2,821 research outputs found
Diagnostic tools for 3D unstructured oceanographic data
Most ocean models in current use are built upon structured meshes. It follows
that most existing tools for extracting diagnostic quantities (volume and
surface integrals, for example) from ocean model output are constructed using
techniques and software tools which assume structured meshes. The greater
complexity inherent in unstructured meshes (especially fully unstructured grids
which are unstructured in the vertical as well as the horizontal direction) has
left some oceanographers, accustomed to traditional methods, unclear on how to
calculate diagnostics on these meshes. In this paper we show that tools for
extracting diagnostic data from the new generation of unstructured ocean models
can be constructed with relative ease using open source software. Higher level
languages such as Python, in conjunction with packages such as NumPy, SciPy,
VTK and MayaVi, provide many of the high-level primitives needed to perform 3D
visualisation and evaluate diagnostic quantities, e.g. density fluxes. We
demonstrate this in the particular case of calculating flux of vector fields
through isosurfaces, using flow data obtained from the unstructured mesh finite
element ocean code ICOM, however this tool can be applied to model output from
any unstructured grid ocean code
Enhancement of deep epileptiform activity in the EEG via 3-D adaptive spatial filtering,
The detection of epileptiform discharges (EDâs) in the electroencephalogram (EEG) is an important component in the diagnosis of epilepsy. However, when the epileptogenic source is located deep in the brain, the EDâs at the scalp are often masked by more superficial, higher-amplitude EEG activity. A
noninvasive technique which uses an adaptive âbeamformerâ spatial filter has been investigated for the enhancement of signals from deep sources in the brain suspected of containing EDâs. A forward three-layer spherical model was used to relate a dipolar source to recorded signals to determine the beamformerâs spatial response constraints. The beamformer adapts, using the least-mean-squares (LMS) algorithm, to reduce signals from sources distant to some arbitrarily defined location in the brain. The beamformer produces three outputs, being the orthogonal components of the signal estimated to have arisen at or near the assumed location. Simulations were performed by using the same forward model
to superimpose realistic EDâs on normal EEG recordings. The simulations show the beamformerâs ability to enhance signals
emanating from deep foci by way of an enhancement ratio (ER), being the improvement in signal-to-noise ratio (SNR) to that observed at any of the scalp electrodes. The performance of the beamformer has been evaluated for 1) the number of scalp electrodes, 2) the recording montage, 3) dependence on the background
EEG, 4) dependence on magnitude, depth, and orientation of epileptogenic focus, and 5) sensitivity to inaccuracies in the estimated location of the focus. Results from the simulations show the beamformerâs performance
to be dependent on the number of electrodes and moderately sensitive to variations in the EEG background. Conversely, its performance appears to be largely independent of the amplitude and morphology of the ED. The dependence studies indicated that the beamformerâs performance was moderately dependent on eccentricity with the ER increasing as the dipolar source and the beamformer were moved from the center to the surface of the brain (1.51â2.26 for radial dipoles and 1.17â2.69 for tangential dipoles). The beamformer was also moderately dependent on variations in polar or azimuthal angle for radial and tangential dipoles. Higher ERâs tended to be seen for locations between electrode sites. The beamformer was more sensitive to inaccuracies in both polar and azimuthal location than depth of the dipolar source.
For polar locations, an ER > 1.0 was achieved when the beamformer was located within 25 of a radial dipole and 35 of a tangential dipole. Similarly, angular ranges of 37.5 and 45 , respectively, for inaccuracies in azimuthal locations. Preliminary results from real EEG records, comprising 12 definite or questionable
epileptiform events, from four patients, demonstrated the beamformerâs ability to enhance these events by a mean 100%
(52%â215%) for referential data and a mean 104% (50%â145%) for bipolar data
Quantum field dynamics of the slow rollover in the linear delta expansion
We show how the linear delta expansion, as applied to the slow-roll
transition in quantum mechanics, can be recast in the closed time-path
formalism. This results in simpler, explicit expressions than were obtained in
the Schr\"odinger formulation and allows for a straightforward generalization
to higher dimensions. Motivated by the success of the method in the
quantum-mechanical problem, where it has been shown to give more accurate
results for longer than existing alternatives, we apply the linear delta
expansion to four-dimensional field theory.
At small times all methods agree. At later times, the first-order linear
delta expansion is consistently higher that Hartree-Fock, but does not show any
sign of a turnover. A turnover emerges in second-order of the method, but the
value of at the
turnover. In subsequent applications of the method we hope to implement the
calculation in the context of an expanding universe, following the line of
earlier calculations by Boyanovsky {\sl et al.}, who used the Hartree-Fock and
large-N methods. It seems clear, however, that the method will become
unreliable as the system enters the reheating stage.Comment: 17 pages, 9 figures, revised version with extra section 4.2 including
second order calculatio
Eruption of primary teeth in South Africans from one year of age
PKErupted primary teeth were recorded in I 446 South African children from five communities. The data were grouped into 3-month age bands and subjected to Probit analysis. Eruption times were similar in boys and girls. Apart from children of Indian descent having significantly fewer incisor teeth erupted at one year compared to the four other groups, there were no significant differences in canine and molar eruption times among the children. This paper defines primary tooth eruption ages in South African children for anthropological, clinical and forensic use
Natural Resources Wales's monitoring networks for groundwater level and quality: the story so far
Natural Resources Wales, which was formed in April 2013, has taken over the functions of the Countryside Council for Wales, Environment Agency Wales and Forestry Commission Wales, as well as some functions of Welsh Government. Its purpose is to ensure that the natural resources of Wales are sustainably maintained, enhanced and used, now and in the future. This includes ensuring that the quality of groundwater, surface water and coastal waters continues to improve.
In Wales, groundwater only contributes around 3% of the total public water supply (Environment Agency, 2008a). However, it is still an important resource in rural areas where records held by local authorities identify at least 21,000 private water supplies, typically comprising shallow wells, boreholes and spring sources. Groundwater also provides baseflow to rivers and groundwater dependent wetlands. Therefore it is important that sufficient data is available to understand, manage, protect, forecast and report on the quality and availability of groundwater
Excitation of High-Spin States by Inelastic Proton Scattering
This work was supported by National Science Foundation Grant PHY 76-84033 and Indiana Universit
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