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November 16

Sci/fi author and gamemaker has Questions on Wigner Energy and future weaponry.

Okay, I have a few questions, but I'm lumping them all together. I'm trying to write a realistic hard-ish sci/fi setting, but I'm having trouble justifying some of the things that are needed. One of the problems is the energy density required for things like portable energy weapons and functional space combat craft. I had an interesting idea, after noticing that Wigner energy has shown energy densities up to 2.7 Kj/g. Which is about as much as theoretical lithium nanotech batteries, and more than some monopropellants. A few questions about this though: 1) that seems to be the highest OBSERVED in a graphite reactor moderator block, could you push it higher if you were intentionally inducing displacements as a means of storing energy? 2) is it possible to get that energy out in a useful manner? 3) is there a better potential source of energy, ideally rechargeable.

My other question is about future weaponry. Are directed-energy weapons viable on a personal scale? They're a sci/fi staple I know, but is it realistic to assume a man-portable laser can do any real damage. Obviously a military would have to see justification for switching from modern small arms, either higher kill potential or greater tactical application. One I can see is the lack of need for lead time (beam traveling at the speed of light as opposed to a bullet moving at a few hundred M/sec) and near-infinite range in a vacuum, another might be ammo considerations, but I'm just not sure. I've read all the articles, but what I really need is a concise rundown on the relative advantages/disadvantages and realism of: Gyroc (gyrojet) firearms, Railgun/Gauss gun/Coilgun, laser, electron beam and conventional firearm. Thanks in advance, 69.210.56.62 (talk) 01:24, 22 November 2008 (UTC)[reply]

Bee stings on different body parts

This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis, prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page.
This question has been removed. Per the reference desk guidelines, the reference desk is not an appropriate place to request medical, legal or other professional advice, including any kind of medical diagnosis or prognosis, or treatment recommendations. For such advice, please see a qualified professional. If you don't believe this is such a request, please explain what you meant to ask, either here or on the Reference Desk's talk page. --~~~~

If you're looking for explanations for your different reactions to bee stings – particularly if you're anticipating getting more, as you keep bees – you should speak to your doctor. We cannot offer an interpretation of your symptoms on Wikipedia. TenOfAllTrades(talk) 00:00, 16 November 2008 (UTC)[reply]

I'm not allergic to bee sting, so a bee sting isn't dangerous, only annoying. I know Ref desk doesn't give medical advice, I'm not looking for medical advice. And it's not the sort of thing I'd waste my doctor's time on. Likewise, I'm not seeking advice on how to treat a bee sting. So it's rather inappropriate to delete my question as asking medical advice. I find it likely that someone reading this reference desk would have an idea as to how apitoxin works, and why it would have significantly different effects on different parts of the body. Biology question, not a medical question.

I'm looking for an answer to a (hopefully simple) question: Why would bee stings to the face just above the moustache and 1cm to the right of the nose; to the upper arm on the biceps; and to the forearm result in very different reactions. Any stings to the forearm are rather nasty, with swelling; stings to face and biceps make a small bump. Why such a vast difference? And note that all these reactions are local reactions and are not dangerous. I'm not seeking advice on what to do about it, only ideas as to why the difference. --Psud (talk) 01:17, 16 November 2008 (UTC)[reply]

Obvious question : Are you sure it was the same species of bee each time? APL (talk) 02:39, 16 November 2008 (UTC)[reply]

Yep. Same colony. --Psud (talk) 03:35, 16 November 2008 (UTC)[reply]

There are too many factors involved to give an answer. Bees do not deliver the same amount of toxin with each sting. Stingers are delivered at different depths. Taking time to remove a stinger increases the amount of toxin delivered. Oily skin (such as that around the face) may have work as an antacid - depending heavily on the person. Rubbing a sting can increase swelling. That is just what comes to mind immediately. I hope it is obvious now that this question is asking for a diagnosis of your specific body and is not a general question about general human anatomy. That is why it is considered medical. It is impossible to diagnose why one part of your body reacts more to a sting than another without performing a physical exam. -- kainaw ™ 04:24, 16 November 2008 (UTC)[reply]

I saw someone stung on the face at or near the location described, and he looked really funny with his eye swollen shut. If the swelling had been on the bicep it would scarcely have been noticeable. That is certainly one difference. Edison (talk) 05:08, 16 November 2008 (UTC)[reply]

