Wikipedia:Reference desk/Archives/Science/2007 December 11

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December 11

How can I dilute perfume?

I have a small quantity of perfume, which I want to dilute. (I got a nifty bottle to put it in, but it doesn't fill it up.) Presumably just using water is a poor idea. I don't really have access to lab ethanol, which would be my first choice; the isopropanol they sell in the store is thirty percent water by volume. Do I need to go to a lab? Should I get a bottle of Everclear? grendel|khan 04:23, 11 December 2007 (UTC)

Perfume#Concentration_levels says ethanol or ethanol and water or jojoba, fractionated coconut oil or wax. The precise percentages for various kinds of perfume are listed there too. SteveBaker (talk) 04:34, 11 December 2007 (UTC)

I'm not sure I'd want to use isopropanol, but if one did want to use it, one can get pretty-much anhydrous isopropanol in the form of gas dryer, sold at your local auto parts store. Be sure to get the iso kind and not the methanol kind. Our article claims Dry gas brand actually is ethanol, but I've never confirmed that, and who knows what denaturing agents have been added?

Atlant (talk) 13:35, 11 December 2007 (UTC)

How about Vodka? That ought to be pretty close to ethanol+water - and the cheap stuff doesn't smell of much. SteveBaker (talk) 14:10, 11 December 2007 (UTC)

I would caution against using isopropanol. For me, at least, isopropanol (even lab-grade pure stuff) has a very distinctive, pungent smell - it may make the perfume smell "off". (Although how long it would take for the isopropanol smell to dissipate after application, I don't know.) Whatever you do, don't use n-propanol or butanol - a colleague of mine got sick everytime she smelled n-propanol. -- 18:44, 11 December 2007 (UTC) —Preceding unsigned comment added by 128.104.112.64 (talk)

Well, you could try to use methyl acetate, it has no smell at all, so i'm sure it will work.

Assuming you are going to use the perfume why dilute it? You'll only empty the bottle using it leaving you in the same situation. Also it may be stating the obious but the best thing to use is more of the same perfume. However you if it is expensive I can see why this is not an option. Thomashauk (talk) 22:04, 11 December 2007 (UTC)

Magical keycard

The door to my old lab was unlocked by waving a keycard in front of what I could only describe as an anonymous blue box with an LED to let you know your card worked. The keycard itself was a flimsy little piece of plastic with a barcode printed on it. There didn't seem to be anything on the card scanner other than the LED, and certainly nothing that resembled a typical barcode scanner. So how does it work? Someguy1221 (talk) 11:58, 11 December 2007 (UTC)

The card probably contained an RFID chip. -- Coneslayer (talk) 12:09, 11 December 2007 (UTC)

Yes. For simple systems the chip just reports a number (the number printed on the barcode); for more advanced (and secure) systems the chip has some brains and does a proper cryptographic challenge-response exchange with the reader (this is more secure because it prevents card cloning and replay attacks). The reader is mostly a dumb radio-relay box which relays between the RFID and a PC somewhere in the building (over a wiring system like ethernet or LonWorks). -- Finlay McWalter | Talk 12:17, 11 December 2007 (UTC)

Yes, the badge you're describing is almost-certainly an RFID-based badge. But for completeness, I'll note that an earlier system (e.g., the "NCS" card) used a badge that you slid through a reader; I'm pretty certain this used Wiegand wires. You may also want to see our Access badge, Common Access Card, ID Card, Keycard, Proximity card, Swipe card, and Wiegand interface articles. (Maybe we need to do some merging?)

Atlant (talk) 13:42, 11 December 2007 (UTC)

I used a friend's RFID reader to try to see whether the keycards we use at work use RFID - and it didn't produce a response - so I doubt they are standard RFID chips. SteveBaker (talk) 14:07, 11 December 2007 (UTC)

What's a "standard RFID" chip? This stuff isn't all that well standardised yet; you might do better with a signal generator and a spectrum analyzer.

Atlant (talk) 17:42, 11 December 2007 (UTC)

Biology Mark Scheme

Can anyone tell me where the mark scheme for the 2006 January, Biology 2801 AS mark Scheme (OCR) is? and why it can't be found?

