Wikipedia:Reference desk/Archives/Science/2007 September 27

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

September 27

eicosanoids

Are Eicosanoids considered fat soluble hormones? —Preceding unsigned comment added by Cgilcher (talk • contribs) 00:03, 27 September 2007 (UTC)

Technically a hormone is any substance carried by the blood that acts on a distant target cell. According to that definition, eicosanoids are technically (fat soluble) hormones. However, in my experience (I'm but a lowly medical student), they're rarely called hormones. --David Iberri (talk) 00:13, 27 September 2007 (UTC)

Fat soluble? Yes. They're even derived from omega-3 & omega-6 fatty acids. Hormones? You'll find them listed at Hormone#Chemical_classes_of_hormones. — Scientizzle 03:54, 27 September 2007 (UTC)

I think Eicosanoids are considered lipids, so they are technically fat.128.163.224.198 00:46, 4 October 2007 (UTC)

Surgery

In order to become a surgeon what type of schools do you have to go to? Would a medical school be enough? I am thinking about pursuing a career in this field so any help would be nice. Thank you —Preceding unsigned comment added by 24.242.119.35 (talk) 01:38, 27 September 2007 (UTC)

In the United States (I see your IP is registered in Texas) a surgeon must complete medical school the same as a physician. This would then be followed by two or more years (I believe) of surgical residency and/or fellowship. Someguy1221 02:33, 27 September 2007 (UTC)

Having said that, surgery is a highly prestigious occupation and it typically attracts the highest salary of any profession. If you are really serious about pursuing it, you should be seeking the advice of a professional career counsellor. That shouldn't be very hard, you should have easy access to one through your school or university. And you generally should be getting marks in the top 5 percent to even be considering it an option. Vespine 06:51, 27 September 2007 (UTC)

Virial Theorem esp. GPE

I am doing an assignment on Dark Matter and I need to know about the Virial Theorem. Most of the derivation of it is too complex for the assingment and my mathematics skills (which are probably about first year uni level) so I really only need to know that it states that KE = -1/2*GPE. However I would like to know how there is an easy way to quickly derive (using as many assumptions as required about the homegeneity/similarity of objects in the group) the mass of the cluster of galaxies. This website: [1] gives a fairly good formula except I dont understand the reason for the value of the total GPE, especially the factor of 1/2. Just in addition, I was wondering whether the tangential velocities of the galaxies is required for the formula for KE or is the radial velocity satisfactory? --AMorris (talk)●(contribs) 02:19, 27 September 2007 (UTC)

I guess you have already looked at Kepler orbits earlier in your course. Just take the simplest case, that of a planet on circular orbit around a star. What is the kinetic energy associated with the orbital velocity and what is the potential energy associated with the planet's distance to the star (as compared to infinite distance)? You'll find that they have opposite signs and the kinetic energy is just one half of the potential one. It s as easy to see that it also holds for elliptic orbits. The factor is still precisely one half for cloud of many small particles of comparable size which all hold fast to each other by gravitation, but to see this you need indeed first learn a bit about Lagrangian and Hamiltonian mechanics. And to your ther question: Yes, for the kinetic energy you need to look at the full velocity, and actually, the tangential velocity is the dominant part. And it is precisely this tangential velocity that is too big to make the kinetic energy only half of the potential one if one calculates the potential energy from the gravitation of the visible galaxies. This is the very reason to infer dark matter halos. Simon A. 08:59, 28 September 2007 (UTC)

second law of thermodynamics

Heat is transfered from a very large mass of water at 91°C to 5kg of air that expands irreversibly in a cylinder-piston device fron 5bars, 42°C to 1bar, 41°C. the air does 2kj of work. determine the heat interaction in the process and entropy growth in the universe. —Preceding unsigned comment added by Fonkynet (talk • contribs) 03:05, 27 September 2007 (UTC)

Please tell me that this isn't ... well, you know. ;-) (Click here for a more detailed explanation) - hydnjo talk 03:46, 27 September 2007 (UTC)

<smacks forehead>Do your own homework! Second law of thermodynamics and many other articles may be useful, be we're not going to do your math and physics problems. — Scientizzle 03:50, 27 September 2007 (UTC)

I agree - we're not doing your homework for you. But if you have a particular part of the problem that you don't understand, explain what it is - and we're definitely going to be here for you. SteveBaker 15:05, 27 September 2007 (UTC)

The continuation of the world as we know it?

