Helicity of convective flows from localized heat source in a rotating layer

Experimental and numerical study of the steady-state cyclonic vortex from isolated heat source in a rotating fluid layer is described. The structure of laboratory cyclonic vortex is similar to the typical structure of tropical cyclones from observational data and numerical modelling including secondary flows in the boundary layer. Differential characteristics of the flow were studied by numerical simulation using CFD software FlowVision. Helicity distribution in rotating fluid layer with localized heat source was analysed. Two mechanisms which play role in helicity generation are found. The first one is the strong correlation of cyclonic vortex and intensive upward motion in the central part of the vessel. The second one is due to large gradients of velocity on the periphery. The integral helicity in the considered case is substantial and its relative level is high

Optical spectra, crystal-field parameters, and magnetic susceptibility of the new multiferroic NdFe3(BO3)4

We report high-resolution optical absorption spectra for NdFe3(BO3)4 trigonal single crystal which is known to exhibit a giant magnetoelectric effect below the temperature of magnetic ordering TN = 33 K. The analysis of the temperature-dependent polarized spectra reveals the energies and, in some cases, symmetries and exchange splittings of Nd3+ 84 Kramers doublets. We perform crystal-field calculations starting from the exchange-charge model, obtain a set of six real crystal-field parameters, and calculate wave functions and magnetic g-factors. In particular, the values g(perpendicular) = 2.385, g(parallel) = 1.376 were found for the Nd3+ ground-state doublet. We obtain Bloc=7.88 T and |JFN|= 0.48 K for the values of the local effective magnetic field at liquid helium temperatures at the Nd3+ site and the Nd - Fe exchange integral, respectively, using the experimentally measured Nd3+ ground-state splitting of 8.8 cm-1. To check reliability of our set of crystal field parameters we model the magnetic susceptibility data from literature. A dimer containing two nearest-neighbor iron ions in the spiral chain is considered to partly account for quasi-one-dimensional properties of iron borates, and then the mean-field approximation is used. The results of calculations with the exchange parameters for Fe3+ ions Jnn = -6.25 K (intra-chain interactions) and Jnnn = -1.92 K (inter-chain interactions) obtained from fitting agree well with the experimental data.Comment: 13 pages, 8 figures, 2 table

New programs for determining the main parameters of open clusters

A set of computer programs for the determination of the main parameters of open clusters, such as color excess, distance, and age, is developed. The set consists of two units. The first unit is designed to search for open clusters in wide fields using JHKs-photometry from various catalogs (2MASS, UKIDSS, VISTA) by identifying areas of high stellar density. The second unit determines the parameters of open clusters by fitting photometric diagrams. This is the unit described in the paper. Probable cluster members are identified by the proximity to the basic sequences on the J-(J - H) and Q-(J - H) diagrams. The color excess is determined by minimizing the deviations of Q values on the Q-(J - H) diagram. Ages and distance moduli are determined by comparing the color-magnitude diagrams with theoretical isochrones. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Inversionless light amplification and optical switching controlled by state-dependent alignment of molecules

We propose a method to achieve amplification without population inversion by anisotropic molecules whose orientation by an external electric field is state-dependent. It is based on decoupling of the lower-state molecules from the resonant light while the excited ones remain emitting. The suitable class of molecules is discussed, the equation for the gain factor is derived, and the magnitude of the inversionless amplification is estimated for the typical experimental conditions. Such switching of the sample from absorbing to amplifying via transparent state is shown to be possible both with the aid of dc and ac control electric fields.Comment: AMS-LaTeX v1.2, 4 pages with 4 figure

Peculiarity of stellar kinematics in the solar vicinity

The peculiar velocities of nearby stars are studied. We determine the solar velocity components from the radial velocities and proper motions of stars and open clusters. We show that nearby stars are not very suitable for the determination of the solar motion components because of peculiarities in their velocity distribution. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim