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April 18

Negative pH of acid mine drainage

Given that the molarity of hydrogen ions in pure sulfuric acid is not much less than the negative of the common log of 18 (the molarity of pure sulfuric acid), how can an aqueous solution (i.e. acid mine drainage) exceed that hydrogen ion concentration with a pH as low as -3.6? I know there's also iron oxidation contributing, but surely it can't be as important as the sulfuric acid present.--Jasper Deng (talk) 06:57, 18 April 2014 (UTC)

The paper traces back to [1]. The sulfate concentration is up to 760 g/L, but sulfuric acid has density 1.84, so it isn't all sulfuric acid (which only has pH -3 according to our article ... which is still lower than -log 18...). There are up to 200 g/L of other minerals present. Someone will have to get the paper to see what they are. Fundamentally, note that pH is not p[H], and that at low pH things get ... strange. According to our article the Nernst equation breaks down. But the bottom line is that you have to know exactly what you're measuring and not assume it means anything else when you're in that territory. Wnt (talk) 21:27, 18 April 2014 (UTC)

I got access to it via JSTOR, but it didn't elaborate too much on how those results were obtained. It did however consider the invalidity of the Nernst equation under those conditions and the need for a different definition of pH.

As I learned it, there was no distinction made between pH and p[H], but I never had to deal with solutions this acidic (i.e. it was a basic chemistry class).--Jasper Deng (talk) 04:48, 20 April 2014 (UTC)

Why is subculturing called passaging?

I've heard the word passaging pronounced with English and with French pronunciation rules. Is French the origin? And we just tack on English endings 'ed' and 'ing'?

If it's from the same root as the horsey sense (to move sideways) then it's from French passager, from Italian passeggiare and normally retains the French pronunciation, as for dressage, though, strangely, neither Wiktionary nor the OED record this fact. Dbfirs 20:59, 19 April 2014 (UTC)

Morphological diversity within a species

Although morphology may not be the best way to classify different species, it can be one practical way. However, even if two species may look very similar, they cannot mate with each other due to geographical isolation, temporal isolation, behavioral isolation, etc. Humans, on the other hand, seem to be the only exception. Humans can look widely different from one another and can potentially all mate with each other, and they are extremely mobile. They can travel from place to place, establish whole communities, and mate with the locals. Is there any other species that is so morphologically diverse as humans, or is this just one trait that makes humans more special and unique? 140.254.226.206 (talk) 14:19, 18 April 2014 (UTC)

Dogs are much more diverse. -- Finlay McWalterᚠTalk 14:21, 18 April 2014 (UTC)

For example, you might get an 8 pound Maltese and an 85 pound Alaskan Malamute; you won't find a tenfold mass differential between folks in one group of humans or another. -- Finlay McWalterᚠTalk 14:25, 18 April 2014 (UTC)

I think it would be best if the Alaskan Malamute is the female and the Maltese is male. The puppies need room to grow. 140.254.226.206 (talk) 14:39, 18 April 2014 (UTC)

Better give the Maltese a stepladder. :-) StuRat (talk) 21:17, 18 April 2014 (UTC)

See out-group homogeneity. We think that humans are different from each other because we are humans, and spent a lifetime trying to identify differences between people (both for good and evil purposes). You probably can't tell monkeys apart, but if you could ask a monkey whether he can tell his mommy apart from his daddy, he'll throw a rotten banana at you. Similarly a monkey might have a hard time distinguishing a black man from a white man, especially if both are fully clothed, and certainly won't understand why groups of seemingly indistinguishable people are trying to exterminate each other (Germans and Jews, Hutus and Tutsis, Turks and Armenians, etc). --Bowlhover (talk) 15:18, 18 April 2014 (UTC)

Yes, I used to be in charge of a breeding colony of Rhesus macaques and, to those of us who worked with them every day, they were all different to look at and quite easy to identify. Richerman (talk) 22:56, 18 April 2014 (UTC)

Humans only look different to us because we have evolved a lot of facial recognition to tell people apart. In part it has to do with our highly social nature, we are one of only a few eusocial mammals. To some hypothetical sentient alien, we'd all look pretty much the same. But sheep faces look very different to other sheep, and wasps look very different to other wasps, even though they all look pretty much the same to us [2] Paper_wasp#Facial_recognition. We are rather unique in our ability to mate with someone born on the other side of the planet. Finlay's dog example is pretty good for diversity, but of course dog breeds as we know them wouldn't exist without all the artificial selection we've put them through. See Sexual_dimorphism for other examples of extreme morphological diversity in non-human animals. (Post-EC:Bowlhover has a good point about outgroup homogeneity, this is in line with the biological examples I've given) (n.b. our article doesn't mention humans as eusocial animals, but E.O. Wilson considers humans to be eusocial, and as one of the most experienced experts in the field, I trust his judgment :)SemanticMantis (talk) 15:19, 18 April 2014 (UTC)

Calling human eusocial seems like a stretch to me -- true, there's a big mystery about homosexuality in mammals, and maybe you could think of it as a non-reproductive caste; or maybe you could argue that some others avoid reproducing for economic or religious reasons and play a similar role, but by and large, humans fail this criterion. In general the rearing of others' offspring seems more than a bit hit and miss. Of course it's just semantics and you can define a term however you like, and biology doesn't know theory. But recognizing facial features seems like a skill suitable for adversaries and competitors, and is often used for this purpose in modern society. Wnt (talk) 21:13, 18 April 2014 (UTC)

My main point is that we are highly social, and highly social animals tend to be better at distinguishing individuals of that species. As you say, it also involves adversaries, competitors (and friends, mates, kin, etc). As for the terminology, I sadly didn't get to ask Wilson how he was thinking about non-reproductive members of humanity, but I bet he'd have an interesting answer :) My own interpretation is that any child that helps rear its siblings, and and ~16-30 yr old that doesn't have children, are both types of humans that help us fit the definition. Also, it would just sound weird to say that humans are "semi-social"! SemanticMantis (talk) 13:39, 19 April 2014 (UTC)

Well, the social nature of modern humans seems largely forced by recent and rapid changes in the environment. I haven't done proper reading on the topic, but IIRC a few of the loci suspected of involvement with autism are also associated with the gregarious phase of locusts. In chimps one of the important genes is present in some individuals and absent in others [3]. So I'm suspicious that if you go back a few tens of thousands of years, that something related to we call autism might have had a fairly high prevalence in the population. I suspect we should even consider the possibility that aspects of the modern environment might provide a different background with epigenetic effects that could cause it to become common again. Admittedly that is a very speculative scenario, but I just mean to illustrate that historically speaking we don't know that humans were really all that social, or would be in more natural environments. Wnt (talk) 14:59, 19 April 2014 (UTC)

Our social behaviors are absolutely under environmental control. I personally think the theory that human civilizations were born from harsh conditions to be quite compelling, e.g. [4]. If life is easy and food grows on trees, why cooperate? But if water is scarce and agriculture is hard, cooperative societies have a strong advantage. But we're rather off-topic now, so I'll just leave it there  :) SemanticMantis (talk) 15:10, 19 April 2014 (UTC)

Correlation for appearance of fruit and vegetables and their quality (redefine quality more than once if you think that helps)

Is there any reason why a particular shade/saturation of colour of, for example, lemons or limes would be of better quality for their zest or juice? I suppose better quality would be highest concentration of components of value including acids, vitamins, oils. Is there any rational reason to go for the regular lemons which look a bit nicer than the anaemic SmartPrice ones? ----Seans Potato Business 15:27, 18 April 2014 (UTC)

If you're happy with the taste of the uglier cheap ones then go with them. Fruits and vegetables sell better when they look prettier, and can be sold at a higher price. I usually take advantadge of this during tomato season - you can pick up a bushel of Roma "seconds" for the price of a half-peck of the pretty ones, but the sauce comes out just as tasty either way. Katie R (talk) 15:48, 18 April 2014 (UTC)

If we define "better quality" as "better tasting," then I think there are several factors to consider: 1. Produce that is ripe tastes better than under/over ripe produce -- this is usually judged by appearance (color) and touch. 2. Some produce appears more attractive in color and size due to chemical treatments or genetic modification, but in this case the appearance is artificially achieved and doesn't correlate to the state of ripeness of the produce. 3. Perceptions of taste are affected by sight -- if a piece of produce appears unattractive then you may not think it tastes good, but perhaps you would find it tasty in a blind taste test. 4. Taste is subjective. Some people may prefer a bland or one-dimensionally sweet version of a piece of fruit versus a "fruitier" more complex-tasting version. Unfortunately I can't find citations for the above. It is sort of "conventional wisdom." You could do an experiment and buy one each of the lemons and do a taste test to see if you prefer one over the other.--Dreamahighway (talk) 16:23, 18 April 2014 (UTC)

Taking a more biological track, note that all our domesticated fruits are based off of wild ancestors that used color, flavor, and nutrition to attract seed dispersers, so, there is a long trend of visually striking food that also tends to taste better. However, under modern breeding, color and shelf-stability often take precedence over actual flavor. Compare the beautiful but bland tomatoes you see on the shelf to a weird looking but delicious heirloom. This is a pop-sci account of a recent finding specifically about good-looking but lame tomatoes [5]. Compare the good looks and early fruiting of e.g. Early Girl to the dark and delicious Cherokee purple. SemanticMantis (talk) 17:01, 18 April 2014 (UTC)

Yes, we are genetically programmed to prefer fruits and vegetables that are good for us, such as colorful ones with lots of phytonutrients. However, marketing guys then use our own biology against us, and add dye or otherwise get unhealthy food to look healthy (like the bag of yellow oranges in a red mesh bag that makes them look orange and ripe).

