Overaluminizing of a CoNiCrAlY Coating by Inward and Outward Diffusion Treatments

Overaluminizing is a commercially accepted treatment to enhance high temperature oxidation resistance of MCrAlY overlay coatings. In the current investigation, a low pressure plasma-sprayed CoNiCrAlY coating was aluminized by two different growth modes: outward growth and inward growth. The resultant microstructures were characterized by means of scanning electron microscopy, energy dispersive spectroscopy, and X-ray diffraction analysis. The results showed that the final microstructure of both types of overaluminized coatings was similar and included Al-rich NiAl and Ni-rich NiAl zones from the top to the bottom. The details of the microstructures are discussed and compared with the results of simple aluminizing of the nickel-based substrate.     

Design of explicit model predictive control for constrained linear systems with disturbances

On-line model predictive control approaches require the online solution of an optimization problem. In contrast, the explicit model predictive control moves major part of computation offline. Therefore, eMPC enables one to implement a MPC in real time for wide range of fast systems. The eMPC approach requires the exact system model and results a piecewise affine control law defined on a polyhedral partition in the state space. As an important limitation, disturbances may reduce performance of the explicit model predictive control. This paper presents efficient approach for handling the problem of using eMPC for constrained systems with disturbances. It proposes an approach to improve performance of the closed loop system by designing a suitable state and disturbance estimator. Conditions for observability of the disturbances are considered and it is depicted that applying the disturbance’s estimation leads to rejection of the response error. It is also shown that the proposed approach prevents the reduction of feasible space. Simulation results illustrate the advantages of this approach.     

“How do you know that I don’t understand?” A look at the future of intelligent tutoring systems

Many software systems would significantly improve performance if they could adapt to the emotional state of the user, for example if Intelligent Tutoring Systems (ITSs), ATM’s, ticketing machines could recognise when users were confused, frustrated or angry they could guide the user back to remedial help systems so improving the service. Many researchers now feel strongly that ITSs would be significantly enhanced if computers could adapt to the emotions of students. This idea has spawned the developing field of affective tutoring systems (ATSs): ATSs are ITSs that are able to adapt to the affective state of students. The term “affective tutoring system” can be traced back as far as Rosalind Picard’s book Affective Computing in 1997.This paper presents research leading to the development of Easy with Eve, an ATS for primary school mathematics. The system utilises a network of computer systems, mainly embedded devices to detect student emotion and other significant bio-signals. It will then adapt to students and displays emotion via a lifelike agent called Eve. Eve’s tutoring adaptations are guided by a case-based method for adapting to student states; this method uses data that was generated by an observational study of human tutors. This paper presents the observational study, the case-based method, the ATS itself and its implementation on a distributed computer systems for real-time performance, and finally the implications of the findings for Human Computer Interaction in general and e-learning in particular. Web-based applications of the technology developed in this research are discussed throughout the paper.     

Corrosion and time dependent passivation of Al 5052 in the presence of H<Subscript>2</Subscript>O<Subscript>2</Subscript>

Corrosion and time–dependent oxide film growth on AA5052 Aluminum alloy in 0.25M Na₂SO₄ solution containing H₂O₂ was studied using electrochemical impedance spectroscopy, potentiodynamic polarization, chronoamperometric and open circuit potential monitoring. It was found that sequential addition of H₂O₂ provokes passivation of AA5052 which ultimately thickens the oxide film and brings slower corrosion rates for AA5052. H2O2 facilitates kinetics of oxide film growth on AA 5052 at 25° and 60 °C which is indicative of formation of a thick barrier film that leads to an increment in the charge transfer resistance. Pitting incubation time increases by introduction of H₂O₂ accompanied by lower pitting and smoother surface morphologies. At short exposure (up to 8 h) to H₂O₂–containing solution, the inductive response at low frequencies predominantly determined the corrosion mechanism of AA5052. On the other hand, at prolonged exposure times (more than 24 h) to 0.25M Na₂SO₄+1vol% H₂O₂ solution, thicker oxide layers resulted in the mixed inductive–Warburg elements in the spectra.     

