The impact of grain boundary character on the size dependence of Bi- crystals

The deformation behavior of metallic single crystals is size dependent, as shown by several studies during the last decade [1]. Nevertheless, real structures exhibit different interfaces like grain, twin or phase boundaries. Due to the possibly higher stresses at the micron scale, the poor availability of dislocation sources and the importance of diffusion in small dimensions the mechanical behavior of samples containing interfaces can considerable differ from bulk materials. Within this study we will show the size scaling behavior of general high angle grain boundaries in copper. The first boundary presented is believed to show extensive dislocation slip transmission at bulk dimensions. The second example acts as perfect obstacle for dislocation slip transfer. In the talk results from in situ scanning electron microscopy (SEM) and in situ µLaue diffraction will be shown. While the SEM data is used to proof slip transmission, µLaue is probing the occurrence of dislocation pile-ups at the grain boundary. The results show that at low plastic strains the size scaling behavior of single and bi-crystalline samples is identical in cases where the grain size is assumed as the critical length scale [2]. It can therefore be concluded that the initial number and size of dislocation sources is dominating not only the deformation behavior of single crystalline pillars, but also for bi-crystals (at low plastic strains) (see Fig. 1a). Thus, the character of the boundary does not play any role for the mechanical properties at the onset of yield! Please click Additional Files below to see the full abstract

Insights into dislocation grain-boundary interaction by X-ray μLaue diffraction

The deformation behavior of metallic single crystals is size dependent, as shown by several studies during the last decade. Nevertheless, real structures exhibit different interfaces like grain, twin or phase boundaries. Due to the possibly higher stresses at the micron scale, the poor availability of dislocation sources and the importance of diffusion in small dimensions the mechanical behavior of samples containing interfaces can considerable differ from bulk material. In the talk we show the first in situ µLaue compression experiments on micron sized, bi-crystalline samples. Three different grain-boundary types will be presented and discussed (i) Large Angle grain Boundaries (LAGBs) acting as strong obstacle for dislocation slip transfer; (ii) LAGBs allowing for easy slip transfer and (iii) coherent sigma 3 twin-boundaries. The talk will focus on pile-up of dislocations, slip transfer mechanisms, storage of dislocations and dislocation networks at the LAGB

A METHOD FOR CALCULATING MECHANICAL CHARACTERISTICS OF INDUCTION MOTORS WITH SQUIRREL-CAGE ROTOR

Purpose. Development of a method for calculating mechanical characteristics of induction motors, taking into consideration saturation of the magnetic path and displacement of the current in the rotor bars. Methodology. The algorithm is based on calculating the steady-state mode of induction motor operation for a set slip, described by a system of non-linear algebraic equations of electrical equilibrium, whereas the mechanical characteristic is evaluated as a set of steady-state modes using parameter continuation method. The idea of the steady-state mode calculation consists in determining vectors of currents and flux linkages of the motor circuits, using which makes it possible to evaluate the electromagnetic torque, active and reactive powers, etc. Results. The study resulted in the development of a method and algorithm for calculating static characteristics of induction motors, which allows looking into the effect of different laws of voltage regulation on the mechanical characteristics, depending on the frequency change. Originality. An algorithm for calculating mechanical characteristics of the squirrel-cage induction motor was developed based on the mathematical model of the induction motor in which electromagnetic parameters are calculated using real saturation curves for the main magnetic flux and leakage fluxes, and displacement of the current in the rotor bars is evaluated by presenting the rotor winding as a multi-layer structure. Applying the transformation of the electrical equilibrium equations into the orthogonal axes enabled a significant reduction of calculation volume without impairing the accuracy of the results. Practical value. The developed algorithm allows studying the effect of different laws of scalar regulation of the voltage on the mechanical characteristics of the induction motor in order to obtain the necessary torque-speed curves for their optimization. It can be used for programming frequency converters

Transboundary Water Institutions in Developing Countries : A Case Study in Afghanistan

