Wikipedia:Reference desk/Archives/Science/2015 April 18

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April 18

Raw meat

Why are humans susceptible to diseases from eating raw meat, but other carnivorous animals can eat raw meat (including birds and swine) with no ill effects? (I tried to find an answer to this in the articles raw meat and carnivore, but didn't see anything. If I missed it, please tell me.)    → Michael J Ⓣ Ⓒ Ⓜ 01:12, 18 April 2015 (UTC)

Their digestive and immune systems are adapted to eating raw meat. Humans are adapted to eating cooked meat. See, for example, the Vermiform appendix, which in humans has been reduced to vestigial organ status because of our change in diet. The book titled Catching Fire: How Cooking Made Us Human extensively covers how the cooking of food changed humans, both societally and biologically. --Jayron32 01:21, 18 April 2015 (UTC)

I'd question the premise of the question that "carnivorous animals can eat raw meat ...with no ill effects". Consider gapeworm as just one counter-example; more here related just to birds. I would expect there to many texts and papers on food-borne animal diseases in veterinary literature (cannot search for specific refs at the moment). Abecedare (talk) 01:33, 18 April 2015 (UTC)

Agreed. Cats and dogs, for example, seem to live much longer as pets than in the wild, and diseases they get from eating raw meat are probably part of the reason. StuRat (talk) 03:58, 18 April 2015 (UTC)

Also see Steak tartare, Mett, Carpaccio, and even medium rare. It's no as if all raw meat is jumping at us with a dagger between its teeth, trying to cut our throats. --Stephan Schulz (talk) 08:34, 18 April 2015 (UTC)

• The two issues with eating raw meat are parasites which have laid eggs in the muscle, which then hatch when eaten uncooked, see schistosomiasis, e.g.; and bacterial infections like Salmonella and Listeria (also E. coli and tuberculosis) due to either indigenous infection or contamination. There's nothing about raw meat itself without some disease agent that is problematic.

μηδείς (talk) 17:53, 18 April 2015 (UTC)

See also here. Count Iblis (talk) 19:15, 18 April 2015 (UTC)

Rotating reference frame

Suppose you have two equal masses that are rotating about each other in circular orbits. Now introduce a particle of negligible mass into the plane of that orbit and you want to observe the path of the particle with respect to the two masses. Will fixing the location of the two masses and observing the particle give you the same results as rotating the reference frame so that the two masses appear fixed? Bubba73 ^{You talkin' to me?} 01:31, 18 April 2015 (UTC)

My understanding of physics is that charging the frame of reference doesn't change the results (other than time dilation being perceived differently for travelers near the speed of light). StuRat (talk) 04:22, 18 April 2015 (UTC)

Then like much else in life you are wrong. Accelerating (eg rotating) reference frames introduce well known effects. Greglocock (talk) 10:37, 18 April 2015 (UTC)

Let's see some sources for that. I can see how looking at a problem a different way can affect our ability to determine the outcome, but not how it can change the outcome. (Reading below, they aren't just talking about changing the frame of reference, but also introducing an additional fictitious force. That's not what I was talking about.) StuRat (talk) 16:35, 18 April 2015 (UTC)

I don't know what you meant to say, but "cha[n]ging the frame of reference doesn't change the results" looks like it is in direct contradiction to the second paragraph of Inertial_frame_of_reference. If you had inserted "inertial" in there I suspect Greg would not have complained. But there are also Non-inertial_reference_frames, and if you use one of those, the results will indeed be different (with respect to the frame, but also with respect to each other), unless you include the appropriate fictitious forces to correct the problem. SemanticMantis (talk) 17:09, 18 April 2015 (UTC)

Well oK, since stu won't do his own research, consider the observations of an inhabitant of a tidally locked binary star system, who uses a ref frame attached to the line joining the two stars. Gravity works as expected near the surface of the star, yet the big star overhead hangs there motionless. If he tries to fire a rocket from one star to the other along that line, it veers off to , as it happens, spinward wrt an outside observer. Greglocock (talk) 00:24, 20 April 2015 (UTC)

Are you asking about two masses in a binary orbit (but with a constant position in the chosen rotating frame) versus two actually stationary masses (separated by a massless strut so that they don't gravitate together)? If so, they're not the same. The acceleration in the nonrotating case is just the sum of the GM/r² accelerations from the two masses, while the acceleration in the rotating case is that plus the centrifugal and Coriolis acceleration. -- BenRG (talk) 05:22, 18 April 2015 (UTC)

