Wikipedia:Reference desk/Archives/Science/2007 January 9

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January 9

How to find a reference...?

How do you find a reference for or locate the manufacture of a Hall effect switch or sensor like one designated as an F41.5Gc? -- Barringa 08:32, 9 January 2007 (UTC)

Try Honeywell SS41. -- 71.100.10.48 02:55, 12 January 2007 (UTC)

Standard taper ground glass joints (glassware): ISO vs. US

I'm trying to understand the difference between US and ISO standard taper (ST) ground glass joints. Are they more or less the same? Both using a xx/yy notation to describe taper diameter and length in mm? Would a ISO ST 29/42 and US ST 29/42 be identical? --Alf 08:02, 9 January 2007 (UTC)

It is possible to work with both at the same time. The US stuf is longer, but has the same diameter at the wider side. The people blive that this is better, but only in an ideal enviroment.--Stone 09:12, 9 January 2007 (UTC)

Thanks for the clarification. If you have the time, do you think you could incorporate some of your knowledge about the difference of these two standards into the Ground glass joint#Conically-tapered joints article? --Alf 09:44, 9 January 2007 (UTC)

Sorry this was for US-long the US is shorter than the ISO but still combinable, as long as the rest of the joint is not in conflict with some parts of the glas aperatus.--Stone 10:52, 9 January 2007 (UTC)

Importance of academic degrees

How important are academic degrees nowadays? Are Ivy league degrees worth the money? —The preceding unsigned comment was added by 132.231.54.1 (talk) 12:54, 9 January 2007 (UTC).

It depends on the field and location. For example, a degree from The Citadel doesn't mean much, unless you live near Charleston, South Carolina. If you do, it is an easy way to get a nice job at most of the local companies. I am a software engineer - which requires a degree to get any respect. I'm switching professions to become a college professor, which requires a graduate degree to even be considered. So, you can see that academic degrees are important in some areas and the college you go to is also important in some areas. --Kainaw ^(talk) 13:52, 9 January 2007 (UTC)

Having an undergrad from a very well known university can definitely get your foot in the door. Most employers respond very positively to "Yale", "Harvard", "Berkeley", etc. as your place of origin. Once you drop down a bit from a world-reknown place, I am not sure that the name means as much to most people. With more advanced degrees I think it depends on what your ambitions are. You are not going to get called up to Wall Street if your business degree is not from some place well-known, but if you weren't aiming at that then it probably matters less. If you are trying to break into academia, having a PhD from a very well known program will definitely make sure you are on the short-list of serious job candidates wherever you apply, which won't automatically get you a job but it sure does help. That's my perception of it, anyway. In most cases the degrees just act to impress upon others what sort of serious candidate you are — you've still got to perform to be successful. --24.147.86.187 15:28, 9 January 2007 (UTC)

If the whole idea of going to university or college for its own sake doesn't strike you as at least somewhat intriguing, you may want to consider your ultimate reasons for going in the first place. Money, a job, a house, a spouse, kids...? Vranak 16:25, 9 January 2007 (UTC)

I chose to go to university so I could meet new people, go somewhere different, spend some time away from home, and learn something I haven't studied at school. The slightly increased chance of getting a job is just an added benefit.Hidden secret 7 19:34, 9 January 2007 (UTC)

Are there some things you can not do if you do not have a degree? Going to university or college is like an operating system for your computer. Going to Havard will probably all a lot of bells and whistles even if you do not graduate like it did for Bill Gates who's parents socialized with the head of IBM, etc. Contacts might be equally or more important than a degree going by the number of millionaires with an 8th grade education or less. Instead of doing basic research in a university/government sponsored lab you could create such a lab of your own Jim Walters. Having a degree - even an incomplete one, is under any circumstance probably better than not having one at all. Barringa 21:25, 9 January 2007 (UTC)

If you are going to do any great work in your life, it will probably not hinge on your having a degree. You might get a degree in the course of doing great work, but it's not like you will say to yourself after four years of college "Ah, I have my degree! Now my life begins!". Vranak

