Sharif Digital Repository

In this paper, we derive a theoretical model for the higher-order four-wave mixing (FWM) power in wavelength division multiplexing networks with non-zero dispersion shifted fibers for the first time. We have investigated the higher-order FWM power theoretically and by numerical simulations. Dividing the fiber into a finite number of elements and applying the boundary conditions allow us to derive an expression for the second-order power penalty. At the end of each element, we derive the first-order FWM power for all wavelengths and use these values to calculate the second-order FWM power in the next element. Consequently, for each channel we can compute the total second-order FWM power... 

In most existing works on the flocking problem, results were obtained for the case where a double integrator dynamic is used to describe motion of agents and virtual leader. These results, however, may not be generalised to agents with general linear dynamic. In this study, it is shown that in the flocking of agents with a linear dynamic, the velocity convergence of agents does not generally lead to the position convergence of informed agents and the position convergence is possible only for a specified group of linear dynamics. In this study, a control protocol is proposed to flock agents with specified linear dynamics and guarantee the velocity convergence of all agents as well as average... 

In this study, flocking of multi-agent systems with virtual leader and linear dynamics is investigated. It is assumed that the dynamics of agents in each dimension is represented by a general second-order linear model. The proposed control protocol is composed of two terms, one for feed backing each agent's states and one for cooperative control. At first, the flocking problem of multi-agent systems with identical agents is discussed and then the proposed protocol is generalised to flock heterogeneous multi-agent systems. Under the proposed algorithm, the velocity convergence of whole group to a velocity of virtual leader is guaranteed while the connectivity of network is preserved and... 

In this work, we study the flocking problem of multi-agent systems with uncertain dynamics subject to actuator failure and external disturbances. By considering some standard assumptions, we propose a robust adaptive fault tolerant protocol for compensating of the actuator bias fault, the partial loss of actuator effectiveness fault, the model uncertainties, and external disturbances. Under the designed protocol, velocity convergence of agents to that of virtual leader is guaranteed while the connectivity preservation of network and collision avoidance among agents are ensured as well. © 2017 ISA  

This paper investigates a new algorithm for flocking of multi-Agent systems with virtual leader. In this algorithm, unlike the existing algorithms, receiving of information by agents are not continuous and it is assumed that each agents receives information of neighbors and virtual leader as sampled data in fixed time intervals. A sufficient condition on sampling period is derived to guarantee the velocity convergence of agents to that of virtual leader, preserve network connectivity, and ensure collision avoidance. Finally, a numerical simulation is provided to illustrate the theoretical results. © 2017 IEEE  

Dual active bridge isolated bidirectional DC converter (DAB-IBDC) has a poor efficiency at light loads and non-unity voltage conversion ratio. In this paper the current stress of the converter is analyzed and the effect of maximum phase shift ratio and leakage inductance on the current stress of the converter is investigated. In order to increase the efficiency of the converter and reduce the current stress, the current stress optimization has been done and the design procedure is presented. Simulation results are used to validate the results of the theoretical analysis. © 2017 IEEE  

This paper studies the leader-follower flocking of multi-agent systems for the linear second-order dynamics, subject to the external disturbance problem. It is assumed that the dynamic of the leader is Lipschitz-type. Also, the velocity is the output of the system, and full-state information is not available for feedback. A distributed full-order observer is employed to estimate every agent's states and external disturbance. A control protocol for each agent is designed based on the measurement of its output/velocity and relative velocity of its neighbors. Under the proposed protocol, the velocity convergence of whole agents to the velocity of the virtual leader is guaranteed as well as the... 

In this paper, we derive a theoretical model for the higher order FWM power in WDM networks with NZDSF fibers for the first time. We have investigated the higher order FWM power theoretically and by numerical simulations. Dividing the fiber into finite number of elements and applying the boundary conditions, allow us derive an expression for second order power penalty. At the end of each element we derive the first order FWM power for all wavelengths and use these values to calculate the second order FWM power in the next element. Consequently, for each channel we can compute the total second order FWM power penalty at the end of the fiber  

In this study, based on the reduced from of elasticity displacement field for a long laminate, an analytical method is established to exactly obtain the interlaminar stresses near the free edges of generally laminated composite plates under the extension and bending. The constant parameters, which describe the global deformation of a laminate, are properly computed by means of the improved first-order shear deformation theory. Reddys layerwise theory is subsequently utilized for analytical and numerical examinations of the boundary layer stresses within arbitrary laminated composite plates. A variety of numerical results are obtained for the interlaminar normal and shear stresses along the... 

