Sharif Digital Repository

Using a generalized Hubbard Hamiltonian, many-electron wavefunctions of negatively charged (NV -) and neutral nitrogen-vacancy (NV 0) centers in diamond were calculated. We report the effect of symmetric relaxation of surrounding atoms on the spin density, calculated from the many electron wavefunctions in the ground and excited states. We evaluated the error, that, arises in estimation of spin density when lattice relaxation effect is neglected in Electron Paramagnetic Resonance experiment and showed that the ground state spin density distribution is accessible in outward relaxations. The computed oscillator strengths give a higher efficiency for the 1.945 eV photoluminescence (PL) line of... 

The biomechanical behavior of brain tissue is needed for predicting the traumatic brain injury (TBI). Each year over 1.5 million people sustain a TBI in the United States. The appropriate coefficients for modeling the injury prediction can be evaluated using experimental data. In the present paper, using an experimental setup on bovine brain tissue, unconfined compression tests at quasi-static strain rates of ϵ 0.0004s-1, 0.008s-1 and 0.4s-1 combined with a stress relaxation test under unconfined uniaxial compression with ϵ 0.67s-1 ramp rate are performed. The fitted viscohyperelastic parameters were utilized by using obtained stressstrain curves. The finite element analysis (FEA) is... 

In this research, the effect of using nanoparticles on the Nusselt number in the natural convection at high Rayleigh numbers has been investigated. A two-component multiple relaxation times lattice Boltzmann code has been developed to investigate the natural convection of nanofluids in a 2D square enclosure. Three main forces, namely, buoyancy, drag, and Brownian forces are included to consider the interactions of the components. The potential force is also added to the model for the interactions among nanoparticles. The effects of Ra number, volume fraction of nanoparticles (ϕ), and size of nanoparticles (λ) have been investigated for two nanofluids (CuO-water and TiO2-water). Five... 

The present experimental study investigated the behavior of hot-mix asphalt (HMA) under repetitive creep and recovery loading. Cylindrical samples of HMA were subjected to trapezoidal and haversine loading followed by unloading. Different amounts of unloading (stress reduction) and relaxation periods (rest periods in complete unloading) were tested. The measured vertical deformation was decomposed into viscoelastic and viscoplastic components. It was observed for cyclic loading that an increase in unloading and/or relaxation period increased the recovery of viscoelastic strain, which in turn increased the accumulated viscoplastic strain in subsequent loading cycles. It appears that... 

Purpose: The purpose of this paper is to investigate the natural convection behavior of nanofluids in an enclosure. The enclosure is a 3D capsule with curved boundaries filled with TiO2-water nanofluid. Design/methodology/approach: In this paper, a multiple relaxation times lattice Boltzmann method (MRT-LBM) has been used. Two-component LBM has been conducted to consider the interaction forces between nanoparticles and the base fluid. Findings: Results show that the enhanced Nusselt number (Nu*) increases with the increase in volume fraction of nanoparticles (ϕ) and Ra number and decrease of nanoparticle size (λ). Additionally, the findings indicate that increasing volume fraction beyond a... 

Different families of the Discrete Vapour Cavity Model (DVCM) are developed, including the frictionless, steady and quasi-steady friction models. A relaxation-dissipation approach is proposed to improve the timing of pressure pulses predicted by the classic DVCM. In this approach, a friction correction factor is introduced into the steady/quasi-steady friction term to reduce the local value of the dissipation term in regions facing with cavitation. The proposed approach is completely consistent with the classical water-hammer framework. The importance of the steady/quasi-steady friction term is investigated by comparing numerical results of different DVCMs with the experimental data for... 

In the near future power systems, efficient management of uncertainties with considering the system constraints without any simplification will be a challenge for system operators. Considering AC constraints leads to providing more accurate schedule of generating units, which can have a significant impact on the reduction of operating costs. Although numerous studies have been done to convexify AC optimal power flow constraints, most of the models are non-linear, which can be intractable for large-scale systems. In this study, a novel linear robust AC model is introduced using a combination of the quadratic convex relaxation (QCR) and the Frank-Wolfe algorithm for linearising the AC... 

Feedback vibration is a standard feature in almost every home video game console controller to vibrate in selected circumstances, such as when the user's character kick the ball or hit the opponent, to immerse the player in the game. In the handheld game consoles this feature causes the handheld game consoles to vibrate. But the handheld game consoles are different than home video game consoles. In this paper we examine the suitability of using feedback vibration in the handheld game consoles. We evaluated feedback vibration popularity among the users. We used Nintendo DS handheld game consoles for this evaluation  

By rapid growth of technology in recent years, many services are provided for disabled people. Using wireless devices such as mobile phones in healthcare is a new idea which is gained attracted by some developers in recent years. On the other hand, nowadays game consoles are not only for playing games, but also have more functions such as using for education. Considering the above mentioned facts, this paper proposes a method to aid speech-impaired children using Nintendo DS Game console. This method helps the speech-impaired children which are not capable of using sign language well to communicate with others until they learn sign language well. Because the Nintendo DS is the most popular... 

