Wikipedia:Reference desk/Archives/Science/2010 July 18

= July 18 =

Nasal passages
Hi. This is not a request for medical advice. Let's say a person suffers a broken nose, leading to a nosebleed. Might the damage cause parts of the brain to be accessible from the nasal passages? The person subsequently develops a common cold. Could sneezing or nose blowing (No article?!) cause parts of the brain to be liquefied and excreted via the nose, or could 'sniffling' result in nasal mucus entering the brain? I am aware of the danger triangle of the face, but this mostly applies to surface cutaneous infections. Might an infection in the nasal cavity, under these circumstances, spread to the brain? Thanks. ~ A H  1 (TCU) 02:04, 18 July 2010 (UTC)
 * The brain is encased in a tough leathery membrane called the dura mater, and there's a large area of sinuses between nose and brain -- also the front part of the brain lies almost entirely above the level of the nose, in fact above the eyes. To expose the brain by hitting the nose, you'd pretty much have to smash the whole face in. Looie496 (talk) 02:33, 18 July 2010 (UTC)
 * Does the danger triangle also include infections of the upper wisdom teeth? Rimush (talk) 08:01, 18 July 2010 (UTC)
 * The danger triangle of the face relates to the very front of the face and relies heavily upon the anterior venous plexi (bilaterally) and ultimately the cavernous sinuses, bilaterally. Because maxillary posterior teeth exist inferior to the maxillary sinus, a spread of infection will either break into one of these sinuses, or more often, through the buccal plate of the alevolar ridge and into the soft tissue of the vestibule (area between teeth and cheek).  Certainly, if an infection is allowed to remain untampered with for long enough, it can spread pretty much anywhere -- but there are also certain common pathways that are way more likely than others.  Dental schools teach that abscesses of the maxillary anterior teeth (that would be incisors and canines) may lead to spread of infection into the danger triangle, but I'd say that even that is pretty uncommon.  DRosenbach  ( Talk 13:54, 18 July 2010 (UTC)


 * So there is no danger of the passage between the brain and nose being broken and punctured like the ancient Egyptians did to their mummies to remove their brains? ~ A H  1 (TCU) 14:53, 18 July 2010 (UTC)


 * If you follow the Egyptians and you're doing it to someone already dead? No. If they're still alive, I'm not sure but I wouldn't worry about it, I'd worry more about the danger of removing their brain...
 * Sorry I couldn't resist Nil Einne (talk) 15:31, 18 July 2010 (UTC)


 * AH1 -- the diagram above may not be the best to use to visualize the relationship of the nose to the brain. I added another that may better suit you.  The "nose" is not really what or where it seems and the term may be confusing.  The nostrils become the nasal cavity as they ascend and it is split in the midsagittal line by the nasal septum.  There is certainly a possiblity of the nasal cavity communicating with not only the inside of the braincase but even of cerebrospinal fluid leaking out of both the ears and the nose after serious trauma like a motor vehicle accident.  But it's way more unlikely for a communication to form between the two areas from a broken nose related to a trip and fall.  Then there are all of the various levels of trauma in between, such as getting smacked in the face by a baseball bat in full swing, etc.  So there's no real way to determine the odds of such a thing happening, but it's certainly possible, as it's listed in BLS texts as a sign of potential brain damage (that is, the leaking of CSF from the ears/nose).  DRosenbach  ( Talk 16:43, 18 July 2010 (UTC)
 * Reading anything about diseases and related stuff on Wikipedia makes it seem like everything is life-threatening and that we are in peril of dying from a number of problems every second. Scary. Rimush (talk) 17:15, 18 July 2010 (UTC)
 * Think of it as "Evolution in action" potential. 87.81.230.195 (talk) 17:25, 18 July 2010 (UTC)
 * Wikipedia does have an obsession over listing the most serious possible causes of any physical symptoms. ~ A H  1 (TCU) 23:59, 18 July 2010 (UTC)
 * Yes, I only meant to explain how difficult it would be for physical damage to the nose to get through to the brain, not to deny the possibility of interaction between sinuses and brain. As an additional note, there is a well-known case in the amnesia literature, of a patient called R.B. who had a fencing accident in which the point of the foil went up his nose and into his brain, causing damage localized to a small midbrain area which nevertheless produced a severe memory impairment.  That's about the only way a blow to the nose can get through to the brain, as far as I can see -- short of a gunshot wound. Looie496 (talk) 17:34, 18 July 2010 (UTC)
 * A woman was killed in Italy by a pointy umbrella that went through her eye and into her brain (someone "stabbed" her on purpose). Rimush (talk) 18:17, 18 July 2010 (UTC)
 * Even without any mechanical trauma, an opening can spontaneously develop which allows cerebrospinal fluid to drain from the region outside the dura mater into the sinuses. I have known of such a case, which resulted in meningitis, and which was later closed by endoscopic microsurgery. Edison (talk) 18:48, 18 July 2010 (UTC)

