Wikipedia:Reference desk archive/Science/2006 August 14

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[edit] casimir effect scale up

Can the casimer effect in theory if not practice yet be scaled up in size and effect range? could we in theory make a repulsive or attractive force from it that could act on larger objects? Is there debate on this subject or is it a flat out no. How then if not by this are scientist proposing right or wrong to produce propulsive force from vacuum energy -- Restless

No. In the Casimir effect, two very closely spaced neutrally charged parallel electrically conducting plates mutually attract because their presence changes the mode structure of the quantum zero point field (ZPF) relative to free space. If the plates are a distance d apart, the force per unit area <cool math stuff I couldn't get to work, sorry> is the reduced Planck’s constant and c is the speed of light in vacuum. The attraction between the two parallel plates can be understood in terms of the pressure of zero-point energy being greater outside the two plates, than in between—the plates snap together. This force is so so small. That is why the Casmir effect could never be scaled up—the mass of the plates would be greater, while the energy pressure continues to stay the same. ...unless you could get them closer and closer together. What would be that limit? Probably the Planck length Where is the article on the Casmir effect?? — [Mac Davis] (talk)

Try Casimir effect. --Lambiam ^Talk 06:18, 14 August 2006 (UTC)

I swear I tried that, even though I thought it was spelled "Casmir." — [Mac Davis] (talk)

What if you could somehow increas the radiation pressure of the zero-point field in one area, would that be able to cause a larger version of the casimir effect? you also never aswered how people are trying to produce propulsive force from zero point energy. restless

Look up for my response to a poster inquiring about some cranky stuff he found at some websites which promote "free energy from the vacuum schemes". Basically, vacuum energy is a legitimate topic in mainstream physics, but the idea that you can use it to do useful work is highly suspect, and in particular, claims that you can use vacuum energy to build a device which would violate the laws of thermodynamics (the term used by many cranks is "over-unity") is definitely cranky.---CH 23:59, 14 August 2006 (UTC)

Hmmm for a mathemetician with with no physics degrees that i have seen in your profile CH, you fling the word crank around alot. SEAS is run by a guy called tom valone I wouldnt call that a crank myself. And hal puthoff who while controverisal in some areas is a well acknowledged expert in vacuum energy [he hosted the NASA talks on alternative energy sources in 2001] agrees with many of these ideas. Just because you dont like his ideas doesnt make him a crank. Furthermore if you look at vacuum energy on this site even it is a huge resevoir of energy, so much that it should be bending time and space. That sounds like energy that can be put to work to me so this fact is not highly suspect, if it were NASA , british aerospace project greenglow, the calphysics institute, the institute for advanced studies in austin and a number of other institutes that are looking into what is not-known [and not highly suspect as you put it] is wether or not we can work with this energy or not with the tools we have at this moment in time. You cannot dismiss this fact. Dont get me wrong i do not beleive in free energy I only beleive that with the right tools we can make the vacuum energy do certain things, perhaps a novel system of propulsion by causeing the waves to effect, or changing them into negative energy like in the casimir effect, but not free energy. Also in closeing attacking the people of these websites is a logical fallicy, you are not disproving the argument only attacking the people. I will not say anything further exept that firstly the statement above is biased, secondly the person posting has no physics qualifications. Commenter

[edit] Birthday

In honor of my birthday (august 14th) I will ask a trivia question and review anyones article of choice if they get it correct. What is the probability that someone shares the same birthday as me if I am in a room with 22 other people? -Ravedave 02:15, 14 August 2006 (UTC)

$1-\left(\frac{364}{365}\right)^{22}$ --Bmk 02:34, 14 August 2006 (UTC)

yup thats it. Birthday Paradox. Which article Do you want reviewed? -Ravedave 02:38, 14 August 2006 (UTC)

The way you've phrased it, 100% (certainly someone somewhere shares your birthday, whether you're in a room with 22 people, or five people, or alone on the top of the Eiffel Tower). But what you probably meant (what is the likelihood that at least one of 22 randomly chosen people will be born on a given day, in this case 14 August) would give an answer more like 6%. (The probability that any one person was born on a certain date (other than 29 February) is about 1/365 or more precisely 4/1461; they are independent events so they are added, so the probability is 88/1461 = 6%). Note that what you have proposed is not the birthday paradox, which asks for the probability of two of 23 people sharing a birthday, rather than specifying the date in advance. Happy Birthday. - Nunh-huh 02:39, 14 August 2006 (UTC)

I relized that shortly after I posted it, however Birthday paradox does have the equasion dmk provided. -Ravedave 02:41, 14 August 2006 (UTC)

And if you prefer digits...0.058571325264343345847099029333104. But I like Nunh-huh's 100% answer. --Bmk 02:46, 14 August 2006 (UTC)

And happy birthday by the way. --Bmk 02:47, 14 August 2006 (UTC)

Now for a harder question: What is the probability it will be your birthday on any given day, if you attend a restaurant that gives away free birthday meals on that day (one that doesn't check ID) ? :-) StuRat 08:35, 14 August 2006 (UTC)

~~I'd say that won't be a constant, it will be a function of how often you visit the restaurant and how good the waiters are at remembering your face.~~ 1/365, because we're all scrupulously honest round here, right? ;-) -- AJR | Talk 12:46, 14 August 2006 (UTC)

Bmk would probably prefer you said 1/365.2425. JackofOz 03:25, 15 August 2006 (UTC)

Unless you're born on February 30. Then it's 1/1461... TERdON 08:34, 22 August 2006 (UTC)

I think you mean Feb 29th. Our calendar never has a Feb 30. StuRat 06:46, 23 August 2006 (UTC)

No, TERdON couldn't have meant 29 Feb. That date is already included in my 365.2425 calculation. Maybe he/she was just overcompensating for the loss of Pluto as a planet. :--) JackofOz 02:18, 25 August 2006 (UTC)

