609 research outputs found
A Formalism for Scattering of Complex Composite Structures. 2 Distributed Reference Points
Recently we developed a formalism for the scattering from linear and acyclic
branched structures build of mutually non-interacting sub-units.{[}C. Svaneborg
and J. S. Pedersen, J. Chem. Phys. 136, 104105 (2012){]} We assumed each
sub-unit has reference points associated with it. These are well defined
positions where sub-units can be linked together. In the present paper, we
generalize the formalism to the case where each reference point can represent a
distribution of potential link positions. We also present a generalized
diagrammatic representation of the formalism. Scattering expressions required
to model rods, polymers, loops, flat circular disks, rigid spheres and
cylinders are derived. and we use them to illustrate the formalism by deriving
the generic scattering expression for micelles and bottle brush structures and
show how the scattering is affected by different choices of potential link
positions.Comment: Paper no. 2 of a serie
Diffraction limited optics for single atom manipulation
We present an optical system designed to capture and observe a single neutral
atom in an optical dipole trap, created by focussing a laser beam using a large
numerical aperture N.A.=0.5 aspheric lens. We experimentally evaluate the
performance of the optical system and show that it is diffraction limited over
a broad spectral range (~ 200 nm) with a large transverse field (+/- 25
microns). The optical tweezer created at the focal point of the lens is able to
trap single atoms of 87Rb and to detect them individually with a large
collection efficiency. We measure the oscillation frequency of the atom in the
dipole trap, and use this value as an independent determination of the waist of
the optical tweezer. Finally, we produce with the same lens two dipole traps
separated by 2.2 microns and show that the imaging system can resolve the two
atoms.Comment: 8 pages, 9 figures; typos corrected and references adde
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
New prenylated quinones from Peperomia galioides
Two new prenylated quinones, piperogalone and galopiperone, and a new prenylated dihydroquinone, hydropiperone, were isolated from #Peperomia galioides H.B.K (#Piperaceae). Hydropiperone exhibited potent antiparasitic activity against three species of #Leishmania$. (Résumé d'auteur
Experimental and modeling study of the autoignition of 1-hexene/iso-octane mixtures at low temperatures
Autoignition delay times have been measured in a rapid compression machine at
Lille at temperatures after compression from 630 to 840 K, pressures from 8 to
14 bar, \Phi = 1 and for a iso octane/1 hexene mixture containing 82%
iso-octane and 18% 1 hexene. Results have shown that this mixture is strongly
more reactive than pure iso-octane, but less reactive than pure 1 hexene. It
exhibits a classical low temperature behaviour, with the appearance of cool
flame and a negative temperature coefficient region. The composition of the
reactive mixture obtained after the cool flame has also been determined. A
detailed kinetic model has been obtained by using the system EXGAS, developed
in Nancy for the automatic generation of kinetic mechanisms, and an acceptable
agreement with the experimental results has been obtained both for autoignition
delay times and for the distribution of products. A flow rate analysis reveals
that the crossed reactions between species coming from both reactants (like
H-abstractions or combinations) are negligible in the main flow consumption of
the studied hydrocarbons. The ways of formation of the main primary products
observed and the most sensitive rate constants have been identified
Orchestrating Tuple-based Languages
The World Wide Web can be thought of as a global computing architecture supporting the deployment of distributed networked applications. Currently, such applications can be programmed by resorting mainly to two distinct paradigms: one devised for orchestrating distributed services, and the other designed for coordinating distributed (possibly mobile) agents. In this paper, the issue of designing a pro-
gramming language aiming at reconciling orchestration and coordination is investigated. Taking as starting point the orchestration calculus Orc and the tuple-based coordination language Klaim, a new formalism is introduced combining concepts and primitives of the original calculi.
To demonstrate feasibility and effectiveness of the proposed approach, a prototype implementation of the new formalism is described and it is then used to tackle a case study dealing with a simplified but realistic electronic marketplace, where a number of on-line stores allow client
applications to access information about their goods and to place orders
Intermittent dislocation flow in viscoplastic deformation
The viscoplastic deformation (creep) of crystalline materials under constant
stress involves the motion of a large number of interacting dislocations.
Analytical methods and sophisticated `dislocation-dynamics' simulations have
proved very effective in the study of dislocation patterning, and have led to
macroscopic constitutive laws of plastic deformation. Yet, a statistical
analysis of the dynamics of an assembly of interacting dislocations has not
hitherto been performed. Here we report acoustic emission measurements on
stressed ice single crystals, the results of which indicate that dislocations
move in a scale-free intermittent fashion. This result is confirmed by
numerical simulations of a model of interacting dislocations that successfully
reproduces the main features of the experiment. We find that dislocations
generate a slowly evolving configuration landscape which coexists with rapid
collective rearrangements. These rearrangements involve a comparatively small
fraction of the dislocations and lead to an intermittent behavior of the net
plastic response. This basic dynamical picture appears to be a generic feature
in the deformation of many other materials. Moreover, it should provide a
framework for discussing fundamental aspects of plasticity, that goes beyond
standard mean-field approaches that see plastic deformation as a smooth laminar
flow
In vitro and in vivo leishmanicidal studies of Peperomia galioides (Piperaceae)
Petroleum ether and methylene chloride extracts of #Peperomia galioides and three phenylated diphenols, grifolic acid, grifolin and piperogalin exhibited in vitro antileishmanial activity. During the course of infection of BALB/c mice with #Leishmania amazonensis, the treatments with each of these compounds did not influence the progression of the disease. (Résumé d'auteur
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