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    Investigation of partial discharge propagation and location in multiple-α and single- α transformer windings using optimized wavelet analysis

    , Article Iranian Journal of Science and Technology, Transaction B: Engineering ; Volume 30, Issue 6 , 2006 , Pages 655-666 ; 03601307 (ISSN) Salay Naderi, M ; Vakilian, M ; Blackburn, T. R ; Phung, T. B ; Salay Naderi, M ; Sharif University of Technology
    2006
    Abstract
    Partial discharges (PD) are recognized as the main cause of the inner insulation deterioration process in power transformers. Therefore, the optimum inner insulation design is one of the challenges a transformer designer is faced with. Transformer strength, especially during transient conditions, is a criterion for transformer insulation designers. This challenge has made designers initiate and employ other types of winding, for example, rather than ordinary layer and disc windings employ the multiple-α windings. Multiple-α windings have a more complicated structure and are comprised of various parts with different physical structures and electrical characteristics. Typical partial discharge... 

    Review of worldwide activities in liquid-fed pulsed plasma thruster

    , Article Journal of Propulsion and Power ; Volume 30, Issue 2 , March-April , 2014 , Pages 253-264 ; ISSN: 07484658 Rezaeiha, A ; Schonherr, T ; Sharif University of Technology
    2014
    Abstract
    A review of worldwide activities in liquid-fed pulsed plasma thruster (LPPT) is discussed. Pulsed plasma thruster are extensively recognized as one of the most promising electric space propulsion systems to perform propulsive tasks on micro- and nanosatellites, including cubesats, because they offer many advantages compared with other electric space propulsion systems. The low plasma exhaust velocity measured by a Langmuir probe showed that thrust is mainly produced by 0.3 μg mass ionized by the first trigger and a much greater quantity of propellant introduced by the main discharge remained neutral at low speed. Various propellant feeding and discharge initiation methods have been applied... 

    Analysis of effective parameters on ablative PPT performance

    , Article Aircraft Engineering and Aerospace Technology ; Volume 84, Issue 4 , 2012 , Pages 231-243 ; 00022667 (ISSN) Rezaeiha, A ; Schönherr, T ; Sharif University of Technology
    2012
    Abstract
    Purpose - The purpose of this paper is to comprehensively review most of the significant works ever done worldwide to study the effects of essential parameters on pulsed plasma thruster (PPT) performance and to analyze the effects of each parameter on PPT performance. Design/methodology/approach - All the important works studying PPT performance are categorized by the parameter they have studied and its effect on the thruster performance, and their works have been reviewed to analyze the influence of each parameter. Findings - The analysis leads to elucidation of the effects of different geometrical parameters including aspect ratio, electrode width, electrode spacing, electrode shape,... 

    Seismic risk analysis with reliability methods, part II: Analysis

    , Article Structural Safety ; Volume 42 , 2013 , Pages 63-74 ; 01674730 (ISSN) Mahsuli, M ; Haukaas, T ; Sharif University of Technology
    2013
    Abstract
    Reliability methods are employed in this paper to analyze the seismic risk to the Vancouver metropolitan region in Canada. The use of reliability methods contrasts with several contemporary approaches for risk analysis. In this paper, two analysis approaches are presented and implemented in a new computer program. One utilizes the first-order and second-order reliability methods together with a hazard combination technique. The other is a sampling-based method that repeatedly generates damage scenarios in the time period of interest. Both strategies employ the same collection of probabilistic models for seismic risk analysis. While the models are presented in the companion paper, this paper... 

    A new approach to optimize the operating conditions of a polymer electrolyte membrane fuel cell based on degradation mechanisms

    , Article Energy Systems ; Volume 4, Issue 3 , 2013 , Pages 219-237 ; 18683967 (ISSN) Roshandel, R ; Parhizgar, T ; Sharif University of Technology
    2013
    Abstract
    Performance degradation remains as one of the primary limitations for practical applications of proton exchange membrane (PEM) fuel cells. The performance of a PEM fuel cell stack is affected by many internal and external factors, such as fuel cell design and assembly, degradation of materials, operational conditions, and impurities or contaminants. Performance degradation is unavoidable, but the degradation rate can be minimized through a comprehensive understanding of degradation and failure mechanisms. In present work, a single PEM fuel cell for stationary applications is investigated. Membrane and catalyst layers (anode and cathode electrodes) are considered as critical components that... 

