9,741 research outputs found

    Optical properties of metal nanoparticles with arbitrary shapes

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    We have studied the optical properties of metallic nanoparticles with arbitrary shape. We performed theoretical calculations of the absorption, extinction and scattering efficiencies, which can be directly compared with experiments, using the Discrete Dipole Approximation (DDA). In this work, the main features in the optical spectra have been investigated depending of the geometry and size of the nanoparticles. The origin of the optical spectra are discussed in terms of the size, shape and material properties of each nanoparticle, showing that a nanoparticle can be distinguish by its optical signature.Comment: 19 pages + 8 figure

    Data reduction in the ITMS system through a data acquisition model with self-adaptive sampling rate

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    Long pulse or steady state operation of fusion experiments require data acquisition and processing systems that reduce the volume of data involved. The availability of self-adaptive sampling rate systems and the use of real-time lossless data compression techniques can help solve these problems. The former is important for continuous adaptation of sampling frequency for experimental requirements. The latter allows the maintenance of continuous digitization under limited memory conditions. This can be achieved by permanent transmission of compressed data to other systems. The compacted transfer ensures the use of minimum bandwidth. This paper presents an implementation based on intelligent test and measurement system (ITMS), a data acquisition system architecture with multiprocessing capabilities that permits it to adapt the system鈥檚 sampling frequency throughout the experiment. The sampling rate can be controlled depending on the experiment鈥檚 specific requirements by using an external dc voltage signal or by defining user events through software. The system takes advantage of the high processing capabilities of the ITMS platform to implement a data reduction mechanism based in lossless data compression algorithms which are themselves based in periodic deltas

    Web based system architecture for long pulse remote experimentation

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    Remote experimentation (RE) methods will be essential in next generation fusion devices. Requirements for long pulse RE will be: on-line data visualization, on-line data acquisition processes monitoring and on-line data acquisition systems interactions (start, stop or set-up modifications). Note that these methods are not oriented to real-time control of fusion plant devices. INDRA Sistemas S.A., CIEMAT (Centro de Investigaciones Energ茅ticas Medioambientales y Tecnol贸gicas) and UPM (Universidad Polit茅cnica de Madrid) have designed a specific software architecture for these purposes. The architecture can be supported on the BeansNet platform, whose integration with an application server provides an adequate solution to the requirements. BeansNet is a JINI based framework developed by INDRA, which makes easy the implementation of a remote experimentation model based on a Service Oriented Architecture. The new software architecture has been designed on the basis of the experience acquired in the development of an upgrade of the TJ-II remote experimentation system

    Magnetic field detection in the B2Vn star HR 7355

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    The B2Vn star HR 7355 is found to be a He-rich magnetic star. Spectropolarimetric data were obtained with FORS1 at UT2 on Paranal observatory to measure the disk-averaged longitudinal magnetic field at various phases of the presumed 0.52 d cycle. A variable magnetic field with strengths between B_z = -2200 and +3200G was found, with confidence limits of 100 to 130G. The field topology is that of an oblique dipole, while the star itself is seen about equator-on. In the intensity spectra the HeI-lines show the typical equivalent width variability of He-strong stars, usually attributed to surface abundance spots. The amplitudes of the equivalent width variability of the HeI lines are extraordinarily strong compared to other cases. These results not only put HR 7355 unambiguously among the early-type magnetic stars, but confirm its outstanding nature: With v sin i = 320 km/s the parameter space in which He-strong stars are known to exist has doubled in terms of rotational velocity.Comment: 6 pages, 5 figures, 1 Table. Accepted for publication in MNRAS Letter

    The (B0+?)+O6 system FN CMa: A case for tidal-pulsational interaction?

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    FN CMa is visually double with a separation of about 0.6arcsec. Sixty high-cadence VLT/UVES spectra permit the A and B components to be disentangled, as the relative contribution of each star to the total light entering the spectrograph fluctuates between exposures due to changes in seeing. Component A exhibits rapid line-profile variations, leading us to attribute the photometric variability seen by HIPPARCOS (with a derived P=0.08866d) to this component. From a total of 122 archival and new echelle spectra it is shown that component A is an SB1 binary with an orbital period of 117.55 days. The eccentricity of 0.6 may result in tidal modulation of the pulsation(s) of component Aa.Comment: 2 pages, 1 figure, IAUS 272 - Active OB Stars: Structure, Evolution, Mass Loss and Critical Limit

    Impacto amplificador del ajuste de inventarios ante choques de demanda seg煤n especificaciones flexibles

