Nanoporosity of fine-crystalline aluminum and an aluminum-based alloy

The presence of nanopores formed during the equal-channel angular pressing of aluminum is revealed using small-angle x-ray scattering. The parameters of nanopores are determined, and a correlation between the level of nanoporosity and the fraction of high-angle grain boundaries is found. The data obtained indicate that the level of nanoporosity can affect the tensile durability of fine-crystalline aluminum in the creep mode. The data on the regularities in the development of nanopores under deformation of the fine-crystalline aluminum-based alloy in the superplasticity mode are obtained.     

Nuclear quantum effects in calculated NMR shieldings of benzene; a Feynman path integral study

The Feynman path integral Monte Carlo approach has been coupled to the gauge including atomic orbital formalism in order to analyse the absolute magnetic shieldings of the benzene nuclei under the conditions of thermal equilibrium. The Hamiltonian employed in the derivation of ensemble averaged NMR quantities is of the Hartree-Fock type. The basis set used is of 6–31G quality. The spatial delocalization of the atoms leads to a deshielding of both types of benzene nuclei relative to the shieldings experienced at the minimum of the potential energy surface. This deshielding has to be traced back to bond length elongations in thermal equilibrium. The influence of the nuclear fluctuations on the NMR parameters of benzene is quantum driven up to temperatures of 400 K; classical fluctuations are of minor importance in this low-temperature window.     

Stereoselective formal [3 + 3] cycloaddition approach to cis-1-azadecalins and synthesis of (-)-4a,8a-diepi-pumiliotoxin C. evidence for the first highly stereoselective 6pi-electron electrocyclic ring closures of 1-azatrienes

Evidence is described here to support that a highly stereoselective 6pi-electron electrocyclic ring closure of 1-azatrienes is a key step in formal [3 + 3] cycloaddition or annulation reactions of chiral vinylogous amides with alpha,beta-unsaturated iminium salts. This would represent the first highly stereoselective 6pi-electron electrocyclic ring closure of 1-azatrienes. We have also unambiguously demonstrated that these specific ring closures are reversible, leading to the major diastereomer that is also thermodynamically more stable, and that a rotation preference likely also plays a role. A synthetic application is illustrated here to stereoselectively transform the resulting dihydropyridines to cis-1-azadecalins with unique anti relative stereochemistry at C2 and C2a, leading to synthesis of epi isomers of (-)-pumiliotoxin C.     

Defect structure and thermomechanical stability of nano- and microcrystalline titanium obtained by different methods of intense plastic deformation

Mechanical stability under prolonged loading and thermostability under annealing have been studied for nano- and microcrystalline titanium obtained by different methods of intense plastic deformation. The effect of nanoporosity and the fraction of high angle boundaries formed due to intense plastic deformation has been revealed and analyzed. It has been established that, depending on the loading or the annealing temperature, thermomechanical stability of titanium can be affected, apart from the above structural characteristics, by either twin grain boundaries or titanium-carbide disperse particles.