Wikipedia:Reference desk/Archives/Science/2007 March 26

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March 26[edit]

Battery operated power strip?[edit]

Is there a way to power a device that needs to plugged into an outlet, such as a lamp, with a battery?

Yes. The usual way is with an inverter, which converts DC to AC (and usually steps up the voltage in the process). Depending on the device to be powered, there may be other solutions as well. --Steve Summit (talk) 00:38, 26 March 2007 (UTC)
Note that permanently running things like incandescent lights off batteries is quite expensive, as the batteries need to be constantly replaced. Using rechargeable batteries is better, but they still have a limited life and will need to be constantly recharged. Lowering the power requirements for the device, such as by going with fluorescent lights instead of incandescent, is a good idea. An uninterruptible power supply will provide battery backup for short periods of time. StuRat 01:39, 26 March 2007 (UTC)
You can buy cheap 12 volt inverters in most car parts stores for around $20 to $30 (I scored a couple of really good ones from WalMart for around $27 recently). They are intended to be plugged into the 12v auxiliary socket of your car - but you can easily wire them up to a stand-alone car battery. A car battery plus inverter will run low wattage things like table lamps for many hours. I keep a couple of old car batteries around (fully charged) and have used them to power a small TV, a 40 watt table lamp and a DVD player for over 6 hours per battery - so these make a cheap alternative to an emergency generator. When you purchase an inverter, you need to check the maximum current they can provide and make sure that you get one with a fuse so you won't damage it if you accidentlly overload it. SteveBaker 03:34, 26 March 2007 (UTC)
The most efficient solution is to use DC appliances powered directly from the batteries. These are made for recreational vehicle and camping applications and for boats. 12 volt compact fluorescent lights are a great choice. For example, one is listed (at the very bottom) at [1] for $12.75, which uses 13 watts to give the brightness of a 60 watt incandescent light. You could also buy an Uninterruptible Power Supply intended for use with computers as a standby power device, charge it up, and use it to power 120 volt ac devices within its power range for a limited time. If the devices uses far less power than the maximum rating of the UPS, it would be able to power it for far longer than the rated backup time. Edison 14:31, 26 March 2007 (UTC)

Or you could attach the battery to an electrical generator so that it creates electricity as it falls, and then lift it back up again and let it fall again, thereby transfering both your energy and the batteries energy into electricity which can then be used for other things :] HS7 17:56, 26 March 2007 (UTC)

HS7 - please cease putting these intentionally misleading replies into honestly asked questions - it is a form of vandalism. If you do not cease forthwith I'm going to complain to the admins. SteveBaker 03:08, 27 March 2007 (UTC)
I think it was just a joke. StuRat 03:12, 27 March 2007 (UTC)
And a pretty good one, I thought, evoking the classic method (er, classic alternative method, if you insist) of determining the height of a building using a barometer. (And it certainly wasn't misleading, once you figured out what he meant.) —Steve Summit (talk) 23:01, 27 March 2007 (UTC)

It's not misleading, it would actually work, I just happen to be more practically minded than most people :) HS7 14:34, 27 March 2007 (UTC)

It's exceedingly misleading. Go calculate what it would take to power a mains-powered 120v lamp by your means. It's ridiculous. SteveBaker 04:14, 28 March 2007 (UTC)


6N Chromosome Number[edit]

One of my reproduction problems has me stuck. Banana plants have a 6N chromosome number and thus cannot reproduce sexually. Why is this. I am thinking that after the first meiotic division each of the two cells would have 3N chromosomes and wouldn't be able to undergo a second meiotic division because there is no way to split up these chromosomes evenly, but I am not sure if my thinking is right. Can anyone give any other suggesions? Thanks! 02:03, 26 March 2007 (UTC)purecontrol

Your thinking is right. See this page on polyploid plants. Briefly, "In the formation of gametes during normal meiosis, homologous chromosomes must pair up with each other during synapsis of prophase I. Like other odd polyploids (with 3 sets of chromosomes), bananas are sterile and seedless because one set of chromosomes (A or B) has no homologous set to pair up with during synapsis of meiosis. Therefore meiosis does not proceed normally, and viable gametes (sex cells) are not produced. Since banana fruits (technically berrylike ripened ovaries) develop without fertilization they are termed parthenocarpic. Without viable seeds, banana plants must be propagated vegetatively (asexually) by planting corms, pieces of corms or sucker sprouts." - Nunh-huh 04:37, 26 March 2007 (UTC)


