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    Integrating module checking and deduction in a formal proof for the perlman Spanning Tree Protocol (STP)

    , Article Journal of Universal Computer Science ; Volume 13, Issue 13 , 2007 , Pages 2076-2104 ; 0958695X (ISSN) Hojjat, H ; Nakhost, H ; Sirjani, M ; Sharif University of Technology
    2007
    Abstract
    In the IEEE 802.1D standard for the Media Access Control layer (MAC layer) bridges, there is an STP (Spanning Tree Protocol) definition, based on the algorithm that was proposed by Radia Perlman. In this paper, we give a formal proof for correctness of the STP algorithm by showing that finally a single node is selected as the root of the tree and the loops are eliminated correctly. We use formal inductive reasoning to establish these requirements. In order to ensure that the bridges behave correctly regardless of the topology of the surrounding bridges and LANs, the Rebeca, modular verification techniques are applied. These techniques are shown to be efficiently applicable in model checking... 

    Optimal active control of vehicle suspension system including time delay and preview for rough roads

    , Article JVC/Journal of Vibration and Control ; Volume 8, Issue 7 , 2002 , Pages 967-991 ; 10775463 (ISSN) Marzbanrad, J ; Ahmardi, G ; Hojjat, Y ; Zohoor, H ; Sharif University of Technology
    SAGE Publications Inc  2002
    Abstract
    An optimal preview control of a vehicle suspension system traveling on a rough road is studied. A three-dimensional seven degree-of-freedom car-riding model and several descriptions of the road surface roughness heights, including haversine (hole/bump) and stochastic filtered white noise models, are used in the analysis. It is assumed that contact-less sensors affixed to the vehicle front bumper measure the road surface height at some distances in the front of the car. The suspension systems are optimized with respect to ride comfort and road holding preferences including accelerations of the sprung mass, tire deflection, suspension rattle space and control force. The performance and power... 

    Stochastic optimal preview control of a vehicle suspension

    , Article Journal of Sound and Vibration ; Volume 275, Issue 3-5 , 2004 , Pages 973-990 ; 0022460X (ISSN) Marzbanrad, J ; Ahmadi, G ; Zohoor, H ; Hojjat, Y ; Sharif University of Technology
    Academic Press  2004
    Abstract
    Stochastic optimal control of a vehicle suspension on a random road is studied. The road roughness height is modelled as a filtered white noise stochastic process and a four-degree-of-freedom half-car model is used in the analysis. It is assumed that a sensor is mounted in the front bumper that measures the road irregularity at some distances in the front of the vehicle. Two other sensors also measure relative velocities of the vehicle body with respect to the unsprung masses in the vehicle suspension spaces. All measurements are assumed to be conducted in a noisy environment. The state variables of the vehicle system are estimated using a method similar to the Kalman filter. The suspension... 

    Partial order reduction for timed actors

    , Article 13th International Conference on Verified Software: Theories, Tools, and Experiments, VSTTE 2021 and 14th International Workshop on Numerical Software Verification, NSV 2021, 18 October 2021 through 19 October 2021 ; Volume 13124 LNCS , 2022 , Pages 43-60 ; 03029743 (ISSN); 9783030955601 (ISBN) Bagheri, M ; Sirjani, M ; Khamespanah, E ; Hojjat, H ; Movaghar, A ; Sharif University of Technology
    Springer Science and Business Media Deutschland GmbH  2022
    Abstract
    We propose a compositional approach for the Partial Order Reduction (POR) in the state space generation of asynchronous timed actors. We define the concept of independent actors as the actors that do not send messages to a common actor. The approach avoids exploring unnecessary interleaving of executions of independent actors. It performs on a component-based model where actors from different components, except for the actors on borders, are independent. To alleviate the effect of the cross-border messages, we enforce a delay condition, ensuring that an actor introduces a delay in its execution before sending a message across the border of its component. Within each time unit, our technique... 

    Flight envelope expansion in landing phase using classic, intelligent and adaptive controllers [electronic resource]

    , Article Journal of aircraft ; 2006, Vol. 43, No. 1 Malaek .S. M. B ; Izadi, Hojjat Allah ; Pakme, Mehrdad
    Abstract
    An expanding flight envelope in the landing phase of a typical jet transport aircraft in presence of strong wind shears using a learning capable control system (LCCS) is investigated. The idea stems fromhuman beings functional architecture that gives them the ability to do more as they age and gain more experience. With the knowledge that classical controllers lack sufficient generality to cope with nonlinear as well as uncertain phenomenon such as turbulent air, the focuse is on different types of intelligent controllers due to their learning and nonlinear generalization capabilities as candidates for the landing flight phase. It is shown that the latter class of controllers could be used... 

