1,282 research outputs found
Equations of state and stability of MgSiO perovskite and post-perovskite phases from quantum Monte Carlo simulations
We have performed quantum Monte Carlo (QMC) simulations and density
functional theory (DFT) calculations to study the equations of state of
MgSiO perovskite (Pv) and post-perovskite (PPv), up to the pressure and
temperature conditions of the base of Earth's lower mantle. The ground state
energies were derived using QMC and the temperature dependent Helmholtz free
energies were calculated within the quasi-harmonic approximation and density
functional perturbation theory. The equations of state for both phases of
MgSiO agree well with experiments, and better than those from generalized
gradient approximation (GGA) calculations. The Pv-PPv phase boundary calculated
from our QMC equations of states is also consistent with experiments, and
better than previous LDA calculations. We discuss the implications for double
crossing of the Pv-PPv boundary in the Earth
Rocky core solubility in Jupiter and giant exoplanets
Gas giants are believed to form by the accretion of hydrogen-helium gas
around an initial protocore of rock and ice. The question of whether the rocky
parts of the core dissolve into the fluid H-He layers following formation has
significant implications for planetary structure and evolution. Here we use ab
initio calculations to study rock solubility in fluid hydrogen, choosing MgO as
a representative example of planetary rocky materials, and find MgO to be
highly soluble in H for temperatures in excess of approximately 10000 K,
implying significant redistribution of rocky core material in Jupiter and
larger exoplanets
Mixed neutron-star-plus-wormhole systems: Equilibrium configurations
We study gravitationally bound, spherically symmetric equilibrium
configurations consisting of ordinary (neutron-star) matter and of a
phantom/ghost scalar field which provides the nontrivial topology in the
system. For such mixed configurations, we show the existence of static,
regular, asymptotically flat general relativistic solutions. Based on the
energy approach, we discuss the stability as a function of the core density of
the neutron matter for various sizes of the wormhole throat.Comment: 18 pages, 3 figures, minor corrections to content, references added,
version published in PR
Multisphalerons in the Weinberg-Salam Theory
We construct multisphaleron solutions in the Weinberg-Salam theory. The
multisphaleron solutions carry Chern-Simons charge , where is an
integer, counting the winding of the fields in the azimuthal angle. The
well-known sphaleron has . The multisphalerons possess axial symmetry and
parity reflection symmetry. We vary the Higgs mass and the mixing angle. For
small the energies of the multisphalerons are on the order of times the
energy of the sphaleron and their magnetic dipole moments are on the order of
times the magnetic dipole moment of the sphaleron.Comment: 18 pages, latex, 17 figures in uuencoded postscript files. THU-94/1
Manifolds with 1/4-pinched flag curvature
We say that a nonnegatively curved manifold has quarter pinched flag
curvature if for any two planes which intersect in a line the ratio of their
sectional curvature is bounded above by 4. We show that these manifolds have
nonnegative complex sectional curvature. By combining with a theorem of Brendle
and Schoen it follows that any positively curved manifold with strictly quarter
pinched flag curvature must be a space form. This in turn generalizes a result
of Andrews and Nguyen in dimension 4. For odd dimensional manifolds we obtain
results for the case that the flag curvature is pinched with some constant
below one quarter, one of which generalizes a recent work of Petersen and Tao
Static black hole solutions with axial symmetry
We construct a new class of asymptotically flat black hole solutions in
Einstein-Yang-Mills and Einstein-Yang-Mills-dilaton theory. These black hole
solutions are static, and they have a regular event horizon. However, they
possess only axial symmetry. Like their regular counterparts, the black hole
solutions are characterized by two integers, the winding number and the
node number of the gauge field functions.Comment: 14 pages, including 4 postscript figures, LaTe
Oral and intestinal dysbiosis in Parkinson's disease.
