Papers by Ebrahim Foulaadvand
Anti-resonance in a one-dimensional chain of driven coupled oscillators
American Journal of Physics, 2014
We investigate a driven system of N one-dimensional coupled oscillators with identical masses. Th... more We investigate a driven system of N one-dimensional coupled oscillators with identical masses. The first mass is connected to a sinusoidal driving force of frequency ω. In the steady state, when all the masses perform simple harmonic motion, we analytically obtain the dependence of their amplitudes on ω and show that there are resonance and anti-resonance frequencies. At an anti-resonance frequency, the amplitude of one of the masses becomes exactly zero. The mass directly connected to the driving force has the largest number of anti-resonance frequencies, N – 1. The phase of each mass's motion is either 0 or π with respect to the driving force. The case where damping forces are present is also considered, and the amplitude dependence on driving frequency is analytically obtained. In the presence of damping, there is no anti-resonance.
International Journal of Modern Physics C, Apr 1, 2010
We have employed the steepest descent method to optimise the variational ground state quantum Mon... more We have employed the steepest descent method to optimise the variational ground state quantum Monte Carlo wave function for He, Li, Be, B and C atoms. We have used both the direct energy minimisation and the variance minimisation approaches. Our calculations show that in spite of receiving insufficient attention, the steepest descent method can successfully minimise the wave function. All the derivatives of the trial wave function respect to spatial coordinates and variational parameters have been computed analytically. Our ground state energies are in a very good agreement with those obtained with diffusion quantum Monte Carlo method (DMC) and the exact results.
American Journal of Physics, Mar 1, 2017
A model of a one-dimensional mass-spring chain with mass or spring defects is investigated. With ... more A model of a one-dimensional mass-spring chain with mass or spring defects is investigated. With a mass defect, all oscillators except the central one have the same mass, and with a spring defect, all the springs except those connected to the central oscillator have the same stiffness constant. The motion is assumed to be one-dimensional and frictionless, and both ends of the chain are assumed to be fixed. The system vibrational modes are obtained analytically, and it is shown that if the defective mass is lighter than the others, then a high frequency mode appears in which the amplitudes decrease exponentially with the distance from the defect. In this sense, the mode is localized in space. If the defect mass is greater than the others, then there will be no localized mode and all modes are extended throughout the system. Analogously, for some values of the defective spring constant, there may be one or two localized modes. If the two defected spring constants are less than that of the others, there is no localized mode. V
Premium Forecasting of an Insurance Company
The Application of Econophysics, 2004
We present an analytical study of an insurance company. The company’s performance is modeled on a... more We present an analytical study of an insurance company. The company’s performance is modeled on a statistical basis. The predicted annual income of the company is evaluated in terms of insurance parameters namely the premium, the total number of insured, average loss claims etc. We restrict ourselves to a single insurance class the so-calledautorriobilrinsururmce. We obtain the corresponding risk as well as ruin probability in terms of premium. Furthermore, we obtain the optimal premium p opt which maximizes the comany’s
Traffic and Granular Flow'07, 2009
We have developed a modified Nagel-Schreckenberg cellular automata model for describing a conflic... more We have developed a modified Nagel-Schreckenberg cellular automata model for describing a conflicting vehicular traffic flow at the intersection of two streets. No traffic lights control the traffic flow. The approaching cars to the intersection yield to each other to avoid collision. Closed boundary condition is applied to the streets. Extensive Monte Carlo simulations is taken into account to find the model characteristics. In particular, we obtain the fundamental diagrams and show that the effect of interaction of two streets can be regarded as a dynamic impurity located at the intersection point. Our results suggest that yielding mechanism gives rise to a high total flow throughout the intersection especially in the low density regime. In some ranges of densities, yielding mechanism even improves and regulates the flow in comparison to the absence of perpendicular flow.
Thermodynamics Properties of One-Dimensional Z 3 Quantum Potts Chain
Modern Physics Letters B, 1997
The method of Discretized Path Integral Representation (DPIR) is used to convert the one-dimensio... more The method of Discretized Path Integral Representation (DPIR) is used to convert the one-dimensional quantum Z3 Potts chain into a two-dimensional classical Interaction-Round a Face (IRF) model. Then we use the Double-Chain approximation to obtain the free energy and thermodynamic properties of the model.
