Sharif Digital Repository

Efficiency of a power amplifier (PA) as the most power consuming block of a cellular transmitter is crucial. In modern wireless communication systems, the use of spectrally efficient modulation scheme will result in signals with high peak to average power ratio. This means that a cellular PA operates at average output power most often. Thus, low PBO efficiency of a cellular PA could result in lower battery life and thermal problems. As a result, the PA power back-off (PBO) efficiency is as important as its peak efficiency in these applications. In conventional classes of PA like class AB and B, efficiency rapidly degrades with output power reduction. Thus, PBO efficiency improvement... 

Futures exchanges require a margin requirement that ensures their competitiveness and protects against default risk. The purpose of a margin requirement is to protect a clearinghouse from members’ defaults resulting from big losses due to adverse movement of futures prices. Extreme movements are central to the margin setting problem, because only a large price variation may cause brokers to incur losses. So in this study according to recent default in gold futures in Iran Mercantile Exchange we apply extreme value theory for computing unconditional and conditional optimal margin levels based on Block-Maxima and Peak over threshold approaches.The results show that at very high confidence... 

In this study, by performing a series of experiments, the effect of the presence of cylinders on the formation of vortices and the interaction of cylinders on each other and, finally, transverse propagation in a steady flow are investigated. The cylinder cylinders that are in the direction of the motion of the water, have a significant effect on the hydrodynamic aspects and propagation in these streams. In the pattern of flow around cylindrical cylinders, with increasing Reynolds number, the vortex behind the stem begins to oscillate and when they reach, vortices flow into the stream. The flow velocity field, the formation and vortex fluctuation, affects the process of particle propagation...