Thanks —Preceding unsigned comment added by 213.106.248.77 (talk) 12:34, 11 December 2007 (UTC)

I can add only that this user is talking about AS levels in the United Kingdom (I think). Don't know where you find the "mark scheme" (do you mean the full course specification or the coursework mark scheme?). We had it provided by our teachers. --Seans Potato Business 12:44, 11 December 2007 (UTC)

My guess would be that they're doing a past paper from last January to help revise, and they'd like the mark scheme to check their answers (and possibly improve their knowledge of how the questions are marked). Skittle (talk) 17:13, 11 December 2007 (UTC)

I guess you're right (my eyes skipped over January). We got those from our teachers, too... --Seans Potato Business 17:37, 11 December 2007 (UTC)

Hollow Earth theory and why we can't drill deeper than 15 miles into earth

Sorry if this has been asked before, but even if it has it's good to review...
I've read the article Hollow Earth and it mentions that the deepest that man has dug into the earth is 15 miles. Why haven't we or why can't we drill deeper? And I take it this is 15 miles below sea level.
Secondly the article fails to explain exactly why we can dispel the idea that the earth might be hollow or have deep cavernous enclaves where it may be possible to survive. As an encyclopedia I think it should, encyclopedically expound on why modern science can so easily rule out any such possibility.
What's also interesting is that surely satelites and other technology could relatively easily check for openings at the poles.
And finally, why does the wikiword digging resolve to Death of a Naturalist? Surely we have an article on digging? Found it: excavation. But still.
Thanks Rfwoolf (talk) 13:33, 11 December 2007 (UTC)

OT, but... I changed the redirect to Excavation. What links here doesn't support the redirect to Death of a Naturalist. --Elliskev 13:52, 11 December 2007 (UTC)

The article Mohole may be of interest. DuncanHill (talk) 13:36, 11 December 2007 (UTC)

I would guess that the propagation characteristics of seismic waves (from earthquakes and/or nuclear bomb tests) and the precise mapping of the earth's gravitational field would help to rule out hollow earth theories. -- Coneslayer (talk) 13:38, 11 December 2007 (UTC)

(ec)We can be confident that the Earth does not contain significant voids by observing the propagation of seismic waves - places of different density cause the wave to refract and diffract. By observing this we've obtained a reasonable (to a first order) approximation of the structure of the Earth. That's a crude tool, so we can't entirely rule out their being small voids, but there's no evidence of them. You'll see stuff like this, which talk about an "ocean" under China - but they're being somewhat poetic in calling it that - it's "big area of wet rock" really: the researcher is quoted in that article saysing "It would still look like solid rock ... You would have to put it in the lab to find the water in it." -- Finlay McWalter | Talk 13:45, 11 December 2007 (UTC)

But if the Earth isn't hollow, then where do those weird glowing guys from the Adventures of Superman come from?

Atlant (talk) 13:52, 11 December 2007 (UTC)

Lots of reasons:

1. Certainly we can time the arrival of seismic waves from a distant event as they arrive at different seismographs around the world. We can tell from when they arrive and how attenuated they are the speed and distance travelled. This means we can know for sure that the waves didn't travel around the surface of the earth in a thin shell but instead took a short cut through the center of the earth. From the way they are attenuated and diffracted, we can tell the density of the material through which they travelled - and therefore that they didn't travel through a few thousand miles of air (or whatever the hollow earth is supposed to be filled with). It's completely conclusive proof that the earth is solid with a molten iron core.
2. Think about what it would take to prevent rocks on the inside of the sphere from falling off and accumulating at the center of the earth...gradually filling in the middle and eventually resulting in total collapse to a much smaller planet.
3. We've figured out that the earth/moon system was formed from collision of two smaller planets early in earth's history. There is no reasonable model for how anything hollow could arise from such a thing.
4. In order for the earth to have as much gravity as the earth actually does have, it either has to be solid - or somewhere below the surface there would have to be a layer of extremely dense material - much denser than any material we know of - except perhaps neutron-star material - and that wouldn't be able to hold together under as little gravity as the earth actually has.
5. If there were no large mass of spinning iron at the center of the earth, how would we explain the earth's magnetic field?
6. Where does all the lava come from when a volcano erupts?

So this lame-assed theory is busted, busted, busted and busted! It's hard to imagine how anyone could ever have thought it was true.

Drilling that deep is tough because the amount of friction on the walls of the drill tube gets larger and larger the deeper you go and eventually, the top end of the tube can't transmit that much power without crumpling. Conventional drilling gear can't go that deep - so you need entirely custom built gear - it's not cheap and research dollars are limited! Of course we don't have to drill down there to understand what's going on that deep. We have these (slightly inconvenient) things called volcanoes that provide us with plenty of material from deeper than 15 miles that we can study.

