Wikipedia:Reference desk/Archives/Science/2006 September 15

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September 15

To the ends of spacetime itself!

On a related note, (and I'm sure this is already adressed elsewhere, sorry) if I could travel for any set amount of time in one direction as fast as desired, would I come to some boundry-like feature? If I come to such a feature, what would its nature be? --Amanaplanacanalpanama 00:19, 15 September 2006 (UTC)

No since ,as it says above, the univerese is not bounded!--Light current 00:23, 15 September 2006 (UTC)

Okay, but what happens as I travel? --Amanaplanacanalpanama 00:26, 15 September 2006 (UTC)

You eventually get bak to wher you started from--Light current 01:04, 15 September 2006 (UTC)

Hopefully with a lot of frequent flyer points and a T-shirt that says "I went to the edge of the universe and all I got was this lousy shirt." Clarityfiend 02:10, 15 September 2006 (UTC)

That is not for sure. — [Mac Davis](talk) (New! SUPERDESK|Help me improve)05:00, 15 September 2006 (UTC)

Because the three dimensional universe has a fourth-dimensional fold upon itself, right? Are we quite confident about that? Are there alternative ideas? What if I could travel in the fourth dimension too?--Amanaplanacanalpanama 02:12, 15 September 2006 (UTC)

I've never even heard that before outside of science fiction. A forth spatial dimension folded upon itself? Not mainstream — [Mac Davis](talk) (New! SUPERDESK|Help me improve)05:00, 15 September 2006 (UTC)

You are doing it right now! the 4 th dimension is time.--Light current 02:18, 15 September 2006 (UTC)

An element of doubt will exist until we actually go to the edge of the universe and see for ourselves. Don't wait for it.  freshofftheufoΓΛĿЌ  02:19, 15 September 2006 (UTC)

You can never get to the 'edge'. There are no edges like there are no edges on the surface of a sphere.--Light current 02:21, 15 September 2006 (UTC)

Henceforth, there will always be people who doubt the true shape of the universe. Did you not sense the irony in my comment?  freshofftheufoΓΛĿЌ  04:51, 15 September 2006 (UTC)

There are plenty of alternative ideas: see Shape of the Universe. I think modern observations support a spatially finite universe, but I'm not sure. It's absolutely conceivable that the universe doesn't fold upon itself, and we probably need better observations to prove it or rule it out. Melchoir 02:22, 15 September 2006 (UTC)

There are three definitions of universe floating around here. Observable universe, accessible universe, and Universe. The first is what we can see. If we wait, the observable universe expands because our past light cone includes more and more space. The accessible universe could be defined as the set of all points with a connected path to them (the canonical path is one that goes backwards in time to nearly the Big Bang, travels a little sideways (in space), then forward in time to the destination point. Thus, the accessible universe is larger than the observable universe but should have the same physics and similar structure as our observable universe. The capital Universe is everything, which might include higher dimensions, superstrings, branes, parallel universes, and even weirder things. The Universe as just defined has ontological problems, much like rank-into-rank cardinals, largely as a reflection of our ignorance about the subject.

Currently, if you were to travel at a feasible velocity (less than the speed of light), we can show that even if the Universe were closed, bounded, and connected, you'd never return to your starting point because of a Hubble expansion and the acceleration of the metric expansion of space. To be blunt, space is appearing faster than you could possibly cross it. -- Fuzzyeric 04:29, 15 September 2006 (UTC)

Right. If spacetime has either an edge or "wraps around," these features are currently completely inaccesible to us. In principle, if the universe collapsed again this could change. -- SCZenz 07:26, 15 September 2006 (UTC)

When you say "the observable universe expands because our past light cone includes more and more space" that sounds as if space = time. DirkvdM 09:05, 15 September 2006 (UTC)

I don't think that was what was meant. Since light travels at a finite speed, it takes a certain amount of time for light from distant parts of the universe to reach us. The longer we wait, the more light from ever more distant parts of the universe reaches us - that's why the observable universe (not the universe itself) can be said to be expanding over time. -- Ferkelparade π 09:15, 15 September 2006 (UTC)

That's why it's often referred to as spacetime.

So I believe the question can be rephrased as this: theoretically speaking, could there be a galaxy somewhere in which the inhabitants look towards one side of their sky and see stars and galaxies (everything that we see when we look up) and on the other side of their sky, do they see blackness (the edge)? I find this unlikely, but I can't quite justify why. Thoughts? - R_Lee_E (talk, contribs) 14:15, 15 September 2006 (UTC)

An edge like that would disobey the Cosmological Principle, and I'm not aware of a good reason to think the principle is wrong. Melchoir 17:28, 15 September 2006 (UTC)

There sure doesn't appear to be any such place, at least not for 13 billion light years in any direction. There are some vague ideas that maybe the universe's fundamental physical constants could be different in other Hubble volumes, and then presumably on the border there'd be galaxies on one side and crazy-go-nuts chaos on the other; but there's no obserervations that confirm this, and the details of the transition would vary tremendously from model to model. -- SCZenz 19:51, 15 September 2006 (UTC)

Thank you for your responses, everybody. --Amanaplanacanalpanama 03:50, 18 September 2006 (UTC)

Why is glass clear?