Could blood flow or muscle make a difference? Face has plenty of muscle near the surface around the mouth, the biceps is a muscle, the forearm has practically no muscles... doesn't it? --121.127.209.126 (talk) 07:29, 16 November 2008 (UTC)[reply]

That ain't it. The forearm has plenty of muscles, including almost all of those that control motions of the fingers and wrist. There are a few intrinsic muscles of the hand, but most hand strength comes from the forearm muscles. --Scray (talk) 01:21, 17 November 2008 (UTC)[reply]

Surface area of the internet

Is it at all possible to calculate this, or am I being mocked by this guy at work? —Preceding unsigned comment added by 81.77.235.192 (talk) 00:27, 16 November 2008 (UTC)[reply]

It would require a lot more clarity on the terms to know if it even made sense. Does "this guy" mean the physical architecture of the internet? If that's the case then it can be calculated as an elaborate Fermi problem. Does he mean the amount of physical space the entire internet would take up if, say, printed onto paper? Or is it implying there is a physical space in the logical manipulation of bits that make up our electronic conversations, the abstract logical space between my screen and yours that constitutes the system of communication and distribution that we call "the internet"? (In the latter case, I don't think it is calculable.) In any case, it is a query that, if you want to appear smart, you answer with more queries that show how smart you are, that you recognize that this is by itself not a clear question. --98.217.8.46 (talk) 00:38, 16 November 2008 (UTC)[reply]

This looks like a nonsensical question. Its sort of like asking what shape is the color red. It seems to lack any connection to reality. If we take the internet as merely the sum total of the information it contains, well information has no "shape" and as such, has no surface area... --Jayron32.talk.contribs 00:47, 16 November 2008 (UTC)[reply]

Isn't the Internet a series of tubes, whose surface area can easily be calculated? Clarityfiend (talk) 01:15, 16 November 2008 (UTC)[reply]

I can't think of any aspect of the Internet that has "area". The volume of all of the equipment is something one could imagine calculating - or maybe the total distance between nodes - the total number of bytes of data? But the AREA?!? I don't know what that means. Unless you're doing some kind of 'space-filling-curve' fractal kinda thing? Like this: (ob. XKCD link). Maybe the total area of all of the web pages if you printed them out on legal-sized paper? (But with dynamic-content pages, the answer could maybe be "infinite")...Meh - put this one on the "unanswerable-unless-clarified" pile. SteveBaker (talk) 01:21, 16 November 2008 (UTC)[reply]

If you have lots of spare computer time and don't want to donate it to more reasonable causes (e.g. distributed computing for science projects) you might take the following approach: Since the internet is all about moving information in electronic form, you could roughly estimate the average number of electrons involved in moving the bits of internet information at any given time. You might then also estimate an area for 2D mapping as described by Steve. (And have another decade worth of discussions as to what would count as internet related movements of electrons, what volume of space that would cover and how to convert that into a 2D figure.) You could then expand on that by including the space occupied by atoms dedicated to storing web pages and other auxiliary elements necessary to keep the internet going. So I'd go with 42. Challenge your co-worker to prove it's wrong! 76.97.245.5 (talk) 05:00, 16 November 2008 (UTC)[reply]

He might want a Fractal dimension on networks. Dmcq (talk) 09:58, 17 November 2008 (UTC)[reply]

How much is 8x10¹⁷ coulombs?

The Orders of magnitude (charge) article is woefully incomplete. I've calculated that an 8x10¹⁷C charge is enough for the Abraham-Lorentz force to cause the Earth to spiral into the Sun in about 5.5 billion years, and I want to know how much that really is, besides enough to make 80 million tonnes of aluminum. Also, does outer space follow the normal laws of electricity well enough to give it a resistance? If so, what is it? I want to use that to figure out exactly how hard it would be to apply a charge to the Earth. — DanielLC 01:59, 16 November 2008 (UTC)[reply]

Well, according to the Faraday constant, 96,485 coulombs equals the charge carried by exactly 1 mole of electrons. So 8x10¹⁷ coulombs is the charge of 4.6x10⁴⁶ electrons, or roughly the number of electrons in 7.7x10¹⁹ kilograms of hydrogen. This is about the mass of a medium-to-smallish sized asteroid. To put this in other terms, an ampere is a coulomb/second, so if this charge were carried by a current of 8x10¹⁷ amperes, at say a potential of 120 V (house current), it would use 9.6x10¹⁹ kilowatts; or in one second would use 2.6x10¹⁶ kilowatt hours of electricity. According to my latest electric bill, the current rate of $.099 per kWh means that driving 8x10¹⁷ coulombs of electic charge through my household circuit for 1 second would cost me $2.64x10¹⁵. That's 2.6 quintillion dollars, or significantly more than the entire supply of all cash, goods, and services of the entire world. Do either of these calculations help put it into scale for you? --Jayron32.talk.contribs 02:50, 16 November 2008 (UTC)[reply]