SteveBaker (talk) 14:02, 11 December 2007 (UTC)

Interesting. Obviously there's magma if you go deep enough.. 64.236.121.129 (talk) 14:07, 11 December 2007 (UTC)

No, magma (i.e. liquid rock) forms at high temperatures and low pressures. At high temperatures and high pressures, rock is a plastic solid (think modeling clay or cheese). It will deform over time as a result of stress, but nearly all of the Earth's crust and mantle is a solid. Dragons flight (talk) 14:24, 11 December 2007 (UTC)

The article on Magma says that it can be found beneath the earth's crust. If you drill deep enough, logically, you'll come across it. Especially if you hit a Magma chamber. 64.236.121.129 (talk) 14:48, 11 December 2007 (UTC)

No, nearly all magma forms at local hot spots within a few km of the surface, i.e. hot and relatively low pressure. The bulk is solid and at many locations drilling straight down need never encounter magma. Dragons flight (talk) 14:51, 11 December 2007 (UTC)

No offense, but the article says magma can be found beneath the earth's crust, and I trust that over you. 64.236.121.129 (talk) 16:10, 11 December 2007 (UTC)

They're both right. The earth's crust is very thin in places. Friday (talk) 16:15, 11 December 2007 (UTC)

The article does not imply that magma is present everywhere beneath the earth's crust, and it certainly is not. Dragons flight is correct. Cheers Geologyguy (talk) 16:19, 11 December 2007 (UTC)

The mantle is a rheid, a form of viscous solid. I've clarified this in magma. Magma is molten rock found beneath the Earth surface, but it is certainly not the case that molten rock occurs everywhere under the crust or even in most places. Dragons flight (talk) 16:28, 11 December 2007 (UTC)

Thanks for the answers SteveBaker and all, but I'd still like them to dig mega-deep. What for? For the hell of it, I don't know. I did come across Chikyu Hakken which seems to be the latest attempt to drill deep - but doesn't even intend to beat the record. I mean, 12 miles, that's not even that deep! Furthermore, some of the theories (crackpost or otherwise) don't propose an entirely hollow earth, just "hollow parts". I suppose cosmologically they know how the earth was formed and they ruled out any hollowness up to a certain point. But maybe not Rfwoolf (talk) 14:29, 11 December 2007 (UTC)

"For the hell of it" is not usually persuasive to people for sponsoring extremely expensive scientific endeavors. Anyway, you're arguing a sort of "hollow earth of the gaps" now, retreating to anything that you don't think for sure has been discounted. In the end you're going to be arguing that caves are really all the hollow earth people really mean! --24.147.86.187 (talk) 15:46, 11 December 2007 (UTC)

"you're arguing a sort of 'hollow earth of the graps' now" - I am not arguing anything. Please read the question, and I originally asked "deep cavernous enclaves". If you have no interest in hypothetical, philosophical or scientific questions then you won't appreciate most of the questions on the reference desk. You'll also notice that "for the hell of it" has a pun. Tee hee Rfwoolf (talk) 20:54, 11 December 2007 (UTC)

A solid earth with "hollow parts" would mean...caves? Well, yes - there are caves - I've even been inside some of them. Does that count as a "hollow earth"? If so, it's a rather less exciting thing than I'd imagined! Of course beyond a certain depth, you can't even have caves because the air inside would start to act like a bubble that would float upwards...and beyond an even deeper depth, the air inside would liquify under the pressure - so no more caves beyond that. (I love "hollow earth of the gaps" btw, very poetic!) SteveBaker (talk) 18:21, 11 December 2007 (UTC)

I think the closest we'll get to a hollow earth is a hypothetical dyson sphere.

Actually, the hole by Chikyu Hakken aims to be 7 km (4.3 mi) deep (although they're already starting below sea level). The Kola Superdeep Borehole in Russia was and is the biggest at 12.2 km (7.6 mi) -- MacAddct  1984 ^{(talk • contribs)} 16:32, 11 December 2007 (UTC)

But Dyson spheres can't work - for precisely the same reason that hollow planets can't. Even if you spin them really fast - there is no way to stop them collapsing in on themselves as a result of their own gravitation. SteveBaker (talk) 18:21, 11 December 2007 (UTC)

While there are lots of problems with constructing a Dyson sphere or hollow planet, I don't think rigidity against self-gravity is one of them. An Earth-sized metal shell 3m thick would have only a few millionths the mass of the actual planet. Given that, I think traditional construction materials/methods have enough structural rigidity to resist the much reduced gravity. Dragons flight (talk) 18:40, 11 December 2007 (UTC)

A Dyson sphere is meant to enclose a star (like the sun), so it should be (about) the size of the earth's orbit, not just the size of the earth. -- Coneslayer (talk) 19:00, 11 December 2007 (UTC)

