Sharif Digital Repository

We introduce a modified-firing-rate model based on Hebbian-type changing synaptic connections. The existence and stability of solutions such as rest state, bumps, and traveling waves are shown for this type of model. Three types of kernels, namely exponential, Mexican hat, and periodic synaptic connections, are considered. In the former two cases, the existence of a rest state solution is proved and the conditions for their stability are found. Bump solutions are shown for two kinds of synaptic kernels, and their stability is investigated by constructing a corresponding Evans function that holds for a specific range of values of the kernel coefficient strength (KCS). Applying a similar... 

In this study, we assess the feasibility of a Hybrid Renewable Energy System (HRES) for the residential area of Hengam Island, Iran. The optimal system design, based on the analysis of minimum CO2 emissions, unmet electric load and capacity shortage, reveals that a hybrid system consisting of 12,779,267 kW (55.8% of production) of solar PV panels and 10,141,978 kW (44.2% of production) of wind turbines is the most suitable for this case study. This configuration ensures zero CO2 emissions and high reliability over a 25-year project lifetime, with an unmet electric load of 164 kWh per year and a capacity shortage of 5245 kWh per year. However, this case has a high initial cost of equipment,... 

The wireless sensor networks include a lot of sensor nodes with a limited energy distributed in a limited geography area. One of the important issues in these networks is the increased longevity of a network. In a wireless sensor network a long connecting distance between sensors and sink uses a lot of energy and decreases the longevity of network. Since clustering can decrease requirement of using energy for wireless sensor networks, we are following an intelligent technique for forming and managing clusters in this article. With clustering wireless sensor network and using a genetic algorithms we can decrease the connecting distance a little, so the longevity of network will be more. The... 

This paper deals with vibrational behaviors of blades with cracks which are key components in rotating machines. However, since modelling and analysis of real blade is a complex problem, a simplified cantilever beam with both chordwise (in X-Y plane) and flapwise (in X-Z plane) motion are modeled instead. Finite Element Method (FEM) is used to model beam and to investigate its natural frequencies with a crack. Finally a limit function using modal data is developed and reliability analysis of beam model is performed. © 2017 IEEE  

An experimental study was conducted to investigate the extraction of oxidized sulfur compounds from gas oil. Solvents used for this purpose included acetone, acetonitrile, methanol and propanol. The effect of solvent concentration, solvent to gas oil ratio, temperature, time and number of stages was studied. To select the best solvent and conditions for extraction, two criteria were considered: high desulfurization and more hydrocarbon recovery. Results showed that extraction time and temperature have no significant effect. Methanol for low ability of extraction of oxidized sulfur compounds and propanol for low hydrocarbon recovery were excluded from further experiments. After the tests, the... 

Wind generated sea states are more accurately modeled by short-crested wave fields. Whether or not these short-crested waves can induce larger response amplitudes in floating offshore structures is of great concern to offshore engineers. In this paper, the hydrodynamics of a moored semisubmersible in short-crested wave fields is investigated. Morison-based motion equations with nonlinear damping terms are used to analyze the dynamic behavior of the structure. A generalized three-parameter short-crested wave field is introduced as the incident wave. The effect of transverse phase lag, wave propagation angle and different ratios of in-line and transverse wave numbers are studied on the force... 

With the rapid proliferation of residential rooftop photovoltaic (PV) systems, current and voltage unbalance issues have become a matter of great concern in low voltage (LV) distribution feeders. To overcome the issues, this study proposes a model to optimally rephase customers and PVs among the three phases via static transfer switches (STSs). The optimal STS placement is also considered in the model to achieve a cost effective solution with optimum number and location of STSs. The objective is to minimise total energy losses caused by current unbalance, minimise the number of STSs, and keep voltage unbalance along the feeder within the acceptable range. The model is solved via a... 

Ab initio density functional theory calculations were used to investigate cohesive, electronic, and structural properties of cagelike and spherical hydrogen terminated nanoparticles of diamond. Unlike cagelike nanodiamond particles, the variation of calculated energies of spherical ones is not monotonic. The variation range of the calculated energies and bond lengths of cagelike nanoparticles is much tighter than the variation range of spherical ones. In contrast to spherical nanodiamond particles, the C-C bond lengths of all cagelike nanoclusters are very similar to the bond length of bulk diamond. The comparison of stability, electronic highest occupied molecular orbital-lowest unoccupied... 

A realistic and practicable modeling of unbalanced distribution networks (DNs) is the missing link in most studies undertaken in these networks, e.g., optimal power flow (OPF), energy markets, etc. To address the issue, this letter proposes an unbalanced linear three-phase four-wire power flow (PF) model based on current injection equations at nodes. Also, the ZIP representation is considered for loads. The model can be easily generalized for unbalanced three-wire networks with minor changes and assumptions. Hence, the scope of the proposed method can be extended to cover both low-voltage and medium-voltage DNs. The performance of the proposed model is verified through simulations on two... 

Purpose: The purpose of our study is to examine the functioning of internal capital markets (ICMs) within business groups in Iran. We document how the ultimate owner's economic interests in affiliated firms influence their investment and dividend policies. Design/methodology/approach: Using hand-collected data on the ownership structures of Iranian firms, we first identify group-affiliated firms using Almeida et al.’s (2011) method. Having identified business groups, we test a number of hypotheses concerning the dynamics of the ICMs and the implications of the ultimate owner’s incentives for affiliated firms’ behavior. Findings: We first demonstrate that investments of group-affiliated firms... 