Then there's the fact that "perfect" fruit or veggies often require the use of artificial fertilizers and pesticides, either of which may be harmful to humans and/or the environment. StuRat (talk) 17:29, 18 April 2014 (UTC)

Statically determinate structure

1 - Are there any easy ways to determine whether a structure is statically determinate? I always miss whether it is and end up doing a stiffness analysis unnecessarily.
2 - In a stiffness matrix, how do you identify the free nodes. I thought all nodes that arent fixed are free nodes but I was told roller and pin supports are also treated as fixed nodes, if they're not nodes which are being analysed, which doesn't make sense to me. 3 - Am I correct in assuming that where there is a force on a member such a axial, shear or a moment, the row on the stiffness matrix, representing that force, becomes 0?

Clover345 (talk) 16:29, 18 April 2014 (UTC)

Regarding your first question: Have you looked at our Statically indeterminate article? Basically if you have more unknowns than equations, it is indeterminate.--146.163.159.12 (talk) 17:53, 18 April 2014 (UTC)--Dreamahighway (talk) 17:54, 18 April 2014 (UTC)

thanks but I meant by just looking at it, without writing down any equations. Clover345 (talk) 18:05, 18 April 2014 (UTC)

See also Underdetermined_system. Unless you've done so many of these problems that you've developed a strong intuition, you have to do at least a quick check on how many constraints and how many unknowns there are. SemanticMantis (talk) 15:02, 19 April 2014 (UTC)

Storing food at temperature fluctuating between -20 and -40 better or worse than constant -20?

Would storing food at a fluctuating temperature between -40 and -20 cause it to degenerate in a way that it wouldn't at a constant -20? ----Seans Potato Business 17:32, 18 April 2014 (UTC)

Celsius, Fahrenheit, or Kelvin? HiLo48 (talk) 17:56, 18 April 2014 (UTC)

It is fairly obvious that it's not Kelvin, unless you're in the habit of storing your food below absolute zero. (+)H₃N-Protein\Chemist-CO₂(-) 18:00, 18 April 2014 (UTC)

Given your username, Sean, I have to ask - does the food in question consist of potatoes? --Demiurge1000 (talk) 18:03, 18 April 2014 (UTC)

Potatoes are not involved at any level beyond that at which they exist in the mean average content of a Western European domestic freezer. ----Seans Potato Business 20:04, 18 April 2014 (UTC)

For what it's worth -40C is exactly the same temperature as -40F. So for the sake of simplicity, you could just read the question as "What happens if you raise/lower the temperature of food without going above the melting temperature of water?" in which case degrees C versus degrees F is pretty much irrelevant.(+)H₃N-Protein\Chemist-CO₂(-) 18:06, 18 April 2014 (UTC)

Well, you have two competing processes which will degrade food. There are chemical reactions, which occur less at lower temperatures, so from that POV a colder average is better. Then there's the thermal expansion and contraction cycles a varying temperature will cause. Since the temp stays below freezing, the expansion and contraction will be minimal. Still, with enough cycles, you might eventually get cracks propagating in hard foods (and most food is hard at those temps). So, I'm not sure which is better, it all depends on the relative scales of the two types of food degradation. StuRat (talk) 18:34, 18 April 2014 (UTC)

I've not noticed any real difference in the taste of caribou meat that has been harvested in the fall and stored outside over the winter. Nor have I heard of anyone getting sick from eating it in the spring. However, this is more a gradual change from −20 °C (−4 °F) to −40 °C (−40 °F) and back rather than rapid changes. See Cambridge Bay#Climate for where I am referring to. CBWeather, Talk, Seal meat for supper? 00:49, 19 April 2014 (UTC)

I take it the polar bears are all hibernating then ? Otherwise that temptation would presumably be too much for them. StuRat (talk) 00:52, 19 April 2014 (UTC)

No bears (polar) around here and as yet few grizzly. Loose dogs and foxes would be the culprits but who stores their food on the ground. Just get them up out of the way. CBWeather, Talk, Seal meat for supper? 02:37, 19 April 2014 (UTC)

Too bad that won't work against our squirrels. No bird feeder is safe around here. StuRat (talk) 02:56, 19 April 2014 (UTC)

Frozen food loses nutrients gradually anyway, frozen vegetables after 6 months or so, and frozen meat a few months after that. But as long as it stays frozen, it's still safe to cook and eat the food. I can't think of where anyone would get a chance to try storing food at -40F / C, other than the far north. OttawaAC (talk) 02:04, 19 April 2014 (UTC)

Source on frozen food losing nutrients? 86.128.79.70 (talk) 04:26, 19 April 2014 (UTC)

Frozen food#Effect on nutrients. Further reading has revealed that my food storage notions are based on FDA food storage guidelines that are themselves based on a perceived deterioration in quality, not nutrient levels. OttawaAC (talk) 13:49, 19 April 2014 (UTC)

StuRat, you could add another degradation mechanism: dehydration. Something stored at a constant temperature is more likely to have fewer (temporary) temperature differentials, which could lead to food losing moisture while another part of the freezer is colder than the food, which will not necessarily be reversed. This could be exacerbated by regular cycling of the temperature. Of course, this process does not need any cycling, only a temperature differential. For example, if the food is warmed by conduction from the shelf it rests on, and the heat is removed by a refrigerating element on inside the wall of the freezer compartment, there could be a continual migration of moisture sublimating from the food to the colder cooling element. —Quondum 04:43, 19 April 2014 (UTC)

Yes, that's the classic freezer burn, but good containers can reduce that. StuRat (talk) 23:20, 19 April 2014 (UTC)

Wigner effect and graphite density

In graphite-moderated nuclear reactors, can the Wigner effect be mitigated by producing graphite with more vacancy defects than other types (which would therefore be less dense), so that most of the displacements caused by each neutron amount to migrations of the existing vacancies rather than the creation of new Frenkel defects? NeonMerlin 18:02, 18 April 2014 (UTC)

April 19

What flowers are these?

the pink and white ones --78.148.106.196 (talk) 09:23, 19 April 2014 (UTC)

Could they be all white flowers which have been given red dye, at the stem ? StuRat (talk) 10:12, 19 April 2014 (UTC)

They are carnations, or Dianthus caryophyllus to give them their full name, and some of them look like that naturally. --TammyMoet (talk) 12:47, 19 April 2014 (UTC)

Yes, no dye used. They have been bred to look like this. (Red and white are natural colours for Dianthus, but this combination does not occur in the wild.) Dbfirs 06:40, 20 April 2014 (UTC)

Theme park rides

Are theme park rides designed by civil or mechanical engineers or both? Clover345 (talk) 09:50, 19 April 2014 (UTC)

That would be mostly mechanical engineering, but often some civil engineering (and several other disciplines) would be involved. If you read those articles they are fairly clear (though I was surprised to see a picture of the International Space Station in the lead of the civil engineering article).--Shantavira|^{feed me} 10:47, 19 April 2014 (UTC)

Really? I thought most of it would be structural and geotechnical engineering. I can understand the mechanical elements if it being mechanical engineering but what about the track structure, support structure, foundation, ride station etc. Clover345 (talk) 13:24, 19 April 2014 (UTC)

Why not perform a case-study? Let's take a look at a project orchestrated by Walt Disney Imagineering from two aspects: the portions of the project under the creative direction of the Disney group; and the portions of the project that are inevitably contracted to other companies.

Wikipedia has thorough articles on about every major theme park attraction: for example, the latest mouse ride.

You can also see what type of people Disney hires: the Disney Imagineering Professional Internships careers page has a lot of openings for (...you guessed it...) software, graphics design, business and marketing. There are some openings for the more hard-core engineering disciplines, but those are pretty rare. A recent humor-article on Cracked, 6 Things Nobody Tells You About Working at Disney World, focused on the in-park internships, and provides an interesting insight into the types of work a Disney corporate intern or employee can expect. Once in a while, you might even find something as technical as Animatronics Intern.

So, if Disney has decided to focus on the creative side, somebody else must be engineering and constructing the projects. Possibly the most famous cases are the Monorails at the Disney resorts. Famously, ALWEG engineered and built the first monorail in 1959; and in the 1960s they were replaced by MBB. Disney also operates a cruise line; but as the animation and film industry has little overlap with the operation of a large marine vessel, they subcontract the operation to BAE Systems. I specifically recall the Disney World Skyway at the Florida park; that item was built by Von Roll Holding, an industrial conglomerate that's mostly owned by Bombardier Inc.. Its construction and operational history is plagued by drama, and it has always inspired me to research the conglomerates who build my ski-lifts. (My favorite resort has a huge poster of the commando-looking engineers from Doppelmayr construction firm moving massive construction equipment over cliffs in the Sierra Nevada mountains - you can see some historic photos in their brochure series, Die Welt der Seilbahnen). The recurring theme you might see is that Disney subcontracts the heavy-lifting to major engineering and aerospace conglomerates - groups like BAE and Bechtel and Lockheed. In return, Disney Corporation helps out the defense industry reciprocally by camouflaging aerospace and defense factories so they look like theme parks from the air. But in all seriousness, if you're the sort of person who is attentive to detail, the next time you walk around a Disney-branded theme-park, you might start spotting the not-so-subtle corporate logos of a lot of other companies - particularly, the aerospace and defense supergiants - plastered on the sides of all the mechanical parts of the ride. Most kids are too busy paying attention to the cartoon characters to spot that stuff.

