Strongly interacting σ\sigma-electrons and MgB2_2 superconductivity

MgB$(p^{n_{\sigma}}p^{n_{\pi}})_{2}$ is classified as a system with strongly interacting $\sigma$-electrons and non-correlated $\pi$-electrons of boron ions. The kinematic and Coulomb interaction V between the orbitally degenerated $\sigma$-electrons provide the superconducting state with an anisotropic gap of s*-wave symmetry. The critical temperature $T_c$ has a non-monotonic dependence on the distance r between the centers of gravity of $\sigma$- and $\pi$-bands. MgB$_2$ corresponds to r=0.085 eV and V=0.45 eV in our model with flat bands. The derived superconducting density of electronic states is in good agreement with available experimental and theoretical data. The possibilities for increasing $T_c$ are discussed.Comment: 8 pages, 4 figure

The tight-binding approach to the corundum-structure d compounds

The analysis of electronic structures has been carried out for the transition-metal compounds showing the corundum-type crystal symmetry using the suggested tight-binding method for interacting bands. With the self-consistent field approximation, the branches of the electronic spectra and energy gaps have been analytically calculated. The role of the electron correlations was found to be decisive for the dielectrization of spectra for which no additional assumptions, e.g. the existence of spin- or charge-density waves, was necessary. The data obtained provide an explanation for the appearance of the insulator state in such compounds as Ti2O3, V2O 3, Cr2O3, alpha -Mn2O3 and alpha -Fe2O3. The calculated values of band gaps agree reasonably with the experimental data available. The Peierls problem is solved for the corundum-structure d compounds

Ультразвуковая диагностика заболеваний органов билиопанкреатодуоденальной области : учебное пособие

В учебном пособии представлены авторские методики ультразвукового исследования печени, желчного пузыря, желчевыводящих протоков, большого сосочка двенадцатиперстной кишки и поджелудочной железы. На основании авторских методик осмотра органов билиопанкреатодуоденальной области показаны новые возможности ультразвукового исследования в диагностике заболеваний этих органов. Для повышения квалификации врачей ультразвуковой диагностики. Учебное пособие выполнено в рамках инновационной образовательной программы Российского университета дружбы народов, направление «Комплекс экспортоориентированных инновационных образовательных программ по приоритетным направлениям науки и технологий», и входит в состав учебно-методического комплекса, включающего описание курса, программу и электронный учебник

Statistical mechanics of base stacking and pairing in DNA melting

We propose a statistical mechanics model for DNA melting in which base stacking and pairing are explicitly introduced as distinct degrees of freedom. Unlike previous approaches, this model describes thermal denaturation of DNA secondary structure in the whole experimentally accessible temperature range. Base pairing is described through a zipper model, base stacking through an Ising model. We present experimental data on the unstacking transition, obtained exploiting the observation that at moderately low pH this transition is moved down to experimentally accessible temperatures. These measurements confirm that the Ising model approach is indeed a good description of base stacking. On the other hand, comparison with the experiments points to the limitations of the simple zipper model description of base pairing.Comment: 13 pages with figure

Exciton Lines in Luminescence Spectra of NixZn1-xO under Inner Shell Excitation

AbstractThe paper presents the results of the study of two narrow luminescence lines I1 and I2 at the energies of 3.339 and 3.393eV respectively in NiO and solid state solution Ni0.6Zn0.4O. The luminescence spectroscopy with a sub-nanosecond time resolution upon selective photoexcitation in the energy range of absorption of the inner shells Zn M- and Ni L2,3- edges of Zn- and Ni- ions was used to promote proposed earlier mechanism of origin of luminescence lines I1 and I2. Photoluminescence decay kinetics of NiO and solid state solution Ni0.6Zn0.4O under soft x-ray excitation are discussed. The doublet of I1 and I2 lines is believed to arise due to the radiative annihilation of p-d excitons