Isn't it possible for GPS equipped units of all kinds, types and sizes to be programmed with "no trespass" zones that inclused a good safety margin to keep users out of trouble with foreign governments or even local law? 02:14, 26 March 2007 (UTC)

Not sure what you mean by "unit", but I don't see why not. --Bmk 02:34, 26 March 2007 (UTC)
Cell phones to patrol boats... 05:15, 26 March 2007 (UTC)
GPS just gives coordinates (and maybe the time) but nothing more. Yes, devices can be programmed to associate ranges of coordinates with trespass zones or any other zones, but retrofitting all existing GPS software to include it would be a very costly and difficult undertaking, and unless required by law would be unlikely to occur. —Pengo 13:27, 26 March 2007 (UTC)
Also note that such zones are dynamic, as areas may be shut down or have their zones extended due to terrorist threats, etc., with little warning. Thus, keeping the device updated would be a problem. You could download new info to it each day via a wireless Internet connection, but there's no guarantee that governments would supply this info electronically in a timely manner. StuRat 15:19, 26 March 2007 (UTC)
The united states can turn off or degrade the un-encrypted signal (what civilians use) form the sattelites at will. This can be used to stop non-US-military recievers from working worldwide, or in a large geographical area. Degradation within a precisely defined area like you describe is not possible. See the article on GPS edit: re-reading your question there is no reason this couldn't be done but it would require cooperation from every single gps unit in use which seems infeasible. No doubt some digital maps included in the units will have relevant info such as restricted areas but there is no way to mandate this or make sure this info is up to date. I could always build my own GPS reciever that has no knowlege of these zones. -- Diletante 17:17, 26 March 2007 (UTC)

Airplane GPS's routinely include airspaces and warnings as you approach them. Also, they can create spaces around other airplanes using ADS-B or Mode S traffic alerting. But it has nothing to do with the GPS system, rather it's the mapping and tracking software that's provided by the manufacturer. GPS only provides coordinates (acutally, I think it only provides time and satellite ID number IIRC). Anything that relates to a map or is a derived quantity such as velocity or track is provided by software. --Tbeatty 08:50, 27 March 2007 (UTC)

What are the Effects of Orgasm/Ejaculation Cessation in Males[edit]

I am curious about this subject on three points:

1) Changes physiologically to the male body over a period of days, weeks, months, and years when orgasms and ejaculation is stopped. (i.e. increase in size of testes, higher risk of heart attack due to hardening of blood vessels, or etc.)

2) Chemical changes in the brain and/or chemical makeup of bodily fluids. (i.e levels of seratonin, dopamine, and etc.)

3) Psylogical effects of cessation. (i.e. irriation, nervousness, elation, hyperactivity, or etc.)

Thanks. -- 02:43, 26 March 2007 (UTC)

More frequent messy sheets ...assuming you mean Orgasm/Ejaculation casued by masturbation or Sexual intercourse. 05:17, 26 March 2007 (UTC)
For the first answer, I am personally skeptical and would like to see a reference. For the first question, it is normally taken to be unhealthy for a male to go without ejaculating for more than about two weeks. Although the prostate fluid can be reabsorbed, the prostate should be drained fairly frequently studies show, and the male has a higher chance of prostate cancer and more disorders of the prostate if it is not. I would not recommend it. To keep this from happening in a male that cannot or has trouble ejaculating normally, the solution is prostate milking. Psychological effects probably would not be all that bad unless he was teased or tempted or really wanted to. I don't believe there would be any problems or much change necessarily on chemical balances in the brain or in the blood, would there? [Mαc Δαvιs] (How's my driving?) ❖ 07:02, 26 March 2007 (UTC)
Jeez, Mac. Your answers should come with a warning label: This health advice is being provided by a teenager who often has no clue what he is talking about but is never in doubt. —The preceding unsigned comment was added by (talk) 11:33, 26 March 2007 (UTC).
Sorry, read it on Wikipedia. If you don't think it's right I'd be glad to see some references. As for my rechecking, I didn't find where I read it on Wikipedia, but I did find "Sterilization by vasectomy may increase the risk of prostate cancer, though there are conflicting data.[1] More frequent ejaculation also may decrease a man's risk of prostate cancer. One study showed that men who ejaculated five times a week in their 20s had a decreased rate of prostate cancer, though others have shown no benefit.[2][3]" Oh, and thanks for signing out dedicated user, so no body knows who you are. [Mαc Δαvιs] (How's my driving?) ❖ 17:58, 26 March 2007 (UTC)
See the "Medical aspects of abstinence" subsection of Sexual abstinence, and the "Benefits" subsection of Masturbation. MrRedact 10:11, 26 March 2007 (UTC)