But the reality is, very few corporations have the expertise in the sorts of specialized engineering that a theme-park ride actually requires. Structurally, it requires moving around massive quantities of heavy material and equipment and setting up construction-facilities in remote swampland. This is the sort of thing that military logistics contractors and oil companies excel at: mobilizing the manpower and engineering to construct massive single-purpose projects; over-engineering complex-systems to provide simplicity, safety, and (best-effort)-idiot-proofing.

These corporations hire civil engineers, mechanical engineers, aerospace engineers, a wide variety of technicians and experts, and they directly hire (and subcontract) for a large volume of unskilled labor. If you want to work on such a project, you have a better chance applying to, say, Boeing or Schlumberger, than Disney; but you still have to be really talented and lucky and competitive to get assigned to a really cool theme-park project.

Meanwhile, Disney Corporation handles the branding and the marketing, and the "theming" of the park.

If you study major theme parks operated on behalf of other conglomerates, you will probably find the same trends.

Nimur (talk) 17:07, 19 April 2014 (UTC)

thanks for the detailed answer. Wouldn't most parks employ a small engineering team though, maybe within their project management group? Clover345 (talk) 17:41, 19 April 2014 (UTC)

I think most theme parks, even the ones owned by companies that do nothing but operate theme parks like Cedar Fair, don't design and build their own rides. Individual parks probably don't have enough new construction on a regular basis to justify a full-time engineering department to design them. But there are several companies that do specialize in theme park rides like Mondial, Bolliger & Mabillard, and Intamin.

As for the original question, I imagine it would depend on the type of ride. For something relatively simple like a conventional roller coaster or river rafting ride, I imagine it would probably be about equal between the mechanical and structural designs. But for more exotic rides like roller coasters launched with linear induction motors and things like this, the mechanical design is probably a little more involved. Mr.Z-man 17:42, 19 April 2014 (UTC)

I imagine that most modern theme park rides also involve a fair bit of electrical engineering and computer engineering for the power, automation, and safety features. shoy (reactions) 13:45, 21 April 2014 (UTC)

Innovationin engineering and design

Do you think all engineering disciplines have just as much scope for innovation as each other? Clover345 (talk) 16:35, 19 April 2014 (UTC)

I think it's reasonable to accept that as a starting position and instead put the onus on arguing that they don't. — Lomn 16:50, 19 April 2014 (UTC)

I don't think "innovation" is well-defined or easily-compared, either. It is nearly impossible to provide a total ordering amongst various innovations, so we can't say whether one accomplishment was more innovative than another.

In my experience, "innovative" people need to be generalists who have the ability to quickly become the best specialist on the team. That means you have to be able to become the best at every branch of engineering. Today's problem might be software; tomorrow, it might be glue that isn't sticky enough; and in two weeks, it might be a budget shortfall. Innovation is being able to come up with a new solution that is better than the existing solution, no matter what today's problem is. As my co-worker jokes - "we're software engineers, which is why we have so many oscilloscopes." Nimur (talk) 17:18, 19 April 2014 (UTC)

I would think that in some engineering fields, it's innovate or fail, like consumer electronics, while other engineering fields are far more conservative, like civil engineering, since a new bridge design which collapses because it wasn't completely understood will cause massive lawsuits. See Tacoma Narrows Bridge (1940).

Airplane design is a field where you might think innovation would be needed, but innovations in that field often cause crashes, due to unknown forces and processes, like supersonic flight (turbulence and sonic booms), rectangular windows (force concentration and metal fatigue), composite materials (delamination), and lithium batteries (flammability). Of course, some innovation is needed, but everything needs to be thoroughly tested before it goes into production there, so being conservative makes sense in aeronautics. An exception might be for unmanned vehicles, where accidents are less likely to cause deaths. StuRat (talk) 19:57, 19 April 2014 (UTC)

So would you say there's more innovation in engineering research than in engineering practice? And what about computer science? Is there innovation in that? Clover345 (talk) 16:26, 20 April 2014 (UTC)

Yes to both, although some areas, like consumer electronics, have a lot of innovation in practice, as well. Some areas of computer science are pretty well set, like database design, while others, like microchip design, are very innovative fields. StuRat (talk) 16:38, 20 April 2014 (UTC)

LED bulbs and inteference

Do LED lamps produce interference they way CFCs do? The article doesn't say anything about it, so I assume that they don't. Bubba73 ^{You talkin' to me?} 18:49, 19 April 2014 (UTC)

CFCs usually refer to an unrelated chemical. Are you sure you don't mean CFL, as in compact fluorescent lamp ? Nimur (talk) 19:20, 19 April 2014 (UTC)

Yes, I meant CFL. Bubba73 ^{You talkin' to me?} 20:02, 19 April 2014 (UTC)

So, who you got winning the Grey Cup this year? --Jayron32 22:28, 19 April 2014 (UTC)

Yes, LED bulbs can produce electromagnetic interference. The references I have found (here, here, and here, to start) suggest that this comes from the power circuits driving the LEDs, rather than from the LEDs themselves. There seems to be some wide variance in EMI produced by LED bulbs depending on the type and the manufacturer. - Eron^Talk 19:06, 19 April 2014 (UTC)

I'm getting terrible interference on my electric guitar. Most of the bulbs in our house are CFLs. Some are incandescent and some are LEDs. I'm replacing CFLs by LEDs as they go bad. Bubba73 ^{You talkin' to me?} 20:17, 19 April 2014 (UTC)

You may be getting that interference over the power line, not RF through the air. I experimented with a strat with single-coil pickups, walking around with it hooked up to an iPod via iRig (so there's no ground loop or other mains connection at all) and I can only get an audible buzz when the pickup is < 10cm from the CF bulb's base. With most light fittings, I can't get the pickups close enough to the source of noise for any buzz to be evident. Instead of the expensive business of changing out the bulbs, you might like to first look at eliminating ground loops and, if that's not enough, install a power conditioner in front of the amp. -- Finlay McWalterᚠTalk 10:41, 20 April 2014 (UTC)

I'd go with Finlay McWalte to look at ground loops first. But a word of warning. Some guitarists, having got rid of interference, have then dropped dead the moment they grab hold of the mic (which in my day had chromium plated metal grip and driven by a separate amplifier). Run your problem by a qualified electrician who will know about Z's (simplest way I can put it). If he likes your genre, it won't cost you nothing and may save your life. Also, some stages have power sockets from three different phases. An electrical fault in your equipment can result in lethal voltages between equipment which may be plunged in to different sockets. Modern regulations endeavour to prevent this, but for example: Australians can still plug a hair drier into a socket in their bathroom because the regulators don't believe that their citizens would be so daft as to dry their hair whilst sitting in the bath. Hum. Most Australians I've met are far from daft – but I did say 'most'. So, I think you would be better off genned up on ground loop so that you know how to inform and describe to an electrician your issue.--Aspro (talk) 20:43, 20 April 2014 (UTC)

But isn't Australia better off without those people who see no problem in bathing with their hair dryers ? :-) StuRat (talk) 04:36, 21 April 2014 (UTC)

Eliminating ground loops in house circuits is not a good idea. Most electricians won't know what it is and most residential codes do not allow isolated grounds. Hospital grade outlets and dedicated circuits are really the only foolproof way to eliminate ground loops in power lines. If you still have noise with an isolated circuit, the next step would be to see if the chassis ground can be isolated from circuitry ground. That prevents the neutral/earth ground loop. Do not ever float the chassis to eliminate the noise as it must be tied to earth ground. Noise from CFL's can be propagated on the power line and across transformers so air distance is not very important (X10 and other high freq data is propagated on power lines as well). --DHeyward (talk) 03:37, 22 April 2014 (UTC)

Power factor ?

