An inventory of Lattice Boltzmann models of multiphase flows

This document reports investigations of models of multiphase flows using Lattice Boltzmann methods. The emphasis is on deriving by Chapman-Enskog techniques the corresponding macroscopic equations. The singular interface (Young-Laplace-Gauss) model is described briefly, with a discussion of its limitations. The diffuse interface theory is discussed in more detail, and shown to lead to the singular interface model in the proper asymptotic limit. The Lattice Boltzmann method is presented in its simplest form appropriate for an ideal gas. Four different Lattice Boltzmann models for non-ideal (multi-phase) isothermal flows are then presented in detail, and the resulting macroscopic equations derived. Partly in contradiction with the published literature, it is found that only one of the models gives physically fully acceptable equations. The form of the equation of state for a multiphase system in the density interval above the coexistance line determines surface tension and interface thickness in the diffuse interface theory. The use of this relation for optimizing a numerical model is discussed. The extension of Lattice Boltzmann methods to the non-isothermal situation is discussed summarily.Comment: 59 pages, 5 figure

Effects of international gold market on stock exchange volatility: evidence from asean emerging stock markets

This paper examines behaviors of returns and volatility of ASEAN emerging stock markets (Indonesia, Malaysia, Philippines, Thailand and Vietnam), incorporating with the effects from the international gold market. The estimates of GARCH(1,1) and GJR(1,1) for these stock markets indicate that the GJR(1,1) model is preferred to GARCH(1,1), except Vietnam. However, under the exogenous effects from international gold market such as the 1 day lagged returns and the 1 day lagged volatility of gold, the GARCH(1,1)-X model captures better stock market volatility behavior than GJR(1,1)-X, except Indonesia. Interestingly, gold could be a substitute commodity for stocks in Vietnam and the Philippines, while it could be a complement for stocks in Indonesia, Thailand and Malaysia.Volatility, GARCH-X, Gold effects, ASEAN emerging stock markets

A Forensically Sound Adversary Model for Mobile Devices

In this paper, we propose an adversary model to facilitate forensic investigations of mobile devices (e.g. Android, iOS and Windows smartphones) that can be readily adapted to the latest mobile device technologies. This is essential given the ongoing and rapidly changing nature of mobile device technologies. An integral principle and significant constraint upon forensic practitioners is that of forensic soundness. Our adversary model specifically considers and integrates the constraints of forensic soundness on the adversary, in our case, a forensic practitioner. One construction of the adversary model is an evidence collection and analysis methodology for Android devices. Using the methodology with six popular cloud apps, we were successful in extracting various information of forensic interest in both the external and internal storage of the mobile device

The DKAP Project The Country Report of Vietnam

Viet Nam is at the beginning of the Fourth Industrial Revolution. In order to grasp the opportunities that the revolution has brought about, and to successfully build the society of digital citizens, there must be the demand of enhancing the capacity and capability for students to meet international standards in terms of Information and Communications Technology (ICT) skills. Viet Nam was selected as one of the four countries (Viet Nam, Bangladesh, Fiji, and the Republic of Korea) to join UNESCO Bangkok’s “Digital Kids Asia Pacific (DKAP)” project, a comparative cross-national study with the aim to seek the understanding and address children’s ICT practices, attitudes, behaviors, and competency levels within an educational context. Thanks to the project, the Vietnamese research team completely conducted the survey in twenty (20) schools from five (5) provinces in Viet Nam. With the data on the digital citizenship competency levels of 1,061 10th grade students, the research team discovered the valuable findings to draw an initial big picture for Vietnamese policy makers, educators, and teachers about digital citizenship competencies of 15-year-old Vietnamese students

Locomotion by tangential deformation in a polymeric fluid

In several biologically relevant situations, cell locomotion occurs in polymeric fluids with Weissenberg {number} larger than one. Here we present results of three-dimensional numerical simulations for the steady locomotion of a self-propelled body in a model polymeric (Giesekus) fluid at low Reynolds number. Locomotion is driven by steady tangential deformation at the surface of the body (so-called squirming motion). In the case of a spherical squirmer, we show that the swimming velocity is systematically less than that in a Newtonian fluid, with a minimum occurring for Weissenberg numbers of order one. The rate of work done by the swimmer always goes up compared to that occurring in the Newtonian solvent alone, but is always lower than the power necessary to swim in a Newtonian fluid with the same viscosity. The swimming efficiency, defined as the ratio between the rate of work necessary to pull the body at the swimming speed in the same fluid and the rate of work done by swimming, is found to always be increased in a polymeric fluid. Further analysis reveals that polymeric stresses break the Newtonian front-back symmetry in the flow profile around the body. In particular, a strong negative elastic wake is present behind the swimmer, which correlates with strong polymer stretching, and its intensity increases with Weissenberg number and viscosity contrasts. {The velocity induced by the squirmer is found to decay in space faster than} in a Newtonian flow, with a strong {dependence} on the polymer relaxation time and viscosity. Our computational results are also extended to prolate spheroidal swimmers and smaller polymer stretching are obtained for slender shapes compared to bluff swimmers. The swimmer with an aspect ratio of two is found to be the most hydrodynamically efficient

A Neural Network Analysis of the Effect of Age on Housing Values

Empirical studies using multiple regression find the value of a residential property declines with its age. Because these results confirm the fact of physical deterioration of a house over time, little attention is paid to the statistical technique's inherent shortcomings. Accordingly, this paper uses a neural network, which is able to overcome multiple regression's methodological problems, to re-examine the effect of age on a house's value. We find that a negative relationship of value to age holds only for the first sixteen to twenty years of the life of a house. Then, not only does the decline in value stop, but a house actually starts to experience appreciation related, in part, to its lot size.

PES in upper-catchments of Vietnam : expected differential impact for contrasted farmers

In most upper-catchments of the Northern provinces of Vietnam current land uses are producing negative externalities that affect downstream areas. Slash-and-burn is often blamed as the main cause for the problem. Land uses that would bring about environmental benefits include tree-based land use alternatives and agro-ecological practices (e.g. direct-seeded mulching cropping systems). However, the environmental services these alternative land uses would provide are un-rewarded. Payments for Environmental Services (PES) schemes present a new approach that focuses on creating a conditional benefit transfer between the upland providers of environmental services and the downstream beneficiaries. Agricultural households in upper-catchments have unequal access to natural resources, inducing contrasted farming practices and livelihood strategies. Our main objective was to evaluate the response of contrasted households to PES schemes that would reward them when they set aside some land for forestry projects. We looked at the specificity of PES schemes targeted at agricultural households of the upper-catchments in Northern Vietnam. Based on farm typologies developed earlier and using a simplified farm model, we analyzed how households with different endowments would respond to such PES schemes. (Résumé d'auteur