I believe the seminiferous ducts in the testicles can rupture, causing sharp pain, but no permanent damage. Frequent erections may also be expected. StuRat 15:13, 26 March 2007 (UTC)

Personally I recently lost any desire to do anything like this for a few weeks (I still haven't worked out why) and during that time I didn't notice any physical effects, or any changes to my mood, other than what I would normally expect :) However as for the first reply, I did find that I appeared to recovered this desire whilst asleep :) HS7 17:48, 26 March 2007 (UTC)

This was almost certainly an effect though as it was the only time this has ever happened to me, and it was a few months ago :) HS7 17:52, 26 March 2007 (UTC)

Without suggesting this is necessarily the case with you, such an experience is sometimes a symptom of depression, or a side-effect of the use of certain pharmaceuticals (some legal, some not). JackofOz 04:16, 28 March 2007 (UTC)


  1. ^ Giovannucci, E; Tosteson TD, Speizer FE, Ascherio A, Vessey MP, Colditz GA (Feb 17 1993). "A retrospective cohort study of vasectomy and prostate cancer in US men". JAMA 269 (7): 878–82. PMID 8123059. 
  2. ^ Giles, GG; Severi G; English DR; McCredie MR; Borland R; Boyle P; Hopper JL (Aug 2003). "Sexual factors and prostate cancer". BJU Int 92 (3): 211–6. PMID 12887469. 
  3. ^ Leitzmann, Michael F. (April 7 2004). "Ejaculation Frequency and Subsequent Risk of Prostate Cancer". JAMA 291 (13): 1578–86. 2004;291:1578-1586.  Text " Elizabeth A. Platz, ScD; Meir J. Stampfer, MD; Walter C. Willett, MD; Edward Giovannucci, MD " ignored (help); PMID: 15069045

c:) HS7 21:05, 26 March 2007 (UTC)

Fish and drowning[edit]

Is it possible for fish to drown in water? Uncke Herb 02:58, 26 March 2007 (UTC)

I would hope not seeing that the water is what they extract their oxygen from. See gills.

Fish can 'drown' (if you can call it that) in open air, however, seeing that gills can only extract oxygen from a liquid environment.

Also, gills only work in the fish keeps moving, pushing water through them - I suppose if the fish was paralyzed somehow, or unable to move, it could 'drown' if the water was very still and not moving through their gills at all. Don't quote me on that though, I'm just a linguist, not a marine biologist. -- 03:08, 26 March 2007 (UTC)

By definition, drowning is death due to the interruption of the body's absorbtion of oxygen from the air due to a liquid. Since fish don't have lungs, and don't get oxygen directly from the air, no, they can't drown. However, fish do need oxygen, which they absorb from the water passing through their gills. If they are unable to get enough oxygen this way, for example if they are in water which has insufficient oxygen disolved in it, the fish can die from hypoxia, which is usually the same primary cause of death as with drowning. MrRedact 03:21, 26 March 2007 (UTC)

Although it doesn't mention drowning per se, you might be interested in the article Dead zone (ecology)Pengo 13:23, 26 March 2007 (UTC)

I'm sure I read somewhere that you don't actually have to die to drown, but right now I can't remember what they claimed the actual defenition was :( HS7 17:44, 26 March 2007 (UTC)

I heard once that a salt water fish will drown if you put it into fresh water and a fresh water fish dies of thirst in salt water, i'll have to try to figure out if that's even remotely correct or if it is complete BS. Vespine 23:49, 26 March 2007 (UTC)

The fish may die, but they don't drown. They would suffer from severe electrolyte imbalance. The freshwater fish would suffer from slat poisoning - like humans would if they only drank seawater. The salt water fish would absorb too much freshwater and the kidneys could not cope. Such a death would be slower than the hypoxia death. GB 03:18, 27 March 2007 (UTC)

Naturally Shaped Eyes[edit]

