Quantum-chemical calculations of NMR chemical shifts of organic molecules: XII. Calculation of the 13C NMR chemical shifts of fluoromethanes at the DFT level

Calculation was carried out of chemical shifts in ¹³C NMR spectra for a series of fluoromethanes CH _n F_4?n (n = 0–4) by the methods of the electron density functional theory GIAO-DFT taking in consideration the solvent effect in the framework of the polarizable continuum model Tomasi IEF-PCM. The best results were obtained at the use of Keal-Tozer KT3 functional combined with Pople standard basis sets 6-311G(d,p) and 6-311++G(d,p), and also with Jensen special set pcS-2 containing tight p-functions. The optimum reference in the calculation of chemical shifts in ¹³C NMR spectra for the fluoromethanes series is TMS.     

A Mössbauer study of iron and iron–cobalt nanotubes in polymer ion-track membranes

Iron and iron–cobalt nanostructures that were synthesized in polymer ion-track membranes have been studied via Mössbauer spectroscopy combined with raster electron microscopy, energy-dispersion analysis, and X-ray diffraction data. The obtained nanostructures are single-phase bcc Fe_1–xCo_x nanotubes with a high degree of polycrystallinity, whose length is 12 μm; their diameter is 110 ± 3 nm and the wall thickness is 21 ± 2 nm. Fe²⁺ and Fe³⁺ cations were detected in the nanotubes, which belong to iron salts that were used and formed in the electrochemical deposition. The Fe nanotubes exhibit eventual magnetic moment direction distributions of Fe atoms, whereas Fe/Co nanotubes have a partial magnetic structure along the nanotube axis with a mean value of the angle between the magnetic moment and nanotube axis of 34° ± 2°. Substituting the Fe atom with Co in the nearest environment of the Fe atom within the Fe/Co structure of nanotubes leads to a noticeable increase in the hyperfine magnetic field at the ⁵⁷Fe nuclei (by 8.7 ± 0.4 kOe) and to a slight decrease in the shift of the Mössbauer line (by 0.005 ± 0.004 mm/s).     

Sums of independent poisson subordinators and their connection with strictly α-stable processes of Ornstein-Uhlenbeck type

We describe a construction in which the discrete time of a sequence of independent, identically distributed random variables changes with the Poisson time. The Poisson time is independent of this sequence. The defined process with continuous time is called a random index process. We establish several properties of random index processes. We study asymptotics of sums of independent, identically distributed random index processes in the case where elements of the initial sequence have strictly α-stable distribution. By calculating characteristic functions we establish relationships of these sums with strictly α-stable processes of the Ornstein- Uhlenbeck type. Bibliography: 4 titles. Translated from Zapiski Nauchnykh Seminarov POMI, Vol. 361, 2008, pp. 123–137.     

Comparison of Transmission Electron Microscopy and X-Ray Reflectometry Data in the Study of the Structure of Silicon-Carbon Nanocomposite Films

Crystallography Reports - Vanadium-doped diamond-like silicon-carbon films have been studied by X-ray reflectometry and transmission electron microscopy. A comparison of the data obtained has shown...     

Physical Methods for Determining the Phase Composition of Gallstones

Crystallography Reports - Gallstones with a zonal morphological structure have been studied using X-ray microtomography, X-ray diffraction analysis, Raman spectroscopy, and elemental analysis....