Wikipedia:Reference desk/Archives/Science/August 2005

velocity of a body orbiting the sun in an elliptical orbit

There are some interesting formulas given for determining the velocity of an object at a given point on its orbit, but it's unclear what units are required. The answers I'm getting aren't adding up to anything that makes any sense or agrees with what's in the literature.

Could you clarify this, pleasse? — Preceding unsigned comment added by 69.209.99.84 (talk) 01:06, 20 August 2005 (UTC)

• It would be easier if you'd tell us which formulas you are referring to, please? --jpgordon∇∆∇∆ 01:58, 20 August 2005 (UTC)

• Possibly the one on Elliptic orbit or Orbital speed. 82.210.117.215 08:12, 21 August 2005 (UTC)

Any consistent set of units should work. I'm assuming you're using this equation from elliptic orbit:

$v={\sqrt {2\mu \left({1 \over {r}}-{1 \over {2a}}\right)}}$

where:

• $\mu \,$ is the standard gravitational parameter= $GM$,
• $G$ is the gravitational constant
• $M$ is the mass of the larger body (or actually its reduced mass, I think, but as long as the orbiting body is much smaller than the body it's orbiting we can ignore that for now)
• $r\,$ is the radial distance of orbiting body from central body,
• $a\,\!$ is the length of the semi-major axis of the orbit.

So if you do all the lengths in meters, the mass in kg, and the gravitational constant in m^3/(s^2 kg), you should get your answer in m/s. Alternatively, do the lengths in km, the gravitational constant in km^3/(s^2 kg), and get the velocity in km/s, or even, if you're old-fashioned or American or crazy, do the lengths in ft, the gravitational consant in ft^3/(s^2 slug) and get the velocity in ft/s. The article on the gravitational constant gives it in m^3/(s^2 kg), but strangely the article on the standard gravitational parameter gives it in km^3/s^2. moink 17:59, 22 August 2005 (UTC)

One more quick thing, just in case you're the person who wrote at Talk:Standard gravitational parameter. I glossed over the idea of the reduced mass above, but if you're trying to solve a two-star problem, you should read that article. From what I remember (it's been a long time since I took astrodynamics, hopefully someone will correct me if I'm wrong), in the orbital equations for a two-body problem you should use the reduced mass of the system. When a small object is orbiting a large object, the reduced mass is very close to the mass of the large object. But if they're two objects of comparable size, use the reduced mass. moink 18:04, 22 August 2005 (UTC)

Sickle-cell anemia vs. sickle-cell disease

Traditionally, the hemoglobin disorder that causes misshapen red blood cells was known as "sickle-cell anemia"; now, however, I'm seeing the more general "sickle-cell disease" used, especially in medical journals and such sources as my IB Biology II book.

Is "disease" preferable to "anemia"? My guess is that the naming standards changed because anemia is not the only sympton, but I could be wrong.

Google suggests "anemia" is more common (in all Web results and news results), but there are factors that lean towards the use of "disease," such as the name of the Sickle Cell Disease Association of America and the results of a search of the New England Journal of Medicine website (190 for "disease," 156 for "anemia," and 14 for "anemia").

A search of only university sites yields 399,000 hits for "disease" and 560,000 for "anemia"; the same search for only government sites yields 88,800 and 115,000 hits, respectively. Switching to "disease" would eliminate some thorny American/British spelling issues ("anemia"/"anaemia"). Any advice as far as what our article name should be? Neutrality^talk 04:41, August 20, 2005 (UTC)

It doesn't matter! It's all the same condition. Sickle cell anemia was the original name. Some people prefer SCD because the anemia is often not the major problem for people and SCD reflects the multi-organ nature of the condition. Current American textbooks and medical journal articles tend to prefer SCD. alteripse 09:48, 20 August 2005 (UTC)

Yup. At the Children's Hospital in Detroit, where they see a lot of SCD, they prefer that name too for the reasons Alteripse explained. For more detail, as I understand it, there are four major complications that can arise from SCD, and like he said, anemia itself isn't the real problem. So I would suggest the disease name for the article. - Taxman ^Talk 12:58, August 21, 2005 (UTC)

It seems as though someone has done the move, but not updated the redirects. I would take care of it, but my wife dripped watermelon juice on my mouse (ostensibly by accident), and my efficiency is greatly reduced until the mouse works again. — Pekinensis 19:19, 23 August 2005 (UTC)

Yeah, sure it was your mouse. As for excuses, I've got the one about a dog eating my homework too, but I'll save that one! Just kidding, but there are about a hundred to fix from a glance, so I could use some help. If you can't get to it, I may be able to later today. - Taxman ^Talk 18:08, August 24, 2005 (UTC)

I've been doing some fixing here, to assist Taxman. (Hey, it's a lazy thursday afternoon with nothing better to do..) Kander 13:11, 25 August 2005 (UTC)

earth shift off axis

did the earth really move off its axis? if so how far?and last question,did it cause a difference in the distance from the earth to the moon? (anon)

To whomever may be intelligent enough to answer this question (if it is answerable), I offer this addendum: How can a planet (or ball or any other spinning object) move off an axis? Doesn't whatever imaginary diameter it is currently spinning around just become its new axis? Garrett Albright 11:58, 20 August 2005 (UTC)

The earth already has a tilted axis. If you draw a plane through the sun and planets, the earth doesn't spin on an axis perfectly perpendicular to that plane. This is one thing that helps make the seasons vary. I don't know when the poster of this question is thinking that it "moved". The earth did change it's speed of rotation ever so slightly with the earthquake that caused the tsunami that caused all that damage in the Indian Ocean. See: 2004 Indian Ocean earthquake. Dismas 13:40, 20 August 2005 (UTC)

Also, the earth's axis is not fixed but changes slowly (with respect to the fixed stars). See precession as well as nutation. However, the question appears to concern a more sudden axis change. You may want to look at the (controversial) "earth crust displacement" theory. See Charles Hapgood for that. 82.210.117.55 19:20, 20 August 2005 (UTC)

See swing bowling and reverse swing! Dunc|☺ 19:52, 20 August 2005 (UTC)

If you accept the theory that one of the things that contributed to the Dinosaurs going Extinct had to do with planet Earth getting plastered by a humogous rock from space, that left a crater that is now the Carribean, supposedly when that happened, it had a humogous impact on how the Earth was spinning on the old axis. This theory "explains" how come some Dinosaur bones got dug up in which the critter was frozen, but there was food in its stomache from a climate other than arctic. AlMac|^(talk) 23:24, 20 August 2005 (UTC)

No, that's due to continental drift. For the Antarctic to get moved from the tropics to its current position would require the axial tilt to have previously been near 90°; this would make life impossible. ~~ N (t/c) 23:27, 21 August 2005 (UTC)

Earth's tilt changing enough to move a tropical continent to an artic climate zone is really unbelievable, and would, I assume, leave obvious traces in the geologic magnetic record. If a dinosaur did freeze to death (rather than after the fact) I would be more inclined to credit weather changes due to particles thrown into the air and obscuring the sun. Freezing long after the fact can be explained by continental drift, specifically the breakup of Gondwana. — Laura Scudder | Talk 02:16, 22 August 2005 (UTC)

Discrepant voltage of rechargeable batteries

AA Batteries typically offer 1.5 V. However, NiMH AA batteries offer only 1.2 V. My questions are:

1. Is this in compliance with the relevant ANSI/IEC Standards?
2. Does this noticeably affect NiMH performance in common use?
3. Why aren't NiMH batteries made to provide 1.5 V?

--LizardWizard 00:35, August 21, 2005 (UTC)

Each chemical composition for a voltage cell has its own EMF (voltage). As the engineers and scientists develop new combinations they allow for particular parameters to be within a range. Some of the parameters are: manufacturability, availability of component chemicals, hazardous waste, volatility, size of a cell, charge capacity, number of recharges, cost to consumer, etc, etc, etc. One of the parameters is of course the natural voltage of a particular chemistry. It's a battle of compromise. A combination of compromises that gives the consumer a 10¢ battery that has too low a voltage (say 0.5 volts) will fail in the general marketplace whereas a battery that can be charged a million times and provides exactly 1.5 volts but would cost $100.00 may also not succeed. So, after too many words for your question, if it's available in the consumer marketplace then it's OK for general use. The product that is receiving the energy must also of course be flexible or it will fail in the consumer marketplace. hydnjo talk 01:31, 21 August 2005 (UTC)

Oh, BTW, NiMH at this time has the most rechargeability capability without concern for the memory problem which plagued NiCad technology. This feature alone has propelled NiMH to the leading thechnology choice for most consumer products in the 2004-2005 timeframe. hydnjo talk 04:28, 21 August 2005 (UTC)

On a side note, this is thanks to some nifty solid state chemistry. --HappyCamper 04:36, 21 August 2005 (UTC)

Mathematics: Handshakes

Prove that the number of people who have shaken hands an odd number of times is an even number. --anonym

Do you have a question to ask, or are you just giving us homework problems? ¦ Reisio 07:58, 2005 August 21 (UTC)

Hint: count the number of people-handshakes in two different ways. On the one hand, it is twice the number of handshakes (because there are two people involved in each handshake) so it must be even. On the other hand, it is the sum over all people of the number of times each person has shaken hands. What can you say about the number of odd terms in a sum whose result is even ? Gandalf61 09:54, August 21, 2005 (UTC)

• $H={\frac {P*(P-1)}{2}}$

Where H=handshakes, P=people, (p-1) because out of p people I do not shake hands with myself. There are p*(p-1) encounters, and I divide by 2 because John and Mary shake hands once.

$p*(p-1)\$ has to equal an even number because

$2H=2*(2n+1)=\ even$, where n is any positive integer.

What do you think? Am I wrong? Do you proceed with a different thread of reasoning and would you like explain in a less verbal fashion? --anonym.

Yes, you are wrong. First of all, H is the number of times P people would shake hands if all had to shake hands with each other. The problem never asks about such a case. Second, all you've proven is that 2H is even, which is obvious anyway. See hint above, it pretty much solves the problem for you. Ornil 19:21, 21 August 2005 (UTC)

I get confused starting with "On the other hand, it is the sum over all people of the number of times each person has shaken hands. What can you say about the number of odd terms in a sum whose result is even ?" Can someone symbolically explain this part?--anonym

Classic "double counting" argument. Symbolically:

$\sum _{\mbox{people}}{\mbox{handshakes per person}}=\sum _{\mbox{handshakes}}{\mbox{people per handshake}}=2|{\mbox{handshakes}}|$

$\Rightarrow 2{\big |}\sum _{\mbox{people}}{\mbox{handshakes per person}}$

• Thank for the symbols.

If $2{\big |}\sum _{\mbox{people}}{\mbox{handshakes/person}}\neq P*(P-1),$then what does it equal?

>Suppose there are two people. Then each person shakes hands once.

  People       Handshakes per person
  ------       ---------------------
     2                   1

Now another guy walks into the room. He shakes hands with the two people already there (two handshakes for him), and each of the people already there adds a handshake to his collection (two total for them):

  People       Handshakes per person
  ------       ---------------------
     2                   1
     3                   2

Now another guy walks into the room. He shakes hands with the three people already there (three handshakes for him), and each of the people already there adds a handshake to his collection (three total for them):

  People       Handshakes per person
  ------       ---------------------
     2                   1
     3                   2
     4                   3

If you continue this for a while, you'll see that the number of handshakes per person is odd only when the number of people is even.

> 2H=N*(N-1)

Odd handshakes-->even people, e.g., 45 handshakes-->10 people.

--even people ---does not imply--> odd handshakes because, for example, 24 people shake hands 276 times.

But the basic equation is (handshakes)*2=(people)*(people-1).

-anonym - learning that I was initially right.

But the original problem does not say that everyone shakes hands exactly once with everyone else. In your example, suppose some of the people entering the room only shake hands with a few people, not with everyone already there ? Suppose some pairs of people shake hands more than once ? The number of people who have shaken hands an odd number of times is still always even, but your argument does not work because the total number of handshakes may be more than or less than p(p-1)/2. Gandalf61 09:14, August 23, 2005 (UTC)

• You are right because if there are 24 people, then EACH person has shaken 23 hands; however, the TOTAL number of handshakes is 276, if everyone shakes hands with each other once.

I think I got it right; however, if I still do not understand another aspect of the problem, then let me know. --anonym

Partial Sum

Find a simple formula for $F_{1}^{2}+F_{2}^{2}+F_{3}^{2}+...+F_{n}^{2},$where $F_{k}^{2}$is the kth Fibonacci number. --anonym

Do you have a question to ask, or are you just giving us homework problems? ¦ Reisio 07:59, 2005 August 21 (UTC)

Fibonacci tiling

Hint: what is the area of the rectangle formed by a Fibonacci spiral tiling (the diagram on the right shows a Fibonacci spiral tiling of squares with sides equal to the first 6 Fibonacci numbers). Gandalf61 10:11, August 21, 2005 (UTC)

$F_{1}^{2}+F_{2}^{2}+F_{3}^{2}+...+F_{n}^{2},$is

$\sum _{k=1}^{n}F_{k}^{2}=F_{n}*F_{n+1}$.

In the case of the picture, we have

$\sum _{k=1}^{6}F_{k}^{2}=F_{6}*F_{7}=8*13=104$.

Thank you.--anonym

Mathematical Product

Find the product $\left(1-{\frac {1}{4}}\right)\left(1-{\frac {1}{9}}\right)\left(1-{\frac {1}{16}}\right)...\left(1-{\frac {1}{n^{2}}}\right)$. --anonym

Do you have a question to ask, or are you just giving us homework problems? ¦ Reisio 07:59, 2005 August 21 (UTC)

Check out the article Infinite product first...there is one equation there which seems to almost match the one here...A nice closed form expression exists for the product if you take the limit as n tends to infinity... --HappyCamper 13:43, 21 August 2005 (UTC)

• This problem can be solved without using limits because it is from a pre-calculus contest. I have evaluated the starting factors and think the answer is 1. Am I wrong? --anonym

You are certainly wrong. A product of several terms each less than 1 cannot be 1. Ornil 19:14, 21 August 2005 (UTC)

• anonym may have been thinking about 1/2+1/4+1/8+1/16 .... =1 hydnjo talk 20:50, 22 August 2005 (UTC)

It's pretty simple -- just use brute force. For n=2, of course, it's 3/4. For n=3, it's 4/6. For n=4, it's 5/8. Figure out the relationship between n and the numerator and the denominator, and the answer will fall into place. --jpgordon∇∆∇∆ 19:52, 21 August 2005 (UTC)I know that $\lim _{n\to \infty }{\frac {n^{2}-1}{n^{2}}}=1$.

