Wikipedia:Reference desk/Science

Welcome to the science section
of the Wikipedia reference desk.

skip to bottom

Select a section:

• Computing
• Entertainment
• Humanities
• Language
• Mathematics
• Science
• Miscellaneous
• Archives

Want a faster answer?

Main page: Help searching Wikipedia

   

How can I get my question answered?

• Select the section of the desk that best fits the general topic of your question (see the navigation column to the right).
• Post your question to only one section, providing a short header that gives the topic of your question.
• Type '~~~~' (that is, four tilde characters) at the end – this signs and dates your contribution so we know who wrote what and when.
• Don't post personal contact information – it will be removed. Any answers will be provided here.
• Please be as specific as possible, and include all relevant context – the usefulness of answers may depend on the context.
• Note:
  • We don't answer (and may remove) questions that require medical diagnosis or legal advice.
  • We don't answer requests for opinions, predictions or debate.
  • We don't do your homework for you, though we'll help you past the stuck point.
  • We don't conduct original research or provide a free source of ideas, but we'll help you find information you need.

Ready? Ask a new question!

How do I answer a question?

Main page: Wikipedia:Reference desk/Guidelines

• The best answers address the question directly, and back up facts with wikilinks and links to sources. Do not edit others' comments and do not give any medical or legal advice.

See also:

• Teahouse
• Help desk
• Village pump
• Help manual

July 23

How much water is needed to block various species from reaching an island they would've thrived on if there was a landbridge?

Thus if you find them on the isle they were either introduced or came when there was less water.

How much is needed to allow an average population of at least 0.0000001 but much less than if there was a landbridge? (i.e. pedigree collapse or they can't find each other from too low of a mobility to population density ratio)

This is often prevailing wind and/or current dependent right? Wind and current going towards the island would lengthen this distance. Sagittarian Milky Way (talk) 21:05, 23 July 2018 (UTC)

Some birds can cover 1000's of km of ocean without landing. But there are other birds that don't like to go more than 10m from tree to tree. Over time humans have developed means to colonise land further away, so I suspect that now 20000 km of sea would not stop a human colonisation. But 100,000 km may be too much! Graeme Bartlett (talk) 00:07, 24 July 2018 (UTC)

This is a topic with connections to why Australia has marsupials (kangaroos, koalas, etc) and most of the rest of the world has placental mammals, and there is very little overlap. The standard explanation is the existence of the Wallace Line between Bali and Lombok in Indonesia. It's currently 35 kilometres (22 miles) wide and very deep, but would have been narrower during various ice ages. It has existed for a very long time. The Wallace Line article addresses the question fairly directly, stating "many birds do not cross even the shortest stretches of open ocean water". HiLo48 (talk) 00:19, 24 July 2018 (UTC)

Aren't birds and especially flying insects sometimes blown where they don't want to go by storms? Also I've heard that in Polynesia land birds aren't normally found more than 20 miles from land, or out of sight or something like that. Sagittarian Milky Way (talk) 02:00, 24 July 2018 (UTC)

It would be difficult to give a meaningful figure, because in addition to Island hopping there is thought to be evidence that some terrestrial species have (inadvertantly) spread from one landmass to another by rafting on floating conglomerations of vegetation – even trans-Atlantic dispersal by this mechanism is considered a likely explanation for the spread of some genera. Because such events will have been rare, and successful only by chance, it's difficult to put numerical constraints on the limits to their possible success. {The poster formerly known as 87.81.230.195} 2.219.34.253 (talk) 05:09, 24 July 2018 (UTC)

What about big animals like deer, elephants and bear? Wouldn't they not want to get on cause there's not enough food and freshwater and it might not be able to support their weight? And there must be other animals that wouldn't have their range extended by vegetation rafts, i.e. perigrine falcons maybe? Would they have an interest in making a long voyage on a raft where they can't hunt by slamming animals into the ground? Sagittarian Milky Way (talk) 19:08, 24 July 2018 (UTC)

Peregrine falcons can be blown off course and like any other bird - there are several records of them on Tenerife [1] for instance as vagrants. Mikenorton (talk) 20:16, 24 July 2018 (UTC)

SMW, you are attributing deliberate forward planning to non-sapient creatures, in a scenario where even H. sapiens would not be able to forecast an outcome. Animal dispersion by rafting is purely accidental, with animals inadvertently stranded on such rafts (which can be quite large) very occasionally being lucky enough to survive long enough to come within reach of land again – only one "success" in a million years might be enough to trans-oceanically disperse a given species.

Keep in mind that many large animals can swim surprisingly long distances if they choose, or are forced, to: Elephants have been seen swimming in the Indian ocean miles from land (see also Elephantidae#Evolutionary history); Polar bears routinely swim tens of miles, (and other bears can probably swim quite well); while Scandinavian Elk (aka Moose) are now known to dive several meters in order to feed on lake-bottom vegetation and coastal seaweed. Even sloths have been observed swimming! {The poster formerly known as 87.81.239.195} 90.218.111.216 (talk) 09:54, 25 July 2018 (UTC)

July 24

Removing water to connect all current land...

