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December 2

Rabbit habit

Is it true that rabbits eat their own crap?--213.205.252.104 (talk) 01:45, 2 December 2016 (UTC)[reply]

Read Rabbit#Diet and eating habits. --Jayron 32 02:06, 2 December 2016 (UTC)[reply]

There is a difference between being unable to vomit, and being unable too eat their own vomit. The way the question is phrased makes it all sound rather unpleasant, though in fact the rabbit has evolved a very neat and efficient solution to the problem of getting enough nutrients from a diet that would fairly quickly kill a human. Wymspen (talk) 10:50, 2 December 2016 (UTC)[reply]

I was familiar with the term "pseudorumination", but apparently "caecotrophy" is of relevance. [1] Wnt (talk) 18:53, 2 December 2016 (UTC)[reply]

Cecotrope is the word I know for special feces that serve a nutritive function. 19:30, 2 December 2016 (UTC)

Here is an article about this topic, written by a veterinarian. SemanticMantis (talk) 19:30, 2 December 2016 (UTC)[reply]

Strange we dont have an opinion from our very own rabbit, isnt it?213.205.252.104 (talk) 02:30, 3 December 2016 (UTC)[reply]

Identify a weapon used by the South African Army

This weapon is clearly a rocket/missile launcher, but what type is it? Roger (Dodger67) (talk) 12:46, 2 December 2016 (UTC)[reply]

Starstreak - LML variant, with one of the three positions filled. This article has this picture of the right side of an empty LML for comparison. -- Finlay McWalter··–·Talk 13:07, 2 December 2016 (UTC)[reply]

Thanks, that is conclusive. Roger (Dodger67) (talk) 13:14, 3 December 2016 (UTC)[reply]

What is the reason that not any mammal can be reproductive from another different mammal?

What is the reason that not any animals can be reproductive from another different animal? For example, two mammals like sheep and cow or even a sex of human with dolphin can not results in shared offspring. Just few animals are known to be successful with different mammals, such as: donkeys and horses that make together mule or hinny. so the question is What does make those two different mammals to be successful in reproduction)? is it the number of the chromosomes the key for the issue? and then any mammal which has the same number of chromosomes (2n=46) is matached to be reproductive with human being? 93.126.88.30 (talk) 15:47, 2 December 2016 (UTC)[reply]

Number of chromosomes is a factor, but not the exclusive one. Some mutant animals have extra or fewer chromosomes, yet can still reproduce with others of their species. Also, very different animals that happen to have the same number of chromosomes can not reproduce. To understand this, think about blood type. People with incompatible blood types can not share blood. For organ transplants, there are far more such factors to consider when tissue matching. Well, in our genetics there are even more such factors, making animals with two sets of incompatible genes unable to survive, meaning they may die in utero shortly after conception, if conception even occurs. StuRat (talk)

Organ/blood incompatibility is not the limitation - see chimera (biology). The evolution of reproductive isolation is a trickier thing. See speciation, hybridization. Actually, I remain very curious whether it is possible to select organisms that are good at hybridization, say, if you cross several species and keep selecting for those that form hybrids most effectively. There are naturally occurring animals that are somewhat infamous for their ability to hybridize, e.g. mallards, and conceivably they might show surprising ways to compensate for reproductive barriers. But I don't know any of that, nor is there good reason to think it true! Wnt (talk) 19:41, 2 December 2016 (UTC)[reply]

Regarding chimeras, that's two sets of genetic codes from the same species, so we would expect that sometimes they would be compatible and sometimes not. Perhaps chimera conceptions are far more common than we think, but due to genetic incompatibility many die before the mother is even aware of a pregnancy, and only the few that are genetically compatible survive. StuRat (talk) 03:57, 4 December 2016 (UTC)[reply]

Oh, chimerism is much more fun than that! Look it up... Wnt (talk) 04:02, 5 December 2016 (UTC)[reply]

You may be interested in Humanzee and Mythological hybrid. The answer to your question is that fertilization will not even occur. (But perhaps if the DNA is directly injected into the egg this restriction could be bypassed) Graeme Bartlett (talk) 11:28, 3 December 2016 (UTC)[reply]

Actually, the story with humanzee is that the verdict is still out. In biology the only way you know something is to do the experiment, and in the case of hybridization, it can take many attempts before a single hybrid is obtained. Until someone fesses up to doing the science (with proof, and completed data) nobody knows. Wnt (talk) 12:40, 3 December 2016 (UTC)[reply]

Why do animals have hearts ?

...as opposed to each blood vessel squeezing the blood past the next valve, in a process similar to intestinal peristalsis, only faster. I understand that some simple animals, such as worms, do use such a system, which would appear to be more fault tolerant and thus I would expect evolution to favor it. However, it must not scale up well. Why is this ? StuRat (talk) 15:52, 2 December 2016 (UTC)[reply]

A very round-about way of answering is asking why we have a 4-chamber heart. Consider just the heart and lungs so this doesn't need to take 30 pages of biology... One side takes blood from the lungs, full of oxygen, and pushes it out into the body. The other side takes dirty blood from the body and pushes it into the lungs. That can be done with two hearts. One to pull blood out of the lungs and push it through the body. The other to pull blood from the body and push it into the lungs. Why do we have two of nearly everything and only one heart when our system is designed for two hearts? With one heart, we don't have to keep it in sync. Both sides beat at the same time. It is simpler - and nature seems to like simple things. With that in mind, consider having about 500 miniature valvular hearts throughout the body. There is a lot of redundancy, but there is also a lot of room for error. Throughout evolution, blood circulation was consolidated to a single structure and then that structure split into chambers to perform multiple functions per beat. Please don't read this to imply that "evolution made it that way." As always, evolution is not an engineer. Evolution is just an observation of what happened in the past. 209.149.113.4 (talk) 16:49, 2 December 2016 (UTC)[reply]

Consider a system where an animal had hundreds - or thousands - of pumps distributed throughout their circulatory system. The distribution of nodes might be more fail resistant (not unlike the internet) but what happens if a few of those pumps fail? What happens if they pump out of rhythm? Sometimes it makes sense to put all your eggs in one basket if you're willing to build an extremely reliable basket. Matt Deres (talk) 17:39, 2 December 2016 (UTC)[reply]

The heart does most of the work, but not all the work, in the human circulatory system. Please see the Skeletal-muscle_pump. Dr Dima (talk) 18:40, 2 December 2016 (UTC)[reply]

Of some relevance to this is that some reptiles have a 3-chambered heart - see Reptile#Morphology and physiology. DrChrissy ^(talk) 20:18, 2 December 2016 (UTC)[reply]

Humans have a three chamber heart for a significant time during development. Many people don't fully form a wall dividing the large chamber. It leads to multiple health problems. — Preceding unsigned comment added by 71.85.51.150 (talk) 02:26, 3 December 2016 (UTC)[reply]

Not exactly. See fetal circulation. The fetal heart normally develops four chambers, but there are holes in the septum to allow oxygenated blood from the placenta to mix. These normally close at birth, but sometimes they don't, which can lead to health problems. I think this is what you're referring to. --47.138.163.230 (talk) 04:03, 5 December 2016 (UTC)[reply]

Note that arthropods have an open circulatory system, where their "blood" (formally hemolymph) is not always contained in vessels, so your proposed system wouldn't work for them. I skimmed a few articles but couldn't find anything about the evolution of the circulatory system and whether it evolved independently in vertebrates and invertebrates. If not, the reason would be pretty simple: the heart came first, and closed blood vessels came later. As others have touched on, in general, evolution works on the principle of "good enough". Animals developed a single heart for whatever reason, and it's good enough, so there isn't much selective pressure to develop an alternative. --47.138.163.230 (talk) 23:24, 3 December 2016 (UTC)[reply]

Just looking at humans, heart disease is a major cause of death, and while most women so affected are past their reproductive years, that's not true of men. So, that would put selective pressure on humans. StuRat (talk) 04:01, 4 December 2016 (UTC)[reply]

A bit, but not a lot. Cardiovascular disease generally manifests many years after sexual maturity, so its impact on an animal's reproductive fitness is small. Also, there's an important distinction to make here. Although "heart disease" is often used to mean "cardiovascular disease" (indeed, here on enwp one redirects to the other), the most common type of cardiovascular disease is coronary artery disease. This is not a disease of the heart proper, but rather of the arteries supplying the heart with its blood supply. If you didn't have a heart, you would still be susceptible to atherosclerosis. I also wonder about the feasibility of your proposed system. Arteries already have to be thick to withstand the arterial pressure. If arteries did the actual pumping of blood, they would need even thicker muscle layers. This might cause issues with the amount of space arteries take up, and in getting the blood supply to the muscle layer. --47.138.163.230 (talk) 04:03, 5 December 2016 (UTC)[reply]

The previous statement from StuRat appears to based on the idea that "heart disease" is limited to the heart. That is not common. If birth defects are thrown out, nearly all heart disease is a localized problem caused by cardiovascular disease. Weak arteries, arterial plaque, etc... If modern humans had hundreds of hearts spread out over the body, there is no obvious way how that would limit cardiovascular disease. Without limiting cardiovascular disease, all of the hearts would be under a greater load and risk heart disease. 209.149.113.4 (talk) 16:46, 5 December 2016 (UTC)[reply]

How heartless animals might work

There would be more, but smaller, veins and arteries, with redundancy, so that severing one would not cause death.

