Wikipedia:Reference desk/Archives/Science/2009 October 25

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October 25

Kaposi sarcoma

Is it possible to contract Kaposi sarcoma without having the HIV/AIDS virus? If so, under what circumstances would it be under?72.95.174.219 (talk) 02:19, 25 October 2009 (UTC)

I know nothing about it, but the article on Kaposi sarcoma seems to state that it is caused by the Kaposi's sarcoma-associated herpesvirus, not the Human immunodeficiency virus (HIV). If that virus were transmitted, I guess it might be able to cause a tumor without the presence of HIV. —Dromioofephesus (talk) 02:44, 25 October 2009 (UTC)

(ec) Infection with HHV-8, the virus that causes Kaposi's sarcoma, is much more common than the disease - thus, the disease occurs in only a small minority of people infected with the virus. The disease does occur in people who don't have HIV; for example, "Classic KS" is described in certain populations of Mediterranean men, and "Endemic KS" is described in some parts of Africa. Both are described in our KS article. -- Scray (talk) 02:45, 25 October 2009 (UTC)

The Kaposi sarcoma was discovered in 1872 and this was before any HIV spread in humans.--Stone (talk) 14:24, 25 October 2009 (UTC)

Time machine coin story

I've read an Arabic article here (Google translation) and also another story in Arabic Wikipedia (I marked as citation needed). The articles seemed interesting till I read about an experiment done in 1980s to transport a coin from one place to another via fiber optics. The story told scientists could make the coin vanish for about 1 hour and 6 minutes and then suddenly appeared in the other place. I know it's funny but I'd like to confirm if such stories were originally written in English and where can I prove/disprove about them?--Email4mobile (talk) 05:59, 25 October 2009 (UTC)

I don't know where you could find the stories in English, but for the stories to be true, there would have to be a fundamental change in the laws of physics as we know it or for an event to occur with a fantastically small probability. So I would say that as conclusively as possible, the stories are untrue by Occam's razor, and thus "disproved." Perhaps I am misunderstanding the article though, it is certainly possible for a coin to travel through space and time; just pick up a coin and throw it: See! it just moved through space and time in your reference frame. But I don't think that this is what the article meant. Jkasd 09:14, 25 October 2009 (UTC)

That's (rather slow) teleportation, isn't it? There have been no accepted successful attempts at teleportation other than transferring quantum information from one atom to another (see Quantum teleportation), that wouldn't allow for transporting coins. --Tango (talk) 15:20, 25 October 2009 (UTC)

We have to stick by the mantra that "extraordinary claims require extraordinary evidence". We don't see ANY evidence (apart from one shakey translation of what is evidently not a news or science journal - but perhaps a blog site or something). If this were true - or even CLOSE to being true - there would be immense repercussions. Such a thing could not be kept quiet for 20+ years - the experiment would have been repeated, re-repeated and studied until some kind of an explanation emerged. It is overwhelmingly likely that this is a hoax or some piece of fiction being misrepresented as truth. The translation of that Arabic piece does not suggest anything remotely like a proper scientific experiment - the rambling at the end about Stephen Hawking and others stinks of someone with little scientific knowledge seeking to make their story look more believable by dropping some real physicists' names into the story. I don't believe it for one moment.

If I had to be super-charitable, there is a thin possibility for confusion. The nearest thing I could find to this claim was the success in "teleporting the quantum properties of one atom to another across several feet" - which is an interesting physics experiment - but a heck of a lot different than teleporting a coin...plus I found a news report where the reporter used the analogy of transferring the head/tails state of a coin to that of another coin several feet away. I suppose that a non-English reader might misread that as the actual teleportation of the coin...when in fact, no coin was involved, not even a single atom was teleported - only it's "quantum state"...which is a heck of a lot different from the head/tails state of a coin! However, if that's what really happened then the arabic article has CONSIDERABLY embroidered the story with bullshit details about bell jars and the time delay and all sorts of other things that never happened.

