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    Packet loss replacement in VoIP using a low-order recursive linear prediction method

    , Article Canadian Conference on Electrical and Computer Engineering, 8 May 2011 through 11 May 2011 ; May , 2011 , Pages 000292-000295 ; 08407789 (ISSN) ; 9781424497898 (ISBN) Miralavi, S. R ; Ghorshi, S ; Mortazavi, M ; Pasha, S ; Sharif University of Technology
    In real-time packet-based communication systems, one major problem is misrouted or delayed packets which results in degraded perceived voice quality. If packets are not available on time, the packet is known as lost packet. The easiest task of a network terminal receiver is to replace silence for the duration of lost speech segments. In a high quality communication system, to avoid quality reduction due to packet loss, a suitable method and/or algorithm is needed to replace the missing segments of speech. In this paper, we introduce a low order recursive linear prediction method for replacement of lost speech segment. In this method a normalized least mean square (NLMS) as an adaptive filter... 

    Throughput analysis of a cognitive multi-hop IEEE 802.11-based WLAN overlaid on a cellular network

    , Article 2011 International Conference on Software, Telecommunications and Computer Networks, SoftCOM 2011, 15 September 2011 through 17 September 2011, Split, Hvar, Dubrovnik ; 2011 , Pages 307-311 ; 9789532900262 (ISBN) Soleimani, H ; Ashtiani, F ; Sharif University of Technology
    In this paper, we focus on a cognitive network scenario, comprised of a multi-hop IEEE 802.11-based WLAN overlaid on a cellular network. In this scenario, the wireless nodes in a WLAN, i.e., cognitive nodes, use the downlink frequency channels of the cellular network opportunistically, such that at each packet transmission all idle channels have been exploited. In order to evaluate the capability of the considered cognitive network scenario, we propose an open queueing network model such that different packet transmission phases are mapped onto different queueing nodes. We also map different types of collisions, i.e., collision on control signals as well as collision on data transmission due... 

    Optimal RTU placement in power distribution systems using a novel method based on analytical hierarchical process (AHP)

    , Article 2011 10th International Conference on Environment and Electrical Engineering, EEEIC.EU 2011 - Conference Proceedings, 8 May 2011 through 11 May 2011 ; May , 2011 , Page(s): 1 - 4 ; 9781424487820 (ISBN) Dehghanian, P ; Kazemi, A. R ; Fotuhi Firuzabad, M ; Sharif University of Technology
    In a practical power system, automating all the substations is neither affordable nor economically justifiable. On the other hand, the trend for electric power subsidies elimination in some regions, such as Iran, aggravates this situation. To enhance the cost effectiveness of distribution automation system, this paper proposes a novel applicable qualitative-quantitative method using analytical hierarchical process (AHP) to find the optimum placement of remote terminal units (RTU). Entire attempt is to contribute all the crucial technical and practical parameters related to this problem in order to find the most reliable solution. Optimum number of RTUs is determined using the concepts of... 

    Development of a penetration model for an erosive long rod considering strength effects of colliding materials

    , Article Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science ; Volume 225, Issue 4 , August , 2011 , Pages 965-973 ; 09544062 (ISSN) Nezamabadi, A. R ; Vahedi, K ; Zohoor, H ; Sharif University of Technology
    In this article a simple penetration model for the terminal ballistic of long rod penetrators is developed. The model is to predict the crater depth of a projectile penetrating into a semi-infinite target. A principle objective was to take an account of strength properties of colliding materials using erosive phenomena. The entire velocity regime from low to hypervelocity is analysed. The effect of the penetrator aspect ratio is also considered in the model. The model developed here is based on the steady-state penetration process and is used to compare with existing experimental measurements. The results of the comparison show very good agreement with experimental investigations of other... 