But what does $\prod _{n=2}^{n\to \infty }{\frac {n^{2}-1}{n^{2}}}$

equal?--anonym

This is exactly the same expression as the original expression. Have you tried jpgordon's heuristic? It should be written as

$\prod _{n=2}^{\infty }{\frac {n^{2}-1}{n^{2}}}$ --HappyCamper 17:33, 22 August 2005 (UTC)

>

  1 - 1/4 =  (1 - 1/2)(1 + 1/2) = 1/2 x 3/2

  1 - 1/9 =  (1 - 1/3)(1 + 1/3) = 2/3 x 4/3

  1 - 1/16 = (1 - 1/4)(1 + 1/4) = 3/4 x 5/4

  ...........................................

  1 -1/n^2 = (1 - 1/n)(1 + 1/n) = (n-1)/n x (n+1)/n

If we multiply these all together we get

1/2 x 3/2 x 2/3 x 4/3 x 3/4 x 5/4 x .... x (n-1)/n x (n+1)/n 

All terms cancel except very first and very last giving the result

  1/2 x (n+1)/n

If n -> infinity (n+1)/n -> 1 so the product -> 1/2

--Anonym with Dr. Math's help.

• Right. Or, by my heuristic (brute-force) approach -- hm, 3/4, 4/6, 5/8, oh! That's (n+1)/2n, right? (Easy to prove, he says waving his hand); then the limit also falls in place. --jpgordon∇∆∇∆ 23:45, 24 August 2005 (UTC)

  I'm dying to ask...is the convergence uniform? Is there a product for which the heuristic fails? --HappyCamper 23:47, 24 August 2005 (UTC)

  • Well, it's not a heuristic for the value -- it's a heuristic (I don't think that's the right word, actually) to glean the formula from the first few values of the series. My mind tries immediately to turn series into generating functions: f(n) = f(n - 1) * g(n) sorts of things. So the formula is exact and converges uniformly. --jpgordon∇∆∇∆ 23:58, 24 August 2005 (UTC)
    • Thanks for the explanation. I learned something new today! --HappyCamper 00:15, 25 August 2005 (UTC)

Blood types in bio articles

I've noticed a few biographical articles that had the person's blood type listed. Of those I've seen, all of them concerned someone who was from China or Taiwan. Is this some sort of cultural thing over there? Or is it maybe just coincidence that I ran into the articles that someone pulled info from the same source books or magazines that happen to list this sort of info? Dismas 09:34, 21 August 2005 (UTC)

See Japan_blood_type_theory_of_personality - it seems to be like an astrology type thing MyNameIsClare talk 09:44, 21 August 2005 (UTC)

The closest similar idiocy in the US was the Eat Right for Your Bloodtype book by Peter Adamo, which read as if it were describing how to feed different species of pets (e.g., herbivores vs carnivores) all based on this single inheritable cell surface protein! alteripse 10:40, 21 August 2005 (UTC)

• In some Japanese computer games, you get a character's blood type, as well as their ability to jump and run fast etc, to help make your descision.--Commander Keane 12:26, August 21, 2005 (UTC)

Thanks for the explanations. The more I learn about Japanese culture, the more strange it seems... Which of course begs the question, how weird are we Americans to them? Dismas 13:30, 21 August 2005 (UTC)

First off, remember that "strange" is a loaded word… As my high-school Spanish teacher taught us, "it's not strange, it's different. As an American currently living in Japan, I can attest that it is very different at times. How are Americans portrayed in Japanese culture? That's probably fodder for an entire article… English is used (and often misused) all over the place here. One of the schools I work at (teaching English, natch) is located in a shopping mall, in which nearly every single store has an English name, even though almost all of them are entirely Japanese companies (the The Gap right next to the Starbucks being an exception — right next to, fer crissake). It's kind of odd seeing your language being used solely for ornamental purposes, though I suppose Chinese people feel the same about all these Americans getting Chinese character tattoos without the least clue about what they mean.

Anyway, to sum things up, there's a commercial running on Japanese TV now where a bunch of Japanese people are at a wedding reception, singing a heavily accented version of "If You're Happy and You Know It" while dancing, cutting a cake, and doing other things associated with Western wedding receptions. As we get quick clips of people enjoying themselves at the party, our POV is deliberately drawn to the black man playing the piano to the tune of the song, and the handsome blonde photographer. I could go on, but this reply is getting long enough and I think that says plenty for now -- hit up my Talk page if you'd like to talk about this some more. Garrett Albright 15:16, 21 August 2005 (UTC)

I can't resist adding one more thing; for all that people worry about the McDonaldization of the world, McDonald's is one of the few American (or Japanese, for that matter!) outfits over here that use a logo in Japanese; マクドナルド, "Makudonarudo". Interesting. See the pictures of Japanese restaurants on McDonald's. Garrett Albright 15:21, 21 August 2005 (UTC)

Sudoku

I am stuck on this Sudoku problem and would like some help with it. Ideally, the solution and perhaps an analysis of where I went wrong :-) I don't know where this particular puzzle came from since I found it lying around in the office.

Here's the puzzle

4	6	2		7
5			1		2		6
					3	5	2	4
6	8		2			4
		9		6	5		1
		3	7				5	8
2	5		3		7
		6		5		1		2
	1			2		3		5

I have:

4	6	2	5	7	X		3	1
5			1	4	2		6
			6	X	3	5	2	4
6	8	5	2	X	X	4
		9	X	6	5	2	1	3
		3	7	9	X	6	5	8
2	5		3	1	7			6
		6		5		1		2
	1			2	6	3		5

In particular, something seems incorrect in the middle, but if I backtrack, I find a contradiction! Any tips would be appreciated. --HappyCamper 04:05, 22 August 2005 (UTC)

See, perhaps, http://www.soduku.org.uk/. -- Rick Block (talk) 04:46, August 22, 2005 (UTC)

Nothing seems wrong to me; I solved it and all your numbers are right, though I don't know what the X means. --jpgordon∇∆∇∆ 05:12, 22 August 2005 (UTC)

I have changed the numbers he got wrong to Xes. --R.Koot 05:31, 22 August 2005 (UTC)

• I don't know where you went wrong, but I managed to solve it without problems. You probably had some duplicate numbers in the same row. I suggest you double check before you put them in. - Mgm|^(talk) 08:07, August 22, 2005 (UTC)

  Ah, of course. I put an 8 in the very top X without noticing a 9 in the other row. Thanks! --HappyCamper 10:38, 22 August 2005 (UTC)

This puzzle is interesting because (1) the layout is not symmetric and (2) the initial position has an unusually large number of filled-in cells: in newspapers, puzzles typically have 20–30 filled-in cells in the initial grid. This has 36. So I suspect the puzzle has been generated by computer, and rather naïvely too. Gdr 13:05:53, 2005-08-22 (UTC)

Writing data to a disk

what term is used to refer to the process of writing data to a disk?

• Saving? — JIP | Talk 13:10, 22 August 2005 (UTC)
• Many people will say "burn" when referring to a Compact disc or DVD. Though "writing" is also correct. Dismas 13:19, 22 August 2005 (UTC)
• Writing. ¦ Reisio 13:21, 2005 August 22 (UTC)
• To a hard disk or a magnetic disk, I'd say writing; to a recordable-CD or derivative, I'd say recording. Rob Church ^{Talk | Desk} 01:32, 25 August 2005 (UTC)
• Copying, if the data is going from one medium to another. AlMac|^(talk) 18:19, 25 August 2005 (UTC)
• Outputting, when a computer program outputs data to hard disk, as opposed to sending the data to be viewed on screen. AlMac|^(talk) 18:19, 25 August 2005 (UTC)
• I generally think in terms of saving information and writing files. Ferdinangus 00:26, 23 September 2005 (UTC)

Electric Inductor

Can you explain to a layperson how an inductor differs from a resister? Don't they both lower the flow of electric charge, and thus current? If you can include an anology or picture, it would be excellent; however,I will appreciate any comment. --anonym

• Please read inductor and resistor. They will probably answer your questions. And they have pictures. You can search for answers to questions that you have by entering the term in the "search" box on the left of the Wikipedia screen, and clicking "search". Ground Zero 15:06, 24 August 2005 (UTC)

Quite a few perspectives can be used to answer this question. Sometimes, a resistor is considered to be an energy dissipative element, while an inductor and a capacitor are considered energy storage units. This means that a resistor can't be used to store energy. It simply drains it away in a circuit as heat. Of course, this doesn't mean that resistors aren't useful. All the passive circuit elements have some utility - some are specialized in certain things. Inductors in particular, can store energy due to a magnetic field. Contrast this with a capacitor which stores energy due to an electric field. Check out RL circuit, RC circuit and RLC circuit which might interest you too.

An ideal resistor is a device whose voltage depends on the current "flowing" through it. An ideal inductor is a device whose voltage depends on the change in current which "flows" through it. Typically, inductors and capacitors are considered together in circuit theory, so you also might want to check out capacitor. In very general treatments of circuit analysis, resistors, capacitors and inductors all contribute an impedance to a circuit. Hope this helps! If you need more help, please feel free to return with more comments. :) --HappyCamper 17:58, 24 August 2005 (UTC)

An inductor tries to keep current flowing if it's already flowing, and resists its flow if it's not already flowing. A resistor resists in either situation. Michael Hardy 22:19, 24 August 2005 (UTC)

• Best answer yet to the original request for an explanation to a layperson. hydnjo talk 03:44, 25 August 2005 (UTC)

• I've never thought of the inductor that way before...ah, what an interesting place this is! --HappyCamper 03:06, 27 August 2005 (UTC)

The explanations herein are superb. So I think the voltage of an inductor must be a fuction of the second derivative of charge with respect to time.

--anonym

Yup. Since you mentioned derivatives, I will sprinkle some of my favourite equations here:

For an inductor, it satisfies $v(t)=L{\frac {d}{dt}}i(t)=L{\frac {d^{2}}{dt^{2}}}q(t)$ --HappyCamper 03:07, 27 August 2005 (UTC)

Squares Inside a 6×6 Grid

• Why is the number of 2*2 squares in a 6*6 grid 5^2=25?
• Why is the number of 3*3 squares in a 6*6 grid 4^2=16?
• Why is the number of 4*4 squares in a 6*6 grid 3^2=9?
• Why is the number of 5*5 squares in a 6*6 grid 2^2=4?

I am utterly lost and cannot picture this. [Perhaps, I am dumb, yet I do not wish to remain so.]

--anonym

How many ways are there of putting a length of 2 into a length of 6? 5, because trying to put it in starting at the 6th square would put it partly outside the grid. For a length of 3, you have to remove another, because starting at both the 5th and 6th would put it outside, so it's 4. And so on. Then just square them because there are two dimensions. Frencheigh 20:13, 24 August 2005 (UTC)

It is sometimes helpful to picture the extremes:

• How many 1*1 squares are there in a 6*6 grid? (Hint: 6^2=?)
• How many 6*6 squares are there in a 6*6 grid? (Hint: 1^2=?)
• Got the picture? hydnjo talk 21:24, 24 August 2005 (UTC)

Typesetting tip:

Why is the number of 2×2 squares in a 6×6 grid 5² = 25?

This forum is not limited to plain ASCII. Michael Hardy 22:15, 24 August 2005 (UTC)

• The number of 1×1 squares in a 6×6 grid is 6² = 36.
• The number of 6×6 squares in a 6×6 grid is 1² = 1.

In addition, the total number of squares in a 6×6 grid is $1^{2}+2^{2}+3^{2}+4^{2}+5^{2}+6^{2}=91$.

I thank you for all the responses including the typesetting tip.

--anonym

Let's start with the 6 by 6 square. If you place a small 2 by 2 square inside it, right at the corner, how many squares can it slide horizontally or vertially? In both cases it's 5. So, the total number of 2 by 2 squares in a 6 by 6 square is 5×5=25. Now, use the patterns suggested above and the answer becomes clearer... --HappyCamper 00:58, 25 August 2005 (UTC)

Washington State desert names

What are the names of all the deserts in Washington State. The one in particularly I would like to know is the one that is on the east side of Washington and runs from the Canada/Washington border through Oregon and into California.

Hmm. I live in said desert, and I have no idea. I don't think it has a name. --Matt Yeager 00:49, August 22, 2005 (UTC)

• Isn't that the Columbia Plateau (and the northern part of the Great Basin)? --jpgordon∇∆∇∆ 01:20, 22 August 2005 (UTC)

Astronomy

What are at least four planetary attributes that determine atmospheric composition and behavior of a planet?

1. The size of the planet (because of...)
2. The distance of the planet to the star it revolves around (because...)
3. The speed of rotation of the planet (what might this do?)
4. The location of the planet with respect to debris in space (or this?)
5. The amount of radiation received by the planet...(what happens when radiation hits the atmosphere? Influence of energy?)

Et cetera...

Think: What is an atmosphere? What might influence its thickness? What about its turbulence? What about its colour? Does temperature play a role? What about asteroids? Et cetera, et cetera...

This sounds very much like a homework question, and I'd highly encourage you to think of different reasons why this question is being asked. Be creative: what concepts does your educator want to convey to you? Why might the question be phrased in an open ended manner? There are lots of factors which influence atmospheric composition. To show you understand the concepts, try to give a reason why you think X is a contributing factor for influencing atmospheric charateristics. There might not be a "correct" answer, but there are always well reasoned ones. Aim for these and I think you'd get pretty close to answering what is being asked! :-) --HappyCamper 14:09, 24 August 2005 (UTC)

• Our article on atmosphere may also hold some answers. - Mgm|^(talk) 17:39, August 24, 2005 (UTC)

• Also look at Celestial body atmosphere for additional stuff. hydnjo talk 19:22, 24 August 2005 (UTC)

Rot or Spoil?

