Wikipedia:Reference desk/Archives/Science/2009 November 25

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November 25

Monstrous shape-shifting owl

I've just been sent a link to this YouTube video, which I found really freaky and disturbing, for some reason that I can't quite place my finger on.

http://www.youtube.com/watch?v=Es52WQKLumI

Does anyone know if this owl is actually a real species and can really do this? I'm thinking that while the first display might be real, the second (demonic looking) one is CGI.--84.69.185.215 (talk) 00:38, 25 November 2009 (UTC)

That was really cool. I don't know if it is real or not. I like it. Dauto (talk) 01:02, 25 November 2009 (UTC)

This has come up on the Reference Desk before, see Wikipedia:Reference desk/Archives/Science/2009 July 26#Cat bird owl?. Looie496 (talk) 01:11, 25 November 2009 (UTC)

Northern White-faced Owl also references that video. SteveBaker (talk) 03:57, 25 November 2009 (UTC)

Remarkable as it is it is quite small beer when compared to some of the courting postures of some Birds of Paradise of Asia.This is just one example. [1] Not much of a song but what a super blue smiley face. Richard Avery (talk) 08:46, 25 November 2009 (UTC)

Some more about the species here:[2] Here's pics of it in action:[3][4] Other "scops-owls" adopt a similar thin upright posture with ear tufts.[5][6][7] Fences&Windows 18:33, 25 November 2009 (UTC)

The owl reminds me (facially) somewhat of a Ring-tailed Lemur during the first transformation. It's probably not intentional - but I just thought that I'd make that observation. I felt slightly unsettled myself when I saw the owl's 'demon' form (anyone have any thoughts as to what it's trying to imitate with that?) - which may indeed be *exactly* what the owl wants you to feel. It's something about the way that its eyes appear to change shape that doesn't rest easy with me. --Kurt Shaped Box (talk) 01:34, 26 November 2009 (UTC)

The resemblance to a cat is striking, and a photographer described them as giving a "rarely heard cat-like cry",[8] Some kind of Batesian mimicry might be going on as an adaptation of the defence posture, but that's speculation. The general significance of ear tufts in owls has been discussed on a science blog here, and mimicry of mammalian predators is one suggestion. But other owls do adopt a similar posture, e.g. the Northern Pygmy-owl, in which it is described as a 'concealing' posture,[9] so the appearance to humans of the Northern White-faced Owl could just be a coincidence. Fences&Windows 12:57, 26 November 2009 (UTC)

The advantages of making oneself looking bigger is obvious. But what can be the advantage of making oneself looking smaller and weaker, as in the second posture? --131.188.3.20 (talk) 14:59, 28 November 2009 (UTC)

Concealment. Fences&Windows 18:55, 28 November 2009 (UTC)

The mimicry of cats reminds me that in Chinese, the literal translation of owl is "cat-faced hawk". ~AH1^(TCU) 02:24, 2 December 2009 (UTC)

Early Hominina finding in Americas

What is the oldest known Hominina remains found in Americas before the Homo sapiens arrived here? 174.114.236.41 (talk) 03:12, 25 November 2009 (UTC)

I find this: Models of migration to the New World. Bus stop (talk) 03:16, 25 November 2009 (UTC)

That article is about Homo sapiens, the OP is explicitly asking about pre-Homo sapiens. --Tango (talk) 03:23, 25 November 2009 (UTC)

There were no hominids in the Americas before Homo sapiens. The only primates in the Americas before the arival of Homo sapiens were the New World monkeys, and they are among the most distantly related primates to Homo sapiens around (far more distantly related than any other apes or monkeys). The first Hominids to arrive in the Americas were fully modern Homo sapiens. See Models of migration to the New World. There is some controversy as to the actual date the first people arrived; or from which direction, or whether they arrived in a single migration or in multiple waves, but even the oldest possible date for humans arriving is about 50,000 years ago, and that date is considered pretty old by most mainstream theories, which hold a date of about 17,000 years ago as the first arrival of humans. For comparison, the last non-Homo sapiens hominid, homo erectus, died out some 1,000,000 years ago. There is simply zero fossil evidence for any pre-homo sapiens hominids in the Americas; indeed as noted above, the nearest relatives are actually quite distant, those New World monkeys branched off of the "human family tree" well before any Apes or Old World monkeys did, some hundreds of millions of years ago. --Jayron32 03:26, 25 November 2009 (UTC)

