Science desk
< December 7	<< Nov \| December \| Jan >>	December 9 >

Welcome to the Wikipedia Science Reference Desk Archives
The page you are currently viewing is an archive page. While you can leave answers for any questions shown below, please ask new questions on one of the current reference desk pages.

December 8

tonneau cover areodynamics

A few years back, Mythbusters did a segment comparing the areodynamics of a pick up truck with the tailgate up vs. the tailgate down (with the myth of it being better to have the tailgate down getting busted). Since that time, I have wondered if there have been any studies of the areodynamics of the open truck box vs a tonneau cover vs a fibreglass truck cap. Undoubtedly there are some differences, but are they significant? 99.250.117.26 (talk) 04:13, 8 December 2010 (UTC)[reply]

I don't know about studies, but I would think a cover would have to help, because the wind whips around something fierce in an open-bed pickup. A cap is a different matter, since that puts more of the vehicle into contact with fast-moving air, possible increasing drag. StuRat (talk) 04:43, 8 December 2010 (UTC)[reply]

Why are the planets almost spherical?

Why are the planets almost spherical? —Preceding unsigned comment added by 125.21.50.214 (talk) 08:23, 8 December 2010 (UTC)[reply]

For a detailed discussion, see Hydrostatic equilibrium. The reason is that, when an object reaches a certain size, the force of gravity holding that object together will tend to act uniformly in all directions, compressing that object into a sphere. Planet-sized objects generally meet this definition (indeed, it is one of the definiting characteristics of a planet that seperates planets from other objects, like asteroids). --Jayron32 08:28, 8 December 2010 (UTC)[reply]

As long you do not have a strong rotation of a liquid object in zero gravity the sphere is the energetically most favourable form you can have.--Stone (talk) 09:36, 8 December 2010 (UTC)[reply]

Because if it's not almost spherical, it is - by definition - not a planet. Mitch Ames (talk) 10:17, 8 December 2010 (UTC)[reply]

Sorry, but that definition begs the question, since the definition reads as such because planets are normally almost spherical. If the Earth and the other planets in our solar system most closely resembled a very long cigar, you can bet that the IAU's definition of a planet would not exclude very long cigar-shaped bodies! Thus this definition does nothing to address the OP's question of why the Earth and the other planets in the solar system are nearly spherical instead of, say, most closely resembling a very long cigar. (But you already knew that, that's why your response was small :) ) 88.182.221.18 (talk) 11:51, 8 December 2010 (UTC)[reply]

It's a matter of semantics, I guess, but it depends on how you read the OP's question. If they are wondering why it is that planets formed into rough spheres a few years back, then the hydrostatic equilibrium answer is best. If they are wondering why a planet must be spherical to be deemed a planet, then yes, it's because we are familiar with the shape and put it into the definition of what we call a planet. Dismas|^(talk) 12:02, 8 December 2010 (UTC)[reply]

Note that Mars, being smaller than the Earth, gets to have bigger mountains because gravity is less. Gzuckier (talk) 13:56, 8 December 2010 (UTC)[reply]

Does that apply to Venus or Mercury as well? If not, I would question that conclusion. Googlemeister (talk) 16:00, 8 December 2010 (UTC)[reply]

Venus is not drasticly different in mass from earth. This is confirmed as Maat Mons, the largest shield volcano on Venus is 8 km high as measured from the base. The equivalent peak on earth would be the Hawaiian volcano of Mauna Kea which is 10 km high as measured from its base. Making some allowances for random variables and differing local conditions regarding erosion and composition, these are roughly on the same scale with regard to size. Contrast this with Mars, which is much smaller than earth, at only 1/10th the size, and its equivalent largest shield volcano, Olympus Mons, is 21 km high. --Jayron32 16:17, 8 December 2010 (UTC)[reply]

So it seems that it might be correct if venus and earth are roughly equivalent with both mountains and gravity and mars with less gravity has a bigger mountain, but then wouldn't mercury have an even bigger mountain then mars, or would its proximity to the sun prevent that mountain from forming somehow? Googlemeister (talk) 17:03, 8 December 2010 (UTC)[reply]

Mercury is too small to have a motlen core or techtonic plates! Is this another blow against intelligent design? Slartibartfast or any other intelligent being would make them cubes so as to make mapping and a whole lot of other things easier. --Aspro (talk) 17:07, 8 December 2010 (UTC)[reply]

