Wikipedia:Reference desk/Archives/Science/2014 April 5

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April 5

Biomedical engineering

Why are some parts of biomedical engineering such as biomedical materials, especially fields looking at the materials interaction with bacteria etc, classified as engineering at all? It seems more like biochemistry to me? What engineering principles are used? Clover345 (talk) 00:37, 5 April 2014 (UTC)

Adapting the physical world to suit a human purpose is "engineering." --DHeyward (talk) 11:41, 5 April 2014 (UTC)

Meaning of wine ageing.

I suspect this question has been asked before. Well, I still decided to give it a go. I am primarily interested in fortified wines like port, madeira and sherry. You go to a wine store and see the spread: regular port is between USD 7 and 20 and if it has been aged 10 years or so, the price will be about $30.00. If it is 20 years old you will pay around $50.00 and a 30 year wine will cost you a hundred dollars.

My question is: what is the meaning of wine ageing? What changes in the fortified wine when you keep it stored for many years. The alcohol content is obviously stays the same, then what is the difference? Is it something tangible that can be caught by scientific methods?

I am not really a wine drinker, so the whole thing is mystery to me. I am sure if given two goblets to compare I could not make out which is "better." I presume ageing is done to make the wine "better," correct? Again, better in what sense?

And why does it get better? Why does it not go in the opposite direction? How about wine that gets worse with time? — Preceding unsigned comment added by AboutFace 22 (talk • contribs) 01:38, 5 April 2014 (UTC)

Anecdotally I recall an acquaintance in a position to know (that person actually worked at the plant) told me about a famous Russian vodka made here in the USA, that they produce the liquor in a single production line but pour it in regular and premium bottles. The premium ones of course cost much more. I therefore wonder about the port wine also. As I said I do not drink but buy the stuff for someone who is of my age but does not drive and cannot easily get around.

What if they do not really age the wine but pour young port so to speak and stick an expensive label on it. This question bothers me.

Thanks, --AboutFace 22 (talk) 00:46, 5 April 2014 (UTC)

Have you read Aging of wine? Wine contains a lot of different chemical compounds that affect the flavor (we have a whole article on Wine chemistry). Aging allows time for reactions to occur that, in some wines, do improve the flavor. Fraud does occur, but it's taken pretty seriously. In Portugal, port production is regulated by the Instituto dos Vinhos do Douro e do Porto. Mr.Z-man 01:48, 5 April 2014 (UTC)

Chemical reactions in liquids take milliseconds, not years unless diffusion is involved then they may take minutes but it is hard to imagine any concentration gradients in a bottle of wine. --AboutFace 22 (talk) 13:43, 5 April 2014 (UTC)

Some reactions are quick, and some are slow (mainly organic reactions). If you examine bottles of expired (non-alcoholic) products, you will notice changes in color, consistency, odor, etc., which indicate chemical reactions which took years to complete. Of course, those are subjectively bad reactions, while the aging of wine is subjectively good. However, I do think there is some effect of people saying since it's more expensive, it must be better. See veblen good. StuRat (talk) 14:50, 5 April 2014 (UTC)

The speed of reactions can be dependent on the concentration of chemicals. While wine has a lot of chemicals in it, it's 95+% water and alcohol, most of the rest is acid and sugar. The organic compounds that create the flavor are less than 1%. Each indiviudal component may only be a few hundred ppm. Mr.Z-man 19:09, 5 April 2014 (UTC)

Something I didn't see specified above in Mr.Z-man's otherwise pertinent comments (although it's doubtless mentioned in some of the linked articles) is that such beverages are often aged mostly not in the bottles they're ultimately sold in, but in larger wooden vessels, sometimes ones that have previously been used for different beverages and or ones that have been so used for decades. The chemical reactions that can occur between the beverage being aged, the wood of the vessels, and the residue of previous beverages that have sunk into the wood can be very complex, and our taste buds are quite good at detecting the subtle effects of such changes. {The poster formerly known as 87.81.230.195} 212.95.237.92 (talk) 13:45, 7 April 2014 (UTC)

How many electromagnetic signals are in my room now?

Now that everyone has their very own broadcasting station with mobiles (cell phones to you Yanks), millions of signals that were not extant 25 years ago are moving thru the space in my room. Back one hundred years, there were no television or radio transmissions. But there still would have been signals from space.

Can you tell me, approx. how many

a. signals are moving thru my room now?

b. signals would there have been 30 years ago?

c. signals 100 years ago?

d. 4 billion years ago?

Is there a limit to the number of signals that can be overlapping in a given space?

Is there any credence we should give to the idea that too many such signals can be bad for one’s health? Myles325a (talk) 03:56, 5 April 2014 (UTC)

Sigh. Please don't be obnoxious, Medeis. Perfectly interesting question and correctly asked. Don't troll the questioner. Fgf10 (talk) 16:10, 5 April 2014 (UTC)
The following discussion has been closed. Please do not modify it.
Do you want answers from Yanks? Unsigned, insulting ones? — Preceding unsigned comment added by Medeis (talk • contribs) I don't know why Yanks should insult me, I certainly did not insult them - only pointing out that what we call mobile phones here (in Australia) they call cell phones. Did this have something to do with me not signing my name earlier? That was just an oversight, which I have amended now. Myles325a (talk) 03:56, 5 April 2014 (UTC)

I really think you're asking the wrong question here. The only answer would have to be an infinite number of electromagnetic waves are passing through your room, and always were passing through every point in space. What's really important is the frequency and power level of those waves. The usual threshold at which we would become concerned is when they start to heat things up. Cell phones are at a very low power level, so only the one next to your head could cause this. But if you happen to be right under some power lines, or next to a radio or TV station's broadcast antenna, or in the path of a 2 microwave transmission towers, then you might possibly get enough electromagnetic radiation to be of concern. StuRat (talk) 04:05, 5 April 2014 (UTC)

