August 19

Human cells have 46 chromosomes that can be divided into 23 homologous chromosome pairs ( a maternal and a paternal copy of each chromosome ). My question: is that means the maternal and paternal chromosomes are completely seperate from each other or is it mixed. For example if we assumed that both the eye color gene and the hair color gene are both on the chromosome pair number 5, is it always that the maternal copy of both genes are in one chromosome and the paternal copy in the other chromosome (i.e. seperate) or it is possible that one chromosome contain a paternal eye color gene and a maternal hair color gene (i.e. mixed). Dy yol (talk) 00:15, 19 August 2009 (UTC)[reply]

I don't think they can become mixed in regular cells (although I'm not 100% sure). I do know they can be mixed in gametes by chromosomal crossover, so (to use your example) your children may receive a combination of eye and hair colour genes from you that neither of your parents had, taking one gene from each of them. (Hair and eye colour involve more than one gene each, but it is only an example!) --Tango (talk) 00:21, 19 August 2009 (UTC)[reply]

I didn't think that eye color would be a sex-dependent trait. It shouldn't matter because you don't know whether, say, the father's gene comes from his father or mother (paternal grandpa or grandma). 98.14.222.41 (talk) 01:18, 19 August 2009 (UTC)[reply]

I don't think either I or the OP mentioned sex-dependent traits... --Tango (talk) 01:31, 19 August 2009 (UTC)[reply]

Chromosomes are independent entities, so what you get is what remains forever. Now that's not true for your offspring because, as brought up by Tango, crossing-over can and does occur -- but that's only on the

sister chromatids during mitosis would produce a genotypically and phenotypically identical result to what would have been had crossing over not occurred. Anyway, the only way for maternal and paternal chromosomes to swap would be when they are aligned, and that only occurs during meiosis -- so no, maternal and paternal copies cannot and do not mix. DRosenbach ^{(Talk | Contribs)} 02:32, 19 August 2009 (UTC)[reply

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I'm getting seriously confused. I post replies and they don't show up so I have to repost them. Anyway; some people think otherwise66.133.202.209 (talk) 03:30, 19 August 2009 (UTC)[reply]

DRosenbach is giving you the information that my high-school textbook has for crossing over: only in meiosis. But the truth is more complex:

Mitotic crossing over for sure happens in mammalian cells, even if it is rare (and it's unnecessary, from an evolutionary point of view, because the genetic changes will not be inherited by the offspring, even if they are beneficial). Have a look at the NCBI page above that has an example with flies. The mechanism is not completely understood, but it seems that under some conditions, chromosomes (perhaps by chance) pair during mitosis and can then cross over. There are even some species of fungi that have lost meiosis in their evolution and use mitotic recombination as a way to increase the genetic diversity. But to put it into perspective: In humans, it is a very rare event, and in most cases it might not have phenotypic consequences (because it doesn't matter for most genes on what copy of the chromosome they are located, and/or because only few cells are affected). --TheMaster17 (talk) 08:43, 19 August 2009 (UTC)[reply

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To respond as a purist in a precisely absolute manner, I wouldn't say that maternal vs. paternal chromosome location does not matter. Genetic microdeletion disorders, such as in

Prader-Willi and Angelman syndromes, occur as separate and distinct disorders, despite resulting from identical genetic disturbances -- the latter resulting from disturbance on the maternally-derived chromosome 15, whereas the former relates to the same on paternally-derived chromosome 15. DRosenbach ^{(Talk | Contribs)} 15:41, 19 August 2009 (UTC)[reply

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TheMaster17 did say "most". --Tango (talk) 17:44, 19 August 2009 (UTC)[reply]

And TheRosenbach was only responding as a purist :) DRosenbach ^{(Talk | Contribs)} 23:21, 19 August 2009 (UTC)[reply]

Only about 1% of genes are imprinted, so both "TheMaster" and "TheRosenbach" are technically correct. --- Medical geneticist (talk) 00:24, 20 August 2009 (UTC)[reply]

Oh, yes, I don't dispute either claims, it's the way DRosenbach presented the claims as if they contradicted TheMaster17's that I object to. It is a

strawman argument. I would have preferred something like "Yes, that's true, but it is worth noting that for some genes it can make a very big difference which chromosome they are on. For example...". --Tango (talk) 01:41, 20 August 2009 (UTC)[reply

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I concede and apologize for any belligerence that may have unintentionally been expressed with my aforementioned post -- no disrespect to Master was intended. DRosenbach ^{(Talk | Contribs)} 18:23, 20 August 2009 (UTC)[reply]

(unindent)DRosenbach might be correct in saying that there are some genes for which it is important which copy(silent/expressed) is disrupted by a genetic event, but this was totally not the topic of my post or this question. We are talking about

Since it is not yet understood how maternal vs. paternal deletion results in different disorders, there is no reason to assume that my point is irrelevant. I wonder if there's any data on disorders such as these, in which chromosome source matters, in which swapping during mitosis can be documented. Additionally, crossing-over mustn't absolutely occur with symmetrical portions, albeit any asymmetrical swap would result in genetic defects. DRosenbach ^{(Talk | Contribs)} 18:22, 20 August 2009 (UTC)[reply]

Has there been any proposal for sequestering atmospheric carbon by planting (farming) bamboo? Bamboo being a fast growing plant, I wonder at what rate can carbon be removed from the atmosphere if the plant is farmed on a large scale. In the plan I have in mind, bamboo is cultivated artificially; harvested bamboo wood will be cut, compacted, and stored in underground mine caves. How well will this plan work? --98.114.146.89 (talk) 03:28, 19 August 2009 (UTC)[reply]

The google answer to your 1st question is yes. http://www.google.com/search?hl=en&q=Carbon+sequestration+bamboo&meta= Vespine (talk) 04:55, 19 August 2009 (UTC)[reply]

Why store the bamboo in underground mine caves? Why not use it, say, as a building material? I'm sure it would make a good reinforcing material for concrete, among other things. 98.234.126.251 (talk) 09:44, 19 August 2009 (UTC)[reply]

It's also now used, laminated, for wind mill rotors, or charred and used for soil improvement (see Biochar). But the problem is the sheer amount needed to counteract our CO2 emissions. We need to eliminate about 7 billion tons of Carbon per year to become Carbon-neutral. That's a lot of bamboo. --Stephan Schulz (talk) 12:29, 19 August 2009 (UTC)[reply]

