3,252 research outputs found
Three-loop Euler-Heisenberg Lagrangian and asymptotic analysis in 1+1 QED
In recent years, the Euler-Heisenberg Lagrangian has been shown to be a
useful tool for the analysis of the asymptotic growth of the N-photon
amplitudes at large N. Moreover, certain results and conjectures on its
imaginary part allow one, using Borel analysis, to make predictions for those
amplitudes at large loop orders. Extending work by G.V. Dunne and one of the
authors to the three-loop level, but in the simpler context of 1+1 dimensional
QED, we calculate the corresponding Euler-Heisenberg Lagrangian, analyse its
weak field expansion, and study the congruence with predictions obtained from
worldline instantons. We discuss the relevance of these issues for Cvitanovic's
conjecture.Comment: 8 pages, 1 figure, Talk given by C. Schubert at QFEXT09, Univ. of
Oklahoma, Norman, September 21 - 25, 2009, to appear in the conference
proceeding
New relations between spinor and scalar one-loop effective Lagrangians in constant background fields
Simple new relations are presented between the one-loop effective Lagrangians
of spinor and scalar particles in constant curvature background fields, both
electromagentic and gravitational. These relations go beyond the well-known
cases for self-dual background fields
The Euler-Heisenberg Lagrangian beyond one loop
We review what is presently known about higher loop corrections to the
Euler-Heisenberg Lagrangian and its Scalar QED analogue. The use of those
corrections as a tool for the study of the properties of the QED perturbation
series is outlined. As a further step in a long-term effort to prove or
disprove the convergence of the N photon amplitudes in the quenched
approximation, we present a parameter integral representation of the three-loop
Euler-Heisenberg Lagrangian in 1+1 dimensional QED, obtained in the worldline
formalism.Comment: 11 pages, 2 figures, talk given by Christian Schubert at QFEXT11,
Benasque, Spain, Sept. 18-24, 2011, to appear in the conference proceeding
The economic value of adding capacity at airports – a data-driven model
This article presents a model for the economic value of adding capacity at airports. We start with an extensive literature review, discussing the main findings covering costs and revenues at airports, in particular related to their capacity. We then proceed to an analysis based on a wide range of data sources (financial, operational, quality of service) which have been synthesised into one database. The analysis itself yields interesting results, such as the presence of distinct types of airport and their characteristics. Broadly based on the knowledge gained from the data analysis, we describe a functional model describing the costs and revenues associated with an increase of capacity at an airport. We show how the model can be calibrated with data and present some preliminary results based on the calibration of Paris Charles de Gaulle airport
Kinetic description of fermion flavor mixing and CP-violating sources for baryogenesis
We derive transport equations for fermionic systems with a space-time
dependent mass matrix in flavor space allowing for complex elements leading to
CP violation required for electroweak baryogenesis. By constructing appropriate
projectors in flavor space of the relevant tree level Kadanoff-Baym equations,
we split the constraint equations into "diagonal" and "transversal" parts in
flavor space, and show that they decouple. While the diagonal densities exhibit
standard dispersion relations at leading order in gradients, the transverse
densities exhibit a novel on-shell structure. Next, the kinetic equations are
considered to second order in gradients and the CP-violating source terms are
isolated. This requires a thorough discussion of a flavor independent
definition of charge-parity symmetry operation. To make a link with
baryogenesis in the supersymmetric extension of the Standard Model, we
construct the Green functions for the leading order kinetic operator and solve
the kinetic equations for two mixing fermions (charginos). We take account of
flavor blind damping, and consider the cases of inefficient and moderate
diffusion. The resulting densities are the CP-violating chargino currents that
source baryogenesis.Comment: 33 pages, 6 figure
Generating TV summaries for CE-devices
Automatically generated summaries of TV content are indispensable for content selection and navigation in CE-devices. We show two types of summaries: Short video trailers and visual overviews consisting of representative frames. The demo does not only show the feasibility of the proposed algorithms, but also shows how different types of generated summaries can be used in future CE-devices
Mechanical dynamic load of the LHC arc cryo-magnets during the installation
About 1700 LHC main superconducting dipoles and quadrupoles will have to be transported and handled between the assembly, the magnet measurements and the storage that precedes the final installation in the LHC tunnel. To ensure the required mechanic and geometric integrity of the cryo-magnets, transport specifications and allowed acceleration loads were defined after detailed dynamic analysis. A large number of cryo-magnets are now arriving at CERN on a regular basis. The logistics for the handling and transport are monitored with tri-axial acceleration monitoring devices that are installed on each cryo-magnet. Measurements are made to commission new equipment like overhead cranes, tunnel transport and handling devices to guarantee that the defined acceleration limits are respected. The results from the acceleration monitoring that are stored in the same quality assurance system as the cryo-magnets allowed to give a first idea of the level of the mechanical dynamic load on each magnet throughout the logistics chain and were used to detect details such as out-of-specification accelerations that needed improvement
Double modelling of the dynamic of activities in rural municipalities.
Land use choices and activity prevalence in a selected territory are determined by individual preferences constrained by the characteristic of the analysed zone: population density, soil properties, urbanization level and other similar factors can drive individuals to make different kind of decisions about their occupations. Different approaches can be used to describe land use change, occupation prevalence and their reciprocal inter-relation. In this paper we describe two different kinds of approaches: an agent based model, centred on individual choices and an aggregated model describing the evolution of activity prevalence in terms of coupled differential equation. We use and we compare the two models to analyse the effect of territorial constraints, like the lack of employment in determined sectors, on the possible activity prevalence scenarios.SBIAgro 2009
Using Middle-Out Reasoning to Control the Synthesis of Tail-Recursive Programs
We describe a novel technique for the automatic synthesis of tail-recursive programs. The technique is to specify the required program using the standard equations and then synthesise the tail-recursive program using the proofs as programs technique. This requires the specification to be proved realisable in a constructive logic. Restrictions on the form of the proof ensure that the synthesised program is tail-recursive. Th
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