Wikipedia:Reference desk/Archives/Science/2007 October 5

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[edit] October 5

[edit] Level of fossilization in T.Rex Tissue?

I'm reading a paper published in Science magazine two years ago [1]. It documents a famous finding of soft tissue in T.Rex fossil bone. I'm trying to figure out to what extent the tissue recovered from the bone was fossilized, but I'm just a half-educated layman and I get lost easily in all the big words. First, what precisely is the definition of "fossilization" that a scientist would use? To what extent must the remains of the organism be changed (or do they have to be changed at all)? Second, the paper refers to the tissue having to be "demineralized" before analysis. Does this imply that the tissue had been fossilized, or is it something that you would have to do to any bone to get at the tissue? Thanks! 69.218.205.188 00:23, 5 October 2007 (UTC)

FWIW, bone specimens usually are decalcified before attempting DNA extraction, as it greatly increased the yield, even in fresh bone. - Nunh-huh 00:42, 5 October 2007 (UTC)
I was about to say "that's impossible", but then I read this section in our T. Rex article. The term "fossilisation" usually means that the original tissue has been replaced by minerals. So if soft tissue was found inside a fossilised bone then it would be more correct to say it has been "preserved" rather than "fossilised" - indeed the title of the Science paper, which is cited as a reference in our article, is Soft Tissue Vessels and Cellular Preservation in Tyrannosaurus rex. The "demineralisation" process uses weak acid to dissolve the fossilised bone, and so presumably leave the soft tissue remains behind. The researchers claim to have found blood vessels, tissue that is still flexible, and possibly even blood cells. If this find is confirmed by other researchers then it is a truly astonishing discovery. Gandalf61 09:02, 5 October 2007 (UTC)

[edit] Macaroni and cheese mystery

Say I pour a packet of cheese powder on my macaroni, then I pour a cup of milk onto the powder. But instead of soaking into the powder, the milk just beads up and rolls right off down to the bottom of the bowl. The powder stays totally dry! What's going on? This has bugged me for years. 154.5.195.217 01:20, 5 October 2007 (UTC)

