Corrosion scale dynamics

This work presents a methodology for simulating ionic and electronic grain boundary transport through thin films, scales or membranes with columnar grain structure. In the model developed the grain structure is idealized as a lattice of identical hexagonal cells - a honeycomb pattern. Reactions with the environment constitute the boundary conditions and drive the transport between the surfaces. Time-dependent simulations solving the Poisson equation self-consistently with the Nernst-Planck flux equations for the mobile species are performed. In the resulting Poisson-Nernst-Planck system of equations, the electrostatic potential is obtained from the Poisson equation in its integral form by summation. An object oriented C++ code has been implemented to solve the system of equations numerically. First, the model is used to interpret alumina membrane oxygen permeation experiments, in which different oxygen gas pressures are applied at opposite membrane surfaces and the resulting flux of oxygen molecules through the membrane is measured. Simulation results involving four mobile species, charged aluminum and oxygen vacancies, electrons, and holes, provide a complete description of the measurements. Second, the model is extended to simulate internal oxidation and stress generation within a thin film of alumina at conditions of high-temperature metal oxidation. The steady-state stresses predicted are compatible with experimental measurements of lateral growth stresses in alumina scale growth experiments. The hypothesized p-n ionic transition within the alumina grain boundaries is observed. In limiting cases the more general simulations are closely related to the Wagner theory of metal oxidation. The Wagner theory assumes local ionic equilibrium while the simulation results demonstrate the possibility of a significant deviation from local Schottky equilibrium within an oxide scale at conditions of steady-state growth. The deviation is related to stress generation, and limits the applicability of the Wagner theory.Open Acces

An overview of video recommender systems: state-of-the-art and research issues

Video platforms have become indispensable components within a diverse range of applications, serving various purposes in entertainment, e-learning, corporate training, online documentation, and news provision. As the volume and complexity of video content continue to grow, the need for personalized access features becomes an inevitable requirement to ensure efficient content consumption. To address this need, recommender systems have emerged as helpful tools providing personalized video access. By leveraging past user-specific video consumption data and the preferences of similar users, these systems excel in recommending videos that are highly relevant to individual users. This article presents a comprehensive overview of the current state of video recommender systems (VRS), exploring the algorithms used, their applications, and related aspects. In addition to an in-depth analysis of existing approaches, this review also addresses unresolved research challenges within this domain. These unexplored areas offer exciting opportunities for advancements and innovations, aiming to enhance the accuracy and effectiveness of personalized video recommendations. Overall, this article serves as a valuable resource for researchers, practitioners, and stakeholders in the video domain. It offers insights into cutting-edge algorithms, successful applications, and areas that merit further exploration to advance the field of video recommendation

Tool-support for the analysis of hybrid systems and models

This paper introduces a method and tool-support for the automatic analysis and verification of hybrid and embedded control systems, whose continuous dynamics are often modelled using MATLAB/Simulink. The method is based upon converting system models into the uniform input language of our efficient multi-domain constraint solving library, ABSOLVER, which is then used for subsequent analysis. Basically, ABSOLVER is an extensible SMT-solver which addresses mixed Boolean and (nonlinear) arithmetic constraint problems as they appear in the design of hybrid control systems. It allows the integration and semantic connection of various domain specific solvers via a logical circuit, such that almost arbitrary multi-domain constraint problems can be formulated and solved. Its design has been tailored for extensibility, and thus facilitates the reuse of expert knowledge, in that the most appropriate solver for a given task can be integrated and used. As such the only constraint over the problem domain is the capability of the employed solvers. Our approach to systems verification has been validated in an industrial case study using the model of a car’s steering control system. However, additional benchmarks show that other hard instances of problems could also be solved by ABSOLVER in respectable time, and that for some instances, ABSOLVER’s approach was the only means of solving a problem at all.