Wikipedia:Reference desk/Archives/Science/2013 October 17

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October 17

Second opinion

Light can break Newton's third law – by cheating

Can I justify believing the veracity of the claims made by this experiment.? Plasmic Physics (talk) 00:49, 17 October 2013 (UTC)

You can read the claims made by Ulf himself in his paper. It's rather beyond me, honestly, but he makes no claims about violating the laws of physics. And I wouldn't trust anything you read on New Scientist anyway. Someguy1221 (talk) 01:02, 17 October 2013 (UTC)

I mean, how falsifiable are his claims, and do they stand up to scientific scrutiny? Plasmic Physics (talk) 01:10, 17 October 2013 (UTC)

So far as I can tell, his claims are eminently falsifiable. Unlike earlier theoretical works regarding diametric drives, Ulf's does not require any exotic materials to function (it also doesn't necessarily do anything useful). Anyone with the right expertise and resources should be able to build it, though since I do not have the expertise I have no idea how difficult that would prove. It's worth noting that this was published in Physical Review Letters, which is considered one of the most prestigious journals devoted to physics. So it is a given that this work was reviewed by several independent experts prior to publication. Someguy1221 (talk) 01:24, 17 October 2013 (UTC)

Yes, it's falsifiable, and I see no reason to doubt that the experimental realization was as reported. Note that even in the science-fiction scenario of a negative-mass diametric space drive, you're still not really violating Newton's third law. Instead, it's the consequence of applying Newton's laws to something with negative mass. The idea of breaking Newton's third law seems to have been introduced in the New Scientist report rather than the article itself. --Amble (talk) 05:42, 17 October 2013 (UTC)

I don't see how it happens. The objective appears to want to create a mass difference between two objects. But conservation of energy still applies. There is no such thing as a "rest mass of light." It's not zero. If there is a frequency, it has energy and mass. If it doesn't, it's not light. I can almost grasp a situation where a mass imbalance occurs between the front and rear of a spacecraft but not as a free energy + mass on one side and - mass on the other based on an interference pattern. Maybe a massive amount of light forced into a material withe significant dielectric differences fore and aft but that would just recenter the center of mass and it would return when the beam was stopped. --DHeyward (talk) 10:28, 17 October 2013 (UTC)

The overall conclusion seems to be "something that behaves mathematicaly similar to mass, but allows some probably impossible things (negative mass), behaves as we would expect that impossible thing to behave". As far as I can tell, the "drive" effect is only on the propagation speed of the light pulses, with no effect on the material itself. MChesterMC (talk) 12:33, 17 October 2013 (UTC)

The paper is not talking about photons per se, but about some kind of quasiparticle that corresponds to the light pulses. That is, he's not talking about photons with negative mass, but a phenomenon that behaves like a particle with negative mass. Someguy1221 (talk) 05:38, 18 October 2013 (UTC)

We know the speed of light depends on the dielectric it passes through. Will changing the dielectric in different sections affect mass balance? I would tend to think equivalent mass, wavelength and energy would always balance. Even if a negative mass were created, it would balance. I've never been able to conceive of any type of propulsion that didn't require a loss of mass (i.e. energy). to move an object through a distance. That seems fundamental to me. Perhaps there is a way to make the distances shorter but it's hard to imagine. --DHeyward (talk) 05:27, 18 October 2013 (UTC)

Why do people tie off their arms when shooting up?

Thanks. μηδείς (talk) 01:03, 17 October 2013 (UTC)

The most obvious reason to me, would be to find a good vein. Plasmic Physics (talk) 01:08, 17 October 2013 (UTC)

Yes, it makes the veins pop up a bit. That's standard procedure at my clinic when they need to draw a blood sample. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:18, 17 October 2013 (UTC)

That makes sense. I had thought maybe it had to do with preventing the drug from entering the bloodstream while they were busy injecting it. μηδείς (talk) 02:22, 17 October 2013 (UTC)

They used to tell us in school that the addict would let some blood come into the syringe chamber to dilute the heroin slightly, before injecting the whole mess into the arm. Thankfully, I have no first hand (or arm) knowledge of that process. But it fits with tying off the arm to make the veins pop up and to initially draw blood before injecting it back into the vein. ←Baseball Bugs ^{What's up, Doc?} carrots→ 02:37, 17 October 2013 (UTC)