Tippe top
http://www.xs4all.nl/~fabilsen/tippe-top.pdf I had a question about the explanation given here. It says that L has a constant orientation, but if there's a torque due to friction, then wouldn't L change direction? The only thing I can think of is that the torque due to friction traces a cone during one revolution, so the net torque will just be in the (opposite) direction of L. Is this right? 74.15.137.192 (talk) 03:31, 18 July 2010 (UTC)


 * I'm not familiar with the 'tippe-top' - but I think it's a variant of something called "Tesla's Egg". We had a detailed discussion about that a few months ago Spinning Tesla egg and stability - which I think applies to the tippe-top also.  As I explained at the time - you can get the exact same effect by spinning a regular hard-boiled egg.  Our article: Tesla's Egg of Columbus refers to some very complicated experiment with coils and a copper egg that winds up with the egg standing up on it's tip - but all of that fancy stuff just gets the egg to spin - the standing up on one end part is nothing to do with that (which you can prove by doing the same thing with a tippe-top or a hard boiled egg). SteveBaker (talk) 13:44, 18 July 2010 (UTC)


 * (We should really clean up this explanation and fix the Tesla's Egg of Columbus article to explain it properly). SteveBaker (talk) 13:52, 18 July 2010 (UTC)


 * A discussion of the tippe top is now archived at Reference desk/Archives/Humanities/2010 June 27.
 * -- Wavelength (talk) 23:59, 18 July 2010 (UTC)

Is this cable modem fried from lightning or not? (2 pictures, Cisco EPC2607)
Two pictures: With flash, without flash (click "Visa i full storlek" to show full size, which is blurry 5 MP). It doesn't power up whatsoever. I can't check the transformer simply because the multimeter doesn't fit, and I can't try another transformer because the connector on the only other one I have won't fit into the modem (and also is 12V/1A when the modem wants 15V/1A).

Anyway... Is this the result of lightning or not? The connection went down at a time I was awake but still in bed, according to ping logs; local weather reports haven't reported any lightning nor have I heard any.

Oh, and the copper-colored spots in the pictures are a) located right around a ~5x5mm IC on the other side and b) extremely conductive. Also, everything on the other side looks brand-new - I haven't checked the two ICs that are on top in the pictures though; all three were shielded under metal casings, and I only removed the first (the one closest to the coax connector). -- Aeluwas (talk) 08:07, 18 July 2010 (UTC)


 * When lightning struck our network a few years ago, the router had a burn pattern like the twigs on a branch, so based on that I'd say no. --TammyMoet (talk) 08:16, 18 July 2010 (UTC)


 * Lightning can produce many different effects, but I agree with Tammy that component failure is a more likely cause. How far into the unit does your 15v supply reach, or is there no 15v coming in?    D b f i r s   09:06, 18 July 2010 (UTC)


 * Those copper area don't look broken to me, they seem deliberate. In any case by far the most common failure is a loose or cracked solder joint caused by motion (for example where you plug something in, or where there is a button, or where there is a wire going to the outside world), or less often by heat. If you can find it you should be able to resolder it. If it's a high power connector you will often see burn marks. But for a signal line you won't, and you'll have to look for a cracks. Ariel. (talk) 13:42, 18 July 2010 (UTC)


 * Thanks everyone. As it turns out, the modem might not be broken after all. The power supply, on the other hand, definitely is. Y'know, the thing that's supposed to supply 15 volts... I measured it to 0.01 V, which is way within the margin of error of a cheap multimeter, so it's rather a question whether it simply died, or died and took the modem with it (e.g. due to lightning). Since I'll be getting a new modem (of a different make and model) anyhow, it doesn't really matter; the main reason I asked was to see if those copper areas are normal or not (for future reference :). Judging by the above responses, how pristine everything else looks and the shapes of those areas (no burns or such in the corners, or what have you), I can only assume they're supposed to be there. -- Aeluwas (talk) 14:44, 18 July 2010 (UTC)


 * Those bare areas may have been deliberately left that way in order that they may radiate heat better. Since you said that the components on the other side had metal covers over them - that seems quite plausible.  If the problem happened during a storm, it's possible that a power spike induced by the nearby lightning took out the power supply without anything actually getting struck or damaged.  If your cable had been struck by lightning, there would be all sorts of other signs - scorch marks on the case, damage to the cable itself, etc. SteveBaker (talk) 15:13, 18 July 2010 (UTC)