    Mind-Body Problem from Wittgenstein’s Perspective

    , M.Sc. Thesis Sharif University of Technology Karimi, Ahmad (Author) ; Hojjat, Mino (Supervisor)
    Abstract
    To provide a stable foundation for human knowledge Descartes presumed that human being is composed of two distinct substances, the mind and the body. But, the solution through which he wanted to explain the correlation between these substances, was not accepted by other philosophers, and thereafter this problem was known as mind-body problem. This problem arises some other philosophical problems including solipsism and the problem of other minds. In this thesis, considering the grammar of such words like memory, understanding, and thinking I will show that having an exact description of these concepts we would be able to escape from these inclination to seek something behind these words, and... 

    Designing a System for Pulse Pile-Up Processing in Gamma Ray Spectroscopy Based on Digital Method

    , M.Sc. Thesis Sharif University of Technology Hojjat, Saeed (Author) ; Hosseini, Abolfazl (Supervisor)
    Abstract
    In Radiation Detection Systems applied in Spectroscopy and Imaging, if the rate of particle incidence with detector is high, the output pulses being stacked up on each other will be expected, which is known as “Pulse Pile-up”. Pulse pile-up might result in a serious disorder of energy and timing data expected from the pulses. In recent decades and after successful implementation of pile-up rejection methods on analog circuits, considering development and progression in the field of digital, different algorithms based on pileup correction methods have been developed to obtain all spectrum information, whether energy, rise time and recorded pulses. Such methods can be compared in different... 

    Smart antennas for OFDM-WLANs based on a spatial-temporal multi-scenario channel model

    , Article Iranian Journal of Electrical and Computer Engineering ; Volume 7, Issue 2 , 2008 , Pages 107-114 ; 16820053 (ISSN) Alihemmati, R ; Dadashzadeh, G ; Shishegar, A. A ; Hojjat, N ; Sharif University of Technology
    Jahad Daneshgahi  2008
    Abstract
    combination of smart antenna techniques and OFDM could be considered as a promising solution for improving the performance and enhancing the data rates of next generation wireless communication systems operating in frequency selective fading environments. There are different design parameters which could affect the application of adaptive arrays in OFDM-based systems. Various beam-forming methods in frequency or time domain, different array architectures and various number of array elements are important factors which are able to change the performance and complexity of the system. These parameters may show different effects in different channel conditions. In this paper we implemented a new... 

    A Model for Logistics Management in Natural Disaster Relief

    , M.Sc. Thesis Sharif University of Technology Hojjat Panah, Sharareh (Author) ; Eshghi, Kourosh (Supervisor) ; Najafi, Mehdi (Co-Advisor)
    Abstract
    Research and information available shows that the number of natural disasters are increasing dramatically; hence disaster management is being raised as one of the most important topics in this field. The relief logistics is the greater part of disaster management model.
    In this study, in order to manage the logistics activities effectively in a response phase of an earthquake, a hybrid meta-heuristic algorithm is developed for a transportation network. Then, the proposed algorithm is tested on a small part of Tehran.
     

    Comparison of the smart antenna architectures for OFDM-WLAN systems in a rich multipath environment based on a spatio-temporal channel model

    , Article 2005 IEEE 16th International Symposium on Personal, Indoor and Mobile Radio Communications, PIMRC 2005, Berlin, 11 September 2005 through 14 September 2005 ; Volume 1 , 2005 , Pages 97-101 ; 3800729091 (ISBN); 9783800729098 (ISBN) Alihemmati, R ; Shishegar, A. A ; Hojjat, N ; Dadashzadeh, G ; Boghrati, B ; Mehrtash, A ; Sharif University of Technology
    2005
    Abstract
    The smart antenna technique as a method of improving the physical layer performance of OFDM WLANs is studied. For this purpose, a comparison of the smart antenna architectures for IEEE802.11a WLAN system using pre-FFT and post-FFT array processing with different parameters is represented. Simulations are performed on a new Simulink model for IEEE802.11a system using a spatio-temporal channel modeling which is based on the measured wideband channels in the 5GHz band. Raw bit-error-rate performance for QPSK/16QAM modulations at LOS and NLOS channel scenarios are evaluated and compared. © 2005 IEEE  

    Gas sweetening process optimization with economic, Exergy and Environmental criteria

    , M.Sc. Thesis Sharif University of Technology Ehsani, Hojjat Allah (Author) ; Farhadi, Fathollah (Supervisor) ; Bozorg Mehri, Ramin (Supervisor)
    Abstract
    In the present work, a comprehensive economic, environmental and exergy analysis and multi-objective optimization for gas sweetening plant are provided and the interaction between decision variables in these criterions is discussed. In the first part, potentials of three environmental features (global warming, acid rain, smog formation) of the operational plant are quantified and normalized using life cycle assessment (LCA) for both process waste and utility environmental impacts.Acid rain index is determined as the most important environmental impactindex in this unit. By choosing proper decision variables based on sensitivity analysis, LCA and EA results, optimization is performed to... 

