Wikipedia:Reference desk/Archives/Science/2014 August 18

= August 18 =

Conclusions of an autopsy
A recent case got me to thinking about what information can or cannot be concluded from an autopsy. So, two questions. (1) Can an autopsy determine if the decedent were moving (e.g., running) versus standing still when the decedent was shot? And (2) Can an autopsy determine the position of the decedent's body when he was shot (e.g., whether or not he was holding his hands up in a "surrender" position?)? If indeed the medical examiner can make conclusions about these two matters, how would he do so? Thanks. Joseph A. Spadaro (talk) 04:25, 18 August 2014 (UTC)


 * The position of the body should show if he was running (unless he survived for some time after being shot and changed his position). Also, if he was running on a road or sidewalk, you'd expect abrasions where he slid on the cement.  On grass his clothes should have grass stains.  And the path of the bullet through the body would reveal the position of the part of the body it hit.  If the body was vertical at the time, that would tend to indicate standing, while if it was angled, that would indicate running (accounting for the height and distance at which the bullet was fired).


 * Detecting the hands up position would be a lot trickier. If the shooter was close enough that the victim was sprayed with gunpowder residue, then the location and density of the spray would indicate that the hands were up, but with a distance shot this method wouldn't work.  Blood spatter from the victim could be used in a similar way, but there might not be much spatter, especially if the bullet is small, doesn't exit the body, and the victim was wearing thick clothes, like a winter coat.  On the other hand, with a case like the fatal JFK head shot, there was all kinds of spatter to work with.  StuRat (talk) 04:57, 18 August 2014 (UTC)


 * Thanks. But, I still have some confusion.  You said: The position of the body should show if he was running.  Why is that?  Once you are shot, don't you just sort of "plop" down, regardless of whether you were running or standing still?  You also said: Also, if he was running on a road or sidewalk, you'd expect abrasions where he slid on the cement.  When your body hits the ground, wouldn't you get abrasions either way, whether running or standing still?  Thanks.   Joseph A. Spadaro (talk) 05:31, 18 August 2014 (UTC)


 * At the very least, if he was hit in the back instead of the front, that would indicate he was leaving the scene. ←Baseball Bugs What's up, Doc? carrots→ 06:52, 18 August 2014 (UTC)
 * In the specific case of Shooting of Michael Brown, that doesn't seem to be a significant factor. Okay there are suggestions from witness statements that he was shot in the back, which may be problematic if there's no evidence of sufficient risk to anyone at the time to justify such a shooting. But although it's difficult to say since we only have third party reports of the officers account, the main dispute, as I think the OP knows appears to be whether he was kneeling on the ground facing forward but not moving instead surrendering to the officer, or rushing towards the officer at the time of the fatal shots, after an earlier alleged attempt to grab the officers gun, before he started to run away. Nil Einne (talk) 08:02, 20 August 2014 (UTC)


 * Momentum is a factor here. If the victim is moving quickly, they will keep moving quickly after being shot (unless shot with something large and fast enough to cancel out their forward momentum).  I'd expect there to be a difference between abrasions resulting from a straight fall down or backwards, and abrasions resulting from a fall when running, which results in sliding across the ground for a small distance. MChesterMC (talk) 08:41, 18 August 2014 (UTC)


 * Moment of inertia seems appropriate, as well. Though I'm what "laymen" call an idiot, sometimes. InedibleHulk (talk) 22:02, 18 August 2014 (UTC)


 * A-ha. That all  makes sense.  Thanks!   Joseph A. Spadaro (talk) 08:49, 18 August 2014 (UTC)


 * As for the abrasions, you'd expect them to be longer and deeper if the victim was running when they dropped on cement or stones, or for the grass stains to be darker and longer if they dropped on grass. Of course, if the wounds weren't immediately fatal, they might have stopped running before they dropped.  Regarding the angle of the bullets, the first should best show the initial position of the victim, but with rapid firing the victim's position might not change much between shots.  StuRat (talk) 17:07, 19 August 2014 (UTC)


 * The problematic word here is "concluded" the medical examiner will describe a bunch of facts, that a bullet entered in one location and exited at another, that certain wounds were found, perhaps any signs of intoxication, cause of death (blood loss, brain trauma). It will be the forensic specialists who argue the case in court who will try to convince the jury of their theories of what happened.  They will argue the patterns show he must have been standing, running away, shot while falling, etc. μηδείς (talk) 16:48, 18 August 2014 (UTC)


 * A medical examiner can conclude lots of things, as Steven Hayne illustrated. —Tamfang (talk) 20:03, 18 August 2014 (UTC)