Pearlite determination in plain carbon steel by eddy current method

Eddy current method has been used for the evaluation of pearlitic microstructure in low to high plain carbon steels. Plain carbon steel samples were heat treated in a furnace. Half of these were slowly cooled in the furnace and half in the air. This resulted in different pearlitic microstructures in the samples. Eddy current readings for all the samples were recorded and studied. It was found that eddy current measurement can be used for obtaining reliable and quick detection of pearlitic percentage in plain carbon steels.     

Behavior of 316L stainless steel containing corrosion pits under cyclic loading

The environmental performance of 316L grade stainless steel, in the form of tensile specimens containing a single corrosion pit with various aspect ratios, under cyclic loading in aerated chloride solutions is investigated in this study. Results from environmental tests were compared and contrasted with those obtained using finite element analysis (FEA). Fractography of the failed specimens obtained from experiments revealed that fatigue crack initiation took place at the base of the shallow pit. The crack initiation shifted towards the shoulder and the mouth of the pit for pits of increasing depth. This process is well predicted by FEA, as the strain contour maps show that strain is the highest around the centric strip of the pit. However, for shallow pits, local strain is uniformly distributed around that strip but begins to concentrate more towards the shoulder and the mouth region for increasingly deep pits.     

New procedure to calculate the Hansen solubility parameters of polymers

The simplest experimental method to determine the Hansen solubility parameters (HSPs) for a polymer is to evaluate whether or not it dissolves in selected solvents. Those solvents dissolving the polymer will have HSPs closer to those of the polymer than those that do not. A computer program or graphical method can then be used to find the HSP for the polymer. In this work, an improved method for calculating the HSP of polymers, based on the Nelder–Mead optimization algorithm, is presented. The results of this program fit the data very well. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 31–36, 2007     

Investigation in Mathematical Models of Chloride Diffusion Coefficient in Concrete Exposed to Marine Environment

Degradation of RC （reinforced concrete） in maritime structures has become a worldwide problem due to its excessive costs of maintenance, repair and replacement in addition to its environmental impacts and safety issues. Degradation of both concrete and steel which is the main reason of reduction in the service life of RC structures strongly depends on the diffusion process of moisture and aggressive species. In this paper, the major and popular mathematical models of diffusion process in concrete are surveyed and investigated. Predominantly in these models, the coefficient of chloride diffusion into the concrete is assumed to be constant. Whereas, experimental records indicate that diffusion coefficient is a function of time. Subsequently, data analysis and comparisons between the existing analytical models for predicting the diffusion coefficient with the existing experimental database are carried out in this study. Clearly, these comparisons reveal that there are gaps between the existing mathematical models and previously recorded experimental results. Perhaps, these gaps may be interpreted as influence of the other affecting parameters on the diffusion coefficient such as temperature, aggregate size and relative humidity in addition to the water cement ratio. Accordingly, the existing mathematical models are not adequate enough to predict the diffusion coefficient precisely and further studies need to be performed.     

New moment-rotation equation for welded steel beam-to-column connections

A three-parameter tangent inverse equation is generically proposed for the non-linear moment-rotation (M-θ) relationship of semi-rigid steel beam-to-column connections. The parameters are the initial stiffness, the plastic stiffness, and a reference moment. Two commonly used welded moment connections are picked up for moment-rotation calculation and comparison between the results of the proposed model and those of a detailed nonlinear finite elements modeling. Semi-analytical equations are proposed for calculating the parameters containing basic factors affecting behavior of the connections. The coefficients of the equations are computed based on a data bank developed in this study using the finite element method. A large number of finite elements models covering the whole range of common dimensions of the above connections are analyzed. Accuracy of the finite element model is verified on the basis of the available test results from previous studies. Tensile tests for determination of material properties of weld to be used in the modeling are conducted. Comparison between the results of the semi-analytical equations and the finite element models shows that the proposed model is able to estimate the moment-rotation curves of the welded beam-to-column connections with very good accuracy.