1,124 research outputs found
Single fibre action potentials in skeletal muscle related to recording distances
Single muscle fibre action potentials (SFAPs) are considered to be functions of a bioelectrical source and electrical conductivity parameters of the medium. In most model studies SFAPs are computed as a convolution of the bioelectrical source with a transfer function. Calculated peak-to-peak amplitudes of SFAPs decrease with increasing recording distances. In this paper an experimental validation of model results is presented. Experiments were carried out on the m. extensor digitorum longus (EDL) of the rat. Using a method including fluorescent labelling of the active fibre, the distance between the active fibre and the recording electrode was derived. With another method, the decline of the peak-to-peak amplitude of SFAPs detected along a multi-electrode was obtained. With both experimental methods, in general peak-to-peak amplitudes of SFAPs decreased with increasing recording distances, as was found in model results with present volume conduction theory. However, this behaviour was not found in all experiments. The rate of decline of the peak-to-peak amplitudes with recording distance was always less than in models
IceCube: CubeSat Demonstration of 883-GHz Cloud Ice Radiometer
No abstract availabl
A mathematical model for fibro-proliferative wound healing disorders
The normal process of dermal wound healing fails in some cases, due to fibro-proliferative disorders such as keloid and hypertrophic scars. These types of abnormal healing may be regarded as pathologically excessive responses to wounding in terms of fibroblastic cell profiles and their inflammatory growth-factor mediators. Biologically, these conditions are poorly understood and current medical treatments are thus unreliable.
In this paper, the authors apply an existing deterministic mathematical model for fibroplasia and wound contraction in adult mammalian dermis (Olsenet al., J. theor. Biol. 177, 113–128, 1995) to investigate key clinical problems concerning these healing disorders. A caricature model is proposed which retains the fundamental cellular and chemical components of the full model, in order to analyse the spatiotemporal dynamics of the initiation, progression, cessation and regression of fibro-contractive diseases in relation to normal healing. This model accounts for fibroblastic cell migration, proliferation and death and growth-factor diffusion, production by cells and tissue removal/decay.
Explicit results are obtained in terms of the model processes and parameters. The rate of cellular production of the chemical is shown to be critical to the development of a stable pathological state. Further, cessation and/or regression of the disease depend on appropriate spatiotemporally varying forms for this production rate, which can be understood in terms of the bistability of the normal dermal and pathological steady states—a central property of the model, which is evident from stability and bifurcation analyses.
The work predicts novel, biologically realistic and testable pathogenic and control mechanisms, the understanding of which will lead toward more effective strategies for clinical therapy of fibro-proliferative disorders
Far-infrared edge modes in quantum dots
We have investigated edge modes of different multipolarity sustained by
quantum dots submitted to external magnetic fields. We present a microscopic
description based on a variational solution of the equation of motion for any
axially symmetric confining potential and multipole mode. Numerical results for
dots with different number of electrons whose ground-state is described within
a local Current Density Functional Theory are discussed. Two sum rules, which
are exact within this theory, are derived. In the limit of a large neutral dot
at B=0, we have shown that the classical hydrodynamic dispersion law for edge
waves \omega(q) \sim \sqrt{q \ln (q_0/q)} holds when quantum and finite size
effects are taken into account.Comment: We have changed some figures as well as a part of the tex
Towards understanding edge localised mode mitigation by resonant magnetic perturbations in MAST
Type-I Edge Localised Modes (ELMs) have been mitigated in MAST through the
application of n = 3, 4 and 6 resonant magnetic perturbations (RMPs). For each
toroidal mode number of the non-axisymmetric applied fields, the frequency of
the ELMs has been increased significantly, and the peak heat flux on the
divertor plates reduced commensurately. This increase in ELM frequency occurs
despite a significant drop in the edge pressure gradient, which would be
expected to stabilise the peeling-ballooning modes thought to be responsible
for type-I ELMs. Various mechanisms which could cause a destabilisation of the
peeling-ballooning modes are presented, including pedestal widening, plasma
rotation braking, three dimensional corrugation of the plasma boundary and the
existence of radially extended lobe structures near to the X-point. This leads
to a model aimed at resolving the apparent dichotomy of ELM control, that is to
say ELM suppression occurring due to the pedestal pressure reduction below the
peeling-ballooning stability boundary, whilst the reduction in pressure can
also lead to ELM mitigation, which is ostensibly a destabilisation of
peeling-ballooning modes. In the case of ELM mitigation, the pedestal
broadening, 3d corrugation or lobes near the X-point degrade ballooning
stability so much that the pedestal recovers rapidly to cross the new stability
boundary at lower pressure more frequently, whilst in the case of suppression,
the plasma parameters are such that the particle transport reduces the edge
pressure below the stability boundary which is only mildly affected by
negligible rotation braking, small edge corrugation or short, broad lobe
structures.Comment: 23 pages, 12 figures. Copyright (2013) United Kingdom Atomic Energy
Authority. This article may be downloaded for personal use only. Any other
use requires prior permission of the author and the American Institute of
Physic
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