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June 7

Logarithm of a dimensioned quantity

From Moment magnitude scale:

$M_{\mathrm {w} }$ is a dimensionless number defined by Hiroo Kanamori as

$M_{\mathrm {w} }={\frac {2}{3}}\log _{10}(M_{0})-10.7,$

where $M_{0}$ is the seismic moment in dyne⋅cm (10⁻⁷ N⋅m).

How does it make sense to take the logarithm of a dimensioned quantity and end up with a dimensionless one? 86.171.42.219 (talk) 00:19, 7 June 2016 (UTC)

It makes sense in three cases. The first case is when you are looking not at the value of the logarithm, but at the changes (differences) of that value as a function of something else. For example, a logarithm of signal power is not very useful, but a change in a logarithm of signal power is a measure of the signal attenuation, see decibel. Indeed, difference of logarithms is the same as a logarithm of a ratio, and a ratio of two values of the same quantity (e.g. power) is dimensionless. The second case is when you have a scale, or a fixed standard unit, of a quantity that you take a logarithm of; as in your own example above. In that case you are really taking a logarithm not of a dimensional quantity, but of that quantity divided by that standard unit, which in your case is (10⁻⁷ N⋅m). --Dr Dima (talk) 01:10, 7 June 2016 (UTC) Oops I forgot explain the third case. The third case is when an additive constant is unimportant. For example, entropy is a logarithm of the number of microscopic states availavle to the system at or near its total energy value. "At or near" means that you count the states within a certain (small) energy range, so it is a dimensional quantity, depending on how narrow this energy range is. However, this multiplicative factor of the number of available states becomes an additive constant once you take a logarithm; and that additive constant is not important as it does not affect any of the thermodynamical propoerties of the system. Hope this helps. --Dr Dima (talk) 01:16, 7 June 2016 (UTC)

Thanks. Do you mean to say that "$M_{0}$ is the seismic moment in dyne⋅cm" does not mean that $M_{0}$ is a dimensioned quantity, having units of dyne⋅cm, but is a dimensionless quantity because it has been divided by the reference level of 1 dyne⋅cm? That would make sense with the logarithm (like in decibels), but that is not, to me, what it seems to say. 86.171.42.219 (talk) 01:51, 7 June 2016 (UTC)

Yes, that sort of usage "in dyne⋅cm" means that the variable itself is considered dimensionless. --69.159.60.83 (talk) 05:37, 7 June 2016 (UTC)

I will note that other logarithms of quantities are dimensionless; for example pH is the negative logarithm of H⁺ concentration. Concentration has a measurement of mol/L, but pH is dimensionless. In chemistry, the way that this is worked around is that some measurements are specifically defined as relationships of Thermodynamic activity, which is a) defined as unitless and b) quite literally not directly measurable, so impossible to determine directly. Concentration is used as a sort of "surrogate measurement" in calculations involving the impossible-to-measure concept of "activity", such as both pH and equilibrium constant. So, we say that pH is the negative logarithm of activity, which is unitless but unmeasurable, and so we use molar concentration as a "stand in" for the calculation, since we can measure that, and at low enough concentrations, activity and concentration are proportional anyways. I'm not sure how this works with moment magnitude, but that's the sort of hand-waving we use in chemistry. --Jayron32 05:41, 7 June 2016 (UTC)

Personally, I would tend to write:

$M_{\mathrm {w} }={\frac {2}{3}}\log _{10}\left({M_{0} \over 1\,{\text{dyne-cm}}}\right)-10.7$

or even:

$M_{\mathrm {w} }={\frac {2}{3}}\log _{10}\left({M_{0} \over 10^{16.05}\,{\text{dyne-cm}}}\right)={\frac {2}{3}}\log _{10}\left({M_{0} \over 10^{9.05}\,{\text{N-m}}}\right)$

Which are all ways to describe the moment magnitude, if one treats $M_{0}$ as a dimensioned quantity rather than treating it as dimensionless. However, it isn't uncommon to see formulas presented in such a way that you are expected to take some variable as its dimensionless value in some units (especially in engineering), but personally I find those presentations rather annoying and suboptimal. Dragons flight (talk) 06:27, 7 June 2016 (UTC)

In physics, one doesn't specify in which units quantities have to be filled in in a formula. As long as one uses the basic units of a consistent system of units, the result comes out of the formula in basic units of the same system, whether that be SI or cgs or any other system. Imperial or American customary units are not so consistent, so that becomes very messy and those are avoided in science. If there is a logarithm in the formula, one has to make sure one takes the logarithm of a dimensionless quantity. If it's not dimensionless already, one has to divide by some constant of the same dimensions to make it dimensionless. For sound levels, one divides by a standard flux of $10^{-12}\mathrm {W} /\mathrm {m} ^{2}=10^{-9}\mathrm {erg} /\mathrm {cm} ^{2}$ to calculate decibels, for stellar magnitudes one divides by the flux of Vega. From a theoretical point of view it would make more sense to use some constant of nature, but that's not always practical.

In this case, the explanation going along with the formula suggests a particular unit. This is an implicit way of stating that one should divide by a standard quantity equal to unity when expressed in this particular unit. I would write:

$M_{\mathrm {w} }={\frac {2}{3}}\log _{10}\left({\frac {M_{0}}{M_{\mathrm {std} }}}\right)-10.7$

with $M_{\mathrm {std} }=1\,\mathrm {dyne} \cdot \mathrm {cm} =10^{-7}\,\mathrm {N} \cdot \mathrm {m} =0.08856\,\mathrm {firkin} \cdot \mathrm {furlong} ^{2}/\mathrm {fortnight} ^{2}$ a standard seismic moment. Or I could absorb the 10.7 term into the logarithm and use a different standard moment:

