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October 27

About (vomitting while) pregnant

Is there vomiting after 2 months of pregnant and why? — Preceding unsigned comment added by Titunsam (talk • contribs) 09:58, 27 October 2013 (UTC)

See Morning sickness for our article on the subject. Tevildo (talk) 10:04, 27 October 2013 (UTC)

This may not be the reason though. If you or someone you know is unwell, please seek the advice of a medical professional. 80.254.147.164 (talk) 09:33, 28 October 2013 (UTC)

Insolation as a function of latitude (alone)

Hi! I am looking for a function for the average insolation a a particular latitude gets over a year. Essentially, it's the information in the upper map of the first image in the insolation article, except, well, there's no indication what formula they used to obtain that result. Now, as far as I understand, it should be a matter of integrating the formula for day-averaged insolation, which is given as

${\displaystyle {\overline {Q}}^{\text{day}}={\frac {S_{o}}{\pi }}{\frac {R_{o}^{2}}{R_{E}^{2}}}\left}$,

with ${\displaystyle \sin \delta =\sin \varepsilon ~\sin(\theta -\varpi )\,}$, for θ = 0 to 360°, except that for one thing I'm afraid it exceeds my mathematical abilities, and anyway the formula includes a parameter h₀ for which they give no value (and no way to calculate it). Could you help me out? Thanks :) JaneStillman (talk) 21:13, 27 October 2013 (UTC)

Woolly bear caterpillars

When I was little, my parents told me never to touch caterpillars, so I'd never touched one until a few minutes ago. It's warm outdoors today, and I'm sitting in a chair on the porch; the woolly bear crawled up the chair, up my shirt, and onto my neck — quite surprising, and I had no clue what it was until I'd shaken it off. Two questions arise from this:

1. How do they move? Little feet like centipedes or millipedes, or suction feet like ants, or something else entirely? And how do they climb human skin, since it's so different from everything that they normally climb?
2. Do these caterpillars actively go looking for food, or do they just wander randomly until they happen upon some? I'm left wondering if it thought that I was a food-bearing plant or if it just found me and decided to climb and see what happened.

Nyttend (talk) 21:15, 27 October 2013 (UTC)

Ants have suction-cup feet ? StuRat (talk) 21:28, 27 October 2013 (UTC)

• Our article on caterpillar covers their general leg anatomy, which is the same for the whole order Lepidoptera. At this time of year they are looking for places to overwinter, and not for food. μηδείς (talk) 21:30, 27 October 2013 (UTC)

Ants and caterpillars both have feet with little hooks on them. Ants have legs, but caterpillars have prolegs. Ant feet look like this . Different types of caterpillars have more variety in their feet, some look like this , some look like this . The latter foot may look cup-like, but I don't think any suction per se is involved. Anyway, their feet work just fine on plants, rocks, curtains, siding, and human skin. At the small scale, there is plenty of roughness of little feet to get a grip.

Medeis is right that they are looking to overwinter, but that doesn't mean they aren't also eating...

As for how they forage, that can depend on what kind of "wooly bear" you mean. E.g. Garden_tiger_moth has a fairly general diet, so "find vertical surface and ascend" is a decent strategy, especially considering they were hatched from eggs deposited by flying adults (who probably found an area with a good food source). They probably do also use smell a bit. If you are interested how caterpillars in general find food, I can probably get some decent refs for that. SemanticMantis (talk) 21:48, 27 October 2013 (UTC)

I'd just add, if not handled gently, the hairs do detach and irritate. μηδείς (talk) 22:02, 27 October 2013 (UTC)

What kind of woolly bear — I have no clue. Between colorblindness and no knowledge of entymology, I really know nothing of caterpillars and am unable to describe the ones in question. Since they're so furry and since I've never touched one before, I've never seen feet and didn't know that all caterpillars would have the same general leg anatomy. I admit that I was surprised what it felt like, and somewhat nervous after so doing: my parents always told me that their hairs were irritants, and that's why I've never touched them. Nyttend (talk) 22:10, 27 October 2013 (UTC)

There are several "dangerous" caterpillars including the Hickory Tussock Caterpillar that have Urticating hairs. Rmhermen (talk) 03:11, 28 October 2013 (UTC)

Fukushima radiation on the NW coast of the US

Friends of mine keep sending me alarming articles about how high levels of radiation either have already, or are about to, engulf Oregon, Washington and California from a plume of radiation from Japan. I'm skeptical, but when I looked into the issue I was unable to find published research from anyone actually measuring, or using science to predict, the degree of exposure. There are a lot of statements either reassuring people or whipping up alarm, but little based on actual monitoring. I'm sure I'm looking in the wrong place - but could someone link me to some hard science on the increased dose someone living on the pnw coast is likely to have already, and in the next few years, get? Thanks! — Preceding unsigned comment added by 71.214.113.234 (talk) 23:49, 27 October 2013 (UTC)

The United States Department of Energy is the federal agency that implements policy, and conducts and administers the hard science related to atomic energy and safety. From their website, here is a starter article: ‘’Radiation Monitoring Data for the Fukushima area, (2011), which is a pointer in the right direction. I'll see if I can find any more elaborate reports specifically publishing data and summary results for the Pacific coast of the United States. Nimur (talk) 00:00, 28 October 2013 (UTC)

Thanks - that looks like the Japan data, which is a start - I'm really looking for data on the US PNW coast - really appreciate your help! — Preceding unsigned comment added by 71.214.113.234 (talk) 00:09, 28 October 2013 (UTC)

In fact, a special website was set up on behalf of the President's directive (during the immediate aftermath of the incident) for rhe DOE and NNSA to fully inform the American public and document all data: http://energy.gov/japan2011 - a website most recently updated in January of 2013. After a cursory review of the data, even in the days immediately following the incident, radiation levels measured at several locations in Japan (including Fukushima) were below a level that would ever cause harm, (loosely speaking, at a level below "background radiation" levels, as measured in rem). So it would appear that the hard data contraindicates any significant long-term health hazards resulting from the nuclear incident. That is not to say the incident had no effect - in fact, this review from the DOE's permanent monitoring station at Amchitka indicates a measured biological effect, as published in April 2013: Biological monotoring at Amchitka appears to show impacts from the Fukushima Dai-ichi incident. So, we can summarize that the effects on humans (in Japan, Alaska, and the Pacific coast of the United States) should be "very small," but in deference to scientific observations and careful data analysis, we should qualify that the effects are non-zero. Nimur (talk) 00:15, 28 October 2013 (UTC)

And in case you haven't already found the link, the May 2012 issue of Health Physics was entirely devoted to the Fukushima incident, including nine articles from prominent government scientists in the Department of Energy, and the National Nuclear Security Agency, as well as articles from other points of view, and an editorial called "The States' Perspective" outlining how state governments (including Washington and Oregon) dealt with the public demand for information, and the difficulty of providing factual scientific answers in the hours and days immediately following the incident. In the phrasing of the journal editor, the radiation was "orders of magnitude" below a concerning level - but in the rush to inform the public, some states published data provided by the federal government - the Environmental Protection Agency - which may have led to unnecessary alarm because it was presented without context.

The Fukushima reactor incident has been widely studied from many many points of view - from the view of physicists, biologists, and climatologists; from the view of first responders and nuclear safety and security agencies; from the view of policy makers and governments in the United States, Japan. and elsewhere. There's no shortage of published opinions on the incident. I'm sure we can help you find more information if you seek it. Nimur (talk) 00:40, 28 October 2013 (UTC)

For the enthusiast historians: here's EPA's corollary, http://www.epa.gov/japan2011/ - also archived for posterity. You will note that EPA's March 11 statement has been redacted, even in the historical archive, and the oldest press release is dated March 15, 2011. Nimur (talk) 00:58, 28 October 2013 (UTC)

Thanks - I still have not been able to track down any recent measurement data for the Pacific Northwest Coast - there's plenty of opinion, not many numbers that I can find. Really appreciate the help! — Preceding unsigned comment added by 71.38.131.41 (talk) 01:58, 28 October 2013 (UTC)

The more I look into this the more I think there may not actually be anyone monitoring radiation levels arriving in the PNW - at least not publishing if they are. Anyone found anything different? Thanks! — Preceding unsigned comment added by 71.214.118.54 (talk) 13:59, 28 October 2013 (UTC)

That is not accurate. Every nuclear power station in the United States is continuously monitoring radiation levels inside and outside the facility. You can locate every single facility and check the data for that location. Many laboratories and special sites, like the Hanford Facility in Washington, perform extensive monitoring for various radioactivity and other nuclear activity. A few select sites - like the Amchitka Island station in the Aleutians - perform even more rigorous monitoring. The U.S. Environmental Protection Agency, in conjunction with the USDA, EPA, and FDA, tests food products and milk for nuclear contamination on a constant basis. So far, very little of interest has been found with any relation to the 2011 Japan incident, which is why there aren't very many recent press-statements. Everything that was scientifically valid has probably long faded below the noise floor.

But the problem is, radioactivity is not as simple as some other properties, like "temperature." We can link you to climatology data, where you can view hourly archives of every temperature at every weather station in the USA for the last fifty years. But radiation is not a single parameter; there are many natural and man-made sources, and there are several types of harmful and non-harmful nuclear decay activity and othher radioactivity. For example, if you read the article about Amchitka, you'll see the problems they faced: they have to measure radioactivity level and further normalize by the isotope ratios between Cesium-137 and Cesium-134. The absolute radiation levels are so low that they are unmeasurable with, say, a geiger counter; you need a complete laboratory analysis to tease these details out.

So, if you have a specific request - say, historical data on calcium isotope ratios in milk produced in the Pacific North West, we can find that data for you. (Here's an FDA press-release from early September, on data collected about milk, just a few days before our Government shut down last month; the next data release may be delayed). Or if you want total electron count in Earth's ionosphere as measured by radiosonde, we can find that data for you - here's data for right now, from NOAA'S Space Weather Prediction Center. The data is there, and it's available. But, the consensus by scientists is, those data show no signficant cause-and-effect relationship with the Fukushima Dai-Ichi incident in 2011. So, you'll probably not see a lot of current scientific summary articles putting these pieces together and showing no effect - especially since that work has already been very thoroughly completed in 2011 and 2012. Academic journals do not like to publish statements of fact that confirm the status quo or the null hypothesis. Nimur (talk) 15:48, 28 October 2013 (UTC)

Thanks - I appreciate the thorough response - I'm still left with no real solid data or analysis to show wether or not there is any effect of the ongoing Japan leak on the PNW coast, which is a little frustrating... — Preceding unsigned comment added by 71.214.118.54 (talk) 20:40, 28 October 2013 (UTC)

How to See RadNet Air Monitoring Data, from the EPA... "EPA's nationwide radiation monitoring system, RadNet, consists of two components. First, stationary and deployable air monitors measure radiation 24 hours a day, 7 days a week. The map below provides monitoring results as graphs that are updated several times daily. You can also search the RadNet database in EPA's Central Data Exchange (CDX) to find monitoring data. Second, EPA samples precipitation, drinking water, and milk on a routine schedule and tests them for radiation in a laboratory. The latest RadNet sampling results are available in Envirofacts." I don't know how this type of data could be made any more solid, or the analysis presented in any more straightforward way, unless it explicitly summarized the measurements in response to the Fukushima incident . Nimur (talk) 00:42, 29 October 2013 (UTC)

Hey that's great - that's exactly the kind of thing I was looking for - thanks for pointing me in EXACTLY the right direction! — Preceding unsigned comment added by 71.214.118.54 (talk) 01:56, 29 October 2013 (UTC)

I think that you have the answers you need, but you might find these articles from Snopes.com useful: Fukushima Emergency, Nuclear Fallout map and Giant Killer Hornets. I'll bet that the articles your friends send you are somewhat like those quoted by Snopes, or at least use the same (unreliable or misrepresented) sources. Sjö (talk) 10:25, 29 October 2013 (UTC)

October 28

Ice cube capilliary free energy?

