Wikipedia:Reference desk/Archives/Science/2013 October 19

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October 19

Global warming and agriculture

According to the article on climate change and agriculture, plant yields are expected to decrease as temperatures rise because each plant has an optimal reproductive and growth temperature which if exceeded leads to reduced growth. Why can't we genetically modify crops, whether through genetic engineering or more conventional methods, to have a higher optimal temperature? 74.15.138.165 (talk) 01:44, 19 October 2013 (UTC)

We don't even have to do that, just grow the proper crops for the new climate. For example, places which are no longer subject to winter frost become available for lots of new crops, like oranges. Also, in other cases, an additional harvest may be possible in a year for a given crop. Global climate change is not universally bad, it just requires that we adapt to the new environment, such as moving inland to deal with rising sea levels. StuRat (talk) 01:48, 19 October 2013 (UTC)

Wikipedia is not a source. The Middle Age and Roman warm periods were great for crops in Europe. Temperatures reached a maximum after the last ice age around 2000-3000BC. We are now in the cooling trend of a new ice age, called the neoglaciation. Recent trends have been local blips on that curve. See Canadian ecologist E. C. Pielou's, After the Ice Age, which is searchable at Amazon and well worth reading. μηδείς (talk) 01:59, 19 October 2013 (UTC)

Just to clarify: no credible scientist believes the world is actually cooling, just that it would be cooling if not for CO2 emissions. I assume that's what Medeis meant, although the natural Milankovitch cycles have been completely drowned out by anthropogenic warming in the past century. --Bowlhover (talk) 04:09, 19 October 2013 (UTC)

One century is 0.1% of the cycle of the ice ages, so how is that relevant? (Alternatively, how is the cycle of the ice ages relevant? At any rate, these two things have little bearing on each other.)  Card Zero  (talk) 18:43, 21 October 2013 (UTC)

The problem with climate change is not only the higher average temperatures but also that the changes in the local climate will happen fast and the local climate may well become inherently more variable. Higher evaporation rates will lead to more droughts, while the average amount of rainfall will also increase. This means that you'll have longer and more severe periods of droughts, interrupted by huge and sometimes catastrophic amounts of rainfall. Agriculture under such conditions will become more difficult, this may well lead to the collapse of our civilization. Count Iblis (talk) 02:12, 19 October 2013 (UTC)

You have moved the bar from global warming to climate change. Neat huh? μηδείς (talk) 02:35, 19 October 2013 (UTC)

No moving involved, only clarification. Global warming is the primary and most easily measurable effect, but no serious scientist ever thought that a general warming would have no or insignificant secondary effects on climate. --Stephan Schulz (talk) 18:51, 21 October 2013 (UTC)

This discussion has been closed. Please do not modify it.
The following discussion has been closed. Please do not modify it.
Why are you still allowed to post here? 68.0.144.214 (talk) 03:33, 19 October 2013 (UTC)

It depends on the crop. Field corn, for example, loves heat. But it also needs water at the right times, and a minimal growing season. The length of the growing season varies from north to south in the US. Northern varieties are bred to mature more quickly. If the North's summer becomes a lot longer (which does not really appear to be happening anytime soon), the corn with longer time to maturity could be grown farther north, and total yields would increase - provided the water and nutrients are also there. ←Baseball Bugs ^{What's up, Doc?} carrots→ 04:04, 19 October 2013 (UTC)

The funny thing is that after Trofim Lysenko spent half a century as the epitome of pseudo-science, some people have started actually doing some of those kind of experiments again. Turns out the Russian peasants were right -- crops inherit adaptation to stress conditions [1]. Wnt (talk) 18:13, 23 October 2013 (UTC)

Icebreaker

Three related questions: (1) Is it possible to make a hole in pack ice by firing a torpedo at it, as described in Ice Station Zebra? (2) Is it safely possible to use this method to free a ship trapped in ice? (3) Is it safely possible to free a ship trapped in pack ice by firing a (non-nuclear) cruise missile at the ice? 24.23.196.85 (talk) 02:35, 19 October 2013 (UTC)

The book synopsis for Under Ice: Waldo Lyon and the Development of the Arctic Submarine mentions "the Skate’s torpedo firing into ice", presumably USS Skate (SSN-578). As for (2) and (3), they sound rather dangerous. WAG: You'd probably have to fire very, very close to the ship to have any appreciable effect. Clarityfiend (talk) 04:19, 19 October 2013 (UTC)

As for using a cruise missile, an unguided torpedo is ever so many times cheaper than a Tomahawk missile at USD 1.5 million each. [2] It would be the world's most expensive hole in the ice. Also you'd have to get the thing to explode under the ice, which might not be as easy as it sounds - I'm not sure about that because they don't put the instruction manual on the internet. Alansplodge (talk) 08:35, 19 October 2013 (UTC)

