439 research outputs found
Kolmogorov-Sinai entropy from recurrence times
Observing how long a dynamical system takes to return to some state is one of
the most simple ways to model and quantify its dynamics from data series. This
work proposes two formulas to estimate the KS entropy and a lower bound of it,
a sort of Shannon's entropy per unit of time, from the recurrence times of
chaotic systems. One formula provides the KS entropy and is more theoretically
oriented since one has to measure also the low probable very long returns. The
other provides a lower bound for the KS entropy and is more experimentally
oriented since one has to measure only the high probable short returns. These
formulas are a consequence of the fact that the series of returns do contain
the same information of the trajectory that generated it. That suggests that
recurrence times might be valuable when making models of complex systems
Analytical affinity chromatography-on-a-chip for selective capture and sensitive detection of protein and polynucleotide biomarkers
Affinity Chromatography is a powerful technique which has been applied to the highly selective purification of several biomolecules from complex mixtures. This technique is currently a core technology in the industrial purification of disruptive biopharmaceuticals such as monoclonal antibodies. The use of high affinity ligands, together with densely functionalized three-dimensional solid-phase supports, confers a remarkable analytical potential, making it a current standard for the quantification of several compounds in certified laboratories, ranging from health biomarkers to environmental contaminants. Aiming at extending the application of affinity chromatography to a portable setup, we report the miniaturization of this system down to nL-scale, by trapping Q-sepharose or protein-A agarose beads in microfluidic channels with total volumes ranging from 60 to 210 nL. This versatile and simple platform combined the high surface area and robust surface chemistry provided by the chromatographic media with the high degree of fluidic control, portability, improved reaction kinetics and low reagent expenditure inherent to microfluidics. Furthermore, the microfluidic structures are simple in terms of microfabrication and can be sequentially operated using standard pipette tips and a negative pressure source at the outlet (Figure A). This system was tested within the scope of prostate cancer diagnostics for the capture of protein and polynucleotide biomarkers. Along these lines, prostate specific antigen (PSA) was selectively captured from unprocessed human serum and a 23 bp polynucleotide (ssDNA analogous to micro RNA MIR145) in fetal bovine serum as model matrix, by coupling a monoclonal anti-PSA IgG2a with protein-A beads or a complementary ssDNA strand with Q-sepharose beads, respectively. The assay schematics are described in Figure A. Clinically relevant sensitivities below 10 ng/mL PSA (Figure B) and 10 pM polynucleotide were achieved using a horseradish peroxidase-labelled reporter and measuring chemiluminescence directly on the bead surface. The results demonstrate a high potential for the miniaturization of analytical affinity chromatography, providing good sensitivities in a portable setup, particularly considering the amenability of integrating miniaturized thin-film sensors for optical transduction, as previously demonstrated by our group.
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Symmetry Nonrestoration in a Gross-Neveu Model with Random Chemical Potential
We study the symmetry behavior of the Gross-Neveu model in three and two
dimensions with random chemical potential. This is equivalent to a four-fermion
model with charge conjugation symmetry as well as Z_2 chiral symmetry. At high
temperature the Z_2 chiral symmetry is always restored. In three dimensions the
initially broken charge conjugation symmetry is not restored at high
temperature, irrespective of the value of the disorder strength. In two
dimensions and at zero temperature the charge conjugation symmetry undergoes a
quantum phase transition from a symmetric state (for weak disorder) to a broken
state (for strong disorder) as the disorder strength is varied. For any given
value of disorder strength, the high-temperature behavior of the charge
conjugation symmetry is the same as its zero-temperature behavior. Therefore,
in two dimensions and for strong disorder strength the charge conjugation
symmetry is not restored at high temperature.Comment: 16 pages, 3 figure
Atmospheric effects on extensive air showers observed with the Surface Detector of the Pierre Auger Observatory
Atmospheric parameters, such as pressure (P), temperature (T) and density,
affect the development of extensive air showers initiated by energetic cosmic
rays. We have studied the impact of atmospheric variations on extensive air
showers by means of the surface detector of the Pierre Auger Observatory. The
rate of events shows a ~10% seasonal modulation and ~2% diurnal one. We find
that the observed behaviour is explained by a model including the effects
associated with the variations of pressure and density. The former affects the
longitudinal development of air showers while the latter influences the Moliere
radius and hence the lateral distribution of the shower particles. The model is
validated with full simulations of extensive air showers using atmospheric
profiles measured at the site of the Pierre Auger Observatory.Comment: 24 pages, 9 figures, accepted for publication in Astroparticle
Physic
Update on the correlation of the highest energy cosmic rays with nearby extragalactic matter
Data collected by the Pierre Auger Observatory through 31 August 2007 showed
evidence for anisotropy in the arrival directions of cosmic rays above the
Greisen-Zatsepin-Kuz'min energy threshold, \nobreak{eV}. The
anisotropy was measured by the fraction of arrival directions that are less
than from the position of an active galactic nucleus within 75 Mpc
(using the V\'eron-Cetty and V\'eron catalog). An updated
measurement of this fraction is reported here using the arrival directions of
cosmic rays recorded above the same energy threshold through 31 December 2009.
