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August 28

recharge standard batteries?

Can batteries that are not designed to be rechargable be effectively recharged in a recharger? Bubba73 ^{You talkin' to me?} 00:56, 28 August 2013 (UTC)

No. And it might be dangerous to try. Looie496 (talk) 02:13, 28 August 2013 (UTC)

Thank you. Bubba73 ^{You talkin' to me?} 02:48, 28 August 2013 (UTC)

Resolved

The above answer is incomplete. You can't recharge them with a standard charger, but it is possible with the right equipment. We have an article on this: Recharging alkaline batteries, although the information in it is a bit limited.--Srleffler (talk) 03:42, 28 August 2013 (UTC)

I suspect both our article and the one non peer reviewed source are being a bit liberal with the word "recharge". In general non rechargable batteries produce power using non reversible chemistry (the first step is reversible but the products are absorbed irreversibly by the carbon slush. I suspect what these chargers are doing (with a claim to get 25% of the original charge or similar once only) is not recharging but recovering more of the original charge. If you have a battery in an application which requires close to full power it stops working when it still contains energy. Putting a DC through it, or leaving it in the sun for an hour, might help with this but it is not technically "recharging". It also might be dangerous--BozMo talk 06:02, 28 August 2013 (UTC)

Yes, "recharge" is not the correct technical term for this process, but I don't remember the correct one. I think there is more to it than just recovering the original charge, but it has been many years since I learned about it and I don't remember the details. --Srleffler (talk) 04:13, 29 August 2013 (UTC)

To be clear - using a standard recharger (ie one designed to recharge NiCd or Lion batteries) puts energy into a non-rechargeable alkaline battery without recharging it. With no place to go, that energy turns into heat. The battery gets very hot, and pretty soon, the liquids inside boil. That produces an enormous pressure spike and the battery explodes - splattering sharp bits of metal casing and hot, nasty chemicals in all directions! So DON'T DO THAT!

Several dubious companies and a bunch of well-meaning amateur nut-jobs have come out with so-called "rechargers" for alkaline batteries. I'm not sure what chemistry they are relying on - but they don't work very well. They can't completely recharge the battery - and the battery only survives one or two of these "recharge" cycles before going dead forever. I strongly suspect (without evidence) that User:BozMo is correct about the process merely releasing the final charge that was already inside the battery. One could imagine that by creating heat inside that's enough to cause the contents of the battery to flow more easily (but not become hot enough to boil and explode)...then, perhaps convection currents would slowly stir up the chemicals and bring material that had not yet released it's charge into the main mixture - thereby resurrecting the battery for a little while longer. That's not "recharging" - but it might seem that way. But these rechargers need some sophistication - controlling the voltage and current over time and monitoring the temperature of the batteries. That makes them expensive (or dangerous!) and it would require a heck of a lot of slightly-recharged batteries to pay for the cost of the equipment. Certainly they take a long time to do what they do - and they don't do it very well.

Bottom line is that using regular rechargers with alkaline batteries is VERY DANGEROUS and doesn't work - and the dubious-quality specialist alkaline battery "rechargers" are expensive and don't work well enough to justify buying one. So the simplest answer to this question is "No!". SteveBaker (talk) 13:50, 28 August 2013 (UTC)

Thanks, I was asking about a standard battery charger designed to work on rechargable batteries. Bubba73 ^{You talkin' to me?} 14:10, 28 August 2013 (UTC)

Yeah - DON'T DO THAT! SteveBaker (talk) 03:30, 29 August 2013 (UTC)

I wonder how many of the posters above have actually tried using a charger specially designed for recharging alkalines. I have. It works. It works well. Batteries do not explode or get too hot in the charger. Why dont you people believe what our article says?86.181.30.8 (talk) 13:59, 29 August 2013 (UTC)

Probably because it isn't a good article. There is only one source cited actually on the topic - and that is a review of a single charger on a 'photography community' website. I'm wondering whether the article should be deleted... AndyTheGrump (talk) 14:11, 29 August 2013 (UTC)

No, I wouldn't imply that batteries would explode or overheat in a properly designed alkaline battery recharger - it's when you try to charge them in a NiMH or a NiCd charger or something like that. SteveBaker (talk) 18:16, 30 August 2013 (UTC)

How much would we suffer if Earth was overcast?

Change reality the minimum possible to make it cloudy 24/7, or at least 90 percent coverage. For the purposes of this I'll consider the sun never being uncomfortably bright to stare - or invisible, to be overcast. Sagittarian Milky Way (talk) 03:10, 28 August 2013 (UTC)

What if we could choose the type (stratus, cumulonimbus etc.), or even distribute those by latitude or even sun altitude (-90 to +90 degrees) Sagittarian Milky Way (talk) 03:19, 28 August 2013 (UTC)

See Year Without a Summer, except that your scenario would be quite a bit worse. Looie496 (talk) 03:35, 28 August 2013 (UTC)

Would it be as bad as Nuclear winter? 24.23.196.85 (talk) 06:49, 28 August 2013 (UTC)

I've actually considered this Q before. If the Earth were permanently overcast, we wouldn't know about stars or planets. We would have noticed day and night, though, and possibly noticed the cycles of the moon, not by observing it directly but by noticing the slight change in the light level of the overcast sky on certain nights, and then matching that to the tides. We also wouldn't have shadows cast by the Sun, making it much more difficult to calculate the diameter of the Earth. So, astronomy and geography would suffer quite a bit. We would eventually figure out the diameter of the Earth, after sailing around it, and would eventually see the stars, after we made planes that could fly above the clouds. Then we could begin forming all the astronomical models that in our world happened over thousands of years, based on high altitude observations. So, I think we'd eventually get to the same place we are now, it would just take a bit longer.

If you take it a bit further and imagine a world always covered in ground-level fog (ignoring how plants would get enough light to grow), then flying planes visually would be impossible, as would sailing ships. We wouldn't be able to get from one disconnected continent to another, and would have little reason to think the world was round. The invention of radar would finally allow for airplanes and sea voyages, and from there we would begin the discovery process described above. StuRat (talk) 11:48, 28 August 2013 (UTC)

Well, if we're talking historically then it wouldn't really matter. "Overcast" simply means that the sky is opaque to visible light via scattering of particles (water droplets, dust, soot, etc..) suspended/dispersed in the atmosphere. If for whatever reason the atmosphere were never transparent to visible light in the first place, It's likely we'd simply have wound up with eyes that were sensitive to wavelengths where the effect of scattering is minimal. That's my $0.02 anyway. Scattering intensity depends strongly on particle size and wavelength. (+)H₃N-Protein\Chemist-CO₂(-) 12:19, 28 August 2013 (UTC)

Overcast means opaque to visible light ? That would mean a black sky. More like translucent, I think, where visible light would still be useful. StuRat (talk) 12:23, 28 August 2013 (UTC)

Translucency is basically just light scattering. A thick enough layer of suspended particles in the atmosphere would substantially reduce the transmission of visible light via scattering, and thus make the sky more opaque (no need to invoke 100% opacity here). Since there's a strong angular dependence to the intensity of scattered light, and since you can't exactly change the scattering angle in this scenario, you'd be losing a fair amount of light. It depends somewhat on the size of the particles, but anything big enough to obscure light would work here, I'd expect absorbance to be a relatively minor component in all this. (+)H₃N-Protein\Chemist-CO₂(-) 03:35, 29 August 2013 (UTC)

I believe "opaque", when unqualified, means 100% opaque: [1]. It's like when you say a door is "closed". That means 100% closed, unless you qualify it with "partially closed", "50% closed", etc. Of course, in both cases, "100%" is actually "almost 100%". That is, a photon or two can pass through almost anything, and there are gaps around any door. StuRat (talk) 06:32, 29 August 2013 (UTC)

I don't really see why I would use the colloquial definition of "opaque" when I was clearly discussing optics. (+)H₃N-Protein\Chemist-CO₂(-) 10:27, 29 August 2013 (UTC)

Knowing how and why the earth is so overcast makes a big difference - we can't ignore it.

• If it's surface-level water-vapor cloud - then the increase in albedo of the planet would turn it into an ice-ball pretty quickly - the oceans would freeze and life would either die out - or never develop. However, a surface level water-vapor cloud wouldn't exist in that kind of cold either - so the sky would clear up before that happened.
• If it's a high-altitude water-vapor cloud then it would cause a rapid onset of very severe global warming because water vapor is a much nastier greenhouse gas than CO2 - and then the oceans would boil and the planet would turn into another Venus.
• I suppose a very carefully balanced cloud layer somewhere between those two extremes might keep the planet habitable - but it would be a highly unstable equilibrium - so it would likely flip one way or the other within not too many years (eg A large volcano might add enough material to flip it one way or the other).

Of course you can imagine clouds made of other stuff - but things get complicated to imagine under those circumstances. SteveBaker (talk) 13:31, 28 August 2013 (UTC)

Article on Pharm D

Your outline of the Doctor of Pharmacy is misleading in its outline for education, It does not require 2-4 years + 4 years, The Pharm. D is the entry level for pharmacy requiring the completion of 6 years entered directly from high school. It replaced the Bachelors of Science in Pharmacy, a five year program, with a 6 year program, It is not a graduate degree it is a professional degree. — Preceding unsigned comment added by 76.19.174.161 (talk) 05:59, 28 August 2013 (UTC)

You can make these changes to the article yourself; please include citations to reliable sources OldTimeNESter (talk) 13:09, 28 August 2013 (UTC).

What determines a planet's angle of rotation?

Exactly as the question states. I'm curious as to what factors come into play for determining the angle of a planet's rotation, and why we can see such a wide spectrum of angles, as in the case of say Earth versus Uranus.

Martyk7 (talk) 07:00, 28 August 2013 (UTC)

Second paragraph at Planet#Rotation has some information which might keep you occupied until someone comes along wit more detail. 163.202.48.125 (talk) 08:13, 28 August 2013 (UTC)

In theory they should all start out rotating in the plane of the ecliptic. However, collisions with random sub-planets would soon change the rotational axis. In the case of Earth, for example, one theory of the Moon's formation holds that a giant impact knocked the material loose from Earth which then formed the Moon. Such an impact would also knock the Earth off it's original axis. You might think such impacts would be rare, but in the early solar system, they were probably quite common. They only became rare after most of those objects either impacted somewhere, fell into the Sun, fell into a stable orbit, or left the solar system. Looking at all the craters on the Moon, you can get an idea of how many impacts there have been. The Earth would have far more impacts, but erosion here covered most of them up. StuRat (talk) 11:35, 28 August 2013 (UTC)

Thanks, that's exactly what I was looking for. Martyk7 (talk) 21:53, 29 August 2013 (UTC)

You're quite welcome. StuRat (talk) 05:43, 30 August 2013 (UTC)

Black hole question

Escape velocity is the speed at which an object can leave another's abject gravity WITHOUT further propulsion. So, if someone could go near a black hole with a rocket propulsion, especially if the black hole is a supermassive black hole with reasonable surface gravity, he could enter and get out from event horizon. So, why is ever written that is impossible to escape a black hole, while there is that possibility? I know that isn,t an easy question, but thanks for answering. Francesco. — Preceding unsigned comment added by 95.239.192.85 (talk) 10:00, 28 August 2013 (UTC)

The escape velocity from inside the event horizon is more than c. 163.202.48.126 (talk) 10:44, 28 August 2013 (UTC)

Other strange things happen at the event horizon, such as infinite gravitational red shift. This results in time slowing to a stop from the point of view of the outside world. This means that if you went to the event horizon and survived, you would never return in the life of the universe. And in case you did not get the point of 163.202.48.126, your rocket can never accelerate you to the speed of light, so you will never escape. Graeme Bartlett (talk) 10:58, 28 August 2013 (UTC)

Yes, but the rocket can, as happens with space aircraft, get me outside the event horizon where the escape velocity is less than c; if the surface gravity of a black hole is, for example 10 m/s" (as that of earth) ten meters under is howewer similar and this isn't difficult to get out; the surface gravity is infinite on the singularity, not on event horizon... — Preceding unsigned comment added by 95.239.192.85 (talk) 11:18, 28 August 2013 (UTC)

The gravity at the event horizon of a black hole is a heck of a lot more than that. However, a rocket flying outside the event horizon would be able to escape the black hole at distances where a rock with no propulsion, of the same mass, would fall in. StuRat (talk) 11:29, 28 August 2013 (UTC)

One of the many problems is (as others have pointed out) that relativistic time dilation is caused by gravitational fields - so as you approach the event horizon from outside, from your perspective, the rest of the universe would appear to go into "fast-forward" - and as the gravity increases, the rest of the universe starts to change faster and faster. At the exact boundary of the black hole, time in the rest of the universe is running infinitely fast - which means that whatever ultimate fate befalls the universe, happens instantly. You can't "escape" because from the perspective of the rest of the universe, time for you has stopped and you're frozen forever on the event horizon. SteveBaker (talk) 13:20, 28 August 2013 (UTC)

That is true only if you stay around very close to the event horizon. If you are free-falling through the horizon, the universe outside doesn't appear running infinitely fast. At least according to General Relativity (if it's true, nobody will ever be able to report to the outside, so everybody who wants to know has to fall into the black hole). Icek (talk) 14:31, 28 August 2013 (UTC)

I know, but my point is: as happens with space shuttle, that don't need earth's escape velocity of 11,2 km/s to escape earth's gravity but reaches with rocket engine higher quotas with less gravity and can escape with minor speed (generally 7-8 km/s), so a little under event horizon, far from singularity, the surface gravity is finite and so is possible WITH EXTERNAL PROPULSION get out from event horizon and reaches distance when is possible to escape. The escape velocity is a limit only without further propulsion; with constant pull each speed can be sufficient.95.239.192.85 (talk) 13:22, 28 August 2013 (UTC)

No. The event horizon is by definition, the point (actually boundary) of no return. As the article states, it is "the point at which the gravitational pull becomes so great as to make escape impossible." You could never go fast enough no matter how many rockets you had. Clarityfiend (talk) 13:35, 28 August 2013 (UTC)

Yes, but why? So, ten meters over the surface of a very supermassive black hole the surface gravity is reasonable (it can be even near that of earth if the black hole is very large) and ten meters under becames so strong to be impossible to resist it with even very strong aceleration? This seems to me very strange. The surface gravity on event horizon is finite or infinite?95.239.192.85 (talk) 13:46, 28 August 2013 (UTC)

Ten meters above the event horizon of a supermassive black hole, the effect of gravity is still extremely strong. A supermassive black hole does not at all have anything close to a "reasonable surface gravity", either a little above or a little below the event horizon. I'm not sure where you got the impression that a supermassive black hole can have surface gravity similar to that of Earth. A supermassive black hole can have a density that's less than that of Earth, but that's a different matter. Red Act (talk) 14:22, 28 August 2013 (UTC)

The gravitational acceleration can be made arbitrarily small by making the black hole large enough. Icek (talk) 14:31, 28 August 2013 (UTC)

Indeed; the concept of 'surface gravity' gets really weird when you're near a black hole's event horizon – see surface gravity#Surface gravity of a black hole – and actually varies inversely with the black hole's mass. TenOfAllTrades(talk) 14:39, 28 August 2013 (UTC)

If you approach the event horizon (from the outside of course) very slowly, braking with your rocket engine, then, as SteveBaker pointed out, you will see the universe running at a faster pace, which also means all kind of things will fall into the black hole and onto yourself within a short time (as seen from your perspective); it's more or less like you are traveling at a very large speed (close to the speed of light) relative to nearby galaxies while still being not in the immediate vicinity of large masses. And the equivalent to being at rest at a large distance from the black hole is more or less freely falling into the black hole.

