Wikipedia:Reference desk/Archives/Science/2020 July 11

= July 11 =

seberrhoeic dermatitis
is there a way to know if you have seberrhoeic dermatitis for a fact? — Preceding unsigned comment added by 110.151.69.112 (talk) 10:04, 11 July 2020 (UTC)
 * The fungus Malassezia may be implicated in Seborrhoeic dermatitis. Malassezia may be assayed by microscope and if necessary by culturing skin scrapings in a lipid-supplemented culture medium, see Malassezia Infections in Humans and Animals: Pathophysiology, Detection, and Treatment. — Preceding unsigned comment added by 84.209.119.241 (talk) 10:35, 11 July 2020 (UTC)
 * Yes. See a doctor. He can do the test 84.209.119.241 describes above. --Guy Macon (talk) 17:31, 11 July 2020 (UTC)

Something I've always wondered walking along ~furlong long apartment buildings
You're standing on the standard big ol' empty flat plain that is the spherical cow of land. Empty except it's bisected by a brick wall x feet high where x is 8 to whatever and straightness is very. It is long enough to be essentially acoustically infinite to simplify math. A sound occurs 5'2" above the plane, z feet from you with the wall in between and you stand as close as you can without touching. What does the volume curve look like as you walk away from it? How small do the lengths need to be for refraction to be ignored? I do not notice a difference when the far side of the street is 260 to 320 feet away (the next street), the near side 60 feet less and the barrier is 200 feet wide and c. 10 meters tall (about half radian above the ears at minimum) but the lack of open space prevents experimenting with other numbers. Let's say no wind or rare air density gradients cause there's still lots of variables even with this simplification. Sagittarian Milky Way (talk) 16:26, 11 July 2020 (UTC)


 * "The best known critic of noise barriers in Connecticut was Professor Conrad Hemond from the University of Hartford's College of Engineering. In the mid-1980's, he published an opinion article in a construction industry trade magazine in which he criticized the cost effectiveness of noise barriers. He was also quoted extensively in a September 16, 1985 Hartford Courant article questioning their effectiveness. Hemond stated that noise barriers had a limited effect in an area 150 to 200 feet behind the fence and little or no effect beyond that distance. Within the area close to the wall, noise reductions of 10 decibels were possible, but because noise waves would come over the wall and bend back to the ground after that distance, they would still be high enough to disrupt normal activities. He also stated that any cracks in the wall or separations between the planks would allow the noise to come through at full strength.


 * Whether this means that noise barriers are not effective is a matter of opinion. State officials who worked with noise barriers countered Hemond's criticism with information showing that the barriers generally achieved the purpose for which they were designed; specifically, to reduce the noise at the first row of houses next to the wall by as much as 10 decibels. This reduction results in a 50% reduction in noise as it is perceived at these locations. Noise barriers are not intended to have a greater effect. They also added that since noise perceptions are subjective, the barriers have psychological benefits beyond their actual reduction of noise levels. For example, residents in areas near the barriers have commented that the fences increase their sense of privacy." Source


 * Also see: A reduced-scale railway noise barrier's insertion loss and absorption coefficients: comparison of field measurements and predictions --Guy Macon (talk) 01:46, 12 July 2020 (UTC)


 * Does the shadow edge bend or is it straight? At what size scale do altitude gradient effects become more than a rounding error in an International Standard Atmosphere? Sagittarian Milky Way (talk) 14:54, 12 July 2020 (UTC)

== How many lux is it when the entire horizon is 18 degrees above the Sun, the Moon's well hidden by Earth and you're over the bright pole (23.4 North and one of the Eurasian longitudes?)? ==

How many lux are artificial light? Which metro area is brightest? (apparent magnitude or SI units) Which square arcminute of Earth is highest surface brightness? (magnitude per square arcsecond or SI equivalent) If there were no artificial light how would the lux and surface brightness of the brightest patch of sky compare to the darkest cloudless astronomical dusks on boats?

What's the most you can see from artificial illumination on what would've otherwise been a very dark night at ISS height? 200km up? 100? Can you read newspaper if you're dark adapted?

