Wikipedia:Reference desk/Archives/Science/2009 November 5

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.

November 5

A sculptor who works in dark matter

How would such a sculptor go about it? What would the results look like? or, if invisible, is there any way one could perceive the results?

Thanks

Adambrowne666 (talk) 00:08, 5 November 2009 (UTC)

Nobody even knows for sure what dark matter is, so there is no way anyone could make a sculpture out of it. --Tango (talk) 00:17, 5 November 2009 (UTC)

True. Let's play with the idea though, based more on current theories than on what it is for sure. Adambrowne666 (talk) 00:20, 5 November 2009 (UTC)

I think there are two main theories - either it is regular matter that is just too cold to radiate light (MACHOs), in which case it would be sculpted in the same way as any other regular matter, or it is "weakly interacting massive particles" (WIMPs) which means particles which only interact with other matter through gravity and the weak interaction (which is only really significant in radioactivity). Such matter couldn't be sculpted at all, since there would be no way to hold the dark matter together. --Tango (talk) 01:00, 5 November 2009 (UTC)

Were those acronyms intentional? Seems too unlikely to be a mere conincidence... (MACHO and WIMP, fight!) --antilived^{T | C | G} 05:57, 5 November 2009 (UTC)

Most theories of dark matter would have it be more like a gas (weakly interacting) than a solid, in which case there would be nothing to sculpt. Dragons flight (talk) 00:22, 5 November 2009 (UTC)

And with so little interaction with normal matter, dark matter could not be confined in a gas tank, or cut with with a blade. The only way to control it is with gravity. In any case most of the matter on earth does not give off light, and could be considered dark matter. Graeme Bartlett (talk) 00:46, 5 November 2009 (UTC)

Ok, but ferrofluid isliquid, and can be sculpted, in a manner of speaking. Say we use gravity to shape dark matter. What then? Is there any way of showing off our work? Adambrowne666 (talk) 01:01, 5 November 2009 (UTC)

If you want to use gravity to hold it together you would need to work and store it in a zero-gee environment. If the dark matter is just regular matter then it would reflect light so you could show it off in the same way as any other sculpture. If it is just weakly interacting then I don't think there is any way it could be directly seen. --Tango (talk) 01:05, 5 November 2009 (UTC)

Sounds a bit like it would have to be Conceptual art. AlmostReadytoFly (talk) 09:17, 5 November 2009 (UTC)

Most art galleries today don't show off dark-matter sculptures. Also, many artists fail to be inspired by it as a working material. Bus stop (talk) 15:56, 5 November 2009 (UTC)

Yes, probably right, Tango; there's no way it could be directly seen - aside from the twisted gravity field, is there any way its presence and form could be detected by a person in the same room? what equipment would such a person need to perceive the art? Adambrowne666 (talk) 09:46, 5 November 2009 (UTC)

If it were heavy enough they could detect the gravity directly, especially in they were otherwise in zero-gee. If it were lighter then watching the paths of slow moving ball bearings as you throw them around the room might allow you to detect it, or some kind of smoke generator. --Tango (talk) 15:30, 5 November 2009 (UTC)

Question - assuming the sculptor can assemble this huge amount of dark matter (mass of a small asteroid if you want it to deflect the path of a ball bearing), how do they keep it in one place ? What stops it dropping straight through the floor ? Gandalf61 (talk) 15:40, 5 November 2009 (UTC)

That's why it needs to be stored in zero-gee. Something that heavy would generally accelerate very slowly, so it shouldn't be too difficult to keep it central in the space-borne art gallery by moving the gallery to compensate for its movements. --Tango (talk) 19:52, 5 November 2009 (UTC)

Thanks, all - it's for a story I'm working on, and I think with a bit, or a lot, of fudging, I can work with this stuff to get something fun. Adambrowne666 (talk) 22:46, 6 November 2009 (UTC)

Speculation: Perhaps you could assemble a ball of dark matter 1 decimeter across yet weighing millions of tonnes. This should have a measurable gravitational field. Or maybe it could condense into a streamer of dark matter held together by gravity, yet kept elongated by mixtures of velocities along the stream. Maybe you can sense the presence of darkmatter by its effect on dust or smoke in the air. A fast moving stream may have a gravitomagnetic effect and pull nearby matter in the same direction. Graeme Bartlett (talk) 06:27, 7 November 2009 (UTC)

What cognitive changes take place at birth?

