# Wikipedia:Reference desk/Archives/Science/2011 October 6

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# October 6

## Nepeta cataria

Hello. Can anyone explain why on Nepeta cataria, there is no phylum or class listed in the taxo box? 03:12, 6 October 2011 (UTC)

Angiosperms

Amborella

Nymphaeales

Austrobaileyales

Mesangiospermae

 magnoliids Chloranthales

monocots

 Ceratophyllum eudicots

The phylogeny of the flowering plants, as of APG III (2009).
It's not just catnip really. Those (unranked) 'ranks' above the ordinal level in plants are clades, which do not actually have taxonomic ranks. This is because all plant articles in Wikipedia follow the modern APG III system of the Angiosperm Phylogeny Group. This system is more accurate than the old Linnean system because it uses molecular genetic data for grouping plants. Remember that the Linnean system was established before the discovery of evolution and the DNA. So they were traditionally and inaccurately grouped simply by morphological and biochemical characteristics.
For example, flowering plants (angiosperms) were once grouped into two classes - Monocotyledons and Dicotyledons based on the number of cotyledons. Obviously this is a rather unreliable way to classify plants. APG discovered that though monocots are monophyletic (that is, they are all descendants of a common ancestor), dicots are not. Though most dicots are monophyletic (now grouped into the clade Eudicots - 'true dicots'), not all of them descended from a common ancestor. Magnoliids, for example, exhibit two cotyledons and have been traditionally classified under dicots, but they actually diverged earlier than eudicots (see phylogenetic tree on the right). Some genera, like Amborella, are also basal (arising earlier than other clades) and thus can not be classified under any of the traditional orders (as of APG III, the single species of the genus has been classified under their own order, separate from the rest). Others are simply not well understood like members of the family Sabiaceae, etc.--  04:07, 6 October 2011 (UTC)
I don't think it is true that all Wikipedia plant articles use the modern system, although that is probably a goal -- at the moment there is still a lot of variability. Looie496 (talk) 14:53, 6 October 2011 (UTC)
It's preferred (in angiosperms at least), like animal and microbio taxonomy, there's always disagreement on which should be in which among specialists. Add to that good faith editors that use outdated classifications (bananas and plantains for example, were still classified as Musa × sapientum and Musa × paradisiaca a year ago... :/ Using autotaxoboxes helps standardize things at least, though there are necessary exceptions. --  19:23, 6 October 2011 (UTC)

## induction motor

can a 3HP three phase induction motor be run at single phase by making the single phase winding inside that 3phase motor?? — Preceding unsigned comment added by 115.242.158.41 (talk) 03:57, 6 October 2011 (UTC)

I have not tried to do that. I have run a 3 phase motor on 2 phase power. That is not very uncommon. When the only power available is 1 phase power, a static 1 phase to 3 phase power converter will produce 3 phase power to get a 3 phase motor started. Then, the static converter will drop to 2 phase power to continue running the motor (yes, this can damage 3 phase motors not designed for 2 phase power). I don't see how a single phase will keep it rotating under any load. Unlike a single phase motor, a three phase motor doesn't have a capacitor to rotate the incoming power and create a second phase (technically, single-phase motors convert the power to 2 phase power internally and are really 2 phase motors). It is possible that some very fancy three phase motors are internally six-phase motors (using the same technology as a single phase motor). Then, I'd be certain that if you got it started, you can keep it spinning on a single phase of power. -- kainaw 13:19, 6 October 2011 (UTC)
I've seen three phase motors burn out when only single phase power is furnished to them, but I cannot rule out some motor being capable of being internally rewired to allow single phase operation, perhaps at a reduced HP. I remember hearing one three phase motor driving ventilators slowly wind down over perhaps a 2 minute period when it was single phased while running. It burned out due to the prolonged overload. Engineers have gotten in trouble for failing to provide protection for a motor against such single-phasing, when they specify the protective circuit for a large motor. If the motor is spun up with 3 phase, then "Alternating current fundamentals" by Herman says it will continue to turn if only one phase is powered, with a "greatly reduced capacity." It would overheat and burn out if it were called on to operate the full 3 phase load on 1 phase. A single phase applied to a stopped 3 phase motor would not produce the phase shift or rotating magnetic field needed to start it turning. The question was a bit fuzzy. Did the OP mean "Could a 3 phase motor also be wound with a single phase winding, along with provision for a capacitor?" If so then the answer is likely "Yes." It would not seem efficient or economical to build motors with that capability. Here is an account from 1918 of how someone added an external phase splitter to start a three phase motor, which was then switched to operate direectly from a single phase source when it got up to speed. Edison (talk) 18:41, 6 October 2011 (UTC)
A three phase motor operated from single phase can also be used to produce the missing phases, and thereby power other three phase motors, or produce dangerous and unexpected backfeed on the phases thought to be dead, endangering utility workers. Edison (talk) 15:43, 7 October 2011 (UTC)

