Influence of long-range coulomb interaction and on-site hubbard repulsion on the formation of d-wave copper-pairing in High- Tc cuprates

We develop a diagram technique for the self-consistent treatment of the long-range Coulomb interaction and on-site Hubbard repulsion in the normal and superconducting state of high7-4 cuprates. The resultant analytical expression for the "screened" matrix elements taking into account long-range and on-site repulsion has been derived. In particular, it accounts for processes with and without spin-flip due to an exchange of spin and charge density fluctuations. Furthermore, we derive the expressions for the normal and anomalous self-energy parts near the superconducting transition temperature Tc that takes into account the vertex corrections including crossing diagrams. The contribution of the crossing parts is taken within the ladder approximation (similar to Fluctuation-Exchange approximation) where the role of Hubbard on-site interaction is replaced by the Coulomb matrix element with a spin-flip averaged over the momentum. Finally, the developed scheme allows to analyze the formation of d-wave superconductivity and its stability in presence of the long-range Coulomb repulsion within a self-consistent anisotropic Eliashberg-like approach. © 2004 Plenum Publishing Corporation

МЕТОДИКА ОБРАБОТКИ ЭКСПЕРИМЕНТАЛЬНЫХ ДАННЫХ ПРИ МОДЕЛИРОВАНИИ ДИСПЕРСИИ ИМПЕДАНСА БИОЛОГИЧЕСКИХ ТКАНЕЙ С ПОМОЩЬЮ СХЕМЫ ЗАМЕЩЕНИЯ ФРИКЕ

Purpose. Modeling the dispersion of the biological tissue impedance of vegetable and animal origin using the Fricke equivalent circuit; development of a technique for experimental data processing to determine the approximation coefficients of the dispersion of the biological tissue impedance for this equivalent circuit; study of the features of the equivalent circuit at modeling the dispersion of the impedance, resistance, and reactance; the definition of the frequency domain in which using of the equivalent circuit is correct; revealing and generalization of the main regularities of dissipation of biological tissue impedance of vegetable and animal origin. Methodology. The technique is based on the scientific provisions of theoretical electrical engineering – the theory of the electromagnetic field in nonlinear media in modeling the dispersion of the biological tissue impedance. Results. The electric circuit of the Fricke equivalent circuit allows modeling the dependences of the impedance module of biological tissues, active and reactive components of impedance with acceptable accuracy for practical purposes in the frequency domain from 103 to 106 Hz. The equation of impedance of the Fricke equivalent circuit for biological tissues makes it possible to approximate the frequency dependences of the impedance modulus, active and reactive parts of the total resistance only by using the approximation coefficients corresponding to each part. The developed method for determining the values of the approximation coefficients of the impedance equation for the Fricke equivalent circuit for biological tissues allows to determine these values with high accuracy for various biological tissues. It is shown that the frequency dependences of the active component of the total resistance for tissues of vegetable and animal origin are similar. Originality. The developed technique operates with the normalized values of the impedance modulus of the Fricke equivalent circuit, the active and reactive components of the impedance as a function of frequency, which allows a comparative analysis of the dependencies of these parameters of various biological tissues of plant and animal origin. Practical value. The approximate dependences of the absolute impedance modulus, active and reactive components of the impedance allow modeling processes occurring in biological tissues with the passage of a current of different frequency. Dependence of the impedance of biological tissue can be applied to the design of diagnostic and control equipment to determine the properties of tissues of animal and vegetable origin, including developing more effective medical equipment.Разработана методика обработки экспериментальных данных для определения коэффициентов аппроксимации импеданса биологических тканей растительного и животного происхождения при моделировании дисперсии импеданса с помощью схемы замещения Фрике. Проведен анализ свойств схемы замещения Фрике, ее возможностей и особенностей при моделировании дисперсии импеданса, резистанса и реактанса. Показано, что при нормировании дисперсии активные составляющие импеданса для тканей растительного и животного происхождения подобны

