Sharif Digital Repository

In this paper, we present the most general form for error control coding using finite field multi-rate filters. This method shows how different types of codes can easily be generated by multi-rate filters and filter banks. In all previous works, codes and syndromes were generated using prefilters. Here we present simple multi-rate structures for encoding and generating syndrome. We show that all kinds of arbitrary rate K/L, circulant linear codes can be generated by these structures. Then we claim that a similar simple structure for syndrome generation in all presented cases exist  

In several recent papers, layered waveguide structures with conductive interfaces have been discussed, whose propagation properties are controlled by a transverse voltage. These structures can be used as a dynamic optical read/write memory cell, and programmable optical diffractive element. In this paper, the excitation of surface waves with the presence of interface charges is discussed. Interface charges affect the dispersion of surface waves, and therefore they can be used in various applications such as optical modulators, switches, sensors and filters. These waves can be superior to surface plasmon waves since they are not lossy. The lossless property is satisfied in limited range:... 

In several recent papers, layered waveguide structures with conductive interfaces have been discussed, whose propagation properties are controlled by a transverse voltage. These structures have wide range of applications. In this paper, surface wave excitation on one-dimensional photonic crystals at the presence of interface conductivity is discussed. It is shown that excitation of electromagnetic surface waves can be controlled by the interface conductivity. This property can be used in constructing miscellaneous optical devices such as optical modulators, switches and tunable optical filters. Devices based on these waves can be superior to surface plasmon waves since they are not lossy.... 

In this paper, the excitation of surface waves in the presence of interface charges is discussed. Interface charges affect the dispersion of surface waves, and therefore they can be used in various applications such as optical modulators, switches, sensors and filters. These waves can be superior to surface plasmon waves since they are not lossy. The lossless property is satisfied in a limited range of millimetre waves to far infrared  

A simple yet accurate model for the analysis of coupling between arrayed plasmonic slot cavities and bus/drop metal-dielectric-metal waveguides is presented. The evanescent coupling region is replaced by a transmission line section whose propagation constant and characteristic impedance are given in closed form. The side coupling between the bus waveguide and the slot cavity is modeled together with the direct coupling between the slot cavity and the drop channel. The proposed model is validated by using rigorous numerical method, and is used to design a typical demultiplexer  

We propose a design algorithm for VIPA-based OCOMA encoder used in WOM-compatible COMA networks based on the problem requirements. Analyzing this device by our previous formulation leads to some useful suggestions to improve the device  

In this paper optical filters based on photonic resonant tunneling effect are analyzed by using the polynomial expansion method. Amplitude and phase response together with their dependency on the physical parameters of the filters are also investigated. These steep-edge filters show low insertion loss amplitude response, and linear phase variation in their passband, a suitable feature for WDM and DWDM applications where constant time delay and dispersion free devices are needed. Two kinds of filters, namely discrete level and continuous profile filters are introduced. These structures can be analyzed and designed by using Transfer Matrix Method. However, this approach suffers from inaccuracy... 

Recently, the interaction of electromagnetic waves with conducting interfaces has been studied and several applications have been proposed. In these structures a free two-dimensional interface charge layer is generated at the dielectric interfaces and interesting phenomena are observed. In this paper, the effect of finite charge layer thickness and its asymptotic behaviour towards the conducting interface, where the thin charge layer is modelled via a surface conductivity σs, is thoroughly studied for the first time. Two different regimes are considered: first, propagation of optical waves through subwavelength free charge layers and their corresponding reflection and transmission... 

Feature vector extraction, based on local image texture, is a primitive algorithm for many other applications, like segmentation, clustering and identification. If these feature vectors are a good match to the human visual system (HVS), we can expect to get the appropriate results by using them. Gabor filters has been used for this purpose successfully. In this paper we introduce a novel refinement, with the use of Matching Pursuit (MP) to improve the Gabor based texture feature extractor. With this improvement, we show that the separability of different textures will increase. Another consideration in this work is computation complexity. Therefore, we limit the basis function set to reduce... 