Sometimes they do: [3] :-)Phoenixia1177 (talk) 08:45, 19 October 2013 (UTC)

Gosh! Alansplodge (talk) 19:14, 19 October 2013 (UTC)

(un-indent) Right, a torpedo is MUCH cheaper than a cruise missile -- but suppose there's a ship trapped in pack ice and being slowly crushed by the pressure, no icebreaker can get to it in time, and there's no submarine in the vicinity to fire a torpedo -- only a B-52 armed with cruise missiles (with conventional, non-nuclear warheads, of course). Is the trapped ship done for, in this scenario, or might it be freed without being sunk by the explosion in the process? 24.23.196.85 (talk) 19:32, 19 October 2013 (UTC)

With enough missiles you could free any ship I guess, not sure if one will do much good. A ship won't be crushed if it's trapped in a small isolated ice sheet, it's the pressure from the wind and sea currents on large ice sheets that can crush a ship, the same way it creates pressure ridges. An explosion on the ice will break up the ice in the vicinity and inertia will prevent the force being transmitted through the ice over long distances, but how many cruise missiles it would take and what the optimal distance (or optimal heigh of detonation) would be is anybody's guess...

Explosives were used in an attempt to free the Discovery, see Discovery Expedition: Second relief expedition. Ssscienccce (talk) 12:37, 21 October 2013 (UTC)

In other words, this method is doable, but inefficient and potentially dangerous. Thanks for the info! 24.23.196.85 (talk) 23:58, 21 October 2013 (UTC)

In any case you’ll have to aim very well!!

Iskánder Vigoa Pérez (talk) 04:42, 22 October 2013 (UTC)

Largest and most used Gastroenterology textbook?

What is the largest and most used (by universities) Gastroenterology textbook for students? Thanks. 79.182.146.170 (talk) 02:59, 19 October 2013 (UTC)

Asymmetric reciprocal effects

What are some of the most famous examples of asymmetric reciprocal effects?

What I mean is, you have two parameters, say volume and pressure, or capacitance and voltage -- I chose these randomly, these may not be good choices -- and when you increase one of the two, the other will respond and change, too, by a factor that relates to the increase in the first quantity. But when you reciprocate, i.e., increase the second quantity of the pair instead of the first, the first quantity will not change by the same factor but by much less or much greater a factor.

Apologies for my clumsy (and probably incorrect) use of technical terminology. — Preceding unsigned comment added by 89.204.130.121 (talk) 05:39, 19 October 2013 (UTC)

Anything with a non-linear relationship in it somewhere will be non-reciprocal, as will anything that is what is in electronics termed an active device. For example, all electrical networks consisting of nothing but passive components (ie resistors, capacitors, or inductors) will be reciprocal. A field effect transistor is an example of an active device, it can be set up so that a certain change in gate (input) voltage will produce a large change in drain (output) voltage, but any change in drain voltage forced by external circuitry will not change the input voltage. In radio, probably the most famous non-reciprocal (and active) device is the coherer, used in the early days to detect radio signals and convert them to audible clicks. Coherers compised a quantity of loose metal filings in an insulating (eg glass) tube. The incidence of radio wave energy caused the filings to clump together and drop in resistance, allwing current to flow in headphones. An electromagnet was typically empoyed to bang the side of it and loosen the filling again, ready for the next radio wave pulse. Obviously, no amount of banging or tapping on a coherer will produce radio frequency energy, so the device is clearly non-reciprocal.

Active devices, and non-reciprocal devices, can be made with magnetic materials, as the response of magnetic materials is inherently non-linear. Before the invention and refinement of transistors, magnetic amplifiers where widely used wherever it was desired to control a large current with a small input current - the regulation of factory processes, control systems for aircraft and missiles (use of magnetic amplifiers in missiles for flight path controls began with the very first - the German V2), control of elevators in multi-story buildings, and many more.

A carbon microphone, used in telephones for about 80+ years, is an example of a non-reciprocal active device. Sound pressure in the air causes change in electrical resistance and thus electric signal current. But no amount of electrical signal will produce a sound pressure. Carbon microphones are also an amplifier. Because the energy for the output current comes from a battery, the electrical power output was greater than the sound power input. That was important, as it overcame signal attenuation in the lines, and losses in the receiver, and allowed the deployment of telephone company networks before radio tubes and transistors were invented.

