4,878 research outputs found
Hydrodynamically enforced entropic trapping of Brownian particles
We study the transport of Brownian particles through a corrugated channel
caused by a force field containing curl-free (scalar potential) and
divergence-free (vector potential) parts. We develop a generalized Fick-Jacobs
approach leading to an effective one-dimensional description involving the
potential of mean force. As an application, the interplay of a pressure-driven
flow and an oppositely oriented constant bias is considered. We show that for
certain parameters, the particle diffusion is significantly suppressed via the
property of hyrodynamically enforced entropic particle trapping.Comment: 5 pages, 4 figures, in press with Physical Review Letter
Giant enhancement of hydrodynamically enforced entropic trapping in thin channels
Using our generalized Fick-Jacobs approach [Martens et al., PRL 110, 010601
(2013); Martens et al., Eur. Phys. J. Spec. Topics 222, 2453-2463 (2013)] and
extensive Brownian dynamics simulations, we study particle transport through
three-dimensional periodic channels of different height. Directed motion is
caused by the interplay of constant bias acting along the channel axis and a
pressure-driven flow. The tremendous change of the flow profile shape in
channel direction with the channel height is reflected in a crucial dependence
of the mean particle velocity and the effective diffusion coefficient on the
channel height. In particular, we observe a giant suppression of the effective
diffusivity in thin channels; four orders of magnitude compared to the bulk
value.Comment: 16 pages, 8 figure
Biased Brownian motion in extreme corrugated tubes
Biased Brownian motion of point-size particles in a three-dimensional tube
with smoothly varying cross-section is investigated. In the fashion of our
recent work [Martens et al., PRE 83,051135] we employ an asymptotic analysis to
the stationary probability density in a geometric parameter of the tube
geometry. We demonstrate that the leading order term is equivalent to the
Fick-Jacobs approximation. Expression for the higher order corrections to the
probability density are derived. Using this expansion orders we obtain that in
the diffusion dominated regime the average particle current equals the
zeroth-order Fick-Jacobs result corrected by a factor including the corrugation
of the tube geometry. In particular we demonstrate that this estimate is more
accurate for extreme corrugated geometries compared to the common applied
method using the spatially dependent diffusion coefficient D(x,f). The analytic
findings are corroborated with the finite element calculation of a
sinusoidal-shaped tube.Comment: 10 pages, 4 figure
The Order of Phase Transitions in Barrier Crossing
A spatially extended classical system with metastable states subject to weak
spatiotemporal noise can exhibit a transition in its activation behavior when
one or more external parameters are varied. Depending on the potential, the
transition can be first or second-order, but there exists no systematic theory
of the relation between the order of the transition and the shape of the
potential barrier. In this paper, we address that question in detail for a
general class of systems whose order parameter is describable by a classical
field that can vary both in space and time, and whose zero-noise dynamics are
governed by a smooth polynomial potential. We show that a quartic potential
barrier can only have second-order transitions, confirming an earlier
conjecture [1]. We then derive, through a combination of analytical and
numerical arguments, both necessary conditions and sufficient conditions to
have a first-order vs. a second-order transition in noise-induced activation
behavior, for a large class of systems with smooth polynomial potentials of
arbitrary order. We find in particular that the order of the transition is
especially sensitive to the potential behavior near the top of the barrier.Comment: 8 pages, 6 figures with extended introduction and discussion; version
accepted for publication by Phys. Rev.
