623,264 research outputs found
Towards asteroseismology of the non-radial pulsating sdB star PG 1605+072
The recently discovered new class of sdB pulsators (sdBV) offers a powerful
possibility for the investigation of their interior and thus their evolutionary
history. The first step towards applying asteroseismologic tools is the
identification of pulsation modes. We reoport on simultaneous spectroscopic and
multi-band photometric time series observations of PG 1605+072 and analyse its
radial velocity and light curve.Comment: 4 pages, 3 figures, Proc. XIII Workshop on White Dwarfs, eds. D. de
Martino, R. Kalytis, R. Silvotti, J.E. Solheim, Kluwe
Gauge/Gravity Duality and Hadron Physics at the Light-Front
We discuss some remarkable features of the light-front holographic mapping of
classical gravity in anti-de Sitter space modified by a confining dilaton
background. In particular, we show that a positive-sign dilaton solution
has better chances to describe the correct hadronic
phenomenology than the negative solution extensively
studied in the literature. We also show that the use of twist-scaling
dimensions, instead of canonical dimensions, is required to give a good
description of the spectrum and form factors of hadrons. Another key element is
the explicit connection of AdS modes of total angular momentum with the
internal structure of hadrons and the proper identification of the orbital
angular momentum of the constituents.Comment: Invited talk presented by GdT at XI Hadron Physics, Maresias Beach,
Sao Paulo, Brazil, 21-26 March 201
Estimation of modal parameters ofcivil structures from frequency response function
Este trabajo se centra en estimar los parámetros modales del sistema dinámico que constituye la pasarela peatonal del
Museo de la Ciencia de la ciudad de Valladolid (Spain). El trabajo consiste no sólo en calcular frecuencias propias o naturales y factores de amortiguamiento asociados a cada uno de los modos estimados, como proporcionan muchos programas comerciales a partir de los registros de aceleraciones de ensayos OMA (Operational Modal Analysis) y/o EMA (Experimental Modal Analysis), sino que el objetivo de este articulo es calcular las masas generalizadas correspondientes a cada uno de los modos estimados de la estructura. Para ello, en primer lugar se obtiene una representación del sistema dinámico en el espacio de estados mediante la técnica SSI (Stochastic Subspace Identification), y en segundo lugar se escalan los modos de vibración a partir de la estimación de los residuos de la descomposición en fracciones parciales de la función de respuesta en frecuencia (FRF) de las mediciones. Con este método se consiguen obtener buenas precisiones en los resultados, siempre que se consigan excitar los modos de vibración de los que queramos estimar los parámetros, lo que nos permite simular la respuesta dinámica de la estructura sin tener que recurrir a otros procedimientos como la actualización de un modelo de elementos finitos de la estructura en estudio.This paper focuses on estimating the modal parameters of the dynamic system that constitutes the pedestrian footbridge of the Science Museum of the city of Valladolid (Spain). The work consists not only of calculating natural frequencies and damping factors associated to each of the estimated modes, as many commercial software provide from acceleration measurements of tests OMA (Operational Modal Analysis) and/or EMA (Experimental modal Analysis), but the aim of this paper is to calculate the generalized masses corresponding to each of the estimated modes of the structure. For this purpose, firstly a representation of the dynamic system is obtained in the state space by SSI technique (Stochastic Subspace Identification), and secondly, vibration modes are scaled from the estimation of the residues of the decomposition in partial fractions of the frequency response function (FRF) measurements. This method gets accurate estimations in the results whose vibration modes are excited, allowing the simulation of the dynamic response of the structure without the need for updating a finite element model of the structure under study.Peer Reviewe
Influence of Topological Edge States on the Properties of Al/Bi2Se3/Al Hybrid Josephson Devices
In superconductor-topological insulator-superconductor hybrid junctions, the
barrier edge states are expected to be protected against backscattering, to
generate unconventional proximity effects, and, possibly, to signal the
presence of Majorana fermions. The standards of proximity modes for these types
of structures have to be settled for a neat identification of possible new
entities. Through a systematic and complete set of measurements of the
Josephson properties we find evidence of ballistic transport in coplanar
Al-Bi2Se3-Al junctions that we attribute to a coherent transport through the
topological edge state. The shunting effect of the bulk only influences the
normal transport. This behavior, which can be considered to some extent
universal, is fairly independent of the specific features of superconducting
electrodes. A comparative study of Shubnikov - de Haas oscillations and
Scanning Tunneling Spectroscopy gave an experimental signature compatible with
a two dimensional electron transport channel with a Dirac dispersion relation.
