Wikipedia:Reference desk/Archives/Science/2008 November 22

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November 22[edit]

equatorial water:direction[edit]

dear peoples i believe that water goes down a drain in different direction north and south of the equator,ie, clockwise and anti clockwise,and i would like to know if there is a permanant geographical location where north and south meets. if so,does the water go straight down the drain without clockwise or anti clockwise direction? and,given that the earth wobbles on its rotational axis,could any such location remain static? —Preceding unsigned comment added by (talk) 00:37, 22 November 2008 (UTC)

It's a myth. Water spirals down the drain in a direction that is not in any way related to the rotation of the earth. So the water will spiral (either clockwise or anti-clockwise) whether you're north, south or in the middle - or even on the moon. -- (talk) 01:20, 22 November 2008 (UTC)

And some references:

-- (talk) 01:26, 22 November 2008 (UTC)

Beat me to it they did, here's one more to top things off [1] - (talk) 01:31, 22 November 2008 (UTC)

I suspect that the OP really wants to know what the coriolis effect does at the equator. Ignoring water in a drain, the fact remains that a fluid flowing over a long distance to a region of lower pressure (or lower elevation in the case of flowing water) on the rotating earth will experience a force not in its line of direction. If the low pressure area is centered right on the equator, then yes, the fluid won't rotate around that point. ~Amatulić (talk) 02:02, 22 November 2008 (UTC)

I suggest someone find some satellite photos of storm systems around the equator. They're of the right scale to be affected by coriolis (cyclonic = clockwise in the south, anticlockwise in the north). -- (talk) 02:14, 22 November 2008 (UTC)
The coriolis effect is far too tiny to affect water going down a drain. It does affect large storm systems - but even then, once they are spun up to speed, the coriolis force is dominated by the momentum the storm already has - so even if a clockwise-spinning storm crosses the equator, it's going to keep spinning clockwise for quite a while. So I wouldn't expect to see any especially remarkable at the equator - except, perhaps, the consequences of a clockwise storm hitting a counterclockwise one. SteveBaker (talk) 03:31, 22 November 2008 (UTC)
I believe the lack of coriolis efffect at the equator is precisely why we rarely get hurricanes forming there. StuRat (talk) 06:36, 22 November 2008 (UTC)
Yeah, we've debunked the idea that toilets are effected by the earth;s rotation. As to the effect of the Coriolis Effect at the equator, see Doldrums... 04:14, 22 November 2008 (UTC)
This is more interesting than useful now, but there have been related discussions on the Reference Desk; see [2] and [3]. To respond to StuRat, tropical cyclogenesis says "a minimum distance of 500 km (300 miles) from the equator is normally needed for tropical cyclogenesis".
"if there is a permanant geographical location where north and south meets.[...] given that the earth wobbles on its rotational axis,could any such location remain static?"
I'm not sure what this is asking. Isn't the "geographical location" the equator? As for Earth's wobble, that would be precession, which does not change the orientation of Earth's axis with respect to the planet's surface. What is now the equator will always be the equator. --Bowlhover (talk) 05:14, 23 November 2008 (UTC)
Except that the land masses are all drifting, so the equator won't always pass through Ecuador. StuRat (talk) 16:50, 23 November 2008 (UTC)

Fate of the universe[edit]

Assuming that our present knowledge of quantum mechanics and relativity are both roughly correct and that any discrepancies will be worked out and leave the existing knowledge of those fields intact, is it possible that our far-distant descendents will be able to stop the inevitable doom of the universe? It seems that this would require a reversal of the 2nd law of thermodynamics, and I vaguely remember reading something about a possible microscale violation of it (basically, small beads dragged through a liquid lower the temperature in their trail), but can't remember many details. (talk) 01:17, 22 November 2008 (UTC)

