Wikipedia:Reference desk/Archives/Science/2009 September 28

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September 28

What species is this?

Unidentified spider

So many brown spiders and they all look alike. Does anyone know what species this is? It was taken in Arkansas, near water, if that helps. --ErgoSum•talk•trib 03:11, 28 September 2009 (UTC)

Possibly a nursery-web spider -- family Pisauridae -- but I cannot see the eye arrangement in this picture so I'm really not sure. I can only tell that she's carrying an egg-sack. Hope this helps. --Dr Dima (talk) 16:47, 28 September 2009 (UTC)

second image

Here is a second picture if that helps. This is all I have of the spider. --ErgoSum•talk•trib 23:56, 1 October 2009 (UTC)

carbon monoxide and the Calvin Cycle

Are plants able to carbon-fixate carbon monoxide? I assume it's a bit easier since carbon monoxide has this huge polar effect. It would be opposite of carbon dioxide though (the carbon is negative). Would it be kind of like how plants process cyanide? John Riemann Soong (talk) 05:19, 28 September 2009 (UTC)

[1] p168 section 6.9.3 Not yet found.

CO also affects nitrogen fixation in plants (like CO affects O fixation in humans) [2] page 17 Nitrogenase is the enzyme affected.

There's bacteria that use CO as an energy source in the sea - by oxidation to CO2. And other processes eg [3] 83.100.251.196 (talk) 11:41, 28 September 2009 (UTC)

does hyperconjugation stabilise only cations?

Here's what I understand about hyperconjugation...by orienting the hydrogen atoms' antibonding orbitals towards the positive charge of a carbocation, that's like the same thing as removing electron density from an antibonding orbital. Does this mean that carbanions (and lone pairs, negative charges, etc.) cannot be stabilised by hyperconjugation? Or would it in fact be stabilised by "anti-hyperconjugation" -- where the eclipsed or gauche conformer is more stable than the anti? John Riemann Soong (talk) 06:00, 28 September 2009 (UTC)

Did you mean "orienting the hydrogen atoms' antibonding orbitals towards the positive charge" - the orbitals must have electrons in - in CH bonds these are the bonding orbitals. eg [4] Hyperconjugation

Can carbanions be stabilised by hyperconjugation? - at first no, then yes "antibonding orbital-hyperconjugation stabilisation of carbanions" would be a good term. Yes - I think this does happen - for example elements lower down the periodic table Sulphur , Silicon [5] also search "silicon stabilised adjacent negative charge" etc etc stabilise an adjacent negative charge on carbon - I think this is due to the process you mention.

For first row elements I think the antibonding orbitals do not give any significant stabilisation.83.100.251.196 (talk) 11:51, 28 September 2009 (UTC) (There might be exceptions to this rule in the case of some per-flouro compouns - eg [6] p274 chap 7.1 - this is a special and extreme case - usually ignore)

The term "hyperconjugation carbanions" [7] turns up a lot with respect to P, Si etc.83.100.251.196 (talk) 12:03, 28 September 2009 (UTC)

Well if the pi orbital is empty (like in a carbocation), C-H bonding orbitals want to overlap with the (bonding?) p-orbital, but if it is filled, then the C-H antibonding orbitals want to overlap with the filled bonding p-orbital or the empty antibonding orbital? (What about the case of nonbonding p orbitals?). John Riemann Soong (talk) 16:49, 28 September 2009 (UTC)

Overlap of filled and unfilled orbitals results in net stabilisation, if both the orbitals are half filled (as in CH₃· + CH₃· ) then that forms a bond too. But if both orbitals are fully filled then the molecular orbital formed by overlap of them would have the antibonding, and bonding orbitals filled - so no net bonding or stabilisation eg as in He₂ .

So it's Carbanion + unfilled orbitals = stabilisation when considering hyperconjugation.83.100.251.196 (talk) 18:40, 28 September 2009 (UTC)

Remember that in pi systems (resonance - not hyperconjugation) the inital p(i) orbitals are only half filled83.100.251.196 (talk) 18:42, 28 September 2009 (UTC)

Wait, overlap of a filled bonding and an empty antibonding orbital results in net stabilisation? John Riemann Soong (talk) 18:58, 28 September 2009 (UTC)

if you mean "antibonding" as in ["antibonding" orbital for the C-H bond] in hyperconjugation - yes - but the term "antibonding" has different meanings in different contexts - ie an orbtial may be antibonding in interaction with one atom - but bonding with another.

(edit conflict)I'll start again..

An anti-bonding orbtial can mean two things:

a. When filled with electrons it decreases the bond order -eg pi* orbitals in ethene.

b. When interacting with another orbital it produces an antibonding orbital (see a) - in case b this arises from the degeneracy of the orbitals - eg for H interacting with another H s orbital there is a s orbital that is bonding, and other that is antibonding. Take the other degenerate orbital on the second H and the situation is reversed.

For 'normal' (ie electron balanced) molecules (or parts of molecules) the antibonding orbital is always empty, the bonding orbital is always filled. I'll avoid these terms below:

Carbocation is stabilised by hyperconjugation interaction with a filled (or partially filed) orbital of the right symmetry.

Carboanion is stabilised by hyperconjugation with an empty (or partially empty) orbital of the right symmetry.

83.100.251.196 (talk) 19:06, 28 September 2009 (UTC)

Hmm, is this kinda related to proton sharing (in say an enone). Let me see if I have this right: a carbanion overlaps with a C-H antibonding orbital, weakening the first C-H bond but forming a second partial C-H bond? So it's sort of like a hydrocarbon intramolecular form of hydrogen bonding, and it results in net stabilisation because of delocalisation of charge?

I'm also wondering whether hyperconjugation generally destabilises carbocations. As I recall, the stability is methyl > pri > sec > tert. One professor (not mine though!) suggests this is because of induction, but I think the inductive differences are too weak and I think it's because of C-H repulsion with the carbanion orbitals. John Riemann Soong (talk) 19:25, 28 September 2009 (UTC)

First part yes, second part you wrote carbocation at firsst - carbanions are quite difficult if you are thinking of compounds like MeLi, BuLi, t-BuLi - since they are clusters (see methyllithium for some description) - the actual Me- might not ever exist.. 83.100.251.196 (talk) 19:45, 28 September 2009 (UTC)

ok I'm going to have two more goes at examples - this seems like a good example - consider NCCH₃ (acrylonitrile) - then deprotonate it once..

