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    Optical bistability in fiber ring resonator containing an erbium doped fiber amplifier and quantum dot doped fiber saturable absorber

    , Article Applied Optics ; Volume 51, Issue 29 , 2012 , Pages 7016-7024 ; 1559128X (ISSN) Tofighi, S ; Farshemi, S. S ; Sajjad, B ; Shahshahani, F ; Bahrampour, A. R ; Sharif University of Technology
    2012
    Abstract
    In this paper we study the optical bistability in a double coupler fiber ring resonator which consists of an erbium doped fiber amplifier (EDFA) in half part of the fiber ring and a quantum dot doped fiber (QDF) saturable absorber in the other half. The bistability is provided by the QDF section of the ring resonator. The EDFA is employed to reduce the switching power. The transmitted and reflected bistability characteristics are investigated. It is shown that the switching power for this new bistable device is less than 10 mW  

    Decentralized active power management in multi-agent distribution systems considering congestion issue

    , Article IEEE Transactions on Smart Grid ; Volume 13, Issue 5 , 2022 , Pages 3582-3593 ; 19493053 (ISSN) Tofighi Milani, M ; Fattaheian Dehkordi, S ; Fotuhi Firuzabad, M ; Lehtonen, M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2022
    Abstract
    Recently, due to the restructuring of power systems and the high penetration level of local renewables, distribution systems have encountered with the complexity of power management. Therefore, the modern systems would be operated in a multi-agent structure which facilitates the power management as well as privacy protections of independent entities. In this structure, the distribution system is assumed to compose of several agents who independently schedule their local resources in order to maximize their own profits. Consequently, this paper provides an efficient peer-to-peer (P2P) active power management framework in a multi-agent distribution system while considering network constraints... 

    Distributed reactive power management in multi-agent energy systems considering voltage profile improvement

    , Article IET Generation, Transmission and Distribution ; Volume 17, Issue 21 , 2023 , Pages 4891-4906 ; 17518687 (ISSN) Tofighi Milani, M ; Fattaheian Dehkordi, S ; Fotuhi Firuzabad, M ; Lehtonen, M ; Sharif University of Technology
    John Wiley and Sons Inc  2023
    Abstract
    In recent years, distributed structures have been developed in distribution networks as a result of privatization as well as integration of independently operated distributed energy resources (DERs) into the grid. In this context, effective management techniques seem to be necessary to enable decentralized operation of systems that have been consisted of multiple agents. Accordingly, novel management schemes should be applied in such systems to enable the distributed reactive power management, which would finally improve voltage profile in the network. As a result, this paper develops a distributed algorithm for reactive power management in multi-agent distribution systems with the aim of... 

    Dispersion around a circular cylinder in surface wave motion

    , Article Scientia Iranica ; Vol. 21, issue. 3 , 2014 , p. 548-556 ; 10263098 Tofighi, M. A ; Jamali, M ; Sharif University of Technology
    2014
    Abstract
    In this paper, we examine fluid flow and associated dispersion around a circular cylinder under progressive surface wave motion. The flow field and vortex shedding patterns were studied using flow visualization and Particle Image Velocimetry (PIV). Several patterns of vortex shedding were identified around a single cylinder. The vortex shedding patterns under progressive wave motion are similar to those observed in planar oscillatory flow, except in the way the vortices form and in the orientation they take. The observed vortex patterns in progressive wave motion are more unstable than those in planar oscillatory flow. Using particle tracking and the Lagrangian dispersion method, the... 

    Theoretical model for visible light saturable absorber nanolithography

    , Article Journal of Optics (United Kingdom) ; Volume 14, Issue 12 , 2012 ; 20408978 (ISSN) Tofighi, S ; Bahrampour, A. R ; Sharif University of Technology
    2012
    Abstract
    In this paper a saturable absorber medium is employed as an optical limiter to reduce the spot size to the range of several tens of nanometres. The characteristics of a Gaussian beam are theoretically analysed upon propagation through the saturable absorber medium. Based on Maxwell equations a system of coupled nonlinear ordinary differential equations for intensity, beam radius and beam curvature is obtained. Theoretical analyses and numerical results show that the behaviour of a Gaussian beam in a saturable absorber medium strongly depends on the initial characteristics of the laser beam. Numerical results indicate that, depending on the initial conditions and a suitable saturable absorber... 

