Wikipedia:Reference desk/Archives/Science/2006 August 5

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You can't make a silk purse out of a sow's ear

Some time ago, I heard about a group of researchers at a university extracting a substance strongly resembling silk from pigs' ears, and using it to make a purse. However, I can't find anything about this besides retellings of the story, with various embellishments. Is there any truth to this, or is it another urban legend? --67.185.172.158 04:20, 5 August 2006 (UTC)

I read something like that many years ago. Googled "silk purse" "sow ear" et voila: Arthur D. Little, who studied chemistry at MIT in the 1880's and founded a large consulting firm. He did it in 1921: http://libraries.mit.edu/archives/exhibits/purse/index.html and http://historywired.si.edu/object.cfm?ID=535 Edison 20:09, 5 August 2006 (UTC)

Tails of shrimp, stems of peperoncini, and peels of oranges and banannas

People often think I am some kind of weirdo because I eat the tails of shrimp, stems of peperoncini, and the peels of oranges.

I sortof understand from a taste/texture point of view - shrip tails are really crunchy and hard to eat, peperoncini stems are stringy, and orange/bananna peels are just bitter.

Are any of them bad for you, though? Is it really that weird to eat these things? It just comes from a family where, if you have food, you EAT it. --69.138.61.168 05:12, 5 August 2006 (UTC)

Nope. I've visited parts of the word where these things are considered delicacies - of course, they are prepared differently than what I imagine a typical Wikipedian would. --HappyCamper 05:15, 5 August 2006 (UTC)

One thing to watch out for is that orange peels may have pesticides and dyes in them that are not intended for human consumption. So, you'd better stick with organic oranges if you intend to eat the peels. StuRat 07:19, 5 August 2006 (UTC)

And in the tropics it is often advised to only eat peeled fruit (and to peel it yourself) to avoid diseases. Don't know which ones, though. DirkvdM 09:20, 5 August 2006 (UTC)

Obelix once complained of his belly after eating oysters. Asterix asked him "Don't you take off the shells ?" --DLL 17:19, 6 August 2006 (UTC)

i ned an urgent info

dear sir, i need an urgent info how to separate UREA and CREATININ from a water solution?

please get me the details in this regards as soon as poissible. thanks.. with regards, budhaditya chattopadhyay, bangalore, india BE(medical electronics) <email address removed>

depends on what purpose they need to be seperated for. if you just want to seperate them analytically, i'm sure RP-HPLC will do the trick. If you want to seperate them preperatively, it becomes more tricky. perhaps cation exchange chromatography? you could exploit the charge differences, i imagine creatinine picks up a positive charge at a higher pH than urea. from a quick look, it seems creatinine forms a complex with zinc chloride, you could have a go at that. Xcomradex 07:44, 5 August 2006 (UTC)

Windows Vista

I think I once saw a link to a program (on Wikipedia) that would configure an XP computer to take on the appearance of a Vista-driven one. Does such a program exist?--the ninth bright shiner ^talk 05:56, 5 August 2006 (UTC)

Maybe this helps? [1] --Abdull 10:06, 5 August 2006 (UTC)

possible infant diarrhea epidemic in Detroit's Harper Hospital in 1943

My infant brother died of diarrhea that year and the family story was that many babies died of it at Harper Hospital during the time of the 1943 race riots because they could not separate the well babies from the sick babies during the riot. I recall at one time years ago reading a newspaper clipping about it but cannot find any now. I am a retired reference librarian so I've looked pretty hard under subject headings pertaining to the (1)riots,(2)Harper's history and(3)medicine, but I know the databases are very different today. Thank you. --209.112.212.40 06:12, 5 August 2006 (UTC)

I don't have an answer, but would like to point out that diarrhea isn't a disease, but rather a symptom of many diseases, quite a few of which result from poor sanitation, especially drinking dirty water. It would be important to know the actual disease which caused the fatal diarrhea if you wanted to research it more thoroughly. Also note that simple rehydration therapy (drinking fluids somewhat similar in composition to Gatorade) can prevent death from diarrhea, so I would research whether this was done at that hospital at that time. StuRat 07:10, 5 August 2006 (UTC)