I know, hence the "or" above. Since the questions is about hollow planets, I focused there. Dragons flight (talk) 19:05, 11 December 2007 (UTC)

So if we had a 3cm thick shell the size of the earth - and we spin it so that the equator was supported by centrifugal force against the rather feeble gravity. You could imagine the problem as having two self-supporting hemispheres - each 6300 km in diameter - each supported against their weight in this new, low gravity. The volume of this new earth (assuming the interior is filled with a vacuum) is only about 1.5x10¹³ cubic meters - and if it were made of steel (with a density of 8000kg/m³), it would weigh about 1.2x10¹⁷ kg. The real earth weighs 6x10²⁴kg - so gravity is about five-millionths of a g. So the question is - can an uninterrupted 12 thousand kilometer span of 3cm thick steel support a weight of about 3 million kilograms? Around the equator, you'd have a cross-sectional area of about a million square meters - so I guess there is only about 3kg per square meter of pressure on our shell...so yeah - I guess it might hold up. The trouble is that we know our shell is at least 15km thick because we've drilled down that far. That makes the gravitational forces 500,000 times greater - so we have a more respectible 1/10th g of gravity and each square meter of crust at the equator has to withstand 1.5 million kilograms per square meter of pressure - and the whole thing collapses like a popped balloon. SteveBaker (talk) 06:24, 12 December 2007 (UTC)

I had the pleasure of speaking with a somewhat crazy planetary scientist a few weeks ago (David J. Stevenson), who explained to me that once you have a really deep well to near the mantle, drilling further is very easy. All you have to do is pour several million tons of molten lead into the well, and it will just push its way down through the mantle and into the core, making a nice lead filled well the whole way down (allegedly this wouldn't cost more than the GDP of the United States for one year, so let's do it!). Of course, then you need equipment or probes that can operate in and transmit back from a liquid lead environment, but that's an "engineering problem" so who cares (or use acoustic waves, as in his original proposal which I just found). Someguy1221 (talk) 21:59, 11 December 2007 (UTC)

Just for fun I submit for your horror and

analysis, part of a film that scared the

"holly bejesus" out of me as a kid thinking

about deep holes and what's in 'em:

Rod Serling's "Encounter with the Unknown Part I

Rod Serling's "Encounter with the Unknown Part II

Rod Serling's "Encounter with the Unknown Part III

Saudade7 23:10, 11 December 2007 (UTC)

Not wishing to be mean, but is that film-on-youtube out of copyright? Has it been put up there by the copyright holder? Skittle (talk) 16:42, 13 December 2007 (UTC)

In answer to the poster who asked why we should even bother drilling deep into the Earth, I think the answer is obvious: To see whether the centre is nutty or chewy. Myles325a (talk) 23:46, 17 December 2007 (UTC)

What species of Lotus Flower is this?

What kind of Lotus is this that Salome is holding in her hand? Thanks in Advance. Saudade7 14:21, 11 December 2007 (UTC)

It doesn't look like a lotus at all. It looks like some kind of lily and may simply be from the imagination of the artist. In any case there is not enough detail in the image you have linked. "Lotus" in English refers to Nelumbo nucifera, which is usually pink, although there are white varieties. The only other species of lotus is the American yellow lotus, Nelumbo lutea. Why do you think it is a lotus?--Eriastrum (talk) 18:59, 11 December 2007 (UTC)

Hey, sorry that image was so bad, it is the only one online. It is claimed to be a lotus but all the critics who have written on the painting by Moreau who mention the flower (1880s to present). Many claim it to be an Egyptian or Indian lotus. I looked at all the lotus pictures I could, and when I could find none that matched I came here. It doesn't matter now. It was for an article that I just submitted sans-flower reference, alas. Thanks though Eriastrum! Saudade7 22:52, 11 December 2007 (UTC)

Enzyme Turnover

This is from a biochem test I am studying for. The original question was longer and I am paraphrasing so you arent doing my homework, just helping me double check my answer and logic. In an enzyme with 4 subunits with its unit of activity(amount enzyme hydrolyzes) being 4 micromoles of ester/minute and Vmax is 1400 units per mg of enzyme. What are the moles of substrate hydrolyzed per second per mg of enzyme at saturating substrate levels. Then determine the turnover rate for this enzyme. Saturing substrate levels implies we are using the Vmax which is a rate of turnover. Product/second. The 4 subunit also implies we are dividing the units of activity by 4. Could someone please connect the dots for me?68.41.111.119 (talk) 16:00, 11 December 2007 (UTC)

Just a hint - look at the units of what you have and what you want, and then puzzle it out with something like the factor-label method (or dimensional analysis). (Be careful to make the distinction between things like "micromoles of product" and "micromoles of protein".) -- 18:53, 11 December 2007 (UTC) —Preceding unsigned comment added by 128.104.112.64 (talk)

Can blackholes produce antimatter?

