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January 19

Bleach

If bleach is so harmful to human health, why is it used so widely as a cleaning product and even in swimming pools we swim in? Clover345 (talk) 12:21, 19 January 2014 (UTC)

It's a matter of use and concentration. Dihydrogen monoxide is deadly in large quantities, too, and yet it's in nearly every kind of food and even indispensable for our water supply. I don't think that bleach is used in swimming pools - chlorine, which is an active ingredient in many kinds of bleach is also used for disinfecting swimming pools, but I think the delivery mechanism is quite different. I could be wrong, though - chlorine bleach, ubiquitous in the US, is very rare in Germany. --Stephan Schulz (talk) 12:29, 19 January 2014 (UTC)

See bleach for more information. There are lots of different bleaches.--Shantavira|^{feed me} 13:56, 19 January 2014 (UTC)

I believe Sodium hypochlorite is used in swimming pools sometimes, but generally in home swimming pools rather than larger public ones which may use direct chlorination (i.e. with chlorine gas). We do have an article Swimming pool sanitation which suggests something similar although also suggests only large commercial public swimming pools use direct chlorination.

(Of course not everyone use chlorination, bromination is another alternative and there are other possible methods.)

However people may or may not use sodium hypohlorite in the form of bleach (by which I mean something sold as bleach in the laundry or cleaning section). I think pool supply stores may generally have more specialised products, these may include tablets or powder/granules which I think are normally calcium hypochlorite or sometimes may be lithium hypochlorite, or sodium hypochlorite solutions in higher concentration probably not marketed as bleach. But provided you avoid junk [1], I'm not sure there's any advantage to choosing any of these, I imagine the best is whatever gives you the appropriate concentration for the lowest cost and is easy to store and safely apply. (The only real concern seems to be the calcium contributing to water hardness [2] and of course the difference between storing and applying a solid vs a liquid. I believe you normally have to predissolve the solids to ensure they get properly dissolved.)

I acknowledge, as per the article, swimming pool sanitation can be complicated with regular testing etc required. It seems one common addition is cyanuric acid or alternatively products which contain the already chlorinated cyanurates [[Trichloroisocyanuric acid] or Dichloroisocyanuric acid (these are commonly called stabilised chlorines in pool supplies) as the greatly increase the halflife of the chlorination (increases sunlight stability). And you also have to deal with the pH etc.

But it does seem to me there's also a degree of lack of knowledge. For example, there seems to be a concern over the build up of cyanuric acid when you use the chlorinated cyanurates and the need for water replacement or higher levels of chlorine [3] [4]. But I don't understand why this is a problem, it seems to me the logical thing is to use stabilised chlorines initially and then once you reach a suitable level, only add unstablised chlorines (whether bleach, sodium hypochorlite solutions for pools, calcium hypochlorite tablets without cyanuric acid or whatever) until cyanuric acid levels start to drop to a level below what you want. (This site [5] seems to agree.) Alternatively it may be easier to add the cyanuric acid seperately.

So it wouldn't surprise me if people are using calcium hypochlorite or even sodium hypochlorite solutions sold by pool supply companies when they are actually paying more to achieve the same chlorination as they would achieve using ordinary sodium hypochlorite bleach simply because they never considered it i.e. not for convience or anything else.

BTW AFAIK the situation is similar for disinfection of water. Municipal water supplies usually use direct chlorination. But simply adding sodium hypochloride bleach is recommend for smaller scale operations such as after a natural disaster or in areas without potable water supplies. In fact, the CDC recommends sodium hypochloride over calcium hypochloride tablets because of concerns over the quality and consistency of tablets. [6] I would have thought the same applies to bleach/sodium hypochloride but I guess you don't have to worry about size and perhaps the variation is lower.

Nil Einne (talk) 19:12, 19 January 2014 (UTC)

Many people don't realise that one of the popular sterilising fluids for baby's bottles [7] is basically a dilute solution (16.5%) of Sodium hypochlorite (bleach). The manufacturers do say, however, that "The purification process during the manufacture ensures complete removal of all heavy metal ions, which would normally act as a catalyst to chemically break down many hypochlorites, causing instability". This product can also be used, at the right dilution, for purifying drinking water. Richerman (talk) 19:39, 19 January 2014 (UTC)

Bleach is, according to the EPA, a method of last resort for purifying drinking water. I learned the same advice from "extreme survival"-style camping: bleach is more effective than most of your ordinary camping-gear (like a filter or iodine droplets) at killing the nasties in your drinking water; it's more potent, lasts longer, acts faster, and it can kill you if you use too much in your water purification process. Nimur (talk) 20:06, 19 January 2014 (UTC)

You seem to have indented under the wrong reply - I didn't suggest using household bleach to disinfect water. The 16.5% solution is much safer to use. Richerman (talk) 20:54, 19 January 2014 (UTC)

There would see to be very little difference between using a weak bleach soloution (reading the FAQ, it's 2% *bleach*, 16.5% *salt*) and just using less bleach. The advantage of the baby bottle cleaner seems to come from removing all the heavy metal ions, favouring a safer decomposition of the bleach. Since the ions would presumably be present in the water anyway, you lose this advantage whether you use the solution or just straight bleach. MChesterMC (talk) 09:48, 20 January 2014 (UTC)

Sorry my mistake, it is a 2% solution. However, using a concentrate of a lower dilution (which is actually non-toxic according to their blurb) means that there is no chance of poisoning yourself if you get the dilution wrong. Richerman (talk) 17:16, 20 January 2014 (UTC)

The CDC suggests a bit lower (0.5-1%) although they don't seem to have a problem with diluting bleach to get it [8] but if you're going to store it you may need to raise the pH so it doesn't degrade too quickly (well their info isn't really for the consumer). Interestingly it seems even full strength bleach isn't as dangerous as you may think. They mention many accidental ingestions don't have significant adverse health effects, although you may be able to kill yourself with 250-500mL (they suggest it's unlikely people will accidentally ingest such large quantities because of the taste). On the whole, it sounds like you'd have to get things very wrong although I guess you may think the water is supposed to taste that bad. (It goes without saying you shouldn't intentionally test any of this.) Of course there are other risks like eye injuries or chlorine gas poisoning from careless use or accidental mixing. Nil Einne (talk) 16:38, 21 January 2014 (UTC)

Organic livestock more humane?

Someone told me that organic livestock is more humane from an ethical point of view than regular livestock. Is this true? I've always been skeptical of organic food claims being more healthy and better for the environment, so I'm also skeptical of this claim. ScienceApe (talk) 17:42, 19 January 2014 (UTC)

Exposing "organic livestock" to an environment with a high degree of organic chemistry (extra amounts of pesticides and fertilizers, etc.) seems not to be very humane or ethical.   71.20.250.51 (talk) 18:04, 19 January 2014 (UTC)

There is no reason for organic raising to be more ethical. The animals can still be slaughtered inhumanely and kept in terrible conditions without pesticides. The two are unrelated. Mingmingla (talk) 18:18, 19 January 2014 (UTC)

• Let me point you to our article on organic beef. The part of the USDA rules that is relevant is that organic beef cattle have to be born and raised on pasture, and more importantly, must have unrestricted outdoor access. That means they don't spend time in feedlots, which are usually pretty unpleasant. Looie496 (talk) 18:21, 19 January 2014 (UTC)

(e/c) And presumably such animals benefit from, for example, not being fattened artificially. We could do with an article on organic livestock, it is mentioned only briefly in our organic farming article. The free range article is probably the closest we have.--Shantavira|^{feed me} 18:24, 19 January 2014 (UTC)

Actually, the USDA says "Due to the number of variables involved in pasture-raised agricultural systems, the USDA has not developed a federal definition for pasture-raised products" which means, for example, that an animal which lived its entire life in a pasture and an animal which saw one once on the way to slaughter could both be labelled as "pasture" cattle. Matt Deres (talk) 19:26, 19 January 2014 (UTC)

The standards for USDA and UK Soil Association are here and here. Basically you need to check the label to see which standards apply. There are, of course, other labels that guarantee ethical standards for livestock that are not necessarily organically reared, such as some of the ones shown here. Richerman (talk) 18:56, 19 January 2014 (UTC)

One of the criteria the USDA lists for Organic Beef is the cattle, "Never receive antibiotics". My friend told me that consuming animals being given antibiotics can lead to antibiotic resistance. Is this true? ScienceApe (talk) 16:33, 20 January 2014 (UTC)

The thing to think about is antibiotic resistance in bacteria, not in humans or cattle. And yes, *every* use of antibiotics technically favors antibiotic-resistant bacteria. This is why they don't use antibiotic cleaners in space! This is also why doctors stress not quitting an antibiotic course early. If you want more info on this topic, you should probably open a new thread. SemanticMantis (talk) 16:47, 20 January 2014 (UTC)

(ec) It is possible for the bacterial population in your gut to become resistant, but even if it that didn't happen the indiscriminate use of antibiotics causes resistant organisms to evolve and get into the environment see:[9]. Richerman (talk) 16:54, 20 January 2014 (UTC)

Damaged molecules?

