Wikipedia:Reference desk/Archives/Science/2013 October 24

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October 24

Why does the green of afterimages look so weird?

I don't have colorblindness. Sagittarian Milky Way (talk) 00:25, 24 October 2013 (UTC)

Define "weird". And what "afterimages" are you talking about specifically? ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:35, 24 October 2013 (UTC)

Staring at a compact fluorescent lightbulb for a minute or two, then closing eyes and watching it go greenish teal. It seems too close to ultragreen, which is what green would look like if your red and blue cones didn't work. My monitor's green-blues seem unvivid to me. Which is not unexpected, see the Gamut article. Do I just not look at poisonous tropical frogs and green-blue lasers enough? Sagittarian Milky Way (talk) 05:39, 24 October 2013 (UTC)

Take a break from the serotonergics, and let us know if it changes :-) --Trovatore (talk) 07:44, 24 October 2013 (UTC)

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The following discussion has been closed. Please do not modify it.
Typically you should see complementary colors to whatever you were looking it. It could be that CFC bulbs are not pure white. Take the various tests in Afterimage, and if they don't work out the way they're supposed to, you should consider going to an eye doctor for further testing. ←Baseball Bugs What's up, Doc? carrots→ 06:53, 24 October 2013 (UTC)

Note that our Afterimage article is not usable as a medical test, and we're in no position to advise you that there's something wrong with you if your experience of afterimages is different than it says in our sometimes incomplete text. In any case, it doesn't sound like a huge problem :) And yes, I think there is something weird about green afterimages, especially from the Sun, which I'd guess has to do with receptor photobleaching. (The ability of the eye to see light really does get "used up" to some degree in a very short term - it's mentioned in cone cell, vitamin A Wnt (talk) 18:27, 24 October 2013 (UTC)

I also see a turqoise afterimage when I stared at a filament bulb. Plasmic Physics (talk) 12:35, 24 October 2013 (UTC)

I theorize that this is because the different types of cone cells recover from neural adaptation at different rates - so the afterimage should in fact go through a series of colors. We're not supposed to theorize here, so I looked for a reference: [1] - this page (seems to be from Dresden Tech psych department) says "As you continue to observe the afterimage carefully, it fades and its color changes slightly. This is because your different cones (and chromatic mechanisms) recover from adaptation at different rates." That could be how you get a color afterimage from a white light.  Card Zero  (talk) 21:21, 24 October 2013 (UTC)

Deflection calculation

I'm trying to work out the deflection of a 2kg cube dropped onto a cantilever rod with diameter 16mm and E=200GPa. L=0.6m. So I have I=(pi)(16*10^3)^4/64=3.217*10^9. Then deflection = fl^3/3EI = (19.62)*0.6^3/3*200*9*3.216*10^9=2.27*10^-20m. All calculations are made using SI units. The correct answer should be 15.63mm. I suspect I'm calculating f wrong but I can't figure out how. Clover345 (talk) 17:39, 24 October 2013 (UTC)

16 mm = 16*10^(-3) m. Count Iblis (talk) 20:31, 24 October 2013 (UTC)

Also, I think you should be measuring the moment of inertia I about an axis along the centre of the beam, in which case it is (pi)d^4/32, not (pi)d^4/64. So I should be 6.434*10^-9. Gandalf61 (talk) 09:08, 25 October 2013 (UTC)

Can lungs by cleaned by inhaling a spray of lung macrophages?

In a BBC documentary they showed how after exposure to even mild air pollution you get a lot of particles in your lungs, you could clearly see macrophages busy with cleaning up the mess. But the rate at which they can work is rather limited, it's not sufficient to deal with even mild air pollution if you are exposed to that frequently. I was wondering if one could grow lung macrophages in the lab and inhale a high dose of those when exposed to air pollution.

Count Iblis (talk) 20:44, 24 October 2013 (UTC)

You wouldn't want to be using other people's macrophages. Acquired immunity. Maybe something like this could be done in the future when the technology and capital were available to give everyone his own clone bank. μηδείς (talk) 21:52, 24 October 2013 (UTC)

Macrophages tend to do some heavy-duty demolition work. The body would make more if more worked better. Often interventions seek more to turn off inflammation than to turn it on. Macrophages release cytokines^[2] and can mediate fibrosis of the lungs.^[3] (random references, not necessarily the best - you could find many making related statements) Wnt (talk) 02:11, 25 October 2013 (UTC)

Plugged noses

Why, in general, do noses get plugged and congested, and how does nasal spray clear them? EDIT: I've read the article Nasal congestion, but it lists causes, but not how it actually happens. How do the blood vessels actually cause the blockage? Mingmingla (talk) 23:55, 24 October 2013 (UTC)

You may find some useful info in Nasal spray. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:29, 25 October 2013 (UTC)

There are two different things here which might be confused here. Nasal sinuses can blocked, and there swollen blood vessels may play a part, and the nose itself can also be blocked, but that's more likely to be due to mucus (snot). StuRat (talk) 03:19, 25 October 2013 (UTC)

Swelling of the mucosa lining the nose accounts for most nasal blocking. The mucosa swells in response to infection or allergy to inhaled particles. You may also find nasal polyps worth reading. Most nasal spray contain a mild steroid or some other medication that reduces the swelling. The efficacy of these sprays can vary enormously. Richard Avery (talk) 07:13, 25 October 2013 (UTC)

Thanks for asking, reminded me of this interesting phenomenon: Nasal cycle. alternating partial congestion and decongestion of the nasal cavities in humans, with a cycle of 2.5 hours. Article could do with some more sources though.

The article about nasal sprays may be emphasizing the steroids too much, I would guess that normal decongestants are more common, these can be pseudoephedrine, oxymetazoline, phenylephrine or xylometazoline. They cause vasoconstriction (narrowing of blood vessels), that narrowing also reduces fluids "leaking" into the tissue, and decrease mucus production. They either cause vasoconstriction directly by binding to α-adrenergic receptors, or in the case of pseudoephedrine do that indirectly by triggering the release of noradrenaline, which binds to the receptor. Ssscienccce (talk) 20:43, 25 October 2013 (UTC)