Wikipedia:Reference desk/Archives/Science/2008 March 2

Science desk
< March 1	<< Feb | March | Apr >>	March 3 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

March 2

Stoichiometric flame

I am burning Isopropyl alcohol as a fuel. Isopropyl alcohol has the chemical formula C₃H₈O. I'm pretty sure I have the equation right but wanted to double check. I get C₃H₈O + 5-O₂ > 3-CO₂ + 4-H₂O + O. The free atom of oxygen seems to confirm my observation of complete combustion occurring under laminar (non-turbulent) flow using uncontaminated fuel, resulting in a flame that is perfectly stoichiometric. —Preceding unsigned comment added by 71.100.9.109 (talk) 04:05, 2 March 2008 (UTC)

Wait, why would you get an atom of free oxygen? The combustion equation for isopropanol is 2 C₃H₈O + 9 O₂ -> 6 CO₂ + 8 H₂O .Someguy1221 (talk) 04:18, 2 March 2008 (UTC)

...okay, my chemistry is a little rusty. Instead of an equation resulting in a free atom of oxygen I need to increase the number of molecules of Isopropyl until the equation is perfectly balanced. The flame would still be stoichiometric although very sensitive to non-laminar flow and/or fuel/air contaminants. —Preceding unsigned comment added by 71.100.9.109 (talk) 04:25, 2 March 2008 (UTC)

Analog Electric Gaussian Filter

Is there a device that reasonably approximates a Gaussian filter? There are digital Gaussian filters, of course, which make calculations to convolve a signal with a Gaussian function to blur images (for instance). But is there any physical device that gives a similar effect without digital computation? It needs to have an approximately Gaussian impulse response. Any dimension would be interesting. 75.168.199.1 (talk) 05:00, 2 March 2008 (UTC) Craig

Are you thinking of building something yourself, or did you just want to buy it off the shelf? If the latter, you are probably out of luck. It must be possible to calculate the filter elements for this as a Cauer or Sallen Key topology implementation but I have no references. This paper [1]expresses an approximation of the Gaussian filter as a number of cascade stages of $H(\omega )=Sinc(k_{n}\omega )$. This *looks* like it ought to transform into a circuit implementation but my maths is too crap to do it. If I had been asked to do this while I was still a design engineer, my approach, if I could not find a tame mathematician, would be to feed a vague approximation (Butterworth filter for example) into a network analysis program and then to hand adjust the component values with successive approximations until I got near enough to the desired result. Complete bodge, I know, but it should work. SpinningSpark 16:51, 2 March 2008 (UTC)

I'm going to be bold and say No. Here's my reasoning:

• True Gaussian filters have infinite duration in time, (which can be worked around with feedback), but furthermore they are not causal (since half of them occurs in future-time!)
• Digital filters work around this by windowing, truncating and introducing a constant time-delay.
• Analog delay lines are not easy to build and are rarely linear with frequency.
• If it could be built, surely a commercial part would exist, and I've not found any.

The question specifically asked for a "reasonable approximation" to a Gaussian filter, at which point I would demand a definition of "reasonable approximation," then suggest a Butterworth or Sallen-Key filter. Nimur (talk) 17:28, 2 March 2008 (UTC)

My reading of the OPs request was that he needs the output to be Gaussian in time domain to an input of a dirac pulse. In the same way that an ideal low pass filter will output a Sinc pulse in response to a dirac pulse, but with only the 0 to ∞ half and missing the -∞ to 0 half, I was assuming that the OP required the 0 to ∞ portion of the Gaussian pulse only. If that is right, my suggestion should work. If he needs the full pulse, you are right, he cannot do it precisely and will need a delay line going back to whatever point is his minimum required accuracy. I might mention at this point that I found this[2] patent claiming to make a quasi-gaussian filter out of directional couplers (microwave band) but did not include it in my previous post because, quite frankly, I cannot understand what it is claiming to be doing.