Interaction of the first electron in the p orbital on C (ie the negative charge) with one of the cyanide (CN) pi _bonding orbitals produces pi system stabilisation - this is a major effect. (here I assume the CH2 is sp2, and the negative charge is in the p orbital)

But additionally interaction of the same p orbital with the CN pi antibonding orbital does this:

NC-CH2-  >>>  -N=C=CH2

This is a minor stabilisation - here it works because N is more electronegative than C, and thus stabilises the negative charge. - So this can be expected to contribute to stabilisation - this is similar to hyperconjugation (in some ways)

Note that this doesn't work when using allyl carboanion, since the resonance structure is the same as the starting structure - ie interaction with the antibonding orbital give no stabilisation, but interaction with the bonding orbital does.83.100.251.196 (talk) 19:45, 28 September 2009 (UTC)

Here's the second part - consider C₂^--CF₃ ... now consider on of the C-F antibonding (unfilled) orbitals being donated into by the negative charge on C.. If this is brought to it's logical conclusion you get this reaction:

CH2--CF3 >>> CH2=CF2 + F-

The idea of one of the bonds being weaken by some types of htperconjugation is absolutely right - in the case above you can see that F- is a stable anion - of course in the case of hyperconjugation it doesn't go all the way - you could still view the hyperconjugation as a resonance hybrid between the two (with the balance very much on the left).83.100.251.196 (talk) 19:45, 28 September 2009 (UTC)

Hmm, that's curious -- the induction effect parallels the hyperconjugation effect. Is it possible to separate the two effects? I mean, one is carried out via bonds and the other through space, right? John Riemann Soong (talk) 19:53, 28 September 2009 (UTC)

If you are doing a full molecular orbital treatment including the difference in nuclear charge between nuclei then you don't need to consider anything else - the method should explain every property..

Before chemists had MO methods they noticed that molecular properties could be explained by combining several different techniques - electron counting (pairing), valence pair repulsion, resonance structures, inductive effects, long range steric effects.. etc - if you can sensibly combine all these you should get a very good understanding of molecules, AND get the same results as those obtained from a supercomputer guessing a MO structures (and cheaper too).

But it's important to note that both are describing the same thing - the second set are empirical - based on a lot of observations of different molecules. The MO methods are more mathematical/computational - and require less empirical knowledge (or non at all). but don't mix the two up in explanations - a molecules reactivity or structure can be explained through either. Only if your MO calculation is very simple (ignoring a lot of factors) do you need to use empirical methods to 'fine tune' the answer.

To fully explain the inductive effect in MO calculations I think you would need to include nuclear charge and hyperconjugation.83.100.251.196 (talk) 20:16, 28 September 2009 (UTC)

Were MO calculations expensive back then? They seem pretty simple now -- I just load up a program on the library computer (2.6 GHz) and hit "calculate"! As long as I'm not doing something like a majorly large protein it gets done within 30 seconds to 10 minutes. (That was when I was doing beta-carotene derivatives or something.)

So is in fact hyperconjugation one of the "root causes" of the inductive effect? I don't quite get your answer. Both induction and hyperconjugation aren't MO explanations, aren't they? John Riemann Soong (talk) 20:38, 28 September 2009 (UTC)

(Yes - back then 2.6GHz was science fiction) It depends on how good your MO program is - simple ones just calculate direct interactions (some early ones used a lot of heavy approximations), you could check how good it is by using the fluorocyclobutane anion in the example linked above - the CF3 fluorines should be split in energy as described in the article (they'd still be split in energy/bond length in the protonated neutral form too - MO should do this too). I've no idea how good they are generally nowadays.

Inductive effect is mostly dipolar/electrostatic (or dipole conducted through conjugated system) - hyperconjugation should be a smaller effect on top of that.

MO calculations are explanations unto themselves - hyperconjugation is easier to explain in terms of molecular orbitals, the inductive effect is more an empirical non MO explanation. Non of the methods listed above 'explains' MO calculations as such - but the results of MO calculations can be compared to the 'hand waving' efforts of these empirical methods - in general there should be a match in the conclusions (usually is).

I suppose it depends on what you mean by separate - could be to attempt to measure the extent of each - specially prepared molecules (with the substituents held in place by rings) could be prepared to compare with non constrained (linear or branching), and/or molecules that were constrained so as to not have good inductive or hyperconjugative effects. Deviations from expected hammett derived activities would be another way that has been tried.83.100.251.196 (talk) 20:23, 28 September 2009 (UTC)

Neutron bomb question

Our article on Neutron bomb states that neutrons released from a nuclear explosion will not travel very far in air. But yet, that contradicts a statement in this rather well written analysis on Fourth Generation Nuclear Weapons, namely pure fusion bombs. http://arxiv.org/PS_cache/physics/pdf/0510/0510071v5.pdf it states in the target coupling section,

"Heat the volume of a material. Penetrating high energy radiations (neutrons, pions,15 or highenergy gammarays) will easily cross a low density intervening medium such as air and deposit their energy deep into any high density material. As a result, a substantial (i.e., centimeter to meter thick)layer of a bomb irradiated material can be brought to a temperature sufficiently high for it to melt, vaporize, or even explode."

So isn't it true that neutrons can penetrate easily through air? It seems logical, they are neutral after all, and are high energy (14 Mev in the case of a pure fusion bomb), so I would think they can penetrate through air easily. ScienceApe (talk) 06:29, 28 September 2009 (UTC)

Our article on neutron radiation agrees with you - it says "Because neutrons are uncharged, they are more penetrating than alpha radiation or beta radiation. In some cases they are more penetrating than gamma radiation, which is impeded in materials of high atomic number". The passage that you refer to in the neutron bomb article is confusing and may be plain wrong. Possibly it is confusing the fast neutrons produced by nuclear reactions with slower thermal neutrons, which are absorbed much more easily. Gandalf61 (talk) 09:02, 28 September 2009 (UTC)

There are a few different things going on here that you're each taking out of context.

