1,204 research outputs found
Stability Analysis of Single-Phase Low-Voltage AC Microgrids With Constant Power Terminals
This express brief presents the stability analysis of single-phase microgrids (SP-MG) operating under master-slave connection with constant power terminals. The SP-MG is composed of linear elements, nonlinear loads and distributed generators modeled as P Q constant terminals interconnected through power electronic converters. A Lyapunov?s direct method through a Hamiltonian representation of the grid is used to demonstrate stability. The non-autonomous model of the SP-MG is transformed into an autonomous equivalent model based on the dynamics of the error. The proposed analysis shows that if there exists an admissible trajectory x * solution of the power flow equations then the SP-MG is stable in the sense of Lyapunov.Fil: Montoya, O. D.. Universidad Tecnologica de Bolivar; ColombiaFil: Garces, A.. Universidad Tecnológica de Pereira; ColombiaFil: Avila Becerril, S.. Universidad Nacional Autónoma de México; MéxicoFil: Espinosa Pérez, G.. Universidad Nacional Autónoma de México; MéxicoFil: Serra, Federico Martin. Universidad Nacional de San Luis. Facultad de Ingeniería y Ciencias Agropecuarias. Laboratorio de Control Automático; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - San Luis. Instituto de Investigaciones en Tecnología Química. Universidad Nacional de San Luis. Facultad de Química, Bioquímica y Farmacia. Instituto de Investigaciones en Tecnología Química; Argentin
Comprehensive transient-state study for CARMENES-NIR high thermal stability
CARMENES has been proposed as a next-generation instrument for the 3.5m Calar
Alto Telescope. Its objective is finding habitable exoplanets around M dwarfs
through radial velocity measurements (m/s level) in the near-infrared.
Consequently, the NIR spectrograph is highly constraint regarding
thermal/mechanical requirements. As a first approach, the thermal stability has
been limited to \pm 0.01K (within year period) over a working temperature of
243K. This can be achieved by means of several temperature-controlled rooms.
The options considered to minimise the complexity of the thermal design are
here presented, as well as the transient-state thermal analyses realised to
make the best choice
Estudio experimental de la relación presión vs temperatura a volumen y cantidad de sustancia constantes para aire
Se revisa la enseñanza experimental de la Termodinámica que se realiza en nuestra facultad y se presentar una propuesta experimental sencilla, rápida, repetible y reproducible para realizar en el laboratorio de Termodinámica y que permite ilustrar la conducta de la presión de un gas (aire) en función de la temperatura, a volumen y cantidad de sustancia constantes (ley de Guy-Lussac). Del análisis de la gráfica presión absoluta vs temperatura absoluta se puede estimar el valor del cero absoluto de temperatura. Además, se puede discutir la importancia del concepto "absoluto" al construir y analizar conducta de gráficas que no incluyan una o dos propiedades absolutas
Beta-decay of nuclei around Se-90. Search for signatures of a N=56 sub-shell closure relevant the r-process
Nuclear structure plays a significant role on the rapid neutron capture
process (r-process) since shapes evolve with the emergence of shells and
sub-shells. There was some indication in neighboring nuclei that we might find
examples of a new N=56 sub-shell, which may give rise to a doubly magic Se-90
nucleus. Beta-decay half lives of nuclei around Se-90 have been measured to
determine if this nucleus has in fact a doubly-magic character. The
fragmentation of Xe-136 beam at the National Superconducting Cyclotron
Laboratory at Michigan State University was used to create a cocktail of nuclei
in the A=90 region. We have measured the half lives of twenty-two nuclei near
the r-process path in the A=90 region. The half lives of As-88 and Se-90 have
been measured for the first time. The values were compared with theoretical
predictions in the search for nuclear-deformation signatures of a N=56
sub-shell, and its possible role in the emergence of a potential doubly-magic
Se-90. The impact of such hypothesis on the synthesis of heavy nuclei,
particularly in the production of Sr, Y and Zr elements was investigated with a
weak r-process network. The new half lives agree with results obtained from a
standard global QRPA model used in r-process calculations, indicating that
Se-90 has a quadrupole shape incompatible with a closed N=56 sub-shell in this
region. The impact of the measured Se-90 half-life in comparison with a former
theoretical predication associated with a spherical half-life on the
weak-r-process is shown to be strong
Beta-decay half-lives and beta-delayed neutron emission probabilities of nuclei in the region below A=110, relevant for the r-process
Measurements of the beta-decay properties of r-process nuclei below A=110
have been completed at the National Superconducting Cyclotron Laboratory, at
Michigan State University. Beta-decay half-lives for Y-105, Zr-106,107 and
Mo-111, along with beta-delayed neutron emission probabilities of Y-104,
Mo-109,110 and upper limits for Y-105, Zr-103,104,105,106,107 and Mo-108,111
have been measured for the first time. Studies on the basis of the quasi-random
phase approximation are used to analyze the ground-state deformation of these
nuclei.Comment: 21 pages, 10 figures, article accepted for publication in Physical
Review
Generalized Weyl Solutions
It was shown by Weyl that the general static axisymmetric solution of the
vacuum Einstein equations in four dimensions is given in terms of a single
axisymmetric solution of the Laplace equation in three-dimensional flat space.
Weyl's construction is generalized here to arbitrary dimension . The
general solution of the D-dimensional vacuum Einstein equations that admits D-2
orthogonal commuting non-null Killing vector fields is given either in terms of
D-3 independent axisymmetric solutions of Laplace's equation in
three-dimensional flat space or by D-4 independent solutions of Laplace's
equation in two-dimensional flat space. Explicit examples of new solutions are
given. These include a five-dimensional asymptotically flat ``black ring'' with
an event horizon of topology S^1 x S^2 held in equilibrium by a conical
singularity in the form of a disc.Comment: 50 pages, 10 figures; v2: minor improvement
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