Wikipedia:Reference desk/Archives/Science/2018 May 23

= May 23 =

Mass spectrometry
In an ordinary, commercial single quadrupole ICP mass spectrometer (such as an Agilent 7800), what happens to all of the ions that hit the detector? I presume that there must be some mechanism to clear them off, otherwise they'd just build up and eventually ruin the detector. 202.155.85.18 (talk) 09:26, 23 May 2018 (UTC)
 * The ions will be neutralised by electrons, react with the detector or turn into a gas. Things need to be cleaned inside it. There is a vacuum pump to remove what turns into a gas, and the detector should be changed in the yearly maintenance. see https://www.agilent.com/cs/library/technicaloverviews/public/5991-9342EN-cost-of-ownership-icp-ms-technicaloverview.pdf page 4. Graeme Bartlett (talk) 10:02, 23 May 2018 (UTC)
 * Gunk (the technical term) does build up inside of mass spectrometers, and they do need to be disassembled and cleaned regularly to address this. While many of the ions will grab an electron and dissipate as a gas when the system is vented at various times, plenty of gunk collects on the components after regular use.  The components need to be taken out, disassembled, cleaned, and re-assembled.  I've not used that specific model, but I suspect the processes are similar for any Mass Spec.  The documentation above notes the need to periodically clean the "ion lenses", which IIRC are metal plates that carry an adjustable voltage to allow the ion beam to be focused.  This was the most fidly bit in the cleaning process.  Source: My first job as a chemist was doing exactly that.  It was 22 years ago, so things may have changed a bit, as well.  -- Jayron 32 14:04, 23 May 2018 (UTC)

What's the strongly orange-colored fungus that grows in the Mid Atlantic states?
Sagittarian Milky Way (talk) 14:11, 23 May 2018 (UTC)
 * Most likely Fuligo septica, also called the "dog vomit slime mold". It isn't confined to the Mid Atlantic states, but is found worldwide. -- Jayron 32 14:52, 23 May 2018 (UTC)
 * That's a terrestrial fungus, you're not going to find that in the middle of the Atlantic, like the OP is asking about. 131.251.254.154 (talk) 14:57, 23 May 2018 (UTC)
 * Mid-Atlantic (United States) is terrestrial. ←Baseball Bugs What's up, Doc? carrots→ 15:06, 23 May 2018 (UTC)
 * What an illogical and confusing name! Fair enough, I stand corrected. 131.251.254.154 (talk) 15:38, 23 May 2018 (UTC)
 * You do know that "I hadn't heard it before now" is not a synonym for "illogical". The states are located along the middle part of the Atlantic coastline of North America.  Thus, mid-Atlantic.  There are other places in the world named for the bodies of water they are near, such as the Pacific Northwest, the Eastern Mediterranean, etc.  It's more surprising you've never heard of regions of land named after some combination of a direction + body of water. -- Jayron 32 15:48, 23 May 2018 (UTC)
 * To be fair to the IP, without specification, to anyone not from the US, Mid-Atlantic would clearly refer to the middle of the Atlantic, as in Mid-Atlantic Ridge. It is a confusing usage. Fgf10 (talk) 21:22, 23 May 2018 (UTC)
 * To be fair to Jayron, logic would tell you that their are no states in the middle of the Atlantic Ocean. ←Baseball Bugs What's up, Doc? carrots→ 01:49, 24 May 2018 (UTC)


