Wikipedia:Reference desk/Archives/Science/2011 September 7

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September 7

Helium-3 fusion

Other than the scarcity of helium-3, is there any other disadvantage to using it as a fusion fuel rather than deuterium and tritium? --76.211.90.74 (talk) 00:25, 7 September 2011 (UTC)

The fact that it won't work with muon-catalyzed fusion? 67.169.177.176 (talk) 00:50, 7 September 2011 (UTC)

Is that outweighed by the fact that it doesn't produce radioactive waste like D-D and D-T fusion? --76.211.90.74 (talk) 02:25, 7 September 2011 (UTC)

What waste are you talking about? Dauto (talk) 04:16, 7 September 2011 (UTC)

He/she prob'ly means neutron radiation. I'd say it depends on the application. If the reaction is to be used to power a spaceship, then light weight and a high power-to-weight ratio are the most essential requirements, in which case muon-catalyzed is the way to go. On the other hand, if it's to be used in a stationary electricity-generating application, then He-3 could be used, for better PR if nothing else. 67.169.177.176 (talk) 06:17, 7 September 2011 (UTC)

I think helium-3 has a lower cross section for fusion reactions than DT, i.e. it is harder to use. No doubt you'll be interested in aneutronic fusion . 157.193.175.207 (talk) 11:15, 7 September 2011 (UTC)

If your primary goal is to avoid radioactive waste (such as that caused by fast neutrons from most forms of fusion) use boron-11+proton aneutronic fusion. The people at http://focusfusion.org can tell you all about why it is more advantageous than alternative lines of fusion research at present. Note also that this is only useful for long term spacecraft because there is essentially no chance that any form of nuclear or alternative renewable energy will be less expensive than wind power over the next century. 208.54.86.137 (talk) 23:54, 7 September 2011 (UTC)

Nuclear fission energy is cost-competitive with wind energy at this time. And, if fusion is to be used for spacecraft propulsion, then the primary goal would be to produce the most power with the least weight, not to avoid neutron radiation. 67.169.177.176 (talk) 01:52, 8 September 2011 (UTC)

No, fission costs five times per kilowatt hour what wind does in the US, and kills ten times as many people if you include the long term risks of above ground dry cask storage as is the norm in the US. On spacecraft, the safety of the crew during and after the mission should be the paramount goal. What good is sending a crew to another planet if they are fried upon arrival? 69.171.160.194 (talk) 23:33, 8 September 2011 (UTC)

Those sure are some hand waving statistics you're citing (an honest assessment on the power of nuclear requires taking into account the lifetime production of the plant — nuclear fission has the highest capital costs, but its long term operation is quite cheap) along with the clever assumption that above ground dry cask is going to be the long term storage method (nobody thinks that — it's just what is being done because the politics of picking an underground storage site have been protracted, in no part due to anti-nuke hysteria). Plenty of astronauts have flown with fission reactors, plenty of sailors rely on them daily, and in space, the waste issue is a non-issue. It's completely silly to refer to astronauts who use nuclear fission as "friend upon arrival." I'm also unclear how wind power is going to work in outer space! --Mr.98 (talk) 00:14, 9 September 2011 (UTC)

Yeah, here's your lifetime assessment of nuclear power costs in the US. I hope some day you have the chance to think about how to dispose of waste created by fast neutrons in space. If you just jettison used shielding, then shielding becomes a consumable in your mass budget, which quickly outweighs the lesser power output of aneutronic fusion. 69.171.160.217 (talk) 03:14, 9 September 2011 (UTC)

Page not found. :-( In any case, my overall point is that coming up with numbers requires lot of assumptions, some arbitrary, some not. I could happily cite back things from pro-nuke thinktanks arguing that wind is less cost effective in the long run. My overall point is just that these numbers are tough to come up with, and blithely choosing the set of numbers that fits your political platform is dumb and unproductive.

Anyway, if you set it up intelligently, you wouldn't need to jettison the shielding at all. If so, you'd be doing it at the very end of the mission. There is no reason to think that nuclear reactors could not be used for space in more or less the same capacity they are used in submarines. I don't see fusion changing this except for creating even less waste and radiation than fission. Depending on your fusion scheme, the fast neutrons need not really create "waste" at all — e.g. they could be enriching a secondary fuel system (e.g. lithium into tritium). But any real discussion of that would require a much more concrete idea of what kind of reactor one was using. --Mr.98 (talk) 15:13, 9 September 2011 (UTC)

In any case, ThinkProgress is a highly partisan, far-left POV source and therefore any info that comes from it fails to meet either the WP:RS or the WP:NPOV requirements. You prob'ly wouldn't trust far-right, Tea Party-backed websites for info, so by the same standards ThinkProgress and similar websites are not to be trusted either. Or has there been a decision to convert Wikipedia into Commiepedia? 67.169.177.176 (talk) 00:14, 10 September 2011 (UTC)

