Wikipedia:Reference desk/Archives/Science/2009 September 16

= September 16 =

What is "absolute mass"
What is meant by the term "absolute mass?" --Simeon24601 (talk) 00:02, 16 September 2009 (UTC)


 * See Atomic mass unit. SteveBaker (talk) 00:10, 16 September 2009 (UTC)
 * It's in direct comparison to a relative mass (i.e. the ratio with respect to a second mass). In general, "absolute mass" would be measured in a standard unit (such as kilograms), while "relative mass" should be dimensionless.  Nimur (talk) 14:33, 16 September 2009 (UTC)

Michelson-Morely Experiment
Let's imagine that we have the typical setup of a M-M interferometer, as shown in the picture, and that there is actually an ether, with the earth travelling through it at a speed v. The lengths of each arm are l. Normally the analysis for this setup is done where one arm is parallel to v, where the time delay between the paths is v^2*l/c^3. My question is(yes it is a homework question, but I've worked on the problem already and just need a hint) to show that the formula for this time delay if one arm is at an angle of θ to v is v^2*l*cos^2(θ)/c^3. My approach was say that ether was moving with respect to the experiment. The velocity vector of light observed from our reference frame would therefore be equal to the vector sum of the actual velocity of light and the velocity of the ether. Using the law of cosines, I managed to get what appears to be the exact formula for this time delay. But the formula's really messy, and I can't for the life of me see how it would reduce to v^2*l*cos^2(θ)/c^3. There's also a lot of algebra and trig identities involved...the math is a bit involved seeing as how the final answer is so simple. Is there a simple way of going about this? —Preceding unsigned comment added by 76.68.245.124 (talk) 06:44, 16 September 2009 (UTC)

Sorry, I forgot to include the picture.


 * I suspect v^2*l*cos^2(θ)/c^3 is a first order approximation. The exact value probably isn't going to come out to anything nice, but v is assumed to be much smaller than c so higher order terms are going to be negligible. Rckrone (talk) 16:58, 16 September 2009 (UTC)


 * Since you did not post your calculations, there is no way to verify wheather you have made any mistakes. Nevertheless I suggest you should check if the angle you define as theta is indeed the same angle the problem defines as theta. Dauto (talk) 18:55, 16 September 2009 (UTC)

neurovegetative
What does neurovegetative mean, as in "neurovegetative symptoms"? Lova Falk (talk) 10:52, 16 September 2009 (UTC)


 * The term Neurovegetative system is a redirect to Autonomic nervous system; I am pretty sure that unqualified, the term "neurovegetative" refers to loss of consiousness, either temporarily or permanently, as in Persistent vegetative state. -- Jayron  32  11:59, 16 September 2009 (UTC)


 * More specifically, a 'vegatative state' is one in which the patient is no longer comatose – indeed, may be awake – but has no awareness or apparent consciousness. The article on PVS linked by Jayron32 has a bit more description and details.  TenOfAllTrades(talk) 13:03, 16 September 2009 (UTC)
 * Thank you, but actually I don't think this is correct. For instance this sentence: "A relationship between neurovegetative symptoms and an increased risk of sudden infant death (SID) has been frequently described. Such symptoms are vomiting because of gastroesophageal reflux, breathing disorders while nutritive sucking, excessive sweating during sleep, prolonged apneas and apneas with associated symptoms, further unexplained episodes of cyanosis, pallor and loss of muscle tone." (http://www.websciences.org/cftemplate/NAPS/archives/indiv.cfm?ID=19973095). In this article vomiting, breathing disorders etc. are examples of neurovegetative symptoms, but I would like to get an exact definition instead of examples. Lova Falk (talk) 13:50, 16 September 2009 (UTC)
 * In that context neurovegetative = autonomic system exactly, which was the first guess I made. All of the symptoms are events of the autonomic nervous system, which means that they occur outside of conscious control (things like vomiting and breathing regulation).  What it is saying is that events controled by the autonomic nervous system are closely linked to SIDS.  -- Jayron  32  17:12, 16 September 2009 (UTC)

Glomerular filtration rate
In terms of eGFR, what's the sense of the 1.2 and 0.75 coefficients for blacks and females, respectively? Are blacks assumed to be bulkier and have greater metabolism, the same way in which I sense females are assumed to be more slender? Would black females be 0.9, a combination of the two? This would seem to skew the results for a large subset of skinny black men and an even larger subset of black females, who I can't seem to conjure up as being necessarily less slender than white females.  DRosenbach  ( Talk 14:27, 16 September 2009 (UTC)
 * That article cites several sources for the equations. Since these are empirical formulae to describe clinical data, it is unlikely that there is a better source than the original research articles, which are linked in the footnotes of renal function.  This one explains some of the statistical derivation; and this one establishes the +1.21 "ethnicity bias".  Nimur (talk) 14:38, 16 September 2009 (UTC)
 * Thanx!  DRosenbach  ( Talk 14:56, 16 September 2009 (UTC)

