2,361 research outputs found
Mass inflation in f(R) gravity: A conjecture on the resolution of the mass inflation singularity
We study gravitational collapse of a charged black hole in f(R) gravity using
double-null formalism. We require cosmological stability to f(R) models; we
used the Starobinsky model and the R + (1/2)cR^2 model. Charged black holes in
f(R) gravity can have a new type of singularity due to higher curvature
corrections, the so-called f(R)-induced singularity, although it is highly
model-dependent. As the advanced time increases, the internal structure will
approach the Cauchy horizon, which may not be an inner apparent horizon. There
is mass inflation as one approaches the Cauchy horizon and hence the Cauchy
horizon may be a curvature singularity with nonzero area. However, the Ricci
scalar is finite for an out-going null observer. This can be integrated as
follows: Cosmologically stable higher curvature corrections of the Ricci scalar
made it bounded even in the presence of mass inflation. Finally, we conjecture
that if there is a general action including general higher curvature
corrections with cosmological stability, then the corrections can make all
curvature components finite even in the presence of mass inflation. This might
help us to resolve the problem of inner horizon instability of regular black
hole models.Comment: 31 pages, 15 figure
A Numerical Investigation of the Effects of Classical Phase Space Structure on a Quantum System
We present a detailed numerical study of a chaotic classical system and its
quantum counterpart. The system is a special case of a kicked rotor and for
certain parameter values possesses cantori dividing chaotic regions of the
classical phase space. We investigate the diffusion of particles through a
cantorus; classical diffusion is observed but quantum diffusion is only
significant when the classical phase space area escaping through the cantorus
per kicking period greatly exceeds Planck's constant. A quantum analysis
confirms that the cantori act as barriers. We numerically estimate the
classical phase space flux through the cantorus per kick and relate this
quantity to the behaviour of the quantum system. We introduce decoherence via
environmental interactions with the quantum system and observe the subsequent
increase in the transport of quantum particles through the boundary.Comment: 15 pages, 22 figure
Camera distortion self-calibration using the plumb-line constraint and minimal Hough entropy
In this paper we present a simple and robust method for self-correction of
camera distortion using single images of scenes which contain straight lines.
Since the most common distortion can be modelled as radial distortion, we
illustrate the method using the Harris radial distortion model, but the method
is applicable to any distortion model. The method is based on transforming the
edgels of the distorted image to a 1-D angular Hough space, and optimizing the
distortion correction parameters which minimize the entropy of the
corresponding normalized histogram. Properly corrected imagery will have fewer
curved lines, and therefore less spread in Hough space. Since the method does
not rely on any image structure beyond the existence of edgels sharing some
common orientations and does not use edge fitting, it is applicable to a wide
variety of image types. For instance, it can be applied equally well to images
of texture with weak but dominant orientations, or images with strong vanishing
points. Finally, the method is performed on both synthetic and real data
revealing that it is particularly robust to noise.Comment: 9 pages, 5 figures Corrected errors in equation 1
Spatial Degrees of Freedom in Everett Quantum Mechanics
Stapp claims that, when spatial degrees of freedom are taken into account,
Everett quantum mechanics is ambiguous due to a "core basis problem." To
examine an aspect of this claim I generalize the ideal measurement model to
include translational degrees of freedom for both the measured system and the
measuring apparatus. Analysis of this generalized model using the Everett
interpretation in the Heisenberg picture shows that it makes unambiguous
predictions for the possible results of measurements and their respective
probabilities. The presence of translational degrees of freedom for the
measuring apparatus affects the probabilities of measurement outcomes in the
same way that a mixed state for the measured system would. Examination of a
measurement scenario involving several observers illustrates the consistency of
the model with perceived spatial localization of the measuring apparatus.Comment: 34 pp., no figs. Introduction, discussion revised. Material
tangential to main point remove
Entropy of Lovelock Black Holes
A general formula for the entropy of stationary black holes in Lovelock
gravity theories is obtained by integrating the first law of black hole
mechanics, which is derived by Hamiltonian methods. The entropy is not simply
one quarter of the surface area of the horizon, but also includes a sum of
intrinsic curvature invariants integrated over a cross section of the horizon.Comment: 15 pages, plain Latex, NSF-ITP-93-4
Selenium Content of Forage and Hay Crops in the Pacific Northwest
A map illustrating the Se content of forage and hay
crops in different sections of the Pacific Northwest was
prepared, based on analyses of crop samples. The primary
criterion used in mapping was to delineate areas
where forage and hay crops generally contain insufficient
Se to meet requirements of lambs and calves, and thus
prevent white muscle disease (WMD) and other Se-responsive
diseases. The minimal requirement may vary
from 0.03 to 0.10 ppm Se in the diet, depending upon the
diet level of vitamin E and possibly other substances.
