Wikipedia:Reference desk/Archives/Science/2008 April 24

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

April 24

any botanists here?

Our Rosette (botany) article sucks. Can someone (a) fix the wording (especially the confused second sentence), and (b) suggest some other common examples? (I'll be glad to try to take some more pictures. At the very least I'll have to try to take a better picture of a dandelion.) —Steve Summit (talk) 00:33, 24 April 2008 (UTC)

Hi Steve, after seeing your note I expanded the article. From this[1] it looks like succulents come into it in some way. Since they're lumped under "borderline" cases you might need to check it. What's wrong with the dandelion pic? Maybe a cross section would be nice. Julia Rossi (talk) 03:41, 24 April 2008 (UTC)

Thanks! But (not to sound like a schoolmarm grading your work, I hope) this sentence:

Often, perennial plants whose foliage dies and the remaining vegetation protects the plant.

is still not a sentence, and this sentence:

This is an example of a modified stem.

has what my schoolmarm always used to call a Vague Pronoun Reference, i.e., what does the 'This' refer to?

The picture is small and fuzzy, and you can't really tell what's going on; you can barely tell it's a dandelion, and it's not obvious what the "rosette" form is. I'll try to take a better one. (Lord knows, I've got plenty of subjects!) —Steve Summit (talk) 03:50, 24 April 2008 (UTC)

Yeah I was working on it, so you need to peek again and fix anything funny. Ha. I'm in a dandelion kingdom too. : ) Julia Rossi (talk) 03:58, 24 April 2008 (UTC)

Okay, I've got the wording mostly fixed up. One more question: what is it that's explained in the second paragraph under "Form"? —Steve Summit (talk) 04:20, 24 April 2008 (UTC)

Form : takes in the structure, relationship of the parts and variations within it throug examples. I've never collab'ed with anyone before this is fun. Julia Rossi (talk) 04:41, 24 April 2008 (UTC)

I went and monkeyed with it. I took out Paris quadrifolia because it has a whorl, not a rosette. There was some odd cut-and-paste detritus that I tried to sort out with me knowing approximately jack about plants. I can't believe a fern belongs here. If I remember my high-school biology, and I sincerely doubt it, ferns don't even have leaves. --Milkbreath (talk) 10:49, 24 April 2008 (UTC)

Hi Milkbreath, be gentle with the little article and put that bushknife down. As it happens, ferns do have leaves see[2] for the difference between the word "frond", "leaf" and the historical background. The ref for the fern also uses rosette for its structure. High school biology is very much subject to ideas in the section "Buffer for speech" above. In the article whorl it also applies as a less technical, alternative description of rosette. not – In some examples I got there was a diff between the rosette and leaves that grew higher on the stem. So when you say you know "jack" and monkeyed with it, is that helping? Julia Rossi (talk) 11:17, 24 April 2008 (UTC)

I'm exaggerating my ignorance out of humility, I hope. I'm a fast study, and I poked around a bit yesterday before giving up and praying for a real botanist. Are you indeed a botanist? I'm impressed. If so, I'll sheathe my machete until the facts are sorted out, at which time I'll timidly knock and humbly beg to be allowed to take a tiny snip here and there with my little pruners in your dreams. If not, stay a few steps behind me till I've cleared a path. --Milkbreath (talk) 11:49, 24 April 2008 (UTC)

In flinging my body across the fern bit so hope didn't squash it, or you. I knocked the article together after SirSummit's plea so it's hardly seamless as yet. Botanist? More like horticulture drop-out. Bush hats all around, your turn -- Julia Rossi (talk) 11:57, 24 April 2008 (UTC)

I've hacked a clearing into the article talk page where we can sit and sort this out over tea like the civilized people we all strive to be, especially the strivers. Thanks for the hat. --Milkbreath (talk) 12:13, 24 April 2008 (UTC)

I'm being humble too because early on, SirSummit called me a botany goddess and I forgot. Make mine Lady Grey black no sugar. Striving is all – collabaway, m'man.  ; ) Julia Rossi (talk) 12:45, 24 April 2008 (UTC)

Impacts, Ballistics, and Mass.

