Wikipedia:Reference desk/Archives/Science/2009 December 12

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

December 12

Hedgehog exercise

This BBC News article discusses an obese hedgehog.

• Fat albino hedgehog put on weight-loss regime.

To exercise him, the veterinarians have put the hedgehog in a bathtub to swim around as part of his weight-loss regimen. Is this standard procedure for exercising a hedgehog? I would have expected a "hamster-wheel" would be more common. Anyway, I know there's a few hedgehog experts on the desk, so I figured I'd solicit their input on this unusual exercise regimen. Nimur (talk) 00:39, 12 December 2009 (UTC)

Domesticated hedgehog may have some useful information. There are also external links to follow, you may be able to find more by poking around some of those. --Jayron32 01:19, 12 December 2009 (UTC)

A standard hamster/mouse wheel is unacceptable for a hedgehog. They often step into the gaps between the spokes and suffer injury (including broken toes). Instead, a hedgehog wheel is commonly referred to as a "bucket wheel" because it is like a shallow bucket placed on its side. Many people actually make their own from buckets. On average, a hedgehog will run about 3 miles each night. The bathtub regimen is not extremely common. Many hedgehogs are afraid of water. Those that like water will spend hours swimming around. Those that are scared of it do nothing except fight to get out of the water (I've got some pretty good claw marks as scared hedgehogs have clawed right up my arm to my shoulder). Some hedgehogs are scared of water and won't run in a wheel. For them, they need exploring activities. It is common to hide their food in a lot of hard-to-reach places. Then, they have to run around and try to figure out how to get their food. All in all - there isn't such thing as a single hedgehog personality. Like all other animals, each has its own personality. -- kainaw™ 01:36, 12 December 2009 (UTC)

Ah. The hazard of getting feet trapped in wheels seems like a motive for finding alternative exercise ideas. From the news story, there are several other news articles linked about obese hedgehogs, [1], [2]. Is this a common problem, or is it just getting disproportionate media attention because of the "weird" factor? Nimur (talk) 01:47, 12 December 2009 (UTC)

In captivity, hedgehogs regularly become obese. Hypertension, diabetes, and hypercholesterolemia are common. This leads to heart attacks, stroke, liver failure, and high rates of cancer. The issue isn't simply captivity. It is that the hedgehogs get plenty of food (most of it rather unhealthy food) and very little exercise. In the wild, hedgehogs span many miles searching for food every night. Relatively, imagine if your main purpose each day was to run a marathon to get a good meal. Sure - you have all day to run the marathon, but the meal won't do much to offset the calories burned getting to it. There is another issue - winter. Hedgehogs are said to hibernate. They don't truly hibernate, but they do spend most of winter holed up and waiting for the weather to get warmer. To last a long time, they need to fatten up. So, this is the time of year that European hedgehogs tend to get rather plump. -- kainaw™ 02:24, 12 December 2009 (UTC)

nitromethane

Is the pka given for this substance the value of nitromethane as an acid, or its conjugate acid (nitromethane is acting like a base)? I really can't see an acidic proton in nitromethane ... unless nitromethide carbanion is really that stable? John Riemann Soong (talk) 02:19, 12 December 2009 (UTC)

It is the pKa of losing a C-H hydrogen. If you read the article on nitromethane, the acidity of the compound and its uses specifically because of this acidity are discussed in the Uses section. The Nitroaldol reaction makes use of this acidity of nitromethane. --Jayron32 05:23, 12 December 2009 (UTC)

How was the international prototype for the metre made?

How was the 1889 version of international prototype for the metre made? —Preceding unsigned comment added by 173.49.9.184 (talk) 04:06, 12 December 2009 (UTC)

The French version of the article explains this in detail. In short, they kept making copies of the 1799 prototype until they got one whose length could not be distinguished from that of the original. --Heron (talk) 15:06, 12 December 2009 (UTC)

Thanks. --173.49.9.184 (talk) 15:53, 12 December 2009 (UTC)

"Bleeding like a stuck pig"

Do hogs bleed more easily than other animals? Or is this phrase a vague allusion to something literary or historic? 24.93.116.128 (talk) 05:14, 12 December 2009 (UTC)

