Plastic response of a 2D Lennard-Jones amorphous solid: Detailed analysis of the local rearrangements at very slow strain rate

We analyze in detail the atomistic response of a model amorphous material submitted to plastic shear in the athermal, quasi-static limit. After a linear stress-strain behavior, the system undergoes a noisy plastic flow. We show that the plastic flow is spatially heterogeneous. Two kinds of plastic events occur in the system: quadrupolar localized rearrangements, and shear bands. The analysis of the individual motion of a particle shows also two regimes: a hyper-diffusive regime followed by a diffusive regime, even at zero temperature.     

Approximations rationnelles des valeurs de la fonction Gamma aux rationnels

As a corollary of a more general result, we present new rational approximations un/vn to the value of the Gamma function at a given rational point, where un and vn are solutions of a linear recurrence of order 3 with polynomials coefficients.     

Analyse du codage de l'information en tomographie longitudinale a haute resolution

Using a 3-D Fourier analysis, we investigate the nature of the informations contained in the high resolution motion pinhole recordings. We show that these images can be interpreted as parallel projections of a distorted 3-D emitting object. Thus, the use of the 3-D central slice theorem and the circular motion of the pinhole show that a 3-D Fourier region remains unexplored. Such a fact leads to a notable degradation of objects containing only very low spatial frequencies. But, in other cases, this degradation is generally less important (heart imaging for instance) and the improvement in resolution of this method proves to be appreciable when analysing local defects of fixation in nuclear medicine.     

High-speed roll coating with complex rheology fluids

The flow of high solids content suspensions and coating colors through the deformable gap of counter-rotating rolls at high speed was investigated. Measurements of nip pressure profiles in a laboratory film coater were conducted and flow visualization experiments downstream the nip were carried out. A high-speed video system allowed showing the formation, elongation and break up of filaments that yield the misting droplets. The role of rheology on misting was also investigated using shear and extensional data. Results show that misting, mainly generated by film splitting, is reduced when the extensional viscosity of the color is larger.     

A three-dimensional fictitious domain method for incompressible fluid flow problems

A new Galerkin finite element method for the solution of the Navier–Stokes equations in enclosures containing internal parts which may be moving is presented. Dubbed the virtual finite element method, it is based upon optimization techniques and belongs to the class of fictitious domain methods. Only one volumetric mesh representing the enclosure without its internal parts needs to be generated. These are rather discretized using control points on which kinematic constraints are enforced and introduced into the mathematical formulation by means of Lagrange multipliers. Consequently, the meshing of the computational domain is much easier than with classical finite element approaches. First, the methodology will be presented in detail. It will then be validated in the case of the two-dimensional Couette cylinder problem for which an analytical solution is available. Finally, the three-dimensional fluid flow inside a mechanically agitated vessel will be investigated. The accuracy of the numerical results will be assessed through a comparison with experimental data and results obtained with a standard finite element method. © 1997 John Wiley & Sons, Ltd.     

Synthesis of novel graft polyhydroxyalkanoates

Graft copolymers were synthesized by direct condensation of methoxy-poly(ethylene glycol) (MePEG) or methoxy-poly(lactic acid) (MePLA) onto a reactive polyhydroxyalkanoate (PHA) backbone in organic solvent. Side carboxylic groups of the PHA were coupled with end hydroxyl groups of MePEG or MePLA in the presence of N,N′-dicylohexylcarbodiimide (DCC). Graft copolymers were characterized by ¹H NMR spectroscopy and size exclusion chromatography (SEC). NMR spectra of PHA-g-PEG and PHA-g-PLA showed the presence of significant amounts of PEG and PLA, respectively. No noticeable unreacted PEG or PLA were detected in SEC chromatograms. Grafting of hydrophilic polymers chains as PEG or biodegradable oligomers as PLA onto PHA backbone will generate polyesters with a more rapid water uptake and faster biodegradation rates. These PHA polymers conjugates could be interesting for bioactive agent delivery systems.     

Completely superhydrophobic PDMS surfaces for microfluidics

This study presents a straightforward two-step fabrication process of durable, completely superhydrophobic microchannels in PDMS. First, a composite material of PDMS/PTFE particles is prepared and used to replicate a master microstructure. Superhydrophobic surfaces are formed by subsequent plasma treatment, in which the PDMS is isotropically etched and PTFE particles are excavated. We compare the advancing and receding contact angles of intrinsic PDMS samples and composite PTFE/PDMS samples (1 wt %, 8 wt %, and 15 wt % PTFE particle concentration) and demonstrate that both the horizontal and vertical surfaces are indeed superhydrophobic. The best superhydrophobicity is observed for samples with a PTFE particle concentration of 15 wt %, which have advancing and receding contact angles of 159° ± 4° and 158° ± 3°, respectively.     

Cell–cell interactions via non-covalent click chemistry

Metabolic glycoengineering with unnatural sugars became a valuable tool for introducing recognition markers on the cell membranes via bioorthogonal chemistry. By using this strategy, we functionalized the surface of tumor and T cells using complementary artificial markers based on both β-cyclodextrins (β-CDs) and adamantyl trimers, respectively. Once tied on cell surfaces, the artificial markers induced cell–cell adhesion through non-covalent click chemistry. These unnatural interactions between A459 lung tumor cells and Jurkat T cells triggered the activation of natural killer (NK) cells thanks to the increased production of interleukin-2 (IL-2) in the vicinity of cancer cells, leading ultimately to their cytolysis. The ready-to-use surface markers designed in this study can be easily inserted on the membrane of a wide range of cells previously submitted to metabolic glycoengineering, thereby offering a simple way to investigate and manipulate intercellular interactions.

We designed complementary artificial markers that were introduced on the surface of cells previously modified by metabolic glycoengineering. These recognition markers enable unnatural cell–cell adhesion through non-covalent click chemistry.