19,565 research outputs found
STV-based Video Feature Processing for Action Recognition
In comparison to still image-based processes, video features can provide rich and intuitive information about dynamic events occurred over a period of time, such as human actions, crowd behaviours, and other subject pattern changes. Although substantial progresses have been made in the last decade on image processing and seen its successful applications in face matching and object recognition, video-based event detection still remains one of the most difficult challenges in computer vision research due to its complex continuous or discrete input signals, arbitrary dynamic feature definitions, and the often ambiguous analytical methods. In this paper, a Spatio-Temporal Volume (STV) and region intersection (RI) based 3D shape-matching method has been proposed to facilitate the definition and recognition of human actions recorded in videos. The distinctive characteristics and the performance gain of the devised approach stemmed from a coefficient factor-boosted 3D region intersection and matching mechanism developed in this research. This paper also reported the investigation into techniques for efficient STV data filtering to reduce the amount of voxels (volumetric-pixels) that need to be processed in each operational cycle in the implemented system. The encouraging features and improvements on the operational performance registered in the experiments have been discussed at the end
On Statistical Aspects of Qjets
The process by which jet algorithms construct jets and subjets is inherently
ambiguous and equally well motivated algorithms often return very different
answers. The Qjets procedure was introduced by the authors to account for this
ambiguity by considering many reconstructions of a jet at once, allowing one to
assign a weight to each interpretation of the jet. Employing these weighted
interpretations leads to an improvement in the statistical stability of many
measurements. Here we explore in detail the statistical properties of these
sets of weighted measurements and demonstrate how they can be used to improve
the reach of jet-based studies.Comment: 29 pages, 6 figures. References added, minor modification of the
text. This version to appear in JHE
Jet Substructure at the Tevatron and LHC: New results, new tools, new benchmarks
In this report we review recent theoretical progress and the latest
experimental results in jet substructure from the Tevatron and the LHC. We
review the status of and outlook for calculation and simulation tools for
studying jet substructure. Following up on the report of the Boost 2010
workshop, we present a new set of benchmark comparisons of substructure
techniques, focusing on the set of variables and grooming methods that are
collectively known as "top taggers". To facilitate further exploration, we have
attempted to collect, harmonise, and publish software implementations of these
techniques.Comment: 53 pages, 17 figures. L. Asquith, S. Rappoccio, C. K. Vermilion,
editors; v2: minor edits from journal revision
Structure of Fat Jets at the Tevatron and Beyond
Boosted resonances is a highly probable and enthusiastic scenario in any
process probing the electroweak scale. Such objects when decaying into jets can
easily blend with the cornucopia of jets from hard relative light QCD states.
We review jet observables and algorithms that can contribute to the
identification of highly boosted heavy jets and the possible searches that can
make use of such substructure information. We also review previous studies by
CDF on boosted jets and its measurements on specific jet shapes.Comment: invited review for a special "Top and flavour physics in the LHC era"
issue of The European Physical Journal C, we invite comments regarding
contents of the review; v2 added references and institutional preprint
number
Blending bias impacts the host halo masses derived from a cross-correlation analysis of bright sub-millimetre galaxies
Placing bright sub-millimetre galaxies (SMGs) within the broader context of
galaxy formation and evolution requires accurate measurements of their
clustering, which can constrain the masses of their host dark matter halos.
Recent work has shown that the clustering measurements of these galaxies may be
affected by a `blending bias,' which results in the angular correlation
function of the sources extracted from single-dish imaging surveys being
boosted relative to that of the underlying galaxies. This is due to confusion
introduced by the coarse angular resolution of the single-dish telescope and
could lead to the inferred halo masses being significantly overestimated. We
investigate the extent to which this bias affects the measurement of the
correlation function of SMGs when it is derived via a cross-correlation with a
more abundant galaxy population. We find that the blending bias is essentially
the same as in the auto-correlation case and conclude that the best way to
reduce its effects is to calculate the angular correlation function using SMGs
in narrow redshift bins. Blending bias causes the inferred host halo masses of
the SMGs to be overestimated by a factor of when a redshift interval of
is used. However, this reduces to a factor of for . The broadening of photometric redshift probability distributions with
increasing redshift can therefore impart a mild halo `downsizing' effect onto
the inferred host halo masses, though this trend is not as strong as seen in
recent observational studies.Comment: 10 pages, 9 figures, 1 table. Accepted to MNRA
Resolving Boosted Jets with XCone
We show how the recently proposed XCone jet algorithm smoothly interpolates
between resolved and boosted kinematics. When using standard jet algorithms to
reconstruct the decays of hadronic resonances like top quarks and Higgs bosons,
one typically needs separate analysis strategies to handle the resolved regime
of well-separated jets and the boosted regime of fat jets with substructure.