In a control experiment, two ice cubes are created in a freezer and they are placed in a dish of water. They are well separated and stay where they are until they melt. X amount of energy was used to pump water out the dish into an ice cube mould. In the second experiment they are placed closer together and capilary action makes them move together. If they stayed solid it would take just as much energy to move them apart. But if they melt and the same process as in the control experiment takes place, have we "separated" them for nothing, gaining free energy in the process? How can the freezer retroactively "know" the fate of the ice cubes (or the pump) to satisfy the second law of thermodynamics? (Trevor Loughlin) — Preceding unsigned comment added by 91.224.27.231 (talk) 13:11, 28 October 2013 (UTC)

Touching or no, how could they stay solid after being placed in water? ←Baseball Bugs carrots→ 14:19, 28 October 2013 (UTC)

You are failing to account for the work you performed in moving the ice cubes. If there is a potential energy gradient that depends on the separation distance (and there is a tiny one, due to the effects of surface tension and capillary action), then you will feel a force along the direction of separation, when you are moving and placing the ice cubes in the tray of water.

But, that is a tiny effect. It is so small that it is dwarfed by the air resistance acting on the ice cube as you lift it and place it in the diah of water; the air resistance is yet another non-zero effect that we can neglect because its magnitude is so small.

Were we to set up a controlled experiment to measure such an effect, we would need to manage all other sources of error to ensure that our tiny, non-zero physical process - the potential energy gradient related to the surface mechanics of capillary action - does not get lost in noise. Nimur (talk) 16:12, 28 October 2013 (UTC)

Touching a black dwarf

I know they probably do not exist yet, but they are predicted to exist if a white dwarf cools down. I was wondering, is it possible for a person to actually touch it, or would they be killed some other force? What would happen if hydrogen or any other peice of matter touches it? It's supposedly pure electrons, I'm just wondering what a solid object made of electrons might be like and if it can actually be touched like any other solid. Would some process occur that causes things to rapidly heat up if other matter touches a black dwarf? ScienceApe (talk) 17:31, 28 October 2013 (UTC)

It should feel just like a solid material, the only problem that I can see is that to touch it you have to go down the surface where the gravitational acceleration will be about 5000 g. Count Iblis (talk) 17:54, 28 October 2013 (UTC)

Note that we do have a black dwarf article. StuRat (talk) 18:29, 28 October 2013 (UTC)

The incredible surface gravity would crush the person against the surface and the atoms of the person's body would be incorporated into the star. Resistance would be futile... Dauto (talk) 19:00, 28 October 2013 (UTC)

Only if it was a superconductor. :-) StuRat (talk) 19:02, 28 October 2013 (UTC)

I believe it would inherently be so, being electron-degenerate matter (even though the article doesn't mention this). — Quondum 03:11, 29 October 2013 (UTC)

What would be the drifting velocity of an electron at those densities? Plasmic Physics (talk) 02:10, 29 October 2013 (UTC)

@ScienceApe: "It's supposedly pure electrons": Not quite, it is a plasma of nuclei and electrons.

@Plasmic Physics: Since the electrons are predominantly (or almost entirely) in the degenerate state, I understand that this implies that they will be superconducting. Not sure this answers your question? — Quondum 03:11, 29 October 2013 (UTC)

No matter what kind of gravity the outside of an object is under (even a neutron star - look at the structure image) the pressure will be very low in the outer atomic layer, and it will therefore not be degenerate matter. Wnt (talk) 16:42, 29 October 2013 (UTC)

True. The outer layer would probably be normal matter. In further response to "or would they be killed some other force", and assuming we are not concerned about the effect of 5000 g ("It's not the fall that kills you, it's the sudden stop at the end"), there is another factor to consider: the tidal forces, which I suspect will rip a person apart before they get near the surface, though I do not have figures. — Quondum 22:22, 29 October 2013 (UTC)

Infrared and microwave radiation

When directing equally strong infrared or microwave radiation towards a human, why is microwave radiation more harmful even though its wavelength is longer? Th4n3r (talk) 18:16, 28 October 2013 (UTC)

Infrared creates heat right on the surface of the skin or clothes, where it can quickly dissipate into the air, while microwaves of the frequency used in microwave ovens penetrate maybe an inch, and that heat doesn't dissipate nearly so quickly. Also, microwaves cause arcing when they hit metal parts, such as in a pacemaker. StuRat (talk) 18:22, 28 October 2013 (UTC)

Thank you. Th4n3r (talk) 19:46, 28 October 2013 (UTC)

I think most of the difference is with resonant absorption peaks of liquid water. I believe arcing is only a problem within the cavity and standing waves (a microwave oven cavity supports a finite set of TE modes and metals disrupt that and induce high currents and voltages. I suppose a wire of a pacemaker might have a microwave resonance but it seems unlikely.) I don't know if it's true that all frequencies considered "microwave" would be more harmful than all frequencies considered "infrared." It would depend on how the human body and it's constituents react. Throughout the EM spectrum the body is transparent, reflective and absorbent of different frequencies depending on the chemical. Pulse oximetry is one example of how spectral differences exist and can be used. Microwave ovens cook through a specific resonance with water but a microwave speed measuring gun doesn't have the same effect. --DHeyward (talk) 11:15, 30 October 2013 (UTC)

Yes, that's why I said "microwaves of the frequency used in microwave ovens". StuRat (talk) 21:58, 30 October 2013 (UTC)

Sorry if I misunderstood. The frequency heating water would be independant of the cavity. The arcing of a pacemeker (or any metal) is very dependent on the cavity so is not likely the same issue as a person standing near a radiating source vs. a piece of metal with a gradient against the electric field in a cavity. The cavity wants to have a static field while the metal wants an equipotential surface (and a 0 electric field at the cavity boundary). This can cause arcing. Outside the cavity, metal isn't really an issue. Think of a piece of aluminum that spans from the TE10 peak field to near he cavity edge. The aluminum will want to have an equipotential surface but the charge will be moved the the edge closest to the cavity edge. This can create heating currents and arcing voltages. But outside the cavity it just reflects the energy. --DHeyward (talk) 07:05, 31 October 2013 (UTC)

How to research symbols?

If you find some formula or symbol that you don't understand and doesn't even know the name of it, how would you look it up by yourself?

Take for example:

${\displaystyle \sum _{k=1}^{n}k}$

or

${\displaystyle {n \choose k}}$

Where would you go to know what they mean? Is there some tool where you could proceed in a tree-like manner until you find what you are looking for? Or maybe some tool where you draw them and it outputs the name?OsmanRF34 (talk) 19:12, 28 October 2013 (UTC)

List of mathematical symbols gives many of the more common maths symbols. There is a separate maths reference desk, for symbols in science it would depend on what area you were interested in. Dmcq (talk) 20:04, 28 October 2013 (UTC)

TinEye supposedly lets you supply a picture and scans the web for similar pics. I've never had much luck using it myself, though, so I can't recommend it. StuRat (talk) 21:42, 28 October 2013 (UTC)

Google Images has the same functionality - and works a lot better, IMHO. However, it wouldn't help with things like:

${\displaystyle {n \choose k}}$

where a simple parenthesis symbol is being used for (in this case) notating a column vector rather than the more common use of grouping arithmetic operations (eg. 4x(3+1)=16). SteveBaker (talk) 03:45, 29 October 2013 (UTC)

It would depend on context, but that's almost certainly a binomial coefficient, not a column vector. Red Act (talk) 08:05, 29 October 2013 (UTC)

And, of course, this is the ideal place (either the Math or Science Desk). Draw a symbol, upload it here, and there's an excellent chance somebody will tell you what it is. StuRat (talk) 21:44, 28 October 2013 (UTC)

Yeah - that's a sure-fire way to find out - but it typically takes a few hours to get an answer. 03:45, 29 October 2013 (UTC)

Symbols.com has the great idea of an index of symbols searchable by graphic form but has a woefully small database. They have some math and logic symbols but seem more aimed at mystic users. SpinningSpark 19:02, 29 October 2013 (UTC)

October 29

Voltage divider.

I'm trying to use a simple voltage divider to allow me to measure a variable resistance that ranges from around 10k ohm down to nearly zero using an Atmel microcontroller (like in an Arduino). The circuit is the one shown at right (from our Voltage divider article - which I've read).

Vin is 5 volts and the analog-to-digital converter is connected to Vout and measures 0 to 5 volts with a precision of one part in 1024. I'm trying to figure out whether I should make R₁ or R₂ be the variable resistor - and what value to use for the other (fixed) resistor. From the math:

V_out/V_in = R₂ / (R₁ + R₂)

Which suggests that if R₁ is the variable resistor, then R₂ should be very small in order to use the entire range of the AtoD converter. (For example, if R₂ is 10k ohms - then all of my results will be in the range 2.5v to 5.0v and I'll be wasting one whole bit of the result...but if it's just 10 ohms, then I'd be using almost the entire range of the AtoD. I'm betting that something will go horribly wrong if I make R₂ be as small as 10 ohms. What's the gotcha and what's the recommended value?

(I'm not really interested in investigating more complicated circuits - I'm engineering down to a price here!).

