Solitary Wave Transformation Due to a Change in Polarity

Solitary wave transformation in a zone with sign-variable coefficient for the quadratic nonlinear term is studied for the variable-coefficient Korteweg–de Vries equation. Such a change of sign implies a change in polarity for the solitary wave solutions of this equation. This situation can be realized for internal waves in a stratified ocean, when the pycnocline lies halfway between the seabed and the sea surface. The width of the transition zone of the variable nonlinear coefficient is allowed to vary over a wide range. In the case of a short transition zone it is shown using asymptotic theory that there is no solitary wave generation after passage through the turning point, where the coefficient of the quadratic nonlinear term goes to zero. In the case of a very wide transition zone it is shown that one or more solitary waves of the opposite polarity are generated after passage through the turning point. Here, asymptotic methods are effective only for the first (adiabatic) stage when the solitary wave is approaching the turning point. The results from the asymptotic theories are confirmed by direct numerical simulation. The hypothesis that the pedestal behind the solitary wave approaching the turning point has a significant role on the generation of the terminal solitary wave after the transition zone is examined. It is shown that the pedestal is not the sole contributor to the amplitude of the terminal solitary wave. A negative disturbance at the turning point due to the transformation in the zone of the variable nonlinear coefficient contributes as much to the process of the generation of the terminal solitary waves.     

Spectral and luminescent properties of mono- and binuclear cyclometalated complexes of Pd(II) and Pt(II) based on 4,6-diphenylpyrimidine with ethylenediamine and orthophenanthroline

The [M(N_^∧N)(Hdphpm)]ClO₄ and [(M(N_^∧N))₂(μ-dphpm)](ClO₄)₂ complexes (M = Pd(II), Pt(II); (N_^∧N) is ethylenediamine (En) and orthophenanthroline (Phen); Hdphpm^? and dphpm^2? are the mono- and bisdeprotonated forms of 4,6-diphenylpyrimidine) are obtained and characterized by ¹H NMR spectroscopy and electronic absorption and emission spectroscopy. The magnetic nonequivalence of protons of (N_^∧N) ligands is explained by a difference in the trans-effect of the carbanion and pyrimidine parts of the cyclometalated ligand. The long-wavelength absorption bands and the vibrationally structured luminescence bands of ethylenediamine complexes are attributed to optical transitions in the {M(Hdphpm)} and {M₂(μ-dphpm)} metal-complex fragments. The complexes with orthophenanthroline exhibit two low-energy optical transitions involving π* orbitals localized on the cyclometalated and chelating ligands; the difference in their energies depends on the metal and is much larger for Pt(II) than for Pd(II). It is found that the replacement of Pd(II) by Pt(II) in the [(M(phen))₂(μ-dphpm)]²⁺ complexes changes the direction of the photoexcitation energy degradation due to the energy transfer between the {M₂(μ-dphpm)} bridging fragment and peripheral phenanthroline ligands.     

Properties and structural state of the surface layer in a zirconium alloy modified by a pulsed electron beam and saturated by hydrogen

A pulsed action of an electron beam on a Zr-1% Nb zirconium alloy is studied. Alloy samples are irradiated by three 50-μs pulses at an energy density of 15–25 J/cm², a power of (3–6) × 10⁴ W/cm², a current density of 10–50 A/cm², and an electron energy of 18 keV. This method of processing is found to modify the surface layer of the alloy without changing the structure-phase state of its volume. This surface modification increases the hydrogen saturation resistance of the alloy.     

Metal-Carbon Composites Based on Carbonized Melamine-Formaldehyde Polymer and Their Electrocatalytic Properties

Russian Journal of Electrochemistry - Metal/N-doped carbon (M/C–N) composites were prepared using the melamine-formaldehyde polymer (MFP) as a source of C–N carbon and a metal salt...     

Macro-N-heterocyclic compounds: X-ray photoelectron spectra and structure

Bi-, tri-, and tetradentate macroheterocylic ligands, i.e., structural analogs of phthalocyanine, are studied by X-ray photoelectron spectroscopy. The X-ray photoelectron spectra of N1s lines of the nitrogen atoms of these compounds are analyzed. The binding energies and integrated intensities of N1s lines of the nitrogen atoms are determined and the effective charges on the nitrogen atoms are calculated. The structures of bi-, tri-and tetradentate macroheterocyclic ligands containing isoindole, benzene, and pyridine fragments are established on the basis of the data obtained.     