Healthy liver
What food/drink is good to keep the liver healthy and look after it? Thanks for info. --AlexSuricata (talk) 15:22, 16 September 2009 (UTC)


 * The liver is perfectly capable and has been designed and developed over millions of years to stay healthy as long as it is not abused with unhealthy food or drink. I would have serious doubts about any food, drink or other product that claims to make your liver healthy in the absence of any pathology. Bear in mind 'detox' is an advertising weasel word little used by proper doctors. 86.4.181.14 (talk) 17:00, 16 September 2009 (UTC)
 * That would be pathosis. Pathology is the study of disease.  DRosenbach  ( Talk 02:20, 17 September 2009 (UTC)


 * It's more like what food/drink is NOT good. Too much fatty food, too much alcohol, to name two. Baseball Bugs What's up, Doc? carrots 02:27, 17 September 2009 (UTC)


 * In the UK medical staff talk about 'pathology' meaning the presence of disease. "I can find no evidence of brain pathology in this patient" for example. 86.4.186.107 (talk) 06:28, 17 September 2009 (UTC)

is it common for people to sneeze after taking cough medicine
and if so why do they do that? —Preceding unsigned comment added by 218.186.12.249 (talk) 15:54, 16 September 2009 (UTC)
 * People sneeze for the strangest reasons. exposure to Sunlight or chocolate, being sexually aroused or having a full stomach are all documented examples. There was an article on it in the 15th of April 2009 issue of New Scientist if you'r interested and can get hold of it at a library.


 * That said, I seem to recall that sneezes can be induced by an increased serotonin level. Cough syrup often include Dextromethorphan which is Serotonergic, which means it can increase the serotonin level. So that's a possible explanation for why cough syrup makes a person sneeze.


 * As an aside, you may want to see Dextromethorphan for drugs that should not be taken at the same time as one is using cough syrup, but apart from that we're not allowed to give medical advice here at the reference desk. EverGreg (talk) 19:56, 16 September 2009 (UTC)


 * Perhaps a simpler explanation is that cough syrups often have aromatic substances in them (to help clear your nose or something, I suppose) - so it could easily be that this is somehow irritating the lining of you nasal passages and causing a sneeze. SteveBaker (talk) 12:16, 17 September 2009 (UTC)
 * Aromatic substances? Yeah, many of'em can make you wanna sneeze alright.  ;-) 98.234.126.251 (talk) 03:36, 19 September 2009 (UTC)

Help identifying an insect (and maybe a flower)
I'd like to identify the hummingbird moth I've photographed so that it can be inserted into the appropriate article. At the moment it's located here, on Flickr, but once it's been identified I'll add it to Commons. It looks to have a distinctive red blotch on its back, but none of the species of the hemaris genus seem to have this marking as far as Wikipedia is concerned. Any help will be gratefully appreciated! To aid your efforts, the photo was taken in the south of France. I have no idea where to begin in identifying the flower, though. Seegoon (talk) 17:21, 16 September 2009 (UTC)
 * Looks to me like, not a Hemaris genus Hummingbird moth (more often called Sphinx moths in the UK), but a Macroglossum genus Hawk moth, specifically a Hummingbird Hawk-moth Macroglossum stellatarum (both Hemaris and Macroglossum fall within the Sphingidae family). The russet-brown dorsal patch may be a local sub-species variation, or particular to one sex.
 * I'm not so good with garden plants, but the flower might be a cultivar of Phlox. I'll delve into my Mother's more extensive garden reference books when I visit her tomorrow, unless someone else has already come up with a firm ID. 87.81.230.195 (talk) 17:57, 16 September 2009 (UTC)
 * I agree; definitely doesn't look like a Hemaris, which apparently all have windows in their wings. These M. stellatarum pics show a bit of a reddish patch on the back:, .  The parent site has a ton of Sphinx pics: .  --Sean 18:44, 16 September 2009 (UTC)
 *   You are the windows in my wings.... --Trovatore (talk) 01:23, 17 September 2009 (UTC)
 * Yes, now I look at these further pictures of life-worn individuals, rather than idealised illustrations from books, I realise that the reddish patches are actually areas of 'naked' thorax, which in a pristine specimen is entirely covered by the greyish thorax scales/hair. 87.81.230.195 (talk) 19:28, 16 September 2009 (UTC)


 * I think the flower is Cape Plumbago, Plumbago auriculata.--Eriastrum (talk) 23:52, 16 September 2009 (UTC)
 * You guys astonish me. I expected a couple of shots in the dark at best, but this is impressive. Collaboration in motion. Thank you all! Seegoon (talk) 18:38, 17 September 2009 (UTC)

how to make a mini hot-plate?
how do i make a mini hot-plate? prefibly about an inch long and wide. —Preceding unsigned comment added by DanielTrox (talk • contribs) 19:06, 16 September 2009 (UTC)