Yes, that is what I was asking, thanks. Bubba73 ^{You talkin' to me?} 05:37, 18 April 2015 (UTC)

Add (after ec): The problem you (ie Bubba73) are describing is called the Circular restricted three body problem. You can solve it in the rotating-frame of reference as long as you introduce the needed fictitious forces to account for the non-inertial frame. See here for solutions to the problem in both the inertial and the rotating frame of reference. Abecedare (talk) 05:25, 18 April 2015 (UTC)

Thanks Bubba73 ^{You talkin' to me?} 14:21, 18 April 2015 (UTC)

Resolved

Effect of an astrophysical jet on stellar bodies

What kind of damage would a close-range astrophysical jet do to an object such as a moon, a planet, a star, or a solar system. The beams are powerful enough to create plumes millions of light-years across, but I don't know if that is just the effect it has on gas. Would it be able to tear a rocky planet apart? — Melab±1 ☎ 01:34, 18 April 2015 (UTC)

See Gamma-ray_burst#Rate_of_occurrence_and_potential_effects_on_life_on_Earth, to wit "However, if a GRB were to occur within the Milky Way, and its emission were beamed straight towards Earth, the effects could be devastating for the planet." Do some searches in Google for "Gamma-ray bursts", which is what these events have become known as in the popular press, for some doomsday scenarios. --Jayron32 01:39, 18 April 2015 (UTC)

Not what I was talking about. I was thinking of the possibility of the jet being something that could tear a star apart. — Melab±1 ☎ 02:44, 18 April 2015 (UTC)

I should think the distance would be critical, not because the jet will slow down much, but because it will spread out. So, a nearby planet might be quickly eroded away, while one on the other side of the galaxy might barely have any effects (I'm picturing something like an aurora). StuRat (talk) 04:19, 18 April 2015 (UTC)

Supposedly, the jet is as thin as a pencil when it starts out (source: Scientific American). — Melab±1 ☎ 04:34, 18 April 2015 (UTC)

According to gamma ray burst, a typical GRB beam represents about 10⁴⁴ J of energy, or roughly the 0.05% of the sun's mass energy equivalent. The gravitational binding energy of the Earth is about 10³² J and Jupiter is about 10³⁶ J. Given that the beam has orders of magnitude more energy than that, it seems likely that a direct hit by such a beam at close range would totally destroy the affected planet. Dragons flight (talk) 04:56, 18 April 2015 (UTC)

I don't think electromagnetic radiation would be capable of tearing a planet or a star apart. It would have to be gases and plasma. Though maybe I am wrong on this count. — Melab±1 ☎ 05:32, 18 April 2015 (UTC)

It depends very much on the duration and dispersion. If it's "as thin as a pencil", and only is on for a short duration, it might just push a hole through the planet and leave on the other side. This would probably still have massive secondary effects, but it would not tear the planet apart. On the other hand, if the beam spread out to the diameter of the Earth and hit it with 10⁴⁴ J, all that would be left would be a rapidly expanding cloud of superheated plasma. However, astrophysical jets and gamma ray bursts are two quite different phenomena. --Stephan Schulz (talk) 08:42, 18 April 2015 (UTC)

In case it is unclear, gamma ray bursts are believed to be a specific kind of astrophysical jet. Since Melab didn't specify what kind of jet, I thought they were a fine choice to consider. Dragons flight (talk) 18:06, 18 April 2015 (UTC)

Right. I was thinking more about the gas jets emitted by quasars or protostars. ---Stephan Schulz (talk) 18:10, 18 April 2015 (UTC)

Yeah, but a gamma-ray burst couldn't do that because it is just radiation. — Melab±1 ☎ 17:41, 18 April 2015 (UTC)

Why not? A microwave oven just uses radiation and it cooks our food much faster that a typical oven. A laser is just radiation, and we have lasers that cut steel. Any matter that was placed directly in the path of a GRB at close range would immediately be heated to ridiculous temperatures and expand with incredible force as a superheated plasma. A GRB carries a trillion times the energy needed to vaporize the Earth, and more than a million times as much momentum as is needed to launch the planet into deep space. The only real question in my mind is whether a narrow jet would punch a hole completely through a planet rather than blowing it apart. Personally, I tend to imagine the explosive effects of the heated plasma disrupting the whole planet, though I'm not entirely sure. Dragons flight (talk) 18:06, 18 April 2015 (UTC)