58.167.234.97 (talk) 06:03, 19 October 2013 (UTC)

That is very useful information to have, thank you very much. But unless I misunderstand you, the examples you give are of non-reciprocal relations only, whereas I am looking for reciprocal but not symmetric relations. (I increase parameter A from 30 to 40 and parameter B consequently increases from 100 to 101. But when I increase parameter B from 101 to 102, parameter A increases only from 40 to 41.) --89.204.130.121 (talk) 06:22, 19 October 2013 (UTC)

I gave you exactly what you asked for. My examples were:-

• Coherer: parameter A is field strength of radio frequency; paramter B is DC current. A affects B but B has no effect on A.
• Field effect transistor: Parameter A is gate voltage; parameter B is drain voltage. Again A affects B but B has no effect on A.
• Carbon microphone: parameter A is sound power; parameter B is electrical signal power.
• Another example is magnetostriction: In certain materials, a magnetic field causes the material to change in length and so apply pressure to something. But applying a pressure change does not produce a magnetic field.

Your use of the term "symmetrical" is what engineers term "reciprocal". "Reciprocal" to a mathematian means dividing into one, but to an engineer it means the translation of energy goes both ways between port A and port B. If changing A from 30 to 40 causes B to go from 100 to 101, AND if changing B form 100 to 101 (or changing it from 101 to 102) causes A to change from 30 to 40, then engineers would call it a reciprocal device. They would call it symmetrical if ALSO changing B from 100 to 99 would cause A to change from 30 to 20. That is, the change (on either side) had the same effect in both polarities. Almost all active devices are non-symmetric to some degree, as they are to a certain extent non-linear. (non linearity is of course the source of harmomic distortion in amplifiers) Electronic tubes follow a 3/2 power law. FETs are square law at low currents.

Perhaps you could give a set of numbers showing what you mean by reciprocal" AND "non-symmetric", as all my examples illustrate an, albiet more at a greater extreme, principle embodied in the numbers you used.

58.167.234.97 (talk) 06:51, 19 October 2013 (UTC)

Perhaps I should say "mutually influencing" instead of reciprocal? Other than that, I can't think of anything else that I could say to make my question clearer. (And I've given a set of numbers exemplifying what I mean in my previous post.) --89.204.130.121 (talk) 07:19, 19 October 2013 (UTC)

(I see that you've added some text to your latest reply in between my reading it and my posting of a response. Thanks but my question still remains. And in case the answer is, No that is impossible, nothing in nature works that way: Is that so not only for two mutually influencing parameters directly coupled to each other but also if they are just two mutually influencing parameters in a complex environment with many intervening links in one or more (non-linear?) cause-and-effect chain(s)? --89.204.130.121 (talk) 07:27, 19 October 2013 (UTC)

I'll have another go at making this clear for you. Here are the basic principles:-

• I'll use the term network. A network can be a network of electronic parts, mechnical parts, or whatever. In many fields, the term is system.
• Parts can be passive or active.
• Passive means that there is a one-to-one correspondence between a quantity and another quantity. A pipe is a passive part - the quantity of water leaving equals the quantity entering. Change one and teh other must change equallly - in sign and in magnitude. An electronic resistor is a passive part. The current in it is directly proportional to the voltage across it. Change either, and the other must also change in proportion, in sign, and in ratio.
• An active device is a device where one quantity controls another quantity. One example is a water tap - the position of the tap handle controls the water flow. Another example is a catalyst - the concentration of a catalyst (you can call this your "a") control the rate of reaction (your "B") of two other chemicals. Another example is a filed effect transistor - the gate voltage controls the flow of current in the drain.
• Practical parts can be almost ideal passives (eg electronic resistor), almost ideal actives (a transistor), or a mix of the two (eg a thermistor).
• A part can be linear, or non-linear.
• A linear part means that a change of x% in one quantity always occurs with the same x% change in another quantity - regardless of polarity, magnitude and offset from zero. An example is a resistor - a change in x volts will always cause the same y amps in current, regardless of whether it is a change from a to a plus x, or b to b plus x.
• A non-linear part means that the change in one quantity varies in magnitude, even when the change in the other quantity is always the same, when the offset from zero is changed. An example is a diode. As voltage is increased, the current increases ever more dramatically.
• A non-linear device is always non-symmetrical - that is a negative change has a different magnitude effect than an equal positive change. — Preceding unsigned comment added by 58.167.234.97 (talk) 11:07, 19 October 2013 (UTC)
• A network or system can comprise any number of linear, non-linear, passive, and active devices.
• A reciprocal network or system is where two quantities (your "A' and "B") each have an equal effect on each other.
• A network or system comprising only of pure linear passive parts is always reciprocal.
• A network or system containing at least one non-linear part or at least one active part will have a degree of non-reciprocity.

