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    Speed/accuracy trade-off between the habitual and the goal-directed processes

    , Article PLoS Computational Biology ; Volume 7, Issue 5 , 2011 ; 1553734X (ISSN) Keramati, M ; Dezfouli, A ; Piray, P ; Sharif University of Technology
    Instrumental responses are hypothesized to be of two kinds: habitual and goal-directed, mediated by the sensorimotor and the associative cortico-basal ganglia circuits, respectively. The existence of the two heterogeneous associative learning mechanisms can be hypothesized to arise from the comparative advantages that they have at different stages of learning. In this paper, we assume that the goal-directed system is behaviourally flexible, but slow in choice selection. The habitual system, in contrast, is fast in responding, but inflexible in adapting its behavioural strategy to new conditions. Based on these assumptions and using the computational theory of reinforcement learning, we... 

    Individual differences in nucleus accumbens dopamine receptors predict development of addiction-like behavior: A computational approach

    , Article Neural Computation ; Volume 22, Issue 9 , 2010 , Pages 2334-2368 ; 08997667 (ISSN) Piray, P ; Keramati, M. M ; Dezfouli, A ; Lucas, C ; Mokri, A ; Sharif University of Technology
    Clinical and experimental observations show individual differences in the development of addiction. Increasing evidence supports the hypothesis that dopamine receptor availability in the nucleus accumbens (NAc) predisposes drug reinforcement. Here, modeling striatal-midbrain dopaminergic circuit, we propose a reinforcement learning model for addiction based on the actor-critic model of striatum. Modeling dopamine receptors in the NAc as modulators of learning rate for appetitive-but not aversive-stimuli in the critic-but not the actor-we define vulnerability to addiction as a relatively lower learning rate for the appetitive stimuli, compared to aversive stimuli, in the critic. We... 

    Secrecy capacity scaling in large cooperative wireless networks

    , Article IEEE Transactions on Information Theory ; Volume 63, Issue 3 , 2017 , Pages 1923-1939 ; 00189448 (ISSN) Mirmohseni, M ; Papadimitratos, P. P ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2017
    We investigate large wireless networks subject to security constraints. In contrast to point-to-point, interferencelimited communications considered in prior works, we propose active cooperative relaying-based schemes. We consider a network with nl legitimate nodes, ne eavesdroppers, and path loss exponent α ≥ 2. As long as n2e (log(ne))γ = o(nl ), for some positive γ , we show that one can obtain unbounded secure aggregate rate. This means zero-cost secure communication, given fixed total power constraint for the entire network. We achieve this result through: 1) the source using Wyner randomized encoder and a serial (multi-stage) block Markov scheme, to cooperate with the relays and 2) the... 

    Fast estimation of connectivity in fractured reservoirs using percolation theory

    , Article SPE Journal ; Volume 12, Issue 2 , 2007 , Pages 167-178 ; 1086055X (ISSN) Masihi, M ; King, P. R ; Nuratza, P ; Sharif University of Technology
    Society of Petroleum Engineers (SPE)  2007
    Investigating the impact of geological uncertainty (i.e., spatial distribution of fractures) on reservoir performance may aid management decisions. The conventional approach to address this is to build a number of possible reservoir models, upscale them, and then run flow simulations. The problem with this approach is that it is computationally very expensive. In this study, we use another approach based on the permeability contrasts that control the flow, called percolation approach. This assumes that the permeability disorder of a rock can be simplified to either permeable or impermeable. The advantage is that by using some universal laws from percolation theory, the effect of the complex... 

    A new decoding scheme for errorless codes for overloaded CDMA with active user detection

    , Article 2011 18th International Conference on Telecommunications, ICT 2011, Ayia Napa, 8 May 2011 through 11 May 2011 ; 2011 , Pages 201-205 ; 9781457700248 (ISBN) Mousavi, A ; Pad, P ; Delgosha, P ; Marvasti, F ; Sharif University of Technology
    Recently, a new class of binary codes for overloaded CDMA systems are proposed that not only has the ability of errorless communication but also suitable for detecting active users. These codes are called COWDA. In [1], a Maximum Likelihood (ML) decoder is proposed for this class of codes. Although the proposed scheme for coding/decoding shows impressive performance, the decoder can be significantly improved. In this paper, by assuming practical conditions for the traffic in the system, we suggest and prove an algorithm that increases the performance of the decoder several orders of magnitude (the Bit-Error-Rate (BER) is divided by a factor of about 400 in some E b/N0's). The algorithm... 

