Wikipedia:Reference desk/Archives/Science/2009 August 16

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August 16

orbital

in niobium, what can be the possible orbital arrangement? i think it should be - 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d3

but in my book the last two are - 5s1 4d4

which one is correct and why (the half-filled orbital concept can't come here as d3 isn't half-filled)? —Preceding unsigned comment added by 122.50.129.193 (talk) 02:59, 16 August 2009 (UTC)

The huristic you have learned to fill electron orbitals in order is only an approximation, the actual filled orbitals will differ slightly. The "half filled" rule which applies to Chromium and Copper are an attempt to "justify" variations from the strict rules. Remember that the electron filling rules are a human invention, and that the elements themselves were not necessarily informed of the rules; even if they were they are not bound to follow them. If you are trying to get a homework problem right, you should probably just follow the rules and use the expected 5s2 4d3 configuration. The actual configuration has been experimentally confirmed to be 5s1 4d4 since it better explains niobium's +4 oxidation state (see Niobium); a state that would be unlikely to exist if the configuration were 5s2 4d3 (where you would ONLY expect the +3 and +5 states). Just remember that real, physical data will sometimes contradict the little games we invent to explain electron configuration. The standard orbital filling model works MOST of the time, with a few notable exceptions. The "half-filled" rule your teacher taught you is a kludge designed to explain away elements like chromium and copper; niobium cannot be explained away by anything except "the model does not work for that one". --Jayron32 03:51, 16 August 2009 (UTC)

The rules are a simple generalisation of the Schrodinger equation so you don't have to perform Hartree-Fock equations every time you want to estimate how orbitals are filled. John Riemann Soong (talk) 21:03, 16 August 2009 (UTC)

Chirping transformer

Why is the power adapter of my computer chirping like a bird, at a rate of roughly 1 chirp per second? Yes, I know it's malfunctioning; I just want to know how the malfunction is causing it to chirp. --99.237.234.104 (talk) 03:11, 16 August 2009 (UTC)

Does it have a built-in fan? (Most desktop power supplies do.) Probably the fan is wobbling slightly. That can produce very regular "chirping" noises. APL (talk) 05:33, 16 August 2009 (UTC)

No, this is a laptop adapter. I'm sure the sound is coming from the power adapter, not the laptop itself. --99.237.234.104 (talk) 06:09, 16 August 2009 (UTC)

Switched mode power supplies can make a noise ,probably due to varying forces on components (capacitors etc) as an input voltage is chopped to maintain output voltage.

Is it very loud?83.100.250.79 (talk) 12:16, 16 August 2009 (UTC)

I would suspect a capacitor is about to fail, or a capacitor has already failed, and there is a new resonant frequency in the supply. Not much should be happening at 1 Hz in an AC-DC power supply - low frequencies typically involve the large, front-end holding capacitors, but those usually are calibrated for kilohertz-ish time constants. Unfortunately it's very hard to diagnose; capacitor failure doesn't always leave any visible signs. Another possibility is that there is a short circuit somewhere in your load (on the computer motherboard) and the failsafe shutdown (if your PSU has one) is triggering at 1Hz and immediately restarting. Nimur (talk) 18:40, 16 August 2009 (UTC)

Capacitance and materials

I'm currently learning about capacitors, and trying to understand the concept of capacitance. Is it dependent upon the material which the capacitor's plates are made out of? Mo-Al (talk) 08:02, 16 August 2009 (UTC)

No but it depends hugely on the material between and around the plates and the area of the surface. --BozMo talk 08:06, 16 August 2009 (UTC)

Also the geometry(shape and size) of the capacitor.[[1]]--Leon (talk) 14:34, 16 August 2009 (UTC)

Capacitance. Cuddlyable3 (talk) 16:08, 16 August 2009 (UTC)

Well, of course the plates have to be made of something pretty highly conductive, e.g., a metal. And the number of free electrons has to be sufficient. But those are very minimal requirements. Looie496 (talk) 17:53, 16 August 2009 (UTC)

So does this mean that two capacitors that are of the same shape, and have the same dilectric, but whose plates are made of different (conductive) materials will have the same capacitance? Mo-Al (talk) 19:04, 16 August 2009 (UTC)

Sure, to within a reasonable accuracy. But when you try it in the lab in my experience if the dilectric is ionic it is difficult to eliminate battery effects as well and they are obviously dependent on the metal. So don't try and prove it as a school physics project unless you are incredibly careful--BozMo talk 19:41, 16 August 2009 (UTC)

A spelling error shall be stamped out with extreme prejudice before the infection spreads further. The word is DIELECTRIC. Cuddlyable3 (talk) 22:09, 16 August 2009 (UTC)

Cast iron stove paint

I am really after someone who know about paints. Sorry that the story is a bit long. I live in a cool climate (UK) with an (old) outdoor swimming pool. Since I have effectively unlimited free wood (I burn about 6 tonnes a year heating the house) I built a bonfire boiler out of scrap lying in the garden to heat the swimming pool. It cost around 50 USD to do and works pretty well (200 degree litres a minute) and over a few days makes an impact on the pool so I am keen to prolong its life. The top part of the boiler (hood and chimneys basically) is made from an old broken Victorian cast iron "Loughborough" boiler and weighs about 150kg. This cast iron has been outside in all weathers for at least a century (it was left under a tree in our garden along with a Victorian bathing hut and all sorts of nonsense) and is still mainly sound. This top piece sits above a steel pipe circulating heating fluid and is double skinned. Nonetheless to get good heat transfer I routed the fire vents through the skins on the way to the chimney and the outside surface of it gets pretty hot. Once I started using this boiler I noticed the rate of rusting of the cast iron had accelerated considerably presumably because the heat was stripping off protective layers. I tried cleaning it and putting two brands of "stove paint" on it but each only lasted one cycle of burn-rain-burn. So I tried "Hammerite" which weathers incredibly well on other iron/steel but had already discolored and I guess is degrading. Questions (1) is there some kind of enamel paint which would do better in rust-heat-rain (2) is it worth trying to cover the Hammerite with stove paint on the basis the degrading requires contact with air and the stove paint might well have failed because of a rusting process under the paint (3) do any primers survive this kind of heat? Hammerite and stove paint both say don't prime (4) Any other ideas? I could I guess cover the whole surface with fire cement but that would be a bit ugly and it is not clear to me if that would survive either. --BozMo talk 08:05, 16 August 2009 (UTC)