It refers to the practice of Exsanguination in the slaughter of an animal. When you want to kill a pig, it is common practice to drain the blood as fast as possible from the meat, the article on Slaughterhouse describes the process in some detail. So when you "bleed like a stuck pig", it means you are bleeding like you are being drained of your blood in a slaughterhouse. --Jayron32 05:20, 12 December 2009 (UTC)

There is a passage in Jude the Obscure in which a character (Jude's unsympathetic wife) instructs Jude that the swine's blood vessel should be lightly nicked, so that the blood would drain slowly, resulting in less blood in the meat. Jude cannot stand to see the animal suffer and kills it quickly, enraging his wife. --Trovatore (talk) 23:22, 12 December 2009 (UTC)

There's some weird sex stuff going on in that book. There's the scene towards the begining where the chicks who are butchering the pig pelt him with the pigs penis. Thomas Hardy was not a stable dude. --Jayron32 05:02, 13 December 2009 (UTC)

Due to the sizes of the animals, it was more common to send cattle to a slaughterhouse for butchering, while smaller animals like chickens, sheep and even pigs you could do yourself at home. So the "average joe" may be more familiar with seeing stuck pigs. It may also have to do with the spiked club once used to kill pigs. The only people I know who have home butchered cows used bullets for the first step. Rmhermen (talk) 14:26, 12 December 2009 (UTC)

According to Jewish law and to Muslim law, animals must be slaughtered by a single cut to the throat while the animal is still conscious, see this article, Cuddlyable3 (talk) 23:14, 12 December 2009 (UTC)

According to Jewish law and to Muslim law, you can't eat pigs! --Dweller (talk) 16:45, 14 December 2009 (UTC)

Perhaps it is "bleating" like stuck pig. I never heard the phrase. But a pig that is "stuck" in some way probably complains loudly. Only problem is that "bleating like a stuck pig" gets zero Google hits. Bus stop (talk) 22:11, 14 December 2009 (UTC)

Pigs don't bleat; they squeal. "Squealing like a stuck pig" gets hits, but it may be an eggcorn. AlmostReadytoFly (talk) 15:33, 15 December 2009 (UTC)

Enzymes

I was under the impression that enzymes simply increase the rate of a reaction (my college bio text book says this). However denaturing certain enzymes can result in certain products from not being produced. But if they only increase the rate, shouldn't the products be formed without the enzyme, but only at a slower rate? So I'm a bit confused as to the nature of enzymes. ScienceApe (talk) 08:32, 12 December 2009 (UTC)

Yes, sometimes the uncatalysed reaction is just REALLY slow, so slow that in a biological system it basically doesn't occur. And also, some enzymes couple 2 reactions - 1 thermodynamically favourable with an unfavourable reaction, in essence driving the second reaction against the direction it would proceed without an enzyme, and using the first reaction to provide the "fuel" to do this. Aaadddaaammm (talk) 09:33, 12 December 2009 (UTC)

To expand on what Aaaddaammm is saying, the uncatalyzed reaction may occur so slowly as to take thousands or millions of years under uncatalyzed reaction conditions. So essentially, enzymes do "make" reactions occur which would otherwise be impossible (or, at least, impossible to work in a living system). --Jayron32 15:16, 12 December 2009 (UTC)

I see, thank you. But what about something like RNA polymerase for example. From what I understand it's the only way to make RNA. Can RNA be produced without RNA polymerase, just very slowly? ScienceApe (talk) 17:13, 12 December 2009 (UTC)

RNA polymerase is special stuff in that it takes a template DNA strand, and uses it to specifically reduce the activation energy barrier to sequentially adding an appropriate RNA base (A, G, C, or U) to the growing RNA strand. (That's a bit of a simplification, because the addition is a multistep process which includes a host of other enzymes, too.) For just random concatenation of RNA bases, you can drive the process using nothing more complicated than ultraviolet light. (See, for example, RNA world hypothesis.) Of course, once you start to have lots of complicated RNA floating around, it can do some simply marvellous stuff — including catalyze the formation of more RNA polymers. Modern RNA still forms a number of important enzymes, collectively called ribozymes. TenOfAllTrades(talk) 17:46, 12 December 2009 (UTC) (expanded, TenOfAllTrades(talk) 00:26, 13 December 2009 (UTC))

So you can transcribe RNA using just ultraviolet light? ScienceApe (talk) 01:21, 13 December 2009 (UTC)