Does bread rot or spoil? Or is there another term applied for bread? --anonym

• Bread goes stale, or even mouldy. Warofdreams 16:40, 24 August 2005 (UTC)

...and eventually rots. All these states spoil the bread. Shantavira 16:52, 24 August 2005 (UTC)

swelling of female organs

I am 27 years old. Two years ago I had my 3rd child. Every delivery I have been though I have had natural birth. During these births I have torn or been cut bewteen the vagina and anus. Well I am now noticing that were the doctors have sown me up is begining to tear and there is some swelling and tissue that is extruding out. I have also had my tubs tied if maybe that maks a differance. I am lost for words and scared to go to the doctor. Please if you can give me some insite it will be greatful. Thanks anon

There are many potential side effects to episiotemies. I think you should see your doctor about it right away. It is not at all unusual to suffer side effects from this procedure, so don't be shy about telling your doctor. — Laura Scudder | Talk 01:53, 25 August 2005 (UTC)

Agreed. It is vital that you consult a doctor immediately, and put out of your mind using internet forums as a primary source of medical advice. Believe me, your doctor will have seen this kind of thing many times, and it will not be anything like as scarry or embarrasing as you are fearing. Trollderella 06:34, 25 August 2005 (UTC)

Agree also. Please see your doctor as soon as possible. Whatever problems you have are far more likely to get worse rather than better the longer you go without treatment. --bodnotbod 20:02, August 25, 2005 (UTC)

What the others said is true, but I want to emphasize "don't be afraid". You definitely need to see a doctor, but you'll be okay. After all, there are no vital organs down there. The doctor will fix you up. — Pekinensis 21:27, 25 August 2005 (UTC)

From talk:Septic tank

How long do septic tanks (systems) last? We are in the process of buying a 20 year old home with the existing septic tank, what questions or concerns should I have? 67.184.249.226 (talk · contribs)

Highly dependant on how well the previous owner(s) cared for and maintained the system. At the very least the there should be documentation as to how often the tank was pumped out. Every year or two is good, every five years or so is not so good. There are so many variables (I just mentioned one of them) that it really is difficult to answer the question quantitatively. A well designed and maintained system can be fine for a 60+ years whereas a poorly designed and/or maintained system may fail after 20 or 30 years. Best bet, hire a professional to inspect the entire system. A couple of hundred dollars will buy either lots of peace of mind or a significant reduction in the value of the home. hydnjo talk 20:04, 20 August 2005 (UTC)

BTW, the septic tank itself rarely fails. The usual failure mode is the leach field (or leach(ing) bed) which becomes clogged and unable to percolate (perc) properly. Your home inspection company or your home appraisal company (not the seller's real estate agent) should be of help in this matter. hydnjo talk 20:34, 20 August 2005 (UTC)

I have a question.....

The south asian subcontinentis separated from the rest of asia by the?

A. Himalayas and the Hindu Kush
B. Nile Valley
C. Ganges
D. Arabian peninsula
Question contributed by 67.182.209.137 hydnjo talk 02:12, 21 August 2005 (UTC)

Why do I feel like saying Go little sparrow, and use this idea to help you find food. And then little sparrow, you will not only not go hungry but you will pass this on to your offspring, and they also will not go hungry. hydnjo talk 02:24, 21 August 2005 (UTC)

Why take the word of a stranger and risk getting the wrong answer. Please read South Asia and the answer may become obvious. If after reading the article you are still confused as to the answer then, by all means, c'mon back and we'll give you some additional help. hydnjo talk 01:06, 21 August 2005 (UTC)

Also realize that this is not a place for direct answers to homework questions. ¦ Reisio 01:13, 2005 August 21 (UTC)

Maybe the IP was a somehow involved with Who Wants to be Millionaire? :-) --HappyCamper 02:48, 21 August 2005 (UTC)

Perhaps. Does that somehow make us complicit or even better, beneficiaries. Go Fundraising. hydnjo talk 03:06, 21 August 2005 (UTC)

tv show northern exposure

what network is northern exposure now on being hallmark doesn't have it on anymore? thank you

If you're asking what television network originally aired Northern Exposure, it's CBS. See our Northern Exposure article for more. Garrett Albright 01:36, 22 August 2005 (UTC)

Um, I think our reader wants to know what network, if any, is currently screening the show in the United States. The answer may, sadly, be "none"; Yahoo's TV guide doesn't reveal any cable, satellite, or free-to-air broadcaster showing the program at present. However, you can buy the first three seasons on DVD, for instance from Amazon.com. I think it's highly likely that subsequent series of this well-loved show will be released in the future. --Robert Merkel 01:50, 22 August 2005 (UTC)

ent_fire code

I want to know what the word or code is to make an npc move or attack.

jtl--24.255.95.187 00:44, 23 August 2005 (UTC)

Personally I prefer to modify the game binary in a hex editor myself...seriously, what game are you referring to? There's thousands of them :)--Robert Merkel

Don't reply to this - go to Wikipedia:Reference_desk#Half_Life_2_code ¦ Reisio 00:05, 2005 August 24 (UTC)

Half Life 2 code

Can someone tell me the code to make an npc attack and fight in a multiplayer game?

shortyjtl--24.255.95.187 23:07, 23 August 2005 (UTC)

See ent_fire code above. Elf | Talk 00:28, 24 August 2005 (UTC)

Annuities

If I invest in monthly ordinary annuities, do I have set aside a fixed amount of my income to pay for the annuity every month? Or do I receive a fixed monthly amount? --anonym

• Bread goes stale. You invest a lump sum in an annuity, which then pays you monthly (e.g.) income. Unless you are a financial institution, then you receive the lump sum, and pay the annuity. Ground Zero 15:02, 24 August 2005 (UTC)

• Where are you located? In the United States, there is the concept of a deferred annuity in which there is an accumulation phase where you can invest various amounts to build up the account value, and then later annuitize it, which means to turn it into a stream of lifetime payments. Here we call a pure annuity (no accumulation phase) an immediate annuity because it starts the stream of income immediately. I can't see the sense of generating taxable income immediately at the same time as when you are saving money into the annuity, especially when there are other options. Though outside the US, I don't know what those options are. See our annuity article for more. - Taxman ^Talk 16:57, August 24, 2005 (UTC)

Do banks or other financial institutions offer annuities in perpetuity to their customers? --anonym

• Annuities are offered to individuals during their life-spans. When you die, the annuity ends. The pay-out of the annuity is usually based on your expected remaining life-span. Some financial instutions may offer a lump-sum pay-out to your estate if your die within a short period of time. In the past, "perpetual bonds" were issued, which continue to pay interest to this day. These are not annuities per se. I do not believe that anybody issues these anymore. A bank, building society, credit union or insurance agent would be able to give you more information on annuities. Ground Zero 16:19, 24 August 2005 (UTC)
• In the US only insurance companies can issue annuities because they are insuring (guaranteeing based on their assets only) that they can continue making the annuity payments for the life of the annuitant or for a period certain. - Taxman ^Talk 16:57, August 24, 2005 (UTC)

There are financial instruments that pay out in perpetuity. For example I inherited War Bonds from a relative, who bought them for a one-off payment. They could not be cashed in but would pay out an annual sum. Since they were bought in the war their annual payment would now be a couple of pennies, and I have no idea what happened to them. DJ Clayworth 18:36, 24 August 2005 (UTC)

Did you read the annuity and pension articles? Trollderella 19:29, 24 August 2005 (UTC)

• I will read them. Thank you.

--anonym

Maths: regular tetrahedron inside a sphere

I understand that inside any sphere you can place a regular tetrahedron which touches the surface of the sphere at each of its four vertices. Now, if that sphere is the planet earth, I'd like to think there's a way (a formula, a spreadsheet, a simple piece of software) to calculate the latitude and longitude of each of the four points of the (regular) tetrahedron. My A-level maths just isn't up to the job. Of course, because there are an infinite number of different ways to position a tetrahedron inside a sphere I would need to input a starting point, e.g. the latitude and longitude of one of the vertices (and one other parameter, probably an angle?), and the formula/spreadsheet/program would provide the lat and long of the other three points.

Now, my questions are: Has anyone out there done this already? Can any wikipedia readers/contributors do this for me? If not, can anyone suggest anyone they know who would be knowledgeable enough and kind enough to help me out? Thanks a million ... Nick

Well, this isn't the simplest method, but it'll work. In cartesian coordinates, our four points would be

$\mathbf {r} _{n}=(x_{n},y_{n},z_{n})=R_{E}(\sin \phi _{n}\cos \theta _{n},\sin \phi _{n}\sin \theta _{n},\cos \phi _{n})$ for n = 1, 2, 3, 4

where $\phi _{n}$ and $\theta _{n}$ are the latitude and longitude of each point respectively. The condition for the tetrahedron formed by these four points to be regular is that $(\mathbf {r} _{n}-\mathbf {r} _{m})^{2}$ is the same for each $n\neq m$. So you can pick your first point. Then you still have to pick the longitude of one other point before the location of the rest of the points will be determined by solving that set of equations (which, I might add, Mathematica or Maple would be all too happy to do for you).

The alternate way to do it is to rotate your set of known solutions from above. In other words, if I want one vertex at some crazy latitude and longitude, I can simply multiple the solutions to the case where one vertex is at the North Pole by the appropriate rotation matrix to land that vertex at the desired latitude and longitude. If need be you could find that matrix by taking the general formula for a 3D rotation matrix and solving

$\left({\begin{matrix}\sin \phi \cos \theta \\\sin \phi \sin \theta \\\cos \phi \end{matrix}}\right)=R\left({\begin{matrix}1\\0\\0\end{matrix}}\right)$

where the vector on the left is where you want the North Pole (represented by the vector on the right) to end up after being hit by the rotation matrix R. This would still leave you freedom for how the other three points are oriented about your first vertex. It's arguable whether this is any easier than the method above, but they'd both work. — Laura Scudder | Talk 18:04, 26 August 2005 (UTC)

• Laura's contribution here is excellent and looks to have set us on the right road, but in light of what she says isn't it possible to actually solve the equations she has provided, so that a general formula can be written for say $\theta _{2}$, $\phi _{3}$, $\theta _{3}$, $\phi _{4}$, $\theta _{4}$ in terms of say $\phi _{1}$, $\theta _{1}$ and $\phi _{2}$? I can't see that there is a need for a tool like Mathematica to solve for particluar values when a general-purpose trigonometric formula seems likely to be derivable(though at present rather elusive).
  • I recommended Mathematica because I don't particularly enjoy doing that much algebra for the general solution (I took the classic textbook out and left it to the reader). It should be doable by hand with a good amount of algebra and a few trig substitutions, just as you suggest. — Laura Scudder | Talk 21:20, 26 August 2005 (UTC)

• So, I'll paraphrase my original question, since my own trig/algebra is too rusty: Has anyone out there done this already? Do any wikipedia readers/contributors have the right amount of non-rusty trig and algebra to do this for me? If not, can anyone suggest someone they know who would be knowledgeable enough and kind enough to help me out? ... Nick

How about this approach instead? Take advantage of the antisymmetry of the tetrahedron with respect to a cube. Place one of the corners of the cube where one point of the tetrahedron is, and use the rest of the symmetry to figure out the coordinates of the other points...after all, we are almost trained to think in Cartesian space (but I'm archiving at the moment, so I haven't read the rest of the question...but maybe a good idea to work with?) --HappyCamper 01:04, 31 August 2005 (UTC)

If I calculated correctly: Let {x,y,z}={sin(long),cos(long),cos(lat)} and then lat=arccos(z) and long=arctan(x/y) if y>0 or long=arctan(x/y)+180° if y<0. Remember that {a,b,c}×{d,e,f}={bf−ce,cd−af,ae−bd}. Then, given the points A and B, the other two points on the tetrahedron are ±√(3/8)(A×B)−(1/2)(A+B). A and B must have the distance √(2/3) from each other. Κσυπ Cyp   13:15, 31 August 2005 (UTC)

Testing randomness

How can one test the randomness of a set of numbers? --anon 19:29, 24 August 2005 (UTC)

Check out the random article, it is really very tricky. What exactly do you want to know? When people are 'testing the randomness' of numbers, they are usually estimating a probability that a certain series of numbers occured randomly, a central concept in statistics. Give us a bit more detail. Trollderella 19:40, 24 August 2005 (UTC)

Given two sequences of numbers, in the range [0, 5000], one was generated "randomly", and the other was not. I need to determine which was not random (the random one is supposed to be a uniform distribution over the integers within the range). --anon 19:45, 24 August 2005 (UTC)

I'm not trying to be difficult, but if there is a "uniform distribution", then those numbers aren't really random, are they? -Aranel ("Sarah") 23:22, 24 August 2005 (UTC)h value has an equal probability of appearing. If I generate a series of numbers by throwing two dice and recording the sum, the series will be random but not uniform. most random (and pesudo-random) number generators create (or approximate) a uniform distribution, but some intentionally generate non-uniform but random distributuions. DES ^(talk) 02:15, 25 August 2005 (UTC)

To say tha a random sequence has a "uniform distributuon" means that eac

Actually after about five seconds of thought I more or less get it. But it depends on the size of the set of numbers. If there are, say, only five numbers, and they are uniformly distributed, that would be highly suspicious. The uniformity of the distribution becomes a more useful indicator as the size of the set increases. It is also more useful applied as an average—you would expect there to be some clumps and some large, open gaps, but in general it should average out about even if the set is truly random. -Aranel ("Sarah") 02:24, 25 August 2005 (UTC)

Have you looked at the frequency of each integer? Are you interested in the sequence, or the distribution of the integers? Trollderella 20:01, 24 August 2005 (UTC)

Looking at the frequency, each number appears at most once. (The sequences are rather short.) I am interested mainly in the distribution of the integers. --anon 20:04, 24 August 2005 (UTC)

The shorter the sequence the more difficult the task. Taking a two random number sequence in the range [0, 5000] that you specified, the two numbers would be identical every 5000 times or so. hydnjo talk 22:22, 24 August 2005 (UTC)

This may be a pretty good question if it is made precise. As it is, it's too vague to know what you mean. Michael Hardy 22:29, 24 August 2005 (UTC)

I assume that the random set has a uniform distribution. The easiest way is to look at the average value. This would 2500. So add up all the numbers in the set and divide by the $|S|$, the number of elements in the set. The random set should be the one closest to 2500. You can also look at the average deviation from the average. This should be 1250.25. Calculate

$\sum _{i=0}^{|S|-1}|S_{i}-2500|$ for a set S.

