Wikipedia:Reference desk/Archives/Science/2010 June 27

Science desk
< June 26	<< May | June | Jul >>	June 28 >

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.

June 27

endocrine disruptors

Are all nitric substances endocrine disruptors or just potassium nitrate? for example, are amyl nitrate and nitric acid endocrine disruptors? —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 01:21, 27 June 2010 (UTC)

Nitric acid is too darn corrosive to be an "endocrine disruptor" -- if you get some of it inside your body, it will burn you from the inside out before any endocrine disruption can take place. Don't know about amyl nitrate, though. FWiW 67.170.215.166 (talk) 02:39, 27 June 2010 (UTC)

To the OP: can you please cite the sources of the statement that potassium nitrate is an endocrine disruptor? I'm not being negative, I'm just curious. Potassium nitrate is routinely used as a food additive, and has LD50 of several g/kg weight, comparable to that of the table salt. How does it affect the human endocrine system? --Dr Dima (talk) 06:34, 27 June 2010 (UTC)

to dr. dima: http://pubs.acs.org/doi/abs/10.1021/es032437n —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 08:25, 27 June 2010 (UTC)

It says that nitrates are suspected, not proven, to be endocrine disruptors. 67.170.215.166 (talk) 09:04, 27 June 2010 (UTC)

For a direct reference, one could look at this article which finds no evidence that nitrates have an endocrine disrupting effect during male rat embryogenesis. It's a pretty limited scope of investigation, but you could track down any references they cite that have shown evidence for nitrates as endocrine disruptors. --- Medical geneticist (talk) 11:57, 27 June 2010 (UTC)

This ref, for example, shows in vitro endocrine disruption by inorganic nitrate (with all due caveats, what happens to mouse tumour cells in a Petri dish might not necessarily happen in the human body). But to answer the question posed, all the studies we're citing are looking at inorganic nitrate, so sodium nitrate would be equivalent to potassium nitrate. The hypothesis is that endocrine disruption comes from production of nitric oxide in inconvenient places, so that would imply that you'd get similar results from amyl nitrite (or amyl nitrate, but fewer people sniff amyl nitrate!). The big difference is the exposure profile: if you're going around sniffing enough amyl nitrite to cause serious endocrine disruption (assuming the hypotheses are correct), you would have many, many other health problems first! Inorganic nitrate, on the other hand, is a well known contaminent in drinking water around the world, and people exposed literally from the day their born until the day they die. As such, it's potentially a much bigger problem, and several groups have looked for effects on human reproduction, without much success from the studies I've seen. Physchim62 (talk) 16:17, 27 June 2010 (UTC)

what about Nitric acid in water ? —Preceding unsigned comment added by Alexsmith44 (talk • contribs) 20:09, 27 June 2010 (UTC)

Nitric acid in water is a source of inorganic nitrate, in that sense it is no different from potassium nitrate; however, it is not a major source of human nitrate intake. Physchim62 (talk) 00:18, 28 June 2010 (UTC)

Or, to put it another way, cyanide is a very potent disruptor of your endocrine system (among other bodily functions), but it is not helpful to label potassium cyanide as an "endocrine disruptor". Physchim62 (talk) 00:20, 28 June 2010 (UTC)

Fan curve derivation

How is the fan curve - pressure vs volume flow rate - derived? In other words how is it related to the specifics of the fan (no of blades, blade angle, blade length etc)? Also how is the efficicency curve of the fan derived (if it can be derived - Im not talking about the friction loss in bearings etc but the hydraulic losses which depend on geometry)? If the answers to the above are not available, can someone tell me how the efficiency varies with fan rpm? Im not talking about ways to calculate/measure the above but get an equation for it. Thanks—Preceding unsigned comment added by 125.17.148.2 (talk) 08:11, 27 June 2010

You may get some information from this designer of industrial fans or through the Fan Manufacturers Association. Cuddlyable3 (talk) 23:44, 27 June 2010 (UTC)

The Navier-Stokes equations are used with numerical methods, usually either differential equation solvers or similar forms of simulation (including, in some cases, Boltzman particle simulation by Monte Carlo methods) to design fluid dynamic shapes, including fans and propellers. Why Other (talk) 00:54, 28 June 2010 (UTC)

