Wikipedia:Reference desk/Archives/Science/2014 May 7

= May 7 =

legal, medical...electrical?  Why are my lights flickering???
I don't see why not. So, why have the ceiling lights in several rooms started flickering incessantly! What does this mean? For several days they've been doing this. Any clues? BTW is this bad for my other electronics? (like laptop adapter) which I assume condition the power so I don't see this except in my lights.

Note: it's not actually every light, there are just two rooms that flicker, and I just remembered that other lamps (desk lamps) plugged in in those rooms are fine.

Why would the ceiling fixture in two rooms start flickering really badly? They're NOT on the same part of the network. (different fuses).

Thanks. 212.96.61.236 (talk) 00:49, 7 May 2014 (UTC)


 * What type of bulb, how old, what type of fixture, etc.? ←Baseball Bugs What's up, Doc? carrots→ 01:19, 7 May 2014 (UTC)


 * If they are fluorescent then this can happen for a couple reasons. Either A) the bulb is going bad or B) the ballast is going bad.  If they're incandescent, I have no idea.  Dismas |(talk) 01:21, 7 May 2014 (UTC)


 * Well, if this was deep winter (which it is not) I would have said that the the flickering luminescencenties where florescent lights chilling out.  Yet what are they ? Incandescent or florescent? Do you suffer brownouts etc. We can deal with the laptops and other stuff latter--Aspro (talk) 01:24, 7 May 2014 (UTC)

incandescent. would the ballast go if I had a too large wattage in there? (e.g. 110 watts if it's rated for 90 that sort of thing). 212.96.61.236 (talk) 02:32, 7 May 2014 (UTC)


 * Incandescent bulbs (the kind with tiny heated coils of wire) don't have "ballast" - the ballasted lights are the florescent bulbs (both the long, straight ones and the coiled CFL bulbs).  Incandescent bulbs could only flicker if there were a change in the supply voltage - either because of some problem at the source - or a loose connection someplace.
 * Florescent tubes do indeed flicker if they get old - or if they are cold - or if the supply voltage is a little too low. Replace one or both of them and see if the problem goes away.
 * It's likely that the ceiling light fixtures are on a different circuit to the wall sockets - so the fact that your desk lamps work doesn't prove much. If they are on different circuits - then it's hard to imagine how they could be flickering and not other lights in the house.  It's possible that they aren't screwed into their sockets tightly enough - then some source of vibration might cause flickering.
 * You should really try to get to the bottom of this because there may be some kind of arcing going on - and that's the kind of thing that causes electrical fires.
 * I'd replace the bulbs - crank up the heat so the rooms aren't freezing cold - and if the problem persists, call an electrician without delay. SteveBaker (talk) 04:46, 7 May 2014 (UTC)


 * I'm thinking you could try flipping off all breakers and turning them on one by one. If you can show that when each of two different breakers is turned on, each of two different lights flickers, it tends to argue for a coincidence, unless there's something wrong with the power going to the house (which, if you can show, the electric company should have to fix at its own expense).  If you have one breaker where the lights don't flicker when it's on, but you turn on another breaker with flickering lights and they all start flickering, well, that does sound like a Rambo First Blood type power scenario. Wnt (talk) 05:38, 7 May 2014 (UTC)


 * It's probably something much simpler: A laser printer, photocopier, or other such device. They always make lights flicker. Large power tools, or pumps can cause it too. So can an A/C (and considering it just started, if you are in a hot location this might be the cause). Ariel. (talk) 06:04, 7 May 2014 (UTC)


 * Ariel, do you have very poor load regulation where you live? A sudden large load will cause lights to dim slightly, but I wouldn't call it flickering.  Perhaps we are just using the word differently?  If the flickering involves just small changes in brightness then Ariel's explanation of other equipment is the most probably, but if it involves rapid on-and-off then there is a fault somewhere and it needs urgent attention.  It's possible that there are two coincidental faults within the lamps.  You can rule this out by swapping with the desk lamp that you know is working, or trying a new lamp bulb.   D b f i r s   06:52, 7 May 2014 (UTC)