The set that is closest to 1250.25 should again be the random set. --R.Koot 00:27, 25 August 2005 (UTC)

In addition, if the sets are small, I would be skeptical that the random one does indeed have a uniform distribution. Trollderella 01:04, 25 August 2005 (UTC)

Uniform distribution would be a property of the random number generator used. As this sounds like a homework assignment I think this method should work. --R.Koot 01:08, 25 August 2005 (UTC)

Am I wrong in thinking that uniform distribution would not necesarily be a property of small, random sets sampled 'in the wild'? Trollderella 01:24, 25 August 2005 (UTC)

No, I just assume the set were generated by a RNG, and are large enough to satify the proberties above with a high probability. --R.Koot 01:26, 25 August 2005 (UTC)

This is an enormously complex topic and has been the subject of reams of research; as well as being a fundamental problem in statistics it has massive applications in cryptography. It is also of pragmatic interest to researchers in physics and chemistry in their simulations, who want numbers that are "random enough" but want them as quickly as possible. It's also something that keeps online casino proprietors awake at night; if their random number generators are insufficiently random they'll lose a lot of money very quickly. The random number article has some pointers to start with. You might also want to have a look at Donald Knuth's The Art of Computer Programming - while the specific algorithms he suggests are obsolete some of the randomness-testing techniques aren't. However, if your interest is because you want a good random number generator for some project my sincere advice to you is to have a look in the literature and pick one. The Mersenne Twister has got some attention recently as both fast and good for simulation purposes, for instance, but is useless for the cryptographic and online casino purposes mentioned above.--Robert Merkel 03:22, 25 August 2005 (UTC)

horizont

How can I measure the distance where I'm standing from an open field such as a beach to the horizon

See the horizon article, which tells you precisely this. Shantavira 17:11, 25 August 2005 (UTC)

4 Your coverage of Vespasian does not include the fact that his family, and himself, were Mule breeders! The fact that his father was a "equestrian," does not mention "Mules."

Unidentified insect on a stick!

What in the world is it? It looks very similar to a fly to me, but it's only 20-30 times bigger..

Also, I would like to preserve it. If i keep it in a peanut butter jar, will it stay in good condition? What about if I put it in acrylic resin?

--Phroziac ^(talk) 16:26, 24 August 2005 (UTC)

It is a cicada. See our insect collecting article for links on how to mount them. In a case protected from water spills, etc, they generally keep for years, so your jar should be fine, though restricting the air flow in a tight jar may actually be worse rather than better. I guess they'll mold eventually, so you could use some preservative, but since they are so common, you could always just get another. - Taxman ^Talk 16:47, August 24, 2005 (UTC)

You could preserve it in an alcohol mixture. If I recall correctly, which I doubt, it should be 30% ethanol and 70% water. Although it may actually be 50/50. I dropped out of my entomology class. --Lord Voldemort ^{(Dark Mark)} 16:57, 24 August 2005 (UTC)

From the last external link in the insect collecting article, it says "Since insects have a hard shell or exoskeleton and all of the soft parts are on the inside, they tend to keep rather well after drying, even for long periods of time. Only a small amount of maintenance is necessary to keep them in good condition. Many specimens in museums today are over one hundred years old and look just as they did on the day they were collected.". It also mentions alcohol only for soft bodied insects. The cicada is hard bodied so it should be fine. - Taxman ^Talk 18:01, August 24, 2005 (UTC)

Cool! Thanks :) --Phroziac ^(talk) 17:04, 24 August 2005 (UTC)

Large cicadas, like large beetles, can rot internally if pinned straight off. Removing the innards and stuffing with cotton wool or similar is sometimes useful if you wan tto keep it dry. I can't see exactly how large the cicada in the photo is, however, so this may not be necessary. 80.255 18:11, 24 August 2005 (UTC)

It is 1 3/4" long. It wasn't my choice to jab it with a stick, my dad kinda did that when i showed it to him. I have epoxied the stick to the inside of a peanut butter jar lid, with JB weld, and have a pair of needlenose pliars holding it up. Will make a neat display when it dries. And if it doesn't work, then oh well, it didn't cost me anything to do. --Phroziac ^(talk) 18:32, 24 August 2005 (UTC)

The food clasification of a pumpkin

Is a pumpkin a starch?And is any squash a starch or carbohydrate?

• You'd best start with our articles on pumpkins, squash and starch. You need to realize that neither of the two vegetables (or are they fruits?) are made up of one type of molecule. But I do think they contain some type of sugar which is a carbohydrate. - Mgm|^(talk) 18:14, August 22, 2005 (UTC)

"It tastes like chicken."

A few stand-up comedians have commented on the real-world phenomenon of people who have eaten exotic (to a Westerner's palate) animals reporting that the animal tastes "like chicken".

What I'm wondering is whether any chemical analyses have been done of different meats that shows that the cooked flesh of various animals is near-identical and would account for the similarity in taste. --bodnotbod 01:09, August 23, 2005 (UTC)

When I was in high school, I believed trilobites would taste like shrimps while dinosaurs would taste like chicken jerky. I still think so. -- Toytoy 01:19, August 23, 2005 (UTC)

Well you're wrong. Sorry I've said too much.

I've recently been reading Harold McGee's book "McGee on Food and Cooking: An Encyclopedia of Kitchen Science, History and Culture" (he has written other similar titles). Apparently the muscle fibres of meat are fairly similar across species but the real difference lies in the fat (which being a storage organ, stores any fat-soluble molecules that the animals may ingest) - apparently lamb/sheep meat has a lot of thymol in it. Also the gut bacteria and their breakdown products will differ among different species and that will contribute to the taste as well. It's a fascinating book! Jo Brodie, 16:42 GMT or BST - I can never remember ;-), Aug 30, 2005

botany

can beetroot leaves be eaten? duncan

Yes, you can use them in a salad. [1] --R.Koot 01:32, 25 August 2005 (UTC)

Chard is the same plant, bred for its leaves. Eating qualities are similar. Personally, I find both a little harsh raw, and would advise at least a brief steaming. — Pekinensis 02:20, 25 August 2005 (UTC)

Mosquito immunity

I have an unusual condition which earned me much envy over a summer spent on the Chesapeake Bay and in the Maine woods: I am almost immune to mosquito bites. When I am bitten all traces of the bite disappear within fifteen minutes (sometimes literally right before my eyes), while everyone else I know retains an itchy welt for days on end. Does anyone know why this might be? (Sad to say, I lack a similar immunity to the bites of horseflies and black flies and the stings of jellyfish.)

--edward

Hi Edward. I don't know where you live, but we in India have never heard of an itchy welt for days on end [following a mosquito bite]. It is common here to see all traces of the bite disappear within fifteen minutes. So, I don't think you've an unusual condition. -- Sundar ^{\talk \contribs} 04:48, August 25, 2005 (UTC)

You must be having an alien blood group. :) I have noticed that mosquitoes tend to go for certain kinds of people. For example, I've noticed that mosquitoes hover around some people in the same room I am in, whereas they rarely come near me. (Oh, and yes I have a bath daily :D ) =Nichalp «Talk»= 07:43, August 25, 2005 (UTC)

Ha, ha. I wasn't telling that mosquitoes don't bite me, but simply that the symptoms last no longer than 15 minutes. But, of course, the mosquitoes tend to bite my mother more than me. (I too do take bath daily ;) -- Sundar ^{\talk \contribs} 13:07, August 25, 2005 (UTC)

I don't know how "special" you are in this case. I used to work at a Boy Scout camp for a few summers. While there the staff would get used to the mosquitoes to the point that none of us used any sort of repellent. The Scouts that would show up every week would be putting on repellant and slapping mosquitos all around us but the staff member would be able to stand there and not even notice the bugs. To this day, mosquitos don't bother me unless there's one buzzing around my ear while I'm trying to sleep. Dismas 11:29, 25 August 2005 (UTC)

As with other immunological reactions, "naturally acquired desensitization to mosquito bites occurs during long-term exposure." [2] Gdr 12:36:32, 2005-08-25 (UTC)

Far Side of Earth

If Moon has a far side, is there an earth equivalent? That is, when standing on moon, will one always only see, say, the Western Hemisphere? --Menchi 20:50, 25 August 2005 (UTC)

No. Observers on the Moon would see the Earth rotate below them once every 23h56min or so. If this were during the period when the Moon is "new" (as seen from the Earth), the relevant parts of the Earth's surface would be sunlight. Physchim62 21:17, 25 August 2005 (UTC)

What about the poles? If the earth's axis of rotation is angeled compared to the moons orbit around the earth (which is the case isn't it?), you wouldn't be able to a part of the north or south pole. This would then switch as the moon rotates around the earth, allowing you to see the entire earth, if it wasn't for the requirement of the moon being new. --R.Koot 21:33, 25 August 2005 (UTC)

Yes, part of one of the polar regions would be invisible throughout the fourteen day "Full Earth". However, this is not quite the same as the "Far Side of the Earth", because all parts of the Earth's surface would be visible at some point during the (terrestrial) year (as Fvw points out below). Physchim62 23:29, 25 August 2005 (UTC)

Keep in mind that if there were such a spot, there'd be a part of the earth's surface from which you could never see the moon. --fvw* 21:27, August 25, 2005 (UTC)

Language codes

In HTML, you can mark text as being in English with either <meta http-equiv="Content-Language" content="en-gb">, or with <div lang="en">. How do you mark text as being in quenya and other fictional languages? Ojw 16:10, 21 August 2005 (UTC)

HTML language tags are described in detail here and use ISO 639 country codes. ISO 639 seems to have an entry for some fictional languages, e.g. Klingon (tlh), but not Quenya (or Sindarin, or even Elvish). x-quenya is probably as good as anything. -- Rick Block (talk) 18:08, August 21, 2005 (UTC)

Teaching HTML to kids

I'm teaching my daughter and neice HTML. The only thing is I don't know that much myself, i feel as if I am only one step ahead of them. Anyway I don't want to teach bad habits, and I don't want them to have to unlearn later, stuff I taught wrongly in the first place. So I'm thinking use tags for structure rather than display, concentrate on content over style, XHTML,and CSS. Does anyone have any advice for me? The girls are 13 and 12. Can anyone recommend any good tutorials on the web that they can work through? We have an idea for content, we thought a kids version of the not pr0n game. We'll need javascript for the level passwords, and i don't know any javascript so a kids tutorial on how to do that would also be useful. TIA Theresa Knott (a tenth stroke) 00:19, 26 August 2005 (UTC)

I don't know about a "kids' tutorial", but if it helps I was about that age when I got into HTML. Two sites I recommend (and used heavily) for tutorials in HTML and Javascript are HTMLGoodies and Webmonkey. On Webmonkey, I especially recommend the frame picnic tutorial and Thau's Javascript Tutorial. Also, make sure they start out typing tags and attributes in lower-case. Apparently, it's required by XHTML, and I'm never going to get used to that now. Remember to validate everything you make at the W3 Validator. It works for CSS and XHTML. Superm401 | Talk 03:19, August 26, 2005 (UTC)

I will second the HTMLGoodie recommendation, and add this short anecdote . . . One day several years ago I was stuck in a corporate classroom being taught something or other and I decided to make more productive use of my time by reading Thau's Javascript Tutorial. It was indeed useful, but one of the links buried within the lessons went to a website called "Bianca's Smut Shack." Luckily nobody seemed to be monitoring net-usage very closely that day, but it's something to be aware of if 12 and 13 year olds are involved. LarryMac 17:53, 26 August 2005 (UTC)

Thank you I shall take a look. As for Bianca's Smut Shack, thanks for the warning but it's pretty nigh on impossible to keep kids away from -everything- and to be honest I don't care if they see nudity or mild porn. (There's a lot more important stuff to worry about than that). Theresa Knott (a tenth stroke) 23:36, 26 August 2005 (UTC)

Superm, you need to use http:// for your links to work: HTMLGoodies and W3 Validator. Anyway, Theresa, why not just pick up XHTML and JavaScript tutorial books from your local (or virtual) bookstore? They may not be directly oriented toward kids, but they won't have anything offensive in them either. Personally, I find books easier to learn from than online tutorials. Garrett Albright 12:23, 26 August 2005 (UTC)

Well we'll do that as well. Theresa Knott (a tenth stroke) 23:36, 26 August 2005 (UTC)

I apologize for the bad links. I suppose I forget for a moment that they would actually be parsed as links, rather than displayed as text. Please don't assume that means you should ignore my advice on this topic. I'm well aware that HTML requires the protocol to be specified in links(as well it should). As for the Smut Shack, I never noticed any link to it when I read the tutorial. A little investigation now reveals a vague line in his bio saying "he is a core troll at bianca's" and I do see references to Bianca's Smut Shack elsewhere on wired, but there is never a specific link to the site in the actual tutorial, according to Google. If it is there, could you say where in the tutorial you found it? Superm401 | Talk 01:12, August 29, 2005 (UTC)

It all depends on how you learn best. I've always found the "look at the source code for something similar to what you want and tweak it until you understand how it works" method is better than books or tutorials for me. — Laura Scudder | Talk 17:05, 26 August 2005 (UTC)

Be sure not to use FrontPage (or even worse, Word!) if they're going to use WYSIWYG at some point. It might be quick and easy to create a page, yes, but you end up with horrible, messy code. --Pidgeot (t) (c) (e) 00:15, 27 August 2005 (UTC)

Identification of earth-crawling insect

I hope this is the right category (biology/etymology). I need help identifying a burrowing insect; I don't have a picture but I do have a description. For a long time I thought they were millipedes -- but a recent Google Image Search for "millipede" indicates that millipedes are nowhere near as tiny as the things I'm talking about. Nor are they centipedes. These are very small, but they do have tons of legs and an elongated body. I usually see them in clusters, rarely alone, and they have a urine-like odor to them (quite a strong urine-like odor if you get a whole handful of these critters, too). Body usually brown, with shiny yellow or dark-orange legs. They seem to shrivel up and dehydrate if left in the sun for more than 8-10 minutes. Here in California but I think I remember seeing them in the northern part of North Carolina as well, so I don't think they're too specific to any particular region in the United States. --69.234.223.139 04:14, 26 August 2005 (UTC)

• I think we can safely say you have there a millipede, or a centipede (not strictly an insect). See those articles to determine the difference. These critters come in thousands of different colours and sizes, so it would be difficult to say which species you have there. Some are indeed very small, and even the big species will have babies. If you can manage to count the legs, it will help you identify the species. Shantavira 08:21, 26 August 2005 (UTC)

Semi-conductors

I want to know how one decides what should be the doping impurity for a particular kind of semi-conductor?