I don't think the decline of the universe is in any way preventable - but that doesn't mean that they can't survive. The amount of available energy can never go completely to zero. The trick will be to live more slowly as the energy declines. You have to imagine some kind of technology that's way beyond where we are now - one perhaps where our intelligences are stored on computers of some kind rather than biological brains. Then - as the energy available declines by half, you simply perform your calculations half as fast. Gradually our future selves would 'think' more and more slowly - using less and less energy until it might take a million years to accumulate enough energy to have a thought. But if the universe never COMPLETELY runs out of energy - and if it will indeed last forever - then this is a viable strategy. SteveBaker (talk) 03:23, 22 November 2008 (UTC)
SteveBaker has roughly the right idea. Heat death is an asymptotic condition, not a finish line. Though the question remains what happens once the ammount of usable energy in the universe reaches levels below the Planck constant... (oh, and the universe is not running out of energy. The energy will always be there. The universe is gaining entropy, which is a slightly different idea. </pedanticrant>.) 04:07, 22 November 2008 (UTC)
Sure - I was (loosely) talking about available energy. As entropy does its thing and most of the energy has diffused out into forms that make it impossible to collect - the amount of available energy will asymptote towards zero. But surely only the average energy will fall below the plank constant - the number of particles with enough energy for our future selves to collect and use will asymptote toward zero also. So we sit there with our battery charger and our "just greater than plank-constant" energy/particle collector and we sit there - just above absolute zero charging our tiny batteries. When we have scraped enough energy together - our super-low-power brain/computer runs one clock cycle - then, with the battery once more drained, we wait for enough more particles to come along to do it again. It will eventually take an exceedingly long time for this to happen - particles with enough energy to kick some into our battery would start to come along less and less often - so our brains would run more and more slowly.
From our perspective it would be like time started to run faster and faster - but with the universe being such an amazingly boring and slow-moving place - that would hardly matter. Indeed, that would presumably be a benefit because it would attune our minds to the pace at which interesting events are happening.
We might have to think more slowly anyway because such a high-entropy device as a chunk of carefully doped silicon or nanotechnological push-rod memory would become hard to maintain with the stretching of space becoming noticable on the timescales of our thoughts. So perhaps we'd be using the spin on a single electron as a 1 bit storage element and super-low energy photons to pass information between them. As space stretches and our minds become physically larger - the time it would take for information to pass through it could become ridiculously large anyway - so a slower pace of thought would likely become inevitable. But infinity is a very large number - we aren't in any hurry. SteveBaker (talk) 14:04, 22 November 2008 (UTC)
Depending on how quickly our thoughts slow down, we may only be able to have a finite number of thoughts in an infinite amount of time. In that case, infinity, while very large, wouldn't be large enough. (This is the exact opposite of Tipler's Omega Point.) --Tango (talk) 15:09, 22 November 2008 (UTC)
Classically you never reach absolute zero, but quantum mechanically you can and do—there are only finitely many energy levels between the current state and the ground state. Maybe you can avoid that in a system that grows without bound, but in ΛCDM no system (with a density much lower than the dark energy density) can grow beyond ≈ 30 billion light years in diameter while still remaining in mutual contact. I'm pretty sure QM plus GR with a positive cosmological constant leads to an unambiguous "no" on this one. Of course, my assumptions might be wrong (especially the one about there being a cosmological constant.) -- BenRG (talk) 23:26, 22 November 2008 (UTC)
Might it be the case that by the time that by the time the heat death of the universe becomes a problem, humanity (or whatever humanity has evolved into by then) will have figured out a way to crack open a gateway in the fabric of reality and go 'elsewhere', where conditions are more hospitable? Or does it not work like that? --Kurt Shaped Box (talk) 09:25, 22 November 2008 (UTC)
Yes. --Stephan Schulz (talk) 09:37, 22 November 2008 (UTC)
It's impossible to speculate. With what we know now - categorically, no. But who knows what peculiar stuff will show up at the margins in the future. I read yesterday that a pocket of dark matter has been located 'only' 2000 light years from us. It's likely that being able to study that would reveal all sorts of aspects of the universe that we don't currently understand. But we don't know what we don't know - so speculation about radical new physics is impossible. However, what I said above about slowing the pace of thought in order to make use of declining amounts of energy doesn't violate any physics that we're currently aware of - so it's possible that this could be the way to survive the entropy death of the universe - and we can reasonably speculate about that using only what we currently believe to be true. SteveBaker (talk) 14:04, 22 November 2008 (UTC)
"It's impossible to speculate." You must be joking!  :o) - CBHA (talk) 17:16, 22 November 2008 (UTC)
I believe the Doomsday argument may apply. If people are going to be around forever, than we would almost surely be living so far from when the universe, human race, etc. started that we wouldn't be able to comprehend how long ago it was. — DanielLC 18:15, 22 November 2008 (UTC)
However if human thought is going to slow down in the future that could compensate - in terms of percieved time, we may not be that near the beginning. --Tango (talk) 18:41, 22 November 2008 (UTC)
One idea is to look at The Last Question, which is too good and too short to spoil here. And (not to assign homework or anything), His Master's Voice by Stanislaw Lem ends with very interesting thoughts along these lines. zafiroblue05 | Talk 01:50, 23 November 2008 (UTC)
Stanisław, please. The slash makes the l into a w. Algebraist 01:55, 23 November 2008 (UTC)