Having a degree is like having a car... you can't walk or ride a bicycle on some roads or get to where you are going as fast. 71.100.10.48 03:00, 12 January 2007 (UTC)

As Mark Twain said, "Never let your schooling interfere with your education." — Michael J 18:02, 21 January 2007 (UTC)

Cosmic inflation

I'm attempting to write an essay on cosmic inflation, but am having a little trouble understanding the jargon in the article - I've interpretated the majority of it, but I don't see anything explaining why inflation ceased - did the decaying vacuum energy simply reach its new, more stable minimum?

Thanks, 130.209.6.40 13:40, 9 January 2007 (UTC)

Didn't it slow down because of gravity attracting everything towards everything else, and now they think the whole thing is going to collapse on itself.Hidden secret 7 19:31, 9 January 2007 (UTC)

Your guess is pretty much correct. The inflaton (no, I haven't missed an i there) field reached a lower, stable potential. What sort of level is this essay supposed to be? And are you versed in quantum field theory?

To be honest, I don't think I have to be that deep - it's for a group report on Cosmology, and the other topics are "easy" things like the expansion of the universe, and the CMBR, so I think it's more hand-wavey than anything else. I've got it pretty much done, with a summary of the process, some of the objections to the HBB model it explains, and now I'm just looking for criticisms. I've only been able to find two in my references, but the Cosmic inflation article doesn't really seem to have any. I've got that it predicts the wrong value of Ω₀, and that the mechanism for why it stops isn't understood...but I'd really like more than that. Am I missing any crucial ones? I fear I'm in over my head... Icthyos 17:12, 10 January 2007 (UTC)

Other criticisms I can think of off the top of my head are: If inflation did happen why haven't we detected any cosmic strings? Why is there still a little bit of inflation going on today? Why is the energy of free space so much higher than that required by inflation? —The preceding unsigned comment was added by 86.145.254.48 (talk) 19:27, 11 January 2007 (UTC).

trivias about sounds...

^{Superscript text} _could you please help me to find some of the most interesting trivias about sounds?,got a hard time seeking for some,;p 203.215.116.127 15:22, 9 January 2007 (UTC)heartbreaker203.215.116.127 15:22, 9 January 2007 (UTC)

The russians discovered that people can hear a much higher pitch of sound if whatever is producing the sound is touching the person hearing it.Hidden secret 7 19:28, 9 January 2007 (UTC)

The Mosquito is quite an interesting sonic device, and there's also ultrasound, used for medical tests. StuRat 04:08, 10 January 2007 (UTC)

Why does catnip have that kind of effect on cats?

Hi all. I was wondering why catnip has that kind of effect on cats? I was reading up in your article, but could find no mention of what the actual mechanism was. Maybe one of you biology-savvy individuals could explain it better? Much help appreciated ! Xhin 15:28, 9 January 2007 (UTC)

The mechanism actually isn't very well understood, though some aspects of it are. The cat's receptor for nepetalactone is in the vomeronasal organ, located above the feline palate, and the response is similar to a sexual response, but the exact nerve pathways involved are not, I think, known. - Nunh-huh 18:14, 9 January 2007 (UTC)

Following on from Nunh-huh, at the vomeronasal organ (VNO) the nepetalactone is hypothesized to bind to one or more G-protein coupled receptors on the surface of sensory neurons which are found in the sensory layer of the organ. Via a signal transduction pathway (probably involving a G-protein and a transient receptor potential channel) an influx of calcium ions occurs creates an action potential along the axon of the neuron. The sensory neurons of the VNO project to a region of the olfactory bulb called the accessory olfactory bulb where multiple neurons (each apparently expressing a single receptor type) synapse at special neuropil called glomeruli. Here the neurons synapse with mitral cells which, in turn, project to various brain loci, including the amygdala, where the signals are integrated into behavioural signals. It is at this point the pathway enters a bit of a black box. However, there is some evidence of projections to the hypothalamus, which in turn regulates a neuroendocrine response via the pituitary. These hormones would mediate the "sexual response" noted above. That is "how" it is thought to work, "why" is currently unknown. Though one might speculate that the chemical probably hijacks the pathway normally influenced by a cat pheromone. The fact that it only elicits such a response in a proportion of cats - and that it is such a dramatic response - suggests that a genetic element might be involved that is enriched for in domesticated breeds. Rockpocket 08:31, 10 January 2007 (UTC)