SteveBaker (talk) 02:57, 29 October 2013 (UTC)

Wouldn't it be simpler to use a three terminal variable resistor, with one end of the resistor connected to +5 V, the other end to ground, and the wiper connected to the A/D converter? This would assure a low (0.5 mA) current through the resistor and a negligible current through the wiper. Jc3s5h (talk) 03:14, 29 October 2013 (UTC)

If I was using a potentiometer - yes. That would be nice because R₁+R₂ is a constant and V_out is directly proportional to R₂ - but I'm not. There is just one external variable resistance that I'm measuring and R₂ is fixed. (Although if there was a good reason to do it, I could make R₂ be the variable one and R₁ be the fixed resistance. SteveBaker (talk) 03:39, 29 October 2013 (UTC)

On the "betting that something will go horribly wrong", you need to watch the potential power dissipation in each of the resistors, e.g. 0.5 A and 2.5 W with your value of 10 ohm. That's a pretty hefty resistor, and may cost a few cents more. If your variable resistor can dissipate less power than the fixed resistor, it may overheat when it is at a similar value. Another gotcha is that over most of the range of the variable resistor (> 10 ohm), your resolution is going to be far worse than if you use a larger fixed resistor. You should plot the resolution over the whole range, and how it is spread over the range compared to where you want it. For example, you may want substantially more resolution at lowish values of resistance at the expense of at the high resistance end, in which case you could use a lowish value (e.g. 1 kiloohm, 90% of your ADC range, quite nonlinear; 10 kiloohm: substantially more linear, 50% of the ADC range). In your diagram, which resistor is which makes no real difference: the results are simply reversed, non-linearities and all (subtract from 1023). — Quondum 03:48, 29 October 2013 (UTC)

Another, slightly more complicated way of doing it (I know you said you're not interested, but it's still cheap) is to convert the resistance into a delay and measure that. 555 timer IC#Example applications gives a good example of how the dirt-cheap and ubiquitous 555 timer (or similar methods) were used to measure the position of joysticks, which produced a variable resistance and had to be read with a digital device. Basically, you charge a capacitor and the resistance determines how long it takes to charge it. You can time that and know what the resistance is. The accuracy isn't great, but it is simple to set up in a way that doesn't damage components with too much current, which can be a serious problem for reading the whole range with a voltage divider. Katie R (talk) 11:47, 29 October 2013 (UTC)

The key thing the 555 brings to the table here is the ability to send a trigger pulse then wait for a response using all digital I/O. Since you have an analog input, you could just watch the voltage of the capacitor directly as it charges from a digital output if you want to avoid the chip. Katie R (talk) 11:49, 29 October 2013 (UTC)

An important piece missing is tolerance and accuracy. If your fixed resistor is 5% but 10k, you can forget being accurate at the low end. You would already be bit limited 10 ohms/bit, but also +/- 500 ohms (50 bits) for resistor tolerance. Without knowing your tolerance for error and where you need accuracy, it's not very tractable. Other alternatives are to use a equal voltage divider to supply the reference voltage to the A/D (zero it out) and then have the same circuit with the DUT in parallel to R2. The more you can ratio out error, the better your accuracy. With just the voltage divider, resistor tolerance, temperature and device selection will all impact your measurement and at the low end, it will be useless. You always want to be close to full scale.--DHeyward (talk) 12:52, 29 October 2013 (UTC)

You know more about this than I do, but my thought is that whatever you're using this for, wasting power is always bad, so you want as high a value as possible for R1 so that no matter what goes wrong with the rest of the circuit, you know your power isn't peeing away through it. You then want your other variable resistor to also be as high as possible so that you can get nearly the full range by turning it up higher than R1. Which gets us to the brass tacks: what is the resistance of your voltmeter really? A hypothetical voltmeter passes zero current, so you could use a chunk of wood for R1 and R2 and move the probe needle back and forth on it. Unfortunately this is not a purely hypothetical voltmeter, so you need R1 << maximum R2 << Rvoltmeter. Wnt (talk) 16:35, 29 October 2013 (UTC)

If you want to use a simple voltage divider, I would choose two fixed resistors, with R₁+R_var in place of R₁, R_var being the variable resistor now. V_out/V_in = R₂ / (R₁ + R_var + R₂). With R₁= 100 R₂ = 1000, R_var between 0 and 10k, Vout will be between 0.45 and 4.55V (assuming 5V input). Absolute precision goes down when the variable resistance rises, but the relative precision will be highest when R_var equals R₁+R₂. Example: Voltage difference between R_var = 100 and = 110 is 0.0344V, between 2000 and 2200 it's 0.098V, between 8000 and 8800 it's 0.044V. Ssscienccce (talk) 08:36, 30 October 2013 (UTC)

Replace R2 with alow value capacitor, make Vin come from an output of the u controller and use software (free) to. work out the restance:)--31.55.113.25 (talk) 22:28, 30 October 2013 (UTC)

Questions about Dietry Fibers

1) Why fibers are not considered Essential nutrients?

2) What is the main source of the most coveted source for insoluble fiber by humans?

3) Is there such a concept "correct ratio between soluble and insoluble fiber in a human's diet?"

Thanks very much for an answer. 109.65.50.176 (talk) 05:48, 29 October 2013 (UTC)

I numbered your Q's for easier response:

1) A nutrient is something you digest. Since fiber is not digested, it's not a nutrient. At least that's true of non-nutritive fiber. StuRat (talk) 21:59, 29 October 2013 (UTC)

Wouldn't retrograde amnesia erase a person's mental illnesses too?

If an adult with several mental illnesses or emotional problems and specific fears had an accident and woke up in the hospital with no memories at all like that was their first second being alive, wouldn't their mental illnesses, emotional problems and specific fears be gone too? — Preceding unsigned comment added by 174.65.23.49 (talk) 07:03, 29 October 2013 (UTC)

No. There are multiple problems with that idea, one of which is that mental illnesses aren't purely based on what's in a person's episodic and declarative memory. See Causes of mental disorders. Red Act (talk) 07:57, 29 October 2013 (UTC)

Life is not like a video game. We can't reset back to an earlier time. Mental disease will no more disappear just because of forgetting than grey hair will turn black. Dmcq (talk) 11:08, 29 October 2013 (UTC)

What would or could be forgotten is whatever was experienced previously. Also, is the hypothetical person able to speak and do other things normally? ←Baseball Bugs carrots→ 11:17, 29 October 2013 (UTC)

It depends on the extent of the damage that caused the amnesia. Different areas of the brain cover different functions, so damage to one (for example, to the ability to recall memories) would not necessarily cause problems for other areas of the brain (for example, language processing or physical coordination). --Jayron32 12:15, 29 October 2013 (UTC)

• The answer is a bit complicated, and involves several factors.

1. It is common in movies and TV shows for somebody to wake up with no memory whatsoever, but that almost never happens in real life. Genuine retrograde amnesia eliminates memory for the recent past -- sometimes extending back for years -- but almost always leaves memory from childhood intact. There are a few exceptions, but most of them have dubious features -- in some cases it is not clear whether people are faking TV-style amnesia in order to avoid answering awkward questions.
2. The idea that all, or most, mental illness results from traumatic experience is a relic of Freudian theory that is now rejected by the great majority of psychiatrists.

So the bottom line is that (a) that doesn't happen, and (b) it wouldn't eliminate most types of mental illness even if it did. Looie496 (talk) 16:59, 29 October 2013 (UTC)

Meck, Su has this kind of retrograde amnesia and though it is rare she isn't the only person to have a complete loss of all memories. Baseball_Bugs, in this case the person would be like an infant and would have to be taught everything again. — Preceding unsigned comment added by 174.65.23.49 (talk) 02:30, 30 October 2013 (UTC)

I remember that happened to Lt. Uhura once. They managed to re-teach her everything by the very next episode! --Trovatore (talk) 02:35, 30 October 2013 (UTC)

I'm sure Kirk volunteered to show her where she sleeps at night. StuRat (talk) 02:40, 30 October 2013 (UTC)

I looked up the Su Meck case, and while it's mostly popular-press stuff, it is very much an impressive story. --Trovatore (talk) 02:53, 30 October 2013 (UTC)

Even in cases where mental illness might be caused (or triggered) by trauma, erasing the memories of the traumatic experiences would not erase the mental effects of the traumatic experiences. My cat doesn't have to specifically remember being sprayed with water to react to the sight of a spray bottle. thx1138 (talk) 18:07, 31 October 2013 (UTC)

Side-stick controls in cockpits

This is just a quick question: when Airbus designed the Airbus A320, the first fly-by-wire airliner, what were the reasons why they decided to use side-stick controls (which, at the time, was probably unheard of for commercial aircraft) instead of the conventional yokes, and what were the reasons why Boeing decided not to use side-stick controls in the Boeing 777 and Boeing 787 Dreamliner? Also, what are the advantages and disadvantages of using side-stick controls in commercial aircraft cockpits? I have read our Misplaced Pages articles for yokes and side-sticks, but they do not elaborate on the information I want answered here. Narutolovehinata5 10:39, 29 October 2013 (UTC)

As a pilot that flies small planes, the Cirrus SR22 vs Cessna 210 (and both are mechanical, not fly-by-wire), the sidestick is out of the way of the display and doesn't feel all that different from the left seat (captains seat) than a traditional center yoke. There is also the feeling of more room. The downside is that the left/right seat switches are reversed (some would be anyway for throttle control while PTT). An obvious advantage of the center yoke is either hand can fly and either pilot can see and reach the other yoke. The requirements for the quick donning mask, for instance, might be easier to accomplish with this feature. Even the fly-by-wire yokes have mechanical feedbacks to mimic what would be felt in a traditional mechanical yoke so the transition is easier like the buffet before a stall is mimicked (I'm not sure about side-stick though). Personally, I like the Cirrus side stick just for the added space. Side stick fighter planes normally have the stick on the right with throttle control either on the stick or left side so opposite the captain's seat. In the end though, it comes down to transition time. If everything looks and works the same and the only difference is fly-by-wire vs hydraulic, a transition will be much easier. If there a number of differences, like how/when the autothrottle engages/disengages or where switches are located (stick or console), transition time can be longer, more expensive and possibly less safe. I suspect the yoke and controls on the yoke, the travel distance for rotation, bank angle for standard rate turn, etc, all match previous Boeing airplanes and makes transitioning easier and quicker (cheaper). The crash in San Francisco recently was attributed initially to a small difference in autothrottle behavior between types. Small things that change can have large consequences even if the change appears good on paper. --DHeyward (talk) 12:04, 29 October 2013 (UTC)

In jet airliners like Airbus and Boeing, the pilots actually spend a very small percentage of the flight with hands on the control - most of the time the aircraft is being flown by the autopilot. Pilots spend a much greater percentage of their time monitoring instruments, monitoring information displays and doing things with documents - hence the attraction of the Airbus strategy of providing a stick at the side of the pilot and a tray table directly in front. All flight controls are fully powered by servo motors so a large stick with a large moment arm is not necessary. And why has Boeing stayed with the conventional control yoke? Probably because Boeing is the market leader so it doesn't need to try new strategies as Airbus does in an attempt to establish its product and then increase market share. Also, Boeing places great importance on what its established customers say and want in their future aircraft. It seems likely to me that when Boeing asks its established customers and their pilots, all say they are entirely happy with what they have at present. Dolphin (t) 12:23, 29 October 2013 (UTC)

It is worth noting that the most important differences between the Boeing and Airbus fly-by-wire control really aren't in the shape and position of the yoke or side-stick, but rather in the way that the aircraft's computer interprets, responds to, and feeds back pressure on the yoke or stick. There is much information and discussion (correct and otherwise) available in online fora; see for instance . (You will find many online flamewars about flight envelope protection philosophies of Boeing versus Airbus.) The Airbus system has a number of unambiguous benefits from a design and economics standpoint—it is lighter and mechanically simpler; it seems to be ergonomically preferable (less tiring for pilots, room for a tray in front of the pilot, no problems with controls obstructing the view of instruments); removing the yoke allows the cockpit to be slightly shallower from front to back.

The safety question is difficult to settle. What you will find fairly readily are a small number of edge-case incidents and crashes which each side's proponents like to cite over and over, saying "in this tiny one-off case, our preferred technology could have/did save(d) the day". TenOfAllTrades(talk) 16:55, 30 October 2013 (UTC)

Animal learning by experiences of other animals without direct exposure themselves...