"Transcribe" implies that you can control the order of bases in the created RNA, and that's not what TenOfAllTrades said. With UV light you just get some random RNA (think monkeys with typewriters). If you're really lucky it will turn out to be a ribozyme that does something interesting, and if you're really really lucky, "something interesting" will involve catalyzing transcription of RNA. Once you get there, you're golden. –Henning Makholm (talk) 02:04, 13 December 2009 (UTC)

So then for all intents and purposes, RNA polymerase, an enzyme, makes messenger RNA. ScienceApe (talk) 07:06, 13 December 2009 (UTC)

Yes. Both this example and the fact provided Adam above hit on extremely important concepts in biochemistry. We always say that enzymes accelerate a particular reaction, but when you are trying to consider what happens in the absence of the enzyme, you have to think about all the other reactions that can happen. In the case of RNA polymerization, the mRNA product of transcription is one possible product of the polymerization of N ribonucleotide triphosphates. There are, in fact, N⁴ conceivable products. In the case of an ATP hydrolysis driven reaction, a conceivable set or products is ADP plus inorganic phosphate, with the enzyme's substrate left unaltered. An enzyme "makes a reaction happen" by lowering the activation energy for one particular reaction amongst the many reactions possible with a given set of reactants. Someguy1221 (talk) 07:19, 13 December 2009 (UTC)

The templated polymerization of ribonucleotides (i.e. the reaction which RNA polymerase catalyzes) will occur on it's own (theoretically). The problem is that it is *so* slow uncatalyzed that all the other reactions which can conceivably occur to the substrates (such as hydrolysis, Maillard reactions, non-specific polymerization, etc., etc.) will go to completion thousands of years before you'll get appreciable amounts of desired product. It's not just that enzymes increase the rates of reaction, but they increase the rates of *specific* reactions, while leaving the other, undesirable reactions slow. -- 128.104.112.87 (talk) 15:55, 14 December 2009 (UTC)

Russian rocket failure

Is this for real? http://www.nzherald.co.nz/world/news/video.cfm?c_id=2&gal_cid=2&gallery_id=108562 Aaadddaaammm (talk) 09:38, 12 December 2009 (UTC)

Yes. The spiral was seen by hundreds of people in northern Europe. The most likely explanation is a Russian ICBM test where the rocket went out of control. spaceweather.com has a write up on it, and the rocket plume of the boost phase of the rocket is visible and normal in at least one photo of the spiral. --121.127.200.51 (talk) 10:10, 12 December 2009 (UTC)

There was a discussion on this earlier. We have an article 2009 Norwegian spiral anomaly Nil Einne (talk) 13:03, 12 December 2009 (UTC)

And just as a note, "spiral in the sky" seems odd if you haven't seen something like that before, but many failed missile tests look like that and produce distinctive spiral smoke shapes. E.g. [3] and [4]—when you have one part of a missile spewing out heat and it gets off-center, you easily get spiral-like activity. What's interesting in the Norway case is how high it was and how the period of the spiral looks so perfect, but you'll notice in the videos that most are showing a clip of just a second or two in length—it disperses immediately afterwards. It is fairly what you'd expect it to look like if, say, the third-stage of an SLBM failed to detach from the main body and spun it around. --Mr.98 (talk) 14:18, 12 December 2009 (UTC)

And just another note... another possibility that has not been discussed seriously, but doesn't quite fall into "conspiracy theory" territory, is that this is a test or failure of a different type of weapon. In their book Nuclear Express, Thomas C. Reed and Danny B. Stillman (the latter of whom was a Los Alamos scientist), report on a mysterious, not-fully-understood weapon that the USSR and China had both been developing, that they term "domes of light". Some of the description from their book, and the photos they reproduced, are visible here. The spiral on the Norwegian thing says "missile test gone awry" to me, but I remember reading about the "domes of light" sometime back and finding them pretty odd as well. Just putting that out there! --Mr.98 (talk) 14:30, 12 December 2009 (UTC)

That sounds vaguely like the conspiracy theories surrounding HAARP and its Russian counterpart SURA (neither of which is at all near Norway or the White Sea). But then what use is a sci-fi death ray if you can't blow up far away things (like test missiles over the White Sea). 87.115.47.74 (talk) 00:08, 13 December 2009 (UTC)

