6,454 research outputs found
A pedo-geomorphological classification and map of the Holocene sediments in the coastal plain of the three Guianas
Stiboka onderzoe
The dish-Rankine SCSTPE program (Engineering Experiment no. 1)
Activities planned for phase 2 Of the Small Community Solar Thermal Power Experiment (PFDR) program are summarized with emphasis on a dish-Rankine point focusing distributed receiver solar thermal electric system. Major design efforts include: (1) development of an advanced concept indirect-heated receiver;(2) development of hardware and software for a totally unmanned power plant control system; (3) implementation of a hybrid digital simulator which will validate plant operation prior to field testing; and (4) the acquisition of an efficient organic Rankine cycle power conversion unit. Preliminary performance analyses indicate that a mass-produced dish-Rankine PFDR system is potentially capable of producing electricity at a levelized busbar energy cost of 60 to 70 mills per KWh and with a capital cost of about $1300 per KW
BV analysis for covariant and non-covariant actions
The equivalence between the covariant and the non-covariant version of a
constrained system is shown to hold after quantization in the framework of the
field-antifield formalism. Our study covers the cases of Electromagnetism and
Yang-Mills fields and sheds light on some aspects of the Faddeev-Popov method,
for both the coratiant and non-covariant approaches, which had not been fully
clarified in the literature.Comment: 21 pages, preprint # UTTG-02-93, UB-ECM-PF 93/5. To appear in Phys.
Rev.
The influence of magnetic field geometry on magnetars X-ray spectra
Nowadays, the analysis of the X-ray spectra of magnetically powered neutron
stars or magnetars is one of the most valuable tools to gain insight into the
physical processes occurring in their interiors and magnetospheres. In
particular, the magnetospheric plasma leaves a strong imprint on the observed
X-ray spectrum by means of Compton up-scattering of the thermal radiation
coming from the star surface. Motivated by the increased quality of the
observational data, much theoretical work has been devoted to develop Monte
Carlo (MC) codes that incorporate the effects of resonant Compton scattering in
the modeling of radiative transfer of photons through the magnetosphere. The
two key ingredients in this simulations are the kinetic plasma properties and
the magnetic field (MF) configuration. The MF geometry is expected to be
complex, but up to now only mathematically simple solutions (self-similar
solutions) have been employed. In this work, we discuss the effects of new,
more realistic, MF geometries on synthetic spectra. We use new force-free
solutions in a previously developed MC code to assess the influence of MF
geometry on the emerging spectra. Our main result is that the shape of the
final spectrum is mostly sensitive to uncertain parameters of the
magnetospheric plasma, but the MF geometry plays an important role on the
angle-dependence of the spectra.Comment: 6 pages, 4 figures To appear in Proceedings of II Iberian Nuclear
Astrophysics Meeting held in Salamanca, September 22-23, 201
Remarks on the consistency of minimal deviations from General Relativity
We study the consequences of the modification of the phase space structure of
General Relativity imposed by breaking the full diffeomorphism invariance but
retaining the time foliation preserving diffeomorphisms. We examine the
different sectors in phase space that satisfy the new structure of constraints.
For some sectors we find an infinite tower of constraints. In spite of that, we
also show that these sectors allow for solutions, among them some well known
families of black hole and cosmologies which fulfill all the constraints. We
raise some physical concerns on the consequences of an absolute Galilean time,
on the thermodynamical pathologies of such models and on their unusual vacuum
structure.Comment: latex 28 pages, 1 figure. Added comments and a reference. Text
improved
Quantum Interference and Decoherence in Single-Molecule Junctions: How Vibrations Induce Electrical Current
Quantum interference effects and decoherence mechanisms in single-molecule
junctions are analyzed employing a nonequilibrium Green's function approach.
Electrons tunneling through quasi-degenerate states of a nanoscale molecular
junction exhibit interference effects. We show that electronic-vibrational
coupling, inherent to any molecular junction, strongly quenches such
interference effects. As a result, the electrical current can be significantly
larger than without electronic-vibrational coupling. The analysis reveals that
the quenching of quantum interference is particularly pronounced if the
junction is vibrationally highly excited, e.g. due to current-induced
nonequilibrium effects in the resonant transport regime.Comment: 11 pages, 4 figure
Optimization of the e-e- option for the ILC
The e-e- running mode is one of the interesting physics options at the
International Linear Collider (ILC). The luminosity for e-e- collisions is
reduced by the beam-beam effects. The resulting beamstrahlung energy loss and
beam-beam deflection angles as function of the vertical transverse offset are
different compared to the e+e- collisions. In this paper, the dependence of
these observables with the offset for different beam sizes has been analyzed to
optimize performances for the e-e- mode, taking into account the requirements
of the beam-beam deflection based intra-train feedback system. A first study of
the implications for the final focus and extraction line optics is also
presented for the cases of the 20 mrad and 2 mrad ILC base line crossing angle
geometries
On the equivalence of the Einstein-Hilbert and the Einstein-Palatini formulations of general relativity for an arbitrary connection
In the framework of the Einstein-Palatini formalism, even though the
projective transformation connecting the arbitrary connection with the Levi
Civita connection has been floating in the literature for a long time and
perhaps the result was implicitly known in the affine gravity community, yet as
far as we know Julia and Silva were the first to realise its gauge character.
We rederive this result by using the Rosenfeld-Dirac-Bergmann approach to
constrained Hamiltonian systems and do a comprehensive self contained analysis
establishing the equivalence of the Einstein-Palatini and the metric
formulations without having to impose the gauge choice that the connection is
symmetric. We also make contact with the the Einstein-Cartan theory when the
matter Lagrangian has fermions.Comment: 18 pages. Slight change in the title and wording of some sections to
emphasize the main results. References added. Matches published versio
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