Міжнародна наукова конференція «Шляхи розвитку науково-технічного співробітництва Росії, України і Білорусі»

7 жовтня 2011 року у Москві, у приміщенні Президії РАН на Ленінському проспекті 32А, відбулася міжнародна наукова конференція «Шляхи розвитку науково-технічного співробітництва Росії, України і Білорусі». Конференція була організована Інститутом проблем розвитку науки РАН (ІПРАН РАН) за підтримки Президії РАН. У ролі партнерської організації1виступив Російський гуманітарний науковий фонд

Radio Properties of the γ\gamma-ray Emitting CSO Candidate 2234+282

Most of the gamma-ray emitting active galactic nuclei (AGN) are blazars, although there is still a small fraction of non-blazar AGN in the Fermi/LAT catalog. Among these misaligned gamma-ray-emitting AGN, a few can be classified as Compact Symmetric Objects (CSOs). In contrast to blazars in which gamma-ray emission is generally thought to originate from highly beamed relativistic jets, the source of gamma-ray emission in unbeamed CSOs remains an open question. The rarity of the gamma-ray emitting CSOs is a mystery as well. Here we present the radio properties of the gamma-ray CSO candidate 2234+282.Comment: 4 pages, accepted for publication in Astronomische Nachrichte

Gamma-ray emission from the solar halo and disk: a study with EGRET data

Context: The Sun has recently been predicted to be an extended source of gamma-ray emission, produced by inverse-Compton (IC) scattering of cosmic-ray (CR) electrons on the solar radiation field. The emission was predicted to be extended and a confusing foreground for the diffuse extragalactic background even at large angular distances from the Sun. The solar disk is also expected to be a steady gamma-ray source. While these emissions are expected to be readily detectable in the future by GLAST, the situation for available EGRET data is more challenging. Aims: The theory of gamma-ray emission from IC scattering on the solar radiation field by Galactic CR electrons is given in detail. This is used as the basis for detection and model verification using EGRET data. Methods: We present a detailed study of the solar emission using the EGRET database, accounting for the effect of the emission from 3C 279, the moon, and other sources, which interfere with the solar emission. The analysis was performed for 2 energy ranges, above 300 MeV and for 100-300 MeV, as well as for the combination to improve the detection statistics. The technique was tested on the moon signal, with our results consistent with previous work. Results: Analyzing the EGRET database, we find evidence of emission from the solar disk and its halo. The observations are compared with our model for the extended emission. The spectrum of the solar disk emission and the spectrum of the extended emission have been obtained. The spectrum of the moon is also given. Conclusions: The observed intensity distribution and the flux are consistent with the predicted model of IC gamma-rays from the halo around the Sun.Comment: Corrected typos, added acknowledgements. A&A in pres

Polaronic Heat Capacity in The Anderson - Hasegawa Model

An exact treatment of the Anderson - Hasegawa two - site model, incorporating the presence of superexchange and polarons, is used to compute the heat capacity. The calculated results point to the dominance of the lattice contribution, especially in the ferromagnetic regime. This behavior is in qualitative agreement with experimental findings.Comment: 9 pages, Revtex, 4 postscript figure

Modification of the Landau-Lifshitz Equation in the Presence of a Spin-Polarized Current in CMR and GMR Materials

We derive a continuum equation for the magnetization of a conducting ferromagnet in the presence of a spin-polarized current. Current effects enter in the form of a topological term in the Landau-Lifshitz equation . In the stationary situation the problem maps onto the motion of a classical charged particle in the field of a magnetic monopole. The spatial dependence of the magnetization is calculated for a one-dimensional geometry and suggestions for experimental observation are made. We also consider time-dependent solutions and predict a spin-wave instability for large currents.Comment: 4 two-column pages in RevTex, 3 ps-figure

Numerical Study of Excited States in the Shastry-Sutherland Model

We investigate excited states of the Shastry-Sutherland model using a kind of variational method. Starting from various trial states which include one or two triplet dimers, we numerically pursue the best evaluation of the energy for each set of quantum numbers. We present the energy difference as a function of either the coupling ratio or the momentum and compare them with the perturbative calculations. Our data suggest that the helical order phase exists between the singlet dimer phase and the magnetically ordered phase. In comparison with the experimental data we can estimate the intra-dimer coupling J and the inter-dimer coupling J' for SrCu2(BO3)2 : J'/J =0.65 and J = 87K.Comment: 15pages, 5figures to be published in JPS