There's a lot of controversy about when exactly killing a fetus/baby becomes murder. One common belief is that it's at (or possibly a little after) the moment of birth. This would only make sense if there are significant cognitive changes caused by being born. I wouldn't find it at all surprising, but it seems strange that I've never heard anything about it one way or another. Is it just impossible to test? If not, what changes take place? Is it generally considered by people in that field to be something necessary for sentience? — DanielLC 00:09, 5 November 2009 (UTC)

I don't think there are any significant cognitive changes that abruptly occur at birth. However, at birth the baby goes from receiving nutrition and oxygen through the umbilical cord to breathing independently and requiring oral food. I know some people place special significance on that first breath, and on the independence from the systems of the mother. I don't think many people worry about sentience per se. Dragons flight (talk) 00:18, 5 November 2009 (UTC)

If it were so, babies born by caesarean section would not be sentient. There is no sharp dividing line: babies born a little before 22 weeks have lived to be sentient, even though there are several important developments in the body and brain between even 34 weeks and the 'mature' 37 weeks. Really, how sentient do you consider a 4 week old baby? Does it have enough experience to understand the world well enough to be considered sentient? Time was, doctors regularly performed surgery on babies and little children without anaesthetic on the basis that they weren't mature enough to really feel pain: they were just reacting instinctively. We now know this is bunk (I know a few older ex-nurses who still go pale at the memory, horrified at what they had been doing once the evidence came in). I don't think there is consensus on a stage of development at which sufficient sentience has developed that the being can feel pain, and doctors carrying out pre-birth procedures have to balance many factors and possible outcomes when deciding what to do. Of course, they may be carrying out these procedures on babies who in other circumstances would be classified only as foetuses.

But given we do not generally consider it murder to kill non-human animals, despite the increasing evidence (staring any observant human in the face) that many species are self-aware and really do suffer when in pain (possible definitions of sentience), I don't think it would really sway anyone. After all, we generally consider it far worse to kill a month-old child than a 5-year-old chimp, even if the chimp can demonstrate its sentience much more fully than the child. 86.142.224.71 (talk) 00:36, 5 November 2009 (UTC)

And there is also the class of the severely retarded or mentally disabled who never pass into a "too little sentience, OK to kill" category (other than brain death). --Mr.98 (talk) 01:07, 5 November 2009 (UTC)

Here you're confounding sentience with cognitive power. They're quite different conceptually. Sentience is the capacity to experience qualia. I see no reason to think that the severely mentally disabled are less sentient than the rest of us. Of course, by the very nature of qualia, we can never really know, one way or another — see solipsism and animism for two opposite conclusions on the question, neither of which is really susceptible to scientific inquiry. --Trovatore (talk) 04:41, 5 November 2009 (UTC)

My belief is that people define words like "life" and "murder" in such a way as to support the rules they want people to follow -- that is, people start with the conclusions, and then work out the premises that are needed to derive those conclusions. Looie496 (talk) 02:30, 5 November 2009 (UTC)

I'd argue that the initial assertion is not accurate. I don't know of anyone or any culture who believes killing a baby in utero a week before it is due would not be murder. Even the most ardent pro choice supporters I know would not argue it is fine to kill a baby just before it is born. A far more commenly held belief in the past was that the quickening was an indicaton of when a foetus became a real person with a soul, there fore capable of being murdered. Vespine (talk) 04:18, 5 November 2009 (UTC)

The following is not given as legal advice. But contrary to the assertion by Vespine, many legal jurisdictions in the U.S. formerly required that a baby be born alive for its subsequent killing to be murder. Killing of a fetus=murder is a modern legal development in the U.S. See a legal textbook on "born alive" statutes:[1]. Under common law, killing of a fetus was not homicide. Edison (talk) 19:50, 5 November 2009 (UTC)

According to Late-term abortion#Legal restrictions on later abortion, in 54 of the 152 most populous nations, abortion is legal at any stage. — DanielLC 05:48, 5 November 2009 (UTC)

That section is a bit nebulous. If you read the reference associated with that section's content, it's not entirely clear that that math is exact. The review groups countries into how they are restricted on availability, such as to save the woman's life or for socioeconomic reasons; a gestational limit isn't one of those categories. A gestational limit is only noted for countries with no other restrictions and of those, only four have laws that don't specify a limit - Canada, China, North Korea, and Vietnam. So, other countries may or may not have gestational limits regulating abortions in addition to their other restrictions, but there's no way to tell based on that reference. Mind you, all of that is from 12 years ago, so many things may have changed. ~ Amory (u • t • c) 15:16, 5 November 2009 (UTC)