Cohesion, team mental models, and collective efficacy: Towards an integrated framework of team dynamics in sport
A nomological network on team dynamics in sports consisting of a multi-framework perspective is introduced and tested. The aim was to explore the interrelationship among cohesion, team mental models (TMM), collective-efficacy (CE), and perceived performance potential (PPP). Three hundred and forty college-aged soccer players representing 17 different teams (8 female and 9 male) participated in the study. They responded to surveys on team cohesion, TMM, CE and PPP. Results are congruent with the theoretical conceptualization of a parsimonious view of team dynamics in sports. Specifically, cohesion was found to be an exogenous variable predicting both TMM and CE beliefs. TMM and CE were correlated and predicted PPP, which in turn accounted for 59% of the variance of objective performance scores as measured by teams’ season record. From a theoretical standpoint, findings resulted in a parsimonious view of team dynamics, which may represent an initial step towards clarifying the epistemological roots and nomological network of various team-level properties. From an applied standpoint, results suggest that team expertise starts with the establishment of team cohesion. Following the establishment of cohesiveness, teammates are able to advance team-related schemas and a collective sense of confidence. Limitations and key directions for future research are outlined
How entropy and hydrodynamics cooperate in rectifying particle transport
Using the analytical Fick-Jacobs approximation formalism and extensive
Brownian dynamics simulations we study particle transport through
two-dimensional periodic channels with triangularly shaped walls. Directed
motion is caused by the interplay of constant bias acting along the channel
axis and a pressure-driven flow. In particular, we analyze the particle
mobility and the effective diffusion coefficient. The mechanisms of entropic
rectification is revealed in channels with a broken spatial reflection symmetry
in presence of hydrodynamically enforced entropic trapping. Due to the combined
action of the forcing and the pressure-driven flow field, efficient
rectification with a drastically reduced diffusivity is achieved.Comment: 11 pages, 7 figure
Presence of Chlamydia, Mycoplasma, Ureaplasma, and Other Bacteria in the Upper and Lower Genital Tracts of Fertile and Infertile Populations
Objective: The genital mycoplasmas (Mycoplasma hominis and
Ureaplasma urealyticum) and Chlamydia trachomatis have been implicated as possible
etiologic factors in infertility. Their role in patients with infertility needs to be further defined
Effects of intervention upon precompetition state anxiety in elite junior tennis players: The relevance of the matching hypothesis
Reproduced with permission of publisher from:
Terry, P., Coakley, L., & Karageorghis, C. Effects of intervention upon precompetition state anxiety in elite junior tennis players: the relevance of the matching hypothesis. Perceptual and Motor Skills, 1995, 81, 287-296. © Perceptual and Motor Skills 1995The matching hypothesis proposes that interventions for anxiety should be matched to the modality in which anxiety is experienced. This study investigated the relevance of the matching hypothesis for anxiety interventions in tennis. Elite junior tennis players (N = 100; Age: M = 13.9 yr., SD = 1.8 yr.) completed the Competitive State Anxiety Inventory-2 before and after one of four randomly assigned intervention strategies approximately one hour prior to competition at a National Junior Championship. A two-factor multivariate analysis of variance (group x time) with repeated measures on the time factor gave no significant main effect by group but indicated significant reductions in somatic anxiety and cognitive anxiety and a significant increase in self-confidence following intervention. A significant group by time interaction emerged for self-confidence. The results question the need to match intervention strategy to the mode of anxiety experienced
Predicting swimming performance using state anxiety
Competitive state anxiety is a common response to stressful competitive sports situations that could affect athletic performance. The effects of state anxiety on swimming performance need further inquiry. The aim of the study was to determine the component of state anxiety that best predicts swimming performance. A quantitative, cross-sectional study design that made use of the Competitive State Anxiety Inventory-2 to measure precompetitive state anxiety was used. A total of 61 male high school swimmers whose age ranged between 14 and 19 years (M = 16.16, standard deviation = 1.66 years) completed the Competitive State Anxiety Inventory-2 1 hr before competing in a 50-m individual swimming event. Performance was evaluated using finishing position. Due to the relatively short duration of the 50-m event, the available literature would suggest that Somatic Anxiety would have a greater effect on Performance - there is not enough time to allow cognitive anxiety to have a detrimental impact on performance. Thus, it was hypothesized that somatic rather than cognitive anxiety will best predict swimming performance. It emerged that both cognitive (b =.787; p <.001) and somatic anxieties (b =.840; p <.001) can independently predict swimming performance. However, when both cognitive and somatic anxieties were regressed onto swimming performance, somatic anxiety partially dominated cognitive anxiety (b =.626; p <.001) and became the significant predictor of swimming performance. It is recommended that swimmers and swimming coaches make use of specific intervention strategies that eradicate the detrimental effects of somatic anxiety immediately before competition.IS
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