Wikipedia:Reference desk/Archives/Science/2007 July 17

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July 17[edit]


Why is it considered bad luck to kill an Albatross? -- 01:25, 17 July 2007 (UTC)

The Rime of the Ancient Mariner is relevant, there is also some information in the article Albatross. My understanding has always been that albatrosses are the souls of drowned sailors. DuncanHill 01:29, 17 July 2007 (UTC)

How to apply heat-conduction formulas? (Hopefully my last Wx-sim question!)[edit]

(My apologies for the barrage of wx-sim related questions -- in trying to do my own research, I've run up against a seemlingly endless stream of helpful formulae which leave-out the units or the application!)

Pre-question: Would it be helpful if, once I get these things all figured out (search this page for "weather-sim"), I added some examples to the relevant wiki-pages? There are lots of helpful pages with formulae and coefficients, but which lack examples & units for the laymen.

The real Question (short): I'm not quite sure how to apply the heat transfer equations for heat conduction; could someone please provide an example?

More detail: (EDIT: (I forgot to mention in the original) this is for a grossly simplified weather-sim for a game. I'm willing to take lots of shortcuts & approximations, the goal is more to give "realistic appearances" rather than "true to life" actual physics.)

For example, let's say I have a sandstone "rod", 1m^2 in area, 3m long. It's 40°C at one end and 20°C at the other end, in a smooth gradient. I want to apply conduction equasions, so we'll ignore radiation & convection. To idealize the situation, we'll also ignore any heat conducted into space, and just say that the rod conduction is "pure." (I know, I know...) Let's say an hour passes; what is the temperature at both ends of the rod?

Heat conduction tells me that the basic formua is

 \frac{\Delta Q}{\Delta t} = -k A \frac{\Delta T}{\Delta x}


Q is the amount of heat transferred,
t is the time taken,
k is the material's conductivity.,
A is the cross-sectional surface area,
\Delta T is the temperature difference between the ends,
\Delta x is the distance between the ends.

Checking the links in the question, and several related sites, applying to our example, I get

 \frac{\Delta Q}{\Delta t}  = -2.4 * 1 \frac{20}{3}


 \frac{\Delta Q}{\Delta t}  = -2.4 * 6.667

Follow up: What to do with numbers so far?[edit]

So now my questions are:

  • What is the units for Q?
  • What is the units for t?

Assuming seconds, I get

 \frac{\Delta Q}{3600}  = -2.4 * 6.667


 \Delta Q = -2.4 * 6.667 * 3600 = -57,600

but, um... what do I do with that number in order to determine the ending temps of both ends of the rod?

Might Q be in watts? So, I subtract 57.6kW from one end and add it to the other? (I thought I had a formula for how to do that, but could someone help me convert that to °C, just for example?)

Btw: Hats off to you guys who know all this stuff. I know it's not magic, but it's pretty darned close!

Thanks! Oliepedia 03:21, 17 July 2007 (UTC)

You've picked a real tough problem here. Digging through my heat transfer book, I can't find any simple relationships for the situation you have, which is one-dimensional conduction with adiabatic boundary conditions at both ends (no heat transfer in or out of either end). Unless someone finds a way I've overlooked, it looks like you'll have to apply Fourier's Law. You're on the right track with what you have, but you've made an incorrect assumption to arrive at the equation you give (and which is given in the article). Namely, there must be heat flux through the ends of the rod. If you're willing to make that assumption, then you're on the right track. If the ends of the rod must be adiabatic, we have to start with the general form (for Cartesian coordinates)
\frac{\partial}{\partial x}\left(k\frac{\partial T(x,y,z,t)}{\partial x}\right)+\frac{\partial}{\partial y}\left(k\frac{\partial T(x,y,z,t)}{\partial y}\right)+\frac{\partial}{\partial z}\left(k\frac{\partial T(x,y,z,t)}{\partial z}\right)+q^m=\rho\cdot c_p \frac{\partial T(x,y,z,t)}{\partial t}
Since this is one dimensional, the above boils down to
where \rho is the material density, cp is the specific heat, and k is the thermal conductivity. This is a partial differential equation, which is best solved numerically. I'll leave that up to you. Sorry about the format of the equations, if someone wants to put them in Tex, please do.--anonymous6494 04:21, 17 July 2007 (UTC)

I'm happy to have heat-flux through the rod-ends (uh... what does that mean?!) if it makes the math simpler. See edit, above. Oh, heck, I'll repeat it, here: (I forgot to mention in the original) this is for a grossly simplified weather-sim for a game. I'm willing to take lots of shortcuts & approximations, the goal is more to give "realistic appearances" rather than "true to life" actual physics.