Mewow! Perhaps you could add that to the catnip article?--Shantavira 09:02, 10 January 2007 (UTC)

Evolution of organs

How do organs evolve when the intermediary step to the organ seem to bring no advantage to the animal? For example, take the elephant ear. I understand how useful their large ears are in present-day elephants, but I don't see how ancestral elephants with slightly bigger ears have advantage over others. For example, how can an ancestral elephant with an ear that's one milimeter larger in diameter be more successful than other elephants with a one milimeter smaller ear? I can understand how other organs, such as eyes, vertebrae ears, limbs, etc. would have advantageous intermediary forms, but not in organs that seemingly don't have such advantage. Is it genetic drift, or something else? Thanks in advance for any insight.128.163.224.198 19:02, 9 January 2007 (UTC)

An elephant's ears are an important cooling system for the animal. Consider larger ears==>better cooling==>better survivability. Ear size differences among different species correlates with climate. But also, how do you know the change was milimeter at a time? Perhaps the gene that regulates ear growth became virtually non-functional via a point mutation, leading to massive overgrowth? DMacks 19:39, 9 January 2007 (UTC)

Oh, to add more, a better example would be the evolution of bird wings, rather than elephant ears. How can a partially developed wing be useful to the animal?128.163.224.198 19:06, 9 January 2007 (UTC)

They now believe the appearance of bird wings was spontanious, caused by the spread of recessive alelles through a population of reptiles. I can't remeber what this is called now, but you might be able to find out more looking up evolution, or archaeopteryx.Hidden secret 7 19:26, 9 January 2007 (UTC)

One possible mechanism: Small wings are good for improving traction while running, larger wings are better, absurdly large wings give the ability to glide and later fly (birds).

Another mechanism: small skin flaps between limbs are good for longer jumps. Larger skin flaps improve on this (flying squirrel). Very large skin flaps give the ability to fly (bat). --Carnildo 19:52, 9 January 2007 (UTC)

Feathers#Evolution says that feature probably evolved for insulation, not for flight, and then got "hijacked" for an entirely different purpose. So they wouldn't have to suddenly be flight-worthy all at once. Clarityfiend 20:56, 9 January 2007 (UTC)

So the elephants genes were mangled and their ears suddenly went mad? Does the fossil record support this? I don't have a museum in my house, but the internet might know.Hidden secret 7 20:06, 9 January 2007 (UTC)

For example, how can an ancestral elephant with an ear that's one milimeter larger in diameter be more successful than other elephants with a one milimeter smaller ear?

That's easy to explain. Think about heatsinks for CPU in ordinary PC. The earliest CPU for PC have no heatsink. The problem is that those CPU cannot exceed a certain rate of heat release without failure. The first heatsinks are tiny (compare with today), but they give the those CPU evolutionary advantages over those without heatsinks because they can run "hotter". The next heatsinks are slightly bigger and so even more evolutionary advantages. Over the years, the heatsink got bigger and bigger. But they hit an evolutionary roadblock. So the next mutation are heatsinks with fans. The first heatsink fans are small and weak. Then they evolve bigger and faster. So you see, every small steps in evolution gives the animal advantages. Every millimeter counts!!! 202.168.50.40

