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    Emergence of Hopf bifurcation in an extended SIR dynamic

    , Article PLoS ONE ; Volume 17, Issue 10 October , 2022 ; 19326203 (ISSN) Roostaei, A ; Barzegar, H ; Ghanbarnejad, F ; Sharif University of Technology
    Public Library of Science  2022
    Abstract
    In this paper, the original SIR model is improved by considering a new compartment, representing the hospitalization of critical cases. A system of differential equations with four blocks is developed to analyze the treatment of severe cases in an Intensive Care Unit (ICU). The outgoing rate of the infected individuals who survive is divided into nI and bI/1+b where the second term represents the transition rate of critical cases that are hospitalized in ICU. The findings demonstrate the existence of forward, backward and Hopf bifurcations in various ranges of parameters. © 2022 Roostaei et al. This is an open access article distributed under the terms of the Creative Commons Attribution... 

    Emergency Medical Service Centers Location

    , M.Sc. Thesis Sharif University of Technology Roostaei, Ali (Author) ; Eshghi, Kourosh (Supervisor)
    Abstract
    The Emergency Medical Services (EMS) have a major role in decreasing the mortality rate and reducing the non-reversible effects of injuries by on time care to patients and transporting them to hospitals if it is needed. Since there is an important goal directly related to the human life, any research or study to improve the performance of EMS is highly recommended. One of the most important parameters in evaluation of EMS is to measure the coverage time of a demand. The locations of EMS play substantial role to decrease the response time. So the locations of EMS stations are very important especially in large and populated cities. Mainly, there are three problems that EMS managers should... 

    Study on Biodiesel Production Using Engineered Lipases

    , M.Sc. Thesis Sharif University of Technology Char Roostaei, Hamzeh (Author) ; Kazemeini, Mohammad (Supervisor)
    Abstract
    Biodiesel has drawn the attention of many researches to itself as a replacing source for crude oil, recently. Transesterification is one of the most popular methods used for biodiesel production. Enzyme transesterification is a more simple method in comparison with acidic or basic transesterification. However, the high price and low yield of enzyme transesterification has caused many obstacles in its application. Enzyme engineering has gained much attention as a way to improve enzyme performance. In this thesis, biodiesel production by a native enzyme named Bacillus thermocatenulatus, and two engineered-enzymes is studied. First, effective parameters and variables in biodiesel production by... 

    Investigation of the Effect of Slip Length on the Electrokinetic Behavior of Conical-Shaped Nanochannels

    , M.Sc. Thesis Sharif University of Technology Roostaei, Mahmoud (Author) ; Mohammadi, Ali Asghar (Supervisor)
    Abstract
    Conical nanochannels have desirable electrokinetic properties due to asymmetry,including ionic current rectification and ion selectivity. The present study numerically addressed the effect of slip length on the ionic current rectification and ion selectivity in conical-shaped electrolyte-loaded nanochannels with and without a coated polyelectrolyte layer. The electrolyte was considered a salted incompressible Newtonian fluid. The polyelectrolyte layer was also modeled as a rigid and charged porous solid saturated with a salted Newtonian fluid. The electrolyte-polyelectrolyte layer interface was modeled as a surface, considering ion partitioning with distinct physical properties across the... 

    Numerical Modeling and Experimental Investigation of the Efficiency of the Laser-assisted Machining for Ceramics

    , Ph.D. Dissertation Sharif University of Technology Roostaei, Hossein (Author) ; Movahhedy, Mohammad Reza (Supervisor) ; Shoja Razavi, Reza (Co-Supervisor)
    Abstract
    Laser-assisted machining is nowadays considered as an alternative to conventional machining processes including ceramics grinding, which has provided the basis for extensive experimental and numerical studies in this field. Since the main difference between laser-assisted machining and conventional machining is in the presence of lasers, the main purpose of this study was to investigate the effects of laser on the laser assisted machining process. In this regard, in the first step the process of laser heating to the ceramic workpiece has been studied experimentally and numerically by finite element method. The material used in this research is a slip cast fused silica ceramic. The... 

    Analysis of Heat Transfer in Laser Assisted Machining of Slip Cast Fused Silica Ceramics

    , Article 7th CIRP Conference on High Performance Cutting, HPC 2016, 31 May 2016 through 2 June 2016 ; Volume 46 , 2016 , Pages 571-574 ; 22128271 (ISSN) Roostaei, H ; Movahhedy, M. R ; Ihlefeldt S ; Wertheim R ; Hochmuth C ; Putz M ; Sharif University of Technology
    Elsevier  2016
    Abstract
    Machining of ceramics often involves many challenges due to their high hardness, brittleness, and low thermal properties. Laser assisted machining (LAM) is a promising technology for improving the machinability of hard-to-cut materials. In this work, laser assisted machining of slip cast fused silica (SCFS) ceramics is investigated by presenting a numerical thermal analysis of laser effects on material behaviour. A transient three-dimensional heat transfer analysis for laser assisted turning of SCFS is performed using finite element method. Temperature distributions in SCFS cylindrical specimens are obtained. Experimental results are provided to validate the numerical results  

    Channelopathy-related SCN10A gene variants predict cerebellar dysfunction in multiple sclerosis

