# Extracts from the Internet

## A sterile neutrino

According to some theoretical models, along with the electron, muon, and tau neutrinos - elementary particles which interact extremely weakly with matter - there also exist so-called sterile neutrinos, whose interaction is even weaker than that. Scientists working with the Super-Kamiokande detector in Japan have recently suggested the existence of neutrino oscillations, i. e., of processes in which muon neutrinos transform into tau and, possibly, sterile varieties. The origin of muon neutrinos is the decay of muons produced by cosmic rays in the upper atmosphere. A new analysis of data has shown, however, that neutrino oscillations - if they at all exist - occur between muon and tau neutrinos only and do not involve the hypothetical sterile variety. Source: http://prl.aps.org

## The smallest nanotubes

One of the most promising lines of research in solid state physics and microelectronics is that dealing with carbon nanotubes - microscopic hollow cylinders of carbon with walls just one atom thick. Apart from offering unique electrical properties, nanotubes also have good heat conductivity (see Uspekhi 170, 1142 (2000)). A Japan team working in collaboration with Hong Kong University has succeeded in fabricating the smallest nanotubes ever observed, whose diameter, a mere 0.5 nanometer, represents the lower theoretical limit for the nanodevice. Source: http://www.sciam.com/news/110600/4.html

## Surface acoustic waves

A Japanese scientist Y Tsukahara and his colleagues performed an experiment in which sound traveled along and around the surface of a small glass sphere. To avoid the strong dispersion of the surface acoustic wave (known as the Rayleigh wave), a tightly focused wave was used in the piezoelectric generator and a wave packet of special shape was employed. Source: Physics News Update, Number 509

## Vortex inside a vortex

Researchers at the University of California have been studying the behaviour of vortices placed within a larger-sized vortex. Since vortices in a real liquid are rather difficult to study because of viscosity, the UC team employed a magnetized two- dimensional electron gas with properties close to those of an ideal liquid, and used a photocathode to create in it electron vortices of required configuration. A small vortex so produced first circulated together with the material of the larger one, and then within its orbit a oppositely spinning vortex-like hole' developed, whose growth ultimately made the motion of the entire system chaotic. This effect had been predicted theoretically earlier. Similar phenomena may occur in oceanic vortices and in the dense atmospheres of giant planets. Source: Phys.Rev.Lett. 85 4052 2000

## Plasma lens

Electron and positron beams are usually focused be means of the magnetic quadrupole lens, but this technique does not work for beam energies above a few GeV. Researchers at the Stanford Linear Accelerator Center (SLAC) in the USA now have discovered that plasma placed in a magnetic field has better focusing properties than those obtained by simply using a magnetic field - presumably because the Coulomb repulsion between beam particles is overridden by the attraction of oppositely charged plasma particles. Using a plasma lens, the experiment E150 group achieved a three-fold narrowing of a 30-GeV electron beam and has been able for the first time to focus a positron beam of the same energy. Source: Physics News Update, Number 508

## Iron line in the spectrum of a gamma-ray-burst

The observation of the optical and X-ray afterglow of gamma-ray bursts is a solid evidence for their cosmological origin, but even within the cosmological scenario a number of hypotheses, such as colliding neutron stars, hypernovae', cosmic string vibration, etc., still continue to compete. Now Chandra observations will possibly narrow the choice after the spectrum of the X-ray afterglow of the gamma-ray burst GRB991216 has for the first time revealed the presence of iron emission lines. From the redshift and width of the lines, the distance to and some characteristics of the burster were determined. It turned out that matter flies away from the burst at about 0.1 of the speed of light and that the mass within a radius of 1-2 light days is at least one tenth of the solar mass. While reminiscent of the `hypernova' model, this picture implies more energy release than previously thought. Source: http://chandra.harvard.edu

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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