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March 25

Heart disease

Can heart disease cause a rash on the patient's chest (and in particular, a red mark shaped like the letter "A")? Note: this is NOT medical advice (as you can hopefully see from the link). 24.5.122.13 (talk) 01:39, 25 March 2014 (UTC)[reply]

Why would you think that it could ? StuRat (talk) 03:21, 25 March 2014 (UTC)[reply]

See [1] for more relevant inspiration. Wnt (talk) 04:15, 25 March 2014 (UTC)[reply]

True enough -- but do you suppose the Reverend branded himself as a form of penance? 24.5.122.13 (talk) 06:25, 25 March 2014 (UTC)[reply]

It's a long blathery tale told from a mad perspective, which doesn't even say exactly what was there, if anything - for all I know he could have imagined it, it might have been supposed to be a divine manifestation, he scratched it into his flesh over and over again with his fingernails, who knows? What I do know is that there's a sternum, a not inconsiderable mass of bone, separating the heart from the skin except in certain cases of congenital malformation. Any relation with heart disease would have to be an incredible Rube Goldberg biological mechanism. Wnt (talk) 15:31, 25 March 2014 (UTC)[reply]

Thanks for the answers, everyone! The reason why I asked is because the Reverend's physical symptoms (weakness, unhealthy pallor, chest pains) are unmistakably those of heart disease. However, considering what you told me, and what the book says, the most likely explanation is that his remorse for his transgression (and not just for the act itself, but for seeing Hester suffer public ostracism while himself being unfairly spared from it), and the stress caused by the need to hide it from the public, both exacerbated his heart disease and also drove him to brand himself as an act of penance (among other things such as rigorous fasting, nighttime vigils, self-flagellation, etc.) 24.5.122.13 (talk) 22:53, 26 March 2014 (UTC)[reply]

What might happen in a wall wart if connected across a battery?

I made my own dynamo-powered bike light with a very simple circuit which charges some NiCad cells to keep the light on when I stop at traffic lights. Due to a disconnected wire, I used it without input which of course drained the cells. I tried to the charge them in a manner I did once before - by connecting via crocodile jumper leads to a variable wall wart power supply. Now I'm trying to do the same thing but the light on the power supply turns off whenever connected across my cells. What might be happening inside that power supply? Does it short the batteries? I imagine it was never designed for this purpose but it did work once before set at 6 V and at 7.5 V (I have five cells connected to form a ~6 V battery) --129.215.47.59 (talk) 12:04, 25 March 2014 (UTC)[reply]

I'd guess the cells are fried. If you lucky one is fried and the others are OK. If you had a multi-meter you could test to see if there is any juice left in them, normal discharged cells will still read 0.1V–1V. If you lucky the power supply has some short circuit protection and its detecting a short and switching off, if your unlucky you have fried the power supply as well. Normally when charging the current is limited to prevent the batteries over heating or over charging, connecting them straight across the power supply didn't have such protection. See Rechargable batteries--Salix alba (talk): 15:06, 25 March 2014 (UTC)[reply]

I think a miscommunication occurred. The battery has open circuit voltage 5.9 V and the charger, still set to 6 V is at 6.02 V (plus or minus whatever), according to my multimeter. I didn't leave them charging and come back. I attempted to initiate charge and no current would flow (and the light on the power supply would go out) whereupon I left everything disconnected and posted here. 129.215.47.59 (talk) 17:09, 25 March 2014 (UTC)[reply]

It sounds as if your power supply has a current limiter and switches off because it thinks it is being short-circuited. Try putting a small resistance in series with the circuit to limit the current that is drawn. Why not just recharge the cells with your bike dynamo (with the lights turned off)? Dbfirs 17:33, 25 March 2014 (UTC)[reply]

....Wall wart? ( link added at 22:58, March 25, 2014‎ by Medeis. )

Yes, thanks for the helpful link, Medeis. I'd never heard them called that until I started reading Wikipedia Reference Desk a few years ago. I don't actually have any of mine plugged into walls, but it's an amusing analogy. Dbfirs 13:32, 27 March 2014 (UTC)[reply]

Magnet motor

Hi, on WP Their is a redirection on Magnet motor to Perpetual motion. Don't magnets lose there magnetism over the years? What do you think of those videos [2] [3] [4]. --YB ^✍ 14:32, 25 March 2014 (UTC)[reply]

All videos showing free energy from magnets are fake. There is no exception to this. Magnets can indeed loose their magnetism.217.158.236.14 (talk) 15:07, 25 March 2014 (UTC)[reply]

As a general rule, nearly all "science" videos on YouTube are fakes. Sure, there are a few honest people making nice videos of real effects - but they are BY FAR outnumbered by the pathetic fakes and camera tricks. When you see an amazing effect on a YouTube video, it's about 90% certain that it's a fake.

The confusion that nearly everyone who proposes these things has is that they confuse the physics concept of a "Force" with the concept of "Energy" or "Work". Something can exert a force without consuming any energy. If you hang a weight on the end of a chain, the chain is exerting a force on the object (in this case, it's equal and opposite to the gravitational pull of the earth). But nobody thinks the chain is going to lose it's ability to support weight because it somehow "runs down" like a dead battery. Magnets are the exact same deal - they can support a weight against gravity without consuming energy in the process.

However, as soon as you get something moving as a result of a force, some energy had to be expended to make that happen - and once it's gone into moving the object, the energy is lost to whatever set it in motion. Magnets don't contain any special energy source - so they can't be used to "power" a machine. That's why 100% of "magnet motor" videos are faked. These machines cannot possibly work - but it's not because the magnet might "run down" - that's a complete red herring.

Sure, you can use a magnet to pick up (say) a steel ball-bearing from a table...but that's a one-time thing. Once the ball-bearing is stuck to the magnet, you've got to use some energy to pull it away again - and the amount you need is more than the energy that was required to put the ball-bearing there in the first place. So you can't use this to make perpetual motion.

It's just the same as using gravity to do the same job. You can roll a ball down a hill - but to do that a second time, you have to expend some energy to raise the ball back to the top again. You can't make a perpetual motion machine from gravity either.

SteveBaker (talk) 21:30, 25 March 2014 (UTC)[reply]

The above lecture contains almost only correct usages of the contraction "it's" meaning "it is". 84.209.89.214 (talk) 00:12, 26 March 2014 (UTC) [reply]

Now don't be sad, ’cause six out of seven ain't bad. —Tamfang (talk) 05:30, 26 March 2014 (UTC)[reply]

As to how the fakery is done in this case, notice in the first video that the device the magnetic gizmo is attached to is supposed to be a generator, but that isn't what it is. The metal cylinder is suggestive of a generator housing, but it's a plain cylinder of metal, without any heat sink fins or at least air holes to help cool off the windings that one would expect on a real generator of that size. Also, in addition to the expected wires that carry the power from the back end of the "generator", there's also an extra small pair of wires coming out of the rotor end of the "generator", which wouldn't make any sense if that device was really a generator. The other end of that pair of wires, which go to the magnetic gizmo, would also make no sense if the "generator" was really a generator. The magnetic gizmo is supposedly a purely mechanical device (it doesn't contain any windings or other visible circuitry) that produces its own energy, so why would it need power supplied to it from the generator? I think the paper with "challenge to all the engineers" written on it a bunch of times that's wrapped around the top of the "generator" is there to help with the illusion by helping to hide the fact that that metal cylinder really doesn't look all that realistically like a generator. I think the "generator housing" is what contains the batteries that are really powering everything, as well as the motor that keeps the useless but impressive magnetic gizmo in motion. The small pair of wires that don't make sense if you assume the setup isn't fake make total sense if you assume that in reality, those wires are attached to a switch connected to the gizmo housing such that shutting the gizmo housing is what switches on the motor and external circuit.

Hopefully this "explanation" will be adequate for me to get my payment from the free energy suppression conspiracy consortium. Red Act (talk) 05:46, 26 March 2014 (UTC)[reply]

Actually, a buried power cable into the base of the fan would also work as the power source, instead of batteries in the motor housing. The fan is never lifted, it's always plugged in while the device is running, and it's sitting on a patch of dirt next to the patio instead of being on the patio like everything else is. Red Act (talk) 06:16, 26 March 2014 (UTC)[reply]

The point is that magnet motor should not be called a perpetual movement machine because magnets lose their magnetism after a while.--YB ^✍ 14:56, 26 March 2014 (UTC)[reply]

I think the amount of energy stored in a permanent magnet must be small, but how do you calculate it? I'm thinking the magnetic field necessarily contains some energy, but that doesn't speak of the magnet itself. Another way I look at it gets a different result: take two strong magnets sitting on a table at rest. They snap to each other, liberating a small amount of extractable energy in the process. Now in order to demagnetize them, you need to put that energy back in, so when stuck together they actually have less energy than demagnetized magnets... right? But... if you chop up and randomize a magnet into itty bitty pieces, letting them all reassort to neutralize each other, doesn't that get the most energy out of them? Oh phooey, I confused myself this time. But looking at a paper from 1953 there seems to be a formula, based on the idea that a material usually adopts a magnetization state that minimizes its free energy as one would expect; it still needs some unpacking to get to a number though. Wnt (talk) 15:07, 26 March 2014 (UTC)[reply]

No, magnets losing their magnetism over time is irrelevant. The phrase "perpetual motion machines" isn't used to describe a set of devices which are actually capable of running literally forever. Instead, it's used to describe a set of devices which are intended by their inventor to be capable of violating the first and/or second laws of thermodynamics. All "perpetual motion machines" would stop functioning eventually due to wearing out in one way or another. But the more important problem that makes such devices be called a "perpetual motion machine" is that they are incapable of violating the laws of thermodynamics as intended even initially, long before wearing out would ever become an issue.

