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Application of the characteristic green's function technique in closed-form derivation of spatial green's function of finite dielectric structures
, Article CEM 2013 - Computational Electromagnetics International Workshop ; number 6617132 , 2013 , Pages 54-55 ; 9781479914326 (ISBN) ; Shishegar, A. A ; Faraji Dana, R ; Sharif University of Technology
2013
Abstract
A closed-form spatial Green's function for finite dielectric structures is derived by using a combination of the characteristic Green's function (CGF) and rational function fitting method (RFFM). CGF-RFFM represents both of the discrete and continuous spectrum contributions efficiently by using the modified VECTFIT algorithm. To obtain more accurate results, reflection coefficient correction due to the surface waves (SWs) incident on the the end-facet is considered. The main advantage of this method lies in its speed as well as accuracy. Excellent agreements with the rigorous method of moments (MoM) are shown in several examples
Innovative performance of Iranian knowledge-based firms: Large firms or SMEs?
, Article Technological Forecasting and Social Change ; May , 2016 ; 00401625 (ISSN) ; Bagheri Nasrabadi, M ; Yazdi, N ; Babakhan, A. R ; Sharif University of Technology
Elsevier Inc
2016
Abstract
The debate over innovativeness of large firms and SMEs, which was bolded by Schumpeter, still continues under mixed empirical evidences. There are several implications for this debate including policy orientation in support of large firms or SMEs. But there is a scarce of studies in developing countries and no such study in Iran yet. The present study has explored the proportionality of increase of innovation activity versus firm size within 522 Iranian knowledge-based firms categorized in 9 industries. Innovation activity was measured by R&D expenditure while firm size stood for number of employees. Using log-log regression in the first phase, it was found that R&D expenditure confirms a...
Sampling and Distortion Tradeoffs for Band-limited Periodic Signals
, Ph.D. Dissertation Sharif University of Technology ; Marvasti, Farokh (Supervisor)
Abstract
One of the funadmental problems in signal processing is finding the best sampling strategy of a continuous time signal, and then finding the best strategy for compressing the obtained signal samples. The sampling and compression steps are designed with the aim of minimizing the distortion of the reconstructed signal. The problem of finding the best sampling strategy has been widely studied in the signal processing literature. In particular, the Nyquist–Shannon sampling theorem gives a sufficient condition for perfect reconstruction of a continuous-time signal of finite bandwidth. Most of the signal processing literature deals with deterministic signals, with relatively less attention paid to...
A GPU based simulation platform for adaptive frequency Hopf oscillators
, Article ICEE 2012 - 20th Iranian Conference on Electrical Engineering ; 2012 , Pages 884-888 ; 9781467311489 (ISBN) ; Maleki, M. A ; Ahmadi, A ; Bavandpour, M ; Maharatna, K ; Zwolinski, M ; Sharif University of Technology
2012
Abstract
In this paper we demonstrate a dynamical system simulator that runs on a single GPU. The model (running on an NVIDIA GT325M with 1GB of memory) is up to 50 times faster than a CPU version when more than 10 million adaptive Hopf oscillators have been simulated. The simulation shows that the oscillators tune to the correct frequencies for both discrete and continuous spectra. Due to its dynamic nature the system is also capable to track non-stationary spectra. With the help of this model the frequency spectrum of an ECG signal (as a non-stationary signal) obtained and was showed that frequency domain representation of signal (i.e. FFT) is the same as one MATLAB generates
Innovative performance of iranian knowledge-based firms: large firms or SMEs?
, Article Technological Forecasting and Social Change ; Volume 122 , 2017 , Pages 179-185 ; 00401625 (ISSN) ; Bagheri Nasrabadi, M ; Yazdi, N ; Babakhan, A. R ; Sharif University of Technology
Abstract
The debate over innovativeness of large firms and SMEs, which was bolded by Schumpeter, still continues under mixed empirical evidences. There are several implications for this debate including policy orientation in support of large firms or SMEs. But there is a scarce of studies in developing countries and no such study in Iran yet. The present study has explored the proportionality of increase of innovation activity versus firm size within 522 Iranian knowledge-based firms categorized in 9 industries. Innovation activity was measured by R&D expenditure while firm size stood for number of employees. Using log–log regression in the first phase, it was found that R&D expenditure confirms a...
Combination of characteristic Green's function technique and rational function fitting method for computation of modal reflectivity at the optical waveguide end-facet
, Article PHOTOPTICS 2015 - 3rd International Conference on Photonics, Optics and Laser Technology, Proceedings, 12 March 2015 through 14 March 2015 ; Volume 2 , 2015 , Pages 14-21 ; 9789897580932 (ISBN) ; Shishegar, A. A ; Institute for Systems and Technologies of Information, Control and Communication (INSTICC) ; Sharif University of Technology
SciTePress
2015
Abstract
A novel method for computation of modal reflectivity at optical waveguide end-facet is presented. The method is based on the characteristic Green's function (CGF) technique. Using separability assumption of the structure and rational function fitting method (RFFM), a closed-form field expression is derived for optical planar waveguide. The uniform derived expression consists of discrete and continuous spectrum contributions which denotes guided and radiation modes effects respectively. An optimization problem is then defined to calculate the exact reflection coefficients at the end-facet for all extracted poles obtained from rational function fitting step. The proposed CGF-RFFM-optimization...
A moment method analysis of the gain spectrum in bi-directionally pumped Raman amplifiers through continuous-spectrum radiation
, Article Optics and Laser Technology ; Volume 42, Issue 2 , 2010 , Pages 332-335 ; 00303992 (ISSN) ; Pourmoghadas, A ; Sharif University of Technology
2010
Abstract
A semi-analytical method is proposed to solve the equations governing a bi-directionally pumped Raman amplifier through continuous-spectrum radiation. The governing equations are systems of uncountable Nonlinear Ordinary Differential Equation (NODE). By applying the moment method, the uncountable system of NODE is reduced to a system of finite number of NODEs. This system of equations is solved numerically and the results are compared with that of the full numerical method. It was shown that the moment method is a powerful and efficient technique for the analysis of a bi-directionally pumped Raman amplifier through continuous-spectrum radiation