    Analysis of transient response and instability in fiber ring resonators containing an erbium-doped fiber amplifier and quantum dot-doped fiber saturable absorber

    , Article Journal of the Optical Society of America B: Optical Physics ; Volume 30, Issue 12 , December , 2013 , Pages 3215-3224 ; 07403224 (ISSN) Tofighi, S ; Bahrampour, A. R ; Sharif University of Technology
    Optical Society of American (OSA)  2013
    Abstract
    In this paper, the transient response of a double coupler fiber ring resonator containing an erbium-doped fiber amplifier (EDFA) in half part of the fiber ring resonator and a quantum dot-doped fiber (QDF) saturable absorber in the other half, is investigated. It is demonstrated that, depending on the device parameters and the input power of the signal and pump, various types of dynamic behaviors (such as bistability, monostability, and regenerative pulsation) can be observed in this intrinsic, optical bistable device. The proposed device can be exploited by optical communication networks to realize all-optical functionalities  

    All-optical controlled switching in centrally coupled circular array of nonlinear optical fibers

    , Article Applied Optics ; Volume 52, Issue 25 , Sep , 2013 , Pages 6131-6137 ; 1559128X (ISSN) Tofighi, S ; Bahrampour, A. R ; Sharif University of Technology
    Optical Society of American (OSA)  2013
    Abstract
    We show that, in a nonlinear centrally coupled circular array of evanescently coupled fibers, the coupling dynamics of a weak signal beam can be efficiently influenced by a high-power control beam that induces nonlinear defects. When the intense control beam is launched into the central core and one core in the periphery, then localized solitons are formed and cause the fibers with induced defects (defected fibers) to decouple from the other array elements. In the presence of a high-intensity control beam, the propagation of weak signal is restricted to the defected optical fibers. The weak signal periodically couples between the induced defects. This oscillatory behavior depends on the sign... 

    Visible Light Saturable Absorber Near-Field Nanolithography

    , Ph.D. Dissertation Sharif University of Technology Tofighi, Sara (Author) ; Bahrampour, Ali Reaz (Supervisor)

    Acoustical gas-leak detection in the presence of multiple reflections, dispersion, and uncorrelated noise using optimized residual complexity

    , Article Journal of the Acoustical Society of America ; Volume 140, Issue 3 , 2016 , Pages 1817-1827 ; 00014966 (ISSN) Ahmadi, A. M ; Amjadi, A ; Bahrampour, A. R ; Ravanbod, H ; Tofighi, S ; Sharif University of Technology
    Acoustical Society of America  2016
    Abstract
    Precise acoustical leak detection calls for robust time-delay estimates, which minimize the probability of false alarms in the face of dispersive propagation, multiple reflections, and uncorrelated background noise. Providing evidence that higher order modes and multi-reflected signals behave like sets of correlated noise, this work uses a regression model to optimize residual complexity in the presence of both correlated and uncorrelated noise. This optimized residual complexity (ORC) is highly robust since it takes into account both the level and complexity of noise. The lower complexity of the dispersive modes and multiple reflections, compared to the complexity of the plane mode, points... 

    Effect of Aquatic Plants on Hydrodynamic and Dispersion in the Wave Motion

    , Ph.D. Dissertation Sharif University of Technology Tofighi, Mohammad Ali (Author) ; Jamali, Mirmosadegh (Supervisor)
    Abstract
    Aquatic plants play an important role in water environment. Increasing drag force, distorting the velocity and turbulence structures and other related parameters, are the results of the presences of plants. These changes affect the dispersion and mass transport in the aquatic areas. This thesis presents laboratory visualizations and measurements of wave motion, and passive solute surface dispersion (longitudinal and lateral) in arrays of cylinders, a model for emergent, rigid aquatic plants. In the range of (where is Keulegan–Carpenter number, is the maximum oscillatory velocity perpendicular to the cylinder axis, is the period of oscillation, and is the diameter of the cylinder), and (where... 