Besides, magnets can hold their magnetism for centuries. A perpetual motion machine that uses magnets would fail due to wear on its bearings long before demagnetization would be the expected failure mode. Red Act (talk) 17:40, 26 March 2014 (UTC)[reply]

I think there's some confusion here. Magnets do not contain energy.217.158.236.14 (talk) 16:15, 26 March 2014 (UTC)[reply]

E = MC^2. Which implies that Wnt's two magnets will have a (very slightly) greater mass when separated than they do when they come together. (See also this old ref desk discussion on the increase in mass of an alarm clock spring resulting from it being wound up [5]). AndyTheGrump (talk) 16:25, 26 March 2014 (UTC)[reply]

And it takes a certain amount of energy to unstick two magnets. But it's not the point.--YB ^✍ 16:39, 26 March 2014 (UTC)[reply]

Wow, it would be easy to miss that you tweaked "point" to link to magnetic bearing. However, magnetic bearings would be inadequate to keep a device rotating without energy input until demagnetization became an issue. Magnetic bearings use permanent magnets to provide the bias field, but usually require active control coils for stability purposes, due to Earnshaw's theorem. Those active control coils consume energy due to resistance in the coils resulting in Joule heating. A homopolar electrodynamic bearing doesn't require control coils, but it works due to induced eddy currents. Those eddy currents again cause energy loss due to Joule heating, causing the rotor to slow down until it ultimately stops. Red Act (talk) 03:43, 27 March 2014 (UTC)[reply]

Even an electron, which really does spin forever, is not a perpetual motion machine, because a "perpetual motion machine" is a device that violates the first or second law of thermodynamics and not, despite the name, one that moves forever. All this discussion of whether a device made of magnets will eventually spin down seems irrelevant. Getting back to the original question of whether "magnet motor" should link to "perpetual motion", I think it probably shouldn't because the phrase could just as well refer to an ordinary electric motor. -- BenRG (talk) 07:50, 27 March 2014 (UTC)[reply]

Except electrons don't actually spin at all, they just have a property called spin. DMacks (talk) 04:11, 28 March 2014 (UTC)[reply]

Amber-colored vertical displays

What are these vertical, amber-colored displays? What do they do? Why don't they just use normal LCD monitors? -- Toytoy (talk) 16:41, 25 March 2014 (UTC)[reply]

The look like old Monochrome monitors from the 1980s. As to why they use them, perhaps they are connected to a system that uses them and has not been upgraded. The principle "if it ain't broke, don't fix it" may apply here. --Jayron32 16:51, 25 March 2014 (UTC)[reply]

And it looks like it's only used to display text data, where color isn't all that useful. Also, you don't have to worry about picking colors so the colorblind can still read it properly (unless they do something really stupid, like green text on a red background). StuRat (talk) 16:55, 25 March 2014 (UTC)[reply]

Very first Ghit for mission control amber suggests they show the console DVIS panel (Digital Voice Intercom System).--Shantavira|^{feed me} 17:00, 25 March 2014 (UTC)[reply]

Yes, they're the DVIS keysets which allow controllers to connect into different voice channels (like a phone conferencing system, where the conferences are on all the time). info. DVIS is the second generation system, consisting of an amber aviation-grade touchscreen; the first generation was VIS, which had a physical button for each channel, and DVIS was replaced with DVICE, which is a more modern LCD touchscreen. Photos of all three are here. -- Finlay McWalterჷTalk 17:16, 25 March 2014 (UTC)[reply]

A little bit more about DVIS operation is here. -- Finlay McWalterჷTalk 17:33, 25 March 2014 (UTC)[reply]

The display looks a lot like the "plasma panel" invented at the University of Illinois in 1964, later marketed by IBM, which used a flat neon based panel which could both store a display and was touch sensitive. It may be a precursor of today's plasma TV displays( which don't have the touch sensitive feature). Edison (talk) 16:51, 26 March 2014 (UTC)[reply]

March 26

Kessler Corporation? A background check.

we can't give legal advice, of which this is a classic case. μηδείς (talk) 03:05, 26 March 2014 (UTC)[reply]

The following discussion has been closed. Please do not modify it.

I recently got a patent and it has been published. Lo and behold a couple of weeks later I got a letter from the above firm offering their services (for a substantial fee) to help me to find manufacturers interested in implementing the invention. I have already set different plans in motion and this offer is not on my map but I am still curious. I want to keep various options open. I wonder if anybody heard about the company (positive or negative) and could shed any light. Thank you --AboutFace 22 (talk) 00:47, 26 March 2014 (UTC)[reply]

You could check with BBB, they have a review: Accredited A+ —71.20.250.51 (talk) 01:06, 26 March 2014 (UTC)[reply]

If you have a patent you should be seeking advice from a patent lawyer, not some random people on the internet. μηδείς (talk) 03:05, 26 March 2014 (UTC)[reply]

Closed per μηδείς (talk) 03:05, 26 March 2014 (UTC) as a request for legal advice.[reply]
μηδείς (talk) 03:05, 26 March 2014 (UTC)[reply]

What is your reason for treating the question as a request for legal advice? It's not a question whose answer requires knowledge of the law or application of legal principles. --173.49.81.186 (talk) 04:21, 26 March 2014 (UTC)[reply]

The BBB is a 501(c)(6) non-profit Accreditation organization. "Background checks" on companies is mostly what they do. In the US, that's the 1st place most people look to check the reputation of a (US) company. —71.20.250.51 (talk) 05:05, 26 March 2014 (UTC)[reply]

I appreciate the comment by the poster who objected to defining my OP as a request for legal advice. It was far from what I had in mind. I want to see if anybody had experience dealing with this company on a practical level. The original issue (obtaining the patent) was perfectly scientific, so this is its extension. --AboutFace 22 (talk) 14:22, 26 March 2014 (UTC)[reply]

This is in no way a request for legal advice. It's a request for information about a business, which was prompted by that business contacting the asker in relation to a published patent (itself a legal document, but that's irrelevant). Even if the question was asking for an opinion on a firm of lawyers, it wouldn't be legal advice ("You don't need to talk to an X lawyer about this" - Possibly legal advice, "Y,Z & Q LLP are a terrible law firm, all of their letters were printed on rabid bobcats which made them extremely hard to read" - not legal advice). As it is, the question isn't even related to patent law, just a company offering to help commercialise an invention, and using patent publications to find clients. MChesterMC (talk) 16:47, 26 March 2014 (UTC)[reply]

This is a reference desk. Maybe the OP could specify some matter we can help with, like the company's contact numbers, any news they have been mentioned in in the last few years. WE cannot give our own opinions of the company itself (see the section on opinions at the top of this page) or offer original research WP:OR or comment on their reliability or busniess practicess, which my subject us to suit for defamation, or give advice on patents ourselves, since that is indeed legal advice. IP 71 has given a helpful comment. μηδείς (talk) 17:34, 26 March 2014 (UTC)[reply]

The OP didn't ask for opinion. (His request was certainly not umambiguously a request for opinion, and arguably not one.) Even if he did, the helpful response would be to tell others to refrain from offering opinion, not to hastily declare the question "closed". Posters of questions may not always phrase the question the best possible way at first; useful answers can nevertheless be provided, not necessarily to the original question as asked, but to the question that the OP should have asked instead. In this case, the OP was really asked for input to help to form an opinion about an entity. What other people may have "heard" need not be subjective opinions, they can be verifiable facts. They can take the form of honors and recognitions, rankings, metrics of past performance, records of criminal conviction/civil penalties etc. --173.49.81.186 (talk) 02:51, 27 March 2014 (UTC)[reply]

IP;DR. μηδείς (talk) 18:07, 27 March 2014 (UTC)[reply]

Again I appreciate all comments. I've been surprised by the reaction. No hard feelings though. Wikipedia is a great place and the issue actually kind of faded in the background for me now. --AboutFace 22 (talk) 14:32, 30 March 2014 (UTC)[reply]

Dowmo alloy electrical resistivity vs temperature

Does anybody know where I can find information on the resistivity versus temperature characteristics of "dowmo" alloy (tungsten & molybdenum 50:50)? I need it over the range 300 K to at least 1200 K, so Mitchell's formula is unlikely to be accuate. Worthing's formula might be. I found nothing via Google. I know it's about the same as pure tungsten at the high end of the range, so even a single measured value near 300 K would help a lot. 120.145.131.60 (talk) 03:14, 26 March 2014 (UTC)[reply]

Light bulb brightness in circuits

Hey everyone, I have two questions relating to physics and electricity. I think I did them right, but I just wanted to double check:

A resistor measuring 330Ω and 3.1V, and an LED measuring 190Ω and 1.8V, are placed in series, both with a current of 9.5mA. If another resistor is added in series to the circuit, would the brightness of the LED change? I said no, because if the current is the same throughout the entire circuit in series, there would be no difference if another resistor was added, only the voltage would change.
The first resistor and LED (from the above question) are placed in series again, but the two are in parallel to a third resistor. If the resistance of both resistors increases, what would happen to the brightness of the LED? Here I said that the brightness would change because while voltage is equal throughout, and resistance increases, current must decrease throughout the circuit and so the brightness decreases.

Was I right? Thanks everyone. 64.229.204.125 (talk) 03:18, 26 March 2014 (UTC)[reply]

The question is incompletely stated. The current and voltage are also determined by the rest of the circuit, so rearranging things can change both the total voltage and current. It is likely that the implicit assumption that you were intended to make (but this reflects badly on whoever set the question) is that the source of the current is a battery or power supply of negligible internal resistance (this should have been made explicit in the question). From the initial setup, this is a voltage of 3.1V + 1.8V = 4.9V. You were then presumably supposed to make inferences about the voltage vs. current characteristics of each component and how this would affect the current in the diode in each new configuration. This gives you different results in the first question. In the second question, while your final answer is correct, the voltage does not stay the same throughout due to the different voltage vs. current characteristics of a LED and a resistor. —Quondum 04:02, 26 March 2014 (UTC)[reply]

IF the current through the series circuit is constant then you are right that the LED brightness doesn't change. Two problems: a) it's rather unusual to power a circuit from a constant current supply. For example a battery gives a constant voltage and adding a series resistor would reduce brightness. b) Ohm's law applies to the resistor exactly so 3.1V across a 330 resistor causes a current of 9.394mA, not 9.5mA. (A LED has non-linear I-V characteristic so Ohm's law cannot apply to it.) I have provided links to articles in Simple Wikipedia that may be helpful. The same subjects are covered in higher detail in Wikipedia.
IF the supply is a constant voltage then the 3rd resistor across the supply has no effect on the current in the LED, and you are correct that the LED brightness decreases when its own series resistor is increased. 84.209.89.214 (talk) 01:14, 27 March 2014 (UTC)[reply]

Sorry, I should elaborate on a few details. 1) There are only 2 significant digits to work with, so 330Ω was rounded up. 2) the circuit was completed on a breadboard, with the current being direct, but plugged into a power outlet. 64.229.204.125 (talk) 01:55, 27 March 2014 (UTC)[reply]

The exact behaviour will depend on the characteristics of the power supply. Many lab DC power supplies are constant voltage (to 2 s.f.), but some LED power supplies attempt constant current. Dbfirs 13:28, 27 March 2014 (UTC)[reply]

A note regarding rounding of the resistor value: 330Ω is widely recognized as a preferred value in the standard E12 series. These are values that approximate an exponential series and have already been rounded to 2 significant figures. The picture shows a typical resistor whose color bands orange-orange-brown-gold identify its value as 330 ohms +/-5%. 84.209.89.214 (talk) 13:21, 28 March 2014 (UTC)[reply]

Military careers

Is the military a good career for people who find desk work stressful? As although military is stressful it's a different type of stress to that of desk work. 82.132.244.5 (talk) 14:11, 26 March 2014 (UTC)[reply]

Yes, there's very little chance of being blown up by a roadside bomb if you're merely working at a desk. You might also want to look for numbers on the quantity of combat troops vs. the quantity of support personnel, many of which have... desk jobs. ←Baseball Bugs ^{What's up, Doc?} carrots→ 14:21, 26 March 2014 (UTC)[reply]

Different people find different types of careers "stressful" based on their aptitude and personality. That is, while one person may be energized and well suited to something like being a police officer, another person would find it highly stressful and unpleasant. There's no universal set of values for this thing. If you are in the United States and are interested in a career in the U.S. military, it is often recommended that you take the Armed Services Vocational Aptitude Battery test, which is designed to find a recruit's strengths and weaknesses, hopefully to place them on a career track to which they are well suited. I see by the geolocation of your IP that you are in the UK, so perhaps the UK has a similar method of evaluating potential military recruits for jobs they are well suited for. You may want to into that. --Jayron32 16:45, 26 March 2014 (UTC)[reply]

What did Folding @ Home accomplish?

