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March 17

Meaning of ground state chemistry notation

I have a paper which apparently uses the notation ³P to identify oxygen atoms in the ground state, as distinct from ¹D and ¹S for oxygen atoms in an excited state. The wikipedia page for oxygen says that the (presumably) ground state oxygen electron configuration is 1s²2s²2p⁴, as do other web sites (the superscripts are the number of electrons in each mode), such as http://periodictable.com/Elements/008/data.html. How does the notation ³P identify the ground state, or, how does it relate to the notation given in the websites? Wickwack124.182.39.88 (talk) 04:34, 17 March 2012 (UTC)

That's the term symbol which is used in addition to the electron configuration to indicate the total angular momentum in the particular configuration. The superscript number is the value 2S+1, where "S" is the sum of all m_s values for all electrons. Thus, for an oxygen atom in the ground state, you have 1s2 (a +1/2 and a -1/2 spins) 2s2 (a +1/2 and a -1/2 spins) and 2p4 (3x +1/2 and only one -1/2 spins). That gives S=1 (all s values cancel except in the 2p orbital, where one +1/2 cancels a -1/2, but there are 2 +1/2 spins left over). So that makes the superscript 2S+1=3. The big letter P is the value "L" in the term symbol, where "L" is the sum of all "m_l" values. For s orbitals, m_l=0, and for p orbitals m_l=+1, 0, -1 for each p orbital. So for oxygen, for all 8 electrons, you have L 0+0(1s) +0+0 (2s) +1+1+0-1 (2p) = 1, so L = 1, which is P. (basically, Capital letters are the sum of the individual lowercase letters in the Term Symbol). The rules for constructing a term symbol for the ground state of an atom are described by Hund's rules. Excited states have electrons in different sets of quantum numbers, so have different term symbols. It is possible for two atoms to have the same notional electron configuration and have different term symbols; for example there are multiple ways that 2p4 could be organized into the three degenerate p orbitals, and only those with the term symbol ³P are considered the "ground state". Organizations that give different term symbols are considered excited states. --Jayron32 05:19, 17 March 2012 (UTC)

Are the concepts of closed space and sliders real concepts?

So I am a big fan of The Melancholy of Haruhi Suzumiya, which is a science-fiction series. In that anime, there are alien, time travelers and ESPers. Obviously, aliens are an established concept in science, as well as time travel, and ESP is being researched by some people. However, in that series, there is mention of so-called "closed space", where ESPers can travel to, and "sliders", who apparently can switch between dimensions. I think the "closed space" concept is made-up by Tanigawa Nagaru, but what about sliders? Has there ever been scientific theories or conspiracies about their existance? Asking this in the Science RefDesk instead of the Entertainment one since I am more interested in Haruhi Suzumiya's scientific basis. Narutolovehinata5 ^tccsdnew 10:04, 17 March 2012 (UTC)

Essentially all serious scientific proposals involving spacelike dimensions beyond the three dimensions of everyday life contemplate that such dimensions would be subatomic in size, so no person would ever be directly aware of them. They are also usually closed in the sense that the two dimensional surface along a very long pipe is closed along the circumference of the pipe's cross sections but not along its length. The reason for those attributes is usually to accommodate the unification of the physical forces, which is motivated by (what could be a merely coincidental) fact that all physical forces appear to be very similar at high energies. However, the prospect of multiple timelike dimensions is sort of an open question which would allow for all kinds of interesting physics. In general though, it is unlikely but there are a number of possibilities around the basic objections. Npmay (talk) 10:35, 17 March 2012 (UTC)

That's not the answer to my question. My question is, are the terms "closed space" and "sliders" made-up or not, or are there actual scientific theories about them that call them as such. Narutolovehinata5 ^tccsdnew 11:00, 17 March 2012 (UTC)

Closed space is an actual mathematical attribute of spatial dimensions which has scientific theories about it calling it such; it is usually called a closed manifold. Sliders are entirely fictional concepts which are certainly not possible without dimensional attributes that are almost never considered seriously in science. Npmay (talk) 11:20, 17 March 2012 (UTC)

Opon review of the fictional literature cited in the original question, I find the Yuki Nagato character most believable, although the most persuasive evidence of extraterrestrial life on Earth is invariably dismissed by serious scientists, but not, in my opinion, for good reasons.

Furthermore, I would say the "closed space" concept is probably less similar to a closed manifold and more similar to a macroscopic brane intersection between multiverses, which is, well, let's just call it fringe science. When branes as scientists theorize them collide, they do things like cause big bangs more often than they open dimensional portals from which one can fight monsters with psionic powers. Npmay (talk) 12:06, 17 March 2012 (UTC)

I'm tempted to think that "sliders" is a reference to Sliders rather than any real physics. Wnt (talk) 20:03, 17 March 2012 (UTC)

how do bridge makers model stresses

in general it seems easy enough to imagine things that support compression or pull, and so there must be software where you can just combine rods and suspending things at all angles you want, specify their attributes and see if the whole thing collapses or how it acts. so what is it? --80.99.254.208 (talk) 11:33, 17 March 2012 (UTC)

Physical modeling with finite element analysis CAD software is usually very accurate, but is almost always checked in practice with physical scale models for new structures of nontrivial complexity. Npmay (talk) 11:53, 17 March 2012 (UTC)

You seem like you know a bit about this subject. Could you explain it. --80.99.254.208 (talk) 12:10, 17 March 2012 (UTC)

Have a look at that article and this video. Npmay (talk) 12:39, 17 March 2012 (UTC)

Not quite professional grade, but I recommend anyone interested in learning the basics try out the bridge builder series of games (some are free or free trial). It lets you visualize the stresses, and you will very quickly get better at building bridges :) SemanticMantis (talk) 14:41, 17 March 2012 (UTC)

I was about to say the same thing, online there's "Bridge Thing" and "Cargo Bridge". Also, sites about building bridges from toothpicks give good info, and there's the bridge design software West Point Bridge Designer, free to download. 84.197.178.75 (talk) 14:49, 17 March 2012 (UTC)

The basics of bridge building have been known for centuries, but some considerations, like wind-loading, resonance, and metal fatigue, have only been fully understood in the last few decades. See Tacoma Narrows Bridge (1940) for a case where the first two issues caused a collapse. StuRat (talk) 21:10, 17 March 2012 (UTC)

Software to draw schematic diagrams?

Hey, is there any software that can be used to draw schematic diagrams of machines or any device for that matter? And I don't mean CAD software, they're used for engineering drawings only. What I mean is something that can be used to draw stuff like this See, I'm reduced to uploading my horrible drawings to Wikipedia. Thanks! Lynch7 16:53, 17 March 2012 (UTC)

If you're just looking for a free package to make diagrams for Wikipedia, then Inkscape is good and it is in Wikipedia's preferred SVG format. SpinningSpark 17:27, 17 March 2012 (UTC)

If Inkscape has too high a learning curve, LibreOffice Draw might do. Npmay (talk) 21:01, 17 March 2012 (UTC)

You wouldn't want to blow $5000 and many hours of leaning to use on professional CAD programs like Autocad, but purchasing a consumer grade CAD product like DesignCAD ($200 or so) is well worth the ease in which you can make very nice drawings with very little learning effort. With a few hours practice it becomes quicker than hand sketching. I find it is very nice for doing custom graphs with special axis too. For example I used it to graph viscosity of mineral oil versus temperature - this requires a [log of (log + K)] scale, not possible in Excel. Keit58.170.182.237 (talk) 04:24, 18 March 2012 (UTC)

crypto rands automatically good for monte carlo?

Is any random number source that's good for crypto automatically good for a monte carlo simulation? (i.e. the monte carlo converges on whatever you would see in the wild with those natural conditions/percentages/whatever, rather than ever converging on some fluke of the RNG.

to illustrate what I'm talking about, int rand() % x is not a good way to monte carlo random integers betwen 0 inclusive and x exclusive, because lower ones tend to come up more than higher ones. Likewise it would be a terrible choice for a crypto secure random integer.

So, my question is about the general case: if something is good enough for cryptography, is it good enough to monte carlo nature with? (i.e. all i have to worry about is finding a crypto library of random numbers, and I can go on my merry way assuming each random number is as good as forking to a random universe to continue, with equal distributin in each random universe...) forgive me if this belongs on the comp sci desk. --80.99.254.208 (talk) 18:55, 17 March 2012 (UTC)

Well, cryptography is pretty notorious for not being as good as claimed - it's hard for the user to tell, after all. It's not my field, but I should think that if your monte carlo acts aberrantly, you're already well on the way to cracking the encryption. So I'd ask ... would it be newsworthy that the encryption that you're using had just been cracked by accident? Wnt (talk) 20:01, 17 March 2012 (UTC)

The needs of cryptography, and those of Monte-Carlo methods, are somewhat different. In principle, for example, a bitstream PRNG used for cryptography in certain ways (say, to get initialization vectors) could tolerate some slight bias (say, 50.1% 1s and 49.9% 0s), because bias per se is unlikely to help an attacker much. However, for Monte-Carlo applications, you don't want bias.

That said, as far as I know, cryptographic PRNGs are all unbiased.

The main downside of using a cryptographic PRNG for Monte Carlo is likely to be speed. Monte-Carlo methods typically need random values in huge torrents; getting those from RC4 or something may be a bit slow.

Then there's a different issue: Are you sure you really want pseudo-random numbers at all? Many Monte-Carlo type algos work better when you give them self-avoiding sequences (let's see if subrandom comes up blue), because you don't waste time exploring points of the space that have already been explored. There's a good practical treatment of some of these in Numerical Recipes in C. --Trovatore (talk) 20:12, 17 March 2012 (UTC)

Well, Numerical Recipes is blue. DMacks (talk) 08:03, 18 March 2012 (UTC)

Why is the urinalysis called also: "Routine and Microscopy"?

I would like to understand it, thank you. — Preceding unsigned comment added by 176.13.203.54 (talk) 20:21, 17 March 2012 (UTC)

You don't say where you saw this, but it was likely on a lab slip where someone places a check-mark by the tests they want to order. One might want to order a routine urinalysis, or an examination of the urine under a microscope, or both. If you want both, you'll check off "routine and microscopy". The reason these are separated is that a routine urinalysis consists of chemical tests, and can be done very simply with a urinalysis dipstick, and it can be completely automated, making that part of the test cheaper than a microscopic examination, which requires spinning the urine in a centrifuge and examination by an actual person with a microscope. Our urinalysis article is a little misleading, because "Routine and Microscopy" is not a synonym for urinalysis, but rather an abbreviation of "routine urinalysis and microscopy". A routine urinalysis would include chemical tests for pH, specific gravity, glucose, ketones, protein, nitrite, blood (red blood cells (RBCs)), and leukocyte esterase (from white blood cells (WBCs)) - bilirubin or urobilinogen or other tests may also sometimes be included. But because there can be false positive chemical tests for blood and WBCs, so these would ordinarily be confirmed by microscopic examination, where one can actually see RBCs or WBCs (or other abnormal urine contents) if present. - Nunh-huh 20:51, 17 March 2012 (UTC)

Thank you for help. 176.13.203.54 (talk) 21:42, 17 March 2012 (UTC)

You're more than welcome. By the way, the combination of a routine urinalysis with a microscopic examination of the urine is sometimes called a "complete urinalysis". - Nunh-huh 21:58, 17 March 2012 (UTC)

Thank you. By the way, you're a good explainer and I wish to meet yuu here a lot in the down the road.176.13.203.54 (talk) 23:06, 17 March 2012 (UTC)

Yes, thanks for your analysis of urinalysis. StuRat (talk) 02:28, 18 March 2012 (UTC)

Why is the Urine culture called also Diaslide?

I don't understand it. thank you for help. 176.13.203.54 (talk) 20:49, 17 March 2012 (UTC)

Diaslide is a trademark for a specific brand of urine culture test. Just like "Bic" is the trademark for a specific brand of pen. - Nunh-huh 20:53, 17 March 2012 (UTC)

Youtube has a video showing it in use.[1]--Aspro (talk) 20:56, 17 March 2012 (UTC)

And I imagine it's short for "DIAgnostic microscope SLIDE culture". StuRat (talk) 20:59, 17 March 2012 (UTC)

The relativity of time.

Could time be the big and small force? — Preceding unsigned comment added by 192.148.117.95 (talk) 23:11, 17 March 2012 (UTC)

vanessa1234394!

tahliabrehm — Preceding unsigned comment added by Tahlia1234 (talk • contribs) 23:22, 17 March 2012 (UTC)

Dunno. Give up! What’s the answer?--Aspro (talk) 00:05, 18 March 2012 (UTC)

If you mean the strong nuclear force and weak nuclear force, then no, absolutely not, not any more than time can be the tomato in your salad. StuRat (talk) 01:59, 18 March 2012 (UTC)

According to Gary Larson, Einstein proved that time is actually money. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:20, 18 March 2012 (UTC)

March 18

Element

Resolved

What chemical compound is produced when carbon monofluoride and thulium are combined, if any? 71.146.8.88 (talk) 01:45, 18 March 2012 (UTC)

I assume that a redox reaction will take place at high temperatures, to form carbon and trifluoridothulium. Plasmic Physics (talk) 02:13, 18 March 2012 (UTC)

Thulium can also from a carbide. At low temperatures graphene fluoride or your carbon monofluoride are quite unreactive. Graeme Bartlett (talk) 10:07, 18 March 2012 (UTC)

Thanks. 71.146.8.88 (talk) 18:43, 18 March 2012 (UTC)

Thanks. 71.146.8.88 (talk) 18:45, 18 March 2012 (UTC)

Physics. Adding vectors.