What exactly are you counting as an "electromagnetic signal"? An electromagnetic signal usually refers to electromagnetic radiation that's being varied in some intentional way in order to communicate information. But your question assumes that there were "signals from space" 100 years ago, even though 100 years ago there was nothing in space that was produced by humans that was intentionally varying electromagnetic radiation in order to communicate information. Are you counting (extremely weak) electromagnetic signals produced by whatever non-human civilizations there may be in the universe? Or are you counting electromagnetic radiation produced by natural processes, that isn't intentionally communicating information? And if you're counting electromagnetic radiation produced by natural processes, what counts as "one signal"? Each star in the visible universe produces electromagnetic radiation, for example, but other natural sources of electromagnetic radiation, such as the cosmic microwave background radiation, aren't so easily separated into a discrete, finite number of sources, unless you're counting individual photons. What lower limit, if any, are you using for how strong electromagnetic radiation needs to be in order to count toward the signal count? And what frequency range, if any, are you limiting your definition to? The answer to your question could be anything ranging from "zero" to "a practically infinite number", depending on how you define what "one electromagnetic signal" means. Red Act (talk) 05:56, 5 April 2014 (UTC)

It can be quantified by calculating the entropy of the electromagnetic background (thermal noise, mobile phone signals etc. etc.) per unit volume. The difference between this entropy and that of perfect white noise with k_B replaced by 1/Log(2)is the number of bits of information that one could in principle extract from the radiation (the contents of the mobile phone calls, some details about stars, the non-uniform microwave background giving away clues about the early universe etc. etc.) Count Iblis (talk) 15:01, 5 April 2014 (UTC)

a. and b.

The electromagnetic signals of interest need to be defined because there are more of them in your (unshielded) room that there is room for full-coverage receiving equipment. Consider just one broadcasting band 540-1610 kHz where in the Americas stations are allocated frequencies with 10 kHz spacing: that suggests 100 music programs can co-exist in the band without interference but in practice there are many more transmitted and your domestic receiver will pick up only a few satisfactorily. Wikipedia has an incomplete List of European medium wave transmitters.

c.

The OP and RedAct are is wrong about "back 100 years": in 1914 there were many radio transmissions. Hertz had demonstrated wave propagation through space (1873), both Popov and Marconi had built radio receivers (1895), voice transmission by radio had been demonstrated in Brazil (1900) and if you picked up a spark-gap wireless telegraph signal on 15 April 1912 it could have been the last one from RMS Titanic. A time traveller equipped with a modern sensitive radio receiver would hear dozens of signals, mostly in Morse code.

How was I wrong? I didn't assume there were no radio transmissions 100 years ago, just that there were no signals from space. 100 years ago well predates Sputnik or Vostok. Red Act (talk) 20:55, 5 April 2014 (UTC)

RedAct you wrote "nothing in space", not "signals from space". I accept now that you meant "no man-made signals were produced in space" not "no man-made signals penetrated into space" and have edited my post by striking accordingly. 84.209.89.214 (talk) 21:55, 5 April 2014 (UTC)

d.

4 billion years ago there were no man-made electromagnetic signals but the Cosmic background radiation remnant of the (presumed) Big Bang, modulated emissions from pulsars and occasional bursts from solar flares and planetary atmospheric discharges.

Overlapping electromagnetic signals

In a vacuum, air or any material with linear permeability any number of electromagnetic fields may overlapp since their vector component fields superimpose and do not interfere unless the peak magnetic field causes saturation or the peak electric field causes Electrical breakdown. The latter puts air into a hot plasma state.

Popular Culture: Contact (1997 film)

Relevant to the question, the opening scene of the movie is a three-minute computer-generated sequence, beginning with a view of Earth from high in the exosphere and listening in on numerous radio waves of modern programming emitting from the planet. The viewpoint then recedes, passing the Moon, Mars, and other features of the solar system, then to the Oort cloud, interstellar space, the Local Bubble, the Milky Way, other galaxies of the Local Group, and eventually into deep space. As this occurs, the radio signals start to drop out and reflect older programming, representing the distance these signals would have traveled at the speed of light, eventually becoming silent as the distance becomes much greater. 84.209.89.214 (talk) 16:26, 5 April 2014 (UTC)

Photos of meteor in dark flight

See this: http://www.universetoday.com/110963/norwegian-skydiver-almost-gets-hit-by-falling-meteor-and-captures-it-on-film/

If the rock is moving past at 300 km/hr, shouldn't its image be blurred? Bubba73 ^{You talkin' to me?} 03:03, 5 April 2014 (UTC)

Well, they might have been using a high speed camera to catch skydivers without making them into a blur. StuRat (talk) 04:13, 5 April 2014 (UTC)

If you watch the actual video, it goes past so fast that you barely see it, so I agree it was a high speed camera. And a website like that really should know the difference between a meteor (which it wasn't) and a meteoroid (which it maybe was).--Shantavira|^{feed me} 09:12, 5 April 2014 (UTC)

Were they sky diving in space? Dbfirs 15:49, 6 April 2014 (UTC)

I'm not buying it. The chance of being hit by a meteorite is very low. Of being hit while skydiving must be a million times lower. During the period the chute is actually open, less than that. (but I suppose many skydivers have cameras, so that doesn't divide any further) So we should look for other explanations. What I think we're seeing is that somehow a pebble was packed in on top of the chute last time and fell off when it was opened. In particular, this is why the 'meteor' is following a parabolic trajectory rather than a linear one. Otherwise, I think they should be searching the area for lifeforms, because I don't trust meteors that make course corrections. Wnt (talk) 12:20, 5 April 2014 (UTC)

