281 research outputs found
Effect of ionic radii on the Curie temperature in Ba1-x-ySrxCayTiO3 compounds
<p>A series of Ba<sub>1-x-y</sub>Sr<sub>x</sub>Ca<sub>y</sub>TiO<sub>3</sub> compounds were prepared with varying average ionic radii and cation disorder on A-site. All samples showed typical ferroelectric behavior. A simple empirical equation correlated Curie temperature, <em>T<sub>C</sub></em>, with the values of ionic radii of A-site cations. This correlation was related to the distortion of TiO<sub>6</sub> octahedra observed during neutron diffraction studies. The equation was used for the selection of compounds with predetermined values of <em>T<sub>C</sub></em>. The effects of A-site ionic radii on the temperatures of phase transitions in Ba<sub>1-x-y</sub>Sr<sub>x</sub>Ca<sub>y</sub>TiO<sub>3</sub> were discussed. </p
Comment to the paper : Collapse of the vortex-lattice inductance and shear modulus at the melting transition in untwinned YBaCuO, by Matl \QTR{em}{et al.}
In a recent paper, Matl et al present a high-frequency study of the complex
resistivity of a pinned vortex lattice in YBaCuO . They focus on the
inductive-to-resistive transition which is investigated as a function of
temperature at a constant field T, so that the transition is associated
with the vanishing of vortex pinning strength. To our view, their conclusions
rely on a rather brittle experimental body and the collapse of C66 results from
an involved analysis of the finite frequency corrections to .
These corrections are not necessary since the complex frequency spectrum has
been previously interpreted by the two modes model, first proposed for low Tc
materials. We think that it is more adequate to interpret the present data and
should be at least considered.Comment: 4pages tex. submitted to PR
Learning to imitate facial expressions through sound
The question of how young infants learn to imitate others’ facial expressions has been central in developmental psychology for decades. Facial imitation has been argued to constitute a particularly challenging learning task for infants because facial expressions are perceptually opaque: infants cannot see changes in their own facial configuration when they execute a motor program, so how do they learn to match these gestures with those of their interacting partners? Here we argue that this apparent paradox mainly appears if one focuses only on the visual modality, as most existing work in this field has done so far. When considering other modalities, in particular the auditory modality, many facial expressions are not actually perceptually opaque. In fact, every orolabial expression that is accompanied by vocalisations has specific acoustic consequences, which means that it is relatively transparent in the auditory modality. Here, we describe how this relative perceptual transparency can allow infants to accrue experience relevant for orolabial, facial imitation every time they vocalise. We then detail two specific mechanisms that could support facial imitation learning through the auditory modality. First, we review evidence showing that experiencing correlated proprioceptive and auditory feedback when they vocalise – even when they are alone – enables infants to build audio-motor maps that could later support facial imitation of orolabial actions. Second, we show how these maps could also be used by infants to support imitation even for silent, orolabial facial expressions at a later stage. By considering non-visual perceptual domains, this paper expands our understanding of the ontogeny of facial imitation and offers new directions for future investigations
Atteinte pulmonaire sévère au cours de la neurofibromatose de type 1
Type 1 neurofibromatosis (NF1) is a hereditary disease inherited as an autosomal dominant. Respiratory involvement is rare. We report the case of a woman suffering from NF1 with mutation of the corresponding gene and with respiratory involvement combining diffuse parenchymatous lesions, severe precapillary pulmonary hypertension and an enlarging, spiculated pulmonary nodule, very suspicious of malignancy, though histological examination was not possible on account of the patient\u27s poor respiratory function. There was progressive deterioration of the patient\u27s respiratory condition, leading to death, despite the introduction of oral therapy combining a phosphodiesterase 5 inhibitor and an endothelin receptor antagonist. Our case illustrates the development of multiple severe respiratory pathologies in the setting of NF1. The specific contribution of the NF1 gene mutation in the pathophysiology of these different pulmonary manifestations needs to be examined in detail
Internal convection in thermoelectric generator models
Coupling between heat and electrical currents is at the heart of
thermoelectric processes. From a thermal viewpoint this may be seen as an
additional thermal flux linked to the appearance of electrical current in a
given thermoelectric system. Since this additional flux is associated to the
global displacement of charge carriers in the system, it can be qualified as
convective in opposition to the conductive part associated with both phonons
transport and heat transport by electrons under open circuit condition, as,
e.g., in the Wiedemann-Franz relation. In this article we demonstrate that
considering the convective part of the thermal flux allows both new insight
into the thermoelectric energy conversion and the derivation of the maximum
power condition for generators with realistic thermal coupling.Comment: 8 pages, 3 figure
A linear nonequilibrium thermodynamics approach to optimization of thermoelectric devices
Improvement of thermoelectric systems in terms of performance and range of
applications relies on progress in materials science and optimization of device
operation. In this chapter, we focuse on optimization by taking into account
the interaction of the system with its environment. For this purpose, we
consider the illustrative case of a thermoelectric generator coupled to two
temperature baths via heat exchangers characterized by a thermal resistance,
and we analyze its working conditions. Our main message is that both electrical
and thermal impedance matching conditions must be met for optimal device
performance. Our analysis is fundamentally based on linear nonequilibrium
thermodynamics using the force-flux formalism. An outlook on mesoscopic systems
is also given.Comment: Chapter 14 in "Thermoelectric Nanomaterials", Editors Kunihito
Koumoto and Takao Mori, Springer Series in Materials Science Volume 182
(2013
Form-function relationship in the amplitude and frequency modulations of infant - directed speech: A predictive processing perspective
Infants prefer infant-directed speech (IDS) over adult-directed speech (ADS). IDS is thought to serve specific functions compared to ADS:
- Attracting infant attention to the speech signal
- Conveying clear opportunities for easier word segmentation.
