47, 49Ti NMR spectra of half-sandwich titanium(IV) complexes

The 47, 49Ti chemical shifts, resonance line half-widths (Deltanu1/2) and energies of the first electronic charge-transfer transitions (lambdamax1.CT) of Cp'TiX3, where Cp' = eta5-C5H5 (Cp), eta5-C5H4Me (MeCp), eta5-C5HMe4 (Me4Cp), eta5-C5Me5 (Me5Cp), eta5-C5H4SiMe3 (SiCp), eta5-C5H4SnMe3 (SnCp) and eta5-C5H4SiMe2Cl (Si'Cp) and X = Cl, Br, I and OBut, half-sandwich complexes are reported. For the compounds studied, a direct linear relationship between delta(49Ti) and lambdamax1.CT was found.     

Flexible H2O2 in water: electronic structure from photoelectron spectroscopy and ab initio calculations

The effect of hydration on the electronic structure of H(2)O(2) is investigated by liquid-jet photoelectron spectroscopy measurements and ab initio calculations. Experimental valence electron binding energies of the H(2)O(2) orbitals in water are, on average, 1.9 eV red-shifted with respect to the gas-phase molecule. A smaller width of the first peak was observed in the photoelectron spectrum from the solution. Our experiment is complemented by simulated photoelectron spectra, calculated at the ab initio level of theory (with EOM-IP-CCSD and DFT methods), and using path-integral sampling of the ground-state density. The observed shift in ionization energy upon solvation is attributed to a combination of nonspecific electrostatic effects (long-range polarization) and of the specific interactions between H(2)O(2) and H(2)O molecules in the first solvation shell. Changes in peak widths are found to result from merging of the two lowest ionized states of H(2)O(2) in water due to conformational changes upon solvation. Hydration effects on H(2)O(2) are stronger than on the H(2)O molecule. In addition to valence spectra, we report oxygen 1s core-level photoelectron spectra from H(2)O(2)(aq), and observed energies and spectral intensities are discussed qualitatively.     

On the distance spectral radius of cacti

A cactus is a connected graph in which any two cycles have at most one common vertex. In this article, we determine the unique graph with minimal distance spectral radius in the class of all cacti with n vertices and k cycles. Also, we determine the unique graph with minimal distance spectral radius in the class of all cacti with n vertices and r pendent vertices. Moreover, we determine the class of cacti in which the maximal distance spectral radius among all cacti with n vertices and k cycles is attained.     

Eigenmobilities in background electrolytes for capillary zone electrophoresis: II. Eigenpeaks in univalent weak electrolytes

We analyze in detail a mathematical model of capillary zone electrophoresis (CZE) based on the conception of eigenmobilities, which are eigenvalues of the matrix tied to the linearized continuity equations. Our model considers CZE systems, where constituents are weak electrolytes and where pH of the background electrolyte may reach the full range from 0 to 14. Both hydrogen and hydroxide ions are taken into account in relations for conductivity and electroneutrality. An electrophoretic system with N constituents has N eigenmobilities. We reveal that two of the eigenmobilities have a special meaning as they exist due to the presence of hydrogen ions and hydroxide ions (in water solutions). These two eigenmobilities are responsible for the existence of two corresponding system zones (system peaks). We show that the stationary zone (injection zone, water zone, gap, peak, dip) is in many common background electrolytes composed of these two eigenzones which overlap, due to their very low electrophoretic mobility, into one zone. Other eigenmobilities give rise to system zones originating due to a possible existence of double (or multiple) coconstituents in the background electrolyte. The last group of eigenmobilities is connected with the movement of eigenzones accompanying analytes and enabling their indirect UV or conductivity detection. The model allows assessing experimentally available quantities such as effective mobility of the analyte, molar conductivity detection response, transfer ratio, and relative velocity slope and gives a picture about migration of analytes, their electromigration dispersion and signals obtained in detectors. It allows computer simulation of electropherograms and enables optimization of background electrolytes.     

Effect of sol–gel-based silica buffer layer on the formation of NaA zeolite membrane

The support substrates were modified with sol?Cgel-based silica coating as intermediate buffer layer followed by NaA zeolite seed (prepared hydrothermally at 85?°C for 3?h) coating with 2?wt% aqueous dispersion. The secondary crystallization of NaA zeolite in the silica-seed-coated supports was carried out hydrothermally through crystal growth process at 65?°C for 4 and 8?h (single-stage each), (6?+?4) and (6?+?6)?h (double-stage each), and (6?+?4?+?2) and (6?+?4?+?4)?h (triple-stage each). The crystallization behaviours of the prepared NaA membranes were studied by X-ray diffraction, and the microstructures of the same films were observed by field emission scanning electron microscope. The efficiency of the membranes was tested with gas permeation study. The double-stage secondary crystallization at 65?°C for (6?+?4)?h showed highly interlocked NaA grains in the membrane and it rendered the permeance values of 3.7?×?10^?8?mol?m^?2?s^?1?Pa^?1 and 15.9?×?10^?8 for single gas, nitrogen (N₂) and hydrogen (H₂) respectively with the ideal selectivity of 4.3.     

Determination of arsenic by cathodic stripping voltammetry at a hanging mercury drop electrode

Arsenic (III), respectively arsenic(V) after the reduction were determined in model solutions and some inorganic and organic materials by fast scan differential pulse cathodic stripping voltammetry and by direct current cathodic stripping voltammetry with a rapid increase of potential. The accumulation on a hanging mercury drop electrode followed by cathodic stripping was carried out in 0.7–0.8M HCl or 1–2M H₂SO₄ solutions containing Cu(II)-ions. Detection limits calculated from regression parameters was determined to be under 1 ng/ml for the samples containing very low arsenic concentrations. The relative standard deviation did not reach 8% for arsenic contents about of 5 ng/ml.     

Computing generalized inverses of a rational matrix and applications

In this paper we investigate symbolic implementation of two modifications of the Leverrier-Faddeev algorithm, which are applicable in computation of the Moore-Penrose and the Drazin inverse of rational matrices. We introduce an algorithm for computation of the Drazin inverse of rational matrices. This algorithm represents an extension of the papers [11] and [14]. and a continuation of the papers [15, 16]. The symbolic implementation of these algorithms in the package mathEmatica is developed. A few matrix equations are solved by means of the Drazin inverse and the Moore-Penrose inverse of rational matrices.     

Nonlinear standing waves in 2-D acoustic resonators

This paper deals with 2-D simulation of finite-amplitude standing waves behavior in rectangular acoustic resonators. Set of three partial differential equations in third approximation formulated in conservative form is derived from fundamental equations of gas dynamics. These equations form a closed set for two components of acoustic velocity vector and density, the equations account for external driving force, gas dynamic nonlinearities and thermoviscous dissipation. Pressure is obtained from solution of the set by means of an analytical formula. The equations are formulated in the Cartesian coordinate system. The model equations set is solved numerically in time domain using a central semi-discrete difference scheme developed for integration of sets of convection-diffusion equations with two or more spatial coordinates. Numerical results show various patterns of acoustic field in resonators driven using vibrating piston with spatial distribution of velocity. Excitation of lateral shock-wave mode is observed when resonant conditions are fulfilled for longitudinal as well as for transversal direction along the resonator cavity.