I participated in the Folding @ Home program for a few years with a couple PS3s and home computers. The promise was that it might cure diseases and discover new treatments. But did it? --209.203.125.162 (talk) 17:28, 26 March 2014 (UTC)[reply]

Have you read Folding@home? It lists several conditions (such as Alzheimer's and Huntington's) where the program has been useful. I don't believe the project is intended to find cures itself, but to provide information that other researchers can use. Rojomoke (talk) 17:51, 26 March 2014 (UTC)[reply]

I seem to recall a few instances where it produced homology models that were usable starting points for molecular replacement, but I don't really have any sources for that. Actually, here's a source, although this was actually using data from Foldit not from Folding@home: Nat Struct Mol Biol. Sep 18, 2011; 18(10): 1175–1177. For what it's worth, it still seems like traditional homology modeling has a much higher success rate. (+)H₃N-Protein\Chemist-CO₂(-) 18:28, 26 March 2014 (UTC)[reply]

Eating nitrocellulose

What would happen if you eat some nitrocellulose?

Is it poisoning, or would it be much like eating regular cellulose? 91.77.188.8 (talk) 17:43, 26 March 2014 (UTC)[reply]

I am assuming that you are asking what would happen to a typical adult human being when he eats nitrocellulose? 140.254.227.69 (talk) 17:57, 26 March 2014 (UTC)[reply]

According to the encyclopedia britannica, nitrocellulose is used in gunpowder and explosives. Hmmm... I don't think you want to ingest that, because that sounds like smoking a cigarette. A pack of toxins into your bloodstream. 140.254.227.69 (talk) 18:02, 26 March 2014 (UTC)[reply]

Being explosive doesn't automatically mean it's not edible. Nitroglycerin, for example, is ingested as a heart medication. See Nitroglycerin#Medical use. StuRat (talk) 00:55, 27 March 2014 (UTC)[reply]

It's still a drug. Drugs that are intended to be ingested into the body should be carefully considered (including receiving advice from a licensed physician), because the ordinary person is unlearned in medicine and chemistry. 164.107.189.137 (talk) 20:40, 28 March 2014 (UTC)[reply]

I'm not advising that anyone take it as a med, just noting that it is prescribed as such. StuRat (talk) 20:22, 29 March 2014 (UTC)[reply]

I must add that safeness of chemical compounds has nothing to do with the name. The name is just used to describe the chemical structure or components. In order to identify the safeness of a compound, you may want to look up Material safety data sheet. 140.254.227.69 (talk) 18:12, 26 March 2014 (UTC)[reply]

According to the Nitrocellulose Safety Data Sheet, there are several problems associated with even getting close to the substance, let alone ingesting it. Always handle unknown chemicals with care. Wear gloves and goggles and maybe a lab apron, though, in most cases, you probably don't need a lab apron. (I never used one, and gloves are usually appropriate in a biomedical lab that deals with biohazards and stuff.) 140.254.227.69 (talk) 18:26, 26 March 2014 (UTC)[reply]

Nitrocellulose paper is very commonly used in western blots as a substrate onto which to transfer protein from an SDS gel, and although it is (obviously) flammable if exposed to an ignition source, I don't think it's quite so super hazardous to handle as long as you don't set it on fire. To answer the OP's question though, no, you shouldn't eat it. FYI, that's the answer to virtually every question that starts with "Is this [random thing I found in lab] safe to eat..". The answer is always "no". (+)H₃N-Protein\Chemist-CO₂(-) 18:40, 26 March 2014 (UTC)[reply]

Indeed, "should I eat it?" should always be followed with the question "is it food?" If the latter is "no" a safe assumption is that the former should be "no" also. --Jayron32 23:13, 26 March 2014 (UTC)[reply]

Is it possible to return the pulse by CPR when having asystole in the heart?

Someone told me that the pulse can not return by CPR if the heart has total asystole. He told me that when the pulse return it says that the heart had only a few contractions before, and that is the reason why the pulse returned (about 10 for a minute). Is it right or not? 213.57.123.85 (talk) 18:48, 26 March 2014 (UTC)[reply]

CPR (but not defibrilation) is still indicated in case of asystole. Recovery, while unlikely, is still possible. Ruslik_Zero 19:20, 26 March 2014 (UTC)[reply]

I know that CPR (without defbriliation) is still indicated in case of the asystole. But it's definitely not the question... The question is What had been under the chest before you returned the pulse. Was it total asystole or was it a few contractions. I hope I explain myself well, because English is not my mother language. 213.57.123.85 (talk) 19:54, 26 March 2014 (UTC)[reply]

During a cardiac arrest, the aim is to defibrillate the patient to achieve a return of spontaneous circulation (ROSC). Asystole is a non-shockable heart rhythm (i.e. it is not to be defibrillated). If the patient is in asystole, CPR is performed to try and change the heart's rhythm into a shockable rhythm, so that the patient may then be defibrillated. (I am an advanced life support trained final year medical student.)

The masses and tensions of violin strings

I've been trying to find masses and tensions for a real life violin string, so that I can make realistic physics problems about the wave speed and frequencies. All I can find in web searches are physics problems posted to sites like answers.com. They give masses on the order of ~0.500 grams. Is that realistic? That tends to lead to tensions on the order of hundreds of Newtons. Are violin strings really under tensions that huge?Inkan1969 (talk) 19:27, 26 March 2014 (UTC)[reply]

Basic physics of the violin points us to this chart which gives tensions. -- Finlay McWalterჷTalk 19:42, 26 March 2014 (UTC)[reply]

Thank you for the link. I couldn't find an article like that.Inkan1969 (talk) 19:48, 26 March 2014 (UTC)[reply]

This (which assumes equal tension on each string) gives corresponding gauges in metres, and this table (from the same folks) gives gauges and mass per metre - note that these are for natural gut core strings; steel core strings will surely be quite different. -- Finlay McWalterჷTalk 20:10, 26 March 2014 (UTC)[reply]

These are tensions in the 40 to 80 N range, so not quite in to the hundreds. Guitar strings are tensioned to about double that. A pretty thorough list of tensions for various strings (for guitars and related instruments) is here. -- Finlay McWalterჷTalk 20:28, 26 March 2014 (UTC)[reply]

Clean burning

Are there any solids that burn entirely without leaving any leftovers on the surface they have been ignited at.

I know some liquids like alcohol might have such properties, but it what about solids? 91.77.160.11 (talk) 20:04, 26 March 2014 (UTC)[reply]

A thought in the right direction but not a full response. In order to leave no leftovers the combustion reaction would have ideally have to be a complete combustion, where all the reaction products are gas, which then disperses.

One class of solid materials which as far as I know undergo complete combustion to gas are explosives, However they do so sufficently quickly that they also take out the ignition surface.Sfan00 IMG (talk) 22:56, 26 March 2014 (UTC)[reply]

I agree that leaving no left-overs implies the reaction products are solely gases, but that's quite common: for example pure sulfur (solid) burns in oxygen to give sulfur dioxide (gas). Incidentally, some solids can completely dissociate into gases without burning: ammonium chloride (solid) becomes ammonia (gas) and hydrogen chloride (gas). --RexxS (talk) 23:09, 26 March 2014 (UTC)[reply]

Diamond, though again the fire will damage the fireplace. Jim.henderson (talk) 23:03, 26 March 2014 (UTC)[reply]

Nitrocellulose comes pretty close. Magicians use it as "flash paper" because after burning it leaves almost no visible ash or smoke. Nitrocellulose was also used as the basis for early types of smokeless powder, the lack of solid particulate in the combustion process is what makes the smokeless (since smoke is basically solid combustion products dispersed in air). --Jayron32 23:11, 26 March 2014 (UTC)[reply]

If you burn them hot enough, the solid hydrocarbons will produce only carbon dioxide and water vapor. (If you can't manage a hot enough flame, you get soot.) --Carnildo (talk) 02:59, 27 March 2014 (UTC)[reply]

Regarding the comment that only gases should be produced: I agree, but keep in mind that they may not be gases at room temperature, only at the combustion temperature. Water vapor is a good example, but there may be other products which are either liquids or solids at room temperature, but are vapors when they leave the fire. Of course, solids that then redeposit when they cool may not meet your standard for "clean burning", but liquids which recondense might, if they are clear and harmless, like water vapor. StuRat (talk) 03:12, 27 March 2014 (UTC)[reply]

As long as it's partial pressure remains below the vapor pressure, the water vapor produced during hydrocarbon combustion remains a vapor at ambient temperature as well. It wouldn't start condensing unless the air was locally at 100% relative humidity for the ambient temperature. --Jayron32 08:43, 27 March 2014 (UTC)[reply]

Right, but it will eventually condense somewhere, even if it has to wait for winter or travel to Antarctica. With water this isn't a problem, of course, as it still qualifies as "clean". StuRat (talk) 13:21, 27 March 2014 (UTC)[reply]

Ashless filter paper is specifically designed to burn without leaving a solid residue, for use in labs. shoy (reactions) 12:52, 27 March 2014 (UTC)[reply]

A lump of pure carbon, burned in a sufficient quantity of pure oxygen could only produce CO and CO2...right? You can only get compounds of carbon and oxygen formed from it - and CO and CO2 are the only two. The only other possibility is that you get some unburned carbon left behind (maybe as soot) - but if you're at the ignition temperature, that too will burn. So the resulting mix could only possibly contain O2, CO and CO2. I'm sure there are a bazillion other reactions for which that's true.

But if you're burning it in air - which is an incredibly complex mix of gasses, then there could be all sorts of other byproducts of combustion, and ruling out the possibility that any of those are not gasses would be tricky. So at some level, it's going to be hard to prove that you'd get perfect combustion with only gaseous byproducts with any solid material as the starting point...but at a practical level, I'm sure there are many, many combustion reactions that are "close enough". SteveBaker (talk) 14:46, 27 March 2014 (UTC)[reply]

Reversible cycle

A classic method of showing that the Carnot cycle has the maximum efficiency between two given temperatures depends on its reversibility.: If a more efficient heat cycle existed, the reversible Carnot cycle can be used as a heat pump to pump all the heat lost by the more efficient engine out of the heat dump and either use it as work or return it to the heat reservoir. But the two engines combined then form a 100% efficient perpetual motion machine. A more detailed explanation of that scenario is shown here. The Carnot+better combo can also be used to make heat flow from the colder dump to the warmer reservoir without any work.