 * Do you have a dimmer switch? My mum's lights flickered and it proved to be dirty tracks on a dimmer switch; replacing the switch was pretty easy and the lights stopped flickering. 129.215.47.59 (talk) 10:43, 7 May 2014 (UTC)


 * That's an interesting explanation - but the "several rooms" part of the OP's description is the problem here. Dirty dimmer tracks, or loose bulb or bad florescent tube ballast - any of those could affect ONE light fitting - but it's a hell of a stretch to have a coincidence that affects multiple light fittings.


 * But if we look for a common source, we know it's not the whole-house wiring or the power supplied to the house by the electricity utility. It also can't be something like A/C or heat turning on because that would be on a separate circuit - and if it can affect the lighting circuit, it would affect the table lamps too.


 * So we have to conclude that it's got to be something that's common to a bunch of rooms - but different for the wall socket circuits.  The things that are common to all ceiling lights - but different for wall sockets is the circuitry from the fuse/breaker box up to the outlets.  That sounds like faulty wiring or a bad breaker/fusebox circuit.  Those things are dangerous (at least, potentially) because they may arc and cause fires.  So calling an electrician is strongly indicated here.


 * That said, I suppose we should look at the realms of "coincidence". Perhaps these are florescent tubes that were all purchased from the same supplier on the same day and have been through the same cycles of hot and cold weather.  It's plausible that they all have failed ballasts.  Perhaps the same person installed a bunch of lightbulbs and didn't tighten any of them up enough because they didn't know how tight to make them?  These are pretty unlikely - but they are VERY easy to test for.  Just replace the light in one of the affected rooms.  If that room stops flickering and the other rooms continue to flicker - then you can just do the same thing in all of the rooms and your problems are solved.   If swapping out the light in one room doesn't fix anything - then you need to call an electrician ASAP.


 * SteveBaker (talk) 17:39, 7 May 2014 (UTC)


 * Power line flicker ??--109.151.101.168 (talk) 14:40, 11 May 2014 (UTC)


 * I had this same issue, and it did indeed turn out to be arcing between the wires, with sparks flying. Very dangerous.  Since you said these are incandescent lights, none of the explanations with fluorescent light flicker and ballasts apply, so arcing (an intermittent short circuit or open circuit) is a real concern.  I suggest you go to the fuse box and turn off the breaker for that circuit immediately, to prevent a fire (just turning the lights off might not prevent a fire, if a short circuit is before the switch).  Since the wall sockets seem to be on another circuit, you can plug lamps into those until you can get an electrician to fix your wiring issue.  BTW, is this an older home ?  Mine was built in the 1920's, and has rather old and substandard wiring, as a result. StuRat (talk) 15:17, 11 May 2014 (UTC)

Three Pairs of Legs
Insects have three pairs of legs. PERIOD.

Some insects have two pairs of wings. Some only have one pair of wings and the unused pair is reduced. Many other insects have no wings.

Some vertebrates have four legs. Some have two. Some have none.

Some insects have very long hind legs.

''' Why can't there be some evolutionary situations where insects were FORCED to walk on four or two legs with the unused legs reduced to very small sizes? '''

Insects are great in number. Their lives are very short. Their evolution shall be quick. At least in comparison with larger vertebrate animals.