There is some dispute about which was the last non-Homo sapiens hominid - it depends on whether you consider Neanderthals to be a subspecies of Homo sapiens or not (the experts can't agree). If you consider them a separate species then that moves to date from which Homo sapiens have been alone to, possibly, 30,000 years ago (although probably more). However, they were in Europe, not the Americas. --Tango (talk) 03:30, 25 November 2009 (UTC)

There is also Homo floresiensis, aka. "The hobbit", which may or may not have been a subspecies of Homo sapiens or a distinct species. Given that there are no actual extant hominids besides homo sapiens, it is hard to say whether any of these examples are "subspecies" or "species" - level relatives, it probably has a lot more to do with politics than real science as to which side of the debate one falls. Still, no fossil evidence of any of these hominids, or indeed of any other, before the arrival of modern Homo sapiens. --Jayron32 03:33, 25 November 2009 (UTC)

(Just today - and reported right there on the Wikipedia front page - is news that some rather convincing new studies show that florensiensis was indeed a separate species.) SteveBaker (talk) 04:31, 25 November 2009 (UTC)

Well, there ya go. But floresiensis wasn't in the Americas either. --Jayron32 04:36, 25 November 2009 (UTC)

Indeed not. SteveBaker (talk) 04:57, 25 November 2009 (UTC)

But is it possible that the early distantly related New World Monkeys may have evolved into hominids, then became extinct prior to the arrival of homo sapiens? ~AH1^(TCU) 02:21, 2 December 2009 (UTC)

Hood Canal "tide computer"

Tide predictor, 1921

I came across this interesting snippet in the 'forum' posts at the end of this:

"...until very recent times the Ptolemaic theory was sufficient to calculate tide tables and it was a whole lot easier to use it rather than to puzzle out multi-body solutions with Newton's formula. The ancient Ptolemaic tables were good enough. At the Hood Canal locks here in Seattle there used to be a giant analog computer consisting of a heavy chain about fifteen feet long. The chain was fixed on one end and stretched horizontally with a series of pulleys representing the celestial bodies each able to indent the stretched chain and make it shorter or longer. The free end culminated in a pointer that moved up and down a scale indicating the expected tide."

I can't find anything about this on the web - does anyone have any more information about it? Hood Canal has nothing about it. Tide-predicting machine has a lot of discussion of these kinds of gizmo but nothing there sounds like it would have fifteen feet of "heavy chain" - it seems to discuss relatively delicate-looking gadgets.

SteveBaker (talk) 03:48, 25 November 2009 (UTC)

Um...since the Hood Canal isn't really a canal, but rather a fjord, why would it have locks? --jpgordon^{::==( o )} 05:32, 25 November 2009 (UTC)

Wow. I did find the thing. "Old Brass Brains", they called it; it was used until 1965! Don't know the Hood Canal connection. This is from Technical World magazine in 1921; it's on page 205. It's a big download! There's also a modern writeup about it and others here. So cool! (--jpgordon^{::==( o )} 06:21, 25 November 2009 (UTC)

Of course, I could have just looked more closely at tide-predicting machine. But it was fun research. Anyway, "Old Brass Brains" was big! It weighed 2500 pounds and was 11.5 feet tall. So "heavy chains" might be accurate. --jpgordon^{::==( o )} 06:33, 25 November 2009 (UTC)

I had looked at the "Old Brass Brains" thing before I posted the question - but I didn't see the Hood Canal connection - and big though it is - it didn't seem like it would have 15 feet of "heavy chain" - and what chain it has isn't "stretched horizontally", it seems to zig-zag through the mechanism. It's clear that the person who I quoted (above) didn't understand the machine. Unless the one he's talking about is very different from the "normal" mechanical tide predictors, it would be summing an empirically derived Fourier series to make the predictions - not employing some kind of ancient Ptolomaic theory of how sun, moon and planets move as implied by "pulleys representing the celestial bodies". Mathematically and mechanically, the results might be kinda similar - you're adding circular motions - but "Old Brass Brains" certainly isn't using Ptolomaic principles. That's why I wanted to find out more about this supposed Hood Canal machine in Seattle. SteveBaker (talk) 14:30, 25 November 2009 (UTC)

