Wikipedia:Reference desk/Archives/Science/2009 August 20

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August 20

Motion, then no motion, in optical illusion

This link is to an optical illusion. When I look at it, I perceive a lot of motion in the image for around 3 seconds, by the end of which the motion has slowed down and stopped. If I continue to stare at the same place, there is no additional motion. If I move my eyes to a different location in the image, I see another 3 seconds of motion which then slows down and stops. Is there a writeup somewhere on why I am perceiving motion that then stops after a short, seemingly consistent, time? Our optical illusion article is disappointingly short. Tempshill (talk) 05:39, 20 August 2009 (UTC)

There is a large class of optical illusions that exploit the fact that our visual cortex is hard-wired to infer 3D structure of objects from illumination and shading. In this illusion, there exists a near order of light-and-shade directions, creating the illusory "direction of illumination" in each small part of the image. Thus, any small part looks like a valid "3D". However, the global 3D structure is invalid; thus shifting the gaze makes the perceived image distort and undulate for a while, until out visual cortex "gives up" finding a meaningful global 3D solution. This seems to take a few seconds, and repeats itself after each saccade or gaze shift. --Dr Dima (talk) 06:10, 20 August 2009 (UTC)

By the way, this very illusion picture is included in the Peripheral drift illusion article for some reason. However, I think that this is not a peripheral drift illusion at all. Indeed, there is no sawtooth intensity gradient in any of the ellipses, and the perceived direction of motion is not always the same. --Dr Dima (talk) 06:25, 20 August 2009 (UTC)

I get almost continual motion, also attempting to mimic the effect using random angular displacements (ie see the black.white circles hidden behind the blue) - gives a vague effect, but not as good.

random displacement pseudo code - works - but not very well

{{{2}}}

It looks like the angular displacements form some sort of orbit (ie some special Vector field ?)- for this to work well - maybe it would be a good idea to ask the creator how they did it, and where the idea came from?83.100.250.79 (talk) 11:27, 20 August 2009 (UTC)

how to get into research?

i am a medico.i am interested o become a biomedical scientist.how do i get into that?what should i do?like-projects to be done,etc. —Preceding unsigned comment added by 115.184.225.12 (talk) 06:52, 20 August 2009 (UTC)

What do you mean by "medico"? Medical student? To become a professional researcher you usually need to do a PhD. If you are a med student you will have tutors and lecturers that will be able to advise you on that. --Tango (talk) 06:56, 20 August 2009 (UTC)

"Medico" in Italian means "doctor", as does "médico" in Spanish. However, the IP address is in India, and I don’t know how the term is used there. Red Act (talk) 07:49, 20 August 2009 (UTC)

Either an MD or a PhD is capable of becoming a professional biomedical researcher, though it does vary somewhat depending on the field. Either way, you'll probably need to look into a post-doctoral research position, and it sounds as though you will have a lot of catching up to do in terms of reading science journals, developing expertise in your area of interest, etc. In academia, depending on your level of experience and success, it might take two post-docs before you've developed into an independent researcher with enough credentials to be hired by a university or other research institution. If you're not interested in establishing your own lab and would be just as happy as part of a larger team you might consider going into industry. Tango's advice is good -- try talking to other people at your institution who are doing research and find out how they got into the field. See if you can find a researcher willing to take an inexperienced trainee and show them how to get started, and go from there. Here are a few links to get you started: Science careers forum, "Career" area for the journal Science, "Jobs" area for the journal Nature. --- Medical geneticist (talk) 11:37, 20 August 2009 (UTC)

It's almost impossible to learn how to do that kind of research without participating in a group that does it. Most people learn as students at a university, but it is possible to start as a "technician" working for a laboratory if there is no way to get accepted as a student. Looie496 (talk) 16:44, 21 August 2009 (UTC)

Time Machine and Law of conservation of energy.

There have been many debate regarding the possibility of constructing a time machine. I'm curious about the fact that wheather the use of time machine would violate the law of conservation of energy. Consider the whole universe as a single system at this moment; now if we send anything to the future(or past)then the system will lose energy(as matter is energy). Consider another scenerio ; if we use time machine to send something back at a time when even the big bang did'nt happened; then the balance of total matter in the universe would be disrupted. Does these scenerio contradicts with the law of conservation of energy?