Accurate analogue delay lines are not easy to build. Accurate analogue anything are not easy to build, which is why analogue filters, especially ones using wound components, are badly out of fashion now (wish I'd known that at Uni - a lot of classes I could have skipped). My opinion is that this is the reason there is no component on the market and hence my original comment that the OP would be out of luck if he wants it OTS. One solution I have used in the past to meet the requirement for a delay line when working in the audio band is to use an acoustic echo chamber. These are large (eg bed sized) and expensive but the OP did say "any dimension". Perhaps the OP could let us know what band he is working in which would narrow down the possible solutions.

And why does it have to be analog? SpinningSpark 20:28, 2 March 2008 (UTC)

I'm only interested theoretically whether such a circuit can exist, I'm not interested in building one for a home project. There's a new mathematical approximation scheme that takes advantage of sums of Gaussians with a single variance, and I'm wondering if a Gaussian filter (because of its linearity) has any possible practical application in signal generation.

Yes. I would judge the circuit to be a reasonable approximation to a Gaussian filter based almost entirely on how close its impulse response is to a Gaussian function; i.e., its output needs to be Gaussian in time domain to an input of a dirac pulse, as SpinningSpark said. Any mean or variance is acceptable, but I do need it for all time and not just 0 to ∞. I'm assuming since the Gaussian drops off so quickly away from its mean, it is for all practical purposes 0 there. The delay criticism sounds valid, though. Reverb would mean the death of this approach.

"If it could be built, surely a commercial part would exist" is honestly the most helpful possible answer I imagined when I wrote the question. I have no practical experience with electronics, so I was hoping for this sort of expertise. Pressing on, though, I found the Bessel filter seems to have an approximately Gaussian impulse response, which I say based (entirely) on looking at the graph on p. 11 of [3]. How close does that mean it is to a theoretical Gaussian filter? (The so-called "Gaussian to 12db" filter on p. 14 has an impulse response that is a bad approximation to a Gaussian.) Is there any other circuit design that has a more accurate Gaussian impulse response? My ignorance and inexperience in this area is regrettably profound, but this limited intuition leads me to think that a Gaussian response should not be impossible (or even impractical) to generate.75.168.188.2 (talk) 21:05, 2 March 2008 (UTC) Craig

It must be analog for this imagined implementation, because I assume there would be a prohibitive time lag in processing the digital Gaussian filter of streams of real-time data. I may be wrong about that, though.75.168.188.2 (talk) 21:22, 2 March 2008 (UTC) Craig

WP has ref Wikipedia_talk:WikiProject_Electronics/Archive_1 —Preceding unsigned comment added by 79.76.194.191 (talk) 01:20, 3 March 2008 (UTC)

Blue flower identification

Unidentified blue flowers

I took this photo at the Honolulu Zoo, and was wondering what type of flower it was. A quick search and I came up with Blue Petunias, but I wanted a second opinion. I know, like birds, flowers can look very similar and it can take a trained eye to identify them. So.... if anybody knows, please let me know! --ErgoSum88 (talk) 08:43, 2 March 2008 (UTC)

Plumbago or Plumbaginaceae should fill you in. Julia Rossi (talk) 09:44, 2 March 2008 (UTC)

Wow, that was fast. Thank you! --ErgoSum88 (talk) 10:35, 2 March 2008 (UTC)

Definitely Plumbago auriculata. Although native to South Africa, it is commonly planted as an ornamental shrub throughout the milder parts of the United States, including Hawaii.--Eriastrum (talk) 16:52, 2 March 2008 (UTC)

Taq polymerase storage

If Taq polymerase is good to go at 95 C, why does it need to be stored at -20? How quickly will it break down at room temperature? --Seans Potato Business 08:49, 2 March 2008 (UTC)

I usually see a labeled shelf life of a year-ish at -20, so I'd bet it's not so great at room temperature...and at 95 it only has to last for a few hours, usually. Someguy1221 (talk) 14:51, 2 March 2008 (UTC)

All enzymes for molecular biology, whether they be ligases, endonucleases, or polymerases should be stored in glycerol at -20C unfrozen. As someguy pointed out, it has a tremendously long shelf life. Taq poly is thermostable, which means it can operate at 95 degrees, but that's not the way to preserve it. At room temperature, the enzyme would still be functional, but it would be unsuitable for use in PCR after a few weeks. It's just terrible lab practice. Wisdom89 _{(T / ^C)} 16:05, 2 March 2008 (UTC)

At the lab where I'm doing my internship, I've been told to do PCR reactions by making the PCR "master mix" with everything in it except Taq (which is kept on ice). Then I add template to the reaction tubes and then I add Taq to the master mix and distribute it among the reaction tubes. I think this is going unnecessarily far to protect the Taq. I think that it would be easier in some cases to add the Taq to the master mix, distribute it among the reaction tubes and THEN add the template (and take it to the PCR machine). I think the Taq would be fine.