So we may conclude that either: (a) this never happened...or... (b) there is no evidence that it ever happened...or... (c) the story in arabic is mere confusion of the experiment I explained above...or... (d) that it's a hoax. If one or more of those things is true (which is surely the case) - then this should be deleted from the Arabic Wikipedia immediately. A little blue "citation required" tag is only appropriate when the fact in question is not seriously disputed but a citation is needed. In this case, the "fact" is very seriously disputed and should be deleted until/unless at least one solid reference can be found (ie a Peer-reviewed scientific paper in respectable journal). Nothing less than that standard of proof would be acceptable for such an outrageous claim! SteveBaker (talk) 19:58, 25 October 2009 (UTC)

If someone could actually do this, they would be the most famous scientist in the world and the experiment would have been world news - it's clearly bollocks. --Cameron Scott (talk) 20:00, 25 October 2009 (UTC)

Some joker is trying to pull the fiber over your optics. Clarityfiend (talk) 23:05, 25 October 2009 (UTC)

heck, happens in my house every day. I'm always not finding something where i'm sure i put it, and then it turns up somewhere else. Gzuckier (talk) 03:24, 26 October 2009 (UTC)

Just today, I lost some important keys for several minutes, then I found that they had been teleported to "the last place I looked." Edison (talk) 04:11, 27 October 2009 (UTC)

All I can say is thank you all for your quick response regarding this topic and I'm really sorry for replaying too late. I've revised the wikipedia article (here are the Arabic new article and old article) and found that someone has already deleted the paragraph related to science experiments.--Email4mobile (talk) 16:28, 12 November 2009 (UTC)

What is this boat.

Doing some google earth, I came across a boat at 40°48.655′N 14°5.602′E (near Italy). The google maps image is the one I'm referring to (although other provides may use the same image. There's a large ship (290 feet (88 m)) and in the middle of the ship is what looks like a giant screw, or a tank, like a door in a ship. What is the purpose of that central structure, and what kind of ship is this? I imagine it's some sort of liquid transport, but it doesn't look like most oil barges I've seen. Shadowjams (talk) 07:57, 25 October 2009 (UTC)

Probably a Pipe-laying ship. See the seventh drawing from the top at this site - the drawing shows a ship with two reels rather than one, but the basic arrangement is the same. Tevildo (talk) 08:20, 25 October 2009 (UTC)

Wow! Neat image. I agree with Tevildo. Or it might be a Cable-laying ship. —Steve Summit (talk) 17:07, 25 October 2009 (UTC)

Thanks. Those both look like matches. It's a curious ship design I'd never seen before. Shadowjams (talk) 20:07, 25 October 2009 (UTC)

lipids

How does trans fatty acids and unsaturated fatty acids corelate to LDL? —Preceding unsigned comment added by 122.169.11.39 (talk) 08:41, 25 October 2009 (UTC)

Trans fat raises your LDL levels, lowers your HDL levels, and is even worse for you than saturated fat. Replacing part of the saturated fat and trans fat in one's diet with naturally occurring unsaturated fat will generally result in lower LDL levels. Trans fat is actually a type of unsaturated fat, but it's a different kind of isomer than the kind of unsaturated fat (cis fat) that occurs naturally in vegetable oils, oil that hasn't been artificially hydrogenated. Red Act (talk) 13:12, 25 October 2009 (UTC)

yeah. as the diagrams in trans fat and saturated fat show, they both have nice orderly carbon chains that pack tightly and are both solid at room temp, while cis fat unsaturated fats have a kink in them that inhibits packing so they're fluid at room temp. so, it appears that it's not so much the saturated or unsaturated nature of the fats that affects the body as their fluidity; less fluid fats drive up the bad LDL and down the good HDL, more fluid fats the opposite. Gzuckier (talk) 03:15, 26 October 2009 (UTC)

Mixture of gases

I have been working on the following exercise:

A mixture of gases He and O₂ has a density of 0.518 g/L at 25ºC and 721 mmHg. What is the percentage in mass of He in this mixture?

I have tried both using the ideal gas formula (which failed, because I know neither V nor n) and the following proportions formula:

$32x+4(1-x)=1$

Where 32 and 4 are the molar masses of O₂ and He, and x is the decimal proportion of O₂ in the mixture.

