Extracts from the Internet


Quantized displacements

Vibrations of a microscopic silicon lever between quantum-mechanically discrete positions were observed in an experiment at Boston University. The experimental sample was prepared by lithography and placed in a magnetic field. Passing an alternating current through the lever caused it to vibrate at about 1 GHz, the maximum vibrational frequency ever experimentally achieved for a macroscopic object. Whereas at a high enough temperature the lever behaved as a classical object with a continuous set of spatial positions, at a temperature of about 1 mK only discrete displacements became possible for the lever. Source: Physics News Update, Number 702

New exciplex molecules

The term exciplexes refers to molecules that can only be stable when electronically excited. Such molecules were first discovered in 1995 as a combination of two cesium atoms and two helium atoms and have been observed in this form in liquid helium, on the surface of nanodroplets, and in cold gas. It was found that the molecule decomposes if an excited cesium atom makes a transition to its ground state. Now P.Moroshkin and his colleagues from the University of Fribourg in Switzerland have for the first time discovered exciplexes in a sample of solid helium, with as much as the seven helium atoms being coupled to a cesium atom in the molecule. The team doped solid helium-4 with cesium atoms at a temperature of 1.5 K and a pressure of 31.6 atm. Then atoms in the sample were excited by laser light and the fluorescence emission spectrum was recorded - to reveal two spectral signatures of bound molecular state in the far infrared, one from exciplexes previously observed in liquid helium, the other being due to new molecules, seven-member rings of helium atoms with cesium atoms at the center. Source: Phys. Rev. Lett. 94 063001 (2005)

Ultrashort laser pulse

S Harris and his colleagues from Stanford University have created a source of ultrashort laser pulses in the optical range (wavelength of 650 nm). The pulses last for only 1.6 fs, a record-short duration corresponding to as little as 0.8 vibration cycles. The team decomposed sapphire laser light into harmonics by passing it through deuterium gas, changed the harmonics' phases using a liquid crystal modulator, and then passed the beam through xenon gas. The nonlinear transformation undergone by the light resulted in a sequence of 1.6-fs pulses at an interval of 11 fs. By varying the phase shift, pulses with different time profiles were produced. Source: Phys. Rev. Lett. 94 033904 (2005)

Organic LEDs and the fullerenes

Organic LEDs significantly improve their characteristics when doped with fullerene C60 molecules, researchers in South Korea have shown. An organic LED - a layer of organic material sandwiched between and receiving injected electrons and holes from two contacts - emits radiation due to the recombination of excitons (bound electron-hole pairs). Doping the organic layer changes the mobility of its charge carriers. J.Y.Lee and J.H.Kwon found that doping with 3% of fullerene molecules results in a fivefold increase in hole mobility, leading to a 30% increase in the luminance of an LED and doubling its service life. Source: Appl. Phys. Lett. 86 063514 (2005)

Baryons in the Universe

It is currently believed that 95% of the mass in the universe is in the form of dark matter and dark energy (or quintessence), entities whose nature is still unknown. The remaining 5% is ordinary matter, or baryons. Of these latter only half has been directly observed (in the form of stars and gas); the remaining half has thus far escaped detection. This puzzle may have now been solved by a Chandra study of the emission spectrum from the active galaxy Markarian 421. The study revealed the absorption lines of oxygen and nitrogen in the spectra of two intergalactic gas clouds 150 and 380 light years from Earth - suggesting such clouds to be the repository of the missing baryonic matter. Source: Nature 433 495 (2005)

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The Extracts from the Internet is a section of Uspekhi Fizicheskih Nauk (Physics Uspekhi) — the monthly rewiew journal of the current state of the most topical problems in physics and in associated fields. The presented News is devoted to the fundamental discoveries of physics and astrophysics.

Permanent editor is Yu.N. Eroshenko.

It is compiled from a multitude of Internet sources.

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