Wikipedia:Reference desk/Archives/Science/2009 February 24

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February 24

Measuring digits

Is there an easy way to measure the length of ones digits accurately? My left thumb is noticably (to me, not so much to other people) stumpier than my right, and I think it's because of the length of my first and second digit, as opposed to the position/length of the nail (which is also short, I believe as a result of the short digits), but I can't figure out a way to measure the lengths accurately to within 1mm or so, because I don't have any expensive measuring equipment. Any ideas? Thanks! 219.102.220.90 (talk) 00:40, 24 February 2009 (UTC)

A clear plastic tube, such as a coin tube, should do the trick. Insert your finger in as far as possible and mark the depth. Repeat and compare. -- Tcncv (talk) 01:21, 24 February 2009 (UTC)

The other option is tracing round your hands onto a piece of paper, then you can measure with a ruler. You would need to trace very carefully, though - keep the pencil vertical the whole time. --Tango (talk) 15:06, 24 February 2009 (UTC)

Extend your thumb, first and second finger at right angles to one another. Then use a ruler to measure each in turn as the side of a triangle. Cuddlyable3 (talk) 19:17, 24 February 2009 (UTC)

One biometric security device for confirming identity uses the lengths of the fingers. It was pretty good at distinguishing the hand of the person being checked from other random hands, and far faster than fingerprint or retinal scan. I believe some early ones used pegs which fit between the fingers and position sensors for the length, but now they seem to use electrical conduction. See [1]. A flatplate scanner can also be used [2]. Edison (talk) 00:02, 25 February 2009 (UTC)

I got a plastic vernier caliper at a dollar store (for one dollar) a few years ago. That is probably the simplest way to measure accurately. You can get fairly nice digital calipers from places like Harbor Freight for under 10 bucks, but be careful ordering from them, they will spam your mailbox with catalogs afterwards. I'm guessing you want accurate measurements because of this story.207.241.239.70 (talk) 06:18, 27 February 2009 (UTC)

The atmosphere on comet Lulin

This article on the comet states: Lulin has a greenish cast because sunlight illuminates two gases — cyanogen and diatomic carbon — in its Jupiter-sized atmosphere.

Am I supposed to believe that the comet has a big enough gravity field to hold gas at a range equivalent to the radius of Jupiter?? I can't find a source that states the estimated size of the comet, but I find it hard to believe it has enough mass to support such a size. 219.102.220.90 (talk) 01:39, 24 February 2009 (UTC)

Gravity of Comet Lulin may not be holding that gas in place, instead it is probably flowing outward from the comet, and dispersing in interplanetary space. What is there is travelling in the same orbit as the comet, with some being blown out into the cometary tail. Graeme Bartlett (talk) 03:47, 24 February 2009 (UTC)

Doesn't "atmosphere" imply that it is being held within the gravity field? 210.254.117.186 (talk) 13:50, 24 February 2009 (UTC)

Yes, they're using the wrong (or, at least, imprecise) word. It's called a coma. --Tango (talk) 15:03, 24 February 2009 (UTC)

Unfortunately, that news article is correctly quoting a NASA press release. In other NASA press releases, it is called a coma. In the one being quoted, it is called an atmosphere. -- kainaw™ 15:08, 24 February 2009 (UTC)

I guess we have to go with "imprecise" rather than "wrong", then. --Tango (talk) 19:14, 24 February 2009 (UTC)

Comets' comae can easily be larger than Jupiter, even larger than the Sun. In fact, Comet McNaught's coma was larger than the Sun, and Comet Holmes' coma was much, much larger than that. ~AH1^(TCU) 22:10, 24 February 2009 (UTC)

Well I guess they can be arbitrarily large/long can't they, assuming gas is being pumped out constantly. Either way that settles it, thanks everyone! 219.102.220.90 (talk) 00:15, 25 February 2009 (UTC)

Yes, it really depends on how you define the edge. There is no clear end to the coma, it just gets thinner and thinner. Of course, similarly, there is no clear end to Jupiter or the Sun, so as long as you use the same definition you can get meaningful comparisons. --Tango (talk) 14:23, 25 February 2009 (UTC)

Requirements for being published in Science Mag: Policy Forum

What are the requirements for having a piece published in the "Policy Forum" section of Science (journal)? The WP article says that research articles are peer reviewed, but what about the Policy Forum section? What is the scope of this section? Thanks, NJGW (talk) 02:06, 24 February 2009 (UTC)

Have you tried contacting them directly? Their website is linked from our article, and if you click the "feedback" link on their homepage, they have a means to contact the editors and ask a question directly of them. --Jayron32.talk.contribs 02:10, 24 February 2009 (UTC)

The "Informational URL" listed in our article points to the "Information for Authors" webpage, from which you can find information about the submission process, selection criteria, etc. DMacks (talk) 02:13, 24 February 2009 (UTC)

Editorial articles (signed or unsigned) for science journals are generally not peer-reviewed. (They are, as the name suggests, provided at the pleasure of the editor.) --98.217.14.211 (talk) 02:14, 24 February 2009 (UTC) nevermind, the Policy Forum articles don't seem to be editorials. I suspect they are peer-reviewed in one way or another, based on the way they are presented (identical to the research articles). --98.217.14.211 (talk) 02:17, 24 February 2009 (UTC)

Thanks for the tips. All that the info for authors states is that the "broadly accessible commentary... presents issues related to the intersections between science and society that have policy implications." NJGW (talk) 02:46, 24 February 2009 (UTC)

The authors'-info page has a link to "Contributors FAQ", on which "What kinds of manuscripts does Science consider?" which notes: "A variety of material under the general heading of Commentary -- including Editorials, Book Reviews, Education Forums, Policy Forums, Perspectives, and Reviews -- is usually solicited by Science editors, although on occasion the editors will consider unsolicited manuscripts of these types." So it's not clear there whether it's peer-reviewed, but it's definitely not open-submission. DMacks (talk) 02:59, 24 February 2009 (UTC)

Amoebas and White Blood Cells

We all know that amoebas and white blood cells send out pseudopodia to engulf their prey or pathogens (respectively). Here's a picture of a mouse macrophage sending out pseudopodia to engulf two bacteria.

My question is: without a nervous system, eyes, or any kind of control system, how do amoebas and white blood cells have the coordination to know how to engulf something, much less reach out long "arms" like in that picture? To my understanding, cells are basically just little bubbles floating around, and it boggles my mind to think they can do such coordinated tasks. Inasilentway (talk) 02:43, 24 February 2009 (UTC)

Well, they're not such coordinated tasks; they are by and large simple trophisms. Specific stimuli for phagocytosis in the immune system are discussed here. - Nunh-huh 03:29, 24 February 2009 (UTC)

Did you mean tropisms? AndrewWTaylor (talk) 09:43, 24 February 2009 (UTC)

Oops, indeed I did. - Nunh-huh 04:04, 25 February 2009 (UTC)

Phagocytosis in three easy steps

(e/c) I hope you don't mind, but I reduced the size of your picture to assist those people viewing this page with restricted bandwidth. A basic answer to your question can be found at Pseudopod. Unicellular locomotion is a fascinating subject, and involves a co-ordinated process of protein interactions at the lamellipodium. It includes microfilamental structural elements and lots of other proteins (such as the Rho family of small Ras-related GTPases) that regulate the actin polymerization/depolymerization. This process essentially creates a cytoskeletal "treadmill" on which the cell can extend processes or move itself.