The low cycle fatigue René 80, a Ni-base superalloy, was studied at temperature of 871 °C, R = (εmin/εmax) = 0 and strain rate of about 2 × 10-3 s-1. The dislocation structure and failure surface observations were evaluated through TEM and SEM. TEM studies showed that at Δεt = 0.8% during the first cycle the dislocations formed a hexagonal network in the γ-phase matrix. When the number of cycles increased, the density of dislocations increased as well. At N = Nf and Δεt = 0.8% the cutting of γ′ precipitates took place. SEM studies at Δεt = 0.8% and N = Nf showed that fatigue crack initiation generally occurred at the surface, where it is depleted of the γ′ phase as a result of oxidation by... 

Fixed gain controllers for automatic generation control are designed at nominal operating conditions and fail to provide best control performance over a wide range of operating conditions. So, to keep system performance near its optimum, it is desirable to track the operating conditions and use updated parameters to compute control gains. A control scheme based on artificial neuro-fuzzy inference system (ANFIS), which is trained by the results of off-line studies obtained using particle swarm optimization, is proposed in this paper to optimize and update control gains in real-time according to load variations. Also, frequency relaxation is implemented using ANFIS. The efficiency of the... 

In the traditional agri-fresh food supply chain (AFSC), geographically dispersed small farmers transport their products individually to the market for sale. This leads to a higher transportation cost, which is the primary cause of farmers’ low profitability. This paper formulates a traditional product movement problem in AFSC. First, the aggregate product movement model is combined with the vehicle routing model to redesign an existing AFSC (the ETKA Company; the most extensive domestic agri-fresh food supply chain in Iran) based on the available data. For the four-echelon, multi-period supply chain under investigation, a mixed integer linear programming (MILP) model is developed for the... 

The folding rates of protein were shown to correlate with the degree of heterogeneity in the formation of native contacts. It was shown that both experimental rates and simulated free energy barriers for 2-state proteins depend on the degree of heterogeneity present in the folding process. Heterogeneity due to variance in the distribution of native loop lengths, and variance in the distribution of φ values, were observed to increase folding rates and reduce folding barriers. The observed effect due to φ variance was found to be the most statistically significant, because φ variance captures both heterogeneity arising from native topology and that arising from energetics  

Train scheduling has been one of the significant issues in the railway industry in recent years since it has an important role in efficacy of railway infrastructure. In this paper, the timetabling problem of a multiple-tracked railway network is discussed. More specifically, a general model is presented here in which a set of operational and safety requirements is considered. The model handles the trains overtaking in stations and considers the stations' capacity. The objective function is to minimize the total travel time. Unfortunately, the problem is NP-hard, and real-sized problems cannot be solved in an acceptable amount of time. In order to reduce the processing time, we presented some... 

Hybrid FVM-LBM schemes are developed in the past few years to use capabilities of both Navier-Stokes based finite volume method (FVM) and lattice Boltzmann method (LBM) to solve macro-meso multiscale problems. In this scheme, the major task is to develop some lifting relations that reconstruct distribution functions in LBM sub-domain from macroscopic variables and their derivatives. The macroscopic variables are computed using Navier-Stokes based FVM in macroscale sub-domain, while distribution functions are computed using LBM in mesoscale sub-domain. The pioneer works in this area used the single relaxation time (SRT) version of LBM. However, it is known that the numerical stability and... 

Scheduling under nonrenewable resources is one of the challenging issues in project scheduling problems. There are many cases where the projects are subject to some nonrenewable resources. In most of the literature, nonrenewable resources are assumed to be available in full amount at the beginning of the project. However, in practice, it is prevalent that these resources are procured along the project horizon. This paper studies the generalized resource-constrained project scheduling problem (RCPSP) where, in addition to renewable resources, nonrenewable resources are considered, such as budget or consuming materials by the project activities. As the problem is NP-hard, some sub-algorithm... 

The relationship between unpaired electron delocalization and nearest-neighbor atomic relaxations in the vacancies of diamond has been determined in order to understand the microscopic reason behind the neighboring atomic relaxation. The Density Functional Theory (DFT) cluster method is applied to calculate the single-electron wavefunction of the vacancy in different charge states. Depending on the charge and spin state of the vacancies, at outward relaxations, 84-90% of the unpaired electron densities are localized on the first neighboring atoms. The calculated spin localizations on the first neighboring atoms in the ground state of the negatively charged vacancy and in the spin quintet...