NOTE: I'm the topic creator, just answering with a different computer/IP address here. Back to the question; I can understand how "every millimeter counts", but in the case of elephant ears I question its impact as a whole. There might be other environmental pressures that trump whatever advantage a milimeter brings (or not really "trump", but make them almost insignificant that the "big ear genes" don't get passed down that many more than small ear genes). For a trait to be passed down at more frequency than others, it must have absolute advantage over others. So, say that there are vicious predators of ancestral elephants. In this case, elephants with longer and stronger legs will survive better and increase its genes in the population. But, those with a milimeter larger ears will not pass more genes because the biggest pressure in the species will select those with better predator-evasion physique, not, say, temperature regulation that the large ears bring. And remember, the ear is only a milimeter larger; while it is an advantage to the animal, it doesn't have that big of an advantage for its genes to be passed down more frequently due to other environmental pressures.

Take another practical example, this time relating to us humans. We acknowledge that better vision makes a better organism. So even though we say that better vision is an advantage, how come we don't have everyone with "super eyes" compared to previous generations? (Our vision as a species probably has stayed more or less the same over the millenias. Pure speculation, but I don't see how it doesn't make sense). That's because, I think, there are other outside factors that selects other things, but not so much the vision. Early hominids with better communication skills, intelligence, and stronger legs had better chance to group together and evade predators; there are those with better vision, but the vision that they have don't offer too much of an advantage (if they don't have the three factors I listed in the previous sentence) that their genes become more frequent in future populations (again, because environmental pressures selected other things beside better vision).

So the only scenario I can think of that allows gradual enlargment of the elephant ear is if the environmental pressure demands larger ears and less everything else. (I guess I just answered my question there :-) ) Is what I'm saying a part of any specific evolutionary theory, so I can look it up? 128.163.80.164 22:23, 9 January 2007 (UTC)

"Environment" means more than just the physical environment, of course; it can also mean "mating pressures" and other things which come under the rubric of sexual selection. As to your question about the "less everything else," what you are really getting at, I think, is that the need for big ears needs to be evolutionary such an advantage that not having them becomes a disadvantage. There are rather complicated statistical models describing how strong these sorts of pressures need to be either way, if I recall. Additionally it is worth remembering that things need not evolve together at all—independent evolution of certain traits can come together in a favorable way as well, and some traits need not even evolve perfectly at all. --24.147.86.187 03:33, 10 January 2007 (UTC)

NOTE: I'm the topic creator, just answering with a different computer/IP address here. You hit my point right on the head there. So, would my analysis be correct? And is there any specific, named theory that describes what I talk about (by that I mean the evolution of a specific trait vs. relevant outside pressure)? From my limited knowledge of evolution, what I described seems to make the most sense to me in the evolution of organs, so if anyone can point out to me other sources regarding it, I'd appreciate it. 128.163.174.129 21:24, 10 January 2007 (UTC)

The questions you are asking are typically grouped into a school of thought known as Irreducible complexity. I think you will find the best answers to your questions in that article, as well as Evidence_of_evolution#Evidence from comparative anatomy, Evidence_of_evolution#Vestigial organis and especially Evolution of the eye. -- dpotter 21:19, 9 January 2007 (UTC)

NOTE: I'm the topic creator, just answering with a different computer/IP address here. Thanks, Dpotter. Just to note, however, I believe that evolution and common descent are the best scientific explanation of speciation. I'm not too fond of IC, ID, Creationism or anything like that in terms of providing the best scientific explanation of diversity. My question here is not so much to question evolution in general, but is about my curiosity in the specific mechanisms of evolution that may have occured.128.163.80.164 22:23, 9 January 2007 (UTC)

No one has yet mentioned the OBVIOUS ONE!:) Elephant ears of course would have started evolving for the same reason as human ears, for better hearing!! Which has very obvious advantages, hearing predators and such.. Vespine 21:34, 9 January 2007 (UTC)

I've heard that it actually takes only a very small advantage to drive change. Vultur

