Volterra difference equations

This dissertation consists of five papers in which discrete Volterra equations of different types and orders are studied and results regarding the behavior of their solutions are established. The first paper presents some fundamental results about subexponential sequences. It also illustrates the subexponential solutions of scalar linear Volterra sum-difference equations are asymptotically stable. The exact value of the rate of convergence of asymptotically stable solutions is found by determining the asymptotic behavior of the transient renewal equations. The study of subexponential solutions is also continued in the second and third articles. The second paper investigates the same equation using the same process as considered in the first paper. The discussion focuses on a positive lower bound of the rate of convergence of the asymptotically stable solutions. The third paper addresses the rate of convergence of the solutions of scalar linear Volterra sum-difference equations with delay. The result is proved by developing the rate of convergence of transient renewal delay difference equations. The fourth paper discusses the existence of bounded solutions on an unbounded domain of more general nonlinear Volterra sum-difference equations using the Schaefer fixed point theorem and the Lyapunov direct method. The fifth paper examines the asymptotic behavior of nonoscillatory solutions of higher-order integro-dynamic equations and establishes some new criteria based on so-called time scales, which unifies and extends both discrete and continuous mathematical analysis. Beside these five research papers that focus on discrete Volterra equations, this dissertation also contains an introduction, a section on difference calculus, a section on time scales calculus, and a conclusion. --Abstract, page v

Master of Science

dissertationPower converters are frequently exposed to electrical stresses such as over voltage, over current and switching impulses during their regular operations. These stresses may not result in immediate failure of a power converter. However, over longer periods they cause gradual degradation of critical components inside the converter, which ultimately leads to a complete failure of the converter. Failure of a power converter might disrupt the operation of the entire system, occasionally causing catastrophic outcomes. Estimating a converter's state of health and predicting the remaining life involves extensive research in semiconductor device physics and circuit theory, and is both important and challenging. There is always a dire need to determine the level of aging in power converters so that an approximate time to failure could be predicted. A reflectometry technique was applied to power converters to identify failure and aging associated to critical components inside a power converter. In addition, mechanisms for gradual shift in measurable electrical parameters of power converter components over long durations have been studied under the scope of the project. While there exist several other techniques for predicting reliability and aging of power converters, they are limited to characterizing isolated components only. Whereas using the proposed technique, estimating the component degradation in energized circuits is possible. Spread spectrum time domain reflectometry (SSTDR) has been commercially used for detecting aircraft wiring faults during the last decade, however, it was never applied to components in a power converter. During the preliminary stage of this project SSTDR was applied to a DC-DC converter circuit, and several key parameters such as MOSFETs ON resistance was extracted to characterize MOSFET aging. Later on, this technique was applied to different other components in an H-bridge AC-AC converter for failure rate estimation and reliability analysis. The MTTF (mean time to failure) was calculated based on the SSTDR generated data. The conducted research has initiated other SSTDR based prognostics and state of health measurement methods applicable to PV panels, electric machines and batteries

ミトコンドリアDNA及び、マイクロサテライトマーカーに基づくバングラデシュとその周辺諸国に産するトラフガエル類の系統関係及び集団構造に関する研究

内容の要約広島大学(Hiroshima University)博士(理学)Doctor of Sciencedoctora

Use of spread spectrum time domain reflectometry to estimate state of health of power converters

pre-printA new online measurement and analysis method has been presented in this paper to identify the state of health of power converter circuits. Using spread spectrum time domain reflectometry (SSTDR), impedance in the various current paths inside the converter as well as any fault can be identified without interrupting the circuit's normal operation. Multiple sets of test data have been generated while the SSTDR process is applied to each of the components i.e. the power MOSFETs, the dc bus capacitor and the load. These obtained test data are analyzed to show how these test results are consistent with the impedances in various current paths. An impedance matrix was formed for a non-aged converter and a corresponding matrix using SSTDR data was formed as well. The matrices could be formed for any power converter, and the impedance matrix for the non-aged converter could be considered as a "Reference matrix" for comparison purpose. By comparing these two matrices, the variation in path impedances due to aging could be determined. This research aims to identify the measurable quantities to characterize the aging process, their origins of these quantities and propose convenient methods to measure them

