Wikipedia:Reference desk/Archives/Science/2018 May 25

= May 25 =

Laurel-Yanny followup
There was a question recently about the "Laurel-Yanny" thing which has since been archived. This is a followup FYI: This guy, the voice behind the "Laurel-Yanny" thing, says the reason people are hearing different things is a result of different frequencies of their listening devices. ←Baseball Bugs What's up, Doc? carrots→ 05:37, 25 May 2018 (UTC)

Car engine = kW/hp calculation
What is the correct kW/hp or hp/kW for car engines??

I've seen some sources online saying

1kW = 1.3hp

1kW = 1.341hp

1hp - 0.74kW

1hp = 0.7476kW

and at Toyota_Celica I saw this:

77 kW / 103 hp

What is the correct calculation for hp-to-kW and kW-to-hp, especially for articles on vehicles sold in Australia, New Zealand and South Africa where kW is widely used?

I want to ensure things are accurate, but have no idea! --Chelston-temp-1 (talk) 12:25, 25 May 2018 (UTC)


 * For what it's worth, our article on horsepower shows the origin of several similar-but-not-identical figures, so at least you can see where the different conversion factors come from. I can't tell you which one is correct for your particular situation, mind you, but maybe that information can get you started in the right direction.... TenOfAllTrades(talk) 13:02, 25 May 2018 (UTC)


 * No hp conversion is correct(or wrong indeed). Hp is not a standardized unit of measure. Use kW if being precise matters. Use hp if it doesn't (in ads, for example).31.4.131.201 (talk) 14:11, 26 May 2018 (UTC)


 * There are two issues here - how many W in a hp? (746 is pretty much universal, especially today) and then how is "car engine power" to be measured?  In particular, is this the output power of the engine, that engine power less the power needed to drive the essential ancillaries (oil pump, water pump, alternator etc.), or the power at the wheels?  There is also the issue of how the engine is run when determining this - how long it has to sustain such a power, what air temperature it does it at, etc.  These measurement differences make a lot more difference to the numbers than the small (and now mostly historical) variations in W/hp. Andy Dingley (talk) 14:25, 26 May 2018 (UTC)

Compressing the H and O of one liter of water
If we separate the H and O from 1 l of water into the two gases (H2 and O2), and then try to compress each one in a bottle of 1/2 l: how difficult would it be? If the matter is the same, why would they separated need more space? --Doroletho (talk) 13:12, 25 May 2018 (UTC)
 * This is a standard unit conversion or dimensional analysis type of problem. Convert the volume of water to the number of moles (using density and molecular weight) of the H2 and O2, then you can try using the ideal gas law determine the gas pressure of that number of moles when compressed to your volume at whatever temperature you like. I suspect the pressure will be enormous, probably enough that it's not an "ideal gas", but it will git you a hint of how different gases (typical density: 25 L/mole at room temp and atmospheric pressure) and liquids (18 mL/mole for water) are at the molecular level. DMacks (talk) 13:21, 25 May 2018 (UTC)


 * Weirdly enough, there seems to be no good sources online for density-vs-pressure diagrams for O2.
 * I would guess that the real question behind OP's question is why H2O is liquid at room temperature/pressure when neither H2 nor O2 is; or equivalently, how come that the H2O molecule can be packed much more densely than H2 or O2 at room TP; or, yet equivalently, how come intermolecular forces between H2O molecules are much stronger than between H2 or O2 molecules. One answer to the latter is that water is a polar molecule and hydrogen bonds stabilize the liquid form (from our article, A polar molecule in general has a higher boiling point [than a nonpolar molecule], because the dipole–dipole interaction between polar molecules results in stronger intermolecular attractions.). However, I am not sure it is the only answer - it would imply that for any atomic species A, B that can combine into a nonpolar molecule AxBy, if A2 and B2 are gaseous species in a certain condition of temperature and pressure then AxBy also is, which seems quite a strong assertion. Off the top of my head I could find no counterexample: only two simple molecules fit the "gaseous single-atoms refs but liquid molecule" bill, water and nitrogen dioxide, both of which are polar. Tigraan Click here to contact me 15:16, 25 May 2018 (UTC)