$M_{\mathrm {w} }={\frac {2}{3}}\log _{10}\left({\frac {M_{0}}{M_{\mathrm {std} }^{\prime }}}\right)$

with $M_{\mathrm {std} }^{\prime }=1.122\cdot 10^{16}\,\mathrm {dyne} \cdot \mathrm {cm} =1.122\cdot 10^{9}\,\mathrm {N} \cdot \mathrm {m} =9.937\cdot 10^{14}\,\mathrm {fir} \cdot \mathrm {fur} ^{2}/\mathrm {ftn} ^{2}=0.5736\,E_{\mathrm {Planck} }$. That's not a nice value in any system (although it's quite close to unity on the Planck scale), but that quantity was chosen to keep close to an earlier seismic scale, developed before seismic moments were properly understood. PiusImpavidus (talk) 10:58, 7 June 2016 (UTC)

Unless anyone can cite Hiroo Kanamori calling $M_{\mathrm {w} }$ dimensionless the gentleman is being misrepresented, because it does not make sense at all. AllBestFaith (talk) 11:32, 7 June 2016 (UTC)

It looks like the original author didn't worry about units - you see that surprisingly often; many people just want to plug numbers into formulas without thinking about them as carrying units with them. What gets interesting is that I would think you can actually carry unit analysis into the realm of logarithms (even though that article explicitly states that they are undefined!) For example, you might say (assuming base 10 for the moment) that log (10 N m) = 1 + log N + log m. You could write something like log m = 2 + log cm or log N = log kg + log m - 2 log s, I think. In which case we could "fix" the above formula by adding "- log N - log m" at the end of it. Note: don't do this! Use Dragons flight's second formula instead, as it has the minor advantage of being sane. But you should be able to, I think. Wnt (talk) 12:58, 7 June 2016 (UTC)

Is "10 N m" really 10 multiplied by "N" multiplied by "m"? Anyway, I find it hard to see what meaning could be ascribed to "1 + log N + log m"! 86.171.42.219 (talk) 21:57, 7 June 2016 (UTC)

I would say yes, at least in the sense that if you keep track of them you can tot them all up to 0. Now to come up with a meaning for a value of "2 + log m" on its own would be harder; yet it seems like it would be a dead giveaway that your pre-log value should have been divided by some reference value - in meters. I suppose it means it's 100 relative to the comparable exponent value for 1 meter. Wnt (talk) 00:11, 8 June 2016 (UTC)

Yes, you can think of N and m as constants equal to the ratios between those units and the "true units" (Planck units, if you like, but it doesn't matter). Then log m is simply the logarithm of the ratio, and represents a shift of the zero point from "true zero". It's not common, but there's nothing insane about it; it's an internally consistent approach. -- BenRG (talk) 02:28, 8 June 2016 (UTC)

Rate of genetic similarities

Modern academia put the DNA similarity between humans and chimps at 95%-99%, as per Human_evolution#Evidence_from_molecular_biology. And in cats, for example, it's reportedly a whooping 90% of homologous genes shared with humans. That seems quite high, as at around 90% of genetic similarities I'd expect some stronger resemblance, such as between modern humans and Neanderthals, and in cats I'd expect around 65-70%. Is it some sort of non-coding DNA that is not responsible for morphological and physiological features? Brandmeister^talk 14:02, 7 June 2016 (UTC)

All the studies make lots of suppositions - including the ones that a "minor difference" is, in fact, of little concern, and that all species have similar rates of change in DNA as their similar species have. Also, the fact is that their is apparently quite substantial variability within human DNA - vide the recent studies that a significant proportion of modern human DNA is likely inherited from "extinct pre-Homo Sapiens species". (Many people appear to have up to about 4% Neanderthal DNA, many have up to about 5% Denisovan DNA, and there is a really good chance that several other "extinct species" also have DNA found in modern human populations, and totally dwarfing the chimp DNA position). Using an analog - the difference between the Davenport electric car's "MNA (Motor Nucleic Acid)" and the Tesla Model S's MNA is extremely small indeed. Yet one might find it not that difficult to spot differences. Collect (talk) 14:20, 7 June 2016 (UTC)

• The genes that make up our appearance are only a small fraction of the total genome. Most of the enzymes and structural proteins are largely similar between all mammals, and in some cases all species. And are cats and humans really that different? Two eyes, four limbs, same internal organs etc. We have about 24% genetic homology with grapes.... (many other species here) Fgf10 (talk) 15:06, 7 June 2016 (UTC)

Trying to spell that out a little more: so many genes have to do with biochemical machinery, and this machinery is/has been broadly conserved via stabilizing selection. How to cells transport things? How do cells metabolize? Then there are many genes that have ontogenetic roles and are related to tissue and organ formation. But cats have skin, and fat, and muscle, and hair... and though those things are a little different in cats, they have most of the same tissue types and organs that work in mostly the same way. Also, homology is not identity. Finally, OP may be interested in reading up on Evolutionary_developmental_biology, aka "Evo-devo", a field that makes much of the similarities (and differences) between a fetal human and a fetal cat. SemanticMantis (talk) 15:24, 7 June 2016 (UTC)

This appears to be a handy overview of nearly all differences between cats and humans, from skeletal system to muscular, nervous, digestive, etc. If the 90% assertion on human similarity is true, are the remaining 10% able to encode all those anatomical and physiological differences? Brandmeister^talk 21:02, 7 June 2016 (UTC)

Hey that's a pretty cool slide set- thanks! My understanding is that there are two sources of differences between a cat and human. One source is that 10% of genes that occur in humans but have no analog in cats. But the other source is that the genes we "share" are not 100% identical, they are merely homologous forms. So while cats and humans have many similar genes, a given shared gene will not be identical. See here [1] for some specific examples of how homologous genes are similar different. I'm not sure which of these sources is more responsible for the differences, nor to if that question even makes sense. Also consider that by this reckoning, you and I have 100% of our genes (i.e. loci) in common, yet we have differences, due to having different alleles. I'm now past my point of expertise. Perhaps User:Fgf10 or User:Wnt can expand on this or tell me if I said anything incorrect :) SemanticMantis (talk) 15:12, 8 June 2016 (UTC)