I am a novelist and I am currently in the process of brainstorming. One one way I brainstorm is by making Character Profiles. So, right now I am currently searching for information on naturally shaped eyes such as Almond-eyed, Round-eyed, Wide-set Eyed, etc. I've searched everywhere but can't find anything.... Can you be born with almond-shaped eyes? Or do you just use make-up like I've been seeing in the search engines? I hope not. What I require is a full and complete list of all the naturally shaped eyes and their descriptions. Zen 03:04, 26 March 2007 (UTC)

I can be quite sure someone can be born with almond-shaped eyes. I am surrounded by a diverse cross-section of asian women at my workplace whose eye shapes can attest to this. As a fellow writer, I suggest just look go to a Wal-Mart or somewhere and just look at some people and see what kind of eye shapes you like. The best examples are always real life. -- 03:14, 26 March 2007 (UTC)
You could just start collecting pictures of different eye-shapes, but personally I feel they rarely add something to a character. No one would worry if you left it out. - Mgm|(talk) 07:51, 26 March 2007 (UTC)
Using eye shape as substitute for characterization is really crappy writing though. It is little better than the medieval assumption that physiognomy reveals character (i.e., ugly must indicate evil). alteripse 11:26, 26 March 2007 (UTC)
The "shape" to which you refer is actually a combination of the contour of the eyelid and relative position of the eye sockets in the skull. Perhaps seeking resources dealing with ophthalmic anatomy would provide significant information on these and related matters; see those pages for links. -- Deborahjay 17:19, 26 March 2007 (UTC)

On another note - retinal scans seem to be less practical than iris recognition since the newer technique can be performed at oblique angles, in uncontrolled lighting, and cope with other real-world constraints. Researchers in both of these fields maintain large academic databases of eye photos for testing purposes. You might investigate to see if you can find public access to these data sets. Nimur 16:05, 29 March 2007 (UTC)

Images and database access are available for free, apparently. Nimur 16:09, 29 March 2007 (UTC)

First personal knowledge of sex[edit]

Where do kids normally learn about erection, ejaculation and orgasm, i.e., from another person sneaking into their bedrooms while they are asleep and doing the "nasty" to, on or for them or from fondling themselves and accidentally causing an erection, ejaculation and orgasm? —The preceding unsigned comment was added by (talk) 05:37, 26 March 2007 (UTC).

The first of the two options you list sounds like you're basically talking about child sexual abuse. There are statistics about its prevalence in the Epidemiology section of that article. There are also some statistics in the "Sibling incest between children" section of the incest article. I realize this information isn't quite what you're asking for, but it at least gives some information about early sexual experiences.
As far as the second option, the "Masturbation frequency, age and sex" section of the masturbation article gives some statistics about childhood masturbation.
The two options you give aren't the only two ways for children to learn about erection, ejaculation, and orgasm. For example, they could also learn about those topics by hearing or reading about them. MrRedact 08:20, 26 March 2007 (UTC)
Or watching practically any movie rated anything about PG-13. Granted, that knowledge will not be entirely accurate but then again much of what people learn about sex early on isn't. -- 14:01, 26 March 2007 (UTC

US territory Antarctica and Who has control over the south pole[edit]

The US has the right to claim territory in Antarctica why havent they claimed any yet? Who has control over the south pole —The preceding unsigned comment was added by (talk) 06:29, 26 March 2007 (UTC).

The U.S. is a signatory of the Antarctic Treaty. No new territorial claims can be asserted while the treaty is in force. - Nunh-huh 06:57, 26 March 2007 (UTC)
And the reason everyone signed that treaty rather than fight over control of Antarctica is that ownership of Antarctica wouldn't be profitable at present. Agriculture wouldn't work there and factories are impractical. Mining/drilling for petroleum is limited because most of the continent is covered by glaciers. While it's possible to drill holes through thick glaciers, they are constantly moving, so the hole would need to be continuously redrilled. The cost of getting workers and equipment to the work site would also be quite high. Of course, if a large petroleum deposit is found there and the world was running out of petroleum, that could change things. Perhaps the treaty would be modified to allow extraction. StuRat 14:52, 26 March 2007 (UTC)

I would assume the South Pole is owned by the US as they have a research base built right on top of it :) HS7 17:39, 26 March 2007 (UTC)

"The Soviet Union and the United States both filed reservations against the restriction on new " i take that as the us has the right to claim territory so my question is why hasn't the us or Russia claimed any territory but we have the south pole so it doesn't matter ;)

Officially the US doesn't 'own' the South Pole, but most of the people working there are american, so it is almost the same :) HS7 21:04, 26 March 2007 (UTC)

