Wikipedia:Reference desk/Archives/Science/2017 January 29

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January 29

Strange sticky brown condensation on bathroom wall

Runners of brown condensation on bathroom wall

I understand why one would have rivulets of water on a bathroom wall after a shower on an otherwise cold morning. I'm curious where the sticky brown nature of them is coming from. I've seen it before in a previous residence in another state, too. Some facts:

• This is our master bathroom, connected to our bedroom, which has a HEPA air filter running in it 24 hours/day, so the air should be pretty clean.
• Nobody in the house smokes. This is California (southern part of SF Bay), almost nobody smokes in the area.
• The walls are recently (within the last year) painted with a high quality latex enamel. I recall this was happening on the previous paint though.
• The shower water is clean, but does seem to have some iron content, although I wouldn't expect iron particulates to be part of water vapor.
• Even if the brown color were due to iron, it wouldn't account for the fact that the "head" of each runner remains sticky to the touch even after drying out for a couple of days.

Any thoughts? When I put tap water in a glass and let it evaporate, there is no sticky brown residue left behind. ~Anachronist (talk) 01:55, 29 January 2017 (UTC)

Anyone in your home smoke? Someguy1221 (talk) 01:57, 29 January 2017 (UTC)

No smokers. Forgot to add that. Done. ~Anachronist (talk) 01:59, 29 January 2017 (UTC)

Q. What's brown and sticky? A. A stick. Aye thang yew! DuncanHill (talk) 02:01, 29 January 2017 (UTC)

Hah. I wouldn't have been able to resist that joke either if someone else had started this section! ~Anachronist (talk) 02:07, 29 January 2017 (UTC)

The OP may be using a propriety bathroom cleaner that contains glycerin to impart that shiny look. Try a doing a control trial. Cleaning two or three areas with just good old fashioned distilled vinegar. They may mist during a shower but not run so much. That is the purpose of adding glycerine. It is hygroscopic and a wetting agent. It prevents the surface tension forming little globules of water fogging up mirrors, chrome taps, etc. – thus maintain that shiny look. But when the surface becomes too wet, the rivulets form and run down under gravity taking the sticky glycerine with them. Also, take a clean tissue soaked in vinegar and wipe down a few clean looking surfaces. The invisible fine coating of dust which was upon them should be apparent on the tissue. COI: I stopped using these products a long time ago. Not because vinegar was far cheaper but that in the long run it performed better. --Aspro (talk) 13:50, 29 January 2017 (UTC)

@Aspro:. Well, the only thing I've ever cleaned the walls with, since repainting them, is a clean damp towel. The problem doesn't appear on the shower walls (which is a manufactured stone material), it's the walls all around the bathroom (painted sheetrock). The paint is new too.

I gotta try vinegar though. Thanks for the suggestion. Just straight vinegar or do you dilute it? ~Anachronist (talk) 07:42, 30 January 2017 (UTC)

@Anachronist: For dilution, this (I think) is a good enough guide as any. [1]. Although it mentions its good for drains too, if your drains smell in hot weather, its because of thermopilic bacteria. Find it better after draining a hot bath to run some cold water down the drain after (to cool it down) and then add a little ordinary cheap household ammonia (buy it by the gallon as it less expensive). Do please however read this as well, as vinegar is not a panacea for all cases: Alternative Hard Surface Cleaners. As a rough guide: If you can still smell vinegar (or ammonia) after a few hours, it has been soaked up by something that need a better dirt remover. It is these little details that cause most people to ignore alternatives that work very well and spend more time using the more expensive multi-purpose propriety products which produce mediocre results. Also, a lot of interior paint interoperates glycerine and some bacteria can metabolise it. So vinegar on those surfaces are probably the best bet. Hope this helps.--Aspro (talk) 22:49, 30 January 2017 (UTC)

Oh. One last thought. If your reconstituted stone is granitic in nature, vinegar will be OK on that too but is if it is some sort of calcareous reconstituted marble, the acid will degrade it, as will some proprietary products.--Aspro (talk) 23:01, 30 January 2017 (UTC)

This looks exactly like what happened in my parent's guest bathroom when mold grew on the wall due to condensation above the point where the tiling ended. The mold was not obvious except when you looked for it, but any humidity in the air would condense, and an hour after you showered there would be brown rivulets. My dad installed a vent fan, and when I visit I make a point of washing the shower walls from the ceiling to the top of the tiled area, and the problem has ceased. μηδείς (talk) 17:41, 29 January 2017 (UTC)

@Medeis:. Hmm. Mold? Last year I would have agreed, but now...

You see, just last year we tore out the entire wet area (bathtub+shower including the surround), from floor to ceiling, and replaced it with a new bathtub surrounded with solid manufactured stone sheets (because I hated cleaning the grout between the old tiles, now there's no grout). Outside that wet area, the walls and ceiling were left standing, just stripped of old paint and repainted. The ceiling already has a vent fan, which is on the same circuit as the light (you can't turn it off separately). Before we replaced the wet area, there were mildew stains in the old grout in places. But we don't have a mold problem now as far as I can tell.

There are no brown rivulets in the wet area, even the back wall where the shower doesn't hit and all it gets is condensation. The rivulets occur only on the painted sheetrock walls outside the wet area.