[edit] Insect identification

Strange insect

I found this insect which had apparently crawled out of my lawn onto the side of the curb and emerged from its chrysalis. After a few hours it flew away. Anyone know what it is? Thanks, --Bmk 02:21, 14 August 2006 (UTC)

Some sort of Cicada apparently. Pretty interesting bugs. -Ravedave 02:29, 14 August 2006 (UTC)

Thanks! I think that's the one! The picture on the cicada page was great. Extra points to anyone who can tell me what species this one is. It was seen in upstate NY, USA. --Bmk 02:58, 14 August 2006 (UTC)

I looks like the one in the template to me which is of the genus Tibicen. I am guessing the one in your picture has light color becuase it hasnt matured. -Ravedave 04:21, 14 August 2006 (UTC)

Compare this picture. --Lambiam ^Talk 06:26, 14 August 2006 (UTC)

Check out http://www.boingboing.net/2006/07/24/online_bug_identific.html for bug ID services. --Kjoonlee 10:21, 14 August 2006 (UTC)

Tibicen it appears to be! Extra points all around. Thanks folks --bmk

As a side, somewhat irrelevant note, cicadas are what makes the loud, constant buzzing noise in many forest areas. In the Florida (where I live) wilderness it is easily identified if cicadas are in proximity (which they mostly are) and an appropriate nickname for their sound would be the white noise of the wilderness. Not many people I know actually know where this sound comes from, but if they read this now they know. Also, when I traveled to Costa Rica I found gargantuan cicadas that where nearly half a foot long. Pretty amazing, huh?--Porsche997SBS 20:24, 26 August 2006 (UTC)

[edit] non-chlorine bleach

Does it clean as effectively as chlorine bleach?

Depends on what you're cleaning. I've never tried laundry, but fo whackin' out a person, no, the chlorine bleach works much better. — [Mac Davis] (talk)

What do you do when your clothes start to smell? freshofftheufo ΓΛĿЌ 11:14, 14 August 2006 (UTC)

Stop using the stuff. DirkvdM 12:06, 14 August 2006 (UTC)

[edit] Reasons for car batteries going flat?

The battery in my car keeps going flat if i don't use it for a couple of days. Yet I've had the battery tested and they say there is nothing wrong with it. Could there be another reason?

Probably your Alternator. Unless you are leaving your lights on. :) -Ravedave 04:15, 14 August 2006 (UTC)

I should probably explain more. Your Alternator is what charges your battery when you are driving. So if its not chanrging your battery then it will go dead from beign used, but not charged. Also I have heard of stuff like hood lights staying on. -Ravedave 04:24, 14 August 2006 (UTC)

If it is the alternator, and you have full gauges, the battery voltage will read a bit low. Look for that. StuRat 08:29, 14 August 2006 (UTC)

Also, you could have an intermittent short circuit. For example, I had an 83 Trans Am which had an intermittent short in the passenger power door lock, which would eventually drain the battery. StuRat 08:26, 14 August 2006 (UTC)

Is it winter where you are? Old car batteries tend to go flat if just left in the cold.

Actually, batteries last longer in the cold. However, if they do go completely dead, they can freeze and split open, and thus be destroyed, by the cold. Also, it takes more juice to start a cold car, due to the sluggish cold oil, so a poorly charged battery will become more apparent in cold weather. StuRat 19:43, 14 August 2006 (UTC)

Make sure you didn't put it in backwards! I always do that with my batteries. freshofftheufo ΓΛĿЌ 11:13, 14 August 2006 (UTC)

and if you've recently put in car electronics, you might have stuffed the wiring up so it draws current even when the ignition is off. it happens. Xcomradex 12:01, 14 August 2006 (UTC)

There have been cases where the car's key fob receiver gets repeatedly activated, either by an external radio source (case study here) or by the fob itself being left overnight near the car (can't find a ref. for this, but read it a few days ago). This keeps the car's electrical systems continually awake and quickly drains the battery. --Heron 17:34, 14 August 2006 (UTC)

Sometimes car batteries just get old and need replacing! BenC7 02:16, 15 August 2006 (UTC)

As a person who has delt with bad car batteries (and bad cars) more times than I would like to admit, there are MANY reasons your battery might go bad. A bad alternator is the most likely cause, but also there are cells inside a batter that hold about 3/4 H2SO4 and 1/4 water. If the water evaporates, the battery efficiency is severely compromised. You can rememedy this by pouring a small amount of distilled water into the cells (NOT TAP WATER, this will cause a violent reaction that will spew acid on you) of a completely cold battery. Also, sometimes the terminals become corroded, which will cause bad connections between the power cables and the terminals; a solution of 1/2 baking soda and 1/2 water will take that corrosion right off in most cases. Frequent jumping and subsuquent light driving also ruins batteries because they cannot retain a good change, and then you have to jump them again...a cycle of pain. Sometimes batties just wear out...for a good one, 5-7 years or more, a cheap one, about 2 years. Hope that helps. --69.138.61.168 03:45, 15 August 2006 (UTC)

There is a rectifier in the alternator which converts the AC current to DC, if this is defective, the alternator will run AC current through the battery which will ruin it.

Check the glove box light and the trunk light. Make sure they are not staying on.

Wouldn't adding any water to concentrated H2SO4 cause a highly exothermic reaction (generates heat) that could splash acid on you? --Shanedidona 13:00, 23 August 2006 (UTC)

[edit] Chronic cough

My 6 years old daughter has chronic cough for more than one month. (Her cough starts when she goes to bed, during night and before she wakes up.)First it started with having caught cold and treated with antibiotic but her cough continued. When she was only 5 months years old, she was hospitalized by diagnosis of "Whooping cough" for 2 months. Now is there any relation between her chronic cough and this childhood disease? Is it a symptom of other disease or as her doctor says it could be an allergy?