I am trying to ascertain the size and magnitude of damage a 'Orbital Weapons Platform', falling from orbit, would cause in terms of craters, etc. Given the object has roughly the mass of a big avg. city bus, possibly 50-100% denser, whatever is feasible, it's a hypothetical modern-era object that fell from orbit, I'm sure there is some natural curve for velocity here, it obviously couldn't be moving the speed of a comet or some-such. How high would the impact crater walls be? Is it feasible it has rutted up a trench in it's wake, on say a moderately shallow trajectory? Would any of it actually survive? It's a tough military-grade object. —Preceding unsigned comment added by 68.221.126.35 (talk) 00:38, 24 April 2008 (UTC)

Here's a start: Impact depth. As to how large the impacting object would actually be after travelling through the atmosphere: depends. Franamax (talk) 01:18, 24 April 2008 (UTC)

Not sure how to respond in this area. That helped some, I just don't have the math background to really comprehend the outcome. Some advice in that regard would help greatly. —Preceding unsigned comment added by IamSamoth (talk • contribs) 02:28, 24 April 2008 (UTC)

I'd ballpark it as approximately a Skylab-type impact. Pieces survive, but there's no crater to speak of. An orbital weapons platform is not a single monolithic hunk of metal, and is not designed for re-entry, so expecting it not to break up while falling is unreasonable. — Lomn 02:49, 24 April 2008 (UTC)

You might enjoy our Kinetic bombardment article (which includes the concept of "Rods from God").

Atlant (talk) 12:48, 24 April 2008 (UTC)

Hi. As for the impact, the Asteroid impact simulator from LPL Arizona may be helpful, but it is more accurate in depicting asteroid and comet collisions. Thanks. ~AH1^(TCU) 00:57, 25 April 2008 (UTC)

Atmospheric_reentry#Uncontrolled_and_unprotected_reentries has a picture of MIR breaking up and burning up on its way down. Too bad they put it into the Pacific, but luckily for us, Skylab hit Australia. It says "Of satellites that reenter, approximately 10-40% of the mass of the object is likely to reach the surface of the Earth." If you want your space thingie to be more robust than the average satellite, you might bump that to, oh, 50 to 80 percent. Earth_orbit#Geocentric_orbit_types shows an orbital speed of 8 km/s for low orbit, so that's your initial speed. Reentry capsule shows an impact speed of "over 300 mph" for a Soyuz 1 capsule whose chutes failed to open. This is roughly the speed of a rather slow-moving airplane, so you can get some idea of the ground deformation you might expect when it hits. Impact crater deals with high-speed collisions, much, much faster than you get with falling man-made junk, so the crater made by junk would not be round like the crater made by space objects. A low angle combined with sloping ground could easily produce a furrow. --Milkbreath (talk) 01:39, 25 April 2008 (UTC)

Wow! Thanks all! Great info, awesome calulator! :) TYVM! —Preceding unsigned comment added by IamSamoth (talk • contribs) 13:25, 26 April 2008 (UTC)

JSTOR access

Any eggheads here with a JSTOR subscription? Help is needed here. Franamax (talk) 00:54, 24 April 2008 (UTC)

This has been done by Someguy1221, thanks Someguy, double-plus-good of you.