CFL's seem to create some type of weird problem with the power factor or some such thing, which I've observed when I put them on the same circuit with a regular fluorescent light, all triggered by a motion detector. The lights wouldn't start until I added an incandescent bulb to the circuit, too. I wonder if LED lights also have this problem, or if they would work like an incandescent and smooth everything out ? StuRat (talk) 19:51, 19 April 2014 (UTC)

The motion detector is probably trying to bleed through a small current through the CFL to operate itself, so it may need a lower resistance item in the circuit to work. Graeme Bartlett (talk) 20:40, 19 April 2014 (UTC)

So do CFLs have high resistance, until they turn on, then drop to low resistance ? And would LEDs exhibit this behavior, too, or behave like incandescents ? StuRat (talk) 21:18, 19 April 2014 (UTC)

If I'm not mistaken, CFLs do have a high resistance at first because enough power has to be put into them to get the gas inside to fluoresce. Once the gas is fluorescing, then the resistance goes down. That is one of the problems (only one?) in getting CFLs to dim. LEDs can and do dim depending on the power that they are supplied, so I would expect them to allow a certain amount of power through without any observable light. Dismas|^(talk) 03:01, 20 April 2014 (UTC)

Interesting. So dimmable CFLs should work then, too ? StuRat (talk) 03:05, 20 April 2014 (UTC)

Good luck. Dimmable CFLs don't even work with all dimmers (I know, because I have one). As for LED's, It would seem to depend on the circuitry used for lighting but they can have ballasts, too, and that circuit combined with the motion sensor circuit would determine how "on" is achieved. --DHeyward (talk) 03:37, 22 April 2014 (UTC)

Yottabytes stored in all servers worldwide?

Does of you have any reliable information on how many bytes of data (ranging from text to movies) are stored in all the servers worldwide? One server alone in Utah is said to be able to store 1 yottabyte of data. 112.198.90.173 (talk) 21:20, 19 April 2014 (UTC)

Wired handwavily estimated that NSA's Utah Data Center could "handle yottabytes" (where "handle" does mean "store"), but Forbes estimated (with slightly less guessing, but still lots and lots) that it could store "3 and 12 exabytes", much less than a yottabyte. -- Finlay McWalterᚠTalk 21:44, 19 April 2014 (UTC)

"Handle" might mean "process". So, they might well process 1 yottabyte of data in a year, but only decide 3 and 12 exabytes of it is worth storing. StuRat (talk) 00:51, 20 April 2014 (UTC)

Grr, I meant to write "Handle" does not mean "store". -- Finlay McWalterᚠTalk 08:36, 20 April 2014 (UTC)

But are there any data how many bytes of data of humankind ranging from private data to govern databases are currently stored in the servers of the world, meaning the sum of all data produced by humankind since inception of data gathering? 112.198.90.161 (talk) 07:05, 20 April 2014 (UTC)

Our articles on Exabyte and Zettabyte have better information than Yottabyte. Dbfirs 07:17, 20 April 2014 (UTC)

No. Companies tend to keep that kind of thing secret. We can place some limits based on the number of hard drives sold. That suggests a few tens of Exabytes at most.©Geni (talk) 10:13, 20 April 2014 (UTC)

That's only data stored online, though (meaning "quickly retrievable", not "Internet accessible"). The amount of data archived on tape may be orders of magnitude higher. "The sum of all data produced by humankind" would be still larger, since a lot of it has been lost. For example, the Large Hadron Collider's detectors produce about one petabyte per second of raw data, which would fill the entire world's supply of online storage in a matter of hours. The vast majority of it is discarded without ever being written to disk (they try to keep the most interesting events). -- BenRG (talk) 00:46, 21 April 2014 (UTC)

Replacing harmful flora with innocuous flora as a cure

You have probably already heard of people with colitis being treated by cleansing their intestinal tract and then deliberately repopulating it with a collection of different organisms, usually obtained from a healthy individual. It made me wonder about other ailments that arise from a disturbance in flora. For instance there's a suggested relationship between certain species of Malassezia (a yeast) and dandruff and seborrhoeic dermatitis and related skin disorders. Would it not be a good idea to try to cleanse the skin and then supplant those yeasts with less problematic ones? The same with acne, too. When I was a spotty kid, I got some sort of infection in the corner of my mouth which was easily treated with an antibiotic cream and didn't come back. The cream also reduced my spots but they came back after discontinuation of that cream. Maybe if I'd replaced the bacteria with a type that didn't have any involvement in acne, I'd have been "cured". I'm reckoning there are other afflictions that could be handled similarly but can't think of any at the moment. Do my suggestions make sense or is there a flaw I'm not seeing? I guess obtaining the alternative flora in appropriate ratios might be difficult. I know those "good bacteria" yoghurts are a crock because they don't represent the variety of bacteria in a healthy intestinal tract. --129.215.47.59 (talk) 22:52, 19 April 2014 (UTC)

The difference is that you can control which organism enter your intestines more easily than the bacteria which contact your skin. But, in areas where the person can control what goes in and out, your suggestion does make sense. For example, vaginal yeast infections could be controlled by introducing "good" organisms. (Douching seems to be the cause of many yeast infections, because it removes those good organisms.) StuRat (talk) 23:18, 19 April 2014 (UTC)

• For reference, the OP seems to be hinting at gut flora and perhaps fecal transplants. Also probably the human microbiome. Last sentence seems a bit WP:SOAP, but we do have articles on yogurt and Fermentation_(food). That will be a good start with references, I'll think more and come back later :) SemanticMantis (talk) 23:28, 19 April 2014 (UTC)

The last sentence might be incorrect but was based in the fact that there are hundreds of species of bacteria in the healthy gut and there are less than 20 in probiotic yoghurt. Finding sources for how many different yoghurts contain is proving difficult. I've only found two sources so far. "It has three times the amount of probiotics that are in yogurt. This is because of the fact that in order to ferment a milk with kefir, 10 to 20 different types of probiotic bacteria and yeasts should be mixed" "A popular brand called Lifeway has 12 species or cultures." 129.215.47.59 (talk) 01:18, 20 April 2014 (UTC)

It's possible that only a few are often lost from the intestines, and in need or replenishment. StuRat (talk) 03:03, 20 April 2014 (UTC)

The reason your acne came back was because it's etiology is more complex than a simple bacterial infection (it is caused initially by hormonal changes) and the treatment didn't last long enough. It usually takes a number of months to clear it up. see [6]. Richerman (talk) 09:55, 20 April 2014 (UTC)

April 20

If it's called cardiac arrest when the heart suddenly stops...

...what's it called when the brain suddenly stops? Ac05number1 (talk) 02:37, 20 April 2014 (UTC)

Brain death. Dismas|^(talk) 02:54, 20 April 2014 (UTC)

Even in total brain death, parts of the brain, like the brain stem, may remain active. StuRat (talk) 02:59, 20 April 2014 (UTC)

That's not correct. See brain death#Medical criteria. Looie496 (talk) 13:26, 20 April 2014 (UTC)

I don't think it stops suddenly. The heart doesn't usually completely stop all at once either, just parts of it stop or pump out of sequence. StuRat (talk) 02:57, 20 April 2014 (UTC)

• In some contexts, where a "cardiac arrest" is called a "heart attack", a Stroke is sometimes called a "brain attack". --Jayron32 03:06, 20 April 2014 (UTC)

Why does the term "cerebral arrest" not exist? -- Jack of Oz ^{[pleasantries]} 07:34, 20 April 2014 (UTC)

There's no accounting for the quirks of English. But consider this: The term "arrest" means to stop.[7] It occurs to me that the term "arrest" in any context usually refers to a sudden or swift action - like it's either beating or it isn't. In the case of the heart, if it stops beating it's pretty obvious just from listening to the chest. The brain doesn't "beat" like the heart does. It requires medical equipment to detect its activity, or lack thereof. ←Baseball Bugs ^{What's up, Doc?} carrots→ 07:46, 20 April 2014 (UTC)

Cerebral arrests are the Thought Police's job. —Tamfang (talk) 08:44, 20 April 2014 (UTC)

Cool. I'm sometimes tempted to make a citizen's cerebral arrest. Of course, in my particular case, it would be a cerebral citizen's arrest.  :) -- Jack of Oz ^{[pleasantries]} 09:02, 20 April 2014 (UTC)

• "Cardiac arrest" means that the heart suddenly stops pumping blood, but in almost every case the individual muscle fibers continue to contract for a while. What happens is that they lose their global synchrony, resulting in fibrillation. The most directly analogous phenomenon in the brain is an epileptic seizure. Those are rarely fatal, though, because they eventually end and don't cause the heart to stop. Breathing may stop for a while, but it usually resumes after the seizure ends. Looie496 (talk) 13:21, 20 April 2014 (UTC)

Yes but the brain can also go into a loop vis avis BB.31.55.123.188 (talk) 00:47, 21 April 2014 (UTC)

The end of LADEE

From IB Times: "Before LADEE crashed into the lunar surface, the spacecraft reached speeds of 3,600 miles per hour, and it most likely broke apart before impact."

What could cause LADEE to break up before impact? Bubba73 ^{You talkin' to me?} 05:24, 20 April 2014 (UTC)

I can think of two reasons why a plunging satellite might break up, but neither seems strong enough on the Moon to have that effect:

1) Hitting the atmosphere. The Moon has a very thin atmosphere, so even at 3600 mph, this doesn't seem likely to cause it to break up, to me, even considering that the satellite isn't designed to withstand re-entry.

