Sharif Digital Repository

To investigate the factors influencing the luminescent properties of polymetallic cycloplatinated complexes a detailed study of the photophysical and structural properties of the heteronuclear complexes [Pt2Me 2(bhq)2(μ-dppy)2Ag2(μ-acetone) ](BF4)2, 2, [PtMe(bhq)(dppy)Tl]PF6, 3, and [Pt2Me2(bhq)2(dppy)2Tl]PF 6, 4, [bhq = benzo[h]quinoline, dppy = 2-(diphenylphosphino)pyridine] was conducted. Complexes 3 and 4 synthesized by the reaction of [PtMe(bhq)(dppy)], 1, with TlPF6 (1 or 1/2 equiv.) and stabilized by unsupported Pt-Tl bonds as revealed by multinuclear NMR spectroscopy and confirmed by X-ray crystallography for 3. DFT calculations for the previously reported butterfly Pt2Ag2 cluster 2... 

The objective of this paper is to present some novel insights for solving a second stage creep problem in metal matrix composites. First, a new analytical approach is developed for obtaining some unknowns in second stage creep of short fiber composites under an applied axial load. The unknowns are the radial, circumferential, axial, shear and equivalent stresses, which are determined by approximation of creep constitutive equations and using proper assumed displacement rates. A nonlinear differential equation is solved employing suitable and correct approximate assumptions. Then, the difference of the stress components utilizing creep constitutive equations and assumed displacement rates is... 

Single-layer reduced graphene oxide nanoribbons (rGONRs) were obtained through an oxidative unzipping of multi-walled carbon nanotubes and a subsequent deoxygenation by hydrazine and bovine serum albumin. Human mesenchymal stem cells (hMSCs) were isolated from umbilical cord blood and used for checking the concentration- and time-dependent cyto- and geno-toxic effects of the rGONRs and reduced graphene oxide sheets (rGOSs). The cell viability assay indicated significant cytotoxic effects of 10 μg/mL rGONRs after 1 h exposure time, while the rGOSs exhibited the same cytotoxicity at concentration of 100 μg/mL after 96 h. The oxidative stress was found as the main mechanism involved in the... 

In this paper, the concentrations of fission products and fuel isotopes as well as the changes of the thermo-neutronic parameters of the Bushehr's VVER-1000 reactor were studied during the initial startup and the first cycle. In order to perform the time-dependent cell calculations and obtain the concentration of fuel elements, the WIMSD5-B code was used. Besides, by utilizing the CITATION-LDI2 code, the effective multiplication factor and the thermal power distribution of the reactor were calculated. A computer program (WERL code) was designed in order to perform accurate calculation of the temperature distribution of the reactor core. For this purpose, the Ross-Stoute, Weisman, and... 

The ever increasing applications of shape memory polymers have motivated the development of appropriate constitutive models for these materials. In this work, we present a 3 D constitutive model for shape memory polymers under time-dependent multiaxial thermomechanical loadings in the small strain regime. The derivation is based on an additive decomposition of the strain into six parts and satisfying the second law of thermodynamics in Clausius-Duhem inequality form. In the constitutive model, the evolution laws for internal variables are derived during both cooling and heating thermomechanical loadings. The viscous effects are also fully accounted for in the proposed model. Further, we... 

A general method for deriving electromagnetic particle in cell (EMPIC) algorithms has been given by Eastwood [Comput. Phys. Commun. 64, 252 (1991)]. This method devises variation of the action-integral to find discrete governing equations. The most important advantage of this method is automatic inclusion of the time coordinate via the action integral into the computational domain. This inclusion is inevitable because electromagnetic algorithms are based on time evolution of the system from its initial state. The drawback of this method is that it is rather abstract. This causes obscurity of particle-mesh interactions and makes it hard to analyze physical treatments of the computational... 

In this work, a boundary element formulation for 2D linear viscoelastic solid polymers subjected to body force of gravity has been presented. Structural analysis of solid polymers is one of the most important subjects in advanced engineering structures. From basic assumptions of the viscoelastic constitutive equations and the weighted residual techniques, a simple but effective boundary element formulation is implemented for standard linear solid (SLS) model. The SLS model provides an approximate representation of observed behavior of a real advanced polymer in its viscoelastic range. This approach avoids the use of relaxation functions and mathematical transformations, and it is able to... 

In this paper, a recurrent neural network model is developed in order to forecast the energy consumption as a complex nonlinear function of gross domestic product (GDP) and population in Iran. This intelligent model is trained by total energy consumption data as output and the population and GDP as inputs during 1976-2001, while 5 annual data points of the following years (2002-2006) are used to validate the model. It can describe time dependencies efficiently and the convergence rate is much faster. This model forecasts the trend of energy consumption annually. Simulation results show that this model can predict energy consumption in Iran with acceptable accuracy. It is expected that this... 

The large amplitude free vibration of an unsymmetrically laminated composite beam (LCB) on a nonlinear elastic foundation subjected to axial load has been studied. The equation of motion for the axial and transverse deformations of a geometrically nonlinear LCB is derived. Using the Ritz method, the governing equation is reduced to a time-dependent Duffing equation with quadratic and cubic nonlinearities. The homotopy analysis method (HAM) is used to obtain exact expressions for the dynamic response of the LCB. This study shows that the third-order approximation of the HAM leads to highly accurate solutions that are valid for a wide range of vibration amplitudes. The effects of different... 

