Wikipedia:Reference desk/Archives/Science/2008 September 1

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September 1

Luciferin

How did this compound get its name? I assume it was someone versed in Christian mythology, but who was it?CalamusFortis 00:02, 1 September 2008 (UTC)

I can't give a who, but maybe a why. "Lucifer" simply means "light-bringer", which is what Luciferins do. The relation to the devil may be coincidental. Paragon¹²³²¹ 00:59, 1 September 2008 (UTC)

Yes - I agree. Our article on Lucifer says that the name means "Light bringer" or "Morning Light" - originally meaning the planet Venus. It suggests that the use of the name to apply to Satan is a relatively modern confusion. Lucifer was originally some much hated tyrant King of Babylon...or perhaps Tyre, Lebanon...who subsequently was confused with the Devil. The article is hard-going...I don't recommend attempting to glean anything more meaningful from it unless you are already enough of a linguist to not need to read it! SteveBaker (talk) 03:47, 1 September 2008 (UTC)

As for the who, according to the OED the word was first used (in the French form luciférine) in 1887 by one R. Dubois, in volume 105 of a journal identified by the abbreviation Compt. Rend., which I assume was Comptes Rendus de l'Académie des Sciences. And yes, as explained above, the word has nothing to do with the Devil. Deor (talk) 12:58, 1 September 2008 (UTC)

Here is the link to the article of Dubois Recherches sur la fonction photogénique .--Stone (talk) 21:24, 1 September 2008 (UTC)

Actually, I believe this is the article that the OED refers to. Dubois coins the name luciférine near the bottom of page 691. Deor (talk) 10:45, 2 September 2008 (UTC)

Amount of Potassium iodide in Iodized salt

From Potassium iodide they say that an adult should take 130 mg of it after being exposed to radiation. Hypothetically, how much iodized salt would be equivalent of 130 mg of Potassium Iodide? Would it matter whether it was Potassium iodide or Potassium iodate? From what I understand of Radiation poisoning this only protects the thyroid from Radioactive iodine, which makes me wonder: Would this kind of action really have much of an impact on survival percentages? Thanks. Anythingapplied (talk) 00:17, 1 September 2008 (UTC)

My container of Morton's says that 1 serving (0.25 teaspoons) contains 130 micrograms of Potassium Iodide. So thats 1000 servings to get the thyroid blocking that I assume you're asking about. 1000 servings = 250 Teaspoons, or about 5 cups! I think the sodium would be more toxic than the radiation at that concentration. But yes, KI only protects the thyroid from uptake of radioactive iodine, which is a by-product of a nuclear chain reaction. Arakunem^Talk 01:18, 1 September 2008 (UTC)

Indeed the LD₅₀ of salt is 3 g/kg in rats. Presuming it's fairly similar for humans, that's 300g for a 100kg human. Presuming you can actually consume that much salt I wouldn't think your chances of survival as very high Nil Einne (talk) 09:26, 1 September 2008 (UTC)

Looks like 1 cups of salt is about 300g, so 5 would no doubt result in a very low survival probability. Anythingapplied (talk) —Preceding undated comment was added at 14:55, 2 September 2008 (UTC)

According to one reference from the KI article [1] thyroid cancer rates increased 30- to 60-fold in very young children after the Chernobyl accident. Looking at statistics for thyroid cancer incidence in the UK [2] and using the general rate of 2.5 per 100,000 people, that would mean maybe 1 in 1,000 people would be protected from cancer. That gets a little confusing though when you look at the age-distribution graph, the normal thyroid cancer rate in children under 10 is close to zero. However, since radioactive iodine is known as a risk factor and has a short half-life, and it is very easy and cheap to give people near nuclear plants emergency kits with KI tablets, it makes sense to do so. Note though, the article doesn't say "after being exposed to radiation", KI is used before or during exposure to radioactive isotopes from an accidental release from a nuclear plant (or heaven forfend, bomb fallout) - the theory being to flood the body with stable iodine to prevent the radioactive iodine from being taken up by the thyroid. Franamax (talk) 11:32, 1 September 2008 (UTC)