Yeah. But as I said -- there don't appear to be any locks in the Hood Not-really-a-canal. --jpgordon^{::==( o )} 15:38, 25 November 2009 (UTC)

Why would anyone make such a large tidal calculator as Old Brass Brains and not scale it down to a portable device like the Antikythera mechanism? How many of the Fourier series coefficients (up to 24 on one machine) correspond to identifiable astronomic influences? Cuddlyable3 (talk) 18:37, 25 November 2009 (UTC)

Seattle has Chittenden Locks - I don't think I'd describe them as being on the Hood Canal - but they are close enough that maybe someone could assume that they were. Still no sign of a tide predictor there though. SteveBaker (talk) 23:38, 25 November 2009 (UTC)

Type of truss bridge

Is the upper drawing a Warren truss bridge? I would guess so from attempting to read the description (I don't know French), but it differs from the lower drawing, which we currently use to illustrate the Warren section of truss bridge — the upper drawing has vertical supports, which are entirely missing from the lower drawing. If it's not a Warren, what is it? Nyttend (talk) 04:54, 25 November 2009 (UTC)

By the way, the reason that I'm asking is that I'm trying to ascertain the type of bridge shown in the photo. Nyttend (talk) 05:14, 25 November 2009 (UTC)

(ec) List of truss types identifies the lower image as a Warren (non-polar) truss - which agrees with the main article. The upper image does not appear in any of those types because the diagonal elements alternate in direction - unlike a Howe truss - and has verticals, unlike a Warran (non-polar) truss. The (french) caption says "Warren avec montants" - "avec" means "with" - so this is a Warren truss with "montants". My wife (who is French) says that "montants" are the vertical elements in window frames (the horizontal bits are "traverses")...and Wiktionary says that a montant is any vertical piece of carpentry in a framework. So evidently, your bottom image is a bona-fide Warren truss - and your top image is a modified version of a Warren - with those vertical bits (the montants) added in for whatever reason. SteveBaker (talk) 05:17, 25 November 2009 (UTC)

Well, now you've confused things - the photo you just added has only every second "montant" present! So that's yet another variation! I'm guessing though that this is still a Warren truss. SteveBaker (talk) 05:19, 25 November 2009 (UTC)

Briefly skimming an old engineering book I happen to have here at home - the critical thing about a Warren truss is how the weight is distributed between compressive and tensile forces in the diagonal elements. The Howe truss has all of the diagonals in the left-hand half of the span going from bottom-left to top-right and all the ones on the other side going the other way. A Pratt truss does the complete opposite - and which one you use depends on the building materials you have (are they better in tension or compression?) and whether you expect the truss to be fairly evenly loaded along it's entire length - or have a small, heavy load at just one point along the truss. It seems that the Warren design (by alternating the diagonals) is some kind of compromise between the two. The vertical elements...I have no clue...they seem to play little part in the discussion of the relative merits of the three designs - but so many real bridges seem to have them that they must be important in some manner. SteveBaker (talk) 05:32, 25 November 2009 (UTC)

Thanks for the details; I've never quite understood the different types of trusses, so I wasn't at all sure that the montants weren't significant for the type of truss. If you're an engineer, you may find this location quite interesting: it's the Deep Cut of the Miami and Erie Canal. Nyttend (talk) 05:47, 25 November 2009 (UTC)

By the way - I doubt that "montant" is the right word for the upright beams in bridge structures. It's evidently the right word in French - but probably not in English. I was merely using the word as a shorthand for whatever the correct term is! SteveBaker (talk) 06:01, 25 November 2009 (UTC)

According to this [10], it is a "varying depth Warren truss". --Cookatoo.ergo.ZooM (talk) 09:11, 25 November 2009 (UTC)