A general note here, are people aware of Wikipedia:WikiProject Resource Exchange where you can ask for subscription-only content from volunteers? I'd encourage anyone with such access to list there. Thanks! Franamax (talk) 04:04, 24 April 2008 (UTC)

It occurs to me that page could be much better advertised than it is, considering the relative dearth of posts there. Someguy1221 (talk) 04:22, 24 April 2008 (UTC)

Thanks - it's now in my notebook. Julia Rossi (talk) 04:58, 24 April 2008 (UTC)

I'm actually stunned by my discovery of that project. So many times, I've chased a lead, only to end up at a "subscription needed" roadblock. It should be way more well known. Any ideas on how to publicize it, to get volunteers and requesters, are welcome. I've started out at WikiProject Science. Franamax (talk) 05:35, 24 April 2008 (UTC)

Even slipping it into relevant moments for the compelled-to-lookup refdeskers, or at stumped talk pages would make a difference. It did to me, Julia Rossi (talk) 05:48, 24 April 2008 (UTC)

Evolution

Who coined the term "evolution" (I suspect it was either Lamarck or Darwin, but I'm not sure)? BeefJeaunt (talk) 01:32, 24 April 2008 (UTC)

Keep in mind that the definition of "evolution" applies to much more than the evolution of the species. According to Merriam-Webster, the term originated in english in 1622, from Latin. Another question might be, "Who was the first to use the term 'Evolution' in its biological context?" You may find History of evolutionary thought interesting. Someguy1221 (talk) 04:01, 24 April 2008 (UTC)

Though used in early Greek thought, this[3] cites Albrecht von Haller (1708-1777), "coiner of the word 'evolution' in biology", and refers to Wikipedia. (Though I wouldn't put it past von Haller, couldn't find it in the tl article.) Julia Rossi (talk) 04:23, 24 April 2008 (UTC)

Another peek shows his backup: "It was coined in 1744 as a biological term by the Swiss biologist Albrecht von Haller (1708-1777), to describe the preformationist theory that embryos grew from homunculi enclosed in the egg or sperm (Gould, 1977, pp.28-29, 1978, p.34). "Evolution" in this sense meant the progressive unfolding of structures that were already present in a prepackaged form (Bowler, 1989, p.9; Jaki, 1988, p.189)." In case you're working on the article Evolution (term) -- Julia Rossi (talk) 04:36, 24 April 2008 (UTC)

It's worth noting that Lamarck referred to his theory as transmutation, whereas Darwin only uses the word once—as a verb, at that—in the entirety of Origin of Species, and that's the very last word of the book ("There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved."). The term would have been, however, quite familiar to Darwin's public by the time he was writing Origin of Species, as it was used in precisely this way all throughout Vestiges of the Natural History of Creation, which was an immensely popular pre-Darwinian book describing something akin to biological evolution (taking its cue from stellar evolution—"We see a gradual evolution of high from low, of complicated from simple, of special from general, all in unvarying order, and therefore all natural, although all of divine ordination"). --Captain Ref Desk (talk) 13:58, 24 April 2008 (UTC)

Nitro

What is the cost of nitrogen in it's gas state? —Preceding unsigned comment added by 76.14.124.175 (talk) 04:45, 24 April 2008 (UTC)

Try this link [4]. Wisdom89 _{(T / ^C)} 04:50, 24 April 2008 (UTC)

This might be useful to you too [5]. Wisdom89 _{(T / ^C)} 04:51, 24 April 2008 (UTC)

(e.c X 2) $33 (AUD) for 'High Purity' in a size G from BOC plus cylinder rental, I think this is a bulk price though..--Shniken1 (talk) 04:54, 24 April 2008 (UTC)

Gaseous nitrogen is available very cheaply as long as you don't mind it being mixed with 20% oxygen and various other trace impurities. Gandalf61 (talk) 09:30, 24 April 2008 (UTC)

:-) StuRat (talk) 01:06, 25 April 2008 (UTC)

Gecko and Spiders (Melbourne, Australia)

What species am I? (flickr)
Black line = 10mm.

I'm wonder what species this gecko I found in my mailbox is.

