Spontaneous coherent phase transition of polaritons in CdTe microcavities

We report on evidence for polariton condensation out of a reservoir of incoherent polaritons. Polariton population and first-order coherence are investigated by spectroscopic imaging of the far-field emission of a CdTe-based microcavity under nonresonant pumping. With increasing pumping power, stimulated emission with thresholdlike behavior and spectral narrowing is observed in the strong exciton-photon coupling regime. We show that it comes from a narrow ring in k space, exhibiting enhanced spatial and angular coherence at the stimulation onset.     

Modeling the electric field third-order nonlinear responses of an infinite aggregate of hexatriene chains using the electrostatic interaction model

A classical electrostatic polarization scheme using the additive distribution procedure has been applied to determine the static longitudinal polarizability and second hyperpolarizability of a all-trans hexatriene molecule in an infinite stretched fiber. The parameters have been derived from ab initio coupled-perturbed Hartree-Fock calculations and the electrostatic scheme has been validated via comparison with ab initio results on small clusters. Upon packing, the polarizability of all-trans hexatriene increases by 7% whereas the second hyperpolarizability increases by as much as 61%. These increases result from the balance between the enhancement of the (hyper)polarizability due to collinear packing and the reduction associated with lateral packing.     

Investigation of a new thermosensitive block copolymer micelle: hydrolysis, disruption, and release

Thermosensitive polymer micelles are generally obtained with block copolymers in which one block exhibits a lower critical solution temperature in aqueous solution. We investigate a different design that is based on the use of one block bearing a thermally labile side group, whose hydrolysis upon heating shifts the hydrophilic-hydrophobic balance toward the destabilization of block copolymer micelles. Atom transfer radical polymerization was utilized to synthesize a series of diblock copolymers composed of hydrophilic poly(ethylene oxide) (PEO) and hydrophobic poly(2-tetrahydropyranyl methacrylate) (PTHPMA). We show that micelles of PEO-b-PTHPMA in aqueous solution can be destabilized as a result of the thermosensitive hydrolytic cleavage of tetrahydropyranyl (THP) groups that transforms PTHPMA into hydrophilic poly(methacrylic acid). The three related processes occurring in aqueous solution, namely, hydrolytic cleavage of THP, destabilization of micelles, and release of loaded Nile Red (NR), were investigated simultaneously using 1H NMR, dynamic light scattering, and fluorescence spectroscopy, respectively. At 80 degrees C, the results suggest that the three events proceed with a similar kinetics. Although slower than at elevated temperatures, the disruption of PEO-b-PTHPMA micelles can take place at the body temperature (approximately 37 degrees C), and the release kinetics of NR can be adjusted by changing the relative lengths of the two blocks or the pH of the solution.     

On the automorphism group of the asymptotic pants complex of an infinite surface of genus zero

The braided Thompson group is an asymptotic mapping class group of a sphere punctured along the standard Cantor set, endowed with a rigid structure. Inspired from the case of finite type surfaces we consider a Hatcher–Thurston cell complex whose vertices are asymptotically trivial pants decompositions. We prove that the automorphism group of this complex is also an asymptotic mapping class group in a weaker sense. Moreover is obtained by by first adding new elements called half‐twists and further completing it.     

Copper‐Catalyzed Oxidation of Alkanes with H2O2 under a Fenton‐like Regime

Copper complexes bearing readily available ligand systems catalyzed the oxidation of alkanes with H₂O₂ as the oxidant with high efficiency in remarkable yields (50–60 %). The reactions proceeded with unprecedented selectivity to give alkyl hydroperoxides as the major products. Detailed scrutiny of the reaction mechanism suggests the involvement of C‐centered and O‐centered radicals generated in a Fenton‐like fashion.     

Catalytic Enantioselective [10+4] Cycloadditions

The first peri‐ and stereoselective [10+4] cycloaddition between catalytically generated amino isobenzofulvenes and electron‐deficient dienes is described. The highly stereoselective catalytic [10+4] cycloaddition exhibits a broad scope with high yields, reflecting a robust higher‐order cycloaddition. Experimental and computational investigations support a kinetic distribution of intermediate rotamers dictating the enantioselectivity, which relies heavily on additive effects.     

N-particles Approximation of the Vlasov Equations with Singular Potential

We prove the convergence in any time interval of a point-particle approximation of the Vlasov equation by particles initially equally separated for a force in 1/|x|^α, with . We introduce discrete versions of the L ^∞ norm and time averages of the force-field. The core of the proof is to show that these quantities are bounded and that consequently the minimal distance between particles in the phase space is bounded from below.     

Acido-triggered nonlinear optical switches: benzazolo-oxazolidines

This work is the continuation of our previous experimental and theoretical studies aiming at designing efficient nonlinear optical (NLO) switches derived from the benzazolo-oxazolidine core. Here, we report the synthesis and the characterization of the linear and nonlinear optical properties of benzothiazolo[2,3-b]oxazolidine acidochromes by means of hyper-Rayleigh scattering as well as quantum chemical calculations. It is shown that these new derivatives incorporating a benzothiazole subunit exhibit very high static first hyperpolarizability values in their acido-generated form. On the basis of previously reported NLO responses of indolino- and benzimidazolo-oxazolidines, structure-properties relationships within the benzazolo-oxazolidine series are proposed.