Loading...
Search for:
parameters-selection
0.006 seconds
An efficient parameter selection criterion for image denoising
, Article 5th IEEE International Symposium on Signal Processing and Information Technology, Athens, 18 December 2005 through 21 December 2005 ; Volume 2005 , 2005 , Pages 872-877 ; Kasaei, S ; Marvasti, F ; Sharif University of Technology
2005
Abstract
The performance of most image denoising systems depends on some parameters which should be set carefully based on noise distribution and its variance. As in some applications noise characteristics are unknown, in this research, a criterion which its minimization leads to the best parameter set up is introduced. The proposed criterion is evaluated for the wavelet shrinkage image denoising algorithm using the cross validation procedure. The criterion is tested for some different values of thresholds, and the output leading to the minimum criterion value is selected as the final denoised output. The resulting outputs of our method and the previous threshold selection scheme for the wavelet...
Optimization of Support Vector Regression Parameters Using Firefly Algorithm
, M.Sc. Thesis Sharif University of Technology ; Mahdavi-Amiri, Nezameddin (Supervisor)
Abstract
Support vector regression (SVR) in the field of machine learning attracted much attention because of its attractive features and high efficiency for high-dimensional and nonlinear data. Although support vector regression has shown to be very effective for prediction problems, it is necessary to adjust the parameters contained therein to obtain the desired output with error rates. In the past, this was done manually, by trial and error. Over time and by development of optimization algorithms, one of the newest methods to solve such problems is the meta-heuristic optimization algorithms. Therefore, in this thesis, we use the firefly optimization algorithm, which is a population-based...
Rainbow table TMTO attack optimization considering online sequential search time
, Article 2014 International Congress on Technology, Communication and Knowledge, ICTCK 2014, 26 November 2014 through 27 November 2014 ; 2015 ; 9781479980215 (ISBN) ; Jahromi, M. M ; Rezaiy, H. R ; Sharif University of Technology
Institute of Electrical and Electronics Engineers Inc
2015
Abstract
In this paper, we propose an optimized parameter selection procedure for rainbow table Time Memory Trade-Off (TMTO) attack with sequential online search. Unlike previous works that mainly deal with minimizing required memory in the rainbow table TMTO attack we simultaneously focus on the required memory and online search time. Our parameter selection technique is optimized regarding the minimization of the required memory subject to a certain success probability and a maximum online search time. Obtained results are two compact mathematical expressions for determining rainbow table TMTO attack parameters, number and length of chains. The application of our optimized parameter selection...
Generalized OOC assisted PPM and overlapping PPM, considering thermal noise and APD effect
, Article Journal of Optical Communications and Networking ; Volume 5, Issue 7 , 2013 , Pages 696-703 ; 19430620 (ISSN) ; Pakravan, M. R ; Sharif University of Technology
Abstract
The effect of thermal noise and avalanche photodiode (APD) noise in a code division multiple access (CDMA) system using generalized optical orthogonal codes (GOOC) are investigated for the first time. The modulations used are pulse position modulation (PPM) and overlapping PPM (OPPM). Double optical hardlimiter receiver structure is selected because of its efficient performance. We show that, in a system with all mentioned noise sources, known parameter values, and a bit error rate of 10-7, GOOC codes with cross correlation (λ) equal to 2 support 20 more users compared to strict OOC. We have also analyzed the spectral efficiency of the GOOC OPPM system and compared it with GOOC PPM. The...
An efficient scanning algorithm for improving accuracy based on minimising part warping in selected laser sintering process
, Article Virtual and Physical Prototyping ; Volume 14, Issue 1 , 2019 , Pages 59-78 ; 17452759 (ISSN) ; Movahhedy, M. R ; Khodaygan, S ; Sharif University of Technology
Taylor and Francis Ltd
2019
Abstract
In the selective laser sintering (SLS) method, layers of powder are scanned by a laser beam and sintered. The thermal gradients created by laser heating and the subsequent cooling of the sintered sections results in thermal stresses and part warping in the final part. Thermal gradients are dependent on the scanning algorithm, in particular, the scan vector length. In this work, an efficient scanning algorithm for the SLS process is presented with the aim to minimise the part warping in the final part due to thermally induced residual stresses, while maintaining the production time at a minimum. The proposed algorithm is implemented in a finite element simulation and scanning parameters...
A multiscale phase field method for joint segmentation-rigid registration application to motion estimation of human knee joint
, Article Biomedical Engineering - Applications, Basis and Communications ; Volume 23, Issue 6 , 2011 , Pages 445-456 ; 10162372 (ISSN) ; Esfandiarpour, F ; Shakourirad, A ; Farahmand, F ; Sharif University of Technology
2011
Abstract
Image based registration of rigid objects has been frequently addressed in the literature to obtain an object's motion parameters. In this paper, a new approach of joint segmentation-rigid registration, within the variational framework of the phase field approximation of the Mumford-Shah's functional, is proposed. The defined functional consists of two Mumford-Shah equations, extracting the discontinuity set of the reference and target images due to a rigid spatial transformation. Multiscale minimization of the proposed functional after finite element discretization provided a sub-pixel, robust algorithm for edge extraction as well as edge based rigid registration. The implementation...