The cheese is greasy and contains fat that repells water in the way you say. If you can melt the cheese you find that the fat is actually in very small droplets and can disperse in the milk if it is mixed. Graeme Bartlett 01:30, 5 October 2007 (UTC)
I had no idea that cheese came in powdered form. Is it dehydrated? Nimur 02:51, 5 October 2007 (UTC)
Umm, you obviously never ate Kraft Mac and Cheese. Powdered cheese is common knowledge. 64.236.121.129 13:40, 10 October 2007 (UTC)
Yes, in a little packet that comes in the Kraft Macaroni and Cheese package (or several other brands). You must not be from the US if you don't know about powdered cheese. I don't think the earlier explanation is correct, however, as the cheese packet does not contain much fat. That is supplied by milk and butter which are added to the mix. StuRat 04:17, 5 October 2007 (UTC)
I'm not sure of the cause, but chocolate powder in milk does the same thing. A boundary layer seems to form between the milk and powder which can only be broken up by vigorous stirring. StuRat 04:23, 5 October 2007 (UTC)
The best plan is to add a small amount of milk to the powder in a cup, mix it well into a half-runny paste, add enough more milk to enable it to coat the macaroni, mix it again, pour it onto the macaroni, and pour the remaining milk on top. -- JackofOz 04:59, 5 October 2007 (UTC)
Right, but I think the original poster was looking for an explanation of why the powder won't dissolve more easily. StuRat 06:03, 5 October 2007 (UTC)
Reading between the lines of the question, it seemed apparent that 154.5 wasn't aware there was a way to counteract the problem. Often, when people ask "Why is it so?", they also want to know "How can I make it be different?". -- JackofOz 01:53, 7 October 2007 (UTC)
No, I was just curious as to what was happening. I'll continue just spending a minute stirring it up after adding the milk. Quite a curious effect though. Thanks all! 154.5.195.217 23:24, 8 October 2007 (UTC)
  • It's certainly not due to any fat content, because talcum powder behaves in the exact same way. I think it has to do with wetting and hydrophobicity. Here are the ingredients of the "cheese" packet: Whey, Milkfat, Milk Protein Concentrate, Salt, Calcium Carbonate, Sodium Tripolyphosphate, Contains Less than 2% of: Citric Acid, Sodium Phosphate, Lactic Acid, Milk, Yellow 5, Yellow 6, Enzymes, Cheese Culture. --Sean 12:47, 5 October 2007 (UTC)
General rule: Any product that contains the word "American" and "Cheese" in it should be avoided at all cost. American cheese is bland beyond belief - the only difference between the different kinds is the colour. Somehow they've even found a way to pursuade the French to make stuff that looks just like Brie and even comes in one of those little round wooden boxes - but which tastes of exactly nothing and goes hard as it 'matures' instead of turning into a pungent creamy liquid as should be the case. I don't know how they do this...or why...but it's a fact. I bought some 'Munster' in the supermarket the other day - this is one of the strongest smelliest cheeses you can find in a French supermarket - and this stuff smells and tastes of precisely nothing. As far as I can tell is exactly the same stuff as their "Sharp cheddar" - but without the orange food colouring. "Sharp cheddar" has definitely not been within several thousand miles of Cheddar gorge - and is only sharp in the sense that a marshmallow is. My wife (who is French) found an interesting little cheese shop in Dallas - it turns out that the cheeses they keep are exactly the same as the ones in WalMart except that some have little bits of nuts in them. Hence we may deduce that the strange orange powder that comes with Mac'N'Cheez is some fascinating chemical substance with all sorts of interesting properties...none of which should encourage you to actually eat the stuff. SteveBaker 13:44, 5 October 2007 (UTC)
What you describe is processed cheese. The main ingredient is soybean oil, versus milk/cream for real cheese. Note, though that real cheeses are also made in the US. I do, however, agree that "American cheese" seems to be a keyword for processed cheese. I would expect that if you bought "sharp cheddar" in the US, it would indeed be real cheddar, unless it had some disclaimer on the label like "processed", "cheese food", "cheese product", or "artificial".
Another hint, any cheese that comes sliced in tiny plastic wrappers is also likely to be "processed cheese". (Cheeses sliced with tiny pieces of waxed paper between them tend to be real, however.) Most Americans are rather disgusted by smelly cheeses, however, so you will find a rather small market for limberger, etc.StuRat 17:38, 5 October 2007 (UTC)
It's not cheese if you can't smell it from three counties away! DuncanHill 18:59, 5 October 2007 (UTC)
My wife comes from Lille - and their local cheese ("Vieux Lille") is reputed to be the strongest flavored cheese in the world. She claims that there is a law to prevent one from carrying Vieux Lille in a Parisian Taxi! SteveBaker 17:54, 6 October 2007 (UTC)
My favorite euphemism in this vein is "processed cheese food product". Corvus cornix 01:48, 7 October 2007 (UTC)

[edit] digestive tract

05:02, 5 October 2007 (UTC)05:02, 5 October 2007 (UTC)~~m4.239.243.165 05:02, 5 October 2007 (UTC)Is it neccessary to have a bowel movement everyday? And is there a certain number of bowel movements a person should have per day?4.239.243.165 05:02, 5 October 2007 (UTC)

