1,218 research outputs found
Accidental suppression of Landau damping of the transverse breathing mode in elongated Bose-Einstein condensates
We study transverse radial oscillations of an elongated Bose-Einstein
condensate using finite temperature simulations, in the context of a recent
experiment at ENS. We demonstrate the existence of a mode corresponding to an
in-phase collective oscillation of both the condensate and thermal cloud.
Excitation of this mode accounts for the very small damping rate observed
experimentally, and we find excellent quantitative agreement between experiment
and theory. In contrast to other condensate modes, interatomic collisions are
found to be the dominant damping mechanism in this case.Comment: 4 pages, 3 figure
A Dynamical Self-Consistent Finite Temperature Kinetic Theory: The ZNG Scheme
We review a self-consistent scheme for modelling trapped weakly-interacting
quantum gases at temperatures where the condensate coexists with a significant
thermal cloud. This method has been applied to atomic gases by Zaremba, Nikuni,
and Griffin, and is often referred to as ZNG. It describes both
mean-field-dominated and hydrodynamic regimes, except at very low temperatures
or in the regime of large fluctuations. Condensate dynamics are described by a
dissipative Gross-Pitaevskii equation (or the corresponding quantum
hydrodynamic equation with a source term), while the non-condensate evolution
is represented by a quantum Boltzmann equation, which additionally includes
collisional processes which transfer atoms between these two subsystems. In the
mean-field-dominated regime collisions are treated perturbatively and the full
distribution function is needed to describe the thermal cloud, while in the
hydrodynamic regime the system is parametrised in terms of a set of local
variables. Applications to finite temperature induced damping of collective
modes and vortices in the mean-field-dominated regime are presented.Comment: Unedited version of chapter to appear in Quantum Gases: Finite
Temperature and Non-Equilibrium Dynamics (Vol. 1 Cold Atoms Series). N.P.
Proukakis, S.A. Gardiner, M.J. Davis and M.H. Szymanska, eds. Imperial
College Press, London (in press). See
http://www.icpress.co.uk/physics/p817.htm
Multi-site mean-field theory for cold bosonic atoms in optical lattices
We present a detailed derivation of a multi-site mean-field theory (MSMFT)
used to describe the Mott-insulator to superfluid transition of bosonic atoms
in optical lattices. The approach is based on partitioning the lattice into
small clusters which are decoupled by means of a mean field approximation. This
approximation invokes local superfluid order parameters defined for each of the
boundary sites of the cluster. The resulting MSMFT grand potential has a
non-trivial topology as a function of the various order parameters. An
understanding of this topology provides two different criteria for the
determination of the Mott insulator superfluid phase boundaries. We apply this
formalism to -dimensional hypercubic lattices in one, two and three
dimensions, and demonstrate the improvement in the estimation of the phase
boundaries when MSMFT is utilized for increasingly larger clusters, with the
best quantitative agreement found for . The MSMFT is then used to examine
a linear dimer chain in which the on-site energies within the dimer have an
energy separation of . This system has a complicated phase diagram
within the parameter space of the model, with many distinct Mott phases
separated by superfluid regions.Comment: 30 pages, 23 figures, accepted for publication in Phys. Rev.
Evaluation of a semi-active gravity gradient system. Volume I - Technical summary
Semi-active gravity gradient system for attitude control of earth oriented spacecraf
Evaluation of a semi-active gravity gradient system. Volume II - Appendices
Evaluation of semi-active gravity gradient system - appendixe
The level of chemokine CXCL5 in the cerebrospinal fluid is increased during the first 24 hours of ischaemic stroke and correlates with the size of early brain damage
Inflammation is an important feature of the pathophysiological response to
ischaemic stroke. The ischaemic brain-invading leukocytes, neutrophils in particular,
contribute to the exacerbation of tissue injury in stroke. Chemokines are
a growing family of proteins performing chemotactic activity on selective leukocyte
subpopulations. Chemokines are broadly divided into two major subfamilies on
the basis of the arrangement of the two N-terminal cysteine residues, CXC and CC,
depending on whether the first two cysteine residues have an amino acid between
them (CXC) or are adjacent (CC). CXC chemokines possessing, close to the
N terminus, the amino acid sequence glutamic acid-leucine-arginine (ELR motif)
specifically act on neutrophils. CXCL5 is one of the ELR-expressing CXC chemokines
and is a potent neutrophil attractant and activator. The objective of the study
was to detect CXCL5 levels in the cerebrospinal fluid (CSF) and sera of stroke
patients and to investigate the relation between these levels and the volume of
brain computed tomography (CT) hypodense areas representing early ischaemic
lesions. A total of 23 ischaemic stroke patients were studied. CSF and blood sampling
and brain CT were performed within the first 24 hours of stroke. The control
group consisted of 15 patients with tension headache. CXCL5 levels were determined
by the ELISA method. CSF CXCL5 levels in stroke patients were significantly
higher in comparison with the control group (38.2 ± 18.4 pg/ml vs. 18.7 ± 8.2 pg/ml; p < 0.001). No significant differences in serum CXCL5 levels were
found between the stroke patients and the control group. CSF CXCL5 levels correlated
positively with the volume of early brain CT hypodense areas (p < 0.0001).
The results suggest that CXCL5 may play a role in the inflammatory reaction during
the early phase of ischaemic stroke
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