497 research outputs found
Chemical analysis and aqueous solution properties of Charged Amphiphilic Block Copolymers PBA-b-PAA synthesized by MADIX
We have linked the structural and dynamic properties in aqueous solution of
amphiphilic charged diblock copolymers poly(butyl acrylate)-b-poly(acrylic
acid), PBA-b-PAA, synthesized by controlled radical polymerization, with the
physico-chemical characteristics of the samples. Despite product imperfections,
the samples self-assemble in melt and aqueous solutions as predicted by
monodisperse microphase separation theory. However, the PBA core are abnormally
large; the swelling of PBA cores is not due to AA (the Flory parameter
chiPBA/PAA, determined at 0.25, means strong segregation), but to h-PBA
homopolymers (content determined by Liquid Chromatography at the Point of
Exclusion and Adsorption Transition LC-PEAT). Beside the dominant population of
micelles detected by scattering experiments, capillary electrophoresis CE
analysis permitted detection of two other populations, one of h-PAA, and the
other of free PBA-b-PAA chains, that have very short PBA blocks and never
self-assemble. Despite the presence of these free unimers, the self-assembly in
solution was found out of equilibrium: the aggregation state is history
dependant and no unimer exchange between micelles occurs over months
(time-evolution SANS). The high PBA/water interfacial tension, measured at 20
mN/m, prohibits unimer exchange between micelles. PBA-b-PAA solution systems
are neither at thermal equilibrium nor completely frozen systems: internal
fractionation of individual aggregates can occur.Comment: 32 pages, 16 figures and 4 tables submitted to Journal of Interface
and Colloidal Scienc
Can the jamming transition be described using equilibrium statistical mechanics?
When materials such as foams or emulsions are compressed, they display solid
behaviour above the so-called `jamming' transition. Because compression is done
out-of-equilibrium in the absence of thermal fluctuations, jamming appears as a
new kind of a nonequilibrium phase transition. In this proceeding paper, we
suggest that tools from equilibrium statistical mechanics can in fact be used
to describe many specific features of the jamming transition. Our strategy is
to introduce thermal fluctuations and use statistical mechanics to describe the
complex phase behaviour of systems of soft repulsive particles, before sending
temperature to zero at the end of the calculation. We show that currently
available implementations of standard tools such as integral equations,
mode-coupling theory, or replica calculations all break down at low temperature
and large density, but we suggest that new analytical schemes can be developed
to provide a fully microscopic, quantitative description of the jamming
transition.Comment: 8 pages, 6 figs. Talk presented at Statphys24 (July 2010, Cairns,
Australia
Reaction â¶Li(p, Îâșâș)â¶He At 1.04 GeV And The ÎâN Interaction
The reaction â¶Li(p, Îâșâș)â¶He has been studied at 1.04 GeV for transferred momenta ranging from 0.11 to 0.35 (GeV/c)2. An exponential decrease of the cross section is observed. A Glauber-type calculation is presented. The possibility of extracting information on Ï(ÎN) and α(ÎN) is discussed
La recherche expĂ©rimentale en aĂ©rodynamique Ă lâONERA â Lâexemple du buffet transsonique
International audienceThe paper reviews research conducted at ONERA over the last thirty years on the transonic buffet. We first present the transonic buffet phenomenon and we explain its importance for aeronautical applications. Then, a distinction is made between the 2D buffet produced by an airfoil and the 3D buffet that characterizes swept wings of finite span. The 2D buffet amounts to a pure oscillation of the shock phase-locked with the detachment and reattachment of the boundary layer downstream, whereas the 3D buffet takes the form of a pocket of broadband perturbations located in a limitedportion of the wing. We recall that these mechanisms were first studied in the 1980s through a series of tests conducted in the transonic wind tunnel ONERA T2 at Toulouse and in the large transonic wind tunnel ONERA S2Ma at Modane. Since this pioneering