As a point of comparison, only 784Million tons of corn and 600Million tons of rice are grown per year. (According to their WP articles.) APL (talk) 13:24, 19 August 2009 (UTC)[reply]

Quibble: Those numbers presumably only weigh the edible part (and the corncobs) and don't weigh all the rest, yes? Tempshill (talk) 17:08, 19 August 2009 (UTC)[reply]

I assume you are correct. But even if you multiply them by ten it's still a daunting comparison. APL (talk) 19:56, 19 August 2009 (UTC)[reply]

Why store it in underground mine caves? I know that bamboo is used for making furniture and as a flooring material. If it is widely accepted by consumers as an alternative to wood from trees, that'd be great. If not, you need to put a huge amount of it somewhere where it won't catch fire easily and turn back into atmospheric CO₂. Hence the idea. --98.114.146.89 (talk) 12:42, 19 August 2009 (UTC)[reply]

Couldn't you burn it underground without O2 and it would become charcoal and store the carbon that way? It would take less room and be more stable. Googlemeister (talk) 13:14, 19 August 2009 (UTC)[reply]

Burn without O2? How? Dauto (talk) 17:41, 19 August 2009 (UTC)[reply]

Well technically it isn't "burning". The process is called pyrolysis. You would need a heat source of course, but if your mine is really deep, you will get that for free. Googlemeister (talk) 18:13, 19 August 2009 (UTC)[reply]

100 years from now how much of that furniture would still be intact and not rotting in a landfill or used as firewood? 200 years? 1,000 years? Carbon sequestering has to be long-term or its not worth doing. APL (talk) 13:24, 19 August 2009 (UTC)[reply]

Removing millions of tons of carbon from the atmosphere for 200 years sounds worthwhile to me. You really don't think doing so for 1,000 years sounds worthwhile? (Aside from the bamboo proposal) Tempshill (talk) 17:08, 19 August 2009 (UTC)[reply]

Bamboo might not be the best plant for the purpose, at least not everywhere. It converts CO2 to biomass faster than any other plant, but it seems to be difficult to get it to grow vigorously in lots of climates. In lots of places growing trees and then burying them might work better; in other places growing weeds might be best. In any case, I personally believe this idea should get a lot more attention than it has so far. Currently the biggest difficulty is that even with massive economies of scale it's hard for the grow-plants-and-bury-them solution to reach prices below $100 per ton of carbon, but carbon credits trade on the exchanges at less than 1/10 that price. Looie496 (talk) 15:58, 19 August 2009 (UTC)[reply]

Bamboo gains height amazingly quickly - but having recently hacked down a minor forest of the stuff growing alongside the driveway of my house - I can tell you that it's mostly air! The stems are of course completely hollow and the leaves are pretty thin and skimpy. I doubt that they lock up as much mass as some plants that you'd think of as slower growing.

But in any case, to 'sequester' CO2, you have to harvest the bamboo and store it someplace where it won't ever decompose - if it's used for anything or burned or just left to rot, the CO2 will escape again.

If you form a mental picture of a 3 mile long coal train trundling into a power station (and they'll do that two or three times a DAY for a large power station) - and then imagine that same train trundling back out again, laden with freshly cut bamboo - you can tell that the acreage/manpower/machinery needed to keep those trains fully laden would be truly immense. The amount of energy required to cut and haul the stuff over all of that area and then to bury it somewhere (like in a coal mine) would be horrifying! Then realise that the amount of CO2 produced by a rail car full of coal is much heavier than the weight of the coal itself (because the coal is almost all carbon - and you're adding two oxygen atoms to every atom of carbon to turn it into CO2 and more atoms of hydrogen when you turn that into plant carbohydrates)...so for every trainload of coal you bring in - you need more than a trainload (by weight) of bamboo heading out again...and the volume of the bamboo (because it's full of air) is much MUCH bigger than the volume of coal...means that you need more bamboo trains than coal trains - and there isn't enough space in the coalmine to bury the stuff.

Suppose instead, you dispense with the coal train - and just cut the bamboo and feed it into the boilers of the power station. Now you have a closed loop system...all of the CO2 produced by the power station gets "recycled" into bamboo...which is burned by the power station...which produces CO2 that goes back into more bamboo. This is a fully sustainable model - you never run out of bamboo - you never run out of places to put the stuff. The ash from burning the bamboo should contain most of the minerals needed to fertilise the stuff. Furthermore, you have no more coal mines and no more coal trains...saving more pollution, energy, etc.

So why don't we have bamboo (or other plants) feeding power stations? Well, when you calculate the amount of land area you'd need to feed the USA's existing coal fired power stations with fast-growing-plant farms - the answer turns out to be about the area of the whole of North America! So this approach doesn't work either.

Bottom line is that using large plants of any kind to sequester the insane quantities of CO2 that we're generating simply won't work. The volume just isn't there. Even if there was, you'd be better off burning the plant material than the coal...but even that won't work. The reason we burn coal, oil and natural gas in the first place is because they are pure, concentrated biomass - they represent millions of years of carbon sequestration by plants. If you burn millions of years of sequestered carbon over a few hundred years - you can't expect plants to be able to reabsorb it all...you know it's got to take millions of years for that to happen.

SteveBaker (talk) 18:35, 19 August 2009 (UTC)[reply]

I have a picture in my head of an ancient human race burying huge quantities of trees saying, "This will solve the CO2 problem we have!" They die off and the pits with the trees in them turn into oil. Googlemeister (talk) 18:45, 19 August 2009 (UTC) [reply]

It was a trap! The dinosaurs intentionally sequestered all of this carbon knowing that it would form an irresistible fuel source to the civilization that would one day be built by the mammals that were even then starting to gain numbers. Now we're starting to turn the global climate back into a dinosaur friendly one, triggering a second age of dinosaurs. I tell you, those lizards had tremendous foresight. APL (talk) 19:22, 19 August 2009 (UTC)[reply]

We don't really need to take the carbon out of circulation forever -- if we can take it away for 100 years, we'll have enough time to get a handle on the problem. I've seen calculations showing that burying plant matter 10 feet underground is enough to accomplish that. If you look at the CO2 curve, you see a quite substantial yearly oscillation superimposed on the secular trend. That oscillation is believed to result from yearly plant growth and decay in the northern hemisphere. If we could remove just one or two percent of the annual plant growth from the system, it would go a long way toward solving our problem. Looie496 (talk) 19:18, 19 August 2009 (UTC)[reply]

