Wikipedia:Reference desk/Archives/Science/2011 September 2

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September 2

Polythene molecules

Hi, I found this on a website:

"Linear polyethylene is pretty big, with molecular weight of 200,000 to 500,000, but it can be made even higher. Polyethylene with molecular weights of three to six million is called ultra-high molecular weight polyethylene, or UHMWPE. It can be used to make fibers which are so strong they are even better than Kevlar for bullet proof vests."

If each "unit" of the molecule, CH₂, has molecular weight 14, and the C-C bond length is 0.153 nm (which I found on another site), then 500,000-weight polythene molecules should be about 5 microns long, and 5,000,000-weight polythene molecules should be about 50 microns long. Have I done that calculation correctly?

Secondly, if polythene could be made with molecules say 30 cm long, then would the material be super-super-strong? Apart from possibly greater strength, would its appearance be substantially the same as that of ordinary polythene? 86.179.1.213 (talk) 00:56, 2 September 2011 (UTC)

No, it's incorrect. You have neglected the <CC bond angle, and treated the chain as straight, instead of a zig-zagging conformation. I don't have an answer for the second question. Plasmic Physics (talk) 01:06, 2 September 2011 (UTC)

We have articles covering the range of different polyethylene (note the spelling!) materials: Linear low-density polyethylene, High-density polyethylene, and Ultra-high-molecular-weight polyethylene. Interestingly, they discuss material properties and some discuss the origin of them, but none discuss the actual linear strength of individual polymer chains. The tensile strength of macroscopic fibers is in part because it's hard for separate polymer chains to slide past each other (so "longer leads to stronger") in addition to it being hard for a single chain to stretch (or even rip apart at exceptionally high forces). The chains in the materials commonly used aren't long enough to actually be gripping two ends of a single chain as your 30-cm example would allow. You're right that it might be even stronger strong because chain slippage (leading to fraying of the chains from each other) would not be relevant. I don't know if actual measurements have been made of simple polyethylene-chain linear strengths (approximated as elastic stretching a spring), but I assume they have because they have for some more complicated biopolymers (see Worm-like chain#Stretching Worm-like Chain Polymers—you can skip the math if you like). DMacks (talk) 07:52, 2 September 2011 (UTC)

"Polyethylene or polythene (IUPAC name polyethene or poly(methylene)) is the most widely used plastic..." This isn't a spelling issue: the words are in free variation. Polythene is more common in lay contexts, polyethylene in IUPAC compliant ones. I'm not the OP, I just wanted to note this is not a spelling issue. 86.164.62.111 (talk) 09:39, 2 September 2011 (UTC)

Polyethylene is the normal word in the States. --Trovatore (talk) 06:46, 3 September 2011 (UTC)

Interesting thanks! I've never seen that alt spelling used in any context (I've worked in recycling and science worlds in the US). DMacks (talk) 10:24, 2 September 2011 (UTC)

I think many Americans first encountered that spelling by way of Mr. Lennon. Deor (talk) 11:11, 2 September 2011 (UTC)

• (OP) Yes, "polythene" is the usual layperson's word in the UK. Here it says that the force needed to break a C-C bond is 1600 pN. So if we knew how many polythene molecules per cross-sectional area then we could work out the tensile strength of some super-polythene with 30 cm molecules. What would the (average) cross-sectional molecular separation be? Would it be slightly more than the C-C bond length? A lot more? Does anyone know? 86.177.107.255 (talk) 17:27, 2 September 2011 (UTC)

Using tidal power to generate electricity

I have a little fishing hut in south Louisiana. Its not much more than a single room with a bunk bed, a mini-refrigerator, a single light bulb, and one power outlet we use to charge the cell phone and operate an AM/FM radio for entertainment. So we use very little power, and currently rely on a propane generator. My question is, when the tide come in and out twice a day, it is a very powerful surge, to the point that an unsteady footing would result in a grown man falling over if he were to stand in the surge. Is there a way to harness this power? All my Internet searches have resulted explanations of commercial tidal-power generation...but nothing for a simple dwelling, or everyday use. Any ideas? Quinn ^{❀ BEAUTIFUL DAY} 03:05, 2 September 2011 (UTC)

It is possible, of course, but there are lots of drawbacks, like your generator getting various sea life encrusted on it, the whole apparatus washing away during a storm, needing enough batteries to "tide you over" between tides, etc. I picture a wheel with fins on it you could lower into the water when present and remove (to avoid encrustation) when absent, which would drive a small generator and charge a series of car batteries. You would then power the hut off those car batteries. You'd need an alternator to power an A/C outlet. StuRat (talk) 03:25, 2 September 2011 (UTC)

We have an article on pico hydro, which while not specifically addressing tidal power generation, may still be of interest. -- 223.207.148.174 (talk) 05:32, 2 September 2011 (UTC)

You are in a very exceptional situation, most dwellings would never have alocal access to tides, therefore, there is no commercial interest in developing something that could power you. You could invent your own device based on standard hydro-power mechanisms, though, something like sturat was describing. Let us know if you do and how much power you end up generating. --Lgriot (talk) 08:28, 2 September 2011 (UTC)