XCone, by contrast, is an exclusive cone jet algorithm that always returns a
fixed number of jets, so jet regions remain resolved even when (sub)jets are
overlapping in the boosted regime. In this paper, we perform three LHC case
studies---dijet resonances, Higgs decays to bottom quarks, and all-hadronic top
pairs---that demonstrate the physics applications of XCone over a wide
kinematic range.Comment: 36 pages, 25 figures, 1 table; v2: references added; v3: discussion
added and new appendix B to match JHEP versio
ArborZ: Photometric Redshifts Using Boosted Decision Trees
Precision photometric redshifts will be essential for extracting cosmological
parameters from the next generation of wide-area imaging surveys. In this paper
we introduce a photometric redshift algorithm, ArborZ, based on the
machine-learning technique of Boosted Decision Trees. We study the algorithm
using galaxies from the Sloan Digital Sky Survey and from mock catalogs
intended to simulate both the SDSS and the upcoming Dark Energy Survey. We show
that it improves upon the performance of existing algorithms. Moreover, the
method naturally leads to the reconstruction of a full probability density
function (PDF) for the photometric redshift of each galaxy, not merely a single
"best estimate" and error, and also provides a photo-z quality figure-of-merit
for each galaxy that can be used to reject outliers. We show that the stacked
PDFs yield a more accurate reconstruction of the redshift distribution N(z). We
discuss limitations of the current algorithm and ideas for future work.Comment: 10 pages, 13 figures, submitted to Ap
Convolved Substructure: Analytically Decorrelating Jet Substructure Observables
A number of recent applications of jet substructure, in particular searches
for light new particles, require substructure observables that are decorrelated
with the jet mass. In this paper we introduce the Convolved SubStructure (CSS)
approach, which uses a theoretical understanding of the observable to
decorrelate the complete shape of its distribution. This decorrelation is
performed by convolution with a shape function whose parameters and mass
dependence are derived analytically. We consider in detail the case of the
observable and perform an illustrative case study using a search for a
light hadronically decaying . We find that the CSS approach completely
decorrelates the observable over a wide range of masses. Our approach
highlights the importance of improving the theoretical understanding of jet
substructure observables to exploit increasingly subtle features for
performance.Comment: 20 pages, 11 figures. v2. Corrected typo in legend in Figure 5.
Updated Figure 11, minor modification to conclusions on discrimination power.
v3. Updated to published version. Minor typos correcte
Luminosity Functions of Lyman Alpha Emitting Galaxies and Cosmic Reionization of Hydrogen
Recent observations imply that the observed number counts of Lya Emitters
(LAEs) evolved significantly between z=5.7 and z=6.5. It has been suggested
that this was due to a rapid evolution in the ionisation state, and hence
transmission of the IGM which caused Lya flux from z=6.5 galaxies to be more
strongly suppressed. In this paper we consider the joint evolution of the Lya
and UV luminosity functions (LFs) and show that the IGM transmission evolved
between z=6.5 and z=5.7 by a factor 1.1 <R < 1.8 (95% CL). This result is
insensitive to the underlying model of the Lya LF (as well as cosmic variance).
Using a model for IGM transmission, we find that the evolution of the mean IGM
density through cosmic expansion alone may result in a value for the ratio of
transmissions as high as R=1.3. Thus, the existing LFs do not provide evidence
for overlap. Furthermore, the constraint R<1.8 suggests that the Universe at
z=6.5 was more than half ionised by volume, i.e. x_i,V>0.5.Comment: MNRAS in press. Constraints from rest-frame UV LF added. Discussion
added on cosmic variance. Lower limit on x_i,V lowered to 0.5 (from 0.8
LEAD Program Evaluation: Recidivism Report
The LEAD program was established in 2011 as a means of diverting those suspected of low-level drug and prostitution criminal activity to case management and other supportive services instead of jail and prosecution. The primary aim of the LEAD program is to reduce criminal recidivism. Secondary aims include reductions in criminal justice service utilization and associated costs as well as improvements for psychosocial, housing and quality-of-life outcomes. Because LEAD is the first known pre-booking diversion program of its kind in the United States, an evaluation is critically needed to inform key stakeholders, policy makers, and other interested parties of its impact. The evaluation of the LEAD program described in this report represents a response to this need.Background: This report was written by the University of Washington LEAD Evaluation Team at the request of the LEAD Policy Coordinating Group and fulfills the first of three LEAD evaluation aims. Purpose: This report describes findings from a quantitative analysis comparing outcomes for LEAD participants versus "system-as-usual" control participants on shorter- and longer-term changes on recidivism outcomes, including arrests (i.e., being taken into custody by legal authority) and criminal charges (i.e., filing of a criminal case in court). Arrests and criminal charges were chosen as the recidivism outcomes because they likely reflect individual behavior more than convictions, which are more heavily impacted by criminal justice system variables external to the individual. Findings: Analyses indicated statistically significant recidivism improvement for the LEAD group compared to the control group on some shorter- and longer-term outcomes
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