Also, I dropped from pre-calc. So, while I get the general concepts, I can't always read all the equations (plus, it's been 30+ years, so details like units escape me.) That's why I was looking for an example walk-through with numbers. I'm hoping to come out of this with something like "So, as you can see, after an hour, the rod will have a smooth temperature gradient, ranging from 35.78°C to 23.9826°C" (numbers made-up for example only.)

Thanks! Oliepedia 04:47, 17 July 2007 (UTC)

Q is in Joules, its a unit of energy. What happens next depends on where that energy is going. Depending on what the "rod" is anchored to (if anything) it will flow from the stuff at one end to the stuff other. Or in the case of a free floating rod, you can imagine the energy going from the hot "half" of the rod to the cold "half". But anyway, the piece of the puzzle you are missing is \Delta Q = M c \Delta T, where M is the mass of stuff the energy is moving in to (or coming out of), c is the specific heat which is simply a constant that varies by material, and \Delta T is the resulting change in temperature. Dragons flight 05:58, 17 July 2007 (UTC)
PS. Please note that the \Delta T I just used, is the change in local temperature for a given amount of energy transfer and is different than the \Delta T you used above to describe the difference in temperature across the two ends. Dragons flight 06:05, 17 July 2007 (UTC)
Since you are going to run it as a weather sim, don't bother trying to solve this analytically; you'll have to convert it to a numerical solution anyways. Since this is a partial differential equation, I would advise using the Crank-Nicolson numerical method to solve the BVP. First discretize with respect to \Delta x with a second-order centered finite difference, then with the algebraic mean of the forward Euler method and backward Euler method for \Delta t. It also allows you to declare adiabatic/insulated/fixed-temperature boundary conditions with minor modifications to the code. Titoxd(?!? - cool stuff) 06:12, 17 July 2007 (UTC)

Follow up: Attempt to apply formulae[edit]

Leaving off with  \Delta Q = -2.4 * 6.667 * 3600 = -57,600 (above), and tossing in Dragons Flight's \Delta Q = M c \Delta T, which I'll switch around to

\Delta T = \frac {\Delta Q} {M c}

(since I'm trying to solve for  \Delta T), and since I know the density of my sandstone (2.323) gives me M=6,969,000g (for 3m^3), and a c of 0.92 for sandstone, I now get:

\Delta T = 0.008983885156

(Hmm, well, I guess it WAS a 3m rod, and only a 20°C differential for an hour...) So, ~0.009°C temp change at both ends -- does that seemreasonable to everyone? (Later, I'll do it with a shallower pool of water, something with which I'm more familiar and better able to speculate the correctness of the answer.)

Just to make sure I've got it, though (and, remember, we're doing gross simplifications & uber-idealization, here -- eliminating all the complicating factors like radiation, conduction, external objects, etc.) -- since 57.6kj "left" one end of the rod (in order to heat the other), then the "hot half" is going to cool-down by the same amount that the "cool half" warms up, and that amount will be my \Delta T, in °C, right?

A big thank you to everyone for your patience in getting me through all this. I'll need to read-up on wiki standards and then see if I can't back-fill some of these examples into the relevant pages. Oliepedia 15:16, 17 July 2007 (UTC)

canebreak or timber rattlesnake / range to desert West Texas?[edit]

I ran across a rattlesnake last weekend, and based on Wikipedia articles and photos, decided it looked like an excellent example of a timber or canebreak rattlesnake. Problem is, the wikipedia article and other sources describe it's range as the Eastern US, possibly including eastern Texas. I ran across my snake about as far west in Texas as possible -- in the Franklin Mountains above El Paso, Texas. (that's about as far west as Denver, Albuquerque, etc.)

Is the article wrong? If so, I don't really feel qualified to edit it. Anyone want to look at my photos or video? I'm wondering if anyone specializing in rattlesnakes would be interested in knowing about timber rattlers living in the desert southwest. My father, who's been in El Paso for 86 years says he's never seen one like that before (we usually see diamondbacks.)

One photo can be seen at:

I have more, as well as some .avi video files (not as high res as the stills.)

UPDATE: nevermind, he's positively a Banded Rock Rattlesnake. I found a good description and photo that identifies him as such, a known resident of the Franklin mountains.

Blyon3 03:22, 17 July 2007 (UTC)blyon3

Proof (if ever it were needed) of the wiseness of Wikipedias' WP:NOR policy. Even if you had found a canebreak snake in the Franklin mountains, you should not have changed the article since your finding of the snake would count as "original research" - which Wikipedia does not allow. What you would have had to do would be to find a book (ideally) or a reputable web site that stated that canebreak snakes were found in that region. SteveBaker 10:59, 17 July 2007 (UTC)

oxygen enriched v. anti-oxidant[edit]

To whom it may concern:

I attended an event where a promoter was handing out bottles of oxygenated water. I've also read about oxygen bars and the indulgent few who sleep in hyper-baric oxygen chambers.

