18 research outputs found
High-accuracy numerical models of Brownian thermal noise in thin mirror coatings
Brownian coating thermal noise in detector test masses is limiting the
sensitivity of current gravitational-wave detectors on Earth. Therefore,
accurate numerical models can inform the ongoing effort to minimize Brownian
coating thermal noise in current and future gravitational-wave detectors. Such
numerical models typically require significant computational resources and
time, and often involve closed-source commercial codes. In contrast,
open-source codes give complete visibility and control of the simulated physics
and enable direct assessment of the numerical accuracy. In this article, we use
the open-source SpECTRE numerical-relativity code and adopt a novel
discontinuous Galerkin numerical method to model Brownian coating thermal
noise. We demonstrate that SpECTRE achieves significantly higher accuracy than
a previous approach at a fraction of the computational cost. Furthermore, we
numerically model Brownian coating thermal noise in multiple sub-wavelength
crystalline coating layers for the first time. Our new numerical method has the
potential to enable fast exploration of realistic mirror configurations, and
hence to guide the search for optimal mirror geometries, beam shapes and
coating materials for gravitational-wave detectors.Comment: 9 pages, 5 figures. Results are reproducible with the ancillary input
file
A scalable elliptic solver with task-based parallelism for the SpECTRE numerical relativity code
Elliptic partial differential equations must be solved numerically for many
problems in numerical relativity, such as initial data for every simulation of
merging black holes and neutron stars. Existing elliptic solvers can take
multiple days to solve these problems at high resolution and when matter is
involved, because they are either hard to parallelize or require a large amount
of computational resources. Here we present a new solver for linear and
non-linear elliptic problems that is designed to scale with resolution and to
parallelize on computing clusters. To achieve this we employ a discontinuous
Galerkin discretization, an iterative multigrid-Schwarz preconditioned
Newton-Krylov algorithm, and a task-based parallelism paradigm. To accelerate
convergence of the elliptic solver we have developed novel
subdomain-preconditioning techniques. We find that our multigrid-Schwarz
preconditioned elliptic solves achieve iteration counts that are independent of
resolution, and our task-based parallel programs scale over 200 million degrees
of freedom to at least a few thousand cores. Our new code solves a classic
black-hole binary initial-data problem faster than the spectral code SpEC when
distributed to only eight cores, and in a fraction of the time on more cores.
It is publicly accessible in the next-generation SpECTRE numerical relativity
code. Our results pave the way for highly-parallel elliptic solves in numerical
relativity and beyond.Comment: 24 pages, 18 figures. Results are reproducible with the ancillary
input file
Omecamtiv mecarbil in chronic heart failure with reduced ejection fraction, GALACTICâHF: baseline characteristics and comparison with contemporary clinical trials
Aims:
The safety and efficacy of the novel selective cardiac myosin activator, omecamtiv mecarbil, in patients with heart failure with reduced ejection fraction (HFrEF) is tested in the Global Approach to Lowering Adverse Cardiac outcomes Through Improving Contractility in Heart Failure (GALACTICâHF) trial. Here we describe the baseline characteristics of participants in GALACTICâHF and how these compare with other contemporary trials.
Methods and Results:
Adults with established HFrEF, New York Heart Association functional class (NYHA)ââ„âII, EF â€35%, elevated natriuretic peptides and either current hospitalization for HF or history of hospitalization/ emergency department visit for HF within a year were randomized to either placebo or omecamtiv mecarbil (pharmacokineticâguided dosing: 25, 37.5 or 50âmg bid). 8256 patients [male (79%), nonâwhite (22%), mean age 65âyears] were enrolled with a mean EF 27%, ischemic etiology in 54%, NYHA II 53% and III/IV 47%, and median NTâproBNP 1971âpg/mL. HF therapies at baseline were among the most effectively employed in contemporary HF trials. GALACTICâHF randomized patients representative of recent HF registries and trials with substantial numbers of patients also having characteristics understudied in previous trials including more from North America (n = 1386), enrolled as inpatients (n = 2084), systolic blood pressureâ<â100âmmHg (n = 1127), estimated glomerular filtration rate <â30âmL/min/1.73 m2 (n = 528), and treated with sacubitrilâvalsartan at baseline (n = 1594).
Conclusions:
GALACTICâHF enrolled a wellâtreated, highârisk population from both inpatient and outpatient settings, which will provide a definitive evaluation of the efficacy and safety of this novel therapy, as well as informing its potential future implementation
Simulating magnetized neutron stars with discontinuous Galerkin methods
Discontinuous Galerkin methods are popular because they can achieve high order where the solution is smooth, because they can capture shocks while needing only nearest-neighbor communication, and because they are relatively easy to formulate on complex meshes. We perform a detailed comparison of various limiting strategies presented in the literature applied to the equations of general relativistic magnetohydrodynamics. We compare the standard minmod/Lambda Pi(N) limiter, the hierarchical limiter of Krivodonova, the simple WENO limiter, the HWENO limiter, and a discontinuous Galerkin-finite-difference hybrid method. The ultimate goal is to understand what limiting strategies are able to robustly simulate magnetized Tolman-Oppenheimer-Volkoff stars without any fine-tuning of parameters. Among the limiters explored here, the only limiting strategy we can endorse is a discontinuous Galerkin-finitedifference hybrid method
SpECTRE
<p>SpECTRE is an open-source code for multi-scale, multi-physics problems in astrophysics and gravitational physics. In the future, we hope that it can be applied to problems across discipline boundaries in fluid dynamics, geoscience, plasma physics, nuclear physics, and engineering. It runs at petascale and is designed for future exascale computers.</p>
<p>SpECTRE is being developed in support of our collaborative Simulating eXtreme Spacetimes (SXS) research program into the multi-messenger astrophysics of neutron star mergers, core-collapse supernovae, and gamma-ray bursts.</p>