29,700 research outputs found
Black hole singularities: a numerical approach
The singularity structure of charged spherical collapse is studied by
considering the evolution of the gravity-scalar field system. A detailed
examination of the geometry at late times strongly suggests the validity of the
mass-inflation scenario~\cite{PI:90}. Although the area of the two-spheres
remains finite at the Cauchy horizon, its generators are eventually focused to
zero radius. Thus the null, mass-inflation singularity {\em generally}\/
precedes a crushing singularity deep inside the black hole core. This
central singularity is spacelike.Comment: 4 pages Phys. Rev. style including five figures, provided as
compressed postscript files. To appear in Physical Review Letter
Computing the merger of black-hole binaries: the IBBH problem
Gravitational radiation arising from the inspiral and merger of binary black
holes (BBH's) is a promising candidate for detection by kilometer-scale
interferometric gravitational wave observatories. This paper discusses a
serious obstacle to searches for such radiation and to the interpretation of
any observed waves: the inability of current computational techniques to evolve
a BBH through its last ~10 orbits of inspiral (~100 radians of
gravitational-wave phase). A new set of numerical-relativity techniques is
proposed for solving this ``Intermediate Binary Black Hole'' (IBBH) problem:
(i) numerical evolutions performed in coordinates co-rotating with the BBH, in
which the metric coefficients evolve on the long timescale of inspiral, and
(ii) techniques for mathematically freezing out gravitational degrees of
freedom that are not excited by the waves.Comment: 6 pages RevTe
Spatially resolved electrochemistry in ionic liquids : surface structure effects on triiodide reduction at platinum electrodes
Understanding the relationship between electrochemical activity and electrode structure is vital for improving the efficiency of dye-sensitized solar cells. Here, the reduction of triiodide to iodide in 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIm][BF4]) room temperature ionic liquid (RTIL) is investigated on polycrystalline platinum using scanning electrochemical cell microscopy (SECCM) and correlated to the crystallographic orientation from electron backscatter diffraction (EBSD). Although the rate determining step in all grains was the first electron transfer, significant grain-dependent variations in activity were revealed, with grains with a dominant (110) crystallographic character exhibiting higher catalytic activity compared to those with a major (100) orientation. The SECCM technique is demonstrated to resolve heterogeneity in activity, highlighting that methods incorporating polycrystalline electrodes miss vital details for understanding and optimizing electrocatalysts. An additional advantage of the SECCM over single-crystal techniques is its ability to probe high index facets
Upper limits on gravitational-wave signals based on loudest events
Searches for gravitational-wave bursts have often focused on the loudest
event(s) in searching for detections and in determining upper limits on
astrophysical populations. Typical upper limits have been reported on event
rates and event amplitudes which can then be translated into constraints on
astrophysical populations. We describe the mathematical construction of such
upper limits.Comment: 8 pages, 1 figur
ECONOMIC EFFECTS OF COPPER-NICKEL DEVELOPMENT IN NORTHEAST MINNESOTA
Computer simulations of industry gross output, employment and earnings changes associated with alternative copper-nickel development scenarios are presented in this report. The direct and indirect economic effects of seven development scenarios are projected for a mining impact Study Area in St. Louis County, Minnesota.Community/Rural/Urban Development, Resource /Energy Economics and Policy,
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