Also, a couple of days ago, someone left an expensive Taq on ice overnight, so it was discovered floating about the next day. Despite my (admittedly weak) protest, it was thrown away (I suggested they could at least test it before throwing away the whole vial). Was this a waste? I'm not sure what kind of Taq it was, except that it wasn't one with red dye in it. ----Seans Potato Business 16:31, 2 March 2008 (UTC)

Whenever I do PCR, I create a master mix with all the reagents (excluding the template of course) including the polymerase. It works just fine. However, bear in mind that usually you make a little more of the MM before distributing, and thus you actually use less enzyme than you add, and it's expensive - but the cost might be negligible. Also, I agree, throwing away the entire tube of enzyme like that was really wasteful. It was probably fine. Wisdom89 _{(T / ^C)} 19:15, 2 March 2008 (UTC)

Burning CuSO4-solution on paper

Hi Science, I need some help with a science project on the side of school.

I have made a paper structure stiffened by chickenwire, covered by cut paper, glued together (quite a bit of glue, around a pound's worth or more). Now, what I seek is to make a solution of water and CuSO4 (readily available), which when lit on fire, will burn green. All is good so far, but upon burning, I fear this will result in unhealthy amounts of SO3 (which follows from balancing the combustion equation). I am attempting to make perhaps around an entire litre of CuSO4, and the paper structure has an area of approximately 2 square meters.

The lighting on fire will take place outdoors, and I will have to be situated upwind (and nobody downwind). Is there no way I can add something to the solution, or apply after the coat, that will bind the SO3 at the stage of combustion, so that the health hazard is reduced? Don't be afraid of answering or guessing, since my professor has a degree in nonorganic chemistry, and whatever I do it will be carefully monitored if at all allowed. Thoughts related to other sides of the matter are also welcomed. Thank you!81.93.102.185 (talk) 11:02, 2 March 2008 (UTC)

A solution of CuSO4 and water will not burn! Did you mean you were going to soak the paper in the solution of CuSO4? If so, you won't see a lot of green because there won't be enough Cu to form a color (there will be the occasional green flash). I've tried this and speak from experience. No need to worry about SO3 production: it takes a lot of energy to dehydrate a sulfate. Delmlsfan (talk) 17:08, 2 March 2008 (UTC)

Or, you can put the CuSO4 in pure ethanol, which will burn. We used to put a lot of various salts in ethanol to make rainbow flames. I can not specifically remember if we used CuSO4 for our green flames (some salts dissolve very well in ethanol, and others do not). Also, I don't recall if there was any chemical reaction at all regarding the CuSO4 salt; it may have just been heated and providing color to the ethanol flame via atomic emission. In that case, there will be no harmful sulfur-containing gas. Nimur (talk) 17:30, 2 March 2008 (UTC)

@Delmlsfan: I believe it's obvious from what I wrote, that the solution will be used to coat the paper structure, and this is then lit on fire. Pardon my inaccuracies. I have also attempted to light this on fire, producing a green hint in the otherwise yellow and orange flame. I thought the matter was simply to increase the copper sulfate in the solution.

Now, if the flashpoint of the paper (newspaper type) is around 400ish, shouldn't it be fairly easy to light in fact ONLY the coat on fire, even if it has soaked the paper? To have a trail of the coat extend from the paper structure over to a metal plate, and light the coat on fire where it is on the plate, should the fire not then spread at an even 100 C over to the paper, and there avoid lighting it on fire? 81.93.102.185 (talk) 18:40, 2 March 2008 (UTC)

Don't think the amount of SO3 will be dangerous (as another states) - as an alternative convert the copper sulphate to copper hydroxide or copper oxide by adding base. Then use the oxide/hydroxide in your paint (note you could mix it with wallpaper paste)