Here's the archive link it was written by a CPA co-author of Economics of Nuclear and Coal Power (Praeger, 1976) but just happened to be hosted by Climate Progress. I doubt there are any designs which contemplate recycling fast neutrons. They're isotropic. 69.171.160.254 (talk) 19:51, 10 September 2011 (UTC)

The Tokamak incorporates a lithium-6 "blanket" to produce tritium from fast-neutron fission. As far as the article "just happened" to be hosted by Climate Progress, I strongly doubt it -- like all partisan sites, they're extremely careful to pick only those authors who share their views. 67.169.177.176 (talk) 04:12, 11 September 2011 (UTC)

Here's an article that presents the other side of the story about nuclear power costs: http://neinuclearnotes.blogspot.com/2009/07/critique-of-craig-severances-new.html. 67.169.177.176 (talk) 04:44, 11 September 2011 (UTC)

High Speed Train Design

In high speed trains, what are the advantages and disadvantages of using 1) power cars vs. powered axles throughout the train and 2) Jacobs bogies vs. conventional bogies? 169.234.102.200 (talk) 06:26, 7 September 2011 (UTC)

(1) Power cars obviate the need for high-voltage wiring through the passenger cars, and (in diesel/gas turbine trains) allow more powerful engines to be used, plus they may offer better crash protection, but they're heavier, tear up the track more, are more prone to wheelslip, and the power equipment takes up the whole car. Powered axles throughout the train save weight, reduce wheelslip, allow more passenger space, reduce track wear, and (in electric trains) may allow more total power to be installed, but they reduce crash protection and require high-voltage wiring and equipment in passenger cars. (2) Jacobs bogies reduce weight and rolling friction, but then you can't add more cars to meet extra demand or cut out a car for maintenance (a common failing of the early streamliners); conventional bogies allow easy reshuffling of the consist, and also reduce axle loading (and therefore track wear), but increase weight and friction. 67.169.177.176 (talk) 06:42, 7 September 2011 (UTC)

amount of grain to amount of product ratio

I am not interested in cost or other factors in the making of a product like bread from wheat but only in the maximum amount of bread that can be made from each type of grain. In other words if I have a certain volume or weight of wheat how much bread I can make versus the amount of bread I can make if I use corn instead to make bread. In addition I am not just interested in one product like bread but in all of the products that can be made by grains. All I need is a list of products for each grain and the amount of product to amount of grain ratio. My question is: where can I find a list of grains, their products and the ratio of grain to product. --DeeperQA (talk) 07:54, 7 September 2011 (UTC)

(edit conflict) It varies a huge amount depending on the properties of the grain: hardness, moisture content, protein—each of these varies, not just per crop variety but per field and per plant. I suppose looking at bread recipes will give you a rough idea, but even then the type/amount of grain is not the primary factor in the volume of a loaf of bread; yeast, other ingredients, technique etc. would (I estimate) have a greater influence. I think the reason you're not having luck with this question is that it's unanswerable with any degree of accuracy. Sorry Jebus989^✰ 09:34, 7 September 2011 (UTC)

The other thing to consider is that only grains that contain gluten will make good yeast-risen bread. This will limit you to wheat and the wheat-varietals, and to some lesser extent rye, although rye gluten is not as satisfactory; most home and commercially-produced rye breads have a significant ratio of wheat flour added to the rye. Grains such as oats and corn (maize) do not have useable gluten for yeast bread. However, you could make chemically-risen baked goods using single or double-acting baking powder, or baking soda. Also, some grains are amenable to self-fermentation to raise the "bread."--Romantic Mollusk (talk) 12:37, 7 September 2011 (UTC)

I tried to answer this above, when DeeperQA asked the first time, and maybe I was too technical. Let me try again.

Start here, Bread Composition from the WikiBook Cookbook. "One pound (500 g) of flour will yield a standard loaf of bread, or two French loaves." Do you see the problem yet? Simply by varying the cooking-style alone, we get a variation of a factor of 2x in the resultant product - starting with the exact same ingredients. This says nothing about the ratios of grain to flour, type of wheat, fineness of the milling, or acres of wheat for a kilogram of grain; are we keeping or discarding the bran; whether this is Kansas or Nebraska wheat, or wheat from Norway or the Ukraine; was fertilizer used, and what effect did it have on the protein content of the flour? Will yeast be used, or are we baking unleavened bread? Each of these can provide a similar 2x or 10x or 100x variability in the process.