I don't mean the process of birth itself. There is are a lot more sensations when you're born. Things actually happen. Before you're born, there's no point in having any significant brain activity. By the way, I was reading the abortion page and it said that there's some controversy that fetuses might feel pain. This seems rather silly, as they must be sentient to feel pain, and if they are, it's bad to kill them because it's murder. Is the idea that they're like animals for a period, and they have sentience, but no right to life? — DanielLC 05:48, 5 November 2009 (UTC)

Yes. And babies do have significant brain activity before birth and it may be meaningful and they feel pain by most definitions. It's all about definitions really so people who work in words feel okay about it as we have no objective way of measuring sentience or pain and there is no objective reason for them to mean anything anyway, they are not like the amount of energy one can get from a lump of coal or anything like that. Dmcq (talk) 12:23, 5 November 2009 (UTC)

Maximum rate of a energy delivered for a given voltage

I am trying to understand if, given a voltage and a duration, whether it is possible to calculate the maximum amount of electrical energy that can be delivered. To put this in context I am trying to judge the maximum amount of energy it might take to recharge this car given just the voltage and the duration of energy delivery (100 volts - 180 minutes, 200 volts - 100 minutes). I understand that the voltage does not have an exact correlation with how much energy is drawn (my kettle draws 2kwh, and my phone charger much less, even though they are both plugged into a 240v socket), but I want to understand whether there is a maximum rate of energy transfer for a given voltage (or do other things, current?, come into play). Sorry, electricity has always been a big blind spot for me. Any help appreciated. BurningFridge (talk) 00:30, 5 November 2009 (UTC)

See the article on Electric power. In summary (and ignoring power factor) the energy transfer is a function of voltage, current and time. Power (watts) = voltage (volts) x current (amps); energy (joules) = power (watts) x time (seconds). Thus for any given voltage, the maximum energy transfer is a function of the current. In Australia, normal household power outlets are rated at a maximum 10A, although you can get 15A sockets. Mitch Ames (talk) 01:01, 5 November 2009 (UTC)

The likely reason for the disparity (twice the voltage but not half the time) is likely to be to do with the need to limit battery overheating and perhaps also due to inefficiencies through the charging circuit which may worsen as the voltage gets bigger. The physics of recharging batteries is rather complicated. SteveBaker (talk) 01:14, 5 November 2009 (UTC)

Some people find the Hydraulic analogy helps understanding of electricity. The difference between the OP's kettle and phone charger is that the kettle has much lower resistance R (ohms) than the charger. The power taken from the 240V supply is inversely proportional to R so the kettle takes the greater power. (We can calculate the kettle resistance R = 240 x 240 / 2000 = 28.8 ohm.) In principle, from a given voltage one can draw any power by connecting a load of appropriate R. In practice the power delivery is stopped if current I = 240 / R (amps) exceeds the current rating in amps of the fuse. In order to calculate the energy (joules) = power (watts) x time (seconds) for charging the car one needs to know the current drawn from the supply during the charge cycle. Cuddlyable3 (talk) 01:28, 5 November 2009 (UTC)

Indeed, that's true. But it doesn't help much because those car chargers that attempt to charge as quickly as possible don't draw (or supply) continuous amounts of constant current - they have to monitor battery temperature and voltage and vary the amount of current as the batteries are charged in order to prolong their life while minimizing the recharge time. Therefore the actual recharge time will depend on the ambient temperature and the amount of ventilation keeping the batteries cool. It's not easy to calculate without understanding the details of what the charger is doing, how the battery temperature changes, how heat is lost from the battery compartment, etc. SteveBaker (talk) 12:50, 5 November 2009 (UTC)

That's also true. To find the energy consumed one must measure how the current varies as a function of time during the charge cycle and integrate (i.e. find the area under the i = f(t) curve) to get the overall current x time product. To find the energy actually delivered to the battery one has to integrate over time the product of charge current and voltage, both varying. Energy delivered to the battery is less than energy consumed because inefficiency of the charger wastes the difference as heat. During use the battery will again deliver less energy than that with which it was charged. Cuddlyable3 (talk) 19:42, 5 November 2009 (UTC)

