Wikipedia:Reference desk/Archives/Science/2012 July 28

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July 28[edit]

Cloning[edit]

How far has science made progress with cloning in the last 10 years? Bulkbot84 (talk) 05:04, 28 July 2012 (UTC)

Have you read the cloning article? Looie496 (talk) 05:14, 28 July 2012 (UTC)
You may be interested in List of animals that have been cloned. 203.27.72.5 (talk) 05:17, 28 July 2012 (UTC)

Psychology and historical context[edit]

I am interested in finding out what areas were considered mainstream psychology, and what areas were considered fringe psychology, in the late 1970s. Can anyone give me any pointers please? --TammyMoet (talk) 09:27, 28 July 2012 (UTC)

This is about when homosexuality went from being classified as a mental disease to an alternative lifestyle. So, before the 1970's, studying the "mental disease of homosexuality" would have been mainstream, while, after the 1970's, those who still believed in that would have been thought of as just a fringe group. StuRat (talk) 09:59, 28 July 2012 (UTC)
Assuming you meant psychiatry (treatment & management of disease) What is considered a mental disease requiring prescribed treatment or management, and what is just considered a bit odd by lay persons, has always varied from region to region. Diagnostic rigor has always varied considerably from region to region. An extreme example of the variation significant up to the 1970's is classification of political/economic views - In the USA, seriously objecting to the system of government would only have been viewed as being a bit stupid at worst, and maybe just exercising your rights. In Iron Curtain countries, it could get you admitted to a mental assylum. For an American view of diagnostic criteria, you might like to dig out old versions of the Diagnostic and Statistical Manual of Mental Disorders (DSM) published by the American Psychiatric Association. It's updated about every 10 years or so. Any good university library should have every version.
Assuming you meant psychology (understanding of normal behaviour & capability)- developmental psychology, industrial psychology, etc), then you need to look at things like aptitude testing for emploment, aptitude testing for allocation for suitable school clases etc. For example, Raven's Progressive Matrices was considered a good tool for determining whether you would make a good clerk, tradesman, etc, up to perhaps the 1960's, then went out of fashion, and now in the 2010's, back in fashion again. Up to the 1960's IQ testing was considered objective good stuff, then progressively less well thought of. In the 1960's, if you applied for a job in Australian Government Service, you would have sat a three-part exam: an IQ test, a raven-style test combined with a basic arithmetic test, and a general knowlege test. If they needed 15 people, and you scored in the top 15, you got the job. No employer would be that silly now - they would at least interview you and check references.
Wickwack121.221.223.145 (talk) 12:14, 28 July 2012 (UTC)
Oh that makes sense: I did my psychology degree in 1980, and in the last semester we studied things like graphology, personality tests, hypnotherapy. I've been racking my brains trying to think (a) why we would have studied them and (b) what else we would have studied. Hence the question. Any other suggestions are welcomed. --TammyMoet (talk) 14:07, 28 July 2012 (UTC)
Graphology is quite old I think. You might want to look at Ink Blot Testing. I think it faded out in the 1960's, but many American industrial psychologists were fans of the ink-blot test - a very subjective and dubious method of ascertaining personality traits and fitness for work. If I remember correctly, the US Navy in the 1950's and 1960's required yearly fitness reports for senior officers, and it incuded a psychological report, usually based on ink blot testing. By the 1970's, at least in my country (Australia), the term "ink-blot merchant" came into use for when one wanted to refer to an industrial psychologist in a derogatory way (now an obsolete term). Wickwack124.178.33.116 (talk) 15:30, 28 July 2012 (UTC)
Yes I remember looking at Rorschach tests, but I think it was right at the start of my degree as part of the History of Psychology. Thanks also for "industrial psychologist" - I remember looking at that field because of the Milk Round (where companies tried to woo final year students) getting me an interview at a car parts factory. I didn't get it. --TammyMoet (talk) 17:04, 28 July 2012 (UTC)
I was given a Rorschach inkblot in the early 90s, so it was still somewhat in use at that point. And, um, I'm feeling much better now... :) Matt Deres (talk) 23:06, 29 July 2012 (UTC)
You might be interested in the fact that it was considered normal for adults to be sexually attracted to teenagers in that era, but that has recently become such an extreme controversy in the latest revision of the DSM in progress that some of its editors want to declare such attraction to be an abnormal mental illness. I am not making this up! PMID 21110392, PMID 21389170, PMID 20336359, PMID 18923891, PMID 18686026, PMID 21389175.... 207.224.43.139 (talk) 21:53, 28 July 2012 (UTC)