If I had to guess a disease that would cause an epidemic of diarrhea affecting infants in a hospital, I would tend to assume either cholera or amoebic dysentery. Our article on diarrhea discusses these and more. --ByeByeBaby 13:36, 7 August 2006 (UTC)

As a relative you should be able to get a copy of the death certificate which should list the exact cause. (in 1940s terminology.) Rmhermen 00:18, 9 August 2006 (UTC)

I've been quite disappointed with death certificates. They frequently just seem to take a guess at the cause, or just list a symptom. It probably just lists "diarrhea" as the cause of death, or maybe "dehydration". Considering that resources are allocated based on the fatality rates of various diseases, it doesn't seem right that death certs are so sloppy in listing the cause of death. StuRat 22:10, 9 August 2006 (UTC)

Chromatography

SIR, I am not able to understand the basic concept of chromatography hence i am fasing problem to learn and understand it.

1) For, eg. " In chromatography , the sample is applied at one end of the porous support which holds the stationary phase and the mobile phase is made to flow over it". The various constituents in the sample gets seperated due to difference in their distribution behaviour.

Now, the stationary phase is the porous support or the sample which is applied? What it is ment by distribution behaviour?

2) The various chromatographic techniques can be classified depanding upon the forces of interacting phenomenon between the solute molecules and the stationary phase.

Now which is the solute molecule and whice is stationary phase, Can you give me any example.

3) Can you explain me the principle of gel- filtration chromatography in simple english.

Thank you. —The preceding unsigned comment was added by Jimitshah123 (talk • contribs) .

I changed the formatting to make your questions easier to read. What are you quoting here? It's not the article Chromatography. Maybe you should start by reading that. —Keenan Pepper 06:32, 5 August 2006 (UTC)

The "simple English" WP has no Chromatography article. Imagine what concepts could be operated to deliver something readable for one only acquainted with simple words (but shall such words be enough when it comes to facing the study of a "problem".) There ought to be a ferryman and it should be the teacher : Why don't they get asked first ? --DLL 17:13, 6 August 2006 (UTC)

atomic physcis

which has higher energy the nuclear fusion or nuclear fission?

nuclear fusion + nuclear fission. Have fun with your homework =D --mboverload@ 06:59, 5 August 2006 (UTC)

Fission and fusion are processes that convert energy from one form into another. It doesn't make sense to say they "have energy". Atomic nuclei have different amounts of energy, as shown in Image:AvgBindingEnergyPerNucleon.jpg, and that's what makes fission and fusion possible. —Keenan Pepper 07:14, 5 August 2006 (UTC)

Fusion generally releases more energy. This is what you should write down. — [Mac Davis] (talk)

...that is, fusion of a given mass generally releases more energy than fission of an identical mass. Fusion also requires much more energy to initiate. StuRat 20:32, 5 August 2006 (UTC)

Since when do we just tell people what to write down?? —Keenan Pepper 05:14, 6 August 2006 (UTC)

Beware that they don't write down you name too. The parents might sue you if the pupil gets convinced of obtaining extra help. --DLL 17:06, 6 August 2006 (UTC)

Three times the same optical phenomenon?

What are the differences between anthelia, glory (optical phenomenon) and heiligenschein? --Abdull 10:04, 5 August 2006 (UTC)

Well spotted. I'm pretty sure these are the same phenomenon. The articles need to be merged (anyone?). Anthelia is the plural, by the way, and duplicates anthelion.--Shantavira 15:30, 5 August 2006 (UTC)

go ahead and merge it abdull. be bold

Actually, sudden mergers can upset some people. It might be wiser to apply {{mergeto}} and {{mergefrom}} and see who rises to comment. Melchoir 17:05, 5 August 2006 (UTC)

It looks to me as though "anathelia" and "glory" should be merged, but "heiligenschein" is different (for example, it doesn't seem to have rainbow colors). --Trovatore 05:39, 6 August 2006 (UTC)