``Flux'' state in double exchange model

We study the ground state properties of the double-exchange systems. The phase factor of the hopping matrix elements arises from $t_{2g}$ spin texture in two or more dimensions. A novel ``flux'' state is stabilized against the canted antiferromagnetic and spiral spin states. In a certain range of hole doping, the phase separation occurs between the ``flux'' state and antiferromagnetic states. Constructing a trial state which provides the rigorous upper bound on the ground state, we show that the metallic canted antiferromagnetic state is not stable in the double exchange model.Comment: REVTEX, 8 pages and 4 PS figure

Long-term photometric monitoring of RR Lyr stars in M3

The period-change behaviour of 134 RR Lyrae stars in the globular cluster Messier 3 (M3) is investigated on the ~120-year time base of the photometric observations. The mean period-change rates (\beta \approx 0.01 d Myr^-1) of the subsamples of variables exhibiting the most regular behaviour are in good agreement with theoretical expectations based on Horizontal-Branch stellar evolution models. However, a large fraction of variables show period changes that contradict the evolutionary expectations. Among the 134 stars studied, the period-change behaviour of only 54 variables is regular (constant or linearly changing), slight irregularities are superimposed on the regular variations in 23 cases and the remaining 57 stars display irregular period variations. The light curve of ~50 per cent of the RRab stars is not stable, i.e., these variables exhibit Blazhko modulation. The large fraction of variables with peculiar behaviour (showing light-curve modulation and/or irregular O-C variation) indicate that, probably, variables with regular period changes incompatible with their evolutionary stages also could display some kind of instability of the pulsation light curve and/or period, but the available observations have not disclosed it yet. The temporal appearence of the Blazhko effect in some stars, and the 70-90 years long regular changes preceded or followed by irregular, rapid changes of the pulsation period in some cases support this hypothesis. [...] Abstract truncated due to the limitations of astroph. See full abstract in the paper.Comment: 22 pages, 14 figures, accepted for publication in MNRA

Quantum phase transition in a minimal model for the Kondo effect in a Josephson junction

We propose a minimal model for the Josephson current through a quantum dot in a Kondo regime. We start with the model that consists of an Anderson impurity connected to two superconducting (SC) leads with the gaps $\Delta_{\alpha}=|\Delta_{\alpha}| e^{i \theta_{\alpha}}$, where $\alpha = L, R$ for the lead at left and right. We show that, when one of the SC gaps is much larger than the others $|\Delta_L| \gg |\Delta_R|$, the starting model can be mapped exactly onto the single-channel model, which consists of the right lead of $\Delta_R$ and the Anderson impurity with an extra onsite SC gap of $\Delta_d \equiv \Gamma_L e^{i \theta_L}$. Here $\theta_L$ and $\Gamma_L$ are defined with respect to the starting model, and $\Gamma_L$ is the level width due to the coupling with the left lead. Based on this simplified model, we study the ground-state properties for the asymmetric gap, $|\Delta_L| \gg |\Delta_R|$, using the numerical renormalization group (NRG) method. The results show that the phase difference of the SC gaps $\phi \equiv \theta_R -\theta_L$, which induces the Josephson current, disturbs the screening of the local moment to destabilize the singlet ground state typical of the Kondo system. It can also drive the quantum phase transition to a magnetic doublet ground state, and at the critical point the Josephson current shows a discontinuous change. The asymmetry of the two SC gaps causes a re-entrant magnetic phase, in which the in-gap bound state lies close to the Fermi level.Comment: 23 pages, 13 figures, typos are correcte

The Gamma Ray Detection Capabilities of the Alpha Magnetic Spectrometer

The modeled performance of the Alpha Magnetic Spectrometer (AMS) as a high energy (0.3 to 100 GeV) gamma-ray detector is described, and its gamma ray astrophysics objectives are discussed.Comment: Latex2e file; 33 pages of text, 20 EPS figures. Accepted for publication in Astroparticle Physics. Correction to affiliations; no modifications of tex