How much would the sea level have to drop to have all *current* above the water land to be connected by land? And what would be the last piece of current land to be connected?Naraht (talk) 15:14, 24 July 2018 (UTC)

Does that include middle-of-the-ocean features such as Hawaii? ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:31, 24 July 2018 (UTC)

Yes. And Pitcairn, Bermuda, Kerguelen, etc....Naraht (talk) 15:33, 24 July 2018 (UTC)

To connect Mauna Kea to mainland, you would have to drain several miles of water. ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:47, 24 July 2018 (UTC)

Any idea how to get more accurate information? (A decent map of depths of the Pacific would probably help, but I haven't found a great one) For Hawaii, it is entirely possible that the land bridge that gets revealed connects Mauna Kea to Kamchatka along the Hawaiian–Emperor seamount chain, but I'm not sure on the depths of some of the gaps in the chain?Naraht (talk) 18:02, 24 July 2018 (UTC)

In Google Images, there are various topographic maps of the ocean floor. This NG item[2] allows you to look at portions of it. The Hawaiian Ridge is a series of volcanoes which go way down deep, as are many of the other Pacific islands. ←Baseball Bugs ^{What's up, Doc?} carrots→ 18:33, 24 July 2018 (UTC)

Agreed, but the question is whether there are gaps in the Hawaiian-Emperor that go all the way down to the general seafloor or whether it stays significantly above that level as is true between Hawaii and Oahu.Naraht (talk) 19:46, 24 July 2018 (UTC)

You can download a detailed (30 arc second) grid of global bathymetry from GEBCO here. With the appropriate software you could mess about with a colour bar until you found what you were looking for. Mikenorton (talk) 19:57, 24 July 2018 (UTC)

In case you didn't know: Puerto Rico is surrounded by water. 2600:8806:4802:C700:19EF:9053:95DC:1C0A (talk) 21:05, 24 July 2018 (UTC)

Thanks, Donald. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:15, 24 July 2018 (UTC)

A related question [3].--Wikimedes (talk) 05:48, 25 July 2018 (UTC)

How do weeds manage to grow without a drop of water in the soil?

Not a drop of rain in two months, and yet I have to remove weed in the garden. I need to water the plants to prevent them from drying out in these extremely dry conditions, yet the weeds germinate and grow. How do these plants get enough water? Count Iblis (talk) 15:48, 24 July 2018 (UTC)

It's at least partly a circular problem: plants are called weeds because they grow where they're not supposed to. Plants with higher tolerance for dehydration would have an advantage filling that niche, so it makes sense that many weeds would survive/thrive while other plants dried out and died - if they didn't, they wouldn't out-compete your tomatoes and dahlias. So what makes them dehydration tolerant? Well, there are many adaptations that will play a part (pore placement and density, gross morphology, waxy coatings, the use of taproots, and so on. Weeds rarely spend a lot of energy on fleshy fruit or showy blooms (though there are some exceptions), and that also reduces their need. Matt Deres (talk) 16:21, 24 July 2018 (UTC)

Are you sure they're not coming up from the roots of weeds you've previously tried to remove? Anyway I've heard weed is associated with Satanism so it must be able to cope well with the heat ;-) Dmcq (talk) 16:24, 24 July 2018 (UTC)

There are indeed plants with deeper roots, but I'm puzzled about new weeds that germinate and have tiny roots when I pull them out. Somehow these tiny roots were able to extract water from the bone dry soil. So, it must be what Matt Deres says about losing less water than other plants, but there must also be mechanisms that allow water to be extracted from the top layers of the soil. Perhaps some of the water at greater depths in the soil evaporates and at night when the top layers of the soil cool down, the water vapor makes it there via pores and condenses there? Count Iblis (talk) 17:17, 24 July 2018 (UTC)

I suppose some weeds are better at conserving water but I think most just are far better at extracting the water and leaving the soil too dry for other plants - it is a major way they outcompete other plants I believe. Dmcq (talk) 17:50, 24 July 2018 (UTC)

If actual data doesn't match your assumption, it is quite likely your assumption is wrong. You have assumed the soil has zero water. Plants are growing in it. Therefore, your assumption is wrong. To have assumptions impervious to contrary evidence is a problem... --Jayron32 18:02, 24 July 2018 (UTC)

One way to get water in the top of the soil is via dew or frost. Before sunrise the soil surface may be moist, but when you look in the afternoon all that moisture may have evaporated. Graeme Bartlett (talk) 03:11, 25 July 2018 (UTC)

Deploying Compost in Extreme Heat.

I know that in the UAE and Saudi Arabia when farmers plant they have little water retention in sandy soils. Why cant they just compost all the organics from the big cities or ship in organics from other places for composting and plant in that. Is there something specific that happens to high organics soils(IE. Compost) when it is exposed to dry heat? Is this sustainable. Looking for someone to prove sustainability or not. If you have questions on more info Please Ask. — Preceding unsigned comment added by Mason201 (talk • contribs) 17:10, 24 July 2018 (UTC)

[ http://hal.cirad.fr/docs/00/18/03/35/PDF/Bahri.pdf ]

Abstract:

Water reuse in Tunisia: Stakes and prospects. In the arid and semi-arid region, countries like Tunisia are facing increasingly serious water shortage problems. According to forecasts, increased domestic and industrial water consumption by the year 2020 may cause a decrease in the volume of fresh water available for Tunisian agriculture. It is therefore important to develop additional water resources as well as protect the existing ones. One way to cope with these problems is to reuse wastewater in agriculture. Therefore and before launching the water reuse policy, a research program was undertaken...

--Guy Macon (talk) 17:44, 24 July 2018 (UTC)

Composting requires the presence of air. Water is needed in the right amounts to maintain activity without causing anaerobic conditions; the air/water balance is critical to maintaining high temperatures (135°-160° F / 50° - 70° C) until organic solid wastes decompose. Urine, itself useful as a nitrogen-rich fertilizer, is a suitable additive to a compost pile. DroneB (talk) 17:46, 24 July 2018 (UTC)

In addition to that, an obvious question is, why compost in the desert anyway? I mean the idea of composting waste from their own cities may make some sense. But what's the purpose of shipping in organic waste from elsewhere? Maybe you've never composted but if you ever did you'd know that the volume of what you start with is a lot more than what you end up with. [4] So there are at least 2 and probably more (shipping organic waste around seems a good way to ensure lots of problems with pests etc) problems with shipping in the waste and composting it on site. If the idea made any sense, it would seem better to simply compost it somewhere else and ship in the compost. BTW perhaps Desert greening will be of some interest. You'd note that it doesn't really mention shipping in compost or soil at massive scale as part of the process. Nil Einne (talk) 23:05, 24 July 2018 (UTC)