A simple and efficient transmission line model is proposed here to study how the transmission characteristics of photonic crystal waveguides are tailored by introduction of stubs patterned in the photonic crystal lattice. It is shown that band-pass and band-stop optical filters can be easily designed and optimized when stubs of appropriate length are brought in. Since the lengths of the designed stubs are not necessarily integer multiples of the photonic crystal lattice constant, a geometric shift in a portion of the photonic crystal structure is shown to be essential. The proposed model is verified by using a rigorous numerical method. An excellent agreement is observed between the... 

This paper deals with the low voltage ride-through (LVRT) control of wind turbines with doubly fed induction generators (DFIGs) under symmetrical voltage dips. The investigation first develops a mathematical formula for the rotor current and rotor voltage when DFIG is subjected to a symmetrical voltage dip. From the analysis, the reasons of rotor inrush current and factors influencing it are inferred. Then, a control scheme enhancing the wind turbine LVRT capability is designed and simulated. The proposed control scheme consists of a nonlinear control strategy applied to the rotor-side converter and a dc-link voltage control applied to the grid-side converter. It improves the damping of DFIG... 

Faraday cups (FCs) have been used to measure charged particle beams currents for a wide variety of experiments since the early days of particle accelerators. The major error source in FC performance is the escape of ejected electrons produced by energetic particles striking with interior metal surfaces of the FC. To avoid this problem, electrostatic and magnetic guard rings are used. Some kinds of non-symmetrical electrostatic FC with superior performance than traditional cylindrically symmetric FC have been reported. Here, we propose a novel non-symmetrical electrostatic FC structure, and a method to compare different non-symmetrical FCs. The purpose of this design is to recapture energetic... 

An approximate and accurate enough multi-conductor transmission line model is developed for analysis of side-coupled metal-insulator-metal (MIM) waveguides. MIM waveguides have been already modeled by single conductor transmission lines. Here, the side coupling effects that exist between neighboring plasmonic structures are taken into account by finding appropriate values for distributed mutual inductance and mutual capacitance between every two neighboring conductors in the conventional single-conductor transmission line models. In this manner, multi-conductor transmission line models are introduced. Closed-form expressions are given for the transmission and reflection of miscellaneous MIM... 

This paper is concerned with the investigation of an optical band-pass filter based on subwavelength surface plasmon polaritons. The transmission characteristics are numerically analyzed by the finite-difference time-domain method, and simulation results reveal that the structure has a band-pass filtering characteristic. The metal–insulator–metal plasmonic nanostructure is implemented by several vertical rectangular cavities across an optical waveguide. The metal and dielectric materials utilized for the realization of the filter are silver and air, respectively. Furthermore, the performance can be efficiently modified by tuning the geometric parameters such as the cavities’ length and width... 

Despite various optical realizations of convolutional neural networks (CNNs), optical implementation of nonlinear activation functions and pooling operations are still challenging problems. In this regard, this paper proposes an optical saturable absorption nonlinearity and its atomic-level model, as well as two various optical pooling operations, namely optical average pooling and optical motion pooling, by means of 4f optical correlators. Proposing these optical building blocks not only speed up the neural networks due to negligible optical processing latency, but also facilitate the concatenation of optical convolutional layers with no optoelectrical conversions in-between, as the... 

A novel filter for use in three-phase power systems is introduced. When the input to the filter is a balanced three-phase set of signals, the filter suppresses noise and distortions and extracts a smooth three-phase fundamental component. When the input signal to the filter is unbalanced, it extracts the fundamental positive-sequence component of the input signal. The filter also estimates the magnitude, phase angle, and frequency of the signal and adaptively follows the variations in all these three variables. The characteristics of the filter, including its mathematical equations, stability analysis, steady state, and dynamic responses, are discussed in this paper. The filter highly...