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

Weighted ergodic theorems for Banach-Kantorovich lattice Lp(∇^,μ^)L_{p}(\hat{\nabla},\hat{\mu})

In the present paper we prove weighted ergodic theorems and multiparameter weighted ergodic theorems for positive contractions acting on $L_p(\hat{\nabla},\hat{\mu})$. Our main tool is the use of methods of measurable bundles of Banach-Kantorovich lattices.Comment: 11 page

Theoretical studies of nonradiative 4f-4f multiphonon transitions in dielectric crystals containing rare earth ions

Detailed calculations have been performed of multiphonon relaxation rates of optical excitations in Nd-doped LiYF4 and Pr-doped CsCdBr3 crystals in the frameworks of the exchange charge model of the crystal fields and rigid ion harmonic models of lattice dynamics. It is shown that the empirical energy gap low emerges from the exponential diminishing of spectral densities of n-phonon correlation functions with the increase of an order n. Calculated transition probabilities for 2-, 3-phonon processes agree with experimental data. However, for energy gaps exceeding the maximum phonon energy more than twice, the existing theory which neglects the lattice anharmonicity brings about underestimated relaxation rates. © 2007 Elsevier B.V. All rights reserved

PREDICTION OF THROMBOEMBOLISM IN PATIENTS WITH LONG-LASTING ATRIAL FIBRILLATION

The aim of the study. Comparative analysis of the risk assessment of thromboembolism by CHADS2 and CHA2DS2-VASc scores, and to study the preventive effectiveness of different antithrombotic agents in patients with long-lasting аtrial fibrillation (AF) at 1 year follow-up. Materials and methods. The study included 108 patients aged 38 to 78 years old (mean age 62,6±8,4 years) with persistent or permanent AF. In 93.5% of patients revealed coronary artery disease and / or arterial hypertension, in 6.5% - non-coronary heart diseases. The risk of tromboembolism assessed by CHADS2 and CHA2DS2-VASc scores. Results. Patients at low risk of tromboembolism, according to CHADS2 score was 2.8%, in their absence, on a CHA2DS2-VASc score. Patients with moderate risk of tromboembolism, in these scores were 63.9% and 7,4% (χ2=72.653; p=0.000) respectively, and a high risk of tromboembolism - 33,3% and 92,6% (χ2=78,796, p=0.000) respectively. Depending on the ways to prevent tromboembolism, patients were divided into 2 groups. 1st group included patients treated with warfarin (n=90), and the endpoints were observed in 5.6% of patients. 2nd group included patients (n=18) treated with acetylsalicylic acid (ASA) and the end point was observed in 27.8% of patients. Conclusion. The introduction of a new CHA2DS2-VASc score led to an increase number of patients, who need mandatory anticoagulant therapy by 2.8 times. In the group of patients with atrial fibrillation treated with warfarin compared with a group of patients treated with aspirin, where cases of ischemic stroke have developed less often, and their clinical manifestation are less pronounced and are characterized by a benign course

Optical spectroscopy of Yb2Ti2O7 and Y2Ti2O7: Yb3+ and crystal-field parameters in rare-earth titanate pyrochlores

Optical absorption spectra of the Yb2Ti2O7 single crystals and luminescence spectra of the Y2Ti 2O7:Yb (1%) polycrystalline samples were registered at temperatures 4.2-300 K. These spectra and earlier published data on magnetic properties of Yb3+ ions and on the temperature dependence of the electric field gradient at Yb nuclei in Yb2Ti2O 7 were used to analyze the crystal-field parameters in rare-earth titanates with the pyrochlore structure. The self-consistent sets of crystal-field parameters for rare-earth ions in the 16d sites with the D 3d symmetry that describe satisfactory all known single-ion magnetic properties and low-energy excitations in R2Ti2O 7 crystals (R=Tb, Ho, Er, Tm, Yb) are presented

Stark structure of the Yb3+ ion levels in (YbxY 1-x)2Ti2O7 and the crystal field in rare-earth titanates with a pyrochlore structure

The absorption spectra of Yb2Ti2O7 single crystals and the luminescence and luminescence excitation spectra of Y 2Ti2O7: Yb (1%) polycrystals were studied in the temperature range 4.2-300 K. The spectra were analyzed in terms of the crystal-field theory and the exchange-charge model. Based on the set of crystal-field parameters found for Yb2Ti2O7, analogous sets of parameters were determined for other rare-earth titanates and proved to be in reasonable agreement with all available experimental data. © 2005 Pleiades Publishing, Inc

Innovative Education as a Factor of Social Progress

The article reveals the historical and pedagogical aspect of the role of education as the main factor in the development of society, shows the importance of decrees and resolutions of the President of the Republic of Uzbekistan on the radical improvement and modernization of the system of continuous education at the present stage.The article proposes the idea that the basis of social progress is the whole set of scientific activities, scientific discoveries, scientific research and achievements of the luminaries of science of past eras. This means that the education system and its content, being dialectically interconnected with production, becomes a locomotive for the development of man and society. In other words, modern knowledge is the spiritual foundation and the driving force behind the progress of social practice and social skills. As a conclusion, the constructive influence of education on the degree of social progress, on the economy, political development, a person's standard of living, family relations is substantiated