Wikipedia:Reference desk/Archives/Science/2008 July 1

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July 1

Adultration

how to cure adultration in products purchased from the market? —Preceding unsigned comment added by Jasleen302 (talk • contribs) 12:00, 28 June 2008 (UTC)

Best to avoid buying them in the first place. Check your product carefully before you buy, and insist on a pure product. Buying this sort of stuff will just encourage more adulteration. What products are you having trouble with. Graeme Bartlett (talk) 01:57, 1 July 2008 (UTC)

By having an effective network of inspectors, checking for adulteration, and with the power to take action when it is found? (if I have understood the question correctly?)87.102.86.73 (talk) 09:58, 1 July 2008 (UTC)

This has been a problem for a long time, and it ebbs and flows with waves of government regulation and deregulation. The classical (fictionalized) work on this is Upton Sinclair's muckraking novel The Jungle.

Atlant (talk) 16:57, 1 July 2008 (UTC)

Unmanned Aircraft

I was watching a documentary, Regulus - The First Nuclear Missile Submarines, after WW2, in that it states how they managed to make the missile from remote go up and down, right and left, and eventually land. More information: [1]. Anyways if can control a missile from remote, why has there been no unmanned aircraft yet? Like a remote control one? I mean with the GPS and satellite technology it is possible. Is the United States Forces holding back on something they have in secret? --69.156.94.136 (talk) 01:17, 1 July 2008 (UTC)

There are unmanned aircraft. They don't even need to be remote controlled, they can be controlled by computer AI. Unmanned combat aircraft are probably the future of air warfare. Bombers and attack aircraft will be first. Followed by fighter aircraft.ScienceApe (talk) 01:29, 1 July 2008 (UTC)

It's not a secret, and it's not being held back. The MQ-1 Predator is a remotely-controlled unmanned aerial vehicle that fills a variety of roles, including precision bombing. It has been flying armed missions since at least 2001. TenOfAllTrades(talk) 02:24, 1 July 2008 (UTC)

Coming soon to an administration near you: Ender's Game.

Atlant (talk) 16:55, 1 July 2008 (UTC)

Modern commercial airliners with an autopilot are virtually unmanned aircraft, see this section Autopilot#Modern autopilots, and potentially only need a pilot for taxiing. Human pilots are almost a back up system to the aircraft autopilot and to provide a sense of security to the passengers. Tobyc75 (talk) 17:59, 2 July 2008 (UTC)

Freezing Cheese: Good or Bad

I wanted some input on freezing cheese. I'm taking a five hour flight and want to take a two pound block of cheese with me. I know that many people say, cheese shouldn't be refrigerated because it inhibits the life, and flavor inside the cheese, But hey I'm an American. And I know that freezing turns the moisture inside items into sharp shards, basically perforating what ever your freezing from the inside. But is freezing cheese GOOD or BAD? —Preceding unsigned comment added by Semi-smart (talk • contribs) 03:34, 1 July 2008 (UTC)

Freezing cheese is mostly successful, hard or soft, but not ricotta, so anything close and without moisture traps inside. Julia Rossi (talk) 07:07, 1 July 2008 (UTC)

Freezing cheddar is no good, it destroys the texture and it all goes crumbly. Parmesan powder freezes OK though. For a short flight like this, just pre cool it in the fridge, and then wrap it in something insulated like bubble wrap to keep it cool. Graeme Bartlett (talk) 07:13, 1 July 2008 (UTC)

But freezing cheddar is fine if you're going to use it in cooking, since the texture won't matter [2]. My Googling suggests that this is true of a lot of cheeses... in applications where texture doesn't matter, freezing is usually fine. --Allen (talk) 07:18, 1 July 2008 (UTC)

I have successfully frozen Stilton style blue cheese, flavour and texture were unaffected after 3 months. Richard Avery (talk) 07:25, 1 July 2008 (UTC)