Why, for example, is glass see-through, and a material like iron a metallic grey? What physical or chemical properties determine that difference? Ellen U.

THe plasmon frequency?--Light current 02:12, 15 September 2006 (UTC)

Probably for the same reasons we discussed a few days ago on this same wiki page here, and that's even very near the top of the table of contents? DMacks 03:03, 15 September 2006 (UTC)

Its not quite the same question tho' is it? Ellen is also asking why iron looks like it does!--Light current 03:06, 15 September 2006 (UTC)

Drinking Electrolyzed Baking-soda Solution

In the electrolysis of a solution of baking soda (sodium bicarbonate, NaHCO₃) in distilled water, is caustic lyme (sodium hydroxide, NaOH) produced?  If so, is there any way of neutralizing it, so as to make the solution safe again for ingestion?

Yes. NaHCO₃ -> Na⁺ + HCO₃^- q.v. carbonic acid. The formation of NaOH will be limited by the concentration of OH^- (one part in 10⁷ by default (q.v. pH)) and competition with the formation of Na₂CO₃ (q.v. soda ash) and NaHCO₃ (q.v. baking soda) as mentioned in the sodium article.

The sodium hydroxide article references an external MSDS which should give toxicity information. Together with your estimate of the concentration of NaOH based on the three-way race above, you should be able to judge if the concentration is unsafe. -- Fuzzyeric 04:42, 15 September 2006 (UTC)

Puzzled about your use of q.v. Can you say what it stands for?--Light current 23:54, 15 September 2006 (UTC)

quod vide = "see" - Nunh-huh 03:02, 16 September 2006 (UTC)

Yup. List of Latin phrases (P–Z) has "quod vide (q.v.)" -- "which see". Although the notes there claim that this should be a suffixed annotation, I've never seen it used other than as a prefix, like "e.g." ("exempli gratia" in the "E"s). -- Fuzzyeric 03:13, 16 September 2006 (UTC)

Battery Capacity

How is it possible to measure the capacity of low voltage high current devices?

Charge em up then discharge em a number of times, integrating the area under the current/time graph and averaging the results?--Light current 19:54, 15 September 2006 (UTC)

First determine what final voltage constitutes the battery being discharged. Then determine your discharge rate. You can connect it to a constant resistance load, and the current will drop as the voltage drops. Or you could discharge it at a constant current draw. If it is driving an uninterruptible power supply, the discharge current may actually increase as the battery discharges, as the inverter draws more current at lower voltage to maintain constant power output.Edison 23:49, 15 September 2006 (UTC)

Computer Software

How does the computer distinguish between shutdown and restart command from software?

Each command probably has a different value with specific instructions. --Proficient 05:58, 15 September 2006 (UTC)

You should probably ask this at the computing reference desk. You might consider rephrasing the question as well; I don't know what you want as answer (we can give you the layman's version, or start discussing the details of system calls. The shutdown article might be helpful. --Robert Merkel 06:03, 15 September 2006 (UTC)

ppDDT and opDDT

ppDDT and opDDT are forms of DDT but what are they exactly? (Please add the info to the DDT article too) —Pengo ^{talk · contribs} 06:00, 15 September 2006 (UTC)

The "o" and "p" refer to the positions of the Cl atoms on the benzene rings relative to the position where the rings bond to the central carbon (the standard "ortho" and "para" substituent designations). I added a note about it to the DDT article. DMacks 06:25, 15 September 2006 (UTC)

The German Wikipedia article on DDT has an illustration showing the pp'-isomer (4,4'-DDT), the op'-isomer (2,4'-DDT), as well as the pp'-isomer of DDD (4,4'-DDD). ---Sluzzelin 06:36, 15 September 2006 (UTC)

diet coke.

Hi, I would like to know YOUR opinions on diet coke and its effect on health. Please dont just send me a link to the coke page or aspartame page! I drink about 1-2 litres a day every day. There seems to be one camp that saas its bad for you and one camp saying its as harmless as water. please dont quote the penny cleaning story either as our stomachs secrete hydrochloric acid anyway!!

Please help as Im very confused about this issue.

