Science desk
< September 26	<< Aug \| September \| Oct >>	September 28 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

September 27

magnetic sensor

does anyone know the basic design of a magnetic sensor? (accurate, fast, sensitive, and Price) also, i would like to know if, where, and for what price, i can get such a sensor. thanks, 70.114.254.43 (talk) 01:02, 27 September 2012 (UTC)[reply]

Have you read Magnetometer? Plasmic Physics (talk) 01:05, 27 September 2012 (UTC)[reply]

If you have some understanding of electronics, I recommend going to a good library (eg local university library) and searching thru the magazine Wireless World. An excellent article on the operation and home construction of a very good fluxgate magnetometer was published in this magazine in the 1980's. Many electronics hobbyist stores and electronics part suppliers (Eg RS Components) carry Hall Effect sensors, but these are rather insensitive. Keit124.178.132.245 (talk) 01:42, 27 September 2012 (UTC)[reply]

It all depends on what you need it for. Do you want to count rotations of a wheel that has a magnet on it, or do you want to detect iron objects 10 meter deep in the ground? You've got a Hall effect sensor for a dollar, a portable cesium vapor magnetometer will cost you twenty thousand. Ssscienccce (talk) 20:57, 27 September 2012 (UTC)[reply]

If you want to measure the earth's magnetic field a DIY proton precession magnetometer kit can be bought for a few hundred dollars - in addition all you need are the basic skills and tools to assemble electronic components. Roger (talk) 11:02, 29 September 2012 (UTC)[reply]

Ganglion cyst

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.

--Jayron32 02:01, 27 September 2012 (UTC)[reply]

See discussion here: Wikipedia_talk:Reference_desk#Medical_advice_question_removed. StuRat (talk) 02:10, 27 September 2012 (UTC)[reply]

Could someone fix the Ununtrium articles, I don't trust my science skills

WikiProject Reference Desk Article Collaboration

This question inspired an article to be created or enhanced:

Ununtrium

Please consider contributing

Hello, It appears the following articles require being updated in light of the recent synthesis of ununtrium.

Ordinarily I would make the edits myself but am not a scientist and I do not trust myself to do so. In particular, there are some claims to earlier synthesis and I don't know how to determine which claims should be given priority in our articles.

Thanks. user:Agradman, logged out and editing as 99.100.214.111 (talk) 05:16, 27 September 2012 (UTC)[reply]

That's super cool! But this isn't really the place to make such requests. I think the talk pages of those articles are probably more suitable. Though no doubt you will reach a broader "sciency" audience of wiki editors here then just on those talk pages.. Also, keep in mind, an article in a newspaper isn't really a great source for "bleeding edge science" (not that I'm saying these claims aren't true), but usually it takes a little bit of consensus building before the very latest science makes it into a encyclopedic article. The finding hasn't even yet been confirmed. Vespine (talk) 05:30, 27 September 2012 (UTC)[reply]

Actually, this is really the place to make such a request. The Wikipedia:WikiProject Reference Desk Article Collaboration was created to facilitate the improving of articles by collaboration at the ref desks. I'm heading off to sleep myself soon, but there are many people here who would likely help with the request. Give it some time for people to come by and check it out, and I'm sure someone (if not me by tomorrow) will look this over and see if there isn't some way we can pitch in and help. --Jayron32 05:51, 27 September 2012 (UTC)[reply]

If anyone needs me, I'll just be over there eating my words... ;) Vespine (talk) 06:51, 27 September 2012 (UTC)[reply]

I have a recipe for a lovely salad that would complement that dish beautifully. -- Jack of Oz (Talk) 09:51, 27 September 2012 (UTC) [reply]

I've gone ahead and added a short sentence to the article Ununtrium, as the anouncement itself is probably as significant as anything else in the article, which discusses prior abortive attempts towards synthesis. I think we should probably wait to adding it to the other two articles noted until this is published in a peer-reviewed journal, which the L.A. Times notes has not been done yet. When it does appear in such a journal, we can expand more and put it in the other lists as "official". --Jayron32 13:46, 27 September 2012 (UTC)[reply]

Technically this isn't a new synthesis, but rather a confirmation of the old one from 2004. RIKEN did in fact synthesize IUPAC's discovery criteria when IUPAC reviewed the claims for the element with Z ≥ 113 last year. But now RIKEN synthesized it again, the new decay chain does have anchors to known isotopes, thus confirming the isotope ²⁷⁸113 beyond reasonable doubt. It's not an official discovery yet – IUPAC hasn't mentioned anything yet AFAIK – but we can probably expect them to say something about this within the next few years. (Note, however, that the JINR has also claimed that they synthesised element 113 just six months before RIKEN did.) Double sharp (talk) 14:59, 27 September 2012 (UTC)[reply]