As usual, you might get better answers by paying a person with years of expertise, accountability, and far more information about your daughter, rather than anonymouse volunteers with unknown qualifications whom you cannot hold responsible. You don't specify some important details, but let's assume you are a middle class American mother and you daughter is basically healthy and growing well with no serious disease since pertussis in infancy. Some of the likely possibilities:

She hasn't finished recovering from her viral respiratory infection
She has an asthmatic cough from an environmental trigger (outdoor or indoor source)
She has an asthmatic cough from a persistent sinusitis
She has a habit cough (this is the typical age) or a psychogenic cough

There are many uncommon possibilities

A foreign body in a bronchus
Persistent gastroesophageal reflux
Tuberculosis or rarer lung infections
Tic or other neurologic cause
Cystic fibrosis
Hypersensitivity pneumonitis (e.g., histoplasmosis, or your local favorite)
A vascular malformation in the chest
Several types of immunodeficiency

There are many more rarer possibilities that you don't even want to know about. If she definitely had pertussis in infancy it is unlikely to recur. How certain was that diagnosis? Despite immunization?

If it isn't gone in a another couple of weeks, go see someone more knowledgeable and responsible than we are. alteripse 11:44, 14 August 2006 (UTC)

If she's had a chronic cough for more than a month, the time to see the pediatrician is NOW. StuRat 21:16, 14 August 2006 (UTC)

Another possibility, especially since you said this only happens when she lies down to sleep, is acid reflux disease. This means that the valve at the top of the stomach fails to prevent acid from entering the esophagus. During the day, gravity performs this function, but not when you lie down. StuRat 21:22, 14 August 2006 (UTC)

Oops, I see that was already listed, under the name gastroesophageal reflux. StuRat 21:24, 14 August 2006 (UTC)

Is her bed next to an outside wall? That's often the coldest part of the house, and I've sometimes had persistent nocturnal coughing for that reason. —Tamfang 07:12, 15 August 2006 (UTC)

[edit] Formula for calculating the Heating Load in KW of Convectional oven

Dear sir,

I am intrested to know that how to know the heating load in KW of convectional Heating oven if I know the Volume of Oven in Cumbic Meter and Weight of Material which has been put inside the oven and set temperature upto what time. I am also intrested to know, How Much Initial heating time effect the Heating load.

As I know the Heating Load is depend upon Set Temperature, Volume of Heating oven, Materail in side the Oven, Air Inside the oven, Thickness of Insulation, Heating up time, Ambient temperature. I am really intrested to know the optimum formula for calculating the heating load of conveyorised and batch oven.

[edit] Biggest cells, and hen's eggs?

How big is the biggest cell (animal, plant, or fungus) please? I remember as a schoolboy wondering about unfertilized hen's eggs. Now while it is extremely unlikely they are just one large cell, just how many cells do they have in them?

The largest known cell is actually the Ostrich Egg, I'm pretty amazed by that as well. PvT 10:46, 14 August 2006 (UTC)

Contrary to popular belief, and to thier names, ostrich and hen's eggs (and any other poultry eggs) are not single cells. In the yolk of the egg, there is just one single cell - that of the embryo, which divides and grows during the incubation of the egg. As for your original question, I'd say that the biggest cells would be those of some single celled organisms, such as algaes. Martinp23 12:14, 14 August 2006 (UTC)

I would have to say that some plant cells are large enough to actually see with a nude eye. I recall those are the largest known. — [Mac Davis] (talk)

Caulerpa (a green alga) are pretty big. Each plant is a single cell (albeit with multiple nuclei) and the whole organism can grow to be about 3 meters long. TenOfAllTrades(talk) 15:13, 14 August 2006 (UTC)

Looks like we have our answer!! — [Mac Davis] (talk)

It says in the Ostrich entry that the eggs are the world's largest single cells. If that is not true, then the entry needs to be changed. I'm rather sceptical as a cell that size would have tremendous problems with respiration. But if it is the case, what do the yolk and egg correspond to? If there is just one little cell in an unfertilized egg, where is it? And the sac (correct spelling I think) containing the yolk, or the membrain inside the shell, how were those made? It could have been made of specialized cells. Cells<-->eggs are still a mystery. If an Ostrich egg truely is a cell then it must be bigger in volume than the algae cell, even if its 3m long.

I thought that in an unfertilised bird's egg the yolk is one great big haploid cell, with no cell membrane between the chromosome-containing non-yolky clear cytoplasm on one side, and the rest of the yolk - a telolecithal cell which will undergo meroblastic cleavage. Is that right? Strange how difficult it is to get real hard facts on this. A fertilised egg, by the time it is laid, is multicellular (already 60000 cells), and the blastodermal cells are separated from the yolk that has no nucleus, so that does not count as a single cell. How long can a giraffe's spinal nerves be (bonus: has only one nucleus), and how big are the the neurons of giant squids? What would be the size of the (multinucleate) muscle cells of an elephant or a whale? --Seejyb 23:36, 14 August 2006 (UTC)

[edit] Electrical Engineering

My question is a very ODD one .

The question is : -

Out of AC and DC voltages which poses a repulsive shock and which an attractive shock ?

Please reply soon .

I'm not sure what you mean by a "repulsive" or "attractive" shock. They both are pretty unpleasant if the voltage is high enough, so I guess they're both pretty repulsive to me :). But seriously, I think what you may be referring to is the way that strong electric currents cause muscles to contract, resulting in a person being unable to release the source of the voltage (the actual reason is that flexors are usually stronger than extensors, so when they both contract, the flexors win). Other than that, I think you should read our article on electricity to get the basics down. --Bmk 12:54, 14 August 2006 (UTC)

I think I know what the confusion is here. In modern electric fences, they frequently turn the voltage on and off every second or so. This allows people who get zapped by them to let go, and thus survive. This is unrelated to A/C versus D/C, however. StuRat 21:10, 14 August 2006 (UTC)

Can you be more specific with your question? --Proficient 21:36, 17 August 2006 (UTC)

Neither is very attractive -- in fact both are quite shocking and repulsive! (sorry!)--Light current 05:44, 19 August 2006 (UTC)

[edit] Why the male Warbler builds unused nests?