As you say, there are different opinions, no doubt here on the reference desk as anywhere else. If you've thoroughly read up on the subject you will have to decide for yourself. Personally, I wouldn't touch the stuff, but that's just because I don't like it. I don't think you can beat a good cup of tea. I start with three mugs of tea every morning, drink coffee in the afternoon, and fruit juice in the evening, or hot chocolate depending on the weather. There will be people who don't think that's a good regime either.--Shantavira 11:01, 15 September 2006 (UTC)

I could just tell you were English :). --liquidGhoul 12:28, 15 September 2006 (UTC)

Those artificial sweeteners are nasty chemicals, I would ban them. Or, if a neutral research firm had 1100 test subjects exposed to those chemicals daily, then studied them over the course of their lifetimes, and showed no increase in any major diseases over the control group, then I might accept them as safe. Short of that, I would drink something natural and known to be safe, not take my chances on those artificial chemical cocktails. StuRat 12:19, 15 September 2006 (UTC)

?? I can't believe you can say that. Aspertame is a harmless chemical to humans that passes right through the digestive tract and into the feces because the body does not know what to do with it but to think it tastes sweet. Actually I see now that there is an actual Aspartame controversy. — [Mac Davis](talk) (New! SUPERDESK|Help me improve)14:39, 15 September 2006 (UTC)

That article shows that it does not pass right thru the system, but is broken down into all sorts of nasty chemicals in the body, like formaldehyde. Even those who support using aspartame admit that these breakdown products exist, they just deny that they are harmful in those quantities. StuRat 23:56, 15 September 2006 (UTC)

As Shantavira said, there is differing opinion on the subject, and you seem to be quite well read on this topic. Irrespective of that, something to consider: yes, your stomach does produce acid. But it's also well known that increasing the acidity of your stomach contents does bad things for you (why do you think people take antiacid tablets?). Coke is moderately acid stuff, and if you're drinking 1-2 liters of the stuff a day it will make your stomach more acid. Do that continuously and you'll probably get heartburn and other ailments unless you have also taken a liking to bicarbonate of soda. Is that such a good idea? Baseline, if you want my (non-expert) opinion is that Coke is fine in reasonable quantities, but if I were you I'd cut down. Try fruit juices, or simply water (with a bit of flavouring, such as a bit of lemon juice, if the taste is too bland for you). Plus, you won't have to go to the bathroom so often (Coke is a strong laxative, as you've no doubt noticed) — QuantumEleven 13:04, 15 September 2006 (UTC)

and yet artifical sweetners are safer than natural orange juice. Xcomradex

(edit conflict) I don't want to get into a war about natural vs artificial, and I'm no expert on the subject, but that would surprise me greatly. Do you have any sources to back that up, XComradex? — QuantumEleven 13:25, 15 September 2006 (UTC)

Go by QuantumEleven's advice. I ised to drink coffee but stopped for some reason and switched(?) to plain water. Now I do enjoy just plain water. I do take a cup of coffee when it is too cold but otherwise it is just water for me. I really like it. Try it. -- Wikicheng 13:21, 15 September 2006 (UTC)

While I'm unsure of the health effects of drinking large amounts of diet soda, anything taken to excess is bad for you. I recommend drinking water. When I left home to go to college, I gave up soda, as I had sold my car, and soda took up too much space in my backpack when I rode back to my dorm from the grocery store. I started drinking Tang, and then later I started just drinking water. Since then I've lost thirty pounds and I've never been healthier. I would attribute the lost weight not just to the lack of soda, but from getting exercise by riding my bike. I also found that it was easy to drink water often if you have a Brita filter in the fridge. That way, you always open the door and are greeted by a container of cold water. Gary 15:05, 15 September 2006 (UTC)

I think aspartame has a relatively good track record, but 1-2 liters a day of anything that's not just plain-ol' water is probably a bad idea...moderation would be my advice. Of all the studies I've looked at, excessive aspartame = bad in certain model systems. (but who is surprised by that? show me a chemical given in high doses that doesn't cause negative effects...) It can't be bad for you to consume less aspartame, though, right? Try to limit your consumption a bit--if you can get down to a can a day (replacing some or all of the volume with water) you might reap the benefits of less caffeine, healthier teeth and a fatter wallet. -- Scientizzle 18:39, 15 September 2006 (UTC)

I knew someone about 50 yrs of age, drank a large bottle of coke every day, plus other sweet drinks. Ended up with diabetes.--Light current 19:48, 15 September 2006 (UTC)

1)The question was about diet coke, which would not affect sugar metabolism much; 2)Not much evidence that sugar consumption causes diabetes, other than it causing obesity which makes Type 2 diabetes more likely. 3)I believe constant consumption of diet coke can discolor your teeth and tends to etch away enamel. Carbonated beverages are also said to produce flatulence. Edison 23:55, 15 September 2006 (UTC)

How much sugar is in 2l of diet coke?--Light current 00:21, 16 September 2006 (UTC)

Apparently none Mattopaedia 08:49, 16 September 2006 (UTC)

Go read the label on a bottle, and multiply the grams of sugar per serving by the number of serving per container. StuRat 06:35, 16 September 2006 (UTC)

I dont touch the filthy stuff! Arrgh. Only pure amber nectar 4 me!--Light current 22:59, 16 September 2006 (UTC)