Most important genes of life[edit]

Are there any genes, which are identical (or highly similar) among all cellular live forms? With no known exceptions. --Ewigekrieg (talk) 13:47, 28 July 2012 (UTC)

You might refine your search by reading about metabolic pathways, such as glycolysis, that are common amongst nearly all known biological organisms. The genetic and other biochemical structures that regulate such pathways provide strong evidence for common ancestry between almost all Earth life-forms. You may also want to read Last universal ancestor, which discusses the scientific study to determine whether Earth life descends from a single source. This entire field presents many questions whose answers are difficult to determine with certainty. We have very limited capability to decipher "fossil" biochemistry evidence; so we must often test our hypotheses by tracing back biochemical evidence from present-day data. There is a lot of scientific data, and there are many good theories, but there will be several questions that can't be answered conclusively. "No known exceptions" is almost always impossible in observational science. A better way to frame the question is: when we find an exception, what does that imply? Does it provide evidence that life on Earth originated multiple times, or that it diverged evolutionarily? Does it provide concrete evidence, as many scientists theorize, for extraterrestrial origin of some biochemical material present in today's Earth life? On the same line of reasoning: if we cannot find any exceptions, how should we formulate our theory? Nimur (talk) 15:11, 28 July 2012 (UTC)
You may also find this week's post on NASA's main astrobiology page interesting: “How Life Turned Left”, regarding biochemical chirality. This is a topic I've heard a lot about, the claim is (loosely) that "all" biologically-created organic molecules have the same chirality. I've seen ths claim a lot, and it seems to be a really significant empirical discovery; but as I am not a chemist, I don't fully understand the evidence or the implications. Nimur (talk) 15:21, 28 July 2012 (UTC)

Ribosomal genes are the most conserved, since they deal with gene transcription. "The 16S and 23S ribosomal RNA genes scored as the most highly conserved sequences." μηδείς (talk) 18:19, 28 July 2012 (UTC)

See conserved genes, 16S ribosomal RNA, and 23S ribosomal RNA. μηδείς (talk) 21:15, 28 July 2012 (UTC)
Yes. In fact, most housekeeping genes are like that, to varying degrees. This is especially true if we restrict what we mean by conserved to the general 3-d structure of the protein and its interaction sites. Yaniv256 (talk) 01:53, 29 July 2012 (UTC)

Wireless energy[edit]

From what I assume about wireless energy transfers is, electrons are sent wirelessly to loads that need it. But similar to radiation, won't electrons flying around a room pose a threat to human life (causing diseases like cancer?) Thanks, 64.229.5.242 (talk) 16:32, 28 July 2012 (UTC)

Electrons as radiation are called beta particles and can cause molecular damage leading to cancer, but there are no electrons involved in wireless energy transfer. -- BenRG (talk) 16:55, 28 July 2012 (UTC)
Most wireless energy transfer occurs without the bulk movement of charge. That means the energy is carried by an electromagnetic wave, not by moving electrons. For the same reason that light can travel in a vacuum - electric and magnetic fields can exist independent of any transmission medium or "substrate" - energy can propagate (wirelessly) via an electromagnetic wave even when there is no movement of electric charge or matter. In most practical systems that have been built to-date - inductive energy transfer - the energy takes the form of an evanescent wave. Nimur (talk) 17:52, 28 July 2012 (UTC)

What would it be like to walk on Gliese 581g?[edit]

What would it feel like for a human being from Earth if they could walk on the surface of a planet with 1.5 or more time the gravity of Earth? If the atmosphere was also denser, what would it feel like to walk through it? And would that mean it was harder to see long distances?184.147.121.51 (talk) 18:12, 28 July 2012 (UTC)

