Wikipedia:Reference desk/Archives/Science/2007 April 30

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April 30

Random Numberon calculator

Any idea how does a calculator produce a Random Number?? —The preceding unsigned comment was added by 210.212.194.209 (talk) 08:12, 30 April 2007 (UTC).

See Pseudorandom number generator. Simon A. 09:07, 30 April 2007 (UTC)

Some calculators use physical characteristics of their microprocessors to drive a hardware random number generator. Here is a hardware-level description of how random numbers can be generated using the clock systems in a family of Texas Instrument microprocessors. Gandalf61 09:26, 30 April 2007 (UTC)

So if you buy two brand new calculators and hit "Random number" will they both bring up the same number? Aaadddaaammm 09:29, 30 April 2007 (UTC)

Not if they use a hardware random number generator, or even a pseudo-random number generator (PRNG) seeded by some hardware characteristic that is difficult to replicate. A seed based on the number of microprocessor clock cycles since the calculator was switched on, for example, would be very difficult to replicate exactly on two different calculators - and the output of a good PRNG will be very sensitive to small differences in the seed. Gandalf61 10:47, 30 April 2007 (UTC)

Exactly, imagine the clock on the little microprocessor is ticking a few million times per second. If you counted the number of clock ticks and displayed (say) just the righthand three digits of the number when the user hit the RND button - then the result would depend on when you hit the button - and unless you could do that with a precision of maybe a thousandth of a second, the number you'd get back would look pretty random! If you then (in effect) scramble those numbers by pushing them into a PRNG and the result will be a very high quality random number. You can't use just the clock by itself if the calculator is programmable - because there would be a risk that the number of instructions between two consecutive calls to the random number generator would produce results that were very similar - but using the clock to seed a PRNG fixes that. SteveBaker 12:07, 30 April 2007 (UTC)

Weight Loss Overnight

I'm monitoring my weight for health reasons at the moment, and as I was curious I weighed myself before going to sleep for the night, and straight away when I woke up. Before sleep I was 15 stone 10 pounds, but 8 or 9 hours later after sleep my weight was 15 stone 6 pounds.

Does anyone know where that 4 pounds went to? Surely I didnt sweat it?

ta -stubblychin —The preceding unsigned comment was added by 213.212.70.122 (talk) 08:14, 30 April 2007 (UTC).

Well, you may have sweated (or exhaled) some moisture - and you shed some dead skin cells and you inhaled lightweight oxygen and breathed out heavy carbon dioxide in its place - but I agree that four pounds sounds way too much. My best guess is that your bathroom scales just aren't that accurate. All it would take would be a 2% error - and I bet you can make the reading change that much by shifting your weight from one foot to another or leaning forwards or backwards or perhaps by getting off and then back on again. SteveBaker 11:46, 30 April 2007 (UTC)

Do an experiment. Place something of constant mass on your scales. Do it at various times of the day. Record down all the values. It should show the same value everytime, if not then your scales are not accurate. 1.8 kg / 99.88kg = 0.0182 hmmnn.. Perhaps your scales are only accurate at 1.8% at around 90-100kg. Ohanian 12:26, 30 April 2007 (UTC)

Actually, I've done this a few times over the last couple of days, and they are a pair of (supposedly) accurate digital scales. I had lost 2 pounds this morning overnight and I checked it twice. My girlfriend had lost even more! I'll test the same weighted thing on it though. Maybe it is atmospheric. -stubblychin

If you took a dump consider that water weighs about a pound a pint and solid waste is also dense. Edison 14:21, 30 April 2007 (UTC)

Yea, you probably just urinated and forgot about it. StuRat 17:45, 30 April 2007 (UTC)

Yeah! a pint of water weighs a pound and a quarter (in UK) so if you exhale a couple of pints overnight (not unknown) you have 2.5 lbs! —The preceding unsigned comment was added by 88.109.137.137 (talk) 21:25, 30 April 2007 (UTC).