P.S. Please don't put it as an "official" discovery yet, even when the article is published in a peer-reviewed journal. That would have to wait until IUPAC acknowledges the discovery. If it takes as long as it did with elements 112, 114, and 116, then we might have to wait until 2016 for that to happen. It might take less or more time, but we don't know yet. Double sharp (talk) 15:31, 1 October 2012 (UTC)[reply]

Benefits/effects of fasting

I stumbled across this video and wondered whether the various claims it makes for the medical benefits of fasting stack up scientifically. Do they? --Dweller (talk) 13:32, 27 September 2012 (UTC)[reply]

Every person and every manner of fasting will be different, and so one should be wary of generalities. The Ramadan fast described in the video is of course different from the garden-variety hunger strike. Also note that Ramadan does not fall on a fixed schedule, nor is it observed in a fixed location, so the schedule of fasting for those practicing it will vary. As a rule, of course, humans are designed to be able to survive periods without food and drink as a matter of necessity; on the other hand, the urges people feel are usually (but not always) a guide to what is physically healthy.

To give a taste of the complexity of one specific instance, consider the guidelines used for diabetes: [1]. Various levels of risk exist depending on many medical parameters and the current mode of treatment. They can participate in the fast, but only with careful preparation. Obviously the nighttime period when food is eaten, and how insulin and blood sugar is managed then, and how much is eaten, is of key importance. On the other hand, a very low calorie diet, verging on a true fast, can be an excellent intervention for type 2 diabetics. So the net benefit/risk depends on many factors that go beyond the fast itself. Wnt (talk) 16:16, 27 September 2012 (UTC)[reply]

Another thing which I'll only ask - I haven't thought how to do a search for it! - is whether survival without water is something that can be "learned" or adapted to. After all, Islam has been prevalent in desert regions. If people don't drink anything for 12 hours for 30 days, does this make them more able to survive if they, say, get lost in a desert or have to make a sudden retreat over a vast expanse of arid landscape at some other time of the year? Wnt (talk) 16:22, 27 September 2012 (UTC)[reply]

Intermittent fasting and fasting has info. The health effects section in the fasting article seem to focus more on caloric restriction, not necessarily part of fasting or involving fasting. Speculation about the slowing of the aging process, and the potential to increase maximum life span in that regard is based on experiments with mice, and recent results of a long term study involving rhesus monkeys show no effect. The article on intermittent fasting mentions that eating a single meal per day worsens some cardiovascular disease risk factors. The claims in the video about removal of toxins, I'm not sure if these have any medical basis, doesn't look like it according to the detoxification (alternative medicine) article. If fasting offers health benefits, it would likely have to be done on a regular basis I suspect. Take physical exercise, doctors wouldn't advice you to do that one month each year. Ssscienccce (talk) 17:26, 27 September 2012 (UTC)[reply]

Every seventh ocean wave larger?

Is it true that every seventh ocean wave is larger? My casual observations seem to indicate that it is true, and I can see how that can happen by waves of two different frequencies combining. Bubba73 ^{You talkin' to me?} 13:45, 27 September 2012 (UTC)[reply]

Sneaker wave describes the "seventh wave" belief as folklore, but also says it has "some scientific basis, due to the occurrence of wave groups at sea". Gandalf61 (talk) 15:20, 27 September 2012 (UTC)[reply]

After spending many years studying wave mechanics (and watching the ocean - there's no substitute for empirical observations to enhance one's knowledge of physics!), I'm actually very confused by this belief, which cannot possibly be true. The swells of the ocean consist of a continuously varying motion of water, in which energy can propagate as a wave. Each crest or trough does not constitute a distinct wave. In fact, it is non-trivial to "count" the number of wave crests that have passed, unless you are very careful to define what constitutes a "crest" (presumably, by band limiting your observations). So, it's not clear how you would count "every seventh wave." See also: Crest (physics). Nimur (talk) 17:30, 27 September 2012 (UTC)[reply]

I'm thinking about ones that come up on shore. Bubba73 ^{You talkin' to me?} 19:28, 27 September 2012 (UTC)[reply]

I suspect the difficulty of definition is what makes the idea "true" - if you get your choice of three different "waves" for your measurement, on average the one you pick will be larger. Wnt (talk) 20:01, 27 September 2012 (UTC)[reply]