Insect from eastern Quebec

Graceful insect

Hello. Can you identify this little fellow who landed on my front door this morning (or last night..). I live in Rimouski suburb, Quebec Canada, in an open landscape of bungalows, many trees and several patches of mixed forest, a few hundred meters of St-Lawrence estuary. Body length : 1cm, wings span 2,5 cm. Thank you. Dhatier (talk) 17:45, 24 July 2018 (UTC)

I'm pretty sure it's a type of paleoptera (i.e. mayfly, dragonfly, or damselfly), though a rather more ornate one than I have ever seen. Maybe that will lead you in the right direction, though there are thousands of different species. --Jayron32 18:12, 24 July 2018 (UTC)

Looks like a rose plume moth Cnaemidophorus rhododactyla. Mikenorton (talk) 18:19, 24 July 2018 (UTC)

Agreed. T shapes are usually some sort of plume moth (although our local ones are ghostly white). Andy Dingley (talk) 18:30, 24 July 2018 (UTC)

Cnaemidophorus rhododactyla confirmed by numerous images on Google. Thank you very much. Dhatier (talk) 18:45, 24 July 2018 (UTC)

July 25

Why can Labrador get so hot?

North West River Northwest River
The highest known North American temperature east of Ontario and New York happened here in 1914.
Coordinates: 53°31′31.32″N 60°08′41.80″W

List of extreme temperatures in Canada. Also has exceeded the all-time highs of DC, Philly, Toronto, Ottawa, Windsor, Detroit, O'Hare, Indianapolis and Columbus and only 0.9F less than Ontario (108F). Sagittarian Milky Way (talk) 22:48, 25 July 2018 (UTC)

Not a complete answer, but there were heat records in many parts of the world this year, with a crisis in Japan at the moment. Co2 levels also fluctuated less, remaining high (with average level higher every year). Extreme weather events are predicted to rise as global warming pursues. Forest fires are regular in many areas and increasing, dumping more Co2 and the warming of permafrost is a concern as more methane is not converted before reaching the surface (with a temporary effect higher than that of Co2). There are fears about reaching tipping points and it's very difficult to determine when one will be attained; runaway changes are considered possible when one or more such tipping points are reached. About Labrador this year specifically, I'll let others expand (obviously, specific events cannot directly be linked to global trends). —PaleoNeonate – 23:28, 25 July 2018 (UTC)

The highest known temperature east of Ontario and New York was not only so far north but also outside the modern warming era or the Dust Bowl which makes it even more unusual. Sagittarian Milky Way (talk) 00:40, 26 July 2018 (UTC)

I am intensely skeptical of that information. The table with that value was added on March 21 of this year, with no sources, by an editor who has repeatedly run into trouble due to adding unsourced information to articles. It is not uncommon for locations that are far inland to reach very high temperatures, even if they are far to the north, but for a coastal location to reach such a temperature would really be anomalous. Anything is possible, of course, but I would like to see some evidence. Looie496 (talk) 03:06, 26 July 2018 (UTC)

There really seems to be a record of that temperature, the Canadian government list it [5]. There is some similar scepticism of that temperature in this discussion [6] (which was how I worked out to use that site) and [7]. Nil Einne (talk) 12:18, 26 July 2018 (UTC)

Further found [8] and sort of [9]. This post in the first discussion [10] is most interesting as it includes a response from Environment Canada which included an image of the original paper record [11] confirming it's not simply a modern data entry error. (Although IMO one of the responses in that thread is a little harsh. It sounds like whoever responded primarily felt they were being asked if there was some data entry error and confirmed there wasn't with the original records. They may not have felt it worthwhile going through the process of annotating or removing a single potentially spurious record.) BTW, in case there is some remaining confusion because of PaleoNeonate's post, we aren't AFAIK talking about anything this year or as SMW said anywhere close to modern times but a record from 1914. Nil Einne (talk) 12:39, 26 July 2018 (UTC)

Wow. I still think there must be an error somewhere, though. As one of those linked posts says, if the high was 65 the day before and the day after, and it rained on that day, it's very difficult to imagine how the temp could have reached 107. Looie496 (talk) 14:04, 26 July 2018 (UTC)

One thing to remember is that climate is complex, and that temperatures (both averages and extremes) are only partly a function of latitude. You can see this sort of thing at U.S. state temperature extremes. The state with the lowest record high temperature? Hawaii. The state closest to the equator. This is true because temperature is a factor of many things, besides latitude there are wind currents, proximity to large bodies of water, temperature of that water, local terrain, elevation, etc. etc. Microclimates can also be similarly weird; one of the most famous microclimates in North America is San Francisco, which is frequently 10-20 degrees F colder than places only a few miles away; (There's a frequently mis-attributed aphorism that goes "The coldest winter I ever saw was the summer I spent in San Francisco") the average July high is 66.5F for San Francisco, and 72.0F for Oakland, a 5.5F difference is impressive given that the cities are connected by a bridge. All that goes to say that simply being far in the north does not disqualify some specific location in Newfoundland from having some unusual microclimate, given the variety of factors at play. --Jayron32 15:20, 26 July 2018 (UTC)

It might be useful to examine the temperature records of adjacent stations, also newspapers covering the area - these often contain a day-to-day weather record. See List of newspapers in Canada. Here are the figures for five stations in the area:

Date                  Station          Max (°C.)                       Min. (°C.)            
1914 August 11        Burin            23.9                            12.8
                      Fogo             23.3                            15.6 
                      North West River 41.7X                           10.0
                      St Georges       24.4                            15.6
                      St John's        23.9                            19.8