You appear to be right. From this abstract it says that a gamma-ray burst can melt materials over 300 light-years away. — Melab±1 ☎ 03:30, 19 April 2015 (UTC)

(ec)You mean like a laser is just radiation? As in laser drilling or laser cutting or laser ablation? --Stephan Schulz (talk) 18:08, 18 April 2015 (UTC)

Exactly: and the take-away message is that you cannot rely on your intuition when dealing with high energy radiation. You have no intuition about these phenomena: there is no natural way for you to ever experience such high-energy events.

This is one of the reasons why nuclear engineering students are taught about the hole-to-China problem. At first, all the nuclear engineering students are laughing off the silly idea, because it seems so preposterous. And then, they do some calculations, and look some numbers up in tables, and recognize that a critical mass chunk of plutonium is more dense than the floor, and more dense than the concrete foundation, and more dense than the substrata, and ... more dense than the iron core of the Earth ... and before long, nobody is laughing, and everyone is struggling to figure out where the thought-experiment went awry.

The issue is not whether these earth-shattering events can occur: it's that you can't rely on the way you intuitively expect materials to behave when you have exactly no first-hand experience with such energy.

Don't rely on intuition when dealing with exotic high energy materials or radiation: shut up and calculate. Nimur (talk) 15:42, 19 April 2015 (UTC)

That seems silly in that, if something could sink to the center of the Earth, it would stay there, not continue on to China. (Of course, the reality of a nuclear meltdown is that the nuclear core melts the surrounding materials and mixes with it, until it's diluted enough to no longer melt the material underneath it.) StuRat (talk) 19:08, 19 April 2015 (UTC)

Dropping an object through a hole in the Earth is a standard homework problem in the section on harmonic oscillators! If we do not account for viscous forces, the object dropped through the Earth's center will return to its initial height above ground. You may be forgetting to conserve energy: when an object sinks to the center of the Earth, it has considerable and non-negligible velocity!

In reality, there is strong evidence that this is what energizes the center of the Earth: natural, geophysically occurring radioactive material inside the Earth is a source of new heat added to our dynamic planet. Whether you intuitively find this silly or not, thar be uranium and plutonium, bouncing and convecting through layers of semi-liquified rock down thar.

Nimur (talk) 19:36, 19 April 2015 (UTC)

That bit about neglecting "viscous forces" is what makes it silly, putting it into the spherical cow category. Why would anyone think that a sinking nuclear reactor core wouldn't be slowed by passing through thousands of miles of rock and magma ? (In reality it's stopped by them.) Your model sound more like what might happen if a small black hole fell through the Earth. StuRat (talk) 04:59, 20 April 2015 (UTC)

A microwave doesn't give off so much energy, it's just that its radiation quickly heats the water content of food by causing the hydrogen bonds of the water molecules to vibrate. μηδείς (talk) 00:05, 19 April 2015 (UTC)

Health effects of mixed triglycerides

This was listed on my Campbell's Soup "Healthy Request" Cream of Mushroom ingredients. I found an explanation for what they are here: [1]. However, I haven't found anything on the potential health effects of this ingredient. Any ideas ? StuRat (talk) 04:02, 18 April 2015 (UTC)

Triglycerides? -- Jack of Oz ^{[pleasantries]} 04:07, 18 April 2015 (UTC)

Yes, fixed in title. StuRat (talk) 04:16, 18 April 2015 (UTC)

The Mayo clinic is always a good place to start for this kind of thing [2]. The article clearly states that your body can create/assemble trigycerides out of simple carbohydrates - I did not see any mention of avoiding them in dietary intake. We also have Triglyceride#Guidelines, which contains several additional refs. SemanticMantis (talk) 14:24, 18 April 2015 (UTC)

Both refs so far are a little off - the first, though correct, is from 1919, and for example makes a distinction with which I'm unfamiliar, if it is even used at all: "Each of these three substances has exactly the same composition, though the constitution is different for each." Today I think when people speak of chemical composition they don't discount isomers of any variety. The second is good as it goes, but it is talking about the safety of triglycerides in blood, which are presumably assembled in accordance with sane genetic rules much of the time. The problem is, this is actually a regulatory question rather than a scientific question, and "mixed triglycerides" is a very expansive term. I am very suspicious that somehow what is indicated really covers an interesterification reaction in which dubiously edible ingredients are mixed into compounds that may not be naturally derived.