    Model enrichment: Concept, measurement, and application

    , Article Journal of Simulation ; Volume 6, Issue 2 , 2012 , Pages 125-140 ; 17477778 (ISSN) Yavari, E ; Roeder, T ; Sharif University of Technology
    2012
    Abstract
    Simplicity and validity are recognized as important attributes of an effective simulation model. However, some disagreement exists both on the definitions of these concepts and on quantitative measures for them. This paper introduces Enrichment Level (EL) for (simulation) models. The EL is a quantitative measure to compare the effectiveness of alternative models when used in a particular project. While there is no conceptual restriction on expanding the EL, it currently captures the bias, speed, variance, and scope of a model as the main contributing enrichment factors. This paper explores these factors and suggests a utility-based method to combine them according to the relative importance... 

    Sensitivity measures for optimal mitigation of risk and reduction of model uncertainty

    , Article Reliability Engineering and System Safety ; Volume 117 , 2013 , Pages 9-20 ; 09518320 (ISSN) Mahsuli, M ; Haukaas, T ; Sharif University of Technology
    2013
    Abstract
    This paper presents a new set of reliability sensitivity measures. The purpose is to identify the optimal manner in which to mitigate risk to civil infrastructure, and reduce model uncertainty in order to improve risk estimates. Three measures are presented. One identifies the infrastructure components that should be prioritized for retrofit. Another measure identifies the infrastructure that should be prioritized for more refined modeling. The third measure identifies the models that should be prioritized in research to improve models, for example by gathering new data. The developments are presented in the context of a region with 622 buildings that are subjected to seismicity from several... 

    Seismic risk analysis with reliability methods, part I: Models

    , Article Structural Safety ; Volume 42 , 2013 , Pages 54-62 ; 01674730 (ISSN) Mahsuli, M ; Haukaas, T ; Sharif University of Technology
    2013
    Abstract
    A library of probabilistic models for prediction of seismic risk is presented. The models are specifically intended for use with reliability methods to compute event probabilities, such as seismic loss probabilities. Several models are presented here for the first time. In particular, new and generic models are proposed for earthquake location, regional loss, building response, building damage, and building loss. Each model is presented with an explanation of its development and a discussion of its predictions. In addition, models from the literature are " smoothed" to make them amenable to reliability analysis. The models are implemented in a new computer program that is tailored for... 

    Degradation based optimization framework for long term applications of energy systems, case study: Solid oxide fuel cell stacks

    , Article Energy ; Volume 107 , 2016 , Pages 172-181 ; 03605442 (ISSN) Roshandel, R ; Parhizkar, T ; Sharif University of Technology
    Elsevier Ltd  2016
    Abstract
    Depletion of fossil fuels has increased the pressure on energy systems to operate in the most efficient and economical mode. This tendency promotes energy systems to operate at optimum operating conditions, which maximizes the system profit over lifetime. Recently, there have been many attempts to maximize lifetime profit. Most of them concentrate on the power generation aspect without incorporating further aspects such as system degradation and profitability through lifetime. However, the main intention of the system operators is to optimize the profitability of system at the moment of operation and not the total profitability through the system lifetime. In this study a novel approach is... 

    SRAM leakage reduction by row/column redundancy under random within-die delay variation

    , Article IEEE Transactions on Very Large Scale Integration (VLSI) Systems ; Volume 18, Issue 12 , 2010 , Pages 1660-1671 ; 10638210 (ISSN) Goudarzi, M ; Ishihara, T ; Sharif University of Technology
    2010
    Abstract
    Share of leakage in total power consumption of static RAM (SRAM) memories is increasing with technology scaling. Reverse body biasing increases threshold voltage (Vth), which exponentially reduces subthreshold leakage, but it increases SRAM access delay. Traditionally, when all cells of an SRAM block used to have almost the same delay, within-die variations are increasingly widening the delay distribution of cells even within a single SRAM block, and hence, most of these cells are substantially faster than the delay set for the entire block. Consequently, after the reverse body biasing and the resulting delay rise, only a small number of cells violate the original delay of the SRAM block; we... 