In other words, observer bias causes the result to seem true, because the observer may selectively define when a "wave" arrives, allowing them to fit the expected result. Nimur (talk) 22:16, 27 September 2012 (UTC)[reply]

For what it is worth, there is this. I know it is just a blog and carries very little weight. Bubba73 ^{You talkin' to me?} 01:51, 28 September 2012 (UTC)[reply]

And this oceanography textbook says that there is no fixed ratio of when larger waves occur. Bubba73 ^{You talkin' to me?} 02:01, 28 September 2012 (UTC)[reply]

I suppose you van get swells from different sources with different wavelength making a regular pattern of bigger and smaller waves. I have spent plenty of time as school looking out the window looking at waves. Sometimes it seems to be true and other times not. Graeme Bartlett (talk) 11:14, 28 September 2012 (UTC)[reply]

The shape of the coast could cause wave patterns in certain spots. But this is not permanent: the tide makes the sea level go up and down, and the shape of the coast changes slightly. For example, in San Sebastián there is an old prison wall in the left side of the bay. In very low tides the wall surfaces from the water and there are almost no waves in the left side of the bay. As the tide goes up the wall goes underwater again, and the waves get stronger again. I suppose that the waves on the right side are also affected, because of Interference (wave propagation).

Also, a wind may be blowing in the sea with a certain force in a certain direction for a certain time, and cause a certain pattern. But minutes later the wind will change slightly, and cause slightly different waves, just different enough to change the pattern.

Finally, sea wave are not predictable at all, probably because stuff like Fluid dynamics is too affected by chaos theories (you can't predict the exact motion of a fluid, you can just make a guess of the most probable motion). And I suppose that waves don't have a single point of origin, they are the result of Interference (wave propagation), with many points of origin influencing the waves. And every point of origin changes over time, causing all time of interactions when the waves interfere. You will randomly get waves that are weaker or stronger than predicted by the pattern, and every once in a while you will get a Rogue wave that can sink a ship. --Enric Naval (talk) 11:33, 29 September 2012 (UTC)[reply]

Around here, the wind is almost always blowing in from the ocean. Bubba73 ^{You talkin' to me?} 01:43, 30 September 2012 (UTC)[reply]

Color of the ocean

What determines whether the ocean appears blue-green, blue, or violet? From the shore it seems to me that there are distinct zones with pretty sharp dividing lines -- blue-green near shore, then vivid blue, then violet farther out. A reference in Ocean#Physical Properties mentions Colored Dissolved Organic Matter, but that's all I can find. I get the impression that depth of water near the shore matters, with very shallow water being more blue-green (perhaps because of the color properties of the sand underneath?). Also does the angle of the sun matter? What else? Duoduoduo (talk) 16:38, 27 September 2012 (UTC)[reply]

See Color of water. --Jayron32 17:12, 27 September 2012 (UTC)[reply]

Thanks, very helpful. But I still wonder why there appear to be very sharp dividing lines between different color regions of the sea as visible from the shore. Know anything about that? Duoduoduo (talk) 18:31, 27 September 2012 (UTC)[reply]

Water which is of different salinity, or which contains differing concentrations of dissolved solids, doesn't readily mix as one would think. That is, different regions of water with different "stuff" in it will tend to remain seperate for a long time, sometimes indefinitely, which is why you can find differences in coloration and sharp dividing lines as you note. See this video which uses different colored sugar water of differing concentrations to demonstrate the effect. --Jayron32 19:39, 27 September 2012 (UTC)[reply]

What lies underneath the water also matters, if the water is shallow enough for light to reflect off the bottom. So, water above white sand will look much lighter blue or green than water above dark green seaweed or above a trench too deep for light to reflect off the bottom. This effect is stronger if looking at the water from above. Therefore, since the nature of the bottom of the sea can change rapidly, so can the apparent color of the water above it: [2]. StuRat (talk) 02:27, 28 September 2012 (UTC)[reply]

Slowing 'death by burning'

In the legend of the Ten Martyrs, it is said that damp wool was placed on the chest of Haninah ben Teradion in order to prolong his suffering. My question relates to the fact that it shouldn't matter how long one's heart is prevented from succumbing to burning if one's head is not similarly wrapped or placed in damp wool. Perhaps this portion is fabricated too, along with the joining of all ten rabbis together into one story when their deaths really occurred years apart. DRosenbach ^{(Talk | Contribs)} 18:53, 27 September 2012 (UTC)[reply]

