Sharif Digital Repository

This paper provides a perspective on the current knowledge and potential areas of future research related to electrostatics in fluidized beds. Aspects addressed include characterization techniques, charge generation and dissipation mechanisms, interplay between the electrostatics and hydrodynamics, charge control methods, applications of tribo-electrostatic fluidization systems, and computational simulations which account for electrostatic charges. This is a complex research field involving fluid mechanics, powders and electrical physics, with potential rewards in terms of safety, process monitoring and new applications. © 2018 Elsevier B.V  

This paper is concerned with the stability of nonlinear Lipschitz systems subject to bounded process and measurement noises when transmission from sensor to controller is subject to distortion due to quantization. A stabilizing technique and a sufficient condition relating transmission rate to Lipschitz coefficients are presented for almost sure asymptotic bounded stability of nonlinear uncertain Lipschitz systems. In the absence of process and measurement noises, it is shown that the proposed stabilizing technique results in almost sure asymptotic stability. Computer simulations illustrate the satisfactory performance of the proposed technique for almost sure asymptotic bounded stability... 

Cascaded H-bridge converter has been utilized recently in different high-power applications due to its modular and simple structure. In order to have a balanced operation after a fault occurrence in this converter, it is necessary to detect the switch fault and its location. In this paper, a fast power-switch fault detection method is presented to identify a fault and its location. Only one voltage measurement per phase is required by this method, and the fault detection is faster compared to the existing methods. Moreover, it is suitable for implementation on an FPGA device due to the use of simple math, relational, and state machine blocks. The proposed method is verified by computer... 

Two-dimensional (2D) and three-dimensional (3D) numerical simulations of an external compression supersonic ramped inlet are presented for a free stream Mach number of 2. A comparison made between numerical results and experimental data showed that multi-block structured gird using standard k - " turbulence model gives acceptable results. The shape of present inlet diffuser was transformed gradually into a circular one to encompass the Aerodynamic Interface Plane (AIP). It was observed that the 3D simulation predicted a more accurate static pressure distribution during the length of supersonic inlet and total pressure distribution at the AIP in comparison with the 2D one. Further, a better... 

We have compared the gas phase thermochemical properties of aspartame (artificial sweetener) and α- and β-glucose. These parameters include metal ion affinities with Li+-, Na+-, K+-, Mg+2-, Ca+2-, Fe+2-, Zn+2-ions, and chloride ion affinity by using DFT calculations. For example, for aspartame, the affinity values for the above described metal ions are, respectively, 86.5, 63.2, 44.2, 255.4, 178.4, 235.4, and 300.4, and for β-glucose are 65.2, 47.3 32.9, 212.9, 140.2, 190.1, and 250.0 kcal mol-1, respectively. The study shows differences between the intrinsic chemistry of aspartame and glucose. © 2008 Elsevier Ltd. All rights reserved  

The main objective of perforating is to connect the wellbore to the reservoir zone by creating tunnels through casing and damaged zone into the undamaged rock. The process of detonating perforation charges generally causes damage due to crushed rock material around the perforation tunnels. There are different methods used to mitigate damage due to perforation, such as static and dynamic underbalanced perforation. In static underbalanced perforation, conventional high shot density perforating guns are run in underbalanced conditions in order to have clean-up after perforation. In dynamic underbalanced perforation, a specific gun design associated with gun puncher charges provides dynamic... 

Though wound healing process is well-researched, this area is poorly known. One reason is that all interactions have not been discovered, the main reason, though, is that the involved processes interact in a very complicated manner with nonlinear feedback. Such complex feedback mechanisms can be easily addressed by mathematical modeling. This paper contains a review of the mathematical modeling of cell interaction with extracellular matrix components during the process of dermal wound healing with focusing on remodeling phase. The models are of partial differential equation type and solved by finite element method. © 2009 IEEE  

A novel combination of discontinuous molecular dynamics and the Langevin equation, together with an intermediate-resolution model of proteins, is used to carry out long (several microsecond) simulations in order to study transport of proteins in nanopores. We simulated single-domain proteins with the α-helical native structure. Both attractive and repulsive interaction potentials between the proteins and the pores' walls are considered. The diffusivity D of the proteins is computed not only under the bulk conditions but also as a function of their "length" (the number of the amino-acid groups), temperature T, pore size, and interaction potentials with the walls. Compared with the... 

A mathematical model was developed to describe the performance of nanoparticulate mixed oxide pseudocapacitors based on RuO 2-MO 2 (M being another suitable transition metal) under galvanostatic charge/discharge regime. Both double layer and faradaic processes were taken into account. The effects of the active material's particle size and composition were examined. Furthermore, the influence of discharge current on the extents of double layer and faradaic contributions was analyzed. The model analysis showed that the energy density declined upon increasing the volume fraction of larger particles. © 2008 Springer-Verlag  

Urban transportation is one of the main sources of air pollution in mega cities, and urban job related trips can effectively influence the state of air quality. Tehran, the capital of Iran, with a population of 7.3 million, was selected for this study. The present model is designed to investigate the effect on traffic of the business working hours of different occupations and, as a result, on the status of air pollution. Daily job, non-job and recreational trips using the present vehicle fleet is a major factor affecting air pollution in Tehran. In the context of the present study, the necessary information was utilized to define some relations between job trips and pollutant emissions. The... 

