Wikipedia:Reference desk/Archives/Science/2014 September 20

= September 20 =

birth control
If the failure rate of mirena is 0.2, how come i saw a study saying that it's higher? 24.207.79.50 (talk) 00:05, 20 September 2014 (UTC)


 * One obvious flaw in most of the birth control statistics is that they assume they are used properly. When you factor in human error, especially when people may be somewhat distracted, the failure rate is a lot higher.  However, since Mirena is an IUD, and those are inserted well in advance, this isn't an issue.  Thus our article lists both "Perfect use" and "Typical use" failure rates of 0.2%. StuRat (talk) 02:08, 20 September 2014 (UTC)


 * The 0.2% comes from a study of 1169 Swedish and Finnish women age 18-35 that was conducted as part of the clinical trials to establish the efficacy of the implant. Specifically, the 0.2% refers to the chance of becoming pregnant during the first year after implantation.  As is typically the case, results established during approval trials become the "approved" facts for discussing a new treatment.  In some cases, subsequent evidence suggests that the initial conclusions about efficacy should be revised, but getting such revisions into the official drug literature is difficult due to the extensive regulations surrounding prescription meds.  Looking at this particular trial, some points stick out.  For one, Swedish and Finnish women are likely to be for the most part racially and culturally homogeneous, so it is possible that women from other ethnic groups or with different lifestyles might have a somewhat different responses to the treatment.  Secondly, 0.2% of 1169 women is a fancy way of saying that exactly 2 women in the trial became pregnant during the first year.  When you are talking about single digit numbers of events, there is some inherent uncertainty.  If I repeated the trial with another 1200 women, I might get 2 again, or I might get 6, or 0, or some other small number.  That randomness associated with rare events will make this result a bit uncertain.  I could well be that the drug companies got lucky with that initial study and the true failure rate is a bit higher.  On the other hand, even if the true failure rate were ten times higher (2%), it would still be very effective compared to most typical use contraceptives.  Dragons flight (talk) 04:34, 20 September 2014 (UTC)


 * Yea, that should be about a 3% margin of error, so they should say it has a 0.2% failure rate ±3.0%, although a -2.8% failure rate makes no sense (unless it terminates that many existing pregnancies ?), so a 0-3% failure rate is probably the best way to put it. StuRat (talk) 22:42, 20 September 2014 (UTC)

Or maybe it's because the study was done over 8 years instead of just one year.They only seemed to mention the percentage of people who got pregnant over the entire period of time instead of the percentage for each single year. Do you think that would be correct?24.207.79.50 (talk) 00:24, 21 September 2014 (UTC)

I guess no one has come to answer my question further. Perhaps that means i'm going too off topic, or simply end of discussion? — Preceding unsigned comment added by 199.119.235.184 (talk) 06:21, 21 September 2014 (UTC)


 * Not necessarily. The Wikipedia Reference desk is manned by volunteers, if nobody has any useful information to contribute, you may not get a complete or meaningful answer.  In this case, you may just be asking us to guess what was in the minds of the authors of the study - and we can't do that.   A better bet might be for you to locate one of the study authors and ask them the question directly.  SteveBaker (talk) 20:16, 23 September 2014 (UTC)

Eunuchs, Estrogen, and Erections
I read somewhere that estrogen (or something along those lines) can boost a eunuch's sex drive and allow him to have more frequent erections. Is this true? And Yes, this is a completely serious question. Futurist110 (talk) 07:35, 20 September 2014 (UTC)


 * These may be of use, . The degree appears to be variable. Phoenixia1177 (talk) 10:16, 20 September 2014 (UTC)


 * Thank you very much for these links. Do you and/or anyone else here have any additional links which address this question of mine? Futurist110 (talk) 02:54, 21 September 2014 (UTC)

Simple mechanical system that satisfies Newton's laws but is not Hamiltonian
Does anyone have such an example? I need it for a presentation. Thanks!--Leon (talk) 18:08, 20 September 2014 (UTC)
 * Any mechanical system with dissipation (friction). Ruslik_ Zero 19:16, 20 September 2014 (UTC)