^Topic 64.236.121.129 (talk) 16:07, 11 December 2007 (UTC)

If Hawking radiation occurs, then either of a particle-antiparticle pair can escape a black hole. I'm not sure if this is what you've got in mind when you say "produce", though. — Lomn 16:29, 11 December 2007 (UTC)

Yes, that counts. 64.236.121.129 (talk) 17:09, 11 December 2007 (UTC)

Christmas trees

How many needles are on the average 8 foot tall blue spruce Christmas tree208.54.7.184 (talk) 16:45, 11 December 2007 (UTC)

Assuming the needles on a Christmas tree are close to the surface the number of needles will be approximately proportional to the area of a cone of the same size (dicounting the bottom). Just count the number of needles in a unit square and multiply by the are and that will be close enough.

More accurate would be to consider the volume in which there are needles which will be the volume of a cone the same size of the tree - the volume of the cone in which there are not needles multiplied by the number of needles per unit volume.

Finding all this is an exercise for the reader. Thomashauk (talk) 21:51, 11 December 2007 (UTC)

I don't know about your Christmas tree, but the ones I've seen are not anything close to "a cone surface of needles". Instead there are lots of concave regions that seem to have at least as much surface as the full-tree cone. That is, it looks like it has deep pockets, where the sides of the pockets (the "depth" dimension) is larger than the bottom (the cross-section parallel to the tree cone). Fractal surfaces are fun. DMacks (talk) 03:01, 12 December 2007 (UTC)

It's much more likely to be proportional to the volume of a cone. But unless someone is going to actually go and count the number of needles on (say) a 10cm section of branch - then figure out the average total branch length within a particular volume - then go on to figure the volume of an 8 foot tree - we aren't likely to be able to figure this out. Knowing what the answer is proportional to is really not too relevent at this stage! Since our tree at home is plastic...that's not really good research material!

Well, let's shoot for some sort of a number at least. On the basis of the detailed photo at right, there appears to be about 200 needles on one 15cm length of branch. So lets go with 13 needles per centimeter of branch. Estimating the branch length per unit volume is tougher without an actual tree to measure - but on the very rough basis of the second photo at right, I'd say that there is probably about 5 branches going through every 10cm x 10cm x 10cm cube of tree volume - which is half a meter of branch length per liter of tree. Which gives us about 0.6 million needles per cubic meter. The cone of this tree appears to have a diameter roughly equal to it's height - but I doubt that's true for an 8' tree - so I'm going to arbitarily guess that our 8' tree is really 2 meters tall (the bottom part doesn't have any branches) with a base radius of maybe 0.75 meters. The volume of a cone is pi.h.r²/3 which means that we have about 1.2 cubic meters of branches...about three quarters of million needles altogether. There are some horrible guesstimates along the way to this number - so I'm going to stick a healthy error bar on that and say "Anywhere between 200,000 and 2 million needles depending on the species and how many there are on your living room carpet.". Feel free to shoot down that number - but until someone actually goes and measures a real tree for us, that's the best answer you're going to get. SteveBaker (talk) 05:50, 12 December 2007 (UTC)

Eat it! Fruit rinds

I would like to know if there's a pleasant, healthy way to acquire the nutrition present in orange rinds that would otherwise go to waste. Candying them seems neither healthy nor efficient (wasted sugar, unless you can keep it somewhere for later reuse) while making tea from them includes all the fun of the pesticides. Is the best option to boil (to cleanse) them and then eat them after that? --Seans Potato Business 17:33, 11 December 2007 (UTC)

How about use them as compost to grow something else that you can then eat? Personally that seems a lot easier than trying to find ways to eat something which is not terribly good tasting. --24.147.86.187 (talk) 19:07, 11 December 2007 (UTC)

I just did a cursory search of our medical journals to see if there is anything on using orange peels in human diets. All that came up was a few studies on using orange peels to remove cadmium ions from aqueous solutions. I have to assume that by "orange peels" it is referring to the rind of the fruit we call an orange and not some weird medical term for some sort of lab device. So, if you have a lot of aqueous solutions polluted with cadmium ions, you can use your orange peels to remove them. -- kainaw™ 19:14, 11 December 2007 (UTC)