On the flip side many food and nutritional products boast of their anti-oxidant properties.

Obviously, oxygen is essential resource for much of life on earth and yet I also know that it is an essential part of the fire triangle - fuel, oxygen, heat.

Is there a different value to the way that oxygen is consumed – breathed v. infused in water v. part of the molecular structure of the food/water itself?

Should there be an RDA for oxygen?

David —Preceding unsigned comment added by Carbon333 (talkcontribs)

On the one hand, you need enough O2 to perform your metabolic conversions. RDA is "that much" (depends on your weight, metabolism, physical activity, etc.) On the other hand, anti-oxidants are things which slow the oxidation process, and are reputed by some to be a preventative against cancer [citation needed]. Since cancer is basically cell-replication-gone-haywire, perhaps the idea is that anti-oxidents "slow down the fire" to a "safe and sane" level. I'm not 100% sure on that part, but it sort of follows reason.
At any rate, you need O2. Also, Oxygen at pressure (i.e., breathing compressed O2 under water) can be toxic to the point of fatality. Breathing oxygen enhanced air even at surface pressures certainly accelerates metabolic processes. You can debate whether that's benefitial (gives you a lift) or harmful (over-works your system.) Oliepedia 04:54, 17 July 2007 (UTC)
Okay, there's a lot of confusion here. First of all, an antioxidant is not something that fights or inhibits oxygen in particular. An antioxidant is something that prevents oxidation. Oxidation is the removal of electrons from a chemical. Elemental oxygen is a familiar oxidizing agent, but certainly not the only one. The similar sound of the words oxygen and oxidize is a historical accident, so try not to let it confuse you.
Second of all, you need to breathe oxygen in order to live. Your lungs are your only organs capable of getting oxygen to the bloodstream anywhere near efficiently enough. Drinking water with oxygen dissolved in it will not do you any good if you are asphyxiating. In fact I'll go ahead and say that it probably won't do you any good under any circumstances. It's a scam. —Keenan Pepper 07:28, 17 July 2007 (UTC)
As for bottled oxygenated water (stub required), it's highly recommended if you happen to be a fish. Otherwise, scam is probably the most appropriate term.--Shantavira|feed me 07:41, 17 July 2007 (UTC)
If you aren't getting enough oxygen, your body will make you breathe faster. Simple as that. You don't need to "supplement" the oxygen that you are breathing. It doesn't work that way. Inhalation is by far and away the most efficient way of getting the oxygen you need. As other have said, oxygen infused water sounds like complete bunk. Capuchin 07:48, 17 July 2007 (UTC)
The urge to breathe is actually due to a build up in Carbon Dioxide. If there is a lack of oxygen in the air, you probably wouldn't notice and you would either faint or die, depending on the circumstances. Most Water is already oxygenated in a way anyway, see Dissolved Oxygen for more info.--GTPoompt(talk) 12:42, 17 July 2007 (UTC)
Under normal conditions, the solubility of oxygen in fresh water tops out at 14.6 mg/L. (That's under regular atmospheric pressure; at 4°C and three atmospheres – the pressure inside a soda can[1] – that limit increases to about 35 mg/L[2]. Meanwhile, the density of oxygen is about 1.4 grams per liter (1400 mg/L) at room temperature. The air around us is about 20% oxygen, giving a concentration of about 280 mg/L. Draw what conclusions you like. TenOfAllTrades(talk) 12:53, 17 July 2007 (UTC)
As I recall, the above numbers are one of the primary reasons why humans can't breathe water (another major one is the unsuitability of the lungs to circulate something as dense as water), as contrasted with being simply unable to process the water at all. You may be interested in reading liquid breathing. — Lomn 13:18, 17 July 2007 (UTC)
Also remember to compare how much air you breathe compared to how much water you drink. Capuchin 10:58, 18 July 2007 (UTC)
The oxygenated water is just a gimmick. might taste better. Certainly, water with all the gas removed from it tastes kinda flat. As to the folks who are consuming more oxygen for their health, unless they have severe lung problems this is also dumb. On the other hand, as you note, evidence is that free radicals and their oxidative properties are part of the aging process. Oxygen is, after all, a corrosive gas, which was toxic to the lifeforms existing when algae first started pumping it into the air; some of them still remain, Clostridium for instance (as in, botuslism, which can only survive in the absence of oxygen, as in canned food). The rest of us made our peace with it and even learned to use it under controlled circumstances, but the concept that sleeping under a hyperbaric tent is good for you is akin to all the other bright ideas Michael Jackson has. On the other other hand, nobody sleeps under a low-oxygen tent to reduce free radical formation, because you'd need somebody monitoring your brain waves and blood O2 level continually to make sure you weren't nosediving into a coma. Gzuckier 14:32, 17 July 2007 (UTC)
I have seen oxygen bars advertising that they mitigate the effects of altitude sickness in the Colorado mountains. Whether this is true or not I don't know, but it makes sense because part of altitude sickness is caused by the lower partial pressure of oxygen. Sifaka talk 05:57, 18 July 2007 (UTC)

