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| Issue 11, 2024 |
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Extracts from the Internet | ||
Replication of states in a quantum dot1 June 2010A.M. Burke and his colleagues at the Arizona State University found that magnetoresistance in an open quantum dot is distributed in the form of rhomboid periodic structures. A quantum dot of dimensions 1.1 × 1.1 µm was prepared by etching and electron-beam lithography in a thin layer of InAs. The scanning gate microscope used in these experiments fixed the variations of magnetoresistance in the quantum dot (produced in response to perturbations introduced by the field of the microscope tip) as a function of the magnetic field. The repeated periodic structures identified in a quantum dot can be described by the the so-called scar wave function of electrons. The data agree well with the concept of “Quantum Darwinism” proposed by W. Zurek (Los Alamos National Laboratory) in 2003. In this model, which describes the transition from the quantum state to the classical one, the decoherence of the very stable quantum state (pointer state) is accompanied with its replication in the classical environment. Repetitive structures in the quantum dot are interpreted by the authors as classical copies of the same pointer state that went through decoherence. Source: Phys. Rev. Lett. 104 176801 (2010) Dipolar intermolecular interactions in ultracold gases1 June 2010Researchers at the University of Colorado and National Institute of Standards and Technologies (NIST) studied for the first time the properties of the ultracold gas consisting of polar fermion molecules 40K87Rb characterized by long-range potential of dipole-dipole pair interaction. Molecules in one of the states of hyperfine splitting of nuclear levels were obtained by sending laser light onto a mixture of potassium and rubidium atoms cooled in nonuniform magnetic field. The induced electric dipole moment of 40K87Rb molecules of magnitude up to 0.22 D is dictated by the intensity of the external electric field and this relationship creates the possiblities for controlling the properties of the gas. The molecules of 40K87Rb placed in electric field interact anisotropically. If a collision occurs with relative velocity directed along the field, the interactions between molecules become attractive as these are collisions between opposite charges of dipoles oriented along the field. In collisions in the transverse direction, molecules are more often repelled, and the rate of inelastic processes (chemical reactions) is lower. The anisotropy of pair interactions of molecules manifested itself, in particular, in anisotropic thermalization of the gas, i.e. in different relaxation rates of the components of velocity along and transversely to the electric field. Source: Nature 464 1324 (2010) Melting mechanism in plasma-dust crystals1 June 2010L. Couedel and his colleagues at the Max Planck Institute for Extraterrestrial Physics (Germany) found that the melting of two-dimensional plasma-dust crystals takes place in view of the crossing and the resonance relations of the two branches of the dusty-plasma oscillations. The mechanism of melting was theoretically predicted by A.V. Ivlev and G. Morfil in 2000 for the one-dimensional case. Plasma-dust crystals are defined as an ordered state of dust particles in dusty plasmas (for details see V.E. Fortov et al. Phys. Usp. 47 447 (2004)). In this experiment dusty plasmas were created in the chamber above a planar electrode generating high-frequency discharge at a frequency of 13.56 MHz. The discharge-ionized argon was kept at at a pressure of 0.4 Pa; it had an admixture of dust, namely, particles of melamine formaldehyde 9 µm in size. The structure of the obtained plasma-dust crystals was studied using high-speed video recording in reflected laser light. The development of instability was accompanied by an increase in the kinetic energy of the particles of dust during the melting of plasma-dust crystals, which was caused by the decrease in the discharge power or by lowering of pressure of the gas. Three branches of dusty plasma oscillations were observed in these experiments. Crossing and the resonance coupling of the transverse mode (relative to the plane of the electrode) and one of the two longitudinal modes of oscillation were observed near the melting point, which corresponds exactly to the theoretical model. Source: Phys. Rev. Lett. 104 195001 (2010) Intergalactic magnetic field1 June 2010S. Ando (California Institute of Technology) and A. Kusenko (University of California and University of Tokio) determined for the first time the strength and characteristic scale of intergalactic magnetic fields. The magnetic field was found from the effect of diffuse emission (halo) of gamma radiation around the active galactic nuclei which themselves are pointlike gamma sources. The halo is due to deflections in the magnetic field of charged particles of the electromagnetic cascades produced by high-energy gamma-ray photons interacting with background radiation. The observed angular scale and brightness of the halo correspond to the magnitude of the magnetic field B ≈ 10-15(λB/1 kpc)-1/2 gauss where λB < 10-100 kpc is the correlation length of magnetic fields; in fact, larger scales are not excluded. It is rather difficult to measure reliably the profile of the gamma halo around an individual active galactic nucleus and the decisive factor proved to be that the statistical study used a set of 170 bright active nuclei observed by the Space Telescope Fermi-LAT. It was established that the gamma-ray halo is not produced by observation errors or by the emission of extended objects around galactic nuclei since the scale of such objects would be about 5-15 Mpc. The knowledge of intergalactic magnetic fields is important for cosmic ray physics and gamma-ray astronomy. It is possible that these fields are remnants of a very early universe (of an inflationary stage or a cosmological phase transition), and that primary magnetic fields in galaxies and stars have been strengthened by the dynamo mechanism. Source: arXiv:1005.1924v1 [astro-ph.HE] Black hole shifted along the jet in M871 June 2010Observations using the Hubble Space Telescope revealed that the supermassive black hole in M87 is shifted from the galactic center by 6.8 ± 0.8 pc. Isophotes of the central bulge of the galaxy were plotted and their geometric center was determined. The black hole which is a pointlike source of radiation is displaced from the above center along the line of the relativistic jet towards the less bright counterjet. Several possible causes of the displacement of the black hole are discussed. It is possible that the black hole gets the recoil in response to jet emission (this mechanism of acceleration of black holes was suggested by I.S. Shklovsky in 1982) while the depth of the gravitational potential well in the nucleus of the galaxy M87 is insufficiently large for retaining the black hole at its center. The black hole can form a binary system with another black hole or feel the gravitational attraction of a massive star cluster, which would also have led to its displacement away from the center of the galaxy. A black hole could have formed by a merger of two black holes and get the recoil momentum via the anisotropic emission of gravitational waves. The latter scenario and I.S. Shklovsky's mechanism yield a correct order of magnitude for the displacement and are regarded as the most likely, but the exact cause of the displacement of the black hole remains unclear. Source: arXiv:1005.2173v1 [astro-ph.CO] |
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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