A Novel Three-Level Isolated AC-DC PFC Power Converter Topology with Reduced Number of Switches

The three-level isolated AC-DC power factor corrected (PFC) converter provides safe and more efficient power conversion. In comparison with two-level, three-level PFC converter has the advantages of low total harmonic distortion, low device voltage rating, low di/dt, better output performance, high power factor, and low switching losses at higher switching frequencies. The high frequency transformer (HFT) grants galvanic isolation, steps up or down secondary voltage, and limits damage in case of a fault current. The existing three-level converter based on solid-state transformer (SST) topologies convert ac power from the electrical grid to a dc load while maintaining at least the minimum requirements set by the international standards (i.e., high power factor and low total harmonic distortion). The SST topologies with the capability of controlling intermediate dc-bus and output voltage simultaneously require two full bridges at the primary and secondary side of the HFT. As the power level increases, the number of cascaded bridges increases accordingly, and the price associated with these semiconductor devices becomes highly expensive. As result, the demand of converting high power level led to emphasis on high performance and cost-effective power conversion topology. The aim of this dissertation is to develop a new low-cost and high-performance three-level isolated AC-DC (PFC) converter topology. The proposed topology replaces the conventional three-level inverter in the secondary side of the HFT by only two switches and four diodes while still maintaining the basic functionality of a three-level converter (i.e., regulating the output voltage, controlling the dc-bus voltage to be within desired limits). The advantages of this new topology are: (1) low conduction losses; (2) low-cost; (3) no need to consider the issue of the power backflow; (4) zero-voltage switching (ZVS) and zero-current switching (ZCS) at turn ON are inherently guaranteed without any extra control effort. Two isolated three-level AC-DC power converter topologies are developed and investigated through the dissertation. First topology is based on the neutral point clamping (NPC) converter, and the second topology composed of the T-type converter. Two scale-down prototypes rated at 900-W and 1kW, 200 V are built to test the overall performance of the proposed topologies. The first and second topologies exhibit 94.5 % and 95.8 % efficiency scaled at a nominal power, respectively. The secondary bridge (novel circuit) in both topologies, which consists of two switches and four diodes, has 99.34 % practical efficiency

Barriers of confronting intellectual extremism in saudi universities from the point of view of postgraduate students

This study aims to identify the barriers facing Saudi universities in confronting intellectual extremism from the point of view of their postgraduate students. To achieve the objective of the study, a purposive sample of 133 postgraduate students in Saudi universities was selected. The study followed the descriptive survey method, through a questionnaire prepared by the researcher to collect information related to the study. The results of the study showed a number of barriers facing Saudi universities to confront the intellectual extremism, which came as follows: the weakness of activating the role of the intellectual awareness unit at the university, the absence of courses topics dealing with the phenomenon of intellectual extremism, the weakness of legislation on negative intellectual phenomena, the poor means of purposeful entertainment in universities, and the weakness of the complementary relationship between the university and society. At the end of the study, the researcher presented a number of recommendations and suggestions that will help Saudi universities to carry out their role and duties with regard to confronting intellectual extremism among their students

AN ANALYSIS OF CUTANEOUS LEISHMANIASIS (CL) IN ALDAWADMI GOVERNORATE, SAUDI ARABIA USING GEOGRAPHICAL INFORMATION SYSTEM (GIS)

Leishmaniasis has been described by the World Health Organisation as a ‘neglected disease’ and not well understood, which reflects the variations in transmission cycle, reservoirs, vectors, clinical manifestations, and its associations with many human factors. One country where Cutaneous Leishmaniasis (CL) is a major health issue is Saudi Arabia. This thesis investigates factors influencing the prevalence of CL in Al-Dawadmi Governorate, Saudi Arabia in the period between January 2006 and April 2011 from a multidisciplinary perspective. Meteorological data were used to investigate the influence of climatic variables on the seasonality of CL in the study area. The research also involved surveys of land use / cover around six communities in the protectorate and a case-control study of 125 CL cases and 125 controls to assess the role of socio-economic factors. Additionally, an assessment was made of CL cases that were not officially reported to the health authority. Four main factors were found to influence the prevalence of CL cases in the governorate. There was a very strong, temporally-lagged, relationship between monthly temperature and rainfall and reporting of CL cases. Within individual communities, the case-control results indicated there was a strong association between the presence of certain land cover types or land uses within 300 metre and the probability of contracting CL. A number of socio-economic and demographic factors were also found to be correlated with a higher risk of contracting CL. In addition, socio-economic factors and contrasts in accessibility to health services influenced the reporting of CL cases to the authorities. Overall, the results suggest that a multi-faceted approach to reducing the prevalence of CL is required. Public authorities need to be aware of the meteorological trigger conditions, undertake reservoir eradication activities in certain circumstances, improve access to key diagnostic health services and, most cost-effectively, undertake initiatives to improve public awareness of the key risk factors, relevant mitigation measures and the advantages of seeking prompt treatment

Foreign Policy from Khatami to Ahmadinejad There is One Foreign Policy in Iran, which is Khamenei's Foreign Policy

This Article is part of an MA thesis: "Iran Wilayat al Faqih System of Governance and Public Policymaking" which tried to investigate the challenges that public policy in Iran is facing under Wilayat al Faqih system of governance. The article here deals with foreign policy making in Iran from Khatami to Ahmadinejad in regards to both Iran regional roleand Iran-U.S. relations. It sheds light on the challenges that are facing Iranian foreign policy making which can affect both the regime and the ideology of Wilayat al Faqih itself. It also, discusses series of problems that are challenging the authority of the supreme leader which resulted in a power struggle between the supreme leader (representative of the Wilayat al Faqih institution) and the president (representative of the Republican institution) inside the system of governance when it comes to policymaking. The contradictory roles between both is a result of the president limited power in formulating foreign policies, together with his ideological preferences that is different from the supreme leader. The Article concludes by stating that such power struggle between the offices may impact Iran's domestic policies but not Iranian foreign policies, as Iran is becoming a regional power

Between the Supreme Leader and the President: Understanding Wilayat al Faqih (Iranian) System of Governance

This paper is going to explain Wilayat al Faqih (Iranian) system of governance by looking at it from institutional and elite theory approach. The paper will try also to look at the so called “president dilemma” within Wilayat al Faqih system of governance, which is represented by the power struggle between the institution of the supreme leader and the institution of the president in public policy making. This power struggle revealed the weakness of the ideology and the institution of Wilayat al Faqih founded by the leader of the Iranian revolution, Khomeini. And became to open the door for many questions of whether or not the Wilayat al Faqih ideology and institution can lead to a constitutional crisis, if not what kind of future is held for both the institution of the supreme leader and the institution of the president under its system