I can't believe no-one's come up with this yet. Most artificial sweeteners in soft drinks are derived from phenylalanine. It is metabolised, otherwise there would be no problem with phenylketonuric people consuming it. Thats what I know. This is my opinion: I've also heard that some people believe that it increases total body phospate somehow. If thats true, then it could possibly also lead to osteoporosis in the longer term (look up the physiology of calcium-phosphate regulation if you don't follow) - although I don't know if theres any studies around that lend any credible evidence to that. But as the others have said - you can't go too far wrong with good ol' water. Mattopaedia 08:49, 16 September 2006 (UTC)

Digital camera image size ratio

After some browsing of the relevant articles I couldn't find the answer to this, so I'm hoping one of the Ref Desk wizards can help me. Why is it that most (I think all except digital SLRs, but I could be wrong since I've never owned a digital SLR) digital cameras take images that have a size ratio of about 1.3 to 1, whereas film cameras (specifically, 35mm) take pictures that are about 1.5 to 1? This has gotten me into trouble several times when developing photos, as I have to remember if I have to develop them at 10x13cm or 10x15cm. Is there any reason for this discrepancy? Thanks! — QuantumEleven 11:15, 15 September 2006 (UTC)

I would guess that's so they will more closely match the common computer monitor aspect ratios:

640/480	=	1.33
800/600	=	1.33
1280/1024	=	1.25
1600/1200	=	1.33

This allows them to display on the entire computer screen, without distortion. StuRat 12:05, 15 September 2006 (UTC)

Aspect ratio of pictures etc

Tv started with an aspect ratio of 4:3 (ie 4 horiz x 3 vertical). I know not how this originated but it seems to have been perpetuated in computer monitors. Of course the new standard HDTV has a ratio of 16:9. Perhaps the old photographic plates were also 4:3?--Light current 18:36, 15 September 2006 (UTC)

I would think the golden ratio would be aesthetically best, perhaps everything should use that ? StuRat 23:27, 15 September 2006 (UTC)

Interestingly 16/9 = 1.7777777 which is fairly near the golden ratio! 8-)--Light current 23:42, 15 September 2006 (UTC)

I would kick the golden ratio's ass in a fight. That is all. Melchoir 04:43, 16 September 2006 (UTC)

What does that statement mean?--Light current 23:03, 16 September 2006 (UTC)

Academy ratio (1.375:1) was established for movies in 1928 and Academy ratio was essentially the only ratio used until 1952. This ratio was adopted for television and then monitors. For stills, 135 film was a cartridge format introduced in 1935 that has a 24 x 36 mm ratio (1.5:1). See film formats to be astonished by the wide range of film formats that have been in use since 1895. APS for instance is a still film format that is designed to accept all three aspect ratios (4:3, 3:2, 16:9). -- Fuzzyeric 05:06, 16 September 2006 (UTC)

Impregnating the female population of Europe

For some time it's been accepted that every man has enough sperm in a single ejaculation to impregnate all the women in Europe. What would be the consequences if one did. The practicalities of how are unimportant (as it's impossible), just assume its magic or sufficiently advanced technology. I know there would be major social & economc upheaval, litigation, divorces, etc but what I'm interested in is the long term evolution of the people of Europe. If all the women of childbearing age in Europe (I estimate female population of Europe to be around 355,000,000 & child bearing women to be half this at 177,500,00) were to get pregnant with the same man's child there would be a lot of duplication of genes across the population so how would this population develop (assuming that it isn't possible for all the children to breed with someone outside Europe) over the course of several generations? Would they develop into another species through the accumulation of certain genes or combinations of genes? AllanHainey 11:24, 15 September 2006 (UTC)

In the short term you'd see an increase in recessive genetic disorders. In the long term, the defective recessive genes would be largely removed from the gene pool. Of course, if the father was a particularly good genetic specimen, you would also dramatically improve the European gene pool, while, if he was a rather poor specimen, then you would seriously degrade the European gene pool. In any case, Europeans would be more homogenous (similar), as a result. StuRat 11:58, 15 September 2006 (UTC)

"Better" guys are usually more able to impreganate females than not as good guys. Same with females. — [Mac Davis](talk) (New! SUPERDESK|Help me improve)14:41, 15 September 2006 (UTC)

Whoa! Better source that...females impregnating females? ;) Durova 00:24, 16 September 2006 (UTC)

Actually, total scum are the best at impregnating large numbers of women, by promising them everything, impregnating them, then dumping them immediately and moving on. This has rather negative implications for the genetic future of the world. StuRat 17:10, 18 September 2006 (UTC)

Didn't Genghis Khan conduct this experiment? --Zeizmic 16:32, 15 September 2006 (UTC)

