect? Alansplodge (talk) 17:36, 17 February 2013 (UTC)[reply]

That was my thought. Perhaps his vision just needs correction, and a pinhole lens corrects it to the point where his brain can assign depths more accurately than it can with blurry objects. StuRat (talk) 23:36, 17 February 2013 (UTC)[reply]

velocity of meteor

NASA gives the aphelion of the Russian meteor at about 2.5 AU. Suppose you want to calculate the speed of it when it crosses the Earth's orbit, assuming that the Earth is not there. Can you calculate the difference in potential energy between 1 AU and 2.5 AUs and assume that is converted into kinetic energy? Bubba73 ^{You talkin' to me?} 20:53, 17 February 2013 (UTC)[reply]

Yes, you can, but this gives only a lower bound, since you'd have to add the kinetic energy at aphelion to this to get the total kinetic energy. --Roentgenium111 (talk) 21:24, 17 February 2013 (UTC)[reply]

Underground bunker effects of the Russian meteoroid?

Would a underground survivalist type of bunker 2 - 4 meters down with 10 cm concrete walls be affected from the 2013 Russian meteor event in any significant manner ..? Missile bunkers are protected from shock waves by having most interior equipment mounted on springs. Perhaps a meteor ground impact would be different and blast the walls located underground with shock waves much in the same manner that sea waves become larger closer to the beach. I find the behaviour of underground shock waves hard to predict and their behavior when they encounter a sharp density change that perhaps results in a superposition reflection that result in an force from the surrounding ground that cracks the walls. Electron9 (talk) 22:41, 17 February 2013 (UTC)[reply]

An underground bunker is going way too far. Any modern building in a first-world country could have survived the meteor with minimal damage, provided it was built to code. Most of the damage the meteor caused was broken glass, but most glass windows nowadays are shatter-proof. See this discussion above. --140.180.243.51 (talk) 23:17, 17 February 2013 (UTC)[reply]

Why didn't Earth's gravity capture the asteroid 2012 DA14?

What I'm really asking is in what approach, distance, and speed should the asteroid that passed a little bit over 17,000 miles above the earth have approached earth in order for the earth's gravity to have captured it in such a way that the asteroid would have become earth's second moon? I ask because many of the planets' moons in the solar system, like the moons of Mars and many of the small moons of the Gas Giants, are actually asteroids that were captured by the planets' gravity in the distant past. 71.98.163.183 (talk) 00:06, 18 February 2013 (UTC)[reply]

@@ Line 434: / Line 434: @@
 :An underground bunker is going way too far.  Any modern building in a first-world country could have survived the meteor with minimal damage, provided it was built to code.  Most of the damage the meteor caused was broken glass, but most glass windows nowadays are shatter-proof.  See [http://en.wikipedia.org/wiki/Wikipedia:Reference_desk/Science#Window_glass this discussion] above.  --[[Special:Contributions/140.180.243.51|140.180.243.51]] ([[User talk:140.180.243.51|talk]]) 23:17, 17 February 2013 (UTC)
+== Why didn't Earth's gravity capture the asteroid 2012 DA14? ==
+What I'm really asking is in what approach, distance, and speed should the asteroid that passed a little bit over 17,000 miles above the earth have approached earth in order for the earth's gravity to have captured it in such a way that the asteroid would have become earth's second moon? I ask because many of the planets' moons in the solar system, like the moons of Mars and many of the small moons of the Gas Giants, are actually asteroids that were captured by the planets' gravity in the distant past. [[Special:Contributions/71.98.163.183|71.98.163.183]] ([[User talk:71.98.163.183|talk]]) 00:06, 18 February 2013 (UTC)