    Comparison characteristics of family and demographic of children with antenatal hydronephrosis between 2nd and 3rd trimesters of gestation

    , Article Iranian Journal of Public Health ; Volume 47, Issue 2 , February , 2018 , Pages 273-279 ; 22516085 (ISSN) Nazemipour, M ; Kajbafzadeh, A. M ; Mohammad, K ; Rahimi Foroushani, A ; Hojjat, A ; Seyedtabib, M ; Nazemipour, A ; Mahmoudi, M ; Sharif University of Technology
    Iranian Journal of Public Health  2018
    Abstract
    Background: The aim of this study was comparison characteristics of family and demographics of children with antenatal hydronephrosis, in 2nd and 3rd trimester of pregnancy, in order to the need for postnatal management. Methods: This cross-sectional study described some information from family of children with antenatal hydronephrosis, at the Pediatric Urology Research Center of Children’s Hospital Medical Center of Tehran University of Medical Sciences. Data for 193 children, admitted in 2012-2013, were collected retrospectively. They were allocated to two groups of 2nd and 3rd trimester, based on the time of diagnosis antenatal hydronephrosis. Data analysis was done using SPSS.... 

    Nonlinear interstory drift contours for idealized forward directivity pulses using "modified fish-bone" models

    , Article Advances in Structural Engineering ; Volume 18, Issue 5 , May , 2015 , Pages 603-627 ; 13694332 (ISSN) Khalo, A. R ; Khosravi, H ; Jamnani, H. H ; Sharif University of Technology
    Multi-Science Publishing Co. Ltd  2015
    Abstract
    Four 5-, 10-, 20- and 30-story moment frames, representing low-, mid-, and two high-rise structures, were subjected to a great number of idealized directivity pulses. The amplitudes and periods of pulses vary from 0.02 g to 1.0 g and 0.5 to 12 sec, respectively. Over 1400 nonlinear dynamic analyses of low- to high-rise moment frames were performed which were feasible through using modified fish-bone model. The distribution of interstory drift along the height was studied and two applied contours were proposed: (i) the maximum interstory drift contour, and (ii) the critical story contour. These contours were demonstrated versus the ratio of natural period of the structure to the pulse period... 

    Analysis of singularities of a 3DOF parallel manipulator based on a novel geometrical method

    , Article 8th Biennial ASME Conference on Engineering Systems Design and Analysis, ESDA2006, Torino, 4 July 2006 through 7 July 2006 ; Volume 2006 , 2006 ; 0791837793 (ISBN); 9780791837795 (ISBN) Pendar, H ; Sadeghian, H ; Roozbehani, H ; Zohoor, H ; Sharif University of Technology
    2006
    Abstract
    In this article singular points of a parallel manipulator are obtained based on a novel geometrical method. Here we introduce the constrained plain method (CPM) and some of its application in parallel mechanism. Given the definition of constraint plane (CP) and infinite constraint plane (ICP) the dependency conditions of constraints is achieved with the use of a new theorem based on the Ceva geometrical theorem. The direction of angular velocity of a body is achieved by having three ICPs with the use of another theorem. Finally, with the use of the above two novel theorems singularities of the 3UPF_PU mechanism are obtained. It should be emphasized that this method is completely geometrical,... 

    Melting enthalpy and entropy of freestanding metallic nanoparticles based on cohesive energy and average coordination number

    , Article Journal of Physical Chemistry C ; Volume 115, Issue 35 , August , 2011 , Pages 17310-17313 ; 19327447 (ISSN) Omid, H ; Delavari H., H ; Madaah Hosseini, H. R ; Sharif University of Technology
    2011
    Abstract
    An analytical model is proposed to study the effect of particle size on melting enthalpy and entropy of metallic nanoparticles (NPs). The Mott's and Regel's equations for melting entropy in the combination of core average coordination number (CAC) and surface average coordination number (SAC) of freestanding NPs are considered. Clusters of icosahedral (IC), body centered cubic (BCC), and body centered tetragonal (BCT) structure without any vacancies and defects are modeled. Using the variable coordination number made this model to be in good agreement with experimental and molecular dynamic (MD) results of different crystal structures. The model predicts melting entropy and enthalpy of... 

