8,385 research outputs found
Systematic Differential Renormalization to All Orders
We present a systematic implementation of differential renormalization to all
orders in perturbation theory. The method is applied to individual Feynamn
graphs written in coordinate space. After isolating every singularity. which
appears in a bare diagram, we define a subtraction procedure which consists in
replacing the core of the singularity by its renormalized form givenby a
differential formula. The organizationof subtractions in subgraphs relies in
Bogoliubov's formula, fulfilling the requirements of locality, unitarity and
Lorentz invariance. Our method bypasses the use of an intermediate
regularization andautomatically delivers renormalized amplitudes which obey
renormalization group equations.Comment: TEX, 20 pages, UB-ECM-PF 93/4, 1 figureavailable upon reques
Trinets encode tree-child and level-2 phylogenetic networks
Phylogenetic networks generalize evolutionary trees, and are commonly used to represent evolutionary histories of species that undergo reticulate evolutionary processes such as hybridization, recombination and lateral gene transfer. Recently, there has been great interest in trying to develop methods to construct rooted phylogenetic networks from triplets, that is rooted trees on three species. However, although triplets determine or encode rooted phylogenetic trees, they do not in general encode rooted phylogenetic networks, which is a potential issue for any such method. Motivated by this fact, Huber and Moulton recently introduced trinets as a natural extension of rooted triplets to networks. In particular, they showed that level-1 level-1 phylogenetic networks are encoded by their trinets, and also conjectured that all “recoverable” rooted phylogenetic networks are encoded by their trinets. Here we prove that recoverable binary level-2 networks and binary tree-child networks are also encoded by their trinets. To do this we prove two decomposition theorems based on trinets which hold for all recoverable binary rooted phylogenetic networks. Our results provide some additional evidence in support of the conjecture that trinets encode all recoverable rooted phylogenetic networks, and could also lead to new approaches to construct phylogenetic networks from trinets
Nonperturbative results on the quark-gluon vertex
We present analytical and numerical results for the Dirac form factor of the
quark-gluon vertex in the quark symmetric limit, where the incoming and
outgoing quark momenta have the same magnitude but opposite sign. To accomplish
this, we compute the relevant components of the quark-ghost scattering kernel
at the one-loop dressed approximation, using as basic ingredients the full
quark propagator, obtained as a solution of the quark gap equation, and the
gluon propagator and ghost dressing function, obtained from large-volume
lattice simulations.Comment: 8 pages, 6 figures. Talk presented by A.C.A at Xth Quark Confinement
and the Hadron Spectrum, 8-12 October 2012, TUM Campus Garching, Munich,
German
Weighted Traces on Algebras of Pseudo-Differential Operators and Geometry of Loop Groups
Using {\it weighted traces} which are linear functionals of the type defined on the whole
algebra of (classical) pseudo-differential operators (P.D.O.s) and where is
some positive invertible elliptic operator, we investigate the geometry of loop
groups in the light of the cohomology of pseudo-differential operators. We set
up a geometric framework to study a class of infinite dimensional manifolds in
which we recover some results on the geometry of loop groups, using again
weighted traces. Along the way, we investigate properties of extensions of the
Radul and Schwinger cocycles defined with the help of weighted traces.Comment: 36 page
Development of polymer network of phenolic and epoxies resins mixed with linseed oil: pilot study
Epoxy resin was mixed with phenolic resins in different percentages by weight. Composite 40/60 means the proportion by weight of epoxy resin is 40 percent. It was found that only composites 50/50 and 40/60 could be cured in ambient conditions. Dynamic mechanical analysis showed that only these two composites form interpenetrating polymer network. The addition of linseed oil to the two resins results also in the formation of interpenetrating network irrespective of proportion by weight of the resins; the mechanical properties will only be better when the percentage by weight of epoxy resin is higher; the aim of reducing cost and at the same time maintaining the mechanical properties cannot be fully achieved because epoxy resin is much more expensive than its counterpart
Anomalies of the infrared-active phonons in underdoped YBCO as an evidence for the intra-bilayer Josephson effect
The spectra of the far-infrared c-axis conductivity of underdoped YBCO
crystals exhibit dramatic changes of some of the phonon peaks when going from
the normal to the superconducting state. We show that the most striking of
these anomalies can be naturally explained by changes of the local fields
acting on the ions arising from the onset of inter- and intra-bilayer Josephson
effects.Comment: Revtex, epsf, 6 pages, 3 figures encapsulated in tex
Structured learning of assignment models for neuron reconstruction to minimize topological errors
© 20xx IEEE. Personal use of this material is permitted. Permission from IEEE must be obtained for all other uses, in any current or future media, including reprinting/republishing this material for advertising or promotional purposes, creating new collective works, for resale or redistribution to servers or lists, or reuse of any copyrighted component of this work in other works.Structured learning provides a powerful framework for empirical risk minimization on the predictions of
structured models. It allows end-to-end learning of model parameters to minimize an application specific loss function. This framework is particularly well suited for discrete optimization models that are used for neuron reconstruction from anisotropic electron microscopy (EM) volumes. However, current methods are still learning unary potentials by training a classifier that is agnostic about the model it is used in. We believe the reason for that lies in the difficulties of (1) finding a representative training sample, and (2) designing an application specific loss function that captures the quality of a proposed solution. In this paper, we show how to find a representative training sample from human generated ground truth, and propose a loss function that is suitable to minimize topological errors in the reconstruction. We compare different training methods on two challenging EM-datasets. Our structured learning approach shows consistently higher reconstruction accuracy than other current learning methods.Peer ReviewedPostprint (author's final draft
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