Please give the price in pounds. You are British, live in Britain, and many readers here are British. 78.147.255.120 (talk) 10:45, 16 August 2009 (UTC)

How is that of any relevance to the question? --antilived^{T | C | G} 10:48, 16 August 2009 (UTC)

It is relevant to the question because the OP is British, lives in Britain, and many readers here are British, yet strangely has not given the amount in British currency. 78.147.255.120 (talk) 13:05, 16 August 2009 (UTC)

More British people understand foreign currencies than the other way round. Say 30 guineas anyway. --BozMo talk 14:39, 16 August 2009 (UTC)

He can quote the cost in dollars as well as pounds to be polite to both our British and our American chums. I'm sure he did not pay the costs in dollars. 78.144.207.41 (talk) 17:00, 16 August 2009 (UTC)

He may quote prices in any currency he likes. Local or foreign, common or obscure. We do not need self-appointed culture police running around telling people to be true to their home currency. APL (talk) 18:32, 16 August 2009 (UTC)

1)Perhaps you can put a roof over the entire contraption to keep it dry? 2)You can also try to add a zinc sacrificial anode. 3)I have no idea if you could galvanize the thing. -Arch dude (talk) 11:15, 16 August 2009 (UTC)

(after research) take a look at Electroplating#Brush electroplating. -Arch dude (talk) 11:33, 16 August 2009 (UTC)

The problem with galvanizing I think it the heating. When I have had galvanized garden incinerators in the past the galvanization tends to strip as soon as they are in use. And in case our friend above protests about a Brit using US spelling unusually "z" in these words is correct usage in British English as always practiced by the Cambridge University Press (even though some Brits use s also). --BozMo talk 14:39, 16 August 2009 (UTC)

The OPs problem is similar to that of painting a car exhaust system. Look at [2]. Cuddlyable3 (talk) 16:03, 16 August 2009 (UTC)

You could try going to a car parts store and buying the stuff you use to paint car engine parts with. It's generally resistant to pretty high temperatures - check what it says on the can. SteveBaker (talk) 23:18, 16 August 2009 (UTC)

Another suggestion from the field: You need to get every last speck of rust off the original piece, and whatever you put on as the first coat over it has to "bond" to the bare iron. Inquire of a really old-time "plumbing and heating" contractor -- you're looking for guys who work on steam heating systems rather than "heating and air conditioning" guys, who are just sheet metal benders -- and ask who they subcontract (or hire out?) radiator refinishing to.

That said, however, it is possible that the temperatures at which your're working are just too high for any kind of paint. The same guys could probably advise you on that!

For the record, it doesn't matter at all whether the price is quoted in pounds or dollars or won :-)

--DaHorsesMouth (talk) 02:25, 17 August 2009 (UTC)

What is the conversion between pounds, bob, and guineas? U.S. hardware stores (iron mongers to Brits) sell high temp paints which seem to last better than what you report. They are intended for barbecues. I believe Rustoleum sells "Barbecue Black." Also look into paints used on steam locomotives. Edison (talk) 03:49, 17 August 2009 (UTC)

1 guinea = 1 pound + 1 bob

1 pound = 20 bob

1 bob = 1 shilling

--TammyMoet (talk) 13:35, 17 August 2009 (UTC)

Does exercise make people less drunk?

I alcohol can be used as a source of energy by humans. Does that mean you can " burn it away " by doing exercise? In other words: if I'm drunk will I be sober faster if I jog a few kilometers? (providing of course that I am still able to walk properly)PvT (talk) 11:01, 16 August 2009 (UTC)

Not really ... alcohol isn't like blood sugar, and it isn't a "preferred carbohydrate". See Ethanol metabolism#Thermodynamic_Considerations. Where the metabolism of sugars and the metabolism of alcohol merges is when they are converted into an acetyl group and bound as a thioester with coenzyme A to form acetyl-CoA. The first step of ethanol metabolism involves its conversion into acetaldehyde, and this *costs* energy (it's endergonic). Arguably, this is the "slow step" of the reaction, and why it takes so long to clear ethanol from the body. Unlike glycolysis, this first step doesn't give you any payoff, so less incentive for the body to use it. There's some minor payoff when acetaldehyde gets converted into acetic acid, but this is quite small compared to say, the decarboxylation step of pyruvic acid metabolism, in the oxidative metabolism of sugars (where a whole molecule of carbon dioxide is released).

The really big payoff of ethanol metabolism is when acetic acid is converted to acetyl-CoA and then the oxidised into water and carbon dioxide. But the sheer majority of ethanol never gets converted into an acetyl group on acetyl-CoA ... it gets converted to acetic acid which is then filtered out by your kidneys. Alcohol is treated as a toxin in your body. Unlike say, glucose, which enter the cell via special glucose channels, there are no special "alcohol channels" to allow ethanol molecules to pass through cell membranes ... say muscle cells. So what happens to alcohol in the bloodstream? It must be processed by liver cells who allow toxins to pass through them so enzymes can process them. (Liver cells get regularly killed by all this toxic waste handling of course, which is why your liver is one of those special organs that can grow back.) What will liver cells do with acetic acid? Probably nothing -- they aren't the ones doing the muscle work. They die, get recycled, the acetic acid ends up in your kidneys and it's passed out as urine (after you drink lots of water to allow renal excretion).

Note you really can't do anything to increase the rate of BAC removal ... you can do symptomatic things that make you feel somewhat better, but the only way to increase the rate of BAC removal is to increase the efficacy of your liver cells. (gene enhancement ... better enzymes ... more liver cells... etc.) And of course if you regularly poison your liver cells, your liver will slow down as well. Furthermore, alcohol is such a minor carbohydrate that even if muscle cells did metabolise alcohol, when you exercise you'd be mainly using sugar, and once in a while, every 100 ATP cycles or so, alcohol would be picked to be metabolised (if muscle cells would use alcohol at all). Alcohol metabolism evolved as a means of dealing with the alcohol toxins of bacteria, not for energy processing. It's probably very good that your muscles don't try to metabolise alcohol -- muscle cells don't grow back as easily as liver cells, you see. John Riemann Soong (talk) 13:46, 16 August 2009 (UTC)

See also Ethanol metabolism#Common_Misconceptions. "There is a common misconception that drinking alcohol leads to weight gain. This has never been proven in the literature and is the subject of ongoing debate among experts..." John Riemann Soong (talk) 13:47, 16 August 2009 (UTC)