I'm still really sceptical that the scales are that accurate. Perhaps the things are temperature sensitive and maybe it's colder in your bathroom in the morning than the evening? Maybe the battery in the scales is going flat and giving a different reading each time. There are a bunch of reasons why the scales could have a 2% error (and now you are telling us that this time it's only 2lbs which is a 1% error) - all of those are more likely than that you lost 2lbs overnight just by sleeping! You say "supposedly accurate" - but how accurate do you expect them to be?! A 1% error for a consumer grade product like that is not at all unreasonable...particularly because they have to weigh you when you are standing a bit off to one side or wobbling a bit as it weighs you. The error bars are just too large with a machine like that to claim a scientific result. SteveBaker 02:37, 1 May 2007 (UTC)

For what it's worth, I have no problems thinking you could lose a few lbs overnight. According to my scale, it happens to me sometimes. My weight seems to fluctuate pretty regularly throughout the day. Maybe my scale is wonky, but I have no reason to particularly doubt it. Friday (talk) 02:44, 1 May 2007 (UTC)

Well, I guess we could figure this out. If you take an average of 18 breaths per minute with a tidal volume of 500ml per breath - then over (say) 8 hours of sleep - you'll have taken in 4320 liters (4.32 m³)of dry air and expelled it at somewhere near body temperature and at 100% humidity...then about 3% of that (by mass) is water vapour - 4.3 cubic meters of air at 1.2kg/m³ means that assuming the air you are breathing is utterly dry - and what you breath out is 100% humidity then at most - you breathed out 0.15kg of water....that's just about a third of a pound. In reality it'll be a lot less than that because you are unlikely to be breathing in utterly dry air - in part because a lot of the air in the room is what you just breathed out! Also the 18 full breaths per minute with 500ml tidal volume is for someone who is awake - you breath more slowly and less deeply when you are asleep. I'd bet that the total is more like 0.1 lbs due to breathing. Now - how about perspiration? Well, this article says that when you are doing a high activity cardiovascular workout, you can sweat 1.2lbs in an hour. If you are claiming to have sweated that amount over maybe 2 or 3 hours of sleep?! And in any case - just think how wet your bed would be if you tipped two to four pounds of water into it each night! No way! NO! Simply not possible. I would be very surprised if you were sweating at even a tenth of that rate. Your scales simply aren't accurate enough - period. SteveBaker 03:25, 1 May 2007 (UTC)

Could it be air pressure changes due to temperature? Or maybe you are wearing different clothes?

A change in air pressure wouldn't affect your true weight - so we'd be talking about how it might affect your scales. If it's an fancy digital gizmo then it's probably using the piezoelectric effect - it it's an old style mechanical one then it's using simple springs and stuff - neither of those mechanisms would be affected by air pressure changes. Temperature changes could make a significant enough difference though. If different clothes were being worn then 'Duh!' - but I presume our questioner has more intelligence than that! SteveBaker 21:57, 1 May 2007 (UTC)

Any reports of Abduction phenomenon in the neighborhood? Succubi? Vampires? Missing kidneys [1]? Edison 19:36, 1 May 2007 (UTC)

people lose weight all the time they aren't eating as their body uses its stores of energy (fat), basically to keep you alive all night :) Whilst sleep doesn't need much energy, if you spend enough time doing it, it can soon add up :) Try finding your BMR, then working out how much of the day you spend asleep and see how much enery that is :) I'm sure someone could tell you how much fat you would have to burn using that much energy :) HS7 16:11, 2 May 2007 (UTC)

But the energy doesn't weigh anything (well, e=mc² but c is huge - so m is quite utterly negligable). What has weight is the byproducts - which includes: Pee and pooh (ruled out because nobody visited the bathroom between weighings), water - exhaled and sweated, CO₂ breathed out. I did the math (see above) - all of those come to a fraction of a pound. Sorry - but your explanation simply doesn't fly. SteveBaker 00:02, 4 May 2007 (UTC)

Global Warming

It was suggested that if ocean going ships were to spread plankton (or some other organism) as they were passing then they would absorb excess CO2 and convert it to carbonates.Any idea why has that not been implemented? —The preceding unsigned comment was added by 210.212.194.209 (talk) 08:19, 30 April 2007 (UTC).

