1,512 research outputs found
Towards a Mini-App for Smoothed Particle Hydrodynamics at Exascale
The smoothed particle hydrodynamics (SPH) technique is a purely Lagrangian
method, used in numerical simulations of fluids in astrophysics and
computational fluid dynamics, among many other fields. SPH simulations with
detailed physics represent computationally-demanding calculations. The
parallelization of SPH codes is not trivial due to the absence of a structured
grid. Additionally, the performance of the SPH codes can be, in general,
adversely impacted by several factors, such as multiple time-stepping,
long-range interactions, and/or boundary conditions. This work presents
insights into the current performance and functionalities of three SPH codes:
SPHYNX, ChaNGa, and SPH-flow. These codes are the starting point of an
interdisciplinary co-design project, SPH-EXA, for the development of an
Exascale-ready SPH mini-app. To gain such insights, a rotating square patch
test was implemented as a common test simulation for the three SPH codes and
analyzed on two modern HPC systems. Furthermore, to stress the differences with
the codes stemming from the astrophysics community (SPHYNX and ChaNGa), an
additional test case, the Evrard collapse, has also been carried out. This work
extrapolates the common basic SPH features in the three codes for the purpose
of consolidating them into a pure-SPH, Exascale-ready, optimized, mini-app.
Moreover, the outcome of this serves as direct feedback to the parent codes, to
improve their performance and overall scalability.Comment: 18 pages, 4 figures, 5 tables, 2018 IEEE International Conference on
Cluster Computing proceedings for WRAp1
SPH-EXA: Enhancing the Scalability of SPH codes Via an Exascale-Ready SPH Mini-App
Numerical simulations of fluids in astrophysics and computational fluid
dynamics (CFD) are among the most computationally-demanding calculations, in
terms of sustained floating-point operations per second, or FLOP/s. It is
expected that these numerical simulations will significantly benefit from the
future Exascale computing infrastructures, that will perform 10^18 FLOP/s. The
performance of the SPH codes is, in general, adversely impacted by several
factors, such as multiple time-stepping, long-range interactions, and/or
boundary conditions. In this work an extensive study of three SPH
implementations SPHYNX, ChaNGa, and XXX is performed, to gain insights and to
expose any limitations and characteristics of the codes. These codes are the
starting point of an interdisciplinary co-design project, SPH-EXA, for the
development of an Exascale-ready SPH mini-app. We implemented a rotating square
patch as a joint test simulation for the three SPH codes and analyzed their
performance on a modern HPC system, Piz Daint. The performance profiling and
scalability analysis conducted on the three parent codes allowed to expose
their performance issues, such as load imbalance, both in MPI and OpenMP.
Two-level load balancing has been successfully applied to SPHYNX to overcome
its load imbalance. The performance analysis shapes and drives the design of
the SPH-EXA mini-app towards the use of efficient parallelization methods,
fault-tolerance mechanisms, and load balancing approaches.Comment: arXiv admin note: substantial text overlap with arXiv:1809.0801
Contribution to the search for binaries among Am stars - VII. Orbital elements of seven new spectroscopic binaries, implications on tidal effects
International audienceWe present the results of a radial-velocity study of seven Am stars (HD 3970, 35035, 93946, 151746, 153286, 204751 and 224002) observed at the Observatoire de Haute-Provence (OHP) and the Cambridge Observatories with CORAVEL instruments. We find that these systems are single-lined spectroscopic binaries whose orbital elements are determined for the first time. Among this sample, HD 35035 and 153286 have long periods, with P = 2.8 and 9.5yr, respectively, which is rather unusual for Am stars. Four systems have orbits with large eccentricities (with e >= 0.4). Physical parameters are inferred from this study for the primaries of those systems. We then investigate the influence of tidal interaction, which has already led to the synchronism of the primaries and/or to the circularization of the orbits of some systems belonging to this sample. We extend this study to the list of 33 objects studied in this series of papers and derive values of the critical fractional radii r = R/a for circularization and synchronization of Am-type binaries. We find that the stars with r >~ 0.15 are orbiting on circular orbits and that synchronism is likely for all components with r >~ 0.20
Repeated games for eikonal equations, integral curvature flows and non-linear parabolic integro-differential equations
The main purpose of this paper is to approximate several non-local evolution
equations by zero-sum repeated games in the spirit of the previous works of
Kohn and the second author (2006 and 2009): general fully non-linear parabolic
integro-differential equations on the one hand, and the integral curvature flow