I am faced with this problem: we have a 200N (newton) force heading west. we have two 200N forces heading off 30 degrees, one in a NE direction one in a SE direction. The net force is equal to 200 newtons in a east direction. We need to find the missing force which will make the net force equal to 200N E. I have tried using trig to find the magnitude of the two 200N forces but still cant find the answer. Paradoxical 0^2 (talk) 02:11, 18 March 2012 (UTC)

First, ignore all those vectors you started with. Since you know the resultant vector, they don't matter. Now, break down the desired 200N vector in the NE direction to the components headed North and East, then subtract the resultant 200N vector headed East from the East component, to get the final amount you want headed East (it will actually be negative, meaning West). Then combine this West component with the North component to get the missing vector. If you show your work, we will check it for you. If my explanation doesn't make sense, please let me know. StuRat (talk) 02:22, 18 March 2012 (UTC)

(edit conflict)Since the NE and SE forces are symmetrical about the East-West axis, their North-South components cancel out. Use Pythagoras theory to calculate the East-West components of the NE and SE forces (treat their given values as their respective hypotineuses). Once you have them, it is simply a case of adding or substracting them from or to the West force, and calculating the difference with the net force. Remember to assign the correct sign to each direction (possitive/negative) to each cardinality. Plasmic Physics (talk) 02:24, 18 March 2012 (UTC)

Still don't understand,here is all the working out i have:

cos(45)*200N=105.064398N
(I believe this is the right way to get the adj side here)
so we have to have 105.064398+(-200N)+x=200N
this x≈294.936 N
this is clearly not right.
by the way the answer given is 53.6 N east

Paradoxical 0^2 (talk) 04:04, 18 March 2012 (UTC)

Your calculator is set to radians, not degrees. 200×cos(45°) = is 141.421356. However, I don't get the given answer. Perhaps I don't understand the problem. In your original post, does "The net force is equal to 200 newtons in a east direction" mean the net force of all 3 original vectors, or only the two vectors at 30 degree angles ? StuRat (talk) 04:11, 18 March 2012 (UTC)

that is the net force with the vector that we are trying to find, i belive that is called the resultant vectorParadoxical 0^2 (talk) 04:28, 18 March 2012 (UTC)

that is with all the vectors added up we are left with a 200N final vectorParadoxical 0^2 (talk) 04:30, 18 March 2012 (UTC)

including the vector we are trying to find Paradoxical 0^2 (talk) 04:32, 18 March 2012 (UTC)

Also, are those vectors 30 degrees above and below straight East ? If so, where does the 45 degree angle come in ? StuRat (talk) 04:11, 18 March 2012 (UTC)

whoops, but still the answer aint right Paradoxical 0^2 (talk) 04:37, 18 March 2012 (UTC)

http://content.jacplus.com.au/secure/ebooks/07314/0731408209/14/image_n/nt0030-y.gif here is the question — Preceding unsigned comment added by Paradoxical 0^2 (talk • contribs) 04:43, 18 March 2012 (UTC)

That requires an account to view it. Can you do a screen grab and upload it here ? I can help you if you don't know how. StuRat (talk) 04:46, 18 March 2012 (UTC)

How do you do that? — Preceding unsigned comment added by Paradoxical 0^2 (talk • contribs) 04:49, 18 March 2012 (UTC)

There are 4 steps:

1) Do the screen grab.

2) Save the image as a JPG (or PNG, GIF, PDF, or TIF).

3) Upload to Wikipedia.

4) Display it here.

Do you need help with all 4 steps ? StuRat (talk) 04:59, 18 March 2012 (UTC)

[2] Paradoxical 0^2 (talk) 05:00, 18 March 2012 (UTC)

I made it a link. It's rather blurry and there's no text. Can you zoom in on it before you do the screen grab and include any text ? (The text might be for a whole group of problems, not just this one.) StuRat (talk) 05:05, 18 March 2012 (UTC)

I understand the problem without needing to see a copy of what's printed in the book. The description of the problem in the first paragraph above seems to me like a perfectly reasonable description of the problem, and indeed has an answer of 53.6 N east. But your math is making three mistakes, only two of which have already been identified above:

• The problem says the angle involved is 30 degrees, but in your first equation, you're using 45 degrees.
• You need to calculate the cosine using degrees on your calculator, not radians.
• There are two vectors each contributing a force of 200 cos 30 N in the easterly direction, but your second equation only includes the easterly contribution of one of those two vectors. Red Act (talk) 05:44, 18 March 2012 (UTC)

Here's the answer:

Let North and East be positive.

X = 200 N (East) + 200 N (West) - 200 N (North-East) x cos(30°) - 200 N (South-East) x cos(30°)

X = 53.6 N (East)

Plasmic Physics (talk) 05:57, 18 March 2012 (UTC)

I don't understand how you can add 200 East and 200 West. Shouldn't they cancel each other out ? StuRat (talk) 06:01, 18 March 2012 (UTC)

No, because they have the opposite sign, and substracting a negative results in addition. It is a result of rearanging the original equation. Plasmic Physics (talk) 06:04, 18 March 2012 (UTC)

Thanks very much guys! sorry for being such a pain. Paradoxical 0^2 (talk) 06:10, 18 March 2012 (UTC)

Here it is with a force diagram. For some reason they omitted vector D, the one we are trying to find, from your diagram:

                      B
                  * 
              *  
A <-------+------->D
              *
                  * 
                      C

Resultant = east component of B + east component of C + D - A

200 = 200(cos(30°)) + 200(cos(30°)) + D - 200

400 = 200(cos(30°)) + 200(cos(30°)) + D

400 = 400(cos(30°)) + D

400 = 400(0.866) + D

400 = 346.4 + D

400 - 346.4 = D

53.6 = D. StuRat (talk) 06:16, 18 March 2012 (UTC)

Resolved

Always being able to feel your heart beating is not normal?

In primary school when taught about how to measure heart rate, I noted that I could actually always feel my heart beating. So, I never have to bother trying to find my pulse. I did realize at the time that this means that most people cannot (always) feel their own heart beating, but I didn't make too much out of this. No doctor has ever found a problem with my heart, and I am extremely fit. However, I've never heard of people who don't have heart disease who can always feel their heart beating. Count Iblis (talk) 02:50, 18 March 2012 (UTC)

I can't feel it, but can hear it when my blood pressure is high. StuRat (talk) 02:57, 18 March 2012 (UTC)

I also used to be able to hear it in one ear when holding my head in a certain position for several years. But that was after I suffered an injury to that ear. But just being able to feel it is actually very handy, I don't need heart rate monitors when exercising, I just need to look at my wach while running! Count Iblis (talk) 03:12, 18 March 2012 (UTC)

Have you tested this to check if your reckoning of your heart rate matches with the account of a pulse meter? SkyMachine ⁽⁺⁺⁾ 06:45, 18 March 2012 (UTC)

It really amazes me that anyone would not feel it. I mean, I feel each heartbeat at the heart, with a sensation that varies according to diastolic blood pressure; I feel it at the inside of my elbows, with a sensation that changes when systolic blood pressure goes over 140; I typically feel it in my toes, legs, hands, abdominal organs (hard to tell which is which though), and many other places. I would say that even the cerebral arteries have a noticeable pulse sensation, especially if my blood pressure gets up over 150 for some reason. And there's also a small degree of control over all the arteries also, though it's hard to tell how much is manipulation of blood pressure in general. (At one point, trying to experiment with or "improve" cerebral blood flow, I actually managed to give myself a painless but quite disturbing ocular migraine; I've generally discontinued that research... I actually suspect that the "emotion" of shame/embarrassment is mostly a sensation of vasoconstriction somewhere near Broca's area, and ensuing results) But an exception to all this is that for some reason the aorta seems devoid of sensation. Wnt (talk) 15:14, 18 March 2012 (UTC)

WNT, do/did you also feel it when your blood pressure is/was 120? My uncle can also feel every beat, but then he has extremely high blood pressure (220 sometimes even higher) due to a coarctation of the aorta. Count Iblis (talk) 23:16, 18 March 2012 (UTC)

Oh, absolutely. In fact, when my blood pressure used to go a bit low when dieting (I think it was a mild instance of orthostatic hypotension) it produced a very distinct and somewhat unpleasant sensation, like my heart had to "suck in blood", which as I understand actually does happen when pressure in the vena cava is low enough. Wnt (talk) 15:27, 19 March 2012 (UTC)

SkyMachine, yes, it is the same (within measurement error, I obviously get the average over, say, ten seconds instead of instanteneous values). When I'm exercising I typically run at such a speed that the heart rate is between 150 bpm and 160 bpm. I simply start running at a speed that feels right to me and only then do I check my heart rate. It is then almost always what it should be. My resting heart rate is around 40 bpm, a bit higher than that when I've done strenuous exercise the day before and the day before that. Occasionally, when I take longer breaks from exercising (I normally exercise 5 times per week, but every few weeks I'll have 3 days of no exercise at all), my heart rate sometimes drops to 37 bpm. Count Iblis (talk) 23:19, 18 March 2012 (UTC)

It's possible for an awareness of one's heartbeat to be a sign of any of a number of health problems, not just heart disease. Given that the question involves a specific individual, it would be a violation of the reference desk's "no medical advice" guideline for me to list the various possible diagnoses, or probably even to mention the article that I'm getting this information from. So ask your doctor as to whether it may be indicative of a health problem in your case. Red Act (talk) 01:47, 19 March 2012 (UTC)

Surely you jest. No doctor has ever asked me if I could feel my own heartbeat - I daresay I'll not receive any professional medical advice on that subject this side of the grave. Wnt (talk) 15:28, 19 March 2012 (UTC)

So what if no doctor has ever asked you if you could feel your own heartbeat? There are lots of symptoms that no doctor has ever asked you about, because there are lots of diseases that your doctors have never had a reason to suspect that you might have. Just because you have never had any indication of a health problem that might prompt your doctor to ask you if you could feel your own heartbeat, doesn't imply that the same is true of the OP. Red Act (talk) 16:27, 19 March 2012 (UTC)

Honestly I think that not being able to feel your own heartbeat sounds like the pathological condition. It seems obvious enough that direct sensation of the process gives useful feedback (e.g. when eating a little Epsom salt would be good). There are specific mechanisms to mediate the sensation. [3] So far as I know it is common for traditional meditation practices to focus on such sensation, and while health claims for them may be controversial, who calls such practices pathological? Wnt (talk) 21:19, 19 March 2012 (UTC)

Incidentally, are those of us who feel our heartbeats the only ones aware of skipped heartbeats, or do the others become aware of it only in that circumstance? Wnt (talk) 15:52, 19 March 2012 (UTC)

Moving your hand in front of your closed eyes in a pitch-dark room

I noted that I can actually "see" something moving in my field of vision when I do this, even though it should be impossible to see anything at all. Is this caused by the brain always taking into account the way body parts move in front of the field of vision when processing visual information? I can imagine that the algorithm used by the brain is not perfect and if there is nothing to see at all, you could be seeing an artifact of the algorithm... Count Iblis (talk) 03:29, 18 March 2012 (UTC)

I doubt if your room is really pitch black. Likely some starlight, etc., filters in through the windows, even on moonless nights. This isn't enough light for you to actually see, but is enough for what you describe. To have a room really be completely dark would require no windows, and seals around all the doors. StuRat (talk) 04:42, 18 March 2012 (UTC)

I'm going to agree with StuRat, considering that as few as nine photons will cause your brain to register having seen something. Someguy1221 (talk) 04:54, 18 March 2012 (UTC)

Nine photons and/or or a really, really shallow wave of light. --134.255.75.71 (talk) 07:29, 18 March 2012 (UTC)

To test this you should repeat the same scenario but get someone else to move their hands in front of your closed eyes and see if you can still determine when they are moving as opposed to being at rest. SkyMachine ⁽⁺⁺⁾ 07:43, 18 March 2012 (UTC)

And you may still be able to detect this without vision, by feeling the draft, hearing the movement or sensing the changed electrostatic environment. Even blocking the ambient noise can be detected. Graeme Bartlett (talk) 09:28, 18 March 2012 (UTC)

You can control for these variables if you put some thought into it. The question is how is the mind percieving the movement? Is it outside sensory data that is being recieved, or is the mind constructing the sense of a hand moving because it already knows the hand is moving. The mind might just be predicting where the hand might be in the absense of confirming sensory data from the eyes. SkyMachine ⁽⁺⁺⁾ 09:39, 18 March 2012 (UTC)

Not only that, it's ridiculously easy to control for! Insider the dark house, find a door with a window in it (making the rooms on either side "pitch black" by covering any other sources of light into the rooms) and have someone on the other side either do the movement quietly or not move at all when you tell them loudly through the door. Your eye can be right against the window, they can stand back but move their hand close by the window when they hear your muffled request to do so. (or they can do nothing and see if you read a false positive). Tell them what you think, and within short order they'll tell you if you're getting it right. --80.99.254.208 (talk) 12:56, 18 March 2012 (UTC)

I used to do a bit of caving. When the all the lights are turned out in a cave, you can see nothing at all, absolutely nothing but blackness, except mayber a bit of retained vision. Alansplodge (talk) 22:39, 18 March 2012 (UTC)

I've noticed too that I can sort of vaguely sense my hand in a totally dark room. And I can assure you it was totally dark. The human eye does have an extremly weak response to infrared. So I tried an experiment with a black painted roughly forearm sized piece of metal warm to 35 C. Results were inconclusive though - I could feel the warmth on my skin if I brought it within 200-300 mm of my face. There is another possibility: Most people know that the eye has 2 kinds of light sensor - the rods and cones. Rods and cones produce the conscous perception of light. But there is a third kind of sensor in the eye - modified ganglion cells. Mammals have these for sychnonising the body circadian rythm to the night-day cycle. Not a lot is known about these sensors. Maybe these respond to infrared as well as visible light, and maybe there is some crosstalk into the conscious perception, as adjacent ganglion cells process the output of the rods and cones. Ratbone124.178.47.224 (talk) 13:19, 18 March 2012 (UTC)