You'll also be continuing a venerable (pre-electric) tradition: see for example Eling Tide Mill. {The poster formerly known as 87.81.230.195} 90.197.66.179 (talk) 11:45, 2 September 2011 (UTC)

Supposing you can built and install this kind of equipment, the power you gonna get will be very small. Refering to Betz' law the energy of the tidal current is given by : $P_{\rm {max}}={\begin{matrix}{\frac {16}{27}}\cdot {\frac {1}{2}}\end{matrix}}\cdot \rho \cdot S\cdot v^{3}$ Suppose you can get all the kinetic energy with a 1 square meter equipement in a 0,5 m/s tidal current with no friction and a perfect generator, you could only get a electric power of 40W ! The fact is that tidal currents are very small in most areas, only few spots on the costs can reach interesting tidal current values worth installing power generation capacities.--Franssoua (talk) 14:10, 2 September 2011 (UTC)

I'm surprised nobody's realized that the OP is asking about the tide but (s)he probably mean to ask about wave power which is entirely another matter. 24.73.119.146 (talk) 19:12, 2 September 2011 (UTC)

I have to disagree: I think the details the OP gives show that he's clearly intending to ask about tidal power, not wave power. However, Quinn (aka David) will probably come back and clarify if you're right and the rest of us wrong. {The poster formerly known as 87.81.230.195} 90.200.79.225 (talk) 19:43, 2 September 2011 (UTC)

Nope, definitely not wave power. My hut is on a pretty narrow inlet of salt water, so it kind of funnels the tides in an out in a fast current. We go from about 3 ft of water to ~6 ft (I've never really measured) in a short amount of time (say, maybe-2 hours), depending on the tide...so you can imagine the "power" of the water flow. A few "neighbors" in similar situation have types of water wheels, but they don't seem to serve any purpose other than being conversation pieces. I am definitely not one to go invent something like this. And few other searches around the web seem to indicate that the tide change, though drastic, is not prolonged enough to generate anything other that a slight re-charge of batteries, and I might be better off doing something with solar panels, since the area is basically marsh, and there's pretty much no shade. Both technologies are still, unfortunately, pretty expensive for a fishing camp I inhabit, sporadically, maybe 3 weeks out of the year. 71.195.140.199 (talk) 00:39, 3 September 2011 (UTC)

Whoops, that was me above. Quinn ^{❀ BEAUTIFUL DAY} 00:41, 3 September 2011 (UTC)

Plug-in, portable solar panels might be best, then, since you could take them home with you and prop them up in a window to get some use out of them all the time. They would slightly reduce your home electric bill. About the shed, do you spend the night there ? If so, then there's the issue of how to run the mini-fridge overnight. You might want to continue to use propane then, since using solar for that would involve lots of batteries and bigger solar panels. Or you could just have it full of ice packs, to keep it somewhat cool overnight. Not appropriate for things like egg salad, but OK for soft drinks. StuRat (talk) 01:04, 3 September 2011 (UTC)

Yeah, I might stay there 4 nights at the most; but usually just for a weekend. We keep the beers/sodas/snacks in an ice chest...the mini-fridge is basically used for keeping the bait and the fish we catch cool until we're ready to leave, since you don't really want to combine dead fish/bait in the same place as your food/drinks. But the whole "free energy" thing is turning out to be one of those ideas that sounds great, but is simply not practical...especially for an old shed that'll probably get blown away in the next hurricane anyway. I like the portable solar panel idea, though, and may see about incorporating that, 'cause I'd have some uses for those around my home as well. Thanks everyone. Quinn ^☂THUNDER 02:16, 3 September 2011 (UTC)

Blood-vein, Mr. Schmidt and taxon authorities

My slowly ongoing project in fiwiki is to at least redlink all taxon authorities. However I drew a blank with Mr. Schmidt in Blood-vein (Timandra comae). Google tells me his first name starts with an A, but there my googling skills end. Any help on finding full names of taxon authorities in general is also appreciated, since I somehow feel that this isn't going to be the only tricky one I'm going to encounter. --Albval (talk) 05:25, 2 September 2011 (UTC)

His name was Anton Schmidt, and the title of the original paper was "Ein neue Timandra-Form aus Spanien” (A new form of Timandra from Spain) published in Internationale Entomologische Zeitschrift 25(6) (1931):57-59.

A very good source for a lot of names is tierdoku.com. That's where I found his name:

http://tierdoku.com/index.php?title=Ampfer-Spanner

It includes full biographies for many of the most noted zoologists (but unfortunately not Anton Schmidt), but doesn't help much with less noted ones. The site is in German, though. Dominus Vobisdu (talk) 07:34, 2 September 2011 (UTC)

Many thanks! I can read (but not speak or write) German adequately, so the site helps my project a lot. --Albval (talk) 07:44, 2 September 2011 (UTC)

Are there any experts who can answer my question? (hand sanitizing)

It's been said that cleaning your hands with soap and water, or a hand sanitizer will eliminate most organisms that are not part of your normal body flora. I want to eliminate ALL of the organisms that are not a part of my normal body flora, not MOST. So I was wondering, is it possible to get rid of all the germs on my hands? If so, how can I do it? If not, why not?98.234.170.202 (talk) 06:40, 2 September 2011 (UTC)

