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June 22

Refractometry, part 2

So how do they prepare a thin slice of a translucent/opaque mineral for refractometry? What special tools (if any) do they need for this? 67.164.54.236 (talk) 00:59, 22 June 2016 (UTC)[reply]

Normally they would cut off a slice with a diamond cutting wheel, then flatten a surface on a faceting machine. It can be glued to a glass slide with canada balsam. Then sliced off again, and then ground down to the thinness required. Lapidary is the topic about shaping stones and minerals. However to measure refractive index, it can also be done by crushing into small fragments that might be transparent, and then putting them in different immersion liquids, such as diiodomethane or α-monochloronaphthaline. There is the Duc de Chaulnes method, oblique illumination method, and Becke line method and observation of relief. My reference is "An Introduction to the Methods of Optical Crystallography" by F Donald Bloss.Graeme Bartlett (talk) 01:26, 22 June 2016 (UTC)[reply]

So is it possible to do the job with a glass-cutting knife and a sander/bench grinder? Or do you have to use a powered diamond cutter and a faceting machine? (Call me Mr. Cheapskate, but these specialized lapidary tools cost a lot more than the generic ones I hope to use -- and I'm not trying to make jewelry, but to make a thin slice for spectroscopic analysis.) 67.164.54.236 (talk) 11:26, 23 June 2016 (UTC)[reply]

It is possible to use cheap equipment, it depends on how much you want to do. Also how hard is your opaque mineral? A bench grinder may be emery, and same with the paper. So you could probably do minerals up to hardness 8.5, but the harder the longer it takes. Also the average bench grinder does not have sealed bearings, and if you get rock/mineral dust inside it will be destroyed. Also something may overheat without water cooling, so you will have to stop and start once again after the sample cools. It is a lot of work to polish by hand on emery paper. I have done this with marble and granite, which is not that hard, but it still takes a long time by hand. But a small area of a few square millimeters should be possible with a couple of hours of grinding and polishing. You will want to get a mirror smooth finish. Graeme Bartlett (talk) 13:26, 23 June 2016 (UTC)[reply]

Thank you! FYI, the mineral in question is (or, rather, should be) between 5 and 6 on the Mohs scale -- so I think I should be OK, as long as the dust doesn't get inside. 67.164.54.236 (talk) 00:51, 24 June 2016 (UTC)[reply]

Just out of curiosity ... couldn't you measure refractive index directly by firing a pulsed laser at a sample and measuring the time delay for the first light to pass through the sample, even if it were nearly opaque? Wnt (talk) 19:15, 23 June 2016 (UTC)[reply]

Yes in principle. But a pulsed laser has a broad wavelength spectrum that will suffer Dispersion which reduces measurement accuracy. See Dispersion#Dispersion in gemology. The same problem arises in measuring emission times of pulsars. AllBestFaith (talk) 21:36, 23 June 2016 (UTC)[reply]

MOSFET driving several LEDs simultaneously

I'm trying to use a MOSFET to turn on/off several LEDs simultaneously like so[1] (only two LEDs shown). Do I need a resistor in series with the drain of Q1? Or the source of Q1? Or would that be extraneous?

I will be driving the MOSFET with the 3.3v GPIO of a microcontroller. Do I need a small resistor in front of Q1's gate to protect it? Johnson&Johnson&Son (talk) 04:48, 22 June 2016 (UTC)[reply]

The devices shown are two opto-couplers driven by a MOSFET. So long as the values for R3 and R1 are appropriate, the MOSFET will not be damaged, since its drain current will be limited by those resistors. So you do not need a resistor in series with the drain. A series resistor in the gate lead would be wise, since current will flow in the gate-source circuit when the drive voltage is made positive. This resistor will also act as a stopper for RF energy picked up from say, a nearby radio transmitter or internet router. It should be connected directly at the gate terminal and a suitable value might be 47K. On the other side of that resistor (the GPIO side), you should connect a resistor of say 4.7K to ground, so that if the triggering voltage becomes indeterminate due to disconnection of the GPIO terminal, the gate is pulled down to ground and the LEDs stay off instead of perhaps flickering. Akld guy (talk) 08:18, 22 June 2016 (UTC)[reply]

See Your µCPU what is the low output voltage? Tie the gate of the MOSFET to GND using a resistor located next to the MOSFET. Keep the gate wire as short as possible. You are using opto-couplers? Make sure there's no solder flux or dirt under the coupler device. Clean before operate on hazardous voltage. --Hans Haase (有问题吗) 11:38, 22 June 2016 (UTC)[reply]

Intestinal gas exchange

Recently, while experiencing a bit of bloat, I was wondering: Do gases in the intestine enter the blood stream to any measurable degree? I would think that if nutrients and water can cross over, then at least some amount of gas would also find its way across. On the other hand, there can't be too much gas exchange otherwise gas buildup wouldn't tend to be much of a problem. If there is some gas exchange, does that cause any problems with blood chemistry and the like? Dragons flight (talk) 07:24, 22 June 2016 (UTC)[reply]