The varying depth refers to the polygonal arrangement of the chords, not the upright posts. We are still looking for a name for a Warren truss with posts. SpinningSpark 12:59, 25 November 2009 (UTC)

This page and this page call it a "subdivided Warren truss". If you want a fancy architectural term for the vertical members, you could call them mullions. Gandalf61 (talk) 13:25, 25 November 2009 (UTC)

Yeah, doesn't seem to have an actual name, just Warren truss with verticals seems the most usual description. The vertical members, according to this book, are called posts and hangers depending on whether they are taking a compressive or tensile load. SpinningSpark 13:31, 25 November 2009 (UTC)

Mullion is a term used in connection with windows and doors and other openings. The side of a bridge is not intended as an opening (either for people of light) so I think it would be unlikely to be used. SpinningSpark 13:41, 25 November 2009 (UTC)

Dehumidifiers and climate change control

Given water vapour's role in the greenhouse effect, could large-scale dehumidifiers be used to offset emissions of other greenhouse gases and control climate change? NeonMerlin 05:25, 25 November 2009 (UTC)

No. --Jayron32 05:27, 25 November 2009 (UTC)

Well, yes and no. Water vapor is itself a greenhouse gas - so I suppose a dehumidification of the upper atmosphere would help to alleviate the greenhouse effect. However, water droplets in the form of clouds and fog banks are very bright and reflect sunlight back out into space - keeping the earth cooler. So in that regard, getting rid of the clouds would make matters worse. (This was noted in the days after the 9/11 terrorist attacks when all North American airliners were grounded. The lack of contrails - which are mostly white water vapor - caused a noticable increase in temperatures throughout the USA.)

But either way, it's crazy to imagine that we could build dehumidifiers on a large enough scale to make any impact without burning so much energy to drive them that our net carbon footprint would go through the roof!

So "No" for a couple of reasons. SteveBaker (talk) 05:40, 25 November 2009 (UTC)

If you could then you could water the entire Sahara with the water taken out of the atmosphere...--BozMo talk 07:10, 25 November 2009 (UTC)

Also, don't dehumidifiers generate a lot of heat in their operation? I suspect the heat generated would be more than the heat allowed to escape into space by the reduced water vapour in the air, even without factoring in the albedo effects. --Tango (talk) 23:32, 25 November 2009 (UTC)

Unlike other greenhouse gasses, water vapor is fairly self-regulating: on average, the atmosphere is fairly close to saturation, so any increase in evaporation will be countered by an increase in rainfall. --Carnildo (talk) 02:02, 26 November 2009 (UTC)

The Thermohaline circulation means that there is naturally, on average, more water vapour in some places than in others. So taking vapour out of the atmosphere could result in more or less heat in some areas, resulting in storms, displaced quasi-stationary highs and lows, wind patterns...and ultimately the Thermohaline itself. But this is mostly speculation. ~AH1^(TCU) 02:17, 2 December 2009 (UTC)

do blue tulips occur in nature?

Tulipa sylvestris

do blue tulips occur in nature?

Define "natural". Tulips are a highly cultivated genus of plants, see tulip. Like maize and other highly cultivated plants, it is doubtful if you have ever seen a truly "wild" tulip before (you may have seen feral tulips, but that is different than a truly wild species). There is apparently a variety called "Tulipa sylvestris" which is known as the "wild" tulip; however we have no article on this, so I have no reference for what "natural" tulips look like. --Jayron32 05:34, 25 November 2009 (UTC)

Type "Tulipa sylvestris" into Google Images and you'll be greeted by a ton of bright yellow flowers with petals that are much more open than the classical idea of what a Tulip should be. So, no - no blue tulips in the wild...or red ones, or orange ones...just yellow. SteveBaker (talk) 05:55, 25 November 2009 (UTC)

Photoshop trumps nature. Cuddlyable3 (talk) 08:20, 25 November 2009 (UTC)

Eeew!! Are you certain about that? ;-)) Richard Avery (talk) 08:33, 25 November 2009 (UTC)