If this does not satisfy you, I suggest you give a set of numbers that show EACH term that you used. That is, give a set of numbers that show what you mean by non-recipocity, and another set of numbers that show what you mean by non-symmetricality. Then I can give examples to suit each. 58.167.234.97 (talk) 11:02, 19 October 2013 (UTC)

(outdent) You're starting to discuss a great deal of terminology now, which may be a good idea (to make sure we're all on the same page) but maybe not absolutely necessary. Here is your set of numbers:

Reciprocal:

Change in Quantity of A	Resultant Change in Quantity of B
30 -> 40	100 -> 101

Change in Quantity of B	Resultant Change in Quantity of A
100 -> 101	30 -> 40

Symmetrical:

Change in Quantity of A	Resultant Change in Quantity of B
30 -> 40	100 -> 101
40 -> 30	101 -> 100
Change in Quantity of B	Resultant Change in Quantity of A
100 -> 101	30 -> 40
101 -> 100	40 -> 30

But in what I am asking for, numbers might look like this:

Increase in one Quantity	Resultant Increase in other Quantity
QA 30 -> 40	QB 100 -> 101
QB 100 -> 101	QA 30 -> 31
Decrease in one Quantity	Resultant Decrease in other Quantity
QA 40 -> 30	QB 101 -> 100
QB 101 -> 100	QA 40 -> 39

I've called this "asymmetrical", for want of a better word. (Again, A and B are measurable physical parameters, such as volume, pressure, voltage, magnetic field strength, temperature, quantity of an element or compound, acidity, salinity, or whatever else one can imagine.)

Now if you tell me, that's preposterous, nature cannot work that way (or: simple logic tells us this is impossible), then o.k., my follow-up question is this:

Can there be a sufficiently complex system, in which A and B are but two of many distinct but mutually influencing factors, in which the interactions work in such a way that ultimately, changing A impacts B differently than changing B impacts A, in a manner as shown in my table above?

And if my follow-up question is nonsensical because there is something wrong with its internal logic or understanding of nature, please point to the error in my thinking. 89.204.130.121 (talk) 15:11, 19 October 2013 (UTC)

Ok, that makes it clear what you are asking. And I should have picked up what you were getting at earlier. Your third case is what an electrical engineer would call a two-port device with dissimilar forward and reverse gain. "Gain" is the ratio of an output quantity to an input quantity. Devices with dissimilar forward and reverse gain are an important class of non-reciprocal devices. So important that most engineers would just say its non-reciprocal. Many devices and systems in electrical/electronics, mechanics, chemistry, etc have this property. The word assymmetrical is not a bad word for it, but in electrical/electronics, assymetry means something else as previously described. Such devices are not at all remarkable. The examples I gave earlier, carbon microphones, transistors, radio tubes/valves, magnetostrictive devices, chemical catalysts, worm-gear mechanical drives with regard to torque, etc etc, all have dissimilar forward and reverse gain. In carbon microphones, for example, the forward/reverse gain ratio is infinite. In worm gear drives, by altering the gear pitch, you can have pretty much any forward/reverse torque ratio you like. In transistors, the ratio is very high (>1000:1 in low power audio transistors) but you can increase or decrease it by adding circuitry around the transistor. In fact, for any device with any arbitary dissimilar forward/reverse gain ratio, you can in theory add feedback to get any desired ratio. For example, if you feed some of the output back to the input at the right level and in opposite sense/polarity, you can completely cancel out the reverse gain, producing an infinite gain ratio. This is called neutralisation. 58.167.234.97 (talk) 16:00, 19 October 2013 (UTC)

Thank you, this is helpful! 89.204.138.111 (talk) 20:06, 19 October 2013 (UTC)

But just for curiosity's sake: The examples you've given -- water tap, transistor, microphone, worm gear -- are all machines. Can you also name a couple examples of natural systems meeting this definition? 89.204.137.240 (talk) 01:03, 20 October 2013 (UTC)

Don't forget catalysts, which I mentioned. Catalysts can be natural as well as man-made. Biological systems use complex catalyst systems to extract energy from food and use it. There's probably a vast multitude of biological systems that display dissimilar forward/reverse gain. DNA: In the simplest cases, the quantity of an enzymes etc is proportional to the number of genes for that enzyme (other factors also affect the rate of enzyme production), however the quantity of any enzyme does not affect the rate of DNA production. Drugs: Narcotics work because they are closely similar to molecules naturally made in the brain. If you take a narcotic, the brain over time automatically cuts down its own production - that is one of the mechanisms of addiction, because if you stop, you're in trouble until the brain ramps up production again, driving you to take more of the drug. So there narcotic you take can be your Quantity A, the brain's natural production can be regarded as your quantity B. The gain or coupling in each direction is obviously not the same. Various climatic parameters are coupled in more or less complex ways with dissimilar gains. For example an increase in temperature increases average wind strength, and an increase in wind strength affects temperature, but depending on distance from coasts etc, the temperature may increase or decrease. 60.230.213.251 (talk) 01:26, 20 October 2013 (UTC)