With the possibility of humanity destroying itself on one hand, and a technological singularity or immersive virtual reality on the other, what's the probability that the world will continue as we know it for an extended period? — Daniel 03:52, 27 September 2007 (UTC)

Indeed! Infinity rules! - hydnjo talk 03:59, 27 September 2007 (UTC)

If the period is extended for only a short time, then call it hell, call it heaven, it's a probable twelve to seven. 05:37, 27 September 2007 (UTC) —Preceding unsigned comment added by Xn4 (talk • contribs)

We know that the "world" (as in the planet Earth) can't continue indefinitely because the Sun will give up and die in a billion years or so. I find it hard to imagine humanity destroying itself completely - I can't really imagine any catastrophy that we could suffer that would wipe us all out. There are enough deep bunkers and remote communities with stores of food, water and power to let enough of us to survive most things - albeit with a very reduced population size. The 'singularity' is a slightly different matter - it's very nature means that we can't predict beyond it - but it's not entirely clear that it will actually happen at any time in the future. I would feel much more comfortable about the future of humanity if we had a 'backup' planet - a population of a few thousand people in a self-sustaining community on (say) Mars would be a great way to ensure we could survive most things. But in the long term (beyond about hundred million years) we really need to start thinking about having a backup star or two as well as a backup planet. SteveBaker 15:01, 27 September 2007 (UTC)

If civilization is destroyed, even if humanity survives, I'd consider that the world ending as we know it. How about this: what's the general consensus on the idea that within a few centuries A) civilization will be destroyed, or B) humanity will be able to change their environment, which may be real or virtual, to pretty much anything they want it to be? How about if you change B to being so technologically advanced that any more advancement beyond that time is all but unnoticeable?

By the way, I understand Steve fine, but what are hydnjo and Xn4 talking about? — Daniel 22:09, 27 September 2007 (UTC)

If civilisation collapsed - yet there were enough people left to preserve genetic diversity and retain knowledge - I think we'd have civilisation back on the road again within a few generations. Human population can easily double every generation if we want it to - a thousand survivors could become a million people within 10 generations - 200 years maybe. But as for the time until humanity is destroyed, how could be possibly answer that? We can't predict that planet-killing meteor strike - we don't know when a pandemic disease might strike - we have no clue about the various weird deaths like a black hole eating our sun or a nearby star going nova. These things aren't very predictable...or we'd be predicting them. If we can get a colony started, self-sufficient and viable on Mars, then I'd say that nothing will annihilate our civilisation. If we can't then it's a totally unpredictable thing - so no answer is possible. SteveBaker 23:07, 27 September 2007 (UTC)

I don't think it could start back up so soon. The rise of civilization as we know it depended on things like large deposits of metals with low melting points at or near the earth's surface; we have used a lot of those up. And of course we have gone trhough millions of years worth of fossil fuels. Eran of Arcadia 20:45, 1 October 2007 (UTC)

photon and magnet .

does magnetic or electric field can affect photon in any way ? photon consist of a electro-magnetic field but it does not seems to by effected either by electric or by magnetic field ; why ? please explain clearly . place interesting external links (if possible) . —Preceding unsigned comment added by Shamiul (talk • contribs) 06:31, 27 September 2007 (UTC)

Static electromagnetic fields do not effect each other or passing photons (electromagnetic waves). This is thanks to the superposition principle, which, while a mathematical concept, happens to apply to electromagnetic fields. However, when an electromagnetic wave passes through matter, the electrons within are disturbed by the field, and will generate their own electromagnetic waves. The net result of these waves is what accounts for reflection and refraction, as well as more complex phenomena such as birefringence. Under cetain conditions, external magnetic fields can also perturb the passing of an EM wave through matter, as in the Faraday effect. I've deliberately taken a Maxwellian approach to this question and ignored quantum electrodynamics, because it scares me. Someguy1221 07:51, 27 September 2007 (UTC)

Sodium potassium pump

Exactly during which phase of the action potential does the sodium potassium pump start working? Lova Falk 07:02, 27 September 2007 (UTC)

The sodium potassium pump never stops working. However, its action is sufficiently slow as to not interfere with the actions of the channels. Someguy1221 07:53, 27 September 2007 (UTC)

Thank you! Does that mean that already during the falling phase of the action potential, lots of sodium ions are pumped back into the extracellullar fluid? Or is the pump so slow (or inefficient) that during hyperpolarization there are still lots of sodium ions in the cell and lots of potassium ions on the outside? Lova Falk 08:13, 27 September 2007 (UTC)