That is a cool slide set. But it's worth adding that while "the" human and "the" cat are different, individuals may be less so. A particular human may lack a vermiform appendix, or have the left common carotid artery arise somewhere other than the aorta, thus resembling the case for the cat. But of course, all this anatomy is very roughly 100 times more ancient than the unique features of modern human beings. The truth is, we still have no idea what features make humans so unusual in their behavior, nor is any existing theory truly sufficient to rule out qualia in a rock or a computer keyboard, let alone a cat. Wnt (talk) 22:02, 8 June 2016 (UTC)

Surnames dying out

I think we have an article on this, if I could only remember what it is called. In a society where family names descend by patrilineality, at some point rarer names will die out, because sooner or later all the children in a given generation will be girls, and will not pass the name on to their children. (Ignore sexism, single mothers, and volitional name changes - this is a thought experiment.) The model that shows how this works can be applied to other things transmitted by descent such as genes. Am I mis-remembering? What is this phenomenon called, and what application does it have in current research of any fields? Carbon Caryatid (talk) 17:36, 7 June 2016 (UTC)

Galton–Watson process. --Jayron32 17:44, 7 June 2016 (UTC)

Elementary, my dear Galton! Thanks. Carbon Caryatid (talk) 18:21, 7 June 2016 (UTC)

Colloquially called "daughtering-out". - Nunh-huh 00:21, 8 June 2016 (UTC)

Does this mean that eventually everyone will be named Smith? ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:50, 7 June 2016 (UTC)

I'm Brian! DMacks (talk) 18:57, 7 June 2016 (UTC)

No. Read sections 2 and 3 of the linked article, which give conditions for extinction of a name. Note that extinction in finite time is always possible, so persistence of a name for all time is necessarily a probabilistic notion. As explained in the "examples" section, real-world names seldom conform exactly to this model. And if one name was likely to increase while others diminish, smart money is on Wáng/Wong over Smith, which is actually a fairly uncommon name. SemanticMantis (talk) 19:41, 7 June 2016 (UTC)

Smith is the most common surname in America, though obviously there are a lot more Chinese than Americans. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:52, 8 June 2016 (UTC)

The article Y-chromosomal Adam says we are all patrilineally descended from a common male ancestor who lived 200,000 to 300,000 years ago. So equating the Y chromsome lineage to surnames, this implies that all other surnames that coexisted with his died out at some point (with no changing of surnames allowed). Is that right? (Also the same applies to Mitochondrial Eve). Loraof (talk) 21:27, 7 June 2016 (UTC)

That common ancestor lived hundreds of thousands of years before there were surnames. But no other man with a Y-chromosome at that time has any male descendants alive with that chromosome. - Nunh-huh 00:20, 8 June 2016 (UTC)

Sure, and in that case, the other haplogroups/surnames had a positive chance for extinction in finite time. The fact that they did die out doesn't mean they had to, and none of this means we should a priori expect one surname to eventually exclude the others. It's always possible for everyone not named Hernandez to die tomorrow, right? So we cannot ever say with certainty that a haplogroup/surname will persist indefinitely. Under the model assumptions, we can sometimes say that a given lineage will almost surely go extinct. SemanticMantis (talk) 15:02, 8 June 2016 (UTC)

What is the term for stoppage or accumulation of blood in the lower part of the body?

What is the term for stoppage or accumulation of blood or fluid in the lower part of the body or other organs? (under influence of gravity. for example by bad blood circulation or even after death). There is a word that should start with the prefix hypo-xxx 93.126.88.30 (talk) 20:07, 7 June 2016 (UTC)

After death: Livor mortis. --NorwegianBlue ^talk 20:15, 7 June 2016 (UTC)

Indeed, it is hypostasis as mentioned in the article that you linked. Thank you! 93.126.88.30 (talk) 20:34, 7 June 2016 (UTC)

Edema is accumulation of fluid (mostly water). It's commonly in the lower part of the body, due to gravity, in people who are upright most of the day. For those who are bedridden, the accumulation may be more towards the back, depending to the position of the patient. It's common to rotate the patient to even it out. Compression stockings are used to limit accumulation in the feet, but unless they have a graduated reduction in compression near the top, the patient can get the "muffin top" effect where all the accumulation pools right above the stockings. Phlebitis, an inflamation of the veins, often in the legs, is also related. StuRat (talk) 17:14, 8 June 2016 (UTC)

You might also look at Ascites. DrChrissy ^(talk) 17:25, 8 June 2016 (UTC)

I thought I might find it in g-suit but it's not there. DrChrissy ^(talk) 17:23, 8 June 2016 (UTC)

Wacom share holding stock

Would you buy a piece of the company? Is it worth - or did they stopped to built interesting things and the company was years ago more interesting for investment? --Ip80.123 (talk) 23:53, 7 June 2016 (UTC)

The Refdesk doesn't give advice, especially not professional advice. It also doesn't make unsourced predictions, especially when assuming a perfect market the existing price would be assumed to approximate the best rational estimate, within some unknown and doubtless financially interesting margin of error. If you go to Humanities and ask where to look up stock predictions they might help you though. Wnt (talk) 00:14, 8 June 2016 (UTC)

Here's some general advice about the stock market, from Will Rogers: "Buy only good stock. Wait till the price goes up, then sell it. If it don't go up... don't buy it!" ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:38, 8 June 2016 (UTC)

June 8

Minimum spring outer diameter for a given wire diameter

Is there a formula, table, or some sort of back-of-the-envelop approximation for calculating the minimum spring outer diameter for a given wire diameter?

