27,727 research outputs found
Two-fluid behavior of the Kondo lattice in the 1/N slave boson approach
It has been recently shown by Nakatsuji, Pines, and Fisk [S. Nakatsuji, D.
Pines, and Z. Fisk, Phys. Rev. Lett. 92, 016401 (2004)] from the
phenomenological analysis of experiments in Ce1-xLaxCoIn5 and CeIrIn5 that
thermodynamic and transport properties of Kondo lattices below coherence
temperature can be very successfully described in terms of a two-fluid model,
with Kondo impurity and heavy electron Fermi liquid contributions. We analyze
thermodynamic properties of Kondo lattices using 1/N slave boson treatment of
the periodic Anderson model and show that these two contributions indeed arise
below the coherence temperature. We find that the Kondo impurity contribution
to thermodynamics corresponds to thermal excitations into the flat portion of
the energy spectrum.Comment: 7 pages, 2 figure
Commutating brushes tested in dc motors in dry argon atmospheres
Test apparatus, procedures, and results are given for dc-motor brushes operating in dry argon. Minimum concentrations of argon impurities are also determined
Phase 1 of the automated array assembly task of the low cost silicon solar array project
The results of a study of process variables and solar cell variables are presented. Interactions between variables and their effects upon control ranges of the variables are identified. The results of a cost analysis for manufacturing solar cells are discussed. The cost analysis includes a sensitivity analysis of a number of cost factors
Phase 1 of the automated array assembly task of the low cost silicon solar array project
The state of technology readiness for the automated production of solar cells and modules is reviewed. Individual process steps and process sequences for making solar cells and modules were evaluated both technically and economically. High efficiency with a suggested cell goal of 15% was stressed. It is concluded that the technology exists to manufacture solar cells which will meet program goals
Exploring the formation by core accretion and the luminosity evolution of directly imaged planets: The case of HIP 65426 b
A low-mass companion to the two-solar mass star HIP65426 has recently been
detected by SPHERE at around 100 au from its host. Explaining the presence of
super-Jovian planets at large separations, as revealed by direct imaging, is
currently an open question.
We want to derive statistical constraints on the mass and initial entropy of
HIP65426b and to explore possible formation pathways of directly imaged objects
within the core-accretion paradigm, focusing on HIP65426b.
Constraints on the planet's mass and post-formation entropy are derived from
its age and luminosity combined with cooling models. For the first time, the
results of population synthesis are also used to inform the results. Then, a
formation model that includes N-body dynamics with several embryos per disc is
used to study possible formation histories and the properties of possible
additional companions. Finally, the outcomes of two- and three-planet
scattering in the post-disc phase are analysed, taking tides into account.
The mass of HIP65426b is found to be Mp = 9.9 +1.1 -1.8 MJ using the hot
population and Mp = 10.9 +1.4 -2.0 MJ with the cold-nominal population. Core
formation at small separations from the star followed by outward scattering and
runaway accretion at a few hundred AU succeeds in reproducing the mass and
separation of HIP65426b. Alternatively, systems having two or more giant
planets close enough to be on an unstable orbit at disc dispersal are likely to
end up with one planet on a wide HIP65426b-like orbit with a relatively high
eccentricity (>~ 0.5).
If this scattering scenario explains its formation, HIP65426b is predicted to
have a high eccentricity and to be accompanied by one or several roughly
Jovian-mass planets at smaller semi-major axes, which also could have a high
eccentricity. This could be tested by further direct-imaging as well as
radial-velocity observations.Comment: 17 pages, 11 figures. A&A in press. Bern EXoplanet cooling curves
(BEX) available upon request. v2: Language and other minor changes; Fig. 4
now has labels summarising a possible formation pathway discussed in the tex
Quantum Fermion Hair
It is shown that the Dirac operator in the background of a magnetic
%Reissner-Nordstr\"om black hole and a Euclidean vortex possesses normalizable
zero modes in theories containing superconducting cosmic strings. One
consequence of these zero modes is the presence of a fermion condensate around
magnetically charged black holes which violates global quantum numbers.Comment: 16pp (harvmac (l)) and 2 figs.(not included
Double Well Potential: Perturbation Theory, Tunneling, WKB (beyond instantons)
A simple approximate solution for the quantum-mechanical quartic oscillator
in the double-well regime at arbitrary is
presented. It is based on a combining of perturbation theory near true minima
of the potential, semi-classical approximation at large distances and a
description of tunneling under the barrier. It provides 9-10 significant digits
in energies and gives for wavefunctions the relative deviation in real
-space less than .Comment: 13 pages, invited talk at "Crossing the boundaries: Gauge dynamics at
strong coupling (Shifmania)", Minneapolis, May 14-17, 200
Conductance of a spin-1 quantum dot: the two-stage Kondo effect
We discuss the physics of a of a spin-1 quantum dot, coupled to two metallic
leads and develop a simple model for the temperature dependence of its
conductance. Such quantum dots are described by a two-channel Kondo model with
asymmetric coupling constants and the spin screening of the dot by the leads is
expected to proceed via a two-stage process. When the Kondo temperatures of
each channel are widely separated, on cooling, the dot passes through a broad
cross-over regime dominated by underscreened Kondo physics. A singular, or
non-fermi liquid correction to the conductance develops in this regime. At the
lowest temperatures, destructive interference between resonant scattering in
both channels leads to the eventual suppression of the conductance of the dot.
We develop a model to describe the growth, and ultimate suppression of the
conductance in the two channel Kondo model as it is screened successively by
its two channels. Our model is based upon large-N approximation in which the
localized spin degrees of freedom are described using the Schwinger boson
formalism.Comment: 16 pages, 10 figure
Microlensing of Extended Stellar Sources
We investigate the feasibility of reconstructing the radial intensity profile
of extended stellar sources by inverting their microlensed light curves. Using
a simple, linear, limb darkening law as an illustration, we show that the
intensity profile can be accurately determined, at least over the outer part of
the stellar disc, with realistic light curve sampling and photometric errors.
The principal requirement is that the impact parameter of the lens be less than
or equal to the stellar radius. Thus, the analysis of microlensing events
provides a powerful method for testing stellar atmosphere models.Comment: 4 pages LaTeX, to appear in New Astronomy Reviews - proceedings of
the Oxford Workshop `Gravitational Lensing: Nature's Own Weighing Scales'.
Uses elsart.cls. Paper also available at
ftp://info.astro.gla.ac.uk/pub/martin/extended.p
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