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    Control of discrete time chaotic systems via combination of linear and nonlinear dynamic programming

    , Article Journal of Computational and Nonlinear Dynamics ; Vol. 10, Issue. 1 , 2014 ; ISSN: 15551415 Merat, K ; Chekan, J. A ; Salarieh, H ; Alasty, A ; Sharif University of Technology
    Abstract
    In this article by introducing and subsequently applying the Min-Max method, chaos has been suppressed in discrete time systems. By using this nonlinear technique, the chaotic behavior of Behrens-Feichtinger model is stabilized on its first and second-order unstable fixed points (UFP) in presence and absence of noise signal. In this step, a comparison has also been carried out among the proposed Min-Max controller and the Pyragas delayed feedback control method. Next, to reduce the computation required for controller design, the clustering method has been introduced as a quantization method in the Min-Max control approach. To improve the performance of the acquired controller through... 

    Simulation of endurance time excitations via wavelet transform

    , Article Iranian Journal of Science and Technology - Transactions of Civil Engineering ; Volume 43, Issue 3 , 2019 , Pages 429-443 ; 22286160 (ISSN) Mashayekhi, M ; Estekanchi, H. E ; Vafai, H ; Sharif University of Technology
    Springer International Publishing  2019
    Abstract
    This paper puts forth a wavelet-based methodology for generating endurance time (ET) excitations. Conventional simulating practice expresses signals by acceleration values which are then computed via unconstrained nonlinear optimization. Dynamic characteristics of signals, including frequency content, are not represented directly in this type of variable definition. In this study, a new algorithm is developed to generate ET excitations in discrete wavelet transform (DWT) space. In this algorithm, signals are represented by transform coefficients. In addition, objective functions are modified in order to obtain transform coefficients and return the objective function values. The proposed... 

    Bohmian approach to spin-dependent time of arrival for particles in a uniform field and for particles passing through a barrier

    , Article Journal of Physics A: Mathematical and Theoretical ; Volume 41, Issue 37 , 13 August , 2008 ; 17518113 (ISSN) Mousavi, S. V ; Golshani, M ; Sharif University of Technology
    2008
    Abstract
    The de Broglie-Bohm interpretation of quantum mechanics with and without spin-dependence is used to determine electron trajectories, arrival-time distribution of electrons and the mean arrival time of spin-1/2 particles (including electrons) in the presence of a uniform field and a barrier separately. The difference for the mean arrival times, which are calculated with different guidance equations, is examined versus mass of the arriving particle and versus group velocity of the arriving electron wave packet and also versus the width of the barrier. Numerical calculations show that these differences are of the order of 10-18-10-17 s. Another feature of the modified guidance law is that... 

    Space/query-time tradeoff for computing the visibility polygon

    , Article Computational Geometry: Theory and Applications ; Volume 46, Issue 3 , April , 2013 , Pages 371-381 ; 09257721 (ISSN) Nouri Baygi, M ; Ghodsi, M ; Sharif University of Technology
    2013
    Abstract
    In this paper, we consider the problem of computing the visibility polygon (VP) of a query point q (or VP(q)) in a scene consisting of some obstacles with total complexity of n. We show that the combinatorial representation of VP(q) can be computed in logarithmic time by preprocessing the scene in O( n4logn) time and using O( n4) space. We can also report the actual VP(q) in additional O(|VP(q)|) time. As a main result of this paper, we will prove that we can have a tradeoff between the query time and the preprocessing time/space. In other words, we will show that using O(m) space, we can obtain O( n2log(m/n)/m) query time, where m is a parameter satisfying n2≤m≤ n4. For example, when m= n3,... 

    The level crossing and inverse statistic analysis of German stock market index (DAX) and daily oil price time series

    , Article Physica A: Statistical Mechanics and its Applications ; Volume 391, Issue 1-2 , 2012 , Pages 209-216 ; 03784371 (ISSN) Shayeganfar, F ; Hölling, M ; Peinke, J ; Rahimi Tabar, M. Reza ; Sharif University of Technology
    2012
    Abstract
    The level crossing and inverse statistics analysis of DAX and oil price time series are given. We determine the average frequency of positive-slope crossings, να+, where Tα=1να+ is the average waiting time for observing the level α again. We estimate the probability P(K,α), which provides us the probability of observing K times of the level α with positive slope, in time scale Tα. For analyzed time series, we found that maximum K is about ≈6. We show that by using the level crossing analysis one can estimate how the DAX and oil time series will develop. We carry out the same analysis for the increments of DAX and oil price log-returns (which is known as inverse statistics), and provide the... 

