77 research outputs found
The Implementation of the Shear Correlation Function and the Matter Power Spectrum in R
Weak gravitational lensing is an important tool in understanding the large-scale structure of the universe. One component in understanding the effect of weak gravitational lensing is the shear correlation function and matter power spectrum. The calculation of these values is often complicated and time consuming. In order to decrease the cost of these calculations they were implemented in R using parallelization. This resulted in the calculations completing faster and the process to be easily changed in order to fit the need of each researcher using the algorithms created in R
Galactos: Computing the Anisotropic 3-Point Correlation Function for 2 Billion Galaxies
The nature of dark energy and the complete theory of gravity are two central
questions currently facing cosmology. A vital tool for addressing them is the
3-point correlation function (3PCF), which probes deviations from a spatially
random distribution of galaxies. However, the 3PCF's formidable computational
expense has prevented its application to astronomical surveys comprising
millions to billions of galaxies. We present Galactos, a high-performance
implementation of a novel, O(N^2) algorithm that uses a load-balanced k-d tree
and spherical harmonic expansions to compute the anisotropic 3PCF. Our
implementation is optimized for the Intel Xeon Phi architecture, exploiting
SIMD parallelism, instruction and thread concurrency, and significant L1 and L2
cache reuse, reaching 39% of peak performance on a single node. Galactos scales
to the full Cori system, achieving 9.8PF (peak) and 5.06PF (sustained) across
9636 nodes, making the 3PCF easily computable for all galaxies in the
observable universe.Comment: 11 pages, 7 figures, accepted to SuperComputing 201
Climate of the Field: Snowmass 2021
How are formal policies put in place to create an inclusive, equitable, safe
environment? How do these differ between different communities of practice
(institutions, labs, collaborations, working groups)? What policies towards a
more equitable community are working? For those that aren't working, what
external support is needed in order to make them more effective? We present a
discussion of the current climate of the field in high energy particle physics
and astrophysics (HEPA), as well as current efforts toward making the community
a more diverse, inclusive, and equitable environment. We also present issues
facing both institutions and HEPA collaborations, with a set of interviews with
a selection of HEPA collaboration DEI leaders. We encourage the HEPA community
and the institutions & agencies that support it to think critically about the
prioritization of people in HEPA over the coming decade, and what resources and
policies need to be in place in order to protect and elevate minoritized
populations within the HEPA community.Comment: Contribution to Snowmass 202
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
Guidelines for the good practice of surface wave analysis: a product of the InterPACIFIC project
Surface wave methods gained in the past decades a primary role in many seismic
projects. Specifically, they are often used to retrieve a 1D shear wave velocity model or to
estimate the VS,30 at a site. The complexity of the interpretation process and the variety of
possible approaches to surface wave analysis make it very hard to set a fixed standard to
assure quality and reliability of the results. The present guidelines provide practical information on the acquisition and analysis of surface wave data by giving some basic
principles and specific suggestions related to the most common situations. They are primarily
targeted to non-expert users approaching surface wave testing, but can be useful to
specialists in the field as a general reference. The guidelines are based on the experience
gained within the InterPACIFIC project and on the expertise of the participants in
acquisition and analysis of surface wave data.Published2367-24205T. Sismologia, geofisica e geologia per l'ingegneria sismicaJCR Journa
PRENOLIN project. Results of the validation phase at sendai site
One of the objectives of the PRENOLIN project is the assessment of uncertainties associated with non-linear simulation of 1D site effects. An international benchmark is underway to test several numerical codes, including various non-linear soil constitutive models, to compute the non-linear seismic site response. The preliminary verification phase (i.e. comparison between numerical codes on simple, idealistic cases) is now followed by the validation phase, which compares predictions of such numerical estimations with actual strong motion data recorded from well-known sites. The benchmark presently involves 21 teams and 21 different non-linear computations. Extensive site characterization was performed at three sites of the Japanese KiK-net and PARI networks. This paper focuses on SENDAI site. The first results indicate that a careful analysis of the data for the lab measurement is required. The linear site response is overestimated while the non-linear effects are underestimated in the first iteration. According to these observations, a first set of recommendations for defining the non-linear soil parameters from lab measurements is proposed. PRENOLIN is part of two larger projects: SINAPS@, funded by the ANR (French National Research Agency) and SIGMA, funded by a consortium of nuclear operators (EDF, CEA, AREVA, ENL)
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