In order to have a more complete picture, you have to consider space-time geometry (details are in the article Schwarzschild metric). Before anything else, you need to know what the coordinates actually mean: You can measure the circumference of a circle around the black hole at a constant distance from the center. The radial coordinate r is the radius that this circle would have in flat space. And the time coordinate is the time that an observer would measure very far away from the black hole. If you now look at the coefficients of the time coordinate differential squared (dt²) and the radial coordinate differential squared (dr²), you should notice that these coefficients switch signs at r = r_S (the Schwarzschild radius). That means that inside the event horizon, the radial direction effectively isn't a spatial direction anymore, but it's a time-like direction. I.e. it is as impossible to go to a larger r as it is impossible to travel to the past.

Icek (talk) 14:31, 28 August 2013 (UTC)

Question: So the only "direction" you can point your hpothetical rocket is the future - towards the singularity? 163.202.48.125 (talk) 14:51, 28 August 2013 (UTC)

Are you pointing rockets in a "future" direction on the surface of Earth? If you cannot do that, then you cannot do that inside a black hole either. Space there has 2 "circular" dimensions along the surface of an imagined sphere around the singularity, and 1 other dimension (corresponding to the Schwarzschild time coordinate). You can move in this 3-dimensional space. But note that the size of the 2 closed (circular) dimensions becomes smaller as time passes (proper time that is measured by your clock, as opposed to coordinate time). Icek (talk) 16:00, 28 August 2013 (UTC)

Your explanation is interesting. So the black hole can't be leaved because space-time. Howewer, to answer to other utents: what matters in escaping, if you have a rocket, isn't the speed but the acceleration you reach: if the surface gravity is 10 km/s^2 and your acceleration is 11 km/s^2 you can win gravity and escape (mantaining that acceleration, obviously) no matter how fast you go and how high could be escape velocity. For this reason i said that could be theoretically possible to escpape a black hole, especially if very large (10^10-10^12 solar masses) — Preceding unsigned comment added by 95.239.192.85 (talk) 14:55, 28 August 2013 (UTC)

No, you cannot. You need to get the energy for acceleration from somewhere. And the potential energy for lifting an object out of a black hole is greater than the mass-equivalent of the object. So even if you successively convert all your object into energy and use it to accelerate the rest, you will not be able to lift it out of the black hole. Indeed, whenever lift anything with a reaction drive out of a gravity field, you want to accelerate as fast as possible - otherwise you waste energy simply by lifting fuel. And if you drive that to the limit, you want to accelerate your ship immediately to c (you cannot do better), and we know that that is not enough to escape the black hole. --Stephan Schulz (talk) 15:38, 28 August 2013 (UTC)

Before thinking about acceleration, think about velocity (and let's stay on radial paths for the sake of simplicity). You might think of dr/dt (how much the radial coordinate of an object changes as its time coordinate changes by one (sufficiently small) unit) as the velocity, but that is only a kind of coordinate velocity. In the Schwarzschild metric, outside the event horizon, this coordinate velocity is limited to $c(1-{\frac {r_{S}}{r}})$ in the same way that it is limited to c in flat spacetime.

And if you accelerate with your rocket engine near the event horizon, the acceleration you measured with the same rocket configuration in flat spacetime is now proper acceleration. Already in flat spacetime, proper acceleration a' of an object moving with respect to the observer is not equal to coordinate acceleration a (otherwise you could simply accelerate past the speed c), but it's

$a'={\frac {a}{(1-{\frac {v^{2}}{c^{2}}})^{\frac {3}{2}}}}$

(if the acceleration is along the same direction as the velocity v)

So I hope you can imagine (or even calculate by a few manipulations of the Schwarzschild metric equations) that an acceleration a bit larger than the gravitational acceleration isn't going to give you the speed you might have hoped for, and therefore the transition from above to below the event horizon isn't as discontinuous as it might have seemed.

Icek (talk) 16:00, 28 August 2013 (UTC)

What the OP needs to understand is that when you are inside of a black hole, even if you are moving outwards (so to speak) at the speed of light, you're are still moving towards the center. There is no path out. Dauto (talk) 16:05, 28 August 2013 (UTC)

Look at that Penrose diagram. The center of the black hole is the red line, the black hole is the triangle next to the red line and the rest of the diagram represents the whole universe outside of the black hole. Objects traveling at the speed of light follow diagonal lines at 45 degrees. If you're inside of the hole, no matter how fast you're going "outwards" you will still eventually reach the center of the hole. Dauto (talk) 16:16, 28 August 2013 (UTC)

As pointed out, the term "surface gravity" has problems in that I presume you're thinking of that term in the Newtonian sense, but the Newtonian concept of surface gravity becomes meaningless at a black hole's event horizon. As TenOfAllTrades pointed out, there does exist an alternative definition of the phrase "surface gravity", which is basically the Newtonian surface gravity renormalized by multiplying it by the gravitational redshift factor, and that renormalized value does go to zero as M increases. However, that's very different from there being something close to a Newtonian surface gravity that's close to zero close to an event horizon.

Avoiding the problematic term "surface gravity", and being super pedantic in order to be precise, the proper acceleration required to keep you at an r Schwarzchild coordinate that's ten meters greater than the black hole's Schwarzchild radius (which is at the event horizon) increases to infinity as the black hole's size increases to infinity, i.e., as the black hole's mass increases to infinity. Icek's statement at 14:31 that the acceleration can be made smaller by increasing the black hole's size is incorrect. An acceleration vastly greater than 10 m/s² is required to keep you at an r Schwarzchild coordinate that's ten meters greater than the Schwarzchild radius even with a black hole with a mass about that a star, and instead dealing with a supermassive black hole only makes the required acceleration much larger, not smaller. Red Act (talk) 16:47, 28 August 2013 (UTC)

Whoops. According to the top equation here and doing a little math, the proper acceleration required to stay a fixed δr above the event horizon only increases with increasing R_s up to R_s = 2 δr, beyond which contrary to my expectation it decreases. So I struck out my post, which apparently is incorrect. Red Act (talk) 18:54, 28 August 2013 (UTC)

So the surface gravity is infinite not only on the singularity, but even on the event horizon? Why (I believed only singularity had an infinite surface gravity)?95.239.192.85 ([[User talk: 95.239.192.85|talk]]) 16:58, 28 August 2013 (UTC)

What you said earlier was correct. The surface gravity is inversely proportional to the mass. But that doesn't mean that you can hover at the surface by accelerating outwards, and that's what Red Act was explaining. Your difficulty understanding the difference comes from the fact that you're imagining a black hole to be an object embedded in a Euclidean space (That's the most natural thing to do, but it is wrong). All it means is that if you fall into the black hole you will find yourself accelerating towards the center at that finite acceleration. If you try to hover by blasting your rocket engines, you will still find yourself approaching the center, though a bit more slowly. You cannot simply subtract one acceleration from the other since you are not in a Euclidean space. Dauto (talk) 17:32, 28 August 2013 (UTC)

It's worse than that; the longest (in proper time) worldlines there are the geodesics. Accelerating (even "outwards") gets you there faster, at least in your estimation. I'm not sure what it does in terms of "outside time" — whether, for instance, accelerating would allow you to rendezvous with a colleague who fell in shortly after you. --Tardis (talk) 13:07, 29 August 2013 (UTC)

• What the OP needs to realize is that a speed limit is hard to break when you can't go any faster. You just simply can't get up to the speed to go out, even though your jets are blasting away - all they're really doing is increasing your relativistic mass and various other weird relativity parameters at that point. Wnt (talk) 18:55, 28 August 2013 (UTC)

The point of the question is that it is possible to leave a planet without ever reaching its scape velocity, so why can't one leave a B-hole without ever reaching c? Answer: The whole idea that c is the scape velocity of a B-hole is wrong to begin with. It's an oversimplification. Dauto (talk) 19:01, 28 August 2013 (UTC)

Yeah, you're right. I'm thinking of something relative to spacetime but that's not the same thing. Wnt (talk) 04:19, 31 August 2013 (UTC)

So, if I understood, the space time on the event horizon is so curved that you could only go into black hole and in every direction you move get into it. Another question: on object when reaches event horizon it's said that stops to esternal observer, but this is only an optical illusion, because black holes in reality increase their mass by absorbing other stars that even to esternal viewers as we are, fall into black holes (even to our proper time, black holes increase their mass, not only to objects that fall into).95.239.192.85 (talk) 00:51, 29 August 2013 (UTC)

Yes, all directions lead to the center, but the horizon itself doesn't have to be particularly curved. Curvature is proportional to surface gravity. Being a B-hole is a global property, not a local property. There is nothing particularly special about the horizon itself. We might be crossing some gigantic B-hole horizon right now as we speak (type) and not know it. Dauto (talk) 12:15, 29 August 2013 (UTC)

Looking up "black hole" and "unbreakable rope" got me to this [2] which says (p.105-110 or so) that there is a "maximum force" c⁴/4G, which limits the ability of a rope to hold someone suspended inside the horizon, etc. But I could use some further explanation of the details and rationale myself. Wnt (talk) 04:19, 31 August 2013 (UTC)

Enthalpy of formation

I'm trying to calculate the enthalpy of formation for molecular lithium hydride, and I'm coming up with an incorrect answer. What am I missing?

• Molar enthalpy of fusion of lithium
• Molar enthalpy of vaporisation of lithium
• Half molar bond-dissociation enthalpy of hydrogen
• Negative molar bond-dissociation enthalpy of lithium hydride

I should get ~141 kJ mol⁻¹, but my answer is >300 kJ mol⁻¹. Plasmic Physics (talk) 14:29, 28 August 2013 (UTC)

What is your source for your numbers so we can check the data? --Jayron32 14:48, 28 August 2013 (UTC)

• Lithium
• ' '
• Bond-dissociation energy
• [3] (Table 2, D_e for X ¹Σ⁺) Plasmic Physics (talk) 23:09, 28 August 2013 (UTC)

It's been a long while since I've done somehing like this, but does the fact that lithium hydride is solid at STP change the answer at all? It seems like the enthalpy of fusion/vaporisation (which will have to be theoretical, since LiH decomposes before it vaporises) should "give some energy back" MChesterMC (talk) 08:29, 29 August 2013 (UTC)

I'm not trying to find the standard enthalpy of formation. Molecular LiH does actually exist. Plasmic Physics (talk) 22:24, 29 August 2013 (UTC)

Rope stretch

In rock climbing (a sport which I have recently taken up) there are two types of nylon kernmantle rope generally used. Dynamic rope has significant elasticity to act as a shock absorber and reduce peak impact forces during a fall (they will typically stretch around 30-40% of their length during a simulated fall of an 80kg load a distance 1.77x the length of the rope). "Static" rope on the other hand has much less stretch and is a better choice for abseiling (rappelling) and hauling loads since dynamic rope can end up rather annoyingly bouncy in these applications.

My question is: what is the difference between static and dynamic climbing rope which results in the difference in elasticity - is it different monomers, a different polymer chain length, a different weave pattern or something else? Thanks, Equisetum (talk | contributions) 15:11, 28 August 2013 (UTC).