You may be confusing hyperpolarization and repolarization. Regardless, during each the sodium potassium pump is, correct, far too slow affect either of these processes in the short term. Interestingly enough, the diagrams in my biology notes show the pump to be inactive during the action potential, but make utterly no mention of this in text (neither do our articles), and I'm willing to chalk it up to an inexplicable error...unless someone wants to point out that these diagrams are actually right. Someguy1221 08:36, 27 September 2007 (UTC)

I meant hyperpolarization as the undershoot phase in the action potential (before it returns to the resting phase). The reason why I ask this question is because, in a couple of pictures and animations such as this one, they show an influx of sodium ions into the cell during the rising phase (picture 5/8 in the animation), less sodium ions inside the cell during the falling phase (picture 6/8), and none at all during the hyperpolarization (picture 7/8). So I wonder how the sodium ions got out again. From your answer, I understand it's not the pump. Or is it a mistake (or simplification) in the animation? Should there still be quite a few sodium ions inside the cell during hyperpolarization that eventually are pumped out by the pump? Lova Falk 12:11, 27 September 2007 (UTC)

There's a lot of simplifications used to explain the action potential. In that animation, I think they just made the ions disappear to unclutter the image. The Na+/K+-ATPases are responsible for "reseting" the membrane potential during the refractory period after the undershoot. The pumps should essentially remain on as long as there's sufficient ATP.

One of the common misconceptions about action potentials is that the depolarization and repolarization are the result of large changes in ion concentration. In fact, the important element is actually the electrical current generated by moving charges (ions) that creates a local voltage drop. This change in local voltage activates nearby voltage-gated ion channels to continue directional conduction. The fact that action potentials don't need wide swings in ion concentrations means that the pumps can keep chugging along and reset the membrane potential in relatively short order. — Scientizzle 15:37, 27 September 2007 (UTC)

Thank you both of you! Lova Falk 16:46, 27 September 2007 (UTC)

Central Valley result of impact event...?

Is there a theory that the Central Valley (in California) is the remnant of an impact event, perhaps as old as when the Moon was created? I have heard that this was investigated to the point where surveys have been done to look for signs of impact. yet without positive results.

The reason for my curiosity is based on the following:

1. The current shape of Central Valley being due to geological activity which as compressed a more or less round or elliptical impact site into a relatively narrow elongated site.
2. The moon resulted from such an impact.
3. As you travel toward LA and leave the Central Valley you can see very large rock strata that is turned upward as you would expect along the periphery of an impact site.
4. Throughout Montana and the Southwest, all the way from LA to Texas especially in Arizonian and New Mexico, there are great piles of homogeneous rock and dirt which are of course large enough to be called mountains but which fit the pattern of a large amount of Earth which was ejected by impact landing in great piles as it returned.

What knowledge do you have of such a theory and what conclusions do you know about that have been reached? Clem 08:41, 27 September 2007 (UTC)

Searching through google and half a dozen astronomical journals, I have found all of nothing on anything like this theory. Someguy1221 08:53, 27 September 2007 (UTC)

I'm pretty sure the theory is not original since I recall posting a question about it several years ago to a geo at Stanford and he responded that nothing to indicate such an impact occured has ever been found, after numerous drillings and the like. Clem 10:08, 27 September 2007 (UTC)

Also, please note (if you take the Giant impact hypothesis as a given) that the impact that created the moon likely reduced the Earth into a molten ball, in addition to throwing up far more material than would a meteor that leaves only a few hundred mile wide crater, and Central Valley (California) offers a non-impact way of forming it. Now, my first two points don't preclude the possibility of millions of tons of debris raining down on a solid Earth for some time after the moon's formation, but I have no idea on that one. Someguy1221 09:03, 27 September 2007 (UTC)

Perhaps not the Moon but certainly a large body... the upturned strata can be explained by subduction forces but not the great piles of rock and dirt debris throughout the Southwest. Only comparison with the underlying material, I suppose, can determine if these piles rained down, grew up or whatever. Clem 10:08, 27 September 2007 (UTC)

Next time, please be more specific - I had to read halfway through the question to get an idea which Central Valley you were talking about. I was thinking Costa Rica (because I've been there and that's the only place where I've ever heard the term). DirkvdM 10:30, 27 September 2007 (UTC)

Three problems with this theory:

• Our section on geology of the Central Valley describes a very different, non-impact origin for the Central Valley.
• The Central Valley is much younger than the hypothetical impact event that created the Moon, which would have happened more than 4.5 billion years ago.
• An impact event large event to form the Moon would have re-formed the whole surface of the Earth - it wouldn't leave any identifiable local features. Gandalf61 10:54, 27 September 2007 (UTC)

quanta

1. If N atoms have equally spaced energy levels (separation = q) and energy (total energy =E) is distributed randomly amongst the atoms in packets of energy q .. what is the name (if any) of the corresponding distribution. (as an average of all the possible combinations equally weighted) (I'm not asking for the equation)