I redirected anthelion and anthelia into glory (optical phenomenon) without merging. Heiligenschein needs a little bit more work, since the glory article needs to note that the phenomenon can occur on dewy grass. Gdr 11:52, 6 August 2006 (UTC)

But the point is, I think it's a different phenomenon on the dewey grass, since you don't see rainbow bands of color, just white. --Trovatore 17:09, 6 August 2006 (UTC)

Yes, it's a different phenomenon altogether. If you follow one of the external links from heiligenschein you'll see that the explanation has to do with the drops of water focusing the sunlight on the blade of grass behind them, then acting as a lens from the point of view of the viewer. A glory, on the other hand, has to do with surface waves of light on the water drop itself. So please don't merge these; they seem to be quite distinct. --Trovatore 17:30, 6 August 2006 (UTC)

The other side of the Big Bank

After the Big Bang, why is it that the Universe is expanding in one general direction? If this is not the case, then what is on the other side of the initial point of the Big Bang?

--Dparisi 16:38, 5 August 2006 (UTC)

In one general direction? It expands forward in time. If it expands backward in time from its starting point, I don't think we'd know. In most (all?) big bang scenarios, time started at the initial point and so nothing was before it because there was no time before it. digfarenough (talk) 16:53, 5 August 2006 (UTC)

In some branches of String Theory it is possible that there was a 'before the big bang'.

I think that Dparisi is under the impression that the universe is moving out into the left (or right). In reality, because the universe itself is expanding (not a bunch of things moving away into the universe), it makes no sense to say that it is expanding in a direction. Space is just getting bigger. —Daniel (‽) 17:39, 5 August 2006 (UTC)

One way to visualise this is as a balloon with dots on it. When you blow up the balloon, all the dots move away from each other. We observe (almost) all stars around us moving away from us, so the conclusion was that we must be part of an 'expanding balloon', ie the universe is expanding. Of course one flaw here is that you can see that the balloon is expanding in relation to its surroundings (the other option would be that everything else is getting smaller, which would be silly). But the universe is everything, so what do you measure its size against? Don't we have to assume that the size of the universe is fixed? (if it indeed is everything) DirkvdM 17:48, 5 August 2006 (UTC)

It is usual to say that all the galaxies in the Universe are moving away from us as opposed to most stars (although as all the stars in the Universe apart from the ones in our galaxy are moving away from us). The balloon analogy can be better expressed by affixing coins to the balloon (top represent galaxies) as these wont expand with the expansion of the balloon. The only real problem with the balloon analogy is that the curvature of a balloon is positive and the curvature of the Universe is zero. This analogy is useful for demonstrating that the big bang happened both everywhere and nowhere.
We measure the size of the Universe from the inside by using standard candles to determine the rate of expansion (the Hubble Constant). Once we know this value the age of the Universe can be established then, by association, the size of the visible Universe. We do not know how big the Universe it is, but it is a fair bet that the visible Universe is not the whole Universe. I'm not sure why one would assume the size of the Universe is fixed.
The Universe is expanding in either 4, 10, 11 or 26 dimensions; depending on which theory you take to be true.

Since at least one of those dimensions is time, what exactly does "expanding in the temporal direction" mean ? Getting older ? I guess I'm "expanding in a temporal direction", too, then (not to mention a couple of spatial dimensions). :-) StuRat 20:24, 5 August 2006 (UTC)

See arrow of time. --Fastfission 21:41, 5 August 2006 (UTC)

For one, the big bang is just a theory. Nothing can prove that it happened. Why would you assume that it is expanding? All things we observe in the universe are in an orbit around something. So it is possible that we , our galaxy, could be in orbit around something. This would be a large orbit that would be impossible for us to observe in our short life time. So we would assume that everything is moving away from us when it realy is not. For example, Haley's comet comes roughly every 80 years. For half of its trip it is moving away from us. The other half it is moving towards us. If this orbit was 1 million yeears insead of 80 it would be imposible for us to tell that it was in an orbit.