To really get all scientific, their response should be random, and not influenced by whether you got it right before. They can memorize 10 responses beforehand, for example, after flipping coins to see what they'll do. Or they can do more than 15 if they have something they can feel (a baille sheet?) taped to the wall that tells them their response). The weaker your ability to see them, the more tests you need to establish statistical confidence. --80.99.254.208 (talk) 12:54, 18 March 2012 (UTC)

also I should mention that a hidden assumption is that a person is very good at being at the other side, like a game where they're trying to be stealthy. I think as hunters (hide and seek etc) we are very good at being stealthy and have fun doing so in a game context. So all they would do is quietly slowly move their hand in front of the window or not, and otherwise not 'give away their position'. --80.99.254.208 (talk) 13:12, 18 March 2012 (UTC)

• To interpret this I should ask a related question: how common is it for people to start dreaming when in the dark? I used to do work in darkroom where it was inappropriate to use a safe light for what could be over an hour, and it was absolutely routine for me to see/imagine all sorts of things despite concentrating on the task at hand. For me these were 1) blue and occasionally yellow wave patterns 2) rarely, a photorealistic "rehash" of recent unfamiliar visual stimuli - for example, if playing cards for the first time in a year the patterns would then show up during the same day 3) faint, ghostly, indistinct, mostly blue dream images of all varieties. This third type is relevant here - when moving a hand in front of my face, I might see something like that, though then again, the hand might not stay where it was supposed to be, or it might segue into monsters and maidens. Is that the way it works for other people? Wnt (talk) 15:25, 18 March 2012 (UTC)

I second the caving story, underground, you can not see your hand waving in front of your face even with your eyes OPEN. I think "expectation" would play a large part in this. I've waled through my house a few times when it has been very dark and a couple of times I'll get a really impending feeling that i'm about to walk into something or bump into something and when I eventually get the light on, I'll realise that the chair I thought was there was actually moved, or I wasn't in exactly the spot I thought I was. Vespine (talk) 23:31, 18 March 2012 (UTC)

I just repeated this experiment in a completely dark room with eyes closed with also one hand covering my eyes and with the other I wave in the field of vision. I can vaguely see something moving, it doesn't make any difference whether or not the other hand is covering my eyes. It seems to me that somehow information from the part of the brain involved in motor control influences the part involved in vision... Count Iblis (talk) 23:29, 18 March 2012 (UTC)

Maybe these Grid cells have something to do with it. SkyMachine ⁽⁺⁺⁾ 07:31, 19 March 2012 (UTC)

Interesting! Note also that what I'm sensing is more a sense of motion without seeing much. It is very similar to trying to spot a very faint object, say M51 using 8 by 40 binos. Where I live there is quite some light polution and M51 is a threshold object for my 8 by 40 bino. Only when conditions are optimal can you spot it in your peripheral vision when moving your binos up and down a bit. You then get the sense that there is something there, but you don't actually see it. For objects that are a bit brighter like M33 you see it in the peripheral vision without having to move the binos up and down, and then you do actually see something. Count Iblis (talk) 14:51, 19 March 2012 (UTC)

Oh, and just a final thought, In order to rule out this being just a result of proprioception or blind tracking of the hand by the eye, you can hold some hand sized implement to extend your reach so that the implement is being waved before your eyes but your hand is not in your "field of vision," and if you still detect motion it would lean toward an interpretation of subtle sensory detection. SkyMachine ⁽⁺⁺⁾ 11:21, 20 March 2012 (UTC)

I would like to comment that it's very difficult to get into a room with absolutely zero photons, even if you got drastic, covered all the windows with thick blackout curtains, and lined the walls with lead. Even if we constrain ourselves to only counting photons with energies that are unambigously within the visible spectrum, it's still very hard to get into a room with absolutely zero visible photons. As has been pointed out, the human eye can detect a very tiny number of photons; but there are constraints on the minimum number of photons are necessary to form an image. "Pitch black" is a weakly defined term, but it shouldn't be construed as "zero visible light." In very dark rooms, your eye, like an artificial imaging sensor, will be limited by photon noise, and in the extremum case of detecting a single photon, seeing the motion of your hand is physically indistinguishable from seeing "not the motion of your hand." Nimur (talk) 18:17, 19 March 2012 (UTC)

I'm quite surprised that no one has linked to blindsight yet. Maybe not directly related, but it's still a very poorly understood phenomenon. Try this little test; you may surprise yourself. -RunningOnBrains^(talk) 02:03, 21 March 2012 (UTC)

Correct me if I am wrong. Rods are black and white eye sensors that deal with low light. Cones are the colour ones that need higher light. The minimum sensitivty for a rod is the same as that of a candle 14 miles away.--Canoe1967 (talk) 09:09, 23 March 2012 (UTC)

Tiger cognition

Hi I would like to learn more about tiger cognition. I read the article on elephant cognition, and I want to know the same type of information, but for tigers (brain size/mass/structure, use of tools, language, self-awareness, etc). The Tiger article itself doesn't address these either. Any help is appreciated. Thanks.--99.179.20.157 (talk) 03:31, 18 March 2012 (UTC)

One interesting measure of their intelligence is that they only attack from the back, when their prey is the most helpless. They do this by recognizing the face of the animal they are attacking (not each particular face, just that it is a face). We know this because people in tiger-infested areas of India have learned to wear face-masks on the backs of their heads, which protects them from attacks. So apparently tigers aren't smart enough to distinguish a real face from a cheap plastic mask. StuRat (talk) 04:39, 18 March 2012 (UTC)

Er, citation needed? AndyTheGrump (talk) 04:59, 18 March 2012 (UTC)

Not sure why you don't believe me, but sure, here you go: [4]. StuRat (talk) 05:09, 18 March 2012 (UTC)

They're not fooled. They just see how silly the mask looks, and feel really, really sad for you. Someguy1221 (talk) 05:21, 18 March 2012 (UTC)

Or maybe they can't attack because they are doubled over laughing. StuRat (talk) 05:43, 18 March 2012 (UTC)

Alright, having actually looked into this now, there is precious little research done on tiger cognition specifically. You may have far more luck asking about cat cognition in general. If I had more time at the moment I'd actually look into that and give you a real answer. Someguy1221 (talk) 05:47, 18 March 2012 (UTC)

OK, that sounds reasonable. Cats have been given the mirror test, and are smart enough to figure out that their reflection is an illusion, and ignore it thereafter. However, they aren't smart enough to figure out that they are seeing an image of themselves, so apparently lack of concept of "self", which also implies an inability to empathize with others/see things from another POV. StuRat (talk) 05:55, 18 March 2012 (UTC)

I'm not sure that a solitary predator has any need to 'empathize with others'. See Ludwig Wittgenstein, and his comments about lions speaking (though come to think of it, lions, as social animals, may have more of a need for empathy than tigers...) AndyTheGrump (talk) 06:23, 18 March 2012 (UTC)

It could be helpful for a tiger. For example, knowing that the villagers of the person they are about to kill will get very upset and come after the tiger with guns might be a good thing to understand. Or, on a more basic level, knowing that the prey animal will run towards the pack when threatened might enable them to figure out that they need to position themselves between it and the pack before they pounce. If you're unable to think about what others are thinking, this type of reasoning becomes more difficult. We could eventually get to game theory, where we also consider other's reactions to our actions, based on their actions, based on our actions, etc. StuRat (talk) 06:34, 18 March 2012 (UTC)

The issue here is that you're conflating "knowing what others are thinking" with "observing repeated actions." A tiger can observe that prey generally try to reach the herd for safety without necessarily understanding "the prey thinks it will be safer in the herd." That's what makes it so difficult to understand animal cognition. As another example, a crow that has learned cars are really good at cracking nuts open doesn't know anything about what the driver of the car is thinking. — The Hand That Feeds You:^Bite 14:39, 21 March 2012 (UTC)

Agreed, except that you said "reach the heard for safety". The tiger wouldn't know why the prey does this, just would note that it does run to the herd. If it did know why, the advantage would be the ability to predict how the prey might behave without having several failed hunts first. StuRat (talk) 23:27, 21 March 2012 (UTC)

which branch of statistics

which branch of statistics (or other science, but I assume with the tools of modern statistics) deals with which religion is most likely to be true.

(Obviously 'we can't know for sure' 100.000...%, a hundred sigmas, as an almighty Taco could have fabricated all the evidence, implicating some nonexistent God) — Preceding unsigned comment added by 149.200.102.16 (talk) 14:57, 18 March 2012 (UTC)

I'm not sure what the origin of the story is (maybe they know on Humanities) but there's an old story about the Emperor of a faraway land, who had never been seen by the people. [5] Desiring to make a statue of him, they needed to find the length of his nose, so a vote was held, and the results were averaged to get a figure. (Hmmm, maybe it should have been a median... [6] ;) That's all statistics can do for religion. One can find deep philosophical truths, but striking an average of the responses has nothing to do with it. Wnt (talk) 16:08, 18 March 2012 (UTC)

For what it's worth, Feynman retells that story in Surely You're Joking, Mr. Feynman!, without giving a source. -- BenRG (talk) 19:57, 18 March 2012 (UTC)

Religion is a matter of faith, and is entirely unconnected with how likely it is to be true. Science cannot help with questions of religion, if it could they would no longer be questions of faith and no longer a matter of religion. SpinningSpark 17:23, 18 March 2012 (UTC)

Obviously religions make a lot of factual statements that can be tested. Christianity says that someone named Yeshua lived in Judea at a certain time and did various things, some of them witnessed by a large number of people. Buddhism says that desire is the cause of suffering. These are statements that can be tested against available evidence. The fact that some people will ignore the results is beside the point. -- BenRG (talk) 19:57, 18 March 2012 (UTC)

You can't quantify uncertainty in precise numerical terms except in very limited circumstances. If you're measuring the average of a numerical property (like nose length) across a population, and you have an accurate list of the members of that population and the ability to compel anyone you choose to submit to the measurement, you can pick a random sample and calculate a degree of confidence in your estimate of the mean. In any vaguer circumstance, you get much vaguer results. When the thing you're trying to test is a vague statement about a historical event and the evidence is whatever historical documents happened to survive, you can't come close to attaching a numeric confidence level to your conclusions. -- BenRG (talk) 19:57, 18 March 2012 (UTC)

Perhaps it's the branch known as "Figures don't lie, but liars do figure." ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:36, 18 March 2012 (UTC)

I imagine more recent religions are designed to match what science tells us about the world a bit more than ancient religions. Have the crystal vibration nuts adapted their "religion" to string theory yet ? StuRat (talk) 02:20, 19 March 2012 (UTC)

Maybe somewhat, but even the newer religions contain testable hypotheses that contradict scientific evidence, in part due to science having progressed since the religion was created. As an example, the Book of Mormon has been around for less than 200 years, but its account of the origins of native Americans conflicts with genetic analysis that has been possible since around the late 1990s; see Genetics and the Book of Mormon. As an even more recent example, Scientology has only been around since the early 1950's, but Scientology's chronology of the universe, which includes events that supposedly took place as long ago as 7 x 10⁸⁵ years ago, conflicts with the actual age of the universe (about 13.7 x 10⁹ years), which has only really been accurately known since the first accurate measurement of the Hubble constant, in 1958. Red Act (talk) 04:35, 19 March 2012 (UTC)

Your last statement is too generous to Scientology. The early estimates of the Hubble constant were inaccurate, but only by a factor of six or so. Similarly, we had estimates for the age of the Earth and the age of the oldest stars that were roughly several billions of years well before Scientology was invented. Anything proposed to occur more than ~10×10¹⁰ years ago would have been clearly inconsistent with Science even in 1950s. Dragons flight (talk) 05:04, 19 March 2012 (UTC)

Yeah, I was already thinking of rewriting the last sentence of my post above, since it doesn't adequately reflect the state of physical cosmology at the time of Scientology's creation. At the time of Scientology's creation in the early 1950's, it wasn't even really clear yet that the universe hadn't been around forever. The derivation of the Friedmann equations and Hubble's law, and Hubble's observation thereof, all took place in the 1920's. But there was an alternative Steady State theory that had just come out in 1948, that allowed for a static universe. Indeed, the term "Big Bang" was coined as a pejorative term in 1949 by a Steady State theorist. It wasn't really until some observations in the 1960s, especially the discovery of the cosmic microwave background radiation in 1965, that the Big Bang theory emerged as the clear winner among the two competing theories. So Scientology's use of a set of times far older than the actual age of the universe by itself didn't really clearly contradict science yet in the 1950s. Red Act (talk) 07:26, 19 March 2012 (UTC)

To be clear, no religion can be proved bogus in this way, because religion can be interpreted differently.* For example, a religion could define a "year" as changing in length in proportion to the age of the Universe (i.e. a logarithmic scale). This is entirely reasonable since otherwise in the first nanosecond of the universe objects could move all the way from one end of the universe to the other in a second. In our modern time it makes 1/15,000,000,000 difference in the length of one year to the next, which nobody would notice. Religion can only be scientifically disproved when it comes out and starts telling scientists what they should be seeing, i.e. making testable predictions. As long as they stay in their own domain, they are invulnerable. Wnt (talk) 02:49, 22 March 2012 (UTC)

* Whether Scientology is a religion, or merely a way of doing quack psychiatry without a license, is another question...

Surely anyone hoping that statistics can help to justify religion needs to look at Lies, damned lies, and statistics, "particularly the use of statistics to bolster weak arguments". HiLo48 (talk) 18:32, 19 March 2012 (UTC)

Thomas Bayes a theologian, invented Baysian statistics. Graeme Bartlett (talk) 08:59, 21 March 2012 (UTC)

why does the chain make a 'triangle' shape between front (pedal) gear, back (wheel) gear, and this arm, on high-quality bikes?

