5,607 research outputs found
Universal properties of distorted Kerr-Newman black holes
We discuss universal properties of axisymmetric and stationary configurations
consisting of a central black hole and surrounding matter in Einstein-Maxwell
theory. In particular, we find that certain physical equations and inequalities
(involving angular momentum, electric charge and horizon area) are not
restricted to the Kerr-Newman solution but can be generalized to the situation
where the black hole is distorted by an arbitrary axisymmetric and stationary
surrounding matter distribution.Comment: 7 page
The interior of axisymmetric and stationary black holes: Numerical and analytical studies
We investigate the interior hyperbolic region of axisymmetric and stationary
black holes surrounded by a matter distribution. First, we treat the
corresponding initial value problem of the hyperbolic Einstein equations
numerically in terms of a single-domain fully pseudo-spectral scheme.
Thereafter, a rigorous mathematical approach is given, in which soliton methods
are utilized to derive an explicit relation between the event horizon and an
inner Cauchy horizon. This horizon arises as the boundary of the future domain
of dependence of the event horizon. Our numerical studies provide strong
evidence for the validity of the universal relation \Ap\Am = (8\pi J)^2 where
\Ap and \Am are the areas of event and inner Cauchy horizon respectively,
and denotes the angular momentum. With our analytical considerations we are
able to prove this relation rigorously.Comment: Proceedings of the Spanish Relativity Meeting ERE 2010, 10 pages, 5
figure
Questioning the existence of a unique ground state structure for Si clusters
Density functional and quantum Monte Carlo calculations challenge the
existence of a unique ground state structure for certain Si clusters. For Si
clusters with more than a dozen atoms the lowest ten isomers are close in
energy and for some clusters entropic effects can change the energetic ordering
of the configurations. Isotope pure configurations with rotational symmetry and
symmetric configurations containing one additional isotope are disfavored by
these effects. Comparisons with experiment are thus difficult since a mixture
of configurations is to be expected at thermal equilibrium
Alleviation of the Fermion-sign problem by optimization of many-body wave functions
We present a simple, robust and highly efficient method for optimizing all
parameters of many-body wave functions in quantum Monte Carlo calculations,
applicable to continuum systems and lattice models. Based on a strong
zero-variance principle, diagonalization of the Hamiltonian matrix in the space
spanned by the wav e function and its derivatives determines the optimal
parameters. It systematically reduces the fixed-node error, as demonstrated by
the calculation of the binding energy of the small but challenging C
molecule to the experimental accuracy of 0.02 eV
Quantum noise of non-ideal Sagnac speed meter interferometer with asymmetries
The speed meter concept has been identified as a technique that can
potentially provide laser-interferometric measurements at a sensitivity level
which surpasses the Standard Quantum Limit (SQL) over a broad frequency range.
As with other sub-SQL measurement techniques, losses play a central role in
speed meter interferometers and they ultimately determine the quantum noise
limited sensitivity that can be achieved. So far in the literature, the quantum
noise limited sensitivity has only been derived for lossless or lossy cases
using certain approximations (for instance that the arm cavity round trip loss
is small compared to the arm cavity mirror transmission). In this article we
present a generalised, analytical treatment of losses in speed meters that
allows accurate calculation of the quantum noise limited sensitivity of Sagnac
speed meters with arm cavities. In addition, our analysis allows us to take
into account potential imperfections in the interferometer such as an
asymmetric beam splitter or differences of the reflectivities of the two arm
cavity input mirrors. Finally,we use the examples of the proof-of-concept
Sagnac speed meter currently under construction in Glasgow and a potential
implementation of a Sagnac speed meter in the Einstein Telescope (ET) to
illustrate how our findings affect Sagnac speed meters with meter- and
kilometre-long baselines.Comment: 22 pages, 8 figures, 1 table, (minor corrections and changes made to
text and figures in version 2
Implicit self-consistent electrolyte model in plane-wave density-functional theory
The ab-initio computational treatment of electrochemical systems requires an
appropriate treatment of the solid/liquid interfaces. A fully quantum
mechanical treatment of the interface is computationally demanding due to the
large number of degrees of freedom involved. In this work, we describe a
computationally efficient model where the electrode part of the interface is
described at the density-functional theory (DFT) level, and the electrolyte
part is represented through an implicit solvation model based on the
Poisson-Boltzmann equation. We describe the implementation of the linearized
Poisson-Boltzmann equation into the Vienna Ab-initio Simulation Package (VASP),
a widely used DFT code, followed by validation and benchmarking of the method.
To demonstrate the utility of the implicit electrolyte model, we apply it to
study the surface energy of Cu crystal facets in an aqueous electrolyte as a
function of applied electric potential. We show that the applied potential
enables the control of the shape of nanocrystals from an octahedral to a
truncated octahedral morphology with increasing potential
Collisions of rigidly rotating disks of dust in General Relativity
We discuss inelastic collisions of two rotating disks by using the
conservation laws for baryonic mass and angular momentum. In particular, we
formulate conditions for the formation of a new disk after the collision and
calculate the total energy loss to obtain upper limits for the emitted
gravitational energy.Comment: 30 pages, 9 figure
First phylogenetic analyses of galaxy evolution
The Hubble tuning fork diagram, based on morphology, has always been the
preferred scheme for classification of galaxies and is still the only one
originally built from historical/evolutionary relationships. At the opposite,
biologists have long taken into account the parenthood links of living entities
for classification purposes. Assuming branching evolution of galaxies as a
"descent with modification", we show that the concepts and tools of
phylogenetic systematics widely used in biology can be heuristically transposed
to the case of galaxies. This approach that we call "astrocladistics" has been
first applied to Dwarf Galaxies of the Local Group and provides the first
evolutionary galaxy tree. The cladogram is sufficiently solid to support the
existence of a hierarchical organization in the diversity of galaxies, making
it possible to track ancestral types of galaxies. We also find that morphology
is a summary of more fundamental properties. Astrocladistics applied to
cosmology simulated galaxies can, unsurprisingly, reconstruct the correct
"genealogy". It reveals evolutionary lineages, divergences from common
ancestors, character evolution behaviours and shows how mergers organize galaxy
diversity. Application to real normal galaxies is in progress. Astrocladistics
opens a new way to analyse galaxy evolution and a path towards a new
systematics of galaxies
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