This study addresses the questions: 1) What kind of transboundary water management institution is needed for Afghanistan; and 2) what expertise is required for the institution and which stakeholders should be involved? The establishment of a transboundary water resources management institution/unit is an essential step for Afghanistan in order to tackle the transboundary waters issue with its co-riparian states. The research also indicated the primary challenges and obstacles (ranging from political matters to technical issues) that a developing country like Afghanistan should anticipate while creating a transboundary waters institution. This study also focused on the perceived risks of cooperation over transboundary water resources from the Afghan standpoint. Furthermore, it reviewed the experience of cooperation between Afghanistan and Iran over the Helmand waters negotiation in 1973. To address the aforementioned questions, I Interviewed transboundary water experts of Afghanistan, applied the risk and opportunities to cooperation framework, used the available literature and secondary data on the topic, and used the situation mapping tool for the Helmand Basin case. At present, lack of technical knowledge, data gaps, weak bargaining and negotiation skills relative to co-riparian states, lack of public support to transboundary waters negotiations – due to lack of awareness of the topic - doubts on faithfulness of co-riparian states on delivering benefits, and the existence of various stakeholders of transboundary waters in the Afghan government are the main concerns. On whether Afghanistan should cooperate or not, the study found that none of the interviewees opposed transboundary water negotiations. However, there were two camps regarding the timing of dialogues with co-riparians. The first group of participants was in favor of dialogue initiation with co-riparian states for now, and the eventual negotiation of water treaties or agreements in the future. The second group opposes current negotiations - this camp wants Afghanistan’s government to start preparing and enhancing its technical knowledge and capacity, bargaining skills, and institutional arrangements for future negotiations. Study results showed existing political will toward transboundary water cooperation and the availability of abundant funding from the donor agencies, as well as from the government of Afghanistan to transboundary waters. Recommendations were made for the design and structure of a transboundary water resources management unit, believed to be the first of its kind in the world. In addition, this study identified the perceived risks to cooperation, and, based on those identified risks, offered risk reduction strategies as well

KOPEKЦIЯ OБ'ЄMУAMHIOTИЧHOЇ РІДИНИ У BAГITHИХ ПРИ IДIOПATИЧHOMУ MAЛOBOДДI.

It was estabiished that the deveiopment of idiopathic oiigohydramnios important roie of increasing piasma osmoiarity mother. Hidratatsiyna therapy can not oniyincrease the amount of amniotic fiuid butaiso improve the iife support systems of the fetus.Уcтaнoвленo, что в развитии идиoпaтичеcкoгo маловодия важная роль принадлежит повышению ocмoляpнocти плазмы крови матери. Гидратационная терапия позволяет не только увеличить объем амниотиче^ой жидкости, но и улучшить жизнеобетечение плода. Встановлено, що в розвитку ідіопатичного маловоддя важлива роль належить підвищенню ocмoляpнocтi плазми крові матері. Гідратаційна терапія дозволяє не тільки збільшити об'єм амніотичної рідини але й покращити життєзабезпечення плода

The innovative component of the system of economic security of Ukrainian transportation industry enterprises

Рассматривается необходимость активизации инновационной деятельности в транспортной отрасли. Исследуются возможности кластерной концепции в формировании системы экономической безопасности предприятий транспортного комплекса за счет активизации инновационного развития

Математическая модель и характеристики асинхронного двигателя при питании от источника тока