You will note the red "X" against the North West River maximum. This suggests it was picked up as an anomaly at the time. 86.133.26.146 (talk) 17:32, 26 July 2018 (UTC)

There is also a red X by the original data record for "107" above. Also note there is a column "Range" to the right, which has an entry "57" (which is "107" - "50"). The weather was given as some letter, which I assume means clear, for the morning, with "overcast" in the afternoon, and "rain and heavy thunderstorm" as a note. Which is what you'd expect with that kind of high temperature! Finally, note the sequence of high temperatures: 97 62 63 71 70 64 65 66 75 107+ 65 86 76 62 63 65 63 65 50 49 68 65 63 74 78 74 . Putting those in LibreOffice Calc and doing STDEV.S(that range of values) I get 12.41, which sounds at least about right. The average is 69.46, so this value is at 3.02 standard deviations out. That means there is only a 0.27% (1/370) chance of such a value occurring, according to standard deviation. (It seemed faster to check that table than remember the function name...) Nonetheless, in a dozen such months, one time it could happen by chance. The value is still suspect, of course, because any 1% chance of error is more likely than that it is correct (that is, until you read the post above; with confirmation, its chance of being correct is much higher than the 1% error) -- but we certainly don't know it is wrong. Wnt (talk) 22:27, 26 July 2018 (UTC)

To me it looks more like a + or straight cross than an x unless it was added at an extreme angle. See also this rotated version. [12]. I was thinking of it before and it seems to be a clear highlighting. But whether it was intended to indicate the value was in doubt or could be an error or an anomaly, or simply noting it was unusual high or maybe that it was the highest value, I'm not sure. I'm leaning towards it simply being because it's the highest value. There look to be two bars which similar denote the lowest minimum values. I was originally confused about these because I thought they were underlining two random values with nothing special. But looking more carefully I realised they are probably a bar above the two 38 values which are the lowest minimum values for that month. Nil Einne (talk) 10:21, 27 July 2018 (UTC)

Not sure why this doesn't break the Second Law of Thermodynamics

I'll assume it doesn't, but I can't see why. Advice welcome, I've been scratching my head for a decade.

Imagine the Earth were so far from the Sun, that there was no solar heating, and it had no internal radioactive decay ; would its atmosphere ( probably needing to be only Helium, to be a gas at 6 Kelvin ) be the same temperature on the surface, as at say 10 kilometres altitude ? If so, how would a molecule of air moving vertically, in the Earth's gravitational field, keep the same kinetic energy ( and hence velocity and hence temperature ), as it gained or lost the gravitational potential energy, of that 10 km of height ? Air molecules may well interact, sharing and equalising their kinetic energy ; but over any finite change of height, there must be an equal and opposite change of kinetic energy. If this were not true, a molecule of air which was moving upwards, would continue at the same speed, indefinitely, until it escaped to space ; and that would seem to break the even-more unbreakable First Law.

If the gas particles do exhibit "ballistic" behaviour ( like mortar shells ), and this maintains a permanent temperature gradient with height, which could be used to drive a heat engine ; a planet with such an atmosphere, could continuously generate mechanical power, as it absorbed heat energy from the 6 Kelvin afterglow of the Big Bang.

The continuous absorption of heat to generate power, would seem to break the Second Law.

Thanks. GeoffAvogadro (talk) 23:21, 25 July 2018 (UTC)

I think you're getting lost in complexities, but the clean and simple answer is that air temperature decreases with height: this is called the adiabatic lapse rate. The physical reason for this is that at lower altitudes, there is more gravitational potential energy; at higher altitudes, individual molecules have expended kinetic energy to work against gravity.

There are many confounding extra details that make atmospheric science so much fun; but at the basic level, there absolutely is a statistical reduction in kinetic energy for air molecules as their altitude increases.

Above a certain height, the sparsity of the gas molecules becomes very low, and some different properties of thermal and chemical physics begin to dominate: this region is called the ionosphere (and/or the thermosphere, or magnetosphere, depending on which classification scheme you're using; these terms are sometimes used interchangeably, but they actually specify sub-regions that describe the details of the molecules and ions at specific altitudes and atmospheric conditions).

Nimur (talk) 23:34, 25 July 2018 (UTC)

The answer is that in that scenario the entire atmosphere would be in thermal equilibrium with the cosmic background radiation, at a temperature of 2.8 K. But basically there wouldn't be any atmosphere -- even helium would be in a liquid state at that temperature. You would only have a few stray molecules that randomly escape from the surface, hardly denser than outer space. Looie496 (talk) 02:45, 26 July 2018 (UTC)

Helium is a liquid at that temperature at atmospheric pressure. You'd need to check the phase diagram of helium to see what state it would be in at the pressures you are thinking of. Also, if helium is escaping from the surface and dissipating into the atmosphere at a greater rate than it is condensing, it is not in equilibrium; your planet is losing mass, which means even at the same temperature, you're losing thermal energy. --Jayron32 18:03, 27 July 2018 (UTC)

Good point about pressure. Looking at the phase diagrams at http://ltl.tkk.fi/research/theory/helium.html, it appears that at the cosmic background temperature, you could have an atmosphere of up to two Earth-atmospheres in pressure composed almost entirely of ³He, above an ocean of liquid helium. The other stable isotope, ⁴He, would be liquid down to a much lower pressure. Looie496 (talk) 20:42, 27 July 2018 (UTC)

It is true that in the absence of surface heating the atmosphere will gradually become isothermic. So, there is no contradiction with the second law. Molecules going up will be slowed by the gravity but will gain energy in collisions with molecules going down and therefore accelerated by the gravity. This picture is only true on spatial scales above the mean free path length in gas. Below this length the gas kinetic model (and thermodynamics generally) is not applicable and the gas behaves like a cloud of free particles which happens, for example, in exospheres. Ruslik_Zero 06:46, 26 July 2018 (UTC)