Using that logic you would expect about half of the galaxies to be moving towards us and half away, but almost everything is moving away. StuRat 05:35, 6 August 2006 (UTC)

If we could measure its trajectory precisely enough we could observe a certain curvature that corresponds with an orbit (would that be a hyperbola?). So the limiting factor is not time but precision. DirkvdM 09:17, 6 August 2006 (UTC)

Mind you, other galaxies are not just moving away from us, but accelerating away. Something that a little theory of mine predicted! See my talk page. The problem is that gravity should provide a countering force, ultimately causing the Universe to collapse on itself again (if there is enough matter in the Universe). But the opposite happens. My theory, however, actually uses gravity to explain this. If our galaxy is collapsing in on itself, we will be accelerating towards its centre, and thus away from other galaxies and silly us think that they are accelerating away from us. Once again we regard ourselves as the the unchanging centre of the Universe. When will we ever learn?

Still, there is the problem that local dynamics (within our galaxy) don't seem to fit in with this theory. Or do they? DirkvdM 09:12, 6 August 2006 (UTC)

All the glaxies are moving away from each other, not only away from us. Following the cosmological principle we certainly do not regard ourselves as the centre of the Universe. That gravity should be pulling everything together is correct, however there is a force driving everything apart (see cosmological constant). If DirkvdM's theory that the Universe is collapsing is correct, there would be evidence for this in changes in the cosmic microwave background. The collapsing Universe theory also doesn't explain why the further away galaxies are, the faster they are moving away from us. If this was caused by gravity the opposite should be true. It is also interesting to note that there are some theories suggesting that, over extremely large distances, gravity might be replusive.

Einstein called the cosmological constant the biggest mistake of his life. It has been re-introduced just to explain away the acceleration, but is not really based on anything, afaik. But my idea of falling towards some great attractor would mean that the further away something is, the faster it would accelerate away from us. That's a prediction I made (although at first I saw it as a flaw) before it was found to be true. That's a theoretician's wet dream and that's the reason I keep on persisting in it, despite the fact that I barely know what I'm talking about. :) DirkvdM 12:22, 7 August 2006 (UTC)

If all gallaxies are moving away from some center point then there should be some other gallaxies moving at the same speed in the same direction as us.

The universe is a four dimentional object and so no adequate explanation can be given to explain its shape or structure to someone who cannot percieve the fourth dimention. It has no centre point, Bill Bryson likened this to taking a person from a universe where there are only 2 dimentions to a sphere, the would find it incomprehendable that they could walk all round it and find no edges, and as such we cannot comprehend how we can travel indefeinitely in any direction at an infinite speed and find no edge, there is no edge that we can comprehend. If you travelled in a straight line for long enough, you would eventually return to your starting point, such is the shape of the universe. As a result there is no centre point. Galaxies are all moving apart. But not from a point that we can comprhend. Philc _T^E_C^I 00:49, 7 August 2006 (UTC)

If we travel long enough in one direction we will return to our starting point? That means that in reality everything is on a colision course. Which means that the universe is not expanding nor is the other galaxies moving father away from us.ĎÀČ

It is possible that if you travel far enough in one direction you will arrive back at your starting point, but it is not possible to test this theory.

Just imagine crossing the entire universe and then missing your starting point by 10 m. Then you'd have to start all over again. Ad infinitum. QED (I think). DirkvdM 08:08, 8 August 2006 (UTC)

Just to return to the original topic as shown in the title, on the other side of the Big Bank is probably the Big Mall, the Big Carpark, the Big Newsagent, the Big Lawyer's office and the Big Optometrist.  :--) JackofOz 14:16, 9 August 2006 (UTC)

Photorespiration in wild soybeans

Is photorespiration lower or higher in wild relatives of soybeans compared to normal soybeans? Why?--Patchouli 18:10, 5 August 2006 (UTC)

Kinetics of Oxalate/Permanganate

I'm a senior high school student doing (or will start doing) a kinetic study of the permanganate/oxalate reaction for my final grade 12 year. I have an idea of what I'm going to do and how I'm going about it, but I have a few questions about the experiment.
The equation for the reaction is the following: 2 MnO₄^-(aq) + 5 C₂O₄^2-(aq) + 16 H⁺(aq) --> 2Mn²⁺(aq) + 10 CO₂(aq) + 8 H₂O (l)

1. The reaction is very often mentioned as autocatalytic, which I have no reason to doubt. The problem is that most sources do not explain why this is so. The closest to an answer I've seen is something to do with the manganous ion produced collides with manganese complexes and this speeds up the reaction, but even then I could be wrong since I saw this in one source that tried to explain it. Then that doesn't really help me either, even if its correct. Some clarity on that would be appreciated.