I thought athletes sleep in hypobaric chambers to increase their amount of red blood cells so they can carry more oxygen quickly and have better stamina. It will increase the chance of getting a stroke or (myocardial)infarction though because the blood is thicker. Hyperbaric chambers are used to relieve altitude sickness. --antilivedT | C | G 06:01, 18 July 2007 (UTC)

Coconut Husks and Water Absoprtion[edit]

My question on 11 July, should I say, as a whole fruit, the skin of the coconut is water-proof (does not absorb water), and the fact that the inner part of it contains husks, shell, flesh, coconut juice and some amount of air - to explain why it is float from island to island as a form of dispersal. Should I say too that coconut husks absorb water while the coir fibres that are found between the skin and the husks is relatively water-proof but still absorb water to certain extend ( if you soak the coir fibres in the water, it will swell and soften - to explain the absorption ). (Teng)

Yes, I stated all these points. You can follow the experimental procedure that I suggested to obtain an idea of absorption. It'll be fun for your son! Capuchin 07:49, 17 July 2007 (UTC)

Water Stain Removal on Standard Steel SUS430[edit]

Pls help. Whats the best cleaning solution for the water stain on standard steel? I use Nitric Acid still can't remove. HFI a bit strong... 09:13, 17 July 2007 (UTC)

Is this rust? Better to use a file, wire brush, or steel wool in that case. What sort of item is it?--Shantavira|feed me 12:54, 17 July 2007 (UTC)

Follow-Up: Its not realy a rust, more of water spot which scattered all over the surface of HDD Cover. Can't use file ot steel wool as it will leave scratches on the surface. 04:33, 18 July 2007 (UTC)

You can purchase stainless steel polish for cleaning saucepans and cutlery. It probably has somehting like toothpaste in it. GB 07:13, 18 July 2007 (UTC)

One thing I would do would be to repeat the stain all over the cover - eg wipe with a damp wet cloth - then your cover would be a different shade of steel (greyer) but at least it would look uniform. I'm guessing that the surface is 'burnished' in someway to give a 'rough industrial' effect rather than being highly polished.. If it's just a water stain the staining might by due to salts (water hardness) - I'd try something alcoholic (but pure) - you could use isopropyl alcohol if you can get it.. or even vodka. Be careful on any plastic parts with the solvents - especially lacqueered bits. By the way did the nitric do nothing - I'd imagine it making the stain worse.. ps how did it happen ? are you sure it's water - not grease? 18:16, 18 July 2007 (UTC)

Cottage Grove seismic zone in Southern Illinois[edit]

I have been searching for information on fault locations and seismic history for this area. I have been able to ascertain it is a series of strike/slip faults on the eastern edge of the New Madrid system near the start of the Wabash Valley system and that some of its features interfere with coal mining in the region, but little to nothing on its seismic history and potential hazards. We are particularly interested in information pertaining to the area within a 50-mile radius of the Harrisburg (IL) quadrangle. 13:58, 17 July 2007 (UTC)goldcatt

This PDF may provide some guidance. So far as I could determine in a quick search, it is not particularly active sesimically. The Illinois Geological Survey would be your best source of authoritative information. Cheers Geologyguy 17:45, 17 July 2007 (UTC)

The Skimmer - how does it avoid injury whilst feeding?[edit]

After watching the videos linked from the Skimmer article, it made me wonder how on earth these birds avoid accidents whilst feeding. Flying rapidly along, just above the surface of the water with the lower mandible trailing in the drink seems like a recipe for disaster. What if there was tangled plant matter, or even worse - a rock (hello broken jaw!) just under the surface? Has anyone seen Skimmers feeding in real life? Do they often injure themselves whilst going about their business? --Kurt Shaped Box 15:12, 17 July 2007 (UTC)