    Slack clustering for scheduling frame-based tasks on multicore embedded systems

    , Article Microelectronics Journal ; Volume 81 , 2018 , Pages 144-153 ; 00262692 (ISSN) Poursafaei, F ; Bazzaz, M ; Mohajjel Kafshdooz, M ; Ejlali, A ; Sharif University of Technology
    Elsevier Ltd  2018
    Abstract
    Adopting multicore platforms is a general trend in real-time embedded systems. However, integrating tasks with different real-time constraints into a single platform presents new design challenges. While it must be guaranteed that hard real-time tasks are able to meet their deadline even in worst case scenarios, firm real-time tasks should be scheduled in a way to achieve high system utilization in order to provide a better quality of service. In this paper, we propose a scheduling scheme for frame-based tasks on real-time multicore embedded systems which is able to guarantee the schedulability of the hard real-time tasks, while it improves the number of executed firm real-time tasks.... 

    Finite-time stabilisation of a class of time-varying nonlinear systems by a mixed event-based and continuous-time strategy

    , Article International Journal of Systems Science ; 2021 ; 00207721 (ISSN) Ghazisaeedi, H.R ; Tavazoei, M. S ; Sharif University of Technology
    Taylor and Francis Ltd  2021
    Abstract
    In this paper, a mixed event-triggered and continuous-time control method is proposed, which can guarantee finite-time stabilisation of the fixed point in a class of time-varying nonlinear systems. Benefiting from an event-triggered framework, which is constructed based on the indefinite Lyapunov theory, the communication/computation costs in the transient time can be reduced by using the proposed method. In a special case, this method is converted to a fully event-triggered control strategy for asymptotic stabilisation of the fixed point in the considered class of time-varying nonlinear systems. The effectiveness of the proposed method is verified by numerical simulations. © 2021 Informa UK... 

    A new approach for calculation of relaxation time and magnetic anisotropy of ferrofluids containing superparmagnetic nanoparticles

    , Article Journal of Mining and Metallurgy, Section B: Metallurgy ; Volume 48, Issue 1 , 2012 , Pages 81-88 ; 14505339 (ISSN) Ahmadi, R ; Hosseini, H. R. M ; Sharif University of Technology
    2012
    Abstract
    In this work, a new approach is described for the calculation of the relaxation time and magnetic anisotropy energy of magnetic nanoparticles. Ferrofluids containing monodispersed magnetite nanoparticles were synthesized via hydrothermal method and then heated using the 10 kA/m external AC magnetic fields in three different frequencies: 10, 50 and 100 kHz. By measuring the temperature variations during the application of the magnetic field, the total magnetic time constant including both Brownian and Neel relaxation times can be calculated. By measuring the magnetic core size and hydrodynamic size of particles, the magnetic anisotropy can be calculated too. Synthesized ferrofluids were... 

    Nanoparticle-based optical sensor arrays

    , Article Nanoscale ; v. 9 , 2017 , pages 16546 – 16563 ; 2040-3364 Hormozi-Nezhad, M. R ; Bigdeli, Arafeh ; Ghasemi, Forough ; Golmohammadi, Hamed ; Abbasi-Moayed, Samira ; Farahmand Nejad, M. Amin ; Fahimi-Kashani, Nafiseh ; Jafarinejad, Somayeh ; Shahrajabian, Maryam ; Sharif University of Technology
    Royal Society of Chemistry  2017
    Abstract
    As in many other methods that have integrated nanoparticles (NPs), the chemical nose/tongue strategy has also progressed greatly since the entrance of NPs into this field. The fascinating tunable physicochemical properties of NPs have made them powerful candidates for array-based sensing platforms and have enabled the development of real-time, sensitive and portable systems that are able to target complex mixtures of analytes. In particular, the unique optical properties of NPs have a key role in providing promising array-based sensing approaches. This review will describe the main aspects and processes of most common NP-based optical sensor arrays. The fundamental steps in the design of a... 

