45 research outputs found
On the accuracy of the Perturbative Approach for Strong Lensing: Local Distortion for Pseudo-Elliptical Models
The Perturbative Approach (PA) introduced by \citet{alard07} provides
analytic solutions for gravitational arcs by solving the lens equation
linearized around the Einstein ring solution. This is a powerful method for
lens inversion and simulations in that it can be used, in principle, for
generic lens models. In this paper we aim to quantify the domain of validity of
this method for three quantities derived from the linearized mapping: caustics,
critical curves, and the deformation cross section (i.e. the arc cross section
in the infinitesimal circular source approximation). We consider lens models
with elliptical potentials, in particular the Singular Isothermal Elliptic
Potential and Pseudo-Elliptical Navarro--Frenk--White models. We show that the
PA is exact for this first model. For the second, we obtain constraints on the
model parameter space (given by the potential ellipticity parameter
and characteristic convergence ) such that the PA is
accurate for the aforementioned quantities. In this process we obtain analytic
expressions for several lensing functions, which are valid for the PA in
general. The determination of this domain of validity could have significant
implications for the use of the PA, but it still needs to be probed with
extended sources.Comment: Accepted for publication in MNRA
Effect of Pre-Harvest Treatment on Yield, Maturity and Quality of Flame Seedless Grape (Vitis vinifera L.)
To improve fruit quality in grape cv. Flame Seedless, application of Ethephon (400 and 500 ppm) and trunk girdling was done at veraison stage. Cluster thinning was done by retaining 100, 75 and 50% of total number of bunches on the vines, and, the rest were removed immediately after full bloom. Highest yield was obtained in the treatment 100% Crop load + 500ppm Ethephon, followed by 75% Crop load + 500ppm Ethephon. The treatment of 50% Crop load + 500ppm Ethephon resulted in maximum bunch weight, lowest percentage of uneven coloured berries, maximum TSS, minimum acidity and maximum TSS:acid ratio, maximum anthocyanin content, advanced maturity by 9 days and had maximum sensory rating. But, in this treatment, yield was significantly lower than in treatments where either 75% or 100% Crop load was retained. Thus, considering yield as well as quality parameters, the treatment 75% Crop load + 500ppm Ethephon was found to be the best
En bloc excision and autogenous fibular reconstruction for aggressive giant cell tumor of distal radius: a report of 12 cases and review of literature
<p>Abstract</p> <p>Introduction</p> <p>Giant cell tumor (GCT) of distal radius follows a comparatively aggressive behaviour. Wide excision is the management of choice, but this creates a defect at the distal end of radius. The preffered modalities for reconstruction of such a defect include vascularized/non-vascularized bone graft, osteoarticular allografts and custom-made prosthesis. We here present our experience with wide resection and non-vascularised autogenous fibula grafting for GCT of distal radius.</p> <p>Materials and methods</p> <p>Twelve patients with a mean age of 34.7 years (21-43 years) with Campanacci Grade II/III GCT of distal radius were managed with wide excision of tumor and reconstruction with ipsilateral nonvascularised fibula, fixed with small fragment plate to the remnant of the radius. Primary autogenous iliac crest grafting was done at the fibuloradial junction in all the patients.</p> <p>Results</p> <p>Mean follow up period was 5.8 years (8.2-3.7 years). Average time for union at fibuloradial junction was 33 weeks (14-69 weeks). Mean grip strength of involved side was 71% (42-86%). The average range of movements were 52° forearm supination, 37° forearm pronation, 42° of wrist palmerflexion and 31° of wrist dorsiflexion with combined movements of 162°. Overall revised musculoskeletal tumor society (MSTS) score averaged 91.38% (76.67-93.33%) with five excellent, four good and three satisfactory results. There were no cases with graft related complications or deep infections, 3 cases with wrist subluxation, 2 cases with non union (which subsequently united with bone grafting) and 1 case of tumor recurrence.</p> <p>Conclusion</p> <p>Although complication rate is high, autogenous non-vascularised fibular autograft reconstruction of distal radius can be considered as a reasonable option after en bloc excision of Grade II/III GCT.</p
The Third Gravitational Lensing Accuracy Testing (GREAT3) Challenge Handbook
The GRavitational lEnsing Accuracy Testing 3 (GREAT3) challenge is the third
in a series of image analysis challenges, with a goal of testing and
facilitating the development of methods for analyzing astronomical images that
