100,343 research outputs found
Regular binary thermal lattice-gases
We analyze the power spectrum of a regular binary thermal lattice gas in two
dimensions and derive a Landau-Placzek formula, describing the power spectrum
in the low-wavelength, low frequency domain, for both the full mixture and a
single component in the binary mixture. The theoretical results are compared
with simulations performed on this model and show a perfect agreement. The
power spectrums are found to be similar in structure as the ones obtained for
the continuous theory, in which the central peak is a complicated superposition
of entropy and concentration contributions, due to the coupling of the
fluctuations in these quantities. Spectra based on the relative difference
between both components have in general additional Brillouin peaks as a
consequence of the equipartition failure.Comment: 20 pages including 9 figures in RevTex
PyFrac: A planar 3D hydraulic fracture simulator
Fluid driven fractures propagate in the upper earth crust either naturally or
in response to engineered fluid injections. The quantitative prediction of
their evolution is critical in order to better understand their dynamics as
well as to optimize their creation. We present a Python implementation of an
open-source hydraulic fracture propagation simulator based on the implicit
level set algorithm originally developed by Peirce & Detournay (2008) -- "An
implicit level set method for modeling hydraulically driven fractures". Comp.
Meth. Appl. Mech. Engng, (33-40):2858--2885. This algorithm couples a finite
discretization of the fracture with the use of the near tip asymptotic
solutions of a steadily propagating semi-infinite hydraulic fracture. This
allows to resolve the multi-scale processes governing hydraulic fracture growth
accurately, even with relatively coarse meshes. We present an overview of the
mathematical formulation, the numerical scheme and the details of our
implementation. A series of problems including a radial hydraulic fracture
verification benchmark, the propagation of a height contained hydraulic
fracture, the lateral spreading of a magmatic dyke and the handling of fracture
closure are presented to demonstrate the capabilities, accuracy and robustness
of the implemented algorithm
Signal Detection for QPSK Based Cognitive Radio Systems using Support Vector Machines
Cognitive radio based network enables opportunistic dynamic spectrum access by sensing, adopting and utilizing the unused portion of licensed spectrum bands. Cognitive radio is intelligent enough to adapt the communication parameters of the unused licensed spectrum. Spectrum sensing is one of the most important tasks of the cognitive radio cycle. In this paper, the auto-correlation function kernel based Support Vector Machine (SVM) classifier along with Welch's Periodogram detector is successfully implemented for the detection of four QPSK (Quadrature Phase Shift Keying) based signals propagating through an AWGN (Additive White Gaussian Noise) channel. It is shown that the combination of statistical signal processing and machine learning concepts improve the spectrum sensing process and spectrum sensing is possible even at low Signal to Noise Ratio (SNR) values up to -50 dB
A general theory of linear cosmological perturbations: bimetric theories
We implement the method developed in [1] to construct the most general
parametrised action for linear cosmological perturbations of bimetric theories
of gravity. Specifically, we consider perturbations around a homogeneous and
isotropic background, and identify the complete form of the action invariant
under diffeomorphism transformations, as well as the number of free parameters
characterising this cosmological class of theories. We discuss, in detail, the
case without derivative interactions, and compare our results with those found
in massive bigravity.Comment: Published version with extra comments in conclusio
Electromagnetic wave propagation inside a material medium: an effective geometry interpretation
We present a method developed to deal with electromagnetic wave propagation
inside a material medium that reacts, in general, non-linearly to the field
strength. We work in the context of Maxwell' s theory in the low frequency
limit and obtain a geometrical representation of light paths for each case
presented. The isotropic case and artificial birefringence caused by an
external electric field are analyzed as an application of the formalism and the
effective geometry associated to the wave propagation is exhibited.Comment: REVTeX file, 6 pages. Version to appear in Phys. Lett.
(Curvature)^2-Terms for Supergravity in Three Dimension
We investigate the effect of (Curvature)^2-terms on N=1 and N=2 supergravity
in three dimensions. We use the off-shell component fields (e_\mu{}^m,
\psi_\mu, S) for N=1 and (e_\mu{}^m, \psi_\mu, \psi_\mu^*, A_\mu, B, B^*) for
N=2 supergravity. The S, A_\mu and B are respectively a real scalar, a real
vector and a complex scalar auxiliary fields. Both for N=1 and N=2, only two
invariant actions for (Curvature)^2-terms exist, while only the actions with
(Scalar Curvature)^2 are free of negative energy ghosts. Interestingly, the
originally non-physical graviton and gravitino fields start propagating,
together with the scalar field S for the N=1 case, or the complex scalar B and
the longitudinal component \partial_\mu A^\mu for N=2. These new propagating
fields form two new physical massive supermultiplets of spins (1/2,0) with 2 x
(1+1) degrees of freedom for the N=1 case, and two physical massive N=2
supermultiplets of spins (1/2,1/2,0,0) with 2 x (2+2) degrees of freedom for
the N=2 case.Comment: 14 pages, no figure
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