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    Tunable delay line based on Fourier-transformation and linear phase modulation with high time-bandwidth product

    , Article Photonische Netze - 13. ITG-Fachtagung 2020 ; 2020 , Pages 229-231 Mokhtari, A ; Preubler, S ; Jamshidi, K ; Akbari, M ; Schneider, T ; Sharif University of Technology
    VDE Verlag GmbH  2020
    We recruit basic properties of Fourier transformation to realize an electrically tunable delay line and increase the delay by creating a loop in the structure. The proposed method has been experimentally tested and verified for up to 5 roundtrips. The relative delay/advancement was increased up to 5 times compared to the original setup while preserving the original setup's advantages. © VDE VERLAG GMBH  

    The design of PIP controller for a thermal system with large time delay

    , Article World Academy of Science, Engineering and Technology ; Volume 32 , 2009 , Pages 890-894 ; 2010376X (ISSN) Zareh, S. H ; Sarrafan, A ; Ghaemi Osgouie, K ; Sharif University of Technology
    This paper will first describe predictor controllers when the proportional-integral-derivative (PID) controllers are inactive for procedures that have large delay time (LDT) in transfer stage. Therefore in those states, the predictor controllers are better than the PID controllers, then compares three types of predictor controllers. The value of these controller's parameters are obtained by trial and error method, so here an effort has been made to obtain these parameters by Ziegler-Nichols method. Eventually in this paper Ziegler-Nichols method has been described and finally, a PIP controller has been designed for a thermal system, which circulates hot air to keep the temperature of a... 

    Criteria of Choosing Intersection or Roundabout Based on Delay Time, Fuel Consumption, and Environmental Factors

    , M.Sc. Thesis Sharif University of Technology Mohammadi, Mansour (Author) ; Nassiri, Habibollah (Supervisor)
    Nowadays, there are three factors in traffic issues, which are very important. These factors are delay time, fuel consumption and environmental pollution. A good choice of the type of traffic nodes (intersection and roundabout) can play an important role in reducing some of the traffic problems such as: the amount of vehicles' delay time, energy consumption and pollution due to the transport system. In this study, we try to identify factors that influence delay time, fuel consumption and air pollution in different types of intersections and roundabout. According to previous studies, these factors were such as: variables of each route volume, distribution of through, right turn and left turn... 

    Leak Detection in Gasand oil Pipeline Using Acousticemission

    , M.Sc. Thesis Sharif University of Technology Ranjbar, Alireza (Author) ; Zohoor, Hassan (Supervisor)
    Pipelines are main means of gas and oil transfer, and thus, leak detection in them for prevention or control of contingencies is highly important. Examination of acoustic waves resulted from diverse vibrational characteristics of damaged points has led to possibility of invention of varied industrial tools for non-destructive test. This research’s objective is examining acoustic and vibrational signals propagated by leakage point as a tool for locating leakage’s place and accuracy assessment of them in leak detection. For leak detection of the devised experimental system, a new method has been employed to calculate time delay; this method, which is called Residual Complexity, is based on... 

    MiNDSTEp differential photometry of the gravitationally lensed quasars WFI 2033-4723 and HE 0047-1756: microlensing and a new time delay

    , Article Astronomy and Astrophysics ; Volume 597 , 2017 ; 00046361 (ISSN) Giannini, E ; Schmidt, R. W ; Wambsganss, J ; Alsubai, K ; Andersen, J. M ; Anguita, T ; Bozza, V ; Bramich, D. M ; Browne, P ; Calchi Novati, S ; Damerdji, Y ; Diehl, C ; Dodds, P ; Dominik, M ; Elyiv, A ; Fang, X ; Figuera Jaimes, R ; Finet, F ; Gerner, T ; Gu, S ; Hardis, S ; Harpsøe, K ; Hinse, T. C ; Hornstrup, A ; Hundertmark, M ; Jessen Hansen, J ; Jørgensen, U. G ; Juncher, D ; Kains, N ; Kerins, E ; Korhonen, H ; Liebig, C ; Lund, M. N ; Lundkvist, M. S ; Maier, G ; Mancini, L ; Masi, G ; Mathiasen, M ; Penny, M ; Proft, S ; Rabus, M ; Rahvar, S ; Ricci, D ; Scarpetta, G ; Sahu, K ; Schäfer, S ; Schönebeck, F ; Skottfelt, J ; Snodgrass, C ; Southworth, J ; Surdej, J ; Tregloan Reed, J ; Vilela, C ; Wertz, O ; Zimmer, F ; Sharif University of Technology
    Aims. We present V and R photometry of the gravitationally lensed quasars WFI 2033-4723 and HE 0047-1756. The data were taken by the MiNDSTEp collaboration with the 1.54 m Danish telescope at the ESO La Silla observatory from 2008 to 2012. Methods. Differential photometry has been carried out using the image subtraction method as implemented in the HOTPAnTS package, additionally using GALFIT for quasar photometry. Results. The quasar WFI 2033-4723 showed brightness variations of order 0.5 mag in V and R during the campaign. The two lensed components of quasar HE 0047-1756 varied by 0.2-0.3 mag within five years. We provide, for the first time, an estimate of the time delay of component B... 