So what is basically the equation for the fan curve - and the fan efficiency? I know most things ultimately trace their origins through Navier Stokes but it is far too complicated for me to derive it from there. Does anyone have the equation(s)? Thanks —Preceding unsigned comment added by 125.17.148.2 (talk) 10:38, 28 June 2010

you will need to ask this question on the math reference desk because in its simplest case it's a 3-D PDE solution. You should also specify bthe fluid (air) material (steel, plastic) and its tensile strength, density, and smoothness, which influences the transitions between laminar and turbulent flow. 208.54.14.90 (talk) 16:21, 28 June 2010 (UTC)

'Metallic conduction' in non metals

Hi. Any examples of metallic conduction (and hence metallic appearance) in non-metals other than poly(sulphurnitride) eg eg, excluding heavily doped polymers such as poly-enes? (ie from a pure compound). Not semiconductors please. ie conductivity better than 100 Ω^-1cm^-1 or thereabouts. 83.100.183.236 (talk) 14:27, 27 June 2010 (UTC)

Carbon nanotubes are good thermal conductors. --The High Fin Sperm Whale 16:59, 27 June 2010 (UTC)

Graphite is a pretty decent electrical conductor, it's even used in old-fashioned voltage regulators and such as a variable resistance element. (Note that diamond is non-conductive.) Clear skies to you 67.170.215.166 (talk) 01:40, 28 June 2010 (UTC)

According to our Molecular electronics article, various charge transfer complexes can easily give you "resistivities as low as 8 ohms-cm", and can go down to the metallic region. General research tip: once you have a read ref, try to search for other articles that cite it or later publications from its authors. Any good followup or later major discovery on a topic will cite precedent/previous work, and few PIs do not publish "just one article" on a breakthrough topic. DMacks (talk) 16:00, 28 June 2010 (UTC)

Metallic appearance

Similar to above question, excluding metal (and metal based powders) are there any pigments or other compounds that have a metallic appearance (specifically - any used as a metallic pigment) ? Thanks. 83.100.183.236 (talk) 14:30, 27 June 2010 (UTC)

Some phthalocyanate dyes (what, no article?) can have a metallic appearance. FWiW 67.170.215.166 (talk) 01:44, 28 June 2010 (UTC)

Did you mean Category:Phthalocyanines - as far as I know - they don't..87.102.11.74 (talk) 02:14, 28 June 2010 (UTC)

Well, maybe it's a different kind of dye (something other than phthalocyanines), but I'm pretty sure that there are organic dyes that have a metallic appearance. FWiW 67.170.215.166 (talk) 01:07, 29 June 2010 (UTC)

Can woodlice breath underwater?

82.43.90.93 (talk) 14:51, 27 June 2010 (UTC)

Certain types can as they live in water! But regarding the more common land species, I'm not sure. Regards, --—Cyclonenim | Chat  15:45, 27 June 2010 (UTC)

No, terrestial types can't. They will drown if put in the water. --The High Fin Sperm Whale 16:57, 27 June 2010 (UTC)

Their oxygen requirement must be tiny. They have spiracles rather than lungs. Wouldnt they be able to absorb enough oxygen from water? 92.29.119.46 (talk) 19:20, 29 June 2010 (UTC)

oysters

af2ter opening some oysters from the delaware bay I have found what appears to be some sort of a crab living inside the shell.Can someone identify the creature & provide some info (does it spend its entire life there,how does it get there etc...) ? —Preceding unsigned comment added by Dvp56 (talk • contribs) 15:57, 27 June 2010 (UTC)

Oysters do snap shut if disturbed. The crab could have crawled into the oyster, and the oyster would have closed its shell, trapping the crab. --The High Fin Sperm Whale 16:53, 27 June 2010 (UTC)

Is the crab living inside the shell with a live oyster, or is it living in an empty shell? Hermit crabs will live in discarded or empty shells of other critters... I've not seen one use a bivalve shell in this way, but the world is a diverse place, and I don't see why there wouldn't be some variety or species that has that behavior. --Jayron32 22:19, 27 June 2010 (UTC)

See oyster crab. I've seen these crabs many times when eating oysters from North Carolina. I eat them right along with their delicious hosts! --Sean 14:42, 28 June 2010 (UTC)

Is the oyster crab a parasite, or is it living in the oyster shell a benefit to the oyster somehow? Googlemeister (talk) 16:21, 28 June 2010 (UTC)

Switching mobile phones while flying.

