2,833 research outputs found
Exact and Truncated Dynamics in Nonequilibrium Field Theory
Nonperturbative dynamics of quantum fields out of equilibrium is often
described by the time evolution of a hierarchy of correlation functions, using
approximation methods such as Hartree, large N, and nPI-effective action
techniques. These truncation schemes can be implemented equally well in a
classical statistical system, where results can be tested by comparison with
the complete nonlinear evolution obtained by numerical methods. For a 1+1
dimensional scalar field we find that the early-time behaviour is reproduced
qualitatively by the Hartree dynamics. The inclusion of direct scattering
improves this to the quantitative level. We show that the emergence of
nonthermal temperature profiles at intermediate times can be understood in
terms of the fixed points of the evolution equations in the Hartree
approximation. The form of the profile depends explicitly on the initial
ensemble. While the truncated evolution equations do not seem to be able to get
away from the fixed point, the full nonlinear evolution shows thermalization
with a (surprisingly) slow relaxation.Comment: 30 pages with 12 eps figures, minor changes; to appear in Phys.Rev.
Oscillatory behavior of the in-medium interparticle potential in hot gauge system with scalar bound states
We investigate the in-medium interparticle potential of hot gauge system with
bound states by employing the QED and scalar QED coupling. At finite
temperature an oscillatory behavior of the potential has been found as well as
its variation in terms of different free parameters. We expect the competition
among the parameters will lead to an appropriate interparticle potential which
could be extended to discuss the fluid properties of QGP with scalar bound
states
Transport of a colloidal particle driven across a temporally oscillating optical potential energy landscape
A colloidal particle is driven across a temporally oscillating one-dimensional optical potential energy landscape and its particle motion is analysed. Different modes of dynamic mode locking are observed and are confirmed with the use of phase portraits. The effect of the oscillation frequency on the mode locked step width is addressed and the results are discussed in light of a high-frequency theory and compared to simulations. Furthermore, the influence of the coupling between the particle and the optical landscape on mode locking is probed by increasing the maximum depth of the optical landscape. Stronger coupling is seen to increase the width of mode locked steps. Finally, transport across the temporally oscillating landscape is studied by measuring the effective diffusion coefficient of a mobile particle, which is seen to be highly sensitive to the driving velocity and mode locking
An in vitro study of the adhesion of blood platelets onto vascular catheters. Part I
The adhesion of human blood platelets onto vascular catheters was studied using a specially designed perfusion chamber. Polyurethane catheters were exposed to citrated human blood for different periods (up to 20 min) and at different wall shear rates (190, 260, 330 sec-1). The rate of platelet adhesion was determined using 111In-labeled platelets, while the morphology of adhering platelets was investigated using scanning electron microscopy. A linear increase in platelet adhesion was found within the first 10 min of perfusion, after which a plateau value was reached. The number of adhering platelets did not vary significantly with the shear rates applied, which may indicate that within the range of shear rates studied, the adhesion of platelets onto the catheter surface is mainly determined by the rate of the reaction between the platelets and the material surface. Catheters coated with a conjugate of heparin and albumin showed a four- to five-fold reduction in platelet adhesion as compared to uncoated catheters. This reduction in platelet adhesion was not only due to the presence of albumin moieties at the surface but also to the presence of heparin residues in the adsorbed albumin-heparin conjugate
Melting Spectral Functions of the Scalar and Vector Mesons in a Holographic QCD Model
We investigate the finite-temperature spectral functions of heavy quarkonia
by using the soft-wall AdS/QCD model. We discuss the scalar, the pseudo-scalar,
the vector, and the axial-vector mesons and compare their qualitative features
of the melting temperature and growing width. We find that the axial-vector
meson melts earlier than the vector meson, while there appears only a slight
difference between the scalar and pseudo-scalar mesons which also melt earlier
than the vector meson.Comment: 27 pages, 10 figure
The goal dependent automaticity of drinking habits
In recent treatments of habitual social behaviour, habits are conceptualised as a form of goal-directed automatic behaviour that are mentally represented as goal-action links. Three experiments tested this conceptualisation in the context of students’ drinking (alcohol consumption) habits. Participants were randomly assigned to conditions where either a goal related to drinking behaviour (socialising) was activated, or an unrelated goal was activated. In addition, participants’ drinking habits were measured. The dependent variable in Experiments 1 and 2 was readiness to drink, operationalised by speed of responding to the action concept “drinking” in a verb verification task. Experiment 3 used uptake of a voucher to measure drinking behaviour. Findings supported the view that when habits are established, simply activating a goal related to the focal behaviour automatically elicits that behaviour. These findings are consistent with a goal-dependent conception of habit. Possibilities for interventions designed to attenuate undesirable habitual behaviours are considered
Self-assembly and crystallisation of indented colloids at a planar wall
We report experimental and simulation studies of the structure of a monolayer
of indented ("lock and key") colloids, on a planar surface. On adding a
non-absorbing polymer with prescribed radius and volume fraction, depletion
interactions are induced between the colloids, with controlled range and
strength. For spherical particles, this leads to crystallisation, but the
indented colloids crystallise less easily than spheres, in both simulation and
experiment. Nevertheless, simulations show that indented colloids do form
plastic (rotator) crystals. We discuss the conditions under which this occurs,
and the possibilities of lower-symmetry crystal states. We also comment on the
kinetic accessibility of these states.Comment: 8 pages, 8 figure
- …