    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
    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... 

    Performance and exhaust emission characteristics of a spark ignition engine operated with gasoline and CNG blend

    , Article Proceedings of the Spring Technical Conference of the ASME Internal Combustion Engine Division ; 2012 , Pages 179-187 ; 15296598 (ISSN) ; 9780791844663 (ISBN) Dashti, M ; Hamidi, A. A ; Mozafari, A. A ; Sharif University of Technology
    Using CNG as an additive for gasoline is a proper choice due to higher octane number of CNG enriched gasoline with respect to that of gasoline. As a result, it is possible to use gasoline with lower octane number in the engine. This would also mean the increase of compression ratio in SI engines resulting in higher performance and lower gasoline consumption. Over the years, the use of simulation codes to model the thermodynamic cycle of an internal combustion engine have developed tools for more efficient engine designs and fuel combustion. In this study, a thermodynamic cycle simulation of a conventional four-stroke spark-ignition engine has been developed. The model is used to study the... 

    Observer-based adaptive neural network controller for uncertain nonlinear systems with unknown control directions subject to input time delay and saturation

    , Article Information Sciences ; Volume 418-419 , 2017 , Pages 717-737 ; 00200255 (ISSN) Khajeh Talkhoncheh, M ; Shahrokhi, M ; Askari, M. R ; Sharif University of Technology
    This paper addresses the design of an observer based adaptive neural controller for a class of strict-feedback nonlinear uncertain systems subject to input delay, saturation and unknown direction. The input delay has been handled using an integral compensator term in the controller design. A neural network observer has been developed to estimate the unmeasured states. In the observer design, the Lipschitz condition has been relaxed. To solve the problem of unknown control directions, the Nussbaum gain function has been applied in the backstepping controller design. “The explosion of complexity” occurred in the traditional backstepping technique has been avoided utilizing the dynamic surface... 

    Adaptive fuzzy decentralized control for a class of MIMO large-scale nonlinear state delay systems with unmodeled dynamics subject to unknown input saturation and infinite number of actuator failures

    , Article Information Sciences ; Volume 475 , 2019 , Pages 121-141 ; 00200255 (ISSN) Moradvandi, A ; Shahrokhi, M ; Malek, S. A ; Sharif University of Technology
    Elsevier Inc  2019
    This paper addresses design of an adaptive fuzzy decentralized fault-tolerant controller for a class of uncertain multi-input multi-output (MIMO) large-scale nonlinear systems with unmodeled dynamics subject to unknown state time-varying delay, external disturbances, unknown input saturation and actuator faults. It is shown that the proposed fault-tolerant control (FTC) scheme can handle infinite number of actuator failures including partial and total loss of effectiveness. System uncertainties have been approximated by the fuzzy logic systems (FLSs). To cope with the unknown state time-varying delay, the Razumikhin lemma has been utilized and unmodeled dynamics has been tackled by... 

    Novel trombone topology for wideband true-time-delay implementation

    , Article IEEE Transactions on Microwave Theory and Techniques ; Volume 68, Issue 4 , 2020 , Pages 1542-1552 Ghazizadeh, M. H ; Medi, A ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2020
    A novel trombone topology has been introduced for achieving controllable true time delay. The prominent aspect of the proposed topology is the ability to provide discrete variable delay with minimum insertion loss variation with delay settings. Furthermore, the effects of source impedance, output load, and line-terminating loads' impedance mismatch on group delay variation are theoretically investigated for the proposed trombone topology. Moreover, based on this new topology, a prototype trombone delay circuit has been designed and fabricated in 0.18- mu ext{m} CMOS technology, operating over the frequency bandwidth of 8-18 GHz. This 3-bit delay integrated circuit provides a maximum delay... 