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    La presente investigaci贸n aproxima cuantitativamente las relaciones din谩micas potencialmente asim茅tricas entre el crecimiento del PBI, del acervo de inventarios y de tres componentes de la demanda agregada (la demanda interna p煤blica, la demanda interna privada y, en particular, la demanda externa por exportaciones) durante la experiencia peruana de crecimiento basado en el mercado (1993-2010). Para capturar la potencial presencia de asimetr铆as en el vector de medias condicionales, se propone un modelo din谩mico flexible (VAR neuronal), una distribuci贸n t de Student para el vector de perturbaciones asociado, as铆 como un modelo de heterosced谩sticidad din谩mica (ARCH) para su matriz de co-varianzas condicionales. Los par谩metros de ambos momentos condicionales son robustos ante la presencia de observaciones at铆picas -outliers- debido a que los vectores de perturbaciones son realizaciones de una distribuci贸n t de Student multi-variada, lo que adem谩s reduce la presencia de asimetr铆as espurias en las medias condicionales. Al cubrir el costo computacional requerido, la aproximaci贸n de los par谩metros logra develar la presencia de incentivos para mantener inventarios que son adicionales al tradicional suavizamiento de la producci贸n. Un par谩metro estad铆sticamente diferente de cero en la estructura contempor谩nea indica que un choque positivo en el ritmo de crecimiento de la demanda privada ser谩 absorbido principalmente por un aumento m谩s que proporcional en el choque del ritmo de la producci贸n. Este impacto amplificador ("des-moderador") de los choques de demanda sobre la evoluci贸n de la producci贸n es consistente con los c谩lculos de la incidencia promedio del crecimiento de la inversi贸n en inventarios en el crecimiento del producto real durante 4 recesiones recientes y se explicar铆a por el ciclo agregado de los inventarios (aunque no necesariamente de bienes finales).Inventarios, Fluctuaciones en los negocios.

    Redes neuronales para predecir el tipo de cambio diario

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    Un problema recurrente es que los modelos estructurales de determinaci贸n del tipo de cambio no logran predecirlo con mayor precisi贸n que un camino aleatorio. El objetivo de la presente investigaci贸n es verificar si es posible obtener proyecciones relativamente precisas generadas por un grupo de modelos econom茅tricos para el tipo de cambio diario sobre la base de la muestra disponible enero 2004 - setiembre 2008. Los modelos a compararse en t茅rminos predictivos son: (a) camino aleatorio en el nivel del tipo de cambio; (b) auto-regresi贸n con p rezagos en la variaci贸n del tipo de cambio; (c) perceptrones con p rezagos en la variaci贸n del tipo de cambio y (d) auto-regresi贸n fraccional con p rezagos en el nivel del tipo de cambio. Los resultados obtenidos confirman que los perceptrones poseen la capacidad para anticipar el patr贸n de los movimientos diarios en el tipo de cambio, especialmente cuando se utiliza el spread entre el tipo de cambio venta y compra como porcentaje del tipo de cambio promedio de estas dos cotizaciones, la depreciaci贸n diaria del yen contra el d贸lar americano y el diferencial de tasas dom茅sticas de inter茅s interbancarias en ambas monedas.Auge crediticio, pol铆tica monetaria

    2020 CARES Act 鈥 APOYO FINANCIERO PARA PEQUE脩AS EMPRESAS

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    Ya sea que un negocio se vea afectado por desastres relacionados con el clima, la construcci贸n de carreteras o las recesiones econ贸micas repentinas, tener un plan para mitigar los impactos puede ser crucial para la supervivencia inmediata y a largo plazo del negocio. Circunstancias imprevistas, como la pandemia de COVID-19, pueden requerir que los propietarios reeval煤en sus modelos de negocios, reduzcan los costos operativos y busquen apoyos financieros externos, todo para mantener el flujo de efectivo y abrir el negocio. Para ayudar a las peque帽as empresas durante la pandemia, el 27 de marzo se promulg贸 la Ley de Ayuda y Seguridad Econ贸mica Coronavirus (CARES) el cual incluye $ 349 mil millones en ayuda para peque帽as empresas y trabajadores estadounidenses. El prop贸sito y la elegibilidad var铆an con cada programa, as铆 que comun铆quese con su agencia financiera local, Nebraska Business Development Center (NBDC), Small Business Administration -Espa帽ol (SBA-Spanis) o NE CVI Extension Latino Small Business Program para obtener la informaci贸n m谩s reciente sobre 2020 CARES Act y la asistencia para la solicitud
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