Is it really necessary to turn our mobile phones off while flying in airplanes, as instructed? Or it is just a fear of new technology like putting off our shoes from the room where computers were used.I myself have never turned off my mobile phone while travelling in airplanes, but just put it in silence mode.This is just to check what will happen and nothing has happened.I am a very frequent flyer. —Preceding unsigned comment added by 113.199.218.23 (talk) 16:06, 27 June 2010 (UTC)

A relative who is a pilot tells me that mobile phone signals can mess with the navigational equipment — if I remember rightly, the VOR, among other things. While flying light aircraft, he is permitted to send text messages (there are plenty of times when he has a minute to type the message), because the text is just a quick burst of signals, while talking on the phone involves several minutes of constant signals. The point of turning your phone off is to ensure that you don't talk on it: having the phone on isn't by itself a problem. Nyttend (talk) 16:12, 27 June 2010 (UTC)

In addition to interfering with the plane's equipment (which isn't really a problem on modern passenger jets - they all have appropriate shielding), it can cause problems with the phone network due to you being a similar distance from lots of cell towers (since the distance between the cell towers is small compared to your height above them). Two non-neighbouring towers will assume that no phone will be communicating with both of them, so they will often use the same channels. Your phone will realise there is a low signal and boost power (flattening your battery quite quickly) and at that higher power will be able to communicate with both towers, causing lots of confusion. --Tango (talk) 16:26, 27 June 2010 (UTC)

We have a pretty lengthy article on this: Mobile phones on aircraft. Comet Tuttle (talk) 17:45, 27 June 2010 (UTC)

I hope never to share an airplane with someone who disobeys the safety instructions (every time and frequently!) just to check what will happen because whatever happens happens to everyone on board. Cuddlyable3 (talk) 23:37, 27 June 2010 (UTC)

If mobile phones were really that dangerous to the aircraft, they wouldn't let you take them on board! Physchim62 (talk) 23:40, 27 June 2010 (UTC)

What a nonsensical statement, Physchim, you should know better than that! 67.170.215.166 (talk) 01:48, 28 June 2010 (UTC)

Recently I have seen a larger number of people agreeing that the ban on mobile phones on planes doesn't make sense technically. However, the airlines and others don't object because no one wants to be stuck next to someone yelling into their phone the entire flight. It would make flying worse than it already is. After reading some extremely technical discussions of this on Slashdot I am of this persuasion. --mboverload@ 23:45, 27 June 2010 (UTC)

The fact that there's an agreement among "large numbers of people" that the ban doesn't make sense is irrelevant, since most of these people are not experts on the subject. As for the technical issues involved, I can tell y'all with certainty (having a private pilot's license with an instrument rating) that the VOR, ILS and comm radios installed on all aircraft as per FAA regulations all operate in the VHF band, which is the very same band used by cell phone networks. This raises the possibility of electromagnetic interference with the plane's radios and navigation systems, and while the likelihood of this happening is pretty low (because there's only a slight possibility of any particular cell phone being on the same channel as the plane's radios), if it does happen it can be very dangerous because the pilot would then have a hard time communicating with ATC and/or wouldn't be able to follow the VOR radial/ILS beam. It's ESPECIALLY dangerous during an instrument approach because while the pilot of a modern jetliner often has backup navigation systems for cruise flight (inertial, GPS, celestial, etc.), during an instrument approach he/she is totally dependent on ILS, and any interference with the ILS beam could easily lead to a CFIT-type crash with no survivors. Clear skies to you 67.170.215.166 (talk) 02:10, 28 June 2010 (UTC)

I'm almost a private pilot (hopefully take the checkride soon). My understanding is that I would have the authority to authorize (within reason) or ban whichever handheld electronics I see fit from a FAA legality standpoint. From an FCC standpoint, it is illegal to use a cellphone in flight, even if I authorize it. Period. When it comes down to it, if the flight crew, be it in a plane like I fly or a commercial airliner, says that you can't use your cellphone, it is highly illegal to do so, regardless of how much sense it makes. Heck, the flight crew could ban pet rocks, and you could be sent to jail (in theory) for refusing, purely because the law gives them complete and ultimate authority over anything and everything that happens on and around the aircraft. Falconus^{p t c} 05:10, 28 June 2010 (UTC)

P.S. 67.170 is right. While it probably won't cause a safety issue on a commercial airliner, you can't know that for certain, so don't try it, especially in clouds and on landing. Being out of contact with the world for a few hours won't hurt you. Falconus^{p t c} 05:14, 28 June 2010 (UTC)