It is possible to remove all bacteria, yeasts and whatnot from your hands, but then you'll be removing all of them. There is no way to differentiate between normal bacterial flora and "germs" when cleaning your hands. Not to mention some parts of your hands are removed as well (probably most of your epidermis, for example). --Albval (talk) 06:50, 2 September 2011 (UTC)

It's possible to remove all of them? How can I do that (and what's epidermis?)? 98.234.170.202 (talk) 06:55, 2 September 2011 (UTC)

I added to the title to make it useful. Epidermis is the outer layer of skin. I imagine submerging your hands in bleach might kill them all off. However, what you need to realize is that some bacteria are helpful. There was a problem, for example, when adult diapers were treated with a chemical (something hexaflouride, I think) which killed off all the bacteria. When you do this, other nasties which were controlled by the helpful bacteria then begin to grow. StuRat (talk) 07:02, 2 September 2011 (UTC)

And something that kills all of the bacteria will be (very) harmful to your hands as well, bleach and heat/fire being the most common answers. --Albval (talk) 07:14, 2 September 2011 (UTC)

"Normal" body flora includes plenty of bacteria of constantly varying extraction. The purpose of washing hands is to reduce the bacterial load, not eliminate it entirely. You absolutely can not eliminate all the germs on your hands without for example, surgical scrubbing followed by powerful antibiotic wash, but there is no reason you should want to unless you are touching a severely immunocompromised person; in which case wearing gloves is far easier. 76.254.20.205 (talk) 09:22, 2 September 2011 (UTC)

Even surgical scrubbing followed by a sterilizing wash won't eliminate all microorganisms -- there is, for example, no procedure that makes it acceptable for a surgeon to work without gloves. Looie496 (talk) 15:41, 2 September 2011 (UTC)

Killing off 99.9% of the harmful bacteria, for example, increases the likelihood of superbugs via disruptive selection. Each person's hands has a unique composition of bacteria, and the human body contains more bacteria than normal body cells. ~AH1 ^(discuss!) 23:17, 2 September 2011 (UTC)

Mold VS Mildew

I have been in the mold remediation business for over 11 years and performed these services around the world. During this time I have met and worked with several professionals within the industry and hence learned/aquired a great amount of knowledge. However I do not know the difference between mold and mildew. Here is why I'm asking this question. When the "Mold Frenzy" began hitting the USA in the mid 90's, most notibly the Ballard case in Texas and Brockovitch case in California, mold slowly became a dreaded "4-letter" word and hence the industry started to utilize the word Mildew instead. This supposedly was a way to calm any concerns or panics that our clients may of had because mildew was never associated with the terms "Black mold" or "Toxic mold". So, with that brief history is there a simple answer that may be given to the difference between mold and mildew. Such as "Mildew requires photosynthesis to grow" if this statement is correct? --CMjeter (talk) 08:03, 2 September 2011 (UTC)

Mildew is simply a term for unsightly molds that grow in damp places like bathrooms and basements and can damage walls, books, and other objects. Mildew is also used for certain fungal plant diseases. Dominus Vobisdu (talk) 08:22, 2 September 2011 (UTC)

In very humid climates mildew is different (and much more damaging to various natural textiles) than the sort of tile grout growth found in kitchens and bathrooms in more arid regions. 76.254.20.205 (talk) 18:22, 2 September 2011 (UTC)

You don't need a humid climate. Just a humid environment. For example, one of the worst cases of mildew I've seen was in sunny San Diego. A tenant had painted his whole apartment with cheap water-based paint and left for a few days, leaving the apartment shut up. There was a luxurious layer of mildew covering just about everything organic in the apartment when he got back. The carpets and upholstered furniture had to be discarded, and all clothing and bedding had to be washed. My friend and I were called in to repaint the apartment, which proved difficult and very costly. Every surface had to be scrubbed with bleach, scrubbed again with TSP, thoroughly dried, sealed, covered with a base coat, and painted with high-quality paint to give satifactory results.

The humid environment doesn't have to be all that big, either. The space under a sink or near an air vent can become humid enough to permit damaging mildew to grow. Dominus Vobisdu (talk) 02:29, 3 September 2011 (UTC)

This is all great information but the topic is headed in the wrong direction. The question is "is there a difference between mold or mildew" and is there a scientific explination to differentiate the 2 terms?--CMjeter (talk) 18:54, 4 September 2011 (UTC)

As I've written already, mildew is simply 1) another name for any mold that disfigures the surfaces of walls, furniture, books and other items in humid environments; or 2) the name of particular fungal diseases of plants (downy mildew and powdery mildew). As your question was about the former, no, there is no scientific distinction between them. Any hyphal fungus that disfigures surfaces can be referred to as either mold or mildew, with no difference implied. They can be used, and are used, interchangeably. The term mold likewise does not refer to any particular taxonomic group of fungi, but refers to any fungus that is growing with a hyphal growth pattern, as opposed to yeast, which is any fungus growing with a unicellular growth pattern. A particular species can grow as either a mold or a yeast, depending on environmental conditions. Dominus Vobisdu (talk) 22:58, 5 September 2011 (UTC)

scientific method

what are the tenets of the traditional scientific method? what is wrong with their account of science? — Preceding unsigned comment added by 41.204.186.18 (talk) 09:09, 2 September 2011 (UTC)

