Fast electro-optical mode in photo-aligned reflective deformed helix ferroelectric liquid crystal cells

The electro-optical behavior of deformed helix ferroelectric liquid crystal in reflective mode is described in this paper. The electrically controlled reflectance has been measured at subkilohertz driving voltage frequency for different polarizations of the incident light and compared quite successfully with the simulation results.     

Suppression of parasitic lasing in high energy, high repetition rate Ti:sapphire laser amplifiers

Transverse parasitic lasing is well known for limiting the signal gain and the pulse energy that can be extracted from Ti:sapphire petawatt amplifiers. We have developed a technique for suppressing these parasitic lasing modes based on perfect refractive index-matching liquid doped with a broad-bandwidth absorber to suppress the transverse lasing while ensuring proper heat removal from the Ti:sapphire crystal. The 800 nm laser output with a bandwidth of 41 nm (FWHM) and peak energy of 22.7 J at a repetition rate of 1 Hz is demonstrated.     

Drug recrystallization using supercritical anti-solvent (SAS) process with impinging jets: Effect of process parameters

The aim of this study is to improve mixing in supercritical anti-solvent process (SAS) with impinging jets in order to form finer particles of sulfathiazole, a poorly water-soluble drug. The influence of several process parameters upon the powder characteristics is studied. Parameters are jets' velocity (0.25 m s^?1 to 25.92 m s^?1), molar ratio solvent/CO₂ (2.5% to 20%), temperature (313 K to 343 K), pressure (10 MPa to 20 MPa) and sulfathiazole concentration in the organic solution (0.5% to 1.8%). Two solvents are used: acetone and methanol. Smaller particles with a more homogeneous morphology are obtained from acetone solutions. For the smallest jets' velocity, corresponding to a non-atomized jet, the stable polymorphic form is obtained, pure or in mixture. At this velocity, pressure is the most influential parameter controlling the polymorphic nature of the powder formed. The pure stable polymorph is formed at 20 MPa. Concerning the particle size, the most influential parameters are temperature and sulfathiazole concentration.The use of impinging jets with different process parameters allows the crystallization of four polymorphs among the five known, and particle sizes are varied. This work demonstrates the studied device ability of the polymorph and the size control. A comparison with the classical SAS process shows that particle size, size distribution and morphology of particles crystallized with impinging jets are different from the ones obtained with classical SAS introduction device in similar operating conditions. Mean particle sizes are significantly smaller and size distributions are narrower with impinging jets device.     

Hamiltonian group actions on symplectic Deligne–Mumford stacks and toric orbifolds

We develop differential and symplectic geometry of differentiable Deligne–Mumford stacks (orbifolds) including Hamiltonian group actions and symplectic reduction. As an application we construct new examples of symplectic toric DM stacks.     

Lower compactness estimates for scalar balance laws

In this paper, we study the compactness in L of the semigroup (St)_t≥0 of entropy weak solutions to strictly convex scalar conservation laws in one space dimension. The compactness of St for each t > 0 was established by P. D. Lax. Upper estimates for the Kolmogorov e‐entropy of the image of bounded sets in L¹ n L^∞ through S_t were given by C. De Lellis and F. Golse. Here we provide lower estimates on this e‐entropy of the same order as the one established by De Lellis and Golse, thus showing that such an e‐entropy is of size ≈ 1/ε. Moreover, we extend these estimates of compactness to the case of convex balance laws. © 2012 Wiley Periodicals, Inc.     

The congruence subgroup problem for branch groups

We state and study the congruence subgroup problem for groups acting on rooted trees, and for branch groups in particular. The problem is reduced to the computation of the congruence kernel, which we split into two parts: the branch kernel and the rigid kernel. In the case of regular branch groups, we prove that the first one is abelian while the second has finite exponent. We also establish some rigidity results concerning these kernels.     

Engineered 3D microporous gelatin scaffolds to study cell migration

Here we present a facile method to fabricate microporous hydrogel scaffolds that can be functionalized with a chemokine gradient. These scaffolds allow studying cellular responses in a 3D environment.     

Influence of the heat treatment conditions on the formation of CuFe2O4 from mechanical milled precursors oxides

Stoichiometric mixture of CuO and ??-Fe₂O₃ milled in air up to 30?h was subjected to different heat treatments. The evolution of the heat treated milled powders was investigated by X-ray diffraction (XRD). The CuFe₂O₄ was partially obtained by milling, the material consisting in a mixture of phases. By applying different heat treatments in air and in vacuum, for 2?C6?h, in 500?C800?°C temperature range the phases composition of the milled samples is changed. A heat treatment at 500?°C in vacuum favours the formation of delafossite (CuFeO₂) and tenorite (CuO) phases. If the same heat treatment is made in air, the CuFe₂O₄ phase formation with a cubic structure is favoured. Differential scanning calorimetry (DSC) investigation realised in Ar atmosphere revealed two large exothermic peaks. The first one is associated with the formation of the delafossite and tenorite phases and the second one with the formation of CuFe₂O₄. The XRD patterns of the samples subjected to the DSC measurements present maxima corresponding to the delafossite and cuprospinel (CuFe₂O₄) phases. For the heat treatment at 600?°C in air the phases present in the sample are the same as for the annealing performed at 500?°C: CuFe₂O₄, ??-Fe₂O₃ and CuO. The heat treatment in air at 800?°C leads to the complete reaction between the different phases and the formation of CuFe₂O₄ phase in whole the sample volume. The CuFe₂O₄ ferrite crystallises after this heat treatment in two crystal systems: cubic and tetragonal.