Because the article says they are in the same family as gulls, I have to assume they have similar eyesight. Gulls can easily see fish (and other objects) in the water. So, the skimmer must be able to see the fish it is "skimming". -- Kainaw(what?) 15:18, 17 July 2007 (UTC)
I have occasionally watched Black Skimmers feeding at Morro Bay in California, and as I recall when they hit something and/or catch something (hard to tell which) their head and lower mandible moves very quickly backwards (as if they were tucking their head underneath their body and trying to touch their underside--hard to describe). So I assume that if their lower mandible did hit some solid object their head and bill would simply move backwards out of danger. Also their lower mandible doesn't extend very deep into the water, so the chance of their hitting something solid that they could not see would be pretty small. On the other hand when they are feeding they seem to be moving very, very fast! Please note this is purely on the basis of my own observations and I could be completely wrong.--Eriastrum 16:38, 17 July 2007 (UTC)
Your observations make sense when you consider the mechanics of the situation. Sorry, I'm not a physics student, so I don't know the correct terminology here - but striking and underwater object 'stiff' (i.e. without using its flexible neck to absorb some of the force of impact) would cause the bird to either 'break' or be flipped forwards, like a human going through a car windscreen, wouldn't it? --Kurt Shaped Box 22:34, 17 July 2007 (UTC)
Yes, the head would experience increased drag and thus deceleration, but the body would continue moving at the same speed. Capuchin 06:48, 19 July 2007 (UTC)

Kerala Fever and Blood Platelet count[edit]


My mother is very sick and she is hospitalized. The doctor says it is only a viral fever. The platelet count is very low. She had the same issue about 2 years ago. Then it became very dangerous and she had to receive the platelet component from a donor. Sine we are aware that for last few years it is repeating at Kerala during the monsoon season, we had taken enough care to maintain hygienic and healthy environment at our house. But still, she got it again; she is only around 60 years old.

We all have got viral fever in the past; but never happend the issue of platelet count. The doctor’s explanations are not convincing enough. As our politicians are stonehearted creatures who are getting ready to face the disaster by preparing mass condolence messages, we desperately hope whether Wikipedia could immediately mobilize the work of some experts on the issue.

I would like to know

1. Under what circumstances (diseases) the platelet count can go down.

2. Is the level of seriousness of the issue (lower count of platelets) is different under different root causes?

3. What is the relation between ordinary viral fever and platelet count? Why not all people have the issue of platelet count go get affected by viral fever?

4. At Kerala, this issue has become so wider spread only since last few years. About a few years ago, there was a strange phenomenon of ‘coloured rain’ at different parts of Kerala. There were news paper reports saying that analysis showed the rainwater contain unknown life forms that might have come from some asteroids. a. The Kerala fever and this ‘coloured rain’ has any connection?

b. What really caused the coloured rain?

c. Could it be the hand work of some inhuman research organizations experimenting with ‘rain cloud engineering’?

5. How serious is the ‘Kerala Fever’?

6. Why it is repeating each year?

7. How can people escape from it?

For medical advice you should consult a doctor. For extraterrestrial advice you should consult a scientologist. Lanfear's Bane
To find out more about platelets, you can read about platelets. The red rain in Kerala was caused by colored algae spores, which possibly looked extraterrestrial to someone who has no idea what algae spores look like. If you don't trust your doctor, find another one. 17:43, 17 July 2007 (UTC)
  1. See thrombocytopenia.
  2. Yes.
  3. It depends; see your doctor.
  4. a) The Kerala Fever you're referring to is probably Chikungunya. It is caused by a virus transmitted via mosquitoes. b) The red rain in Kerala was (most likely) caused by algal spores. c) See weather control, and no.
  5. See Chikungunya.
  6. There's no vaccine, and it's hard to get rid of mosquitoes.
  7. Avoid mosquitoes.
Please speak to a physician to discuss specific personal health issues. TenOfAllTrades(talk) 17:47, 17 July 2007 (UTC)

Is this real?[edit]

Ballard score, uncategorized for ages, unlinked to, I don't know anything about. It's way out of my field, but... I can't tell if it should stay or go and unfortunately I don't know what Wiki-Projects to notify about it... 17:02, 17 July 2007 (UTC)

It should be under Ballard Maturational Assessment. And, it is used to assess gestational age. -- Kainaw(what?) 17:28, 17 July 2007 (UTC)
Yes check.svg Done Moved it to that title--VectorPotentialTalk 17:35, 17 July 2007 (UTC)
Just thought to add a link to a BMA form, -- Kainaw(what?) 17:28, 17 July 2007 (UTC)
Just need some links to it from the relevant articels and it'll be fine, thanx. 14:58, 18 July 2007 (UTC)

shielding angle and protective margin[edit]

