Wikipedia:Reference desk/Archives/Science/2011 May 27

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May 27

Dialyses machines!

what are two challenges that face us as we try to develope effective portable dialyses machines? — Preceding unsigned comment added by Faridehm (talk • contribs) 02:29, 27 May 2011 (UTC)

1) Making them simple to use.

2) Making them customizable (different flow rates, etc.) StuRat (talk) 04:08, 27 May 2011 (UTC)

True dialysis precludes active transport. Kidneys can dump through lots of unwanted stuff through a porous membrane, then pull back the water and whatever the body actually wants through a less porous membrane, leaving the unwanted stuff behind. As a result dialysis involves running a lot of water, one way or another.

I think the kind of dialysis machine the patient wants comes either from modest change in the "ethics" surrounding organ transplants (i.e. donation by default) or else from a tissue printer. Wnt (talk) 05:37, 28 May 2011 (UTC)

PH Rate?

Why Alcohol stimulates hydrochloric acid secretion in the stomach and suppresses of ADH?what happen to respiratory rate and the volume and the pH IN URINE? — Preceding unsigned comment added by Faridehm (talk • contribs) 02:35, 27 May 2011 (UTC)

This is your third homework question in three days. I draw your attention to this statement at the top of this page: "If your question is homework, show that you have attempted an answer first, and we will try to help you past the stuck point. If you don't show an effort, you probably won't get help. The reference desk will not do your homework for you." Axl ¤ [Talk] 10:18, 27 May 2011 (UTC)

Decay energy

What's the decay energy of ²³⁹Np? (And how can I find the decay energy for all the isotopes?) Lanthanum-138 (talk) 05:28, 27 May 2011 (UTC)

The Isotopes of neptunium article lists the mass of ²³⁹Np as 239.052939 u. If you subtract off the masses of the daughter particles, namely 239.052156 u for the ²³⁹Pu and 0.000549 u for the electron, you get a difference of 0.000234 u, which is equivalent to a decay energy of 218 keV. Red Act (talk) 06:55, 27 May 2011 (UTC)

Thank you! Lanthanum-138 (talk) 10:54, 27 May 2011 (UTC)

Climate change

Caution: I am not a troll, and I believe the scientific consensus on climate change. I just want to clarify my own understanding.

As I understand it, there have been periods of warming and cooling in the past. Why is global warming an issue now? Is it because it is happening more quickly now? But if so, according to Dansgaard–Oeschger event, in the past there have been instances of warming up to 8 degrees over 40 years. Why wasn't it a problem then, but is a problem now? Thanks. 74.15.138.241 (talk) 07:48, 27 May 2011 (UTC)

Two things: First, who said it wasn't a problem before? Unusually hot or cold periods will have a profound effect on e.g. farming and wildlife which can lead to famine. As our article Bond event mentions, the last such event corresponds roughly with the Migration Period, and it might or might not be more than a coincidence. Because of recentism and the spotty historical records from the time I think we tend to underestimate the environmental disasters of historic time.

Secondly, there is today more people on the Earth than there has ever been before. That means that there's not as much space and the natural resources aren't as abundant. I can imagine that if the sea level rose 3-4 feet those who lived near the shore could relocate and rebuild their settlement somewhere else. That is not as easy today, partly because we have invested in buildings and infrastructure that to a large degree are near the shorelines. Sjö (talk) 10:59, 27 May 2011 (UTC)

Note also that past civilizations have ended as a result of climate change that was much, much milder than what is likely to happen as a result of global warming. Climate change can destroy civilization by making agriculture difficult. An advanced civilization depends on an efficient agricultural system where little manpower is needed to produce the food for the entire civilization. This is in contrast to primitive hunter-gatherer civilizations were people have to work hard for their food. Such civilizations are far more resistant against climate change, because they can adapt more easily to changing circumstances.

If e.g., India and China were unable to produce the rice and grain for their own population, then they have enough financial reserves to buy what they need from the World market. However, this situation can only last a few years at most, because the rest of the World cannot compensate for the loss of the production of the food for 2.5 billion people. So, the price of food would then skyrocket.