What did you wash your walls with? I'd like to try that to see if it fixes the problem. ~Anachronist (talk) 07:42, 30 January 2017 (UTC)

I've had this happen too. It's from condensation. ([2], [3]). Color can be dirt, iron in water, mold, etc. Increased ventilation should help reduce it. Personally, I've used a light bleach solution (about 10%) to scrub it off, but I don't rinse with fresh water. I leave the bleach-water dry on the wall in inhibit further growth. EvergreenFir (talk) 23:17, 30 January 2017 (UTC)

It's not possible to diagnose at a distance, but there was no known mold in the wall problem involved in my parents' case. In any case, I use Scrubbibg Bubbles with Bleach when I can get it. The vent fan and a rub-down every three months has prevented a recurrence. μηδείς (talk) 00:07, 31 January 2017 (UTC)

Aspro, EvergreenFir and Medeis: Thank you all for your replies. I have the scrubbing bubbles stuff but never thought to use it on painted walls; I've just used it on the manufactured stone walls around the wet area. I'll try the vinegar solution on the walls too, although I suspect I shouldn't use it on the stone, which looks like it may be made from marble dust (but I have a sample I can test it on). Since these rivulets are distributed in a fairly uniform density on the walls, I could try different things in different sections too.

After reading through the links you all provided, I conclude that my problem is called surfactant leaching. Most of the paint manufacturers have some information about this appearance of these sticky weeping brown streaks, and it's apparently more prevalent with latex paints than oil-based paints. The thing is, the published advice to wipe it off a couple of times and the problem will go away isn't quite right in my case. I'm likely going to need to try something stronger than soapy water. ~Anachronist (talk) 06:54, 31 January 2017 (UTC)

...and, it looks like the Wikipedia article is exudate, which mentions latex. I'll add my picture there. ~Anachronist (talk) 07:59, 31 January 2017 (UTC)

Water gurgles and urine

It seems to notice when I urinate after hearing a lot of gurgles in the stomach caused by water I just drank, I notice that my urine I excrete afterwards tend to be more bubbly. Is it really true that more (and especially more loud) stomach gurgles from water tend to make urine more bubbly? Also it seems that a lot of times when my stomach gurgles after drinking up to two cups of water at a time, it tends to not make me much more urging nor even noticeably more urging to urinate even after several hours, while not so much gurgles tend to urge me to urinate more and sooner. Does the duration and loudness of water gurgles really influence the urging and timing to urinate? PlanetStar 03:53, 29 January 2017 (UTC)

Lots of possible causes for bubbles in urine - have a read here - http://www.md-health.com/Bubbles-In-Urine.html - and have it checked out if anything medical seems to match your case. Wymspen (talk) 11:51, 29 January 2017 (UTC)

There's no connection whatsoever between the gastrointestinal tract and the kidneys. The urine is filtered from the blood by the kidneys, not excreted by the intestines. That being said, having gas or fullness of the intestines can make you want to urinate or make urination more difficult depending on what organs are pressing on which. But bubbles in the urine (I assume you don't just mean froth in the bowl caused by an urgent micturation) would be a medical issue for which you should probably seek medical advice. There's also fistula, which is a serious medical condition--so see a doctor. μηδείς (talk) 17:37, 29 January 2017 (UTC)

Machining is so boring!

How does one level in a boring bar so that it's exactly and precisely at the center of the hole to be enlarged? I know how to level in a tool bit in a toolpost -- make one or more facing cuts and adjust the height until the cut is perfectly smooth -- but that doesn't apply to a boring bar, does it? 2601:646:8E01:7E0B:50AD:44BE:5728:6813 (talk) 07:46, 29 January 2017 (UTC)

In much the same way as for a conventional lathe tool, there is no reason to think that on-centre is the right height. I suggest that typical external diameters are turned with the tip of the tool below centre, and internal diameters are turned with the tip of the tool above centre. The reason is obvious. Greglocock (talk) 10:34, 29 January 2017 (UTC)

• What's a boring bar here? Between centres, or a cantilevered bar in the toolpost?

A between centres bar is fixed relative to the lathe bed - so you have to level and raise the workpiece, rather than the tool. For this reason boring is often done early (or used to be, in the real hand-alignment era) and the other machining is then laid out relative to the bored hole afterwards. It's often more accurate to mark off from the bored hole than to bore to the mark.

As to how it's levelled, then that depends on the work and size. You might shim it on a lathe bed or cross slide. On a mill you can probably use the bed leadscrews, and shims for levelling. A big casting (one you can walk through) might be set up on a few screw jacks.

There's absolutely no reason for a toolpost boring bar to be on centre. All that matters is the tool angle, which can be done either by moving the tool up and down (as is easiest for a typical turning tool) or by rotating the angle of the tool. For a circular boring bar though, it's often much easier to rotate the bar and tool slightly. Also these bars are often run upside down on the back of the hole, as it improves visibility and chip clearance. Andy Dingley (talk) 12:00, 29 January 2017 (UTC)

In professional production a "drill guide" is used in your part fixture construction. Sorry, im a german professional and thus im not shure i used the common terms my fellow english professionals use. The german term is "Bohrhülse". Put that into yahoo or google and check what images are offered. If you need more precission you have to switch from using drills to using a "wolhaupter" tool. --Kharon (talk) 20:48, 29 January 2017 (UTC)

