6,098 research outputs found
Unitarity of black hole evaporation in final-state projection models
Almheiri et al. have emphasized that otherwise reasonable beliefs about black
hole evaporation are incompatible with the monogamy of quantum entanglement, a
general property of quantum mechanics. We investigate the final-state
projection model of black hole evaporation proposed by Horowitz and Maldacena,
pointing out that this model admits cloning of quantum states and polygamous
entanglement, allowing unitarity of the evaporation process to be reconciled
with smoothness of the black hole event horizon. Though the model seems to
require carefully tuned dynamics to ensure exact unitarity of the black hole
S-matrix, for a generic final-state boundary condition the deviations from
unitarity are exponentially small in the black hole entropy; furthermore
observers inside black holes need not detect any deviations from standard
quantum mechanics. Though measurements performed inside old black holes could
potentially produce causality-violating phenomena, the computational complexity
of decoding the Hawking radiation may render the causality violation
unobservable. Final-state projection models illustrate how inviolable
principles of standard quantum mechanics might be circumvented in a theory of
quantum gravity.Comment: (v3) 27 pages, 16 figures. Expanded discussion of measurements inside
black hole
Identifiability of Large Phylogenetic Mixture Models
Phylogenetic mixture models are statistical models of character evolution
allowing for heterogeneity. Each of the classes in some unknown partition of
the characters may evolve by different processes, or even along different
trees. The fundamental question of whether parameters of such a model are
identifiable is difficult to address, due to the complexity of the
parameterization. We analyze mixture models on large trees, with many mixture
components, showing that both numerical and tree parameters are indeed
identifiable in these models when all trees are the same. We also explore the
extent to which our algebraic techniques can be employed to extend the result
to mixtures on different trees.Comment: 15 page
The vertical distribution of iron stable isotopes in the North Atlantic near Bermuda
Seawater dissolved iron isotope ratios (δ^(56)Fe) have been measured in the North Atlantic near Bermuda. In a full-depth profile, seawater dissolved δ^(56)Fe is isotopically heavy compared to crustal values throughout the water column (δ^(56)Fe_(IRMM-014) = +0.30‰ to +0.71‰). Iron isotope ratios are relatively homogenous in the upper water column (between +0.30‰ to +0.45‰ above 1500 m), and δ^(56)Fe increases below this to a maximum of +0.71‰ at 2500 m, decreasing again to +0.35‰ at 4200 m. The δ^(56)Fe profile is very different from the iron concentration profile; in the upper water column [Fe] is variable while δ^(56)Fe is relatively constant, and in the deeper water column δ^(56)Fe varies while [Fe] remains relatively constant. The δ^(56)Fe profile is also not well correlated with other hydrographic tracers in the North Atlantic such as temperature, salinity, or the concentrations of oxygen, phosphate, silica, and CFC-11. The dissimilarity between δ^(56)Fe profiles and profiles of [Fe] and other hydrographic tracers shows that Fe isotope ratios provide a unique sort of information about ocean chemistry, and they suggest that Fe isotopes may therefore be a valuable new tool for tracing the global sources, sinks, and biogeochemical cycling of Fe
Mississippi River Research Conclusions Executive Summary
Briefing paper requested by Senator Bond detailing the conclusions from the Mississippi River research to date.Agricultural and Food Policy, Environmental Economics and Policy,
IMPACT OF NEW FARM BILL PROVISIONS ON OPTIMAL RESOURCE ALLOCATION ON HIGHLY ERODIBLE SOILS
The study focuses on incentives to produce crops under reduced tillage systems on highly erodible soils. A mixed integer, mathematical programming model was developed to identify optimal resource use under alternative farm program provisions. A positive counter cyclical payment only reinforces the incentive to comply with NRCS soil erosion constrains.Crop Production/Industries,
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