Scientific research stations are allowed under the treaty. StuRat 21:13, 26 March 2007 (UTC)

I think the US policy basically is that they're in theory against territorial division of Antarctica, but if the Antarctic Treaty system ever collapses, they reserve the right to get in on the action.--Pharos 19:24, 27 March 2007 (UTC)

true cause[edit]

Is it possible to cause someone to die without triggering an investigation that would reveal the true casue of their death? 06:30, 26 March 2007 (UTC)

Yes, especially if no body knew they died. Plenty[citation needed] of agents that worked for the United States Central Intelligence Agency have died without an investigation being triggered[citation needed]. The investigation would be illegal[citation needed] anyway. [Mαc Δαvιs] (How's my driving?) ❖ 06:56, 26 March 2007 (UTC)
Mac Davis, ... what do you know about the CIA? 1. It's a government agency, and its employees are monitored. If they were to die, some form of investigation would happen. 2. It is not a movie or comic book, and there aren't "secret agents without an identity." The original questioner should realize that the "true cause of death" is only determined as far as people care to find additional information. Consider soldiers killed in active-duty overseas - many of them are simply considered "killed by enemy action," and further investigation would probably not reveal more information than that. Is it true? Is it false? It's irrelevant unless somebody demands more facts. Nimur 16:18, 29 March 2007 (UTC)
Normally a doctor would have to sign a death certificate to say that a person has died, if there is a body. If there are any suspiscious circumstances, that is when the police will investigate, or if no apparent cause or an unusual one then there could be a post mortem to determine what happened. So the death of very old or very sick people often has no investigation. GB 09:30, 26 March 2007 (UTC)


which of the following is only once characterized and what is the reason for it?

1. Genome
2. Proteome
3. Transcriptome
4. Metabolome 10:41, 26 March 2007 (UTC)

This is quite clearly a homework question, and the reference desk policy is that we don't give answers to homework questions. Perhaps if you read the articles on genome, proteome, transcriptome, and metabolome, you would gain enough information to answer your question. MrRedact 10:57, 26 March 2007 (UTC)

It's a weird question, though. I can't figure out what his/her teacher is getting at. What do you think "characterized" means in this context, or is it being misused? alteripse 11:25, 26 March 2007 (UTC)
Characterized may mean measured or determined, so for example if a genome is determined 100% correctly, then it will be the same in all the cells of the organism, whereas the proteome may vary depending on the type of cell producing different products. However even a genome will change due to mutation, variation amoungst individuals, and breeding. GB 02:59, 27 March 2007 (UTC)

Computer radiation[edit]

I have bad vision, mainly due to overuse of my computer, and I realized that my vision is worst as it gets darker, while nearly "non-damaged" as it gets sunnier. Does this mean that computer radiation can cause somewhat of a night blindness? O, and do lcd screens radiate less? 12:18, 26 March 2007 (UTC)

Its possible that in the brighter light, your eyes 'stop down' thus giving you improved depth of field. Conversely, in dim light, your irises open up giving you less ability to focus easily. I wouldnt think that monitors can cause night blindness, but if you are at all worried, go to the optitican to get your eyes checked and mention the problem to him/her.
I would imaginre that LCD sceeens, becasue of the way they work would generate few or zero X Rays compared to CRT monitors (which geneate bit from the back normally. —The preceding unsigned comment was added by (talk) 12:46, 26 March 2007 (UTC).

Maybe you have bad night vision? --Shanedidona 13:44, 26 March 2007 (UTC)

Availability of light certainly has an effect on vision in general, and becomes incredibly noticeable when you have vision impairment of some sort. Even people who have very little vision impairment (like myself) generally notice a difference between sunlight and artificial light in terms of their vision (in sunlight I can read things from very far away; in artificial light of any sort I require glasses to see details at any distance). It doesn't have anything to do with radiation, at least not in the sense you probably mean it (radiation, strictly speaking, includes visible light and heat as well, but I am assuming you mean its more nefarious definitions which do not at all come into play in computer monitors — if they did they would never be approved for sale). -- 14:05, 26 March 2007 (UTC)

Why do you believe that your bad vision is related to your computer? See Rhodopsin for how night vision works. Sometimes called Visual purple. Don't see how it's related to computer use though. --Tbeatty 07:45, 27 March 2007 (UTC)

