Sharif Digital Repository

Synchronization is a phenomenon that occurs in systems of interacting units, and is widespread in nature, society and technology. Recent studies have enlightened us regarding the interplay between synchronization dynamics and interaction structure. However, most of these studies neglect that real-world networks may actually be directed and disconnected. Here, we study the synchronization of directed networks with multiple leaders using the Kuramoto model. We found that in networks with high driving strength, the steady-state frequency of each node is determined by the linear combination of leaders natural frequencies, with structural coe?cients that can be calculated using the eigenvectors... 

In this paper the principles of submarine dynamics modeling have been gathered as distinguished steps. Of course, in these few pages the details cannot be discussed and the formulae cannot be proved. The interested reader has to study more detailed references to attain a better perception of the subject. The paper, in addition to gathering and editing principles, has gone through offering simplifications in each part of modeling. Such simplifications will result in a good approximation of submarine dynamic behavior, which is exactly complicated in reality. In higher levels of modeling each part can be completed and details can be processed  

We analyze the impact of loss in lattices of coupled optical waveguides and find that, in such a case, the hopping between adjacent waveguides is necessarily complex. This results not only in a transition of the light spreading from ballistic to diffusive, but also in a new kind of diffraction that is caused by loss dispersion. We prove our theoretical results with experimental observations  

Using the cross-correlation of the wavelet transformation, we propose a general method of studying the scale dependence of the direction of coupling for coupled time series. The method is first demonstrated by applying it to coupled van der Pol forced oscillators and coupled nonlinear stochastic equations. We then apply the method to the analysis of the log-return time series of the stock values of the IBM and General Electric (GE) companies. Our analysis indicates that, on average, IBM stocks react earlier to possible common sector price movements than those of GE  

Jumps are discontinuous variations in time series and one expects that the higher jump activity will cause higher uncertainty in the stochastic behavior of measured time series. Here we study jump events in beat-to-beat fluctuations in the heart rates of healthy subjects, as well as those with congestive heart failure (CHF). The analysis shows that the interbeat time series belong to the class of non-continuous stochastic processes. The estimated drift and diffusion coefficients and jump characteristics of healthy and CHF subjects reveal the distinguishability of two subjects. © 2019 IOP Publishing Ltd and SISSA Medialab srl  

The conventional finite element method has been used successfully in linear and nonlinear analyses in concrete chimney structures. The method can be performed by subdividing the large structure into small uniform elements having approximate shape functions. Although this replaces a single complicated structural system into a number of simple uniform elements, in cases of tall concrete chimney structures with cracking and crushing behavior in concrete material and yielding in the reinforcement, the computer time and memory can be large. Hence, it is desirable to search for a procedure requiring a fewer number of elements and also less computer time and effort to model a structure. In this... 

In this work, the effects of dynamic strain aging and dynamic recovery on metal flow during warm working are studied. Compression experiments are utilized to assess the flow behavior of a low carbon steel under warm deformation conditions. Then, a two dimensional finite element routine is coupled with dynamic recovery and dynamic strain aging models. In this way, the temperature and the velocity fields are predicted during warm working operations with regard to the effects of dynamic recovery and dynamic strain aging. Warm rolling tests are performed in order to verify the modelling results. Comparison between the predicted and measured roll forces shows reliability of the employed model  

A new control law for direct yaw moment control of an electric vehicle is developed. Although this study is considered as part of a global control system for the traction control of a four motorized wheel electric vehicle, but the results of this study is quite general and can be applied to other types of vehicles. The dynamic model of the system has been analyzed and, in accordance with the optimal control theory, an optimal controller is designed. Two different versions of the control law have been considered and the performance of each version has been separately studied and compared with each other. Finally, the numerical simulation of the vehicle-handling model with and without the use... 

The emergence of synchronization among a set of individual oscillators that are coupled in a network is an amazing physical phenomenon that appears in many different systems, from natural sciences to even human behavior. The phenomenon has attracted the attention of many researchers in many fields of science and engineering by the science behind its unique collective behavior without some kind of external organization. One of the most popular models for the dynamical evolution of coupled phase oscillators is the Kuramoto model, which gives a simple yet powerful formalization together with a numerical measure called the degree of synchronization. The crucial role of structural properties of... 