2) Tidal effects. Here the near side of the object is pulled more than the far side. This caused Comet Shoemaker–Levy 9 to break up before it hit Jupiter. But, the Moon's gravity is far less than Jupiter's, so this seems unlikely. StuRat (talk) 07:18, 20 April 2014 (UTC)

Yes, but it had been orbiting only about 1 mile above the surface for a while, without breaking up. Bubba73 ^{You talkin' to me?} 08:20, 20 April 2014 (UTC)

I think it's just an error by the IB Times. The NASA press release says it broke up "during impact". -- BenRG (talk) 08:05, 20 April 2014 (UTC)

Probably. Bubba73 ^{You talkin' to me?} 08:20, 20 April 2014 (UTC)

I don't think either knows for sure. I suspect it loses stability in flight and begins cartwheeling. The centrifugal force rips it apart. --DHeyward (talk) 15:39, 22 April 2014 (UTC)

What strain/breed of Columbia livia/Columbia livia domestica is the common white dove?

I have a problem with the so-called white doves (it's Easter day, after all... happy Easter to everyone!). This article says the most common strain of white doves is the Stielbacht, a breed or strain that does not apperar in this list. Should it be added or is it something different from a proper breed?--Carnby (talk) 10:04, 20 April 2014 (UTC)

It's not Columbia, but Columba, which is mentioned.

Resolved? - ¡Ouch! (^{hurt me} / _{more pain}) 06:03, 22 April 2014 (UTC)

Nodal loads on shear and moment diagrams

How do you represent nodal loads on shear and moment diagrams. As far as I know, these diagrams, always start and end at 0. So if for example, a simply supported beam has a uniform load on it but also a nodal load on 1 support. How do you factor this in? If I simply draw the uniform load on the diagrams and then put in the nodal load, the diagrams wouldn't end at 0 and hence the beam wouldn't be in equilibrium. Clover345 (talk) 14:35, 20 April 2014 (UTC)

Do I need to perform a HIV test?

For more than a year, I have been having my hair cut at a nearby barber shop (around 10+ times). The barber always cuts my chin when shaving, maybe because my beard is hard. He used his fingers cleaning the blood, and I did not notice it until recently. I have 2 flus, 1 at the time being, and 1 long ago I cannot remember. 3 months ago I had a muscle pain in my left leg which lasted for nearly 2 months. I felt extreme pain when I stretched my leg or performed a high kick. Currently it has not fully gone, but is negligible. I am 25, healthy. I don't care much about the flus, but the leg pain was really unusual.

Although I got cut many times, I know the risk is very small. The number of HIV infected people going to the same barber shop is small, the number of people getting cut is small, the chance between 2 bleeding people is small. But I am still worry about my unusual leg pain. Are there many causes for such pain? I do not really want to take a HIV test because of the discriminations. People here consider only those with social issues (drug, have sex with prostitutes, etc...) are vulnerable to the disease and need such kind of test. -- 222.252.79.24 (talk) 14:39, 20 April 2014 (UTC)

We cannot give you medical advice or diagnosis. See your doctor (and change your barber).--Shantavira|^{feed me} 14:49, 20 April 2014 (UTC)

For the benefit of other respondents, the IP geolocates to Vietnam (technically Hanoi, but I have doubts Vietnamese geolocation is that accurate). Nil Einne (talk) 16:25, 20 April 2014 (UTC)

222.252.79.24 - Be careful when looking for these kinds of things on the Internet; many people answer confidently without knowing what they're talking about and it's very easy to get bad information. Most doctors will not give definitive answers to these kinds of questions over the internet, nevermind us non-doctors, so as already stated we cannot give medical advice here. If you've not seen them already, there's an article on HIV/AIDS tagged as "good article" (high quality) as well as on Misconceptions about HIV/AIDS. The US government has a website for HIV/AIDS information that might be useful (aids.gov) and the AIDS Healthcare Foundation also operates in Vietnam, offering various services including testing. But it would be best to just call your local doctor who would be best able to point you in the right directions and answer questions you have. --— Rhododendrites ^talk |  17:55, 20 April 2014 (UTC)

Is the stigma or social discrimination attached to merely taking the HIV test, or to failing the test? ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:39, 21 April 2014 (UTC)

It is apply to both those who apply the test, and those who are HIV-positive, although the latter being worse. The stigma even comes from your beloved relatives. I had a drugged cousin who died of this disease around 10 years ago. My uncle (his father) sent him to a drug treatment camp, only for him to be beaten badly by others. Other relatives, including my parents, did not give him any concerns. No treatment was given, and he died when he was at my age, 5 years after the infection. Sad story. I think I will have an anonymous test in the next few months anyway, although I highly doubt if I am really in trouble with this cursed disease. -- 222.252.79.24 (talk) 12:20, 21 April 2014 (UTC)

Acacia motteana and Acacia podalyriifolia

I have read that Acacia motteana and Acacia podalyriifolia are two names for the same species. Do you know if it's true?--Carnby (talk) 14:54, 20 April 2014 (UTC)

This page says so - assuming that "sin." means "synonym". I couldn't find the use of A. motteana on any English language website. Alansplodge (talk) 22:07, 20 April 2014 (UTC)

Revision strategy

How do you revise for physics exams? Past papers and example questions? Do you have to time yourself? I find it too hard to time unless I've done every type of question possible which isn't always feasible as there's too many possible types. 90.205.212.104 (talk) 16:20, 20 April 2014 (UTC)

Your tutor will be able to guide you better than we can. Every course has a syllabus, and you will be asked questions on what you have covered from the syllabus. Your tutor will tell you whether there will be multiple choice questions on the paper, and how to complete the paper if there is. He/she will also be able to provide you with past papers. You only need to revise what is on the syllabus. --TammyMoet (talk) 18:59, 20 April 2014 (UTC)

Yes, your teacher will be the best guide, because we don't know what exam or syllabus you are studying for, but past papers are an excellent way to revise , provided that they are on the same syllabus as your exam. Understanding is more important than timing, but it would be useful to try an occasional times paper just to check that you are not working too slowly. Have you not done a "mock" paper? Dbfirs 20:27, 20 April 2014 (UTC)

Read and re read your notes whilst subjecting yuorself to physical pain such as sitting on your leg. In this way, the knowledge will embed itself in your brain.31.55.123.188 (talk) 00:21, 21 April 2014 (UTC)

I made it a point to perform all my studying for the Private Pilot Knowledge Test using only my cockpit kneeboard as my writing surface, and occasionally studying in unusual attitudes... because if I could perform well in those conditions, I could ace the written test in normal desk conditions. Quoting an archived newsletter, "...Quality unusual attitude training creates a unique environment in which to learn how to override the potentially debilitating mental inertia that accompanies the normal shock of an unexpected loss of control." As physics written tests go, this exam was one of the easiest I've had to endure, but I also spent more time studying for it than any previous exam I had taken. Nimur (talk) 21:48, 21 April 2014 (UTC)

Is "revision" British English for studying ? StuRat (talk) 22:46, 21 April 2014 (UTC)

Yes. Think of re-vision as re-viewing. --50.100.193.30 (talk) 23:01, 21 April 2014 (UTC)

Seems potentially confusing, where "note revision" could either mean modifying your notes or studying them. StuRat (talk) 23:11, 21 April 2014 (UTC)

Yes, potentially confusing to American readers, but not in the UK where I used to re-write my notes (onto small cards that I carried round with me to look at in boring moments) as part of my revision (studying, reviewing) for exams. This British sense of the verb to revise is restricted to education, but has been in use since 1886 (first unambiguous usage with this sense in The Lancet). It's sense 3 in Wiktionary, marked as UK, Australia, New Zealand. Dbfirs 09:23, 22 April 2014 (UTC)

microscopy

compare the limit resolution of air and oil — Preceding unsigned comment added by 115.240.159.50 (talk) 17:07, 20 April 2014 (UTC)

Please do your own homework.

Welcome to the Wikipedia Reference Desk. Your question appears to be a homework question. I apologize if this is a misinterpretation, but it is our aim here not to do people's homework for them, but to merely aid them in doing it themselves. Letting someone else do your homework does not help you learn nearly as much as doing it yourself. Please attempt to solve the problem or answer the question yourself first. If you need help with a specific part of your homework, feel free to tell us where you are stuck and ask for help. If you need help grasping the concept of a problem, by all means let us know. --Jayron32 19:43, 20 April 2014 (UTC)

We have articles on both Oil immersion and Water immersion objective. Personally speaking, my objectives seem to improve when I am immersed in a good Single malt whisky. Hope this helps.--Aspro (talk) 22:02, 20 April 2014 (UTC)

But even macroscopic details become blurry after a while. DMacks (talk) 02:59, 21 April 2014 (UTC)

Location of the big bang and size of the universe

The observable universe is centred on Earth and it's unknown how big the universe is with some saying that it's infinite. I have a couple of questions, though I imagine you guys will have to correct me on a lot.

I see in the news every so often that new and improved telescopes have revealed how the very early universe took shape after the big bang. Does that mean in the observable universe we can see or almost see the location of the big bang and the very first galaxies?