They engulf something on detecting it by a surface receptor. This creates in intracellular signaling cascade that results in phagocytosis. Our phagocyte article is also very informative about this process. Rockpocket 03:33, 24 February 2009 (UTC)

Cells are far more than "little bubbles floating around". And yes, they are unfathomably complex. An entire field of biology is devoted to understanding cell biology, including (but not limited to) cell motility, chemotaxis, intracellular communication, intracellular signaling, molecular control of gene expression, protein synthesis, endocytosis and exocytosis, cell division, programmed cell death, and many other topics. Cell biology is fundamental to the understanding of development in multicellular organisms, as well as much of what we know about disease. I highly recommend this series of online seminars, from the American Society for Cell Biology. --- Medical geneticist (talk) 15:09, 24 February 2009 (UTC)

As mentioned, macrophage has receptors that bind to bacterial surface. Bacterial surface has unique signatures, or common molecular patterns, that the macrophage are able to recognize. Also, when there's an infection, we produce antibodies (proteins that bind to the invaders). The antibody-bacteria complexes are like extra glue, making it easier for macrophages to attach and eat up the bacteria. The receptor make-up of the macrophage is very complex as to be able to recognize invaders. Check out http://www.ncbi.nlm.nih.gov/books/bv.fcgi?highlight=macrophage&rid=imm.figgrp.157 199.76.164.202 (talk) 03:39, 25 February 2009 (UTC)

If you think white blood cells or amobea are "simple" bubbles just floating around, have a read of Chromosome and DNA ;) Vespine (talk) 05:59, 26 February 2009 (UTC) 05:56, 26 February 2009 (UTC)

Photosynthesis

if u were to feed a plant sugar through the roots, would the plant need leavs(or photosynthesis)?

This, erm, documentary explains how the human equivalent to the above question works. --Jayron32.talk.contribs 06:20, 24 February 2009 (UTC)

Only if you would consider fungi to be plants and their mycelium to be roots. They are generally considered to be different. For "ordinary plants there's a problem because the sugar is transported in the Phloem from the leaves to the roots, the xylem transports salts and water from the roots to the leaves. AFAIK it doesn't work in reverse.--76.97.245.5 (talk) 08:01, 24 February 2009 (UTC)

You should look at the substances used to prolong the life of cut flowers, these are usually just vitamin B. Graeme Bartlett (talk) 22:37, 24 February 2009 (UTC)

This is exactly what parasitic plants such as striga do but they still need leaves etc so that they can set seed.Smartse (talk) 20:16, 28 February 2009 (UTC)

low radiation

would low levels of radiaton from a red laser pointer help of harm light loving plants?

Your Question is quite difficult to understand, but as far as i know, a laser Pointer does not produce what is commonly called radiation (its actually ionizing radiation). Also the wavelength of red light (around 700 nm) is not absorbed by either of the two chlorophylls so it probably wouldn't even give the plant energy... But what do you mean with "help of harm?"--91.6.42.166 (talk) 08:51, 24 February 2009 (UTC)

Probably meant "help or harm". Clarityfiend (talk) 08:53, 24 February 2009 (UTC)

91.6.42.166 is wrong about red light not being useful to plants energetically. The exact opposite is true. Photosystem I and Photosystem II (our plant articles are so deficient...), the big two light absorbing components of the electron transport chain necessary for photosynthesis, optimally operate in the red end of the spectrum at 700 and 680 nanometers respectively. In fact photosystems I and II are often called P700 and P680. There is a famous experiment by German plant physiologist T. W. Engelmann in 1881 which used filamentous algae and mobile aerobic bacteria. Engelmann used a prism to split white light up into the colors of the spectrum and laid some algae across the length of it. The oxygen-needing bacteria would congregate around where the algae was maximally performing photosythesis (and making the most oxygen) The results he found were that the bacteria congregated most strongly around the red end of the spectrum, and slightly less so around the blue. Of all the individual wavelengths, red light produced the most photosynthesis. See a pictoral representation of the results here.

As for the laser pointer question the answer is no. Most red light lasers operate in the 650 to 680 nm range rather than 700nm. I did some rough order of magnitude calculations and it appears that leaving a plant with 20 or so quarter sized leaves even in partial sun will deliver much more usable energy to the plant than with a handheld laser pointer, especially taking into account that the photosystems saturate above a certain photon density. An intense enough laser pointer could cause photobleaching and thermal damage to the photosynthetic machinery, but full sunlight can do this too. Plants have evolved robust ways of dealing with this sort of damage through repair mechanisms and by minimizing light exposure by turning the leaves parallel to the sun's rays, relocating chloroplasts so they are stacked on top of one another, and decreasing the number of photosystems and photosynthetic compounds. Plant physiology is pretty interesting. 152.16.253.109 (talk) 21:26, 25 February 2009 (UTC)

Latent index and manifest index (in psychology)

I would be very grateful if somebody could explain the terms latent index and manifest index for me in the following sentence that I found in an article:
"Factors represented by circles (e.g., early childhood adversity) constitute latent indexes of primary theoretical constructs (i.e, they are respectively composed of correlated but conceptually distinct elements). Genetic factors constitute a manifest index and are therefore represented by a box (see Bollen, 1989, for conventions relating to path model representation)."
By the way, Bollen 1989 is a book that I haven't read - and do not wish to read :) Lova Falk (talk) 09:06, 24 February 2009 (UTC)

My guess is that by latent index the author means something that is hidden and not directly measurable (although still having an effect); while manifest index is something that is measurable (by examining the genes). I think it likely that the two terms are something made up by the author and are not standard terminology. 'Index' is probably used in the sense that, for example, IQ is an index of actual intelligence.

For example, someone's current personality is a result of the "manifest index" of their genes, and the "latent index" of the traces of their childhood upbringing. 89.240.206.134 (talk) 21:16, 2 March 2009 (UTC)

Ripen my mango

Does anyone know how to ripen a mango? Or do I just have to leave it and wait? My inclination would be to put it on a sunny windowsill, but Moseley is cold and grey at this time of year.--Shantavira|^{feed me} 09:50, 24 February 2009 (UTC)

Ethylene might work. They build countermeasures into fruit containers and warehouses so the fruit will stay fresh longer. Some fruit emit it naturally, so all you have to do is toss one of those into a plastic bag with your mango. 76.97.245.5 (talk) 11:08, 24 February 2009 (UTC)

If it's an ethylene-ripened fruit, then putting it near an old apple or banana, both of which produce ethylene as they become over-ripened, should work. --Jayron32.talk.contribs 12:12, 24 February 2009 (UTC)

According to [3] and [http://www3.interscience.wiley.com/journal/119468364/abstract mangos are indeed ethylene sensitive Nil Einne (talk) 12:26, 24 February 2009 (UTC)

In which case, putting it next to an old banana is your best option. --Tango (talk) 14:46, 24 February 2009 (UTC)

Thanks. Yes, I had forgotten the old banana-in-the-plastic-bag trick.--Shantavira|^{feed me} 17:56, 24 February 2009 (UTC)

Make it a paper bag instead. Plastic bags keep moisture trapped against the fruit, encouraging rot. Matt Deres (talk) 21:44, 24 February 2009 (UTC)