Intravenous therapy#Hypodermic needle mentions the practice of pulling up a bit of blood as a way to verify that the needle is actually in a vein. DMacks (talk) 06:10, 17 October 2013 (UTC)

Yer but just remember to release the pressure before you actually inject all you junky scumbags! :-) Die Antwoorde (talk) 07:35, 17 October 2013 (UTC)

"Only dopes use dope." ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:11, 17 October 2013 (UTC)

Apparently, [they don't always do it.] OsmanRF34 (talk) 11:16, 17 October 2013 (UTC)

This came up because of the ltest episode of Homeland, and wasn't meant as a venue for bashing people. μηδείς (talk) 16:25, 17 October 2013 (UTC)

I'm quoting Cheech and Chong, FYI. ←Baseball Bugs ^{What's up, Doc?} carrots→ 22:21, 17 October 2013 (UTC)

If you donate blood (in the UK at least), they use a Sphygmomanometer to achieve the same effect. At a blood donor session a few years ago, I was asked if I wouldn't mind being used for training of a new staff member. When I agreed, the Cockney nurse called across the crowded room "Oi! Come and have a go at this one, he's got veins like drainpipes!" Alansplodge (talk) 09:44, 18 October 2013 (UTC)

I used to inject animals with drugs on a regular basis. When you're giving an intravenous injection you need to raise the vein to ensure that it's easy to find and you can get into it without the needle going through the other side. You can do this by applying heat to the skin, applying an irritant to the skin (not considered ethical these days), or applying pressure to the vein to temporarily stop the flow and raise the vein by back pressure. As said above, you push the needle into the vein and then pull the syringe plunger back to suck up a little blood to ensure you are in a vein, then release the pressure and inject. I have seen nurses use a disposable rubber glove to tie off the arm for this purpose. Of course if you miss the vein and inject anyway you can cause tissue damage at the injection site and the drug will not be metabolised at the correct rate. If you regularly inject into the same veins they eventually collapse and it gets harder to find them. That's why junkies are always searching for veins they haven't used before and end up injecting in all sorts of strange places. Richerman (talk) 12:00, 18 October 2013 (UTC)

Why do the veins collapse? Do they come back? Isn't that bad for circulation? And what if they're just drawing some (non-large) amount of blood, as nothing noxious or osmotically active is injected into the vein, wouldn't the vein stay healthy? Sagittarian Milky Way (talk) 22:56, 18 October 2013 (UTC)

To an extent, the blood system is like the road system, blood can find alternate return routes. (They can take vessels from your leg to reuse in your heart, for example.) But obviously shutting down a vein in your elbow is not good, and damage builds up. See krokodil and do a NSFW google image search for the fun you can have with impure drugs!) Even if the injections are harmless there is still mechanical damage from the needle. Someone else will have to comment on self-repair, but my suspicion is that there is a point of no return of scarring and so forth. I spent about six months with an IV which had to be moved at least twice a day, but after ten years I am unaware of any permanent damage. μηδείς (talk) 00:48, 19 October 2013 (UTC)

I don't understand -- what does a Russian satirical magazine have to do with IV injections? 24.23.196.85 (talk) 02:27, 19 October 2013 (UTC)

Hehe. I am sure there's a disambig link at the top of that page. μηδείς (talk) 02:37, 19 October 2013 (UTC)

Fish tank

Hi! I’m back again one more time… last days I pass by this little country hotel that have an awesome aquarium in the lobby and watching the fishes made me remember when I was a kid and have lot of fishes in tiny fishbowls… so one thing came after another and somehow I finished buying a couple of glasses and wow… it seems that I’m going to make a fish tank for my living room… of course it wouldn’t be as large as the one in the hotel, but I don’t know if, at my intended dimensions, the vertical water column pressure effect could be an important issue to consider.

my question is: how can I calculate the pressure that the glass and the glue/sealant will have to hold?

I know how to get the average pressure of the whole tank, but my principal concern is in the stress concentration at lower part of it

I’m thinking in something like 145cm width by 60 cm height by 50 cm depth more or less

thanks!!