By "dubiously edible" I mean things like PGPR - it may sound like a storybook villain's scheme, but the reason why American chocolate has tasted so crappy the past couple of decades is that the big companies have been making it out of castor oil (much of it grown in Middle Eastern plantations that doubtless do nothing at all untoward with the hundreds of tons of ricin that potentially could be extracted from the beans; it isn't produced in the U.S. because of security concerns... !) By "not naturally derived"... I don't really know whether abnormal triglyceride mixtures have potential health effects, and I'm not convinced anyone has ever really checked. In theory they should be broken down in digestion before they cause trouble, but... biology doesn't know theory.

That said, I still don't know whether Campbell is using "mixed triglycerides" to frustrate your knowledge of what fats went in, or if it is simply a required regulatory term. If the food industry's lobbyists did their job, of course, it should be both. Wnt (talk) 15:47, 18 April 2015 (UTC)

Do we even know that ingestion of triglycerides leads to triglycerides in the blood? I noticed a conspicuous absence of the suggestion that lowering dietary intake could lower blood levels. I know that doesn't prove anything, but I'd think the mayoclinic would at least mention dietary intake if they thought it had anything to do with blood concentrations... SemanticMantis (talk) 16:33, 18 April 2015 (UTC)

As a general rule, lipases digest triglycerides into their component fatty acids before they are taken into the body. But where there's an enzyme, there's usually some wild-card molecule that resists it, or inhibits it, or destroys it; orlistat is an example but I'd guess not the only one. In theory, undigested triglycerides are excreted in feces without further effect, but... Wnt (talk) 19:18, 18 April 2015 (UTC)

Yes, undigested fats, in quantity, lead to anal leakage, hence the notorious warning, from Alli, not to wear white pants. StuRat (talk) 19:34, 18 April 2015 (UTC)

There is nothing wrong per sa with triglycerides in a balanced diet. Most body fat consist of triglycerides. It is too much triglycerides in a diet that has health implications. A can of soup is not likely to push you over the edge. However, an investment in a kitchen blender to make ones own soup is a better and taster option. Mushrooms give a good umami taste, so no need for added sodium glutamate. Many shops to-day, sell dried seaweed and so that can be used for other soups.--Aspro (talk) 16:37, 18 April 2015 (UTC)

The "mixed" seems to have gotten lost in my Q. I wanted to know, specifically, whether "mixed" triglycerides are better or worse than "unmixed". StuRat (talk) 20:07, 18 April 2015 (UTC)

Would be very surprised if you could get a can of soup, or cook up your own concoction without having a 'mix' and they are all fuel to the body. So in answer to your question: I can't see any difference.--Aspro (talk) 21:38, 18 April 2015 (UTC)

Well, I think it's like asking whether wheat is better than bread made out of mixed grains. "What grains?" "Mixed grains." "Mixed out of what?" "Mixed is mixed." I tend to have less confidence but I can't really say why. Wnt (talk) 15:36, 19 April 2015 (UTC)

36 miles of cycling - time?

In a month I'll be doing a triathlon. The cycling part is 36 miles / 58 km. I've noticed while training that I struggle with not having a "goal" to work towards that feels official or standard or expected. Would any one be able to suggest a reasonably good completion time for a female who's not an athlete? I believe the course will be mostly flat with only small hills. I'm not expecting to win or anything. Just want to make the training more concrete. Ta! Julia\^talk 17:23, 18 April 2015 (UTC)

Thirty six miles on a bike is not an exceptionally long distance, but it's worth checking with a health professional if you aren't used to this kind of intense exercise.

Your pace will also depend significantly on other factors, like the terrain, the weather, the type and condition of your bicycle, and so on. Our article on bicycle performance has a section on typical speeds.

A healthy individual who is not an athlete might expect to sustain a reasonable average speed - say, 12 or 15 mile per hour continuously to complete 36 miles in about two and a half hours. If there is terrain, it might be difficult to maintain this average speed.

