21,189 research outputs found
Making electromagnetic wavelets
Electromagnetic wavelets are constructed using scalar wavelets as
superpotentials, together with an appropriate polarization. It is shown that
oblate spheroidal antennas, which are ideal for their production and reception,
can be made by deforming and merging two branch cuts. This determines a unique
field on the interior of the spheroid which gives the boundary conditions for
the surface charge-current density necessary to radiate the wavelets. These
sources are computed, including the impulse response of the antenna.Comment: 29 pages, 4 figures; minor corrections and addition
Thermal coupling of a heat flux sensor
The conditions of thermal coupling were investigated in relationship to the development of sensors for local thermal flux measurements of component surfaces. The dependence of the transfer function on heat conductivity coefficient of the measured object and the influence of the contact resistance at the sensor boundaries are discussed in terms of known results and investigations
The position of gas turbine power plants with respect to the emission of nitrogen oxides by fossil-fueled energy installations
The amount of nitrogen oxides introduced into the atmosphere by gas turbines is very significant in relation to the total amount of nitrogen oxide emissions produced by chemical installations and combustion engines. Turbine manufacturers are therefore working to develop combustion chambers with sufficiently low nitrogen oxide emission concentrations. Attention is given to aspects of nitrogen oxide formation in gas turbines, the parameters which determine this formation, and suitable approaches to reducing nitrogen oxide emissions
Chiral -exchange NN-potentials: Two-loop contributions
We calculate in heavy baryon chiral perturbation theory the local
NN-potentials generated by the two-pion exchange diagrams at two-loop order. We
give explicit expressions for the mass-spectra (or imaginary parts) of the
corresponding isoscalar and isovector central, spin-spin and tensor
NN-amplitudes. We find from two-loop two-pion exchange a sizeable isoscalar
central repulsion which amounts to MeV at fm. There is a
similarly strong isovector central attraction which however originates mainly
from the third order low energy constants entering the chiral -scattering amplitude. We also evaluate the one-loop -exchange diagram
with two second order chiral -vertices proportional to the low
energy constants as well as the first relativistic 1/M-correction
to the -exchange diagrams with one such vertex. The diagrammatic results
presented here are relevant components of the chiral NN-potential at
next-to-next-to-next-to-leading order.Comment: 6 pages, 2 figure
Spectral functions of nucleon form factors: Three-pion continua at low energies
We study the imaginary parts of the isoscalar electromagnetic and isovector
axial form factors of the nucleon close to the -threshold in covariant
baryon chiral perturbation theory. At the two-loop level, the contributions
arising from leading and next-to-leading order chiral -vertices, as well
as pion-induced excitations of virtual -isobars, are calculated.
It is found that the heavy baryon treatment overestimates substantially these
-continua. From a phenomenological analysis, that includes the narrow
-resonance or the broad -resonance, one can recognize small
windows near threshold, where chiral -dynamics prevails. However, in the
case of the isoscalar electromagnetic form factors , the
radiative correction provided by the -intermediate state turns out
to be of similar size.Comment: 12 pages, 9 figures, accepted for publication in Eur. Phys. J.
Dominant -exchange nucleon-nucleon interaction: Spin-spin and tensor potentials
We calculate at two-loop order in chiral perturbation theory the
electromagnetic corrections to the two-pion exchange nucleon-nucleon
interaction that is generated by the isovector spin-flip
contact-vertex proportional to the large low-energy constant GeV. We find that the respective -exchange potentials
contain sizeable isospin-breaking components which reach up to -4% of
corresponding isovector -exchange potentials. The typical values of these
novel charge-independence breaking spin-spin and tensor potentials are MeV and MeV, at a nucleon distance of fm. The
charge-symmetry breaking spin-spin and tensor potentials come out a factor of
2.4 smaller. Our analytical results for these presumably dominant
isospin-violating spin-spin and tensor NN-forces are in a form such that they
can be easily implemented into phase-shift analyses and few-body calculations.Comment: 7 pages, 1 figure, 2 tables, to be published in Physical Review C:
Brief report
Chiral -exchange NN-potentials: Results for diagrams proportional to g_A^4 and g_A^6
We calculate in (two-loop) chiral perturbation theory the local NN-potentials
generated by the three-pion exchange diagrams proportional to g_A^4 and g_A^6.
Surprisingly, we find that the total isoscalar central -exchange
potential vanishes identically. The individually largest -exchange
potentials are of isoscalar spin-spin, isovector central and isoscalar tensor
type. For these potentials simple analytical expressions can be given. The
strength of these dominant -exchange potentials at r=1.0 fm is 4.6 MeV,
2.9 MeV and 1.4 MeV, respectively. Furthermore, we observe that the spin-spin
and tensor potentials due to the diagrams proportional to g_A^6 do not exist in
the infinite nucleon mass limit.Comment: 8 pages, 5 figure
Electromagnetic corrections to the dominant two-pion exchange nucleon-nucleon potential
We calculate at two-loop order in chiral perturbation theory the
electromagnetic corrections to the dominant two-pion exchange nucleon-nucleon
interaction that is generated by the isoscalar contact-vertex
proportional to the large low-energy constant . We find that the
respective -exchange potential contains sizeable isospin-breaking
components which amount to about -1% of the strongly attractive isoscalar
central -exchange potential. The typical value of these novel
charge-independence and charge-symmetry breaking central potentials is MeV at a nucleon distance of fm. Our analytical result
for this presumably dominant -exchange interaction is in a form
such that it can be easily implemented into phase-shift analyses and few-body
calculations.Comment: 7 pages, 1 figure, to be published in Physical Review C (2006): Brief
Report
Well-Ordered Philosophy? Reflections on Kitcher's Proposal for a Renewal of Philosophy.
In his recent article Philosophy Inside Out, Philip Kitcher presents a metaphilosophical outlook that aims at nothing less than a renewal of philosophy. His idea is to draw philosophers’ attention away from “timeless questions” in the so-called “core areas” of philosophy. Instead, philosophers should address questions that matter to human lives. The aim of this paper is twofold: first, to reconstruct Kitcher’s view of how philosophy should be renewed; second, to point out some difficulties relating to his position. These difficulties concern the integration of his naturalism into the pragmatic vision of philosophy, the role of putative philosophical experts, and the ideal status of the program of well-ordered inquiry
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