1,054 research outputs found
Risk Factors for Hospital Malpractice Exposure: Implications for Managers and Insurers
The possibility of identifying certain variables that might serve as predictors of above- or below-average medical malpractice claims experience was explored. Results showed that it is possible to identify significant risk factors
White Dwarf Mergers on Adaptive Meshes I. Methodology and Code Verification
The Type Ia supernova progenitor problem is one of the most perplexing and
exciting problems in astrophysics, requiring detailed numerical modeling to
complement observations of these explosions. One possible progenitor that has
merited recent theoretical attention is the white dwarf merger scenario, which
has the potential to naturally explain many of the observed characteristics of
Type Ia supernovae. To date there have been relatively few self-consistent
simulations of merging white dwarf systems using mesh-based hydrodynamics. This
is the first paper in a series describing simulations of these systems using a
hydrodynamics code with adaptive mesh refinement. In this paper we describe our
numerical methodology and discuss our implementation in the compressible
hydrodynamics code CASTRO, which solves the Euler equations, and the Poisson
equation for self-gravity, and couples the gravitational and rotation forces to
the hydrodynamics. Standard techniques for coupling gravitation and rotation
forces to the hydrodynamics do not adequately conserve the total energy of the
system for our problem, but recent advances in the literature allow progress
and we discuss our implementation here. We present a set of test problems
demonstrating the extent to which our software sufficiently models a system
where large amounts of mass are advected on the computational domain over long
timescales. Future papers in this series will describe our treatment of the
initial conditions of these systems and will examine the early phases of the
merger to determine its viability for triggering a thermonuclear detonation.Comment: Accepted for publication in the Astrophysical Journa
World-sheet Instantons via the Myers Effect and N=1^* Quiver Superpotentials
In this note we explore the stringy interpretation of non-perturbative
effects in N=1^* deformations of the A_{k-1} quiver models. For certain types
of deformations we argue that the massive vacua are described by Nk fractional
D3-branes at the orbifold polarizing into k concentric 5-brane spheres each
carrying fractional brane charge. The polarization of the D3-branes induces a
polarization of D-instantons into string world-sheets wrapped on the Myers
spheres. We show that the superpotentials in these models are indeed generated
by these world-sheet instantons. We point out that for certain parameter values
the condensates yield the exact superpotential for a relevant deformation of
the Klebanov-Witten conifold theory.Comment: 24 pages, JHEP, some small errors and typos correcte
Quantum Wall Crossing in N=2 Gauge Theories
We study refined and motivic wall-crossing formulas in N=2 supersymmetric
gauge theories with SU(2) gauge group and N_f < 4 matter hypermultiplets in the
fundamental representation. Such gauge theories provide an excellent testing
ground for the conjecture that "refined = motivic."Comment: 24 pages, 4 figure
Reverse geometric engineering of singularities
One can geometrically engineer supersymmetric field theories theories by
placing D-branes at or near singularities. The opposite process is described,
where one can reconstruct the singularities from quiver theories. The
description is in terms of a noncommutative quiver algebra which is constructed
from the quiver diagram and the superpotential. The center of this
noncommutative algebra is a commutative algebra, which is the ring of
holomorphic functions on a variety V. If certain algebraic conditions are met,
then the reverse geometric engineering produces V as the geometry that D-branes
probe. It is also argued that the identification of V is invariant under
Seiberg dualities.Comment: 17 pages, Latex. v2: updates reference
Massless D-Branes on Calabi-Yau Threefolds and Monodromy
We analyze the link between the occurrence of massless B-type D-branes for
specific values of moduli and monodromy around such points in the moduli space.
This allows us to propose a classification of all massless B-type D-branes at
any point in the moduli space of Calabi-Yau's. This classification then
justifies a previous conjecture due to Horja for the general form of monodromy.
Our analysis is based on using monodromies around points in moduli space where
a single D-brane becomes massless to generate monodromies around points where
an infinite number become massless. We discuss the various possibilities within
the classification.Comment: 29 pages, LaTeX2e, 3 figures, author order fixe
The Breakdown of Topology at Small Scales
We discuss how a topology (the Zariski topology) on a space can appear to
break down at small distances due to D-brane decay. The mechanism proposed
coincides perfectly with the phase picture of Calabi-Yau moduli spaces. The
topology breaks down as one approaches non-geometric phases. This picture is
not without its limitations, which are also discussed.Comment: 12 pages, 2 figure
A Geometric Unification of Dualities
We study the dynamics of a large class of N=1 quiver theories, geometrically
realized by type IIB D-brane probes wrapping cycles of local Calabi-Yau
threefolds. These include N=2 (affine) A-D-E quiver theories deformed by
superpotential terms, as well as chiral N=1 quiver theories obtained in the
presence of vanishing 4-cycles inside a Calabi-Yau. We consider the various
possible geometric transitions of the 3-fold and show that they correspond to
Seiberg-like dualities (represented by Weyl reflections in the A-D-E case or
`mutations' of bundles in the case of vanishing 4-cycles) or large N dualities
involving gaugino condensates (generalized conifold transitions). Also duality
cascades are naturally realized in these classes of theories, and are related
to the affine Weyl group symmetry in the A-D-E case.Comment: 94 pages, 18 figures. Added referenc
Accumulation of glial fibrillary acidic protein and histone H4 in brain storage bodies of Tibetan terriers with hereditary neuronal ceroid lipofuscinosis
The neuronal ceroid lipofuscinoses (NCLs) are inherited neurodegenerative diseases characterized by massive accumulation of autofluorescent storage bodies in neurons and other cells. A late-onset form of NCL occurs in Tibetan terrier dogs. Gel electrophoretic analyses of isolated storage body proteins from brains of affected dogs indicated that a protein of approximately 50 kDa was consistently prominent and a 16 kDa component was present in some brain storage body preparations. Mass spectral analysis identified the 50 kDa protein as glial fibrillary acidic protein (GFAP), isoform 2. GFAP identification was supported by immunoblot and immunohistochemical analyses. Histone H4 was the major protein in the 16 kDa component. Specific accumulation of GFAP and histone H4 in storage bodies has not been previously reported for any of the NCLs. Tibetan terrier NCL may be the canine correlate of one of the human adult-onset NCLs for which the genetic bases and storage body compositions have not yet been determined
L-functions with large analytic rank and abelian varieties with large algebraic rank over function fields
The goal of this paper is to explain how a simple but apparently new fact of
linear algebra together with the cohomological interpretation of L-functions
allows one to produce many examples of L-functions over function fields
vanishing to high order at the center point of their functional equation. The
main application is that for every prime p and every integer g>0 there are
absolutely simple abelian varieties of dimension g over Fp(t) for which the BSD
conjecture holds and which have arbitrarily large rank.Comment: To appear in Inventiones Mathematica
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