It helps if you provide a link to the subject you are talking about. Gliese 581g. μηδείς (talk) 18:15, 28 July 2012 (UTC)
The gravity would be fairly easy to simulate, aboard the "vomit comet", for example. A more convenient, but not quite as good, simulation can be obtained by carrying weights all over your body equal to half your body mass.
Thicker atmosphere would make movement more like swimming, but would also reduce your apparent mass weight, due to buoyancy. It would make it harder to see through, if it was identical the Earth atmosphere other than density. However, it might have fewer particulates, and thus be clearer, as high gravity would tend to cause particulates to settle out quicker. StuRat (talk) 18:33, 28 July 2012 (UTC)
StuRat, buoyancy has no effect on mass - apparent or otherwise. You can model buoyant force as a change in net weight (though it's more physical and more common to model buoyancy as a separate force); but it's incredibly uncommon to model buoyant force as a change in mass. Please don't confuse weight and mass. Nimur (talk) 18:41, 28 July 2012 (UTC)
OK, fine, "apparent weight", although the only two ways individual humans have to infer mass is from weight and inertia, both of which would appear reduced in a thick atmosphere (the gravitational attraction caused by each person is a third method, but beyond our ability to perceive without powerful instruments). StuRat (talk) 19:02, 28 July 2012 (UTC)
Buoyancy reduces apparent weight but not inertia. The friction of a thicker atmosphere might well reduce momentum in some situations, but might also increase "apparent inertia" in others. Dbfirs 08:11, 29 July 2012 (UTC)
How would a thicker atmosphere increase the apparent inertia of a person ? It seems to me you will be slowed more by the thick atmosphere than you would in a thinner atmosphere. StuRat (talk) 08:25, 29 July 2012 (UTC)
It would be pretty easy to distinguish higher air resistance from a change in inertia. More air resistance would make it more difficult to pick up speed (think about trying to walk underwater), which is vaguely similar to having higher inertia. However, once you are moving and started to coast, the increased air resistance would slow you down faster, which is vaguely similar to having lower inertia (consider throwing a piece of paper vs throwing a metal sheet the same size - the paper slows down faster). In reality, air density simply doesn't have any effect on inertia and cannot be meaningfully modelled as a change in inertia. --Tango (talk) 17:12, 29 July 2012 (UTC)
An atmosphere 10 times as dense as earth's would buoy about 1.5% of a person's weight, see the calculation below. That effect would be unnoticeable. μηδείς (talk) 19:39, 28 July 2012 (UTC)
(Edit conflict)
This question should really be broken down into its constituent sub-questions:
  • What would it be like on Gliese 581g? In truth, we don't know, because we know very little about Gliese 581g. What we do know was learned through indirect observations - the way its parent star wobbles - from which we fit model parameters based on what we know about sun-and-planet systems.
  • What does 1.5g gravity feel like? This one is fairly easy: you would weigh 1.5 times as much; you would be heavier. We can "easily" simulate 1.5 g forces using airplanes, or elevators, and so forth.
  • Would the atmosphere be denser? Probably, yes, if all else is equal; because that fits our model of atmospheric formation. We have an article on atmospheric modeling. And, if you study aerodynamics, you will some-day encounter the Standard Atmosphere; if you study astronautics or planetary science, you will extend the standard atmosphere to a general atmospheric model for any gas mixture on any planet under any other circumstance. I recommend Lissauer and de Pater's Planetary Science text if you're interested in following such details with scientific rigor.
  • Would it be hard to see through a denser atmosphere? All else equal, yes; we have an article on optical density. We also have the somewhat more practical article, visibility, about the concept used in meteorology. It would be difficult to estimate how much the optical density changes, without knowing a lot about the other atmospheric parameters. For example, consider the atmosphere on Mars: all other things are not equal: the temperature, pressure, and gas composition are totally different from Earth. The Martian air is much much thinner - nearly a vacuum, compared to Earth's surface - and yet, the major optical attenuators are aerosols, fogs, and hazes. Even thin air can be optically dense.
Nimur (talk) 18:39, 28 July 2012 (UTC)
  • A human weighing 200lbs occupies about 89 liters of space, about four moles of gas at standard temperature and pressure. Four moles of O2 weighs about 0.128kg. In a breathable atmosphere 10 times as dense as the earth's the 200lb man's body would displace a little under three pounds of gas, the weight of a full bladder and a good bowel movement. He would not notice that difference. μηδείς (talk) 19:25, 28 July 2012 (UTC)
Perhaps the greatest effect of denser atmosphere would be increase difficulty in exhaling? While it may not be especially difficult to breathe while awake, I wonder if sleep apnea would be more common in a dense atmosphere scenario. BigNate37(T) 19:43, 28 July 2012 (UTC)
No, the higher pressure would be equal inside and outside your lungs. A higher vapor density of Oxygen would actually make it easier to breath, to the point of getting too much O2. μηδείς (talk) 19:47, 28 July 2012 (UTC)
It would take more effort to exchange a full lung's worth of air, since it now has more mass. However, since you would need less air to get the same oxygen, you might breath less often, and take shallower breaths, when resting. But, of course, the higher gravity and the extra effort to move through the thicker atmosphere (especially on a windy day) would also increase the amount of energy needed to move around, and thus increase your respiration rate. StuRat (talk) 19:59, 28 July 2012 (UTC)