 * I guess I'd start with something like a soldering iron - you can pick them up pretty cheap - then you just need to figure a way to keep it in good thermal contact with the underside of your small metal plate. I'd probably dismantle the iron and just keep the heater and associated wiring.  You can even get soldering irons with adjustable temperature. SteveBaker (talk) 19:11, 16 September 2009 (UTC)


 * No liability is assumed in the event of injury or damage from experimenting with a red hot object. Use extreme caution. Avoid using a resistance heat element like ones in a toaster, which have the line voltage present on the resistance wire, or anything with an energized conductors exposed. Photographic supply and art supply houses sell "tacking irons," used in dry-mounting art or photos. They have an insulated handle and a small heated area. Some have a heat control. Attaching a soldering gun to a small metal plate might do the trick. Edison (talk) 20:25, 16 September 2009 (UTC)


 * Most electronic stores sell miniature heaters. They are resistors that generate a lot of heat.  The resistor is usually wrapped in a metal heat shield to help dissipate the heat.  They get pretty hot - but maybe not as hot as you like.  I've only used them for temperature control for camera housing units.  If it gets too cold inside the unit, I send electricity to the heater (resistor) until it warms up. --  k a i n a w &trade; 02:08, 17 September 2009 (UTC)

ok, well i allso need to know how to create a housing for the wires (if i go with taking apart a soldering Iron) that will allow me to have the hotplate in the center of a glass dome. i was considering a up-stim of glass but im afrade it might melt the wiring. because the plate will be getting to about 320'-370'F

There is a commercial thing that you can place in a microwave oven to make a small furnace. My friend uses it to make glass jewelry. Polypipe Wrangler (talk) 06:16, 22 September 2009 (UTC)

Electron microscope?
Hey, y'all, what's up? So the other day in Biology class, we were talking about microscopes. My teacher mentioned something about an electron microscope, and said something like they cost 7 billion dollars or something. He also said there's this one school that has one. So I was wondering, what would happen if someone dropped it? I need to get this off my mind 'fore I do something stupid. Thanks. --Evan —Preceding unsigned comment added by 99.61.157.103 (talk) 22:14, 16 September 2009 (UTC)


 * You can't "drop" an electron microscope (of any type). They take up a space of at least several cubic metres. Even lifting one up would require Heraclean strength. By the way, I think you mean seven million dollars, not seven billion.  Intelligent  sium  22:17, 16 September 2009 (UTC)


 * cf home made electron microscope, which Wired says cost $10,000 -- Finlay McWalter • Talk 23:13, 16 September 2009 (UTC)


 * (ec) Most of them aren't worth nearly that much. Right now on eBay you can have an as-is may-be-incomplete buy-it-now transmission electron microscope for less than five thousand U.S. dollars.  More realistically, you can get working, good-quality used TEMs and SEMs from a few tens of thousands of dollars up.  (All the bells and whistles will run you a quarter million or so, used.)  If you tried hard and bought a lot of ancillary accessories (or picked up a bunch of features not actually part of the imaging side of the instrument), I suppose you might be able to spend seven million on a new EM.
 * Any decently-sized university science department will have one or more, as do many large hospitals. You won't be able to drop one, because as Intelligentsium notes, you wouldn't be able to lift it in the first place.  A good running tackle might screw up the alignment of the optics, though. TenOfAllTrades(talk) 23:18, 16 September 2009 (UTC)
 * Large SEMs and TEMs weights hundreds of kg and cannot be lifted by human, but small tabletop SEMs weights only about 40-50kg an is of size of about 2 to 3 ATX cases, so these can be picked up (and dropped (if unlucky)). -Yyy (talk) 09:28, 17 September 2009 (UTC)

As it happens, my son went to the only high school in the USA to have a working electron microscope (or so they claim). The School of Science and Engineering in Dallas, Texas. [Their website has a short video about it]. SteveBaker (talk) 01:10, 17 September 2009 (UTC)
 * Maybe one of the few. A more credible claim would be only-in-state, similar to what is said about this one in Connecticut. And there's this one in Washington state. DMacks (talk) 01:25, 17 September 2009 (UTC)
 * I would guess that a reasonable entry-level scanning electron microscope costs only a few thousand dollars; this is not so different from a high-quality optical stereomicroscope price. I've found a few on eBay for about $3000 in "as-is" condition (presumably functional).  As far as damage, I'd be more worried about clogging the vacuum system or putting the wrong kind of lube on the roughing pump - these are the sort of "newbie hazards" that can destroy or damage such equipment (hopefully nobody's clumsy enough to drop the gear, but I can imagine some transport hazards).  Nimur (talk) 02:36, 17 September 2009 (UTC)