527 research outputs found

    MATLAB/Simulink Implementation and Analysis of Three Pulse-Width-Modulation (PWM) Techniques

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    With advances in solid-state power electronic devices and microprocessors, various pulse-width-modulation (PWM) techniques have been developed for industrial applications. For example, PWM-based three-phase voltage source inverters (VSI) convert DC power to AC power with variable voltage magnitude and variable frequency. This thesis discusses the advantages and drawbacks of three different PWM techniques: the sinusoidalPWM(SPWM) technique, the third-harmonic-injection PWM(THIPWM) technique, and the space-vector PWM (SVPWM) technique. These three methods are compared by discussing their ease of implementation and by analyzing the output harmonic spectra of various output voltages (poles voltages, line-to-neutral voltages, and line-to-line voltages) and their total harmonic distortion (THD). The simulation results show that both the THIPWM and SVPWM techniques have lower total harmonic distortion than the SPWM technique. The THIPWM and SVPWM techniques in the under-modulation region can both increase the fundamental output voltage by 15.5% over the SPWM technique. Moreover, the SVPWM technique can increase the fundamental output by about 5% in each of the overmodulation regions 1 and 2, respectively

    Entwicklung und Realisierung eines echtzeitfĂ€higen Millimeterwellen-Abbildungssystems fĂŒr Nahbereichsanwendungen

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    The realization of a real time millimetre-wave imaging system for nearfield applications represents a great challenge. Particularly, due to economic reasons, it is currently impossible to realize a scanning system with a huge amount of millimetre-wave transmitters and receivers. Therefore, in the context of this work a new imaging concept has been developed. An investigation concerning its potential for a high-resolution, real time imaging system has been carried out. The system is able to scan a large measurement area (approx. 1 square metre) within 15s and additionally offers the possibility of an automated material recognition. This goal has been achieved with a four channel broadband heterodyne system, and the performance of the setup has been verified with numerous measurement results.Die Realisierung eines echtzeitfĂ€higen bildgebenden Millimeterwellensystems fĂŒr Anwendungen im Nahfeldbereich stellt eine große Herausforderung dar. Vor allem im Millimeterwellenbereich ist es aus KostengrĂŒnden derzeit nicht möglich, fĂŒr eine große AbtastflĂ€che eine komplette Anordnung aus Sende-/Empfangselementen aufzubauen. Deshalb wurde im Rahmen dieser Arbeit ein neuartiges Abbildungskonzept entwickelt und bezĂŒglich seines Potenzials fĂŒr die Erzeugung hochaufgelöster Abbildungen im Quasi-Echtzeitbetrieb untersucht. Das Gesamtsystem ist in der Lage, eine große MessflĂ€che (ca. 1 Quadratmeter) innerhalb von 15s abzutasten und verfĂŒgt weiterhin ĂŒber die Möglichkeit einer automatisierten Materialerkennung. Dieses Ziel wurde mit einem vierkanaligen breitbandigen Heterodynsystem erreicht und anhand zahlreicher Messungen demonstriert

    Some Impact of the English Competence Assessment Test Based on Output Standards on English Teaching at Tan Trao University

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    The standardized English proficiency assessment has yielded significant and positive impacts on the English teaching and learning processes at Tan Trao University. This assessment not only serves as a tool to evaluate students' English proficiency but also constitutes an integral component of the educational process, encompassing curriculum design and instructional methodologies. One of the paramount effects of this assessment is the establishment of clear standards regarding proficiency levels and requisite skills. This initiative provides educators and students with a precise understanding of the competencies required for English language acquisition. Consequently, the university can devise tailored language programs that ensure students are equipped with the necessary skills to thrive in academic and professional environments. Furthermore, the assessment instills a sense of pressure on students as they prepare and engage in a high-stakes testing environment. However, this pressure serves as a motivator for students to enhance their individual English proficiency. Consequently, students are propelled towards autonomy and responsibility in their English language learning endeavors, whether through supplemental coursework or independent study. the assessment fosters improvements in the quality of English language instruction at the university. Educators must possess comprehensive knowledge of the assessment's content and requisite skills, prompting them to explore and implement effective pedagogical strategies. This results in a diversification of teaching methodologies, ranging from the utilization of extensive learning resources to the organization of practical activities and classroom discussions.&nbsp

    Perfectionism, motivational orientation and academic performance

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    The present study examined the association between perfectionism and academic performance, as well as how motivational orientations (fear of failure and achievement motivation) and achievement goals (performance-approach, performance-avoidance, and mastery goals) are interrelated in predicting marks. Two hundred and eight university students completed a questionnaire package that included eight perfectionism subscales, and measures of achievement motivation, trait test anxiety, and achievement goal scales early in the fall semester. Marks in Introduction to Psychology (December exam) were used as a measure of academic performance. Perfectionism made independent contributions to the prediction of marks above and beyond that accounted for by motivational orientations and achievement goals, with significant unique contributions made by the personal standards, parental expectations, and organization perfectionism subscales. Students who had higher personal standards, lower parental expectations and lower organization attained higher marks. In addition, those who had a fear of failure orientation, as well as those who endorsed performance-avoidance goals generally obtained lower grades

    Help or Hurt? The Impact of ESG on Firm Performance in S&P 500 Non-Financial Firms

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    The paper aims to investigate the impact of ESG practice on firms’ financial performance in the context of U.S. market from 2018 to 2020. The paper examines a sample of 57 U.S. non-financial firms belonging to the S&P 500. The Two-Stage Least Squares (2SLS) estimation is employed with an instrumental variable - the political views of the states where the studied firms are located. The paper shows that having a better practice of ESG could enhance firms’ financial performance measured by ROA, ROE, and TobinQ. These findings are consistent with the stakeholder-focused theory instead of shareholder-focus perspective. In addition, the magnitude of the influence of the ESG practice on TobinQ is significantly higher than that of the ESG-ROA and ESG-ROE relations. It reveals that the ESG benefits could make the firms appear more attractive to investors, creating higher market values of the firms’ assets and then higher TobinQ ratio. Not as the TobinQ enhancement, the significant improvement in ROA and ROE would be realized in the long run rather than short term. The low managerial ownership in the U.S. market may increase the chance of ESG overinvestment by the firms’ managers, hence reducing firm value. However, under the pressure of the investors’ strong demand for socially responsible investing, the U.S. firms tend to become involved in ESG activities, obtaining a strong stakeholder commitment and thus creating additional firm value in the long run
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