I don't understand how that chart supports your contention that 100 year carbon sequestering would have a long-term impact. It seems to show that the annual variation is irrelevant to the overall trend, which I think is the opposite of what you were trying to say. Do you have a cite? APL (talk) 19:29, 19 August 2009 (UTC)[reply]

My apologies, I mixed two points in one paragraph, thereby violating the rules of good writing. The chart has no relation to 100 year sequestering, its point is just to show that the effects of plant growth on atmospheric CO2 levels are large enough to make it worthwhile trying to exploit them. My source for the point re 100 year sequestering is this paper, which drew some attention last year. Looie496 (talk) 21:51, 19 August 2009 (UTC)[reply]

What a 100 year sequestering would do would be to borrow from the future - and hand our grandkids a problem WAY harder than the one we're trying to solve. When those plants break down and return their CO2 to the atmosphere - it'll dump OUR CO2 into THEIR atmosphere. But a 1 or 2% change is hopeless - we need something like an 80% reduction. I don't see where this percentage gain comes from anyway - the graph you posted clearly shows that the annual variation in CO2 levels due to the absorption of CO2 by all of the plants across the entire planet is about the same as 3 years of human-induced atmospheric CO2 growth...that's easy to see - right? So to cut our emissions by 1%, we'd have to bury one third of one percent of all plantlife production across the entire planet! Do you have ANY conception of how many plants that is?! The idea of deforesting (and de-grassing and de-marine-planktoning) one third of a percent of the earth's surface...a third of the area of the USA...every single year...wow! SteveBaker (talk) 01:53, 20 August 2009 (UTC)[reply]

Borrowing from the future seems reasonable to me. We're still developing low-carbon technology and moving towards a low-carbon (I can't see us being sustainably carbon neutral, but that isn't really required) economy. In 100 years (if we get our acts together) we should have all those technologies and lifestyle changes and will be able to handle the stored CO2 being released then. The problem we face isn't really getting an 80% reduction, it is getting an 80% reduction quickly enough to minimise damage. That said, even if sequestering 1-2% of plant growth a year would be enough to make a big difference, that is an absolutely enormous amount of biomatter to store. If Steve's estimates (which I haven't checked) are correct and we need to store a third, it is definitely impossible - what would all the animals eat? We would have to increase plant growth by 1/3 and store that extra growth, and I can't see where we would grow those plants. Ocean algae might be an option, but I have no idea where you would store it. --Tango (talk) 02:11, 20 August 2009 (UTC)[reply]

Well, some in the oil industry inject CO2 into oil wells to facilitate better oil flow. Logically then, we should be able to inject a large amount of CO2 into empty natural gas caverns which we then cap? I don't know how many tons we could stash doing that, but it might be pretty significant. Googlemeister (talk) 13:22, 20 August 2009 (UTC)[reply]

You have to get the CO2 out of the atmosphere first. --Tango (talk) 13:43, 20 August 2009 (UTC)[reply]

Not necessarily -- you could get the CO2 directly from the industrial source that produces CO2 emissions and inject it directly into the cavern. (This would work especially well with

adiabatic compression.) 98.234.126.251 (talk) 00:12, 21 August 2009 (UTC)[reply

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Why does a jet of water under the influence of gravity adopt the shape of a parabola? I know why a single drop of water would, but a single drop of water is not the same thing as a continuous jet of water, where the centre of mass doesn't move. —Preceding unsigned comment added by 76.69.240.190 (talk) 04:04, 19 August 2009 (UTC)[reply]

Water in a stream is only "held together" by Surface tension which is fairly weak. Each "piece" of the water, whether a droplet or part of a stream will still be affected by gravity the same way. The only thing that makes it a stream is that there is enough water all travelling in a similar enough direction with a similar enough velocity so as the surface tension prevents it from flying apart. You can see this when a stream isn't "quite" enough in the same direction and it starts as a continuous stream but after a while breaks up, this can also be caused by turbulence and wind and anything else which moves the "droplets" enough apart for surface tension to be overcome. Vespine (talk) 04:12, 19 August 2009 (UTC)[reply]

When I watch streams of water from fountains they always seem to start breaking up almost exactly at the peak, any idea why that would be? --Tango (talk) 05:03, 19 August 2009 (UTC)[reply]

The slower the water is moving, the thicker the stream has to be to accommodate the same rate of water. As it reaches the peak and slows down, the water is basically running into itself a little bit which perturbs some bits of it from the uniform parabola trajectory. In addition, as the water speeds up again on the way down and the steam becomes less dense, the surface tension probably plays some role in pulling it into separate beads rather than stretching out into a narrower but continuous stream. Rckrone (talk) 05:41, 19 August 2009 (UTC)[reply]

I think the key word actually is "seem". If you photograph the rising jet of a fountain, you often find that what looked like a continuous stream of water actually consisted of drops close together. See this one, for example. It's breaking into drops very soon after leaving the jets. --Anonymous, 06:03 UTC, August 19, 2009.

There's a kind of fountain we have at our melbourne casino which is all fancy and computer controlled, it shoots powerful coherent and consistent streams of water into the air, which travel along a predictable path and land in the same spot every time. It's like a "water display" rather then a fountain. All the water in each stream is shot in a very controlled way at the same velocity and direction. This creates quite a striking effect since the water jet stops well before the leading edge of the water has hit the ground, o for a while you have what looks like a straight cable of water almost sailing trough the air. So it's at least possible to keep the water from breaking up noticably. I've tried a few googles and i can't find any pictures or what it might be called. Vespine (talk) 06:50, 19 August 2009 (UTC)[reply]

Those are the kind of fountains I'm talking about. [1] There are some. --Tango (talk) 18:05, 19 August 2009 (UTC)[reply]

(EC)Why does a jet of water not equal a stream of drops of water? Edison (talk) 04:13, 19 August 2009 (UTC)[reply]

The assertion that the "center of mass" doesn't move is completely wrong. There is a constant mass flux; and the center of mass must include the water which accumulates on the other end of the jet. The center of mass argument really doesn't even have anything to do with the effect of gravity though - consider a hanging rope - it takes a Catenary shape, even if the center of mass is truly stationary. Gravity is still present, and it exerts a force on each particle of water in the stream, whether that particle of water is moving or stationary. Nimur (talk) 06:50, 19 August 2009 (UTC)[reply]

