4,571 research outputs found
Adherence to secondary stroke prevention strategies - Results from the German stroke data bank
Only very limited data are available concerning patient adherence to antithrombotic medication intended to prevent a recurrent stroke. Reduced adherence and compliance could significantly influence the effects of any stroke prevention strategies. This study from a large stroke data bank provides representative data concerning the rate of stroke victims adhering to their recommended preventive medication. During a 2-year period beginning January 1, 1998, all patients with acute stroke or TIA in 23 neurological departments with an acute stroke unit were included in the German Stroke Data Bank. Data were collected prospectively, reviewed, validated and processed in a central data management unit. Only 12 centers with a follow-up rate of 80% or higher were included in this evaluation. 3,420 patients were followed up after 3 months, and 2,640 patients were followed up one year after their stroke. After one year, 96% of all patients reported still adhere to at least one medical stroke prevention strategy. Of the patients receiving aspirin at discharge, 92.6% reported to use that medication after 3 months and 84% after one year, while 81.6 and 61.6% were the respective figures for clopidogrel, and 85.2 and 77.4% for oral anticoagulation. Most patients who changed medication switched from aspirin to clopidogrel. Under the conditions of this observational study, adherence to stroke prevention strategies is excellent. The highest adherence rate is noticed for aspirin and oral anticoagulation. After one year, very few patients stopped taking stroke preventive medication. Copyright (C) 2003 S. Karger AG, Basel
Patterns of convection in rotating spherical shells
Patterns of convection in internally heated, self-gravitating rotating
spherical fluid shells are investigated through numerical simulations. While
turbulent states are of primary interest in planetary and stellar applications
the present paper emphasizes more regular dynamical features at Rayleigh
numbers not far above threshold which are similar to those which might be
observed in laboratory or space experiments. Amplitude vacillations and spatial
modulations of convection columns are common features at moderate and large
Prandtl numbers. In the low Prandtl number regime equatorially attached
convection evolves differently with increasing Rayleigh number and exhibits an
early transition into a chaotic state. Relationships of the dynamical features
to coherent structures in fully turbulent convection states are emphasized
Elastic turbulence in shear banding wormlike micelles
We study the dynamics of the Taylor-Couette flow of shear banding wormlike
micelles. We focus on the high shear rate branch of the flow curve and show
that for sufficiently high Weissenberg numbers, this branch becomes unstable.
This instability is strongly sub-critical and is associated with a shear stress
jump. We find that this increase of the flow resistance is related to the
nucleation of turbulence. The flow pattern shows similarities with the elastic
turbulence, so far only observed for polymer solutions. The unstable character
of this branch led us to propose a scenario that could account for the recent
observations of Taylor-like vortices during the shear banding flow of wormlike
micelles
Emergence of pointer states in a non-perturbative environment
We show that the pointer basis distinguished by collisional decoherence
consists of exponentially localized, solitonic wave packets. Based on the
orthogonal unraveling of the quantum master equation, we characterize their
formation and dynamics, and we demonstrate that the statistical weights arising
from an initial superposition state are given by the required projection. Since
the spatial width of the pointer states can be obtained by accounting for the
gas environment in a microscopically realistic fashion, one may thus calculate
the coherence length of a strongly interacting gas.Comment: 8 pages, 1 figure; corresponds to published versio
Localized transverse bursts in inclined layer convection
We investigate a novel bursting state in inclined layer thermal convection in
which convection rolls exhibit intermittent, localized, transverse bursts. With
increasing temperature difference, the bursts increase in duration and number
while exhibiting a characteristic wavenumber, magnitude, and size. We propose a
mechanism which describes the duration of the observed bursting intervals and
compare our results to bursting processes in other systems.Comment: 4 pages, 8 figure
Generation and Structure of Solitary Rossby Vortices in Rotating Fluids
The formation of zonal flows and vortices in the generalized
Charney-Hasegawa-Mima equation is studied. We focus on the regime when the size
of structures is comparable to or larger than the deformation (Rossby) radius.
Numerical simulations show the formation of anticyclonic vortices in unstable
shear flows and ring-like vortices with quiescent cores and vorticity
concentrated in a ring. Physical mechanisms that lead to these phenomena and
their relevance to turbulence in planetary atmospheres are discussed.Comment: 3 pages in REVTeX, 5 postscript figures separately, submitted to
Phys. Rev.
Hysteresis phenomenon in turbulent convection
Coherent large-scale circulations of turbulent thermal convection in air have
been studied experimentally in a rectangular box heated from below and cooled
from above using Particle Image Velocimetry. The hysteresis phenomenon in
turbulent convection was found by varying the temperature difference between
the bottom and the top walls of the chamber (the Rayleigh number was changed
within the range of ). The hysteresis loop comprises the one-cell
and two-cells flow patterns while the aspect ratio is kept constant (). We found that the change of the sign of the degree of the anisotropy of
turbulence was accompanied by the change of the flow pattern. The developed
theory of coherent structures in turbulent convection (Elperin et al. 2002;
2005) is in agreement with the experimental observations. The observed coherent
structures are superimposed on a small-scale turbulent convection. The
redistribution of the turbulent heat flux plays a crucial role in the formation
of coherent large-scale circulations in turbulent convection.Comment: 10 pages, 9 figures, REVTEX4, Experiments in Fluids, 2006, in pres
Scaling properties of granular materials
Given an assembly of viscoelastic spheres with certain material properties,
we raise the question how the macroscopic properties of the assembly will
change if all lengths of the system, i.e. radii, container size etc., are
scaled by a constant. The result leads to a method to scale down experiments to
lab-size.Comment: 4 pages, 2 figure
Square patterns in Rayleigh-Benard convection with rotation about a vertical axis
We present experimental results for Rayleigh-Benard convection with rotation
about a vertical axis at dimensionless rotation rates in the range 0 to 250 and
upto 20% above the onset. Critical Rayleigh numbers and wavenumbers agree with
predictions of linear stability analysis. For rotation rates greater than 70
and close to onset, the patterns are cellular with local four-fold coordination
and differ from the theoretically expected Kuppers-Lortz unstable state. Stable
as well as intermittent defect-free square lattices exist over certain
parameter ranges. Over other ranges defects dynamically disrupt the lattice but
cellular flow and local four-fold coordination is maintained.Comment: ReVTeX, 4 pages, 7 eps figures include
Effects of non-resonant interaction in ensembles of phase oscillators
We consider general properties of groups of interacting oscillators, for
which the natural frequencies are not in resonance. Such groups interact via
non-oscillating collective variables like the amplitudes of the order
parameters defined for each group. We treat the phase dynamics of the groups
using the Ott-Antonsen ansatz and reduce it to a system of coupled equations
for the order parameters. We describe different regimes of co-synchrony in the
groups. For a large number of groups, heteroclinic cycles, corresponding to a
sequental synchronous activity of groups, and chaotic states, where the order
parameters oscillate irregularly, are possible.Comment: 21 pages, 7 fig
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