2,630 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
Local dependence of ion temperature gradient on magnetic configuration, rotational shear and turbulent heat flux in MAST
Experimental data from the Mega Amp Spherical Tokamak (MAST) is used to show
that the inverse gradient scale length of the ion temperature R/LTi (normalized
to the major radius R) has its strongest local correlation with the rotational
shear and the pitch angle of the magnetic field (or, equivalently, an inverse
correlation with q/{\epsilon}, the safety factor/the inverse aspect ratio).
Furthermore, R/LTi is found to be inversely correlated with the
gyro-Bohm-normalized local turbulent heat flux estimated from the density
fluctuation level measured using a 2D Beam Emission Spectroscopy (BES)
diagnostic. These results can be explained in terms of the conjecture that the
turbulent system adjusts to keep R/LTi close to a certain critical value
(marginal for the excitation of turbulence) determined by local equilibrium
parameters (although not necessarily by linear stability).Comment: 6 pages, 3 figures, submitted to PR
Photoionization models of the CALIFA HII regions. I. Hybrid models
Photoionization models of HII regions require as input a description of the
ionizing SED and of the gas distribution, in terms of ionization parameter U
and chemical abundances (e.g. O/H and N/O). A strong degeneracy exists between
the hardness of the SED and U, which in turn leads to high uncertainties in the
determination of the other parameters, including abundances. One way to resolve
the degeneracy is to fix one of the parameters using additional information.
For each of the ~ 20000 sources of the CALIFA HII regions catalog, a grid of
photoionization models is computed assuming the ionizing SED being described by
the underlying stellar population obtained from spectral synthesis modeling.
The ionizing SED is then defined as the sum of various stellar bursts of
different ages and metallicities. This solves the degeneracy between the shape
of the ionizing SED and U. The nebular metallicity (associated to O/H) is
defined using the classical strong line method O3N2 (which gives to our models
the status of "hybrids"). The remaining free parameters are the abundance ratio
N/O and the ionization parameter U, which are determined by looking for the
model fitting [NII]/Ha and [OIII]/Hb. The models are also selected to fit
[OII]/Hb. This process leads to a set of ~ 3200 models that reproduce
simultaneously the three observations.
We find that the regions associated to young stellar bursts suffer leaking of
the ionizing photons, the proportion of escaping photons having a median of
80\%. The set of photoionization models satisfactorily reproduces the electron
temperature derived from the [OIII]4363/5007 line ratio. We determine new
relations between the ionization parameter U and the [OII]/[OIII] or
[SII]/[SIII] line ratios. New relations between N/O and O/H and between U and
O/H are also determined.
All the models are publicly available on the 3MdB database.Comment: Accepted for publication in A&
A flexible and optimal approach for appointment scheduling in healthcare
Appointment scheduling is generally applied in outpatient clinics and other healthcare services. The challenge in scheduling is to find a strategy for dealing with variability and unpredictability in service duration and patient arrivals. The consequences of an ineffective strategy include long waiting times for patients and idle time for the healthcare provider. In turn, these have implications for the perceived quality, cost-efficiency, and capacity of healthcare services. The generation of optimal schedules is a notoriously intractable problem, and earlier attempts at designing effective strategies for appointment scheduling were based on approximation, simulation, or simplification. We propose a novel strategy for scheduling that exploits three tactical ideas to make the problem manageable. We compare the proposed strategy to other approaches, and show that it matches or outperforms competing methods in terms of flexibility, ease of use, and speed. More importantly, it outperforms competing approaches nearly uniformly in approaching the desired balance between waiting and idle times as specified in a chosen objective function. Therefore, the strategy is a good basis for further enrichments
Microstability analysis of pellet fuelled discharges in MAST
Reactor grade plasmas are likely to be fuelled by pellet injection. This
technique transiently perturbs the profiles, driving the density profile hollow
and flattening the edge temperature profile. After the pellet perturbation, the
density and temperature profiles relax towards their quasi-steady-state shape.
Microinstabilities influence plasma confinement and will play a role in
determining the evolution of the profiles in pellet fuelled plasmas. In this
paper we present the microstability analysis of pellet fuelled H-mode MAST
plasmas. Taking advantage of the unique capabilities of the MAST Thomson
scattering system and the possibility of synchronizing the eight lasers with
the pellet injection, we were able to measure the evolution of the post-pellet
electron density and temperature profiles with high temporal and spatial
resolution. These profiles, together with ion temperature profiles measured
using a charge exchange diagnostic, were used to produce equilibria suitable
for microstability analysis of the equilibrium changes induced by pellet
injection. This analysis, carried out using the local gyrokinetic code GS2,
reveals that the microstability properties are extremely sensitive to the rapid
and large transient excursions of the density and temperature profiles, which
also change collisionality and beta e significantly in the region most strongly
affected by the pellet ablation.Comment: 21 pages, 10 figures. This is an author-created, un-copyedited
version of an article submitted for publication in Plasma Physics and
Controlled Fusion. IOP Publishing Ltd is not responsible for any errors or
omissions in this version of the manuscript or any version derived from i
- …