排序方式： 共有19条查询结果，搜索用时 15 毫秒
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Ahmed Bendib Aissa Chouder Kamel Kara Abdelhammid Kherbachi Said Barkat Walid Issa 《Journal of The Franklin Institute》2019,356(13):6842-6874
In a microgrid (MG) topology, the secondary control is introduced to compensate for the voltage amplitude and frequency deviations, mainly caused by the inherent characteristics of the droop control strategy. This paper proposes an accurate approach to derive small signal models of the frequency and amplitude voltage at the point of common coupling (PCC) of a single-phase MG by analyzing the dynamics of the second-order generalized integrator-based frequency-locked loop (SOGI-FLL). The frequency estimate model is then introduced in the frequency restoration control loop, while the derived model of the amplitude estimate is introduced for the voltage restoration loop. Based on the obtained models, the MG stability analysis and proposed controllers’ parameters tuning are carried out. Also, this study includes the modeling and design of the synchronization control loop that enables a seamless transition from island mode to grid-connected mode operation. Simulation and practical experiments of a hierarchical control scheme, including traditional droop control and the proposed secondary control for two single-phase parallel inverters, are implemented to confirm the effectiveness and the robustness of the proposal under different operating conditions. The obtained results validate the proposed modeling approach to provide the expected transient response and disturbance rejection in the MG. 相似文献
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This article presents a new approach to modeling information flows within today's information systems environments characterized by electronic commerce. We treat information as a resource whose value is fundamentally multidimensional in nature. In this article we consider the economic and psychological dimensions of the value of information. It is argued that it is meaningless to model the value of information in isolation away from the context and the specific parties between which this information is exchanged. We therefore focus exclusively on modeling information flows rather than information itself. To achieve this, we propose a formal framework for describing transactions involving information flows. The framework consists of a generalized model for representing information transactions and for defining a set of fundamental properties of multiparty transactions. These properties are fairness, constructiveness, and monopoly. Where applicable, they are defined for individuals, transactions, and a system of transactions. The proposed model reveals the nature of individual transactions and markets, and consequently has important implications for simulation of market scenarios and to help arrive at effective policies for pricing and market regulations. 相似文献
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Nabeel Al-Qirim Ali Tarhini Kamel Rouibah Serhani Mohamd Aishah Rashid Yammahi Maraim Ahmed Yammahi 《Education and Information Technologies》2018,23(1):129-142
This research examines the learning preferences of students in UAE University (UAEU). The uniqueness of this research emanates from the fact that no prior research examined this area from the UAE’s perspective. Thus, this research embarks on the fact that student learning strategies vary from one country to another due to many factors. This research utilizes six learning strategies extended from the literature and attempts to examine their importance on UAEU students using survey research. The selected learning strategies were students” motivation, time-poorness, mastery effort, assessment focus, competitiveness, and listening. This research provided interesting insights and contrasts pertaining to the learning strategies of UAEU students. Implications are discussed highlighting different theoretical as well as professional contributions and contentions and portrayed a path where pending issues could be addressed by future research. 相似文献
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Walid E. Zahran Kholoud A. Salah El-Dien Philip G. Kamel Ahmed Shawky El-Sawaby 《Indian journal of clinical biochemistry : IJCB》2013,28(2):141-146
Tumor necrosis factor (TNF-α) is a cytokine involved in systemic inflammation during acute phase reactions. The current study was designed to investigate the levels of pro-inflammatory cytokine (TNF-α) along with the anti-inflammatory cytokine (IL-10) during progression of non-alcoholic fatty liver disease (NAFLD) from simple steatosis to non-alcoholic steatohepatitis (NASH) and fibrosis in diabetic patients, and correlate the levels of cytokines with the progression of NAFLD. Fifty-two diabetic patients compared to 18 healthy controls were participated in this study. Based on clinical diagnosis, patients were divided into three groups: simple steatosis, NASH and fibrosis. Serum liver function tests, fasting blood glucose, bilirubin, ALT, AST, TNF-α, IL-10 and lipid profile were measured. TNF-α levels were significantly higher in NAFLD patients compared to control subjects with a significant positive correlation with body mass index and fasting blood glucose (FBG) but with negative correlation with IL-10. Serum IL-10 levels were significantly lower in NAFLD patients compared with controls. A positive correlation between IL-10 and HDL-C with concomitant negative correlation between IL-10 and FBG and triacylglycerides was found. Cytokine analyses showed that there was a prominent imbalance between TNF-α and IL-10 in patients with NAFLD, and this imbalance increase by increasing the progression of NAFLD especially in obese diabetic patients. TNF-α and IL-10 could be used in diagnosis and follow-up of NAFLD stages in a way to avoid liver biopsies in greater proportion of patients. 相似文献
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A tracer study of Lebanese upper secondary school students 总被引：1，自引：0，他引：1
Barend Vlaardingerbroek Kamel Dallal George Rizkallah Jihan Rabah 《International Journal of Educational Development》2007