That's very interesting. Speaking of climatic parameters, we know from paleoclimatic records that in Earth history, an increase in temperatures generally was followed by an increase in carbon dioxide, but not the other way around or not as often. Could the temp v. CO2 relationship be an example of dissimilar forward/reverse gain? You mentioned feedbacks. How well are all the intervening feedbacks between CO2 change and temp change that may damp so-called climate sensitivity understood? Can the principle of dissimilar forward/reverse gain help us better understand the lull in global warming since 1998? 89.204.137.240 (talk) 02:04, 20 October 2013 (UTC)

I don't want to take this any further as I am not a climate scientist. I am an electrical engineer. While engineers have a lot of good mathermatical tools that helps their understanding of non-electrical subjects, there is a danger in straying from one's qualified field. However, my impression is that climate science is not well understood, as the complexity of the calculations demand a super-computer. And even then, too many simplifications have to be made in order to make the problem manageable. I suggest you ask your question on climate modelling again, without all the preample that is in this question. Then any climate scientists in Wikiland may answer you. When questions and their answers get too long, it tends to inhibit others from reading it all. 60.230.213.251 (talk) 06:28, 20 October 2013 (UTC)

i ask you again:is there any picture or graphic of the mixed flow compressor from the Pratt and Whitney pw610f?

is there any picture of this compressorß cause i surfed the internet and found the patent but there is no picture about this compressor and google gives e nothing aswell and surfing the internet in general helped nothing. so i give you the question again is there any picture of this compressor?Saludacymbals (talk) 15:02, 19 October 2013 (UTC)

You can get patents from various online sources. The patent should have a diagram, but on some online sources you only get teh overview text. So, if you tell us the patent number, the patent titel and assingnee, and which site you got that from, we'll have a chance to find another online patent source that has the diagram(s). 58.167.234.97 (talk) 15:40, 19 October 2013 (UTC)

Assingee is PRATT & WHITNEY CANADA CORP. the patent number is EP 1322865 B1 the title is Mixed flow and centrifugal compressor for gas turbine engine but there is only the cuttet diagram and no picture of the compressor section and google and internet dont shows more Saludacymbals (talk) 20:57, 19 October 2013 (UTC)

Haven't found one... Ssscienccce (talk) 15:05, 21 October 2013 (UTC)

Special dietary treatments for Autism

Is there published research on the effectiveness of special diets, such as the Specific Carbohydrate Diet, in controlling autism/ADHD?

This is a field of medicine where research is scant. Many parents treat or control their child's autism with special diets they believe to work, or drugs like ritalin the consequences of which haven't even been confirmed - for example whether it changes the patient's blood pressure. Authoritative publications like Proceedings of the Royal Society B, The Lancet and so on simply haven't covered in in the same way as, say, lung cancer or Alzheimer's Disease. I'm looking for sources like professional journals and books. Thanks 92.28.225.238 (talk) 15:47, 19 October 2013 (UTC)

There is quite a bit of published research -- not all of it high-quality though. See https://www.aacp.com/pdf%2F2104%2F2104ACP_Review2.pdf for a systematic review that discusses diet along with other treatments. Looie496 (talk) 16:05, 19 October 2013 (UTC)

Note that, although both autism and ADHD can lead to social interaction problems, the two conditions are quite different. Also with high functioning autism, it can be strongly argued that it is wrong to try to correct it. A degree of autism allows high achievement in subjects requiring technical detail and is thus of benefit to society. Many autistics like themselves just as they are, thank you very much. Whether or not ADHD is a real disease is controversial. The incidence of ADHD diagnosis is high in cultures where parents and teachers are taught/counselled/compelled not to use corporal punishment, whereas in previous generations the offender would have got a good smack or the cane, and that would quickly end the problematic behaviour. This is not to suggest that their cannot be a disease or gene expression problem leading to ADHD, but it is very likley that many diagnosed with ADHD do not have anything wrong with them other than just needing discipline. 58.167.234.97 (talk) 16:15, 19 October 2013 (UTC)

Autism and ADHD are comorbid conditions - meaning that if you have one of them, the odds of you also having the other is significantly higher than for the general public.

There are ways to alleviate the symptoms of ADHD (eg with drugs like ritalin) but there is nothing that helps with Autism - other than teaching sufferers social skills and such - which helps them to live with the symptoms without in any way diminishing them.