From purely theoretical considerations of the physics of electricity, any given voltage could deliver any given amount of energy in a given time, if the circuit impedance were made low enough. The impedance of the load and the impedance of the source are what limit the current. Additionally the fuse or circuit breaker in the supply, along with the electronics of the battery charging circuit are the practically limiting variables. Edison (talk) 19:45, 5 November 2009 (UTC)

Flame tests

Will metal ions with different charges (i.e. Fe3+ and Fe2+) produce different colors in flame tests? 76.204.127.175 (talk) 03:53, 5 November 2009 (UTC)

That's a good question. If you haven't already, see emission spectrum. In this situation, it might be helpful to imagine a Bohr model. Under controlled circumstances, we should say that the tempurature is the same for both tests, because varying temperatures can effect the color. Fe+2 is the ion of iron, with 3 energy levels. When excited, we could say that the electrons jump up 3 energy levels, then fall to their original orbital energy level, releasing a photon of light. This is complexely measured in an emission spectrum.

An emission spectrum of Fe+2

Let's say that for some reason, an electron was taken from the atom of iron, making it Fe+3. If this was able to be maintained, (it would be somewhat difficult to keep the unstable Fe+3 from reacting, unless in a container of inert gas) and it was excited, the electrons would only manage to jump up 2 energy levels. To the naked eye, one might not be able to distinguish different colors, but the emission spectrum would be the tell-all. It would be slightly different than a Fe+2 ion. If you have any questions, ask here or on my talk page :). Letter ⁷ _{it's the best letter :)} 13:51, 5 November 2009 (UTC)

Also when we are calm we could say that the electrons, when excited, jump up 3 energy levels. Cuddlyable3 (talk) 19:23, 5 November 2009 (UTC)

What is the capacitance of a black hole?

The article "Detecting Energy Emissions from a Rotating Black Hole" at [2] (free subscription required to view) makes the statement in passing that the capacitance of a black hole C = 1/M (approximately). I guess these are in natural units. Does anyone happen to know where this relationship is derived or explained, and what the units are? The Wikipedia article on natural units [3] doesn't define capacitance or voltage.

Trevor Turton —Preceding unsigned comment added by Tijaska (talk • contribs) 04:17, 5 November 2009 (UTC)

This abstract says "The notion of electric capacitance for a black hole is introduced", so might be worth a look. --Sean 17:47, 5 November 2009 (UTC)

Naively, I'd expect it to be similar to the self-capacitance of an isolated sphere, $C=4\pi \epsilon _{0}R={8\pi GM\epsilon _{0} \over c^{2}}$, where R is the Schwarzchild radius, but your reference suggests that's not even the right proportionality. So obviously more complicated effects matter. Dragons flight (talk) 18:32, 5 November 2009 (UTC)

Natural units of charge are chosen so that G = 1/4πε₀. With all factors added back in, C = 1/M should become C = 4πε₀ħ / cM, but you probably shouldn't take my word on that. Membrane paradigm has a tiny bit on this subject and lists some references. -- BenRG (talk) 18:43, 5 November 2009 (UTC)

cosmatics

How cosmatics are manufactured, tell me complete procedure —Preceding unsigned comment added by 119.152.59.27 (talk) 06:36, 5 November 2009 (UTC)

_{I have slightly reformatted your question to make it easier to read. Richard Avery (talk) 08:30, 5 November 2009 (UTC)}

What kind of cosmetics? There are lots of different types. AlmostReadytoFly (talk) 09:12, 5 November 2009 (UTC)

It's not very different from any other chemical product manufacture. Generally, a pigment (coloring chemical) is added to a binder (like a wax or a synthetic oil - or an alcohol, in some cases); fragrance may also be added. Finally, the stock mixture will be cut and packaged by special-purpose machinery. The actual procedure will depend on the type in question. Hopefully a quality-control process is in place to help ensure the safety of the finished product. Nimur (talk) 17:55, 5 November 2009 (UTC)

Insolation

How to find solar insolation patterns at various points in the jupiter's atmosphere. A comparison with earth is needed —Preceding unsigned comment added by 220.225.125.246 (talk) 09:16, 5 November 2009 (UTC)

Figuring out the insolation at the top of the atmosphere is easy. It looks like all the trigonometry is worked out in the insolation article, whereas the parameters of Jupiter orbit are given, not surprisingly, in the Jupiter (planet) article. Now, the insolation within the atmosphere is very much more tricky. Strictly speaking, you need to model the absorption and the scattering of light at every position at every wavelength into every direction. This requires a full 3D radiation transfer model. As Gandalf said, "this foe is beyond any of you..." --Dr Dima (talk) 10:32, 5 November 2009 (UTC)