I know you just want a number. Part of thinking like a quantitative scientist is being able to resolve a question with a numerical answer; but the more important part of quantitative science is formulating a question so that the answer is meaningful. Now, if you want, we can make all sorts of assumptions, to give you a simplistic single-number answer: assume an acre of wheat, grown in Kansas, harvested with a 2007-year-model John Deere Combine, milled on a commercial production line, with 10% product loss to rats, producing XXX grams of flour, baked by an artisan French baker with a flour-to-bread ratio of ... blah blah blah. You see the problem? Every one of these stages amplifies the uncertainty, and if we specify the constraints, we end up with a preposterous answer subject to a huge string of qualifications that are not generally valid.

So - we can not answer your question, because the correct number has a variance many orders of magnitude larger than is reasonable to report. When you say that you aren't interested in other factors, like processing efficiency or cost, you are effectively saying "I don't care if my answer is reasonable or anywhere close to correct, because I don't need details." Well, if you are willing to ignore all details about a very detailed process, we can simply say, "the ratio of grain to bread is 1:1 (ignoring details)." Nimur (talk) 15:24, 7 September 2011 (UTC)

Nimur - Thanks for both of your detailed answers. The problem you may not understand is that whenever or wherever there is s difference in grain or product a separate entry will solve the problem. The idea of using energy content of the grain and its products (as Modocc points out below) may solve the problem in terms of ratio since ratio is all I am concerned about in the end. --DeeperQA (talk) 20:01, 7 September 2011 (UTC)

DeeperQA, precisely how much grain is used per product varies. However, one can easily research the number of energy-sustaining meals, say for a 2000 calorie/day diet, that a flour (or for any food for that matter) is capable of providing. For instance, my box of dry 100% whole wheat pasta has 210/56 calorie/gram. --Modocc (talk) 18:34, 7 September 2011 (UTC)

Thanks Modocc. I did not have my thinking cap on. The ratio of energy content does provide a numerical ratio solution. --DeeperQA (talk) 20:01, 7 September 2011 (UTC)

Good. Our article on food energy goes into some detail on how the nutritional value is calculated too. --Modocc (talk) 20:08, 7 September 2011 (UTC)

What is a "PETE stamp"?

Here's an example Jebus989^✰ 09:37, 7 September 2011 (UTC)

What is a PETE stamp in the following context?

Are the printing materials ABS and PLA used for 3D printing recyclable? And if so, is there any way to add the correct PETE stamp to a printed object? Context.

ABS is recyclable, and PLA is not (cost effectively, yet.) The symbol for ABS is the same three arrow triangle with "ABS" instead of a resin number in the middle. 69.171.160.217 (talk) 23:50, 8 September 2011 (UTC)

Is it some kind of environmental, food safety or recycling regulation named after a commonly used plastic, polyethylene terephthalate? Where is PETE stamp described (on Wikipedia or elsewhere)?

--Mortense (talk) 09:26, 7 September 2011 (UTC)

"PETE stamp" sounds like the Resin identification code insignia (the standard "recycling" numbered symbols), but PETE itself is #1 whereas ABS composite seems more like #7 (not sure though). Maybe mis-used (overly specific) terminology in that forum-post? DMacks (talk) 09:35, 7 September 2011 (UTC)

No, ABS just has "ABS" in the middle of the three arrow triangle, not a resin number. Although '7' is used for "other" resins, the recycling process involved is different for ABS so it is marked differently. 69.171.160.217 (talk) 23:56, 8 September 2011 (UTC)

For more information you can see the below link: http://scifun.chem.wisc.edu/chemweek/polymers/polymers.html

spectral absorption lines

Where can I view the spectral absorption intensity line graph of the materials used to make solar cell p-n junctions? --DeeperQA (talk) 20:47, 7 September 2011 (UTC)

There are many such materials, and their spectrum is often available via a literature search on their Chemical Abstracts number. 69.171.160.217 (talk) 23:52, 8 September 2011 (UTC)

Monthly-disposable contact lenses - why dispose?

Is there a good reason that I can only work monthly-disposable contact lenses for a month before disposal or is it just to maintain the income of the manufacturer? Won't proteases remove any protein build-up? — Preceding unsigned comment added by 2.216.135.109 (talk) 22:26, 7 September 2011 (UTC)

The article Contact lens discusses the different types of lenses and their durations. ←Baseball Bugs ^{What's up, Doc?} carrots→ 00:33, 8 September 2011 (UTC)

Not changing your lenses will just maintain the income of the manufacturers of conjunctivitis medicine. So you need to decide who to give your money to, the people who make your lenses, or the people who make that goopy antibiotic you have to drizzle in your eye a few times a day. --Jayron32 04:38, 8 September 2011 (UTC)

Since you get that from other people, do you regularly share your contacts with others ? If not, I think the far more reasonable approach is to use the lenses until they have a visible protein growth that isn't removed with cleaning. This may be either before or after the magic 30 days pass (or do the lenses miraculously last a bit longer on months with 31 days and not quite so long in February ?). StuRat (talk) 04:48, 8 September 2011 (UTC)