I mean flying insects may not need all these six legs. It's not my business but it looks nice to me if they have fewer legs. -- Toytoy (talk) 04:24, 7 May 2014 (UTC)


 * Preying mantis, water striders and ambush bugs have their front pair of legs modified to function more like arms...they walk on four legs. SteveBaker (talk) 04:37, 7 May 2014 (UTC)
 * Praying mantis, to be precise. Actually, both. To paraphrase another regular, "preying" would slightly altar the meaning in this case. - ¡Ouch! (hurt me / more pain) 06:14, 7 May 2014 (UTC)


 * Butterflies in Nymphalidae and Riodinidae have the front legs are much reduced in size. They've gone from being walking appendages to having a sensory role.  See .  Changes like this are reasonably common in evolution, yet the basic groundplans of the phyla have proved remarkably resilient overall. Wnt (talk) 04:54, 7 May 2014 (UTC)


 * The larval stage of many butterflies, moths, etc. have many legs - little stubby ones. ←Baseball Bugs What's up, Doc? carrots→ 04:58, 7 May 2014 (UTC)


 * Purists call those prolegs. If you want to be expansive, practically anything that expresses Distalless can count as a modified leg. Wnt (talk) 05:56, 7 May 2014 (UTC)


 * It's worth noting that the number of legs (or leg-like structures) is tied to the segmentation of the thorax and that the legs, like all forms of animal locomotion, have evolved a highly complex and interdependent form of mechanical interaction; if a random mutation caused an insect to be born with only for of these appendages, it is unlikely to be advantageous such as to increase the likelihood of the trait being selected for, unless a part of a complex of evolution towards some more beneficial function, as on cases noted above. On a side note, this comment -- "It's not my business but it looks nice to me if they have fewer legs." -- makes me lament that Toy will never get a chance to realize their true destiny as a member of Rasczak's Roughnecks.  S n o w  talk 06:09, 7 May 2014 (UTC)

I like the previous answer. Segmented bodies could have resulted in a design which is highly unlikely to tolerate mutations. If this part breaks, it breaks everything.

However, primates have a pair of arms and hands. They are very useful. I can be an expert witness. Birds have a pair of wings. They are also very useful. "And the LORD God said unto the serpent, Because thou hast done this, thou art cursed above all cattle, and above every beast of the field; upon thy belly shalt thou go, and dust shalt thou eat all the days of thy life" Genesis 3:14. Anyway, I don't think snakes are very unhappy with their bodies. Whales have a pair of flippers and almost vanished pieces of bones as their hind legs.

Most of the vertebrate animals either make very good use of their four legs (dogs, horses ...) or a pair of legs evolved to become even more useful tools. Some of them can live without legs at all.

It still makes me wonder why insects have not evolved more ways to use or lose their legs.

They are just about everywhere. Sea, air, land, ground, from the north to the south, in deserts, jungles, ..... There shall be a place where evolutionary pressure is so strong and unusual that some adult insects actually get rid of a couple of pairs of legs. -- Toytoy (talk) 12:52, 7 May 2014 (UTC)


 * Strepsiptera females are legless. Wnt (talk) 15:50, 7 May 2014 (UTC)


 * What evolutionary pressure would give a small four-legged critter an advantage over a six-legged one? ←Baseball Bugs What's up, Doc? carrots→ 15:54, 7 May 2014 (UTC)


 * Losing some part of the body that's not being used is always an evolutionary advantage. The energy cost to build and maintain unneeded body parts is high - so mutations that remove truly unneeded parts have an advantage over the status-quo and should come to dominate the species.  This is most obviously visible the case of animals that wind up trapped for many generations in deep caves (see Troglofauna).  They mutate to become blind and to lose pigmentation in an amazingly short amount of time.  This blindness has evolved independently in hundreds of cave-dwelling species, so it must be a highly advantageous change.  In fact, nearly all species of animals that live in deep caves have evolved in this way...so it's obviously an easy and compellingly good change for them.