Resolved

on a high-quality bike like this: http://www.bike-trend.com/wp-content/uploads/2009/06/gt-force-carbon-pro-2009.jpg why does the chain not go directly between the forward and after gears, both above and below - instead, below an arm makes it form a triangle (in case it isn't clear what I'm saying I drew the triangle here in red: http://imgur.com/cFFIH.jpg -- the green is what I would expect instead of the red triangle. To get the green, you would just reflect the top half the chain makes going from back gear to front pedal, reflected horizontally so it looks the same below (result: http://imgur.com/xf083 )....soo...why the triangle? --79.122.101.84 (talk) 18:36, 18 March 2012 (UTC)

The gear assembly hanging down is the derailleur, which is there to move the chain back and forth between the different gear ratios on the wheel hub.--Aspro (talk) 18:48, 18 March 2012 (UTC)

As always, one can usually consult a Wikipedia article on this very subject and we do indeed have one: Derailleur gears.--Aspro (talk) 18:52, 18 March 2012 (UTC)

The question is, why such a large triangle? The last picture I ended up drawing looks fixed-gear; obviously you would need different amounts of chain to connect different sized gears. But the picture I showed seems to show that the angle (the angle of the triangle corner that is closest to the right/front of the bike) is much larger than necessary. Does this have some benefit? 79.122.101.84 (talk) 19:00, 18 March 2012 (UTC)

The gears have all the same tooth pitch but different 'diameters' . With many gears, one not only has the problem of needing the angle of the chain to be kept as near perpendicular to the wheel hub axial but also take up the slack as it moves to smaller diameter gears. A slack chain is liable to jump off the sprockets. The more slack to be taken up the longer the derailleur arm.--Aspro (talk) 19:13, 18 March 2012 (UTC)

Even good bikes (like mine) with internal hub gearing often have a "derailleur", or at least the cage. The idea here is to take up the extra slack the chain develops as it slowly wears out, so it won't slip or jump of. --Stephan Schulz (talk) 23:57, 18 March 2012 (UTC)

Why such a large triangle? we have an article section for that Fifelfoo (talk) 03:06, 19 March 2012 (UTC)

Hey, thanks! The article was too technical for me to digest when you first linked it, but linking the section, I think I understand. It wasn't what I expected. (I expected an answer that would show that for some reason it's better for the chain to come up at closer to vertical as it makes it's way up the back gear and toward the front pedal: hence a larger triangle gets it closer to that. (it's taken up at an angle closer to vertical, not completely horizontal). Alternately, I thought the angle might have fed the chain better due to some other consideratio, like this design is more immune to a twig etc getting stuck in there, I don't know exactly. Anyway thanks for clearing it up! It seems the answer is almost 100% just about the "slack" that is represented by the amount of chain that's needed to connect the two smallest and the two largest possible gears. We can mark this resolved. --80.99.254.208 (talk) 09:29, 19 March 2012 (UTC)

Quite so. As the article mentions, if you have two rings in front (unlike the bike in your picture, which has three), there is less "slack" that needs to be handled, and so the "derailleur" does not need to be as big (compare).--Itinerant1 (talk) 23:53, 19 March 2012 (UTC)

Gynandromorphs and intersex

can we call a gynandromorph a "partial intersexed creature" ?. thanks. 109.64.44.20 (talk) 18:42, 18 March 2012 (UTC)

See Intersex#"True_hermaphroditism". Note, however, that there is a certain amount of room for play in these definitions; conceivably, I can picture a case of something/someone who is a gynandromorph in the sense that, oh, the Y chromosome was lost in the skin of his left hand, so that tissue is XO female, but I wouldn't call him an intersex. Wnt (talk) 19:20, 18 March 2012 (UTC)

looking for a book in microscopy

i need a book that shows authorized real and pure (UN-edited) Photographs of atoms (via scanning tunneling microscope for example) and even such photos ("captures") of molecules. if the book contains photographs of cells, proteins and all other "family members", than it will be blessed. much thanks guys. 109.64.44.20 (talk) 18:56, 18 March 2012 (UTC)

Are you looking for a textbook on scientific microscopy, or for a coffee-table book with attractive microphotographs? 87.113.82.247 (talk) 19:08, 18 March 2012 (UTC)

By "authorized" do you mean "public domain" or "copyleft", etc., or something else? You might try PubMed Central and/or ArXiv for papers instead of looking for a whole book... Wnt (talk) 19:46, 18 March 2012 (UTC)

Here's an arXiv paper with STM pictures of graphene, with focus on the individual carbon atoms (pages 10-12). Any general biology book will have plenty of photos of cells, but photos of individual proteins will be a lot harder to find though - in fact, I don't think any exist, since proteins have a complex non-cystalline 3D structure which can't be scanned with current microscopes (strictly speaking, none of the pictures are photographs, since light is far too imprecise to take images on the scale of individual atoms. Scanning tunnelling microscopes work by basically moving a very fine needle over the object being imaged, using the movement of electrons from the molecule to the needle to work out the structure of the molecule). Hope this helps. Smurrayinchester 21:39, 18 March 2012 (UTC)

Ah, here's a paper in Nature which seems to have STM images of proteins. Here's an atomic force microscopy image of part of a protein too (I know AFM can indirectly measure proteins, but I didn't realise it could make direct images too). Smurrayinchester 21:46, 18 March 2012 (UTC)

Hi. i am the asker, well, indeed, i need a "coffe-table" book. in "authorized" i mean that the author worked very hard to legally put the content in his book... :) will download the articels right now. thanks! 81.218.145.251 (talk) 17:47, 19 March 2012 (UTC)

It sounds like you might be after something like this which has images showing both extremes of scale and everything in between (power of ten style). Oh actually, this looks even more what like what you want. SmartSE (talk) 22:09, 19 March 2012 (UTC)

Pentacene also has an image (bigger here) of it from an atomic force microscope which I think is/was one the best atomic images so far. SmartSE (talk) 22:14, 19 March 2012 (UTC)

March 19

Why do energy saving lights (Compact fluorescent lamp) stop working?

Excluding external factors, which could break the lamp physically, what makes it stop working? Does any sort of chemical reaction take place in the gas? — Preceding unsigned comment added by 186.106.190.177 (talk) 00:10, 19 March 2012 (UTC)

The UV arc is sustained by gaseous mercury. This eventually gets absorbed by the phosphorous coating and even the glass tube. Eventually there is not enough. That’s when candles and reed lamps come back into their own – as God intended.. --Aspro (talk) 00:33, 19 March 2012 (UTC)

There are several different ways that a fluorescent bulb or tube may eventually fail. In addition to mercury depletion (which manifests as pink tubes) a number of of other failure modes are listed at fluorescent lamp#End of life. TenOfAllTrades(talk) 00:43, 19 March 2012 (UTC)

The most common failure "symptom" I see is black deposits on the glass at the electrode ends, what is the process there? Roger (talk) 10:34, 19 March 2012 (UTC)

It's in the article section that I linked...check the section about sputtering of the emission mix. TenOfAllTrades(talk) 15:16, 19 March 2012 (UTC)

For CFL's it's more likely the electronic ballast that fails: From reference 63 of the Compact fluorescent lamp article:

• Ontario’s Electrical Safety Authority will issue a warning later this week to notify users of the unexpected way compact flourescent light bulbs expire at the end of their long lifespan. Ted Olchena, a provincial code engineer with the authority said he plans to post the warning on its website. The bulbs come to an end by charring around the base, producing smoke and emitting a bad smell. That has scared some homeowners into calling fire departments, he said. But there have been no reports of fires resulting from flourescent bulbs in Ontario, Olchena said. The upcoming advisory will explain that this is a normal way for those energy­efficient bulbs, (which can last up to 10,000 hours) die.

84.197.178.75 (talk) 16:34, 19 March 2012 (UTC)

Arecibo message detection distance

How far away could the Arecibo message possibly be detected? Bubba73 ^{You talkin' to me?} 01:16, 19 March 2012 (UTC)

In the best case scenario, the Arecibo message is received at another planet while that planet has its own Arecibo-sized dish pointed directly at Earth. In this case, even a pessimistic estimate gives the Arecibo a detectable range of 10,000 light years [7]. In that same page, it is noted that Frank Drake claims the technology exists to boost this range ten-fold. It's hard to imaging, however, that we'd manage to land the message right on an equivalent detector. I recall seeing a calculation (but I can't recall where), that a modern radio receiver without a directional dish like Arecibo would detect the message from ~400 light years at most. A non-directional emitter and a non-directional detector would have a drastically reduced range, and with modern equipment (I'm told), you may have trouble communicating with Alpha Centauri. Someguy1221 (talk) 04:09, 19 March 2012 (UTC)

Polyethylene II

In the previous question, it was established that both cyclobutane and but-2-ene are possible dimers of polyethylene.

Which one has the lowest ground state?

What are the end groups of longer polyethylene polymers - what is the identity of the icosamer?

Plasmic Physics (talk) 02:09, 19 March 2012 (UTC)

Because all 3 substances (cyclobutane, (Z)-2-butene and (E)-2-butene) are gases under standard conditions, the standard enthalpies of formation should answer your question. According to the NIST Chemistry Webbook, it is -10.8±1.0 kJ/mol for (E)-2-butene and -7.7±1.3 kJ/mol for (Z)-2-butene. According to this, the standard enthalpy of formation of cyclobutane is +53 kJ/mol, so (E)-2-butene should have the lowest ground state. Icek (talk) 12:12, 19 March 2012 (UTC)

Seems useful to link your previous question. Here it is. Note carefully that I never said "2-butene" was necessarily the isomer. One of the neat tricks of catalysts is that they don't reduce the activation energy every reaction you can imagine, therefore the result is not strictly "most stable of all isomers you can imagine" (as if it were a free-for-all equilibrium ruled by LeChatelier). DMacks (talk) 04:40, 20 March 2012 (UTC)

OK. I'm asking these questions to find the habit of polyethylene polymers — what an individual molecule looks like. Plasmic Physics (talk) 00:44, 21 March 2012 (UTC)

LED lamp

I got an LED lamp today to replace a Compact fluorescent lamp. The quality of light is poor and it gets very hot. Why does it get hot? It is LED and every other LED I've ever seen never got hot. — Preceding unsigned comment added by 98.145.71.230 (talk) 06:14, 19 March 2012 (UTC)

It's unclear to me what other LEDs you've (ever) seen. All LEDs generate heat. It just depends on the amount. I don't know the number or type of LEDs on your light. But if it's intended to replace a compact fluorescent lamp then this is probably at least 8W in total. This isn't comparable to a single 5mm LED, not even say a 5050 LED. Even a 1W power LED is potentially an order of magnitude less (although if you've ever dealt with even a 1W LED at close to maximum rated current I'm sure you'll know LEDs do generate heat). If you have LED/s using a large amount of power in a small volume the heat becomes more obvious (a much more difficult to deal with). Also as mentioned in our LED article, LEDs exhibit droop meaning as the current through the LED increases the efficiency goes down, i.e. percentage of heat to useful light goes up. Dealing with heat output is in fact one of the big issues when designing bulb replacement LEDs, unlike with incandescents and to a lesser extent CFLs, LEDs really don't like heat, efficiency goes down (since current is generally fixed this means the light gets less bright) and LED lifespan will also decrease significantly if it's hot for a long time. It's easy to design for heatsinking requirements in purposely designed fixtures although with high power LEDs heat is always something you have to deal with in some way. (E.g. if you're dealing with the raw emitter you can easily kill the LED if you don't attach it to a heatsink.)

Using a large number of efficient power LEDs like the Cree XM-L at a low current would improve efficiency (although you also have to consider driver efficiency) but this significantly raises cost and may make design more difficult particularly if you need high surface brightness. And many manufacturers just use cheap generic Chinese LEDs with unclear efficiency and poor/inaccurate CCT binning and poor CCT rather then those from Nichia or Cree or other Japanese and American manufacturers who have high efficient LEDs generally with good binning etc. (Of course using cheaper Chinese LEDs may be better if you do get decent efficiency and you can afford to use more so don't need to drive them so hard.) Also LEDs are more efficient at high correlated colour temperatures whereas many people in the Western world prefer lower CCTs more comparable to incandescents, and higher colour rendering index LEDs are also less efficient. So ultimately it's a tradeoff between many factors.

Nil Einne (talk) 07:08, 19 March 2012 (UTC)

If by "very hot" you mean "too hot to touch", then it does sound like something is wrong. Is the lamp inside a fixture ? I believe LED lamps are normally designed to be used without a fixture, to allow cooling. I also agree with Nil that your household current may be too high. The driver is supposed to be able to compensate for that, but it sounds like yours isn't (either by design or defect). So, short answer is that the lamp doesn't seem to work for your application, so I suggest you return it and go with a compact fluorescent bulb. StuRat (talk) 07:18, 19 March 2012 (UTC)

Here's the relevant section from our article:

A single LED is a low-voltage solid state device and cannot be directly operated on standard high-voltage AC power without circuitry to control the voltage applied and the current flow through the lamp. In principle a series diode and resistor could be used to control the voltage polarity and to limit the current, but this would be very inefficient since most of the applied power would be dissipated by the resistor. A series string of LEDs would minimize dropped-voltage losses, but one LED failure would extinguish the whole string. Paralleled strings increase reliability by providing redundancy. In practice, three or more strings are usually used.