    Estimation of the Effective Permeability of Heterogeneous Porous Media by Using Percolation Concepts

    , Article Transport in Porous Media ; Volume 114, Issue 1 , 2016 , Pages 169-199 ; 01693913 (ISSN) Masihi, M ; Gago, P. A ; King, P. R ; Sharif University of Technology
    Springer Netherlands  2016
    In this paper we present new methods to estimate the effective permeability (keff) of heterogeneous porous media with a wide distribution of permeabilities and various underlying structures, using percolation concepts. We first set a threshold permeability (kth) on the permeability density function and use standard algorithms from percolation theory to check whether the high permeable grid blocks (i.e., those with permeability higher than kth) with occupied fraction of “p” first forms a cluster connecting two opposite sides of the system in the direction of the flow (high permeability flow pathway). Then we estimate the effective permeability of the heterogeneous porous media in different... 

    Percolation-based effective permeability estimation in real heterogeneous porous media

    , Article 15th European Conference on the Mathematics of Oil Recovery, 29 August 2016 through 1 September 2016 ; 2016 ; 9462821933 (ISBN); 9789462821934 (ISBN) Masihi, M ; Gago, P ; King, P ; DCSE; Schlumberger; Shell ; Sharif University of Technology
    European Association of Geoscientists and Engineers  2016
    It has long been understood that flow behavior in heterogeneous porous media is largely controlled by the continuity of permeability contrasts. With this in mind, we are looking in new methods for a fast estimation of the effective permeability which concentrates on the properties of the percolating cluster. From percolation concepts we use a threshold permeability value (Kth) by which the gridblocks with the highest permeability values connect two opposite side of the system in the direction of the flow. Those methods can be applied to heterogeneous media of a range of permeabilities distribution and various underlying structures. We use power law relations and weighted power averages that... 

    Optimization of sputtering parameters for the deposition of low resistivity indium tin oxide thin films

    , Article Acta Metallurgica Sinica (English Letters) ; Vol. 27, issue. 2 , Apr , 2014 , p. 324-330 Yasrebi, N ; Bagheri, B ; Yazdanfar, P ; Rashidian, B ; Sasanpour, P ; Sharif University of Technology
    Indium tin oxide (ITO) thin films have been deposited using RF sputtering technique at different pressures, RF powers, and substrate temperatures. Variations in surface morphology, optical properties, and film resistances were measured and analyzed. It is shown that a very low value of sheet resistance (1.96 ω/sq.) can be achieved with suitable arrangement of the deposition experiments. First, at constant RF power, deposition at different pressure values is done, and the condition for achieving minimum sheet resistance (26.43 ω/sq.) is found. In the next step, different values of RF powers are tried, while keeping the pressure fixed on the previously found minimum point (1-2 Pa). Finally,... 

    Comparative assessment of gasification based coal power plants with various CO2 capture technologies producing electricity and hydrogen

    , Article Energy and Fuels ; Volume 28, Issue 2 , 20 February , 2014 , Pages 1028-1040 ; ISSN: 08870624 Mukherjee, S ; Kumar, P ; Hosseini, A ; Yang, A ; Fennell, P ; Sharif University of Technology
    Seven different types of gasification-based coal conversion processes for producing mainly electricity and in some cases hydrogen (H2), with and without carbon dioxide (CO2) capture, were compared on a consistent basis through simulation studies. The flowsheet for each process was developed in a chemical process simulation tool "Aspen Plus". The pressure swing adsorption (PSA), physical absorption (Selexol), and chemical looping combustion (CLC) technologies were separately analyzed for processes with CO2 capture. The performances of the above three capture technologies were compared with respect to energetic and exergetic efficiencies, and the level of CO2 emission. The effect of air... 

    Synthesis of nanosize single-crystal hydroxyapatite via mechanochemical method

    , Article Materials Letters ; Volume 63, Issue 5 , 2009 , Pages 543-546 ; 0167577X (ISSN) Nasiri Tabrizi, B ; Honarmandi, P ; Ebrahimi Kahrizsangi, R ; Honarmandi, P ; Sharif University of Technology
    Single-crystal hydroxyapatite (HAp) nanorods and nanogranules have been synthesized successfully by a mechanochemical process using two distinct experimental procedures. The experimental outcomes are characterized by transmission electron microscopy (TEM), and powder X-ray diffraction (XRD) techniques. In this work, the feasibility of using polymeric milling media to prepare hydroxyapatite nanoparticles is described. The resulting hydroxyapatite powder exhibits an average size of about 20 to 23 nm. Final results indicate that the proposed synthesis strategy provides a facile pathway to obtain single-crystal HAp with high quality and suitable morphology. © 2008 Elsevier B.V. All rights... 