 * Similarly, if an insect could survive perfectly well with just four legs, it would need to eat less because of that - which means it could survive when food is sparse - which is a clear evolutionary advantage. However, this doesn't seem to happen.  There are two possibilities:
 * One difficulty is that there generally isn't a separate set of genes for each pair of legs - the same gene makes a pair of legs on each of the three major body parts. So it's hard for a mutation that drops one pair of legs to appear.  However, (as I pointed out way up top there), there are plenty of insects with modified forelegs...presumably they could be further modified to get smaller and smaller to the point of vanishing.  But the legs can't just disappear in one generation.
 * The fact that we don't see many four-legged insects (or six-legged ones with modified forelimbs) means that there must be significant advantage to having six legs - and the fact that most other animals of that size also have more than four legs (spiders, for example) suggests that there really is some major advantage to that body plan. If anything, we see small animals with more legs (centipedes, millipedes and the pro-legged larval stages of many insects) - which suggests that at this small scale, more legs is better.
 * In larger scaled animals, it becomes clear that fewer legs are better - four or even two seems to work great for anything bigger than an inch or two long. It would be interesting to understand why that might be...but it does seem to be a rule. SteveBaker (talk) 17:21, 7 May 2014 (UTC)


 * Well there's another factor to consider -- we don't know that it hasn't happened; the number of extant species is the smallest, most miniscule drop of water in the bucket of species that has ever existed, hexapods included. It's possible, though I certainly know of no research suggesting it, that such a species existed at some time, only to be out-competed by their contemporaries and quickly disappear. But that's pure speculation, and there's another element of an answer to your question which I'd focus on instead -- there's really no reason to be surprised at the retention of this design feature, even taking into account the factors you've listed above arguing for diversity of physiology (quick lifespans/breeding cycles, large numbers and global distribution).  Afterall, six legs are very useful to have, in the ecological niche of the insect especially.  They give advantages for locomotion, stability, speed, environmental alteration (for nesters and trap builders), hunting (for predators) and are just generally suited to their vertically-oriented physiology.  The musculature of an insect also generates more locomotive force for the creature, relative to its mass, as scale makes all of the difference in this case, so the trade-off of use versus caloric requirement to accommodate it has an even higher net benefit in general.


 * Lastly, and perhaps most importantly, it's not generally easy to lose an evolved trait; a structure as a complex as a leg is coded for in multiple genes, meaning the chance of random mutation removing a pair in any immediate fashion is highly unlikely (more likely as a mutation leading to useless legs, which would be a serious detriment to the bugger in question, significantly reducing it's chances of living to breed and pass on the trait). The fact that evolved traits tend to persist even if a change in ecological conditions renders them less adaptive or altogether useless, is a good part of why many organisms have vestigial structures and why regressive traits tend to be fairly rare and often viewed as confounding when they do occur (for example, in the famous tetra cavefish).    So since the legs are so beneficial and since they would need to regress out of existence over a sustained period of genetic adaptation favoured by environmental factors, it's not altogether surprising that they have not, except in cases where a pair of legs (usually the forelegs) have adapted to a new function other than locomotion, in which case that new selected-for purposes is the driver. Remember also that this is partly a matter of taxonomical definition: there are plenty of arthropods which evolved, or inherited and maintained, differing numbers of legs -- we just happen to have classified the ones with six legs together because of this feature (hexapoda as aterm directly references their six-leggedness) amongst other observable phenotypical traits, though certainly they also share a common ancestry.   So the question might as well be, why haven't any arthropods evolved to walk on four or two legs, or ecdysozoans in general?  And the answer in all cases (generic as I recognize it to be in relation to the nature of your inquiry): that's just not the way that chance circumstance worked out with regard to the ecological context and the biophysical limitations at work.  S n o w  talk 16:12, 7 May 2014 (UTC)


