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Old 2004-02-04, 13:07   #23
only_human
 
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Some years back I came across a statement that claims about optical properties of polar bear fur were grossly misstated. A brief google search just now pulled up this site:Is polar bear hair fiber optic? The accompanying references are grouped into skeptical and supportive categories and are quite extensive.
Quote:
This website is an attempt to document the extent to which one myth -- the claim that polar bear hairs behave as optical fibers for ultraviolet light -- has permeated the popular science media, from the US to the UK, Australia, Canada, Russia, Switzerland, Norway, and Japan
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Old 2004-02-05, 23:45   #24
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Quote:
Originally Posted by garo
Okie.... This site should help:
http://www.nsf.gov/od/lpa/nstw/teach...cte/clrbr1.htm

So the hair is transparent allowing some transmission and some reflection and some TIR.

Why does fibre-optic cables appear white when they are transparent? Does their cylindrical shape have something to do with it?

[PS: The questions above are rhetorical.]
What about FRUSTRATED total internal reflection (FTIR)? Did any of you make that lab exercise during your physics studies?
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Old 2004-02-06, 07:58   #25
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Speaking of frustrated, here is an optical bench experiment done on polar bear hair by D. W. Koon and C. L. Jahncke, Physics Dept., St. Lawrence University:FOUL(UP): A Fiber-Optic Ursine Link (Universal Prototype) D. W. Koon maintains the site I quoted in an earlier message.
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Old 2004-02-24, 15:15   #26
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http://story.news.yahoo.com/news?tmp...re_green_bears
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Old 2004-02-24, 16:25   #27
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You beat me to it. Here is the story:


Polar Bears at Singapore Zoo Turn Green

SINGAPORE (AP) - Life in the balmy tropics has made polar bears Inuka and Sheba go green with algae.

The usually white coats of Sheba and her 13-year-old son Inuka, Singapore Zoo's two polar bears, turned green a few weeks ago from algae growing in their hollow hair shafts, said Vincent Tan, a spokesman for the zoo.

``The harmless algae is the result of Singapore's warm and humid tropical conditions,'' Tan said.

Polar bears have clear hair shafts which appear white because they reflect light.

Sheba's coat was successfully bleached with hydrogen peroxide 2 1/2 weeks ago and Inuka will be given a similar treatment in 3 weeks time, Tan said.

The zoo wanted to observe Sheba's reaction to the treatment before bleaching Inuka, he said.

For now, Inuka remains mottled with bright grass-colored splotches behind his ears, on his back and legs.

Three polar bears at the San Diego Zoo developed similarly green coats in 1979 but were cured with a salt solution, according to the Web site of Polar Bears International, a nonprofit conservation group based in North America.
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Old 2004-08-04, 14:58   #28
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To explain the south east north thing better, put your finger at the top of a globe and move it down an inch. Turn the globe until your finger slides one inch. Move it up an inch. Your finger is in the original spot!
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Old 2008-09-09, 13:08   #29
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More algae:

http://news.yahoo.com/s/ap/20080907/...an_green_bears
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Old 2008-09-09, 13:40   #30
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I recently found a completely new set of solutions, for which the answer is "various shades of brown".

The phrase "travels one mile due east" means "travel one mile towards the longitude of Greenwich while maintaining a constant distance from the north pole (or equator or south pole)".

The North American plate is subject to continental drift. Not only is it heading westwards on average, it is also rotating. Pick a spot such that the combination of continental drift and rotation combines such that after drifting west one mile that spot is due south of the starting point. Walk very slowly on the eastward leg of the journey.


Paul

Last fiddled with by xilman on 2008-09-09 at 13:40
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Old 2008-09-09, 13:50   #31
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Since it would seem that all the continental plates are in motion, how do we know where the starting point is/was? The magnetic field flips about, the crust plates are moving, the mantle is moving, the outer and inner cores are rotating, the spin axis wobbles etc. Is there some fixed reference point we can refer to so we can know we have returned to the starting point?

Firstly, I think before we can really, completely, and finally, solve the bear colour problem, we must solve how to define the location of the start point.
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Old 2008-09-09, 17:02   #32
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Quote:
Originally Posted by retina View Post
Since it would seem that all the continental plates are in motion, how do we know where the starting point is/was? The magnetic field flips about, the crust plates are moving, the mantle is moving, the outer and inner cores are rotating, the spin axis wobbles etc. Is there some fixed reference point we can refer to so we can know we have returned to the starting point?

Firstly, I think before we can really, completely, and finally, solve the bear colour problem, we must solve how to define the location of the start point.
By definition, the zero of longitude passes through the centre of a particular telescope in Greenwich and the North and South poles lie on the earth's rotation axis. That fully fixes the coordinate system. Any given place on the earth will wander around as time passes. Notice that even the aforementioned telescope can, and does, drift north and south by this definition but it is the only place on the surface of the earth which remains at 0 longitude for the rest of the life of the earth (which means we'd better take good care of it!)

Paul
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Old 2008-09-09, 21:16   #33
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Quote:
Originally Posted by xilman View Post
I recently found a completely new set of solutions, for which the answer is "various shades of brown".

The phrase "travels one mile due east" means "travel one mile towards the longitude of Greenwich while maintaining a constant distance from the north pole (or equator or south pole)".

The North American plate is subject to continental drift. Not only is it heading westwards on average, it is also rotating. Pick a spot such that the combination of continental drift and rotation combines such that after drifting west one mile that spot is due south of the starting point. Walk very slowly on the eastward leg of the journey.


Paul
This is similar to my initial line of thought - what if the hunter is on a giant moving iceberg?
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