By the way the fountains where the water looks like a pipe, that's called

Dmcq (talk) 09:05, 19 August 2009 (UTC)[reply

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The

Mythbusters have tried on several occasions to get a jet of water to conduct electricity - which would require a continuous stream - and they've always had a hell of a hard time getting that to work. The reason being that very often, what LOOKS like a continuous stream is actually a broken up series of droplets. I think that what our senses tell us about "continuous" streams of liquid is very often wrong. SteveBaker (talk) 17:45, 19 August 2009 (UTC)[reply

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So the bottom line is that if it is low viscosity, it will move as an idealized stream of fluid with no significant interactions. If it is high viscosity, the parcels of fluid will interact, and this makes the calculation of the shape more complicated. Awickert (talk) 23:35, 19 August 2009 (UTC)[reply]

someone answer my question —Preceding unsigned comment added by 74.65.3.30 (talk) 05:50, 19 August 2009 (UTC)[reply]

I presume you’re referring to your most recent question on the Science reference desk, the suppository question that you asked two days ago? It’s kind of a difficult question to answer, since it isn’t possible to go back to the 90’s and check out the various brands of suppositories that were available back then. The reference desk volunteers can’t always figure everything out for sure. It’s looking like the glycerin capsule hypothesis is likely to be the best guess that anyone here can come up with. In particular, maybe the tin of suppositories got hot, which melted the glycerin capsules? It’s just a guess, but guesses are likely to be the best that anyone here will be able to provide for you in this case. Sorry. Red Act (talk) 06:30, 19 August 2009 (UTC)[reply]

The people who answer questions here do it for fun. Treating us like servants takes all the fun out of it. Regards, Looie496 (talk) 15:49, 19 August 2009 (UTC)[reply]

Everyone who is likely to be able to answer your question has already read it - and (presumably) decided they don't know how to answer it. Generally, if you don't get an answer in a few days, you'll never get one - no matter how many times you re-ask it. Sorry - but this desk is manned by a bunch of enthusiasts - there are no guarantees. SteveBaker (talk) 17:38, 19 August 2009 (UTC)[reply]

Would widely spaced video cameras with a good quality microphones at a live rock concert come close in fidelity and stereo reproduction to directly "plugging in" to the microphones/instruments of the bands I want to film? And in the case of directly "plugging in", what sort of skills, equipment and general hassle/extra equipment setup time are involved, bearing in mind that I am not a professional recording technician (or camera man for that matter?)Trevor Loughlin (talk) 08:00, 19 August 2009 (UTC)[reply]

You don't want them so widely spaced that they pick up the audience more than the music. If I were to record it, I'd actually patch right into the band's microphones and pick-ups from electric guitars and other instruments. Then I'd also have some microphones placed near the audience. Record them all onto different tracks so you can mix them later. Sometimes crowd noise is nice, other times it ruins everything, like if one person has a coughing fit during the quiet parts of Stairway to Heaven. StuRat (talk) 11:47, 19 August 2009 (UTC)[reply]

If you had two video cameras and each recorded the sound on its own, you would get monophonic souns. It would not be simple (if even possible) to combine the two separate sound recordings to get stereo, since they would not be adequately synchronized. If you could record 2 sound tracks on one camera, via a long cord, with the mic from one camera and the line out from the other camera, or a mic cord from the other camera, it would be stereophonic, but people would trip over the cord unless it was taped down. Edison (talk) 13:42, 19 August 2009 (UTC)[reply]

Per Edison & Sturat, there are issues associated with recording from within the crowd. As to recording from the sound mixer ... synchronisation may be the major issue here. The sound desk has input channels for each of the microphones & direct inputs from the band; typically these'll be mixed down to a couple of channels, being a stereo left & right. For practical purposes, you'll be limited to taking a stereo feed from the desk. It'll be mixed for the speakers in the auditorium and may not be the best mix for playback; but will always tend to be better than a crowd recording since it lacks the hacking cough of the person behind you. The desk feed will tend to lack crowd noise; you need to decide whether you want such noise in your film. If you can capture the feed from the desk into your camera; no problem. If you cannot, then you have the problem of synching an audio soundtrack onto the video. How you go forward depends in part on how much you can influence the engineering of the gig - can you get a feed, can you get crowd noise mixed in, &c. There are more complex ways of doing the job (to do with timecoding recordings, and separate mixing desks for the recording, but your post indicates you have limited experience, so we'll leave those to one side for now. --Tagishsimon (talk)

Certainly, if you can get it, take the mix out of the back of the mixing desk. If you need the crowd for a more "live" feel - then point another microphone from the stage out towards the crowd, record that separately and mix it in later. That lets you fade the crowd down during the music and bring it back up in the gaps between the music...or whatever you want to do. SteveBaker (talk) 17:34, 19 August 2009 (UTC)[reply]

Audience recordings don't sound anything like board tapes, but they are very listenable and they have their aficionados. You can do pretty well with a single video camera or portable stereo recorder. If you want to do better (it gets outside of my range of experience) you need real microphones with mic stands, from what everyone tells me. www.taperssection.com is a good discussion forum for all aspects of this stuff. 70.90.174.101 (talk) 00:55, 20 August 2009 (UTC)[reply]

I read some years ago about removing the crowd noise using a number of microphones, I think it was from Qunitiq, the math was fairly advanced with tensors and suchlike but I'm sure there must be software for that sort of thing by now. However using the microphones on the stage is the obvious way to go rather than trying to patch up afterwards.

Dmcq (talk) 09:03, 20 August 2009 (UTC)[reply

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Just occurred to me the same sort of thing is probably what's used in

Dmcq (talk) 09:14, 20 August 2009 (UTC)[reply

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At least I've sorted the cable tripping problem! http://www.fencerecords.com/beefboard/viewtopic.php?t=16931 —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 10:37, 20 August 2009 (UTC)[reply]

A question for all the professional pilots here: What is the minimum cloud ceiling and visibility for an NDB landing approach? Also, how are the NDB landing procedures different from, say, those for a VOR landing approach (in which I'm very well briefed)? Assume a 15-knot crosswind blowing directly (or almost directly) across the runway. Thanks in advance! 98.234.126.251 (talk) 09:20, 19 August 2009 (UTC)[reply]

Simply, all non-precision instrument approaches have a Minimum Descent Altitude (MDA), a Missed Approach Point (MAP) and a minimum required Runway Visual Range (RVR). These numbers are not fixed, they are specified in the relevant approach plate and differ for each airport, runway and approach. MDA and RVR may even differ from airplane to airplane. Once arriving at the MAP, the approach becomes visual; the pilot, having established visual contact with the runway, may descent below the MDA and land visually. If the cloud base is lower than the MDA, the pilot arriving at the MAP won't be able to see the runway enough to continue the approach safely and will abort, followed by the missed approach procedure, which is also explained on the same plate.

