Sharif Digital Repository

Time reversal is a technique in which a signal is pre-filtered such that it focuses both in time and space. Spatial focusing reduces interference to other co-existing systems and temporal focusing concentrates the received power in a very short interval. Energy detector is a practical receiver for ultra-wideband (UWB) time reversed signals due to its low-complexity and low-cost implementation. However, selection of an optimum integration interval to minimize the bit error rate is a major problem. Weighted energy detection is an effective technique to overcome this problem and enhance the performance of energy detectors. However, this improvement is achieved at the expense of non-trivial... 

The algebraic multigrid (AMG) algorithm as a preconditioner to the Krylov subspace methods has drawn the attention of many researchers in solving fluid flow and heat transfer problems. However, the efficient employment of this solver needs experience, because users have to quantify several important parameters. In this work, we choose a hybrid finite-volume element method and quantify the optimum magnitudes for those parameters. To generalize our results, two sets of fluid flow governing equations, the thermobuoyant flow and confined diffusion flame, are studied and the optimum values are determined. The results indicate that the AMG can be very effective if a proper storage method is chosen... 

Study on the potential abilities of the proportional-integral-weighted (PIw) controllers, as a recently proposed generalization for proportional-integral (PI) controllers, can be useful for improving the performance of traditional control systems. In this paper, adaptive PI and adaptive PIw controllers are designed to be used in control of a special class of nonlinear uncertain systems based on the Lyapanuv stability theorem. The effectiveness of the proposed controllers is illustrated by applying the proposed schemes to a Continuous Stirred-Tank Reactor (CSTR) system with an unknown parameter. Simulation results indicate that using adaptive PIw controllers, in comparison to using the... 

Shell galaxies are understood to form through the collision of a dwarf galaxy with an elliptical galaxy. Shell structures and kinematics have been noted to be independent tools to measure the gravitational potential of the shell galaxies. We compare theoretically the formation of shells in Type I shell galaxies in different gravity theories in this work because this is so far missing in the literature. We include Newtonian plus dark halo gravity, and two non-Newtonian gravity models, MOG and MOND, in identical initial systems. We investigate the effect of dynamical friction, which by slowing down the dwarf galaxy in the dark halo models limits the range of shell radii to low values. Under... 

The rise of the damage to energy systems caused by both natural and man-made disruptive events and the connection between energy systems and socio-economic systems have motivated the study of energy system resilience. This paper conceptualizes and comprehensively presents a systematic review of the recent literature focused on the analytical, technical, and mathematical points from the standpoint of the energy systems facing disruptive events. To this end, five phases are developed. Firstly, the concept of the energy system resilience is presented, and then the energy resilience characters and the resilience states are introduced and connected. Thirdly, the formulation and indicators of the... 

The rise of the damage to energy systems caused by both natural and man-made disruptive events and the connection between energy systems and socio-economic systems have motivated the study of energy system resilience. This paper conceptualizes and comprehensively presents a systematic review of the recent literature focused on the analytical, technical, and mathematical points from the standpoint of the energy systems facing disruptive events. To this end, five phases are developed. Firstly, the concept of the energy system resilience is presented, and then the energy resilience characters and the resilience states are introduced and connected. Thirdly, the formulation and indicators of the... 

In this paper, we have proposed a dual-channel supply chain model in uncertain environment to analyze the demand of manufacturer and retailer demand in which the profit being maximized. Linguistic terms are also utilized to establish two fuzzy systems for estimating the demand in direct and retail channels. In order to do that, a mathematical model is proposed based on decentralized situation of supply chain. To solve the model, we have developed a hybrid solution method of genetic algorithm, fuzzy system, and L-P metric. Finally, several test problems are first generated; then, the computational results are analyzed. © 2017 World Scientific Publishing Company  

There is a unanimous agreement that "systems thinking" helps both individuals and organizations make more intelligent and more effective decisions. On the other hand, the unsatisfactory rate of systems thinking evolution among managers, collegians, students and other stratums raises this question that, why such a useful, discriminating and tasteful concept in theory, does not spread with the desirable pace in practice. Where exactly does the problem originate from? The tragedy is more sensible when noting the fact that even those who know the concept methodically do not apply it in action and in their decisions. Unfortunately, despite relatively numerous literatures on changing beliefs,... 

Following the approach of the induced-matter theory, we investigate the cosmological implications of a five-dimensional Brans-Dicke (BD) theory, and propose to explain the acceleration of the universe. After inducing in a four-dimensional hypersurface, we classify the energy-momentum tensor into two parts in a way that, one part represents all kind of the matter (the baryonic and dark) and the other one contains every extra terms emerging from the scale factor of the fifth dimension and the scalar field, which we consider as the energy-momentum tensor of dark energy. We also separate the energy-momentum conservation equation into two conservation equations, one for matter and the other for... 

In this study, we present a vast boundary condition treatment to simulate gas flow through microfilters using direct simulation Monte Carlo (DSMC) method. We examine the effects of different boundary condition treatments on the density, pressure, and velocity distributions and suggest the best conditions to simulate gas flow through microfilters. We also refine the effects of upstream and downstream locations on the solution. The results show that uniform distributions can be achieved if we apply the inlet/outlet boundary condition at appropriate upstream and downstream distances. We also show that all the suggested boundary conditions suitably predict the pressure drop coefficient factor... 

In the present study, the thermal characteristics of electroosmotic flow of power-law fluids in rectangular microchannels in the presence of pressure gradient are investigated. The governing equations for fully developed flow under H1 thermal boundary conditions are first made dimensionless and subsequently solved through a finite difference procedure for a non-uniform grid. The influence of the major parameters on thermal features of the flow such as the temperature distribution and Nusselt number is discussed by a complete parametric study. The results reveal that the channel aspect ratio and the non-Newtonian characteristic of the fluid can affect the thermal behavior of the flow. It is... 

In this paper, the fully developed electroosmotic flow of power-law fluids in rectangular microchannels in the presence of pressure gradient is analyzed. The electrical potential and momentum equations are numerically solved through a finite difference procedure for a non-uniform grid. A complete parametric study reveals that the pressure effects are more pronounced at higher values of the channel aspect ratio and smaller values of the flow behavior index. The Poiseuille number is found to be an increasing function of the channel aspect ratio for pressure assisted flow and a decreasing function of this parameter for pressure opposed flow. It is also observed that the Poiseuille number is... 

Energy is one of the most important social and economic infrastructures and human life is strongly depends on it. In recent years, the occurrence of natural disasters such as drought as a high-impact low-probability event is undeniable. So, energy planning in the disruption situation is necessary in order to anticipate and maintain the performance of the energy system in optimal condition. This paper focuses on developing a hybrid long-term framework for evaluating the energy system resilience based on sustainability concept against drought. The model bridges the gap between long-term energy system planning in macro level and short-term switching operations or micro level modeling approach...