Mercury also presents interesting problems because of its proximity to the sun; it experiences something like tectonic acivity, though not from inside forces but outside ones. The surface of Mercury is buckled by tidal forces it experiences from the nearby sun. Mercury doesn't have volcanoes, per se, but it does have interesting features like buckles and escarpments and impact craters. See geology of Mercury for more. --Jayron32 17:14, 8 December 2010 (UTC)[reply]

Walking on a cubic planet might not be easier when you encountered the transition from one face of the cube to another. Those people who frequently had to cross this divider might be plagued with tendinitis of the ankle or something. Bus stop (talk) 17:12, 8 December 2010 (UTC)[reply]

Ah. Now you're trying to baffle me with science :-)--Aspro (talk) 17:23, 8 December 2010 (UTC)[reply]

Anticipating the next question. No, a planet does not need to be 'molten' in order to form into a sphere. Rock is plastic when subjected to planet forming pressures. One only has to visit a mine to see upage, downage, etc., as the rock expands in response to the overlying rock (and thus the pressure) being removed.--Aspro (talk) 17:23, 8 December 2010 (UTC)[reply]

Here’s another way to look at it. There is a mutual gravitational attraction between atoms/molecules. If a planet had the shape of a cube, an atom/molecule at a corner of the cube would experience a certain gravitational force tending to pull it toward the center of the cube. This force would be due to all atoms/molecules to the opposite corner. An atom/molecule at the center of one of the faces of the cube would have less force pulling it toward the center. (The atom/molecule at he center of the face has less material between it and the opposite face of the cube, as compared with a corner atom/molecule.) Therefore if the planetary material its plastic, the corner atoms would move toward the center and the face atoms, experiencing less force, would be pushed away from the center. One of the things affecting the plasticity of the planet would be its total mass.

Volcano benefits?

Do eruption of volcano have any benefits? —Preceding unsigned comment added by 125.21.50.214 (talk) 08:50, 8 December 2010 (UTC)[reply]

Volcanoes produce gaseous sulfur dioxide, which reacts with OH and water in the stratosphere to create sulfate aerosols, which contribute to global dimming for a couple years after the eruption. Global dimming helps offset global warming, so that's generally a beneficial thing. Unfortunately, sulfur dioxide and sulfates in the atmosphere also result in acid rain, so the sulfate aerosols aren't purely beneficial. Red Act (talk) 09:51, 8 December 2010 (UTC)[reply]

Do volcano play any role in the process of evolution? —Preceding unsigned comment added by 125.21.50.214 (talk) 09:55, 8 December 2010 (UTC)[reply]

Some rather basic information about the benefits of volcanoes - As well as Red Act's notes, they can also increase the fertility of land in the area surrounding the volcano and tourism, according to the source

/edit - A better source with some references you may find interesting Darigan (talk)

The Earth's earliest atmosphere came primarily from gasses produced by volcanoes[1], and volcanic gasses were an important contributor to the Earth's second atmosphere (see History of Earth#Origin of the oceans and atmosphere). The beginning of life on Earth occurred toward the beginning of Earth's second atmosphere. So volcanic gasses played an important role in the creation of the environment within which life began. It's questionable as to whether life on Earth would have even arisen at all, if it weren't for volcanic gasses. Red Act (talk) 11:08, 8 December 2010 (UTC)[reply]

Farmland near volcanoes has very good soil, and they also attract tourists. Here's a page listing some of the benefits 82.44.55.25 (talk) 12:14, 8 December 2010 (UTC)[reply]

Yes, dirt from weathered volcanic rock or ash mixed with local mud has lots of air, plenty of nutrient minerals, and energy sources for both anaerobic and aerobic bacteria; so it makes a wonderful loose richly fertile soil. See [2]. Ginger Conspiracy (talk) 14:48, 8 December 2010 (UTC)[reply]

Carbon cycle; carbon dioxide gets quasi-permanently tied up reacting with silicate minerals. When these compounds are subducted they are broken down by the heat underground, and the carbon dioxide gets released back into the atmosphere via volcanic eruption. Gzuckier (talk) 14:06, 8 December 2010 (UTC)[reply]