Resolved

 – 17:43, 20 January 2014 (UTC)

A "nutrition expert" interviewed on a TV health segment mentioned that commercial processing of vegetable oils "damages the oil molecule". This sounds like BS to me; either a molecule is what it is, or it isn't, right? Or, is it possible to "damage a molecule" such that it looses its health benefit? ~:71.20.250.51 (talk) 21:28, 19 January 2014 (UTC)

Well, sure; molecules can get changed in all kinds of ways. Just consider what a hamburger patty goes through as it goes from being raw to being cooked to being burnt to being nothing but charcoal. Eating that lump of black char is unlikely to provide much in the way of vitamins. Could you provide more detail about what the oil supposedly went through to become less nutritious? Did it have to do with hydrogenation? Matt Deres (talk) 21:50, 19 January 2014 (UTC)

That changes molecules from one molecule to other molecule(s). Processing doesn't "damage" an oil molecule (right?). -Re: "more details" --this post is in response to what seemed like mumbo-jumbo from an "expert" on TV (the processed oil you buy at a store is no good, etc.); this was on network programming, not an infomercial. ~:71.20.250.51 (talk) 22:04, 19 January 2014 (UTC)

Sure. Damage = change from useful to less useful. If I take a hammer to a window, I change it. Into something less useful. Changes to oil molecules that make them less useful could reasonably be described as damage. --Jayron32 23:41, 19 January 2014 (UTC)

You can "damage" some molecules - like when you denature proteins (cooking egg whites, for instance). I don't think this is possible for oils. The usual problem with oils is when the molecules are changed into other molecules by adding hydrogen to it. Trans fat is created this way. 75.41.109.190 (talk) 22:33, 19 January 2014 (UTC)

So, (let's say) you take oil from the Borobudur Ubatuba plant, and send some to the EvilFood Industrial Processing Corp., and some to the GreenyGood Food Coddler's Co-op., you could end up with two different Borobudur Ubatuba oils? ~:71.20.250.51 (talk) 00:09, 20 January 2014 (UTC)

• The most common processes that damage oils and other lipids are known as rancidification -- that article will give you more information. However there are also other processes that can occur. For example if you put oil

together with something that is strongly alkaline, the result is soap -- something you don't want in your food. Looie496 (talk) 05:15, 20 January 2014 (UTC)

This is becoming an argument about terminology. Sure, if you "change" a molecule, you'll have to either change the number and type of atoms within it (which makes a "different" molecule) - or you might possibly make it be folded differently.

Cyclohexane (to pick a very simple example) can fold into several different shapes (called "Chair", "Half Chair", "Boat" and "Twist-boat") - those forms all have the same chemical formula, the same number and type of atoms - and they are even connected together in the same way - so they are all "Cyclohexane". But I suppose that if you wanted "chair-Cyclohexane" and some process turned it into "boat-Cyclohexane" - you might say that it had been "damaged" by the process because the chemical properties have been slightly changed...but it's only a matter of terminology to say whether that's the "same" molecule or a "different" molecule -and "damaged" is such a loaded word in a situation where the molecule can trivially be flipped back into the preferred form. When we get to something as complicated as an "oil" - molecules will be changing and flipping shape all the time - so if you just do nothing whatever to a bucket of the stuff, it would slowly change (by some definitions of the word "change"). Perhaps that can be considered "damage" or perhaps "improvement" - or "unchanged" - depending on what use you're planning to put it to.

But even when the number of atoms changes - we have a terminology issue in the case of any long-chain molecule. We simply don't consider a molecule with 10,000 repeated units to be a "different" molecule from one with (say) 9,500 units. So you could take a polyethylene molecule, chop it in half - and you'd still say that you have "polyethylene" - even though the properties have changed and the strict chemical formula is different.

So I'm not sure this question is really very meaningful without a lot of clarification about the terminology we're using - and the purpose to which it'll ultimately be used.

SteveBaker (talk) 16:27, 20 January 2014 (UTC)

Thank you everyone, this does clarify the subject for me. I hadn't considered Protein folding, Molecular clustering, etc. Perhaps the "expert" wasn't totally off-base afterall. ~Eric:71.20.250.51 (talk) 17:43, 20 January 2014 (UTC)

Well, I wouldn't go that far! Nutritionalists (especially the ones interviewed on TV shows) aren't chemists! There is no such thing as "an oil molecule" - vegetable oil is a complicated mixture of many different chemicals - and clearly it's very likely that any sort of processing will change both configuration and chemical formula of the resulting molecules. The big question is whether this constitutes "damage" - in the sense of the oil not being so useful after this processing stage. Clearly, these commercial processes wouldn't be applied to the oil if there was no benefit to the manufacturer - perhaps they're improving shelf life - or making the stuff clearer and more visually appealing in a bottle on the supermarket shelves. It's plausible that something they do to "improve" it from their perspective also "damages" it from the perspective of the nutritionalist by (say) removing some flavors, vitamins or fibre. I'd bet that almost any change could be viewed as "damage" from someone's point of view.

The nutritionalist's answer is (IMHO) premium bullshit because it's a vague and lazy description. Had we been told "commercial processing lowers the boiling point, making it harder to cook without it smoking"...or..."commercial processing removes the longer chain molecules ruining the texture of bread made with it"...or whatever - then I'd listen and take note - but this sounds far too much like a blanket "Commercially processed anything is unspeakably horrible" kind of a claim, tossing in the word "molecule" because it sounds scientific - which is common amongst people who speak about food on mindlessly stupid TV health shows!

SteveBaker (talk) 00:28, 21 January 2014 (UTC)

Metric expansion of space

A doubt about metric expansion of space: the galaxies that now are, for example, receeding from us at 100 km/s did ever receed from us at that speed or when they were nearer they receeded more slowly? If yes, this would contrast with the extimations of universe age, because it was calculated assuming that the recession was constant. 95.235.225.100 (talk) 22:06, 19 January 2014 (UTC)

No one assumes the recession is constant through time. The rate of expansion changes through time due to both the slowing effect of gravitational attraction and the accelerating effect of dark energy. Dragons flight (talk) 05:28, 20 January 2014 (UTC)

Coming up with an estimate of the age of the universe by simply assuming that the Hubble parameter has had about the same value during the life of the universe works surprisingly well. Even Alan Sandage's 1958 estimate for H of 75 (km/s)/Mpc amounts to a Hubble time of 13.05 billion years, and the current measured value for H of 67.80±0.77 (km/s)/Mpc amounts to a Hubble time of 14.43 billion years, both of which are surprisingly close to the current best measurement for the age of the universe of 13.798±0.037 billion years. However, it's been a long time since the determination of the age of the universe was done so crudely by professionals in the field.

Yes, it was discovered in 1998 that the expansion of the universe is accelerating slightly (see Accelerating universe), but the surprise in that observation wasn't that the Hubble parameter hasn't been precisely constant, but rather that the expansion of the universe wasn't decelerating somewhat. I.e., before 1998's observation, the presumption was that the deceleration parameter was likely positive, not that the deceleration parameter was zero.