It is perfectly possible to make a high-stretch dynamic rope and a low-stretch static rope out of the same materials. In the dynamic rope, the sheath is braided, and the core is filled with loosely twisted fibers, which are not themselves laid together, like this:[4], which allows them to slip against eachother, and against the sheath. After a drop, the sheath may be the only structural part remaining intact: the energy of the fall is absorbed in part by the friction of the core fibers pulling apart (this is why you don't use dynamic rope to bear human loads after it's been used to break a big fall). For a a static rope, (which may or may not have a braided sheath), the core is composed of fibers, laid into yarn, which is in turn laid into a solid, twisted cord, like this:[5], or in some cases a solid braid(see other pics in previous link). For actual rope products on the market, different fibers may be used, but the principle differences in performance of dynamic vs. static cordage are due to the structural properties of how the fibers are arranged. Of course, if you have spare sections of each, just do some dissecting! SemanticMantis (talk) 15:31, 28 August 2013 (UTC)

Update, if you read all of rope carefully, it says that dynamic kernmantle has the core fibers chopped into shorter sections, and the static kernmantle has both longer fibers, and less twist on the core. A conventionally laid or braided rope of the same fiber would have intermediate stretch, between the dynamic and static. SemanticMantis (talk) 15:37, 28 August 2013 (UTC)

Excellent answers, thank you. I should have done some dissection since I just retired my father's old dynamic rope and had some offcuts of static cord I used for re-slinging some nuts, but then, these were from different manufacturers and one was new and the other 20 years old (don't worry - it hasn't been used for over 10 years, I know that climbing ropes have limited lifespan), so I would hardly be controlling my variables very well! Equisetum (talk | contributions) 16:05, 28 August 2013 (UTC)

Homophobia

Is finding homosexual sex (or more broadly a kind of sex that does not fit one's sexuality) "icky" a learned behavior or is it an inherent part of human behavior. personally I don't find any kind of sex icky, including those kinds that don't fit my sexuality, though I don't find them attractive either. But many other people seem to genuinely disgusted by it even though they are not homophobes (or heterophobes?)--Irrational number (talk) 16:18, 28 August 2013 (UTC)

It's natural behavior, what happens is that a straight person will imagine him/herself to be in the position of the gay person and then judges that to be icky, obviously this is caused by this imagined scenario not being consistent with his/her own sexual preference. Count Iblis (talk) 16:36, 28 August 2013 (UTC)

Source for that? This is a complicated matter not helped by the fact that sexuality is something of a spectrum. 163.202.48.125 (talk) 16:41, 28 August 2013 (UTC)

Not to mention that homosexuality has been very differently treated in different societies (see e.g. the uber-macho Sacred Band of Thebes), and that at least in societies with general sexual taboos, many people often find all kind of sex "icky" - from kids to stereotypical "spinsters" to Lady Hillingdon of "Lie Back and Think of England" fame. --Stephan Schulz (talk) 17:43, 28 August 2013 (UTC)

The elephant in the room here is that when people think of straight sex, they tend to think of a penis penetrating a vagina, and when they think of gay male sex, they tend to think of a penis penetrating an anus. We know what comes out of anuses, and that's where the ickiness factor comes in. Well, just as penis-vagina contact is SO NOT the only kind of straight sex, penis-anus contact is SO NOT the only kind of gay male sex. Oh, I've had many discussions with people who say that these other activities are not really "sex", they're just foreplay or "fooling around" or whatever one does in the lead-up to actual sex. That is just so much garbage. So, we need to be really clear what we're talking about when we say "sex". -- Jack of Oz ^{[pleasantries]} 21:28, 28 August 2013 (UTC)

There's a certain amount of "ickiness" in sex in general, although "messiness" might be the better way to put it. It reminds me of an extremely old joke from Woody Allen: "Q: Is sex dirty? A: Only if you're doing it right." ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:17, 28 August 2013 (UTC)

• This may be of some interest: Disgust#Evolutionary_significance, also Evolution_of_morality#Disgust. If I recall, I think Richard Dawkins or similar did a program about where disgust comes from. The analogy used in it was that the thought of two ugly people having sex gives one a feeling of disgust but rationally one can see that the disgust mechanism doesn't indicate whether something is right or wrong, IRWolfie- (talk) 22:31, 28 August 2013 (UTC)

@ Jack above, a better solution than such clarity might be a boycott on answering any heterosexuals' questions on gay sex until they have tried it first. Kind of like the homework rule, above, "we'll get you over the stuck part". μηδείς (talk) 00:53, 29 August 2013 (UTC)

Yuck Medeis, did you have to choose those words? - ¡Ouch! (^{hurt me} / _{more pain}) 07:45, 29 August 2013 (UTC)

I thought you liked pain. Be careful of what you ask for. You'll get it, but it may not be exactly what you had in mind. -- Jack of Oz ^{[pleasantries]} 08:27, 29 August 2013 (UTC)

Well played... - ¡Ouch! (^{hurt me} / _{more pain}) 09:19, 30 August 2013 (UTC)

I don't have the answer, but I don't think "picturing it" explains it- even if picturing it causes some to feel disgust, it obviously doesn't in others. Moreover, lot's of men enjoy anal sex with a female partner and, yet, find the imagery of it with another male disgusting; and the same goes for other sex acts they would enjoy with a woman. Finally, I, personally, think it all seems pretty hot to picture, and to do, (either gender) and have felt this way since a young age- By numbers, I would definitely be labeled as straight, and, while this is all anecdotal, I can't imagine my perspective/experience is uncommon to the point of anomaly. In other words, "picturing it" causing disgust in some is what needs explained, not an explanation.Phoenixia1177 (talk) 03:44, 29 August 2013 (UTC)

I still don't have an answer for you, but you may find our articles: Homosexuality and psychology, Biology and sexual orientation, Societal attitudes toward homosexuality, Sexual norm, Heteronormativity, and Homophobia as a good place to start; especially the portions talking about societal attitudes. I'll be honest, this is one of those areas that's a giant morass of studies, politics, and sociology- in other words, it's gigantic and half of it's science, half of it's philosophy, half of it's pedantry, and half of it's bullshit (not exclusive halves:-) ). Because of my last sentence I'm not going to attempt any type of summation, better just to read through the articles and see if they takes you somewhere with a satisfying answer.Phoenixia1177 (talk) 09:40, 29 August 2013 (UTC)

Weather and sleep

So I live in Tehran and as you can tell it has a very polluted air. And I usually feel tired when I wake up, even when I wake up spontaneously (without an alarm clock) and I sleep in the normal time interval people sleep. And I found out that in the other cities that I've been to, although they are in very different locations of the country, I sleep very well, independent of the time interval, and I wake up feeling fresh, I wonder what is this related to... --Irrational number (talk) 16:23, 28 August 2013 (UTC)

Might be related to the fact that big cities suck? Dauto (talk) 16:28, 28 August 2013 (UTC)

Perhaps also noise perturbing sleep? Count Iblis (talk) 16:30, 28 August 2013 (UTC)

can't be it my room is quiet.--Irrational number (talk) 16:47, 28 August 2013 (UTC)

If your room isn't very dark, then that could also perturb your sleep. But if it really has to do with the polluted air, that would suggest that you may have apnea due to the air causing breathing problems that you may not notice when you are awake. Then it's best to see a doctor to get a sleep test done and test for allergies, asthma etc. Count Iblis (talk) 16:58, 28 August 2013 (UTC)

We may be straying into MedAdvice land here.. 163.202.48.125 (talk) 16:42, 28 August 2013 (UTC)

AW COME ON! let me ask it in a different way "does the weather of the place you sleep in affect the quality of your sleep in any way"? Is that better? I'm just curious about something!--Irrational number (talk) 16:47, 28 August 2013 (UTC)

From an anecdotal level (but confirmed by many), yes, absolutely. If it is too hot at night, I sleep badly. Somewhat surprisingly, heat during the day does not seem to be similarly bad (but maybe I'm just more tired because of little sleep at night ;-). --Stephan Schulz (talk) 17:45, 28 August 2013 (UTC)

The Med Advice police needs to chill out. We are just taking about a topic here. I still think the general suckyness of big cities is the culprit. Dauto (talk) 17:47, 28 August 2013 (UTC)

The line was crossed when Count Iblis suggested apnea as a medical cause - which could be construed as making a diagnosis - a clear violation of Kainaw's Criteria. SteveBaker (talk) 19:50, 28 August 2013 (UTC)

I think he said the best thing is to go see a doctor which doesn't break the rules. I think I'm gonna make a diagnosis as well: Half of the inhabitants of this forum are obsessed - You know who you are. Dauto (talk) 20:20, 28 August 2013 (UTC)

There's a big difference between:

• "Go and see a doctor, who is the most appropriate source of advice about problems with the functioning of your body", and
• "Go and see a doctor, because you may have apnea / cancer / a brain tumour / cholera / AIDS / the bubonic plague / an infestation of cockroaches in your guts / whatever" . -- Jack of Oz ^{[pleasantries]} 21:16, 28 August 2013 (UTC)

• In the US we have lots of ads on TV that say "If you have symptom X, then you may have syndrome Y, so ask your doctor about it" (who will then prescribe their dangerous meds instead of sensibly suggesting lifestyle changes). We even have ads that say "You wouldn't want a doctor to do your job, so don't try to do his" (just take whatever crazy drugs he prescribes and shut up). I wish the makers of those ads could be convicted of practicing medicine without a license. StuRat (talk) 06:23, 29 August 2013 (UTC)

Some people have looked into a weather/sleep or air pollution/sleep connection. Plugging air pollution sleep into PubMed I get these hits:

• Association between PM10 exposure and sleep of Egyptian school children ("There were statistically significant associations between particulate matter with an aerodynamic diameter <10 µm (PM10) exposure and DIMS and sleep hyperhidrosis (P?<?0.05)")
• Is sleep apnea a winter disease?: meteorologic and sleep laboratory evidence collected over 1 decade ("More sleep-disordered breathing events were recorded in winter than in other seasons. This finding suggests that obstructive sleep apnea severity may be associated with other seasonal epidemiologic phenomena")
• Association between exposure to secondhand smoke and sleep bruxism in children: a randomised control study ("High and moderate exposure to SHS is associated with sleep bruxism characterised by teeth grinding or clenching movements during sleep in children")

Perhaps the scientists here can tell you if these studies seem reasonable. None of them are a body of evidence, just single studies. 184.147.119.141 (talk) 00:29, 29 August 2013 (UTC)

Is there a physical barrier between the peritoneum and fallopian tube?

If not, what keeps all that stuff from just leaking out?

Thanks, Saintrain (talk) 20:41, 28 August 2013 (UTC)

Our internal organs don't just float; there is all manner of connective tissue holding things together. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:14, 28 August 2013 (UTC)

Sorry, wrong term. I meant "peritoneal cavity". (A little learning, something, something, spring.)

According to Ovary, "The ovaries are not attached to the fallopian tubes ..." and "The ovaries are uncovered in the peritoneal cavity ...", and, from Fallopian_tube#Anatomy, "The tubal ostium is the point where the tubal canal meets the peritoneal cavity ...". Since the fallopian tubes and ovaries have no physical (direct) connection, that implies that the tubes are open to the peritoneal cavity. So, why no leakage? Saintrain (talk) 22:52, 28 August 2013 (UTC)

I hope it's OK to quote non-WP sources :-), from The peritoneal environment in endometriosis,

"Fallopian tubes and ovaries are bathed in PF [peritoneal fluid]. Oocytes are

exposed to the peritoneal environment even after they are

captured by the fimbria because the Fallopian tube is a

conduit freely communicating with the peritoneal cavity.

Spermatozoa are exposed to PF factors in the Fallopian

tube before and during fertilization. The embryo undergoes

early development in the Fallopian tube. where it is also

potentially exposed to cellular and soluble components of

PF. There is evidence suggesting that at least some of the

uterine fluid may be of peritoneal origin (Casslen. 1986)."

Saintrain (talk) 23:09, 28 August 2013 (UTC)

Abdominal pregnancy can occur when an embryo floats from the fallopian tube into the abdomen and implants on internal organs. Based on this and on Saintrain's second source regarding PF in fallopian tubes, it appears that "leakage" does occur. 198.190.231.15 (talk) 16:54, 29 August 2013 (UTC)

• This question always has freaked me out. In addition, I had to get a procedure where they stuck a tube only slightly thinner than a drinking straw into my abdomen to drain fluid after an operation, leaving a puncture shaped scar, yet when I asked the doctor said there was no need to suture it. μηδείς (talk) 00:50, 29 August 2013 (UTC)

August 29

Can't remember the name of a medical condition

An elderly acquaintance was recently diagnosed with a medical condition, and I can't remember its name. All I know is that it's causing severe pain in her back, and the condition's name begins with "arach", but the condition apparently doesn't have anything to do with spiders. Any clue what I could be thinking of? Nyttend (talk) 01:36, 29 August 2013 (UTC)

It isn't Sciatica is it? --Jayron32 01:38, 29 August 2013 (UTC)

Arachnoiditis Hot Stop talk-contribs 01:46, 29 August 2013 (UTC)

The name "arachnoiditis" sounds right, and the description in the article sounds a lot like the symptoms that she's experiencing. Thanks! Nyttend (talk) 02:15, 29 August 2013 (UTC)

Helpful advice: next time try typing in the words you know first for sure, "back pain", to google, and then start typing a...r...a...c...h... and it will fill in the answer for you. μηδείς (talk) 02:53, 29 August 2013 (UTC)

You just gave away my secret. Hot Stop talk-contribs 03:50, 29 August 2013 (UTC)

Didn't even think of that...Nyttend (talk) 03:54, 29 August 2013 (UTC)

That's why I get paid so much. μηδείς (talk) 05:34, 29 August 2013 (UTC)

And you are worth every cent we pay you, maybe even twice as much. StuRat (talk) 06:12, 29 August 2013 (UTC)

I can never seem to remember the name for the medical condition, aphasia. :-) StuRat (talk) 06:12, 29 August 2013 (UTC)

I'm sure I know it, but I usually just can't quite conjure up the name for presque vu. DMacks (talk) 06:17, 29 August 2013 (UTC)

Just read schizophrenia – great article, made me think twice. - ¡Ouch! (^{hurt me} / _{more pain}) 08:02, 29 August 2013 (UTC)

What are you telling us about our question, Ouch? Nyttend (talk) Nyttend (talk) 11:11, 29 August 2013 (UTC)

The condition's connection with spiders is only in the name, as "arachnoid" means "cobweb-like".[6] ←Baseball Bugs ^{What's up, Doc?} carrots→ 11:40, 29 August 2013 (UTC)

The reference is to the arachnoid mater, a thin and spiderweb-like layer of tissue that encloses the brain and spinal cord, between the dura mater and pia mater. Looie496 (talk) 22:09, 29 August 2013 (UTC)

Elysium – "open to space" space station?