    Heuristic guess-and-determine attacks on stream ciphers

    , Article IET Information Security ; Volume 3, Issue 2 , 2009 , Pages 66-73 ; 17518709 (ISSN) Ahmadi, H ; Eghlidos, T ; Sharif University of Technology
    2009
    Abstract
    Guess-and-determine (GD) attacks are general attacks on stream ciphers, which have often been implemented in an ad hoc manner. The authors introduce a heuristic approach to the design of GD attacks, that is a dynamic programming method using a Viterbi-like algorithm which is a well-known decoding algorithm for convolutional codes. The authors also show that with this method, the resulting GD attacks, named heuristic GD (HGD) attacks, on TIPSY, SNOW1 and SNOW2 lead to less computational complexity than the previously known GD attacks. The main advantage of HGD attacks, over ad hoc GD attacks, is that while being powerful, they can be designed algorithmically for classes of stream ciphers,... 

    Rubber-toughened epoxies: A critical review

    , Article Polymer Reviews ; Volume 49, Issue 3 , 2009 , Pages 201-225 ; 15583724 (ISSN) Bagheri, R ; Marouf, B. T ; Pearson, R. A
    2009
    Abstract
    Epoxy resins have been used as structural materials since the late 1940s. Despite their desirable properties such as high strength, excellent creep resistance, and good adhesion, they suffer from low fracture energy. Rubber modification as a major toughening approach to overcome the inherent brittleness of epoxy polymers was introduced during the early 1970s. Since then, a large number of investigations have been conducted to elucidate different aspects of rubber-toughened epoxies. The present work is a critical review of the field focusing on the important parameters affecting rubber-toughening. The studies reviewed are classified in five categories including roles of matrix ductility,... 

    Practical next bit test for evaluating pseudorandom sequences

    , Article Scientia Iranica ; Volume 16, Issue 1 D , 2009 , Pages 19-33 ; 10263098 (ISSN) Lavasani, A ; Eghlidos, T ; Sharif University of Technology
    2009
    Abstract
    The Next Bit Test briefly states that a sequence is random if and only if, given any i bits of the sequence, it is not possible to predict the next bit of the sequence with a probability of success significantly greater than 1/2. In 1996, Sadeghiyan and Mohajeri proposed a so-called "new universal test for bit strings", based on the theoretical next bit test. In this paper, we study different aspects of this test and show its weakness. Then, we improve it both theoretically and practically for better classification of the sequences. As a result, a Practical Next Bit (PNB) test is introduced in two Global and Local versions and a histogram, which gives an impression of the global evaluation... 

    A lattice-based changeable threshold multi-secret sharing scheme and its application to threshold cryptography

    , Article Scientia Iranica ; Volume 24, Issue 3 , 2017 , Pages 1448-1457 ; 10263098 (ISSN) Pilaram, H ; Eghlidos, T ; Sharif University of Technology
    Sharif University of Technology  2017
    Abstract
    In this paper, we propose a threshold increasing algorithm for a (t; n) latticebased Threshold Multi-Stage Secret Sharing (TMSSS) scheme. To realize the changeability feature, we use the zero addition protocol to construct a new (t0; n) TMSSS scheme. Therefore, the new scheme enjoys the significant feature of threshold changeability along with the inherited features of being multi-stage, multi-use, and verifiable derived from our previously proposed lattice-based TMSSS scheme. Furthermore, we use the improved TMSSS scheme to propose a threshold decryption algorithm for the Learning With Error (LWE) based public key encryption scheme based on the study of Lindner and Peikert. For threshold... 

    An efficient lattice based multi-stage secret sharing scheme

    , Article IEEE Transactions on Dependable and Secure Computing ; Volume 14, Issue 1 , 2017 , Pages 2-8 ; 15455971 (ISSN) Pilaram, H ; Eghlidos, T ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2017
    Abstract
    In this paper, we construct a lattice based (t, n) threshold multi-stage secret sharing (MSSS) scheme according to Ajtai's construction for one-way functions. In an MSSS scheme, the authorized subsets of participants can recover a subset of secrets at each stage while other secrets remain undisclosed. In this paper, each secret is a vector from a t-dimensional lattice and the basis of each lattice is kept private. A t-subset of n participants can recover the secret(s) using their assigned shares. Using a lattice based one-way function, even after some secrets are revealed, the computational security of the unrecovered secrets is provided against quantum computers. The scheme is multi-use in... 

