7,088 research outputs found
Towards a cross-correlation approach to strong-field dynamics in Black Hole spacetimes
The qualitative and quantitative understanding of near-horizon gravitational
dynamics in the strong-field regime represents a challenge both at a
fundamental level and in astrophysical applications. Recent advances in
numerical relativity and in the geometric characterization of black hole
horizons open new conceptual and technical avenues into the problem. We discuss
here a research methodology in which spacetime dynamics is probed through the
cross-correlation of geometric quantities constructed on the black hole horizon
and on null infinity. These two hypersurfaces respond to evolving gravitational
fields in the bulk, providing canonical "test screens" in a "scattering"-like
perspective onto spacetime dynamics. More specifically, we adopt a 3+1 Initial
Value Problem approach to the construction of generic spacetimes and discuss
the role and properties of dynamical trapping horizons as canonical inner
"screens" in this context. We apply these ideas and techniques to the study of
the recoil dynamics in post-merger binary black holes, an important issue in
supermassive galactic black hole mergers.Comment: 16 pages, 5 figures, contribution to the proceedings volume of the
Spanish Relativity Meeting ERE2011: "Towards new paradigms", Madrid, Spain,
29 Aug-2 Sep 201
Exchange Rates and the International Adjustments Process
macroeconomics, exchange rates
Profitability, Employment and Structural Adjustment in France
In this paper, we present a dynamic model which explains output, enployment and energy consumption in the French manufacturing sector in terms of the expectedand actual path of wage rates and energy prices in units of output. The modelhas two distinguishing features: First, the rate of capacity utilization isdetermined explicitly from profit-maximizing behavior and it is viewed as the crucial adjusting variable in the short run. Second, we assume complete lack of substitutability between capital, labor and energy inputs ex post.The model is motivated by a brief discussion of French growth, focusing on the decline of profitability and employment in manufacturing, and simulated using annual data from 1950 to 1979. The wage explosion and the energy shock of the early seventies are interpreted (in a model allowing for overhead labor) in terms of changes in expected real factor prices,and their effects on the utilizationand the profitability of each vintage are quantified. Aggregating over vintages,the model generates the observed decline in profitability and utilization of existing capacity. The results of the simulation are very encouraging, and a simultaneous estimation of the model under static expectations is rejected by the data. There are two limitations of the analysis which will be relaxed in further work. Investment is exogenous and open-economy aspects only appear indirectly, say via constraints on the energy price and the price of output.
Charge and momentum transfer in supercooled melts: Why should their relaxation times differ?
The steady state values of the viscosity and the intrinsic ionic-conductivity
of quenched melts are computed, in terms of independently measurable
quantities. The frequency dependence of the ac dielectric response is
estimated. The discrepancy between the corresponding characteristic relaxation
times is only apparent; it does not imply distinct mechanisms, but stems from
the intrinsic barrier distribution for -relaxation in supercooled
fluids and glasses. This type of intrinsic ``decoupling'' is argued not to
exceed four orders in magnitude, for known glassformers. We explain the origin
of the discrepancy between the stretching exponent , as extracted from
and the dielectric modulus data. The actual width of the
barrier distribution always grows with lowering the temperature. The contrary
is an artifact of the large contribution of the dc-conductivity component to
the modulus data. The methodology allows one to single out other contributions
to the conductivity, as in ``superionic'' liquids or when charge carriers are
delocalized, implying that in those systems, charge transfer does not require
structural reconfiguration.Comment: submitted to J Chem Phy
Electric and magnetic fields effects on the excitonic properties of elliptic core-multishell quantum wires
The effect of eccentricity distortions of core-multishell quantum wires on
their electron, hole and exciton states is theoretically investigated. Within
the effective mass approximation, the Schrodinger equation is numerically
solved for electrons and holes in systems with single and double radial
heterostructures, and the exciton binding energy is calculated by means of a
variational approach. We show that the energy spectrum of a core-multishell
heterostructure with eccentricity distortions, as well as its magnetic field
dependence, are very sensitive to the direction of an externally applied
electric field, an effect that can be used to identify the eccentricity of the
system. For a double heterostructure, the eccentricities of the inner and outer
shells play an important role on the excitonic binding energy, specially in the
presence of external magnetic fields, and lead to drastic modifications in the
oscillator strength.Comment: 17 pages, 10 figure
Gravitational and magnetosonic waves in gamma-ray bursts
One of the possible sources of gamma-ray bursts are merging, compact
neutronstar binaries. More than 90% of the binding energy of such a binary is
released in the form of gravitational waves (GWs) in the last few seconds of
the spiral-in phase before the formation of a black hole. In this article we
investigate whether a fraction of this GW-energy is transferred to
magnetohydrodynamic waves in the magnetized plasma wind around the binary.
Using the 3+1 orthonormal tedrad formalism, we study the propagation of a
monochromatic, plane fronted, linearly polarized GW perpendicular to the
ambient magnetic field in an ultra-relativistic wind, first in the comoving and
then in the observer frame. A closed set of general relativistic
magnetohydrodynamic equations is derived in the form of conservation laws for
electric charge, matter energy, momentum and magnetic energy densities. We
linearize these equations under the action of a monochromatic GW, which acts as
a driver and find that fast magneto-acoustic waves grow, with amplitudes
proportional to the GW amplitude and frequency and the strength of the
background magnetic field.Comment: Accepted for publication in Astronomy & Astrophysics (A&A). 7 pages,
1 figur
Gravitational wave recoil in Robinson-Trautman spacetimes
We consider the gravitational recoil due to non-reflection-symmetric
gravitational wave emission in the context of axisymmetric Robinson-Trautman
spacetimes. We show that regular initial data evolve generically into a final
configuration corresponding to a Schwarzschild black-hole moving with constant
speed. For the case of (reflection-)symmetric initial configurations, the mass
of the remnant black-hole and the total energy radiated away are completely
determined by the initial data, allowing us to obtain analytical expressions
for some recent numerical results that have been appeared in the literature.
Moreover, by using the Galerkin spectral method to analyze the non-linear
regime of the Robinson-Trautman equations, we show that the recoil velocity can
be estimated with good accuracy from some asymmetry measures (namely the first
odd moments) of the initial data. The extension for the non-axisymmetric case
and the implications of our results for realistic situations involving head-on
collision of two black holes are also discussed.Comment: 9 pages, 6 figures, final version to appear in PR
Cultivo de fruteiras em sistemas agroflorestais.
O que são Sistemas Agroflorestais (SAF). O novo conceito de sistemas agroflorestais. Interações entre componentes em sistemas agroflorestais. Critérios para escolha de espécies frutÃferas para comporem sistemas agroflorestais. Diagnóstico de problemas de uso da terra e o desenho tecnologias agroflorestais
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