## homology / analogy of env viral coat proteins, across mammals and Drosophila

I'm designing the beginnings of a selective intercellular transport protocol, and I'd like to take advantage of some of the interesting properties exhibited by HIV env (perhaps make a pseudotype). I note that Drosophila has some endogeneous retroviruses, such as gypsy which too, codes for an "env-like" protein. However, when I actually do a BLAST search between gypsy env and HIV env, the alignment is quite poor, on both a protein level (for gypsy open reading frame 3, which codes for env, and HIV gp120 / gp160 etc.) and a nucleotide level -- often the query coverage is less than 20%. How possible is that HIV env and gypsy env would just keep a few conserved domains and rapidly mutate all the non-critical domains, and that BLAST scores aren't useful for detecting homology between retroviruses of distant species?

Other than the receptors, are there significant differences in the mechanisms of HIV-1 env and gypsy env? Could I use HIV env in Drosophila? This is because the required receptors on the target cell required for gypsy env to induce efficient infections remain poorly-characterised, unlike the receptors/coreceptors required for HIV env. elle vécut heureuse à jamais (be free) 05:05, 6 October 2011 (UTC)

It may be difficult to identify homology, particularly if the entry process has diverged substantially (i.e. if very little homology exists). For a search like this, I would expect PSI-BLAST (PMID 9254694, available as an algorithm choice on the BLAST page) to be more useful for your purpose than BLAST. PSI-BLAST forms a PSSM from BLAST results, and uses the highest-scoring positions in an iterative BLAST search - it's a remarkably powerful process! -- Scray (talk) 02:05, 7 October 2011 (UTC)

## Eating "unpleasant" foods

There are many foods that people eat routinely that are in some sense "unpleasant", such as spicy, sour, and bitter foods. Many of these contain chemical irritants that "burn" your mouth or otherwise might discourage some people from eating them, and yet many of us (myself included) enjoy eating them frequently. Presumably such qualities originally evolved to discourage animals from eating these plants, though now they are paradoxically the reason that we intentionally cultivate many foods for consumption.

Now, what I am really wondering about is whether the irritants in "unpleasant" foods have an impact beyond the mouth and immediate process of eating them. For example, does eating such foods also tend to irritate the stomach or bowel in a way that can make people more prone to digestive problems such as stomach aches, heart burns, diarrhea, etc? I know people who have given such an explanation for not eating spicy food, but I'm not sure if there is good empirical evidence for this or not. Dragons flight (talk) 07:56, 6 October 2011 (UTC)

Strictly hearsay, but I've known people who said they ate stuff that was so strong and spicy they could feel it all the way through their digestive systems. ←Baseball Bugs What's up, Doc? carrots→ 09:42, 6 October 2011 (UTC)
Eating certain spicy foods, irritates the digestive tract. Normally, this is not a problem however, regular consumption of such foods can result in ulceration which may lead to further complications. In fact, it has been proven that daily consumption of curries usually causes the stomach lining to thin considerably. Plasmic Physics (talk) 09:55, 6 October 2011 (UTC)
[citation needed]. For decades it was believed that alcohol and spicy foods caused peptic ulcers, but that was shown to be a myth wasn't it? [1][2][3]. Our article and those external links generally say that spicy food may aggravate an existing ulcer, but they don't cause them. The last link even suggests that spicy food may partially protect against ulcer formation in healthy people. Since the 2005 Nobel prize was awarded for showing that most ulcers are caused by bacteria, I pretty much assumed that we would be discussing other kinds of digestive problems when I asked the question. Also, where are you getting the curry info from? Dragons flight (talk) 18:59, 6 October 2011 (UTC)
It's difficult to track down the original research paper, but the main point is that acute gastritis is caused by the phenolic compounds present in "hot" foods, such as capsaicin, this compound induces the secretion of hydrochloric acid in a similiar way that alcohol does. The increased acidity of the stomach acid erodes the stomach lining, and causes inflamation. Curries have a complex chemical makeup, while they contain many healthy chemicals, they also contain unhealthy ones. It's like a candle, oxygen feeds a flame, but if air flow is too great, it extinguishes the candle. The short of it is, moderation is a virtue. Plasmic Physics (talk) 00:57, 7 October 2011 (UTC)
Within the last ten or so years I read an article about chicken farmers feeding hot pepper to the hens. They (the hens, not the farmers) didn't mind the flavor, it discouraged rodents from eating the feed, and somehow the irritation of the digestive system made the hens healthier. Now when I search for "hen pepper health" all I find are chicken soup recipes. I did find refs for using pepper in bird seed to discourage squirrels, which say that birds do not mind the hot pepper taste:[4] Edison (talk) 15:55, 7 October 2011 (UTC)
Yes, most/all? birds aren't sensitive to capsaicin, it's usually suggested the capsaicin evolved in chillis partially for this reason as it discourages mammals from eating the fruit but not birds who are the better seed dispersal agent (for those plants), see Chili pepper#Evolutionary advantages. Nil Einne (talk) 17:08, 7 October 2011 (UTC)
I saw the headline for this a few hours ago but it just occured to me it has some minor relevence here, there can be acute problems [5] [6] [7]. I noticed Capsaicin#Effects of dietary consumption which is of greater relevence (that article also mentions the acute effecs). Nil Einne (talk) 17:15, 7 October 2011 (UTC)
I don't see what is so unpleansant about sour things. I drink vinegar, and eat lemons as if they were oranges. Plasmic Physics (talk) 23:28, 10 October 2011 (UTC)

