20,833 research outputs found
A target guided subband filter for acoustic event detection in noisy environments using wavelet packets
This paper deals with acoustic event detection (AED), such as screams, gunshots, and explosions, in noisy environments. The main aim is to improve the detection performance under adverse conditions with a very low signal-to-noise ratio (SNR). A novel filtering method combined with an energy detector is presented. The wavelet packet transform (WPT) is first used for time-frequency representation of the acoustic signals. The proposed filter in the wavelet packet domain then uses a priori knowledge of the target event and an estimate of noise features to selectively suppress the background noise. It is in fact a content-aware band-pass filter which can automatically pass the frequency bands that are more significant in the target than in the noise. Theoretical analysis shows that the proposed filtering method is capable of enhancing the target content while suppressing the background noise for signals with a low SNR. A condition to increase the probability of correct detection is also obtained. Experiments have been carried out on a large dataset of acoustic events that are contaminated by different types of environmental noise and white noise with varying SNRs. Results show that the proposed method is more robust and better adapted to noise than ordinary energy detectors, and it can work even with an SNR as low as -15 dB. A practical system for real time processing and multi-target detection is also proposed in this work
Neutrino physics with multi-ton scale liquid xenon detectors
We study the sensitivity of large-scale xenon detectors to low-energy solar
neutrinos, to coherent neutrino-nucleus scattering and to neutrinoless double
beta decay. As a concrete example, we consider the xenon part of the proposed
DARWIN (Dark Matter WIMP Search with Noble Liquids) experiment. We perform
detailed Monte Carlo simulations of the expected backgrounds, considering
realistic energy resolutions and thresholds in the detector. In a low-energy
window of 2-30 keV, where the sensitivity to solar pp and Be-neutrinos is
highest, an integrated pp-neutrino rate of 5900 events can be reached in a
fiducial mass of 14 tons of natural xenon, after 5 years of data. The
pp-neutrino flux could thus be measured with a statistical uncertainty around
1%, reaching the precision of solar model predictions. These low-energy solar
neutrinos will be the limiting background to the dark matter search channel for
WIMP-nucleon cross sections below 210 cm and WIMP
masses around 50 GeVc, for an assumed 99.5% rejection of
electronic recoils due to elastic neutrino-electron scatters. Nuclear recoils
from coherent scattering of solar neutrinos will limit the sensitivity to WIMP
masses below 6 GeVc to cross sections above
410cm. DARWIN could reach a competitive half-life
sensitivity of 5.610 y to the neutrinoless double beta decay of
Xe after 5 years of data, using 6 tons of natural xenon in the central
detector region.Comment: 17 pages, 4 figure
A Dual-phase Xenon TPC for Scintillation and Ionisation Yield Measurements in Liquid Xenon
A small-scale, two-phase (liquid/gas) xenon time projection chamber (Xurich
II) was designed, constructed and is under operation at the University of
Zurich. Its main purpose is to investigate the microphysics of particle
interactions in liquid xenon at energies below 50 keV, which are relevant for
rare event searches using xenon as target material. Here we describe in detail
the detector, its associated infrastructure, and the signal identification
algorithm developed for processing and analysing the data. We present the first
characterisation of the new instrument with calibration data from an internal
83m-Kr source. The zero-field light yield is 15.0 and 14.0 photoelectrons/keV
at 9.4 keV and 32.1 keV, respectively, and the corresponding values at an
electron drift field of 1 kV/cm are 10.8 and 7.9 photoelectrons/keV. The charge
yields at these energies are 28 and 31 electrons/keV, with the proportional
scintillation yield of 24 photoelectrons per one electron extracted into the
gas phase, and an electron lifetime of 200 s. The relative energy
resolution, , is 11.9 % and 5.8 % at 9.4 keV and 32.1 keV,
respectively using a linear combination of the scintillation and ionisation
signals. We conclude with measurements of the electron drift velocity at
various electric fields, and compare these to literature values.Comment: 11 pages, 14 figure
Photon counting compressive depth mapping
We demonstrate a compressed sensing, photon counting lidar system based on
the single-pixel camera. Our technique recovers both depth and intensity maps
from a single under-sampled set of incoherent, linear projections of a scene of
interest at ultra-low light levels around 0.5 picowatts. Only two-dimensional
reconstructions are required to image a three-dimensional scene. We demonstrate
intensity imaging and depth mapping at 256 x 256 pixel transverse resolution
with acquisition times as short as 3 seconds. We also show novelty filtering,
reconstructing only the difference between two instances of a scene. Finally,
we acquire 32 x 32 pixel real-time video for three-dimensional object tracking
at 14 frames-per-second.Comment: 16 pages, 8 figure
The future of gamma-ray astronomy
The field of gamma-ray astronomy has experienced impressive progress over the
last decade. Thanks to the advent of a new generation of imaging air Cherenkov
telescopes (H.E.S.S., MAGIC, VERITAS) and thanks to the launch of the Fermi-LAT
satellite, several thousand gamma-ray sources are known today, revealing an
unexpected ubiquity of particle acceleration processes in the Universe. Major
scientific challenges are still ahead, such as the identification of the nature
of Dark Matter, the discovery and understanding of the sources of cosmic rays,
or the comprehension of the particle acceleration processes that are at work in
the various objects. This paper presents some of the instruments and mission
concepts that will address these challenges over the next decades.Comment: To be published in Comptes Rendus Physique (2016
Search for low-mass WIMPs in a 0.6 kg day exposure of the DAMIC experiment at SNOLAB
We present results of a dark matter search performed with a 0.6 kg day
exposure of the DAMIC experiment at the SNOLAB underground laboratory. We
measure the energy spectrum of ionization events in the bulk silicon of
charge-coupled devices down to a signal of 60 eV electron equivalent. The data
are consistent with radiogenic backgrounds, and constraints on the
spin-independent WIMP-nucleon elastic-scattering cross section are accordingly
placed. A region of parameter space relevant to the potential signal from the
CDMS-II Si experiment is excluded using the same target for the first time.
This result obtained with a limited exposure demonstrates the potential to
explore the low-mass WIMP region (<10 GeV/) of the upcoming DAMIC100, a
100 g detector currently being installed in SNOLAB.Comment: 11 pages, 11 figure
- …