Reduction of spurious velocity in finite difference lattice Boltzmann models for liquid - vapor systems

The origin of the spurious interface velocity in finite difference lattice Boltzmann models for liquid - vapor systems is related to the first order upwind scheme used to compute the space derivatives in the evolution equations. A correction force term is introduced to eliminate the spurious velocity. The correction term helps to recover sharp interfaces and sets the phase diagram close to the one derived using the Maxwell construction.Comment: 22 pages, 10 figures (submitted to International Journal of Modern Physics C- Physics and Computers

A lattice Boltzmann study of phase separation in liquid-vapor systems with gravity

Phase separation of a two-dimensional van der Waals fluid subject to a gravitational force is studied by numerical simulations based on lattice Boltzmann methods (LBM) implemented with a finite difference scheme. A growth exponent $\alpha=1$ is measured in the direction of the external force.Comment: To appear in Communications in Computational Physics (CiCP

Investigating the Impact of Social Interactions in Adaptive E-Learning by Learning Behaviour Analysis

Adaptive Educational Hypermedia Systems (AEHSs) allow for personalization of e-learning. Social media tools enable learners to create, publish and share their study, and facilitate interaction and collaboration. The integration of social media tools into AEHS offers novel opportunities for learner engagement and extended user modelling, and thereby fosters so-called Social Personalized Adaptive E-learning Environments (SPAEEs). However, there has been a lack of empirical design and evaluation to elaborate methods for SPAEEs. The goal of the research, therefore, is to investigate 1) the learning behaviour patterns within SPAEEs and the use of these patterns for learner engagement, 2) the evaluation methodologies for SPAEEs, and 3) the design principles for SPAEEs. Topolor4 is an SPAEE that has been under iterative development for achieving our research goals. The first prototype was used as an online learning system for MSc level students in the Department of Computer Science, at the University of Warwick, and usage data was anonymously collected for analysis. This poster focuses on system features and learning behaviour analysis. We first present the methodologies applied in the research, followed by the social and adaptive features that Topolor provides. Then we revisit the analysis of learning behaviours. Finally, we propose the follow-up work based on the evaluation results

Social E-Learning in Topolor: a Case Study

Social e-learning is a process through which learners achieve their learning goals via social interactions with each other by sharing knowledge, skills, abilities and educational materials. Adaptive e-learning enables adaptation and personalization of the learning process, based on learner needs, knowledge, preferences and other characteristics. In this paper, we present a case study that analyzes the social interaction features of a social personalized adaptive e-learning system developed at the University of Warwick, called Topolor. We discuss the results of a quantitative case study that evaluates the perceived usefulness and usability. The results demonstrate a generally high level of learner satisfaction with their learning experience. We extend the discussion of the results to explore future research directions and suggest further improvements for the studied social personalized adaptive e-learning system

To Build Light Gamification upon Social Interactions: Requirement Analysis for the Next Version of Topolor

The introduction of social dimension enables traditional adaptive educational hypermedia systems to provide more versatile personalized services. Topolor has been developed to investigate the impacts of social interaction and feasible engagement strategies in such a system. We have evaluated Topolor’s social features from the perspectives of usefulness and ease of use. We intend to develop the next version of Topolor, starting with enhancing relatively lower rated social features. This paper presents our plan of building light gamification upon the evaluated social interaction features with relatively lower rating

Creep-Fatigue Crack Growth in Power Plant Components

In components operating at high temperature, the presence of defect, that may derive from manufacturing process or operating under critical conditions, could raise to creep-fatigue crack growth even at low loading conditions. Creep- fatigue experimental tests have been performed on P91 material, at 600 °C according to ASTM E2760-10 standard, with focus on the effects of the initial nominal stress intensity factor range, ranging between 16 and 22 MPa m 0.5, and the hold time, ranging between 0.1 and 10 hours. The results will be presented in the paper, together with their application for residual life prediction of a power plant cracked pipe, as case study

A Social Personalized Adaptive E-Learning Environment: A Case Study in Topolor

Adaptive e-Learning is a process where learning contents are delivered to learners adaptively, namely, the appropriate contents are delivered to the learners in an appropriate way at an appropriate time based on the learners' needs, knowledge, preferences and other characteristics. Social e-Learning is a process where connections are made among like-minded learners, so they can achieve learning goals via communication and interaction with each other by sharing knowledge, skills, abilities and materials. This paper reports an extended case study that investigated the influence of social interactions in an adaptive e-Learning environment, by analyzing the usage of social interaction features of a Social Personalized Adaptive E-Learning Environment (SPAEE), named Topolor, which strives to combine the advantages from both social e-Learning and adaptive e-Learning. We present the results of a quantitative case study that evaluates the perceived usefulness and ease of use. The results indicated high satisfaction from the students who were using Topolor for their study and helped us with the evaluation processes. Based on the results, we discuss the follow-up work plan for the further improvements for Topolor

On the number of solutions of a transcendental equation arising in the theory of gravitational lensing

The equation in the title describes the number of bright images of a point source under lensing by an elliptic object with isothermal density. We prove that this equation has at most 6 solutions. Any number of solutions from 1 to 6 can actually occur.Comment: 26 pages, 12 figure

Lattice Boltzmann study on Kelvin-Helmholtz instability: the roles of velocity and density gradients

A two-dimensional lattice Boltzmann model with 19 discrete velocities for compressible Euler equations is proposed (D2V19-LBM). The fifth-order Weighted Essentially Non-Oscillatory (5th-WENO) finite difference scheme is employed to calculate the convection term of the lattice Boltzmann equation. The validity of the model is verified by comparing simulation results of the Sod shock tube with its corresponding analytical solutions. The velocity and density gradient effects on the Kelvin-Helmholtz instability (KHI) are investigated using the proposed model. Sharp density contours are obtained in our simulations. It is found that, the linear growth rate $\gamma$ for the KHI decreases with increasing the width of velocity transition layer ${D_{v}}$ but increases with increasing the width of density transition layer ${D_{\rho}}$. After the initial transient period and before the vortex has been well formed, the linear growth rates, $\gamma_v$ and $\gamma_{\rho}$, vary with ${D_{v}}$ and ${D_{\rho}}$ approximately in the following way, $\ln\gamma_{v}=a-bD_{v}$ and $\gamma_{\rho}=c+e\ln D_{\rho} ({D_{\rho}}<{D_{\rho}^{E}})$, where $a$, $b$, $c$ and $e$ are fitting parameters and ${D_{\rho}^{E}}$ is the effective interaction width of density transition layer. When ${D_{\rho}}>{D_{\rho}^{E}}$ the linear growth rate $\gamma_{\rho}$ does not vary significantly any more. One can use the hybrid effects of velocity and density transition layers to stabilize the KHI. Our numerical simulation results are in general agreement with the analytical results [L. F. Wang, \emph{et al.}, Phys. Plasma \textbf{17}, 042103 (2010)].Comment: Accepted for publication in PR