    Migrating to Cloud-Native architectures using microservices: An experience report

    , Article Workshops on CLIoT, WAS4FI, SeaClouds, CloudWay, IDEA, FedCloudNet 2015 held in conjunction with European Conference on Service-Oriented and Cloud Computing, ESOCC 2015, 15 September 2015 through 17 September 2015 ; Volume 567 , 2016 , Pages 201-215 ; 18650929 (ISSN); 9783319333120 (ISBN) Balalaie, A ; Heydarnoori, A ; Jamshidi, P ; Celesti A ; Leitner P ; Sharif University of Technology
    Springer Verlag  2016
    Migration to the cloud has been a popular topic in industry and academia in recent years. Despite many benefits that the cloud presents, such as high availability and scalability, most of the on-premise application architectures are not ready to fully exploit the benefits of this environment, and adapting them to this environment is a non-trivial task. Microservices have appeared recently as novel architectural styles that are native to the cloud. These cloud-native architectures can facilitate migrating on-premise architectures to fully benefit from the cloud environments because non-functional attributes, like scalability, are inherent in this style. The existing approaches on cloud... 

    Study the effect of connectivity between two wells on secondary recovery efficiency using percolation approach

    , Article 15th European Conference on the Mathematics of Oil Recovery, ECMOR 2016, 29 August 2016 through 1 September 2016 ; 2016 ; 9462821933 (ISBN); 9789462821934 (ISBN) Sadeghnejad, S ; Masihi, M ; King, P. R ; Gago, P. A ; Sharif University of Technology
    European Association of Geoscientists and Engineers, EAGE  2016
    Estimating available hydrocarbon to be produced during secondary oil recovery is an ongoing activity in field development. The primary plan is normally scheduled during early stage of field's life through master development plan studies. During this period, due to the lake of certain data, estimation of the field efficiency is usually based on rules of thumb and not detailed field characterization. Hence, there is a great motivation to produce simpler physically-based methodologies. The minimum necessity inputs of percolation approach make it a useful tool for foration performance prediction. This approach enables us to attain a better assessment of the efficiency of secondary recovery... 

    Modeling of CO2-brine interfacial tension: Application to enhanced oil recovery

    , Article Petroleum Science and Technology ; Volume 35, Issue 23 , 2017 , Pages 2179-2186 ; 10916466 (ISSN) Madani, M ; Abbasi, P ; Baghban, A ; Zargar, G ; Abbasi, P ; Sharif University of Technology
    Development of reliable and accurate models to estimate carbon dioxide–brine interfacial tension (IFT) is necessary, since its experimental measurement is time-consuming and requires expensive experimental apparatus as well as complicated interpretation procedure. In the current study, feed forward artificial neural network is used for estimation of CO2–brine IFT based on data from published literature which consists of a number of carbon dioxide–brine interfacial tension data covering broad ranges of temperature, total salinity, mole fractions of impure components and pressure. Trial-and-error method is utilized to optimize the artificial neural network topology in order to enhance its... 

    Improved advection algorithm of computational modeling of free surface flow using structured grids

    , Article Computer Methods in Applied Mechanics and Engineering ; Volume 195, Issue 7-8 , 2006 , Pages 775-795 ; 00457825 (ISSN) Babaei, R ; Abdollahi, J ; Homayonifar, P ; Varahram, N ; Davami, P ; Sharif University of Technology
    In the present study a finite difference method has been developed to model the transient fluid flow and heat transfer. A single fluid has been selected for modeling of mold filling and The SOLA-VOF 3D technique was modified to increase the accuracy of simulation of filling phenomena for shape castings. The model was then evaluated with the experimental methods. Refereeing to the experimental and simulation results a good consistency and the accuracy of the suggested model are confirmed. © 2005 Published by Elsevier B.V  

    Modelling of air pressure effects in casting moulds

    , Article Modelling and Simulation in Materials Science and Engineering ; Volume 13, Issue 6 , 2005 , Pages 903-917 ; 09650393 (ISSN) Attar, E ; Homayonifar, P ; Babaei, R ; Asgari, K ; Davami, P ; Sharif University of Technology
    In the casting process, as a mould is filled with molten metal, air escapes through the vents. Air pressure in the mould cavity has serious effects upon the filling behaviour such as surface profile of the molten metal and filling time. In this project a computational model was developed for calculation of air pressure during the mould filling. A 3D single phase code based on the SOLA-VOF algorithm was used for the prediction of the fluid flow. The ideal gas assumption, conservation of mass equation and Bernoulli law were used for the calculation of air pressure. A new algorithm was developed to interpolate air pressure on the surface cells. The creation of air pressure was correlated with... 