2. Alternatively. If N atoms have equally spaced energy levels (separation = q) and energy (total energy =E) is distributed randomly amongst the atoms so that each possible distinct distribution is counted only once.. What is the name for this distribution (again as an average of the different possible energy distributions each equally weighted) (eg the atoms can be considered labelled so that energy distributions of E=3 over 3 atoms (q=1) has possible distributions including (3,0,0) and (0,3,0) and (0,0,3) that all count once.)

2b. Also does anyone know (link?) what happens when I don't 'label' the atoms so that in the above example (3,0,0) and (0,3,0) and (0,0,3) are only counted as one possible contribution?83.100.254.236 13:11, 27 September 2007 (UTC)

I'm looking for distributions (science or maths) that correspond to either of the two above when the energy levels have constant difference (even if this condition is a specific case within the distribution). Thanks.83.100.254.236 13:11, 27 September 2007 (UTC) (and no degenerate energy levels in my examples if you were wondering)

I believe this is all answered by the Boltzmann distribution, my personal favorite physics equation. The question of whether distinct distributions (2 and 2b) are counted once or degenerately (the same as saying all particles are identical or all particles are distinct) merely affects how many energy states are included in the Boltzmann distribution. Someguy1221 18:16, 27 September 2007 (UTC)

Erm the ditribution I got from 2 wasn't the same as the Boltzmann distribution.. I don't actually know what the distribution is like for 2b - I haven't been able to work it out yet.. (the difference between 2 and the Boltzmann distribution is that in 2 the average of microstates is taken whereas bolztmann takes the microstate with the highest 'entropy' (a micro state is (3,0,0) or (2,1,0) etc in the example I gave) see boltzmann for his definition of entropy in this case)87.102.83.163 17:00, 28 September 2007 (UTC)

Anyone recognise distributions (including continuous ones) that at least match the shapes of the above.87.102.83.163 16:37, 28 September 2007 (UTC)

These are particular cases of Maxwell-Boltzmann statistics and Bose-Einstein statistics. Just plug in the energy levels. If you further require that no two atoms be in the same state, you get Fermi-Dirac statistics instead. I don't understand the difference between (1) and (2a), since the atoms are distinguishable in both cases. --Reuben 17:54, 28 September 2007 (UTC)

The difference between 1 and 2 is in the case given above- for the state (3,0,0) there is one way to obtain the state in 1, but for the state (1,1,1) there are 6 (3!) ways to obtain the state in 1. So in 1 each state is not equally likely.87.102.83.163 19:37, 28 September 2007 (UTC)

Are you saying that in (1), you mean not only the atoms but also the quanta of energy to be labeled and distinguishable? In that case, 2(a) and 2(b) are Maxwell-Boltzmann and Bose-Einstein respectively, but (1) doesn't seem to correspond to anything very physical. --Reuben 19:45, 28 September 2007 (UTC)

Effectively yes (for type 1) - I would put it this way - that the energy is quantised and comes in chunks of energy q only. It does give a fairly good model of blackbody radiation. (does this distribution have a mathematical name - also I'd like to know more about getting a continuous version of this - ie not quantised ..)

For type 2 : Bose einstein statistics looks promising - I found this page http://hyperphysics.phy-astr.gsu.edu/hbase/quantum/disbex.html#c1 that seems to show that I'm using the same method to calculate states in 2 as is used in bose-einstein - so that's good - however - I get probability of 'atom' having energy E is proportional to (k-E)^N-2 - ie the shape of the graph depends on the number of molecules (as is easily tested with small numbers of molecules without a derivation) - the bose-einstein equation doesn't do that - so I'd like to ask 3. why? and 4. Is there a distribution function (something I can look up) that does take into account the numbers of molecules..87.102.83.163 19:56, 28 September 2007 (UTC)

It seems reasonable to begin an accounting of the quanta of action that take place in ergonomic work or exercises. The number of quanta won't be exact, they are so small. But it won't be less than, say, 10^10 quanta for lifting a curling iron, and it won't be more than 10^40. Progressive estimates can narrow the number a great deal. SyntheticET (talk) 04:03, 22 December 2008 (UTC)

Enkephalin and enkephaline

Enkephalin has its own article in Wikipedia, enkephaline is redirected to endorphin. Is this really correct?? Lova Falk 13:18, 27 September 2007 (UTC)

Enkephalin is an endorphin, it looks like enkephaline is a french spelling of enkaphalin, but seems to refer to a family of enkephalins? so maybe should redirect to enkephalin, though the current redirect is not really wrong - just not specific enough.83.100.254.236 13:22, 27 September 2007 (UTC)

I don't think enkephaline is actaully an english word...83.100.254.236 13:24, 27 September 2007 (UTC)

I found enkephaline in an english book (Kolb & Whishaw: Fundamentals of Human Neuropsychology).