In the context of neutron bomb radiation effects, "very far" means on the scale of, say, many meters. A 10kt fission weapon will put out very high energy neutrons for only some 800 yards or so. 800 yards is only "small" in the context of nuclear weapon explosions! Thus the article says:

Neutron bombs have low explosive yields compared with other nuclear weapons. This is because neutrons are absorbed by air, so a high-yield neutron bomb is not able to radiate neutrons beyond its blast range and so would have no destructive advantage over a normal hydrogen bomb.

AFIAK this is generally accurate except that the neutrons are not "absorbed" but "scattered". It's not a question of penetration in the sense used by "neutron radiation", it's about the fact that neutrons scatter off of light elements (oxygen, hydrogen) very easily, and by doing so, lose their energy (and thus become less of an effects problem). So if you set off a "regular sized" nuclear bomb, the range of neutron effects is going to be a lot smaller than the blast and other radiation effects, and thus not be of much use. In a neutron bomb, you use a low yield weapon, modified to increase radiation output, so that the radiation goes well beyond the blast and heat effects. Again, the distances/times involved are only "small" when compared to the other effects of a nuclear explosion, which are huge!

The article linked to above refers to radiation transport (which is what the paper refers to), inside an actual hydrogen bomb—it's talking about a couple of yards at most, usually just a few feet with modern warheads. Neutrons have no problem penetrating air at that distance. That's not what the neutron bomb paragraph is referring to at all.

There is a lot of discussion on this in Chapter VIII of Glasstone and Dolan's The Effects of Nuclear Weapons, 1977 edn. But it's important not to take these statements out of context and to start applying them from one domain to another. Neutrons are highly penetrating on table-top experiment. When you're talking about over the course of a mile through air, they scatter out comparatively quickly. --Mr.98 (talk) 14:58, 28 September 2009 (UTC)

Source transformation..........

This is something which I was wondering about........ I know that in principle, a 1A current source in parallel with a 1 ohm resistance is the same as a 1V voltage source in series with a 1 ohm resistance. My question is, how do you differentiate between the two ? Say you have 2 black boxes, totally identical from the outside. Say you can't open them and look inside. All you have is two terminals poking out of each box. One of them contains an ideal Voltage source in series with a resistance, and the other an ideal current source with a parallel resistance. How do you say which is which ? Is there any means at all......? Rkr1991 ^{(Wanna chat?)} 07:16, 28 September 2009 (UTC)

Yes, of course there is! You just connect the terminals across a one ohm resistance and measure the current or voltage. The series arrangement will have 0.5 volts and 0.5 amps. The parallel arrangement (There is no such thing as a 1A current source, so I've assumed one volt EMF) will have 1 volt and one amp (assuming no voltage drop in the source). Your hypothetical parallel arrangement would never be sold as a product because there would be a constant one amp internal drain on the source, though I suppose such an arrangement might be used in some voltage stabilising circuits. apology below Dbfirs 08:06, 28 September 2009 (UTC)

Read Current source. Agreed, there's no such thing as an ideal current source, but assuming there is, how do you differentiate it then is my question. Of course you can't replace that by a voltage source again, like how you explained. I am asking how to differentiate like how i asked. Rkr1991 ^{(Wanna chat?)} 08:39, 28 September 2009 (UTC)

No, you can't differentiate them at all. When Norton and Thévenin called them equivalent circuits, they really meant it. What Dbfirs is forgetting is that the current from the 1 A source will divide equally between the internal 1 ohm resistor and the external 1 ohm resistor, resulting in 0.5 A in each. Thus the current and voltage in the external resistor will be the same in both cases. --Heron (talk) 09:51, 28 September 2009 (UTC)

OK, but they are equivalent only if we assume Ohm's law right ? Isn't it possible to bring some sort of a situation where Ohm's law is no longer a good enough approximation, and hence we would be able to differentiate ? Or would they, even under such conditions, produce exactly the same outputs ? Rkr1991 ^{(Wanna chat?)} 10:43, 28 September 2009 (UTC)

Yes you can tell the difference. The box containing the current source is dissipating 1W internally which can be felt as warmth. The other box is cold. Previous answers are below the standard that the OP has a right to expect. Cuddlyable3 (talk) 12:07, 28 September 2009 (UTC)

Great answer. Thanks, everyone. Rkr1991 ^{(Wanna chat?)} 13:36, 28 September 2009 (UTC)

More methods:
#1 Place the two boxes in identical parallel universes. Measure the time to reach heat death in each universe. The universe with the voltage source dies second.
#2 The black paint on the box with the current source dries quicker. Cuddlyable3 (talk) 15:34, 28 September 2009 (UTC)

Apologies to Rkr1991 for misunderstanding the question. I should have read the article first, even if the device doesn't exist. Dbfirs 18:00, 28 September 2009 (UTC)

There is no difference, even in terms of power dissipated. Edison (talk) 19:12, 28 September 2009 (UTC)

... except internally? Dbfirs 21:37, 28 September 2009 (UTC)

Edison please explain why you think I am mistaken. Cuddlyable3 (talk) 21:46, 28 September 2009 (UTC)

Yes, AFAIK, Cuddlyable's answer seems perfectly reasonable.Rkr1991 ^{(Wanna chat?)} 07:44, 29 September 2009 (UTC)

genius

do geniuses live long?

What makes you think they would ? Rkr1991 ^{(Wanna chat?)} 07:43, 28 September 2009 (UTC)

Some do, some don't (just like the rest of us). Has anyone done any research? There does seem to be a slight bias towards dying young amongst geniuses. Do some burn out, or is this just media hype? Dbfirs 08:19, 28 September 2009 (UTC)

To answer your question: "Further evidence for a positive relation of intelligence and suicide mortality is provided by the observation of excess suicide prevalence in the Terman Genetic Study of Genius sample, relative to the general population." from Voracek, M. 2004. National intelligence and suicide rate: an ecological study of 85 countries. Personality and Individual Differences, 37, 543-553.--droptone (talk) 12:47, 28 September 2009 (UTC)

IQ is associated with mortality:

It has recently been discovered that people with lower IQs tend to die younger than people with higher IQs. This association is found whether psychometric intelligence is measured in childhood (Deary, Whiteman, Starr, Whalley, & Fox, 2004; Osler et al., 2003; Whalley & Deary, 2001), early adulthood (O’Toole, 1990; O’Toole & Stankov, 1992), middle age (Pavlik et al., 2003), or old age (Korten et al., 1999). For example, Whalley and Deary (2001) traced 80% of people born in 1921 who took part in the Scottish Mental Survey of 1932 in Aberdeen city (n52,230 from 2,792). They used medical and public databases to find whether people were still alive at age 76 in 1997, 65 years after the IQ test. People with a standard-deviation (15-point) disadvantage in IQ score relative to others at age 11 were only 79% as likely to live to age 76. Further linkage studies of the Scottish Mental Survey 1932 found that lower childhood IQ is associated with earlier death from a variety of diseases, including cardiovascular disease (Hart, Taylor et al., 2003) and stomach and lung cancers (Deary, Whalley, & Starr, 2003). (from Deary, I.J. and Der, G. 2005. Reaction time explains IQ's association with death. Psychological Science, 16, 64-69)

Do you specifically want to know if this trend is continues as the IQ gets increasingly high?--droptone (talk) 12:38, 28 September 2009 (UTC)

And to answer your question specifically, here is a quote from Martin, L.T. and Kubzansky, L.D. 2005. Childhood Cognitive Performance and Risk of Mortality: A Prospective Cohort Study of Gifted Individuals. American Journal of Epidemiology, 162, 887-890: A 15-point advantage in childhood IQ was significantly associated with a decreased risk of mortality (hazard ratio = 0.68, 95% confidence interval: 0.49, 0.93) for IQ scores up to 163; beyond that, the risk of death plateaued.--droptone (talk) 12:47, 28 September 2009 (UTC)

I think it depends on the type of genius. Lots of artistic geniuses seem to die young, perhaps because artistic genius is strongly associated with risky or self-destructive behavior. "Intellectual" geniuses don't seem to follow this pattern, though. (Disclaimer: this is just my own impressions; never seen any data on the question.) Looie496 (talk) 15:57, 28 September 2009 (UTC)

Mozart, George Gershwin, and Irving Thalberg come to mind as artistic geniuses who died young, although it was disease and not lifestyle that got them, as far as I know. On the other hand, Aaron Copland and Irving Berlin both lived to be about 100. →Baseball Bugs ^{What's up, Doc?} carrots 06:12, 29 September 2009 (UTC)

They lived pretty long compared to maths genius Évariste Galois.... --Pykk (talk) 18:28, 29 September 2009 (UTC)

If geniuses died very young - we wouldn't know they were geniuses. That must tend to skew the numbers upwards. SteveBaker (talk) 21:50, 28 September 2009 (UTC)

This is interesting and all but then the question becomes why do people with higher IQ live longer? My guess is it is simply because they come from more wealth, on average, since IQ is not just about how quickly you can learn but also about what you know. More wealth means better education and they are also able to focus on education as opposed to someone who is very poor and has to work early to help the family. So they know more than those exact same people would know if they were very poor. And, a wealthier person is probably less likely to do a very dangerous job, such as being a miner. And, diet is going to be different as well which could have a large effect on life. For those who know more than me, do you think this sounds right or not? Thanks. StatisticsMan (talk) 15:19, 4 October 2009 (UTC)

Innovations in the last 50 years.

I believe there havent been any 'breakthrough' innovations in the past 50 years, in the field of science, or otherwise. Something on the scale of the invention of steam engine, electricity, computer etc.

You have to define breakthrough. Many scientists would disagree with you, though: Sanger sequencing (1975) made it possible to analyze, with modifications over the years, entire genomes; and restriction enzymes (1970) made molecular cloning possible, and with it most modern understanding of molecular biology. Someguy1221 (talk) 08:25, 28 September 2009 (UTC)

The Integrated circuit is now just out of your 50-year limit, but developments in data transmission have been phenomenal in the last twenty years. Does this count as "breakthrough"? Dbfirs 08:28, 28 September 2009 (UTC)

Electricity is not an invention, it's a natural phenomenon. For breakthroughs, consider the Internet, and the WWW that runs on top of it. GPS. If you allow for scientific breakthroughs, dark matter and dark energy are recent and fundamental. The superposition calculus is cool. Most of genetic engineering and DNA releated techniques post-date 1959. The first heart transplant was in 1967, and the moon landing in 1969. Of course, most newer inventions rely on older ones - but in that sense, there has been no breakthrough since some ape hit another with a rock for the first time. --Stephan Schulz (talk) 08:32, 28 September 2009 (UTC)

Yes Stephan, Internet is a good example. Landing on the moon was not something innovative. My point is that we might have become more intelligent in using old inventions and modifying them, but we have lost creativity with regard to new ideas.

Well the personal computer really falls into that range, and that was certainly game changing. How about cell phones and portable music players? Polymerase chain reaction is a good one too. ~ Amory (user • talk • contribs) 11:08, 28 September 2009 (UTC)

Has the OP delivered a declaration or a challenge? I can't see a question. The time from making an invention to it being recognized as having been a 'breakthrough' can be long so it is premature to conclude about recent inventions. Like Stephan Schulz comments about electricity, all inventions are discoveries of principles that were already there, just waiting to be invented.Cuddlyable3 (talk) 11:52, 28 September 2009 (UTC)

Transistor seems to be 55 years old in its present form. Pocket calculator appears to date from 1970, and believe me, it was truly groundbreaking for those of us who couldn't get the hang of either mental arithmetic or slide rules! --TammyMoet (talk) 11:58, 28 September 2009 (UTC)

Other great inventions of the past 50 years. Nuclear magnetic resonance is a bit old (1930's and 1940's), but its cousin Magnetic resonance imaging became practical in 1973 or so, and it is undoubtedly one of the most important modern medical diagnostic tools. Also, while Sputnik falls just barely outside this range (1957), the first practical Communications satellite was put into orbit in 1962 (see Telstar), and communications sattelites are hugely important to the modern world. If we ever move from the carbon economy to the hydrogen economy, then Fuel cells would be a huge innovation. While the principle was devised in the 1830's, the first modern fuel cells used in transportation came about in 1959-1960, so that falls just inside the 50 year window. --Jayron32 14:03, 28 September 2009 (UTC)

If you are only talking about the sorts of things that reconfigure entire societies and economies, the personal computer (something that is quite different from the previous ideas of the "computer") and the internet (and the developments in telecommunications that have been simultaneous with it) probably rank the highest. They are the backbone of our information society and have radically changed how the world works in the past few decades, with no signs of letting up. Additionally, the development of psychoactive medications has been a major game-changer for a lot of people, and signals a very different era in regards to making sense of our own minds that existed previously. And of course there are the advanced genetic techniques which are only now just beginning to have a real impact, but promise a lot more in the future.

