2,477 research outputs found
N=2 Coset Compactifications with Non-Diagonal Invariants
We consider 4-dimensional string models obtained by tensoring N=2 coset
theories with non-diagonal modular invariants. We present results from a
systematic analysis including moddings by discrete symmetries.Comment: 29 page
Piogranuloma estéril idiopático canino
En este artÃculo se presenta un caso clÃnico de piogranuloma estéril idiopático en un perro, macho, de raza Rottweiler, de seis años de edad, con múltiples nódulos quÃsticos, ulcerados y sangrantes a nivel perianal, prepucial y del labio inferior. Se discute acerca del diagnóstico, pronóstico y tratamiento.In this paper we present a case report of idiopathic stèrile pyogranuloma, on a six year-old, male, Rottweiler dog, with multiple haemorrhagic, cystic, ulcerated nodules on the lower lip, prepuce, and perineum. We describe the clinical findings, diagnosis and therapeutical approach
Heterotic strings on T3/ℤ2, Nikulin involutions and M-theory
We first describe the low energy dynamics of ten dimensional heterotic supergravity compactified on the smooth, flat 3-manifold , without supersymmetry, and explain how it arises from flat heterotic gauge fields. The semi-classical theory has both Coulomb and Higgs branches of non-supersymmetric vacua. We then give an exact worldsheet description as asymmetric orbifolds of , where the orbifold generator involves a Nikulin non-symplectic involution of the even self-dual lattice . Along the way we briefly compare our findings with M-theory on . Our construction gives a novel CFT description of the semi-classical field theory moduli space. In particular, the Wilson line parameters in the lattice of signature which is invariant under , and in its orthogonal complement , correspond respectively to Coulomb and Higgs branch moduli. There is a rich pattern of transitions amongst Higgs and Coulomb branches which we describe using the worldsheet theory
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Concentration of Random-Coding Error Exponents
This paper studies the error exponent of i.i.d. randomly generated codes used for transmission over discrete memoryless channels with maximum likelihood decoding. Specifically, this paper shows that the error exponent of a code, defined as the negative normalized logarithm of the probability of error, converges in probability to the typical error exponent. For high rates, the result is a consequence of the fact that the random-coding error exponent and the sphere-packing error exponent coincide. For low rates, instead, the proof of convergence is based on the fact that the union bound accurately characterizes the probability of error
Stringy Tachyonic Instabilities of Non-Supersymmetric Ricci Flat Backgrounds
Superstring/M-theory compactified on compact Ricci flat manifolds have recently been conjectured to exhibit instabilities whenever the metrics do not have special holonomy. We use worldsheet conformal field theory to investigate instabilities of Type II superstring theories on compact, Ricci flat, spin 3-manifolds including a worldsheet description of their spin structures. The instabilities are signalled by the appearance of stringy tachyons at small radius and a negative (1-loop) vacuum energy density at large radius. We briefly discuss the extension to higher dimensions
Kinetico-mechanistic study on the C-H bond activation of primary benzylamines; cooperative and solid-state cyclopalladation on dimeric complexesss
The cyclometallation reactions of dinuclear μ-acetato complexes of the type [Pd(AcO)(μ-AcO)L]2 (L = 4-RC6H4CH2NH2, R = H, Cl, F, CF3), a process found to occur readily even in the solid state, have been studied from a kinetico-mechanistic perspective. Data indicate that the dinuclear acetato bridged derivatives are excellent starting materials to activate carbon-hydrogen bonds in a facile way. In all cases the established concerted ambiphilic proton abstraction by a coordinated acetato ligand has been proved. The metallation has also been found to occur in a cooperative manner, with the metallation of the first palladium unit of the dimeric complex being rate determining; no intermediate mono-metallated compounds are observed in any of the processes. The kinetically favoured bis-cyclopalladated compound obtained after complete C-H bond activation does not correspond to the final isolated XRD-characterized complexes. This species, bearing the classical open-book dimeric form, has a much more complex structure than the final isolated compound, with different types of acetato ligand
Thick disk accretion in Kerr space-time with arbitrary spin parameters
In this paper we extend our previous works on spherically symmetric accretion
onto black holes and super-spinars to the case in which the fluid has a finite
angular momentum initially. We run 2.5D and 3D general relativistic
hydrodynamic simulations of the accretion of a fat disk. We study how the
accretion process changes by changing the values of the parameters of our
model. We show that the value of the fluid angular momentum critically
determines turn-on and off the production of powerful equatorial outflows
around super-spinars. For corotating disks, equatorial outflows are efficiently
generated, even for relatively low spin parameters or relatively large
super-spinar radii. For counterrotating disks, equatorial outflows are instead
significantly suppressed, and they are possible only in limited cases. We also
study accretion around a tilted disk.Comment: 11 pages, 10 figure
Relativistic Hydrodynamics around Black Holes and Horizon Adapted Coordinate Systems
Despite the fact that the Schwarzschild and Kerr solutions for the Einstein
equations, when written in standard Schwarzschild and Boyer-Lindquist
coordinates, present coordinate singularities, all numerical studies of
accretion flows onto collapsed objects have been widely using them over the
years. This approach introduces conceptual and practical complications in
places where a smooth solution should be guaranteed, i.e., at the gravitational
radius. In the present paper, we propose an alternative way of solving the
general relativistic hydrodynamic equations in background (fixed) black hole
spacetimes. We identify classes of coordinates in which the (possibly rotating)
black hole metric is free of coordinate singularities at the horizon,
independent of time, and admits a spacelike decomposition. In the spherically
symmetric, non-rotating case, we re-derive exact solutions for dust and perfect
fluid accretion in Eddington-Finkelstein coordinates, and compare with
numerical hydrodynamic integrations. We perform representative axisymmetric
computations. These demonstrations suggest that the use of those coordinate
systems carries significant improvements over the standard approach, especially
for higher dimensional studies.Comment: 10 pages, 4 postscript figures, accepted for publication in Phys.
Rev.
Broadband distortion modeling in Lyman- forest BAO fitting
In recent years, the Lyman- absorption observed in the spectra of
high-redshift quasars has been used as a tracer of large-scale structure by
means of the three-dimensional Lyman- forest auto-correlation function
at redshift , but the need to fit the quasar continuum in every
absorption spectrum introduces a broadband distortion that is difficult to
correct and causes a systematic error for measuring any broadband properties.
We describe a -space model for this broadband distortion based on a
multiplicative correction to the power spectrum of the transmitted flux
fraction that suppresses power on scales corresponding to the typical length of
a Lyman- forest spectrum. Implementing the distortion model in fits for
the baryon acoustic oscillation (BAO) peak position in the Lyman-
forest auto-correlation, we find that the fitting method recovers the input
values of the linear bias parameter and the redshift-space distortion
parameter for mock data sets with a systematic error of less than
0.5\%. Applied to the auto-correlation measured for BOSS Data Release 11, our
method improves on the previous treatment of broadband distortions in BAO
fitting by providing a better fit to the data using fewer parameters and
reducing the statistical errors on and the combination
by more than a factor of seven. The measured values at
redshift are $\beta_{F}=1.39^{+0.11\ +0.24\ +0.38}_{-0.10\ -0.19\
-0.28}b_{F}(1+\beta_{F})=-0.374^{+0.007\ +0.013\ +0.020}_{-0.007\
-0.014\ -0.022}\sigma\sigma\sigma$ statistical errors). Our
fitting software and the input files needed to reproduce our main results are
publicly available.Comment: 28 pages, 15 figures, matches the published versio
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