Flower Identification[edit]

What is the name of the plant in this picture?--Abhishek Jacob (talk) 09:47, 22 November 2008 (UTC)

What a beautiful flower. It is a Heliconia rostrata. Richard Avery (talk) 12:20, 22 November 2008 (UTC)
Psst Richard A, do you mean Heliconia bihai? [No, you're right, the bihai is erect instead.] Julia Rossi (talk) 12:30, 22 November 2008 (UTC)
Yes, well, if you're looking from Oz it would be up the other way! ;-)) Richard Avery (talk) 15:35, 22 November 2008 (UTC)
No, no! Cameras sold in the southern hemisphere are designed to invert the image to compensate for that!  :-) SteveBaker (talk) 15:14, 24 November 2008 (UTC)
Haha, time to stop walking on my hands then,  :) Julia Rossi (talk) 07:37, 25 November 2008 (UTC)

Air conditioning plant sizing[edit]

Hi there, I regularly build 3D models of buildings (for fun/creative fulfilment whatever you want to call it) and being a perfectionist, I like to make things accurate. One thing I am never sure about is how much space in the building I should allow for mechanical services (ventilation plant, boilers etc). I have read quite a bit about the subject in so much as how these things work and I like to think I have a reasonable knowledge of that side of things but I have no idea at all about sizing - how much space I need to allow in the building to accomodate plant rooms etc.

I am currently sketching out floor plans for a large building I plan to construct a virtual model of and need some guidance on plant sizing. I have several large spaces that are 250 sq m by 9 m high (ie 2250 cu m if my calculations are correct.) that will need cooling, I would estimate 20 air changes per hour. How large (phyically) would the air handling unit for each of these spaces need to be? There is no need for refrigeration locally in these plant rooms as the site will be supplied with chilled water from a central plant. Does the plant room need to be more than one floor high?

As well as the aforementioned large production areas requiring local air handling units, other areas of the building used for storage and smaller production areas require air conditioning to a lesser degree, say 5 air changes per hour. The total space reuiring this is 30,000 cubic metres. I plan to put air handling plants on the roof to serve this but again, how large would they need to be? I plan to have three units so each one would need to serve 10,000 cubic metres. Again, these would served with centralised chilled water.

The next question concerns the chilled water plant itself. I currently have a double hight space of 234 sq m allocated for the chiller plant; is this large enough, bearing in mind the above requirements?

Finally, how much space do I need to allow for the cooling towers to serve the chiller plant?

Any suggestions/ideas would be much appreciated. I have read the article here on Air Handler and Googled the subject but I have not found any useful information on plant sizing.


Arthur —Preceding unsigned comment added by (talk) 10:51, 22 November 2008 (UTC)

I can't give a numeric answer, but do have some factors to consider:
1) What's the initial source of energy for the A/C ? More space (and ventilation) is required for a natural gas fired A/C unit than an electric one.
2) When will the water-chilling portion of the A/C be operated ? If operated "on demand", the storage tank would be smaller, but, if operated at night only, you could take advantage of lower rates and avoid losing A/C during summer brown-outs/black-outs.
3) Consider that it may be necessary to change the cooling technology used over the life of the building, as petroleum prices skyrocket and new technologies become available. Thus, make your design as flexible as possible. For example, you could make the rooms larger than needed and use the extra space for storage. This storage space could be re-purposed in the future, though, if a new technology is put in place for the A/C which requires more space. StuRat (talk) 15:43, 22 November 2008 (UTC)

Name of old mechanical airport/rail schedule signs?[edit]

I am trying to locate information about the old type of signs in airports and railway stations that consisted of small static signs rotated around a horizontal axis in the middle like a rolodex. The problem is I do not know what they were called and all current equipment is digital, does anybody know what this technology was called? —Preceding unsigned comment added by Caisys (talkcontribs) 17:21, 22 November 2008 (UTC)