[un-indent] Maybe I misspoke in the original question -- what I meant is that I need to level in the boring bar such that the cutting point is EXACTLY AND PRECISELY on the diameter of the workpiece (within 1/32 of an inch or less), NOT on a chord of it. And yes, in my case it IS important (in fact, to call it "important" is an understatement, because the right word is IMPERATIVE) -- if the cutting point is even slightly above or below the diameter of the workpiece, this will lead to false readings on the cross-slide, which in turn can mess up the final diameter of the bored hole -- and in my case, the diameter, runout and cylindricity of the hole MUST be held to within 1/200 of an inch! (And yes, for the record, I'll be using a toolpost boring bar -- for one thing, I don't have any other sort, and even if I did, adjusting the chuck after each pass would simply be too time-consuming, not to mention imprecise.) Also, laying out the other machining relative to the hole is NOT an option -- I'll be starting out with a hex bar (due to the need to create a flange for the wrench), so I will have to turn the piece BEFORE any drilling or boring, in order to make it fit into a 4-jaw chuck. 2601:646:8E01:7E0B:904E:8E2E:48D1:CC6E (talk) 01:14, 30 January 2017 (UTC)

You can not drill with a position precission of 1/200 inch with drills on a boring bar. I will simply cite myself: "If you need more precission you have to switch from using drills to using a "wolhaupter" tool". You probably even have to switch to a Milling machine for such precission. --Kharon (talk) 17:20, 30 January 2017 (UTC)

• Bang the boring bar roughly in the toolpost, adjust it somehow so that it cuts OK, then get boring. Don't believe a word the cross slide tells you, gauge it as you go. It can be worth making plug Go/No Go gauges beforehand - especially as it's much easier to achieve accuracy on an external diameter than an internal.

You can't bore to 5 thou surface finish with the level of tooling that you seem to have, you'd have to ream it to the final diameter anyway. You also need to start distinguishing between surface finish, diameter, position, angular alignment and bellmouthing. You might well bore it to be accurately placed, then let a reamer handle the diameter and surface. You can buy reamers in most sizes, you can get adjustable reamers (tricky to set them to be parallel cylinders to this level), or it's not even that hard to make a reamer, if you only need to use it a few times. It's even possible (not too hard or expensive) to have a reamer made - have one ground accurately to size by a toolroom with an accurate centreless grinder, then fluted and hardened. Andy Dingley (talk) 23:10, 30 January 2017 (UTC)

(sigh) All right then, it looks like it's micrometer time (I don't like it because it will take so much longer, but quality is more important). BTW, I'll take your advice and use a reamer -- if they have one in 1 3/8 inch diameter (do they?) 2601:646:8E01:7E0B:F88D:DE34:7772:8E5B (talk) 02:53, 31 January 2017 (UTC)

Tools are available for all common Machine taper. Sounds like yours is a standard "Morse", which is the most common. A reamer will just follow the existing hole tho. It wont correct if your drill moves out of its starting center, which drills always do to some extend. A "wolhaupter" tool will correct that perfectly instead, with much higher precission. They where not invented and they are not widely used whereever needed just bcause they look so much cooler that a drill or reamer you know?! Anyway go buy a reamer and try. Not that big investment and seemingly the only way you are willing to learn. --Kharon (talk) 22:31, 31 January 2017 (UTC)

Except that for this part of the hole, I'll be using a boring bar rather than a drill. 2601:646:8E01:7E0B:1C2B:1B0E:6B82:7D00 (talk) 00:18, 1 February 2017 (UTC)

Feynman Lectures. Lecture 46. Ch.46-3 [4]

...

If we solve the equations of motion, we may get certain functions such as t+t²+t³. We claim that another solution would be −t+t²−t³. In other words, if we substitute −t everywhere for t throughout the entire solution, we will once again get a solution of the same equation. This follows from the fact that if we substitute −t for t in the original differential equation, nothing is changed, since only second derivatives with respect to t appear.

— Feynman • Leighton • Sands, The Feynman Lectures on Physics, Volume I

For equation $x(t)=t+t^{2}+t^{3}$ we have:

$v(t)={\tfrac {d}{dt}}x(t)=1+2t+3t^{2}\implies v_{0}=1$

$a(t)={\tfrac {d^{2}}{dt^{2}}}x(t)=2+6t$

Original differential equation is therefore ${\tfrac {d^{2}}{dt^{2}}}x(t)=2+6t$.
If we substitute $-t$ for $t$ , we get ${\tfrac {d^{2}}{dt^{2}}}x(t)=2-6t$
— absolutely different equation with solution $x(t)=t+t^{2}-t^{3}$, since $v_{0}=1$. And equation $x(t)=-t+t^{2}-t^{3}$ is a solution neither for ${\tfrac {d^{2}}{dt^{2}}}x(t)=2+6t$ nor for ${\tfrac {d^{2}}{dt^{2}}}x(t)=2-6t$.
Suggest please, how can be proved Feynman's hypothesis.
Username160611000000 (talk) 09:40, 29 January 2017 (UTC)

From the wording of that piece (I have not read through for the full context), I expect Feynman is assuming that the equation being solved is time-independent (which is one of the features of physical laws) other than through the second time derivative, but may depend on the variable(s) (including derivatives of any order with respect to space). Thus, your derivation of the original differential equation is not valid in this context; it is not the only differential equation with this solution. Remember that the equation need not be linear. —Quondum 13:35, 29 January 2017 (UTC)