201.220.215.14 (talk) 05:07, 17 October 2013 (UTC)

Go to your local pet supply shop and buy one that's already properly constructed. ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:09, 17 October 2013 (UTC)

Seconding Bugs. Apart from any questions of sufficient mechanical strength, how do you know what glues and sealants, which will be in contact with the water, will or will not have a poisonous effect on the plants, fish etc in the tank? {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:50, 17 October 2013 (UTC)

Haha… no no I already bought the glasses, and besides let’s assume that here there isn’t anything like a “pet supply shop” plus building up the thing is part of the fun…

isn’t any physic or math formula that allow you to obtain the pressure in the edges of the tank?

the seller told me that the glass will hold up for that dimensions, my major concern is for the glue

the glue will be something silicon based

Iskánder Vigoa Pérez (talk) 13:59, 17 October 2013 (UTC)

P = ρgh. Where rho is defined as the density of water at a desired temperature, g is gravitational acceleration (choose standard or local), and h is the depth of water measured from the surface. This will yield the pressure as a function of depth. Plasmic Physics (talk) 14:09, 17 October 2013 (UTC)

While I agree that it seems odd to try to build an aquarium yourself, I will try to answer as best I can. Some thoughts:

1) You said you only bought 2 sheets of glass ? The usual aquarium has glass on 5 of the 6 sides. Do you intend to put something other than glass on the bottom and 2 of the sides ? Or do you intend to try to cut the glass yourself ? And do you have a lid ?

2) The pressure will be solely based on the depth of the water. However, you also need to consider that the glass will tend to bow out more, the greater the area over which the pressure is applied.

3) I suggest you add a physical support at the bottom, like a wooden frame to hold it all together. Then the load on the adhesive will be far less. Here's a top view of what I have in mind:

  +---+-----------------------+---+
  |   |         WOOD          |   |
  |   +-----------------------+   |
  | W |                       | W |
  | O |       AQUARIUM        | O |
  | O |                       | O |
  | D |                       | D |
  |   +-----------------------+   |
  |   |         WOOD          |   |
  +---+-----------------------+---+

You might also extend the wooden frame to have vertical posts along each of the 4 edges, and a repeat of the bottom wooden form at the top. Wood is far easier to work with than glass, and doesn't shatter if you mess up. StuRat (talk) 14:18, 17 October 2013 (UTC)

Not that it's any of my business, as it's your project - but isn't the kind of question an engineer would ask before buying the glass? ←Baseball Bugs ^{What's up, Doc?} carrots→ 15:18, 17 October 2013 (UTC)

the man that sold me the glass told me that it would support the pressure and give me total warranty, the glass is almost 8mm, now I’ll buy the glue, so I’m asking

Iskánder Vigoa Pérez (talk) 15:58, 17 October 2013 (UTC)

thanks… that’s exactly the formula I was looking for

stu, I have the total glass area and know a man that will cut into the five rectangles that I need

thanks for the answers

Iskánder Vigoa Pérez (talk) 15:58, 17 October 2013 (UTC)

A silicone glue is normally used to hold and seal the panes together. You want to be careful to get 100% silicone - a lot of the caulks and glues sold will have a small amount of fungicides or other chemicals in them, because they're normally used in bathrooms or kitchens and it is nice not to worry about mildew growth. In an aquarium, the fungicide can dissolve into the water, potentially causing health problems for your fish. Do you have a solution for filtration and aeration? Katie R (talk) 16:54, 17 October 2013 (UTC)

You might want to try browsing through this magazine (or even take out a subscription) for informed advice in this area. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 18:00, 17 October 2013 (UTC)

Well… the height is 0.6 and the density will be in-between 995 and 997 so the glue in the bottom will have to hold max 5.98 kP… that’s 0.87 psi I’m right?