Vaguely, maybe, but it's not, and the source of it is much better than the normal conspiracy nonsense. The authors of that particular book are not kooks, and the book itself has been well-reviewed all over the place. One sign that this particular theory is not just kook-land is the fact that the authors readily admit they aren't really sure how it works (rather than spinning out endless Tesla-based theories). --Mr.98 (talk) 18:40, 13 December 2009 (UTC)

Cavity Preparations-Dentistry

What are the recent modifications made in outline form of class 1 cavities (with faciolingual extentions)n class 2 cavities for amalgam restorations? <ref>Fundamentals in cavity preparations</ref>—Preceding unsigned comment added by DOC PANU (talk • contribs)

Is this homework? Fences&Windows 14:41, 12 December 2009 (UTC)

You may find the information here. Cuddlyable3 (talk) 23:03, 12 December 2009 (UTC)

Your question is very vague -- could you be more specific, please? DRosenbach ^{(Talk | Contribs)} 14:12, 13 December 2009 (UTC)

no transmission for a car?

Why does a car need a transmission and an airplane doesn't? I'm not sure, but it looks like propeller aircraft have propellers somehow attached to the engines' crankshaft; would it possible to do the same with a car so engine speed would be directly proportional to car speed? 70.144.137.239 (talk) 14:36, 12 December 2009 (UTC)

A modern propeller driven plane will generally have a variable pitch propeller - and that is (in effect) a continuously variable transmission - when the propeller blades are parallel to the circle in which they travel, the blades generate almost zero thrust - as you increase the pitch of the blades, the 'gear ratio' gets higher - suitable for flying at higher speeds. Prop planes that don't have that are essentially "stuck in one gear" - which is a compromise between performance and idle. But aircraft don't have much problems with stop-and-go traffic - once they are moving, their power needs are over a fairly small band - and the range of RPM's they need isn't that great. Also, you can't stall a plane's engine in the way that you can stall a car engine. If you bring your car to a dead stop using the brakes in a high gear - the engine RPM will drop so low that the engine will be unable to keep running. In an airplane, on the ground, the propeller can continue to rotate when the brakes are on and the plane is stationary - so you don't need a clutch or a neutral gear either.

Having said that - I recall that at least one design of Russian or maybe Czech fighter from the WWII era did actually have a gearbox. Sadly, I can't recall the model number - so no link.

SteveBaker (talk) 15:21, 12 December 2009 (UTC)

As far as I know cars with electric motors (e.g. Tesla Roadster) actually go all the way down to zero RPM, they don't have the stalling or motor starting issues that regular engines have that would necessitate the need for a clutch, torque converter or gearbox. In principle they could couple the the motor directly onto the crankshaft (especially in the case of the Tesla which has a 1-speed gearbox). However there are practical considerations and advantages to have at least a neutral gear (free-wheeling downhill without excessive engine braking is one) as well as several gears. As Steve points out, a plane or boat operates in a VERY limited RPM range. If you had to stick with only 1 gear in a (electric) car it would simultaneously need to be short enough to pull away from standstill (while loaded to its maximum allowable weight) and at the same time long enough to cruise at top speed within the engine's operating range (typically 12,000 RPM for an electric motor). The Tesla can do this because it is a light sports car with no boot space and only 2 seats. The max. weight is not excessive so the gearing isn't TOO compromised on the "short" side. Zunaid 16:04, 12 December 2009 (UTC)

Our turbofan article has a very brief section discussing gearboxes for aircraft engines. The gearing is very different from a car transmission. Nimur (talk) 17:31, 12 December 2009 (UTC)

Yeah - some planes do have gearing - but it's not a shiftable gearbox - it's just a way to get the engine RPM down to a reasonable fan/propeller speed. Helicopters have much fancier gearboxes - but again, they aren't shiftable - they are a constant ratio. SteveBaker (talk) 22:16, 12 December 2009 (UTC)

I'll digress into trains and talk about diesel ones. Most of these are actually diesel-electric: the diesel engine drives a generator, at a narrow range of speeds, and electric motors drive the wheels. No gearbox needed since the electric motors can handle the full range of speeds needed. But there have been some diesel-hydraulic trains, based on a torque converter like in an automatic-transmission car; the Budd Rail Diesel Cars once common on secondary passenger services in Canada and the US are one example. And there have even been "diesel-mechanical" trains with a gearbox; these used to be common on secondary passenger routes in Britain. --Anonymous, 20:47 UTC, December 12, 2009.

