Wikipedia:Reference desk/Archives/Science/2016 October 29

= October 29 =

component type ID
what is this diode(?) ? On the PCB, the designator is SGxxx and the symbol is like this: o---><---o Thanks everyone in advance! Asmrulz (talk) 03:37, 29 October 2016 (UTC)
 * The colour band numbering suggests 53±2%. If it was a diode you would put "1N" on the front. 1N532, but since the red is offset it looks more like a tolerance. THis may not be a diode. Graeme Bartlett (talk) 04:01, 29 October 2016 (UTC)
 * It might be a transient-voltage-suppression diode. Though at first I thought it looked like a fuse: http://www.slimlab.net/mirror/fusecolours/fusecolours.htm but the colours don't decode to anything. Graeme Bartlett (talk) 04:29, 29 October 2016 (UTC)
 * I don't think this looks much like a diode. The internal structure looks much more like a resistor, although the clear glass packaging would be unusual.  If it is a resistor, I don't think the offset red band is a tolerance, resistor colour codes are a minimum of three bands and this has only three.  More likely the offset is to indicate which end to read it from.  I would also read the centre band as brown rather than orange; 53 is not a preferred number whereas 51 is on the E24 series.  That would make its value 5.1kΩ.  Have you tried measuring it?
 * I have seen diodes colour coded in this way, for instance the common 1N4148 diode is marked with Y-BN-Y-S colour bands by some manufacturers, and the "1N" is just implied. However, 1N512 is a large diode with a threaded stud. SpinningSpark 09:29, 29 October 2016 (UTC)
 * It feels plastic-y and doesn't measure as anything (open loop) in either direction Asmrulz (talk) 10:08, 29 October 2016 (UTC)
 * If that's the case it would not be a fuse, diode or resistor. (but could be a blown fuse.) transient-voltage-suppression diode is still possible as it will only conduct when the voltage is high. Graeme Bartlett (talk) 12:56, 29 October 2016 (UTC)
 * The pictured component is a spark gap surge protector. AllBestFaith (talk) 12:58, 29 October 2016 (UTC)
 * Yup, put a coil across it, is arcing. Thanks everyone Asmrulz (talk) 14:07, 29 October 2016 (UTC)

Best substance to absorb moisture from a damp item upon contact
I am looking for a substance that will absorb moisture directly from a damp item upon contact. I have been looking into desiccants (specifically activated carbon because of it's easy regeneration properties and additional odor removal characteristics) as well as super absorbent polymers. However, the only evidence I can find regarding desiccant moisture absorption is dealing with removal of moisture in the air and the SAPs absorbing liquid that has been directly poured onto the polymer.

Is there a material out there that can remove moisture from a damp item? Preferably a material that can be reused and can maintain it's absorption properties if contained in a non-woven/fabric covering. — Preceding unsigned comment added by 146.88.42.76 (talk) 04:51, 29 October 2016 (UTC)


 * Powdered calcium chloride can do this, but it's not reusable. 2601:646:8E01:7E0B:411:FA40:3178:507F (talk) 06:36, 29 October 2016 (UTC)


 * Are you concerned about transfer of the dessicant to the item? Calcium chloride would be a problem there.
 * I would look at fuller's earth. This is cheaply available as cat litter (the grey mineral cat litter) and can be powdered further in a coffee grinder (cheap whirling blades type). It's inert, absorbent and can be regenerated by oven drying.
 * I'd also consider using a towel. This is already "its own fabric covering" and can be applied and removed cleanly and easily. Well laundered (older) cotton towels are fairly fibre free, and microfibre fabrics work well too. Andy Dingley (talk) 09:24, 29 October 2016 (UTC)


 * Sawdust or fine wood chippings, possibly, if it's dried out after use.--TammyMoet (talk) 10:38, 29 October 2016 (UTC)
 * Vermiculite is often used as an absorbent. -- Jayron 32 10:47, 29 October 2016 (UTC)


 * It would help if you inform us of what the item was. For instance, once having finished the wet process of making gunpowder one uses distilled alcohols for fast desiccation before the nitrate can form large crystals. If you have been looking at polymers, you will ready know about how to rejuvenate silica-gel in order to use it again. Then there is vacuum freeze drying and many other techniques. However, there is not one method that suits all cases. --Aspro (talk) 12:20, 29 October 2016 (UTC)
 * Indeed. Fuller's earth will work great on some items, while ShamWow may be more effective on others. Drying cabinet may be the best bet for other things. SemanticMantis (talk) 15:27, 29 October 2016 (UTC)


