Isolated horizons in numerical relativity: constructing the excised Kerr spacetime in Dirac gauge

Using a constrained formalism for Einstein equations in Dirac gauge, we propose to compute excised quasistationary initial data for black hole spacetimes in full general relativity. Vacuum spacetime settings are numerically constructed by using the isolated horizon formalism; we especially tackle the conformal metric part of our equations, assuming global stationarity. We show that a no-boundary treatment can be used on the horizon for the equation related to the conformal metric. We relate this finding to previous suggestions in the literature, and use our results to assess the widely used conformally flat approximation for computing black hole initial data.Comment: 3 pages, 1 figure; to appear in the proceedings of the 12th Marcel Grossmann meeting on general relativit

A numerical study of Penrose-like inequalities in a family of axially symmetric initial data

Our current picture of black hole gravitational collapse relies on two assumptions: i) the resulting singularity is hidden behind an event horizon -- weak cosmic censorship conjecture -- and ii) spacetime eventually settles down to a stationarity state. In this setting, it follows that the minimal area containing an apparent horizon is bound by the square of the total ADM mass (Penrose inequality conjecture). Following Dain et al. 2002, we construct numerically a family of axisymmetric initial data with one or several marginally trapped surfaces. Penrose and related geometric inequalities are discused for these data. As a by-product, it is shown how Penrose inequality can be used as a diagnosis for an apparent horizon finder numerical routine.Comment: Contribution to the "Encuentros Relativistas Espanoles - Spanish Relativity Meeting ERE07" Proceedings, Tenerife, Spain (September 2007

Application of initial data sequences to the study of Black Hole dynamical trapping horizons

Non-continuous "jumps" of Apparent Horizons occur generically in 3+1 (binary) black hole evolutions. The dynamical trapping horizon framework suggests a spacetime picture in which these "Apparent Horizon jumps" are understood as spatial cuts of a single spacetime hypersurface foliated by (compact) marginally outer trapped surfaces. We present here some work in progress which makes use of uni-parametric sequences of (axisymmetric) binary black hole initial data for exploring the plausibility of this spacetime picture. The modelling of Einstein evolutions by sequences of initial data has proved to be a successful methodological tool in other settings for the understanding of certain qualitative features of evolutions in restricted physical regimes.Comment: Contribution to the proceedings volume of the Spanish Relativity Meeting 2008: Physics and Mathematics of Gravitation, Salamanca, Spain, 15-19 Sep 200

An excision scheme for black holes in constrained evolution formulations: spherically symmetric case

Excision techniques are used in order to deal with black holes in numerical simulations of Einstein equations and consist in removing a topological sphere containing the physical singularity from the numerical domain, applying instead appropriate boundary conditions at the excised surface. In this work we present recent developments of this technique in the case of constrained formulations of Einstein equations and for spherically symmetric spacetimes. We present a new set of boundary conditions to apply to the elliptic system in the fully-constrained formalism of Bonazzola et al. (2004), at an arbitrary coordinate sphere inside the apparent horizon. Analytical properties of this system of boundary conditions are studied and, under some assumptions, an exponential convergence toward the stationary solution is exhibited for the vacuum spacetime. This is verified in numerical examples, together with the applicability in the case of the accretion of a scalar field onto a Schwarzschild black hole. We also present the successful use of the excision technique in the collapse of a neutron star to a black hole, when excision is switched on during the simulation, after the formation of the apparent horizon. This allows the accretion of matter remaining outside the excision surface and for the stable long-term evolution of the newly formed black hole.Comment: 14 pages, 9 figures. New section added and changes included according to published articl

Kadath: a spectral solver for theoretical physics

Kadath is a library that implements spectral methods in a very modular manner. It is designed to solve a wide class of problems that arise in the context of theoretical physics. Several types of coordinates are implemented and additional geometries can be easily encoded. Partial differential equations of various types are discretized by means of spectral methods. The resulting system is solved using a Newton-Raphson iteration. Doing so, Kadath is able to deal with strongly non-linear situations. The algorithms are validated by applying the library to four different problems of contemporary physics, in the fields of gauge field theory and general relativityComment: Accepted to Journal of Computational Physic

Mutual Fund Size and Fund Performance

Masteroppgave(MSc) in Master of Science in Business, Finance - Handelshøyskolen BI, 2019This thesis studies the relationship between size and performance for 67 equity mutual funds in Norway, using a 14 years dataset free of survivorship bias from January 2005 to December 2018. We construct three portfolios based on the funds’ size and evaluate their performance by looking at their risk-adjusted return estimated from various factor models. We find no significant evidence that Norwegian mutual funds are able to beat their benchmark, both gross of fees and net of fees. Further, we study the relationship between fund size and performance while controlling for different fund characteristics. We find a statistically significant negative relationship between fund size and performance. Thus, our results indicate that size matters for mutual fund performance in Norway. We suggest that these findings come from price mechanisms, complex decisionmaking processes, and the fact that the Norwegian mutual fund market has a narrow asset base that could cause investors to dilute their best ideas

Interprofessional Learning in the Simulation Laboratory : Nursing and Pharmacy Students’ Experiences

Background: Using simulation as an educational method to learn collaborative practice requires the involvement of various professional education programs where the intention is to learn from, with, and about each other. Methods: is study describes pharmacy and nursing students´ experiences with interprofessional education. Aer interprofessional simulation, three focus group interviews with bachelor students were conducted. e data were analysed using Giorgi’s qualitative content analysis method. Findings: e students found that IPE closed knowledge gaps, change a stereotypical perception of professional roles, and enhance patient safety. Full-scale simulation appears to be an effective arena for learning clinical judgement, improving communication skills, and developing knowledge of pharmacodynamics. Conclusion: Interprofessional education may be necessary for professionals to enhance their ability to interact more effectively in the future.publishedVersio

Adult and paediatric mortality patterns in a referral hospital in Liberia 1 year after the end of the war

The aim of this study was to describe and analyse hospital mortality patterns after the Liberian war. Data were collected retrospectively from January to July 2005 in a referral hospital in Monrovia, Liberia. The overall fatality rate was 17.2% (438/2543) of medical admissions. One-third of deaths occurred in the first 24h. The adult fatality rate was 23.3% (241/1034). Non-infectious diseases accounted for 56% of the adult deaths. The main causes of death were meningitis (16%), stroke (14%) and heart failure (10%). Associated fatality rates were 48%, 54% and 31% respectively. The paediatric fatality rate was 13.1% (197/1509). Infectious diseases caused 66% of paediatric deaths. In infants <1 month old, the fatality rate was 18% and main causes of death were neonatal sepsis (47%), respiratory distress (24%) and prematurity (18%). The main causes of death in infants > or =1 month old were respiratory infections (27%), malaria (23%) and severe malnutrition (16%). Associated fatality rates were 12%, 10% and 19%. Fatality rates were similar to those found in other sub-Saharan countries without a previous conflict. Early deaths could decrease through recognition and early referral of severe cases from health centres to the hospital and through assessment and priority treatment of these patients at arrival