287 research outputs found
Spatial prediction models for landslide hazards: review, comparison and evaluation
The predictive power of logistic regression, support vector machines and bootstrap-aggregated classification trees (bagging, double-bagging) is compared using misclassification error rates on independent test data sets. Based on a resampling approach that takes into account spatial autocorrelation, error rates for predicting 'present' and 'future' landslides are estimated within and outside the training area. In a case study from the Ecuadorian Andes, logistic regression with stepwise backward variable selection yields lowest error rates and demonstrates the best generalization capabilities. The evaluation outside the training area reveals that tree-based methods tend to overfit the data
The penetration of plasma clouds across magnetic boundaries : the role of high frequency oscillations
Experiments are reported where a collisionfree plasma cloud penetrates a
magnetic barrier by self-polarization. We here focus on the resulting anomalous
magnetic field diffusion into the plasma cloud, two orders of magnitude faster
than classical, which is one important aspect of the plasma cloud penetration
mechanism. Without such fast magnetic diffusion, clouds with kinetic beta below
unity would not be able to penetrate magnetic barriers at all. Tailor-made
diagnostics has been used for measurements in the parameter range with the
kinetic beta ? 0.5 to 10, and with normalized width w/r(gi) of the order of
unity. Experimental data on hf fluctuations in density and in electric field
has been combined to yield the effective anomalous transverse resistivity
eta(EFF). It is concluded that they are both dominated by highly nonlinear
oscillations in the lower hybrid range, driven by a strong diamagnetic current
loop that is set up in the plasma in the penetration process. The anomalous
magnetic diffusion rate, calculated from the resistivity eta(EFF), is
consistent with single-shot multi-probe array measurements of the diamagnetic
cavity and the associated quasi-dc electric structure. An interpretation of the
instability measurements in terms of the resistive term in the generalized (low
frequency) Ohm's law is given.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
Conditions for plasmoid penetration across magnetic barriers
The penetration of plasma clouds, or plasmoids, across abrupt magnetic
barriers (of the scale less than a few ion gyro radii, using the plasmoid
directed velocity) is studied. The insight gained earlier, from experimental
and computer simulation investigations of a case study, is generalised into
other parameter regimes. It is concluded for what parameters a plasmoid should
be expected to penetrate the magnetic barrier through self-polarization,
penetrate through magnetic expulsion, or be rejected from the barrier. The
scaling parameters are n(e), v(0), B(perp), m(i), T(i), and the width w of the
plasmoid. The scaling is based on a model for strongly driven, nonlinear
magnetic field diffusion into a plasma, which is a generalization of the
laboratory findings. The results are applied to experiments earlier reported in
the literature, and also to the proposed application of impulsive penetration
of plasmoids from the solar wind into the Earth's magnetosphere.Comment: 12th International Congress on Plasma Physics, 25-29 October 2004,
Nice (France
Рентгенометрический анализ кинематики L4-L5 И L5-S1 позвоночных сегментов в III стадии дегенеративного процесса
ПОЗВОНОЧНИКА БОЛЕЗНИОСТЕОХОНДРОЗОСТЕОХОНДРИТГРЫЖА МЕЖПОЗВОНОЧНОГО ДИСКАМЕЖПОЗВОНКОВОГО ДИСКА СМЕЩЕНИЕРЕНТГЕНОГРАФИ
On the electron energy distribution function in the high power impulse magnetron sputtering discharge
We apply the Ionization Region Model (IRM) and the Orsay Boltzmann equation
for ELectrons coupled with Ionization and eXcited states kinetics (OBELIX)
model to study the electron kinetics of a high power impulse magnetron
sputtering (HiPIMS) discharge. In the IRM the bulk (cold) electrons are assumed
to exhibit a Maxwellian energy distribution and the secondary (hot) electrons,
emitted from the target surface upon ion bombardment, are treated as a high
energy tail, while in the OBELIX the electron energy distribution is calculated
self-consistently using an isotropic Boltzmann equation. The two models are
merged in the sense that the output from the IRM is used as an input for
OBELIX. The temporal evolutions of the particle densities are found to agree
very well between the two models. Furthermore, a very good agreement is
demonstrated between the bi-Maxwellian electron energy distribution assumed by
the IRM and the electron energy distribution calculated by the OBELIX model. It
can therefore be concluded that assuming a bi-Maxwellian electron energy
distribution, constituting a cold bulk electron group and a hot secondary
electron group, is a good approximation for modeling the HiPIMS discharge
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