Split-flap display, like the Solari departure board? DMacks (talk) 17:28, 22 November 2008 (UTC)
Thats right thanks a lot —Preceding unsigned comment added by Caisys (talkcontribs) 19:53, 22 November 2008 (UTC)

states of matter[edit]

how many states of matter are there? and what are they? which conditions facilitate their existence? —Preceding unsigned comment added by (talk) 17:42, 22 November 2008 (UTC)

Try State of matter. --Tango (talk) 17:44, 22 November 2008 (UTC)
Or read the textbook your teacher gave you. --Shaggorama (talk) 20:02, 22 November 2008 (UTC)
But be aware that if the textbook gives an answer, that answer is wrong. The true situation, as described in the article Tango linked to, is that there is no general agreement as to what constitutes a state of matter, nor as to how many there are. Algebraist 12:36, 23 November 2008 (UTC)
In the view of some of these people, there are only 50 states that matter. Clarityfiend (talk) 04:30, 23 November 2008 (UTC)
I was under the impression most of those people think some states don't matter Nil Einne (talk) 07:54, 23 November 2008 (UTC)
It might depend what state you're in, Julia Rossi (talk) 00:50, 24 November 2008 (UTC)
  • High school text books generally name 3 (solid, liquid and gas), but sometimes plasma is considered one too and there's bound to be more. Basically, there's no agreement. - Mgm|(talk) 00:39, 27 November 2008 (UTC)

false positive in blood test[edit]

I am 61 yrs old, female, and was recently hospitalized with a mild heart attack. One of the physicians said that marijuana showed up in the blood tests. I explained that I had taken one capsule of boswellia serrata that day for inflammation in my hands and had taken senna, but certainly had no exposure to marijuana. When I asked if there could have been a false positive, the doctor said no. As boswellia is from the resinous plant frankincense, could the chemical composition have similarities to marijuana, which is also resinous, that could trigger a false positive in the type of testing which is done to detect marijuana in the bloodstream? There is no way I came in contact with marijuana and would like an explanation for the false results. I am uncomfortable with the doctor's definitive assertion of no possibility of error and of that result appearing on my medical records. —Preceding unsigned comment added by (talk) 19:06, 22 November 2008 (UTC)

No test is perfect so there is always a chance of a false positive. I don't know how they test for marijuana so I have no idea what could cause a false positive, but there will be things that will (mixing up your blood sample with that of a marijuana user, for example - assuming it's a half decent hospital, the chances of that are very remote, but they aren't zero). --Tango (talk) 19:12, 22 November 2008 (UTC)
The test is usually for 11-nor-9-Carboxy-THC which can show a positive days after consumption. This site says Ibuprofen will show a false positive for cannabis. SpinningSpark 19:37, 22 November 2008 (UTC)
And this site has a more comprehensive list of pills for false positives. SpinningSpark 19:47, 22 November 2008 (UTC)
Not only do all tests have false positives, but one of the most common reasons for a false positive is a lab screw-up. It's more likely that the lab mixed up samples than it is that you had a false positive for a biochemical reason, so it's probably someone else's positive result. It's certainly not worth worrying about; an isolated result in a big thick chart won't get anyone's attention. It's a little odd, though, to do a blood test for marijuana; most such tests are done on urine - maybe you just got that part confused. Otherwise it would be a rather wasteful way for your doctor to be spending your money - urine toxicology screens are cheap, blood toxicology screens expensive. - Nunh-huh 03:41, 23 November 2008 (UTC)
I'm not an expert but I was under the impression toxicology tests are usually comprehensive so if they decided to do a toxiclogy test, they would have looked for all common toxins. Obviously they wouldn't have ordered a test specifically for marijuana. In more general terms, while the doctors claim it couldn't have been a false positive may have been misleading, I would say it's not surprising, they probably get a lot of people who claim it's a false positive when it isn't so find it more convenient to say it wasn't (since 99% of the time they would be right) Nil Einne (talk) 07:51, 23 November 2008 (UTC)
Yes, they would have ordered a screening test, which would include marijuana, but it would ordinarily have been on urine, and not on blood. Such screening tests are certainly not comprehensive - they by necessity must test for only the most common toxins - almost always less than twenty specific tests. But the tests are chosen to be non-specific, so that entire classes of drugs (benzodiazepams, barbiturates, etc.) can be tested for with one test. This nonspecificity is one reason why screening tests have to be confirmed with a second, more specific test, before they are taken as proven. The only blood test that might routinely be ordered on blood is a blood alcohol level. - Nunh-huh 16:47, 23 November 2008 (UTC)
By comprehensive, I mean comprehensive for common toxins, not comprehensive as in liable to pick up all the millions of possible toxins out there. Sorry if I wasn't clear Nil Einne (talk) 10:27, 24 November 2008 (UTC)