 * Disposable diapers are designed for contact moisture removal. If the moisture is clean water only, the diaper can be dried and reused, but it may be more cost-effective to just throw it away. If you have ever fished a diaper out of the toilet after baby throws it in there as a experiment, you know how much water a diaper can hold -Arch dude (talk) 16:22, 29 October 2016 (UTC)
 * The "magic" in this case is courtesy of sodium polyacrylate which can absorb several hundred times its own mass of water. Roger (Dodger67) (talk) 15:27, 30 October 2016 (UTC)
 * After reading the diaper article, I now see that some diaper products are designed to be slightly less than optimal at removing moisture from the skin, so baby will feel a small amount of discomfort to hasten potty training. You should avoid these products, perhaps by using diaper for newborns or using a different product like a tampon. -Arch dude (talk) 01:40, 31 October 2016 (UTC)

A hypothetical idea
Suppose a universe has four spatial dimensions, but gravitational force is not proportional to acceleration, but to jerk. Would there be stable orbits? 93.142.81.244 (talk) 18:16, 29 October 2016 (UTC)
 * See Anthropic principle and the linked articles for our coverage of this issue. Tevildo (talk) 18:29, 29 October 2016 (UTC)
 * But there the force of gravitation is still mass × acceleration, so the gravitational acceleration is constant. I'm talking about mass × jerk, where the Δacceleration would be constant. For example, suppose a jerk of j = 1 m/s3 is applied to a standing body. After five seconds, a = jt = 5 m/s2, v = jt2/2 = 12.5 m/s, s = jt3/6 ≈ 21 m. I wonder if that could solve the instability of orbits. I suppose this is useless in our own universe, where acceleration is constant but I wonder if anyone has tried this? 93.142.81.244 (talk) 18:43, 29 October 2016 (UTC)
 * The initial problem with that idea is that Newton's first law would become "if the net force acting on an object is zero, then the acceleration of the object is constant", so the speed of all bodies in free space would tend to become infinite. Tevildo (talk) 09:41, 30 October 2016 (UTC)

Do athletes live longer?
Another thing that has been bugging me. Exercise is supposed to be healthy and increase our lifespan, and who exercises more than the athletes? But the thing is, when you exercise you breathe in more air, which contains lots of O2. Similarly, if you drink more water, which is also something that athletes do and is supposed to be healthy, you drive extra oxygen atoms through your body. Shouldn't all that oxidation kill us faster? 93.142.81.244 (talk) 18:30, 29 October 2016 (UTC)


 * One leading cause of death is heart failure (alongside cancer). Sport can considerably help here. Add to it that other pretty common causes of death are diabetes and simple falls. Sport also reduces the incidence of this. If you are active, you also have a lower chance of developing dementia.
 * Do not assume though that the more sport you do the healthier you are. Professional athletes might have a shorter lifespan compared to reasonable active people who bike, walk, play soccer, and lift moderate weights. Going to the extreme can also be pretty bad. Sumo wrestlers might have a lifespan 10 years below average, for example. Llaanngg (talk) 18:37, 29 October 2016 (UTC)
 * Well, I'd expect injuries from full contact fighting sports to overwhelm any benefits. 93.142.81.244 (talk) 18:50, 29 October 2016 (UTC)


 * Well, that was a useless pile of personal opinion. Changes to life expectancy due to athleticism has been studied quite a bit. For example here is a meta-study that examines 54 primary studies regarding the life expectancy of athletes. It goes into some detail and has a sizable bibliography for your perusal. This article discusses some of the factors that probably lead to the greater lifespan. And here's an easy-to-read newspaper article that relates the basics of a smaller study involving Tour de France competitors. If you're interested in the negative health effects of oxygen, our article at oxidative stress is a pretty good start. Presumably, the health benefits outweigh the problems, but I didn't immediately find anything the discussed that particular topic directly. Matt Deres (talk) 18:57, 29 October 2016 (UTC)


 * Personal opinion? Amazingly what I said, although did not have more than one source can be corroborated even by your sources: "Physical activity reduces many major mortality risk factors including arterial hypertension, diabetes mellitus type 2, dyslipidemia, coronary heart disease, stroke"Llaanngg (talk) 19:19, 29 October 2016 (UTC)