 * Of course, he can conclude all sorts of things, such as cause and approximate time of death, type of weapon used, trajectory of a bullet though the body. He can have his own theory, if asked to testify as a witness.  But he can't conclude guilt or criminal fact in the legal sense, which is what the OP seems to be getting at, given the recent shooting in MO. μηδείς (talk) 22:13, 18 August 2014 (UTC)
 * Though, of course, he may be getting at The Huston Plan. Inconclusive, I declare. InedibleHulk (talk) 22:20, 18 August 2014 (UTC)

Thanks, all. Joseph A. Spadaro (talk) 21:03, 19 August 2014 (UTC)

Mayer bullets
There is an article on Russian Wikipedia about something called Mayer bullets or Mayer slugs. According to Google translate the article seems to say these are used in shotguns. How does that work exactly? Is a cartridge full of propellant loaded behind the slug? Are the Russians still using muzzle loaders? Our article on shotgun slugs seems to show the slug always crimped to a shell, but in the images in the Russian article just shows the slugs by themselves. SpinningSpark 10:48, 18 August 2014 (UTC)


 * My guess is that they are a normal type of slug, normally fired from a complete shell. I think they are just pictured solo for illustrative convenience. If you do an image search for shotgun slug, you'll see lots of photos where the slugs are removed from the shell for comparison purposes. Here's an article all about modern slugs, and it mentions a guy named Mayer, but it's probably not the same Mayer SemanticMantis (talk) 14:58, 18 August 2014 (UTC)


 * Yup, not the same Mayer. That's Steve Mayer of Winchester, we're looking for A. K. Mayer (А. К. Майера) who invented a slug in 1963. SpinningSpark 16:22, 18 August 2014 (UTC)


 * They certainly seem to be on sale as bullets only without a shell . SpinningSpark 16:54, 18 August 2014 (UTC)


 * I found a video where a guy is shooting them. I have no idea how they are commonly sold, but he shows the single slugs, then packs one into a shell, then fires it from a seemingly normal Break_action shotgun . This video seems to be the same guy, and shows a little more about how the shell is assembled . I found the videos by searching /Майера ружье/, with the second word meaning "shotgun" in Russian, according to google translate. SemanticMantis (talk) 21:58, 18 August 2014 (UTC)
 * Thanks, that about answers it then. SpinningSpark 23:57, 18 August 2014 (UTC)

Nuclear contrail thingies
Yeah, I'm sure that's not the correct term, but since I have no idea what they are, I also have no idea what their name is. You can see them in the image at right; I've seen better images of them before but wasn't able to find any with a quick check of Commons. They are quite distinct white-ish lines of what look like water vapor, and they seem to have a strange habit of appearing in the area of nuclear weapon tests. I have a guess as to what they are, but it's probably wrong, and I'm sure someone here knows. Thanks in advance! Evan (talk&#124;contribs) 16:05, 18 August 2014 (UTC)
 * They are smoke trails from small rockets launched just prior to the nuclear detonation. The visual distortion of the trails provides information about the detonation. Trying to find the relevant articles... DMacks (talk) 16:11, 18 August 2014 (UTC)
 * Mentioned with cite at Effects of nuclear explosions. I know I've seen more detail of the history of this use (originally discovered accidentally!). DMacks (talk) 16:21, 18 August 2014 (UTC)
 * Fantastic! Thanks for the speedy response. Evan (talk&#124;contribs) 16:24, 18 August 2014 (UTC)


 * How about an entire book on the history and role of such rockets? NASA Sounding Rockets, 1958-1968: A Historical Summary.  This book focuses on civilian sounding rockets, including many that were fired at White Sands, but if I recall, it also has a section on the early Army rockets launched during the Trinity test in 1945.  The photograph posted in the original question is a 1953 test at a different Department of Energy facility, the Nevada Test Site.  Those sounding rockets were almost certainly small Army rockets and their smoke-trails would have been used as an indicator of the winds aloft (after the blast) at various distances.  For some tests, the rockets would also be equipped with radiological, physical, and chemical detection and sample-collection equipment.  You can find historical records of such tests from the Nevada Test Site's OpenLibrary web-page, hosted by the Department of Energy's Office of Scientific and Technical Information.  In just a few moments of browsing, I found a technical report on the specific purpose of sounding rockets during Operation Hardtack, Aircraft and Rocket Fallout (1959).  If you're interested in the exact test pictured above (Upshot-Knothole Grable, (1953)), I'm sure you can spend a few more hours browsing those resources.  Nimur (talk) 17:16, 18 August 2014 (UTC)