On an episode of MythBusters, they concluded that is was plausible that exercise could help lessen the effects of alcohol: MythBusters_(2008_season)#Stone_Cold_Sober —Preceding unsigned comment added by 173.62.219.247 (talk) 13:53, 16 August 2009 (UTC)

I think the effect is purely symptomatic. Receiving vigourous nervous system input of course, would be a stimulatory effect that could potentially alleviate the neurodepressive effects of alcohol if the right stimulation is applied. Besides, breathalyser tests aren't really that reliable as blood tests. (The first can only be used as a reasonable warrant for an arrest. You need a blood test to secure a conviction.) I have no idea why getting slapped in the face will lower your BAC. John Riemann Soong (talk) 13:58, 16 August 2009 (UTC)

A simplistic guess would be: slap in face → anger / increased sympathetic activity → increased blood flow to liver → increased ethanol metabolism.

Did they definitely say that BAC lowered after being slapped in the face though? and was it statistically significant? --Mark PEA (talk) 15:46, 16 August 2009 (UTC)

It's a bit more complicated than that. Alcohol, along with benzodiazepine and barbiturate tranquilizers, has effects on the brain that are strongly arousal-dependent. The underlying causes are not fully understood, but the effect is so strong that a dose can be fatal if the subject falls asleep but survivable if the subject is kept awake by slapping, cold-showers, etc. The concentration of the drug in the blood doesn't change much, but the way the brain responds to it does. Looie496 (talk) 17:50, 16 August 2009 (UTC)

What I have taken away from this thread is that if I am ever stopped for suspected driving while intoxicated, after consuming a few beers, and told that after some period I will be tested for blood alcohol, my best strategy is to continuously slap myself in the face, while avoiding other forms of exercise. Has anyone tried this? Edison (talk) 03:44, 17 August 2009 (UTC)

Actually, you should do nothing at all, allow yourself to test positive, be convicted, and lose your licence. This is the smartest thing to suggest to anyone stupid enough to drive while intoxicated. On the other hand, when you show up black and blue from having slapped yourself repeatedly, you could create a diversion by claiming you were beaten by the cops, ;-) Maedin\^talk 11:59, 17 August 2009 (UTC)

That would be a utilitarian's opinion on what to do. Most people, however, care more about themselves than other people, so the prospect of having one's licence revoked, losing one's job, etc. is not favorable, therefore they will choose to slap themselves. --Mark PEA (talk) 16:25, 17 August 2009 (UTC)

Actually, "burning it away" is the only thing you won't achieve! If you do exercise, you will increase your breathing rate and thus increase the amount of alcohol that "evaporates" through your lungs (in normal circumstances, i.e. at rest, that is about 1 to 5 % of total alcohol disposal, and incidentally that is what gets measured in a Breathalyzer). In addition to the effect on your actual blood alcohol content, hyperventilation will give you a significantly lower reading on the breathalizer, while hypoventilation will give you a significantly higher reading (about 30% both ways). So, if you think you're borderline, at least don't hold your breath before taking the breathalyzer test!! :-)

Exercising will also lead you to "sweat it away" a little bit (about 0.5% at rest). The rest goes to kidneys and liver. If you decide to exercise, while you're at it you could drink water, which will lower you blood alcohol content, and consume fructose which will speed up metabolism. Stefano (talk) 22:31, 19 August 2009 (UTC)

The flip side is that vigorous exercise could lead to loss of water from the body, which can actually increase your BAC. So if you try to lower your BAC by exercising, make absolutely sure that you drink lots of water to prevent this tactic from backfiring. 98.234.126.251 (talk) 00:38, 20 August 2009 (UTC)

Does a compressed spring weigh more than an uncompressed one?

Einstein established an equivalence between mass and energy with E = mc^2. If energy and mass are thus equivalent, this means it makes sense to talk about the total "mass-energy" of a particular system, in that a body's mass is actually the total energy contained within.

Does this mean that a compressed spring, since it stores potential energy, will weigh more than an uncompressed (but otherwise identical) spring?

67.172.215.13 (talk) 12:44, 16 August 2009 (UTC)

Yes exactly, it has more mass. Dmcq (talk) 12:55, 16 August 2009 (UTC)

Really? Then does a rock have more mass when I hold it over my head than it does when on the ground? Wikiant (talk) 12:59, 16 August 2009 (UTC)

Ever so slightly. The energy of the rock is many times (many orders of magnitude) greater than the 10 J or so you gain by holding it over the ground. In a compressed spring, what you are doing is pushing atomic nuclei ever so slightly (this is elastic deformation)) beyond their optimal distances, and this stores energy in the form of greater electrostatic repulsion. In effect this makes the nuclei and the electrons ever slightly more massive, but the difference is so miniscule it cannot be measured reliably. John Riemann Soong (talk) 13:13, 16 August 2009 (UTC)

Hmmm. Are you sure about the rock? I can see the spring, easily. But the rock gains potential energy, and that energy is no really inherent in the rock, but depends on the gravitational field of the rock and the Earth. By Chuck-Norris-symmetry, if you lift the rock, the Earth should also gain mass. Does it gain more or less than the rock? Or the same? Or does this depend on the observer? --Stephan Schulz (talk) 14:32, 16 August 2009 (UTC)

I mean, I really should say the Earth-rock-lifter system. Separating masses attracted to each other is like separating attractive charges. I really don't know a lot about relativity, but my impression is that rest mass doesn't increase, so who gains the increased mass is indeed observer-dependent. John Riemann Soong (talk) 14:38, 16 August 2009 (UTC)

But that suggests that, as the rock moves an infinite distance away from the earth, the earth-rock system approaches infinite mass, no? Wikiant (talk) 15:47, 16 August 2009 (UTC)

You only need a finite amount of energy to reach escape velocity. Dmcq (talk) 16:27, 16 August 2009 (UTC)

And that's because of the inverse square law ... as masses separate the gravitational attraction between them rapidly decreases. John Riemann Soong (talk)

The compressed spring is used as an example in our article on mass–energy equivalence, which says "A spring's mass increases whenever it is put into compression or tension. Its added mass arises from the added potential energy stored within it, which is bound in the stretched chemical (electron) bonds linking the atoms within the spring". Chemical bonds are electrostatic, so the additional energy/mass is stored in the electromagnetic field. Similarly, when you lift a rock, the additional energy/mass is stored in the gravitational field. Gandalf61 (talk) 14:54, 16 August 2009 (UTC)