Also there's a bunch of spiders I've taken photos of with poor or minimal IDs. Anyone want to have a go at giving an ID? This Spiders of Australia site is quite good, but I've given up. (link) —Pengo 05:04, 24 April 2008 (UTC)

This [6] little fellow seems to match the photo and the habitat. Richard Avery (talk) 17:47, 24 April 2008 (UTC)

Name of anticipatory effect in experiments?

Does anyone know what the proper term is for the effect where subjects try and anticipate the results the experimenter is trying to achieve, and respond accordingly? There's a specific term I'm thinking of, but I can't quite remember it. All suggestions welcome... thanks --131.111.135.84 (talk) 06:10, 24 April 2008 (UTC)

Subject-expectancy effect? — Kieff | Talk 06:24, 24 April 2008 (UTC)

That's it - and not sure how I missed it in the first place. Thanks! --131.111.135.84 (talk) 09:49, 24 April 2008 (UTC)

Sometimes known as demand characteristics and also see Hawthorne effect. --Mark PEA (talk) 15:50, 24 April 2008 (UTC)

Variegation in wild pigeon populations

I live on the 20th floor of an apartment complex in the centre of Sydney and feed various birds from my balcony, including lorikeets and pigeons (even though the feeding of pigeons is frowned upon). The lorikeets are very beautiful, feisty, and demanding, but are picky eaters. Nevertheless, I feed as many as I can to encourage them to live in the city. The pigeons will eat any old bread or seed, but they are numerous, and I only feed “special” ones which have particularly striking plumage, or are especially friendly. Every day, I see a large flock of these pigeons—many of them my own visitors—hanging about the park outside the complex, and being fed by residents and passers-by. I am no pigeon fancier, but I have noticed that our local flock seem to have a much wider variety of plumages on show than flocks in other areas. Hardly two birds look alike, and several have stunning red and white necks that made me think at first that they must be products of some interspecies mating. This is very different to other flocks I have seen in which the great bulk of their constituents could be clones.

Typically, in many other areas, people indiscriminately throw breadcrumbs at a seething mass of birds in a park, but in my local situation, residents can only feed a few birds at a time from their small balconies, and inevitably favour the prettier and more affectionate ones. I got the idea that perhaps the feeding patterns of the area had contributed to this variability. As this pattern of feeding has been going on for at least 40 years, I am wondering if there has been a form of selection pressure that has led to larger than normal variability in plumage patterns and colourings, and whether anything like this occurs in other pigeon groupings in comparable circumstances. Myles325a (talk) 07:47, 24 April 2008 (UTC)

Your observations are very interesting, although I could make no guess as to how valid they are. All I can say is there are many varieties of pigeons, as they have been domesticated for many centuries. The first chapter of Darwin's Origin of Species is largely dedicated to them, as examples of non-natural selection. Thanks for sharing. —Pengo 11:02, 24 April 2008 (UTC)

Yeah, it's hard to say. I would never underestimate the power of evolution to surprise; plus recently scientists have been observing more instances of short-term evolution. So, I'd say it's possible that feeding patterns have affected the plumage phenotypes of the local flock, but very difficult to say for sure. --Bmk (talk) 13:50, 24 April 2008 (UTC)

See Heike crab for another interesting example of unintentional artificial selection. StuRat (talk) 00:51, 25 April 2008 (UTC)

Aircraft noise

I live about 5 miles from a major airport. I've sometimes heard an echoing sort of aircraft noise that drops very rapidly in pitch from very high to very low in just three or four seconds, from silence into silence. I'm sure it's nothing to do with the Doppler effect as it happens so quickly and the sound is not overhead. I have come up with a theory based on the fact that (1) I live on a hillside (2) now that I come to think about it, I associate the sound with overcast weather conditions. Could it be that a sound wave is oscillating between the ground and the cloud base, and because this distance rapidly becomes greater as the aircraft moves "downhill", the frequency suddenly drops? Is the cloud base substantial enough to reflect this sound wave?--Shantavira|^{feed me} 08:26, 24 April 2008 (UTC)