 * Yes, a lot of damage is caused by metabolism, but almost all that damage has to be repaired, otherwise we would not live very long (if you shut off the self repair mechanisms in a healthy teenager, that teenager would look like a 100 year old within a few years and then die). So, longevity comes down to how well the body is capable of repairing itself. This has a strong genetic component, which explains why many super centenarians (people who have lived beyond the age of 110) actually did not stick to healthy lifestyles (most people do not stick to healthy lifestyles, the super centenarians are a self-selected group out of the pool containing everyone who happen to have good genes for self-repair). E.g., Calment smoked cigarettes from the age of 21 (1896) to 117 (1992). So, the huge damage done by smoking which would have caused most people to not reach their maximum possible age, did not significantly affect her, because the repair mechanisms at work in her body repaired the damage done by smoking much better than in most other people, without that mechanism at work in her body she would not have reached anywhere near her record breaking age, even if she had lived according to the most healthy lifestyle you can imagine.


 * Now, if you exercise a lot, then you will do a lot more damage to your body. But note that the reason why exercise improves physical fitness is due to the body repairing itself. After damage has been done the body will not simply restore itself in its previous state it will go beyond that making itself stronger than it was before. A system that has to maintain itself would not be stable if the extra repairs in response to more damage done, would not lead to it becoming a bit stronger. Damage done via exercise is extra damage on top of all the processes in the body that lead to decay. The body is constantly at work to counter these processes. Exercise will stimulate the self-repair mechanisms, the ramped up metabolism will do more damage, but the net effect of all processes taken together is that your body becomes stronger and fitter. Longevity will increase provided you stick to your exercise routine well into old age. Genes that in people destined to become super centenarians are always switched on by default, may be switched off in normal people by default, but they can be switched on if you exercise a lot. While the variant of these genes may be different in non-super centenarians making them less effective, it will still be a huge benefit to switch them on. So, it's best to stick to Jack LaLanne's routine and keep on exercising. Count Iblis (talk) 19:02, 29 October 2016 (UTC)


 * Nitpick said: "if you shut off the self repair mechanisms in a healthy teenager, that teenager would look like a 100 year old within a few years and then die"
 * I'm afraid that is a gross overestimation of the survival time in such a situation. Death would occur in a matter of hours at most, not years. Just one such mechanism; the constant replacement of the stomach lining, if stopped would cause the stomach acid to dissolve the stomach and then move on to the rest of the viscera, but by then the victim would already have bled out and died. Roger (Dodger67) (talk) 15:44, 30 October 2016 (UTC)


 * This and this provide a few different perspectives on the matter. -- Jayron 32 20:38, 29 October 2016 (UTC)
 * To focus purely on one thing in the OP: drinking more water doesn't really "drive extra oxygen atoms through your body". It is technically true, since water molecules contain oxygen atoms, but your body doesn't split water molecules apart to get at the hydrogen and oxygen. Respiration actually produces water. Plants, and other photosynthetic organisms, are the ones that take up water to use it as an electron donor, yielding oxygen as a waste product. The reason you need to drink water is to replenish excreted water. --47.138.165.200 (talk) 21:47, 29 October 2016 (UTC)
 * Thinking further about this... does this mean that respiration is an antioxidative process? 93.142.81.244 (talk) 00:46, 30 October 2016 (UTC)
 * There isn't really such a thing as an "antioxidative process". Aerobic metabolism is a redox process, which involves oxidizing "fuel" like sugars and fatty acids and reducing oxygen. This inevitably generates reactive oxygen species as a byproduct, which is why aerobic organisms have antioxidants, to counteract this. --47.138.165.200 (talk) 06:52, 31 October 2016 (UTC)

Thanks, guys. I guess it's more complicated than I thought. 93.142.81.244 (talk) 22:43, 29 October 2016 (UTC)
 * A thing to keep in mind in general (touched on in some of the responses above) is that athletes (in the American English sense of the word) are people who compete. Sometimes (actually, very often) competitive sport has exigencies that don't match up well with personal fitness.
 * This is a peeve of mine with regard to high-school athletics in the United States, especially football. High-school football forces the school day to start very early, so that the team can run practices afterwards.  Any time it is questioned, the first arrow from the defenders' quiver is that American kids are fat and unhealthy and need physical education.
 * And that part is certainly true. What's not clear at all is that football is at all a good way to make them more fit.  Getting smacked on the head is not an intuitive way to improve your physical health. --Trovatore (talk) 22:57, 29 October 2016 (UTC)
 * Aside for anyone who was confused by my "American English" comment: It seems that in Commonwealth English, "athletics" is not competitive sport in general, but one particular competitive sport, the one that on this side of the pond we call "track and field".  So in England, say, a student who plays rugby or cricket does not count as an "athlete". --Trovatore (talk) 23:06, 29 October 2016 (UTC)
 * Yeah, I meant athlete as a competitive sports player, not just Usain Bolt etc. 93.142.81.244 (talk) 00:46, 30 October 2016 (UTC)
 * Also, in American English, football means American football, which is a rougher game than association football. Robert McClenon (talk) 00:54, 30 October 2016 (UTC)
 * I would be very suspicious of this explanation for the early school day. My guess (and it's just a guess) is that parents want to see kids safely off to the school bus, or at the very least awake and dressed, before they head out the door to work.  Kids being what they are, if they come home at 3 and the parent comes home at 5, they may get in a little trouble... but if the parent leaves at 8 and the kids are supposed to get on the bus at 10, there's no telling what would happen. Wnt (talk) 13:12, 30 October 2016 (UTC)