In the recent movie “Elysium”, Elysium is a rotating space station orbiting Earth, designed as a luxurious gated suburb for the world’s wealthiest. These types of space stations mimic gravity by rotating giant rings in which people can reside (as made famous in the movie 2001). It appears that they could indeed work very much as depicted in that film. But in the movie Elysium, the station has a feature I have never seen depicted before, and I very much doubt could work. The rings of the space station are al fresco, that is, they have no covering at all. The idea is that the rotational velocity that provides the “gravity”, also keeps the air from expanding. (The depth of Elysium’s atmosphere appears to be no more than half a mile or so, at the most.) I suppose the designers would have considered:

"Earth is a rotating space station with gravity, and no hard covering between it and the vacuum of space, and Elysium is a rotating space station which mimics gravity, so why should it have a hard cover either?"

link

I wrote in an IMDB msg board that air pressure would immediately make the air boil away on Elysium, and that on Earth it takes miles of atmosphere to get the pressure we have at ground level. This blooper is not recognised as such in the “blooper list” of the movie, and I can only think that most people are not aware of how wrong it is. Unless, of course it is I who am wrong....Could that be possible? Myles325a (talk) 07:12, 29 August 2013 (UTC)

Air pressure on Earth is about 100,000 Pa, and that would be needed on the space station as well. One cubic meter of air weighs in at just above 1kg, so 500m of air would weigh 500kg per square, which is 5000N at 1.0g. So we have 5000 Pa, not 100,000 Pa. The factor of twenty means that the air would be gone quite fast, even by that ballpark estimate. - ¡Ouch! (^{hurt me} / _{more pain}) 07:50, 29 August 2013 (UTC)

OP myles325a back live. Thanks One.Ouch, but could you and succeeding posters spell out jargon properly? I don't know what a PA is; I gather it is an initialism. Anyway, I'm getting the drift, but a more accessible explanation would be appreciated. Myles325a (talk) 08:22, 29 August 2013 (UTC)

I presume Pa = Pascal (unit). I haven't seen the film (or even heard of it until now) but surely another problem is that it would be impossible to maintain a survivable temperature in the "open air". AndrewWTaylor (talk) 08:31, 29 August 2013 (UTC)

For Niven's Ringworld, the open architecture is plausible (even if the ringworld itself is not ;-). But then the "walls" of the Ringworld are 1000 miles high, not half a mile. At 1000 miles, the atmosphere is essentially all below you. --Stephan Schulz (talk) 09:12, 29 August 2013 (UTC)

Also see Orbitals, Halos and Bishop Rings. But these fictional/hypothetical structures all appear to be much larger than the Elysium space station, and depend on some form of unobtainium (such as Niven's scrith) to keep them in one piece. Gandalf61 (talk) 09:33, 29 August 2013 (UTC)

The Halos in your link make extensive use of hyper-dimensional architecture, metamaterials, nanomaterials, and exotic matter (to manipulate space-time), it does not rely on simple Newtonian mechanics to function. Plasmic Physics (talk) 12:26, 29 August 2013 (UTC)

Yes, that's the sort of thing I loosely filed under "unobtanium". Gandalf61 (talk) 16:25, 29 August 2013 (UTC)

In a thread elsewhere on this page, I linked to a review of the film by Gary Westfahl, in which he touches on this topic. Deor (talk) 13:02, 29 August 2013 (UTC)

The basic issue is that the scale height of an atmosphere doesn't permit this. Any atmosphere of Earthlike temperature and composition under Earthlike gravity is going to have a scale height of about 7.5 kilometers, which means that the pressure at the top of a 500-meter wall (1/15 of a scale height) is going to be around 95% of the surface pressure. If you want a 500-meter wall to retain an atmosphere, you'll need to reduce the scale height, either by using a denser gas (sulfur hexafluoride has a scale height of 1.5 km, still too much), or by increasing gravity (a surface gravity 70 times that of Earth's will drop the scale height to 107 meters, putting the top of the wall above 99% of the atmosphere). Reducing the temperature isn't an option, because by the time you get it low enough (3.5 kelvin), not even helium is a gas. --Carnildo (talk) 23:57, 29 August 2013 (UTC)

I think Carnildo has got it right. Summarising a few points, which might not be obvious to the OP (or which could do with a bit of clarification at any rate), we can say that the earth's gravity is due to its mass, but that on Elysium is due to rotation. If it is due to an artificial gravity machine (I don't think the film actually explained this), then all bets are off. Supposing it is rotation, the atmosphere is only kept in place as long as it lies beneath the walls. If it spills over at all, its angular momentum will carry it off into space. So unless the atmosphere at the top is allowed to boil off, whilst keeping the atmosphere below at some constant density, it will all float upwards, then away. But as Carnildo's link shows, the atmospheric density declines as a function of temperature, density and gravity, and none of these are arbitrary, if we are to create livable conditions. IBE (talk) 08:44, 30 August 2013 (UTC)

How was the moon created?

how was it made — Preceding unsigned comment added by 196.29.167.50 (talk) 08:47, 29 August 2013 (UTC)

See Moon#Formation and the articles linked from there. Rojomoke (talk) 08:55, 29 August 2013 (UTC)

A 2013 hypothesis suggests that the Moon formed from debris ejected from a cataclysmic thermonuclear detonation of the core of proto-Earth. Plasmic Physics (talk) 12:06, 29 August 2013 (UTC)

If our own articles aren't enough for you, could you supply a reference for your alternative? Rojomoke (talk) 12:13, 29 August 2013 (UTC)

[7]. Plasmic Physics (talk) 12:17, 29 August 2013 (UTC)

What would such a detonation look like, would the Earth vapourise, or will gaint asteroids be thrown out, or something in between? Plasmic Physics (talk) 01:40, 30 August 2013 (UTC)

"Despite what the revisionist historians tell you, there is no mention of the 'moon' anywhere in literature or historical documents -- anywhere -- before 1950. That is when it was initially launched." 178.48.114.143 (talk) 23:45, 29 August 2013 (UTC)

"O, swear not by the moon, the fickle moon, the inconstant moon, that monthly changes in her circle orb, Lest that thy love prove likewise variable" SteveBaker (talk) 17:56, 30 August 2013 (UTC)

Antoher black hole question

Excuse me, I have another question about black holes: if they increase their mass by absorbing other stars even to us external observers, the fact about an object that stops on the event horizon is only an optical illusion (inother the gravitational time dilatation is valid even if object is on free fall?)? Thanks for your patience.95.234.63.70 (talk) 10:43, 29 August 2013 (UTC)

No, it is not an illusion, rather it is physical reality imposed by the principle of relativity: the notion that there is no universal frame of reference. In simplest terms, how you observe what happens at the event horizon depends on where you do the observing. To the person observing from the outside, the object falling into the black hole stops at the event horizon, while to that object itself, nothing special happens. They keep falling, without any special event that would even tell them they crossed it. The difference in observations between te two situation is nothing like an optical illusion. It's just that different observers in different frames of reference observe the event differently. That's what relativity means. --Jayron32 11:14, 29 August 2013 (UTC)

Both the external and internal points of view are real, hence the name relativity. Dauto (talk) 12:28, 29 August 2013 (UTC)

There is a complication here; unlike in Special Relativity there is no unambiguous way an observer can say when an event happened at a different location. This is not a problem in special relativity. So, the OP does have a point, you can't simply say that when the light signals arrive, that's when the event happens in your frame as that's not true in Special Relativity.

You can e.g. consider sending the infalling observer a message via light signals. What you find is that a message sent later than a certain time will never be received by the infalling observer. Count Iblis (talk) 13:10, 29 August 2013 (UTC)

Yes, but the problem is: we (external observer) see black holes absorbing other stars and so increasing their mass, we don,t see star stopping at horizon's surface (it's probably that the object stop its time but we see it equally falling into black hole). 95.234.63.70 (talk) 13:29, 29 August 2013 (UTC)

We would never see a star cross the event horizon, in practice we simply measure the mass of a black hole by considering how fast stars orbit it, so everything that is just outside the event horizon will then also be attributed to the mass of the black hole. Count Iblis (talk) 13:40, 29 August 2013 (UTC)

When we say that "the object stops at the event horizon" - we mean that each individual subatomic particle stops at the event horizon. So don't imagine a planet, buried forever, half inside and half outside of a black sphere. A better mental image is that as the planet (star, rock, spaceship) heads towards the black hole, tidal forces rip it apart - and eventually, rip even the atoms apart. From an outside observer's perspective, time for each individual quark (or whatever) slows right down and stops at the precise instant it hits the event horizon. The event horizon itself grows with each new addition of mass - so those objects do cross the event horizon and vanish - even from our perspective. But the idea that it's black at all is a bit misleading - these objects that are falling into the black hole are emitting immense amounts of radiation - some of which is visible from far away and is further smashing up the incoming stuff. The event horizon itself must have a fantastically small layer of sub-atomic mush that (to us) seems to be going slower and slower. But the actual appearance is even more confusing than that because gravitational red-shift is shifting the frequencies of light (and radio and X-rays, etc) so far off the chart that they'll be indetectable anyway. Roll in quantum effects and black-hole evaporation, hawking radiation...it's not a simple picture to imagine.

SteveBaker (talk) 13:41, 29 August 2013 (UTC)

This could be certainly possible for stellar black hole, but for very supermassive black holes with irrilevant tidal force and low surface gravity, a compact object wouldn't ripped apart. Inother, on a freefall is still valid the gravitational time dilatation? It isn't valid only if the object oppose resistance to gravity?80.116.228.11 (talk) 14:14, 29 August 2013 (UTC)

Gravitational time dilation still aplies for free falling objects plus there will also be some Doppler red shifting due to the motion of the object. The star certainly never reaches the horizon due to the (infinite) gravitational time dilation. Not only that, if quantum effects are included (as shown by Leonard Susskind), the individual particle orbitals enlarge until they wrap around the B-hole covering the whole surface. Off course, from the point of view of the falling object, none of that happens Dauto (talk) 15:21, 29 August 2013 (UTC)

Ageing

Is there an age where every organ of the body is at peak performance and nothing is growing or declining, since apparently growth and decline happens at different ages for different parts of the body？Clover345 (talk) 12:29, 29 August 2013 (UTC)

No. Life operates at the edge of chaos, and stasis is death (at least, according to Stuart Kauffman). See section 4.5.1 here [8], which summarizes some of Kauffman's work on gene expression in complex networks. Gene expression is basically what controls developmental biology, and also senescence. I'd also recommend "At Home in the Universe" [9], but you'd have to go to a library or buy it. SemanticMantis (talk) 14:51, 29 August 2013 (UTC)

Most aspects of physical and mental performance peak in the age range 20-25 for men, a bit younger for women, if I've grasped the data correctly. However, maximum strength for weightlifters peaks later, in the 30s, I believe. Looie496 (talk) 16:37, 29 August 2013 (UTC)

Also, memory power, ability to absorb more education and raw thinking speed are all places where younger people do well - but cunning, knowledge and "wisdom" are attributes associated with older people. On that basis alone, I'd say that there is no particular age at which you can say that the brain is at it's peak. SteveBaker (talk) 17:54, 30 August 2013 (UTC)

BMI

Is BMI an accurate measure of body faT? For instance would a body builder have a low BMI or a High one because he has very little fat but a lot of muscle?--86.181.30.8 (talk) 14:09, 29 August 2013 (UTC)

No it isn't very accurate and recent reseach points out to problems with using the MBI. The BMI is, however, a good general indicator, but it can be misleading. A body builder can have a high BMI while having an extremly low body fat percentage. People of Asian origin can have a low BMI while having a lot of fat, putting them at high risk of developing heart disease and diabetes. Count Iblis (talk) 14:59, 29 August 2013 (UTC)

(ec) No, it's certainly not accurate. Our Body mass index article has a section Body_mass_index#Limitations_and_shortcomings which you should probably read. It was always intended as a statistical means to estimate body fat over a large number of people - using it for an individual is problematic and has huge possibilities of error. However, it's extremely easy to measure - and it can provide a useful (if highly approximate) answer for some applications. SteveBaker (talk) 15:03, 29 August 2013 (UTC)

FAT

Does eating fat, on its own, make one fat?--86.181.30.8 (talk) 14:16, 29 August 2013 (UTC)

No, and not even a high total calory intake will on its own make one fat. Controlled experiments have consistently failed to demonstrate a link between diet and obesity. That doesn't mean that such a link over a long period does exist, just that it isn't as simple as eating too much for a while and putting on weight as a result. Count Iblis (talk) 15:02, 29 August 2013 (UTC)

I agree it's not as simple as that...but the ways in which it's not simple need to be explained very clearly before making such an extreme claim. You need to be VERY careful about how you phrase that - it's misleading in the extreme to say that your diet doesn't affect whether you're obese or not - and many, MANY sources would disagree with that. I think Count Iblis needs to provide us with some very good references for this rather extreme claim - and explain in considerably more detail what is meant by it. His preceding statement is horribly misleading! SteveBaker (talk) 15:11, 29 August 2013 (UTC)

No, if you kept your exercise schedule the same and instead of eating (say) 2,000 calories of carbohydrates each day (sugars, starches, etc) - you switched to eating 2,000 calories of fat instead - then you would be unlikely to change weight significantly as a result. Other health indicators such as cholesterol might go badly wrong - but the calorie intake is the same, it won't make you fatter. However, if you're eating a good diet and then add 2,000 calories of fat to your diet each day - then you'll put on weight rather rapidly! SteveBaker (talk) 15:11, 29 August 2013 (UTC)

Forgive me for not trusting the comments above, I had to look it up.

Here's a ref that is relevant to the question.