I've used my computer more than any sane person should, and when I'm not on my computer i'm watching TV, however in the 4 years between getting my eyes tested, only one eye changed by 0.5 (and that's probably down to my own error in judgement during the test). My prescription is very weak anyway. So for me I don't see any connection between the two, as Tbeatty says. Capuchin 11:54, 27 March 2007 (UTC)
(I started the question) Wow, you are lucky. I had very sharp vision until three years ago when I discovered the addicting world of computer games. I spent around 8 hours a day during summer playing those things. When I came back to school I realized that my vision is not sharp anymore. I have many friends who also got glasses this way. /By your comments I am guessing that my bad vision is due to the computer games and not computer in general/.
Now I realized that my night vision has way more deteriorated that my day vision so I was asking if there is a connection between "computer radiation (or whatever that emits from the computer and ruins your vision)" and night vision? 12:36, 27 March 2007 (UTC)
Oh, computer games, yes, I played those, more than 8 hours a day. Are you sure it's not something else, and the computer usage is conincidental, for example, puberty? Capuchin 06:36, 28 March 2007 (UTC)

van der waals question[edit]

Hi I was recently reading your Casimir effect page, and it claims that the Van der Waals force is a similar effect. Can i clear something up? does the Van der Waals force, utilise quantum vacuum fluctuations? or is it just a similar effect with other EM sources? - Seatle —The preceding unsigned comment was added by (talk) 13:25, 26 March 2007 (UTC).

It is more similar to other electromagnetic bonding—it commonly arises from the polarization of molecules into dipoles. It does not have to do with virtual particles or vacuum energy or anything like that. [Mαc Δαvιs] (How's my driving?) ❖ 17:47, 26 March 2007 (UTC)
The polarization of nonpolar molecules into dipoles does depend on the quantum mechanical view of electron distribution in molecules. London forces should be helpful. —LestatdeLioncourt 18:13, 26 March 2007 (UTC)

Memorial size for traffic deaths versus deaths from military conflict[edit]

If a memorial wall was built for traffic deaths each year how much bigger or smaller would each memorial be compared to the Vietnam Memorial for deaths in the USA and Vietnam since the Vietnamese war ended? 13:34, 26 March 2007 (UTC)

This sounds like a homework question. It requires four numbers, two of which you can get easily, one of which takes a little more hunting, and the last you have to calculate. You need to know the size of the Vietnam Memorial as well as the number of names (deaths) on it. These are easily found from the Vietnam Veterans Memorial article. Then you need to know the number of traffic deaths per year, and figure out what the proportional size of the memorial would be if it were allocating the same amount of space-per-death as the Vietname Memorial. You can get the statistics from the US Census website if you hunt around (look for mortality statistics), and then it is up to you to do the calculation of size from that. -- 14:08, 26 March 2007 (UTC)

And if it is homework, and exactly as you have put here, don't forget to point out that it could be any size depending on how big the writing is :] HS7 17:31, 26 March 2007 (UTC)

Blackhole evaporation[edit]

Why and how a blackhole evapoarates? By definition, a blackhole is intense concentration of matter, wherefrom absolutely nothing, not even light can escape due to its collosal gravity. How then a black hole is said to be radiating energy / mass? Aren't these cutting-edge-physisists faltering in thier own beliefs? —The preceding unsigned comment was added by (talk) 16:15, 26 March 2007 (UTC).

Have you read the article on black holes? It discusses these issues. The gist of things is that we don't really know whether black holes can evaporate (the theory that postulates that they can isn't yet supported by evidence), and we don't know why relativistic jets form (they are indeed a bit of a paradox). -- mattb @ 2007-03-26T16:27Z
Black holes are theorized to evaporate due to Hawking radiation. This happens due to almost a loophole in physics, which some things actually do happen because of these "loopholes." Hawking radiation was thought of as a solution to the black hole information paradox. [Mαc Δαvιs] (How's my driving?) ❖ 17:26, 26 March 2007 (UTC)
To elaborate on Mac Davis's answer (in what may be a grossly oversimplified view of things, because I'm just an armchair astronomer): virtual particles are constantly being created at the event horizon of the black hole (just as they would anywhere else). These particles are always being created and destroyed (they annihilate each other because the are a particle-antiparticle pair). Sometimes, one of the particles will get sucked into the black hole, so the other doesn't get annihilated. This particle is released "from the black hole". In this sense, black holes continuously emit radiation. Again, I'm no expert, but I think this is will give you a basic idea of how thing are happening. —LestatdeLioncourt 18:20, 26 March 2007 (UTC)
Yeah, Hawking Radiation is all you need to take away from this. How relativistic jets form in the accretion disks of Black Holes isn't clear, but that's not a particularly big deal. WilyD 18:34, 26 March 2007 (UTC)

