2,538 research outputs found
Reproducibility in the diagnosis of needle core biopsies of non-palpable breast lesions: an international study using virtual slides published on the world-wide web
Multicolor observations of the Hubble Deep Field South
We present a deep multicolor (UBVIJsHKs) catalog of galaxies in the HDF-S,
based on observations obtained with the HST WFPC2 in 1998 and VLT-ISAAC in
1999. The photometric procedures were tuned to derive a catalog optimized for
the estimation of photometric redshifts. In particular we adopted a
``conservative'' detection threshold which resulted in a list of 1611 objects.
The behavior of the observed source counts is in general agreement with the
result of Casertano et al. (2000) in the HDF-S and Williams et al. (1996) in
the HDF-N, while the corresponding counts in the HDF-N provided by
Fernandez-Soto et al. (1999) are systematically lower by a factor 1.5 beyond
I_AB=26. After correcting for the incompleteness of the source counts, the
object surface density at I_AB<27.5 is estimated to be 220 per square arcmin,
providing an estimate of the Extragalactic Background Light in the I band
consistent with the work of Madau & Pozzetti(2000). The comparison between the
median V-I color in the HDF-North and South shows a significant difference
around I_AB~26, possibly due to the presence of large scale structure at z~1 in
the HDF-N. High-z galaxy candidates (90 U dropout and 17 B dropout) were
selected by means of color diagrams, down to a magnitude I_AB=27, with a
surface density of (21+-1) and (3.9+-0.9) per square arcmin, respectively. 11
EROs (with (I-K)_AB>2.7) were selected down to K_AB=24, plus 3 objects whose
upper limit to the Ks flux is still compatible with the selection criterion.
The corresponding surface density of EROs is (2.5+-0.8) per sq.arcmin
((3.2+-0.9) per sq.arcmin if we include the three Ks upper limits). They show a
remarkably non-uniform spatial distribution and are classified with roughly
equal fractions in the categories of elliptical and starburst galaxies.Comment: 36 pages Latex, with 12 PostScript figures. Accepted for publication
in Astronomical Journa
Validation of a patient-specific system for mandible-first bimaxillary surgery: ramus and implant positioning precision assessment and guide design comparison
In orthognathic surgery, the use of patient-specific osteosynthesis devices is a novel approach used to transfer the virtual surgical plan to the patient. The aim of this study is to analyse the quality of mandibular anatomy reproduction using a mandible-first mandibular-PSI guided procedure on 22 patients. Three different positioning guide designs were compared in terms of osteosynthesis plate positioning and mandibular anatomical outcome. PSIs and positioning guides were designed according to virtual surgical plan and 3D printed using biocompatible materials. A CBCT scan was performed 1 month after surgery and postoperative mandibular models were segmented for comparison against the surgical plan. A precision comparison was carried out among the three groups. Correlations between obtained rami and plates discrepancies and between planned rami displacements and obtained rami discrepancies were calculated. Intraoperatively, all PSIs were successfully applied. The procedure was found to be accurate in planned mandibular anatomy reproduction. Different guide designs did not differ in mandibular outcome precision. Plate positional discrepancies influenced the corresponding ramus position, mainly in roll angle and vertical translation. Ramus planned displacement was found to be a further potential source of inaccuracy, possibly due to osteosynthesis surface interference
An Atlas of Monte Carlo Models of Dust Extinction in Galaxies for Cosmological Applications
We present an extensive study of the radiative transfer in dusty galaxies
based on Monte Carlo simulations. The main output of these simulations are the
attenuation curves (i.e. the ratio between the observed,
dust extinguished, total intensity to the intrinsic unextinguished one of the
galaxy as a function of wavelength). We have explored the dependence of on a conspicuous set of quantities (Hubble type, inclination, dust
optical thickness, dust distribution and extinction properties) for a large
wavelength interval, ranging from 1250\AA to the K band, thus finally providing
a comprehensive atlas of dust extinction in galaxies, which is electronically
available. This study is particularly suitable for inclusion into galaxy
formation evolution models and to directly interpret observational data on high
redshift galaxies.Comment: 29 pages, aasms4.sty, LaTeX, 5 figures. ApJSS, accepte
Operator product expansion of higher rank Wilson loops from D-branes and matrix models
In this paper we study correlation functions of circular Wilson loops in
higher dimensional representations with chiral primary operators of N=4 super
Yang-Mills theory. This is done using the recently established relation between
higher rank Wilson loops in gauge theory and D-branes with electric fluxes in
supergravity. We verify our results with a matrix model computation, finding
perfect agreement in both the symmetric and the antisymmetric case.Comment: 28 pages, latex; v2: minor misprints corrected, references adde
Polyhedra in loop quantum gravity
Interwiners are the building blocks of spin-network states. The space of
intertwiners is the quantization of a classical symplectic manifold introduced
by Kapovich and Millson. Here we show that a theorem by Minkowski allows us to
interpret generic configurations in this space as bounded convex polyhedra in
Euclidean space: a polyhedron is uniquely described by the areas and normals to
its faces. We provide a reconstruction of the geometry of the polyhedron: we
give formulas for the edge lengths, the volume and the adjacency of its faces.