When the mango is ripe, it should be deep yellow (no green and not too brown), soft, and sweet rather than sour. ~AH1^(TCU) 22:06, 24 February 2009 (UTC)

You don't really need a bag at all, unless you are in a hurry. Just being in the same fruit bowl as a bunch of ripe bananas will do the job. --Tango (talk) 00:18, 25 February 2009 (UTC)

adrenal and gonadal androgen

Do I understand correctly from the article on androgens that there exist adrenal androgens, produced in the adrenal gland, and gonadal androgens, produced in the testes?
And, next question, do females produce just as much adrenal androgens as males? Lova Falk (talk) 10:06, 24 February 2009 (UTC)

You understand correctly. The adrenal glands produce three main types of hormones: glucocorticoids that have a role in the stress response and glucose homeostasis, mineralocorticoids that help regulate the salt/water balance, and androgens that are involved in the process of adrenarche (i.e. pre-puberty where pubic hair and body odor begin to develop). I don't know if there are(changing my wording... thanks, 159.14.241.253) specifically what the quantified differences in adrenal androgen output are between females and males, but during puberty the effects are dominated by gonadal production of testosterone in males (testes)and estrogen in females (ovaries). Abnormal adrenal steroid production is a key pathophysiologic mechanism in congenital adrenal hyperplasia. --- Medical geneticist (talk) 15:25, 24 February 2009 (UTC)

Of course there are age and sex differences in adrenal androgen production. All questions about normal human steroid hormone levels are only answerable for specified age and sex. Here, browse away to your heart's content. http://www.esoterix.com/files/expected_values.pdf —Preceding unsigned comment added by 159.14.241.253 (talk) 15:44, 24 February 2009 (UTC)

Scientist head of states!

Apart from Chaim Weizman and A.P.J.Abdul Kalam ,are there any instances of scientists heading a state?(Ramanathan) —Preceding unsigned comment added by 212.247.70.129 (talk) 12:25, 24 February 2009 (UTC)

An interesting non-example is that Einstein was asked to be Israel's second president after Weizman died, but he declined. --Sean 12:57, 24 February 2009 (UTC)

Weizman and Kalam are not scientists, but engineers. Very good engineers, no doubt, but not scientists. I found one, maybe, head-of-state scientist in Wikipedia, Stanislau Shushkevich, "first leader and head of state of independent Belarus after the dissolution of the Soviet Union". What the article means by "scientist" is impossible to tell, since it gives no examples of any discoveries of his, and the references are in Russian. --Milkbreath (talk) 13:14, 24 February 2009 (UTC)

Weizmann was a chemist, just FYI. He studied in chemistry, he did work in chemistry. Yes, there were industrial applications but that doesn't make him any less a chemist than Fritz Haber. From what I can tell, Shushkevich was a professor of nuclear physics (ядерной физики). --140.247.243.27 (talk) 21:09, 25 February 2009 (UTC)

Angela Merkel has a physics PhD, which is a lot closer to be a scientist than most, though she hasn't been an active researcher for decades. Dragons flight (talk) 13:16, 24 February 2009 (UTC)

Margaret Thatcher has a chemistry degree and worked as a research chemist before entering politics. Gandalf61 (talk) 14:43, 24 February 2009 (UTC)

I don't know whether the distinction is important to the OP, but Merkel and Thatcher are/were heads of government, not heads of state (also, Merkel's article seems to say that her PhD was in quantum chemistry, not physics). 81.98.38.48 (talk) 10:32, 1 March 2009 (UTC)

Thomas Jefferson lacked any formal degree in sciences, but he was an avid researcher, and his work in fields such as botany and zoology and archeology could easily qualify him as a scientist. --Jayron32.talk.contribs 16:45, 24 February 2009 (UTC)

Adding to the list of female chemists, on a more unpleasant note, Elena Ceauşescu was a polymer chemist. She was only deputy Prime Minister, but was often rumored to have been the brains behind her husband. --Pykk (talk) 18:49, 24 February 2009 (UTC)

The article suggests she may not really have been a chemist and instead relied on other people to do the work for her Nil Einne (talk) 03:37, 25 February 2009 (UTC)

Ephraim Katzir, president of Israel, was a scientist. Also, Chaim Weizmann was actually a chemist / biochemist rather than an engineer, AFAIK; our article, too, says "chemist" rather than "engineer". --Dr Dima (talk) 00:25, 25 February 2009 (UTC)

Right, but as the "father of industrial fermentation", I figured Weizmann for a chemical engineer. "Chemist" doesn't necessarily mean "scientist", but the line is blurry, so he can come in for my money. --Milkbreath (talk) 00:34, 25 February 2009 (UTC)

If you're the father of figuring out how to turn some bench science into engineering science, it doesn't make you an engineer and not a scientist. It makes you a pretty impressive scientist! --140.247.243.27 (talk) 21:09, 25 February 2009 (UTC)

Woodrow Wilson was a political scientist. -- Mwalcoff (talk) 04:20, 26 February 2009 (UTC)

Though not a very good one. —Tamfang (talk) 22:14, 2 March 2009 (UTC)

Abel Pacheco was a psychiatrist who did some scientific research (which may or may not count). Rockpocket 06:55, 26 February 2009 (UTC)

Bamir Topi, president of Albania, has a PhD in vetinary science. Bosnia's president Boris Tadić used to be a psychologist. Abdullah Gül, the president of Turkey, appears to have a PhD in economics, as does Yayi Boni, the president of Benin, and Aníbal Cavaco Silva, president of Portugal. Chile's president Michelle Bachelet is a doctor of medicine. Abdul Kalam, a former president of India, used to be an engineer, and Costa Rica's president, Óscar Arias Sánchez, has a PhD in political science. I found all of these by picking entries at random from List of heads of state by diplomatic precedence. 81.98.38.48 (talk) 10:58, 1 March 2009 (UTC)

a pill i found

a friend of mine dropped a round white tablet in my car and now i'm curious what it is. it has a few numbers on it on two rows. 44 and 438 on the second row. —Preceding unsigned comment added by 98.210.135.91 (talk) 13:19, 24 February 2009 (UTC)

A Google search for "44 438 pill" finds several sources agreeing that it's 200mg of Ibuprofen, like this pill. jeffjon (talk) 13:52, 24 February 2009 (UTC)

Ibuprofen! Duh, what a disappointment. Richard Avery (talk) 14:42, 24 February 2009 (UTC)

This inspired me to take a closer look at the ibuprofen pills nearest my desk (also 200 mg), which came from Walgreens: they're red and say 44/291. Where do the numbers come from? —Tamfang (talk) 00:15, 3 March 2009 (UTC)

Singapore history

Hi all, I am currently doing a history assignment. I am supposed to gather accounts of people living from the previous generations to give an account of Singapore during their time and suggest the history od modern singapore. Please give me your account of Singapore and how it was like. Thank you very much.(you could help me by helping me find accounts of other people). —Preceding unsigned comment added by Invisiblebug590 (talk • contribs) 13:34, 24 February 2009 (UTC)

That's not really the kind of references we can help with. I can point you to History of Singapore if you want the facts, but if you want personal accounts you will have to find them yourself, I'm afraid. --Tango (talk) 14:44, 24 February 2009 (UTC)

This newsreel gives an account of pre-WW2 colonial Singapore. Cuddlyable3 (talk) 19:02, 24 February 2009 (UTC)