I always thought of it as a product of the uncertainty principle. For a very short period of time, energy can exist that satisfies E*t = h. This energy is in the form of a particle and an anti-particle. Normally this energy is unmeasurable per the uncertainty principle. However, if this creation occurs exactly at the event horizon, one of the particles is captured by the black hole and the other particle escapes instead of being annihilited in recombination. The particle that escaped had energy/mass from the black hole and eventually the entire black hole will evaporate. There is a lot more mathematics involved especially if the black hole is spinning but the principle is that uncertainty means that some events cannot be ruled out and indeed must happen if QM is correct. --Tbeatty 07:58, 27 March 2007 (UTC)

Ionic Equations[edit]

I would appreciate any help on how to balance ionic equations.

I've checked the articles here and searched the internet extensively, but to no avail.

I also know nothing of redox/oxidation/reduction etc.; since I haven't yet covered that in school, so I need to know hot to balance the aforementioned equations without any knowledge of redox reactions or electrolytes.

I can balance normal chemical equations, but not ionic ones.

An example of what I cant solve, would be:

Pb2+(aq) + OH- ---> Pb(OH)2(s)

--Xanton111 17:08, 26 March 2007 (UTC)

the 2+ counts as 2, therefore needing to be neutralised by 2 1-s (shown just as -s):) HS7 17:23, 26 March 2007 (UTC)

I just need to know:

a) The "goal" of solving the equations. b) The method of solving them, while making sure the mass is equal on both sides as well as the charge.

a) is to make the charge multiplied by the number of molecules/atoms for each different molecule/atom the same ie. b) 2 molecules of charge +3 and 3 or charge -2, giving 6 each :) As for making the mass equal, I have no idea, but you will need the Relative Atomic/Molecular Masses for each molecule/atom :( HS7 17:35, 26 March 2007 (UTC)

If you already have the equation, as you do, but without coefficients, then you only need to worry about balancing the number of atoms. I find a chart useful for this:
Reactants | Products
  1 Pb    |   1 Pb
  1 O     |   2 O
  1 H     |   2 H
So, it is apparent that we need to add an extra O and H to the reactants to get them to balance:
Pb2+(aq) + 2OH- ---> Pb(OH)2(s)
This gives us:
Reactants | Products
  1 Pb    |   1 Pb
  2 O     |   2 O
  2 H     |   2 H
If the atoms balance then the masses will balance automatically. In this case, the atomic masses for Pb, O, and H are approximately 207, 16, and 1 grams/mole, so we would have 207 + 32 + 2 or 241 grams per mole on both sides. Note that balancing the number of atoms on each side can be far more complex, requiring an iterative process, in some cases. StuRat 18:06, 26 March 2007 (UTC)

Sorry about my answer, I wasn't thinking properly :( HS7 14:08, 27 March 2007 (UTC)

Warning: Thinking improperly is punishable as thoughtcrime. :-) StuRat 17:15, 28 March 2007 (UTC)

Mie Scattering and Cylinders[edit]

Can Mie Scattering have a >1% effect on UV-Vis measurements of nanoporous membranes? (Pores are 200nm in diameter and .5mm long, centers ~500nm apart, alumina membrane refractive index=1.6) There are papers that analytically take Generalized Mie Theory from spheres to infinitely long ellipsoids (taken to be cylinders), but I not only cannot interpret the purely theoretical papers but I also am unsure of whether the lack of a cylinder scatters in a similar fashion as an actual cylinder (I assume so -- just switch the indices of refraction of the solid and air). Why am I asking? I am seeing some funky business in transmittance and reflectance measurements.Chillliman 17:13, 26 March 2007 (UTC)Chillliman

A quick rough answer would be yes, as the 200nm would be on the same order of magnitude as your UV wavelength. However if the light is propogating parallel to a straight cylynder there may not be much effect. But are your pores straight cylinders, or randomly aligned as in a sponge? If you look at how much of the surface is pore it would be approx 200/500 squared or 0.16 - so there may be a 16% effect compared to pure alumina on the gross material point of view.