    Well-conditioned sensor placement for range-only localization

    , Article 2011 4th IFIP International Conference on New Technologies, Mobility and Security, NTMS 2011 - Proceedings, 7 February 2011 through 10 February 2011 ; February , 2011 , Page(s): 1 - 5 ; ISSN : 21574952 ; 9781424487042 (ISBN) Shadi, K ; Dehghani, H. L ; Gholampour, I ; Sharif University of Technology
    This paper addresses the optimality of Network topology for localization purposes when measurements are range-only. Localization procedures based on TOA and TDOA range measurements are considered in this paper. As of now, the optimal placement of fixed terminals to locate mobile terminals has been studied based on Cramer-Rao Lower Bound (CRLB). CRLB is a universal bound on the variance of a general unbiased estimator and therefore is not dependent to the estimator and methods of localization. Here we introduce another algorithm dependent criterion, based on perturbation theory of linear equations. Different optimal topologies are presented using the new criterion. These optimal topologies,... 

    A new distributed uplink packet scheduling algorithm in WiMAX newtorks

    , Article Proceedings of the 2010 2nd International Conference on Future Computer and Communication, ICFCC 2010, 21 May 2010 through 24 May 2010 ; Volume 2 , May , 2010 , Pages V2232-V2236 ; 9781424458226 (ISBN) Nazari, S ; Beigy, H ; Sharif University of Technology
    Worldwide interoperability for Microwave Access (WiMAX) is designed to support a wide range of Quality of Service (QoS) requirements for different applications. Unlike the single service networks, a priority based mechanism is needed for specifying the transmission order of packets belonging to different traffic sources according to their QoS characteristics, which is called packet scheduling. In WiMAX standard, packet scheduling algorithm is not defined and its design is left for researchers. In this work, we propose a distributed uplink packet scheduling algorithm. In the proposed algorithm, when uplink capacity cannot satisfy the required resource of connections, according to traffic... 

    Reliability evaluation of an HVDC transmission system tapped by a VSC station

    , Article IEEE Transactions on Power Delivery ; Volume 25, Issue 3 , April , 2010 , Pages 1962-1970 ; 08858977 (ISSN) Zadkhast, S ; Fotuhi Firuzabad, M ; Aminifar, F ; Billinton, R ; Faried, S. O ; Edris, A. A ; Sharif University of Technology
    Reliability evaluation of multiterminal HVDC systems has received very little attention in the past. This paper presents reliability modeling and analysis of an HVDC transmission system incorporating a voltage-sourced converter (VSC) tapping station. The use of VSC tapping stations enables the supply of power along the route to areas with comparatively little consumption. In this paper, a comprehensive detailed reliability model is developed and then converted to a manageable and computationally efficient model. Using this equivalent reliability model, various reliability indices are calculated at the load point of the system and the impacts of the VSC tapping station on these indices are... 

    Purification and characterization of a novel biosurfactant produced by Bacillus licheniformis MS3

    , Article World Journal of Microbiology and Biotechnology ; Volume 26, Issue 5 , 2010 , Pages 871-878 ; 09593993 (ISSN) Biria, D ; Maghsoudi, E ; Roostaazad, R ; Dadafarin, H ; Sahebghadam Lotfi, A ; Amoozegar, M. A ; Sharif University of Technology
    The physical properties and chemical structure of a new biosurfactant (licheniformin) produced by Bacillus licheniformis MS3 were investigated. The purified biosurfactant was identified as a lipopeptide with amino acid sequence of Gly, Ala, Val, Asp, Ser, Gly, Tyr and a lactone linkage between the carboxyl group of Aspargine and hydroxyl group of Tyrosine residue. The fatty acid moiety was attached to N-terminal amino acid residue through an amide bond. The purified licheniformin could lower the surface tension of water from 72 to 38 mN/m at concentrations higher than 15 μg/mL and its relative emulsion volume (EV%) was equal to 36%. It also showed stable surface activity over a wide range of... 

