1,164 research outputs found
A crystallographic, spectroscopic and magnetic study of the [Co(dpk. OH)(dpk. OCH3)(NCO)2]2 compound
Ellipticals at z=0 from Self-Consistent Hydrodynamical Simulations: Clues on Age Effects in their Stellar Populations
We present results of a study of the stellar age distributions in the sample
of elliptical-like objects (ELOs) identified at z=0 in four simulations
operating in the context of a concordance cosmological model. The simulations
show that the formation of most stars in each ELO of the sample is a
consequence of violent dynamical events, either fast multiclump collapse at
high z, or mergers at lower z. This second way can explain the age spread as
well as the dynamical peculiarities observed in some ellipticals, but its
relative weight is never dominant and decreases as the ELO mass at the halo
scale, , increases, to such an extent that some recent mergers
contributing an important fraction to the total ELO mass can possibly
contribute only a small fraction of new born stars. More massive objects have
older means and narrower spreads in their stellar age distributions than less
massive ones. The ELO sample shows also a tight correlation between
and the central stellar l.o.s. velocity dispersion, . This gives
a trend of the means and spreads of ELO stellar populations with
that is consistent, even quantitatively, with the age effects observationally
detected in the stellar populations of elliptical galaxies. Therefore, these
effects can be explained as the observational manifestation of the intrinsic
correlations found in the ELO sample between and the properties of
the stellar age distribution, on the one hand, and and
, on the other hand. These correlations hint, for the first time,
at a possible way to reconcile age effects in ellipticals, and, particularly,
the increase of ratios with , with the
hierarchical clustering paradigm.Comment: 13 pages, 2 figures, accepted for publication in Astrophysical
Journal Letter
Diseño metodológico de un sistema de medición del desempeño para la cadena de suministros de astilleros en Colombia
The design of a performance measurement system for the Colombian shipyard supply chain is shown in this paper, using a model that integrates the principles of the Balanced Scorecard with the fuzzy sets theory to treat uncertainty associated with selected logistics indicators, enabling better supply chain management.El presente artículo muestra el diseño de un sistema de medición del desempeño para la cadena de suministros de los astilleros colombianos, usando un modelo que integra los principios del Balanced Scorecard con la teoría de conjuntos difusos para el tratamiento de la incertidumbre asociada a los indicadores logísticos seleccionados, posibilitando mejor gestión de dicha cadena
Band-gap engineering of Cu2ZnSn1-xGe xS4 single crystals and influence of the surface properties
Thin film solar cells based on Cu2ZnSn(S,Se)4 are very promising, because they contain earth-abundant elements and show high absorptivity. However, the performance of these solar cells needs to be improved in order to reach efficiencies as high as that reported for Cu(In,Ga)Se 2-based devices. This study investigates the potential of band-gap engineering of Cu2ZnSn1-xGexS 4 single crystals grown by chemical vapour transport as a function of the [Ge]/([Sn] + [Ge]) atomic ratio. The fundamental band gap E0 is found to change from 1.59 to 1.94 eV when the Ge content is increased from x = 0.1 to x = 0.5, as determined from spectroscopic ellipsometry measurements. This knowledge opens a route to enhancing the performance of kesterite-based photovoltaic devices by a Ge-graded absorber layer. Furthermore, the formation of GeO2 on the surface of the as-grown samples was detected by X-ray photoelectron spectroscopy, having an important impact on the effective optical response of the material. This should be also taken into account when designing photovoltaic solar cellsRC acknowledges financial support from Spanish MINECO within the program Ramón y Cajal (RYC-2011-08521). This work was supported by the Marie Curie-IRSES project (PVICOKEST, GA: 269167), MINECO projects (KEST-PV, ENE2010-21541-C03-01/-02/-03) and Marie Curie-ITN project (KESTCELL, GA: 316488
Micromagnetic simulations of interacting dipoles on a fcc lattice: Application to nanoparticle assemblies
Micromagnetic simulations are used to examine the effects of cubic and axial
anisotropy, magnetostatic interactions and temperature on M-H loops for a