Hm. You may be interested in Auto-da-fé, Death by burning, Tunica molesta (though that is a stub) and Sanbenito for what sounds like similar garments, though of the opposite effect. Maybe something was confused in the translation? --Jayron32 19:36, 27 September 2012 (UTC)[reply]

Is it possible that by "chest" they mean the entire trunk of the body, so as to ensure that the extremities and genitals would be worst affected? (Assuming the head remained somewhere out of the fire and visible so that they could get their special pleasure out of watching him scream) Wnt (talk) 19:59, 27 September 2012 (UTC)[reply]

Oh, what a dreadful thing to ask about. However, as you have asked. This is my take (without any citations to back it up). The executioners had probably watched many immolations and worked out how to prolong consciousness in the victim -by trial and error. The evaperative cooling effect and insulating properties of damp wool strategically placed may have keep the victim conscious for longer. The inhalation of fire kills in about twenty to thirty seconds but some placement of wet material may provide temporary relief. The brain -within the bony cranial cavity- is very well supplied with blood. With the flames liking up towards the nether regions the hart is probably pumping quite well – therefore, external heat to the skull is unlikely to induce acute heat-stroke if another parts of the body is sufficiently cool. Also, the historical accounts maybe over simplified as to the exact placement of the wool -so I don't think you will be able to get a definitive answer. Why do you ask? Has your local political representative done anything that you think deserves a slow roasting upon a spit?--Aspro (talk) 20:13, 27 September 2012 (UTC)[reply]

Post Script: The executioners time and expertise may have been wasted though. Whilst talking to people undergoing skin-grafts due to burns, they said that (and I paraphrase here) “what with the adrenalin flowing an' all, I did not realize that the heat was burning me” In other words: some tried to fight the fire when they really should have got out fast. So the martyrs may have quickly become anesthetized to the effects of the flames. In some situations (as had been also described by solder wounded in battle), the human body can sometimes block out pain that would normally immobilize the average John Doe in the street.--Aspro (talk) 20:33, 27 September 2012 (UTC)[reply]

That may be the case for people actively engaged in something important enough to ignore the flames; from personal experience I can say that suffering third degree burns and being unable to escape the flames is bloody painful all the way. Ssscienccce (talk) 08:35, 28 September 2012 (UTC)[reply]

Magnetic potential from current densitty

The current density on a disc of radius R is $K(r)=r^{3}(-\sin \phi {\hat {x}}+\cos \phi {\hat {y}})$ . Calculate the magnetic vector potential. From ${\frac {\mu _{0}}{4\pi }}\int \int _{A}{\frac {K(r)}{|x{\hat {x}}+y{\hat {y}}+z{\hat {z}}-r(\sin \phi {\hat {x}}+\cos \phi {\hat {y}})|}}dA$ I get ${\frac {\mu _{0}}{4\pi }}\int _{0}^{2\pi }\int _{0}^{R}{\frac {r^{4}(-\sin \phi {\hat {x}}+\cos \phi {\hat {y}})}{(x^{2}-2xr\cos \phi +y^{2}-2yr\sin \phi +r^{2}+z^{2})^{\frac {1}{2}}}}drd\phi$ . Can I evaluate the intigral, or is there an other way to get the magnetic potential?--150.203.114.14 (talk) 20:49, 27 September 2012 (UTC)[reply]

Is this homework? Whoop whoop pull up ^{Bitching Betty | Averted crashes} 20:57, 27 September 2012 (UTC)[reply]

Probably, but this looks like a nice bit of transpositions to keep our brain cells from ceasing up. Just like my cat, I like to isolate the μ's...--Aspro (talk) 21:11, 27 September 2012 (UTC)[reply]

Yes, it is but I have shown my current working.--150.203.114.14 (talk) 21:01, 27 September 2012 (UTC)[reply]

Are you sure you stated the problem completely? Often problems like this only want the vector potential over a restricted region. For example, if you only wanted the potential along the z-axis, then the integral is solvable. I'm not sure if the general case can be integrated. Dragons flight (talk) 21:12, 28 September 2012 (UTC)[reply]

Hm, maybe; the next part of the question is to find the magnetic field at points on the z-axis by taking the curl, but to take the curl you still need to know the vector potential in all space (or at least some neighbourhood around the z-axis) don't you? 150.203.114.14 (talk) 00:45, 29 September 2012 (UTC)[reply]

