4,464 research outputs found
Superconductivity in the Kondo lattice model
We study the Kondo lattice model with additional attractive interaction
between the conduction electrons within the dynamical mean-field theory using
the numerical renormalization group to solve the effective quantum impurity
problem. In addition to normal-state and magnetic phases we also allow for the
occurrence of a superconducting phase. In the normal phase we observe a very
sensitive dependence of the low-energy scale on the conduction-electron
interaction. We discuss the dependence of the superconducting transition on the
interplay between attractive interaction and Kondo exchange.Comment: Submitted to ICM 2009 Conference Proceeding
Simulation of Stratospheric Water Vapor Trends: Impact on Stratospheric Ozone Chemistry
A transient model simulation of the 40-year time
period 1960 to 1999 with the coupled climate-chemistry
model (CCM) ECHAM4.L39(DLR)/CHEM shows a stratospheric
water vapor increase over the last two decades of
0.7 ppmv and, additionally, a short-term increase after major
volcanic eruptions. Furthermore, a long-term decrease in
global total ozone as well as a short-term ozone decline in the
tropics after volcanic eruptions are modeled. In order to understand
the resulting effects of the water vapor changes on
lower stratospheric ozone chemistry, different perturbation
simulations were performed with the CCM ECHAM4.L39-
(DLR)/CHEM feeding the water vapor perturbations only to
the chemistry part. Two different long-term perturbations of
lower stratospheric water vapor, +1 ppmv and +5 ppmv, and a
short-term perturbation of +2 ppmv with an e-folding time of
two months were applied. An additional stratospheric water
vapor amount of 1 ppmv results in a 5–10% OH increase in
the tropical lower stratosphere between 100 and 30 hPa. As
a direct consequence of the OH increase the ozone destruction
by the HOx cycle becomes 6.4% more effective. Coupling
processes between the HOx-family and the NOx/ClOxfamily
also affect the ozone destruction by other catalytic
reaction cycles. The NOx cycle becomes 1.6% less effective,
whereas the effectiveness of the ClOx cycle is again
slightly enhanced. A long-term water vapor increase does
not only affect gas-phase chemistry, but also heterogeneous
ozone chemistry in polar regions. The model results indicate
an enhanced heterogeneous ozone depletion during antarctic
spring due to a longer PSC existence period. In contrast,
PSC formation in the northern hemisphere polar vortex and
therefore heterogeneous ozone depletion during arctic spring
are not affected by the water vapor increase, because of the
less PSC activity. Finally, this study shows that 10% of the
global total ozone decline in the transient model run can
be explained by the modeled water vapor increase, but the
simulated tropical ozone decrease after volcanic eruptions is
caused dynamically rather than chemically
Automated Model Selection with AMSFin a production process of the automotive industry
Machine learning, statistics and knowledge engineering provide a broad variety of supervised learning algorithms for classification. In this paper we introduce the Automated Model Selection Framework (AMSF) which presents automatic and semi-automatic methods to select classifiers. To achieve this we split up the selection process into three distinct phases. Two of those select algorithms by static rules which are derived from a manually created knowledgebase. At this stage of AMSF the user can choose between different rankers in the third phase. Currently, we use instance based learning and a scoring scheme for ranking the classifiers. After evaluation of different rankers we will recommend the most successful to the user by default. Besides describing the architecture and design issues, we additionally point out the versatile ways AMSF is applied in a production process of the automotive industr
Charge gaps and quasiparticle bands of the ionic Hubbard model
The ionic Hubbard model on a cubic lattice is investigated using analytical
approximations and Wilson's renormalization group for the charge excitation
spectrum. Near the Mott insulating regime, where the Hubbard repulsion starts
to dominate all energies, the formation of correlated bands is described. The
corresponding partial spectral weights and local densities of states show
characteristic features, which compare well with a hybridized-band picture
appropriate for the regime at small , which at half-filling is known as a
band insulator. In particular, a narrow charge gap is obtained at half-filling,
and the distribution of spectral quasi-particle weight reflects the fundamental
hybridization mechanism of the model
Permanent generic relatedness and silent change
Given the assertion of a relation between two types, like: “Epidermis
has part some Keratinocyte”, we define silent change as any kind of change of the instance-relata of the relation in question that does not change the truth-value of the respective type-level assertion. Such assertions are notoriously difficult to model in OWL 2. To address this problem, we distinguish different modes of type-level relatedness giving rise to this problem and describe a conservative extension to the BFO top-level ontology that allows expressing these modes
Self-consistent Treatment of Crystal-Electric-Field-Levels in the Anderson Lattice
We consider an Anderson lattice model with a spin 1/2 degenerated conduction
electron band and localized ionic CEF-levels, classified according to the
irreducible representation of the point group of the lattice. We present the
self-consistency equations for local approximations ("
approximation) for the periodic Anderson model. It leads to a matrix
formulation of the effective local density of states and the lattice
-Green's function. We derive the quasi-particle life-time which enters the
Boltzmann transport equations. The impact of a -dependent hybridization is
discussed. We prove that vertex corrections will vanish, as long as all states
of an irreducible representation couple to the conduction electron band with a
hybridization matrix element of the same parity.Comment: 3 pages, REVTeX type, proceedings of SCES96 Z\"uric
A Fermi Sea of Heavy Electrons (a Kondo Lattice) is Never a Fermi Liquid
I demonstrate a contradiction which arises if we assume that the Fermi
surface in a heavy electron metal represents a finite jump in occupancy
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