Well orange peel is used to make orange zest, marmalade, orange oil and pectin. You can eat these if sufficiently diluted. Would you rather extract the protein and vitamins? Graeme Bartlett (talk) 20:11, 11 December 2007 (UTC)

And underneath the thin zest is the white "pith", which is bitter and unpleasant to eat. -- Coneslayer (talk) 20:26, 11 December 2007 (UTC)

But full of nutrients, I hear. --Seans Potato Business 20:30, 11 December 2007 (UTC)

From which sources? I hear such claims all too often... Icek (talk) 22:38, 11 December 2007 (UTC)

Sources? Well, let's start with Wikipedia to begin with. The white pith that lies between the outer rind and inner fruit of oranges contains massive amounts of the bioflavonoids hesperidin, quercetin, rutin (a glycoside of quercetin), and tangeritin. Bioflavonoids have been clinically proven to be very important for many reasons, including the treatment of allergens, viruses, and carcinogens, and in the prevention of heart disease and cancer. They also greatly help the human body assimilate vitamin C, so that if you eat an orange and strip off all the pith, you will be impeding your body's ability to utilize all of the vitamin C that is in the rest of the fruit. This is why it is better to drink orange juice that contains pulp - without the pulp the orange juice is more or less just flavored, sweetened water, as far as the dietary benefits it can give you. The pulp (or pith) is what allows your body to absorb the vitamin C in the juice. -- Saukkomies 14:09, 12 December 2007 (UTC)

Yes, I ask for sources, not additional claims. And by the way, ascorbic acid is absorbed equally well whether it is in oranges, in orange juice or in pure form. Icek (talk) 22:49, 12 December 2007 (UTC)

(resetting margin)Well, Icek, it appears we're in the game of trumping each other's ace. I looked at the full text of the citation you gave for The Journal of Nutrition article published in 1993, which being 14 years old is sort of pushing the envelope in a field such as nutritional science, but hey, I'm impressed frankly that someone came up with even that! So my hat's off to you, friend! So yes, I realized I was guilty of posting a claim without supportive evidence, and it comes to mind that I should know better than that, but hey, sometimes I walk into walls and put my shirt on inside out, and well, sorry about that. So to rectify my lack of sense, I dug around a bit and came up with an article from The Journal of Biological Chemistry, dated 2002 that directly addresses the issue.

So to compare what we've come up with so far, you asked to see sources for the claim that Seans made about orange rind pith being full of nutrients. I believe I addressed this by providing several sources in my post above, most notably a wiki article that discusses this. I then made a claim about how the bioflavonoids in orange rind pith aid the absorption of vitamin C in the human body, but did not provide sources. You then apparently neglected to notice that I provided sources, but in your frank manner pointed out that I'd neglected to source my own new claim. I then went out and found a source that discusses this, and to my surprise I discover that the study that this article discusses actually demonstrates that both of our claims are false! Namely, that bioflavonoids do indeed have an effect on the absorption of vitamin c (ascorbic acid) which contradicts the article you cited, but then it goes on to show that this effect is actually contrary to what I was claiming - that bioflavonoids actually inhibit the absorption of ascorbic acid! So we're both busted!

Allow me to present some brief excerpts (which since they are merely short quotes are supported by copyright law to include here) that provide the main thesis of each of our articles regarding this subject. Note that when I insert space in the quote (by using three dots ...), that I'm only cutting out references to other articles or studies, not content. First from the article you cited from The Journal of Nutrition:

"Early reports have suggested little difference in ascorbic acid bioavailability from fruits or vegetables compared with synthetic ascorbic acid...Small numbers of subjects and insensitive techniques may, however, have obscured differences in these studies. Although few studies have assessed the impact of such factors as the fiber or mineral content of a meal or the presence or absence of other substances including bioflavonoids...on vitamin C absorption in vivo, the bioavailability of other substances, such as carotenoids, does seem to be affected by dietary factors."

So what this article is saying is that --- they don't know. If you go back and examine it, you'll pick that up in the article. It does say that ascorbic acid seems to be absorbed equally well whether it's being ingested in oranges, orange juice or in pure form, which is what you said, but they then go on to state that not enough studies have been done - not enough data have been gathered as of the date of that article (1993) to firmly state whether the presence of bioflanonoids has an effect on the absorption of ascorbic acid. To report that this article firmly states that ascorbic acid is NOT effected by the presence of bioflavonoids would, therefore, be inaccurate.