    Fast and accurate time delay estimation in noisy environments

    , Article 2nd Microwave and Radar Week in Poland - International Radar Symposium, IRS 2006, Krakow, 24 May 2006 through 26 May 2006 ; 2006 ; 8372076219 (ISBN); 9788372076212 (ISBN) Bayat, S ; Emadi, M ; Mousavi, M. R ; Jafargholi, A ; Sharif University of Technology
    The problem of time delay estimation (TDE) in the presence of zero mean white Gaussian noise is addressed. A novel and efficient algorithm for obtaining Conditional Maximum Likelihood (CML) estimates of delays, attenuation factors and the number of paths from a transmitter to a receiver is introduced. This approach is quite suitable for the cases in which time delay difference is less than the duration of signal autocorrelation  

    Voltage and frequency consensusability of autonomous microgrids over fading channels

    , Article IEEE Transactions on Energy Conversion ; Volume 36, Issue 1 , 2021 , Pages 149-158 ; 08858969 (ISSN) Mahdian Dehkordi, N ; Khorsandi, A ; Baghaee, H. R ; Sadati, N ; Shirvani Moghaddam, S ; Guerrero, J. M ; Sharif University of Technology
    Institute of Electrical and Electronics Engineers Inc  2021
    In this article, a novel cooperative secondary voltage/frequency control considering time-varying delays and noises in fading channels is presented for an autonomous alternating current (AC) voltage sourced-based converter (VSC)-based microgrid (MG), including inverter-interfaced distributed generations (DGs). Fading phenomenon makes complex random fluctuations on the voltage and frequency of every DG received from its neighbor DGs. In multi-agent cooperative systems, in addition to the total additive noise and time-variant delay, a multiplicative complex random variable is considered to model the main received signal and its replicas due to multipath propagation. The proposed... 

    Adaptive online prediction of operator position in teleoperation with unknown time-varying delay: simulation and experiments

    , Article Neural Computing and Applications ; Volume 33, Issue 13 , 2021 , Pages 7575-7592 ; 09410643 (ISSN) Nikpour, M ; Yazdankhoo, B ; Beigzadeh, B ; Meghdari, A ; Sharif University of Technology
    Springer Science and Business Media Deutschland GmbH  2021
    One of the most important problems in teleoperation systems is time delay and packet loss in the communication channel, which can affect transparency and stability. One way to overcome the time delay effects in a teleoperation system is to predict the master-side motion. In this way, when data is received in the slave side, it will be considered as the current position of the master robot and, thus, complete transparency could be achieved. The majority of the previous works regarding operator position prediction have considered known and constant time delay in the system; however, in the real applications, time delay is unknown and variable. In this paper, an adaptive online prediction... 

    Computational analysis of ground effects on the dynamical behavior of unconfined two-phase clouds in view of detonability studies

    , Article Scientia Iranica ; Volume 12, Issue 4 , 2005 , Pages 414-425 ; 10263098 (ISSN) Mazaheri, K ; Doustdar, M. M ; Hosseinalipour, M ; Sharif University of Technology
    Sharif University of Technology  2005
    A numerical analysis has been performed to investigate the ground effects on the main parameters of a two-phase unconfined cloud of fuel and air to study its detonability. Equivalence ratio, turbulence intensity, cloud shape and volume, uniformity, temperature gradient and delay time distribution are the most important factors that affect the detonability of a vapor cloud. The effects of the altitude of the dispersing device from the ground on these significant factors have been demonstrated. A modified KIVA-based program has been employed to carry out the computations. A finite volume method is used to solve the equations describing the gas phase. A discrete particle technique is applied to... 

    A bee colony task scheduling algorithm in computational grids

    , Article Communications in Computer and Information Science, 7 July 2011 through 9 July 2011 ; Volume 188 CCIS, Issue PART 1 , July , 2011 , Pages 200-210 ; 18650929 (ISSN) ; 9783642223884 (ISBN) Mousavinasab, Z ; Entezari Maleki, R ; Movaghar, A ; Springer ; Sharif University of Technology
    The efficient scheduling of the independent and sequential tasks on distributed and heterogeneous computing resources within grid computing environments is an NP-complete problem. Therefore, using heuristic approaches to solve the scheduling problem is a very common and also acceptable method in these environments. In this paper, a new task scheduling algorithm based on bee colony optimization approach is proposed. The algorithm uses artificial bees to appropriately schedule the submitted tasks to the grid resources. Applying the proposed algorithm to the grid computing environments, the maximum delay and finish times of the tasks are reduced. Furthermore, the total makespan of the... 

