Sharif Digital Repository

The effect of substrate temperature on epitaxial growth of Y1Ba2Cu3O7−x film deposited on (100) crystalline lanthanum aluminate (LAO) substrates by RF Sputtering method has been investigated. The crystal mismatch between film and substrate is about 1.6%. The sputtering was carried out in vacuum with base pressure better than 10−5 Torr and 10/20 Pa oxygen/argon partial pressures. Substrate temperature at this condition is about 730 °C based on Bormann–Hammond diagram. As well known, because of the small lattice mismatch between YBCO and LAO, fabricated thin films are not perfectly c-axis and there is tendency to form a/b-axis regions in the film. Due to substantial effects of the density and... 

During the past two decades, the lattice Boltzmann (LB) method has been introduced as a class of computational fluid dynamic methods for fluid flow simulations. In this method, instead of solving the Navier Stocks equation, the Boltzmann equation is solved to simulate the flow of a fluid. This method was originally developed based on uniform grids. However, in order to model complex geometries such as porous media, it can be very slow in comparison with other techniques such as finite differences and finite elements. To eliminate this limitation, a number of studies have aimed to formulate the lattice Boltzmann on the unstructured grids. This paper deals with simulating fluid flow through a... 

Bi-directional RSFQ benefits from using both positive and negative SFQ pulses to manipulate and transfer digital data. This allows more flexibility in the design of simpler circuits with enhanced performance. On the other hand, using the AC bias current, one can replace on-chip resistive current distributors with inductors. This resembles RQL logic, but in contrast to RQL, it is possible to use the well-established standard RSFQ cells in bi-directional RSFQ. These two advantages (energy-efficient computation and flexibility in design) make bi-directional RSFQ a powerful tool in next-generation supercomputers and also compatible with ultra-low-temperature quantum computers. In this work, to... 

During the past two decades, the lattice Boltzmann (LB) method has been introduced as a class of computational fluid dynamic methods for fluid flow simulations. In this method, instead of solving the Navier Stocks equation, the Boltzmann equation is solved to simulate the flow of a fluid. This method was originally developed based on uniform grids. However, in order to model complex geometries such as porous media, it can be very slow in comparison with other techniques such as finite differences and finite elements. To eliminate this limitation, a number of studies have aimed to formulate the lattice Boltzmann on the unstructured grids. This paper deals with simulating fluid flow through a... 

One of the most prominent concerns of human societies, especially in advanced countries, is how to manage and consume energy in a manner that not only energy demand would be supplied but also a minimum amount of pollution enters the environment. In this case, production and consumption resources of energy and carbon dioxides emission sources have to be identified. Optimizing the consumption schedule can reduce fossil fuel consumption and carbon dioxide emission. This project aims to design and plan a multi-energy carrier microgrid that facilitates reaching a low carbon society. In this manner, utilizing modeling techniques of carbon dioxide flow in energy systems offers a good estimation for... 

SbCl3 supported on montmorillonite K-10 is an efficient catalyst for the ring opening of epoxides with aromatic amines under solvent-free conditions and microwave irradiation to give the corresponding b-amino alcohols in high yields with high regioselectivity  

Presence of fracture roughness and occurrence of nonlinear flow complicate fluid flow through rock fractures. This paper presents a qualitative and quantitative study on the effects of fracture wall surface roughness on flow behavior using direct flow simulation on artificial fractures. Previous studies have highlighted the importance of roughness on linear and nonlinear flow through rock fractures. Therefore, considering fracture roughness to propose models for the linear and nonlinear flow parameters seems to be necessary. In the current report, lattice Boltzmann method is used to numerically simulate fluid flow through different fracture realizations. Flow simulations are conducted over a... 