The best current measurements of the age of the universe use observational data from NASA's Wilkinson Microwave Anisotropy Probe and the Planck spacecraft, and use the complicated ΛCDM model of the universe, which is a lot more sophisticated than simply assuming that the Hubble parameter has been constant, and estimating the age of the universe as its inverse. Red Act (talk) 06:50, 20 January 2014 (UTC)

The image on the right shows why the naive estimates of universe age based on constant expansion speed worked so well—the linear extrapolation (solid line) happens to intersect the horizontal axis at almost the same place as the ΛCDM curve (dashed line). -- BenRG (talk) 20:28, 21 January 2014 (UTC)

I meant if, as example, 6,9 billions years ago (the half the universe's age) the same galaxies were receeding from us at (adproximately) half the speed today or their velocity was more or less that of present. Thanks for answering.93.45.32.204 (talk) 16:56, 20 January 2014 (UTC)

Their past velocities relative to us would be similar to present. Dragons flight (talk) 01:41, 21 January 2014 (UTC)

This is a good question, and can be answered with mathematical precision. The universe's expansion rate is given by the Friedmann equations. In particular, the Hubble "constant" at any given time is:

${\frac {H^{2}}{H_{0}^{2}}}=\Omega _{R}a^{-4}+\Omega _{M}a^{-3}+\Omega _{k}a^{-2}+\Omega _{\Lambda }.$

where H is the Hubble constant, H_0 is its present value, a is the scale factor (1 today, 0.5 when the universe was 50% the modern size, etc), and the rest are constants. In our universe, following the lambda-CDM model, $\Omega _{R}$ and $\Omega _{k}$ are nearly 0, $\Omega _{M}=0.272$, and $\Omega _{\Lambda }=0.728$. Since H is by definition da/dt divided by a, we have:

${\frac {da}{dt}}=H_{0}a*{\sqrt {0.272a^{-3}+0.728}}$

To my surprise, this can be solved analytically, and the result is:

$a=0.72*sinh^{2/3}(1.28H_{0}t)$

Next we just need to compute da/dt:

$da/dt=0.61H_{0}*sinh^{1/3}(1.28H_{0}t)cosh(1.28H_{0}t)$

Click here to see a graph of this function. The x axis represents time, where 1 is roughly the current age of the universe. The y axis is the ratio of your hypothetical galaxy's recession speed to its current recession speed. For example, the graph is roughly 0.95 at a time of 0.5. This means that 6.8 billion years ago, a galaxy that's receding at 100 km/s today was receding at 95 km/s.

BTW can someone please check my calculations? I have an inkling that something's wrong, because I don't remember the Friedmann equations being analytically solvable for lambda-CDM and was shocked that they had a simple solution. --Bowlhover (talk) 08:32, 21 January 2014 (UTC)

I found the same solution and I was surprised for the same reason, but I don't see how it can be wrong. Maybe we should publish. -- BenRG (talk) 20:28, 21 January 2014 (UTC)

Outside my expertise, but this unpublished manuscript seems relevant "Solution of the Friedman Equation, Determining ... Acceleration and Age of the Universe "[10], also these course notes [11] Still, just a preprint, and I don't have time to compare your work to theirs :) SemanticMantis (talk) 15:08, 22 January 2014 (UTC)

Situations where a law change allowed researchers to gather useful data due to before/after comparisons?

I'm looking for examples where important social science data was able to be gathered because a new law went into effect, which allowed for before/after comparisons.

I'm especially interested in examples where the new law was initially rolled out to only a subset of the population, and that population subset was determined by something random like the last digit of their SSN or license plate, and this allowed researchers to treat it as a [inadvertent] randomized controlled trial.

Anywhere in the world is fine. --Hirsutism (talk) 22:22, 19 January 2014 (UTC)

I'm not sure this is exactly what you're after - because it's not "social science" and not exactly a "law" that was involved. But when the 9-11 attacks in Sept 2011 forced every passenger plane in the USA (and most in Canada) to be grounded for three days, researchers were finally able to deduce what effect their contrails had on the weather - showing a variation of between one and two degrees centigrade while the aircraft were grounded. This is an experiment that would be impossible to conduct without a fortuitous governmental imposition like that. Fortuitous things like long power-outages reveal all sorts of interesting things such as changes in birth rate, crimes and even literacy (parents read to their TV-deprived children after that massive power outage in the Northern USA - and enough of them stuck with doing it after the power came back on to make a measurable difference to childhood literacy rates over the next year or so)...but again, that's not a law that was passed. SteveBaker (talk) 16:09, 20 January 2014 (UTC)

Cite, please, for the "1–2 degrees Celsius"? --50.100.193.107 (talk) 22:05, 21 January 2014 (UTC)

There's a bit on it in our contrail article, and you can follow references from there. Looks like the day/night temperature swing was slightly larger during that period: Contrail#September_11.2C_2001_climate_impact_study Katie R (talk) 16:32, 22 January 2014 (UTC)

• What you are looking for is a specific type of Natural experiment. That term is very common in biological sciences (e.g. before/after analysis of a hurricane), but it applies equally well to the social sciences, when the researchers are not in control of the treatment or grouping. Here is an example I recall, "Does Daylight Saving Time Save Energy? Evidence from a Natural Experiment in Indiana" [12], that made use of different counties changing their time at different times. It's in an economics journal, and is focused on energy, but the ultimate drivers are sociological processes. Anyway, with the right term in mind, searching google scholar for /"natural experiment" law sociology/ (e.g. here [13]) produces myriad relevant hits, touching on child labor, recycling practices, etc., so that should get you started. SemanticMantis (talk) 17:07, 20 January 2014 (UTC)

One example is that in 2008 Oregon Expanded Medicaid to included low income uninsured adults. However, there was a lottery as there were only 30,000 openings out of 90,000 applicants. They have now been able to compare health care usage and health outcomes for two very similar groups where the only difference appears to be random selection to the insured vs uninsured group. see:http://www.latimes.com/science/sciencenow/la-sci-sn-expanding-medicaid-increases-emergency-room-visits-study-finds-20140102,0,2102014.story#axzz2rA2rAqvD — Preceding unsigned comment added by 166.107.101.87 (talk) 20:31, 22 January 2014 (UTC)

January 20

Some articles are unclear

I cannot understand what is said by the articles: protist and algae. The article protist includes algae int it and says that protists are eukaryotic. But the aticle about algae includes cyanobacterias which are prokaryotic. These articles' facts are opposing each other. The article about cyanobacteria includes the cyanobacteria into bacteria domain. But in the article algae there are sentences like this:

• Most algae except cyanobacteria contain chloroplasts

So if algae are protists(as mentioned) and protists are eukaryotes (as mentioned), then cyanobacterias should not be included in algae because they don't have a membrane bounded nucleus. What can we do? --G.Kiruthikan (talk) 04:47, 20 January 2014 (UTC)

Did you read the lead of the algae article? I think it answers your questions. Basically the answer is that the protist article should have said that they include some types of algae. Looie496 (talk) 05:09, 20 January 2014 (UTC)

"It depends who you ask, and when," to some degree. Have a look at some of the most common classification schemes in use today. Some articles are surely using different schema. We can even find and cite sources that give contradictory correct answers!

I'm actually much more interested in this problem that Wikipedia articles contradict each other!

When I went to lower-grade school, our text-books used the five-kingdom classification method (bacteria, protists, fungi, plants, and animals). This was mostly consistent with what I "knew" to be correct; I had read, cover-to-cover, my home library copy of the 1967 World Book Encyclopedia, and it used a similar categorization. By the time I went to high-school biology, our text-books had switched to the "2.5 kingdom" (archaea, bacteria, everything-else) schema. Everything seemed wrong! Even the waterbears were in the wrong chapter of my high-school book, and there can be no doubt what they are! I got into a lot of trouble with my teacher by making noise about that issue. (If only more people could get so passionate about these important flaws in school biology textbooks!)

