Search results for "Dynamic"

Zone of Proximal Development (ZPD) as an Emergent System: A Dynamic Systems Theory Perspective

2016

This paper sets out to present a novel construal of one of the notions of Vygotskian cultural-historical theory viz., zone of proximal development (ZPD) drawing upon dynamic systems theory. The principal thesis maintains that ZDP is an emergent and dynamic system which is engendered by a dialectical concatenation of psychogenesic and sociogenesic facets of human development over time. It is reasoned that Vygotskian cultural-historical theory of human development, by invoking dialectical logic, has transcended Cartesian substance dualism and in turn has proffered a monistic and process-anchored ontology for emerging becoming of human consciousness. Likewise, it is contended that dynamic syst…

A phenomenological approach to the mechanical breakdown of anodic oxide films on zirconium

1986

Abstract A phenomenological theory of the mechanical breakdown of films growing on valve metals during galvanostatic oxidation is presented and discussed in detail for ZrO2 anodic films. It is shown that the mechanical breakdown voltage, Vmb, can be linearly related to the logarithm of the anodizing current density both in the case of constant and variable critical thickness, Lc, at which the breakdown occurs. It is also shown that the Amb and Bmb parameters of the relationship: Vmb = Amb + Bmb log i are strictly related to the kinetic parameters of growth of the films in the different solutions. The expressions of Amb and Bmb parameters are derived for films grown in the presence as well a…

An Interfacial Thermodynamic Model for the Oxidation Kinetics of a Metal: Epitaxial Stress Effects

2004

Mechanical Stresses: Inhibitor of Catalyst of High Temperature Oxidation?

2001

Oxidation of metals is a complex reaction in which mechanical and chemical phenomena occur. A dynamic and macroscopic model is developed in order to simulate oxidation kinetics of a metal. It includes the stress/diffusion coupling in the bulk and the interfacial phenomena at metal/oxide interface. Its application to the Zr/ZrO 2 system shows the important role of stress field distribution in oxide on kinetic behavior. According to the sign of stress gradient in the oxide scale, the oxidation rate can speed up or slow down. The calculated kinetic curves could he fitted using a k p .t 1/n law where n and kp vary all over the process, like for the experimental kinetic curves.

Flash synthesis of zirconia nanoparticles by microwave forced hydrolysis

2001

Forced hydrolysis preparation of zirconia sols and powders by microwave heating of zirconium tetrachloride solutions at temperatures equal to 180 °C leads in a few minutes to monodispersed nanoscale zirconia particles. Synthesis was performed in a microwave reactor called the RAMO system. This microwave reactor was designed by the authors. This flash-synthesis process combines the advantages of forced hydrolysis (homogeneous precipitation) and microwave heating (very fast heating rates). The sols and powders were characterized by x-ray diffraction,photon correlation spectroscopy (PCS), small-angle x-ray scattering, and transmission electron microscopy. Sols are colloidally stable, which mea…

Y:BaZrO 3 Perovskite Compounds II: Designing Protonic Conduction by using MD Models

2011

The proton dynamics in Y-doped BaZrO(3) derivatives, in particular the different dopant environments within a Pm3m cubic framework, were studied by using classical molecular dynamics (MD) calculations. Single- and double substitution of zirconium by yttrium atoms was considered. The presence of yttrium induced variations in the surrounding oxygen sites, according to their local geometrical arrangements. The differences among such distinct oxygen sites became evident when protons interacted with them and upon changes in the temperature. So, different proton transfer pathways, which had different energy barriers, characterized the topologically different oxygen sites. The experimental proton-…

Fast Secure Routing for Highly Mobile Large-Scale Ad-Hoc Vehicular Networks

2009

In highly mobile large-scale vehicular ad-hoc networks, routing protocols must be fast and efficient in terms of low routing discovery delay and communication overhead to support the applications such as car talk. Such requirement becomes more difficult to achieve when inducing security enhancement to tackle the authentication of routing messages. In this paper, we propose a lightweight (fast) secure routing protocol, Secure Proactive Tree-based Routing (SPTR) to hit these two points. SPTR makes use of the characteristics of VANET networks, that is, the traffic originates from or terminates at the gateway or road side unit. SPRT also takes advantages of certificate-less ID-based cryptograph…

Multipath extensions to the DYMO routing protocol

2007

Multipath routing is a technique that can improve performance, specially in mobile ad hoc networks. Due to traffic dispersion it can perform load balancing; minimize the energy consumed by nodes or prevent traffic analysis. In this work we focus on enhancing the DYMO protocol to support multipath routing. We study the impact of traffic dispersion on both UDP and TCP traffic when varying a set of parameters.

New treatment for stress urinary incontinence

2003

Objective: The aim of this study is to evaluate the safety and efficacy of the Zuidex implacement for the treatment of type III incontinence. Methods: We evaluated 36 women (median age 51) with type III ( MUCP<20 cm H2O and VLPP<60 cm H2O), with fixed urethra demonstrated (Delta Value<30 at Q-tip test). 21 (58.3%) had undergone previous continence surgery .They were recluted by a complete urogynaecological work-up( Vaginal profile, Q- tip test, Endoscopy and Urodynamic study, one hour Pad test, Ultrasonography). We defined as cured patients that were dry after the implant was performed, and as improved those who decreased in number of pads and symptoms.We underwent all patients an intrauret…

LC3 A Spatial-temporal Data Model to Study Qualified Land Cover Changes

2015

International audience; Land cover changes caused by humans have reached points never witnessed in history before. Consequences of these changes are environmental degradation, pollution of water, biodiversity loss and climate change among others. It is in this frame that the interest of the scientific community for this type of events has increased in the last decades. Nowadays, researchers have access to sophisticated monitoring tools and techniques. However, the new threat is that over abundance of information would hide relevant facts and processes. In our research we use data from the CORINE (Coordination of Information on the Environment) program. This program has compiled land cover i…