Kinetic modeling of high temperature oxidation of Ni-base alloys

The rates of isothermal and cyclic oxidation and the elemental concentration profiles as a function of time of oxidation for a few Ni-base superalloys were determined through a modified Wagner’s oxidation model and the solution of coupled elemental diffusion equations. Thermodynamically calculated interfacial elemental concentrations and oxygen partial pressures for the multi-component Ni-base alloys were used as boundary conditions for the solution of Wagner’s equation and the elemental coupled diffusion equations (for Cr, Al and O). The multiple elemental diffusion and mass conservation equations were solved using a numerical procedure. The dependence of self/tracer-diffusivities of Cr, Al and O in the corundum phase on the oxygen partial pressures was deduced using a genetic algorithm based optimization procedure incorporating the experimental parabolic rate constants for several Ni-base alloys. Rates of cyclic oxidation were then deduced from the deterministic interfacial cyclic oxidation spalling model (DICOSM) developed by Smialek [1]. The calculated oxidation rates were in reasonable agreement with the experimental values for a range of multi-component Ni-base alloys.     

Diameter-dependent coloration of silver nanowires

Silver nanowires were synthesized with a green method and characterized with microscopic and diffractometric methods. The correlation between the colors of the nanowires deposited on a solid substrate and their diameters was explored. Silver nanowires that appear similar in color in the optical micrographs have very similar diameters as determined by atomic force microscopy. We have summarized the diameter-dependent coloration for these silver nanowires. An optical interference model was applied to explain such correlation. In addition, microreflectance spectra were obtained from individual nanowires and the observed spectra can be explained with the optical interference theory. This work provides a cheap, quick and simple screening method for studying the diameter distribution of silver nanowires, as well as the diameter variations of individual silver nanowires, without complicated sample preparation.     

Heat exchanger fouling model and preventive maintenance scheduling tool

The crude preheat train (CPT) in a petroleum refinery consists of a set of large heat exchangers which recovers the waste heat from product streams to preheat the crude oil. In these exchangers the overall heat transfer coefficient reduces significantly during operation due to fouling. The rate of fouling is highly dependent on the properties of the crude blends being processed as well as the operating temperature and flow conditions. The objective of this paper is to develop a predictive model using statistical methods which can a priori predict the rate of the fouling and the decrease in heat transfer efficiency in a heat exchanger. A neural network based fouling model has been developed using historical plant operating data. Root mean square error (RMSE) of the predictions in tube- and shell-side outlet temperatures of 1.83% and 0.93%, respectively, with a correlation coefficient, R², of 0.98 and correct directional change (CDC) values of more than 92% show that the model is adequately accurate. A case study illustrates the methodology by which the predictive model can be used to develop a preventive maintenance scheduling tool.     

Hydrogen separation through the use of mixed oxygen ion and electron conducting membranes (I): theoretical analysis

Membrane-based processes are becoming increasingly important in the field of industrial gas separation. Such processes are attractive from the standpoint of high separation selectivity and high conversion ratios in cases involving gas phase and gas–solid reactions. In particular, the application of dense ceramic mixed ionic and electronic conducting membranes to separate gases such as oxygen through ambipolar transport of oxygen ions and electrons and hydrogen through ambipolar transport of protons and electrons from gas mixtures at elevated temperatures (>500°C) is gaining increasing importance. As a specific example, the requirement of high-purity tonnage hydrogen with less than 10 ppm carbon monoxide impurity levels would be absolutely essential for low-temperature proton exchange membrane fuel cells to gain wide market acceptance. We analyze herein a novel membrane-based hydrogen separation process which has heretofore not been widely reported in the literature.     

Adaptive Modeling of Analog/RF Circuits for Efficient Fault Response Evaluation

In this paper, we propose a methodology for adaptive modeling of analog/RF circuits. This modeling technique is specifically geared towards evaluating the response of a faulty circuit in terms of its specifications and/or measurements. The goal of this modeling approach is to compute important test metrics, such as fail probability, fault coverage, and/or yield coverage of a given measurement under process variations. Once the models for the faulty and fault-free circuit are generated, we can simply use Monte-Carlo sampling (as opposed to Monte-Carlo simulations) to compute these statistical parameters with high accuracy. We use the error budget that is defined in terms of computing the statistical metrics and the position of the threshold(s) to decide how precisely we need to extract the necessary models. Experiments on LNA and Mixer confirm that the proposed techniques can reduce the number of necessary simulations by factor of 7 respectively, in the computation of the fail probability.     

Multimodal image/video fusion rule using generalized pixel significance based on statistical properties of the neighborhood

Image fusion has been receiving increasing attention in the research community with the aim of investigating general formal solutions to a wide spectrum of applications such as multifocus, multiexposure, multispectral ( $IR$ -visible) and multimodal medical (CT and MRI) image and video fusion. While there exist many fusion techniques for each of these applications, it is difficult to formulate a common fusion technique that works equally well for all these applications. This is mainly because of the different characteristics of the images involved in various applications and the correspondingly different requirements on the fused image. In this work, we propose a common generalized fusion framework for all these classes, based on the statistical properties of local neighborhood of a pixel. As the eigenvalue of the unbiased estimate of the covariance matrix of an image block depends on the strength of edges in that block, we propose to employ it to compute a quantity we call as the significance of a pixel. This generalized pixel significance in turn can be used as a measure of the useful information content in that block, and hence can be used in the fusion process. Several data sets were fused to compare the results with various recently published methods. The analysis shows that for all the image types into consideration, the proposed methods improve the quality of the fused image, both visually and quantitatively, by preserving all the relevant information.     

A phase diagram approach to study liquation cracking in alloy 718

The constitutional liquation of NbC wrought alloy 718 is discussed in terms of a diffusion couple between NbC and they matrix in a pseudo-ternary of γ-NbC-Laves. Theoretical arguments are presented to show that the diffusion path cannot be a straight line connecting the terminal compositions. Experimental results indicate the existence of the NbC-γ diffusion couple and also support the hypothesis that the diffusion path is not a straight line connecting NbC and γ. Consequently, the temperature at which carbide liquation can occur is below the equilibrium NbC solidus, and hence, carbide liquation is constitutional in nature. The lowest temperature at which carbide liquation initiates depends upon the extent of deviation of the diffusion path from the straight line path. The dependence of the relative volume fractions of carbide and Laves phase in cast alloys on Nb/C ratio is explained using the γ-NbC-Laves pseudo-ternary. The Laves phase present in cast alloys is shown to liquate at the terminal eutectic temperature of the alloy, which could be lower than the carbide liquation temperature.     

Intel 870: a building block for cost-effective, scalable servers

Architects based the Intel 870 system architecture on the scalability port, a coherent system interconnect. The system's building-block approach lets a single chip set support a wide range of server segments.     

A cubic element program for the solution of Laplace-type equations based on the boundary element method

This paper presents a program written in C language for the solution of Laplace's equations in two dimensions employing cubic boundary elements. The program imposes no restriction on the number of elements to be used in the analysis. Since it makes efficient use of memory it can be used to solve fairly large-sized problems even on a personal computer. Numerical examples are presented to illustrate the accuracy of the results obtained.