Sharif Digital Repository

We propose a new system which can generate digital holograms using natural color information. The proposed system can generate about 10 digital holographic video frames per a second using about 6K light sources  

When the periodic permittivity of two-dimensional (2D) photonic crystal (PC) can be separated in x- and y- coordinates, one can consider the structure as two separate 1D photonic crystals, one of them being periodic in x coordinate and the other in y coordinate. If it is possible to find a proper separable permittivity function, we can approximate a 2D PC with two distinct 1D structures. One of the advantages is rapid calculation the density of state of a 2D PC. In this article an analytical calculation of the density of states for such a 2D PC has been done with the aim of taking this advantage. For calculating the density of states we use the effective resonance approach to analyze the 1D... 

A simple analytic formula is derived to extract tiny dispersion fluctuations along highly nonlinear fibers from distributed measurements of parametric gain. A refined BOTDA scheme, suitable to track Kerr processes, enables low noise measurements  

Supply function equilibrium (SFE) is often used to describe the behavior of generating companies in electricity markets. However, comprehensive analytical description of supply function models is rarely available in the literature. In this paper, using some analytical calculations, a novel direct approach is proposed to compute the Nash equilibrium (NE) of the supply function model under uniform marginal pricing mechanism. An explicit mathematical proof for its existence and uniqueness is also presented. The proposed methodology is then generalized to accommodate practical market constraints. In addition, a new concept of robust NE is introduced and calculated based on this approach.... 

In this paper, an analytical method for calculation of the dose equivalent (DE) of coordinate surfaces of the Cartesian geometry is presented. DE of rectangular surfaces of gamma radiation emitters is calculated. The developed analytical method changes rectangular surface to multiple polar regions by dividing its surface into four types of sectors. By this method, the calculation of the dose is converted into calculation of simple mathematical series. The dose of rectangular shape sources for different gamma radiation emitters at different distances to target is calculated and the results are compared with MCNP code. Results show very good agreement. Advantages of the developed method are:... 

This paper proposes a novel, one-part, variable capacitor, using semi-conducting carbon nanotube (CNT). This variable capacitor works based on the change in the electronic structure of CNTs under applied voltage and deformations. Positive and negative charges are stored at both ends of a non-zero band gap nanotube which works as metallic electrodes in parallel plate capacitors. Also the neutral strip in the middle acts as the dielectric part of a conventional capacitor under the influence of an external electric field. Mechanical strains on carbon nanotube change its band gap energy and thus the length of neutral strip and charged regions. The lengths of these parts are primarily dependent... 

In this paper, we consider the problem of optimum rate adaptation and power allocation to maximize the delay-limited throughput (DLT) in a time-correlated 2×1 MISO Rayleigh fading channel with Hybrid ARQ in Chase-Combining mode (HARQ-CC). To this aim, we have first formulated the DLT equation based on the outage probability for 2×1 MISO-HARQ channel. We show that exact analytical calculation of the outage probability is not tractable. Therefore, we approximate the outage probability using a log-normal approximation approach. Based on such approximation, optimal rate and power allocations are derived. Finally, using Monte-Carlo simulation, we show that the approximation method provides... 

In this paper by solving Dirac equation, we present an analytical solution to calculate energy levels and wave functions of mono- and bilayer graphene quantum dots. By supposing circular quantum dots, we solve Dirac equation and obtain energy levels and band gap with relations in a new closed and practical form. The energy levels are correlated with a radial quantum number and radius of quantum dots. In addition to monolayer quantum dots, AA- and AB-stacked bilayer quantum dots are investigated and their energy levels and band gap are calculated as well. Also, we analyze the influence of the quantum dots size on their energy spectrum. It can be observed that the band gap decreases as quantum... 

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... 

The field of any point source which is broadened equally in all directions without any limitation to its range is within category of the inverse square law (ISL). As a case study, the dose equivalent (DE) rate is calculated. For calculating the DE rate, the radiation source can be divided into multiple layers and each layer is fractionated to multiple rectangular surfaces. Each rectangular surface can be replaced with three types of sectors. The DE rate of a source on a target is then sum of DE rates of sectors. The developed method is independent of the target position relative to the source and is used for the dose calculation of any arbitrary arrangement of source and target. As an... 

A new structure for the compression surfaces of a supersonic inlet is proposed which has improved the target performance parameter i.e. total pressure recovery ratio. This idea resulted in development of a new type of supersonic inlet, utilized four ramps and a cone simultaneously as the compression surfaces. A prototype of the proposed inlet has been designed for a free stream Mach number of 3 and its performance has been evaluated via numerical simulation for both design and off-design conditions. The performance of the newly designed inlet has been compared to the existing experimental data of two double-cone inlets. The acquired data are further compared with analytical calculations of... 

We propose an accurate analytical model for a circularly polarized antenna comprising a normally magnetized, grounded ferrite disk with a metalized top surface. The antenna is assumed to be excited by a conventional current probe. In the case of a thin ferrite disk, the electromagnetic fields of the dominant mode of the antenna do not vary in the direction normal to the disk. However, with increasing thickness of the ferrite disk, higher order modes start to affect antenna characteristics such as resonance frequency. This work presents an analysis of the structure that takes into account all higher modes of the antenna. To validate the theoretical calculations, HFSS simulations are... 

By detailed analytical treatment of the shock dynamics in the Burgers turbulence with large scale forcing we calculate the velocity structure functions between pairs of points displaced both in time and space. Our analytical treatment verifies the so-called Taylor's frozen-flow hypothesis without relying on any closure and under very general assumptions. We discuss the limitation of the hypothesis and show that it is valid up to time scales smaller than the correlation time scale of temporal velocity correlation function. We support the analytical calculation by performing numerical simulation of the periodically kicked Burgers equation. © 2008 The American Physical Society  

Soft errors caused by particles strike in combinational parts of digital circuits are a major concern in the design of reliable circuits. Several techniques have been presented to protect combinational logic and reduce the overall circuit Soft Error Rate (SER). Such techniques, however, typically come at the cost of significant area and performance overheads. This paper presents a low area and zero-delay overhead method to protect digital circuits' combinational parts against particles strike. This method is made up of a combination of two sub-methods: (1) a SER estimation method based on signal probability, called Estimation by Characterizing Input Patterns (ECIP) and (2) a protection... 

A new severe plastic deformation (SPD) method entitled Tube Channel Pressing (TCP) is proposed. In this study, the ability of TCP on strength improvement and grain refinement is assessed. This method is based on pressing a tube through a tubular channel die with a neck zone. Utilization of a mandrel fitted inside the tube prevents the crumpling of tube and preserves its initial dimension. Due to the symmetric design, after one pass, the die is rotated upside down and the second pass is applied by pressing the tube in inverse direction. Ultimate strength of a commercial purity aluminum tube after 5 successful passes is improved to 2 times of the initial strength. Analytical calculations and... 

A terahertz modulator based on the Type-II superconductor flux flow oscillator has been proposed. Analytical calculations are presented and the effects of intrinsic and extrinsic parameters such as disorder strength of crystal, penetration depth, frequency, and amplitude of the modulated current on the radiation power spectrum have been studied. The proposed structure also exhibits a mixer-like behavior, in the sense that its output harmonics range from the washboard frequency up to the superconductor gap frequency, so the input signal is practically mixed with the washboard frequency and its harmonics. The modulation index for each harmonic of this modulator has also been investigated. This...