Have you read Scientific method? 76.254.20.205 (talk) 09:13, 2 September 2011 (UTC)

Properly the scientific method is a matter of philosophy rather than science, and as such it's not really one thing you can nail down but many related things. The hypothetico-deductive model is not really that different from the intuitive trial and error approach of the ancients. At the same time adding a control group is an important refinement, and further refinements (sometimes debatable) constantly emerge - double-blind studies, crossover studies and meta-analysis for example. When used properly, the scientific method is just a way of saying you've thought over how to do an experiment so that it proves what you think - but when improperly interpreted, you get people denouncing all the scientists of ancient times as being irrelevant because they didn't know Francis Bacon. Of course a certain amount of frustration at ancient authors is to be expected, because they didn't have monks copy out every result from a hundred experiments they did or heard of to see whether a given imported herb was useful for patients with a given disease. But I suspect often such work was done in one form or another, and I think it's unscientific, even cult-like, when people dismiss their results out of hand because "science wasn't invented yet". Wnt (talk) 09:32, 2 September 2011 (UTC)

The main problem with an account of science that relies upon a single scientific method is that no single such method exists, or has ever been used by scientists. Different scientists in different fields use different methodologies, and they are essentially never the method displayed in high school science fairs (form a question, propose a hypothesis, conduct the experiment, revise the hypothesis, publish the conclusion). Real life examples of scientists, past and present, show a lot more "messiness" in how they choose their problems of interests, how they attack them, how they filter over their data to figure out what is real and what is not, and so on. The belief in a unitary "scientific method" is a convenient falsehood that children are told to encourage them to think about knowledge in a systematic fashion, but it is not a reflection of the reality of scientific practice. (This in no way need disparage scientific practice, any more than disbelief of the stork disparages childbirth.) --Mr.98 (talk) 14:26, 2 September 2011 (UTC)

There are universal threads within the philosophy of science which one can distill out, however. Certain things like a) being organized in your thinking b) having goals in mind c) developing testable ideas d) developing reasonable experiments to test those ideas e) being skeptical f) universality and repeatability (i.e. anyone can do it, and the results should work always) g) a negative result is still a result, and probably several other concepts. What makes science work is that it is different than other ways of thinking, than other paradigms. --Jayron32 15:50, 2 September 2011 (UTC)

Unfortunately there's no really great way to distinguish a specifically scientific method (see demarcation problem), and much of what you've listed is only distinguishable long in hindsight (which makes it not so useful as a prescriptive and only problematically useful as a descriptive). So that doesn't really change things a whole lot, unfortunately. There's plenty of what all would consider to be "science", historically and presently, that doesn't fit into those criteria you've mentioned. --Mr.98 (talk) 21:42, 2 September 2011 (UTC)

I think observation, inductive reasoning, hypothesis and experiment (or in layman's terms, trial and error), are instinctive and ancient. Any plumber called to a home collects the data, forms a hypothesis, and tests it; if they lacked a scientific mindset, they would be very poor plumbers indeed. I don't know, but I suspect the plumbers in ancient Rome were just as scientific in their approach. I think that it is the small technical refinements that modern scientific method emerges - starting with the conscious use of a control group, which implies the planned decision to set up identical experimental groups and treat them differently. I think that any ancient herbalist knew to take a substance and give it to patients it's supposed to help and note down what happens - what's not so clear to me is whether they could find it in themselves, their ethics, and the tolerance of their patients to sacrifice the quality of care by giving half a treatment they believe to be less effective. I won't rule out that they did it, though, and in any case economic limitations probably caused such contrasts to occur whether they wanted them or not. Likewise meta-analysis implies a certain added level of sophistication, in which clinical studies are done with enough consistency and regularity (often perforce, due to the need to study people at many different hospitals) that people can actually tot up averages of the results of multiple studies and hope they really mean something. Wnt (talk) 22:20, 2 September 2011 (UTC)

They're not instinctive, they're not ancient. It wasn't anything like what Aristotle was doing, for one simple example. Consider that one of the major learned debates (Hobbes v. Boyle) in the 17th century was whether induction or deduction should be used to generate knowledge — it was essentially a debate about whether experimentation could create "real" philosophical knowledge. (The modern echo of this sort of discussion is the still relevant question for many people about whether scriptural knowledge or scientific knowledge should be believed.) Either one dilutes what "science" means to the point where every shaman and plumber is a scientist, or you have to assert that it's something much more recent... --Mr.98 (talk) 22:25, 2 September 2011 (UTC)

Despite some significant advances, 17th century Europe was still fairly backward about many things. I don't think it's right to assume that people in 10th century Turkey or ancient Sumeria didn't have a more scientific orientation. What I do know is that people somehow were capable of producing effective drugs many millennia ago - products like aspirin, colchicine, and morphine are sometimes a little better, sometimes a little worse than the equivalent remedies compounded in the 5th to 3rd millennium B.C. The ability of ancient physicians to develop such products implies some kind of working scientific process, even if we don't have the details on what it was. Wnt (talk) 18:36, 4 September 2011 (UTC)