work, progress in the measurement techniques has led to the constitution of a comprehensive database of the 2D buffet that we describe. This database, obtained in the wind tunnel ONERA S3Ch at Meudon, has been extensively used to validate various CFD tools, with the latter being used in turn to investigate the buffet physics. We illustrate this collaboration between simulation and physics by recalling that a linear stability analysis of accurate Reynolds-Averaged-Navier-Stokes (RANS) solutions made it possible to prove that the buffet on a 2D airfoil stems from a global instability mechanism.We also review more recent tests done in the case of a laminar airfoil, which reveal very distinct behaviors of the buffet flow. This illustrates how sensitive the buffet is to the nature of the boundary layer. The last section of the paper gives a short overview of advanced simulations for these different test cases. In the conclusion, we list research perspectives, which include some more general topics such as data assimilation.L'article passe en revue les recherches menĂ©es Ă l'ONERA au cours des trente derniĂšres annĂ©es sur le buffet transsonique. Nous prĂ©sentons d'abord le phĂ©nomĂšne du buffet transsonique et nous expliquons son importance pour les applications aĂ©ronautiques. On distingue ensuite le buffet 2D produit par une aile bidimensionnelle et le buffet 3D qui caractĂ©rise les ailes en flĂšches dâenvergure finie. Le buffet 2D se prĂ©sente sous la forme dâune oscillation dâensemble de tout lâĂ©coulement couplant un dĂ©placement de lâonde de choc et le dĂ©collement de la couche limite en aval de ce choc. Le buffet 3D prend quant Ă lui la forme d'une poche de perturbations localisĂ©es dans une portion limitĂ©e de l'aile. Nous rappelons que ces mĂ©canismes ont d'abord Ă©tĂ© Ă©tudiĂ©s Ă lâONERA dans les annĂ©es 80 Ă travers une sĂ©rie de tests rĂ©alisĂ©s dans la soufflerie transsonique T2 Ă Toulouse et dans la grande soufflerie transsonique S2 de Modane. Ces travaux pionniers ont ensuite Ă©tĂ© approfondis dans la soufflerie S3Ch de Meudon de maniĂšre Ă Ă©laborer une base de donnĂ©es complĂšte du buffet 2D sur une aile 2D en rĂ©gime turbulent, que nous dĂ©crivons. Cette base de donnĂ©es a Ă©tĂ© utilisĂ©e de façon extensive, Ă lâONERA et dans dâautres institutions pour valider diffĂ©rents outils de simulation, ces derniers Ă©tant alors utilisĂ©s Ă leur tour pour Ă©tudier la physique du buffet. Nous illustrons cette collaboration entre la simulation et la physique en rappelant qu'une analyse de stabilitĂ© linĂ©aire de solutions prĂ©cises des Ă©quations de Navier-Stokes moyennĂ©es au sens de Reynolds (RANS) a permis de prouver que le buffet 2D provient d'un mĂ©canisme d'instabilitĂ© globale. Nous passons Ă©galement en revue des essais plus rĂ©cents rĂ©alisĂ©s dans la soufflerie S3Ch sur le cas d'une aile 2D laminaire qui rĂ©vĂšlent des comportements trĂšs distincts par rapport au cas turbulent. Cela illustre la sensibilitĂ© du buffet Ă la nature de la couche limite. Le dernier paragraphe du document donne un bref aperçu des simulations avancĂ©es de ces diffĂ©rents cas tests. Dans la conclusion, nous Ă©numĂ©rons les perspectives de recherche sur le sujet, qui incluent aussi des thĂ©matiques mĂ©thodologiques plus gĂ©nĂ©rales telles que l'assimilation de donnĂ©es
Phase Behavior of Polyelectrolyte Block Copolymers in Mixed Solvents
We have studied the phase behavior of the poly(n-butyl
acrylate)-b-poly(acrylic acid) block copolymer in a mixture of two miscible
solvents, water and tetrahydrofuran (THF). The techniques used to examine the
different polymers, structures and phases formed in mixed solvents were static
and dynamic light scattering, small-angle neutron scattering, nuclear magnetic
resonance and fluorescence microscopy. By lowering the water/THF mixing ratio
X, the sequence unimers, micron-sized droplets, polymeric micelles was
observed. The transition between unimers and the micron-sized droplets occurred
at X = 0.75, whereas the microstructuration into core-shell polymeric micelles
was effective below X = 0.4. At intermediate mixing ratios, a coexistence
between the micron-sized droplets and the polymeric micelles was observed.
