380 research outputs found
SANS evidence for the dispersion of nanoparticles in W-1Y₂O₃ and W-1La₂O₃ processed by hot isostatic pressing
The development of a dispersion of nanoparticles in the W–1%Y₂O₃ and W–1%La₂O₃ (wt%) alloys processed by hot isostatic pressing have been investigated using small-angle neutron scattering. The analyses of the scattering data using the Beaucage unified approach reveal the presence of a bi-modal distribution of spherical scattering centers with sizes of less of 180 nm in these alloys. The mode values of these centers are found at ~ 10 and 40 nm in W–1%Y₂O₃, and at ~ 15 and 80 nm in W–1%La₂O₃ . The scanning electron microscopy analyses showed the presence of small second phase particles. The contribution of the pore space to the scattering curves has been analyzed using the results obtained for pure W processed following the same procedure used for the alloys, and the porosity measurements of the samples.The present work was supported by the Consejería de Educación
de la Comunidad de Madrid, through the program ESTRUMAT CM
S2009MAT 1585 and by the Ministerio de Innovación y Ciencia (project ENE2008 06403 C06 04). The additional financial support from
EURATOM/CIEMAT association through contract EFDA WP11 MAT
WWALLOY is also acknowledged.Publicad
On Limitations of the Ultrasonic Characterization of Pieces Manufactured with Highly Attenuating Materials
Some technical aspects of two Spanish cooperation projects, funded by DPI and Innpacto Programs of the R&D National Plan, are discussed. The objective is to analyze the common belief about than the ultrasonic testing in MHz range is not a tool utilizable to detect internal flaws in highly attenuating pieces made of coarse-grained steel. In fact high-strength steels, used in some safe industrial infrastructures of energy & transport sectors, are difficult to be inspected using the conventional “state of the art” in ultrasonic technology, due to their internal microstructures are very attenuating and coarse-grained.
It is studied if this inspection difficulty could be overcome by finding intense interrogating pulses and advanced signal processing of the acquired echoes. A possible solution would depend on drastically improving signal-to-noise-ratios, by applying new advances on: ultrasonic transduction, HV electronics for intense pulsed driving of the testing probes, and an “ad-hoc” digital processing or focusing of the received noisy signals, in function of each material to be inspected.
To attain this challenging aim on robust steel pieces would open the possibility of obtaining improvements in inspecting critical industrial components made of highly attenuating & dispersive materials, as new composites in aeronautic and motorway bridges, or new metallic alloys in nuclear area, where additional testing limitations often appear.The Spanish I+D National Plan (MINECO), by funding the Projects: Fundamental Research / DPI2011 – 22438,
and INNPACTO Program / IMAAD - IPT-020000-2010-0004
Mechanical properties of freely suspended atomically thin dielectric layers of mica
We have studied the elastic deformation of freely suspended atomically thin
sheets of muscovite mica, a widely used electrical insulator in its bulk form.
Using an atomic force microscope, we carried out bending test experiments to
determine the Young's modulus and the initial pre-tension of mica nanosheets
with thicknesses ranging from 14 layers down to just one bilayer. We found that
their Young's modulus is high (190 GPa), in agreement with the bulk value,
which indicates that the exfoliation procedure employed to fabricate these
nanolayers does not introduce a noticeable amount of defects. Additionally,
ultrathin mica shows low pre-strain and can withstand reversible deformations
up to tens of nanometers without breaking. The low pre-tension and high Young's
modulus and breaking force found in these ultrathin mica layers demonstrates
their prospective use as a complement for graphene in applications requiring
flexible insulating materials or as reinforcement in nanocomposites.Comment: 9 pages, 5 figures, selected as cover of Nano Research, Volume 5,
Number 8 (2012
Programa de rehabilitación cardíaca mediante un entrenamiento de tenis adaptado
The aims of this study were to determine the effect of a cardiac rehabilitation program, based on the adjustment of a sports modality (tennis), on differentes laboratory analysis variables (triglycerides, cholesterol,cholesterol LDL, cholesterol HDL and glucose ) And and on an exercise stress test (metabolics equivalent-METs-, time of effort, systolic pressure, dyastolic pressure, maximum cardiac frecuencia and double product). The study involved 7 patients with low risk myocardial heart attack. The ages was include between 48 and 63 years old. By the end of the program, which has lasted 3 months, triglycerides, cholesterol, exercise capacity and double product had improved significantly (p<.005 for all).Los objetivos de este estudio son evaluar los efectos de nuestro programa de rehabilitación cardiaca, basado en la adaptación de una modalidad deportiva (tenis), sobre diferentes variables del perfil lipídico (triglicéridos, colesterol, cLDL, cHDL, y glucosa) así como en la prueba de esfuerzo (MET, tiempo de esfuerzo, presión sistólica, presión diastólica, frecuencia cardíaca máxima y doble producto). Analizamos a 7 pacientes con infarto agudo de miocardio de bajo riesgo. Las edades estaban comprendidas entre los 48 y 63 años. Tras la realización del programa, que ha tenido 3 meses de duración, se han producido mejoras significativas a nivel de triglicéridos, colesterol, capacidad funcional valorada en equivalentes metabólicos y doble producto (p<.005 para todos)
Mechanical properties of freely suspended semiconducting graphene-like layers based on MoS2
We fabricate freely suspended nanosheets of molybdenum disulphide (MoS2) which are characterized by quantitative optical microscopy and high-resolution friction force microscopy. We study the elastic deformation of freely suspended nanosheets of MoS2 using an atomic force microscope. The Young's modulus and the initial pre-tension of the nanosheets are determined by performing a nanoscopic version of a bending test experiment. MoS2 sheets show high elasticity and an extremely high Young's modulus (0.30 TPa, 50% larger than steel). These results make them a potential alternative to graphene in applications requiring flexible semiconductor materials
Engineering bound states in the continuum at telecom wavelengths with non-Bravais lattices
Various optical phenomena can be induced in periodic arrays of nanoparticles
by the radiative coupling of the local dipoles in each particle. Probably the
most impressive example is bound states in the continuum (BICs), which are
electromagnetic modes with a dispersion inside the light cone but infinite
lifetime, i.e., modes that cannot leak to the continuum. Symmetry-protected
BICs appear at highly symmetric points in the dispersion of periodic systems.