Another section talks about the use of a rectifier to convert A/C to DC. Either you have a low quality LED lamp that's using a resistor, or the heat is coming from the rectifier. In either case, it's just no good for your application. If you're dead set on going with LEDs, you might try hooking up a dimmer switch, so you can reduce the excess voltage and current that way. StuRat (talk) 07:31, 19 March 2012 (UTC)

There's a lot of confusing info above. The 'household current' has nothing to do with it being too high (the statement doesn't actually make sense) and I never suggested it did. If the light is very poorly designed, it may be designed for 220V and if the OP's voltage is 240V this won't work so well but there's no real reason to think this is the problem. It's fairly unlikely in a LED lamp replacement (for starters the only way you could use a resistor is if the lamp had a very large number of LEDs in series), most do use buck drivers. Far more likely if the lamp does get too hot it just means whoever designed the lamp didn't heatsink it properly. Also as I explained above, while some of the heat is coming from the driver, a big part of it is in fact coming from the LED. The idea LEDs don't generate heat is false. Nil Einne (talk) 08:40, 19 March 2012 (UTC)

Nobody said that. They should generate some heat, yes, but far less than an incandescent light, due to the much higher efficiency. Therefore, even an LED lamp without a heatsink shouldn't get as hot as an incandescent. From the OP's words "very hot", it sounds like it is getting that hot, so something is defective. Regarding your statement that "it may be designed for 220V and if the OP's voltage is 240V this won't work so well but there's no real reason to think this is the problem", why isn't the excess heat a reason to suspect this ? StuRat (talk) 08:50, 19 March 2012 (UTC)

I agree with Nil Einne. Competent designers of ANY electronic equipment design it to cope with reasonably expected input voltage ranges. For sale in countries variously noted as 220V/230V/240V, the recommended upper design limit is 254V. There's no reason for a LED light design engineer not to go for the same 254V limit. Leds dissipate power so naturally they get hot, not fogetting energy losses in the power convertor cicuit. High power LEDs dissipate a lot of power in a very small space, so, naturally, if not adequately heatsinked, they will get very hot. Keit121.215.133.147 (talk) 12:49, 19 March 2012 (UTC)

Any LED lamp designed to fit a standard incandescent fixture should be properly heatsinked and shouldn't be producing poor quality light. It sounds like something is not working as intended, or the bulb doesn't fit the lighting needs of the poster. The fact that a competently designed bulb should work properly doesn't really tell us anything about whether this bulb is working properly. Rckrone (talk) 14:59, 19 March 2012 (UTC)

Note that 'poor quality light' was undefined. As I stated in my first reply, a lot of people in the Western world appear to prefer warm white lamps similar to incandescents but it's not a universal preference so there's no reason why someone shouldn't produce a cool white LED lamp. If the problem is colour temperature then the fact the OP doesn't like it doesn't tell us the bulb isn't properly designed. If the problem is poor CRI, again since it gives higher efficiency and since some people may not feel the need for high CRI, it seems to me there's no reason why a designer needs to only use higher CRI LEDs. And again if the OP made a poor choice in CRI it's not the fault of the designer. This is particularly true if these factors were part of the product packaging, documentation or advertising. If the LED has a fairly unusual tint, as can be particular problem with cheap Chinese LEDs, then you can perhaps argue it was a poor design choice. Nil Einne (talk) 15:42, 20 March 2012 (UTC)

I once bought a batch of "cheap" 12 v led lamps for halogen lamp fixtures. The 20 or so leds gave less light than a single 20mA led. There's money to make, and led lamps are easy to produce, in contrast to for example fluorescent lamps. Makes it ideal for businesses specializing in fake merchandise 84.197.178.75 (talk) 15:02, 19 March 2012 (UTC)

Agreed, talking about how it should work is irrelevant, as clearly it's not working as it should. A lot of these are probably made in China, by people who either don't know how to do it right or don't care, with either no regulations or no enforcement of regulations requiring them to do it properly. Considering all the cases of poison in items coming out of China, it should be no surprise that they also make some defective products. As for the retailer, they probably never tested the item, and, even if a substantial number of returns occur, they still might well make a profit if this LED lamp is considerably cheaper for them to buy, from those who don't return it. StuRat (talk) 19:20, 19 March 2012 (UTC)

I question whether we have conclusive evidence the lamp isn't working properly since we have no real idea what the OP means 'gets very hot' and 'quality of light is poor'. It's possible the OP simply has unrealistic expectations and made a poor choice given their personal preference, the details of the light being fully disclosed in the packaging, advertising or website info. It actually wouldn't surprise me if the LED lamp is poorly designed since as I said in my first reply this is a very common problem in the LED replacement lamp world but without more evidence it's just an educated guess. Nil Einne (talk) 15:42, 20 March 2012 (UTC)

Actually an LED lamp can get fairly hot. It probably shouldn't be as hot as an incandecent, but it could easily be too hot too hold for any length of time. This isn't ideal for efficiency or lifespan reasons but it also depends on the LED as some are rated to handle higher temperatures then others. (E.g. the Cree XM-L is rated for a junction temperature of up to 150 degrees C.) Note that one of the reasons for the increased efficiency of LEDs is because they don't produce much light in the infrared unlike with incandescents, so just looking at the increased efficiency and saying it shouldn't get so hot is misleading. And how hot the light feels also depends a lot on various factors too, like where the heat is concentrated and whether your exposed to it. E.g. halogens tend to be more efficient then normal incandescents but try touch an exposed halogen and you will likely burn yourself (and break the lamp). While you can burn yourself on incandescents, it's far less likely if you're careful. (Halogens of course are designed to get hot.)

And an LED lamp intended for a compact fluourescent lamp replacement without any heatsinking will either be so dim to be useless or heat up very quickly and kill itself, so in that respect you're correct it won't get hot if you leave it for long enough. (Note I never said 'no heatsinking' I just said insufficient.) To be blunt, it sounds like you have no real experience with high output LEDs and don't really appreciate how much heat they can produce (again let's ignore the driver circuitry). I'm not saying this is unusual, until I myself had experience, I didn't really appreciate this either but it does mean you should be careful when providing advice.

P.S. I realised some of my earlier statements may have been misleading. Although high CRI LEDs are less efficient, it doesn't mean they generate a substanially greater amount of heat. One of the reasons for the lower efficiency is undoutedly because of the different wavelength profile needed for higher CRI which results in a light with a lower apparent brightness.

P.P.S. There's no reason to think it's the problem because the chance someone would design an LED lamp in a way that it will do that is slim. As I've said, if it's not designed to accept 240V, the most likely thing is it will die when you try to use 240V with it. And there's no reason to think it wasn't simply insufficient heatsinking or poor design in general, which is a far more common problem in the LED replacement lamp world.

P.P.S. Just to be clear, I don't disagree with APL that one of the common flaws in LED replacement lamps is poor driver circuitry, which may get very hot. However one of the flaws in design is the electronics themselves aren't heatsinked nor connected to the LED heatsinking (and thermal transfer through the circuit board is usually limited). So usually the driver circuitry may get very hot but it won't affect the LED or heatsink temperature that much. Note that even though electronic design may be poor and get hot, it doesn't mean it's using a linear regulator or resistor. Vvery likely it is using a buck driver, just a poorly designed one.

Nil Einne (talk) 15:25, 20 March 2012 (UTC)

I've noticed that some of the cheap no-name brand of LED bulbs have cheap ancillary electronics (Primarily a rectifier, I assume?) that overheat like crazy and eventually burn themselves out. Which is too bad because the LEDs themselves run cool and will last for a very long time, it seems like a shame to connect them to a circuit board that's perpetually on the verge of setting itself on fire. APL (talk) 11:45, 20 March 2012 (UTC)

Questions for the OP (so we never buy this product):

1) Where was this product manufactured ?

2) What is the brand name ? StuRat (talk) 19:23, 19 March 2012 (UTC)

OT but if you want an LED replacement lamp which really doesn't get hot, you could try something made using [8] ;-) Of course given that we're talking about LEDs using picowatts, you'll have a very, very, very, very dim light even if you use 1000 of them. Nil Einne (talk) 16:00, 20 March 2012 (UTC)

We should probably compare the heat generated by LED lamps with that from CFL's, of identical wattage. Since they are both supposed to be about the same efficiency (with LED perhaps a bit better), they should both produce a similar total amount of waste heat. And CFLs I've used (up to 23 watts) only get warm, not too hot to touch, as incandescents of the same luminosity (100 watts) do. StuRat (talk) 21:57, 20 March 2012 (UTC)

LED lighting is an important technology which is likely changing in efficiency, cost, and construction. If someone familiar with the technology ( as several posters here seem to be) would update the article LED lamp, it would be a great benefit to Wikipedia. The article is full of "as of 2010" statements, so reading the article is like, well, reading about something in an old Encyclopedia Britannica. As for the heat buildup causing degradation of light output, why do new LED light fixtures have to imitate olf incandescent light bulbs? Incandescents have by nature a tiny filament, and commonly are behind a much larger diffuser such as a piece of opal glass or ground glass. If an LED light is going to last for years or decades, why not make have an array of LEDs that are spread over an area comparable to the diffuser placed over an incandescent bulb? That way the heat dissipation is less of a problem. Going forward, why would all LED lamps have to screw into an old incandescent lamp socket. rather than being a new fixture, for new construction? It should at least be an option. In the beginning of incandescent bulb use, some were installed in old gas lights, with the wires run through the gas pipe, but we did not insist on maintaining that style of fixture going forward. Edison (talk) 14:56, 21 March 2012 (UTC)

Geomagnetic calculator

Hey!Can anyone please tell me that this calculator,http://wdc.kugi.kyoto-u.ac.jp/igrf/point/index.html , provided north latitude and east longitude , altitude and year , gives geomagnetic field values in ECI or ECEF or in any other frame of reference? Any genuine info? Thanks --111.68.97.146 (talk) 07:09, 19 March 2012 (UTC)

Have your read through their PDF file ? Maybe there's more info in there: [9]. StuRat (talk) 05:03, 20 March 2012 (UTC)

Theoretically, under controlled circumstances, can plants live indefinitely?

Plants, especially trees, can live a very long time (especially when they are not cut). But is it possible, that under certain controlled circumstances (such as in a well-maintained greenery or something, or under a glass structure like I sometimes see in movies), they can live indefinitely? If not, exactly how can they die without natural disasters or animal intervention? Narutolovehinata5 ^tccsdnew 07:24, 19 March 2012 (UTC)

I believe, in theory, yes, some plants can live forever (others have a fixed lifespan). However, in practice, changing conditions in any given area will eventually kill them, especially since they can't evolve to better fit those changing conditions. Since the ice age cycle is on the order of tens of thousands of years, that may set the practical limit. StuRat (talk) 07:39, 19 March 2012 (UTC)

With technological intervention anything possible under the laws of physics is not off limit. You could have surgeons replace parts of the tree as they wear out using cloned parts. You can strengthen part of it with bionic components. Genetic errors can be undone if you keep a record of the original genome. You could mount the whole tree in side a artificial environment that will control environmental conditions to keep them constantly favorable, and mount the whole thing on rocket engines so that the tree can escape the Earth in the event of an impending asteroid impact. You may even wish to move the tree out side of the galaxy to escape gamma ray bursts etc. But left to its own without this help it will die. SkyMachine ⁽⁺⁺⁾ 08:04, 19 March 2012 (UTC)

See also Lomatia tasmanica (which might have been cloning itself for up to 135,000 years).--Shantavira|^{feed me} 08:22, 19 March 2012 (UTC)

What a sad cycle and waste of potential. At first, it just didn't have any plants to produce with sexually, it ends up cloning itself, and before you know you spend 135,000 years having no one but yourself. Sad but true. --80.99.254.208 (talk) 09:23, 19 March 2012 (UTC)

A relevant (though short) article is indeterminate growth, which is what allows some plants to have no theoretical upper bounds to their life spans. Given clonal growth, we also have to be careful about the notion of 'individual'. For instance, the L. tasmanica link above states that the genetic material is very old, but no one plant lives for that long. You may also be interested in Pando, who has been living in the same place for ~80,000 years. Lastly, even something as common and 'simple' as a dandelion has no fixed limits on longevity. SemanticMantis (talk) 12:52, 19 March 2012 (UTC)

There's a jellyfish that has the potential for immortality, Turritopsis nutricula. See also the tree Pinus longaeva and the article Immortality 84.197.178.75 (talk) 15:13, 19 March 2012 (UTC)

non-metal, non-nitrogenous acidic cations

What would be a counterion that would buffer carbonate's basicity that doesn't contain nitrogen or heavy metals? Are there any water-stable stabilised organic cations? — Preceding unsigned comment added by 74.65.209.218 (talk) 08:27, 19 March 2012 (UTC)

I've used various phosphoranes (analogous to protonated nitrogen) as acids. All sorts of cryptands and crown-ethers can complex your choice of cation (and perhaps protect it from whatever concerns you about metals or nitrogen). Lots of borates exist with various pKa ranges. But what do you really mean by "buffer carbonate's basicity"? Carbonate is a base and carbonate/bicarbonate is already a buffer. If carbonate is too basic, bicarbonate gets you closer to neutral. Seems like you've got some context in mind...don't know what it is so it's hard to recommend something useful. DMacks (talk) 17:22, 20 March 2012 (UTC)

Ramjet

Why don't the expanding gases at the exhaust of a ramjet prevent the flow of air going into the inlet? Surely there is more pressure at the exhaust end than the inlet end; so what stops the gases going back toward the inlet? --92.28.88.124 (talk) 09:47, 19 March 2012 (UTC)

I would think that the forward motion of the engine combined with the rearward motion of the exhaust would keep the exhaust gasses from looping back around to the inlet. Or am I mis-reading your question? Dismas|^(talk) 10:00, 19 March 2012 (UTC)

Im talking about the internal situation.--92.28.88.124 (talk) 10:02, 19 March 2012 (UTC)

In the internal situation, the fuel-air mixture is moving toward the exhaust at a good pace. There is also a lot more open space behind the combustion chamber than in front of it. Both of these combine to produce a net forward thrust. I'm not a rocket scientist, so I cant gild that explanation with fancy words or math. Someguy1221 (talk) 10:06, 19 March 2012 (UTC)

It may be the OP meant by "flow of air going back the inlet" mean internal backflow and not an external loop around. I'm not a ramjet expert either, but I think you'll find that the answer lies in the physics of flame propagation. More space behind the combustion chamber compared to that in front is not the crucial factor in ramjet operation.

First, fuel can be arranged to squirt into the combustion chamber in the direction facing the exhaust. As the fuel moves toward the rear it get progressively burnt, resulting in ever increasing gas temperature and ever increasing gas velocity as seen moving toward the rear orrifice. Any tendency for flame to propagate forawards should be inhibited by the incomming relatively cold air. Picturing a ramjet side-on, if the aircraft is travelling at a certain speed, that will be the airspeed just in fron of the intake. As the air moves towards the combustion area, the air velocity drops due mainly to compression, but also due to friction. At the point where the fuel is injected the velocity is minimum. Progressively combining chemically with the fuel, air velocity progressively increases again reaching a value at the exhaust nozzle significantly greater that the initial intake velocity and producing a large forward reaction force driving the whole thing forward. This is not realy much different to a bunsen burner. A bunsen burner burning will push down a bit harder than just its weight, but of course not enough to be significant.