Combining the different aforementioned techniques, it was concluded that the
droplet dispersion resulted from a solvent partitioning that was induced by the
hydrophobic blocks. Comparison of poly(n-butyl acrylate) homopolymers and
poly(n-butyl acrylate)-b-poly(acrylic acid) block copolymers suggested that the
droplets were rich in THF and concentrated in copolymers and that they were
stabilized by the hydrophilic poly(acrylic acid) moieties.Comment: 11 pages, 12 figures, to appear in Macromolecule
Microscopic theory of the jamming transition of harmonic spheres
We develop a microscopic theory to analyze the phase behaviour and compute
correlation functions of dense assemblies of soft repulsive particles both at
finite temperature, as in colloidal materials, and at vanishing temperature, a
situation relevant for granular materials and emulsions. We use a mean-field
statistical mechanical approach which combines elements of liquid state theory
to replica calculations to obtain quantitative predictions for the location of
phase boundaries, macroscopic thermodynamic properties and microstructure of
the system. We focus in particular on the derivation of scaling properties
emerging in the vicinity of the jamming transition occurring at large density
and zero temperature. The new predictions we obtain for pair correlation
functions near contact are tested using computer simulations. Our work also
clarifies the conceptual nature of the jamming transition, and its relation to
the phenomenon of the glass transition observed in atomic liquids.Comment: 31 pages, 18 figures; long version of arXiv:1011.563
NOVIWAM : Five European countries together for improving water quality and water use efficiency
The European NOVIWAM (NOvel Integrated Water Management Systems for Southern European Regions, www.noviwam.eu) program aims to promote interregional co-operation in the field of water management tools and methods. One of its originality is to analyze in depth the relations between decision makers, stakeholders and researchers in order to disseminate know-how and technologies, and to tackle the compelling water management problems faced in the Euro-Mediterranean climate regions. In a first period, aiming at a good ecological and chemical state of waters and at a sustainable and efficient resource management, five European countries/regions (Albania, Cyprus, Poitou-Charentes in France, Northern Region in Portugal and Andalusia in Spain) are working together. The program will thus contribute to the objectives of the European Water Framework Directive. But additionally, the NOVIWAM program will establish a schedule for the implementation of a « Join action plan », trying to involve other countries into it, and generalize the conclusions of this three year work at a regional and international level.NOVIWAM (Grant Agreement nÂș 245460
Computational Model of the Insect Pheromone Transduction Cascade
A biophysical model of receptor potential generation in the male moth olfactory receptor neuron is presented. It takes into account all pre-effector processesâthe translocation of pheromone molecules from air to sensillum lymph, their deactivation and interaction with the receptors, and the G-protein and effector enzyme activationâand focuses on the main post-effector processes. These processes involve the production and degradation of second messengers (IP3 and DAG), the opening and closing of a series of ionic channels (IP3-gated Ca2+ channel, DAG-gated cationic channel, Ca2+-gated Clâ channel, and Ca2+- and voltage-gated K+ channel), and Ca2+ extrusion mechanisms. The whole network is regulated by modulators (protein kinase C and Ca2+-calmodulin) that exert feedback inhibition on the effector and channels. The evolution in time of these linked chemical species and currents and the resulting membrane potentials in response to single pulse stimulation of various intensities were simulated. The unknown parameter values were fitted by comparison to the amplitude and temporal characteristics (rising and falling times) of the experimentally measured receptor potential at various pheromone doses. The model obtained captures the main features of the doseâresponse curves: the wide dynamic range of six decades with the same amplitudes as the experimental data, the short rising time, and the long falling time. It also reproduces the second messenger kinetics. It suggests that the two main types of depolarizing ionic channels play different roles at low and high pheromone concentrations; the DAG-gated cationic channel plays the major role for depolarization at low concentrations, and the Ca2+-gated Clâ channel plays the major role for depolarization at middle and high concentrations. Several testable predictions are proposed, and future developments are discussed
Genomic innovations, transcriptional plasticity and gene loss underlying the evolution and divergence of two highly polyphagous and invasive <i>Helicoverpa</i> pest species
BACKGROUND: Helicoverpa armigera and Helicoverpa zea are major caterpillar pests of Old and New World agriculture, respectively. Both, particularly H. armigera, are extremely polyphagous, and H. armigera has developed resistance to many insecticides. Here we use comparative genomics, transcriptomics and resequencing to elucidate the genetic basis for their properties as pests. RESULTS: We find that, prior to their divergence about 1.5 Mya, the H. armigera/H. zea lineage had accumulated up to more than 100 more members of specific detoxification and digestion gene families and more than 100 extra gustatory receptor genes, compared to other lepidopterans with narrower host ranges. The two genomes remain very similar in gene content and order, but H. armigera is more polymorphic overall, and H. zea has lost several detoxification genes, as well as about 50 gustatory receptor genes. It also lacks certain genes and alleles conferring insecticide resistance found in H. armigera. Non-synonymous sites in the expanded gene families above are rapidly diverging, both between paralogues and between orthologues in the two species. Whole genome transcriptomic analyses of H. armigera larvae show widely divergent responses to different host plants, including responses among many of the duplicated detoxification and digestion genes. CONCLUSIONS: The extreme polyphagy of the two heliothines is associated with extensive amplification and neofunctionalisation of genes involved in host finding and use, coupled with versatile transcriptional responses on different hosts. H. armigera's invasion of the Americas in recent years means that hybridisation could generate populations that are both locally adapted and insecticide resistant
- âŠ