Sharif Digital Repository

Rarefied gas flow in micro/nano electro mechanical systems (MEMS/NEMS) does not perform exactly as that in macro-scale devices. The main goal in this study is to investigate mixed subsonic-supersonic flows in micro/nano channels and nozzles and to provide physical descriptions on their behaviors. We use DSMC method as a reliable numerical tool to extend our simulation. It is because the DSMC provides accurate solution for the Boltzmann equations over the entire range of rarefied flow regime or Knudsen numbers. As is known, the appearance of oblique/normal shocks at the inlet of a channel or a nozzle adds to the complexity of internal flow field analyses. We found some very unique physical... 

Kinetic theory based numerical scheme such as direct simulation Monte Carlo (DSMC) and information preservation (IP) schemes properly solve micro-nano flow problems in transition and free molecular regimes. However, the high computational cost of these methods encourages the researchers toward extending the applicability of the continuumbased equations beyond the slip flow regime. In addition to correct velocity profile, the continuum-based equations should predict accurate mass flow rate magnitude. The secondorder velocity slip models derived from the kinetic theory provide accurate velocity profiles up to Kn=0.5; however, they yield erroneous mass flow rate magnitudes because the basic... 

We investigate the efficiency of a parallel direct simulation Monte Carlo (PDSMC) algorithm in solving the rarefied subsonic flow through a nanochannel. We use MPI library to transfer data between the processors. It is observed that PDSMC solver shows ideal speed up if sufficient workload is provided for each of processors. Additionally, this study shows that the computational time and speed up of the extended PDSMC solver do not depend (or slightly depend) on the number of cells. In contrary, increasing the total number of particles would result in a better efficiency of the PDSMC  

Choreography description languages aim at specifying from a global point of view interactions among a set of services involved in a new system. From this specification, local implementations or peers can be automatically generated. Generation of peers that precisely implement the choreography specification is not always possible: This problem is known as realizability. When peers corresponding to this specification are being executed we may want to modify the choreography specification and reconfigure dynamically the system. This is the case for instance if we add or remove interactions due to the addition of functionalities to the system at hand or the loss of a service. In this article, we... 

The kinetic-theory-based numerical schemes, such as direct simulation Monte Carlo (DSMC) and information preservation (IP), can be readily used to solve transition flow regimes. However, their high computational cost still promotes the researchers to extend the Navier-Stokes (NS) equations beyond the slip flow and to the transition regime applications. Evidently, a suitable extension would accurately predict both the local velocity profiles and the mass flow rate magnitude as well as the streamwise pressure distribution. The second-order slip velocity model derived from kinetic theory can provide relatively accurate velocity profiles up to a Knudsen (Kn) number of around 0.5; however, its... 

In this paper we have proposed an efficient method based on Genetic Algorithms (GAs) to design quantum cellular automata (QCA) circuits with minimum possible number of gates. The basic gates used to design these circuits are 2-input and 3-input NAND gates in addition to inverter gate. Due to use of these two types of NAND gates and their contradictory effects, a new fitness function has been defined. In addition, in this method we have used a type of mutation operator that can significantly help the GA to avoid local optima. The results show that the proposed approach is very efficient in deriving NAND based QCA designs  

Service-oriented computing has emerged as a new software development paradigm that enables implementation of Web accessible software systems that are composed of distributed services which interact with each other via exchanging messages. Modeling and analysis of interactions among services is a crucial problem in this domain. Interactions among a set of services that participate in a service composition can be described from a global point of view as a choreography. Choreographies can be specified using specification languages such as Web Services Choreography Description Language (WS-CDL) and visualized using graphical formalisms such as collaboration diagrams. In this paper, we present an... 

This paper presents the homotopy series solution of the Navier-Stokes and energy equations for non-Newtonian flows. Three different problems, Couette flow, Poiseuille flow and Couette-Poiseuille flow have been investigated. For all three cases, the nonlinear momentum and energy equations have been solved using the homotopy method and analytical approximations for the velocity and the temperature distribution have been obtained. The current results agree well with those obtained by the homotopy perturbation method derived by Siddiqui et al (2008 Chaos Solitons Fractals36 182-92). In addition to providing analytical solutions, this paper draws attention to interesting physical phenomena... 

We use a direct simulation Monte Carlo (DSMC) method to simulate gas heating/cooling and choked subsonic flows in micro/nanoscale channels subject to either constant wall temperature or constant/variable heat flux boundary conditions. We show the effects of applying various boundary conditions on the mass flow rate and the flow parameters. We also show that it is necessary to add a buffer zone at the end of the channel if we wish to simulate more realistic conditions at the channel outlet. We also discuss why applying equilibrium-based Maxwellian distribution on molecules coming from the channel outlet, where the flow is nonequilibrium, will not disturb the DSMC solution. The current... 

