8,877 research outputs found
Using state space differential geometry for nonlinear blind source separation
Given a time series of multicomponent measurements of an evolving stimulus,
nonlinear blind source separation (BSS) seeks to find a "source" time series,
comprised of statistically independent combinations of the measured components.
In this paper, we seek a source time series with local velocity cross
correlations that vanish everywhere in stimulus state space. However, in an
earlier paper the local velocity correlation matrix was shown to constitute a
metric on state space. Therefore, nonlinear BSS maps onto a problem of
differential geometry: given the metric observed in the measurement coordinate
system, find another coordinate system in which the metric is diagonal
everywhere. We show how to determine if the observed data are separable in this
way, and, if they are, we show how to construct the required transformation to
the source coordinate system, which is essentially unique except for an unknown
rotation that can be found by applying the methods of linear BSS. Thus, the
proposed technique solves nonlinear BSS in many situations or, at least,
reduces it to linear BSS, without the use of probabilistic, parametric, or
iterative procedures. This paper also describes a generalization of this
methodology that performs nonlinear independent subspace separation. In every
case, the resulting decomposition of the observed data is an intrinsic property
of the stimulus' evolution in the sense that it does not depend on the way the
observer chooses to view it (e.g., the choice of the observing machine's
sensors). In other words, the decomposition is a property of the evolution of
the "real" stimulus that is "out there" broadcasting energy to the observer.
The technique is illustrated with analytic and numerical examples.Comment: Contains 14 pages and 3 figures. For related papers, see
http://www.geocities.com/dlevin2001/ . New version is identical to original
version except for URL in the bylin
The pinewood nematode, Bursaphelenchus xylophilus, in Madeira Island
The environmental conditions in Madeira Island are favorable
for the presence and dissemination of the pinewood
nematode (PWN), Bursaphelenchus xylophilus. Five hundred
Pinus pinaster wood samples were collected in several
forest areas and PWN was detected in 22.8 % of the
samples. Bursaphelenchus xylophilus isolates from Madeira
Island displayed the species-specific diagnostic characters.
A morphological variation in the female tail terminus was
detected. In most females, the tail presented a broadly
rounded terminus and, occasionally, a digitate terminus with
a terminal nipple-like extension resembling a mucro. PCR
ITS-RFLP analysis revealed that Madeira Island isolates
exhibited patterns specific to the species B. xylophilus and
similar to virulent isolates. Amplified ITS regions were
further sequenced and no genetic diversity was found for
this genomic region among 17 Portuguese isolates (Madeira
Island and Continental Portugal). Phylogenetic analysis
revealed that Portuguese isolates grouped with isolates from
China, Korea and one isolate from Japa
Electromagnetic radiation from collisions at almost the speed of light: an extremely relativistic charged particle falling into a Schwarzschild black hole
We investigate the electromagnetic radiation released during the high energy
collision of a charged point particle with a four-dimensional Schwarzschild
black hole. We show that the spectra is flat, and well described by a classical
calculation. We also compare the total electromagnetic and gravitational
energies emitted, and find that the former is supressed in relation to the
latter for very high energies. These results could apply to the astrophysical
world in the case charged stars and small charged black holes are out there
colliding into large black holes, and to a very high energy collision
experiment in a four-dimensional world. In this latter scenario the calculation
is to be used for the moments just after the black hole formation, when the
collision of charged debris with the newly formed black hole is certainly
expected. Since the calculation is four-dimensional, it does not directly apply
to Tev-scale gravity black holes, as these inhabit a world of six to eleven
dimensions, although our results should qualitatively hold when extrapolated
with some care to higher dimensions.Comment: 6 pages, 2 figure
Truncated states obtained by iteration
Quantum states of the electromagnetic field are of considerable importance,
finding potential application in various areas of physics, as diverse as solid