 * Just to give the details of the calculation that DMacks suggested -- an atom of H2O weighs about 18 atomic mass units (16 for the O and 1 each for the two Hs). So 1 liter = 1000 grams of water contains 1000/18 = 55.5 moles of water molecules.  After splitting them, you have 55.5 moles of oxygen atoms which forms 27.8 moles of diatomic oxygen molecules.  Similarly, you have 111 moles of hydrogen atoms which forms 55.5 moles of hydrogen molecules.  One mole of any ideal gas occupies 22.4 liters, so the 55.5 moles of hydrogen would occupy 1243 liters at standard temperature and pressure.  Therefore it would need to be compressed to 2486 atmospheres of pressure to fit in 0.5 liters.  The oxygen, having only half as many molecules, would need to be compressed to 1243 atmospheres. CodeTalker (talk) 17:02, 25 May 2018 (UTC)
 * ...assuming isothermal compression and that the ideal gas law applies, of course, which most certainly is not the case (as hinted to by DMacks). Such pressures are extremely high (higher than e.g. the critical point of pretty much every standard gas). Tigraan Click here to contact me 09:00, 28 May 2018 (UTC)

Quantum spin
Can the spin of an electron be approximated by viewing an electron to be shaped like a spindle torus that is also knotted, where helical rotation occurs about the locus of the torus? Plasmic Physics (talk) 14:08, 25 May 2018 (UTC)


 * Electrons don't spin. The concept of spin is used to approximate the concept of a magnetic moment and magnetic deflection. Unlike real items that spin, electrons can spin in only two directions and the energy, whatever energy you want to discuss, of the spin is limited to very specific values. 209.149.113.5 (talk) 15:20, 25 May 2018 (UTC)


 * Per 209; electron spin is not "spin" in a classical sense. Spin (physics) refers to an intrinsic property which behaves like angular momentum, but it is using the term "spin" as an analogy, not to say that the electron actually spins.  To say that a subatomic particle has "spin" is akin to saying quarks have color.  It's a word that we can use to represent a phenomenon, which closely matches the mathematics necessary to account for that phenomenon, but it's not actually that thing.  -- Jayron 32 17:23, 25 May 2018 (UTC)
 * Well, come on, it doesn't just "behave like" angular momentum. It is angular momentum.  Angular momentum is a conserved quantity.  If you send right-circularly-polarized light through a medium that converts it to left-circularly-polarized light, the angular momentum has to go somewhere; presumably there is a torque on the medium that a sufficiently sensitive experiment can measure. --Trovatore (talk) 01:48, 26 May 2018 (UTC)
 * Yes, but the thing is, you're not supposed to think about the election as a spinning ball, because that introduces so sorts of problems that we needn't get into here. I wasn't referring to the fact that elections didn't have angular momentum, just that you can't visualize what the thing is that is spinning.  There's no thing to spin in the way that, say, the Earth spins around it's axis.  It's just that the electron, whatever it is, has intrinsic angular momentum.  As soon as you ask "how do I picture it spinning in a way that makes sense by analogy to an shape I could make" the answer is "shut up and calculate."  Or another way: there is no adequate image you could conceive.  There is just the angular momentum and The electron has it.-- Jayron 32 03:02, 26 May 2018 (UTC)
 * Yes, but what actually makes the above description inadequate? Plasmic Physics (talk) 03:18, 26 May 2018 (UTC)
 * I know precisely that 'spin' is used as a abstract concept in quantum mechanics. What I am asking is if the electron actually spins, but not about an axis per se. Plasmic Physics (talk) 22:28, 25 May 2018 (UTC)
 * One wonders if an electron is like a ball at all.... Abductive  (reasoning) 01:10, 26 May 2018 (UTC)


 * Electron and other QM spins are very often described with spin vectors, which more or less imply the spin has a somewhat discernable direction. The degree to which these vectors are known is limited, among other things, by the requirement that Planck-based quantized units of angular momentum be transferred in any interaction.  The weird part is that if you start reading about nuclear magnetic resonance, suddenly spin starts to become incredibly real - for example, see the illustration in spin echo, where the spin magnetization of individual nuclei seems to be realigned precisely.  I still don't claim to fully understand how this is consistent with the it's-just-QM stuff we hear elsewhere (and above). Wnt (talk) 01:42, 26 May 2018 (UTC)
 * I recall reading somewhere, "You can think of quantum spin as just like a spinning top, except there is no top." --47.146.63.87 (talk) 21:22, 27 May 2018 (UTC)

What makes a ruminant's milk more dangerous than human breastmilk that it needs to be pasteurized before consumption?
Raw, unpasteurized milk can carry dangerous bacteria such as Salmonella, E. coli, and Listeria, which are responsible for causing numerous foodborne illnesses. How do the bacteria get inside the ruminant's milk in the first place? Perhaps, the bacteria find their way in the milk supply, because the farm is a dirty place, and a cow's feces can wind up in the milk supply? Or does the milk directly from the cow contain those bacteria similar to how human mothers carry bacteria and viruses in their own milk supply? If the bacteria/viruses are in the mother's milk supply, then will the calf become sick from drinking the cow's milk? If the calf is fed through a bottle unpasteurized cow's milk, then can the calf still become sick? Or do humans become sick because they have more dedicate stomachs than calves do and cannot destroy the bacteria and thus need pasteurization to kill the bacteria for them? SSS (talk) 15:16, 25 May 2018 (UTC)