I agree with Graeme Bartlett that the best way to deal with this would be to just cool it and keep it cool by insulating it. A simple way to do this would be to buy a small cooler -- I've seen ones that are about the size of a small handbag -- and sticking a couple of ice packs in with the cheese. (The "ice pack" article appears to deal only with the medical ice packs, but what I mean is the thing that is also called a "freezer block" or "ice brick", a rigid plastic brick filled with water that you can freeze and then use to keep things cool, the mainstay of coolers all over the world. (Can it be that we really don't have an article for them, or am I just completely blanking on the terminology here?)) Depending on where you are and how paranoid they are about you using your cheese to destroy the plane in midair, taking that with you as carry-on might be problematic, but you could just stick it in your bag and check it.

That said, a cheaper and more low-tech approach would be simply wrapping the refrigerated cheese tightly in newspaper. It makes a pretty good insulator, and you could always stick in an ice pack with the cheese to make sure it stays cool, if you're worried about that, but the newspaper by itself will probably do the trick, if the cheese is cool to begin with. You can probably get some extra mileage out of the newspaper by sticking it in the fridge with the cheese so it's also cool. As long as the newspaper is dry (water conducts heat very well), it'll work just fine. -- Captain Disdain (talk) 11:02, 1 July 2008 (UTC)

Why don't you test it out? Try freezing a bit and seeing whether it survives. I would be interested in hearing your results. Plasticup ^T/C 13:01, 1 July 2008 (UTC)~

I say screw it. The flight is only 5 hours pal, leaving cheese out of the fridge for that long probably won't be that bad for it. Moreover, if it's 2 pounds of cheese it should hold a temperature for a while. I'm all for captain disdain's strategy of insulating the cheese. But for the record, remember that if you're flight is international they're probably going to take the cheese at customs. --Shaggorama (talk) 16:46, 1 July 2008 (UTC)

When we returned from France, we brought back a variety of cheeses, probably mostly of the semi-dry styles. They were wrapped well in butcher paper at the cheese shop and we then closed the cheese shop's plastic bag as well as we could and chucked them in the middle of the clothes in our luggage. Between the insulation of the clothing and the likely cold baggage hold of the plane, they survived the ten-ish hour trip just fine. And even though the cheeses were from (gasp!) France, we declared them at American customs and were still allowed back into the country, cheeses and and all. (The preceding does not constitute legal advice; it just recounts Wikipedian's one anecdote.)

Atlant (talk) 16:53, 1 July 2008 (UTC)

This might help clarify matters. [3] But be sure to print out a copy to hold under their noses in case someone makes a fuss. OR: I've encountered customs officials anywhere from waving people through to trying to declare that permitted goods were not so. (Chocolate could cause all sorts of delays in NY for a couple of years while back, but that seems to have dissipated. I assume some overzealous supervisor got retired.) As for transporting the cheese, if you have the spare luggage capacity you might freeze a couple of those soft Ice packs you can buy at drugstores or pharmacies or the like. If you are squeezing for space and weight a wet T-shirt or towel might do the trick to prevent your cheese from suffering in case your luggage ends up baking in the summer sun for a couple of hours instead of going directly from the cool terminal to the cold cargo hold. NB: make sure to unpack immediately once you're home and air out the luggage to prevent moisture damage. Bubble wrap suggested above would additionally prevent your cheese from turning into cheese crumble, thanks to baggage handling. Remember you won't be able to take it as carry-on [4]. 80.171.254.148 (talk) 01:33, 3 July 2008 (UTC)

The recommendation for hard cheese is probably good for customs reasons as well; you want to avoid bringing back anything like Abbaye de Citeaux, Chevrotin and Chabichou du Poitou, "the forbidden cheeses", which have a moisture content that makes U.S. Customs uncomfortable. (What is specifically banned is raw milk cheese aged less than 60 days, or aged more than 60 days but having a moisture content of more than 67% water). This is sad for Americans, because, in the words of the Amateur Gourmet, the "high moisture content gives a creamy, luxurious texture and the raw milk lends it complexity and depth." You will have to enjoy these abroad.... - Nunh-huh 02:59, 3 July 2008 (UTC)