In order to get any kind of time machine you need to use General Relativity (with some extra bits added in), and energy isn't really conserved in GR (there is a concept of conservation of energy, but it isn't very general). There is an explanation here, but it is a little technical (it was the first Google hit, someone else might know of a better explanation or be able to write one themselves). --Tango (talk) 13:01, 20 August 2009 (UTC)

Tango, You don't believe in the Cosmic censorship hypothesis? Wow! --BozMo talk 13:36, 20 August 2009 (UTC)

I never said that. The question only makes sense if we assume time travel is possible, so I answered based on that assumption. --Tango (talk) 13:46, 20 August 2009 (UTC)

Ok, I took the question the other way round. Time travel almost certainly allows the free creation of energy and perpetual motion machine, and also the break down of determinism etc etc but since we think its impossible we don't spend a whole load of time trying to work out, to see if it could only be impossible for one reason but be consistent with the other ones. Perhaps we should but it seems a bit like arguing over how many angels could sit on a pin head to me. --BozMo talk 16:52, 20 August 2009 (UTC)

I. Why would sending something back in time remove energy from the universe...you must thinking fourth dimensionally! If time is merely another axis on the space-time continuum graph, no energy is removed from the universe any more so than energy is removed from the universe when you travel from New York City to London -- the energy (and mass) is merely moved within the universe. So too are mass and energy conserved within the universe when time is the medium of travel.

II. Hmmm...if time began at the Big Bang, it would be impossible to travel to before the Big Bang -- it would be like trying to travel from the 86th floor of the Empire State Building in 2009 to the same location in January of 1930. Since construction of the building only began in late January of that year, one could not travel to that place because there was no that place at that time. DRosenbach ^{(Talk | Contribs)} 13:04, 20 August 2009 (UTC)

The law of conservation of energy states that there's a constant amount of energy in a closed system at all times. Not that if you add up all the energy in it ever, it would come to a total. That kind of goes without saying. — DanielLC 15:48, 20 August 2009 (UTC)

That's because whomever wrote the law wasn't thinking fourth dimensionally either. DRosenbach ^{(Talk | Contribs)} 23:39, 20 August 2009 (UTC)

(stupid edit conflict) Conservation of energy is not a problem, that is why there is a law of conservation of energy, because it is always conserved. A bigger issue however would be the second law of thermodynamics, as going back in time would mean decreasing entropy (think: carbon dioxide + water -> hydrocarbon). Physics isn't my area however, so I'm certain someone will reply with an answer explaining how the second law isn't violated by travelling into the past. --Mark PEA (talk) 13:14, 20 August 2009 (UTC)

Without providing a full justification, bear in mind that the second law in no way prohibits the localized decrease of entropy (else Wikipedia wouldn't be here), provided that entropy generally increases. So long as the time machine consumes power, this one isn't a sticking point. — Lomn 13:38, 20 August 2009 (UTC)

Thanks, that explains it. Although it brings up new speculations of why a future generation would want to input such vast amounts of energy to get back in time. But that is way off topic. --Mark PEA (talk) 14:18, 20 August 2009 (UTC)

What if there was a drought one year and a really bad harvest? It would be great to be able to send some of next year's harvest back in time to tide you over. I can see plenty of benefits to time travel. --Tango (talk) 14:46, 20 August 2009 (UTC)

We can do that now. It's the reason financial markets exist. Wikiant (talk) 14:56, 20 August 2009 (UTC)

Financial markets allow us to buy food before it is grown, but they don't allow us to eat it. --Tango (talk) 18:46, 20 August 2009 (UTC)

Actually, the past generations would need to input vast amounts of energy to receive the time-traveller. The future generations would be able to get (almost) as much energy as the past generations consume. — DanielLC 15:48, 20 August 2009 (UTC)

I think all these issues arise from trying to apply concepts that just don't apply if time travel is possible. Conservation requires the ability to take time-slices (and see that the quantity is the same in all of them) and the 2nd law of thermodynamics requires a nice simple linear time dimension where the concepts of "past" and "future" make sense. If spacetime is all wrapped around on itself so as to allow closed timelike curves (ie. time travel) then those things are simply impossible and the whole concepts cease to exist (at least globally, you might be able to manage locally). Energy is neither conserved or not conserved in such a universe because conservation makes no sense (which will really piss off the environmentalists! ;)). --Tango (talk) 14:43, 20 August 2009 (UTC)

Of course there are time machines. They will be invented circa 2750. However, while the inventors finally found a way to move material through time, they realized another problem they hadn't considered—moving material through space, instantaneously. The first experiment sent a chimp back in time one year. At first, they wondered why the chimp didn't appear in the lab one year earlier, then it hit them. The chimp arrived at the exact same place it was, but with the earth circling the sun, and the whole solar system moving, the chimp moved through time to a place in open space and promptly died. Next, they put the chimp in a spacesuit, but that simply left the chimp in space, thousands of miles away from the earth, to slowly die.