If you are flying a pure VOR or NDB approach without the DME, the MAP will be right above the radio beacon. Straight-in landings are generally prohibited in such circumstances. As NDBs are non-directional (duh!), you cannot set the course on OBS and follow the needle during the approach; an NDB approach may or may not be flown differently compared with a VOR approach of the same runway. Also NDBs are less precise than VORs, the MDA for an NDB approach will be higher than its VOR counterpart.

Winds are not found on the approach plates or procedures. They are a part of the aircraft's specifications, namely the 'Maximum Demonstrated Crosswind Component' for takeoff and landing. 88.242.250.37 (talk) 10:53, 24 August 2009 (UTC)[reply]

So from what you're saying, an NDB approach is not much different from a VOR approach, except that you can't use the OBS and that the MDA is higher. That's pretty much what I wanted to know, thanks! (BTW, in the scenario I have in mind, the beacon is near the approach end of the runway and aligned with it, sort of like a LOM (Locator Outer Marker) but closer to the runway.) Just one more thing, what would be a ballpark figure for a typical NDB approach MDA in these circumstances? 1000 feet AGL, maybe less? 98.234.126.251 (talk) 23:29, 24 August 2009 (UTC)[reply]

An NDB approach can be flown exactly the same as a VOR approach of the same runway (MDA and all) or it may be completely different. You can't use the OBS; you use Automatic Direction Finder for NDBs. When MDA is expressed with respect to the ground, it becomes 'Minimum Descent Height' (MDH). Generally speaking, MDH for NDB approaches vary between 400 to 700 ft AGL, sometimes higher, 1000 ft or more. It depends on the surrounding terrain. If you are writing a story, the best approach (pun intended) is finding the charts of your airport. 88.242.224.97 (talk) 05:18, 25 August 2009 (UTC)[reply]

OK, thank you very much. I can't get ahold of the approach plates for that tundra airstrip, regrettably, but the terrain there is pretty flat, so I think I'll just pick a number on the low side of the range, just to be plausible ;-) Well, thanks again, and clear skies to you! 98.234.126.251 (talk) 07:15, 25 August 2009 (UTC)[reply]

What are the key differences between the early teen years (appx.13-14), mid teen years (appx.15-16) and late teen years (appx.17-19). Early and mid teens seem very similar and late teens seem similar to early 20s but yet they're teens. 86.138.238.2 (talk) 10:36, 19 August 2009 (UTC)[reply]

The stage in their education, their closeness to 'adulthood', the legal allowances. See

Adolesence and the many links/pages within. 194.221.133.226 (talk) 11:17, 19 August 2009 (UTC)[reply

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Sorry but you need to be more specific with regard to what you are asking. Are you asking about the biological/physiological transitions during the teen period, social (as 194.221.133.226 pointed out in age of consent, but there will be others such as age of voting, drinking alcohol, etc.) or physchological?

Well it's the science desk, not the humanties or social law desk - so I would assume biological.

Good point, but it's sometimes easy to speculate that it has been posted in the wrong section. This reads like a psychology question, not a biological one. Hence my query. I suppose you could take out the social point, though. In any case, the main biological changes are related to varying regulation in hormones in the body, changes in growth patterns and in physiological changes such as development of pubic hair etc. Adolescence has more information. —Preceding unsigned comment added by 157.203.42.175 (talk) 12:32, 19 August 2009 (UTC)[reply]

I consider developmental psychology as a science, not humanities. Edison (talk) 13:39, 19 August 2009 (UTC)[reply]

The difference is - they are progressively older, and so progressively more adult.83.100.250.79 (talk) 12:28, 19 August 2009 (UTC)[reply]

Thank you for that profound insight - without careful, knowledgeable researchers such as yourself, I have no idea how the ref desk could function. SteveBaker (talk) 17:24, 19 August 2009 (UTC)[reply]

Early and mid teens seem very similar and late teens seem similar to early 20s but yet they're teens. Well, yes. Someone who is 18 is a lot closer to 20 than 15 or 13. The reason they are called a "teen" is because of the number - thirteen, nineteen, etc., and so has nothing to do with actual maturity. At any rate, to completely and utterly generalize and stereotype, 13 and 14 year olds are just beginning to mature, likely starting puberty, and are gaining some independence. 15 and 16 year olds continue the trend, with more responsibilities, more maturity, and usually starting to finish their growth spurt. People 17, 18, and 19 years of age tend to look forward more, and usually try to act more adult and mature, in terms of independence and decision-making, which is helped by finishing high school and maybe looking toward college. These are all subject to radical changes based on nationality, culture, and so on, in addition to my earlier disclaimer. ~ Amory (user • talk • contribs) 12:49, 19 August 2009 (UTC)[reply]

So, what is it that makes 17-19 year olds not adults psychologically (putting legal factors aside). 86.138.6.31 (talk) 15:04, 19 August 2009 (UTC)[reply]

Third molars will generally not erupt earlier than 18, although they may take until 21 or later to erupt, if they ever do. This would work for determining the dental-age of a patient. There is also the skeletal age, mental age and probably many other "ages" that different practitioners utilize. There are also sexual changes that occur, but I'll leave that for the

endocrinologists. DRosenbach ^{(Talk | Contribs)} 15:46, 19 August 2009 (UTC)[reply

]

These classifications are problematic as the variance between individuals is such that a trained psychologist could not reliably determine whether an individual was 19 years old or 20 years old despite that they are classified separately. At best, he could give a probability estimate, but he could not definitively state as a fact that the person in question is 19 or 20 based solely on observation. Googlemeister (talk) 15:51, 19 August 2009 (UTC)[reply]

It's a good question, and it's rather difficult to defend the legal stances in most countries that have a specific cutoff date: After that date, you're an adult; and before that date, you're legally a child. The answer is ostensibly "experience" but there's nothing to guarantee that any particular 20 year old has more life experience than any particular 16 year old. Tempshill (talk) 17:03, 19 August 2009 (UTC)[reply]

Here's a quick test: Be 17. Then, a few years later, be 20. There is a world of difference, even if your actual world hasn't changed much. Any 20 year old can see they are a complete world apart from a high school kid, especially mentally. Despite the painfully early onset of age-related deterioration at 27-30, the body is still developing into the 20s, and often to a fair degree after. That's where one of the arguments for a drinking age of 21 comes from. I (amusingly) call it the Pokémon effect: At low levels/ages, a difference of a level/year or two makes a difference (Level 5 Pidgy will beat a Level 3 Pidgy) but when you level-up/get older, the difference doesn't matter as much (L50 Charizard can lose to a L40 one). ~ Amory (user • talk • contribs) 01:51, 20 August 2009 (UTC)[reply]

• 13-14: Happy (many sources of wonder and amazement)
• 15-16: Excitable (many exciting girls)
• 17-19: Manic-depressive and quite insane (damn, I think my soul is broken)

I can only speak for myself of course. Vranak (talk) 16:34, 19 August 2009 (UTC)[reply]

This question is not going to have a satisfactory answer. There are few groups more heterogeneous than an age group. Anyone who deals with adolescents of a given age -- or is an adolescent -- will tell you there are vast differences among people of the same age. Hopefully, a given person will be more mature and experienced at 20 than at 17 and moreso at 17 than at 14. But everyone matures at different rates. For example, some girls get their first period at age 9; others not until age 15. If such a basic physical trait can happen at such widely varying ages, no doubt the same could be said for aspects of mental or emotional maturity. And it's not as simple as saying that someone matures at a given age. There are many aspects to both emotional and physical maturity. In some ways, I demonstrated "adult" sensibility when I was 12 or 13; in other ways, I acted childlike even when 19 or 20. I get particularly frustrated when someone tries to attribute a characteristic to an adolescent age group. We often hear about how teen drivers (presumably 16-17) can be "reckless" and "think they're invincible." But when I was 16-17, I was so nervous about driving that I was afraid to change lanes! -- Mwalcoff (talk) 03:24, 20 August 2009 (UTC)[reply]

Where can I find out how many people are allergic to Actinidain? Googlemeister (talk) 16:45, 19 August 2009 (UTC)[reply]

I am going to make the assumption that you are interested in statistics pertaining to kiwifruit in general. According to the literature, the rates of allergies to kiwi and other foods vary by population. Another review paper of kiwifruit allergies didn't present any figures on the overall rate which suggests that by at least 2003 there hasn't been a comprehensive study on the rate of kiwifruit allergies in various populations. This paper only generally states that there has been an increase in the number of reported kiwifruit allergies. I found those papers by the way using google with the search term 'kiwifruit allergy rate.' Further examination for fruit allergy rates didn't lead to any hard numbers that included kiwifruit either. 152.16.15.144 (talk) 23:42, 19 August 2009 (UTC)[reply]

My mother says she left Wicca partly because she felt too many of its members were paranoid or had other symptoms of mental illness. Are Wiccans less mentally healthy on average than members of other religions, and do they tend toward the same types of mental illness in the same relative proportions? NeonMerlin 19:12, 19 August 2009 (UTC)[reply]

That's an interesting question. Speaking purely from personal observation, I identify with certain subcultures more then the mainstream and I used to frequent alternative night clubs like goth and industrial clubs when I was younger. They sometimes get lumped together, goth/metal/industrial, because those kind of scenes do tend to attract certain similar fringes of society, people who don't "fit in" with the mainstream. So they are typically over represented with people who have alternate beliefs, odd personalities, unusually creative, more introvert or extrovert then "normal", that kind of thing. Within those groups I could confidently say there would also be an over representation of people with genuine mental "issues", (since a lot of mental issues make it harder to identify with the mainstream) and also people who believe/practice Wicca. How much those 2 groups overlap, I could not say but I would not find a correlation at all surprising. That is not to say there is a direct causal correlation, as in "it takes a person with mental problems to believe in Wicca", I don't believe that, but more plausibly that people with mental problems have a harder time fitting into a mainstream, therefore they may have a higher predisposition to be drawn to alternative views, like Wicca. Vespine (talk) 01:59, 20 August 2009 (UTC)[reply]

I think Vespine probably has it right: the general ethos of Wicca is non-judgemental, tolerant and welcoming to diverse and sometimes unusual belief clusters and personalities, so people with them tend to gravitate there. A not-dissimilar situation exists in the Science Fiction Fan community, which contains a higher than average proportion of people noticably on the Aspergers/Autism spectrum (both examples are based on my personal observations from within). However, I suspect that investigation of some non-Wiccan (or indeed non-neopagan) religious organisations/cults might reveal much higher proportions of those with dysfunctional mental states: I'm thinking of some Southern-USA schismatic Christian fundamentalist churches, and of Sc!ent0l0gy (excuse the hopefully search-engine baffling transliteration, they're notoriously litigious) which – as anyone who'se read their promotional literature and questionnaires will know - appear actively to target those with mental health issues.

A properly conducted scientific study of the broad question might be interesting, but I fear would be both highly contentious and open to misuse. 87.81.230.195 (talk) 04:54, 20 August 2009 (UTC)[reply]

Another possibility when comparing religious groups is that any relatively new religious group will have almost exclusively converts as members, while a well-established

Here's how to test this hypothesis: examine Wiccans who were raised Wiccan, and converts to Lutheranism who had been raised in a religion that is hostile to Lutheranism. If the hypothesis is true, then raised-Wiccans will be less "crazy" than convert-Wiccans, and convert-Lutherans will be more "crazy" than raised-Lutherans. --FOo (talk) 09:54, 20 August 2009 (UTC)[reply]

I would think it would largely depend on how mental illnesses are defined. One old definition is "those who are mentally abnormal, that is, outside the norm". This would likely include just about all Wiccans, as well as homosexuals and many others. If you go with a more narrow definition, like "those who, due to their mental state, are a physical danger to themselves or others", then I doubt if Wiccans have a significantly higher rate than others. There could even be an argument that "letting yourself go" periodically, such as dancing naked and primal screams (do Wiccans do those things ?) might help relieve stress and thus make you healthier physically and mentally than in a typical repressive religion. StuRat (talk) 12:56, 20 August 2009 (UTC)[reply]