Also note boric acid/borax also produce green flames - not health hazards here I can think of.87.102.93.158 (talk) 11:16, 3 March 2008 (UTC)

Women discharging too much of seminal fluid during intercourse affects their health

Hai, i have heard that women who discharge too much of seminal fluid during intercourse have their health affected and feel week , is it true? —Preceding unsigned comment added by 122.164.123.155 (talk) 14:45, 2 March 2008 (UTC)

If women are discharging seminal fluid, they're probably not a woman... -- MacAddct  1984 ^{(talk • contribs)} 16:28, 2 March 2008 (UTC)

The reference desk cannot and will not answer medical questions. Nimur (talk) 17:32, 2 March 2008 (UTC)

It only happens during "Feel Week", which starts on 29 February (and only occurs in leap years). (This is so named because many women don't actually want to propose to anyone - maybe they're already happily married, maybe they prefer to remain single, whatever - but most women like to cop a nice feel of another person's butt, crotch or chest, and they're allowed a whole week once every 4 years when they can do this to unsuspecting passers-by without fear of being charged with sexual harrassment.) For the remaining 207.6 weeks of the olympiad, nothing remotely like this is known to science.  :) -- JackofOz (talk) 00:51, 3 March 2008 (UTC)

If you mean they feel weak if they don't retain seminal fluid discharged into them, then the long-standing safe use of condoms would suggest that what you heard is wrong. AlmostReadytoFly (talk) 09:20, 3 March 2008 (UTC)

Perhaps the OP is really asking about Skene's gland (warning contains gynecological imagery). Vranak (talk) 21:31, 3 March 2008 (UTC)

Fat Content In Soap?

If you gently place a bar of soap in water, it will float. Then how come me, covered in soap, wont float? Sounds pretty stupid I know, but think about it; Soap is supposed to displace water.--Sam Science (talk) 15:21, 2 March 2008 (UTC)

I just tried three different brands - they all sank. Regarding displacement, I think you are confused between Archimedes principle and the surfactant properties of soap. Soap is not fat, it is a salt of a fatty acid. Click on the blue words to see those articles. SpinningSpark 15:43, 2 March 2008 (UTC)

Most people do float in water, whether covered in soap or not, otherwise it would be very difficult for you to swim. Divers need weights to keeep themselves underwater. Soap will not normally float, unless you shape it like a boat.--Shantavira|^{feed me} 16:38, 2 March 2008 (UTC)

Ivory soap floats.--Eriastrum (talk) 16:48, 2 March 2008 (UTC)

What's specifically important there is that Ivory (and other floating soaps) are specifically aerated to allow them to float; "pure" soaps generally do not. This is analogous to pumice. — Lomn 17:01, 2 March 2008 (UTC)

Even if the soap material itself does float (i.e., not just because it's aerated, is carved out like a canoe, or has other physical attributes), covering yourself with it just adds a relatively small amount of bouyancy to your otherwise-apparently-sinky body. If you're 5 pounds heavier than the water you displace, then adding to that something that is less than 5 pounds lighter than the water it displaces will still make a net effect of "heavier than the water being displaced". DMacks (talk) 20:27, 2 March 2008 (UTC)

What is "first-strand DNA"?

What is "first-strand DNA"? ----Seans Potato Business 15:28, 2 March 2008 (UTC)

I think it just refers to the "first strand" of DNA extracted or synthesized (if the synthesis was from RNA). The only literal definition I could find was "For purposes of the present invention, first strand DNA is defined as initial DNA transcript produced from isolated viral DNA," from this patent. I've seen the term used in plenty of papers that weren't discussing viruses, but my first sentence here seems to fit all those uses I have seen of it. Someguy1221 (talk) 15:54, 2 March 2008 (UTC)

When performing RT-PCR, the first-strand DNA is the single strand of DNA synthesized by Reverse transcriptase from an RNA template. This first strand is then used to make a complementary DNA strand, and thus double-stranded DNA. -- Flyguy649 ^talk 05:51, 3 March 2008 (UTC)

Removal of sand from Sand Hills of Nebraska

Why couldn't sand from the Sand Hills of ND be relocated to beach areas suffering from chronic erosion? —Preceding unsigned comment added by Fredcowie (talk • contribs) 15:33, 2 March 2008 (UTC)