The problem of moving material through time was hard, but moving it through time to exactly coincide with a livable space at that same time proved insurmountable. You can look it up, it's the 310 millionth article in Wikipedia (or will be).--SPhilbrickT 16:02, 20 August 2009 (UTC)

They'll solve that problem in 2751, when they define the location of the time machine to be at rest with respect to the universe. Then the rest of the galaxy can spiral away and they won't have to care. — Lomn 17:55, 20 August 2009 (UTC)

Except that the time machine accelerates. What they need to do is take where the time machine is now, and where they want the object, and define those as the same place. — DanielLC 21:29, 20 August 2009 (UTC)

Why soy wax?

Soy candles are made from partially hydrogenated soybean oil. But why is it just soybean oil that's so treated? Why isn't there canola/corn/olive/etc. wax from partially hydrogenated canola/corn/olive/etc. oils? Is there some physical property of soybean oil (fatty acid chain length or the like) which makes it ideally suited for wax making, or is it just an economic reason (soybean oil is cheaper/more readily available, or a soy="healthy alternative" association in the target market)? -- 128.104.112.102 (talk) 15:20, 20 August 2009 (UTC)

Soybean oil is much more readily available than corn oil or olive oil. (BTW, when they hydrogenate it, the product is technically not a wax, but a saturated triglyceride similar to margarine or tallow.) 98.234.126.251 (talk) 00:18, 21 August 2009 (UTC)

As for "physical properties" of soybean oil, they're not that much different from the other oils you mentioned, so I'd say that economic reasons are prob'ly why they use soybean oil and not the others. 98.234.126.251 (talk) 00:31, 21 August 2009 (UTC)

LED

What's the largest a single LED bulb can be? —Preceding unsigned comment added by 82.43.89.136 (talk) 16:04, 20 August 2009 (UTC)

An LED simply needs a PN junction (with suitable material properties to emit light) - so it seems likely that a vertically stacked PN junction could be made over the entire area of a single silicon wafer (which are now upwards of 30 cm diameter circles). The physical challenges of supplying current uniformly over such a large area seem like the first hurdle to overcome; defect resistance might be another issue (though in a research setting, this might be an acceptable nuisance to the yield). I can't think of any reason why an arbitrarily-large surface-area PN junction would not act as an LED. The next question is naturally going to be, how do you define a single LED? One single wafer die, or one single packaged component, etc? Or do you mean a different scale, such as largest possible power output? Nimur (talk) 16:38, 20 August 2009 (UTC)

I'm not really sure about the technical stuff, I was just wondering how big theoretically one of these could be made. —Preceding unsigned comment added by 82.43.89.136 (talk) 19:18, 20 August 2009 (UTC)

Sorry if I used too much jargon - as I mentioned, there's no reason why you couldn't create one of those with a 30-cm diameter using present-day technology. The hardest part would be powering it in a way that makes the entire device light up. If you wanted to create several hundred individual LED semiconductor elements, and package them in the same plastic lens cap, then you could probably make an arbitrarily large (hundreds of feet wide and then some) version, if you had enough power to light it up. I make no claim about the limits of practicality and the economics of manufacturing such devices; the usefulness of the resulting light source is also questionable. If you are looking for the largest LED you can buy from a manufacturer today (not hypothetical), I suggest you search for ultrabright LEDs at your favorite electronics vendor (DigiKey, Mouser, and Newark Electronics all are suitable web-based distributors). You can also contact Cree Inc. directly (they manufacture a lot of the LEDs you can buy). Their sales team can assist you, if you want to discuss an industrial-scale purchase (thousands of units and above; or custom designs, etc.). Nimur (talk) 20:58, 20 August 2009 (UTC)

I doubt you could actually make one anything like that size. Silicon is a quite strong semiconducting element and so can be made into large wafers. LEDs are typically made from III-V semiconductors (like GaAs) and these are much more fragile, and thus much smaller. I don't know how large the biggest are, though. --Phil Holmes (talk) 14:38, 22 August 2009 (UTC)

I've been playing with lots of LEDs recently and the biggest ones i've seen which are still cheap and easy to get are these 20mm ones. I know that's not huge, but for a single element LED, they are as big as I've seen.. Then of course if you need a bigger light source, you can get EL backlight sheets up to A2 size which are cuttable to size. But I wouldn't call them cheap. Vespine (talk) 22:57, 20 August 2009 (UTC)

Thanks everyone! —Preceding unsigned comment added by 82.43.89.136 (talk) 12:11, 21 August 2009 (UTC)

Wireless electricity

I was recently burned by a joke product that offered wireless electricty. It worked effectively like a infrared wireless network in that it was specifically direction, and the two ends had to be pointed at eachother.

I've found out this isn't a real product... yet.

What I'm wondering is where is this product in development or research. Are we close? If we are, how would you guess something like this would work, and what would some risks be?

I've read about telsa coils and while they demonstrate what is technically wireless electricity, it isn't exactly a good idea to have in your house :).

