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    Multi-user opportunistic spectrum access with channel impairments [electronic resource]

    , Article AEU - International Journal of Electronics and Communications ; Volume 67, Issue 11, November 2013, Pages 955–966 Majd, A. (Sayyed Arash) ; Salehkalybar, S ; Pakravan, M. R ; Sharif University of Technology
    In this paper, we study the impact of sensing error and channel fading on the decision process of a multiple secondary user network in a primary network whose channel occupancy states are modelled as a Bernoulli process. We present a randomized access strategy to maximize total secondary network throughput. The proposed method guarantees that the probability of collision between primary and secondary users in each channel is less than the predefined value of Pc = ξ. To find the optimal access strategy, we formulate secondary network throughput as an optimization problem. Then, using the KKT method to find the solution, we break the original problem into multiple sub-problems. Then, we employ... 

    Graph homomorphisms and nodal domains [electronic resource]

    , Article Linear Algebra and its Applications ; 2006, Volume 418, Issue 1, Pages 44–52 Daneshgar, A. (Amir) ; Sharif University of Technology
    In this paper, we derive some necessary spectral conditions for the existence of graph homomorphisms in which we also consider some parameters related to the corresponding eigenspaces such as nodal domains. In this approach, we consider the combinatorial Laplacian and co-Laplacian as well as the adjacency matrix. Also, we present some applications in graph decompositions where we prove a general version of Fisher’s inequality for G-designs  

    Effects of design parameters and A f temperature on superelastic behaviour of Nitinol stent for application in biliary duct: finite element analysis [electronic resource]

    , Article Materials Technology: Advanced Performance Materials ; Vol. 29, No. 2, 2014, 65-75 Nematzadeh, F. (Fardin) ; Sadrnezhaad, K ; Sharif University of Technology
    For more than a decade, stent implantation has been strategically used for solving gastrointestinal dilemmas such as biliary stenosis. Predicaments like insufficient radial strength, low twisting ability, inappropriate dynamic behaviour and restenosis are expected to be solved by the introduction of new designs. Superelastic Nitinol stent is an interesting alternative for minimising these tight spots. The application of finite element method to predict metallurgical and geometric behaviour of superelastic Nitinol stents for biliary duct dilatation is supported by conventional crimp tests. Model calculations show that all stents encounter the highest stress in their intersegment curvature.... 

    An efficient tabu search algorithm for the single row facility location problem [electronic resource]

    , Article European Journal Of Operational Research ; Vol. 205, No. 1, pp. 98-105 Samarghandi, H. (Hamed) ; Eshghi, Kourosh ; Sharif University of Technology
    The general goal of the facility layout problem is to arrange a given number of facilities to minimize the total cost associated with the known or projected interactions between them. One of the special classes of the facility layout problem is the Single Row Facility Layout Problem (SRFLP), which consists of finding an optimal linear placement of rectangular facilities with varying dimensions on a straight line. This paper first presents and proves a theorem to find the optimal solution of a special case of SRFLP. The results obtained by this theorem prove to be very useful in reducing the computational efforts when a new algorithm based on tabu search for the SRFLP is proposed in this... 

    Ant colony algorithm for the shortest loop design problem [electronic resource]

    , Article Computers and Industrial Engineering, Elsevier ; Volume 50, Issue 4, August 2006, Pages 358–366 Eshghi, K. (Kourosh) ; Kazemi, Morteza ; Sharif University of Technology
    In this paper, a new algorithm for solving the shortest loop design problem is presented. The shortest loop design problem is to find the shortest loop for an automated guided vehicle covering at least one edge of each department of a block layout. In this paper, first it is shown that this problem can be represented as a graph model. The properties of the presented model enable us to design a meta-heuristic based on ant colony system algorithm for solving the shortest loop design problem. Computational results show the efficiency of our algorithm in compare to the other techniques  

    Novel probabilistic bounds on power level profile of spectrally-encoded spread-time CDMA signals [electronic resource]

    , Article IEEE Transactions on Wireless Communications ; Vol. 8, No. 5, PP. 2296-2301, May 2009 Mashhadi, S. (Saeed) ; Sharif University Of Technology
    In this letter we introduce an effective tool to demonstrate signal power behavior of a typical spectrally encoded spread-time (SE/ST) CDMA system using probabilistic approach. By defining power level profile (PLP), as the probability of stretching instantaneous power from a pre-specified threshold, we can find novel upper bounds on the signal power profile. We discuss various properties owing to PLP and elaborate on the main parameters affecting the PLP value. We present three theorems, propose some simple upper bounds on the PLP, and give an insight on the main contributions of the results. We introduce a fundamental parameter, namely ß, as a key design parameter which relates the most... 