IUPAC nomenclature of an organic compound with one double bond at one end and one triple bond at the other end?
What is it called? Is it an alkene or alkyne? 71.79.234.132 (talk) 18:45, 20 September 2014 (UTC)
 * It "is" a molecule with both:) This is one advantage of the "new" rules for ene/yne, using infix numbers (as a simple case, "but-1-ene") rather than giving greater emphasis of it as the parent chain itself (old name "1-butene"). Your case is just some carbon-chain that happens to have two functional groups. So vinylacetylene lists in its infobox "but-1-en-3-yne" with the two modifiers ordered by normal ordering rules (alphabetical/numerical precedence). But using synonym in the infobox using older naming pattern is "3-butene-1-yne", which is confusing as hell regarding precedence and parent+modification patterns. DMacks (talk) 19:19, 20 September 2014 (UTC)
 * Found the authoritative answer: IUPAC nomenclature of organic chemistry 1993 recommendations rule "R-3.1.1 Suffixes denoting multiple bonds" says in part:
 * The presence of both double and triple bonds is similarly denoted by endings such as "-enyne", "-adienyne", "-enediyne", etc. Numbers as low as possible are given to double and triple bonds as a set, even though this may at times give "-yne" a lower number than "-ene". If a choice remains, preference for low locants is given to the double bonds.
 * which matches the patterns used in the example I noted earlier. DMacks (talk) 19:38, 20 September 2014 (UTC)

Nocturnal animals
Kind of a silly question, but: how do nocturnal animals sleep through the noise made by diurnal ones? I have been out birdwatching at a local park around sunrise, and I often see a Black-crowned Night Heron trying to settle down to sleep on a tree branch, while all around it the other birds are singing and squawking and generally making a racket. Not to mention all the noises generated by humans. 75.4.18.101 (talk) 19:46, 20 September 2014 (UTC)


 * How do humans sleep through traffic noise? Our brains filter out known harmless background noise when we're asleep, and only wake up if an unexpected noise occurs. I expect it is the same for most animals. CS Miller (talk) 20:38, 20 September 2014 (UTC)


 * Yes, that's accustomization. Country folk can't sleep in the city, because of all the noise from traffic and the subway, while city folk can't sleep in the country because of those crickets, bullfrogs, owls, etc.  But after a while they will get used to it and be able to sleep again.  In the case of nocturnal animals, they may have even evolved a permanent way to ignore certain sounds.  (Probably not closable ears, as it's far simpler to suppress the sound in the brain than there.) StuRat (talk) 21:27, 20 September 2014 (UTC)


 * In the early 18th century, people who came to New York City couldn't sleep because of the frogs. It was much smaller then. (even 1810s City Hall was further than a large pond) Sagittarian Milky Way (talk) 02:46, 23 September 2014 (UTC)


 * (OP here, my IP may have changed.) Thanks for the responses. I wonder if there are local variations in what sounds nocturnal animals can sleep through, or individual ones (my sister sleeps through earthquakes, I am woken up by a raccoon on the roof). 75.4.18.101 (talk) 00:18, 21 September 2014 (UTC)


 * So there's this guy who lives in a house in the country. Every night the Midnight Special goes by on a distant railroad track and blows its horn, but the guy always sleeps through it. One night the Midnight Special doesn't blow its horn. The guy wakes up and says, "What was that?" ←Baseball Bugs What's up, Doc? carrots→ 00:39, 21 September 2014 (UTC)


 * The accustomization would be pretty specific for an animal that depends on hearing things while it's asleep to make sure it doesn't become some diurnal critter's lunch. They would likely take cues from the various noises even a familiar non-threatening critter might make, i.e. they'd subconsciously distinguish between a bird's mating call and its alarm call.  I myself work nights and have 5 dogs.  I often sleep through them barking at people walking down the road in front of my house (from what my wife informs me of) but will wake up if they are barking at someone coming up the drive.  Dismas |(talk) 01:09, 21 September 2014 (UTC)