To add to what others have said, there is lots of variation in any population; consider that it's not hugely unusual to find adult human males taller than 2m (6'6") or shorter than 1.65m (5'5") - a difference of more than 20% in height. Consider also that large animals have a smaller surface-area to volume ratio and so are more likely to struggle to dissipate heat (as in a simple model - heat is generated by every cell in the body -> roughly proporional to volume. Heat can be dissipated only by the skin around the edge of the animal). Elephant ears provide a cooling mechanism for the elephant. Larger ears allows an elephant to lose heat more quickly. What if that means that an elephant can run further/faster from predators without overheating? That will certainly give a large-eared elephant a definite advantage over smaller-eared ones and increase the survival rates. It needn't be millimeter changes in ear size - if human heights can vary by 20%, so could elephant ear sizes. So if the survival rates of large-eared elephants increases (even slightly), then there is a trend for large-ear genes to be passed on to offspring in favour of small-ear genes. Over many hundreds of generations, larger-eared elephants become the norm in the population Richard B 14:56, 15 January 2007 (UTC)

Chemistry Trouble

Hey, I'm revising for Chemistry and have just done a past paper for my AQA Chemistry A-Level. I've just tried the AQA website, and it's not working! My friends have also found it down. I was hoping that you'd be able to confirm whether I'm write for this question.

You're given the formula for the decomposition of Lead(II)Nitrate

2Pb(NO₃)₂ → 2PbO + 4NO₂ + O₂

and then told to work out the number of moles using the Ideal Gas Equation, being told that the sample was heated until decomposition was complete. Using the information provided you get 0.00361 mol (to 3 s.f.) (500K, 100kPa, 1.50x10^-4m³, T=8.31JK^-1mol^-1)

The followup question asks for the number of moles of NO₂ and then the mass.

How would you tackle this followup. I'm pretty confident but want to check!

Thanks, --86.137.233.160 19:50, 9 January 2007 (UTC)

I think you are not giving us some info. You are looking for moles of what? You obtained .00361 mol of what? And what was the info provided? Maybe a more word-for-word description of the problem is in order. --Bennybp 21:55, 9 January 2007 (UTC)

unfitness test

This isn't about medical advice, I am just interested in knowing weather it is normal when my pulse rate gets over 220 that it feels like someone is squeezing my trachaea, my whole body is pulsating as blood flows through it and air is forced our of my lungs every time my heart beats. Is this beacuse I am very unfit, or just the usual side effects of a high pulse rate?Hidden secret 7 20:02, 9 January 2007 (UTC)

I would suspect that the latter is a symptom of the former. Vranak

Do you know how on all those fitness machines, they say "See doctor before commencing any fitness program!"? I think that is good advice. --Zeizmic 23:35, 9 January 2007 (UTC)

If your heart rate gets above 220 often, you're probably unfit. Regardless, try to exercise more than you do now, and see a doctor if you're worried. --Bowlhover 03:10, 10 January 2007 (UTC)

It has never gone above 180 before, and I have started exercizing more, which is why it was so high. I did the same thing again today and it seems slightly better. I hope.Hidden secret 7 13:46, 10 January 2007 (UTC)

Typically in exercise, your target heart rate should be 65-85% of your "maximal" heart rate. To calculate your maximal rate, take 220 minus your age. A heart rate over 200 in an adult is indicative of ventricular tachycardia, a potentially fatal heart rythm. You should probably talk to your doctor about your exercise regimin or about being tested with a Holter monitor. Andrewjuren(talk) 07:48, 11 January 2007 (UTC)

I don't think I have that, I hope not :( Is there any way to tell without seeing a doctor :? And I am not an adult yet :)Hidden secret 7 18:35, 11 January 2007 (UTC)

Galinstan?

