A Bi-Polar Triple-Output Converter with Duty Cycle Estimation

This paper proposes a triple output converter with buck, boost and inverted outputs and controlled through duty cycle estimation. In the existing converter, to generate the negative output, the power flows from load to the supply (from the boost output to the supply) during a part of the cycle, which increases cycle time and losses, and reduces the power level. To overcome this, a modified converter with a main and an auxiliary inductance and with reduced number of switches is proposed. The converter can operate in continuous and discontinuous conduction modes and the outputs can be independently controlled. An analysis of the converter is done for both modes. A simplified control of the converter through duty cycle estimation is suggested to regulate the outputs, which does not have the constraint that the current ripple has to be small. The control works both in the continuous and discontinuous modes. The simulation results closely match with the analysis. A prototype of the converter is constructed with a Spartan FPGA system and results have been presented.

Novel forward mode AC/AC converters with high frequency link

A circuit configuration and a circuit topologic family of the novel forward mode AC/AC converters with high frequency link are presented. The circuit configuration is constituted of input cycloconverter, high frequency transformer, output cycloconverter, input and output filters. The circuit topologic family includes eight circuit topologies, such as full-bridge-full-wave mode, etc. The bi-polarity phase-shifted control strategy and steady principles are thoroughly investigated. The output characteristics are obtained. By using the bi-polarity phase-shifted control strategy with phase-shifted control between the output cycloconveter and the input cycloconverter, commutation overlap period of the output cycloconverter, and polarity selection of the output filtering inductance current and the input voltage, the leakage inductance energy and the output filtering inductance current are naturally commutated, and surge voltage and surge current of the cycloconverters are overcome. The converters have such advantages as simple topology, two-stage power conversions(LFAC/HFAC/LFAC), bi-directional power flow, high frequency electrical isolation, good output waveforms, and strong ability to stabilize voltage. The converters lay key technical foundation on a new-type of regulated sinusoidal AC power supplies and electronic transformers. The correction and advancement of the converters are well verified by a principle test.

DISTRIBUTION OF VOTAW'S λ_1(vc) CRITERION FOR TESTING COMPOUND SYMMETRY OF A COVARIANCE MATRIX

The distribution of Votaw’s λ1（vc） criterion for testing compound symmetryof the covariance matrix of a t-variate Gaussian model has been obtained in terms ofMeijer’s G-function as well as in computable series form. Special cases of the densityhave also been derived using reduction formulae for G-function.

BRICS and Geopolitics： A Match Made in Heaven？

We are living in a multi-polar world under the greater influence of one power. After the shutdown of the government in the US, it can be said that the sole power is about to be challenged. This paper hopes to establish the fact that the future of the international system will continue to be multi-polar. Economic groupings like the Brazil, Russia, India, China, and South Africa （BRICS）, Mexico, Indonesia, Singapore and Turkey （MIST） and others denote to this. These groupings may present an alternative to geographically locked but indispensible European Union. Despite the system being multi-polar, the United States dominates the international system. This paper deals with the BRICS countries that propose a bid for power in international relations. Will they have equidistant power form one another or will there be a hierarchy in between them？ Can they take/make economic or political decisions？ Is a geographically spread power structure more effective in controlling the balances between war and peace？ Can they remain objective on trouble spots that may arise in Europe, the Middle East, the Balkans, Asia and the Americas？ This paper hopes to achieve the goal of providing a framework for understanding a multi-polar approach to international relations based on the collaboration of BRICS countries. The first part will be the theoretical framework of the paper. The second part will be concerned with American supremacy in foreign relations and the need to question it. The third part will deal with emerging powers but since the most influential ＂power politics＂ are steered by China and Russia the main emphasis will be on them. The last part will come to the conclusion.

A Seven-year Experience for The Surgical Radiofrequency Ablation in Patients With Atrial Fibrillation

Objective A 7-year experience for the treatment strategy using mono- and bi-polar radiofrequency （RF） ablation procedures in a heterogeneous group of patients was reported. Methods Between July 2003 and May 2009, the data of 314 consecutive patients aged 13 -75 （48.70 ± 11.09 ）undergone the radiofrequency ablation procedure for atrial fibrillation （AF） associated with concomitant cardiac surgery were analyzed. Monopolar was used for 91 patients; Medtronic bi-polar RF ablation procedure for 92 patients and Atricure RF ablation procedure for 131 patients. All patients were combined with valve surgery. Regular follow-ups were performed at 3, 6 month after surgery. Results Hospital mortality after combined open heart and surgical RF ablation was 0 %. The success rates for sinus rhythm conversion with monopolar RF were 73.6 % immediately, 74. 7 % at 3 months, 79. 1% at 6 months ; with Medtronic bi- polar RF, the rates were 78.3 % immediately, 82. 8 % at 3 months, 84 % at 6 months ; with Atricure bi-polar RF, the rates were 82. 4 % immediately, 84. 1% at 3 months, 83.9 % at 6 months. Conclusions The use of RF ablation procedures is a safe and efficient option to cure AF during open heart surgery in a selective group of patients.