Did you give your permission for a marijuana test? All tests performed by a doctor should be fully consented before-hand. Donek (talk) 14:48, 23 November 2008 (UTC)

In the U.S., at any rate, she would have signed a consent when she was hospitalized which would be deemed to cover all ordinary tests. Separate informed consent signatures would be required for risky procedures, but not urine or blood tests. - Nunh-huh 16:50, 23 November 2008 (UTC)
Please ask the poster what country they are in before making such sweeping statements. SpinningSpark 16:55, 23 November 2008 (UTC)
Not aimed at you Nunh-huh - I missed the fact that you had posted while I was typing. SpinningSpark 16:57, 23 November 2008 (UTC)
Isn't it the case that the patient has to give consent for blood/urine/whatever to be taken for the test - but what tests are done after that point using the same fluids do not require further consent? Taking the fluids without consent would be assault. But testing something already given with consent but without specifying the precise tests to be done is only illegal if you are the police or some other government agency because then it would constitute an illegal search. I'm pretty sure that (for example) some hospitals do routine testing for things like HIV/AIDS when taking blood for other purposes - as much for the safety of their own staff as for the benefit of the patient. I agree though that the jurisdiction you happen to be in makes a huge difference - in some US states it's illegal to do an HIV test without jumping through all sorts of legal hoops. At any rate - we aren't allowed to give legal advice here - so we should really just say "If you think you were tested without your consent - get in touch with a lawyer." SteveBaker (talk) 15:11, 24 November 2008 (UTC)
Better yet, if you think you were tested without your consent, forget about it. You'd have to have damages before you can sue, and you're not going to get much for a (purportedly) erroneous positive result that had no other consequences. - Nunh-huh 23:57, 24 November 2008 (UTC)

The Rydberg Constant in Balmer's Formula[edit]

Okay so in my optics class, we were doing experiments to determine the characteristic wavelengths of hydrogen (using diffraction grating) and then comparing them to the known values. Before the lab, in the theory section in our lab manual, there is a little problem which we cannot figure out. The author states the four postulates of the Bohr theory and then says that using these postulates, it is possible to derive an expression for the energy of the stationary states as given by

where n=1,2,3,4,...

And then the frequency of those transition is given by

where n=3,4,5,6,... Then on the next line he says that using , which we know is true for all waves, gives that

On the wiki page, the Rydberg constant has both a c and h cubed in the denominator. So does that mean the expression for f is wrong? Or is it the expression for energy? Which one is wrong and what are the correct expressions? We were trying to go from frequency to wavelength by just substituting f=c/lambda and then dividing by c but we don't get the same thing.

Another question is, when electron jumps from one stationary state to another, they don't have to jump to a consecutive state, right? Can they skip three stationary states and then jump to the fourth one?----A Real Kaiser...NOT! (talk) 22:47, 22 November 2008 (UTC)

The expression for f is wrong. It's equal to , which is an energy. To get the frequency you need to use E = hf. Then you can substitute f = c/λ and you should get Wikipedia's formula.
It looks like the author also forgot to divide by c on the right side and added an extra e0 to the denominator. --Bowlhover (talk) 02:40, 23 November 2008 (UTC)
Electrons can jump between non-consecutive energy levels. You're calculating the energies/frequencies/wavelengths of transitions from level n > 2 to level 2 (the Balmer series), and those transitions skip at least one energy level when n > 3. -- BenRG (talk) 23:14, 22 November 2008 (UTC)

