Novel addition reactions of titanacycle phosphonates by tuning of Ti(O-i-Pr)4/2i-PrMgCl

Di- or tri-substituted vinylphosphonates, 2-5, can be obtained in a highly regio- and stereoselective manner from 1-alkynylphosphonates, by manipulation of Ti(O-i-Pr)4/2i-PrMgCl.     

Growth of Sr6Rh5O15 single crystals from high-temperature solutions: structure determination using the traditional 3-D and the 4-D superspace group methods and magnetic measurements on oriented single crystals

Single crystals of Sr6Rh5O15 were grown from a molten potassium carbonate flux. The structure was solved by both the traditional 3-D crystallographic approach and the 4-D superspace group approach using JANA2000. Both methods produced an equivalent structure determination, thereby confirming the 4-D superspace group approach as an effective structure solution method for 3-D commensurate composite structures. Sr6Rh5O15 corresponds to the n = 1, m = 1 member of the A3n+3mA'nB3m+nO9m+6n family of 2H hexagonal perovskite-related oxides. This compound is characterized by pseudo-one-dimensional polyhedral chains of four face-sharing RhO6 octahedra followed by one RhO6 trigonal prism. These chains in turn are separated by [Sr](infinity) chains. Magnetic measurements were carried out on oriented single crystals, and a very large magnetic anisotropy in the magnetic susceptibility was observed.     

On the stability of Langmuir films of pyramidic mesogens

Pyramidic mesogens forming thermotropic liquid crystal bulk phases were spread in an air-water interface. Pressure surface measurements and polarizing microscopy on the Langmuir films were used to characterize the various states of these pyramidic-like molecules. For two compounds bearing short lateral aliphatic chains, the surface pressure isotherms exhibit a large plateau region corresponding to a metastable monolayer in which the molecules may adopt an 'edge-on' arrangement. The coexistence of multilayered, anisotropic, slowly growing domains with the monolayer in the plateau region has been observed at long time scale. The film area relaxation kinetics at constant surface pressure show the existence of two nucleation mechanisms for the formation of these domains.     

Titanium-mediated addition of diallylsilanes to oxalyl chloride: formation of a diquinane

The titanium tetrachloride mediated reaction of the cis,cis-2,6-dimethyl-1,8-bis(trimethylsilyl)-2,6-octadiene with oxalyl chloride yielded 1-hydroxy-4-methyl-8-(1-propen-2-yl)bicyclo[3.3.0]oct-3-en-2-one of which the structure was confirmed by X-ray crystallographic analysis.     

A straightforward approach to N-substituted-2H-indazol-2-amines through reductive cyclization

A versatile two-step, one-pot reaction to access N-substituted-2H-indazol-2-amine derivatives has been elaborated. A diverse set of analogues was obtained by a sequential hydrazone formation and reductive cyclization in moderate to good yields from readily available starting materials. The strategy tolerates a broad range of substitutions pattern and functional groups allowing further derivatizations.     

Normal forms, stability and splitting of invariant manifolds I. Gevrey Hamiltonians

In this paper, we give a new construction of resonant normal forms with a small remainder for near-integrable Hamiltonians at a quasi-periodic frequency. The construction is based on the special case of a periodic frequency, a Diophantine result concerning the approximation of a vector by independent periodic vectors and a technique of composition of periodic averaging. It enables us to deal with non-analytic Hamiltonians, and in this first part we will focus on Gevrey Hamiltonians and derive normal forms with an exponentially small remainder. This extends a result which was known for analytic Hamiltonians, and only in the periodic case for Gevrey Hamiltonians. As applications, we obtain an exponentially large upper bound on the stability time for the evolution of the action variables and an exponentially small upper bound on the splitting of invariant manifolds for hyperbolic tori, generalizing corresponding results for analytic Hamiltonians.     

Numerical investigation of a broadband coherent supercontinuum generation in Ga8Sb32S60 chalcogenide photonic crystal fiber with all-normal dispersion

All normal dispersion (ANDi) and highly nonlinear chalcogenide glass photonic crystal fiber (PCF) is proposed and numerically investigated for a broad, coherent and ultra-flat mid-infrared supercontinuum generation. The proposed PCF consists of a solid core made of Ga₈Sb₃₂S₆₀ glass surrounded by seven rings of air holes arranged in a triangular lattice. We show by employing the finite difference frequency domain (FDFD) method that the Ga₈Sb₃₂S₆₀ PCF dispersion properties can be engineered by carefully adjusting the air holes diameter in the cladding region and ANDi regime is achieved over the entire range of wavelengths with a zero chromatic dispersion around 4.5?μm. Moreover, we demonstrate that injecting 50?fs width and 20?kW peak power laser pulses (corresponding to a pulse energy of 1.06?nJ) at a pump wavelength of 4.5?μm into a 1?cm long ANDi Ga₈Sb₃₂S₆₀ PCF generates a broad, flat-top and perfectly coherent SC spectrum extending from 1.65?μm to 9.24?μm at the 20?dB spectral flatness. These results make the proposed Ga₈Sb₃₂S₆₀ PCF an excellent candidate for various important mid-infrared region applications including mid-infrared spectroscopy, medical imaging, optical coherence tomography and materials characterization.