They weren't hit and estimate it as around 5Kg which is considerably bigger than a pebble. I think one would notice packing that up with a chute! Dmcq (talk) 14:54, 5 April 2014 (UTC)

I don't believe it. I don't think that with a camera shooting bright sunlit sky with very fast settings (which should have a small aperature) you could tell the difference between a pebble next to the camera and a large stone ten times further away. As I recall the original article even said that the skydivers didn't notice the rock themselves; this image is all we have. It's true that even the original article (which seems to have come out first in English then in Norwegian a day later) was dated 4/3. But I think someone had April Fool's jollies out of this. Wnt (talk) 16:10, 5 April 2014 (UTC)

I believe there are more small meteors than you might think. Most just go by without anyone noticing. On a regular security camera, for example, such a small object would be a blur or would fall between frames entirely, so we'd never hear about it. Only when one falls near a high speed camera is anything worth mentioning captured. As far as it's apparent motion, remember that the camera is moving, too, and the spin of the object may cause some deflection from a straight path, as it does with a baseball. StuRat (talk) 15:04, 5 April 2014 (UTC)

Well, the Antarctic meteorites should give a number; I don't think of it as high overall. I need to balance the very unlikely chance of the real scenario against the far more likely chance of the hoax. If it can plausibly be a hoax, it is. It's the same principle as with crytozoology. Wnt (talk) 16:12, 5 April 2014 (UTC)

It would be great if they could find the rock. They should know approximately where it is. Bubba73 ^{You talkin' to me?} 16:21, 5 April 2014 (UTC)

Very approximately. And that film was a few years ago, so the hole it made may well have filled in by now. StuRat (talk) 18:14, 5 April 2014 (UTC)

Wnt, why do you reckon a skydiver is at "a million times" less risk of meeting a meteorite than someone not skydiving? —Tamfang (talk) 06:59, 6 April 2014 (UTC)

That's not quite what Wnt wrote. Skydivers seldom spend more than a millionth of their lifetime actually skydiving. I share Wnt's scepticism. Meteors are rare in the lower atmosphere, so we should look first for an explanation with higher probability. Dbfirs 12:20, 6 April 2014 (UTC)

Well, the chances of me being hit by one while saying grace at Sunday dinner would then be a million times less than for ordinary folk too. Are you sure you and Wnt thought this one out?

I think we are arguing at cross-purposes on the probabilities. Perhaps it's just a difference in the way we use the language? Dbfirs 21:58, 9 April 2014 (UTC)

Also, as most meteorites burn up, they would be rarer on the ground than in the lower atmosphere, but more common in the lower atmosphere than they are in the upper atmosphere and in space. What's your point? Myles325a (talk) 03:42, 9 April 2014 (UTC)

No meteorites burn up completely: they all (or at least the meteorite part) hit the ground, by definition. If this was a meteor that was going to burn up then wouldn't it be glowing from ram pressure? Dbfirs 21:58, 9 April 2014 (UTC)

btw, I believe there are two recorded cases of people being hit by a meteor in all of history, and one of a dog. So the chances are very low indeed. Myles325a (talk) 03:42, 9 April 2014 (UTC)

But the relevant question is what proportion of the outdoor filming with high speed cameras is done by skydivers. I bet that's considerably higher. StuRat (talk) 14:52, 6 April 2014 (UTC)

I believe that the proportion of filmed encounters with meteors correlates very closely with instances in which cameras were present in the vicinity. Myles325a (talk) 03:42, 9 April 2014 (UTC)

Are you claiming that meteorites can be detected only by high-speed cameras? Dbfirs 15:43, 6 April 2014 (UTC)

For small ones like this, yes, as it would either fall between frames or just be an unrecognizable blur on a normal speed camera. A larger object that leaves a trail behind it can be filmed with a normal camera, as in the recent one in Russia. But those are rare. StuRat (talk) 16:06, 6 April 2014 (UTC)

Back to the original question: the one website has a diagram that suggests that the frame interval is 1/30 sec. The blur seems to be far less than 1% of the travel distance between frames, which implies an exposure time of less than 1/3000 sec. The wide depth of focus suggests a tiny aperture setting. The lack of distortion implies an actual shutter (simply scanning the exposed pixels from the sensor element results in distortion for moving objects). In such a small commercial camera, this combination of attributes surprises me, but some camera fundi could comment. My expectation would be to see blurring unless the camera is truly exceptional. —Quondum 19:06, 6 April 2014 (UTC)

When taking pictures (or video) in broad daylight, shutter speeds on the order of 1/2000 of a second are nothing unusual. --Carnildo (talk) 02:53, 9 April 2014 (UTC)

• StuRat nearly has a valid objection, but ... no. I think that if someone had footage from a regular building security camera of a meteorite landing in the parking lot next to someone walking in, it would have hit the big time. Even more so if it landed in a lawn or garden plot and started a fire around it. I should also add that I went back and looked at the video, and it's just a few seconds from the moment the chute opens until the rock falls past - really, it seems like almost too short a time until we recall that the skydiver is rapidly decelerating once the chute opens and the rock retains its inertia. There's simply nothing unlikely about a pebble coming out like this, especially not this time of year. Sure, the guy ought to have gotten every last pebble out when he packed the chute, but parachutes are big, ground is full of stones, and he has other things he's worried about like whether he's folding it right so it will really open. I also encourage people to rethink any consideration of how the skydiver's motion could have distorted the rock's trajectory. We see the background sharp and crisp; he's not twisting within the duration of the exposure. The only question is whether his velocity relative to a distant meteor travelling at colossal speed is going to change by a visible proportion, creating a parabolic arc, within a single set of superimposed high-speed frames, and if so, whether it's going to change so that the meteor is going faster and faster toward the ground. I really don't think so! Come on, April Fools is over, this is busted. Wnt (talk) 20:13, 6 April 2014 (UTC)