Nevertheless, I just keep getting rubbish results, instead of the actual result, which is 19.9% He. What am I doing wrong? Should I try another approach? Thank you. Leptictidium (mt) 09:48, 25 October 2009 (UTC)

The ideal gas law (pV = nRT) is the right approach. You know R and T. Assume a fixed volume (say, 1 litre). The overall mass of the system is then ρ V (and you're given ρ, the density). n_He = m_He / M_He, where m_He is the mass of helium in the system (which you don't know), and M_He is the molar mass of helium (4.0 g/mol) - similarly for the O₂. p_He + p_O2 is the total pressure of the system, by Dalton's law, and you're given that value (721 mmHg). Substitute the ideal gas law values for p_He and p_O2 in the Dalton's law equation, and you should have enough to calculate the ratio m_He/m_O2. Tevildo (talk) 10:50, 25 October 2009 (UTC)

Thank you, but... How am I supposed to calculate p_He without knowing n_He, or vice versa? Leptictidium (mt) 11:29, 25 October 2009 (UTC)

The Dalton's Law equation is $p_{He}+p_{O_{2}}=p_{total}$. From the ideal gas law, we get $p_{He}={\frac {m_{He}RT}{M_{He}V}}$ and $p_{O2}={\frac {m_{O_{2}}RT}{M_{O_{2}}V}}$ The two equations you need to solve are: ${\begin{aligned}{\frac {m_{He}RT}{M_{He}V}}+{\frac {m_{O_{2}}RT}{M_{O_{2}}V}}&=p_{total}\\m_{He}+m_{O_{2}}&=m_{total}=V\rho \end{aligned}}$ R, M_He, and M_O2 are known physical constants. p_total, T, and ρ are given in the question. If we assume V = 1.0, we can solve the equations for m_He and m_O2. (Perhaps start by rearranging the second equation to give m_He in terms of m_O2?) Tevildo (talk) 12:07, 25 October 2009 (UTC)

Coffee Stain

When coffee stains, water colour and other ink stains start out with lot of water and then dry out, why does the dye accumulate at the periphery? I am trying to simulate coffee stain effect. If the dye is supposed to diffuse, then it should spread evenly, right? Is there a wiki article on the physical mechanism behind this ink spreading? —Preceding unsigned comment added by 59.93.1.138 (talk) 10:55, 25 October 2009 (UTC)

Basically, what happens is that the dye gets carried along with the solvent. The articles I can think of that come the closest to addressing this kind of phenomenon are paper chromatography and thin layer chromatography. Unfortunately, those articles don't go into a whole lot of technical detail about the mechanisms involved. Red Act (talk) 11:40, 25 October 2009 (UTC)

Umm. Is this obvious or am I missing something? It doesn't seem to me to be quite like paper chromatography because all the coffee is added well mixed (versus solvent washed past the solute). However, even for initially well mixed coffee the solvent will eventually be fairly evenly spread but the concentration in it won't be. All the time the stain is spreading the leading edge is both thinner than the bulk of the fluid behind it (so evaporating proportionately upwards more) and evaporating in the coplanar direction into the carpet (so it has an extra surface). So it is continually getting more concentrated than the bulk of the coffee. Hence a darker ring. That make sense? --BozMo talk 21:04, 25 October 2009 (UTC)

Whoops. You're right; the situation is rather different from paper chromatography. Please disregard my answer. Red Act (talk) 22:38, 25 October 2009 (UTC)

The physical basis of the phenomenon is described in Contact line deposits in an evaporating drop, Deegan et al , Phys Rev E, 2000. Looie496 (talk) 21:07, 25 October 2009 (UTC)

Thanks I'll look into the pdf. It seems exactly the thing I'm looking for. How did you mange to find that paper? I couldn't think of any thing to google but 'coffee stain'. The other contents of the site also seem very interesting. 59.93.8.217 (talk) 13:25, 26 October 2009 (UTC)

@BozMo: Are you implying that

1. Solute dissolved in the amount of water that evaporates will settle
2. The extra evaporation at the edges cause more deposition
3. Fluid from the bulk now flows (along with solute) to the edge to replace the the water lost
4. Total height of the spill decreases until all of the water is gone? 59.93.8.217 (talk) 13:25, 26 October 2009 (UTC)

The first point is not needed for the explanation to work but the other three look good to me. The first one is only true once saturation has been reached and the concentration gradient may even cause osmosis I don't know. Please note though my research was nonlinear fast combusting shock-waved exploding type flows and I never even taught the slow stuff or deposit forming. --BozMo talk 15:13, 26 October 2009 (UTC)

Was gentian violet ever a commonly used antiseptic in the U.S?

