Nonlinear optical properties of regioregular main‐chain polyesters

We have prepared new polyesters containing quadratic, nonlinear optical (NLO) active chromophores covalently incorporated into the main chain. In these polymers, the sequence of the chromophore units along the main chain is rigorously head to tail. All the polyesters are processable, both in the melt and in solution. For one polyester, a full second‐order NLO characterization has been performed. An out‐of‐resonance d₃₃ coefficient of 21 pm/V at 1368 nm has been measured. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2719–2725, 2007     

Cluster approach in first-principle calculations for ferroelectrics

It is shown that, proceeding from the first principles, it is possible to separate the contributions from short-and long-range interactions to the lattice dynamics and dielectric properties of crystalline dielectrics. The cluster calculations of local force constants and potentials for the matrix and impurity atoms in ferroelectrics with the perovskite structure were made by the Hartree-Fock MOLCAO-SCF method. The parameters of the Devonshire-Slater-Barrett single-ion model are calculated for barium titanate and potassium niobate. The influence of the quantum statistics on the Curie temperature in these ferroelectrics and the isotope effect in barium titanate are also considered.     

Carbide precipitates in solution-quenched PH13-8 Mo stainless steel: A small-angle neutron scattering investigation

This paper deals with the small-angle neutron scattering (SANS) investigation on solution-quenched PH13-8 Mo stainless steel. From the nature of the variation of the functionality of the profiles for varying specimen thickness and also from the transmission electron microscopy (TEM), it has been established that the small-angle scattering signal predominantly originates from the block-like metallic carbide precipitates in the specimen. The contribution due to double Bragg reflection is not significant in the present case. The single scattering profile has been extracted from the experimental profiles corresponding to different values of specimen thickness. In order to avoid complexity and non-uniqueness of the multi-parameter minimization for randomly oriented polydisperse block-like precipitate model, the data have been analyzed assuming randomly oriented polydisperse cylindrical particle model with a locked aspect ratio.     

Kinetic C<Subscript>(2)-H</Subscript> exchange study of<Emphasis Type="Italic">Cis</Emphasis>-[(en)<Subscript>2</Subscript>Co(HIm)(enH)]Br<Subscript>4</Subscript> by NMR spectroscopy: Evidence for the acidity of C<Subscript>(2)-H</Subscript> proton

C_(2)-H exchange incis-[(en)₂Co(HIm)(enH)]Br₄ (Im, imidazole; en, ethylenediamine) was studied over a pD range of 9.4 to 10.2 at 60°C where thecis-[(en)₂Co(Him)(enH)]⁴⁺ andcis-[(en)₂Co(HIm)(en)]³⁺ are the species present in significant concentrations.Cis-[(en)₂Co(HIm)(enH)]⁴⁺ has pK_a1 7.86 and pK_a2 9.82 with pK_a1 corresponding to coordinated enH ionization and pK_a2 to ImH ionization. The kinetic data may be interpreted in terms of an intramolecular H-D exchange mechanism, where the “dangling”-ND₂CH₂CH₂ND₂ group acts as a base to remove the imidazole C_(2)-H proton from the coordinated DIm moiety.     

<Superscript>6</Superscript>He + <Superscript>6</Superscript>He Clustering of <Superscript>12</Superscript>Be in a Microscopic Algebraic Approach

The norm kernel of the A=12 system composed of two ⁶He clusters, and the L=0 basis functions (in the SU(3) and angular momentum-coupled schemes) are analytically obtained in the Fock-Bargmann space. The norm kernel has a diagonal form in the former basis, but the asymptotic conditions are naturally defined in the latter one. The system is a good illustration for the method of projection of the norm kernel to the basis functions in the presence of SU(3) degeneracy that was proposed by the authors. The coupled-channel problem is considered in the algebraic version of the resonating-group method, with the multiple decay thresholds being properly accounted for. The structure of the ground state of ¹²Be obtained in the approximation of zero-range nuclear force is compared with the shell-model predictions. In the continuum part of the spectrum, the S-matrix is constructed, the asymptotic normalization coefficients are deduced and their energy dependence is analyzed.     

Computation of triple differential cross-sections with the inclusion of exchange effects in atomic K-shell ionization by relativistic electrons for symmetric geometry

The triple differential cross-section for K-shell ionization of silver and copper atoms by relativistic electrons have been computed in the coplanar symmetric geometry with the inclusion of exchange effects following the multiple scattering theory of Das and Seal [1] multiplied by suitable spinors. Present computed results are marginally improved in some cases from the previous computed results [2]. Present results are compared with measured values [3] and with previous computation results [2]. Some other theoretical computational results are also presented here for comparison.      

Degradative chain transfer in vinyl acetate polymerizations using toluene as solvent

In this work, we propose that retardation in vinyl acetate polymerization rate in the presence of toluene is due to degradative chain transfer. The transfer constant to toluene (C_trs) determined using the Mayo method is equal to 3.8 × 10^?3, which is remarkably similar to the value calculated from the rate data, assuming degradative chain transfer (2.7 × 10^?3). Simulations, including chain‐length‐dependent termination, were carried out to compare our degradative chain transfer model with experimental results. The conversion–time profiles showed excellent agreement between experiment and simulation. Good agreement was found for the M_n data as a function of conversion. The experimental and simulation data strongly support the postulate that degradative chain transfer is the dominant kinetic mechanism. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3620–3625, 2007     

Polarization locking and nonparaxial spatial solitons in media with electronic Kerr nonlinearity

The polarization structure of nonparaxial spatial solitons in a transparent medium with the electronic mechanism of Kerr nonlinearity is studied theoretically. It is demonstrated analytically in the weak nonparaxiality approximation that the regime of polarization locking, in which all the field components have the same propagation constant, is the only stable regime. Estimates of the rate of transition of the initial metastable regime of rotation of the polarization ellipse to the regime of polarization locking are presented. Based on a numerical solution of the nonlinear Maxwell equations, the presence of the nonparaxial regime of polarization locking is confirmed and the main characteristics of the corresponding spatial solitons are obtained.     

Content and Methodological Provision of the Basic Course of Analytical Chemistry

Russian standards in training conventional graduates and bachelors are considered. These standards determine the status and volume of analytical chemistry courses at different higher educational institutions. An analysis of the educational standards, standard curricula, and the aims of teaching analytical chemistry suggests the advisability of changing the content of the course, particularly at industrial (branch) higher educational institutions. The provision of the analytical chemistry course with special literature (manuals, textbooks), equipment, and computer software is considered.     

Structure and morphology of laser-ablated WO3 thin films

The structure and surface morphology of WO₃ thin films deposited by a laser-ablation technique have been found to be strongly dependent on the deposition conditions and the nature of the substrate. By precisely controlling the substrate temperature and the oxygen partial pressure, amorphous, polycrystalline, nano-crystalline and iso-epitaxial WO₃ thin films were successfully grown. The structure and surface morphological features of the films from X-ray diffraction and atomic force microscopy data are described in relation to the deposition conditions. PACS 81.15.Fg; 68.55.-a; 68.37.Ps