Note that there is no reason to suspect there have been "fewer" creative things at all. Compared to the other time periods you are indirectly mentioning, we invent and move forward at a blinding pace. --Mr.98 (talk) 15:33, 28 September 2009 (UTC)

In many cases there have been decades between an innovation and the time it was recognized as a "breakthrough" -- electricity and the steam engine are examples. Fusion power generation, which was developed within the past 50 years, is currently in a state comparable to the earliest electrical generators. Gene sequencing (already mentioned above) has already shown itself as a major breakthrough. Superconductivity is still moving toward widespread usefulness. In fact I think an argument could be made that major breakthroughs have been happening faster than ever. Looie496 (talk) 15:51, 28 September 2009 (UTC)

There are some pretty huge inventions in the last 50 years listed in Timeline of historic inventions, some of the most important of which have not been mentioned above. I think perhaps perhaps hugely important inventions occur so frequently now, that we aren't as impressed by each of them as we would otherwise be. It's like we've grown to expect huge inventions. Red Act (talk) 17:42, 28 September 2009 (UTC)

I'm pretty sure we've had a similar question before and we came up with a similar answer, it depends on your definitions however there have been some very major changes even in the past 20 years which have substantially changed the way many people in developing countries live and work and many people would argue things are changing far faster now then before. Nil Einne (talk) 18:44, 28 September 2009 (UTC)

I would call manned spaceflight a pretty dramatic development of the past 50 years. Robotic exploration of the other planets is pretty dramatic as well. The Cat scan and MRI for medical imaging have reduced the need for exploratory surgery and are a quantum leap ahead of older Xray capabilities. Endoscopic surgery for tumors or defects of the base of the brain i a similar leap forward, compared to older brain surgery techniques. In the power industry, SCADA and computerized relaying were a dramatic breakthrough, compared to older remote control systems and electromechanical relaying, respectively. In the military/spying/assassination field, remote control airplanes which can circle invisibly for tens of hours and then hit a target with Hellfire missiles give dramatic new capabilities. Edison (talk) 19:06, 28 September 2009 (UTC)

I think the changes over the past 50 years are more than simple individual inventions - we've largely transitioned from the industrial age to the information age. As people describe changes in "ages" like that - we've only really had: stone age, iron age, the agricultural age, industrial age and now, the information age...that last change having happened almost entirely in the past 50 years. Not many generations of humans have lived through such a dramatic change. Many of us are able to make a living producing nothing but bits and bytes - with no physical/tangiable 'thing' coming out of the process. Google makes 20 billion dollars a year in a business sector that has only existed for 10 years! We are seriously able to say that all of human knowledge is available to any human who can afford a few hundred dollars to get online. We can communicate around the planet so easily that we've forgotten what it was like to have to wait for news to arrive. The idea that for $1 you could have literally any piece of music you could think of available to listen to within maybe 30 seconds of feeling the desire to do that...that's just stunning. I can talk to my car - tell it to communicate with my cellphone to call my wife on her cell phone - which in turn talks to her car to tell it that the phone is ringing. The car obligingly turns down the radio so she can hear. She tells her car to answer the phone...then we can talk - while on the move - from almost anywhere in the world to almost anywhere in the world.

Admittedly we've had many of the individual inventions for more than 50 years - but the integration of them into one massively interconnected whole is something that was inconceivable in the 1950's. All of this would have been like science fiction to people from the 1950's.

21:47, 28 September 2009 (UTC)

It also depends on the field you are looking at. In the field of music and music production the last 50 years has been essentially one long sustained period of innovation. Pfly (talk) 05:15, 29 September 2009 (UTC)

Betelgeuse Supernova

The article on the star Betelgeuse suggests that it may go supernova within a time to be observable by human civilization and possibly within a lifespan of humans alive today. If Betelgeuse were to do that, what would happen to the Earth? Would there be a danger from the radiation put off by a massive star exploding within a few hundred light years? Would it be dangerous to watch the explosion itself occur? What would it look like? 63.245.144.68 (talk) 11:09, 28 September 2009 (UTC)

Our article states rather clearly: "Since its rotational axis is not toward the Earth and also because of its 430 light year distance, Betelgeuse's supernova will not cause a gamma ray burst in the direction of Earth large enough to damage its ecosystems." What more are you looking for? -- kainaw™ 12:45, 28 September 2009 (UTC)

lol my phisics teacher was talking about this. He said that its a very slim chance.

The crazy thing is that it might have gone supernova when humans were running around the planet on wooden sailing ships, and we still would not know that it happened! Googlemeister (talk) 13:31, 28 September 2009 (UTC)

I'd say that was more paradoxical than crazy.

A paradox requires some kind of contradiction. There is no contradiction involved in the speed of light being finite. --Tango (talk) 15:37, 28 September 2009 (UTC)

Humans never ran around the planet on wooden sailing ships though one sailed around it on one. Cuddlyable3 (talk) 15:51, 28 September 2009 (UTC)

au contraire Googlemeister (talk) 19:09, 28 September 2009 (UTC)

From memory of movies (not a good source I know) it was uncommon to run around on wooden sailing ships, particularly if another ship is shooting at you or about to board you (or vice versa). Besides sounds like good exercise and they didn't have treadmills in those days Nil Einne (talk) 18:39, 28 September 2009 (UTC)

See Near-Earth supernova. SUch an event would likely only affect the Earth if within about 100 light years, which makes Betelgeuse an order of magnitude too far away to have any substantial effect should it go kaboom. Such events HAVE occured, though not on a human time scale, supernovas that affect the earth only happen about once every 1,000,000,000 which means there have only been 4-5 since the solar system formed. There have been supernova which have been observed in human history, see Crab Nebula, though that one is an order of magnitude FARTHER away than Betelgeuse. --Jayron32 13:54, 28 September 2009 (UTC)