QAM query

Hello to all Please if some one can guide me about data rates of different catagerizes of QAM that is the data rate of 8-QAM, 16-QAM, 32-QAM, 64-QAM, 128-QAM, 256-QAM

thanks —Preceding unsigned comment added by Arsalan 80 (talk • contribs) 04:29, 1 July 2008 (UTC)

The different rates will depend on what bandwidth in general you want. For particular applications such as digital television or ADSL the appropriate standard will specify the rates to select from. With 8-QAM you will get 3 bits per symbol, 16-QAM will give you 4 bits per symbol, and so on till 256-QAM with 8 bits per symbol. Graeme Bartlett (talk) 06:18, 1 July 2008 (UTC)

statistics

what the the distinction between simulation,models,and experiments? —Preceding unsigned comment added by 72.75.74.106 (talk) 11:46, 1 July 2008 (UTC)

Experiments are tests on real-world things that yield real-world data. Simulations are more like thought-experiments. They are involve creating a model to imitate the real thing. Plasticup ^T/C 11:58, 1 July 2008 (UTC)

In my experience, a model is something that is fed into a simulation to give it the information needed to simulate, so to speak. Said in another way, the model is the abstraction and the simulator takes that abstraction and performs calculations on it to produce an expected result. The Monte Carlo method is a good example of this. The model is the input and the simulation is the action taken on it and the final result. In common parlance, they are often used interchangeably. An experiment is a totally different thing. It is an empirical study of something. Rather than having a known model, a series of observations are taken and analysed. In some cases, a model fit can be used to test a hypothesis. It is important to note that the experiment is totally based on observation. Simulation and modelling can be used to create a hypothesis, but experimentation is usually necessary to reject or not reject a hypothesis. Gjmulhol (talk) 12:06, 1 July 2008 (UTC)

A model can be more than just an idea. In biology, a model could be a live mouse, used to "simulate" a human for a particular purpose. Someguy1221 (talk) 03:22, 3 July 2008 (UTC)

Help with electronics

redirected from Wikipedia:Reference desk/Computing#Help with electronics

I have just begun building a guitar pedal, but no have no electronics expereience, but a good deal of knowledge (theoretical knowledge) of the subject.

I have become stuck where the schematic tells me to connect to ground.

I am soldering to a sheet of stripboard, and it has a thin copper track running down both sides of the board, but with no holes in them; Is this where i should connect grounded connections to? And do i connect all grounded connections to the one place, or should i cut the track so as to separate them from one another?

Any help would be much appreciated.

Thank you!! —Preceding unsigned comment added by 212.46.129.226 (talk) 09:33, 1 July 2008 (UTC)

If this is a standalone pedal (not powered by a wall outlet), it is very possible that you do not have ground inside the footpedal at all. In that case, I would assume that you are using a 1/4" plug from the guitar/amp and assume that the shielding of that connector is ground. So, attach there. If, instead, you are powering this from a wall outlet, ensure you are using a grounded plug (three prongs in the U.S.). Then, you will have ground where the power is soldered onto the board. Because this is an audio device, be wary of ground loops. If you ground your pedal and plug it into one outlet, then plug the guitar/amp into another outlet, it is possible that they do not share the same ground. You can easily get a hum or buzz on the speakers. So, inside the pedal, ensure you connect the ground from your power input to the ground on the shield of the cable from the guitar/amp. Then, you will joining the possible difference in grounds and eliminating the buzz. -- kainaw™ 12:54, 1 July 2008 (UTC)

Additional Help with Electronics

Thanks to kainaw for answering my previous question about grounding, but i still have some queries.

When you say to connect to the ground from the guitar jack, do you mean the input or the output jack?

And does it matter whether i connect all the grounded connections directly to the ground terminal of the jack, or if i connect them all (Including the ground from the jack) to the copper track at the side of the stripboard?