Not really. It's true that some percentage (5%? 20%? i can't be bothered looking it up) of people in the UK have Genghis's genes, but that number is more a matter of statistics than of his sexual prowess. That is, the same stat would be true of many other people who were alive at the time of Khan. Simple the DNA has diffused throughout the population. I could probably explain this better but it's 3am. As for the original question, yes, as mentioned there would be many recessive traits coming out as Europeans would have no one to breed with but their half-brothers and half-sisters unless they left Europe. These don't get bred out that quickly as that's the nature of resessive traits. It would be similar to the founder effect. —Pengo ^{talk · contribs} 17:26, 15 September 2006 (UTC)

If the single man was the bearer of any low-frequency alleles (which, statistically, any single person is likely to have a handful), you'd have a most profound disruption of genetic drift. As Stu pointed out, if any of those alleles are associated with autosomal recessive diseases, the overall incidence of such diseases would increase. If he's got an autosomal dominant condition, it could have even more drastic effects on the overall poplulation. Overall, though, there will be a dramatic increase in the frequency of each of his alleles in the general population.

Now, looking at future generations: the production of a roughly a 170 million half-siblings would lead to increased consanguinity in the production of future generations. This could potentially lead to something akin to a founder effect under the right circumstances (small rural areas of Europe, especially). A hundred generations later, our Don Juan's genetic effect would still be noticable, but probably mostly in isolated regions. With increased globalization, the effects of pseudo-random assortive mating would smooth out many of the negative consequences of a drastic decrease in genetic variability within the European population. -- Scientizzle 18:27, 15 September 2006 (UTC)

If the Great Impregnator were Prince Charles, the population of Europe would tend to have ears that stuck out a bit. There was a sci-fi story aboout a world where one man's dream was to have sex with all the women. He got his wish, and only he could father children. It got old after a whileEdison 23:58, 15 September 2006 (UTC)

It's been done a number of times in science fiction; the TV show Sliders had a variation on the topic. But you may well be thinking of Alfred Bester's short story 5,271,009. --Robert Merkel 11:10, 16 September 2006 (UTC)

msin i

I was wondering if someone might (gently) explain "msin i" as a formula for determining planetary mass boundaries. The only answer I've found is this but I'm still befuddled. The sentence it pertains to (that I'd like to unpack in an article): "Throughout the habitable zone around Barnard's star, i.e. 0.034-0.082 AU, we exclude planets with msin i> 7.5 mEarth and m> 3.1 mNeptune." Marskell 14:33, 15 September 2006 (UTC)

Looks like it's mass * sin(i), since the author mentions angle i. Clarityfiend 19:34, 15 September 2006 (UTC)

Ok, then. Any more explanatory answer welcome. Marskell 21:51, 15 September 2006 (UTC)

The article is describing the detection of extrasolar planets by "wobble". The magnitude of the wobble is proportional to the mass of the planet and the sine of the (edge on) angle of the orbit, called "iota" there. A better way to write your expression is "exclude planets with $m\sin(\iota )\ >\ 7.5\ m_{Earth}\$ and $m>3.1\ m_{Neptune}\$ ." This means that they're ignoring planets producing wobbles bigger than would be produced by a planet 7.5-times as heavy as the Earth in an orbit that was perpendicular to the line of sight to the planet and ignoring planets more than 3.1-times more massive than Neptune. -- Fuzzyeric 03:25, 16 September 2006 (UTC)

If a planet's orbit is perpendicular to the line of sight its detection is much more difficult, correct? If it's perfectly perpendicular there will be no red/blue shift at all relative to the observer and thus no radial velocity detection available (?). How, in this case, is the measurement for an orbit perpendicular to the line of sight so precise? I'm no doubt ass-backwards, but I'd expect the more precise boundary for a parallel orbit as this would create a maximal "wobble" to the observer. Marskell 05:57, 16 September 2006 (UTC)

You're right (your reference even says so in the first sentence). But I have a question for you: why does sin(i) appear only in one of the inequalities? Clarityfiend 18:42, 16 September 2006 (UTC)

The primary source [1] states "determine upper limits to the projected mass msin i and to the true mass". The second figure is true mass: no body >3.1 Neptunes, period. Marskell 09:32, 17 September 2006 (UTC)

Extrasolar planets describes both transverse wobble (photographically detected) and longitudinal wobble (Doppler shift detected). The article's abstract isn't sufficiently detailed to indicate which is being talked about. It would make as much sense using appropriate combinations of "orbit vector defined by displacement vector most parallel to line of sight", "orbit vector defined by angular momentum covector", "wobble measured photographically", "wobble measured spectrally". -- Fuzzyeric 21:46, 17 September 2006 (UTC)

Riiight. Marskell 21:02, 18 September 2006 (UTC)

Cystic Fibrosis

Can people in their 80s live with CF all there life without knowing it?

My 83 year old brother-in law has terminal CF, is at home and administered Hospice care. He never smoked, is a WW2 combat vetran, and was an avid walker till recently when, after short walks, he began labored breathing.

I have read most of Wikipedia articles concerning CF, but don't find any referance to late diagnosis, for the first time, of CF at his age , hence, my question.