A more seasoned cyclist can sustain 25 miles per hour for over an hour, but if there is terrain or weather, this is probably an unreasonable average speed for 36 miles. As our article on cycling for sport indicates, a world-class race cyclist can sustain over 40 mph for an extended period of time.

Nimur (talk) 17:40, 18 April 2015 (UTC)

That seems like a bit of an exaggeration, more like >40 km/h, not 40 mph over large distances, as indicated by the article you linked. The current world record for 1 hour is only 32.6 miles. Nobody can cycle at 40 mph for longer than a minute (not counting going downhill, of course). - Lindert (talk) 23:04, 18 April 2015 (UTC)

The only real way to get a metric is to look at past results for that particular triathlon (which are almost always posted on the web), and look at the times for women in the same age bracket. The distance you specify is none of the standard triathlon distances (Olympic distance is 25 miles, half ironman 56 miles) so it's not ideal for us to scale results from other events, but we can look at the 2011 Santa Cruz Sentinel triathlon, which is Olympic distance, as an example. Looking at the results for that group, you see a twofold variation (the slowest rider took around twice as long as the fastest); I'd expect your event will probably fall into the same distribution. You can look at those speeds, slow them down by maybe 10% because of the longer distance you have, and you have a ballpark range to work off. -- Finlay McWalterᚠTalk 17:57, 18 April 2015 (UTC)

I should explain the spread (which is obviously much greater than you'd get in a high level event) - it's down to wider range of experience you'll find in a typical open-access (that is, not elite-level) mass participation distance event. The fastest people are typically very experienced athletes with dozens of events behind them, often current (or in older age groups, former) club or collegiate-level competitive athletes. The slowest are first or second timers, often doing it for charity, who are happy just to have finished. Where you fall in that experience range largely determines where you'll fall in the result range. -- Finlay McWalterᚠTalk 18:08, 18 April 2015 (UTC)

Thank you, great information! I average about 17.5 mph but I've also not been able to sustain this over 36 miles, only more like 20 to 25. It's road cycling so at least I don't have to worry about terrain so much. So it seems that if I could finish the cycling part in an hour and a half, I'd be doing well. Julia\^talk 22:22, 18 April 2015 (UTC)

You would be doing very well indeed. 36 miles in 90 minutes is 24 mph, which is tough to sustain for that distance. My best ever was 25 mph for 10 miles but quite a lot less for 25 miles.--Phil Holmes (talk) 11:28, 19 April 2015 (UTC)

The tricky thing in a triathalon is that you can't go all-out in the cycling section if you still have to retain stamina for the other parts. I'd expect your speeds to be significantly lower than cyclists in a straight road race. So I'd agree that you have to find actual triathalon times - preferably from past years of the event that you're entering. SteveBaker (talk) 04:39, 20 April 2015 (UTC)

CNC Router Table build material

Im considering purchasing a CNC router. There appears to be basically two materials from which these machines for sale are made: thick plywood, and (cast?)aluminium alloy. Which material would give the most rigidity to the machine if they were both of similar thickness?--BoldEditor (talk) 20:22, 18 April 2015 (UTC)

That might well depend on the particular plywood, and the particular alloy. I suspect that a typical aluminium alloy of the type likely to be used in such circumstances might be more rigid than a typical plywood, but to give a definitive answer would require more information. There are other considerations than simple rigidity though - plywood may absorb moisture over time and warp, for example. Certainly the use of wood for precision machine tools isn't the norm. AndyTheGrump (talk) 20:31, 18 April 2015 (UTC)

The use of plywood seems unusual, yes, but I suspect there is a reason, such as wood being better at absorbing vibrations. Unabsorbed vibrations could leave a trace in the final products. StuRat (talk) 20:37, 18 April 2015 (UTC)

To answer ATGs remark re moisture, I am assuming that the plywood wood be marine grade.--BoldEditor (talk) 20:44, 18 April 2015 (UTC)

The precision of the bed isn't the issue - the precision of the rails on which the motion platform runs is the critical factor. A lot depends on what kind of CNC machine you're considering. The large format routers are generally used for milling material that itself is liable to warp and twist - and having a heavy plywood bed isn't a huge deal. The small routers are typically used for milling metal and plastic - and those are frequently small enough to have a metal bed. There are MANY kinds of machine, with different materials, dimensions and precision requirements - so it's tough to generalize. SteveBaker (talk) 04:34, 20 April 2015 (UTC)