What is the absolute magnitude and lumenage of the artificial light of the world's brightest metro area from the brightest angle when it's millions of miles away? What is the absolute magnitude of a Hiroshima or Tsar Bomba fireball? How bright can the artificial part of a hemisphere's get if you're over the right place (don't know if it's over the tropics or not) at "globe looks orthographic" distances"? You see few streetlight bulbs from above, only reflected light, so at "Earth is tiny" distances being right over a bright continent like Europe might not be decisive like how it'd be for maximizing artificial light at medium altitudes. Sagittarian Milky Way (talk) 19:13, 11 July 2020 (UTC)
 * I find this question hard to parse. If the "entire horizon is 18 degrees above the Sun, something either geographically or astronomically fairly unusual has taken place. Your local horizon is also not that relevant for the luminosity of the sky. If you mean that it's clearly after twilight (i.e. the sun is more than 18 degrees below nominal horizon), our article Sky brightness has some information (although I don't know how to convert the units there). --Stephan Schulz (talk) 21:06, 11 July 2020 (UTC)
 * It means the entire horizon is 18 degrees above the Sun. I am guessing that the "bright pole" for the tip of Earth's "hyperumbra" (spirit of the astronomical twilight rule not the letter, which is "Sun (90 plus 18) degrees from the zenith" and would fail at this altitude of ~100 ~50 million feet) is something like https://www.fourmilab.ch/cgi-bin/Earth?di=B7EC8051F5D91BD47F89F415E268883F04E8F4D19B88D8BE449162CC43710E286817C6FC8A97CC5F3D592AF49033742CD9A31838F4240EF32D67C465AA663C7DFB3794FBD50CCD737055998500062026652781D806F323C4ED44704DF8F3F2FCC6DB946405 this, the place where the hyperumbra cone tip gets the most artificial illumination. Sagittarian Milky Way (talk) 14:30, 12 July 2020 (UTC)


 * Crap, I made math error, actual altitude is only about 14230km which would dim the lights of Japan and Britain a lot with atmospheric extinction and buildings and terrain blocking some: . Maybe somewhere in the North Atlantic is brighter. Sagittarian Milky Way (talk) 16:14, 12 July 2020 (UTC)

Butter
This is kind of a weird question, but:

After you melt butter, is there any way to turn it back into its "original", solid form? (I don't mean freezing the liquid butter, because that would just produce butter-flavored ice. I mean the actual, original substance.)

Thank you, Heyoostorm (talk) 20:00, 11 July 2020 (UTC)


 * Not sure if this helps, but I know from experience and observation that heating butter in order to melt it results in changes. The solid portions separate from the water portions, and the heat causes changes in the butter solids. Some "water" is lost to evaporation. In that case the answer is NO!


 * However, if a "stick" of butter is left out at room temp for a period of time, it will be so soft that it yields to the pressure of a finger, ie squishy :-). At this point, it can be returned to refrigeration, and re-solidify with no discernable degredation, (barring some sort of scientific analysis, of course). Hope this helps.  Tribe of Tiger Let's Purrfect!  21:55, 11 July 2020 (UTC)

Thanks so much, both of you! You each answered a different part of the question, and it really cleared it up for me. :) Heyoostorm (talk) 23:01, 11 July 2020 (UTC)
 * There's also ghee. It melts at a certain temperature, but on cooling it returns to its prior state. --  Jack of Oz   [pleasantries]  01:29, 12 July 2020 (UTC)
 * Even if you freeze the liquefied butter, it will not result in butter-flavored ice. You might get cold butter with some ice crystals.