Uh, unless there's some subtlety I'm missing here, you couldn't drive a heat engine with the atmospheric temperature gradient because to move the hotter air away from the surface you have to do work against Earth's gravity. Also, I know this is a spherical cow kind of thought experiment, but as Looie496 noted, at that temperature you'd just have frozen volatiles on the planet's surface, with a tiny amount of sublimated vapor, as seen on worlds like Pluto. And there'd be no appreciable amount of helium; Earth's gravity is too weak to hold on to hydrogen or helium. --47.146.63.87 (talk) 06:59, 26 July 2018 (UTC)

I thought that the cosmic background radiation plus starlight gave a higher equilibrium temperature than the cosmic background radiation alone. Obviously this would differ (in the galaxy core? in the empty spaces between galaxies? Any large clouds nearby?) but the interesting number would be for a planet in the spiral arm, roughly where our sun is. --Guy Macon (talk) 06:59, 26 July 2018 (UTC)

The vast majority of cosmic rays originate from outside our own galaxy. The intensity may actually increase as you move to regions of lower stellar density, due to reduced shielding from cosmic rays by stellar magnetic fields. Someguy1221 (talk) 22:28, 27 July 2018 (UTC)

"Cosmic background radiation" properly refers to the relic radiation from photon decoupling that pervades the universe. This is what the original poster was referring to. I don't doubt sometimes the term is used sloppily to include cosmic rays, but in strict scientific terms this is wrong, as they're two totally different things. --47.146.63.87 (talk) 06:39, 28 July 2018 (UTC)

Nah, i just had a total brain fart reading Guy's post, and thought he wrote 'cosmic rays'. Someguy1221 (talk) 19:32, 28 July 2018 (UTC)

Yes, obviously this depends on distance. Pluto for instance gets down to about 33 kelvin; the heat sources are a mixture of the Sun's heat, Pluto's internal heat, and probably some tidal flexing from Charon. --47.146.63.87 (talk) 06:39, 28 July 2018 (UTC)

Assuming the background temperature was enough to keep helium a gas then the temperature of the air would be the same at all heights. It being different on earth is because the earths atmosphere is nowhere near an equilibrium, we have the sun shining down and various interactions between the gas and the radiation. The energy of the molecules would get spread out, they don't just fall from space to the ground. Just having molecules falling straight up and down isn't a stable equilibrium. Dmcq (talk) 11:37, 26 July 2018 (UTC)

July 26

Stomach usually gurgles on the left side

This question is not for diagnosis but for curiosity. I hear that my stomach usually gurgles on the left side rather than on the right. Why most of the gurgles occur on the left side rather than about the same on both sides? PlanetStar 05:32, 26 July 2018 (UTC)

Your stomach is mostly on the left side of your body. --76.69.47.228 (talk) 05:47, 26 July 2018 (UTC)

But the gurgles sometimes occur on the right side of the abdomen. The stomach were referring to is a bean-shaped organ above the intestines. The gurgles doesn't just occur in the stomach, it also occurs in the intestine, which is evenly spread from left to right. Maybe most gurgles occurring on the right side is intestinal gurgles, but maybe most intestinal gurgles occur on the left side; if so, what's the cause of occurring mostly on one side of the intestine? PlanetStar 04:33, 27 July 2018 (UTC)

I suppose that what is gurgling is not the stomach as a whole but the pylorus, which is clearly located on one side of the body, by most humans the right one. Maybe you have it on the other side? Also gurgling of the intestine is possibly not evenly distributed but happens e.g. only at the interface between colon and ileum, or only in its descending or ascending but not horizontal segments. 194.174.76.21 (talk) 16:07, 27 July 2018 (UTC) Marco Pagliero Berlin

Not eating or drinking before surgery

A family member had to have several minor surgeries, I made a comment to the doctor that "your instructions said no food or drink after midnight for a 7AM surgery, and later we got the exact same instructions for a 5PM surgery." To his credit, he listened and now gives the instruction "no food for ten hours before the surgery, and no water for four hours before the surgery". Needless to say, we follow the instructions no matter what they are. Only an idiot ignores doctors orders.

This got me to thinking and researching. I believe that these restrictions are to reduce the chance of you vomiting while under anesthesia and then sucking some of that stomach acid down your windpipe. So has anyone done a study about how long food and water stay in the stomach? And does the sphincter valve that empties the stomach slowly meter out the contents to the intestines or does it let the stomach work on the food for a while and then dump the result into the intestines? Please note that I am asking for sources, not opinions. --Guy Macon (talk) 06:53, 26 July 2018 (UTC)

You are correct about the purpose: see nil per os and aspiration pneumonia. Chyme states, with no given source: Depending on the quantity and contents of the meal, the stomach will digest the food into chyme in anywhere between 40 minutes to a few hours. However, you can vomit material from the small intestine if vomiting is sufficiently vigorous; such vomiting can often be identified by the presence of greenish bile in the vomit. It sounds like they want all food to have passed into the large intestine. --47.146.63.87 (talk) 07:10, 26 July 2018 (UTC)

Thanks! Good info. I see that Nothing by mouth says "The American Board of Anesthesiology recommends that patients should not eat solid food for at least 8 hours prior to a procedure, and should not drink even clear liquids for at least 2 hours prior". Looks like the doctor added a couple of hours to that just to be safe. Also, he has you show up two hours before the surgery and they put you on an IV, so from a standpoint of thirst/dehydration its only two hours with no water.