Thanks again for your help —Preceding unsigned comment added by 212.46.129.226 (talk) 13:41, 1 July 2008 (UTC)

"Ground" is often used in an imprecise way. The two most common usages are as "Ground"/"Earth" (yes I know this has reused "Ground") for the purpose of one or more of safety and screening/shielding and as 0V. Eventually Ground/Earthwants to get connected to a physical Ground - eg a copper rod stuck into the planet's soil. For this to work well as a safety connection, it wants to be well connected "in all directions". For it to work well as screening, you don't want current to flow through it, so only one connection to each bit of ground should be made, ideally in a star configuration but at worst as a tree configuration branching out from the trunk where the copper rod is. The other common usage informally means 0V. This has come about since often the 0V terminal of a PSU gets connected to ground to "stop it floating". This often creates loops and current flows in screening circuitry. With your pedals etc, you want all the 0V connected to each other once (no loops). A starter would be to see if, without your circuit in place the screen of the Inlet jack was connected somehow to the screen of the Outlet jack. If not, connect your ground signal to BOTH outers, otherwise choose one - the most convenient. There is an element of art rather than science about getting ground/0V/earth/screening right. -- SGBailey (talk) 13:52, 1 July 2008 (UTC)

To expand on SGBailey's point, "ground" in the context in which you're asking means "the reference voltage" (which we conventionally then call "0 volts"). All other signals in the circuit are measured "in reference" to this point, "the ground". For your guitar effects pedal, both the input and output jacks each have an outer terminal which should be connected to "the ground" (reference voltage) in your circuit.

Odds are that your guitar effects pedal should be designed to operate solely from battery power. Otherwise, any connection to mains/line power, even through a power supply/wall wart, is likely to cause a ground loop and that can induce your guitar amplifier to produce noise, hum, and other nasty stuff.

Atlant (talk) 16:42, 1 July 2008 (UTC)

A good book you might want to look into is "Do-It-Yourself Projects fo Guitarists" by Craig Anderton. I used to know a great website too, but I can't find it right now. --Shaggorama (talk) 16:09, 4 July 2008 (UTC)

Figure of the Earth image

I can't find this anywhere. I would like to know if there is an image which shows the figure of the earth without the water on it. I.e. only the rock part of the earth. Does such an image exist?  — Adriaan (T★C) 13:44, 1 July 2008 (UTC)

Bathymetry, [5]? -- Coneslayer (talk) 13:46, 1 July 2008 (UTC)

No, not what I'm looking for. I was wondering if there was a pic in true colour of the earth, just with the water edited out. Something like an artist's impression of what the earth would look like if all the water suddenly disappeared. Like a 3D pic of an object supposed to be the earth - but without water.  — Adriaan (T★C) 15:52, 1 July 2008 (UTC)

How about Mars? --Shaggorama (talk) 16:40, 1 July 2008 (UTC)

There's a 2D texture here. You could create a 3D image out of it quite easily with Xplanet. — Matt Eason ^{(Talk • Contribs)} 20:03, 1 July 2008 (UTC)

Space program benefits

In reading about the ancillary benefits of NASA's space program in articles like this and this, it strikes me that most the advances that are mentioned aren't dependent on the space travel part of the equation. Rather, they were inspired or triggered by space travel, but could just as easily have been developed for the same cost for a land-based application. For example, water filtration was (according to the NASA site above) developed in part for the Apollo program, but it's not as though it couldn't have been developed for non-space applications. Are there practical benefits to the space program, readily apparent to regular folks, that could only come with space travel? jeffjon (talk) 14:28, 1 July 2008 (UTC)

Define 'regularly apparent to regular folk'. There are thousands of experiments in space, many of which will have furthered our understanding of the world and how things react in given situations. Do you just want a list of products that use techniques based on the space program? Or do wooly benefits such as "improving the knowledge of mankind" and "continuing the exploration of the universe"? Personally I find that when people start to try to qualify the value of Nasa based on products/technological developments overlook the strongest argument for the space-program - that there's a universe out there that holds limitless possibilities and the more we go out there and the further we venture the more interesting things we will find. Of course this is from an exploratory enthusiast who supports the cause, certainly there are plenty of worthy groups vying for already scarce government funding. 194.221.133.226 (talk) 15:02, 1 July 2008 (UTC)

