22,095 research outputs found
Comparing Feature Detectors: A bias in the repeatability criteria, and how to correct it
Most computer vision application rely on algorithms finding local
correspondences between different images. These algorithms detect and compare
stable local invariant descriptors centered at scale-invariant keypoints.
Because of the importance of the problem, new keypoint detectors and
descriptors are constantly being proposed, each one claiming to perform better
(or to be complementary) to the preceding ones. This raises the question of a
fair comparison between very diverse methods. This evaluation has been mainly
based on a repeatability criterion of the keypoints under a series of image
perturbations (blur, illumination, noise, rotations, homotheties, homographies,
etc). In this paper, we argue that the classic repeatability criterion is
biased towards algorithms producing redundant overlapped detections. To
compensate this bias, we propose a variant of the repeatability rate taking
into account the descriptors overlap. We apply this variant to revisit the
popular benchmark by Mikolajczyk et al., on classic and new feature detectors.
Experimental evidence shows that the hierarchy of these feature detectors is
severely disrupted by the amended comparator.Comment: Fixed typo in affiliation
Dust Measurements in the Outer Solar System
Dust measurements in the outer solar system are reviewed. Only the plasma
wave instrument on board Voyagers 1 and 2 recorded impacts in the
Edgeworth-Kuiper belt (EKB). Pioneers 10 and 11 measured a constant dust flux
of 10-micron-sized particles out to 20 AU. Dust detectors on board Ulysses and
Galileo uniquely identified micron-sized interstellar grains passing through
the planetary system. Impacts of interstellar dust grains onto big EKB objects
generate at least about a ton per second of micron-sized secondaries that are
dispersed by Poynting-Robertson effect and Lorentz force. We conclude that
impacts of interstellar particles are also responsible for the loss of dust
grains at the inner edge of the EKB. While new dust measurements in the EKB are
in an early planning stage, several missions (Cassini and STARDUST) are en
route to analyze interstellar dust in much more detail.Comment: 10 pages, 5 figures, Proceedings of the ESO workshop on ``Minor
bodies in the outer solar system'
CMB Telescopes and Optical Systems
The cosmic microwave background radiation (CMB) is now firmly established as
a fundamental and essential probe of the geometry, constituents, and birth of
the Universe. The CMB is a potent observable because it can be measured with
precision and accuracy. Just as importantly, theoretical models of the Universe
can predict the characteristics of the CMB to high accuracy, and those
predictions can be directly compared to observations. There are multiple
aspects associated with making a precise measurement. In this review, we focus
on optical components for the instrumentation used to measure the CMB
polarization and temperature anisotropy. We begin with an overview of general
considerations for CMB observations and discuss common concepts used in the
community. We next consider a variety of alternatives available for a designer
of a CMB telescope. Our discussion is guided by the ground and balloon-based
instruments that have been implemented over the years. In the same vein, we
compare the arc-minute resolution Atacama Cosmology Telescope (ACT) and the
South Pole Telescope (SPT). CMB interferometers are presented briefly. We
conclude with a comparison of the four CMB satellites, Relikt, COBE, WMAP, and
Planck, to demonstrate a remarkable evolution in design, sensitivity,
resolution, and complexity over the past thirty years.Comment: To appear in: Planets, Stars and Stellar Systems (PSSS), Volume 1:
Telescopes and Instrumentatio
PLASMON EFFECTS IN SOLID-STATE RADIATION DETECTORS
We have examined the role of plasmons on the electron energy response of solid-state (Si and Ge) radiation detectors. We found that at the level of parts per thousand, internal-conversion electron calibration techniques do not suffice to yield an adequate response function. In particular, spectral distortions in the detection of low-energy beta-particles have been found which are not accounted for by the usual calibration methods. Thus, a small but significant error can arise from energy loss to low-energy plasmons in Si and Ge detectors. The proximity of the plasmon energy to the end-point singularity and the quadratic form of the beta-decay spectrum may account for the effect interpreted as a 17 keV neutrino. Similar errors can also arise in other subtle solid-state measurements as, for example, in the X-ray edge absorption and emission spectra of metals and semiconductors
Neural-Attention-Based Deep Learning Architectures for Modeling Traffic Dynamics on Lane Graphs
Deep neural networks can be powerful tools, but require careful
application-specific design to ensure that the most informative relationships
in the data are learnable. In this paper, we apply deep neural networks to the
nonlinear spatiotemporal physics problem of vehicle traffic dynamics. We
consider problems of estimating macroscopic quantities (e.g., the queue at an
intersection) at a lane level. First-principles modeling at the lane scale has
been a challenge due to complexities in modeling social behaviors like lane
changes, and those behaviors' resultant macro-scale effects. Following domain
knowledge that upstream/downstream lanes and neighboring lanes affect each
others' traffic flows in distinct ways, we apply a form of neural attention
that allows the neural network layers to aggregate information from different
lanes in different manners. Using a microscopic traffic simulator as a testbed,
we obtain results showing that an attentional neural network model can use
information from nearby lanes to improve predictions, and, that explicitly
encoding the lane-to-lane relationship types significantly improves
performance. We also demonstrate the transfer of our learned neural network to
a more complex road network, discuss how its performance degradation may be
attributable to new traffic behaviors induced by increased topological
complexity, and motivate learning dynamics models from many road network
topologies.Comment: To appear at 2019 IEEE Conference on Intelligent Transportation
System
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