1,944 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
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
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
High-resolution, 3D radiative transfer modelling : V. A detailed model of the M 51 interacting pair
Context. Investigating the dust heating mechanisms in galaxies provides a deeper understanding of how the internal energy balance drives their evolution. Over the last decade radiative transfer simulations based on the Monte Carlo method have emphasised the role of the various stellar populations heating the diffuse dust. Beyond the expected heating through ongoing star formation, older stellar populations (>= 8 Gyr) and even active galactic nuclei can both contribute energy to the infrared emission of diffuse dust.Aims. In this particular study we examine how the radiation of an external heating source, such as the less massive galaxy NGC 5195 in the M 51 interacting system, could affect the heating of the diffuse dust of its parent galaxy NGC 5194, and vice versa. Our goal is to quantify the exchange of energy between the two galaxies by mapping the 3D distribution of their radiation field.Methods. We used SKIRT, a state-of-the-art 3D Monte Carlo radiative transfer code, to construct the 3D model of the radiation field of M 51, following the methodology defined in the DustPedia framework. In the interest of modelling, the assumed centre-to-centre distance separation between the two galaxies is similar to 10 kpc.Results. Our model is able to reproduce the global spectral energy distribution of the system, and it matches the resolved optical and infrared images fairly well. In total, 40.7% of the intrinsic stellar radiation of the combined system is absorbed by dust. Furthermore, we quantify the contribution of the various dust heating sources in the system, and find that the young stellar population of NGC 5194 is the predominant dust-heating agent, with a global heating fraction of 71.2%. Another 23% is provided by the older stellar population of the same galaxy, while the remaining 5.8% has its origin in NGC 5195. Locally, we find that the regions of NGC 5194 closer to NGC 5195 are significantly affected by the radiation field of the latter, with the absorbed energy fraction rising up to 38%. The contribution of NGC 5195 remains under the percentage level in the outskirts of the disc of NGC 5194. This is the first time that the heating of the diffuse dust by a companion galaxy is quantified in a nearby interacting system
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