 * (OP, maybe I should make an account:) On the other hand (in my particular case), there don't seem to be any predators here that could kill a Night Heron. Even Buteo hawks probably couldn't take one down, or easily maneuver through the trees where they doze. So maybe these birds can afford to "tune out" better than some. 75.4.18.101 (talk) 01:49, 21 September 2014 (UTC)
 * Yes, by all means make an account. It is easy and free.--Srleffler (talk) 18:19, 21 September 2014 (UTC)
 * It's also not required. There are advantages, though. ←Baseball Bugs What's up, Doc? carrots→ 01:46, 22 September 2014 (UTC)


 * I spent sixth moths in the hospital on an IV that had to be changed every 8 hours, with nurses chatting outside my door, with a patient in the bed next to me. After about the third night I could sleep through anything but the IV needle re-insertion.  Animals get used to sleeping, and I even saw my sister train my nephew to sleep on a regular schedule rather than cry when he was a newborn.  It's like feeding a spoiled dog hard kibble.  They might refuse the first night, but they'll get hungry enough to eat anything, eventually. μηδείς (talk) 17:27, 21 September 2014 (UTC)


 * Another factor here may be that since nocturnal animals have evolved to sleep during the day, their brains may be configured to get more alert when there is little noise while a lot of background noise will help to fall asleep. Count Iblis (talk) 17:45, 21 September 2014 (UTC)

bug ID
Hello, could someone please tell me what bug this is. Specifically if it's a parasite, like a louse or a flea. Here is another pic taken using a scanner (warning, nasty.) If it helps, I'm in western Central Europe Asmrulz (talk) 20:45, 20 September 2014 (UTC)


 * Looks like a louse to me. But there's many hundreds of species, and only a few are known to infest humans.  Being a louse doesn't mean it's a problem, per se. -- Jayron  32  20:49, 20 September 2014 (UTC)


 * F*** :( What do I do now? Asmrulz (talk) 21:05, 20 September 2014 (UTC)


 * Depends. Based on the odds, there's a 0.1% chance it's one of the species that infest humans (3000 species of louse; only 3 are problems for people).  So, you could do nothing.  -- Jayron  32  21:18, 20 September 2014 (UTC)


 * However, since it looks like he found it in his bathroom, not on the back of a Sumatran tiger, that rather changes the odds, don't you think ? It looks like it's belly is full of blood too, so it just fed on either a human or pet in the house.  I'd have everyone check for bug bites and watch any pets (except fish) for signs of scratching.  There are methods for killing lice on either humans or pets, but first you have to figure out which it is. StuRat (talk) 21:34, 20 September 2014 (UTC)
 * Maybe he has a tiger as a pet. It's been known to happen. ←Baseball Bugs What's up, Doc? carrots→ 10:12, 21 September 2014 (UTC)
 * not just known to happen. Happens too much. There are more tigers kept as pets in the United States alone than there are tigers in the wild.  See  -- Jayron  32  19:23, 22 September 2014 (UTC)
 * Judging by what looks like blood in its digestive tract, it is probably a parasite. In any case, Diatomaceous earth is a possible non-toxic solution for that sort of critter.   — 71.20.250.51 (talk) 01:21, 21 September 2014 (UTC) —I hate to nit-pick, but head lice might require a different solution, and of course, Wikipedia has an article on that: Treatment of human head lice


 * This critter is so hard to see it may as well be a cricket for all I can tell, but if it is a louse they are very easy to deal with, your pharmacists will provide an over-the-counter shampoo/lotion and further instructions. μηδείς (talk) 17:20, 21 September 2014 (UTC)

Thank you very much to all who replied. This is indeed from the bathroom. I don't think I have anything in my scalp, but I'll be checking once every few days. I find these often on books and stuff. This would indicate booklice, but the thing is, they don't suck blood whereas in the photo it clearly has, as StuRat has noted, blood in its intestine. Could be I have those AND those... :(( Asmrulz (talk) 21:10, 22 September 2014 (UTC)