High-friction coating for bike rims to improve braking efficiency?
I'm going to try new brake pads for my caliper brakes, but I wondered whether the rims (apparently steel rims are poor braking surfaces) could also be coated with something to increase the coefficient of friction, ideally without unduly wearing-out the brake pads or quickly being destroyed in use? Seans Potato Business 11:24, 18 July 2010 (UTC)


 * Is this a pedal-powered bike or a motorbike? I'm guessing pedal-powered because of the rims. New brakes, or recently adjusted old brakes, will stop you very abruptly. This can be moderated by applying the brakes gently. High-friction rims would give you no choice in the matter, causing a stomach-wrenching halt every time, so I think it's a bad idea. 213.122.67.124 (talk) 12:14, 18 July 2010 (UTC)
 * Caliper breaks seems to indicate bicycle. It's probably possible to go with surface coating, but for modern (aluminium) rims and decent quality brake pads (I use CoolStop on my mountain bike with Shimano LX V Brakes, and Magura brake pads with the HS11 the on my commuting bike), there is no need. Both braking performance and brake pad lifetime are excellent in dry weather and plenty good enough if it rains. For more extreme needs, check out disk brakes. --Stephan Schulz (talk) 12:24, 18 July 2010 (UTC)
 * Steel rims are actually excellent. That's what cars use. For brakes you don't want too much sticktion - you want friction. It needs to be very smooth, and non sticky. Ariel. (talk) 13:46, 18 July 2010 (UTC)
 * Yes, exactly. You want to be able to use your brakes gradually to slow yourself down at a reasonable rate.  Correctly set up bike brakes (even on a smooth steel rim) are more than able to throw you over the handlebars and/or lock up the wheels and put you into a skid.  What you need is a controllable amount of friction that allows you to apply anything from the most gentle slowdown to a full-scale lock-up-the-wheels skid.  Having an unnecessarily large amount of friction will make the bike harder to control because the slightest touch on the brakes could result in a skid or an over-the-handlebars event.  Also (as Ariel points out), there is an important difference between 'sticktion' (static friction) and dynamic friction.  If the material has a high coefficient of static friction then it's much easier to lock up the wheels.  If all you needed for really good bike brakes was the maximum amount of friction - then you could just shove a stick between wheel spokes and frame!  What you need is (a) good pads - which you must change when they wear down and (b) correct adjustment of the cable from the brake lever to the caliper so that the lever cannot be pulled all the way back to the end-stop, no matter how much force you apply.  This second thing is the most common problem with bike brakes (especially the back ones) because the cables gradually stretch with use leading to a situation where the brakes would be perfectly able to stop you if only you could apply enough pressure to them without hitting the end-stop first.  The back wheel brakes suffer the most from that because the cable is longer. SteveBaker (talk) 15:05, 18 July 2010 (UTC)
 * That's a little bit oversimplified. If you're riding downhill or at high speed, the main braking force should be applied to the rear wheel, to avoid flipping you over the front.  In my experience, it's really hard to apply enough force to the rear brake to lock it up when you're going fast, even with new brakes.  But I definitely agree that roughening the rim is a bad idea.  If nothing else, it will grind away the rubber in the brake in no time. Looie496 (talk) 18:00, 18 July 2010 (UTC)
 * Well, no, I'm not so sure I agree about the rear-v-front thing. You have to keep the front braking light enough to avoid an endo, yes, that's true.  But short of that, front braking pushes your front tire downwards into the roadway and improves your grip on the road.  They tell me that the best balance is around 70-30 with the heavier braking in front.
 * Now I can't really claim experience on this, even though I bike a lot on hills, because I'm cautious and don't really let the bike get very close to losing traction (at least on the downhills). So if you have any pointers to studies on this, I'd be interested in seeing them. --Trovatore (talk) 21:19, 18 July 2010 (UTC)
 * The best thing to do would be to replace the rims with aluminium ones - an expensive proposition, but possibly worthwhile. Bicycling Science by D. G. Wilson quotes this paper from 1971: steel rims lost 90+% of braking power when wet. If your bike is anything like the ancient contraption I use at university, and you often ride in rain, I'd put serious thought into upgrading for safety reasons: if it rains during the course of a lecture, I have to use "sneaker brakes" on the way back. If your bike is newer, modern brake pads might have improved the situation, but it's up to you to judge. Brammers (talk/c) 20:48, 18 July 2010 (UTC)
 * Addendum after archiving: a company called Rigida (website) sell rims that have been coated with tungsten carbide. A review in the CTC's Cycle magazine says they are highly effective but will chew through anything but the hardest brake blocks. Brammers (talk/c) 11:16, 28 July 2010 (UTC)