Even if they caught it hitting the ground, I wouldn't expect a fireball from a rock this small, just a hole appearing in the lawn with some mud sprayed out. Of course, in that case, they could find it and dig it out, so that would make it more interesting than just the video alone. StuRat (talk) 20:39, 6 April 2014 (UTC)

For action shots in daylight I believe exposure times of about 1/1000 second per frame are quite usual. I believe the pixels are captured then shifted out serially out rather than there being any scanning of the pixels. Dmcq (talk) 20:27, 6 April 2014 (UTC)

I know that exposures of about that length are used in still cameras, but what about video cameras? The article says that that it was traveling 300 km/hour. That is 83 meters per second. With an exposure of 0.001 second, it would move 8cm during the exposure. It doesn't look like it is blurred that much to me, although the exposure could be much shorter than 0.001 seconds. Bubba73 ^{You talkin' to me?} 04:24, 9 April 2014 (UTC)

Filtered milk - contaminated after opening? Why filters and not irradiation?

At my local supermarket there's the option of milk that's been filtered to keep it fresher for longer. To what extent do the milk-spoiling organisms come from the milk compared to being introduced when the bottle is opened and contents decanted?

Why don't they use gamma irradiation instead of filters? Also, wouldn't irradiation be preferable;e to UHT which alters the milk? --78.148.110.69 (talk) 13:00, 5 April 2014 (UTC)

Dairy products suffer from vitamin destruction and the creation of off-flavours when irradiated.[1]--Aspro (talk) 14:23, 5 April 2014 (UTC)

Let me just add a note that the IP of the person who asked the question geolocates to the UK. Looie496 (talk) 14:27, 5 April 2014 (UTC)

While I don't have a direct comment on the relative effects, it's worth remembering that there will often be at least a few days between packaging and opening the milk container. Even more if you often buy more than one bottle at a time but don't drink it that fast. And of course one advantage if this does work is you can do this to an even greater extent if it fits your lifestyle. And the stores themselves don't have to ensure their stock rotates so quickly.

And obviously the bacteria (including spores) in the milk are problematic otherwise your unopened refrigerated milk container wouldn't spoil within 2 - 3 weeks while your unopened unrefrigerated UHT milk container would last months or even years. (In case there's any confusion, although I can't find a ref which directly states this, while the UHT process does cause some changes which some find undesirable, the reason why it lasts longer is because of the much more effective sterilisation.)

In other words, if the filtering does work well, it would make the milk fresh for longer to some extent depending on the particular case. I don't know about your particular milk but [2] mentions a refrigerated shelf life of 60 to 90 days for an unopened container.

(Edit: Note that that source is from 2013 so I'm not sure if there will be anything on the market yet although it sounds like [3] this has been an active area of research recently. From what I can tell there is also some confusion because some extended shelf life milk which seems to generally anything which lasts more than 21 days or so milk just uses microfiltration and HTST pasteurisation, but others uses higher temperature treatements as well as microfiltration. Yet others just use high temperatures. And it varies whether the fat/cream is processed the same or subjected to UHT. There are also other possible steps like UV treatment. [4] (see also comments) [5] [6]. The journal source only used HTST and the other processes but achieves 60-90 days which I think may be partially why it's recent research. It sounds like in the UK microfiltration is the norm, but possibly also higher heat treatment. Our pasteurisation article also discusses the issues briefly. One thing the first (Dr. Gail Barnes) source mentions that's probably relevant although it may be obvious, you need to make sure you post processing such as packaging steps are good enough for your purposes, probably aseptic. So it may also be that your microfiltered milk has this done better too. And it also helps if you are careful with your input. And yes I recognise that this doesn't answer that well what appears to be your main question namely how much of a different this will make after you open the milk.)

As for when the container is opened, obviously if it's fresher from the beginning it may last longer. You shouldn't expect miracles since even UHT milk refrigerated before opening, carefully decanted and closed each time doesn't generally last more than 3 or 4 weeks at the extreme end from my personal experience so I don't see any reason to expect any of this to be better. (May be if you only ever open, decant and close in a laminar flow hood you can stretch it?)

Edit: I should clarify I only read the abstract and I'm not sure the research in the Journal of Dairy Science article was using unopened packaging. It's possible they weren't but were testing in conditions unlikely to be achieved in most real life ones, such as the laminar flow hood I earlier suggested. In other words, I'm pretty sure they were primarily thinking of an unopened packaging shelf life situation since as I suggested and I guess also StuRat below, it's generally difficult to prevent contamination after opening; and milk is a good culture media.

Edit2: Also there is some mention in Microfiltration#Dairy Processing and Milk#Microfiltration but it doesn't add much.

Nil Einne (talk) 14:48, 5 April 2014 (UTC)

The opening on the top of most milk containers is a problem, letting bacteria drop in whenever the cap is off. The air which rushes in to replace the lost milk will also contain bacteria. Milk bags can solve the second problem, as they are flexible and can be reduced in size to match the lower volume of milk. As far as not letting bacteria drop in from above, a system like some ketchup squeeze bottles use, where they open at the bottom, might work. Of course, ketchup is thicker, so avoiding spills would be trickier with milk. Another way to reduce spoilage is smaller containers, ideally single use. This can mean more packaging waste, though, so reusable glass bottles would be best for the environment and also eliminate leaching of plasticizers into the milk. StuRat (talk) 15:22, 5 April 2014 (UTC)

OMG, I had no idea that there was such a thing, as opposed to a "figure"-ative term. :) Wnt (talk) 16:14, 5 April 2014 (UTC)

Yes, for most Americans, the effort to get your hands on some milk bags will be a giant bust. StuRat (talk) 16:58, 5 April 2014 (UTC)

