Sharif Digital Repository

Three dimensional calculations of electronic dynamics of CH4 in a strong laser field are presented with time-dependent density-functional theory. Time evolution of dipole moment and electron localization function is presented. The dependence of dissociation rate on the laser characters is shown and optimal effective parameters are evaluated. The optimum field leads to 76% dissociation probability for Gaussian envelope and 40 fs (FWHM) at 10 16 W cm-2. The dissociation probability is calculated by optimum convolution of dual short pulses. By combining of field assisted dissociation process and Ehrenfest molecular dynamics, time variation of bond length, velocity and orientation effect are... 

In transient liquid phase (TLP) bonding for commercial applications, one of the important key parameters is the holding time required for complete isothermal solidification tIS, which is a prerequisite for obtaining a proper bond microstructure. The objective of the study is to analyse the isothermal solidification kinetics during TLP bonding of cast IN718 nickel based superalloy. Experiments for TLP bonding were carried out using a Ni-7Cr-4.5Si-3Fe-3.2B (wt-%) amorphous interlayer at several bonding temperatures (1273-1373 K). The time required to obtain TLP joints free from centreline eutectic microconstituents was experimentally determined. Considering the solidification behaviour of... 

We investigate the time-dependent evolution of thin liquid films over inclined substrates using a multi-component lattice Boltzmann algorithm. Substrates with and without grooves are considered and the effects of the inclination angle on the dynamics and the coating of the substrates are studied. Our results indicate that the dynamics is enhanced and the ridge height and its displacement are increased by increasing the inclination angle. However, by increasing the inclination angle the maximum depth that can be successfully coated is reduced. Also, although for any given groove depth the width should be larger than a critical value for successful coating, the critical width decreases for... 

A series of experimentally synthesized metal free organic dyes based on the 2-Cyano-3-(5-(5'-(4-(diphenylamino)phenyl)-4,4'-dihexyl-2,2'-bithiazol-5-yl)thiophen-2-yl)acrylic acid (dye 1) were investigated, based on computational methods to shed light on how a tiny difference in π-linker of sensitizer, C[tbnd]C and thiophene moiety as the additional π spacer group in dyes 2 and 3 respectively, has a significant impact on the short-circuit photocurrent densities (JSC) in Dye-sensitized solar cells (DSSCs). Although dyes 2 and 3 have similar redshifts in comparison to dye 1 in the UV–vis absorption spectra, there is a significant difference between JSC values of these dyes resulting in... 

Emergence of high pseudo-magnetic field as a result of mechanical deformations is one of the intriguing characteristics of the graphene honeycomb structure. For a time-dependent nonuniform strain and in the context of Berry curvature approach, the topological charge pumping is studied theoretically. Calculations have been performed in time–momentum parametric space. Within the Berry curvature approach, it has been revealed that time-dependent deformations result in nonzero valley-dependent charge pumping in the gapped graphene when there is a population imbalance between the valleys. This indicates that the valley polarization can be measured by the amount of topological charge pumping in... 

Concrete is a heterogeneous material with a wide variety of usage in structural design. Concrete under tension exhibits strain softening, i.e., a negative slope in the stress-deformation diagrams. Different softening curves have been proposed in the literature to interpret this phenomenon. In current research, a new softening curve for concrete has been proposed by using the newly introduced concept of fractal geometry. This new softening curve is denominated a 'Quasi-fractal' softening curve and consists of two parts, a linear portion at the beginning and an exponential portion in the rest of the curve. A comparison of a "Quasi-fractal" softening curve with a set of proposed experimental... 

Purpose - This study aims to present compatible computational fluid dynamics procedure for calculation of incompressible three-dimensional time-dependent flow with complicated free surface deformation. A computer software is developed and validated using a variety of academic test cases. Design/methodology/approach - Two fluids are modeled as a single continuum with a fluid property jump at the interface by solving a scalar transport equation for volume fraction. In conjunction, the conservation equations for mass and momentum are solved using fractional step method. Here, a finite volume discretisation and colocated arrangement are used. Findings - The developed code results in accurate... 

