Simulation of three mutually coupled oscillators

In a practical multipurpose high frequency circuit, different oscillators are not completely isolated from each other. Instead, they interact with the environment, or with other oscillator. The interference between different oscillators may lead to generation of undesired signals. Therefore, the effect of oscillators on each other must be considered in the circuit design. As oscillators have nonlinear behavior, simulation of some of them which are coupled to each other needs more attention. In this report we present a mathematical model for three mutually coupled voltage controlled oscillators and solve it by a numerical method. The approach is illustrated by numerical experiments on realistic designs

A Three-Level Single Stage A-Source Inverter With the Ability to Generate Active Voltage Vector During Shoot-Through State

Single-stage boosting capability of impedance network (IN) inverters makes this family of inverters an attractive choice for DC/AC applications with low input DC voltage. A specific time of shoot-through (ST) state is required to achieve the required voltage gain. Conventionally ST state and zero output voltage vector should be applied simultaneously. This constraint limits the modulation index and increases the voltage stress of the semiconductor devices, particularly for applications requiring a high boosting factor. In this paper, as the boosting stage for a three-level inverter, a new modified configuration of A-source IN with two series outputs is proposed and connected to a 10-switches three-level inverter. Besides generating two outputs by a single IN, the proposed DC/AC inverter is able to apply an active voltage vector during the ST state. This capability improves the DC/AC voltage gain, increases the modulation index, and decreases the required ST time. The operation principles are described, and the steady-state relations are derived. It is compared with other magnetically coupled INs in terms of boost factor and voltage stress of switches. Considering the 10-switches three-level inverter as the front-end inverter, an adopted maximum boost strategy using the space vector modulation is developed targeting minimum ST time. Finally, a laboratory prototype of the converter is developed, and several tests are carried out. The results validate the given theories and simulations.© The Authors. Published by IEEE. This work is licensed under a Creative Commons Attribution 4.0 License. For more information, see https://creativecommons.org/licenses/by/4.0/fi=vertaisarvioitu|en=peerReviewed

ПАРАЛЛЕЛЬНАЯ ИТЕРАЦИОННАЯ РЕКОНСТРУКЦИЯ ФАНТОМА CATPHAN ПО ЭКСПЕРИМЕНТАЛЬНЫМ ДАННЫМ

The principles of fast parallel iterative algorithms based on the use of graphics accelerators and OpenGL library are considered in the paper. The proposed approach provides simultaneous minimization of the residuals of the desired solution and total variation of the reconstructed three- dimensional image. The number of necessary input data, i. e. conical X-ray projections, can be reduced several times. It means in a corresponding number of times the possibility to reduce radiation exposure to the patient. At the same time maintain the necessary contrast and spatial resolution of threedimensional image of the patient. Heuristic iterative algorithm can be used as an alternative to the well-known three-dimensional Feldkamp algorithm.Рассматриваются принципы создания быстрых параллельных итерационных алгоритмов, основанных на использовании графических ускорителей и библиотеки OpenGL. Предложенные подходы обеспечивают одновременную минимизацию невязки искомого решения и тотальной вариации реконструируемого трехмерного изображения. При этом число необходимых исходных данных (конических рентгеновских проекций), а значит, и лучевая нагрузка на пациента при сохранении необходимого контраста и пространственного разрешения трехмерного изображения могут быть уменьшены в несколько раз. Предложенный эвристический итерационный алгоритм может быть использован как альтернатива известному трехмерному алгоритму Фельдкампа

Students’ Educational Problems, Presented in the University’s Educational Councils from 2002 to 2005, Shahrekord University of Medical Sciences

Background & Objective : An educational council, one of the most important parts of each university, plays the main role in solving students’ educational problems. This study was aimed to analyze the students’ educational problems in Shahrekord University of Medical Sciences, according to the councils’ minutes from 2002 to 2005. Methods : In this study, 333 cases of the students’ educational problems were extracted from the minutes of 66 educational councils’ meetings during a period of four years. They were analyzed according to the students’ study field, level, turn (morning or evening courses), sex, and the state of being native. Results : Among all, request for omitting a course, educational leave, and registering a course were the most frequent problems. Non native students’ educational problems were more than native ones (6.8% and 4.3% respectively) and males’ problems (9.8%) were more than females’ (3.8%) (p=0.0001). Educational problems among students of medicine (8.4%), radiology (7.6%), and field of fighting against diseases (5.9%) were more frequent than others. The difference between the frequency of problems in the students attending morning classes (5.3%) and those attending evening classes (5.2%) was not significant. Conclusion : This study revealed that the students’ educational problems were different in various study fields. There were significantly more problems in male and non native students (who are less supported by the families) compared to female and native ones. Family, financial and health problems, lack of enough knowledge among students and tutors about educational rules stood amongst the most important factors leading to the students’ educational problems. Keywords: Student’s educational problem, Educational council, University of Medical Sciences