Now for my article, which appeared 9 years after yours in The Journal of Biological Chemistry. Here's the citation. It's entitled "Flavonoid inhibition of sodium-dependent vitamin C transporter 1 (SVCT1) and glucose transporter isoform 2 (GLUT2), intestinal transporters for vitamin C and Glucose." Here's the excerpt:

"We propose that novel functions of flavonoids may be to distribute nutrient absorption throughout the small intestine or to frankly inhibit absorption. Flavonoids in vivo might possibly delay or inhibit ascorbate and glucose absorption by more than one pathway... The data in this paper suggest that flavonoids could inhibit transport of ascorbate and glucose from the intestinal lumen into cells."

Not to put all my eggs in one basket, I went ahead and dug around some more, and came up with the following article in The Journal of Nutrition appearing in May of 2000 that supports the same claim as the one I cited above that bioflavonoids suppress the absorption of ascorbic acid.

In my digging, I came across numerous articles that provided hard substantial evidence showing that bioflavonoids (again, that are found a lot in orange pith) have incredible benefits for all manner of things. Thus, at least we can state with some authority that eating orange rind pith is good for you... Saukkomies 23:34, 12 December 2007 (UTC)

Thank you for the interesting and informative answer. What I dispute is not that the flavonoids are contained in the white pith, but that they are nutrients - they do not seem to be essential for human survival. Seans' claim that the pith is "full of nutrients" is misleading. Sugar is "full of nutrients" (about 100%); in comparison, white orange pith is devoid of nutrients. Of course Seans probably wanted to say something different, but I don't know exactly what.

Showing that some flavonoids from the pith are beneficial in some circumstances (if you were digging for something else, I guess you didn't read these articles very carefully; neither did I, but I'm hesitant to conclude too much only because there is a large amount of studies without knowing about their quality and exact nature) does not show that the pith itself is beneficial; it may contain harmful substances as well. What causes its bitter taste? Natural poisonous substances are (for obvious evolutionary reasons) often bitter, but of course that doesn't prove anything. Icek (talk) 07:45, 13 December 2007 (UTC)

We're on the same field now I think, Icek. Thanks for the discussion. I do think that not everything that has a bitter taste is necessarily harmful. Take for instance chocolate, which in its pure form is extremely bitter, as is the coffee bean, white willow bark (where they get aspirin from), tea leaves, dandelion leaves (which have a lot of beneficial ingredients in them and are good in salads), etc. Saukkomies 10:36, 13 December 2007 (UTC)

Yes, but I would be more cautious when saying that something is "good for you". The white pulp is usually not eaten, and that may also explain the apparent discrepancy between "my" ascorbic acid study and "your" ascorbic acid studies. By the way, I don't think that my study being older makes it necessarily worse, as the measurement of ascorbic acid plasma levels is a relatively straightforward procedure and I don't think that they are that much better at doing it now than 14 years ago.

Considering bitter substances: Interestingly, cocoa is relatively poisonous for some other mammals like dogs (see the Wikipedia article on theobromine, the main cocoa alkaloid). Icek (talk) 02:47, 14 December 2007 (UTC)

Certified organic oranges shouldn't have any pesticide on them. Also, try throwing some orange zest into a stirfry. Vranak (talk) 20:38, 11 December 2007 (UTC)

Just FYI, citrus fruits are often (in addition to being treated with pesticides while on the tree) treated with a certain wax after harvest to prevent mold from growing. I often see the label saying that the wax contains 2-Phenylphenol, thiabendazole and imazalil. Icek (talk) 22:36, 11 December 2007 (UTC)

Gravitational effect of an ellipsoid

I want to create a simulation of how satellites orbit around earth. I've done this in the past with perfectly uniform spheres or spheres consisting of concentric regions of varying density as both of these can be approximated by a point mass (assume Newtonian mechanics). I do this numerically by taking very small time steps and adding an acceleration on the satellite which resulted from the gravity at its current location.

I know that earth is not a perfect sphere and there are some good Reference ellipsoids. First, do these only offer an approximation for the shape of earth's surface or are they also usable approximations for orbital calculations? Secondly, is there an analytical solution or even a good numerical one for calculating acceleration at a 3D coordinate relative to such an ellipsoid? I'm guessing they can't as easily be reduced as a sphere to something elementary.

Why I'm so interested in the ellipsoid approximation is to see if I can simulate (for fun) the effects of orbital precession. It might be that I need to use an even more complex geoid approximation or relativity but I'm hoping not as I only have a moderately powerful CPU. 41.243.33.25 (talk) 20:04, 11 December 2007 (UTC) Eon Zuurmond

It depends on the orbit, for an orbit around the equator there would be no difference, for other orbits however I am unsure.

