12,897 research outputs found
Asymmetric velocity correlations in shearing media
A model of soft frictionless disks in two dimensions at zero temperature is
simulated with a shearing dynamics to study various kinds of asymmetries in
sheared systems. We examine both single particle properties, the spatial
velocity correlation function, and a correlation function designed to separate
clockwise and counter-clockwise rotational fields from one another. Among the
rich and interesting behaviors we find that the velocity correlation along the
two different diagonals corresponding to compression and dilation,
respectively, are almost identical and, furthermore, that a feature in one of
the correlation functions is directly related to irreversible plastic events
Diffusion and Velocity Auto-Correlation in Shearing Granular Media
We perform numerical simulations to examine particle diffusion at steady
shear in a model granular material in two dimensions at the jamming density and
zero temperature. We confirm findings by others that the diffusion constant
depends on shear rate as with , and set out to
determine a relation between and other exponents that characterize the
jamming transition. We then examine the the velocity auto-correlation function,
note that it is governed by two processes with different time scales, and
identify a new fundamental exponent, , that characterizes an algebraic
decay of correlations with time
Using shared online blogs to structure and support informal coach learning. Part 2: The participants’ view and implications for coach education
In part one of this paper, Stoszkowski and Collins (2015) showed that shared online blogs were a useful tool to structure and support the informal learning of a cohort of final year undergraduate sports coaching students. The aim of the present study was to offer insight into student coaches’ perceptions of their use and experiences of structured group blogging for reflection and learning. Twenty-three student coaches (5 females, 18 males), purposely sampled from the original study, took part in four semi-structured focus group interviews. Interview data were inductively analysed. Student coaches were generally very positive about their learning experiences and the pedagogical approach employed. This was especially apparent in terms of perceived increases in levels of reflection, knowledge acquisition and improvements in coaching practice; changes corroborated by the data presented in part one. A range of reasons emerged for these outcomes, alongside several potential limiters of engagement in shared group blogging as a learning endeavour. Whilst these findings support recent, and growing proposals to systematically incorporate Web 2.0 technologies such as blogs into coach education pedagogy, several key considerations for the process of using such tools are outlined. Finally, the implications for coach educators are discussed
Vortex glass transitions in disordered three-dimensional XY models: Simulations for several different sets of parameters
The anisotropic frustrated 3D XY model with strong disorder in the coupling
constants is studied as a model of a disordered superconductor in an applied
magnetic field. Simulations with the exchange Monte Carlo method are performed
for frustrations f=1/5 and f=1/4, corresponding to two different values of the
magnetic field along the z direction. The anisotropy is also varied. The
determination of the helicity modulus from twist histograms is discussed in
some detail and the helicity modulus is used in finite size scaling analyses of
the vortex glass transition. The general picture is that the behavior in [Phys.
Rev. Lett. 91, 077002 (2003)] is confirmed. For strong (e.g. isotropic)
coupling in the z direction the helicity modulus fails to scale and it is
argued that this is due to a too small effective randomness of such systems for
the accessible system sizes
Duality in Shearing Rheology Near the Athermal Jamming Transition
We consider the rheology of soft-core frictionless disks in two dimensions in
the neighborhood of the athermal jamming transition. From numerical simulations
of bidisperse, overdamped, particles, we argue that the divergence of the
viscosity below jamming is characteristic of the hard-core limit, independent
of the particular soft-core interaction. We develop a mapping from soft-core to
hard-core particles that recovers all the critical behavior found in earlier
scaling analyses. Using this mapping we derive a duality relation that gives
the exponent of the non-linear Herschel-Bulkley rheology above jamming in terms
of the exponent of the diverging viscosity below jamming.Comment: 5 pages, 4 figures. Manuscript revisions: new title, additional text
concerning connections to experiment, revised Fig. 4, other minor changes and
clarifications in text. Conclusions remain essentially unchanged. Accepted
for publication in Phys. Rev. Let
Two phase transitions in the fully frustrated model
The fully frustrated model on a square lattice is studied by means of
Monte Carlo simulations. A Kosterlitz-Thouless transition is found at , followed by an ordinary Ising transition at a slightly
higher temperature, . The non-Ising exponents reported by
others, are explained as a failure of finite size scaling due to the screening
length associated with the nearby Kosterlitz-Thouless transition.Comment: REVTEX file, 8 pages, 5 figures in uuencoded postscrip
The Impact of NLO-Corrections on the Determination of the $\bar{u},\bar{d} Content of Nucleons from Drell-Yan Production
The interpretation of Drell-Yan production in terms of the antiquark
densities depends on NLO corrections. Besides the NLO corrections to the
familiar annihilation , there is a
substantial contribution from the QCD Compton subprocesses and . The beam and target
dependence of the two classes of corrections is different. We discuss the
impact of this difference on the determination of the
asymmetry in the proton from the comparison of the and Drell-Yan
production.Comment: 4 pages, 1 eps-figure. To be published in Proceedings of DIS'9
Semi-leptonic B decays into higher charmed resonances
We apply HQET to semi-leptonic meson decays into a variety of excited
charm states. Using three realistic meson models with fermionic light degrees
of freedom, we examine the extent that the sum of exclusive single charmed
states account for the inclusive semi-leptonic decay rate. The consistency
of form factors with the Bjorken and Voloshin sum rules is also investigated.Comment: Latex, 27 pages. A few references and errors corrected, to appear in
Phys. Rev.
Dynamic Approach to the Fully Frustrated XY Model
Using Monte Carlo simulations, we systematically investigate the
non-equilibrium dynamics of the chiral degree of freedom in the two-dimensional
fully frustrated XY model. The critical initial increase of the staggered
chiral magnetization is observed. By means of the short-time dynamics approach,
we estimate the second order phase transition temperature and all the
dynamic and static critical exponents , z, and .Comment: 5 pages with 6 figures include
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