There are a few cultivars that approach blue: for example 'Blue Parrot', seen here [11]. As for naturally occuring species (about 150 [12] ), I don't think there are any blue species, although there are certainly purplish species. --Eriastrum (talk) 00:08, 26 November 2009 (UTC)

North Sea gas

In The Death of Regginald Perrin by David Nobbs, Jimmy attempts suicide by putting his head in the oven, and Reggie laughs at his ineptitude: "North Sea gas isn't poisonous." I thought this was either a bizarre blunder by the author, or exceedingly obscure humor. But now I'm reading a story by P. D. James in which a murder attempt fails: "The conversion, that's why. We're on natural gas from this evening. That North Sea stuff. It isn't poisonous. The two men from the Gas Board came just after nine o'clock."

What the heck do they pump out of the North Sea? Hydrogen? —Tamfang (talk) 05:28, 25 November 2009 (UTC)

North Sea Gas (aka "Natural" gas) is mostly Methane - which isn't poisonous. If the air gets too full of the stuff - it would eventually displace all of the oxygen and you'd suffocate - but that's not really likely from a gas oven. The biggest concern would be explosions. The old "Coal Gas" or "Town Gas" that was used in the UK before the North Sea oil boom was a mixture of hydrogen, methane and carbon monoxide. The carbon monoxide would kill you pretty quickly. I'm pretty sure the UK was in that transition period right when Reggie Perrin was imagining his mother in law as a hippo - so it's perhaps understandable that someone would still attempt suicide that way if they didn't know any better. Maybe the advertising of the benefits of the new gas was highly prevalent at the time the series was made - so perhaps the implication was that the guy who was attempting this was an idiot for not knowing about that. SteveBaker (talk) 05:50, 25 November 2009 (UTC)

For the record, natural gas is not a term that applies just to "North Sea Gas" — reading through the article, "natural gas" appears to be a super-generalization, describing many variants. Comet Tuttle (talk) 19:02, 25 November 2009 (UTC)

I was an accident investigator for Shell when Tokyo switched. Funnily the pattern of failed suicides (booze, oven, wake up with headache) was sometimes followed by lighting a cigarette and starting a non fatal gas explosion. When I left they were looking at smart meters to contact the police for suspected suicide. It is similar to using car exhaust to kill yourself when you have a Cat Converter on the car. --BozMo talk 07:03, 25 November 2009 (UTC)

Oh, there goes that plan. Thanks, all, for the clarification. —Tamfang (talk) 07:07, 25 November 2009 (UTC)

At the time of the changeover there was a lot of public debate over North Sea gas being odourless. I believe something is added to it to give it a human detectable odour but it is very mild compared to the strongly sulfurous smell of the old coal gas and this led to some public concern. It was a stock response from industry and government spokesmen that there was no need to do anything about this because the gas is not poisonous. The issue was therefore likely to be in people's minds at the time and they would have got the joke. SpinningSpark 12:23, 25 November 2009 (UTC)

Seriously? "Not poisonous" is not much comfort when your house goes up like a bomb. Was there an uptick in explosions corresponding to the downtick in poisonings? --Trovatore (talk) 18:15, 25 November 2009 (UTC)

I doubt that - if someone dies from carbon monoxide poisoning with their head in a gas oven - they are unlikely to turn it off afterwards! Hence, probably, the number of explosions would be pretty similar. But once people knew that this was not a viable suicide technique - the rate of explosions due to that ought to have dropped substantially. SteveBaker (talk) 23:01, 25 November 2009 (UTC)

Do they not use Butanethiol in the UK? --Jmeden2000 (talk) 16:04, 25 November 2009 (UTC)

Yes, I think that's what is used, and I know it is a very nasty chemical in high concentrations. But it is used in tiny quantities and definitely does not smell anywhere near as repulsive as coal gas. One whiff of that had us immediately opening all the windows to dispel it. Natural gas simply does not cause that same reaction in people. At least, with the additives used in Britain, I could not speak for elsewhere. SpinningSpark 17:35, 25 November 2009 (UTC)