It is also quite difficult to use cell phones at high altitude because the cell towers are designed to cover the ground. They try to design the towers so that it is not wasting energy straight up. A friend of mine who is a CAP pilot tells me that he can have 4 bars on the ground, but the same place at 5,000 ft AGL, he will have no signal. Also, on a commercial airline, it is good to turn your phone off because I have found that finding a new cell tower every 20 seconds drains the battery like there is no tomorrow (and no I was not trying to talk on it). 65.121.141.34 (talk) 13:45, 28 June 2010 (UTC)

Superoxide reactivity

I was under the assumption that superoxide reactivity is a result of the superoxide having such a great affinity for electrons that it grabs electrons from surrounding molecules (DNA, membrane phospolipids, etc.), thereby contributing to the danger to biologic viability in the immediate area of superoxide concentration. Is this accurate? How does the electron affinity of the deficient valence shell of a single oxygen atom (as in a superoxide) differ from the deficient valence shells of two oxygen atoms (as in binary oxygen) to produce such a reactive substance? DRosenbach ^{(Talk | Contribs)} 16:59, 27 June 2010 (UTC)

Yes I think that as an oxidizing agent it snatches electrons from reducible substances, creating lots of havoc. --Chemicalinterest (talk) 17:38, 27 June 2010 (UTC)

It's also a radical (chemistry), which gives it a direct method of attack on just about any inorganic substance eg:

R-H + O₂^-· → R· + HO-O^- (forms peroxide and a radical)

It's its radical nature in addition to the oxidising properties that makes it particularly harmful. This can be put another way by showing its reaction with water:

O₂^-· +H₂O → HO₂^- + HO·

ie hydrogen peroxide anion and a hydroxyl radical

Didn't understand the second part of your question, the electron affinities of O, and O₂ are given at Electron affinity (data page). I think the answer you are looking for is "molecular oxygen is less reactive since the bond dissociation energy is high.." O^-is even more reactive than O₂^- - a reason why it isn't usually found. 83.100.183.236 (talk) 18:15, 27 June 2010 (UTC)

Superoxide usually reacts as a reducing agent, giving up a single spare electron to produce O₂. The reason that it causes damage is the radicals it forms by one-electron reduction, which tend to go on and react with other cell components in a pretty uncontrolled way. Physchim62 (talk) 22:30, 27 June 2010 (UTC)

Superoxide is more reactive despite paradoxically being a) an anion, which theoretically should reduce its electrophilicity b) in a more reduced state. This is because the diradical species of normal O2 is quite stable, preventing spontaneous reactions while the superoxide is an unstable monoradical ... kinetically more unstable. The energy barrier is lower. There is almost no activation energy involved in radical-radical interactions.

Also, polarised molecules tend to be more reactive than molecules without a permanent dipole moment. John Riemann Soong (talk) 05:31, 28 June 2010 (UTC)

Superoxide has no permanent dipole moment: the unpaired electron is delocalized over both oxygen atoms. Physchim62 (talk) 10:08, 28 June 2010 (UTC)

Ants

When a queen bee dies, the female workers start to lay their own eggs as the queen isn't producing the pheromone anymore. Does the same happen in an ants nest when the queen ant dies? 82.43.90.93 (talk) 17:02, 27 June 2010 (UTC)

According to E. O. Wilson's wonderful article/story "Trailhead", the answer is basically "yes". "Soldier-queens" begin laying eggs, no longer inhibited by the queen's pheromones. However, the eggs are unfertilized and are thus all male drones, which can then go aid the beginning of new colonies, but their original colony will eventually die out after the queen has died. --Mr.98 (talk) 18:05, 27 June 2010 (UTC)

I'm only really familiar with honey bees (my grandfather is a bee-keeper), so other bees may be different, but that isn't my understanding of how it works. The workers don't start laying eggs (I don't think they are capable of laying). Rather, they start feeding royal jelly to existing larva (there is always some brood in a hive, I believe) so they become queens. It is also possible that there will already be a virgin queen in the hive who will simply take over as queen. I have no idea how it works with ants. --Tango (talk) 19:38, 27 June 2010 (UTC)

I know that some ant colonies have multiple queens,such as the Tapinoma sessile. 65.121.141.34 (talk) 13:39, 28 June 2010 (UTC)

It's true that they'll make a new queen with royal jelly if possible, but it's not always possible (a new hive might never have had a queen, for example). Worker bees can indeed lay eggs, but they're not very good at it --their patterns are spotty, and they'll sometimes lay more than one egg per cell -- and they're not fertilized, so can only lay eggs that will become males (drones). Sounds the same for ants, according to Sr. 98. Ants and bees have many similarities. --Sean 14:49, 28 June 2010 (UTC)

Scientific term for species who don't take care of their young.