What had happened is that over the years, new scientific research has enabled us to classify the same organisms in many different ways. There is no single canonically-correct way to classify an organism; and if you assume that some microorganism must be either a protist or a cyanobacteria, you'd better be very sure you know exactly how you've defined those classifications. Sometimes, superficial treatments about science portray a level of consistency that doesn't really exist in the research community. Molecular biologists may prefer one classification scheme, while zoologists prefer a different scheme, while ecological conservation policy-makers use a totally different type of taxonomy. Classification schemes for organisms are not "facts;" they are positions that are put forward by prominent researchers. Old-fashioned publications, like paper encyclopedias and schoolbooks, had an editorial board who would convene, and there would be a top-down commandment specifying that one set of "facts" was canonically correct and reflected the current state of scientific knowledge (at least for the purposes of that year's publication). That's not how science works - if anything, Wikipedia is giving you more "correctness" by presenting contradictory information and letting you make the critical judgement.

If you are classifying an organism, you need to know which scheme you're using, and what basis is the standard for determining taxa. You should be aware that different sources and authors may use different schema. Particularly at Wikipedia, we are an encyclopedia edited by many individuals, and with very little coherent editorial oversight; nobody here is "the Chief Editor" who commands top-down that all articles shall use schema X. So, at a superficial inspection, our articles may contradict each other. Nimur (talk) 10:30, 20 January 2014 (UTC)

• In addition to Nimur's good points above, the reason it is hard to reconcile "protist" with "algae" is that neither of these groupings are currently believed to be clades. They are both highly polyphyletic, and so they don't make much sense in relation to each other, or to our more modern systematics. You might also be interested in Phylogenetic_nomenclature#Philosophy. Finally, if you read carefully, I don't think our article protist actually says or even implies that all algae are protists. SemanticMantis (talk) 00:07, 21 January 2014 (UTC)

I have now understood why there were contradictions. But we should make sure that other readers will not get any of the contradictions. Then all will got complicated. (I don't know the grammer well). Some books say that the classification of protists is not natural but rather it is artificial. They say that protists include organisms with many different evolutionary traits and no very recent evolutionary similarities. So regarding this point I think that there is no way of getting out of this complication. The only thing that matters is that according to Wikipedia's article, all protists are eukaryotic. So I think there is a small possibility of excluding cyanobacterias from protists.--G.Kiruthikan (talk) 02:43, 22 January 2014 (UTC)

How do resistors suppress RF interference?

Every since I started messing with cars I've heard that automobile spark plugs and their the wires contain resistors. Supposedly this eliminates RF noise from interfering with radio reception. On Wikipedia's Spark Plug page I found this statement:

The central electrode is connected to the terminal through an internal wire and commonly a ceramic series resistance to reduce emission of RF noise from the sparking.

That's great. Why does it work? — Preceding unsigned comment added by 50.43.12.61 (talk) 06:48, 20 January 2014 (UTC)

Same reason that a shock absorber reduces mechanical vibrations. 67.169.83.209 (talk) 09:52, 20 January 2014 (UTC)

Schematic showing how a wave flows down a lossless transmission line. Red color indicates high voltage, and blue indicates low voltage. Black dots represent electrons. The line is terminated at an impedance-matched load resistor (box on right), which fully absorbs the wave.

It works via (electro magnectic) transmission line theory. A wave is produced and the wave travels down the transmission line and hits the end of the transmission line and bounces back. Each time it travels down the transmission line it releases RF. It does this trillions of times by bouncing back and forth, back and forth endlessly. To stop this, put a resistor in series with the transmission line. The resistor is tune so that to the wave it looks like an infinite transmission line. As the wave travels down the transmission line, it is absorbed by the resistor and does not bounce backwards because as far as the wave is concerned it is going down an infinite transmission line. 220.239.51.150 (talk) 10:39, 20 January 2014 (UTC)

I think DHeyward is right about the spark plugs, but on a semi-unrelated note, I don't understand this animation. Is the resistor the whole rectangle of wire, or just the wide part? Either way, how can the electron density in the rectangular part be constant in both position and time? The effect of the resistor should be distributed along its length. I can't see any way of interpreting the image such that it's correct. -- BenRG (talk) 20:34, 21 January 2014 (UTC)

Just the end. A transmission line has an inherent impedance related to the permittivity and permeability of the dielectric as well as its structure dimensions. Energy is stored and transmitted in the field which is the picture. Waveguides are usually TE modes while coaxial cable and power lines are TEM modes. When wavelengths are short compared to the length of the lines, reflections can occur (I like to think of it as the source and load are unaware of each other at initiation and the speed of propagation in the dielectric means the model is a full power transmitter and the load reflects back what it cannot absorb. - YMMV with that though experiment. Transmission lines are often many wavelengths of the source frequency.) Impedance matching the source to the transmission line to the load minimizes reflected energy back to the source. Smith chart and S-parameters are normally the way transmission line matching is analyzed and corrected using power. Ionizing breakdown is a complex impedance (plasmas in waveguide is similar) that a simple resistor cannot match but can limit. The 5k resistor appears as the source impedance for a short circuit limiting what energy is in the spark. --DHeyward (talk) 04:28, 22 January 2014 (UTC)

Until the air breakdown voltage is reached, there is no current. When the breakdown voltage is reached and the conductive channel is formed, it's very low resistance. A resistor in series limits the total current and therefore the total energy available for the RF impulse. Resistors of 5k are typical. It has nothing to do with RF line matching. It's function is to produce a spark with the minimum energy necessary and therefore the least RF energy produced. --DHeyward (talk) 08:13, 21 January 2014 (UTC)

Wavelength of electromagnetic radiations emitted by different excited lead isotopes

Do the different isotopes of lead emit electromagnetic radiations of different wavelengths? or Do all four isotopes emit electromagnetic radiations of same wavelengths when they are decaying? — Preceding unsigned comment added by 27.62.251.166 (talk) 13:11, 20 January 2014 (UTC)

Yes, different isotopes have slightly different molecular spectra due to a difference in nuclear structure. However, these effects are much larger in lighter elements. In lead, which is the heaviest stable element, it may be hard to measure the difference in wavelength between isotopes, but in principle it should be possible. See this article from Encyclopedia Brittanica. The naturally occuring isotopes of lead are observationally stable (see isotopes of lead), so they do not typically decay, but when you compare e.g. Pb-210 with Pb-211 or Pb-214 the energies associated with the decay process differ significantly. - Lindert (talk) 13:47, 20 January 2014 (UTC)

I want to know whether it fixed that a particular isotope would emit electromagnetic radiations (EMR) having only a certain specified range of wavelengths (i.e., wavelength of EMR emitted by Pb-210 is different from Pb-211) or the wavelengths of EMR emitted is independent of the isotope used. 106.216.118.149 (talk) 14:45, 20 January 2014 (UTC)

The gamma rays emitted by the decaying nuclei are all different frequencies. However when lead decays it turns into different isotopes of different elements. So your ²¹⁰Pb gives off gamma rays that belong to Bismuth 210m at an energy of 271.3 keV. In the table in the isotopes of lead article you can see the numbers with m1, m2... after them, these give off the gamma rays listed and are all different energies, and belong to lead.

Food chemistry, eggs, milk, and salt

Hello, I witnessed some curious behavior making breakfast recently, and hope you can help clear it up. I whisked two eggs together in a clear measuring cup, until fairly homogenous. I then added a bit (15-20cc) of whole milk, and did not stir. Both eggs and milk were roughly the same temperature, straight from the fridge. The resulting mixture had a distinctly inhomogenous, marbled look, which is as expected (basically like this [14], but even less mixed, and with less milk. The important part is the borders are very sharp).

When I sprinkled a few shakes of salt on top, the veins of milk on the surface started wiggling and writhing, making the previously sharp and stable milk/egg border roil. It really caught my eye, as it reminded me of Diffusion-limited_aggregation or vortex shedding or some other clever pattern formation thing.