Chest of drawers: noise
How can a person build (or retrofit) a chest of drawers so as to minimize the noise caused by the drawers being slid in and out? —Wavelength (talk) 20:55, 20 September 2014 (UTC)


 * WD-40. -- Jayron  32  21:00, 20 September 2014 (UTC)


 * Well, some drawers have little wheels under the drawers on which they slide in and out on. In that case, some lubricant at the axles of those wheels might indeed help.  Others just slide directly on the surface.  In this case, reducing the friction of those surfaces is in order, and, if both the drawer and cabinet are wood, perhaps furniture wax might be the best option.  Talc (baby powder) could also work, but expect some of it to get on things in the drawer and nearby.  You could also retrofit the drawers with wheels, but that's a major project, and may require reducing the height of the drawers to make room.  Also, if a wheel is off the track, that may cause noise, too, so check for that.


 * The first step is to pull a drawer all the way out, look at what's on the bottom, then look in the hole to see where the wear patterns are. If you see sawdust, that's a clue that something is rubbing directly against the wood.  It's also possible the sides or top of the drawer are rubbing, but the drawer would probably be hard to open then.  In that case, you'd need to sand down the drawer so it fits properly.  StuRat (talk) 21:44, 20 September 2014 (UTC)


 * Rub pencil lead (graphite) on the runners. Oldie but a goldie. DuncanHill (talk) 21:59, 20 September 2014 (UTC)
 * Soap, or candle-wax, can also be used. DuncanHill (talk) 22:04, 20 September 2014 (UTC)
 * French chalk (which redirects to "Talc", but it's not the same thing as talcum powder) is the traditional substance. Tevildo (talk) 22:12, 20 September 2014 (UTC)
 * Traditional where? I'm with Duncan. My old Scottish woodwork teacher taught me about candle wax 50 years ago. No mess. Long lasting. HiLo48 (talk) 22:18, 20 September 2014 (UTC)
 * Well, it's what my grandfather used to use. And see this site (other suppliers of such materials are available), where "Fix Sticky Drawers" ooer missus! is listed as one of its uses.  But wax will also work, I agree. Tevildo (talk) 22:41, 20 September 2014 (UTC)

Thank you all for your answers. Instead of a lubricant, I am looking for a solution in the actual design of the chest of drawers, either by the shapes of its components or by its material(s), which might include metal or plastic (even if only as coverings on contact surfaces). The choice of wood(s) is also of interest. —Wavelength (talk) 23:33, 20 September 2014 (UTC)
 * Drawer slides come in a variety of types and quality. A ball-bearing suspension drawer slide is smooth and quiet.  There are even smooth-close types, etc.  I don't want to endorse a particular brand, but this site is quite informative (videos, etc.), no matter which brand you choose:  — I noticed there is something called 'Sliding Compound', "for wood or metal".   — 71.20.250.51 (talk) 01:46, 21 September 2014 (UTC)
 * Since searching for "slider compound" will give you results about "sliding compound miter saw", I guess I need to provide the trade-name: Slipit© Sliding Compound.  — 71.20.250.51 (talk) 01:56, 21 September 2014 (UTC)
 * Thank you for this information about prefabricated drawers.
 * —Wavelength (talk) 22:21, 21 September 2014 (UTC)
 * Perhaps you misunderstood. Drawer slides not only relate to prefab drawers, they are hardware that can be purchased separately and applied to DIY projects. 71.20.250.51 (talk) 01:14, 22 September 2014 (UTC)
 * Thank you for this clarification.
 * —Wavelength (talk) 01:19, 22 September 2014 (UTC)


 * If you're considering changing the design of an old wood-sliding-on-wood drawer to make it move more easily, then I'd suggest buying some PTFE tape and sticking that onto one of the surfaces. PTFE is really slippery and avoids having wax or talc from an upper drawer falling down into the drawer below.  SteveBaker (talk) 15:54, 22 September 2014 (UTC)