So, if this becomes a visible phenomenon during our lifetimes (say, in the next 50 years), shouldn't we be using the past tense in terms of whether the supernova might have occurred about 400 years ago? I realize that many of you know this, I just think it's interesting as a grammatical and conceptual construct - we're hypothesizing that something may have happened about 400 years ago so that we can see it soon, and yet there will be no way for us to know whether it happened (during Shakespeare's lifetime) except when it becomes visible. --Scray (talk) 15:53, 28 September 2009 (UTC)

Potentially Hazardous Objects are rather more of a risk.--Shantavira|^{feed me} 16:08, 28 September 2009 (UTC)

In my experience, it is more common to use the present tense to described events for which the light is just reaching us. It is only when writing for people with little knowledge of astronomy that anyone makes any mention of the fact that it actually happened many years ago. You may also be interested in Relativity of simultaneity, not strictly relevant to your question, but a related topic. --Tango (talk) 17:13, 28 September 2009 (UTC)

Just Imagine, "Supernova -2584371A" :) Sagittarian Milky Way (talk) 19:07, 28 September 2009 (UTC)

Surveying a pyramid

A Gravimeter can be both portable and very sensitive. What would be the resolution achievable by an array of gravimeters used to survey Khufu's pyramid for cavities? Cuddlyable3 (talk) 15:46, 28 September 2009 (UTC)

What really causes the resting cell membrane potential (in animal cells)?

I'm taking Anatomy and Physiology and our course book "Human Anatomy and Physiology" eighth edition by E. Marieb and K. Hoehn published by Benjamin Cummings states that the resting cell membrane potential is caused by the diffusion of Ka+.

However it seems to me that the KA+ ions are passively responding to the forces applied by the concentration gradient and electrical charge difference so that Ka+ is at equilibrium. It seems to me that what CAUSES both the concentration gradients and the voltage differential is NA+ being pumped out of the cell by the Sodium-potasium pump. Since the pump pushes out 3 NA+ ions and only brings in 2 KA+ ions, it would seem to me that the voltage difference is due to this "active" work and not the passive response of the KA+ ions to these forces.

I've looked at several on-line sources including the wikipedia article on cell membrane potential and most of them seem to attribute the voltage differential to KA+ diffusion.

Can anyone provide additional information so that I may understand why the voltage differential is attributed to KA+ diffusion and not the active Na+ pump?

Curious-BioPhysStudent (talk) 16:04, 28 September 2009 (UTC) Curious-BioPhysStudent

• Mmm... Maybe you are considering two different kinds of potential; the negatives charges exceed in the inner side of the membrane, due to the presence of undiffusable, charged proteic anions in the cell. This causes the K+, wich can enter easily the cell, to be brought passively in the inner side, and the Ca2+ to be brought in the outer one. That's what happens in erythrocytes, wich have membrane a potential of about -10 mV. --87.1.124.116 (talk) 17:58, 28 September 2009 (UTC)

• • You could try reading articles such as Resting potential which discuss the subject in detail, and follow various bluelinks from that article to find other info. --Jayron32 18:44, 28 September 2009 (UTC)

The OP is correct that nearly all the work of setting up the membrane potential is done by the sodium-potassium exchange pump, which is powered by ATP. However, the precise voltage that results depends on many other factors, including the permeability of the membrane to Na⁺, K⁺, Ca⁺⁺, and Cl^- ions.

• • • Thanks! —Preceding unsigned comment added by Curious-BioPhysStudent (talk • contribs) 14:31, 30 September 2009 (UTC)

Turning a car 90 degrees

Hi. Assume you have two cars, which both have front wheels that turn to the same maximum angle, but fixed rear wheels. The cars have different spacing between the front pairs of wheels and the back pair of wheels (because the cars are different lengths), and also different spacing between the wheels in each pair (because the cars are wider). Is there a formula to calculate how quickly the back end will turn 90 degress given the angle of the front wheels, the space between a pair of wheels and the space between the front and back pair of wheels (assuming that factors such as downforce etc are equal). I am trying to picture how to figure out how different sized cars would compare in terms of turning 90 degrees into a parking space, but can't find any online sources. Would appreciate any help you could give. Thanks Jimmy Laser (talk) 16:26, 28 September 2009 (UTC)

Our article, Turning radius, might help. I think the turning radius can be estimated from the wheel base, the angle the tires are at with respect to the ground, vehicle length, and so forth; but other experimental details can also affect the result. Nimur (talk) 16:59, 28 September 2009 (UTC)

Thanks, I had looked at that article and also the links it has, but I cannot see anywhere that directly discusses a calculation. I am also not sure if turning circle is exactly the same because the real issue is how soon does the backend finish the 90 degree turn (it probably is the same, but I am just having trouble picturing it). I imagine that the experimental details do make a big difference, but am trying to understand just the hypothetical impact of varying the distances between tires. I imagine it is just a case of working out the forces on the backend of the car, but just don't know how to figure this out. Thanks for your help so far. Jimmy Laser (talk) 17:46, 28 September 2009 (UTC)

Ideally the turning radius should only depend on the maximum angle of the wheels and the length of the car. To find the center of curvature (the point around which the turning car rotates) draw a line along the axis of rotation of the rear wheels, and a line along the axis of rotation of each of the front wheels. Where the lines intersect are your centers of curvature. You'll notice that you get a different point for each front wheel, but the effective center of curvature is probably going to be somewhere in between (probably right in the middle if you're driving slowly). The wider the car, the larger the discrepancy between the two front wheels, but otherwise width shouldn't play a significant factor in turning radius. The turning radius will be proportional to the length of the car. Rckrone (talk) 17:50, 28 September 2009 (UTC)

Apparently car steering corrects for the discrepancy between the centers of curvature of the two front tires (see Ackermann steering geometry), so the angles of the two wheels won't be the same when turning like I assumed above. Rckrone (talk) 18:07, 28 September 2009 (UTC)

Don't forget the differential, which controls the angular speed of each wheel, too. Nimur (talk) 04:19, 30 September 2009 (UTC)

Potatoes no good?