Volcanoes also provide scientists with a method of studying the Earth's interior (such as by sampling gases and magma/lava), and diamonds and other gems are sometimes found in extinct (or at least dormant) volcanoes. StuRat (talk) 14:34, 8 December 2010 (UTC)[reply]

I read somewhere that the steam given off by volcanoes is what formed the oceans eventually. Can anyone confirm this? ScienceApe (talk) 15:03, 8 December 2010 (UTC)[reply]

Nope, we got the volatiles pounded out of us by the Giant impact hypothesis. The oceans are all imported water. Volcanoes are good for recycling. Planets without them are lifeless. Hcobb (talk) 15:10, 8 December 2010 (UTC)[reply]

Pseudo-morning sickness

Some years ago, I would occasionally wake up in the morning too warm, though not really feverish, and nauseous at the thought of food. I was never noticeably ill apart from those symptoms, and it was always gone by midday. What might have been going on? As this isn't a current issue for me (hasn't happened in probably three years), I'm not really breaking the "no medical advice" thing, am I? ;-) — Preceding unsigned comment added by RandomLurker (talk • contribs) 13:47, 8 December 2010 (UTC)[reply]

Maybe you really were too warm. A room temperature which was fine during the day might have been too much when you were under the blankets. The other symptoms might have been a result of being overheated. You didn't list your age and gender, but if you are an older female, perhaps hot flashes due to menopause might also cause such symptoms. StuRat (talk) 13:58, 8 December 2010 (UTC)[reply]

What often baffles people (and their GP's) is when they have developed an intolerance to a commonly eaten food. Food intolerance. Some specialist still refer to this by their old names of delayed allergy or masked allergy. As it can take hours for the symptoms to come on, it is very easy to fail to make the connection. Morning fatigue, nausea, feeling hot and a host of other possible symptoms caused by this can often be dispersed by just a bit of vigorous exercise. A good sign that this is indeed the problem is if the exercise initially may one feel a lot worse before feeling better. It is common as well, that the symptoms can change overtime, which adds to the difficulty of working out the cause. Eating a very varied diet appears to help avoid it developing in the first place. --Aspro (talk) 16:55, 8 December 2010 (UTC)[reply]

Dreams

When people dream, the content of the dreams is usually stored in short term memory and discarded when the person wakes up. How might a hypothetical human brain be switched to storing dream material to long term memory? 93.85.8.58 (talk) 16:36, 8 December 2010 (UTC)[reply]

A voice recorder and/or a notepad and pencil on the nightstand plus a programmable alarm clock telling you to remember to rehearse the memories of your dream as well as you can while you reach for the recorder or pencil and paper. Set the alarm to 2-3 hours before you usually get up so you have a better chance of interrupting REM sleep. Don't be discouraged if you can't remember any dreams -- if you get awoken during non-REM sleep you might not be having any. Please remember that dreams are really strange, and the various theories ascribing meaning to dreams have never been verified. However, if you are struggling through a surrealist writing assignment, no problem! Ginger Conspiracy (talk) 17:12, 8 December 2010 (UTC)[reply]

That's the usual method, but it's conceivable that a drug could be invented for this. Current belief is that the storage of memory in the brain depends on a process called long-term potentiation, which strengthens the synaptic connections between neurons. This process has two phases, an early phase that produces a memory trace lasting only a few minutes, and a later "consolidation" phase producing memory traces that last much longer. It seems likely that the consolidation part is somehow suppressed during dreaming, although we don't understand why (it may have something to do with the drastic reduction in norepinephrine during dreaming). If a drug could be invented that would block the suppression of the consolidation phase, presumably the result would be that we would remember our dreams as well as our ordinary experiences. This is of course all very speculative... Looie496 (talk) 17:21, 8 December 2010 (UTC)[reply]

There might be a tradeoff. Might you not relegate normal wakefulness memory establishment to a status of secondary importance at the same time that you are elevating the purposeless memory establishment of the dreams that occur in sleep? We establish many memories during wakefulness that are apparently abandoned soon after they are no longer needed. It is just a guess—but our intellectual capacities may be limited to remembering things only to a limited degree. Bus stop (talk) 17:32, 8 December 2010 (UTC)[reply]

I'm certainly not saying this would be useful, just that it might be possible. Looie496 (talk) 17:42, 8 December 2010 (UTC)[reply]

Dark matter: black holes

It's dark matter awareness week \o/ I attended along with a previous series of cosmology, astronomy, and astrophysics lectures on dark matter and very closely related topics, and have been reading journal and arXiv papers and emailing various experts in the field. I've come to the conclusion that Paul Frampton is right about dark matter being mostly black holes.[3] Is there any observational evidence against this possibility at all?