[This] link claims the UK smell is due to a blend of mercaptans and sulphides. But a trace of any thiol is going to smell enough to detect. I would suspect a blend is used so that the gas detector vans can check the ratio of the odourants and confirm a gas leak - it might be that a nearby plant could be using one of the components, but the ratio in the detector would then be different. LPG uses ethanethiol to make it smell - I think the butanethiol is too high boiling here - it would tend to concentrate towards the end of the bottle - I know that the ethanthiol has a small tendency to do that - and I can tell (on the boat) when the bottle is starting to get low by the smell of the cooker.  Ronhjones  ^(Talk) 19:35, 25 November 2009 (UTC)

Someone should really move that article to butyl mercaptan in accordance with WP:COMMONNAME. In my opinion the chemistry editors are overly respectful of IUPAC's silly nomenclature. But I'm not a chemist so I won't do it myself. --Trovatore (talk) 18:12, 25 November 2009 (UTC)

See a full account in Kreitman, Norman (1976). "The coal gas story. United Kingdom suicide rates, 1960-71". Br J Prev Soc Med. 30 (2): 86–93.. Fences&Windows 18:02, 25 November 2009 (UTC)

overies

wat happens if the size of overies s larger??? —Preceding unsigned comment added by Shilpa.upadhya (talk • contribs) 07:37, 25 November 2009 (UTC)

A common cause of swollen ovaries is a cyst or PCOS. We have an article about PCOS[13] and there is more information on the web.Cuddlyable3 (talk) 08:14, 25 November 2009 (UTC)

Balancing chemical equations

Is there any real, concrete method for balancing chemical equations? If not, can anyone offer any advice or tips? Thank you. —Preceding unsigned comment added by 161.165.196.84 (talk) 08:51, 25 November 2009 (UTC)

There must be such methods, because automatic equation balancers exist, e.g. http://www.webqc.org/balance.php.

Does Chemical equation#Balancing chemical equations help?

A good tip is to start by balancing one particular element (i.e. making sure there are equal numbers of the chosen element on both sides of the equation) and then putting in enough of the other elements to make the required product.

Ben (talk) 11:54, 25 November 2009 (UTC)

Chemical equations can be written as simultaneous equations requiring integer solutions. Written in that form, any linear equation solver like Gaussian elimination or linear programming, or a complicated optimization method, can be applied. Finally, for convenience, the result is usually reduced by dividing out any common integer factors, if the solution method doesn't already take care of this. Nimur (talk) 13:34, 25 November 2009 (UTC)

The best tip I give my students is that, if done correctly, the last element always balances itself; so if there is some element which is complicating the solution because it appears in multiple compounds on each side of the equation (oxygen does this often), leave THAT element till last, and it will work itself out. Additionally, some equations may seem to never balance; my suggestion in these cases is to consider using fractional coefficients and then multiply out to get rid of the fractions. Just a few tips. --Jayron32 04:28, 26 November 2009 (UTC)

How does an increased heart-rate stimulate the body's metabolism?

Obviously, excersise raises one's metabolism (although scientifically speaking, I'm not sure why), but how does just having an increased heart-rate (perhaps by consuming caffiene)stimulate the metabolism? Thank you.161.165.196.84 (talk) 09:27, 25 November 2009 (UTC)

(For the impact of exercise on the body, see Exercise physiology.) I don't know the actual biochemistry involved, but by definition, the energy used by the heart would increase if its output were to increase. Zain Ebrahim (talk) 14:09, 25 November 2009 (UTC)

I think we need to start by asking whether the body's metabolism is stimulated by increased heart rate. There are many ways to increase the heart rate, and many of those could affect metabolism in ways that don't directly involve the heart. One way to separate the effects would be to use an implanted cardiac pacemaker to increase the heart rate directly. Speeding up the heart above normal rate using a pacemaker is called ventricular overdrive pacing redlink!, and is used diagnostically and therapeutically in tachycardia. I haven't found a reliable source for this (yet), but my own experience suggests that metabolism is not globally increased during this maneuver. It is clear that cardiac metabolism is increased (PMID 8261221), as Zain has pointed out. -- Scray (talk) 14:24, 25 November 2009 (UTC)

exercising raises one's metabolism for that particular part of the body exercised, there is increase of heart rate and respiratory rate (by both neurological and hormonal activation), with corresponding increase in metabolic activity in terms of cardiac muscle as well as the respiratory muscles. while doing exercise, organic acids and products of anaerobic respiration such as lactic acid will be released into circulation, and these will be metabolised by the liver, and this would lead to increase in metabolic rate in liver as well. bubu~ (talk) 15:29, 25 November 2009 (UTC)