Apart from the expense, beaches suffering chronic erosion will continue to erode. So it would be a perpetual thing. Cheers Geologyguy (talk) 15:41, 2 March 2008 (UTC)

Sand will easily wash away. Large chunks of concrete last much longer, if the goal is to protect homes on the beach. Of course, large chunks of concrete make for a lousy beach for swimmers and sunbathers, so another approach is to construct a breakwater (structure) to protect the beach from wave erosion, then add more sand. It's normally cheapest to dredge the sand up from the bottom of a nearby lake, river, or other body of water, especially where a deeper channel is desired for ships. StuRat (talk) 19:43, 3 March 2008 (UTC)

chemistry

how to produce hydrogen at home —Preceding unsigned comment added by 117.193.96.108 (talk) 15:49, 2 March 2008 (UTC)

Simple Electrolysis. Wisdom89 _{(T / ^C)} 16:06, 2 March 2008 (UTC)

(after edit conflict) By electrolysis of a solution where water is the solvent. See [4] for an efficient way to produce large quantities of hydrogen. Using this method, with a few modifications, I was able to make about ten bottles. --Bowlhover (talk) 16:11, 2 March 2008 (UTC)

Be aware, of course, that if hydrogen mixes with oxygen, it is highly reactive (explosive). --98.217.18.109 (talk) 16:48, 2 March 2008 (UTC)

Did you read the reference Bowlhover cited? It covers the safety aspects quite well. —Steve Summit (talk) 16:54, 2 March 2008 (UTC)

I did. I just wanted to re-emphasize it, like I would with anyone contemplating to do something that could be hazardous! --98.217.18.109 (talk) 20:21, 2 March 2008 (UTC)

Steel hand soap?

Hi. I have a bar of soap, triangular and made by company Michaelangelo in Germany, that is completely made from stainless steel. It removes odours, and does not lather. How does it work, and does it combine steel with water causing a molecular chemical reaction that peels away odours, and an unrelated question: can banana oil remove tough stains the way Stainz-R-Out does? Thanks. ~AH1^(TCU) 16:39, 2 March 2008 (UTC)

Completely made from stainless steel? Maybe you mean they use microparticles as an abrasive. It seems very unlikely that pure steel can form anything remotely soap-like.

• Stainless steel soap - solid evidence that Wikipedia organizes all of the world's information. Nimur (talk) 17:34, 2 March 2008 (UTC)

Wow! I've said it before -- WHAAOE! —Steve Summit (talk) 18:12, 2 March 2008 (UTC)

It seems likely that the odour molecules will bind preferentially to the metal (and not your hand), some people suggest that once on the metal, they odour molecules will be de-odorised - with the metal surface having a catalytic effect (probably oxidation)

Banana Oil - it might work on some stains - ... I can't say much more - might be good at grease spots - Sounds a bit unusual to try to use it..87.102.93.158 (talk) 11:12, 3 March 2008 (UTC)

Remember, the metal ONLY removes odors. Don't expect to be able to remove residues or bacteria. -- User:Mac_Davis 00:09, 4 March 2008 (UTC) —Preceding unsigned comment added by 216.120.217.92 (talk)

Firefox

Moved question to the Computing Reference Desk

Non-exorcise calories

Does the body use a lot of energy for functions outside of exercise and movement? Like brain activity, hair growth, blood cell production, etc, or is it a minuscule amount compared to exercise? 69.77.237.158 (talk) 22:25, 2 March 2008 (UTC)

Certainly! For example, in the USA, many people eat around 2,000 calories per day, do not exercise at all, and do not gain (much) weight. Most of your energy goes to keeping warm and keeping your systems in operation. Anyway, an exorcism would only take off 21 grams. :) -- Sean —Preceding unsigned comment added by 69.134.115.242 (talk) 22:42, 2 March 2008 (UTC)

But don't forget the weight of all the pea soup (and pee) that is expelled during the process. :-) StuRat (talk) 19:28, 3 March 2008 (UTC)

The base energy need of the body, without exercise, is called the basal metabolic rate. StuRat (talk) 19:28, 3 March 2008 (UTC)

