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Mashhad, Iran

Islamic Azad University of Mashhad is a university in Mashhad, Iran. It was established in 1982, and offers Bachelor, Master, PhD and M.D. degrees. It is famous for the quality and toughness of its undergraduate education and the success of its students in many national competitions and exams. Wikipedia.

Comparing simulation results with experimental findings, it is found that considering nonlinear optical gain is quite essential to accurately obtain dynamic and static characteristics of self-Assembled quantum-dot lasers (SAQDLs). In fact, the nonlinear optical gain prevents extreme decline or growth of photon population as the time increases and of output power as the injected current enhances. It also results in multi-mode lasing and increasing the number of lasing modes with elevation of the injected current. In addition, the best performance of SAQDLs, at a certain injected current, depends on homogeneous and inhomogeneous broadening. Thermal carrier excitation results in degradation of light-current characteristics. It also leads to a red shift in dominant lasing modes at low injected currents, the dominant lasing modes move toward higher energies as the current enhances until the most dominant mode becomes the central one. © 2012 Optical Society of America. Source

Mehmannavaz M.R.,Islamic Azad University at Mashhad | Sattari H.,Islamic Azad University at Tabriz
Laser Physics Letters | Year: 2015

We propose a model for a quintuple coupled quantum dot system based on a GaAs/AlGaAs heterostructure. Then, we analyze the optical bistability (OB) and optical multistability (OM) behaviours and transition between the regimes at a wavelength of λ = 1.550 μm. We take the benefit of consecutive and parallel interdot tunnelling and an incoherent pumping field for electrical and even optical control of the processes. It is shown that OB, OM and transition between them can be accomplished and controlled by adjusting the rate of the inter-dot tunnellings (electrical bias), probe wavelength detuning and rate of the optical incoherent pumping field. By proper choice of the controlling parameters, the bistable hysteresis loop becomes narrower, which makes it easier for the cavity field to reach saturation. We interpret the OB and OM behaviours by discussing the absorption of the active medium. We also investigate switching time between the two stable states when the output field jumps from a lower branch to an upper branch. Such a controllable OB/OM and transition between them in multiple QD molecules at a wavelength of 1.550 μm, may provide some new possibilities for technological applications in optoelectronics, solid-state quantum information science and systems dealing with signal processing. © 2015 Astro Ltd. Source

A novel catalytic synthesis of biscoumarins from 4-hydroxycoumarin and aromatic aldehydes has been developed. The reaction occurs in ethanol in the presence of tetrabutylammonium hexatungstate [TBA] 2[W 6O 19] as catalyst to give the corresponding products in high yields. This new approach has short reaction times, clean reaction profiles, and simple experimental and workup procedures. Moreover, the catalyst can be easily recovered by filtration and used at least three times with only slight reduction in its catalytic activity. Source

Barati R.,Islamic Azad University at Mashhad
KSCE Journal of Civil Engineering | Year: 2013

The Muskingum model continues to be a popular procedure for river flood routing. An important aspect in nonlinear Muskingum models is the calibration of the model parameters. The current study presents the application of commonly available spreadsheet software, Microsoft Excel 2010, for the purpose of estimating the parameters of nonlinear Muskingum routing models. Main advantage of this approach is that it can calibrate the parameters using two different ways without knowing the exact details of optimization techniques. These procedures consist of (1) Generalized Reduced Gradient (GRG) solver and (2) evolutionary solver. The first one needs the initial values assumption for the parameter estimation while the latter requires the determination of the algorithm parameters. The results of the simulation of an example that is a benchmark problem for parameter estimation of the nonlinear Muskingum models indicate that Excel solver is a promising way to reduce problems of the parameter estimation of the nonlinear Muskingum routing models. Furthermore, the results indicate that the efficiency of Excel solver for the parameter estimation of the models can be increased, if both GRG and evolutionary solvers are used together. © 2013 Korean Society of Civil Engineers and Springer-Verlag Berlin Heidelberg. Source

Alamatian J.,Islamic Azad University at Mashhad
Computers and Structures | Year: 2013

This paper prepares new features for applying the Dynamic Relaxation (DR) method in buckling and post-buckling structural analyses. Here, controlling the displacement's increment is the main concept so that the minimum residual displacement and the minimum kinetic energy criteria are designed for updating the load factor in DR iterations. These new formulations do not affect the DR's stability and they are successfully applied to both viscous and kinetic DR algorithms. Numerical analyses of structures with snap-through and snap-back behaviors show that the accuracy and the convergence rate of the suggested methods are higher than the well-known existing approaches such as the arc-length technique, especially, if they are combined with the kinetic DR algorithm. Calculating the buckling load is another interesting application of the proposed methods, performed here. In this manner, the suggested DR algorithms could numerically present the accurate buckling load of structures. © 2012 Elsevier Ltd. All rights reserved. Source

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