6,066 research outputs found
An intrinsic Proper Generalized Decomposition for parametric symmetric elliptic problems
We introduce in this paper a technique for the reduced order approximation of
parametric symmetric elliptic partial differential equations. For any given
dimension, we prove the existence of an optimal subspace of at most that
dimension which realizes the best approximation in mean of the error with
respect to the parameter in the quadratic norm associated to the elliptic
operator, between the exact solution and the Galerkin solution calculated on
the subspace. This is analogous to the best approximation property of the
Proper Orthogonal Decomposition (POD) subspaces, excepting that in our case the
norm is parameter-depending, and then the POD optimal sub-spaces cannot be
characterized by means of a spectral problem. We apply a deflation technique to
build a series of approximating solutions on finite-dimensional optimal
subspaces, directly in the on-line step. We prove that the partial sums
converge to the continuous solutions, in mean quadratic elliptic norm.Comment: 18 page
Understanding chemical evolution in resolved galaxies -- I The local star fraction-metallicity relation
This work studies the relation between gas-phase oxygen abundance and
stellar-to-gas fraction in nearby galaxies. We first derive the theoretical
prediction, and argue that this relation is fundamental, in the sense that it
must be verified regardless of the details of the gas accretion and star
formation histories. Moreover, it should hold on "local" scales, i.e. in
regions of the order of 1 kpc. These predictions are then compared with a set
of spectroscopic observations, including both integrated and resolved data.
Although the results depend somewhat on the adopted metallicity calibration,
observed galaxies are consistent with the predicted relation, imposing tight
constraints on the mass-loading factor of (enriched) galactic winds. The
proposed parametrization of the star fraction-metallicity relation is able to
describe the observed dependence of the oxygen abundance on gas mass at fixed
stellar mass. However, the "local" mass-metallicity relation also depends on
the relation between stellar and gas surface densities.Comment: 10 pages, 4 figures. Matches accepted version (significant typo
corrected
Imposición y bienestar social bajo discriminación espacial de precios
Este trabajo analiza los efectos de la imposición directa e indirecta sobre el bienestar social, en un modelo de entrada en el que las empresas practican discriminación espacial de precios. Se muestra que en un oligopolio la imposición directa puede afectar positiva o negativamente al bienestar social, mientras la imposición indirecta es neutral. Cuando el mercado está monopolizado en ausencia de impuestos, los efectos de los impuestos nunca pueden ser beneficiosos desde la perspectiva del bienestar social.Discriminación espacial de precios, impuestos directos, impuestos indirectos.
Phase-dependent exciton transport and energy harvesting from thermal environments
Non-Markovian effects in the evolution of open quantum systems have recently
attracted widespread interest, particularly in the context of assessing the
efficiency of energy and charge transfer in nanoscale biomolecular networks and
quantum technologies. With the aid of many-body simulation methods, we uncover
and analyse an ultrafast environmental process that causes energy relaxation in
the reduced system to depend explicitly on the phase relation of the initial
state preparation. Remarkably, for particular phases and system parameters, the
net energy flow is uphill, transiently violating the principle of detailed
balance, and implying that energy is spontaneously taken up from the
environment. A theoretical analysis reveals that non-secular contributions,
significant only within the environmental correlation time, underlie this
effect. This suggests that environmental energy harvesting will be observable
across a wide range of coupled quantum systems.Comment: 5 + 4 pages, 3 + 2 figures. Comments welcom
Vacuum fluctuations and the conditional homodyne detection of squeezed light
Conditional homodyne detection of quadrature squeezing is compared with
standard nonconditional detection. Whereas the latter identifies
nonclassicality in a quantitative way, as a reduction of the noise power below
the shot noise level, conditional detection makes a qualitative distinction
between vacuum state squeezing and squeezed classical noise. Implications of
this comparison for the realistic interpretation of vacuum fluctuations
(stochastic electrodynamics) are discussed.Comment: 14 pages, 7 figures, to appear in J. Opt. B: Quantum Semiclass. Op
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