    Polarization maintaining optical fiber multi-intruder sensor

    , Article Optics and Laser Technology ; Volume 44, Issue 7 , October , 2012 , Pages 2026-2031 ; 00303992 (ISSN) Bahrampour, A. R ; Bathaee, M ; Tofighi, S ; Bahrampour, A ; Farman, F ; Vali, M ; Sharif University of Technology
    Elsevier  2012
    Abstract
    In this paper, an optical fiber multi-intruder sensor based on polarization maintaining optical fiber (PMF), without any interferometric fiber loop, is introduced. To map the local coordinates of intruders on the beating spectrum of the output modes, radiation from a ramp frequency modulated laser is injected at the input of PMF optical fiber sensor. It is shown that the local coordinates and some characteristics of intruders can be obtained by the measurement of the frequencies and amplitudes of the output mode beating spectrum. Generally the number of beating frequencies is more than the number of intruders. Among the beating frequencies, a group with maximum signal to noise ratio is... 

    Saturable absorber nanolithography by vectorial nonparaxial gaussian beam

    , Article 3rd Mediterranean Photonics Conference, MePhoCo ; 7 - 9 May , 2014 , pp. 1 - 3 ; ISBN: 9781479948185 Tofighi, S ; Afsary, M ; Bahrampour, A. R ; Sharif University of Technology
    2014
    Abstract
    The non-paraxial and vectorial effects have an important role in the dynamics of highly confined beam in nonlinear medium. In this paper, we study the vectorial non-paraxial propagation of Gaussian field in the saturable absorber media numerically with the aim of nano-lithography. It is shown that in the optimal regimes for nanolithography, the mutual coupling between components of optical field and mode coupling between different orders of Hermite-Gaussian mode lead to generation of various patterns upon propagation through saturable absorber media. The vectorial effect is responsible for the symmetry breaking. For converging input beam, while the intense part of the beam goes toward the... 

    Optimum quantum state of light for gravitational-wave interferometry

    , Article Optics Communications ; Volume 283, Issue 6 , 2010 , Pages 1012-1016 ; 00304018 (ISSN) Tofighi, S ; Bahrampour, A. R ; Shojai, F ; Sharif University of Technology
    2010
    Abstract
    The laser interferometric gravitational-wave detectors are sensitive to the quantum state of light employed in the dark port of interferometric system. In this paper a general quantum state for the dark input port is assumed. The quantum state of light is expanded versus the Fock states. The quantum noise of interferometric system is computed as a function of the quantum state of light. The variational method and the genetic algorithm are employed to determine the coefficients of the dark input port and the laser input power for the minimization of the quantum noise. Calculation shows that the optimum quantum state for the dark input port is very close to the vacuum squeezed state. For this... 

    A theoretical multi-reflection method for analysis of optomechanical behavior of the Fabry-Perot cavity with moving boundary condition

    , Article Optics Communications ; Volume 284, Issue 19 , 2011 , Pages 4789-4794 ; 00304018 (ISSN) Bahrampour, A. R ; Vahedi, M ; Abdi, M ; Ghobadi, R ; Golshani, M ; Tofighi, S ; Parvin, B ; Sharif University of Technology
    2011
    Abstract
    The opto-mechanical coupling and the generation of Stokes and anti-Stokes frequencies in the in-band and intra-band regimes of operation of the Fabry-Perot cavity with a moving mirror on the basis of multi-reflection method (MRM) are described by a unique theory. The frequency characteristic function of the Fabry-Perot filter is modified. By increasing the amplitude of mirror oscillation the Fabry-Perot bandwidth increases and normal mode splitting occurred. The conversion efficiencies of the Stokes and anti-Stokes frequencies versus the mechanical amplitude of oscillation have an optimum value. Also, the delay function corresponding to the radiation pressure is obtained  

    Efficient Distributed Management of Local Resources in Multi-agent Distribution Systems

    , M.Sc. Thesis Sharif University of Technology Tofighi Milani, Mahyar (Author) ; Fotuhi Firuzabad, Mahmud (Supervisor)
    Abstract
    Nowadays, with the expansion of restructuring and privatization in power systems, energy markets are growing rapidly, within distribution networks. In order for such markets to be implemented in practice, the technical constraints and issues of the distribution network, which are mainly the power loss and congestion of lines and also the bus voltage violations, must also be considered within the framework provided for them. Hence, this dissertation presents some new structures for Peer-to-peer (P2P) energy markets, in which the technical issues of the distribution network could be considered. Moreover, a model predictive control method is used in the proposed structures of this dissertation... 