The universe was only 630 million years old when GRB 090423 exploded and it took 13 billion years for that light to reach us. Similar to the above question, since we know GRB's location and how long is ago it exploded (relevant because everything is moving away from the big bang), doesn't that give us some clue as to the size of the universe and the location of the big bang? And would the location of the big bang be the centre of the universe, roughly, as everything in the universes exploded outwards from that location? Thanks, 92.16.58.122 (talk) 18:15, 20 April 2014 (UTC)

I know that the universe was just a small ball then it got much larger when the big bang occurred, like a balloon, so my question of location is whether the small ball expanded uniformly and so our knowledge of the early galaxies mean we know where the centre is and the length of time it took for that light to reach us mean we can guess the size of the universe. 92.16.58.122 (talk) 18:35, 20 April 2014 (UTC)

The usual analogy used for the young is to imagine the universe as the surface of a balloon. Draw a load of galaxies on a deflated balloon, then inflate it. The galaxies move further apart, but none of them are the centre. There is no location where the big bang started. The galaxies are not expanding away from the centre, they are expanding away from each other. There is no centre. The big bang wasn't an explosion of matter into space: it is the beginning of time and space as we know it, and space expands like the surface of a balloon.

This is exactly the right question for you to ask, to find out more about the big bang. So, well done. 86.146.28.229 (talk) 19:12, 20 April 2014 (UTC)

I see, thanks. So does GRB 090423's (former) location give us some clue as to the size of the universe? I imagine at 630 million years, the universe was much closer together/smaller than it is now. 92.16.58.122 (talk) 20:10, 20 April 2014 (UTC)

Not necessarily. We have some sense for the size of the observable universe, which includes ALL parts of the universe we can get ANY information about. Since the universe is actually larger than what we can observe, and by definition what we cannot observe we have no information about, we can only speculate about the actual size of the entire universe. You may find good reading at Universe#Size, age, contents, structure, and laws and Shape of the universe. The first section starts with the sentence "The size of the Universe is unknown; it may be infinite." That's about all we can say. --Jayron32 20:18, 20 April 2014 (UTC)

Also, I read that because everything is moving further away there are some stars that we'll never see because the light can't reach us. With better telescopes would that change? 92.16.58.122 (talk) 20:13, 20 April 2014 (UTC)

Nope. Telescopes can only capture light that we get; if the light never gets here, no matter how good our telescopes, we'll never see it.--Jayron32 20:18, 20 April 2014 (UTC)

Future horizon explains this at little more.--Aspro (talk) 21:13, 20 April 2014 (UTC)

The crucial point is that the universe is (or seems to be) homogeneous. This implies that there's no place where the big bang happened, and relics of the big bang (such as the CMBR) fill the universe uniformly. The matter that emitted the CMBR that we see now is now a certain distance away, and in that sense we're seeing faraway objects when we see the CMBR, but if we were somewhere else in the universe we would see similar CMBR from a different set of objects at the appropriate distance from that location. -- BenRG (talk) 01:08, 21 April 2014 (UTC)

(EC) The closest thing to the Big Bang that it's possible to see is the last scattering surface, which existed around the time of the recombination, about 378,000 years after the Big Bang. It isn't possible to see anything that existed earlier than that time because before that time, the universe was so dense that it was opaque. The light from that last scattering surface is called the cosmic microwave background, which we can still detect. But the cosmic microwave background comes to us from all directions equally, instead of coming from one particular direction, due to the expansion of the universe being an expansion of space itself, not an expansion of the universe into previously empty space outside of the universe. I.e., there is no direction that points toward the Big Bang, except that if you count time as a "direction", then the direction that points toward the Big Bang is "backwards in time". That perspective of "backwards in time" being very much like a "direction" is a standard perspective in Einstein's theory of relativity. Red Act (talk) 01:30, 21 April 2014 (UTC)

Also, if you have the math for it (I don't, but someone might) Minkowski space would be a useful read. --Jayron32 02:15, 21 April 2014 (UTC)

"Dense" isn't quite the right word; as per the name "recombination", the universe was hot enough prior to that time that it was a plasma and thus (more) opaque to radiation. (Pressure ionization does occur, but not at densities 10^-20 that of water like at recombination.) --Tardis (talk) 02:37, 21 April 2014 (UTC)

Point taken. I have struck out the problematic phrase. Red Act (talk) 05:50, 21 April 2014 (UTC)

does anything not sink to the ocean floor?

does anything not sink to the ocean floor? — Preceding unsigned comment added by Wilburlou544 (talk • contribs) 22:18, 20 April 2014 (UTC)

Yes, any object with a lower average density than seawater (about 1.025 grams per milliliter) will float. The volume used in determining that "average density" includes any volume of air that's unable to be replaced by water; see Archimedes' principle and buoyancy. Red Act (talk) 23:18, 20 April 2014 (UTC)

See Great Pacific garbage patch for an awful example... OttawaAC (talk) 01:25, 21 April 2014 (UTC)

An interesting variation on the OPs question (and possibly what they meant to ask): is there anything that will sink in water but not ultimately come to rest on the seafloor? I.e., something that will stop falling at a certain point and just sort of float about 20,000 feet down (or whatever). The answer to that question is also yes, and buoyancy is again the reason. Evan ^{(talk|contribs)} 02:23, 21 April 2014 (UTC)

The density of seawater is only a few percent more at the floor of the ocean than at the surface, due to the low compressibility of water, so the large majority of objects will either sink to the ocean floor or float. But yes, there do exist objects that have a density within the necessary range to maintain an intermediate elevation. For objects in or around that density range, the compressibility of the object would be an important consideration, too, i.e., the density of the object is going to change some depending on how deep it is, too, due to the pressure of the surrounding water. Red Act (talk) 03:41, 21 April 2014 (UTC)

I interpreted this Q differently: "Is there any living sea creature, which, when dead, won't eventually sink to the ocean floor ?". In this case I'd say that the decomposition process will eventually reduce the organism to microscopic floating particles and a portion which sinks, such as bones. StuRat (talk) 22:50, 21 April 2014 (UTC)

Just because it's relevant and awesome, behold the recently discovered Osedax. Also relevant is marine snow. SemanticMantis (talk) 00:05, 22 April 2014 (UTC)

I think the giant isopods at those whale falls are even cooler. StuRat (talk) 01:38, 22 April 2014 (UTC)

My guess was that the question was about flight 370. Red Act (talk) 00:10, 22 April 2014 (UTC)

April 21

Bazhin Gap

In the Nanga Parbat there is a high altitude gap/saddle called "Bazhin Gap". What does "Bazhin" refer to? Local dialect? A name of a person? The expression seems to be mentioned for the first time in the 1930ies. Any lead is appreciated. GEEZER^{nil nisi bene} 10:18, 21 April 2014 (UTC)

Probably a person. Note that there is also a "Bazhin Glacier" nearby. Looie496 (talk) 14:06, 21 April 2014 (UTC)

don't put warm food in fridge?

I had some leftovers that I was going to save in the fridge, but my mom says don't do that since they are still warm. I'm supposed to leave them on the counter til they reach room temperature before refrigerating. She says the same thing when we buy warm stuff from the store. What's the issue here? Does the quicker temperature change mess up the food in some way? Does putting the warm stuff (just an unfinished meal, not anything large) in the fridge temporarily warm up the fridge interior enough to speed the spoilage of other food in the fridge? Or is the whole thing just silly? Thanks. 98.207.66.10 (talk) 19:33, 21 April 2014 (UTC)

"Make sure food has cooled down before you put it in the fridge," says Philippa Hudson, senior lecturer in food safety at Bournemouth University.

"If the food is still hot it will raise the temperature in the fridge, which isn't safe as it can promote bacterial growth." [8] 86.146.28.229 (talk) 20:09, 21 April 2014 (UTC)

See also Danger zone (food safety). If you place an overhot item in the fridge, you increase the chance of raising the temperature of all of the other food around it to temperatures that promote unhealthy bacterial growth. --Jayron32 20:12, 21 April 2014 (UTC)

The U.S. Department of Agriculture says "Hot food can be placed directly in the refrigerator or it can be rapidly chilled in an ice or cold water bath before refrigerating."[9] The U.S. Food and Drug Administration says "Leftovers … need to be refrigerated or frozen within two hours … . Despite what some people believe, putting hot food in the refrigerator doesn't harm the appliance."[10] The Washington State Department of Health labels the idea that you shouldn't put hot foods in the fridge a "myth", and says "Hot food can be placed in the refrigerator."[11] Red Act (talk) 20:24, 21 April 2014 (UTC)

I do wonder if there are climate and cultural differences. The stereotype is that Americans have larger, more powerful fridges than Britons: I know that I have watched the temperature in my fridge rise out of the safe zone, when I have overloaded it. And American food safety advice I have seen seems to assume a much warmer environment than British food safety advice: perhaps in line with the jokes about room temperature being laughably unrealistic in British labs. And every bit of American advice which claims it is a myth, that I have seen, also has a note about if you left the food to cool and forgot about it for hours, which perhaps shows the motive for the advice. This would explain why the official governmental advice from the NHS, supported by expert advice, is to allow food to cool before putting it in the fridge, whereas the official governmental advice in America is to not worry about that. 86.146.28.229 (talk) 20:31, 21 April 2014 (UTC)

I'd say it depends. If you have a powerful, almost empty fridge, containing food that doesn't really need refrigeration anyway (like fruit), and the food you want to put in isn't all that hot, but might tend to spoil quickly, then go for it. On the other hand, if it's very hot, doesn't need refrigeration all that much, and you will need to cram it in right next to some foods that really need to be properly refrigerated (like egg salad), and your fridge can barely keep up with what's already in it, then wait. StuRat (talk) 22:57, 21 April 2014 (UTC)