A field has mass? A spring weighs more when it is compressed? Cuddlyable3 (talk) 15:45, 16 August 2009 (UTC)

You've got it. Energy is put in to lift a rock. That energy has an associated mass and the gravitational field gains that amount of mass when the energy is used to lift the rock. So if the spring is used to lift the rock the spring loses mass but the whole system still has the same amount of mass. Dmcq (talk) 16:25, 16 August 2009 (UTC)

I'm sorry, but this isn't making sense. I've heard two contradictory statements: (1) increase the distance between rock and earth and the earth-rock system gains mass, and (2) as masses separate, gravitational attraction decreases (implying that the potential energy of the rock declines and therefore the mass of the earth-rock system decreases). It appears that, as the rock-earth distance approaches infinity, the mass of the system approaches infinity if (1) is true and zero if (2) is true. Which is it? Wikiant (talk) 18:39, 16 August 2009 (UTC)

The error is "gravitational attraction decreases, implying that the potential energy declines." The correct statement is that as they separate, the gravitation attraction decreases, therefore the potential energy increases more slowly. What you have to remember is that the potential energy you add to a rock by lifting it depends on the total work you did to lift it -- the higher you go, the more potential energy it has. That's why it does more damage if you drop it from 50 feet than if you drop it from 5 inches. If you lift it so high that gravity is noticeably weaker, that doesn't change the fact that you're still adding potential energy as you lift it further -- you just aren't doing it as fast. --Anonymous, 19:03 UTC, August 16, 2009.

And as for (1) vs. (2), neither one is true. The correct statement is that as the potential energy (and therefore the mass) increases more and more slowly, it asymptotically approaches a limiting value. Specifically, the most energy you can add to a rock (more precisely, to the Earth/rock system) by lifting the rock away from the Earth's surface (all the way to infinity) is GMm/r, where G is Newton's gravitational constant, M and m are the masses of the Earth and the rock, and r is the Earth's radius. (See under potential energy.) This corresponds to a mass increase of GMm/rc², which if I calculate correctly comes out to about something on the order of 1/1,000,000,000 of the rock's mass m. --Anonymous, 19:10 UTC, August 16, 2009.

Excellent! Thanks. Wikiant (talk) 20:09, 16 August 2009 (UTC)

But does this mean that if two linked springs were rotated around each other (in outer space),and one was compressed during half of the cycle, wouldn't the center of mass alter to allow a (very weak) reactionless drive to be created, in violation of Newtons third law of motion!?Trevor Loughlin (talk) 02:56, 17 August 2009 (UTC)

Please understand that a spring powered clock theoretically gains mass when you wind it, just as a grandfather clock with a weight to power it gains mass when you elevate the weight. If I accelerate my car to 125 miles per hour (200 km/h), as I did in my misspent youth, it also gains mass, but no practical scale could ever measure the mass increase. It would be many orders of magnitude smaller than the resolution of practical scales. In cyclotrons, the mass increase of the particles accelerated to an appreciable fraction of the speed of light has to be taken into account or the devices would not work. We can confirm relativistic mass increase, experimentally, in extreme cases, but we cannot observe it in everyday situations. Edison (talk) 03:39, 17 August 2009 (UTC)

As for what Trevor said if your spring setup is what I think it is (so that when one spring is compressed the other spring is stretched) to me it seems it wouldn't work because (besides the whole violating the 3rd law part) when you stretch a spring 1 m you store the same amount of energy as if you compressed it 1 m, so the center of mass wouldn't change. Also last month in Scientific American there was an article about moving yourself through space by flailing your arms and legs. From what I remember it works because of the curvature of space (and so is very neglible unless you are standing next to a black hole). Suppose you are standing on a curved surface (like the Earth). You walk in a straight line, after some miles turn 60 degrees, and repeat till you have walked three straight lines forming what would be a triangle. If you calculate the center of mass as the point connecting all the meridians of the sides, and then do it again as as the point 2/3 of the way down from one of the vertex's (which should bring the same point) you get different points. This difference (the fact your center of mass isn't precisely defined) allows you to move yourself (instead of just moving forward and coming back) —Preceding unsigned comment added by 66.133.202.209 (talk) 04:09, 17 August 2009 (UTC)

Listen guys, I have a big huge suspension spring in my basement, I stood on the bathroom scale and squeezed it. Nothing happened.</extreme intentional ignorance for the purpose of humor>ZS 11:49, 17 August 2009 (UTC)

Of course not. The energy that went into the spring, making it heavier, came from the chemical potential in your muscles. So the overall energy content of the system (you+spring) did not change. You need to weigh just the uncompressed spring, then compress it and re-weight. Alternatively, you can weigh yourself before and after the exercise, and subtract your body weight to cancel for the energy (and hence mass) you lost. --Stephan Schulz (talk) 12:10, 17 August 2009 (UTC)

Each spring is left to spring back to its normal state, not "stretched" during part of the cycle, but is compressed during the other part. But the power to weight of such a device (even if it worked ,which I don't know) would not have a practical application. But supposing you had two linked cyclotrons loaded with relativistic charged particles- protons for example swinging around each other, and switched one cyclotron off during part of the cycle? Would the centre of mass alter in a way sufficient for practical reactionless drive-or have I simply thought up a new version of "EM drive"-I don't know if this works either, though the Chinese are working on it now apparently. Also, if a spacecraft is ever constructed to achieve relativistic speeds, would the increase in mass cause the craft to collapse in on itself with gravitational effects?Trevor Loughlin (talk) 12:07, 17 August 2009 (UTC)

No. The rest mass doesn't change, and the spacecraft always perceives itself "at rest". — Lomn 13:04, 17 August 2009 (UTC)

If you turn off your cyclotron the protons travel in a straight line and crash into the sides of the tunnel. I'm not understanding your design... (either the springs one or the cyclotron one). Could you describe how one of them works in detail? What is causing this periodic compression and relaxation of the springs, for example? --Tango (talk) 13:14, 17 August 2009 (UTC)

On releasing trevor's spring all I can foresee is that simple harmonic motion ensues, with the energy that was potential, now oscillating to and fro from kinetic. Energy cannot be destroyed trevor, and so unless some sort of object leaves the system the mass of the system will remain the same. Elocute (talk) 21:47, 17 August 2009 (UTC)