Why are potatoes not counted as one of your 5 vegetables a day?--CruelSea (talk) 17:22, 28 September 2009 (UTC)

I would suspect because while they contain some minerals and vitamins (vitamin C in particular), potatoes are mostly starch and water, i.e. carbohydrates. Much of the vitamin content is also lost in typical preparations. That said, a typical Secundo in Italy can have boiled potatoes or even fries as a side just as well as steamed broccoli. --Stephan Schulz (talk) 17:44, 28 September 2009 (UTC)

Potatoes, like maize and some others, are nutrutionally much closer to breads, and so usually get counted among those, even if part of a side dish. Culinarily, most cuisines would treat Potatoes like a "starch", much like pasta or rice, rather than a vegetable. See vegetable for further information. --Jayron32 18:38, 28 September 2009 (UTC)

from a biochemical basis, "vegetables" is a loose term. it includes things where we eat the leaves and other green parts, which supply one group of nutrients, things where we eat the fruits, like tomatoes and peppers and so on, which are nutritionally closer to their biolgical class, fruits and berries, and things like roots which are a mixed bag with sometimes leafy type nutrients (sweet potatoes, carrots, etc. for instance) and sometimes not so much. then there's rice, which is really a grain, of course. Gzuckier (talk) 20:12, 28 September 2009 (UTC)

However, making a salad from the leaves of potato plants would NOT be recommended. →Baseball Bugs ^{What's up, Doc?} carrots 06:08, 29 September 2009 (UTC)

Agree, not only is it toxic, but it would probably taste terrible! Googlemeister (talk) 15:17, 29 September 2009 (UTC)

Especially if you throw in some rhubarb leaves and crushed acorns. Top that off with some chocolates for dessert - maybe some crunchy frog or anthrax ripple. →Baseball Bugs ^{What's up, Doc?} carrots 17:50, 29 September 2009 (UTC)

Breed of dog with the most powerful sense of smell & Police dog breed

What is the breed of dog with the most powerful sense of smell? 87.1.124.116 (talk) 17:39, 28 September 2009 (UTC)

What are the most important features for a breed of dog used by policemen for discovering drugs or corpses? 87.1.124.116 (talk) 17:39, 28 September 2009 (UTC)

The Scent hound article says those dogs are generally considered to have the greatest sense of smell; you'll probably have to dig through the breed links in that article for specific breeds. The article Police dog has a list of breeds used for that profession (and the list itself has its own article, linked to in the Police Dog article). Detection dog has a few links to explore. Comet Tuttle (talk) 18:08, 28 September 2009 (UTC)

The Black and Tan coon hound probably has the most sensitive ability to detect and follow cold scent. Other factors may dictate the use of bloodhounds for tracking people. Edison (talk) 19:01, 28 September 2009 (UTC)

(ec)Have read the article Police dog? It mentions Labrador Retriever, Springer Spaniel, Bloodhound and Beagle as breeds able to sniff out bombs and drugs. Beagles are used in airports because they do not worry most passengers. Desireable qualities in a police dog are intelligence, loyalty, and a willingness to be trained and worked. Dog breeds that have extraordinary sensitive noses are Scent hounds one of which is the Bloodhound. Cuddlyable3 (talk) 21:10, 28 September 2009 (UTC)

Wow, that helps. Thank you, friends. I have a last question: wich is the canid in general with the most powerful sense of smell? 87.10.128.11 (talk) 01:40, 29 September 2009 (UTC)

emulsifiers

i need a comprehensive list of E numbers and their sourceMihir1825 (talk) 18:36, 28 September 2009 (UTC)

i have tried best to collect present info from this encyclopedia, but it is not sufficient. i need to know thoroughly the source of emulsifiers being veg or non veg.

I have removed the copied list of text. Interested readers can find the list at E number. There's not really a need to duplicate the whole thing here. If your concern is over keeping "kosher" or "halal", there is this resource: [8] which lists the additives acording to religious dietary traditions, but it does not explicitly list the original source of the additives. --Jayron32 18:41, 28 September 2009 (UTC)

Perhaps the OP is vegan? Nil Einne (talk) 19:28, 28 September 2009 (UTC)

Furthermore, for people with strict dietary practices, like vegans OR people with religious restrictions, may find that sticking to Whole foods may be easier than trying to track down the source of every additive. --Jayron32 20:20, 28 September 2009 (UTC)

By the way the E in E-number doesn't stand for emulsifier.83.100.251.196 (talk) 20:54, 28 September 2009 (UTC)

Here http://www.veggieglobal.com/nutrition/non-vegetarian-food-additives.htm or http://www.vegsoc.org/info/enumbers.html 83.100.251.196 (talk) 20:57, 28 September 2009 (UTC)

Human Mind Altering Parasites, Bugs, etc

Are there other human mind-altering parasites or bugs besides Toxoplasma gondii? I am looking for something like Dicrocoelium dendriticum that affects ants. --Reticuli88 (talk) 18:51, 28 September 2009 (UTC)

Rabies? Nil Einne (talk) 19:24, 28 September 2009 (UTC)

High fevers can cause delusions and can be induced by a great number of pathogens such as that which causes Dengue Fever or malaria. PS that Toxoplasma gondii is one of the more interesting species I have heard of. Making mice attarcted to cats! Googlemeister (talk) 19:35, 28 September 2009 (UTC)

depends on your definitions and where you draw the lines. No doubt that somebody with a bad cold behaves and thinks differently than when he's in good shape, for instance. Gzuckier (talk) 20:05, 28 September 2009 (UTC)

A Drug dealer is a human mind altering parasite. Cuddlyable3 (talk) 21:40, 28 September 2009 (UTC)

Religion. Imagine Reason (talk) 14:48, 30 September 2009 (UTC)

Mushrooms

Are mushrooms considered more plant than animal?--Reticuli88 (talk) 18:54, 28 September 2009 (UTC)

Mushrooms are fungus which is neither plant nor animal. Therefore, comparing them to either a plant or animals is going to be kind of like trying to determine if an airplane or a car is more like a boat. It is mostly stationary like a plant and has cell walls, but the material of the cell walls is not the same as plants. Googlemeister (talk) 19:06, 28 September 2009 (UTC)