1 gram of hydrogen is roughly one mole, so it would hold 96,485 coulombs. This would mean that it would take roughly 8e12 grams, or 8e9 kilograms of hydrogen, not 8e19. — DanielLC 03:28, 16 November 2008 (UTC)[reply]

Dang. Yer right. Musta hit the extra "1" key somewhere. But the household cost is right, no?!? --Jayron32.talk.contribs 21:06, 16 November 2008 (UTC)[reply]

I just calculated that the energy required to launch that many electrons out of orbit is about 3.6e-10 joules. Moving the electrons to your house would require all the supplies of the entire world, but you could move them into space with the energy gained from the nuclear fission of ten atoms. I suppose getting them through the atmosphere would be the hard part. Anyway, making the Earth fall into the Sun conventionally would take about 8e26 kilowatt hours, so this still might work better. — DanielLC 03:56, 16 November 2008 (UTC)[reply]

If you're waiting 5.5 billion years, the Sun will have expanded into a red giant and possibly engulfed the Earth anyway (and if it doesn't, it will certainly be much closer), so you can save yourself the trouble!

Chances are the sun's expansion will push the earth out further though, in any event we're talking an astronomical (no pun intended) amount of time here though. 00:54, 22 November 2008 (UTC)

--Tango (talk) 23:56, 16 November 2008 (UTC)[reply]

I figured taking longer than that would be cheating, so I set that as the upper limit. I suppose what I should be saying is that it would take at least 8e17 C. So, about the resistance of space? — DanielLC 05:06, 17 November 2008 (UTC)[reply]

The resistance in space is pretty frigging huge. You need a series of actual atoms to transfer electrons along; and atoms are few and far between in space, so the resistance is likely, um, excuse the pun, "astronomically high". --Jayron32.talk.contribs 15:36, 17 November 2008 (UTC)[reply]

Does black hole evaporation violate the second law of thermodynamics?

A black hole sucks enormous amounts of matter and energy into it, presumably (correct me if I am wrong) including the microwave background radiation from the ongoing cooling of our universe after the big bang. But having re-concentrated all this energy, the hole slowly shrinks and evaporates due to Hawking radiation, violently releasing this energy all at once when it is small enough. Surley this violates the second law of thermodynamics? Could the universe be a perpetual motion machine? —Preceding unsigned comment added by Trevor Loughlin (talk • contribs) 04:43, 16 November 2008 (UTC)[reply]

Well - the energy goes into the black hole as organized, structured matter - stars and such - and comes out as photons hurtling off in random directions. That means that mass/energy was conserved but disorder increased - and that's pretty much what you'd expect with the second law. I guess I don't see the problem. SteveBaker (talk) 05:16, 16 November 2008 (UTC)[reply]

True about the stars. But what about the low grade energy in the form of microwaves that it sucks in? I assume that as the black hole shrinks the hawking radiation it gives out is of a higher grade, X-Rays for example.

Yes, during the last moments of evaporation, the black hole will almost certainly produce extremely energetic particles - "almost" as in "we don't have a good theory of quantum gravitation to know better". But you need to look at the complete lifetime of the black hole. You cannot make a black hole from just low-energy photons, but need some initial mass that collapses. Whatever started the black hole lost an enormous amount of information in this collapse. So yes, some of the Hawking radiation particles will have more energy than some of the cosmic microwave background that goes into it. But on average, particles escaping from the black hole will be of individually lower energy than those that went into it, and hence have a higher overall entropy. BTW, currently (in cosmological times, so give or take a few billion years) a stellar-sized black hole gets more energy from the microwave background than it loses due to Hawking radiation. Before a black hole can effectively evaporate, the universe has to expand quite a bit. --Stephan Schulz (talk) 11:19, 16 November 2008 (UTC)[reply]

The mass at which a black hole's temperature matches the current CMBR temperature (2.7 K) is about 2×10⁻⁸ solar masses. So, regardless of a black hole's initial size, it will radiate all but 2×10⁻⁸ solar masses of its energy at a temperature below 2.7 K. For a black hole of one solar mass that's 99.999998%. That's ignoring the further absorption of CMBR radiation that Stephan Schulz mentioned. -- BenRG (talk) 14:02, 16 November 2008 (UTC)[reply]

Paradox

^{Moved to the humantities desk here by an I.P. user. —Cyclonenim (talk · contribs · email) 12:59, 16 November 2008 (UTC)}[reply]

Bad smelling, but delicious?