. Methods and mathematical models for studying the modes and characteristics of the three-phase squirrel-cage induction motor with the power supplied to the stator winding from the current source have been developed. The specific features of the algorithms for calculating transients, steady-state modes and static characteristics are discussed. The results of the calculation of the processes and characteristics of induction motors with the power supply from the current source and the voltage source are compared. Steady-state and dynamic modes cannot be studied with a sufficient adequacy based on the known equivalent circuits; this requires using dynamic parameters, which are the elements of the Jacobi matrix of the system of equations of the electromechanical equilibrium. In the mathematical model, the state equations of the stator and rotor circuits are written in the fixed two-phase coordinate system. The transients are described by the system of differential equations of electrical equilibrium of the transformed circuits of the motor and the equation of the rotor motion and the steady-state modes by the system of algebraic equation. The developed algorithms are based on the mathematical model of the motor in which the magnetic path saturation and skin effect in the squirrel-cage bars are taken into consideration. The magnetic path saturation is accounted for by using the real characteristics of magnetizing by the main magnetic flux and leakage fluxes of the stator and rotor windings. Based on them, the differential inductances are calculated, which are the elements of the Jacobi matrix of the system of equations describing the dynamic modes and static characteristic. In order to take into account the skin effect in the squirrel-cage rotor, each bar along with the squirrel-cage rings is divided height-wise into several elements. As a result, the mathematical model considers the equivalent circuits of the rotor with different parameters which are connected by mutual inductance. The non-linear system of algebraic equations of electrical equilibrium describing the steady-state modes is solved by the parameter continuation method. To calculate the static characteristics, the differential method combined with the Newton’s Iterative refinement is used.Разработаны методы и математические модели для исследования режимов и характеристик трехфазного асинхронного двигателя с короткозамкнутым ротором при питании обмотки статора от источника тока. Изложены особенности созданных на их основе алгоритмов расчета переходных процессов, установившихся режимов и статических характеристик. Приведено сравнение результатов расчета процессов и характеристик асинхронных двигателей при питании от источника тока и источника напряжения. Исследование установившихся и динамических режимов не может быть осуществлено с достаточной адекватностью на основе известных схем замещения и требует использования динамических параметров, являющихся элементами матрицы Якоби системы уравнений электромеханического равновесия. В математической модели уравнения состояния контуров статора и ротора составлены в неподвижной двухфазной системе координат. Переходные процессы описываются системой дифференциальных уравнений электрического равновесия преобразованных контуров двигателя и уравнением движения ротора, а установившиеся режимы – системой алгебраических уравнений. В основу разработанных алгоритмов положена математическая модель двигателя, в которой учитываются насыщение магнитопровода и явление скин-эффекта в стержнях короткозамкнутой обмотки. Для учета насыщения используются реальные характеристики намагничивания основным магнитным потоком и потоками рассеяния обмоток статора и ротора. На их основе вычисляются дифференциальные индуктивности, которые являются элементами матрицы Якоби систем уравнений, описывающих динамические режимы и статические характеристики. С целью учета скин-эффекта в обмотке короткозамкнутого ротора каждый стержень вместе с короткозамыкающими кольцами разбивается по высоте на несколько элементов. В результате в математической модели рассматриваются эквивалентные обмотки ротора с разными по значению параметрами, между которыми существуют взаимоиндуктивные связи. Решение нелинейной системы алгебраических уравнений электрического равновесия, которой описываются установившиеся режимы, выполняется методом продолжения по параметру. Для расчета статических характеристик используется дифференциальный метод в сочетании с итерационным уточнением методом Ньютона

Orientation dependence of dislocation transmission through twin-boundaries studied by in situ μLaue diffraction

It is well known that the grain boundaries (GBs) act as a barrier for dislocation motion (Clark 1992), leading to the well-known strength increase with reduced grain size, as explained by the Hall-Petch relation. Unfortunately the strength increase often leads to a reduction of ductility, except one example: Nano-twinned microstructures. The twin-boundary (TB) dislocation interaction is still not thoroughly understood (Imrich 2014, Gumbsch 2006). Recent developments in deforming micron sized samples on synchrotron beamlines allow to study the interplay of the single dislocation with a specific grain boundary. In present work we conduct in situ compression on micron-sized copper specimens with differently oriented coherent Σ3 twin boundaries. The samples were grown by the Bridgman method and subsequently fabricated using FIB milling. The in situ Laue microdiffraction experiments (µLaue) were performed on BM32 at the ESRF synchrotron light source. The experiments allow a clear insight into the stress state, and the density and type of geometrically necessary dislocations stored inside the material during compression. The complementary in situ scanning electron microscope (SEM) experiments further allow to analyze slip transfer by slip step analysis. The discussion will concentrate on the dislocation transmission mechanism through the TB and the necessity to store dislocations in some specific loading directions as against others