Wave equation

I'm having trouble understanding waves. I find wave equation explainations insufficient. I can see how rates of speed in circular motion can translate to expressed different kinds/shapes of waves and appreciate the descriptive graph/animations on the wikipedia pages for waves and trigonometry. But I don't believe it sufficiently explains why concepts of trigonometry like sin,cos which a beginner like myself associates with triangles are brought into describing waves, there is a connection gap. Can anyone elaborate on how sin, sohcahtoa, e.g. opposites divided by hypotenuse (one never sees this process taking place and which parts they correspond to in the waves) relate/interact to aspects of the waves. Thanks in advance for any insight here. —Preceding unsigned comment added by Dbjohn (talk • contribs) 15:15, 24 February 2009 (UTC)

You associate trigonometry with geometric shapes like triangles, but that mathematics can be applied to a very large set of geometric and other conceptual problems. In many ways, you can think of a wave equation as "some parameter" (such as pressure), traversing around unit-circle. This means that it is repetitive, cyclic, and can be described as a "phase" (angle) parameter and a strength (magnitude) parameter. The conceptual leap from physical space to phase space is a big one - when "pressure" goes through an angle from 0 to 360°, the pressure isn't "moving" anywhere (although the wave may actually propagate as a result). The wave equation, for whichever physical situation you are considering, will describe the relationship between the phase of the parameter and its spatial coordinate (position) as a function of time. Let me know if you need some more clarification; this is conceptually a big leap, but after you can bridge the ideas, things will seem much simpler. Nimur (talk) 17:59, 24 February 2009 (UTC)

I suggest you look at these two figures[4][5]. In the second figure only the lengths marked sin and cos are of interest. There you have your right triangle where AO is the hypotenuse. Think of the hypotenuse continually rotating anticlockwise so angle theta keeps increasing. The sin and cos values vary over time (angle) as shown in the first figure. In practical terms, either could be the voltage wave produced by a rotating generator. Cuddlyable3 (talk) 18:39, 24 February 2009 (UTC)

Band-stop filters

I am considering using a digital filter to remove electrical background noise from facial surface EMG data. I have seen a number of different band-stop ranges in the literature to remove 60 Hz (I am in the USA), but there is no particular theoretical justification I can find regarding why one would use a particular range (for example, 59-61 Hz as opposed to 58-62 Hz). Is this an arbitrary decision? Does anyone here know what the standard deviation for 60 Hz mains hum is? Thanks, PotionsMasterSnape (talk) 15:37, 24 February 2009 (UTC)

Utility_frequency#Long-term_stability_and_clock_synchronization ~<0.1% deviation per day. —Preceding unsigned comment added by 213.249.232.187 (talk) 16:00, 24 February 2009 (UTC)

Two things come to mind: There might be times when you'll be getting power from a generator that won't have such a tight frequency spec. I looked online, and the specs I saw just said "60 Hz". The lack of an expressed tolerance bodes ill for their accuracy, I think. The other thing might be only in my fevered brain, but I imagine it's possible that line hum could feed some low-Q stray resonance in a circuit close to 60 Hz. --Milkbreath (talk) 16:13, 24 February 2009 (UTC)

Our article on Utility frequency notes that utilities try to keep quite close to the nominal frequency so that synchronous clocks only deviate a few seconds from actual time. That article says that utilityes may start automatic load shedding when the frequecy drops as much as, say .5 Hz from a nominal 60 Hz. to prevent a widespread blackout due to inadequate generation online to serve the connected load. So +/- .5 Hz should cover extreme frequency deviations, and a somewhat tighter band (+/- .1 Hz?) should cover normal day to day deviations, outside of system instability or overloads. If the power is provided by stand-alone generators, then the frequency deviation could be much wider, perhaps several Hz.Outlet power or even the power on the utility feeders also contains harmonic multiples of the mains frequency, the amount varying greatly depending on transformer balancing and the loads customers have connected. Edison (talk) 17:32, 24 February 2009 (UTC)

I've spent a lot of time filtering out power-line harmonics (and going to great lengths to avoid power-lines in the first place). Your particular measurements will have to dictate your removal method for power-line harmonics (have you looked at an FFT of your recording? You can probably see the 60Hz hum spike). In many cases, a narrow notch-filter works well; sometimes, I've used noise-fillers or statistical estimators to interpolate in the frequency or time domains to smooth out the final signal. The power-line hum can vary by a large amount from place to place; its mean frequency might not be exactly on 60 Hz; its amplitude fluctuates by extreme amounts (I have seen 100 dB range) based on the actual amount of current in the lines and how well your receiver couples in to it at any given instant). I have seen bandwidths of more than 20Hz on pathological datasets. It will largely be arbitrary; you can make an intelligent nonlinear filter or estimator to automate the estimation of the filter parameters, depending on your needs. (E.g. measure the original signal's frequency spectrum; estimate the f3db width of the spike closest to 60 Hz, and make a new notch-filter based on those). Nimur (talk) 18:06, 24 February 2009 (UTC)

You may also want to remove harmonics of the 60Hz such as 120 or 180Hz which are also likely to be present, especially if you have mains power supplies nearby. And if you want your system to work in other countries you may want to stop out 50Hz instead. If you make a very narrow bandstop filter it will have a high Q, and a long delay, so as to be more a problem for real time results. You should also look at the side effect on your signals, try to minimize the phase shift near the stop point. This can happen with the Gaussian filter but there will be a trade off with the shape of the stop band. Graeme Bartlett (talk) 22:30, 24 February 2009 (UTC)

Conservation of mass

The law of conservation of mass states that the sum total of mass in a system remains constant no matter what, right? Visualize the following situation: A couple (male and female) of animals (cows, dogs, goats, or even humans) is kept in a closed chamber for a year. The chamber is stocked with enough food to last them for quite a while. After a year, the food reserve is finished, and the female has borne a child. Does the law of conservation of mass apply here?? The food is finished, and there is addition of a third organism. How can the sum total of all the masses still be the same?? Thanks in advance. 117.194.230.71 (talk) 15:58, 24 February 2009 (UTC)

Enough food, water, and air to last a year would be a much larger amount of mass than most people would imagine. It would be many, many times the size of the third organism - the vast majority would be actually converted to waste solid, liquid, and gas. arimareiji (talk) 16:05, 24 February 2009 (UTC)

And don't forget heat, which hasn't really been discussed in the original scenario. Remember that conservation of mass applies to closed systems, meaning no heat in or out of the chamber, which will introduce all sorts of issues. Arakunem^Talk 16:11, 24 February 2009 (UTC)

(EC) Yes. Everything would tally up, assuming you have a way of totalling ALL of the energy in this closed system (i.e. the masses of the people/goats/pink mongooses and all the food, plus the thermal energy "waste", because E=mc²), and I'm assuming you mean properly "closed", as in, say, a hermetically sealed chamber.--Rixxin (talk) 16:09, 24 February 2009 (UTC)

The heat released from the system is NOT converted to or from mass. It comes from chemical potential energy stored between atoms in chemical bonds and is NOT from mass-to-energy conversion which requires a very specific sort of thing, i.e. nuclear fission. If you have a truly closed system, the mass will not change at all, and there is no need to invoke E=mc² to make it happen. The existing atoms in the closed system don't disappear, and no new atoms are created out of whole cloth. Since a closed system will have, atom-for-atom, the same exact atoms in it over any length of time, regardless of how those atoms are physically rearranged over time, the entire system will retain a constant mass. QED. --Jayron32.talk.contribs 16:36, 24 February 2009 (UTC)