Basically you're saying:

1. enkephalin = enkephaline
2. there are different kinds of endorphins, and enkephalin is one of them. (This is how I interpret your writing an endorphin.)

Are you sure this is correct? Lova Falk 13:31, 27 September 2007 (UTC)

The consensus at the AFD that made enkephaline a redirect was that it is a mis/alt-spelling of enkephalin. Since enkephalin was a redirect then, enkephaline was redirected straight to endorphin. Thus I have just changed enkephaline to redirect to enkephalin. I hope this is correct. btw, enkephalin is strictly speaking two endorphins, met- and leu-. Algebraist 16:02, 27 September 2007 (UTC)

The issue of the extra e is solved, but I'm still confused about enkephalin being two endorphins. Why does neither the article on enkephalin nor the article on endorphin mention this? Why does the article Opioid peptide name three opioid peptides produced by the body and not mention that enkephalin is an endorphin?? I'm sorry for being so stubborn, but it just doesn't make sense to me that enkephalin is an endorphin. Lova Falk 16:56, 27 September 2007 (UTC)

I expanded the section Opioid peptides produced by the body. Goodman & Gilman's The Pharmacological Basis of Therapeutics is sorta the bible for these kinds of things and it uses "endogenous opioid peptides" as the general term for which there are three well-characterized families, enkephalins, endorphins and dynorphins. Since these three families of opioid peptides are produced by homologous genes, things can get a bit confused, particularly since the met-enkephalin peptide sequence is coded for by both the enkephalin gene and the endorphin gene (also known as the POMC gene) and the leu-enkephalin peptide sequence is coded for by both the enkephalin gene and the dynorphin gene. The peptides were found and named first and only later were the genes sequenced, so the nomenclature is a bit of a mess. --JWSchmidt 03:16, 28 September 2007 (UTC)

Thank you! I added your comment to Enkephalin. Lova Falk 15:05, 28 September 2007 (UTC)

decline of the human body

I am a 24 year old male who is very athletic. I can run really fast, jump high, and I am very flexibile. I play a lot of sports, especially basketball. I wanted to know at what age does the body start to slow down? How many more years do I have left until I won't be able to run fast or jump high and overall start to loose my abilities? —Preceding unsigned comment added by 68.223.217.95 (talk) 15:51, 27 September 2007 (UTC)

One way of finding an answer to your question is to check for each ability at what ages professional athletes are at their peak. For instance, gymnasts (for flexibility) usually reach their peak performance at a much younger age than runners do. Lova Falk 17:04, 27 September 2007 (UTC)

I'm sure its different for everybody. Brett Favre is pushing 38 and he still dominates the NFL. Tiki Barber was only like 31 when he retired. —Preceding unsigned comment added by 128.101.53.147 (talk) 18:24, 27 September 2007 (UTC)

Of course it's also individual, and injuries can complicate matters. But you can calculate averages. Lova Falk 18:44, 27 September 2007 (UTC)

Also, keep in mind that as you age, your speed goes down, but your endurance goes up. This is why, for example, top sprinters tend to be in their 20s, but top endurance runners tend to be in their 30s or 40s. --Carnildo 23:30, 27 September 2007 (UTC)

In many important physiological aspects, it is all downhill after age 19. Intellectually, it has been said that mathematicians make their best contributions by age 35. Then there is the truism "Age and guile beat youth and talent, every time." Edison 04:29, 28 September 2007 (UTC)

In other words, it's gradual. Your abilities will very slowly diminish. On the other hand, your experience will grow and that experience will help you make better use of the physical abilities you have. So that will compensate for a while. I'd say that on average the effect of declining physical abilities will start to have a bigger effect than the experience in one's forties. But that also depends on what kind of activity we're talking about, more physical, like running or rowing, or more skill-based, like hiking or sailing. Also, it depends on how much you wear out your body. Such as with sports. Physical exercise (eg taking the stairs instead of the lift) is good, but sports tend to put too much ('unnatural') stress on specific body parts (think tennis-elbow and football-knee). Especially if you stick to just one sport and/or do it more fanatically. If you want to stay fit as long as possible, then forget about sports and get your exercise from ordinary daily activities, preferably as varied as possible. If that's not enough exercise for you, then maybe do several sports and don't try to excel at them. In other words, remain active, but don't overdo it either. DirkvdM 06:57, 28 September 2007 (UTC)

