Dynamics of the Spatial Structure of a Microsecond Pulsed Barrier Discharge Initiated in Atmospheric Pressure Air in the Point–Plane Geometry at Different Polarities of Feed Voltage

Technical Physics - The evolution of a microsecond pulsed barrier discharge initiated in atmospheric pressure air in the point–plane electrode geometry has been investigated using streak...     

Dynamics of the Initial Stage of the Spark and Diffuse Discharges in Air in a Point–Plane Gap at Different Parameters of the Tip Electrode

Technical Physics - Dynamics of the initial stage of discharge in air is studied at atmospheric pressure in a point–plane gap at different parameters of the tip electrode and lengths of the...     

Approximate chemical analysis of volcanic glasses using Raman spectroscopy

The effect of chemical composition on the Raman spectra of a series of natural calcalkaline silicate glasses has been quantified by performing electron microprobe analyses and obtaining Raman spectra on glassy filaments (~450 µm) derived from a magma mingling experiment. The results provide a robust compositionally‐dependent database for the Raman spectra of natural silicate glasses along the calcalkaline series. An empirical model based on both the acquired Raman spectra and an ideal mixing equation between calcalkaline basaltic and rhyolitic end‐members is constructed enabling the estimation of the chemical composition and degree of polymerization of silicate glasses using Raman spectra. The model is relatively insensitive to acquisition conditions and has been validated using the MPI‐DING geochemical standard glasses 1 as well as further samples. The methods and model developed here offer several advantages compared with other analytical and spectroscopic methods such as infrared spectroscopy, X‐ray fluorescence spectroscopy, electron and ion microprobe analyses, inasmuch as Raman spectroscopy can be performed with a high spatial resolution (1 µm²) without the need for any sample preparation as a nondestructive technique. This study represents an advance in efforts to provide the first database of Raman spectra for natural silicate glasses and yields a new approach for the treatment of Raman spectra, which allows us to extract approximate information about the chemical composition of natural silicate glasses using Raman spectroscopy. We anticipate its application in handheld in situ terrestrial field studies of silicate glasses under extreme conditions (e.g. extraterrestrial and submarine environments). © 2015 The Authors Journal of Raman Spectroscopy Published by John Wiley & Sons Ltd     

Supramolecular chirogenesis in zinc porphyrins: mechanism, role of guest structure, and application for the absolute configuration determination.

The achiral syn folded (face-to-face conformation) host molecule of the ethane-bridged bis(zinc porphyrin) transforms into the corresponding chiral extended anti bis-ligated species in the presence of enantiopure amine guests. The mechanism of the supramolecular chirogenesis is based upon the screw formation in bis(zinc porphyrin), arising from steric interactions between the largest substituent at the ligand's asymmetric carbon and peripheral alkyl groups of the neighboring porphyrin ring pointing toward the covalent bridge. The screw direction is determined by the guest's (amines) absolute configuration resulting in a positive chirality induced by (S)-enantiomers due to formation of the right-handed screw, and a negative chirality produced by the left-handed screw of (R)-enantiomers. The screw magnitude is strongly dependent upon the structure of the chiral guests. The amines with bulkier substituents result in stronger CD signals and larger (1)H NMR resonance splittings of enantiotopic protons. This system possesses a high degree of chiroptical activity, which allows the differentiation of one of the smallest homologous elements of organic chemistry, that is, the methyl and ethyl groups attached to the asymmetric carbon, and additionally, which senses a remote chiral center at a position beta to the amine binding group.     

Large Deviation Probabilities for Random Walks with Semiexponential Distributions

Siberian Mathematical Journal -     

An IR spectroscopic study of acid centers on the surface of Al,Zr silica gels

Acid centers of Al, Zr silica gels with approximately equal aluminum ion contents (∼2.4% Al₂O₃) and various concentrations of Zr ions were studied by IR spectroscopy using the deuteroacetonitrile molecule as a probe. The surface of such samples was found to contain Lewis acid centers of two types, coordination unsaturated (I) silicon and (II) zirconium ions. An increase in the content of zirconium ions was accompanied by a decrease in the intensity of the 2328 cm⁻¹ band in the IR spectra. This band was characteristic of interaction of CD₃CN with Lewis acid centers of type I. The suggestion was made that this was caused by a decrease in the accessibility of coordination unsaturated silicon ions to CD₃CN molecules.