7,687 research outputs found
Lithium in field Am and normal A-F-type stars
Preliminary abundances of lithium and a few other elements have been obtained
for 31 field Am stars with good Hipparcos parallaxes, as well as for 36 normal
A and F stars. Radial and projected rotational velocities were determined as
well. We examine the Li abundance as a function of the stellar parameters: for
normal stars, it is clearly bimodal for Teff < 7500 K, while Am-Fm stars are
all somewhat Li-deficient in this range. The most Li-deficient stars - either
Am or normal - tend to be at least slightly evolved, but the reverse is not
true.Comment: 4 pages, 2 figures, poster presented at the conference "Element
stratification in stars, 40 years of atomic diffusion", eds. G. Alecian, O.
Richard and S. Vauclair, EAS Publication Series, in pres
Interface Engineering to Create a Strong Spin Filter Contact to Silicon
Integrating epitaxial and ferromagnetic Europium Oxide (EuO) directly on
silicon is a perfect route to enrich silicon nanotechnology with spin filter
functionality.
To date, the inherent chemical reactivity between EuO and Si has prevented a
heteroepitaxial integration without significant contaminations of the interface
with Eu silicides and Si oxides.
We present a solution to this long-standing problem by applying two
complementary passivation techniques for the reactive EuO/Si interface:
() an hydrogen-Si passivation and () the
application of oxygen-protective Eu monolayers --- without using any additional
buffer layers.
By careful chemical depth profiling of the oxide-semiconductor interface via
hard x-ray photoemission spectroscopy, we show how to systematically minimize
both Eu silicide and Si oxide formation to the sub-monolayer regime --- and how
to ultimately interface-engineer chemically clean, heteroepitaxial and
ferromagnetic EuO/Si in order to create a strong spin filter contact to
silicon.Comment: 11 pages of scientific paper, 10 high-resolution color figures.
Supplemental information on the thermodynamic problem available (PDF).
High-resolution abstract graphic available (PNG). Original research (2016
Local monotonicity of Riemannian and Finsler volume with respect to boundary distances
We show that the volume of a simple Riemannian metric on is locally
monotone with respect to its boundary distance function. Namely if is a
simple metric on and is sufficiently close to and induces
boundary distances greater or equal to those of , then . Furthermore, the same holds for Finsler metrics and the
Holmes--Thompson definition of volume. As an application, we give a new proof
of the injectivity of the geodesic ray transform for a simple Finsler metric.Comment: 13 pages, v3: minor corrections and clarifications, to appear in
Geometriae Dedicat
Percepção de incongruências no contorno entonacional de frases e de melodias por crianças com, ou sem, treino musical
A prosódia está relacionada com a materialização da linguagem enquanto estÃmulo acústico. Constituem
aspectos da prosódia a entoação, o ritmo, a intensidade e as pausas linguÃsticas (Ladefoged, 1982). Alguns
destes aspectos são comuns à música. No caso da entoação da fala, esta é análoga à melodia em música. A
prosódia de uma frase falada e a melodia de um trecho musical apresentam componentes estruturais muito
semelhantes.
O presente estudo aborda esta questão do ponto de vista psicológico. Trata-se de um estudo sobre a
percepção de melodias e de prosódia, realizado no seguimento de Schön et al (2002), cuja problemática está
centrada no contorno da frequência fundamental ( fo) da entoação em fala e da melodia em música. Pretendese
averiguar se há ou não uma correlação entre a percepção prosódica e a percepção melódica; e se a
aprendizagem musical pode potenciar o desenvolvimento da capacidade de percepção prosódica,
nomeadamente no que diz respeito ao contorno entonacional. A metodologia empregue é comportamental
(medida dos tempos de reacção, percentagem de repostas correctas e sensibilidade, d’). Os participantes do
estudo são dois grupos de crianças do 4.º ano de escolaridade: um com aprendizagem musical desde o 1.º ano
de escolaridade e outro sem aprendizagem musical formal. Os resultados indicaram que não existem
diferenças significativas entre os dois grupos de crianças. Contudo, as crianças com melhor performance na
tarefa musical, independentemente do grupo a que pertencem, são as que têm melhor performance na tarefa
de linguagem. Este facto pode ser indicador de uma predisposição musical que pode influenciar o
desenvolvimento da percepção das caracterÃsticas entonacionais da linguagem
Dihydroxyacetone conversion into lactic acid in an aqueous medium in the presence of metal salts: influence of the ionic thermodynamic equilibrium on the reaction performance
International audienceThe catalytic conversion of dihydroxyacetone (DHA) to lactic acid (LA) via pyruvaldehyde (PA) in aqueous media was studied using different homogeneous metal salts. A kinetic model was developed and the parameters corresponding to each reaction steps were estimated. Agreement between experiments and simulated results was excellent and the performance of the different catalysts was consistent with previous studies described in the literature. Aluminium salts, which show the best performance, were tested in a whole range of concentrations and at different pH, in order to identify the catalytically active ionic species. It was confirmed that the DHA to pyruvaldehyde (PA) dehydration step is catalyzed by both Brønsted and Lewis acids whereas the consecutive reaction of PA to LA is solely catalyzed by Lewis acids. Moreover, comparing thermodynamic analysis of the reaction media and kinetic parameters demonstrated that cationic hydroxyl-aluminium complexes [Al(OH)h] (3-h)+ formed in situ by the hydrolysis of the aluminium aqua complexes like [Al(OH2)6] 3+ are the most active Lewis acids
Ab Initio Study of Hybrid b-bar-gb Mesons
Hybrid b-bar-gb molecules in which the heavy b-bar-b pair is bound together
by the excited gluon field g are studied using the Born-Oppenheimer expansion
and numerical simulations. The consistency of results from the two approaches
reveals a simple and compelling physical picture for heavy hybrid states.Comment: 4 pages, 3 figures, uses REVTeX and epsf, final published versio
New limits for neutrinoless tau decays
Neutrinoless 3-prong tau lepton decays into a charged lepton and either two charged particles or one neutral meson have been searched for using 4.79fb^(-1) of data collected with the CLEO II detector at Cornell Electron Storage Ring. This analysis represents an update of a previous study and the addition of six decay channels. In all channels the numbers of events found are compatible with background estimates and branching fraction upper limits are set for 28 different decay modes. These limits are either more stringent than those set previously or represent the first attempt to find these decays
Z boson transverse momentum spectrum from the lepton angular distributions
In view of recent discussions concerning the possibly limiting energy
resolution systematics on the measurement of the Z boson transverse momentum
distribution at hadron colliders, we propose a novel measurement method based
on the angular distributions of the decay leptons. We also introduce a
phenomenological parametrization of the transverse momentum distribution that
adapts well to all currently available predictions, a useful tool to quantify
their differences.Comment: 12 pages, 6 figure
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