It is also possible for certain individuals to regulate their own heartrate through techniques. But please do not try this at home. ~AH1^(TCU) 02:11, 2 December 2009 (UTC)

Freezing contents of deeply chilled liquid.

What happens to a deeply chilled, but unfrozen drink; that in the few seconds,usually a bottle container, is opened, the liquid freezes immediately? In the many discussions held about this phenomenon, none could come up with a convincing answer. Some tried to say that when the oxygen enters the bottle container, it makes the liquid to freeze. It was not convincing since the oxygen entering the top of the bottle is warmer than the inside of the bottle. Please help41.17.171.15 (talk) 12:00, 25 November 2009 (UTC)

The liquid has been supercooled but freezing will not start unless there are small particles present that allow nucleation to begin. Opening the bottle releases bubbles which provoke the nucleation process. SpinningSpark 12:07, 25 November 2009 (UTC)

It could be that, or it could be that the phase diagram of water indicates that there is an inverse relationship between pressure and phase for water; that is water under higher pressure tends to be more likely to be a liquid, and it actually freezes as the pressure decreases. Additionally, the released gas can cause adiabatic cooling in the liquid (open a can of soda, its temperature will drop slighlty but measurably as the bubbles are released). I think it is some combination of these three effects; though I think that Spinningsparks answer on supercooling is likely the dominant effect here, the other two effects may play some role as well. --Jayron32 04:24, 26 November 2009 (UTC)

Finding power factor

Suppose I find the time delay between the voltage and current waveforms and divide that by the time period of half a cycle. Then subtracting it from 1, won't that give me the power factor? If not, please suggest how to. I want to avoid finding out phasor angular difference. 218.248.80.112 (talk) 14:18, 25 November 2009 (UTC)

The time delay to the crest of the current sine wrt the crest of the voltage sine is only part of the power factor calculation (namely the leading/lagging portion) you still need to know the total power drawn vs the peak of the current sine (apparent power) to figure out what the number should be. If the current sine is perfectly identical to the voltage sine this might be a simple process (mathematically) if not you will need to perform some advanced calculations. Hope this helps! --Jmeden2000 (talk) 15:56, 25 November 2009 (UTC)

What Jmeden2000 is alluding to is that the power factor may vary if your current and voltage waveforms aren't perfect sinusoids. If they are not, then all bets are off, and simple power-factor formulae are useless - you will need to perform a full integral over the waveforms, $\int V(t)I(t)dt$.

In any case, your approach will yield:

$PF\approx 1-\Delta t\times 2/T$

This is approximately, but not exactly equal, to $\cos(\phi )$ (the correct value of the power factor), for sufficiently small $\phi$ and perfect sinusoids. I think you're missing a factor of pi, too. You probably meant:

$PF\approx 1-2\pi \Delta t/T$

...which is sort of like a first-order taylor series approximation of a cosine. (But not a correct one).

The degree of applicability of this engineering approximation will depend on your application's precision needs. I can't think of any engineering application today where this approximation would be useful, because calculating the true phase difference and computing its cosine is trivial on even the most reduced forms of computers, microcontrollers, or even analog signal conditioners. Nimur (talk) 17:41, 25 November 2009 (UTC)

After re-reading your question, it sounds like you just want to avoid using phasors. That's fine - but your approach has already calculated the angular difference in the time-domain (without using phasors): $\phi =2\pi \Delta t/T$. Is there any reason you don't want to use cosine? Nimur (talk) 18:01, 25 November 2009 (UTC)