Properties of alcohols

what are he properties for the following alcohols and their chemical formulae:

1. DL-2-pentanol
2. pentan-1-0l
3. octanol-1-0l
4. ethanol
5. butan-1-ol
6. n-porpyl

send to email address removed —Preceding unsigned comment added by 120.18.247.221 (talk) 11:40, 5 November 2009 (UTC)

Wikipedia gets copied mercilessly across the internet. It's a bad idea to put your email address on this website, as it will likely attract much more spam than you want. Falconus^{p t c} 12:39, 5 November 2009 (UTC)

We do not answer questions by email - you have to return here to find responses - and we remove people's email addresses if they provide them. We have articles on pentanol, octanol, ethanol, butanol and propanol which (I believe) will answer all of your questions. SteveBaker (talk) 12:42, 5 November 2009 (UTC)

(edit conflict)

1. See Amyl alcohol
2. See Amyl alcohol
3. See octanol
4. See ethanol
5. See butanol
6. propyl?

These pages generally give the formulae and properties. AlmostReadytoFly (talk) 12:49, 5 November 2009 (UTC)

Uncompressed image file formats other than .bmp files

What other file formats are there, apart from BMP files, that are uncompressed and can be processed as a raw bit stream? I require to know the exact file structure of these formats.Csanghamitra (talk) 15:34, 5 November 2009 (UTC)

The results for searching this includes:

[4], [5]

This question belongs on the Computing desk, I think. Imagine Reason (talk) 16:22, 5 November 2009 (UTC)

TIFF files are commonly used by image processing people. They can store uncompressed data. PNG can store with lossless compression (but compressed), depending on whether your software tool supports this feature. Our Comparison of graphics file formats article allows you to sort by compression technique. If you're looking specifically for no compression, your options are narrowed down pretty significantly; lossless compression preserves information but is a bit more work for you as a programmer. "Anything" can be handled as a bitstream, but it sounds like you want to be able to seek to a specific pixel location without decoding any other values - that is a bitmap by definition; and you probably want a .BMP or TIFF container format. Nimur (talk) 18:02, 5 November 2009 (UTC)

There aren't many formats that guarantee uncompressed data. PNG and TIFF are probably the best choices for LOSSLESS compression (as opposed to GIF and JPEG which have LOSSY compression). But I'm struggling to think of any format that has no compression whatever. The old "SGI" image format has only run-length encoding - it's relatively easy to unpack yourself. If you use the GIMP package for saving files, it has a "Save" format called "Raw image data" that is literally just a bunch of bytes with the pixels in it...that's guaranteed to be uncompressed and has no "structure" whatever. These days, most people just grab the freeware libPNG or libTIFF libraries and let them do the unpacking. Both can deliver a simple array of bytes to your application code. SteveBaker (talk) 18:44, 5 November 2009 (UTC)

No. Strictly speaking the GIF format gives compression with NO LOSS and certainly nothing like the distortion artifacts that strong JPEG compression produces. It is true that the number of different colours in an image may need to be reduced to keep within the maximum 256 colours that GIF can handle, but beyond that the GIF format has LOSSLESS compression. Cuddlyable3 (talk) 19:02, 5 November 2009 (UTC)

Well, yes - in the special case where your image happens to have that few colors and the conversion tool makes up a palette on-the-fly rather than using a standardized one...you're right - but those are very special circumstances. In general, it's lossy. SteveBaker (talk) 22:02, 5 November 2009 (UTC)

This is why lossy compression is often defined in terms of generational loss—otherwise you risk having to classify every format as lossy because it demands a grid of pixels and at most 256 levels per channel and so on. GIF is only defined for input images of 256 colors or less, and compresses those without loss, so it's normally classified as lossless. At some level it's all relative; you could define the input of MP3 as just those waveforms that can be produced by a reference decoder, and a good enough lossy encoder can avoid all generational loss (most encoders in the wild are not that good). But GIF is normally considered lossless. -- BenRG (talk) 22:37, 5 November 2009 (UTC)

The GIF format allows using multiple 16x16 pixel tiles with individual palettes to achieve 24-bit (over 16 million) colours in a file.Cuddlyable3 (talk) 23:21, 8 November 2009 (UTC)

Vector graphic formats are compact and unsuitable for lossy compression. The OP does not exclude mentioning the uncompressed audio formats WAV and PCM. Cuddlyable3 (talk) 19:15, 5 November 2009 (UTC)