“ The percentage of energy from dietary fat is widely believed to be an important determinant of body fat, and several mechanisms have been proposed to account for such a relation. Comparisons of both diets and the prevalence of obesity between affluent and poor countries have been used to support a causal association, but these contrasts are seriously confounded by differences in physical activity and food availability. Within areas of similar economic development, regional intake of fat and prevalence of obesity have not been positively correlated. ... ... Moreover, within the United States, a substantial decline in the percentage of energy from fat consumed during the past two decades has corresponded with a massive increase in obesity. Diets high in fat do not appear to be the primary cause of the high prevalence of excess body fat in our society, and reductions in fat will not be a solution. ”

Emphasis added by me. From here [10], an article from The American Journal of Clinical nutrition, 1998. SemanticMantis (talk) 15:16, 29 August 2013 (UTC)

Yes - but that's not what Count Iblis said. He said (in essence) that calorie intake isn't the culprit and that diet doesn't matter - and without some pretty strong evidence, I have to call "bullshit" on that claim. The reason that decreasing fat intake doesn't reduce obesity is that people eat more carbohydrates (sugar, starch) to make up for it. Total calorie intake is the key - and it doesn't matter all that much where the calories come from. SteveBaker (talk) 17:40, 29 August 2013 (UTC)

Despite my phrasing, I wasn't really responding to you or Iblis, just providing a ref that I thought addressed the OP's question. I've stricken part of my post to make my intent more clear. SemanticMantis (talk) 17:55, 29 August 2013 (UTC)

See also Mediterranean diet, which is rather high in fat, and recently attracted lots of attention as a rather healthy diet (see refs in article). SemanticMantis (talk) 15:18, 29 August 2013 (UTC)

I don't know what you have in mind when you ask the question. If you are asking whether we accumulate the fat that we eat as fat in our body, then the answer is definitely no. Out bodies produce their own fat to store energy. But the fat that we eat has lots of calories, which make us fat. OsmanRF34 (talk) 17:28, 29 August 2013 (UTC)

The core determinant of weight is calories eaten vs. calories burned. If you eat a (say) 2000 calorie diet, and maintain the same activity schedule, the exact composition of the diet is of decidedly secondary consideration. But some diets are easier to maintain than others, and some (different ones, of course ;-) diets make it easier to exercise well. If you manage to eat a reasonable amount of your calories as fat without overeating in total, that's generally fine. --Stephan Schulz (talk) 17:36, 29 August 2013 (UTC)

Indeed, and a reasonable rule-of-thumb is that: weightGainedInPounds = (caloriesEaten - caloriesBurned)/3500

All diets that actually work have to play with how many calories your eat, or how many you burn, or some combination of the two. Mediterranean diets replace carbohydrates with fat - and hope that you'll be fooled into eating less calories because of it. But if you eat too much fat you'll put on weight despite not eating a single unit of carbohydrate. SteveBaker (talk) 17:52, 29 August 2013 (UTC)

Of course, one of the factors in overeating is the desire to eat itself. Different foods have a different affect on the sense of satiation; and foods that make you feel fuller with less calories are generally considered preferrable, if only because a person who is satiated (full) will eat less calories if their diet contains more foods that "fill you up" while providing less calories. Without going into exhaustive detail as to which foods tend to be more satiating; that has to be a factor in considering a healthy diet, from an "obesity-avoidance" perspective. People who are less hungry eat less food, so foods that fill you up and provide less calories in doing so are, on the balance, better for you. --Jayron32 18:11, 29 August 2013 (UTC)

I think the OP's question has been answered, but there is the question about what I wrote about total calory intake. What I'm saying is that it is not a universially valid statement to say that a big increase in calory intake will lead to a big weight gain. That doesn't mean that it will lead to weight gain in some people (paticularly if you are already obese, your weight will be more sensitive to the calory intake). But controlled experiments on people who are deliberately given way more to eat than they normally do (e.g. 5000 Kcal/day instead of 2500 Kcal/day) have debunked the simple calories in - calories out = weight gain model, see e.g. this documentary:

"In 1967, a medical researcher, Ethan Sims, carried out an experiment at Vermont state prison in the US. He recruited inmates to eat as much as they could to gain 25% of their body weight, in return for early release from prison.

Some of the volunteers could not reach the target however hard they tried, even though they were eating 10,000 calories a day. Sims's conclusion was that for some, obesity is nearly impossible.

It was with this in mind that 10 slim volunteers - who were not dieters - convened in more hospitable circumstances, for a recent experiment devised by the BBC's Horizon documentary. The 10 spent four weeks gorging on as much pizza, chips, ice cream and chocolate as they could, while doing no exercise, and severely limiting the amount they walked."

Count Iblis (talk) 18:37, 29 August 2013 (UTC)

The calories in vs. calories out model has not been debunked. More likely we just have a tendency to give wrong estimates of both variables. Calories in ones mouth may be consumed by gut flora or excreted intact. Calories out is impacted by basal metabolic rate, which may not be as constant as some would believe. Someguy1221 (talk) 21:01, 29 August 2013 (UTC)

Now what you said makes sense. Although I wouldn't dismiss Steve Baker's formula. In thermodynamic terms, it's true that 1 pound of fat equals 3600 kcal. But it appears that not all the calories that you intake can be stored. I would just expand the formula to include things about current weight and amount of extra kcal (the first 3600 extra kcal might give you an extra pound, but the same can't be true for the following groups of 3600 kcal). OsmanRF34 (talk) 18:46, 29 August 2013 (UTC)

Yes, the body will increase its metabolic rate to compensate for the increased calory intake. Without such a mechanism, eating slightly less would lead you to eventually starve to death. If you eat 2500 Kcal per day and you have a stable weight, then you won't starve to death if you start to eat 2400 Kcal per day and at the same time start to exercise a lot more. What happens is that your body will eventually start to burn 2400 Kcal per day. This is possible because the amount of calories used during heavy exercise isn't that much, the body can easily compensate for that by adjusting the metabolic rate.

Exercise is still important for maintaining a healthy weight, not because you burn a significant amount of calories, but because it enables this feedback mechanism to operate better. Count Iblis (talk) 20:28, 29 August 2013 (UTC)

But it's essential to note that the finding on calorie intake vs. calorie use only works in one direction. It violates no scientific principles for the body to eliminate excess calories without exercise, whether by increasing metabolic rate or by simply passing the excess through digestive tract without uptake, and simply allowing the gut flora to consume those calories. But if you start consuming fewer calories than your body intakes (or start burning more), you must be burning fat or something else to compensate. Someguy1221 (talk) 20:58, 29 August 2013 (UTC)

What Iblis has found is that sometimes, some people, under some conditions, can eat a lot of calories and not gain weight. Extrapolating the results of highly limited experiments is a suspicious way of making sweeping generalizations about all of humanity, doubly so when one merely cherry picks those specific experiments that happen to confirm the conclusion one had reached prior to searching for evidence in the first place. --Jayron32 22:43, 29 August 2013 (UTC)

Jack Sprat, for example. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:30, 29 August 2013 (UTC)

dog intelligence ranking

This is just a personal issue for me but Australian shepherds are listed as average intelligence while they and Border Collie rule the agility world, not the domain of dumb dogs. And to be truthful, most people pick agility dogs so they will be easy to train. Something is wrong with Coren's list. Maybe the new book about Chaser, the Border Collie, will be better. — Preceding unsigned comment added by Aikenite (talk • contribs) 22:52, 29 August 2013 (UTC)

Interesting, but this page is for asking questions, not to be used as a forum for expressing opinions. Looie496 (talk) 00:14, 30 August 2013 (UTC)

The OP has opened an interesting topic. Intelligence in dogs is an ill-defined thing. Dog intelligence and The Intelligence of Dogs seem to be our main articles, with the latter being about Coren's book, referred to in the OP's question. Some think that being reliably obedient and easy to train to perform tricks is a sign of intelligence, but we would probably ask serious questions about a human with such traits. Others suggest that the sneaky, disobedient dogs, like my beagle who stole half my lunch off the kitchen bench I didn't think he could reach when my back was turned, are smarter. Until we can agree on that, we won't agree on which are the intelligent breeds. HiLo48 (talk) 06:18, 30 August 2013 (UTC)

I agree - I had a relatively disobedient lab mix ("Sarah") and a very well-behaved, trainable god-knows-what mix ("Sam"). Sarah learned (by herself) that scratching at the back door would get one of us humans to come to the door and let her in. No amount of training would get her to stop scratching the paint off of the door...and the only way to save the door was to let her in...Argh! Then, one day while working in the back yard, I saw Sam standing patiently looking at the back door in the hope that by sheer force of will, it might maybe open...Sarah rushed all the way across the yard, scraped frantically at the back door - then ran away and went back to what she was doing as my wife opened it. Seems pretty obvious that she did that to let Sam in - knowing that he wasn't smart enough to do it for himself! When I mentioned this to my wife, she said that she'd seen that happen several times before. So, on the basis of that small measure, I'd definitely argue that "intelligence" and "trainability" were not only different - but possibly complete opposites.

That said, Border Collie's are very trainable - and they seem pretty intelligent too...but it's hard to know for sure.

Clearly, we don't have a good definition of "intelligence" - even in humans where we could measure it if only we knew what it was. (It's widely recognized that IQ tests don't measure what most people think of as intelligence). Doing that in dogs would be just about impossible. So I don't think there is a good answer to this. HOWEVER: It clearly is possible to measure such attibutes as "trainability" and "obedience" with simple statistical measures. SteveBaker (talk) 15:20, 30 August 2013 (UTC)

I have dreaded what the dog genome project would uncover about the basis of instilling trainability and obedience. But I haven't heard much out of it since [11]. (Selective sweeps from the farm-fox experiment are also potentially informative; I see here they were doing basic mapping with backcrosses.) I'm thinking "quiet ... too quiet". Wnt (talk) 15:26, 31 August 2013 (UTC)

August 30

determining probabilities from rate laws

For something like radioactibe decay, the rate law is ${\frac {dN}{dt}}=-\lambda N$. and for a general chemical reaction it is usually something like ${\frac {dN}{dt}}=kN^{x}$ (see rate law). Is it possible to deduce from the rate laws the probability that a reaction occurs after a particular elapsed time? 130.56.84.66 (talk) 02:20, 30 August 2013 (UTC)

The answer is essentially "yes, but...". the k term in the rate law you quoted implies an constant. In practice for chemical reactions it is a complex function of temperature. The temperature dependence is often modelled by the modified Arrhenius equation. Reactions can be considered as two sorts: a) reactions that are single step, or are time dominated by one of several steps, and b) reactions that comprise two or more steps where none dominates. Reactions of the first type show an exponentially decaying rate easily (trivially) determined from the rate equation. Reactions of the second type typically show a delay period in which not a lot happens, followed by a relatively sudden or dramatic increase in the production of product (and heat). Combustion reactions are of this sort. A "simple" example is the reaction of hydrogen and oxygen. The final stable product is water vapour, but there are several steps on the way involving over 120 simple reactions between 6 intermediate species such as OH, HO2 etc. To determine both the initial delay and the subsequent reaction rate, you need to solve the reaction rate equations for each step as a set of simultaneous non-linear equations. You probably learnt how to manually solve simultaneous linear equations in high school, using two and three equation examples. If so, you'll know that the amount of work rises very rapidly with the number of equations. To do this for real chemical reactions can take a LOT of computer time. And I do mean a lot. For working it out for say the combustion of gasoline, you need a super computer grinding away for weeks.

A practical issue is that the constants you need to use in the modified Arrhenious equation to calculate k are often not known for the reactions you are interested in. And considerable laboratory ingenuity is required to measure them.

Much the same applies to radioactive decay, however with radioactive decay unlike chemistry, there is quite often single step or single time dominant step. Even when there isn't, there are far fewer component reactions for each intermediate species than is usually the case in chemistry. So the calculation of radioactive decay is generally easy, not requiring a lot of computer time.

124.178.41.65 (talk) 03:40, 30 August 2013 (UTC)

Can you tell a person's race through genetics?

Through molecular genetics can you tell a person's race? Say if a person is black, white, native can it be found through genes? — Preceding unsigned comment added by 74.14.31.85 (talk) 03:42, 30 August 2013 (UTC)

Physical characteristics would be defined by the genes, sure. See Phenotype. ←Baseball Bugs ^{What's up, Doc?} carrots→ 03:52, 30 August 2013 (UTC)

But how can you tell the person's race, isn't there more to race like IQ averages? Wasn't that proven to be almost completely hereditary? — Preceding unsigned comment added by 74.14.31.85 (talk) 03:56, 30 August 2013 (UTC)

Why was this question removed, if I say something wrong please correct me? — Preceding unsigned comment added by 74.14.31.85 (talk) 04:05, 30 August 2013 (UTC)

Race and intelligence are unrelated, as you well know. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:30, 30 August 2013 (UTC)

24.23.196.85 (talk) 05:58, 30 August 2013 (UTC)

Citation needed? See the discussions below. You're obviously a race-baiting troll. I don't know why this thread is being allowed to stand. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:40, 30 August 2013 (UTC)

Actually, Wikipedia has an article on this subject: Race and intelligence. There is certainly a correlation between race and intelligence. As always, correlation does not equal causation. Furthermore, calling people "trolls" is most uncivil. Race, per se, can be a very sensitive issue, but that doesn't mean we can't talk about it in academic discourse. Therefore, if you want to engage in an discussion about race and intelligence, you have to provide references to support your point. The OP's question is concerned with the idea that a person's race can be determined by genetics. In reality, a person's race can be determined by many attributes, including place of origin. Now, if individuals live together, they may mate among each other and thus produce similar genes. Therefore, race may be attributed to place of origin or common ancestry. Perhaps, a similar scenario would be dog breeds. 164.107.102.219 (talk) 21:35, 30 August 2013 (UTC)

The OP's question implies you could discern the race in part by discerning the presumed intelligence level in their DNA (if such a thing is even measurable). That's a nakedly racist idea. And thoroughly bogus. There are lots and lots of very smart black people in this world, and lots and lots of very dumb white people. And genes aren't going to contain whatever "average" a race allegedly has, they are going to contain whatever level that individual has. Intelligence is in individuals, not in races. ←Baseball Bugs ^{What's up, Doc?} carrots→ 12:03, 31 August 2013 (UTC)

And, in many peoples' eyes, black, white and native aren't races. HiLo48 (talk) 06:10, 30 August 2013 (UTC)

Here in the Eastern Hemisphere, 'black' and 'white' are approximate descriptions of the people who are 'native'. AlexTiefling (talk) 09:02, 30 August 2013 (UTC)

Race is partially genetic, but it's also partially cultural. So, identical twins might both be determined to be the same race, genetically, but, if raised in different cultures, might self-identify themselves as different races, and might appear to be different races to everyone else. For example, whether a black person wears their hair in an afro, or straightens it, will greatly affect how they are perceived. StuRat (talk) 06:14, 30 August 2013 (UTC)

The short answer is "no". A longer answer can be found by reading our article on race and genetics which says:

In everyday life many societies classify populations into groups based on phenotypical traits and impressions of probable geographic ancestry and socio-economic status - these are the groups we tend to call "races". Because the patterns of variation of human genetic traits are clinal, with a gradual change in trait frequency between population clusters, it is possible to statistically correlate clusters of physical traits with individual geographic ancestry. The frequencies of allelles tend to form clusters where populations live closely together and interact over periods of time. This is due to endogamy within kin groups and lineages or national, cultural or linguistic boundaries. This causes genetic clusters to correlate statistically with population groups when a number of alleles are evaluated.