Physics of mace (club)-like weapons[edit]

If you have several different versions of a blunt weapon, which consist of a heavy ball attached to a handle (flexible or not) or a chain, like a mace (club) or flail (weapon). What's the difference, regarding the impact force, between the versions? OsmanRF34 (talk) 19:03, 28 July 2012 (UTC)

You're probably asking about the potential to get it going faster, like a whip, but a whip works by having the tip be lighter than the the rest, not heavier, so I don't think that would happen here, or at least not to the same extent. StuRat (talk) 19:14, 28 July 2012 (UTC)
But, doesn't it make any difference if the handle is a chain or a rod? (given the same mass). — Preceding unsigned comment added by OsmanRF34 (talkcontribs) 19:24, 28 July 2012 (UTC)
Not sure if it would make any difference in the force it would deliver unopposed, but it certainly would make other differences. The chain mace would be more portable, could be easier to use at less than the total length, and would be harder for the enemy to stop by grabbing at the shaft. It would also eliminate force or vibration on the hands when it strikes an object. StuRat (talk) 19:35, 28 July 2012 (UTC)
A mace can be modelled in a similar way to a baseball bat or golf club, both of which have ample physical analyses out there. Using a club-like weapon (or any rigid weapon, including a fist) allows for follow-through, where the user attempts to put the weapon "through" the target; follow-through allows the user to continue imparting force through the weapon after the point of initial contact. Contrast with a flail: the user must first accelerate the striking mass, at which point the force of impact is effected by the mass' momentum alone, with no means for the user to supply additional force on impact. I'm afraid I'm ill-prepared to discuss it quantitatively, though. Another obvious difference is that a rigid weapon allows for more precise control (given sufficient strength) whereas a flail must be accelerated towards the target with some foresight. Changing angle of attack or aborting an attack with flail is very difficult, and potentially very unsafe. In a combat scenario, it would be difficult to avoid telegraphing your movements. Those are trade-offs against the disadvantages Stu mentions above in using a club in a combat scenario. BigNate37(T) 19:37, 28 July 2012 (UTC)
The amount of force you can exert after contact is quite low. Considering the baseball example, if you started with the baseball stationary and in contact with the ball (let's say a T-ball setup), how far do you think you could move the ball ? StuRat (talk) 20:07, 28 July 2012 (UTC)
Your example is not quite a correct analogy. It precludes the possibility of flex in the weapon due to initial force, which prevents prolonging the time of impulse. Were the follow through as ineffective at imparting force as you imply, golf clubs and hockey sticks would not be designed for extra flex. However, I suppose with an effective grip and stance I could move said ball something like 5–15m, which is perhaps an order of magnitude less than a full swing, a non-negligible amount of force. BigNate37(T) 20:21, 28 July 2012 (UTC)
That flex is mostly due to force exerted prior to contact, not after. That 5-15m seems rather high, to me. Time for an experiment ! StuRat (talk) 21:40, 28 July 2012 (UTC)
Right, the flex and impulse extension is not itself providing supplemental acceleration, but by extending contact time, I'm asserting that it widens the window during which the follow through adds force. Perhaps snap shot vs. slap shot is a more appropriate analog? It's easy enough to find sources that admit flex is important, but it's harder to find anything that specifically addresses the matter of follow through force or lack thereof. BigNate37(T) 15:32, 29 July 2012 (UTC)
I don't think it's a good analogy to using a mace in combat, because you can maintain contact for a long time and distance with the hockey stick, since the puck is so light (even the baseball analogy was generous in this regard). Presumably you can't accelerate a (much heavier) enemy with a mace in a similar fashion. StuRat (talk) 19:11, 29 July 2012 (UTC)
Well, a rigid club striking an opponent should have ample contact time too, but for a different reason. Rather than displacing the target, you are deforming it via an inelastic collision. But perhaps I've stated my thoughts as clearly as I can, and now I'm just repeating myself. BigNate37(T) 19:27, 29 July 2012 (UTC)
Do you have a baseball and bat ? If so, I'd like you do that experiment to see if you can get 5-15m. (If you lack a t-ball setup, you can just place the ball on a porch or ledge, but no fair kicking the baseball bat.) StuRat (talk) 19:11, 29 July 2012 (UTC)
I do not have access to a baseball bat or a tee. I'm also not convinced a ledge or railing is a practical replacement tee, either, unless we substitute a softball or something with a sufficiently large diameter to allow the bat to clear the "tee." I could try that with my goalie stick and a floor hockey ball when I get back home next week, but that's essentially just going to be a wrist shot, and the outcome of that thought experiment isn't in question. BigNate37(T) 19:27, 29 July 2012 (UTC)
  • From the latter article, "The chief tactical virtue of the two-handed flail was its capacity to defeat a defender's shield or avoid it entirely." You know how today we see stories about weird curved guns from World War II that could shoot around corners? Well, this is a club that can shoot around corners. Or at least that's my guess. Wnt (talk) 14:31, 1 August 2012 (UTC)

