10,420 research outputs found
Effect of Multiple Higgs Fields on the Phase Structure of the SU(2)-Higgs Model
The SU(2)-Higgs model, with a single Higgs field in the fundamental
representation and a quartic self-interaction, has a Higgs region and a
confinement region which are analytically connected in the parameter space of
the theory; these regions thus represent a single phase. The effect of multiple
Higgs fields on this phase structure is examined via Monte Carlo lattice
simulations. For the case of N>=2 identical Higgs fields, there is no remaining
analytic connection between the Higgs and confinement regions, at least when
Lagrangian terms that directly couple different Higgs flavours are omitted. An
explanation of this result in terms of enhancement from overlapping phase
transitions is explored for N=2 by introducing an asymmetry in the hopping
parameters of the Higgs fields. It is found that an enhancement of the phase
transitions can still occur for a moderate (10%) asymmetry in the resulting
hopping parameters.Comment: 10 pages, 8 figures. References updated and minor typos correcte
Modeling Merging Galaxies using MINGA - Improving Restricted N-body by Dynamical Friction
Modeling interacting galaxies to reproduce observed systems is still a
challenge due to the extended parameter space (among other problems). Orbit and
basic galaxy parameters can be tackled by fast simulation techniques like the
restricted N-body method, applied in the fundamental work by Toomre & Toomre
(1972). This approach allows today for the study of millions of models in a
short time. One difficulty for the classical restricted N-body method is the
missing orbital decay, not allowing for galaxy mergers. Here we present an
extension of the restricted N-body method including dynamical friction. This
treatment has been developed by a quantitative comparison with a set of
self-consistent merger simulations. By varying the dynamical friction
(formalism, strength and direction), we selected the best-fitting parameters
for a set of more than 250000 simulations. We show that our treatment reliably
reproduces the orbital decay and tidal features of merging disk galaxies for
mass ratios up to q=1/3 between host and satellite. We implemented this
technique into our genetic algorithm based modeling code MINGA and present
first results.Comment: To be published in the proceedings of the "Galactic and Stellar
Dynamics 2008" conference. 4 pages, 4 figures, 2 table
Meromorphy and topology of localized solutions in the Thomas–MHD model
The one-dimensional MHD system first introduced by J.H. Thomas [Phys. Fluids 11, 1245 (1968)] as a model of the dynamo effect is thoroughly studied in the limit of large magnetic Prandtl number. The focus is on two types of localized solutions involving shocks (antishocks) and hollow (bump) waves. Numerical simulations suggest phenomenological rules concerning their generation, stability and basin of attraction. Their topology, amplitude and thickness are compared favourably with those of the meromorphic travelling waves, which are obtained exactly, and respectively those of asymptotic descriptions involving rational or degenerate elliptic functions. The meromorphy bars the existence of certain configurations, while others are explained by assuming imaginary residues. These explanations are tested using the numerical amplitude and phase of the Fourier transforms as probes of the analyticity properties. Theoretically, the proof of the partial integrability backs up the role ascribed to meromorphy. Practically, predictions are derived for MHD plasmas
Accurate calculation of the solutions to the Thomas-Fermi equations
We obtain highly accurate solutions to the Thomas-Fermi equations for atoms
and atoms in very strong magnetic fields. We apply the Pad\'e-Hankel method,
numerical integration, power series with Pad\'e and Hermite-Pad\'e approximants
and Chebyshev polynomials. Both the slope at origin and the location of the
right boundary in the magnetic-field case are given with unprecedented
accuracy
Chandrasekhar's Dynamical Friction and non-extensive statistics
The motion of a point like object of mass passing through the background
potential of massive collisionless particles () suffers a steady
deceleration named dynamical friction. In his classical work, Chandrasekhar
assumed a Maxwellian velocity distribution in the halo and neglected the self
gravity of the wake induced by the gravitational focusing of the mass . In
this paper, by relaxing the validity of the Maxwellian distribution due to the
presence of long range forces, we derive an analytical formula for the
dynamical friction in the context of the -nonextensive kinetic theory. In
the extensive limiting case (), the classical Gaussian Chandrasekhar
result is recovered. As an application, the dynamical friction timescale for
Globular Clusters spiraling to the galactic center is explicitly obtained. Our
results suggest that the problem concerning the large timescale as derived by
numerical -body simulations or semi-analytical models can be understood as a
departure from the standard extensive Maxwellian regime as measured by the
Tsallis nonextensive -parameter.Comment: 16pp 5 figs, revised and extended version of arXiv:1202.1873 .
Accepted for publication by JCA
Low frequency elastic wave propagation in 2D locally resonant phononic crystal with asymmetric resonator
The resonance modes and the related effects to the transmission of elastic
waves in a two dimensional phononic crystal formed by periodic arrangements of
a two blocks unit cell in one direction are studied. The unit cell consists of
two asymmetric elliptic cylinders coated with silicon rubber and embedded in a
rigid matrix. The modes are obtained by the semi-analytic method in the least
square collocation scheme and confirmed by the finite element method
simulations. Two resonance modes, corresponding to the vibration of the
cylinder along the long and short axes, give rise to resonance reflections of
elastic waves. One mode in between the two modes, related to the opposite
vibration of the two cylinders in the unit cell in the direction along the
layer, results in the total transmission of elastic waves due to zero effective
mass density at the frequency. The resonance frequency of this new mode changes
continuously with the orientation angle of the elliptic resonator.Comment: 17 pages, 7 figure
OEXP Analysis Tools Workshop
This publication summarizes the software needs and available analysis tools presented at the OEXP Analysis Tools Workshop held at the NASA Langley Research Center, Hampton, Virginia on June 21 to 22, 1988. The objective of the workshop was to identify available spacecraft system (and subsystem) analysis and engineering design tools, and mission planning and analysis software that could be used for various NASA Office of Exploration (code Z) studies, specifically lunar and Mars missions
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