state physics, quantum communication and cosmology. In this paper we introduce
the concept of truncated states obtained via iterative processes (TSI) and
study its statistical features, making an analogy with dynamical systems theory
(DST). As a specific example, we have studied TSI for the doubling and the
logistic functions, which are standard functions in studying chaos. TSI for
both the doubling and logistic functions exhibit certain similar patterns when
their statistical features are compared from the point of view of DST. A
general method to engineer TSI in the running-wave domain is employed, which
includes the errors due to the nonidealities of detectors and photocounts.Comment: 10 pages, 22 figure
Late-Time Tails of Wave Propagation in Higher Dimensional Spacetimes
We study the late-time tails appearing in the propagation of massless fields
(scalar, electromagnetic and gravitational) in the vicinities of a
D-dimensional Schwarzschild black hole. We find that at late times the fields
always exhibit a power-law falloff, but the power-law is highly sensitive to
the dimensionality of the spacetime. Accordingly, for odd D>3 we find that the
field behaves as t^[-(2l+D-2)] at late times, where l is the angular index
determining the angular dependence of the field. This behavior is entirely due
to D being odd, it does not depend on the presence of a black hole in the
spacetime. Indeed this tails is already present in the flat space Green's
function. On the other hand, for even D>4 the field decays as t^[-(2l+3D-8)],
and this time there is no contribution from the flat background. This power-law
is entirely due to the presence of the black hole. The D=4 case is special and
exhibits, as is well known, the t^[-(2l+3)] behavior. In the extra dimensional
scenario for our Universe, our results are strictly correct if the extra
dimensions are infinite, but also give a good description of the late time
behaviour of any field if the large extra dimensions are large enough.Comment: 6 pages, 3 figures, RevTeX4. Version to appear in Rapid
Communications of Physical Review
Solvability of subprincipal type operators
In this paper we consider the solvability of pseudodifferential operators in
the case when the principal symbol vanishes of order at a nonradial
involutive manifold . We shall assume that the operator is of
subprincipal type, which means that the :th inhomogeneous blowup at
of the refined principal symbol is of principal type with Hamilton
vector field parallel to the base , but transversal to the symplectic
leaves of at the characteristics. When this blowup
reduces to the subprincipal symbol. We also assume that the blowup is
essentially constant on the leaves of , and does not satisfying the
Nirenberg-Treves condition (). We also have conditions on the vanishing
of the normal gradient and the Hessian of the blowup at the characteristics.
Under these conditions, we show that is not solvable.Comment: Changed the formulation of Theorem 2.15, added an assuption.
Corrected errors and clarified the arguments. Added reference
Time of Admission to Intensive Care Unit, Strained Capacity, and Mortality: a Retrospective Cohort Study
Purpose: We sought to study the association between afterhours ICU admission and ICU mortality considering measures of strained ICU capacity.
Materials and methods: Retrospective analysis of 4141 admissions to 2 ICUs in Lisbon, Portugal (06/2016-06/2018). Primary exposure was ICU admission on 20:00 h-07:59 h. Primary outcome was ICU mortality. Measures of strained ICU capacity were: bed occupancy rate ≥ 90% and cluster of ICU admissions 2 h before or following index admission.
Results: There were 1581 (38.2%) afterhours ICU admissions. Median APACHE II score (19 vs. 20) was similar between patients admitted afterhours and others (P = .27). Patients admitted afterhours had higher crude ICU mortality (15.4% vs. 21.9%; P < .001), but similar adjusted ICU mortality (aOR [95%CI] = 1.15 [0.97-1.38]; P = .12). While bed occupancy rate ≥ 90% was more frequent in patients admitted afterhours (23.1% vs. 29.1%) or deceased in ICU (23.6% vs. 33.7%), cluster of ICU admissions was more frequent in patients admitted during daytime hours (75.2% vs. 58.9%) or that survived the ICU stay (70.1% vs. 63.9%; P ≤ .001 for all). These measures of strained ICU capacity were not associated with adjusted ICU mortality (P ≥ .10 for both).
Conclusions: Afterhours ICU admission and measures of strained ICU capacity were associated with crude but not adjusted ICU mortality.info:eu-repo/semantics/publishedVersio
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