No, he's right. E=mc² applies to all forms of energy, including chemical bond energies. It's just that the amount of energy change associated with breaking chemical bonds is so tiny that the mass change is nearly always below the limit of detectability. If you burn and dissipate the heat from 600,000 gallons of gasoline the resulting CO2 + H2O would be about 1 gram lighter than the sum of the initial gasoline + oxygen. Dragons flight (talk) 16:52, 24 February 2009 (UTC)

I think the first two sentences of this section of the E=mc² article might shed some light on, if not settle, the matter.--Rixxin (talk) 17:12, 24 February 2009 (UTC)

I think the question is whether the light will settle into mass, not matter. --140.247.243.27 (talk) 21:14, 25 February 2009 (UTC)

Mass-energy equivalence is tossed around a lot these days. In this case, it is correct that energy-changes could result in minute mass changes, but those are truly minuscule and absolutely negligible for the purposes of this scenario. The original poster is probably just underestimating how much food it really takes - maybe some statistics on agriculture will help. A cow can consume 300 pounds of water in a single day. In a year, this will equate to tens of thousands of pounds of water. Does this help put into perspective? Nimur (talk) 18:15, 24 February 2009 (UTC)

Or even just consider the air: According to Oxygen: "An adult human in rest inhales 1.8 to 2.4 grams of oxygen per minute." We'll call that 2 grams. That's 2g*60*24=2880g per day. That works out to just over 1 tonne of oxygen in a year (which will have been converted into CO₂). The newborn baby might have a mass of about 5kg, it's neglibible. --Tango (talk) 18:50, 24 February 2009 (UTC)

Well conservation of mass mostly applies to chemistry now (where E=mc² can be safely neglected, as mentioned). And if you view this from a chemical viewpoint, it's not very strange. Humans catalyze the reaction: Food + O₂ ---> Excrement + CO₂ + Babies. --Pykk (talk) 19:00, 24 February 2009 (UTC)

Are there any other catalysts (other than other lifeforms) that catalyse a reaction that creates the catalyst? --Tango (talk) 19:07, 24 February 2009 (UTC)

Yep. See autocatalysis. There are a number of chemical reactions where one of the products is a catalyst of the reaction; these reactions will start slowly (if at all), and accelerate (as more product/catalyst is generated) until the supply of raw materials is depleted. TenOfAllTrades(talk) 20:03, 24 February 2009 (UTC)

There's a lot of math here to answer a simple question. Isn't the more obvious answer that the original questioner forgot about poop? APL (talk) 20:10, 24 February 2009 (UTC)

Yep - this stuff about E=mc² is really a red herring. That's so negligable - we can ignore it for all practical purposes. So long as the container is absolutely air-tight (gas tight), water-tight and no solids, liquids or gasses come into or out of the container for the whole duration of the experiment - then the contents of the container will weigh exactly the same at the beginning as at the end. SteveBaker (talk) 20:54, 24 February 2009 (UTC)

By my extremely rough calculations, the energy losses would correspond to about 10kg over a year. That's pretty small compared to the tonnes of food, air and water than would be required, but it is probably measurable if you tried hard enough. However, if energy can be lost from the container, it may be possible for it to be gained as well (sunlight coming in the window, for example), so it's rather more difficult to work out what would happen to the mass. --Tango (talk) 21:10, 24 February 2009 (UTC)

Of course, I only realise I divided by c and not c^2 immeadiately after clicking "save"... my rough calculations actually come out at about 30μg. Ok, that's negligible! --Tango (talk) 21:13, 24 February 2009 (UTC)

Antoine Lavoisier was a pivotal figure in the discovery of the law of conservation of mass. Unfortunately, he was caught up in the french revolution and lost his head. Vespine (talk) 04:25, 26 February 2009 (UTC)

Ketonuria caused by a high protein diet.

Hi I read the article on ketonuria which states that the condition can be caused by a high protein low carbohydrate diet. My question is why? Say we had a non-diabetic individual who ate nothing but high protein foods such as meat and fish. Would not their bodies be converting the amino acids produced from the digestion of their food to glycogen by the process of gluconeogenesis? Why would their body then need to metabolise fats (it is my understanding that the catabolism of fatty acids produces ketones) for energy if glycogen can be produced from the protein they are eating? Would I be right in thinking that the person's body would not be able to get all the energy it would need from glycogen produced by the gluconeogenesis of amino acids and so fatty acids would need to be broken down to provide additional energy. Hope this makes sense and any suggestions would be great. —Preceding unsigned comment added by 139.222.240.66 (talk) 16:04, 24 February 2009 (UTC)

• It's simplest to answer your second question first, actually.

1. The body is very efficient at breaking down glucose into smaller particles and energy.
2. The body is very inefficient at driving the same cycle in reverse to turn small particles into glucose. (gluconeogenesis)
3. Functionally, the brain will not operate on any fuel other than glucose. If your brain stops, you die.
4. Gluconeogenesis is a last-ditch emergency effort by the body to keep from dying.
5. Anything becomes fair game as a matter of survival - fat and muscle included.

• Back to the first question:

1. Remember point #2 above - it's somewhat akin to trying to drive a water wheel backwards.
2. You get a lot of the components for gluconeogenesis building up / pooling.
3. Those components are high-energy, i.e. very reactive chemically.
4. They're almost as happy to start engaging in side-reactions with themselves (condensation) as they are to be driven through gluconeogensis.
5. The products of those side-reactions are ketones.

• As you can imagine, this type of diet is very effective - but it's also a very bad idea if you prefer long-term survival. It plays hell with your liver and glucose regulation, among several other niceties. arimareiji (talk) 17:14, 24 February 2009 (UTC)

The article on ketogenic diet and particularly the mechanism of action section may be helpful. If your body is in starvation mode (or thinks that it is in starvation mode) then any glucose made via gluconeogenesis will go straight to the blood stream and not be converted back into glycogen, which is the storage form. The hormones that control this process (insulin and glucagon) have opposing roles and once you're in a catabolic state the breakdown of fatty acids will be an integral part of the process. By the way, the above statement that "the brain will not operate on any fuel other than glucose" is incorrect. The brain CAN and DOES utilize energy sources other than glucose, namely the ketone bodies that are produced during starvation. --- Medical geneticist (talk) 17:52, 24 February 2009 (UTC)

Please note that I already qualified the statement with "functionally" for the exact reason that you specified. arimareiji (talk) 18:32, 24 February 2009 (UTC)

Thank you very much for your help to both of you. —Preceding unsigned comment added by 139.222.241.116 (talk) 09:56, 25 February 2009 (UTC)

The answer can be made a lot simpler. Insulin levels are primarily determined by carbohydrate intake (carbohydrates stimulate insulin secretion). The processes of ketogenesis are amplified whenever insulin levels fall below a threshold level, and suppressed when insulin levels rise. Although a few other factors besides carb intake affect insulin secretion, and a few other factors besides insulin levels affect ketogenesis, the basic answer to the question is this simple. 159.14.241.230 (talk) 19:52, 25 February 2009 (UTC)

You could make it simpler yet and say "Because it just does." arimareiji (talk) 23:14, 25 February 2009 (UTC)

