Generalized Snell's law

http://www.sciencemag.org/content/334/6054/333.full

Conventional optical components rely on gradual phase shifts accumulated during light propagation to shape light beams. New degrees of freedom are attained by introducing abrupt phase changes over the scale of the wavelength. A two-dimensional array of optical resonators with spatially varying phase response and subwavelength separation can imprint such phase discontinuities on propagating light as it traverses the interface between two media. Anomalous reflection and refraction phenomena are observed in this regime in optically thin arrays of metallic antennas on silicon with a linear phase variation along the interface, which are in excellent agreement with generalized laws derived from Fermat’s principle. Phase discontinuities provide great flexibility in the design of light beams, as illustrated by the generation of optical vortices through use of planar designer metallic interfaces.

Converting mechnical energy by surface tension

Hey, someday you may charge your phone by just walking around !
[http://www.physicstoday.org/daily_edition/physics_update/a_microfluidics_path_to_harvesting_mechanical_energy]

Imagine a drop of water on a solid, pulled up into a ball by surface tension. The simple application of voltage between liquid and solid alters the interfacial energy and prompts the droplet to spread out, an effect known as electrowetting; the greater the voltage, the greater the spread. In the past decade, researchers exploiting the effect have developed, among other applications, liquid lenses with voltage-tunable focal lengths and microfluidic circuits that store and steer droplets without the need for pumps or mixers. Tom Krupenkin and Ashley Taylor at the University of Wisconsin–Madison have now developed an approach that runs the process in reverse—converting the mechanical energy of liquid motion into electrical current. In one implementation, they pressurized a fluidic channel to force a train of mercury droplets past dielectric-coated electrodes connected to a bias voltage on the order of tens of volts. As the overlap area between the droplets and electrodes changed, so did the charge stored at their interface, giving rise to an alternating current that can drive a load. The researchers measured a few milliwatts from a channel containing 22 droplets. But from their model of the process they calculate that average powers of 1 W or more could easily be generated in a fluidic device with 1000 flowing droplets. The devices are small enough to fit into a pair of shoes; with each step, fluid is squirted back and forth between the heel and toe. (T. Krupenkin, J. A. Taylor, Nat. Commun. 2, 448, 2011.)—R. Mark Wilson

A One-Way Wall of Silence

In a previous entry I highlighted this work. Here is another citation of it [http://www.sciencemag.org/content/331/6022/twil.full?sa_campaign=Email/toc/3316022twil]:

The recent development of metamaterials and photonic crystals has provided a route to control the propagation of electromagnetic waves through the engineered structure of a material. Combined with transformation optics, such control is rewriting the expected rules of behavior governing the propagation of electromagnetic waves, and offers myriad possibilities ranging from imaging to communications and stealth applications. Sound is also a wave, and so the manipulation of acoustic waves may be expected to carry over by analogy to their electromagnetic counterparts. Li et al. present a sonic crystal composed of a periodic array of steel rods, the geometry of which was selected to give rise to a band gap, whereby the transmission of sound waves in a specific frequency range is prohibited in one direction but allowed in the opposite direction. The authors also show that by mechanically changing the spacing of the array (by rotating the square steel rods), the diode-like behavior can be switched on and off. A range of applications might be expected to follow, from acoustic isolation and filtering to ultrasound imaging.

Phys. Rev. Lett. 106, 84301 (2011).

What happend at the Fukushima reactor ?

The 9.0 level earthquake took place in Japan and caused damage to the nuclear reactors. Now the media are disseminating and making up all kinds of bells and whistles around a possible disaster like Chernobly catastrophe. And the mass and some activists rise to protest against nuclear plants plan. So, the earnest question is, is the nuclear industry really so unsafe ? Here is an excellent article speaking of this. His view is that, the event in Japan witnessed the success of the modern technology, rather than a failure that is spread so widely in the media.

As a nuclear engineer, it is depressing to read the recent reports on the Fukushima nuclear incident — not because of the incident itself (at this point I strongly believe that we will remember Fukushima as evidence of how safe nuclear power is when done right) — but because the media coverage of the event has been rife with errors so glaring that I have to wonder if anyone in the world of journalism has ever taken a physics class. My favorite: in one article, boric acid was described as a “nutrient absorber” instead of a “neutron absorber.” How many editors signed off on that line without asking, “Why would a nuclear reactor need to absorb nutrients?”

Whether it is confusion of radiation with radioactive material, flailing comparisons to past accidents, or hopeless misuse of terminology, reporting on Fukushima has been a mix of hype and speculation entirely devoid of useful information. Let’s set the record straight: the situation is under control, it is unlikely that the nuclear fuel has melted, the risk to the public is effectively zero, and, depending on whether facts on the ground have been reported correctly, it is possible that the reactors will remain capable of producing power in the future.

Henry's design was found an error

This interesting study has acquired attention from Nature Physics. The authors reveal an error with Henry's design on display in Princeton University.

In 1831, Henry invented a battery-powered rocking-beam motor that he later described as the first electromagnetic machine. He repeatedly modified the design over his career, but only one version of a motor actually constructed by Henry is known to exist. This version is in a collection of Henry instruments at Princeton University. We found that the Princeton motor cannot have operated in the
form that was displayed as early as 1884. We found evidence in several historical documents and in the instrument itself that the field magnet shown with the motor is a mistake. Instead of a single horizontal bar magnet, the motor was designed to use two elliptical magnets. We presume the error was made by whoever assembled the first public display. We modeled the dynamics of Henry’s vibrating motor and compared our results to the operation of a replica motor. Modeling provides
insight into how the motor is able to vibrate indefinitely even in the presence of energy loss due to friction. © 2011 American Association of Physics Teachers.
DOI: 10.1119/1.3531940