The OP did specify image file formats. (I'm unclear why bringing in vectors is relevant... it seems rather clear they mean bitmaps). --98.217.71.237 (talk) 20:37, 5 November 2009 (UTC)

Thank you, you are right and I strike the mention of audio. Vector graphic image formats are examples of uncompressed image file formats, so they are relevant to the OP who excluded one but did not insist on only raster formats. Cuddlyable3 (talk) 00:41, 6 November 2009 (UTC)

A very nice format -- because of its openness, simplicity, and the number of tools available for manipulating it -- is NetPBM. —Steve Summit (talk) 23:27, 5 November 2009 (UTC)

TGA images can be stored uncompressed (and BMP supports run-length compression, though almost nobody uses it). Various digital camera raw formats are also uncompressed, but it takes a good deal of post-processing to turn them into usable images. --Carnildo (talk) 23:47, 5 November 2009 (UTC)

XBM Would be the easiest one, all it contains is a C array with values for each pixel. Problem is that it's in monochrome, but you can probably easily convert say a PNG to XBM by converting it to different channels first(hence the monochrome) then to 3 XBM files.

Sticking finger

Why do we feel sticky when we press a finger on frozen ice in the freezer of a refrigerator? —Preceding unsigned comment added by Cssivakumar (talk • contribs) 18:51, 5 November 2009 (UTC)

Because your finger has slightly frozen to the ice. More fully, the heat from your finger slightly melted the ice. However, if you touch something sufficiently cold, the surface of your finger loses heat faster than the whatever-it-is gains heat, and the just-melted water quickly re-freezes. — Lomn 19:13, 5 November 2009 (UTC)

The effect is much greater if your finger is already wet - that leads to cold burns. --Tango (talk) 19:48, 5 November 2009 (UTC)

For this same reason, if you are in a very cold climate, like where there is snow around, do NOT touch your tongue to anything like a light post or fire hydrant. Even if someone double dares you to do it. Vespine (talk) 03:45, 9 November 2009 (UTC)

Solitude drove the old hermit crab insane.

Are there any hermit crabs that actively kill shell-living critters for their houses? Vitriol (talk) 18:52, 5 November 2009 (UTC)

They don't unless they have to. If they cannot find a discarded shell they will attack a shelled-creature and nick their house. It's usually only a problem in home aquariums, as the natural environment is littered with suitable "crabitation". Fribbler (talk) 19:00, 5 November 2009 (UTC)

'Diesel' engine

Trying to make sense of second paragraph in [A http://railroad.100megsfree5.com/L8/GazTurbo-GT101.html] , the engine may be called 'СПГГ' (russian/cyrllic type) [B http://images.google.co.uk/images?hl=en&q=%D0%A1%D0%9F%D0%93%D0%93&um=1&ie=UTF-8&sa=N&tab=wi] - is the loco engine same type as here [C http://dic.academic.ru/dic.nsf/ruwiki/1140871].?

Also does this type have an article / english name? Following on I'd like to ask if anyone knows how the fuel/air (?) is injected into 'small cylinder' following release of pressurised combusted gas into turbine as shown in third link (C above) - there must be some sort of 'tappet valve' activated on return stroke to allow recharge of fuel air mixture? anyone know? Thanks..83.100.251.196 (talk) 18:53, 5 November 2009 (UTC)

We have Gas turbine locomotive and Gas turbine-electric locomotive. Commons has a picture of the GT101, but only the Russian Wikipedia links to it. We have an article GT 101, which appears to be a similar German -- not Russian -- thing, but perhaps they're related. --Sean 20:33, 5 November 2009 (UTC)

Thanks (I think GT is gas turbine in many languages and GT 101 is a coincidence) - it seems it's more common that I though - part of it is called a Free-piston engine - it was the valve or equivalent arrangements in this engine that I was wondering about.83.100.251.196 (talk) 22:45, 5 November 2009 (UTC)

I think I've found the answer here [6] fig 12.5 it looks like they are simple one way valves.

It didn't think to look at gas turbine locomotive - I thought it was to obscure to be mentioned..but there were similar things in france and sweden...