A proper vertex coloring of a graph G is called a dynamic coloring if for every vertex ν with degree at least 2, the neighbors of ν receive at least two different colors. It was conjectured that if G is a regular graph, then χ2(G) - χ (G) ≤ 2. In this paper we prove that, apart from the cycles C4 and C5 and the complete bipartite graphs Kn,n, every strongly regular graph G, satisfies χ2(G) - χ (G) ≤ 1  

In this paper, "Subspace" method is generalized to asymmetrical case. In the new algorithm described here, "Lanczos" method is used to find the first subspace and to solve the eigenvalue problem resulted in generalized subspace method. To solve the standard eigenvalue problem developed by "Lanczos" method "Jacoby" method is used. If eigenvalue problem includes damping matrix, that will be imported in new defined mass and stiffness matrices  

Choreography description languages aim at specifying from a global point of view interactions among a set of services involved in a new system. From this specification, local implementations or peers can be automatically generated. Generation of peers that precisely implement the choreography specification is not always possible: This problem is known as realizability. When peers corresponding to this specification are being executed we may want to modify the choreography specification and reconfigure dynamically the system. This is the case for instance if we add or remove interactions due to the addition of functionalities to the system at hand or the loss of a service. In this article, we... 

In this chapter we reconstruct stochastic dynamical equations with known drift and diffusion coefficients, as well as known properties of jumps, jump amplitude and jump rate from synthetic time series, sampled with time interval τ. The examples have Langevin (white noise- and Lévy noise-driven) and jump-diffusion dynamical equations. We also study the estimation of the Kramers–Moyal coefficients for “phase” dynamics that enable us to investigate the phenomenon of synchronisation in systems with interaction. © 2019, Springer Nature Switzerland AG  

In this chapter we reconstruct stochastic dynamical equations with known drift and diffusion coefficients, as well as known properties of jumps, jump amplitude and jump rate from synthetic time series, sampled with time interval τ. The examples have Langevin (white noise- and Lévy noise-driven) and jump-diffusion dynamical equations. We also study the estimation of the Kramers–Moyal coefficients for “phase” dynamics that enable us to investigate the phenomenon of synchronisation in systems with interaction. © 2019, Springer Nature Switzerland AG  

This paper presents the kinematics and dynamic modeling of a three-link (3-DOF) underwater manipulator where the effects of hydrodynamic forces are investigated. In our investigation, drag and added mass coefficients are not considered as constants. In contrast, the drag coefficient is a variable with respect to all relative parameters. Experiments were conducted to validate the hydrodynamic model for a one degree-of-freedom manipulator up to a three degrees-of-freedom manipulator. Finally, the numerical and experimental results are compared and thoroughly discussed  

In this paper, a comprehensive model is used to describe dynamic behavior of SDA and its components during stepwise motion. In this model, Hamilton’s principle and Newton's method are used to extract dynamic equations of the SDA plate and dynamic equation for the linear motion of SDA. Comparison between the modeling results and available experimental data shows that this model is very effective in predicting some design objectives such as step size and output force for this type of actuators  

In this article, we study the formation of nanomeniscus around a nanoneedle using molecular dynamics simulation approach. The results reveal three distinct phases in the time-evolution of meniscus before equilibrium according to the contact angle, meniscus height, and potential energy. In addition, we investigated the correlation between the nanoneedle diameter and nanomeniscus characteristics. The results have applications in various fields such as scanning probe microscopy and rheological measurements  

Quantum mechanics imposes a fundamental bound on the minimum time required for the quantum systems to evolve between two states of interest. This bound introduces a limit on the speed of the dynamical evolution of the systems, known as the quantum speed limit. We show that black holes can drastically affect the speed limit of a fermionic quantum system subjected to an open quantum dynamics. As we demonstrate, the quantum speed limit can enhance at the vicinity of a black hole's event horizon in the Schwarzschild spacetime. © 2020 The Author(s)  

In this study, we explore the possibility of dynamic object manipulation of objects using a series of manipulators. Here, two three-active-link manipulators have been considered and the generality of the idea to a series of manipulator is developed easily. So without any gripper, and in an unstable grasp manner, we try to throw an object by a manipulator and catch It with another. Also we can consider the impacts generated in the moment of throwing and catching objects, as some disturbance and therefore we damp it. Finally we deal with the whole manipulation process as a system with some noise and disturbance and try to demonstrate its stability. All results have been validated with the aid... 

In this paper, an effective way is proposed for reduction of oscillations in the response of dynamical systems. In this regard, it is analytically shown that the undesirable oscillations in the response of dynamical systems can be reduced using a simple input shaping fractional order filter. The effectiveness of the proposed fractional calculus based technique is numerically verified in reduction of oscillations in a mass-spring-damper system, a low-pass Chebyshev filter, and a PI-controlled two-mass drive system