Ghorine 15:16, 15 September 2006 (UTC)

Well, usually cystic fibrosis is diagnosed very early and, without dedicated treatment, is still largely fatal by young adulthood. The list of notable people with cystic fibrosis has some examples of folks that have lived relatively long and successful lives with CF.

If I were to hazard a guess here, perhaps the CF alleles your brother-in law possess are of the relatively healthier variety. There are effectively five classes of CFTR mutation (more info here) that range from defective protein production with premature termination of CFTR production to simply reduced overall synthesis of CFTR. A person's two alleles will combine to determine overall CFTR function and symptoms follow from there. There are also at least four known autosomal dominant alleles that confer relatively minor effects. Whatever the combination, maybe it took eighty years to do what often happens to children and teenagers with the most common mutations.

It is unusual to have such a late diagnosis, but there seems to be plenty of genetics info that would suggest it's not unlikely. Best of luck to your brother-in law. -- Scientizzle 18:07, 15 September 2006 (UTC)

While exceedingly uncommon, it's certainly possible to have mutations which are mild enough to give a mild disease which doesn't present until late in life. Some people have mutations with no pulmonary symptoms (such as those diagnosed after infertility evaluations). Maybe it occurs more often than we know and no one checks for it! InvictaHOG 22:44, 15 September 2006 (UTC)

mesotechnology

what exactly is the principle of mesotechnology?if i am to do a seminar on this topic from where can i achieve enough and more information regarding this technology? —Preceding unsigned comment added by 220.226.49.86 (talk • contribs)

Our article on Mesotechnology might be a good place to start. -- Plutortalkcontribs 16:25, 15 September 2006 (UTC)

vitamins and supplements

I would like to know if there is and honest/ethical source that does studies on the benefits of vitmins and supplements. I am looking at hsn right now and Andrew Lessman is giving some very interesting information on supplements... I would like to know if there is an support for the statements he is making and where a average person can look for an unbiased/ researched opinion... thanks

The problem, I think, is that there is really nowhere an "average person" can go look for unbiased research opinions. A lot of medical literature on the subject will have improtant confounding biases (which may not easily be observed) such as one or more of the authors receiving some benefit form a large vitamin company, for example. Advertising and advertorials are more about marketing than good scientific evidence. You can search public domain medical databases like pubmed if you like, but if you're not au fait with medical terminology and statistics what you find may be hard to interpret. Much of what I've read over the years in the medical literature about vitamin and mineral supplements suggests there is no evidence they are any more effective at improving health & well-being than placebo. This is for the average, well nourished, western civilisation adult. There is evidence to suggest vitamin supplementation is important in certain health conditions, such as Iron and vitamin C in anaemia, zinc and vitamin C for wound healing, thiamine to limit chemically induced brain damage, vitamine B6 for leg cramps in pregnancy. General supplementation is also believed to benefit chronically malnourished individuals such as those with anorexia nervosa. So if you're fit & well, eat fresh friut & veg, don't eat many processed foods or fast foods, don't smoke & don't drink too much alcohol, you are probably wasting your money buying supplements. And anything some guy on TV tells you that sounds too good to be true, probably is. By the way, don't forget to sign your posts. Mattopaedia 03:14, 16 September 2006 (UTC)

I take a vitamin and mineral supplement every day, so I'm biased. Vitamin D has been recently shown to reduce many cancer rates, as has selenium. British people are thought to be deficient in selenium since we not longer import bread-flours from selenium-rich areas of North America. But selenium can also be obtained in abundance by eating one brazil nut a day, and there is firm evidence that people who eat nuts regularly (unroasted, non-salted) live longer. I choose a pill that includes iodine, as I wonder I might be otherwise deficient, but iodine can be found in seafood. The bad and dangerous thing to do is to consume more than the recommended daily allowance (RDA), since some vitamins such as Vitamin D for example are dangerous at only a little above the RDA, or can result in deficiencies in other nutrients. Vitamin C in unnaturally high doses causes kidney damage. So stick to a pill with only the RDA or less in it. And pregant women or those seeking to become so, should seek medical advice, including regarding folic acid.

Seagulls and slightly past-the-date sausages?

I have a pack of sausages in my fridge that I didn't manage to eat by the expiry date and they have started to go slightly 'off' (turned greyish with a little bit of mold starting). Are they safe to feed to the seagulls like this (raw too)? I don't want to see food go to waste but I don't want to make the gulls sick either. --84.67.70.185 16:41, 15 September 2006 (UTC)

I'd cut off the moldy parts, then cook them, then give them to the seagulls. If that's too much trouble, just toss them in the garbage. StuRat 17:30, 15 September 2006 (UTC)

I'm pretty sure the sausages would eventually be eaten by something (perhaps seagulls, perhaps another animal or insect) even if you just toss it out. Maybe let the gulls decide if they want it (i.e. leave it outside on the ground or something). —AySz88\^-^ 18:27, 15 September 2006 (UTC)

I believe most food molds are carcinogenic, except presumably those in cheese. I remember reading a detailed article in the online Spiked magazine written by a professor who said that although mold may only appear on a small part of the fruit or vegetable, the carcinogens will have spread through most of it. I expect the same is true with sausages. I think it would be ethical to feed the sausages to gulls, as they won't live long enough to develop cancer. My guess is they may prefer them uncooked, as this is closer to their natural food, but who knows?