Here's an afterthought - does anyone know if the concentration of ketones in the urine would significantly differ between a non-diabetic person on a high protein diet and person who has undiagnosed type 1 diabetes? I expect the diabetic would have a greater concentration of ketones in the urine. Could a person on a high protein diet give themselves ketoacidosis by eating protein rich foods exclusively? I believe a people persue a high protein diets to try and put on muscle mass, but surely then, persuing a high protein diet to such extremes that only protein rich foods were eaten would be counter-productive to trying to put on muscle mass as it would just result in ketogenesis which depletes fat reserves and causes muscle wasting. Once again thanks to all that have helped. Any thoughts? —Preceding unsigned comment added by 139.222.241.116 (talk) 11:13, 26 February 2009 (UTC)

Blood and urine ketone levels can reach much higher levels (like >10x) in diabetic ketoacidosis compared to ordinary low-carb ketosis, because even the low levels of insulin in starving healthy people are enough to prevent the extreme degree of ketosis that leads to DKA. Ketogenic diets are used in the treatment of several conditions, especially difficult-to-control epilepsy. A high fat diet is more effective than a high protein diet for maintaining ketosis. PS, I just looked at the ketogenic diet article-- it is superb: kudoes to user:colin and others. 159.14.241.230 (talk) 13:52, 26 February 2009 (UTC)

Have a look at rabbit starvation, when people live entirely off meat which has very little or no fat. See particularly the reference link at the bottom of that page. 89.241.154.51 (talk) 21:45, 1 March 2009 (UTC)

Tiny Springs

Hello. I think I may wish to acquire tiny springs - 1mm diameter, length >3mm.

Does anyone know where I could get such things (UK), the springs preferably should be slightly compressable, and on the weaker side of spring constant (for their size).

Alternatively (my main question) - how could I turn tiny coils of wire into tiny springs (in real life practice) - what substance should I used, and what are the ways of making wire springy (copper wire as bought makes a coil - but isn't springy)

Thanks. FengRail (talk) 21:45, 24 February 2009 (UTC)

Google, in their "sponsored links" section, has several spring manufacturers and sellers, as seen here: in this google search. If you refine your search, you may find one to meet your need. --Jayron32.talk.contribs 16:16, 24 February 2009 (UTC)

Could you cut a bit of a spring from a "clicky" biro?--82.70.123.254 (talk) 16:25, 24 February 2009 (UTC)

Remember, 1 mm isn't much thinner than your fingernails in cross-section. arimareiji (talk) 16:29, 24 February 2009 (UTC)

Most devices that small utilise tiny pads of foam rubber instead.--Shantavira|^{feed me} 18:01, 24 February 2009 (UTC)

McMaster-Carr, my preferred mechanical stock supplier, has springs down to 0.12 inch (3mm) outer diameter. Nimur (talk) 18:18, 24 February 2009 (UTC)

You'll find a spring of about the size you are looking for inside a leather watch strap pin. You know, that metal tube with a sprung tip at each end that fastens the strap to the watch and to the buckle. --Heron (talk) 19:09, 24 February 2009 (UTC)

Yes that's the sort of thing - thank you. I might need a few but I guess that if I buy 100 they won't cost much.

• By the way I'm still interested in making my own...(I think the watch spring pins might be just over 1mm, .... mmmh - are ladies watch pins smaller?) If anyone can give material hints....FengRail (talk) 21:45, 24 February 2009 (UTC)

Hop over to your local dollar store and grab a selection of their $ 1 each watches. Some, but not all have a spring like what you are looking for under the battery. If you are lucky you might even find one model that has springs at the "push buttons". You could also contact your local watch repair shop and ask them if they have any. Unless you can talk them out of a couple of irreparable broken movements, the brand name stuff is likely going to cost you an arm and a leg. I tried to find a source online, but there are only a handful of manufacturers that actually make watch movements. So the springs aren't a mainstream item. Your local goldsmith will be able to point you towards a source for fine wire to make your own springs.76.97.245.5 (talk) 01:00, 25 February 2009 (UTC)

The springs under the pushbuttons will be leaf springs. I think FengRail wants a coil spring. The spring pins that hold the watchband on as Heron suggested are the most obvious source. If you want to wind your own from spring steel I expect you'd have to heat treat them. 207.241.239.70 (talk) 06:40, 27 February 2009 (UTC)

Botany of antractica

Are there any plants naturally occuring in Antactica? Simply south is this a buffet? 18:23, 24 February 2009 (UTC)

Yes - Flora of Antarctica should give you more detail. DuncanHill (talk) 18:27, 24 February 2009 (UTC)

Thanks. Simply south is this a buffet? 00:59, 27 February 2009 (UTC)

Sexuality being decided?

I just had an argument with a friend today who said she believed that our sexuality (ie: gay/straight/transexual/whatever) was decided for us, chemically, before we are born. I argued that there was no evidence for this and that it was much more likely that one of the trillion influences on our development have an effect at some point which eventually determin how we feel about ourselves sexually. I wondered if there is any scientific evidence either way? Is there really (as she claims) a bunch of chromosomes that are instrumental in deciding our sexual fate before we are born? Has there ever been any social studies to explore the possibillity that a certain type of upbringing is more likely to produce a homosexual? I put this on the science desk to limit the level of 'opinion' that a question like this might generate, so please try and keep answers as factual as possible, thanks.91.111.86.8 (talk) 20:04, 24 February 2009 (UTC)

Here's a relevant article: Biology_and_sexual_orientation. Friday (talk) 20:09, 24 February 2009 (UTC)

Another suitable article (well, it is more of a stub) is Xq28 and the references. --Cookatoo.ergo.ZooM (talk) 20:12, 24 February 2009 (UTC)

In the purest sense, a gene for outright homosexuality would be selected out of the gene pool in a single generation. So we know it can't be as simple as that. Such complex behaviors are highly likely to be a combination of nature and nurture - genes and upbringing. Bisexuality could perhaps be a gene because it wouldn't out and out prevent itself from being passed on to the next generation (although you'd still imagine it would be strongly selected against over a number of generations unless it conferred some other benefits that ultimately (and paradoxically) aided reproduction). SteveBaker (talk) 20:47, 24 February 2009 (UTC)

A dominant gene for homosexuality would be selected out in a single generation (assuming culture allowed it - plenty of homosexuals have married and had children since that was what was expected of them by society), a recessive gene could last longer, particularly if being a carrier held some advantage (like with sickle cell anaemia). One (very small, perhaps) advantage of being a carrier of the homosexual gene would be that you are likely to have homosexual siblings that wouldn't have children of their own so could help you support yours. (That's more of a mitigation of the disadvantage than an outright advantage, I suppose.) However, I agree, there is clearly something more going on than a single gene. --Tango (talk) 20:58, 24 February 2009 (UTC)

(See also, kin selection. Note though that it is certainly not the case that 100% of all homosexuals do not reproduce genetically. In fact one can probably make the argument that the history of homosexual oppression in the last few hundred years would have led to more homosexuals reproducing than the current more liberal sentiment, as I suspect those in the closet have kids more often than those out of it do.) --98.217.14.211 (talk) 05:21, 25 February 2009 (UTC)

It's possible that homosexual individuals who do not have children provide some benefit to their own close family members. If so, then while not themselves reproducing, those with a homosexuality trait may indirectly encourage the propagation of their own genes (via their siblings). I seem to recall reading about such a hypothesis once in a sociobiology class I took many, many moons ago. I'll see if I can find a source when I get home. – ClockworkSoul 22:27, 24 February 2009 (UTC)

