22,855 research outputs found
Planet Shadows in Protoplanetary Disks. I: Temperature Perturbations
Planets embedded in optically thick passive accretion disks are expected to
produce perturbations in the density and temperature structure of the disk. We
calculate the magnitudes of these perturbations for a range of planet masses
and distances. The model predicts the formation of a shadow at the position of
the planet paired with a brightening just beyond the shadow. We improve on
previous work on the subject by self-consistently calculating the temperature
and density structures under the assumption of hydrostatic equilibrium and
taking the full three-dimensional shape of the disk into account rather than
assuming a plane-parallel disk. While the excursion in temperatures is less
than in previous models, the spatial size of the perturbation is larger. We
demonstrate that a self-consistent calculation of the density and temperature
structure of the disk has a large effect on the disk model. In addition, the
temperature structure in the disk is highly sensitive to the angle of incidence
of stellar irradition at the surface, so accurately calculating the shape of
the disk surface is crucial for modeling the thermal structure of the disk.Comment: 14 pages, 14 figures. To appear in Ap
Nonuniqueness for the kinetic Fokker-Planck equation with inelastic boundary conditions
We describe the structure of solutions of the kinetic Fokker-Planck equations
in domains with boundaries near the singular set in one-space dimension. We
study in particular the behaviour of the solutions of this equation for
inelastic boundary conditions which are characterized by means of a coefficient
describing the amount of energy lost in the collisions of the particles
with the boundaries of the domain. A peculiar feature of this problem is the
onset of a critical exponent rc which follows from the analysis of McKean (cf.
[26]) of the properties of the stochastic process associated to the
Fokker-Planck equation under consideration. In this paper, we prove rigorously
that the solutions of the considered problem are nonunique if and
unique if . In particular, this nonuniqueness explains the
different behaviours found in the physics literature for numerical simulations
of the stochastic differential equation associated to the Fokker-Planck
equation. In the proof of the results of this paper we use several asymptotic
formulas and computations in the companion paper [16].Comment: 64 pages, 1 figure. Previous version has been split into tw
Constraints on the Formation of the Planet Around HD188753A
The claimed discovery of a Jupiter-mass planet in the close triple star
system HD 188753 poses a problem for planet formation theory. A circumstellar
disk around the planet's parent star would be truncated close to the star,
leaving little material available for planet formation. In this paper, we
attempt to model a protoplanetary disk around HD 188753A using a fairly simple
alpha-disk model, exploring a range of parameters constrained by observations
of T Tauri-type stars. The disk is truncated to within 1.5 to 2.7 AU, depending
on model parameters. We find that the in situ formation of the planet around HD
188753A is implausible.Comment: Accepted version, to appear in ApJ. 23 pages, 5 figures (3 in color
Strong pinning of vortices by antiferromagnetic domain boundaries in CeCo(InCd)
We have studied the isothermal magnetization of
CeCo(InCd) with = 0.0075 and 0.01 down to 50 mK. Pronounced
field-history dependent phenomena occur in the coexistence regime of the
superconducting and antiferromagnetic phases. At low-fields, a phenomenological
model of magnetic-flux entry well explains implying the dominance of
bulk pinning effect. However, unless crystallographic quenched disorder is
hysteretic, the asymmetric peak effect (ASPE) which appears at higher fields
cannot be explained by the pinning of vortices due to material defects. Also
the temperature dependence of the ASPE deviates from the conventional scenario
for the peak effect. Comparison of our thermodynamic phase diagrams with those
from previous neutron scattering and magnetoresistance experiments indicates
that the pinning of vortices takes place at the field-history dependent
antiferromagnetic domain boundaries.Comment: 13 pages,4 figures, to be published in New Journal of Physic
Role of the fast kinetics of pyroglutamate-modified amyloid-β oligomers in membrane binding and membrane permeability.
Membrane permeability to ions and small molecules is believed to be a critical step in the pathology of Alzheimer's disease (AD). Interactions of oligomers formed by amyloid-β (Aβ) peptides with the plasma cell membrane are believed to play a fundamental role in the processes leading to membrane permeability. Among the family of Aβs, pyroglutamate (pE)-modified Aβ peptides constitute the most abundant oligomeric species in the brains of AD patients. Although membrane permeability mechanisms have been studied for full-length Aβ1-40/42 peptides, these have not been sufficiently characterized for the more abundant AβpE3-42 fragment. Here we have compared the adsorbed and membrane-inserted oligomeric species of AβpE3-42 and Aβ1-42 peptides. We find lower concentrations and larger dimensions for both species of membrane-associated AβpE3-42 oligomers. The larger dimensions are attributed to the faster self-assembly kinetics of AβpE3-42, and the lower concentrations are attributed to weaker interactions with zwitterionic lipid headgroups. While adsorbed oligomers produced little or no significant membrane structural damage, increased membrane permeabilization to ionic species is understood in terms of enlarged membrane-inserted oligomers. Membrane-inserted AβpE3-42 oligomers were also found to modify the mechanical properties of the membrane. Taken together, our results suggest that membrane-inserted oligomers are the primary species responsible for membrane permeability
Blowup of Jang's equation at outermost marginally trapped surfaces
The aim of this paper is to collect some facts about the blowup of Jang's
equation. First, we discuss how to construct solutions that blow up at an
outermost MOTS. Second, we exclude the possibility that there are extra blowup
surfaces in data sets with non-positive mean curvature. Then we investigate the
rate of convergence of the blowup to a cylinder near a strictly stable MOTS and
show exponential convergence near a strictly stable MOTS.Comment: 15 pages. This revision corrects some typo
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