Let's say the spring wire diameter is 1 mm. A 5 mm outer diameter spring is possible given this wire size; but a 4 mm outer diameter spring would not be possible. Thus the minimum spring outer diameter is somewhere between 4 mm and 5 mm. How do I go about calculating or approximating this minimum outer diameter? Johnson&Johnson&Son (talk) 07:34, 8 June 2016 (UTC)

Yes. I use a slide rule for this. It's a specialised slide rule, given away some time in the 1970s as a design aid by a spring winding factory. If you talk to any spring maker, they will help you out with this - either with a table in their catalogue, a simple spreadsheet or computer program, or maybe even a slide rule. Andy Dingley (talk) 11:39, 8 June 2016 (UTC)

Wikipedia articles are Coil spring and Spring (device). Here is an American spring catalog search site which converts inch measurements to mm. The extended search for extension springs made of 1.0414 mm diameter wire finds minimum outer diameter 5.9436 mm in stock. AllBestFaith (talk) 13:21, 8 June 2016 (UTC)

Talk to a manufacturer. Bear in mind they are talking about what is easy to make on their standard machines, so far as I know an ID of almost zero would work as a spring, but would be very hard to make (3d print it but that will have horrid material properties compared with spring steel). Now, the usual equations won't work, you'd need to FEA it or do some hard maths. The fatigue life, in particular, is likely to be horrific, as the most central fibre is almost in tension and compression. Greglocock (talk) 02:35, 9 June 2016 (UTC)

I talked to a manufacturer and that's where they told me that for a 1 mm diameter wire, 5 mm OD was feasible but 4 mm OD wasn't. They weren't able to tell me exactly what the minimum was, other than "somewhere between 4 mm and 5 mm“. Johnson&Johnson&Son (talk) 10:07, 9 June 2016 (UTC)

There's a minimum interior diameter because otherwise the strain becomes excessive.

This is one reason for the use of Belleville washers, rather than coil springs. Andy Dingley (talk) 11:04, 9 June 2016 (UTC)

Question about sperm temperature

A mans nutsack is on the outside of the body because sperm die if they are too hot, right? Otherwise they'd be kept safe inside his body instead of dangling dangerously outside. So how come when he puts his sperm inside the womans belly to make her pregnant the sperm don't die from the internal heat of the woman? (I assume men and women measure the same temperature?)

Basically how come the sperm die at body temperature inside the man, but don't die inside the woman? 200.94.21.194 (talk) 18:42, 8 June 2016 (UTC)

It's not that sperm die at body temperature; it's that spermatogenesis doesn't work as well. Sperm also travel through the male's body during ejaculation (note: NSFW images in article), so even before entering the vagina they already encounter higher temperatures. (Also, "nutsack"? Maybe use "testicles" on the science desk?) --71.110.8.102 (talk) 22:04, 8 June 2016 (UTC)

Maybe the OP was talking about this kind of thing. And speaking of "spilling seed", the OP should be advised that the methods illustrated in that secnd article are unlikely to result in impregnation. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:29, 8 June 2016 (UTC)

Très amusante, except that those are not nuts. Richard Avery (talk) 06:38, 9 June 2016 (UTC)

That's OK, this is even more illustrative. ←Baseball Bugs ^{What's up, Doc?} carrots→ 06:44, 9 June 2016 (UTC)

This is an interesting one - I'll need more time to figure it out, if I ever do. There are forum postings available via [2] and [3] that shed some light. It is noted that elephants are "primary testicond" animals, i.e. that have never had testes descend. This is somehow used to try to claim that they evolved for aquatic life ... even though they never evolved to have a scrotum in the first place ... [4] I would like to see more evidence of basal "primary testicond" mammals before I try to impose any sense on that, but in any case the testicles are definitely way up inside, like ovaries -- see [5]. So it is not impossible to produce sperm inside the body. But is it more difficult? So far the most appealing of the speculations at those forums I saw was the notion that since sperm are highly specialized, stripped-down cells, they need to damp down their metabolism to live longer, i.e. by being cooler. But I have no idea if that has any truth to it. Wnt (talk) 14:46, 9 June 2016 (UTC)

I'm not sure what you're saying about the elephant exactly. What you linked says the same thing as other sources: elephants have internal testes because they're descended from aquatic ancestors. Aquatic mammals have internal testes to reduce drag. Mammals with internal testes cool them below body temperature using blood vessels that bring cool blood from the skin. --71.110.8.102 (talk) 15:31, 9 June 2016 (UTC)

I often wonder why lists/discussions of mammals with internal testicles miss out the Hyrax. This small lagamorph-sized animal tends to rule out that internal testes might be due to some animal-size/thermoregulation issue. I have often wondered why, if some mammals can reproduce successfully with internal testes, do not all mammals have internal testes. After all, I would have thought the selection pressure on catching your scrotum on a branch would have been very high given that a split scrotum would likely reduce your fitness to zero. DrChrissy ^(talk) 16:49, 9 June 2016 (UTC)

Well, a hyrax is more or less an elephant, at the level of generalization we're using (they're both Afrotheria). Hyraxes have body temperature 35 to 37 C [6] and our article on elephant says they're 36 C, so both are just a little cooler than humans (but don't tell them that). And at least the Testicles article only talks about special cooling in aquatic mammals that have re-evolved internal testes, not in these guys. Plus, birds endure even hotter body temperatures with internal testes. The rhinoceros is another one of the primary testiconds (but within Boreoeutheria), and they have body temperature of 100 F [7]. So it seems like we might have to cast our gaze elsewhere, like basal mutation rate ... sigh, what are the odds I can find the basal mutation rate of a rhinoceros...? Well, I'll be -- found something pretty close, anyway, here: [8] They actually represent one of the slower-varying clades, as is Xenarthra, another primary testicond. But humans are also slow. I'm thinking lifespan may be a confounder here, but at first blush I have to say, I'm not buying the idea that internal testicles impose some huge mutation burden. Wnt (talk) 19:56, 9 June 2016 (UTC)

Sperm competition can shed some light on why many/some mammals have a sort of Red Queen's Race going on with testicle size/sperm output, and external testes may be part of that. But sexual selection and and cultural/behavioral stuff also clouds this for anything but the most solitary of species. Also evolution of anisogamy is a distant symmetry breaker that I think has shaped a lot of this evolution. SemanticMantis (talk) 15:00, 10 June 2016 (UTC)

Baby spiders

I recall reading back in the '80s in The Encyclopedia of Igorance (eds: Ronald Duncan, Miranda Weston-Smith) about an experiment involving baby spiders with results that could not be explained by known mechanisms. The experiment was simple: hatch spiders in a controlled environment, devoid of any food or water source. Soon their mass and volume will greatly increase (I forget the stats) -- it was (is?) unknown how they were able to create the complex molecules presumably from "thin air". --Has this since been explained? ~107.15.152.93 (talk) 20:04, 8 June 2016 (UTC)

I don't know about that study, but I remember reading that some baby spiders catch pollen and dust on their webs, and that can sustain them. Graeme Bartlett (talk) 22:34, 8 June 2016 (UTC)

Spider cannibalism both of the mother and of fellow hatchlings ([9]) can be a factor, so I would be suspicious that the experiment did not take an accurate count of the number of spiders at beginning and end. Wnt (talk) 14:50, 9 June 2016 (UTC)

How does capillary phenomena play a role in eye irrigation and nosebleeds?

