Sharif Digital Repository

In this article, we present the room-temperature current-voltage characteristics of a nanometer scale (100×100 nm2) metal-oxide-semiconductor capacitor containing few (less than 100) silicon nanoparticles. The layer of silicon nanoparticles is synthesized within the oxide of this capacitor by ultra low-energy ion implantation and annealing. Current fluctuations in the form of discrete current steps and sharp peaks appeared in the static and dynamic I (V) characteristics of the capacitor. These features have been associated to quantized charging and discharging of the nanoparticles and the resulting Coulomb interaction to the tunneling current. © 2005 American Institute of Physics  

Probabilistic thermal buckling analysis of composite plates with temperature-dependent properties under stochastic thermal fields is performed by developing a new temperature increment-based algorithm for solving the stochastic nonlinear equation. The temperature distribution is assumed to be a stochastic Gaussian field which leads to spatially varying stochastic mechanical properties. The stochastic thermal field is decomposed by applying the Karhunen–Loeve theorem. The combination of stochastic assumed mode method and polynomial chaos is proposed as an alternative solution for the time-consuming stochastic finite element method. The uncertainty of the critical temperature is studied by... 

In this work, thermo-mechanical behavior of an aluminum alloy during gas tungsten arc welding (GTAW) is studied using a three-dimensional mathematical model. The model can be employed to determine residual stresses and their distribution after the welding operation. The effects of the strain hardening and the temperature dependency of material properties have also been considered in the calculations. Model validation has been performed using experimental measurements of residual stress by means of hole-drilling technique. The measurements have been carried out at the heat affected zone (HAZ) and base metal next to the welding line. In addition, microstructural observations have been made to... 

Design and development of FGMs as the heat treatable materials for high-temperature environments with thermal protection require understanding of exact temperature and thermal stress distribution in the transient state. This information is primary tool in the design and optimization of the devices for failure prevention. Frequently FGMs are used in many applications that presumably produce thermal energy transport via wave propagation. In this study, transient non-Fourier temperature and associated thermal stresses in a functionally graded slab symmetrically heated on both sides are determined. Hyperbolic heat conduction equation in terms of heat flux is used for obtaining temperature... 

In this paper, we study the frost formation and growth at the walls of a duct with uniform wall temperature variation. The simulation is performed for laminar flow regime considering suitable semi-empirical models incorporated with computational fluid dynamics (CFD) method. The frost growth is considered to be normal to the duct surface. Since the duct aspect ratio is high, we perform our simulations in two-dimensional zones. To simulate the frost layer properly, we solve both the energy and mass balance equations implementing some semi-empirical correlations on the frost side. At this stage, we suitably predict the required heat flux value at the solid boundary and the heat transfer... 

Purpose - The purpose of this paper is to propose a mathematical model to estimate required energy and temperature distribution during cold extrusion process. Design/methodology/approach - An admissible velocity field is generated based on stream function technique. Then, the required energy and the temperature distributions in the metal and the extrusion die are determined by a coupled upper bound-finite element analysis. Findings - To examine the proposed model, cold extrusion of AA6061-10%SiCp is considered and the predicted extrusion force-displacement diagrams in different reductions are compared with the experimental ones and reasonable agreement is observed. Furthermore, it... 

The major source of energy is fossil fuels, known as hydrocarbon containing C and H as the main elements. The heat generated from combustion of these fuels is used in power generation cycles to generate electricity. Main products of a hydrocarbon combustion reaction are water and carbon dioxide, but due to some reasons such as excessive temperature and inappropriate air-fuel mixing, always some pollutants are formed. One of the major concerns of recent years are NOx pollutants, which is mostly generated in the high temperature combustions. According to the geographical and economic issues, most countries are using coal as fuel and many researches have been conducted about pollutant formation... 

A numerical approach has been developed based on the stream function technique and the finite element analysis to predict required power and temperature rise in wire drawing processes. An admissible velocity field is first proposed using a stream function and then power consumption in the wire drawing is optimized to achieve sensible and unique deformation geometry. In addition, the finite element method together with axi-symmetric Petrov-Galerkin algorithm is coupled with the deformation model to assess the temperature distribution in both the deforming wire and the die during the process. The work hardening effects are also considered in the model both in the deformation zone and on the... 

In this paper, structural and electrical transport properties of hexagonal, 4H-type, BaRu1-xMnxO3 (x=0-0.3), synthesized by the solid-state reaction method at ambient pressure, have been presented. Electrical transport properties are measured over a temperature range of 10300 K in the magnetic field up to 15 kOe. The low temperature resistivity (10K