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On the positive definiteness of polarity coincidence correlation coefficient matrix
, Article IEEE Signal Processing Letters ; Volume 15 , January , 2008 , Pages 73-76 ; 10709908 (ISSN) ; Nayebi, M. M ; Aref, M. R ; Sharif University of Technology
2008
Abstract
Polarity coincidence correlator (PCC), when used to estimate the covariance matrix on an element-by-element basis, may not yield a positive semi-definite (PSD) estimate. Devlin et al. (Devlin, 1975) claimed that element-wise PCC is not guaranteed to be PSD in dimensions p > 3 for real signals. However, no justification or proof was available on this issue. In this letter, it is proved that for real signals with p ≤ 3 and for complex signals with p ≤ 2, a PSD estimate is guaranteed. Counterexamples are presented for higher dimensions which yield invalid covariance estimates. © 2007 IEEE
Optimization of higher order pulse shapers used for reduction of noise in amplifier circuits
, Article Scientia Iranica ; Volume 12, Issue 1 , 2005 , Pages 75-82 ; 10263098 (ISSN) ; Sharif University of Technology
Sharif University of Technology
2005
Abstract
Active components in amplifiers generate noise. Thus, amplifiers too, produce noise at their output and, therefore, increase the input signal to noise ratio. This is an undesirable feature, more particularly when one is dealing with weak input signals already combined with noise. Thus, reducing amplifiers' noise becomes a necessity for some applications. To overcome this problem, one approach consists of improving electronic device technology. Another approach is the use of advanced techniques in designing low noise amplifiers by taking advantage of pulse shapers. Pulse shapers generally consist of calculated filters made of integrator(s) and differentiator(s) that limit properly the...
A new IR-UWB pulse to mitigate coexistence issues of UWB and narrowband systems
, Article 2013 21st Iranian Conference on Electrical Engineering ; May , 2013 , Page(s): 1 - 5 ; 9781467356343 (ISBN) ; Nezhad, A. Z ; Fotowat Ahmady, A ; Sharif University of Technology
2013
Abstract
A new Ultra Wideband (UWB) pulse shape is proposed to mitigate coexistence issues of IEEE802.11.a WLAN and Impulse Radio UWB (IR-UWB) systems. The proposed method is applicable to the reduction of any given narrowband (NB) interference into UWB systems. This pulse shape is based on frequency up-converting of first derivative of Gaussian pulse which has an adjustable null in Power Spectral Density (PSD) depending on up-converting frequency. Both analytical and simulation results with an adaptive receiver show that an UWB system with interference from a WLAN has noticeable improved performance when using the proposed pulse in comparison with using conventional modulated Gaussian pulse
The effect of intense short pulse laser shapes on generating of the optimum wakefield and dissociation of methane molecule
, Article Laser and Particle Beams ; Volume 30, Issue 3 , May , 2012 , Pages 357-367 ; 02630346 (ISSN) ; Zare, S ; Navid, H. A ; Dehghani, Z ; Sadighi Bonabi, R ; Sharif University of Technology
2012
Abstract
The optimum convolution of dual short pulse for producing the maximum wakefield and the highest dissociation probability of CH4 has been investigated. By using three fundamental shapes of pulses though four different arrangements, the generated wake are considered in plasma. It is found that when the first and second pulses were rectangular-triangular and sinusoidal pulse shapes, respectively, the resultant wakefield amplitude is the highest. This effect opens up a new novel way by pulse shaping mechanism in the photo dissociation dynamics of molecules and controlling of chemical reactions in the desired channels by short pulse intense lasers for reducing the computation time of genetic...
Optimal control of dissociation of nitrogen molecule with intense ultra-short laser pulse shaping
, Article Journal of Molecular Structure ; Volume 1083 , March , 2015 , Pages 121-126 ; 00222860 (ISSN) ; Irani, E ; Sadighi Bonabi, R ; Sharif University of Technology
Elsevier
2015
Abstract
(GraphPresented) The quantum optimal control theory in conjunction with time dependent density functional theory is used to optimize the laser pulse shape for dissociation of nitrogen molecule. For several initial peak intensities and frequency ranges, the optimum shapes are produced and compared to determine the most efficient pulse. Ehrenfest molecular dynamics model is also used to test the dissociation process. The corresponding snapshots of density and time dependent electron localization function are presented. It is noticed that when the frequency ranges of laser pulses are doubled, it leads to 60% faster dissociation of N2 molecule
Optimization of two tailored rectangular femtosecond laser pulses in methane dissociation
, Article Proceedings of SPIE - The International Society for Optical Engineering, 12 April 2010 through 16 April 2010 ; Volume 7721 , April , 2010 ; 0277786X (ISSN) ; 9780819481948 (ISBN) ; Dehghani, Z ; Irani, E ; The Society of Photo-Optical Instrumentation Engineers (SPIE); Brussels Photonics Team (B-PHOT); Brussels-Capital Region; Fonds Wetenschappelijk Onderzoek (FWO); International Commission for Optics (ICO) ; Sharif University of Technology
2010
Abstract
Based on the quantum mechanics principles and classically calculated dressed potential surfaces by using field assisted dissociation model the dissociation probability for CH4 + molecule exposed with a 100 femtosecond 8 Jcm-2 Ti:sapphire laser pulses is calculated. Using the gradient optimization method two tailored rectangular laser pulses for controlling the dissociation of C-H bond of CH4 + molecule along laser pulse direction is found. In the proposed optimization method, the complicacy of solving Schrodinger wave equation is reduced by using classical method and in contrast to the usual controlling and pulse shaping methods of chemical reactions, the experimental data is not needed and...
Application of the splitting approach to solve population balance equations in chemical processes
, Article Chemical Engineering and Technology ; Volume 32, Issue 12 , 2009 , Pages 1894-1900 ; 09307516 (ISSN) ; Baghaei, A ; Sarrafi, A ; Sharif University of Technology
Abstract
Different processes in chemical industries deal with particles and multiphase flow. In such processes, particle or bubble size distribution (PSD) influences the final product quality and also process design. On the other hand, solutions to the dominant hydrodynamic and thermo-kinetic equations ignoring these distributions will make it impossible to accurately simulate these processes. Solutions to population balance equations (PBE's) are needed to attain the PSD. One of the most common methods for the solution of a PBE is the classes method (CM). However, as this method requires a large number of classes to give a reasonable result, it needs a huge amount of calculations and time. To...