Ratbone120.145.147.138 (talk) 12:36, 19 March 2012 (UTC)

Think of it this way: if there were "reversed" flow in the engine, the combustion could not continue indefinitely. So, the flow reversal would self-limit; the combustion would cease; the overpressure would dissipate; and the forward flow would resume. Combustion could then restart. If the engine is poorly designed, this could result in a combustion oscillation; the absolute worst-case scenario would be a complete flow-reversal with hot exhaust-gases impinging on forward components of the engine; but in less severe cases, you'll just see high-frequency variations in the chamber pressure, turbine speed, and so on (in a ramjet, there's not a lot to "see," but you'll have poor below-spec I_sp and pressure oscillation). You may also see another symptom of this: "chuffing," or incomplete burning, resulting in gasps of sooty smoke blowing out of the back of the engine. Properly-operated, properly designed engines do not do this. You can see chuffing in a solid-rocket booster in this amazing composite video of the Space Shuttle Solid Rocket Boosters. (It should be noted, solid rockets are not ramjets, but the point is that a rocket engine "out-of-spec" will have reversed flow). What is occuring at ~5m40s into the video is that after the engine has already extinguished, and is falling back toward Earth's surface, atmospheric pressure is rising, so oxygen re-enters the combustion chamber, re-igniting the last remnants of the fuel. When this combusts, it overpressures, and blows the atmospheric oxygen back out, extinguishing the SRB again, decreasing the pressure in the combustion bore; ... allowing atmospheric oxygen back in, reigniting... hence "chuffing" or combustion oscillation. Again, let me reiterate: this is "out-of-spec" operation, in this case occurring long after the SRB has separated and completed its mission. Well-designed motors (ramjet, SRB, or otherwise) do not exhibit reversed flow during normal operation. Nimur (talk) 17:27, 19 March 2012 (UTC)

Also, on the specific subject of ramjets, don't forget the immense stagnation pressure on the forward air. The entire principle of a ramjet is based on balancing static and combustion pressures, which is why they work in sparse air at high mach numbers. Nimur (talk) 17:34, 19 March 2012 (UTC)

There is an exception, A valveless pulse jet is based on reversal of flow, and oscillation. 84.197.178.75 (talk) 17:51, 19 March 2012 (UTC)

Valid point... pulse jets are a sort of exception to almost all of my earlier explanation. But, at the risk of angering the pulse-jet fans, as far as I'm concerned, pulse-jets are "hypothetical." Lemme know next time you see one flying! Nimur (talk) 18:00, 19 March 2012 (UTC)

So it seems that Nimur is saying it is the stagnation pressure that prevents the combustion pressure pushing too far back (ie creating a balance). The ramjet article glosses over this point and i think the actual operation needs expanding much much further. Im not qualified to do it.--92.25.96.193 (talk) 19:04, 19 March 2012 (UTC)

The British saw lots of them in 1944 ;-). Nice videos on youtube of model airplanes with pulsejet engines. Very fast, very loud... 84.197.178.75 (talk) 18:22, 19 March 2012 (UTC)

Just in case you didn't get 84.197's point, see V-1 flying bomb which was powered by an Argus As 014 pulse jet. Over 8,000 were sent towards London in 1944. One threw my grandmother's Victorian dining table through a partition wall, then some windows and out into the street, so I doubt that it's really "hypothetical". We still have the table. Alansplodge (talk) 20:40, 19 March 2012 (UTC)

By all means, I'm familiar with the V-1, and I'm familiar with its characterization as a pulse-jet. I would prefer to call it a "poorly calibrated, primitive hybrid liquid-fuel/atmospheric-oxygen rocket." At this point we're mincing terms, though. It's regrettable about the table (is it still intact?), though I'm sure it's a fantastic antique/discussion-piece. Nimur (talk) 20:49, 19 March 2012 (UTC)

Yes, still intact - it's a very solid lump of oak. And you're quite right, you don't see many about these days, thank goodness. Alansplodge (talk) 21:05, 19 March 2012 (UTC)

Ah! make do and mend, that's the spirit. None of this new-fangled fabby-dabby Reduce, Reuse, Recycle. Thincat (talk) 22:09, 19 March 2012 (UTC)

Was this dining table laid at the time? I could be the source (HP obviously) for the rumors that the Nazi's had created flying saucers but then again...--Aspro (talk) 22:31, 19 March 2012 (UTC)

Reinforcing what Ratbone posted. The thrust is the result of accelerating the 'mass' of air passing through. Its reaction and not pressure that is important here because a jet doesn’t 'push' against anything. To put it in context: in the case of a jetboat, it is more efficient when the water is ejected out above the waterline rather than below it. The air coming into a ram is forced to slow down before it enters the combustion chamber and that increases the pressure well above that of the exhaust pressure -which is lower because it accelerates.--Aspro (talk) 22:14, 19 March 2012 (UTC)

Blimey! An apparently "straight" question from someone in LC's neighborhood. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:58, 20 March 2012 (UTC)

Just to sum up and clarify what I and Aspro have said:-

The air at the intake port is at the natural air pressure and temperature and the velocity relative to the engine is the aircraft forward velocity. As the air goes down the intake throat it is progressively compressed - this progressively reduces its velocity and also increases its temperature somewhat. The air velocity is minimum in the throat where the fuel is injected. At the point of injection, the fraction of fuel burnt is zero. As the air moves further towards the rear, the percentage fuel burnt gradually increases. The pressure, meanwhile, must pregressively decrease from its maximum at the point of fuel injection, back to natural atmosphere pressure at the exhaust port. As the fuel is progressivel burnt, towards 100% burnt at the exhaust port, the combustion progressively raises temperature and velocity, such that the the exhaust velocity considerably exceeds the intake velocity. As the pressure is maximum where the fuel is injected, and the flame is directed rearwards, any tendency to burn toward the front is inhibited. The excess air velocity of the exhaust/combustion product preduces a net reaction force driving the whole thing forward. Ratbone58.167.242.221 (talk) 08:47, 20 March 2012 (UTC)

So which part of the engine does the exhaust gases push against to give the vehicle forward momentum?--92.25.96.193 (talk) 17:42, 20 March 2012 (UTC)

That's a good question to ask but difficult to answer simply because it depends on the direction of the 'force vectors' which change throughout the length of the engine and in particular after the compression stage (before the compression stage they are negative) but I imagine that statement doesn't leave you any the wiser. So lets construction a Pons asinorum. If a hot gas is allowed to expand -it cools (bad). Therefore, the gas must be constrained radially so that it accelerates rearward only. All those surfaces that lay towards the perpendicular plane to the rearward axial flow have a higher force vector that points forward (or the push that your looking for). Yet, remember that that that is due to the initial compression. As the exhaust gas accelerates rearwards, its pressure starts to drop leaving behind it high pressure regions (the push – in all ways -it both accelerates and helps to maintain the pressure brought about due to the reduction of velocity of the incoming air and exerts pressure on the walls of the engine). Yet the main sum of the vector forces propels the aircraft forwards. That's also why a ram jet can't produce static thrust. In other words its only by stint of its forward momentum that the intake air can get compressed. The fuel's heat energy then ensure that the compressed air mass wants to expand and the design of the engine ensures that it only has one direction in which to do that. Though, I'm sure there must be an easier way to explain all this. You may have noticed also, that the upper stages engines of heavy transport rockets (Arian etc.) have an extended nozzles. This is so that at the low ambient pressure of the upper atmosphere, some of the radial velocity potential of the expanding exhaust gas a it leaves the throat can be captured as forward thrust. Don't tell me, your next question will be “why then don't we see more ram jet powered aircraft.” --Aspro (talk) 20:38, 20 March 2012 (UTC)

Where does the reaction push back on? I'll see if I can make it simpler. The ramjet article, http://en.wikipedia.org/wiki/Ramjet has diagrams that are more complex than they need to be in order to understand the principle. The simplest ramjet comprises a cylinder, open at both ends, with an internal narrowing in the midle, like a venturi, but it is important to note that the mode of operation is not as a venturi (ie it is not about increasing velocity, it is about increasing pressure) It is the internal narrowing that causes the compression. This compression does of course mean that there is pressure against surfaces forward of, and just at, the point where it is narrowest. This pressure is acting acting against inward sloping surfaces as the narrowest point is approached. - the vector sum of all this distributed force impedes the forward motion of the engine/aircraft. The fuel is injected at the narrowest point, directed rearwards. Combustion causes temperature rise - this means that for the same pressure a larger volume must be provided. So, as the combusting air & fuel procedes toward the exhaust orrifice, an expanding of the tube is provided, so that pressure is back to atmospheric at the exhasut nozzle. Since the temperature after the narrowest point is greater than the temperature before the narrowest point, there is a greater surface area to push on, to accomodate the greater volume required. So, even though the expansion side pressure gradient is a almost a mirror of the compression pressure gradient, the greater engine surface subject to expansion side pressure means a greater total force than the net force on the compression side. Prctical ramjets don't have to have a narrowing of the tube - they can have an co-axial tapered plug, as shown in many drawings. This does not change the principle. Ratbone121.221.30.213 (talk) 02:40, 21 March 2012 (UTC)

additions and corrections update

I recently came across a possible addition to your "Neutrinos" definition. I hope I am doing this correctly. Consider the following artical from March 19, 2012, Lab New Daily: (link) — Preceding unsigned comment added by Drummer1088 (talk • contribs) 18:06, 19 March 2012 (UTC)

Thanks for the link. It is not necessary to copy/paste the entire article here; please see our Wikipedia:Copy-paste guidelines. I have removed the verbatim text of the article you pasted above, per our copyrights policy. I'll read through the article to see if there's anything new that should be added to our article; was there a specific item you felt was important from this article? Nimur (talk) 18:22, 19 March 2012 (UTC)

After review, our main neutrino article, and the more recent Faster-than-light neutrino anomaly, both already include reference to the official OPERA statement from February, 2012, which reflects that the experimental was most probably beset by instrumentation errors. Both articles seem to correctly indicate that the earlier reports of a faster-than-light speed have been debated, and are widely considered to have been in error, though the results are not "completely" discredited. Both articles also correctly indicate that further research by independent labs, including the ICARUS group, are being undertaken. Nimur (talk) 19:06, 19 March 2012 (UTC)

Liposuction to produce biofuel

I asked previously if it was possible to use animal fat to produce biofuel, and the answer was affirmative. So it got me thinking, is it possible for the government to offer free liposuction to fat people in exchange for their fat which could then be turned into biofuel? Is this economically feasible? ScienceApe (talk) 21:59, 19 March 2012 (UTC)

Whilst I'm sure it is feasible, it could never be economically viable - think about how much liposuction costs, compared to how much fat you get. Even with the price of petrol as high as it is here in the UK, it would probably be at least 100 times as expensive to remove that from a person. SmartSE (talk) 22:02, 19 March 2012 (UTC)

(WP:EC, I basically agree with Smartse above) In short, no, it is not economically feasible. The small amount of energy gained from the fat of even a large human is of negligible value compared to large institutional infrastructure and expert labor costs. A more reasonable idea is salvaging used deep fryer oil from restaurants. One such application of this is biodiesel. SemanticMantis (talk) 22:07, 19 March 2012 (UTC)

At a 20% fat to electricity conversion efficiency, 1 pound of fat is approximately equal to 1 kilowatt-hour of electricity, which is worth USD$ 0.10 to 0.15, depending on the exact location. --Itinerant1 (talk) 23:31, 19 March 2012 (UTC)

The medical cost of extracting the fat would indeed make the value of the human fat negligible. The fat, however, is sometimes used on other parts of the person's body (e.g. breast augmentation). Human faeces, on the other hand, might well be a somewhat more viable resource (and have long been used for this purpose in rural areas, I believe) to produce Biogas. 58.111.224.202 (talk) 03:24, 20 March 2012 (UTC)

Note that the Nazis did use human fat as fuel in extermination camps, but it was only economically viable because of how cheaply they got it, without the need for surgery. StuRat (talk) 03:38, 20 March 2012 (UTC)

Do you have a citation for this? It seems like it would have been more trouble than it's worth, besides perhaps a few candles or lamps for novelty's sake. This is especially true when you consider that most people who'd spent any time in those camps did not really have a lot of body fat. APL (talk) 11:36, 20 March 2012 (UTC)

This compilation of graphic testimonies discusses the fuel requirements for cremation in Auschwitz. It notes that some groups of bodies were relatively healthier vs others that were emaciated, and that the healthier ones required less external fuel supply in the crematoria--even though there would be more material needing to be incinerated--due to their own ability to fuel the fire. DMacks (talk) 17:10, 20 March 2012 (UTC)

Yes, one of the defenses the Nazis used at the Nuremberg Trials was to claim that they couldn't have murdered and incinerated the number of people claimed, because the camps didn't requisition enough coal for that. And, indeed, the figures for the amount of coal they used only seemed to be enough to heat the barracks, not to run crematoria. However, once the fuel value of the fat was figured in, in all made sense. Also note that a good portion of the people were sent to the crematoria upon arrival in the camps. Our view is biased, because the only ones we have on film are the few skeleton-like survivors or skeleton-like detainees who died in the last few weeks before liberation. The plump detainees who were killed years earlier were long gone. StuRat (talk) 21:38, 20 March 2012 (UTC)

Wouldn't it have been protein and other components as well (excluding some such as bone and water perhaps)? According to Body fat percentage the average is around 25% (depending on gender, age and other factors) but it seems likely the average there would be significantly lower. [10] suggests the protein content is something like 16%. [11] gives 16.6% for protein and 14.9% for fat. I don't actually know what sort of figures we can expect for holocaust victims, given the atrocious conditions including starvation many likely only had muscle left for fuel. Those who were better off would have had more fat, but I wonder whether the protein was often just as big a contributor to body weight differences. Remembering that even if they had just arrived, very often they would still have been in poor conditions beforehand so I suspect even many of those who had just arrived weren't exactly 'plump' (nor very fit/muscular) even if they weren't the horrificly emancipated victims common in picture. The over double energy density of fat does mean fat may have been a bigger contributor even if body fat percentage was only 10% but I don't know if it's accurate to suggest it was primarily fat that was used as fuel. Nil Einne (talk) 00:15, 21 March 2012 (UTC)

Fat contains 9 kilocalories per gram, while protein only contains 4, so fat provides the majority of the fuel value. I believe almost all of that 4 is used in incinerating the meat itself (specifically, in vaporizing the water contained therein), so there is little or no excess energy provided by protein (unless it was dessicated first). Try lighting a slab of lean meat on fire. It doesn't work. Fat, on the other hand, burns well, once you get it started (anything which acts as a wick helps a lot). StuRat (talk) 02:07, 21 March 2012 (UTC)

But consider that Nazis weren't just rounding up people in the streets and sending them straight to extermination camps. Many (probably most?) victims came there from ghettos like Warsaw ghetto or internment camps like Westerbork transit camp, where they lived for years on extremely restricted food rations.