The change of the applied field in a medium containing anisotropic magnetic grains, makes the number of magnetic moments in the field direction, and in the opposite direction to vary. Near H = Hc, probability of transition between the two minimum energies (SW model) increases strongly and the magnetization of system varies rapidly. We measured the time dependence of magnetization for various Fe1-xCOx samples, in the presence of some step fields. These samples were grown via solving iron, and cobalt salts with borohydride and then, heat treatment was accomplished on them. The results of time measurement of magnetization in step fields reveals a linear proportionality between coercivity and... 

The stability analysis of cantilevered curved microtubules in axons regarding various size elements and using the generalized differential quadrature method for solving equations is reported. The impacts of covering MAP Tau proteins along with cytoplasm are taken into account as the elastic medium. Curved cylindrical nanoshell considering thick wall is used to model the microtubules. The factor of length scale (l/R = 0.2) used in modified couple stress theory would result in more accuracy when it comes to comparison with experiments, while alternative theories presented in this paper provide less precise outcomes. Due to the reported precise results, at the lower value of the time-dependent... 

This article presents the cyclic behavior of the A356.0 aluminum alloy under low-cycle fatigue (or isothermal) and thermo-mechanical fatigue loadings. Since the thermo-mechanical fatigue (TMF) test is time consuming and has high costs in comparison to low-cycle fatigue (LCF) tests, the purpose of this research is to use LCF test results to predict the TMF behavior of the material. A time-independent model, considering the combined nonlinear isotropic/kinematic hardening law, was used to predict the TMF behavior of the material. Material constants of this model were calibrated based on room-temperature and high-temperature low-cycle fatigue tests. The nonlinear isotropic/kinematic hardening... 

Time-dependent model is presented to simulate random lasers in the presence of an inhomogeneous gain medium. PbSe quantum dots (QDs) with an arbitrary size distribution are treated as an inhomogeneous gain medium. By introducing inhomogeneity of the PbSe QDs in polarization, rate, and Maxwell's equations, our model is constructed for a one-dimensional disordered system. By employing the finite difference time-domain method, the governing equations are numerically solved and lasing spectra and spatial distribution of the electric field are calculated. The effect of increasing the pumping rate on the laser characteristics is investigated. The results show that the number of lasing modes and... 

Calcium is a highly widespread and versatile intracellular ion that can control a wide range of temporal dynamics in the brain such as synaptic plasticity. This brief presents a novel and efficient digital circuit for implementing a calcium-based plasticity model aimed at reproducing relevant biological dynamics. Accordingly, we investigate the feasibility of the proposed model in a minimal neural network stressing on the effect of calcium oscillations on synaptic plasticity with various neuronal stimulation protocols. MATLAB simulations and physical implementations on field-programmable gate array confirm that the proposed model, with considerably low hardware overhead, can fairly mimic the... 

We study the quantum plasmonic features of gold and silver nanoparticles using TD-DFT+TB, a new density functional theory approach to the calculation of excited states, which combines a full DFT ground state with tight-binding approximations in the linear response calculation. In this framework, the optical properties of closed-shell Ag, Au and bimetallic Ag-Au nanoparticles with tetrahedral symmetry (with 20, 56, 120, and 165 atoms) and icosahedral structure (with 13, 55, and 147 atoms) were obtained and compared to full linear response time-dependent density functional theory (TD-DFT) as a reference and also to time-dependent density functional based tight binding (TD-DFTB) as a low-cost... 

The safety and optimal performance of nuclear reactors require online monitoring in the core. The present paper describes a method that avoids the solution of the time-dependent neutron diffusion equation, and it uses online readings of the fixed in-core neutron detectors to reconstruct the three-dimensional (3D) neutron flux distribution. The essential idea of the nodal synthesis method is the separation of time and space-dependence of the neutron flux distribution. The time-dependent section of the flux distribution is determined by in-core neutron detector readings, and the space-dependent section is obtained from pre-computed harmonics of the neutron diffusion equation. In online... 

The safety and optimal performance of nuclear reactors require online monitoring in the core. The present paper describes a method that avoids the solution of the time-dependent neutron diffusion equation, and it uses online readings of the fixed in-core neutron detectors to reconstruct the three-dimensional (3D) neutron flux distribution. The essential idea of the nodal synthesis method is the separation of time and space-dependence of the neutron flux distribution. The time-dependent section of the flux distribution is determined by in-core neutron detector readings, and the space-dependent section is obtained from pre-computed harmonics of the neutron diffusion equation. In online...