Thanks. —Preceding unsigned comment added by 148.134.37.3 (talk) 16:56, 20 August 2009 (UTC)

This somewhat recent article in PopSci looks like the most promising thing that I have seen, though that was a year and a half ago. —Akrabbim^talk 17:02, 20 August 2009 (UTC)

WP:OR: I have personally seen inductive heaters on stoves; short-range wireless chargers for cellular phones (and similar devices)[1], and contact chargers to replace the "plug" in "plug-in hybrid" - all of these use electromagnetic propagation with the express purpose of power-transfer. Not all of these qualify as consumer-ready products, but there is a spectrum of technology readiness (and some media coverage, too). In addition, there is widespread use of RADAR, which transmits very significant amounts of power wirelessly (though not with the intenion of "powering" a device on the other end). You should carefully consider the difference between transmitting power wirelessly (in the form of transmitting and receiving electromagnetic signals), and transmitting power for the purpose of powering a device. Most power-transmission schemes are so inefficient that actually powering the device is not worthwhile. Nimur (talk) 17:53, 20 August 2009 (UTC)

There is one very common use of wireless power that I can think of. The teeny-tiny RFID tags you find in things like keyless entry car keys, some store products, security badges, etc are powered (briefly) by the scanner that's querying them. SteveBaker (talk) 18:46, 20 August 2009 (UTC)

Another notable, if not widespread, use is the linear induction motor. I have ridden trains powered by these in several cities. Of course, the power is only transmitted wirelessly for a few inches or centimeters. --Anonymous, 19:11 UTC, August 20/09.

James May and his Twentieth Century claim that some of the oldest commercial radios used an extremely long cable to both pick up the signal and produce the power for a pair of headphones (then known as "telephones"). Does this count as wireless energy? Vimescarrot (talk) 19:27, 20 August 2009 (UTC)

Absolutely - if you ever built a crystal radio as a kid or hobbyist, your ultra-high-impedance earphone was connected to an otherwise entirely passive device (no amplifier!) Any sound-waves that were generated were powered entirely by the (very low) received radio power, and downmixed to baseband by the crystal diode. Nimur (talk) 21:04, 20 August 2009 (UTC)

Inductively powered trams - [2] or [3] 83.100.250.79 (talk) 21:06, 20 August 2009 (UTC)

Nikola Tesla invented his coil for, among other things, wireless power transmission. --Jayron32 21:07, 20 August 2009 (UTC)

See wireless energy transfer. 70.90.174.101 (talk) 03:27, 25 August 2009 (UTC)

Taking a picture of the past

I know time travel is considered theoretically impossible, but is there a reason it would not be possible to take a picture of the past? Since you would only be impacting photons and photons' experience the entirety of time instantly it seems that observing them would not defy causality.

So could I build a machine to take a picture of during the Elizabethan era? TheFutureAwaits (talk) 18:19, 20 August 2009 (UTC)

The real problem with time travel is the problem of time travel. In other words, the reason why there are so many speculations is because it's fairly certain that it can never be achieved, and as such, each author, director, etc. takes a license in generating his or her own rules that would apply. So your question is not a bad one -- your presumption would sort of undermine the laws of physics as dictated by Gale and Zemeckis in Back to the future, but nothing dictates that their laws are any more cogent than any one else's. So no, you can argue that time itself and the experiences that occur within it should not be able to effect an already-taken photograph. But in the same vein, a time machine should not be able to tap into time and effect it at all, thus undermining time travel altogether. DRosenbach ^{(Talk | Contribs)} 18:36, 20 August 2009 (UTC)

Not any more. However, if you put a large (LARGE!!!) mirror onto a spacecraft and shot it off into deep space at some reasonable fraction of the speed of light - and then parked your mirror (say) 50 light years away - then you'd be able to point your super-powerful telescope at the mirror and take photos of the earth as it was 100 years ago. Sadly, since nobody had the foresight to do that, we have no chance to take photos of the Elizabethans. Even if your spacecraft can go at 99.999% of the speed of light, you can never use it to take pictures from before the time it was launched.

They didn't lack the foresight so much as they lacked the technology, and if you do have the technology it's easier and better to just take photos and store them locally. -- BenRG (talk) 19:21, 20 August 2009 (UTC)

To riff further on the giant space mirror idea, there exists the possibility that aliens 1000 light years away built a giant space mirror 999 years ago, and that next year we'll suddenly be able to see what was happening on Earth 2000 years prior (handwaving all the telescope problems, naturally). This routes around the problem of seeing something before the mirror was constructed, but only because of the sheer fluke of its existence. Such time travel, in effect, works only by accident, never by intent. — Lomn 20:08, 20 August 2009 (UTC)