(edit conflict)There are many areas of disagreement among scientists, one of them being the hidden debate over the degree which materialism dominates the scientific method, and another over reductionism vs. holistic methods. Most of these controversies reflect differences between Scientific disciplines and patterns of thinking among specific scientists. Another matter of intense debate is when a new falsifiable hypothesis, theory or unrepeated observation is scruitinized using scientific skepticism, whether scientists attempt to explain a phenomenon using known parameters or completely explain away the phenomenon, under the line of extraordinary claims require extraordinary evidence. As a result, -isms in science are usually not falsifiable, any more than the usefulness of pattern recognition is falsifiable. Many tenets of scientific canon have a cultural background. Science undergoes various paradigm shifts, and interdisciplinary approaches to subjects are becoming more popular as the need for solutions to today's problems from various points of view is ever-increasing. Another area of disagreement is conforming to a generalist vs. specialist approach to science in today's world. See also scientism. ~AH1 ^(discuss!) 22:38, 2 September 2011 (UTC)

See logic, inductive logic and deductive logic. ~AH1 ^(discuss!) 22:38, 2 September 2011 (UTC)

Also take a look at meta-analysis, and one meta-analyst's essay: Why most published research findings are false (and this video). ~AH1 ^(discuss!) 22:41, 2 September 2011 (UTC)

Yet another issue is that in some fields including astrophysics and climatology, more than one reason (ie. more than one hypothesis) may explain the causes of an observed phenomenon or change. When factions of scientists want to reject all but one hypothesis, problems may occur in the form of incomplete explanation. ~AH1 ^(discuss!) 22:49, 2 September 2011 (UTC)

In the above mentioned fields, computer modelling is typically used over actual manipulations of the subject matter, for obvious reasons. The inherent chaoticity in some dynamical systems contributes to higher difficulty in testing hypotheses. ~AH1 ^(discuss!) 22:52, 2 September 2011 (UTC)

Caffeol

Is there a single unique compound called caffeol, or is it fairy dust? I find very few modern scholarly sources mentioning it in detail. If it does exist, what is its structure? Why has it vanished into obscurity? Plasmic Physics (talk) 10:19, 2 September 2011 (UTC)

After striking out in PubChem,^[1] I turned to Google, and found the blog of someone who had walked this road before. [2] He leads us to [3] which describes that caffeol is an aromatic distillate with many components, which is further modified by Maillard reaction during heating. It apparently is about 250 mg/kg of coffee, a pretty small amount. The book is pretty detailed, but even so I'm a bit puzzled how to define caffeol, because it's historical in nature and I'm not sure how many of the components are truly part of "caffeol" rather than simply "components of the coffee aroma". Wnt (talk) 15:29, 2 September 2011 (UTC)

Essential oils of any plant substance are usually dozens if not hundreds of different aromatic oils and esters, which is why artificial flavors -- which usually only have 1-3 synthetic components -- are usually distinguishable from the flavor they are supposed to represent. 76.254.20.205 (talk) 18:20, 2 September 2011 (UTC)

That is as far as what I got in Google, I searched PubChem, SpiderChem, ChEBI, MeSH, nothing. The closest thing I found on PubChem was a compounds containing the functional group called caffeoyl, which refers to 3-(3,4-dihydroxyphenyl)prop-2-enoyl. Plasmic Physics (talk) 22:13, 2 September 2011 (UTC)

So caffeol is a distillate, not a unique substance. I've done some more reading and found that furfuryl meracaptol is the main component of caffeol, partial to the coffee aroma. I've started an article stub on it: furan-2-ylmethanethiol. Plasmic Physics (talk) 07:16, 3 September 2011 (UTC)

I wouldn't really consider it accurate to pinpoint that particular chemical as the key component of 'caffeol'. 'Caffeol' really is a magic catchall term for the origin of the cofee aroma, as the kinds of compounds are produced during roasting and therefore extremely variable. Various studies since the original coining of the term 'caffeol' by Bernheimer in 1880, have identified 850 different compounds, all of them contributing to the aroma of coffee. -- Obsidi♠n Soul 09:56, 4 September 2011 (UTC)

OK well, the sample extract in the study I read, detected it to contribute the strongest to the aroma tested. Plasmic Physics (talk) 10:29, 4 September 2011 (UTC)

Electromagnetic pump for ionic liquids

Can an electromagnetic pump be used to pump molten salts or ionic liquids as it is used for pumping liquid metals (without electrolytic effects)?--86.125.191.228 (talk) 10:49, 2 September 2011 (UTC)

Yes, these are sometimes used in nuclear reactors, but they aren't practical in (m)any other applications. 76.254.20.205 (talk) 18:14, 2 September 2011 (UTC)

Capt. Marko Ramius would beg to differ on the last point... 67.169.177.176 (talk) 06:10, 3 September 2011 (UTC)

Earthquakes

Why have there been so many large earthquakes the past few years? --76.211.88.37 (talk) 12:02, 2 September 2011 (UTC)

It's not obvious to me that there have been more large earthquakes in recent years than previously. There is more media coverage now. Increasing populations mean the more people are affected. It would be interesting to look at absolute figures for the earthquakes themselves. HiLo48 (talk) 12:08, 2 September 2011 (UTC)

