19 research outputs found
Numerical Brill-Lindquist initial data with a Schwarzschildean end at spatial infinity
We construct numerically time-symmetric initial data that are
Schwarzschildean at spatial infinity and Brill-Lindquist in the interior. The
transition between these two data sets takes place along a finite gluing region
equipped with an axisymmetric Brill wave metric. The construction is based on
an application of Corvino's gluing method using Brill waves due to Giulini and
Holzegel. Here, we use a gluing function that includes a simple angular
dependence. We also investigate the dependence of the ADM mass of our
construction on the details of the gluing procedure.Comment: 6 pages, 1 figure, 1 table. Conference proceedings for the Spanish
Relativity Meeting, Valencia 201
COFFEE -- An MPI-parallelized Python package for the numerical evolution of differential equations
COFFEE (ConFormal Field Equation Evolver) is a Python package primarily
developed to numerically evolve systems of partial differential equations over
time using the method of lines. It includes a variety of time integrators and
finite differencing stencils with the summation-by-parts property, as well as
pseudo-spectral functionality for angular derivatives of spin-weighted
functions. Some additional capabilities include being MPI-parallelisable on a
variety of different geometries, HDF data output and post processing scripts to
visualize data, and an actions class that allows users to create code for
analysis after each timestep.Comment: 12 pages, 1 figure, accepted to be published in Software
Numerical construction of initial data for Einstein's equations with static extension to space-like infinity
We describe a numerical method to construct Cauchy data extending to
space-like infinity based on Corvino's (2000) gluing method. Adopting the
setting of Giulini and Holzegel (2005), we restrict ourselves here to vacuum
axisymmetric spacetimes and glue a Schwarzschildean end to Brill-Lindquist data
describing two non-rotating black holes. Our numerical implementation is based
on pseudo-spectral methods, and we carry out extensive convergence tests to
check the validity of our numerical results. We also investigate the dependence
of the total ADM mass on the details of the gluing construction.Comment: 20 pages, 13 figures. Agrees with the published versio
Second release of the CoRe database of binary neutron star merger waveforms
We present the second data release of gravitational waveforms from binary
neutron star merger simulations performed by the Computational Relativity
(CoRe) collaboration. The current database consists of 254 different binary
neutron star configurations and a total of 590 individual numerical-relativity
simulations using various grid resolutions. The released waveform data contain
the strain and the Weyl curvature multipoles up to . They span a
significant portion of the mass, mass-ratio,spin and eccentricity parameter
space and include targeted configurations to the events GW170817 and GW190425.
CoRe simulations are performed with 18 different equations of state, seven of
which are finite temperature models, and three of which account for
non-hadronic degrees of freedom. About half of the released data are computed
with high-order hydrodynamics schemes for tens of orbits to merger; the other
half is computed with advanced microphysics. We showcase a standard waveform
error analysis and discuss the accuracy of the database in terms of
faithfulness. We present ready-to-use fitting formulas for equation of
state-insensitive relations at merger (e.g. merger frequency), luminosity peak,
and post-merger spectrum.Comment: 33 pages, 14 figure
The Generalised Conformal Field Equations Near Spatial Infinity
The linearised general conformal field equations in their first and second order form are used to study the behaviour of the spin-2 zero-rest-mass equation on Minkowski background in the vicinity of space-like infinity
The Generalised Conformal Field Equations Near Spatial Infinity
The linearised general conformal field equations in their first and second order form are used to study the behaviour of the spin-2 zero-rest-mass equation on Minkowski background in the vicinity of space-like infinity
A Prospective Cohort Study Assessing the Impact of Fixed Orthodontic Appliances on Saliva Properties and Oral Microbial Flora.
Purpose: Orthodontic treatment may introduce a risk to the integrity of enamel due to plaque accumulation and colonisation by oral microbes. This prospective cohort study observed the effect of fixed, self-ligating orthodontic appliances on saliva properties and oral microbial flora.
Materials and Methods: Thirty adolescent patients were recruited (13 female, 17 male, mean age 13.97 ± 2.07 years). Saliva samples were collected before placement of fixed orthodontic appliances (T0), and 4 (T1) and 12 (T2) weeks later. Salivary pH, flow rate and buffering capacity were recorded. All saliva samples were cultured on agar plates for 2 days. Salivary prevalence of Neisseria spp., streptococci, Staphylococcus aureus, coagulase-negative staphylococci and Candida albicans were assessed.
Results: High buffering capacity was reported in 21 patients at T0, 22 patients at T1 and in 28 patients at T2. Saliva flow rate also increased over time (7.08 ml/5 min at T0, 7.93 ml/5 min at T1 and 8.35 ml/5min at T2). Mean pH was 7.63 at T0, 7.67 at T1 and 7.78 at T2. There was no evidence that either pH or the number of colonies of any of the microbial species changed over time.
Conclusion: The increased buffering capacity of saliva as well as the salivary flow rate after initial bonding might be protective against the development of dental caries. Current microbial findings indicate that initiation of orthodontic treatment may not be associated with significant changes in oral microbial flora
Entropy-limited higher-order central scheme for neutron star merger simulations
Numerical relativity simulations are the only way to calculate exact
gravitational waveforms from binary neutron star mergers and to design
templates for gravitational-wave astronomy. The accuracy of these numerical
calculations is critical in quantifying tidal effects near merger that are
currently one of the main sources of uncertainty in merger waveforms. In this
work, we explore the use of an entropy-based flux-limiting scheme for
high-order, convergent simulations of neutron star spacetimes. The scheme
effectively tracks the stellar surface and physical shocks using the residual
of the entropy equation thus allowing the use of unlimited central flux schemes
in regions of smooth flow. We perform the first neutron star merger simulations
with such a method and demonstrate up to fourth-order convergence in the
gravitational waveform phase. The scheme reduces the phase error up to a factor
five when compared to state-of-the-art high-order characteristic schemes and
can be employed for producing faithful tidal waveforms for gravitational-wave
modelling.Comment: 22 pages, 21 figure
Effects of Self-ligating Orthodontic Appliances on the Periodontal Health of Adolescents: A Prospective Cohort Study.
PURPOSE
To evaluate the association between orthodontic treatment with fixed appliances and periodontal health during treatment by examining gingival inflammation indices and saliva properties.
MATERIALS AND METHODS
Thirty consecutive orthodontic patients, aged 11-18 years old, who were eligible for fixed orthodontic appliances, were included in the study. Plaque index (PI), gingival index (GI), salivary pH and flow rate were recorded at three timepoints: immediately before placement of orthodontic fixed appliances (T0), and 1 (T1) and 3 months (T2) after bonding.
RESULTS
The hypothesis that PI would remain constant across timepoints was rejected. PI increased over time (0 to 1 scale, T1-T0: mean diff. = 0.10, 95% CI = 0.03, 0.18, p = 0.01; T2-T0: mean diff. = 0.16, 95% CI = 0.08, 0.24, p < 0.001). On the other hand, GI changed statistically significantly over time (p = 0.05). Patients' age was not a predictor for PI change (p = 0.93), but it was for GI (p = 0.01). As anticipated, average PI was found to be higher for the mandibular dentition by 0.10 (95% CI = 0.04, 0.16) and the labial surfaces of teeth of both jaws by 0.51 (95% CI = 0.45, 0.57).
CONCLUSIONS
Within the framework of the current study, orthodontic treatment appeared to affect the periodontal health of patients, but the changes were clinically negligible and not consistently statistically significant