From 3 a day to once every 3 days is the guideline I heard, and that's the latest poop. StuRat 05:51, 5 October 2007 (UTC)
Quite. I once heard that nothing varied so much between humans as much as this statistic. It depends a lot on what you eat. Once every three days was normal for me as a kid, because I was fed hardly any roughage.--Shantavira|feed me 17:37, 5 October 2007 (UTC)
In Western societies, people generally defecate two or three times a day, but it’s an individual matter. All the advice about the importance of regular bowel movements notwithstanding, some people defecate just once a week and are perfectly healthy. Constipation isn’t defined by the frequency of bowel movements, but by whether someone has difficulty when they have one. —Preceding unsigned comment added by 88.109.121.209 (talk) 19:53, 5 October 2007 (UTC)
It's my understanding that keeping feces in the bowel for long periods is associated with higher colon cancer rates. --Sean 14:19, 6 October 2007 (UTC)
I've also heard reports that colon cancer incidence is higher among individuals who feel constipated (eg, [2]). Note that that doesn't suggest anything about causation (not that you're suggesting causation, Sean), just that there's an association. It might be explained by some confounding variable, eg, that some underlying condition predisposes individuals to both colon cancer and constipation, not that longstanding or frequent constipation causes colon cancer. --David Iberri (talk) 15:49, 7 October 2007 (UTC)

[edit] Klebsiella Infection

What is the acceptable colony count of Klebsiella per Milligram?

Diya Mukherjee —Preceding unsigned comment added by Diya2710 (talk • contribs) 07:38, 5 October 2007 (UTC)

It's impossible to answer the question for at least two reasons. First, you haven't specifed what is being counted (though I suspect you're talking about urine). Second, colony counts alone are not diagnostic of anything: a colony count has to be considered in light of actual clinical conditions (symptoms of the person, reason for the testing, the presence or absence of instrumentation). As such, a colony count really needs to be evaluated by the treating physician or other medical practitioner. For example, if a patient has an indwelling urinary catheter and a colony count of 10,000, it might be considered a colonization requiring no treatment (in the absence of symptoms), and it might also be considered an infection requiring treatment (in the presence of fever or other symptoms). Similarly, the significance of the presence of Klebsiella in sputum would depend on the clinical setting in order to distinguish between colonization and infection. - Nunh-huh 17:37, 5 October 2007 (UTC)


This sounds like either a homework question or medical advice. The Reference Desk has a policy of not answering either. If homework, look it up yourself (e.g. in your textbook or class material). If medical advice, talk to a licensed medical professional. -- 72.33.121.200 18:58, 5 October 2007 (UTC)
It sounds like neither. A homework question would be more exactly phrased, and medical advice would pertain to a clinical question rather than an abstract one about lab values. - Nunh-huh 20:02, 5 October 2007 (UTC)

[edit] What kind of lock / key combination is this?

I need access to this common type of lock to open a panel but I don't know the name of the lock / key I need to get hold of to open it. These things open pretty easily and I have a feeling some thin pliers might do the job, but is there a particular name? Thanks.

http://img515.imageshack.us/img515/862/lockfh6.png

Looks like a meter cabinet - I think (in the UK) you should be able to get one from Screwfix, B&Q, Homebase etc. They are just called "meter cabinet keys". DuncanHill 08:48, 5 October 2007 (UTC)

[edit] aids

why aids donot spread by mosquito bite? —Preceding unsigned comment added by 202.177.155.94 (talk) 10:45, 5 October 2007 (UTC)

HIV_and_AIDS_misconceptions#HIV_is_transmitted_by_mosquitoes--Mostargue 11:13, 5 October 2007 (UTC)

[edit] unlitateral carotid ligation

What is unlitateral carotid ligation? Does it just mean that the two carotid arteries are connected? What would serve as the conduit? It's used or was used, as part of an animal model for cerebral ischemia. --Seans Potato Business 13:43, 5 October 2007 (UTC)

