APS Physics Tip Sheet – Jul 8, 2014
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Simple Molecules for Accurate Clocks
A team of researchers from Germany, Bulgaria and Russia has suggested that some of the simplest molecules, such as molecular hydrogen, could be used to build a new class of ultraprecise clocks. In the proposed scheme, the rate at which the clock ticks would be determined by a combination of molecular transitions whose shifts due to external perturbations would cancel out, yielding a very stable frequency. The authors’ calculations suggest a potential order-of-magnitude improvement compared to the best existing schemes based on atoms.
* Stephan Schiller (contact author), D. Bakalov, V.I. Korobov, “The simplest Molecules and Clocks,”Physical Review Letters (published Jul 8)
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The Physics of Drop Impact
When a drop hits a surface, the resulting outcome depends critically on the surrounding gas.
A drop falling onto a surface may either spread in a smooth blob, or splash and disintegrate into smaller droplets, but the factors determining which of these two outcomes occurs are not entirely clear. Researchers in Spain used high-speed cameras to film droplets of different liquids as they fell onto a solid surface at varying speed. The analysis of the experiments allowed the authors to derive criteria for predicting when a drop splashes. The researchers conclude that a so-far under-appreciated factor—the gas surrounding the droplet—plays a crucial role because it determines the aerodynamic lift that propels the sheet of impacting liquid upwards until it ruptures. The model may find a wide range of applications, from inkjet printing to surface coating technologies.
* G. Riboux, José Manuel Gordillo (contact author), “Experiments of drops impacting a smooth solid surface: A model of the critical impact speed for drop splashing,” Physical Review Letters (expected publication date: Jul 11)
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Building a Gamma-Ray Laser with Antimatter
Calculations suggest that an efficient gamma-ray laser could be built using a Bose-Einstein condensate of electron-antielectron pairs.
Recent proposals have suggested that gamma ray lasers could be built if a Bose-Einstein condensate of positronium—atoms made of an electron and an antielectron (positron)—became available. In such schemes, gamma rays would be generated by the annihilation of electrons with antielectrons and amplified in a cavity formed by two mirrors. But the lack of mirrors that can reflect gamma rays would still pose a key obstacle to the realization of such lasers. Researchers in Armenia have now reported calculations suggesting that with the appropriate parameter choice lasing would be so efficient that an intense gamma-ray beam could be generated in a single pass, without requiring mirrors. Gamma ray lasers could have a number of important applications, from high-resolution imaging to new ways of controlling nuclear reactions.
* Hamlet K. Avetissian (contact author), A.K. Avetissian, G.F. Mkrtchian., “Self-amplified gamma-ray laser on positronium atoms from Bose-Einstein condensate,” Physical Review Letters (expected publication date: Jul 10)
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Journal articles and preprints are available to journalists on request.
Matteo Rini, PhD
Deputy Editor, Physics