It may sound like a confusing or misleading title, but what I am getting at is the instance of having an animal experience some sort of distress by a specific type of predator that looks a particular way. Instead of reacting by instinct, the animal that experiences the stress passes on the learning or conditioning by communication or language, no matter how rudimentary it is. That way, successive generations of the same species can learn who to avoid rather than relying on instinct all the time. In a similar story about lyre birds, if I remember correctly, young male lyre birds can learn the songs of older lyre birds and imitate them. I am wondering if there are any more specific cases in the animal kingdom, but are more sophisticated/complex than the ones I've described and are occurring in nonhuman species. I already know that humans can do it. So, please don't list homo sapiens or any member of the homo genus unless it is an exception. 140.254.227.60 (talk) 13:32, 29 October 2013 (UTC)

It has been shown shown that primates do not have an inborn fear of predators such as snakes but they learn this behaviour from other primates. However, although they can be conditioned in the lab to fear predators by showing them videos of other members of their species showing a fear response, the same process won't necessarily condition them to fear other objects. As it says here "When videos were spliced so that identical displays of fear were modeled in response to toy snakes and flowers, or to toy crocodiles and rabbits( (M. Cook & Mineka, 1991), the lab-reared monkeys showed substantial conditioning to toy snakes and crocodiles, but not to flowers and toy rabbits". So they suggest that there is also an evolutionary component to the selective learning. Richerman (talk) 14:23, 29 October 2013 (UTC)

Concidentally or otherwise, the information you're stating was covered in an NPR discussion just yesterday. :) Which means there could be a link to it on their website, if someone wants to hear more about it. ←Baseball Bugs carrots→ 23:19, 29 October 2013 (UTC)

Are you going to link the article? 140.254.226.247 (talk) 16:18, 30 October 2013 (UTC)

We have a moderately lengthy article on observational learning, with some material about animals. A Google Scholar search for "observational learning animals" will give you a lot more material -- for example, rats learning which foods are good to eat by observing other rats. Looie496 (talk) 16:44, 29 October 2013 (UTC)

There was a study of crows which seemed to show that they recognize specific humans and pass a fear to those individual humans on to others. The people wore masks which made identifying them a bit easier, though. StuRat (talk) 22:05, 29 October 2013 (UTC)

Might be the masks made them scarier. As this BBC thing I just read suggests, humans are naturally freaked by not-quite-human faces, due to the expectation of a regular one. Crows have lived among us as long as we have, so it seems (to me) they could have the same issue. Might be why scarecrows exist. InedibleHulk (talk) 06:04, October 30, 2013 (UTC)

One of my psychology students had trained a rat to press a lever repeatedly to get a reward, and wanted to see if a "student rat" could learn to press the lever to get the reward just by watching the "teacher rat" do the act. The result was that Student rat just hung around by the water dipper to enjoy the reward which was earned by the Teacher rat. The Student did not learn that pressing the lever was what brought the reward. Edison (talk) 04:24, 30 October 2013 (UTC)

And did they call this Student Rat a StuRat, for short ? :-) StuRat (talk) 17:07, 31 October 2013 (UTC)

Does anybody know how many citations an article has been cited?

Does anybody know how many citations an article has been cited? I know there is a function on some website that allows people to track how many people have cited the article in their own articles as part of their references/citations/bibliographies. By the way, have there been documented cases where scientists harshly criticized their rivals' work, where both scientific teams are engaged in the same field and both want the glory of making some important distinguished landmark? I seem to recall a story in the field of chemistry about some guy who discovered Helium and then lost to the guy who discovered Hydrogen... or was it the reverse? I forget. 140.254.227.60 (talk) 14:19, 29 October 2013 (UTC)

To answer the first part of your question, the number of times a scientific publication is cited is the main criterion used to decide its quality and it is something academics are obsessed with. There are a number of ways find out see: for example or google "how many times has my article been cited" As for the second part - scientific rivalry often spills over into harsh criticism of one anothers' work, and the awarding of the Nobel prizes are often a great source of controversy as to whether the recipient really should have got the credit - see Nobel Prize controversies. Richerman (talk) 14:37, 29 October 2013 (UTC)

I beg to differ that it is not academics who are obsessed with citation count, but the people who evaluate academics (for allocating university rankings, research funding, etc). I'm sure most academics would happily not care about such dubious measures but are forced to if they are to survive. 31.52.246.217 (talk) 23:17, 30 October 2013 (UTC)

• If you look up an article on Google Scholar, it will show you the number of citations and allow you to list the citing articles. The number is often not completely accurate -- if it is important, you should check through the list to make sure that each entry is legitimate. Looie496 (talk) 16:48, 29 October 2013 (UTC)

Google Scholar is a useful tool but it has the drawback that it only includes journals that have been indexed online. In some fields this can omit the majority of publications. SpinningSpark 17:27, 29 October 2013 (UTC)

The old standard was ISI Web of Science, but in some way that I don't understand they made themselves so much of a pain in the ass for so many researchers to use (both in terms of interface and who was allowed access from where) that for a while they've seemed to have become more obscure. Wnt (talk) 21:11, 29 October 2013 (UTC)

Fighting scientist? doi:10.1029/2011JE003880 against doi:10.1029/2010JE003599. Or an old example: The discovery of thallium doi:10.1098/rsnr.1984.0005. The favorite one is Cassiopeium and Aldebaranium are no elements because the French chemist was heading the naming committee and not the Austrian chemist. The bloody fight about polywater and the devastating resistance about plate tectonics are other examples.--Stone (talk) 12:30, 30 October 2013 (UTC)

If your German is good enough just read what Hermann Kolbe wrote about his colleagues in his journal (one example of many is doi:10.1002/prac.18820260121).--Stone (talk) 12:33, 30 October 2013 (UTC)

My German is extremely poor. A translation of the document or a summary written in English would be helpful. Thanks. 140.254.226.247 (talk) 15:55, 30 October 2013 (UTC)

"...Adolf von Baeyer is an excellent experimentor, but he is only an empiricist, lacking sense and capability, and his interpretations of his experiments show particular deficiency in his familiarity with the principles of true science..." To make it clear 1905 Baeyer was awarded the Nobel Prize in Chemistry.--Stone (talk) 19:01, 30 October 2013 (UTC)

October 30

The term for the tendency for dominant entities to get more dominant

Like Microsoft, planets, armies, wealthy individuals, etc. Being big helps them get bigger. Is it a maths thing? It seems to be everywhere. It seems that on Earth, it's fueled by money, and people jump into exploit the phenomenon. It seems to have a runaway effect. What's the term? It there one? Anna Frodesiak (talk) 05:13, 30 October 2013 (UTC)

Oh, and thank you, by the way. :) Anna Frodesiak (talk) 05:18, 30 October 2013 (UTC)

Well, the opposite and ultimately triumphant tendency is regression to the mean. - Nunh-huh 06:27, 30 October 2013 (UTC)

The rich get richer and the poor get poorer. Clarityfiend (talk) 06:58, 30 October 2013 (UTC)

I'm not 100% certain what it is you are looking for, so here's a bunch of things that might be of interest: Matthew effect, Tipping point (sociology), Network effect, Virtuous circle and vicious circle, Positive feedback, Reflexivity (social theory), Bifurcation theory, Threshold model. Do any of these fit the bill for the type of thing you are looking for? If so, I can help you find more specific details; or if not, what is missing (so i can narrow it down)?Phoenixia1177 (talk) 07:30, 30 October 2013 (UTC)

Wow! Holy moly! Yes, it's all of those, somehow. Those are some of the most interesting articles I've ever seen. I'm just getting started on them and it will take me a while. Thank you very, very much!

Okay, I will return the favour. Here's something I made up: Tell a friend you can make a specific word come to mind. Write down "What???" on a bit of paper and fold it up. Then ask your friend: "Okay, ready? Are you sure? Okay, concentrate. Now, think of an animal between one and ten." Anna Frodesiak (talk) 08:09, 30 October 2013 (UTC)

No problem:-) I'll dig around when I get home and see if I can find something with more details. --I like your trick, I'm going to use it at work:-)Phoenixia1177 (talk) 08:15, 30 October 2013 (UTC)

Where someone might respond, "Between one and ten inclusive or exclusive?" ←Baseball Bugs carrots→ 09:48, 30 October 2013 (UTC)

Or another wise guy might say, "Three-toed sloth." ←Baseball Bugs carrots→ 09:51, 30 October 2013 (UTC)

Or they might say, "My dog." Then you say, "What?" And they say, "My dog just turned seven." ←Baseball Bugs carrots→ 09:53, 30 October 2013 (UTC)

So if you're asking this to a group, you could resort to this Casey Stengelism: "OK, everybody line up... alphabetically by height." ←Baseball Bugs carrots→ 09:53, 30 October 2013 (UTC)

At first I was confused. Then more confused. Then I finally got it. I think your friends think more than mine. Mine all just said "What???" :) Anna Frodesiak (talk) 11:16, 30 October 2013 (UTC)

Economies of scale would be a likely explanation. Ssscienccce (talk) 08:59, 30 October 2013 (UTC)

Money equates to power. Also described as, "The Golden Rule: Whoever has the gold, makes the rules." ←Baseball Bugs carrots→ 09:46, 30 October 2013 (UTC)

Ah, another good article to absorb. Thank you. Anna Frodesiak (talk) 11:16, 30 October 2013 (UTC)

See also Snowball Effect. uhhlive (talk) 13:11, 30 October 2013 (UTC)

It's important to realize that that "Golden Rule" assumes that everyone has at least some theoretical access to gold. If literally one guy had literally all the world's gold, then gold would be come worthless as money. ←Baseball Bugs carrots→ 22:50, 30 October 2013 (UTC)

Economists like to call this Natural monopoly. Jørgen (talk) 13:37, 30 October 2013 (UTC)

Another term is critical mass. Our article is strictly about the nuclear sense of the term, but it also has broader meaning similar to "tipping point". StuRat (talk) 15:07, 30 October 2013 (UTC)

And, another important concept is that all such effects only operate within a certain range. That is, we don't have one person or company that owns everything, on nation that is able to conquer the world, one animal which replaces all the rest, etc. The reason is that at some point a significant diseconomy of scale also kicks in. In the case of business, this leads to a specific ideal firm size. In another field, you also get a stable population size for a given species, even a very successful one. I don't think even black holes are expected to contain the entire universe, due to Hawking radiation and other effects. StuRat (talk) 15:07, 30 October 2013 (UTC)

And we'll throw in logistic growth for a bit more abstract mathematical fun. TenOfAllTrades(talk) 15:52, 30 October 2013 (UTC)

And I'll throw in network effect - the nature of consumers to gravitate toward the most established product/service providers (applies more to some industries than others). Someguy1221 (talk) 22:51, 30 October 2013 (UTC)

I'm going to toss Turing Patterns into the ring. Not strictly examples of this phenomenon, but interesting and related nevertheless. More generally it sounds like you would be interested in reading about pattern formation. If so I can highly recommend the series of books by Philip Ball entitled "Nature's Patterns, A Tapestry in Three Parts" Equisetum (talk | contributions) 23:50, 30 October 2013 (UTC)

I'm absolutely astonished at how much great content there is on this sort of thing. And all these articles get tons of page visits. Misplaced Pages builders are gooooooooooood. Anna Frodesiak (talk) 00:01, 31 October 2013 (UTC)

Heisenberg's delusion of adequately well behaved standard reality?