To answer you other question: yes it only protects against ragiation-induced thyroid cancer and not against cancers cause by any of the other isotopes that are released by a nuclear weapon or accident. However, since this one cnacer represents the biggest single health risk from such an incident, so yes it's worth tryin to defend against. Duringhte cold war, the US government seriously considered a law to require that all households keep a package of potassium iodide tablets (to be distributed by teh electric power company and taped to the fuse box, oddly enough.) The plan was abandoned due to concerns that more deaths would occur due to failure to follow the directions on the package than could be averted by proper use. -Arch dude (talk) 16:17, 1 September 2008 (UTC)

Hmm...that distribution scheme actually makes a remarkable amount of sense. Every home should have a fuse box, and every homeowner ought to know where it is. having the electric company deliver the tablets ensures that every household will get some, and having the electric company staff tape the packet to the fuse box guarantees that the homeowner won't forget and misplace the tablets. Since KI tablets have an essentially unlimited shelf life, the job only has to be done once. Keeping them out of the medicine cabinet prevents them being thrown out accidentally when cleaning out the cabinet, and means that they won't get misplaced or damaged (transferred to a different drawer in the bathroom, moved to a first aid kit that gets left in the car or at the cottage, dropped in the sink and soaked, etc.). In homes with a basement, the fuse box is almost always located there rather than on the main floor of the house—if you've taken cover in your basement during a nuclear attack, you won't have to go upstairs to the bathroom – risking exposure to radiation and additional blasts – to find your KI tablets. TenOfAllTrades(talk) 16:44, 1 September 2008 (UTC)

Potassium iodide tablets are available from internet sources by mail order [3] , with no prescription needed. Just keep'em near your radiation monitor [4] and hope you never need them. Edison2 (talk) 18:03, 1 September 2008 (UTC)

Digital data over radio transmitter

Hello, can i KNow more about transmitting difital data using a Radio Transmitter? Thanks. Praveen Pkmchoudhari (talk) 02:02, 1 September 2008 (UTC)

Well, that's a big subject. Television is about to be transmitted digitally in the USA, we have digital cell phones, we have WiFi connections between computers in our homes, some radio controlled toys use digital commands, radio is used to send commands to the two NASA rovers driving around on Mars...where would you like us to start? Essentially, we have a radio wave that's oscillating at some frequency ("pitch") and at some amplitude ("volume") - you can send digital data (which is basically just a string of 1's and 0's) by changing the frequency a little bit for a '1' and not changing it when there is a '0' (which would be like an FM radio station sends analog audio) - or you can sent the radio wave at full strength for a '1' and turn it way down (or even, off altogether) for a '0' (like an AM radio station sends analog audio by varying the "amplitude" of the radio wave). Do this very rapidly and you can send quite a bit of data in a short time. But there are lots of much more complicated and subtle ways that this can be done.

Perhaps if you could be a bit more specific, we could help you out with a much more detailed explanation. SteveBaker (talk) 02:48, 1 September 2008 (UTC)

The article Packet Radio may help. It's all about trasnmitting digital data using a Ham Radio. APL (talk) 03:07, 1 September 2008 (UTC)

(I don't know about this but I gave your question a title so it's easier to find and neater looking. Sorry for this is minor inconvenience! 88.211.96.3 (talk) 08:42, 1 September 2008 (UTC) )

The magical blue smoke

You know when you get a bit of electronic equipment such as a CRT monitor or a TV, and it dies and sometimes you get pale blue smoke (which my Dad jokingly tells me is the magic blue smoke that makes the TV work). What is this smoke made of and what causes it? Also is there a way to tell what things would produce said mystic smoke when they die, and under what circumstances? 88.211.96.3 (talk) 08:45, 1 September 2008 (UTC)

Magic blue smoke. Yes, wiki has an article on everything. Dragons flight (talk) 09:06, 1 September 2008 (UTC)

applications of lagrangian dynamics

could you plz suggest a website where I can find problems and applications relating to the use of Euler-Lagrangian equations? I am still learning the elementary concepts in Lagrangian dynamics..so, plz see that the problems are not too complicated..thanx.. —Preceding unsigned comment added by 59.93.90.44 (talk) 08:59, 1 September 2008 (UTC)

thin layer chromatography

In TLC, I've always known of the Rf value as the retardation factor, but recently I've seen it referred to as "relative frontal mobility". Anyone else heard of this terminology? Is it correct/acceptable? --TomDæmon (talk) 09:31, 1 September 2008 (UTC)