You first need to have the plankton. Therefore, the idea is not to spread plankton itself, but rather to fertilize the ocean with iron in order to stimulate the growth of algae and other plankton living an algae. This idea, including the problems, is discussed in the iron fertilization article. Simon A. 09:11, 30 April 2007 (UTC)

Agreed, as much plankton as can grow (under current conditions) is currently growing. Thus, to make more grow, we need to change the conditions. StuRat 17:41, 30 April 2007 (UTC)

There's also the general concern that the environment should not be tinkered with lightly. One would want to explore the possible side-effects from such a scheme very carefully — otherwise you could quite possibly end up with the very common situation in the history of purposeful environmental meddling where 1. you end up creating a new calamity where one didn't exist and 2. you don't even end up really accomplishing what you set out to accomplish. --24.147.86.187 01:46, 1 May 2007 (UTC)

Why is the F/A-18 Hornet so good?

Looking at the characteristics of the F-14 Tomcat with the F-18, the F-14 excels in nearly all areas, the most obvious being its speed (Mach 2.34 vs Mach 1.8). The Tomcat has a greater combat radius, and can carry nearly twice as much weight in equipment. So why were they all changed to F-18s in every squadron after 2006? They are so slow they could not catch even the oldest types of MiGs. This strange aircraft replacement can be observed in some post-Warsaw Pact European countries, where the good old MiG-21s are being replaced with the newer, more expensive, and less proficient Grippens. No conspiracy theories and nasty money things please. --V. Szabolcs 08:30, 30 April 2007 (UTC)

Costs and agility. - Dammit 09:59, 30 April 2007 (UTC)

Well, "nasty money things" is hard to avoid. The F-14 is quite the modern marvel of engineering and electronics, but the frames are becoming old, and it is quite a tormenting task to overhaul a F-14, whereas the F-18 may be considered better on these areas. Logistics is very important, extremely much so aboard aircraft carriers and such. Also when you say "good old MiG-21", it is true that these aircraft have a very good performance history, but the agility is nowhere near what the Swedish Grippen has to offer. Also consider the fact that as airframes age, you can only adjust them so much to carry new equipment (see F-16 Falcon) before in the long run, a new frame is preferable. If this does not answer your question well enough, do let us know. 81.93.102.185 10:59, 30 April 2007 (UTC)

The mission of these aircraft has also changed quite a bit. US aircraft are not likely to be dogfighting with other modern planes at close quarters (especially the US Navy/Marines aircraft - dogfighting is for F16's). For most missions these guys will be undertaking, it's down to stealth, long range targetting, fancy sensors to be able to find the enemy while they are still 60 miles away, stability as a camera platform and fuel capacity. Lifetime operating costs and mission flexibility are more important than capital costs and ability to excel in one particular area. Top speed is largely irrelevent. If the enemy have fighter aircraft at all, they will mostly be taken out by trashing their airfields from high altitude, radar-invisible bombers or cruise missiles - and if any do make it into combat, long range air-to-air missiles are what wins the battle - not flying really fast in tight circles blazing away with machine guns like in the movies. Remember the first Gulf war? Saddam flew what was left of his airforce to Iran to avoid them getting splatted. Since then, I doubt that the US Airforce/Navy/Marines has faced a single enemy plane! SteveBaker 11:59, 30 April 2007 (UTC)

Agreed. The major current threats to fixed-wing aircraft are surface-to-air missiles, small arms fire at take-off and landing (for land-based planes), and mechanical failure (with sand as a contributing factor). StuRat 17:36, 30 April 2007 (UTC)

I believe the F-14 is considered a much better combat fighter and has all the things you mentioned including a much better radar. The F/A-18 is single man crewed and has much better ground attack capabilities. Every air wing on a carrier can now carry out ground attack missions which makes them significantly more effective in operations such as Iraq and Afghanistan. The Super Hornet closes the gap in interceptor capability. Essentially variants on the F/A-18 are used for every role and this helps reduce cost, improve aircraft availability (all spares are the same and allow cannabilism in a pinch), reduce crew training (both support and flight), standardized ordninance, improved overall program cost and the reliability of more modern airframes (the F/A-18 is still 20 years old, super hornet is newer). The current mission of the U.S. Navy is threat projection. this is somewhat different from the cold war role of Nuclear Strike Force. --Tbeatty 07:03, 1 May 2007 (UTC)

what is science?