Obviously, I'm aware that the technology is far beyond what we can do even now - the gigantic mirror, the close-to-light-speed rocket that carries it, the spectacularly good aiming you'd need to make the mirror point back towards the orbiting earth with such precision, the amazing telescope you'd need...the public will to spend all that money on a project that even their grandchildren are not going to benefit from! So this is firmly a 'thought experiment'. However, there are plenty of advantages over simply taking some photos and storing them in a vault for the same amount of time. The problem with doing that is that it's only with a lot of hindsight that you know what's going to be interesting and what isn't. If you had enough of these 'thought experiment' mirrors at appropriate places, you could answer questions like "What happened to Amelia Earhart?", "What was the Tunguska event?", "Did someone fire from the grassy knoll?" - all things that only prove interesting enough (or possible at all) to photograph with the benefit of hindsight. Of course you could argue for millions of orbitting cameras that took continous video footage of the entire planet just in case...but that's hardly any easier than the 100 ly mirror approach. SteveBaker (talk) 23:29, 20 August 2009 (UTC)

Of course, we'd need another close-to-light-speed rocket to deliver a corrective lense once the first mirror was found to have a flaw. APL (talk) 01:45, 21 August 2009 (UTC)

A machine that "takes pictures of the past" isn't subject to any of the traditional time travel paradoxes, as you say, but it has nothing to do with photons not experiencing time. There's just no logical contradiction involved in preserving a complete record of the past. -- BenRG (talk) 19:21, 20 August 2009 (UTC)

Okay, cool! So then, how could one go about building such a device? I mean besides the mirror idea which would limit your ability to see the past beyond its construction. TheFutureAwaits (talk) 20:20, 20 August 2009 (UTC)

You Sill might not be able to do it because you might not be able to get clear LOS on the event, say if it is indoors, or the sun, moon or clouds would be in the way. Or it might be dark. Not a chance that you would get a satisfactory solution. Googlemeister (talk) 14:39, 21 August 2009 (UTC)

Just because it's not logically contradictory doesn't mean there's any way to build one. There's no logical contradiction in teleportation or curing cancer by prayer either, they just happen to not actually work. -- BenRG (talk) 20:49, 20 August 2009 (UTC)

<nitpick alert> Technically speaking, every picture you take is of the past, just not very far into it. Photograph the Moon and you're looking about a second and a quarter into the past. </nitpick alert> Clarityfiend (talk) 22:25, 20 August 2009 (UTC)

If there were a gravitational lens or two of just the right size and location, there might be millennia-old images of Earth shooting through space that could actually be intercepted by an appropriately targeted spacecraft. Actually doing so would probably be close enough to impossible, though. Confusing Manifestation(Say hi!) 02:35, 21 August 2009 (UTC)

There is a theory that space is closed,and that(assuming you were in the same place for billions of years) if you could see far enough you would see the back of your own head-which of course would be billions of years in the past due to the time taken by the light. The mirror idea would NOT be able to see points before the rocket was sent, because it would have to exceed light speed-and even if some technology made this possible, you would then be able to travel back in time in person rather than merely observe an image. But there is no sign of such a technology so far, and many scientists think never.80.2.202.175 (talk) 02:53, 21 August 2009 (UTC)

Are Monkeys Taxa

Hey,

I am not a monkey expert in the slightest, but need to know if monkeys are considered Taxa? If they are I will put the Taxobox back up on the monkey article. Thanks!--Gordonrox24 | ^Talk 18:23, 20 August 2009 (UTC)

They are not. The monkey article's lead (as it stands now) gets it right: "The New World monkeys are classified within the parvorder Platyrrhini, whereas the Old World monkeys (superfamily Cercopithecoidea) form part of the parvorder Catarrhini, which also includes the apes. Thus, scientifically speaking, monkeys are paraphyletic (not a single coherent group) and Old World monkeys are actually more closely related to the apes than they are to the New World monkeys." Rlendog (talk) 18:34, 20 August 2009 (UTC)

As I said, I am not a monkey or science expert. If you can make that line make sense enough to answer the question, all the power to you! Thanks!--Gordonrox24 | ^Talk 18:36, 20 August 2009 (UTC)

To put into laymans' terms, Rlendog has explained that the two common groups of monkeys ("Old World" and "New World" monkeys) are classified separately (two different groups). The first group, "Old World" monkeys, are not even a complete group, because that group also includes apes (which are not scientifically called monkeys). Specifically, there should be two separate taxoboxes - which appears to be the case at Old World monkey and New World monkey. The main monkey article could duplicate these two boxes, as it is a common name for distinct taxa. Nimur (talk) 19:17, 20 August 2009 (UTC)

Temperature of fire

Hi Can anyone tell me the temperature of the coil of a one KW bar electric fire?

Thank you for your assistance in advance!