The article contact lens says one risk is allergic conjunctivitis, and the article conjunctivitis lists a variety of causes, including allergies and physical irritation. Conjunctivitis isn't always viral or bacterial, and if sharing contact lenses was its only cause, it'd be a lot less common. --Colapeninsula (talk) 11:10, 8 September 2011 (UTC)

This is why I go for daily disposables. No fuss, no muss.--24.228.90.14 (talk) 12:45, 8 September 2011 (UTC)

Contact lenses can certainly be used for some period beyond a precise month - but the safety range is likely only a week or so beyond the month. Proper cleaning is one key, of course. Collect (talk) 12:10, 8 September 2011 (UTC)

Eastern equine encephalitis in maine

Have there been any cases of Eastern equine encephalitis virus in maine this year (in animals or people). — Preceding unsigned comment added by 169.244.148.235 (talk) 22:53, 7 September 2011 (UTC)

According to [1] and associated pages, there have been no human or veterinary cases in Maine in 2011. There was however a single positive finding from a dead bird back in February. Dragons flight (talk) 23:20, 7 September 2011 (UTC)

But that map does not show the recent human case of EEE in southeast Massachusetts either, so is it accurate? — Preceding unsigned comment added by 169.244.148.235 (talk) 23:23, 7 September 2011 (UTC)

The data is from the Centers for Disease Control (CDC) and updated weekly. I'd say that this is as reliable as one can expect. The recent report of EEE in the news may not have been confirmed by the CDC yet, or if confirmed now, it may not have been ready for the last update. Dragons flight (talk) 23:37, 7 September 2011 (UTC)

Star formation and ideal gas law

The first step of star formation: gravitational collapse of a giant molecular cloud

My question is: is it possible to happen?

The Ideal gas law states:

pV=nRT

where: p is the pressure; V is the volume; n is the number of moles; R=0.0821 L atm mol-1 K-1 (that is, R is the gas constant); T is the temperature.

According to this law: where nRT is finite (as it always is for any given amount of gas), and pressure approaches zero (as it is in the vacuum of space), V approaches infinity. That is, a gas will spread indefinitely in a vacuum.

Further, as T increases (as it must if a hydrogen cloud is to grow warmer on its way toward fusion), the expansion pressure of the gas cloud will increase. In other words, the warmer the hydrogen cloud gets, the more it will spread.

Maybe you want to visit Giant_molecular_cloud#Star_formation.

Before I give the address of the website I found this problem, I want someone to answer me first.

Aquitania (talk) 23:47, 7 September 2011 (UTC)

It is true that the pressure approaches zero in a vacuum but the hydrogen is not in a vacuum, its inside of a cloud filled with (wait for it) hydrogen! The pressure will not be zero. Dauto (talk) 23:53, 7 September 2011 (UTC)

Giant_molecular_cloud#Star_formation is a summary of the more detailed article on Star formation which mentions Jeans mass and also different compression events that can trigger a gravitational collapse. --Modocc (talk) 02:06, 8 September 2011 (UTC)

Note that a gas in vacuum when it expands in space, will do work against the gravitational field generated by itself. If you ignore gravity, an ideal gas would not cool when it expands in vacuum. When a gas contracts due to gravity, it will heat up, causing the pressure to rise, preventing further collapse. So, normally a gas is stable against collapse. But the clouds we're talking about here are opaque to its own thermal radiation. This allows it to lose energy when it contracts; the pressure stays low enough for the contraction to go on. Count Iblis (talk) 03:41, 8 September 2011 (UTC)

The ideal gas law is based on the idea of ideal gases. Ideal gases are not real gases, and real gases deviate from the ideal gas law at extreme temperatures and pressures; at the temperatures and pressures found in a star, the ideal gas law is likely VERY far off from reality. --Jayron32 04:36, 8 September 2011 (UTC)

Actually, Jayron the ideal gas law works pretty well for the temperatures and pressures inside most stars. Dauto (talk) 13:58, 8 September 2011 (UTC)

Isn't the material in stars plasma rather then gas? Googlemeister (talk) 18:09, 8 September 2011 (UTC)

Yes, of course. Dauto (talk) 19:34, 8 September 2011 (UTC)

So then as plasma is a completely different state of matter, applying the ideal gas law to hydrogen plasma is about as useful as applying the ideal gas law to liquid nitrogen. Googlemeister (talk) 19:44, 8 September 2011 (UTC)

The ideal gas law works well in this situation. See for instance stellar structure and note the use of a state equation based on two assumtions

• adiabatic convection
• mono-atomic ideal gas.

Dauto (talk) 20:00, 8 September 2011 (UTC)

Everything else being equal, making a gas hotter tends to make it more ideal. Plasma is just a form of ionized gas and can often be treated as an ideal gas (provided any associated electromagnetic fields are not too large). Dragons flight (talk) 22:16, 8 September 2011 (UTC)