of an interface (Imbert, 2008) on the other hand. In order to do so, we start
by constructing such a game for eikonal equations whose speed has a
non-constant sign. This provides a (discrete) deterministic control
interpretation of these evolution equations. In all our games, two players
choose positions successively, and their final payoff is determined by their
positions and additional parameters of choice. Because of the non-locality of
the problems approximated, by contrast with local problems, their choices have
to "collect" information far from their current position. For integral
curvature flows, players choose hypersurfaces in the whole space and positions
on these hypersurfaces. For parabolic integro-differential equations, players
choose smooth functions on the whole space
Characterizing Metabolic Alterations in Palbociclib-Resistant ER+ Breast Cancer
Characterizing Metabolic Alterations in Palbociclib-Resistant ER+ Breast Cancer
Jessica Shunnarah1, Susan M. Dougherty2, Yoannis Imbert-Fernandez3
1ULBB Program, 2Department of Medicine, University of Louisville
Abstract
Diverse mechanisms of resistance to inhibitors of cyclin dependent kinases 4 and 6 (CDK4/6) have been described including cell cycle alterations and metabolic changes. Palbociclib was the first CDK4/6inhibitor approved against estrogen receptor positive (ER+) breast cancer however, the development of resistance has limited its success. This study investigates the changes in the expression of key metabolic enzymes using an in vivo model of palbociclib resistance. Palbociclib-resistant patient derive xenografts (PDXs) were generated by treating NSG mice that had ER+ breast cancer was implanted into the mammary fat pat of NSG mice with palbociclib until the tumors grew in the presence of the drug.. At endpoint, the tumors were harvested, flash frozen, and pulverized for western blot analysis. Our analysis shows the up regulation in some of the metabolic enzymes. We have concluded that resistance to palbociclib ER+ breast cancer increases the expression of Glutaminase (GLS1) in the presence and absence of palbociclib. Palbociclib treatment also leads to an increase 6-phosphofructo-2 kinase/fructose-2,6-biphosphotase-3 (PFKFB3) and Glucose-6-phosphate dehydrogenase (G6PDH) and transketolase in both palbociclib-sensitive and palbociclib-resistant PDX models.
Keywords: Palbociclib, estrogen receptor positive, patient derive xenograft, glutaminase, 6-phosphofructo-2 kinase/fructo, glucose-6-phosphate dehydrogenas
Orbital and physical parameters of eclipsing binaries from the ASAS catalogue -- I. A sample of systems with components' masses between 1 and 2 M
We derive the absolute physical and orbital parameters for a sample of 18
detached eclipsing binaries from the \emph{All Sky Automated Survey} (ASAS)
database based on the available photometry and our own radial velocity
measurements. The radial velocities (RVs) are computed using spectra we
collected with the 3.9-m Anglo-Australian Telescope and its \emph{University
College London Echelle Spectrograph} and the 1.9-m SAAO Radcliffe telescope and
its \emph{Grating Instrument for Radiation Analysis with a Fibre Fed Echelle}.
In order to obtain as precise RVs as possible, most of the systems were
observed with an iodine cell available at the AAT/UCLES and/or analyzed using
the two-dimensional cross-correlation technique (TODCOR). The RVs were measured
with TODCOR using synthetic template spectra as references. However, for two
objects we used our own approach to the tomographic disentangling of the binary
spectra to provide observed template spectra for the RV measurements and to
improve the RV precision even more. For one of these binaries, AI Phe, we were
able to the obtain an orbital solution with an RV of 62 and 24 m s
for the primary and secondary respectively. For this system, the precision in
is 0.08%. For the analysis, we used the photometry available in
the ASAS database. We combined the RV and light curves using PHOEBE and JKTEBOP
codes to obtain the absolute physical parameters of the systems. Having precise
RVs we were able to reach 0.2 % precision (or better) in masses in
several cases but in radii, due to the limited precision of the ASAS
photometry, we were able to reach a precision of only 1% in one case and 3-5 %
in a few more cases. For the majority of our objects, the orbital and physical
analysis is presented for the first time.Comment: 16 pages, 2 figures, 6 tables in the main text, 1 table in appendix,
to appear in MNRA
On the Numerical Approximations of an Optimal Correction Problem
The numerical solution of an optimal correction problem for a damped random linear oscillator is studied. A numerical algorithm for the discretized system of the associated dynamic programming equation is given. To initiate the computation, we adopt a numerical scheme derived from the deterministic version of the problem. Next, a correction-type algorithm based on a discrete maximum principle is introduced to ensure the convergence of the iteration procedure
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