Since smell is so closely related to our sense of taste, is it possible for anything to smell terrible, but actually taste delicious? --69.151.187.196 (talk) 17:04, 16 November 2008 (UTC

Well, there is the durian, which is the edible fruit of Durio zibethinus, a tree which grows in southeast Asis. The durian smells awful but tastes delicious.

My parents love Gorgonzola cheese. I hate the smell(!), and they don't like it either, but they love the taste. -- Aeluwas (talk) 17:46, 16 November 2008 (UTC)[reply]

I can confirm that durian smells awful, I've never been able to pluck up the courage to see what it tastes like! --Tango (talk) 18:32, 16 November 2008 (UTC)[reply]

Kimchi is the worst smelling popular food that I've smelled. People who like really like it. I can't get past the smell to eat it. I do agree with Aeluwas. Many cheeses smell terrible, but I haven't had a cheese that I didn't like. Now that I think of it, fish smells terrible also, but I like fish also. A especially like to put stinky little sardines on roasted red peppers and sprinkle with blue cheese. -- kainaw ™ 18:00, 16 November 2008 (UTC)[reply]

There are a number of cruciferous vegetables which "smell like farts" when you cook them, like broccoli, cabbage, and brussels sprouts, but taste good when you eat them. StuRat (talk) 19:48, 16 November 2008 (UTC)[reply]

Read the article on the durian, and also there's stinky tofu. Thanks. ~A H 1^(TCU) 19:56, 16 November 2008 (UTC)[reply]

I like a good "stinky cheese" like Gorgonzola or Roquefort or Camembert. A friend of mine, who also likes them, described them thusly "They smell like old sweat-socks, but not in a bad way". That about sums it up. --Jayron32.talk.contribs 21:02, 16 November 2008 (UTC)[reply]

I really like durian in a paste form, but maybe being mixed with other stuff dilutes the smell. There's also shrimp paste or belacan. Julia Rossi (talk) 07:25, 17 November 2008 (UTC)[reply]

There's often specific rules forbidding the possession of durians in places where the smell could cause problems like in airplanes. Dmcq (talk) 09:52, 17 November 2008 (UTC)[reply]

I had a small part of a durian milkshake once. Only once. And only part. Leave the durian for the orang-utans and give me a strawberry smoothie any day. The smell was mostly covered by the sweetener and dairy/thickener, but the taste was horrid. Fresh (and not-so fresh) fish can smell bad, but cooked fish smells delicious, so I don't think that's a great example. It seems to me that the best examples would include foods heavily flavoured by tastes our taste buds can interpret directly (i.e. sweet, salty, sour, bitter, as those might be pleasant flavours that could overwhelm a noxious smell. Matt Deres (talk) 21:17, 17 November 2008 (UTC)[reply]

Medical advice

Where I am now, if you only have the public health insurance, you have to wait some weeks until a doctor sees you. And then he will take only a few minutes - between 3 and 5 - to reach a diagnosis. Would such a diagnosis be more accurate than googling or consulting wikipedia? Are laypersons able to make a better (self-)diagnosis, if they invest more time to understand their illness?--Mr.K. (talk) 18:31, 16 November 2008 (UTC)[reply]

Where are you? It sounds like somewhere without any real medical facilities, so is there are treatment available even if you do get a diagnosis? A qualified doctor is likely to know if the diagnosis they reach in a few minutes is reliable or not and they'll know whether or not to refer you on for more tests, but if there aren't any more tests available it doesn't make a lot of difference. --Tango (talk) 18:57, 16 November 2008 (UTC)[reply]

First, I doubt that your description applies in general. In nearly all public health systems, emergencies are treated out of order. And the time taken for a diagnosis will depend on the symptoms of your disease, although too little time for this is a very frequent problem in many (not just public) health systems. As for the quality of the diagnosis, I would trust an expert more. Experience counts for a lot, as does formal education. And an individual simply does not have the tools for a proper diagnosis in non-trivial cases, like a laboratory for a complete blood test, EEG and EKG equipment, or culturing. Indeed, an individual probably have trouble doing trivial things like looking into his or her ears or listening for pulmonary sounds. Of course physicians are not perfect, and if a patient has an idea and concrete symptoms, (s)he should mention it to the diagnostician. --Stephan Schulz (talk) 19:13, 16 November 2008 (UTC)[reply]