Each valved segment would contract X milliseconds after the previous segment, or after Y milliseconds, if no signal is received. The brain would send out signals modifying X and Y, to increase the blood circulation rate during athletic events, slow it down while sleeping, etc.

So, if this system just wouldn't keep up for animals with a fast metabolic rate, how about slower animals, like sloths ? StuRat (talk) 13:38, 4 December 2016 (UTC)[reply]

I think we need to be very careful about terminology here. This sub-thread heading uses the word "heartless". Even a tube-like structure such as discussed above is called a "heart" - see Heart#Invertebrate. DrChrissy ^(talk) 23:56, 4 December 2016 (UTC)[reply]

If you did that, then such an animal might have thousands of "hearts". I think a different name would be in order. StuRat (talk) 05:06, 5 December 2016 (UTC)[reply]

"The heart in arthropods is typically a muscular tube that runs the length of the body, under the back and from the base of the head." This is a quote from Heart (my emphasis). DrChrissy ^(talk) 20:24, 5 December 2016 (UTC)[reply]

Yes, but note the "a" in the quote. When you have thousands of them working in unison, they are more of a collective heart, rather than thousands of individual hearts. For comparison, look at a compound eye, where each individual lens segment is not called an eye, but rather the collection of many is. StuRat (talk) 03:37, 6 December 2016 (UTC)[reply]

Sea anemone. Count Iblis (talk) 08:20, 5 December 2016 (UTC)[reply]

Atomic particle identification

I don't know how to express the following, please try to understand:

There is a particle you find sometimes after an artificial (man made) atom collision that exists in two places at the same time. Does anyone know what the name is? 103.230.104.6 (talk) 18:20, 2 December 2016 (UTC)[reply]

I believe that applies to all sub-atomic particles, before or after collisions. See wave function and Heisenberg uncertainty principle. StuRat (talk) 18:57, 2 December 2016 (UTC)[reply]

I'm not thinking of anything specific either, but see two-slit experiment. Wnt (talk) 18:58, 2 December 2016 (UTC)[reply]

Yes, that might be what they meant. There's no collision involved, but the particle sent towards the slits behaves as if it travels through both slits at the same time. Here we get into wave-particle duality. StuRat (talk) 19:00, 2 December 2016 (UTC)[reply]

Are you guys sure, cause I'm not. All I recall (which could be wrong), a rare particle displays in two places at the same time (sometimes) after bursting an atom, in less than a milli/nano second or so. They are identical/twins. 103.230.104.18 (talk) 08:10, 3 December 2016 (UTC)[reply]

Some sort of quantum entanglement, such as this experiment? DMacks (talk) 10:48, 3 December 2016 (UTC)[reply]

And some type of quarks spontaneously change type. Seems less likely to be what you heard though. StuRat (talk) 03:53, 4 December 2016 (UTC)[reply]

supermassive black holes

Scientists have found black holes that are several billion solar masses. Is there evidence or scientific speculation of much more massive black holes, perhaps trillions, octillions or even more solar masses?144.35.45.53 (talk) 19:26, 2 December 2016 (UTC)[reply]

See Supermassive black holes, which states that there is no known mechanism for the generation of so-called ultramassive black holes, and that there is thought to be a limit of the size. Robert McClenon (talk) 21:17, 2 December 2016 (UTC)[reply]

The actual paper that produced that claim [2] only states that black holes cannot grow beyond this size through the consumption of an accretion disk, while they can still grow further through black hole collisions. The maximum size of a black hole that expands through accretion is proposed to be 50 billion solar masses in ordinary conditions, and 270 billion solar masses in "perfect" conditions. Black holes beyond this size, not having a visible accretion disk, would be hard to detect. Someguy1221 (talk) 22:48, 2 December 2016 (UTC)[reply]

Ultramassive black holes might be detectable by the effect of their gravitational field on nearby galaxies or by gravitational lensing. Graeme Bartlett (talk) 11:54, 3 December 2016 (UTC)[reply]

alcohol hand gel

Please can you tell me what percentage of alcohol this specific product contains, and whether or not it will kill most bacteria and fungi within 30 seconds. The page is vague and does not say. I see these hand gels in hospitals and I want to know if they would be effective. Thanks for your help. — Preceding unsigned comment added by 125.141.200.13 (talk) 19:59, 2 December 2016 (UTC)[reply]

You might do better by asking the makers.

As to its effectiveness, then many products will kill or remove "most" bacteria. However that's nothing like effective enough. Even the much touted TV advert claims of "Kills 99% of all known germs" are nothing like effective enough - 1% of a contamination remaining will still be "contaminated", in practical terms.

Alcohol gels are remarkably effective though, compared to handwashing with soap. Their other advantage is that they're effective even with poor technique - unlike soap, which needs conscientious scrubbing to be comparably effective. Andy Dingley (talk) 21:54, 2 December 2016 (UTC)[reply]

^{[citation needed]} on all of that. Our article covers some of the details, which suggest that the situation is much more complicated than the opinions expressed above. Matt Deres (talk) 17:12, 3 December 2016 (UTC)[reply]

FYI, I had to reload your link as the first time I clicked it, I was redirected to the suppliers homepage. Anyway, the SDS for product 5665-02-INT00 is here: [3] It doesn't discuss effectiveness, but it does identify the key ingredients as Sodium Laureth Sulfate >=1 to <5 and Cocamidopropyl Betaine >=1 to <5. I would describe this as a standard hand soap. It has no particularly special properties and though all soaps are effective are removing bacteria, this one has no claim to being special in that regard. Please note that the manufacturer, Purell, also makes products that are intended for healthcare use, including ones certified for use by surgeons and others requiring a highly effective antibacterial soap. Some of those products come in similar form factors, so if you were expecting this soap to be especially germicidal, perhaps you indicated the wrong product number. Dragons flight (talk) 22:37, 2 December 2016 (UTC)[reply]

Agree with Dragons flight. This product doesn't even appear to be marketed as a hand sanitizer, but rather as a hand soap. It likely doesn't contain alcohol as an active ingredient. As a side note, most hand sanitizers, including for hospital use, contain somewhere around 70% ethyl alcohol or isopropyl alcohol. This is the percentage recommended by the CDC for use under biosafety conditions. https://www.cdc.gov/biosafety/publications/bmbl5/bmbl5_appendixb.pdf --OuroborosCobra (talk) 00:23, 4 December 2016 (UTC)[reply]

According to the bottle I have here, the ingredients are; "Aqua, Sodium Laureth Sulfate, Cocamidopropyl Betaine, Critic Acid, Disodium Cocoamphodiacetate, Glycerin, PEG-80 Sorbitan Laurate, Polyqautermium-39, Benzyl Alcohol, Sodium Benzoate", however it does not give percentages.— Preceding unsigned comment added by 125.141.200.13 (talk) 00:54, 4 December 2016‎ (UTC)[reply]

The alcohol on their (benzyl alcohol) isn't one commonly used for sanitization of surfaces. It is so far down the ingredient list that I also doubt that as the use. The sodium benzoate, for example, is a preservative. This is hand soap, not hand sanitizer. Remember that the lower something is on an ingredient list, generally the lower its percentage in the product. --OuroborosCobra (talk) 02:02, 4 December 2016 (UTC)[reply]

December 3

Is Glicine not chiral?

In this video (10:20>) the woman says that the Glycine is not chiral because it has 2 different group only rather than four. Then I can understand from her things that amino acid can be chiral just in case that it has 4 different groups. But I don't understand why when even it has only two different groups it can not be chiral, here is the group of the left side can be on the right and vice versa and it is chiral since it has a mirror image as well. 93.126.88.30 (talk) 02:00, 3 December 2016 (UTC)[reply]

This is one of those questions where it would help if you had something physical to model the molecule with, like any stick-and-ball molecule kit. If you were to build both glycine and any mirror-image, you would find that you could make the two molecules identical simply by rotating bonds or the whole model around, and therefore conclude that all mirrored forms of glycine are actually glycine. Someguy1221 (talk) 02:13, 3 December 2016 (UTC)[reply]

I do have a physical model here and I still don't understand why it's not chiral if you rotate it the same as doing with the hand. 93.126.88.30 (talk) 02:58, 3 December 2016 (UTC)[reply]

I'm sorry, I guess I don't fully understand what the hangup is. If you take like, clay or plastic models of the left- and right-hand, it's quickly obvious that no amount of rotations will make them identical. Someguy1221 (talk) 03:20, 3 December 2016 (UTC)[reply]

Take a pair of gloves that have different "left" vs "right" gloves. Put the left one on your left hand. Now take it off and the left one on your right hand (or instead now put the right glove on your left hand). If these results feel different to you, then your hands are not identical. DMacks (talk) 10:40, 3 December 2016 (UTC)[reply]

Note that "two different groups" is not correct for this structure, nor is it what is needed in this context. The requirement for chirality of this sort of structure is "all four different", so "any two (or more) the same" makes it nonchiral because that would mean there would only be less than four different. DMacks (talk) 10:44, 3 December 2016 (UTC)[reply]

There is no carbon atom with 4 different things attached. If you put a mirror in the plane of the carbon atoms and oxygens, you can see that its reflection is identical. Graeme Bartlett (talk) 11:19, 3 December 2016 (UTC)[reply]

The physical model might mislead you. The thing to bear in mind with chirality is that it's not merely whether you can pick up a model molecule and tell if you've inverted it in a mirror - can you tell if you've inverted it after you allow every bond that rotates to do so freely? The mirror image glycine may look different, but I guarantee you can twist some bonds around and get back where you started. You might play with [4] which is a free open source chemical modeling program.