The heterobinuclear cyclometalated PtII-AuI complexes of the type [MePt(bhq)(μ-dppy)AuL]PF6, in which, bhq = benzo{h}quinoline, dppy = 2-diphenylphosphinopyridine, L = PPh3, 5; PPh2Me, 6; PPhMe2, 7; have been prepared by reaction of the mononuclear platinum(II) complex [MePt(bhq)(dppy)], 1, with 1 equiv. [AuL]+. Also, the reaction of complex 1 with 1 equiv AuCl(SMe2) at -60 °C gave the neutral heterobinuclear complex [MePt(bhq)(μ-dppy)AuCl], 8. All of the complexes were characterized using NMR spectroscopy and elemental microanalysis and complexes 5 and 8 were further identified by single crystal X-ray structure determination. Time-dependent density functional theory (TD-DFT) is used to... 

(GraphPresented) The quantum optimal control theory in conjunction with time dependent density functional theory is used to optimize the laser pulse shape for dissociation of nitrogen molecule. For several initial peak intensities and frequency ranges, the optimum shapes are produced and compared to determine the most efficient pulse. Ehrenfest molecular dynamics model is also used to test the dissociation process. The corresponding snapshots of density and time dependent electron localization function are presented. It is noticed that when the frequency ranges of laser pulses are doubled, it leads to 60% faster dissociation of N2 molecule  

In this study, the fundamental problem of unsteady blood flow in a tube with multi-stenosis is studied. An appropriate shape of the time-dependent multi-stenosis which is overlapping in the realm of formation of arterial narrowing is constructed mathematically. Blood is considered as a viscoelastic fluid characterized by the Oldroyd-B model. For the numerical solution of the problem, which is described by a coupled, non-linear system of partial differential equations (PDEs), with appropriate boundary conditions, the finite difference scheme is adopted. The solution is obtained by the development of an efficient numerical methodology based on the predictor-corrector method. The effects of... 

In this paper, the synchronization of a pair of pacemaker cells as Sino-Atrial (SA) and Atrio-Ventricullar (AV) nodes have been studied and a new approach for synchronization, based on the concept of Phase Response Curve (PRC), has been proposed. The paper starts with presenting the necessary and sufficient conditions for synchronization in terms of the PRC parameters. Such conditions are time dependent and thus, the paper proceeds with deriving some sufficient conditions, which are not time dependent. The time-delay between the firing time of SA node and when it reaches the AV node is also considered. When the conditions for spontaneous synchronization are not valid, the synchronization is... 

Load Balancing has many applications in various systems, but specifically plays a major role in the efficiency of parallel and distributed systems. In these systems, by load balancing we mean scheduling the jobs in a way that every job could be executed concurrently while it is mapped to a processing unit, such as a processor (in a multi-processor system) or a computer (in a grid computer). By developing effective methods the whole program time execution will be decreased and process utilization will be optimized. In this paper, a solution is proposed for dynamic load balancing. Because of the NP-hard nature of the problem, heuristic methods are desired. A simple scheduling method, Round... 

This study reports on the simulation of temperature distribution of human tooth under a laser beam based on non-Fourier models. The temperature in the tooth depth that directly results from the conduction heat transfer process is caused by the lengthy thermal relaxation time in the tooth layers. A detailed tooth composed of enamel, dentin, and pulp with unstructured shape, uneven boundaries, and realistic thicknesses was considered. A finite difference scheme was separately adopted to solve time-dependent equations in solid layers and soft tissue of the tooth. In this study, a dual-phase-lag non-Fourier heat conduction model was applied to evaluate temperature distribution induced by laser... 

The multielectron dissociative ionization of CH4 and CH2O molecules has been investigated using optimum convolution of different dual tailored short laser pulses. Based on three dimensional molecular dynamics simulations and TDDFT approach, the dissociation probability is enhanced by designing the dual chirped-chirped laser pulses and chirped-ordinary laser pulses for formaldehyde molecule. However, it is interesting to notice that the sensitivity of enhanced dissociation probability into different tailored laser pulses is not significant for methane molecule. In this presented modifications, time variation of bond length, velocity, time dependent electron localization function and evolution... 

We proposed a modeling procedure to calculate the impact of temperature on the detection efficiency in photodetectors based on CdTe materials. Temperature increase impacts on the electrical properties of the materials such as carrier mobility and carrier recombination lifetime. This impact which can be effective in some cases has been normally ignored in the modeling approaches presented in the literature. Here we show that increasing the temperature from 190 K to 300 K not reduces the mobility of both electrons and holes but also significantly reduces the carrier lifetime. The result will impact on electric-field within the depletion width of the device, drift and diffusion lengths which... 

This paper investigates the dynamic response of a clamped-free CNT-reinforced-MRE beam which is actuated by the combination of a constant and a harmonic time-dependent magnetic field. Using Hamilton's principle, the equation of motion has been obtained and discretized using the Galerkin method. This procedure transforms the governing PDE equation of motion into a nonlinear ODE equation in the form of the nonlinear Mathieu equation with cubic damping. Then, the method of multiple scales is employed to obtain the dynamic response of the system. Furthermore, a stability analysis is also performed and the effects of a magnetic field on the dynamic response and stability of the system is... 

Extensive experimental studies have been performed to investigate the unsteady boundary layer behavior over a plunging wind turbine blade section. The studies have been undertaken at various combinations of reduced frequencies, Reynolds numbers, and locations. A boundary layer rake has been carefully manufactured and utilized for velocity measurements inside the unsteady boundary layer. The measurement has been conducted in pre-static stall conditions. The reduced frequency and free stream velocity have varied from 0.005 to 0.1, and 30 to 60 m/s, respectively. To cover all possible scenarios, the streamwise positions of measurements have been chosen to be in favorable (x/c = 0.37), almost...