Sharif Digital Repository

This paper investigates various approaches to relieve the transient stability constraint in restructured power systems. The approaches adopted fall into two broad categories: those based on eliminating the constraint in the least-cost way and those based on eliminating with the least possible rescheduling. The latter group can, on the other hand, emerge in the form of a pool-protected policy in which the bilateral contracts are rescheduled to maintain the stability or in the form of a contract-protected policy in which the realizable bilateral contracts are maximized while minimizing the rescheduling in pool market. Transient energy function (TEF) method is used as a tool to calculate the... 

In this study, the issue of allocating the cost of transient stability relief in a bilateral electricity market is investigated. The results of a constrained generation scheduling problem can be utilised in two ways to price the cost of a constraint. In the first method, which is the basis of nodal pricing, the Lagrange multipliers of the nodal power balance constraint are used as the price of electricity at various buses. In the second method, which is used in this study, the constraint relief scheme is based on a bid-based adjustment market of increments and decrements offered by generators to be involved in the constraint relief process. In the scheme used in this study, the cost of... 

In this paper, we analyze the performance of a nonlinear two-photon-absorption (TPA) receiver and compare its performance with that of a single-photon-absorption (SPA) receiver in the context of spectral-phase-encoded optical code-division multiple access (CDMA) technique. The performances for the above systems are evaluated for two different transmission scenarios, namely, asynchronous and slot-level synchronous transmitters. Performance evaluation includes different sources of degradation such as multiple-access interference, noise due to optical amplification, shot noise, and thermal noise. In obtaining the performance, the mean and variance of the received signal in each of the above... 

In this paper, the authors study the performance of a two-photon absorption (TPA) receiver in a typical communication system employing an optical amplifier. For the study, the authors develop a comprehensive performance analysis, taking into account noises due to an optical amplifier, shot noise, and thermal noise, using Gaussian approximation technique. In evaluating the performance of the system using this technique, the mean and the variance of the received signal will be derived. Comparing the results of receivers using the TPA process with that of a typical single-photon absorption (SPA) structure leads the authors to conclude that TPA receivers can be used when the speed of the... 

This paper describes a study of the performance of various configurations for placing multiple optical amplifiers in a typical coherent ultrashort light pulse code-division multiple access (CULP-CDMA) communication system using the additive noise model. For this study, a comprehensive performance analysis was developed that takes into account multiple-access noise, noise due to optical amplifiers, and thermal noise using the saddle-point approximation technique. Prior to obtaining the overall system performance, the input/output statistical models for different elements of the system such as encoders/decoders, star coupler, and optical amplifiers were obtained. Performance comparisons... 

In the present study, considering two-dimensional porosity distribution through a functionally graded porous (FGP) beam, its optimal distributions are obtained. A multi-objective optimization problem is defined to maximize critical buckling load and minimize mass of the beam, simultaneously. To this end, Timoshenko beam theory is employed and equilibrium equations for two-dimensional functionally graded porous (2D-FGP) beam are derived. For the solution, we present generalized differential quadrature method (GDQM) and consider two symmetric boundary conditions (Clamped-Clamped and Hinged-Hinged). Solving generalized eigenvalue problem, critical buckling load for 2D-FGP beam is then obtained.... 

In this paper, assuming porosity varies only along thickness direction, its optimal distributions in functionally graded porous (FGP) beams are tailored. Two multi-objective optimization problems are defined. In the first one, critical buckling load and mass are optimized simultaneously while in the second one, we concentrate on simultaneous optimization of mass and fundamental frequency. Employing Timoshenko beam theory, we present governing equations for a FGP beam. For the solution, we use Ritz method and propose appropriate trial functions according to the boundary conditions (Hinged-Hinged, Clamped-Clamped, Clamped-Hinged and Clamped-Free). Since the porosity distribution along... 

This research addresses the escalation of the ‘discourse of going’ among Iranian educated people in recent years through highlighting the influential role played by for-profit study abroad institutions. Utilizing a discourse-analytic approach, we engage the theoretical concept of chronotope, caliberation, and commodification to investigate the ways through which for-profit study abroad institutions represent the images of ‘life beyond’. The data were obtained in interview sessions with ten certified Iranian study-abroad institutions. The results of the data analysis revealed two main themes, namely, hypothetical utopia there and dystopia here as well as success here-and-now and...