I had to skip all those integrations and all because I am implementing this on an 8051 microcontroller which does not have any floating point capability and only 8bit math. So that was also the reason of not producing the cosine.. I think I will extend this project to simple power factor improvement (like connecting a capacitor through relay for low power angle) and protection (cutting of the circuit for very low power angle). Any suggestions ? And btw thanks for the analysis.. 218.248.80.112 (talk) 09:50, 26 November 2009 (UTC)

Fixed point math throws some kinks in to things, but you can still compute cosine with a lookup table. But, if your only actions are to throw a relay or two, you may as well just solve for the phase difference that you want to use as trigger points (instead of power factor). You might also want to be aware that simply throwing a relay to change the circuit may result in a phase oscillation - for example, you may be right on the edge of an acceptable phase error, throw the relay, and then fall just on the other side, un-trigger the relay... in other words, unless you analyze the closed loop circuit, including your software logic, you may have created an unstable circuit. The correct way to design such a power factor correction circuit is a little bit more complicated. For example, take a look at Fairchild Semiconductor's Application Note AN-42047 - Power Factor Correction Basics. They detail the theory and practice of PFC circuits, and pitch some of their products that do this for you. Nimur (talk) 15:12, 26 November 2009 (UTC)

Certainly you could use a lookup table for cosine - and if you need higher precision and/or are too limited on memory to get the precision you desire then you can dramatically improve the results by doing a simple linear interpolation of two consecutive table entries. SteveBaker (talk) 17:33, 26 November 2009 (UTC)

Ionic food preserver

Does anyone have any idea how this "ionic preserver" works to prevent mould growth, banana pigmentation, and the various other food spoilages that they are claiming? I searched Google but couldn't find a thing. The only clue from the food preservation article is nitrites and sulphites, but surely the device would run out of them eventually and there is no mention of a plug-in pack or the like. --Mark PEA (talk) 17:02, 25 November 2009 (UTC)

Ionising air will produce ozone. The Wikipedia article on ozone says it can be used as a disinfectant for killing bacteria on food and to kill mold spores. I'm not sure if this is the specific mechanism for the "ionic preserver", or if the preserver would produce a sufficient concentration of ozone to do anything.

Here is a scientific paper saying that negative ions preserve lettuce; they seem to reduce water loss (which would cause drying). --Maltelauridsbrigge (talk) 17:26, 25 November 2009 (UTC)

Ozone reduces the ripening of bananas by reacting with, and hence eliminating, ethylene which is the chemical that causes bananas to ripen.[14][15][16]

Air ioniser and Air_purifier#Air_ionizers_and_ozone will tell you more about this idea in general, but not this specific product. The idea has been around since at least the 1950s.[17] Negative ions and ozone may restrict the growth of microorganisms.[18] Here's a study of the use of an ionizer in a domestic fridge that says it is effective:[19] Fences&Windows 17:51, 25 November 2009 (UTC)

Okay, so basically it is 3O₂ -> 2O₃. Aerobes don't proliferate, cheese doesn't dry out, etc. I do wonder about the safety of the product though, I'm guessing there aren't any longitudinal studies looking at respiratory diseases of those who have these in their fridge. --Mark PEA (talk) 18:35, 25 November 2009 (UTC)

It's a UK advert - which is good, because it will have to tell the truth (or the ASA will jump on them like a ton of bricks) - it's main claim as I see it is "it reduces the damaging gases involved in food decay" - I would guess that it will keep down the concentration of ethylene, that would slow down any ripening process, and if the food doesn't over-ripen, it won't go bad so fast.  Ronhjones  ^(Talk) 00:45, 26 November 2009 (UTC)

Ozone is a strong oxidiser and will cleave unsaturated compounds by ozonolysis. Ozone will react with ethylene (possibly into formaldehyde units) cuz of the unsaturated pi bond. The side effect of applying ozone for too long I think is rancidification. John Riemann Soong (talk) 13:03, 26 November 2009 (UTC)

This just reminded me of an A-level chemistry lecture I had a couple of years ago. Paintings discolour overtime due to UV light homolysing O₂ in the atmosphere, leading to O₃ and subsequent ozonolysis of the unsaturated glycerides in the paint. --Mark PEA (talk) 17:40, 27 November 2009 (UTC)