will be used to measure weak gravitational lensing. This measurement requires
extremely precise estimation of very small galaxy shape distortions, in the
presence of far larger intrinsic galaxy shapes and distortions due to the
blurring kernel caused by the atmosphere, telescope optics, and instrumental
effects. The GREAT3 challenge is posed to the astronomy, machine learning, and
statistics communities, and includes tests of three specific effects that are
of immediate relevance to upcoming weak lensing surveys, two of which have
never been tested in a community challenge before. These effects include
realistically complex galaxy models based on high-resolution imaging from
space; spatially varying, physically-motivated blurring kernel; and combination
of multiple different exposures. To facilitate entry by people new to the
field, and for use as a diagnostic tool, the simulation software for the
challenge is publicly available, though the exact parameters used for the
challenge are blinded. Sample scripts to analyze the challenge data using
existing methods will also be provided. See http://great3challenge.info and
http://great3.projects.phys.ucl.ac.uk/leaderboard/ for more information.Comment: 30 pages, 13 figures, submitted for publication, with minor edits
(v2) to address comments from the anonymous referee. Simulated data are
available for download and participants can find more information at
http://great3.projects.phys.ucl.ac.uk/leaderboard
GREAT3 results I: systematic errors in shear estimation and the impact of real galaxy morphology
We present first results from the third GRavitational lEnsing Accuracy
Testing (GREAT3) challenge, the third in a sequence of challenges for testing
methods of inferring weak gravitational lensing shear distortions from
simulated galaxy images. GREAT3 was divided into experiments to test three
specific questions, and included simulated space- and ground-based data with
constant or cosmologically-varying shear fields. The simplest (control)
experiment included parametric galaxies with a realistic distribution of
signal-to-noise, size, and ellipticity, and a complex point spread function
(PSF). The other experiments tested the additional impact of realistic galaxy
morphology, multiple exposure imaging, and the uncertainty about a
spatially-varying PSF; the last two questions will be explored in Paper II. The
24 participating teams competed to estimate lensing shears to within systematic
error tolerances for upcoming Stage-IV dark energy surveys, making 1525
submissions overall. GREAT3 saw considerable variety and innovation in the
types of methods applied. Several teams now meet or exceed the targets in many
of the tests conducted (to within the statistical errors). We conclude that the
presence of realistic galaxy morphology in simulations changes shear
calibration biases by per cent for a wide range of methods. Other
effects such as truncation biases due to finite galaxy postage stamps, and the
impact of galaxy type as measured by the S\'{e}rsic index, are quantified for
the first time. Our results generalize previous studies regarding sensitivities
to galaxy size and signal-to-noise, and to PSF properties such as seeing and
defocus. Almost all methods' results support the simple model in which additive
shear biases depend linearly on PSF ellipticity.Comment: 32 pages + 15 pages of technical appendices; 28 figures; submitted to
MNRAS; latest version has minor updates in presentation of 4 figures, no
changes in content or conclusion
Environmental sustainability in basic research:a perspective from HECAP+
The climate crisis and the degradation of the world's ecosystems require humanity to take immediate action. The international scientific community has a responsibility to limit the negative environmental impacts of basic research. The HECAP+ communities (High Energy Physics, Cosmology, Astroparticle Physics, and Hadron and Nuclear Physics) make use of common and similar experimental infrastructure, such as accelerators and observatories, and rely similarly on the processing of big data. Our communities therefore face similar challenges to improving the sustainability of our research. This document aims to reflect on the environmental impacts of our work practices and research infrastructure, to highlight best practice, to make recommendations for positive changes, and to identify the opportunities and challenges that such changes present for wider aspects of social responsibility
Environmental sustainability in basic research: a perspective from HECAP+
The climate crisis and the degradation of the world's ecosystems require
humanity to take immediate action. The international scientific community has a
responsibility to limit the negative environmental impacts of basic research.