Many of these gases dissolve freely into the bloodstream, but they also dissolve freely out of it, making it possible to test them on the breath, etc. [2][3]. The second source seems to suggest that swallowed nitrogen is more persistent than oxygen, which is absorbed; meanwhile carbon dioxide can enter. Only 1/3 of people have the secret mutant power to generate methane; the rest have to content themselves with farting hydrogen and CO2. But I feel like I don't really have the answer, because I'd want to see rates of production and diffusion to get a full picture - I'm assuming it's all a matter of kinetics. Wnt (talk) 12:08, 22 June 2016 (UTC)[reply]

Finasteride and fertility.

Does Finasteride decrease the sperm count and thereby making one impotent ? — Preceding unsigned comment added by 182.18.177.78 (talk) 08:02, 22 June 2016 (UTC)[reply]

Physicians use Finasteride primarily to treat BPH, informally known as an enlarged prostate, and the FDA approved label reports cases of diminished libido or erectile dysfunction. Finasteride partially inhibits 5α-reductase with side effects that include reduced Epididymis (outlet tube from testicle) and decreased sperm motility. Suspected Male impotence connected with BPH treatment can have many causes which will not be diagnosed on this ref. desk and should be resolved in consultation with a urologist who may prescribe any of a number of medications with different side effects. For example, Dutasteride is an alternative 5α-reductase inhibitor to Finasteride, with a different risk profile. AllBestFaith (talk) 11:46, 22 June 2016 (UTC)[reply]

Note that decreased sperm count doesn't directly lead to impotence - lots of guys are shooting blanks and never know it until they start wondering why no babies are coming out! Wnt (talk) 12:10, 22 June 2016 (UTC)[reply]

We may suppose that infertility is an undesirable side effect of BPH medication. However Silodosin in contrast to other α₁ blockers has shown promise as both a BPH medication and as a chemical contraceptive for men, see Silodosin#Pharmacology. AllBestFaith (talk) 18:23, 23 June 2016 (UTC)[reply]

Seeing a rocket go up

If a Long March 7 rocket launches at sunset 19:30, 2016 06 25 around 126 degrees to the southeast, around 100 km away, will we see it go up from the top of a building in Haikou? Anna Frodesiak (talk) 10:36, 22 June 2016 (UTC)[reply]

The human eye should certainly be able to see that amount of light at that distance - experiments showed that the eye can actually see a candle flame at 30 miles! However - it will rather depend on the weather! http://www.livescience.com/33895-human-eye.html Wymspen (talk) 11:49, 22 June 2016 (UTC)[reply]

And you'll see it when it's just less than 1km from the ground, fwiw, based on a quick scan of this table --Tagishsimon (talk) 11:59, 22 June 2016 (UTC)[reply]

Thank you, Wymspen and Tagishsimon!

Anna Frodesiak (talk) 21:14, 22 June 2016 (UTC)[reply]

Magnetic field influence in neutron

Does the applying of a magnetic field influence the average lifetime of a neutron by increasing or decreasing from the value of approximately 15 minutes in absence of field?--82.137.9.64 (talk) 12:23, 22 June 2016 (UTC)[reply]

Possibly, but by only an infinitesimally small amount. Ruslik_Zero 14:22, 22 June 2016 (UTC)[reply]

Neutron half life is unaffected by magnetic field strength in ordinary contexts. It is suspected to decrease, however, in magnetic fields stronger than 10⁸ tesla. Magnetic fields as this strength would only be found at the surface of a magnetar or possibly inside a star that is in the process of collapsing into a black hole. However, a magnetar will still contain neutrons since neutron half life is increased by matter density in a way that more than cancels out its dependence on magnetic field strength http://journals.aps.org/pr/pdf/10.1103/PhysRev.187.2141]. Someguy1221 (talk) 04:41, 23 June 2016 (UTC)[reply]

Which tetrapod group could evolve into a new class?

I wonder whether exists a tetrapod group which can evolve in a reasonable amount of time (ten-twenty million years?) into a new class of organisms as different as are mammals or birds.--Carnby (talk) 13:57, 22 June 2016 (UTC)[reply]

My WP:CRYSTAL is cloudy, cannot read. You may be interested in exaptation, mutation rate, rate of evolution, and Error_catastrophe. Also this [4] article on a rapidly evolving group of fish looks interesting. SemanticMantis (talk) 15:15, 22 June 2016 (UTC)[reply]

Agree with the above, but see also species problem. The concept of species is fraught with exceptions and hard-cases and it's much more easily defined than "class" or "family". A new class could be created at any time by deciding to organize phylogeny slightly differently. Matt Deres (talk) 16:16, 22 June 2016 (UTC)[reply]