2. The reaction procedes in an acidic solution. Would the rate law look like this: rate = k[MnO₄^-]^x[C₂O₄^2-]^y or do I have to add the proton (like [H⁺]^z) to the equation?

3. I've read some experiment writeups where sulfuric acid was added to the reaction. Does it have to do with the reaction needing to be acidified? Would it be required if I used say oxalic acid instead of sodium oxalate (although oxalic acid isn't very strong)? Another explanation I've found is that it destroys the permanganate and speeds up the reaction and otherwise this reaction would take too long. Any ideas?

Thanks in advance.--72.56.179.48 19:35, 5 August 2006 (UTC) Adam Friedman

If you look at the basic equation you have written, you will see that it requires, at least theoretically, for two negative ions to react together. This would indicate that the reaction has high activation energy. You must look at the way the two manganese-containing ions react together. Secondly, you cannot predict the rate equation by looking at the balanced chemical equation. Rate equations can only be worked out by a series of experiments, for example, varying the concentration of H⁺ ions. Thirdly, the reaction is a very heavy consumer of H⁺ ions. These can only be provided by a strong acid. The original ethanedioic acid is far to weak to do this.--G N Frykman 21:01, 5 August 2006 (UTC)

Thanks for the above. Regarding the interactions of the manganese ions, is there a relatively simple way to explain it? I mean the manganese ion in permangante is reduced the 2+ state, so it must collide/interact. But can someone offer some sort of explanation regarding the interaction of the manganese ions and how this contributes to the autocatalytic nature of the reaction? (Or perhaps offer a basic idea of an experiment I could do...)

Thanks Again. --72.56.179.48 01:08, 6 August 2006 (UTC)

I didn't want to give you all the answers at once! Manganate(VII) and manganese(II) ions react together in a reverse disproportionation reaction to produce manganese(III) ions. It is these which oxidise the ethandioate ions to carbon dioxide. You will see that, as opposed to two negative ions reacting together, we now have a positive ion and a negative ion reacting. This can't happen, of course, until some manganese(II) ions have been produced by the slow reaction of the two negative ions. There is a hint of an experiment that you could do on the page autocatalysis.--G N Frykman 09:11, 6 August 2006 (UTC)

Yes, its ok not to want to give me all the answers all at once. Now that it was brought to my attention, I remember seeing in a journal article I read what is presumed to happen in the reaction in terms of how the maganese ions are reduced. They had three equations, and one of them was something like the following: Mn (VII) + Mn (II) → Mn (III) + Mn (VI).
Then it says that the 3+ species is destroyed in a reaction with the oxalate species, actually now I that I think of it, like you mentioned. So I offer my thanks. I will next check the autocatalysis page. Again, thanks. --72.56.179.48 19:06, 6 August 2006 (UTC)

electromagnetic fields and radiation pressure

What is the difference between the lorentz force exerted by electrostatic and electromagnetic fields and the raditation pressure of electromagnetic radiation pressure. Secondly I saw an article in the 70s where small glass balls were levitated by electromagnetic radiation pressure, what is the largest and heaviest object moved by radiation pressure to date? Curiosgeorge

It's worth reading the articles
The most important difference between them is that the Lorentz Force only acts on charged particles; radiation pressure can be exerted on anything. The Lorentz force will also make charged particles move along curves, rather than straight lines. I'm afraid I don't know what the most massive objects moved by radiation pressure (in an experimental setting) are, but using radiation pressure to propel spacecraft is an active area of research.

