Sharif Digital Repository

In this article design and operation of a plastic optical fiber (POF) sensor based on the unconventional light leakage from one fiber to another one causing intensity modulation are presented. The dominant loss mechanism was found to be the evanescent loss and based on this phenomenon the optical fiber sensor was designed. The penetration depth of evanescent wave as a function of different refractive index of cladding was calculated. Operation of this sensor was tested as a liquid level sensor for different liquids and the experimental results are compared. The dry (air interface layer) and wet output (liquid interface layer) signals for this probe were measured for a series of measurements... 

This study is concerned with a theoretical and laboratory investigation of selective withdrawal of a linearly stratified fluid through a line sink at the base of a reservoir with a side contraction. The width-averaged equations of motion are solved numerically. The evolution of selective withdrawal and the flow properties at the steady state are studied. Using the numerical results, an equation is proposed for the withdrawal layer thickness, the critical Froude number, and the density thickness. For comparison, experiments were conducted in a flume and particle image velocimetry technique was used to capture the flow field upstream of a contraction during evolution of selective withdrawal.... 

Heavy metal removal from water and wastewater was investigated by using raw and modified diatomite from Iranian mines. Modification of diatomite was done by impregnating the diatomite surface with 0.35 g of manganese oxide in one gram of diatomite. This modified diatomite was named Mn-Diatomite. The surface area measurements for Mn-diatomite showed a 2.2 fold increase, hence higher removal capacity for the heavy metals. The results of the removal showed an increase in adsorption capacity which was for Pb2+ about 40 mg/g, for Ni 2+ about 34mg/g and for Cu2+ about 33mg/g. The filtration quality of diatomite was significantly enhanced with surface modification by manganese oxide  

An efficient numerical method for simulation of casting solidification is presented. The presented method is based on a stable explicit finite difference solution of the heat equation in conjunction with the temperature recovery method to incorporate latent heat effect. The computational cost of the presented method is approximately the same as an explicit method (per time step), while it is free from the time step limitation due to the stability criterion. A simple domain decomposition method is included to improve the computational performance of the presented method. The efficiency, stability and accuracy of the presented method are supported with illustrative examples. Copyright © 2007... 

The optimal design of a casting feeding system is considered. The problem is formulated as the volume constrained topology optimization and is solved with the finite element analysis, explicit design sensitivity, and numerical optimization. In contrast to the traditional topology optimization where the objective function is defined on the design space, in the presented method, the design space is a subset of the complement of the objective function space. To accelerate optimization procedure, the nonlinear unsteady heat transfer equation is approximated with a Poisson-like equation. The feasibility of the presented method is supported with illustrative examples. © 2007 Springer-Verlag  

In this study, design and operation of a cylindrical capacitive sensor based on the dielectric and reactance capacitance changes of the gap medium is reported. The proposed system was used to determine the electrical properties of different water liquids as a result of the capacitance variations. For capacitance measurement, the cylindrical gap can be filled up by water liquids under study, the electrical characteristics of different water liquids, mixture of ethanol and water, mixture of methanol and water, mixture of petroleum and water and other liquid mixtures were studied. In this research a big difference about 16200 nF was noticed in the measured capacitance of the corresponding... 

We have studied the effect of anisotropies on the quantum phase transition of the Kondo necklace model in dimensions D=1, 2, and 3. Both the anisotropy δ of the intersite interaction term and anisotropy Δ of the on-site Kondo interaction have been included. We use a bond operator method with constraints implemented in mean-field approximation. Starting from the paramagnetic phase we determine the critical ratio (t J)c of the quantum critical point and associated scaling exponents of the Kondo-singlet gap. We show that in the case of easy-axis type anisotropy δ>1 a qualitatively different behavior in comparison to the conventional Kondo necklace model with (δ,Δ) = (0,1) appears. We have also... 

Let D be a division ring with center F and n {greater than or slanted equal to} 1 a natural number. For S ⊆ Mn(D) the commuting graph of S, denoted by Γ(S), is the graph with vertex set S{minus 45 degree rule}Z(S) such that distinct vertices a and b are adjacent if and only if ab = ba. In this paper we prove that if n > 2 and A, N, I, T are the sets of all non-invertible, nilpotent, idempotent matrices, and involutions, respectively, then for any division ring D, Γ ( A ), Γ ( N ), Γ ( I ), and Γ ( T ) are connected graphs. We show that if n > 2 and U is the set of all upper triangular matrices, then for every algebraic division ring D, Γ ( U ) is a connected graph. Also it is shown that if R... 

In the reliability analysis of systems, all system components are often assumed independent and failure of any component does not depend on any other component. One of the reasons for doing so is that considerations of calculation and elegance typically pull in simplicity. But in real-world applications, there are very complex systems with lots of subsystems and a choice of multiple components that may interact with each other. Therefore, components of the system can be affected by the occurrence of a failure in any of the components. The purpose of this paper is to give an explicit formula for the computation of the reliability of a system with two parallel active components and one spare... 

The probability of failure estimation of composite structures under applied loads is an inevitable requirement given the uncertainties related to the material properties, loads, and boundary conditions. The properties of composite materials have more scatter due to non-homogeneity and anisotropic characteristics, and manufacturing defects. In this paper, the reliability of S2-Glass/Epoxy laminate composite materials containing a central circular hole under static tensile load is presented. Failure in fiber-reinforced plastic structures, since individual faults in each ply cannot be traced, is a random process due to the scatter caused by the behavior of the material. According to the... 