So if you take a large enough population there may be some statistical correlations between genotype and geographic ancestry, but at the level of individuals the answer is still "no". Certainly there is no genetic definition of "race". Gandalf61 (talk) 08:28, 30 August 2013 (UTC)

You can reasonnably reliably identify someone's ancestry through genetics. Some genes are more common amoung certain populations, so you can make a good guess of where their ancestors used to live if you find several of these population-specific genes. --Lgriot (talk) 08:58, 30 August 2013 (UTC)

Really ? So how does that work ? If there is an allele X that is very common in population Y and very rare outside of population Y then you can conclude that someone with allele X probably has at least one ancestor from population Y - but that could be a single lone ancestor. This tells you nothing about the overall span or distribution of their ancestry. Gandalf61 (talk) 09:36, 30 August 2013 (UTC)

Here is some data, as of 2008: [12]

"Using only genetic data, the researchers were able to assign, on average, 50% of European individuals to within 400 kilometers of their correct country of origin. But there was one caveat: all four grandparents of an individual had to come from the same European country for the assignment to be correct. People with mixed European ancestry tended to show up between the locations of their ancestors."

A thing to remember is that you're not just looking at one allele, you're looking at tens of thousands of alleles. So statistical correlations do come into play, even for DNA taken from a single individual. Jheald (talk) 10:08, 30 August 2013 (UTC)

With more complicated ancestries, you can estimate where each part of each chromosome is likely to have originated geographically. Here is what 23 & Me reckoned they could achieve in 2012 [13] -- scroll down about two-thirds of the page for their estimates of where each part of each of the two copies of one customer's Chromosome 2 originated. Jheald (talk) 10:22, 30 August 2013 (UTC)

23 & Me makes money by selling DNA test kits, so they are not a reliable source of information on this. This article from the Telegraph reports the views of academics on genetic ancestry tests and concludes that they are "genetic astrology". Gandalf61 (talk) 10:38, 30 August 2013 (UTC)

I'd tend to trust the data and the science and what's been published by scientists actually working in this area, rather than a few rent-a-quotes rounded up by the Telegraph.

When you can see with your own eyes the clear geographical clustering in the principal-components scatterplots, it is fatuous to deny that that clustering exists.

The algorithms 23 & Me are running for the chromosome plots are very standard data-mining changepoint detection methods, and the results are pretty much exactly what you would expect. They make sense, biologically and genetically.

The weakness is that so far they have very little comparison data for genomes from outside Europe, apart from the specific individuals in the 1000 genomes project. So their identifications of the origins of non-European parts of the chromosomes are really rather vague at the moment, and should only be considered provisional -- in time, with better reference data, it should be possible to be much more specific; and it may turn out that some of the "nearest best guess" from current data may not be quite right.

In the media article, I can understand distaste at some of the rather strident hype from people like Brian Sykes or Alistair Moffat encouraging people to identify with a "tribe" according to which Y-DNA Haplogroup they belong to, and then identify with Richard III or whoever -- when this only accounts for one part of their ancestry, and may have come into the country in many different ways. I can see why somebody might challenge that this is no more significant than somebody's star-sign. But on the other hand, if somebody in the UK has particular forms of a Haplogroup I Y-chromosome, one can say with pretty much certainty that that mutation originated in Scandinavia and was brought over by the Vikings. That only gives one line of ancestry, but go far enough back to a time when there was much less population migration for much of the population, and it probably does indicate that a grandfather or great-grandfather or great-great-grandfather came from a part of the country that had a considerable Viking ancestry. Similarly, if you look at enough Y-STR markers, there may be a particular detailed pattern that indicates that that chromosome came from a particular Ashkenazi Jewish ancestry; or a particular lineage from the Indian subcontinent. Yes, there were mistakes made when people over-claimed too early, using too few markers, before it was better known how widespread or not those combinations were in particular populations. (Some of the early claims made for the so-called Cohen Modal Haplotype based only only 6 markers, rather than up to 37 or 67 that are typical today, are such an example). But we now have that data, so we now know just how specific a particular combination of markers is.

With autosomal data, we are not at that stage yet for non-European populations. We don't yet have enough data from enough different parts of the world outside Europe to be able to definitively say in detail how geographically widespread particular values for particular genetic markers may be, and in just which populations they may or may not be most common. So this is why the ancestry assignments outside Europe for parts of chromosomes are pretty vague, and for the moment should be regarded only as provisional. But they will inevitably get better, more detailed and more certain, as more reference data comes in. The underlying science is sound. Jheald (talk) 11:52, 30 August 2013 (UTC)

This guide] from Sense About Science is a detailed objective critique of the marketing claims of 23andMe and similar commercial organisations. "Genetic ancestry tests use some techniques that have been developed by researchers for studying differences in DNA across many groups of people. The things we know about genetic ancestry, almost without exception, are about the genetic history of whole populations.Companies use techniques from this field and sell their findings to people who want to find out about their personal history. The techniques were not designed for this. The information they give is not unique to any individual." Gandalf61 (talk) 12:27, 30 August 2013 (UTC)

I think it's a fair message that you need to have your eyes open to the limitations of what a genetic test can tell you. And you should know exactly how high resolution a test you're getting. There are certainly inflated claims being made to tell you "your ancestry" on the basis of just quite a low-resolution test -- perhaps just the Y or mtDNA haplogroup; so the comments on the limitations of a test like that, and the generic un-personalised people might get back from perhaps just a dozen standard scripts (which may also perhaps be rather fanciful) are entirely on-point. Perhaps that isn't much more meaningful than a star-sign. But at the same time, that's not necessarily all one can learn, even from just the Y or mt-DNA.

On Y-DNA and mtDNA testing, they don't really say anything different from what I've said above: that each of these can only tell you about one particular line out of many. And strictly speaking it will only relate to people sharing that DNA today. On the other hand, a 37- or 67-marker Y-STR test are specific enough that they may clearly indicate that particular line is specifically related to a cluster of Ashkenazi Jewish lineages; or corresponds to a Y-STR signature strongly found in present-day Scandinavia. Does that mean you are a "Viking"? No. Does that mean that you had a direct male-line ancestor who was a Viking? If that's your Y-STR signature, then almost certainly. Is that fact, concerning just one line out of many, of interest to you? That depends on you. And of course, most likely you will get something much less revealing -- eg a very generic West European Haplogroup R1b ancestry; or alternatively, something less easily interpreted, for example a Haplogroup T ancestry like Thomas Jefferson, for which various possible routes have been suggested.

When we come to autosomal DNA, which is probably going to be the most revealing test for this Ref-desk question, there are a couple of good caveats that they make -- for example, that one can only fully securely relate what is found to the genetics of present-day populations, because there's a limit to how confident we can be about the geographical ancestral genetics; and also, purely due to randomness, the proportions of DNA correlating to particular geographical groups will only roughly correspond to the proportion of ancestry, because some ancestors won't be represented in the inherited DNA at all; and others will be more strongly represented.

What I think the pamphlet fails to connect with (disappointingly, given the high calibre of the advisors consulted) is the statistical power of moidern high-throughput genetics. It cites a paper (5) that considers what you can learn from ten to twenty loci. But the SNP chips used by 23 & Me are testing 500,000 loci. That makes it possible to do qualitatively different sorts of analyses.

The pamphlet highlights that "the Scottish Highlands do have some genetic differences from the bulk of the population, but they are not big". But with 500,000 probes, you have enough statistical power to start to pull out those differences. "There is no such thing as a ‘Scottish gene'"; but with 500,000 probes you can distinguish between really quite subtly-different probability distributions -- as the scatterplot from 23 & Me demonstrates. There is only "gradual genetic change and mixing", even across "strong cultural boundaries, such as between the Germanic and Romance language groups in Europe". But this is exactly in line with the 2008 data I quoted above, which found that "the researchers were able to assign, on average, 50% of European individuals to within 400 kilometers of their correct country of origin."

There's a relationship between how different the probability distributions are, and how many DNA loci you need from a DNA fragment to identify cluster membership and a changepoint from one cluster to another. If the populations are very distinct, you may be able to identify even quite closely spaced changepoints along the chromosome -- as the Chromosome 2 pics linked above appear to demonstrate, still being able to sharply identify the recombination points of DNA from different continents even at a depth of several generations on. If the populations are less distinct -- different European countries, say -- identifying the points along the chromosome where the DNA inheritance switches from one country to another may be much more difficult, for anything other than the very most recent ancestors.

So there certainly are some real limits to the resolution. But given that the question at the top referred to "races" -- which we might take as a not-particualarly-good shorthand for roughly continental-level population clustering, then, yes, as the Chromosome 2 pics demonstrate, it probably is possible to estimate pretty sharply which parts of which chromosomes came from which continents.

You would be relating bits of your DNA to *groups* of people, rather than getting a detailed personal history. And these are indeed groups that would have been characterised on a population-level, and are going to be pretty generic, so not going to point to any specific ancestor. (Though you might find a chunk of your DNA happens to match the corresponding chunk of somebody else's on the programme, establishing a common ancestor). However, I don't see how a breakdown of which part of your DNA comes from which group (or indeed which continent) could be said to be anything other than "unique to the individual".

Is the information going to be personally meaningful? Depends on what the individual finds meaningful, personally. Jheald (talk) 16:01, 30 August 2013 (UTC)

23andme offers "country of origin" analysis, and if it shows, based on genetic analysis that Person A is 99% European, while person B is 76% Sub-Saharan African, it is pretty clear which will have the Black physical characteristics and which will have the Caucasian characteristics. No one would be confused, looking at their pictures, as to which one was of mostly European and which one was of mostly African ancestry. "Race" is a social construct, such as Jim Crow laws or German Nuremberg Laws which made someone a Black or Jew based on "one drop of blood," or one great-great grandparent of the discriminated-against race. But there are readily detectable genetic indices of where ones ancestors lived. Edison (talk) 22:19, 30 August 2013 (UTC)

• There are definitely people who claim they can reconstruct a face from DNA now [14] or in the near future [15]. But the former is an artist, and the latter is a company page about a future product (and their table of faces according to a gradation from male to female pegs my BS-ometer, because how would they get an intermediate value?). Our article on DNA profiling doesn't cover it. As of 2004 it was pretty crude [16] but one expects improvements. We'd really need to get a list of every product on the market and evaluate each one skeptically. Wnt (talk) 16:12, 31 August 2013 (UTC)

Isn't the answer here simply, "maybe, depending on what you mean by race"? If the subject has the alleles that produce the West African version of sickle-cell, or the Jewish version of Tay-Sachs, can't we draw the obvious conclusions? μηδείς (talk) 03:30, 1 September 2013 (UTC)

Yes. We can draw the conclusion that someone doesn't understand genetics. Alleles for the "West African version of sickle-cell" aren't confined to West Africans, and alleles for the "Jewish version of Tay-Sachs" aren't confined to Jews... AndyTheGrump (talk) 03:37, 1 September 2013 (UTC)

L-system and proportions

Hello. As far as I understand from the article, the commands for drawing a fractal using L system (if we draw it using turtle graphics) don't deal with the proportions of the fractal and the fact that in many fractals, deeper the recursion, smaller the segments added. Am I right? for example, the rules for Lévy C curve don't treat the fact that each segment is replaced by 2 segments that are smaller version of the initial segment (they are divided by sqrt(2)). Why is That?

Thanks! 94.159.221.4 (talk) 07:34, 30 August 2013 (UTC)

Your are correct - the iterated replacement rules in an L-system give a scale-free description of a fractal structure. How you then interpret the L-system strings to construct a family of geometric curves is up to you. You can rescale at each iteration, making each segment smaller and smaller so that overall size of the curve (as measured by, say, the width and height of a rectangle that contains it) remains the same. Or you can keep each segment the same size, in which case the overall size of the curve increases with each iteration. Both interpretations are valid - neither one is more "correct" than the other. Gandalf61 (talk) 08:56, 30 August 2013 (UTC)

Thank you very much! maybe it's worth mentioning in the article itself. 94.159.221.4 (talk) 11:19, 30 August 2013 (UTC)

Correlation between adultery and education level?

I found this interesting Psychology report on the web.

Whisman & Snyder (2007) also found support that the likelihood of infidelity decreases the more religious you are, as you age, or if you’re better educated. They also found that the risk for cheating was greater for women who were remarried (compared to those who were on their first marriage), or for either gender with the greater number of sexual partners you have.

I can easily find a possible reason for the correlation between religiosity and adultery or age and adultery. But the correlation between education level and adultery is what I find interesting. The article cites the source, and I try to find the source on the web, which brings me to the original article. Sadly, the original article doesn't really seem to support the notion of education level and adultery, besides reporting the negative correlation in the table. There is no verbal coverage on this topic. I am wondering if similar research has been done on the correlation between adultery and education level, or the possible reported reasons and explanations for why this phenomenon may be the case. 164.107.102.232 (talk) 13:54, 30 August 2013 (UTC)

DNFT--see banned user Wickwack at talk
The following discussion has been closed. Please do not modify it.
There is a vast multitude of survey based pschology "findings" out there. Most are pretty dubious, inclding those reported every month in Scientific American Mind, and in professional journals. However, I don't find the claim that the risk of infidelity is less for the better educated at all surprising. The better educated are often (but certainly not always!) the more intelligent. That confers at least three factors: The more intelligent probably made a better and more thought out choice of partner to marry, rather than just go on lust or infatuation. They are better able to be led by their brain (seeing the negative consequences of infidelity) rather than being led by their hormones when meeting, as will inevitably happen sooner or later, an available person more sexy than their marriage partner. They are better able to reason out a commitment to do nothing that could potentially harm their children or affect their relationship with inlaws etc. A succesful infidelity-free marriage is based on three things: a) Commitment, b) Each has something the other needs, and c) a "circuit breaker" for the inevitable occaisonal silly argument. The more educated have demonstrated, whether they are intelligent or not, an ability to committ to something hard but durable - their education. The more intelligent probably have just as many "domestic tiffs" as the less bright, but are better able to get past them and get back to harmonious living. Finally, the less intelligent a person is, the more they view things as "all about me". The more intelligent tend to view things as "more about you". 124.178.41.65 (talk) 15:57, 30 August 2013 (UTC)

Interesting theory. Can you define what you mean by "intelligent" and "educated"? It appears that you use those two words differently. What type of "intelligence" are you talking about? I would have thought that there are so many confounds in regards to adultery that it would be nearly impossible to generalize accurately the relationships between adultery and its presumed causes. In addition, I think one explanation is to combine age, religion, and education into one big pot. Perhaps, as people grow older, they become wiser, more religious, and more educated - and thus less likely to cheat against each other. Many religions are deeply philosophical and may put people in what I call "deep thinking mode", a state in which people just stay calm, meditate, and think. And all that deep thinking and reasonings against unwise sexual intercourse make people less likely to commit adultery. It's a thought. 164.107.102.30 (talk) 16:56, 30 August 2013 (UTC)

Note that 124 is a banned sockpuppet so their responses are not welcome. Nil Einne (talk) 08:24, 31 August 2013 (UTC)

Of course there is an underlying assumption here that infidelity is necessarily a bad thing. Our society has basically said that it's a bad thing - but that doesn't mean that it is. From an evolutionary perspective, there is benefit to males in doing this because increasing the number of females he mates with increases the number of copies of his genes that make it into the next generation. It might be (and I have no evidence for this) that the impulse for males to be adulterous might not be negatively correlated with intelligence at all - completely the opposite in fact.