For the record, it's extremely arguable whether or not Brett Favre currently "dominates" the NFL, but it's nonetheless impressive that he's still playing and winning games at his age. 38.112.225.84 13:57, 28 September 2007 (UTC)

chemistry/food-grade

I am looking for information on what compound 1036 is.

207.41.37.140 15:54, 27 September 2007 (UTC)Rachel

3-methyl-6-(ethoxycarbonylbutoxy)-2-oxo-1,2-dihydroquinoxaline Someguy1221 18:38, 27 September 2007 (UTC)

Positronium energy levels and instability

Why is the "reduced mass" used for energy level calculations in positronium but not in hydrogen. What quantum mechanical forces lead to instability of positronium.68.226.119.129 18:07, 27 September 2007 (UTC)

1. It should be reduced mass for the hydrogen atom too, but the electron mass and reduced mass are only different by about 0.05%, so the distinction is usually ignored as negligible. 2. In the ground state, the electron and positron wave functions overlap quite considerably. They annihilate. See positronium for decay channels. --Reuben 18:14, 27 September 2007 (UTC)

Ummm, no. The reduced mass is ${m_{1}m_{2}} \over {m_{1}+m_{2}}$ and hence the reduced mass of the electron in positronium is half the electron's normal mass. 136.152.153.30 21:26, 28 September 2007 (UTC)

You're talking about positronium. I was explaining why the distinction is not necessary for the hydrogen atom. --Reuben 21:43, 28 September 2007 (UTC)

Proper temperature for deep freeze?

My deep freeze has a digital display showing the current temp inside. How cold should I set it? I don't want to set it unnecessarily cold and waste electricity. --24.249.108.133 18:15, 27 September 2007 (UTC)

Deep freeze = standard home freezer which is possibly attached to the refrigerator? Dismas|^(talk) 19:07, 27 September 2007 (UTC)

Freezers are conventionally set at 0F/-18C. Colder probably makes things last longer but uses more energy, and "longer" is asymptotic anyway -- things last a long, long time at 0F.

FYI: In American usage, "deep freeze" usually refers to a separate freezer unit, often chucked off in the garage or basement because they're not accessed all that often. These units are frequently horizontally-oriented with the door opening upwards so that the spill they least amount of cold air when the top (door) is opened. Baskets within allow easy access into the freezer to get at things down by the bottom.

Atlant 19:14, 27 September 2007 (UTC)

Interesting that there isn't an entry on these, eh? BTW, my deep freeze has a fridge-like vertical orientation. --24.249.108.133 21:58, 27 September 2007 (UTC)

In English/English, the kind that you put in the garage are 'chest freezers' - but the term 'deep freezer' refers to how cold they are kept rather than how physically deep they are. I'm surprised that -18C is right - I thought it was much warmer than that. -7C or so. The only requirement is for everything inside to be frozen and there aren't many foods that are still liquid below that. (Although concentrated brine solutions won't freeze until -21C. The amount of heat leaking into your freezer (and therefore the amount of electricity you'll need to run the thing) is proportional to the square of the difference in temperature between the air and the freezer. If your room temperature is (say) 20C and you keep your freezer at -18C then you'll be using 38² 'units' of electricity - at (say) -8C, it's only 28²...that's about half as much! So running your freezer colder than it needs to be is not cheap! SteveBaker 22:54, 27 September 2007 (UTC)

Even in American English, technically speaking, I think you're correct about "chest freezer" and "deep freeze", but colloquially, I think it's more common to refer to the freezer-only unit, whether upright or horizontal, as the "deep freeze".