In this work, the rising of a single bubble in a quiescent liquid under microgravity condition was simulated. In addition to general studies of microgravity effects, the initiation of hydrodynamic convection, solely due to the variations of interface curvature (surface tension force) and thus the generation of shearing forces at the interfaces, was also studied. Then, the variation of surface tension due to the temperature gradient (Marangoni convection), which can initiate the onset of convection even in the absence of buoyancy, was studied. The related unsteady incompressible full Navier-Stokes equations were solved using a finite difference method with a structured staggered grid. The... 

There have been significant advances in fabrication of high-density microelectrode arrays using silicon micromachining technology in neural signal recording systems. The interface between microelectrodes and chemical environment brings great interest to researchers working on extracellular stimulation. This interface is quite complex and must be modeled carefully to match experimental results. Computer simulation is a method to increase the knowledge about these arrays and to this end the finite element method provides a strong environment for investigation of relative changes of the electrical field extension surrounding an electrode positioned in chemical environment. In this paper FEM... 

In this paper, we propose an approach for routing in SPEED protocol considering residual energy in routing decisions. Due to the limited energy of a sensor node, energyefficient routing is a very important issue in sensor networks. This approach finds energy-efficient paths for delayconstrained data in real-time traffic. The SPEED protocol does not consider any energy metric in its routing. In our approach, routing is based on a weight function, which is a combination of the three factors: Delay, Energy & Speed. Here, the node with the greatest value in the weight function is to be selected as the next hop forwarding. We increase the network lifetime by considering energy metric in routing... 

Although several analytical models have been proposed for wireless sensor networks (WSNs) with different capabilities, very few of them consider the effect of general service distribution as well as design constraints on network performance. This paper presents a new analytical model to compute message latency in a WSN with loop-free Bellman Ford routing strategy. The model considers limited buffer size for each node using M/G/1/k queuing system. Also, contention probability and resource utilization are suitably modeled. The results obtained from simulation experiments confirm that the model exhibits a high degree of accuracy for various network configurations. © 2009 IEEE  

This study investigates the effects of wall heating and skin friction on the characteristics of a compressible turbulent flow in developing and developed regions of a pipe. The numerical solution is performed by finite-element-based finite volume method applied on unstructured grids. A modified κ-ε model with a two-layer equation for the near-wall region and a compressibility correction are used to predict turbulent viscosity. The results show that shear stress in fully developed flow is nearly constant from the centerline up to 75% of the pipe radius, then increases sharply next to the wall, and the ratio of the turbulent viscosity to the molecular one is less than 0.2. Under a uniform wall... 

This paper presents a hybrid adaptive network based fuzzy inference system (ANFIS), computer simulation and time series algorithm to estimate and predict electricity consumption estimation. The difficulty with electricity consumption estimation modeling approach such as time series is the reason for proposing the hybrid approach of this study. The algorithm is ideal for uncertain, ambiguous and complex estimation and forecasting. Computer simulation is developed to generate random variables for monthly electricity consumption. Various structures of ANFIS are examined and the preferred model is selected for estimation by the proposed algorithm. Finally, the preferred ANFIS and time series... 

In this article, the flow behavior around a NACA 0012 airfoil which is oscillating with different Reynolds numbers and in various amplitudes has been investigated numerically. Numerical simulations have been performed with ANSYS software. First, the 2-D geometry has been studied in different Reynolds numbers and angles of attack with various numerical methods in its static condition. This analysis was to choose the best turbulent model and comparing the grids to have the optimum one for dynamic simulations. Because the analysis was to study the blades of wind turbines, the Reynolds numbers were not arbitrary. They were in the range of 9.71e5 to 22.65e5. The angle of attack was in the range... 

The use of cooperative schemes in wireless networks has recently attracted much attention in scenarios where application of multipleantenna systems is impractical. In such scenarios, the requirement of having full channel state information (CSI) at the receiver side can be relaxed by using differential distributed (DD) transmission schemes. However, in the DD schemes proposed so far, the decoding complexity as well as the delay requirements increase with the number of relays. In this paper, we propose a low-rate feedback-based DD approach (with one-bit feedback per relay) that enjoys full diversity, linear maximum likelihood (ML) decoding complexity, and unrestrictive delay requirements. In... 

In this paper, we propose a new analytical model in order to evaluate the throughput of a wireless tandem network coding. Our analytical model is based on a multi-class open queueing network. In this model, we include two basic processes of network coding, i.e., packets combination and packets multicasting, in a suitable way considering the constraints of the queueing networks. To this end, we consider the coded packets as new classes of customers. In our model we consider the arrival and departure rates in and from the wireless nodes in steady state. By solving the related traffic equations and applying the stability condition, we compute the maximum stable throughput, i.e., the maximum... 

Motivated by applications of sensor networks, there has been growing interest in monitoring large scale distributed systems. In these applications, we usually wish to monitor a global system condition defined as a function of local network elements parameters. In this paper, we study Reactive Monitoring in sensor networks, which has the benefit of operating in a decentralized manner. Our primary concern in adopting such a monitoring paradigm is reducing the communication cost which is the dominant factor of energy drain in wireless sensor networks. In this study, we address the reactive aggregate monitoring problem by casting the underlying threshold assignment as an optimization problem....