What do you mean by shielding angle of a transmission line and what are its recommended values? What is protective margin and what are its recommended values> Thank you for your reply. —Preceding unsigned comment added by (talkcontribs)

Never heard of the term shielding angle. What sort of transmission line are you asking about?--Tugjob 01:18, 18 July 2007 (UTC)

gapless surge divertor[edit]

I have two questions. What are the advantages of gapless surge diverters? What are the differences between a surge diverter and a surge absorber? —Preceding unsigned comment added by (talkcontribs)

I would say that an absorber totally dissipates the energy of the surge, whereas a diverter reflects it.--Tugjob 01:15, 18 July 2007 (UTC)

In some lightning arrester (divertor) systems for example for Ham Radio Antennae's they have a gapped diverter which in effect says " if the voltage is high enough it will divert ( jump the gap) to the most conducive ground (a very well grounded contact). The con to the gapped system is that it also conducts some (too much and it frys your radio) of the surge to the device its supposed to protect. The PRO is that it does divert most of the lightning bolt safely away to ground preventing a fire in "most" cases. Its alot better than nothing but not perfect. By the same token, the consumer 'surge protector' you buy to plug your pc into are also not 100% .. advice use two back to back in series for more protection. I've seen phone type surge protectors absolutely charred and burnt thru (although the phone co denies this vehemnently to avoid lawsuits).

In a gapless system they must have found a way to do away with the gap.  Probably a solid state DIODE or other device that is actually in my opinion more
prone to breakdown.. and more expensive to replace.  Best advice use both types in series for lightning.
 ALso have a very good lightning rod system for the whole house (standard in use for hundreds of years
- ben franklin) with heavy copper cable to very good heavy 8 foot copper rod into ground all the way until
only 2" are above ground to bolt cabl to. 
  The surge absorber is probably just another name for a  surge protector.  
 IFF you can invent a true high wattage surge absorber (a giant battery) you can "slay the dragon" so to speak and
capture lightning bolts for use to power cities.  TripleBatteryLife 16:27, 23 July 2007 (UTC)

Power Systems[edit]

What are the differences between the two types of lightning strokes: A stroke and B stroke on transmission lines? —Preceding unsigned comment added by (talkcontribs)

three questions in power systems[edit]

What is an isolator? What is a back flashover? What are the types of lightning strokes that can cause such back flashovers of line insulators? What is surge impedance of a transmission line and what are its significances? —Preceding unsigned comment added by (talkcontribs)

I suggest you re read your lecture notes!--Tugjob 01:20, 18 July 2007 (UTC)

gapless surge diverter[edit]

can someone briefly describe the working and construction of a gapless surge diverter? Thanks for ur help. —Preceding unsigned comment added by (talkcontribs)

See transient suppressor--Tugjob 01:11, 18 July 2007 (UTC)

Uncertainty in various fields[edit]

(This question was originally asked at the Mathematics Reference Desk but editors there suggested the Science desk was more appropriate.)

When giving error limits, there is almost always an uncertainty associated with the limits. For example, the August 2007 edition of Scientific American contains a graph on page 67 that shows various causes of radiative forcing which are thought to be driving global warming, and for each forcing an error bar is shown, which represent a 90 percent liklihood that the value lies within the error bar. Similarly, page 66 contains the statement "the updated trend over 1906 to 2005 is now 0.6 ± 0.2 degree C." There must be some unstated uncertainty associated with this tolerance; perhaps the phrase realy means there is a 90 percent probability that the trend lies between 0.4 and 0.8 degree C.

What I would like to know is whether there is/are document(s) that state what level of uncertainty is usually used in various fields when there isn't enough information to rigorously choose an uncertainty level? If this had been a biology article instead of a climate article, would the uncertainty level have been 95 percent rather than 90 percent?

I understand that on rare occasions, the economic consequences of the measurement falling outside the error bounds is known, and the budget available to deal with the outliers is known, so an appropriate error bound can be rigorously calculated, but this seldom is the case. --Gerry Ashton 22:03, 16 July 2007 (UTC)