Atlant 23:08, 27 September 2007 (UTC)

When attached to the refrigerator it is often referred to as the freezer compartment and its temperature is usually not owner adjustable. - hydnjo talk 11:37, 28 September 2007 (UTC) Oops, strike "not". - hydnjo talk 21:17, 28 September 2007 (UTC)

The temperature of the freezer compartment is always adjustable, it's just that the temperature of the refrigerator compartment may track along with it (or vice-versa, depending on your point of view). But in most American kitchen 'friges (with a separate door for the freezer compartment), some provision is made to adjust the temperature of the compartments separately. Low-end friges let you manually set an air door (damper) that varies the relative amount of cooling between the two compartments. Higher-end fridges have separate thermostats that probably automatically affect an air door; I haven't taken mine apart yet. ;)

Atlant 15:55, 28 September 2007 (UTC)

I know that -18C is often the recommended storage temperature for ice cream. Whether it makes a significant different to the texture or taste I don't know. Also I don't think the only requirement is that everything is frozen. You ideally want most things to be a few degrees below their freezing temperature since otherwise they may thaw too quickly. I'm not saying -8C doesn't achieve this simply pointing out everything being frozen isn't usually sufficient. Also I would expect the actual temperature inside the freezer is allowed to vary by at least 1-2 degrees. The freezer turns on when it's above the high threshold and turns off when below the low threshold (similar to the way the fridge part works). Nil Einne 14:52, 28 September 2007 (UTC)

My experience is that small changes in temperature have big effects on the texture of ice cream, especially the more-watery varieties.

Atlant 15:44, 28 September 2007 (UTC)

Lower temperatures also help to stave off the effects of freezer burn. 136.152.153.30 21:33, 28 September 2007 (UTC)

A few points on why a lower temp than freezing may be needed. One is that many frozen foods contain fat or oils, which substantially lowers their freezing temp. Another is that adding a large room temperature object (say the carcass of a turkey after a meal) can melt things around it. Every time a frost-freeze cycle occurs the food degrades further, so you want to avoid this, if at all possible. StuRat 22:49, 28 September 2007 (UTC)

I don't think that's true. Fat and oils don't dissolve in water - they forms an emulsion, which is really just teeny-tiny bubbles of oil floating in the water - and that doesn't change the freezing points of either substance. AFAIK, the lowest temperatures you can get are with salt. In fact, the one thing that lends some credance to the -18C figure is that it is zero Fahrenheit. The Fahrenheit temperature scale was designed such that 0F was the coldest temperature that could be obtained in a laboratory at the time - using salt and water (100F was thought to be human body temperature at the time). But Mr Fahrenheit wasn't much of an experimenter and he got both ends off the scale off by a few degrees and actually, you can get water down a few degrees below 0F with a really concentrated salt solution. SteveBaker 01:17, 29 September 2007 (UTC)

I didn't say oils mixed with water. I'm quite clear on oils and waters forming an emulsion, as I mentioned just recently here. I said that some "foods contain fat or oils, which substantially lowers their freezing temp". That means that to be frozen solid, the oils must be frozen, too, which have a much lower freezing temp than water. (I suppose you can leave the oils in liquid form, but that leaves them free to migrate, which can cause the food quality to diminish.) StuRat 02:06, 29 September 2007 (UTC)

I did find the proper 'official' temperature for freezing foods. In the UK (at least) frozen foods are labelled with their storage life against the temperature of the freezer using a 'star rating' - so the amount of time you can keep food depends on the star rating of your freezer:

One Star = -6°C

Two Stars = -12°C

Three Stars = -18°C

Four Stars = -18°C - but with a 'fast freeze' setting down to -26C

So you could save a LOT of energy by adjusting your freezer down to -6C and pretending you only have a one-star freezer - but you'd have to be aware that you are reducing the amount of time that your food will remain in good shape. Bacteria can't grow at -6C - so that's not the issue...it's purely the texture, flavor and such that suffers at warmer settings over long periods. SteveBaker 01:33, 29 September 2007 (UTC)

Wouldn't that be setting the temp "up" to -6°C ? StuRat 01:54, 29 September 2007 (UTC)

neurophysiology

im looking for a few pointers how to write a 3000-5000 word essay on the reason why even though you are running after a bus for example,you can still read the number on the bus with reference to the nervous system and responses Saradennehy 19:48, 27 September 2007 (UTC)

The tell them three times rule of thumb may apply. Introduction -- Tell them what your are going to tell them. Body -- Tell them. Conclusion -- Tell them what you told them. Lazyquasar 23:33, 27 September 2007 (UTC)

Oh, hey, you're looking for a specific reflex. I'm not going to tell you what it is, because I think you're doing homework. However, there is a link to it at Eye movement. Let us know if you run into trouble! --Mdwyer 01:28, 28 September 2007 (UTC)

If I'm not mistaken, Steven Rose uses that very example in his book The 21st century brain explaining how we can identify a big red patch moving accross our field of vision as a bus and act instinctively upon that realisation (such as jumping out of the way). This might touch on your subject (is it vision and body coordination?). It's a classic that should be in your college library. 80.200.155.140 00:13, 30 September 2007 (UTC)