 * The OP brought up the subject of the serpent and the biblical reference. The twisty path of some snakes is not unlike the gait of a typical reptile, whose legs are spread to the sides rather than being "under" the animal. Some snakes can move pretty fast. In the case of reptiles, there might have actually been an evolutionary advantage to not having legs. ←Baseball Bugs What's up, Doc? carrots→ 18:25, 7 May 2014 (UTC)
 * I don't think so. The fastest snake is reputed to be the Black Mamba - and it can get up over 10mph in short spurts.  A fit human can beat that - but the snake is definitely in with a chance!  The fastest of the large lizards is the Perentie monitor lizard, can hit 25mph - and the monitor lizards are the closest lizards to the snakes, from an evolutionary perspective.  Smaller lizards such as the common gecko can easily hit 30mph.
 * I'm sure that you could find are a few of the faster snakes that could move faster a few of the slower lizards - but that's not likely to be due to the lack or presence of legs so much as metabolic reasons. A "typical" snake can't come close to the speed of a "typical" lizard - and not by a small amount...snakes mostly move at maybe 5mph and lizards at 15 to 20mph...so having legs CLEARLY gives you a huge advantage in speed. The advantages for snakes in not having legs probably relates more to the ability to move through dense terrain...and that's much harder to quantify than straight line speed on open ground. SteveBaker (talk) 18:48, 7 May 2014 (UTC)


 * To your last sentence: absolutely yes! Suffice to so say that if it weren't advantageous in some ecological niche to be a legless reptile, we would not have snakes. (The caveat is that not every trait of a species is necessarily an adaptive trait, but for something as drastic as leglessness I think the adaptiveness of that feature is fairly incontrovertible.) SemanticMantis (talk) 20:02, 7 May 2014 (UTC)

1,2-Dichloroethene and chloro(fluoro)amine
At what temperature, do electronic excitations and relaxations cause 1,2-Dichloroethene to equilibrate to a mixture with an equimolar ratio of cis to trans isomers?

How cold must it become before the mean life-time of (R)-chloro(fluoro)amine molecules increases to a second? Plasmic Physics (talk) 08:05, 7 May 2014 (UTC)


 * (1) Cis-trans isomers do NOT "equilibrate" under ANYTHING resembling normal conditions. (2) IDK. 24.5.122.13 (talk) 22:44, 7 May 2014 (UTC)


 * That is why I do not place a constraint on temperature conditions. Plasmic Physics (talk) 02:34, 8 May 2014 (UTC)


 * Even at high temperatures, 1,2-dichloroethylene would most likely pyrolyze before it even starts equilibrating. 24.5.122.13 (talk) 05:35, 8 May 2014 (UTC)


 * There shouldn't be a cut-off temperature, the equilibrating rate should be a continuous function of temperature. That is a statistical inevitability due to the definition of temperature as the mean energy of a system. Meaning that there is will always be a non-zero fraction of the bulk substance which will have sufficient energy for a transition. Granted, the rate of pyrolyzation may become an important factor. Plasmic Physics (talk) 22:11, 8 May 2014 (UTC)


 * Given that the energy required to break the other bonds in the compound is comparable to the energy required to force rotation around the double bond, you won't actually be able to establish an 'equilibrium' in any meaningful sense. Popping loose a chlorine atom is almost as energetically likely as rotation about the double bond.  So what you'll see isn't a mixture of cis- and trans-DCE, but instead a rapidly-disappearing pool of your starting enantiomer that becomes lightly contaminated with a small population of the other enantiomer for a short period of time before you end up with an ugly haze of free radicals, hydrogen chloride, and crud.  (Please conduct this experiment in a well-ventilated area.)
 * In any event, the original question is predicated on an incorrect assumption. Even if DCE were perfectly durable with respect to heat and the only reaction it was capable of was cis-trans racemization, the equilibrium would never be an equimolar mixture at any real temperature; the two isomers have different energies. TenOfAllTrades(talk) 22:54, 8 May 2014 (UTC)
 * I wasn't quite sure how to get to this one, but... shouldn't you be able to favor rotation over other decompositions by hitting the compound with bright monochromatic light of just the right frequency to provide the needed activation energy? (Or is it of a hypothetical rotational mode...?)  Perhaps accompanied by some other frequencies that (maybe?) help to induce emission of photons in order to cool the excited molecules back down before they do something ugly?  I feel like there ought to be a lot more photochemistry going on than I know of. Wnt (talk) 03:36, 9 May 2014 (UTC)
 * That would just favor formation of free radicals. Now, there's ONE thing I know of that MIGHT cause dichloroethylene isomers to interconvert, and that's an acid catalyst -- but even then, you'll get some major side reactions like addition. 24.5.122.13 (talk) 04:26, 9 May 2014 (UTC)
 * Yes, they do have different energies, but states are populated in ratios which are dependent on temperature. Plasmic Physics (talk) 11:48, 9 May 2014 (UTC)
 * Don't teach your grandmother to suck eggs. Given two states with different energies, at what temperature is the Boltzmann factor equal to 1.0&mdash;that is, the ratio of the two populations is 1:1, giving equimolar amounts in each state? TenOfAllTrades(talk) 13:11, 9 May 2014 (UTC)