 * Our article on pasteurization suggests that the danger in raw milk came from contaminants in the milk supply chain: "Milk is an excellent medium for microbial growth, and when stored at ambient temperature bacteria and other pathogens soon proliferate ... Prior to industrialization, dairy cows were kept in urban areas to limit the time between milk production and consumption hence the risk of disease transmission via raw milk was reduced. As urban densities increased and supply chains lengthened to the distance from country to city, raw milk (often days old) became recognized as a source of disease." Gandalf61 (talk) 15:30, 25 May 2018 (UTC)


 * Oct 1871: Fire started in cow barn 1 kilometer from Chicago Loop, entire Downtown burned.
 * Sept 1873-1879: the Great Depression (the actual contemporary name).
 * Sept 1882: First commercial central power plant in America opens in Manhattan. Practical skyscrapers now possible.
 * 1884: World's first skyscraper is in Chicago. Has strong culture of skyscrapers ever since.
 * Thus the early 21st century's tallest building was caused by Civil War-ish milk bacteria. (the "military occupation junta" only stopped 1870, the Sears Tower roof was only surpassed 2003-04) Sagittarian Milky Way (talk) 01:11, 27 May 2018 (UTC)


 * As above; if we drank bovine milk straight from the cow like a calf does, microbial proliferation wouldn't be an issue. But simple refrigeration isn't enough to retard bacterial growth in such a nutrient-rich environment, so in the time it takes to package, transport and sell that raw milk, any bacteria that have been introduced to the milk grow like they're in a Petri dish. NorthBySouthBaranof (talk) 15:35, 25 May 2018 (UTC)
 * It would be helpful if you provided a ref for how fast bacteria grow in properly refrigerated raw cow’s milk. That is contrary to what I remember from my high school science course before quick analysis of DNA existed . Edison (talk) 17:19, 25 May 2018 (UTC)
 * I tried Googling, but articles on the time course of bacterial growth in raw cow milk under refrigeration name scores of bacteria types without clarifying which cause illness in human consumers and which are innocuous. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC520874/ Says that in 24 hours some microbe species actually disappeared while others proliferated. Another article said that in zealously sanitized dairy barns the bad bacteria showed up in the milk in higher concentrations that when some normal bacteria found on the teat survive. Edison (talk) 17:35, 25 May 2018 (UTC)
 * In times when wet nurses might be infected with syphilis, a better solution was proposed: that infants whose mothers could not nurse them should suckle directly from goats. Healthy animals, clean udders, no supply chain, no bacterial disease. On the other hand, when human milk is used by hospitals now, part of the function of human milk banks is to check that no nasties have accumulated - I believe they do this by freezing and pasteurising. Carbon Caryatid (talk) 22:53, 25 May 2018 (UTC)
 * At the end of the 1950es they introduced pasteurization in my country (Italy) mainly because Tuberculosis: many cows had it, the agents passed internally from the cow directly to the milk and humans could get the illness from the milk. By now there are virtually no more tuberculotic cows in western Europe and pasteurization is meant mainly to fight contaminants in the milk supply chain like Salmonella and Listeria 2003:F5:6F03:8B00:81B4:3C23:FFC8:8DE0 (talk) 13:11, 31 May 2018 (UTC) Marco Pagliero Berlin

What does it mean “patient K”?
I found the same question in other forum and nobody answered it but it's interesting for me: What does it mean "patient K"? I googled it to find an answer, but I found a lot of results without explanation to this term. What is "patient K"? "Clinical Example: Patient K., 54 years old, during 15 years has been suffering from type II DM (Diabetes Mellitus) with periodic phenomena of decompensation... (Obesity and Diabetes Mellitus - Book)" --93.126.116.89 (talk) 22:02, 25 May 2018 (UTC)
 * They referred to a patient using a letter instead of their real name. Alternatively, that's just the initial of their first or last name.  Ian.thomson (talk) 22:05, 25 May 2018 (UTC)
 * Yep. You can go searching medical case reports and you'll find every letter used this way. Someguy1221 (talk) 03:16, 26 May 2018 (UTC)
 * One of the more famous examples being HM (patient). --47.146.63.87 (talk) 05:19, 26 May 2018 (UTC)