What's going on here? Something to do with surface tensions? Ions? Would there be any real "reactions" leading to a reaction-diffusion system? Anyway, I highly suggest you take a look next time you make scrambled eggs. Thanks! SemanticMantis (talk) 18:11, 20 January 2014 (UTC)

I'm not sure, but I think this may have to do with the changes in osmotic pressure caused by addition of salt. 67.169.83.209 (talk) 02:15, 21 January 2014 (UTC)

I don't really know about the reaction, but I was always told not to add salt before the eggs are cooked because it can make them rubbery. Hot Stop 04:32, 21 January 2014 (UTC)

Some sources say this [15], but a number disagree [16] [17] [18]. Nil Einne (talk) 17:43, 21 January 2014 (UTC)

Foo yung

Are Chinese foo yungs healthy? Clover345 (talk) 22:18, 20 January 2014 (UTC)

"Yes" and "no". They essentially share ingredients with omelets. Your question has been answered on several sites; e.g.: an authoritative one→[19] ~:71.20.250.51 (talk) 22:46, 20 January 2014 (UTC)

Rubbing Alcohol

I was talking to my neighbor recently, and he recommended applying Rubbing_alcohol to a sore muscle, and vigorously rubbing it in to provide relief. Thus, the name rubbing alcohol. The article here makes no mention of such a use, or why it is called rubbing alcohol. I have no intention of trying this, but I was curious. Is this a common, safe, or valid use of the product? Cthulhu42 (talk) 22:36, 20 January 2014 (UTC)

The bottle I have handy has instructions that say exactly that, so I assume it's at least common and/or safe. As to how valid it is, I don't know. When the alcohol evaporates, it will cool your skin, but I don't think much of that effect would even reach your muscles, let alone what benefit it would provide. Matt Deres (talk) 00:29, 21 January 2014 (UTC)

It says here " According to Medical Dictionary, the name "rubbing alcohol" stems from its use in the past as a medicinal rubdown, although this is not as common of an application now". It also describes the reasons for that usage under the heading 'Liniment for muscle aches'. Richerman (talk) 00:35, 21 January 2014 (UTC)

That's a placebo, except for the fact that rubbing with an antiseptic is less likely to cause infected skin lesions than rubbing without. Also, for all medical questions, consult a health care professional instead of the reference desks, thanks! 193.138.222.5 (talk) 03:19, 21 January 2014 (UTC)

Evaporative cooling would be similar to ice, I would think. --DHeyward (talk) 04:04, 21 January 2014 (UTC)

I believe the "effective" ingredient in 'rubbing alcohol' is the "rubbing". ~:71.20.250.51 (talk) 06:36, 21 January 2014 (UTC)

If you live in the US, then I think that I think yours neighbors reference to "rubbing alcohol" dates back to the laws of prohibition era. It was the only spirit people could legally bye over the counter. This alcohol was the base for making Liniment. Alcohol on its on is only good for cooling and dehydrating Trench foot conditions, etc. Medicated "rubbing alcohol" was much better for soothing muscle complaints (but dreadful for drinking). However, it is extremely difficult to bye now on the North American continent because no pharmaceutical companies hold patents to make it worth selling.--Aspro (talk) 19:06, 21 January 2014 (UTC)

January 21

Old French mechanical signals

How exactly did the mechanical ralentissement (slow 30) signal work? Was the mechanical vane operated from the signal box via the lever frame, or was it directly linked to the switch and the associated rappel de ralentissement signal? Also, how exactly did it produce the two yellow lights in the closed position, and the single green in the open? Were there two (or three) separate color lamps, or only one lamp fitted with movable color filters linked to the vane? Thanks in advance! 67.169.83.209 (talk) 03:37, 21 January 2014 (UTC)

I forwarded this query to Clive Feather, who has kindly replied as follows:

From http://www.carreweb.fr/stfr/sl_en.html and other pages (found by searching for "French railway signalling" or similar), it is clear that Ralentissment 30 is an aspect shown at the running signal (like "Medium to Clear" in North American practice). For the mechanical layout, you have a Carré above a Ral30. If the lever for the main route is pulled, only the Carré rotates. If the lever for the diverging route is pulled, both rotate.

If you asked me to implement this, I'd use an inverted slot mechanism. You have three bars that are centre pivoted on the same axis. A weight holds the left side down by default. The wire from the main lever pulls on the right end of bar 1. The wire from the diverging lever runs through the Ral30 rotation mechanism and pulls on the right end of bar 3. Bars 1 and 3 each have a short bar at right angles that crosses over to bar 2. So if either lever is pulled, the right end of bar 2 is pushed down by the relevant short bar; this in turn pulls the Carré rotation mechanism. When the lever is replaced, the weight on bar 2 rotates the Carré back again. (It's an "inverted" slot because the standard slot is an "and" gate, not an "or".)

Rappel de ralentissment is like the UK double yellow; it's a preliminary warning used when the signals are closer togther. The mechanical version would be driven from the same lever or from the equivalent of a distant signal lever.

It's clear from the images that there are three separate lamps.

-- Clive D.W. Feather

Forwarded (and lightly copedited/wikified) by: --50.100.193.107 (talk) 21:28, 22 January 2014 (UTC)

Thanks! So it is operated from the lever frame and not linked directly to the switch mechanism, right? 67.169.83.209 (talk) 03:50, 23 January 2014 (UTC)

what is the difference between chemistry and biochemistry in the blood test

I have noticed that there are two kinds of blood tetsts. One is chemistry, and the two is biochemistry. So what is the different between the two? which kinds of tests are included in the chemistry or biochemistry blood tests. 194.114.146.227 (talk) 05:53, 21 January 2014 (UTC)

See Blood test#Types of blood tests. Red Act (talk) 07:02, 21 January 2014 (UTC)

thank you. But it doesn't answer on my question: What does define a bihemiemical blood test as biochemical test? 194.114.146.227 (talk) 09:43, 21 January 2014 (UTC)

Chemical tests relate to things like simple ions (e.g. Na+, K+) and pH. Biochemical tests look for larger molecules, for example certain serum proteins e.g. serum albumin. --—Cyclonenim | Chat  09:27, 21 January 2014 (UTC)

Thank you. So I can understand that the chemical blood test is looking for the elements or the ions of them in the blood while the biochemical tests is looking for molecule. Am I right? 194.114.146.227 (talk) 09:43, 21 January 2014 (UTC)

Not quite. Biochemical tests are a subset of chemical tests. A biochemical test is a chemical test that detects or quantifies a biomolecule. If you want to reserve the name "chemical test" to "chemical tests that are not biochemical tests", they would still include ions composed of several atoms, such as phosphate, and dissolved gases such as ammonia. --NorwegianBlue ^talk 20:46, 21 January 2014 (UTC) — Preceding unsigned comment added by 109.189.65.217 (talk)

Identify this animal

What animal is this? [20] — Preceding unsigned comment added by Bobatnet (talk • contribs) 10:17, 21 January 2014‎

a monitor lizard? —Tamfang (talk) 11:00, 21 January 2014 (UTC)

A legavaan? A white-throated Rock_monitor. 196.214.78.114 (talk) 13:14, 21 January 2014 (UTC)

A bengal monitor, I think. Mikenorton (talk) 21:09, 21 January 2014 (UTC)

Goanna? HiLo48 (talk) 06:04, 22 January 2014 (UTC)

Looks like a Lace Monitor (varanus varius) to me, quite a big one. There's not many monitors that have those spots. Tom duF (talk) 07:01, 22 January 2014 (UTC)

"Alabama Rot" in the UK

The BBC reports that 17 dogs across Britain have been killed by "Alabama Rot". However an article mentioning Alabama rot says that it is "Idiopathic cutaneous and renal glomerular disease", affects only Greyhounds, and is associated with them eating raw meat. What makes them think that the cases in the UK are the same disease, it sounds quite different. -- Q Chris (talk) 10:59, 21 January 2014 (UTC)

The BBC report does not say that, but maybe it has been updated since you read it. Suggest you read it again.--Shantavira|^{feed me} 11:47, 21 January 2014 (UTC)

You're right it changed! -- Q Chris (talk) 13:29, 21 January 2014 (UTC)

The BBC article says it's "similar to Alabama rot" - not that it is that. Both diseases involve skin lesions in the early stages, Idiopathic just means that the cause is unknown, and "renal glomerular disease" means it affects the kidneys (see Glomerulus), which probably means it leads to renal (kidney) failure, like the disease in the BBC article. The second article says Alabama rot has "only been reported in greyhounds". That doesn't mean it only affects greyhounds - only they it hasn't been seen in other breeds yet. Richerman (talk) 13:21, 21 January 2014 (UTC)

Not to be confused with the live concert CD: Alabama Rot in the UK      —(sorry, couldn't resist. 71.20.250.51 (talk) 18:53, 21 January 2014 (UTC)}

Metric expansion of space 2

So, as I seen from the graphic, the recession velocity didn't change too much with the time. My final question is: if there wasn't that difference, how is possible that the limit of our observable universe is 46 billion light-years, where the recession speed is three times c (the light's speed)? This would mean that the recession velocity would have at least triplied from the time the radiation that reacht us was emitted, a thing that according to the graphic is impossible (the highest difference isn't more than 20%). Thanks for answering and excuse me for my insistence. 93.45.32.204 (talk) 12:56, 21 January 2014 (UTC)

It doesn't mean that at all. Suppose that 6 billion years ago, the universe was 50% its current size, so a=0.5. A photon travels for 1 year across the universe. That one light-year would be two light-years today, giving the impression that the ancient photon traveled at 2c.

