2,527 research outputs found
Dual-species quantum degeneracy of potassium-40 and rubidium-87 on an atom chip
In this article we review our recent experiments with a 40K-87Rb mixture. We
demonstrate rapid sympathetic cooling of a 40K-87Rb mixture to dual quantum
degeneracy on an atom chip. We also provide details on efficient BEC
production, species-selective magnetic confinement, and progress toward
integration of an optical lattice with an atom chip. The efficiency of our
evaporation allows us to reach dual degeneracy after just 6 s of evaporation -
more rapidly than in conventional magnetic traps. When optimizing evaporative
cooling for efficient evaporation of 87Rb alone we achieve BEC after just 4 s
of evaporation and an 8 s total cycle time.Comment: 8 pages, 4 figures. To be published in the Proceedings of the 20th
International Conference on Atomic Physics, 2006 (Innsbruck, Austria
A homomorphism between link and XXZ modules over the periodic Temperley-Lieb algebra
We study finite loop models on a lattice wrapped around a cylinder. A section
of the cylinder has N sites. We use a family of link modules over the periodic
Temperley-Lieb algebra EPTL_N(\beta, \alpha) introduced by Martin and Saleur,
and Graham and Lehrer. These are labeled by the numbers of sites N and of
defects d, and extend the standard modules of the original Temperley-Lieb
algebra. Beside the defining parameters \beta=u^2+u^{-2} with u=e^{i\lambda/2}
(weight of contractible loops) and \alpha (weight of non-contractible loops),
this family also depends on a twist parameter v that keeps track of how the
defects wind around the cylinder. The transfer matrix T_N(\lambda, \nu) depends
on the anisotropy \nu and the spectral parameter \lambda that fixes the model.
(The thermodynamic limit of T_N is believed to describe a conformal field
theory of central charge c=1-6\lambda^2/(\pi(\lambda-\pi)).)
The family of periodic XXZ Hamiltonians is extended to depend on this new
parameter v and the relationship between this family and the loop models is
established. The Gram determinant for the natural bilinear form on these link
modules is shown to factorize in terms of an intertwiner i_N^d between these
link representations and the eigenspaces of S^z of the XXZ models. This map is
shown to be an isomorphism for generic values of u and v and the critical
curves in the plane of these parameters for which i_N^d fails to be an
isomorphism are given.Comment: Replacement of "The Gram matrix as a connection between periodic loop
models and XXZ Hamiltonians", 31 page
Remarks on the extension of the Ricci flow
We present two new conditions to extend the Ricci flow on a compact manifold
over a finite time, which are improvements of some known extension theorems.Comment: 9 pages, to appear in Journal of Geometric Analysi
The one-dimensional Keller-Segel model with fractional diffusion of cells
We investigate the one-dimensional Keller-Segel model where the diffusion is
replaced by a non-local operator, namely the fractional diffusion with exponent
. We prove some features related to the classical
two-dimensional Keller-Segel system: blow-up may or may not occur depending on
the initial data. More precisely a singularity appears in finite time when
and the initial configuration of cells is sufficiently concentrated.
On the opposite, global existence holds true for if the initial
density is small enough in the sense of the norm.Comment: 12 page
Interlayer Quasiparticle Transport in the Vortex State of Josephson Coupled Superconductors
We calculate the dependence of the interlayer quasiparticle conductivity,
, in a Josephson coupled d-wave superconductor on the magnetic field
B||c and the temperature T. We consider a clean superconductor with resonant
impurity scattering and a dominant coherent interlayer tunneling. When pancake
vortices in adjacent layers are weakly correlated at low T the conductivity
increases sharply with B before reaching an extended region of slow linear
growth, while at high T it initially decreases and then reaches the same linear
regime. For correlated pancakes increases much more strongly with
the applied field.Comment: 4 pages, 3 figure
Regularization of Linear Ill-posed Problems by the Augmented Lagrangian Method and Variational Inequalities
We study the application of the Augmented Lagrangian Method to the solution
of linear ill-posed problems. Previously, linear convergence rates with respect
to the Bregman distance have been derived under the classical assumption of a
standard source condition. Using the method of variational inequalities, we
extend these results in this paper to convergence rates of lower order, both
for the case of an a priori parameter choice and an a posteriori choice based
on Morozov's discrepancy principle. In addition, our approach allows the
derivation of convergence rates with respect to distance measures different
from the Bregman distance. As a particular application, we consider sparsity
promoting regularization, where we derive a range of convergence rates with
respect to the norm under the assumption of restricted injectivity in
conjunction with generalized source conditions of H\"older type
SLE local martingales in logarithmic representations
A space of local martingales of SLE type growth processes forms a
representation of Virasoro algebra, but apart from a few simplest cases not
much is known about this representation. The purpose of this article is to
exhibit examples of representations where L_0 is not diagonalizable - a
phenomenon characteristic of logarithmic conformal field theory. Furthermore,
we observe that the local martingales bear a close relation with the fusion
product of the boundary changing fields.
Our examples reproduce first of all many familiar logarithmic representations
at certain rational values of the central charge. In particular we discuss the
case of SLE(kappa=6) describing the exploration path in critical percolation,
and its relation with the question of operator content of the appropriate
conformal field theory of zero central charge. In this case one encounters
logarithms in a probabilistically transparent way, through conditioning on a
crossing event. But we also observe that some quite natural SLE variants
exhibit logarithmic behavior at all values of kappa, thus at all central
charges and not only at specific rational values.Comment: 40 pages, 7 figures. v3: completely rewritten, new title, new result
General existence proof for rest frame systems in asymptotically flat space-time
We report a new result on the nice section construction used in the
definition of rest frame systems in general relativity. This construction is
needed in the study of non trivial gravitational radiating systems. We prove
existence, regularity and non-self-crossing property of solutions of the nice
section equation for general asymptotically flat space times. This proves a
conjecture enunciated in a previous work.Comment: 14 pages, no figures, LaTeX 2
Asymptotic behaviour of random tridiagonal Markov chains in biological applications
Discrete-time discrete-state random Markov chains with a tridiagonal
generator are shown to have a random attractor consisting of singleton subsets,
essentially a random path, in the simplex of probability vectors. The proof
uses the Hilbert projection metric and the fact that the linear cocycle
generated by the Markov chain is a uniformly contractive mapping of the
positive cone into itself. The proof does not involve probabilistic properties
of the sample path and is thus equally valid in the nonautonomous deterministic
context of Markov chains with, say, periodically varying transitions
probabilities, in which case the attractor is a periodic path.Comment: 13 pages, 22 bibliography references, submitted to DCDS-B, added
references and minor correction
A single hollow beam optical trap for cold atoms
We present an optical trap for atoms that we have developed for precision
spectroscopy measurements. Cold atoms are captured in a dark region of space
inside a blue-detuned hollow laser beam formed by an axicon. We analyze the
light potential in a ray optics picture and experimentally demonstrate trapping
of laser-cooled metastable xenon atoms.Comment: 12 pages, 8 figure
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