7,952 research outputs found
On the -limit for a non-uniformly bounded sequence of two phase metric functionals
In this study we consider the -limit of a highly oscillatory
Riemannian metric length functional as its period tends to 0. The metric
coefficient takes values in either or where and . We
find that for a large class of metrics, in particular those metrics whose
surface of discontinuity forms a differentiable manifold, the -limit
exists, as in the uniformly bounded case. However, when one attempts to
determine the -limit for the corresponding boundary value problem, the
existence of the -limit depends on the value of . Specifically, we
show that the power is critical in that the -limit exists for , whereas it ceases to exist for . The results here have
applications in both nonlinear optics and the effective description of a
Hamiltonian particle in a discontinuous potential.Comment: 31 pages, 1 figure. Submitte
Single crystal growth and anisotropy of CeRuPO
We report on the single crystal growth of the ferromagnetic Kondo lattice
system CeRuPO using a Sn flux method. Magnetic susceptibility and electrical
resistivity measurements indicate strong anisotropy of this structurally
layered compound. They evidence that the magnetic moments order
ferromagnetically along the c-direction of the tetragonal unit cell, whereas
the crystal electric field (CEF) anisotropy favors the ab-plane. Therefore,
CeRuPO presents the unusual case within rare earth systems, where the
anisotropy of the interionic exchange interaction overcomes the single ion
anisotropy due to the CEF interaction.Comment: 13 pages, 7 figures, high quality figures:
http://www.cpfs.mpg.de/~krellner
High-sensitivity tool for studying phonon related mechanical losses in low loss materials
Fundamental mechanical loss mechanisms exist even in very pure materials, for
instance, due to the interactions of excited acoustic waves with thermal
phonons. A reduction of these losses in a certain frequency range is desired in
high precision instruments like gravitational wave detectors. Systematic
analyses of the mechanical losses in those low loss materials are essential for
this aim, performed in a highly sensitive experimental set-up. Our novel method
of mechanical spectroscopy, cryogenic resonant acoustic spectroscopy of bulk
materials (CRA spectroscopy), is well suited to systematically determine losses
at the resonant frequencies of the samples of less than 10^(-9) in the wide
temperature range from 5 to 300 K. A high precision set-up in a specially built
cryostat allows contactless excitation and readout of the oscillations of the
sample. The experimental set-up and measuring procedure are described.
Limitations to our experiment due to external loss mechanisms are analysed. The
influence of the suspension system as well as the sample preparation is
explained.Comment: 4 pages, 3 figures, proceedings of PHONONS07, submitted to Journal of
Physics: Conference Serie
Influence of a small fraction of individuals with enhanced mutations on a population genetic pool
Computer simulations of the Penna ageing model suggest that already a small
fraction of births with enhanced number of new mutations can negatively
influence the whole population.Comment: 10 pages including 6 figures; draf
Jahn-Teller effect versus Hund's rule coupling in C60N-
We propose variational states for the ground state and the low-energy
collective rotator excitations in negatively charged C60N- ions (N=1...5). The
approach includes the linear electron-phonon coupling and the Coulomb
interaction on the same level. The electron-phonon coupling is treated within
the effective mode approximation (EMA) which yields the linear t_{1u} x H_g
Jahn-Teller problem whereas the Coulomb interaction gives rise to Hund's rule
coupling for N=2,3,4. The Hamiltonian has accidental SO(3) symmetry which
allows an elegant formulation in terms of angular momenta. Trial states are
constructed from coherent states and using projection operators onto angular
momentum subspaces which results in good variational states for the complete
parameter range. The evaluation of the corresponding energies is to a large
extent analytical. We use the approach for a detailed analysis of the
competition between Jahn-Teller effect and Hund's rule coupling, which
determines the spin state for N=2,3,4. We calculate the low-spin/high-spin gap
for N=2,3,4 as a function of the Hund's rule coupling constant J. We find that
the experimentally measured gaps suggest a coupling constant in the range
J=60-80meV. Using a finite value for J, we recalculate the ground state
energies of the C60N- ions and find that the Jahn-Teller energy gain is partly
counterbalanced by the Hund's rule coupling. In particular, the ground state
energies for N=2,3,4 are almost equal
Dissipation-preserving discretization of the Cahn--Hilliard equation with dynamic boundary conditions
This paper deals with time stepping schemes for the Cahn--Hilliard equation
with three different types of dynamic boundary conditions. The proposed schemes
of first and second order are mass-conservative and energy-dissipative and --
as they are based on a formulation as a coupled system of partial differential
equations -- allow different spatial discretizations in the bulk and on the
boundary. The latter enables refinements on the boundary without an adaptation
of the mesh in the interior of the domain. The resulting computational gain is
illustrated in numerical experiments
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