If there is a name (person?) for the "free piston / gas turbine combination" it would be interesting, or is the free piston engine always assumed coupled to a gas turbine??83.100.251.196 (talk) 22:50, 5 November 2009 (UTC)

Drosophila melanogaster and human genome homology

Is there a published estimate of how many similar genes we and the fruit fly have? The Drosophila melanogaster article has some numbers, but I contested them on the talk page years ago, sadly without good sources. Now a prominent Finnish newspaper stated on their science pages that the genetic similarity is 66%, but that I just can't make myself believe (and therefore I hesitate to use that as a reference in the Finnish featured DM article) Any ideas about reliable homology percentage estimates? --Albval (talk) 20:25, 5 November 2009 (UTC)

Actually, I'm surprised it's so little. Remember that most of that genome is comprised of things to make cells run - all sorts of complicated biochemistry that's very similar - if not identical - between a fruit fly and a human. SteveBaker (talk) 21:58, 5 November 2009 (UTC)

I did a little research and found the BBC saying it was 60% (but no reliable sources, really). I'm a little surprised it is so low too - I've heard similar figures for bananas and surely we have a lot more in common with fruit flies than bananas. There are different ways to measure genetic similarity, though. For example, do you include differences in non-coding DNA or not? --Tango (talk) 22:26, 5 November 2009 (UTC)

Well, they are fruit flies. ~ Amory (u • t • c) 22:39, 5 November 2009 (UTC)

It wouldn't be possible to compare non-coding regions between fruit flies and humans -- there's no way to figure out what a given part should be compared to. Looie496 (talk) 23:58, 5 November 2009 (UTC)

It's possible to compare the non-coding regions that are linked to a particular gene, such as introns. It's also possible to compare non-coding regions of more recently diverged organisms, such as humans to mice, as the sequence of chromosomal rearrangements can be deduced, and the non-coding regions aligned. However, you are correct, that there would be no way to know how to align the non-coding regions of humans and fruit flies. Anyway, I've been trying to find something, anything, to answer the OP's question. As with others, I have found some news reports that give a number, but I haven't found any reliable sources on the matter outside of research reports related to only a specific gene, and not the whole genome. Someguy1221 (talk) 01:10, 6 November 2009 (UTC)

77% of human disease genes have versions or "cognates" in Drosophila.[7] Fences&Windows 04:12, 6 November 2009 (UTC)

I haven't checked in a few years. 60-77% sounds correct as a rough estimate. I'll go see if I can scare up some better numbers. -- Flyguy649 ^talk 05:50, 6 November 2009 (UTC)

The 2003 Drosophila fly community White Paper states that greater than 60% of Drosophila genes have human counterparts with the 70% figure describing similarities to disease-associated genes [8]. I'll see if there's anything more recent, but I'd be surprised if it's in a paper. This degree of conservation between flies and humans was really surprising when it was first discovered in the early part of the millennium. Now it's accepted as fact. At the time of the big genome sequencing projects, the estimate for the number of human genes ranged from 50,000-100,000. Researchers were shocked to find that there are only 23,000 or so genes in humans (flies have ~14,000) .-- Flyguy649 ^talk 06:18, 6 November 2009 (UTC)

Feels somewhat strange to me that there aren't any more detailed comparative analyses made, especially when you see different kinds of human-mouse and human-fly similarity percentages in the popular media quite often. Or is it computationally just too hard to figure out, which DNA stretches actually are homologous? Or is it just not scientifically interesting enough? Anyway, your estimate is good enough for me, the exact percentage the newspaper article gave just made me wonder if there really was a study wrom which the newspaper article had taken its figures. Now it seems that the journalist just took the numbers out of thin air... --Albval (talk) 08:43, 6 November 2009 (UTC)

Coincidentally, I was reading The Greatest Show on Earth: The Evidence for Evolution last night and Dawkins makes a good point about these percentage-identical measurements for DNA. As he explains, if you're comparing the individual C, G, A and T base-pairs - then you get a different answer depending on how you handle missing, inserted or repeated sequence comparisons. If you are talking about codons, you get another different answer because there are cases where two or more different codons produce identical proteins - do you count those as "different" or not? If you are talking about genes - then you get another different answer because two genes only have to differ by one letter to be "different" and that means that there is a much greater probability of two genes being different than two base-pairs, so the percentage-different numbers are much higher. If you compare entire chromosomes then the probability of any two creatures - even closely related members of the same species - being anything other than 100% different is almost zero. Worse still, some animals have much the same genes - but arranged on totally different chromosomes - are those very different or very similar? So unless you are VERY careful about the level of comparison and the method of accounting for differences - then you can't give a definitive answer. That means that the 'popular-science' answers like "Chimpanzees and Humans have 98% identical DNA" doesn't mean very much.