If you used Heisenberg's box cutter to open the impenetrable cardboard box and dump Schrödinger's cat into a region governed only by classical physics, wouldn't the poor beast die instantly in the flash of an Ultraviolet catastrophe?

I.e. what color of wallpaper is used to paper over the cracks of the run down and condemned poorhouse where classical physics has been left to die in when the physicist makes some sort of effort to separate herself from quantum reality by suggesting that the padded room she's in is not part of all that quantum weirdness "out there"? Is there a well defined "classical model" that actually works, or is it all just Heisenberg's delusion of adequately well behaved standard reality, that breaks down if you poke at any of the walls? Hcobb (talk) 13:19, 30 October 2013 (UTC)

If I not misunderstood your question, some model of a "classic" can be - The movement of the particles back and forth in time many times. Therefore statistics, Therefore possibilities, Therefore the "reality" stabilizing on part of the particles, so the "universes" are multiple . thanks Water Nosfim — Preceding unsigned comment added by 192.116.142.154 (talk) 14:06, 30 October 2013 (UTC)

I don't think you're going to get a better answer than Water Nosfim's to this one. Maybe you could rephrase the question? -- BenRG (talk) 18:14, 30 October 2013 (UTC)

The real question is how classical physics emerges as an approximation of quantum physics in a certain limit. (Just as relativistic kinematics reduce to Newtonian for low relative speeds.) This is a thorny question. The short answer is decoherence, which explains why we see an adequately well behaved standard reality in which interference effects, superposition, etc. are not obvious. It's not that some systems are fundamentally classical instead of quantum, it's just that classical physics is a good enough description of some things and not others. --Amble (talk) 19:45, 30 October 2013 (UTC)

For that matter, much of the Copenhagen interpretation is just pure nonsense, honestly, having done far more harm than good to the advancement of scientific thought. Ideas of superposition, entanglement, and collapsing wavefunctions continue to spur us on into research of fictitious "quantum computers" and the like...meanwhile we just drift further and further from, well, reality. Go figure. Sebastian Garth (talk) 07:23, 31 October 2013 (UTC)

Superposition, entanglement, and quantum computers are in no way dependent on the Copenhagen interpretation. --Amble (talk) 08:37, 31 October 2013 (UTC)

Let me rephrase that: the vast majority of Copenhagen-like interpretations are pure nonsense. More specifically, they all arise from a misinterpretation of the implications of probability with respect to physics; rather than seeing it as the mere necessity to consider all of the probabilistic "degrees of freedom" inherent in a system, they instead take the analogy too far, as it were, constructing a sort of hocus-pocus holographic multiverse of quantum weirdness in the process. Quantum computers are a direct result of such interpretations and thus nothing more than an interesting thought experiment. Sebastian Garth (talk) 15:53, 31 October 2013 (UTC)

That's quite a tangle of misconceptions. --Amble (talk) 18:12, 31 October 2013 (UTC)

You may be surprised to find that a few others agree with my assessment. But hey - what could they possibly know about all that? Sebastian Garth (talk) 19:49, 31 October 2013 (UTC)

Thanks, but I'll take modern experimental and theoretical work in quantum information over a local hidden variables interpretation that has been shown to be inadequate many decades ago. And I have no idea why you believe that quantum computers depend on any particular interpretation of quantum mechanics. They don't. --Amble (talk) 20:16, 31 October 2013 (UTC)

Bell test experiments is the relevant article, although the experiments are unlikely to convince the OP. Tevildo (talk) 21:45, 31 October 2013 (UTC)

Bell's experiments have their own set of problems and besides that don't in any way invalidate what I have said. You can use quantum equations without having to accept that they are inherently "real" (just as you can use probability in many other fields without having to draw any such conclusions). Sebastian Garth (talk) 22:34, 31 October 2013 (UTC)

They most certainly do. To quote the first line of the article, in fact:

"A quantum computer (also known as a quantum supercomputer) is a computation device that makes direct use of quantum-mechanical phenomena, such as superposition and entanglement, to perform operations on data".

Superposition and entanglement are merely (the Copenhagen-type variety of) interpretations of the possible implications posed by the equations used in quantum mechanics. Furthermore, from the first line from quantum superposition:

"Quantum superposition is a fundamental principle of quantum mechanics that holds that a physical system—such as an electron—exists partly in all its particular theoretically possible states (or, configuration of its properties) simultaneously; but when measured or observed, it gives a result corresponding to only one of the possible configurations (as described in interpretation of quantum mechanics)".

Finally, from the article on quantum entanglement:

"Quantum entanglement is a product of quantum superposition.".

So you see, all of these ideas are indeed connected. It's no wonder people like Stephen Hawking are so much more popular than Einstein in this day and age - science has become a mythological free-for-all, sadly... Sebastian Garth (talk) 21:04, 31 October 2013 (UTC)

To the extent that the theories are predictive and validated by experiment, they are valuable models. Mathematical models describe what we observe. To the extent quantum mechanics lends itself to the description of observation (and the effect observation has on the experiment), is very well documented. I think everyone realizes that a description of a thing is not the thing itself. But if it's sufficiently detailed to predict behavior of the thing, then it's a pretty good model. As far as I can tell, QM's basic premise is the observer is part of the system. Probabilities arise from the uncertainties introduced by the observer. Superposition for example, describes all the observable states for an electron. It's a useful description and model but we can't create an electron from it. We also can't observe a state not part of the superposition description nor can we violate some of the fundamental underpinnings. Until that happens, it's a pretty good model. --DHeyward (talk) 23:33, 31 October 2013 (UTC)

The crux of the problem is are you trying to determine the state of the cat without measuring it? --DHeyward (talk) 07:33, 31 October 2013 (UTC)

Put the cat back in the box and measure the observable O = |dead><alive| + |alive><dead|. Count Iblis (talk) 16:04, 31 October 2013 (UTC)

Division by nothing

I know that division by zero is not mathematical, but what do you get if you divide something with nothing? — Preceding unsigned comment added by 128.214.166.7 (talk) 13:22, 30 October 2013 (UTC)

By this mean insted of 5/0 trying for to do example 5/ — Preceding unsigned comment added by 128.214.166.7 (talk) 13:23, 30 October 2013 (UTC)

According to quantum physics, there is no nothing, so division is well bounded. Alternatively, you can roll up the Complex plane into the Riemann sphere by adding an infinity point, giving a result for every use of the division operator. Hcobb (talk) 13:28, 30 October 2013 (UTC)

Not sure this is a science question more a maths one. But this video has a good explination. Zero and nothing are the same thing.Dja1979 (talk) 13:59, 30 October 2013 (UTC)

• It depends on the system you are operating in. In most programming languages, "5/0" will give you a floating point exception, whereas "5/" will give a syntax error when you try to compile the program. Looie496 (talk) 14:36, 30 October 2013 (UTC)

Looie496's answer is excellent - because at the core, our original question is not well-defined. In English, we use the word "division" to refer to many related mathematical concepts, including the calculation of the multiplicative inverse and the left-multiplication by the adjoint or conjugate. In these cases, we can explicitly define a mathematical result. If you use a programming language to ask the question, you are forced to be very specific; and depending on what you ask, we can provide the result. In English, your words leave enough ambiguity about your intent that we can't answer very specifically.

Speaking of programming - I recently did battle with the innards of a mathematical representation in the C++ Standard Template Library. I was winning the battle, but I realized I had lost the war when I discovered that my predecessor had overloaded arithmetic operations, including /, as unary predicate operators so that he could divide by nothing while iterating over empty sets. I saw red-links, and knew I had crossed over the edge of reason and had reached the limit of human knowledge. Nimur (talk) 15:57, 30 October 2013 (UTC)

http://en.wikipedia.org/Division_by_zero 217.158.236.14 (talk) 14:56, 30 October 2013 (UTC)

You have lack of information about the denominator, so the outcome fo the division is not known. But what you can say is that the amount of information about the outcome will increase by 2 <Log|x|>, where you have to average over all possible inputs. Count Iblis (talk) 15:53, 30 October 2013 (UTC)

What the OP is calling "nothing" is actually the "empty set". Any computer language worth its salt will have a trap for undefined operations like that. I tried it in Oracle SQL, and 5 over null is... surprise! ...null. ←Baseball Bugs carrots→ 16:38, 30 October 2013 (UTC)

The question is not answerable. The OP admits that division by zero is not defined, but then asks what happens when you do it. It's not that it is forbidden, it's simply not defined. Some calculators/computers will raise some type of error that you could catch, like any other logical error. However, you can still approach it as much as you want OsmanRF34 (talk) 19:46, 30 October 2013 (UTC)

Division by zero is well-defined in some contexts — see our article on division by zero for a discussion, or go straight to Riemann sphere for the most important example. But what "division by nothing" is supposed to mean, I'm not sure. Zero is a thing, and the empty set is also a thing, so neither of them is "nothing". Maybe it's more of a language question? If you divide five by nothing, literally speaking, you just didn't do anything, so there is no result of this action, because there wasn't any action. --Trovatore (talk) 19:56, 30 October 2013 (UTC)

In that sense, it's no different from dividing 5 by an apple. That doesn't work either. Most computers and calculators nowadays will pre-empt division by 0 and flag it as an error. But I recall a few decades ago, a mechanical calculator. If you divided X by Y, it would compute it, apparently by figuring out what Z x Y would equate to X. All well and good, until you divided 1 by 0. Then it would start calculating the Z value mechanically. Basically it would just start counting up. The machine had maybe 15 or 20 digits, and although it seemed to be going pretty fast, each power of 10 would naturally take 10 times as long to switch to the next high-order digit as did the next lower-order digit. I figured it would have to have run for days or maybe weeks before it would hit the last digit. So I stopped that experiment, and never did learn what would have happened once it reached all 9's. ←Baseball Bugs carrots→ 22:43, 30 October 2013 (UTC)

Well, no, it is different. Dividing 5 by an apple doesn't make sense, but it could make sense if you specified what new meaning of "divide" you have in mind. Similarly with dividing by zero (though there well-established meanings already exist) or dividing by the empty set (where they don't, as far as I know) — those are both things. But the word "nothing" does not refer to a thing; it has a different linguistic function altogether. --Trovatore (talk) 22:47, 30 October 2013 (UTC)

I think the short, complex answer is infinity. Division by zero is undefined in the real number system, but in Calculus and other higher math, we can argue it is conceptually equal to infinity. Or we might say, "approaching infinity" since it cannot be reached. In other words, how many times does 0 go into some finite number? Infinite number of times. - 76.17.125.137 (talk) 01:59, 31 October 2013 (UTC)

If ∞ = 1/0, then 0 = 1/∞. Count Iblis (talk) 02:06, 31 October 2013 (UTC)

• Let me just say Hcobb's answer is no, good. Concepts are not physical objects, no more than motherhood has a molecular weight. The statement is a category error. μηδείς (talk) 02:31, 31 October 2013 (UTC)

