514 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
Anisotropy in Homogeneous Rotating Turbulence
The effective stress tensor of a homogeneous turbulent rotating fluid is
anisotropic. This leads us to consider the most general axisymmetric four-rank
``viscosity tensor'' for a Newtonian fluid and the new terms in the turbulent
effective force on large scales that arise from it, in addition to the
microscopic viscous force. Some of these terms involve couplings to vorticity
and others are angular momentum non conserving (in the rotating frame).
Furthermore, we explore the constraints on the response function and the
two-point velocity correlation due to axisymmetry. Finally, we compare our
viscosity tensor with other four-rank tensors defined in current approaches to
non-rotating anisotropic turbulence.Comment: 14 pages, RevTe
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
Quasi-static magnetohydrodynamic turbulence at high Reynolds number
We analyse the anisotropy of homogeneous turbulence in an electrically
conducting fluid submitted to a uniform magnetic field, for low magnetic
Reynolds number, in the quasi- static approximation. We interpret disagreeing
previous predictions between linearized theory and simulations: in the linear
limit, the kinetic energy of transverse velocity components, normal to the
magnetic field, decays faster than the kinetic energy of the axial component,
along the magnetic field (Moffatt (1967)); whereas many numerical studies
predict a final state characterised by dominant energy of transverse velocity
components. We investigate the corresponding nonlinear phenomenon using Direct
Numerical Simulations of freely-decaying turbulence, and a two-point
statistical spectral closure based on the Eddy Damped Quasi-Normal Markovian
model. The transition from the three-dimensional turbulent flow to a
"two-and-a-half-dimensional" flow (Montgomery & Turner (1982)) is a result of
the combined effects of short-time linear Joule dissipation and longer time
nonlinear creation of polarisation anisotropy. It is this combination of linear
and nonlinear effects which explains the disagreement between predictions from
linearized theory and results from numerical simulations. The transition is
characterized by the elongation of turbulent structures along the applied
magnetic field, and by the strong anisotropy of directional two-point
correlation spectra, in agreement with experimental evidence. Inertial
equatorial transfers in both DNS and the model are presented to describe in
detail the most important equilibrium dynamics. Spectral scalings are
maintained in high Reynolds number turbulence attainable only with the EDQNM
model, which also provides simplified modelling of the asymptotic state of
quasi-static MHD turbulence.Comment: Journal of Fluid Mechanics, 201
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
Identification and functional characterization of the pheromone biosynthesis activating neuropeptide receptor isoforms from Mamestra brassicae
Communication : 28th Conference of European Comparative Endocrinologists ; Organisme : European Society for Comparative Endocrinology (ESCE), Louvain, Belgique ; date de début de l'événement : 2016-08-21, date de fin de l'évenement : 2016-08-25International audienceIn most moth species, including Mamestra brassicae, pheromone biosynthesis activating neuropeptide (PBAN) regulates pheromone production. Generally, PBAN acts directly on the pheromone gland (PG) cells via its specific G protein-coupled receptor (i.e. PBANR) with Ca2+ as a second messenger. In this study, we identified cDNAs encoding three variants (A, B and C) of the M. brassicae PBANR (Mambr-PBANR). The full-length coding sequences were transiently expressed in cultured Trichoplusia ni cells and Sf9 cells for functional characterization. All three isoforms dose-dependently mobilized extracellular Ca2+ in response to PBAN analogs with Mambr-PBANR-C exhibiting the greatest sensitivity. Fluorescent confocal microscopy imaging studies demonstrated binding of a rhodamine red-labeled ligand (RR10CPBAN) to all three Mambr-PBANR isoforms. RR10CPBAN binding did not trigger ligand-induced internalization in cells expressing PBANR-A, but did in cells expressing the PBANR-B and-C isoforms. Furthermore, activation of the PBANR-B and-C isoforms with the 18 amino acid Mambr-pheromonotropin resulted in co-localization with a Drosophila melanogaster arrestin homolog (Kurtz), whereas stimulation with an unrelated peptide had no effect. PCR-based profiling of the three transcripts revealed a basal level of expression throughout development with a dramatic increase in PG transcripts from the day of adult emergence with PBANR-C being the most abundant
Interactions between Magnetic Nanowires and Living Cells : Uptake, Toxicity and Degradation
We report on the uptake, toxicity and degradation of magnetic nanowires by
NIH/3T3 mouse fibroblasts. Magnetic nanowires of diameters 200 nm and lengths
comprised between 1 {\mu}m and 40 {\mu}m are fabricated by controlled assembly
of iron oxide ({\gamma}-Fe2O3) nanoparticles. Using optical and electron
microscopy, we show that after 24 h incubation the wires are internalized by
the cells and located either in membrane-bound compartments or dispersed in the
cytosol. Using fluorescence microscopy, the membrane-bound compartments were
identified as late endosomal/lysosomal endosomes labeled with lysosomal
associated membrane protein (Lamp1). Toxicity assays evaluating the
mitochondrial activity, cell proliferation and production of reactive oxygen
species show that the wires do not display acute short-term (< 100 h) toxicity
towards the cells. Interestingly, the cells are able to degrade the wires and
to transform them into smaller aggregates, even in short time periods (days).