John d —Preceding unsigned comment added by 78.149.141.93 (talk) 20:02, 20 August 2009 (UTC)

I don't believe that your question is answerable; or rather, that any answer I would give would be synthetic. Assuming 1KW is the rate at which heat energy is produced, the temperature will depend on the temperature of the environment. That's all the power dictates. And one would have to factor in the heat capacity of the electric fire itself. Also, why must the temperature be homogeneous throughout the fire? --Leon 20:58, 20 August 2009 (UTC) —Preceding unsigned comment added by Star trooper man (talk • contribs)

What colour does the coil glow?83.100.250.79 (talk) 21:02, 20 August 2009 (UTC)

Was anyone else confused by the question's terminology? I think the OP means an electric fireplace, not an electrical fire. Nimur (talk) 21:11, 20 August 2009 (UTC)

Or just an electric heater. Anyway, as noted, the best easy way to tell the temperature is to look at the color of the hot wires. See the table at Thermal radiation#Subjective colors. (Obviously this will only give you an approximation, as the temperature will probably be between two of the numbers shown.) --Anonymous, 21:37 UTC, August 20/09.

In the UK, it's common for people to refer to a fireplace-looking electric heater as an 'electric fire'. Fluorescent lights sometimes have a 'starter motor' too. --Kurt Shaped Box (talk) 00:54, 21 August 2009 (UTC)

I'm not sure where the OP is from, but an electrical heater that uses a coiled resistance element round a ceramic core has been called an "electric fire" in the UK for a long time, so I presume this is what is being referred to. They tend to glow dull red, so my guess (from my memory of furnaces in a clean room) is that the element is probably at about 900 celsius. --Phil Holmes (talk) 14:34, 22 August 2009 (UTC)

So are you saying the table I linked to above is wrong? --Anon, 01:35 UTC, August 23, 2009.

In my experiences with furnaces, yes. Whether these have different radiation charateristics than metal objects in free air, I don't know. --Phil Holmes (talk) 10:53, 23 August 2009 (UTC)

Trans-fat binder ?

Fat binder pills exist which, when taken with fatty meals, will bind with fats and thus make them unavailable for digestion. Chitin is one such substance. The problem is that this causes the infamous "anal leakage" problem, as large quantities of bound fat come out the other end. My idea is to make the fat binder specific to trans-fats, which are much worse for our health than regular fats and also come in small enough quantities (a few grams a day), that anal leakage shouldn't be a problem. So, is it possible to make fat binders trans-fat specific, and is anybody working on this ? StuRat (talk) 20:06, 20 August 2009 (UTC)

The assertion that trans-fats are any worse for us than other fats is erroneous. Trans-fats are essentially no worse than saturated cis-fats. Trans-unsaturated are merely worse than cis-unsaturated fats. And while we have a use for at least some saturated fat in our diet, we have no need for trans-unsaturated. DRosenbach ^{(Talk | Contribs)} 23:43, 20 August 2009 (UTC)

I refer you to the last paragraph of the intro to our article on trans-fats, which contains many references (see the article for those):

"Unlike other dietary fats, trans fats are not essential, and they do not promote good health.[1] The consumption of trans fats increases one's risk of coronary heart disease[2] by raising levels of "bad" LDL cholesterol and lowering levels of "good" HDL cholesterol.[3] Health authorities worldwide recommend that consumption of trans fat be reduced to trace amounts. Trans fats from partially hydrogenated oils are more harmful than naturally occurring oils.[4]" StuRat (talk) 00:34, 21 August 2009 (UTC)

The only sentence you presented that serves to contradict my statements is the last, and note 4 is unobtainable without a subscription, so I plead "unable to defend my position" rather than defend it at this time. DRosenbach ^{(Talk | Contribs)} 01:14, 21 August 2009 (UTC)

What exactly do you mean by saturated cis-fats? As I understand it the whole notion of cis and trans makes sense only at a double bond. --Trovatore (talk) 01:28, 21 August 2009 (UTC)

You are correct -- my fingers were faster than my brain! I meant to explain how trans and cis formation make a difference. Macromolecularly speaking, saturated fat appears as a straight hydrocarbon, and when saturated hydrocarbons exist as part of phospholipids, the phospholipids are able to pack tightly together, thus decreasing the fluidity of the membrane they construct. Classically, it was said that unsaturated hydrocarbons form phospholipids that are kinked, because of a double bond at which bond angles differ from the standard tetrahedron formation, thus allowing for less packing and more fluidity and better physiological results. When trans-fat began to be understood better, is was seen that they were double kinked, but immediately adjacent to each other, so that the end result was a hydrocarbon chain that is nearly as straight as a saturated chain. Thus, trans-formation hydrocarbons produce phospholipid bilayer membranes that are just as packed and viscous as saturated fat. Thank you for that catch. DRosenbach ^{(Talk | Contribs)} 03:23, 21 August 2009 (UTC)