Was gentian violet ever a commonly used antiseptic in the U.S.? If it was, when did its use begin to decline? —Preceding unsigned comment added by 98.114.98.236 (talk) 14:39, 25 October 2009 (UTC)

Well, the first thing that pops to mind was that various characters in the novel Catch-22 were always getting their toes and gums painted with the stuff, and in fact this tidbit is mentioned in our article on gentian violet. [Don't tell the notability police, though; they've got it in for "in popular culture" sections.] Does that article give you any useful information on your question? —Steve Summit (talk) 17:01, 25 October 2009 (UTC)

You can search in Google Books advanced search, varying the time period. I see no results for gentian violet as an antiseptic before 1871, then lots thereafter, once there was the concept of an "antiseptic" after germs were theorized. Try searching one decade at a time. Certainly it was at times a commonly used antiseptic in the U.S. Some problems have been observed: A recent mention is [1]. Edison (talk) 04:08, 27 October 2009 (UTC)

Hippo teeth

I'm trying to help a six year old with homework (so this is homework, but not mine!). While I've found plenty of descriptions of hippo teeth (and pictures, yuck!), I've not been able to answer a question of why their teeth are like this! Anyone? --Dweller (talk) 17:06, 25 October 2009 (UTC)

The general rule with teeth is 1. consider what they eat, and 2. if they have things like tusks, consider how they fight. --Mr.98 (talk) 17:17, 25 October 2009 (UTC)

Like what, exactly? From a evolutionary perspective, utilizing natural selection, favorable random mutations are passed onto offspring at a greater rate than unfavorable random mutations and non-mutations, thus establishing greater and greater diversity between species. So it must have been that such teeth favored the species leading up to and including the modern-day hippo. As a dentist, I can say with some experience and context that hippo teeth, and for that matter, the teeth, skulls and skeletal patterns of almost all organisms are a real wonder. When taken on a whole, most everything about everything is actually a wonder, if considered in that context. DRosenbach ^{(Talk | Contribs)} 17:38, 25 October 2009 (UTC)

Sorry -- I was assuming you meant your question on a very general level. If, though, by why you meant "how does it come about" or "what processes occur in the periodontium and related structures such that the teeth exist in the manner and environment that they do", you might want to contact the chair of vertebrate zoology at your local natural history museum -- the answer will likely be too complex for a six year old's homework, though...with references made to structures and processes the likes of dental lamina, cementum, odontoblasts and amelogenesis. DRosenbach ^{(Talk | Contribs)} 18:41, 25 October 2009 (UTC)

I think... you have missed the point about the "hippo", here. It is a 6-year-old's question regarding a specific animal, not a general question about "what is evolution, and what does it mean?" --Mr.98 (talk) 20:26, 25 October 2009 (UTC)

My point was that although the teacher may not understand this (and it might often be that 1st grade teachers lack understanding of this caliber), the father should understand that it's a silly question -- once one asks about a hippo's teeth, why not ask about a manatee's fluke and a walrus's tusks. Then let's ask about the innumerable other specialty items that most animals possess. The kid wasn't asking the question -- it was the father, so I figured the father could use a response to sort of smooth over the intensity of the question's focus on hippos -- the same answer applies for all animals' specialty items. DRosenbach ^{(Talk | Contribs)} 01:24, 26 October 2009 (UTC)

For a 6 year-old's homework - it would be plenty good enough to say that the hippo's teeth evolved the way they did to allow them to eat the food that's available for them in the places where they live. So look up what a hippo eats - and try to understand why their teeth make that easier for them. SteveBaker (talk) 19:23, 25 October 2009 (UTC)

In addition to the topic of eating, I think Mr. 98 was right to highlight the role that tusks might play in "social interaction". -- Scray (talk) 19:29, 25 October 2009 (UTC)

Yes, I wasn't trying to be obtuse... I just wanted to structure the inquiry a bit better, and I thought that was clear. Hippo's teeth do two things: they let it chew the leafy material that they eat (those rough, herbivore molars), but more notably (what distinguishes their jaws from, say, cows, in the most obvious way), the front tusks are used for sparring with other hippos (sexual selection), and for self-defense. These are both clear from the hippo page on here, if you are looking for the right things. --Mr.98 (talk) 20:14, 25 October 2009 (UTC)