(Annoying pedantry follows) Note that it is possible, rarely, to have a chiral molecule without any chiral centers because its geometry does not allow free rotation - for example, C(CH3)=C=C(CH2CH3)(a cumulated diene) has no carbons with four distinct ligands, but it is non-superimposable if the ethyl goes right instead of left - that is an enantiomer since you can see it would be a mirror image to swap those. I imagine that there are some compounds that are achiral at room temperature because we assume that their conformation changes constantly, yet become chiral if they are kept at cryogenic temperatures because they no longer can access the higher-energy states needed to rotate all sigma bonds freely. Wnt (talk) 12:06, 3 December 2016 (UTC)[reply]

Atropisomers have the thermal/kinetic barrier to rotation on a single bond you describe. These and the allene case are examples of axial chirality. DMacks (talk) 20:58, 3 December 2016 (UTC)[reply]

It's not even necessary to have π systems around for a molecule to be chiral. Spiro compounds can also be chiral. (Imagine a molecule with two pyrrolidine rings connected at the carbon to the left of each nitrogen in the ring, and with the other carbon next to this connecting point double-bonded to an oxygen atom. The central carbon must be tetrahedral, so the rings are orthogonal and there can be no plane of symmetry.) A molecule with a plane of symmetry or centre of symmetry cannot be chiral, but a molecule with an axis of symmetry can be. Double sharp (talk) 04:54, 4 December 2016 (UTC)[reply]

This description is confusing...do you mean two 2-pyrrolidones that form a spiro compound by virtue of sharing single carbon as their respective C3 positions? That sort of chirality thing is mentioned at the spiro compound article. DMacks (talk) 21:06, 4 December 2016 (UTC)[reply]

Yes, that's the one! Thank you and sorry for the obtuse description! Double sharp (talk) 03:22, 5 December 2016 (UTC)[reply]

2,7-Diazaspiro[4.4]nonane-1,6-dione (CAS# 36817-39-7) if anyone is interested. DMacks (talk) 06:06, 5 December 2016 (UTC)[reply]

One of my teaching examples is 1,7-dioxaspiro[5.5]undecane, a sex pheremone of the olive fruit fly, where one enantiomer is active against males and the other against females. For a review, see Mori, Kenji (2011). "Chirality and bioactivity". Chimica Oggi. 29 (4): 40–43. DMacks (talk) 21:32, 4 December 2016 (UTC)[reply]

I should add we have an article on glycine, though it lacks the usual pretty picture. See [5] for that. Wnt (talk) 12:43, 3 December 2016 (UTC)[reply]

What does the word "cis" (of cis isomer) stand for?

I know what it is cis but I don't know what is the meaning of the word itself.93.126.88.30 (talk) 03:00, 3 December 2016 (UTC)[reply]

It means "on this side of", the OED has "Latin cis prep. ‘on this side of’, opposed to trans or ultra, across, beyond; also used in comb. as in cis-alpīnus, cis-montānus, lying on this side the Alps or the mountains, cis-rhenānus on this side the Rhine, cis-tiberis on this side the Tiber. The two first of these esp. continued in use in medieval Latin in reference to Rome and Italy, whence Italian cisalpino, French cisalpin, cismontain, cisalpine adj., cismontane adj." and for the chemical sense "Designating a compound in which two atoms or groups are situated on the same side of some plane of symmetry passing through the compound; cis-trans isomerism, a form of isomerism in which in one isomer two identical groups are on the same side of the plane of a double bond whereas in the other isomer they are on opposite sides; so cis-trans isomer". See also Cis–trans isomerism for discussion of its use in chemistry. DuncanHill (talk) 03:16, 3 December 2016 (UTC)[reply]

Thank you. I've read the article here before I asked my question. Now I understand that the meaning of "cis" in Latin is "on the same side". I think that such essential information should be in the article which talks about the cis isomer.93.126.88.30 (talk) 04:44, 3 December 2016 (UTC)[reply]

If you mean the article Duncan cited, it's there in the first paragraph:

The terms “cis” and “trans” are from Latin.

--76.71.5.45 (talk) 05:24, 3 December 2016 (UTC)[reply]

And does that sentence tell you what the word means? —Tamfang (talk) 20:32, 3 December 2016 (UTC)[reply]

Nowadays "cisgender" is probably the cis- heard most often outside of chemistry. Wnt (talk) 11:46, 3 December 2016 (UTC)[reply]

Historic examples not referring to Rome: Cisplatina, Cisleithania, Ciskei. —Tamfang (talk) 20:44, 3 December 2016 (UTC)[reply]

The Cissy is a tangentally related South Park episode. StuRat (talk) 13:44, 4 December 2016 (UTC) [reply]

What do the letters Pk stands for in chemistry (acids & basis)?

I know the meaning but not what each letter stands for. By gogleing I didn't find the answer.

93.126.88.30 (talk) 04:43, 3 December 2016 (UTC)[reply]

p = -log, K = the constant for which you want to find the -log. 2601:646:8E01:7E0B:4194:43D8:DAB4:1C6C (talk) 05:53, 3 December 2016 (UTC)[reply]

It might stand for concentration of potassium K. See pH. Dolphin (t) 06:17, 3 December 2016 (UTC)[reply]

PH#History discusses the historical meaning of "p". Sørensen never stated exactly why he chose "p", but it is generally thought to mean logarithmic power, as the IP above me stated. "K" has a long history of being used as a reaction constant in chemistry, at least since 1864 (see Law_of_mass_action#History), though I haven't found any explanation as to why the authors chose K, though it could be as simple as the fact that "constant" in Norwegian (the native language of the first author I know to have used it) is konstant. Someguy1221 (talk) 06:22, 3 December 2016 (UTC)[reply]

In my chemistry class I remember it stood for "puissance", the French word for power. Doesn't mean that's right though. Graeme Bartlett (talk) 11:15, 3 December 2016 (UTC)[reply]

And similarly I remember hearing that it was from the German Potenz. That one is somewhat appealing because it means "power" in the mathematical sense, as opposed to the other senses of the English word (which would be instead probably Kraft or Macht). OTOH, there have been so many explanations of the "p" notation that I think it's safe to say that "nobody knows, but 'power of hydrogen' is as good an answer as any". Double sharp (talk) 05:09, 4 December 2016 (UTC)[reply]

I assume everyone is talking about pK_a, not p[K⁺] or pH or p[H⁺] etc., though that is indeed the place to look about "p" notation. It is the inverse log (p) of the acid constant, a type of equilibrium constant. Wnt (talk) 11:44, 3 December 2016 (UTC)[reply]

What the heck is a "wedge connector", and should there be a Wikipedia article about it?

Hello RD/S folks,
I deleted the article "Wedge connector" as a copyvio/advertising only page. Copyvio/advertising only pages I know about. Electrical connectors, not so much. And by "not so much", I mean that "me and a soldering iron" might be a plausible redirect to WP:CIR.
I've googled, and would appear to me that this thingumabob is a type of connector for power lines, particularly near electrical substations.
Should there be an article, or section in an article, about "wedge connectors"?
Pete AU aka --Shirt58 (talk) 09:12, 3 December 2016 (UTC)[reply]

Hi Shirt58 it's a "widget" used on high voltage powerlines. I found a few possible sources that might be able to start an article:

http://www.te.com/documentation/whitepapers/pdf/5jot_1.pdf
https://www.researchgate.net/publication/3620625_Wedge-connector_technology_in_power_utility_applications
https://books.google.com/books?id=YTjMBQAAQBAJ&pg=PA290&lpg=PA290&dq="wedge+connector"&source=bl&ots=wASBZfr1Rd&sig=9NqLZZnlhDQL0udGhHV2upVZSBo&hl=en&sa=X&ved=0ahUKEwjo8N2WntrQAhVELMAKHX_fB604ChDoAQg5MAg#v=onepage&q=%22wedge%20connector%22&f=false

Roger (Dodger67) (talk) 09:41, 4 December 2016 (UTC)[reply]

24v from PSU

On this page someone commented;

To get 24vdc, you can use +12 as positive terminal, and use -12 as ground terminal..voltage is potential difference, thats might be the reason you dont get voltage from second psu unit-no difference(+12v vs +12vs difference is 0v)..imagine two AA batteries connected in series..it will produce 3v, but actually you can tap the middle point as GND and came up with -1.5v on negative & +1.5v on positive terminal..that is basically concept of terminal +VE,-VE, & GND..

