2,160 research outputs found
Four wave mixing oscillation in a semiconductor microcavity: Generation of two correlated polariton populations
We demonstrate a novel kind of polariton four wave mixing oscillation. Two
pump polaritons scatter towards final states that emit two beams of equal
intensity, separated both spatially and in polarization with respect to the
pumps. The measurement of the intensity fluctuations of the emitted light
demonstrates that the final states are strongly correlated.Comment: 5 pages, 5 figures In this strongly revised version several new
experimental data are adde
Proton-electron mass ratio from HD revisited
We present a new derivation of the proton-electron mass ratio from the
hydrogen molecular ion, HD. The derivation entails the adjustment of the
mass ratio in highly precise theory so as to reproduce accurately measured
ro-vibrational frequencies. This work is motivated by recent improvements of
the theory, as well as the more accurate value of the electron mass in the
recently published CODATA-14 set of fundamental constants, which justifies
using it as input data in the adjustment, rather than the proton mass value as
done in previous works. This leads to significantly different sensitivity
coefficients and, consequently, a different value and larger uncertainty margin
of the proton-electron mass ratio as obtained from HD
Evaluation of binomial double sums involving absolute values
We show that double sums of the form can always be
expressed in terms of a linear combination of just four functions, namely
, , , and , with
coefficients that are rational in . We provide two different proofs: one is
algorithmic and uses the second author's computer algebra package Sigma; the
second is based on complex contour integrals. In many instances, these results
are extended to double sums of the above form where is
replaced by with independent parameter .Comment: AmS-LaTeX, 42 pages; substantial revision: several additional and
more general results, see Proposition 11 and Theorems 15-1
Creep feeding studies with lambs
This bulletin is a report on Department of Animal Husbandry Research Project 142, 'Method of Lamb Production'--P. [2].Digitized 2007 AES.Includes bibliographical references (page 16)
Static Safety for an Actor Dedicated Process Calculus by Abstract Interpretation
The actor model eases the definition of concurrent programs with non uniform
behaviors. Static analysis of such a model was previously done in a data-flow
oriented way, with type systems. This approach was based on constraint set
resolution and was not able to deal with precise properties for communications
of behaviors. We present here a new approach, control-flow oriented, based on
the abstract interpretation framework, able to deal with communication of
behaviors. Within our new analyses, we are able to verify most of the previous
properties we observed as well as new ones, principally based on occurrence
counting
A bone grease processing station at the Mitchell Prehistoric Indian Village: archaeological evidence for the exploitation of bone fats
© Association for Environmental Archaeology 2015. Author's accepted manuscript version deposited in accordance with SHERPA RoMEO guidelines. The definitive version is available at http://www.maneyonline.com/doi/abs/10.1179/1749631414Y.0000000035.Recent excavations at the Mitchell Prehistoric Indian Village, an Initial Middle Missouri site in Mitchell, South Dakota have revealed a large, clay-lined feature filled with fractured and fragmented bison bones. Fracture and fragmentation analysis, along with taphonomic evidence, suggests that the bones preserved within the feature represent evidence of prehistoric bone marrow and bone grease exploitation. Further, the character of the feature suggests that it served as a bone grease processing station. Bone fat exploitation is an activity that is frequently cited as a causal explanation for the nature of many fractured and fragmented bone assemblages in prehistory, and zooarchaeological assemblages have frequently been studied as evidence of bone fat exploitation. The Mitchell example provides some of the first direct, in-situ archaeological evidence of a bone grease processing feature, and this interpretation is sustained by substantial analytical evidence suggesting bone fat exploitation. This new evidence provides a clearer concept of the nature of bone fat exploitation in prehistory as well as an indication of the scale and degree to which bone grease exploitation occurred at the Mitchell site. Finally, this research demonstrates the importance of careful zooarchaeological and taphonomic analysis for the interpretation of both artifactual remains as well as archaeological features
Fish assemblage change following the structural restoration of a degraded stream
