18,483 research outputs found
Speech and language difficulties in children with and without a family history of dyslexia
Comorbidity between SLI and dyslexia is well documented. Researchers have variously argued that dyslexia is a separate disorder from SLI, or that children with dyslexia show a subset of the difficulties shown in SLI. This study examines these hypotheses by assessing whether family history of dyslexia and speech and language difficulties are separable risk factors for literacy difficulties. Forty-six children with a family risk of dyslexia (FRD) and 36 children receiving speech therapy (SLT) were compared to 128 typically developing children. A substantial number (41.3%) of the children with FRD had received SLT. The nature of their difficulties did not differ in severity or form from those shown by the other children in SLT. However, both SLT and FRD were independent risk factors in predicting reading difficulties both concurrently and 6 months later. It is argued that the results are best explained in terms of Pennington's (2006) multiple deficits model
Structural Relaxation and Mode Coupling in a Simple Liquid: Depolarized Light Scattering in Benzene
We have measured depolarized light scattering in liquid benzene over the
whole accessible temperature range and over four decades in frequency. Between
40 and 180 GHz we find a susceptibility peak due to structural relaxation. This
peak shows stretching and time-temperature scaling as known from
relaxation in glass-forming materials. A simple mode-coupling model provides
consistent fits of the entire data set. We conclude that structural relaxation
in simple liquids and relaxation in glass-forming materials are
physically the same. A deeper understanding of simple liquids is reached by
applying concepts that were originally developed in the context of
glass-transition research.Comment: submitted to New J. Phy
Evidence from Rb–Sr mineral ages for multiple orogenic events in the Caledonides of Shetland, Scotland
Shetland occupies a unique central location within the North Atlantic Caledonides. Thirty-three new high-precision Rb–Sr mineral ages indicate a polyorogenic history. Ages of 723–702 Ma obtained from the vicinity of the Wester Keolka Shear Zone indicate a Neoproterozoic (Knoydartian) age and preclude its correlation with the Silurian Moine Thrust. Ordovician ages of c. 480–443 Ma obtained from the Yell Sound Group and the East Mainland Succession constrain deformation fabrics and metamorphic assemblages to have formed during Grampian accretionary orogenic events, broadly contemporaneously with orogenesis of the Dalradian Supergroup in Ireland and mainland Scotland. The relative paucity of Silurian ages is attributed to a likely location at a high structural level in the Scandian nappe pile relative to mainland Scotland. Ages of c. 416 and c. 411 Ma for the Uyea Shear Zone suggest a late orogenic evolution that has more in common with East Greenland and Norway than with northern mainland Scotland
Reactive self-heating model of aluminum spherical nanoparticles
Aluminum-oxygen reaction is important in many highly energetic, high pressure
generating systems. Recent experiments with nanostructured thermites suggest
that oxidation of aluminum nanoparticles occurs in a few microseconds. Such
rapid reaction cannot be explained by a conventional diffusion-based mechanism.
We present a rapid oxidation model of a spherical aluminum nanoparticle, using
Cabrera-Mott moving boundary mechanism, and taking self-heating into account.
In our model, electric potential solves the nonlinear Poisson equation. In
contrast with the Coulomb potential, a "double-layer" type solution for the
potential and self-heating leads to enhanced oxidation rates. At maximal
reaction temperature of 2000 C, our model predicts overall oxidation time scale
in microseconds range, in agreement with experimental evidence.Comment: submitte
Elastic waves and transition to elastic turbulence in a two-dimensional viscoelastic Kolmogorov flow
We investigate the dynamics of the two-dimensional periodic Kolmogorov flow
of a viscoelastic fluid, described by the Oldroyd-B model, by means of direct
numerical simulations. Above a critical Weissenberg number the flow displays a
transition from stationary to randomly fluctuating states, via periodic ones.
The increasing complexity of the flow in both time and space at progressively
higher values of elasticity accompanies the establishment of mixing features.
The peculiar dynamical behavior observed in the simulations is found to be
related to the appearance of filamental propagating patterns, which develop
even in the limit of very small inertial non-linearities, thanks to the
feedback of elastic forces on the flow.Comment: 10 pages, 14 figure
Thermodiffusion in model nanofluids by molecular dynamics simulations
In this work, a new algorithm is proposed to compute single particle
(infinite dilution) thermodiffusion using Non-Equilibrium Molecular Dynamics
simulations through the estimation of the thermophoretic force that applies on
a solute particle. This scheme is shown to provide consistent results for
simple Lennard-Jones fluids and for model nanofluids (spherical non-metallic
nanoparticles + Lennard-Jones fluid) where it appears that thermodiffusion
amplitude, as well as thermal conductivity, decrease with nanoparticles
concentration. Then, in nanofluids in the liquid state, by changing the nature
of the nanoparticle (size, mass and internal stiffness) and of the solvent
(quality and viscosity) various trends are exhibited. In all cases the single
particle thermodiffusion is positive, i.e. the nanoparticle tends to migrate
toward the cold area. The single particle thermal diffusion 2 coefficient is
shown to be independent of the size of the nanoparticle (diameter of 0.8 to 4
nm), whereas it increases with the quality of the solvent and is inversely
proportional to the viscosity of the fluid. In addition, this coefficient is
shown to be independent of the mass of the nanoparticle and to increase with
the stiffness of the nanoparticle internal bonds. Besides, for these
configurations, the mass diffusion coefficient behavior appears to be
consistent with a Stokes-Einstein like law
XMM-Newton and INTEGRAL analysis of the Supergiant Fast X-ray Transient IGR J17354-3255
We present the results of combined INTEGRAL and XMM-Newton observations of
the supergiant fast X-ray transient (SFXT) IGR J173543255. Three XMM-Newton
observations of lengths 33.4 ks, 32.5 ks and 21.9 ks were undertaken, the first
an initial pointing to identify the correct source in the field of view and the
latter two performed around periastron. Simultaneous INTEGRAL observations
across of the orbital cycle were analysed but the source was neither
detected by IBIS/ISGRI nor by JEM-X. The XMM-Newton light curves display a
range of moderately bright X-ray activity but there are no particularly strong
flares or outbursts in any of the three observations. We show that the spectral
shape measured by XMM-Newton can be fitted by a consistent model throughout the
observation, suggesting that the observed flux variations are driven by
obscuration from a wind of varying density rather than changes in accretion
mode. The simultaneous INTEGRAL data rule out simple extrapolation of the
simple powerlaw model beyond the XMM-Newton energy range.Comment: 13 pages, 9 figures, This article has been accepted for publication
in Monthly Notices of the Royal Astronomical Society Published by Oxford
University Pres
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