That explanation went entirely over my head. Please explain in idiot terms how to get 24v from a PSU that has 12v and -12v lines? I know nothing about electricity theory. — Preceding unsigned comment added by 125.141.200.13 (talk) 18:30, 3 December 2016‎ (UTC)[reply]

The difference between 12V and –12V is 24V (basic math, nothing to do specifically with electricity). So if you call the –12V line the "ground" for your circuit, then the 12V line is 24V higher than it. DMacks (talk) 20:54, 3 December 2016 (UTC)[reply]

Eh? 12 minus -12 is 0 isn't it? 125.141.200.13 (talk) 00:55, 4 December 2016 (UTC)[reply]

No. Maybe not having a good understanding of the idea of Negative numbers and Arithmetic involving negative numbers is the key to your original confusion? DMacks (talk) 03:50, 4 December 2016 (UTC)[reply]

The OP is wrong in subtracting because the two supplies are effectively in series, as in his illustration with the two AA batteries, so their voltages should be added, not subtracted. So it's 12 plus 12. Akld guy (talk) 18:13, 4 December 2016 (UTC)[reply]

Sorry for being dense but wouldn't -12 + 12 also be 0? 125.141.200.13 (talk) 00:59, 5 December 2016 (UTC)[reply]

No. The +ve of the negative supply is connected to the -ve of the positive supply, just like the two series-connected AA cells, so the voltages add. The total voltage from the -ve terminal to the +ve terminal is 24V. Akld guy (talk) 06:03, 5 December 2016 (UTC)[reply]

This usually works just fine, but some power supplies get confused and shut down. This is especially likely when the +12V puts out more current than the -12V -- the -12V circuit might not like being driven backwards like that. --Guy Macon (talk) 21:06, 3 December 2016 (UTC)[reply]

Yes, the negative lead of the 24V device can be connected to the -12V line and the positive lead to the +12V line. All will be well, with a couple of caveats: there must be no DC path of any kind from the 24V device to the power supply's common ground (the mid-point). This applies to all inputs and outputs of the device. So for instance, if a 24V amplifier is connected in this way, its input connection must have no common path (called a ground loop) via its own wiring or via any other device, to that mid-point. Such a path would probably exist with a 12V preamplifier ahead of a 24V amplifier; the common ground of the preamp and amplifier would result in a path through the preamp, probably causing serious damage. Also, if the case of the 24V device is internally connected to one of the device's DC leads, great care must be taken that it does not accidentally come in contact with the mid-point or with the case of some associated device connected to the same power supply. For audio devices, an audio transformer will provide the required isolation, but of course the characteristics of the transformer must be chosen so as to not impair the frequency range and other performance aspects of the device. Akld guy (talk) 21:25, 3 December 2016 (UTC)[reply]

It's not a well-written page and they don't seem to appreciate the several drawbacks to this. A 10Ω 10W load resistor on the 5V rail is a bit crude and it will be a full 10W load, so that's a bunch of heat to get rid of.

One issue in particular is that -ve supplies on PC power supplies are just there to support low current devices, originally serial ports. These supplies are completely unbalanced, in terms of how much current the +ve can supply vs. the -ve. So that if you use a PC supply as a 24V supply, it "works" (with the ground offset problem mentioned above), but it will be a great big PSU that still only achieves a very low useful current.

If you need a 24V supply, then my route these days is eBay and the vast range of cheap DC-DC boost converters now available. Often based on the LM2596 and LM2621 ICs. They're cheap, they deliver several A and they only cost a few quid. Andy Dingley (talk) 21:45, 3 December 2016 (UTC)[reply]

I should point out that 10R at 5V is 2.5 W, not 10. V²/R. Tevildo (talk) 22:08, 3 December 2016 (UTC)[reply]

Science or Science Fiction? Professionals’ Discursive Construction of Climate Change

I saw this in my Twitter feed: http://oss.sagepub.com/content/33/11/1477.full Is this a reputable journal? Is it a reputable article? It's being cited to back the claim that the majority of scientists are skeptical of global warming "crisis". A Quest For Knowledge (talk) 19:35, 3 December 2016 (UTC)[reply]

The claim is bogus for it was not a representative survey of scientists even according to the authors of the study. --Modocc (talk) 20:55, 3 December 2016 (UTC)[reply]

It certainly is bogus for supporting the claim that the majority of scientists are skeptical of a global warming crisis, but would be a reliable source concerning what was actually studied, which the paper describes as:

"To address this, we reconstruct the frames of one group of experts who have not received much attention in previous research and yet play a central role in understanding industry responses – professional experts in petroleum and related industries." and "To answer this question, we consider how climate change is constructed by professional engineers and geoscientists in the province of Alberta, Canada"

It is the improper changing of "professional engineers and geoscientists in the province of Alberta, Canada" to "all scientists" that is completely bogus. --Guy Macon (talk) 21:19, 3 December 2016 (UTC)[reply]

Yep on a quick read of the article I agree. It is just a study of how people don't want to think they are part of a problem and like to stand up for the company and industry they work for. Not exactly surprising, it is the strength and extent of the effect most people don't understand. Even scientists are unfortunately prone to that - it is one of the things they have to learn to guard against and work hard to maintain. Dmcq (talk) 12:28, 4 December 2016 (UTC)[reply]

"It is difficult to get a man to understand something, when his salary depends upon his not understanding it!" - Upton Sinclair, American writer. Wikiquote. Carbon Caryatid (talk) 17:22, 5 December 2016 (UTC)[reply]

Fishing spider in the house

I found a fishing spider in my kitchen. We imported some of these in the house as stowaways on the Christmas tree a few years ago, but I'm guessing they live in the garden or on the outside walls as I rarely see them, and this one could've got in while the balcony door was open. I suppose it might have come in to protect itself from the cold (it's 0 to -5 C outside and 14 C in the kitchen). I can't find much info about this species, aside from guessing that it won't be eating much here, considering it feeds on passing insects. Do you think it'll have better chances of survival outside? FWIW I'm pretty sure it's a female as it's the biggest one I've ever seen. 93.142.67.37 (talk) 22:28, 3 December 2016 (UTC)[reply]

I know next to nothing about this spider, but I believe that in general, animals behave in a way that is best for them. Of course they sometimes will not, but that is the basis of natural selection. We could start a debate about the morals and ethics of "interfering" with wildlife, but if you have no objection to her presence in your residence, I would just leave her alone. DrChrissy ^(talk) 22:45, 3 December 2016 (UTC)[reply]

Alright, thanks. I like spiders anyway, I'm just afraid that she might starve here. I'm going to leave a window cracked open overnight in case she decides she doesn't like it here. 93.142.67.37 (talk) 00:10, 4 December 2016 (UTC)[reply]

I like spiders too. I rarely brush away their cobwebs in my flat and I am always amazed they manage to find food here. Maybe one of our entemological friends can tell us how much/frequently they need to feed on. The open window sounds like a great idea. DrChrissy ^(talk) 00:30, 4 December 2016 (UTC)[reply]

It may be better to relocate spiders back outside to ensure that they might at least have a chance of producing their own progeny. A modern home, may offer a few prime spidery [des res] locations. Yet, if the food is not there they die within months. One only has to look around a bachelor pad (whose owner is lackadaisical when it comes to using a feather duster) that there are not many spidery des res locations in a house ( in comparison with a garden). So if one see a spider, where one saw one the year before, it is probably a different spider that’s moved in to occupy that exact same spot. A UV florescent dye is available that can be applied to such small critters with a artists paint brush to identified them as individuals, (up and till the time they moult that is). Got no references to hand but I think they only moult once a year unless they are getting lots to eat and I think they can only survive months without any subsidence in a dry, heated environment. The UV dye will also make it easier to locate the shrivelled up remains, that air currents may cast into a dark and dusty corner; post-mortem. Some ecologists have argued ( and me thinks convincingly) that the abundant wild life around the Chernobyl nuclear plant is not evidence of wild life thriving there and producing their own progeny but rather shows that as soon as an ecological niche becomes vacant, due to the failure of the indigenous species successfully breed , wildlife from outside the area quickly move in to fill the emptying niche . So, one may be ignorantly allowing ones home to become a place of solitude and slow starvation by inaction as I don't think an open window will provide a sufficient hint.--Aspro (talk) 18:38, 4 December 2016 (UTC)[reply]

Well, we stopped cleaning up spiderwebs several years back and since then we've had far less problems with colds and allergies, not to mention less flies and mosquitoes, so I think they've got to be eating something after all. Also, the tree incident happened three years ago and I had never seen a fishing spider before that in my life, so I think this is likely one of the spiders that arrived then or their offspring, and not a random neighborhood spider who wandered inside. 93.142.67.37 (talk) 19:20, 4 December 2016 (UTC)[reply]

