Memory function formalism approach to electrical conductivity and optical response of dilute magnetic semiconductors

A combination of the memory function formalism and time-dependent density-functional theory is applied to transport in dilute magnetic semiconductors. The approach considers spin and charge disorder and electron-electron interaction on an equal footing. Within the weak disorder limit and using a simple parabolic approximation for the valence band we show that Coulomb and exchange scattering contributions to the resistivity in GaMnAs are of the same order of magnitude. The positional correlations of defects result in a significant increase of Coulomb scattering, while the suppression of localized spin fluctuations in the ferromagnetic phase contributes substantially to the experimentally observed drop of resistivity below T_c. A proper treatment of dynamical screening and collective excitations is essential for an accurate description of infrared absorption.Comment: Proceedings of the 13th Brazilian Workshop on Semiconductors Physic

Sickness rate and disability resulting from diseases of the nervous system: leading factors and ways of prevention.

Over the past 10 years the total number of patients with diseases of the nervous system in Europe makes up 127,200,000 people, that is almost 25,8 % of the population have neurological pathology. Currently in Ukraine 1 654 875 patients with different neurological disorders are registered, in 78 % of cases disability develops which substantially worsens quality of life. By the assessment of WHO in 2012, more than 1 billion people are disabiled (15 % of the world population), of them – 2,8 million people are in Ukraine. Nervous diseases and their consequences will occupy the leading cause of disability among able-bodied population before 2020. The socio-economic aspect of the problem lies in the fact that by indices of person-years of life (index DALY) WHO evaluates disability as the global burden of diseases for the society, and most of the authors consider prevention of disability as the most economically expedient medical intervention. On this basis state Program «Health 2020: Ukrainian dimension» was approved considering new statutes of the new European politics, international experience on prevention of diseases and disability

Hydro-thermodynamic model of deep-water hydraulic lift of 3-phase fluid considering heat-mass-exchange processes

Purpose. To justify theoretical dependences of the main flow parameters of 3-phase streams for modeling the process of hydraulic hoisting of polymetallic nodules in the flow section of the deep-water air-lift for various structures of heterogeneous fluid flow. Methods. Theoretical studies allowed to establish dependences of the main flow parameters of 3-phase streams transporting solid material in a vertical pipeline. Findings. We obtained dependences describing the main characteristics of 3-phase flows in vertical pipelines and calculation formulas for determining the flow parameters of polymetallic nodules hydraulic hoisting for different flow patterns of the fluid. An approach to the development of a mathematical treatment of the mechanism underlying solid materials transportation in the carrying fluid is proposed. Originality. A thermohydrodynamic model of the rising pipe of the deep-water air-lift hydraulic hoisting is developed taking into account the heat-mass exchange processes with different structures of the 3-phase fluid. Practical implications. We developed and prepared for trial operation the software simulating transitional operation modes of deep-water hydraulic lifts transporting polymetallic nodules.Цель. Обоснование теоретических зависимостей основных расходных параметров 3-х фазных потоков для моделирования процесса гидроподъема полиметаллических конкреций в проточной части глубоководного эрлифта для различных структур течения гетерогенной смеси. Методика. Теоретическими исследованиями установлены зависимости основных расходных параметров 3-х фазных потоков, транспортирующих твердый материал в вертикальном трубопроводе. Результаты. Получены зависимости основных характеристик 3-х фазных течений в вертикальных трубопроводах и расчетные формулы для определения расходных параметров процесса гидроподъема полиметаллических конкреций при различных структурах течения смеси. Предложен подход к разработке математического описания механизма транспортирования твердых материалов в составе несущей гидросмеси. Научная новизна. Разработана термогидродинамическая модель подъемной трубы глубоководного эрлифтного гидроподъема учитывающая тепломассообменные процессы при различных структурах 3-х фазной смеси. Практическая значимость. Разработана и приготовлена к опытной эксплуатации программа, моделирующая рабочие переходные режимы глубоководных гидроподъемов, транспортирующих полиметаллические конкреции.Мета. Обґрунтування теоретичних залежностей основних витратних параметрів 3-х фазних потоків для моделювання процесу гідропідйому поліметалічних конкрецій в проточній частині глибоководного ерліфта для різних структур течії гетерогенної суміші. Методика. Теоретичними дослідженнями встановлено залежності основних витратних параметрів 3-х фазних потоків, що транспортують твердий матеріал у вертикальному трубопроводі. Результати. Отримано залежності основних характеристик 3-х фазних потоків у вертикальних трубопроводах та розрахункові формули для визначення витратних параметрів процесу гідропідйому поліметалічних конкрецій при різних структурах течії суміші. Запропоновано підхід до розробки математичного описання механізму транспортування твердих матеріалів у складі несучої гідросуміші. Наукова новизна. Розроблена термогідродинамічна модель підйомної труби глибоководного ерліфтного гідропідйому, що враховує тепломасообмінні процеси при різних структурах 3-х фазної суміші. Практична значимість. Розроблена й підготована до дослідної експлуатації програма, що моделює робочі перехідні режими глибоководних гідропідйомів, що транспортують поліметалічні конкреції.Авторы данной работы выражают благодарность за содействие в подготовке статьи заведующему кафедры строительной, теоретической и прикладной механики Д.Л. Колосову, а также сотрудникам кафедры горной механики Национального горного университета

Response properties of III-V dilute magnetic semiconductors: interplay of disorder, dynamical electron-electron interactions and band-structure effects