So, what you're saying is that we should go back to the milkman bringing pints of milk in reusable glass bottles to our doorstep. I can tell you from experience that the problem I had with this was that the bottles never seemed to completely lose the smell of stale milk, which put me off drinking the fresh milk. 86.146.28.229 (talk) 07:21, 6 April 2014 (UTC)

That's inadequate cleaning or perhaps the milk at the top had gone bad. They should avoid screw tops, as those are difficult to clean. A disposable cork might work better. I don't think the porch is an appropriate place to leave milk, as it gets warm there, especially if the sunlight hits it, and the labor cost of the delivery has to increase the price significantly. I'd still deliver it in stores, but in single-use glass containers, like a quart, pint or half-pint (depending on the family size). They can have a deposit on them to encourage people to recycle. StuRat (talk) 16:50, 6 April 2014 (UTC)

Well obviously it was improper cleaning, but my point is that when everyone actually used them (and they were cheap, because everyone used them: the delivery cost was no higher than the labour cost involved in delivering and setting bottles out in a supermarket, really) this was a problem. So I doubt it would be less of a problem for future implementations. And they weren't screw top: they were foil-top, to maximise hygiene and minimise costs. The bottles were returned by simply leaving them out to be collected when the next milk was delivered. The doorstep was considered an appropriate place to leave it for generations of people, since when people get up at a reasonable time in a temperate climate there is no issue: prior to that, the milkman came around with his horse and wagon, with a large vat of milk that released milk from a tap at the bottom (just like you said), and people took out their own containers to fill. You might think that it would in theory be unsuitable, but in practice for many years it actually was suitable, even if people round where you live don't do it. There were pint bottles, and rarely-used half-pint bottles, and third of a pint bottles to deliver to schools. People ordered however many pints they wanted (a quart bottle would surely cause problems, since it would be open for longer, and would also make the delivery and cleaning more complicated), and opened each sealed bottle as they used the last. But I could never switch back to communal, reusable glass bottles for milk, because my experience is that the industrial cleaning process doesn't completely eliminate the smell. 212.183.128.252 (talk) 08:19, 7 April 2014 (UTC)

How long ago was this ? They might have better cleaning methods now (UV lasers ?). StuRat (talk) 19:28, 7 April 2014 (UTC)

It was about 15 years ago, now. There were definitely better, more thorough cleaning methods available, even then, but the cost would quickly become prohibitive. 86.146.28.229 (talk) 12:16, 9 April 2014 (UTC)

Two million pints a day still delivered in glass bottles, though they are becoming rarer.[7] Dbfirs 22:15, 9 April 2014 (UTC)

Also note that many people have an irrational fear of irradiation, thinking that the food itself then becomes radioactive. This is rather ironic, since they don't worry about foods which are naturally radioactive, like bananas. StuRat (talk) 15:24, 5 April 2014 (UTC)

You are not allowed to sell irradiated milk in the UK.[8] Thincat (talk) 17:00, 5 April 2014 (UTC)

And why when the governmental Food Standards Agency says it is "a safe and effective way to kill bacteria in foods and extend its shelf life". It's because of lobby groups such as The Food Commission.[9] Thincat (talk) 17:15, 5 April 2014 (UTC)

And I see Long-life milk which is common in the EU, meets consumer resistance in the US. It seems irradiated milk in the US is ultraviolet treated,[10] not gamma radiation – I don't know if this is done in the UK (EU). Thincat (talk) 18:03, 5 April 2014 (UTC)

Hmm...the sentence "in the American market, consumers have been uneasy about consuming milk that is not delivered under refrigeration, and have been much more reluctant to buy it" in the UHT article not supported with a citation, so it should be treated with suspicion. Richerman (talk) 18:21, 5 April 2014 (UTC)

I'm not impressed by regulations against irradiation - I tend to think commercial interests like the idea of people throwing food away and buying more. But... irradiation isn't guaranteed to have no effect. Ionizing radiation can produce double-strand breaks in DNA to kill microbes, and it is true that many enzymes or mechanical agitation produce DNA with similar breaks. But there might be other molecules that radiation breaks in a place that few if any enzymes do. So I can't rule out the possibility of a harmful effect. Nonetheless, I wish we'd let people try more things experimentally, with labelling ... and also that we'd be faster to recognize when things like partially hydrogenated oil are not food and should not be labelled as such. Wnt (talk) 19:15, 5 April 2014 (UTC)

I wonder if there's any risk that irradiation could cause a mutation, say like the ones that causes mad-cow disease, by altering some proteins in the milk. StuRat (talk) 20:43, 5 April 2014 (UTC)

There's really no remotely plausible mechanism for that to occur.(+)H₃N-Protein\Chemist-CO₂(-) 02:10, 7 April 2014 (UTC)

Mad Cow disease? Now there is a thought! The protein has to get deformed by some agent initially. Expression of cellular isoform of prion protein on the surface of peripheral blood lymphocytes among women exposed to low doses of ionizing radiation. Still, I will never have to worry about contracting Mad Cows disease because I'm a helicopter. It is a sham that irradiation won't make milk radioactive, because if it did, it would be easier to see it glowing in the dark it when the fridge light has blown. It would also aid, my secret night-time food raids to the kitchen when everyone else is sleeping. We need (I need) genetically modified cows with some jellyfish genes, to create glow in the dark milk. Oh, and cheese cake. Err,.. Yes you scientists out there, concentrate on developing the cheesecake first.--Aspro (talk) 01:32, 6 April 2014 (UTC)

And if the milk is radioactive, you won't even need to warm it up ! StuRat (talk) 02:17, 6 April 2014 (UTC)