Where can I find information on the liquid metal Galinstan? The wiki article did not have the physical properties I was looking for. (Viscosity, thermal conductivity, etc.) —The preceding unsigned comment was added by 216.182.144.119 (talk)

An MSDS is often a good source for physical properties. There's a link to one at the end of the galinstan article. DMacks 20:34, 9 January 2007 (UTC)

Two Hybrid Screening In Yeast

When talking about yeast cells used in two-hybrid screening, is it appropriate to call the yeast cell a 'host', 'model' or something else? --Username132 (talk) 21:06, 9 January 2007 (UTC)

Two-hybrid screening --JWSchmidt 04:26, 10 January 2007 (UTC)

Sorry but I don't think the article answers my question. As it happens I'm working on that article and that's why I asked the question (for a subheading). --Username132 (talk) 21:38, 10 January 2007 (UTC)

The plasmids are introduced into the yeast cells by a process that is generally called transfection. After the plasmids have entered the cells, the cells are called "tranfected cells". The tranfected cells are subjected to selection conditions: growth in a defined culture medium that only allows tranfected cells to survive if those cells can form a functional transcription complex formed by the physical interaction of two "transfected proteins". "Transfected proteins" meaning that they are proteins expressed from the plasmids that were transfected into the cells. --JWSchmidt 04:26, 11 January 2007 (UTC)

Elemental form

Is 3Co in its elemental form? 141.158.99.155 21:29, 9 January 2007 (UTC)

Do you mean Co₃? A substance that's in its elemental form has only one element in its molecules; it's not a chemical compound. Co₃ has 3 cobalt atoms, so the short answer to your question is yes. --Bowlhover 03:05, 10 January 2007 (UTC)

How would a molecule not be a chemical compound? A real question might be whether Co₃ is a naturally-occurring allotrope of cobalt. DMacks 07:49, 11 January 2007 (UTC)

If you think about band theory and all that, then technically any metal in the form M_n is still in its elemental form where M = any metal and n = any number of atoms. Therefore Co is in it's elemental form whether it is written as 3Co (ie three moles of Cobalt) or Co₃. It is certainly not an allotrope.

And a compound usually has more than one type of atom, or, if it is a p block element, more than one atom (eg O₂, CO, S₈, GaN, LiCl etc)

Stui 21:21, 17 January 2007 (UTC)

How's it done?

How was this done? http://ebaumsworld.com/2006/03/magnet.html Thanks!! Reywas92^Talk_Sigs 21:52, 9 January 2007 (UTC)

That's an example of a superconductor. The black material is superconducting below a certain temperature. I assume that's liquid nitrogen poured onto it, this lowers the temperature and causes it to superconduct. When a material superconducts it does not admit any magnetic fields. The magnet will therefore not approach within a certain distance depending on its strength. This causes it to hover.
Contrary to popular belief this is not quite how bullet trains work. They mearly use very good conductors, not superconductors. I hope this helps. —The preceding unsigned comment was added by 81.153.52.250 (talk) 22:45, 9 January 2007 (UTC).

• Clarification: The term "bullet train" is usually used for fast conventional trains. This person is talking about maglev trains. --Anon, Jan. 10, 07:42 (UTC).

How does the superconductor and the piece of metal stay a fixed different from eachother? —The preceding unsigned comment was added by 138.29.51.251 (talk) 23:09, 9 January 2007 (UTC).

Two answers: (1) The magnet settles downward until the upwards repulsive force from the superconductor becomes equal to the downward force of gravity, just like whenever a weight is placed on a spring, for example. If that were all that was going on, however, the magnet would probably slide off to the side as if it rolled off a ball. But it doesn't, so there is more going on: (2) You probably noted that the magnet appeared to become "stuck" at a particular point and orientation in space above the superconductor. This is because these are "type 2 superconductor|"type 2"]] superconductors, which do not exclude the magnetic flux completely, but instead allow a few thin tubes of magnetic flux ("flux vortices") to go through. These tubes tend to get stuck ("pinned") at defects inside the superconductor, and since the flux is connected to the magnet (in a sense) this makes the magnet "get stuck" too. --mglg_(talk) 02:18, 10 January 2007 (UTC)

The article for more information is the Meissner effect. X [Mac Davis] (DESK|How's my driving?) 17:45, 10 January 2007 (UTC)

Reversible Gas Turbines

Kindly explain what is a reversible Gas Turbine —The preceding unsigned comment was added by 213.130.123.28 (talk) 10:33, 9 January 2007 (UTC).