The Lorentz force is the force that electromagnetic fields exert on charge particles. "Radiation pressure" is an interesting macroscopic example of the Lorentz force, but nonetheless they are really the same phenomenon. Both the lorentz force and radiation pressure only affect charged particles. Luckily, most matter is made of charge particles - protons and electrons. You might be interested in the Yarkovsky effect, which is an interesting example of the momentum of radiation affecting astronomical bodies in an unusual way. --Bmk 01:57, 6 August 2006 (UTC)

The radiation pressure exerted on an area, A, is given by (dp/dt)/A (where p is momentum). This does not involve any charges. It's an application of conservation of momentum.

There can be no radiation pressure without charges. All atomic matter consists of charges - electrons and protons. The only way for radiation to exert a pressure on a solid is if the solid contains charges; the electromagnetic field only interacts with charged particles. --198.125.178.207 18:47, 7 August 2006 (UTC)

That's not right, light carries momentum and when it is absorbed or reflected by an object, it transfers that momentum to the object. Light even though it does not have mass, has energy, and therefore can transfer momentum. This is an often overlooked effect of relativity. Dan 15:15, 10 August 2006 (UTC)

Vinegar reacts with hairspray to form a solid

A strange elastic white porous soild formed when I poured vinegar into a hairspary formula (40% alcohol) at room temperature and standard pressure. I smell the ethyl acetate, but that doesn't explain the solid. Can someone tell me what happened?

Do the ingredients of the hairspray list something like sodium benzoate? You have probably precipitated the insoluble acid (eg benzoic acid) of a soluble salt by lowering the pH.--G N Frykman 20:52, 5 August 2006 (UTC)

I once had to inject small amounts of benzoic acid into rubber-stoppered vials via a small guage needle and syringe. I can attest to the fact that benzoic acid is indeed very stringy and very sticky. Indeed, I'm pretty sure I never was able to get it in, and had to pick another chemical.Tuckerekcut 23:52, 5 August 2006 (UTC)

Nitpick: you can't pour anything into a formula because that's something abstract. Referring to the mix in the canister as a 'formula' is commercial blah. DirkvdM 09:27, 6 August 2006 (UTC)

Counter-nitpick: Any mother or half-interested father knows that what goes into a baby's bottle is usually called a 'formula'. Scientists are humans too (mostly).  :--) JackofOz 01:32, 7 August 2006 (UTC)

I think any combination of chemicals can be called a formula. — [Mac Davis] (talk)

Well formulated. DirkvdM 08:08, 8 August 2006 (UTC)

Nice, a precipitation. --Proficient 04:29, 9 August 2006 (UTC)

Intercalating agents and you

I'm a labworker and during my work I get into contact with many nasty substances like ethidium bromide and DAPI. I tend to handle these substances (even in heavily diluted form) as if they were death incarnate. Sadly I'm also an incredible clutz and did get some DAPI on me and possibly in me. Of course I freaked out like no tomorrow especially because there is so very little known about the substance at hand. There are however quite a few other substances like this like Benzopyrene and Alfatoxin both of which, if I can believe the wikipedia articles, occur in my toast with peanutbutter (all be it in small doses).

Yet both these substances are flagged as highly carcinogenic (just like ethidium bromide and DAPI). So why aren't we dying of cancer left and right. Given the world we live in, with it's smoke, bbq's and crispy brown baked bacon, we should be accumalating this crud in our system at a staggering rate. So what gives? Am I missing something here? Can the body " deal " with these molecules shunting themselves between our precious base pairs thus causing happy frame shift mutations and the like? - Pascal

First, are you sure they accumulate instead of passing through the system ? Second, perhaps the dosage is insufficient to cause a problem. Third, perhaps it's not in a harmful form (for example, elemental mercury is far less dangerous than methyl mercury). StuRat 21:43, 5 August 2006 (UTC)

