沉积硫酸盐对Fe-20Cr合金800℃氧化行为的影响

采用动力学测量、SEM、X-射线等手段研究了沉积硫酸盐对Fe-20Cr合金800℃氧化行为的影响.结果表明,沉积盐引起Fe-20Cr合金加速氧化.     

Optimal discrete systems with prescribed eigenvalues

In this article, the problem of the numerical computation of the stabilising solution of the game theoretic algebraic Riccati equation is investigated. The Riccati equation under consideration occurs in connection with the solution of the H _∞ control problem for a class of stochastic systems affected by state-dependent and control-dependent white noise and subjected to Markovian jumping. The stabilising solution of the considered game theoretic Riccati equation is obtained as a limit of a sequence of approximations constructed based on stabilising solutions of a sequence of algebraic Riccati equations of stochastic control with definite sign of the quadratic part. The proposed algorithm extends to this general framework the method proposed in Lanzon, Feng, Anderson, and Rotkowitz (Lanzon, A., Feng, Y., Anderson, B.D.O., and Rotkowitz, M. (2008), ‘Computing the Positive Stabilizing Solution to Algebraic Riccati Equations with an Indefinite Quadratic Term Viaa Recursive Method,’ IEEE Transactions on Automatic Control, 53, pp. 2280–2291). In the proof of the convergence of the proposed algorithm different concepts associated the generalised Lyapunov operators as stability, stabilisability and detectability are widely involved. The efficiency of the proposed algorithm is demonstrated by several numerical experiments.     

Time-optimal output regulators for linear multivariable discrete-time systems Part 1. Right invertible decouplable systems

Corsetti and Houpis (1985) presented a simple algebraic solution for the timeoptimal output regulator problem. This solution has been obtained for a special class of right invertible decouplable systems S(A, B, C) satisfying the condition that CB is of full rank. In this paper a general method is presented to extend the results of Corsetti and Houpis to all classes of right invertible decouplable systems S(A, B, C, E). It is shown that a simple state feedback control law drives each output of S(A, B, C, E) in a minimum number of steps equal to the order of the associated infinite zero. This state feedback represents the optimal solution for the considered time-optimal output regulator problem. A class of optimal solutions, parametrized by a free parameter matrix K, is obtained for non-square systems. The properties of the resulting optimal closed-loop system is given and a numerical example is worked out to illustrate the generality and feasibility of the proposed method.     

A new systematic firefly algorithm for forecasting the durability of reinforced recycled aggregate concrete

This study presents a new systematic algorithm to optimize the durability of reinforced recycled aggregate concrete. The proposed algorithm integrates machine learning with a new version of the firefly algorithm called chaotic based firefly algorithm (CFA) to evolve a rational and efficient predictive model. The CFA optimizer is augmented with chaotic maps and Lévy flight to improve the firefly performance in forecasting the chloride penetrability of strengthened recycled aggregate concrete (RAC). A comprehensive and credible database of distinctive chloride migration coefficient results is used to establish the developed algorithm. A dataset composite of nine effective parameters, including concrete components and fundamental characteristics of recycled aggregate (RA), is used as input to predict the migration coefficient of strengthened RAC as output. k-fold cross validation algorithm is utilized to validate the hybrid algorithm. Three numerical benchmark analyses are applied to prove the superiority and applicability of the CFA algorithm in predicting chloride penetrability. Results show that the developed CFA approach significantly outperforms the firefly algorithm on almost tested functions and demonstrates powerful prediction. In addition, the proposed strategy can be an active tool to recognize the contradictions in the experimental results and can be especially beneficial for assessing the chloride resistance of RAC.     