    Stable regions in the parameter space of delays for LTI fractional-order systems with two delays

    , Article Signal Processing ; Volume 107 , February , 2015 , Pages 415-424 ; 01651684 (ISSN) Mesbahi, A ; Haeri, M ; Sharif University of Technology
    Elsevier  2015
    This paper studies fractional-order systems of retarded type with two independent delays, and determines the stability regions in spaces of delays. In this approach, an auxiliary polynomial is employed to calculate all purely imaginary roots of the characteristic equation of the system on the imaginary axis. Since roots of the characteristic equation are continuous with respect to delays, these purely imaginary roots determine the stability regions in delay space. Also, the necessary and sufficient condition for stability independent of delays is developed for the systems. Furthermore, a simple inequality constraint is established to obtain pure imaginary poles of the scalar systems.... 

    The control of a thermal system with large time delay using of LQG and lead-compensator

    , Article 2010 IEEE International Conference on Mechatronics and Automation, ICMA 2010, 4 August 2010 through 7 August 2010 ; August , 2010 , Pages 1842-1847 ; 9781424451418 (ISBN) Zareh, S. H ; Jahromi, A. F ; Abbasi, M ; Khayyat, A. A ; Sharif University of Technology
    This paper will first describe the Linear-Quadratic-Gaussian (LQG) and Lead-Compensator when the Proportional-Integral-Derivative (PID) controllers are inactive for procedures that have large delay time (LDT) in transfer stage. Therefore in those states, LQG and Lead Compensator perform better than the PID controllers. The constrained LQG is optimal and stabilizing. The solution algorithm is guaranteed to terminate in finite time with a computational cost that has a reasonable upper bound compared to the minimal cost for computing the optimal solution. In this work all actual working area condition for instance noises and disturbances are considered. Eventually, LQG and Lead Compensator have... 

    The design of LQR and fuzzy logic controller for a thermal system with large time delay

    , Article Proceedings of the 2010 International Conference on Mechanical, Industrial, and Manufacturing Technologies, MIMT 2010, 22 January 2010 through 24 January 2010 ; January , 2010 , Pages 293-298 ; 9780791859544 (ISBN) Zareh, S. H ; Jahromi, A. F ; Sarafan, A ; Akbar Khayyat, A. A ; Sharif University of Technology
    This paper will first describe the Linear Quadratic Regulator (LQR) and Fuzzy logic controller when the Proportional-Integral-Derivative (PID) controllers are inactive for procedures that have large delay time (LDT) in transfer stage. Therefore in those states, LQR and Fuzzy controllers perform better than the PID controllers. The constrained LQR is optimal and stabilizing. The solution algorithm is guaranteed to terminate in finite time with a computational cost that has a reasonable upper bound compared to the minimal cost for computing the optimal solution. The system determines the amount of fuel required from a fuzzy algorithm to arrive at the desired temperature. The parameters of the... 

    Multifractal analysis of light scattering-intensity fluctuations

    , Article Physical Review E - Statistical, Nonlinear, and Soft Matter Physics ; Volume 80, Issue 6 , 2009 ; 15393755 (ISSN) Shayeganfar, F ; Jabbari Farouji, S ; Movahed, M. S ; Jafari, G. R ; Rahimi Tabar, M. R ; Sharif University of Technology
    We provide a simple interpretation of non-Gaussian nature of the light scattering-intensity fluctuations from an aging colloidal suspension of Laponite using the multiplicative cascade model, Markovian method, and volatility correlations. The cascade model and Markovian method enable us to reproduce most of recent empirical findings: long-range volatility correlations and non-Gaussian statistics of intensity fluctuations. We provide evidence that the intensity increments Δx (τ) =I (t+τ) -I (t), upon different delay time scales τ, can be described as a Markovian process evolving in τ. Thus, the τ dependence of the probability density function p (Δx,τ) on the delay time scale τ can be... 

    An improved macro-model for simulation of single electron transistor (SET) using HSPICE

    , Article TIC-STH'09: 2009 IEEE Toronto International Conference - Science and Technology for Humanity, 26 September 2009 through 27 September 2009, Toronto, ON ; 2009 , Pages 1000-1004 ; 9781424438785 (ISBN) Karimian, M ; Dousti, M ; Pouyan, M ; Faez, R ; Sharif University of Technology
    To get a more accurate model for simulation of single electron transistors (SETs), we have proposed a new macromodel that includes the ability of electron tunneling time calculation. In our proposed model, we have modified the previous models and applied some basic corrections to their formulas. In addition, we have added a switched capacitor circuit, as a quantizer, to calculate the electron tunneling time. We used HSPICE for high-speed simulation and observed that the simulation results obtained from our model matched more closely with that of SIMON 2.0. We also could evaluate the time of electron tunneling through the barrier by using the quantizer. Clearly, our macro-model gives more...