6,651 research outputs found
Practical Open-Loop Optimistic Planning
We consider the problem of online planning in a Markov Decision Process when
given only access to a generative model, restricted to open-loop policies -
i.e. sequences of actions - and under budget constraint. In this setting, the
Open-Loop Optimistic Planning (OLOP) algorithm enjoys good theoretical
guarantees but is overly conservative in practice, as we show in numerical
experiments. We propose a modified version of the algorithm with tighter
upper-confidence bounds, KLOLOP, that leads to better practical performances
while retaining the sample complexity bound. Finally, we propose an efficient
implementation that significantly improves the time complexity of both
algorithms
Problems in Attempting to Translate Statuory Standards into Emission Limitations under Air and Water Pollution Control Legislation
Mineralization of an Axially Aligned Collagenous Matrix: A Morphological Study
Bone can be described as a highly ordered composite of type I collagen integrated with an inorganic mineral phase. In vitro models of bone mineralization using collagenous substrates have been reported in the literature. This study reports an in vitro system of mineralized reconstituted collagen fibers, with aligned fibrillar substructure. The collagen fibers were mineralized in a double diffusion chamber saturated with respect to calcium and phosphate. The morphology and ultrastructure of the mineral precipitate were evaluated as a function of the pH of the incubating media. Brushite crystal was observed at acidic pH. Large rectangular crystals formed at pH 5.15 and appear to associate with the collagen fibers. At neutral and alkaline pHs, hydroxyapatite crystals were observed in association with the collagen fibers . Spherical aggregates of hydroxyapatite crystals were seen at neutral and alkaline pHs, but these structures were reduced in size when formed on collagen at alkaline pH. On close examination these spherical structures were found to be hollow when viewed in cross section.
The crystals precipitated within the interior of the collagen fiber at neutral and alkaline pHs were comparable in both size and shape to crystals observed in mineralized turkey tendon and skeletal tissues. These preliminary observations indicate that with further refinement the reconstituted collagen fibers may prove useful in model systems for the study of collagen mediated mineralization in vitro. In addition, mineralization of collagenous matrices may lead to the development of biomaterials for bone repair and replacement
Polaritons and Pairing Phenomena in Bose--Hubbard Mixtures
Motivated by recent experiments on cold atomic gases in ultra high finesse
optical cavities, we consider the problem of a two-band Bose--Hubbard model
coupled to quantum light. Photoexcitation promotes carriers between the bands
and we study the non-trivial interplay between Mott insulating behavior and
superfluidity. The model displays a global U(1) X U(1) symmetry which supports
the coexistence of Mott insulating and superfluid phases, and yields a rich
phase diagram with multicritical points. This symmetry property is shared by
several other problems of current experimental interest, including
two-component Bose gases in optical lattices, and the bosonic BEC-BCS crossover
problem for atom-molecule mixtures induced by a Feshbach resonance. We
corroborate our findings by numerical simulations.Comment: 4 pages, 3 figure
Lower Cretaceous Pre-Batholithic Rocks of Northern Baja California, Mexico
Cretaceous fossils have been found at scattered localities in the pre-batholithic metamorphic rocks of northern Baja California by investigators during the past half-century. The resulting information has been inadequate, however, for the explanation of regional stratigraphic and structural relations, particularly those correlations between the less metamorphosed coastal sections and the more deformed rocks of the mountainous interior
Cardiac output during CPR: a comparison of two methods
Simultaneous Fick and saline dilution methods were compared for measuring cardiac output during experimental cardiac arrest and resuscitation in anesthetized dogs. During cardiopulmonary resuscitation (CPR) cardiac output averaged 53 ± 30 ml/min-kg (42% of pre-arrest values). Values obtained using the Fick vs. saline methods were highly correlated (r = 0.96), and were not statistically different (t = 1.47, df = 16)
Bose--Hubbard Models Coupled to Cavity Light Fields
Recent experiments on strongly coupled cavity quantum electrodynamics present
new directions in "matter-light" systems. Following on from our previous work
[Phys. Rev. Lett. 102, 135301 (2009)] we investigate Bose-Hubbard models
coupled to a cavity light field. We discuss the emergence of photoexcitations
or "polaritons" within the Mott phase, and obtain the complete variational
phase diagram. Exploiting connections to the super-radiance transition in the
Dicke model we discuss the nature of polariton condensation within this novel
state. Incorporating the effects of carrier superfluidity, we identify a
first-order transition between the superradiant Mott phase and the single
component atomic superfluid. The overall predictions of mean field theory are
in excellent agreement with exact diagonalization and we provide details of
superfluid fractions, density fluctuations, and finite size effects. We
highlight connections to recent work on coupled cavity arrays.Comment: 16 pages, 17 figure
Effects of nitrogen additions on above- and belowground carbon dynamics in two tropical forests
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