Alas, I remember the first time I spilled EtBr on myself. I freaked out too, but my reaction was decidedly less pronounced the 100th time. I'm not sure what the wikipedia article says (perhaps I'll stop by later), but EtBr (as well as DAPI) is not carcinogenic per say, but mutagenic. Much like UV radiation and charred carbohydrates, it is advisable to limit exposure, but don't worry so much that it takes over your life. From what I have learned from working with some geneticists who were working on their degrees before Watson and Crick even published, use gloves whenever possible (nitrile gloves) and if you spill a little you spill a little. In situations where you are working with visible dilutions (solutions which are visibly colored by the stain, red for EtBr, or blue/green for DAPI) double glove, and walk don't run to the shower if you spill on yourself. Gels (even mildly colored ones) are usually not a big deal for contact exposure because not much chemical is available at the surface. Basically, freaking out about a spill isn't gonna help you much, and as long as you haven't succombed to any toxic effects, the mutagenic effects can't generally be reversed specifically after the fact. Really the best protection is to stay healthy with a good diet and plenty of excersize. The human body has a slew of cancer-peventing mechanisms, utilizing many levels of protection at different teirs of biology (i.e. promoters/demoters in genes all the way to cells that scavenge for budding neoplasms). In short, lots of stuff can cause cancer, but we have pretty good defences. The goal is limited exposure, not necessarily zero exposure.Tuckerekcut 23:48, 5 August 2006 (UTC)

Good points made above. I also work in a lab and agree that you have to accept some element of risk, but work to minimize it. The point i wanted to make is that we simply do not know what the mong term effects of working with substances like EtBr or DAPI is. It could well be that they are carcinogenic to humans even at a very limited exposure, but corrolating increased cancer rates with lab workers will be very difficult to do. A lot of chemicals we are exposed to are called carcinogenic, usually because in some study somewhere - after exposure to ridiculously high doses - mice were shown to have an increase in tumour development compared to controls. If you live in California you would be amazed at the things that, according to state law, must be explained to you that they could cause cancer.

Poor old Marie Curie found out that working with material we do not fully understand can have pretty nasty effects, that is why we treat lab chemicals with such care, probably more than we strictly need to, on the principle it is better safe than sorry (and also to stop litigation based on the due care an employer owes their workers). That said, risk is relative, if i were you i would worry looking left and right when crossing the road than about suffering from EtBr exposure. Rockpocket 03:44, 6 August 2006 (UTC)

Thanks for the replies guys. I had already talked to the institute's doctor and he had already assured me that I didn't have to much to worry about, but your words of wisdom are always welcome. Also thanks for the advice for wearing nitrile gloves. I used to wear those dinky medical examination gloves (standard in our institute) untill I found those nitrile gloves. The nitrile gloves fit me better, cover the wrist area well and offer better protection so I'm sticking with them. Though I won't be returning to the labs soon (It was an internship of mine) I feel better prepared now.

I heard in a documentary on the Chernobyl accident that exposure to moderate doses of radiation aren't as harmful as one might expect from the effects of higher doses and might actually even have a positive effect, almost like a vaccination, causing the body to counteract cancer even though the doses aren't high enough for it. But that is speculation. DirkvdM 09:44, 6 August 2006 (UTC)

One of the reason that medium levels of radiation are often safer than low levels of them is because of the way that radiation affects the cell. In a rather simplistic form: if one particle hits the cell, you get a mutation (and potentially cancer). If two hits the cell, the cell just dies. So there is supposedly a level in between low and high in which cancer is less likely, since most of the cells that would be cancerous would end up just getting killed instead of surviving from their exposure. Or something along these lines. There is a lot of uncertainty and debate on the question of low-level radiation, I should point out. --Fastfission 16:29, 9 August 2006 (UTC)

actually the phenomenon is well precendented. it thought it was called hysteresis, but the wiki article doesn't mention much about its relevance to biology. it might be another h-word. Xcomradex 11:13, 6 August 2006 (UTC)

Just to be clear, the reason for using nitrile gloves goes beyond mechanical resilience. Ethidium Bromide is able to migrate through latex barriers with little difficulty (a phenomenon not often observed because latex so effectively stops the primary solvent for EtBr, water); and based on its similar ability to cross cell membranes, DAPI is likely to be able to do this too. Thus nitrile gloves offer barrier protection from these stains while latex gloves do not. I'm not so sure about other materials, though.Tuckerekcut 23:18, 6 August 2006 (UTC)

Strangely enough everyone in the institute uses latex gloves for just about anything. This makes sense because heck I could only scrounge up 1 box of nitril gloves in the intire institute. I think the institute needs to adjust it's safety protocols. - Pascal

how a snowboarder turns around while on the air

As far as I am concerned, things need stable things to move. (Car-Road, Boat-sea). So how a snowboarder turns around in the air an astronout in space without touching anything else. if so which musles are more likely to be used while in the action? Any relevant answer would be much appreciated...

