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| Issue 12, 2024 |
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Extracts from the Internet | ||
Pear-shaped atomic nuclei1 June 2013L.P. Gaffney (University of Liverpool, UK) et al. have reliably demonstrated for the first time that perturbations may result in octupole distribution of nucleons inside radon and radium nuclei, i.e. in pear-shaped deviations from symmetry of these nuclei. Non-spherical nuclei were studied in many experiments but in most cases these were elongated or collapsed ellipsoids of revolution, i.e. showed quadrupole distribution; only weak ambiguous indications were obtained in the past concerning lopsided pear-shaped nuclei. In this new experiment, 220Rn and 224Ra nuclei were born in collisions of a beam of protons with uranium carbide target at the REX-ISOLDE facility at CERN. After further acceleration, these nuclei flew through layers of nickel, cadmium or tin. In the course of Coulombic interactions with nuclei in these layers, some of the 220Rn and 224Ra nuclei would undergo excitation. Reverse transitions would cause emission of gamma photons in such a way that pear-shaped nuclei revealed additional transitions between rotational levels of unequal parity. It was this characteristic spectrum of gamma emission that provided the evidence that the excited nuclei had octupole distribution of nucleons. The octupole deformation occurred either statically for a long time (in the case of 224Ra), or the oscillating nuclei would get pear-shaped periodically (220Rn). The study of pear-shaped nuclei is important not only for the verification of theoretical models of the atomic nucleus, but also for searching for off-Standard models of elementary particles, since in the case of octupole distribution the electric dipole moment of nuclei might be enhanced by as much as two-to-three orders of magnitude. The nuclear electric dipole moment has not been detected so far but the very fact of its absence at the achieved level of accuracy has already imposed constraints on possible extensions of the Standard Model. Source: Nature 497 199 (2013) The quantum Hong – Ou – Mandel effect for microwave photons1 June 2013The quantum Hong – Ou – Mandel effect consists in the following: when nearly indistinguishable photons from two sources pass simultaneously through a light splitter, these photons are detected in pairs on one side of the optical splitter considerably more often than on both sides. This effect is implied by the Bose statistics of photons and cannot be explained in terms of the classical (nonquantum) physics. In the past the Hong – Ou – Mandel effect was only observed in experiments with laser photons in the optical range. A. Wallraff (ETH in Zurich, Switzerland) and his colleagues are the first to detect the Hong – Ou – Mandel effect for photons of microwave radiation. In their experiment, photons in single-photon Fock states were emitted by two generators based on transmon qubits. By smoothly varying the phase difference between the generators, it was possible to make the states of the photons more or less similar and to identify the moment when the Hong – Ou – Mandel effect set in. The splitter was made of intersecting microwave waveguides, while the photons were detected by measuring the correlation functions of the electromagnetic field at the outputs of the two waveguides after splitting. Owing to the possibility of controlling the microwave generators, the Hong – Ou – Mandel effect was measured in better detail than in optical experiments. The quantum properties of microwave photons may find application in quantum communication devices. Source: Nature Physics 9 345 (2013) Uniform Bose – Einstein condensate1 June 2013Typically the Bose – Einstein condensate of atoms is created in a trap with harmonic potential, in which the density of the condensate increases towords the center. However, in a number of applications it would be preferable to work with a uniform condensate. In the past, a condensate that is uniform in one direction only was created only in quasi-one-dimensional linear or toroidal traps. A group of researchers at the The Cavendish Laboratory of the Cambridge University (UK) were able for the first time to produce a uniform condensate of rubidium atoms in a three-dimensional trap. The trap was prepared by three laser beams: a hollow cylindrical beam and two flat beams intersecting the cylinder one. After the initial evaporative cooling, the potential inside the trap was made flat and the gravitational field was compensated out by applying a constant-gradient magnetic field. As a result, a uniform Bose – Einstein condensate was created in the trap. The observation of the condensate was run both in real time, by the absorption method, and at the stage of free expansion of the atomic cloud once the trap potential was turned off. In contrast to the the case of a harmonic potential, the transition to the condensate state was not accompanied with spatial separation of the components or sharp visible changes. At the same time, the momentum distribution of atoms, measured at the expansion stage, had bimodal anisotropic shape which corresponded to the flat potential without spherical symmetry. Source: Phys. Rev. Lett. 110 200406 (2013) Gamma horizon1 June 2013A. Dominguez (University of California at Riverside, USA) et al. recorded for the first time and with high statistical significance the effect of damping of gamma-ray emission from blazars (active galaxies with jets directed at the Earth) owing to creation of e+e- pairs in the interaction between γ-photons and extragalactic background radiation. It was not possible until recently to achieve reliable recording of the gamma horizon in view of the low statistics of blazar observations and uncertainties in spectra. The new work is largely free of these factors, owing to the method applied. Dominguez et al. observed 15 blazars, each in a wide range from radio to gamma frequencies simultaneously. The data on gamma radiation were obtained from the Fermi Space Telescope and the atmospheric Cherenkov detectors. The universal model of the synchrotron Compton radiation with self-absorption that was used to model the initial spectrum, predicted the evolution of the spectrum with sufficient reliability, owing to normalization at a wide range of frequencies. It was therefore possible for the first time to identify the gamma horizon in the observational data at red shifts z ≤ 1. For instance, it was found to be at E0 ≈ 10-30 TeV at low z ≈ 0.01 and then decreases by approximately two orders of magnitude at z ≈ 1. Source: arXiv:1305.2162 [astro-ph.CO] The MASTER-II network of robotic optical telescopes1 June 2013This communication presents the results obtained by the Russian network of robotic optical telescopes MASTER-II (Mobile astronomical network of robotic optical telescopes) built by V.M. Lipunov (Sternberg State Astronomical Institute, MSU) and his colleagues. The Russian segment of the network was completed and began regular operations at the end of year 2010. The network is composed of nine optical telescopes that cover the skies from the European part of Russia to the Far East. The most important results of the network MASTER-II was the discovery of hundreds of optical transients (315 by May 2013). Among them we found optical afterglow of gamma-ray bursts, nova and supernova stars, flashes in quasars and in lacertids (emission in relativistic plasmas in the vicinity of supermassive black holes) and other optical objects with short lifetimes. Searching for optical afterglow from gamma bursts is the main task of the MASTER-II networks. Telescopes are capable of rapid automatic focusing to the sky areas defined with known coordinates sent from space gamma telescopes. Photometric measurements of light curves from optical binaries were carried out, sometimes for two polarizations at the same time. At the moment MASTER-II completes the record-high number of first recordings of aftergrow events among robotic networks. Two types of bursts were identified in observations by the MASTER-II networks: with synchronous and with independent variations of signals in the soft and hard parts of the spectrum. MASTER-II observed 387 cosmological supernovas, of which 111 — for the first time. Network expansion and its use for searching for smallish asteroids and warning about dangerous approaches to the Earth have been contemplated. Source: Astronomy Reports 57 233 (2013) |
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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