Division by nothing produces the IP address 128.214.166.7, if you want it to. The word "nothing" in mathematics would most commonly mean "0", but not necessarily, and even what "0" means depends on the context. More importantly, the expression "5/" by itself or more generally "x/" by itself doesn't have any well-established mathematical meaning. So by talking about "x/" you're creating new mathematics (which is a perfectly legitimate thing to do), and you're free to define what you mean by "x/" without it even causing confusion due to your meaning being different from some usual meaning of that expression. In particular, you're free to define a function called "division by nothing", which is denoted by the symbol "/" using postfix notation , such that ${\displaystyle /\colon \mathbb {R} \rightarrow \mathbb {IP} }$, where ${\displaystyle \mathbb {R} }$ as usual means the set of reals and ${\displaystyle \mathbb {IP} }$ means the set of IP addresses, and for all x, x/ = 128.214.166.7 . I'm not a mathematician, so a professional mathematician might express the definition of the function a little better than I did, but my point is that you're free to define what "division by nothing" means however you want to. Red Act (talk) 03:10, 31 October 2013 (UTC)

"The word nothing in mathematics would most commonly mean 0"? No. Where do you get that? 0 is very definitely something; it is absolutely not nothing. --Trovatore (talk) 03:40, 31 October 2013 (UTC)

Well, the word "nothing" is certainly sometimes used in mathematical contexts to mean zero; here is the title of an article in Scientific American, as well as the title of book written by a mathematician, that uses "nothing" to mean "zero". The word is also sometimes used to mean the empty set. The word is also sometimes used to mean neither of those things. The whole point of my sentence is that the meaning of the word "nothing" depends on the context. There is no established context I'm aware of in which "division by nothing" is defined, so creating a new context in which it is defined doesn't conflict with any existing definition. Red Act (talk) 04:51, 31 October 2013 (UTC)

The subtitle in your link is just a witticism, not a genuine use of "nothing" to mean "zero".

The thing is that nothing is used as a noun phrase, but it is not interpreted as having a referent; when it appears in a sentence, it's normally to be interpreted as the universal quantification of a negative statement. "I saw nothing" doesn't mean "I saw x, which is nothing"; rather, it means "for every x, I did not see x". So if you divide by zero, you may or may not get a definite answer, depending on the context. But if you divide by nothing, you just don't divide by anything. --Trovatore (talk) 08:26, 31 October 2013 (UTC)

Perhaps the article subtitle can be dismissed as a witticism, but the book title "The Nothing that Is: A Natural History of Zero" mentioned in the article isn't just using a witticism as far as I can tell. But I think it's all moot, because I think the term "nothing" is only used in very informal mathematical contexts, and mainstream math doesn't have a rigorous concept called "nothing". At least, Nothing#Mathematics doesn't list any possible meaning other than zero or the empty set, and I think in formal settings mathematicians would use one of those two terms instead of "nothing", when they want to talk about zero or the empty set. If you're aware of a reliable source containing a rigorous mathematical treatment of "nothing" as being defined as something other than zero or the empty set, please give a citation, so that the Nothing#Mathematics section can be updated. Red Act (talk) 09:51, 31 October 2013 (UTC)

Of course there is no "rigorous mathematical treatment of 'nothing'". That's the whole point of what I was saying — the word "nothing" looks syntactically like something that should have a referent (because it constitutes a noun phrase), but in the actual semantics of the English language, it serves a different function and does not have a referent. So there can't be a mathematical (or, indeed, any) treatment of it, because there is no "it". --Trovatore (talk) 20:26, 31 October 2013 (UTC)

I think I see your point, and I agree with what I think your point is. The English sentence "I saw nothing" means something like "the number of objects that I saw was zero", or "the set of objects that I saw was empty", not "I saw the number zero" or "I saw the empty set". Similarly, the phrase "division by nothing" means something like "the number of numbers being divided by is zero", or "the set of numbers being divided by is empty", not "division by zero" or "division by the empty set". That's consistent with my treatment of the "division by nothing" function above. The function in question is a function that has one argument that's labeled as being a "numerator", and zero arguments that are labeled as being a "denominator", not a function which has one "numerator" argument and one "denominator" argument whose value is zero, or whose value is the empty set. Red Act (talk) 22:09, 31 October 2013 (UTC)

It simply doesn't make sense to not have a denominator, it's a non-function. It is possible to have the denominator as undefined, but must still be something. Plasmic Physics (talk) 03:19, 31 October 2013 (UTC)

The "division by nothing" function I defined has a domain of ${\displaystyle \mathbb {R} }$, not ${\displaystyle \mathbb {R} \times \mathbb {R} }$. I.e., the "division by nothing" function doesn't have a denominator, by definition. Red Act (talk) 03:55, 31 October 2013 (UTC)

You've got it wrong, the domain is ${\displaystyle \mathbb {R} \times }$, not ${\displaystyle \mathbb {R} }$. Plasmic Physics (talk) 04:07, 31 October 2013 (UTC)

ERROR: Parsing failure (EXPECTED OPERAND). Plasmic Physics (talk) 06:16, 31 October 2013 (UTC)

It doesn't make sense for the expression "x/" to not have a denominator, if the symbol "/" in that expression is referring to the standard division function whose domain is ${\displaystyle \mathbb {R} \times \mathbb {R} }$. But that doesn't mean that somebody can't define a new function that uses the same symbol, whose domain is just ${\displaystyle \mathbb {R} }$. And if the domain is just ${\displaystyle \mathbb {R} }$, and the symbol for the new function is defined as being used after the function's argument (similar to x! for the factorial function), then the expression "x/", where ${\displaystyle x\in \mathbb {R} }$, is perfectly well defined for that new function. Red Act (talk) 06:21, 31 October 2013 (UTC)

Well, that is bit a useless answer. The OP has already defined / as division. You're basically saying, that hypothetically, if you had a million dollars, then you would have a million dollars. It is a self-evident statement, which has no real bearing on the OP's question. Plasmic Physics (talk) 07:24, 31 October 2013 (UTC)

Baseball, the empty set is no equivalent to nothing. Nothing has no mathematical definition, or any definition for that matter, the empty set is by no means equivalent to nothing - the empty set is a useful mathematical tool.

The OP most certainly has not defined "/" as being the normal division function. The normal division function is defined as a function whose domain is ${\displaystyle \mathbb {R} \times \mathbb {R} }$. But the OP has explicitly specified that the "division" function being referred to does not involve a denominator of zero. The "division" function being referred to also doesn't have a denominator that's a non-zero real, either; the expression "5/" only shows the function as having one argument, i.e., it doesn't have any kind of denominator (i.e. second argument) at all. It's possible to define a new function that meets the OP's criteria, but none of the standard functions called "division" do. Red Act (talk) 09:23, 31 October 2013 (UTC)

Where has the OP given this liberty to redefine division? Plasmic Physics (talk) 21:27, 31 October 2013 (UTC)

My first post above, at 03:10 31 October 2013, points out to the OP that if he wants to, he can take the liberty of choosing to define "division by nothing" in such a way that his question makes sense, without conflicting with existing mathematics. The function I supplied was merely an example of a function that would work for that purpose. The question is not consistent with the normal division function whose domain is ${\displaystyle \mathbb {R} \times \mathbb {R} }$. If an alternative function is not considered, then the question has no more meaning than "what is the square root of a unicorn?" Red Act (talk) 23:17, 31 October 2013 (UTC)

this is more of a mathematics function. Often the answer depends not on the fixed number division, but rather whether the numerator converges faster or slower to 0 than the denominator. --DHeyward (talk) 07:18, 31 October 2013 (UTC)

Drinking Ethanol, does it makes you live longer?

I have seem to be found very contradictory claims on alcohol (as a popular beverage) where it says that drinking it will make you live longer, or have healthier life, other claims that drinking alcohol, is bad for health, and should be avoided at all costs.

There doesn't seem to be a consensus about it, so is it really true that drinking alcohol makes you live longer, or it's just a myth? Thank you. 190.60.93.218 (talk) 17:29, 30 October 2013 (UTC)

You may be interested in our articles Long-term effects of alcohol and Health effects of wine. It is true that some studies have found that regular moderate consumers of alcohol (or sometimes specifically wine) seem to live longer, or gain other health benefits. It should also be obvious from the first article that excessive alcohol consumption over a long period of time seems to be extremely bad for you. So the conclusion is less "avoid at all costs" and more "everything in moderation". But you have to keep in mind that most of these long-term studies are looking at correlation only, and correlation does not imply causation. Someguy1221 (talk) 17:57, 30 October 2013 (UTC)

Note that the studies on wine of which I am aware do not cite ethanol as the beneficial substance, but rather other compounds found in wine (see the article cited above for more information) Equisetum (talk | contributions) 23:34, 30 October 2013 (UTC)

Of course excessive consumption in bad for you, that's pretty much the definition of excessive consumption - "the amount which is bad for you" MChesterMC (talk) 09:40, 31 October 2013 (UTC)

And the big difference is what you would be drinking, otherwise. If soda, especially soda with artificial sweeteners, then a bit of alcohol is a favorable alternative. StuRat (talk) 21:55, 30 October 2013 (UTC)

Yeah, if instead of ethanol you decide to drink methanol you'll live a much shorter life. OsmanRF34 (talk) 22:02, 30 October 2013 (UTC)

"especially soda with artificial sweeteners"? Excuse me? citation please... Diet_soda#Health_concerns, mayo clinic "Artificial sweeteners and other sugar substitutes", national cancer institute - Artificial Sweeteners fact sheet Vespine (talk) 23:40, 30 October 2013 (UTC)

Well, you had a citation right in our Wikpedia article: . That concluded that diet soda and regular soda are equally unhealthy. However, they made the assumption that equal quantities were consumed, ignoring the fact that many will drink more diet soda, since they aren't as worried about the calories. When you factor that in, diet sodas are worse. StuRat (talk) 01:38, 31 October 2013 (UTC)

A you say? Oh and speaking of needed citations, where's the one for the claim alcohol is preferable to soft drinks? The link you provided says nothing useful to either query. In fact it doesn't even say what you claimed it said. (It doesn't say they are equally unhealthy, it only says people who consumed diet drinks also had similar health risks and goes on to note the evidence is quite contentious and particularly mentions there are a bunch of confounding factors like people consuming diet drinks because they already had health problems, as μηδείς mentions below. I would also note since the study appears to be an observational study, it seems unlikely any 'assumptions' were made about equal consumption.)