We don't entirely understand why Autism happens - and it's really only a description of a collection of symptoms - not all of which apply to all sufferers, so there could be many underlying conditions that produce the symptom group that we call "Autism". Worse still, it's a spectrum condition - varying from people who are almost normal to people who are profoundly cut off from the rest of the world.

I have Aspergers' Syndrome - which is now 'officially' called "High functioning Autism". There are some common symptoms that I don't have (eg extreme sensitivity to certain sounds and smells) - but I do have the social interaction issues and the beneficial symptoms such as improved mental focus and the inability to empathically understand how other people are feeling. For all of that, I'm one of the lucky ones who doesn't want to be cured.

Having met people with many more of the symptoms - it's really hard to believe that there is just one underlying condition - which means that it's highly unlikely that there can be just one cure. For that reason, I am super-suspicious of "cures" that are just anecdotally supplied.

I think that many parents of the less severely afflicted kids are being quite cruel to their children because they don't understand what's really going on. I have seen parents who tried to "cure" the social interaction problems by creating a meet-up group where all of their children could meet up and play together. For someone with Asperger's, it's hard to imagine anything more horrible than doing this!

It's also worth mentioning that the idea that innoculations are the cause of Autism is busted, busted, busted. For chrissakes don't avoid innoculations for your kids in order to "prevent" them getting Autism...it won't work and it's a dangerous thing to do.

SteveBaker (talk) 20:36, 19 October 2013 (UTC)

Autisma is a spectrum disorder. No two autistic persons are alike in their symptoms. For some children, parentally or teacher driven social interaction may be cruel or it may not be. A couple of things:-

• Generally, high functioning autistics (Aspergers) gain good, even very good, social interaction later in life. That's because they have enough built-in social function to learn from their experience. The best time to learn is when you are young. So an autistic child may be uncomfortable in social groups, but the experience will give him a better adult life. Sometimes you have to be cruel to be kind. Like birds, who when hatched don't know how to fly and must learn from watching parents, all people have to learn how to do social interaction. It's just that for normal people, learning it is easy, but for autistics it is hard. High functioning autistics learn social skills and can end up as good at as anybody - it just takes them longer to do it. The earlier they start the better, just as playing piano is difficult - but start at age 5 (ie as soon as the arms and hands are big enough), practice every day and you can eventually be very good.
• Like other brain aberations leading to poor social skills, many autistics may have poor social skills and lack the ability to bond with friends. But that doesn't mean they don't crave friendship and human interaction. Some couldn't care less, but some do care. Often, childhood social interaction doesn't result in the autistic child gaining lots of friends, but the frienship bonds they do form can after a while be very strong and last a lifetime.

60.230.213.251 (talk) 01:42, 20 October 2013 (UTC)

Thank you. 92.28.225.238 (talk) 08:54, 20 October 2013 (UTC)

There are a handful of reports about "purine autism" (autism with hyperuricosuria), a pretty small subset of people who have specific issues with purine metabolism, and even a claim that the drug allopurinol can address it [4]. I think potentially a number of traditional Chinese gout remedies that work by a similar principle of inhibiting xanthine oxidase, such as cassia/cinnamon, would have a related beneficial effect, though not as potent, but I don't think any real parent would want to fool around with an experiment on top of an experiment where their kids are concerned, so I don't think there's any data on that! But though there's a lot of research about metabolic variations in autism, I don't feel like much of it has carried through, and of course simply diagnosing and subcategorizing the condition into several subtypes is a step that, though needed, isn't even being done yet on a regular basis. Wnt (talk) 16:05, 20 October 2013 (UTC)

To follow up, it looks like there is some Chinese traditional medicine basis for dealing with autism, though it is hard to tell the difference between truly traditional treatment for the "Syndrome of five delays" and modern ideas to repurpose existing medicines for other conditions [5]. Still, various sources of unknown veracity such as [6] lead me to think that there is an acknowledged relationship between autism and "kidney qi" and "liver qi" which seem otherwise involved in metabolic disturbances such as gout, and herbs recommended for it do indeed include cinnamon, among many many others. As hard as it is to pick through information like this, I suspect that any nutritional help for autism is more likely to come from a careful, skeptical, systematic examination of the existing body of semi-empirical observations than from some sudden inspiration based on the genetic or neurological data. Wnt (talk) 16:39, 20 October 2013 (UTC)

There are indication that vitamin D is involved in autism. The evidence is not conclusive and sometimes contradictory, but this may be because wat is considered to be a normal vitamin D level may still be way too low. If the hypothesis that normal calcidiol levels should be around 120 nmol/l or higher is correct, then the autism epidemic in the West may well be the making of the medical community itself. The medical community had issued RDAs for vitamin D that were too low by today's standards, and today's standards are not compatible with what is observed in indigenous people in Africa. Particularly during pregnacy there is a big problem.