FTIR spectra and conformations of 2`-deoxyuridine in Kr matrices

The Fourier transform infrared spectra in the range 4000–200 cm⁻¹ of pyrimidine nucleoside 2'-deoxyuridine (dU) have been obtained in the low temperature inert Kr matrices. For the first time, instead of a usual flat mirror, a low temperature one-coordinate retroreflector was used as the matrix substrate. Owing to this, the matrix setup is insensitive to dip angle vibrations of the cryostat and is favourable to work with thinner matrix layers. Of two syn-conformers with dU_s1 and dU_s2 (stabilized by the intramolecular hydrogen bond O5'H…O2), only dT_s2 conformer with C2'-endo structure of the ribose ring was uniquely quenched. The height of the interconversion barrier of the minor syn-conformer dU_s1 was estimated to be below 0.7 kcal/mole. It was shown that the energy relaxation of impurities in Kr is slower than in Ar matrices

The most recent (682-792 C.E.) volcanic eruption in the Jombolok lava field, East Sayan, Central Asia triggered exodus of Mongolian pre-Chinggis Khaan tribes (778-786 C.E.)

International audienceThis study presents new data on one of the most recent (historical) volcanic eruptions in Central Asia. The Jombolok lava field located in the East Sayan Mountains (Southern Siberia) was formed during Late Pleistocene and Holocene times. At least four phases of volcanic activity have been identified and evidences associated with the last phase have been found in the upper reaches of the Khi-Gol valley and in the Oka-Jombolok basin. The volcanic activity is represented by young basaltic lava located among older lavas. Live and dead trees have been sampled in the young lava field. Nine fragments of wood have been found embedded in lavas of the latest eruption. Dendrochronological analysis, radiocarbon dating and the analysis of historical chronicles have shown that the latest eruption occurred during the period 682-792 A.D. The volcanic activity possibly triggered the migration of Mongolian tribes out of the locality known in historical chronicles as Ergune-Kun towards the Onon River, which, 400 years later, became the place of birth and rise of Chinggis Khaan

Two−photon Processes in Organometallic Molecules and Clusters: T−T Absorption of Group IV Metal Complexes

Triplet – triplet absorption of d0 metal complexes was for the first time revealed and studied by means of pulse photolysis and electron-exchange (Dexter) resonant energy transfer energy transfer. When you are citing the document, use the following link http://essuir.sumdu.edu.ua/handle/123456789/3539

Comparative Analysis of Various Superconducting and Non-Superconducting Fault Current Limiting Devices Designed for Operation in a 110kV/100 MW Power Network

AbstractAs it is known one of the most promising fault current limiting (FCL) devices for high-power electric networks can be the so-called transformer type superconducting fault current limiter (SFCL) with the primary winding connected to the load in series and the secondary one shortened by a fast-acting circuit-breaker. These devices when made of conventional materials can be very large and expensive – e.g., for a 100 MW circuit under protection the total mass of copper winding conductors can exceed 15 tons and the heat losses in a normal operating mode can be more than 200kW. Therefore, using of high-temperature superconductors (HTSC) can be a solution which can sufficiently improve the mass, geometrical and operational characteristics of an FCL. Unlike other superconducting AC devices, the magnetic field in SFCL does not exceed 0.1 – 0.2 T what allows using HTSC windings even at a comparatively high level of AC losses existing nowadays. In this paper is performed a comparative analysis of various designs of SCFL with the non-superconducting FCL. It has been shown that the former have a mass by an order of magnitude lower than the latter and the rate of lowering of heat losses in a normal operating mode is the same. The equalization of costs of both designs is expected to be reached within the nearest 3 – 5 five years

On the nature of ferromagnetism in diluted magnetic semiconductors: GaAs:Mn, GaP:Mn

A microscopic Hamiltonian for interacting manganese impurities in diluted magnetic semiconductors (DMS) is derived. It is shown that in p -type III-V DMS the indirect exchange between Mn impurities has similarities with the Zener mechanism in transition metal oxides. Here the mobile holes and localized states near the top of the valence band play the role of unoccupied oxygen orbitals which induce ferromagnetism. The Curie temperature estimated from the proposed kinematic exchange agrees with recent experiments on GaAs:Mn. The model is also applicable to the GaP:Mn system.Comment: 10 pages, 3 figures. Submitted to Europhysics Letters, June 25, 200