Why are highly nitrated compounds explosive?CalamusFortis 20:39, 19 August 2009 (UTC)[reply]

this website contains an excellent review of the thermochemistry of explosives like nitrates. The deal with nitrated compounds is that they are essentially "self-oxidizing"; its not that the combustion of a nitrated compound necessarily releases more energy, its that it releases that energy MUCH faster than a standard combustion because the oxidizer (the nitro group) is in the compound itself. The limiting factor in the speed of a standard combustion is the relative diffuse nature of the oxidizer; atmospheric oxygen is only about 20% of the atmosphere, and as a gas, it is also about 1/1000 the concentration of a liquid or solid. So your oxidizer in a standard open-air combustion is about 1/5000 as effective as it would be if you were dealing with pure, condensed oxygen, like liquid oxygen. With a nitrated organic compound, since the oxidizer is part of the molecule itself, it works essentially instantaneously, and there's enough of it around. --Jayron32 22:54, 19 August 2009 (UTC)[reply]

A few weeks back I made a composter out of an old plastic trash can. Following instructions, I cut a number of holes and duct taped them with plastic window screening. I then loaded it up with shredded paper and dried leaves (carbon rich "brown" waste) and old produce and grass clippings (nitrogen rich "green" waste). Per the instructions I found online, the ratio of green to brown by volume was approximately 1:4 or 1:6. The first week we had a dry spell and nothing seemed to happen. Apparently I wring out my sponges harder than most people do as my definition of a "wrung-out sponge" was too dry. Adding substantially more water and moving the composter into the shade helped and soon I felt the distinctive heat of decomposition when I turned the contents over.

After about a week, though, the heat went away and decomposition seems to have stopped. Dampening and aerating seem to do nothing. There is no unusual smell (i.e. ammonia) as indicated in various troubleshooting hints in the instructions. As of last night, the grass clippings seem to be mostly gone. I found other instructions (at http://www.ehow.com/how_16876_make-compost-bin.html which I can't link to because of a wikipedia link block) calling for a 1:1 ratio. The

This weekend, I will mow my lawn and add more clippings to see how that works. In the meantime, though, I thought I'd post here to see if anyone can suggest other things I might need to look at if that doesn't work out. So, three questions:

• Does my diagnosis of too little green waste sound plausible?
• If the diagnosis is wrong and the grass clippings don't work, what should I do? (FYI, I'd really rather not dig out a pH meter or anything arcane like that)
• Also, should I count this last week as a "lost week" in my two to four week cycle before I can use the compost?

Thanks

--KNHaw ^(talk) 22:03, 19 August 2009 (UTC)[reply]

I looked at"Back to basics," (1981) by Readers' Digest. It is an excellent guide to lots of "back to the land" farming techniques. They say the optimum size for a compost pile is 4 feet, since a small pile loses heat too rapidly. They start with 2-3 inches of course material like cornstalks, twigs or straw, to promote ventilation. Only one such bottom layer is called for. They layer 3-6 inches of garden waste or dead leaves, 2-3 inches of manure (or a light sprinkling of synthetic fertilizer) to supply nitrogen, then a thin layer of garden soil. Repeat until the compost bin is full. Leave the top saucer shaped to hold water. Too little water and the breakdown comes to a halt. In dry weather, water it every few days. In rainy weather cover it with a tarp to prevent too much water. Turn it weekly. It is done when it no longer gives off heat and the material is "brown and crumbly." Compost does not have to look like dirt to be done. It can still be recognizable in form as leaves and grass, but should be dark or brown. They suggest the process can be complete in 2 weeks. So: was there an adequate nitrogen source? You might try adding manure or fertilizer. Was the volume large enough to hold heat? Did you add soil, so the needed microorganisms are plentiful? From my experience the manure or fertilizer and the layers of soil are important for speedy breakdown and heat. If it is not going to get hot, perhaps earthworms could do the composting for you. They crawl around, multiply, and turn old grass clippings into rich brown soil. Edison (talk) 01:21, 20 August 2009 (UTC)[reply]

OR: It may also be that your compost got too hot and was sterilized. Adding earthworms might work, but they don't like it too toasty either. Depending on what you use to treat your lawn and what type of grass you have, clippings may not be a good thing to put in your compost. Some grass types don't compost well and some lawn treatments can mess up the ecosystem in your compost. If you have oak trees then maybe your "leaf matter" is to blame. 71.236.26.74 (talk) 11:55, 20 August 2009 (UTC)[reply]

I agree that a very critical factor for composting is scale (it affects moisture level, temperature loss etc etc.). I think this is much more critical than composition. Most people seem to reckon a cubic metre is a minimum for general conditions so I wonder if your "plastic bin" is big enough? How much grass cutting do you get each time you mow the lawn? The first 48 hours with moist fresh cut grass is the hottest (50C is easy if you have a few cubic metres of squashed clippings each cut in my experience, in rough terms in the UK you get about a cubic metre per acre mown) and the steam which rises from the compost helps to moisten everything else. If you cannot get a cubic metre of compost together my advice would be to bury what you have in the soil and it will degrade there ok. --BozMo talk 12:37, 20 August 2009 (UTC)[reply]

I was also going to suggest earthworms. They put holes in the compost heap, allowing water and air to permeate it, and also directly break down the compost. I wouldn't be so focused on getting the composting done quickly, but just leave the worms enough time to work their magic. If you have to turn the compost heap periodically you may miss days or just get sick of it entirely, whereas the worms will never give up. I'd also compost in a hole you dig, rather than in a plastic bin, which could limit air and water flow. So, basically, let nature do the composting for you. StuRat (talk) 12:43, 20 August 2009 (UTC)[reply]

Looking at the instructions you linked to, my guess would be A) not enough material overall to keep heat up, and B) not enough aeration through the ventilation holes. You might want to take a look at this (pdf) link from NCSU's School of Agriculture, or this one from Cornell's Waste Management Institute. You sound like you've read up on this pretty well, so a lot of information may be things you already know, but I like the way the schools lay the information out, and you can trust that you're not reading something from someone who "swears to god they did thus-and-such, and got amazing results." Reading the forums on Gardenweb on the subject, every time you add new material to the container-type composters, you're starting the process over, in terms of week-count.