Here's a partial answer. Unlitateral carotid ligation is the tying off of one of the two carotid arteries, which supply the head and (most importantly) the brain. Normally, this should not cause problems because of the Circle of Willis, which is a circular arterial loop fed by both internal carotid arteries. However, if one of the carotids is partially or completely occluded (e.g. with atherosclerotic plaques), it would be dangerous to ligate the carotid on the other side. -- Flyguy649 talk contribs 15:43, 5 October 2007 (UTC)
(after edit conflict) Unilateral carotid artery ligation is the closure of the carotid artery on one side. The artery is not rerouted or attached anywhere else; it's just closed. It is indeed used in animal cerebral ischemia studies. See for example Guri Bronner, Kendall Mitchell and Frank A Welsh "Cerebrovascular Adaptation After Unilateral Carotid Artery Ligation in the Rat: Preservation of Blood Flow and ATP During Forebrain Ischemia" in the Journal of Cerebral Blood Flow & Metabolism (1998) 18: 118–121 [3].
It turns out that closure of one carotid artery doesn't typically have any serious effects in an otherwise healthy rat's brain. There's sufficient redundancy in the blood vessels of the rat's brain to maintain an adequate supply of blood to the affected hemisphere of the brain. However, combining this closure with other stresses (hypoxia, closure of additional vessels, etc.) will cause damage—there's not as much 'reserve capacity' in the system. Some researchers have looked at the ability of the rat's brain to adapt to closure of one or more major vessels to model chronic disease in humans; the paper I linked above showed that closing one carotid artery results in adaptive vascular changes in as little as three days. (This can happen in humans as well; there are cases of patients with both of their carotid arteries completely closed—their brains get sufficient blood through vertebral arteries that have expanded to take up the slack.) TenOfAllTrades(talk) 15:47, 5 October 2007 (UTC)
Thank you both. I see how "unilateral" was pointing in this direction, and checking that article, I gather "ligation" refers to the closure of the vessel ends created by cutting through it. --Seans Potato Business 18:25, 5 October 2007 (UTC)
"Ligature" refers to closing it by tying (see wiktionary:ligature; compare to ligature strangulation). However, practically , it doesn't matter how one of the carotids is blocked. -- Flyguy649 talk contribs 21:05, 5 October 2007 (UTC)

[edit] Petroleum jelly

Is there a silicon based equivalent for Petroleum jelly? 71.100.9.205 17:36, 5 October 2007 (UTC)

For what use? Shoe shine? Lip moistener? Spitball doctoring? Personal lubricant? People use petroleum jelly for many different things, so you'll have to clarify what you want the silicone equivalent for. Note also that silicon is a chemical element, while silicone is the slippery rubbery stuff. --Sean 17:56, 5 October 2007 (UTC)
To compare its physical, mechanical and thermal properties for a school project? —Preceding unsigned comment added by 71.100.9.205 (talk) 18:07, 5 October 2007 (UTC)


Silicone grease probably. You should be able to get some at a car parts store. (Note that's silicone - although it contains silicon). SteveBaker 18:32, 5 October 2007 (UTC)
Is there any real difference between generic silicone O-ring sealing greases and a specialized silicone grease like Dow Molykote 55? Kel - Ex-web.god 20:37, 5 October 2007 (UTC)
Well, Dow chemicals describe this stuff as "Phenyl-methyl" silicone grease - so it obviously has chemicals in it in addition to simple silicone grease - but what these actually do - and whether that makes this stuff actually better than regular silicone grease - is anyones guess. SteveBaker 17:47, 6 October 2007 (UTC)

[edit] Modulation techniques book

Can someone give me the name of some good books on modulation techniques for wireless communication systems? I'm particularly interested in information about QAM and the various forms of PSK, which I think are the most used modulation formats and also OFDM. I would appreciate your help, thanks! 217.129.207.58 21:28, 5 October 2007 (UTC)

Look for Signal processing, modulation and noise by J.A.Betts (Dept Electronics Univ of Southampton). Published by Hodder and Stoughton 1970 (reprinted 1975 and maybe later) ISBN N0: 340 09895 3 (paperback) or 0 340 05212 0 (Case bound) —Preceding unsigned comment added by 88.109.121.209 (talk) 22:22, 5 October 2007 (UTC)
Proakis and Manolakis Digital Signal Processing is a good start, and though it's not extremely thorough in the actual modulation architecture, it will provide the processing techniques you need to use, which will assist your understanding. Nimur 22:51, 5 October 2007 (UTC)

[edit] Preferential Solubility?