Weather conditions may make the sound more audible, but I think the rapid change in frequency is more likley to be due to changes in the aircrafts' thrust during their climb or descent phase, rather than any more complex explanation. Gandalf61 (talk) 08:41, 24 April 2008 (UTC)

I agree but gusting etc is also possible. You are proposing some sort of waveguide I think but I doubt the density difference moving from air to cloud is enough set one up. A cloud base (or temperature inversion) will reflect some sound but not enough to set up a standing oscillation I think. Also the frequency of audible sound is too high compared to the distances. --BozMo talk 09:09, 24 April 2008 (UTC)

Could you maybe be confusing the engines with the hydraulics? It could just be the hydraulics lowering the flaps.Luxosus (talk) 13:43, 24 April 2008 (UTC)

It seems quite unlikely that you'd hear hydraulics operating from that distance. — Lomn 15:07, 24 April 2008 (UTC)

Is the sound anything at all like an indecisive whistle (ie, with no clear association in terms of meaning connected to familiar whistle signals)? If you could somehow record this, I'm sure it would be quickly identified. Any further description of the sound would also help. 81.93.102.185 (talk) 17:14, 24 April 2008 (UTC)

You could be hearing the thrust reversers or spoilers activating on landing: they both change pitch and volume rapidly as the airplane slows down. --Carnildo (talk) 20:16, 24 April 2008 (UTC)

Annealing of Copper CuSn6

What is the procedure of annealing Copper CuSn6? Including at what temparature to heat how long and what temparature to cool and through what period of time? —Preceding unsigned comment added by 122.166.11.179 (talk) 11:01, 24 April 2008 (UTC)

Annealing (metallurgy) may be able to help you. Stifle (talk) 13:15, 24 April 2008 (UTC)

Speed of Tennis

The game of tennis can be played on different surfaces. The news often mentions that a grass surface is "faster" than a clay surface. What is meant by "faster" in this context? Astronaut (talk) 11:59, 24 April 2008 (UTC)

"Faster" here means that the ball loses less energy when contacting the ground, allowing it to move faster. Only applicable after a bounce, obviously. This similarly affects how quickly the players are able to move about the court. — Lomn 12:58, 24 April 2008 (UTC)

Grass also bounces much less, so the ball seems to come onto the player faster. Luxosus (talk) 13:46, 24 April 2008 (UTC)

As a tennis player, the term "faster" means how quickly the ball goes from side to the other, and how its trajectory is affected by the court (after the bounce). For example, clay courts are considered the "slowest" courts because the loose clay takes any spin from the ball and emphasises it; a topspin ball will bounce higher and further on clay than on a "hard-court" or grass. Grass, alternately, is the "fastest" because of the tendency of the ball to skid on the surface when it makes contact, making the trajectory more horizontally locked. Hard courts are the middle-ground, though even at the high-school level a easily discernable difference is commonplace depending on the roughness of the courts, the specific materials the court is made of, and the weather conditions. From what Lomn said, I shall digress. Each court has its own pace, but different players move better on different services. For example, current world #2 Raphael Nadal is the best mover on clay, while world #1 Roger Federer is the best mover on grass. It all depends on the style of movement the player utilizes. Though, I will give you the benefit of the doubt for that argument, since sliding is much easier to do on clay courts, and allows you to get to shots you otherwise wouldn't have gotten to.

Also, any court is subject to "speed" changes due to weather. Clay courts become faster when dry, grass courts slow down when dry. Hard courts are just a pain to play on when wet.

