361 research outputs found
Recurrent neural networks and proper orthogonal decomposition with interval data for real-time predictions of mechanised tunnelling processes
A surrogate modelling strategy for predictions of interval settlement fields in real time during machine driven construction of tunnels, accounting for uncertain geotechnical parameters in terms of intervals, is presented in the paper. Artificial Neural Network and Proper Orthogonal Decomposition approaches are combined to approximate and predict tunnelling induced time variant surface settlement fields computed by a process-oriented finite element simulation model. The surrogate models are generated, trained and tested in the design (offline) stage of a tunnel project based on finite element analyses to compute the surface settlements for selected scenarios of the tunnelling process steering parameters taking uncertain geotechnical parameters by means of possible ranges (intervals) into account. The resulting mappings of time constant geotechnical interval parameters and time variant deterministic steering parameters onto the time variant interval settlement field are solved offline by optimisation and online by interval analyses approaches using the midpoint-radius representation of interval data. During the tunnel construction, the surrogate model is designed to be used in real-time to predict interval fields of the surface settlements in each stage of the advancement of the tunnel boring machine for selected realisations of the steering parameters to support the steering decisions of the machine driver
Structure Formation, Melting, and the Optical Properties of Gold/DNA Nanocomposites: Effects of Relaxation Time
We present a model for structure formation, melting, and optical properties
of gold/DNA nanocomposites. These composites consist of a collection of gold
nanoparticles (of radius 50 nm or less) which are bound together by links made
up of DNA strands. In our structural model, the nanocomposite forms from a
series of Monte Carlo steps, each involving reaction-limited cluster-cluster
aggregation (RLCA) followed by dehybridization of the DNA links. These links
form with a probability which depends on temperature and particle
radius . The final structure depends on the number of monomers (i. e. gold
nanoparticles) , , and the relaxation time. At low temperature, the
model results in an RLCA cluster. But after a long enough relaxation time, the
nanocomposite reduces to a compact, non-fractal cluster. We calculate the
optical properties of the resulting aggregates using the Discrete Dipole
Approximation. Despite the restructuring, the melting transition (as seen in
the extinction coefficient at wavelength 520 nm) remains sharp, and the melting
temperature increases with increasing as found in our previous
percolation model. However, restructuring increases the corresponding link
fraction at melting to a value well above the percolation threshold. Our
calculated extinction cross section agrees qualitatively with experiments on
gold/DNA composites. It also shows a characteristic ``rebound effect,''
resulting from incomplete relaxation, which has also been seen in some
experiments. We discuss briefly how our results relate to a possible sol-gel
transition in these aggregates.Comment: 12 pages, 10 figure
Category-specific video summarization
International audienceIn large video collections with clusters of typical categories, such as ''birthday party'' or ''flash-mob'', category-specific video summarization can produce higher quality video summaries than unsupervised approaches that are blind to the video category. Given a video from a known category, our approach first efficiently performs a temporal segmentation into semantically-consistent segments, delimited not only by shot boundaries but also general change points. Then, equipped with an SVM classifier, our approach assigns importance scores to each segment. The resulting video assembles the sequence of segments with the highest scores. The obtained video summary is therefore both short and highly informative. Experimental results on videos from the multimedia event detection (MED) dataset of TRECVID'11 show that our approach produces video summaries with higher relevance than the state of the art
A Measurement of Time-Averaged Aerosol Optical Depth using Air-Showers Observed in Stereo by HiRes
Air fluorescence measurements of cosmic ray energy must be corrected for
attenuation of the atmosphere. In this paper we show that the air-showers
themselves can yield a measurement of the aerosol attenuation in terms of
optical depth, time-averaged over extended periods. Although the technique
lacks statistical power to make the critical hourly measurements that only
specialized active instruments can achieve, we note the technique does not
depend on absolute calibration of the detector hardware, and requires no
additional equipment beyond the fluorescence detectors that observe the air
showers. This paper describes the technique, and presents results based on
analysis of 1258 air-showers observed in stereo by the High Resolution Fly's
Eye over a four year span.Comment: 7 pages, 3 figures, accepted for publication by Astroparticle Physics
Journa
Search for Global Dipole Enhancements in the HiRes-I Monocular Data above 10^{18.5} eV
Several proposed source models for Ultra-High Energy Cosmic Rays (UHECRs)
consist of dipole distributions oriented towards major astrophysical landmarks
such as the galactic center, M87, or Centaurus A. We use a comparison between
real data and simulated data to show that the HiRes-I monocular data for
energies above 10^{18.5} eV is, in fact, consistent with an isotropic source
model. We then explore methods to quantify our sensitivity to dipole source
models oriented towards the Galactic Center, M87, and Centaurus A.Comment: 17 pages, 31 figure
Observation of the Ankle and Evidence for a High-Energy Break in the Cosmic Ray Spectrum
We have measured the cosmic ray spectrum at energies above eV using
the two air fluorescence detectors of the High Resolution Fly's Eye experiment
operating in monocular mode. We describe the detector, PMT and atmospheric
calibrations, and the analysis techniques for the two detectors. We fit the
spectrum to models describing galactic and extragalactic sources. Our measured
spectrum gives an observation of a feature known as the ``ankle'' near eV, and strong evidence for a suppression near eV.Comment: 14 pages, 9 figures. To appear in Physics Letters B. Accepted versio
Measurement of the scintillation time spectra and pulse-shape discrimination of low-energy beta and nuclear recoils in liquid argon with DEAP-1
The DEAP-1 low-background liquid argon detector was used to measure
scintillation pulse shapes of electron and nuclear recoil events and to
demonstrate the feasibility of pulse-shape discrimination (PSD) down to an
electron-equivalent energy of 20 keV.