Assume I have two substances of differing solubility in water: A=250mg/mL and B=50mg/mL. Excluding any temperature and pressure variables, what happens when I add 250mg of A and 50mg of B in 1mL of water concurrently? I assume both substances partially dissolve, but in roughly what amount or ratio? Also, what happens when A and B are added to the water consecutively? Last question: what's the name of the rule/law/effect/whatever that governs this effect? Kel - Ex-web.god 23:07, 5 October 2007 (UTC)

I think you are likely looking for the common ion effect. We would need to know more information to tell you specifically what would happen, but this has hints of a homework problem. Someguy1221 00:15, 6 October 2007 (UTC)
Hmm. I never would have guessed my writing style could be confused with that of a 12-year-old. Regardless, were this a homework problem, I'd have asked it a decade ago, when I was still in college. :) This is for my own education. Anyway, what further information do you need that would make any difference? The solubility figures above weren't from any specific substances, but if it makes a difference, I'd say any random hydrochloride (or sulfate) salts. Kel - Ex-web.god 00:39, 6 October 2007 (UTC)
To a first approximation, this turns out not to be the case: the basic rule is that the concentration of one substance in a solution will not affect the solubility of another. This is because the solubility of a substance is not determined by "the amount of dissolved stuff the water can hold", but by a chemical equilibrium at the interface between the solution and the solid substance. Basically, the substance dissolves at a constant rate (per unit area), but also precipitates back at a rate proportional to its concentration (again per unit area). In a saturated solution these two rates will be equal, and no more of the substance can dissolve.
Of course, these rules do have exceptions. One is the "common ion effect" already mentioned above: if the substance split into multiple components when dissolving, the concentrations of all those components will affect the precipitation rate. Another is that, to be precise, the word "concentration" in all of the above really needs to be replaced with chemical activity, a more complicated measure that tends to be proportional to the concentration in dilute solutions but deviates from it in more concentrated ones. The activity can also depend on the general ionic strength of the solution: essentially, as the solution gets concentrated enough, the different dissolved substances start interacting with one another. Our article on the solubility equilibrium lists several more such effects, and also describes the matter in general. —Ilmari Karonen (talk) 15:33, 6 October 2007 (UTC)

[edit] Scarlet Macaw

Should his claws cut into and hurt my shoulders like that? I only got him recently and he seems to really dig in and hold on when he sits up there. —Preceding unsigned comment added by 81.79.213.158 (talk) 23:45, 5 October 2007 (UTC)

Excluding the possibility that he really dislikes you, I'd say it's because his claws are designed to grab a branch. Your shoulder is too big, so he needs to squeeze harder to get a good grip. It might help if you wore a strong (for you), yet thin (for him), shirt. And preferably just one (so not a shirt and a t-shirt). DirkvdM 09:01, 6 October 2007 (UTC)
Your avian veterinarian can trim your macaw's talons (and beak, if you wish). We have this done with our sun conure because she really, really likes to cuddle within our clothes, but her sharp little talons can do a number on one's skin when they are "fully sharp". You don't want too much trimmed, though, or your bird won't be able to perch easily.
Atlant 23:39, 6 October 2007 (UTC)

[edit] Glucose in benedict's solution

When one puts glucose into a dialysis tubing and into a test tube of Benedict's Solution and heats it in a water bath, the Benedict's solution inside the test tube turns an opaque yellow. But does the glucose inside the dialysis tubing (which is inside the test tube) also turn yellow? I guess in short, will the Benedict's solution diffuse into the dialysis tubing? Thanks. Acceptable 23:46, 5 October 2007 (UTC)

Try Benedict's reagent. --JWSchmidt 15:28, 6 October 2007 (UTC)