Nil Einne (talk) 04:43, 31 October 2013 (UTC)

Try this one then: . StuRat (talk) 05:01, 31 October 2013 (UTC)

Actually, an antidote to methanol poisoning is ethanol. They compete for the metabolic pathways so it becomes a rate equation as to which wins. The liver clears both but too high of the intermediate metabolites can cause blindness and death for methanol but if you can reduce the rate of methanol metabolism and spread it out through the ingestion of ethanol, you may live and also see the benefits of a beer. The liver prefers metabolizing ethanol over methanol and keeps the intermediate toxins at bay. YMMV and don't try at home. --DHeyward (talk) 08:00, 31 October 2013 (UTC)

I imagine if they catch they methanol poisoning early enough, they would induce vomiting or pump the stomach. StuRat (talk) 17:03, 31 October 2013 (UTC)

• Can you give a mechanism as to why diet soda is worse? Wouldn't it simply make sent that people who drink diet soda do so in a significant part because they are already heavy or diabetic, hence a less healthy cohort? μηδείς (talk) 02:28, 31 October 2013 (UTC)

• I believe the suspected mechanism is as follows: Your body starts to produce insulin as soon as sugar is consumed, so it will be in place as it is digested, to prevent a blood sugar spike. However, artificial sugars fool your body into thinking you consumed sugar, so the insulin is still produced, causing your blood sugar to crash. Your body then responds to this by increasing your cravings for sugar. You then eat some real sugar. You thus suffer all the consequences of consuming sugar, plus the consequences of the blood sugar crash beforehand. StuRat (talk) 04:59, 31 October 2013 (UTC)

The difficulty is that the studies that show that moderate amounts of alcohol are beneficial don't present an underlying mechanism. It's perfectly possible that, for example, people who drink "socially" are getting the benefit from being social - not from the actual alcohol...or that people who are naturally more healthy are happier than people who aren't, and are therefore more likely to drink moderately. It's very difficult to disentangle cause from effect here. SteveBaker (talk) 05:59, 31 October 2013 (UTC)

I know of one abstainer who admits that the only reason he is alive is because he used to drink enormous amounts of booze, it was that or top himself. So he reckons that despite the damage it did him, at least he is alive, 30 years later. (cite: Ross Fitzgerald in The Australian) Greglocock (talk) 23:35, 31 October 2013 (UTC)

Practically visible universe stops growing

When will that happen? The visible universe will grow forever (and never exceed 2.36 times the space) but all but our cluster will become too redshifted to detect. What's the real ratio then? — Preceding unsigned comment added by 12.196.0.56 (talk) 20:31, 30 October 2013 (UTC)

Eventually, there will likely be nothing left to detect at all; see Heat death of the universe. For a timeline of what will happen before then, see Future of an expanding universe. And although there is a growing consensus that the universe will continue to expand forever, there are dissenting opinions; see Ultimate fate of the universe. Red Act (talk) 00:55, 31 October 2013 (UTC)

Long after you have died. You will either obtain the answer through divine intervention or simply cease to care. :) --DHeyward (talk) 08:41, 31 October 2013 (UTC)

XENON-100 project regarding dark matter detection?

Is there any short description of the XENON-100 project? or if someone cares to convert the PhD publications into an wikipedia article.. I'm particulary interested in how they physically accomplish this. Electron9 (talk) 22:00, 30 October 2013 (UTC)

You have already found the short description of the project. "XENON is a next-generation Dark Matter Direct Detection experiment, which will use liquid xenon as a sensitive detector medium to search for WIMPs (Weakly Interacting Massive Particles)." If you are not familiar with gas scintillation, the Misplaced Pages article may help. Nimur (talk) 22:53, 30 October 2013 (UTC)

Makes me wonder if there's other methods to detect dark matter other than scintillation or WIMP. Perhaps like interaction with a field rather than with a mass.. Electron9 (talk) 23:02, 30 October 2013 (UTC)

There are a variety of approaches to direct detection. (Note that WIMPs are a type of dark matter candidate, not a detection method.) Other channels are used to search for WIMPs: XENON-100 uses ionization and scintillation, and other projects also use phonons or heat. COUPP uses bubble nucleation. The Axion Dark Matter Experiment looks for a different candidate, axions, by searching for their interaction with the electromagnetic field in a cavity. --Amble (talk) 00:43, 31 October 2013 (UTC)

We do already have an article for the Xenon family of experiments that includes Xenon100: XENON Dark Matter Search Experiment. Funny that you ask about Xenon-100 on the day that LUX, a very similar but competing experiment, released its first results. --Amble (talk) 06:23, 31 October 2013 (UTC)

October 31

Testing for Pink Noise

I am aware of statistical tests for white noise in a real signal (Box-Pierce, Ljung-Box tests) and red noise (Percival test) but am unaware of any statistical tests for pink noise in a signal and cannot find any literature on this, only properties of pink noise and the generation of pink noise. Does anyone know of any? — Preceding unsigned comment added by 211.31.25.66 (talk) 07:48, 31 October 2013 (UTC)

Articles related to Flicker noise have detection and elimination techniques. Suppressing flicker noise below the thermal noise floor is generally the goal. Double correlated sampling and chopper stabilization are techniques to move the flicker noise below thermal noise. detection is basically all 1/f noise is pink noise. --DHeyward (talk) 08:11, 31 October 2013 (UTC)

I think it's important to point out the distinction between pink noise and flicker noise, which our articles don't make clear. Pink noise is any noise with a 1/f (3 dB per octave) spectral density. Flicker noise is a type of pink noise produced in electronic devices. The two terms aren't synonymous. Tevildo (talk) 22:14, 31 October 2013 (UTC)

Flicker noise does from the description seem to resemble shoot noise but where every single electron contributes and thus it looks different but have the same base? Electron9 (talk) 23:39, 31 October 2013 (UTC)

Shot noise has a white (frequency-independent) spectral density, not a pink (1/f) density. I'm afraid I don't understand the rest of your question. Tevildo (talk) 00:06, 1 November 2013 (UTC)

It is indeed important to realsise that there is a very important difference between flicker noise (also known as 1/f noise) (f for frequency) and pink noise. The Misplaced Pages artcilces on flicker noise and pink noise are all mixed up - the authors have been confused on the meaning of "1/f".

Flicker noise arises in vacuum tube cathodes, junctions between thin metal films, and junctions between metals and semiconductors, has a power spectrum that drops 6 db for each octave increase in frequency, and rises in proportion to the square of the DC current thru the junction. Saying that it drops 6 dB for each octave increase in frequency is or couse the same as saying flicker noise voltage is proportional to 1 / frequency. Since power is proportional to voltage squared, power drops 4:1 for each 2:1 increase in frequency.

Pink noise is white noise that has been filtered to produce a power spectrum that drops 3 dB (ie power halves) for each octave increase in frequency. When expresed as a voltage, pink noise halves for each 4:1 increase in frequency. Because of this, pink noise cannot be produced by a cpacitor shunting a noise current source. In analogue circuits, pink noise is produced by a complex network og capacitors and resistors that approximates an impedance proportional to (1/f), not 1/f.

One way to prove out pink noise is to inverse filter it (i.e., use an A = k.f1/2 filter) back to white noise in a finite bandwidth and then apply the usual tests for band limited white noise.

Note: Those of us old enough to have worked with vacuum tube operational amplifiers, and those of us who are old enough to have listened to the amplified Low frequency noise from the early junction transistors (eg OC71, AC125, Japanese HJ15, etc) know why popcorn noise is called popcorn noise. And we know it is random, but it sure doesn't sound like pink noise or filtered thermal noise.

A classic textbook that covers white, coloured, and popcorn noise is: Electrical Noise by W R Bennet, McGraw Hill 1960. An oldie but a goodie. Poporn noise discussion starts on Page 87.

127.0.0.1 (talk) 00:24, 1 November 2013 (UTC)

Agriculture and global food supply

Can you tell me what the current amount of staple foods needed for the world supply is? I want to know the amount of food produced for at least 3 staples and the total world population of those 3 staples.--131.96.121.122 (talk) 13:53, 31 October 2013 (UTC)

• Is meat one staple, grain another staple, and fruits still another staple?

• Also, if meat is one staple, does this mean that beef, mutton, pork, and chicken meat are all one staple?--131.96.121.122 (talk) 14:40, 31 October 2013 (UTC)

I think you misunderstand the concept of a staple food. There is never more than one staple in a given community with a common diet. --Trovatore (talk) 18:31, 31 October 2013 (UTC)

World Population in 50 years

What is the projected increase in world population for the next 50 years? (If you can, give me a weblink, too.)--131.96.121.122 (talk) 13:55, 31 October 2013 (UTC)

Population growth has a projection. OsmanRF34 (talk) 14:09, 31 October 2013 (UTC)

So, we're looking at a world population of 10 billion in 2063.--131.96.121.122 (talk) 14:18, 31 October 2013 (UTC)

Trousers

Cuold you please explain me how wearing two trousers (or, in general, wearing multiple layers of clothes) produce warmth?

Sorry for a stupid qestion, but I really don't know. --Roman1969 (talk) 14:44, 31 October 2013 (UTC)

This will trap a layer of air between the clothes, and air has a very low thermal conductivity coefficient. So, what then happens is that the same amount of heat that your body produces must still escape via your clothes, but this heat will escape from the top layer of your clothes, So at that top layer the temperature will be the same (because heat transfer depends on the temperature difference and the heat transfer between the top layer and the air will be the same). Then the hat transfer from your body to that top layer must also be the same in bith cases, but nowwith more air trapped between the top layer and your body, the tamperature difference must be larger, so the temperature at your skin will be larger. Count Iblis (talk) 14:56, 31 October 2013 (UTC)

An air layer is part of the answer, but two layers of the same material also cuts in half the heat transferred by conduction through the fabric, and also decreases the flow of cold wind if the fabric is porous enough to allow any air current. Edison (talk) 18:55, 31 October 2013 (UTC)

Layers also provide another advantage: It's important to prevent sweat from building up, which can then make you very cold and uncomfortable later. With layers, you can add or remove layers as needed, to keep comfortable. If you had a single, thick item of clothing, you would lose this flexibility. StuRat (talk) 16:49, 31 October 2013 (UTC)

This is probably clear, but just in case: Clothing doesn't produce any warmth, it is only your body that produces warmth. Clothes only reduce the heat loss of the body. You can wrap a stone in as many layers as you wish and it will not warm up.86.179.30.226 (talk) 22:41, 31 October 2013 (UTC)

RPG-29

I have a curiosity about RPG-29 rocket: in its technical description is said that it could penetrate 750 mm of RHA (Rolled homogenous armour) or 1500 mm of reinforced concrete. This sound to me very strange: the reinforced concrete has a tensile strength of 12-15 megapascal and the RHA of 1000-1200 megapascal (80 times higher). How it's possible so low difference beetwen the two penetration? Isn't maybe the data for RHA overstimed or there is any other reason? 80.116.228.89 (talk) 17:37, 31 October 2013 (UTC)

An RPG uses a shaped charge. The liner of the charge is compressed into a narrow jet of metal moving at speeds up to 14 km/s. At those speeds, the strength of the armor plays a minor role, it's mainly the density or weight that determines how far the charge penetrates, that's why some tanks use depleted uranium in their armor. Ssscienccce (talk) 18:26, 31 October 2013 (UTC)

See also composite armour, that mentions that fused silica glass had a higher stopping power than steel (not sure that can be explained by density). To defend against hollow (shaped) charges, explosive reactive armor has been developed: an explosion moves part of the armor while the jet of the shaped charge is penetrating, disrupting the shape of the jet and diminishing the penetrating depth. To defeat reactive armor, the RPG-29 and other HEAT rockets use two shaped charges, the first will trigger the explosive charge in the armor, the second strikes milliseconds later, when the armor isn't "reactive". Ssscienccce (talk) 19:13, 31 October 2013 (UTC)

'Real world length contraction' moved to archives. Why?