I've seen so many people spending lots of money looking for nonbaryonic explanations, and they always freely admit that nobody has ever found any evidence for such new kinds of particles, I'm wondering what's going on. The evidence for nonbaryonic cold dark matter is exceptionally flimsy, but it does seem to be entrenched. Why? Ginger Conspiracy (talk) 16:41, 8 December 2010 (UTC)[reply]

I think its largely because the evidence for baryonic dark matter, or the "its just a bunch of black holes we haven't accounted for yet" theory is equally as sparse. Dark matter is pretty much an ad-hoc hypothesis to explain certain fundemental deviations from the predicted universe from the observed universe. While there are strong opinions regarding what it might be (or even if it exists at all). It seems likely to exist, given that it is the most plausible explanation for the observations, but as it has never been directly observed, any such propositions are lacking in the sort of verification which would take one proposal "over the top" to become established, accepted theory. What we are left with instead is a lot of propositions of varying likelyhood. Personally, from all of the reading I have done (which is probably not as much as you), I consider myself somewhat noncomittal on the issue. Until there exists some definitive way to verify one of these theories, none seems to be worth "believing in". --Jayron32 16:54, 8 December 2010 (UTC)[reply]

There's zero evidence for the new particles, but at least the intermediate-mass black holes have GCIRS 13E and M82 X-1. I think we need microlensing sky surveys (looking for arc and crescent shapes in sky survey data) and better names for these things than GCRIS 13E and M82 X-1. Ginger Conspiracy (talk) 17:10, 8 December 2010 (UTC)[reply]

Most physicists accept the conclusions of big bang nucleosynthesis, which models the population of primordial atoms as a consequence of the Big Bang. By looking at the concentrations of hydrogen, helium, beryllium, lithium, and their isotopes, scientists can place constraints on the amount of baryonic matter existing immediately after the Big Bang. The measurements of ~8 different isotopes are mutually consistent with theoretical expectations only if we assume that baryons make up about 3.5 to 5% of the closure density. Estimates of total matter are currently about 28% of the closure density, which is far larger than the uncertainties reported for nucleosynthesis. If most of the total matter were baryonic then nucleosynthesis would predict primordial concentrations of deuterium and lithium that differ by more than an order of magnitude from their observed values. Of course it is always possible that something is wrong with either the theory or the measurements, but because it is a relatively simple theory constrained by multiple independent measurements, most people give it a lot of credence. The implication though is that most of the mass in the universe must be in some form other than baryons. Whether that is WIMPs, primordial black holes, sterile neutrinos, axions, or something else is still a matter of debate and active searches. (Note: Primordial black holes are consistent with the nucleosynthesis results only if they form before nucleosynthesis. Black holes created afterwards wouldn't be able to explain dark matter in a way that is consistent with nucleosynthesis.) Dragons flight (talk) 17:18, 8 December 2010 (UTC)[reply]

After more than a month of searching, I haven't been able to find the source for the deuterium and lithium predictions. Do you know where that comes from? If it is from [4] then which passages in it actually support the assertion? Ginger Conspiracy (talk) 17:48, 8 December 2010 (UTC)[reply]

Many places. For a recent review, you might try: [5] For an older, and somewhat more technical discussion, perhaps: [6] Dragons flight (talk) 18:04, 8 December 2010 (UTC)[reply]

Thank you! Ginger Conspiracy (talk) 18:46, 8 December 2010 (UTC)[reply]

Cheapest source of ethanol for sterlisation

At my institute, from the "Stores" department, which stocks most commonly used materials, we can get 2.5l 96% ethanol for just over £8 or 2.5l absolute ethanol for just over £6. Obviously there's something wrong if the prices are that way around. Does someone know a cheaper source of ethanol (for sterilisation purposes), taking into account delivery charges? ----Seans Potato Business 17:21, 8 December 2010 (UTC)[reply]