1) I have read the following phrase in the book "Nano-Surface Chemistry" (p.289) "Capillary phenomena are also essential in tribology and in many biological systems, such as blood circulation and eye irrigation". How does it plays role in eye irrigation? 2) In a English-Spanish I've read: "Nosebleeds are caused by the rupture of a small blood vessel called a capillary in the nose." Is there any relation between the capillary phenomena to the rupture or to the mechanical going of the blood outside? 93.126.88.30 (talk) 23:37, 8 June 2016 (UTC)

The word "capillary" originally meant "pertaining to the hair" ([10]). Capillary blood vessels were so named because they are very thin, like hair. Very thin glass tubes are also called capillary tubes for the same reason. Capillary phenomena or capillary action is the tendency for liquid to flow into narrow spaces, first noticed in glass capillary tubes. So capillary action is not really related to capillary blood vessels except that they both come from the same root word. CodeTalker (talk) 02:00, 9 June 2016 (UTC)

But I saw many sources (except of this that I've already brought) which claims that capillary phenomena does relate to blood circulation. What is the explanation? 93.126.88.30 (talk) 11:28, 9 June 2016 (UTC)

As mentioned above, capillary action occurs in many situations, but if your "many sources" claim that it is the main cause of blood flow in capillary blood vessels, then there's something wrong. Dbfirs 09:40, 10 June 2016 (UTC)

As for the first question, tears form a thin film on the eyeball when they're dragged across by the eyelids. The various components of tears play a role in maintaining this film, and the physics are somewhat complex. The film is essential so tears coat the whole eye and don't evaporate away quickly. --71.110.8.102 (talk) 03:29, 9 June 2016 (UTC)

Elements 119-120

Now that official names of elements 113-118 have been proposed to become standard, can anyone find out what's going on with elements 119 and 120 (the elements of the next row of the s-block)?? By the end of 2016 some of the labs should start working on trying to create these elements whatever way they can. Georgia guy (talk) 23:43, 8 June 2016 (UTC)

The story so far is at ununennium and unbinilium. I imagine that now that 113–118 have IUPAC approval (despite having failed miserably at guessing the names that weren't revealed well in advance), the labs will indeed make another push for 119 and 120. Whether they will work is another story! Double sharp (talk) 12:18, 9 June 2016 (UTC)

Does human body have a surfactant in another place in the body except of in the lungs?

or it is the only one surfactant in the body? 93.126.88.30 (talk) 23:49, 8 June 2016 (UTC)

I expect there are many, and many compounds will have some surfactant behaviour even if it's not their primary function. One obvious one leaps out though, and that's bile, which emulsifies fats as part of the digestive process. Andy Dingley (talk) 01:11, 9 June 2016 (UTC)

How about the cell membrane of every cell in the body? EdChem (talk) 14:51, 9 June 2016 (UTC)

June 9

Is there a relation between capillary action and capillary blood vessels?

Kindly I would like to get sources for the answer. 93.126.88.30 (talk) 16:21, 9 June 2016 (UTC)

Read capillary and capillary action. The word "capillary" itself refers to hair, i.e. a fine strand of something. ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:25, 9 June 2016 (UTC)

There is not a direct relationship because the blood does not depend on capillary action to make it flow. The blood flow is caused by vascular pressure from the heart and is regulated in the capillary by the Bayliss effect. AllBestFaith (talk) 23:38, 9 June 2016 (UTC)

Corporate culture in emergency services

In general, do emergency services personnel and frontline healthcare staff feel like corporate slaves? Are there any studies on this? 2A02:C7D:B965:D700:E0F6:67A9:FE9A:3BD (talk) 16:39, 9 June 2016 (UTC)

Clarify what you mean by "slaves". No one is being forced to work there. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:33, 9 June 2016 (UTC)

Are you unfamiliar with the term "wage slavery"? OP is using the term in a related, metaphorical manner. Also, the phrase "feel like" is not usually used as a synonym for "is a literal example of". SemanticMantis (talk) 19:34, 9 June 2016 (UTC)

Here [11] [12] [13] [14] are a selection of studies regarding some mix of mental health, job satisfaction and stress of emergency services personnel. The last one, on ambulance personnel, finds that

“ Approximately a third of the sample reported high levels of general psychopathology, burnout and posttraumatic symptoms. Burnout was associated with less job satisfaction, longer time in service, less recovery time between incidents, and more frequent exposure to incidents. ”

Hope that helps, SemanticMantis (talk) 19:34, 9 June 2016 (UTC)

Measuring strike on ball. with simple devices

If I connect a pressure gauge to a football ball and kick it, measuring the added pressure (gauge goes up to 100 psi) how can I convert this to force? — Preceding unsigned comment added by 212.163.6.23 (talk) 18:52, 9 June 2016 (UTC)

Alternatively: could I attach the ball with a cord to a post kick it and see how many times it spins around the post? It would be like a Tetherball, but at floor level. — Preceding unsigned comment added by 212.163.6.23 (talk) 18:55, 9 June 2016 (UTC)

See the table at the bottom of our force article, and decide exactly what it is you want to measure. "Strike" isn't a term used in mechanics, but there's force, impulse (force * time), momentum (mass * velocity), kinetic energy, and more esoteric things like jerk (d³x/dt³) and action. All such quantities are measurable (directly or indirectly), but we'll need to know which one you're interested in before we can tell you how to measure it. Tevildo (talk) 22:13, 9 June 2016 (UTC)

