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| Issue 12, 2024 |
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Extracts from the Internet | ||
Investigation of decays of 19Ne nuclei1 September 2012Measurements of lifetimes of neutrons and of the electron asymmetry in their decays is important for more precise determination of the element Vud of the Cabibbo – Kobayashi – Maskawa matrix and for recalculating constraints on the hypothetical right-handed weak currents. However, higher accuracy is achieved not in experiments with individual neutrons but in β-decay experiments of 19Ne nuclei, despite certain complications connected with the structure of these nuclei. According to the new experiments carried out on the isotope separator and accelerator TRIUMF (Vancouver, Canada), the half-life of the 19Ne nucleus is 17.262 ± 0.007 s, which differs by 2.5 σ from the value measured earlier in other experiments. The measured value of the asymmetry parameter Aβ deviates to some extent from the predictions of the Standard Model. At the moment the cause of these deviations remains unknown. Source: Phys. Rev. Lett. 109 042301 (2012) Josephson effect in superconductor-topological insulator systems1 September 2012Researchers at Stanford University and the National Accelerator Laboratory SLAC (USA) discovered unusual properties of the Josephson contact in the hybrid system composed of two superconductors separated by a thin layer of topological insulator Bi2Se3. The titanium and aluminum contacts were deposited onto the Bi2Se3 substrate by electron lithography and the gap between the contacts acted as quantum barrier. Two important differences from familiar Josephson contacts were found; there is no complete explanation for them yet. First, the product of critical current by contact resistance in the normal phase was found inversely proportional to contact width while in conventional Josephson contacts this product is constant. Second, the first minimum of the oscillating supercurrent is produced at a magnetic field which is five times weaker than the corresponding quantity for the minimum quantum flux of the magnetic field possible for a given area of the contact. Source: Phys. Rev. Lett. 109 056803 (2012) Transistor based on phase transition1 September 2012M. Nakano and his colleagues in Japan demonstrated a field-effect transistor based on the “dielectric--metal” bulk phase transition triggered by the electric field. In the past it was only possible to induce this transition in layers of nanometer thickness as the Thomas – Fermi screening did not allow the field to penetrate deeper into the film. VO2 films 10 to 70 nm thick were grown on the TiO2 substrates by laser deposition. Vanadium dioxide VO2 is the Mott insulator, hence the name “Mott transistor” for the new promising device. The important new feature of the experiment lied in covering the VO2 film with a drop of organic ionic liquid into which the transistor gate was immersed. The voltage of only ≈ 1 V generated in the surface layer of VO2 a strong electric field which induced a phase transition to metallic state not only at the surface but also in the bulk of the VO2 film, and this increased the total conductivity of the film by two orders of magnitude. No such effect could be obtained with solid contacts without ionic liquid. The mechanism of the phase transition of the first kind in the bulk of VO2 (evidenced by the hysteresis curve) has not been determined yet. One possibility is that the Thomas – Fermi screening is overcome due to the correlation between electrons and the collective interaction between electrons and the crystal lattice. Source: Nature 487 459 (2012) Kinematiñ Sunyaev-Zel'dovich effect1 September 2012Observations of the microwave background radiation with the radiotelescope Atacama Cosmology Telescope reliably recorded for the first time the kinematic Sunyaev – Zel'dovich effect. In contrast to the ordinary Sunyaev – Zel'dovich effect which was first observed in 1983, the kinematic effect is associated with the motion of clusters relative to the average Hubble flow. Such motion, known as peculiar, is a consequence of gravitational instability and occurs simultaneously with increasing density perturbations which initiate the formation of galaxy clusters. Scattering of microwave background photons by the gas of the moving cluster results in a slight shift of the brightness temperature in proportion to the peculiar velocity along the line of sight. In contrast to previously used methods, the new study measured the relative velocities in closely spaced pairs of clusters from the BOSS galaxy survey. Their positions were compared with a map of the distribution of microway background radiation at the frequency 148 GHz on the patch of the sky measuring 3° × 110°. The effect has been registered not for individual objects (this was prevented by the weakness of signals at the noise level) but for a statistically large set of clusters. The results obtained are in good agreement with the theory of large-scale structures in the standard cosmological model. Source: Phys. Rev. Lett. 109 041101 (2012) Dark matter in the vicinity of the Sun1 September 2012S. Garbari (Institute for Theoretical Physics, University of Zurich, Switzerland) et al carried out a new study of the distribution of dark matter (hidden mass) in the galactic neighborhood of the Solar System by studying the kinematics of 2016 stars (orange dwarfs of spectral type K) and also analyzing the solutions of the Jeans equation and numerical modeling of the mass distribution and the dynamics of the stars in the galaxy. Modeling helped to create test catalogs for testing statistical hypotheses; this reduced to a minimum the number of model assumptions that were made in previous papers and sometimes led to erroneous results. The final result demonstrates that the local density of dark matter in the vicinity of the solar system is 0.85+0.57-0.50 GeV cm-3. Models of the spherical halo of the Galaxy typically yield somewhat lower mean values like 0.3 GeV cm-3. If this discrepancy is not a statistical fluctuation, then it could be explained as a result of oblateness of the Galactic halo or of the presence of an additional dark matter disk. Source: arXiv:1206.0015v2 [astro-ph.GA] |
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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