As a passing note, if the stomach empties too quickly after for instance gastric reduction surgery it causes the imaginatively named Dumping syndrome, not a pleasant experience. Richard Avery (talk) 12:30, 26 July 2018 (UTC)

Does anyone know how long it takes for food to get past the "vomiting from the small intestine" state? And whether it can happen under anesthesia? --Guy Macon (talk) 17:42, 26 July 2018 (UTC)

I'm not finding anything definitive and searching has already ruined my lunch. :) I will point out the article on fecal vomiting, which suggests that, in rare cases, there is not really a limit (unless it's already pooped out the other end). Matt Deres (talk) 17:44, 27 July 2018 (UTC)

Small intestine transit time ranges from 15 minutes to 5 hours. In 83% of those studied, transit time was less than 2 hours, and mean transit time was 84 minutes. [13] Probably once you're past the duodenum the exit route will no longer be up. - Nunh-huh 17:58, 27 July 2018 (UTC)

Seeking an identification for this caterpillar found in garden. Somerset UK

Hi folks

I found this caterpillar in the garden this afternoon and I'm hoping someone can identify it. It was about 4 inches inches long and fairly thick. I've attached some pics the last of which was after I had gently brushed against it with a twig, this appears to have made it change it's head shape into something broader and more threatening, as a defensive measure no doubt.

This was all happening in Somerset UK in case that helps identify the creature.

• 
• 
• 
• 

Many thanks Gareth — Preceding unsigned comment added by Hermitical (talk • contribs) 20:18, 26 July 2018 (UTC)

Looks like a Deilephila elpenor, an Elephant Hawk Moth.Mikenorton (talk) 20:52, 26 July 2018 (UTC)

(ec)I googled "caterpillars with segments that look like eyes" an this ite turned up: [14] They actually think it looks like a snake. Be that as it may, they're saying it's the "Deilephila elpenor, known as the Elephant Hawk-moth". ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:53, 26 July 2018 (UTC)

And given Mikenorton's confirmation, it looks like you've got some new illustrations to add to the article! ←Baseball Bugs ^{What's up, Doc?} carrots→ 20:55, 26 July 2018 (UTC)

Many thanks for all your help. It was an incredible sight! Do you really think I should add any/all of these photos to the Deilephila elpenor article? Hermitical (talk) 18:04, 27 July 2018 (UTC)

You could add them to commons:Category:Deilephila elpenor (caterpillar). Mikenorton (talk) 18:30, 27 July 2018 (UTC)

July 27

Definition of episomal

Is it correct to call a non-integrating plasmid episomal if it's in a eukaryotic cell and does not replicate in that cell? Is the ability to replicate in the cell in question necessary to meet the definition of episomal? Thanks. --185.230.100.66 (talk) 06:28, 27 July 2018 (UTC)

The ability to replicate independently of the nucleus is the defining characteristic of Plasmid DNA, while some suggest that the term episome be abandoned or modified to refer to viruses that may be replicated in the nucleus, see Plasmid#Episomes. DroneB (talk) 12:57, 27 July 2018 (UTC)

AA and KSD

Every aldosterone antagonist that I see is also a potassium-sparing diuretic. Are there any aldosterone antagonists that are not potassium-sparing? 209.149.113.5 (talk) 18:46, 27 July 2018 (UTC)

I think by definition no, because that's just literally what happens when you antagonize the aldosterone receptor (unless there's something else going on with the patient's kidneys). To do something else would require significant off-target activity, at which point I suspect it would not be placed in that class of drug. Someguy1221 (talk) 22:34, 27 July 2018 (UTC)

July 28

Hearing: difference in sensitivity to harmonics and intermodulation.

The reproduction of sound through electronic devices inherently involves "non-linear distortion". It has been known for a very long time that distortion occurs in two forms: harmonic (extra tones in harmonic relationship to source fundamentals) and intermodulation (non-harmonic extra tones that are the sum or subtraction of source tones), and that the ear is both more sensitive to, and finds it more objectionable, to the intermodulation form. For example, the motion picture industry devised a specification and test (the SMPTE test) for maximum allowable intermodulation almost as soon as sound movies were devised. Harmonic distortion they weren't much concerned about.

It seems that this extra sensitivity to intermod is inherent in the structure of the inner ear. Almost all natural sounds contain lots of harmonics. Intermod pretty much does not occur in nature. Does anyone know what evolutionary advantage this has conferred, remembering that human evolution is essentially stopped at the caveman era, or perhaps at the stone age era, when there was certainly no high quality electronic sound? Or is it that excess sensitivity to intermod conferred no evolutionary disadvantage? One would think that as harmonics are normal in nature, that that is what we ought to be most sensitive to. 118.209.51.33 (talk) 16:37, 28 July 2018 (UTC)

Evolution hasn’t stopped. There was not a ‘direction of travel’ of evolution to arrive at where we are now, for humans, giraffes, hippopotami, or dinosaurs etc. — Preceding unsigned comment added by 82.38.221.49 (talk) 17:30, 28 July 2018 (UTC)

So? How does that help?118.209.58.85 (talk) 16:24, 29 July 2018 (UTC)

Human hearing ability has ceased to be a parameter for evolutionary selection since our hominid ancestors struggled in a predatory environment. Our hearing sensitivity and frequency range have become inferior to the cats and dogs around us, though we claim to have developed a finer tuned cultural appreciation of sound (music) than they. We also value our hearing directionality, a hangover from the use of hearing in stealthy stalking or predator avoidance, enough to invest in Stereophonic sound reproducers. This direction sensitivity depends on relative signal phases at each ear (compare with Phased array ultrasonics). A reason intermodulation tones are objectionable is that they can only confuse detection of a sound's direction while harmonic distortion of a single tone does not impede hearing where it originates. DroneB (talk) 13:20, 30 July 2018 (UTC)

If I understand this question, the OP is asking whether the aesthetic appreciation for sound is derived from an evolutionary tendency - and in specific, if there is an evolutionary reason to prefer certain harmonic tones, as opposed to non-harmonic combinations.