I'd also caution the results of studies that do not control for intelligent people being smart enough to get away with it more often - resulting in under-reporting of their infidelity rates.

We'd also have to be careful about our definitions of the term. Technically, it means having sex with someone else while you're still married - but what about when people are married, but separated? SteveBaker (talk) 17:47, 30 August 2013 (UTC)

Using the term "evolution" with "good" or "bad" is extremely misleading. First of all, the good/bad dichotomy may refer to morality, and by saying that "because evolutionary forces made us this way", you are automatically making a claim that somehow nature can make so-called "good" or "bad" choices. That is extremely misleading by itself. Second of all, you are assuming that the spreading of genes is desirable, when in reality it may not be in all situations. For instance, a counter-argument would be that males that invest time, effort, and commitment in the raising of the offspring ensure the viability and fertility of the next generation, while males that invest less time in such behaviors and more time in one-night-stands with various women may produce children living in destitute conditions, and such children may be left on the streets to die. Therefore, you cannot assign "good" or "bad" characteristics to nature. 164.107.102.219 (talk) 20:23, 30 August 2013 (UTC)

Ferdinand Richters (1849-1914) and Tardigrades - help!

Hello all,
Apparently Ferdinand Richters was the authority for any number of Tardigrade familia, genera and species: see Richtersius coronifer. I'm not being much use google-fu wise for the article.
Help me out here! Pete aka --Shirt58 (talk) 16:04, 30 August 2013 (UTC)

What do you need to know? I don't see a question here. SteveBaker (talk) 18:17, 30 August 2013 (UTC)

I think Shirt wants refs/sources confirming or counter-indicating Richters as the authority of the Tardigrade genera. But maybe I'm reading too much into it, or perhaps OP will clarify. SemanticMantis (talk) 18:24, 30 August 2013 (UTC)

Shirt created the Ferdinand Richters article, which currently contains one sentence. I think Shirt is looking for more information to put in the article. Looie496 (talk) 23:00, 30 August 2013 (UTC)

Here are 4 sources, Shirt: [17], [18], [19], [20]. They came from googling "Ferdinand Richters 1849 1914". -- Jack of Oz ^{[pleasantries]} 23:17, 30 August 2013 (UTC)

Thanks all. As SemanticMantis said, I'm looking for refs that verify that Richters was the binomial authority for Richtersius coronifer. And as Looie496 said, yep, I'm looking for more content for the article. De mortuis nihil nisi bonu notwithstanding, obituaries are good for verifying dates of birth and death. Looking for input from folks who have access to scholarly journals. Pete aka --Shirt58 (talk) 12:40, 31 August 2013 (UTC)

Linear bench power supply for charging batteries

Mastech says their linear bench power supplies cannot be used to charge batteries or provide power for electroplating. They recommend specific models for those applications which have over-voltage and over-current protection. Why can't their linear power supplies also have over-voltage and over-current protection? --89.241.229.123 (talk) 18:39, 30 August 2013 (UTC)

Because both those applications tend to use very high current (or at least, there is a high risk of creating a short-circuit), and even the circuit-breakers and fuses built into bench power-supplies will have operational limitations beyond which they can not be reliably assured to provide protection. For example, see fuse breaking capacity and the corresponding section in our article on circuit-breakers. If an application is known to exceed the design capability of the protection circuitry, then the protection-circuitry is not safe and reliable. For those applications, a higher-grade protection-circuit is recommended. Nimur (talk) 20:31, 30 August 2013 (UTC)

It would not be a matter of "can't", it would be that Mastech did not put such protection in. This would be because it would have cost more, or degraded other specifications (such as size, accuracy or efficiency). For charging batteries you often need a specific charger that will not damage the batteries with overheat or overcharge, and yet not take too long. Graeme Bartlett (talk) 21:47, 30 August 2013 (UTC)

August 31

DNA and heredity

Hello. Perhaps this is a simple question and I'm just not seeing an answer anywhere, but I'm trying to understand if (for example) I, as a male, could have inherited any traits from my paternal grandmother. In this scenario, my father would have inherited a Y chromosome from his dad and an X chromosome from his mom. He would have passed the Y chromosome (i.e. only his father's genetic material, not his mother's) on to me and my X chromosome would come from my mother. Is this right? Or is there some other process whereby I would have inherited genetic material from my father's mother?--William Thweatt ^TalkContribs 01:04, 31 August 2013 (UTC)

You have another 22 chromosome pairs besides X and Y, which come from both of your parents, and are constructed from DNA passed on by all four of your grandparents. See the introduction of Human genome. Someguy1221 (talk) 01:23, 31 August 2013 (UTC)

More specifically, you've inherited 25% of your genetics from your paternal grandmother. As you have from your other three genetic grandparents. --Jayron32 01:29, 31 August 2013 (UTC)

Ah, yes. It's all coming back to me now. Thanks all. It's been a long time since Biology 101 for me. :) --William Thweatt ^TalkContribs 01:42, 31 August 2013 (UTC)

The 25% is a good approximation, but you might actually inherit slightly more from your paternal grandfather than your paternal grandmother, since you definitely have his Y and have only a 50% chance of having that grandmother's X. Also, sometimes genes can jump from one chromosome to another. StuRat (talk) 02:43, 31 August 2013 (UTC)

Presuming that William is male, he has zero chance of having that grandmother's X. A man's X always comes from his mother. (A woman gets one from her mother and one from her father.) Looie496 (talk) 02:58, 31 August 2013 (UTC)

Good point. Correcting for that, with 46 chromosomes, a male should, on average get 1 (Y) + 44/4 chromosomes from his paternal grandfather, 44/4 chromosomes from his paternal grandmother (no sex chromosome), and 1/2 + 44/4 chromosomes from the additional two maternal grandparents, as either might contribute the X. So, that's 12 + 11 + 11.5 + 11.5 = 46. As a percentage, that works out to be 26%, 24%, 25%, and 25%. StuRat (talk) 10:10, 31 August 2013 (UTC)

There's no either, just as with autosomes both maternal grandparent will contribute to the X chromosome a male inherits as recombination will almost definitely occur (if it does not, this generally means major problems so the whole calculation may be out of wack). In case this is still confusing, this means the X chromosome the male inherits from his mother is not her father's X chromosome nor her mother's X chromosome but a chromosome combining their two (maternal grandparents) chromosomes in some way. (The X chromosome the maternal grandmother contributes is likewise a combination of the two X chromosomes she has. In fact even the X chromosome from the father is not simply the X chromosome he inherits from his mother but a combination of his X and Y chromosomes although the Pseudoautosomal regions are small enough that it doesn't really screw up your statistics to assume it is.) Also I question the usefulness of counting percentages in terms of number of chromosomes, it makes much more sense to either use base pairs or perhaps genes (the former is of course far simpler than the later), and the differing size of the chromosomes means the values you will get will be sufficiently different. Nil Einne (talk) 16:05, 31 August 2013 (UTC)

If we're just talking about autosomal DNA here, the 25% has to be understood as a statistical average. When germ cells (sperm and eggs) are made, genetic recombination causes the paternal and maternal copies of each pair of chromosomes to exchange some DNA. This means that while you carry 22 autosomes that are entirely paternal and 22 that are entirely maternal, your germ cells carry autosomes that each contain a mix of paternal and maternal DNA. So your children do not carry the exact same chromosomes as you. Since this process is totally random, you may inherit more or less than 25% from each particular grandparent, but the average will be 25%. Someguy1221 (talk) 03:56, 31 August 2013 (UTC)

weathern pattern significance

Back in the early-to-mid 1980s, when I was a kid, I heard a foghorn sounding off at night during a rainstorm in San Francisco. Why would an authority need to turn on the foghorn during rainy weather at night?142.255.103.121 (talk) 04:09, 31 August 2013 (UTC)

Two reasons: (1) On a rainy night, it IS harder to see than on a clear day (anyone who's ever flown a small plane on a rainy night can appreciate just how much); and (2) even more importantly, along seashores (especially in the area around Frisco), such weather can often cause the cloud base to sink and ground fog to form -- hence the need for the foghorn. 24.23.196.85 (talk) 04:51, 31 August 2013 (UTC)

Same thing for a rainstorm during the day, right?142.255.103.121 (talk) 19:17, 31 August 2013 (UTC)

Calling it a "fog" horn is a bit of a misnomer - it's really a "poor visibility" horn. Hence it's gotta be sounded in heavy rain or snow as well as in fog. Also in an era before weather satellites and weather radar - nobody knew what the visibility would be like further from shore - so you'd definitely want to err on the side of caution. SteveBaker (talk) 21:56, 31 August 2013 (UTC)

Are dogs born in winter less smelly than dogs born in summer?

Just heard one of my friends say so--朝鲜的轮子 (talk) 04:57, 31 August 2013 (UTC)

I wouldn't think so, although an outdoor poo will smell less in winter, as it will rapidly cool and freeze. Of course, if you don't pick them up, you're in for a rude surprise in spring. :-) StuRat (talk) 09:59, 31 August 2013 (UTC)

If you live in a hot, dry climate the quick drying of the deposits makes them less offensive and problematic than being somewhere where they stay damp and squishable. But all if this has nothing to do with when the dog was born. Had dogs all my life, Never heard of that, and can't think of any reason why that would make a difference. HiLo48 (talk) 22:26, 31 August 2013 (UTC)

I think my friend mean a dog's skin odor. Looked up Dog odor, but found nothing about skin odor except "Dogs only produce sweat on areas not covered with fur, such as the nose and paw pads, unlike humans who sweat almost everywhere. However, they do have sweat glands, called apocrine glands, associated with every hair follicle on their body. The exact function of these glands is not known, but they may produce pheromones or chemical signals for communication with other dogs.".--朝鲜的轮子 (talk) 01:29, 1 September 2013 (UTC)

Polonium hydride

Is it PoH₂ or H₂Po? Double sharp (talk) 15:15, 31 August 2013 (UTC)

There is an article about it Polonium hydride Widneymanor (talk) 16:39, 31 August 2013 (UTC)

Which unfortunately wavers on the issue:( (I suspect Ds knows this, but for others...) The same formula written one way or the other suggests which atom is more cationic vs anionic. Naming it "[some-metal] hydride" (meaning Po is more metallic and has "hydride" anions) contradicts comments about it having chemical analogs to chalcogenides where the Po has anionic forms. So to respond to the question sort-of..."what's really the goal of your question? To understand the nature of the chemical, or to decide how to write it in some [as yet unstated] context?" DMacks (talk) 20:04, 31 August 2013 (UTC)

Yup, the sources I've seen tend to disagree on this! Bagnall calls it polonium hydride with PoH₂ (IIRC), while Thayer (a ref at element 117, talks about heavy main group elements) calls it H₂Po! Po has a slightly lower EN (2.0) than H (2.20); that would imply that Po is the cation, but is there something else at work here? (And should we list it in the Po compounds template under Po(II) or Po(−II)?) It's more of understanding the nature of the compound than writing it.

(Hydrogen astatide has a similar issue with HAt vs AtH...) Double sharp (talk) 03:25, 1 September 2013 (UTC)

...much as which we habitually write "H₂O" rather than "OH₂" or "HOH" or even "HHO". SteveBaker (talk) 21:24, 31 August 2013 (UTC)

For the molecular compound, it should always be written as H₂Po. IUPAC determines the order in empirical formulae to be row 7→ row 2; group 18 → group 1 → group 2 → Actinium → Lawrencium → Lanthanum → Lutetium → group 3 → group 15 → Hydrogen → group 16 → group 17. Plasmic Physics (talk) 21:37, 31 August 2013 (UTC)

But if it really is a hydride rather than a polonide, this would be misleading, which is why I asked the question, albeit not that clearly (I've tried to remedy that now!) Double sharp (talk) 03:27, 1 September 2013 (UTC)

It would not matter, compositional formulae are ignorant of bond-type. Plasmic Physics (talk) 08:40, 1 September 2013 (UTC)

Need help with Calculating the slope of the best fit line from a data table?

Basically we had to calculate the circumference and the diameter of several round objects and convert that into a number closest to PI...

Now we are supposed to Calculate the slope with it but our teacher made no attempt to explain to us how to do it and our textbooks provide no easy to understand way to coincides with the assignment.

Diameter/Independent    Circumference/Dependent  Ratio C/D

     4.5 cm                  10   cm               2.22
     2   cm                   7   cm               3.5
     2.5 cm                   8   cm               3.2
     6.8 cm                  21.8 cm               3.205
     2.9 cm                   8.8 cm               3.034

He was supposed to post a video on Blackboard but he is so computer illiterate that it is sad. He never explains stuff and makes the assignment difficult but does not really teach us how to complete it. I have spent two days on youtube trying to understand this but i feel he pulled this whoel thing out of his @$$! Sorry! — Preceding unsigned comment added by Jheckman1986 (talk • contribs) 20:38, 31 August 2013 (UTC)

The slope of a Simple linear regression without an intercept term is ${\hat {\beta }}=({\overline {xy}})/({\overline {x^{2}}})$, where the overline indicates the mean, y in this case is circumference and x is diameter. However, just calculating the simpler ${\hat {\beta }}=({\overline {y/x}})$ would give you pretty much the same answer in this case. Red Act (talk) 21:20, 31 August 2013 (UTC)

I suspect that the intent here is that you plot a graph of diameter versus circumference. If diameter is the "independent" variable - then it should be plotted along the horizontal X axis and the circumference being "dependent" goes up the vertical Y axis.