From personal experience with a stationary bin made of nailed-together pallets, I can tell you that I very quickly despaired of ever keeping it full enough for hot composting, because the pile shrinks as the material in it settles and breaks down. A bin full to the top with a mix of leaves (raked and pruned), chopped-up weeds (left in the sun for a couple days to kill the roots first), and kitchen scraps would in a week or so collapse to just a foot and a half to two feet of material in the bottom of the bin. I never even had a chance to worry about C:N ratios; I was just trying to find enough stuff to keep the bin full. So I gave up, and now I throw in what I have when I have it, and turn it every week or two, depending on whether I feel like it. I'm not churning out perfect batches of compost every couple of weeks, but I have a place for yard and kitchen waste to go, and it'll become something usable eventually. Good enough for me, but YMMV. Some jerk on the Internet (talk) 13:16, 20 August 2009 (UTC)[reply]

What is the difference between A/California/04/2009 and A/California/05/2009? Are these the old names of two samples, or two different names for the same strain? -- Jeandré (talk), 2009-08-19t22:15z

If you look at those pages, you'll notice some differences; specifically, the section called "Comment" always has some information on the sequence. The first appears to be from a 10 year old male, and the second from a nine year old female. The first was collected on April 1st, and the second on March 30th. Noticing they had the same protein product (PB2) and similar resistances, I BLASTed them against each other, which told me that out of 2280 nucleotides, they had all but two identical. The exact changes are at positions 1218, a guanine for an adenine, and at 1872, a cytosine for a thymine. Hence, they are not the exact same virus, which is why they have different names (the names are based on when they were discovered and published). They are, however, the same strain - a good hint (although by no means definite) is that they are both

H1N1. ~ Amory (user • talk • contribs) 02:12, 20 August 2009 (UTC)[reply

]

It says "tape-like". The article is not recommending using actual tape. It is indicating that they are sometimes treated with an item similar to tape, but specifically designed for that purpose. APL (talk) 00:08, 20 August 2009 (UTC)[reply]

I really, really hate to have to say this, but we cannot give medical advice. Your question may not really be asking for medical advice, so this may not be applicable in this case. Nevertheless, lots of folks with blackheads and pimples end up at the doctor's office after a botched self-treatment. It is really better to go see the doctor first. 90% of the time, the doctor will be able to tell within one minute or less that your visit was unnecessary. It's the other 10% of the time we worry about. Basically, if you are worried enough to ask on this forum, you should go to the doctor so he can reassure you and keep you from doing something stupid. -Arch dude (talk) 01:02, 20 August 2009 (UTC)[reply]

Both of you are beyond intense. I know it said tape-like, I read the article. And I'm not asking how to take my gallbladder out -- take a chill pill! Man... DRosenbach ^{(Talk | Contribs)} 02:17, 20 August 2009 (UTC)[reply]

"Beyond intense"? That's a new one on me, when and where is that slang from? --Tango (talk) 03:30, 20 August 2009 (UTC)[reply]

I am Ultra Intense. APL (talk) 05:21, 20 August 2009 (UTC)[reply]

Is ultra intense beyond intense? Or just a subset? Or do put it a different way, are you disputing that you are beyoond intense of do we have a confession? To the OP if I'm reading your user page right, your a dentist? Do you encourage your patients to ask random strangers on the internet to find out whether using "3 parts baking soda (cleanser) thoroughly with 1 part salt (the abrasive)" or perhaps "with chalk, pulverized brick, or salt as ingredients" as a

mouth wash is a good idea too? Nil Einne (talk) 10:08, 20 August 2009 (UTC)[reply

]

DRosenbach, there is a chance you may harm yourself applying packing tape to your face. Be sure to avoid blocking respiratory orifices and do not put tape directly on the surface of your eyeball. Mac Davis (talk) 03:35, 20 August 2009 (UTC)[reply]

I. Similar to how severe could serve to classify a point on the severity spectrum, I was utilizing intense to refer to a point on the intensity spectrum -- thus, ultraintense, which likely exhibits greater frequency and perhaps lesser amplitude than intense, would be an example of "beyond intense," but would not define it, as beyond intense was meant as merely a relative label rather than a definition of another point along the spectrum. One could, of course, refer to a specific point as beyond intense, but that was not what I was doing.

II. I would encourage my patients to confirm my recommendations with their colleagues -- only one who is insecure and unconfident about his or her recommendations would restrict his or her patients access to other sources of information. Sort of like how China doesn't allow anti-Chinese sentiments to be expressed or disseminated among its masses.

III. I do not consider you all to be random strangers as much as I consider you all to be a fine subset of random strangers, heretofore entitled scientifically-drawn random strangers. I would, and as this case exemplifies, do ask scientific queries of scientifically-driven random stranger -- doesn't everyone else here do the same.

IV. So to summarize, I can use packing tape, as long as I avoid eyes, nose and mouth? DRosenbach ^{(Talk | Contribs)} 12:55, 20 August 2009 (UTC)[reply]

No. I'm fairly sure Mac Davis was being facetious. Use packing tape for your parcels and face cleaning tape for your face. The ref desk can't and won't give you advice on home-made alternatives. --Tango (talk) 13:05, 20 August 2009 (UTC)[reply]

Another one beyond. DRosenbach ^{(Talk | Contribs)} 13:07, 20 August 2009 (UTC)[reply]

I enjoy aiding the science desk's

sebum-absorbent acne tape.[2] Even better, Google Books lets you read this book's sections on acne tape and absorbent paper.[3] Mac Davis (talk) 16:45, 21 August 2009 (UTC)[reply

]

Did you find one on packing tape too? Nil Einne (talk) 21:38, 21 August 2009 (UTC)[reply]

Obviously, what we have here is an opportunity for a clinical trial. The Annals of Improbable Research would probably publish your results. APL (talk) 14:20, 20 August 2009 (UTC)[reply]

Okay thanks for the clarification. As it seems you're the best qualified and I have your attention can you tell me whether using "3 parts baking soda (cleanser) thoroughly with 1 part salt (the abrasive)" or perhaps "with chalk, pulverized brick, or salt as ingredients" as a

mouth wash is a good idea? Cheers. P.S. Are you telling us a dermatologist told you to use packing tape and you just want a confirmation it's a good idea? If not, I don't get the relevance of point II, since it's never a point that was raised by anyone. Nil Einne (talk) 21:33, 21 August 2009 (UTC)[reply

]