But there have been several investigations into this (as you would imagine) and it seems that the local gravity is more important which is caused by differing decities of material in different parts of the earth not just in concentric regions. Thomashauk (talk) 21:57, 11 December 2007 (UTC)

The technical approach is to use a multipole expansion to describe the gravitational potential function to high accuracy from which one can then extract the relevant forces as the gradient of that potential. The low order terms in the multipole can be thought of as ellipsoidal corrections, and subsequent terms build in every more detailed structure. The relevant multipole coefficients have been measured to high accuracy and tables exists somewhere (NASA?). If you are interested in this approach, I'd suggest you google "multipole gravity", etc. Dragons flight (talk) 22:03, 11 December 2007 (UTC)

According to my satellite geodesy text, the derivatives from the multipole expansion are then substituted into the Lagrange perturbation equations, and integration would yield time dependent functions for the Keplerian elements. It's possible to do analytically, but "extremely laborious". The numeric methods are more accurate anyway as the analytic method uses truncated series expansions. Your simulation should result in not only precession, but rotation of the apsides in eccentric orbits.—eric 01:21, 12 December 2007 (UTC)

Cold Chill or Holy Shiver

I have been working on an article for Cold chill and was wondering if anyone could explain the physiology behind music or memories and such causing cold chills. --DatDoo (talk) 22:56, 11 December 2007 (UTC)

Sounds like an example of synesthesia. I would say this is just a miswiring of the brain such that one sense is misinterpreted as another (in this case music is interpreted as cold). StuRat (talk) 04:50, 12 December 2007 (UTC)

Do you know where I might get some sources on that?--DatDoo (talk) 05:11, 12 December 2007 (UTC)

See the further reading, references and external links sections for that article. StuRat (talk) 11:03, 12 December 2007 (UTC)

Hmmm, that doesn't sound quite right. People getting 'the shivers' when experiencing particular pieces of music or memories don't, in my experience, tend to experience the piece of music or memory as being cold. Rather, the 'shiver' response seems to be triggered by a particular emotional sort-of feeling which can cause a 'judder', rather than prolonged shivering or a sensation of cold. This is original research, of course, but I'm rather doubtful this can be put down to synesthesia. Skittle (talk) 16:34, 13 December 2007 (UTC)

In fact, it looks like the first reference in the article has it pretty well; the response being related to the shiver-response to anxiety or fear. Music and memories can certainly cause such emotions, and related feelings which appear to produce the same response. Skittle (talk) 16:37, 13 December 2007 (UTC)

SNRIs/Anti-depressants

(Removed medical question - it is contrary to our policies to answer medical questions) SteveBaker (talk) 05:21, 12 December 2007 (UTC)

Cold confused with wet

Is there a reason why it's often hard to tell the difference between something being just cold rather than wet? I think I find it happening with clothing the most. I assume it's due to the fact that most wet things that we touch are also cold, so items that are just cold we assume there's wetness as well. --MacAddct  1984 ^{(talk • contribs)} 23:54, 11 December 2007 (UTC)

Short answer, as far as I know, is that there is no such thing as a "wetness" receptor. Our brains figure out whether something is wet or not by combining different signals, one being cold. You could probably learn more by reading this and associated articles: Somatosensory system. (EhJJ) 02:04, 12 December 2007 (UTC)

Ah, I like that answer! That actually makes a lot of sense, I'll definitely have to look around more. -- MacAddct  1984 ^{(talk • contribs)} 03:59, 12 December 2007 (UTC)

The human temperature sense is a bit weird. It's not really measuring the temperature per-se but the rate at which heat is being gained or lost through the skin. A chunk of wood feels warmer to the touch than a chunk of metal even if they are at the exact same temperature because the wood doesn't conduct the heat from your skin away as well as the metal does. Liquids feel especially cold because they contact your skin very closely - every little fold and wrinkle is in contact with the liquid - where when you touch a solid object, only a smaller part of the skin is actually in contact. With a dry powder, there are lots of air gaps between the solid particles - so again there is plenty of insulation preventing the heat from being conducted away. So that's the reason why wet things generally feel colder than dry things - even if they are really at the exact same temperature. SteveBaker (talk) 05:19, 12 December 2007 (UTC)

In addition, as the water evaporates, it takes the heat of vaporization away, which further cools down your skin. (This is really obvious when you squirt some more volatile liquid on your hand, like ethanol) 18.96.7.135 (talk) 16:08, 13 December 2007 (UTC)