Even if there were some "plump detainees" on trains to extermination camps, that does not seem adequate to change significantly the amount of needed coal. Modern gas-fired crematoria consume 2000 cubic feet of natural gas per body, which is around 37 kg. Various online sources likewise quote fuel demands of Nazi crematoria at around 30 kg/body.--Itinerant1 (talk) 00:37, 21 March 2012 (UTC)

A bigger problem is that fuel requirement estimates would be normally based on bodies of well-nourished victims in the first place. Cremating bodies of emaciated victims would have required more fuel than average. Saying that not all of them were emaciated does not really help to address the discrepancy. (Which is, by the way, quite large: according to the article linked by DMacks, in order to harmonize data on coal shipments to Auschwitz and conventional Holocaust estimates of the number of prisoners killed there, camp authorities had to be able to manage with 4 kg of coal per body.) --Itinerant1 (talk) 01:46, 21 March 2012 (UTC)

The other major factor is running the crematoria continuously, versus letting them cool off between bodies. The amount of fuel required in the latter case is far greater. The reason is that most of the coal is required up front, to drive off all the water, and then then, later on, the excess energy is released. The difference is therefore whether this heat energy just goes up the chimney, or used to dessicate the next body. StuRat (talk) 02:02, 21 March 2012 (UTC)

But that raises another discrepancy: the article states that it would take 16 tons of coal per day to run all crematoria at Auschwitz if they were operated around-the-clock, on a continuous basis. At that rate, total coal shipments recorded for the period from April to October 1943 (six months) were sufficient to operate crematoria only for about 30 days, even assuming that they didn't use the coal for anything else.--Itinerant1 (talk) 05:42, 21 March 2012 (UTC)

I would guess they only kept one running full-time, and fired up others as the need arose. This would be almost as efficient as keeping them all going continuously. StuRat (talk) 06:37, 21 March 2012 (UTC)

Cecil Adams recently did an article on this : The Straight Dope : Is Excess American Body Fat a Potential Energy Resource?

Hope this helps. APL (talk) 11:33, 20 March 2012 (UTC)

Actually, you can harvest that energy economically, and indeed, with a greater-than-unity gain, if, instead of using liposuction, you simply put the affected people (mumbleincludingmemumble) onto a rational diet. Food calories are very expensive (in energy terms) to produce, so if you let people partially live on their build-in reserves, you do get a large saving in primary energy. And a calorie saves is a calorie gained. Now, about how to make people follow this diet I have no plausible idea... --Stephan Schulz (talk) 18:22, 20 March 2012 (UTC)

One additional factor is that the surgeon performing liposuction will typically extract fat from a limited number of sites in a single procedure, and it is generally considered unsafe to extract more than 5 liters (~10 lbs) of fat at once. A borderline obese person of average height has 30 lbs of excess subcutaneous fat spread under his skin and around 3 lbs of visceral fat inside the abdominal cavity. There are some visible excesses near the abdomen and the hips, but that's only part of total fat. It would be extremely unsafe to remove all excess fat in a single procedure.

One alternative method that could be close to break-even economically is to install stationary bike trainers with power generators in gyms and to hook them up to the grid. It would take a long time to recoup the cost of building and installing the bike trainer. A moderately fit person such as myself might be able to put out 200 watt of useful energy for extended periods of time, producing electricity at the rate of USD$0.03/hour. However, a sufficiently cheap bike trainer that is manned 12 hours a day everyday could pay for itself in several years and begin generating money after that. --Itinerant1 (talk) 20:45, 20 March 2012 (UTC)

March 20

Valerian attracts or repels rats?

Our article Valerian claims that valerian attracts rats, and gives a reference. On the other hand, Eno Raud, Mohaszakállék újabb kalandjai (original title Naksitrallid) shows that the scent of fresh Valerian roots repels rats. Now of course this is a fiction novel so the part about Valerian repelling rats could be just a convenient plot device so that the heroes can keep rats away, but this still seems a strange contradiction. So which one is true? Does Valerian attract or repel rats? Can you find more references? Or maybe I misremember and the novel mentions a different herb used to repel rats? – b_jonas 07:49, 20 March 2012 (UTC)

Asking for clarification: you've got cats in the title and rats in the question. Which is it? I can confirm that valerian attracts some cats, as you can see in cat toys like this one. --TammyMoet (talk) 08:17, 20 March 2012 (UTC)

It also attracts rats, according to the article. Some say it can be planted at the edge of your property to keep them away from the house. 84.197.178.75 (talk) 10:12, 20 March 2012 (UTC)

Sorry, I mean rats. I've fixed the question title. – b_jonas 12:06, 20 March 2012 (UTC)

There is no idea too old or too obvious to patent. The bright side of this is that you can use patent searches to learn about how things were done in ancient times. I present [12]. Wnt (talk) 12:51, 20 March 2012 (UTC)

Why use Valerian. For anyone that has kept rats as pets will know, that they are very cultured creatures. All that a trap needs is a loop tape playing a little of Handel's Water Music to capture their interest, followed by some of Claude Debussy's suite Bergamasque (the de lune bit). That will relax them so much that one can then 'humanly' pick them up by their tail and drop the into the garbage disposal unit.--Aspro (talk) 22:21, 20 March 2012 (UTC)

Or, if you're into visuals, the blender or the microwave. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:49, 20 March 2012 (UTC)

What turn from green to red at the touch of a button?--Aspro (talk) 01:40, 21 March 2012 (UTC)

Aspro: if valerian attracted both cats and rats, it would be an all in one solution: the arriving cats would eat the gathered rats. There's be no need for an adhesive, nor for dumping the rats to the garbage can. You'd only need to change the valerian frequently. (Or is it the other way? Maybe valerian isn't effective as a rat bait at all, no matter how sophisticated traps you use with it, because the cats scare the rats away?) – b_jonas 09:28, 21 March 2012 (UTC)

TNO: major problem with "orbital characteristics"-data

90377 Sedna (edit | talk | history | protect | delete | links | watch | logs | views)

• 90377 Sedna German Wikipedia
• (90377) Sedna Spanish Wikipedia
• (90377) Sedna Italian Wikipedia
• (90377) Sedna French Wikipedia

09:49, 20 March 2012 (UTC): Hello! Having a look at the values of the major orbital characteristics of Sedna given by various language-specific Wikipedias reveals a rather less than awe- and confidence-inspiring chaos of different values. I realize that these stem in part from osculating orbits, different epochs, etc., etc. Correctly interpreting the JPL-Horizon's output isn't easy, either (a guideline for that might be useful, by the way). Anyway, the current state of things does not inspire trust in Wikipedia's reliability. Is there no way to consistently choose a set of values people can rely on and reasonably reflect reality (no one will use Wikipedia-data to calculate actual orbits)? The current orbit of a TNOs does have a specific orbital period after all, a specific aphelion, a specific perihelion, etc. (even if the location of the last aphelion was not the same one as the next one will be). What do you think? The sample data for Sedna (harvested on March 22, 2012), illustrating the problem:

Sedna: orbital values in various Wikipedias

Data	en.wiki	de.wiki	fr.wiki	it.wiki	es.wiki
e	0,8527	0,8478	0,85	0,855	0,857
a	518,57	501,2	505,754	525,606	n/a
Perihelion	76,361	76,31	76,057	76,156	76
Aphelion	937	926	935,451	975,056	850
Orb. Period	11400	12059,06	10500 to 12000	12050,32	10500

This is the English Wikipedia and we have no control over, or even collaboration with, other language projects. We can only answer for what is in our own article. The five articles you have looked at all have very different quality status. The en article is FA status (the highest) and will have been thoroughly reviewed and can be expected to be well sourced. The next highest is the de article with GA status. The it and fr articles are only B Class and the sp article is unclassified and appears to be entirely unsourced as far as I can tell.

The orbital elements in our article are sourced to the JPL Small Body Database Browser which I would have thought is a reliable source. However, looking on that page it seems to have been recently updated (14 March) and now has data that disagrees with all the articles; for instance e=0.8590486217687489. SpinningSpark 12:52, 20 March 2012 (UTC)

I think what's going on here is that a single source keeps updating the data as it gets more results, and it gets updated in the Wikipedias at random times, either directly or (for smaller Wikipedias) perhaps by copying from this article. The German infobox repeatedly changed, for example, especially around 2006. Wnt (talk) 12:59, 20 March 2012 (UTC)

The first report in 2004, based on data from 2001 (precovery) to 2003, gave error margins for their calculations. For example the perihelion was most likely to be within about 7 AU of the 76 AU perihelion estimate. When I see an orbit fit (www.boulder.swri.edu/~buie/kbo/astrom/90377.html) giving 76.13229114 as value (based on 1990 to 2009 data), and all error terms equal to zero, I'm wondering about standards in astronomy...

(BTW: Minute of arc gives wrong value for second of arc in lede, third sentence, missing a factor 60) 84.197.178.75 (talk) 14:03, 20 March 2012 (UTC)

Audio oscillators

What is the main cuase of harmonic distortion in audio oscillators? I have a theory that it is the ampliude stabilising system that cuases this and that it is predominantly second harmonic due to the full wave rectifiaction of the the signal in the control circuit. Would i be correct, and can anyone shed any light on design of ultra low distortion oscillators (say -100 dBc)? Thanks --92.25.96.193 (talk) 14:50, 20 March 2012 (UTC)

It's a bit useless to discuss the root-cause of distortion in a circuit without specifying the circuit. There are thousands of designs for audio amplifiers, audio-frequency oscillators, low-noise amplifiers, and power amplifiers. There are thousands of components that you can use to build them. Each design, and each implementation thereof, will have its own limitations; so if you want to start talking about 100dB of dynamic range, you need to more precisely describe the circuit you are using. Have you considered starting with a basic text on amplifier design? Do you need help locating such a text? Nimur (talk) 18:21, 20 March 2012 (UTC)

I think he means sinus wave oscillators. These have to have gain at small signals > 1 but ned to be amplitude limited. When this happens by clipping, there's much distortion. Clever way to solve this was the Wien bridge oscillator that uses an incandescent lamp as PTC thermistor. 84.197.178.75 (talk) 18:50, 20 March 2012 (UTC)

This might help: http://www.moorepage.net/RC.html looks at the circuits used in some commercial designs. 84.197.178.75 (talk) 19:02, 20 March 2012 (UTC)

Oscillators such as Wein bridge that utilise a temperature sensitive resistance (thermistor or tungsten filament) to vary feedback and control amplitude are indeed subject to 2nd harmonic distortion. The temperature sensitive resistance tends to be at a slightly different temperature during the + half cycle compared to the - half, leading to 2nd harmonic distortion, worsening at low frequencies.

Oscillators using a semiconductor variable resistance (eg FET) to control amplitude also have predominately 2nd harmonic distortion as the control FET or transistor also inherently has a resistance proportional to the oscillation voltage across it. In theory this can be cancelled out by injecting a fraction of the oscillation voltage onto the gate in addition to the feedback control voltage. However it is virtually impossible to get the cancellation exactly right.

The amplifier used to make the oscillator distorts of course like any amplifier. As an amplifier in an oscillator will normally be class A, the distortion will again be mainly 2nd harmonic.

Oscillators based on the tranditional Wien configuration have an additional distortion mode. Both the + and - inputs to the amplifier together swing at signal frequency a significant voltage above and below earth. So amplifier common mode distortion adds to the problem. The differential input stage of such amplifiers adds odd-order harmonic distortion.

Oscillators based on state-variable circuits use only inverting input amplifier stages, thus eliminating common mode distortion, and eliminating the impossible-to-cancel odd-order distortion of differential inputs. It amuses me to see just about every text on audio oscillators devote much sapce to wein bridge oscillators, which should have been consigned to the rubish bin decades ago, for this reason.

If a fixed frequency not too low is required, an LC tuned circuit approach can be used. Since the output can be taken frm the LC tank, and not from the amplifer output, any amplifier distortion (which should already be at least 40 dB down, is attentuated by the LC tank, and such attenuation exceeding 60 dB or more is quite easy. Things like LCR bridges were often built with LC oscillators, as a very simple one-transistor circuit built cheap as chips could reliably give lower distortion than carefully built wein oscillators requiring 4 or more transistors.

With state variable oscillators, outputs are available in-phase and out-of-phase. These can be summed with an opamp. The fundamental will cancel, leaving the even order distortion. This can be injected back in to cancel the even order distortion at the user output. Some extremely low distortion oscillators have been made with this technique.

By using an integrator circuit, an output 90 degrees out of phase is available. The zero crossings of this can be used to synchnonously gate the peaks of the main output into a sampel & hold circuit, giving a DC voltage directly proportional to output. If the frequency determining circuit has a high Q, it can be driven by a shaped square wave, derived from the DC voltage from the sample and hold. In this way the 2nd harmonic ditortion from temperature dependedent amplitude control is completely eliminated. However the action of the sample and hold means that energy at sub-harmonics may be present. Never the less, circuits of oscillators with distortion 120 dB down have been built with this technique. The magazine Wireless World / Electronics World has covered all these techniques over recent years.