collection of magnetic dipoles on fcc and sc lattices. We employ a simple model
of interacting dipoles that represent single-domain particles in an attempt to
explain recent experimental data on ordered arrays of magnetoferritin
nanoparticles that demonstrate the crucial role of interactions between
particles in a fcc lattice. Significant agreement between the simulation and
experimental results is achieved, and the impact of intra-particle degrees of
freedom and surface effects on thermal fluctuations are investigated.Comment: 10 pages, 9 figure
Spectroscopic ellipsometry study of Cu2ZnSnS4 bulk poly-crystals
The linear optical properties of Cu2ZnSnS4 bulk poly-crystals have been investigated using spectroscopic ellipsometry in the range of 1.2-4.6 eV at room temperature. The characteristic features identified in the optical spectra are explained by using the Adachi analytical model for the interband transitions at the corresponding critical points in the Brillouin zone. The experimental data have been modeled over the entire spectral range taking into account the lowest E0 transition near the fundamental absorption edge and E1A and E1B higher energy interband transitions. In addition, the spectral dependences of the refractive index, extinction coefficient, absorption coefficient, and normal-incidence reflectivity values have been accurately determined and are provided since they are essential data for the design of Cu2ZnSnS4 based optoelectronic devicesThe research leading to the presented results was partially
supported by the European Project INFINITE-CELL (Ref.
H2020-MSCA-RISE-2017-777968, 2017–2021, www.infinitecell.eu)
and the Spanish MINECO Projects “WINCOST”
(ENE2016-80788-C5-2-R) and PHOTOMANA (TEC2015-
69916-C2-1-R). The authors from the Institute of Applied
Physics appreciate the financial support from STCU 6224 and
from the Institutional Project No. CSSDT 15.817.02.04
The Behaviour Of Cosmological Models With Varying-G
We provide a detailed analysis of Friedmann-Robertson-Walker universes in a
wide range of scalar-tensor theories of gravity. We apply solution-generating
methods to three parametrised classes of scalar-tensor theory which lead
naturally to general relativity in the weak-field limit. We restrict the
parameters which specify these theories by the requirements imposed by the
weak-field tests of gravitation theories in the solar system and by the
requirement that viable cosmological solutions be obtained. We construct a
range of exact solutions for open, closed, and flat isotropic universes
containing matter with equation of state and in vacuum.
We study the range of early and late-time behaviours displayed, examine when
there is a `bounce' at early times, and expansion maxima in closed models.Comment: 58 pages LaTeX, 6 postscript figures, uses eps
Reduction of optical crosstalk in SiPMs due to coupled light guides and investigation of other properties demonstrated with the SensL MicroFJ-60035-TSV
The optical coupling of light guides to Silicon Photomultipliers (SiPMs)
influences the probability for optical crosstalk. Measurements of the crosstalk
probability and the relative gain of 122 SiPMs of type SensL MicroFJ-60035-TSV
are presented. Semi-conductor photo sensors have replaced photo multiplier
tubes in numerous applications featuring single-photon resolution,
insensitivity to magnetic fields, higher robustness and enhanced photo
detection efficiency at lower operation voltage and lower costs. Light guides
are used to increase the comparably small photo sensitive area of SiPMs. Their
optical coupling changes the surface conditions of the sensor and influences
the probability for crosstalk photons to leave the sensor without inducing
secondary breakdowns. This study compares properties of sensors that are
optically coupled to light guides with bare sensors, operated at nominal bias
voltage. It demonstrates, that the optical coupling to a light guide
significantly reduces the crosstalk probability of the measured sensors
On integrability of Hirota-Kimura type discretizations
We give an overview of the integrability of the Hirota-Kimura discretization
method applied to algebraically completely integrable (a.c.i.) systems with
quadratic vector fields. Along with the description of the basic mechanism of
integrability (Hirota-Kimura bases), we provide the reader with a fairly
complete list of the currently available results for concrete a.c.i. systems.Comment: 47 pages, some minor change
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