In this study, the authors investigate the problem of source localisation based on the time difference of arrival (TDOA) in a group of sensors. Aiming to minimise the squared range-difference errors, the problem leads to a quadratically constrained quadratic programme. It is well known that this approach results in a non-convex optimisation problem. By proposing a relaxation technique, they show that the optimisation problem would be transformed to a convex one which can be solved by semi-definite programming (SDP) and Lagrange multiplier methods. Moreover, these methods offer the exact solution of the original problem and the affirmation of its uniqueness. In contrast to other complicated... 

We prepared Cu nanoparticles in a-C:H thin films by co-deposition of RF-sputtering and RF-PECVD methods at room temperature. By increasing Cu content in these films a nonmetalmetal (NM) transition is observed. This transition is explainable by the power law of percolation theory. The critical metal content is obtained 56% and the critical exponent is obtained 1.6, which is larger than the exponent for 2 dimension systems and smaller than the one for 3 dimension systems. The electrical conductivity of dielectric samples was explained by tunneling. Activation tunneling energy that was obtained from temperature dependence of electrical resistivity correlates with near infrared absorption peak... 

This article endeavors to present the impact of conducting robot-assisted music-based intervention sessions for children with low-functioning (LF) autism. To this end, a drum/xylophone playing robot is used to teach basic concepts of how to play the instruments to four participants with LF autism during nine educational sessions. The main findings of this study are compared to similar studies conducted with children with high-functioning autism. Our main findings indicated that the stereotyped behaviors of all the subjects decreased during the course of the program with an approximate large Cohen’s d effect size. Moreover, the children showed some improvement in imitation, joint attention,... 

Distributed energy resources (DERs) play an important role in the future vision of distribution energy networks. This paper with the aim of promoting DERs role in energy markets proposes a new framework for the optimal bidding strategy of a Technical Virtual Power Plant (TVPP) in different markets. In the proposed framework, it is assumed that the TVPP energy power is distributed throughout a multi-carrier energy network (MCEN) which consists of district heat networks (DHNs) and a distributed electricity network (DEN). In the MCEN, CHP units are the linkage between DHNs and DEN. With the goal of maximizing the profit of TVPP in different local and wholesale energy markets, a bi-level... 

Many-electron calculations based on a generalized Hubbard Hamiltonian for electronic states of the diamond vacancies are reported. The model does not use the configuration interaction (CI) method and proper tetrahedral symmetry and spin properties of the defect are included in the Hamiltonian. Atomic orbital bases are introduced for the Hamiltonian calculation. Excited states of both neutral and negatively charged vacancies in diamond are calculated. The calculated values for the experimentally observed first dipole transition energies of the vacancies in diamond, GR1 and ND1 bands, are in good agreement with experiment. To obtain these results, we used a semi-empirical Hamiltonian... 

New chemical process design strategies utilizing computer-aided molecular design (CAMD) can provide significant improvements in process safety by designing chemicals with required target properties and the substitution of safer chemicals. An important aspect of this methodology concerns the prediction of properties given the molecular structure. This study utilizes one such emerging method for prediction of a hazardous property, flash point (FP), which is in the center of attention in safety studies. Using such a reliable data set comprising 1651 organic and inorganic chemicals, from 79 diverse material classes, and robust dynamic binary particle swarm optimization for the feature selection... 

A generalized Hubbard model based on a molecular approach is used to calculate many electron wavefunctions of diamond vacancies. We have calculated the oscillator strength of the dipole transition rates from the ground states of the neutral and negatively charged vacancies. The ratio of the oscillator strengths is in very good quantitative agreement with the reported optical spectroscopic data. Electronic configurations in the ground and dipole allowed excited states are presented. With the proposed picture, the much larger oscillator strength of the negatively charged vacancy with respect to other experimentally investigated color centers N-V, H3, X3 and H4 is explained  

This study comprehensively assesses the release rate of biocides, corrosion effects related to antifouling, and the physical properties of different paint types. Tests were conducted to measure thickness, viscosity, hardness, bending, adhesion, gloss, impact resistance, abrasion resistance, scratch resistance, polarization, and salt spray. The paints evaluated include resin-based, acrylic-based, epoxy-based, and vinyl-based formulations. The study investigates the influence of biocide content, biocide particle size, and immersion time on release rate using a lab-scale setup. Results showed that acrylic-based paints had a higher biocide release rate due to faster hydrolysis, while smaller... 

To improve the thermal stability of starch in water-based drilling fluid, monoethanolamine (MEA) was added, and the effect was investigated by laboratory experiment. The experimental results show that the addition of monoethanolamine (MEA) increases the apparent viscosity, plastic viscosity, dynamic shear force, and static shear force of the drilling fluid, and reduces the filtration rate of drilling fluid and thickness of mud cake apparently. By creating hydrogen bonds with starch polymer, the monoethanolamine can prevent hydrolysis of starch at high temperature. Starch, as a natural polymer, is able to improve the rheological properties and reduce filtration of drilling fluid, but it works... 

Virtual Reality (VR) technology is a growing technology that has been used in various fields of psychology, education, and therapy. One group of potential users of VR are children with autism who need education and have poor social interactions; this technology could help them improve their social skills through real-world simulation. In this study, we evaluated the feasibility of conducting virtual music education programs with automatic assessment system for children with autism at treatment/research centers without the need to purchase a robot, resulting in the possibility of offering schedules on a larger scale and at a lower cost. Intervention sessions were conducted for five children...