I think the point is that if you take

$x(t)=-t+t^{2}-t^{3}$

$v(t)={\tfrac {d}{dt}}x(t)=-1+2t-3t^{2}\implies v_{0}=-1$

$a(t)={\tfrac {d^{2}}{dt^{2}}}x(t)=2-6t$

That's all the same, except t has the opposite sign, and its velocity has the opposite sign for any t, compared to -t in the original equation. Wnt (talk) 13:39, 29 January 2017 (UTC)

That's all the same - The derivation is same. But the equation is not the same. Feynman says: In other words, if we substitute −t everywhere for t throughout the entire solution, we will once again get a solution of the same equation.Username160611000000 (talk) 14:46, 29 January 2017 (UTC)

As far as understanding what Feynman meant, this might be side-tracking. It is trivially true that if one substitutes $t\mapsto -t$ throughout, including $\partial /\partial t\mapsto \partial /\partial (-t)$, that every time-reverse solution will be a solution of the time-reversed equations in any system whatsoever. This brings no understanding to physics. What Feynman was saying is that we cannot distinguish the forward time direction from the backward time direction given only the equations governing motion of a system when the only time-dependence is the second derivative (very easy to prove that this is so). That is to say, a time-reversal of a solution is also a solution to the same equation (without the substitution $t\mapsto -t$ in the equation). —Quondum 14:40, 29 January 2017 (UTC)

If sign of dt-s changes then ${\tfrac {d}{-dt}}{\tfrac {dx}{-dt}}=+{\tfrac {d}{dt}}{\tfrac {dx}{dt}}$. So the equation ${\tfrac {d^{2}x}{dt^{2}}}=2+6t$ transforms to $+{\tfrac {d^{2}x}{dt^{2}}}=2-6t$. Again whatever you do , you get different equation. Such manipulations with signs, that Feynman would wish, are possible only when second derivative is constant. Username160611000000 (talk) 15:52, 29 January 2017 (UTC)

"... are possible only when second derivative is constant" – not true; it is always possible without constraints on the derivatives such as this. Consider the equation ${\tfrac {d^{3}}{dt^{3}}}x=6$, with a solution $x=t^{3}+2t^{2}+3t+4$. If we substitute $t\mapsto -t$ everywhere as you say, we get a solution $x=(-t)^{3}+2(-t)^{2}+3(-t)+4=-t^{3}+2t^{2}-3t+4$ to ${\tfrac {d^{3}}{d(-t)^{3}}}x=6$, i.e. ${\tfrac {d^{3}}{dt^{3}}}x=-6$.

"... whatever you do, you get different equation" – not true; consider the equation ${\tfrac {d^{2}}{dt^{2}}}x=-x$, with a solution $x=\cos t+2\sin t$. If we time-reverse the solution as $x=\cos(-t)+2\sin(-t)=\cos t-2\sin t$, this is also a solution to the original unmodified equation ${\tfrac {d^{2}}{dt^{2}}}x=-x$. —Quondum 16:39, 29 January 2017 (UTC)

I think we should not digress from the solution $t+t^{2}+t^{3}$ and related differential equation. Username160611000000 (talk) 07:19, 30 January 2017 (UTC)

we get a solution $x=(-t)^{3}+2(-t)^{2}+3(-t)+4=-t^{3}+2t^{2}-3t+4$ to ${\tfrac {d^{3}}{d(-t)^{3}}}x=6$, i.e. ${\tfrac {d^{3}}{dt^{3}}}x=-6$ - So you get the solution of the different differential equation. But Feynman states that the solution with substitution (-t for t) is the solution of the original differential equation. Username160611000000 (talk) 07:26, 30 January 2017 (UTC)

You have chosen a differential equation that not satisfy Feynman's description. —Quondum 12:07, 30 January 2017 (UTC)

• The argument in the quote is probably "if function t→f(t) satisfies the differential equation, then function t→f(-t) satisfies it as well". "The same equation" refers to the differential equation. It does not follow that f(t)=f(-t) for all t.

You need to assimilate an assertion's logic before diving into calculations. You have already been told Feynmann's courses are not great as introductory courses, precisely because he is extremely sloppy in the language (is that sentence a restatement of the previous equation? a new hypothesis? the result of the combination of previous calculations?). This is a prime example of it. Tigraan^{Click here to contact me} 17:40, 30 January 2017 (UTC)

Medical terminology may please be explained in simple English

Homogeneously enhancing mass lesion of 30 x 28 x 25 mm in the right cavernous sinus. Anteriorly, the mass is reaching upto the orbital apex, encasing the right ICA and causing indentation upon the right temporal lobe. Differential diagnosis includes schwannoma and meningioma.