Optimized Tra卤c Flow at a Single Intersection: Tra卤c Responsive Signalization
Scientific Reports
We investigate the optimal orientation for a fixed flat plate solar collector using the clear sky... more We investigate the optimal orientation for a fixed flat plate solar collector using the clear sky model. The ground reflection component of irradiation that hits the collector’s surface is ignored due to its relatively small magnitude when compared to the direct beam and sky diffusive components. Analytical calculations demonstrate that regardless of the collector’s latitude, the most effective azimuthal angle, $$\gamma ^*$$ γ ∗ , is 0, which generally corresponds to a North–South direction. However, the optimal tilt angle, $$\beta ^*$$ β ∗ , is dependent on both the Day of Year (DoY) and the collector’s local latitude. For latitudes typical of mid-altitude climate zones, we can calculate the optimal tilt angle and the maximum energy that the collector can harvest during each DoY. We compare the maximum daily received energy—which is the sum of the direct beam and sky diffusive energies—associated with this optimal orientation to their corresponding values when the flat plate track...
arXiv (Cornell University), Jun 12, 2010
Forced oscillation of a system composed of two pendulums coupled by a spring in the presence of d... more Forced oscillation of a system composed of two pendulums coupled by a spring in the presence of damping is investigated. In the steady state and within the small angle approximation we solve the system equations of motion and obtain the amplitudes and phases of in terms of the frequency of the sinusoidal driving force. The resonance frequencies are obtained and the amplitude ratio is discussed in details. Contrary to a single oscillator, in this two-degree of freedom system four resonant frequencies, which are close to mode frequencies, appear. Within the pass-band interval the system is shown to exhibit a rich and complicated behaviour. It is shown that damping crucially affects the system properties. Under certain circumstances, the amplitude of the oscillator which is directly connected to the driving force becomes smaller than the one far from it. Particularly we show the existence of a driving frequency at which the connected oscillator's amplitude goes zero.
We have employed the steepest descent method to optimise the variational ground state quantum Mon... more We have employed the steepest descent method to optimise the variational ground state quantum Monte Carlo wave function for He, Li, Be, B and C atoms. We have used both the direct energy minimisation and the variance minimisation approaches. Our calculations show that in spite of receiving insufficient attention, the steepest descent method can successfully minimise the wave function. All the derivatives of the trial wave function respect to spatial coordinates and variational parameters have been computed analytically. Our ground state energies are in a very good agreement with those obtained with diffusion quantum Monte Carlo method (DMC) and the exact results.
Scientific Reports, 2021
We analytically, experimentally and computationally explore the solar radiation flux distribution... more We analytically, experimentally and computationally explore the solar radiation flux distribution in the interior region of a spherical mirror and compare it to that of a paraboloidal one with the same aperture area. Our investigation has been performed in the framework of geometrical optics. It is shown that despite one can assign a quasi focus, at half the radius, to a spherical mirror, the light concentration occurs as well on an extended line region which starts at half-radius on the optical axis. In contrast to a paraboloidal concentrator, a spherical mirror can concentrate the radiation parallel to its optical axis both in a point-focus and in a line-focus manner. The envelope of the reflected rays is also obtained. It is shown that the flux distribution has an axial symmetry. The radial dependence of the flux on a flat circular receiver is obtained. The flux longitudinal dependence is shown to exhibit three distinctive regions in the interval [0, R] (R is mirror radius). We o...
We consider the exclusion process on a ring with time-dependent defective bonds at which the hopi... more We consider the exclusion process on a ring with time-dependent defective bonds at which the hoping rate periodically switches between zero and one. This system models main roads in city traffics, intersecting with perpendicular streets. We explore basic properties of the system, in particular dependence of the vehicular flow on the parameters of signalization as well as the system size and the car density. We investigate various types of the spatial distribution of the vehicular density, and show existence of a shock profile. We also measure waiting time behind traffic lights, and examine its relationship with the traffic flow.
Journal of Statistical Mechanics: Theory and Experiment, 2017
We provide insights into energetics of a Brownian oscillator in contact with a heat bath and driv... more We provide insights into energetics of a Brownian oscillator in contact with a heat bath and driven by an external unbiased time-periodic force that takes the system out of thermodynamic equilibrium. Solving the corresponding Langevin equation, we compute average kinetic and potential energies in the long-time stationary state. We also derive the energy balance equation and study the energy flow in the system. In particular, we identify the energy delivered by the external force, the energy dissipated by a thermal bath and the energy provided by thermal equilibrium fluctuations. Next, we illustrate Jarzynski work-fluctuation relation and consider the stationary state fluctuation theorem for the total work done on the system by the external force. Finally, by determining time scales in the system, we analyze the strong damping regime and discuss the problem of overdamped dynamics when inertial effects can be neglected.
Physical Review E, 2017
We consider the exclusion process on a ring with time-dependent defective bonds at which the hopp... more We consider the exclusion process on a ring with time-dependent defective bonds at which the hopping rate periodically switches between zero and one. This system models main roads in city traffics, intersecting with perpendicular streets. We explore basic properties of the system, in particular dependence of the vehicular flow on the parameters of signalization as well as the system size and the car density. We investigate various types of the spatial distribution of the vehicular density, and show existence of a shock profile. We also measure waiting time behind traffic lights, and examine its relationship with the traffic flow.