Predicting the failure probability of composite laminates under fatigue loading has many uncertainties, such as material properties, loading, boundary conditions, etc. In this paper, the failure probability of pin-loaded composite laminates is investigated. For this purpose, the continuum damage mechanics (CDM) theory has been combined with Monte Carlo Simulation (MCS) as a physics of failure tool to predict the failure of composite laminates in different directions (fibers, matrix, and shear) to calculate the probability of failure of the composite laminates under fatigue loading. Therefore, the failure function will be formed using the CDM theory and random variables identified. Finally,... 

A new group explicit method for solution of diffusion equation is presented. This method is based on domain decomposition concept and using asymmetric Saul'yev schemes for internal nodes of each sub-domain and alternating group explicit method for sub-domain's interfacial nodes. This new method has several advantages such as: good parallelism, unconditional stability, fully explicit nature and better accuracy than original Saul'yev schemes. The details of implementation and proving stability are briefly discussed. Numerical experiments on stability and accuracy are also presented. © 2006 Elsevier Inc. All rights reserved  

One of the most important goals of any organization for a product that goes into the design or manufacturing process is to improve its reliability. Reliability growth is defined as improving a product's criteria (input parameters) during operation using changes in design or production. This paper presents a hardware-centric approach for the reliability growth of systems following normal distribution based on the Non-Homogeneous Poisson Process (NHPP). To reach this goal, the reliability growth modeling equations for the NHPP with the assumption of the normal distribution for failure data are extracted and obtained. Then, the maximum likelihood estimation technique based on the... 

An iterative reconstruction-based method for suppression of clipping distortion in OFDM systems is proposed. Analysing the performance of the proposed method in Rician fading channels shows that it outperforms similar techniques, i.e. DFT-based reconstruction and iterative cancellation methods, on both BER performance and computational complexity. © IEE, 2005  

Marine accidents are some of the risk sources on human life at sea and also make the founded budget to be sank to the deep. In order to prevent these damages and losses, it is necessary to do a proper understanding of these accidents. Offshore systems as of the main parts of ocean structures and their accidents are considered here in this paper. From 1975 some data showing offshore accidents are captured in the Worldwide Offshore Accident Databank (WOAD), which are the main data bank to be used in this study. These data are about offshore damages and collapses due to Fires, Blowout, Anchor failure, Capsize, Explosion, etc. The main scope of the study is on fixed offshores, named jackets... 

In this paper, the production of lactic acid from deproteinized whey, using immobilized Lactobacillus casei on wood chips is investigated. The immobilization process was considered on various supports like wood chips, brick particle and porous glass by adsorption and on eggshell with glutaraldehyde by covalent bonding. Wood chips demonstrated the highest adsorption among all the supports and, therefore, was chosen as the best support for production. Batch production was studied at four temperatures and three different pH after five days. The highest concentration of lactic acid (16 g/1) was observed at T = 28°C and pH = 5.5. The optimum condition of temperature and pH for the continuous... 

An approximate method is presented that can be used to determine the non-linear behaviour of a new structural bracing system called the `Disposable Knee Bracing'. In this framing system, a special form of diagonal brace connected to a knee element instead of beam-column joint, is investigated. The diagonal element provides lateral stiffness during moderate earthquakes. However, the knee element is designed to have three plastic joints for dissipation of the energy caused by strong earthquake. This article demonstrates the transformation of a complex problem into a new, practical set of design charts and graphs. First, by studying of the elastic behaviour of the system, a suitable shape and... 

For environmental and economic reasons, the development of leight materials matching the mechanical requirements to highly loaded structural components in the transportation industry, in particular in the automotive industry, is continuously increasing within the recent years. Alloy properties can only marginally be improved by conventional metallurgical procedures, as for instance by alloying techniques and by heat treatment, due to the thermodynamic laws. However, by combination of metallic materials with different reinforcement composites and by application of various production technologies composite materials can be produced with a wide variation in composition and properties. The... 

In this study, the kinetics of nanocrystallization of amorphous Fe 73.5Si13.5B9Nb3Cu1 (F1) and Fe77Si11B9Nb2.4Cu0.6 (F2) alloys is investigated. The microstructure and magnetic properties of the nanocrystalline alloys are compared. The crystallization temperature of F2 alloy is shifted towards lower temperatures with respect to F1. Thus, the crystalline volume fraction and the crystalline grain size at specific annealing temperature for the F2 alloy are higher than for the F1 alloy, accounting for the higher coercive force of F2 alloy with respect to the one of F1 alloy. According to isoconversional methods, the activation energy for crystallization is variable as a function of transformed... 

When cracks along rivet holes and other highly stressed regions of mostly aged aircrafts are found, usually repairs are being made to arrest these cracks. Patches provide an innovative repair technique, which can enhance the way aircrafts are maintained. Composite patch design along with axiomatic design technique deployment is a possibility. Axiomatic Design (AD) is expressed as a system design methodology that is applicable to creation of a new design, analysis and improvement of an existing design. While, here Patch Design system architecture is expressed as application of principles of axiomatic design on top level requirements with consideration of design parameters and constraints. A...