A new neutron study of the short range order inversion in Fe1−x_{1-x}Crx_x

We have performed new neutron diffuse scattering measurements in Fe$_{1-x}$Cr$_x$ solid solutions, in a concentration range 0$<$x$<$0.15, where the atomic distribution shows an inversion of the short range order. By optimizing the signal-background ratio, we obtain an accurate determination of the concentration of inversion x$_0$ =0.110(5). We determine the near neighbor atomic short range order parameters and pair potentials, which change sign at x$_0$. The experimental results are compared with previous first principle calculations and atomistic simulations.Comment: 6 pages; 6 figure

Critical Dynamics of Magnets

We review our current understanding of the critical dynamics of magnets above and below the transition temperature with focus on the effects due to the dipole--dipole interaction present in all real magnets. Significant progress in our understanding of real ferromagnets in the vicinity of the critical point has been made in the last decade through improved experimental techniques and theoretical advances in taking into account realistic spin-spin interactions. We start our review with a discussion of the theoretical results for the critical dynamics based on recent renormalization group, mode coupling and spin wave theories. A detailed comparison is made of the theory with experimental results obtained by different measuring techniques, such as neutron scattering, hyperfine interaction, muon--spin--resonance, electron--spin--resonance, and magnetic relaxation, in various materials. Furthermore we discuss the effects of dipolar interaction on the critical dynamics of three--dimensional isotropic antiferromagnets and uniaxial ferromagnets. Special attention is also paid to a discussion of the consequences of dipolar anisotropies on the existence of magnetic order and the spin--wave spectrum in two--dimensional ferromagnets and antiferromagnets. We close our review with a formulation of critical dynamics in terms of nonlinear Langevin equations.Comment: Review article (154 pages, figures included

An Analytic Study of the Professional Development Research in Early Childhood Education

The goal of this study was to examine empirical research on the design, delivery, and measurement of the effects of professional development (PD) for early childhood educators in order to provide insight into what the field has accomplished as well as suggest directions for future PD programs and research. Through the use of rigorous inclusion criteria outlined by S. M. Wilson, R. E. Floden, and J. Ferrini-Mundy (2001), 73 studies were included and analyzed. On average, 25% (M = 12.68, SD = 9.99) of references in each study were specifically about PD. The majority of studies (n = 39) targeted some form of language and literacy instruction, whereas only 5 studies targeted math and 1 study targeted science. A total of 35 different delivery mechanisms were used to provide PD, with 40 studies including some form of coaching and 45 including training workshops. The studies used a wide range of methods to measure PD-related outcomes: 51% (n = 37) of studies examined changes in teacher practice, 18% (n = 13) measured changes in teachers’ knowledge, 40% (n = 29) measured changes in children’s learning, and 11% (n = 8) measured changes in children’s behavior. Practice or Policy: Based on the results of this study, there are 4 major ways in which PD for early childhood educators can be developed. Researchers and providers of PD should (a) continue to draw from multiple resources to inform PD implementation designs, (b) include more diversity in the content of instruction targeted by PD, (c) experiment with innovative formats for delivering PD, and (d) create better means of evaluating PD

Emerging issues and current trends in assistive technology use 2007-1010: practising, assisting and enabling learning for all

Following an earlier review in 2007, a further review of the academic literature relating to the uses of assistive technology (AT) by children and young people was completed, covering the period 2007-2011. As in the earlier review, a tripartite taxonomy: technology uses to train or practise, technology uses to assist learning and technology uses to enable learning, was used in order to structure the findings. The key markers for research in this field and during these three years were user involvement, AT on mobile mainstream devices, the visibility of AT, technology for interaction and collaboration, new and developing interfaces and inclusive design principles. The paper concludes by locating these developments within the broader framework of the Digital Divide

Effectiveness of physical therapy interventions for children with cerebral palsy: A systematic review

Background To assess the effectiveness of physical therapy (PT) interventions on functioning in children with cerebral palsy (CP). Methods A search was made in Medline, Cinahl, PEDro and the Cochrane library for the period 1990 to February 2007. Only randomized controlled trials (RCTs) on PT interventions in children with diagnosed CP were included. Two reviewers independently assessed the methodological quality and extracted the data. The outcomes measured in the trials were classified using the International Classification of Functioning, Disability and Health (ICF). Results Twenty-two trials were identified. Eight intervention categories were distinguished. Four trials were of high methodological quality. Moderate evidence of effectiveness was established for two intervention categories: effectiveness of upper extremity treatments on attained goals and active supination, and of prehensile hand treatment and neurodevelopmental therapy (NDT) or NDT twice a week on developmental status, and of constraint-induced therapy on amount and quality of hand use. Moderate evidence of ineffectiveness was found of strength training on walking speed and stride length. Conflicting evidence was found for strength training on gross motor function. For the other intervention categories the evidence was limited due to low methodological quality and the statistically insignificant results of the studies. Conclusion Due to limitations in methodological quality and variations in population, interventions and outcomes, mostly limited evidence on the effectiveness of most PT interventions is available through RCTs. Moderate evidence was found for some effectiveness of upper extremity training. Well-designed trials are needed especially for focused PT interventions.BioMed Central Open acces