Measuring the change in pressure only allows you to calculate the change in volume because by Boyle's law the pressure is inversely proportional to the volume. However more information is needed about the geometry of the deformation of the football, and the elasticity of its material, before you can calculate the mechanical force of the kick. Consider instead kicking the ball straight up and having an observer record the height it reaches $h$. Then you know the energy imparted by your kick is the ball's potential energy $mgh,$ where $m$ is in kg, $g$ is 9.81 and $h$ is in metres, plus some unaccounted loss to air resistance. AllBestFaith (talk) 23:26, 9 June 2016 (UTC)

Scientific principles in engineering

Could you argue that the basic scientific principle in all the engineering disciplines are the same? 2A02:C7D:B965:D700:4058:E3A:59C2:BE6D (talk) 19:48, 9 June 2016 (UTC)

Tempting to say yes, but in practice electrical engineering is mostly concerned with stuff where Newton's laws aren't much help, whereas they are fundamental to mechanical engineering. Not too sure about the lookup table merchants, I assume they sometimes use some physics. Greglocock (talk) 00:18, 10 June 2016 (UTC)

"lookup table merchants"- I assume that's a vaguely insulting phrase for a type of engineer but I can't figure out which one? Anyway, the scientific principles are the same, even if some engineers don't use them. It's not like Newton's laws fail to work for electrical engineers :) SemanticMantis (talk) 14:55, 10 June 2016 (UTC)

Electronic engineering, I would imagine. Historically, electronic systems were adjusted (a process commonly known as "calibration", but see below) using trimmers and similar mechanical devices: today, they're built with fixed components, and the various settings required on the system to give the correct outputs for a given set of inputs are stored on the device in a lookup table. Our coverage of the issue is surprisingly thin - our article Calibration only covers calibration sensu strictu, the measurement of a parameter against a traceable standard; Adjustment (disambiguation) suggests that adjustment is the same thing as calibration, which it ain't. Tevildo (talk) 19:13, 10 June 2016 (UTC)

Lookup table merchant=Any type of engineering where the analysis is entirely defined by a set of codes typically with step by step procedures written down as well. Not electronic engineering. Incidentally SemanticMantis, obviously the laws of the universe still apply, that was probably the most redundant answer I have ever seen.Greglocock (talk) 23:13, 10 June 2016 (UTC)

I would suggest reading What Engineers Know and How They Know It (the whole book, not the wiki article). Unsurprisingly it's a series of essays on topics which engineers know something about, and how they came to know this. The chapter on flush riveting though is, surprisingly, riveting. Andy Dingley (talk) 20:02, 10 June 2016 (UTC)

June 10

What chewing gums supply urea for healthy teeth?

I read that urea is used to give sugar-free chewing gum its texture and also that urea in gum is good for the teeth. Then, I looked at all the different kinds of gum I have at home, and none of them lists "urea" or "carbamide" on the list of ingredients. Is urea found in all sugar-free gums (to provide texture) or only in certain brands (to help reduce salivary pH)?174.131.42.212 (talk) 03:25, 10 June 2016 (UTC)

I can't identify a chewing gum brand but note that US Patent no. 7595065 mentions urea and is assigned to Wrigley's. A Danish Committee reported that Urea is used in unspecified sugar-free chewing gum to adjust the texture but concluded use of urea at levels of up to 3% was of no toxicological concern. See also Effect of urea in sugar-free chewing gums on pH recovery in human dental plaque evaluated with three different methods. and The Effect of Chewing Urea-Containing Gum on Plaque Acidogenic and Alkaligenic Parameters. AllBestFaith (talk) 09:33, 10 June 2016 (UTC)

Civil engineering

Is civil engineering the engineering discipline which is most business like (spending more time managing stakeholders, considering costs etc) and less technical (calculation, solving scientific problems etc) ? 94.10.246.129 (talk) 20:05, 10 June 2016 (UTC)

It involves both, but is built on calculation and the application of solutions to technical problems. It's a wide field, of course: designers of structures are very much involved in calculation, to the extent that some of them have speciated into Structural Engineers. Cost remains an important consideration for designers, and designers must manage their stakeholders. Site engineers are very much more concerned with the efficient and proper applications of bricks & concrete to an a priori design and arguably their job involves greater stakeholder management and a strong strand of operational cost control. --Tagishsimon (talk) 20:29, 10 June 2016 (UTC)

Yes but is it more like this than for example, mechanical engineering or electrical or biomedical, where the main aim is to design and make a product? 2A02:C7D:B965:D700:F1C9:FB26:2235:BD09 (talk) 21:58, 10 June 2016 (UTC)

In general, yes, I suspect civil engineers tend to spend more time dealing directly with clients than other types of engineer do. However I can assure you that most automotive engineers think about cost rather a lot.Greglocock (talk) 23:52, 10 June 2016 (UTC)

So why is that because surely all engineers are developing products or solutions for clients? 2A02:C7D:B965:D700:6CE5:9C2C:E21A:EBB2 (talk) 12:44, 11 June 2016 (UTC)

This is completely ObPersonal and unreferenced, but my perception is that, to the extent it's true, it's because the clients of civil engineers, more often and to a greater extent than in other types of engineering, do not actually know what they really want or need. There ought to be a term for this. {The poster formerly known as 87.81.230.195} 5.66.223.127 (talk) 20:24, 11 June 2016 (UTC)

Could people get good at sports betting, or is it always gambling?