    Multi-evaporator Joule-Thomson cryogenic refrigeration cycles created by pumping and suction mechanisms

    , Article Applied Thermal Engineering ; Volume 175 , 2020 Rostamzadeh, H ; Gholizadeh, T ; Sharif University of Technology
    Elsevier Ltd  2020
    Abstract
    Due to the simple structure and low production cost of Joule-Thomson (JT) refrigeration cycles, these cryogenic systems have widely been used in many food or medicine industries. However, in many scenarios, two or even three cryogenic temperatures are needed to simultaneously supply different cryogenic cooling loads since each product has its own comfort low-temperature range. In this case, multi-evaporator JT systems can be a promising solution to address several cryogenic temperatures via employing different evaporators. Following this objective, an innovative triple-evaporator JT cycle is proposed, where the pressure difference between evaporators is created via a pumping mechanism by... 

    A new, publicly verifiable, secret sharing scheme

    , Article Scientia Iranica ; Volume 15, Issue 2 , 2008 , Pages 246-251 ; 10263098 (ISSN) Behnad, A ; Eghlidos, T ; Sharif University of Technology
    Sharif University of Technology  2008
    Abstract
    A Publicly Verifiable Secret Sharing (PVSS) scheme, as introduced by Stadler, has a feature where anyone, besides the participants, can verify the validity of the shares distributed by the dealer. Schoenmakers added a new feature, by providing a proof of correctness of the shares released by the players in the reconstruction process. This protocol is claimed to be an improvement on Stadler's and Fujisaki-Okamoto's, both in efficiency and in the type of intractability assumptions. However, Young-Yung improved Schoenmakers' PVSS, using a Discrete-Log instead of a Decision Diffie-Hellman. In this paper, a new PVSS is presented, having an intrinsic difference with its predecessors, that is, the... 

    An adaptive self-regular proximity based large-update IPM for LO

    , Article Optimization Methods and Software ; Volume 20, Issue 1 , 2005 , Pages 169-185 ; 10556788 (ISSN) Salahi, M ; Terlaky, T ; Sharif University of Technology
    Taylor and Francis Inc  2005
    Abstract
    Primal-dual interior-point methods (IPMs) have shown their power in solving large classes of optimization problems. However, there is still a discrepancy between the practical behavior of these algorithms and their theoretical worst-case complexity results with respect to the update strategies of the duality gap parameter in the algorithm. Recently, this discrepancy was significantly reduced by Peng, J., Roos, C. and Terlaky, T., 2002, Self-Regularity: A New Paradigm for Primal-Dual Interior-Point Algorithms (Princeton, NJ: Princeton University Press) who introduced a new family of self-regular (SR)-proximity functions based IPMs. In this paper, based on a class of SR proximities, we propose... 

    ZnS nanocrystals embedded in SiO2 matrix

    , Article Physica E: Low-Dimensional Systems and Nanostructures ; Volume 21, Issue 1 , 2004 , Pages 96-102 ; 13869477 (ISSN) Taghavinia, N ; Yao, T ; Sharif University of Technology
    2004
    Abstract
    Growing nanocrystals in a matrix is a way to have separate, non-agglomerated nanoparticles, which are surface passivated and stabilized against environmental attacks. To create nanocrystals of the desired size and properties in a matrix, it is required that the growth parameters are properly tuned. In this work, we study the growth parameters for ZnS nanocrystals in an SiO2 matrix. Samples were prepared by cosputtering of SiO 2 and ZnS on a silica substrate, followed by annealing at different temperatures. Two categories of samples with low-content ZnS (4 mol%) and high-content ZnS (15 mol%) were examined. In the low-content samples, ZnS nanocrystals are not formed below 900°C annealing... 

    Fluid particle diffusion through high-hematocrit blood flow within a capillary tube

    , Article Journal of Biomechanics ; Volume 44, Issue 1 , Jan , 2011 , Pages 170-175 ; 00219290 (ISSN) Saadatmand, M ; Ishikawa, T ; Matsuki, N ; Jafar Abdekhodaie, M ; Imai, Y ; Ueno, H ; Yamaguchi, T ; Sharif University of Technology
    2011
    Abstract
    Fluid particle diffusion through blood flow within a capillary tube is an important phenomenon to understand, especially for studies in mass transport in the microcirculation as well as in solving technical issues involved in mixing in biomedical microdevices. In this paper, the spreading of tracer particles through up to 20% hematocrit blood, flowing in a capillary tube, was studied using a confocal micro-PTV system. We tracked hundreds of particles in high-hematocrit blood and measured the radial dispersion coefficient. Results yielded significant enhancement of the particle diffusion, due to a micron-scale flow-field generated by red blood cell motions. By increasing the flow rate, the...