28,622 research outputs found
Airborne lidar measurements of El Chichon stratospheric aerosols, January 1984
A lidar-equipped NASA Electra aircraft was flown in January 1984 between the latitude of 38 and 90 deg N. One of the primary purposes of this mission was to determine the spatial distribution and aerosol characteristics of El Chichon produced stratospheric material. Lidar data from that portion of the flight mission between 38 deg N and 77 deg N is presented. Representative profiles of lidar backscatter ratio, a plot of the integral backscattering function versus latitude, and contours of backscatter mixing ratio versus altitude and latitude are given. In addition, tables containing numerical values of the backscatter ratio and backscattering function versus altitude are applied for each profile. These data clearly show that material produced by the El Chichon eruptions of late March-early April 1982 had spread throughout the latitudes covered by this mission, and that the most massive portion of the material resided north of 55 deg N and was concentrated below 17 km in a layer that peaked at 13 to 15 km. In this latitude region, peak backscatter ratios at a wavelength of 0.6943 microns were approximately 3 and the peak integrated backscattering function was about 15 X 10 to the -4/sr corresponding to a peak optical depth of approximately 0.07. This report presents the results of this mission in a ready-to-use format for atmospheric and climatic studies
Energy flow polynomials: A complete linear basis for jet substructure
We introduce the energy flow polynomials: a complete set of jet substructure
observables which form a discrete linear basis for all infrared- and
collinear-safe observables. Energy flow polynomials are multiparticle energy
correlators with specific angular structures that are a direct consequence of
infrared and collinear safety. We establish a powerful graph-theoretic
representation of the energy flow polynomials which allows us to design
efficient algorithms for their computation. Many common jet observables are
exact linear combinations of energy flow polynomials, and we demonstrate the
linear spanning nature of the energy flow basis by performing regression for
several common jet observables. Using linear classification with energy flow
polynomials, we achieve excellent performance on three representative jet
tagging problems: quark/gluon discrimination, boosted W tagging, and boosted
top tagging. The energy flow basis provides a systematic framework for complete
investigations of jet substructure using linear methods.Comment: 41+15 pages, 13 figures, 5 tables; v2: updated to match JHEP versio
Measuring Up 2006: The National Report Card on Higher Education
Measures the performance of the U.S. and of each state in providing education and training beyond high school. Compares national and state higher education performance with other nations
An operational definition of quark and gluon jets
While "quark" and "gluon" jets are often treated as separate, well-defined
objects in both theoretical and experimental contexts, no precise, practical,
and hadron-level definition of jet flavor presently exists. To remedy this
issue, we develop and advocate for a data-driven, operational definition of
quark and gluon jets that is readily applicable at colliders. Rather than
specifying a per-jet flavor label, we aggregately define quark and gluon jets
at the distribution level in terms of measured hadronic cross sections.
Intuitively, quark and gluon jets emerge as the two maximally separable
categories within two jet samples in data. Benefiting from recent work on
data-driven classifiers and topic modeling for jets, we show that the practical
tools needed to implement our definition already exist for experimental
applications. As an informative example, we demonstrate the power of our
operational definition using Z+jet and dijet samples, illustrating that pure
quark and gluon distributions and fractions can be successfully extracted in a
fully well-defined manner.Comment: 38 pages, 10 figures, 1 table; v2: updated to match JHEP versio
Heegaard genus, cut number, weak p-congruence, and quantum invariants
We use quantum invariants to define a 3-manifold invariant j_p which lies in
the non-negative integers. We relate j_p to the Heegard genus, and the cut
number. We show that j_$ is an invariant of weak p-congruence.Comment: to appear in JKTR. 8pages 1 figur
Observations and Analysis of High-Resolution Magnetic Field Structures in Molecular Clouds
Recent high-angular-resolution (up to 0.7") dust polarization observations
toward star forming regions are summarized. With the Sub-Millimeter Array, the
emission from the dense structures is traced and resolved. The detected
magnetic field morphologies vary from hourglass-like structures to isolated
patches depending on the evolutionary stage of the source. These observed
features have also served as a testbed to develop new analysis methods, with a
particular focus on quantifying the role of the magnetic field in the star
formation process.Comment: 4 pages, 2 figures; To appear in Proceedings of Magnetic Fields in
the Universe: From Laboratory and Stars to Primordial Structures Aug. 21st -
27th 2011, Zakopane, Poland Eds. M. Soida, K. Otmianowska-Mazur, E.M. de
Gouveia Dal Pino & A. Lazaria
The jet-disk symbiosis without maximal jets: 1-D hydrodynamical jets revisited
In this work we discuss the recent criticism by Zdziarski of the maximal jet
model derived in Falcke & Biermann (1995). We agree with Zdziarski that in
general a jet's internal energy is not bounded by its rest-mass energy density.