You can change your direction in the sense of turning around by simply shifting your own weight around. You can't change the path you are on very radically though—i.e. if you were thrown to the left, you could just throw yourself to the right without some sort of friction involved. --Fastfission 23:29, 5 August 2006 (UTC)

When snowboarders go for a jump, they give themselves some angular momentum by pushing off in the right way. Since they are also moving quickly through the air standing on a large board, there is significant air resistance which they can use to turn themselves. --Bmk 02:00, 6 August 2006 (UTC)

If an astronaut can't push against anything, that means his centre of gravity can't move. But that doesn't mean he can't turn around his own axis. If he stretches out his arms and swings them both to the left, his body will rotate to the right. His arms will wrap around his body, thus accelerating the rotation, like a figure skater. This rotation will continue until he moves his arms back again. To come to a stop he would have to do the same in reverse. If he would just move his arms back along his body (not outstretched) the rotation would merely be diminished. I think. Even thought the reasoning sounds right, it still feel counterintuitive, so I understand your question. I have wondered the same thing about 'accelerating' on a swing. I still find it hard to reason how this would be possible, but the person on the swing is excerting energy and that has to go somewhere. DirkvdM 10:09, 6 August 2006 (UTC)

The astronaut would only continue spinning until his arms stopped moving, then he would stop spinning; conservation of momentum prohibits him (or her) from gaining angular momentum. Basically, he can swing his arms, and his body will rotate a certain amount, but it will not continue to rotate unless he rips off his arms and throws them across his spacecraft, which is strictly against NASA regulations. --Bmk 13:25, 6 August 2006 (UTC)

Citation needed ? --DLL 16:59, 6 August 2006 (UTC)

How would you explain being able to increase the amplitude on a swing without violating the conservation of momentum? DirkvdM 13:35, 7 August 2006 (UTC)

Interesting question - after thinking about it, i think the way a person is able to increase their energy while swinging is because they are connected to the swing set by the rope. Basically, when they are swinging, they can use their muscles to elevate their body by pulling on the rope, thus adding potential energy to the motion, which is converted to more kinetic energy when they stop pulling. Momentum is conserved in the earth-swinger system. Oh, and by the way, I should have cited conservation of angular momentum in my first comment. --18.239.6.57 15:02, 7 August 2006 (UTC)

The arguments of conservation of momentum (be it linear or angular) or energy and such take a step back, looking at the system as closed and saying nothing can enter or escape. You say the person on the swing converts energy stored in their body to create (angular) motion. Can't the astronaut do the same? Then again, I recognise that they couldn't create linear motion that way, so I'm still stuck on this level. But in detail, the trick is to give the impulse in one direction with outstretched arms and then moves the arms back along the body. I'm not sure they would keep on spinning (I suppose they wouldn't), but if they keep on repeating this, they could keep on turning. DirkvdM 08:20, 8 August 2006 (UTC)

Right - the trick with the swinger is the system in which angular momentum is conserved is the entire swingset-swinger system. In the case of the astronaut, there's only the astronaut - if he wishes to have some angular momentum, there are no other parts of the system to which he can impart the opposite angular momentum to maintain conservation (unless he's allowed to blow air). And the astronaut would not actually be able to keep on turning - his angle will be limited (this is all neglecting air resistance, which would allow him through use of aerodynamics to gain angular momentum). Try it on a good swiveling chair - one with very low turning resistance. You should be able to verify that without the help of the resistance on the chair bearings, you are not able to continue turning after you arms are maximally twisted and stop twisting. --Bmk 20:19, 8 August 2006 (UTC)

Interesting. --Proficient 04:30, 9 August 2006 (UTC)