УСТАНОВИВШИЕСЯ РЕЖИМЫ И СТАТИЧЕСКИЕ ХАРАКТЕРИСТИКИ ТРЕХФАЗНОГО АСИНХРОННОГО ДВИГАТЕЛЯ ПРИ ПИТАНИИ ОТ ОДНОФАЗНОЙ СЕТИ

A mathematical model is developed to study the operation of three-phase asynchronous motor with squirrel-cage rotor when the stator winding is powered from a single phase network. To create a rotating magnetic field one of the phases is fed through the capacitor. Due to the asymmetry of power feed not only transients, but the steady-state regimes are dynamic, so they are described by differential equations in any coordinate system. Their study cannot be carried out with sufficient adequacy on the basis of known equivalent circuits and require the use of dynamic parameters. In the mathematical model the state equations of the circuits of the stator and rotor are composed in the stationary three phase coordinate system. Calculation of the established mode is performed by solving the boundary problem that makes it possible to obtain the coordinate dependences over the period, without calculation of the transient process. In order to perform it, the original nonlinear differential equations are algebraized by approximating the variables with the use of cubic splines. The resulting nonlinear system of algebraic equations is a discrete analogue of the initial system of differential equations. It is solved by parameter continuation method. To calculate the static characteristics as a function of a certain variable, the system is analytically differentiated, and then numerically integrated over this variable. In the process of integration, Newton's refinement is performed at each step or at every few steps, making it possible to implement the integration in just a few steps using Euler's method. Jacobi matrices in both cases are the same. To account for the current displacement in the rods of the squirrel-cage rotor, each of them, along with the squirrel-cage rings, is divided in height into several elements. This results in several squirrel-cage rotor windings which are represented by three-phase windings with magnetic coupling between them.Разработана математическая модель для исследования работы трехфазного асинхронного двигателя с короткозамкнутым ротором при питании обмотки статора от однофазной сети. Для создания вращающегося магнитного поля одна из фаз питается через конденсатор. Вследствие несимметрии не только переходные процессы, но и установившиеся режимы являются динамическими, поэтому в любой системе координат описываются дифференциальными уравнениями. Их исследование не может быть с достаточной адекватностью осуществлено на основе известных схем замещения и требует использования динамических параметров. В математической модели уравнения состояния контуров статора и ротора составлены в неподвижной трехфазной системе координат. Расчет установившегося режима выполняется путем решения краевой задачи, что дает возможность получить зависимости координат на периоде, не прибегая к расчету переходного процесса. Для этого исходные нелинейные дифференциальные уравнения алгебраизируются путем аппроксимации переменных кубическими сплайнами. Полученная нелинейная система алгебраических уравнений является дискретным аналогом исходной системы дифференциальных уравнений. Ее решение выполняется методом продолжения по параметру. Для расчета статических характеристик как функции некоторой переменной данная система дифференцируется аналитически, а затем интегрируется численным методом по этой переменной. В процессе интегрирования на каждом шаге или через несколько шагов производится уточнение методом Ньютона, что дает возможность осуществить интегрирование методом Эйлера за несколько шагов. Матрицы Якоби в обоих случаях совпадают. Для учета вытеснения тока в стержнях короткозамкнутого ротора каждый стержень вместе с короткозамыкающими кольцами разбивается по высоте на несколько элементов. В результате на роторе получаем несколько короткозамкнутых обмоток, эквивалентирующихся трехфазными обмотками, между которыми существуют магнитные связи