    Random data and key generation evaluation of some commercial tokens and smart cards

    , Article 2014 11th International ISC Conference on Information Security and Cryptology, ISCISC 2014 ; 2014 , p. 49-54 Boorghany, A ; Sarmadi, S. B ; Yousefi, P ; Gorji, P ; Jalili, R ; Sharif University of Technology
    In this paper, we report our evaluation of the strength of random number generator and RSA key-pair generator of some commercially available constrained hardware modules, i.e., tokens and smart cards. That was motivated after recent related attacks to RSA public keys, which are generated by constrained network devices and smart cards, and turned out to be insecure due to low-quality randomness. Those attacks are mostly computing pair-wise GCD between the moduli in public keys, and resulted in breaking several thousands of these keys. Our results show that most of the tested hardware modules behave well. However, some have abnormal or weak random generators which seem to be unsuitable for... 

    Stability and size-dependency of temperature-related Cauchy-Born hypothesis

    , Article Computational Materials Science ; Volume 50, Issue 5 , March , 2011 , Pages 1731-1743 ; 09270256 (ISSN) Khoei, A. R ; Ghahremani, P ; Abdolhosseini Qomi, M. J ; Banihashemi, P ; Sharif University of Technology
    In continuum mechanics, the constitutive models are usually based on the Cauchy-Born (CB) hypothesis which seeks the intrinsic characteristics of the material via the atomistic information and it is valid in small deformation. The main purpose of this paper is to investigate the temperature effect on the stability and size-dependency of Cauchy-Born hypothesis. Three-dimensional temperature-related Cauchy-Born formulations are developed for crystalline structure and the stability and size-dependency of temperature-related Cauchy-Born hypothesis are investigated by means of direct comparison between atomistic and continuous mediums. In order to control the temperature effect, the Nose-Hoover... 

    A simplified model for the flow inside cascade impactor

    , Article ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE) ; Volume 7 A , November , 2013 ; 9780791856314 (ISBN) Mehr, S. M. N ; Sohrabi, S ; Falsafi, P ; Gorji, P ; ASME ; Sharif University of Technology
    American Society of Mechanical Engineers (ASME)  2013
    In this paper we developed a new mathematical model for the flow inside cascade impactors and via this simplified model, we determined the particle size distribution by a fast and low cost computational method. Using cascade impactors for determining the particle size distribution, one can use comprehensive CFD methods to fully simulate the particle traces. Although the results from those CFD analyses can be very accurate, usually that is not a time and cost efficient routine. In contrast, we showed that by using our proposed calculation we can estimate the particle size distribution very fast and yet with the slight error -comparing to the results from CFD method. Cascade impactors are... 

    Improvement of airlift pump performance based on the exergy analysis

    , Article Proceedings of the 23rd International Conference on Efficiency, Cost, Optimization, Simulation, and Environmental Impact of Energy Systems, ECOS 2010, 14 June 2010 through 17 June 2010, Lausanne ; Volume 1 , 2010 , Pages 489-497 ; 9781456303006 (ISBN) Ghanbarzadeh, S ; Hanafizadeh, P ; Gholampour, P ; Shams, H ; Saidi, M. H ; Sharif University of Technology
    Aabo Akademi University  2010
    Airlift systems (ALS) are widely used in various fields such as petroleum and oil extracting industries. As gas-liquid two phase flow is the main part of the flow through these systems, the analysis of such systems accompanies with problems of two phase flow modeling. However, exergy analysis could be a simple method for modeling of airlift systems. In the present study, an analytical model based on thermodynamic principles has been implemented on each phase to analyze the performance of airlift systems. The experimental data were collected at a large scale multiphase flow test rig for the airlift pump with 6m height and diameter of 50 mm. Finally, irreversibility terms, energy destruction,... 

    Distributed Primary and secondary power sharing in a droop-controlled lvdc microgrid with merged AC and DC characteristics

    , Article IEEE Transactions on Smart Grid ; Volume 9, Issue 3 , 2018 , Pages 2284-2294 ; 19493053 (ISSN) Peyghami, S ; Mokhtari, H ; Loh, P. C ; Davari, P ; Blaabjerg, F ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2018
    In an ac microgrid, a common frequency exists for coordinating active power sharing among droop-controlled sources. A common frequency is absent in a dc microgrid, leaving only the dc source voltages for coordinating active power sharing. That causes sharing error and poorer voltage regulation in dc microgrids, which in most cases, are solved by a secondary control layer reinforced by an extensive communication network. To avoid such an infrastructure and its accompanied complications, this paper proposes an alternative droop scheme for low-voltage dc microgrid with both primary power sharing and secondary voltage regulation merged. The main idea is to introduce a non-zero unifying frequency...