    Demand response participation in wholesale energy markets

    , Article IEEE Power and Energy Society General Meeting ; 2012 ; ISSN: 19449925 ; ISBN: 9781470000000 Parvania, M ; Fotuhi-Firuzabad, M ; Shahidehpour, M ; Sharif University of Technology
    This paper summarizes a presentation to be given at the IEEE Power and Energy Society 2012 General Meeting, in the panel session Demand response: analytics, practice, and challenges in smart grid environment. The paper elaborates participation of demand response (DR) resources in electricity markets. Specially, different types of DR participation in the wholesale energy markets are discussed. Then, two DR program designs are presented which aim to enable customers' participation in day-ahead energy markets. The paper continues with presenting the modified structure of the day-ahead energy market in presence of the DR programs. The offer packages specifically designed for DR participation in... 

    Design and routine test optimization of modern protection systems with reliability and economic constraints

    , Article IEEE Transactions on Power Delivery ; Vol. 27, issue. 1 , 2012 , p. 271-278 ; ISSN: 08858977 Etemadi, A. H ; Fotuhi-Firuzabad, M ; Sharif University of Technology
    This paper approaches the topic of protection system reliability from an economic point of view by 1) designing an optimal modern protective relay based on a prescribed level of reliability subject to economic constraints and 2) determining optimal routine test intervals by balancing the cost of routine tests and losses due to relay failure. This paper proposes a method that enables the designer to optimally select hardware and software components of a digital protective relay to gain the highest possible overall reliability with a restricted budget. This design can be viewed as a reliability and redundancy allocation problem for which a new easy-to-implement algorithm is proposed. In... 

    Chaos control in single mode approximation of T-AFM systems using nonlinear delayed feedback based on sliding mode control

    , Article 2007 Proceedings of the ASME International Design Engineering Technical Conferences and Computers and Information in Engineering Conference ; Volume 3 PART B , 2008 , Pages 725-730 ; ISBN: 9780791848043 Sadeghian, H ; Salarieh, H ; Arjmand, M. T ; Alasty, A ; Sharif University of Technology
    The taping mode Atomic Force Microscopic (T-AFM) can be properly described by a sinusoidal excitation of its base and nonlinear potential interaction with sample. Thus the cantilever may cause chaotic behavior which decreases the performance of the sample topography. In this paper a nonlinear delayed feedback control.is proposed to control.chaos in a single mode approximation of a T-AFM system. Assuming model parameters uncertainties, the first order Unstable Periodic Orbits (UPOs) of the system is stabilized using the sliding nonlinear delayed feedback control. The effectiveness of the presented methods is numerically verified and the results show the high performance of the control.er  

    Design for scalability in enterprise SSDs

    , Article Parallel Architectures and Compilation Techniques - Conference Proceedings, PACT ; 24-27 August , 2014 , p. 417-429 ; ISSN: 1089795X ; ISBN: 9781450328098 Tavakkol, A ; Arjomand, M ; Sarbazi-Azad, H ; Sharif University of Technology
    Solid State Drives (SSDs) have recently emerged as a high speed random access alternative to classical magnetic disks. To date, SSD designs have been largely based on multi-channel bus architecture that confronts serious scalability problems in high-end enterprise SSDs with dozens of flash memory chips and a gigabyte host interface. This forces the community to rapidly change the bus-based inter-flash standards to respond to ever increasing application demands. In this paper, we first give a deep look at how different flash parameters and SSD internal designs affect the actual performance and scalability of the conventional architecture. Our experiments show that SSD performance improvement... 