I’m getting something wrong here? I’m approximating everything toward my security and yet it seems so little…

katie as far as I know for the filtration all I need to do is buy a filter and for the aeration plants and a bubble device; someone told me the same thing about the glue…

Thanks for your time, and for the link to the magazine, it’s very interesting… — Preceding unsigned comment added by Iskander HFC (talk • contribs) 22:49, 17 October 2013 (UTC)

That is approximately correct. Plasmic Physics (talk) 23:12, 17 October 2013 (UTC)

And that's not as little as you think. Using dimensions for the long sides of 145 cm width by 60 cm height, or 57 inches by 24 inches, I get an area of 1368 square inches. Multiply that by an average pressure of 0.87/2 psi, and I get a force of 595 pounds. That's a lot of force to expect glue alone to hold (not completely impossible, though). Thus my suggestions for a wooden support frame. StuRat (talk) 03:10, 18 October 2013 (UTC)

You should also remember that the most important dimension that restricts the amount of fish you can keep in the tank is the surface area of the water. This is because the gas exchange nearly all takes place at the surface, so you can't keep as many fish in a tall thin tank as you can in a low wide one that holds the same volume of water - as it doesn't absorb as much oxygen see:[1]. Aerating the water with a pump increases the surface area by agitating the water but that is, of course, only effective as long as the pump keeps working see:[2]. Richerman (talk) 12:32, 18 October 2013 (UTC)

Note that for example this glue manufacturer does not recommend it being used for more than 30 gallons (114 l) and/or water height more than 18 inch or 46 cm. Ssscienccce (talk) 12:46, 18 October 2013 (UTC)

thanks for all the links… very interesting stuff… I’ll try don’t place to many fishes in there, btw the aquariums in the photos here in Wikipedia and at practicalfishkeeping are way better than the one I saw in the hotel, and [Aquascaping] has some beautiful photos too… I hope mine resemble some of those

Iskánder Vigoa Pérez (talk) 17:28, 19 October 2013 (UTC)

Good scholarly sources

Are Razib Khan and Dienekes Pontikos blog good sources when it comes to human race classification? — Preceding unsigned comment added by 70.31.154.71 (talk) 08:57, 17 October 2013 (UTC)

Blogs are not considered as reliable sources on Wikipedia unless written by people who are acknowledged experts in the field or are under editorial control. See WP:RS. Dmcq (talk) 09:17, 17 October 2013 (UTC)

Dienekes and Razib Khan are both experts — Preceding unsigned comment added by 70.31.154.71 (talk) 09:29, 17 October 2013 (UTC)

You seem to have decided already that they are "experts". This is highly debatable - see also this. The idea that "human race classification" is a matter for a Science reference desk - when so much is based on social and cultural factors - is itself somewhat dubious. Ghmyrtle (talk) 10:04, 17 October 2013 (UTC)

Razib Khan seems to get a little bit respectability since his blog is hosted by Discovery Channel. He also has been cited thoroughly through out Wikipedia.OsmanRF34 (talk) 11:27, 17 October 2013 (UTC)

Thanks for help, turns out neither are actually experts, and no one even knows Dienekes identity. Razib Khan does have some academic background but his science seems to be criticized a lot — Preceding unsigned comment added by 70.31.154.71 (talk) 15:43, 17 October 2013 (UTC)

Generally for a good scholarly source I would tend to set the bar a bit higher than wikipedia's definition of good sources (which is fine - since Wikipedia obviously needs to deal with plenty of non-scholarly sources as well). I would like to see something that has either been peer-reviewed or draws on peer-reviewed research in the making of all of its claims (such as a review article or monograph ). The University of Illinois generally agrees. Now that isn't to say that other good sources don't exist, it's the "scholarly" bit that is lacking in other sources, rather than necessarily the "good". I personally don't know of any blogs which undergo peer review, and even if they refer exclusively to peer-reviewed research, I don't think I could get away with citing a blog in an academic paper (unless the paper was on the phenomenon of blogging!), so I would say that currently no blogs are good scholarly sources. Equisetum (talk | contributions) 14:40, 18 October 2013 (UTC)

Drinking coke

As I understand correctly, 100 years ago, the favorite route of administration of cocaine was drinking it. Today it seems to be snorting it. Why the shift? OsmanRF34 (talk) 11:25, 17 October 2013 (UTC)