Protonotaria citrea - (Boddaert, 1783) Prothonotary Warbler Unique Identifier: ELEMENT_GLOBAL.2.100372 Element Code: ABPBX07010

I have read :

The Prothonotary Warbler is a small songbird of the New World warbler family. It breeds in hardwood swamps in southern Canada and the eastern United States, nesting in a cavity. The male often builds several incomplete unused nests in his territory; the female builds the real nest. It winters in the West Indies, Central America and northern South America. This bird was named after officials in the Roman Catholic Church known as the protonotarii, who wore golden robes.

Most activities in the animal kingdom have a biological advantage, I was wondering if the male bird does this activity, as a method of fooling predators. ie, the predator will see the false nest and attempt to steal eggs from that nest....

Any information about this would be much appreciated.

It is an interesting division of labour. The male typically selects several potential nesting sites in advance, and "illustrates" their suitability by building a dummy nest, using moss. It's a bit like a real-estate agent dressing up a place for viewers. When a female arrives, the male shows her around, and if she is sufficiently impressed by one of these sites, she'll turn it into a real nest. As a male you always wonder: "What does woman want?" By selecting several sites, the male increases the likelihood that the female will like one of them. --Lambiam ^Talk 01:10, 15 August 2006 (UTC)

[edit] This piece of 'equipment'?

I have been challenged to find out the name of this piece of equipment, I can only guess it is used somewhere in science but having looked through various lists on here of science equipment and clicking on the ones that I hadn't heard of hasn't actually got me anywhere. The piece of equipment is linked below.

http://img136.imageshack.us/my.php?image=6iu2.jpg

I'm guessing the image is probably somewhere on wiki. Thanks. ~~

Warning. The link opens a popup that crashes Konqueror. DirkvdM 12:15, 14 August 2006 (UTC)

Looks like an empty Stevenson screen. DirkvdM 12:15, 14 August 2006 (UTC)

Thanks, I found the exact image on google images when I searched it so I guess that you're right. Sorry if it crashes Konqueror, I'd only tried it on Firefox. ~~

Crashes Konqueror 3.2 on Mac OS X Tiger as well. O_o --M1ss1ontom a rs2k4 ^{(T | C | @)} 23:05, 23 August 2006 (UTC)

[edit] gold - precious metal

what makes gold so precious? what quality does it have that is of so much value?

1) It is scarce. That alone makes people want it. Which makes it more scarce, etc. Which is a bloody shame, because this jewellery-nonsense forces up the prices also for

2) practical implementations. It is one of a sel;ct group of chemicals that are not very reactive. In plain English, it doesn't rust. For that reason it is used for electrical connections because they are especially prone to rust, which reduces their conductivity, their very reason for existence. DirkvdM 12:24, 14 August 2006 (UTC)

Practicality aside, if you've ever held 99.9% pure gold in the sunlight, it is just so incredibly pretty! I think that's the real reason :) --Bmk 12:56, 14 August 2006 (UTC)

Because it's so non-reactive, it's one of a very few elements that are commonly found in the pure form (nuggets). This meant that it was one of the first elements to be discovered in antiquity, so people started figuring out how to make pretty things out of gold long before they did so with other things. Result: several millennia of accumlated cultural mystique. --Pyroclastic 19:10, 14 August 2006 (UTC)

Gold just has lots of practical applications in industry. For the same reason copper is actually rather valuable — a couple bucks a pound. --Cyde Weys 17:03, 14 August 2006 (UTC)

Gold is quite ductile (soft), which makes it easy to work with. It's also highly electrically conductive, which makes it good for wiring (except it costs too much for most wiring), and, as previously noted, it doesn't oxidize, like iron (to form rust), silver (to form tarnish), copper (to form that nasty green stuff), or aluminum (to form white spots). If it was plentiful enough (and thus cheap), we might even make car body panels out of it. StuRat 21:04, 14 August 2006 (UTC)

Copper is so valuable that it's being stolen frequently. Recently, a nearby school had ten classrooms flooded because thieves broke in to steal the copper pipes. User:Zoe|(talk) 02:19, 15 August 2006 (UTC)

copper is also running out, hence the price hike. Xcomradex 07:59, 15 August 2006 (UTC)

I thought i would throw in that Silver is a better room temperature conductor than gold, and that gold car panels would be impractically soft and heavy, high grade aluminum would be a more feasible corrosion-resistant choice. --66.195.232.121 13:37, 15 August 2006 (UTC)

Silver wouldn't be as good as gold for electrical use, because it tarnishes, and the silver oxide would prevent electricity from flowing across electrical contacts. Gold isn't any softer than the plastic body panels used on many cars. And aluminum gets those ugly white spots of aluminum oxide. StuRat 18:47, 15 August 2006 (UTC)

Technically silver tarnish is really Silver Sulfide, as it reacts slowly with Hydrogen Sulfide found in trace amounts in the air. Over time the black tarnish builds up.

I never thought about copper being valuable, but then you must think about the prices of some higher end heat sinks to see its value. --Proficient 21:41, 17 August 2006 (UTC)

[edit] Human Decomposition

How long do you have to wait until all that's left of a corpse is a skeleton? --Burbster 12:09, 14 August 2006 (UTC)

Longer than you'll live if it's in a bog. So if ou don't slide into the bog yourself, you'd decompose before the other body. More in general, this depends to a large degree on how much oxygen the body is exposed to. And the temperature also makes a big differnce. This was asked before, but I can't find the thread. DirkvdM 12:29, 14 August 2006 (UTC)

This depends enormously on its environment. See decomposition. --Shantavira 12:30, 14 August 2006 (UTC)

If the environment is a vat of strong acid, a few seconds. If the environment is a inter-galactic void, never. StuRat 20:59, 14 August 2006 (UTC)