The problem with the question in many contexts is that, if one were to say "This is 100% choice" then it many people take this to mean "this is a valid reason to discriminate against someone who is homosexual", and yet we have laws in most western nations that disallow discrimination based BOTH on genetic-based traits (such as gender or skin tone), choice-based traits (such as religion), and environmentally-determined traits (such as historical national origin). The reality is likely that, like every single behavioral trait we experience, there are some combinations of genetics, environment, and choice involved in it, and every individual has a unique melange of these factors determining their own unique personalaties. To isolate one factor of a personality and say "This bit here, this bit must be all genetic" or "This bit here, this bit must be all choice" is wrong for several reasons. First, its never all genetic or all choice or all environment, and secondly, you cannot isolate a single aspect of someone's life in that way and treat its cause in isolation from the rest of their personality. Its just not that simple. --Jayron32.talk.contribs 04:59, 25 February 2009 (UTC)

There is no doubt that there is much to be said in terms of political correctness for there being a genetic component - but science is what science is - and sometimes the truth just isn't politically correct. It's perfectly possible for there to be no genetic component whatever - although it's extremely hard to imagine that a purely genetic reason is a possibility. I agree that the most likely explanation is a mixture of genetics and upbringing - but I don't think we know that yet. SteveBaker (talk) 16:55, 25 February 2009 (UTC)

Clockwork, there may be some benefit to the family of a homosexual but notice that this sort of explanation isn't used for anything else. You don't speak of the (any type of trait that makes him highly unlikely to reproduce, like being infertile or disgustingly unattractive, etc) Uncle being selected for by natural selection because he provides benefits for his kin.--droptone (talk) 13:11, 25 February 2009 (UTC)

The simplest answer to that is kin selection. Most of what I would say is included or linked in that article. If you treat humans as social creatures that evolved in tribes, rather than individually, a lot of things make more sense; competing tribes try to out-survive each other. 79.66.56.21 (talk) 16:18, 25 February 2009 (UTC)

Kin selection is a rather weak form of selection. It can explain things like that we tend to live past child-rearing age...but for something as specifically significant to reproduction as homosexuality - I think that's a long stretch! Even tribes need people to breed - and specifically in a small tribe where there is likely to be much inbreeding - a latent gene such as this would have to be would doom the tribe pretty solidly. If there is a genetic component to this - it really can't be the whole answer. SteveBaker (talk) 16:55, 25 February 2009 (UTC)

I would doubt it is the whole picture (seriously doubt it), and there are many proposed ways in which selection may work on genes giving an increased tendency towards homosexuality (aiding with rearing nephews and nieces, increased fertility in women who carry the genes that tend to be associated with homosexuality in men, etc). Tribes do indeed need people to breed, but they don't necessarily need all members to breed. Particularly not all men. But anyway, that is beside the point; I was replying to the claim that this reasoning is only ever applied to homosexuality. Kin selection is a wider thing applied in more areas than merely sexual orientation, and that is what my reply was supposed to indicate. 79.66.56.21 (talk) 22:05, 25 February 2009 (UTC)

E.O. Wilson is the one who suggested homosexuality and kin selection are likely related; if I recall, he points out (in On Human Nature) that tribes that had, say, 1/10th of the men who were on whole more dedicated to the support of others in the tribe (and not breeding), and are willing to help with "women's work" would be quite an advantage over time. But it's a 1970s sort of argument on many fronts. Part of the difficult here is that we are used to, in the west, defining homosexuality/heterosexuality as some sort of simple binary. While I don't think sexuality is as evenly distributed on the bell curve as, say, Kinsey argued, the idea that there should be some sort of behavioral spectrum seems fairly likely (given that almost all other behaviors exist on such a spectrum). What we call "homosexuality" could really just be the extreme case of a more subtle effect, one that really only manifests when you start talking about really large sample sizes. Obviously cultural/environmental values must play into it in some way as well, of course. --140.247.11.54 (talk) 01:59, 26 February 2009 (UTC)

"Specifically significant to reproduction as homosexuality" - pardon, but kin selection allows selecting for infertile-by-birth members; homosexuality - which, if viewed entirely from a breeding standpoint offers similar advantages without the lock-in cost - in extremis, a tribe with one homosexual and one alternate sex can procreate, a tribe with one infertile-by-birth eusocietic member and one alternate sex is doomed. 98.169.163.20 (talk) 07:23, 27 February 2009 (UTC)

It's worth remembering that 'determined before birth' does not mean 'determined entirely genetically'. There are many traits where conditions in the womb and other things have some effect but which are determined largely or completely before birth Nil Einne (talk) 02:43, 26 February 2009 (UTC)

Exactly. I'd say the actual decision comes from the womb, hence the reason why there's about a 50% concordance rate among identical twins, but only a 25% concordance rate among fraternal twins. They're exposed to the same womb, but because their brains are developing at significantly different rates (as opposed to only slightly different rates), the effect of a hormone surge at one period is less likely to affect both of them at the same time. Thus, the "gay gene" is, I would argue, a "womb instability gene," and not causal to being gay or not-- it would merely influence how unstable the womb is. Combined with womb memory research finding that the more kids a female has, the greater the likelihood that subsequent children will turn out gay, I'd say there's ample evidence to suggest the womb is at fault-- not simple genetics.

It makes sense, too, as a population control mechanism, and it's presumably why homosexuality is rampant in higher order animals (including aves and mammalia). The easier it is for them to survive in their environment, the more likely it is for them to overpopulate, exhaust their resources, and die off. In this instance, survival of the fittest creates a situation where the fittest would die and therefore not be the fittest. Thus the "womb instability gene" probably came along as a way to naturally mediate overpopulation without the danger of creating underpopulation, thereby continuing the trend of "fittest" without worry of the fittest multiplying like rabbits with no fox to eat them.

Thus, the "gay gene" (or really, "womb instability gene") is simply another evolutionary advancement: it prevents the species from sexually selecting for totally gay/asexual in times of plenty, thus dying out; it allows for a gay member to reproduce during a population crisis without guaranteeing homosexuality to its offspring (thus preventing dying out); and, finally, at the same it prevents the species from staying totally heterosexual, which, when it comes to high-order animals like humans, would also result in the species dying out. As a spillover benefit, gays still retain mothering and fathering instincts and are able to care for abandoned children or children whose parents have died, thereby also increasing the chances of successful continuance of the species when, under certain circumstances, the abandoned child's lineage would die out when the child did.

Taken in this light, the persecution of gays is actually what's more logically unnatural—not gay people themselves—while the uninhibited population growth by forcing gays into lives of procreation actually worsens the problem and makes it more likely that humans will die off due to overpopulation.