    LYSO based precision timing calorimeters

    , Article Journal of Physics: Conference Series, 15 May 2016 through 20 May 2016 ; Volume 928, Issue 1 , 2017 ; 17426588 (ISSN) Bornheim, A ; Apresyan, A ; Ronzhin, A ; Xie, S ; Duarte, J ; Spiropulu, M ; Trevor, J ; Anderson, D ; Pena, C ; Hassanshahi, M. H ; Sharif University of Technology
    Abstract
    In this report we outline the study of the development of calorimeter detectors using bright scintillating crystals. We discuss how timing information with a precision of a few tens of pico seconds and below can significantly improve the reconstruction of the physics events under challenging high pileup conditions to be faced at the High-Luminosity LHC or a future hadron collider. The particular challenge in measuring the time of arrival of a high energy photon lies in the stochastic component of the distance of initial conversion and the size of the electromagnetic shower. We present studies and measurements from test beams for calorimeter based timing measurements to explore the ultimate... 

    Decomposition and robust non-fragile stabilisation of singular time-delay systems

    , Article IET Control Theory and Applications ; Volume 12, Issue 13 , 2018 , Pages 1882-1888 ; 17518644 (ISSN) Zahedi, F ; Haeri, M ; Sharif University of Technology
    Abstract
    This study presents a new approach to decompose singular time-delay systems (STDSs) in a way that they can be transformable to normal time-delay systems (TDSs) with a lower order. Necessary and sufficient conditions are provided to determine which STDSs can be transformed to TDSs. Also, a stabilisation method is provided to stabilise the system, while the time delay in the system can belong to several distinct intervals or even everywhere. The proposed method is non-fragile towards controller parameters. This method also reveals one of the many applicable situations of the proposed decomposition. The effectiveness of the proposed method is illustrated through some examples. © 2018 The... 

    On AdS/CFT of galilean conformal field theories

    , Article Journal of High Energy Physics ; Volume 2009, Issue 8 , 2009 ; 11266708 (ISSN) Alishahiha, M ; Davody, A ; Vahedi, A ; Sharif University of Technology
    2009
    Abstract
    We study a new contraction of a d+1 dimensional relativistic conformal algebra where n+1 directions remain unchanged. For n = 0,1 the resultant algebras admit infinite dimensional extension containing one and two copies of Virasoro algebra, respectively. For 1$">n>1 the obtained algebra is finite dimensional containing an so(2,n+1) subalgebra. The gravity dual is provided by taking a Newton-Cartan like limit of the Einstein's equations of AdS space which singles out an AdS n+2 spacetime. The infinite dimensional extension of n = 0,1 cases may be understood from the fact that the dual gravities contain AdS 2 and AdS 3 factor, respectively. We also explore how the AdS/CFT correspondence works... 

    An applicable count rate saturation correction approach on gamma camera for I-131 labeled radiopharmaceuticals

    , Article Results in Physics ; Volume 12 , 2019 , Pages 1901-1904 ; 22113797 (ISSN) Haghighatafshar, M ; Piruzan, E ; Entezarmahdi, S. M ; Shekoohi Shooli, F ; Parishan, M. R ; Sharif University of Technology
    Elsevier B.V  2019
    Abstract
    Background: Gamma camera count rate saturation and high-rate dead time are the most important problems of quantitative measurement in dosimetric studies. In this study, we aimed to assess an algorithm for correction of the measured counting rates in the entire energy spectrum (327–400 keV) for camera dead-time effects. Methods: In our study, whole body (WB) scan was performed by using a tissue-equivalent phantom, and that the radioactive Iodine (I-131) source with activities of 0.3, 0.6, 1.2, 1.5, 2.07, 2.7, 3.7, and 5.55 GBq was applied. WB scans of the 20% width energy windows were acquired for 420 s. Results: Camera dead-time parameters were obtained from different activities of I-131 in... 