Although the addition of nonequivalent lattice points in a unit cell is an easy
and straightforward way of tuning the symmetry, BICs in such particle lattice,
i.e., non-Bravais lattice, are less explored among periodic systems. Starting
from a periodic square lattice of Si nanodisks, we have prepared three
non-Bravais lattices by detuning size and position of the second disk in the
unit cell. Diffraction-induced coupling excites magnetic/electric dipoles in
each nanodisk, producing two surface lattice resonances at the point
with a band gap in between. %of 41 meV.
The high/low energy branch becomes a BIC for the size/position-detuned array,
respectively, while both branches are bright (or leaky) when both size and
position are detuned simultaneously. The role of magnetic and electric
resonances in dielectric nanoparticles and the change of BIC to bright
character of the modes is explained by the two different origins of BICs in the
detuned arrays, which is further discussed with the aid of a coupled electric
and magnetic dipole model. This study gives a simple way of tuning BICs at
telecom wavelengths in non-Bravais lattices, including both plasmonic and
dielectric systems, thus scalable to a wide range of frequencies.Comment: 26 pages, 5 figure
Importance of the resonance frequencies of the vocal tract in estimating articulatory positions
La inversión articulatoria, cuyo objetivo es estimar la posición de los órganos articuladores a partir de la
información contenida en la señal de voz, ofrece una variedad de potenciales aplicaciones en el campo de la voz; sin embargo,
este es un problema aún por resolver. En este sentido, buscar representaciones con la capacidad de incrementar el desempeño de
los sistemas de inversión articulatoria es una tarea importante. El presente trabajo analiza la relevancia de los formantes como
entrada para los sistemas de inversión articulatoria. Para ello se implementa un análisis analítico y estadístico. En el caso analítico
se utiliza un sintetizador articulario, el cual simula la ecuación de tubos concatenados que modelan el tracto vocal. Para el análisis
estadístico se estudian datos reales provenientes de un articulógrafo electromagnético para los cuales se estima la asociación entre
las características acústicas y los movimientos de los órganos articuladores. A modo de medida de asociación estadística se utiliza
la medida de información . Los resultados entregados por el análisis son corroborados en un sistema de inversión articulatoria
basado en redes neuronales. Se observa una mejora en el valor de error cuadrático medio del 2,2% y para el caso de la medida de
desempeño de la correlación, una mejora del 2,8%.Acoustic-to-Articulatory inversion, which seeks to estimate an articulator position using the acoustic information
in the speech signal, offers several potential applications in the field of speech processing. In this context, it is important to use
acoustic parameters with the ability to increase the performance of acoustic-to-articulatory inversion systems. This paper analyzes
the importance of formants as inputs to such inversion systems from an analytical and a statistical perspective. The former is
based on an articulatory synthesizer that simulates the voice signal from the vocal tract. The statistical analysis is based on real
data provided by an electromagnetic articulograph, for which we estimate the statistical association between acoustic features and
articulator movement. As a measure of statistical association, the information measure is utilized. The results are tested on a neuralnetwork-
based Acoustic-to-Articulatory inversion system. The use of formants as inputs led to an improvement of 2.2% and 2.8%
in the root-mean-square error and correlation values, respectively
Análisis de la tolerancia al ruido de características basadas en dinámica no lineal sobre señales fonocardiográficas
Una propiedad muy deseable en sistemas de detección automática de patologías es la robustez ante el ruido, tal que su presencia no afecte notablemente la habilidad de detectar patologías. El presente trabajo estudia la capacidad discriminatoria que características de la dinámica no lineal, en particular, el Exponente de Hurst, el Máximo Exponente de Lyapunov y la Dimensión de Correlación, puedan proveer en la detección de soplos cardíacos usando señales fonocardiográficas contaminadas con diferentes niveles de ruido. A su vez se hacen comparaciones con características obtenidas a partir de representaciones tiempo frecuencia. Los resultados muestran la fortaleza de las características basadas en dinámica no lineal para tareas de clasificación de estados funcionales, aún sobre señales con altos niveles de ruido.A very desirable attribute in automatic pathology detection systems is noise robustness, such that the presence of noise should not significantly affect the ability to detect pathologies. This paper explores the discriminatory potential that nonlinear dynamic features, in particular, the Hurst exponent, the maximum Lyapunov exponent and correlation dimension, can provide in the detection of heart murmurs using phonocardiographic signals contaminated with different levels of noise. At the same time comparing with features obtained from time frequency representations. The results show the strength of features based on nonlinear dynamics for functional state classification tasks, even on signals with high noise levels
Room Temperature Exciton-Polariton Condensation in Silicon Metasurfaces Emerging from Bound States in the Continuum
We show the first experimental demonstration of room-temperature
exciton-polariton (EP) condensation from a bound state in the continuum (BIC).
This demonstration is achieved by strongly coupling stable excitons in an
organic perylene dye with the extremely long-lived BIC in a dielectric
metasurface of silicon nanoparticles. The long lifetime of the BIC, mainly due
to the suppression of radiation leakage, allows for EP thermalization to the
ground state before decaying. This property results in a condensation threshold
of less than 5 \mu J cm^{-2}, one order of magnitude lower that the lasing
threshold reported in similar systems in the weak coupling limit
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