With looming food shortages, the countries that are able to produce food would keep it for themselves; there would no longer be free trade between countries. E.g. if the US still produces more than enough grain, they would have to close their market, to make sure Americans have enough to eat. But the moment you close the market for one product, the entire free trade system will collapse (e.g., Saudi Arabia won't sell oil to the US, if the US is not going to sell them grain), triggering the collapse of the World economy. As a result, the total agricultural output would sink to a much lower level. Eventually, all supermarkets will be empty, people living in cities will starve to death. Count Iblis (talk) 15:00, 27 May 2011 (UTC)

Also, you can consult Ask the Experts: Your weather questions answered - USATODAY.com.

—Wavelength (talk) 15:52, 27 May 2011 (UTC)

Thanks. Oh, and which civilization ended because of climate change? 74.15.138.241 (talk) 16:41, 27 May 2011 (UTC)

There's a list of possible ones at Historical impacts of climate change Dmcq (talk) 17:43, 27 May 2011 (UTC)

dsp3 and d2sp3 hybridisations

I know that sp3d and sp3d2 are not same as dsp3 and d2sp3, but I am unable to get clarity. Can you please give few examples of dsp3 and d2sp3 hybridizations? — Preceding unsigned comment added by Krishnashyam94 (talk • contribs) 09:55, 27 May 2011 (UTC) --Krishnashyam94 (talk) 12:58, 27 May 2011 (UTC) --Krishnashyam94 (talk) 10:54, 28 May 2011 (UTC)

Dipole moment of BF3

Generally all trigonal planar molecules (of same type of bonded atoms)have dipole moment as zero. I have a doubt regarding BF3, As there is a dative bond from one of the Fluorine atoms to Boron atom. Does that dative bond alter the net dipole moment of molecule, as the dative bond has got some dipole moment and the dipole moment due to the remaining 3 sigma bonds between boron and fluorine atoms is zero? — Preceding unsigned comment added by Krishnashyam94 (talk • contribs) 10:18, 27 May 2011 (UTC)

Boron trifluoride is our article on the topic. The molecule is symmetrical with each bond equivalent so there is no dipole moment. Here I will put in a plug for the article on boron monofluoride which would have a dipole moment. Graeme Bartlett (talk) 12:27, 27 May 2011 (UTC)

Is co-ordinate covalent bond between one of the fluorine atoms and the boron atom absent?--Krishnashyam94 (talk) 13:03, 27 May 2011 (UTC)

There is no co-ordinate bonding in trifluoroborane/trifluoridoboron, aren't you perhaps refering to tetrafluoroboranuide/tetrafluoridoborate(1-)? Plasmic Physics (talk) 14:20, 27 May 2011 (UTC)

Graeme: just a friendly note, "schakel" is equivalent to "link" in english as in a link in a chain. Plasmic Physics (talk) 14:26, 27 May 2011 (UTC)

See orbital hybridisation, especially sp² hybridization. While the example of ethylene given there is not symmetric, picture that, but without the extra p orbital (because it's empty in boron). Wnt (talk) 15:43, 28 May 2011 (UTC)

HgCl2

Is HgCl2 ionic or can we give predict its structure using VSEPR theory? i.e., is it covalent? — Preceding unsigned comment added by Krishnashyam94 (talk • contribs) 10:21, 27 May 2011 (UTC)

It is mainly covalent with a linear digonal coordination geometry, and a nihilohedral molecular shape, meaning the molecule is not polyhedral. Plasmic Physics (talk) 12:39, 27 May 2011 (UTC)

Read mercuric chloride Graeme Bartlett (talk) 12:43, 27 May 2011 (UTC)

Speed of radio waves through the earth compared to light in fiber optic cable on the surface

Imagine I want to send messages from Sidney to London at the fatest speed possible (microseconds matter) based on triggers, which are public electronicly generated events in Sydney (for example a price movement on the Sydney stock exchange). I am a large organisation with huge funding resources and so I can lay some underwater fiber optics cable as straight as possible between the 2 locations. I have secured all the agreements necessary with the countries that are in between, so the cable will be authorised to go over land where needed. Now my competitor wants to beat me to it, that is send the same message based on the same trigger faster than me between the 2 locations. They are looking at their options, but I have the best hardware commercially available. Would they be able to use radio waves through the earth to be faster? I was wondering if very low frequency radio waves could make it through the earth in direct line? Second question: would these radio waves be nearly as fast as the speed of light? Or would the loss of speed mean that their message actually arrives after mine, even though their distance travelled is shorter than mine? --Lgriot (talk) 10:46, 27 May 2011 (UTC)

