113 research outputs found
Massive vector fields on the Schwarzschild spacetime: quasinormal modes and bound states
We study the propagation of a massive vector or Proca field on the
Schwarzschild spacetime. The field equations are reduced to a one-dimensional
wave equation for the odd-parity part of the field and two coupled equations
for the even-parity part of the field. We use numerical techniques based on
solving (scalar or matrix-valued) three-term recurrence relations to compute
the spectra of both quasi-normal modes and quasi-bound states, which have no
massless analogue, complemented in the latter case by a forward-integration
method. We study the radial equations analytically in both the near-horizon and
far-field regions and use a matching procedure to compute the associated
spectra in the small-mass limit. Finally, we comment on extending our results
to the Kerr geometry and its phenomenological relevance for hidden photons
arising e.g. in string theory compactifications.Comment: 15 pages, 8 figures; minor corrections, to be published in Phys. Rev.
The effect of mildronate on the circadion biorhythm of the parametrs of the excretory renal function
Bound states of spin-half particles in a static gravitational field close to the black hole field
We consider the bound-state energy levels of a spin-1/2 fermion in the
gravitational field of a near-black hole object. In the limit that the metric
of the body becomes singular, all binding energies tend to the rest-mass energy
(i.e. total energy approaches zero). We present calculations of the ground
state energy for three specific interior metrics (Florides, Soffel and
Schwarzschild) for which the spectrum collapses and becomes quasi-continuous in
the singular metric limit. The lack of zero or negative energy states prior to
this limit being reached prevents particle pair production occurring.
Therefore, in contrast to the Coulomb case, no pairs are produced in the
non-singular static metric. For the Florides and Soffel metrics the singularity
occurs in the black hole limit, while for the Schwarzschild interior metric it
corresponds to infinite pressure at the centre. The behaviour of the energy
level spectrum is discussed in the context of the semi-classical approximation
and using general properties of the metric.Comment: 16 pages, 6 Figures. Submitted to General Relativity and Gravitatio
Resonance and absorption spectra of the Schwarzschild black hole for massive scalar perturbations: a complex angular momentum analysis
We reexamine some aspects of scattering by a Schwarzschild black hole in the
framework of complex angular momentum techniques. More precisely, we consider,
for massive scalar perturbations, the high-energy behavior of the resonance
spectrum and of the absorption cross section by emphasizing analytically the
role of the mass. This is achieved (i) by deriving asymptotic expansions for
the Regge poles of the -matrix and then for the associated weakly damped
quasinormal frequencies and (ii) by taking into account the analytic structure
of the greybody factors which allows us to extract by resummation the physical
information encoded in the absorption cross section.Comment: v2: Minor changes to match the published version. v3: Typos correcte
Warm-Start AlphaZero Self-Play Search Enhancements
Recently, AlphaZero has achieved landmark results in deep reinforcement
learning, by providing a single self-play architecture that learned three
different games at super human level. AlphaZero is a large and complicated
system with many parameters, and success requires much compute power and
fine-tuning. Reproducing results in other games is a challenge, and many
researchers are looking for ways to improve results while reducing
computational demands. AlphaZero's design is purely based on self-play and
makes no use of labeled expert data ordomain specific enhancements; it is
designed to learn from scratch. We propose a novel approach to deal with this
cold-start problem by employing simple search enhancements at the beginning
phase of self-play training, namely Rollout, Rapid Action Value Estimate (RAVE)
and dynamically weighted combinations of these with the neural network, and
Rolling Horizon Evolutionary Algorithms (RHEA). Our experiments indicate that
most of these enhancements improve the performance of their baseline player in
three different (small) board games, with especially RAVE based variants
playing strongly
From Chalcogen Bonding to SâÏ Interactions in Hybrid Perovskite Photovoltaics
The stability of hybrid organicâinorganic halide perovskite semiconductors remains a significant obstacle to their application in photovoltaics. To this end, the use of lowâdimensional (LD) perovskites, which incorporate hydrophobic organic moieties, provides an effective strategy to improve their stability, yet often at the expense of their performance. To address this limitation, supramolecular engineering of noncovalent interactions between organic and inorganic components has shown potential by relying on hydrogen bonding and conventional van der Waals interactions. Here, the capacity to access novel LD perovskite structures that uniquely assemble through unorthodox Sâmediated interactions is explored by incorporating benzothiadiazoleâbased moieties. The formation of Sâmediated LD structures is demonstrated, including oneâdimensional (1D) and layered twoâdimensional (2D) perovskite phases assembled via chalcogen bonding and SâÏ interactions, through a combination of techniques, such as single crystal and thin film Xâray diffraction, as well as solidâstate NMR spectroscopy, complemented by molecular dynamics simulations, density functional theory calculations, and optoelectronic characterization, revealing superior conductivities of Sâmediated LD perovskites. The resulting materials are applied in nâiâp and pâiân perovskite solar cells, demonstrating enhancements in performance and operational stability that reveal a versatile supramolecular strategy in photovoltaics
