Sharif Digital Repository

In linear particle accelerators used for free-electron lasers, it is often required that the electron bunches experience the same electric field as they pass through the accelerating structures. For radio frequency (RF) pulsed mode machines, like the SwissFEL, this means that the amplitude and phase of the RF pulses feeding the structures through the waveguides should be kept constant over the pulselength. This raises an interesting problem that can be addressed by an iterative learning control (ILC) technique. This method manipulates the input waveforms iteratively, in order to generate flat amplitude and phase pulses at the output of the system. In this paper, we introduce two ILC... 

In this study, high harmonic generation from a multi-atomic nitrous oxide molecule was investigated. A comprehensive three-dimensional calculation of the molecular dynamics and electron trajectories through an accurate time-dependent density functional theory was conducted to efficiently explore a broad harmonic plateau. The effects of multi-electron and inner orbitals on the harmonic spectrum and generated coherent attosecond pulses were analyzed. The role of the valence electrons in controlling the process and extending the harmonic plateau was investigated. The main issue of producing a super-continuum harmonic spectrum via a frequency shift was considered. The time-frequency... 

Availability of low-cost range sensors and the development of relatively robust algorithms for the extraction of skeleton joint locations have inspired many researchers to develop human activity recognition methods using 3-D data. In this paper, an effective method for the recognition of human activities from the normalized joint trajectories is proposed. We represent the actions as multidimensional signals and introduce a novel method for generating action templates by averaging the samples in a “dynamic time” sense. Then, in order to deal with the variations in speed and style of performing actions, we warp the samples with action templates by an efficient algorithm and employ wavelet... 

Experimental acoustic cell separation methods have been widely used to perform separation for different types of blood cells. However, numerical simulation of acoustic cell separation has not gained enough attention and needs further investigation since by using numerical methods, it is possible to optimize different parameters involved in the design of an acoustic device and calculate particle trajectories in a simple and low cost manner before spending time and effort for fabricating these devices. In this study, we present a comprehensive finite element-based simulation of acoustic separation of platelets, red blood cells and white blood cells, using standing surface acoustic waves... 

In the present work, an efficient method is theoretically investigated for extending high-order harmonics and ultrashort attosecond pulse generation in N2 and CO molecules by using the time-dependent density functional theory approach. Our results show that by utilizing chirped laser field in the presence of a low frequency field, not only is the harmonic cutoff extended remarkably but also the single short quantum trajectory is selected to contribute to the harmonic spectra. When a low frequency field is added to the two-color chirped laser field, the long quantum trajectories are suppressed and only the short quantum trajectories contribute to the higher harmonic emission mechanism. As a... 

Rhythmic activities such as swimming stroke in the human body are learnable through conscious trainings. Inspiringly, the main objective of this study is to develop a control framework to reproduce the described functionality in the imitating robots. To do so, a two layer supervisory controller is proposed. The high-level controller, which acts as the conscious controller during trainings, is a supervisory dynamic-based controller and uses all system sensory data to generate stable rhythmic movements. On the other hand, the low-level controller in this structure is a distributed trajectory-based controller network. Each node in this network is an oscillatory dynamical system which has the... 

Reference trajectory management is a method to modify reference trajectories for the faulty system. The modified reference trajectories define new maneuvers for the system to retain its pre-fault dynamic performance. Controller reconfiguration is another method to handle faults in the system, for instance by adjusting the controller parameters (coefficients). Both of these two methods have been considered in the literature and are proven to be capable of handling various faults. However, the comparison of these two methods has not been considered sufficiently. In this paper, a controller reconfiguration mechanism and a reference trajectory management are proposed for the spacecraft attitude... 

This paper proposes a new method for view-invariant action recognition that utilizes the temporal position of skeletal joints obtained by Kinect sensor. In this method, the actions are represented as sequences of several pre-defined poses. After pre-processing, which includes skeleton alignment and scaling, the appropriate feature vectors are obtained for recognizing and discriminating the pose of every frame by the proposed Fisherposes method. The proposed regularized Mahalanobis distance metric is used in order to recognize both the involuntary and highly made-up actions at the same time. Hidden Markov model (HMM) is then used to classify the action related to an input sequence of poses.... 

This study investigates an ethanol liquid jet subjected to combination of an air crossflow and a normal electric field. The results on the liquid jet trajectory and subsequent droplets flight paths are presented. The liquid jet trajectory was found as a function of two non-dimensional quantities; the liquid jet to the crossflow momentum ratio and the electroinertial number. The electroinertial number is defined as the ratio between the liquid jet specific momentum and the electric force. A correlation is introduced for the jet trajectory in low crossflow speeds and electric field intensities. The same two quantities control the detached droplets flight paths. Satellite droplets flight angles... 