Hope I helped. —Preceding unsigned comment added by EWHS (talk • contribs) 16:26, 26 April 2008 (UTC)

polar molecular solids

the force of interaction in polar solid is that of a dipole-dipole interaction which is strong and thus they have a high melting point.yet they are in the form of gases or liquids in room temperature?why? —Preceding unsigned comment added by Arya237 (talk • contribs) 16:22, 24 April 2008 (UTC)

Everything is relative. The general patterns you mention only hold if all other properties are equivalent. And "room temperature" is an arbitrary cutoff you have chosen. Dipolar interactions are strong, but weaker than ionic interactions, and heavier molecules tend to have higher mp/bp. To see a specific trend, one must pick molecules that minimize other trends (i.e., compare tert-butanol and neopentane). The trend even holds for things that "are in the form of gases or liquids (at) room temperature", except that again it's the relative effect (the interaction makes the mp higher than it would be in the absence of that interaction): compare water and dimethyl ether and propane. DMacks (talk) 18:03, 24 April 2008 (UTC)

Insolubility of Sulphur in water.

Common salt and Sugar are soluble in water while Sulphur is not.Why Sulphur is insoluble in water?Explain. —Preceding unsigned comment added by Geniuskrishna (talk • contribs) 17:09, 24 April 2008 (UTC)

You may find the solubility and chemical polarity articles helpful. Note that sulfur is a pure element; salt is an ionic compound and sugar is can form hydrogen bonds; pure sulfur has neither of these features and so it does not readily dissolve in water. Nimur (talk) 17:28, 24 April 2008 (UTC)

Heart monitors -- what do they mean?

Can someone explain the symbols found on a heart monitor -- such as ECG, HR, PR, SpO2, Oxy CRG, ST, RESP, NIBP? --70.167.58.6 (talk) 17:30, 24 April 2008 (UTC)

That's the trouble with buying on e-bay there's never a users manual. Richard Avery (talk) 17:43, 24 April 2008 (UTC)

Here is what I know-

• Electrocardiogram (ECG)
• Heart rate (HR)
• Pulse rate (PR) (I am not an expert, but I think this is identical to heart-rate - it may be probed from elsewhere on the patient such as a finger-tip sensor).
• SpO2 (Oxygen saturation in blood)
• Cardiorespirogram (Oxy CRG) - combined ECG and breathing-rate chart
• ST segment of the healthy electrocardiogram signal output. See this diagram or the waves section of the ECG article.
• Respiratory rate (RESP)
• Non-invasive blood pressure monitor (NIBP)

Hope this helps, Nimur (talk) 17:51, 24 April 2008 (UTC)

Thanks! Really helpful! What entry should all these abbreviations be in? --70.167.58.6 (talk) 20:46, 24 April 2008 (UTC)

Some of them should be in List of acronyms and initialisms, but they aren't. I looked for "ECG", for instance, and it wasn't there. I'll put it in now. --Milkbreath (talk) 21:19, 24 April 2008 (UTC)

You may be looking for this :) Regards, CycloneNimrod^Talk? 22:23, 24 April 2008 (UTC)

Doh! (But some should be in both places.) --Milkbreath (talk) 23:14, 24 April 2008 (UTC)

Note also that ECG is sometimes written EKG, from the German language spelling. Nimur (talk) 05:35, 25 April 2008 (UTC)

I've only heard it called an EKG....--Shniken1 (talk) 07:01, 25 April 2008 (UTC)

Shniken1, I can guarantee you that, in Britain at least, it's called an ECG. They are the same thing. Regards, CycloneNimrod^Talk? 07:50, 25 April 2008 (UTC)

If you want to learn how to interpret an ECG, I strongly suggest thumbing through an ALS or paramedicine guide from your local library, or poking around online. there are a few websites i've come across maintained by nurses and paramedics intended to provide ECG tutorials, including collections of many ECG strips to practice identifying arrhythmias. --Shaggorama (talk) 05:48, 29 April 2008 (UTC)

Fish species with edible roe

Does anyone know of a good list of fish species with edible roe? Is most roe edible? At the moment I'm trying to figure out the edibility of white bass roe, with no luck so far. I've also failed to find similar information on other species. Thanks - Qatter (talk) 19:05, 24 April 2008 (UTC)

