Snakes' virtual glasses, leopard spots and all-optical transistors

APS Physics tip sheet #64



Master painter Albrecht Durer's rabbit would look like a smudge (top right) to a snake relying on uncorrected images from heat sensing pit organs. But a virtual lens in the...
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Virtual Lens May Improve Heat Vision in Snakes
Andreas B. Sichert, Paul Friedel, and J. Leo van Hemmen
Physical Review Letters (forthcoming article, available to journalists on request)
"Snakes On Plane": en.wikipedia.org/wiki/Snakes_on_a_plane

Even in the dark, snakes on a plane (at least those of the pit viper and boa varieties) could keep a close watch on terrorized passengers and crew thanks to small cavities near their snouts known as pit organs. The organs are sensitive to the infrared radiation emitted by warm prey such as rats, rabbits, and Samuel L. Jackson. An optical analysis of pit organs suggests that snakes shouldn't be able to use the organ to track prey very well because the pit aperture is large and the organ is not very deep. However, studies have shown that snakes can localize heat sources to a surprisingly accurate resolution of five degrees (roughly the angular width of "Snakes on a Plane" costar Rachel Blanchard at three meters). Physicists at the Technische Universität München believe the solution to the paradox could be a network of neurons in the snakes' brains –a kind of snake brain firmware - that provides image enhancement as though the snakes were wearing virtual corrective lenses. Because snakes' brains are small, the physicists kept their model of an image enhancing network simple. They discovered that even a crude network dramatically improves infrared imaging - which you might want to keep in mind if you ever book a flight on a snake-infested airline.



Leopard kittens (top left) and jaguar kittens (top right) both begin life with spotted pelts. A two-stage Turing-pattern model may explain why leopards eventually end up with rosette decorations (lower...
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A Model of Changing Leopard Spots
R. T. Liu, S. S. Liaw, and P. K. Maini
Physical Review E
http://link.aps.org/abstract/PRE/v74/e011914

Leopard's spots and Zebra's stripes inspired the ancient myths famously retold in Kipling's "Just So Stories." They also led legendary mathematician Alan Turing to suggest that some patterns in nature are due to various chemicals, or morphogens, diffusing across surfaces and forming shapes where they interact. Few Turing-type models, however, addressed the fact that such patterns may evolve over time. A two-stage variation of Turing's model, recently developed by physicists at Taiwan's National Chung-Hsing University and Oxford's Mathematical Institute, duplicates the changes in the patterns on leopards and jaguars as the animals age. Both felines sport simple spots when they are kittens. By the time they're adults, Jaguar's spots have turned to polygons, while Leopard wears rosettes. The researchers' model replicates the changes each of the species experiences, provided that the model parameters are tuned in different ways after the initial spots have formed. No one has ever found the morphogens that might be responsible for decorative animal pelts, which potentially makes Turing pattern morphogens the "Just So Story" of modern biology. Still, the researchers are encouraged by the fact that their model easily accounts for the big cats' complex and changing patterns, and are hopeful that experimentalists will soon track morphogen chemicals down.



This schematic conceptually shows how a control beam (green) and a signal beam (red) interact through plasmons on a gold film pierced with an array of holes. The squiggly lines...
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An All-Optical Transistor Breakthrough
G. A. Wurtz, R. Pollard, and A.V. Zayats
Physical Review Letters (forthcoming article, available to journalists on request)

All-optical circuit components are light-based analogues of electrical transistors and other devices. They are among the most eagerly anticipated technological advances, with the potential to revolutionize computers and communications. But all-optical devices built in the past have been far too large and power hungry to be practical. Physicists at the Queen's University in Belfast appear to have solved the problems with a prototype optical amplifier that is both small and low power. The key to the device is a layer of gold film pierced by an array of holes 0.2 millionths of a meter in diameter and coated in a layer of polymer. The researchers shine two beams of light on the structure: a signal beam and a control beam. When the beams strike the patterned film they produce plasmons, which are essentially blobs of electron gas near the surface of a metal. Varying the intensity and the color of the control beam causes the plasmons to interact in ways that enhance or decrease the transmission of the signal beam through the film. That is, the film acts as an all-optical transistor, with the potential to serve as a building block in optical circuits and optical versions of microelectronic devices.

Multiple Choice Makes Better Tests
Michael Scott, Tim Stelzer, and Gary Gladding
Physical Review Special Topics – Physics Education Research
http://link.aps.org/abstract/PRSTPER/v2/e020102

Multiple-choice tests are better than test questions that require students to work out extended problems with a pencil and paper, according to a study of physics undergrads at the University of Illinois, Urbana-Champaign. While a comparison with longer format tests showed that multiple-choice questions were roughly as good at evaluating students' relative performance, there are additional benefits to eliminating calculation-crammed test booklets. Multiple choice tests ease grading demands in large classes, reduce grading ambiguity and inconsistencies between graders, and severely cut back on the numbers of students contesting grades. While standardized test questions for exams like the SATs and GREs undergo rigorous evaluations, the Illinois study focused on tests designed by instructors with little or no formal training in writing exam questions. Nevertheless, the researchers conclude that multiple choice exams in the University's physics classes A) are just as reliable and valid as other types of tests in gauging students' understanding of class material, B) are as good or better than traditional format tests at assessing relative rankings of students in a class, C) effectively eliminate student complaints about grading fairness, D) all of the above. (Answer: D)

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Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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