I'm new here... wondering why discussion of my question "'Real World' Length Contraction" was deleted from the current menu and moved to the archives, while, for instance the "vomiting while pregnant" question and others remains on the up-front menu. Wherever I raise the question of a variously contracted Earth diameter, or contracted distances between stars... depending on all varieties of relativistic frames, I am either called a crank (and banned from science forums) or told that challenging mainstream length contraction is inappropriate... or the topic is hidden in the backwaters, like the archives here. Will someone here please explain why my question was brushed aside as above with no answer? Thanks — Preceding unsigned comment added by 63.155.141.178 (talk) 17:58, 31 October 2013 (UTC)

I just asked about the above but forgot the headline... and the question disappeared. — Preceding unsigned comment added by 63.155.141.178 (talk) 18:04, 31 October 2013 (UTC)

Because questions 5 days old are archived automatically. Ssscienccce (talk) 18:12, 31 October 2013 (UTC)

If there's more you feel needs to be explored, feel free to open a new question along those lines. Ideally, don't just ask the same question (unless, say, no one responded at all), but focus on what you feel was not addressed. --Trovatore (talk) 18:16, 31 October 2013 (UTC)

Thanks. The question was left hanging at the challenge of a shrinking Earth diameter, depending on the velocity and direction of relativistic frames observing it. The muon question was also left unanswered. I'll open a new question on those cases of supposed contraction specifically.

The point is that you come over as quite hostile. You're essentially saying "I don't believe in Special Relativity - it's impossible" - which is not asking us a question. In fact, you're entirely wrong. Special relativity is true - it's one of the better tested scientific theories - and much of what happens in the universe can only be explained by it being true. People have gone so far as to measure the ticking of the clocks on actual, for real spacecraft to see if time is slowed for them - and it is. If you own a GPS unit - you may be surprised to know that there is software inside that little box that has to compensate for both special and general relativity in calculating where you are in the world. This stuff really isn't up for debate.

So we're telling you the answer - "The Truth". It's OK if you don't fully understand it - by all means, ask for clarification. But issuing "challenges" and being generally combative is hostile to our volunteer staff, who's mission here is to tell you the truth and explain it if you don't understand. We're not here to disprove or challenge whatever wonky ideas you may have of your own. If you wish to dismiss all of mainstream science on this point and ignore what 100% of the respondents here are telling you, that's fine - go away and be flat out wrong someplace else. But please don't argue with us. We're telling you the truth as researched most carefully by hundreds of people who were all a lot smarter than any of us here!

Subjects like relativity and quantum theory are strongly contrary to "common sense" - but that's not because they're wrong - it's because we humans have evolved in a world where nothing much moves anywhere near to the speed of light (except light) and all of the objects we deal with routinely are bigger by far than an atom. The "common sense" that we evolved as stone-age hunter-gatherers on the African plains is pretty much useless for explaining what goes on in realms that it did not evolve to handle...so we find it hard to get our heads around the reality of the universe at these crazy speeds and scales. I forget who said it, but: It's not natures' duty to be understandable by mankind.

Perhaps you'd do our volunteers the kindness of toning down your rhetoric - and rather than telling us that this is all wrong and impossible (which it's definitely not), confine yourself to politely requesting clarifications for the parts that you don't understand. Do that, and things will progress more smoothly.

SteveBaker (talk) 21:38, 31 October 2013 (UTC)

I didn't read all that, but you apparently missed his question, the OP asked for an explanation or the underlying mechanisms regarding length contractions. Not that hard is it? --Modocc (talk) 00:17, 1 November 2013 (UTC)

Contracted Earth diameter and atmosphere depth

My "real world length contraction" question was moved to the archives (after the 5 day limit, I'm told... but doesn't seem to apply to other topics), so here are the unanswered challenges from that exchange: If a relativistic frame (future ship or whatever) approaches Earth in the direction of its axis at .866c, special relativity (SR) says that it will measure the polar diameter to be about 4000 miles. Then if it turns around and approaches at the same velocity in the direction of the equatorial diameter, that will now be measured as 4000 miles, and the polar diameter will have restored to its proper length just under 8000 miles. SR insists that all frames are equally valid, so then Earth must "morph" with every possible velocity and direction from which it could (relativistically) be observed. True of false?

Muons traveling through our atmosphere have higher velocities than lab-accelerated muons, so they decay more slowly ("live longer") and therefore travel further than lab muons, so they can reach Earth's surface. SR claims that the depth/thickness of the atmosphere contracts "for those muons." But the atmosphere remains about 1000 km all around Earth at all times, not contracted by what incoming muons would "observe." Different observations can not change physical objects or distances. SR claims that it does. SR advocates now have another 5 days to reply to this challenge. — Preceding unsigned comment added by 63.155.141.178 (talk) 18:51, 31 October 2013 (UTC)

SR says that the squared invariant distance between two points in space-time (x,y,z,t) and (x',y',z',t') is

s^2 = (t-t')^2 -

where the time and the positions are measured in the same units (so the speed of light, is set equal to 1). So, SR disputes the validity of Pythagoras' formula and it disputes that time intervals are invariant. Count Iblis (talk) 19:32, 31 October 2013 (UTC)

I don't see your problem here. Relativity says that sizes, masses, rate of passage of time and a bunch of other things depend on the frame of reference of the observer. In your example, people approaching the earth from different directions and speeds would indeed see the earth as having different sizes and shapes simultaneously. The idea that two people perceive things differently because they are moving at different speeds and directions should come as no surprise to you.

It's not quite a correct analogy - but consider the doppler effect for sound.

There is a person driving a fast car along a straight road and a person standing still at the side of the road. As he's driving along, the first guy leans on the horn and hears a sound of constant pitch as he passes the guy who's standing still. But the guy standing on the side of the road hears a higher pitched sound as the car approaches him and a lower pitched sound as it passes him and heads off into the distance. Ask the two people what pitch the horn had and they'll disagree. The horn doesn't have to have two pitches simultaneously - it's just that the frame of reference for the two observers is different. Position 100 people at different points along the road, all moving at different speeds and you'll get 100 different perceptions of the exact pitch of the car horn.

CAVEAT: This isn't actually a very good analogy because sound exhibits doppler differently from the way light does - but the point is that it's OK that an object can simultaneously be perceived as being many different sizes, masses, etc by different observers.

As I said before, you have to read (and completely understand) things like the Ladder paradox. In that example, a fast-moving 20' ladder fits into a 10' building - from the point of view of an observer standing next to the building - and the 20' ladder moves through the 5' building from the point of view of an observer riding on the ladder. This is entirely non-contradictory - but it is confusing as all hell for people who aren't comfortable with special relativity.

So the answer to your first question is that the earth doesn't "morph" - it simply "is" a whole bunch of different sizes (etc) depending on the frame of reference of the observer.

Your description of what happens with Muons is correct. From our point of view, they are moving ungodly fast, so time for them has slowed down - so they make it through the atmosphere without decaying. From the muons' point of view, time is ticking along normally - but the earth (and it's atmosphere) has contracted to a nearly flat circle and the atmosphere is so thin that it can make it through easily. This is not contradictory - it's an entirely consistent story - and the outcome (that the muon makes it through the atmosphere) is perfectly correct from both viewpoints.

You boldly assert that "Different observations can not change physical objects or distances." - but you are quite wrong. That is exactly what does happen. Consider the behavior of muons to be proof of that. There have been numerous other experiments that demonstrate this kind of thing. Special relativity is a proven fact - weird though it seems. You really can fit a 20' ladder into a 10' building if you move it fast enough...but if you're sitting on the ladder, things seem VERY different.

But think back to my (technically, rather bad) car horn analogy. Different observations of the car horn did change the frequency at which the various observers heard the sound. This is just like that (although the analogy is only perfect for lightwaves - not sound).

SteveBaker (talk) 21:17, 31 October 2013 (UTC)

If I might indulge in a bit of devil's advocacy - the statement "different observations cannot change physical objects" is correct (in this context, although we might get to the Copenhagen Interpretation soon). Different observations change the values of measured times and distances for a given (unchanging) physical object. The object doesn't change, although its length does. Tevildo (talk) 21:23, 31 October 2013 (UTC)

Yes...we should perhaps think of the "rest length" of an object (like it's "rest mass") as being a constant that doesn't change, and that all practical measurements of the object are a combination of the rest-length and a scaling factor that depends on relative motion. Splitting the length into those two parts resolves the confusion. The object's rest-length is an unchanging property of the object itself but it's modified by a factor that is observer-dependent. However, the key point here is that this second factor isn't like an optical illusion or seeing something in a distorted mirror. The point of the Ladder paradox is that a fast-moving object doesn't just look smaller - it will actually fit into a smaller space...from the perspective of some observers.

SteveBaker (talk) 21:46, 31 October 2013 (UTC)

Your "challenge" is like saying that the rules of perspective require objects to grow and shrink. The only difference between that case and this one is that there aren't a bunch of dumb popular books telling you that perspective means that the size of objects is "relative to the observer" and that that has profound philosophical implications. Ignore the second-rate philosophy and you'll be fine -- BenRG (talk) 21:39, 31 October 2013 (UTC)

I like that analogy...but we have to be a little careful though. The moon seems like it would fit into a matchbox because of perspective - but we know that it's not "really" that small and that it won't fit into such a small space. With Special Relativity, if the moon were moving so fast that it appeared to be that small, it really would fit into a matchbox. SteveBaker (talk) 21:49, 31 October 2013 (UTC)

Well, no, for a couple of reasons. First of all, length contraction is only in the direction of motion, so you'd need a Moon-sized matchbox in the other two directions. Then, yes, in the matchbox's frame of reference, you could (very briefly!) have the Moon contained within the top and bottom of the matchbox, say a centimeter apart, but only because you don't agree with the Moon about simultaneity. You'd have to let the Moon in, close the box (that might involve moving the top faster than the speed of light, but whatevs), then bask in the satisfaction that the Moon is inside the box before it obliterates the other side. From the point of view of a lunar observer, the events happen in a different order. --Trovatore (talk) 21:55, 31 October 2013 (UTC)

SSRI/SSNRI WITHDRAWAL

Can someone please add SAVELLA (Milnacipran) withdrawals in with the other SSRI/SSNRI Withdrawal symptoms? It is a fairly new medication, though it has severe withdrawal symptoms, very similar to others you have listed on the page. I would just like others to be informed about coming off this medication.

Thank you kindly,

Laurie Hart — Preceding unsigned comment added by 2602:30A:C0CB:4D60:78B7:92FD:3CA1:56C6 (talk) 19:17, 31 October 2013 (UTC)

If you have a reliable source that supports the change, then be bold and add it, or make a suggestion on the article's talk page. RudolfRed (talk) 20:27, 31 October 2013 (UTC)

Effect of poor Eyesight on life skill development

Can poor eyesight through childhood and adolescence cause any significant lack of life skill development, knowledge etc? Clover345 (talk) 22:25, 31 October 2013 (UTC)

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