Cod, salmon, herring, alaska pollock and burbot are all roe-able, as it were; the article on roe has a list of different types, actually. As for white bass, they release their roe straight into running water, so i'm guessing its not eaten due to the difficulty of obtaining it. Ironholds (talk) 22:34, 24 April 2008 (UTC)

Most roe is collected by "milking" it from the fish directly, so I don't think that'd be an issue for commercial caviar or sushi consumption. -- Kesh (talk) 21:54, 25 April 2008 (UTC)

Is simply tasting the white bass roe something you'd be willing to try? If it looks at all appetizing, go for it. Vranak (talk) 22:43, 24 April 2008 (UTC)

Ion thruster in the atmosphere

The article about ion thruster points out that the mechanism are only practical in outer space. However, can/have we fly/flied with an ion thruster on Earth? (even if commercially is senseless). 217.168.3.246 (talk) 20:12, 24 April 2008 (UTC)

Nope. One of the primary reasons that ion thrusters are outer-space suitable is their very low thrust. You would as soon fly on Earth by flapping your arms. — Lomn 21:06, 24 April 2008 (UTC)

Okay, and its low thrust is due to technical problems that could be resolved or physically impossible? 217.168.3.246 (talk) 22:45, 24 April 2008 (UTC)

A thrusting force will accelerate an object in an atmosphere until the air resistance imposes an equally opposing force, then acceleration will stop. In the case of an ion thruster, the force is so small (atomic particles being ejected, very low mass output) that even the smallest breeze would be enough to counteract its thrust.

The low thrust isn't a "technical problem". Think of analogies with other technologies: A solid-fuel rocket motor can't be throttled. A turbine jet can't propel an airplane to hypersonic speeds. A propeller thruster can't propel an airplane to supersonic speeds. An ion thruster can't propel anything in an atmosphere. These aren't "technical problems", they are simply features of each technology. ~Amatulić (talk) 22:55, 24 April 2008 (UTC)

What if you ionize a lot of air with an air ioniser and then accelerate this mass of air? 217.168.3.246 (talk) 00:08, 25 April 2008 (UTC)

So, ion thrusters depend on the fuel being nearly wholly ionized (a large fraction of the propellant must be ionized in order for them to work). It is very difficult to fully ionize air at atmospheric densities. There is simply too much matter in air to ionize all at once. Even if you achieved full ionization of air, the resulting plasma would vaporize any nozzle or thruster chamber - no magnetic field we could ever produce in a rocket would be sufficient to contain or collimate an atmospheric density plasma. And an air ionizer merely ionizes a tiny fraction of the air - not nearly enough to produce thrust against the accompanying atmospheric drag; also the electromagnetic effects responsible for ion thruster operation would not work if the ions were in a dense mishmash of neutral atoms. Ion thrusters work by ionizing very diffuse streams of gas and accelerating the resulting plasma to high speeds. The short answer is, atmospheric ion thrusters aren't inherently impossible, but they are fully out of our forseeable grasp in terms of materials and technology. --Bmk (talk) 00:32, 25 April 2008 (UTC)

While people can't fly on them, there are "Ionocraft" which can fly using ion propulsion in the atmosphere thanks to the Biefeld-Brown effect and EHD thrusters, which are similar to but different than ion thrusters. You may have seen one on the Mythbusters anti-gravity episode. -- HiEv 05:23, 25 April 2008 (UTC)

That is. Is it theoretical possible to build a plane based on a EHD thrusters motor? 217.168.1.182 (talk) 10:41, 25 April 2008 (UTC)

Theoretically, maybe, but practically, I would say "no". The article shows a thruster 2 meters wide that produces only 2 Newtons of thrust (0.45 pounds of force). Critical specs for an airplane powerplant would be thrust/weight ratio, input power, and size.

Thrust/weight: terrible. The thrust produced is a small fraction of the weight of the device including power supply. To get sufficient thrust, your airplane is likely to be too heavy to lift off.