Thanks, I see. At least this identifies the issue, of warm food in the fridge transferring heat to other food. Of course letting the warm food sit outside the fridge probably attracts even more bacteria, but whatever. 98.207.66.10 (talk) 01:09, 22 April 2014 (UTC)

• This really depends on the food and circumstances. Soup in a pot with a lid that forms a seal can be brought to a boil and served, then left on the stove with the lid closed, be removed from heat, and let cool overnight. As long as the lid is not removed and the stock was boiling it is sterile. Leaving out uncovered eggs or dairy to cool is foolish. Bacterial growth is normally most rapid around body temperature. The worst thing to do is to let food sit warm. It's an easy way to get you restaurant shut down. Food should be under 40 or over 140F. If your fridge is from the 1940's a warm pot might be a problem, but letting a newer model run to cool the food is better than kidney failure. μηδείς (talk) 02:53, 22 April 2014 (UTC)

Hypoxia

I have read the article on hypoxia, but it did not answer my questions. What are the cumulative effects of marginal hypoxia? What would the main symptoms be? Thank you. — Preceding unsigned comment added by 62.56.71.197 (talk) 21:45, 21 April 2014 (UTC)

I'm not an expert on hypoxia, but I suppose drowsiness and fatigue would be two of the most likely symptoms/effects. FWiW 24.5.122.13 (talk) 05:48, 22 April 2014 (UTC)

Rust treatment

Steel gasoline (UK: petrol) tanks of cars and motorcycles that have internal rust are difficult to clean, access is only via by small openings and most of the inner surface is out of sight. Vinegar which is mainly dilute Acetic acid is suggested in online videos as a rust remover so I experimented by letting the head of a rusty screw soak overnight in a teaspoonful of concentrated "Vinegar Essence 35%" which is cheap (and is probably safer than an industrial chemical such as phosphoric acid). The pictures show my results which are promising. The questions are:

1. Surface rust on the screw has blossomed into a powdery scale (center pic). This happens above the submerged part of the screw. I suppose capillary action and/or a reaction in air occur. Can anyone explain what chemical reaction is likely here?
2. The converted rust could be washed off with warm water (right pic). The bolt head is now almost rust free, and I can repeat the treatment. But in the case of a fuel tank I suspect the acid etched surface will be prone to rust again quickly. My question is what is a good way to finish the vinegar treatment? I am considering alternatives such as rinsing with Kerosene, Gasoline or with dilute caustic soda ? JustAnotherUploader (talk) 23:50, 21 April 2014 (UTC)

I'm wondering if it makes economic sense to try to remove rust from a gas tank, instead of replacing it. To remove the rust you will have to remove the gas tank (which is quite a job, in the case of a car), drain it, then use quite a bit of whatever rust removing agent you decide on, then rinse that, then coat it with a large quantity of some type of anti-rust treatment, then maybe let it cure for a while, then rinse again, dry all the water out, then re-install. The labor and other costs of all this sounds like it would exceed that of a new tank (or maybe a used one from a junkyard). Perhaps an exception might exist for old tanks for which no replacement can be found, or when you need to keep the original parts intact in a classic vehicle. StuRat (talk) 01:26, 22 April 2014 (UTC)

• I have to agree with Stu. Have a professional replace the tank. The last thing you need is rust particles flowing upstream into the engineworks. Pennywise, poundfoolish. μηδείς (talk) 02:40, 22 April 2014 (UTC)

April 22

Which covalent bonds are broken in DNA cleavage by nucleases?

When DNA is cleaved by restriction endonucleases, meganucleases, engineered zinc finger nucleases/TALENs or Cas9 which covalent bonds are broken? Are they different for each type and if so, does that affect the repair mechanisms? --78.148.106.196 (talk) 00:47, 22 April 2014 (UTC)

I suggest you read the first sentence in nuclease, and our article on DNA. There is only one bond to be cleaved in DNA. Fgf10 (talk) 07:08, 22 April 2014 (UTC)

I think I can see five potential bonds that could be cleaved. What makes you so sure that all enzymes cleave cleanly at that point? --78.148.106.196 (talk) 10:58, 22 April 2014 (UTC)

Only likely (from a chemical standpoint) possibilities, given we are talking about the phosphodiester bonds of the backbone linkage, are the two P–O (those O being the 3' and 5' on the adjacent deoxyribose parts of the two DNA residues). The two O–C are comparatively harder to break. And the C^5'–C^4' is not at all fragile. The question of "which P–O" is a reasonable one. Assuming the phosphate remains attached to one of the two DNA residues, does it stay with 3' (breaking off the next one's 5') or vice versa? DMacks (talk) 14:56, 22 April 2014 (UTC)

I think it's going to be a while before I can answer my own question. I know that some of the enzymes form covalent bonds with the DNA which are then broken. Also, since the restriction endonucleases, Cas9 and the business ends of ZFNs and TALENs all derive from an evolutionary need to protect bacteria from invading phage and plasmids, I think it stands to reason that the DNA might be cleaved in such a way that it couldn't easily be ligated back together. I don't know nearly as much as I'd like to about DNA repair. Some day... 78.148.106.196 (talk) 19:46, 22 April 2014 (UTC)

Rotary cannon and super capacitors

The M61 Vulcan compared to the Gryazev-Shipunov GSh-6-23 has a slower rate of fire and has a slower "spin up" time. The article says this is due to the GSh-6-23 using a gas operating system instead of an electrical system to cycle the weapon. I was wondering if a rotary cannon were powered by super capacitors, would they have more power, and therefore spin up faster and have a rate of fire comparable to the gas operating rotary cannon? Also on a related note, would super capacitors grant electric cars greater acceleration? ScienceApe (talk) 00:59, 22 April 2014 (UTC)

My guess is that you are not on the right track. The reason the electrical system would be "slower" I doubt is because of the power delivery, which is probably from the vehicle. It seem far more likely to me that it is a synchronization or motor speed issue, there’s also heat dissipation and many other factors to consider. These guns are designed with many specifications in mind, including weight, cost and serviceability, not just “rate of fire”. No doubt you COULD make a faster firing, electrically powered rotary cannon, could you do it with super capacitors? I don’t really see why you’d bother, there are perfectly serviceable high speed motors, I don’t think power delivery is the limiting factor there. As for cars, power delivery ‘’might’’ be a factor, but no doubt weight and cost are also, and I don’t think electric cars have a problem with acceleration, the major problem for electric cars is range, so weight plays a more important factor. Vespine (talk) 02:17, 22 April 2014 (UTC)

Have a read of the applications section of the Supercapacitor article, if you haven't already. You'll get a good idea of the kinds of situations supercapacitors are being used in, they generally supplement systems where batteries are already used or only small amounts of power are required. They might be used in electric cars, but it would be more to save the batteries from spikes in current drain which could reduce their (usually expensive) life, rather then to "supercharge" the acceleration or anything like that. Vespine (talk) 02:24, 22 April 2014 (UTC)

Right, as for electric cars, I would guess that the acceleration is actually limited by the computer to act more like a traditional gas-powered car. In a conventional internal combustion engine, torque increases with engine RPM and will eventually decrease at even higher RPMs (see Power band), hence the need for transmissions with multiple gear ratios. This isn't the case with electric motors. Electric motors can produce maximum torque instantly. So the actual acceleration is probably limited to keep people from doing a burnout every time they tap the accelerator. Though they certainly can if you want, the Tesla Model S has a 0-60 time of ~4 seconds, comparable to a Corvette. And then there's the EV-converted 1972 Datsun that can do it under 2 seconds, comparable to an F1 car.

Another benefit to using supercapacitors in vehicles though is their short charge time. They can be fully charged in minutes rather than hours. So for vehicles that stop a lot at predictable locations for short periods of time like buses, you can build electric vehicles that can run all day without needing continuous overhead wires like a trolleybus. Mr.Z-man 03:34, 22 April 2014 (UTC)

To touch the gun part of the question, there are newer Vulcan cannon which have both an increased ROF and shorter spin-up interval; they achieve that through decreased spun mass rather than better motors (or a Tim Taylor-esque "more power" approach). Other guns (including the XM301, no image though) feature a truncated-conic (rather than cylindric) barrel array, where the muzzles are at the narrow end. This does not only (slightly) decrease spun mass, but it limits the energy taken to spin the array, because a lower linear velocity will translate to the same angular velocity. The fact that the muzzle velocity vector and the axis are no longer parallel is accounted for easily.