Depends on the molarity of the strong acid. It might take considerably longer than a few seconds. --Amanaplanacanalpanama 21:41, 16 August 2006 (UTC)

Okay, let's say instead for three different environments: Out in the open air at moderate humditiy, in a shallow grave and in a coffin buried deep underground. --Burbster 23:32, 16 August 2006 (UTC)

You're asking purely for academic reasons? Rentwa 20:11, 26 August 2006 (UTC)

[edit] The 'save' button is teasing me

Because three questions up Konqueror crashed, I switched to Mozilla and now I notice the strange effect that when I hit the 'save page' button, the screen moves up a bit. Only when I hit it a second time does it work. Is the button teasing me? DirkvdM 12:31, 14 August 2006 (UTC)

I've had the same thing for a while now, on my Linux machine. --Zeizmic 12:36, 14 August 2006 (UTC)

Because the questioner is using Konqueror, I assume he is using KDE. I use Firefox in KDE and have no issues with the save button. --Kainaw ^(talk) 16:59, 14 August 2006 (UTC)

I have issues like this occasionally with Firefox on Windows. My only guess is that, for whatever reason, when you try to click the button it instantaneously re-renders the page such that the new location of the save button is no longer under the mouse pointer, and thus, it doesn't get clicked. This might be JavaScript-related. --Cyde Weys 17:02, 14 August 2006 (UTC)

This occasionally happens with all my Windows applications. Clicking on the scroll bar clears it for me.--Shantavira 17:31, 14 August 2006 (UTC)

I am indeed using KDE (under Suse). And it might indeed have something to do with Javascript. Between the edit frame and the options above it, there is some space. When I hit the save button, this space disappears. It might indeed re-render then. But when I hit the top of the save button, it doesn't move up enough and there is no problem (the button works). I don't have Javascript enabled for Konqueror, so that may be it. Nothing to do with the OS, the DE or the browser. DirkvdM 17:50, 14 August 2006 (UTC)

This actually has to do with your Wikipedia preferences. If you go to your preferences and the Editing tab, at the very bottom is a option saying "Prompt me when entering a blank edit summary". If you checked it, then if you enter nothing or enter /*(text)*/ in the edit summary and click save, at the top you will get a message telling you: "You have not provided an edit summary. If you click Save again, your edit will be saved without one." Only if you click save again, it will save. --Yanwen 18:14, 14 August 2006 (UTC)

No, that's not it - I don't have that checked. It is Javascript. I just disabled it and the problem is gone. DirkvdM 09:05, 15 August 2006 (UTC)

[edit] If mountains have effect on earth Consistency and stabilizing?

the earth has move (in orbit) and shake. if mountain effect it and other things similar these? —The preceding unsigned comment was added by 194.225.166.13 (talk • contribs) .

I'm not exactly sure what you're asking, but let me point out a few things that may be relevant. The overall shape of the Earth is practically a perfect sphere: the equatorial bulge is small and Mount Everest is even smaller. I don't see how mountains could have any "stabilizing" effect on earthquakes. In fact, the same tectonic activity that produced the mountains could also produce earthquakes, so I'd say earthquakes are more likely to occur in mountainous regions, not less. —Keenan Pepper 16:06, 14 August 2006 (UTC)

I think the question is if mountains cause earthquakes. The answer would then be that they are both caused by tectonic plate movement and volcanic activity.

The plates of the Earth's crust move about (extremely slowly) and collide with each other, pushing up mountains (like the Himalaya). This causes friction, which also causes earthquakes.
Below that crust is lava, which sometimes breaks through and causes volcanoes, another type of mountain (like the ones in Indonesia). And this also causes earthquakes.

So mountains don't really cause earthquakes, but the two have a common cause, so that's why earthquakes occur in mountainous areas. If your English isn't good enough to read these articles, you might want to have a look at the Simple English Wikipedia. It is not quite as extensive as the 'normal' Wikipedia, though. DirkvdM 18:13, 14 August 2006 (UTC)

Although I'm not quite sure what the question is, I suspect it may be related to the recent news item that the 2004 Indian Ocean earthquake had perceptibly altered GPS satellite orbits. --Lambiam ^Talk 00:52, 15 August 2006 (UTC)

I think the question-asker may be referring (knowingly or unknowingly) to Milankovitch cycles rather than earthquakes. Do mountains have an effect on orbital parameters? might be what is being asked, I think - much like if you stick a blob of something to a ball it will affect how it spins. With regards to the Earth, the answer is no. If the earth was scaled down to 7 or 8 centimetres across, it would be smoother than a billiard ball. Mountains are not large enough with respect to the Earth to make any difference to its orbit, spin, precession, etc. BenC7 02:32, 15 August 2006 (UTC)

He could also be asking about isostasy. Tito xd^(?!?) 07:24, 17 August 2006 (UTC)

[edit] Instrument

http://img136.imageshack.us/my.php?image=6iu2.jpg

Could someone kindly tell me what this scientific instrument is...it looks like a beehive but i`m relatively sure it`s not.

That is a weather station, where anyone interested in measuring the weather puts instruments such as barometers and thermometers, where they are subjectedto the atmosphere but protected from the elements. Martinp23 14:40, 14 August 2006 (UTC)

Are you the same person? We just had this question a few hours ago. The answer is Stevenson screen. — [Mac Davis] (talk)

[edit] artificial insemination

Can all animals be inseminated artificially?