    On the temperature and residual stress field during grinding

    , Article WCE 2010 - World Congress on Engineering 2010, 30 June 2010 through 2 July 2010 ; Volume 2 , 2010 , Pages 1196-1200 ; 9789881821072 (ISBN) H-Gangaraj, S. M ; Farrahi, G. H ; Ghadbeigi, H ; Sharif University of Technology
    2010
    Abstract
    Grinding is widely used for manufacturing of components that require fine surface finish and good dimensional accuracy. In this study a thermo-mechanical finite element analysis is conducted to find out how grinding parameters can affect temperature and residual stress distribution in the workpiece. Results of parametric study presented in this work indicate, by carefully selecting the grinding parameters, minimum thermal and mechanical damage can be achieved. Higher workpiece velocities produce higher surface residual stress. By increasing depths of cut, depth of tensile residual stresses increases. Convection heat coefficient does not have any considerable effect on surface residual stress... 

    A new lattic LP-based post filter for adaptive noise cancellers in mobile and vehicular applications

    , Article Proceedings of the 8th IEEE International Symposium on Signal Processing and Information Technology, ISSPIT 2008, 16 December 2008 through 19 December 2008, Sarajevo ; 2008 , Pages 407-412 ; 9781424435555 (ISBN) Khorram, S ; Sameti, H ; Veisi, H ; Abutalebi, H. R ; Sharif University of Technology
    2008
    Abstract
    Adaptive Noise Cancellation (ANC) is a well-known technique for background noise reduction in automobile and vehicular environments. The noise fields in automobile and other vehicle interior obey the diffuse noise field model closely. On the other hand, the ANC does not provide sufficient noise reduction in the diffuse noise fields. In this paper, a new multistage post-filter is designed for ANC as a solution to diffuse noise conditions. The designed post-filter is a single channel Linear Prediction (LP) based speech enhancement system. The LP is performed by an adaptive lattice filter and attempts to extract speech components by using intermediate ANC signals. The post-filter has no... 

    Finite element analysis of shot-peening effect on fretting fatigue parameters

    , Article Tribology International ; Volume 44, Issue 11 , 2011 , Pages 1583-1588 ; 0301679X (ISSN) H-Gangaraj, S. M ; Alvandi Tabrizi, Y ; Farrahi, G. H ; Majzoobi, G. H ; Ghadbeigi, H ; Sharif University of Technology
    2011
    Abstract
    Shot peening is widely used to improve the fretting fatigue strength of critical surfaces. Fretting fatigue occurs in contacting parts that are subjected to fluctuating loads and sliding movements at the same time. This paper presents a sequential finite element simulation to investigate the shot peening effects on normal stress, shear stress, bulk stress and slip amplitude, which are considered to be the controlling parameters of fretting damage. The results demonstrated that among the modifications related to shot peening, compressive residual stress has a dominant effect on the fretting parameters  

    Mechanically activated synthesis of single crystalline MgO nanostructures

    , Article Journal of Alloys and Compounds ; Volume 506, Issue 2 , September , 2010 , Pages 715-720 ; 09258388 (ISSN) Nusheh, M ; Yoozbashizadeh, H ; Askari, M ; Kobatake, H ; Fukuyama, H ; Sharif University of Technology
    2010
    Abstract
    One-dimensional (1D) MgO structures were successfully synthesized via carbothermic reduction of mechanically activated mixture of MgO and graphite. Mechanical activation of source materials before carbothermic reduction can substantially enhance the formation of MgO products at a temperature (1000 °C) relatively lower than that required in previous approaches (≥1200 °C). However, the morphology of MgO formed is dependent on the degree of mechanical activation and the condition of the subsequent carbothermic reduction. Two distinctive morphologies were found for MgO products synthesized using our method: single crystalline nanorods with rectangular cross-sections whose diameters range from 50... 

    Boundary control design for vibration suppression and attitude control of flexible satellites with multi-section appendages

    , Article Acta Astronautica ; Volume 173 , 2020 , Pages 22-30 Ataei, M. M ; Salarieh, H ; Nejat Pishkenari, H ; Jalili, H ; Sharif University of Technology
    Elsevier Ltd  2020
    Abstract
    Attitude and vibration control of a general form of flexible satellites is addressed in this paper. Partial differential dynamic equations are derived considering new details such as multi sectioned solar panels and elastic connections between main hub and solar panels. Boundary control approach is adopted to eliminate simplification errors of discrete models, using just one actuator in the hub. Asymptotic stability of attitude dynamics is proved for a group of boundary controllers and necessary conditions for asymptotic stability of vibrations are discussed. Being independent of modeling accuracy and using easily measurable feedbacks are among advantages of the proposed class of...