The important thing is that the energy in the spring is conserved like any other mass. It isn't created when the spring is compressed, it flows from somewhere. Your perpetual motion device with compressed springs won't work for the same reason all those clever perpetual motion devices with shifting weights won't work. The same physical principles apply. -- BenRG (talk) 09:45, 18 August 2009 (UTC)

Toothpastes with two anti-bacterial ingredients

Which toothpastes, particularly those available in the UK, have two or more anti-bacterial ingredients please? Mentadent P is one, but few places stock it. 78.147.255.120 (talk) 13:01, 16 August 2009 (UTC)

Excuse my ignorance, but why does the number of such ingredients matter? Surely its their efficacy?--Leon (talk) 14:31, 16 August 2009 (UTC)

See here http://jac.oxfordjournals.org/cgi/content/full/45/2/153#SEC4 Note: I am not looking for a debate on the merits or otherwise of various toothpaste ingredients. Thanks. 78.144.207.41 (talk) 16:51, 16 August 2009 (UTC)

Is it possible for mouth bacteria to develop resistance against antibacterial ingredients? John Riemann Soong (talk) 14:47, 16 August 2009 (UTC)

Certainly, and the flora in the human mouth are legion both in number of species and number of organisms (even after brushing, flossing, and using mouthwash). Sterilization of the mouth is not feasible (perhaps not even desirable), so what's the point of using antibacterial toothpaste unless it has been demonstrated, in carefully-controlled studies, to reduce a major problem (e.g. caries and/or gingivitis) without causing short- or long-term problems? Without such evidence, this practice could cause much more harm than good. This is all general comment and is not meant to substitute for or diminish any advice you might be given by a health professional. --Scray (talk) 15:36, 16 August 2009 (UTC)

Is anyone going to answer the question asked please? 78.144.207.41 (talk) 16:41, 16 August 2009 (UTC)

Up till today I wasn't aware of a toothpaste with more than one antibacterial agent - unless you include fluoride, the only antibacterial agent I'm aware of in toothpaste (UK) is Triclosan. Perhaps there aren't any?83.100.250.79 (talk) 21:32, 16 August 2009 (UTC)

According to [3] (not the greatest of sources), it has triclosan and Zinc Citrate. I also came across this rather old study [4] which compares the activity levels. There also seem to be a lot of studies looking into the effects of the triclosan/zinc citrate combo [5] Nil Einne (talk) 22:50, 16 August 2009 (UTC)

This is a Science reference desk, so you're going to find it rather difficult to avoid discussion on which agents are truly "antibacterial" in anything other than the marketing literature. Many anitbacterials (antibiotics) have the perverse effect of actually promoting bacterial growth by eliminating beneficial (commensal) bacteria and promoting resistance in general when used in improper doses, so the focus here is rightly on whether the toothpastes in reality have a two-component action. Perhaps you would like to rephrase your question as "Which toothpastes claim to have two anti-bacterial ingredients?" - and then it becomes more of a RefMisc question than a RefScience question... Franamax (talk) 23:54, 16 August 2009 (UTC)

What sort of ridiculous people do you take us for? Do not use the science reference desk to ask questions that will be answered by those who answer by using Google to search for answers -- use Google yourself and spare us. DRosenbach ^{(Talk | Contribs)} 03:09, 17 August 2009 (UTC)

Please do not assume yourself to be ridiculous, or be emotive. It is impossible to predict beforehand if answers to questions asked will have answers from specialised knowledge, or just Google 'research' prompted by the question. Even with the latter, searchers may turn up information that the OP had not found despite spending some time previously searching, as happened in my case. 78.144.246.133 (talk) 12:48, 17 August 2009 (UTC)

Impossible to predict...quite presumtuous. DRosenbach ^{(Talk | Contribs)} 22:33, 17 August 2009 (UTC)

From a lead given above, I have found this http://www.ncbi.nlm.nih.gov/pubmed/9238875 which indicates that Crest Complete, Mentadent, and Colgate Total are such toothpastes. Crest Complete is said to be the most effective, while Colgate Total is not effective. However the study is open to question by apparantly being funded by the manufacturer of Crest Complete. 78.144.246.133 (talk) 12:48, 17 August 2009 (UTC)

De Havilland Dragon Rapide

What is the small propeller on the upper wing of this plane? —Preceding unsigned comment added by 217.30.185.1 (talk) 14:47, 16 August 2009 (UTC)

(Guessing) It looks unnecessarily large to be (only) an airspeed sensor. I think it is an air-powered electric generator. Cuddlyable3 (talk) 15:22, 16 August 2009 (UTC)

It is a wind-powered electric generator http://www.iaopa.eu/mediaServlet/storage/gamag/apr06/Rapide.pdf. MilborneOne (talk) 15:35, 16 August 2009 (UTC)

Fluorescent light comes on only after long, variable delay. Probable cause?

Here's a real-life puzzler: Fluorescent lights in a fixture would come on only after a long, variable delay (20 – 30 mins., sometimes longer). The fixture may have an electronic ballast (no starter is visible where it can be replaced easily). What might be the cause of the strange behavior? —Preceding unsigned comment added by 173.49.16.37 (talk) 15:31, 16 August 2009 (UTC)

Do the filaments at each end of the fluorescent tube glow during the start delay? If yes then try a new tube. If no then something is wrong with the starter (which is sometimes hard to see behind the tube). Cuddlyable3 (talk) 15:50, 16 August 2009 (UTC)

There's no visible glow during the delay. If you flip the switch to off before the light comes on, you'll see a brief flicker of light. Occasionally flipping the switch back and forth a few times would cause the light to come on without the delay, but that's not always successful. --173.49.16.37 (talk) 16:13, 16 August 2009 (UTC)

That is the symptom of a bad transformer in a "starterless" fixture. Replace the transformer. This is fairly cheap and easy to do (about like repairing a lamp or light fixture) but do not try it yourself unless you are comfortable with electricity. A dead transformer usually (but not always) has exuded some sticky melted tar: if you see tar, you know for sure it's bad. In my house, I gave up and refitted all of my tube flourescent fixtures to use compact flourescents. I removed the old transformers and wiring and added a bunch of screw-type scokets (four dual sockets) to each fixture. The compact flourescents are somewhat less efficient, but with tube flourescents I was always replacing either the bulbs or the transformers, and worrying that badd transformers were killing bulbs or vice versa. With the CFs, you just replace the bulb, the bulbs are each independent, and I can eventually shift to LEDs when they become economical. -Arch dude (talk) 20:14, 16 August 2009 (UTC)