 * Some factors to consider:


 * 1) Some sports cause regular concussions, like boxing and American football, so those can shorten lifespans.


 * 2) Some sports require consuming large numbers of calories, which can cause a problem when the player retires, and needs to immediately downsize their diet or become obese. StuRat (talk) 02:25, 30 October 2016 (UTC)


 * 2b) I can personally vouch for above. Been swimming "athletically" from 12 until 22 when I had to "retire" for health reasons, reccuring sinusitis. I managed +40 kilograms over the next five years. I'm 35 now and I only managed to drop 30 out of those 40. By my estimate I was on 6-7 thousand calories a day when I was training about 30 hours a week. So watch out! 89.120.104.138 (talk) 12:54, 31 October 2016 (UTC)

Is the a/c ventilation system ever big enough so that a person can move through it?
How big can the ventilation system of a/c be? Or is this just a reality bending for movies? --Llaanngg (talk) 18:30, 29 October 2016 (UTC)


 * IIRC, Mythbusters once did an episode about it. It turned out to be impractical even if possible, because anyone moving inside it made a lot of noise, and sound travels very well through metal tubing. 93.142.81.244 (talk) 18:48, 29 October 2016 (UTC)


 * Specifically, see MythBusters (2006 season). --76.71.5.45 (talk) 04:41, 30 October 2016 (UTC)


 * Yes, the idea of sneaking past somebody in the HVAC system is absurd. Also, in No Country for Old Men, a bag of money was slid in and out of the duct-work, which would also have alerted everyone in the motel.  However, hearing something in the duct-work and knowing exactly where it is are two different things.  It would be hard to locate the source of the sound, precisely because sound caries so well to each of the vents.  This might work well in a horror movie, if the baddie was in the HVAC system, but nobody could tell exactly where it was, to run from it.   StuRat (talk) 15:00, 30 October 2016 (UTC)


 * Quite apart from the noise aspect, all of the ventilation ducting I've ever seen (which may not be a representative sample) would, both of itself and in the structures supporting it, be too weak to support the weight of a person crawling through it. {The poster foremrly known as 87.81.230.195} 90.211.130.104 (talk) 05:17, 30 October 2016 (UTC)