The doping changes the band structure or band gap of the material, and it really depends on what the application is. You want to consider the conductivity, and also the number of holes and electrons that will be introduced to the silicon. Also, it depends on whether the substrate is silicon or GaAs for example. Check out the article semiconductor to get some other ideas too. Doping and dopant might be useful too. Hope this helps!--HappyCamper 05:21, 26 August 2005 (UTC)

Telecommunication : 4G/WiMAX

Hello, I would like to know the difference between 4G and WiMAX. Is it the same thing or is the WiMAX a smaller part of 4G?

Thank you,--Rafik 10:15 26/08/2005 Geneva

No they are not. WiMAX is a successor/complement of WiFi that allows wireless communication over greater distances at greater speeds. 4G is a standard for mobile devices that is just vaporware at the moment. 2G refers to the traditional communication using GSM/EDGE. 3G will usually use UMTS but can still use GSM, but usess those transmition standards to send IP packets. 4G might (this is looking into a crystal ball) use WiMAX as it's transmition standard, but will also include other standards. --R.Koot 11:34, 26 August 2005 (UTC)

AAA Battery

• (1) Does my AAA battery (alkaline battery) have an electric indutor or any other circuit element in it?
• (2) Do AA and other kinds of batteries have the same type of circuit? If so, what is the circuit type?

I will highly appreciate any word, analogy, picture, diagram, or explanation that will enable me to understand this topic.

-anonym

Batteries contain no circuits themselves, but are just a set of electrochemical cells (there's a better explaination of the idea at galvanic cell). So there is no circuit until the two ends of the battery are hooked up to other circuit elements. Since inductors dissipate energy by resisting changes in the current, I would doubt anyone would build one into a battery, but real-world batteries are sometimes treated as if they consist of an ideal battery and a resistor in series. — Laura Scudder | Talk 20:02, 26 August 2005 (UTC)

• What is the relation of AA batteries and DC circuits? Is there a DC circuit inside my graphing calculator (TI-83)? Also, am I correct that every portable device such as a flashlight, calculator, et cetera has a DC circuit within it?

--anonym

In circuit theory, you can separate any circuit into its DC and AC component behaviour. That is to say, each and every circuit element is made of a part which affects DC current, and AC current. The DC part is essentially the voltage offset of your circuit. The AC stuff is usually used to represent the signal the you feed into the circuit. Hmm...this discription is sort of vague, but please feel free to come back if you need more help. --HappyCamper 04:52, 27 August 2005 (UTC)

• Let me focus on the circuit of a graphing calculator. Based on the above explanations, if I put a battery inside my calculator, then the battery completes the circuit. Now, this completed circuit has both a DC and an AC part. Did I get this right?

--anonym

Pretty much all electronic devices use direct current, because computer processors and such only work with DC. That means your computer, TV, and just about everything else converts the AC from the wall into DC to use it. (On the other hand, AC is better for strong motors and such, so your blender probably doesn't do this conversion, and your washing machine probably uses both; AC for the moving parts, and converted DC for the electronics.) As there's no need for your calculator to use AC, it powers itself by DC only. DC is the only kind of juice you're getting out of a battery, unless you convert it to AC... I don't think that's even possible, but IANAElectrician. (I might be wrong on other things too, but I know for a fact that your calc is DC only.) Garrett Albright 14:48, 28 August 2005 (UTC)

DC → AC is possible (check out the power inverters that create 120/220 VAC out of a car's 12VDC supply) but I don't recall the details on how. — Lomn | Talk / RfC 13:33:31, 2005-08-31 (UTC)

Photon visibility

Is a photon invisible until it reacts with mater? Are all photons in EM spectrum invisible? Thank you .... Thomas

The act of seeing a photon requires that the photon is destroyed by being absorbed by matter. This is true for all of the spectrum. But since we don't usually say that things are invisible just cause you happen to have your eyes closed, I wouldn't say that photons are invisible until they are seen if you get my distinction. — Laura Scudder | Talk 20:51, 26 August 2005 (UTC)

Soreness and swelling in the armpits

Just today I've developed soreness and small swellings in both armpits. I thought it was just an unpleasant spot (or pimple), but it's rare for me to get spots, rarer for me to get one under the armpit, and unprecedented to get such under both on the same day and they're quite sensitive/sore.

I seem to remember that this is a symptom of the bubonic plague, however I am sensible enough to realise this is an unlikely cause.

Is something up with my lymphatic system?

Note: I realise WP isn't a subsitute for proper medical advice, and if it persists I'll go into the doctor's on Monday... in the meantime I'm interested in theories. I'm going to regret this deicision if someone scares me, obviously, but hey-ho... --bodnotbod 23:42, August 26, 2005 (UTC)

You should go see a doctor - but you alrady know this. However before contemplating lymphomas (Yeah we know you were) think about the following - What were you wearimg today? What has it been washed in? Did you put on deoderant, in short was there anything environmerntal that could have caused this? Theresa Knott (a tenth stroke) 23:57, 26 August 2005 (UTC)

Just a familiar old T-shirt, washed in the usual washing liquid. No deoderant (I didn't leave the house). I can't think of any change to routine. --bodnotbod 00:22, August 27, 2005 (UTC)

Swelling in the lymph nodes is a common symptom for many types of infection. While I would think about potential new environmental factors first, failing that you could also check your other lymph nodes for swelling, too. I would think that since both armpits are affected any infection is not terribly localized, so you'd expect some swelling elsewhere. Try feeling just under the sides of your jawbone like the doctor does when you have a cold. You might need a healthy volunteer for comparison if you're not regularly feeling up necks. — Laura Scudder | Talk 00:27, 27 August 2005 (UTC)

I've got quite a pronounced jawbone, no facial fat and a skinny neck: all ideal terrain to detect swelling. Can't seem to find any, nor any tenderness. I am feeling run down though. I feel like I sometimes do before a rotten cold sets in. Not quite giddy, but slightly as if my balance is pausing a quarter second before catching up with my movements. --bodnotbod 00:32, August 27, 2005 (UTC)

Do you have a thermometer? Theresa Knott (a tenth stroke) 00:34, 27 August 2005 (UTC)

No, I don't have one unfortunately. I think I'll start drinking iced fluids just the same though. --bodnotbod 00:43, August 27, 2005 (UTC)

This doesn't sound like a serious problem, of course, who am I to say that? See a doctor if it still bothers you. I'd wait 24 hours to see if it subsides. Could it be possible that you were bitten by an insect coincidentally, and it happens that you are allergic to their bties? --HappyCamper 03:14, 27 August 2005 (UTC)

No, I don't think bites are likely. I don't get out much (nor does much get in). I no longer seem to have any feelings of something coming on, and the swelling is no more tender than yesterday and may very well have subsided slightly. Things are looking up. My doctor's won't be open til Tuesday since it is a bank holiday here this weekend, I suspect it (whatever it is) will have passed by then. --bodnotbod 20:02, August 28, 2005 (UTC)

Counting

Two cards are chosen in order from a deck. In how many ways can this be done if (a) the first card must be a spade and the second must be a heart? (b) both cards must be a spade? --anonym

Think about it. How many cards are ther in a deck? How many of them are spades? What's the change that the first card is a spade? Right now how many cards are left (after you just removed one)? How many of these are hearts? What's the chance that the second one is a heart? Now you've got two probabilities, what's the change of the first one and the second one both happening? Theresa Knott (a tenth stroke) 01:29, 27 August 2005 (UTC)

This is not a probability question. It is a counting question.

(a) 13×13 = 169.

(b) 13×12 = 156.

Am I right?

--anonym.

Yes you are I misread the question. Theresa Knott (a tenth stroke) 02:15, 27 August 2005 (UTC)

scientific proof

Two questions about Intelligent design:

1. What is your scientific proof that an intelligent designer exist?
2. What exactly are your meterals for a class on intelligent design? What are you going to teach? Do you have a full semeter worth of meteral to teach?

1. The article on Intelligent design describes it as a controversial assertion not a scientific proof.
2. This is an Encyclopaedia not a classroom nor a structured course of study. hydnjo talk 04:57, 27 August 2005 (UTC)

The reference desk is here to answer questions. The way these particular questions are presented implies they were posted by a teacher who is looking for help with lesson plans or curriculum. They also imply that the particular curriculum being formulated is a plan to insert "intelligent design" into a science class. So we can point out that most people agree that "intelligent design" is not a scientific theory, but rather an "argument from improbability/ignorance" or "god-of=the-gaps argument": that is, it's a philosophical or religious "theory" rather than a scientific theory, which would be open to testing and modification. So the correct answer to the first question is "there is no scientific proof that an intelligent designer exists". The answers to the following questions should probably be: I have no materials for such a class, I'm not going to teach it, and there isn't a full semester's worth of material on Intelligent Design: instead I'm going to make sure my class has a solid foundation of scientifically based knowledge of biology. - Nunh-huh 05:07, 27 August 2005 (UTC) (Is this a subtle test of the new "Reference Desk" sorted-into-categories? "Intelligent Design" isn't "science". - Nunh-huh 05:07, 27 August 2005 (UTC)

Regardless, it still shows that we Wikipedians are robust enough to answer any question that shows up on the RD! --HappyCamper 07:00, 27 August 2005 (UTC)

Stuck on 137 GB

As loathe as I am to go to Wikipedia as tech support - hardly the purpose of this site - I'm really running out of options here, so here it goes... I recently installed a Maxtor 200 gb drive in my Gateway 700S desktop. Unfortunately, while I know the drive contains 200 gb, the operating system flat out refuses to recognize that the drive contains anything more than 137 GB.

What makes it doubly weird is that I just flashed my BIOS, and *it* recognizes that there are 200 GB in there. It's just the operating system - Windows XP Professional, SP2 - that's the problem.

I've talked with Gateway tech support, and they say that the only solution is to reformat my main hard drive and reinstall Windows. It strikes me as a bit blunt of a solution, and I'm loathe to do unless I know for certain it'll work. Anyone out there have any more advice for me? I could use a second opinion.

Thanks. --Brasswatchman 03:43, August 27, 2005 (UTC)

Hmm...when you load Windows and right click on the drive, can you attempt a repair and see what happens? --HappyCamper 04:01, 27 August 2005 (UTC)

Sorry, a repair? I don't see that option when I right click on the drive. Perhaps you mean re-formatting the drive? --Brasswatchman 04:20, August 27, 2005 (UTC)

No, not a reformatting. The other day I had a similar problem with my drive. 80 GB, but only showed up as 12 GB. Had something to do with partioning, and all I had to do was to delete it. I did this on another computer, so I don't have screenshots for you at the moment. --HappyCamper 04:48, 27 August 2005 (UTC)

Is it possible that you have a partition on the drive which is less than the full drive size? "Right click" on My Computer and select "Manage". Then choose "Disk Management". XP doesn't provide facilities to resize a partition, so if it is less than full size and you don't want to reformat, you'll need to buy a third-party partition resizing utility, or create a second partition to use the remaining space.-gadfium 07:01, 27 August 2005 (UTC)

There's a (fairly dangerous in ther wrong hands) free util called DELPART which will delete any partition you point it at. And FDISK is normally handly for checking out what partitions are on a device. They should be your friends. --Tagishsimon (talk)

Fdisk is no longer part of Windows XP. Disk Management is the replacement for it. The reply immediately below this with the link to seagate.com is the most useful one.-gadfium 19:40, 27 August 2005 (UTC)

The original releases of Windows XP had trouble seeing more than 137gb of a hard drive - see this link for example. The easiest solution is to partition the drive, something familiar to anyone who remembers the old 2gb limit from days gone by; I would partition a 200gb drive into a 20gb partition for the operating system and other core utilities, and two 80gb partitions for... games and music, for example. -Ashley Pomeroy 14:10, 27 August 2005 (UTC)

Disk Management seems to have done the trick. Thank you all very much. Don't know what I would have done otherwise. :) --Brasswatchman 19:41, August 29, 2005 (UTC)

Conflict between articles - relativity

Two articles (below) disagree on application of SR to accelerated systems. Which is correct ? Can't the 2 editors convene to correct this contradiction?

from "Sagnac effect": The result of the Sagnac experiment has been cited by many as a disproof of the theory of relativity.... The reasoning is that if the speed of light is a constant for the observer, then for the observer on the rotating ring light should take the same time to travel each way and no effect should occur. This argument does not hold because the rotating ring is an accelerated frame of reference, while the constancy of the speed of light (c) applies only in inertial frames of reference.

from "Status of special relativity": A common misstatement about relativity is that SR cannot be used to handle the case of objects and observers who are undergoing acceleration (non-inertial reference frames), but this is incorrect. For an example, see the relativistic rocket problem.

Robert Bennett

• Not a contradiction. Both are true:

1. - According to SR, the speed of light is constant only in inertial (non-accelerated) frames.
2. - It's perfectly possible to calculate, using SR, the behaviour of observers in non-inertial frames. It's just they won't measure the speed of light as a constant. -- DrBob 16:21, 27 August 2005 (UTC)

Printer Issue

I have an all-in-one inkjet printer (Brother MFC-3420). Recently it has been showing white horizontal streak or lines through printed text. I have checked the ink; I have also restarted the printer. However, neither of these actions have proved fruitful. Can anyone tell me how to fix this problem? (I have had the printer for a year and a half.)

