6,024 research outputs found
Outgoing gravitational shock-wave at the inner horizon: The late-time limit of black hole interiors
We investigate the interiors of 3+1 dimensional asymptotically flat charged
and rotating black holes as described by observers who fall into the black
holes at late times, long after any perturbations of the exterior region have
decayed. In the strict limit of late infall times, the initial experiences of
such observers are precisely described by the region of the limiting stationary
geometry to the past of its inner horizon. However, we argue that late
infall-time observers encounter a null shockwave at the location of the
would-be outgoing inner horizon. In particular, for spherically symmetric black
hole spacetimes we demonstrate that freely-falling observers experience a
metric discontinuity across this shock, that is, a gravitational shock-wave.
Furthermore, the magnitude of this shock is at least of order unity. A similar
phenomenon of metric discontinuity appears to take place at the inner horizon
of a generically-perturbed spinning black hole. We compare the properties of
this null shockwave singularity with those of the null weak singularity that
forms at the Cauchy horizon.Comment: 23 pages, 4 figures, minor change
Amino acid classes and the protein folding problem
We present and implement a distance-based clustering of amino acids within
the framework of a statistically derived interaction matrix and show that the
resulting groups faithfully reproduce, for well-designed sequences,
thermodynamic stability in and kinetic accessibility to the native state. A
simple interpretation of the groups is obtained by eigenanalysis of the
interaction matrix.Comment: REVTeX, 11 pages, 4 figures, To appear in J. Chem. Phy
High Energy Hadron-Nucleus Cross Sections and Their Extrapolation to Cosmic Ray Energies
Old models of the scattering of composite systems based on the Glauber model
of multiple diffraction are applied to hadron-nucleus scattering. We obtain an
excellent fit with only two free parameters to the highest energy
hadron-nucleus data available. Because of the quality of the fit and the
simplicity of the model it is argued that it should continue to be reliable up
to the highest cosmic ray energies. Logarithmic extrapolations of proton-proton
and proton-antiproton data are used to calculate the proton-air cross sections
at very high energy. Finally, it is observed that if the exponential behavior
of the proton-antiproton diffraction peak continues into the few TeV energy
range it will violate partial wave unitarity. We propose a simple modification
that will guarantee unitarity throughout the cosmic ray energy region.Comment: 8 pages, 9 postscript figures. This manuscript replaces a partial
manuscript incorrectly submitte
Formation of closed timelike curves in a composite vacuum/dust asymptotically-flat spacetime
We present a new asymptotically-flat time-machine model made solely of vacuum
and dust. The spacetime evolves from a regular spacelike initial hypersurface S
and subsequently develops closed timelike curves. The initial hypersurface S is
asymptotically flat and topologically trivial. The chronology violation occurs
in a compact manner; namely the first closed causal curves form at the boundary
of the future domain of dependence of a compact region in S (the core). This
central core is empty, and so is the external asymptotically flat region. The
intermediate region surrounding the core (the envelope) is made of dust with
positive energy density. This model trivially satisfies the weak, dominant, and
strong energy conditions. Furthermore it is governed by a well-defined system
of field equations which possesses a well-posed initial-value problem.Comment: 15 pages; accepted to Phys. Rev. D (no modifications
Trends and Regional Variation in Hip, Knee and Shoulder Replacement
Analyzes patterns in underuse or overuse of joint replacements among Medicare beneficiaries by geographic regions and race/ethnicity. Explores underlying factors and highlights the need for physician and patient education and shared decision making
Evaluation of diffusive gradients in thin-films using a Diphonix® resin for monitoring dissolved uranium in natural waters
Commercially available Diphonix® resin (TrisKem International) was evaluated as a receiving phase for use with the diffusive gradients in thin-films (DGT) passive sampler for measuring uranium. This resin has a high partition coefficient for actinides and is used in the nuclear industry. Other resins used as receiving phases with DGT for measuring uranium have been prone to saturation and significant chemical interferences. The performance of the device was evaluated in the laboratory and in field trials. In laboratory experiments uptake of uranium (all 100% efficiency) by the resin was unaffected by varying pH (4–9), ionic strength (0.01–1.00 M, as NaNO3) and varying aqueous concentrations of Ca2+ (100–500 mg L−1) and HCO3− (100–500 mg L−1). Due to the high partition coefficient of Diphonex®, several elution techniques for uranium were evaluated. The optimal eluent mixture was 1 M NaOH/1 M H2O2, eluting 90% of the uranium from the resin. Uptake of uranium was linear (R2 = 0.99) over time (5 days) in laboratory experiments using artificial freshwater showing no saturation effects of the resin. In field deployments (River Lambourn, UK) the devices quantitatively accumulated uranium for up to 7 days. In both studies uptake of uranium matched that theoretically predicted for the DGT. Similar experiments in seawater did not follow the DGT theoretical uptake and the Diphonix® appeared to be capacity limited and also affected by matrix interferences. Isotopes of uranium (U235/U238) were measured in both environments with a precision and accuracy of 1.6–2.2% and 1.2–1.4%, respectively. This initial study shows the potential of using Diphonix®-DGT for monitoring of uranium in the aquatic environment
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