9,925 research outputs found
Spin effects in the phasing of gravitational waves from binaries on eccentric orbits
We compute here the spin-orbit and spin-spin couplings needed for an accurate
computation of the phasing of gravitational waves emitted by comparable-mass
binaries on eccentric orbits at the second post-Newtonian (PN) order. We use a
quasi-Keplerian parametrization of the orbit free of divergencies in the zero
eccentricity limit. We find that spin-spin couplings induce a residual
eccentricity for coalescing binaries at 2PN, of the order of
- for supermassive black hole binaries in the LISA band.
Spin-orbit precession also induces a non-trivial pattern in the evolution of
the eccentricity, which could help to reduce the errors on the determination of
the eccentricity and spins in a gravitational wave measurement.Comment: 7 pages, 1 figure; Accepted for publication in Phys. Rev.
A Langevin equation for the energy cascade in fully-developed turbulence
Experimental data from a turbulent jet flow is analysed in terms of an
additive, continuous stochastic process where the usual time variable is
replaced by the scale. We show that the energy transfer through scales is well
described by a linear Langevin equation, and discuss the statistical properties
of the corresponding random force in detail. We find that the autocorrelation
function of the random force decays rapidly: the process is therefore Markov
for scales larger than Kolmogorov's dissipation scale . The corresponding
autocorrelation scale is identified as the elementary step of the energy
cascade. However, the probability distribution function of the random force is
both non-Gaussian and weakly scale-dependent.Comment: 25 pages, 10 figures, elsart.sty, to be published in Physica
Reallocation Problems in Agent Societies: A Local Mechanism to Maximize Social Welfare
Resource reallocation problems are common in real life and therefore gain an increasing interest in Computer Science and Economics. Such problems consider agents living in a society and negotiating their resources with each other in order to improve the welfare of the population. In many studies however, the unrealistic context considered, where agents have a flawless knowledge and unlimited interaction abilities, impedes the application of these techniques in real life problematics. In this paper, we study how agents should behave in order to maximize the welfare of the society. We propose a multi-agent method based on autonomous agents endowed with a local knowledge and local interactions. Our approach features a more realistic environment based on social networks, inside which we provide the behavior for the agents and the negotiation settings required for them to lead the negotiation processes towards socially optimal allocations. We prove that bilateral transactions of restricted cardinality are sufficient in practice to converge towards an optimal solution for different social objectives. An experimental study supports our claims and highlights the impact of a realistic environment on the efficiency of the techniques utilized.Resource Allocation, Negotiation, Social Welfare, Agent Society, Behavior, Emergence
Agricultural Insurances Based on Meteorological Indices: Realizations, Methods and Research Agenda
In many low-income countries, agriculture is mostly rain-fed and yields highly depend on climatic factors. Furthermore, farmers have little access to traditional crop insurance, which suffers from high information asymmetry and transaction costs. Insurances based on meteorological indices could fill this gap since they do not face such drawbacks. However their implementation has been slow so far. In this article, we first describe the most advanced projects that have taken place in developing countries using these types of crop insurances. We then describe the methodology that has been used to design such projects, in order to choose the meteorological index, the indemnity schedule and the insurance premium. We finally draw an agenda for research in economics on this topic. In particular, more research is needed on implementation issues, on the assessment of benefits, on the way to deal with climate change, on the spatial variability of weather and on the interactions with other hedging methods.Agriculture, Insurance, Climatic Risk
Parameter estimation for coalescing massive binary black holes with LISA using the full 2-post-Newtonian gravitational waveform and spin-orbit precession
With one exception, previous analyses of the measurement accuracy of
gravitational wave experiments for comparable-mass binary systems have
neglected either spin-precession effects or subdominant harmonics and amplitude
modulations. Here we give the first explicit description of how these effects
combine to improve parameter estimation. We consider supermassive black hole
binaries as expected to be observed with the planned space-based interferometer
LISA, and study the measurement accuracy for several astrophysically
interesting parameters obtainable taking into account the full 2PN waveform for
spinning bodies, as well as spin-precession effects. We find that for binaries
with a total mass in the range 10^5 M_Sun < M < 10^7 M_Sun at a redshift of 1,
a factor ~1.5 is in general gained in accuracy, with the notable exception of
the determination of the individual masses in equal-mass systems, for which a
factor ~5 can be gained. We also find, as could be expected, that using the
full waveform helps increasing the upper mass limit for detection, which can be
as high as M = 10^8 M_Sun at a redshift of 1, as well as the redshift limit
where some information can be extracted from a system, which is roughly z = 10
for M < 10^7 M_Sun, 1.5-5 times higher than with the restricted waveform. We
computed that the full waveform allows to use supermassive black hole binaries
as standard sirens up to a redshift of z = 1.6, about 0.4 larger than what
previous studies allowed. We found that for lower unequal-mass binary systems,
the measurement accuracy is not as drastically improved as for other systems.
This suggests that for these systems, adding parameters such as eccentricity or
alternative gravity parameters could be achieved without much loss in the
accuracy.Comment: 20 pages, 20 figure
Gravitational wave energy spectrum of hyperbolic encounters
The emission of gravitational waves is studied for a system of massive
objects interacting on hyperbolic orbits within the quadrupole approximation
following the work of Capozziello et al. Here we focus on the derivation of an
analytic formula for the energy spectrum of the emitted waves. We checked
numerically that our formula is in agreement with the two limiting cases for
which results were already available: for the eccentricity {\epsilon} = 1, the
parabolic case whose spectrum was computed by Berry and Gair, and the large
{\epsilon} limit with the formula given by Turner.Comment: 9 pages, 4 figures, Accepted for publication in Physical Review
Shear instability of an axisymmetric air-water coaxial jet
We study the destabilization of a round liquid jet by a fast annular gas
stream. We measure the frequency of the shear instability waves for several
geometries and air/water velocities. We then carry out a linear stability
analysis, and show that there are three competing mechanisms for the
destabilization: a convective instability, an absolute instability driven by
surface tension, and an absolute instability driven by confinement. We compare
the predictions of this analysis with experimental results, and propose scaling
laws for wave frequency in each regime. We finally introduce criteria to
predict the boundaries between these three regimes
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