29,475 research outputs found
T-Duality and Conformal Invariance at Two Loops
We show that the conformal invariance conditions for a general sigma-model
with torsion are invariant under T-duality through two loops.Comment: 21 pages. Uses RevTex. Revised Version with extra references and
typos correcte
Background Rejection in Atmospheric Cherenkov Telescopes using Recurrent Convolutional Neural Networks
In this work, we present a new, high performance algorithm for background
rejection in imaging atmospheric Cherenkov telescopes. We build on the already
popular machine-learning techniques used in gamma-ray astronomy by the
application of the latest techniques in machine learning, namely recurrent and
convolutional neural networks, to the background rejection problem. Use of
these machine-learning techniques addresses some of the key challenges
encountered in the currently implemented algorithms and helps to significantly
increase the background rejection performance at all energies.
We apply these machine learning techniques to the H.E.S.S. telescope array,
first testing their performance on simulated data and then applying the
analysis to two well known gamma-ray sources. With real observational data we
find significantly improved performance over the current standard methods, with
a 20-25\% reduction in the background rate when applying the recurrent neural
network analysis. Importantly, we also find that the convolutional neural
network results are strongly dependent on the sky brightness in the source
region which has important implications for the future implementation of this
method in Cherenkov telescope analysis.Comment: 11 pages, 7 figures. To be submitted to The European Physical Journal
Redundant Array Configurations for 21 cm Cosmology
Realizing the potential of 21 cm tomography to statistically probe the
intergalactic medium before and during the Epoch of Reionization requires large
telescopes and precise control of systematics. Next-generation telescopes are
now being designed and built to meet these challenges, drawing lessons from
first-generation experiments that showed the benefits of densely packed, highly
redundant arrays--in which the same mode on the sky is sampled by many antenna
pairs--for achieving high sensitivity, precise calibration, and robust
foreground mitigation. In this work, we focus on the Hydrogen Epoch of
Reionization Array (HERA) as an interferometer with a dense, redundant core
designed following these lessons to be optimized for 21 cm cosmology. We show
how modestly supplementing or modifying a compact design like HERA's can still
deliver high sensitivity while enhancing strategies for calibration and
foreground mitigation. In particular, we compare the imaging capability of
several array configurations, both instantaneously (to address instrumental and
ionospheric effects) and with rotation synthesis (for foreground removal). We
also examine the effects that configuration has on calibratability using
instantaneous redundancy. We find that improved imaging with sub-aperture
sampling via "off-grid" antennas and increased angular resolution via far-flung
"outrigger" antennas is possible with a redundantly calibratable array
configuration.Comment: 19 pages, 11 figures. Revised to match the accepted ApJ versio
Species Profiles: Life Histories and Environmental Requirements of Coastal Fishes and Invertebrates (Pacific Southwest): Black, green, and red abalones
All abalones belong to the genus
Haliotis sensu latu, family Haliotidae.
The 75 species known worldwide
(Booloot ian et, al. 1962) are anatomically
similar and all are adapted for
attachment to hard substrates. Seven
species are widely distributed along
the coast of California (Cox 1962;
Mottet 19781, of which several are
important in the comercial and sport
fisheries of the Pacific Southwest. (PDF has 19 pages.
The evolution of the self-lensing binary KOI-3278: evidence of extra energy sources during CE evolution
Post-common-envelope binaries (PCEBs) have been frequently used to
observationally constrain models of close-compact-binary evolution, in
particular common-envelope (CE) evolution. However, recent surveys have
detected PCEBs consisting of a white dwarf (WD) exclusively with an M dwarf
companion. Thus, we have been essentially blind with respect to PCEBs with more
massive companions. Recently, the second PCEB consisting of a WD and a G-type
companion, the spectacularly self-lensing binary KOI-3278, has been identified.
This system is different from typical PCEBs not only because of the G-type
companion, but also because of its long orbital period. Here we investigate
whether the existence of KOI-3278 provides new observational constraints on
theories of CE evolution. We reconstruct its evolutionary history and predict
its future using BSE, clarifying the proper use of the binding energy parameter
in this code. We find that a small amount of recombination energy, or any other
source of extra energy, is required to reconstruct the evolutionary history of
KOI-3278. Using BSE we derive progenitor system parameters of M1,i = 2.450
Msun, M2,i = 1.034 Msun, and Porb,i ~ 1300 d. We also find that in ~9 Gyr the
system will go through a second CE phase leaving behind a double WD, consisting
of a C/O WD and a He WD with masses of 0.636 Msun and 0.332 Msun, respectively.
After IK Peg, KOI-3278 is the second PCEB that clearly requires an extra source
of energy, beyond that of orbital energy, to contribute to the CE ejection.
Both systems are special in that they have long orbital periods and massive
secondaries. This may also indicate that the CE efficiency increases with
secondary mass.Comment: Accepted for publication in A&A Letters, 4 pages, 2 figure
Kinetic study of adsorption and photo-decolorization of Reactive Red 198 on TiO2 surface
Recycling and reuse of wastewater after purification will reduce the environmental pollution as well as fulfill the increasing demand of water. Adsorption-based water treatment process is very popular for dye-house wastewater treatment. The present study deals with treatment of wastewater contaminated by reactive dye. TiO2 is used as adsorbent and the spent adsorbent has been regenerated by Advanced Oxidation Process (AOP), without using any other chemicals. TiO2 adsorbs dye molecules and then those dye molecules have been oxidized via a photocatalytic reaction in presence of UV irradiation. Kinetics of dye adsorption and photocatalytic oxidation reaction has been developed in this study. Photocatalyst adsorbent (TiO2) has been reused several times after regeneration. The activity of catalyst decreases after each cycle; due to poisoning cause by intermediate by-products. Kinetic of this catalyst deactivation has been incorporated with L–H model to develop the photocatalytic reaction kinetic model
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