БЫСТРАЯ ИТЕРАЦИОННАЯ КИЛОВОЛЬТНАЯ ТОМОГРАФИЯ В КОНИЧЕСКОМ ПУЧКЕ ЛУЧЕЙ

Creating a fast parallel iterative tomographic algorithms based on the use of graphics accelerators, which simultaneously provide the minimization of residual and total variation of the reconstructed image is an important and urgent task, which is of great scientific and practical importance. Such algorithms can be used, for example, in the implementation of radiation therapy patients, because it is always done pre-computed tomography of patients in order to better identify areas which can then be subjected to radiation exposure. Создание быстрых параллельных итерационных томографических алгоритмов, основанных на использовании графических ускорителей, которые одновременно обеспечивают минимизацию невязки и тотальной вариации реконструированного изображения является важной и актуальной задачей, имеющей большое научное и прикладное значение. Такие алгоритмы могут использоваться, например, при осуществлении радиационной терапии пациентов, потому что предварительно всегда производится компьютерная томография пациентов с целью более точного определения областей, которые потом будут подвергнуты лучевому воздействию

ТРЕХМЕРНАЯ РЕКОНСТРУКЦИЯ ИЗОБРАЖЕНИЙ МЕТОДОМ SART С МИНИМИЗАЦИЕЙ ТОТАЛЬНОЙ ВАРИАЦИИ

Computed tomography is still being intensively studied and widely used to solve a number of industrial and medical applications. The algebraic reconstruction method with simultaneous iterations SART considered in this work as one of the most promising of iterative methods, suitable for the tomographic problems. Graphics processor is used to accelerate the speed of the reconstruction. The method of minimizing the total variation (TV) is used as a priori support for the regularization of the iterative process and to overcome the incompleteness of the information.Компьютерная томография продолжает интенсивно исследоваться и широко используется для решения ряда промышленных и медицинских задач. Алгебраический метод реконструкции с одновременными итерациями SART рассматривается в данной работе как один из перспективных итерационных методов, пригодных для решения томографических задач. Для ускорения быстродействия используется графический процессор. Метод минимизации тотальной вариации (TV) используется как априорная поддержка для регуляризации итерационного процесса и преодоления неполноты информации

Beam-forming module for backhaul link in a Relay-aided 4G network

YesA novel beam-forming module based on Wilkinson power divider technology, including attenuators and phase shifter chips is designed, fabricated and evaluated to be incorporated in a Relay Station connecting it with the Base Station under a 4G network. The proposed module is a 1:8 port circuit, utilizing two substrates, providing approximately 700 MHz bandwidth over 3.5 GHz frequency band and less than −20 dB transmission line coupling. Moreover an external control unit that feeds the beam-forming module with code-words that define the proper amplitude/phase of the excitation currents is established and described. The presented module is connected to a planar array and tested for two beam-forming scenarios, providing satisfactory radiation patterns

ВЫБОР РАЦИОНАЛЬНЫХ ПАРАМЕТРОВ КОНСТРУКЦИИ КАРКАСА МОРСКОЙ ПЛАТФОРМЫ

Creation of a parametric geometrical model of the frame construction of offshore oil platform using special built-in languages of finite-element modeling systems and finite-element model of the construction subject to operational loads is considered. Preparation of an optimization construction model is described, optimization calculations are carried out and recommendations on choosing ra-tional construction parameters are given.Рассматривается создание параметрической геометрической модели конструкции каркаса морской нефтедобывающей платформы с использованием специальных встроенных языков систем конечно-элементного моделирования, а также конечно-элементной модели этой конструкции с уче-том эксплуатационных нагрузок. Описывается подготовка оптимизационной модели конструкции, выполняются оптимизационные расчеты и даются рекомендации по выбору рациональных парамет-ров конструкции

ПАРАМЕТРИЧЕСКАЯ КОНЕЧНО-ЭЛЕМЕНТНАЯ МОДЕЛЬ КЕССОННОЙ КОНСТРУКЦИИ

This research is devoted to the creation of a finite element model of a dry welding box for repairing core oil platform taking into account operational loads.Рассматривается создание параметрической геометрической модели конструкции бокса сухой сварки для ремонта остова нефтедобывающей платформы с использованием специальных встроенных языков систем конечно-элементного моделирования, а также конечно-элементной модели этой конструкции с учетом эксплуатационных нагрузок. Описывается подготовка оптимизационной модели конструкции, выполняются оптимизационные расчеты и даются рекомендации по выбору рациональных параметров конструкции