6,852 research outputs found
Neutrinos and Ultra-High-Energy Cosmic-Ray Nuclei from Blazars
We discuss the production of ultra-high-energy cosmic ray (UHECR) nuclei and
neutrinos from blazars. We compute the nuclear cascade in the jet for both BL
Lac objects and flat-spectrum radio quasars (FSRQs), and in the ambient
radiation zones for FSRQs as well. By modeling representative spectral energy
distributions along the blazar sequence, two distinct regimes are identified,
which we call "nuclear survival" -- typically found in low-luminosity BL Lacs,
and "nuclear cascade" -- typically found in high-luminosity FSRQs. We quantify
how the neutrino and cosmic-ray (CR) emission efficiencies evolve over the
blazar sequence, and demonstrate that neutrinos and CRs come from very
different object classes. For example, high-frequency peaked BL Lacs (HBLs)
tend to produce CRs, and HL-FSRQs are the more efficient neutrino emitters.
This conclusion does not depend on the CR escape mechanism, for which we
discuss two alternatives (diffusive and advective escape). Finally, the
neutrino spectrum from blazars is shown to significantly depend on the
injection composition into the jet, especially in the nuclear cascade case:
Injection compositions heavier than protons lead to reduced neutrino production
at the peak, which moves at the same time to lower energies. Thus, these
sources will exhibit better compatibility with the observed IceCube and UHECR
data.Comment: 23 pages, 20 figure
Cosmic-Ray and Neutrino Emission from Gamma-Ray Bursts with a Nuclear Cascade
We discuss neutrino and cosmic-ray emission from Gamma-Ray Bursts (GRBs) with
the injection of nuclei, where we take into account that a nuclear cascade from
photo-disintegration can fully develop in the source. One of our main
objectives is to test if recent results from the IceCube and the Pierre Auger
Observatory can be accommodated with the paradigm that GRBs are the sources of
Ultra-High Energy Cosmic Rays (UHECRs). While our key results are obtained
using an internal shock model, we discuss how the secondary emission from a GRB
shell can be interpreted in terms of other astrophysical models. It is
demonstrated that the expected neutrino flux from GRBs weakly depends on the
injection composition, which implies that prompt neutrinos from GRBs can
efficiently test the GRB-UHECR paradigm even if the UHECRs are nuclei. We show
that the UHECR spectrum and composition, as measured by the Pierre Auger
Observatory, can be self-consistently reproduced in a combined
source-propagation model. In an attempt to describe the energy range including
the ankle, we find tension with the IceCube bounds from the GRB stacking
analyses. In an alternative scenario, where only the UHECRs beyond the ankle
originate from GRBs, the requirement for a joint description of cosmic-ray and
neutrino observations favors lower luminosities, which does not correspond to
the typical expectation from {\gamma}-ray observations.Comment: 36 pages, 25 figure
Physical Representation-based Predicate Optimization for a Visual Analytics Database
Querying the content of images, video, and other non-textual data sources
requires expensive content extraction methods. Modern extraction techniques are
based on deep convolutional neural networks (CNNs) and can classify objects
within images with astounding accuracy. Unfortunately, these methods are slow:
processing a single image can take about 10 milliseconds on modern GPU-based
hardware. As massive video libraries become ubiquitous, running a content-based
query over millions of video frames is prohibitive.
One promising approach to reduce the runtime cost of queries of visual
content is to use a hierarchical model, such as a cascade, where simple cases
are handled by an inexpensive classifier. Prior work has sought to design
cascades that optimize the computational cost of inference by, for example,
using smaller CNNs. However, we observe that there are critical factors besides
the inference time that dramatically impact the overall query time. Notably, by
treating the physical representation of the input image as part of our query
optimization---that is, by including image transforms, such as resolution
scaling or color-depth reduction, within the cascade---we can optimize data
handling costs and enable drastically more efficient classifier cascades.
In this paper, we propose Tahoma, which generates and evaluates many
potential classifier cascades that jointly optimize the CNN architecture and
input data representation. Our experiments on a subset of ImageNet show that
Tahoma's input transformations speed up cascades by up to 35 times. We also
find up to a 98x speedup over the ResNet50 classifier with no loss in accuracy,
and a 280x speedup if some accuracy is sacrificed.Comment: Camera-ready version of the paper submitted to ICDE 2019, In
Proceedings of the 35th IEEE International Conference on Data Engineering
(ICDE 2019
Object Detection in 20 Years: A Survey
Object detection, as of one the most fundamental and challenging problems in
computer vision, has received great attention in recent years. Its development
in the past two decades can be regarded as an epitome of computer vision
history. If we think of today's object detection as a technical aesthetics
under the power of deep learning, then turning back the clock 20 years we would
witness the wisdom of cold weapon era. This paper extensively reviews 400+
papers of object detection in the light of its technical evolution, spanning
over a quarter-century's time (from the 1990s to 2019). A number of topics have
been covered in this paper, including the milestone detectors in history,
detection datasets, metrics, fundamental building blocks of the detection
system, speed up techniques, and the recent state of the art detection methods.
This paper also reviews some important detection applications, such as
pedestrian detection, face detection, text detection, etc, and makes an in-deep
analysis of their challenges as well as technical improvements in recent years.Comment: This work has been submitted to the IEEE TPAMI for possible
publicatio
Unwinding Inflation
Higher-form flux that extends in all 3+1 dimensions of spacetime is a source
of positive vacuum energy that can drive meta-stable eternal inflation. If the
flux also threads compact extra dimensions, the spontaneous nucleation of a
bubble of brane charged under the flux can trigger a classical cascade that
steadily unwinds many units of flux, gradually decreasing the vacuum energy
while inflating the bubble, until the cascade ends in the self-annihilation of
the brane into radiation. With an initial number of flux quanta Q_{0} \simgeq
N, this can result in N efolds of inflationary expansion while producing a
scale-invariant spectrum of adiabatic density perturbations with amplitude and
tilt consistent with observation. The power spectrum has an oscillatory
component that does not decay away during inflation, relatively large tensor
power, and interesting non-Gaussianities. Unwinding inflation fits naturally
into the string landscape, and our preliminary conclusion is that consistency
with observation can be attained without fine-tuning the string parameters. The
initial conditions necessary for the unwinding phase are produced automatically
by bubble formation, so long as the critical radius of the bubble is smaller
than at least one of the compact dimensions threaded by flux.Comment: 29+15 pages, 10 figures, published versio
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