 * No idea, I'm in the UK (similar climate). Our brightly orange coloured one isn't simply a fungus though, but a lichen. Xanthoria parietina, Caloplaca marina or C. thallincola are all commonly seen (and fairly easily distinguished). Andy Dingley (talk) 15:08, 23 May 2018 (UTC)
 * To be fair, slime molds aren't fungi either. But as many people don't recognize the taxonomy here, "orange slimy stuff" is the best we can go on.  Of course, if SMW really wanted someone to provide useful answers, he'd supply us with a photograph.  -- Jayron 32 15:11, 23 May 2018 (UTC)
 * The phone with the photo got water-damaged and always dies while booting even on AC power. It was on the ground, a pretty saturated orange not yellow, not resembling stereotypical mushrooms, mold, lichen or moss (and the last 2 are symbiotes and plant anyway), had a fairly simple shape without hairs or fuzziness and may have only been attached to the ground in the middle. Thickness was multiple millimeters, length and width both over a centimeter but not over a decimeter and at least a few times the thickness. Thanks for correcting my misconception that slime molds were fungi. Sagittarian Milky Way (talk) 16:15, 23 May 2018 (UTC)
 * I didn't pick one to see if the underside had furrows like mushrooms. Sagittarian Milky Way (talk) 16:24, 23 May 2018 (UTC)
 * Sagittarian Milky Way, they were fungi. See Slime mold: They were originally represented by the subkingdom Gymnomycota in the Fungi kingdom and included the defunct phyla Myxomycota, Acrasiomycota, and Labyrinthulomycota.  Nyttend (talk) 20:46, 23 May 2018 (UTC)
 * But SMW didn't mention "slimy". If it's slimy, then it's likely to be a slime mould or a cyanobacter (we have many local species of Nostoc, greeny brown, under a generic folk name of "witches' butter" - but slime moulds are uncommon). Here at least, "orange stuff visible on a tree or rock" will be one of the orange lichens, far more likely. Andy Dingley (talk) 16:16, 23 May 2018 (UTC)
 * Chicken of the woods is often strikingly orange and common enough in the UK (don't know about Mid Atlantic states). --catslash (talk) 22:59, 23 May 2018 (UTC)
 * Chicken of the woods might be it, or a related species. Sagittarian Milky Way (talk) 23:56, 23 May 2018 (UTC)

Apollo reentry and "equivalent power" for the heatshield?
Does anyone have an estimate for the equivalent power of the Apollo Command Module heatshield during atmospheric re-entry? Just something rough, in terms of initial kinetic energy + potential energy - final KE + PE (at time of parachute deployment), divided by the duration. How does this compare with a Saturn engine? Andy Dingley (talk) 15:03, 23 May 2018 (UTC)


 * How I'd do it: KE+PE in LEO-PE at chute deploymanet/average time for descent to deploymanet of chutes. I'm supposed to be in a meeting so can't actually do that. Greglocock (talk) 22:47, 23 May 2018 (UTC)


 * Did the command module actually brake into LEO? I thought it came in with more energy than that. The max would be the entire energy from The orbital distance of the moon, I think. Final KE at chute deployment must be quite small. The problem in any case is to research the mass of the command module at the point it begins is aerobraking, as it will have thrown away a bunch of stuff earlier. The KE being dissipated will be KE= 0.5*mv2. so what was the mass? -Arch dude (talk) 23:37, 23 May 2018 (UTC)
 * I don't think they entered LEO on the return, it was a direct burn to re-entry, but I assume that the energies were similar, otherwise they would have done so. It's a limit that Apollo must have had sufficient heatshield to cope with at least LEO's energy. It would be interesting to know what the difference in energy (pre-burn) between the return from the translunar orbit and an LEO orbit would have been - was this best dealt with by the SM engine burning longer, or by a larger heatshield? Andy Dingley (talk) 08:52, 24 May 2018 (UTC)
 * It's all about the mass. In general it takes less mass of heat shield than it does of fuel to provide the same braking energy. That's why you use a heat shield at all. Otherwise, the system would have used the rocket all the way down to parachute height. -Arch dude (talk) 20:57, 24 May 2018 (UTC)
 * This NASA document suggest that the heat shield was designed to handle a total heating load of between ~7000 and ~37500 BTU, which is (very) roughly the same number of kilojoule, at a maximum heating rate of between 83 and 425 BTU/ft2-second. With a diameter of 12'10", the heat shield would have an area of approximately 130 square feet, meaning the heat shield (very roughly) had a power equivalent of between 10790 kW and 55250 kW. If you by "Saturn engine" refers to the Rocketdyne F-1 used on the first stage of the Saturn LV, that was rated for maximum trust of 7770 kN. One kilowatt is the same as one kilonewton per second, so the heat shield was about 7 times "more powerful" than the F-1 engine. A direct comparison is kind of pointless, but fun to play with the numbers :) WegianWarrior (talk) 21:53, 24 May 2018 (UTC)
 * Thanks, that's saved me digging out a bunch of numbers. Andy Dingley (talk) 22:25, 24 May 2018 (UTC)
 * There's something funky with your math/units; I'm pretty sure that saying one kilowatt is the same as one kilonewton per second is incorrect. I think you want a kilonewton-meter per second to get the units to work out.
 * (Note that if you presume that the heat shield is 7 times more powerful than the F-1 engine, then you get pulped astronauts. Recall that a force of one newton will accelerate a 1 kg mass at one meter per second per second. The Apollo command module had a mass of about 6000 kg, so a thrust of 7770 kN – 7 770 000 N – will impart an acceleration of about 1300 m/s/s, or about 130 g.  At seven times that force, you're looking at a deceleration of close to a thousand gees, bringing the returning Apollo capsule to rest relative to the Earth in about...one second.  Splat!) TenOfAllTrades(talk) 22:51, 24 May 2018 (UTC)