## Centipedes

Specifically, Scutigera coleoptrata, or the "house centipede". They look like a little mustache running along. Creepy critters. But supposedly they feed on other, creepier critters. One thing is unclear or unstated in the article: Do they pose any threat to humans? That is, do they bite? Or are they harmless? Does anyone here know? Thank you! ←Baseball Bugs What's up, Doc? carrots→ 09:39, 6 October 2011 (UTC)

Some are toxic. Plasmic Physics (talk) 09:46, 6 October 2011 (UTC)
Technically they sting, not bite since their venom organs are attached to their legs. That sting might be painful to humans. Googlemeister (talk) 13:21, 6 October 2011 (UTC)
They don't seem to be considered dangerous to humans. We have the dangerous scolopendrid centipedes (locally known as ulihipan), among which is Ethmostigmus rubripes which can reach a little over six inches in length (compared to one or two inches in American house centipedes). ;) They have the same reputations out here as scorpions (i.e. if you see one inside the house, kill it). --  19:47, 6 October 2011 (UTC)
Centipede bite amazingly .. For the record I was bitten by the European Centipede - not painful like a wasp sting - but very strong - like being kicked by a mule (I never been kicked by a mule so I'm guessing). 87.102.42.171 (talk) 23:21, 6 October 2011 (UTC)
Being kicked by a mule is like being punched in the gut only more painful, it is a truely breathless experience. Plasmic Physics (talk) 02:04, 7 October 2011 (UTC)
How might one get bitten by Scutigera coleoptrata? I've seen them skittering along the floor. I've deliberately stomped out the lives of a few, wearing shoes of course. I can't imagine trying to pick one up in my hands. They move too fast to catch. Bus stop (talk) 02:12, 7 October 2011 (UTC)
A pair of legs on their first trunk segment have been modified into venom-injecting appendages (forcipules). Think of them as poison syringe-tipped hands. This is the origin of the scientific name for their taxon - Chilopoda means "lip leg". Click to see forcipules on Scutigera--  09:14, 7 October 2011 (UTC)
I found myself sharing a bed with one in Turkey once, so I could easily have been 'bitten', although I wasn't. I also managed to catch it in a water bottle and release it in the hotel grounds. Mikenorton (talk) 09:50, 7 October 2011 (UTC)
I think you should be given credit for being kind to centipedes. Did the centipede even say thank you or give you a reduced price coupon to Foot Locker? Bus stop (talk) 16:10, 7 October 2011 (UTC)
Maybe it gave him a "High 100". ←Baseball Bugs What's up, Doc? carrots→ 23:25, 8 October 2011 (UTC)
lol Bus stop (talk) 16:13, 9 October 2011 (UTC)

## Day Length and Seasons

I know that the earth's tilted axis is the primary reason that we have seasons, but how much of an effect does the varying day length have? --CGPGrey (talk) 10:07, 6 October 2011 (UTC)