See nasal administration. It's faster, bypasses irrelevant organs that would try to digest the drug, and can also bypass the blood-brain barrier because the nose has a specially close connection to the brain. (This doesn't really answer why they didn't try snorting it in the first place, as was already done with snuff. Lack of imagination?)  Card Zero  (talk) 12:01, 17 October 2013 (UTC)

One important factor is that it was originally used as a medicine, not a recreational drug. (Coca-Cola was originally a weak concentration of cocaine mixed with cola, sold in syrup form, as a medication.) In that case, you want the slow release you get from the digestion process, not the quick release from snorting it. Indeed, if people didn't figure out that they could get high from refining it further and snorting it, cocaine might still be used as a med today. Also note that heroine and several other illegal recreational drugs also were used as medications originally. StuRat (talk) 14:25, 17 October 2013 (UTC)

What do they put it the fancy energy drinks these days??122.111.240.138 (talk) 15:55, 17 October 2013 (UTC)

Read the Wikipedia article titled Energy drink. --Jayron32 17:03, 17 October 2013 (UTC)

Yer but I dont mean the "generaly included" additives" I'm talking about the colonels secret recipe. And now to ease the side effects we can buy a relaxation drink and human designed additives may be added also maybe. 122.111.240.138 (talk) 18:10, 17 October 2013 (UTC)

Heroin, usually referred to in medical contexts as diamorphine, is actually still used extensively in the UK for the management of both acute and chronic severe pain. Cocaine is still used in several countries as a local anaesthetic in certain specialised situations. Equisetum (talk | contributions) 14:16, 18 October 2013 (UTC)

The crackpot doctor Wilhelm Fliess, a contemporary of Freud, pioneered the application of cocaine to nasal tissues.--Digrpat (talk) 20:41, 17 October 2013 (UTC)

Coca tea is still being sold. Count Iblis (talk) 23:58, 17 October 2013 (UTC)

Certain people seam too like applying the free base to their oral mucosa! 122.111.240.138 (talk) 03:53, 18 October 2013 (UTC)

Thousands of years ago, people chewed coca leaves. Later, Incas chewed leaves when making long treks at high altitudes. I think that Incas already had problems with people getting addicted to coca leaves. Then Spanish conquerors imported them to Europe. And then, centuries later, an American decided to make a medicinal drink with them. He used a cola drink as base, so he called it Coca-Cola.

Coca-Cola, get it? A cola drink with those coca laves that people had been using for centuries and millenia. Now in a more convenient format, faster to take, doesn't leave spots around your mouth, doesn't force you to chew for minutes or hours, lasts longer in storage, etc.

Moreover, cola has caffeine from cola nuts. Coca leaves have undesired side effects, like apathy. You can't work properly under their effects. Caffeine compensates those undesired side effects and makes you more active and awake.

These are the sort of things that made Coca-cola popular. In historical matters, context is very important. --Enric Naval (talk) 17:36, 18 October 2013 (UTC)

Megawats, generating capacity and consumption

A small West African country is said to have 90-100 MW installed generating capacity. There is a proposed bio-fuels project which will grow suger cane, produce ethanol, and use the ethanol to produce 30 MW of electricity, offering 15 MW for sale back to the national grid, and using the other 15 MW for the ethanol plant and related local installations. If I understand, the entire country now uses less than 100 MW. One project can increase production by 30%, but requires 15% of what the entire national grid produces and consumes, just to run the one project (of 12,000 hectares) producing 85,000 cubic metres of ethanol for export. Does that make sense? Are these numbers credible? Thanks if you can make this more understandable. — Preceding unsigned comment added by 193.173.50.222 (talk) 12:09, 17 October 2013 (UTC)

One thing to keep in mind is that it always takes more energy to produce a fuel than you get from it. However, in this case, one of the biggest energy inputs is the sunlight used to grow the sugar cane, so it might be reasonable to expect that the rest of the refining process would take half of the energy produced. I am skeptical, though, that this process is the optimal use of the land and sunlight. Selling the sugar cane instead, or some other crop, might very well make more financial sense. You could also place solar panels there instead, to create electricity directly. However, solar panels are a rather low efficiency way to make electricity, too. StuRat (talk) 14:33, 17 October 2013 (UTC)