(ec)In our article, Hippopotamus, it says that the large canines are used for fighting (either other hippos, or other animals such as crocodiles), and that Hippos mostly eat grass. They need rough molars to chew that. 86.144.144.110 (talk) 20:17, 25 October 2009 (UTC)

The OP might consider explaining to his child that hippo teeth are as they are - gross and ugly - because hippos don't brush. Perhaps this might encourage a lifetime of better dental hygene in the child. B00P (talk) 05:19, 26 October 2009 (UTC)

Thanks chaps, and probably adequate for the 6 year old (particularly comments on tusks and on hygeine). For my own curiosity now, why are hippo teeth (as opposed to tusks) so drastically different from other large herbivores that primarily eat grass? --Dweller (talk) 14:03, 26 October 2009 (UTC)

Other large herbivores generally have fairly impressive horns, which can be used for the same purpose. Tevildo (talk) 21:40, 26 October 2009 (UTC)

Membrane fluidity. What is it good for?

I was taught in class that the fluidity of lipid membranes is a result of the type of lipids of which the membrane is constructed (saturated vs unsaturated, length) and the presence of cholesterol. I was also told that the fluidity of a membrane is important to a cell, that being to rigid is bad. I was never told however, why exactly this is bad. Wikipedia's article on membrane fluidity doesn't really cut it for me.PvT (talk) 17:26, 25 October 2009 (UTC)

I'll tell you that after learning this quite a number of times (high school, college, dental school and now again in post-grad), I found only one or two professors who know enough to actually answer such a question. It is merely explained that membrane fluidity is proportional with the cells' ability to be flexible (in the figurative sense, not only the literal sense) in the face of insult. Rigidity, they explain, is detrimental to the cell's ability to adapt to mechanical forces and mechanical changes in ECM of immeditate vicinity. DRosenbach ^{(Talk | Contribs)} 19:37, 25 October 2009 (UTC)

The interesting thing is that I did a thesis a while back on lipid producing algae. Funny thing is they tend to produce more unsaturated fatty acids in cold waters. Presumably this was to maintain the same level membrane fluidity. These algae would most likely not endure high shear forces in nature nor do they need to phagocytize their food source. To me it appears that something more is going on here then just being able to handle mechanical stress.PvT (talk) 20:08, 25 October 2009 (UTC)

Even if you don't need to handle sheer forces or phagocytize food, you still need to turnover your membrane proteins and lipids. This means that any cell will be continuously exporting and importing material from its membrane, and this will mean extreme local curvature. Cell division will also require a degree of membrane fluidity. Someguy1221 (talk) 22:01, 25 October 2009 (UTC)

yep. warm blooded animal fats: saturated, solid at room temp but fluid at body temp. fish fats: unsaturated, fluid at the cold temps fish live at. plant oils: unsaturated, fluid at room temps where plants live except...... tropical plants like palm or coconut, whose saturated fats are solid at temps up north here, but fluid at the slightly higher temps where they live. which suggests that cell membranes have to not be too solid, but also not too fluid. i don't think we've made more than a dent in the question of membrane function, but there are issues of permeability (gotta keep the inside separate from the outside or you're not a cell), mobility of membrane structures and proteins etc., which have to sort of float around from where they get made to where they need to be, how proteins, which typically have moving parts, function when embedded in a fluid of whatever consistency, and as some guy points out, just the physics of the bending a membrane goes through. maybe when we get a better handle on this stuff we'll be better able to understand the role of cholesterol in the body than we do now. Gzuckier (talk) 03:03, 26 October 2009 (UTC)

Thanks for the answers guys :).PvT (talk) 11:36, 26 October 2009 (UTC)

mental and cognitive development

Hi everyone, I've been given an assignment on child development and the criteria includes mental and cognitive development of a child. My question is, is there a significant difference between a child's mental and cognitive development or are the terms interchangeable? If not, any hints about what I should be including when writing about each of these things? Thanks to anyone who helps! RichYPE (talk) 19:26, 25 October 2009 (UTC)

Those sound like technical jargon words to me -- likely, they require specific definition on the level at which you are being educated. DRosenbach ^{(Talk | Contribs)} 19:40, 25 October 2009 (UTC)

Mental is a general term for anything to do with the mind. Cognitive refers to reasoning and logic. --Tango (talk) 19:43, 25 October 2009 (UTC)

In my opinion (as a behavioral neuroscientist), you should treat the two as meaning the same thing. Looie496 (talk) 20:46, 25 October 2009 (UTC)

