5,767 research outputs found
Submodular Welfare Maximization
An overview of different variants of the submodular welfare maximization
problem in combinatorial auctions. In particular, I studied the existing
algorithmic and game theoretic results for submodular welfare maximization
problem and its applications in other areas such as social networks
Excitation of stellar p-modes by turbulent convection: 1. Theoretical formulation
Stochatic excitation of stellar oscillations by turbulent convection is
investigated and an expression for the power injected into the oscillations by
the turbulent convection of the outer layers is derived which takes into
account excitation through turbulent Reynolds stresses and turbulent entropy
fluctuations. This formulation generalizes results from previous works and is
built so as to enable investigations of various possible spatial and temporal
spectra of stellar turbulent convection. For the Reynolds stress contribution
and assuming the Kolmogorov spectrum we obtain a similar formulation than those
derived by previous authors. The entropy contribution to excitation is found to
originate from the advection of the Eulerian entropy fluctuations by the
turbulent velocity field. Numerical computations in the solar case in a
companion paper indicate that the entropy source term is dominant over Reynold
stress contribution to mode excitation, except at high frequencies.Comment: 14 pages, accepted for publication in A&
The Effect of Large Scale Magnetic Field on Outflow in ADAFs: an Odd Symmetry Configuration
We construct self-similar inflow-outflow solutions for a hot
viscous-resistive accretion flow with large scale magnetic fields that have odd
symmetry with respect to the equatorial plane in , and even symmetry
in and . Following previous authors, we also assume that the
polar velocity is nonzero. We focus on four parameters:
, (the plasma beta parameters for associated with
magnetic field components at the equatorial plane), the magnetic resistivity
, and the density index . The resulting flow
solutions are divided into two parts consisting of an inflow region with a
negative radial velocity (. Our
results show that stronger outflows emerge for smaller
( for ) and larger values of , and
.Comment: 10 pages, 9 figures, Accepted for publication MNRA
Excitation of non-radial stellar oscillations by gravitational waves: a first model
The excitation of solar and solar-like g modes in non-relativistic stars by
arbitrary external gravitational wave fields is studied starting from the full
field equations of general relativity. We develop a formalism that yields the
mean-square amplitudes and surface velocities of global normal modes excited in
such a way. The isotropic elastic sphere model of a star is adopted to
demonstrate this formalism and for calculative simplicity. It is shown that
gravitational waves solely couple to quadrupolar spheroidal eigenmodes and that
normal modes are only sensitive to the spherical component of the gravitational
waves having the same azimuthal order. The mean-square amplitudes in case of
stationary external gravitational waves are given by a simple expression, a
product of a factor depending on the resonant properties of the star and the
power spectral density of the gravitational waves' spherical accelerations.
Both mean-square amplitudes and surface velocities show a characteristic
R^8-dependence (effective R^2-dependence) on the radius of the star. This
finding increases the relevance of this excitation mechanism in case of stars
larger than the Sun.Comment: 8 pages, to be published in MNRAS (in press); corrected typo
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