The semi-empirical Kozeny–Carman (KC) equation is the widely used equation for determining permeability of porous media. Recent studies have shown that KC coefficient (CKC ) is a function of porous media parameters. In this study, the relation between parameters of randomly generated porous media is investigated to improve permeability prediction. In particular, site percolation theory is applied to construct random porous media. The static parameters of porous media, including porosity and specific surface area, are evaluated from porous media structure, and dynamic parameters, tortuosity and permeability, are derived from the results of Lattice Boltzmann fluid flow simulation.... 

The ring-opening reaction of epoxides with thiols by SbCl3 supported on Kieselguhr under solvent-free conditions, afforded high yields of β-hydroxy sulfides. Nucleophilic attack of the thiols occurs regioselectively at the less hindered side of the epoxides. Copyright © Taylor & Francis Group, LLC  

Mg-based metallic glasses are promising materials for biodegradable implants. Understanding atomistic mechanism behind glass formation in these glasses plays a critical role in developing them for future applications. In the present work, we perform a set of molecular dynamics simulations to study structural origin behind glass form ability of Mg-based Mg-Zn metallic glasses at a wide range of compositions. Pair distribution function, Voronoi tessellation and dynamical analysis were adopted to characterize local structures in these glasses. Structural analysis was performed considering both topological and chemical short-range orders. It was found that structure of Mg-Zn metallic glasses... 

Considering the two main categories of rapid single flux quantum gates with destructive and nondestructive readout process, we have investigated the effects of readout cell topology and involved critical parameters on the proper functionality and stability of the states of the newly developed bidirectional T flip-flops (TFFs). It is observed that instabilities and fluctuations in the state of the gate (memory of TFF) after each transition determine the minimum time intervals between the clock pulses set by the ac bias current, further limiting the ultimate operation frequency of the circuits. The absolute values of the current levels of the junctions at each state, which play an important... 

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... 

Computer base and simulation technique have been applied for modeling the semi-solid die filling and part of the solidification process of aluminum A356 alloy. A fairly simple one-phase rheological model has been implemented into a fluid flow finite element software Procast, to solve the partial differential equations. This model is purely viscous nature and is implemented in the power law cut-off model of Procast. The constitutive parameters of this model were determined for a rheocast A356 alloy. Using these parameters and comparing the simulation results with experimental data showed good correlation with the model prediction. The designed die for rheocasting was applied for the... 

In this work, the evolution of the local structure in Cu50-Zr50 bulk metallic glass during glass formation was studied by molecular dynamics simulation. The pair distribution function and Voronoi analysis were adopted to characterize local structures in this alloy. The stability of icosahedral clusters and the role of other local clusters in the formation of icosahedra were evaluated. It was found that the (0,2,8,2) polyhedron is not only the dominant cluster in this alloy, but also the most prone cluster to convert into an icosahedron in the course of cooling. Moreover, it acts as an intermediate state during the icosahedron formation. The onset of stability of icosahedra emerges at the... 

In this work, the evolution of the local structure in Cu50–Zr50 bulk metallic glass during glass formation was studied by molecular dynamics simulation. The pair distribution function and Voronoi analysis were adopted to characterize local structures in this alloy. The stability of icosahedral clusters and the role of other local clusters in the formation of icosahedra were evaluated. It was found that the (0,2,8,2) polyhedron is not only the dominant cluster in this alloy, but also the most prone cluster to convert into an icosahedron in the course of cooling. Moreover, it acts as an intermediate state during the icosahedron formation. The onset of stability of icosahedra emerges at the... 

According to recent studies, Cu–Zr and Ni–Zr binary alloying systems are very similar based on known glass-forming ability criteria, however, they exhibit significant difference in glass-forming ability in practice. In this work, local atomic structures of Cu–Zr and Ni–Zr metallic glasses are studied by molecular dynamics simulation to explain the source of mentioned difference. The total and partial distribution functions, coordination number and voronoi analysis are utilized to characterize the local atomic structures around Zr, Ni and Cu atoms. It was found that the local environment around Zr atoms is almost similar in both systems. The difference in the atomic structure in these systems...