This is a good place to get some numbers to play with. -- kainaw™ 12:58, 2 September 2011 (UTC)

I made 2 graphs to show how many eathquakes occur yearly in the past 40 years with Magnitude > 7 and Magnitude > 8. I let you make your own opinion whether there's more big earthquakes recently. I think a bit statistics would help but I'm not sure it would bring a clear answer since the data set is very small.--Franssoua (talk) 13:37, 2 September 2011 (UTC)

One should be cautious in interpreting plots such as those, as it's worth remembering that earthquakes often come in clusters (with foreshocks and aftershocks) in space and time. Consider, for example, the 2010 magnitude 7+ numbers. Out of 22 quakes listed, it seems apparent that the three quakes on July 23 – falling within a couple of hours and a few miles of one another – are part of the same event and probably would be covered in the media as one disaster, despite counting thrice. On the other hand, there were also strong quakes on 6 April and 9 May with epicenters about 200 km apart, off the coast of Indonesia. They were no doubt occurring on the same fault system and probably as part of the same gelogical event or process, but the two quakes would definitely have been on separate news cycles.) TenOfAllTrades(talk) 14:40, 2 September 2011 (UTC)

Three of the ten largest recorded earthquakes have occurred within the last 7 years (see Lists of earthquakes#Largest earthquakes by magnitude) -- that's a statistical anomaly for sure, but since it is post hoc, it is hard to assess it's significance. I have seen some discussion of it in the literature, but there are no definite conclusions. Looie496 (talk) 15:31, 2 September 2011 (UTC)

Note that large quakes in populated areas get far more coverage than in unpopulated areas. If a quake the size of the one in Japan had occurred in a sparsely populated area, with no video coverage of the event, it wouldn't have been a major news story, but at best a footnote on that day's news. So, the perception that there are more large quakes recently is probably due to them having occurred where they did.

That said, seismic activity can cluster together. A large quake in one place moves the crust of the Earth slightly, causing other misalignments which cause other quakes, etc., within hours, days, or weeks. StuRat (talk) 15:35, 2 September 2011 (UTC)

A 9.0 earthquake would be a big news story no matter where it occurred -- because of its high likelihood of producing a destructive tsunami if nothing else. Of course a 9.0 in, say, Vanuatu, would not draw the same attention as a 9.0 in Japan, but it would still draw attention. Looie496 (talk) 16:25, 2 September 2011 (UTC)

I don't believe such a quake, in the middle of a continent, would have any chance of triggering a tsunami. StuRat (talk) 22:36, 2 September 2011 (UTC)

Also from the list it's not clear it's a 'statistical anomaly for sure'. If we take out all the ones from before ~1900 i.e. as our article notes, the ones which are estimates so their position in the list is unclear as they before the widespread distribution of seismometers, we find that 6 of the top 10 happened in 1960, 1964, 1952, 1965, 1950, 1957. You can put these in various combinations including 3 in a 5-6 year period and another 3 in a 7-8 year period; 6 in a 15-16 year period; 4 in a 8-9 year period and 2 in a 2-3 year period. (Although if you expand it to top 11 you get another for your past 7 years, I'm not sure if it makes sense to restrict it to the top 10 in that fashion anyway since the moment magnitude appears to be the same.) To be fair, 3 of those were in Alaska (although I haven't looked how close they are) and 2 of those less then a year apart so they may have been related, but it still shows the fallacy of calling a statistical anomaly from such limited statistics and without actually looking at the rest of the statistics. P.S. Noticed that our article on the 1960 quake says "This 2010 Chile earthquake may be related or consequential to the 1960 tremor.[17]" Nil Einne (talk) 17:54, 2 September 2011 (UTC)

I am fairly convinced that, due to a number of factors, there is a systematic reporting/detection bias that makes it seem as if extreme natural phenomena of all kinds are increasingly frequent. 86.177.107.255 (talk) 20:31, 2 September 2011 (UTC)

This is a question that the USGS is often asked, their response is here and further statistics can be found here. Mikenorton (talk) 21:54, 2 September 2011 (UTC)

Some geologists speculate that we are currently in an active earthquake cycle, as well as a high volcanic activity cycle. Also, some studies, though not all, have found that large earthquakes often trigger smaller earthquakes several thousand kilometers away that cannot be considered aftershocks. Some zones experience very large earthquakes (M8 and 9) on irregular intervals, such as the Cascadia subduction zone. ~AH1 ^(discuss!) 22:06, 2 September 2011 (UTC)

The same is also true of the Sunda megathrust, which has had three great earthquakes in the period 2004 to 2007, but a long gap before that. There were three relatively closely spaced magnitude 8+ events in 1797, 1833 and 1861 in a previous cycle. Mikenorton (talk) 22:16, 2 September 2011 (UTC)

Could this be a sign that a big mantle plume is approaching the crust and a flood basalt event is imminent? Count Iblis (talk) 23:48, 2 September 2011 (UTC)