Photochemical stability of nitroxyl derivatives

Different classes of compounds with imidazoline radicals were studied by EPR spectroscopy. The effects of light and atmospheric oxygen on the stability of these compounds in alcoholic solutions were investigated. The study of the photochemical stability of rhodium complexes with imidazoline radicals in oxygen-containing and oxygen-free media demonstrated that the photolysis of these compounds in the absence of oxygen causes the disappearance of paramagnetism. The reaction is reversible, and the observed effects are due to the formation of hydroxylamine groups via the interaction between excited nitroxyl radicals and the solvent in the absence of oxygen. When present in this system, oxygen deexcites the nitroxyl groups. A similar effect of oxygen is observed for nitroxyl derivatives of the fullerenes C₆₀ and C₇₀. A quite different photolytic behavior is shown by copper complexes with bidentately bonded nitroxyl radicals. These compounds are stable to photolysis in both oxygen-containing and oxygen-free media. It was demonstrated using phenyl-tert-butylnitrone (PBN) as the spin trap that photolysis in the absence of the trap results in the decomposition of the copper complex to copper metal. It is assumed that PBN incorporates into the complex at free coordination sites and competes with the copper ion in its reaction with the earlier formed radical of the ligand.     

Synthesis of new polycarbonate-polysiloxanes based on oligomeric organosilicon bisphenols

New linear polycarbonate-polysiloxanes are synthesized through the heterophase polycondensation of α,ω-bis[3-(4-hydroxy-3-methoxyphenyl)propyl]oligoorganosiloxanes (P_Si-bisphenols) with α,ω-bis(chloroformato)oligocarbonates (method I), the phosgenation of P_Si-bisphenol-diphenylolpropane mixtures (method II), the interaction of the same bisphenols with bis(4-chloroformatophenyl)propane (method III), and the polycondensation of the latter with P_Si-bisphenol-α,ω-dihydroxyoligocarbonate mixtures (method IV). The highest molecular masses (as high as 130 × 10³ at a degree of multiblockiness of 11–14 block pairs) are inherent in poly-carbonate-polysiloxanes synthesized by methods II and III; moreover, the same copolymers have the highest mechanical characteristics (σ_br and ?_br are as high as 48 MPa and 300%, respectively).     

Physical properties and molecular conformations of indole alkaloids and model protein interactions--theoretical vs. experimental study

The physical properties and molecular structure of five natural indole alkaloids (IAs) and their interaction with protein targets have been studied, experimentally and theoretically. Electronic absorption (EAs) and CD spectroscopy, electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry (MS), as well as imaging mass spectrometric techniques (IMS) were used, analyzing the isolated alkaloids and corresponding IAs/protein molecular complexes. Theoretical quantum chemical DFT calculations were also applied. The mechanism of their biological activity and structure-activity relationship as potential neurologically active compounds were studied, using the model interactions with 5HT2A receptors. The gas-phase stable molecular fragments of the IAs are discussed comparing the experimental mass spectrometric data and theoretical quantum chemical DFT calculations of the different molecular fragments of the IAs.     

Carboxylated and decarboxylated nanotubes studied by X-ray photoelectron spectroscopy

Carbon nanotubes (CNTs) of the conic and cylindrical structure were studied by X-ray photoelectron spectroscopy in the initial state and after carboxylation and decarboxylation reactions. The O=C—O and C—O groups were revealed on the surface of the chemically modified samples. It was found that both the carboxylated and decarboxylated cylindrical CNTs contain a smaller amount of oxygen than the corresponding conic CNTs apparently due to differences in their structures.     

Synthesis and Characterization of Fluorite-Like Ce-Zr-Y-La-O Systems

Ce-Zr-O and Ce-Zr-Y-La-O materials obtained under various conditions and at varying component ratios are characterized. At Ce/Zr ≈ 1, a tetragonal phase that can hardly be distinguished from a cubic phase by X-ray diffraction forms in the ternary system. Raising the precipitation temperature favors the formation of two-phase systems. Promoting the Ce/Zr = 0.26–0.62 materials with both yttrium and lanthanum favors the formation of a single-phase specimen, namely, a (Ce, Zr, Y, La)O₂ fluorite-like solid solution at 600°C. This structure persists up to 1150°C. The specific surface area of the (Ce, Zr, Y, La)O₂ materials is primarily determined by their calcination temperature: S_sp = 50–80 m²/g at 600°C and 0.6–0.8 m²/g at 1150° C. The specimens calcined at 600°C are mesoporous, with uniformly sized pores of mean diameter 32 ± 2 Å, and have no micropores. According to TPR data, the specimens calcined at 600°C are reduced with hydrogen in two steps that can apparently be interpreted as surface and bulk reduction. The Ce/Zr = 0.26 and 0.40 specimens calcined at 1150°C are reduced in a single step, giving rise to TPR peaks at 707 and 686°C, respectively, and their degree of reduction increases with decreasing Ce/Zr.