Now a reversible cycle can be represented as a well defined closed loop on a P-V graph. Here's the Carnot graph. But what confuses me: Isn't ANY cycle that can be represented as a well defined closed loop on a P- V diagram a reversible cycle? Like the Otto cycle and the diesel cycle? Then is reversibility actually a property not exclusive to the Carnot cycle? Further, couldn't I then join a Carnot cycle with a less efficient but reversible cycle (with a well defined closed loop) to make a perpetual motion machine? Thank you in advance.Inkan1969 (talk) 20:22, 26 March 2014 (UTC)[reply]

Our article at Otto cycle states that this cycle comprises four distinct processes - two of them reversible and the other two occurring at constant volume but not reversible. Therefore I don't think it is correct to assume the Otto and the Diesel are reversible. Dolphin (t) 22:03, 26 March 2014 (UTC)[reply]

Clearly Otto is reversible, while Diesel is not, giving us leseiD if we attempt to reverse it. :-) StuRat (talk) 01:42, 27 March 2014 (UTC) [reply]

Wouldn't any cycle which starts with a chemical fuel need to produce that chemical fuel again in order to be fully reversible ? StuRat (talk) 01:42, 27 March 2014 (UTC)[reply]

The air standard cycles, such as Otto and Diesel, disregard the practicalities of where the heat comes from. In order to determine a thermodynamic efficiency, they simply postulate that there is an increase in temperature and pressure at a constant volume. An increase in temperature and pressure at a constant volume won't be reversible. (Good point about the palindrome.) Dolphin (t) 05:52, 27 March 2014 (UTC)[reply]

I thought Palindrome is the other name for Wasilla Airport? ;-) 24.5.122.13 (talk) 06:33, 27 March 2014 (UTC)[reply]

March 27

Meth addicts

Whenever you see photographs of meth addicts, they usually have scabs all over their face, as if they pick at their skin. Why is that? Thanks. Joseph A. Spadaro (talk) 05:02, 27 March 2014 (UTC)[reply]

According to this, they pick their skin obsessively due to a sensory hallucination of bugs crawling beneath the skin. The technical name for that is delusional parasitosis, also known as "crank bugs". Red Act (talk) 05:24, 27 March 2014 (UTC)[reply]

Thanks. Wow, pretty disturbing stuff in that link. Almost sorry that I asked! Ughhhhhhh. Thanks. Joseph A. Spadaro (talk) 15:58, 27 March 2014 (UTC)[reply]

Isn't a secondary reason that they don't feel pain when scratching open their cheeks ? StuRat (talk) 14:11, 28 March 2014 (UTC)[reply]

Angle of penis

Links in this question are NSFW.

The article Erection provides a table with the distribution of erect penis angles. But what does it tell us, how is the angle measured? Few penises are completely uncurved. Take the image in the article: at the root it has an angle of about 70° while at the glans it has an angle of about 35°. Which of the values is the correct one? Or does one have to draw an imaginary line through root and glans and measure the angle of this line?

I have no access to the original paper. Does anybody know or can look it up in the paper?

Also asked on Talk:Erection#Angle a few days ago, but with no answers so far. --31.16.110.207 (talk) 10:26, 27 March 2014 (UTC)[reply]

The excitation phases of an orthodox healthy phallus are quantifiable in terms of a 2-D Euclidean vector (Length, Angle) in the vertical plane, where Angle is readily estimable within ranges of 10 degrees or more, as given in the cited article, from photographs. This data does not apply to the minority of phalli that exhibit curvature, whether the origin of their additional vector curl component be congenital or pathological as observed by Gigot de Peyronie in 1743. Popular culture offers only qualitative, not quantitative, insinght to this non-linear male morphology, as evidenced in the Limerick prose: There was a young fellow of Kent / whose prick was remarkably bent. / To get over the trouble / he bent it in double / so instead of coming he went. 84.209.89.214 (talk) 17:32, 27 March 2014 (UTC)[reply]

Thanks. That's my new favourite limerick. InedibleHulk (talk) 20:10, March 27, 2014 (UTC)

As tedious as this point is, I add that the penis would more normally be described as having curvature rather than curl. Both in regular usage and strictly mathematical senses. Curl applies to vector fields. Penises are usually experienced as localised rather than distributed phenomena.

Agreed, and please sign your posts. The non-linear turgid phallus has a local curvature that could be quantified by a curvature vector, or in a more general 3-D parametric curve fitting method using B-spline analysis and control points.

However existence of distributed phallo-erectile vector fields quantifiable by time-dependent del operators cannot be ruled out. In practice such fields would be quantifiable by teams of volunteer males, selected preferentially for non-paraphilian Hypersexuality but disqualified for hyposexuality, and each fitted with a recording plethysmograph and satellite locator. Such phallometric field data, if collected, would be of direct value to the pornography industry, by extension also to planners of male-directed advertising, and might serve to validate B.Singer's model of sexual arousal (1984) which postulates vectorial responses from subject(s) towards attractive object. 84.209.89.214 (talk) 12:49, 28 March 2014 (UTC)[reply]

This is such jargon its unbelievable. — Preceding unsigned comment added by 84.92.32.38 (talk) 09:15, 30 March 2014 (UTC)[reply]

How do coil cords get kinked up the way they do?

Here's a link to a YouTube video on how to untangle a coiled cord [6]. My question is: how does a coil cord seemingly suddenly develop a "reversal turn" in the middle of the cord in the first place? I have a hard time visualizing it happening, because the cord on either side of the "turn" looks normal, and certainly nobody did anything like the opposite of the procedure in the video to put the "turn" there. Is there a better way than what's in the video to fix the problem? I fixed a coil cord once by shifting the "reversal turn" to one end, one turn at a time. But the thing is, the cord didn't look quite the same afterward. The length of the cord where the shifting of the "reversal turn" has passed through became visibly less tight than before. --96.227.60.84 (talk) 11:50, 27 March 2014 (UTC)[reply]

Original research on my part, but I find the easiest way to fix a telephone cord is to suspend the handset and allow it to spin round a few times, thus more or less correcting itself. How does it get like that? What seems to happen is that someone picks up the handset say with their right hand, and after a while they might pass it to their left hand in order to write something down. It then goes back to their right hand before replacement and during all this it somehow does a complete turn. Over the course of a few weeks, the cumulative twist builds up.--Shantavira|^{feed me} 13:03, 27 March 2014 (UTC)[reply]

Yes, I was just about to post the same comment when I read Shantavira's explanation above. I used to go round the phones at work every week or fortnight, giving them a few twists in the opposite direction (usually anticlockwise), or spinning them to reverse the effect of people adding a clockwise twist when they replaced the handset. Perhaps we had an inadequate proportion of left-handed people? It never happens with my phone at home. Dbfirs 13:12, 27 March 2014 (UTC)[reply]

I've found two seemingly contradictory ways to keep a cord from tangling:

1) Constrain it more. Use zip ties to hold it all together so it can't twist. It also helps to avoid putting as much stress on it when coiling it up, by moving your body over or under the cord when you see it starting to twist, to relieve the stress.

2) Constrain it less. Just leave it all in a pile, rather than trying to make it look neat. You can put it into a trash can, for example, and just let it flop where it will. This puts less twisting stress on it, so the coils don't need to move to relieve the stress. StuRat (talk) 13:16, 27 March 2014 (UTC)[reply]

While cords can be an everyday frustration, understanding the dynamics via knot theory is a rigorous field of math that addresses some of these issues. While it historically was a "pure" and abstract study, it has proven useful for describing certain behavior of DNA. Some relevant articles for cords are Reidemeister_move, twist_(mathematics) and writhe. For the DNA applications, see Writhe#Applications_in_DNA_topology and DNA_supercoil, or check out the work of Craig Benham [7] if you want to see some of the detailed math. SemanticMantis (talk) 16:09, 27 March 2014 (UTC)[reply]

It seems to me that finding ways to prevent regular cords, ropes, wires, etc., from tangling was already a rather practical application of this field of study. It's not just a homeowner annoyance, to people like construction workers who deal with such problems every day, it's a real-world problem. Those who design products like "hose caddies" also must take twisting and tangling into account.

For pure science apps, though, we also have the twisting of tornadoes, especially multiples, and the entanglement of the Sun's magnetic lines of force (which is linked with the sunspot cycle), and many others. StuRat (talk) 14:00, 28 March 2014 (UTC)[reply]

Weights and rest

I heard that weight training (doesn't matter which part of body) shouldn't be done more than two days in a row i.e the third day should be resting or cardio if needed. Is it scientifically sound to say that even if i give rest to my body parts and concentrate on different part the next day still my whole body needs a day of rest ?? — Preceding unsigned comment added by 119.235.54.187 (talk • contribs) 11:54, 27 March 2014‎

Muscles need time to repair themselves. However, I've read that for young people this is a bit different. E.g. in the US army they let the recruits do many pushups every few hours every day. Count Iblis (talk) 15:35, 27 March 2014 (UTC)[reply]

LOL @ "let"...as if the recruits would do constant push-ups, if not held back by their concerned, overprotective drill sergeants. StuRat (talk) 14:18, 28 March 2014 (UTC) [reply]

The lucky ones are allowed to practice this variant. Count Iblis (talk) 18:03, 28 March 2014 (UTC)[reply]

What's the point?

Imagine for a moment that you're able to get one of these things to work. What's the point? As soon as you harness it to do regular work, won't it stop? I can't quite imagine all these people trying for generations to make a self-perpetuating plaything. Nyttend (talk) 12:31, 27 March 2014 (UTC)[reply]

Yes, if we harness it to do regular work it will stop. But it will also stop before being harnessed to do work, just as a result of friction between the moving parts.

Prior to the industrial revolution all work was done by human workers or by animals. Around the start of the industrial revolution, simple machines were invented and built. These were a source of great interest but they all required a person, horse, donkey etc. to drive them. There arose a fascination with the idea of one of these new machines that would run by itself, without input by a person or an animal. In those early days there were no electric motors to conveniently drive these machines so there was a serious incentive to find something (other than people or animals) that would do so. Many people tried, unsuccessfully, and their creations became known as "perpetual motion machines". Ultimately, it was the electric motor and the reciprocating engine that would be put to use driving machines. Dolphin (t) 12:44, 27 March 2014 (UTC)[reply]

Folks who believe in these things hope they can be improved to be "over unity", meaning they generate energy. Simply breaking even, being "at unity", is, as you say, nothing more than a magical toy. -- Finlay McWalterჷTalk 12:49, 27 March 2014 (UTC)[reply]

Well, by all accounts the universe is a perpetual motion machine, creating space and dark energy and mass-energy out of nothing. I wouldn't rule out that someone can come up with a way - who knows, maybe even something that uses magnets - maybe they just need the right idea. But these ... aren't them. Wnt (talk) 13:28, 27 March 2014 (UTC)[reply]

If you could make this (or any other 'perpetual motion' machine) work, then there are two possibilities as to how you hypothetically managed to do that:

You somehow removed 100% of the friction and air resistance from the thing. That would require (at the very least):
1. Encasing it in a vacuum that's even more empty of stray atoms than deepest interstellar space to avoid all of the air-resistance.
2. To somehow avoid atoms that evaporate from the surface of the machine's parts and the container around it from gradually polluting your vacuum and causing "air resistance".
3. You'd also have to avoid photon pressure from remote light sources - so the machine would have to be kept in complete darkness.
4. ...and keep it from being bombarded with radiation of all kinds - including hard-to-stop things like neutrinos...but to do that perfectly requires that you encase it in an infinite thickness of some screening material.
5. Microscopic tidal forces on the machine due to gravitational forces from other objects in the universe would cause the machine to microscopically bend and flex - which would create heating, and therefore slow it's motion...so I guess your machine would need to be placed infinitely far away from any other masses such as galaxies and such.
6. Magnetic fields would also pose a problem because they to can cause "tidal" forces...so you'd better not even think about building a machine with magnets inside it!
You've somehow made it work DESPITE the air resistance, friction, tidal forces, etc, etc. If you could do that then it would actually be an "over unity" machine because it would produce waste heat. You'd be able to use a big pile of them to heat your home during cold winter nights - or to heat water to boiling point and have it run a steam engine to power your car! (All free energy ideas ultimately reduce to some nut wanting to run their car for free...I don't know why that is.) Since the laws of thermodynamics don't permit "over unity" operation, we know that this can't happen.

