2,295 research outputs found
Motor-driven Dynamics of Cytoskeletal FIlaments in Motility Assays
We model analytically the dynamics of a cytoskeletal filament in a motility
assay. The filament is described as rigid rod free to slide in two dimensions.
The motor proteins consist of polymeric tails tethered to the plane and modeled
as linear springs and motor heads that bind to the filament. As in related
models of rigid and soft two-state motors, the binding/unbinding dynamics of
the motor heads and the dependence of the transition rates on the load exerted
by the motor tails play a crucial role in controlling the filament's dynamics.
Our work shows that the filament effectively behaves as a self-propelled rod at
long times, but with non-Markovian noise sources arising from the coupling to
the motor binding/unbinding dynamics. The effective propulsion force of the
filament and the active renormalization of the various friction and diffusion
constants are calculated in terms of microscopic motor and filament parameters.
These quantities could be probed by optical force microscopy.Comment: 13 pages, 8 figures, 1 Tabl
Solvable Examples of Drift and Diffusion of Ions in Non-uniform Electric Fields
The drift and diffusion of a cloud of ions in a fluid are distorted by an
inhomogeneous electric field. If the electric field carries the center of the
distribution in a straight line and the field configuration is suitably
symmetric, the distortion can be calculated analytically. We examine the
specific examples of fields with cylindrical and spherical symmetry in detail
assuming the ion distributions to be of a generally Gaussian form. The effects
of differing diffusion coefficients in the transverse and longitudinal
directions are included
Sex Differences in the Excess Risk of Cardiovascular Diseases Associated with Type 2 Diabetes: Potential Explanations and Clinical Implications
Strong evidence suggests that type 2 diabetes confers a stronger excess risk of cardiovascular diseases in women than in men; with women having a 27Â % higher relative risk of stroke and a 44Â % higher relative risk of coronary heart disease compared with men. The mechanisms that underpin these sex differences in the associations between diabetes and cardiovascular disease risk are not fully understood. Some of the excess risk may be the result of a sex disparity in the management and treatment of diabetes, to the detriment of women. However, accruing evidence suggests that real biological differences between men and women underpin the excess risk of diabetes-related cardiovascular risk in women such that there is a greater decline in risk factor status in women than in men in the transition from normoglycemia to overt diabetes. This greater risk factor decline appears to be associated with women having to put on more weight than men, and thus attain a higher body mass index, to develop diabetes. Further studies addressing the mechanisms responsible for sex differences in the excess risk of cardiovascular diseases associated with diabetes are needed to improve the prevention and management of diabetes in clinical practise
A scanning drift tube apparatus for spatio-temporal mapping of electron swarms
A "scanning" drift tube apparatus, capable of mapping of the spatio-temporal
evolution of electron swarms, developing between two plane electrodes under the
effect of a homogeneous electric field, is presented. The electron swarms are
initiated by photoelectron pulses and the temporal distributions of the
electron flux are recorded while the electrode gap length (at a fixed electric
field strength) is varied. Operation of the system is tested and verified with
argon gas, the measured data are used for the evaluation of the electron bulk
drift velocity. The experimental results for the space-time maps of the
electron swarms - presented here for the first time - also allow clear
observation of deviations from hydrodynamic transport. The swarm maps are also
reproduced by particle simulations
Structural characteristics of positionally-disordered lattices: relation to the first sharp diffraction peak in glasses
Positional disorder has been introduced into the atomic structure of certain
crystalline lattices, and the orientationally-averaged structure factor S(k)
and pair-correlation function g(r) of these disordered lattices have been
studied. Analytical expressions for S(k) and g(r) for Gaussian positional
disorder in 2D and 3D are confirmed with precise numerical simulations. These
analytic results also have a bearing on the unsolved Gauss circle problem in
mathematics. As the positional disorder increases, high-k peaks in S(k) are
destroyed first, eventually leaving a single peak, that with the lowest-k
value. The pair-correlation function for lattices with such high levels of
positional disorder exhibits damped oscillations, with a period equal to the
separation between the furthest-separated (lowest-k) lattice planes. The last
surviving peak in S(k) is, for example for silicon and silica, at a wavevector
nearly identical to that of the experimentally-observed first sharp diffraction
peak (FSDP) in the amorphous phases of those materials. Thus, for these
amorphous materials at least, the FSDP can be regarded as arising from
scattering from atomic configurations equivalent to the single family of
positionally-disordered local Bragg planes having the furthest separation.Comment: v2: changes in response to referees' comments: Figure 2 made more
readable, improved discussion of height of peaks in S(k), other minor changes
4 pages, 3 figures, submitted to Physical Review
Lesbian and bisexual women's experiences of sexuality-based discrimination and their appearance concerns
Lesbian and bisexual women frequently experience sexuality-based discrimination, which is often based on others' judgements about their appearance. This short article aims to explore whether there is a relationship between lesbian and bisexual women's experiences of sexuality-based discrimination and their satisfaction with the way that they look. Findings from an online survey suggest that discrimination is negatively related to appearance satisfaction for lesbian women, but not for bisexual women. It is argued that this difference exists because lesbian appearance norms are more recognisable and distinctive than bisexual women's appearance norms
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