Levelling[edit]

A recent TV programme mentioned that an instrument that had been placed on the moon had to be levelled which made me wonder what was the datum used, what was it levelled against? This raised the same question in my mind, what is the datum on earth, it can't be sea level since that differs everywhere. Any advice please?--85.211.195.59 (talk) 21:14, 28 July 2012 (UTC)

Presumably they mean they used some form of level (such as a laser line level) to make sure the device wasn't at an angle. These use gravity to determine what "level" is. For a large body, this can very closely be approximated as the pull towards the center of the object. StuRat (talk) 21:24, 28 July 2012 (UTC)
As for measuring altitude, sea level does not vary by much, only a few meters, counting tides. I believe they average all those out, however. Rivers and lakes can vary by quite a bit more (usually higher, but sometimes lower, as in the Dead Sea). Rivers also have the problem of varying altitude from source to mouth. These days, I imagine a GPS system is the best way to measure altitude (air pressure is also used, but can vary a bit due to high and low pressure cells, and even more in a hurricane). StuRat (talk) 21:31, 28 July 2012 (UTC)
Whereas on earth the datum used for measuring altitudes is sea level, this obviously can not be used on the moon. Therefor, various organizations such as NASA, the U.S. Geological Survey and others have established an artificial lunar datum plane at approximately 1,738 km from the center of the moon. It varies depending on location because the moon, like the earth, is not quite spherical. The full explanation is here.    → Michael J    06:31, 29 July 2012 (UTC)

NASA has a great amount of information available on specific experiments. If you can recall the mission, or the experiment package, we can probably help you find more specific information. Here's a general overview of Apollo Lunar Surface Experiment Packagess. In many cases, experimental devices were leveled using the UHT (the Universal Handling Tool - a NASA acronym for poking them around in the sand-like regolith with an aluminum pole until they seemed "level"). Other experiments were much more precise. Apollo 17 used a gimballed antenna with 2-axis bubble level lines (similar to what you'd use on Earth). The infamous laser corner-reflectors self-align, because they are corner reflectors, so did not require any precision alignment at all. Nimur (talk) 15:46, 29 July 2012 (UTC)