Personal observations are important and valuable, yet one must be remain aware that this was not a controlled trial and so other factors could be at work here. Glad to hear you're suffering less colds and allergies and in modern draft proofed homes, leaving a window is important in this respect. Especially, if you're cohabiting with young children, which are well known to be very productive virus factories. Cold viruses just love draft free, dry, oxygen deficient environments which causes their hosts mucous membranes to dry out. So continue to keep a window or two open. Not high fan-lights, as they let the hotter air out but the lower ones. An ioniser is also cheap to run and settles both dust and other allergy inducing flotsam an' jetsam that floats around in the air. --Aspro (talk) 20:12, 4 December 2016 (UTC)[reply]

It's probably not going to end up like this case. Count Iblis (talk) 01:16, 4 December 2016 (UTC)[reply]

I've just done a quick search of how often spiders eat. I came across this article[6] which states they (of course there will be species differences) eat 2,000 insects/year. I am really surprised by how high this is as it represents 5.5 insects/day! The other possibility is that she moved in to hibernate - see here[7]. DrChrissy ^(talk) 20:35, 4 December 2016 (UTC)[reply]

Could be, I haven't seen her since last night. Although, it says here that immature adults hibernate, but this one had a leg span well over 5 cm. 93.142.67.37 (talk) 00:21, 5 December 2016 (UTC)[reply]

December 4

Erroneous Recycling

Many types of paper or plastic may appear recyclable to a non-specialist, but are actually technically or legally not recyclable in any given locality, e.g., pizza boxes, styrofoam, paper towels and napkins, granola/candy bar wrappers, etc. If someone deposits one of those items in the recycling can, what generally happens? Is there a huge contamination risk for the recycling facility? Assuming there are human sorters they might fish those items out, but perhaps not 100%... Bottom line -- how big of a problem is it if someone tries to recycle these "non-recyclable" items? --208.58.213.72 (talk) 05:34, 4 December 2016 (UTC)[reply]

I'm not sure, but I'd think the contamination would be relatively minor (unless this is really widespread), given the sheer volume of waste to be recycled. Also, regarding food scraps and such, they would probably tend to be chemically degraded during the paper recycling process (which uses harsh chemicals) and to burn up during plactics recycling (which involves high temperatures). FWIW 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 08:54, 4 December 2016 (UTC)[reply]

I believe recycling centers typically pour items to be recycled out on a large conveyor belt, where people pick out items that can't be recycled, and separate the items that can be recycled into categories, perhaps also using devices such as magnets. StuRat (talk) 15:30, 4 December 2016 (UTC)[reply]

There numerous Internet sites where recyclable items are listed and discussed. For instance here[8]. --AboutFace 22 (talk) 22:45, 4 December 2016 (UTC)[reply]

Thanks, all. However, the issue is not *which types* of items are recyclable, but what happens if someone (inadvertently or not) breaks the rules and non-recyclable items get into the recycling process inadvertently (if they are not spotted or removed by human or mechanical sorters). Thanks.--208.58.213.72 (talk) 03:11, 6 December 2016 (UTC)[reply]

Running crack

Is it possible, in principle, to dissolve cocaine in automotive gasoline, and then to recover it for street sale? Is a near-quantitative recovery possible, or would the process involve unacceptable losses? Would the recovered crack be fit for illicit consumption (note not for medical use), or would there be toxic impurities left which would make it completely unmarketable? 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 09:02, 4 December 2016 (UTC)[reply]

Wikipedia is not in the business of encouraging criminal activity. ←Baseball Bugs ^{What's up, Doc?} carrots→ 09:15, 4 December 2016 (UTC)[reply]

In case you didn't check out my second link, I'm asking this as a James Bond fan, not as a prospective drug runner! 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 11:15, 4 December 2016 (UTC)[reply]

Googling the subject briefly, here is an article that discusses the production of cocaine, which includes dissolving the stuff in gasoline or kerosene. So it sounds like it could work. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:00, 4 December 2016 (UTC)[reply]

All right, so Franz Sanchez can get his $500M worth of crack dissolved in four truckloads of gasoline -- but the question is, could he get it back again (in an alternative timeline where 007 doesn't get all of the stuff burned up along with Sanchez himself, of course)? Just from looking at the properties of cocaine, liquid-liquid extraction with an aqueous solution of e.g. hydrochloric acid might work -- but the question is, (1) would the losses be within acceptable limits (mainly a question of economics), and (2) would there be toxic chemicals from gasoline left in the drug to the point that it would be unfit for sale? 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 12:41, 4 December 2016 (UTC)[reply]

The reason "why" you are asking is not actually a valid defense against the rules of the ref desk, or Wikipedia for that matter. "Can you answer this question that sounds like medial advice, but I'm just curious"? for example. If it sounds like a duck and looks like a duck, the policy still applies. I am not in a position to do a policy search right now but it is against Wikipedia policy to detail how to perform illegal activities and detailed recipes for illicit substances. Having said that, I don't think this particular question crosses that line, simply asking IF it is possible is not really doing anything to encourage or enable it. Vespine (talk) 23:52, 4 December 2016 (UTC)[reply]

There is no such policy - indeed, I actually asked [9]. Preserving ignorance is not our mandate, so when we don't know of any plan to commit a crime that would make us worry about conspiracy prosecution, there's no obstacle. Wnt (talk) 03:18, 5 December 2016 (UTC)[reply]

I'm sure I saw a policy about how much information should be included in our articles about nuclear weapons and recipes for high explosives. Vespine (talk) 03:45, 5 December 2016 (UTC)[reply]

Have you read our articles on nuclear weapons? They're pretty nice. We really don't know how information will be used - odds are, the first person who goes looking through our archives to see if there can be coke in the gas tank will be a nark trying to crack a smuggling ring. I feel bad about that, but not enough to stop talking about fun science. Wnt (talk) 03:55, 5 December 2016 (UTC)[reply]

Yes I have, they're among my fav articles, but they're very "high level", they don't go into details, I'm certain I read somewhere that this was not an accident. I'll see if I can dig it up, this certainly isn't really the place to be debating this. I thought there 'was' a general consensus that detailed recipes for things like high explosives would not be kept on Wikipedia, I might be wrong. Vespine (talk) 21:48, 5 December 2016 (UTC)[reply]

Wikipedia is not supposed to be censored for content. However, too much detail could run afoul of the axiom that Wikipedia is not a "how-to" source. As for making explosives, if the information has a valid source, then it's already public knowledge. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:53, 5 December 2016 (UTC)[reply]

It's not an "axiom", it's a style guideline for how to write an article (I assume you mean WP:NOTHOWTO). Which tells us not to write an article about chocolate chip cookies by saying to mix in the chips and set the oven to 375 degrees. We're not addressing the reader as "you" and giving him commands; we should say "Chocolate chip cookies are typically made at 350 to 425 degrees^[1][2][3]" and give him three recipes to look at instead! The guideline doesn't say anything against telling people to do that on the Refdesk.

As for ethics, well, I come from a country that elected someone based on his promise to torture people, who called up the butcher of Davao to congratulate him for doing it "the right way",^[10] so pardon me if I have a decreasing patience for appeals to my ethics in general, let alone ethics implacably and openly opposed to the stated goal of "Imagine a world in which every single person on the planet is given free access to the sum of all human knowledge." which brought me to the project in the first place. Wnt (talk) 22:54, 5 December 2016 (UTC)[reply]

Our new president promised to torture terrorists, not people -- do you not know the difference, or do you not care?! 2601:646:8E01:7E0B:99F8:B355:9D57:7021 (talk) 02:07, 6 December 2016 (UTC)[reply]

Yes, that's the one. And, yes, more of a suggestion than an axiom. Ethics figure into it when someone tries to give professional advice, which no one here is qualified to do. As for Trump and his "mandate", Hillary got a lot more popular votes than Donald did, but he got the right states. I share your concerns about that, for sure. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:51, 5 December 2016 (UTC)[reply]

Gasoline by definition is made up of volatile hydrocarbons, so in theory anything dissolved in it can be dried out. Cross-border shipping can involve a markup of 100% or more, depending on the border, so it can make financial sense. The interesting part of the question i.e. the part I don't know the answer to is whether cocaine in gasoline will cause trouble with the car. It doesn't seem that different from gasoline components, I suppose -- with the exception of the nitrogen, which makes it an alkaloid. Looking at [11] it appears nitrogen doesn't play that nicely with internal combustion engines. Going through Customs sputtering a thick trail of smoke that drives all the drug hounds wild would not be a tactical move, though it might make for a great movie scene. OTOH there are mechanics who can do marvellous, even miraculous things with an engine, and as I said, I actually have no idea. Wnt (talk) 03:10, 5 December 2016 (UTC)[reply]

Presumably it's in barrels, not in the gas tank. Otherwise you'd be burning away your profits as you drive. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:12, 5 December 2016 (UTC)[reply]

I was thinking more along the lines of a tanker truck, like in these videos. 2601:646:8E01:7E0B:99F8:B355:9D57:7021 (talk) 08:19, 5 December 2016 (UTC)[reply]

Clarification: note this section is appropriately titled - you can dissolve crack cocaine in gasoline, as it is a free base (uncharged), but powder cocaine (cocaine HCl) would not dissolve in an organic solvent (except, perhaps, with a phase transfer catalyst...).