Recently, electrode-based Dielectrophoresis (eDEP) has been used for particle manipulation by means of triangular electrodes. In this theoretical and numerical study, a microchannel with quarter-of-ellipse electrodes is presented and a detailed comparison with triangular electrodes is provided. Electric field, resultant DEP force, and particle trajectories for each microchannel are evaluated by means of COMSOL Multiphysics 4.4. Afterwards, focusing and separation efficiencies of the systems are assessed and compared. Finally, separation efficiency of our proposed model for live and dead cells is compared with that of our previous model published in the literature [1]. It is demonstrated that... 

time-optimal problem for redundantly actuated robots moving on a specified path is a challenging problem. Although the problem is well explored and there are proposed solutions based on phase plane analysis, there are still several unresolved issues regarding calculation of solution curves. In this paper, we explore the characteristics of the maximum velocity curve and propose an efficient algorithm to establish the solution curve. Then we propose a straightforward method to calculate the maximum or minimum possible acceleration on the path based on the pattern of saturated actuators, which substantially reduces the computational cost. Two numerical examples are provided to illustrate the... 

This study considers the detector design and performance analysis in a statistical multiple-input-multiple-output radar. The authors studied this subject under some assumptions such as single point target, Swerling scattering models for radar cross-section and Gaussian interference. The target is assumed to move in a piecewise linear trajectory and multi-scan data is stored. So, the target cell may have changed during the time. A three-dimensional data signal space is generated that involved in observations from multiple scans, then a generalised likelihood ratio test detector is derived that employs consecutive observations in a central unit. Then a sub-optimum detector is introduced in... 

In this paper, two online path planning methods are presented for SURENA III humanoid robot by using model predictive control scheme. The methods are general control schemes which can generate the online motions for walking of a humanoid robot. For lowering computational costs a three dimensional linear inverted pendulum model is used instead of the full dynamical model of the robot. The generated trajectories are then used for computing the zero-moment point (ZMP) of the robot and the joint torques. The resulted joint torques of the two methods are compared to torques obtained from Genetic Algorithm (GA) path planning method presented for SURENA III humanoid robot in previous studies. The... 

In this study, a gait optimization routine is developed to generate walking patterns which demand the lowest friction forces for implementation. The aim of this research is to fully address the question which walking pattern demands the lowest coefficient of friction amongst all feasible patterns?. To this end, first, the kinematic structure of the considered 31 DOF (Degrees of Freedom) humanoid robot is investigated and a closed-form dynamics model for its lower-body is developed. Then, the medium through which the walking pattern generation is conducted is presented. In this medium, after designing trajectories for the feet and the pelvis, the joint space variables are obtained, using the... 

In this paper, the optimal performance of a planar humanlike musculoskeletal arm is investigated during reaching movements employing an optimal control policy. The initial and final states (position and velocity) are the only known data of the response trajectory. Two biomechanical objective functions are taken into account to be minimized as the central nervous system (CNS) strategy: (1) a quadratic function of muscle stresses (or forces), (2) total time of movement plus a quadratic function of muscle stresses. A two-degress of freedom (DOF) nonlinear musculoskeletal arm model (for planar movements) with six muscle actuators and four state variables is used in order to evaluate the proposed... 

A hyper-redundant manipulator is made by mounting the serial and/or parallel mechanisms on top of each other as modules. In discrete actuation, the actuation amounts are a limited number of certain values. It is not feasible to solve the kinematic analysis problems of discretely actuated hyper-redundant manipulators (DAHMs) by using the common methods, which are used for continuous actuated manipulators. In this paper, a new method is proposed to solve the trajectory tracking problem in a static prescribed obstacle field. To date, this problem has not been considered in the literature. The removing first collision (RFC) method, which is originally proposed for solving the inverse kinematic... 

During the past decade, Electro-Hydraulic system has performed a significant role in industrial engineering as an actuator for high performance and precision positioning applications. In this case, many control methods have been developed for an electro-hydraulic actuated clutch. In this paper a Linear Quadratic Regulators (LQR) is proposed to trajectory control of a wet clutch actuated by a hydraulic servo valve mechanism. Simulation study was performed using linearized mathematical model of the system implemented in MATLAB software. Based on the simulation results performance of the proposed controller was evaluated and discussed  

This paper considers the detector design and performance analysis in a widely separated multiple input - multiple output (S-MIMO) radar. We studied this subject under some assumptions such as single point target, Swerling models for radar cross section and Gaussian interference. The target is moving in piecewise linear trajectory and multi-scan data is stored. So, the target cell maybe changed through the time. A GLRT detector is derived that employs all data at once in a central unit. The performance of detector is extracted and numerical simulations verify all results  

In this paper, decentralized control of formation of a special category of leaderfollower networks on bounded velocity trajectories is addressed. The network of the agents in this study is supposed to have a directed graph with a spanning tree rooted at the leader agent. Moreover, follower agents do not receive online or have offine velocity of the desired trajectory, such as in tracking problem of trajectories which are not predefined or when the total bandwidth is narrow. Furthermore, the leader does not receive any information from any agent and its control is fully centralized. In the present study, formation problem is considered a consensus problem. The controller is designed for... 

In this paper, the problem of obtaining the optimal trajectory of a Dual-Arm Cam-Lock (DACL) robot is addressed. The DACL robot is a reconfigurable manipulator consisting of two cooperative arms, which may act separately. These may also be cam-locked in each other in some links and thus lose some degrees of freedom while gaining higher structural stiffness. This will also decrease their workspace volume. It is aimed to obtain the optimal configuration of the robot and the optimal joint trajectories to minimize the consumed energy for following a specific task space path. The Pontryagin's Minimum Principle is utilized with a shooting method to resolve kinematic redundancy. Numerical examples...