During live-fire exercises, many guns are used at a low speed setting (usually half or two thirds of battle speed), and fed training rounds, which are not only cheaper than fully combat-effective rounds, but also easier on the barrels. - ¡Ouch! (^{hurt me} / _{more pain}) 06:59, 22 April 2014 (UTC)

Most modern gatling guns operate using a DC motor to cycle the rounds (chambering, ejecting, etc.) A typical time frame for the gatling gun to reach full fire rate is about 0.4 seconds (see GAU-19). So the super capacitor idea is kind of a moot point. Justin15w (talk) 15:30, 22 April 2014 (UTC)

Mesopotamian units of measure

Dear refence desk

please supply the reference for two specific Sumerian units which are given with precision

first the cubit (kus) of 497 mm

second the mass of the pound (ma-na) of 497.7 grams

Thank you

Roland Boucher Irvine california — Preceding unsigned comment added by 2602:306:CE07:A6D0:21F:F3FF:FECE:3122 (talk) 03:14, 22 April 2014 (UTC)

You already asked here three months ago[12] for support for the cubit being 497mm, which I'm aware that you need to be true in order to support your theory (that I won't link to) that the Sumerians basically invented the metric system 5000 years before the French proposed it. The information you were given last time, that in historical reality the cubit wasn't a precise consistent length but rather varied a bit depending on the precise time and location you're talking about, is still true. Red Act (talk) 05:43, 22 April 2014 (UTC)

It's also important to understand (and accept) that the levels of precision you're expecting did not exist in those days, even in places and timeframes where the units employed were consistent. AlexTiefling (talk) 12:27, 22 April 2014 (UTC)

Hunger hormones VS Appetite hormones

As I know, it is now clear for scientists that Hunger and Appetite are 2 different things - Hunger will always bring appetite but appetite won't necessarily bring hunger.

My question is: Are there any documented Neurochemicals that deals specifically with hunger and others that specifically with appetite? Thanks Ben-Natan (talk) 04:08, 22 April 2014 (UTC)

I don't think your distinction between Hunger and Appetite is standard in the literature, but if you are using "Appetite" to mean the act of eating, then yes, there are biological distinctions. It isn't true, though, that hunger always causes eating. Unfortunately we don't yet have a very deep understanding of either the neurochemistry of hunger or the mechanisms that drive eating. Our article on hunger (motivational state) gives a rather sketchy overview of what is currently known. The hormones leptin and ghrelin seem to be pretty directly related to the sensation of hunger. Looie496 (talk) 14:02, 22 April 2014 (UTC)

Buoancy

If no water is displaced when an object is put in it, then how do objects like leaves float when they do not displace water and thus the water does not have buoyancy force? — Preceding unsigned comment added by 122.150.66.107 (talk) 04:52, 22 April 2014 (UTC)

Anything that floats on water displaces water. See Archimedes principle. Leaves don't displace very much, because they don't weigh very much. --50.100.193.30 (talk) 05:43, 22 April 2014 (UTC)

Perhaps surface tension has something to do with it. Richard Avery (talk) 05:59, 22 April 2014 (UTC)

Yes, surface tension has two effects: firstly, for an unwetted leaf, it moves the displacement of water away from the leaf (but the same amount of water is still displaced, it's just not as obvious); secondly, at the boundary of the container, it allows displaced water to form a meniscus above the edge of the container, preventing overflow. Thus the displacement of a small mass of water is not clearly observable. The displacement will be more clearly visible if you use heavier leaves and add a surfactant (e.g. detergent) to the water next time you try the experiment. Dbfirs 09:07, 22 April 2014 (UTC)

Giant bumblebee

Here in Central California this spring, there seem to be quite a few GIGANTIC black bumblebees (I'd say at least 1.5-2 inches in length, and about the same in wingspan), which I hadn't noticed in previous years. Are these native to California, or are they an invasive species? Are they any more dangerous than ordinary bumblebees (more aggressive/more toxic/etc.)? Thanks in advance! 24.5.122.13 (talk) 05:54, 22 April 2014 (UTC)

Black bees tend to be Carpenter bees, and there are many species of them. Some can get quite large: see [13]. If I had to guess, you have seen some kind of carpenter bee, but more specific than that, it would be hard to say. --Jayron32 12:40, 22 April 2014 (UTC)

There's also the black-chinned hummingbird there. The ones in our article don't look all that black, but here's one that does: [14], which can be mistaken for a giant bee, as it makes a similar sound and also hovers as it goes from flower to flower. (While in motion, the wings are a blur, so you can't see the obvious difference between bird wings and insect wings.) StuRat (talk) 13:38, 22 April 2014 (UTC)

Without pics it's hard to ID conclusively, but Xylocopa_varipuncta is the largest bee native to California. Females are metallic black, males are gold and fluffy. They can reach over an inch long, and can easily seem to reach 2" while on the wing. In general, actual bumble bees (bombus) are not very aggressive. Carpenter bees can be aggressive, but mostly to other bees. This in part comes from different social structures. Most carpenter bees are solitary, and each male will defend an area from other males, while hoping to attract mates. People often think they are a threat, as they will aggregate around e.g. wooden picnic shelters that they have prepared nesting sites in. The bees will then fly at incoming animals to investigate. So, you might feel threatened if one of these comes flying at your head, it actually poses no threat, it just wants to make sure you're not a rival bee. Males can't sting, and you can swat them away with impunity. For fun, you can wad up a bit of paper or aluminum foil and chuck in the direction of such an aggregation. The bee will quickly track that object, and follow it away from you. Since they don't live together in a large colony, they do not cooperatively defend anything, so it is almost impossible to get a swarm of them chasing you (unlike certain wasps, africanized honeybees, etc.) Anyway, just wanted to give you the general info that carpenter bees are nothing to be afraid of. Yellow jackets, however, are horrible jerks, and will seriously ruin your day ;) SemanticMantis (talk) 15:46, 22 April 2014 (UTC)

Do Jews have some African/Black DNA?

All the people that I know are Jewish ethnicity/race have some of the same ethnicity-specific features as Black people including a cloud of big curly hair that grows out like an afro, very full lips and according to a funny book about true stereotypes, a giant penis. Since Jews have some of the features that are unique to African people does that mean they have some African/Black DNA? — Preceding unsigned comment added by 68.8.106.52 (talk) 05:12, April 22, 2014

We all have African DNA. HiLo48 (talk) 09:44, 22 April 2014 (UTC)

More specifically "In paleoanthropology, the recent African origin of modern humans, frequently dubbed the "Out of Africa" theory, is the most widely accepted model describing the geographic origin and early migration of anatomically modern humans." --Jayron32 10:52, 22 April 2014 (UTC)

That's correct, but the "Out of Africa" event occurred over 50,000 years ago. Since then there has been limited genetic mixing between sub-Saharan populations and non-African populations, so the question actually does make some sense at that level. The bigger problem is that there is really no such thing as a "Jewish race", or anything like it, at a biological level. Modern-day Jews derive from a pretty diverse mixture of backgrounds. In any case, as a group, it's extremely unlikely that they have higher levels of sub-Saharan-derived DNA than other people from the same parts of Europe or Asia. (I think the question is probably trolling but I have answered it seriously anyway.) Looie496 (talk) 13:51, 22 April 2014 (UTC)

The question may be related to Ethiopian Jews in Israel. Ruslik_Zero 19:32, 22 April 2014 (UTC)

Baseline fitness

Other than age, what influences natural baseline fitness levels. Without any training, anyone's fitness regresses but what influences the speed of regression and also where the regression stops, other than age. Clover345 (talk) 10:13, 22 April 2014 (UTC)

Physical fitness is a nebulous concept, and not easily quantifiable. There are aspects of fitness (such as the ability to complete certain physical tasks, like run a certain distance, etc.) or things like Basal metabolic rate or Body Mass Index or other such measures which are sometimes used as proxies for fitness, but none of those singularly captures what it means to be "fit". --Jayron32 12:34, 22 April 2014 (UTC)

Hormone levels are important, in particular testosterone in males. Looie496 (talk) 14:47, 22 April 2014 (UTC)

Physical activity an important factor here. If you exercise regularly from a young age onward, you should not notice a significant decline in physical fitness until you start to hit old age. Only if you are an olympic class top sporter who exercises a few hours per day will this be different. A typical 60 year long distance runner who has run for most of his life can perform just as well as when he was 30; exercising regularly will have helped to preserve the physical fitness he had decades ago. Count Iblis (talk) 15:07, 22 April 2014 (UTC)

Urinalysis

Do chlamydia and gonnorhea urine tests involve the same test as a urinalysis looking for white cells, blood etc? If not, why don't they do it along with the std test since they have a sample of urine anyway sand it can't be that expensive to do both? Do these test literally only detect chlamdia and gonnorhea? 90.205.212.104 (talk) 14:14, 22 April 2014 (UTC)

According to http://std.about.com/od/gettingtested/qt/Urine-Testing-For-Gonorrhea-And-Chlamydia.htm, the standard method of testing is to test for the presence of bacterial DNA in the urine. That's quite different from the method of looking for blood cells. Looie496 (talk) 14:46, 22 April 2014 (UTC)

They could also test for LSD metabolites, gold particles, and Borg nanoprobes. The questions invovled are reasonable suspicion of risk, cost-benefit analysis, and informed consent. μηδείς (talk) 16:57, 22 April 2014 (UTC)

Would borg nano probes and gold particles come out in urine? 90.205.212.104 (talk) 18:27, 22 April 2014 (UTC)

Does (or did) any country's military or police use the Desert Eagle pistol?

Question as topic. I thought at one time that the Israeli military and US Special Forces used them, for two examples - but I've been told not. I have been told that most Desert Eagles will only ever be fired at targets, tin cans and water jugs by private owners, because they're not actually that useful, in terms of effectiveness to the military and police, despite being a .50 caliber pistol. Also that they're basically 'more form than function'. Thanks.