At first I was thinking this question would be unapproachable, but it appears that radiation exposure actually prolongs survival in mice exposed to prions [11]. Unfortunately I still don't see a way to get a good reliable stat on how frequently radiation induces prion disease because I assume it must be very rare; still, if the response to radiation protects against prions, it gives a whiff of plausibility that it could be a real consequence of radiation exposure. Still, this is nothing like evidence that irradiated food would have this happen to a meaningful probability. You really have to do the experiment directly. Wnt (talk) 21:03, 6 April 2014 (UTC)

Radiation can't cause mutations of nonliving material. If for instance you were to irradiate a steak, it could of course damage any residual DNA or RNA (that's sort of the point since it inactivates viral and bacterial contaminants). But since it's not part of a living organism anymore, it's not capable of replicating the damaged DNA, or expressing new proteins, so none of that can result in the production of mutant proteins. You could certainly cause some minor degradation of any proteins already present, but you're not going to magically change the sequence, besides people eat denatured protein all the time. Case in point, scrambled egg. The basic take home message here is that you can't "mutate" nonliving matter. That's genetics 101. (+)H₃N-Protein\Chemist-CO₂(-) 02:10, 7 April 2014 (UTC)

But my understanding of mad cow disease prions is that they are mutated proteins. The replication happens by other cells in the cow, or in a human once those prions are introduced there. So, one mutated prion gets in, and it can then be replicated to a dangerous level. Are you saying proteins can never be mutated directly ? StuRat (talk) 02:21, 7 April 2014 (UTC)

Prions are proteins that adopt alternate (or incorrect) folds and then propagate the misfolded form by trapping other unrelated proteins in the same incorrect tertiary structure. The idea being that the disease state is passed on structurally, trapping native proteins in alternate conformations. The initial misfolding event can be the result of a mutation, but the mutation itself can't be passed on to other proteins. A mutation is a change in sequence, so a mutant protein would literally have to have a different primary sequence. (+)H₃N-Protein\Chemist-CO₂(-) 02:31, 7 April 2014 (UTC)

Also, worth clarifying the terminology here: A mutant gene is a gene with a different nucleotide sequence, a mutant protein has a different amino acid sequence. A mutant gene can produce a mutant protein, or it could easily produce a wild-type protein depending on what specific change is made (See also: degenerate codon). The amino acid sequence itself can't replicate though, so one mutant protein can't make another copy of itself. (+)H₃N-Protein\Chemist-CO₂(-) 02:42, 7 April 2014 (UTC)

Sounds like a distinction without a difference to me. That is, you don't count a misfolded prion as being a mutation, but it can still be passed on to somebody who eats it and cause mad cow disease. So then, if radiation can cause a misfolded protein, that's a problem. StuRat (talk) 02:39, 7 April 2014 (UTC)

That's unfortunately, a completely baseless conclusion. Radiation could degrade a protein chemically, maybe even produce amyloid in an extreme case. But suggesting that radiation damage will produce infectious mutant prion proteins out of thin air is essentially invoking magic. Edit: Out of curiosity, where did you even get the idea that radiation causes prion diseases? (+)H₃N-Protein\Chemist-CO₂(-) 02:46, 7 April 2014 (UTC)

I didn't say that it could, I just asked if it's possible, as one example of a possible mutation. Another example would be in a surviving bacterium that might be mutated to be more harmful. StuRat (talk) 03:00, 7 April 2014 (UTC)

Also, some foods remain alive until irradiated, like onions or potatoes or grains which can sprout. I can easily imagine that some cells in the milk also remain alive. StuRat (talk) 13:49, 7 April 2014 (UTC)

Well, they wouldn't be alive anymore after being dosed with high levels of gamma radiation. So, there's still no mechanism for that to cause the overly specific mutations you've invoked above. Contrary to what happens in the comics, exposure to high levels of ionizing radiation tends to cause nonspecific and irreparable DNA damage resulting in either death (fast or slow) or sterility, neither are optimal conditions for passing on genetic material. It also doesn't actually turn you into a big green rage monster. In either case, irradiating food neither causes the food to remain radioactive, nor does it "mutate" the food in any genetic sense of the word. (+)H₃N-Protein\Chemist-CO₂(-) 13:16, 8 April 2014 (UTC)

Just like with antibiotics, the potential nutation danger would be in under-dosed foods. And while most mutations are either deadly or have no effect, a very few help the organism to survive. In the case of harmful bacteria, this could be bad news for us. StuRat (talk) 13:27, 8 April 2014 (UTC)

No, still not plausible. Bacteria can become resistant to the specific chemical mechanism of a particular antibiotic, it's all about the chemistry. Say a small molecule binds to a bacterial ion channel, then there's a strong selective pressure for an ion channel with a slightly different extracellular domain. The only way bacteria can respond to low level DNA damage is with so-called "DNA repair" proteins, allows them to repair minor damage induced by low level UV irradiation. Ionizing radiation is entirely different, if you irradiate a bacteria with gamma radiation you cause genome wide damage to its genetic material, there's no way to adapt to it because you're directly destroying the thing that would allow it to respond. IF you invoke incomplete irradiation, then maybe a few bacteria aren't exposed to the gamma radiation at all, but then there's no selective pressure. High dose ionizing radiation is a horrible way to introduce a stable mutation, chemical or UV methods work way better. For instance, directed evolution screens sometimes work this way. (+)H₃N-Protein\Chemist-CO₂(-) 14:25, 8 April 2014 (UTC)