    OD3P: On-demand page paired PCM

    , Article Proceedings - Design Automation Conference ; 2-5 June , 2014 , pp. 1-6 ; ISSN: 0738100X ; ISBN: 9781450327305 Asadinia, M ; Arjomand, M ; Sarbazi-Azad, H ; Sharif University of Technology
    With current memory scalability challenges, Phase Change Memory (PCM) is viewed as an attractive replacement to DRAM. The preliminary concern for PCM applicability is its limited write endurance that is highly affected by pro-cess variation in nanometer regime. This increases the vari- ation in cell lifetime resulting in early and sudden reduc- tion in main memory capacity due to wear-out of few cells. When some memory pages reach their endurance limits, other pages may be far from their limits even when using a perfect wear-leveling. Recent studies have proposed redi- rection or correction schemes to alleviate this problem, but all suffer from poor throughput or latency. On contrary, we... 

    Network-on-SSD: A scalable and high-performance communication design paradigm for SSDs

    , Article IEEE Computer Architecture Letters ; Vol. 12, issue 1, Article number 6178186 , 2013 , pp. 5-8 ; ISSN: 15566056 Tavakkol, A ; Arjomand, M ; Sarbazi-Azad, H ; Sharif University of Technology
    In recent years, flash memory solid state disks (SSDs) have shown a great potential to change storage infrastructure because of its advantages of high speed and high throughput random access. This promising storage, however, greatly suffers from performance loss because of frequent ''erase-before-write'' and ''garbage collection'' operations. Thus, novel circuit-level, architectural, and algorithmic techniques are currently explored to address these limitations. In parallel with others, current study investigates replacing shared buses in multi-channel architecture of SSDs with an interconnection network to achieve scalable, high throughput, and reliable SSD storage systems. Roughly... 

    Reconfigurable cluster-based networks-on-chip for application-specific MPSoCs

    , Article Proceedings of the International Conference on Application-Specific Systems, Architectures and Processors ; 9-11 July , 2012 , pp. 153-156 ; ISSN: 10636862 ; ISBN: 9780769547688 Modarressi, M ; Sarbazi-Azad, H ; Sharif University of Technology
    In this paper, we propose a reconfigurable NoC in which a customized topology for a given application can be implemented. In this NoC, the nodes are grouped into some clusters interconnected by a reconfigurable communication infrastructure. The nodes inside a cluster are connected by a fixed topology. From the traffic management perspective, this structure benefits from the interesting characteristics of the mesh topology (efficient handling of local traffic where each node communicates with its neighbors), while avoids its drawbacks (the lack of short paths between remotely located nodes). We then present a design flow that maps the frequently communicating tasks of a given application into... 

    High-endurance and performance-efficient design of hybrid cache architectures through adaptive line replacement

    , Article Proceedings of the International Symposium on Low Power Electronics and Design ; 2011 , p. 79-84 ; ISSN: 15334678 ; ISBN: 9781612846590 Jadidi, A ; Arjomand, M ; Sarbazi-Azad, H ; Sharif University of Technology
    In this paper, we propose a run-time strategy for managing writes onto last level cache in chip multiprocessors where STT-RAM memory is used as baseline technology. To this end, we assume that each cache set is decomposed into limited SRAM lines and large number of STT-RAM lines. SRAM lines are target of frequently-written data and rarely-written or read-only ones are pushed into STT-RAM. As a novel contribution, a low-overhead, fully-hardware technique is utilized to detect write-intensive data blocks of working set and place them into SRAM lines while the remaining data blocks are candidates to be remapped onto STT-RAM blocks during system operation. Therefore, the achieved cache... 

    Performance modeling of the LEACH protocol for mobile wireless sensor networks

    , Article Journal of Parallel and Distributed Computing ; Vol. 71, issue. 6 , 2011 , p. 812-821 ; ISSN: 07437315 Nayebi, A ; Sarbazi-Azad, H ; Sharif University of Technology
    In many wireless sensor network applications, nodes are mobile, while many protocols proposed for these networks assume a static network. Thus, it is important to evaluate if a traditional protocol designed for a static network can tolerate different levels of mobility. This paper provides an analytic model to investigate the effect of mobility on a well-known cluster-based protocol, LEACH. The model evaluates data loss after construction of the clusters due to node mobility, which can be used to estimate a proper update interval to balance the energy and data loss ratio. Thus, the results can help the network designer to adjust the topology update interval given a value of acceptable data... 