Radio waves do not penetrate deeply into the earth due to electrical conductivity due to water or salt or hot ions. Radio propagation talks about how these waves travel. If you could drill a hole in a straight line through the earth and pass an optic fibre through it could take less time than a fibre over the surface of the earth. Perhaps you need to develop an optic fibre with a lower refractive index, or use neutrinos to communicate in a straight line. Radio waves heading into a conductor actually travel much much slower than the speed of light, and attenuate rapidly. Skindepth covers the formulas you need. Graeme Bartlett (talk) 12:56, 27 May 2011 (UTC)

Extremely low frequency radio waves might well penetrate sufficiently, but you'll get into a question of what "faster" means -- the start of the ELF signal will arrive faster than the fiber signal due to distance traveled, but the bandwidth of ELF is so low (on the order of single bits per second, versus fiber's megabits per second and beyond) that any conceivable message -- to include mere authentication that the signal is a message and not a natural transient -- will arrive first via fiber. — Lomn 12:59, 27 May 2011 (UTC)

The great circle distance from Sydney to London is about 17000 km. In vacuum (or air), that is a time-of-flight for light (including radio waves) of about 57 milliseconds. In glass optical fiber (index of refraction about 1.5), the time of flight is about 85 ms. To those numbers, one needs to add the amount of time the signal spends 'stopped' at repeaters and routers. As the other responses note, you're going to have extraordinary (and probably insurmountable) difficulties trying to punch photons at any frequency through the core of the Earth, so you just need to make the round trip as fast as possible. For comparison with reality, this article includes an interview with the CIO of an architectural firm that does worldwide videoconferencing; they report their worst ping time on their private network as being London-Sydney at 290 ms in 2009, and they didn't lay their own private fiber. Since pings are usually reported as round-trip times, they're already doing better than half the speed-of-light-in-fiber limit.

In principle, you could shave 30 milliseconds by setting up a chain of laser repeaters that would allow most of the transmission to happen in open air—but that's orders of magnitude more difficult and costly, and stops working if it starts to rain anywhere along the route. If money's really no object, then you could put a constellation of laser- or radio-linked satellites into low earth orbit and get nearly the same travel time without the weather problems. (You can't go up to geostationary orbit, because that's too far.) TenOfAllTrades(talk) 13:59, 27 May 2011 (UTC)

Brilliant answers, thanks a lot. Extremely low frequency says it allows only several characters per minute, so that seems impossible to properly send a message to react to an event in this manner. We don't have the technology to drill through the core, so unless someone tells me otherwise, I will have to exclude having a straight fiberoptics cable through the Earth. Neutrinos still seem to be an option, as we can probably generate them, but do we have the technology to capture them on the other side? I though they would just go through my receptor in London without even registering, just like they would go through the Earth without hitting anything, so I woouldn't even know a that message has been sent! Air or space lasers: interesting, but the distance is still roughly the same, so the best you can do si the spead of light * 17,000km. The shortest is still through the earth (less than 12,742kms), but it seems there is no known technology that can do this at the moment. --Lgriot (talk) 15:33, 27 May 2011 (UTC)

Neutrino bandwidth is even worse than ELF: current technology requires using a nuclear reactor as the transmitter, and a cave full of high-purity water surrounded by photomultipliers as the receiver. Signaling is done by altering the reactor's power settings and measuring the change in the rate at which the receiver detects neutrinos; at London-Sidney distances, the detection rate would be low enough that I'd be amazed to see transmission rates of more than one character per day. --Carnildo (talk) 00:26, 28 May 2011 (UTC)

http://www.popsci.com/military-aviation-amp-space/article/2009-10/neutrinos-may-someday-provide-high-speed-submarine-communication Hcobb (talk) 15:41, 27 May 2011 (UTC)