Recharging NiMH batteries

Hello. I have a set of NiMH batteries. I also have a charger that states: "Use only with nickel-cadmium batteries." I think that the charger is from before NiMH batteries were commonly commercially available here in the Netherlands. What is the risk if I try to recharge the NiMH batteries with this charger? Could they explode? :wimdw: 16:54, 15 September 2006 (UTC)

You'll wreck the batteries. If you're unlucky, the batteries will leak acid or catch fire. NiCd batteries are very durable when it comes to charging, while NiMH batteries aren't. --Serie 21:52, 15 September 2006 (UTC)

Thanks. :wimdw: 18:51, 16 September 2006 (UTC)

It relates to how the charger senses when to stop charging. One way that works for NiCd cells is to sense the rate of change of the cell voltage as a function of time (dv/dt). This voltage will increase as the battery charges (so dv/dt > 0), but when the battery is fully charged it will start to decrease (dv/dt < 0), and you can sense this and terminate the charge. NiMH cells still do this to a certain extent, but the effect is much smaller. An NiCd charger that looks at dv/dt might therefore overcharge an NiMH cell, which could destroy it, or at least shorten its life.

A lot depends on how much life you're expecting to get out of the set of NiMH batteries and how sophisticated your charger is. The warning probably refers to the idea that the charger is completely unsuitable for recharging primary batteries.

Now whether or not you could charge NiMHs is a somewhat different question. Very old NiCd chargers were not automated at all; you simply charged batteries for a certain number of hours and hoped a) they were "topped up" and b) if they ran "over the top", that the recombination catalyst within the cells was recombining the hydrogen and oxygen that was being evolved by electrolysis. The charge current was usually quite low (<= 1/10 C) so the power that was dissipated by a fully-charged cell wasn't very much. Such a charger could probably do about as good a job recharging NiMH cells as it did with NiCd cells (which was "okay" but not great and certainly not "automatic").

Automated chargers would run into the problems described above by other editors: the "terminal" (end-state) conditions for NiMH batteries are different from NiCd batteries. But it still might be possible to recharge NiMH cells if this is a conventional "slow" charger and you considered the charger to be manually operated and were careful to end that charge cycle after some calculated period of time. If you were to try this, monitoring the cell temperature sounds like a really good idea. I suspect it would be a very bad idea to try this with a "fast" NiCd charger as finding the "end moment" would be too tricky and the results of miscalculation too dangerous.

Atlant 01:12, 20 September 2006 (UTC)

Brille, plural

What's the correct plural of brille? (in the sense of the article).

It could be brille (no plural), brilles, or brillen (from German). I'm not sure which is correct in English, or if multiple are. Most mentions seem to avoid using a plural. —Pengo ^{talk · contribs} 17:10, 15 September 2006 (UTC)

From the use in the article ("All geckos except those in the subfamily Eublepharinae (eyelid geckos) possess brille."), the singular and plural appear to both be 'brille'. -- Plutortalkcontribs 17:15, 15 September 2006 (UTC)

Yeah but I wrote that —Pengo ^{talk · contribs} 17:18, 15 September 2006 (UTC)

The first hit I get for brilles (animals.about.com/od/b/g/brilles.htm) clearly uses it as the plural form. Clarityfiend 19:41, 15 September 2006 (UTC)

Global Warming: ice core question

I have a question about the ice core examinations and how increasing temperatures correlate to increased CO2. In years when the temperature and CO2 are high, doesn't the ice melt--loosing an important piece of the record? Wan't the temperature in the 13th century high enough to melt the ice even on the GISP2 site in Antartica? During interglacials, how can scientists distinguish between years of ice strata when the depth of the ice is unlikely to increase due to summer melting? Is geothermal heating an issue with the 800,000 year old ice core? I'm having trouble understanding the science. Thank you!