 * In round numbers, the loaded Apollo command module came in at around 5500 kg. Atmospheric entry on a lunar return trajectory was at about 11 km/s.  If I haven't lost any powers of 10, that comes out to a kinetic energy of about 300 GJ (gigajoules).  Since kinetic energy goes as velocity squared, the remaining kinetic energy of the capsule is negligible for our purposes.
 * From the start of atmospheric reentry to deploying the drogues takes about 7 minutes on a lunar return trajectory. This NASA document has actual data, showing the acceleration forces felt aboard Apollo 10 during reentry in Figure 4.  There was a relatively rapid rise to about 7 gees, followed by more complex acceleration profile during the remainder of the descent; that works out to an average deceleration force of about 2.5 gees.  Getting rid of 300 GJ over 7 minutes requires dissipating about 700 MJ/s (700 megawatts).
 * Most of that energy ends up carried away by the air, not imparted to the heat shield. (Which is fortunate.  Back-of-the-envelope, 300 GJ is enough thermal energy to completely vaporize 5 tons of aluminum capsule&mdash;4 times over.)
 * Decelerating at an average of 2.5 gees requires a drag force of about 140 kilonewtons (5500 kg times 25 m/s^2). As noted above, the thrust of one first-stage F-1 was 7770 kN: about 50 times as much. TenOfAllTrades(talk) 01:42, 25 May 2018 (UTC)
 * I thought it was carried away as a result of ablation. That's not just the air, but also part of the heat shield itself being converted to gas (and plasma: it's really hot) and being carried away, with its heat, into the air. -Arch dude (talk) 21:53, 25 May 2018 (UTC)
 * That's a common misconception; the ablation of the heat shield does dissipate some of the energy, but only a relatively small fraction. (Again, the kinetic energy shed by the capsule would be sufficient to vaporize the heat shield many times over.) Essentially, the blunt reentry vehicle piles up a bunch of air in front of the vessel; the air is compressed and heated, and spills around and away from the capsule, taking the heat with it.  The heat shield is mostly dealing with radiant heating from this compressed shock layer, rather than direct frictional heating. The shadowgraphs in Atmospheric entry are relevant. TenOfAllTrades(talk) 01:33, 26 May 2018 (UTC)

What makes decibels of whistles higher?
Decibels of whistles for referees vary and the max decibels that I found is 127.6 dB. How does the whistle itself influence the dBs? Wouldn't that be almost 100% dependent on how strongly you blow into it? How does the force of the blowing influence the dB then?--Hofhof (talk) 20:34, 23 May 2018 (UTC)
 * See the quite extensive steam whistle for some pointers. A whistle can be thought of as a "pneumatic spring". See Helmholtz resonator. The energy is provided by the air blast, stored in the reservoir by compressing the air slightly, then released. It's energy from the reservoir that makes the sound, not the moving air. Up to a point, the volume is proportional to the blowing velocity. It is very difficult to increase the sound volume past this by blowing harder, because once the reservoir is operating at its peak, then blowing harder and harder just doesn't change this.
 * Blowing harder may also change the frequency, but this depends on the type of whistle design. Some are optimised to do this (making them almost 'playable'), some to avoid it. Andy Dingley (talk) 21:01, 23 May 2018 (UTC)
 * It's very simple. The whistles go woo woo! --47.146.63.87 (talk) 07:52, 24 May 2018 (UTC)
 * A Decibel abbreviated dB is a ratio on a logarithmic scale and the term 127.6 dB means only "5.012x1012 times as powerful". That usage neglects to explain the power reference (what power is 0 dB?). Sound power levels in decibels are meaningful only when expressed with a suffix to define their reference. For example, the OP might mean dB ref 10−12 W (threshold of hearing), dB(A) (a perceptual frequency-weighted scale) or something else unspecified. DroneB (talk) 11:20, 24 May 2018 (UTC)
 * The OP specifically asked about a whistle that is blown into, such as those used by referees and railway train managers. It takes a certain amount of energy to get the pea in the whistle moving, and this appears to be near the maximum amount of airflow that a person can blow. Consequently, there cannot be much variation in the intensity of the sound. Akld guy (talk) 20:17, 25 May 2018 (UTC)

Weird pond creature
What kind of pond creature is this?