The answer should be a clear and sonorous no, this aesthetic preference is not an evolutionary effect; this is a learned, acculturated phenomenon related to the history and culture that has had a dominant effect on the music and sounds that many of our readers are exposed to.

Our article on Tonality is a good starting place; and our ancillary article, Atonality, has this to say: "the term atonality describes music that does not conform to the system of tonal hierarchies that characterized classical European music between the seventeenth and nineteenth centuries..." (with just massive amounts of citations to great music-theory sources all throughout that article).

So: no, we humans did not have any evolutionary or biological reason to prefer harmonic sounds, nor was there any evolutionary reason to dislike nonharmonic sounds (including, but not limited, to the sounds caused specifically by intermodulation of acoustic frequencies). Any such predisposition that you or others may have is a learned behavior that is heavily influenced by your exposure to the musical traditions of renaissance-era Western European societies, and the more subsequent modern music that developed from those cultures.

Nimur (talk) 05:13, 30 July 2018 (UTC)

These are very definitive statements, but I'm not convinced that they are correct. Harmony actually has a very strong and straightforward physical significance. When you have a simple source of sound, it usually produces a base frequency and a set of "harmonics", that is, tones with frequencies that are integer multiples of the base frequency. As the name indicates, the harmonics harmonize with each other. When you have multiple sound sources, the tones that they produce typically do not harmonize with each other. Therefore, harmony is a signal that a sound comes from a single source. Thus, the ability to perceive harmony goes with the ability to distinguish single sound sources from multiple sound sources. I can't prove that that has evolutionary importance, but it does seem plausible to me. Looie496 (talk) 14:44, 30 July 2018 (UTC)

I don't know enough and haven't put in the time to riddle this out, but there is a lot about harmonics in the cochlea, e.g. [15] I would speculate that there may be a difference in how much the two types of distortion affects the final neural signal, but I don't know that. Wnt (talk) 14:36, 30 July 2018 (UTC)

Red meat and diabetes

Red meat says A 2016 literature review found that for the each additional 50g per day of processed meat (e.g., bacon, ham, hot dogs, sausages) consumed, the risk increased 4% for total prostate cancer, 8% for cancer mortality, 9% for breast cancer, 18% for colorectal cancer, 19% for pancreatic cancer, 13% for stroke, 24% for cardiovascular mortality and 32% for diabetes. The source is [16] ("Free Access"; not sure if that means it's open access or that I can access it due to my on-campus IP address), and most of its references to diabetes are merely comments; the exceptions are Table 1, Figure 2, and Figure 3. [Figure 3 proposes a mechanism whereby various chemicals in red meat trigger insulin resistance.] Am I missing something, or does the author merely give the statistics (with sources, of course) and propose an explanation, or does he give methodology somewhere? Here in the USA, at least, individuals with higher consumption of red meat have disproportionately high rates of general poor eating, including obvious diabetes-associated sugary foods. If the latter, it's still a reasonable thing to state in a research article because it poses a topic for research ("does red meat cause diabetes, or is it associated with something else that causes it?"), but by stating this information where we do in Red meat, we're implying causation, which isn't seemingly appropriate unless the author's reviewing studies with control groups whose diets were similar minus the red meat. Nyttend (talk) 17:06, 28 July 2018 (UTC)

Here's a more rounded source: [17]. 86.131.233.223 (talk) 17:24, 28 July 2018 (UTC)

A more rounded source? That's a news report! I'm seeking something reliable. Nyttend (talk) 19:10, 28 July 2018 (UTC)

These are just correlations that may disappear after appropriate adjustments as already mentioned in the article. Ruslik_Zero 17:40, 28 July 2018 (UTC)

AFAIK, red meat increases bowel and colon cancer from 4-5% to 5-6%, i.e. if one consumes lots of read meant for most of his/her life. Tgeorgescu (talk) 04:17, 29 July 2018 (UTC)

Tractor model (Montana 1991)

• 

Which model is this tractor? --Nato-Strichmännchen (talk) 19:09, 28 July 2018 (UTC)

Looks like an older model of the Massey Ferguson 230. It seems definitively from this company.--Doroletho (talk) 12:18, 29 July 2018 (UTC)

July 29

Force in rocketry, possibly for quarks inside proton, anywhere else?

Hi if t is time, p(t) is momentum of a pointlike object with mass, then classical physics says that p(t)=m(t)v(t) where m and v are mass and velocity of the opject, and that the net force F(t) is p’(t) = m(t)v’(t) + m’(t)v(t). In a rocket if the mass loss due to fuel consumption can make m’(t) a large enough negative number, can m’(t)v(t) become almost as great in magnitude though of opposite sign, to m(t)v’(t)? Is it possible to gain great increases in speed with small amounts of force this way? My second question is if quarks inside a proton could experience relativistic increases or decreases in mass so rapid that the contribution to net force of m’(t)v(t) is comparable or even much greater than that of mv’(t)? My 3rd question is that since the charges on quarks would complicate even the classical picture (what with electromagnetic radiation), are there noncharged particles that experience th strong force in the same way quarks do, so that a similar regime of m’v dominating could exist in a simpler way? Thank you Rich (talk) 03:38, 29 July 2018 (UTC)

Well, according to Newton's law F=m*a. So, in order to accelerate a ship of mass m, one needs a force F, there is no way around that except for gravitational slingshots (using planets/moons). If m diminishes, yes, the acceleration would be higher, but there is a limit to it (i.e. when all fuel got burned). With present-day technology it isn't possible to separate the quarks inside of a proton (anyway, not upon a spaceship). Tgeorgescu (talk) 04:13, 29 July 2018 (UTC)