Yes. Its really the phallus that is artificial, not the semen. I guess the insemination is artificial. Anyway, it doesn't matter if there was copulation involved, the sperm just has to get to the egg. — [Mac Davis] (talk)

Technically, some animals, such as Cnemidophorus lizards, cannot be artificially inseminated, because they don't reproduce sexually. See Parthenogenesis. —Keenan Pepper 16:09, 14 August 2006 (UTC)

Well, you need more than the sperm and the egg. You also need a womb (if you want a baby to come out of it, that is). So you indeed have to enter something in a female, be it a fertilised egg, as it is done with humans, or with a functional dildo, so to say. I can imagine that with some animals that would be problematic, like very small animals (without killing them, which would defeat the purpose). Or with very big ones. Try inseminating a whale (a sperm whale of course :) ). DirkvdM 18:26, 14 August 2006 (UTC)

It might be very difficult for microscopic animals. I wonder if anyone does this for any reason. Also remember that creatures such as sponges and corals are animals. Maybe they could be "artifically inseminated", but it would be much different that the process for a horse or a pig. ike9898 19:49, 14 August 2006 (UTC)

There may be a technical problem for Diplozoon paradoxum. For an illustration of the fused animals, see da:Dobbeltdyr (Diplozoon paradoxum) or the middle of the bottom line of the image at Flatworm. --Lambiam ^Talk 00:35, 15 August 2006 (UTC)

Many animals fertilize externally, in which situation this question is a non sequitur. --Ginkgo100 ^{talk · contribs · e@} 03:46, 15 August 2006 (UTC)

[edit] Maximum velocity of a sailing ship

Can a ship powered only by sail exceed the wind velocity? If so, what is the maximum speed it can reach relative to the wind velocity? --Cyde Weys 16:59, 14 August 2006 (UTC)

If the water current exceeds the wind velocity then the ship can lower its sails and go as fast as the water current. -- C. S. Joiner (talk) 17:25, 14 August 2006 (UTC)

And a more serious answer can be found here: "the motion of the boat creates its own apparent wind, which combines the windspeed vector and the hull speed vector. Sailing into the wind, this can quickly add up to apparent winds of far greater than the true windspeed" -- C. S. Joiner (talk) 17:37, 14 August 2006 (UTC)

Per Csjoiner, yes—modern racing hulls are efficient enough to exceed the wind speed when on a broad or beam reach. (Most sail boats are fastest on a beam reach, though may not be able to exceed the wind's speed.) Ice boats, because they travel on a very low friction surface, can usually easily exceed the wind's speed when reaching. TenOfAllTrades(talk) 17:44, 14 August 2006 (UTC)

The reason for this is that the boat is (at least when on a beam reach or closer to the wind) not mainly powered by the direct force of the wind on the sail. It is driven by the bernoulli effect of the wind blowing across the wing-like shape of the filled sail, and thus is not limited by the velocity of the wind. --198.125.178.207 18:25, 14 August 2006 (UTC)

Hold on. Sailing into the wind? That won't get you anywhere, or do I get the English sailing terms wrong? (If not, the article needs correcting.) But even sailing upwind (at an angle of up to about 45° to the wind) isn't very fast - it just feels very fast. Sailing downwind is a lot faster and quieter. But that way you just get pushed by the wind and you miss out on the wing-effect. Indeed, broad or beam reach (getting the wind from the side) is fastest. That way you can indeed exceed the speed of the wind. Which sounds counterintuitive, but so does the ability to sail upwind (close hauled). Both are possible thanks to the wing-effect.

By the way, if things go just right, the bough can be lifted on to of the bough wave. This has happened to me once (in a Valk or 'falcon' - I thought we had an article on that) and it's a wonderful feeling, like you're flying. What is this called and is this an indication one is exceeding the wind speed?

About the Points of sail article, I disagree with calling running downwind a 'don't go zone'. Getting 'gull wing' right is one of the nicer moments of sailing. DirkvdM 18:45, 14 August 2006 (UTC)

"Sailing into the wind" is indeed a not uncommon (but potentially confusing) way of expressing "sailing upwind". You also hear "sailing against the wind" (which makes me wonder who was the winner), possibly influenced by German gegen den Wind segeln or similar expressions in other Germanic languages. --Lambiam ^Talk 00:21, 15 August 2006 (UTC)

[edit] Sodium azide interferes with SDS-PAGE?

If you have experience with SDS-PAGE, have you ever had a problem with having too much sodium azide in your samples? Would you suspect this would interfere at high concentrations? ike9898 19:10, 14 August 2006 (UTC)

What is the nature of your problem, and what concentration of azide are you using? I can say, however, that I regularly use azide in my peptide samples to prevent bacterial contamination, and I've never had any problem with them (none, at least, that I traced to the presence of azide). – Clockwork Soul 21:33, 14 August 2006 (UTC)

[edit] Formatting an External Harddrive

I have an external USB hard drive. It is currently in NTFS, but I want to format it in FAT32 so that I can use it with my Linux dual boot. Windows XP doesn't let you format it into anything but NTFS and I'm a Linux noob running Ubuntu. I tried GParted, but it doesn't seem to be able to manage externals. Any help? --Russoc4 20:18, 14 August 2006 (UTC)

This is probably a better question for the Computing Reference Desk -- C. S. Joiner (talk) 20:23, 14 August 2006 (UTC)

Oh dear. I didn't realize they made one! Thanks for your help. --Russoc4 20:25, 14 August 2006 (UTC)

Give it to one of your friends that runs a Mac, it only takes a few clicks. — [Mac Davis] (talk)

In the command prompt 'format [drive letter]: /FS:FAT32'

[edit] P = I*V

And now for a completly unrelated question to the one above...

I know that Power in Watts = Current * Voltage. I know that current is the flow of electrons and voltage is the potential energy to push the electrons, , but I'm not sure what that means in practice. Lets say you have a 100W lightbulb. Is there any different in powering it with 20 amps and 5 volts compared to 2 amps and 50 volts? How about for a DC motor? What role do each current and voltage play when powering a motor? I've been wondering about this for a while, but I keep forgetting to ask it.--Russoc4 20:25, 14 August 2006 (UTC)

One quick response--while 20A*5V = 2A*50V in power output, they would work differently based on the limitations of real world material. 20 amps is a lot to send through wires.