Keit124.182.163.120 (talk) 03:23, 21 March 2012 (UTC)

Why does biodiesel have less energy density than regular diesel?

So according to this, http://en.wikipedia.org/wiki/Energy_content_of_biofuel

Biodiesel has really good energy density, but it's still less than regular diesel. Why is this? Isn't petroleum derived from ancient biomass like algae that has been compressed over millions of years? Is the compression a factor? If we compress biodiesel or the oil it's derived from, can we increase the energy density of biodiesel and other derived biofuels? ScienceApe (talk) 16:23, 20 March 2012 (UTC)

Crude-oil components "come from" ancient biomass, but it's a lot different than just various chemicals leached out of the dead stuff...there is a whole slew of chemistry that occurs to transform it into crude oil (see Petroleum#Formation). Diesel fuel#Sources notes that the chemicals in the petroleum-based diesel fuel are simple alkanes and related hydrocarbons, whereas biodiesel is esters (contains oxygen) and often has alkenes in addition to alkanes on the chains. DMacks (talk) 16:43, 20 March 2012 (UTC)

In order to have high energy density, what kind of molecular structures should it be most abundant in? ScienceApe (talk) 18:05, 20 March 2012 (UTC)

There are several ways to measureenergy density, either per unit of mass, or per unit of volume (see tables); if you want it more specific, see heat of combustion, the values in MJ/L. You see for example that cyclopentane has a considerably higher value than pentane, which is still higher than isopentane. But looking at MJ/kg, cyclopentane has the lowest energy density. All these figures don't automatically give you the best fuel since efficiency of a motor depends upon the temperature, and some fuels burn hotter than others; the reaction products are CO2 and H20 mostly, with water vapor containing considerable amounts of energy that you don't use. 84.197.178.75 (talk) 19:41, 20 March 2012 (UTC)

That's not really what I'm asking, I'm asking what chemical structures make a substance have higher energy density (energy per unit of volume). DMacks said that petroleum diesel fuel has alkanes while biodiesel has esters and alkenes. If a substance is abundant in alkanes, does its energy density increase? ScienceApe (talk) 00:21, 21 March 2012 (UTC)

From the different heating values I'd say that for a given number of carbon atoms, energy density drops with the number of hydrogens. Aromatics seem to have higher energy density and alkynes > alkenes > alkanes. Oxygen containing molecules (esters, alcohols) will have lower energy. highly strained molules will have higher energy, but does that also influence the density of the liquid? I don't think there are simple rules to calculate energy density per volume of molecules. 84.197.178.75 (talk) 13:35, 21 March 2012 (UTC)

Has the Sun met blinding stars in its travels?

It is amazing to read in Sirius that in 60,000 years it will brighten noticeably, and in a mere 250,000 years, it will no longer be the brightest star in the sky. These are numbers smaller than the lifespan even of ours, one of the most recent of species. This makes me wonder: has a star such as Rigel, not 25 but rather 96,000 times brighter than the Sun, ever passed by our star during its rounds of the Milky Way? Bear in mind that Sirius has magnitude -1.46 at 8.6 ly, the full Moon -12.74; five orders of magnitude = a 100-fold difference. So Rigel, 3840 times brighter than Sirius, would appear as bright as the full Moon at a distance of 3.28 light-years - but all concentrated into a single point of light. That is (I think) quite unlikely, but it illustrates that life on this planet might have had to deal with unusual conditions - conditions where for whole seasons of the year night would not have been absolute.

How much is now known of the Sun's travels, of its recent neighbors among the stars? How far back can the interactions of local stars be modeled with any confidence?

Oh, and Solar neighborhood is a redlink. Anyone want to get it started? Wnt (talk) 18:19, 20 March 2012 (UTC)

Stellar neighborhood redirects to List of nearest stars. Would you be happy with just another redirect? Jason Quinn (talk) 18:51, 20 March 2012 (UTC)

Hmmm, that list article looks like it is overflowing its bounds - notably List of nearest stars#Future and past is just the sort of thing I was curious about (though I wish there were a video...). It is incomplete, though, as evidenced that checking its entry for Gliese 710 I arrived at Algol, not on that list, which according to its article was a -2.5 magnitude star 7 million years ago. (I doubt it was an eclipsing binary back then, but if it were it might have really mindfreaked our ancestors. ;) )

Judging by the point that Gliese and Algol are now over 50 light-years away, I can see that predicting the close calls past 10 million years may be quite difficult. Still, it might be possible to do on a purely statistical basis...

To give an example of what I mean by "statistical basis", the list gives 5 stars expected to pass within 4 light-years in the next 50,000 years. According to stellar classification, 0.13% of all main sequence stars are class B - 25-30,000 times brighter than the Sun. Taking 50,000/5*0.0013 gives one class B star passing within 4 light years every 7 million years ... well, shoot, that's just balderdash! Some nitpicky little thing about independent observations must apply. I think it's time to let the king's men have another crack at this egg... Wnt (talk) 19:21, 20 March 2012 (UTC)

While it doesn't directly address the question, the Local Bubble is of interest, as is Geminga, which may or may not be responsible for the bubble: both articles give some insight into relatively recent history in this part of the galaxy. Acroterion (talk) 03:13, 21 March 2012 (UTC)

March 21

who is closer phylo-genetically to the human?

Chimps or Bonobos?, and why it's in dispute?, thanks. 109.64.44.20 (talk) 02:35, 21 March 2012 (UTC)

The two Chimpanzee species last share a common ancestor with Homo sapiens around four to six milion years ago, while the last common ancestor of Pan troglodytes and Pan paniscus lived less than a million years ago - they are equally closely related to us. AndyTheGrump (talk) 02:45, 21 March 2012 (UTC)

While AndyTheGrump is scrupulously correct, from a scientific perspective, I can see where the question itself seems important from a psychological/philosophical standpoint. Bonobos like to fuck and cuddle, Chimps like to fight and kill, and as a human, it seems important to us to know what it is in our "nature" to be more like: The loving Bonobo or the violent Chimp. Andy is, of course, correct that we are equally related to both of them; but it doesn't obviate the question, philosophically, which aspect of human nature (the good or the evil, the loving or the hateful, if you will) is "closer" to our true nature. Unfortunately, cladistically that question cannot be answered, for as Andy notes, they're both as related to us as the other. Even if they weren't, however, it still wouldn't answer the question. Closest common ancestor is not going to give any clear indication on behavioral patterns and evolution. --Jayron32 03:21, 21 March 2012 (UTC)

Eh? I love to go on a bit of a rant as much as the next guy, but the question was specifically about Phylogenetics, not philosophy or human nature. I'm not sure where you inferred that from. As to the question, I think using the human family tree analogy is the best way to answer these kinds of questions (along with the kind of answer Andy gave) because we are all so familiar with those. So, you are essentially asking, if your uncle has two kids, your cousins. They are closely related to eachother (they are siblings), but which is more closely related to you? The answer is neither, they are both your 1st cousins. More accurately, the siblings in this example should probably be cousins, but that makes the tree one more level deep which gets very complicated to explain without a diagram. Vespine (talk) 04:49, 21 March 2012 (UTC)

Well, I think Jayron is getting at the issue of what is the ancestral behavior of our ancestors. If you go back to that last common ancestor 4-6 million years ago, did that ancestor act more like a Chimp, a bonobo, a human, or something else entirely? Which animal are we more like, and which animal should we be more like, based on our genetics? With comparative genomics you can infer which mutations occurred in which ancestors and when, but we're left in the dark when it comes to complex animal behaviors, unless they can be causally linked to genes. Someguy1221 (talk) 05:04, 21 March 2012 (UTC)

I think we'd need to inject a little scepticism into Jayron's 'fuck and cuddle' vs 'fight and kill' characterisations of the two species too. While there seems to be evidence to bear this out to some extent, it needs to be pointed out just how limited the data is - and how we may be making invalid comparisons based on differing environments, rather than on any objective difference between the two species. As much as I admire Jane Goodall's seminal work amongst chimpanzees for example, I have to agree with her critics: much of the violence she observed may have been down to the unusual context - artificial provisioning, and a great deal of stress from human encroachment into the ecosystem. Given their obvious intelligence, their intensely social behaviour, and the degree to which chimps pass on knowledge through learning, I see no particular reason to assume that there is any great difference in an 'inherent propensity to violence' between the two species at all - a chimp, like a human being, is born with the potential to become all sorts of individual - and just what sort of individual it becomes will depend very much on the environment it is brought up in - both ecological and social. AndyTheGrump (talk) 05:17, 21 March 2012 (UTC)

I think we could potentially do better than just saying we are each equally related. Just like a person will share more chromosomes with some first cousins than others, either chimps or bonobos presumably share more active genes with us. That is, since we split with our last common ancestor, humans have had some genes changes, and chimps/bonobos have has some genes change. The genes which changed before those two split will presumably not distinguish between the two (unless some of those genes changed back after the final split). However, genes which changed after the final split, but which humans still possess, should exist. I'm not sure if anyone has ever done such a study, though. Since there seems to be very little different between chimps and bonobos other than their behavior, I suspect that genes which control behavior are where the largest changes occurred. Of course, some behavior might also be cultural/learned.

Also note that a comparison of chimp and bonobo genetics might give us great insight into how to predict, and even control, human behavior, so could be quite valuable for our survival as a species. StuRat (talk) 06:30, 21 March 2012 (UTC)

USSR/Russia interplanetary probes

The USSR was an early pioneer in sending probes to the Moon and to Venus. They also sent some to Mars. Why hasn't the USSR/Russia sent probes beyond Venus and Mars? Bubba73 ^{You talkin' to me?} 05:23, 21 March 2012 (UTC)

It likely has a lot to do with cost. Cassini-Huygens cost about US$3.2B and according to Space industry of Russia, their budget as of 2011 is US$3.8B. With the cost of sending people and cargo to the ISS, there isn't much left for probes to the outer planets. Dismas|^(talk) 05:58, 21 March 2012 (UTC)

Maybe if America hadn't been spending so much on interplanetary exploration, we might still have a Shuttle program. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:05, 21 March 2012 (UTC)

Well, there there is money, but it's spent on other things:

2010 NASA budget = $18.724 billion (http://en.wikipedia.org/wiki/NASA_Budget)

2010 Military Budget = $1.03 trillion (http://en.wikipedia.org/wiki/Military_budget_of_the_United_States)

Just saying... 217.158.236.14 (talk) 09:59, 21 March 2012 (UTC)

This is true, but there's no know-how left to send even a smaller probe anywhere. New Horizons cost $650M over 15 years. This would have been within the budget if Russian engineers knew how to build probes. Which they don't, because the last successful Russian/Soviet mission beyond the low Earth orbit took place (IIRC) in 1986.--Itinerant1 (talk) 06:17, 21 March 2012 (UTC)

Correction: I should've said "beyond the geosynchronous orbit". --Itinerant1 (talk) 09:27, 21 March 2012 (UTC)

Because the USSR collapsed in 1991 and very nearly took the entire Soviet space industry under as well. In the 90's, government financing of science was minimal, scientists and engineers were being paid starvation wages, existing technologies were becoming obsolete, and there was no money to develop new ones. Things got a little better in the 00's, but, as of today, starting salary of an engineer or a programmer at NPO Lavochkin is the equivalent of $700/month (this is near Moscow, which is one of the most expensive cities in the world, on par with New York or London.) Russian space industry lost an entire generation of employees because STEM students were going into business or emigrating from the country. The average age of an employee is in the 50's. It's a wonder that Russia can still launch anything at all, let alone send probes beyond Venus and Mars.--Itinerant1 (talk) 06:12, 21 March 2012 (UTC)

Russia has a bit of a curse when it comes to Mars probes. So while it's true that they "sent" a whole bunch of probes to Mars, I don't think that any of them actually got there in one piece and then functioned properly. (Their Venus probes were pretty awesome though. Go figure.) APL (talk) 10:36, 21 March 2012 (UTC)

Ok, I see about the economic problems since 1991. But in the 1970s and 80s we were sending probes to Mercury and the outer planets. Why didn't they do it too? Bubba73 ^{You talkin' to me?} 15:01, 21 March 2012 (UTC)

Solid fluorine

What is the appearance of solid fluorine? Double sharp (talk) 13:39, 21 March 2012 (UTC)

Application for vocational studies in Sweden.

Please sir/madam, kindly direct me on how and when to apply for vocational studies under science department in Sweden. Thanks, am Cosmas from Nigeria. — Preceding unsigned comment added by 95.209.176.236 (talk) 15:00, 21 March 2012 (UTC)

Astatine alpha-decay

I hope you can help me. I am writing astatine and I have a question about its alpha decay characteristics. At-211 has 126 neurtons, which is a magic number. Why then energy of alpha decay of At-211 exceeds that of At-210? Also notable that At-213 (N=128=126+2) has two more protons than 126. Its alpha decay half-life is in accordance: the shortest of all astatine isotopes. IS there a reason why At-211 is not the longest-lived astatine isotope? Thanks--R8R Gtrs (talk) 15:19, 21 March 2012 (UTC)

Recommended reading

I graduate from my computer science bachelor's this year. I've enjoyed the probability and statistics elements of the subject, both taught and extracurricular. These taught courses have been fairly informal (e.g. no precise description of space) - I'd like to improve on this enough that descriptions elsewhere are more easily understandable, but I have also made the deliberate choice to post on this desk rather than the mathematics one. I've enjoyed that much of what I've learned was immediately useful, so I'm particularly interested in algorithmic processes which address practicalities of real-world problems. That's quite general, so I mean things like PCA, Metropolis-Hastings and Levenberg–Marquardt. With this in mind, if wonder if the fine folks of the reference desk can recommend any moderately comprehensive introductory texts? Thanks very much. 77.97.198.48 (talk) 15:31, 21 March 2012 (UTC)