In case there remains any dispute I think this is another key point that wasn't quoted The NAS is concerned "that dietary trans fatty acids are more deleterious with respect to coronary heart disease than saturated fatty acids".[2] This analysis is supported by a 2006 New England Journal of Medicine (NEJM) scientific review that states "from a nutritional standpoint, the consumption of trans fatty acids results in considerable potential harm but no apparent benefit."[4] On a personal note, I'm not aware of any authority that disputes that trans fats are worse then saturated fats or any other naturally occuring fats. I'm of course open to any refs that show otherwise and there is some dispute over how much worse, but that's a different issue. Nil Einne (talk) 20:30, 22 August 2009 (UTC)

Because of these facts and concerns, the NAS has concluded there is no safe level of trans fat consumption. There is no adequate level, recommended daily amount or tolerable upper limit for trans fats. This is because any incremental increase in trans fat intake increases the risk of coronary heart disease

Now can we go back to the original Q, please ? StuRat (talk) 12:38, 21 August 2009 (UTC)

I couldn't find any published articles looking into this. Axl ¤ [Talk] 21:30, 21 August 2009 (UTC)

Thanks for looking. StuRat (talk) 22:14, 21 August 2009 (UTC)

One other comment on a trans-fat blocker: The trans-fats that did "pass thru the system" would be more solid than other fats, and thus less likely to cause "leakage". StuRat (talk) 22:17, 24 August 2009 (UTC)

Physical exercise --> prolonged life. But will i actually have more time? Cardiologist may know?

We all hear daily that physical exercise is good and will make you live longer.

The tough question is: If i spend 30 minutes per day on exercise how many minutes will i grow older from that in the long run? Consider if i did 30 mins a day up from zero per day. I find exercise to be a complete waste of time and its boring. However i might just start if i know i'll gain maybe 50-60 minutes of longer life if i spend 30 minutes per day. Because i deduct the 30 minutes spent on exercise. However if i gain 20 minutes of extra life per 30 minutes spent on exercise i won't spend a second of running unless im in a hurry for something. ;)

But my question is: Where's the breaking point? Whats the uptimum amount of exercise per day/week? 10 mins? 2 hours? My sister who, even though she didn't know the answer, knew who could know it. This was a cardiologist. I've personally no idea what they do.(hey? I drive a forklift for a living ;) )

Anyways i'm really interested in this.

as for the physical stuff: im a 25 year old male my BMI is around 29 but i don't look overweight as such.(noone could tell easily when i went from 70 to nearly 100kg)

I have access to a good area to run in very close by but i lack motivation.

many thanks Troels —Preceding unsigned comment added by 90.184.177.214 (talk) 20:22, 20 August 2009 (UTC)

OK, first you should know that we can't give medical advice. I don't consider this a request for medical advice; more like healthy-lifestyle advice, which is generally thought to be a bit different, though I'm not sure where the line is.

I think you should factor more stuff into your calculation. Suppose you find out that the extra time you get is all spent exercising, which you don't enjoy. Have you considered that you may still enjoy the rest of the time more? You may be healthier, you may be better looking, you may find it easier to attract romantic partners. None of this is guaranteed, but these are the usual trends.

Also running is not the only thing available. Personally I think running is painful and probably damaging (to me, at least). This may depend on your genetic inheritance -- some people have connective tissue that stands up well to running; others don't. If you don't, you may want to look into something like swimming or cycling. Of course you can injure yourself in these sports as well, but I find it's easier to avoid injury than it is with running. (With the caveat that I've heard some weight-bearing exercise is still important -- swimming shouldn't be your only exercise, but it could be the one that burns the bulk of your calories.)

Note that I have no professional qualifications whatsoever in this field and this is not offered as professional advice of any sort; it's just my own impressions. Take it or leave it at your own risk. --Trovatore (talk) 20:43, 20 August 2009 (UTC)

I don't quite think that's the way it works, I don't think anyone has worked it out to "if you run 30 minutes, you'll live 20 minutes longer". Cardiologist is a doctor who specialises in the heart, by the way. Look at it this way, say you live until you are 70 and at age 10 you start doing a 30 minute run every day for your whole life. After 60 years you've completed about 22000 half hour runs, that actually only adds up to 456 days, which is less then a year and a half. I'm pretty sure that leading an active lifestyle adds more then a year and a half to the life expectancy, but it is related to other factors too. This study found 4 factors which together amount to an average 11 year increase in life expectancy. The four factors are: eat 5 servers of fruit and vegetables a day, be active, don't smoke, and drink a little alcohol. But that doesn't mean: "you either do those 4 or you don't, and you either get an extra 11 years or you don't". The general "advice" is it appears better to do those things then not to, on average, nothing is a guarantee, but you have a better chance of living longer if you lead an active lifestyle. Don't ask me to define active lifestyle either but I'll tell you what it isn't: sitting down at work and not doing any exercise. Vespine (talk) 22:41, 20 August 2009 (UTC)

I'd try finding something interesting that had some exercise in it rather than just wasting time doing exercise. Something social where you do different things and need some skill is best for keeping your mind bright as well as keeping your body fit if you ever reach old age, dance or tai chi for instance. Dmcq (talk) 22:52, 20 August 2009 (UTC)

A very interesting read. Many things here are really quite interesting. Especially that report. In any case i realise that finding me the answer im looking for is quite hard. If any med students is looking for a challenge for a report then they're free to use this as theme. I'll keep this bookmarked for a while. Thanks alot.

