66,696 research outputs found
Noise Corruption of Empirical Mode Decomposition and Its Effect on Instantaneous Frequency
Huang's Empirical Mode Decomposition (EMD) is an algorithm for analyzing
nonstationary data that provides a localized time-frequency representation by
decomposing the data into adaptively defined modes. EMD can be used to estimate
a signal's instantaneous frequency (IF) but suffers from poor performance in
the presence of noise. To produce a meaningful IF, each mode of the
decomposition must be nearly monochromatic, a condition that is not guaranteed
by the algorithm and fails to be met when the signal is corrupted by noise. In
this work, the extraction of modes containing both signal and noise is
identified as the cause of poor IF estimation. The specific mechanism by which
such "transition" modes are extracted is detailed and builds on the observation
of Flandrin and Goncalves that EMD acts in a filter bank manner when analyzing
pure noise. The mechanism is shown to be dependent on spectral leak between
modes and the phase of the underlying signal. These ideas are developed through
the use of simple signals and are tested on a synthetic seismic waveform.Comment: 28 pages, 19 figures. High quality color figures available on Daniel
Kaslovsky's website: http://amath.colorado.edu/student/kaslovsk
Gaston Memorial Hospital: Driving Quality Improvement With Data, Guidelines, and Real-Time Feedback
Describes efforts to reduce variance in provider practice patterns through data analysis and benchmarking of process-of-care measures. Discusses strategies such as sharing data, feedback, and best practices in ways physicians can utilize them immediately
Non-Asymptotic Analysis of Tangent Space Perturbation
Constructing an efficient parameterization of a large, noisy data set of
points lying close to a smooth manifold in high dimension remains a fundamental
problem. One approach consists in recovering a local parameterization using the
local tangent plane. Principal component analysis (PCA) is often the tool of
choice, as it returns an optimal basis in the case of noise-free samples from a
linear subspace. To process noisy data samples from a nonlinear manifold, PCA
must be applied locally, at a scale small enough such that the manifold is
approximately linear, but at a scale large enough such that structure may be
discerned from noise. Using eigenspace perturbation theory and non-asymptotic
random matrix theory, we study the stability of the subspace estimated by PCA
as a function of scale, and bound (with high probability) the angle it forms
with the true tangent space. By adaptively selecting the scale that minimizes
this bound, our analysis reveals an appropriate scale for local tangent plane
recovery. We also introduce a geometric uncertainty principle quantifying the
limits of noise-curvature perturbation for stable recovery. With the purpose of
providing perturbation bounds that can be used in practice, we propose plug-in
estimates that make it possible to directly apply the theoretical results to
real data sets.Comment: 53 pages. Revised manuscript with new content addressing application
of results to real data set
Germanium and lead: Significant differences between meteoritic and photospheric abundances?
The order of the Galactic cosmic ray source (GCRS) composition in terms of first ionization potential (FIP) was examined. For most elements, the degree of volatility is (positively) correlated with the value of the FIP, so that it is not easy to distinguish a correlation of GCRS abundances anomalies with FIP from a correlation with volatility. Only a few permit to distinguish between the two kinds of ordering: if they are depleted relative to refractory metals, volatility must be relevant, if not, FIP is relevant. Among them Cu and Zn would seem to favor FIP. Among the best indicators are Ge and Pb. The abundance anomalies in GCRS are defined relative to a standard which, for the heavy elements concerned, is commonly taken as C1 Carbonaceous Chondrites. Photospheric abundances are more directly representative of the protosolar nebula, and hence of ordinary local galactic (LG) matter. The Ge and Pb reference abundance determinations in the Photosphere and in C1 meteorites are examined and their relevance to the problem with FIP vs. volatility in GCRs is discussed
Nanodust detection near 1 AU from spectral analysis of Cassini/RPWS radio data
Nanodust grains of a few nanometer in size are produced near the Sun by
collisional break-up of larger grains and picked-up by the magnetized solar
wind. They have so far been detected at 1 AU by only the two STEREO spacecraft.
Here we analyze the spectra measured by the radio and plasma wave instrument
onboard Cassini during the cruise phase close to Earth orbit; they exhibit
bursty signatures similar to those observed by the same instrument in
association to nanodust stream impacts on Cassini near Jupiter. The observed
wave level and spectral shape reveal impacts of nanoparticles at about 300
km/s, with an average flux compatible with that observed by the radio and
plasma wave instrument onboard STEREO and with the interplanetary flux models
Multiple sources or late injection of short-lived r-nuclides in the early solar system?