It may also help, when thinking about this topic, to remember V = I*R, therefore, P = I²*R, which might make more intuitive sense when thinking about the "roles" of current-voltage-resistance in motor power. -- Scientizzle 21:00, 14 August 2006 (UTC)

One difference between powering a 100 W light bulb with 5 V 20 A or 50 V 2 A is that you would have to use different bulbs. Another difference is that the low voltage case would need power supply wires that have more copper in them, but could get away with less insulation. Since insulation is generally cheaper than copper, higher voltages are generally preferred. In the case of electric motors, the windings for a high voltage motor will have comparatively many turns of thin wire, while the low voltage motor will have fewer turns of thick wire. --Gerry Ashton 23:13, 14 August 2006 (UTC)

Nowadays bulbs may say "100W" while they have much lower wattage but equivalent luminosity, an unfortunate development. Let's assume it is a "true" 100W bulb, which has been designed for use at 120V. Then the current going through will be 100W/120V = 0.833A. It's resistance, using Ohm's Law, is then 120V/0.833A = 144Ω. The latter is an actual physical characteristic of the lamp, independent of the voltage applied. If instead of 120V we apply 60V, we get a current of 60V/144Ω = 0.417A, and a power of 0.417A × 60V = 25W, only a quarter of what it says on the bulb. Likewise, if we apply 240V, we get a power consumption of 400W in the split second before the filament melts. The point is that the wattage listed is not an invariant physical characteristic, but only applies within the design parameters. --Lambiam ^Talk 23:48, 14 August 2006 (UTC)

In many real materials, resistance is a function of temperature. So the 144Ω figure may only apply at the temperature which the filament reaches in operation at that voltage. So it's even more design-specific than you suggest. In general, a bulb will have an output

O (T)

(e.g., blackbody radiation) and a resistance

R (T)

. At equilibrium,

P = V 2 / R = O

, or

V 2 = O (T) R (T)

. Since output tends to increase very rapidly with temperature, even if

d R / d T < 0

we expect to find a balance. (In fact, resistance tends to increase with temperature due to increased disorder within the material.) Of course, even this is a simplification since in reality there will be temperature variations (and thus resistivity variations) within the wire and the current may create complex patterns that are harder to analyze. The important bit with respect to the initial question is that for most things as simple as light bulbs, once you pick the voltage the current is determined, so you can't just "go to" half the voltage and twice the current and "see what happens". Hope this helps. --Tardis 06:49, 15 August 2006 (UTC)

Well, all these answers do help put it into perspective. thanks. --Russoc4 15:38, 15 August 2006 (UTC)

Don't fall into the trap of thinking that P=I*V is true for AC. It is strictly true only for DC. For AC, it is true only for a load which is purely resistive. A resistive load could be a heater or an incandescent light bulb. Any load which is reactive, containing net inductance or capacitance, will consume power less than I*V. High voltage power lines (such as 345 kv) are likely to be capacitive (combination of resistance and capacitance) and the current will lead the voltage. Residential loads, with motors and air conditioners, are likely to be inductive combination of resistance and inductance. In an inductive load the current waveform will lag behind the voltage waveform. The electric meter on your house bills for energy used in kilowatt hours; the reactive current is basically free. Commercial and industrial customers are billed if their power factor is too reactive. The reactive current is termed VARs for "volt-amps reactive" and the power company hates them, since they heat up transformers and distribution lines just like revenue-producing watts. They install capacitor banks to improve the power factor towards unity (neither inductive nor capacitative). Edison 16:51, 15 August 2006 (UTC)

[edit] G2B2... what does it mean?

Trying to figure out what G2B2 means in a medical context, as an adjective applied to a woman, or as a status associated with a woman. --MattShepherd 20:37, 14 August 2006 (UTC)

Perhaps if you provided the specific context in which you heard this term it would be easier for us to figure out what it means. Was it on a lab sheet? ...in a text book? Did you overhear it? Tuckerekcut 20:46, 14 August 2006 (UTC)

Asked in passing by a translator friend, who didn't give me much else to go on. I'll figure it out. --MattShepherd 20:55, 14 August 2006 (UTC)

Did you mean G2P2? It is shorthand for an obstetrical history. "G" (for gravida) refers to the number of pregnancies. "P" (for para) refers to the number of live births. Some include an "A" or "SA" for abortions/miscarriages. G2P1 means 2 pregnancies, 1 delivery (and currently pregnant with the second). G1P2 means 1 pregnancy with a set of twins delivered. - Cybergoth 21:30, 14 August 2006 (UTC)

It might refer to a GABA A receptor structure: a γ2 and a β2 subunit. --Lambiam ^Talk 23:30, 14 August 2006 (UTC)

The way you describe the circumstance in which the term is used would indicate the pregnancy related meaning. "G" does refer to the number of times the woman has fallen pregnant. As noted, the second letter is a capital "P", but these days a somewhat complicated four-digit "code" follows it. The first digit after the P indicates the number of full-term pregnancies (those that lasted > 37 weeks), the second, the number of pregnancies where a premature baby was born (20-37 weeks' pregnancy), the third, the number of pregnancies ending before 20 weeks (spontaneous or induced abortion), and the fourth indicates the number of children living at present. An example would be "G5 P3115", analysed as: G5 = times pregnant, P3xxx = 3 times full-term pregnancies, Px1xx = 1 premature delivery, Pxx1x = 1 miscarriage before 20 weeks, and Pxxx5 = 5 living children. Note that this does not indicate in what sort of combination(s) the 5 living children come from, all one can say is that out of 5 pregnancies, 4 lasted to a viable gestational age. They could all have been twin pregnancies, with three kids having died, one from prematurity, one poisoned by her husband, and one in battle. The coding does not allow for indicating twins, triplets, and such. Note also that if the first three numbers following the P add up to 1 less than the G, then it indicates that the woman is presently pregnant. --Seejyb 01:04, 15 August 2006 (UTC)

[edit] broken neon

Do broken neon tubes release a dangerous amount of mercury vapor? I was in a convenience that had a broken neon sign and I'm wondering if I should bother with going to the doctor. KeeganB