Don't mantle plumes typically take place over hotspots, such as Iceland, Hawaii or Yellowstone? What about Large igneous provinces? ~AH1 ^(discuss!) 00:18, 3 September 2011 (UTC)

climate change

The economics of climate change includes issues to do with; Human Behavior, Economic Development and Negative Nxternalities. discuss these aspects of climate change problem, and give a brief example of how poor countries loose out as a result? how best can one answer the question,i seem to have limited information--Soft tembo (talk) 15:00, 2 September 2011 (UTC)

This looks like a homework question, and the Reference Desk will not do your homework for you. Weren't you given ideas about what to read to answer it? Have you read our Climate change article? Looie496 (talk) 15:21, 2 September 2011 (UTC)

We also have an externality article. —Akrabbim^talk 15:26, 2 September 2011 (UTC)

The Climate change mitigation article might also be helpful. Rckrone (talk) 15:32, 2 September 2011 (UTC)

Some other suggested articles to glance over include economics of climate change, economics of climate change mitigation, peace and conflict studies, politics of climate change, Stern Report, geoengineering, climate change, industry and society, climate change and agriculture, climate change and poverty, and environmental migrant. ~AH1 ^(discuss!) 22:01, 2 September 2011 (UTC)

At what point in the big bang did particles come into existence?

I've been reading the article "Timeline of the big bang," but it seems a little vague. Were they there immediately? (Certainly they were around by the electroweak epoch... but earlier?) --Goodbye Galaxy (talk) 15:23, 2 September 2011 (UTC)

I'm really not being trite, but what is a "particle"? Its all a matter of perspective, and at the scales you are talking about, it isn't really clear that such concepts are necessarily understood in the same way we experience the world with our senses. --Jayron32 15:39, 2 September 2011 (UTC)

Somewhat simplified answer: before the quark epoch the universe is so hot that frequent energetic interactions, high density of virtual particles and continual creation and decay of exotic heavy particles make the questions of particle existence and identity somewhat moot. Once we get into the quark epoch the universe is filled with a quark-gluon plasma of quarks, neutrinos and electrons and their antiparticles, so we can reasonably say that these particles exist at that point, although many are still being annihilated in particle/antiparticle interactions. Once we get into the hadron epoch quarks become confined within hadrons (protons and neutrons, plus their heavier cousins, which eventually decay). Neutrons combine with protons into stable atomic nuclei (helium, lithium and beryllium nuclei) during the first few minutes after the Big Bang. Stable atoms don't form for another 380,000 years. Gandalf61 (talk) 16:00, 2 September 2011 (UTC)

What exactly do you mean by "heavy exotic particles?" Stuff that's not one of these guys? --Goodbye Galaxy (talk) 16:54, 2 September 2011 (UTC)

I still think of anything other than a proton, electron, neutron, or photon as "exotic." The last time I saw a muon was more than six months ago (and all I really saw was a digital readout indicating a large current due to the electrons the muon produced). I have never seen a quark; I have to accept indirect evidence of their existence. If that's not weird enough to be called "exotic," I don't know what is... Nimur (talk) 17:40, 2 September 2011 (UTC)

Quarks are not considered exotic matter any more. Exotic would be anything beyond the standard model. 24.73.119.146 (talk) 18:18, 2 September 2011 (UTC)

In inflationary cosmology, the inflationary era is the earliest state about which anything is known. It's basically a vacuum with a nonzero cosmological constant and a few stray particles (just like the future of our universe according to ΛCDM cosmology, except that the cosmological constant is much larger in inflation). At the end of inflation you suddenly get a hot particle soup by a process called reheating. But until electroweak symmetry breaking (the beginning of the quark epoch) concepts like "photon" and "electron" and "quark" don't really make sense. All particles are exotic. -- BenRG (talk) 03:06, 3 September 2011 (UTC)

Eyes going in different directions

As seen here, it looks like Oprah's eyes go in slightly different directions. What's the name for that? 20.137.18.50 (talk) 16:02, 2 September 2011 (UTC)

Strabismus. —Akrabbim^talk 16:05, 2 September 2011 (UTC)

Of course, not all photographs prove a person has the actual condition. ~AH1 ^(discuss!) 21:56, 2 September 2011 (UTC)

Exactly. The ability to turn the eyes horizontally towards or away from each-other is not only normal but necessary for proper binocular viewing of, respectively, close-by or far-away objects. See Vergence. --Dr Dima (talk) 01:17, 3 September 2011 (UTC)

I couldn't see anything wrong with her eyes in the picture. Dauto (talk) 01:40, 3 September 2011 (UTC)

That's probably because there isn't anything wrong with her eyes in the picture. She is looking into the distance and not at the camera; this may seem like exotropia but probably isn't. --Dr Dima (talk) 02:51, 3 September 2011 (UTC)

Question about the accessible length scales in SAXS? (reworded header)

According to the lede of the Small-angle X-ray scattering article "SAXS is capable of delivering structural information of macromolecules between 5 and 25 nm, of repeat distances in partially ordered systems of up to 150 nm". I'm far from an expert but I thought that most modern synchrotron SAXS beamlines were capable of accessing a much larger q range than that? The website of this beamline at APS seems to imply that they can get to a Dmax of over 500nm with a particular detector configuration. Is it because APS is a 3rd generation light source and the primary reference is the 1982 Glatter and Kratky text (I'm far from an expert but at that time 2nd generation light sources were still state of the art?). I'm only beginning to dive into small-angle scattering, so am unsure if I'm missing something obvious or if the article simply needs to be updated. Thanks. I(q) = User(q)·Talk(q) 16:32, 2 September 2011 (UTC)

Follow up: or is it just that this type of setup is formally considered USAXS (Ultra-Small-Angle X-Ray Scattering)? Thanks again. I(q) = User(q)·Talk(q) 16:36, 2 September 2011 (UTC)

I'll take the dead silence to mean that my second assumption was correct and that it's just a nomenclature thing. I(q) = User(q)·Talk(q) 23:33, 3 September 2011 (UTC)

Sound in space

A star breaks the sound barrier in space?

