Science desk
< May 1	<< Apr \| May \| Jun >>	May 3 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

May 2

In what stage the muscle cell should get the stimulus?

I came across this presentation in which they write that there are 4 steps in muscle contraction: "1. Excitation = nerve impulse, neurotransmitter & excitation of myofiber 2. Coupling = ATP & calcium ions 3. Contraction = muscle cells shorten 4. Relaxation = muscle cell resume normal resting length (ATP)". My question is why the 1st steps isn't considered as relaxation? (I understand that the impulse should not come in the period of relaxation). Based on the reading here on Wikipedia it seems here that the time that the muscle should normally get the stimulus is the latent period. Isn't it? 93.126.116.89 (talk) 00:28, 2 May 2018 (UTC)[reply]

The relaxation period is the time during which the muscle fibers are changing from a contracted state to a resting state. Once the fibers stop changing, the relaxation period is over. Stimuli that arrive during the relaxation period will usually not be fully effective. Is that clear enough? Looie496 (talk) 13:44, 2 May 2018 (UTC)[reply]

Yes, it's clearest! Thank you93.126.116.89 (talk) 02:22, 4 May 2018 (UTC)[reply]

Is the Lepton Number of the Universe a large negative value?

Assuming the Universe's Lepton number started at zero, the electron surplus was balanced by anti-neutrinos and Lepton number was conserved (or at least randomly even) thereafter, then shouldn't the Lepton number of the Universe today be a large negative value?

The problem is the No-hair theorem. Every black hole has a lepton number of zero, no matter how many electrons it eats. Since electrons tend to cluster in galaxies where black holes lurk while neutrinos are spread more evenly the overall balance favors anti-leptons over leptons.

If so, what's the current deficit? Around 1% of the total number of electrons, more or less?

Hcobb (talk) 02:35, 2 May 2018 (UTC)[reply]

Unless I'm missing something, the no-hair theorem the no-hair theorem doesn't say that the black hole can't have a lepton number, just that the lepton number of the black hole can't affect the externally observed parameters (i.e. gravitational and EM properties). Given that there's no way any of the decays which the lepton number is used to explain could occur within a black hole and have an effect outside it, and no limit on the total lepton number for the black hole, I can't see how a contradiction would arise. (of course, whether it's more meaningful to consider a universe with 0 total lepton number but a load of high lepton number black holes, or a universe with a steadily decreasing total lepton number is likely a pretty arbitrary distinction). MChesterMC (talk) 10:58, 2 May 2018 (UTC)[reply]

This paper makes an argument, which I have skimmed in roughly 45 seconds, that seems to be that any other quantum number should have some GUT to explain it that implies that the number isn't really conserved, so black holes with tremendously long lifetimes (or high evaporation energy?) won't. I'll leave it to a better physicist to give a genuine read on this. Wnt (talk) 21:19, 2 May 2018 (UTC)[reply]

Air changes per hour

What is the air changes per hour of a house that is insulated well and has energy efficient double pane windows? I know someone who says that if I cook something with onions and can smell onions the next day that means that the same air from the day before is still there and has not exchanged with outside air. Is that true or false?--User777123 (talk) 04:32, 2 May 2018 (UTC)[reply]

Anecdote is not data, but I agree with /someone/. In our modern energy efficient house I can smell the curry that was cooked the previous day. In my non energy efficient house it clears within a couple of hours. Funnily enough when I asked the builder for the first house to vent the extractor fans to the air rather than the attic he said no. Greglocock (talk) 07:33, 2 May 2018 (UTC)[reply]

Does air changes per hour point you in the right direction? As to the second query, this can be trivially falsified: chemicals from cooking can settle on surfaces. Also, some, but not all of the air may linger. --47.146.63.87 (talk) 07:36, 2 May 2018 (UTC)[reply]

Yes, agreed; this sounds like a "technically true, but practically not so much" kind of thing. Okay, so you fried up some onions yesterday. Assuming the food was eaten, was the pan washed thoroughly? Was the splatter from the oil all wiped up, including the tiny amounts that travel all over, such as the floor? Has the cook themselves washed? Odoriferous compounds could be lurking in many, many places around the kitchen, re-odorizing even perfectly fresh clean air. Matt Deres (talk) 14:27, 2 May 2018 (UTC)[reply]

Onion is particularly hard to clean up odors from; the odiferous compounds are a class of sulfur-containing compounds called thioketones which cling to just about any non-polar hydrocarbon out there, which includes oils (such as are found in skin) and plastics, and such compounds are fantastically resistant to soap as well. There's some reports out there that the smell can be removed by rubbing with a metal object, but this feels (speaking as a chemist) likely hokum; in my experience the only things that work are vinegar or bleach. --Jayron 32 15:53, 2 May 2018 (UTC)[reply]

Yeah, a cool trick is to boil a pot of vinegar on the stove for about 30 minutes. That will knock down all kinds of cooking odors clinging to curtains, wallpaper, etc. Heaviside glow (talk) 20:18, 2 May 2018 (UTC)[reply]

Can those very big square batteries for flashlights leak if stored for years?

Sagittarian Milky Way (talk) 17:03, 2 May 2018 (UTC)[reply]

All batteries can corrode and leak if improperly stored. I assume you mean a Lantern battery, and there are dozens of different chemical compositions of such a battery, including wet lead acid versions and dry cell versions, so knowing what it is made of will help you decide how to properly store it. Here is some general advice on how to properly store batteries. --Jayron 32 17:17, 2 May 2018 (UTC)[reply]

Some lantern batteries (especially ones sold as "heavy duty"[1]) are still zinc/carbon chemistry. Those will absolutely leak all over the place. Other lantern batteries are alkaline batteries[2], just like most normal AAs and will have a similar shelf-life.

Either way, don't count on the battery holding together forever. If you're storing them long-term, there's no harm in assuming they'll leak and taking appropriate precautions. (Like taking them out of devices, and not putting them near anything precious.) ApLundell (talk) 19:17, 2 May 2018 (UTC)[reply]

*Fixed your link. --69.159.62.113 (talk) 21:58, 2 May 2018 (UTC) [reply]

Thank you.ApLundell (talk) 00:16, 3 May 2018 (UTC)[reply]

Batteries have an expiration date/shelf-life. Sometimes it's printed on the package, and not on the battery though. Anyway, I'd say that when properly stored, they won't leak. By properly stored I mean the temperature, humidity they are exposed to. And also whether they are kept mixed with metal objects that could cause a short circuit.--Doroletho (talk) 17:37, 2 May 2018 (UTC)[reply]

Yes. My experience is that it's batteries left in inert devices that are most likely to leak. Inert devices also tend to be left in places that exacerbate the problem: garages and work sheds with little or no temperature and humidity control. Add a little Murphy's law in there and there you go. Matt Deres (talk) 19:38, 2 May 2018 (UTC)[reply]