Question moved here from the Mathematics reference desk.  --Lambiam^Talk 21:52, 9 January 2007 (UTC)

This extract from a research abstract considers one definition, where the turbine can turn in the opposite direction to normal -

Aircraft gas turbine engines, as now configured for ship propulsion, are unidirectional in output rotation and, therefore, require the added complexity of a reversing transmission or a reversible-pitch propeller. This study explores the feasibility of a novel reverse-turbine concept which is configured to adapt to existing free-power turbine engines without additional clutches or separate drive trains. This device, termed the 'isolated reverse turbine,' is sized for meeting that most demanding maneuver for a fixed-pitch propeller-driven frigate or destroyer, namely, the crash reversal maneuver. The reverse-turbine concept would replace the function of the reversing gear or the reversible-pitch propeller; it could also complement electrically actuated reverse transmissions by eliminating the need for braking resistors and switches.

A turbine operating in reverse would of course be a compressor, but the design characteristics of the two devices are somewhat different.81.153.220.80 12:56, 10 January 2007 (UTC)

Reversible implies that the turbine has an efficiency of 1; that is it loses no energy to frictional or viscous effects, and there is no entropy gain. Thus, the process (not the turbine) can be reversed without violating the second law of thermodynamics. It has nothing to do with running the turbine backwards. -anonymous6494 16:54, 10 January 2007 (UTC)

Based on Google hits on the term and the contexts in which the term appears, it doesn't seem that "reversible" is used in the sense of the word in thermodynamics. --71.175.23.226 18:08, 12 January 2007 (UTC)

I see hits for both, but for the sake of argument let's assume we are talking about running a turbine engine in reverse (i.e. as a compressor). The problem with such an engine is that the blades are designed with the direction of flow in mind, so simply running the turbine in reverse will not produce the desired result. An engine designed to do both could be built, of course at the expense of efficiency. It is likely that the reversible turbine would be less attractive (at such low efficiency) than another system, such as an electric motor and battery. anonymous6494 03:14, 13 January 2007 (UTC)

Google hits on the term suggest that reversible gas turbines are most commonly used for ship propulsion. At least in the context of this U.S. patent, a "reversible gas turbine" is one that can reverse the direction in which the output shaft rotates (however accomplished). It's not about running a turbine in reverse and using it as a compressor. --71.175.23.226 13:37, 13 January 2007 (UTC)

Measuring rainfall

Why is rain measured in mm than mL? The Updater 23:22, 9 January 2007 (UTC)

See Rain gauge. --Zeizmic 23:32, 9 January 2007 (UTC)

Kind of like how you wouldn't measure how much snow there is by its volume. I suppose one could measure rain and snow in terms of volume, but that wouldn't be practical. How high those things are from the ground lets us know, for example, how bad a flood or a blizzard is.128.163.80.164 00:33, 10 January 2007 (UTC)

More fundamentally, of course you could measure in litres say, and now you compare the amount of rainfall you had with your neighbour, who also collected rain, but you collected it in a can and your neighbour in a giant tub. Of course she would have more, if measured by volume. Your tiny can could not even hold one litre. So to make this comparable, you have to take the surface area into account over which the rain was collected. And then you get, for instance, as the measure an amount in litres per square metre, L/m², and since 1 L = 0.001 m³, that unit of measurement equals 0.001 m³/m³ = 0.001 m = 1 mm.  --Lambiam^Talk 01:16, 10 January 2007 (UTC)

By the way, what Lambiam just did is called dimensional analysis, and it's a great way to figure why we use the units we use for several things. — Kieff 02:20, 10 January 2007 (UTC)

Like measuring pressure in mm too. :?Hidden secret 7 13:49, 10 January 2007 (UTC)

Pressure measured in terms of length is a reference to gravitational potential energy: height times the acceleration of gravity times the density of the fluid referenced (typically water or mercury) has units of pressure. So for mercury the conversion is (13.534 g/cm³)(9.81 m/s²)=133 Pa/mm. --Tardis 17:41, 10 January 2007 (UTC)