So even a perpetual motion machine that spins and does nothing is impossible. The need to avoid all of those things that would eventually slow it down is an annoying practical problem. As a "thought experiment", you could wave away all of those annoying objections, and the laws of thermodynamics would obediently allow you to build a machine that spins forever - an "at unity" machine rather than an "over unity" device. But as a practical possibility, even with the most extreme engineering imaginable, you can't make a perpetual motion machine that runs at exactly unity.

Perpetual motion of any kind is simply not worth consideration...it can't happen in a real universe.

SteveBaker (talk) 14:29, 27 March 2014 (UTC)[reply]

Well, as I said above, the universe itself seems to run by perpetual motion. In this case, entropy doesn't decrease, so there's no violation of the laws of thermodynamics, even as the amount of matter and energy continually increases. There just needs to be more and more space. I suppose if you had some kind of wannabe 'wormhole generator' that pinches off little vesicles of space and sends them sailing away into some higher dimension, you might be able to similarly claim increased entropy even while producing an unlimited stream of energy. It just requires some ... inspiration. Wnt (talk) 16:48, 27 March 2014 (UTC)[reply]

Superfluid helium-4 would seem to qualify for "unity" perpetual motion, if placed in just the right environment and stirred; mere superconductor rings with current flowing qualify at the electron level. I think. Issue: apparently the helium-4 and superconductors both have some non-superconducting component, and it's not clear to me that doesn't inevitably have a way to stop the motion over time. Wnt (talk) 16:54, 27 March 2014 (UTC)[reply]

Videos of a Brownian ratchet device apparently extracting rotational energy from random particle motions. These perpetual motion demonstrations and the automatic watch pictured give Maxwell's demon some explaining to do. 84.209.89.214 (talk) 16:34, 27 March 2014 (UTC)[reply]

You don't think it's worth evaluating the energy balance in that "granular gas" demonstration (before you start suggesting that the demonstration somehow challenges known physics)? Even if we concede that a bunch of ping-pong balls bouncing around in a plexiglass arena were a reasonable approximation of gas molecules... what energy source is supplying the ping pong balls (or gas molecules)? There's a "thermal gradient" with energy being supplied at the bottom of the container (the machine that's lobbing those ping-pong balls upwards!) That's not perpetual motion, it's extraction of energy from an external heat reservoir. Once that external energy supply runs out - i.e., when you unplug the ping-pong ball "popper" machine - the balls stop bouncing around, and the device goes quiescent. Throw on top of this the millions of "technicalities" about why ping-pong balls are terrible models of gas molecule brownian motion - and that very interesting ratchet demo is actually further evidence for why the Maxwell's demon though-experiment actually shows that the method fails to extract perpetual energy from the gas.

If you want other physicists to explain Maxwell's demon, all you have to do is read any textbook on thermodynamics or any reputable physics website on the internet. Here's a nice one I found at Auburn University, with a fun cartoon of the demon: Maxwell's Demon, from a lecture series on "concepts of science." You can also read our article, why the ratchet fails. Ultimately, it comes down to using a correct definition of thermal equilibrium in the thought-experiment; or, in the practical demonstration, making a device that would hypothetically work, without actually supplying external energy. Nimur (talk) 17:13, 27 March 2014 (UTC)[reply]

The page of videos you linked, made by the Department of Science and Technology of the University of Twente, makes no claim of perpetual motion or free energy. The automatic watch is, of course, wound by motions of the wearer and will run down if not worn. -- BenRG (talk) 17:34, 27 March 2014 (UTC)[reply]

As I said in the last thread, a "perpetual motion machine" is a device that violates the first or second law of thermodynamics and not, despite the name, one that moves forever. -- BenRG (talk) 17:34, 27 March 2014 (UTC)[reply]

Extraction of useful energy on a large scale from tidal forces is uncontroversial, yes? SB suggests above the impossibility of isolating a device such as Brownian ratchet from all "Microscopic tidal forces on the machine due to gravitational forces from other objects in the universe". Please do not interpret the present scientific consensus that perpetual motion is impossible, as it would violate the first or second law of thermodynamics, as also providing the definition of PM. For that we should be allowed our individual understandings of perpetuality that are essentially as finite as ourselves: "For generally the infinite has this mode of existence: one thing is always being taken after another, and each thing that is taken is always finite, but always different. Aristotle, Physics, book 3, chapter 6. 84.209.89.214 (talk) 18:20, 27 March 2014 (UTC)[reply]

You seem to be suggesting that any machine could be considered a perpetual motion machine, for sufficiently small values of "perpetual". I am not sure this is a useful approach - rejecting a scientific definition in what is essentially a question of science (and engineering). - Eron^Talk 18:29, 27 March 2014 (UTC)[reply]

Perpetual motion machines, as defined by a device that outputs more energy than it takes in and can do this indefinitely, violate the first law of thermodynamics. It doesn't matter whether the scientific consensus supports the first law or not--by definition, such a device violates the first law. --Bowlhover (talk) 18:40, 27 March 2014 (UTC)[reply]

Alright... take a region of intergalactic void. Lay two pieces of cable from one end to the other. One is anchored to a heavy object at one end, one is anchored to a heavy object at the other. They receive minimal energy from other regions of space. Nonetheless, as the universe expands, inevitably the two heavy objects drift further and further apart, causing the cables to move relative to one another. Plant generators along the strands to take advantage of this motive force, and enjoy your perpetual motion machine. Wnt (talk) 00:24, 29 March 2014 (UTC)[reply]

Neat but... Wouldn't the molecules in the links of the cables and generators also expand at the same rate and so generate no relative motion? draw your mechanism on an expanding soap bubble. I'm not saying you are wrong, but may have missed something. Greglocock (talk) 00:43, 29 March 2014 (UTC)[reply]

Assuming the temperature remains the same (or colder) the optimum interatom distance should not increase. Of course, the expansion of space should tend to spread the atoms apart, but the point is that a tension force should develop, with the heavy weight at one end determining which way the cable ends up moving under this tension to keep a stationary center of mass. (I recognize of course that this is not a practically workable perpetual motion machine, and that harnessing local gravitational variations in the Solar system would be way more productive, but my point is: the universe is a perpetual motion machine and this energy is extractable, and maybe there's a better way to extract it yet to be discovered. I hate it when people tell us that it's possible there could be a Big Rip or the decay of a false vacuum or the collapse and rebirth of the universe and half a dozen other impossible things, all of which I'm supposed to believe before breakfast, only to be lectured just afterward that it's absurd for me to think perpetual motion can be real. Wnt (talk) 03:59, 29 March 2014 (UTC)[reply]

The incorrect assumptions regarding the metric expansion of space your little "ball and cable" thought experiment introduce are too profound to counter here, so just read the article please. Let me quote the relevent bit, and hope you understand it " Once objects are formed and bound by gravity, they "drop out" of the expansion and do not subsequently expand under the influence of the cosmological metric, there being no force compelling them to do so." Your balls-and-cables will not drift apart under the "force" of the metric expansion of space. They will remain stubbornly stable and do no work for you. Thermodynamics wins again. --Jayron32 04:25, 29 March 2014 (UTC)[reply]

I was careful to specify "intergalactic void". Still, to be clear, two objects that are "at rest" relative to one another, and not subject to a net gravitational pull relative to one another over a few billions of years for whatever reason, whether it is balancing of masses or just being very remote, will end up further away from one another. That's what metric expansion of space means. If gravity does not apply the force to move them together, the force needs to be applied by some other means, which implies that usable work could in concept be harvested. I recognize, of course, that as strong as electromagnetic forces are, building cables that is so long but so light that the masses required to anchor them would not attract one another would be quite implausible - the point of the thought experiment is only that "over unity" can be done.

Perhaps a simpler version of the experiment would be more straightforward: suppose you have a very long piece of very light, very weak string floating in intergalactic space. As space expands, the string must break. Where does the energy to break it come from? This is, as I suggested, a very mild version of the Big Rip scenario where supposedly every atom gets torn apart. How can a force be strong enough to pull apart atoms but not exist? Wnt (talk) 13:14, 29 March 2014 (UTC)[reply]

Again, please provide a reference or stop making these over-unity claims. Even if you could "slow down" a distant galaxy by tying a rope to it and harvest the energy, so what? How does that give you free energy? By analogy, suppose a bomb explodes in space and its pieces go flying in all directions. I can in principle tie a string between one piece of debris and another. The string will break, the pieces slow down, and the energy to break it comes from the kinetic energy of the pieces. After I've connected enough strings between enough pieces, all the pieces will be at rest and I'll be unable to harvest any more energy. You seem to be saying that harvesting energy from the universe is somehow the equivalent of over-unity perpetual motion. Did you realize that the universe has nearly limitless starlight, and that harvesting that is much easier than your scheme (and also not free energy)? --Bowlhover (talk) 16:03, 29 March 2014 (UTC)[reply]

Wnt, please provide a reference or stop repeating your incorrect claims about the expansion of space. The universe is NOT a perpetual motion machine. It is NOT true that matter is being created; in fact, the amount of matter in the universe remains constant, and is being diluted as the universe expands. Your thought experiment does not work, practical or not, because objects bound by electromagnetic or gravitational forces don't expand with the universe. Hence, the Earth, the solar system, and even the Milky Way will be exactly the same size 100 billion years from now--because they're not affected by the metric expansion of space!