White spirit/Mineral turpentine

Is there a difference between white spirit and mineral turpentine? —Ruud 23:08, 27 September 2012 (UTC)[reply]

According to the articles, yes. WS has a mixture of aliphatic and alicyclic C7 to C12 hydrocarbons. MT is a hydrotreated light distillate of petroleum, and consists of a complex mixture of highly refined hydrocarbon distillates mainly in the C9-C16 range. So close relations, but perhaps not on merging terms? --Tagishsimon (talk) 23:19, 27 September 2012 (UTC)[reply]

I don't quite trust what the articles say, however, and several pages on the Internet just point back to Wikipedia... (Surprisingly, the articles turn out to be created by the same person [3] [4].) I'm getting the impression they describe the same class of substances, which can have a range of chemical compositions (the lengths of the hydrocarbons) But I'm neither a professional chemist, nor a painter... —Ruud 23:31, 27 September 2012 (UTC)[reply]

Hmm. You may be right; or it may be a point of view. Inchem gives Mineral turpentine as a common synonym of white spirit, but uses the C7 to C12 definition, which on the face of it excludes the C9-C16. But C9-C16 is not referenced so... --Tagishsimon (talk) 23:39, 27 September 2012 (UTC)[reply]

That reference looks useful and would support them being the same substances. Also, Google tells me C9-C16 would be kerosene. —Ruud 00:12, 28 September 2012 (UTC)[reply]

Our WS article comments "it is merely a light grade of kerosene". Some more digging. Looking only at British Standards, there are a couple for Kerosene - BS2869:2010 and ASTM D3699 - 08, and a separate BS for Mineral Solvents - BS245:1976. There's no stand-alone BS for White Spirit or for Mineral Turpentine ... the first appears as a descriptor of BS254, the second does not. None of this is anywhere near conclusive, however. I've yet to find a standard for MT; I see hints thereof, but looking at something like this explanation of two classes of MT oil, characterised by different boiling ranges, it may just be different nomenclature in different markets. --Tagishsimon (talk) 00:57, 28 September 2012 (UTC)[reply]

I've seen the two products on sale side-by-side at different prices, and the ones I've bought seem to have marginally different odours, but I don't know whether there is an essential difference that is consistent between manufacturers. The two products are very different from kerosene (paraffin in the UK) and from other fuel oils. Dbfirs 07:56, 28 September 2012 (UTC)[reply]

The boiling points in the article are completely wrong, the Avantor reference gives 156 to 202°C;

other source:

Germany: Test Benzine (DIN 51632) : BP 130°C min/ 220°C max

UK: Mineral solvent (white spirit,type A) (BS 245: 1976): BP approx. 130°C min/ 220°C max arom <25%

UK: Mineral solvent (white spirit,type B) (BS 245: 1976): BP approx. 130°C min/ 220°C max arom 25-50%

USA Mineral spirit type 1 - regular (Stoddard solution)(ASTM D235-83): 149°C / 208°

USA Mineral spirit type 2 : 90° to 230°C (C₇ to C₁₂ )

USA Mineral spirit type 3 : 65° to 230°C (C₆ to C₁₃ ) hydrogenated

types 1 to 3 subdivided in 3 techn grades:

"low flash" white spirit, flash point 21-30°C boiling point 130-144°C

"regular flash" white spirit flash point 31-54°C boiling point 145-174°C

"high flash" white spirit flash point > 55°C boiling point 175-200°C

Wait, that doesn't make much sense either, how can types 2 and 3 be "subdivided" in technical grades with much higher boiling points?

For mineral turpentine I find BP 145° / 200°, so it seems more or less the same but that doesn't say anything about aromatics etc.. Ssscienccce (talk) 14:29, 29 September 2012 (UTC)[reply]

coronene (chemical).

The article for "Coronene" lacks all the synonyms for the mineral form of same, and the article and its talk page are enough "locked up" that I can't conveniently pass along the information there. "Dana's New Minerology" 8th edn 1997 has the mineral form under the names Karpatite, Pendletonite and Coronene only. The monograph in the Merck Index 14th edn 2006 for Coronene has the mineral form listed only as Pendletonite. Would you please see to passing this along? TnxC.s.auaeginal (talk)c.s.auaeginal, 27 Sept 2012 Th. —Preceding undated comment added 23:25, 27 September 2012 (UTC)[reply]

Actually the article is unprotected and you should be able to change it by clicking on edit links. I have added a sentence to the article. Graeme Bartlett (talk) 11:01, 28 September 2012 (UTC)[reply]