Think what StuRat is trying to get across to you is that ionising radiation might 'flip' a non pathogenic prion into a pathogenic form. The people that suffered from Kuru (disease) ate the brains of their old folk, whom (one can reason) had more time on this earth to suffer from possible damage from natural radiation. OK, Prions, from all accounts, appear to be very resistant from ionizing radiation damage – yet millions of tax payers money (some of it yours) is currently being spent on building, running, analyzing - neutrino detectors. Events seldom happen. Yet statistically they do and get recorded. Likewise, the prion refolding 'must' happen for a reason – even if the originating spontaneous event happens very rarely. Even if God deems it so – he/she or it would leave evidence of a causative agent. Ok. Prions are small molecules, so gamma rays from Cobalt 60 might just whizz by. But industrial gamma source isotopes are not pure. They will emit more neutrons than your Moms Apple Pie has has calories. Do you know what a neutron can do? The other possibility, is a faulty DNA codon in the cow might create a pathogenic prion. However, that is a might also. So I can not fathom: how you can pontificate with certainty that Sturat's suppositions is is outside consideration. Scientist may be skeptics by nature but they are always ready to question their beliefs in the hope that they might have that Aha moment, which may lead them to sudden realization, new insights, inspiration, recognition, or (what we most of us all hanker towards) comprehension! They don't have a monkeys chance of getting a Noble if they leave higher education, confident in the knowledge that they now know everything. You may have a point but you need to state it.--Aspro (talk) 22:52, 8 April 2014 (UTC)

"Do you know what a neutron can do" To proteins? Yes, as a matter of fact seeing as how doing this to proteins is a major part of my own research. Neutrons interact weakly with light nuclei, they can on occasion "activate" certain transition metals, but that's very rare. One reason neutron scattering is so popular is that in contrast to synchrotron x-rays, neutrons are entirely chemically nondestructive. I'm actually extremely comfortable dismissing baseless pseudo-science, especially when people can't be bothered to even pretend there's a plausible mechanism for the thing they imagine science is doing to them. Is this the science desk, or should we just start calling it the ^ALTscience desk?(+)H₃N-Protein\Chemist-CO₂(-) 00:56, 9 April 2014 (UTC)

What's the thickness of the pleura membrane?

213.57.121.149 (talk) 15:17, 5 April 2014 (UTC)

Your answer is going to vary considerably depending on just how refined a structure you are referring to regarding the pleural membrane, but assuming you are looking at just the visceral pleura, the thickness for a healthy individual is on the order of micrometers (in the ballpark of 30-80µm on average), though there are conditions (notably diffuse pleural thickening) which can increase the thickness by several millimeters. Snow (talk) 03:31, 6 April 2014 (UTC)

Yes, I'm looking for the pleural parietal too. I think there is a differnt of the thickness between the two. And if it's so thin how can it be he can hold whole the volume of the lungs. Thank you. — Preceding unsigned comment added by 194.114.146.227 (talk) 07:59, 6 April 2014 (UTC)

The parietal pleura is even thinner, at about 20µm. As to your second question, I assume by volume of the lungs you are inquiring as to how it contains the pressure of the volume of gas regularly inhaled. If so, the answer is that it does not, in itself, so much perform this function; air is conducted through still more internal structures, notably the bronchi, bronchioles, alveolar ducts, and the alveoli (where the bulk of gas exchange occurs) themselves, all of which is supported by a matrix of connective and vascular tissues. These tissues are more than sufficient, in most circumstances, to resist the pressure of the maximum volume of air. In fact, the function of the pleurae is less to resist internal pressure than it is to regulate it; the intrapleural space is filled with pleural fluid, which increases surface tension and keeps the visceral pleura in contact with the parietal pleura without friction between the two, such that, when the diaphragm contracts, increasing the volume of the thoracic cavity, the volume of the lungs is increased as well, drawing air into the bonchi, by way of the trachea. So in essence these structures are part of the mechanism which regulates volume (and thus pressure) in the lungs, and less so those which resist it. Snow (talk) 11:50, 7 April 2014 (UTC)

Airplane black box

Is there any reason why an airplane black box will "ping" for the specific time period of one month? Or is that just an arbitrary time frame established by the manufacturer of the box? Thanks. Joseph A. Spadaro (talk) 19:07, 5 April 2014 (UTC)

Battery life isn't infinite. However, this article suggest a push to extend the life to 90 days. As technology approves, the size, durability and lifespan of these devices will all optimize. Regulations must be in place to keep up with technology. Mingmingla (talk) 19:58, 5 April 2014 (UTC)

For me this reads like a requirement by a government agency and the manufacturer does exactly what he is obliged to do deliver 30 days of battery life. --Stone (talk) 20:36, 5 April 2014 (UTC)

More likely an international NON-government agency. HiLo48 (talk) 21:42, 5 April 2014 (UTC)

I've spent a good part of my career as an engineer in the provision of battery backup power (Unreakable Power Supplies - UPS) for critical computer systems, police telecommunications, hospitals, etc. The someone who can come up with a battery technology that never suffers unpredicted catastrophic failure upon discharge, offers a reliable discharge time (not forgetting that battery capacity is inherently proportional to temperature, as a battery is essentially a chemical system and all chemical reactions are temperature dependent), and offers a usuable capacity in a resonable size and weight, is a rich someone to whom the world will beat a path to their door. Nickel iron batteies come close when made at high cost. Super-capacitors have great promise. But this business of the black box battery being good for a known length of time is nonsense. 120.145.97.4 (talk) 00:30, 6 April 2014 (UTC)

My understanding is that one month is the GUARANTEED MINIMUM time that a black box will ping -- it might or might not ping for a longer time, but it WON'T stop before one month. 24.5.122.13 (talk) 03:07, 6 April 2014 (UTC)

Right, the 30 days are guaranteed, and there is a safety margin defined by some requirement. I know of a few parts were we have to built in a factor of 1.5 and for others 3 or even more for very dangerous systems. --Stone (talk) 08:45, 6 April 2014 (UTC)

Wikipedia has relevant information at Underwater locator beacon. This article points to a useful external link HERE, although this equipment is very modern and unlikely to be installed in Boeing 777 of the age of MH370. Dolphin (t) 11:00, 6 April 2014 (UTC)