    Cooperative communication with power allocation in downlink CDMA networks

    , Article ATC 2009 - Proceedings of the 2009 International Conference on Advanced Technologies for Communications, 12 October 2009 through 14 October 2009, Hai Phong ; 2009 , Pages 284-288 ; 9781424451395 (ISBN) Abdizadeh, M ; Rad, H. J ; Jafarnia, A ; Sharif University of Technology
    In this paper, we study the downlink of cooperative Direct-Sequence Code Division Multiple Access (DS-CDMA), where a set of Mobile Terminals (MT) are cooperating with the purpose of improving their downlink communications reliability with the Base Station (BS). In order to achieve the spatial diversity, a new cooperation scenario is proposed. Afterward, in addition to multiuser precoding, Maximum Ratio Combining (MRC) according to the Maximum Signal to Noise Ratio (MSNR) criterion at the destination is investigated. Then, the optimal transmission power control strategy under a fixed total power constraint is illustrated and analyzed. Compared with equal transmission power assignment where BS... 

    TSRN: A tabu search-based routing protocol for named data networking

    , Article Wireless Personal Communications ; Volume 101, Issue 3 , 2018 , Pages 1411-1428 ; 09296212 (ISSN) Shariat, Z ; Movaghar, A ; Hosseinzadeh, M ; Sharif University of Technology
    Springer New York LLC  2018
    Information-centric network (ICN) has become a basic research topic with regard to the future architecture of the Internet. Storage and routing data is an important feature of ICN, as it improves network performance and content distribution. One of the challenges in this type of network is the routing problem. The objective of this paper is to propose a routing algorithm in the named data network. Owing to the impressive results presented by the enhanced heuristic methods, tabu search has been selected to develop the proposed algorithm. This work has been carried out in five major steps, Creating the initial solution, The mechanisms of generating a neighborhood, Evaluating the neighbor... 

    A terminal guidance algorithm based on ant colony optimization

    , Article Computers and Electrical Engineering ; Volume 77 , 2019 , Pages 128-146 ; 00457906 (ISSN) Nobahari, H ; Nasrollahi, S ; Sharif University of Technology
    Elsevier Ltd  2019
    In this paper, terminal engagement of a maneuvering target and a pursuer is investigated. A heuristic nonlinear model predictive guidance algorithm is presented. Nonlinear kinematics of the pursuer and the target is utilized to formulate the guidance problem. Also, the target maneuver is assumed to be unknown. The proposed heuristic guidance algorithm uses an ant-based optimization algorithm to estimate simultaneously the states of the pursuer, the maneuver of the target, and the optimal guidance commands. Performance of the new guidance algorithm against maneuvering and non-maneuvering targets is evaluated using numerical simulations. Also, the results of the guidance algorithm are compared... 

    A 3D path planning algorithm based on PSO for autonomous UAVs navigation

    , Article 9th International Conference on Bioinspired Optimization Methods and Their Applications, BIOMA 2020, 19 November 2020 through 20 November 2020 ; Volume 12438 LNCS , 2020 , Pages 268-280 Mirshamsi, A ; Godio, S ; Nobakhti, A ; Primatesta, S ; Dovis, F ; Guglieri, G ; Sharif University of Technology
    Springer Science and Business Media Deutschland GmbH  2020
    In this paper, a new three-dimensional path planning approach with obstacle avoidance for UAVs is proposed. The aim is to provide a computationally-fast on-board sub-optimal solution for collision-free path planning in static environments. The optimal 3D path is an NP (non-deterministic polynomial-time) hard problem which may be solved numerically by global optimization algorithms such as the Particle Swarm Optimization (PSO). Application of PSO to the 3D path planning class of problems faces typical challenges such slow convergence rate. It is shown that the performance may be improved markedly by implementing a novel parallel approach and incorporation of new termination conditions.... 

    On the viscosity of composite suspensions of aluminum and ammonium perchlorate particles dispersed in hydroxyl terminated polybutadiene-New empirical model

    , Article Journal of Colloid and Interface Science ; Volume 299, Issue 2 , 2006 , Pages 962-971 ; 00219797 (ISSN) Arefinia, R ; Shojaei, A ; Sharif University of Technology
    The rheological properties of fuel suspensions with various solid loadings up to close their maximum packing fraction and suspending media having different viscosities are investigated using the rotational viscometer at relatively low shear rates in which suspensions behave as Newtonian fluids. Aluminum (Al) and ammonium perchlorate (AP) particles are major solid components of any solid fuel system which should be distributed uniformly inside a polymeric binder based on hydroxyl terminated polybutadiene (HTPB). The experimental data generated in this investigation indicates that the relative viscosity of the suspensions is independent of viscosity of polymer binder, but in addition to solid... 