Organizing phylogeny differently, a ready-made new class could be Chelonia, couldn't it?--Carnby (talk) 16:40, 22 June 2016 (UTC)[reply]

You would want to look for the current classes which already show great diversity between different sub-groups. Possibly bony v cartilaginous fish, turtles/tortoises v snakes v lizards/crocodilians, penguins v flying birds? Wymspen (talk) 17:59, 22 June 2016 (UTC)[reply]

That would be true if we were fine with arbitrary classification, but the goal is to support these things with scientific evidence. We do get new evidence and shuffle things around quite a bit, but not classes. If you're doing modern systematics (largely via Computational_phylogenetics), classes are actually often easier and less subjective to separate than species are. Families are pretty tough. Given the species problem and the three-domain system, taxonomy gets more anchored and stable at the top and bottom, and it's the middle-to low taxonomic ranks like family that are most arbitrary. Consider that bird taxonomy has shuffled things quite a bit in recent decades, but class Aves has remained unchanged for quite a while. According to Tetrapod#History_of_classification, no tetrapod classes have changed since the reptiles and amphibians were split in 1804. SemanticMantis (talk) 18:40, 22 June 2016 (UTC)[reply]

My point was not about re-classifying existing species. If you are considering where evolution might lead to such a high variance that it was no longer possible to consider all the species involved to belong to the same class, the logical starting point seems to be those classes where a very high level of variance has evolved already. I didn't suggest such a process for an mammalian groups, because the class is more recent, and probably shows less variance than the older ones (though the cetaceans may well be on their way). Wymspen (talk) 20:02, 22 June 2016 (UTC)[reply]

Yes, I took your point, it was fine. I was replying to Matt Deres' comments on creating new classes of extant species, per WP:INDENT style. SemanticMantis (talk) 20:21, 22 June 2016 (UTC)[reply]

The biggest problem with the question as such is that "class" is an artifact of our evolving understanding of evolution and cladistics. That being said, birds and mammals probably would not have become considered new classes, except for extinction events. Given the widespread prevalence and small size of songbirds, rodents, and microchiroptera, my guess is they would probably survive another K/T type event, and speciate quite rapidly.

Bats and whales are diverse enough that were all other mammals to go extinct, there'd be little sense in keeping them closer than turtles an birds. And I agree with the above statement that if you want to go with existing tetrapods, separating off the turtles and crocodiles from the lepidosauria would make the most sense. This is all my POV, of course. μηδείς (talk) 00:44, 23 June 2016 (UTC)[reply]

Yes, there's a lot of philosophy in this question. Cetaceans are indeed even-toed ungulates - zero is even, after all. :) - but cetaceans aren't a class, not even an order (though they were considered such at one time). But surely a bird and a bat are more similar than a whale and a mouse deer? Only with great effort does the taxonomist know what to look for to (rather absurdly, you'd think) dispute this claim.

For everything that's not a bird: note the fur and mammary glands. Note the lack of hollow bones. Note the uterus and lack of cloaca. That the bat is more closely related to the mouse deer and the whale than the crow should be obvious to anyone who's dissected all four. You're right that the number of taxonomic ranks and their names are a bit arbitrary, but the distinction between tetrapod classes is far brighter and more easily supported than e.g. chimps vs. bonobos or any ring species. Class disctinctions are less artificial than species or genera, not more. Another way of saying it: the deeper the cut between two clades, the less debate is possible. SemanticMantis (talk) 20:04, 23 June 2016 (UTC)[reply]

Oh, I'm definitely not denying that the clade distinction is most fundamental and important. But determining the relative importance of characters is not easy; it's only in hindsight we know to look for hairs and to distinguish them from feathers. So to say "a class of organisms as different as mammals or birds" is actually a tautology - whatever makes that group a class will be an important difference from a cladistic point of view, no matter how small and subtle that feature may be. But to the eyes of the layman, it may look like a big nothing, or more closely related species (humans and chimps, say) may seem much more different than the classes as a whole. Wnt (talk) 23:35, 23 June 2016 (UTC)[reply]

It would seem in "true" taxonomy the status of class therefore is not earned by morphological difference, though morphological difference may be its expression ... sort of like grace and good works in theology, perhaps. The penchant of taxonomists seems to be to add superphylum and taxonomic domain near the top of the list, so my guess would be as time goes by, categories ideally would simply work their way up the ranks. The exception being species, with its unique definition, versus genus. But if many species become genera, then genera become families, families become orders, orders become classes. And so any order today has a roughly equal chance, depending on its recent fortunes and changing ecology, of becoming a class. All others need not apply, unless of course they happen to be things that ought to be orders now. Now could there be an event in the next ten million years that is drastic enough that species radiate out into genera? Well, a mass extinction clearing out most existing lifeforms would do the trick, and happy chance, we're in the middle of one. So the odds, I'd say, are looking good. Wnt (talk) 16:43, 23 June 2016 (UTC)[reply]