And this may also be a way to recover it afterward -- simply reconvert it back to the chloride salt, and out of the gasoline it goes straight into the aqueous phase! 2601:646:8E01:7E0B:99F8:B355:9D57:7021 (talk) 02:11, 6 December 2016 (UTC)[reply]

Reflection of light when momentum is transferred

I'm aware of the law that the angle of incidence equals the angle of reflection. However, since some momentum is transferred when light hits a mirror, I was wondering, is this quite true? Of course, in common experience the momentum transferred to the mirror by light is undetectable, but it is there, and if there is some transfer of momentum to the mirror in a direction perpendicular to the normal of the mirror, the angle of reflection should be subtly different to the angle of incidence.--Leon (talk) 10:15, 4 December 2016 (UTC)[reply]

Yes, the angle will change - this is a fairly simple treatment of the problem. For an initially stationary (ν = 0) but low-mass mirror, we can drop the second term (rather than the third) in Equation 6 - derivation of the rest of the calculations is left as an exercise for the reader. Tevildo (talk) 20:26, 4 December 2016 (UTC)[reply]

Whether the angle changes depends on your choice of reference frame. Assuming an instantaneous pulse and a perfectly elastic collision (as Tevildo's source does), wrt the most symmetric frame, the incident and reflected angles are the same. (Also, the frame-independent spacetime angles are the same.) With respect to any other frame, the angles are given by the aberration formula, and will be different in general. The most symmetric frame is the one where the mirror is moving at the same speed in opposite directions before and after the collision.

The derivation in Tevildo's source is more complicated than necessary because it doesn't use the symmetric frame. (The author is aware of that, though, and links some earlier articles that presumably do use an easier derivation.) -- BenRG (talk) 23:51, 5 December 2016 (UTC)[reply]

no information on the bond energies of a pi bond (ALONE), separate from the C=C sigma bond?

Why doesn't our article comment on the bond energies of the C=C pi bond (separate from the sigma bond)? I only ask this because I am drafting tutoring notes and I want to give my students a ballpark figure. Am I correct to guess that a pi bond in say ethylene is around 50 kcal/mol? Yanping Nora Soong (talk) 18:00, 4 December 2016 (UTC)[reply]

This article in J. Chem Ed looks promising. --Jayron 32 14:15, 5 December 2016 (UTC)[reply]

You could use diatomic C₂ (:C=C: with ground state ¹
Σ⁺
_g) to gauge this, since if you draw the MO diagram you'll find that σ and σ* are both fully occupied and the net bond order of two comes only from the π bonds. But do note that strange cases like this are not representative because the presence of a σ bond prevents the π bond from having its optimal bond length, which tends to "want" to be shorter than that of the σ bond between the same two atoms: see this article. The cohesive energy of gaseous C₂ is 609 kJ/mol (two π bonds), not far from that of a "normal" C=C bond at 614 kJ/mol (one σ and one π bond) according to Wikipedia. Double sharp (talk) 15:01, 5 December 2016 (UTC)[reply]

There is a paragraph in pi bond that begins "Pi bonds are usually weaker than sigma bonds." It includes an orbital-overlap explanation but not a quantitative comparison. Later in that article is additional content about the difference of alkane vs alkene (the "ene" detail adding less strength than was present with just the "ane"), and the confounding ideas of differing preferred length/etc that Double sharp notes. The JChemEd article Jayron notes seems at a quick glance to base some pi-strength calculations on cis/trans isomerization kinetics, which relies on the well-disputed idea that such a process involves breaking the pi bond (with the two atoms retaining sp2 nature but rotating their respective planes compared to each other)--see doi:10.1021/ed082p1329. I think our pi bond article needs updating for that! DMacks (talk) 00:44, 6 December 2016 (UTC)[reply]

What large cheap vessel to use for a chloroform vapour bath?

I would like to use a chloroform vapour bath to smooth some tall parts that I intend to 3D print. The pieces will be 33 cm tall. I can get a PP bucket and lid at a resonable price but the Cole Palmer website says PP will perform adequately although it will be attacked while two other websites suggest it will be unacceptable. Could the bucket be coated with anything cheap? I want to use this container many times and although the container won't be full of liquid chloroform there will be paper towels lining the walls soaked with chloroform. Thanks for any suggestions. ----Seans Potato Business 18:14, 4 December 2016 (UTC)[reply]

I'm naturally lazy, so I would first try lining it with some cheap Jumbo Size Turkey Roasting Bags being nylon they should be resistant to chloroform and more than large enough to contain said object. But why consider just a bucket. The local scrap yard may have many a 5 gallon drum or other metal container where chloroform attack is not going to be a problem. P.S. Doing this in a well ventilated area means doing it outside in the open air. Not only is the vapor explosive but it can bring on cardiac arrest.--Aspro (talk) 19:28, 4 December 2016 (UTC)[reply]

While there are obvious health hazards associated with chloroform use (likely carcinogen, and if you can smell the vapor you're likely over the airborne concentration permitted in the workplace), chloroform – as liquid or vapor – is not flammable or explosive. If you expose it to flame or high heat, it can produce some nasty decomposition products, though. Please be sure you're familiar with all the hazards associated with this chemical (and also the appropriate, safe, legal methods for disposal of chlorinated solvents) before using chloroform.

Most important, please don't trust random individuals on the Ref Desk to provide you with safety training or advice; unfortunately, there are a few regulars here who give very confident and assertive advice without actually knowing what they're talking about. Start with the appropriate safety data sheet (several are linked from Chloroform (data page)). TenOfAllTrades(talk) 19:53, 4 December 2016 (UTC)[reply]

TenOfAllTrades as always give good advice not to take what we say here as gospel and to seek qualified advice. His own utterance give proof to this when he sates as liquid or vapor – is not flammable or explosive. Using analytical quality chloroform perhaps, according to the data sheets he quotes. But we don't know the grade/quality nor contaminates in the OP's work place which can cause a chloroform fuelled explosion, so one should always consider it to be potentially explosive. “However, the addition of small amounts, of any flammable compound or an increase in oxygen content will make chloroform flammable.” So now the OP has some advice from just not any old editor to do it out in the open unless he a has qualified staff and a fully equipped lab, and obviously, should he have such a lab, equipped with a fume cupboard, he would'nt need to be asking this question here.--Aspro (talk) 20:49, 4 December 2016 (UTC)[reply]

It ought to go without saying that stuff to which you've added other, different stuff isn't quite the same stuff as stuff without the other added stuff. It's certainly true that someone unaware of that principle shouldn't go near chemistry...or the kitchen. TenOfAllTrades(talk) 01:07, 5 December 2016 (UTC)[reply]

I tried "chloroform vapor bath" and "chloroform vapour bath" through Google and found a total of four hits - one here - two of which say in the snippet it's 61 degrees C. So I have to ask... where is the original source or reference for this idea? Maybe you have some other process in mind, like chloroform vapor polishing, which turns up just a few hits; there are apparently a lot of other kinds of vapor polishing. The most familiar meeting of chloroform and polypropylene to me is in the Eppendorf tube, a kind of centrifuge tube. See [12] - the polymer will definitely resist, but the plasticizer of this anonymous bucket may not be built according to Eppendorf's standard for tubes they know people will do their plasmid minipreps in. There are apparently some issues with certain metals like magnesium and aluminum also though. [13] Wnt (talk) 03:39, 5 December 2016 (UTC)[reply]

December 5

What is the difference between these two glycines?

I saw these two illustrations in the article Glycine: and I don't understand what are the differences between these two structures. If it's the same molecule why they are different while using skeletal structure?

93.126.88.30 (talk) 00:07, 5 December 2016 (UTC)[reply]

Zwitterion. TenOfAllTrades(talk) 01:08, 5 December 2016 (UTC)[reply]

Thank you. I know what is zwitterion but I'm not talking about the plus and minus signs that make it zwitterion. I am talking about the structure. It says that there are here TWO types of skeletal structure with different positions with different number of elements (H3N vs.NH2) 93.126.88.30 (talk) 02:11, 5 December 2016 (UTC)[reply]

There's not a different number of elements. The H3N+ (or NH3+, if you want to more easily compare to NH2) is just the amine group protonated with a hydrogen. What had been a COOH is now a COO-, as it lost a hydrogen when it was deprotonated. The skeletal structure doesn't appear any different either. The second structure is merely rotated about 45 degrees clockwise from the first structure in space, but the connectivity is identical. It's as if you picked up the entire physical molecule, rotated it, and set it down. The central carbon is still SP2 hybridized. The only difference is, as TenOfAllTrades said, that the second structure is the zwitterion form. --OuroborosCobra (talk) 03:21, 5 December 2016 (UTC)[reply]

The neutral and zwitterionic forms are tautomers. The only difference is the location of one of the protons.