Can this medical report/terminology please be explained in a simple English for a common man to understand!Kvees (talk) 14:34, 29 January 2017 (UTC)

This answer is not to be construed as medical advice. Basically it means that there is a roughly spherical tumor an inch or so in diameter directly under the brain, behind the eyes, and impinging on the brain -- the tumor probably results from cancer of the membranes that surround the brain. Looie496 (talk) 15:34, 29 January 2017 (UTC)

If you're going to use the word 'cancer' you need also to point out that many schwannomas and meningiomas are benign. - Nunh-huh 15:57, 29 January 2017 (UTC)

What does "homogeneously enhancing" mean in the context? I suppose the phrase contrasts with "heterogeneously enhancing", but what would heterogeneous enhancement be like? --100.34.204.4 (talk) 21:08, 29 January 2017 (UTC)

"Homogenously enhancing" means that the radiocontrast (dye) is taken up uniformly by the mass, not by some parts more than others. Non-homogenous enhancement might show focal areas where the dye isn't taken up. "Ring enhancement" would be used if the dye were taken up by the outside of the mass but didn't spread to the inside, so it would show up as a ring in the x-ray. Radiologists expect to see different kinds of enhancement based on what is causing the lesion. -Nunh-huh 01:17, 30 January 2017 (UTC)

• We have articles on both schwannoma and meningioma. According to our articles, all schwannomas and most meningiomas are benign (i.e., non-cancerous). However, note the phrase "differential diagnosis includes..." This means that the radiologist can't say for sure that the mass is not something else. Now that you have researched this a little, Talk to the radiologist. We can help you understand the words, but we cannot help you understand the underlying imaging, much less what is actually going on. (And I hope things work out OK for the patient and everyone concerned) -Arch dude (talk) 02:40, 30 January 2017 (UTC)

Bear in mind that "benign" has a different meaning here than in normal English: it means "non-cancerous", not "non-harmful". A benign brain tumor that grows in the wrong place can be fatal; it will definitely not be benign in the normal sense of the word. Nyttend (talk) 01:20, 31 January 2017 (UTC)

Drug addiction when you don't enjoy the drug

I'm not sure I fully understand the concept of addiction, but in as much as I do, it revolves around a rewarding stimulus. However, it is not clear if the so-called "reward system" has to entail pleasure. Further, it seems possible to feel pleasure and displeasure at the same time, caused by the same collection of stimuli e.g. smoking contains nicotine, but someone may not like the action of smoking itself. So, is it possible to be addicted to a drug when you don't enjoy it at any stage? What about other sorts of addiction?--Leon (talk) 15:22, 29 January 2017 (UTC)

A large body of research has led drug investigators to make a distinction between "pleasure" and "reward". This has been framed in various ways -- Kent Berridge, for example, calls the two constructs "seeking" and "liking". Some drugs, such as cocaine, have their most direct effects on the "reward" system; others, such has heroin, more directly affect the "pleasure" system. Thus it is theoretically possible to have a drug that is rewarding without causing pleasure; however at a practical level I am not aware of any such drug. Our article on pleasure and the reward system discuss these concepts in greater depth, with pointers to the relevant literature. Looie496 (talk) 15:42, 29 January 2017 (UTC)

• There is a definite distinction between physical dependence and psychological addiction. The two phenomena may and often overlap, but they are different things. People can be dependent on drugs from which they gain no pleasure, which is one reason why many drugs come with the instruction "do not stop taking without doctor's advice". One example might be sedatives taken at bedtime or anti-convulsants that provide no psychological high when not abused. Cold turkey withdrawal from certain benzos can cause death.

I take a benzodiazepine at bedtime for a sleep disorder. I don't take it while awake, I don't get high, but the withdrawal symptoms if I miss it for 48 hours are severe high blood pressure and tremors. I would have to be weened off it, and am considering doing so, since I have found a safer alpha-blocker that seems to serve the same purpose. Conversely, I smoked weed daily for 14 years, and quit cold turkey in 2004. I missed it quite strongly for a few days and was irritable, but suffered no physical effects at all. μηδείς (talk) 17:24, 29 January 2017 (UTC)

The idea that Benzos provide "no psychological high when not abused" is questionable, as is defining "abuse". The Rolling Stones realized something was amiss with the use of these drugs way back in 1966. I don't think the medical profession had yet caught on to the problem? These housewives may have been using the drug at "normal dose ranges", but the medical and psychological issues surrounding such use are profound. Eliyohub (talk) 15:56, 30 January 2017 (UTC)

Jacqueline Susann came to similar conclusions around the same time. {The poster formerly known as 87.81.230.195} 94.12.94.189 (talk) 16:07, 30 January 2017 (UTC)

She took four more, outside the door, is different from I take two before I snooze. I have no temptation to take them otherwise, and have been on the same dose for almost two decades--not the usual course of pleasure-seeking psychological dependence. μηδείς (talk) 00:02, 31 January 2017 (UTC)

boiling water that already were boiled and cooled

Is there a scientific basis for the claim that water that already were boiled and cooled again, in the next time the boiling will be faster relative to water that not boiled before? If there is, what is the explanation for that? 93.126.88.30 (talk) 16:02, 29 January 2017 (UTC)

Where have you seen this claim? ←Baseball Bugs ^{What's up, Doc?} carrots→ 16:48, 29 January 2017 (UTC)

I have heard it. I wouldn't be surprised if it has not already been addressed in the archives (although it sounds like nonsense to me). μηδείς (talk) 17:28, 29 January 2017 (UTC)

It sounds a bit like the old wives' tale that hot water will turn to ice faster than cold water will. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:57, 29 January 2017 (UTC)

Please get you facts right before pontificating here. The Mpemba effect is hardly "an old wives tale" - would you call Aristotle, Francis Bacon or René Descartes old wives? - and it does appear to be valid under certain circumstances.[5][6] Richerman (talk) 19:19, 29 January 2017 (UTC)

Is that the same Aristotle who said that heavy objects fall faster than light objects? ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:49, 29 January 2017 (UTC)

I assume that you are aware of the fact that this is generally true, right? Try a hammer and a feather. --Stephan Schulz (talk) 16:39, 30 January 2017 (UTC)