A rigorous, peer-reviewed scientific journal will always explain the meaning of an error bar or interval in a figure, and explain how it is derived. Unfortunately, publications meant for popular consumption usually omit the details of these derivations. (Scientific American – well-written and generally high-quality though it may be – is no exception.) In order to get the information about how these values are derived, you need to go back to the primary sources. I'm going to assume that the Scientific American figure you're referring to is similar to the one in our Image:Radiative-forcings.svg, which in turn is based on the IPCC's Fourth Assessment Report; you'll have to look through that document to see how they arrived at those particular confidence intervals.
Different fields of study will tend to have different standards for evidence and reporting, and even within a field (and indeed even between papers in a single journal) there are apt to be differences depending on circumstances. To get an idea of acceptable standards of evidence and statistical significance, you might be well-advised to pull a few journals from the relevant field and look at the statistical tests used. TenOfAllTrades(talk) 21:04, 17 July 2007 (UTC)
In general, a point on graph represents a measurement of some sort. It may represent a single datum, or it may represent the mean (or other statistic) of a set of data. If it represents a single measurement, (for example, a reading from a voltmeter) then the uncertainty of the measurement is based on the precision of the instrument and the experimental setup, as calibrated during other experimental runs. The calibration is done using statistical methods. In either case, we are now in the realm of statistics. The "error bounds" given in any particular case represent a crude representation of the underlying statistical methodology. Basically, you are getting three points (the datum, the lower bound, and the upper bound) of what is actually a continuous statistical curve. You must go back to the original report to discover which particular curve these three points represent. If for some reason you disagree with the statistical model used by the author, you must go all the way back to the original data. In many cases, the author assumes a gaussian distribution. In this case the author can use the mean and the standard deviation as the three points. If the underlying distribution is not gaussian, the result is misleading. -Arch dude 03:15, 18 July 2007 (UTC)
As far as I know, and certainly in physics, the plus/minus errors on a number represent one standard deviation. That is a 68% probability. People will also tend to prove things up to a certain confidence limit, 95% is a standard choice. Somehow being used to more precise fields of physics 90% doesn't seem that convincing, but I suppose it is quite high really. Cyta 07:19, 18 July 2007 (UTC)
I think you may be confusing a p-value with a confidence interval. The former is a way of evaluating whether or not there is a statistically significant difference between two values. The latter is a way of expressing the uncertainty in a measured or calculated value.
In other words, the apples-to-apples comparison you should be making is between standard deviations and confidence intervals as ways of expressing uncertainty. For a normally distributed variable, a 95% CI is going to be 2 SD, a 90% CI a bit less (but still much larger than 1 SD error bars). CI's have the advantage of not necessarily implying a normal distribution, of course. As you've probably noticed, if certain conditions are met it is entirely possible to have two values with partially-overlapping distributions still be statistically significantly different. TenOfAllTrades(talk) 13:16, 18 July 2007 (UTC)

Chemistry and Childbirth[edit]

How does chemistry relate to childbirth? 21:01, 17 July 2007 (UTC)

That's a bit broad. Narrowing your question would help us answer it. For instance, are you interested in the chemicals (hormones, etc.) that dominate during pregnancy, labor-inducing drugs, contraceptives, etc? Help us help you. --David Iberri (talk) 02:24, 18 July 2007 (UTC)


im looking for the best available thermoconductor to extract heat from hot air, i need to find the most efficient way of doing it , colud anyone help me with this please

Best depends on many things - are you after the cheapest, the longest lasting, the least maintenance, what sort of temperature range does it have to work over (sub freezing, or over boiling point of water?). and by efficient do you mean to cool the air as fast as possible, or as cold as possible, or using the least energy possible? Water in a copper pipe is a way to do it, but if you have a narrow range of temperature, a liquid that boils at your temperature can extract heat quickly. Have a look at how airconditioners work! GB 22:22, 17 July 2007 (UTC)

sorry, i think i didnt mean thermoconduction here , i forgot to mention that i need to extract heat form hot air and turn it to electrical current , in the most cost efficient way possible ,this would be used at the same time to generate electricity and prevent the system from overheating , im planing on using a lot of these conductors in a tube and passing the air contained in the system trough the tube and back in the system to be heated again , the only thing is i dont know what kind of conductors to use.

Have you considered using something other than air for your heat exchange? -- JSBillings 13:24, 18 July 2007 (UTC)

not really since im pretty sure it would increase the cost a lot and i coudnt have fluids go inside the main chamber where all of the heat if generated and needs to come out quickly to keep from over heating , the unit would be sealed tough so i could use an other gas than but i dont know anything about gas thermoconductivity , i could surround the main chamber in fluid filled pipes but im not sure if that would be enough

why is it[edit]

that generally men have darker skin than women? —Preceding unsigned comment added by Jolly hockey sticks what (talkcontribs) 22:10, 17 July 2007

Do they? Never noticed. Where do you live? Simon A. 22:21, 17 July 2007 (UTC)
Men often spend more time outdoors in the sun, therefore get a tan and are less likely to use daycream. GB 22:25, 17 July 2007 (UTC)
Oh, that really depends on where you live/work. The dynamic could be easily reversed (except that daycream part). Someguy1221 23:55, 17 July 2007 (UTC)
In some cultures it's considered more attractive for females to be lighter skinned, while not necessarily for males. --antilivedT | C | G 05:53, 18 July 2007 (UTC)
How is "asian people" a culture? --Edward Morgan Blake 09:43, 21 July 2007 (UTC)

So, just how does a gull's eyesight compare to that of your average human's?[edit]

(Question in relation to the Skimmer thread above - not just another self-indulgent seagull query, hehehe).