Decades of anthropogenic pressure have harmed riverscapes throughout North America by degrading habitats and water quality and can result in the extirpation of sensitive aquatic taxa. Local stream restoration projects have increased in frequency, but monitoring is still infrequent. In 2010, Kickapoo Creek in East Central Illinois was subjected to a stream restoration project that included implementation of artificial riffles, riprap, scouring keys, and riparian vegetation. We monitored the restoration efforts for 6years after the restoration through annual sampling efforts at restored and reference sites to determine changes in habitat and fish assemblage using standard habitat sampling and electrofishing techniques. We observed distinct temporal and spatial shifts in physico-chemical parameters along with changes in fish community structure. Although biotic integrity remained moderately low in reference assemblages, restored reaches showed 3-year delay in response to restoration, with biotic integrity positively linked to additional instream habitat and altered channel morphology. Larger substrate sizes, submerged terrestrial vegetation, and newly formed scour pools along with reduced siltation were found in the restored sites, in contrast to the reference sites. These changes resulted in increased species diversity, reduced number of opportunistic species and consequently an overall increase in health of fish communities. We also observed recruitment of habitat specialists and increase in species with reproductive strategies that rely on complex substrates. The results of this study highlight some of the complex dynamics driving reach-scale restoration projects. We demonstrate the usefulness of structural restoration as a management tool to increase biotic integrity through long-term alteration of critical habitat. The delay in the response of species to the restoration efforts emphasizes the need for long-term continuous temporal and spatial monitoring
Simulations of energetic beam deposition: from picoseconds to seconds
We present a new method for simulating crystal growth by energetic beam
deposition. The method combines a Kinetic Monte-Carlo simulation for the
thermal surface diffusion with a small scale molecular dynamics simulation of
every single deposition event. We have implemented the method using the
effective medium theory as a model potential for the atomic interactions, and
present simulations for Ag/Ag(111) and Pt/Pt(111) for incoming energies up to
35 eV. The method is capable of following the growth of several monolayers at
realistic growth rates of 1 monolayer per second, correctly accounting for both
energy-induced atomic mobility and thermal surface diffusion. We find that the
energy influences island and step densities and can induce layer-by-layer
growth. We find an optimal energy for layer-by-layer growth (25 eV for Ag),
which correlates with where the net impact-induced downward interlayer
transport is at a maximum. A high step density is needed for energy induced
layer-by-layer growth, hence the effect dies away at increased temperatures,
where thermal surface diffusion reduces the step density. As part of the
development of the method, we present molecular dynamics simulations of single
atom-surface collisions on flat parts of the surface and near straight steps,
we identify microscopic mechanisms by which the energy influences the growth,
and we discuss the nature of the energy-induced atomic mobility
Simplifying Multiple Sums in Difference Fields
In this survey article we present difference field algorithms for symbolic
summation. Special emphasize is put on new aspects in how the summation
problems are rephrased in terms of difference fields, how the problems are
solved there, and how the derived results in the given difference field can be
reinterpreted as solutions of the input problem. The algorithms are illustrated
with the Mathematica package \SigmaP\ by discovering and proving new harmonic
number identities extending those from (Paule and Schneider, 2003). In
addition, the newly developed package \texttt{EvaluateMultiSums} is introduced
that combines the presented tools. In this way, large scale summation problems
for the evaluation of Feynman diagrams in QCD (Quantum ChromoDynamics) can be
solved completely automatically.Comment: Uses svmult.cls, to appear as contribution in the book "Computer
Algebra in Quantum Field Theory: Integration, Summation and Special
Functions" (www.Springer.com
POOL development status and production experience
The pool of persistent objects for LHC (POOL) project, part of the large Hadron collider (LHC) computing grid (LCG), is now entering its third year of active development. POOL provides the baseline persistency framework for three LHC experiments. It is based on a strict component model, insulating experiment software from a variety of storage technologies. This paper gives a brief overview of the POOL architecture, its main design principles and the experience gained with integration into LHC experiment frameworks. It also presents recent developments in the POOL works areas of relational database abstraction and object storage into relational database management systems (RDBMS) systems
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