Input power: You need too much input power to get just a little bit of thrust. 100W per Newton is 1 horsepower to produce 7.5 lb of force; you're better off using that 1 horsepower to drive a propeller.

Size: The size of the power supply and thruster could well be bigger than the airplane you want to put it in.

If an EHD thruster can (as the article claims) achieve near 100% electrical to mechanical conversion efficiency, then maybe it's possible theoretically to build an airplane based on it, but acheiving that efficiency may mean even more sacrifices in thrust/weight, size, and input power. ~Amatulić (talk) 18:49, 25 April 2008 (UTC)

Musing over my Cider

Greetings, reference desk.

This afternoon, while nattering with a college friend over the finer details of next weeks presentation, I noticed something strange in my pint of cider. My friend and I decided to call it Bertie, and I'm hoping you can tell me what Bertie was... here are the specifics:

• It was a pint of Bulmers.
• It was full
• Bertie appeared to be a tiny, pale yellow/white (though the cider may have stained him) speck, almost indiscernible, on the bottom of my glass (on the inside, in the cider)
• He was stuck to the bottom
• He emitted bubbles, about the same size as himself (very tiny), at a rate of about 8-10 per second, which all rose straight up to the top
• He was the only thing emitting bubbles, the rest of the cider was still
• He was stuck fast, I could rotate the pint 360 degrees and return him to his original position before the stream of bubbles had time to deviation the position at the other end from where the bubbles met the surface
• I could smell nothing near the rim of the pint but cider
• Towards the end of the pint, as I drank, it became shallow enough so that as I drank Bertie would be exposed to air, upon re-submergence, Bertie would not emit bubbles for a few seconds, then would gradually being and raise his bubble rate until he was at maximum bubblefication after 5-10 seconds or so.
• Bubblefication went on at a steady rate (8-10 a second) throughout the 45 minutes that I was sipping this pint (slow day)

My friend and I theorized that either Bertie was some sort of organism that respired cider, or some speck of something or other that reacted with the cider to produce oxygen, CO2 or something like that.

So... who or what is Bertie?! A pint to whomever tells me!

Regards, SGGH ^speak! 22:42, 24 April 2008 (UTC)

Bertie is likely a little speck of crud that resulted from incomplete dishwashing. By providing a rough surface – in contrast to the smooth surface of the rest of the interior of the pint glass – Bertie acted as a nucleation site for the formation of bubbles. (A scratch or other defect in the glass would do the same thing.) The bubbles are just carbon dioxide slowly coming out of solution from the cider; no chemical reaction is occurring. TenOfAllTrades(talk) 22:56, 24 April 2008 (UTC)

Right. And as for the curious time delay after exposure to air and then re-submergence -- I'm guessing that what was happening for those 5-10 seconds was that the released CO₂ was first filling Bertie's nooks and crannies, or forming a big enough bubble to overcome the cider's surface tension, at which point bubbles could again break free and form the stream. —Steve Summit (talk) 00:42, 25 April 2008 (UTC)

Another vote for a speck of dust acting as a nucleation site. This is far more likely than a living organism. Nimur (talk) 05:38, 25 April 2008 (UTC)

Interesting! Shame though, I thought perhaps I had discovered a new species (then murdered it when I finished my drink) oh well. Thanks guys! SGGH ^speak! 08:46, 25 April 2008 (UTC)

Cider is apple juice at a waypoint on the road to becoming Vinegar. In a program on semantics in the 1960's Mr. Wizard noted that one could sometimes find Mother in a bottle of vinegar, so perhaps Bertie is a very young Mother. See, for instance [7], where Mother/Bertie (formal name acetobacter) is said to be present in some cider vinegar. Was your cider a bit sour? [8] confirms the presence of acetobacter in cider. Edison (talk) 01:34, 26 April 2008 (UTC)