A google search would suggest it used at least by some. Retention factor is also possible, of course. --Cameron* 11:09, 1 September 2008 (UTC)

MRI machine

Hi

I wanted to know about the cryogen used in MRI machine and can liquid helium be replaced by liquid nitrogen? —Preceding unsigned comment added by Hetal R Shah (talk • contribs) 09:35, 1 September 2008 (UTC)

This depends on the machine using high temperature superconductors. See MRI#Magnet: However, despite its cost, helium cooled superconducting magnets are the most common type found in MRI scanners today. --Ayacop (talk) 10:01, 1 September 2008 (UTC)

The liquid Helium flask will be surrounded by liquid Nitrogen to maintain the Helium at its very low temperature. Liquid Nitrogen is much much cheaper than liquid Helium and is thus periodically topped up preventing the need to replace the expensive liquid Helium. Jdrewitt (talk) 10:26, 1 September 2008 (UTC)

Additionally, no you cannot replace the Helium with Nitrogen because the superconducting coil must remain at a temperature below T_C, the critical temperature where the superconductivity characteristics occur. If the magnet was cooled by liquid Helium originally (i.e. down to less than 4.2 K) then T_C will be far too low for Nitrogen to achieve since Nitrogen freezes at 63 K. See Superconducting magnet. Jdrewitt (talk) 11:38, 1 September 2008 (UTC)

Comercial MRI use Niobium-tin with critical temperature 18.3 kelvins. So Liquid nitrogen with 77K is not sufficient. With other superconducting material maybe but with the stuff maketed now. NO!--Stone (talk) 21:10, 1 September 2008 (UTC)

How can we calculate the chemical energy of a body?

How can we calculate the chemical energy of a body? Can we do that by using the calorific value of it and simply multiplying it by the mass?Anirban Chatterje (talk) 09:38, 1 September 2008 (UTC)

Did you read the article on internal energy? --Ayacop (talk) 10:07, 1 September 2008 (UTC)

Yes, I did.But the thing is that,only the Equation U=3RT/2 can be received.But how can I apply this in case of chemical compounds?Anirban Chatterje (talk) 18:40, 1 September 2008 (UTC)

Mortality of acute pancreatitis

Why is the mortality of acute pacreatitis so high? What are the mortality rates? I am not asking medical advice. —Preceding unsigned comment added by 217.227.75.39 (talk) 10:56, 1 September 2008 (UTC)

The pancreas is a rather important organ, and you only have one of them. Is it really surprising that a major condition affecting it has a high mortality rate? Cardiac arrhythmias tend to be rather bad too Nil Einne (talk) 12:39, 1 September 2008 (UTC)

The pancreas is fragile, and pretty damn important. Pancreatic cancer is a particlarly devastating condition, where Wikipedia states that there is roughly a 5% 5-year survival. Although, my Oxford Handbook of Medicine states that carcinoma of the pancreas carries a less than 2% 5-year survival with a mean survival of 6 months. That said, a procedure called pancreaticoduodenectomy can increase the prognosis to 5-14% —Cyclonenim (talk · contribs · email) 15:08, 1 September 2008 (UTC)

The low survival rate for pancreatic cancer is because it doesn't have well-defined symptoms until the cancer has reached a very advanced stage. The survival rate for early-stage pancreatic cancer is similar to that of any other cancer. --Carnildo (talk) 22:41, 2 September 2008 (UTC)

One way to think about it is as a positive-feedback loop. The pancreas produces zymogens that are usually involved in digesting our food after being pumped through the pancreatic duct into the duodenum (and then activated there, where the lining of the intestine keeps them from harming the host). In pancreatitis, these enzymes become active in the pancreas proper, and begin digesting - a bit like a fire at a fuel refinery. With the proximity of major arteries and bacteria-filled intestines, this makes for a lethal combination. Scray (talk) 15:06, 1 September 2008 (UTC)

This article discusses the high incidence of multiorgan failure in acute pancreatitis. Axl (talk) 18:35, 4 September 2008 (UTC)

regarding physics olympiad

what is the syllabus for physics olynpiad —Preceding unsigned comment added by 122.167.99.51 (talk) 13:29, 1 September 2008 (UTC)