We describe the effects of the mistake on conclusions that have been made using
the maximal jet model and show when a maximal jet is an appropriate assumption.
The maximal jet model was used to derive a 1-D hydrodynamical model of jets in
agnjet, a model that does multiwavelength fitting of quiescent/hard state X-ray
binaries and low-luminosity active galactic nuclei. We correct algebraic
mistakes made in the derivation of the 1-D Euler equation and relax the maximal
jet assumption. We show that the corrections cause minor differences as long as
the jet has a small opening angle and a small terminal Lorentz factor. We find
that the major conclusion from the maximal jet model, the jet-disk symbiosis,
can be generally applied to astrophysical jets. We also show that isothermal
jets are required to match the flat radio spectra seen in low-luminosity X-ray
binaries and active galactic nuclei, in agreement with other works.Comment: 7 pages, accepted by A&
Learning to Classify from Impure Samples with High-Dimensional Data
A persistent challenge in practical classification tasks is that labeled
training sets are not always available. In particle physics, this challenge is
surmounted by the use of simulations. These simulations accurately reproduce
most features of data, but cannot be trusted to capture all of the complex
correlations exploitable by modern machine learning methods. Recent work in
weakly supervised learning has shown that simple, low-dimensional classifiers
can be trained using only the impure mixtures present in data. Here, we
demonstrate that complex, high-dimensional classifiers can also be trained on
impure mixtures using weak supervision techniques, with performance comparable
to what could be achieved with pure samples. Using weak supervision will
therefore allow us to avoid relying exclusively on simulations for
high-dimensional classification. This work opens the door to a new regime
whereby complex models are trained directly on data, providing direct access to
probe the underlying physics.Comment: 6 pages, 2 tables, 2 figures. v2: updated to match PRD versio
Pileup Mitigation with Machine Learning (PUMML)
Pileup involves the contamination of the energy distribution arising from the
primary collision of interest (leading vertex) by radiation from soft
collisions (pileup). We develop a new technique for removing this contamination
using machine learning and convolutional neural networks. The network takes as
input the energy distribution of charged leading vertex particles, charged
pileup particles, and all neutral particles and outputs the energy distribution
of particles coming from leading vertex alone. The PUMML algorithm performs
remarkably well at eliminating pileup distortion on a wide range of simple and
complex jet observables. We test the robustness of the algorithm in a number of
ways and discuss how the network can be trained directly on data.Comment: 20 pages, 8 figures, 2 tables. Updated to JHEP versio
OmniFold: A Method to Simultaneously Unfold All Observables
Collider data must be corrected for detector effects ("unfolded") to be
compared with many theoretical calculations and measurements from other
experiments. Unfolding is traditionally done for individual, binned observables
without including all information relevant for characterizing the detector
response. We introduce OmniFold, an unfolding method that iteratively reweights
a simulated dataset, using machine learning to capitalize on all available
information. Our approach is unbinned, works for arbitrarily high-dimensional
data, and naturally incorporates information from the full phase space. We
illustrate this technique on a realistic jet substructure example from the
Large Hadron Collider and compare it to standard binned unfolding methods. This
new paradigm enables the simultaneous measurement of all observables, including
those not yet invented at the time of the analysis.Comment: 8 pages, 3 figures, 1 table, 1 poem; v2: updated to approximate PRL
versio
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