No, F=ma when m’(t)=0.Rich (talk) 05:37, 29 July 2018 (UTC)

if one has to look at the the rocket case as a closed constant mass system that includes the exhaust gases, as i just learned a few seconds ago, how does one deal with a case where mass isnt being lost by or gained by something like fuel consumption, but instead by relativistic mass increase?Rich (talk) 05:50, 29 July 2018 (UTC)

In Newtonian mechanics the change in mass is not part of the force equation. If the mass is changing over time/space that will be included in calculations of impulse and work, but that's it. In the relativistic case, you simply use a corrected force equation, like p = γm₀v, F = dp/dt. Someguy1221 (talk) 07:56, 29 July 2018 (UTC)

In "to accelerate a ship of mass m, one needs a force F, there is no way around that except for gravitational slingshots" there is no 'except'. No force == no acceleration. In a gravitational slingshot gravity is the force accelerating the spaceship. Doroletho (talk) 15:01, 29 July 2018 (UTC)

The chain rule derivative you do looks right. As said above, the first term is F = ma. The other term makes it F = ma + m'v. This extra term distinguishes Newtonian momentum from relativistic momentum. The classic case where this matters is that you can take a particle, put it in an accelerator and keep applying force to it, and after a while v scarcely changes - it's moving near the speed of light. Instead the relativistic mass keeps going up and up. To be sure, relativistic mass, while sensible as ever, is presently out of vogue, and you would be encouraged to do relativistic problems using a different formalism and a different definition of "mass"; hence instead of saying p = mv you say p = γm₀v. But F is still dp/dt, and γm₀ is still relativistic mass. Our article on momentum points at variable-mass system. But you have to watch the assumptions in those problems because mass never just "varies" (apart from the relativistic effects); it always comes or leaves taking its own momentum with it. Wnt (talk) 15:00, 29 July 2018 (UTC)

Sonorescence

The old Chambers Dictionary from 1908 defines sonorescence as the property of emitting sound under intermittent radiant heat or light. I can find this mentioned in some older books, e.g. Rubber World vol. 68 (1923): "In this application hard rubber is particularly valuable owing to the accuracy with which it can be machined and also to its remarkable sonorescent quality." Yet Wikipedia has no entry for sonorescence and I've never heard of this property before. Is it real, or was it an old erroneous belief? Does it have a different name today? Equinox ◑ 16:34, 29 July 2018 (UTC)

According to the latest OED (draft third edition of June 2017) the term is now obsolete, but the definition was: "The production of audible sounds by a substance when it absorbs periodically modulated light (or other electromagnetic radiation); the ability of a substance to do this." The OED also comments: "Now sometimes called the optoacoustic or photoacoustic effect." Dbfirs 16:39, 29 July 2018 (UTC)

Thanks; just made a redirect. Equinox ◑ 16:42, 29 July 2018 (UTC)

You beat me to it! Dbfirs 16:43, 29 July 2018 (UTC)

Different expression levels from same reporter inserted into the same place in the genome

I used homology directed repair to get a cassette expressing a fluorescent protein and (eukaryotic) antibiotic resistance gene in a specific place in the genome of a cell line. The cells were cultured under selective medium but for some reason they all show different levels of expression of the fluorescent protein. Why might that happen? It would be interesting to culture them in a live cell imaging microscope to see if high-fluorescence cells divide into high-fluorescence daughter cells but I'm not going to have the opportunity. The cells in this image are fully confluent because I was about to extract the DNA from them but the variation in expression exists at lower confluence also.

Maybe it's an oversimplification to think they're all the same cells and they actually have developed their own epigenetic deviations which have resulting in the differing expression? They were all resistant to that antibiotic though and the antibiotic was expressed from the same transcript as the fluorescent protein via a 2A sequence. --129.215.47.59 (talk) 18:33, 29 July 2018 (UTC)

This is the expected result for most things. I mean, not necessarily that level of variance between clonal cells, but variance in general. "Stochastic gene expression" is virtually an entire field of study at this point. I would recommend going to your favorite research search engine and search for recent reviews on that topic. The stochasticity can arise from transcription factor abundance/activity/binding, epigenetic marks, transcript stability, or translation rates. Or even protein stability. It's a whole field! Some genes are more prone to this than others, and variance can also be influenced by environmental factors and genetic background. If the cells were recently transfected and not subject to clonal expansion yet, whether the transgene is likely to be identical in each would depend on the method by which you got it in there. Someguy1221 (talk) 02:24, 30 July 2018 (UTC)

This [maybe not -- see below] likely has to do with heterochromatin formation or other epigenetic aspects of the genome. See position-effect variegation as one example, though to be sure I don't know whether you have yours next to heterochromatin. Note though that putting multiple copies of something into the genome will make heterochromatin; it's the body's despamming mechanism. Steve Henikoff put out a lot of the key papers in the area. There are some neat examples - the Pigmented Extraepidermal Tissues mutant reportedly formed five different sublineages with different (internal) pigmentation patterns from a single originating mutant [18] though four were lost during an air conditioner outage. I should also comment that "unstable transgene expression" is typically downward and hence disappointing - it was not that uncommon for lines of transgenic mice to just stop producing the transcript as a new heterochromatin region became established, though modern methods allow for better control over both the position and the number of copies.

Actually looking at your picture though, I realize this might be simpler than my first thought. It is possible that some variable aspect of the plating is influencing the expression -- for example, the cells might be at different points of the cell cycle, or some might be experiencing contact inhibition while others aren't, or many other things. The effects I described above should be somewhat clonal in nature, but it looks like you grew up those cells together, and there's no obvious correlation between neighboring cells. There's a lot of variation, but not variegation. If I saw patches of lower expression it would be more likely to be a DNA-based effect. See if you can synchronize these cells in the cell cycle and look at them at known times and/or with cell cycle markers as controls. Wnt (talk) 14:29, 30 July 2018 (UTC)