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| Issue 10, 2024 |
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Extracts from the Internet | ||
Bs-meson oscillations1 May 2006The most accurate measurements to date of the fast oscillations of the Bs-meson into its antiparticle have been made at the Tevatron proton-antiproton collider at Fermilab. A Bs-meson consists of a b quark and an s antiquark. CP violation allows mesons to transform to antiparticles and back again. Previous experiments have only been able to establish the lower and upper bounds for the rate of such transformations. Now the international CDF cooperation has very accurately determined the oscillation rate to be 3x1012Hz based on a four-year study of meson oscillations at the Tevatron. While this value agrees well with Standard Model calculations, supersymmetry theory in its simplest from predicts a somewhat higher oscillating rate - suggesting that the new CDF results place strong constraints on theories beyond the Standard Model. Source: http://www.fnal.gov/pub/presspass/press_releases/CDF_04-11-06.html Superconductivity stability against magnetic field1 May 2006
Superconducting films
The practical application of superconductors
is limited by magnetic field's destructive effect on
superconductivity. X.S.Wu and his colleagues at Louisiana State
University have found that depositing a thin layer of gold on a
beryllium film greatly increases the critical magnetic field for
destroying superconductivity in beryllium. Beryllium films in the
thickness range d=2-30nm, coated with a layer of gold 0.2nm thick,
were made by depositing atoms onto a glass substrate in vacuum. For
smaller values of d, an order of magnitude increase was obtained in
the critical magnetic field. The layer of gold does not affect the
value of the superconducting gap but changes the spin state of
electron Cooper pairs. Interaction with the large charges of gold
nuclei enhances the stability of the pairs.
Source: Phys. Rev. Lett. 96 127002 (2006) Localized vibrations in a uranium crystal1 May 2006M.Manley and his colleagues from the US and Germany have discovered three-dimensional localized acoustic modes in a single crystal of uranium for the first time. The existence of 3D localized modes was predicted theoretically 20 years ago but heretofore never confirmed experimentally. The new experiment, a joint effort between Argonne and Oak Ridge National Labs, used inelastic X-ray and neutron scattering techniques to obtain dispersion curves for a uranium crystal. On heating to a temperature of 450K, the crystal displayed a vibration energy peak on a small scale of as little as two near- neighbor atoms. The crucial point was that the vibrations were localized like resting solitons rather than spreading through the crystal. A strong electron-phonon coupling is believed to give rise to this acoustic mode. Source: Phys. Rev. Lett. 96 125501 (2006) Thin film magnetism1 May 2006F.E.Gabaly and his colleagues studied the magnetization profile of ferromagnetic films of cobalt as thin as one, two, or three atomic layer thick. The high-precision technique the team used deposited cobalt atoms one-by-one on a ruthenium substrate - to produce cobalt islands that were about 10 mkm across and contained equal numbers of atomic layers. To control the thickness and magnetization of the layers, spin polarized electron beam technology was used. The team observed that the magnetic moment lies in or perpendicular to the plane of the film depending on whether the film is one- or three-atom thick or two-atom thick, respectively. To explain the observed effect, first-principles theoretical calculations were performed. There are a number of factors contributing to the energy of a ferromagnetic film, including particularly the dipole-dipole interaction between cobalt atoms, the cobalt layer separation, and separations between the cobalt layers and the substrate. Importantly, these separations change as each new layer of cobalt atoms is added to the system. What the calculations revealed is that, in complete agreement with experiment, one- and three-layer films do indeed energetically favor in-plane magnetization, whereas two-layer films favor perpendicular-to-plane magnetization. This work may find application in developing macroscopic magnetic information carriers, according to the researchers. Source: Phys. Rev. Lett. 96 147202 (2006) How rare isotopes formed1 May 2006Current theory says that light chemical elements in the Universe are of primordial origin or, alternatively, emerged from quiet nuclear reactions in stars; and that elements heavier than iron were formed via proton capture processes in supernova explosions. While this picture is by and large adequate in explaining the abundances of chemical elements, it fails for some rare isotopes, like those of molybdenum and ruthenium, because the proton capture mechanism is not efficient enough for them to form. Now C.Frohlich of the University of Basel, Switzerland, and her colleagues have proposed a theoretical model that explains the formation of rare isotopes. Neutron stars, which are created in many supernovas, are known to produce powerful antineutrino fluxes. According to the Basel team, protons absorb antineutrinos to form neutrons that are readily captured by nuclei, increasing strong interaction within a nucleus to the point where the capture of additional protons becomes possible. This model successfully explains the heretofore mysterious origin of rare isotopes. Source: Phys. Rev. Lett. 96 142502 (2006) |
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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