--anonym

Sounds like the cartridge is running out of ink, or that it has dried up. Have you bought a new cartridge? Another possibility is that its clogged up. Try cleaning the head carefully with some wipes and see if it helps. --HappyCamper 04:45, 27 August 2005 (UTC)

Clogged jets on the printer head is my guess. It is possible to soak it in water (just the tip of the print head itself, not the electronics) but there may be further damage so that may not work. -- WormRunner | Talk 05:15, 27 August 2005 (UTC)

Radii for an approximate ellipse

How would you construct an approximate ellipse using two radii only? What would be the ratio of the lenght of the two radii, for a known ratio of the lengths of major and minor axies (say 1:1.3) ? thanks chrish

Some questions for you:

• What is an "approximate ellipse"?
• What is the radius of an ellipse?
• Do you allow rotations, or do the axes have to lie on a predetermined set of coordinate axes?

--Smack (talk) 18:50, 27 August 2005 (UTC)

I'm not sure if this is what you're after, but interesting anyway: If you're trying to draw an ellipse you don't need to be approximate at all. Just take a short length of non-stretchy string, tie the ends to two push-pins. Put some paper on cardboard and push the pins in any two spots (if they're really far apart you'll get a really flat ellipse; close together you'll get a more round one). Use the string to guide the path of the pencil by keeping the string taut like in this picture. To get specific semimajor and -minor axes, use the pythagorean theorem to figure out the distance between the push-pins and length of the string like they do here. — Laura Scudder | Talk 20:42, 27 August 2005 (UTC)

- an oval is probably a more appropriate term for my 'approximate ellipse' When making 'elliptical' paving for a terrace each section of paving is made by packing the material into a mould to set. the constraints of manufacture are such that each mould section can only be a true radii. thus the need to breakdown an ellipse into an approximation with a number of sections of different true radii. since each mould is quite costly the cheapest method is to form an approximate ellipse or oval using two radii only. one larger radius centred on the minor axis and a smaller one on the major axis so that the circumferences meet at a common tangential point. it would be useful to have a correlation between the ratio of axies and radii so that for a given set of axies lengths and one chosen radii the second radii could be calculated. at present this is only found by trial and error, with paper and compasses. chrish

Electro magnetic Pulse and deisel engines

Hi, I have just seen War of the Worlds and note that all the cars (and everything else) was stopped by the EMP. But I've also been told by an ex-mechanic that a deisel engine would not be affected in the same way as it works on compression ignition. So as long as it was running when the EMP struck it should continue. Have I got one over on Mr Spielberg?

That may have been true at an earlier time (pre-electronics) but today's engines and automobiles have quite a bit of electronic stuff controlling their operation. However, even back then, hand cranking a deisel engine would pose quite a challenge. Today, no microchip, no run. hydnjo talk 16:00, 27 August 2005 (UTC)

Electromotive Force and Voltage

Can you explain to a layperson the difference between emf and voltage?

--anonym

Tricky! Check out electromotive force and voltage to get some ideas for starters. I personally don't know what the difference definitively is - in fact, thinking that they are the same thing has always worked for me. Maybe some more knowledgable Wikipedian can help out here. --HappyCamper 01:02, 28 August 2005 (UTC)

Unfortunately those two articles are, hmmmm, non-optimally written! Electromotive force is only used in connection with a generator (which might be, for example, a battery or a mains socket): it is the electrical potential difference (voltage) between the poles when no current is flowing. Theoretically, it cannot be measured directly, but can be extrapolated from measurements at non-zero current: in practice, modern voltmeters draw so little current that there is usually no need for a correction. Electrical potential difference (usually known as voltage) is defined between any two points in a circuit, notably between the poles of a power source in normal use: the same (theoretical) measurement problems apply. HappyCamper is correct in implying that there is rarely a need to distinguish between the two. Physchim62 01:42, 28 August 2005 (UTC)

I should add that the measured voltage is always lower than the theoretical emf, because no real voltmeter has infinite resistance. Again, in practice, there is rarely a problem. Physchim62 01:46, 28 August 2005 (UTC)

Faraday's Law of Induction

How is $v(t)=L{\frac {d}{dt}}i(t)=L{\frac {d^{2}}{dt^{2}}}q(t)$ related to$E=-{\frac {d\phi _{B}}{dt}}$?

1. Why is there a negative sign in Faraday's Law of Induction?
2. What is magnetic flux in simple terms?
3. How is magnetic flux related to the change in current?

Please add anything that might amplify my understanding.

--anonym

Math equation - the question as it is asked doesn't really make sense. Well, I guess you could set V = E, but that really doesn't tell you much. Where did the equation come from?

1. Faraday's law of induction has a negative sign because of Lenz's law. It has to do with conservation of energy. If it had a positive sign, it would essentially mean some really weird physics would happen: Take a coil, and put a magnet right beside it. Nudge the magnet into the coil so that an emf results. This emf would then suck the magnent in further, and create more emf, et cetera...You would be creating energy! The negative sign is there to ensure that this situation cannot occur.
2. Handwavy definition: "Magnetic flux" is a measure of the amount of the magnetism passing through an area. Flux generally means "stuff going through something".
3. Check out SI units. In particular, notice that magnetic flux is measured in Webers. A Weber is a Volt*second, or Watts / (amps/second) --> hence, magnetic flux is Watts divided by the change in current over time. In other words, its a measure of how much energy can be delivered by a unit change in current over time. But admittingly, I'm not as sure of these answers as I would like to be. Hopefully some other Wikipedian will come by and comment too... --HappyCamper 01:22, 28 August 2005 (UTC)

Induce

In electromagnetism, does induce mean to bring about a change in current? --anonym

What's the full context? I guess "yes but not always", it really depends on the context. --HappyCamper 01:23, 28 August 2005 (UTC)

• [Michael] Faraday concluded that although a steady magnetic field produces no current, a changing magnetic field can produce an electric current. Such a current is called an induced current.... Motion or change of [the magnet] is required to induce an emf.

My source is Physics, 5th edition, by Dougals Giancoli, p.623.

--anonym

In your above contexts you could replace induce with bring about a change in or create a (fill in the blank) where there wasn't one. The word induced is helpful to let us know that this current or that emf isn't around because the wire's hooked up to some battery, but it was created by a changing magnetic field. It effectively tells us the proximate cause of the current. — Laura Scudder | Talk 19:19, 29 August 2005 (UTC)

Light through vacuum

Can a ray of light travel through vacuum? And does is have mass? If it doesnt, then is it affected by gravity?--203.92.55.61 04:33, 28 August 2005 (UTC)Royd

Yes, no, yes.

1. Light can travel through a vacuum - if it couldn't, you wouldn't be able to see the stars or the sun.

2. Light is made up of photons, which don't have (rest) mass, however...

3. ...they are still affected by gravity despite being massless. A beam of light will be deflected by a gravitational field, because photons have momentum, as predicted by general relativity; this leads to interesting effects like gravitational lensing.

Hope that made some sense! Shimgray 04:48, 28 August 2005 (UTC)

Increase Fret board length of guitar

I have an acoustic box guitar with 12 playable frets. Is there anyway i can increase the length of the fret board to accomodate atleast 22 frets without affecting the overall physics of the guitar? No modifications on the body is permitted. --203.92.55.61 05:22, 28 August 2005 (UTC)StratOnLSD

Hmm...to compensate, you'd need to change the tension in the strings, and this may not give a very desirable sound. Maybe there are other ideas out there? --HappyCamper 05:59, 28 August 2005 (UTC)

Not really, as the frets are at fixed proportions of the length of the open string (this is why there are different distances between the frets). By the time you have had a new fret board constructed and fitted to your guitar, you would be better off by a completely new model. Physchim62 17:28, 29 August 2005 (UTC)

It's pretty impossible to cut any more frets in a guitar without getting a new fingerboard, at least in my experience. However, with a little knowhow, you can make a new fretboard for your guitar, keeping the original bodywork. You can have up to about 30 frets cut into your fingerboard, assuming your fingers are small enough - Ron Jarzombek, guitarist for Spastic Ink and WatchTower makes his own guitars with up to 29 frets. Not sure whether it would work quite as well on an acoustic! Good site for instrument-making links - http://www.mimf.com/link.htm . Also, there's a cool fret calculator program here - http://www.dougsparling.com/software/fretcalc/ . Hope this helps. --Lawrence Dunn <e-mail removed>

Counting Straight Lines Formed by Dots

Twelve dots are drawn on a page in such a way that no three are collinear. How many straight lines can be formed by joining the dots?

--anonym

66. David Sneek 08:16, 28 August 2005 (UTC)

Ok, I'll play:

No three are collinear, and so every combination of two dots define a unique line. n! / (n-r)! = 12! / 10! = 12* 11 = 132. Two dots can be chosen from twelve dots in 132 different ways. - Nunh-huh 08:29, 28 August 2005 (UTC)

But didn't you count every line twice? David Sneek 08:54, 28 August 2005 (UTC)

• • 66 is right. The formula is n*(n-1)/2. Me and my generating functions again: the values starting at n=3 are 3, 6, 10, 15...; the generating function is f(n) = f(n-1) + (n-1). It's the number of sides plus the number of diagonals in an n-gon. --jpgordon∇∆∇∆ 17:33, 28 August 2005 (UTC)

$C(12,2)={\frac {12!}{2!10!}}={\frac {12\times 11}{2}}=66.$. Every 2 dots form a line.

--anonym

Yep, forgot the 2! in the denominator. 66 it is. - Nunh-huh 21:33, 28 August 2005 (UTC)

Counting the Ways to Choose a Delegation

Three delegates are to be chosen from a group of four lawyers, a priest, and three professors. In how many ways can the delegation be chosen if it must include at least one professor?

--anonym

21. David Sneek 08:22, 28 August 2005 (UTC)

Let me play:

• Professors: A,B,C;
• others: L1,L2,L3,L4,P1
• Enumerate the possible groups of three:

1: A + B + C

2-6: A + B + (L1, L2, L3, L4, or P1)

7-11: A + C + (L1, L2, L3, L4, or P1)

12-16: B + C + (L1, L2, L3, L4, or P1)

17: A + L1 + L2

18: A + L1 + L3

19: A + L1 + L4

20: A + L1 + P1

21: A + L2 + L3

22: A + L2 + L4

23: A + L2 + P1

24: A + L3 + L4

25: A + L3 + P1

26: A + L4 + P1

27: B + L1 + L2

28: B + L1 + L3

29: B + L1 + L4

30: B + L1 + P1

31: B + L2 + L3

32: B + L2 + L4

33: B + L2 + P1

34: B + L3 + L4

35: B + L3 + P1

36: B + L4 + P1

37: C + L1 + L2

38: C + L1 + L3

39: C + L1 + L4

40: C + L1 + P1

41: C + L2 + L3

42: C + L2 + L4

43: C + L2 + P1

44: C + L3 + L4

45: C + L3 + P1

46: C + L4 + P1

-- Nunh-huh 08:29, 28 August 2005 (UTC)

You must have one professor, and there are seven others. Your options number 1 * 7 * 6. More precisely, you have a choice of three for the first option which must be a professor, but there are three choices, so 3 * 7 * 6 * 1/3, since any of the initial three professors will work. I am not a statistics student, so prefer any answer which explicitly explains why I'm wrong.-gadfium 08:46, 28 August 2005 (UTC)

My feeling on reflection is that Nunh-huh is right and I'm wrong, but I can't explain why. The approach of enumerating the possibilities is unanswerable, but doesn't translate for greater numbers.-gadfium 09:34, 28 August 2005 (UTC)

There are three possibilites. If there is exactly one professor in the group, s/he could be chosen in three ways. The second delegate should be one of the four lawyers and the priest, so s/he could be chosen in five ways. The third could be chosen from the remaining lawyers and priests in four ways. That makes 3 * 5 * 4 = 60 ways. If there is exactly two professors in the group, there are three choices of which professor to omit. The third delegate is chosen the same way as above, so there are five choices. That makes 3 * 5 = 15 ways. The third possibility, that all delegates are professors, can be done in only one way. Summing it up gives a total of 76 ways.

If it doesn't matter which professor or lawyer you choose, there are far fewer choices. Only two of the delegates are then interesting, as the first will always be a professor. The second and third could be two professors, a professor and a lawyer, a professor and the priest, two lawyers, or a lawyer and the priest, five ways in all. There exists probably some formula to calculate that, but I can't remember it now. Hope that helps. Maybe the article on combinatorics gives some clues too. --130.238.5.5 11:00, 28 August 2005 (UTC)

It's 46, as follows. 30 delegations including exactly 1 professor because 3 ways to choose the professor and 5x4/2=10 ways to choose other two delegates from five candidates (solution above gives 60 delegations for this case, but this is double counting). 15 delegations including exactly 2 professors because 3 ways to choose 2 professors from 3 and 5 ways to choose the one remaining delegate. 1 delegation including exactly 3 professors because no other delegates to choose. 30+15+1=46. Nunh-huh is right. Gandalf61 11:21, August 28, 2005 (UTC)

Perhaps this is more simple. There are 56 ways of picking three delegates from the eight candidates: 8!/(5!*3!)=56. There are 10 ways of picking three delegates without picking a professor, i.e. from the four lawyers and the priest only: 5!/(3!*2!)=10. And 56-10=46. David Sneek 13:25, 28 August 2005 (UTC)

An alternative is to express it as subproblems:

• How many ways are there to choose a delegation with A?
• How many ways are there to choose a delegation with B, but without A?
• How many ways are there to choose a delegation with C, and no other professors?

A generic formula for each of those subproblems is ${\frac {P\times C\times (C-1)}{P\times 2!}}$, where P is the number of professors one may choose from, and C is the number of people to choose from after selecting the required professor.