Decoration of vertically aligned TiO2 nanotube arrays with WO3 particles for hydrogen fuel production

WO₃ decorated photoelectrodes of titanium nanotube arrays (W-oxide TNTAs) were synthesized via a two-step process, namely, electrochemical oxidation of titanium foil and electrodeposition of W-oxide for various interval times of 1, 2, 3, 5, and 20 min to improve the photoelectrochemical performance and the amount of hydrogen generated. The synthesized photoelectrodes were characterized by various characterization techniques. The presence of tungsten in the modified TNTAs was confirmed using energy dispersive X-ray spectroscopy (EDX). Field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscope (HRTEM) proved the deposition of W-oxide as small particles staked up on the surface of the tubes at lower deposition time whereas longer times produced large and aggregate particles to mostly cover the surface of TiO₂ nanotubes. Additionally, the incorporation of WO₃ resulted in a shift of the absorption edge toward visible light as confirmed by UV-Vis diffuse reflectance spectroscopy and a decrease in the estimated band gap energy values hence, modified TNTAs facilitated a more efficient utilization of solar light for water splitting. From the photoelectrochemical measurement data, the optimal photoelectrode produced after 2 min of deposition time improved the photo conversion efficiency and the hydrogen generation by 30% compared to that of the pure TNTA.     

Effects of Mechanical Processing on Semiconducting Properties of Barium Titanate

Semiconducting barium titanate elements with positive temperature coefficient of resistance (PTCR) are usually subjected to different degrees of stress levels during processing operations like grinding, ultrasonic drilling, and slicing, etc. In this work we have examined the influence of these operations on the semiconducting properties of PTCR barium titanate using X-ray diffraction and electrical resistivity measurements.     

HEATING UNIFORMITY AND RATES IN A DOMESTIC MICROWAVE COMBINATION OVEN

Physics-based modeling complemented with magnetic resonance imaging (MRI) for validation can provide a novel means to understand and thereby optimize combination heating processes. The objectives of this study were to compare heating patterns in a combination of radiant, forced air and microwave oven measured by MRI with those predicted by coupled electromagnetics-heat transfer model; quantify speed and uniformity of heating for the different combination modes; determine the effect of food dielectric properties on heating patterns; and delineate the nature of individual heating modes and their combinations. The modes of radiant heating through heating elements and forced convection by fan led to a more uniform heating compared with the faster (but less uniform) heating method provided by the microwaves. Combination methods were faster than radiant, forced-air and microwave-only heating. Although the speed of heating increased appreciably for combination modes, the nonuniformity of heating did not increase as much.

PRACTICAL APPLICATIONS

The results from the study can be used to develop design recommendations/guidelines for combination heating for different thermal processes such as baking, broiling, roasting and reheating of different materials, grouping them based on their properties. The research can benefit the consumers, food services and equipment manufacturers to understand the combination heating process in a better way and to, thereby, use it efficiently. Without a fundamental understanding of the effect of various combinations, optimization of heating can be intractable. The fundamental approach used in this study would, therefore, help consumers and food services in preparation of safe and high-quality foods through combination heating. The work would also help equipment manufacturers in optimizing the designs of combination-heating ovens.     

Implementation of two-level algorithms using fixed-point arithmetic

The effect of using fixed-point arithmetic in the digital implementation of two-level control algorithms is examined in this paper. Analytical expressions are developed to predict the change in the expected minimum cost and associated matrices. It is shown that there is a favourable match between the analytical predictions and averaged simulation experiments. The use of finite-precision machines increases the expected theoretical minimum cost and makes the two-level algorithm become slow and thus require excessive iterations to converge.     

Determination of invariant zeros and zero directions of the system S(A,B, C,E)

Mita (1977) presented a simple method for the invariant zeros of a linear multivariable system by constructing its maximal unobservable subspace (MUS). However, the results of this method have been restricted to a class of controllable and right invertible systems satisfying the diagonal decoupling condition and described by the triple (A,B,C). Here, a general method based on the theory of decoupling extends Mita's results for all classes of systems described by the 4-tuples (A, B, C, E) with no special requirements. The MUS of all classes of such systems is simply constructed and its order is given in terms of the system order n and the infinite zeros or the minimal observability indices of the system. In addition, the invariant zeros and zero directions are found from the eigenvalues and eigenvectors of a reduced-order matrix having the dimension of the MUS obtained directly from the state-space parameters. Algorithms are presented for the invariant zeros and zero directions of invertible decouplable (or non-decouplable) systems S(A, B, C, E) and all classes of invertible and non-invertible systems S(A, B, C, E). Numerical examples demonstrate the generality and feasibility of the proposed method.