I suggest the articles Season and Seasonal lag. ←Baseball Bugs What's up, Doc? carrots→ 10:22, 6 October 2011 (UTC)
There is no mention of the % effect that day length has on seasons in those articles. --CGPGrey (talk) 10:27, 6 October 2011 (UTC)
That might be a bit more detail than an encyclopedia would get into. OR, it might just be that no one has researched it and added it. Obviously, the length of the day has a qualitative effect on both atmospheric and oceanic temperatures. An exact percentage might be hard to come by, as it's liable to vary from season to season, due to factors such as el nino, la nina, and any number of other things. ←Baseball Bugs What's up, Doc? carrots→ 10:32, 6 October 2011 (UTC)
Part of the problem is that it would essentially be a 3-dimensional table: One dimension would be the average daily temperature. Another would be the number of hours and minutes of sunlight per day. The third dimension would be the latitude. Obviously, a lot of info, and probably beyond the scope of a wikipedia article. Have you tried googling this subject? ←Baseball Bugs What's up, Doc? carrots→ 10:38, 6 October 2011 (UTC)
The inclination of the Earth's axis relative to the Earth's orbital plane causes the cyclic variation in the duration of daylight and solar heating, and this variation causes the seasons. Therefore it is reasonable to say that the seasons are due entirely (100%) to inclination of the Earth's axis. Dolphin (t) 10:54, 6 October 2011 (UTC)
But that's not the whole story, otherwise the coldest day of the year would be the Winter Solstice and the hottest day would be the Summer Solstice (or the opposite in the southern hemisphere). But thanks to seasonal lag, the coldest day of the year is liable to be in early February, and the hottest day in early August, by which time the days are longer than the winter solstice and shorter than the summer solstice, respectively. And besides, the OP apparently wants numbers rather than qualitative observations. ←Baseball Bugs What's up, Doc? carrots→ 11:00, 6 October 2011 (UTC)
I agree that the seasonal extreme temperatures don't occur on the solstices, but that doesn't detract from the fact that the Earth's seasonal variations are due 100% to the inclination of the Earth's axis relative to its orbital plane. All other observations, such as seasonal variation in duration of solar radiation and seasonal variation in ocean temperatures, are consequences of the Earth's inclination, not independent causes of seasonal variation. Dolphin (t) 11:12, 6 October 2011 (UTC)
OK. So the simple answer to the OP's question is, indeed, 100 percent. One way to look at it is to look at the extremes. The poles never get warm, but they are not as cold in their respective summertimes when they get 24-hour sunlight, vs. wintertimes when they get none. And at the equator, it's pretty much the same all year around, apart from daily variations due to weather changes. ←Baseball Bugs What's up, Doc? carrots→ 11:16, 6 October 2011 (UTC)
I understand that the seasons are caused 100% due to the tilt, but that's not my question. There is increased solar radiation during the summer because the hemisphere is 'facing' the sun, but there is also increased radiation because the duration of exposure is also increased. How much of the increase in solar radiation is attributable to the increase in day length? --CGPGrey (talk) 13:49, 6 October 2011 (UTC)
Here's a plot of solar irradiance during the summer and winter solstices for 40° of latitude [[8]]. The increase in solar radiation is the area between the two curves. You're asking which fraction of the area is due to the summer curve being higher, and which fraction of the area is due to the summer curve being wider. I don't think that's mathematically defined. 98.248.42.252 (talk) 15:59, 6 October 2011 (UTC)
Isn't the increased duration of exposure also caused by the axial tilt? The sun is up longer because the hemisphere is tilted toward the sun. thx1138 (talk) 16:46, 6 October 2011 (UTC)
I disagree with Dolphin's assertion that the Earth's axial inclination is responsible for 100% of the seasonal variations. Because the Earth's orbit is also slightly eccentric, its distance from the Sun varies by about 5,000,000km (about 3.34%) between aphelion (currently around 04 July) and perihelion (03 January), resulting in about 6.9% greater insolation at perihelion. This certainly must have some effect on seasonal temperature variations (ameliorating Northern hemisphere winter temperatures, for example), though as our Earth's orbit article states, the effect is not great compared to that of axial tilt. Nevertheless it is important when considering the Milankovitch cycles. {The poster formerly known as 87.81.230.195} 90.197.66.175 (talk) 13:57, 6 October 2011 (UTC)
The Earth's tilt is 100% of the reason for the existing seasons, but yes, winter in the Northern hemisphere would be a few % colder (probably only 1 or 2%, depending on what you measure percentages of) if the Earth were at its furthest point from the sun instead of its nearest point. The proportion that is attributable to angle of incidence, compared with the effect day length, will depend not just on latitude but on cloud cover, wind speed and direction, and probably several other factors, so it is unlikely that we can find an answer to the question. We need to decide what we are measuring the proportion of (probably temperature, but this has a fixed point only at −459.67 °F). I wonder if anyone has published any research comparing angle of incidence effect with day length effect. They would be difficult to separate because they are closely related. Dbfirs 12:07, 7 October 2011 (UTC)

## oxidation no. in halogens

my teacher said that oxidation no. of Halogens like fluorine and iodine in their peracids is +7 not -1 like HClO4 but i want to know the other peracids which i must calculate the oxidation no. of their halogens by +7 not -1 — Preceding unsigned comment added by Mido22 (talkcontribs) 13:00, 6 October 2011 (UTC)