(after ec) : OK let's start from the last question. No, electrons do not have to "jump" to consecutive "states". (Actually, n is not a "state", it is a configuration that is made up of 2n2 distinct states; and electron does not "jump", it makes a transition; but that does not matter now). When electron makes a radiative transition in which its principal quantum number changes from n=3 to n=2, it emits a photon in Balmer alpha line. Transitions from n=4 to n=2 give Balmer beta, n=5 to n=2 give Balmer gamma, and so on. Now, for the first part of your question, the best reference is the NRL Plasma Formulary here. This being homework, I am officially precluded from checking your math; but everything you need is in the NRL Formulary. Just make sure you stick with the SI units and don't mix SI units with cgs units. All the best, --Dr Dima (talk) 23:24, 22 November 2008 (UTC)

Actually, this was not homework. This was a lab (which we already did by the way) and this theory was just something we read before we did the lab but we didn't go into much detail because our teacher keeps deferring everything and tells that you will do more in upper division and grad school. My class is actually a lower division undergrad physics. It is the first calculus based physics class we can take. It is just that the author of the lab manual gave us these formulas and we all knew that there is a typo so we were trying to figure it out. That is it! Thanks both of you. We got it now. It makes much more sense. That formulary looks pretty handy.----A Real Kaiser...NOT! (talk) 23:32, 22 November 2008 (UTC)

Plaster Glue?[edit]

What's the best way to repair a broken plaster statue? I have all the pieces, but I'm not sure what to stick them together with. I don't want them falling apart again, but I also want to leave as little visible seam as possible. Black Carrot (talk) 23:27, 22 November 2008 (UTC)

I would go for a two-part epoxy myself, although I did find this what kind of glue do I use to repair a plaster statue (not you is it?) which says that there is a concrete and plaster glue at all hardware stores (never seen it myself). You will need to sand the joints after, not a problem if your statue is painted as the touch-up will cover any marks but would need to be done with great care if it is bare as colour of the glue will get rubbed in to the surrounding plaster. If you want maximum strength bear in mind that generally fast setting epoxies have lower final strength than the regular ones. That means you want to work out how to clamp the pieces before you start spreading glue. If this is the Venus de Milo you are repairing strike all the above and go see an expert. SpinningSpark 00:08, 23 November 2008 (UTC)

I don't see any mention of plaster glue on the Home Depot or Hobby Lobby websites, but maybe I'm searching wrong. I'll try out the epoxy. What would you recommend to hold the pieces while they dry? It's a big hollow statue, about three feet high, and the plaster is a quarter-inch thick shell painted mostly black. Black Carrot (talk) 01:10, 23 November 2008 (UTC)

How about duct tape? —Preceding unsigned comment added by (talk) 02:01, 23 November 2008 (UTC)

The handyman's secret weapon? I don't think I'm that desperate yet. Black Carrot (talk) 03:48, 23 November 2008 (UTC)
The oracle of all things sticky [4] says superglue. Personally, I'd probably go with slow epoxy - but it's not runny so the two halves won't fit perfectly back together because of the layer of glue. It'll also ooze out everywhere and you'll have to wipe it off while it's still wet. So maybe superglue (which is very runny) is a better choice. My concern with superglue is that it's not as strong as epoxy. If you do go with superglue - pick a slow one...the ones that dry in seconds are a pain. I like Zap. SteveBaker (talk) 03:59, 23 November 2008 (UTC)
Fresh plaster to make the repairs could make sense. I'd use the harder plaster to join the pieces, then fill the joins with a softer finishing plaster. It depends on the relationship of the pieces when you're talking about holding them together – they could be supported in place with packing or sand, taped in place (masking tape is good, the right kind doesn't leave sticky residue), or strapping – much the same as if you're gluing wood/furniture pieces together. Whatever keeps them from shifting. Julia Rossi (talk) 06:59, 23 November 2008 (UTC)

I saw something that suggested white elmer's glue. It would be easier to work with than epoxy or superglue, but how well do you think it would hold plaster together? Black Carrot (talk) 23:16, 23 November 2008 (UTC)

Found this among comments that it takes longer to dry, is thinner and may not last ("elmers is water based......if u dont care that your project may not stand the test of time then use elmers"). The article Elmer's Products, Inc. only presents it as a product for sale, so no durability/strength tests here. From a conservation pov, it's better to use similar material to the object – so, do you want to repair it or restore it? to show someone it isn't broken, or as a sculpture? Julia Rossi (talk) 23:35, 23 November 2008 (UTC)