Consider, for example, the following two DNA chunks (evidently taken from feline DNA!):

   CATCATCATCATCATCATCA...
   CATGATCATCATCATCATCA...
      ^

They clearly differ in only one letter - and also only in one codon (a codon is a group of 3 letters). But what about:

   CATCATCATCATCATCATCA...
   CATATCATCATCATCATGCA...
      ^             ^

These differ by the deletion of one base-pair (a 'C') near the beginning and the insertion of another letter (a 'G') near the end. Should we say that they are nearly identical because they differ by only two base-pairs? Well, not really - the codons in the middle are completely different and would produce radically different proteins. So do these two animals have 90% identical DNA (two changes in 20 letters) or are they only 30% identical (14 differences in 20 letters) or are they 0% identical (because these two chunks would code for completely different proteins)?

SteveBaker (talk) 13:52, 6 November 2009 (UTC)

I see the difficulty in base-pair/codon -level comparisions, but homologous genes shouldn't (in my opinion) be too hard to find. There will be differences even in the amino acid level of course, but the "gene" is the same. So basically if you could find all the genes in the fruit fly and in human that have shared ancestry and then divide that by total, you'd get the "popular science" answer. I'm just wondering if it is too hard to do or too silly to do, because it seems that nobody really has done it? Or am I just missing something? Albval (talk) 18:58, 6 November 2009 (UTC)

The 60% figure may come from a quote by Gerry Rubin in 2000 from when the Drosophila genome was sequenced: "Of the 289 genetic flaws known to cause disease in humans, says Rubin, they have found Drosophila homologues for 60 percent and for 70 percent of the genes involved in human cancers".[9] He was referring to the finding published in Science that "The fly has orthologs to 177 of the 289 human disease genes examined."[10] The details of that study are here:[11] The 77% I quoted above is from 2001; both studies looked at orthologues of disease genes. Bier quotes it in 2002 as "75% of human genetic disease genes have clear homologues in the fly"[12], also cited here:[13] Another study from 2004, also looking at disease genes, found 1406 orthologues in Drosophila to the 2757 human disease genes in the OMIM Morbid Map, which works out as 51%.[14] A similar study using I think the same program found 774 Drosophila orthologues to 1180 human disease genes, i.e. 65.6%.[15]

The results depend on what stringency is used to decide whether a gene is an orthologue or not; the range I've found is 51-77% of human disease genes have Drosophila orthologues. I don't know that anyone has bothered doing the study for every fruit fly and human gene.

By way of contrast, a 2004 study found that 99.5% of human disease genes are found in rats: "Of the 1,112 human disease genes examined, evidence that all are represented as functional genes in the rat genome was found, except for ... six genes."[16] Fences&Windows 22:38, 8 November 2009 (UTC)

Wow, that was very thorough and helpful answer. Thank you very much for your help, all of you! --Albval (talk) 08:43, 9 November 2009 (UTC)

Hydrogen orbital average radius in terms of energy level.

What is the mathematical relationship between the average radius of an electron's orbit around a proton in terms of the electron's energy level? -Craig Pemberton (talk) 22:48, 5 November 2009 (UTC)

Average radius is [ 3n^2 - l(l+1) ] / 2 in atomic units. Here n is principal quantum number, l is orbital quantum number. Is that what you are asking? --Dr Dima (talk) 22:55, 5 November 2009 (UTC)

(edit conflict) It starts with Electric_potential#Electric_potentials_due_to_point_charges (this gives the relationship between potential energy and distance) - but to be accurate you need an average weighted properly by the probability distribution of the electron's likely hood at a given distance. (ie a mean average is not good) - that is the classical method to do it. You could just use a mean average anyway..83.100.251.196 (talk) 22:58, 5 November 2009 (UTC)

For the Bohr-model hydrogen atom, r_n = n² * (5.30 x 10^-11 m) where:

• r_n = the radius of energy level with principle quantum number n

There is also likely a more general equation for calculating the radius of any one-electron atom (such as He⁺¹ and Li⁺²), but that is the one I found for the Bohr-model hydrogen atom. Note that the Bohr model is a pretty limited model. It works VERY well for one electron systems because it is basically a two-body problem. For any system with 2 or more electrons, you have a n-body problem, which is a chaotic system and where you cannot mathematically predict things like energy level radius and even the energies of those levels directly. --Jayron32 04:46, 6 November 2009 (UTC)