Disc brakes — bikes
Why are the discs not a simple circular configuration? They follow a path that diverges from the plain circular form that one might expect. The divergence is regularly corrected, so that the overall configuration is circular. But why the periodic squiggles out of simple circularity? Click on the pic to enlarge it. It's a very nice photograph. Bus stop (talk) 15:25, 18 July 2010 (UTC)
 * Personally I think it's simply to make it look cool. Same for the holes. (If you are trying to save weight, there are better ways, like an internal grid, layered with thin smooth metal.) Ariel. (talk) 15:44, 18 July 2010 (UTC)
 * Agree about the form. As for the holes, they both safe weight and help dissipate heat, so I do think they have a function. --Stephan Schulz (talk) 15:50, 18 July 2010 (UTC)
 * The holes do not dissipate heat. They put them in cars not to dissipate heat but to release outgassing from the pads. Ariel. (talk) 15:52, 18 July 2010 (UTC)
 * Might it be to dislodge foreign matter like mud that might get splashed in there? I'm just guessing. Bus stop (talk) 16:10, 18 July 2010 (UTC)
 * See Disc brake, which mentions these ideas and could use some actual citations to support them. DMacks (talk) 17:31, 19 July 2010 (UTC)
 * A solid disk, I hypothesize, would be harder to get traction on than a disk with holes in it. And solid disk does have less heat dispersion than a holey one, but I doubt this really matters due to the fact that mountain bikes (unlike motorcycles, which have similar brake designs) don't usually weigh hundreds of pounds or go 100kph. The more important dispersion, I think, is of stress - a lot of circular saw blades have funky grooves in them to spread out mechanical stress from the workpiece, and this brake disk looks pretty thin so it probably needs all the strength it can get. But the most likely reason for the holes is that unlike a bulky frame (which only adds net weight), a bulky brake disk has to be spun around with the wheel, adding difficulty not only in net weight but in effort required to pedal the bike. So it's more important to save weight on the wheels than anywhere else. ZigSaw 14:33, 20 July 2010 (UTC)

Infrared thermometer
Is there a way to measure the room temperature / ambient temperature with an infrared thermometer? It seems that they must always measure the temperature of the surface of some object. --Yanwen (talk) 20:28, 18 July 2010 (UTC)
 * Infrared thermometer relies on the infrared being reflected back into the sensor, that's why you can't measure the actual temperature of the air, because it doesn't reflect. But depending on the situation, you can make some reasonable assumptions. In a room, most soft furnishings and other objects IN the room will be pretty close to the air temperature in the room. Stay away from windows and doors and anything that has been in or near direct sunlight.. Even if you can get just a piece of paper and let it rest in the room for a few minutes, I don't see why that wouldn't work.. Vespine (talk) 23:09, 18 July 2010 (UTC)
 * I'm afraid that is completely incorrect. It's not reflected IR that is used, it is emitted IR. It's the thermal radiation of the object (which, for objects at everyday temperatures, will be predominantly IR) that is being detected. Reflected light doesn't tell you anything about the temperature of the object, it just tells you about its colour and the colour of the light it is reflecting. The air does emit thermal radiation in exactly the same way as any other matter, however there really isn't very much air (about 1.2kg/m3, compared to around 1800kg/m3 for brick), which is why it doesn't emit a noticeable amount (this is also why the flame produced by complete combustion is almost invisible: red-hot air doesn't emit a significant amount of radiation, even though it is visible radiation, it is only when there are soot particles in the air that you get a visible flame, since the soot particles at the same temperature emit much more light, since there is much more matter there). --Tango (talk) 00:17, 19 July 2010 (UTC)
 * I admit you are right Tango however I don't think i'm "completely wrong". If anything i'm half wrong ;) . I'm wrong about how the IR thermometer worked, fair enough, but that's not even what the OP was actually asking, you didn't even address that. I think i still came to the right conclusions about that.. Vespine (talk) 01:21, 19 July 2010 (UTC)
 * Just to be clear, the little red light on the infrared thermometers is for targeting purposes only. The thermometer would work fine without it, but you wouldn't be able to accurately know what you were measuring the temperature of... Hense the little red laser to know where you are aiming.  -- Jayron  32  03:30, 19 July 2010 (UTC)
 * Ok, your first sentence was completely wrong! The rest was ok. --Tango (talk) 13:33, 19 July 2010 (UTC)