Transforming the fish value chain in Bangladesh: What a gender lens brings

Peer Revie

Characterization of aging process in power converters using spread spectrum time domain reflectometry

pre-printThis paper aims to find a new technique to predict the state of health of power converters by characterizing the most vulnerable components in the converter without affecting the normal circuit operation. Spread spectrum time domain reflectometry (SSTDR) can detect most of the aged components inside the converter while the converter is operational. Semiconductor switches and electrolytic capacitors are the two most sensitive components in power converter circuits, and this paper demonstrated how SSTDR can be used to determine the degradation of these components. Multiple sets of test data have been generated while the SSTDR process is applied to the power MOSFETs, IGBTs connected in a chopper circuit and to the aluminum electrolytic capacitors connected in an RC circuit. Analysis is done on these obtained test data to show how the SSTDR generated data are consistent with the aging of power MOSFETs, IGBTs and electrolytic capacitors

Quantifying device degradation in live power converters using SSTDR assisted impedance Matrix

pre-printA noninterfering measurement technique designed around spread spectrum time domain reflectometry (SSTDR) has been proposed in this paper to identify the level of aging associated with power semiconductor switches inside a live converter circuit. Power MOSFETs are one of the most age-sensitive components in power converter circuits, and this paper demonstrates how SSTDR can be used to determine the characteristic degradation of the switching MOSFETs used in various power converters. An SSTDR technique was applied to determine the aging in power MOSFETs, while they remained energized in live circuits. In addition, SSTDR was applied to various test nodes of an H-bridge ac-ac converter, and multiple impedance matrices were created based on the measured reflections. An error minimization technique has been developed to locate and determine the origin and amount of aging in this circuit, and this technique provides key information about the level of aging associated to the components of interest. By conducting component level failure analysis, the overall reliability of an H-bridge ac-ac converter has been derived and incorporated in this paper

A relational study on consumer promotion, price Perception, service quality perception and brand loyalty in the context of telecommunication industry in Bangladesh

This internship report is submitted in a partial fulfillment of the requirements for the degree of Bachelor of Business Administration,2013.Cataloged from PDF version of Internship report.Includes bibliographical references (page 84).Consumer promotion, in general, is a very expensive issue. Therefore, it is imperative that consumer promotions and other dependent elements have to be studied to make sure that if a consumer promotion activity is implemented, it is a highly effective one. This way, precious monetary resources have the minimum chances of being wasted. To understand the competition in the telecommunication industry better, price perceptions and service quality perceptions on promotion are also considered being worth studying. To look at market share issues, the brand loyalty element should also be explored.This report is directed towards exploring the relationship between consumer promotions, price perception, service quality perceptions and brand loyalty in the telecommunication industry of Bangladesh. Through sizeable literature review and discussions, it is known that there is considerable correlation that exists among the study variables mentioned above. The data sampling was conducted on the customers of different telecom operators. A structured questionnaire was used to find out the views of people regarding consumer promotion in telecom industry of Bangladesh, price perceptions and service quality perceptions about companies’ services and also to find out about brand loyalty in this industry. One Sample T-Test Analysis, Crosstab Analysis and Annova were run on the collected data to analytically explore the relations and their extent. It was found that consumer promotion in the telecommunication industry of Bangladesh communicates the quality of voice clarity and VAS and does not communicate the quality of network availability and internet service to the consumers. Moreover, consumers in the telecommunication industry of Bangladesh perceive that if the price is fair, the quality is moderate. At last but not the lease, occupation and level of income have effect on brand loyalty, whereas gender has no effect on brand loyalty.Nasrin SultanaB. Business Administratio

Fish feed in Bangladesh: Where are the women?

Peer Revie

Rainfall modelling of coastal areas in Bangladesh: extreme-value approach

A series of rainfall data over 48 years in the perio