An ultra-efficient switching method for successive approximation register ADCs is proposed. In this method, the input signals are sampled in a special fashion to reduce the switching energy. Owing to the sampling method, only one reference voltage (Vq=Vref/4) is required to implement the switching steps. Therefore, in addition to reduction in the switching energy (due to the lower supply voltage), the precision of the DAC is improved. The proposed method reduces the switching energy and area by 99.41 and 50%, respectively, compared with the conventional method. © 2016 The Institution of Engineering and Technology  

A highly energy-efficient switching method for capacitor-splitting digital-to-analogue converter (DAC) in successive approximation register (SAR) analogue-to-digital converters (ADCs) is presented. In the proposed DAC, a bottom-plate sampling method is introduced which requires only one reference voltage (Vcm = 1/2Vref) during the entire DAC switching steps. Therefore, in addition to the switching energy reduction, the precision of the DAC is increased since only one reference voltage is used. The DAC average switching energy and the area are reduced by 98.44% and 50% compared with the conventional binary weighted DAC  

A sampling and switching method for a binary weighted digital-to-analogue converter (DAC) in successive approximation register (SAR) analogue-to-digital converters (ADCs) is presented. This sampling method is proposed to reduce the switching energy. Thanks to the proposed switching method, only one reference voltage (Vcm = 1/2 Vref) is required which helps to improve the precision of the DAC along with energy reduction compared with those methods that use more than one reference voltage. The switching energy and area of the DAC reduce by 97.66% and 50% compared with the conventional binary weighted DAC  

The propagation of a Gaussian beam in underdense plasma with upward increasing density ramp is analyzed. In this work are shown that the spot size oscillations of laser beam increases and its amplitude shrinks with proper plasma density ramp. This causes the laser beam to become more focused and penetrations deep into the plasma by reduction of diffraction effect. The related focusing parameters are optimized to get the best possible focusing at the relativistic threshold intensity of Nd-glass laser and the effect of the laser intensity in the self-focusing parameters is also investigated. The analytical calculations are presented and showed more reliable results in comparison to the... 

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... 

A highly energy-efficiency switching procedure for the capacitor-splitting digital-To-Analog converter (DAC) is presented for successive approximation register (SAR) analogue-To-digital converters (ADCs). In this procedure, the MSB capacitor is divided into its binary constituents. All output digital bits, except the least significant bit (LSB), is determined using reference voltage (Vref), while the common-mode voltage (Vcm) is used to determine the LSB. Therefore, the precision of the proposed SAR ADC is independent of the precision of Vcm except in the LSB. This method reduces the area by 75% compared to the conventional binary weighted DAC and reduces the switching energy by 96.89%. ©... 

Animal walking is one of the most robust and adaptive locomotion mechanisms in the nature, involves sophisticated interactions between neural and biomechanical levels. It has been suggested that the coordination of this process is done in a hierarchy of levels. The lower layer contains autonomous interactions between muscles and spinal cord and the higher layer (e.g. the brain cortex) interferes when needed. Inspiringly, in this study we present a hierarchical control architecture with a state of the art intrinsic online learning mechanism for a dynamically walking 5-link biped robot with compliant knee joints. As the biological counterpart, the system is controlled by independent control... 

A high energy-efficiency and low-area switching method is proposed for the successive approximation register analog-to-digital converters. In the proposed scheme, the threshold voltage for comparison is derived from the charge sharing technique and using a voltage source connected to the bottom plates of the digital-to-analogue converter (DAC) capacitors. The switching method achieves an average DAC switching energy and DAC area reduction of 99.15% and 84.27%, respectively, with respect to the conventional method. The differential nonlinearity and integral nonlinearity of the proposed scheme are 0.1288 LSB and 0.1207 LSB, respectively. In addition, in the proposed method, the number of DAC... 

Most of the biped robots are controlled using pre-computed trajectory methods or methods based on multi-body dynamics models. The pre-computed trajectory-based methods are simple; however, a system becomes highly vulnerable to the external disturbances. In contrast, dynamic methods make a system act faster, yet extensive knowledge is required about the kinematics and dynamics of the system. This fact gave rise to the main purpose of this study, i.e., developing a controller for a biped robot to take advantage of the simplicity and computational efficiency of trajectory-based methods and the robustness of the dynamic-based approach. To do so, this paper presents a two-layer hierarchical... 

A high energy-efficiency and low-area switching method is proposed for the successive approximation register analog-to-digital converters. In the proposed scheme, the threshold voltage for comparison is derived from the charge sharing technique and using a voltage source connected to the bottom plates of the digital-to-analogue converter (DAC) capacitors. The switching method achieves an average DAC switching energy and DAC area reduction of 99.15% and 84.27%, respectively, with respect to the conventional method. The differential nonlinearity and integral nonlinearity of the proposed scheme are 0.1288 LSB and 0.1207 LSB, respectively. In addition, in the proposed method, the number of DAC... 

Respiratory drug delivery has been under the research spotlight for the past few decades, mainly due to the high incidence of pulmonary diseases and the fact that this type of delivery offers the highest efficiency for treatment. Despite its invaluable benefits, there are some major drawbacks to respiratory drug delivery, the most important of which being poor delivery efficiency and relatively high drug deposition in undesirable regions, such as the mouth cavity. One way to improve the efficiency of respiratory drug delivery with metered-dose inhalers is placing a respiratory spacer between the inhaler exit and the mouth. It is argued that high drug deposition in the immediate airways of...