Parametric Excitation of Electromagnetic Fields by two Pump Waves

A collisionless plasma in the presence of two monochromatic electric fields is considered. By means of a kinetic analysis, a dispersion relation that governs the excitation of transverse electromagnetic fluctuations is derived and analysed.     

Lactone polymers. II. Hydrodynamic properties and unperturbed dimensions of poly-ε-caprolactone

Poly-ε-caprolactone prepared by a dibutylzinc-catalyzed bulk polymerization process was fractionated, and the solution properties of the fractions were studied in benzene and in dimethylformamide. In these solvents at 30°C the Mark-Houwink relations were [η] = 9.94 × 10^?5 M and [η] = 1.91 × 10^?4 M , respectively. The value of K_Θ was found to vary from 1.1 to 1.2 × 10^?3 when determined by three known extrapolation techniques. Poly-ε-caprolactone chains appear to be quite flexible in solution, and the steric hindrance parameter σ had the low value of 1.37. Root-mean-square end-to-end dimensions were approximated from the experimental data and calculated from the Debye-Bueche and the Kirkwood-Riseman theories.     

Cost and sensitivity of restricted active‐space calculations of metal L‐edge X‐ray absorption spectra

The restricted active‐space (RAS) approach can accurately simulate metal L‐edge X‐ray absorption spectra of first‐row transition metal complexes without the use of any fitting parameters. These characteristics provide a unique capability to identify unknown chemical species and to analyze their electronic structure. To find the best balance between cost and accuracy, the sensitivity of the simulated spectra with respect to the method variables has been tested for two models, [FeCl₆]^3– and [Fe(CN)₆]^3–. For these systems, the reference calculations give deviations, when compared with experiment, of ≤1 eV in peak positions, ≤30% for the relative intensity of major peaks, and ≤50% for minor peaks. When compared with these deviations, the simulated spectra are sensitive to the number of final states, the inclusion of dynamical correlation, and the ionization potential electron affinity shift, in addition to the selection of the active space. The spectra are less sensitive to the quality of the basis set and even a double‐ζ basis gives reasonable results. The inclusion of dynamical correlation through second‐order perturbation theory can be done efficiently using the state‐specific formalism without correlating the core orbitals. Although these observations are not directly transferable to other systems, they can, together with a cost analysis, aid in the design of RAS models and help to extend the use of this powerful approach to a wider range of transition metal systems. © 2015 Wiley Periodicals, Inc.     

Self-assembly of cationic surfactants that contain thioether groups in the hydrophobic tails

Self-assembly in aqueous solutions of cationic surfactants that carry thioether groups in their hydrophobic tails has been investigated. Of particular interest was the identification of possible changes in the aggregate structure due to the presence of sulfur atoms. Solutions of four different compounds [CH(3)CH(2)S(CH(2))(10)N(CH(3))(3)(+)Br(-) (2-10), CH(3)(CH(2))(5)S(CH(2))(6)N(CH(3))(3)(+)Br(-) (6-6), CH(3)(CH(2))(7)S(CH(2))(6)N(CH(3))(3)(+)Br(-) (8-6), and CH(3)(CH(2))(7)S(CH(2))(8)N(CH(3))(3)(+)Br(-) (8-8)] were characterized by (1)H NMR, (13)C NMR, NMR diffusometry, and conductivity measurements. In addition to investigating aqueous solutions containing each of the thioethers present as the sole solute, mixtures of 2-10 or 6-6 with dodecyltrimethylammonium bromide (DTAB) were studied. The addition of a sulfide group to the hydrophobic tail causes an increase in the critical micelle concentration but has a limited effect on the aggregate structure. Micelles are formed at a well-defined concentration for all of the investigated surfactants and surfactant mixtures. However, a comparison of the behavior of concentrated solutions of 8-8 to that of solutions of hexadecyltrimethylammonium bromide (CTAB) of similar concentrations suggests that the presence of a sulfur atom decreases the tendency for micellar growth. This may be a consequence of a slightly higher preference for the micellar surface of a sulfur atom as compared to that of a methylene group in a similar position, an idea that is also supported by results for the surfactant mixtures.     

Electroreductive Desulfurative Transformations with Thioethers as Alkyl Radical Precursors**

Thioethers are highly prevalent functional groups in organic compounds of natural and synthetic origin but remain remarkably underexplored as starting materials in desulfurative transformations. As such, new synthetic methods are highly desirable to unlock the potential of the compound class. In this vein, electrochemistry is an ideal tool to enable new reactivity and selectivity under mild conditions. Herein, we demonstrate the efficient use of aryl alkyl thioethers as alkyl radical precursors in electroreductive transformations, along with mechanistic details. The transformations proceed with complete selectivity for C(sp³)−S bond cleavage, orthogonal to that of established transition metal-catalyzed two-electron routes. We showcase a hydrodesulfurization protocol with broad functional group tolerance, the first example of desulfurative C(sp³)−C(sp³) bond formation in Giese-type cross-coupling and the first protocol for electrocarboxylation of synthetic relevance with thioethers as starting materials. Finally, the compound class is shown to outcompete their well-established sulfone analogues as alkyl radical precursors, demonstrating their synthetic potential for future desulfurative transformations in a one-electron manifold.     

Studies on an ester-modified cationic amphiphile in aqueous systems: behavior of binary solutions and ternary mixtures with conventional surfactants

The aqueous behavior of an ester-modified cationic amphiphile with the molecular structure CH3CH2O(C=O)(CH2)6(C=O)O(CH2)8N+(CH3)3Br-, in the following referred to as A, has been investigated. Systems with A as the only solute, as well as different aqueous mixtures with conventional cationic surfactants, primarily dodecyltrimethylammonium bromide (DTAB), were included in the study. Isotropic solution samples were characterized using 1H NMR, 13C NMR, NMR diffusometry, and conductivity measurements, whereas liquid crystalline samples were investigated by optical polarization microscopy and small-angle X-ray diffraction. The results are compared to the behavior of the binary system of DTAB and water. A does not exhibit a typical surfactant behavior. When it is present as the only solute in a binary aqueous system, it forms neither conventional micelles nor liquid crystalline phases. However, there is clear evidence that it assembles with lower cooperativity into loose clusters at concentrations above 25-30 mM. When A is mixed with DTAB in solution, the two amphiphiles form mixed assemblies, the structure of which varies with the total amphiphile concentration. In concentrated mixtures with alkyltrimethylammonium surfactants, A can participate in hexagonal liquid crystalline phases even when it constitutes a significant fraction of the total amphiphile content.     

On some hyperbolic type equations and weighted anisotropic Hardy operators

We introduce a version of weighted anisotropic Morrey spaces and anisotropic Hardy operators. We find conditions for boundedness of these operators in such spaces. We also reveal the role of these operators in solving some classes of degenerate hyperbolic partial differential equations. Copyright © 2016 John Wiley & Sons, Ltd.