Critical phenomena and neutron scattering (I)

First we recall the expressions of the scattering cross section of thermal neutrons in the vicinity of the critical temperature. Then we strive to present as briefly as possible the earlier theories of critical fluctuations of magnetization (conventional theories), as also the theory of Halperin and Hohenberg that is based upon a generalisation of the concept of scaling laws applied previously to the static critical phenomena. The end of the article is devoted to display the failure of conventional theories in the interpretation of the results obtained by neutron scattering and the experimental verification of scaling laws hypothesis. It is emphasized on the difficulty to find out magnetic materials in the nature thoroughly assimilable to the theoretical systems for which the theory of Halperin and Hohenberg can be applied

Étude de la diffusion critique des neutrons par le fer dans les régions « hydrodynamique » et « quasi hydrodynamique »

With our experiments of neutron scattering by iron above the Curie temperature, the aim is to reach the « hydrodynamic » région defined by the theory of « scaling laws » and to determine the variation of the diffusion constant Λ with the temperature in this région. These experiments bring a check of the recent calculations of the « scaling » function f(K 1/q) made by P. Résibois and C. Piette. These calculations, as also the different measurements performed display the existence of a région called by us « quasi-hydrodynamic » région in which the parameter Λ has not yet the typical law of variation with the temperature of the « hydrodynamic » région. The concept of a « quasi-hydrodynamic » région appears gradually from the analysis of the experimental results. In the « hydrodynamic » region demarcated from the calculations of P. Résibois and C. Piette, the law of variation of the diffusion constante Λ with the temperature can be written : Λ = Λ0(T-Tc/Tc )z. The experimental results lead, concerning Λ 0 and the critical exponent z, to the following values : [FORMULA].Par nos expériences de diffusion des neutrons par le fer au-dessus de la température de Curie nous avons cherché à atteindre la région « hydrodynamique » définie par la théorie dite « des lois d'échelle » et à y déterminer la variation avec la température de la constante de diffusion Λ. Ces expériences apportent une vérification des récents calculs de la fonction « d'échelle » f(K 1/q) effectués par P. Résibois et C. Piette. Ces calculs ainsi que les diverses mesures que nous avons faites ont mis en évidence l'existence d'une région à l'intérieur de laquelle le paramètre Λ n'a pas encore la loi de variation avec la température qui caractérise la région « hydrodynamique ». Cette région, voisine de la région « hydrodynamique », nous l'avons appelée région « quasi hydrodynamique ». Le concept de région « quasi-hydrodynamique » se dégage progressivement au cours de l'analyse des résultats expérimentaux. Dans la région « hydrodynamique » délimitée à partir des calculs de P. Résibois et C. Piette, la loi de variation de la constante de diffusion Λ avec la température s'écrit : Λ= Λ 0(T-Tc/Tc)z. Les résultats expérimentaux conduisent en ce qui concerne Λ0 et l'exposant critique z aux valeurs suivantes : [FORMULE]

DIFFUSION CRITIQUE DES NEUTRONS LENTS PAR LE FER

Dans le cas du fer et à des vecteurs de diffusion q de modules compris entre 1,8 et 7,1 x 10-2 Å-1 nous avons étudié juste au-dessus de la température de Curie (Tc ≤ T ≤ 1,04 Tc) la fonction Relaxation Φ(q, ω) par diffusion des neutrons : la variation de sa largeur à demi-hauteur suivant la température à vecteur q constant mise en évidence dans nos expériences est celle prédite par la récente théorie de Résibois et Piette. Dans la « région hydrodynamique » nous avons trouvé pour l'exposant critique z de la constante de diffusion Λ la valeur : 0,38 ± 0,07.The Relaxation function Φ(q, ω) has been studied in Iron just above the Curie temperature (Tc ≤ T ≤ 1.04 Tc) at scattering vector q in the range 1.8 x 10-2 < |q| < 7.1 x 10-2 Å-1 by neutron scattering : In our experiments the variation of its width at half height displays a behaviour following the temperature at q constant which is predicted by the recent theory of Résibois and Piette. In the hydrodynamic region » the critical exponent z of the diffusion constant Å has been found equal to 0.38 ± 0.07