431 research outputs found
Highly-Resolved Numerical Simulation of the Turbulent Combustion Process in Experimental Burners
This paper presents investigations of experimentally well-characterised turbulent flames with highly-resolved Large Eddy Simulations (LES) and Direct Numerical Simulations (DNS). The combustion process is modelled with a flamelet-based approach, which assumes that the local turbulent flame structure can be described by an ensemble of wrinkled laminar flames. Good agreements between the simulation results and experimental measurement data is achieved. The governing equations are discretised with the Finite Volume Method (FVM). The numerical implementation is tailored for massively parallel simulations on a large number of grid cells. The computational efficiency benefits from the applied simple grid structure and the use of non-blocking Message Passing Interface (MPI) parallelisation
Host-induced gene silencing in the necrotrophic fungal pathogen Sclerotinia sclerotiorum.
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Integrated European materials programme for DEMO applications: recent achievements and challenges
Spin effects in gravitational radiation backreaction II. Finite mass effects
A convenient formalism for averaging the losses produced by gravitational
radiation backreaction over one orbital period was developed in an earlier
paper. In the present paper we generalize this formalism to include the case of
a closed system composed from two bodies of comparable masses, one of them
having the spin S.
We employ the equations of motion given by Barker and O'Connell, where terms
up to linear order in the spin (the spin-orbit interaction terms) are kept. To
obtain the radiative losses up to terms linear in the spin, the equations of
motion are taken to the same order. Then the magnitude L of the angular
momentum L, the angle kappa subtended by S and L and the energy E are
conserved. The analysis of the radial motion leads to a new parametrization of
the orbit.
From the instantaneous gravitational radiation losses computed by Kidder the
leading terms and the spin-orbit terms are taken. Following Apostolatos,
Cutler, Sussman and Thorne, the evolution of the vectors S and L in the
momentary plane spanned by these vectors is separated from the evolution of the
plane in space. The radiation-induced change in the spin is smaller than the
leading-order spin terms in the momentary angular momentum loss. This enables
us to compute the averaged losses in the constants of motion E, L and L_S=L cos
kappa. In the latter, the radiative spin loss terms average to zero. An
alternative description using the orbital elements a,e and kappa is given.
The finite mass effects contribute terms, comparable in magnitude, to the
basic, test-particle spin terms in the averaged losses.Comment: 12 pages, 1 figure, Phys.Rev.D15, March, 199
Generalized quasiperiodic Rauzy tilings
We present a geometrical description of new canonical -dimensional
codimension one quasiperiodic tilings based on generalized Fibonacci sequences.
These tilings are made up of rhombi in 2d and rhombohedra in 3d as the usual
Penrose and icosahedral tilings. Thanks to a natural indexing of the sites
according to their local environment, we easily write down, for any
approximant, the sites coordinates, the connectivity matrix and we compute the
structure factor.Comment: 11 pages, 3 EPS figures, final version with minor change
Reducing orbital eccentricity in binary black hole simulations
Binary black hole simulations starting from quasi-circular (i.e., zero radial
velocity) initial data have orbits with small but non-zero orbital
eccentricities. In this paper the quasi-equilibrium initial-data method is
extended to allow non-zero radial velocities to be specified in binary black
hole initial data. New low-eccentricity initial data are obtained by adjusting
the orbital frequency and radial velocities to minimize the orbital
eccentricity, and the resulting ( orbit) evolutions are compared with
those of quasi-circular initial data. Evolutions of the quasi-circular data
clearly show eccentric orbits, with eccentricity that decays over time. The
precise decay rate depends on the definition of eccentricity; if defined in
terms of variations in the orbital frequency, the decay rate agrees well with
the prediction of Peters (1964). The gravitational waveforms, which contain
cycles in the dominant l=m=2 mode, are largely unaffected by the
eccentricity of the quasi-circular initial data. The overlap between the
dominant mode in the quasi-circular evolution and the same mode in the
low-eccentricity evolution is about 0.99.Comment: 27 pages, 9 figures; various minor clarifications; accepted to the
"New Frontiers" special issue of CQ
Energy spectra, wavefunctions and quantum diffusion for quasiperiodic systems
We study energy spectra, eigenstates and quantum diffusion for one- and
two-dimensional quasiperiodic tight-binding models. As our one-dimensional
model system we choose the silver mean or `octonacci' chain. The
two-dimensional labyrinth tiling, which is related to the octagonal tiling, is
derived from a product of two octonacci chains. This makes it possible to treat
rather large systems numerically. For the octonacci chain, one finds singular
continuous energy spectra and critical eigenstates which is the typical
behaviour for one-dimensional Schr"odinger operators based on substitution
sequences. The energy spectra for the labyrinth tiling can, depending on the
strength of the quasiperiodic modulation, be either band-like or fractal-like.
However, the eigenstates are multifractal. The temporal spreading of a
wavepacket is described in terms of the autocorrelation function C(t) and the
mean square displacement d(t). In all cases, we observe power laws for C(t) and
d(t) with exponents -delta and beta, respectively. For the octonacci chain,
0<delta<1, whereas for the labyrinth tiling a crossover is observed from
delta=1 to 0<delta<1 with increasing modulation strength. Corresponding to the
multifractal eigenstates, we obtain anomalous diffusion with 0<beta<1 for both
systems. Moreover, we find that the behaviour of C(t) and d(t) is independent
of the shape and the location of the initial wavepacket. We use our results to
check several relations between the diffusion exponent beta and the fractal
dimensions of energy spectra and eigenstates that were proposed in the
literature.Comment: 24 pages, REVTeX, 10 PostScript figures included, major revision, new
results adde
Spin effects in gravitational radiation backreaction III. Compact binaries with two spinning components
The secular evolution of a spinning, massive binary system in eccentric orbit
is analyzed, expanding and generalizing our previous treatments of the
Lense-Thirring motion and the one-spin limit. The spin-orbit and spin-spin
effects up to the 3/2 post-Newtonian order are considered, both in the
equations of motion and in the radiative losses. The description of the orbit
in terms of the true anomaly parametrization provides a simple averaging
technique, based on the residue theorem, over eccentric orbits. The evolution
equations of the angle variables characterizing the relative orientation of the
spin and orbital angular momenta reveal a speed-up effect due to the
eccentricity. The dissipative evolutions of the relevant dynamical and angular
variables is presented in the form of a closed system of differential
equations.Comment: 10 pages, 1 figur
Spin-spin effects in radiating compact binaries
The dynamics of a binary system with two spinning components on an eccentric
orbit is studied, with the inclusion of the spin-spin interaction terms
appearing at the second post-Newtonian order. A generalized true anomaly
parametrization properly describes the radial component of the motion. The
average over one radial period of the magnitude of the orbital angular momentum
is found to have no nonradiative secular change. All spin-spin terms
in the secular radiative loss of the energy and magnitude of orbital angular
momentum are given in terms of and other constants of the motion.
Among them, self-interaction spin effects are found, representing the second
post-Newtonian correction to the 3/2 post-Newtonian order Lense-Thirring
approximation.Comment: 12 pages, to appear in Phys. Rev.
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