Lastly, it's true that the amount of dark energy in the universe is increasing. However, if dark energy really is the zero-point energy of space, extracting energy from it is impossible--it is by definition the lowest possible energy. If it's not zero-point energy, then we don't have a plausible physical theory of what it is. You can of course propose a theory where dark energy allows for perpetual motion machines, just as I can propose a theory where dark energy is comprised of angels flapping their wings while dancing on a pinhead, and neither theory is appropriate for the reference desk because no reputable scientist would say either is true. --Bowlhover (talk) 05:20, 29 March 2014 (UTC)[reply]

We had this discussion in a thread above. As the universe expands, Unruh radiation from the retreating "edge of space" produces mass-energy. Indeed, the thread above suggested the universe had only about a Planck mass in a Planck volume early in its development. (Please do correct me if I'm wrong, as I had Bowlhover's impression before, but I think I have it right this time) Wnt (talk) 12:55, 29 March 2014 (UTC)[reply]

I don't know which thread you're talking about, but there is no Unruh radiation from the "edge of space". Please give a reference if you think there is. It's also not true that the universe had a Planck mass early in its development--it's entirely possible that the present-day universe is infinite, which would imply that the universe always had infinite mass and infinite size. --Bowlhover (talk) 16:03, 29 March 2014 (UTC)[reply]

Hunting around, I found a bit of a different reference which gives some sense of the conservation question [8]. I have no idea whether you're going to say this is fringe or old hat, but here's the issue: "While in one view it is speculated that the universe has been evolving with a constant mass but increasing radius, (e.g. Lemaitre [3]), on the alternative view it is variously mentioned in passing that total energy being the sum of the positive energy of matter and the negative energy of the scale factor or radius is what is conserved as the universe evolves [4-6]." And "To obtain Ω ~ 1 immediately after inflation, the mass of the observable universe after the event must not be more than 675kg!" But admittedly that one doesn't say Unruh; someone else mentioned it. Wnt (talk) 22:08, 29 March 2014 (UTC)[reply]

Lots of things that are obvious to us, are obvious because someone discovered it, and stated it as a principle. Many Superseded scientific theories were solid for past generations, but just hilarious fringe theories for us. Take into account too that people back then couldn't understand magnetism and gravity well enough to discard a mechanism build for extracting energy of these too fields. OsmanRF34 (talk) 19:37, 27 March 2014 (UTC)[reply]

Can right handed living organisms be created in the lab?

Synthetic DNA has been created ab initio in the lab, so I was wondering if right handed DNA together with all the right handed variants of the molecules of a simple organism can be synthesized and put together in a cell. Count Iblis (talk) 19:00, 27 March 2014 (UTC)[reply]

Assuming you mean "can" as in "we can do this tomorrow because we know how to do it", then no, I don't think so. We can't even get any sort of totally synthetic thing sustainably reproducing in a lab. AFAIK Synthetic_biology#Synthetic_Cells describes the latest significant published results in the area, but I could be wrong.

Also, I'm not sure what you're getting at with the chirality. We see both right and left-handed DNA in nature, but maybe you are thinking about some novel assembly of the chirality among the important molecules? DNA#Alternate_DNA_structures says a bit about what we do and don't see in nature, and there's a decent table of info at Z-DNA#Comparison_geometries_of_some_DNA_forms. I suspect @Wnt: might have something to add? SemanticMantis (talk) 22:32, 27 March 2014 (UTC)[reply]

I think Count Iblis refers to DNA built from L-deoxyribose. I.e. take a bacterium and create its mirror image. As for the question, I don't know of anything beyond Craig Venter's bacterial chromosome (which presumably could have been synthesized with mirrored molecules without much difficulty, other than the resulting chromosome not working with the enzymes and other molecules in the DNA-free target bacterium). One would have to synthesize a number of proteins from D-amino acids. Icek (talk) 00:38, 28 March 2014 (UTC)[reply]

Ah yes, that makes sense. But your "other than..." strikes me as very apt, and a big obstacle to the fully synthetic creation of some "mirror image" life! SemanticMantis (talk) 15:12, 28 March 2014 (UTC)[reply]

See http://www.darwinismrefuted.com/molecular_biology_04.html.

—Wavelength (talk) 01:40, 28 March 2014 (UTC)[reply]

@SemanticMantis: I have read the articles you linked to, and they are crystal clear. I have two side-questions:

This article Chirality_(chemistry) has it that "all life on Earth being homochiral". Perhaps that phrase should be modified a bit then to mark what is actually homochiral in "all life"?
This article http://www.bbc.com/news/science-environment-26768445 claims to the synthetic dna in cells now being able to reproduce. You added "sustainably". Could you please expand a bit on that? Star Lord - 星王 (talk) 09:53, 28 March 2014 (UTC)[reply]

@DanielDemaret: I'll answer based on my knowledge, but this is not really my area of expertise. 1)I definitley agree that that part of the article should be clarified, but I don't have the expertise (or time to make up for it) right now. I think the issue is sort of the scale of the chirality being discussed. The DNA articles I've linked above both mention different chiralities of the DNA helix being found in nature. So clearly all life isn't homochiral in terms of Nucleic_acid_secondary_structure, but there are other levels of organization above and below that (e.g. quaternary structure, etc.) -- So maybe the "all" is supposed to apply to the chirality of the constituent amino acids, with e.g. all known life using left-handed amino acids (Not sure if that's even true...). Anyway, thinking more on it, I think Iblis was getting at this lower level of amino acid chirality, which does seem to be more uniform across known organisms. However, IMO this makes it even less likely to fully synthesize life that way, esp. since, as I said above, we can't even do the "easy" case yet, using all the same handedness molecules as the natural variants do. Anyway, I'd suggest dropping a note on the talk page, asking for clarification. Hopefully you'll get a response and improvement from an actual subject expert.

2) I'm just being careful and skeptical, and thinking about the ecology of such a critter in a teleological sense (this is closer to my expertise). Reproducing for a few generations doesn't mean it can do so indefinitely, and without human support (we probably wouldn't want that anyway!) Think of an analogy from cloning: Cloning#Dolly_the_sheep was in some sense a "perfect clone", but she experienced rapid senescence, probably because of something to do with her telomeres shortening. Lacking evidence to the contrary, I don't see any reason to believe there is not some kind of breakdown in these synthetic critters that pops up after several generations. Hope that helps, but I better get back to my day job :) SemanticMantis (talk) 15:09, 28 March 2014 (UTC)[reply]

Clear and to the point as ever, @SemanticMantis:, thank you! If I recall the Dolly problem correctly, (I am NOT checking now, this is just from the top of my head), the problem was that the DNA used already had shortened telomeres. This was later rectified with telomerase, which was promoted by Genentech. Star Lord - 星王 (talk) 15:21, 28 March 2014 (UTC)[reply]

Yes, I was asking about creating the mirror image of existing life forms. So, this isn't going to be feasible anytime soon, I guess. Count Iblis (talk) 04:02, 29 March 2014 (UTC)[reply]

It isn't feasible yet, but it might be feasible before too long. Progress in this area has been remarkably rapid, and our synthetic biology article has fallen a bit behind. For example, this report from just a couple of days ago describes the first creation of a fully synthetic chromosome. Looie496 (talk) 15:41, 29 March 2014 (UTC)[reply]

Paid mourning

How does paid mourning work? Ever since reading about it in the Bible as a kid, I've found it hard to understand, since I can't cry when I'm not emotional and not cutting onions. How could paid mourners cry "on command?" 2001:18E8:2:28CA:F000:0:0:BA27 (talk) 19:04, 27 March 2014 (UTC)[reply]

Actors have techniques to enable themselves to cry when necessary. The usual comment you hear is that they think of something sad. Googling "crying on demand" yields various results, starting with this one. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:07, 27 March 2014 (UTC)[reply]

Crying may not even be required but silence, or keening or ululation. Paying mourners dressed in black to march with the body [9]. In New Orleans, they play jazz. You could read Professional mourning but its only a stub. 75.41.109.190 (talk) 12:14, 28 March 2014 (UTC)[reply]

A little more at Funeral#Mutes and professional mourners. Alansplodge (talk) 23:09, 28 March 2014 (UTC)[reply]

March 28

Shark tooth to ID

My daughter found what looks like a shark tooth in her school yard (I'm assuming the previous owner was a grade school kid and not a land-based mako). I've uploaded a few pictures here. Would anyone care to identify what species it's from? I think it's genuine, but if you have reason to doubt that, feel free to say so. Matt Deres (talk) 01:11, 28 March 2014 (UTC)[reply]

I'm no expert, but judging from the size it could be from a great white Hot Stop talk-contribs 01:30, 28 March 2014 (UTC)[reply]

I suspect it was a land shark, delivering a Candygram, that lost the tooth during an attack. :-) StuRat (talk) 03:51, 28 March 2014 (UTC) [reply]

A basic web search turns up [10] - I don't know about this and I'm not enthusiastic about diving into the details there right now, but it seems to offer a way to figure something out. Can the OP or someone else interested try to work through the characteristics and figure out which ones can be deduced from this picture, and if more pictures are necessary? Wnt (talk) 04:36, 28 March 2014 (UTC)[reply]

That's a handy (if daunting) PDF. I'm not going to have time to work through it properly this morning, but maybe I'll send the link on to school with my daughter. Her teacher wanted to use the tooth as a kind of brain teaser anyway; this way they'll get to learn terms like "transverse groove" and "lateral cusplets" as they go. :) Matt Deres (talk) 11:02, 28 March 2014 (UTC)[reply]

Wnt's PDF is about identifying fossilized shark teeth from the Neogene period, so I'm not sure how helpful it will be. John M Baker (talk) 13:44, 28 March 2014 (UTC)[reply]

Since we don't know the tooth's provenance, we really don't know if it is a fossil. Besides, it's a guide for 20 to 3 million years ago, so what's another 20%? Just looking at the pictures it seems to have something in common with Isurus "first (2nd) anterior tooth" - I think I see the central foramen out of focus in the third photo, and the shape and lack of serration seem similar. Working back from that it seems like "root lobes round and extend beyond basal limit of crown" describes this tooth better, which is keyed to Alopias; "basal margin of root broadly arched" also seems to fit that (brings us back to 24b "root lobate") Alas at this point we are back to 23 whether the crown is 'recumbent', which is the sort of glossary term that separates the dilettante from the shark expert. Good thing we're doing this backwards, eh? But 16b lateral cusplets unequal - I think this refers to there being one teeny weeny tooth-like extension on one side and not the other (they use this a bit inconsistently in Figure 16B vs. question 1b...); also 15b; 8b is the lack of serration, whew!; and we're back to not multicusped, not notched. One of these days I'm going to use a taxonomy key the way it's meant to be used, but so far this is about as close as I've come. :) An image search for Alopias teeth turns up lots and lots of examples, and in the first 50 or so none look exactly like this and few much resemble each other either. And I'm not confident about how round is "round" and how far the root has to extend so as not to be "beneath" the crown, and above all, that little cusplet isn't turning up in the pictures I'm sorting through. Maybe it's something else in Lamniformes. There's still a lot that can be done to try to figure this one out. Wnt (talk) 14:40, 28 March 2014 (UTC)[reply]

March 29

Monitoring CNS activity in fine detail

Is there any way to track individual neurone activity in an animal with a central nervous system? Like what time it depolarises and what effects that has on adjacent neurones with which it synapses etc? Is there any way to fix (as in preserve) a brain so that it could be imaged layer by layer, allowing a 3D map of every neurone and every synapse? "This massive chunk communicates with this massive chunk entirely through a massive release of this single neurotransmitter" isn't very informative. --129.215.47.59 (talk) 00:19, 29 March 2014 (UTC)[reply]