According to neon sign, only some neon signs use mercury and it's a drop of it at that. Spread out to an entire convenience store, it's probably fine. AEuSoes1 21:05, 14 August 2006 (UTC)

And since it is elemental mercury in the sign, instead of a vapor, you are in less danger of mercury poisoning than if it were methylmercury or similar. Hyenaste ^(tell) 23:43, 14 August 2006 (UTC)

Doesn't elemental mercury produce a poisonous vapor? Anyway, I forgot to point out that the duplicates of this sign produced blue light, which it caused by mercury. KeeganB

I wouldn't worry to much about your mercury exposure. I myself have come into contact with a solution which contained a small amount of the mercury salt mercury(II)chloride without even knowing what it was till much later. As far as I know elemental mercury is actually quite safe compared to its salts. Seeing how very little is in the tube to begin with I wouldn't think that you have anything to worry about at all short term or long term. PvT 12:36, 15 August 2006 (UTC)

I don't have a scientific basis for questioning that mercury is every bit as deadly as its present reputation. The term "mad as a hatter" is supposed to refer to recognition centuries ago that exposure to mercury caused brain damage. But a few decades ago everyone in chemistry class got to roll some of it around in the palm of his hand and it felt really cool. It would also coat a penny and make it look like a dime. In the late 19th century, gold miners would make up snowball-like wads of gold ore and mercury with their bare hands to extract the precious metal. Electrical experimenters used it all the time for low resistance low friction contact points is circuits. Mr. Wizard on TV kid science shows used mercury many times this way, as for a "jumping spring." 19th century photographers used it to make Daguerrotypes. It was in fever thermometers, which many a child bit through and got mercury in the mouth. It is in the silver amalgam fillings which have been in the mouths of many millions of Americans for many decades. For these reasons, I have to feel a little skepticism about the deadly peril of the vapor from a drop of spilled mercury. Edison 17:05, 15 August 2006 (UTC)

You're right on the first point, you don't have the "scientific basis" for understanding the difference between mercuric nitrate, dimethylmercury, methylmercury, and mercury the element. If I were to follow the reasoning you have just outlined, I would have to conclude that the toxicity of chlorine gas is a myth, after all, people consume sodium chloride all the time, and don't do anything other than raise their blood prease, therefore chlorine isn't really toxic, that's just media hype, bah, brain hurt.--71.247.125.144 03:05, 17 August 2006 (UTC)

Mercury is what is known as a heavy metal poison. What is dangerous about it is it bioaccumulates. This means any taken in to the body is not eliminated very quickly, so if you are exposed to it as a very young child most of it will still be in you when you are very old. Other poisons, like cyanide, will allow you to recover from a less than fatal dose as the poison will be eliminated after a time, a few days maybe. Poisons which bioaccumulate won't do that. Sicne Mercury is a liquid, it has a higher vapor pressure than solids so you can inhale enough to be significant. The amount in a neon tube is not very much, you would have to hang around the convenience store a long time (weeks) with a neon tube breaking nearly every day to have a chance of having problems.

[edit] Mammals and body temperature

Could someone explain why, say, my cat has a different body temperature than myself, even though we share a great deal of temperature-sensitive biochemistry? Peter Grey 23:29, 14 August 2006 (UTC)

Seriously, doesn't it seem odd that mammals have so many genes in common, and these genes govern chemical reactions highly sensitive to temperature, and yet different species have different normal body temperatures? Peter Grey 18:14, 19 August 2006 (UTC)

[edit] digression:individual temperature

Try reading body temperature, particularly the section on variations in body temperature between different mammals. That should give you a start. :-) Anchoress 00:36, 15 August 2006 (UTC)

Thermoregulation discusses temperature variation for an individual, not variations across species. Peter Grey 02:22, 15 August 2006 (UTC)

On a related subject, I remember seeing a chart purporting to show how you can read the temperature in a room from the posture of a resting cat. Wish I could find that again! —Tamfang 06:53, 15 August 2006 (UTC)

They also find the warmest and coolest location in the house. I once found my cat sleeping in the bathroom sink. I thought it's little walnut brain had blown a fuse until I realized the ceramic sink was connected to thick metal pipes filled with cool water, and probably stayed cool all day long. StuRat 07:41, 15 August 2006 (UTC)

[edit] Mushroom clouds

Was the Trinity test the first instance in which the iconic mushroom cloud seared its image into humanity's collective consciousness, or did scientists even before the first nuclear explosion have an idea of what the resultant cloud would look like? --Cyde Weys 23:34, 14 August 2006 (UTC)

Read our article Mushroom cloud; it suggests that they should have known the answer if they asked the question. Probably they were smart enough to figure it out anyway without experimental evidence. I don't remember reading anywhere that they actually wondered or speculated about this aspect, although it appears unlikely to me that they wouldn't have. --Lambiam ^Talk 00:03, 15 August 2006 (UTC)

Note that much smaller conventional explosions also produce mushroom clouds, so people would have known about them long ago. I would even think, under the right circumstances, that a volcano could produce a mushroom cloud. StuRat 00:33, 15 August 2006 (UTC)

Yeah, I've had the experience of seeing an explosion complete with a mushroom cloud less than a mile away. — [Mac Davis] (talk)

Somebody lit a match near the Porta-potties after the chili bake off ? StuRat 07:34, 15 August 2006 (UTC)

Image-google 'volcano "mushroom cloud"' for some nice examples. DirkvdM 09:15, 15 August 2006 (UTC)

Before the Trinity explosion, they did a trial run with 100 tons of TNT to get an idea of what a large explosion would do, and how the radioactive fallout would behave. That explosion also generated a mushroom cloud. --Serie 22:46, 15 August 2006 (UTC)

[edit] Orphaned comment

I'm not sure where this belongs, because it was added to the Science Ref desk after this date had been transcluded:

Straight after exercise jump into icy water, it helps with the recovery process. Einstein's shadow 11:47, 17 August 2006 (UTC)