Journal of Statistical Mechanics: Theory and Experiment, 2016
We discuss two-dimensional diffusion of a Brownian particle confined to a periodic asymmetric cha... more We discuss two-dimensional diffusion of a Brownian particle confined to a periodic asymmetric channel with soft walls modeled by a parabolic potential. In the channel, the particle experiences different thermal noise intensities, or temperatures, in the transversal and longitudinal directions. The model is inspired by the famous Feynman's ratchet and pawl. Although the standard Fick-Jacobs approximation predicts correctly the effective diffusion coefficient, it absolutely fails to capture the ratchet effect. Deriving a correction, which breaks the local detailed balance with the transversal noise source, we obtain a correct mean velocity of the particle and a stationary probability density in the potential unit cell. The derived results are exact for small channel width. Yet, we check by exact numerical calculation that they qualitatively describe the ratchet effect observed for an arbitrary width of the channel.
Entropy, 2017
The stochastic model of the Feynman-Smoluchowski ratchet is proposed and solved using generalizat... more The stochastic model of the Feynman-Smoluchowski ratchet is proposed and solved using generalization of the Fick-Jacobs theory. The theory fully captures nonlinear response of the ratchet to the difference of heat bath temperatures. The ratchet performance is discussed using the mean velocity, the average heat flow between the two heat reservoirs and the figure of merit, which quantifies energetic cost for attaining a certain mean velocity. Limits of the theory are tested comparing its predictions to numerics. We also demonstrate connection between the ratchet effect emerging in the model and rotations of the probability current and explain direction of the mean velocity using simple discrete analogue of the model.
Physical Review E, 2016
We study traffic in a roundabout model, where the dynamics along the interior lane of the roundab... more We study traffic in a roundabout model, where the dynamics along the interior lane of the roundabout are described by the totally asymmetric simple exclusion process (TASEP). Vehicles can enter the interior lane or exit from it via S intersecting streets with given rates, and locally modified dynamics at the junctions take into account that collisions of entering vehicles with vehicles approaching the entrance point from the interior lane should be avoided. A route matrix specifies the probabilities for vehicles to arrive from and to exit to certain intersecting streets. By subdividing the interior lane into segments between consecutive intersecting streets with effective entrance and exit rates, a classification of the stationary roundabout traffic in terms of TASEP multiphases is given, where each segment can be in either the low-density, high-density, or maximum current TASEP phase. A general methodology is developed, which allows one to calculate the multiphases and optimal throughput conditions based on a mean-field treatment. Explicit analytical results from this treatment are derived for equivalent interesting streets. The results are shown to be in good agreement with kinetic Monte Carlo simulations.
Driven binary colloidal mixture in a 2D narrow channel with hard walls
The European Physical Journal E, 2016
Abstract.We have investigated the properties of a driven equi-molar binary colloidal mixture conf... more Abstract.We have investigated the properties of a driven equi-molar binary colloidal mixture confined to a two-dimensional narrow channel. The walls are hard and periodic boundary condition is applied along the channel. Colloidal particles perform Brownian motion in a solvent having a fixed temperature and interact with each other via a Debye-Hückel Coulombic interaction (Yukawa potential). A constant external force drives the colloids along the channel. Two species move oppositely to each other. Hydrodynamic interactions are neglected and the dynamics is assumed to be over-damped. The flow increases nonlinearly with the external force but does not exhibit a notable dependence on channel width. Above a critical driving force the system undergoes a homogeneous-to-laning transition. It is shown that the mean lane width as well as the laning order parameter increases with the channel width. The reentrance effect is observed in the narrow channel geometry.Graphical abstract
Controlling of Vehicular Traffic Flow at an Intersection Via Two Schemes of Traffic Lights
Traffic and Granular Flow '13, 2014
ABSTRACT By means of extensive Monte Carlo simulation, we have investigated the traffic flow char... more ABSTRACT By means of extensive Monte Carlo simulation, we have investigated the traffic flow characteristics in a single signalised intersection via developing Nagel-Schreckenberg cellular automata model. A set of traffic lights operating in two schemes controls the traffic flow. A closed boundary condition is applied to the streets, each of which conducts a unidirectional flow. It is shown that there exists a plateau region in fundamental diagrams inside which the total outflow remains almost.
Physical Review E, 2015
We investigate the diffusion of a rigid rodlike object in a two-dimensional disordered host mediu... more We investigate the diffusion of a rigid rodlike object in a two-dimensional disordered host medium, which consists of static pointlike sources of force. The points are distributed with long-range spatial correlation and interact with the rod via a repulsive potential. The time dependence of the rod's center-of-mass mean-squared displacement and its rotational mean-squared displacement are obtained for various degrees of long-range spatial correlation and rod's lengths. These transport characteristics are compared to those obtained in previous studies for the case of homogeneous distribution of force points. It is shown that existence of long-range correlation among force points makes the center of mass diffusion anomalous.
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Papers by Ebrahim Foulaadvand