At the quantum level, this correspondence allows us to identify an intertwiner
with the state of a quantum polyhedron, thus generalizing the notion of quantum
tetrahedron familiar in the loop quantum gravity literature. Moreover, coherent
intertwiners result to be peaked on the classical geometry of polyhedra. We
discuss the relevance of this result for loop quantum gravity. In particular,
coherent spin-network states with nodes of arbitrary valence represent a
collection of semiclassical polyhedra. Furthermore, we introduce an operator
that measures the volume of a quantum polyhedron and examine its relation with
the standard volume operator of loop quantum gravity. We also comment on the
semiclassical limit of spinfoams with non-simplicial graphs.Comment: 32 pages, many figures. v2 minor correction
The Effect of Light Scattering by Dust in Galactic Halos on Emission Line Ratios
We present results from Monte Carlo simulations describing the radiation
transfer of line emission, produced both by HII regions in the disk
and in the diffuse ionized gas (DIG), through the dust layer of the galaxy
NGC891. This allows us to calculate the amount of light originating in the HII
regions of the disk and scattered by dust at high , and compare it with the
emission produced by recombinations in the DIG. The cuts of photometric and
polarimetric maps along the -axis show that scattered light from HII regions
is still 10\% of that of the DIG at ~pc, whereas the the degree of
linear polarization is small (\%). The importance of these results for the
determination of intrinsic emission line ratios is emphasized, and the
significance and possible implications of dust at high are discussed.Comment: 12 pages, LaTeX (aasms4.sty), 2 figures; ApJ Letters, accepted, June
5t
Area-angle variables for general relativity
We introduce a modified Regge calculus for general relativity on a
triangulated four dimensional Riemannian manifold where the fundamental
variables are areas and a certain class of angles. These variables satisfy
constraints which are local in the triangulation. We expect the formulation to
have applications to classical discrete gravity and non-perturbative approaches
to quantum gravity.Comment: 7 pages, 1 figure. v2 small changes to match published versio
Coupling gauge theory to spinfoam 3d quantum gravity
We construct a spinfoam model for Yang-Mills theory coupled to quantum
gravity in three dimensional riemannian spacetime. We define the partition
function of the coupled system as a power series in g_0^2 G that can be
evaluated order by order using grasping rules and the recoupling theory. With
respect to previous attempts in the literature, this model assigns the
dynamical variables of gravity and Yang-Mills theory to the same simplices of
the spinfoam, and it thus provides transition amplitudes for the spin network
states of the canonical theory. For SU(2) Yang-Mills theory we show explicitly
that the partition function has a semiclassical limit given by the Regge
discretization of the classical Yang-Mills action.Comment: 18 page
Supersymmetric Wilson loops on S^3
This paper studies in great detail a family of supersymmetric Wilson loop
operators in N=4 supersymmetric Yang-Mills theory we have recently found. For a
generic curve on an S^3 in space-time the loops preserve two supercharges but
we will also study special cases which preserve 4, 8 and 16 supercharges. For
certain loops we find the string theory dual explicitly and for the general
case we show that string solutions satisfy a first order differential equation.
This equation expresses the fact that the strings are pseudo-holomorphic with
respect to a novel almost complex structure we construct on AdS_4 x S^2. We
then discuss loops restricted to S^2 and provide evidence that they can be
calculated in terms of similar observables in purely bosonic YM in two
dimensions on the sphere.Comment: Latex, 84 pages, 4 figures. v2: minor changes, references added; to
appear in JHE
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