Mathematically, a photon travels a distance c*dt in time dt. But this distance corresponds to a distance of c*dt/a(t) in today's universe, because the universe has since expanded by a factor of 1/a. To find the size of the observable universe, we integrate c*dt/a from t=0 to t=13.7 billion years:

$R=\int _{0}^{t_{age}}c{\frac {dt}{0.72*sinh^{2/3}(1.28H_{0}t)}}$

$\approx {\frac {3.45c}{H_{0}}}$

where $c/H_{0}$ is very close to 13.6 billion light-years. Multiplying that by 3.45 gives 47 billion light-years. You can see the result of the integral here. --Bowlhover (talk) 21:02, 21 January 2014 (UTC)

The recession speed was generally higher in the past, not lower, which makes sense since gravitational attraction slows expansion down. If it weren't for the cosmological constant, the recession speed would always decrease. The speed goes to infinity at the big bang (in the standard radiation-dominated model without inflation).

The image on the right shows visually what's going on with the distances. Light travels at a "45° angle" relative to the local metric. The earth (brown, left) and a distant quasar (yellow, right) have gone from a few billion light years apart to 28 billion light years apart in 13 billion years, which is an average recession speed of about 2c over that time, but light (red) traveling at a local speed of c can get from one to the other regardless. The geometry just works out that way. It's often said that the distance the light travels early on "counts for more" because the distance it has covered later expands. I'm not sure how much I like that explanation, but it's probably fine if you find it helpful. -- BenRG (talk) 20:47, 21 January 2014 (UTC)

Ancient Mesopotamian units of measurement

Dear Sirs

Regarding mesopotanian measurement standards the talk section describes a potential problem

In the table of values the length of the Cubit and smaller values seens to be consistant but the values fro the larger standards appear to be rounded off

the talk section describes a possinle solution which seems correct to me

IT IS VERY IMPORTANT to researchers like myself to have accurate data

I have been critized for using this Wikepedia reference but am convinced that you are correct in stating the length of the cubit at 497 mm

can you help me overcome my rejection of by reviewers on this single issue

Roland Boucher — Preceding unsigned comment added by Roland Boucher (talk • contribs) 16:33, 21 January 2014 (UTC)

For convenience, this question seems to be about our article Ancient_Mesopotamian_units_of_measurement. That article gives no source for the claim 1 cubit=497mm. Cubit gives some examples of ancient metrology standards that have been recovered, with a range of 518 to 529 mm. It then states that 450mm is an estimate used by biblical scholars.

If I were reviewing your article, I would not allow you to publish 1cubit=497mm based on only a citation to Wikipedia. I looked quickly on google scholar, and found this paper, which is probably citable, [21] and this manuscript [22], which is not citable, though it does have some good references for several types of cubits and metric equivalents that you can read/cite for a peer-reviewed article. If you cannot get access to these articles, I suggest you ask at WP:REX. Finally, if you are seeking to be a good researcher in this field, then you are in the best position to improve these WP articles! You can add the citations that you need for your research to support our articles, and everyone then can benefit from your work! SemanticMantis (talk) 17:45, 21 January 2014 (UTC)

Finding the value for the cubit at the particular time and space that you're researching is essential. For example, the Olympias was a super-carefully researched reconstruction of a Greek trireme (an oared vessel). They spent a small fortune building the thing - and only after they tried putting a crew into it to row it did they discover that they'd used "the wrong cubit" and the ship was much more cramped than it should have been. Given the massive amount of work they put into doing this - this minor catastrophy is a measure of how easy it is to get the wrong cubit. It's really not an easy question to answer - and there is no single answer that's correct over more than a small interval of time and a small geographical region. Worse still, researchers can only really relate these ancient cubit measures to modern units by physically measuring some historical artifact who's dimensions were documented in cubits. We know the dimensions of things like the great pyramid in cubits - and we can measure the real thing and know what size the pyramid builder's cubit was...but if you want to know the size of cubit used by a trireme builder, you're right out of luck because there are no surviving vessels of that kind still around. (I don't recall how the Olympias people figured out how they'd screwed up). SteveBaker (talk) 21:04, 21 January 2014 (UTC)

The other way of finding out is by finding extant physical standard cubits. Our cubit article has photos of a few, and says "Fourteen such rods, including one double cubit rod, were described and compared by Lepsius in 1865" -- so at least some cubits can be "rigorously" converted to metric. As you say though, it really depends on time and place, and those known samples won't necessarily say much about the cubits that Roland needs. I think he could probably dig through the refs I gave above and find an estimate that is at least vaguely for the right time and place. For something this subtle, I think that's far better than relying on the authority of Wikipedia! SemanticMantis (talk) 22:06, 21 January 2014 (UTC)

January 22

Is this right? (Order of reactants)

The problem is Zero, First and Second order reaction rate... things (I'm so screwed I don't even know the correct way to say it. but anyway, I'm not sure if this is correct, but It's what I gleaned from what I've read online:

• A zero order reactant does not affect the rate of reaction if doubled
• a first order reactant makes the rate go two times as fast if doubled
• a second order reactant makes the rate go four times as fast if doubled.

Am I figuring this correctly?--Ye Olde Luke (talk) 04:04, 22 January 2014 (UTC)

According to our article rate equation. A zero-order reaction is at a constant rate with changing concentration of reactant, a first-order reaction is linearly proportional to the concentration of reactant, and a second-order reaction is proportional to the square of the concentration. So yes, the example numbers you cite are correct. SpinningSpark 16:29, 22 January 2014 (UTC)

Polar Bears

If a few polar bears were introduced to Antarctica, what would happen to all the penguins? — Preceding unsigned comment added by 216.114.215.239 (talk) 04:15, 22 January 2014 (UTC)

As long as those polar bears are all male the answer is not much. 220.239.51.150 (talk) 05:46, 22 January 2014 (UTC)

And if they are all female? --Bowlhover (talk) 05:54, 22 January 2014 (UTC)

Still not much. The IP editor is suggesting that they couldn't mate and thus would die off after a few years. Dismas|^(talk) 07:59, 22 January 2014 (UTC)

Polar bears live for around 25 years...if there is going to be ecological damage, I'd expect it to happen long before enough of the bears died out to prevent it. SteveBaker (talk) 16:54, 22 January 2014 (UTC)

It depends greatly how you intepret 'a few'. I would intepret it to be a fairly low number less than 20. 10 polar bears could definitely cause great ecological damage, heck even if only 5 die they could also cause great ecological damage if left unchecked. I mean a single rat, cat or dog can devaste an unadapted population [23]. That said, it's a lot less likely than if you import a breeding group. Nil Einne (talk) 00:14, 23 January 2014 (UTC)

The penguins would be fine. The polar bears couldn't get the wrappers off. Rojomoke (talk) 06:33, 22 January 2014 (UTC)

Some joking is fine, but I think the main focus should be answering the poster's question. That's part of civility.76.218.104.210 (talk) 12:28, 22 January 2014 (UTC)