I've seen it stated that birds generally have better eyesight than humans - but what about the gull family in particular? How do they measure up to us in terms of colour vision, depth/motion perception and general sharpness of sight? --Kurt Shaped Box 22:54, 17 July 2007 (UTC)

Gulls are evidentally UV sensitive [3] Nil Einne 23:22, 17 July 2007 (UTC)
Cool. Do you have a non-blog-related source for that? I'd really like to add this info to the Herring Gull article... --Kurt Shaped Box 23:36, 17 July 2007 (UTC)
Don't know if birder's world counts as a reliable source, but [4] says "Besides hummingbirds and songbirds, parrots and gulls are known to see UV light". Hope you don't mind, I corrected your borken link Capuchin 07:45, 18 July 2007 (UTC)
My understanding is that essentially all birds have much better vision than humans -- and humans (and other primates) have generally better vision than other mammals. While I am not sure about gulls in particular, I think all or nearly all birds have four color receptors rather than the normal two receptors found in mammals. Humans have three (red, green, blue if I'm not mistaken), but one of them is a bit of a kludge and not as good as any of the four that birds have. Also, most or all birds have a variety of other vision-enhancing things, like "oil droplets" in or near the eye lens, to help focus, and better foveas. Some birds even have more than one fovea per eye. My quick search indicated that birds of prey tend to have multiple fovea. While gulls are not birds of prey, they are scanvangers (at least where I live!), which, as I understand it, requires sophisticated vision and flying skills beyond what people commonly think. A google search turned up all kinds of info on bird vision, but it would take more time to find something specific to gulls. I found a few clues while googling, but didn't spend that much time on it. A more determined search would probably turn up gull-specific vision info. Finally.. for some reason I always enjoy pointing out how birds are far superior to humans in both vision and vocalization. We literally cannot conceive of what it would be like to see things the ways birds do. Pfly 08:40, 19 July 2007 (UTC)
AFAIK, birds also have much more efficient respiration and metabolism than humans. They're incredibly well-'designed' for what they do. I'm not too sure about their senses of smell, taste and hearing - I've heard conflicting information. --Kurt Shaped Box 22:53, 19 July 2007 (UTC)
Well, most birds have a really poor sense of smell but there are some really notable exceptions (kiwis, albatrosses, vultures, etc). It doesn't take long to figure out why - a keen nose would require some keen olfactory-sensing brainpower and weight is precious to flying birds; they'd need a really good reason to have a good sniffer. Albatrosses and vultures need it because they scavenge for a good portion of their calories. Kiwis obviously don't have the same weight-worries. On the other side, smell would be of little use in finding seeds, worms, bugs, fish, and live meat - or rather, it would not be as useful as good eyesight, which the bird needs anyway to fly.
I've no idea about the taste sensation in birds. The hearing is probably pretty good (especially in owls) since they need to recognize some pretty complicated songs and oftentimes repeat them back. Matt Deres 20:30, 20 July 2007 (UTC)

How do you control and eliminate the aquatic plant Wolffia (aka Watermeal/Mealweed)?[edit]

Location is central South Carolina; the Wolffia grows extensively in a large pond that has catfish and bream in it that is caught for human consumption. I would like to know what chemical and biological treatments are available and their effectiveness as well as duration of time needed for the treatments. What side effects are there to these treatments? It would also be helpful to know what options are available in preventing its spread in coming years. BotanistWannabe 23:41, 17 July 2007 (UTC)

wolfia is difficult to get rid of - one possible method is to remove all of the plant - but that would be difficult - one possible method would be to use a rolling filtration system similar to that used to harvest algae (it's a bit like an up escalator - with mesh for steps).
alternatively plant competing plants (reeds, bullrush etc) after skimming the wolffia - that should compete for nutrients and limit it's grow back. ( same thing as pdf) gives lots of answers - note the use of carp and water fowl to eat it - ducks are tasty -why not add those! 12:46, 18 July 2007 (UTC)
the above also lists chemical treatments - note that limited amounts of duckweed will proved shelter and food for fish fry. 12:48, 18 July 2007 (UTC)