GB 02:51, 27 March 2007 (UTC)

Some math[edit]

Transferred to WP:RD/MATH#Some math -- atropos235 (blah blah, my past) 23:21, 26 March 2007 (UTC)

Value of fp in the Drake equation[edit]

The Drake equation, used to estimate the number of advanced civilizations in our galaxy, is dependent of several values, one of which is fp-the fraction of stars that have planets. What is the currently accepted (or least controversial) value for this variable? The Drake equation article says that Drake used .5, but considering how much our understanding of extrasolar planets has developed in the past few years, are different figures accepted now? Thanks for any information on this topic. GhostPirate 20:20, 26 March 2007 (UTC)

  • .5 probably isn't crazy. I think any astronomer would agree it's between .1 and 1, and the Drake equation is so imprecise anyhow this number probably isn't a big deal. There are other factors to - fp probably increases with time, for instance (metallicity, actually, but these are related, right?) and who knows what else? My guess is its more like .9 or something, but any good astrophysicist will tell you .5 = .9 WilyD 20:36, 26 March 2007 (UTC)

I don't think we currently have enough data to come up with a good estimate. Current techniques mainly detect only huge planets in nearby systems. It's quite possible that every star has small terrestrial planets, but we just can't detect them yet. StuRat 21:02, 26 March 2007 (UTC)

StuRat summed it up nicely. Current observations focus on stars of about the same mass as the Sun, on the main sequence, but nobody's spent any significant time looking at close or medium binaries, which are fairly common. The (naive) assumption in the past was that these can't form planets, but HD 188753 A put an end to that, and theory is starting to catch up. Of the stars we do look at, about 10% have planets (as it says in the exoplanet article), but - for now - we're limited to gas giants within about 5 astronomical units, or closer bodies down to about 15 Earth masses. Models that "explain" (used loosely) the solar system predict terrestrial planets to be quite common; but then the solar system is something of the odd one out at the moment. Still, expect the number to go up. 0.5 is as good a guess as any, frankly. Spiral Wave 00:47, 27 March 2007 (UTC)
Compared to the uncertainties in the other numbers in the equation, 0.1 to 1.0 is a pretty tight range. I agree that 0.5 is a pretty good number to plug in, but if you really want to look where the uncertainties are, look at almost any of the other 'guesstimated' values! SteveBaker 02:59, 27 March 2007 (UTC)

Neutral methyl orange[edit]

If someone has already answered here than ignore and delete this.

What couler us Methyl orange when mixed into neutral solutions.--I.W 21:08, 26 March 2007 (UTC)

Neutral solutions have a pH of 7. The Methyl orange article says that it is yellow when in solutions with a pH above 4.4 -- atropos235 (blah blah, my past) 22:55, 26 March 2007 (UTC)

GPS Signal degradation[edit]

What is the effect of heavy cloud cover on the signal strength of a conventional automotive GPS receiver? Thanks for any help!

dondd:Dondd 23:23, 26 March 2007 (UTC)

Quite a bit, though I am not expert enough to quantify. Splintercellguy 23:57, 26 March 2007 (UTC)
I've found it to be significant for hand-held GPS's - but the TomTom unit I have in my car doesn't seem to be affected badly enough to cause a loss of navigational ability. The worst conditions for the hand-held units seems to be when you are standing under trees that have been soaked with rain. SteveBaker 02:52, 27 March 2007 (UTC)

Theoretically it should have little effect as the rain drops are small compared with the wavelength of the signal. GPS wavelength is bigger than C band which is little affected by cloud or rain. GB 02:54, 27 March 2007 (UTC)

Hmm, Seeber (2003) Satellite Geodesy, in explaining why higher frequencies are not used (as here would be much less refraction in the ionosphere at higher frequencies) states:

With higher frequencies the atmospheric absorption in the troposphere increases. Without rainfall, the absorption can be neglected for frequencies between 30 MHz and 30 GHz. With precipitation, however, signals in the frequency domain > 1 GHz experience considerable attenuation.

The L1 and L2 GPS frequencies are 1.6 and 1.2 GHz.—eric 21:25, 27 March 2007 (UTC)
Also,our GPS article explains that moisture in the air affects the propagation velocity of the GPS signals. So even if the signal is not attenuated, its accuracy could be significantly compromised, since of course GPS measurements depend intimately on phase and propagation velocity. —Steve Summit (talk) 12:09, 28 March 2007 (UTC)