Well, you could check the local drug store, er, chemist. That seems like a pretty low price, though, considering all the higher expenses involved in running a lab. Looie496 (talk) 17:29, 8 December 2010 (UTC)[reply]

Depends what you are trying to sterilise. Industrial alcohol is used for hypodermic syringes and things. That's usaly cheaper (well it is where I am).--Aspro (talk) 17:28, 8 December 2010 (UTC)[reply]

Not necessarily. As alcohol distills as an azeotrope, absolute ethanol is usually produced by desiccating it with benzene or some other organic molecule. It would be easy enough to leave just enough benzene in the resultant product to render it denatured alcohol, unfit for human consumption. For that reason the absolute ethanol might not be subject to alcohol excise taxes, rendering it cheaper. (£1 per liter does not sound excessive for excise taxes). The cheapest alcohol you'll likely find would be methylated spirits sold by a (house) painting supplier, although whether or not that meets your requirements is another question. Usually there are enough legal and administrative hassles with the purchase of alcohol that most institutions find a single supplier policy is less expensive/easier in the long run, even if some other company has a cheaper sticker price on some item. (P.S. suppliers and shipping costs are likely going to change based on location. Use of £ indicates UK, but where in the UK? London? Glasgow? Belfast? Douglas, even?) -- 174.31.212.34 (talk) 17:39, 8 December 2010 (UTC)[reply]

Fully denatured methylated alcohol leaves a residue and so does surgical spirit. So really need to know the application. --Aspro (talk) 17:48, 8 December 2010 (UTC)[reply]

For a country like the UK you can usually get referrals. This company came up top in a Google search. Call them and see if you're in their delivery area, and if not, ask them who they recommend who is. It looks like you need to fill out a free customs form if you're a non-consumption user to avoid the £20/l tax. Ginger Conspiracy (talk) 19:01, 8 December 2010 (UTC)[reply]

This isn't what you asked, but for sterilization 70% alcohol works better than 96%. Ariel. (talk) 20:02, 8 December 2010 (UTC)[reply]

That surprised me, and I checked - it seems to be accurate. I searched for "sterilization 70% ethanol" and found this book, Disinfection, sterilization, and preservation, with a chapter comparing efficiency of sterilization with various types and grades of alcohols. It seems that in most cases, 70% ethanol kills microbes faster than 95% ethanol. In some cases, the reverse has been shown. It seems to depend on the type of substrate (glass, counter-surface, organic matter, etc.), and the species of bacteria to be destroyed. Nimur (talk) 20:41, 8 December 2010 (UTC)[reply]

I think we can safely presume that the OP already knows the strength of alcohol to use, what he's asking for is the cheapest way to achieve sterility. I was encouraged to use isopropyl alcohol when ever possible as it was the cheapest (I don't know about current prices) but in some applications its toxicity may be problematical if there is going to be some residue left behind. The NHS uses industrial alcohol and you can't go much wrong with that. --Aspro (talk) 21:01, 8 December 2010 (UTC)[reply]

Synthetic Organic Schemes for Pharmaceutical Compounds

I'm interested at looking at the synthetic reactions used to synthesize pharmaceutically relevant compounds. I'd prefer the reaction schemes used for commercial production, but schemes for the original synthesis would be fine, too. Does anyone know of a compilation (e.g. a website or a book) of the reaction pathways used to synthesize commonly used drugs, or would I have to assemble them drug-by-drug? -- 174.31.212.34 (talk) 17:24, 8 December 2010 (UTC)[reply]

There are some books with lots of them collected. K. C. Nicolaou's Classics in Total Synthesis has some ones that are significant (milestones in methodology or structure, etc.). Many recently-developed/currently-used prescription drugs are probably covered by patents and/or obscurely described and/or non-published (gotta protect that income stream!). Journals like Chemical Reviews have articles about classes of them (for example, lots of synthetic approaches towards a common type of structure). But there's no general compilation of them all...too many, too rapidly changing, to redundant or no value-added vs the individual literature for each. DMacks (talk) 18:18, 8 December 2010 (UTC)[reply]

The information you want is spread out in hundreds of journals, books, patents, and even web sites, but there are some databases which try to aggregate it. However, the Chemical Abstracts Service indexes by compound so once you get used to searching it (and there are a lot of programs to help you enter structures, substructures, and do various forms of pattern matching on structure, composition, and reaction surface geometry, even) then you still need access to a large college or university library journal subscription services if you need to do dynamic searching. If you are just starting out you might be more comfortable with SciFinder CAD searching but if you think you can handle a text interface then STN may be for you. Or maybe it sounds like you only need the SYNTHLINE database, which costs $200/hour to search plus $1.50 per bibliographic record or $40 per synthesis record. Ginger Conspiracy (talk) 18:28, 8 December 2010 (UTC)[reply]

Alternatives to silicon for computers?