It's a hot topic. overview fiber optic optical tomography another whole-body fluorescence etc. And of course the old standbys PETT, fMRI. Wnt (talk) 00:34, 29 March 2014 (UTC)[reply]

If you could combine the Brainbow techniques with those used in the Visible Human Project you would be getting towards what you're looking for in the second part of your question. However, I suspect you would need much thinner slices than those used in the VHP. Richerman (talk) 00:40, 30 March 2014 (UTC)[reply]

Not sure you'll have volunteers lined up around the block to have Cre-Lox recombination constructs genetically engineered to express fluorescent proteins in their brains. Really, while Cre/Lox is the better technology, the ability of Golgi's method to stain entire individual neurons while ignoring others is the more remarkable outcome. I don't know if anyone ever has gotten to the bottom of how it works -- if they do, maybe it will allow a "brainbow" like technique on wild-type samples. Wnt (talk) 02:28, 30 March 2014 (UTC)[reply]

The question is about "animals with a central nervous system" - not humans. We don't usually require volunteers for animal experiments in my experience. Richerman (talk) 08:37, 30 March 2014 (UTC)[reply]

True, I was thinking with a different emphasis there (just saw some interesting news about autism and the six cortical layers)^[11][12] Wnt (talk) 15:12, 30 March 2014 (UTC)[reply]

Significance of a Term

In eletrical engineering the equation v(t)= L di/dt when integrated gives a constant of integration C i.e. , i(t)= 1/Lʃ v(t)dt + C.What is the physical significance of this C.117.202.57.197 (talk) 06:50, 29 March 2014 (UTC)[reply]

You can have any constant current you like in an inductance L, it won't cause any voltage drop. That's your C. 84.209.89.214 (talk) 15:24, 29 March 2014 (UTC)[reply]

If the constant current is 0 then what will be the scenario.i.e. can C be equal to 0.117.194.230.123 (talk) 17:10, 29 March 2014 (UTC)[reply]

Yes. 84.209.89.214 (talk) 17:24, 29 March 2014 (UTC)[reply]

Complex Frequency

What is the physical significance of complex frequency in electrical engineering.What is the physical significance of Laplace Transform.It is not at comprehendible to me from the article.What does it mean by moment in context of Laplace Transform.117.202.57.197 (talk) 06:54, 29 March 2014 (UTC)[reply]

Searching for "Complex frequency" in Wikipedia links naturally to an article about the S plane. While an isolated sine wave can be adequately defined by its frequency and amplitude, because we don't care about when it has a particular phase, the phase relations between wave components of different frequencies are often critical when they are present together. A communication system may exploit two independant signal channels on a single frequency carrier wave by separately modulating two phases separated by 90 degrees of the carrier, with either continuous (analog) or binary (digital) modulations. These technologies and indeed any broadband analysis of frequency-selective circuits need frequency components to be measured in frequency, amplitude and phase i.e. a complex value for each frequency. The Laplace transform is often interpreted as a transformation from the time-domain, in which inputs and outputs are functions of time, to the frequency-domain, where the same inputs and outputs are functions of complex angular frequency, in radians per unit time. "Moment" has a mathematical meaning; Moment-generating function may be helpful.84.209.89.214 (talk) 14:49, 29 March 2014 (UTC)[reply]

The complex frequency

\scriptstyle {S}

describes (in general case) exponentially growing or decaying sinusoids. The imaginary part of the

\scriptstyle {S}

is the angular frequency and the real part gives the rate of growth or decay. The general waveform in question is

v(t)=\mathrm {Re} (Ve^{St})

where

\scriptstyle {V}

is a complex constant known as a phasor.

If it's not clear to you why this represents a sinusoid, then see Euler's formula. Writing

\scriptstyle {V}

as an amplitude and phase

\scriptstyle {V=|V|e^{i\arg(V)}}

and

\scriptstyle {S}

as real and imaginary parts

\scriptstyle {S=\sigma +i\omega }

and applying Euler's formula gives

{\begin{aligned}v(t)&=\mathrm {Re} (Ve^{St})\\&=|V|\mathrm {Re} (e^{i(\arg(V)+\omega t)}e^{\sigma t})\\&=|V|\cos(\arg(V)+\omega t)e^{\sigma t}\end{aligned}}

That is (as promised), an exponentially growing sinusoid of angular frequency

\scriptstyle {\omega =\mathrm {Im} (S)}

and rate of growth

\scriptstyle {\sigma =\mathrm {Re} (S)}

. The amplitude is determined by

\scriptstyle {|V|}

and the phase by

\scriptstyle {\arg(V)}

. Each point on the complex S plane is one complex frequency. The imaginary axis of the S-plane represent sinusoids that are neither decaying or growing, the left half of the plane decaying sinusoids and the right half growing sinusoids. The real axis represents exponential decay or growth with no oscillation and the origin is d.c.. --catslash (talk) 22:47, 29 March 2014 (UTC)[reply]

Component of a force

When a force is resolved into two components why is it that we always only consider a horizontal component and a vertical component that are mutually perpendicular. The forces can be balanced only in these two direction. However a force can be resolved into two components in infinte number of ways as long as it obeys parallelogram law of forces. Did Sir Isaac Newton consider forces as vectors and and apply parallelogram law?117.202.57.197 (talk) 07:00, 29 March 2014 (UTC)[reply]

You are correct about the parallelogram of forces. When resolving a force into two components, it is usually to serve a purpose that necessitates the two forces be mutually perpendicular. Those two forces don't have to be parallel to the local horizontal and vertical, but those two orientations are often the only useful ones. Dolphin (t) 11:03, 29 March 2014 (UTC)[reply]

In problems of statics or dynamics involving an inclined plane it is common to resolve forces along directions parallel to and perpendicular to the plane instead of in horizontal and vertical directions. Newton certainly knew about the parallelogram law - he states and proves it in Corollary I of Book I of the Principia Mathematica, straight after he states the three laws of motion. Gandalf61 (talk) 11:32, 29 March 2014 (UTC)[reply]

Gandalf61's link goes to our article on Principia Mathematica (1910) by Bertrand Russell. He probably would have meant Principia, (1687), by Newton. Nimur (talk) 14:26, 29 March 2014 (UTC)[reply]

Oops ... yes. Thank you. Gandalf61 (talk) 18:36, 29 March 2014 (UTC)[reply]

Similarly to resolving forces in those two directions, in ballistics it's also useful to resolve velocity into both horizontal and vertical components. This is because the horizontal velocity will remain unchanged (ignoring air resistance), while the vertical velocity will be affected by gravity. StuRat (talk) 17:48, 29 March 2014 (UTC)[reply]

Dispersion

Why is it that only prisms are used for optical dispersion. For any optical medium of any arbitrary shape does dispersion takes place or does not take place.Is there restriction on the shape of the object for dispersion to take place.Is it possible to subject this type of dispersion if it occurs to mathematical analysis.117.202.57.197 (talk) 07:05, 29 March 2014 (UTC)[reply]

Glass prisms have been used to demonstrate dispersion ever since Isaac Newton in 1666 but they are not the only objects that display optical dispersion i.e. spreading of a white light beam into its constituent spectral colours. Dispersion occurs in raindrops as every natural Rainbow proves, as undesirable Chromatic aberration in simple lenses and in Diffraction gratings. Only the latter seem to make good practical use of dispersion, when they are incorporated in a Spectrometer that can be used to analyse the dispersive properties of different optical glasses. 84.209.89.214 (talk) 14:12, 29 March 2014 (UTC)[reply]

Inorganic chemical synthesis

When the chemists especially the early chemists wanted or wants to produce a particular compound or preparation on what basis does he chose the reagents.Is theresystematin theory or logic or method to arrive at the solution.At the initial stage how does the chemist know about the chemical nature of the product(s) that are produced in a reaction or side reaction.Is it so that in experimental chemistry while finding the chemical nature of a chemical do the chemists react with all other chemical compounds in all possible combinations.Is it possible to predict if two or more chemical substances with known composition react under given conditions.How do the chemists devise or dicover the specific tests for radicals.How and when were the dry and wet tests for acdic and basic radicals discovered or devised.My questions can be extended to the organic chemistry also.I could not find answers to these intiguing questions in any chemistry text at any level.117.202.57.197 (talk) 07:24, 29 March 2014 (UTC)[reply]

See Outline of chemistry and Chemistry. Chemical reactions are governed by certain laws which have become fundamental concepts in chemistry. Wikiversity has started a school of chemistry. 84.209.89.214 (talk) 13:48, 29 March 2014 (UTC)[reply]

Mostly, chemists already have. So if a chemist wants to know how something behaves chemically, he looks it up. In past generations, reference works like the Merck Index and the CRC Handbook of Chemistry and Physics. Of course, the existence of the Web makes such print references superfluous. Further more, even if trying to predict the behavior of novel compounds, they are able to use the results of hundreds of years of chemistry to do Computational chemistry to predict the results of even novel chemical reactions. Of course, they still do the new reactions to confirm the predicted results. --Jayron32 20:41, 29 March 2014 (UTC)[reply]

What's the purpose of this ring on the hard drive motor?

I found a hard drive motor as shown with a smooth metal ring that goes around the shaft on the left. What, does the central shaft expand when the thing heats up and friction gets the ring to catch on and spin? To what purpose does the ring spin? Or is it for bearing purposes? Please someone tell me about this ring's purpose and the details of what goes on with it during operation. Peter Michner (talk) 15:28, 29 March 2014 (UTC)[reply]

Just a guess, bit if they had a vibration problem due to the hard drive hitting it's natural resonance frequency, then adding a metal ring like that to change it's mass, and thus it's harmonic frequency, might be the quick and dirty way to solve the problem. StuRat (talk) 17:57, 29 March 2014 (UTC)[reply]

Lowest temperature during last ice age

Does science have a ballpark of the lowest average low temperature normally occuring on Earth during the last ice age? I know it gets around -60°C quite a bit in Antarctica and some parts of Siberia on a more or less yearly basis — Preceding unsigned comment added by 78.1.186.238 (talk) 17:18, 29 March 2014 (UTC)[reply]

It wouldn't have been anywhere near that low, at least in the tropics. Those temperatures come from getting no light for 6 months. The tropics would have gotten plenty of light in the ice age. Also, if the whole world was that cold, the oceans would have frozen over. This may have happened during the Snowball Earth period, but not during any recent ice age. StuRat (talk) 18:02, 29 March 2014 (UTC)[reply]

Two common errors there, StuRat. Polar night does not last for six months throughout Antarctica. In fact some of Antarctica is north of the Antarctic Circle and so won't experience polar night or the midnight sun. Also take a look at Antarctica#Climate for an explanation of why the place is cold. By the way check Form B and use 0 degrees east or west longitude and 90 degrees south latitude (and then 89 south latitude) to see the sunrise/sunset times. CambridgeBayWeather (talk) 05:13, 30 March 2014 (UTC)[reply]

Yes, I meant at the South Pole, not all of Antarctica. StuRat (talk) 14:58, 30 March 2014 (UTC)[reply]

Surely it was lower than today, right? I'm not talking about the tropics, I'm talking about the mean low winter temperature in the then coldest places on Earth. 78.1.186.238 (talk) 18:05, 29 March 2014 (UTC)[reply]

Yes, lower than today, possibly with a few exception areas due to changing currents, jet streams, etc. StuRat (talk) 18:13, 29 March 2014 (UTC)[reply]

(edit conflict) "Scientists estimate that global average surface temperature was about 5 °C lower than at present, with larger changes at the poles."The Science Museum - Past climates: Ice ages. Alansplodge (talk) 18:16, 29 March 2014 (UTC)[reply]

And in case it isn't obvious, one major reason is the white ice reflecting sunlight back into space, although typically there is some other cause of the ice age initially. StuRat (talk) 18:20, 29 March 2014 (UTC)[reply]

Bioinformatics

Hi, I am starting to take my first steps in this field. I am trying to understand global and local alignments, using dynamic programming. I'm OK with the bio, but not really with the computer stuff. I am doing this alignment with a pen and paper, and want to make sure I'm doing it right. Is there a somewhere online I could put in tow DNA sequences & decide the scores, and as an output get the matrix itself {similar to what appears on this page: http://www.biosym.uzh.ch/modules/models/DNA_Alignment/align.xhtml }? — Preceding unsigned comment added by 164.138.124.238 (talk) 19:50, 29 March 2014 (UTC)[reply]

Cantilever bridges

The Grand Canyon Skywalk is a transparent horseshoe-shaped cantilever bridge whose free end overhangs the canyon in Arizona, USA.