Next, you can (hopefully) observe that those points lie close to a straight line...so you can calculate the slope of a best-fit straight line through those data points and thereby deduce the equation for the circumference of a circle, knowing it's diameter. This is a very valid and scientific way to deduce such a relationship. Mathematicians will of course cringe at this because they have ways to prove beyond doubt that that relationship is...but I'm guessing that this experiment is to help you to understand how scientific relationships are deduced from experimental data.

The way to calculate the slope of a straight line is described in our slope article (look at the first equation).

SteveBaker (talk) 21:22, 31 August 2013 (UTC)

(I fixed the OP's chart.) I think what Steve is saying is to just plot the points and draw in what looks like a good line, then measure it's slope off the graph. There are many mathematical ways you could calculate the best fit line, instead, but each will give a slightly different answer. So, if your teacher didn't specify what to do, I'd take the easy way out and just draw in a line by hand (using a ruler, of course). StuRat (talk) 10:30, 1 September 2013 (UTC)

Throwing away contact lenses

Is there a reason that monthly contact lenses need to be disposed of after a month of use (other than to enable the manufacturer to sell more contact lenses)? — Preceding unsigned comment added by 89.241.229.123 (talk) 21:01, 31 August 2013 (UTC)

Contact_lens#Replacement_schedule says that "Lenses replaced frequently gather fewer deposits of allergens and germs". By allowing gasses and liquids to flow through the lens, it's also possible for germs and allergens to lodge deep inside them where cleaning fluids may not penetrate. The article does also mention that "Quarterly or annual lenses, which used to be very common, have been discontinued by manufacturers who argue they are less comfortable but also can make more profit by forcing consumers over to more frequent replacement schedules." - which kinda backs up your theory that it's to enable them to sell more lenses. HOWEVER: What that sentence neither says nor implies is that you could wear 4-week lenses for months. It's quite possible that 4 week lenses really are only good for 4 weeks - and they the manufacturers simply stopped making the kind that last longer...do not assume that it's safe to use a 4 week lens for many months on the basis of this information...that might be very dangerous. SteveBaker (talk) 21:13, 31 August 2013 (UTC)

Why not sterilize contact lenses using UV radiation or ionizing radiation? Count Iblis (talk) 23:17, 31 August 2013 (UTC)

UV will destroy the polymers in the lens in a matter of hours [21]. 68.0.135.117 (talk) 23:20, 31 August 2013 (UTC)

The protein deposits are what I find to be the worst problem. You can sterilize them with hydrogen peroxide, but the protein deposits don't come off. I tried using bleach on them, but that also damaged the lenses. The original hard contact lenses could probably be cleaned indefinitely, but those really were uncomfortable, and, in my opinion, dangerous (they can cut your eyes). StuRat (talk) 10:21, 1 September 2013 (UTC)

herbicide for vines?

vine on the tree near the azaleas

vine in azaleas

About 2 months ago, vines were taking over our azaleas so bad that I had someone cut them out. It was so bad that they had to cut back most of the azaleas. Now the vines are coming back. Is there a herbicide or something that will get rid of the vines but not hurt the azaleas? Bubba73 ^{You talkin' to me?} 23:46, 31 August 2013 (UTC)

No, not to my knowledge. We have Roundup-ready corn, but not Azaleas. You can also get herbicides that selectively target grasses, but that won't help here either. The best removal tactics may depend in part on what type of vine. Does it have a woody stem? Is it English ivy or virginia creeper or porcelain berry or kudzu (all common and invasiv across much of the USA)? Anyway, for most woody vines, you can paint a small amount of Roundup on the stumps, directly after you cut the vines back. The vines will most likely resprout, but you can repeat the process over the course of a season or two, and the plant will get weaker and weaker each time. There is also some risk to the Azaleas, but if you don't spill any and only directly apply glyphosate to unwanted stumps (ideally on a hot day), you should be ok. SemanticMantis (talk) 00:22, 1 September 2013 (UTC)

(There is something wrong with the sections right now.) Thanks - I don't know what kind of vine it is, but I think it looks like the porcelain berry. I'll try to get a photo tomorrow. Bubba73 ^{You talkin' to me?} 00:42, 1 September 2013 (UTC)

Whoever found they had to cut back your azaleas to get at the vines is grossly negligent. You simply cut the vine stem (species is irrelevant unless it's dodder) at soil level, allow it to die, and then remove it later. There's absolutely no need to harm the plant on which the vine is growing. μηδείς (talk) 03:24, 1 September 2013 (UTC)

You're right - we aren't using them again. My wife was furious. He cleaned out the vines but cost at least a couple of years of growth. My wife and I planted them ourselves a few years ago. The vines are threatening to take over again. Bubba73 ^{You talkin' to me?} 04:25, 1 September 2013 (UTC)

Exactly what is being referred to by "vines" here? In my part of the world the word vine immediately brings up images of grape vines. Those in this section are being described as if they are some sort of weed. Is that the case? HiLo48 (talk) 04:30, 1 September 2013 (UTC)

I was wondering that, too! Whatever the type of weed, applying an appropriate weedkiller with a paintbrush (as described by SemanticMantis above) instead of a spray should stop the regrowth (after cutting down), though this method will require some patience. Make sure that the weedkiller is one rendered harmless by soil so that it doesn't affect the azalea. I've got rid of ground elder amongst other low-growing plants by this method (even though some "experts" claim that this is impossible without digging out). For some woody weeds, a selective hormonal weedkiller such as "SBK" (formerly containing 2,4-Dichlorophenoxyacetic acid and 2,4,5-Trichlorophenoxyacetic acid in the UK) might be quicker, but availability might be restricted by law. I think this has been replaced by Triclopyr for domestic use. Be careful, though, because azaleas are shallow-rooting, so any soil contamination might affect them. The really environmentally friendly method is to regularly remove new growth by hand as it appears, but that's very time-consuming. Dbfirs 08:35, 1 September 2013 (UTC)

See liana. In AU, e.g. cat's claw creeper is considered a weed of national significance [22]. Due to their extensive root systems, and growth of rhizomes and stolons, vines can be very challenging to remove. If you've never had to deal with aggressive, undesirable vines, consider yourself lucky! SemanticMantis (talk) 13:22, 1 September 2013 (UTC)

I've added two photos. Bubba73 ^{You talkin' to me?} 14:38, 1 September 2013 (UTC)

Yeah, that's grape (see leaf here. Contrary to HiLo's response above, grape is very much a weed, at least where I live (SW Ontario). I never tried herbicide in my war against it, but pulling it physically was an unending task. Good luck. :) Matt Deres (talk) 14:56, 1 September 2013 (UTC)

It doesn't produce Grapes, at least it hasn't so far. (Maybe it takes many years to do that.) Bubba73 ^{You talkin' to me?} 15:25, 1 September 2013 (UTC)

Habits

I forgot the name of a condition where sufferers act in odd ways; such as excessively cleaning your hands, a need to position objects in a very specific way, etc. I think its obsessively compulsive disorder or something like that. Pass a Method talk 23:49, 31 August 2013 (UTC)

Obsessive-compulsive disorder. 86.141.185.189 (talk) 23:54, 31 August 2013 (UTC)

September 1

Can it be proven that people dream?

Can it be proven that people dream while they are asleep? Bubba73 ^{You talkin' to me?} 01:06, 1 September 2013 (UTC)

You mean apart from the evidence of their own mouths? Can it be proven that people are merely hallucinating when they relate the details of an alleged "dream" they just had? -- Jack of Oz ^{[pleasantries]} 01:12, 1 September 2013 (UTC)

I have a friend who keeps quoting some unnamed scientist who (according to my friend) says that people just make it up when they wake up. Bubba73 ^{You talkin' to me?} 01:27, 1 September 2013 (UTC)

So why are you asking us, rather than your friend? What would constitute a proof? Has neither of you ever slept next to someone and noticed them dreaming? Maybe your friend is a zombie, and not having a consciousness, finds it impossible to imagine others having mental states? μηδείς (talk) 01:37, 1 September 2013 (UTC)

Because I think he is using it as a way to criticize the scientist. I'm pretty sure that he doesn't doubt that there are dreams, but he criticizes the person who said that they can't be proven (and empiricism - or Positivism). Bubba73 ^{You talkin' to me?} 02:57, 1 September 2013 (UTC)

Oh, well, thank God for that! There are all sorts of problems with naive and traditional empiricism. David Kelley's Evidence of the Senses is a good graduate/upper class-level treatment of some of the problems with and solutions to empiricist problems--although he deals with perception, rather than dreams. μηδείς (talk) 03:18, 1 September 2013 (UTC)

Take two witnesses and you have proof81.218.91.170 (talk) 03:27, 1 September 2013 (UTC)

Naturally we have an article, Dream. There's a lot of content there on neurological aspects of dreams that must go pretty close to proof. HiLo48 (talk) 01:23, 1 September 2013 (UTC)

The OP's friend may very well be thinking of Freud's distinction between the manifest and latent content of dreams - it's not actually mentioned in our article on The Interpretation of Dreams, but see Dream#Dynamic psychiatry. Tevildo (talk) 01:49, 1 September 2013 (UTC)

I should think sleep-walking, talking in one's sleep, etc., show that some type of dreaming occurs, unless you think that's all faked, too. Then there's brain scans which show activity in the part of the brain we associate with dreaming. StuRat (talk) 10:15, 1 September 2013 (UTC)

And the visual part of the brain starts working, even though there is no input from the eyes. Bubba73 ^{You talkin' to me?} 15:51, 1 September 2013 (UTC)

Exercise and blood sugar control in diabetes

I just finished reading the novel One Second After. One of the characters has (type 1) diabetes, and eventually dies from hyperglycemia. I am curious why a lack of insulin would necessarily prove fatal if she were fasting (it's a disaster novel) and exercised. Do diabetics reach some sort of wall that prevents their lowering their blood sugar below a certain point, even with fasting and exercise. I always though exercise necessarily lowered one's blood sugar. (Searches on google lead to a bunch of quackery, and if we have a relevant article, I haven't found it.) Thanks. μηδείς (talk) 04:57, 1 September 2013 (UTC)

Yes, exercise should lower blood sugar. Are you sure the character didn't die from low blood sugar ? That tends to cause immediate death, whereas high blood sugar causes organ damage that leads to eventual death. StuRat (talk) 10:12, 1 September 2013 (UTC)

I don't see how exercise would lower blood sugar unless you were to use more insulin. People with diabetes who do exercise use more insulin to be able to exercise at a high intensity. Count Iblis (talk) 14:27, 1 September 2013 (UTC)

Orchids

There are orchids in all climate zones. But the orchids on sale in western Europe are a smaller choice. Some orchids don't give flowers anymore after one year at home. Are they any tricks? Thx --Chris.urs-o (talk) 08:36, 1 September 2013 (UTC)

This site is probably the best you can get, and here is what they recommend. --TammyMoet (talk) 11:14, 1 September 2013 (UTC)

Thank you --Chris.urs-o (talk) 11:52, 1 September 2013 (UTC)

Coupled atoms

Consider a chain of identical atoms (with mass M) that are connected by springs with alternating spring constants K1 and K2 and nearest neighbour separations of a/2.

Write down an expression for the force experienced the atoms, considering longitudinal motion only and construct a pair of differential equations describing the system.

I find this question puzzling. Is it even solvable, given that there are infinitely many atoms? In the finite case, you have a differential equation for each mass. Why do you only get two differential equations, rather than an infinite number?

150.203.188.147 (talk) 14:11, 1 September 2013 (UTC)

You need to number your atoms (atom 1, atom 2, atom 3... along the chain), then you can write an equation for the force on (and hence the acceleration of) atom n in terms of the positions of atom n - 1, atom n itself and atom n + 1 (you could the positions x_n-1, x_n, and x_n+1). This looks like one equation, but it can be regarded as an infinite number of equations, one for each integer value of n. Actually, since the spring properties alternate, there will be two such equations, one for odd n and one for even n. --catslash (talk) 15:21, 1 September 2013 (UTC)

Wikipedia does not seem to have an article on waves in periodic structures (which is an unfortunate omission). However Léon Brillouin wrote a famous book on the subject, which covers exactly the problem you describe. --catslash (talk) 15:45, 1 September 2013 (UTC)

It's easier to solve when you impose periodic boundary conditions, because then the system is invariant under translations. It is helpful to denote position of the atoms by x_1, y_1, x_2, y_2 etc. so that all the atoms at the positions x_j interact in the same way with their nearest neighbors and also the atoms at the positions y_j interact in the same way with their nearest neighbors. If there are 2N atoms, then the periodic boundary conditions imply that x_{j+N} = x_j and y_{j+N} = y_j. The two sets of differential equations that Catslash mentions can then be solved by performing a Fourier transform, you put:

$x_{j}=\sum _{q=1}^{N}v_{q}\exp \left({\frac {2\pi iqj}{N}}\right)$

$y_{j}=\sum _{q=1}^{N}w_{q}\exp \left({\frac {2\pi iqj}{N}}\right)$

If you substitute this in the differential equations you obtain a decoupled set of differential equations for the v_q and w_q. Count Iblis (talk) 16:29, 1 September 2013 (UTC)

Gravitational time dilation in black holes

If around a black hole the time stops to us external viewers, a black hole to us would never collapse into a singularity but the matter would stop around event horizon and (to us) would never form a singularity! So the idea of a nude singularity would be wrong and a a blck hole would never evaporate (the famous stephen hawking radiation) to us (and to all external universe) because the negative energy's particle would never enter (to us) the black hole! Can someone explain to me this paradox? 80.117.238.25 (talk) 16:48, 1 September 2013 (UTC)