Your "variant 1" is the neutral form that is often quoted for simplicity, even though it actually won't occur at standard conditions: any pH high enough to deprotonate the –NH₃⁺ group to –NH₂ will also deprotonate the –COOH group to –COO⁻. At biological pH, the amine is protonated and the carboxylic acid is deprotonated, giving your "variant 2". Double sharp (talk) 03:28, 5 December 2016 (UTC)[reply]

There is no chemical meaning for which side of the N the H are written ("H₂" on the right of the N in variant 1 vs "H₃" on the left of the N in variant 2). In both cases, and as always for condensed formula details, "adjacency implies connectivity". The bond from the implicit carbon of the CH₂ group goes to the N specifically, so the nitrogen is obviously bonded to that carbon. The 2 or 3 H are written condensed and adjacent to the N, so they are bonded to it. The N has tetrahedral geometry regardless, so there is not an "H2" or "H3" group, nor are the set of N–H bonds all going in any one direction. DMacks (talk) 06:16, 5 December 2016 (UTC)[reply]

Reducing the waiting period to donate blood after male-male sex - practical impact?

Here in Australia, the rules state that a male cannot donate blood for a full 12 months after engaging in anal sex with another male. Many have argued that such a long period is unnecessary - it could be reduced to three months with no risk (feel free to disagree if I've somehow got the science wrong). The "window period" for modern HIV tests is never longer than that, as far as I am aware, and in many cases is shorter.

two questions:

1. Less important question: Would there be any safety risk to the blood supply in terms of avoiding HIV transmission, by reducing the exclusion period after male-male sex from twelve months to three?

2. This is my more important question: How much would such a move practically increase the donor pool? I would assume that the majority of men who have anal sex with men (I avoid the term "gay", as not all such men would identify with the title) would generally not do so on a one-off, or only once a year. Men who engage in this activity would, in general, I assume, tend to do so on a regular basis (i.e. significantly more frequently than once every three months). I know many answers here will be speculative, but I still believe it's a fair question: How many men are excluded by a one-year exclusion period, who would not be excluded by a three month exclusion period? How much of an impact would such a move have on donor numbers and blood stocks? Would it be significant at all? Or would it be trivial, making any rule change have little practical impact?

I don't think any of the answers to this question would potentially fall into the "medical advice" prohibition, as those who make the rules on these matters are at zero risk of taking advice from wikipedia! And the second question is not really a "medical" one in any case. Eliyohub (talk) 09:57, 5 December 2016 (UTC)[reply]

According to the UK's blood service, the 12-month window is to do with Hepatitis B rather than HIV - see the "Why a 12 months deferral?" section here. AndrewWTaylor (talk) 10:08, 5 December 2016 (UTC)[reply]

Hardly a reason - we've had vaccination against Hepatitis B available for many years now. Assuring a donor's vaccination is up to date, no need to defer them at all due to Hepatitis B - they're at near-zero risk. Besides, the reference you provided only says it takes up to 12 months to clear the virus. The window period to potential detection is far shorter, up to six weeks. In addition, if a person tests positive to Hepatitis B "surface antibodies", it indicates that not only are they free of the virus, they are immune (either due to vaccination, or recovery from past infection) Eliyohub (talk) 10:47, 5 December 2016 (UTC)[reply]

It's my impression that when these policies were first drawn up, it was surmised that there were other bloodborne diseases (like "non-A, non-B hepatitis", i.e. mostly hepatitis C) which were not understood, and there was some thinking that there were other unknown risks being addressed. Mixed, of course, with a certain amount of prejudice. There are some other curiosities that have emerged since like GB virus C that may justify a certain amount of ongoing paranoia, though one hopes that the number of diseases circulating undetected is falling. In general the blood banking system needs to think about both known and unknown threats - that said, there may well be different specific criteria to use that secure against them more effectively. Wnt (talk) 11:02, 5 December 2016 (UTC)[reply]

(EC) I found [14] which I think is the most recent review of the behavioural based donor deferral criteria in NZ. It mentions a 6 month deferral was considered but rejected based on what was felt was insufficient evidence that it wouldn't increase the risk. It also mentions other things like why more detailed sexual history (e.g. condom usage) was rejected (again insufficient evidence and what limited evidence there was caused concern as well as concern over whether such questions may be too invasive), why oral sex is included, etc. One thing it does mention is that the older 5 year period was at least partially due to concern over new TTIs. However it doesn't sound like the 12 month period was based on that.

I make no comment on the decisions and accuracy of the information contained in the report, except to note that it says the maximum window period is for hepatitis C which is 94 days. While it doesn't seem there's good evidence sexual activity is a strong risk for hepatitis C infections (except for certain co-occuring infections), since there is some limited evidence it may be the case that a conservative risk assessment would consider 3 months too short. The report does mention that in addition to the window period + margin of error for the test just in case, there is also concern over making the margin of error too short in case people don't remember correctly. Note it would seem easily possibly relying on people to remember if they've been properly (including all courses) remember if they've been vaccinated against Hepatitis B would raise similar concerns although I'm not sure if this arises since it doesn't seem Hepatitis B has the worst window period, e.g. Human T-lymphotropic virus 1 also has a longer window period.

Also the report makes it sound like in some countries (but not NZ anymore) there may be concern over a failure to remove a sample with a positive test result (quarantine failures/release errors). While improving systems to prevent this would be the primary goal, in the mean time reducing detected infections (by removing riskier individuals) may also be implemented to reduce the risk of TTIs, and this was evidently part of the reason for the old 5 year deferral.. Finally the report does mention 6 months was recommended by the blood service in Australia but rejected by the TGF. It is also was implemented in Japan and maybe elsewhere (I didn't look that well). I suspect you can probably find some info on why the TGA rejected the 6 month deferral. It also seems likely that if research in those countries where 6 months was adopted suggests it didn't result in an increase in TTIs, this would be then spread, as the report and other things I've read suggest this is what happened with 12 months.

Nil Einne (talk) 14:38, 5 December 2016 (UTC)[reply]

[15] is the TGA's decision rejecting the 6 month proposal. Nil Einne (talk) 14:45, 5 December 2016 (UTC)[reply]

In the US, ever having had an active case of viral hepatitis permanently excludes one from donating blood. Part of the justification is that a small percentage of infections never clear but have a viral load that persists indefinitely at a low concentration. Of these, a small percentage have traces of a hepatitis virus (usually HBV) but no longer produce sufficient antigens or antibodies to be detectable during a standard blood screen. Dragons flight (talk) 14:06, 5 December 2016 (UTC)[reply]

I've just seen that we have an article on the subject, and also that the 12-month rule is being reviewed in the UK. AndrewWTaylor (talk) 14:22, 5 December 2016 (UTC)[reply]

From men who have sex with men, at least 2.9% of US men (age 15 to 44) had sexual activity with another man in the previous 12 months. [2.9% is the self-reported frequency, the authors believe that such activity is unreported due to perceived bias.] I don't think it is controversial to suggest that most people who have sex try to do so frequently, so much of that 2.9% are probably going to excluded by any choice of waiting period. I would guess that moving from a 12-month wait to a 3-month wait probably wouldn't increase the potential donor pool more than ~1%. Dragons flight (talk) 15:26, 5 December 2016 (UTC)[reply]

Cheeses, Murray and Joseph! I am HIV and Hep A, B, & C, negative, as well as negative for Syphilis, Gonnorhea, and Chlamydia. But I have still been told never to donate blood, given I have had three full transfusions. We do NOT give medical advice, please read WP:DISCLAIMER and then go elsewhere, like to a physician! μηδείς (talk) 04:33, 6 December 2016 (UTC)[reply]

None of the above is medical advice, μηδείς, It's a response to questions about medical regulations and the medical theories and knowledge surrounding them. There is no suggestion whatever that anybody either is or is not going to undergo or avoid any medical procedure as a result of it. {The poster formerly known as 87.81.230.195} 176.248.159.54 (talk) 04:56, 6 December 2016 (UTC)[reply]

Why are mitochondria called "mitochondria"?

I understand—from both the Wikipedia article and the Wiktionary article—that the word mitochondrion is constructed from the classical Greek for "thread" and "granule." My question is, why thread and granule rather than, say, potato and tennis racket?

I can guess that a mitochondrion's gross morphology may have stricken its discoverer(s) as particularly discrete and grain-like. I can also speculate that its strands of DNA may have stood out to the microscopically aided eye. But I know better than to trust my guesswork on a matter about which I am so far from expert.

Could someone please illuminate? And to clarify, although I do welcome guesses better educated than mine, what I'd really love is an authoritative explanation of what actually did inspire the namer, rather than merely what might plausibly have done so.—PaulTanenbaum (talk) 14:08, 5 December 2016 (UTC)[reply]

Read this. --Jayron 32 14:13, 5 December 2016 (UTC)[reply]

(ec) See Carl Benda: 'Because of their tendency to form long chains, he coined the name mitochondria'. AndrewWTaylor (talk) 14:17, 5 December 2016 (UTC)[reply]

Wow, in a mere 5 minutes I got exactly what I'd requested. Thanks!—PaulTanenbaum (talk) 14:28, 5 December 2016 (UTC)[reply]

Is that claim proved scientifically?