Aristotle would have said that two hammers of different weights would fall at speeds proportional to their weights. ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:12, 30 January 2017 (UTC)

And your own links confirm that this notion is generally false. ←Baseball Bugs ^{What's up, Doc?} carrots→ 19:52, 29 January 2017 (UTC)

I think you need to look up the definition of an old wives' tale. Richerman (talk) 23:08, 29 January 2017 (UTC)

A folk tale that's generally false. ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:28, 29 January 2017 (UTC)

The short answer is "no." Shock Brigade Harvester Boris (talk) 18:05, 29 January 2017 (UTC)

It will be slower the next time. If you heat water until you reach boiling point then this will remove the dissolved air in the water. The boiling process involves the formation of water vapor bubbles in the water that rise to the surface. This means that the gas pressure inside the bubbles must be equal to the atmospheric pressure. Now, when you boil water the first time, there will be some air inside these bubbles, this means that the vapor pressure inside the bubble can be a bit less than 1 atmosphere, what matters is that the partial pressure of the vapor plus the partial pressure of the air equals (or exceeds) 1 atmosphere. This means that the temperature at the boiling point will be a bit less.

You can clearly observe this effect by boiling a large amount of water, say, 4 liters of water or more. When the water starts to boil. you'll see many small bubbles. If you keep on letting the water boil, you'll see after about 5 minutes that a few large bubbles have appeared, you don't see many small bubbles anymore. If you keep on boiling for a few more minutes and the cool down the water and then reheat it, you'll see that the water will start to boil with only a few large bubbles. You can then demonstrate that this boiling is happening at a higher temperature where the vapor pressure in the bubbles is larger than the first time, by introducing a large number of air bubbles into the water. You can do that by throwing rice in the water. You can actually turn off the fire and wait for a few seconds until the water looks calm. So, the boiling has stopped, and there is no energy source to keep the water heated. Nevertheless, the water is still at a higher temperature than the first time it boiled. If you now throw some rice in the water, you'll see that the water will boil explosively for a few seconds. What happens is that the air bubbles will fill with water vapor, the total pressure will exceed 1 atmosphere causing the bubbles to grow which leads to faster evaporation of water into the bubbles. Count Iblis (talk) 20:21, 29 January 2017 (UTC)

@Count Iblis: The way I think of it, the length of time to "boil" water means to a "rolling boil", a condition under which dissolved air has been made irrelevant. I have no idea what the heat of solution of oxygen and nitrogen in water may be, and it's aggravating to search, but I at least found a statement the former is positive (which seems like what I'd expect) [7] So if it takes heat to drive these gasses out of solution, it should take technically a shorter time to boil the water the second time. Without knowing the numbers I can't really argue it's insignificant, though I suspect so. Wnt (talk) 02:16, 30 January 2017 (UTC)

• Other semi-obvious observations depending on what "boiled and and cooled again" means:

1. If it means "heated until vapor appears, then left to cool", the evaporating water will be gone, in which case there is less water to boil for the second round, so it is faster (...duh).
2. If it means "completely vaporized then condensed", i.e. distilled, then the water will be more pure which will impact its evaporation point. I am supposed to remember which way the effect goes, but I would rather let someone else answer that toss a coin.

If we are talking about the Mpemba effect then yeah, it's probably bogus. Tigraan^{Click here to contact me} 16:29, 30 January 2017 (UTC)

Solutes raise the boiling point, Tigraan. The bottom line is that boiling is path independent and so, unless there is indeed a chemical difference, pre-boiling will be irrelevant. μηδείς (talk) 23:58, 30 January 2017 (UTC)

password

-Is there a point where the length of a password starts to negatively impact on the crypographic strength? Like if you had a million character password or something? — Preceding unsigned comment added by 177.184.8.123 (talk) 16:31, 29 January 2017 (UTC)

This question might get a quicker and better response at the math desk than here. The only guess I'd have as a layman is that at some point you'd reach diminishing return as the cost of inputting the longer password would not significantly improve the security gained. But that's a guess. μηδείς (talk) 17:31, 29 January 2017 (UTC)

Guesses as laymen is not what the Ref Desk responses should be about, if you don't know, don't respond. Instead, let's use Wikipedia to help, which I believe the Ref Desk is here to do... So we have an article called password strength which may be of interest to the OP. Plenty of information in there. The Rambling Man (talk) 17:38, 29 January 2017 (UTC)

The subject is Cryptography, see the article Password strength. Increasing password length is a straightforward way to increase its resistance to a brute-force "guessing" attack; for an ideal Random password generator entropy, H, is given by the formula

$H=\log _{2}N^{L}=L\log _{2}N=L{\log N \over \log 2}$

where N is the number of possible symbols and L is the number of symbols in the password. H is measured in bits. However people are poor random generators, cryptographic systems are subject to other lines of attack than guessing, and systems that accept arbitrary size passwords generally do so by converting them by a Cryptographic hash function. A secure hash of a million-character password is neither harder nor easier to guess than the hash of a two-character password. There is therefore little point in constructing a very long password to achieve an entropy much higher than is required for the situation (256-bits or 64 hexadecimal digits or 32 character bytes is regarded as secure against casual attacks), the system will never have greater security than is given by the length of its hash function, and use of very long passwords may introduce other weaknesses such as difficulties and delays in remembering, storing, updating and legitimately conveying the password, and will bloat of the message bandwidth. Blooteuth (talk) 17:42, 29 January 2017 (UTC)