    Reconstruction procedure for writing down the langevin and jump-diffusion dynamics from empirical uni- and bivariate time series

    , Article Understanding Complex Systems ; 2019 , Pages 215-226 ; 18600832 (ISSN) Rahimi Tabar, M. R ; Sharif University of Technology
    Springer Verlag  2019
    Abstract
    In this chapter we present the steps of reconstruction procedure for writing down the Langevin and jump diffusion stochastic dynamical equations for uni- and bivariate time series, sampled with time intervals τ. © 2019, Springer Nature Switzerland AG  

    Reconstruction Procedure for Writing Down the Langevin and Jump-Diffusion Dynamics from Empirical Uni- and Bivariate Time Series

    , Article Understanding Complex Systems ; 2019 , Pages 215-226 ; 18600832 (ISSN) Rahimi Tabar, M. R ; Sharif University of Technology
    Springer Verlag  2019
    Abstract
    In this chapter we present the steps of reconstruction procedure for writing down the Langevin and jump diffusion stochastic dynamical equations for uni- and bivariate time series, sampled with time intervals τ. © 2019, Springer Nature Switzerland AG  

    Forecasting smoothed non-stationary time series using genetic algorithms

    , Article International Journal of Modern Physics C ; Volume 18, Issue 6 , 2007 , Pages 1071-1086 ; 01291831 (ISSN) Norouzzadeh, P ; Rahmani, B ; Norouzzadeh, M. S ; Sharif University of Technology
    2007
    Abstract
    We introduce kernel smoothing method to extract the global trend of a time series and remove short time scales variations and fluctuations from it. A multifractal detrended fluctuation analysis (MF-DFA) shows that the multifractality nature of TEPIX returns time series is due to both fatness of the probability density function of returns and long range correlations between them. MF-DFA results help us to understand how genetic algorithm and kernel smoothing methods act. Then we utilize a recently developed genetic algorithm for carrying out successful forecasts of the trend in financial time series and deriving a functional form of Tehran price index (TEPIX) that best approximates the time... 

    Nonlinear charging and transport times in doped nanotubes junctions

    , Article Journal of the Physical Society of Japan ; Volume 74, Issue 2 , 2005 , Pages 515-518 ; 00319015 (ISSN) Esfarjani, K ; Farajian, A. A ; Kawazoe, Y ; Chui, S. T ; Sharif University of Technology
    2005
    Abstract
    The nonlinear capacitance in doped nanotube junctions is calculated self consistently. A negative differential capacitance is observed when the applied bias becomes larger than the pseudogap of the metallic armchair nanotube. For this device, one can deduce a relaxation time of approximately 0.1 fs. Because of its negative differential resistance (NDR), a switching time of less than a femtosecond, i.e., at least three orders smaller than present-day switching times, can also be estimated. This effect is important in designing ultrafast nano-electronic components. ©2005 The Physical Society of Japan  

    Mixed branes at angle in compact spacetime

    , Article Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics ; Volume 475, Issue 1-2 , 2000 , Pages 39-45 ; 03702693 (ISSN) Arfaei, H ; Kamani, D ; Sharif University of Technology
    2000
    Abstract
    In this article the interaction of branes at angles with respect to each other with non-zero internal gauge fields are calculated by construction of the boundary states in spacetime in which some of its directions are compact on tori. The interaction depends on both angle and fields. (C) 2000 Elsevier Science B.V  

    Expounding the Meaning of Time in Evolutionary Process

    , M.Sc. Thesis Sharif University of Technology Arami Manesh, Saber (Author) ; Shafiee, Afshin (Supervisor)
    Abstract
    The question of the time is one of the obscure and challenging subjects which has been discussed as a mysterious problem in various civilizations. In ancient Greece, the question has been debated among the supporters of existence and eternity. We observe the words of Plato, on the existence of the absolute essence of eternity against the change and transition time instantiated as a conducted river in the Heraclitus view. Other discussions focused on the relationship between the change and displacement, or the the spatial relations to which Aristotle paid attention. With the passing of time from the ancient and medieval eras to the Renaissance period, along with the growth of the science in... 

    Phase-induced intensity noise in digital incoherent all-optical tapped-delay line systems [electronic resource]

    , Article Lightwave Technology, Journal of ; 2006, Volume.24 , Issue. 8, p.3059-3072 Mansouri Rad, M. M. (Mohammad Mehdi) ; Salehi, J. A ; Sharif University of Technology
    Abstract
    In this paper, the authors analyze conditions under which they can be certain on the intensity addition of a given device, such as tapped-delay lines, used in digital incoherent all-optical communication systems. A general expression for phase-induced intensity noise that is applicable to all types of semiconductor lasers is derived by defining an optical self-SNR expression that can be used to analyze and measure phase-induced intensity noise. The result shows that in order to have a minimal phase-induced intensity noise in most digital optical incoherent systems, a large optical self-SNR, e.g., 20 dB or more, is needed. This in turn is shown to place a limit on the maximum rate of...