—The preceding unsigned comment was added by 80.87.65.22 (talk) 11:29, 30 April 2007 (UTC).

By the way, you can use the Wikipedia:Sandbox or any of your own pages to do "experiments." The preview button is also probably better than either of those. [Mαc Δαvιs] ❖ 13:36, 30 April 2007 (UTC)

They probably pressed the Example Image button by accident, I've removed it from their post--VectorPotential^Talk 13:39, 30 April 2007 (UTC)

Science has a pretty decent overview... -- mattb 13:45, 30 April 2007 (UTC)

Science is the systematic rational investigations of natural phenomenon. The question you should be asking is "what are rational methods?" and "what are natural phenomenons?". 202.168.50.40 22:09, 30 April 2007 (UTC)

It's not phenomenons, it's phenomena (do do doo doo doo, phenomena) 137.138.46.155 06:59, 1 May 2007 (UTC)

I liked that movie, Phenomenon [Mαc Δαvιs] ❖ 13:11, 1 May 2007 (UTC)

growth plates

how do you know when growth plates are closed or still open without an x-ray or do you need one show it and am i still growing? im turning 16 this year and im currently 5"8 / 5"8.5 (im not sure which one :D ) —The preceding unsigned comment was added by 80.42.1.152 (talk) 13:25, 30 April 2007 (UTC).

well as far as the growing thing yes you are. i belive it was at the age of 20-21 that a person stops growing. thats why they dont recomment Lasic operations on your eyes till then. although i dont think this is relevent to what your asking; it shows how long our bodys keep changing though. Now growth plates ill leave that to someone else User:Maverick423 If It Looks Good Nuke It 13:48, 30 April 2007 (UTC)

What does LASIK have to do with growth plates? Splintercellguy 15:03, 30 April 2007 (UTC)

LASIK is not recommended for people that are still growing. This medical recommendation is an indirect report of when growth stops. Czmtzc 15:23, 30 April 2007 (UTC)

i have good eyesight so i dont really need laser eye surgery :D

Yep it was just to be used as a comparison of when growth stops. =) User:Maverick423 If It Looks Good Nuke It 17:02, 30 April 2007 (UTC)

When you stop growing will probably depend largely on your genetics. Although many do continue growing into their early twenties, some do not. It does depend on the person - and is probably to do with genetics and probably also things like diet etc. It'll generally depend on when you reached puberty. Earlier puberty = stopping growing sooner, generally speaking - although it's probably not quite that simple. I stopped growing when I was 15 at 6'0". One or two in my year at school stopped earlier. Many of my friends were still growing near 18. It all depends - and the only sure way of checking would probably be a bone age test. 83.67.65.69 17:37, 30 April 2007 (UTC)

Picture identification

I saw this strange plant and photographed it. Does anyone know what it is? J Are you green? 22:20, 30 April 2007 (UTC)

Is it right side up, or did you photograph it sideways? Some kind of pollen?--VectorPotential^Talk 23:29, 30 April 2007 (UTC)

Plant location, image with leaves would be helpful bmk

It is right side up; it was growing out of a possibly dead, leafless bush-like plant in an abandoned field. The ball itself was about 2 or 3 cm in diameter if I remember correctly. J Are you green? 01:31, 1 May 2007 (UTC)

By "location", I'm guessing bmk meant something both more and less specific than "an abandoned field", namely: what part of the world? Country/province/state/city? —Steve Summit (talk) 02:19, 2 May 2007 (UTC)

I can't tell for certain if it's from the plant, but there appears to be a strand of silk which might indicate an insect or other animal life which contributes (partially or wholly) to the fuzzy appearance. 128.12.131.62 01:35, 1 May 2007 (UTC)

The underlying brown stalky bits look very much like the old remains of an umbel, the seed bearing part of an Apiaceae plant (such as carrot, fennel, celery etc). But the stalks to the seeds have been broken off. The white fur may be a fungus such as mould. GB 01:24, 2 May 2007 (UTC)