Suppose that silicon were (somehow) rare and pretty expensive. What other materials could we use to make semiconductors? This is for a sci-fi story I'm working on, so I'm looking for something that could be accomplished by a culture with technology no more advanced than our own -- I thought about vacuum tubes but my understanding is it would be extremely difficult if not impossible to build modern computers that aren't the size of houses using them (and even then still pretty tough). Thanks for your help. 96.246.58.133 (talk) 18:56, 8 December 2010 (UTC)[reply]

List of semiconductor materials. You can also make transistors out of carbon nanotubes, but that's very new, expensive, and might end up being impractical or otherwise esoteric. Ginger Conspiracy (talk) 19:05, 8 December 2010 (UTC)[reply]

There is also the question of developing light-based transistor alternatives rather than semiconductor-based. --Jayron32 19:09, 8 December 2010 (UTC)[reply]

Yes, optical computing, about as far along as the carbon nanotubes these days, which isn't saying much (no x86 compatible ICs with millions of gates for at least the next 2-5 years, for both.) Ginger Conspiracy (talk) 19:24, 8 December 2010 (UTC)[reply]

Okay, wow, thanks. Useful list. Offhand do any of you guys know why silicon is preferred over anything else? I'd assumed price, but some of those don't seem like they'd be very rare. Is it just institutional, ie the first transistors were made with silicon and its just what everyone is used to? 96.246.58.133 (talk) 20:02, 8 December 2010 (UTC)[reply]

Actually, the first transistors were not silicon. The first semiconductor diodes were metal/oxide P-N junctions (anecdotally, discovered "accidentally" using oxidized/rusty nails, or delicately balancing a wire against galena or other rock/mineral); and the first practical transistors were III/V semiconductors (see History of the transistor, particularly William Shockley's germanium triode). Silicon, as a semiconductor, requires doping, and by most metrics, silicon is an inferior semiconductor to 3-5 materials. But it is cheap, and it is easy to mass-produce, and it does not "gum up the machinery" as much with impurities, so it is easier to have extremely high quality clean-room and clean-process environments. It is cheaper to acquire raw materials for silicon processing. Modern technologies (that is, things invented in the 1930s-1960s) like feedback control made it possible to deal with the crummy performance of silicon; and the adoption of CMOS over bipolar junction transistors gave silicon a distinct advantage. Finally, the semiconductor era quickly gave way to the digital VLSI era - so it became more important to pack very many small devices very densely (instead of worrying about the quality and electrical performance characteristics of each device). So silicon CMOS VLSI is now the standard for most computer electronics (though it is not the clear winner for technologies like wireless radio, optical (LED and photosensor) electronics, nor for high power systems like solid state relays and power transistors, nor for radiation hardened electronics for spacecraft or scientific applications. This introduction to integrated circuit design gives some good comparisons between bipolar and CMOS (and while you can implement either process on almost all types of semiconductor substrates, in practice, silicon is used for CMOS processes, and alternative technologies are not). Nowadays, if you want to design a semiconductor circuit, your first decision is silicon or not silicon - every performance-spec, theoretical/practical design process, software EDA tool, and even the factories or countries that you can use to manufacture your circuit, will depend on this choice. Nimur (talk) 20:59, 8 December 2010 (UTC)[reply]

When I taught basic electronic components in K-8 classes (long long long ago), I used water. A semiconductor is anything that somehow changes the flow of water. A resistor is a narrower tube. A diode is a one-way valve. A transistor is a valve controlled by pressure on a plunger. There is no reason you couldn't make micro-versions of all plumbing components and push water through them instead of electrons. Of course, water molecules are tremendously larger than electrons, so you will never achieve the same compactness. For a modern computer, you'd still be looking as a device about as large as a room. -- kainaw ™ 19:19, 8 December 2010 (UTC)[reply]