I remember a funny conversation at [8] where I noticed that Kaspersky's password checker could tell me that a password was super secure, then change its mind as I typed more characters. A reason was that a longer password might be one of the 10,000 most common passwords while a truncated one didn't come up on that list. In any case, password strength is sort of a black art, not really a science, since it's predicting behavior. I bet the NSA really does check to see if you used the entire preamble to the Declaration of Independence as your passphrase... Wnt (talk) 02:22, 30 January 2017 (UTC)

Just out of curiousity, did the less-secure-but-longer password form an English word? Simple English words are generally held to be less secure (or perhaps more guessable), so it could be that a nonsense part word 'likin' might be more secure than an English word 'liking', despite being shorter. Matt Deres (talk) 12:10, 30 January 2017 (UTC)

@Matt Deres: I copied the file to Wikipedia:Most common passwords/10000. It contains some real headscratchers: 123qweasdzxc and 8J4yE3Uz for example. More common are entries like PUSSY and knockers ... anything remotely related to sex is one of the most common passwords. Wnt (talk) 23:19, 30 January 2017 (UTC)

@Wnt: Interesting. I'm not surprised 123qweasdzxc is on there; I've used a shorter version of that before on some low-priority passwords, but I'm lost on 8J4yE3Uz. Maybe it's an easy-type password on some other keyboard type I'm not thinking of. Matt Deres (talk) 02:58, 31 January 2017 (UTC)

This 4-year old file suggests that 8J4yE3Uz may be, or have been, used to access pornography sites, which could explain frequent usage of such an unintuitive sequence. Blooteuth (talk) 16:28, 1 February 2017 (UTC)

For a farcical example of the most lax of all password security, see the bizarre success of Gary McKinnon's most primitive of tactics. To quote from our article: In an interview televised on the BBC's Click programme, McKinnon stated that he was able to get into the military's networks simply by using a Perl script that searched for blank passwords; in other words his report suggests that there were computers on these networks with the default passwords active. The MILITARY doesn't think of this problem??? Can anyone explain how this is possible?. Any half-smart system would never allow the use of a "default password". What exactly went wrong here? Has anyone provided any half-credible explanation?

Whatever the explanation, the phenomenon has been widespread and persistent. As described in his autobiographical Surely You're Joking, Mr. Feynman!, Richard Feynman repeatedly demonstrated that he could access military computers (as well as open safes and other combination-protected devices), and was able to do so because he had learned the factory default settings and knew that the majority of military users didn't understand the need to change them.

Historically, miltary handling of computer systems often fell foul of the mismatch between military mindset and civilian nerdthink – my father was involved in the introduction of computers to the then Royal Army Pay Corps, and at one point, after a mixed-rank group had completed a training course provided by the suppliers, the other ranks were all assigned to be programmers and the officers as systems analysts, regardless of their demonstrated suitabilities. {The poster formerly known as 87.81.230.195} 94.12.94.189 (talk) 16:27, 30 January 2017 (UTC)

The obvious problem is that "civilian nerdthink" is generally where the real expertise is. Rare is the soldier who can thwart a FBI Ten Most Wanted Fugitives former member Kevin Mitnick. NASA, from I've heard, has an army of "civilian nerds", who, I would presume, are perfectly capable of going toe-to-toe with a Gary McKinnon. Mckinnon's tricks working against a pentagon computer, your explanation fits. But he claims he got into NASA, which would be far harder, ironically, given the nature of their techie staff. Has the American government ever detailed their allegations against him, and whether NASA was in fact hit? Eliyohub (talk) 17:31, 30 January 2017 (UTC)

A bit like not encypting military drone video feeds, allowing anyone with a radio antenna and some downladable shareware software to view the feed in real time Eliyohub (talk) 12:21, 30 January 2017 (UTC)

A lot of internet's first protocols date back from a golden age where a few bearded researchers shared data files across a network and none really thought about security. Fast forward today, high towers have been built on shaky foundations and none really wants to evacuate the tower for renovations.

Take for instance BGP hijacking. The way routing works is that everyone in the network knows in how much time they can pass a message to their neighbours, and announce it loudly. From the annoucements of your neighbours you can guess how much time you would need to reach your neighbour's neighbour, etc. If A tries to send B a message over the network, A will look among her neighbours which one advertises the shortest time to B, and each successive handler of the packet should do the same until the packet reaches its destination. The problem is that M could falsely claim that he is very very close to B, in order to force the packet go through him (either to eavesdrop the connection, or to censor it).

If a routing protocol was built from scratch this attack would be trivial to eliminate. For instance, everyone signs who is their neighbour and how much time they need to reach any destination, the whole thing is published, and unless there are too many liars it is pretty obvious to spot who tried to hijack traffic (the "second solution" of Byzantine_fault_tolerance#Early_solutions even claims there is no such thing as "too many" if crypto is available). I just made that strategy up, so there probably are easier/faster/better ways to do it. The point is that from basic cryptography your can eliminate the attack, but none thought it would even be necessary when the protocols were designed. Tigraan^{Click here to contact me} 13:20, 30 January 2017 (UTC)

Is there a term for the continents excluding Antarctica?