Comparisons between the predicted abundances of short-lived r-nuclides
(107Pd, 129I, 182Hf, and 244Pu) in the interstellar medium (ISM) and the
observed abundances in the early solar system (ESS) conclusively showed that
these nuclides cannot simply be derived from galactic chemical evolution (GCE)
if synthesized in a unique stellar environment. It was thus suggested that two
di erent types of stars were responsible for the production of light and heavy
r-nuclides. Here, new constraints on the 244Pu=238U production ratio are used
in an open nonlinear GCE model. It is shown that the two r-process scenario
cannot explain the low abundance of 244Pu in the ESS and that this requires
either than actinides be produced at an additional site (A-events) or more
likely, that 129I and 244Pu be inherited from GCE and 107Pd and 182Hf be
injected in the ESS by the explosion of a nearby supernova.Comment: 4 pages, 1 figure, Nucl. Phys. A, in press (proceedings of NIC8
The Solar Wind Energy Flux
The solar-wind energy flux measured near the ecliptic is known to be
independent of the solar-wind speed. Using plasma data from Helios, Ulysses,
and Wind covering a large range of latitudes and time, we show that the
solar-wind energy flux is independent of the solar-wind speed and latitude
within 10%, and that this quantity varies weakly over the solar cycle. In other
words the energy flux appears as a global solar constant. We also show that the
very high speed solar-wind (VSW > 700 km/s) has the same mean energy flux as
the slower wind (VSW < 700 km/s), but with a different histogram. We use this
result to deduce a relation between the solar-wind speed and density, which
formalizes the anti-correlation between these quantities.Comment: 12 pages, 5 figure
Analytic invariant charge and the lattice static quark-antiquark potential
A recently developed model for the QCD analytic invariant charge is compared
with quenched lattice simulation data on the static quark-antiquark potential.
By employing this strong running coupling one is able to obtain the confining
quark-antiquark potential in the framework of the one-gluon exchange model. To
achieve this objective a technique for evaluating the integrals of a required
form is developed. Special attention is paid here to removing the divergences
encountered the calculations. All this enables one to examine the asymptotic
behavior of the potential at both small and large distances with high accuracy.
An explicit expression for the quark-antiquark potential, which interpolates
between these asymptotics, and satisfies the concavity condition, is proposed.
The derived potential coincides with the perturbative results at small
distances, and it is in a good agreement with the lattice data in the
nonperturbative physically-relevant region. An estimation of the parameter
is obtained for the case of pure gluodynamics. It is found to
be consistent with all the previous estimations of in the
framework of approach in hand.Comment: LaTeX2e, 10 pages with 3 EPS figure
Anomalous Josephson effect in semiconducting nanowires as a signature of the topologically nontrivial phase
We study Josephson junctions made of semiconducting nanowires with Rashba
spin-orbit coupling, where superconducting correlations are induced by the
proximity effect. In the presence of a suitably directed magnetic field, the
system displays the anomalous Josephson effect: a nonzero supercurrent in the
absence of a phase bias between two superconductors. We show that this
anomalous current can be increased significantly by tuning the nanowire into
the helical regime. In particular, in a short junction, a large anomalous
current is a signature for topologically nontrivial superconductivity in the
nanowire.Comment: 10 pages, 9 figures; published versio
Interim report on the hydrologic features of the Green Swamp area in Central Florida
The Green Swamp area in central Florida is another
area where man is developing agricultural land from marginal
land. Though the area is by no means as extensive as
that of the Everglades, the present efforts for its development
are similar to the early efforts for developing the Everglades
in that many miles of canals and ditches have been
constructed to improve the drainage.
Lest the early mistakes of the Everglades be repeated,
the Florida Department of Water Resources considered that
an appraisal of the physical and hydrologic features of the
area was needed to determine the broad effects of draining
and developing the swamp. This reconnaissance provides information required
by the State of Florida for determining its responsibility
and policy in regard to the Green Swamp area and
for formulating future plans for water management of the
area.
Some of the features that have been determined are:
the amount of rainfall on the area; the pattern of surfacewater
drainage; the amount and direction of surface-water
runoff; the direction of ground-water movement; the interrelationship
of rainfall, surface water, and ground water;
the effects of improved drainage facilities'; and the effects
of the hydrologic environment on the chemical quality of
water of the area.(PDF contains 106 pages.
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