I'm irresistably reminded of the MONIAC Computer. 87.81.230.195 (talk) 20:21, 8 December 2010 (UTC)[reply]

There are plenty of ways to compute mechanically, which circumvents the need for semiconductors. See e.g. Analytical engine. Using current technology, compact and powerful (though not very general) computers can be built, see e.g. [7]. SemanticMantis (talk) 20:06, 8 December 2010 (UTC)[reply]

Reed relay computers can be built, too. They are more compact than vacuum tubes, but suffer from reliability problems. Nimur (talk) 20:32, 8 December 2010 (UTC)[reply]

Water molecules (~3Å) are quite a bit smaller than the feature size of state-of-the-art CPUs (~320Å), but water is too sticky to force through a pipe that small. I suppose you could make a compact liquid-based CPU with superfluid helium, but it's not very practical. -- BenRG (talk) 02:49, 9 December 2010 (UTC)[reply]

volcanoes

i have been searching for the deration of a volcano. what is it? 24.45.91.137 (talk) 20:40, 8 December 2010 (UTC)[reply]

Do you mean duration of a volcano? Mikenorton (talk) 20:43, 8 December 2010 (UTC)[reply]

yes that is what i mean. 24.45.91.137 (talk) 20:59, 8 December 2010 (UTC) —Preceding unsigned comment added by 24.45.91.137 (talk) 20:53, 8 December 2010 (UTC)[reply]

There is no fixed duration, they can last from day to years. According to volcano: "The lifespan of a volcano can vary from months to several million years" Ariel. (talk) 20:59, 8 December 2010 (UTC)[reply]

and one more thing would 1980 eruption of mount saint helen's be cosidered one of the worlds worst volcano eruption? 24.45.91.137 (talk) 21:07, 8 December 2010 (UTC)[reply]

Far from it. See our article on Volcanic Explosivity Index and our list of largest volcanic eruptions for starting points, and note that you'll have to define the criteria for "worst" (largest? longest? most casualties? most monetary damages?). — Lomn 21:13, 8 December 2010 (UTC)[reply]

Based on any metric, Mt. St Helens isn't a superlative in any category except "Was in the continental United States", That's probably the only reason it was so memorable. It should be noted that the term "volcano" is very broad, it describes a VERY wide range of structures and events which are only very loosely related. Shield volcanos like Mauna Kea are very different than Stratovolcanos like Mount Pinatubo and Mount Vesuvius, and neither one is very much like Cinder cone. Other than the general "hole where stuff comes out of the earth" classification, none of these types of volcanoes has much in common. The erupt very differently, they have very different structures, etc. etc. In general the most destructive type of volcano is a Stratovolcano; all of the really bad "explosive" type eruptions are associated with them. On the other hand, eruptions like Kīlauea (a shield volcano) tend to be not all that destructive comparitively speaking; Kīlauea has been erupting more or less continuously since 1983, and it could best be described as a major annoyance. It does cause some considerable property damage when a lava flow takes out some structures, but it isn't "dangerous" in the sense of killing people like Stratovolcanos are. --Jayron32 21:32, 8 December 2010 (UTC)[reply]

Although a shield volcano can also do a lot of damage if the eruption is extensive enough. For example the eruption that produced the Siberian Traps is widely believed to have been responsible for the Permian–Triassic extinction event, the greatest mass extinction in geological history. Looie496 (talk) 21:58, 8 December 2010 (UTC)[reply]

Actually I heard of a one in lake toba Indonesia that when it erupted that it effected the entire human population and nearly drove us to extinction. Also other other bad eruptions was mount vesuivus at 79 AD produced its famous eruption burying the roman cities of pompeii and herculaneum. Mount Pinatubo in the philipines island of Luzon, Mountserrat in either the leeward islands, Mount Tambora in Indonesia causing the year without a summer. These are few of the famous ones but they are others. --213.94.237.14 (talk) 21:44, 8 December 2010 (UTC)[reply]

See Toba catastrophe theory. Looie496 (talk) 22:00, 8 December 2010 (UTC)[reply]

Some Large igneous provinces can last very long. Also, the Yellowstone supervolcano has been around for over 20 million years, and the Hawaii hotspot likely for over 80 million. ~A H 1^(TCU) 03:45, 11 December 2010 (UTC)[reply]