Note that even if anyone ever gets that to work, the bandwidth given is 100 bps. [1] says 10 bps which I'm more willing to believe. To put that in context, even the original Hayes modem managed 300 bps. Also I would note the concern there isn't latency anyway but communicating with objects deeply underwater (or underground in some other cases). BTW [2] [3] [4] are some examples of current work with neutrinos (and equipment and cost required) and this isn't for communication. About the neutrinos, they seem to be a common topic on the RD Wikipedia:Reference desk/Archives/Science/2009 February 28#Using neutrinos for communication & Wikipedia:Reference desk/Archives/Science/2007 December 18#Possible to use neutrinos for communication?. In another arena, ignoring the very low bandwidth, if you ever try to use VLF or ULF to communicate through the earth you may find as someone here did [5] that your attempts aren't appreciated by those already using those frequencies. I do seem to recall I once (few years ago) read something, I think in New Scientist about communicating through the earth. It was probably some wacky suggestion, can't remember what the idea was but I think it was presented as a low latency solution for normal communication rather then these extremely low bandwidth proposals. Can't seem to find it despite some extensive searching although did find this [6]. If you can't read the whole thing it says near the end "the signal capacity would be just 1 bit per second" Nil Einne (talk) 17:51, 27 May 2011 (UTC)

[7] may be what I'm remembering which I finally found. I'd actually stumbled upon it before but because of the title didn't pay attention to the description. It doesn't mention latency as I thought it did but otherwise may fit what I remembered (and as I guessed did involve neutrinos). Nil Einne (talk) 18:24, 27 May 2011 (UTC)

Neutrinos are extremely hard to detect but extremely hard is NOT the same thing as impossible. See neutrino detector. Unfortunately, producing and detecting them is hard enough to make that idea impractical. Dauto (talk) 19:50, 27 May 2011 (UTC)

Well even less likely are gravitational waves which are even harder to create and detect, and then into the hypothetical axions or tachyons. The lower refractive index optic fibre would be more within human technology capability. Graeme Bartlett (talk) 23:00, 28 May 2011 (UTC)

Distinguishing between whole milk and two-percent milk

Is there any way to distinguish between whole (3.25%, homogenized, of course) milk and two-percent homogenized milk besides tasting it? It might be a fun science project. If you added an equal amount of food coloring to both samples, for instance, would you be able to SEE the difference? Could you tell the difference using some kind of simple test based on the viscosity (thickness) of the milks? Would shining a light (like a flashlight?) over or into each one be useful? Could you smell a difference between the two of them? Would the two-percent milk have a higher pH (since it would contain fewer fatty ACIDS and more water)?174.131.90.154 (talk) 18:04, 27 May 2011 (UTC)

Their density is slightly different so an object will float at different levels above the liquid surface depending on the kind of milk used. Dauto (talk) 19:36, 27 May 2011 (UTC)

That would work, although the density measurement would have to be very precise. The density of unfortified skim milk is only about 0.4% greater than the density of homogenized whole milk,[8] and the difference would be even less if comparing 2% milk to whole milk instead of skim milk to whole milk. Red Act (talk) 20:09, 27 May 2011 (UTC)

Without actually having crunched the numbers, I would think that any good quality laboratory or commercial Hydrometer would be well up to the task. Hydrometers specifically optimised for this exact task are used, and called lactometers. {The poster formerly known as 87.81.230.195} 90.197.66.166 (talk) 22:00, 27 May 2011 (UTC)

One simple low-budget way of distinguishing between the two chemically would be to measure the solubility of some powdered substance in each of the two that's lipophilic and hydrophobic. I'll leave it to the chemists here to suggest specific such substances. Red Act (talk) 19:48, 27 May 2011 (UTC)

I am thinking that the two-percent milk would actually be more dense (although definitely "thinner") because oil is less dense than water. If I used two objects, like two identical small balls, and dropped one in each glass, would I be able to visually tell the difference between them?174.131.90.154 (talk) 20:02, 27 May 2011 (UTC)

At equal temperatures, the viscosity of whole milk is only about 8% greater than the viscosity of skim milk,[9] which is certainly a big enough difference to measure with a viscometer, but likely wouldn't be enough to make an obvious difference if you just drop a ball into each of the two. Red Act (talk) 20:25, 27 May 2011 (UTC)