In the surface dataset using a triple-coincidence tag we found the fraction
of beta events that are misidentified as nuclear recoils to be (90% C.L.) for energies between 43-86 keVee and for a nuclear recoil
acceptance of at least 90%, with 4% systematic uncertainty on the absolute
energy scale. The discrimination measurement on surface was limited by nuclear
recoils induced by cosmic-ray generated neutrons. This was improved by moving
the detector to the SNOLAB underground laboratory, where the reduced background
rate allowed the same measurement with only a double-coincidence tag.
The combined data set contains events. One of those, in the
underground data set, is in the nuclear-recoil region of interest. Taking into
account the expected background of 0.48 events coming from random pileup, the
resulting upper limit on the electronic recoil contamination is
(90% C.L.) between 44-89 keVee and for a nuclear recoil
acceptance of at least 90%, with 6% systematic uncertainty on the absolute
energy scale.
We developed a general mathematical framework to describe PSD parameter
distributions and used it to build an analytical model of the distributions
observed in DEAP-1. Using this model, we project a misidentification fraction
of approx. for an electron-equivalent energy threshold of 15 keV for
a detector with 8 PE/keVee light yield. This reduction enables a search for
spin-independent scattering of WIMPs from 1000 kg of liquid argon with a
WIMP-nucleon cross-section sensitivity of cm, assuming
negligible contribution from nuclear recoil backgrounds.Comment: Accepted for publication in Astroparticle Physic
First Observation of Coherent Production in Neutrino Nucleus Interactions with 2 GeV
The MiniBooNE experiment at Fermilab has amassed the largest sample to date
of s produced in neutral current (NC) neutrino-nucleus interactions at
low energy. This paper reports a measurement of the momentum distribution of
s produced in mineral oil (CH) and the first observation of coherent
production below 2 GeV. In the forward direction, the yield of events
observed above the expectation for resonant production is attributed primarily
to coherent production off carbon, but may also include a small contribution
from diffractive production on hydrogen. Integrated over the MiniBooNE neutrino
flux, the sum of the NC coherent and diffractive modes is found to be (19.5
1.1 (stat) 2.5 (sys))% of all exclusive NC production at
MiniBooNE. These measurements are of immediate utility because they quantify an
important background to MiniBooNE's search for
oscillations.Comment: Submitted to Phys. Lett.
A Likelihood Method for Measuring the Ultrahigh Energy Cosmic Ray Composition
Air fluorescence detectors traditionally determine the dominant chemical
composit ion of the ultrahigh energy cosmic ray flux by comparing the averaged
slant depth of the shower maximum, , as a function of energy to the
slant depths expect ed for various hypothesized primaries. In this paper, we
present a method to make a direct measurement of the expected mean number of
protons and iron by comparing the shap es of the expected
distributions to the distribution for data. The advantages of this method
includes the use of information of the full distribution and its ability to
calculate a flux for various cosmic ray compositi ons. The same method can be
expanded to marginalize uncertainties due to choice of spectra, hadronic models
and atmospheric parameters. We demonstrate the technique with independent
simulated data samples from a parent sample of protons and iron. We accurately
predict the number of protons and iron in the parent sample and show that the
uncertainties are meaningful.Comment: 11 figures, 22 pages, accepted by Astroparticle Physic
Alternative Methods to Finding Patterns in HiRes Stereo Data
In this paper Ultra High Energy Cosmic Rays UHECRs data observed by the HiRes
fluorescence detector in stereo mode is analyzed to search for events in the
sky with an arrival direction lying on a great circle. Such structure is known
as the arc structure. The arc structure is expected when the charged cosmic
rays pass through the galactic magnetic field. The arcs searched for could
represent a broad or a small scale anisotropy depending on the proposed source
model for the UHECRs. The Arcs in this paper are looked for using Hough
transform were Hough transform is a technique used to looking for patterns in
images. No statistically significant arcs were found in this study
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