If someone analyzed scientifically some sport, could he predict results better than the average joe? Could sports betting be a game of ability? At least, this is not like lotteries or roulette where there is a randomizing factor, carefully chosen and audited to be truly random. --Llaanngg (talk) 20:42, 10 June 2016 (UTC)

Yes, it is possible to do better than the average Joe. It is even possible to do better than the average bettor (who is generally more knowledgable than the average guy on the street). However, bookmakers routinely have a margin, referred to as the vigorish, which is essentially their cut. For example, if you and I both bet $1 on a game using a bookie, the winner might get their $1 back plus $0.9 from the loser and the bookmaker keeps $0.10. In order to be profitable at sports gambling you have to be right with a high enough accuracy to overcome the losses due to the house's margin. The accuracy required varies by the sport, because the house margin varies by sport (generally sports regarded as less predictable have a higher margin for the bookmaker). As I recall, in basketball one needs to be on the right side of the over / under line roughly 54% of the time to be profitable over the long-term. That's actually pretty hard, but there are people like Jon Price, Zeljko Ranogajec, and Haralabos Voulgaris [15] that present themselves as professional sports gamblers and claim to have made money over the long-term. I think it is probably possible to predict sports well-enough to be profitable, though one might need to be very selective in one's bets and only bet on contests where you have a strong reason to believe the line offered by the bookie is not a good reflection of the true odds. Dragons flight (talk) 21:39, 10 June 2016 (UTC)

There is at least one Australian David Walsh (art collector) who is registered for tax as a gambler. Greglocock (talk) 23:18, 10 June 2016 (UTC)

Growing Bismuth crystals

What is the best way of growing nice looking Bismuth crystals starting from the metal in 'shot' form?--178.100.75.110 (talk) 23:30, 10 June 2016 (UTC)

Google and Youtube are covered in instructions for these. You could have saved yourself a wait by going direct. Richard Avery (talk) 07:33, 11 June 2016 (UTC)

@Richard Avery: We shouldn't be looking to defer to search engines. They may serve up several sites, but which is best? And will those searches remain usable, will those sites remain in operation? The goal is to bring back the information and integrate it here, just as we do for encyclopedia articles and for the same reason. Someday Google is going to start charging and a lot of the world will lose access, the people who don't matter anyway but still would like to know. Wnt (talk) 15:02, 11 June 2016 (UTC)

Best method? Practice.

Bismuth crystal growing is great fun and low complexity for equipment, but the crystals grow in liquid phase bismuth just where you can't see them. So there's an awful lot about learning the best growth profiles (timing) by repeated experiment, rather than observation.

I'd also suggest an Indian grocers as a source of handy stainless containers in a range of sizes. Then get enough bismuth to work easily with - it's annoying to try and grow them in a teaspoon. A small electric hotplate is useful, but as the thermal mass is high you only need rough power control, not necessarily closed loop control of temperature. A non-contact IR thermometer is cheap and useful though. If you fancy a small electronics project, then PID controller modules are cheap (China via eBay) and that will make you a handy workshop hotplate with temperature control. Andy Dingley (talk) 09:39, 11 June 2016 (UTC)

Maltese pavements

Why are they so slippery even when dry? What is the solution?--178.100.75.110 (talk) 23:33, 10 June 2016 (UTC)

I think some form of evidence is required. I'm only 69 years old but have never heard of that before. Richard Avery (talk) 07:35, 11 June 2016 (UTC)

Times of Malta has a number of letters about it and I have slippped on them myself.--178.100.75.110 (talk) 09:37, 11 June 2016 (UTC)

From what I recall, the pavements in Malta (just like most of the buildings) are made from local limestone. The limestone is relatively soft and tends to get polished with wear, which makes the pavements slippery, particularly when wet, although I've failed to find any good sources for this. I'm not sure what you can do to improve the situation, apart from wearing footwear with better grip. Mikenorton (talk) 12:44, 11 June 2016 (UTC)

Extraordinary, that must make a lot of Maltese cross. Richard Avery (talk) 18:19, 11 June 2016 (UTC)

June 11

Acid pump

Help! I'm looking for a compact, acid-resistant and not too expensive centrifugal pump for an experimental application, but I can't get a quote or even a comparison anywhere without having to enter the company name! I'm not actually affiliated with a company, but am doing the experiments on my own time (or planning to -- I can't get started until I get the pump) -- what should I do? 2601:646:A180:C88C:F88D:DE34:7772:8E5B (talk) 04:15, 11 June 2016 (UTC)

try aliexpress. I'd be more helpful but since your spec is virtually undefined (pH, head, flow rate, etc) then i won't be. Greglocock (talk) 04:38, 11 June 2016 (UTC)

Thanks! And here's the more detailed spec: I'm looking for a pump which can circulate small quantities (<1 L) of dilute phosphoric acid (10% or less) at VERY high pressures (head of 100 m or more). Oh, and it has to run on 60 Hz AC. 2601:646:A180:C88C:7465:D06A:8B2E:A8BD (talk) 04:45, 11 June 2016 (UTC)

I'd be looking at a food processing pump, 10% phosphoric is not scary, and your pressures are pretty trivial. I'd expect a peristaltic pump with silicone tubing would do. BUT. I am not a professional chemist. I have never specced a food industry pump in my life. http://www.welco.net/product/wp1000_1100/wp1000_1100_guide.html So if that is helpful, great, if not, oh well. Greglocock (talk) 05:17, 11 June 2016 (UTC)

That's helpful, but I'd strongly prefer a centrifugal or axial pump -- the downstream setup is a packed-bed reactor which I expect will routinely clog up (in fact, it will be set up for batch operation only due to the product forming a crust and blocking the flow), and in such a setup a positive-displacement pump of any sort could be positively dangerous. Also, if there are pumps which develop even higher pressures, I'd like to see them -- but if not, then 10 bar probably would do. 2601:646:A180:C88C:7465:D06A:8B2E:A8BD (talk) 05:52, 11 June 2016 (UTC)

On second thought, I've looked at the specs, and they do not specify the head -- but they do say the pump should be mounted no more than 2 m above the inlet. If this has to do with the pressure, then it follows that the working pressure is only 0.2 bar or so, and that will NOT do -- I need probably at least 10 bar (corresponding to a head of 100 m), maybe more. 2601:646:A180:C88C:7465:D06A:8B2E:A8BD (talk) 06:01, 11 June 2016 (UTC)

Don't confuse intake pressure and output pressure. http://www.shanleypump.com/corrosive_and_acids_resistant_centrifugal_pumps.html say. Greglocock (talk) 06:57, 11 June 2016 (UTC)

They have PRECISELY what I'm looking for! Thanks a million! Now I just hope I can afford it... 2601:646:A180:C88C:7465:D06A:8B2E:A8BD (talk) 08:22, 11 June 2016 (UTC)