    Improving the performance of deadlock recovery based routing in irregular mesh NoCs using added mesh-like links

    , Article ISCAS 2010 - 2010 IEEE International Symposium on Circuits and Systems: Nano-Bio Circuit Fabrics and Systems ; 2010 , p. 3236-3239 ; ISBN: 9781424453085 Hosseingholi, M ; Ahmadian, A. S ; Sarbazi-Azad, H ; Sharif University of Technology
    Heterogeneity is one of the challenges in the current NoC design which forces designers to consider irregular topologies. Therefore, finding an optimal topology with minimum cost (minimum use of links, buffers, NIs, etc) and power consumption, and maximum flexibility can provide the best cost-performance trade-off. Irregular mesh is a topology which combines the benefits of regularity and advantage of irregularity. Routing algorithms especially those coupled with wormhole switching should deal with deadlock occurrences. Unlike deadlock avoidance-based schemes, deadlock detection and recovery-based routing schemes, do not restrict routing adaptability. In this paper, we modify irregular mesh... 

    Voltage-frequency planning for thermal-aware, low-power design of regular 3-D NoCs

    , Article Proceedings of the IEEE International Conference on VLSI Design ; 2010 , p. 57-62 ; ISSN: 10639667 ; ISBN: 9780769539287 Arjomand, M ; Sarbazi-Azad, H ; Sharif University of Technology
    Network-on-Chip combined with Globally Asynchronous Locally Synchronous paradigm is a promising architecture for easy IP integration and utilization with multiple voltage levels. For power reduction, multiple voltage-frequency levels are successfully applied to 2-D NoCs, but never with a generic approach to 3-D counterparts; in which low heat conductivity of insulator layers makes high dense temperature distribution at layers away from heat sink. In this paper, a thermal-aware methodology for regular 3-D NoCs based on multiple voltage levels is proposed. Given an application task graph, this methodology determines an efficient mapping of tasks onto network tiles, considering inherent... 

    Nonlinear observer design for turbocharger in a SI engine

    , Article Proceedings of the American Control Conference ; 2013 , pp. 5231-5236 ; ISSN: 07431619 ; ISBN: 9781479901777 Salehi, R ; Shahbakhti, M ; Alasty, A ; Vossoughi, G. R ; Sharif University of Technology
    Estimation of major turbocharger variables is essential for proper control and monitoring of a turbocharged engine. This work presents a novel algorithm to estimate turbocharger rotator speed, air temperature downstream a compressor and flow rate over the compressor using mean value models of engine subsystems. A nonlinear Luenberger observer is designed for a 1.7-lit gasoline turbocharged engine. The designed observed is shown analytically to be asymptotically stable. Performance of the designed observer is experimentally validated with the data collected from the engine. The results indicate the observer can capture major turbocharger's rotational dynamics and estimated turbocharger... 

    Nonlinear dynamics and control of bifurcation to regulate the performance of a boiler-turbine unit

    , Article Energy Conversion and Management ; Vol. 68 , 2013 , pp. 105-113 ; ISSN: 01968904 Moradi, H ; Alasty, A ; Vossoughi, G ; Sharif University of Technology
    The economical operations of power plants and environmental awareness are the major factors affecting the importance of control in boiler-turbine units. In this paper, a multivariable nonlinear model of boiler-turbine unit is considered. Drum pressure, electric output and water level of drum (as output variables) are adjusted at desired values by manipulation of valve positions for fuel, steam and feed-water flow rates (as input variables). Nonlinear dynamics of the unit is investigated through the concepts of bifurcation and limit cycles behaviour. In the presence of harmonic disturbances, some coefficients of the dynamic model, fuel and steam flow rates play as the bifurcation parameters.... 

    Design and analysis of a novel two DOF thermal micromanipulator

    , Article 2011 IEEE International Conference on Mechatronics, ICM 2011 - Proceedings ; 2011 , pp. 654-659 ; ISBN: 9781612849836 Pourzand, H ; Ghaemi, R ; Alasty, A ; Sharif University of Technology
    In this paper, a novel thermal microactuator is designed which is capable of producing bi-directional lateral and rotational output and one of its applications as a two DOF micromanipulator is shown. Also, by carefully choosing the doping level, temperature distribution is determined by considering the dependency of silicon's resistivity and conductivity to temperature. Using variable separation method an equation in terms of elliptic integrals is reached and after imposing boundary conditions the exact temperature distribution is obtained numerically. Currents at each branch is updated due to the last temperature distribution and this process is repeated several times until the final...