Luminescent dry-erase boards

At my local pizza parlor, they have a dry-erase board that glows wherever the marker has marked. How does that work? Thanks. —Preceding unsigned comment added by 69.134.115.242 (talk) 22:44, 2 March 2008 (UTC)

It most likely has a black light on it. -- kainaw™ 01:24, 3 March 2008 (UTC)

The ones I've seen are lit from inside, by what may indeed by a black light. There's a transparent sheet over a black background, and light shines through the upper edge of the glass, being mostly invisible except where it hits the neon marker and glows. I can't seem to find anything more technical than that, but that's how it looks to me. jeffjon (talk) 17:54, 3 March 2008 (UTC)

relativity

does the relationship $ke={\frac {1}{2}}\gamma m_{0}v^{2}$ hold up accurately for relativistic speeds, or is it just an approximation? —Preceding unsigned comment added by 172.142.196.236 (talk) 22:50, 2 March 2008 (UTC)

Well, the energy of a particle of mass m₀ and Lorentz factor γ is γm₀c². Subtracting the rest energy, we have a KE of (γ-1)m₀c², which, if my calculations are correct, is ${\frac {\gamma ^{2}}{\gamma +1}}m_{0}v^{2}$. Thus what you have is just an approximation, and an odd one at that. The leading order (in (γ-1)) approximation is just 1/2m₀v², and the next approximation is (I think) ((3γ-1)/4)m₀v². Algebraist 02:23, 3 March 2008 (UTC)

Speaking of relativity-

Sorry to be a pest fellas, but I got another question. The first one was kinda lame, this one is more interesting.

About time dilation. When Einstein said gravity slows time, is time thought of as atom movement? And is this why time is considered a "physical" property? Like if everything around you is moving at the same speed along with your atoms moving at the same rate (20x faster, 100x faster, etc.) you'd percieve time as the rate you're used to, even though you and everything around you is really moving "faster"? Also, its been said that if you fall into a black hole and reach singularity, all of time will have passed by, and you'd know it. How, if you need time itself to think?

We're probably not meant to understand the universe.Sam Science (talk) 23:25, 2 March 2008 (UTC)

Re: "We're probably not meant to understand the universe" well then, speak for yourself Sam. ;-) --hydnjo talk 01:09, 3 March 2008 (UTC)

You're quite right that you could never measure the rate of passage of your own time — what would you use, a clock? — but that's why it's called relativ[e]ity. The presence of a gravitational field within (or of acceleration of) an object causes other observers to see everything in that object happen at a reduced rate.

Similarly, but in reverse, when you fall into a black hole (assuming that you aren't killed first), the intense gravity causes most of the rest of the universe to appear (to you) to be running at ludicrous speed. In fact, as you cross the event horizon, the entire future history of the universe plays out for you, although so radically blue shifted that it's hard to understand (or to survive) the show.

Note that in special relativity, the slowing of clocks (and they only ever slow down, not speed up) is symmetric: A says B is slow precisely to the extent that B says A is slow. (This sounds paradoxical: see relativity of simultaneity.) In general relativity, which encompasses gravity, the slowdown is more "real" in that A says B is slow and B says A is fast. --Tardis (talk) 02:48, 3 March 2008 (UTC)

Small correction - the extreme blue shift phenomena only happens to an observer who attempts to hover just above the event horizon. A free-falling observer experiences much less blue shift. If the black hole is large enough to make tidal forces small then the free-falling observer can cross the event horizon with no adverse effects - although a second distant observer will never see this event. Gandalf61 (talk) 08:50, 3 March 2008 (UTC)

One of Einstein's key axioms is that time is what you measure it to be. It's not something external, some sort of magical fluid we are moving through. That's why he looks at a light clock and says that its behavior in various frames of reference tells us something about time itself. Re-thinking the nature of time and space is pretty much what (special) relativity is all about.

Time is change. Which makes sense if you think about it—every clock is just a little thing which measures regular amounts of change (tick, tock). The difference between something "frozen in time" and something not is change. We can tell when things are "sped up" or "slowed down" because change happens at a different rate. --98.217.18.109 (talk) 03:58, 3 March 2008 (UTC)