18,082 research outputs found
Dimer states in atomic mixtures
A mixture of heavy atoms in a Mott state and light spin-1/2 fermionic atoms
is studied in an optical lattice. Inelastic scattering processes between both
atomic species excite the heavy atoms and renormalize the tunneling rate as
well as the interaction of the light atoms. An effective Hamiltonian for the
latter is derived that describes tunneling of single fermions, tunneling of
fermionic pairs and an exchange of fermionic spins. Low energy states of this
Hamiltonian are a N\'eel state for strong effective repulsion, dimer states for
moderate interaction, and a density wave of paired fermions for strong
effective attraction.Comment: 10 pages, 3 figure, extended versio
S-matrix elements for gauge theories with and without implemented constraints
We derive an expression for the relation between two scattering transition
amplitudes which reflect the same dynamics, but which differ in the description
of their initial and final state vectors. In one version, the incident and
scattered states are elements of a perturbative Fock space, and solve the
eigenvalue problem for the `free' part of the Hamiltonian --- the part that
remains after the interactions between particle excitations have been `switched
off'. Alternatively, the incident and scattered states may be coherent states
that are transforms of these Fock states. In earlier work, we reported on the
scattering amplitudes for QED, in which a unitary transformation relates
perturbative and non-perturbative sets of incident and scattered states. In
this work, we generalize this earlier result to the case of transformations
that are not necessarily unitary and that may not have unique inverses. We
discuss the implication of this relationship for Abelian and non-Abelian gauge
theories in which the `transformed', non-perturbative states implement
constraints, such as Gauss's law.Comment: 8 pages. Invited contribution to Foundation of Physics for an issue
honoring Prof. Lawrence Horwitz on his 65th Birthda
Blood levels of PAF are elevated during induction of immune complex mediated enteropathy in the rat
Intravenous injection into rats of immune complexes (IC) prepared in 5 × antigen excess rapidly induces annular bands of vascular congestion and transmural haemorrhage producing a striped appearance of the small intestine. Indirect evidence suggested a major role for PAF in the induction of lesions. In the present study, we showed that blood and leukocyte levels of PAF were elevated in most rats injected 10 min earlier with sufficient IC to induce lesions of 3+ to 4+ intensity. There was no significant difference in the number of rats with elevated plasma levels of PAF. The possibility that changes in blood PAF levels might be mirrored at sites closer to the lesions was considered. The overall effect of PAF on the small intestine of the rats is to induce stasis of flow; the precise target of PAF in mediating this effect is unknown
Extended Coherence Time with Atom-Number Squeezed Sources
Coherence properties of Bose-Einstein condensates offer the potential for
improved interferometric phase contrast. However, decoherence effects due to
the mean-field interaction shorten the coherence time, thus limiting potential
sensitivity. In this work, we demonstrate increased coherence times with number
squeezed states in an optical lattice using the decay of Bloch oscillations to
probe the coherence time. We extend coherence times by a factor of 2 over those
expected with coherent state BEC interferometry. We observe quantitative
agreement with theory both for the degree of initial number squeezing as well
as for prolonged coherence times.Comment: 4 pages, 4 figure
Discrimination of the Healthy and Sick Cardiac Autonomic Nervous System by a New Wavelet Analysis of Heartbeat Intervals
We demonstrate that it is possible to distinguish with a complete certainty
between healthy subjects and patients with various dysfunctions of the cardiac
nervous system by way of multiresolutional wavelet transform of RR intervals.
We repeated the study of Thurner et al on different ensemble of subjects. We
show that reconstructed series using a filter which discards wavelet
coefficients related with higher scales enables one to classify individuals for
which the method otherwise is inconclusive. We suggest a delimiting diagnostic
value of the standard deviation of the filtered, reconstructed RR interval time
series in the range of (for the above mentioned filter), below
which individuals are at risk.Comment: 5 latex pages (including 6 figures). Accepted in Fractal
Phase coherence of an atomic Mott insulator
We investigate the phase coherence properties of ultracold Bose gases in
optical lattices, with special emphasis on the Mott insulating phase. We show
that phase coherence on short length scales persists even deep in the
insulating phase, preserving a finite visibility of the interference pattern
observed after free expansion. This behavior can be attributed to a coherent
admixture of particle/hole pairs to the perfect Mott state for small but finite
tunneling. In addition, small but reproducible ``kinks'' are seen in the
visibility, in a broad range of atom numbers. We interpret them as signatures
for density redistribution in the shell structure of the trapped Mott
insulator
A variational problem on Stiefel manifolds
In their paper on discrete analogues of some classical systems such as the
rigid body and the geodesic flow on an ellipsoid, Moser and Veselov introduced
their analysis in the general context of flows on Stiefel manifolds. We
consider here a general class of continuous time, quadratic cost, optimal
control problems on Stiefel manifolds, which in the extreme dimensions again
yield these classical physical geodesic flows. We have already shown that this
optimal control setting gives a new symmetric representation of the rigid body
flow and in this paper we extend this representation to the geodesic flow on
the ellipsoid and the more general Stiefel manifold case. The metric we choose
on the Stiefel manifolds is the same as that used in the symmetric
representation of the rigid body flow and that used by Moser and Veselov. In
the extreme cases of the ellipsoid and the rigid body, the geodesic flows are
known to be integrable. We obtain the extremal flows using both variational and
optimal control approaches and elucidate the structure of the flows on general
Stiefel manifolds.Comment: 30 page
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