In other words: ${\begin{matrix}{\frac {3\times 7\times 6}{3\times 2!}}+{\frac {2\times 6\times 5}{2\times 2!}}+{\frac {1\times 5\times 4}{1\times 2!}}&=\\{\frac {126}{6}}+{\frac {60}{4}}+{\frac {20}{2}}&=\\21+15+10&=&46\end{matrix}}$ --Pidgeot (t) (c) (e) 14:03, 28 August 2005 (UTC)

Note that it's a completely different solution if the order you select the people in has any importance. In that case, the result is $(8\times 7\times 6)-(5\times 4\times 3)=336-60=276$ - that is, the number of possible groups (even those with no professors), minus the number of possible groups without a professor (see below for C program that verifies result). --Pidgeot (t) (c) (e) 14:17, 28 August 2005 (UTC)

I'm only a high school maths student, but I get 63: 3 × (7 choose 2) = 63. There are three ways of choosing the professor, and (7 choose 2) ways of choosing the other two delegates. That is, if order is not important. If order is important, then it is 3× 7 × 6 = 126. I'm also assuming the delegate can have more than one professor, as the question above states. Graham 13:23, 29 August 2005 (UTC)

If order is important, you're not factoring in that the professor may be selected at any point. I've just verified my result above with the following C program:

#include<stdio.h>
//1-3=Prof. 1-3, 4=Priest, 5-8=Lawyer 1-4
int main()
{
  int i,j,k;
  int total=0;
  int noprof=0;
  for (i=1;i!=9;i++)
  {
    for (j=1;j!=9;j++)
    {
      for (k=1;k!=9;k++)
      {
        if ((i!=j) && (j!=k) && (i!=k))
        {
          total++;
          if ((i>3) && (j>3) && (k>3))
          {
            noprof++;
          }
        }
      }
    }
  }
  printf("%d/%d with no professor",noprof,total);
}

The output is 60/336 with no professor, proving my result above. --Pidgeot (t) (c) (e) 14:12, 29 August 2005 (UTC)

Scratch that. There are 8 choose 3 = 56 ways of choosing delegates with no restrictions, and 5 choose 3 = 10 ways of choosing a delegate with no professor. So the solution is 56 - 10 = 46, as above. I'll remember that one ... Graham 13:32, 29 August 2005 (UTC)

what is CRDi

What does CRDi technology in Cars stands for? And what is its importance? -Optional Check

I can help you with the first part of your question. Common Rail Direct Injection (CRDi) is the latest technology for diesel engines. Also, I don't really know whether it's a technological or a marketing advance so I'll leave the second part for another Wikipedian. hydnjo talk 13:56, 28 August 2005 (UTC)

It is a genuine technological advance; read the common rail article for an explanation. Basically, a very highly pressurised fuel line (the common rail) feeds electrically-controlled solenoids which inject fuel directly into the engine's combustion chamber, rather than mechanically controlled valves and lower-pressure pumps. The resulting diesel engines (which are almost universally also turbocharged) are very efficient and are also considerably quieter and more refined than earlier designs. Diesels are very popular in Europe, where all fuel is expensive (encouraging fuel efficiency) and gasoline is much more highly taxed than diesel. Unfortunately, I don't have any quantitative figures to hand as to the improvements in efficiency between common rail designs and their predecessors, but I'm sure they're around somewhere.--Robert Merkel 06:22, 30 August 2005 (UTC)

XHTML

Hi, I recently redesigned my site using css, which made it look a LOT better and cleaner. Now, I'm wondering, what advantages would I have in incorporating XHTML into my site? What can XHTML/CSS do that HTML/CSS can't? Also, consider the fact that I'm using PHP code to generate this HTML, so that may also come into play. Or am I already using XHTML and I don't know it? — Ilγαηερ (Tαlκ) 15:37, 28 August 2005 (UTC)

XHTML and HTML are very similar. XHTML is just HTML tweaked to fit within the rules of XML; but since XML itself was based on HTML, it's not that different. (XHTML 2 will be quite different, but it's a good ways off.) The most notable differences from regular HTML are that all tags must be written in lowercase, all values must be surrounded by quotes, and "singleton" tags such as <br> must end with a space and a slash before the >, as in <br />. See the XHTML article for more. So should you switch? It's not imperative, as it will be a long time (if ever) before web browsers are unable to handle standard HTML, but as XHTML is the "now," I would recommend it. By the way, if you're using PHP, do you know about Smarty? I hardly ever go without it in any PHP project, big or small. Garrett Albright 17:37, 28 August 2005 (UTC)

XHTML is HTML that conforms to the XML standards. Read the articels for a thourough overview. It is usually quite trivial to generate valid XHTML form PHP as this was a design goal of XML. Using XHTML doesn't give you that many great advantage, but this are the ones I consider imporatant:

• Even cleaner code
• It allows other people to perform, for example, XSLT tansformations on your page.
• You can embed XSLT code, that is executed on the client side (if the browser supports this (IE6/Firefox)).

--R.Koot 18:13, 28 August 2005 (UTC)

Missing sound control

My sister has got a laptop with Windows 98 OS from my aunt, but the thing fails to make sound when selecting MP3 files (or any other type of sound for that matter). I found the link that's supposed to go to the volume control panel goes to the regular control panel and there's no sound control there. I hear you say: has this thing got a sound card. Yes it does, cause playing CDs works fine. Any idea how to get it working properly? - 82.172.23.66 16:14, 28 August 2005 (UTC)

Try running sndvol32.exe and check the volume settings. Just because CDs play fine doesn't mean MP3s will, as there are different volume settings for those. --Pidgeot (t) (c) (e) 16:52, 28 August 2005 (UTC)

• sndvol32.exe is the "volume control panel" in windows I was referring to in the question. When I click it after finding it in either the start menu or a search window, nothing happens. - Mgm|^(talk) 17:50, August 28, 2005 (UTC)

Does the CD sound play through the speakers connected to the sound card, or to the line out on the CD-drive? --R.Koot 18:15, 28 August 2005 (UTC)

Good idea, I'll check that. - Mgm|^(talk) 18:43, August 28, 2005 (UTC)

• In the mean time, my sister told me she's getting an error when trying to start Windows Media Player telling her the hardware isn't responding. - Mgm|^(talk) 18:43, August 28, 2005 (UTC)

  That points to an issue with Windows not detecting the sound card or experiencing a conflict.

  In relation to the question R.Koot raised above, how are you playing the CDs - that is, what application are you using? --Pidgeot (t) (c) (e) 19:11, 28 August 2005 (UTC)

  I did not read it was a laptop, which means it must play through the soundcard. The error above means that there a no drivers/wrong drivers for the sound card (check with device manager/apparaatbeheer). Having no drivers for the soundcard shouldn't interfere with playing CD audio though, which corresponds with the effect you describe. --R.Koot 19:21, 28 August 2005 (UTC)

• Yep, looks like that's the case. I'll try finding some drivers to install and see if things work better then. - 82.172.23.66 20:29, 28 August 2005 (UTC)

Aromaticity of pentalene

Is pentalene aromatic? According to aromatic hydrocarbon#PAHs, it is. Encyclopedia Britannica says it isn't. [3] Which is correct? ‣ᓛᖁᑐ 16:54, 28 August 2005 (UTC)

• Britannica, unfortunately. Pentalene is non-aromatic, as would be expected from Huckel's rule (there should be an umlaut over the U, but my current keyboard doesn't have them). This was confirmed in 1997 by the first preparation of According to Bally, T. et al. (1997). J. Am. Chem. Soc. 119: 1869–75, who first prepared pentalene, the monomer is extremely unstable! An isomer of pentalene, whose correct name I do not have for the moment but lets call it benzocyclobutene, is a moderately stable [6+2] aromatic. Physchim62 17:43, 29 August 2005 (UTC)

If you allow javascript on wikipedia.org (and the monobook skin possibly), you should see clickable entities on the bottom when editing that allow inserting a bunch of fun characters like umlauts. - Taxman ^Talk 18:21, August 29, 2005 (UTC)

• Good job catching that. That means, that if confirmed by another reliabel source (the ideal way) the pentalene article itself is horribly wrong too. Of course, Hückel's rule itself isn't perfect as its article states. - Taxman ^Talk 18:21, August 29, 2005 (UTC)
  • No, Hückel's rule isn't perfect (which is why it's only a "rule") but it seems to work fine in this case. The pentalene article is wrong, and should be rewritten (my connection time is vrey limted at present, otherwise I'd do it myself). The external link which I added above is actually a copyvio, so only the J. Am. Chem. Soc. reference should go into the article. Physchim62 21:35, 30 August 2005 (UTC)

I wonder if some disambiguation is needed here? I've seen the dianion of pentalene marked as aromatic. --HappyCamper 03:11, 31 August 2005 (UTC)

A google search for pentalene aromatic, pulls up our information and mirrors of it first, but also a few links to pentalene as actually being anti-aromatic like cyclobutadiene. But it does also pull up [4] that notes the dianion is aromatic and [5] that refers to a postulated aromatic dication. I could't access the second, so someone else will have to check. But how important is it is the dianion is aromatic? How often will it exist as a dianion? Also, Wikipedia doesn't know what a dianion is, and while I can assume, can someone with some references available, fix that? Hint, hint. :) - Taxman ^Talk 19:35, August 31, 2005 (UTC)

I'm not so sure, but it's quite important in transition metal chemistry. Take for example this paper which explains quite nicely why the dianion is quite interesting...In particular, take a look at the diagrams. A dianion is an ion with a valence of 2^-. There's also zwitterion which is a chemical species with a net charge of 0, but has simultaneously a 1⁺ and a 1^- charge somewhere. Very common in polymer chemistry. Analogously, there's trianion, et cetera, and their analogous cationic counterparts. These terms aren't really used so much though as a far as I can tell, unless it's in a very specific research context. --HappyCamper 14:26, 3 September 2005 (UTC)

Molecular Biology Question:

• does anyone know the exact name for the Bovasial Protein Complex(BPC)? seems to have slipped my mind at the momement--172.168.17.18 17:53, 28 August 2005 (UTC)

• I belive you're thinking of the fullus shitium, also know as the foundation of modern made up things, like this word you're using in front of Protein--152.163.101.12 21:35, 30 August 2005 (UTC)

Question About a Medical Bill

One of my relatives was hospitalized for two days due to a car accident on the 6th of February, this year. Ever since she has been getting inundated with bills on a regular basis. Some of the items on a most recent bill are

Hospitalization Bill

Item #	Description	Amount	Date
1	Hospital Conslt	$600	2/6/2005
2	Hospital Visit	$300	2/7/2005
3	Hospital Discharge	$300	2/8/2005
4	Suture of Wnds 22 Cm	$1,800	2/6/2005
5	Add 5Cm/Less Rep	$450	2/6/2005

• Is there a doctor of medicine, medical attorney, or anyone knowledgeable about medical bills who can explain items 1 through 3, inclusive. Is it legal for a hospital to charge for these things?
• What is the meaning of item 5?

--anonym

Well, whoever is billing you is the only place that can tell you what these actually mean. They do seem to be coming from a doctor, not a hospital, though perhaps the hospital is billing on behalf of the physician. Whoever is sending the bills should be willing to explain them. As a guess, though: [1] hospital consultation is the fee you pay to a doctor who performed a consultation in the hospital - usually a specialist of some kind. [2] hospital visit is a fee you pay to the doctor who provided routine care in the hospital. [3] hospital discharge is the fee the doctor charges for discharging someone from the hospital. These are fees you are paying the doctor, and are in addition to whatever the hospital charges per day. As for [4] & [5] it seems that they are charges for suturing two wounds ($1800 for the first one, 22 centimeters long, and $450 for the additional one, which was 5 centimeters or less). None of that sounds illegal to me (but what do I know?), as long as they are only charging you once for each service. - Nunh-huh 21:47, 28 August 2005 (UTC)

I can't help you but I don't think we can know if it's illegal or not if we don't know in which country this is. I think that this is something that could vary much from country to country. Jeltz talk 21:57, 28 August 2005 (UTC)

This bill was received from a physician in California, U.S.A. --anonym

Then it looks like it was a surgeon who was called in "on consultation" to suture two wounds (possibly in the Emergency Room), did it, did one followup visit on the day your aunt was admitted to the hospital, and discharged her from the hospital the following day. - Nunh-huh 22:17, 28 August 2005 (UTC)

• In item #5, does Rep = repeat? So does this item mean 5 centimeter or less, repeat?

--anonym

More likely "repair". - Nunh-huh 22:17, 28 August 2005 (UTC)

• Does a hospital not have its own surgeons? I think at least this particular or perhaps all hospitals assign suites to their own surgeons. Later, every time they need a surgeon, they call him. Then for every coming in and going out of the suite or office, the patient get smacked with a bill. (Also, my relative has said that she has paid a cumulative of $40,000.) Am I right about my conjecture? Does a hospital not have its own physicians and nurses? Aren't the consultation, visit, and discharge parts of a huge scam. (She was scanned scores of times, her urine was glanced at an equal number of times, etc.)

--anonym

It's not a scam, it is all in the name of providing good service and getting her healthy. That happens to be expensive, but you can't have it both ways. As for multiple tests, it is of course possible they are duplicating, but it is likely she simply needed them. Also, due to the ease of suing medical practitioners even when they do a great job, there is a certain amount of defensive medicine going on all the time which along with malpractice insurance greatly adds to everyones cost. As to the multiple bills other people have answered why, and I agree consults are very common in order to get the right person (or possibly someone at all if they are very busy) to do the needed work. What may happen is they both bill you to make sure the service gets paid for. Someone will have to wade through all the bills to make sure none of them are double paid. Keep voluminous written records annotated with dates and full names of people you talk to and make them verify what services each bill is for. I also agree with others that the hospital has full time paid staff to help people with this stuff. Make use of them and be persistent. Also be persistent in getting reimbursement from Kaiser as it may take multiple calls, threatening letters and possibly the willingness to sue in court. Hire a competent lawyer of course if need be, but it shouldn't come to that if you are persistent. - Taxman ^Talk 18:36, August 29, 2005 (UTC)

That's pretty much the way it works. The basic hospital rates don't cover physician services, which are billed for separately. - Nunh-huh 23:24, 28 August 2005 (UTC) BTW - if it was a car accident, isn't it covered by insurance? - Nunh-huh 23:29, 28 August 2005 (UTC)

• She has had health insurance, luckily. However, Kaiser Permanente has not readily paid all the bills; in some instances, Kaiser has pointed out that some of the numerous bills were duplicates. By the way, you are right, when you stated that she gets separate bills from the surgeon and the hospital.