A choreography specifies activities and interactions among a set of services from a global point of view. From this specification, local implementations or peers can be automatically generated. Generation of peers that precisely implement the choreography specification is not always possible: this problem is known as realizability. This paper presents an encoding of the Chor choreography calculus into the FSP process algebra. This encoding allows to: (i) validate and verify Chor specifications using the FSP toolbox (LTSA), (ii) generate peer protocols from its choreography specified in Chor, (iii) test for realizability of the Chor specification, and (iv) generate Java code from FSP for... 

The current research uses an unstructured direct simulation Monte Carlo (DSMC) method to numerically investigate supersonic and subsonic flow behavior in micro convergent-divergent nozzle over a wide range of rarefied regimes. The current unstructured DSMC solver has been suitably modified via using uniform distribution of particles, employing proper subcell geometry, and benefiting from an advanced molecular tracking algorithm. Using this solver, we study the effects of back pressure, gas/surface interactions (diffuse/specular reflections), and Knudsen number, on the flow field in micronozzles. We show that high viscous force manifesting in boundary layers prevents supersonic flow formation... 

In this study, we applied the homotopy perturbation (HP) method for solving linear and nonlinear fourth-order boundary value problems. The analytical results of the boundary value problems have been obtained in terms of a convergent series with easily computable components. Comparisons between the results of the HP method and the analytical solution showed that this method gives very precise results with a few terms. In the implied HP method, some unknown parameters in the initial guess are introduced, which are identified after applying boundary conditions. This improvement results in higher accuracy. © 2008 The Royal Swedish Academy of Sciences  

In this study, the supersonic and choked subsonic flows through micro/nano channels are investigated using direct simulation Monte Carlo (DSMC) method. The supersonic case is simulated at different Knudsen numbers covering slip to transition flow regimes, while the effects of inlet Mach and back pressure are studied in details. The inlet/outlet pressure boundary conditions are suitably implemented benefiting from the basics of characteristics theory. A behavior similar to the one predicted by the Fanno theory is observed here; i.e., the supersonic flow velocity decelerates up to a choking condition where any further increase in Knudsen number is impossible unless strong normal/oblique shocks... 

Quantum dots cellular automata is a new computing method in the nanotechnology that has considerable features such as low power, small dimension and high speed switch. A QCA device stores logic based on the position of individual electrons. The fundamental logic elements in QCA are the majority (Fig.1 (a)) and inverter gates (Fig.1 (b)) that operate based on the Coulomb repulsion between electrons [1]  

We have constructed a collaboration network for physicists based in Iran working in different disciplines. By discussing properties like collaborators per author, shortest path, betweenness, and the concept of power in networks for this local model, and comparing with the global model, we understand how a developing country in the Middle East is contributing to the scientific growth in the world statistically. In this comparison, we found some properties of the local model which were not in accordance with the standard global society of science, which should be considered in developing the future policies. Our results show significant differences in factors like the degree and the diameter... 

Anxiety is among the most debilitating nonmotor symptoms of Parkinson's disease (PD). This study aimed to determine how PD patients with low and high levels of anxiety (LA-PD and HA-PD, respectively) compare with age- and sex-matched controls at the level of motor control of reach-to-grasp movements during single- and dual-task conditions with varying complexity. Reach-to-grasp movement kinematics were assessed in 20 LA-PD, 20 HA-PD, and 20 sex- and age-matched healthy controls under single- as well as easy and difficult dual-task conditions. Assessment of PD patients was performed during both the on- and off-drug phases. The results obtained during dual-task conditions reveal deficits in... 

In vivo dose-dependent effects of nanoscale graphene oxide (NGO) sheets on reproduction capability of Balb/C mice were investigated. Biodistribution study of the NGO sheets (intravenously injected into male mice at dose of ∼2000 μg/mL or 4 mg/kg of body weight) showed a high graphene uptake in testis. Hence, in vivo effects of the NGO sheets on important characteristics of spermatozoa (including their viability, morphology, kinetics, DNA damage and chromosomal aberration) were evaluated. Significant in vivo effects was found at the injected concentrations ≥200 μg/mL after (e.g., ∼45% reduction in sperm viability and motility at 2000 μg/mL). Observation of remarkable DNA fragmentations and...