I'd say some combo of self-diagnosis and reliance on a doctor is best. If you have info that might be relevant, tell the doctor, whether they ask for it or not, and also tell them when you think they've made a mistake. For example, if you have symptoms of anemia and the doc prescribes iron and B12, you might want to mention if both your parents had sickle-cell anemia, as you are likely to also have that form. StuRat (talk) 19:44, 16 November 2008 (UTC)[reply]

Do you live in the United States by any chance? Are there any walk-in clinics or family doctors? In Canada we usually get free health care provided that you have a health card. ~A H 1^(TCU) 20:05, 16 November 2008 (UTC)[reply]

The primary problem with self-diagnosis is that people tend to believe that they have whatever illness they are reading about. Also, people do not usually have the ability to run tests. Do you know what your creatinine clearance is? Do you know what your HbA1c level is? What I mainly see is people who go to doctors they don't like and then schedule another appointment with them. Why? Get a new doctor and then another one and then another one until you find one that you like. -- kainaw ™ 20:25, 16 November 2008 (UTC)[reply]

That's not always an option. In the US, many types of insurance limit the number of doctors you are allowed to see to a small list of "approved doctors", and, in some cases, there may only be one accessible doctor on the list. StuRat (talk) 22:11, 16 November 2008 (UTC)[reply]

Then switch insurance companies? --Tango (talk) 23:51, 16 November 2008 (UTC)[reply]

Tango: That's pretty naive - most people who have health insurance get it through their employer - so they have little or no choice as to what insurer they go with - and therefore, little or no choice as to the doctor they get assigned to. Sure, you could change jobs in order to change insurer in order to change doctors - but that's a pretty drastic step and it's REALLY tough to walk the maze of (a) finding a good doctor, then (b) finding the insurers he/she accepts, then (c) finding the companies that offer those insurers, then (d) getting a job with one of those companies. And that assumes that you have the time to make the change (tough when you actually NEED a doctor) - and it assumes that there aren't a million other constraints that prevent you from changing jobs. So, it's naive to assume that people can fix this - they mostly can't. SteveBaker (talk) 01:50, 17 November 2008 (UTC)[reply]

Ok, emigrate to a country with a sensible health system, then! ;) --Tango (talk) 13:37, 17 November 2008 (UTC)[reply]

Which is an EVEN MORE naive answer! Have you any concept at all of how hard it is to emigrate? Visas, work permits...are mostly unobtainable at any price - then you have to find a job from hundreds of miles away - figure a way to transfer money - find somewhere to live - probably learn an entirely new language...and all of this to get to see a different doctor?! You're living in cloud-cuckoo-land! SteveBaker (talk) 00:42, 18 November 2008 (UTC)[reply]

Steve, I think you missed Tango's wink, at the end. StuRat (talk) 19:54, 18 November 2008 (UTC)[reply]

Wikipedia cannot diagnose a condition. Here on the reference desk we're strictly prohibited from attempting to diagnose or suggest treatment for medical problems. The main articles may give you information on which to base a diagnosis - but if you have some particular symptom, how would you know which pages to look up to find the causes? You have a headache - there are probably 100 or more things that could cause it. What are the odds that you'd find all 100 articles? A doctor, on the other hand is supposed to be aware of all 100 conditions - and can look for secondary or tertiary symptoms that might lead to a more accurate determination. Furthermore - the doctor might have a range of treatment options ranging from asperin to brain surgery - and if there is some uncertainty as to the precise cause of your headaches may be able to come up with a treatment that covers all of the possible causes. Furthermore, a doctor can recommend more studies - blood and urine samples, an X-ray or a CAT scan. You can't do that yourself - so you may be working with only a piece of the information. Also, you are biassed - what may seem to you to be an extreme condition because it's been bugging you for a long time - is something that the doctor can assess dispassionately. So - no - you can't use Wikipedia - that's not the business we're in. SteveBaker (talk) 00:52, 17 November 2008 (UTC)[reply]

The doctor isn't likely to consider the rare causes of headaches, either. Or at least not until many years of unsuccessful treatments for the more common causes. StuRat (talk) 01:32, 17 November 2008 (UTC)[reply]