Fluorine does not have a VII oxidation state, only the lower halogens do. All the lower halogens form "peracids" perchloric acid, perbromic acid, periodic acid. It's not just the peracids, where the VII state exits - iodine heptafluoride, dichlorine heptaoxide, the list is really inexhaustive. Plasmic Physics (talk) 13:41, 6 October 2011 (UTC)
Hypofluorous acid is not fluorine in a +7 oxidation state, but it's still pretty damn cool. It's a good source of oxygen radical. elle vécut heureuse à jamais (be free) 23:01, 6 October 2011 (UTC)
Which is the strongest oxidant, chlorine trifluoride, or fluoroantimonic acid? It has been said that in case of an accidental spill of chlorine trifluoride, the most appropriate response is to run. It eats through concrete, don't you know? Plasmic Physics (talk) 01:05, 7 October 2011 (UTC)
It would be good to have a strongest oxidant redirect. A very good substance for stripping electrons off other atoms would be the U92+ ion. Graeme Bartlett (talk) 00:19, 8 October 2011 (UTC)
It's a trick question: The strongest oxidant is a charged capacitor. I think we can get them up to several million volts now. Buddy431 (talk) 04:45, 8 October 2011 (UTC)
I thought that if you work with chemicals, the approperiate response to any accident is to run, because your life is worth more than all the lab devices. In what respect does chlorine trifluoride differ? – b_jonas 18:30, 8 October 2011 (UTC)
What I mean is that it is an unstoppable force, it consumes everything in its path. There is no way for emergency services to control it. It's like perpetually lit thermite, that only stops buring once it is completely consumed. There are very few materials that can withstand it. Plasmic Physics (talk) 23:27, 8 October 2011 (UTC)

## Dark energy and the local cluster

Is the local cluster expanding due to dark energy, contracting due to gravity, or at a steady state (by which I mean, whether it's expanding or contracting is statistically insigificant given the margin of error, or that some parts are expanding and others contracting)?

What can this tell us about dark energy and a possible equation for determining the strength of dark matter in a given area? I'm curious if the evidence points to a cosmological constant (i.e., that the vacuum of space necessarily pushes matter apart as an inherent property) or to a scalar field (e.g., a fifth fundamental force, heretofor undetected).

I'm also curious at what point dark energy seems to overpower gravity; am I correct that the equation for gravity is ${\displaystyle {\frac {k}{r^{2}}}}$ whereas the equation for dark energy is ${\displaystyle {\frac {k}{r^{x}}}}$ where ${\displaystyle 0<}$${\displaystyle x<2}$ (part wherein "${\displaystyle 0" stricken; actually, ${\displaystyle x}$ could theoretically be zero or negative Magog the Ogre (talk) 19:16, 6 October 2011 (UTC)) (it seems most likely to me that ${\displaystyle x=1}$, but I can't make that assumption precisely)? Magog the Ogre (talk) 16:49, 6 October 2011 (UTC)

A scalar field would lead to an attractive force scaling as ${\displaystyle {\frac {k}{r^{2}}}}$ if the particle is massless, so that won't work. Dauto (talk) 17:10, 6 October 2011 (UTC)
Galaxies in the local group tend to be orbit around each other, so overall there isn't any significant expansion or contraction. --Tango (talk) 17:51, 6 October 2011 (UTC)
re: Dauto: according to the article dark energy, scalar fields are in fact considered a possibility, with quintessence and moduli considered subpossibilities.
re: Tango: I'm looking for data that's a bit more specific than that. Magog the Ogre (talk) 19:10, 6 October 2011 (UTC)
What data would you like? --Tango (talk) 21:28, 6 October 2011 (UTC)
The simplest form of dark energy, a cosmological constant, can be approximately represented as ${\displaystyle F\propto kr}$. In other words, the force grows in direct proportion to the separation distance rather than falling off with distance. The effects of dark energy are just barely perceptible on the scale of several billion light years. If dark energy truly has the form given above, then there is no reason to expect that any measurable impact would occur to structures as small as the local cluster. Dragons flight (talk) 19:21, 6 October 2011 (UTC)
re DF: wait - the force actually expands with distance? That means that a galaxy which is 12 billion ly away is pushing on our planet with greater power than a galaxy at 10 billion ly. If this is correct, wouldn't it eventually mean the disintegration of all matter in the universe? (because, as the universe expands, the distance to massive objects becomes greater, and thus more powerful, such that the forces would become incredibly high... or am I wrong?).
re Tango (not responding inline above; honestly I dislike inline comments because it disrupts the flow): what is the redshift/blueshift of other galaxies within the cluster, how does this relate to their distance from ours, and how is this comparable to other galaxies? I'd think that a measurement of the redshift of these galaxies, versus the redshift of other clusters could give us a pretty good estimation of the scales on which dark energy works. Magog the Ogre (talk) 21:37, 6 October 2011 (UTC)
Yes, a cosmological constant dominated universe will eventually enter a period of exponential inflation, and all structures that are not already gravitationally bound will eventually fly so far apart that they are no longer observable. See also: Big Freeze, Dark energy#Implications for the fate of the universe. Dragons flight (talk) 21:46, 6 October 2011 (UTC)
Re Magog the Ogre: Quintessence doesn't produce a repulsive force between objects. Not the way you're thinking. We are not being pushed away by distant galaxies. Quintessence creates an expansion of space (In other words, it's a dynamical form of cosmological constant). That's why the further apart galaxies are, the faster they seem to accelerate from us. That happens because there is more space in between to expand. That can be modeled as a repulsive force that is proportional to the distance as Dragons flight pointed out but it isn't an actual force between distant objects. In fact, An actual force between distant objects that increases with the distance would have to propagate faster than light. Dauto (talk) 01:20, 7 October 2011 (UTC)
Different galaxies within the local group have different redshifts/blueshifts (some of each). There is no correlation between redshift and distance. Redshifts change over time (and change from redshifts to blueshifts and back again) as galaxies move around their elliptical orbits. --Tango (talk) 18:35, 7 October 2011 (UTC)
No it wouldn't. If we can see the galaxy, we can feel the force from it. Magog the Ogre (talk) 01:46, 7 October 2011 (UTC)
Yes, that's right, and as Dragons flight explained above, and I quote "all structures that are not already gravitationally bound will eventually fly so far apart that they are no longer observable". Neither will we be able to see those far away galaxies nor will we be able to fill any force produced by them. They will effectively be beyond the horizon. Dauto (talk) 04:23, 7 October 2011 (UTC)
Are you sure about that? I think that the only reason we won't be able to see them not because they're beyond the event horizon, but because they will be redshifted into the CMBR, meaning there will be too much noise. Magog the Ogre (talk) 15:23, 8 October 2011 (UTC)
Yes, I'm sure. At some distant point galaxies become in fact causally disconnected from us. They are moving away from us faster than the speed of light! (without any contradiction with special relativity). That's what makes it possible for the diameter of the observable universe to be larger than twice the age of the universe (c=1). We see the light of those distant galaxies because they were still causally connected to us back when they produced the light we see now. But they are now causally disconnected so we will never see the light they are producing right now (not even a redshifted version of it). See observable universe. Dauto (talk) 15:18, 9 October 2011 (UTC)
Read also Hubble volume and Event horizon#Particle horizon of the observable universe. --Dauto (talk) 15:40, 9 October 2011 (UTC)