АНАЛИЗ КОНСТРУКЦИЙ ШИХТОВАННЫХ МАГНИТОПРОВОДОВ СИЛОВЫХ ТРЕХФАЗНЫХ ТРАНСФОРМАТОРОВ

Analysis and research into properties and parameters of different-type laminated magnetic cores of three-phase power transformers are conducted. Most of new laminated magnetic core designs are found to have significant shortcomings resulted from design and technological features of their manufacturing. These shortcomings cause increase in ohmic loss in the magnetic core, which eliminates advantages of the new core configurations and makes them uncompetitive as compared with the classical laminated magnetic core design.Проведен анализ и исследование свойств и параметров различных типов шихтованных магнитопроводов силовых трехфазных трансформаторов. Установлено, что большинство новых конструкций шихтованных магнитопроводов, обладают серьезными недостатками, вызванными конструктивными и технологическими особенностями процесса их изготовления. Эти недостатки ведут к увеличению активных потерь в магнитопроводе, что нивелирует их достоинства и не позволяет им конкурировать с классической шихтованной конструкцией магнитопровода.Проведено аналіз та дослідження властивостей й параметрів різних типів шихтованих магнітопроводів силових трифазних трансформаторів. Встановлено, що більшість нових конструкцій шихтованих магнітопроводів мають серйозні недоліками, викликані конструкційними й технологічними особливостями процесу їх виготовлення. Ці недоліки ведуть до збільшення активних втрат у магнітопроводі, що нівелює їх переваги та не дозволяє їм конкурувати із класичною шихтованою конструкцією магнітопроводу

Strong paramagnon scattering in single atom Pd contacts

Among all transition metals, palladium (Pd) has the highest density of states at the Fermi energy at low temperatures yet does not fulfill the Stoner criterion for ferromagnetism. However, its close vicinity to magnetism renders it a nearly ferromagnetic metal, which hosts paramagnons, strongly damped spin fluctuations. Here we compare the total and the differential conductance of mono-atomic contacts consisting of single Pd and Cobalt (Co) atoms between Pd electrodes. Transport measurements reveal a conductance for Co of 1\,G0, while for Pd we obtain 2\,G0. The differential conductance of mono-atomic Pd contacts shows a drop with increasing bias, which gives rise to a peculiar \Lambda-shaped spectrum. Supported by theoretical calculations we correlate this finding with the lifetime of hot quasi-particles in Pd which is strongly influenced by paramagnon scattering. In contrast to this, Co adatoms locally induce magnetic order and transport through single cobalt atoms remains unaffected by paramagnon scattering, consistent with theory.PostprintPeer reviewe

Influence of long-range coulomb interaction and on-site hubbard repulsion on the formation of d-wave copper-pairing in High- Tc cuprates

We develop a diagram technique for the self-consistent treatment of the long-range Coulomb interaction and on-site Hubbard repulsion in the normal and superconducting state of high7-4 cuprates. The resultant analytical expression for the "screened" matrix elements taking into account long-range and on-site repulsion has been derived. In particular, it accounts for processes with and without spin-flip due to an exchange of spin and charge density fluctuations. Furthermore, we derive the expressions for the normal and anomalous self-energy parts near the superconducting transition temperature Tc that takes into account the vertex corrections including crossing diagrams. The contribution of the crossing parts is taken within the ladder approximation (similar to Fluctuation-Exchange approximation) where the role of Hubbard on-site interaction is replaced by the Coulomb matrix element with a spin-flip averaged over the momentum. Finally, the developed scheme allows to analyze the formation of d-wave superconductivity and its stability in presence of the long-range Coulomb repulsion within a self-consistent anisotropic Eliashberg-like approach. © 2004 Plenum Publishing Corporation

On the influence of a square-root van Hove singularity on the critical temperature of high-T_c superconductors

It is shown that the square-root Van Hove singularity in the density of states (DOS), associated with extended saddle-point features in the electronic spectra of cuprates, leads to a nonmonotonic dependence of Tc on the position of the Fermi level. As the result of cancellation of the DOS divergence in the electron-electron coupling constant, renormalized due to the account of strong-coupling effects, Tc approaches zero when Fermi level touches the bottom of the saddle. The Tc dependence on the doped holes' concentration, obtained in the strong coupling approximation, agrees with experimental data for the overdoped cuprate metal-oxides.Comment: LaTeX 2.09, 4 pages, 3 Postscript figures, to be published in JETP Lett. v.67, No.