A reduction of the size of the Bi2Se3 flakes to the nanoscale is an unavoidable
step to drive Josephson junctions in the proper regime to detect possible
distinctive features of Majorana fermions.Comment: 11 pages, 14 figure
The pulsation modes of the pre-white dwarf PG 1159-035
Context. PG 1159-035, a pre-white dwarf with Teff ≃ 140000 K, is the prototype of both two classes: the PG 1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035 photometric data obtained with the Whole Earth Telescope (WET) showed a rich frequency spectrum allowing the identification of 122 pulsation modes. Analyzing the periods of pulsation, it is possible to measure the stellar mass, the rotational period and the inclination of the rotation axis, to estimate an upper limit for the magnetic field, and even to obtain information about the inner stratification of the star.
Aims. We have three principal aims: to increase the number of detected and identified pulsation modes in PG 1159-035, study trapping of the star's pulsation modes, and to improve or constrain the determination of stellar parameters.
Methods. We used all available WET photometric data from 1983, 1985, 1989. 1993 and 2002 to identify the pulsation periods.
Results. We identified 76 additional pulsation modes, increasing to 198 the number of known pulsation modes in PG 1159-035, the largest number of modes detected in any star besides the Sun. From the period spacing we estimated a mass M/M⊙= 0.59 ±0.02 for PG 1159-035, with the uncertainty dominated by the models, not the observation. Deviations in the regular period spacing suggest that some of the pulsation modes are trapped, even though the star is a pre-white dwarf and the gravitational settling is ongoing. The position of the transition zone that causes the mode trapping was calculated at rc/R* = 0.83 ± 0.05. From the multiplet splitting, we calculated the rotational period Prot = 1.3920 ± 0.0008 days and an upper limit for the magnetic field, B < 2000 G. The total power of the pulsation modes at the stellar surface changed less than 30% for ℓ = 1 modes and less than 50% for ℓ = 2 modes. We find no evidence of linear combinations between the 198 pulsation mode frequencies. PG 1159-035 models have not significative convection zones, supporting the hypothesis that nonlinearity arises in the convection zones in cooler pulsating white dwarf stars.La lista completa de autores que integran el documento puede consultarse en el archivo.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat
The pulsation modes of the pre-white dwarf PG 1159-035
Context. PG 1159-035, a pre-white dwarf with Teff ≃ 140000 K, is the prototype of both two classes: the PG 1159 spectroscopic class and the DOV pulsating class. Previous studies of PG 1159-035 photometric data obtained with the Whole Earth Telescope (WET) showed a rich frequency spectrum allowing the identification of 122 pulsation modes. Analyzing the periods of pulsation, it is possible to measure the stellar mass, the rotational period and the inclination of the rotation axis, to estimate an upper limit for the magnetic field, and even to obtain information about the inner stratification of the star.
Aims. We have three principal aims: to increase the number of detected and identified pulsation modes in PG 1159-035, study trapping of the star's pulsation modes, and to improve or constrain the determination of stellar parameters.
Methods. We used all available WET photometric data from 1983, 1985, 1989. 1993 and 2002 to identify the pulsation periods.
Results. We identified 76 additional pulsation modes, increasing to 198 the number of known pulsation modes in PG 1159-035, the largest number of modes detected in any star besides the Sun. From the period spacing we estimated a mass M/M⊙= 0.59 ±0.02 for PG 1159-035, with the uncertainty dominated by the models, not the observation. Deviations in the regular period spacing suggest that some of the pulsation modes are trapped, even though the star is a pre-white dwarf and the gravitational settling is ongoing. The position of the transition zone that causes the mode trapping was calculated at rc/R* = 0.83 ± 0.05. From the multiplet splitting, we calculated the rotational period Prot = 1.3920 ± 0.0008 days and an upper limit for the magnetic field, B < 2000 G. The total power of the pulsation modes at the stellar surface changed less than 30% for ℓ = 1 modes and less than 50% for ℓ = 2 modes. We find no evidence of linear combinations between the 198 pulsation mode frequencies. PG 1159-035 models have not significative convection zones, supporting the hypothesis that nonlinearity arises in the convection zones in cooler pulsating white dwarf stars.La lista completa de autores que integran el documento puede consultarse en el archivo.Facultad de Ciencias Astronómicas y GeofísicasInstituto de Astrofísica de La Plat
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