Yeah - electric motors have a very flat torque-versus-rpm curve - gasoline & diesel engines typically don't. Hence the need for a gearbox to get the gasoline engine to run at the optimum RPM to get the best torque (or the lowest fuel consumption or whatever) at a range of vehicle speeds. With an electric motor, it's not really necessary to shift gears because the torque output is pretty much the same no matter the RPM. Having said that - some electric cars do use a simple two-speed gearbox with a 'starting gear' and a 'running gear'. Hybrid cars (and diesel-electric railroad locomotives) take advantage of that by running the internal-combustion engine at it's absolute best RPM - use the engine to generate electricity - and use the electricity to drive electric motors. That's a neat trick - and it's how hybrid cars get such good gas mileage. But you just don't need that range of RPM's in a low-cost light aircraft. High end prop planes use that variable-pitch prop trick - so they can alter the torque demands at a wide range of speeds without altering the engine RPM by more than it can cope with. SteveBaker (talk) 22:16, 12 December 2009 (UTC)

What happens when a cold-blooded animal gets an infection.

When warm-blooded animals (well, humans, dogs, etc at least) get an infection - their temperature goes up in a fever as their bodies try to kill off the bacteria/virus by making things too hot for them.

How do cold-blooded animals cope under these circumstances? Is there evidence that they'll bask in the sun for longer in an effort to create a hotter situation?

SteveBaker (talk) 15:26, 12 December 2009 (UTC)

Apprently that is the case.[5] There is something called 'behavioral fever' in reptiles, birds, fish and amphibians and it seems to be effective in increasing survival rates following infection. Mikenorton (talk) 17:09, 12 December 2009 (UTC)

It should be noted that the idea that fever is a useful survival technique has been questioned by some researchers. See Fever#Usefulness_of_fever which notes that the notion is not universally accepted that fever is beneficial to the organism as described by SteveBaker. --Jayron32 17:12, 12 December 2009 (UTC)

As a further pedantic note, the main function of fever isn't to make things too hot for the infectious agent, it is to ramp up the activity of the immune system. Looie496 (talk) 17:59, 12 December 2009 (UTC)

Wow! Thanks for the link Mike. So they got snakes to want to be in a warmer place by injecting them with DEAD bacteria?! How did the snakes know they needed to do that if they didn't get sick? (Presuming they didn't get sick from dead bacteria.) That's an interesting result! I'm glad I asked. SteveBaker (talk) 22:05, 12 December 2009 (UTC)

Well the dead bacteria would still contain the antigens which would bind to immunoglobulins. --Mark PEA (talk) 22:12, 12 December 2009 (UTC)

I have not read that study, but I doubt it was due to immunoglobulins, which are generally produced by the adaptive immune system and therefore would only be generated in large amounts if the animal had had that infection before. More likely it's an innate response mediated by LPS and other PAMPs from the bacterial cell, binding to PRRs like TLR4. According to this (free) publication the sensing of bacterial PAMPs by PRRs is conserved throughout vertebrate evolution. -- Scray (talk) 00:36, 13 December 2009 (UTC)

On a more general level than which antigens bind to what, "getting sick" is generally not something the invading bacteria actively do. It is simply the body's reaction to something foreign being there. Feeling sick is how we perceive the immune system's being activated to flush out the invaders before they get many enough to do damage of their own. It seems to work well for modifying our behavior to support the immune reaction; being miserable tends to make the patient lie down, bury himself in blankets and generally conserve as much energy as possible to fighting the infection (as opposed to things that can wait, such as locomotion, gathering food, or preparing for winter). Snakes probably feel it similarly. –Henning Makholm (talk) 01:10, 13 December 2009 (UTC)

M&M

Why are there two "m"s in Mmgy? SpinningSpark 16:48, 12 December 2009 (UTC)

According to our article on the barrel, where a million barrels is sometimes rendered as 1MMbbls, this arises from the use of M to represent a thousand (derived from 'mille'). Mikenorton (talk) 16:56, 12 December 2009 (UTC)

It's worth noting that neither Mmgy and MMbbls are SI units, so they do not abide by SI standard prefixes. Nimur (talk) 17:33, 12 December 2009 (UTC)

Thanks Mike, and thanks also to Nimur, although I did not think for one minute that this was an SI unit. SpinningSpark 18:57, 12 December 2009 (UTC)