Sharif Digital Repository

In this paper the electrical characteristics of a novel nanoscale double-gate MOSFET (DG-MOSFET) have been investigate by a full Quantum Mechanical simulation framework. This framework consists of Non-Equilibrium Green's Function (NEGF) solved self-consistently with Poisson's Equation. Quantum transport equations are solved in two-dimension (2-D) by recursive NEGF method in active area of the device to obtain the charge density and Poisson's equation is solved in entire domain of simulation to get potential profile. Once self-consistently achieved all parameters of interest (e.g. potential profile, charge density, DIBL, etc) can be measured. In this novel DG-MOSFET structure, a front gate... 

In this paper, the influence of the van der Waals force on two main parameters describing an instability point of cantilever type nanomechanical switches, which are the pull-in voltage and deflection are investigated by using a distributed parameter model. The fringing field effect is also taken into account. The nonlinear differential equation of the model is transformed into the integral form by using the Green's function of the cantilever beam. The integral equation is solved analytically by assuming an appropriate shape function for the beam deflection. The detachment length and the minimum initial gap of the cantilever type switches are given, which are the basic design parameters for... 

The work presented here is a study of the steady withdrawal of water from the lens of freshwater situated above the ocean's salt water and within the island. It is the aim of this paper to investigate the process of withdrawal from the lens of freshwater with a view to establishing the critical flow values for withdrawal and the effects of sink location and density differences on these values, and also to determine the effects of relative density differences.Steady solutions are found for the shape of the interface between salt and freshwater beneath a tropical island. A Green_s function approach is used and proves to be much more robust than spectral methods. Computations of the surface... 

In this paper, the influence of the Casimir force on two main parameters describing an instability point of cantilever type nanomechanical switches, which are the pull-in voltage and deflection are investigated by using a distributed parameter beam model. The nonlinear differential equation of the model is transformed into the integral form by using the Green's function of the cantilever beam. The integral equation is solved analytically by assuming an appropriate shape function for the beam deflection. The detachment length and the minimum initial gap of the cantilever type switches are given, which are the basic design parameters for NEMS switches. The pull-in parameters of micromechanical... 

The work presented here is a study of the steady withdrawal of water from the lens of freshwater situated above the ocean's salt water and within the island. It is the aim of this paper to investigate the process of withdrawal from the lens of freshwater with a view to establishing the critical flow values for withdrawal and the effects of sink location and density differences on these values, and also to determine the effects of relative density differences. Steady solutions are found for the shape of the interface between salt and freshwater beneath a tropical island. A Green_s function approach is used and proves to be much more robust than spectral methods. Computations of the surface... 

In this paper, the influence of the van der Waals force on two main parameters describing an instability point of cantilever type nanomechanical switches, which are the pull-in voltage and deflection are investigated by using a distributed parameter beam model. The nonlinear differential equation of the model is transformed into the integral form by using the Green's function of the cantilever beam. The integral equation is solved analytically by assuming an appropriate shape function for the beam deflection. The detachment length and the minimum initial gap of the cantilever type switches are given, which are the basic design parameters for NEMS switches. The pull-in parameters of... 

The vibration response of a Timoshenko beam supported by a viscoelastic foundation with randomly distributed parameters along the beam length and jected to a harmonic moving load, is studied. By means of the first-order two-dimensional regular perturbation method and employing appropriate Green's functions, the dynamic response of the beam consisting of the mean and variance of the deflection and of the bending moment are obtained analytically in integral forms. Results of a field measurement for a test track are utilized to model the uncertainty of the foundation parameters. A frequency analysis is carried out and the effect of the load speed on the response is studied. It is found that the... 

Eringen's nonlocal theory and an accurate determination of the nonlocal kernel functions for hexagonal close-packed (hcp) crystals are of interest. The kernel functions are closely related to the anisotropy as well as any crystalline symmetries. To this end, five new distinct nonlocal kernel functions which have the characteristics of discrete atomistic Green's functions in the stress space are obtained through consideration of the nonlocal dispersion relations associated with certain directions combined with ab initio Density Functional Perturbation Theory (DFPT) calculations of the pertinent phonon frequencies. This is the first work which provides the nonlocal hcp kernel functions... 

In this paper, we study the coherent electronic transport of a periodic quantum wire (P-QW) such as poly-acetylene connected to uniform metallic leads, within the tight-binding (TB) approach and in the ballistic regime. We have calculated the Green's function (GF), density of states (DOS) and the coherent transmission coefficient (TC) fully exactly for a quantum wire. The quasi gap and the energy and wire-length dependence of the GF and conductance for the system are also derived. Finally, we obtain a non-linear equation which gives the bound state energies. Our calculation can be generalized to arbitrary leads and can be applied to molecular wires, polymers, nanocrystals, where results may... 

The response of infinite beams supported by nonlinear viscoelastic foundations subjected to harmonic moving loads is studied. A straightforward solution technique applicable in the frequency domain is presented in this paper. The governing equations are solved using a perturbation method in conjunction with complex Fourier transformation. A closed-formed solution is presented in an integral form based on the presented Green's function and the theorem of residues is used for the calculation of integrals. The solution is directed to compute the deflection and bending moment distribution along the length of the beam. A parametric study is carried out and influences of the load speed and... 

In this paper we have calculated the conductance of a periodic quantum dot attached to metallic leads, within the tight-binding (TB) model and in the ballistic regime. We have calculated the Green's function (GF), density of states (DOS) and the coherent transmission coefficient (TC) fully analytically for an alternating quantum dot (A-QD). The quasi-gap, bound states energies, the energy and dot-size dependence of the GF and conductance for the system are also derived. Finally, we show analytically the conductance can be switched between insulating (OFF) and conducting (ON) states by applying a gate voltage. © 2004 Elsevier B.V. All rights reserved  

A unified and robust method has been introduced to compute magnetostatic and electrostatic fields for nonperiodic excitations in periodically corrugated anisotropic structures. The method extends a previously published concept of modified phased-periodic Green's functions for solving flat-surface problems. Convergent results have been obtained for corrugations with aspect ratios exceeding 15. Novel elemental field distributions are presented as examples  

An efficient hybrid method is presented for the analysis of the interference phenomenon in high frequency communication circuits. The method is based on the transmission line matrix (TLM) method, augmented with a time domain integral formulation using the free space Green's function to account for the radiation of equivalent sources on boundary surfaces. The method is highly effective in reducing the dispersion effects in the TLM method and drastically reduces its computational intensity. © 2003 IEEE  

The elastodynamic behavior of layered media consisting of an arbitrary combination of isotropic and transversely isotropic layers is of great importance for many engineering applications. In this work, some appropriate elastodynamic Green’s functions pertinent to both the displacement and the stress fields are devised so that the problems associated with the n-layer semi-infinite and infinite media with any combinations of transversely isotropic and isotropic layers subjected to surface and buried oblique time-harmonic annular loading can all be treated in a unified manner. The material degeneracy arising due to the scenarios where one or more regions are isotropic is also discussed and...