 * I would love to see someone in Hollywood do this one properly. The ventilation duct to the sinister top secret spy base should quickly reach a comfortable height for walking.  There should be little colored lines on the floor for you to follow with labels so that you can find the vaccine, aliens, self destruct mechanism, head honcho office.  A few times you'd pass other bands of heroes, kids armed with wrenches or some James Bond on a rocket skateboard following their own lines, and a few groups of high-tech janitors in cleansuits burnishing the sides of the duct to keep it cinema-grade clean.  You might find this air duct somewhere off the grand spiral staircase that connects the mezzanine of a 747 with the cargo hold below and the computer rooms on the top floor. Wnt (talk) 13:08, 30 October 2016 (UTC)
 * As an architect, I've seen ductwork up to maybe 5 feet high in a big room with a big air handler, but that tends to be right before or after the main HVAC unit and it rapidly diminishes to two feet max as it branches out, and it's often vertical, with smaller branches running out at each floor. Then there's the air speed - a duct that size is moving lots of air, pushed by a multi-horsepower motor that would tend to move large obstructions along with the air - and a row of turning vanes at every change of direction, balancing dampers, zone dampers ... In an office space the ducts are always much smaller because there's economic pressure to minimize the wasted space above the ceiling. Bruce Willis would have a hard time with such ducts, assuming the whole thing doesn't fall out of the ceiling or the colossal amount of noise he makes doesn't give him away. Bruce is also too big to fit through the distribution registers.  Acroterion   (talk)   14:38, 30 October 2016 (UTC)
 * Also, ducts are dirty as Wnt notes. A further note to Hollywood - when the hero activates the sprinkler system ,only one sprinkler comes on at a time in a normal sprinkler system, the one that gets hot. It spews filthy, greasy black rusty water, because the sprinkler pipes are steel and are rarely flushed after they're installed. The threading is cut using cutting oil, which remains in the system.
 * In jails, even though the heads are tamper-resistant, somebody occasionally sets one off. The cell has to be scrubbed and re-painted (and the inmate scrubbed too, though not painted). As a jail maintenance guy told me, the inmate said "I won't be doing that again!"  Acroterion   (talk)   14:54, 30 October 2016 (UTC)
 * Can't fit through the A/C duct? Take the Jefferies tube! Seriously, though TV Tropes has an intersting writup on this topic. --Guy Macon (talk) 15:49, 30 October 2016 (UTC)
 * That's a good essay. As in lots of movie things, "where's all that light coming from?" is an obvious question too.  Acroterion   (talk)   17:48, 30 October 2016 (UTC)
 * What you say about the sprinkler system is absolutely true, but I do have to wonder why. I mean, it's not like they really only get set off in a fire - there's always some undergrad with a frisbee or an unsung vandal looking to do damage for the hell of it, or the good folks at Prank University just call one of the people who ought to know better on the phone and get them to do it for them.  It would seem to make sense to spare the extra twenty minutes and flush the damn things out. Wnt (talk) 22:54, 30 October 2016 (UTC)
 * They do usually get drained down a couple of times during construction and now and then the fire marshal opens the test port to make sure the alarm works or it's drained for alterations, but there's really no means of actually flushing the system from one end to the other, since it's normally open on only one end. Draining clears out construction debris, but the oil from pipe manufacture and thread sticks around, and the pipe oxidizes a little. Ideally the system reaches an equilibrium and you don't want to introduce oxygenated water on a regular basis. Adding multiple flush points adds cost to a system that's supposed to be affordable protection, and it's usually hard enough in design to find a place to put the main drain where its discharge won't dump dirty water in a public place, much less in several places. The hydraulic calculations are fussy and the designers avoid adding complications.  Acroterion   (talk)   23:11, 30 October 2016 (UTC)
 * Plastic piping is commonly used in residential applications and the water isn't especially dirty. Plastic piping is starting to appear in commercial work but isn't approved everywhere.  Acroterion   (talk)   01:44, 31 October 2016 (UTC)
 * But wouldn't plastic piping be a problem in a fire scenario, because it would melt or even burn and thereby take out the sprinkler system precisely when it's needed most? 2601:646:8E01:7E0B:998F:4012:900C:F798 (talk) 05:06, 31 October 2016 (UTC)
 * There are lots of different kinds of plastic. The correct kinds—I've only seen PEX used in this scenario—are listed if they meet "UL 1821: Thermoplastic Sprinkler Pipe and Fittings for Fire Protection Service" (see also "NFPA 13D: Residential Fire Sprinkler Applications"). DMacks (talk) 05:39, 31 October 2016 (UTC)
 * Plastic is used in residential to keep costs down, encouraging adoption of sprinklers. The plastic is relatively thermally insensitive. A more advanced version is starting to be used in commercial buildings, but most are still done in steel, or rarely in copper.  Acroterion   (talk)  
 * Is there also a noise-based reason for keeping the ducts under a certain size? It has been my general impression that the infrasound gets sharply worse when comparing, oh, maybe 2 and 3 feet diameter ducts.  I remember one supermarket that had a round duct that looked a yard across out in the open under a very high ceiling, and the infrasound near that thing was so loud it made me feel nauseous - enough to make me rush to finish anything in that part of the store during the winter. Wnt (talk) 00:19, 1 November 2016 (UTC)
 * Usually it's the other way around, that ducts are increased in size to keep velocities, static pressure and friction losses down, which keeps air movement noise under control. I suspect the infrasound you were hearing was a fan noise from a unit that was right near the duct opening, either a harmonic in the fan cage or a slightly off-center bearing ("runout") in the motor that created a rumble. Large return ducts in big open spaces are usually close to a unit and transmit machinery noise efficiently. If it's sitting on a roof the relatively flexible roof plane can act as a drum and can amplify the sound. During close-out of construction it's not unusual to have to diagnose and fix various screeches, whines, whooshes and rumbles in HVAC systems. In stores they usually just stock the shelves and open the doors.  Acroterion   (talk)   11:45, 1 November 2016 (UTC)