I saw this video which is viral on Facebook and it claims that the way that people sit on the lavatory seat is not correct and not healthy and the correct way is like animals or as people used to do in the past (read the titles on the video). My question is if it's proved scientifically or it is nonsense? 93.126.88.30 (talk) 15:43, 5 December 2016 (UTC)[reply]

There is some evidence that squatting reduces the amount of straining needed, but at the same time, it's also more difficult than sitting which seems to counteract the benefit. This study, for instance, actually finds squatting seems to increase stroke risk, and advises that at risk of stroke avoid it. Smurrayinchester 16:09, 5 December 2016 (UTC)[reply]

We have an article on this at Defecation postures, but it isn't a very good article.

There is also a video on this on youtube that I found to be hilarious.[16] Also see [17]

But enough of the silliness. What do the sources say?

"Conclusion: The results of the present study suggest that the greater the hip flexion achieved by squatting, the straighter the rectoanal canal will be, and accordingly, less strain will be required for defecation." --Influence of Body Position on Defecation in Humans (Full text here:[18])
"The patients were instructed to defecate using two types of toilet: an unraised, ground-level style (common in Iran), and a bowl with attached tank style (common in Western countries) ... Use of the Iranian-style toilet yielded a much wider anorectal angle, and a larger distance between the perineum and the horizontal plane of the pelvic floor than the European style. Bowel evacuation was also more complete using the Iranian-style toilet" --Impact of ethnic habits on defecographic measurements
"The magnitude of straining during habitual bowel emptying in a sitting posture is at least three-fold more than in a squatting posture and upon urge. The latter defecation posture is typical of latrine pit users in underdeveloped nations. The bowels of Western man are subjected to lifelong excessive pressures which result in protrusions of mucosa through the bowel wall at points of least resistance." --Etiology and pathogenesis of diverticulosis coli: a new approach.
"In conclusion, the present study confirmed that sensation of satisfactory bowel emptying in sitting defecation posture necessitates excessive expulsive effort compared to the squatting posture." --Comparison of Straining During Defecation in Three Positions: Results and Implications for Human Health (Full text here:[19])
"Cardio-vascular events at defecation are to a considerable degree the consequence of an unnatural (for a human being) seating defecation posture on a common toilet bowl or bed pan. The excessive straining expressed in intensively repeated Valsalva Maneuvers ... adversely affecting the cardio-vascular system is the causative factor of defecation syncope and death. The squatting defecation posture is associated with reduced amounts of straining and may prevent many of these tragic cases." --Cardio-vascular events at defecation: are they unavoidable?
"A considerable proportion of the population with normal bowel movement frequency has difficulty emptying their bowels, the principal cause of which is the obstructive nature of the recto-anal angle and its association with the sitting posture normally used in defecation. The only natural defecation posture for a human being is squatting. The alignment of the recto-anal angle associated with squatting permits smooth bowel elimination. This prevents excessive straining with the potential for resultant damage to the recto-anal region and, possibly, to the colon and other organs." --Primary constipation: an underlying mechanism.
"Our result clearly shows that modified commode squatting posture has the highest success rate for the treatment of chronic anal fissure." --Role of defecation postures on the outcome of chronic anal fissure

On the other hand, see the comment above mine for a study on blood pressure in hypertensives during squatting. Also, I can't help but wonder whether it makes a difference whether you squat with a toilet seat supporting your body, as seen in the squatty potty video above, or whether you support your weight with your legs/feet, as is don in Japan. --Guy Macon (talk) 18:16, 5 December 2016 (UTC)[reply]

Arachidyl Alcohol

Arachidyl alcohol page isn't clear on this. Is this substance always derived from groundnut (peanut) oil? And if so, can it cause an allergic response in someone who has a peanut allergy? --TammyMoet (talk) 17:09, 5 December 2016 (UTC)[reply]

Regarding the second question: that would depend on whether or not the person was specifically allergic to this compound. The source of a pure compound makes no difference. It would only cause an allergic reaction in one of two cases: 1) if a person were specifically allergic to this compound or 2) if the compound was laced with impurities that the person WAS allergic to. This article lists the specific molecules that are known to trigger peanut allergies. Arachidyl alcohol is not listed there, they are mostly all proteins. --Jayron 32 18:34, 5 December 2016 (UTC)[reply]

Thank you Jayron that's actually really useful. --TammyMoet (talk) 18:43, 5 December 2016 (UTC)[reply]

Fire safety

request for medical advice

The following discussion has been closed. Please do not modify it.

If the door's hot it's often said to tell the fire department where you are then seal cracks with wet towels. And breathe near the floor and through a wet towel if need be.

Would floating in a cool bathtub further increase the time before injury or death if the firemen take longer than average? Taking trash bag(s) of good air with you and only opening them to breathe? (exhale inside or outside the bag?) Holding your breath after you run out of air below a certain level of smokiness and hope they get there before you have to breathe again? What's the best breathing strategy? How smoky should the air become before holding your breath as long as you can becomes the best strategy? Sagittarian Milky Way (talk) 19:15, 5 December 2016 (UTC)[reply]

The bathtub? Probably not helpful. Most fire deaths are due to smoke inhalation. Trash bags? An interesting idea. I would favor exhaling into the room. You could try doing an experiment with ten bags (to account for the logistics of moving multiple bags of air around) and reporting how long the air lasted. Original research, of course, but I for one would be interested in the answer. How far could you crawl along a smoky hallway using one or two trashbags of air? If you wanted to prepare ahead of time you might consider getting the clothing and breathing gear that firefighters use. --Guy Macon (talk) 20:06, 5 December 2016 (UTC)[reply]

Definitely exhale INSIDE the trashbag, you only consume a fraction of the oxygen from the air in each breath. Air is about 20% oxygen, exhaled air is about 15% oxygen, you can inhale and exhale a bag of air several times before you deplete ALL the oxygen. Vespine (talk) 21:39, 5 December 2016 (UTC)[reply]

How hard is it to tell how close you are to depletion? The above seems risky, because the user may not realize that they are about to deplete all the oxygen and then start inhaling CO, which does not seem likely to have a good result. Also, we should clearly indicate that Wikipedia and its contributors disclaim any responsibility for the results of the proposed techniques described in this thread. Do not try these techniques at home! --03:17, 6 December 2016 (UTC) — Preceding unsigned comment added by 208.58.213.72 (talk)

Smoke hood might be a useful article here (although, unfortunately, it doesn't go into much quantitative detail). Tevildo (talk) 22:12, 5 December 2016 (UTC)[reply]

With all the caveats of NOT TRYING THIS AT HOME! I think you would pass out before you die if you keep inhaling and exhaling into a bag, I don't think you could "keep" breathing into the bag until you die. Unless you stuck your head IN the bag which would definitely be a terrible idea. Vespine (talk) 03:43, 6 December 2016 (UTC)[reply]

Plastic garbage bags would melt if anywhere near heat, and catch fire if near flames. However, if you were in an area with smoke but no fire, that might work. I've myself thought if using a scuba tank in a bathtub. Hopefully that would allow you to survive, unless the building collapses (and even then, a bathtub full of water might offer some protection, say if it falls through the floor). StuRat (talk) 03:43, 6 December 2016 (UTC)[reply]

Ginkgo fruit yield

How much fruit does a mature Ginkgo biloba produce in one season? Surtsicna (talk) 22:08, 5 December 2016 (UTC)[reply]

“

The seed of G. biloba contains a thin-layer nut, which is consumed as food and a medicine throughout the world. Fresh nuts contain about 41% moisture. Dry nuts contain 6% sucrose, 68% starch, 13% protein and 3% fat [27]. The commercial production of Ginkgo nuts has been reported in China for more than 600 years. About 44 cultivars with best performance in growth have been selected, based on quality, size and shape of their nuts and productivity [2] and [28]. These cultivars are propagated by grafting technique using seedling rootstocks. These grafted plants start bearing nuts after 5 years of age. In China, a widely grown cultivar, Dafushon, in Jiangsu Province, produces 5 to 10 kg of nuts by a 15 year old tree and between 50 to 100 kg by a 50 year old tree. One recent production from 700,000 to 800,000 trees produced an average of 6000–7000 tons of dry nuts per year [2].

”

Emphasis mine, from here [20]. That article doesn't clarify if that's a fresh or dry weight, but the cited source probably does. In my experience dry weight is what is usually reported in scientific contexts. Note also that wild types and cultivars not designed specifically for seed production will probably make less seeds, and they can take 20-30 years to mature, a fact stated earlier in the same article. SemanticMantis (talk) 22:19, 5 December 2016 (UTC)[reply]

Within 10 minutes! I had been searching for an hour. Thank you! Surtsicna (talk) 22:37, 5 December 2016 (UTC)[reply]

You're welcome! There are probably other estimates out there, this should be good enough for most casual usage. (It did take me several searches on Google Scholar. I think it was /Gingkgo seed production/ that worked, but part of it was being familiar enough with the literature to know that at least some estimate would certainly be there :) SemanticMantis (talk) 22:43, 5 December 2016 (UTC)[reply]

I am tempted to say "too much" but as a New Yorker, I would compare the yield to a non-cultivated Krabapple or cherry. No one would grow the plant for human consumption. μηδείς (talk) 04:19, 6 December 2016 (UTC)[reply]

December 6