From Chalcogen Bonding to SâÏ Interactions in Hybrid Perovskite Photovoltaics
The stability of hybrid organicâinorganic halide perovskite semiconductors remains a significant obstacle to their application in photovoltaics. To this end, the use of lowâdimensional (LD) perovskites, which incorporate hydrophobic organic moieties, provides an effective strategy to improve their stability, yet often at the expense of their performance. To address this limitation, supramolecular engineering of noncovalent interactions between organic and inorganic components has shown potential by relying on hydrogen bonding and conventional van der Waals interactions. Here, the capacity to access novel LD perovskite structures that uniquely assemble through unorthodox Sâmediated interactions is explored by incorporating benzothiadiazoleâbased moieties. The formation of Sâmediated LD structures is demonstrated, including oneâdimensional (1D) and layered twoâdimensional (2D) perovskite phases assembled via chalcogen bonding and SâÏ interactions, through a combination of techniques, such as single crystal and thin film Xâray diffraction, as well as solidâstate NMR spectroscopy, complemented by molecular dynamics simulations, density functional theory calculations, and optoelectronic characterization, revealing superior conductivities of Sâmediated LD perovskites. The resulting materials are applied in nâiâp and pâiân perovskite solar cells, demonstrating enhancements in performance and operational stability that reveal a versatile supramolecular strategy in photovoltaics
Global maps of the magnetic thickness and magnetization of the Earthâs lithosphere
International audienceWe have constructed global maps of the large-scale magnetic thickness and magnetization of Earth's lithosphere. Deriving such large-scale maps based on lithospheric magnetic field measurements faces the challenge of the masking effect of the core field. In this study, the maps were obtained through analyses in the spectral domain by means of a new regional spatial power spectrum based on the Revised Spherical Cap Harmonic Analysis (R-SCHA) formalism. A series of regional spectral analyses were conducted covering the entire Earth. The R-SCHA surface power spectrum for each region was estimated using the NGDC-720 spherical harmonic (SH) model of the lithospheric magnetic field, which is based on satellite, aeromagnetic, and marine measurements. These observational regional spectra were fitted to a recently proposed statistical expression of the power spectrum of Earth's lithospheric magnetic field, whose free parameters include the thickness and magnetization of the magnetic sources. The resulting global magnetic thickness map is compared to other crustal and magnetic thickness maps based upon different geophysical data. We conclude that the large-scale magnetic thickness of the lithosphere is on average confined to a layer that does not exceed the Moho
Stock markets and effective exchange rates in European countries: threshold cointegration findings
© 2015, Eurasia Business and Economics Society. The nexus between stock markets and exchange rates is examined in the case of eight European countries. The sample consists of four economies with national currencies and four that have adopted the euro. Thus, if differences between the two groups in the relationship governing the two markets exist, they will be unveiled. To this effect, a threshold cointegration methodology is adopted that allows for more reliable inferences to be drawn for both the short and long run nexus between the two markets. Monthly data is used covering the period 01/2000â12/2014. The findings reported herein offer support in favor of the portfolio approach thesis over the recent economic crisis period, but this finding is not the case for the entire sample. Bidirectional causality is found for Norway and the UK, pointing to a currency effect on stock markets. In view of the findings reported herein, policies aiming at reducing uncertainty in the stock markets can exert beneficial effects on currency markets
Continental crust beneath southeast Iceland
The magmatic activity (0â16 Ma) in Iceland is linked to a deep mantle plume that has been active for the past 62 My. Icelandic and northeast Atlantic basalts contain variable proportions of two enriched components, interpreted as recycled oceanic crust supplied by the plume, and subcontinental lithospheric mantle derived from the nearby continental margins. A restricted area in southeast Icelandâand especially the ĂrĂŠfajökull volcanoâis characterized by a unique enriched-mantle component (EM2-like) with elevated 87Sr/86Sr and 207Pb/204Pb. Here, we demonstrate through modeling of SrâNdâPb abundances and isotope ratios that the primitive ĂrĂŠfajökull melts could have assimilated 2â6% of underlying continental crust before differentiating to more evolved melts. From inversion of gravity anomaly data (crustal thickness), analysis of regional magnetic data, and plate reconstructions, we propose that continental crust beneath southeast Iceland is part of âŒ350-km-long and 70-km-wide extension of the Jan Mayen Microcontinent (JMM). The extended JMM was marginal to East Greenland but detached in the Early Eocene (between 52 and 47 Mya); by the Oligocene (27 Mya), all parts of the JMM permanently became part of the Eurasian plate following a westward ridge jump in the direction of the Iceland plume
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