The joke isn't even that unique [24] Nil Einne (talk) 00:14, 23 January 2014 (UTC)

Uniqueness is an absolute, so something either is unique or isn't. This info should allow you to supply perfecter responses in the future. :-) StuRat (talk) 00:26, 23 January 2014 (UTC)

[25], [26], [27], [28], [29], [30], [31], Comparison (grammar)#cite_note-4. Nil Einne (talk) 08:23, 23 January 2014 (UTC)

It's pretty difficult to predict the effect of introducing a non-native species; the oft-quoted examples of brown tree snakes, rabbits in Australia and, to a lesser extent gray squirrels, suggest it may not be good news for the penguins, but food webs are complicated and who knows what trophic cascade may follow. benmoore 13:10, 22 January 2014 (UTC)

Hear, hear! USA government actually promoted planting kudzu in the south, to disastrous effects. Experts usually know enough to know that they cannot predict the long-term outcomes of population dynamics of endemic species when exposed to introduced species. Really, we don't even know if polar bears are any good at catching penguins ;) SemanticMantis (talk) 15:12, 22 January 2014 (UTC)

It's important to note that many (most?) species of penguin don't live anywhere near the antarctic - so while it's possible, and even quite likely that some of them would suffer - it's undoubtedly true that not all of them would even notice. For the antarctic penguins, let's consider what polar bears eat - and how they hunt. Here are some quotes from our Polar bear article:

• "Mature bears tend to eat only the calorie-rich skin and blubber of the seal, whereas younger bears consume the protein-rich red meat. Studies have also photographed polar bears scaling near-vertical cliffs, to eat birds' chicks and eggs. For subadult bears which are independent of their mother but have not yet gained enough experience and body size to successfully hunt seals, scavenging the carcasses from other bears' kills is an important source of nutrition." -- There are plenty of seals in the Antarctic, although not the familiar species that the bear prey on. So we might expect the antarctic seals to have a very hard time of things - they aren't adapted to avoid land-predators, their biggest problem normally being killer whales. Once they get over the 6 months of "jet lag" due to mid-winter being in July, I think this would give the bears the diet they need without too much trouble. Since we know they will take birds eggs and chicks, they might well cause the penguins problems - we know that penguins are completely unafraid of humans - so very likely they'd just stand around looking stupid while the bears grab their eggs and chicks.
• "Most terrestrial animals in the Arctic can outrun the polar bear on land as polar bears overheat quickly, and most marine animals the bear encounters can outswim it. " - so the bears won't be able to catch penguins in the ocean. Whether a penguin can out-run a bear is hard to guess.

My best read on this is that if you could transfer the bears without screwing up their body clocks and have them hibernate at the right times - then they'd survive just fine on seal meat...possibly thriving because the seals don't expect attacks when on land. I think the bears might then not need to resort to hunting penguins - and when they do, it would be chicks and eggs that they'd grab. Since leopard seals are a major predator of penguins - and the seals would be in huge trouble from the bears - the penguins might actually do rather well out of the deal.

Bears prefer to hunt in sea-ice - which will constrain them to the oceans' edge - so some penguins that do their breeding inland might also be OK.

CONCLUSION: Both bears and penguins probably do just fine...very, very bad news for the seal population though. SteveBaker (talk) 16:32, 22 January 2014 (UTC)

See also polar bear which mentions difference between Artic and Antartic seals believed to be partially the result of polar bear predation. I wouldn't BTW underestimate the possible effect of polar bears on Antartic penguins. Seals in the Antartic and of course the terrain are somewhat different from those in the Artic. And more significantly, many examples have shown predatorsorganisms are nothing if not good at adapting to new preyfood species they encounter in a new environment. Several commentators seem to agree [32] [33] [34] [35] [36] [37] [38] [39]. (The first source BTW may be a little confusing, the paper it refers to [40] [41] is not about such long range translocations and in fact specifically mentions polar bears to Antartica as something they are not proposing.) And of course, if they are too successful at hunting seals and you're right there's a good chance to think they will be, they could easily quickly devaste the seal population even more so if you import a breeding group. And as they devaste the seal population and their plentyful food supply runs out, if they weren't already hunting penguins there's a good chance they will start. Nil Einne (talk) 00:14, 23 January 2014 (UTC)

Elephants

Are elephants aware that the main reason they are being hunted by elephant poachers is for the ivory?76.218.104.210 (talk) 12:26, 22 January 2014 (UTC)

It seems like you're asking about awareness on a cognitive level, which seems unlikely. But on a related note, (and I'm not aware of the actual research the press was based on) a few years ago it was claimed (e.g.) that due to the artificial selection imposed on elephants, killing those with the largest tusks, the mean population tusk length was decreasing. I'm not sure how they accounted for survivorship bias and it seems unlikely such a fitness benefit could be realised in such a short time, but then again I think dramatic morphological changes were noted in Atlantic cod in the North Sea before strict fishing restrictions were put in place, so who knows. benmoore 13:03, 22 January 2014 (UTC)

There is simply no way to know what the elephants may or may not be "aware" of. We can't know what any other beings are thinking - I don't know what my next door neighbor is aware of without asking, and how would you ask an elephant? You might possibly be able to prove that they were *UN*aware (eg if the poachers removed the entire elephant carcass before removing the tusks - you'd be fairly sure that the elephants wouldn't know whether they were after the ivory or...the toenails or something) - but even if they saw the tusk removal happening, it's not clear what they would or wouldn't be able to deduce from that. Worse still, you're asking for us to know whether the elephant knows what the poacher is thinking - and that's two levels of unknowability. SteveBaker (talk) 16:13, 22 January 2014 (UTC)

This made me think of the bear that watched its parents get shot and killed and then when faced with the hunter rolled over on its back as if to say "dont shoot me; it seems that you like us to lay still so here you go, but dont kill me" anyone hear of this account or is it some "rural" legend?165.212.189.187 (talk) 16:33, 22 January 2014 (UTC)

I guess what I meant is that it seems the bear deduced (albeit somewhat incorrectly) that the hunter wanted all the bears to "lay still" (be dead).165.212.189.187 (talk) 18:27, 22 January 2014 (UTC)

Consider the human equivalent. If random passersby were targeted by a psycho killer with a particular fixation (say for left-handed people with big noses), would they be able to decipher the reason from a tiny sample set? No. Clarityfiend (talk) 01:41, 23 January 2014 (UTC)

I thought there might be some ways a very elephant-knowledgeable and imaginative human in elephant territory might discern such awareness from elephants' day to day behavior, or devise a clever test for that kind of awareness. Also, I respectfully disagree with Clarityfiend. I dont think the analogy Clarityfiend provided is very close to what's been happening in Chad, according to Wikipedia.--Richard Peterson76.218.104.210 (talk) 09:33, 23 January 2014 (UTC)

Lorentz transformation and Ampere's law

I have been thinking about the derivation of Ampere's law by applying the Lorentz transformation to Coulomb's law. My undergraduate physics text only treats the case of two equal currents with equal charge velocity, but I am having trouble getting the right answer for the more general case. We have two relevant articles, Relativistic electromagnetism and Classical electromagnetism and special relativity, but neither of them directly solves my problem. Here is what I have got;

Consider two parallel lines of charge a distance r apart with a charge density of Q₁ and Q₂ coulombs/metre respectively. In a frame of reference at rest to the charges, the Coulomb force between them is given by,

$F={\frac {Q_{1}Q_{2}}{2\pi \epsilon _{0}r}}$

If the charges are in motion axially (ie, are actually currents) we must apply the Lorentz transformation so that,

$Q'={\frac {Q}{\sqrt {1-v^{2}/c^{2}}}}$

and

$F'={\frac {Q'_{1}Q'_{2}}{2\pi \epsilon _{0}r}}={\frac {Q_{1}Q_{2}}{2\pi \epsilon _{0}r{\sqrt {(1-v_{1}^{2}/c^{2})(1-v_{2}^{2}/c^{2})}}}}$

Note that the velocities can be different even if the two currents are the same. This would pertain, for instance, if one conductor had a much larger cross-section than the other. The amount by which F' exceeds F is the Ampere's force,

