Immersion of Kähler manifolds in the class of convex submanifolds

It is proved that a real complete convex Kähler submanifold in Euclidean space splits as a metric product of two-dimensional surfaces of positive Gaussian curvature in Euclidean 3-space and a Euclidean subspace. A theorem of V. K. Beloshapka and S. N. Bychkov is generalized to the case of convex submanifolds of any codimension.     

Nanoscale yttrium distribution in yttrium-doped ceria powder

The microstructure and geometry of yttrium-doped ceria particles, synthesized by spray pyrolysis (SP), were characterized by transmission electron microscopy, and the distribution of yttrium was investigated by energy-dispersive X-ray spectroscopy (EDX). The yttrium distribution was investigated by considering an electron interaction volume and geometry of the particle in an EDX profile analysis. Two models, linear and non-linear, for the yttrium concentration gradient were tested against the experimental EDX data for hollow particles. The results showed that the linear concentration distribution of yttrium fits the EDX profiles appreciably better than the non-linear concentration gradient model. This suggests that yttrium distribution is mainly controlled by the different diffusion rates of the precursors from the centre to the surface of the particle, which could be related to their different solubilities, during the heating process in SP.     

Palladium‐Catalyzed Amination of 3,5‐Dihalopyridines – a Convenient Route to New Polyazamacrocycles

Pd‐Catalyzed amination of 3,5‐dibromo‐ and 3,5‐dichloropyridine ( 1a and 1b , resp.) with linear polyamines 2 leads to the formation of a new family of pyridine‐containing macrocycles 3 with an ‘exo’‐oriented pyridine N‐atom (Schemes 1 and 2). The dependence of the macrocycle yield on the nature of the halogen atom, the length of the polyamine chain and C/N atom ratio, and the composition of the catalytic system is studied. The synthesis of mono‐ and bis(5‐halopyridin‐3‐yl)‐substituted polyamines 4, 5, 8, 9 , and of 3,5‐bis(polyamino)‐substituted pyridines 6 is described (Schemes 3 and 4), and the use of these compounds as intermediates on the way to the macrocycles 7, 16 , and 18 with larger cavity (‘cyclodimers’ and ‘cyclotrimers’) is demonstrated (Schemes 5–10).     

Aminopyridines as amino components in the catalytic synthesis of α-aminophosphonates

6h-Aminophosphonates containing alicyclic, aromatic, and heterocyclic fragments were obtained in high yields by the Kabachnick—Fields reaction of the corresponding carbonyl compounds with 2-, 3- and 4-aminopyridines and diethyl phosphite using tetra- tert-butyl- phthalocyanine aluminum chloride as the catalyst. 2-, 3-, 4-Aminopyridines were found to vary in their reactivity with ketones and diethyl phosphite in the catalytic three-component one-pot process.     

Molecular structures of arachno-decaborane derivatives 6,9-X2B8H10 (X = CH2, NH, Se) including a gas-phase electron-diffraction study of 6,9-C2B8H14

The molecular structures of the three heterodecaboranes arachno-6,9-C2B8H14, arachno-6,9-N2B8H12, and arachno-6,9-Se2B8H10 have been determined by ab initio MO theory. In addition, the structure of arachno-6,9-C2B8H14 was experimentally determined using gas-phase electron diffraction (GED). The accuracy of all four of these structures has been confirmed by the good agreement of the (11)B chemical shifts calculated at the GIAO-MP2 level with the experimental values. A comparison of the GIAO-HF and GIAO-MP2 methods shows that for these heteroborane clusters, electron correlation effects on the computed delta((11)B) values are quite substantial and that it is necessary to go beyond the HF level in the NMR computation.     

EIT Ground State Cooling Scheme of <Superscript>171</Superscript>Yb<Superscript>+</Superscript> Based on the <Superscript>2</Superscript>S<Subscript>1/2</Subscript>→<Superscript>2</Superscript>P<Subscript>1/2</Subscript> Cooling Transition

We propose a method for EIT ground state cooling of ¹⁷¹Yb+ ion, which involves three light fields with detuning on a MHz scale. The steady-state mean vibrational quantum number is calculated to be less than 0.005. Efficient cooling is achievable in a motional-mode frequency range of 2π · (1.5 ± 0.5 MHz).     

A concerted rational crystallization/amorphization mechanism of Ge2Sb2Te5

Reverse Monte Carlo refinements using electron diffraction data and density functional theory calculations of the local atomic structure of amorphous Ge₂Sb₂Te₅ confirm presence of a noticeable number of four-membered rings with the general Ge(Sb)TeGe(Sb)Te composition similar to the building blocks of its cubic crystalline phase. The persistence of these rings, as well as the presence of the medium range order at the scale of about 1 nm, suggests that the amorphization/crystallization transition in Ge₂Sb₂Te₅ can be modelled with a concerted rotation of the sheets of atom-squares in {1 0 0} faces of cubic subcells of the cubic crystalline phase, similar to Rubik’s cube rotation. This mechanism can produce large models of material that agree with a range of the previous experimental and theoretical studies and also with the experimental electron diffraction data.     

Spin-dependent electron transport in manganite bicrystal junctions

Magnetic bicrystal films and junctions of magnetic La_0.67Sr_0.33MnO₃ (LSMO) and La_0.67Ca_0.33MnO₃ (LCMO) films epitaxially grown on NdGaO₃ substrates with the (110) planes of their two parts misoriented (tilted) at angles of 12°, 22°, 28°, and 38° are investigated. For comparison, bicrystal boundaries with a 90° misorientation of the axes of the NdGaO₃ (110) planes were fabricated. The directions of the axes and the magnetic anisotropy constants of the films on both sides of the boundary are determined by two independent techniques of magnetic resonance spectroscopy. The magnetic misorientation of the axes in the substrate plane has been found to be much smaller than the crystallographic misorientation for tilted bicrystal boundaries, while the crystallographic and magnetic misorientation angles coincide for boundaries with rotation of the axes. An increase in the magnetoresistance and characteristic resistance of bicrystal junctions with increasing misorientation angle was observed experimentally. The magnetoresistance of bicrystal junctions has been calculated by taking into account the uniaxial anisotropy, which has allowed the contributions from the tunneling and anisotropic magnetoresistances to be separated. The largest tunneling magnetoresistance was observed on LCMO bicrystal junctions, in which the characteristic resistance of the boundary is higher than that in LSMO boundaries.     

Properties and structure of oxidized coatings deposited onto Al-Cu and Al-Mg alloys

The results of new studies of creating protective oxide coatings based on Al₂O₃ (Si, Mn) and deposited onto aluminum alloys using electrolyte-plasma oxidation are presented. An analysis is performed by scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), X-ray diffraction, Rutherford backscattering of ⁴He⁺ and protons, nanoindentation, scratching, friction coefficient measurements, and acoustic emission measurements. The results demonstrate that the deposited coatings have a high quality, hardness, and wear resistance and a low thermal diffusivity. Apart from Al₂O₃, the coatings are found to have Si, Mn, C, and Ca. The stoichiometry of the coatings is determined. The density and hardness of the coatings are close to those of ??-Al₂O₃ in the coating on an Al-Cu (D-16) substrate, and these values of the coating on an Al-Mg (S006) are lower by a factor of 1.5.