--slakr^\ talk / 05:43, 26 February 2009 (UTC)

DC power supplies in parallel/series

I am building a guitar pedal at the moment and am having trouble with the power supply. I originally designed the pedal to run on 9V batteries (two of), but as I use a powered pedal board, it seemed a better idea to open it and replace the batteries with DC sockets(two of). I have the correct sockets, and have wired them up in sort of "Y" configuration - where the two tips of the Y connnect to a 9V DC socket (either +ve or -ve), and the bottom tip of the Y is the +ve or -ve supply respectively. Upon use, I have found that it does not work as it used to. It was a distortion pedal, based on the fact that op-amps saturate after a certain level of input - so I think the problem lies in the configuration of the DC supply. Right now, they are connected in some kind of pseudo-parallel configuration, and I am wondering if I connect them in series, will it solve my problem. My thinking is that when batteries are connected in parallel (+ve to +ve and -ve to -ve) the overall voltage is the same, but the current is doubled, whereas when they are connected in series (+ve of one to -ve of the other) the voltage doubles, but the current stays the same. In the battery, however, the +ve and -ve poles are connected via the chemicals in the battery - but with my DC socket, the -ve and +ve poles are isolated from each other, and to connect them (in a series fashion) would ground the power, and thus not be able to power any of my pedals. Is there any way around this?

Summary: How do I connect two DC sockets together (bear in mind, the +ve and -ve terminals are isolated from each other) so that the voltage across the two of them is equal to the sum of the two input DC voltages?

Any help is appreciated. Thanks! —Preceding unsigned comment added by 81.158.231.154 (talk) 20:29, 24 February 2009 (UTC)

You need to know whether the pedal has the two 9 volt batteries driving different parts of the circuit at 9v each - or whether they are in series (to generate an 18 volt supply) or in parallel (to last twice as long or to produce twice as much current as a single battery). I strongly suspect the latter because there aren't many (if any) simple audio circuits that need 18 volts! However, if the two batteries WERE in series - then you just shorted out your power supply because the pedal connected the + of one plug to the - of the other...but they go back to the same power supply via the 'Y' lead! This might have damaged the power supply...or maybe blew a fuze inside - or maybe just caused a thermal trip to trip out...depending on the kind of power supply. If the batteries were in parallel - then there was no point in wiring up two separate jack plugs because they are both going to the same place. In that case the problem might be that your power supply can't produce as much current as two 9v batteries.

At any rate - you cannot double the voltage of a power supply by putting in a 'Y' lead and then connecting the + of one plug to the - of the other. That not only doesn't work - but is highly likely to do damage to the power supply. If you truly need 18 volts (which seems VERY unlikely) then you either have to go back to using 2 batteries - or you need a proper 18 volt power supply.

SteveBaker (talk) 20:41, 24 February 2009 (UTC)

Many op amps require dual (split) supplies; +V and -V, and I would bet that your two 9V batteries were connected in series so one provides the positive and one the negative voltage, with the remaining two battery terminals tied together and connected to the circuit ground. Yeah, powering it with a single supply in a Y won't fly. To power the pedal you will need two 9V DC supplies, such as a pair of "wall wart" transformers. You can put sockets on your pedal that accept the wall warts' plugs. Just be sure they connect to your circuit with the same polarity as your batteries. As an alternative, at thrift shops you can often find wall warts that provide split supplies. Look for one with terminals marked, +9V and -9V, and GND or COM, then connect the COM line to the two (opposite polarity) battery terminals which were tied to the circuit ground. You can tell which ones these are because they are connected together, or you can use an ohmmeter. Then connect the +9V and -9V lines to the remaining + and - battery connectors. If you can't find ±9V transformers, your op amps will probably work ok with any voltage between ±7V and ±15V, as long as both positive and negative voltages are the same. --Chetvorno^TALK 22:40, 24 February 2009 (UTC)

Yes, I am powering an op-amp, and yes, I am using 18V. The op-amp I am using (NE55532) can take a 3V-25V power supply, and so I decided 18V was the most I could feasibly use. Thanks for the tip that I won't be able to generate as much current with two power supplies as with two batteries. I'm just going to revert back to batteries for now. If you can find any kind of information on turning two 9V DC supplies into one 18V DC supply then let me know. Thanks! —Preceding unsigned comment added by 81.158.231.154 (talk) 10:41, 25 February 2009 (UTC)

But why do you need 18v just to generate a few volts of audio signal? You're putting the signal into an amplifier at the end - and it CERTAINLY doesn't want 18 volts of audio! SteveBaker (talk) 16:43, 25 February 2009 (UTC)

The reason for the somewhat crazy voltage requirements are that many op amps (and certainly the NE5532) cannot swing their output close to the supply rails. In the worst case they can only get within 3 V, so a power supply of ±9 V only gives an output dynamic range of ±6 V. There are other reasons to use large supplies for an op amp (eg. better slew rate, better bandwidth) even if the output dynamic range doesn't need to be large. To the OP, if you have a 555 timer and some largish capacitors, you can make a "voltage inverter" which can obtain about -7 or -8 V from a +9V supply (google "voltage inverter" for some circuits). However, these types of circuits are typically charge pump circuits which may have unacceptable ripple voltage. Another way to obtain a dual supply when you only have a single supply is to get a 24 V supply and split it with a 7812, then call the regulated +12 V "ground", the old ground "-12 V" and the old +24 V "+12 V". TI also makes supply splitters (TLE2425 and TLE2426) which are designed for this purpose, so you can try using those if you can find them. 130.194.72.111 (talk) 00:21, 27 February 2009 (UTC)

hydrodynamic and aerodynamic

On the front of large ocean going vessels (and probably other kinds of ships too) there is a bulb shaped thingy (can't remember the name) that aids in the hydrodynamics of the ship. Thus, with this bulb thingy, the ship moves through the water easier (due to a decrease in water resistance). Does this same principle apply to cars, planes and other vehicles as they pass through the air? —Preceding unsigned comment added by 69.77.185.91 (talk) 21:07, 24 February 2009 (UTC)

Oh. I found the name: bulbous bow! D-uh. —Preceding unsigned comment added by 69.77.185.91 (talk) 21:10, 24 February 2009 (UTC)

A bulbous bow works on ships because they're travelling on the interface between air and water. Nothing else travels on such an interface, so you won't see bulbous bows on submarines or airplanes. --Carnildo (talk) 22:58, 24 February 2009 (UTC)

We really need an article about that. Clarityfiend (talk) 23:52, 24 February 2009 (UTC)

Water Hammer Arrestor

When I bought my house, the washing machine was causing bad water hammer, so I installed a water hammer arrestor which solved the problem. Years later, the problem has returned. I think I remember reading something at the time that said that eventually the arrestor fills up with water (or something like that) and something must be done to replenish it.

My question is: What do I need to do to 'replenish' it? Just remove it and shake out the water? Or do I actually need to replace it with a new one?

BTW: We need an article on water hammer arrestors

ike9898 (talk) 22:13, 24 February 2009 (UTC)

Drain out the water. An arrester works by creating an air-filled gap in the water line. Since air is compressible while water isn't, it absorbs the shock rather than transmitting it. --Carnildo (talk) 23:00, 24 February 2009 (UTC)

We've got this article Hydropneumatic device. DuncanHill (talk) 23:01, 24 February 2009 (UTC)

"Drain out the water" is the correct answer. However, it doesn't explain how to do that. What I did was turn off the water at the main line - so no water would flow into the house. Then, I opened all the taps. This pretty much drained all the water out of the lines. Then, I closed all the taps, turned the water back on, and the arrestor started working again. Obviously, this is limited to an arrestor that is higher than the lowest tap - since you can't drain anything below the lowest tap. -- kainaw™ 05:04, 25 February 2009 (UTC)

I have linked the Hydropneumatic device from water hammer arrestor. Graeme Bartlett (talk) 05:18, 25 February 2009 (UTC)