The number of arrival directions has increased from 27 to 69, allowing a more
precise measurement. The correlating fraction is , compared
with expected for isotropic cosmic rays. This is down from the early
estimate of . The enlarged set of arrival directions is
examined also in relation to other populations of nearby extragalactic objects:
galaxies in the 2 Microns All Sky Survey and active galactic nuclei detected in
hard X-rays by the Swift Burst Alert Telescope. A celestial region around the
position of the radiogalaxy Cen A has the largest excess of arrival directions
relative to isotropic expectations. The 2-point autocorrelation function is
shown for the enlarged set of arrival directions and compared to the isotropic
expectation.Comment: Accepted for publication in Astroparticle Physics on 31 August 201
Origins of the Ambient Solar Wind: Implications for Space Weather
The Sun's outer atmosphere is heated to temperatures of millions of degrees,
and solar plasma flows out into interplanetary space at supersonic speeds. This
paper reviews our current understanding of these interrelated problems: coronal
heating and the acceleration of the ambient solar wind. We also discuss where
the community stands in its ability to forecast how variations in the solar
wind (i.e., fast and slow wind streams) impact the Earth. Although the last few
decades have seen significant progress in observations and modeling, we still
do not have a complete understanding of the relevant physical processes, nor do
we have a quantitatively precise census of which coronal structures contribute
to specific types of solar wind. Fast streams are known to be connected to the
central regions of large coronal holes. Slow streams, however, appear to come
from a wide range of sources, including streamers, pseudostreamers, coronal
loops, active regions, and coronal hole boundaries. Complicating our
understanding even more is the fact that processes such as turbulence,
stream-stream interactions, and Coulomb collisions can make it difficult to
unambiguously map a parcel measured at 1 AU back down to its coronal source. We
also review recent progress -- in theoretical modeling, observational data
analysis, and forecasting techniques that sit at the interface between data and
theory -- that gives us hope that the above problems are indeed solvable.Comment: Accepted for publication in Space Science Reviews. Special issue
connected with a 2016 ISSI workshop on "The Scientific Foundations of Space
Weather." 44 pages, 9 figure
The Fluorescence Detector of the Pierre Auger Observatory
The Pierre Auger Observatory is a hybrid detector for ultra-high energy
cosmic rays. It combines a surface array to measure secondary particles at
ground level together with a fluorescence detector to measure the development
of air showers in the atmosphere above the array. The fluorescence detector
comprises 24 large telescopes specialized for measuring the nitrogen
fluorescence caused by charged particles of cosmic ray air showers. In this
paper we describe the components of the fluorescence detector including its
optical system, the design of the camera, the electronics, and the systems for
relative and absolute calibration. We also discuss the operation and the
monitoring of the detector. Finally, we evaluate the detector performance and
precision of shower reconstructions.Comment: 53 pages. Submitted to Nuclear Instruments and Methods in Physics
Research Section
Advanced functionality for radio analysis in the Offline software framework of the Pierre Auger Observatory
The advent of the Auger Engineering Radio Array (AERA) necessitates the
development of a powerful framework for the analysis of radio measurements of
cosmic ray air showers. As AERA performs "radio-hybrid" measurements of air
shower radio emission in coincidence with the surface particle detectors and
fluorescence telescopes of the Pierre Auger Observatory, the radio analysis
functionality had to be incorporated in the existing hybrid analysis solutions
for fluoresence and surface detector data. This goal has been achieved in a
natural way by extending the existing Auger Offline software framework with
radio functionality. In this article, we lay out the design, highlights and
features of the radio extension implemented in the Auger Offline framework. Its
functionality has achieved a high degree of sophistication and offers advanced
features such as vectorial reconstruction of the electric field, advanced
signal processing algorithms, a transparent and efficient handling of FFTs, a
very detailed simulation of detector effects, and the read-in of multiple data
formats including data from various radio simulation codes. The source code of
this radio functionality can be made available to interested parties on
request.Comment: accepted for publication in NIM A, 13 pages, minor corrections to
author list and references in v
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