843 research outputs found
Topography, substratum and benthic macrofaunal relationships on a tropical mesophotic shelf margin, central Great Barrier Reef, Australia
Habitats and ecological communities occurring in the mesophotic region of the central Great Barrier Reef (GBR), Australia, were investigated using autonomous underwater vehicle (AUV) from 51 to 145 m. High-resolution multibeam bathymetry of the outer-shelf at Hydrographers Passage in the central GBR revealed submerged linear reefs with tops at 50, 55, 80, 90, 100 and 130 m separated by flat, sandy inter-reefal areas punctuated by limestone pinnacles. Cluster analysis of AUV images yielded five distinct site groups based on their benthic macrofauna, with rugosity and the presence of limestone reef identified as the most significant abiotic factors explaining the distribution of macrofaunal communities. Reef-associated macrofaunal communities occurred in three distinct depth zones: (1) a shallow (75 m). The effects of depth and microhabitat topography on irradiance most likely play a critical role in controlling vertical zonation on reef substrates. The lower depth limits of zooxanthellate corals are significantly shallower than that observed in many other mesophotic coral ecosystems. This may be a result of resuspension of sediments from the sand sheets by strong currents and/or a consequence of cold water upwelling
Characterising a solid state qubit via environmental noise
We propose a method for characterising the energy level structure of a
solid-state qubit by monitoring the noise level in its environment. We consider
a model persistent-current qubit in a lossy resevoir and demonstrate that the
noise in a classical bias field is a sensitive function of the applied field.Comment: 3 Figure
Immediate reward reinforcement learning for clustering and topology preserving mappings
We extend a reinforcement learning algorithm which has previously been shown to cluster data. Our extension involves creating an underlying latent space with some pre-defined structure which enables us to create a topology preserving mapping. We investigate different forms of the reward function, all of which are created with the intent of merging local and global information, thus avoiding one of the major difficulties with e.g. K-means which is its convergence to local optima depending on the initial values of its parameters. We also show that the method is quite general and can be used with the recently developed method of stochastic weight reinforcement learning [14]
Neutron star properties in the quark-meson coupling model
The effects of internal quark structure of baryons on the composition and
structure of neutron star matter with hyperons are investigated in the
quark-meson coupling (QMC) model. The QMC model is based on mean-field
description of nonoverlapping spherical bags bound by self-consistent exchange
of scalar and vector mesons. The predictions of this model are compared with
quantum hadrodynamic (QHD) model calibrated to reproduce identical nuclear
matter saturation properties. By employing a density dependent bag constant
through direct coupling to the scalar field, the QMC model is found to exhibit
identical properties as QHD near saturation density. Furthermore, this modified
QMC model provides well-behaved and continuous solutions at high densities
relevant to the core of neutron stars. Two additional strange mesons are
introduced which couple only to the strange quark in the QMC model and to the
hyperons in the QHD model. The constitution and structure of stars with
hyperons in the QMC and QHD models reveal interesting differences. This
suggests the importance of quark structure effects in the baryons at high
densities.Comment: 28 pages, 10 figures, to appear in Physical Review
Stochastic Lagrangian Particle Approach to Fractal Navier-Stokes Equations
In this article we study the fractal Navier-Stokes equations by using
stochastic Lagrangian particle path approach in Constantin and Iyer
\cite{Co-Iy}. More precisely, a stochastic representation for the fractal
Navier-Stokes equations is given in terms of stochastic differential equations
driven by L\'evy processes. Basing on this representation, a self-contained
proof for the existence of local unique solution for the fractal Navier-Stokes
equation with initial data in \mW^{1,p} is provided, and in the case of two
dimensions or large viscosity, the existence of global solution is also
obtained. In order to obtain the global existence in any dimensions for large
viscosity, the gradient estimates for L\'evy processes with time dependent and
discontinuous drifts is proved.Comment: 19 page
Comparisons of Statistical Multifragmentation and Evaporation Models for Heavy Ion Collisions
The results from ten statistical multifragmentation models have been compared
with each other using selected experimental observables. Even though details in
any single observable may differ, the general trends among models are similar.
Thus these models and similar ones are very good in providing important physics
insights especially for general properties of the primary fragments and the
multifragmentation process. Mean values and ratios of observables are also less
sensitive to individual differences in the models. In addition to
multifragmentation models, we have compared results from five commonly used
evaporation codes. The fluctuations in isotope yield ratios are found to be a
good indicator to evaluate the sequential decay implementation in the code. The
systems and the observables studied here can be used as benchmarks for the
development of statistical multifragmentation models and evaporation codes.Comment: To appear on Euorpean Physics Journal A as part of the Topical Volume
"Dynamics and Thermodynamics with Nuclear Degrees of Freedo
Covariant Field Equations, Gauge Fields and Conservation Laws from Yang-Mills Matrix Models
The effective geometry and the gravitational coupling of nonabelian gauge and
scalar fields on generic NC branes in Yang-Mills matrix models is determined.
Covariant field equations are derived from the basic matrix equations of
motions, known as Yang-Mills algebra. Remarkably, the equations of motion for
the Poisson structure and for the nonabelian gauge fields follow from a matrix
Noether theorem, and are therefore protected from quantum corrections. This
provides a transparent derivation and generalization of the effective action
governing the SU(n) gauge fields obtained in [1], including the would-be
topological term. In particular, the IKKT matrix model is capable of describing
4-dimensional NC space-times with a general effective metric. Metric
deformations of flat Moyal-Weyl space are briefly discussed.Comment: 31 pages. V2: minor corrections, references adde
Existence and Nonlinear Stability of Rotating Star Solutions of the Compressible Euler-Poisson Equations
We prove existence of rotating star solutions which are steady-state
solutions of the compressible isentropic Euler-Poisson (EP) equations in 3
spatial dimensions, with prescribed angular momentum and total mass. This
problem can be formulated as a variational problem of finding a minimizer of an
energy functional in a broader class of functions having less symmetry than
those functions considered in the classical Auchmuty-Beals paper. We prove the
nonlinear dynamical stability of these solutions with perturbations having the
same total mass and symmetry as the rotating star solution. We also prove local
in time stability of W^{1, \infty}(\RR^3) solutions where the perturbations
are entropy-weak solutions of the EP equations. Finally, we give a uniform (in
time) a-priori estimate for entropy-weak solutions of the EP equations
Is there a Jordan geometry underlying quantum physics?
There have been several propositions for a geometric and essentially
non-linear formulation of quantum mechanics. From a purely mathematical point
of view, the point of view of Jordan algebra theory might give new strength to
such approaches: there is a ``Jordan geometry'' belonging to the Jordan part of
the algebra of observables, in the same way as Lie groups belong to the Lie
part. Both the Lie geometry and the Jordan geometry are well-adapted to
describe certain features of quantum theory. We concentrate here on the
mathematical description of the Jordan geometry and raise some questions
concerning possible relations with foundational issues of quantum theory.Comment: 30 page
Polaron formation for a non-local electron-phonon coupling: A variational wave-function study
We introduce a variational wave-function to study the polaron formation when
the electronic transfer integral depends on the relative displacement between
nearest-neighbor sites giving rise to a non-local electron-phonon coupling with
optical phonon modes. We analyze the ground state properties such as the
energy, the electron-lattice correlation function, the phonon number and the
spectral weight. Variational results are found in good agreement with analytic
weak-coupling perturbative calculations and exact numerical diagonalization of
small clusters. We determine the polaronic phase diagram and we find that the
tendency towards strong localization is hindered from the pathological sign
change of the effective next-nearest-neighbor hopping.Comment: 11 page
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