In order to calculate the lifespan of a volcano, you need to know its geological pressure isosurfaces, which aren't always available from seismic studies. You may need active seismology (e.g., setting off underground explosions to listen to their echos) with a good understanding of the speed of sound in different pressures, temperatures, and compositions. That means you may need to drill for core samples to get complete information, too. It is a very difficult problem, but not insurmountable. Ginger Conspiracy (talk) 05:26, 11 December 2010 (UTC)[reply]

Multiforce members (statics)

Hello,

I did a test yesterday. Got about half way in to the question, then hit a wall. Where do I go from here? I've labelled all the external forces. A and G are hinge supports. The external reactions I am fine with. A sum of the moments at A or G combined with a sum of the x forces reveals Ax and Gx to equal 28 and 32 kN, respectively. The sum of the y forces is thus = 0 = Ay + Gy + 20 kN

EG is a two-force member, and is under 28kN of compression. And then.... I can't go further because the forces acting at D are unknown no matter which of the remaining three members I analyze. If I perform a moment equation at D, all the numbers contradict one-another.

Where do I go from here? - ʄɭoʏɗiaɲ ^τ _¢ 20:40, 8 December 2010 (UTC)[reply]

It might help if you told us what question you were supposed to answer. Looie496 (talk) 20:58, 8 December 2010 (UTC)[reply]

Standard analysis. Need to find all the internal forces acting on each of the members. - ʄɭoʏɗiaɲ ^τ _¢ 21:55, 8 December 2010 (UTC)[reply]

You seem to be ignoring gravity, is that appropriate here? Dragons flight (talk) 22:06, 8 December 2010 (UTC)[reply]

No, the weight of the members themselves is not included, and the structure is assumed to be motionless (statics). - ʄɭoʏɗiaɲ ^τ _¢ 22:19, 8 December 2010 (UTC)[reply]

Some length seems to be missing, either length AB or the distance from member CE to the axis at which the 20kN force is applied. Do you have this info anywhere ? Also, we'd like to see the calcs you did that appear to get contradictory results. StuRat (talk) 00:21, 9 December 2010 (UTC)[reply]

EG is a two-force member, so the stress on EG is purely compressive, and that compressive stress on EG is purely horizontal, so Gy=0. Setting the sum of the y forces to 0 then gives Ay=-20kN. Red Act (talk) 01:30, 9 December 2010 (UTC)[reply]

Sorry, made the diagram quick and left that measurement out. It's 0.4 m between A and B.

For member CDG:

SumM@D = 0 = (20*0.6) - (40*1.3) + (32*1.3) - (Fc*1.2)

That means the x-component of the force acting on B of member ABC must be 26.67 kN ( 28 - 1.33 ). The 4/3 ratio of BCD means the axial force of that x-component is 5/3*26.67 = 44.44445... And if I keep going things just get worse and worse. Not to mention the sum of the x forces on CDG not equalling zero. - ʄɭoʏɗiaɲ ^τ _¢ 03:27, 9 December 2010 (UTC)[reply]

You don't seem to be considering that the 20kn Y force at the end of the member encompassing BD is not applied directly at D but 0.3m away. Arakunem^Talk 20:49, 9 December 2010 (UTC)[reply]

Yep. Got the results back today and that was exactly the problem. I should analyze BDE to find the x component at D, and then a sum of x's on the same member to get Cx. Using that, I analyze ABC to get the x and y component at B and perform a check with member BE - ʄɭoʏɗiaɲ ^τ _¢ 02:21, 10 December 2010 (UTC)[reply]

Acid with nylon

What is the chemical equation for adding an acid (such as sulfuric acid) to nylon?David255 (talk) 23:57, 8 December 2010 (UTC)[reply]

There's one given in the nylon article. DMacks (talk) 00:27, 9 December 2010 (UTC)[reply]

So nylon + dilute acid -> carboxylic acid + amine via nucleophilic substitution?David255 (talk) 01:14, 9 December 2010 (UTC)[reply]

See Nucleophilic acyl substitution for the mechanism. Physchim62 (talk) 01:32, 9 December 2010 (UTC)[reply]

So I take it my equation is right? Thanks for the link...didn't realize there was an article on that!David255 (talk) 01:39, 9 December 2010 (UTC)[reply]