Until very recently the official guidelines were that expecting mothers should not use any vitamin D (due to the now debunked theory that this could cause damage to the unborn child), so their calcidiol levels would be very low. But measurements of the calcidiol levels of pregnant Maasai and Hadzabe women that were performed last year show that they have very high calcidiol levels, some had levels higher than 250 nmol/l (until recently it was thought that 250 nmol/l is the highest level that is obtainable by natural means alone). Also, huge spikes in the calcitriol hormone levels were observed during pregnacy, extremely high levels that according to common wisdom should be dangerously high levels, are apparantly part of the normal pregnancy processes. Count Iblis (talk) 20:02, 20 October 2013 (UTC)

I'm underwhelmed by the study that article is based on, because it shows that people with autism have lower levels of vitamin D -- but that could be because those people simply spend more time indoors, for example. Wnt (talk) 01:26, 21 October 2013 (UTC)

Here are a few Cochrane Reviews on the subject:

• Gluten and casein-free diets for autism spectrum disorder. It concluded, "Research has shown of high rates of use of complementary and alternative therapies (CAM) for children with autism including gluten and/or casein exclusion diets. Current evidence for efficacy of these diets is poor. Large scale, good quality randomised controlled trials are needed."
• Vitamin B6 and magnesium in combination for children with autism spectrum disorder. It concluded: "Due to the small number of studies, the methodological quality of studies, and small sample sizes, no recommendation can be advanced regarding the use of B6-Mg as a treatment for autism."
• Omega-3 fatty acids for autism spectrum disorders (ASD). It concluded: To date there is no high quality evidence that omega-3 fatty acids supplementation is effective for improving core and associated symptoms of ASD. Given the paucity of rigorous studies in this area, there is a need for large well-conducted randomised controlled trials that examine both high and low functioning individuals with ASD, and that have longer follow-up periods.

You can find other autism related related Cochrane reviews here (not all about special diets/supplements). And I want to re-emphasize the message hinted by User:Looie496's above: unless you (ie the OP) are medically trained, or have justifiable confidence in your ability to properly survey and interpret the results, you should really be looking at only high quality reviews and ignoring individual medical reports on the subject. Abecedare (talk) 02:01, 21 October 2013 (UTC)

Quite right. But, again, correlation does not mean cause. It may be that kids with a degree of autism do better because their parents take an interest, and try lots of things - including forcing contact with other kids. And the kids will be aware of their parents' interest, and believe they can interact socially - the placebo effect. Kids whose parents take the easy road and give the child what he wants, i.e., stay in his room and persue his hobby interests, are never going to learn social skills. Heck, even completely normal children will not learn social skills if they don't have contact with other kids. 60.230.213.251 (talk) 05:31, 21 October 2013 (UTC)

Potential Energy and Kinetic Energy

Assuming two massive bodies collided with each other due to gravitational potential energy. In such case, it is expected that collision will result in heat loss. How do we (approximately) calculate this increase in temperature at the surfaces of collision? Can we say that: Heat rise = Kinetic energy difference = potential energy difference? --Almuhammedi (talk) 16:04, 19 October 2013 (UTC)

It's virtually impossible to calculate the temperature right at the surface of collision, because so many factors affect it. In fact it really isn't even meaningful, since the collision surface is obliterated at the instant of collision. Looie496 (talk) 16:08, 19 October 2013 (UTC)

Indeed. In the simple case of two uniform homogenous bodies where nothing gets torn apart and there is no elasticity, the deformation of the surface must take a finite time, and that tiem can be estimated. In that time some of the heat will flow into the bodies within and away from the deformed surface, so there will be a temperature profile. Following the collision, heat will continue to flow within the bodies until the temperature is uniform thoughout. You can easily calculate the final uniform temperature, by relating the kinetic energy to the specific heat. This is a not uncommon question in asked of students in physics courses. By knowing the thermal conductivity of the bodies, you can with a lot more math, calculate the peak surface temperature rise. In reality though, your two massive bodies probably won't be uniform homogenous, will exhibit some elasticity, the elasticity will be non-linear (ie not obey Hook's Law) and some of the material will be sheared/split/broken off. Then a proper cacluation is near impossible. 58.167.234.97 (talk) 16:37, 19 October 2013 (UTC)

You can calculate the total thermal energy added to the colliding bodies - that's easy. But figuring out how much of the heat energy ended up in each body...and precisely where within each body is virtually impossible. It depends on the shapes, the initial temperatures, the material it's made of, the ambient air temperature...a huge number of unknowns.