I would like more information on the Marbled Lungfish (Protopterus aethiopicus). According to Wikipedia, it has 133 billion base pairs in its genome, which is more than 40x the size of the human genome. My questions are as follows:

• How does it fit all of that in each of its cells? Does this animal have any evolutionary adaptations to maintaining such a large genome (wrapping it up more tightly, larger cells on average, more cell space devoted to the nucleus)?
• How much of it is junk DNA?
• How long does mitosis take for this creature? Any special adaptations for this process?

Thanks. --70.122.116.118 (talk) 18:09, 6 October 2011 (UTC)

Disclaimer: I know next to nothing about the genome of the Marbled Lungfish. However, tracing the references from the citation in the artice, the quoted genome size is based on estimates from cell size published in 1972 (here). I can't find anything more recent and it doesn't seem that the lungfish genome is among the 1215 eukaryotic genome projects currently underway. Since the genome size estimates are based on the larger cell size, it appears that the answer to your first question is "unusually large cell size" (1978 article by the same author). Since we don't have an actual genome sequence for the marbled lungfish, the answer to your second question is likely unknown, although based on other genome sequences, there do seem to have been genome duplication events during the evolution of fishes, which might explain its large size. I would predict that the proportion of the genome that is "junk" (terrible term, it just means we don't really know what it does; perhaps plays a structural role or controls gene expression patterns in very complex ways) is somewhat greater than the more compact genomes. I can't find any references that address the last question. The marbled lungfish, as beautiful as it is, does not seem to be one of the favorite model organisms for cell biologists or molecular biologists. --- Medical geneticist (talk) 00:29, 7 October 2011 (UTC)
Actually a Google Scholar search for "Protopterus aethiopicus DNA" finds quite a bit of stuff, some of it pretty recent. One factor is that the species is apparently tetraploid, meaning that it has four copies of every chromosome instead of the usual two. This recent paper, however, suggests that the quoted genome size value may not be all that reliable -- there seem to be substantial discrepancies between studies. Looie496 (talk) 02:27, 7 October 2011 (UTC)

## Damped oscillations in real life

Why do damped oscillations in real life come to a halt when basic damped oscillations studied in physics/differential equations (such as overdamped, underdamped, and critically damped cases arising from second order linear differential equations with constant coefficients) model oscillations that go on forever, even if with decreasing amplitude? — Trevor K. — 20:27, 6 October 2011 (UTC) — Preceding unsigned comment added by Yakeyglee (talkcontribs)