ОПРЕДЕЛЕНИЕ МАГНИТНЫХ ИНДУКЦИЙ В МАГНИТОПРОВОДАХ СИЛОВЫХ ТРАНСФОРМАТОРОВ ПРИ СОВМЕСТНОМ ИСПОЛЬЗОВАНИИ АНИЗОТРОПНОЙ И ИЗОТРОПНОЙ ЭЛЕКТРОТЕХНИЧЕСКИХ СТАЛЕЙ

Purpose. The development of calculation method to determinate the flux densities in different parts of the magnetic cores of distribution transformers, what built from different types magnetic steel (mixed core). Methodology. The method is based on the scientific positions of Theoretical Electrical Engineering – the theory of the electromagnetic field in nonlinear mediums to determine the distribution of magnetic flux in mixed core of transformer, what are using different types of steel what have the different magnetic properties. Results. The developed method gives possible to make calculation of the flux density and influence of skin effect in different parts of the magnetic cores of distribution transformer, where are used mix of grain oriented (GO) and non grain oriented (NGO) steels. Was determinate the general basic conditions for the calculation of flux density in the laminations from grain and non grain oriented steels of the magnetic core: the strength of magnetic field for the laminations of particular part of mixed core is the same; the sum of the magnetic fluxes in GO and NGO steels in particular part of mixed core is equal with the designed magnetic flux in this part of mixed core. Discover, the magnetic flux in mixed core of the transformer has specific distribution between magnetic steels. The flux density is higher in laminations from GO steel and smaller in laminations from the NGO steel. That is happened because for magnetic flux is easier pass through laminations from GO steel, what has better magnetic conductance than laminations from NGO steel. Originality. The common using of different types of magnetic steels in cores for distribution transformers gives possibility to make design of transformer with low level of no load losses, high efficiency and with optimal cost. Practical value. The determination of the flux density in different parts of magnetic core with GO and NGO steels gives possibility make accurate calculation of no load losses and magnetizing current of the transformer.Разработана методика расчета значений магнитных индукций в частях шихтованных магнитопроводов силовых трансформаторов при совместном использовании разных типов электротехнических сталей, в частности – анизотропной и изотропной, позволяющая в дальнейшем рассчитывать потери в магнитопроводах трансформаторов (потери холостого хода) и ток холостого хода.Розроблено методику розрахунку значень магнітних індукцій у частинах шихтованих магнітопроводів силових трансформаторів при спільному використанні різних типів електротехнічних сталей, зокрема – анізотропної й ізотропної, що дозволяє надалі розраховувати втрати в магнітопроводах трансформаторів (втрати холостого ходу) і струм холостого ходу

Health policy formulation process in Zambia : presented at the Zambia Forum For Health Research (ZAMFORH) Workshop held from 3rd - 4th June 2009 at Ibis Gardens

PowerPoint presentationThe presentation focuses on the policy making process in Zambia. Four stages of the policy process are formulation, adoption, implementation, and monitoring and evaluation. Cabinet Liaison Officers (CLOs) are responsible for coordinating all Cabinet business within their Ministries, including the Ministry of Health. The adoption stage refers to a recommended course of action presented before a decision-making body for approval. The key players in the policy adoption stage are the political action committee (PAC), the Minister and the Cabinet. The presentation names some national health policies that have been adopted by Cabinet