--anonym

Many hospitals employ no doctors. Some hospitals employ all the doctors on their staff (closed staff). Some hospitals employ some doctors but also have many community physicians with privileges at the hospital. Fees from doctors employed by the hospital (excluding house staff) are included in the hospital bill; fees from office-based doctors not full-time employees of the hospital will bill separately.

Few seriously ill or injured people get in and out of the hospital without seeing more than one doctor. The consultation charge is from a physician who was advising without providing the principal care (e.g., an internist seeing a trauma surgery patient to manage his diabetes). The hospital visit is the daily care from the principal attending physician (excluding day of admission and discharge). The discharge was for the same physician's hospital visit on day of discharge; it is a higher charge because it usually takes more time and involves discharge planning. If these physician charges were on the hospital bill it means the physician was employed by the hospital. I am less familiar with surgical billing but the final charge is simply for additional suturing beyond the 22 cm; I'm not sure what "less rep" means if it was transcribed correctly.

You have no idea what you are talking about with respect to the relationship of hospital and surgeons. Why would you not expect a surgeon to charge if he/she gets called from the office to see a patient in the hospital? How do you think he/she earns a living?

Finally, why on earth haven't you asked these questions of the hospital? They pay full-time employees to answer these questions. alteripse 17:00, 29 August 2005 (UTC)

Closed-source wiki software

(It said computing questions go here, so...)

Where can I compare and shop for closed-source wiki engines? Comparison of wiki software only lists open source software, and 'wiki' is so hit upon by advertisers that neither Google nor Yahoo can provide effective results. Almafeta 00:19, 29 August 2005 (UTC)

My guess is you won't find very much of it. It's somewhat against the "wiki ethic", to quote a recent answerer. Superm401 | Talk 01:20, August 29, 2005 (UTC)

I don't think it deserves to mentioned in the same sentence, but Microsoft is pushing sharepoint as an alternative to wikis. I don't exactly know what they call it, but I'm sure IBM's Lotus Notes provides something similar. -- Rick Block (talk) 02:17, August 29, 2005 (UTC)

*sigh* Almafeta 16:08, 29 August 2005 (UTC)

then there are literally hundreds of different outfits offerng software for blogging, and interaction between different people blogs. AlMac|^(talk) 03:55, 29 August 2005 (UTC)

Can I ask what the motivation for your question is? Open source doesn't necessarily mean "unsupported", if that's your concern. --Robert Merkel 06:10, 30 August 2005 (UTC)

Just looking for wiki software that doesn't mandate supporting the political goals of the open source movement. (I guess it's worth metioning that for these purposes, BSD is not an open source license.) Almafeta 13:15, 7 September 2005 (UTC)

As I understand it, using media-wiki software in a company for internal purposes is not illegal. It is only altering the software and trying to re-sell it what is illegal. Is question really: Where can I get a wiki engine so I can embbed it into a larger project that I am planning to sell? By the way, let's say I use a mediaWiki sofware as is, without modifuing the source, but I attempt to charge for accessing the content. Is this illegal? --Threner 04:30, 1 September 2005 (UTC)

Absolutely not. However, again, it's somewhat against the "wiki ethic". Superm401 | Talk 21:04, September 4, 2005 (UTC)

What did ancient romans use for medical instruments

Our history of medicine unfortunately doesn't cover ancient Rome, and it looks like we don't have anything on instruments in particular. There's a nice looking collection of pictures of Roman instruments here. If you are interested in tracking down the roots of some of the instruments and methods, Ancient Egyptians were quite renowned for their medical experitise, particularly by Greeks, who seemed to dominate Roman medicine, so I'd bet that some of their instruments carried over. (I'm restraining myself from simply recommending reading Galen.) — Laura Scudder | Talk 06:56, 29 August 2005 (UTC)

Increasing the acceleration of an object under the influence of centripetal force

Dear Sirs,

A question to which I think I know the answer, and which is possibly very easy for you to confirm.

If you have a fixed object at the end of a rod, secured at the other end so it is like the hand of a clock, if you drop the object from position 2 on a clock face, when it reaches position 6 on the face, the mass at the non fixed end will have accelerated to x Metres per second.

If you repeat the procedure, allowing a weight to travel from the fixed point of the rod to the object at the end when it is dropped, when the object at the end reaches position 6 on the clock face, will it's acceleration be greater than the original x metres per second, due to the movement of the weight down the rod to the fixed object. If this assumption is correct, could you tell me what particular laws of physics govern the phenomenon, and could you also confirm that the figure x meters per second would be improved upon if either the mass of the additional weight, or the distance it travelled down the rod were varied. Is ther a calculation to prove this?

Many thanks,

    Bill Friend.

Assuming you're talking about a frictionless, massless rod (I seem to have misplaced mine) attached to a frictionless pivot: in the first case, the gravitational potential energy of the weight at the end of the rod, which is a function of how far it drops in a purely vertical sense, is converted to kinetic energy. In the second case, there are simply two objects to keep track of. The one not at the end of the rod doesn't drop as far, but its potential energy is also converted to kinetic energy, so the answer to your first question is yes. Potential energy is mass x gravity x height. Kinetic energy is (mass x velocity²) / 2. In your case you'll have two masses, two heights, and a single final velocity. If you can't get it from here, please talk to any high school or college physics teacher. -- Rick Block (talk) 13:27, August 29, 2005 (UTC)

science human anatopmy skeletal sysytem

WHAT BONE IN OUR BODY DOES NOT GROW.

• Why the answer to that is simple, travel to the midwest, they don't belive in biology there, so all you'll have to do in BIO class is cut out pictures oif zebras from magazine covers, and make a collage--152.163.101.12 21:33, 30 August 2005 (UTC)

Having begun as a single cell, there seems to be a good argument that all of our bones have grown. — mendel ☎ 19:29, August 29, 2005 (UTC)

• And that some (maybe all) bones eventually stop growing if the individual that owns them gets old enough. - 82.172.23.66 20:01, 29 August 2005 (UTC)

Maybe he/she means a bone that is the same size in a newborn and in an adult. Ornil 20:45, 29 August 2005 (UTC)

There are indeed a number of bones in the human body that do not grow after birth. Hint: there's six of them in every human. Proto t c 13:40, 31 August 2005 (UTC)

What occurred to me when this question was first posted were the inner ear bones. They are formed by 20 weeks and I am skeptical that no growth from first fetal formation occurs, although they may not change much from infancy to adult life, in which case this is one of those annoying, poorly worded questions where we are challenged to guess what misconception the questioner is imagining or what answer the questioner intended us to give instead of the accurate answer to the literal question, which I suspect is "none". alteripse 10:58, 1 September 2005 (UTC)

Perhaps it was written better originally, and this guy just didn't ask it quite right? --Phroziac ^(talk) 13:47, September 4, 2005 (UTC)

Native POSIX Thread Library

In research done by Edward Rice in February of 2004, NPTL was compared to the Windows Threading Library. A program written in Java created multiple threads that ran at the same time. This program was run on both Windows and Linux on a dual boot system Intel non-hyper-threading chipset. It was discovered that Windows handled threads that yielded often better than Red Hat Linux 9, but Red Hat Linux 9 handled threads that yielded less frequently better than Windows. It was concluded that this was the result of the time it takes for a thread to yield and the virtual machine to pick a new one.

Who is Edward Rice? Where is this research? If it isn't available to be read anywhere, why is it referenced in this http://en.wikipedia.org/wiki/NPTL entry.

Thanks much. Christopher Warner 64.61.118.58 17:59, 29 August 2005 (UTC)

Please ask this question at Talk:Native POSIX Thread Library. If you don't get a satisfactory response in a week or so, feel free to to delete the paragraph. -- Rick Block (talk) 01:06, August 30, 2005 (UTC)

Power plant service

How many homes and or business would a 750 megawatt power plant service?

Depends on where you are (due to variations in AC/heating usage, etc.) In the US, expect somewhere between 400 and 1000 homes per MW (hotter places usually needing more power), so about 300,000 - 750,000 houses for a 750 MW plant. Businesses, I've no idea. -- DrBob 19:33, 29 August 2005 (UTC)

Unknown Mental Disorder

I am searching for the name of a mental disorder which i am having trouble even describing. I would like to know what it is called when someone will take events that happen in the world and see it in a way that makes them despise society to the point they feel despression and regret at having lived and seen such things - or even make them feel as though they have to isolate themselves simply because they can no longer stand seeing them or hearing about them. For instance, a racist attack could trigger a spiral of depression for the sufferer who, although understanding the cruel act completely, cannot overcome or get over the incident that happened to someone they may neither know or be the same race as. A further example will be the sufferer witnessing acts such as corruption, be it a from a large corporation or the local newspaper seller who does one dodgy deal ont he side. the sufferer will see such acts and feel overwhelming emotions of despite and hatred for those who would live in such corrupt ways. these two acts, and any other kind of 'wrong' act for that matter, have an effect on the sufferer who feels more than a simple dislike for what they see and know to be wrong, because they have such high ideals of what is just and right, and how the world should be. but how the world is makes them want to remove themselves from society, because they cannot bare the thought that, to them, the world is a place that will never be perfect, or even truely good. i was just wondering what such a condition would be called.

I am not a doctor or psychiatrist, but I might describe such a condition as a combination of post-traumatic stress disorder with uncontrollable empathy. If someone had this condition, though, I would strongly recommend they visit a psychiatrist. Superm401 | Talk 20:01, August 29, 2005 (UTC)

It is not a mental disorder. No specific trauma is mentioned and this is not a recognized aspect of PTSD or any other entity in the DSM-IV-R. We could trivialize it by pointing out how adolescent the combination of naive idealism and excessively harsh judgementalism is. Or we could call it a spiritual disorder. In Christian times and cultures this was termed the recognition of the fallen nature of man, or in the last century as being a soul too delicate for coarse flesh. I also suspect it comes not from an excess of empathy but an unbalanced empathy that cannot recognize the transgressors as being as equally human as the victims. If one cannot stand to live in the real world as it is among sinners, one solution often resorted to in the past is monastic life or simply the isolation of a hermit. With the right public relations support you can become a saint. Or maybe the solution is to become more familiar with the world, more accepting of human nature, and grow up... alteripse 21:18, 29 August 2005 (UTC)

You're probably right. I didn't mean it was precisely PTSD. That was an approximation. Superm401 | Talk 22:15, August 29, 2005 (UTC)

It is of course not a medical term, but the description fits Weltschmerz. (Try pronouncing that if you're Anglo-Saxon.) 82.210.117.215 18:09, 30 August 2005 (UTC)

Excellent! Veltshmairts it is! alteripse 01:20, 31 August 2005 (UTC)

This may be off-topic but the statement, If one cannot stand to live in the real world as it is among sinners, one solution often resorted to in the past is monastic life or simply the isolation of a hermit may not necessarily be completely true. Those who have chosen the monastic/contemplative way of life may not necessarily be "escaping" from the difficult-to-take experiences of the world but primarily aiming at finding a deeper spiritual connection in greater solitude. --Dpr 06:55, 5 September 2005 (UTC)

Line crossing algorithm

Ok, suppose I have a set of pairs of coordinate points representing line segments. What would be the best way to check of any lines cross?--Fangz 22:45, 29 August 2005 (UTC)

A start might be generating equations from the lines and solving the system of each pair. I.E. for a simplified example of only two lines below:

1.(3,5) and (6,11) 2.(5,4) and (7,12)

1.y=2x-1 2.y=4x-16 0=-2x+15 2x=15 x=7.5

They intersect where x=7.5. This is inefficient, but it's an okay idea to start with. Do you get the idea? Superm401 | Talk 23:13, August 29, 2005 (UTC)

• Another similar idea:

First compute the bounding-boxes of each pair of lines. They must overlap if the lines cross (necessary, but not sufficient).

For line segments AB & CD, solve the equations (by separating the x & y components) for s:

$\mathbf {A} +s(\mathbf {B} -\mathbf {A} )=\mathbf {C} +t(\mathbf {D} -\mathbf {C} )$

Bear in mind there may be no solution (lines parallel).

Now compute t from s. If the line segments cross, both s and t must be in the range 0-1. -- DrBob 23:24, 29 August 2005 (UTC)

If you really want the best algorithm for doing this, here's a paper in the Journal of the ACM which contains an optimally-fast algorithm for doing this computation. I haven't read the full paper so I'm not sure how straightforward it is to implement. --Robert Merkel 05:57, 30 August 2005 (UTC)

Understanding Quantum Spin

I am researching the standard model of particle physics and quantum mechanics, in order to get a solid conceptual grasp on the ideas therein. One topic remains quite hard for me to visualize, however: what exactly is quantum spin? I have no formal physics background, but these things interest me _very_ much. Can anyone provide an accurate metaphorical explanation of what quantum spin is?

Thanks in advance, Robert Winslow

• Have you read Spin (physics) (quite scientificly phrased)? Are there any other parts of quantum mechanics you already understand? - 131.211.210.12 08:32, 30 August 2005 (UTC)

• I have a degree in physics and have never really been able to visualise spin either, so don't think your lack of formal physics background is what is holding you back! I tend to think of it as just another quantum number. But this is a cop out. You certainly can't think of it as analogous to a classical spinning particle. Electrons have spin but they are point like particles, and how can a point spin? The spin of an electron does however create a magnetic field ( a magnetic dipole) in the same way that a spinnig ball of charge would create a magnetic dipole, so something is going on. Like I said - I don't really understand. Theresa Knott (a tenth stroke) 22:40, 30 August 2005 (UTC)

• I could be entirely wrong here, but I think I once heard it explained as: imagine having a playing card, an ace of spades, turn it around so the back faces you, turn it around again, now a queen of hearts faces you, turn around again, to have the back face you agian, and turn around another time, to have the ace of spades face you again. That's spin 1/2. (But agian, it could be that I'm talking about something entirely different.) --R.Koot 19:33, 31 August 2005 (UTC)

• Even more confusingly, even though QM spin isn't the same thing as classical spin, things like spin-orbit coupling still happen. Add in the link between spin and statistical mechanics (spin-statistics theorem), and you've got one of the most mysterious bits of QM, which I'm glad I no longer have to think about. -- DrBob 20:34, 31 August 2005 (UTC)