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Few studies have recently supported the preposition that housing price changes in one location can be affected not only by its history but also by housing price changes in other locations (Ripple effect). There are many reasons why housing price changes in some areas may lead housing price movements in the other areas. The possible causes include structural differences and economic interdependence between areas, migration as well as informational factors. This paper examines spatial effects of house price dynamics within Tehran. The first hypothese is that house prices have started rising first in the north and then spread out over the rest of the city. The second hypothesis is that there is a strong price relationship between contiguous districts. Spatial autoregressive (SAR) and vector error-correction (VEC) models are emplyed to estimate the empirical models using quarterly panel data of Tehran housing markets over the period 1991 to 2006. The results confirms that there is a positive spatial interrelationship among districts. Moreover, the findings indicate the evidence of leading role of the district 1 in the northern half of the city while district 2 seems to have a more prominent effect on the center and the west. Furtheremore, the price interdependence of contiguous districts in the north is seen to be more significant and stronger than the south.

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In this paper torque ripple in switched reluctance motor is studied. The presented method in this paper for minimization of torque ripple is based on suitable machine structure obtained from the genetic algorithm (GA) and suitable machine driver. In the presented paper, the parameters of one machine are chosen as the reference machine parameters. Then some parameters of machine are chosen, which have no effects on the characteristics of mechanical, power and volume of reference machine. The desirable machine is simulated by finite element software, and then the torque characteristics are obtained for different machine structure with various machine parameters. Finally, with GA the best parameters for the design of machine with minimum torque ripple are chosen. So this paper presented for the first time an accurate method by finite element method in the process of machine design by GA. The finite element method used in the previously studies in the design of machine only for machine analysis, but in this paper finite element method is used in the process of machine design. So this method of machine design can be replaced to a conventional method. In this paper, the design of SRM driver is presented based on the best machine structure which is chosen from GA. So, the profile of machine torque for this structure has minimum deviation from the ideal torque without the ripple

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Electrostatic motors are presented special advantages compare to electromagnetic motors such as light-weight, compactness and simple to fabricating. Due to these capabilities, recently, many researchers are working on electrostatic motors to make them applicable in industries. Accordingly, in this paper a new design idea for these motors is investigated theoretically and experimentally. This motor has driving electrodes on both rotor and stator, however, no wire is attached to rotor and signals are transferred to rotor using the induction electrodes. Modeling is implemented to study the effective parameters on performance. Then, using the modeling results, the design parameters are optimized using numerical method to improve the torque and minimize the ripple. Optimization findings are identified an optimum value for ratio of width to gap for driving electrodes and an optimum value for ratio of induction electrodes surface to total surface. Finally, the motor performance is evaluated using experimental setup and several experiments.

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The Direct Torque Control (DTC) of Interior Permanent Magnet Synchronous Motor (IPMSM) offers simple structure and fast torque response. The conventional Switching Table-based DTC (ST-DTC) presents some disadvantages like high torque and flux ripple and also variable switching frequency. This paper investigates the improved ST-DTC strategies to reduce both torque and flux ripple in DTC of IPMSM with emphasis on structure simplicity and fast dynamics. New switching table with only two active vectors for each sector is introduced and the torque control hysteresis band is replaced by duty cycle calculation unit. For flux ripple reduction, conventional hysteresis-based controller is replaced by simple dithering technique. The duty cycle calculation unit is implemented to operate on each selected vector with the aim of torque ripple RMS minimization. The increase of switching frequency in ST-DTC because of delay in torque and flux estimation process, actually, is not possible; even when hysteresis bands are sufficiently diminished. This paper incorporates the combination of duty cycle modulated DTC and dithering technique to enlarge switching frequency. It therefore provides smoother waveform concurrently for the motor torque and the flux.  In the proposed method waveform comparison structure for duty cycle calculation is used; hence, the merits of classical ST-DTC, such as fast dynamic and simple structure, are mostly preserved