I'm with you; I think exploration for sake of pure discovery is motivation enough. My wife isn't convinced, so I was trying to come up with a more tangible benefit that she receives for that almost 1% of every dollar she pays in taxes, whether it's a product, a health benefit, a scientific advance with other implications, etc. jeffjon (talk) 15:10, 1 July 2008 (UTC)

IMHO the scientific benefits are good enough. But to counter the "they totally could've been developed anyway" argument, I guess the question is why. Why would any of that be built? Why would the US build a water filter when we've got good tapwater? Necessity is the mother of invention. We need a way to recycle water in space. It also happens to work really well on Earth? We should sell that to the third world and people who are superstitious about tap water! As the first source you cite mentions, if you look at a lot of the products, most of them are saying "NASA was doing this obscure scientific thing and it totally improved this product by leaps and bounds!" Thats pretty damn impressive, and I consider it a good testament to the power of a good R&D budget. EagleFalconn (talk) 15:24, 1 July 2008 (UTC)

I wouldn't expect R&D for space to be any more likely than anything else to have things that help in unexpected ways. If NASA didn't invent water filtration, maybe it wouldn't have occurred to anyone, but, by the same token, maybe there's something that hasn't occurred to us because we weren't spending that money on R&D for something of more obvious practical significance. Doing R&D for something practical has the added advantage of helping in expected ways. For those of you who think NASA does pull its weight, how much of your money do you donate to it? You don't think it's only worth it if it's money the government takes from you forcefully, do you? I'm currently saving up for college, but when I'm done with that, I plan on donating to a microcredit group, like Unitus. I think they have more practical significance than NASA. — DanielLC 15:49, 1 July 2008 (UTC)

Satellites enable my contributions to Wikipedia. There's your human benefit right there. ;-) Plasticup ^T/C 17:11, 1 July 2008 (UTC)

That's a bit of a red herring, isn't it? I don't make voluntary cash donations to my local water treatment plant or the city subway system, but I still think it's worthwhile for those projects to receive funding. If you want to talk about research, in the United States good solid research is carried out or funded by government agencies from the Department of Energy to the Department of Veterans Affairs; I don't make donations to those organizations either. TenOfAllTrades(talk) 17:26, 1 July 2008 (UTC)

Global Positioning System saves a lot of time and needless erring around. LINEAR is another point. And then, for people like me, it's simply interesting and sometimes even exciting to look at real pictures from space. And when I saw Neil Armstrong live on TV stepping on the moon that is something to remember. 77.3.134.249 (talk) 20:27, 1 July 2008 (UTC)

Though I am certainly no expert, I have read in the past that zero gravity experiments have been done on cultures of bacteria. These have shown unique characteristics. I also remember evidence of a super-bug, but I don't remember where that is from. Gravity is vital to life, it is important that we know how plants and animals react in such an environment. From a materials perspective (I am a materials scientist), some crystals and structures can only be formed in a zero-g environment. If extra-planetary colonization ever takes place, it would be good to know how to take advantage of these new, potentially revolutionary structures. Gjmulhol (talk) 11:55, 2 July 2008 (UTC)

Note that just because spinoff products are formed does not necessarily mean that NASA is a good way to get them. If you give me a billion dollars I'm sure I could get you some tangible benefit for it—but would that be a better approach to said products than, say, letting them develop on the free market? That is—the return on R&D in terms of secondary benefits is going to be pretty small, most likely, and not very efficient.

