Les niobates CaUNb2O8 et MThNb2O8 (M = Ca,Sr, Cd). Etude des transformations monoclinique - quadratique

New compounds M^IIThNb₂O₈ with M^II = Ca, Sr, Cd, and CaUNb₂O₈ have been prepared by solid state reaction. These compounds isotypic with the rare-earth niobates LnNbO₄ cristallize in a monoclinic system with space group I2/c. Like the niobates LnNbO₄, they present a displacive and non quenchable transition (monoclinic to tetragonal) which is probably of second order.     

Measurements of the behavioral effects of albino mutation in mice (Mus musculus): Comparisons of coisogenic inbred and hybrid lines.

The effects of the albino gene on mouse behavior were examined, particularly its possible interactions with nonallelic genes (epistasis). More generally, the possible effects of genetic background (inbreeding depression or hybrid vigor) on the effects of the mutation were also considered. Tasks requiring either predominantly motor or predominantly cognitive capacity were studied for coisogenic albino and pigmented mice from either an inbred strain (C57BL/6 c/c vs C57BL/6 +/c) or an F? heterozygous generation (F? c/c vs F? +/c) from a BALB/c?×?C57BL/6 +/c cross. Results show a clear albino gene effect in the 2 lines and provide further evidence that the gene is the effective factor. There was no significant interaction between the mutation and the genotypic group (C57BL/6 or F?), which indicates that the effects of the mutation act approximately in an additive fashion between loci in these groups. (13 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Study of the oxidation kinetics of finely-divided magnetites. II - Influence of chromium substitution

The oxidation kinetics of magnetites substituted by chromium (Fe²⁺Fe³⁺_2?xCr³⁺_x)O^2?₄ (0 < x < 2) into γ(Fe³⁺_1?yCr³⁺_y)₂O^2?₃, (x = 3y), which is a metastable phase, was found out to be ruled by the law of diffusion, under variable working conditions, of vacancies generated at the surface. The chemical diffusion coefficient is a function of the substitution ratio, crystallite size and the number of vacancies in the spinel lattice. Contrary to magnetites substituted by aluminum, the activation energy varies irregularly with the substitution ratio.     

Study of the Action of Static and Dynamic Fusimotor Fibers With a Mechanical Model of the Mammalian Muscle Spindle

A model of the mammalian muscle spindle having three distinct parts is proposed. The three parts, which consist of a mechanical filter, a transducer, and an encoder, are closely related with their physiological counterparts. A study of the generator potentials for the primary and secondary endings of the spindle was performed by means of an analog computer simulation of the model. The afferent responses of the spindle under a phasic stretch with and without fusimotor fibers simulation are also studied. Finally, frequencygrams (see text) are obtained under the condition of ?1 (dynamic) stimulation acting on both nuclear bag and nuclear chain fibers. The model yields results that are directly comparable with physiological data obtained under similar conditions.     

Resonator stability subject to dynamic random-tilt aberration

We derive the behavior of the average exit time (i.e., the number of reflections before escape) of a ray path traveling between two perfect mirrors subject to dynamic random-tilt aberrations. Our calculation is performed in the paraxial approximation. When small random tilts are taken into account, we may consider an asymptotic regime that generically reduces the problem to the study of the exit time from an interval for a harmonic, frictionless oscillator driven by Gaussian white noise. Despite its apparent simplicity, the exact solution of this problem remains an open mathematical challenge, and we propose here a simple approximation scheme. For flat mirrors, the natural frequency of the oscillator vanishes, and, in this case, the average exit time is known exactly. It exhibits a 2/3 scaling-law behavior in terms of the variance of the random tilts. This behavior also follows from our approximation scheme, which establishes the consistency of the scaling law. Our mathematical results are confirmed with simulation experiments.     

Towards efficient data distribution on computational desktop grids with BitTorrent

Datacentric applications are still a challenging issue for large-scale distributed computing systems. The emergence of new protocols and software for collaborative content distribution over the Internet offers a new opportunity for efficient and fast delivery of a high volume of data. This paper presents an evaluation of the BitTorrent protocol for computational desktop grids. We first present a prototype of a generic subsystem dedicated to data management and designed to serve as a building block for any desktop grid system. Based on this prototype we conduct experiments to evaluate the potential of BitTorrent compared to a classical approach based on FTP data server. The preliminary results obtained with a 65-node cluster measure the basic characteristics of BitTorrent in terms of latency and bandwidth and evaluate the scalability of BitTorrent for the delivery of large input files. Moreover, we show that BitTorrent has a considerable latency overhead compared to FTP but clearly outperforms FTP when distributing large files or files to a high number of nodes. Tests on a synthetic application show that BitTorrent significantly increases the communication/computation ratio of the applications eligible to run on a desktop grid system.     

Extension of the Hansen-Bliek Method to Right-Quantified Linear Systems

The problem of finding the smallest box enclosing the united solution set of a linear interval system, also known as the “interval hull” problem, was proven to be NP-hard. However, Hansen, Bliek, and others subsequently, have provided a polynomial-time solution in the case of systems preconditioned by the midpoint inverse matrix. Based upon a similar approach, this paper deals with the interval hull problem in the context of AE-solution sets, where parameters may be given different quantifiers. A polynomial-time algorithm is proposed for computing the hull of AE-solution sets where parameters involved in the matrix are constrained to be existentially quantified. Such AE-solution sets are called right-quantified solution sets. They have recently been shown to be of practical interest.     

Well-structured languages

This paper introduces the notion of well-structured language. A well-structured language can be defined by a labelled well-structured transition system, equipped with an upward-closed set of accepting states. That peculiar class of transition systems has been extensively studied in the field of computer-aided verification, where it has direct an important applications. Petri nets, and their monotonic extensions (like Petri nets with non-blocking arcs or Petri nets with transfer arcs), for instance, are special subclasses of well-structured transition systems. We show that the class of well-structured languages enjoy several important closure properties. We propose several pumping lemmata that are applicable respectively to the whole class of well-structured languages and to the classes of languages recognized by Petri nets or Petri nets with non-blocking arcs. These pumping lemmata allow us to characterize the limits in the expressiveness of these classes of language. Furthermore, we exploit the pumping lemmata to strictly separate the expressive power of Petri nets, Petri nets with non-blocking arcs and Petri nets with transfer arcs.     

Students’ tool-use within a web enhanced course: Explanatory mechanisms of students’ tool-use pattern

The popularity of content management systems (CMSs) in today’s higher education is driven by the assumption that providing a rich toolset and leaving the use of this toolset under learner control will stimulate self-regulated and deeper learning. Current evidence on students’ tool-use within CMS supported courses however tackles this assumption and indicates that CMSs may empower students’ learning only under particular learner-related conditions. The current study addresses this concern and investigates how students’ tool-use within a CMS supported course can be explained in terms of (a) students’ conceptions on the tool functionalities, (b) self-efficacy beliefs for self-regulated learning and (c) goal orientation. Data were collected within a first year undergraduate course ‘Learning and Instruction’. Students’ (n = 182) tool-use within the course was logged throughout the course episode and the influencing variables were measured through questionnaires. K-means cluster analyses revealed four clusters that reflected differences in students’ tool-choice and tool-use throughout the course. Multinominal regression analyses revealed that these tool-use differences could be explained in terms of students’ goal orientation. The study provides thus perspectives in order to capture students’ academic motivation through unobtrusive, behavioral, measures. Furthermore, questions are raised regarding the parallel between students’ tool-use pattern and study strategy use.