2 questions about cantilever bridges 1- do cantilever bridges have a free end when're complete or is it only a method of construction. Where is the free end if it does? 2- Are bascule bridges such as Tower Bridge, cantilevers if we assume the movable part is a fixed end? Clover345 (talk) 22:07, 29 March 2014 (UTC)[reply]

See cantilever bridge. Typically they are attached at both ends, so act ads a dual cantilever (one from each end). However, I can imagine a case where they might not be attached at one end, say to span a fault line. This would allow it to survive a quake, although there might then be a large gap to span to make it safe for traffic again.

Single cantilever bridge over fault line before quake:
------   
   \/

Single cantilever bridge over fault line after quake:
------
   \      
    \/

StuRat (talk) 23:06, 29 March 2014 (UTC)[reply]

Regarding the Grand Canyon Skywalk, I certainly hope it has an anti-slip surface, as otherwise it might become slick when predictably covered with urine. :-) StuRat (talk) 01:31, 30 March 2014 (UTC) [reply]

March 30

Frog tails

Tadpoles and juvenile frogs have tails, adult frogs don't. Do these tails contain bones? How exactly are those tails lost, do the bones vanish or is it that the rest of the body grows backward so the bones become part of the spine? If the bones vanish, how is this accomplished? 95.112.194.18 (talk) 09:33, 30 March 2014 (UTC)[reply]

Frog#metamorphosis doesn't answer that question precisely, but I suspect that some of the references in that section do so. --ColinFine (talk) 10:44, 30 March 2014 (UTC)[reply]

This abstract mentions that the tails do not have any kind of skeleton to them (i.e. no bony or cartilaginous skeleton). In fact, the very first sentence mentions that tadpoles lack vertebrae for most of their body length. Matt Deres (talk) 12:52, 30 March 2014 (UTC)[reply]

In this picture of a mostly translucent tadpole, you can really see how rudimentary their skeleton is. It's also worth noting that the degeneration of the tail appears to be key in developing the strong back legs characteristic of frogs; it's only when those tail muscles shrink away that the legs really begin to bulk up. Matt Deres (talk) 12:56, 30 March 2014 (UTC)[reply]

This is certainly true for tadpoles, but those pictures on wikipedia of juvenile frogs suggest the tail may well have bones. 95.112.194.18 (talk) 13:59, 30 March 2014 (UTC)[reply]

Could you specify which pictures you're looking at? You can link them without posting the picture in full by putting a colon : between the square brackets and the word "File" like this [[:File:Haswell's Frog - Paracrinia haswelli tadpole.jpg]]. Incidentally, the so-called Tailed frog does not actually have a tail at all; the confusion comes from the uniquely shaped cloaca forming a kind of rudimentary penis, and it also has no bones in it. Matt Deres (talk) 15:20, 30 March 2014 (UTC)[reply]

File:Juvenile_Frog_with_tail_top_view_(1).JPG but i think I have seen more pictures (which I can't find again right at the moment) where the apperence looks even more bony. Could still be non-bony tissue, though. 95.112.194.18 (talk) 16:18, 30 March 2014 (UTC)[reply]

Hmmm, according to PMID 17371401 and [13], Megophryidae have supernumerary vertebral centra in their tails that ossify and serve as muscle attachment sites. It could be interesting to go through the taxon and see if this is truly an evolutionary reversal as the authors suggest. In any case, "In all four, the larval tail skeleton undergoes massive reduction, with vertebrae apparently degraded by the action of osteoclasts, leaving only the coccyx and ossified hypochord intact." Wnt (talk) 15:59, 30 March 2014 (UTC)[reply]

I came to think about this question because I was thinking about a (far future) way to do tissue engineering and looked for examples where nature removes bones. 95.112.194.18 (talk) 16:18, 30 March 2014 (UTC)[reply]

Not at an individual scale, but nature has slowly taken my tailbone. In the "far future", we'll almost certainly better understand the steps it took, so could replicate them viably quicker, and tweak where needed. Of course, in the "far future", maybe every house will simply have a biological Game Genie, growing tails like changing shirts. In the "far future", nature will have removed all of our bones the old-fashioned way.

Also, I met a frog with a tail last summer. The frog was about four inches, the tail about one. Didn't notice whether his legs were skinnier than they should have been. If I see him again (somehow), I'll check. InedibleHulk (talk) 17:20, March 30, 2014 (UTC)

need help on this

can any real scientists help me with this? no one here seems to know....

One of the things showed to me was our real time. It seems the Gregorian calendar is incorrect. The problem with it is time. There is no account for the speed the earth is traveling around the sun, and for the sun rotation around the galactic center. This gives us a quarter of a day extra a year. Einstein explained it with his theories of relativity. Once a person reaches the speed of light, time will stop. The earth travels around and gains a quarter of a free day a year. The creator lets it build up and releases every four years on the Gregorian calendar date July the 25th. This day repeats itself. It is a day that has no time. Because we are moving slower than the speed of light we gain time. When you exceed the speed of light we can travel backwards in time. This leads to the famous "twin paradox" in which one twin is rocketed at high speeds flies across the galaxy and back home. Even at a velocity close to the speed of light, the journey would take tens of thousands of years from the vantage point of Earth, but because of his high relative motion the astronaut would age more slowly than he or she would than on Earth, and would return home only a few years older. His twin would be long dead. In a 1905 Einstein predicted that because of the rotation speed of Earth, clocks would also run slower at the Equator than the poles, but that turned out to be wrong. See Einstein actually understood time. I think with a little bit more time Einstein would have figured this out too. E=mc2 and set the speed of light, 186,000 miles per second, as the cosmic speed limit - allows for time to stop. So if you are going slower than the speed of light it will move you forward. Everyone is a time traveler on our ship earth. There are 26 hours in the day. 13 hours of light 13 hours of dark 1 hour = 52 min 1 min = 52 sec 1sec = 52 nanosec 3 times 7 = 21 + 1 for god=22 7/22 = PI PI=3.142857 364 days a year times PI = 1144 Perfect rotation! It is in the math. Every four years we get a free click. The day with no time. 28 days times 13 months = 364 days 12 ages/ 1 age = 2166.7 earth years 26,000 earth years around galaxy 125 years a click = 1 min on watch Remember we have to take in the account that we are moving slower than the speed of light. The faster you go towards the speed of light you gain extra time. Once you exceed the speed of light you can travel backwards in time. So all of you hopeful time travelers you will need to build a craft that can go faster than the speed of light to go back. This is almost impossible, but can be done. In order to go back you need to bend space which allows the astronaut to move faster than the speed of light. In order to bend space you need to create your own gravity. I have drawn a replica watch of earth’s correct time. I guess you can tell I ate the apple of knowledge — Preceding unsigned comment added by 86.6.96.72 (talk) 10:05, 30 March 2014 (UTC)[reply]

You are conflating a whole load of different phenomena which happen to be about time. In particular, there is no connection between the adjustments needed for the Gregorian calendar (which are simply because the period of the Earth's rotation on its axis doesn't divide the period of its rotation about the Sun; and the Julian approximation to it was not quite accurate enough) and relativistic effects. The idea that when you pass the speed of light you can travel backward in time is speculation, and unrelated to the twin paradox. And if you eat of the fruit of the tree of knowledge of good and evil, you will surely die--ColinFine (talk) 10:48, 30 March 2014 (UTC)[reply]

I missed the question amongst the nonsense. But the answer surely rests with the difference between Passover, Westerm easter and Eastern easter. And a nanosecond is 10^-9 seconds. --DHeyward (talk) 11:54, 30 March 2014 (UTC)[reply]

As many physicists have pointed out, the distinction between past, present and future is only a stubbornly persistent illusion. Count Iblis (talk) 14:24, 30 March 2014 (UTC)[reply]

No doubt in the future we will be enlightened and no longer believe this illusion. :) And I think I can guess the species of the apple of knowledge, though I might be wrong. :) Wnt (talk) 14:55, 30 March 2014 (UTC)[reply]

The Einstein clock thing is interesting though: apparently the time dilation from the different amounts of gravity under general relativity exactly cancels out the time dilation from the relative motion of the equatorial observer? [14] But... isn't that only from one point of view? Hmmm... Wnt (talk) 15:03, 30 March 2014 (UTC)[reply]

Free floating arctic ice cap - what happens?

Graphics like the one at [15] show a sometimes much reduced polar ice cap during the summer, which remains attached to Greenland and the Canadian Archipelago. Suppose that global warming this or some future summer sunders this connection completely so that the entire polar ice cap is untethered to any land. Does it

(a) act the same as ever, since land so distant can't possibly transmit a force through cracked and moving ice for hundreds of miles?

(b) start to randomly drift south like any iceberg, some of which are very large after all?

I have this weird horror-movie scenario of a vast but much reduced raft of ice, loaded with starving, desperate polar bears, abruptly washing up on the shores of Scotland, but hopefully that's just stupid. :) Wnt (talk) 15:24, 30 March 2014 (UTC)[reply]

Some scientists are predicting the Arctic ice will entirely disappear by 2015. They do have a word for ice that attaches to land but I forget what it is; one of the implications of it becoming unattached is more Arctic methane being released. Raquel Baranow (talk) 15:46, 30 March 2014 (UTC)[reply]

Hbv indirect transmission

Are there any cases of HBV being transmitted through indirect means such as through contact between breaks in the skin and contaminated surfaces, in particular wet surfaces such as swimming pools?