APS physics tip sheet #55

October 12, 2005

Molecules of light
M. Stratmann, T. Pagel, and F. Mitschke
Physical Review Letters
http://link.aps.org/abstract/PRL/v95/e143902

Researchers at the University of Rostock in Germany have made the world's first molecules of light, which might allow a significant increase in the data transfer rate of fiber optical systems. The molecules are built of solitons, pulses of light that do not dissipate or easily lose their shape like most other types of pulses. Solitons are useful for transmitting information because the signals can travel over long distances without degrading.

Solitons are waves that can have characteristics similar to material particles, like electrons and billiard balls. The researchers claim that this is the first time anyone has made solitons stick together to form structures analogous to molecules.

Fiber optical systems transmit information by sending light signals through a fiber as a combination of zeros (dark) and ones (light). The data transfer rate for binary coding is fast approaching its fundamental limits, but it may be possible to bypass the limit by transmitting information as zeros, ones, and twos with soliton molecules representing the number two.

The Rostock scientists propose that using soliton molecules as the "two" in information coding could take telecommunications technology to the next level without expensive infrastructure upgrades. They also believe that it may eventually be possible to represent higher numbers with molecules comprised of more complex groups of solitons.

Virtual lab class is better than the real thing
N. D. Finkelstein et al.
Physical Review Special Topics - Physics Education Research
http://link.aps.org/abstract/PRSTPER/v1/e010103

Students master concepts and skills more effectively when they work with computer simulations than when they handle real world components and experiments, according to a study of physics lab students. Researchers at the University of Colorado and the Kavli Operating Institute in Santa Barbara reached the conclusion after comparing students studying elementary electrical circuits. One group of students assembled circuits with wires, batteries, resistors and light bulbs, another assembled the same circuits in a graphical computer simulation. Those who performed experiments with computers significantly outperformed students using real world components on tests of their conceptual grasp of physics principles.

Surprisingly, the students interacting with computers also outperformed their peers in a follow up test requiring them to assemble a circuit with real components. The researchers propose that the real world components can add complications and distractions in lab class that slow learning. Computer simulations, on the other hand, are neater, simpler, and provide constraints that prevent distraction. Computer simulations also helped instructors to make more efficient use of their time with students because they were able to focus on concepts rather than the minutia of mechanically assembling circuitry.

Focusing ocean waves for power and mondo surf
Xinhua Hu and C. T. Chan
Physical Review Letters 95, 154501 (2005)
http://link.aps.org/abstract/PRL/v95/e154501

A new water lens may allow engineers to focus ocean waves. Focusing water waves could potentially enhance the output of wave-powered energy generation schemes, protect ocean front real estate from wave damage, and even amplify waves for surfing and other seaside recreation activities.

Researchers from the Hong Kong University of Science and Technology showed that it would be possible to make a lens from an array of vertical cylinders secured below the water, which focus small ocean waves into larger ones.

The researchers reached their conclusions by simulating the propagation of water waves through an array of ocean bottom-mounted cylinders. By varying the size and spacing of the cylinders, they showed that they could control the reflection, transmission and direction of the water waves through the array, in much the same way that mirrors and glass lenses control light.
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American Physical Society

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