This paper presents data arising from a tracer study of 90 terminating Beirut upper secondary school students. Nearly all the students intended to transit to university, about half of them to science and technology programmes, and subsequently did so. Median anticipated earnings upon graduation were realistic, but a lack of information or guidance about higher education and career options was noted by a considerable proportion. The results of the study are discussed with reference to the as yet poorly elucidated dynamics of schooling with regard to attrition and transition to higher education and employment in Lebanon. 相似文献
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Kamel Ariffin Mohd. Atan Rustem Suncheleev Mahendran Shitan Mohd. Shafie Bin Mustafa 《美中教育评论》2008,5(3):1-15
Recent years it has an explosive development of IT technologies. However, the problem of natural integration of modern technologies in teaching and learning mathematics is far from its final solution. In teaching mathematics at universities, these capabilities either are ignored or have extremely limited applications. In our study, we consider animation as one of the tools that could increase students＇ motivation, curiosity and understanding. In order to evaluate the perception about using animation in the study of calculus, a brief survey was conducted in University Utara Malaysia （UUM）. The survey consisted of 17 lecturers and 25 students from UUM. The survey also conducted in UPM （University Putra Malaysia） and UniKL （University Kuala Lumpur）, which comprised of 82 students and 49 students respectively. At the same time, we are interested in whether or not the perception of students differs by factors like gender, age group, entry qualification, program of study and previous grades. This survey was conducted in UPM comprised of 160 students. In this paper, we describe our data and report our findings, make a comparison between students＇ perception in UPM, UUM and UniKL. Further a comparison is also made regarding perception of UniKL students from two different programmes of study. To evaluate the performance of students, a simple comparative experiment between Computer Aided Learning Method （CALM） and the Traditional Learning Method （TLM） conducted in UUM and UPM and we report our preliminary findings in this paper. 相似文献
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Kamel Asali 《International Information and Library Review》2013,45(2):171-183
AbstractLibrary automation assumed a great deal of importance in libraries in the mid 1960’s. Since then it has become a household word in librarianship. Library automation in university libraries in Ghana is a relatively new concept. Even though computers have been installed in the three university libraries in Ghana, computerization has not had much impact on the services provided by these libraries. This paper reviews the computerization projects in the university libraries in Ghana, with a particular reference to the Balme Library of the University of Ghana. Reasons for automation, areas of application and problems associated with automation are discussed. Also highlighted are barriers militating against successful university library automation, like financial problems, attitudinal problems, lack of co-operation among university libraries, hardware and software problems and personnel problems. Recommendations are made for the improvement of automation at the university libraries in Ghana. These include evaluation of existing systems, properly planned automation project, financial support and co-operation among the university libraries. 相似文献
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Kamel Jedidi Venkatram Ramaswamy Wayne S. DeSarbo Michel Wedel 《Structural equation modeling》2013,20(3):266-289
We propose a maximum likelihood framework for estimating finite mixtures of multivariate regression and simultaneous equation models with multiple endogenous variables. The proposed “semi‐parametric” approach posits that the sample of endogenous observations arises from a finite mixture of components (or latent‐classes) of unknown proportions with multiple structural relations implied by the specified model for each latent‐class. We devise an Expectation‐Maximization algorithm in a maximum likelihood framework to simultaneously estimate the class proportions, the class‐specific structural parameters, and posterior probabilities of membership of each observation into each latent‐class. The appropriate number of classes can be chosen using various information‐theoretic heuristics. A data set entailing cross‐sectional observations for a diverse sample of businesses is used to illustrate the proposed approach. 相似文献
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Hannah L. Dinnen Jack Baker Renee Dallal Kristy Brann Paul D. Flaspohler 《Psychology in the schools》2020,57(12):1864-1877
This study explored negative emotional, behavioral, and academic performance outcomes for highly mobile students and potential protective factors. Participants were fourth and fifth-grade students (N = 647, 51% male) from three schools with low socioeconomic status, highly mobile student populations within a large, suburban school district in the midwestern United States. Data were collected through student self-report surveys, teacher-report surveys, and school records. Multilevel moderation analysis tested whether school connectedness (SC) or social and emotional competence (SEC) acted as protective factors for highly mobile students, moderating the effect of school mobility on emotional problems and academic performance. Student mobility was associated with more emotional problems and lower academic performance. In contrast to past research, there was not an association between mobility and behavior problems. Although they did not act as protective factors, SC and SEC were independently associated with fewer emotional problems and stronger reading performance for all students, controlling for mobility. Results build on existing evidence that student mobility has negative effects on emotional and academic outcomes and lend support for interventions focused on enhancing SC and SEC of all students, including those at increased risk due to high mobility. 相似文献