In my opinion a better argument focuses on the BIG, non-spinoff benefits. GPS. Satellite communications. Military advances in rocketry. Advances in computing, robotics, materials science, etc. Water filtration? Not impressive. You could easily have gotten something like that without NASA. But GPS? Probably not. (And while "knowledge for its own sake" works great for people who would post on a board like this, it's not that convincing for the common man. Very little of that knowledge for its own sake has any payoff, and there's a lot of different types of "knowledge for its own sake" that one could be funding, much of it for a lot cheaper than space budgets.) --98.217.8.46 (talk) 18:37, 3 July 2008 (UTC)

physics

Question: When we throw a ball on the wall in a particular direction, then why does the ball comes back to us in some other direction ?'' —Preceding unsigned comment added by 61.2.190.79 (talk) 16:33, 1 July 2008 (UTC)

Start with Reflection (physics), but the most basic principle is that "the angle of incidence equals the angle of reflection". And remember, gravity is constantly working on the path of the ball.

Atlant (talk) 16:37, 1 July 2008 (UTC)

More specifically, for a ball: Deflection (physics). This article could do with expansion though ....Jdrewitt (talk) 16:53, 1 July 2008 (UTC)

More simply: It would take more energy to send the ball back in the direction it came from. Mac Davis (talk) 16:57, 1 July 2008 (UTC)

Well, yes and no; it would just take a corner cube, but gravity is still affecting the track of the ball (which is probably what you were referring to in the need for "more energy").

Atlant (talk) 19:48, 1 July 2008 (UTC)

Also, it is very difficult to throw a ball with zero spin. If you are familiar at all with the sport of tennis you will know that depending on the surface the ball is striking, the spin can change the direction dramatically. This is particularly evident if you use a hard rubber ball on a rough surface (e.g., a lacrosse ball on asphalt). The spin will alternate and dampen until the ball rolls flat. Thus, you see a low, long bounce followed by a short, high bounce, and on and on until the ball flies with negligible spin or it simply starts rolling. Gjmulhol (talk) 11:52, 2 July 2008 (UTC)

Endorphin as drug

Why not simply inject endorphin instead of some artificial substance if the purpose is to feel right? —Preceding unsigned comment added by Mr.K. (talk • contribs) 18:42, 1 July 2008 (UTC)

And where would you obtain the natural endorphins? You can't just buy it. And if you synthesized it, it would then be an artificial rather than "natural" substance. The closest analogue is morphine, which is routinely injected during childbirth and other painful periods. ~Amatulić (talk) 18:53, 1 July 2008 (UTC)

I'm under the impression that one would have to inject the endorphin(s) directly into the brain, which sounds rather messy. --Several Times (talk) 20:13, 1 July 2008 (UTC)

This is a common question with relation to most centrally acting drugs (serotonin vs SSRIs, norepinephrine vs salbutamol, etc). The most common problem with endogenous substances is that they won't cross the blood-brain barrier, other problems are listed in the pharmacokinetics article (absorption, distribution, metabolism and excretion). --82.21.25.219 (talk) 08:21, 2 July 2008 (UTC)

Also note that administering natural endorphins long-term would likely cause the same problems as other such drugs. A tolerance would develop, requiring more and more to get the same effect. And addiction would occur, so people would feel sick if the endorphin supplement was ever stopped. StuRat (talk) 15:42, 2 July 2008 (UTC)

Insulators for copper wiring

I'm wondering if there is any way to accuratly measure the resistivity of a substance...is there a way to get a quantitative value for resistivity in substances that could potentially be used to insulate basic copper wiring? 24.34.168.154 (talk) 18:43, 1 July 2008 (UTC)Fiziks

Using a Megger? Fribbler (talk) 18:46, 1 July 2008 (UTC)

A megger is a good answer if you're interested in the performance of the insulator at relatively high voltages (~1KV), but at lower voltages, one would use a nanoammeter, a voltage source, and some careful experiment design including guarding. Keithley Instruments is a typical vendor of nanoammeters. And here's a good article from EDN about proper techniques: [6].

Atlant (talk) 19:43, 1 July 2008 (UTC)

A Megger will measure the insulation resistance not the material resistivity. There are standard ways to measure resistivity: [7]