Examples of Buffer Solutions

Can you tell me some examples of buffer solutions that work in human body? I need to know them to prepare an assignment.What is their biological imprtance and how does they function? Please, share your knowledge. thanks a lot. —Preceding unsigned comment added by 201.220.222.140 (talk) 20:22, 27 September 2007 (UTC)

Well, the human body uses several buffer systems (not solutions). The two main systems are the bicarbonate/carbonate ionic system, and the phosphate buffer system. I don't see a good overview here on Wikipedia, though you could look at the specifics here. Some explanation can be found at this site. - Nunh-huh 20:41, 27 September 2007 (UTC)

"Oh yeah, a buffer. The family had a lot of buffers!" - hydnjo talk 03:21, 28 September 2007 (UTC)

Physiological Effects of Niacin

I am doing an article on niacin and am trying to simplify a paragraph found at http://www.feinberg.northwestern.edu/nutrition/factsheets/vitamin-b3.html . Could someone explain it to me?

Niacin is an essential vitamin that supports energy metabolism and reactions involving biosynthesis and degradation as part of the pyridine nucleotide coenzymes, nicotinamide adenine dinucleotide (NAD) and nicotinamide adenine dinucleotide phosphate (NADP). The levels of oxidized and reduced forms of these coenzymes establish the redox potential in cells that regulates metabolic activities involving mitochondrial electron transport and numerous enzyme reactions.

Thanks!

Felix 22:23, 27 September 2007 (UTC)

Niacin is a vitamin required to produce NAD and NADP, which govern the redox state of a cell, and thereby regulate its metabolism. - Nunh-huh 22:52, 27 September 2007 (UTC)

Basically, Niacin is required to make NADP and NAD. (Niacin makes up parts of the structures of NADP and NAD.) NADP and NAD are two molecules that help in making stuff that the body needs (biosynthesis). They do this by helping in redox reactions (redox is a type of reaction that transfers electrons from one molecule to another).

The paragraph also talks about NADP and NAD being coenzymes. Coenzymes are molecules that work together with enzymes (proteins that help speed up biological reactions) to complete the reactions. Hope this helps.

128.163.224.222 20:33, 30 September 2007 (UTC)

insect brain

Other than size, what is the difference betweem human and insect brains? Clem 23:47, 27 September 2007 (UTC)

Our insect article discusses the nervous system a bit. An insect barely has anything worth calling a "brain": what passes for a brain is sixed fused ganglia in the head. The insect nervous system is much more "decentralized" than the vertebrate nervous system, with ganglia in various body segments controlling local funcitons. - Nunh-huh 00:25, 28 September 2007 (UTC)

• It also weighs much less. --Sean 03:24, 28 September 2007 (UTC)

Which is a logical result from it being smaller. Duh! :) Keep in mind that a larger body requires a larger brain, just to control the body. As for the mental functions, I was almost tempted to point out that the neocortex gives mammals the ability to learn. But bees can tell each other where a nice and nectary flower field can be found, and that is a form of learning. DirkvdM 07:08, 28 September 2007 (UTC)

"The developing Drosophila melanogaster brain, like the vertebrate brain, contains many compartments that give rise to multiple, anatomically distinct processing centers...." Compartmentalization of visual centers in the Drosophila brain requires Slit and Robo proteins provides a description of the major fly brain regions involved in vision. You can compare these to the major visual centers of the human brain. Exoskeletons impose restrictions on the evolution of sensory organs and brains, but insect brains are as "highly" evolved as human brains. --JWSchmidt 14:25, 28 September 2007 (UTC)

Do you mean to say that the basic functions are the same, but insects just have less of them? Concerning my remark about learning - the example I gave is short-term memory. And I now wonder if that is essentially different from long-term memory or that the latter is just a matter of 'more of the same', therefore spanning a longer time period. However, I doubt that insect brains will be essentially the same as human brains because the two are so different in so many ways. I suppose what matters here is if nerves as we know them evolved before the insect and mammal branches split off from each other. DirkvdM 18:09, 28 September 2007 (UTC)

Invertebrates and vertebrates have been found to use many proteins (example: CREB) in similar ways for making changes in neurons that are required for the storage of long term memories. However, many hundreds of millions of years have passed since there was a common ancestor for insects and vertebrates, so there are very different patterns in how insect and human brains are laid out. A Beetle is very different from a Liebherr T 282B, but are they "essentially" the same? --JWSchmidt 20:29, 28 September 2007 (UTC)