True - he won't investigate the super-rare things - and as you say - he's not going to do CAT scans looking for brain tumors for every patient who walks through the door complaining of a headache. But a decent doctor ought to at least ask whether you have weird visual problems or an adverse reaction to bright light during the headaches - and thereby suspect a migrane - or he might ask whether they occur in the morning right after waking up - and diagnose sleep apnea. There are a few very common diagnostic things that he might ask that you and your unqualified friends might never think to look up. Services like 'Web-MD' might to a better job - but even so, there is no substitute for an expert - even if you only have his attention for a short period. SteveBaker (talk) 01:45, 17 November 2008 (UTC)[reply]

The doc might also send you home with a prescription and schedule an exam later, but if the problem is a carbon monoxide leak in your home you could be dead by then. If you diagnose the problem yourself, however, by doing web searches based on the symptoms, and call the gas department to investigate, you may survive. StuRat (talk) 03:16, 17 November 2008 (UTC)[reply]

The operational words here being "might" and "may". You might also diagnose yourself with a bacterial infection and take antibiotics until you've cured your harmless but persistent viral infection into a multi-antibiotic-resistant pneumonia. Neither is very likely. --Stephan Schulz (talk) 07:48, 17 November 2008 (UTC)[reply]

That why it's important to combine info a doctor has access to, like medical tests, with info only the patient will think is important, like "Something is seriously wrong here, I've never felt like this before". StuRat (talk) 18:13, 17 November 2008 (UTC)[reply]

Here's an unpopular answer: the doctor may only take 3-5 minutes to look at each patient because most people either don't have something he can help with (viral infection) or have something he can write a prescription for quickly (headache, cough, runny nose, ear ache). In places where the health care system is under a great deal of stress it makes sense to rush those sorts of people in and out, so you can focus your efforts on the ones who really need it. If you find yourself being rushed through the exam, consider for yourself what else a reasonable person could have done for you. How much time do you want him to spend on your sniffles? And, as StuRat says, if you do feel something is very wrong, be sure to impress that upon the physician. Matt Deres (talk) 21:27, 17 November 2008 (UTC)[reply]

cables and auto transformer

kindly help me know the advantages, disadvantages and applications of pvc insulated,pvc sheathed,paper insulated and lead sheathed cables.

what could be the danger that may arise by the the use of an auto transformer on high transformation ratio. —Preceding unsigned comment added by 196.46.196.66 (talk) 18:54, 16 November 2008 (UTC)[reply]

All of those insulators, except lead, are flammable, with paper being flammable at the lowest temps. The paper will deteriorate with age and the PVC will deteriorate with exposure to UV light (such as in sunlight). The lead insulation will be heavier, more expensive, and must be properly disposed of to avoid lead contamination of the environment. One advantage to the PVC is that dyes can be mixed in during production to produce brightly colored insulators that won't fade with time, making identification of various wires far easier. StuRat (talk) 19:35, 16 November 2008 (UTC)[reply]

And isn's lead a decent enough conductor to create its own problems? --Jayron32.talk.contribs 20:59, 16 November 2008 (UTC)[reply]

Lead also has a pretty low melting point for a metal. shoy (reactions) 22:44, 16 November 2008 (UTC)[reply]

The lead would be an outer jacket to keep moisture out. Under it, surrounding each conductor, would be an insulator such as paper or plastic. Oil-impregnated paper insulation with a lead outer sheath to keep out moisture has been used over a hundred years, but may be obsolescent, since it takes highly skilled splicers to make the joints and terminations, and they are exposed to lead fumes. Rubber and plastic insulation has been used since the 1940's. XLPE is cross linked polyethylene and is widely used for distribution voltages such as 12 kV. Semiconductor layers may be used around the insulation to control electrical stress gradient, and there may be copper braid for shielding. What kind of cable is insulated with PVC? I have heard of TW and THHN, among other plastic insulation systems. For the autotransformer question, what do you regard as a "high transformation ratio? An autotransformer has only one winding, and has relatively low reactance. I suppose that might be a problem in some circumstances. See Autotransformer#Limitations where it says what could appear on the low voltage tap if there were an open circuit in the turns it covers. This would be more of a problem if the autotransformer were stepping down high voltage, as at a substation, than if it were stepping up low voltage, as at a generating station.Edison (talk) 00:47, 17 November 2008 (UTC)[reply]

The 1957 Underground Systems Reference Book by the EEI talks about PVC being used in low voltage applications, particularly for signal cables. It also mentions it used for street lighting up to 5 kilovolts. 198.29.191.149 (talk) 20:55, 18 November 2008 (UTC)[reply]