 * I don't know what that saying means. I don't know the answer to that. I haven't worked with those types of calculations for several months. Even then, I would have no idea to apply them to general situations. Plasmic Physics (talk) 13:29, 9 May 2014 (UTC)


 * Well, what's the Gibbs free energy of formation for each isomer of 1,2-dichloroethylene? 24.5.122.13 (talk) 19:36, 9 May 2014 (UTC)


 * Useful enlightening answers nonetheless. How about the second query? Plasmic Physics (talk) 11:45, 9 May 2014 (UTC)

Meaning of micro
I have a textbook published in England in 1951. The thickness of certain coatings is given simply as digits following by "μ" e.g., 188μ. What is this likely to be? 188 microinches? 188 micrmeters? 124.182.16.27 (talk) 08:24, 7 May 2014 (UTC)


 * Micrometres. "Micro" is a metric prefix. There are no imperial prefixes that I'm aware of. Plasmic Physics (talk) 08:28, 7 May 2014 (UTC)


 * From the micrometre article: "This came about because, before the official adoption of the unit prefix micro- during the creation of the SI in 1960, the symbol µ was used in isolation to denote the micron." Double sharp (talk) 08:50, 7 May 2014 (UTC)
 * Most likely micrometers yes. To this day, the thickness of sections in histology is frequently referred to (in speech, not in writing) as xx mu. Fgf10 (talk) 09:58, 7 May 2014 (UTC)


 * To be clear, micron. Wnt (talk) 15:51, 7 May 2014 (UTC)
 * My grandfather, born in 1890, worked in precision engineering. The firm used inches generally but would also regularly use µ to mean micron. Here's a graph but I don't know if it proves anything. Thincat (talk) 21:04, 7 May 2014 (UTC)

Adult-onset h(a)emophilia
Does anyone know anything about adult-onset h(a)emophilia? I just heard about someone (in his 70s, if I understood rightly) being so diagnosed, and I'd never heard of such a disease. Nothing in haemophilia appears relevant, and all thirty-or-so Google hits were seemingly porn sites with auto-generated strings of random words. Nyttend (talk) 12:24, 7 May 2014 (UTC)


 * I found some helpful links, World Federation of Hemophilia, ClinicalKey (scroll down to "Acquired Hemophilia", Medscape. DuncanHill (talk) 12:32, 7 May 2014 (UTC)


 * More, NHS, Haemophilia Care. Search for "acquired haemophilia" seems to get best results. DuncanHill (talk) 12:35, 7 May 2014 (UTC)

Organic chemistry
Are there any practical applications for dinitromethane? 24.5.122.13 (talk) 22:46, 7 May 2014 (UTC)
 * It's used as a precursor for many explosives. Metal salts of dinitromethane, especially potassium dinitromethane (KDNM) show up in the synthesis of nitrate explosives, see here for example.  Also, it's used in various steps as parts of some organic synthesis sequences, such as [here].  Looking at the structure, the nitro groups are highly electron withdrawing, making the central carbon very electrophillic, which can be synthetically useful.  -- Jayron  32  23:45, 7 May 2014 (UTC)
 * Thanks! 24.5.122.13 (talk) 01:15, 8 May 2014 (UTC)