Another question: Why aren't there two black boxes, one of which remains with the plane, and another of which is ejected? The one that is ejected (automatically) could be equipped not only with "pinging" ability but with a huge inflatable orange flotation device, which might aid in recovery. Bus stop (talk) 11:42, 6 April 2014 (UTC)

A proposal to this effect has been circulating in the US Congress for several years. This proposal has recently been re-introduced as a result of the search for MH370. See the information supplied by User:BBoniface about the SAFE Act - diff. Dolphin (t) 11:52, 6 April 2014 (UTC)

Given the chilly temperature at the bottom of the ocean, would that extend the batteries' life, or shorten it? ←Baseball Bugs ^{What's up, Doc?} carrots→ 13:18, 6 April 2014 (UTC)

It should slow the reaction extending the life, but on the other hand the maximum current would be reduced, so the useful life could be less. I hope 120 comments on that question. All the best, Rich Farmbrough, 14:19, 6 April 2014 (UTC).

As previously stated, battery discharge time goes down with any reduction in temperature. Mathematical formulae are available to predict the reduction for each type of battery, but I don't know just what battery technology is employed in the black boxes (actually, they are orange). However, googling "deep ocean temperature" throws up a multitude of websites that show that the temperature profile of deep oceans is not simple, and very deep areas may be quite warm. The area where MH370 is thought to have gone down is ~4 km deep and includes an area with underwater volcanoes. Discharge time is also affected by the service life of the battery in a complex way. Many rechargeable battery technologies increase in capacity over time before reducing near end of life.

If I were running the search operation, I would requisition a battery engineer from the manufacturer to review the service life of the particular unit, the performance of other batteries from the same batch, and the water temperatures at the assumed location, and make some sort of estimate of how long it's going to last. There's no such thing as a guarantee in the battery business, but if the design criteria is for a minimum of 30 days for some high percentage of units, then depending on all the factors a particular unit may last 2 or 3 times as long - or it may die today.

Another aspect that the search team should be aware of is that batteries recover somewhat when rested. This means that, depending on the battery technology and the design of the electronics, as the battery gets very weak, the electronics may skip pings. A simple way to exploit the full capacity of a battery is to parallel it with a super-capacitor. The capacitor accumulates energy as the near flat battery manages to dribble it out, and when the capacitor has accumulated enough, the electronics can turn on and send a ping. So, at first, pings are sent regularly at the design intervals. As the battery weakens, the interval between pings can get longer, and perhaps get to a stage where a few pings are sent then a long break before a few more pings, another long break, and so on... I have no idea of whether black boxes employ this technique, which is quite new.

120.145.70.125 (talk) 15:14, 6 April 2014 (UTC)

Thanks, all. Please see my new question below about black boxes (in the April 6 section, entitled "Airplane black box - another question"). Thanks. Joseph A. Spadaro (talk) 15:18, 6 April 2014 (UTC)

Manganese in Steel

I read at several points that the Spartans had superior steel weapons because their iron ore was contaminated with manganese. From my understanding at that point people used bog iron as mains source for iron. I can think of nearly no way how the manganese could come into the iron with the process used at that time. The good thing is that I also could not find a metallurgy or archeology article stating the claimed of manganese in steel in that time period, but it is stated in a good article of wikipedia so it must be true ;-). Is there anybody with a little advice for me?--Stone (talk) 20:35, 5 April 2014 (UTC)

Since bog iron is derived from groundwater, if the groundwater in question naturally contains manganese, so will the bog iron. 24.5.122.13 (talk) 03:01, 6 April 2014 (UTC)

And in fact, according to the article Pyrolusite, manganese is actually often found in bogs. 24.5.122.13 (talk) 06:32, 7 April 2014 (UTC)

A useful-looking source on manganese in bog iron, via a Google search: [12] AndyTheGrump (talk) 07:00, 7 April 2014 (UTC)

Lanthanide oxide crystal structures

Hello. I know that B-type lanthanide oxides can be formed for Pr-Gd (sometimes necessitating high T). According to the book I've got at hand, the B-type structure has three different sites, one of which is distorted capped octahedral, and two different face-capped trigonal prismatic sites. What differs between the two face-capped trigonal prismatic sites ? I can't seem to find any good illustrations of this structure online, so please point one out to me if you can ! Thanks. --2.100.5.77 (talk) 21:51, 5 April 2014 (UTC)

Illustrated at http://www.radiochemistry.org/periodictable/la_series/L12.html. I think this is it also [13] but you will have to register to use the Atom Work site. It looks to be capped at slightly different angles.

table of unit cell structure of Gd2O3 based on http://onlinelibrary.wiley.com/doi/10.1107/S0365110X58002012/pdf

No 	Site 	Atom 	Multi 	symmet 	x 	y 	z 	Occupancy
1 	O1 	O 	4 	m 	0.0259 	0 	0.6562 	1.0
2 	Gd1 	Gd 	4 	m 	0.1346 	0 	0.4900 	1.0
3 	Gd2 	Gd 	4 	m 	0.1899 	0 	0.1378 	1.0
4 	O2 	O 	4 	m 	0.2984 	0 	0.3738 	1.0
5 	O3 	O 	4 	m 	0.3250 	0 	0.0265 	1.0
6 	Gd3 	Gd 	4 	m 	0.4662 	0 	0.1879 	1.0
7 	O4 	O 	4 	m 	0.6289 	0 	0.2864 	1.0
8 	O5 	O 	2 	2/m 	0 	0 	0 	1.0 

The B-type is monoclinic prismatic C2/M. C-type is cubic. A type is P32/m. X-type is Im3m cubic, H-type is P6₃/mmc.[14] Graeme Bartlett (talk) 09:04, 7 April 2014 (UTC)

Awesome, I'll put that into crystalmaker. Cheers ! 2.100.5.77 (talk) 16:31, 8 April 2014 (UTC)