Finding Apparent Horizons in Dynamic 3D Numerical Spacetimes

We have developed a general method for finding apparent horizons in 3D numerical relativity. Instead of solving for the partial differential equation describing the location of the apparent horizons, we expand the closed 2D surfaces in terms of symmetric trace--free tensors and solve for the expansion coefficients using a minimization procedure. Our method is applied to a number of different spacetimes, including numerically constructed spacetimes containing highly distorted axisymmetric black holes in spherical coordinates, and 3D rotating, and colliding black holes in Cartesian coordinates.Comment: 19 pages, 13 figures, LaTex, to appear in Phys. Rev. D. Minor changes mad

Event Horizons in Numerical Relativity I: Methods and Tests

This is the first paper in a series on event horizons in numerical relativity. In this paper we present methods for obtaining the location of an event horizon in a numerically generated spacetime. The location of an event horizon is determined based on two key ideas: (1) integrating backward in time, and (2) integrating the whole horizon surface. The accuracy and efficiency of the methods are examined with various sample spacetimes, including both analytic (Schwarzschild and Kerr) and numerically generated black holes. The numerically evolved spacetimes contain highly distorted black holes, rotating black holes, and colliding black holes. In all cases studied, our methods can find event horizons to within a very small fraction of a grid zone.Comment: 22 pages, LaTeX with RevTeX 3.0 macros, 20 uuencoded gz-compressed postscript figures. Also available at http://jean-luc.ncsa.uiuc.edu/Papers/ Submitted to Physical Review

Morphology-Directed Catalysis with Branched Gold Nanoantennas

We synthesized multibranched gold nanoantennas (MGNs) of two morphologies by varying the core-to-branch ratio. We compared their efficacy in catalytic reduction of <i>p</i>-nitrophenol (PNP) to <i>p</i>-aminiphenol (PAP). We observed that MGNs with shorter protrusions had a faster induction time and higher apparent rate constant, <i>k</i>_app, for PNP catalysis relative to the MGNs with longer protrusions. By examining the reaction as a function of temperature, we observed significantly lower activation energy for the MGNs with shorter protrusions (80 J/g) compared to MGNs with longer protrusions (200 J/g). The Langmuir–Hinshelwood model was used to fit the change in <i>k</i>_app as a function of increasing [PNP], which demonstrated more efficient PNP adsorption on the surfaces of MGNs with shorter protrusions. For the MGNs with longer protrusions, PNP adsorption is affected by the heterogeneity of the surface sites resulting in a lower adsorption coefficient. We attributed the improved efficiency of the MGNs with shorter protrusions to the presence of {100} and {110} crystal planes, which have a high density of atomic steps and kinks that promote higher catalytic activity for PNP degradation. MGNs with long protrusions are bound by low index {111} facets; the highly coordinated atoms of {111} reduce the adsorption efficiency of PNP

Search for intermediate mass black hole binaries in the first observing run of Advanced LIGO

International audienceDuring their first observational run, the two Advanced LIGO detectors attained an unprecedented sensitivity, resulting in the first direct detections of gravitational-wave signals produced by stellar-mass binary black hole systems. This paper reports on an all-sky search for gravitational waves (GWs) from merging intermediate mass black hole binaries (IMBHBs). The combined results from two independent search techniques were used in this study: the first employs a matched-filter algorithm that uses a bank of filters covering the GW signal parameter space, while the second is a generic search for GW transients (bursts). No GWs from IMBHBs were detected; therefore, we constrain the rate of several classes of IMBHB mergers. The most stringent limit is obtained for black holes of individual mass 100  M⊙, with spins aligned with the binary orbital angular momentum. For such systems, the merger rate is constrained to be less than 0.93  Gpc−3 yr−1 in comoving units at the 90% confidence level, an improvement of nearly 2 orders of magnitude over previous upper limits