Assuming you're talking about the International Physics Olympiad, the syllabus is here. Algebraist 13:31, 1 September 2008 (UTC)

There are more "Physics Olympiads". I know of two universities that host events with that specific name. -- kainaw™ 13:35, 1 September 2008 (UTC)

evolution

What is the benefit to male big cat reproductive success of leaving the area and pack. —Preceding unsigned comment added by 194.70.73.98 (talk) 15:44, 1 September 2008 (UTC)

It varies from species to species - but what often happens is that young males are forced to leave the group - one older male remains. The benefit to the older male is obvious - he doesn't need help to impregnate multiple females - so less competition is good. The younger male is forced to leave or get into a fight with the leader which he'd surely lose due to smaller body size and inexperience. The young males go off by themselves for a while - those that survive may eventually return and kick out the old male after some kind of dominance battle. Evolutionary benefits are that weaker males don't get to spread their weak genetics to the next generation. Every animal born is a result of the best male genes available from the previous generation. SteveBaker (talk) 16:08, 1 September 2008 (UTC)

I've been told that lions are the only social cats, having organized groups. What other species have pack dynamics? --Allen (talk) 16:56, 1 September 2008 (UTC)

Define pack dynamics. I'd guess most Bovidae have a top dog and yes, many other mammals, too. --Ayacop (talk) 17:33, 1 September 2008 (UTC)

Sorry; I meant what other cat species. --Allen (talk) 19:38, 1 September 2008 (UTC)

As far as I know, you're right. Lions are the only cat that exhibit pack dynamics. ScienceApe (talk) 21:48, 1 September 2008 (UTC)

Hmm. See feral cat colony, for a counterexample. --Sean 22:26, 1 September 2008 (UTC)

One benefit is to avoid inbreeding. I guess it's especially effective when only one sex is moving. 93.132.132.172 (talk) 18:54, 1 September 2008 (UTC)

Carotid artery

What is the best technique for determining the amount of plaque inside the carotid artery? —Preceding unsigned comment added by 79.76.154.239 (talk) 22:21, 1 September 2008 (UTC)

The usual diagnostic test is carotid ultrasound, with the results reported as carotid plaque area. [5]. "Best" is a matter of opinion, of course. - Nunh-huh 22:27, 1 September 2008 (UTC)

A carotid angiogram might give you more information. CT and MRI's are starting to show promising diagnostic results with the advantage of not being very invasive. Ultrasounds tend to be less exact. OrangeMarlin ^{Talk• Contributions} 02:23, 2 September 2008 (UTC)

It rather depends on one's definition of 'best'. Using appropriate techniques, one can definitely get a very precise measurement (arguably better than ultrasound) using CT or (especially) MR methods. But a precise measurement isn't the only criterion. CT exposes the patient to (a fair bit of) ionizing radiation. Usually carotid occlusion is a problem in an older population, so cancer risk is low, but still worth considering. CT instrumentation is also relatively costly, and (with a few rare exceptions) non-portable. MR imaging equipment is extremely costly, entirely non-portable, and not suitable for patients with certain medical implants or prostheses. Ultrasound, on the other hand, is dirt cheap (compared to the other two, at least), portable, widely available, fast, and 'good enough' for most cases.

Of course, for the absolute most accurate measurement, you have to wait for the patient to die, then cut out the carotid artery and have a look. While this is by far the least expensive and most direct method, it has certain drawbacks. TenOfAllTrades(talk) 02:48, 2 September 2008 (UTC)

Back to the angiogram then, which balances risk to benefit. Of course, there would be other signs of vascular disease that would indicate the need for a carotid angiogram. OrangeMarlin ^{Talk• Contributions} 06:08, 2 September 2008 (UTC)

This question is in regard to galvanizing.

Presently I want to start a galvanizing company and during the research I was asking question about what materials is needed to galvanize a metal. Due to fact that businesses are scared of the competition they would not help me with all the information I was looking for.

I would like to know what is requite to melt a cutlery as in temp which should be applied and how would I be able to keep it into silver. More importantly which metal I should use while I’m still studying galvanizing?

My regards Christian —Preceding unsigned comment added by 41.208.48.160 (talk) 22:33, 1 September 2008 (UTC)

Have you looked at galvanization and its links? Ζρς ι'β' ^¡hábleme! 00:04, 2 September 2008 (UTC)