Ok, so what do they mean to you? --Tango (talk) 21:19, 25 October 2009 (UTC)

Both of them basically mean development of the ability to think. This is a very broad and loosely defined question. You could stretch for a distinction between them but it seems most likely to me that the person who wrote that wasn't trying to be so subtle. Looie496 (talk) 21:28, 25 October 2009 (UTC)

Would you consider developing, for example, the ability to empathise to be part of mental and cognitive development? I would consider it part of mental development but not cognitive. --Tango (talk) 00:38, 26 October 2009 (UTC)

Looie, I have to disagree with you despite your expertise. Cognition is conscious mental reasoning, and mental includes unconscious mechanisms and heuristics, like recognizing shapes and fine motor coordination. Vranak (talk) 22:12, 25 October 2009 (UTC)

According to our Mental retardation article, (lack of) cognitive development is one part of mental retardation, as distinguished from "[an] individuals' functional skills in their environment". Mental development redirects to neural development, but I don't think that's what your teacher means. Developmental psychology might be a useful reference. Tevildo (talk) 21:12, 25 October 2009 (UTC)

Gravitys effect on radioactive decay

Does radioactive elements decay at a different rate in different fields of gravity? The measure given for known elements decay rates are they for G=0 or maybe G does not mean anything in relation to radioactive element decay?

And what happens in layman turns to elements properties in extreme gravity fields (high Gs)? —Preceding unsigned comment added by 85.81.121.107 (talk) 20:05, 25 October 2009 (UTC)

Any effect will only happen where the force of gravity exceeds that of the weak or strong forces involved in the nucleus. You are looking at G=10⁴⁰ or something like that. In neutron stars extreme pressure affects the atoms. Graeme Bartlett (talk) 20:57, 25 October 2009 (UTC)

Radioactive decay will happen slower (from the perspective of a distant observer) in higher gravitational fields due to gravitational time dilation. --Tango (talk) 21:18, 25 October 2009 (UTC)

Me again..

G=10⁴⁰ in relation to the above, is that some kind of point where the forces 'melt' together?

So outside of elements (atoms) traveling near a black hole (horizon) I can assume that decay rates are somewhat universal? Is time dilation accounted for... Neutron stars is not really different elements (atoms) so what is the rule that governs decay rates in a gravity field. Gotta read up on neutron stars. —Preceding unsigned comment added by 85.81.121.107 (talk) 22:40, 25 October 2009 (UTC)

Yes the pressure in a neutron star is what changes the situation, electrons confined to a small space with the nucleus causing then to react with the protons inside. The same thing could happen with neutrinos. One theory about beta decay is that some of the observed effects are due to a vast flow of neutrinos flowing through the nucleus affecting the outcome. We cannot detect all those low energy neutrinos, (unless they make up the dark matter). My very rough G=10⁴⁰ figure would be when the forces combine, the idea was that the weight of a particle in the nucleus would exceed the binding force. Even near this the nucleus could be squashed flat and properties changed. But even in a neutron star you don't get G forces near this. Perhaps when a cosmic ray hits the earth you may get an acceleration like this, with nucleus being disrupted. Graeme Bartlett (talk) 21:08, 26 October 2009 (UTC)

DNA stability vs. RNA

Which contributes more greatly to the chemical stability of DNA when compared to RNA: the fact that it contains thymine (and not uracil, which spontaneously deaminates into cytosine, which would lead to A-U -> G-C mutations), or the fact that it is double-stranded, which, at least to me, seems to protect the bases in a hydrophobic core. Although RNA may form extensive irregular double-stranded secondary structure, it remains single stranded to a significant degree, and so may be more labile because of this. Thanks for the help. —Preceding unsigned comment added by Lashyn (talk • contribs) 21:21, 25 October 2009 (UTC)