This degradation is likely to occur as a consequence of the internal structure
of the wires, which is that of a non-covalently bound aggregate. We anticipate
that this degradation should prevent long-term asbestos-like toxicity effects
related to high aspect ratio morphologies and that these wires represent a
promising class of nanomaterials for cell manipulation and microrheology.Comment: 21 pages 12 figure
Pheromone Binding to General Odorant-binding Proteins from the Navel Orangeworm
General odorant-binding proteins (GOBPs) of moths are postulated to be involved in the reception of semiochemicals other than sex pheromones, the so-called âgeneral odorants.â We have expressed two GOBPs, AtraGOBP1 and AtraGOBP2, which were previously isolated from the antennae of the navel orangeworm, Amyelois transitella. Surprisingly, these two proteins did not bind compounds that are known to attract adult moths, particularly females. The proper folding and functionality of the recombinant proteins was inferred from circular dichroism analysis and demonstration that both GOBPs bound nonanal in a pH-dependent manner. EAG experiments demonstrated that female attractants (1-phenylethanol, propionic acid phenyl ester, and isobutyric acid phenyl ester) are detected with high sensitivity by the antennae of day-0 to day-4 adult females, with response declining in older moths. The same age-dependence was shown for male antennae responding to constituents of the sex pheromone. Interestingly, AtraGOBP2 bound the major constituent of the sex pheromone, Z11Z13-16Ald, with affinity comparable to that shown by a pheromone-binding protein, AtraPBP1. The related alcohol bound to AtraPBP1 with higher affinity than to AtraGOBP2. AtraGOBP1 bound both ligands with low but nearly the same affinity
Modelling of friction stir welding of DH36 steel
A 3-D computational fluid dynamics (CFD) model
was developed to simulate the friction stir welding of 6-mm
plates of DH36 steel in an Eulerian steady-state framework.
The viscosity of steel plate was represented as a non-
Newtonian fluid using a flow stress function. The PCBN-WRe
hybrid tool was modelled in a fully sticking condition with the cooling system effectively represented as a negative heat flux. The model predicted the temperature distribution in the stirred zone (SZ) for six welding speeds including low, intermediate and
high welding speeds. The results showed higher asymmetry in
temperature for high welding speeds. Thermocouple data for the
high welding speed sample showed good agreement with the
CFD model result. The CFD model results were also validated
and compared against previous work carried out on the same
steel grade. The CFD model also predicted defects such as
wormholes and voids which occurred mainly on the advancing
side and are originated due to the local pressure distribution
between the advancing and retreating sides. These defects were
found to be mainly coming from the lack in material flow which
resulted from a stagnant zone formation especially at high tra-
verse speeds. Shear stress on the tool surface was found to in-
crease with increasing tool traverse speed. To produce a âsoundâ
weld, the model showed that the welding speed should remain
between 100 and 350 mm/min. Moreover, to prevent local melt-
ing, the maximum toolâs rotational speed should not exceed
550 RPM
- âŠ