Hi, I'm writing a story, and I want an adjective that means the species does not take care of their offspring. Is there a term for that? --Ye Olde Luke (talk) 19:33, 27 June 2010 (UTC)

I don't have a term to describe the species, but I know there is a range of altricial to precocious to describe birds depending on the level of maturity they possess at the time of hatching. The terms are defined by such things as whether the young hatch naked or with feathers already developed and what type of feathers are present, whether the eyes are open or closed, etc. Perhaps you can take a spin on that and term the species a precocious one if the young do not need the parents' attention. DRosenbach ^{(Talk | Contribs)} 20:04, 27 June 2010 (UTC)

There you go -- you can term the species precocial. DRosenbach ^{(Talk | Contribs)} 20:05, 27 June 2010 (UTC)

From the parental investment article, the term is r-selected, as opposed to K-selected. CS Miller (talk) 20:54, 27 June 2010 (UTC)

or as a made up term "non-incubatory" ?? 83.100.183.236 (talk) 20:55, 27 June 2010 (UTC)

Thanks all! For the species introduction, I think I'm going to use "non-incubatory," but I plan to mention all of these terms at leter parts in the story, since it would get redundant to just keep using "non-incubatory." --Ye Olde Luke (talk) 21:24, 27 June 2010 (UTC)

The common cuckoo is an example. 92.28.242.168 (talk) 21:25, 27 June 2010 (UTC)

Sort of. Except the cuckoo chicks still need to be taken care of, so the cuckoo has developed strategies to get other birds to do the hard work. As explained in the article, this is called brood parasitism, and is a different phenomenon from what the OP is thiking of. I think that sea turtles are a better example. The mother lays the eggs and leaves town, and when they hatch, the young are completely on their own. --Jayron32 22:16, 27 June 2010 (UTC)

The Cuckoo is not the only bird in the Old-World that does that. The wild-cute and water-hen are known to parasitically avail of one another's parental skills. In the Avery manuals I looked-up this is usually referred to as parasitical practice. In the plant life, much the same thing can happen, with honeysuckle for example. It is a plant without roots of it's own, but avails of a neighbour. Again it it referred to as parasitical.MacOfJesus (talk) 23:19, 5 July 2010 (UTC)

Flying wings

I know that flying wing aircraft are stealthy because they reflect radar in few directions. How much more visible would a flying wing be on radar if it had vertical stabilizer/s? Also, do flying wings produce a lot of lift? --The High Fin Sperm Whale 21:54, 27 June 2010 (UTC)

Your questions are very unspecific. I'm not sure what kind of answer you expect other then "a bit" for your 1st question. If stealth is your primary concern, then you don't have them like the B-2 Spirit. For the second question, a lot of lift compared to what? The article says Theoretically the flying wing is the most efficient aircraft configuration what does that suggest? Vespine (talk) 23:01, 27 June 2010 (UTC)

See our article Radar cross-section. It is non-trivial to calculate how many dB additional reflectivity (or how many square meters of effective cross section) are added by adding a new part to an airframe. In practice, you can simulate, estimate, and so forth. Because radio reflectivity is complex and involves complete solutions of the full wavefield, simple approximations are rarely accurate. Furthermore, RADAR cross-sections are directional - so adding a vertical stabilizer might make negligible difference in the head-on view, but seriously increase the plane's reflectivity from the side. Nimur (talk) 23:54, 27 June 2010 (UTC)

The problem with vertical stabilisers is the point where they meet the fuselage. Interior corners make really strong radar reflectors. A corner reflector made of three surfaces at right angles will reliably bounce radar right back to it's source and sticks out like a sore thumb - but any concave junction between two surfaces does that to some degree and is basically undesirable for a stealthy design. SteveBaker (talk) 01:31, 28 June 2010 (UTC)

How would it effect stealth, especially on a flying wing, if the wings were either Dihedral or Anhedral? --The High Fin Sperm Whale 03:24, 28 June 2010 (UTC)

Relatively little because the angle is much larger than a right angle. SteveBaker (talk) 12:47, 28 June 2010 (UTC)