The HECAP+ communities (High Energy Physics, Cosmology, Astroparticle Physics,
and Hadron and Nuclear Physics) make use of common and similar experimental
infrastructure, such as accelerators and observatories, and rely similarly on
the processing of big data. Our communities therefore face similar challenges
to improving the sustainability of our research. This document aims to reflect
on the environmental impacts of our work practices and research infrastructure,
to highlight best practice, to make recommendations for positive changes, and
to identify the opportunities and challenges that such changes present for
wider aspects of social responsibility.Comment: 158 pages, 21 figures; comments welcome. Revisions included in
Version 2.0 are detailed on page 3 of the pdf. If you would like to endorse
this document please visit: https://sustainable-hecap-plus.github.io/. An
HTML version of this document is available at:
https://sustainable-hecap-plus.github.io
GREAT3 results - I. Systematic errors in shear estimation and the impact of real galaxy morphology
We present first results from the third GRavitational lEnsing Accuracy Testing (GREAT3) challenge, the third in a sequence of challenges for testing methods of inferring weak gravitational lensing shear distortions from simulated galaxy images. GREAT3 was divided into experiments to test three specific questions, and included simulated space- and ground-based data with constant or cosmologically varying shear fields. The simplest (control) experiment included parametric galaxies with a realistic distribution of signal-to-noise, size, and ellipticity, and a complex point spread function (PSF). The other experiments tested the additional impact of realistic galaxy morphology, multiple exposure imaging, and the uncertainty about a spatially varying PSF; the last two questions will be explored in Paper II. The 24 participating teams competed to estimate lensing shears to within systematic error tolerances for upcoming Stage-IV dark energy surveys, making 1525 submissions overall. GREAT3 saw considerable variety and innovation in the types of methods applied. Several teams now meet or exceed the targets in many of the tests conducted (to within the statistical errors). We conclude that the presence of realistic galaxy morphology in simulations changes shear calibration biases by âŒ1percent for a wide range of methods. Other effects such as truncation biases due to finite galaxy postage stamps, and the impact of galaxy type as measured by the SĂ©rsic index, are quantified for the first time. Our results generalize previous studies regarding sensitivities to galaxy size and signal-to-noise, and to PSF properties such as seeing and defocus. Almost all methods' results support the simple model in which additive shear biases depend linearly on PSF ellipticit
The Gravity Collective: A Search for the Electromagnetic Counterpart to the Neutron Star-Black Hole Merger GW190814
We present optical follow-up imaging obtained with the Katzman Automatic
Imaging Telescope, Las Cumbres Observatory Global Telescope Network, Nickel
Telescope, Swope Telescope, and Thacher Telescope of the LIGO/Virgo
gravitational wave (GW) signal from the neutron star-black hole (NSBH) merger
GW190814. We searched the GW190814 localization region (19 deg for the
90th percentile best localization), covering a total of 51 deg and 94.6%
of the two-dimensional localization region. Analyzing the properties of 189
transients that we consider as candidate counterparts to the NSBH merger,
including their localizations, discovery times from merger, optical spectra,
likely host-galaxy redshifts, and photometric evolution, we conclude that none
of these objects are likely to be associated with GW190814. Based on this
finding, we consider the likely optical properties of an electromagnetic
counterpart to GW190814, including possible kilonovae and short gamma-ray burst
afterglows. Using the joint limits from our follow-up imaging, we conclude that
a counterpart with an -band decline rate of 0.68 mag day, similar to
the kilonova AT 2017gfo, could peak at an absolute magnitude of at most
mag (50% confidence). Our data are not constraining for ''red'' kilonovae and
rule out ''blue'' kilonovae with (30% confidence). We
strongly rule out all known types of short gamma-ray burst afterglows with
viewing angles 17 assuming an initial jet opening angle of
and explosion energies and circumburst densities similar to
afterglows explored in the literature. Finally, we explore the possibility that
GW190814 merged in the disk of an active galactic nucleus, of which we find
four in the localization region, but we do not find any candidate counterparts
among these sources.Comment: 86 pages, 9 figure