    , Article Neurology ; Volume 86, Issue 5 , 2016 , Pages 410-417 ; 00283878 (ISSN) Roostaei, T ; Sadaghiani, S ; Park, M. T. M ; Mashhadi, R ; Nazeri, A ; Noshad, S ; Salehi, M. J ; Naghibzadeh, M ; Moghadasi, A. N ; Owji, M ; Doosti, R ; Hashemi Taheri, A. P ; Rad, A. S ; Azimi, A ; Chakravarty, M. M ; Voineskos, A. N ; Nazeri, A ; Sahraian, M. A ; Sharif University of Technology
    Lippincott Williams and Wilkins  2016
    Abstract
    Objective: To determine the motor-behavioral and neural correlates of putative functional common variants in the sodium-channel NaV1.8 encoding gene (SCN10A) in vivo in patients with multiple sclerosis (MS). Methods: We recruited 161 patients with relapsing-onset MS and 94 demographically comparable healthy participants. All patients with MS underwent structural MRI and clinical examinations (Expanded Disability Status Scale [EDSS] and Multiple Sclerosis Functional Composite [MSFC]). Whole-brain voxel-wise and cerebellar volumetry were performed to assess differences in regional brain volumes between genotype groups. Resting-state fMRI was acquired from 62 patients with MS to evaluate... 

    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... 

    Characterization and calcination behavior of a low-grade manganese ore

    , Article Materials Today Communications ; Volume 25 , 2020 Cheraghi, A ; Becker, H ; Eftekhari, H ; Yoozbashizadeh, H ; Safarian, J ; Sharif University of Technology
    Elsevier Ltd  2020
    Abstract
    Characterization and calcination behavior of a low-grade manganese ore, as a part of Mn ferroalloys production, was studied by XRF, ex-situ XRD, in-situ XRD, and SEM-EDS techniques. Calcination experiments were carried out at and up to 900 °C (1173 K) in air and argon atmospheres. The samples were in particles and powder forms. The results indicated that both quartz and calcite phases in the ore exhibit a bimodal spatial distribution; as relatively large regions and finely distributed in the Mn- and Fe-containing phases. By Rietveld analysis of the in-situ XRD data, the reactions occurring upon heating during the calcination process were deduced. Thermal decomposition and reactive diffusion... 

    Minimizing the error of time difference of arrival method in mobile networks

    , Article 2005 International Conference on Wirelessand Optical Communications Networks, Dubai, 6 March 2005 through 8 March 2005 ; 2005 , Pages 328-332 ; 0780390199 (ISBN); 9780780390195 (ISBN) Malekitabar, A ; Aghababa, H ; Radfar, M. H ; Khalaj, B. H ; Sharif University of Technology
    2005
    Abstract
    Estimating the position of a mobile set is of great importance in new mobile services. However, in most cases, the accuracy should be less than 100 meters. This accuracy is hard to reach especially in urban areas. The main problem is that there are a lot of obstacles like buildings between the BTS and the mobile set. Thus the time measured between BTS and the mobile set is somehow greater than the time it takes the wave to travel directly between two points. This paper introduces an optimized solution for TDOA as one of the most efficient ways for finding the location of a mobile phone. Considering the standards and limitations of both GSM and UMTS, the Authors present a solution for... 

    A fast and novel method of pattern synthesis for non-uniform phased array antennas

    , Article Proceedings International Radar Symposium, 24 June 2015 through 26 June 2015 ; Volume 2015-August , 2015 , Pages 924-929 ; 21555753 (ISSN) ; 9783954048533 (ISBN); 9783954048533 (ISBN); 9783954048533 (ISBN) Tohidi, E ; Sebt, M. A ; Nayebi, M. M ; Behroozi, H ; Rohling, H ; Rohling, H ; Rohling, H ; Sharif University of Technology
    IEEE Computer Society  2015
    Abstract
    Weighting elements to achieve radiation patterns with desired characteristics is a classical work in phased array antennas. These characteristics can be low sidelobe level, narrow beamwidth, high directivity, pattern nulling in special angle and etc. For each of these characteristics, different methods have been introduced. Most of methods have been presented for uniform arrays, however there are lots of methods to obtain a desired pattern for antennas with non-uniform element distances. The problem with these methods is complexity or not very good results. In this paper, fast and easy methods based on Least Square Error that leads to good results are presented. In addition, weighting of... 

    Size-dependent interaction of an edge dislocation with an elliptical nano-inhomogeneity incorporating interface effects

    , Article International Journal of Solids and Structures ; Volume 49, Issue 5 , March , 2012 , Pages 759-770 ; 00207683 (ISSN) Shodja, H. M ; Ahmadzadeh Bakhshayesh, H ; Gutkin, M. Y
    2012
    Abstract
    The elastic behavior of an edge dislocation, which is positioned outside of a nanoscale elliptical inhomogeneity, is studied within the interface elasticity approach incorporating the elastic moduli and surface tension of the interface. The complex potential function method is used. The dislocation stress field and the image force acting on the dislocation are found and analyzed in detail. The difference between the solutions obtained within the classical-elasticity and interface-elasticity approaches is discussed. It is shown that for the stress field, this difference can be significant in those points of the inhomogeneity-matrix interface, where the radius of curvature is smaller and which... 

    Control of parallel three- phase inverters using optimal control and SVPWM technique

    , Article IEEE International Symposium on Industrial Electronics, 5 July 2009 through 8 July 2009 ; 2009 , Pages 1823-1828 ; 9781424443499 (ISBN) Nazaripouya, H. R ; Mokhtari, H ; Sharif University of Technology
    2009
    Abstract
    In this paper, optimal control strategy is applied to parallel three-phase inverters using SVPWM technique. The three-phase system is transformed to a synchronous-stationary frame, suitable cost functions are defined, and the switching schemes are determined for the inverters. The control strategy minimizes the circulating current between the inverters, therefore, proper load sharing scheme is achieved. Simulations are performed for steady state and load change operation, and the results which show the suitability of the controller are provided. ©2009 IEEE