Although LED fluorescent tube replacements seem more common (at least when I last looked) albeit perhaps can't be considered economical. E.g. [6] Nil Einne (talk) 23:01, 16 August 2009 (UTC)

I could understand a second, or a few seconds to reach full brightness, but 20 minutes is abnormal, and suggestive of some abnormality of the ballast, the starter, the bulb, or the wiring. Edison (talk) 03:30, 17 August 2009 (UTC)

A fluorescent light which is that slow to come on could have a problem with the grounding. There might not be a good ground connection to the case. There might also be a problem with the neutral connections. Edison (talk) 02:36, 18 August 2009 (UTC)

Did anyone else read the headline and think "No, that's not probable cause" ? —Tamfang (talk) 06:32, 6 December 2009 (UTC)

BLAST search always fruitless?

I have reason to believe that GCTGAGAGAGAGAAAAAAAAAAATCAG is part of the human genome but when I go here http://www.ncbi.nlm.nih.gov/genome/seq/BlastGen/BlastGen.cgi?taxid=9606, enter the sequence and click 'begin search', followed by 'view report', I get no matches. I also get the same result even with a simple string like CAT - what am I doing wrong? ----Seans Potato Business 16:39, 16 August 2009 (UTC)

I suspect that the presence of so-called low-complexity sequences (those highly-repetitive portions) are being automagically disregarded by the matching algorithm. Since the bulk of your sequence is low-complexity (highly-repetitive), all hits are getting filtered out. In the query screen that you've linked, look in the 'Optional parameters' box and change the 'Filter' setting from 'default' to 'none'. This will force BLAST to search using the entire sequence. Unfortunately, you're going to get a very large number of hits, as highly-repetitive regions tend to occur frequently by chance (due to gene slippage during copying). TenOfAllTrades(talk) 19:49, 16 August 2009 (UTC)

I'm not saying that slippage would generate the whole sequence spontaneously, only that it can extend the repetitive sections (the multiple GA and A repeats) in this sequence. TenOfAllTrades(talk) 21:35, 16 August 2009 (UTC)

The USCS genome browser places your sequence at chr14:51,714,964-51,714,983 using a BLAT algorithm. From what I understand, BLAT is better for looking for short, exact matches, than BLAST. It seems NCBI used to have an option to "search for short, nearly exact matches" but this is now part of the usual BLAST algorithm. FWIW I also got no hits using the NCBI version of BLAST, changing a couple of parameters. Weird... --- Medical geneticist (talk) 23:09, 16 August 2009 (UTC)

Artificial membrane

Hi, I would like to know if there are artificial membrane capable to separate CO2 and, at the same time, let the O2 and H2O molecules pass. If it is possible, I would like to know some commercial name. Thanks. —Preceding unsigned comment added by 94.163.134.160 (talk) 16:48, 16 August 2009 (UTC)

It sounds like you're looking for a Carbon dioxide scrubber, like you'd find on a Rebreather or a space ship, but they're more complicated than a simple membrane. APL (talk) 18:21, 16 August 2009 (UTC)

Most CO2 scrubbers work by absorption rather than membrane filtration. In the most commonly used type, CO2 is absorbed by metal oxide or hydroxide (often KOH or CaO, sometimes LiOH too) to form the corresponding carbonate, which is then regenerated back to the oxide / hydroxide by heating with the release of CO2 (into a different gas stream, of course). Absorption by amine solution is pretty commonly used too (the amine acts as a Lewis base). And for really thorough CO2 removal (for example, in coal liquefaction plants), physical absorption with refrigerated methanol (at -30 C) is often used -- it's expensive, but it removes CO2 to less than 100 parts per billion. Which method is best for you will of course depend on what you'll be using it for (and especially on the volume-flow of your gas stream, the CO2 partial pressure, and the maximum remaining CO2 level desired). So if you could tell me what is it you're trying to do, I could maybe point you in the right direction. 98.234.126.251 (talk) 01:13, 17 August 2009 (UTC)

Thanks to the both of you. 98.234.126.251, I would like to grow algae, so I need CO2 trapped in the internal side of the membrane (but not as carbonate), and I would like to let O2 and H2O (made from the algae) spread to the external side. —Preceding unsigned comment added by 94.162.2.225 (talk) 01:22, 17 August 2009 (UTC)

Oh -- I was assuming that you wanted to remove CO2 rather than concentrate it. (That's a natural assumption for me, cause most of my experience with CO2 scrubbing is in the context of a coal gasification plant.) Well, for your aquarium, I'd recommend passing the "product stream" (the mixture of O2/H2O/CO2 that comes out of the tank) through activated carbon, which will preferentially adsorb CO2 (but not O2), and then once the carbon is saturated with CO2, passing a stream of water (if the "product stream" is aqueous) or nitrogen (if the "product stream" is gaseous) through the CO2-saturated carbon and back into the tank. That will put the CO2 back into the tank while letting the O2 and H2O out -- essentially doing the same job as the membrane that you were asking about. 98.234.126.251 (talk) 03:20, 17 August 2009 (UTC)

I understand; the matter is that it would be a very large colture volume, so I can't use adsorbtion. It's not easy at all, but you were very kind. —Preceding unsigned comment added by 94.163.139.185 (talk) 12:25, 17 August 2009 (UTC)

Couldn't we use a principle similar to reverse osmosis? Just find membrane holes that will selectively allow oxygen and water, but not carbon dioxide. This seems possible, as CO2 contains 3 heteroatoms, oxygen only contains two, and water only contains one (and the hydrogen atoms should be small in comparison). On the other hand, it could be a problem if CO2 and O2 as linear molecules could slip in via the size of a single heteroatom. But CO2 is heavier than oxygen, so maybe that element could be combined too. How efficient would the CO2 filtration have to be? I mean if this only removes 50% of the CO2 with each pass, that might be good enough for some purposes. John Riemann Soong (talk) 13:23, 17 August 2009 (UTC)

Membranes:

• CO2 selective polymer membranes often contain amino groups -eg search "CO2 membrane selective amine"
• O2 selective membranes incorporate an oxygen carrier eg something like haemoglobin - see http://pubs.acs.org/doi/abs/10.1021/jp9816317
• water is a liquid.. I don't know any trade names. According to thermodyamics you'll have to supply energy to do the separation - probably as a pressure drop accross the membrane.83.100.250.79 (talk) 15:03, 17 August 2009 (UTC)

Zeolites are another possibility - CO2 and O2 are the same width, but CO2 is longer, it also has different chemical properties. Search "zeolite O2 CO2"83.100.250.79 (talk) 15:26, 17 August 2009 (UTC)

Don't you have to supply energy in reverse osmosis too? John Riemann Soong (talk) 20:57, 17 August 2009 (UTC)

Yes83.100.250.79 (talk) 10:38, 18 August 2009 (UTC)

Thanks, John Riemann Soong & 83.100.250.79. I agree, in theory it would be possible to make a membrane capable to saparate CO2 from O2 and H2O. The filtration should be very good, as the passing of the CO2 outside the membrane would result in pollution of the environment, but 50% could be a good start point. The problem is that I can't use any active system, just filtration, because every other method would make the tecnique too expensive, if compared to more classic way of colture: so I can't use matrix of amino groups or oxygen carrier, and neither zeolite, wich adsorbs. —Preceding unsigned comment added by 94.162.12.113 (talk) 12:26, 18 August 2009 (UTC)

I don't know if it's possible to do it any other way than actively (and I assume you mean "active" in the sense of activated carbon and not say, active transport requiring the supply of energy). I wonder if it's possible to borrow some principles of gas chromatography.... and selectively choose solvents which will dissolve CO2, O2, H2O, etc. We might turn water into a gas for this purpose ... but are you sure that an active method would be expensive? I mean, the capital cost would be high, but the maintenance would be low. Whereas if you're vaporising water to try to do the job, that might end up being more efficient in the long run. (You could also turn water into a gas via a vacuum environment of 0.001 atm -- but unless you had a superpowerful vacuum you might have to do this via tiny amounts of water at a time.) John Riemann Soong (talk) 14:37, 18 August 2009 (UTC)

I'd say 83.100 is on the right track -- a good option in the case of your seaweed plantation would be to pass the effluent through a membrane made of a polymer with lots of amino groups, which would selectively adsorb CO2 while letting O2 and H2O pass to the outside, and then when the membrane is saturated, use a reverse flow of water or nitrogen to desorb the CO2 and put it back into the tank. 98.234.126.251 (talk) 22:37, 18 August 2009 (UTC)

Ok, this way appears to be the best solution to the problem; the only real matter, unfortunately, is the same: energy. I will think about it in a deeper way, also starting from what you have written here. Thanks to all the partecipants, you really helped me! —Preceding unsigned comment added by 82.59.65.242 (talk) 16:21, 19 August 2009 (UTC)

Depending on where you're growing this algae -- couldn't you harness the tides or something? The tide going out brings out the H2O and O2, the tide going in restores the CO2... John Riemann Soong (talk) 16:42, 19 August 2009 (UTC)

Oh, that's interesting; the bounding should be weak in this case. This is not perfect yet, but it was such a good idea. If you want, you can leave me a contact; if this tecnique will be used, I would like to keep you name evident!

OK, seaweed grower, where can I leave you my contact info? I don't want to leave it here on the ref desk cause we might both get spammed; besides, this is against wiki policy. 98.234.126.251 (talk) 00:02, 21 August 2009 (UTC)

"Good" or "Bad" Firewood

We recently had a storm come through and damage two trees to the point we had to take them down and cut them into firewood. What level of MMBTU/Chord makes a type of wood a good firewood? Based on that, are the Mulberry and Ash trees we cut good firewood? Ks0stm ^(T•C) 17:46, 16 August 2009 (UTC)

This site [7] has a table listing the MBTU values of various trees. --Cookatoo.ergo.ZooM (talk) 18:46, 16 August 2009 (UTC)

But the critical thing for firewood is not MBTU but water content and how inclined to spit they are. Ash is generally rated as the best possible firewood. The very old rhyme we are all taught is fairly reliable except for Elm which burns fine (but superstition says don't do it)

Beechwood fires are bright and clear
If the logs are kept a year
Chestnut only good they say
If for long it's laid away
Make a fire of elder tree
Death within your house will be
But ash new or ash old
Is fit for a Queen with a crown of gold

Birch and Fir logs burn too fast
Blaze up bright and do not last
It is by the Irish said
Hawthorn bakes the sweetest bread
Elmwood burns like churchyard mould
Even the very flames are cold
But ash green or ash brown
Is fit for a Queen with a golden crown

Poplar gives a bitter smoke
Fills your eyes and makes you choke
Apple wood will scent your room
With an incense-like perfume
Oaken logs, if dry and old
Keep away the winters cold
But ash wet or ash dry
A king shall warm his slippers by.

or another version of the same poem:

Beechwood fires burn  bright and clear
If the logs are kept a year
Store your beech for Christmastide
With new holly laid beside
Chestnuts only good they say
If for years tis stayed away
Birch and firwood burn too fast
Blaze too bright and do not last
Flames from larch will shoot up high
Dangerously the sparks will fly
But Ashwood green and Ashwood brown
Are fit for a Queen with a golden crown

Oaken logs, if dry and old
Keep away the winters cold
Poplar gives a bitter smoke
Fills your eyes and makes you choke
Elmwood burns like churchyard mould
Even the very flames burn cold
Hawthorn bakes the sweetest bread
So it is in Ireland said
Applewood will scent the room
Pears wood smells like a flower in bloom
But Ashwood wet and Ashwood dry
A King may warm his slippers by.

--BozMo talk 19:05, 16 August 2009 (UTC)

DVD lasers

I've seen lots of speculation on the internet about taking the lasers out of DVD-R drives and putting them into flashlights, etc.e.g. These lasers are apparently powerful enough to pop balloons, burn retinas, and other not-very-safe things.

My question: how far can these project? How far are they dangerous? How much exposure would be necessary to, say, damage a human eye in a permanent way? What kind of eye-wear would be protective? The example above has a visibly red laser—what if one used the infrared laser from a CD-R drive? Or the violet laser of a bluray drive? How much of a threat is this, in the end?