Is there a word to describe the continents with the exclusion of Antarctica? I came across the phrase "every inhabitable continent" but Antarctica has 135 permanent residents. "Every non-polar continent" sounds better, though Antarctica is only partially within the Antarctic Circle. Any ideas? - Reidgreg (talk) 17:28, 29 January 2017 (UTC)

What's wrong with "the continents excluding Antarctica"? ←Baseball Bugs ^{What's up, Doc?} carrots→ 17:55, 29 January 2017 (UTC)

Antarctica does not have any permanent residents, all research station personnel are seasonal, nobody stays for more than a year. Roger (Dodger67) (talk) 18:00, 29 January 2017 (UTC)

Our Antarctica article does claim 135 permanent residents, but provides no source, and the Population section and separate Demographics article provide no support for the claim. The figure is found on various other websites, but from a cursory look, none that might not have copied it from here.

As for the actual question, I'd go with habitable continents. Antarctica is only habitable in the same sense that space is. Henry^Flower 20:41, 29 January 2017 (UTC)

p.s.: looking at the talk page for the article, it seems that the claim was added last year, by an editor with an idiosyncratic interpretation of "permanent resident". Henry^Flower 20:47, 29 January 2017 (UTC)

Disagree. Antarctica is habitable in the same sense as, say, New York City is--you've got to wear warm clothes and have heating. Loraof (talk) 20:45, 29 January 2017 (UTC)

Only in winter. Henry has it right. Antarctica is no more habitable than the Moon. ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:03, 29 January 2017 (UTC)

If New York is inhabitable all year round, then so is Antarctica. And you can breathe the air in Antarctica but not on the Moon. Loraof (talk) 21:21, 29 January 2017 (UTC)

The area we now call New York was inhabited by aboriginal peoples for thousands of years prior to the development of modern conveniences. How many aboriginals inhabited Antarctica? ←Baseball Bugs ^{What's up, Doc?} carrots→ 21:30, 29 January 2017 (UTC)

That's a red herring. As far as we know, the place was only first visited by humans in the 19th century. But had Inuits somehow found their way there, they probably wouldn't have had too many problems. -- Jack of Oz ^{[pleasantries]} 21:42, 29 January 2017 (UTC)

Then what is the basis of the OP's question? ←Baseball Bugs ^{What's up, Doc?} carrots→ 23:27, 29 January 2017 (UTC)

People can stay more than a year. In US-based stations, employee contract are seasonal (usually divided into winter and summer blocks), but there is no prohibition on stringing together longer stays. Of course, most people choose not to do that, and the winter work force is much smaller than the summer, but there are a few people that have strung together multiple years on the ice. Dragons flight (talk) 21:17, 29 January 2017 (UTC)

Can they bring their family? Personal ad: Likes long walks on the ice cap, snowboarding, snowshoeing, snowmobiling, being able to do it almost anywhere.. Sagittarian Milky Way (talk) 00:05, 30 January 2017 (UTC)

Demographics of Antarctica lists the names of those actually born in Antarctica (as part of Argentine and Chilean attempts to strengthen claims), and indicates a winter population of about 200. Wymspen (talk) 10:51, 30 January 2017 (UTC)

If I had a wife I certainly wouldn't volunteer to spend multiple years there without her. Sagittarian Milky Way (talk) 11:22, 31 January 2017 (UTC)

Nothing to see here. Collapsed by --Aspro (talk) 23:54, 1 February 2017 (UTC)

A lot of things that we can conceptualize, like "bleached-blond gay campus lecturers" could have a single word, but you have to consider epistemological economy. Having a word for everything is simply too much of a cognitive burden when phrases will do. If you were writing a book comparing Antarctica to the rest of the world you might coin an acronym, like EAC's for extra-Antarctic continents for convenience's sake. Ayn Rand's Introduction to Objectivist Epistemology has a chapter addressing this issue. μηδείς (talk) 21:06, 29 January 2017 (UTC) Nothing to see here. Collapsed by TigraanClick here to contact me 10:24, 31 January 2017 (UTC) I think you had everyone until the last sentence. --Jayron32 11:53, 30 January 2017 (UTC) You need to grow up, Jayron; develop a thick skin and the ability to separate your emotions from your critical thought processes. Criticizing a valid answer that sites a perfectly relevant source because you don't like the politics of the source (who's making an entirely non-political argument) is something out of Cultural Marxism or the Middle Ages. Read the book, and then get back to us. My undergrad philosophy major advisor told me it was the best philosophy book he had read in 10 years, and he had no idea who Rand was. μηδείς (talk) 17:04, 30 January 2017 (UTC) Oh, Lord, I tried to read Ayn Rand once, back when I was far more sympathetic to her politics. OMFG I could have emptied a revolver into her book and no bullet would have made it even a third of the way through! Wnt (talk) 23:36, 30 January 2017 (UTC) Neither of you has read the book I have referenced, it is well under two hundred pages (the second edition has large appendices). This really should be hatted as off-topic ad hominem totally irrelevant to the question at hand. μηδείς (talk) 23:54, 30 January 2017 (UTC) As it was you than brought up A R why don't you hat it all?--Aspro (talk) 00:19, 31 January 2017 (UTC)

Q: Is there a term for the continents excluding Antarctica?

A: Anti-antarcticism. All of the other continents, used to laugh and call it names...

(I'm very sorry.) TenOfAllTrades(talk) 00:05, 2 February 2017 (UTC)