The fat is not the same colour as the rest of the milk. Careful colour measurement might be sufficient to distinguish them. Selection of lighting spectrum to optimize reflection from fat molecules might help.--76.160.195.90 (talk) 17:22, 31 May 2011 (UTC)

Some very useful information here about how small the difference in density and viscosity would really be. Thank you! I once saw a photograph on the Internet comparing glasses of milk. The person who took the photograph said that he used whole milk, two-percent, one-percent, and skimmed. He or she put chocolate syrup in all of them, and the color of each one got progressively darker moving from whole to skimmed milk. Would that actually work with, say, food coloring?174.131.90.154 (talk) 20:57, 27 May 2011 (UTC)

It might. Another suggestion is to shine a light (laser pointer ?) through a fixed thickness of milk to see how much passes through. More light should pass through skim milk. If a light meter is used to register the amount that passes through, this could be made into an objective test. StuRat (talk) 21:15, 27 May 2011 (UTC)

Measuring turbidity by laser or Nephelometer/turbidometer or Secchi disk (possibly requiring standard dilution as a first step) should show the difference. Is the differnce visible to the naked eye? - skim to whole is. Rmhermen (talk) 13:29, 28 May 2011 (UTC)

Muscles in gastrointestinal tract

is there 2 layers of muscles (internal muscularis mucosae and external muscle coat) in g.i. tract in cross section? — Preceding unsigned comment added by 117.201.115.113 (talk) 18:35, 27 May 2011 (UTC)

Yes. See "Small_intestine#Histology" and "Muscular layer". Axl ¤ [Talk] 22:15, 27 May 2011 (UTC)

Where is the best place to go Whale watching for Narwhals?

Where is the best place to go Whale watching for Narwhals? Neptunekh2 (talk) 21:32, 27 May 2011 (UTC)

Narwhals do not live in convenient places for most tourists! Here is a tour company that operates out of Ottawa: Narwhal & Polar Bear Floe Edge Adventure. For an undisclosed amount of money, they will organize a flight for you from Ottawa to Iqaluit, Nunavut, where a small busher will fly you to Pond Inlet; and a "comfortable hotel." Then, "we will conduct various dives in and around ice or if and when the Narwhal are present, we will attempt to dive/snorkel with them." This actually sounds awesome, but I wouldn't be surprised if the price tag is in the tens of thousands of dollars. Nimur (talk) 22:38, 27 May 2011 (UTC)

Another company does the same run; from Pond Inlet, it's $10K; Ottawa to Pond Inlet is around $2500. --jpgordon^{::==( o )} 22:51, 27 May 2011 (UTC)

Wouldn't you go narwhal watching to see narwhals? Just kidding, I'm just being picky! XD Now I'm going to actually be helpful. Here is a Canadian adventure/travel company that offers tours: http://www.canadiantraveladventures.com/narwhal. I hope this helps you! Stripey the crab (talk) 23:42, 29 May 2011 (UTC)

Why is Biology a qualitative science?

Why is Biology the only science where mathematical modelling is rarely used? Is this due to a lack of full udnerstanding of its systems and processes or more to do with its unpredictable nature? Clover345 (talk) 21:39, 27 May 2011 (UTC)

Biology uses a great deal of mathematical modeling, particularly in biophysics. Looie496 (talk) 21:41, 27 May 2011 (UTC)

Yep, your premise is faulty. There are many mathematical models designed, deployed, and researched across the biological sciences. See e.g. FitzHugh–Nagumo_model, Molecular_motor, and links therein. In ecology, see Lotka_volterra, Unified_neutral_theory_of_biodiversity and Storage_effect. It is perhaps more fair to say the biological sciences have not benefited from mathematical modeling until more recently than say, physics or chemistry. Also, if you'll accept wp:or, I am an applied mathematician who uses models to understand biology. SemanticMantis (talk) 21:51, 27 May 2011 (UTC)

See Psychoacoustics. Cuddlyable3 (talk) 12:07, 28 May 2011 (UTC)

Also check out systems biology. At least in molecular biology, pretty much all research is heading in this direction. Aaadddaaammm (talk) 16:46, 29 May 2011 (UTC)