Two independent domains of complexity that are embedded in the speech stream:
- Amplitude complexity: Lower amplitude complexity associates with greater ease in identifying word boundaries
- Frequency complexity: Higher fre q uency complexity associates with more attention eliciting speech attention by inducing uncertaint
Preparing the COROT space mission: new variable stars in the galactic Anticenter direction
The activities related to the preparation of the asteroseismic, photometric
space mission COROT are described. Photoelectric observations, wide--field CCD
photometry, uvbyB calibrations and further time--series have been obtained at
different observatories and telescopes. They have been planned to complete the
COROT programme in the direction of the galactic Anticenter. In addition to
suitable asteroseismic targets covering the different evolutionary stages
between ZAMS and TAMS, we discovered several other variable stars, both
pulsating and geometrical. We compared results on the incidence of variability
in the galactic Center and Anticenter directions. Physical parameters have been
obtained and evolutionary tracks fitting them have been calculated. The
peculiarities of some individual stars alre pointed out. Paper based on
observations collected at the San Pedro Martir, Sierra Nevada, Teide, La Silla,
Haute-Provence and Roque de Los Muchachos (Telescopio Nazionale Galileo and
Mercator telescopes) observatories.Comment: 13 pages, 9 figures. Accepted for The Astronomical Journal (2005 May
volume
Rotation profiles of solar-like stars with magnetic fields
The aim of this work is to investigate rotation profile of solar-like stars
with magnetic fields. A diffusion coefficient of magnetic angular momentum
transport is deduced. Rotating stellar models with different mass are computed
under the effect of the coefficient. Then rotation profiles are obtained from
the theoretical stellar models. The total angular momentum of solar model with
only hydrodynamic instabilities is about 13 times larger than that of the Sun
at the age of the Sun, and this model can not reproduce quasi-solid rotation in
the radiative region. However, not only can the solar model with magnetic
fields reproduce an almost uniform rotation in the radiative region, but its
total angular momentum is consistent with helioseismic result at the level of 3
at the age of the Sun. The rotation of solar-like stars with magnetic
fields is almost uniform in the radiative region. But there is an obvious
transition region of angular velocity between the convective core and the
radiative region of models with 1.2 - 1.5 , where angular velocity
has a sharp radial change, which is different from the rotation profile of the
Sun and massive stars with magnetic fields. Moreover the changes of the angular
velocity in the transition region increase with the increasing in the age and
mass.Comment: Accepted for publication in ChjA
Seismic constraints on the radial dependence of the internal rotation profiles of six Kepler subgiants and young red giants
Context : We still do not know which mechanisms are responsible for the
transport of angular momentum inside stars. The recent detection of mixed modes
that contain the signature of rotation in the spectra of Kepler subgiants and
red giants gives us the opportunity to make progress on this issue.
Aims: Our aim is to probe the radial dependance of the rotation profiles for
a sample of Kepler targets. For this purpose, subgiants and early red giants
are particularly interesting targets because their rotational splittings are
more sensitive to the rotation outside the deeper core than is the case for
their more evolved counterparts.
Methods: We first extract the rotational splittings and frequencies of the
modes for six young Kepler red giants. We then perform a seismic modeling of
these stars using the evolutionary codes CESAM2k and ASTEC. By using the
observed splittings and the rotational kernels of the optimal models, we
perform inversions of the internal rotation profiles of the six stars.
Results: We obtain estimates of the mean rotation rate in the core and in the
convective envelope of these stars. We show that the rotation contrast between
the core and the envelope increases during the subgiant branch. Our results
also suggest that the core of subgiants spins up with time, contrary to the RGB
stars whose core has been shown to spin down. For two of the stars, we show
that a discontinuous rotation profile with a deep discontinuity reproduces the
observed splittings significantly better than a smooth rotation profile.
Interestingly, the depths that are found most probable for the discontinuities
roughly coincide with the location of the H-burning shell, which separates the
layers that contract from those that expand. These results will bring
observational constraints to the scenarios of angular momentum transport in
stars.Comment: Accepted in A&A, 27 pages, 18 figure
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