Most conventional pressure measurements are either in hPa (mbar) or in mmHg/inHg, for the reasons explained above. Titoxd^(?!?) 17:44, 10 January 2007 (UTC)

Thanks for the info. The Updater

sideways in time

Thanks to such science fiction shows as Star Trek we have an understanding of the concept of back and forth in time. But what might "sideways" (left or right) or "diagonally" or "spirally" in time look like? Anyone care to speculate? —The preceding unsigned comment was added by 216.176.54.133 (talk) 23:40, 9 January 2007 (UTC).

"Sideways" doesn't exist in one dimension. If we consider time as some sort of timeline, it can only have "backward" and "forward" directions. — Kieff 23:50, 9 January 2007 (UTC)

Being a creature that occupies four dimensions, which I am aware of at least, I find it really difficult to imagine what one dimension would be like. ;) Have you seen the Back to the future movies?? I think they explain sideways in time fairly well, more the sequels then the original. Basically, time is like a tree, from any point in time, there are an almost infinite number of branches of possible 'futures' that could happen depending on chance and choice. going forward you can only travel down the branches that span from the trunk of the NOW you are in, travelling sideways, you could end up on a branch that branched off BEFORE the now you are in. For example, travel sideways in time to the 2007 where the allies didn't manage to develop nuclear weapons and the axis powers ultimately took over the world. Vespine 00:20, 10 January 2007 (UTC)

Imagining one dimension is easy, you can only go one way. Like time, in this universe, or driving through a tunnel. Imagining multidimensional time is much harder. Philc _T^E_C^I 18:28, 10 January 2007 (UTC)

The way the OP asked the question, it seems he's interested in continuous movement in time, not "jumping". What you described is just jumping to a different timeline altogether. Assuming many timelines side by side, travelling completely "sideways" in time would just move you around the same instant in time, but in different alternative universes. Travelling diagonally, then, would make you pass through a different universe in each subsequent instant forwards (or backwards) in time. That wouldn't be very useful to observe. Unless, of course, alternative universes close to each other had a gradual change. If that was the case, you could see people walking in the streets slowly turning into intelligent chicken-like beings as you travelled diagonally along the alternative universes. — Kieff 00:35, 10 January 2007 (UTC)

Which raises the question, would it be unethical to catch these chicken-like beings, bring them back to our universe, and sell them (after some culinary processing) as Alternative Fried Chicken?  --Lambiam^Talk 01:21, 10 January 2007 (UTC)

From the realm of science fiction or modern physics, moving sideways in time would imply going to another of the nearly infinite number of alternate universes. At each instant, universes should branch out from each possible quantum event. Drop a piece of buttered bread, and it lands butter side up in one universe and butter side down in another. Drop 50 coins and there are universes where all 50 land heads up and every other permutation. Robert A. Heinlein wrote some fun sci-fi about such things. Edison 05:44, 10 January 2007 (UTC)

There is a classic science fiction story whose name escapes me now, about a Catholic priest who travels to another planet where he discovers a civilization of intelligent, peaceful dinosaurs which he comes to admire. But their entire existence begins to undermine his faith that only humans can have souls. User:Zoe|(talk) 18:16, 10 January 2007 (UTC)

Ah, it's A Case of Conscience, by James Blish. User:Zoe|(talk) 18:36, 10 January 2007 (UTC)

How about imaginary time? Also, Stephen Hawking wrote in his book Black Holes and Baby Universes about that I think. Something about time always moves forward, never backward, but we can go at an angle, as in the special theory of relativity. I suppose it just depends on what you put on the other axis, and if time is one dimensional or not. --Bennybp 06:17, 10 January 2007 (UTC)

This is only peripherally relevant, but watching the 2004 movie Sideways is an excellent way of spending time. JackofOz 02:34, 11 January 2007 (UTC)