Splitting of cones of optical axes in gyrotropic crystals in the presence of dichroism

Features of the appearance of conical singularities in the presence of linear dichroism and natural optical activity at the point of intersection of dispersion curves of the principal refractive indices of a crystal have been considered. It has been shown that even insignificant dichroism results in the splitting of cones of optical axes into cones of singular optical axes (in a partial case, cones are degenerate into planes) between which a “gap” with identical velocities of proper waves appears. The splitting angle for the AgGaS₂ crystal is estimated at about 5°.     

同步荧光光谱法测定石油中的晕苯

用苯做溶剂对原油样品进行逐级稀释,恒波长同步荧光法对原油样品中晕苯进行定性、定量分析。分别从溶剂选择、波长差、狭缝宽度等参数对其测定的光谱条件进行优化。实验结果表明：用苯为溶剂、Δλ=6nm,狭缝宽度为2.5nm,为原油样品中晕苯的最佳测试条件。所建立方法测定晕苯的线性范围为0.5—100μg/mL,校准曲线的相关系数r大于0.99,相对标准偏差小于3%（n=5）。该法分析快速、准确,对石化工厂中对原油样品中晕苯的快速检测具有一定的应用价值。     

Theory of Raman light scattering by nanocrystal acoustic vibrations

A theory of Raman scattering of light by acoustic phonons in spherical nanocrystals of zinc-blende and wurtzite semiconductors has been developed with the inclusion of the complex structure of the valence band. The deformation-potential approximation was used to describe the exciton-phonon interaction. It is shown that this approximation allows only Raman scattering processes involving spheroidal acoustic phonons with a total angular momentum F=0 or 2. The effect of phonon quantum confinement on linewidth in Raman scattering spectra and scattered polarization is analyzed. An expression for the shape of the spectral line corresponding to nonresonant scattering from F=0 phonons was obtained. Fiz. Tverd. Tela (St. Petersburg) 41, 1473–1483 (August 1999)     

Interpreting early land management through compound specific stable isotope analyses of archaeological soils

Compound specific stable isotope analyses of managed soils using isotope ratio mass spectrometry have been undertaken as a means of determining early land use practices. delta (15)N amino acid signals demonstrate differences between manured grassland, unmanured grassland and continuous cereal cultivation under long-term experimental land use control conditions, with delta (15)N in hydrophobic amino acids providing the most distinctive signals. Analysis of early modern/medieval and of Bronze age anthropogenic soils from Orkney demonstrates that such signals are retained in archaeological contexts. delta (13)C analyses of n- alkanoic acid components of the fossil, Bronze Age, anthropogenic soils suggest a major terrestrial input to these soils, with uniform composition of formation materials. Surficial soils demonstrate the assimilation of isotopically lighter carbon, providing a means of assessing the mobility of the n- alkanoic acids within soils and sediments. Copyright 1999 John Wiley & Sons, Ltd.     

Heteroleptic cobalt(II) and nickel(II) complexes with iminodiacetic and dicarboxylic acids in aqueous solution

Equilibria in binary and ternary systems containing cobalt(II) and nickel(II) salts, iminodiacetic acid, and dicarboxylates were studied by spectrophotometry at I = 0.1 (NaClO₄) and T = 20 ± 2°C. The molar and proton compositions of the resulting complexes and the pH ranges of their existence were determined. The stability constants of the homo- and heteroleptic complexes were calculated. The pH-distribution of the detected complexes was obtained. The experimental data were analyzed using the mathematical models that predict the existence of a wide spectrum of complex species in solution and allow ignoring those species that are negligible for accurate reproduction of the observed pattern.     

Ionic mobility and structure of glasses in Zrf<Subscript>4</Subscript>—Bif<Subscript>3</Subscript>—Mf<Subscript>2</Subscript> (M = Sr,Ba, Pb) systems according to Nmr,Ir, and Raman spectroscopic data

The NMR (¹⁹F and MAS NMR ¹⁹F), IR, and Raman spectroscopic methods are used to study the ionic mobility and structure of a series of new glasses in ZrF₄—BiF₃—MF₂ (M = Sr, Ba, Pb) systems in a temperature range of 180 K to 500 K. The temperature range, in which diffusion of fluorine ions becomes the dominant form of ionic motion, is determined by the nature of the M₂+ cation. The factors determining the basic model of the structure of glasses in ZrF₄—BiF₃—MF₂ (M = Sr, Ba, Pb) systems and conditions under which bismuth polyhedra can participate in the construction of the glass network are considered. According to the data of impedance spectroscopy, the studied glasses have relatively high ionic conductivity (δ ≥ 10–₄ S/cm above 480 K).     

On some features of the phase diagram of a ferroic with the cubic paraphase

The phase diagram of a ferroic with the paraphase of symmetry O _h has been studied for a three-dimensional order parameter. In the simplest model, which allows for the existence of a phase of the general position, i.e., the triclinic phase, the region of its existence has been investigated analytically. The invariance of the shape of this region is shown. The conditions providing the formation of a “swallowtail”-type feature in the region of existence of the monoclinic phase are considered. A convenient parametrization is proposed for the representation of the phase diagram, including all possible phases.     

Investigation of the influence of gradual substitution K ? Rb on the structure and phase transition in K x Rb1 ? x Pb2Br5 solid solutions

Single crystals of K _x Rb_{1 − x} Pb₂Br₅ solid solutions have been grown and investigated using X-ray diffraction and polarized light microscopy in the temperature range 270–640 K. The regions of existence of the tetragonal (I4/mcm) and monoclinic (P2₁/c) phases have been determined. It has been demonstrated that the partial introduction of rubidium into KPb₂Br₅ leads to an increase in the temperature of the ferroelastic phase transition (P2₁/c↔mmm), so that it approaches the melting temperature. In the solid solutions with x ≈ 0.4−0.5, the temperature region of existence of the orthorhombic phase is narrowed to ≈ 1−2 K. It has been revealed that an increase in the potassium content in the material results in a considerable increase in the incorporation coefficient of Er³⁺ ions. Original Russian Text ? L.I. Isaenko, S.V. Mel’nikova, A.A. Merkulov, V.M. Pashkov, A.Yu. Tarasova, 2009, published in Fizika Tverdogo Tela, 2009, Vol. 51, No. 3, pp. 554–557.