 * ► Sounding rocket.   —E: 71.20.250.51 (talk) 17:41, 18 August 2014 (UTC)
 * Here is the accidental first use of visual effect I was remembering: File:Trinity explosion film strip.jpg. And according to ISBN 9783540304210 page 992, the smoke trails are actually not even from really rockets, just simple mortars (in this context they are only used for the smoke trails, not the object being lofted). DMacks (talk) 16:57, 19 August 2014 (UTC)


 * as stated by others they are rocket smoke trails laid intentionally before the detonation. The intention is to use them as indicators of blast shockwave and turbulence following detonation. In addition to contributing to the general understanding of weapon effects remember that these weapons are from the era of nuclear bombers. When you drop a nuclear bomb the survival of the aircraft and crew is one consideration. To this end one needs to anticipate the weapon effects at altitude in the vicinity of the detonation. http://www.atomcentral.com/atomic-smoke-trails.aspx — Preceding unsigned comment added by 73.170.236.122 (talk) 04:43, 2 September 2016 (UTC)

Water jet cutter as a weapon
About how effective would a water jet cutter be as a weapon?(ignoring the bulk of the surrounding hardware) Would the stream just dissipate into steam after a few feet? 108.170.113.22 (talk) 16:37, 18 August 2014 (UTC)


 * Our article does say "The penetrating power of these tools has led to the exploration of their use as anti-tank weapons but, due to their short range and the advent of composite armour, research was discontinued.[citation needed]". Rojomoke (talk) 16:45, 18 August 2014 (UTC)
 * Yeah I saw that, but ya know. Citation needed, plus I want to know what causes the range to be limited. 108.170.113.22 (talk) 16:57, 18 August 2014 (UTC)
 * Air resistance and turbulent flow limit the effective range at which you can shoot a stream of high-velocity liquid. You read a two-sentence overview at the terminal velocity section of our article on water drops.  Momentum and energy - which you would want to direct into the target - are instead lost to the air around the stream of water as it "sloshes."  The faster you move the water, the more it sloshes, because air flowing past the "edges" of the water stream induces a viscous flow shear force.  Nimur (talk) 17:02, 18 August 2014 (UTC)
 * I remember reading that in the article when I first started at my current job (we have a waterjet cutting machine) and pointing it out to a colleague who laughed. When it comes to steel, particularly thicker/harder steel, it is very slow. To give some numbers, the M1A2 Abrahms tank apparently has armour 120mm thick (according to google, yeesh), the feed rate for that thickness is somewhere in the region of 2-3mm a minute. That means to cut through 1m of steel would take some 6-8 hours. In that time your tank could have driven 250-340 miles-- Jac 16888 Talk 17:34, 18 August 2014 (UTC)
 * The rate at which the machine could cut a slot might not matter if you could aim it sufficiently well - a single penetrating hole one millimeter in diameter would be plenty if you can hit exactly the right spot in the engine bay and have the water jet drill a 1mm hole through some vital engine part or electronics. But I agree that keeping the water flow focussed over significant distances would be the downfall of such a weapon.  I doubt that it's practical beyond a foot or two. SteveBaker (talk) 20:27, 18 August 2014 (UTC)
 * 1mm could take 30 seconds, which a long time considering at the same time a tank-turret is probably turning around to face you-- Jac 16888 Talk 21:48, 18 August 2014 (UTC)
 * That sentence, which evolved out of something posted by someone at Central Michigan University in 2007, was apparently inspired by the use of a water jet cutter in the video game Metal Gear Solid 2. See the original addition.  I can't find anything using Google that would support that sentence, so I removed it.  Red Act (talk) 20:32, 18 August 2014 (UTC)

Would shooting another liquid that has a higher density and/or boiling point at high velocity make a difference? Liquid metal perhaps? 69.121.131.137 (talk) 22:31, 18 August 2014 (UTC)
 * You're on the right way, since most portable anti-tank weapons use metal, which behaves like a liquid at the kind of pressure involved. Generating that kind of pressure (I've read it's in the TPa range, which is more than 107 times atmospheric pressure) using non-destructive equipment (in the sense that it doesn't blow itself apart in the process) is difficult even with today's technology. Sidney Alford lists some shaped charges using water, so the idea isn't flawed as much as it hits its limits if applied to modern armor.
 * Also note that a tag does not necessarily indicate that the tagged statement is dubious; it indicates that a key fact is not backed by a source in the list of references. For dubious statements, we have the [dubious] tag. - ¡Ouch! (hurt me / more pain) 05:49, 19 August 2014 (UTC)
 * It is a common application in manufacturing engineering. See Water jet cutter. It only works on very short distance but is a very cost efficient, precise, fast and reliable technology to cut flat materials like steel plates. But it wouldnt make much sense as a weapon. --Kharon (talk) 16:51, 19 August 2014 (UTC)
 * Note that shaped charges don't work either if the range is too high or too low. If the distance between charge and target surface is off, the effect can be severely diminished or even completely fall flat.
 * From Shaped charge: The location of the charge relative to its target is critical for optimum penetration for two reasons. If the charge is detonated too close there is not enough time for the jet to fully develop. But the jet disintegrates and disperses after a relatively short distance, usually well under 2 meters. At such standoffs, it breaks into particles which tend to tumble and drift off the axis of penetration ; OTOH, a water jet cutter wouldn't work well even at 1m, where the shaped charge only begins to exhibit severe degradation. - ¡Ouch! (hurt me / more pain) 08:33, 20 August 2014 (UTC)