CCM

At most of the sites where cores are located it never gets warm enough to melt (or only very infrequently). Consider that Antarctica has been ice covered for 10s of millions of years, and a warm summer at Vostok Station is a balmy -30 C. At sites where melting does occur, the resulting melt layers are very easy to distinguish from ice formed by compacted snow. Geothermal heating can be an issue and is partially responsible for the formation of subglacial lakes, like Lake Vostok, but I don't believe it is an issue with the recent 800,000 year Dome C core. Dragons flight 17:38, 15 September 2006 (UTC)

In Earth's history, 800.000 years is nothing.That's less than one thousands of its age. And there have only been four major ice ages in the sense that the polar caps melted (wat is coloquially known as an ice age is really a glaciation). The present ice age started 40 million years ago. That's 50 times longer ago than the age of those cores. DirkvdM 07:10, 17 September 2006 (UTC)

Coins

I've been to a mall in the Northeast US where there were these trash can-shaped receptables that people were supposed to put coins into for charity. There was a small slot outside of the can you put the coin into that would align the coin, so that after it dropped out of the slot, it would rotate around and around the upper lid of the bin until it dropped into its hole in the center. Does anybody know if there is a special mathematical curve for this type of lid, and if I can easily make/obtain this as a scientific curio? Thanks, JianLi 22:22, 15 September 2006 (UTC)

I'm imagining a 3D spiral (something between a 2D spiral and a helix). As long as the slope is sufficient to overcome friction, excess slope would just accelerate the coin further. You would have to be rather generous on the slope, though, as the friction may vary quite a bit, depending on the size of the coin and how sticky it is. StuRat 23:21, 15 September 2006 (UTC)

It actually wasn't spiral. Rather, it was merely a curved surface. I think it's called a "coin vortex." Here are some pictures of it on Google [2]. There are references to a "hyperbolic tunnel," but I am skeptical that that is its actual shape. JianLi 01:11, 16 September 2006 (UTC)

Why are you skeptical that it's a hyperboloid ? I still think that the path the coin takes is a 3D spiral, however. StuRat 02:51, 16 September 2006 (UTC)

They're not just in the Northeast. We have them all over the U.S. And not just at malls, although that is likely where you'll find one. Charities often put them in public places because kids want to see coins go down them so they pester their parents for the coins. It gets more money than just setting a bucket up somewhere with a big sign that says "please give". Dismas|^(talk) 17:30, 16 September 2006 (UTC)

I'm not sure that it's a hyperboloid because the website that said it was hyperbolic was a commercial, rather than academic, website. So you think a hyperboloid would work? Could it be any other shape, or any type of hyperboloid? And yes, the path of the coin was spiral; I was just saying the shape of the curve was not spiral since it was a solid surface. JianLi 18:40, 16 September 2006 (UTC)

Of course it is a hyperboloid. In Michigan and Thai mallsI saw them everywhere. — [Mac Davis](talk) (New! SUPERDESK|Help me improve)18:46, 16 September 2006 (UTC)

momentum transfer and air molecules

I recently read two articles one was about acoustic levitation the other about a vortex ring cannon, the vortex ring cannon claims to use momentum tranfer to accelerate air at such speeds and concentration that it can knock a man down. i am wondering if this is how acoustic levitation works [sounds transfers momentum to air, air pushes object] and if there are other methods for producing momentum transfer on air molecules, and how is this different from levitations that transfer momemtum directly to the object?

Robin

Harr! Wasn't there a pirate song about such a phenomenon? Edison 00:00, 16 September 2006 (UTC)

blow the man down??? yea, but the question was does acoustic levitation produced pressure on objects because it is causing momentum transfer between air molecules , and the air pushes the object, Robin

The second reference at acoustic levitation suggests not. It's recoil to phonon radiation pressure, which is not a momentum transfer phenomenon (strictly) with the molecules. Of course, phonons are quasiparticles, so it's easy to ascribe the effect to the motion of the molecules when the form of energy is actually a collective mode. -- Fuzzyeric 03:45, 16 September 2006 (UTC)

So acoustic levitation is not the same as levitating something by superfocussed high intensity momentum transfer in air molecules. i dont think this method exists yet however, but it seems possible vortex rings focuss air enough to repulse even large objects. and apparently this is not acoustic in nature. What are the methods for producing momentum transfer in air molecules

Robin

A vortex-ring is more than just a ring, it also carries some surrounding air, and the whole blob is roughly spherical. The whole blob moves along. So if you could fill the whole thing with smoke, it would resemble a travelling sphere with a ring-shaped flow in its center. If you were struck by a fast-moving sphere of air, as with any other collision you'd absorb momentum. Perhaps it would help your understanding if you imagine the whole thing taking place under water. If you collide with a fast-moving ball of water while under water, it's not much different than colliding with a ball of ice while under water. --Wjbeaty 06:11, 17 September 2006 (UTC)

Best guess based on what definitions I can find of the terms in "superfocussed high intensity momentum transfer in air molecules" is no. Acoustic levitation is based on caoustic waves, which produced a zero expectation displacement in the participating air molecules. (They displace approximately sinusoidally, but they don't have a constantly increasing displacement.) The momentum transfer method is similar to directing a hose at the object -- the participating molecules have constantly increasing displacements (until they hit something in the way).

The momentum transfer method requires a constant supply of air to replace the air that's being jetted away. Acoustic levitation does not because no air is (net) pushed away. -- Fuzzyeric 22:00, 17 September 2006 (UTC)