Thanks.I'm sure I wasn't very clear when I put the question. I'm trying to understand if it is credible that one biofuel factory could be using 15 MW for its activities, while the entire country (Sierra Leone) presently makes due with less than 100 MW. I would think, even in a country with very low generating capacity, that one factory could only use 1%, or a fraction of a percent of all the electricity being used in the entire country. But I don't know much about electricity, (or ethanol production) ... so I was looking for some insight on that. I'm skeptical of the claims, numbers, publicly stated plans of the biofuel investors. Thanks for anyone who has additional information. — Preceding unsigned comment added by 193.173.50.222 (talk) 16:06, 17 October 2013 (UTC)

It looks about right to me, I'm sorry to say. This confirms an installed electricity capacity for Sierra Leone of 100 megawatt in 2010 (hover over the little graph). This confirms the figure for 2013 and says they want to increase production tenfold by 2017. This describes an Ethanol plant in Peru (also sugar cane) generating 37 MW (and potentially exporting 17 MW) to produce 35,000,000 US gallons (130,000 m³) per year. These figures are somewhat larger than the plant you describe but roughly in proportion. Thincat (talk) 20:36, 17 October 2013 (UTC)

How much time should I studying for the astronomy GCSE?

Hf245 (talk) 17:41, 17 October 2013 (UTC)This applies to the UK. I am studying GCSE astronomy as an extra qualification. However, I have only 1 year to complete the 2 year course. I have one lesson for about 1 hour a week. I need to learn the rest at home but I don't know how often I should study and for how long.-

After reviewing the official documentation from the UK's Ofqual website, specifically comparing the recommendations from the five exam administration corporations listed in the GCSE Guide, your first step should be to classify yourself as a "Higher," "Middle," or "Lower" performer; and then cover the syllabus outlined in the order presented. For example, one test administrator, EdExcel, offers the current Astronomy course specification in "linear syllabus" format. That specification is 60 pages long, nearly as lengthy as a high-school-level textbook on astronomy in the United States!

Standardized test assessment, (and standardized learning, for that matter), are complex topics. What do you expect to achieve by learning this material? If you hope only to pass a test, there are excellent study-techniques that will statistically improve your test performance. But if you hope to learn this material to build a baseline for future study and work in scientific fields; or if you enjoy the topic and want to enlighten yourself, your strategy should be entirely different. If you want to enlighten yourself and score at a particular level on the tests, there's probably a middle-ground. Nimur (talk) 17:59, 17 October 2013 (UTC)

A GCSE course is normally taught for between 2.0 and 2.5 hours per week (plus homework assignments), so I suggest that you should spend at least five hours per week to cover the course in one year. If you learn quickly, then you might need less time than this, but you should obtain past papers covering as many years as possible and test your learning on these. A keen interest in the subject often reduces the learning time. Dbfirs 18:22, 17 October 2013 (UTC)

You should not study like that. What you should to is start to study, make sure you can solve the difficult problems and when you are starting to make progress, you can have some idea about how much time it will take to completely master the subject. Studying by the clock is an extremely bad way of studying; the whole point of year long courses is that you can afford to spend a lot of time time on difficult problems that can be done in, say, 5 minutes when you've mastered the subject. Count Iblis (talk) 18:32, 17 October 2013 (UTC)

Yes, I agree (except you should start with the easy problems and go on to the difficult ones later). I assumed that the OP was wanting to budget his time in advance. A solid five hours would not be appropriate for most people. Dbfirs 20:34, 17 October 2013 (UTC)

I don't think we can advise this because it depends on the ability and enthusiasm of the student. Personal experience - I studied, took and passed Music O level in just 8 weeks. I also supported (much later on) a student doing Astronomy GCSE in a similar circumstance to yourself who was already an astronomy geek and we covered the syllabus in a college term (10 weeks). So my recommendation is to study the subject at your own pace. Do what you find interesting. --TammyMoet (talk) 20:40, 17 October 2013 (UTC)

Thanks a lot for your help, I've split the topic up into smaller topics and I do one of them around every other day! :)

Binaural beats

Is there any link between binaural beats, iDosing, and this track? — Preceding unsigned comment added by 184.99.143.31 (talk) 18:25, 17 October 2013 (UTC)