Personally, I'd consider them more plant than animal, but scientifically I believe they have their own kingdom (Fungi), which is closer to animals than plants on the evolutionary cladogram.129.65.196.121 (talk) 19:09, 28 September 2009 (UTC)

See also Opisthokont or [9] for example Nil Einne (talk) 19:20, 28 September 2009 (UTC)

as is often the case, depends on how you define/classify/draw the lines. fungi are biochemically closer to animals (made of chitin, not cellulose; no chlorophyll) but behave more similar to plants, in general. Gzuckier (talk) 20:14, 28 September 2009 (UTC)

Plants are a subclass of algae, which split off from the other eukaryotes before a lot of the other kingdoms did. You really should look into plant and fungi alternation of generations (which give interesting evolutionary clues). Fungi are scavenging heterotrophs and spread much more quickly than do plants (which tend to stay rooted in one location). Remember, sessile sponges are animals too -- happened one day that one line of spongeish organisms decided to have the ability to use their vascular current channels for flotation and propulsion. John Riemann Soong (talk) 23:31, 28 September 2009 (UTC)

supersonic speed

If you have a hypersonic aircraft (say mach 10), would you be able to hear the noise from it's engines while you are flying along? I know on the Concorde jet you could because the speed of sound through metal is like 4x faster then air, but would you still get the noise even if you were surpassing THAT speed? Googlemeister (talk) 19:29, 28 September 2009 (UTC)

Yes you'd definitely hear the sound conducted through the material of the aircraft, though not through the air outside unless you're at the back and the engines are near the body of the aircraft.. The speed the plane goes at makes no difference to what happens inside, you'll still be able to talk to the person next to you. We're all moving far faster than the speed of sound round the sun and you can't even tell it without astronomical measurements. Dmcq (talk) 19:39, 28 September 2009 (UTC)

(ec) I would guess "yes". Speed is relative. You are stationary relative to the engines, so the sounds should have no problem reaching you. --Tango (talk) 19:40, 28 September 2009 (UTC)

True I forgot about the conduction through the aircraft body. What if there was a second such craft flying in formation with me 300ft to my right, could I hear his engines (assuming I could differentiate between his engine noise and my own craft's? Googlemeister (talk) 20:19, 28 September 2009 (UTC)

No, the sound wouldn't be able to reach you. If you have a supersonic plane going overhead you won't hear anything until the plane has gone past and the sonic boom reaches you. Dmcq (talk) 20:41, 28 September 2009 (UTC)

No, the sounds would be carried backwards by the air faster than it propagates, so it would never reach the other plane. --Tango (talk) 20:46, 28 September 2009 (UTC)

If the supersonic aircraft are close enough and long enough for their shock waves to overlap, there would be turbulence and I suspect that sound of the other aircraft would be heard through the airframe.Cuddlyable3 (talk) 21:36, 28 September 2009 (UTC)

Let me expand on the point "speed is relative" made above. What is important is the speed of the transmission medium relative to you and the source of the sound. You will always hear the sound conducted through the body of the aircraft because the speed of the body relative to you and the engines is zero. You will not hear the sound conducted through the air (unless the engines are almost directly in front of you, as Dmcq says) because the speed of the air relative to you and the engines is faster than sound. --Anonymous, 04:28 UTC, September 29, 2009.

In today's technology, building a zero Enertia vehicles (auto or airplane)

Is it possible in today's technology to create a zero-enertia vehicles? --Reticuli88 (talk) 19:46, 28 September 2009 (UTC)

Is zero Inertia what you meant? if so the answer is no - since the mass of the vehicle would have to be 0. Still impossible with todays technology.83.100.251.196 (talk) 19:58, 28 September 2009 (UTC)

I assume that you mean "inertia" rather than "enertia". In that case, no. Inertia is a fundamental property of all mass. Star Trek's "inertial dampening field" remains pure fiction with no basis in reality. — Lomn 19:59, 28 September 2009 (UTC)

The Zero Inertia powertrain is an innovative powertrain concept in which kinetic energy is exchanged between an additional flywheel and a car engine’s inertia. Cuddlyable3 (talk) 21:25, 28 September 2009 (UTC)

That's just a type of regenerative braking isn't it? You would still feel the acceleration, it's not like Star Trek's inertial dampeners. --Tango (talk) 21:53, 28 September 2009 (UTC)

Sorry Inertia is a fallacious concept. Only mass exists and that obeys Newtons laws which did not mention inertia AFAIK--Tappet (talk) 21:32, 29 September 2009 (UTC)

Effects of the acidity of juice

What kind of effects would a very acidic juice have on the human body? Has any research been done about this?--Dlo2012 (talk) 20:36, 28 September 2009 (UTC)

For stuff like lime juice the effect would the same as pickling. For strong acids see John George Haigh who performed the experiment. Dmcq (talk) 20:47, 28 September 2009 (UTC)

I'm sorry, but what I meant was juice that is consumed by a person. Orange juice would be an example.

If you mean naturally occurring strongly acidic juices such as lime juice, then its pH of around 2 is about the same as gastric acid, though the stomach can produce much stronger acid up to 0.8 pH. The stomach is designed to cope with this, but the throat and gullet aren't. Dbfirs 21:28, 28 September 2009 (UTC)

Well I've used lime juice in marinades but to really break meat down you'd want to use enzymes as well like the stomach does. Dmcq (talk) 22:47, 28 September 2009 (UTC)

(original research) When I eat lemons, the juice seems to etch the teeth a bit. Edison (talk) 23:53, 28 September 2009 (UTC)

Not that original! ;-) Dentists warn against drinking strongly acidic juices too often! I use to say that my teeth get a "woollen sweater"... ;-)--Janke | Talk 14:10, 29 September 2009 (UTC)

[A web site ] says the ph of lemon juice is 2.3, lime juice is 1.8-2, orange juice is 3-4, vinegar is 2.4-3.4, stomach acid is 1-3. Those who binge and purge often eat the enamel off their teeth, from the stomach acid. Acid erosion says fruit juice and soft drinks can demineralize teeth and remove enamel. That article says wine (pH 3.0-3.8) can erode teeth. [10] says Coca Cola Classic has a pH of 2.5. Edison (talk) 21:46, 29 September 2009 (UTC)