A theory of the electronic response in spin and charge disordered media is developed with the particular aim to describe III-V dilute magnetic semiconductors like GaMnAs. The theory combines a detailed k.p description of the valence band, in which the itinerant carriers are assumed to reside, with first-principles calculations of disorder contributions using an equation-of-motion approach for the current response function. A fully dynamic treatment of electron-electron interaction is achieved by means of time-dependent density functional theory. It is found that collective excitations within the valence band significantly increase the carrier relaxation rate by providing effective channels for momentum relaxation. This modification of the relaxation rate, however, only has a minor impact on the infrared optical conductivity in GaMnAs, which is mostly determined by the details of the valence band structure and found to be in agreement with experiment.Comment: 15 pages, 9 figure

The experimental measurement of hexapod stiffness

Розроблено модель гексапода і конструкцію вимірювального стенда, запропоновано методику опрацювання результатів вимірювання, що дозволяє визначити вектор узагальненого пружного переміщення платформи гексапода при навантаженні та жорсткість, приведену до точки навантаження. Встановлено залежність приведеної жорсткості від положення рухомої платформи та координат прикладення навантаження.The parallel machine tools stiffness is the most important as to their high accuracy and performance. The hexapods stiffness is considered in the article, as the hexapod is one of the effective machine tools for multiaxis processing. The objective is to experimentally measure the elastic deformation of hexapod platform under loading by the force, to determine the spatial stiffness depending on the position of the moving platform and loading force, to calculate the reduced stiffness at the loading point. The simplified hexapod model is developed and manufactured. The model consists of solid base and the moving platform connected to the base with six variable length struts. Each strut consists of two telescopic tubes with collet clamping device to lock its length. The struts also have the universal joints at both ends. It is possible to change the platform position and orientation arbitrarily within certain range by changing the struts length. Then the platform position can be locked by tightening the collet clamps of each strut. The stiffness of each hexapod strut is measured and its average value is calculated. The measuring bench is designed to measure the solely displacement of platform caused by the struts deformation and exclude the base deformation. With the manufactured equipment it is possible to apply the force to the platform at an arbitrary direction and angle, to simulate the load on the different height of the platform, from the top or the bottom of the platform. The force is created by the screw tensioner and measured with spring force gage dynamometer. The 6x1 spatial force vector is calculated with the force value and its position within the reference frame. The platform displacement is measured by six gages placed around the platform in the particular order. The procedure of experimental data analysis is developed to obtain the generalized spatial displacement from the indicators readings and their position around the movable platform. The 6x1 vector of spatial displacement is obtained for each load and the reduced stiffness is calculated. The relations of elastic deformations from the platform position with the reference to the base and the force position with the reference to the platform are obtained. It is found that when the distance between the loading force and the platform is increased, the longitudinal displacement of the platform center decreases, but the angular displacement increases. This testifies that the longitudinal displacement at the load point is compensated by the displacement caused by the rotation of the moving platform relatively to the center of stiffness. The measurements testified that the maximum stiffness is observed when the moving platform approaches the base. The maximum stiffness is observed when the load is applied at 0.05 to 0.1 m from the joints plane. In this case the stiffness approximately equals the strut stiffness

Transport and optical conductivity in dilute magnetic semiconductors

doi: 10.1088/0953-8984/21/8/084202 http://iopscience.iop.org/0953-8984/21/8/084202/pdf/0953-8984_21_8_084202.pdfA theory of transport in spin and charge disordered media is developed, with a particular emphasis on dilute magnetic semiconductors. The approach is based on the equation of motion for the current-current response function and considers both spin and charge disorder and electron-electron interaction on an equal footing. The formalism is applied to the specific case of Ga1−xMnxAs. Within the single parabolic band approximation it is shown that both spin (p-d exchange) and charge (Coulomb) scattering contributions to the resistivity are of the same order of magnitude and should be treated simultaneously. Positional correlations of charged impurities are shown to significantly increase the Coulomb scattering. In the magnetically ordered phase, the suppression of localized spin fluctuations leads to a sizable reduction of spin scattering, which may contribute to the experimentally observed drop in resistivity below the critical temperature. The developed model allows for a comprehensive treatment of electron-electron interaction, screening and correlation effects by means of time-dependent density-functional theory. It is shown that collective modes and a dynamical treatment of electron-electron interaction are essential for an accurate description of the infrared absorption spectrum.This work was supported by DOE grant no. DE-FG02-05ER46213

Enhanced carrier scattering rates in dilute magnetic semiconductors with correlated impurities

In III-V dilute magnetic semiconductors (DMSs) such as Ga$_{1-x}$Mn$_x$As, the impurity positions tend to be correlated, which can drastically affect the electronic transport properties of these materials. Within the memory function formalism we have derived a general expression for the current relaxation kernel in spin and charge disordered media and have calculated spin and charge scattering rates in the weak-disorder limit. Using a simple model for magnetic impurity clustering, we find a significant enhancement of the charge scattering. The enhancement is sensitive to cluster parameters and may be controllable through post-growth annealing.Comment: 4 pages, 3 figure

Вербалізація гумору в англомовних ситкомах

У статті розглядаються основні методи вербалізації гумору у англомовних ситкомах останнього десятиліття. Увага фокусується на визначенні ролі реалій для досягнення комічності. Досліджено тематику гумору у сучасному медійному просторі, проаналізовані особливості процесу вербалізації гумору у англомовних ситкомах в період від 2000 до 2014 року. (This article observes and discusses methods of humor verbalization in English sitcoms of the previous decade. Attention is focused upon the usage of realia for the sake of humor. The role of humor in contemporary media has been researched, humor verbalization peculiarities of 2000 – 2014 English sitcoms have been analyzed.