 * The deal with butter is that it is an emulsion of three basic ingredients (four if it is salted), those being 1) fat 2) water and 3) "milk solids", which includes all of the things not normally soluble much in either water or fat, things like proteins such as Casein. When you heat butter until it liquifies, you basically disturb the emulsion, causing the three phases to separate.  Sometimes this is a desired result, in applications like ghee and clarified butter, the method removes the milk solids and some of the water, resulting in a significantly different product.  However, when you completely melt a normal stick of butter, and then just let it cool, the three phases don't form the same sort of emulsion as when they started, so you don't get the same stuff back again, it is often grainier and less smooth, and has noticably different phases in it, because you've "broken" the emulsion.  -- Jayron 32 17:24, 15 July 2020 (UTC)

Cat jumping ability (between roofs) while carrying a kitten
How is the usual ability of jumping of a cat influenced by the need to move its (presumably 23-25 days) kitten from a roof of a house extension to the roof of a metal shed nearby the house wall and then from here to the ground? The context of the question is the following:

In the past seven days I've been watching (from the window of a first floor apartment) a cat and its kitten moving from the mentioned roofs to the ground and back, but I've been missing to see the exact moment of the jump of the cat with the kitten by its neck between the ground and the first roof of the metal shed and then to the second roof. So far I've seen the kitten at the ground level only twice since the begining of the watching interval, in the first day and the sixth. At some moments when the kitten was at the ground level and the cat was moving back and forth from the ground to the second roof, the kitten seemed to be requesting by miaowing that its mother move him/her to the second roof. These repeated requests by the kitten were being partially ignored, being done only after some hours after dark. The cat seemed reluctant to move her kitten from the ground to the second roof more than once a day, of course during the mentioned days.--109.166.138.220 (talk) 21:03, 11 July 2020 (UTC)
 * Maybe the cat was reluctant to risk taking the jump in the dark. --Lambiam 18:09, 12 July 2020 (UTC)
 * The kitten at the ground level was miaowing in daylight to be moved up and also some time after dark. At some far moment after dark he could be seen at the second roof level, which implies that the cat was delaying the answer to the request until the moment when the kitten no longer really needed to be on the ground to avoid spending the night in a less safe place. From this behaviour of the parent cat of delaying the answer one can get the impression that jumping with the kitten between the ground and roofs is quite demanding energetically, thus requiring a minimization of the number of this type of moves/jumps. So the (or a rephrasing of the initial) question is: What is the additional energy demand of jumping with the kitten compared to usual jumps without a kitten?--109.166.132.47 (talk) 17:30, 13 July 2020 (UTC) Or perhaps the cat is somehow additionaly stressed by the need to prevent the possible, accidental fall of the kitten while jumping with it? Could this be a reason of the rare(ly observed) carrying of the kitten to the ground and back?--109.166.132.47 (talk) 18:25, 13 July 2020 (UTC)
 * P.S. This morning I've seen the kitten running between the roofs of the (inner) yard of the house. At some moment it was trying to jump over a level difference between roofs (one of the roofs having the shape of a wedge) of about half a meter. It didn't seem very easy, the kitten was making quite an effort to get to the upper level, at some moment the kitten was hanging before succeding to jump.--109.166.132.47 (talk) 17:50, 13 July 2020 (UTC)
 * I haven't seen the kitten on the ground today (and neither (in/over) the two days before). Perhaps this has some significance from an energetic point of view.--109.166.132.47 (talk) 18:03, 13 July 2020 (UTC)
 * This evening I've seen the kitten on the ground, without the cat, at around 25 minutes before the dark, while I was preparing to go at a local store. Then when I was coming back from the store, the kitten was no longer on the ground. After arriving in the room, the kitten could be seen on the second roof, moving and running around, near the cat. (It is kind of annoying to have missed again to see the moment of jumping of the cat with the kitten, kitten presumably not being able to make such big jumps on its own.)--109.166.132.80 (talk) 20:17, 14 July 2020 (UTC)
 * Late in this afternoon I've seen the kitten accidentally falling off the roof of the garage while playing with a twig from a tree near the roof. Once on the ground, he was moving or running around, then sleeping on a ledge attached to the exterior house wall behind the metal shed. Then after a while, at about the same moment as (in) the previous evening, the cat and the kitten were running around the exterior walls of the yard of the house in order that the kitten could be moved up to the roof. The next moments the kitten and the cat could be seen on the roofs from behind where the height to be jumped is lower. Thus the way the kitten was able to be back on the roof remains enigmatic/puzzling re the help of the mother cat due to the fact that the jump could not have been observed directly as expected. They have avoided the more difficult path to arrive back/up on the roofs. --109.166.132.80 (talk) 21:36, 15 July 2020 (UTC)
 * Today the kitten has had the largest observed duration spent on the ground, from about 10:00 AM until an hour after dark. This duration may have been started with another fall from the roof while playing with a twig. Early in the morning, the kitten was moving around on the roof. --109.166.137.83 (talk) 23:59, 17 July 2020 (UTC)
 * The kitten has just fallen to the ground while trying to jump onto the roof of the metal shed next to the house wall.--109.166.137.83 (talk) 17:35, 18 July 2020 (UTC)
 * I've been watching the kitten after the fall for about 3 hours until he has succeded to climb back to the roofs, guided by its mother, on one of the other sides of the yard where there are some means which make the climbing quite easy for a kitten, namely metal wires on one side of the fence and brick contours on the other side, the side of the fence used by the kitten being that with metal wires.--109.166.137.83 (talk) 21:20, 18 July 2020 (UTC)
 * It seems that the kitten hasn't an easy recollection of the paths used to climb the previous nights when on the ground, otherwise it would use the previous knowledge to get to the roofs faster instead of miaowing to its mother when she is not in its visual range. But perhaps it somehows enjoys or at least tries to enjoy the duration spent in the ground with its mother around.--109.166.137.83 (talk) 21:50, 18 July 2020 (UTC)
 * Or perhaps when on the ground and not seeing his mother it gets panicked and thus the memory of the previous knowledge gets somehow blocked.-- 109.166.137.83 (talk) 21:53, 18 July 2020 (UTC)
 * The puzzling aspect re its mother's contribution to getting back to the roofs seems solved--109.166.137.83 (talk) 21:59, 18 July 2020 (UTC)