Troels —Preceding unsigned comment added by 90.184.177.214 (talk) 10:19, 21 August 2009 (UTC)

Why have many (most?) vertebrates not evolved to ejaculate quickly during intercourse?

I recently watched a video of a pair of turtles mating, only to have many other males arrive and attack the male - who is then forced to try and hold on until they get bored. Why have animals like this not evolved to ejaculate very quickly (and the same goes for female stimulation if that aids conception)?

Is it that other factors have evolved instead like ability to withstand attacks, to cleverly avoid attacks or to displace semen from previous males, and factors such as overall strength and fitness being more important in the long run? But still, surely sex is unnecessarily drawn-out?

Jokes and answers appreciated. --ASmartKid (talk) 23:16, 20 August 2009 (UTC)

From what I remember from wildlife documentaries, many African deer can complete the 'physical act of love' very quickly indeed. Mount, *unf*, off in about five seconds. I'm not exactly sure why - but perhaps it's to do with the presence of lions/cheetahs? --Kurt Shaped Box (talk) 23:23, 20 August 2009 (UTC)

Yes, I recall a TV documentary showing a young male chimp (or bonobo, perhaps) surreptitiously copulating with a female that "belonged" to an alpha male. It lasted about three seconds, tops. Deor (talk) 00:25, 21 August 2009 (UTC)

I believe the answer to the OP could lie in Deor's response. Chimps as a species may be less fit because weaker individuals are two-pump chumps. A competing species where only strong males get to impregnate females (because it takes longer) could outcompete the extant species. Quick ejaculation cheats stronger males and perhaps also removes some amount of the females' ability to choose their mates (since it's easier to grab a chimp by the hips and hang on for three seconds than for 10 minutes (trust me)). --Sean 14:33, 21 August 2009 (UTC)

OR ? Cuddlyable3 (talk) 20:51, 22 August 2009 (UTC)

haven't you heard of the story of turtle and the hare? I don't know if your assumption about "most" vertebrates is true at all. From what I've seen, like the above, the majority of mammals do not copulate for long at all, maybe a minute at most. Birds also do not have long love making sessions, though admittedly some have long courtship sessions. I think maybe your own personal human experience, and watching the turtles which are just slow at doing everything, has skewed your perception. There are a lot of vertebrates which don't even copulate and ejaculate seemengly at will, like most fish. (EDIT: Believe it or not, that typo, and pun, was not intended, lol) Vespine (talk) 23:30, 20 August 2009 (UTC)

Yes, you're probably right that many/most species do it quickly. I did find one correspondence that suggested that protracted sex is simply a good way of keeping females from having sex with other males (and possibly also 'using up' their 'appetite for sex'). --ASmartKid (talk) 23:41, 20 August 2009 (UTC)

It could also be that if a male offers more drawn-out sex to a female, then the female would be more likely to come back again to that particular male, increasing the chances of passing his genes to the next generation. Also, in some species, ovulation in the female is actually triggered by sexual stimulation -- and in that case, longer sex could cause more eggs getting into the womb and getting fertilized, hence more cubs being born. FWiW 98.234.126.251 (talk) 00:28, 21 August 2009 (UTC)

I believe the rabbit is one example of ovulation triggered by intercourse. The Wikipedia article is somewhat lacking in detail, but here's an article (PDF) that agrees with me. Note that "there is ... about 10 hr. between mating and actual rupture of the follicle". Those bucks must have some staying power :-)

A team of scientists are visiting Mars where the Martians turn out to be friendly and interested in cultural exchange. The teams agree to demonstrate how each race reproduces. The Martians show first. A Martian with blue hair rubs the front of a Martian with pink hair, then a door opens on the front of the pink Martian and out steps a perfectly formed Martian baby. Now it is the turn of the earth team from whom a man and a woman have volunteered to demonstrate reproduction. After witnessing the act the Martians ask in confusion But where is the baby? The earth scientists reply We have to wait 9 months for the baby. The Martians say If you have to wait so long for a result, why such a rush towards the end? Cuddlyable3 (talk) 20:57, 22 August 2009 (UTC)