    Releasing All-Pairs Shortest Distances of Public Graphs with Differential Privacy

    , M.Sc. Thesis Sharif University of Technology Tofighi Mohammadi, Alireza (Author) ; Ebrahimi Boroojeni, Javad (Supervisor)
    Abstract
    In the context of differential privacy, a data holder has confidential information about users. The goal is to provide a randomized algorithm that takes this information as input and outputs an aggregation of the input. The algorithm must have the property that for any neighboring input pairs, the output distribution of the algorithm is close. One problem in differential privacy research is the release of shortest distances in a weighted graph. This model, first studied by Adam Sealfon, involves an edge-weighted graph G=(V, E) with weights w : E → R, where the topology of the graph is public and the private information is the weight of the edges. The aim is to provide an (ϵ, δ)-DP algorithm... 

    Monitoring of Structure Characteristics, Humidity, Temperature and Torsion Using Optical Fiber Sensor

    , Ph.D. Dissertation Sharif University of Technology Esmailzadeh Noghani, Fereshteh (Author) ; Bahrampour, Alireza (Supervisor) ; Tofighi, Sara (Supervisor)
    Abstract
    Fiber optic sensors have found industrial applications due to their unique characteristics and wide range of environmental parameters. Specifically, distributed optical fiber sensors which have applications in borders protection, intrusion detection, oil and gas leakage detection and smart irrigation of farms and gardens, have attracted significant attention from research groups around the world in recent years. According to the forecasts, among all kind of optical fiber sensors, the temperature and acoustic/vibration sensors will seize the market during the coming years. In this thesis, three kind of optical fiber sensors are proposed for environment health monitoring. First, distributed... 

    The relationship between an EFL teacher's gender and students' willingness to communicate

    , Article International Journal of Communication and Linguistic Studies ; Volume 10, Issue 4 , 2013 , Pages 17-29 ; 23277882 (ISSN) Khosravizadeh, P ; Pakzadian, S. S
    Common Ground Publishing  2013
    Abstract
    Learning a foreign language encompasses a process of trial and error that can lead to the progression of the learner's interlanguage, meaning that the learners make use of their language knowledge that receives feedback and brings about progress through diagnosis of the problems and being corrected by the teacher. Therefore, there exists a need to analyze the underlying reasons causing the students to remain taciturn with a low willingness to communicate (WTC) during a language class. There has been much work done investigating the role of the learner's stable personal characteristics (traits) along with their situational changes at a specific time (states) that influence the student's... 

    An automated simple algorithm for realistic pore network extraction from micro-tomography images

    , Article Journal of Petroleum Science and Engineering ; Vol. 123, issue , 2014 , pp. 164-171 ; ISSN: 09204105 Rabbani, A ; Jamshidi, S ; Salehi, S
    2014
    Abstract
    Using 3-D scanned data to analyze and extract pore network plays a vital role in investigation of porous media's characteristics. In this paper, a new simple method is developed to detect pores and throats for analyzing the connectivity and permeability of the network. This automated method utilizes some of the common and well-known image processing functions which are widely accessible by researchers and this has led to an easy algorithm implementation. In this method, after polishing and quality control of images, using city-block distance function and watershed segmentation algorithm, pores and throats are detected and 3-D network is produced. This method can also be applied on 2-D images... 

    Discrimination of heart arrhythmias using novel features in heart rate phase space

    , Article Computing in Cardiology ; Volume 40 , Sept , 2013 , Pages 1035-1038 ; 23258861 (ISSN); 9781479908844 (ISBN) Moharreri, S ; Rezaei, S ; Salavatian, S
    2013
    Abstract
    In this paper, we try to recognize and distinguish different groups of arrhythmia using novel features which have been obtained from the heart rate's phase space in recent years. For this purpose, we used Triangular Phase Space Mapping (TPSM) and Parabolic Phase Space Mapping (PPSM). For recognition, we used three groups of 15 subjects using the Physionet database (Arrhythmia, Congestive Heart Failure (CHF), and Atrial Fibrillation (AF)) with Normal Sinus Rhythm (NSR). The obtained features discriminate arrhythmia from NSR by p