You could try entering freelance or N/A in the company name field. Worst that's likely to happen is they'll ignore you because they don't think your worth dealing with. Nil Einne (talk) 06:31, 11 June 2016 (UTC)

*you're AllBestFaith (talk) 13:39, 11 June 2016 (UTC)

Given your concerns about clogging the downstream system, you'll want to check the pump's specs (or sales rep) about the risks of "deadheading" (running with outflow blocked). I assume you've already planned for a way to monitor and relieve pressure:) On additional concern for the intake pressure (or height above supply) relevant to centrifugal pumps is that (to quote our article) "Most centrifugal pumps are not self-priming." DMacks (talk) 10:09, 11 June 2016 (UTC)

Bubbles

What causes the sound of bubbles popping? JoshMuirWikipedia (talk) 11:01, 11 June 2016 (UTC)

The surface tension of the liquid slightly pressurizes the interior, and when the layer of liquid goes away suddenly, the gas in the interior expands rapidly with a "pop" sound. --Guy Macon (talk) 12:50, 11 June 2016 (UTC)

Is it the same thing for balloons? It just occurred to me something I heard a while ago about latex exceeding the sound barrier, though I'm not sure if I heard it right. Thanks for your answer though! JoshMuirWikipedia (talk) 13:28, 11 June 2016 (UTC)

This article may be interesting to you. For more detailed information see here The Quixotic Potato (talk) 17:27, 11 June 2016 (UTC)

Confusion about mumps and measles

Mumps and measles has different symptoms but causative virus is same for both. How? — Preceding unsigned comment added by Achyut Prashad Paudel (talk • contribs) 13:12, 11 June 2016 (UTC)

Measles is caused by the Measles virus. Mumps is caused by the Mumps virus. Still confused? AllBestFaith (talk) 13:28, 11 June 2016 (UTC)

Agreed. The measles virus and mumps virus are not the same. The MMR vaccine is a multi-vaccine mixture which vaccinates against both these and the rubella virus, but that's an accident of history, not a sign that they are the same causative agent. -- The Anome (talk)

International Journal of Advanced Research (IJAR), a credible journal?

International Journal of Advanced Research (IJAR) claims on its website to have an impact factor of 5+. www.journalijar.com/Journal website Is this journal reliable and acceptable in academic circles or is it a paid publishing journal? I am curious why this article clai?medly publishing about a new species of plant got published in this journal. Can somebody help? — Preceding unsigned comment added by 117.253.199.233 (talk) 14:17, 11 June 2016 (UTC)

WP:RSN is the best place for this sort of question, but my non-expert answer is "probably not" - see this forum posting. Note also that we do not have an article on the journal, and details of its publisher do not seem to be immediately available. Tevildo (talk) 15:36, 11 June 2016 (UTC)

The journal's subject matter is incredibly broad -- agriculture to psychology to astronomy and everything in between. This raises a huge red flag. Shock Brigade Harvester Boris (talk) 15:48, 11 June 2016 (UTC)

Agreed. The journal is also on Beall’s List of Predatory Publishers 2016[16] DrChrissy ^(talk) 16:22, 11 June 2016 (UTC)

"R^deloc" in a chemical formula

The compound [(R^delocSn)₄S₆](R^deloc=4–(CH2=CH)–C₆H₄) is mentioned at [17] and presumably [18] (though I don't presently have access). I assume there is some kind of electron delocalization implied there, but I've never seen this format and I don't know what it means. The illustration in the sci-news article doesn't even look like it has the phenyls the right way around (wait, no, I get that part now, the 4-(CH2=CH) is just another constituent, not the attachment site), but then again, how can I say that when I don't understand the formula? Wnt (talk) 14:53, 11 June 2016 (UTC)

Certainly an odd way to represent a 4-vinylphenyl substituted Sn atom with a Sn₄S₆ core. [(p-CH₂=CH-C₆H₄-Sn)₄S₆] would be clearer. EdChem (talk) 15:58, 11 June 2016 (UTC)

The underlying Science ref does indeed identify it as R^deloc as mentioned in the sci-news.com highlight. EdChem is correct on its meaning according to the 3D diagrams included in both links. As final confirmation, the supporting material for the Science article says the starting material is "Trichloro(4-vinylphenyl)tin (R^delocSnCl₃, R^deloc = 4-(CH₂=CH)-₆H₄)" and similar naming for the other related compounds they synthesized. DMacks (talk) 18:33, 11 June 2016 (UTC)

Checking Biophysics calculation of cardiogram

The question that I got is: What is the value of a point (1 mm square) horizontally in seconds or milliseconds if the recording speed of the cardiograph is 50 mm/s, 25 mm/s? My answer is: Each big square is equal to 5mm which are divided to 5 small squares of 1mm. and in calibration of 25mm/s it equals to 0.04 sec or 40 ms therefore: 40/5= 8ms. In calibration of 50mm/s we have to multiply the aforementioned value of 25mm/s and therefore it equals to 16ms. (8ms*2=16ms). My answer is correct? 93.126.88.30 (talk) 15:45, 11 June 2016 (UTC)

It's simpler than that. At 50 mm/s, one square is 1/50 = 0.02 s = 20 ms. At 25 mm/s, one square is 1/25 = 0.04 s = 40 ms. 25 mm/s is the standard speed - see Electrocardiograph. Tevildo (talk) 16:32, 11 June 2016 (UTC)

Claim that Pando (tree) is the oldest living organism

Some IP changed the text:

"The root system of Pando, at an estimated 80,000 years old, is among the oldest known living organisms."

to:

"The root system of Pando, at an estimated 80,000 years old, the oldest known living organism."

Is that true? I think the original version is better. The edit could not be undone due to conflicting intermediate edits; it has to be fixed manually.

TIME claims that the Posidonia sea grass meadow may be 100,000 years old! [19] The Quixotic Potato (talk) 16:02, 11 June 2016 (UTC)

Link for the sea grass meadow: Posidonia oceanica. clpo13_(talk) 16:06, 11 June 2016 (UTC)