The model of friction, or other energy-dissipation process in the physics models, is simplified. Also, in real life oscillations below a certain level can't be detected because they are overwhelmed by other motions, electrical noise, or electrical noise and vibration inherent in the measuring device. Jc3s5h (talk) 20:32, 6 October 2011 (UTC)
ec Because those models have been simplified. At some point, the oscillation in a damped system will be below that of molecule vibration. For all intents and purposes, it is no longer oscillating, but in the mathematical model, you can say it is still oscillating even if it is only moving 1x10^-50 m per cycle. Googlemeister (talk) 20:33, 6 October 2011 (UTC)
I would say that the most general explanation falls under the description of stick-slip motion. While the surface-mechanics are still an active area of material science research, stick-slip motion is a very well known model of real-world friction behavior. Basically, what it means is, below a certain velocity, the friction becomes much larger and the object "sticks." We have lots of mathematical models to approximate such behavior: various empirical hysteresis curves can be fit to approximate motion.
More generally, a complicated physical model of friction turns simple harmonic oscillation (the most trivial 2nd order, ordinary differential equation) into a complicated nonlinear differential equation. Nimur (talk) 18:03, 7 October 2011 (UTC)

## Gulf stream

Is the gulf stream or north atlantic drift really moving southwards if so what is causing this. Would the mid atlantic ridge eventually have an impact the gulf stream and north atlantic drift therefore changing the climates of different regions. — Preceding unsigned comment added by 86.41.89.65 (talk) 20:52, 6 October 2011 (UTC)

Between the articles Gulf Stream and Mid-Atlantic Ridge, it appears the ridge is roughly twice the depth of the bottom part of the stream. That doesn't precisely answer your question, though. ←Baseball Bugs What's up, Doc? carrots→ 05:43, 7 October 2011 (UTC)
You would think the first question would be answered in Gulf Stream; it isn't but it is covered in Shutdown of thermohaline circulation. (Some evidence, probably natural but not sure.) Don't know about the second question, presumably ridges do affect the deep ocean currents. Itsmejudith (talk) 10:40, 7 October 2011 (UTC)
You may be interested in the article, Latitude of the Gulf Stream and the Gulf Stream north wall index - unfortunately, it is essentially pure data. The Gulf Stream itself is situated mostly on the North American continental shelf, before departing eastwards near the Outer Banks of North Carolina. It is likely that increased oceanic heat content during the past few decades has both altered the strength of the Gulf stream and its position through additional influxes of warm tropical water and cold Arctic fresh meltwater. As for the Mid-Atlantic ridge, bathymetry usually does affect local sea levels, though I'm not sure about the shape of the ocean currents. It appears that you are asking about the recent tectonic/volcanic activity, and whether any extra heat build up is likely to have affected the Gulf Stream. Any such effect is likely to be slow and long-term, though you can check for any correlations in the data, while remembering that correlation does not imply causation. Additionally, the North Atlantic Oscillation, Arctic oscillation, Arctic dipole anomaly, Azores High position, Atlantic Multidecadal Oscillation and other climate oscillations all affect the atmospheric circulation, and likely the position of the Gulf Stream in association. East of the Grand Banks of Newfoundland, the Gulf Stream becomes the North Atlantic Drift. The following journal articles show some link between the ridge, a geological feature, and the Gulf Stream to North Atlantic Drift: JGR, 1991 and DSR, 1988. See also Irminger Current for the area west of Iceland. ~AH1 (discuss!) 23:09, 7 October 2011 (UTC)

## Spin–lattice relaxation of different substances

I'm looking at T1 and T2 relaxation times in physics labs ... and being experienced in chemical NMR I am rather puzzled over many aspects of NMR that I overlooked. The pathetic strength of the magnetic field we're using means that we have to use 21 MHz signals (rather than say 300 MHz signals) though. For one, though resonance frequency differences between protons in different chemical environments can't really be resolved that well (though we can pick up differences that are sometimes on the order of parts per ten thousand as opposed to million). The other thing is that differences in relaxation times can be very dramatic.

Why would T1 of glycerol (T1 seems to be ~20 ms) be much shorter compared to the T1 of isopropanol and water (both are >1000 ms)? I get the idea that more oily or more solid implies a shorter T1 -- but is glycerol really that much different from ethanol chemically? Why would this be so? And how would chemical properties (solvent effects, chemical activities, densities and so forth) theoretically affect T2?