Komodo dragons: past availability as pets, @ 20 years ago, in US
I just finished reading Komodo dragon. I have a memory that dates to the late 1990s. Someone was telling me about their "housepet" collection of several reptiles, including a Komodo Dragon. I remember him mentioning the glass-sided enclosure where it lived.

I gather that it is now illegal to sell these reptiles, and I wholeheartedly approve. However, is it possible that my memory is correct, and that a US resident might have had access to a Komodo, back in the late 1990s?

Thanks,  Tribe of Tiger Let's Purrfect!  21:21, 11 July 2020 (UTC)
 * Your question is under the assumption he had them legally, right? I mean, the illegal trade and ownership of exotic animals is a big thing in the US. --OuroborosCobra (talk) 21:36, 11 July 2020 (UTC)


 * Thanks for the reply. No, I do not assume that he had them legally, and no surprise to me if he did not. He was merely a casual acquaintance (he gave me a haircut, in a popular salon, two times}, and at the time I was clueless about illegal reptiles, etc. I am curious if laws pertaining to importation/trade were in existence at the time for this lovely "wee beastie", or if they were not well-enforced at the time. Here am I, 20 some years later, recalling this memory with some distress and horror, and wondering..... was this a big thing back then and well-enforced? Regards,  Tribe of Tiger Let's Purrfect!  22:19, 11 July 2020 (UTC)


 * Even if the legality of importing a certain species to the US falls under federal (or international) law, whether it is legal to own one might depend on the particular state, as mentioned briefly at Exotic pet. --174.89.49.204 (talk) 05:45, 12 July 2020 (UTC)


 * It's worth pointing out that Komodos are members of the monitor family and, although they're easily the biggest, the others are also quite large. For example, the crocodile monitor gets up to eight feet. All monitors look broadly similar as well. I guess what I'm getting at is that it may have been a Komodo "cousin". Unless you were an expert, it would be very difficult to tell a young Komodo from some other monitor (of whatever ecological status); it may even have been marketed that way, just as anoles are marketed as chameleons and bala are marketed as sharks, even though they look nothing alike. 64.235.97.146 (talk) 15:08, 13 July 2020 (UTC)


 * I didn't know about the "cousins", and I now suspect that was what he had. I don't think he had the resources to (eventually) care for a full-grown Komodo, i.e. his very own zoo! Thanks to all,  Tribe of Tiger Let's Purrfect!  19:15, 17 July 2020 (UTC)