The Effects of Atmospheric Heat Treatments on TiO\u3csub\u3e2\u3c/sub\u3e Nanotube Anodes for Lithium-Ion Batteries

The effects of various heat treatments on the physical and electrochemical properties of anatase TiO2 nanotubes were studied in this work. Well-ordered TiO2 nanotubes were grown via electrochemical anodization and annealed at 450°C to induce a phase transformation to anatase. The heat treatments were conducted under atmospheres of O2, Ar, N2, and water vapor (WV) to create different point defects. The oxygen-deficient atmospheres were used to generate oxygen vacancies in the TiO2 nanotubes, while the water vapor treatment was used to create Ti vacancies by stabilizing them via the protonation of O sites. Computational models of anatase TiO2 with oxygen or titanium vacancies were created to predict the effect of the defects on the band structure and electrical properties. Two-point conductivity measurements and Mott-Schottky characterizations were conducted to evaluate the electrical conductivity and charge carrier concentration of TiO2 nanotube samples and compared to the predicted effects of the heat treatments. Scanning electron microscopy and x-ray diffraction were used to study the nanostructure morphology. Additional characterization techniques such as Raman spectroscopy were used to study the generation of the respective point defects. The anatase nanotubes synthesized under different atmospheres were then used as anodes in lithium-ion batteries. The N2- and WV-treated samples exhibited the largest increase in capacity, while the Ar-treated sample had a slight capacity increase compared to the stoichiometric O2-treated control sample. Further electrochemical testing revealed that the WV-treated sample had the highest Li diffusivity

On the moving contact line singularity: Asymptotics of a diffuse-interface model

The behaviour of a solid-liquid-gas system near the three-phase contact line is considered using a diffuse-interface model with no-slip at the solid and where the fluid phase is specified by a continuous density field. Relaxation of the classical approach of a sharp liquid-gas interface and careful examination of the asymptotic behaviour as the contact line is approached is shown to resolve the stress and pressure singularities associated with the moving contact line problem. Various features of the model are scrutinised, alongside extensions to incorporate slip, finite-time relaxation of the chemical potential, or a precursor film at the wall.Comment: 14 pages, 3 figure

A comparison of slip, disjoining pressure, and interface formation models for contact line motion through asymptotic analysis of thin two-dimensional droplet spreading

The motion of a contact line is examined, and comparisons drawn, for a variety of models proposed in the literature. Pressure and stress behaviours at the contact line are examined in the prototype system of quasistatic spreading of a thin two-dimensional droplet on a planar substrate. The models analysed include three disjoining pressure models based on van der Waals interactions, a model introduced for polar fluids, and a liquid-gas diffuse-interface model; Navier-slip and two non-linear slip models are investigated, with three microscopic contact angle boundary conditions imposed (two of these contact angle conditions having a contact line velocity dependence); and the interface formation model is also considered. In certain parameter regimes it is shown that all of the models predict the same quasistatic droplet spreading behaviour.Comment: 29 pages, 3 figures, J. Eng. Math. 201

The contact line behaviour of solid-liquid-gas diffuse-interface models

A solid-liquid-gas moving contact line is considered through a diffuse-interface model with the classical boundary condition of no-slip at the solid surface. Examination of the asymptotic behaviour as the contact line is approached shows that the relaxation of the classical model of a sharp liquid-gas interface, whilst retaining the no-slip condition, resolves the stress and pressure singularities associated with the moving contact line problem while the fluid velocity is well defined (not multi-valued). The moving contact line behaviour is analysed for a general problem relevant for any density dependent dynamic viscosity and volume viscosity, and for general microscopic contact angle and double well free-energy forms. Away from the contact line, analysis of the diffuse-interface model shows that the Navier--Stokes equations and classical interfacial boundary conditions are obtained at leading order in the sharp-interface limit, justifying the creeping flow problem imposed in an intermediate region in the seminal work of Seppecher [Int. J. Eng. Sci. 34, 977--992 (1996)]. Corrections to Seppecher's work are given, as an incorrect solution form was originally used.Comment: 33 pages, 3 figure

PROMOTING INTERACTIVITY AND CREATIVITY IN A SCIENCE COURSE

Young people entering the working force are nowadays required to compete not only on skills and education but also on creative thinking. This is because creativity and innovation are a must for businesses and nations which, today more than ever, are required to compete on the creative use of the scarce resources and the identification of new ones. Thus, promoting creative thinking among students, individually and collectively, is an educator’s challenge. This paper presents the efforts made to promote creative thinking in a Human Computer Interaction course and the students’ evaluation of these efforts

A Tool For Teaching Spline Methods In A Computer Graphics Course

The specialized mathematics knowledge covered in a computer graphics course is usually presented to students in an abstract way. Albeit, computer graphics is an application of this (abstract) mathematics, students may find it hard to link them together. In particular one of the most difficult topics to present in a pedagogical manner to junior students in a computer graphics course is spline methods (mathematical method for data smoothing) used for curve/surface modelling. This topic involves mainly the mathematics of parametric functions, piecewise functions, derivatives, matrices, and parametric/geometric continuities. Usually a student has a vague picture of the actual output of the application of this mathematics. Many educators have experienced that students may fully understand splines application, if and when they are assigned a software project to implement splines, and this understanding could still remain vague until the very last stages of the implementation. As an alternative, static pictures may be presented in class to provide an intuitive understanding of splines. This approach is, in effect, similar to viewing a picture in a textbook. A better alternative is for the educator to demonstrate real-time spline generation, since a picture is worth ten thousand words but a moving picture (animation) is worth ten thousand static ones. This paper presents an interactive software program which is used as a tool to introduce important concepts and algorithms of spline methods to computer science and computer engineering students. The software is specially developed for educational purposes, and generates spline curves

Understanding accessibility problems of blind users on the web

The web is an eminently visual medium. However, not everyone accesses web content visually. Research shows that using the web is challenging for blind users. To create a good user experience for blind users on the web, we need a comprehensive understanding of the users’ problems. Currently, there is little knowledge about the problem differences between blind and sighted users, which makes it difficult to suggest and test design solutions that address these problems. This research aims to provide a further understanding of the problems blind users have on the web by comparing and contrasting problems between blind and sighted users and testing how design solutions to prevalent problems benefit blind users’ experience. The first study draws together the research literature into a common unified definition of web accessibility that was used to operationalise studies. The second study compared which verbal protocol (concurrent or retrospective) is better in user-based studies. The results showed that retrospective verbal protocol is a better option for eliciting problems on the web for blind and sighted users. Then, an empirical study compared the problems between blind and sighted users on the web. The results showed that the problems the two user groups encounter largely differ. There are specific problem types distinct to blind users, but also the characteristics of the problem types that had instances by both user groups were very different. Moreover, many problems blind users encounter were in relation to the search and browse features of the websites. A further investigation by two studies with blind users of how specific design solutions to prevalent problems users had (poor page structure, lack of feedback and excessive effort) in this specific design aspect showed that simple design solutions improve specific aspects of users’ experience. Although, for major improvements in the overall user experience a combination of design solutions is needed