14,341 research outputs found
On the usefulness of finding charts Or the runaway carbon stars of the Blanco & McCarthy field 37
We have been recently faced with the problem of cross--identifying stars
recorded in historical catalogues with those extracted from recent fully
digitized surveys (such as DENIS and 2MASS). Positions mentioned in the old
catalogues are frequently of poor precision, but are generally accompanied by
finding charts where the interesting objects are flagged. Those finding charts
are sometimes our only link with the accumulated knowledge of past literature.
While checking the identification of some of these objects in several
catalogues, we had the surprise to discover a number of discrepancies in recent
works.The main reason for these discrepancies was generally the blind
application of the smallest difference in position as the criterion to identify
sources from one historical catalogue to those in more recent surveys. In this
paper we give examples of such misidentifications, and show how we were able to
find and correct them.We present modern procedures to discover and solve
cross--identification problems, such as loading digitized images of the sky
through the Aladin service at CDS, and overlaying entries from historical
catalogues and modern surveys. We conclude that the use of good finding charts
still remains the ultimate (though time--consuming) tool to ascertain
cross--identifications in difficult cases.Comment: 4 pages, 1 figure, accepted by A&
Progression from ocular hypertension to visual field loss in the English hospital eye service
Background There are more than one million National Health Service visits in England and Wales each year for patients with glaucoma or ocular hypertension (OHT). With the ageing population and an increase in optometric testing, the economic burden of glaucoma-related visits is predicted to increase. We examined the conversion rates of OHT to primary open-angle glaucoma (POAG) in England and assessed factors associated with risk of conversion.
Methods Electronic medical records of 45 309 patients from five regionally different glaucoma clinics in England were retrospectively examined. Conversion to POAG from OHT was defined by deterioration in visual field (two consecutive tests classified as stage 1 or worse as per the glaucoma staging system 2). Cox proportional hazards models were used to examine factors (age, sex, treatment status and baseline intraocular pressure (IOP)) associated with conversion.
Results The cumulative risk of conversion to POAG was 17.5% (95% CI 15.4% to 19.6%) at 5 years. Older age (HR 1.35 per decade, 95% CI 1.22 to 1.50, p<0.001) was associated with a higher risk of conversion. IOP-lowering therapy (HR 0.45, 95% CI 0.35 to 0.57, p<0.001) was associated with a lower risk of conversion. Predicted 5-year conversion rates for treated and untreated groups were 14.0% and 26.9%, respectively.
Conclusion Less than one-fifth of OHT patients managed in glaucoma clinics in the UK converted to POAG over a 5-year period, suggesting many patients may require less intensive follow-up. Our study provides real-world evidence for the efficacy of current management (including IOP-lowering treatment) at reducing risk of conversion
Bubbles from Nothing
Within the framework of flux compactifications, we construct an instanton
describing the quantum creation of an open universe from nothing. The solution
has many features in common with the smooth 6d bubble of nothing solutions
discussed recently, where the spacetime is described by a 4d compactification
of a 6d Einstein-Maxwell theory on S^2 stabilized by flux. The four-dimensional
description of this instanton reduces to that of Hawking and Turok. The choice
of parameters uniquely determines all future evolution, which we additionally
find to be stable against bubble of nothing instabilities.Comment: 19 pages, 6 figure
Chiral Superconducting Membranes
We develop the dynamics of the chiral superconducting membranes (with null
current) in an alternative geometric approach either making a Lagrangian
description and a Hamiltonian point of view. Besides of this, we show the
equivalence of the resulting descriptions to the one known Dirac-Nambu-Goto
(DNG) case. Integrability for chiral string model is obtained using a proposed
light-cone gauge. In a similar way, domain walls are integrated by means of a
simple ansatz. We compare the results with recently works appeared in the
literature.Comment: Latex file, 17 pages, no figures. Improved version, typos corrected,
Comments and references adde
Decay of flux vacua to nothing
We construct instanton solutions describing the decay of flux
compactifications of a gauge theory by generalizing the Kaluza-Klein
bubble of nothing. The surface of the bubble is described by a smooth
magnetically charged solitonic brane whose asymptotic flux is precisely that
responsible for stabilizing the 4d compactification. We describe several
instances of bubble geometries for the various vacua occurring in a
Einstein-Maxwell theory namely, AdS_4 x S^2, R^{1,3} x S^2, and dS_4 x S^2.
Unlike conventional solutions, the bubbles of nothing introduced here occur
where a {\em two}-sphere compactification manifold homogeneously degenerates.Comment: 31 pages, 15 figure
On supersymmetric Minkowski vacua in IIB orientifolds
Supersymmetric Minkowski vacua in IIB orientifold compactifications based on
orbifolds with background fluxes and non-perturbative superpotentials are
investigated. Especially, microscopic requirements and difficulties to obtain
such vacua are discussed. We show that orbifold models with one and two complex
structure moduli and supersymmetric 2-form flux can be successfully stabilized
to such vacua. By taking additional gaugino condensation on fixed space-time
filling D3-branes into account also models without complex structure can be
consistently stabilized to Minkowski vacua.Comment: 17 pages, 2 figures; More detailed proof for absence of complex flat
directions in susy AdS vacua given; Footnotes and reference adde
Molecular dynamics of folding of secondary structures in Go-type models of proteins
We consider six different secondary structures of proteins and construct two
types of Go-type off-lattice models: with the steric constraints and without.
The basic aminoacid-aminoacid potential is Lennard Jones for the native
contacts and a soft repulsion for the non-native contacts. The interactions are
chosen to make the target secondary structure be the native state of the
system. We provide a thorough equilibrium and kinetic characterization of the
sequences through the molecular dynamics simulations with the Langevin noise.
Models with the steric constraints are found to be better folders and to be
more stable, especially in the case of the -structures. Phononic spectra
for vibrations around the native states have low frequency gaps that correlate
with the thermodynamic stability. Folding of the secondary structures proceeds
through a well defined sequence of events. For instance, -helices fold
from the ends first. The closer to the native state, the faster establishment
of the contacts. Increasing the system size deteriorates the folding
characteristics. We study the folding times as a function of viscous friction
and find a regime of moderate friction with the linear dependence. We also
consider folding when one end of a structure is pinned which imitates
instantaneous conditions when a protein is being synthesized. We find that,
under such circumstances, folding of helices is faster and of the
-sequences slower.Comment: REVTeX, 14 pages, EPS figures included, JCP in pres
Exact Microscopic Entropy of Non-Supersymmetric Extremal Black Rings
In this brief note we show that the horizon entropy of the largest known
class of non-supersymmetric extremal black rings, with up to six parameters, is
exactly reproduced for all values of the ring radius using the same conformal
field theory of the four-charge four-dimensional black hole. A particularly
simple case is a dipole black ring without any conserved charges. The mass gets
renormalized, but the first corrections it receives can be easily understood as
an interaction potential energy. Finally, we stress that even if the entropy is
correctly reproduced, this only implies that one sector of chiral excitations
has been identified, but an understanding of excitations in the other sector is
still required in order to capture the black ring dynamics.Comment: 7 pages. v2: minor improvements, ref adde
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