Most of the stability differences between RNA and DNA in vivo arise from the abundance of ribonucleases in the cell, which post-dates the "choice" of DNA over RNA as the genetic material of all living organisms. RNA can also exist in a double stranded state, although this is especially unstable due to dsRNA targetting RNases. As for what stability issues may have lead to the initial choice of DNA over RNA long ago, I'd assume (I'm just guessing here) it may have to do with the ability of RNA to self-hydrolyze its phosphodiester bond through a reaction with its 2' hydroxyl group, which is lacking in DNA. As an example of the inherent instability of RNA outside of all other concers, even high purity RNA, stored at -80^oC, may be noticably degraded within years, while similarly purified and stored DNA, even single stranded, will stay good more or less forever. Someguy1221 (talk) 21:53, 25 October 2009 (UTC)

right. not to repeat what you said, but single stranded DNA is more stable because the 2' hydroxyl participates in the hydrolysis of RNA, so its absence makes DNA more stable in general; presumably that led to evolutionary supremacy of organisms using it, and the biological things like T vs U, double stranded, etc. got added later. Gzuckier (talk) 02:48, 26 October 2009 (UTC)

Also, there are nucleotide excision repair enzymes that fix damaged DNA. Mutations of these enzymes can cause xeroderma pigmentosum. Axl ¤ [Talk] 13:32, 26 October 2009 (UTC)

Radioactive Mercury

Which Radioactive Mercury were used in old Analog Telephone Sets Grammar-Phone Turn-table Player? —Preceding unsigned comment added by Fred Emagoro (talk • contribs) 21:57, 25 October 2009 (UTC)

I have a hard time interpreting your Q. Are you perhaps talking about a Gramaphone ? StuRat (talk) 00:49, 26 October 2009 (UTC)

There is no such thing as radioactive mercury. All of the naturally occurring isotopes are stable. The only way to get radioactive mercury is to make it synthetically - like in a nuclear reactor or something. The cost of the stuff would be spectacular. So I'm pretty sure you're mistaken about the radioactive part. Non-radioactive mercury is used in certain types of switches and relays - it's certainly found in old telephones and lots of other pre-modern electronic systems - dunno about gramophones though. SteveBaker (talk) 02:38, 26 October 2009 (UTC)

Perhaps poster makes the common mistake of hearing "isotope" and thinking "radioactivity"? DMacks (talk) 03:14, 26 October 2009 (UTC)

That's possible - but the uses of mercury in such primitive machines as analog telephones and gramophones are not of the kind that could possible care what isotopes are used. SteveBaker (talk) 14:03, 26 October 2009 (UTC)

Another possibility - the OP means "element" rather than "mercury". Tritium was used in luminous telephone dials (see Beta light). Some thermionic valves had thorium in the cathodes, but I don't know whether or not such a valve would be found in a domestic TV set or record player. I suppose it's not impossible that some equipment had radium/zinc sulphide luminous paint applied to it - that was more common in bedside clocks and watches, though. Tevildo (talk) 21:09, 26 October 2009 (UTC)

Analog telephones used carbon granules in the (Thomas Edison) transmitter, and magnets and coils of wire in the (Alexander Bell) earpiece. No mercury was needed. Analog gramophones/phonographs used in the pre-electronic days metallic steel or diamond or sapphire stylus, and an isinglass or metal diaphragm, so again no mercury. More modern electric players used magnet and coiled wire reproducers, or piezoelectric reproducers, and again no mercury. Edison (talk) 03:56, 27 October 2009 (UTC)

NaBH4 versus LiAlH4

Costs, environmental concerns and economics aside, what would be an advantage of using sodium borohydride over lithium aluminum hydride? Is it mainly the lack of reactivity with possible protecting groups, or is there more? John Riemann Soong (talk) 23:50, 25 October 2009 (UTC)

NaBH₄ is mild enough it can be used in aqueous solution. That's a huuuuge gain for industry, for lab-safety, and for organic-waste issues. The idea of "milder" is a whole world itself, not just "doesn't touch a protecting group". Using a milder reagent, one can get selectivity between two unprotected carbonyls (even easily reduce aldehyde in presence of ketone if you're careful). LiAlH₄ is also much more basic as well as more hydride-nucleophilic, so there are base-induced side-reaction issues to consider. DMacks (talk) 03:10, 26 October 2009 (UTC)

I considered that, but pragmatic considerations generally aren't a factor in grading examinations. No one awards you more points if your reaction is more environmentally-friendly! John Riemann Soong (talk) 04:35, 26 October 2009 (UTC)

Maybe not in your class.... DMacks (talk) 04:50, 26 October 2009 (UTC)

...but certainly they would in a class which teaches green chemistry. -- 128.104.112.179 (talk) 17:37, 26 October 2009 (UTC)