Also why is glycerol 1200 times more viscous than isopropanol? elle vécut heureuse à jamais (be free) 20:58, 6 October 2011 (UTC)

More OHs = more hydrogen bonding, so stronger intermolecular forces, so more viscous. --Jayron32 00:04, 7 October 2011 (UTC)
It surely can't be that simple. Water must surely have a stronger and more robust hydrogen-bond network than glycerol. For one, it can pack a lot more hydrogen bonds into a given space. Furthermore, this trend doesn't necessarily hold with other polyols. Furthermore, many viscous liquids aren't even polar. elle vécut heureuse à jamais (be free) 01:48, 7 October 2011 (UTC)
I don't know the answer to this one. The real question is, how do you predict viscosity (in general) from first principles? I found an abstract [9] which says "So in this work, a virial equation for calculating the viscosity of dense liquid was introduced according to correlating the dimensionless residual viscosity and reduced density. Adopting critical parameter (Tc, Pc), molecular mass (M) and accentric factor (ω) as parameters, the calculation can be accomplished. So the calculation of the viscosity of dense liquid is consistent with the calculation of equilibrium properties perfectly over the entire fluid range." This person has a site here but I couldn't get in. Wnt (talk) 03:09, 7 October 2011 (UTC)
Also in general, what would differ between glycerol and isopropanol (there are both organic alcohols) that would make for very long T1 and T2 relaxation times for isopropanol compared to glycerol? Why would spin-spin relaxation times be affected? elle vécut heureuse à jamais (be free) 05:11, 7 October 2011 (UTC)
I can't answer this one. I don't even understand how spin echo can be consistent with what I thought would be the quantization of the nuclear spin each moment is being measured. And I'm not entirely clear on what is being transferred to where with T1 and T2 of these materials. It would be kind if you'd humor me with a description of what you know about this system ... I really hope someone answers your question! Wnt (talk) 17:09, 7 October 2011 (UTC)

## Is there software that can animate chemical reactions?

I would like to be able to set up a reaction and be able to watch it in 2D or 3D, for instance in the reaction CO2 + C > 2 CO I'd like to see the O atom breaking from the first C and then attaching to the second C. I know Chemsketch can animate a molecule, but something that did a reaction would be awesome. Does anything like this exist? Noformation Talk 23:17, 6 October 2011 (UTC)

I doubt it, I don't think that the reaction type can be predicted. Reaction rates, and types can only be found through experimental evidence. Plasmic Physics (talk) 01:00, 7 October 2011 (UTC)
Plasmic Physics is way off. Such methods of animating simple chemical reactions have existed for decades. Here is an abstract from J. Chem. Ed. from 1995 which discusses how to animate such chemical reactions. I can also find any of several dozen more recent articles from J. Chem. Ed. which discuss the use of computer animations in a wide variety of applications. Many of these are simple animations of "ball and stick" or "space-filling" models transfering balls from one molecule to another, but trivially one could show electron flows between molecular orbitals (i.e. between HOMO and LUMO orbitals) that show bonds breaking and forming in simple computer animations, which would match expected mechanisms of such reactions. Like say this video which involves a reaction even more complicated than the one the OP came up with. --Jayron32 04:19, 7 October 2011 (UTC)
While there is software that can animate *some* chemical reactions, there is no software that can accurately animate an arbitrary chemical reaction. Because, as Plasmic Physics points out, there's no way to predict a priori how a particular chemical reaction proceeds. You can have a theory, or make analogies to other chemical reactions, but you have to actually do experiments to find out. Even then it can be hard to figure out and contentious. If your reaction is of a class that's been extensively studied (e.g. SN2, E1, etc.) a program may be able to make a guess of how the reaction goes, but the literature is filled with reactions which look like SN2 (or E1, etc.) reactions, but were later found to use some other mechanism. If all you have is a list of substrates, a list of products, and a set of reaction conditions, no software in the world will be able to give you an accurate animation, unless someone has already done the lab studies. For example, in the CO2 + C > 2 CO case: yes, a C=O bond needs to be broken and the C needs to form a bond with the O, but how does that happen? Is it dissociative, associative, or coordinated? (What happens first, the old bond breaking, the new bond forming, or do they happen at the same time? The transition state might not be 50%/50%, but something like 20%/30% or 60%/55%.) Is it an end-on attack, or does the new carbon form a three member ring across the C=O bond? (Because the latter is how some halogens add to double bonds.) Additionally, you likely don't have monoatomic carbon - it'll be in some sort of particle, so how does surface effects contribute to the reaction mechanism? - You can animate the reaction any way you like, but you can also draw pentavalent carbons. That doesn't mean that's what happens in the lab. -- 174.24.217.108 (talk) 16:52, 7 October 2011 (UTC)
All very true, but it wasn't readily clear if the OP wanted animations for software which animated known mechanisms, or which itself predicted unknown mechanisms. I read the question as the first; rather than the second. So it's OK. You can be correct too. I don't mind that much. It really doesn't bother me that you are correct. --Jayron32 18:32, 7 October 2011 (UTC)
Is it really meaningful to ask how all those bonds change in time and animate it? I thought all that was so quantum (in the derogatory sense) that all you can really tell with simple reactions is that the old molecules go in and the new molecules come out. Now if you took more complicated reactions from oraganic chemistry and large enzymes, you could as what steps you can break it to, but not with a simple one like that carbon monoxide. – b_jonas 18:25, 8 October 2011 (UTC)