It was wriggling about in the water.

Location: England

Cesde v a (talk) 23:42, 23 May 2018 (UTC)


 * Looks like a tadpole of some sort. -- Jayron 32 02:04, 24 May 2018 (UTC)


 * Unfortunately, there's no scale, although the netting mesh suggests that it's small. I Google-imaged "tadpole" and a few photos came up that look kind of like it. ←Baseball Bugs What's up, Doc? carrots→ 03:02, 24 May 2018 (UTC)


 * It is most certainly a tadpole, although very early in its development; you can see the basic morphology from which the torso develops, but the tail lacking any fringe dates this one as a recent hatchling. Its apparent size relative to its level of development is a bit of a confusing factor for me; a more precise location could be instrumental in giving a more precise identification. Right now, my best guess is Rana Temporaria. Sno<b style="color: #b2dffe;">w</b> <b style="color: #d4143a">let's rap</b> 06:48, 24 May 2018 (UTC)
 * Sorry for no scale. Also the picture is rather low quality. From observation, our frogspawn appeared to not have gotten past the initial stage. It just disintegrated. I would have expected a tadpole of this size to definitely have some limbs, and appear a lot darker. I suppose i'll have to wait and see. The timing is right and our frogs are Rana temporaria, although appear a lot darker but I think that's down to water algae content. Thanks for your help, Cesde v a  (talk) 07:48, 24 May 2018 (UTC)


 * I agree that the most confusing aspect is the large size relative to development. Some frogs do have tadpoles that can be several times that apparent size very early in the larval stage, but I am scratching my head all the same as there are only so many species extant in England.  As to colouring, it can vary considerably between populations in a given species, and even within a given population--although European common frogs are usually a little darker, as you note is typical for your local population in the past.  The fact that you describe this specimen as "disintegrating", suggests a possible explanation, though: dead specimens no longer maintain constrained osmotic equilibrium in their tissues and can swell considerably.  The integrity of the torso appears substantial in the picture, but as you note, the quality is so-so. <b style="color: #19a0fd;">S</b><b style="color: #66c0fd">n</b><b style="color: #99d5fe;">o</b><b style="color: #b2dffe;">w</b> <b style="color: #d4143a">let's rap</b> 08:31, 24 May 2018 (UTC)


 * It most certainly is not a tadpole. The colour is wrong, the shape of the body is wrong and the tail is wrong (OK otherwise!) It is the larva of a member of the Eristalini a kind of fly, commonly known as hover flies in the UK. The larva is known as a rat-tailed maggot and what appears to be a tail is in fact a breathing tube. Have a look at this image. Richard Avery (talk) 09:54, 24 May 2018 (UTC) Langegg Rattenschwanzlarve Eristalini.jpg
 * Thank you. That's extraordinary, I never knew hover flies had such interesting larvae. Cesde v a  (talk) 10:09, 24 May 2018 (UTC)
 * As it happens, I took a picture of what I think was hoverfly near the pond the other day. Fly0001.png Cesde v a  (talk) 10:21, 24 May 2018 (UTC)
 * Of course, Wikipedia has an article on... everything! —2606:A000:1126:4CA:0:98F2:CFF6:1782 (talk) 13:27, 24 May 2018 (UTC)


 * Thanks for the link. It seems the larva is an indicator of poor water quality, which is as I suspected. I added some oxygenating plants a few days ago so we'll see how that goes. Cesde v a  (talk)


 * Eristalis interruptus, I would venture. (Though I will stop short of insistence for obvious reasons. ;) <b style="color: #19a0fd;">S</b><b style="color: #66c0fd">n</b><b style="color: #99d5fe;">o</b><b style="color: #b2dffe;">w</b> <b style="color: #d4143a">let's rap</b> 17:32, 24 May 2018 (UTC)


 * I stand corrected! (and a little sheepish). I thought there was something wrong with that tail morphology (there's usually at least a little bilateral fringe on the tail/flage, even very early in development), but I just chalked it up to the photo quality or state of the specimen.  Thanks for rescuing a gung-ho ID--fascinating larval phase/lifecycle for that clade! <b style="color: #19a0fd;">S</b><b style="color: #66c0fd">n</b><b style="color: #99d5fe;">o</b><b style="color: #b2dffe;">w</b> <b style="color: #d4143a">let's rap</b> 17:04, 24 May 2018 (UTC)