Sharif Digital Repository

By examination of the exerted electromagnetic (EM) force on boundary of an object in a few examples, we look into the compatibility of the stress tensors corresponding to different formulas of the EM force density with special relativity. Ampere-Lorentz's formula of the EM force density is physically justifiable in that the electric field and the magnetic flux density act on the densities of the total charges and the total currents, unlike Minkowski's formula which completely excludes the densities of the bounded charges and the bounded currents inside homogeneous media. Abraham's formula is fanciful and devoid of physical meaning. Einstein-Laub's formula seems to include the densities of... 

In this paper, we propose an optimized parameter selection procedure for rainbow table Time Memory Trade-Off (TMTO) attack with sequential online search. Unlike previous works that mainly deal with minimizing required memory in the rainbow table TMTO attack we simultaneously focus on the required memory and online search time. Our parameter selection technique is optimized regarding the minimization of the required memory subject to a certain success probability and a maximum online search time. Obtained results are two compact mathematical expressions for determining rainbow table TMTO attack parameters, number and length of chains. The application of our optimized parameter selection... 

Molecular dynamics simulations were used to propose a closed-form expression for the mobility of the [Formula presented] edge dislocation in low-carbon α-Fe (up to 0.1 at.% C) at temperatures of 300, 400 and 500 K and applied shear stresses of 10–100 MPa. Considering this parameter helps us to understand the effect of damage cascade on the dislocation mobility. The results confirmed that the point defect clusters at the thermal spike stage of the cascade (that they can be considered as an unstable precipitation-like phase), the distance of damage cascade relative to the center of the dislocation core and forming carbon-vacancy (C–V) complexes are some rather stronger obstacles for movement... 

Particle capture at porous media in cross-flow microfiltration is studied to investigate permeability reduction as a function of membrane pore size and particle size distribution. A new model in pore scale and its pertinent mathematical expressions, which consider pore and particle size distribution, are provided. Permeability reduction of the membrane because of size exclusion during particulate suspension flow was predicted using the developed model. It is assumed that the size exclusion is the dominant mechanism of particle retention causes pore blocking and permeability reduction in the porous media.The exact analytical solution of the stochastic model for size exclusion is used to... 

In this paper, a new all-optical phase-locked loop (OPLL) in a TDM system is proposed and analyzed. The scheme relies on using fiber optical parametric amplifier (FOPA) device models and theories. In the proposed OPLL, the local clock pulse stream and the received data signal pulses are fed into the FOPA as its pump and amplified signals, respectively. The power of the resulting, relatively, strong idler signal depends on the phase difference between the local clock and the received data signal pulses, and it is used to reveal the OPLL's error signal. We characterize the mathematical structure of the proposed OPLL and identify its three intrinsic sources of phase noises namely, randomness of... 

Particle capture at porous media in cross-flow microfiltration is studied to investigate permeability reduction as a function of membrane pore size and particle size distribution. A new model in pore scale and its pertinent mathematical expressions, which consider pore and particle size distribution, are provided. Permeability reduction of the membrane because of size exclusion during particulate suspension flow was predicted using the developed model. It is assumed that the size exclusion is the dominant mechanism of particle retention causes pore blocking and permeability reduction in the porous media.The exact analytical solution of the stochastic model for size exclusion is used to... 

Rubberlike materials are characterized by high deformability and reversibility of deformation. From the continuum viewpoint, a strain energy density function is postulated for modeling the behavior of these materials. In this paper, a general form for the strain energy density of these materials is proposed from a phenomenological point of view. Based on the Valanis-Landel hypothesis, the strain energy density of incompressible materials is expressed as the sum of independent functions of the principal stretches meeting the essential requirements on the form of the strain energy density. It is cleared that the appropriate mathematical expressions for constitutive modeling of these materials... 

In this article, a strain energy density function of the Saint Venant-Kirchhoff type is expressed in terms of a Lagrangian deformation measure. Applying the governing postulates to the form of the strain energy density, the mathematical expression of this measure is determined. It is observed that this measure, which is consistent with the strain energy postulates, is a strain type with the characteristic function more rational than that of the Seth-Hill strain measures for hyperelastic materials modelling. In addition, the material parameters are calculated using a novel procedure that is based on the correlation between the values of the strain energy density (rather than the stresses)... 

In this study, some new aspects of adsorption of a fluorochemical onto carbonate rocks as a wettability alteration agent to a gas wetting condition with the potential application for reduction of condensate blockage in gas condensate reservoirs are presented. To achieve this, kinetics, equilibrium, and thermodynamic of the adsorption process besides contact angle, imbibition, and characterization tests are investigated. Results of adsorption experiments revealed that kinetics behavior of the utilized fluorochemical–calcite system obeyed the pseudo-second order kinetics model. There was no change in adsorption after about 20 h. Also, the intraparticle diffusion mechanism was not the only rate... 

The formation of liquid bridge is pertinent to many fields including seepage into underground fractured rocks as an environmental issue and capillary continuity between matrix blocks which controls oil recovery in fractured reservoirs. Evaporation from the surface of liquid bridge into the surrounding gas could affect the stability of liquid bridge and fracture capillary pressure, which is not well discussed in the available literatures. In this research, by the aid of analogy between the diffusive flux and electrostatic potential, a new model for predicting evaporation rate from a liquid bridge inside a horizontal fracture is presented. The proposed model is then coupled with Young-Laplace... 

In this paper an analytical model is proposed to study the nonlinear dynamic behavior of rolling element bearing systems including surface defects. Various surface defects due to local imperfections on raceways and rolling elements are introduced to the proposed model. The contact force of each rolling element described according to nonlinear Hertzian contact deformation and the effect of internal radial clearance has been taken into account. Mathematical expressions were derived for inner race, outer race and rolling element local defects. To overcome the strong nonlinearity of the governing equations of motion, a modified Newmark time integration technique was used to solve the equations... 

In this paper, we analyze and discuss the performance limits of optical clock recovery systems using a phase-locked loop (PLL) structure with nonlinear two-photon absorption (TPA) phase detection scheme. The motivation in analyzing the aforementioned optical PLL with TPA receiver structure is due to a recent successful experiment reported in [8]. We characterize the mathematical structure of PLLs with TPA, so as to evaluate the performance limits on optical clock recovery mechanism. More specifically, we identify two intrinsic sources of phase noise in the system namely, the ON-OFF nature of the incoming data pulses and the detector's shot noise that ultimately limit the performance of the...