Palladium-Catalyzed Asymmetric Hydrophosphination of Internal Alkynes: Highly Regio- and Stereoselective Construction of Axially Chiral Phosphines

Palladium-catalyzed unprecedented atroposelective hydrophosphination of internal alkynes has been realized using diarylphosphines, affording C-N axially chiral trisubstituted olefins (vinylphosphines) in excellent regioselectiviry, (E)-selectivity, and enantioselectivity. The axial chirality was established via integration of hydrophosphination and dynamic kinetic transformation of the alkynes, with both symmetrical and nonsymmetrical secondary phosphines being applicable. In the latter case, additional P-central chirality has been constructed in good diastereoselectivity.

Testing Compound Nucleus Hypothesis Across the 17O Nucleus Excitation

The excited compound nucleus 17O* has been studied over (n,α) and (α,n) cross sections modelling, respectively for 16O and 13C targets in their ground states. The modelling is fulfilled within the Reich-Moore formalism. We were able to calculate the (α,n) cross section by two separate ways: the direct kinematic standard route and by inversion of the (n,α) cross section using the compound nucleus hypothesis. Resonance parameters of the resolved resonance range (0 to 6 MeV) were borrowed from the CIELO project. In a first stage, the modelling is carried out in the referential of the incident particle (either way neutron or α) requesting conversion of the CIELO neutron-type resonance parameters to the α-type. In a second stage, the implementation is uniquely designed in the center of mass system of the excited compound nucleus. The resonance parameters are thus converted in that unique reference framework. The present investigation shows the consistency of the kinetic transformation that relies on the compound nucleus hypothesis.

Cellular Automaton Modeling of Dynamic Recrystallisation Microstructure Evolution for 316LN Stainless Steel

Based on the theoretical model and physical mechanism of dynamic recrystallization (DRX) in metal materials, the dislocation density change, nucleation and grain growth model during the process of DRX are taken into account. And according to the nucleation driven by dislocation and grain growth kinetic, transformation rules are made. A modeling methodology coupling fundamental metallurgical principles based on amended nucleation rate with the cellular automaton (CA) technique is here derived to simulate the 316LN.The two-dimensional CA model uses quadrilateral element and periodic boundary condition and Von-Neumann neighbor type. The influence of strain, strain rate and deformation temperature on dynamic recrystallization volume fraction and average grain size are analyzed on the basis of established CA model.

Heating rate dependence of anatase to rutile transformation

Commercial titania powders were calcined in order to investigate the influence of the heating history on the thermally stable phase (rutile). Temperatures from 620 to 700?C and heating rates from 50 to 300?C/h were used in order to evaluate their influence on the kinetics of transformation and microstructure evolution. The quantitative analysis of anatase-rutile mixtures based on X-ray diffraction intensities was performed. The results were plotted as cumulative transformation rate vs. cumulative coarsening rate in order to address the heating history of the anatase to rutile transformation. As the main result it was found that the amount of anatase transformed into rutile increases with increasing heating rate at fixed soaking time and temperature of calcination. Through linear extrapolation of experimental data obtained from the calcined commercial titania Degussa P25, it was found that 83 nm for the rutile crystallite size is the lowest limit needed for getting 100% of rutile powders. A substantial improvement in the anatase to rutile kinetic transformation was achieved after pressing the starting powders in order to exploit the interface nucleation.