Under normal livestock management practices, WMD
is common when forages and hay contain less than 0.10
ppm Se and the incidence is greater at lower Se levels.
The western half of Washington and Oregon and part
of northern California comprise an extremely low Se
area. The eastern half of Washington, northern Idaho,
extreme western Montana, and the northeast corner of
Oregon comprise a low Se area. Most of the remaining
portion of the Northwest may be considered as variable
in Se, with farm-to-farm variations common, but some
small areas of adequate Se were found and mapped
The New Urban Revival in the United States
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68657/2/10.1080_00420989320081901.pd
Decay of flux vacua to nothing
We construct instanton solutions describing the decay of flux
compactifications of a gauge theory by generalizing the Kaluza-Klein
bubble of nothing. The surface of the bubble is described by a smooth
magnetically charged solitonic brane whose asymptotic flux is precisely that
responsible for stabilizing the 4d compactification. We describe several
instances of bubble geometries for the various vacua occurring in a
Einstein-Maxwell theory namely, AdS_4 x S^2, R^{1,3} x S^2, and dS_4 x S^2.
Unlike conventional solutions, the bubbles of nothing introduced here occur
where a {\em two}-sphere compactification manifold homogeneously degenerates.Comment: 31 pages, 15 figure
Fine Root Productivity and Dynamics on a Forested Floodplain in South Carolina
The highly dynamic, fine-root component of forested wetland ecosystems has received inadequate attention in the literature. Characterizing fine root dynamics is a challenging endeavor in any system, but the difficulties are particularly evident in forested floodplains where frequent hydrologic fluctuations directly influence fine root dynamics. Fine root (\u3c 3mm) biomass, production, and turnover were estimated for three soils exhibiting different drainage patterns within a mixed-oak community on the Coosawhatchie River floodplain, Jasper County, SC. Within a 45-cm deep vertical profile, 74% of total fine root biomass was restricted to the upper 15 cm of the soil surface. Fine root biomass decreased as the soil became less well-drained (e.g., fine root biomass in well-drained soil \u3e intermediately drained soil \u3e poorly drained soil). Fine root productivity was measured for one year using minirhizotrons and in-situ screens. Both methods suggested higher fine root production in better drained soils but showed frequent fluctuations in fine root growth and mortality, suggesting the need for frequent sampling at short intervals (e.g., monthly) to accurately assess fine root growth and turnover. Fine root production, estimated with in-situ screens, was 1.5, 1.8, and 0.9 Mg ha-1 yr-1 in the well-drained, intermediately drained, and poorly drained soils, respectively. Results from minirhizotrons indicated that fine roots in well-drained soils grew to greater depths while fine roots in poorly drained soils were restricted to surface soils. Minirhizotrons also revealed that the distribution of fine roots among morphological classes changed between well-drained and poorly drained soils
Explaining the unobserved: why quantum mechanics is not only about information
A remarkable theorem by Clifton, Bub and Halvorson (2003)(CBH) characterizes
quantum theory in terms of information--theoretic principles. According to Bub
(2004, 2005) the philosophical significance of the theorem is that quantum
theory should be regarded as a ``principle'' theory about (quantum) information
rather than a ``constructive'' theory about the dynamics of quantum systems.
Here we criticize Bub's principle approach arguing that if the mathematical
formalism of quantum mechanics remains intact then there is no escape route
from solving the measurement problem by constructive theories. We further
propose a (Wigner--type) thought experiment that we argue demonstrates that
quantum mechanics on the information--theoretic approach is incomplete.Comment: 34 Page
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