I ask only because I am curious about the blinding-potential that exists out there in the world, were someone to be malicious about it, which is a disturbing thought. I thought one of you mad scientists could fill me in. --98.217.14.211 (talk) 18:16, 16 August 2009 (UTC)

This reference says that DVDs have Class 3B or Class 3R lasers. See Laser safety for precautions. -Arch dude (talk) 19:59, 16 August 2009 (UTC)

A class 3 laser is a fairly dangerous thing. Even a class 2 laser can damage your eye with just a quarter second of exposure. A class 3 laser can wreck your vision in less time than you can blink - so the scope for accidents while messing around with them is significant - it's easy to think you're pointing the laser across the room - then hit a mirror or a window or something and bounce the light back into your eyes. IR and UV lasers are doubly dangerous because you can't tell you're looking into one until you can't see clearly anymore. Even the little class 1 or class 1M lasers in laser pointers can damage your eyes with enough exposure. There really is no such thing as a "safe" laser - even the ones in green laser pointers rely on you looking away and blinking to save your sight.

As to how far they can project...that's the thing about lasers - they don't get dimmer with range (well, at least not very quickly). In theory a laser beam is a parallel beam - so all of the energy stays together instead of safely spreading out like 'ordinary' light. In practice, most lasers are not perfectly parallel - but still, it's kinda meaningless to talk about a "range".

SteveBaker (talk) 23:11, 16 August 2009 (UTC)

What I'm really trying to get at is: let's say there's a huge crowd of people at some kind of major event (let's say, the Superbowl). Could one guy with a CD writing drive laser (which is in the infrared, if I understand the optical drive page correctly, but is still in a wavelength that can do damage) plugged into a big mag-lite be able to secretly do major eye damage to lots of people there? --98.217.14.211 (talk) 00:45, 17 August 2009 (UTC)

OOH! Class 3a lasers can blind you in 1/4 second! Then why are they sold as pointers/cat toys? Could it be because the output is less than 5 milliwatts? How does that compare to the energy (per square mm) falling on the retina when I look at snow or a anything painted white under full sunlight? The BS alert just sounded full volume. Edison (talk) 03:27, 17 August 2009 (UTC)

Luckily for us Edison, we aren't talking about class III A lasers. True their output is less then 5 milliwats, which is why no one considers them dangerous. However a class III A laser isn't a class 3 B laser. Btw I can't remeber the name for the unit that measures the amount of energy from sunlight that falls on the ground. It has some really strange units (not Joules/square meter). Anyone remember? EDIT: I remember now: the unit I was thinking off was the langley (and it was in J/sq. m.

66.133.202.209 (talk) 04:52, 17 August 2009 (UTC)

Yeah - you have to be very careful. The OLD classification scheme used roman numerals and was based on some highly unsound science. The NEW classification uses arabic numerals and is a much more accurate description of the safety of lasers. So a class III laser is like a laser pointer or something - but a class 3 laser is able to blind you before you can blink. SteveBaker (talk) 21:36, 17 August 2009 (UTC)

A quarter of a second is a huge span of time if you're trying to blind someone from across a football stadium. Most people couldn't hit someone's pupil at that range with a rifle, let alone a laser pointer.

To do this you would have do construct a laser pointer with a tripod and a scope. Even then you'd still need tremendous skill and a lot of luck. It'd be a lot easier to just walk up to people and throw bleach in their face. APL (talk) 16:52, 17 August 2009 (UTC)

Right, except you'd get caught if you did that. If you had an infrared laser at some distance in a concealable case, nobody is going to know who did it. That's the issue I'm asking about, in the end. --98.217.14.211 (talk) 19:19, 17 August 2009 (UTC)

You'd either need to be so close to someone that it would be obvious that you were the one with the laser, or you'd need a super elaborate aiming contraption.

You'd never blend into the crowd with a laser-pointer that looks like a sniper-rifle on a tripod. The target you're trying to hit (and maintain contact with) is minuscule even at close range.

(If the laser is IR it's even MORE difficult to aim, because you don't have the red dot to use as reference.) APL (talk) 19:58, 17 August 2009 (UTC)

However, if the target is not one specific person, than it's easy to hit a lot of random people even from a great distance. --79.119.218.161 (talk) 07:49, 22 August 2009 (UTC)

What is the risk of brief laser exposure compared to briefly staring into the sun? Which (comparing the class of laser to a cloudless summer in England for example) would cause permanent damage the quickest? (I have NO plans to try this out!) Also, is staring into a shop laser scanner (out of curiosity at the scintillation effects) dangerous? My retinal scan shows no damage, though perhaps being short-sighted lessens the focus/damage? Trevor Loughlin (talk) 13:07, 17 August 2009 (UTC)

Shop scanners don't point at a single location, they flick rapidly back and forth across a path. So the damage would be less than their power output would imply. Vimescarrot (talk) 14:23, 17 August 2009 (UTC)

There seems to be some doubts up there whether the lasers can damage ones' eyes. I don't think there's ANY doubt that a strong laser can do that, and I imagine that a laser that can pop a balloon is strong enough to damage one's photoreceptors. If a stadium is rather too large to hit a small eye target (which I think is probably true), what about smaller distances? Or put another way—what's the minimum distance (estimated) that this would be a serious problem? (esp. if the one with a laser has both a scope of some sort, and some basic way to stabilize the laser). --98.217.14.211 (talk) 19:19, 17 August 2009 (UTC)

I don't think the lasers used in barcode scanners are class 3 - there is no reason for them to need to be that bright. They're probably class 1 - which are relatively safe. But as Vimescarrot points out - they are scanning so rapidly that the average brightness wouldn't be low enough to hurt you even if they were more powerful than that. The concern with such contraptions is what happens when the mechanism that oscillates the laser breaks...typically, everyone peers into the machine to see what broke! I bought a piece of a supermarket scanner mechanism on eBay for my 3D scanner project - and it doesn't move the laser at all. It has a holographic lens that stretches the laser spot out into a line - which it bounces off mirrors to make the criss-cross pattern. No moving parts...nothing to go wrong. SteveBaker (talk) 21:36, 17 August 2009 (UTC)

Using a scope to point the laser might not be such a good idea. If something reflective gets in the beam path, you have an excellent focussing mechanism pointing right at your own eye! Franamax (talk) 07:06, 18 August 2009 (UTC)

Oooh! I like it! Poetic justice. SteveBaker (talk) 12:32, 18 August 2009 (UTC)