The suspicion of an origin of Parkinson's disease (PD) at the periphery of the body and the involvement of environmental risk factors in the pathogenesis of PD have directed the attention of the scientific community towards the microbiota. The microbiota represents all the microorganisms residing both in and on a host. It plays an essential role in the physiological functioning of the host. In this article, we review the dysbiosis repeatedly demonstrated in PD and how it influences PD symptoms. Dysbiosis is associated with both motor and non-motor PD symptoms. In animal models, dysbiosis only promotes symptoms in individuals genetically susceptible to Parkinson's disease, suggesting that dysbiosis is a risk factor but not a cause of Parkinson's disease. We also review how dysbiosis contributes to the pathophysiology of PD. Dysbiosis induces numerous and complex metabolic changes, resulting in increased intestinal permeability, local and systemic inflammation, production of bacterial amyloid proteins that promote α-synuclein aggregation, as well as a decrease in short-chain fatty acid-producing bacteria that have anti-inflammatory and neuroprotective potential. In addition, we review how dysbiosis decreases the efficacy of dopaminergic treatments. We then discuss the interest of dysbiosis analysis as a biomarker of Parkinson's disease. Finally, we give an overview of how interventions modulating the gut microbiota such as dietary interventions, pro-biotics, intestinal decontamination and fecal microbiota transplantation could influence the course of PD
Stationary Black Holes with Static and Counterrotating Horizons
We show that rotating dyonic black holes with static and counterrotating
horizon exist in Einstein-Maxwell-dilaton theory when the dilaton coupling
constant exceeds the Kaluza-Klein value. The black holes with static horizon
bifurcate from the static black holes. Their mass decreases with increasing
angular momentum, their horizons are prolate.Comment: 4 pages, 6 figure
Kinematics of Metal-Poor Stars in the Galaxy. II. Proper Motions for a Large Non-Kinematically Selected Sample
We present a revised catalog of 2106 Galactic stars, selected without
kinematic bias, and with available radial velocities, distance estimates, and
metal abundances in the range 0.0 <= [Fe/H] <= -4.0. This update of the Beers
and Sommer-Larsen (1995) catalog includes newly-derived homogeneous photometric
distance estimates, revised radial velocities for a number of stars with
recently obtained high-resolution spectra, and refined metallicities for stars
originally identified in the HK objective-prism survey (which account for
nearly half of the catalog) based on a recent re-calibration. A subset of 1258
stars in this catalog have available proper motions, based on measurements
obtained with the Hipparcos astrometry satellite, or taken from the updated
Astrographic Catalogue (AC 2000; second epoch positions from either the Hubble
Space Telescope Guide Star Catalog or the Tycho Catalogue), the Yale/San Juan
Southern Proper Motion (SPM) Catalog 2.0, and the Lick Northern Proper Motion
(NPM1) Catalog. Our present catalog includes 388 RR Lyrae variables (182 of
which are newly added), 38 variables of other types, and 1680 non-variables,
with distances in the range 0.1 to 40 kpc.Comment: 31 pages, including 8 figures, to appear in AJ (June 2000), full
paper with all figures embedded available at
http://pluto.mtk.nao.ac.jp/people/chiba/preprint/halo4
Sequences of Einstein-Yang-Mills-Dilaton Black Holes
Einstein-Yang-Mills-dilaton theory possesses sequences of neutral static
spherically symmetric black hole solutions. The solutions depend on the dilaton
coupling constant and on the horizon. The SU(2) solutions are labelled
by the number of nodes of the single gauge field function, whereas the
SO(3) solutions are labelled by the nodes of both gauge field
functions. The SO(3) solutions form sequences characterized by the node
structure , where is fixed. The sequences of magnetically neutral
solutions tend to magnetically charged limiting solutions. For finite the
SO(3) sequences tend to magnetically charged Einstein-Yang-Mills-dilaton
solutions with nodes and charge . For and the SO(3) sequences tend to Einstein-Maxwell-dilaton solutions with
magnetic charges and , respectively. The latter also
represent the scaled limiting solutions of the SU(2) sequence. The convergence
of the global properties of the black hole solutions, such as mass, dilaton
charge and Hawking temperature, is exponential. The degree of convergence of
the matter and metric functions of the black hole solutions is related to the
relative location of the horizon to the nodes of the corresponding regular
solutions.Comment: 71 pages, Latex2e, 29 ps-figures include
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