In the Yom Kippur War, very low tech predecessors of the water jet cutter were efficiently used as weapons by the Egyptian army on the Bar Lev Line. --Dweller (talk) 12:14, 21 August 2014 (UTC)

Kidney function questions
The other day I started wondering about kidney function. Firstly, does the filtering ability of the kidneys dynamically respond to waste concentrations in the blood? If a person happens to have high levels of urea, or salt, or something else in their blood does the body have the ability to increase the activity of the kidneys, or are they pretty much going to filter the blood at a fixed rate regardless? Secondly, for a fixed level of hydration, if one has more waste in the blood (e.g. urea / excess salt) does that lead the kidneys to excrete more water as well or is the water output about the same but the waste in the urine more concentrated? Dragons flight (talk) 23:10, 18 August 2014 (UTC)


 * First of all, it's important to clarify that the kidney only removes excess organic molecules and/or wastes. The answer to your first question, as far as I can tell, is yes. Refer to Clearance (medicine). Not sure about the answer to your second question, sorry.  ceran  thor 00:25, 19 August 2014 (UTC)


 * The removal of waste and water are largely independent (although obviously some water is needed to carry the waste out). If you drink a very large quantity of water, but don't eat much or do much, your urine will be clear, since it's mostly water.  If you are dehydrated, but have eaten a lot and done a lot of exercise, your urine will be brightly colored, since it's much more concentrated with waste.  Obviously that wouldn't be a safe test, but you can take some vitamin C, instead.  That will turn your urine brighter yellow, which indicates it has a higher concentration of waste (vitamin C, in this case).


 * I suspect that salt is a special case, though, where the concentration of salt in the urine can't be changed much relative to the concentration in the blood. This would explain why eating salty things makes you thirsty, because the salt must be diluted, as it can't easily be removed at high concentrations.  StuRat (talk) 00:38, 19 August 2014 (UTC)


 * I would suggest conceptualizing the kidney as an organ of absorption rather than merely excretion. For the example of Vitamin C, one should realize that all the vitamin C in the serum passes into the renal tubules, and then only a certain amount is reabsorbed. So the kidney isn't responding to a high level of vitamin C and excreting more, it's just excreting all the vitamin C regardless of its blood level, and then reabsorbing the same amount it always does. Salt, as StuRat says, must be considered separately, as it's not a simple matter of passive diffusion; there are a variety of means of regulating salt (active transport, hormones, countercurrent multiplication, etc.). You may be interested in the concept of obligatory water loss, which is the amount of water that must be excreted in order to remove waste products and thereby maintain health.  - Nunh-huh 01:01, 19 August 2014 (UTC)
 * I see we don't have an article on obligatory water loss, but you will find a brief mention in dehydration. - Nunh-huh 01:01, 19 August 2014 (UTC)

Let's take a step back here. Kidney function starts with what seems to be a pretty straightforward filtration in Bowman's capsule, (lovely illustrations in our article!) where most contents of the serum (but not proteins) are allowed to escape into the system. Then here is more activity proximal convoluted tubule where more things can be specifically excreted into this ever-flowing stream. Then this, the loop of Henle and distal convoluted tubule remove things that you want to keep, like water and salt, and finally what is left is collected and dumped. All of this is massive generalization, since each and every cell is a tremendously complicated living thing capable of a vast range of behavior; you'd really have to look up for your molecule of interest what happens. But urea and salt are on the diagram I've added at the top of this section. Note of course that every process done to a solute - filtration, secretion, reabsorption - will tend to be influenced by the internal concentration of whatever it processes by Le Chatelier's principle, linearly if it follows a first order relationship, otherwise in some more complicated way. But it generally is more complicated; the kidneys have primary responsibility for keeping many of the overall concentrations of things in the blood, especially ions, at the right values. For example an ACE inhibitor for high blood pressure ultimately affects sodium reabsorption in the kidney (see angiotensin). Wnt (talk) 12:58, 21 August 2014 (UTC)