What you can say, easily and immediately is that the total heat energy created is equal to the sum of the kinetic energies of the colliding bodies - which (if this is a collision caused entirely by one object falling under gravity onto the other) is equal to the initial gravitational energy. SteveBaker (talk) 20:18, 19 October 2013 (UTC)

No, not correct. In purely elastic deformation, all of the kinetic energy is returned to the two bodies. Two bodies colliding dead on will rebound, heading apart again, without any conversion to heat. If two elastic bodies collide but with a glancing blow and not dead on, part of the knietic energy will end up as the bodies spinning while they fly apart again. For conversion to heat, plastic deformation is required, as Ssscience pointed out below. This generally means that calculating the amount of heat is not trivial, and temperature rise most decidely non-trivial, because plastic deformation, specific heat, and thermal conductivity are all non-linear in real bodies. Not at all easy. 60.230.213.251 (talk) 02:19, 20 October 2013 (UTC)

Without plastic deformation, the decrease in kinetic+potential energy will equal the increase in "heat energy". When plastic deformation has occured, part of the energy may have gone into breaking of inter- or intramolecular bonds, changes in surface energy, stored as internal stress... Ssscienccce (talk) 00:30, 20 October 2013 (UTC)

What you can do here is compute the relative speed just before impact. If this is much more than the speed of sound of the materials the bodies are made of, then you can use the same methods that are used to compute the effect of impacts in the Solar System. A lot is known about this from theory, simulations and experiments, there are ready to use formulas that are derived from these results using scaling relations. Count Iblis (talk) 14:53, 20 October 2013 (UTC)

Recrystalization vs. acid-base extraction

In an experiment in which benzoic acid is purified using two methods, recrystalization (heating and cooling) and acid-base extraction (which involved mixing benzoic acid with ethy acetate and changing its pH in a separatory funnel), which should one should result in a higher percent mass recovery (i.e. recovered mass similar to initial mass)? Also, I have no idea how, but my recovered mass from the extraction method was twice the initial mass. This doesn't seem right. --FutureTrillionaire (talk) 16:18, 19 October 2013 (UTC)

Extraction should give a MUCH higher percent recovery -- recrystallization relies on the decrease in solubility with temperature, so a good portion of your product will go into the waste with the solvent (been there, done that!) As for why your recovered mass is twice the initial mass -- the most likely explanation is that your extracted product still has A LOT of solvent in it (or maybe it somehow reacted with your solvent because of a pH excursion, though I think this is unlikely). 24.23.196.85 (talk) 19:25, 19 October 2013 (UTC)

Cool. Thanks man!--FutureTrillionaire (talk) 19:38, 19 October 2013 (UTC)

With a solubility of 68.0 g/l at 95°C and 2.1 g/l at 10°C (1.7 at 0°; 2.9 at 20°), recrystalisation could be quite efficient, depending on the amount of water used... Ssscienccce (talk) 21:10, 19 October 2013 (UTC)

Health effects of low exposure to pesticides

Is there any evidence of harmful health effects from consuming fruits and vegetables containing a small amount of residual pesticides? The article on health effects of pesticides wasn't clear about this. 74.15.138.165 (talk) 17:20, 19 October 2013 (UTC)

Short answer: yes, see paraquat for example. Nuanced answer: one reason the article is not clear is that the answer is not entirely clear -- among other factors it depends on what pesticide is involved and what amount. There is some reasonably solid evidence that exposure to certain pesticides can increase the likelihood of Parkinson's disease, for example (see our article). Looie496 (talk) 17:40, 19 October 2013 (UTC)

Well, that depends on how small is your small amount -- if you're talking about 1 part per trillion, then no pesticide can possibly have an effect at such a low concentration, whereas if you're talking about, say, 100 parts per million, then long-term harmful effects are very much possible, depending on the pesticide in question. 24.23.196.85 (talk) 19:51, 19 October 2013 (UTC)

What do you mean by exposure? Does that mean exposure at the typical concentrations that you would find on a vegetable in a supermarket? 74.15.138.165 (talk) 20:12, 19 October 2013 (UTC)

Birth defect rates were higher (in U.S., 1996 to 2002) when conceived in the period april to july, same period in which concentration of pesticides in surface water (and possibly tap water) is highest. Increase (in birth defects) was 3%. Doesn't mean causation of course... Ssscienccce (talk) 22:48, 19 October 2013 (UTC)

• There is sometimes a paradoxical measurable benefit from a small exposure to certain toxins. I am annoyed I cannot think of the term for this. Perhaps it will occur to someone else. μηδείς (talk) 00:44, 20 October 2013 (UTC)

Hormesis 89.204.137.240 (talk) 02:52, 20 October 2013 (UTC)

Or Desensitization (medicine), immunization and even homeopathy, 175.38.168.70 (talk) 03:02, 20 October 2013 (UTC)