Some guy I encountered on the internet made the claim that the fact that there's no sound in space is a misconception and that if the sound is loud enough, it can be transmitted through the tiny particles floating in the vacuum. In other words, if the sound is loud enough, you can hear it. Is he full of shit? ScienceApe (talk) 21:35, 2 September 2011 (UTC)

First of all, it all depends on the mode of transmission. Human speech requires air to be present in the lungs, which is an impossibility when a person is exposed to a pure vacuum, since the blood would boil along with other nasty effects. However, if electrical sensors are used to detect subtle vibrations, then the signal is transmitted in the person, then communication may be possible. When discussing other sounds, such as a drum set, sound waves would likely not transmit in a vacuum, but a person listening to a drum on the Moon by pressing his/her ear to the lunar soil may detect seismic vibrations. In higher levels of atmosphere such as the mesosphere (the level of space shuttles), air particles are indeed present, yet I'm uncertain about sound transmission. You may find speed of sound interesting. ~AH1 ^(discuss!) 21:54, 2 September 2011 (UTC)

I've added an interesting picture of Mira above, making a sort of bow wave ahead of it as it passes through the interstellar medium. I suppose that as that wave approaches you, you feel fluctuations in the pressure of the ever so tenuous interstellar gas, which can be considered as a type of sound. The turbulence in its wake probably has some "sonic" aspect to it also. I don't know if this is a true shock wave created by moving faster than sound ... sort of looks like one though. Of course, all these "sounds" are ever so slow and faint, not meant for human ears. I should also note that because atoms in outer space are often ionized, "sound" has a strongly electrical/radio frequency component to it as the ions repel one another - see e.g. [4] for the Cassini Jupiter flyby's detection of ion-acoustic waves which are in low radio frequencies but also represent the compression and expansion of the gas of charged particles. Wnt (talk) 22:07, 2 September 2011 (UTC)

Here is a paper that discusses the possible physics of sound waves in a vacuum, although it is pretty technical. I think this may be the sort of thing the OP's friend was talking about. Looie496 (talk) 22:31, 2 September 2011 (UTC)

They just can't hear you scream. Clarityfiend (talk) 22:41, 2 September 2011 (UTC)

That's not what the original poster asked, but it is a seriously weird idea. ;) He was talking about the particles in space - not asking if the vacuum itself could transmit sounds through fluctuations in its basal energy, permitting the velocity of the aether at last to be measured! Wnt (talk) 16:50, 3 September 2011 (UTC)

The "transmission by particles in space" would require a hell of a lot of particles, since any gap would stop the transmission. It would amount to a continuous piece of material, and yes, a tight string or a stick connection 2 space helmets would allow sound transmission through a vacuum. Edison (talk) 20:32, 3 September 2011 (UTC)

The article on outer space speaks of a mean free path on the order of 1 AU at the edge of the solar system. Clearly "sound" of the type I describe has a very long wavelength - as the photo of the star above suggests. Wnt (talk) 18:24, 4 September 2011 (UTC)

speed of sound

why does sound travel faster in warm air than in cold air? — Preceding unsigned comment added by 175.110.242.217 (talk) 23:27, 2 September 2011 (UTC)

The formula for the speed, IIRC, is 331.4 m/s + 0.606(T°C). ~AH1 ^(discuss!) 00:04, 3 September 2011 (UTC)

Why: According to speed of sound, a lower density allows the sound waves to travel more readily and thus at a vaster speed, and warmer air generally has less density. The fact that warmer particles vibrate and move around faster may also allow the motion transfer of a sound wave to propagate faster. ~AH1 ^(discuss!) 00:11, 3 September 2011 (UTC)

Imagine making a wave in a bathtub full of water. Now imagine doing so in a tub full of honey. You'd expect the thicker fluid to make slower waves, right ? StuRat (talk) 01:09, 3 September 2011 (UTC)

Honey has a high viscosity which is unrelated to the question asked so that analogy doesn't seem to be very helpful. Dauto (talk) 01:37, 3 September 2011 (UTC)

The lower density and sound speed relation does not apply to gasses, In gas it depends on the temperature. The lower density in solids increases the speed of sounds in a solid, if the bulk modulus stays the same. Graeme Bartlett (talk) 04:56, 3 September 2011 (UTC)

Increasing the temperature of a gas changes the speed of sound BECAUSE that change of temperature forces a change of density or a change in pressure and either one of these affects the speed of sound. Dauto (talk) 17:50, 3 September 2011 (UTC)