$F_{\mathrm {m} }=F'-F={\frac {Q_{1}Q_{2}}{2\pi \epsilon _{0}r}}\left[{\frac {1}{\sqrt {(1-v_{1}^{2}/c^{2})(1-v_{2}^{2}/c^{2})}}}-1\right]$

Making the substitutions

$I=Qv$

and

$c^{2}={\frac {1}{\mu _{0}\epsilon _{0}}}$

gives

$F_{\mathrm {m} }={\frac {\mu _{0}I_{1}I_{2}}{2\pi r}}\left[{\frac {c^{2}}{v_{1}v_{2}}}\left({\frac {1}{\sqrt {(1-v_{1}^{2}/c^{2})(1-v_{2}^{2}/c^{2})}}}-1\right)\right]$

which is Ampere's law if the part in square brackets approximates to unity for small (non-relativistic) velocities. Unfortunately, it doesn't. Applying the binomial approximation

$(1+x)^{n}\approx 1+nx,\quad x\ll 1$

to the part in round brackets (I'm not showing all the detail here to keep it short) results in,

$[...]\approx \left[{\frac {c^{2}}{v_{1}v_{2}}}\left({\frac {1}{2}}{\frac {v_{1}^{2}}{c^{2}}}+{\frac {1}{2}}{\frac {v_{2}^{2}}{c^{2}}}\right)\right]$

$={\frac {v_{1}^{2}+v_{2}^{2}}{2v_{1}v_{2}}}$

which is unity when the velocities are equal but is clearly wrong - the expression goes to infinity if one velocity goes to zero. I would like to think that I have invented a new kind of motor with infinite torque, but in reality I have probably just made a mistake. SpinningSpark 12:39, 22 January 2014 (UTC)

$I=Qv$ isn't correct! The proper formula for the drift velocity is $J=\rho v_{\it {avg}}$, where J is the current density (current per unit *area*) and $\rho$ is the charge density (charge per unit **volume**). Alternatively, $Qv={I \over nA}$ where n is the charge carrier density. Not sure how to work those into your expressions, my physics is a touch rusty. MChesterMC (talk) 14:20, 22 January 2014 (UTC)

Starting from,

$J=\rho v$

which we both agree to be correct, and multiplying by cross-sectional area s,

$Js=I=\rho sv$

Since

$\rho s={\frac {Q}{s}}s=Q$

where Q is to be read as charge per unit length (a common enough contrivance in elementary textbooks to avoid having to explicitly include terms for length of the conductors) we have

$I=Qv$

as claimed. SpinningSpark 16:00, 22 January 2014 (UTC)

Sorry, but you made a wrong assumption. You can transfer from one frame of reference to another one, but you can not transfer to two frames of reference simultaneously! If charges are moving with different speeds they are in two different reference frames. So, the textbook is absolutely correct—you can only obtain the Amprere's law by frame transformation if velocities are equal. Ruslik_Zero 19:40, 22 January 2014 (UTC)

So what is the correct approach? I surely need the force between the conductors as observed in the rest frame. SpinningSpark 22:46, 22 January 2014 (UTC)

One approach that works is as follows:

So that there isn't any Coulomb force between the wires as measured in the lab frame, assume that in the lab frame, there is no net charge density on either wire 1 or wire 2. I.e., assume that on wire 1, in addition to the linear charge density $Q_{1}$ of charge carriers traveling at speed $v_{1}$ in the lab frame, there is also a linear charge density $Q_{1}^{*}$ of charges that are stationary in the lab frame, such that in the lab frame, $Q_{1}+Q_{1}^{*}=0$. Similarly, on wire 2, in addition to the linear charge density $Q_{2}$ of charge carriers traveling at speed $v_{2}$ in the lab frame, there is also a linear charge density $Q_{2}^{*}$ of charges that are at rest in the lab frame, such that in the lab frame, $Q_{2}+Q_{2}^{*}=0$.

The total force on wire 1 due to the charge densities on wire 2 is then a sum of four terms, one for each possible combination of a charge density on wire 1 and a charge density on wire 2. Each term is a Coulomb force, except that the charge density on wire 2 needs to be increased by a Lorentz factor to account for the length contraction within the charge density on wire 2 as observed in a frame in which the charge density on wire 1 is at rest. Thus, for each term, the Lorentz factor for the term depends on the relative velocity between the two charge densities involved. The total force per unit length on wire 1 as measured in the lab frame is thus:

$F_{m}={\frac {1}{2\pi \epsilon _{0}r}}\left(Q_{1}\gamma _{12}Q_{2}+Q_{1}\gamma _{10}Q_{2}^{*}+Q_{1}^{*}\gamma _{02}Q_{2}+Q_{1}^{*}\gamma _{00}Q_{2}^{*}\right)\ ,$

where

$\gamma _{ij}={\frac {1}{\sqrt {1-(v_{i}-v_{j})^{2}/c^{2}}}}\ ,$

and for convenience we're defining $v_{0}=0$ for the speed of the lab frame as measured in the lab frame. But since the expression for $F_{m}$ is in the lab frame, we can substitute $Q_{1}^{*}=-Q_{1}$ and $Q_{2}^{*}=-Q_{2}$ to get the simpler

$F_{m}={\frac {Q_{1}Q_{2}}{2\pi \epsilon _{0}r}}\left(\gamma _{12}-\gamma _{10}-\gamma _{02}+\gamma _{00}\right)\ .$

Doing a Taylor expansion of $\gamma _{ij}$ and ignoring terms that are more than quadratic in the velocities gives

$\gamma _{ij}\approx 1+{\frac {v_{i}^{2}}{2c^{2}}}+{\frac {v_{j}^{2}}{2c^{2}}}-{\frac {v_{i}v_{j}}{c^{2}}}\ .$

Substituting this low-speed approximation for $\gamma _{ij}$ in $F_{m}$ and simplifying gives

$F_{m}\approx {\frac {Q_{1}Q_{2}}{2\pi \epsilon _{0}r}}\left(-{\frac {v_{1}v_{2}}{c^{2}}}\right)\ .$

Making the substitutions $I=Qv$ and $c^{2}={\frac {1}{\mu _{0}\epsilon _{0}}}$ then gives

$F_{m}\approx -{\frac {\mu _{0}I_{1}I_{2}}{2\pi r}}\ .$

Red Act (talk) 07:02, 23 January 2014 (UTC)

Thanks for that, and indeed my Physics text also only treats the case of overall neutral conductors as well. It would appear that Ampere's law fails in a charged medium such as a plasma or electron beam. Is that true? The equations I derived above imply that there is a "surplus" force even if one current is zero (contrary to Ampere's law). SpinningSpark 10:04, 23 January 2014 (UTC)

What is Abrogation?

I know the term abrogation in its colloquial and legal senses. But I see that it is widely used in scientific contexts, too, particularly in molecular biology, where it seems to refer to some kind of canceling or preventing of the expression of genes. I've Googled variously but been unable to find a decent definition or explanation of its technical nuances. Anyone resolve the mystery?—PaulTanenbaum (talk) 18:23, 22 January 2014 (UTC)

Don't have a detailed explanation, but Oxford English Dictionary (1997) gives for 'abrogate': "3. Immunol. To suppress or prevent (a physiological process)." Abrogation in this sense first attested in 1959 in Nature: "Abrogation by injected mouse blood of protective effect of foreign bone marrow in lethally X-irradiated mice.". - Lindert (talk) 20:44, 22 January 2014 (UTC)

You pretty much have it. It doesn't refer to any specific biological or experimental process in my experience, and simply refers to the state of some element, not necessarily genetic, not being present or functional. Also, as far as I am aware it is always used in practise to refer to an experimental manipulation, or a mutation, natural or otherwise, and never to a process natural to a wild type organism (for which you might use "repress" or "inhibit" instead). For example you could say "the expression of gene A was found to be abrogated in mutant B" (referring to the expression of a gene not being present any longer) or "inhibitor X was found to completely abrogate the function of protein Y" (referring to the function of a protein not being present any longer). Equisetum (talk | contributions) 11:37, 23 January 2014 (UTC)