    Performance of UWB linked relay network with time-reversed transmission in the presence of channel estimation error

    , Article IEEE Transactions on Wireless Communications ; Volume 11, Issue 8 , 2012 , Pages 2958-2969 ; 15361276 (ISSN) Zeinalpour Yazdi, Z ; Nasiri Kenari, M ; Aazhang, B ; Sharif University of Technology
    In this paper, we present the bit error probability (BEP) of a relay network employing UWB links between its nodes. Since UWB systems can resolve many paths and are thus rich in multipath diversity, the use of the Rake diversity combining is very effective. However, because of the complexity, it is impractical in the scenarios with portable terminals or in the networks with multiple relays. Time-reversal technique, in which the transmitting nodes can do the pre-diversity filtering of UWB signal before transmission, is known as an approach to achieve the performance equivalent to the Rake combining without increasing the receiver complexity. The performance of such a network with simple... 

    Investigation of novel polyurethane elastomeric networks based on polybutadiene-ol/polypropyleneoxide mixture and their structure-properties relationship

    , Article Materials and Design ; Volume 32, Issue 7 , 2011 , Pages 3933-3941 ; 02641275 (ISSN) Amrollahi, M ; Sadeghi, G. M. M ; Kashcooli, Y ; Sharif University of Technology
    Polyurethane elastomer networks were designed and synthesized based on hydroxyl terminated polybutadiene/polypropyleneoxide (HTPB/PPO) mixtures, 2,4-toluene diisocyanate and 1,4-butanediol. Various networks with different molar ratio of HTPB to PPO (0/100, 25/75, 50/50, 75/25 and 100/0) had been prepared. Depending on the length of soft segment, average functionality of polyol mixtures, mechanical and thermal properties of samples were varied. Our observations confirmed that final properties of the networks can be attributed to two synergistic factors: (a) formation of chemical network (crosslinking) and (b) soft segment length. An optimum composition was found. This optimum composition... 

    Modeling nonsaturated contention-based IEEE 802.11 multihop ad hoc networks

    , Article IEEE Transactions on Vehicular Technology ; Volume 58, Issue 7 , 2009 , Pages 3518-3532 ; 00189545 (ISSN) Ghaboosi, K ; Latva-Aho, M ; Xiao, Y ; Khalaj, B. H ; Sharif University of Technology
    The IEEE 802.11 contention-based distributed coordination function has been used in ad hoc networks, and so far, a comprehensive mathematical analysis of such multihop systems has not been reported in the literature due to complicating factors such as hidden terminals and the unreachability problem. In this paper, we propose a new analytical model based on the parallel space-time Markov chain for IEEE 802.11 medium access control (MAC) in multihop ad hoc networks. The proposed scheme is able to model the hidden-terminal and unreachability phenomena. Extensive evaluation is conducted to demonstrate the accuracy of the proposed framework. © 2009 IEEE  

    Producing functional recombinant human keratinocyte growth factor in Pichia pastoris and investigating its protective role against irradiation

    , Article Enzyme and Microbial Technology ; Volume 111 , April , 2018 , Pages 12-20 ; 01410229 (ISSN) Bahadori, Z ; Kalhor, H. R ; Mowla, S. J ; Sharif University of Technology
    Elsevier Inc  2018
    Keratinocyte Growth Factor (KGF) is a paracrine-acting, epithelial mitogen that plays a prominent role in the regeneration of damaged epithelial tissues. In spite of different attempts to produce recombinant human KGF in many organisms, including bacteria, mammalian cells, plant cells and insect cells; production of recombinant form suffers from lower yields and recovery relative to other recombinant proteins of similar size and properties. Due to many advantages of Pichia pastoris expression systems for producing industrial enzymes and pharmaceutical proteins, in this study P. pastoris was chosen as a host for KGF expression. For preparing human KGF coding sequence, MCF-7 cell line was...