Additional raising of the degeneracy of CEF-split Ho3+ ions by antiferromagnetic spin-waves in Ho0.1Y0.9Ba2Cu3O6.13

Inelastic neutron scattering has been employed to study in detail the low-energy crystal-field (CEF) excitations of Ho³⁺ in tetragonal antiferromagnetic (AF) Ho_0.1Y_0.9Ba₂Cu₃O_6.13. We observe a splitting of the lowest excited ₅ doublet atT=1.5 K. This splitting is explained as resulting from the exchange interaction with the AF subsystem of copper spins. The corresponding susceptibility at the Ho³⁺ site has a symmetry lower than the tetragonal one of the CEF potential and, as a result, produces the splitting. The value of the coupling between Ho³⁺ and Cu²⁺ ionsJ _ex=2.4 meV is derived from the experimentally observed value of the splitting E=0.1 meV and parameters of the AF subsystem, known from the neutron scattering experiments. Some possible consequences of the rare-earth (RE)-copper exchange are discussed, including the interaction between RE ions via the virtual exchange by spin waves.     

Fractal structure in base-catalyzed silica aerogels examined by TEM, SAXS and porosimetry

A fractal analysis of three base catalyzed silica aerogels was performed using different experimental techniques: image analysis of electron micrographs, SAXS and study of pore size distribution determined from nitrogen adsorption isotherms. The aerogels appeared to exhibit self-similar properties over the range from 3–10 to 50–130 nm. The values of mass fractal dimension varied from 1.75 to 2.05 depending on the reactants concentration (TEOS, H₂O) and were found to be similar irrespective of the method applied.     

Porous texture characteristics of a homologous series of base-catalyzed silica aerogels

Eighteen samples of base-catalyzed silica aerogels obtained using various tetraethylorthosilicate (TEOS) and water contents in the reaction system were characterized using N₂ adsorption. From the observed pore size distribution and adsorption isotherms the volumetric and surface fractal dimensions were determined and also the range of power-law behaviour of the porous network. The porous texture of both the bulk aerogel and surface of clusters appeared to be dependent on the concentration of reactants. The water content, however, emerges as a factor controlling surface fractal structure, its principal effect being exerted on the pore volume in the mesopore size range.     

Intrinsic symmetry of refracting profiles derived from a parabola

The intrinsic symmetry of kinoform refracting profiles, which determines the possible types of the arrangement of parabolic segments constituting a planar lens on a plane, is considered. It is shown that the intrinsic symmetry of a compound kinoform profile is determined by a symmetry group G consisting of two subgroups G = G _t ? G _m . The elements of subgroup G _m = {E, m ₁, m ₂, m ₃} are symmetry planes such that m ₁ and m ₃ correspond to the reflection of the kinoform profile into itself and m ₂ is a black-white antisymmetry plane. A rule is stated for the assembling of segments in a kinoform lens following from the condition of the conservation of the focal length. For the first time, a subgroup of permutations is introduced into consideration such that its action is reduced to a permutation among single profiles within the common compound set. It is shown that the existence of subgroup G _t determines the properties of lenses that are observed experimentally in the spectral dependences of the lens gain in the focal spot.     

Synthesis in a series of quinoline derivatives

Monomeric substances, 8-methacryloxyquinolines were synthesized with the object of obtaining preparations with prolonged action.For part V, see [1].     

Self-similar solution of the Navier-Stokes equations governing gas flows in rotary logarithmically spiral two-dimensional channels

A self-similar solution of the Navier-Stokes equations governing gas flows with constant transport coefficients in rotary log-spiral two-dimensional channels is obtained and analyzed. The solution and its existence depend on the following dimensionless parameters: the Reynolds number Re; the parameterM _o characterizing the channel rotation; the self-similarity parameters and responsible for the channel shape; the direction of channel rotation; and, finally, the wall temperature ratio. A numerical solution of the system of second-order ordinary differential equations gives the ranges of the governing parameters on which self-similar solutions for the gas flow in a rotary channel can exist.Perm'-Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 6, pp. 44–50, November–December, 1995.     

Exact Solutions of Three Sobolev Equations Containing Fourth-Order Pseudo-Laplacians

Differential Equations - We construct several classes of exact solutions of three nonlinear Sobolev equations containing fourth-order pseudo-Laplacians and describing quasi-stationary processes in...     

Selective Water Sorbents for Multiple Applications, 10. Energy Storage Ability

The application of new selective water sorbents for storage of low temperature heat is analyzed. Values of energy storage ability E are measured by a DSC technique for more than fifteen samples of selective water sorbents based on silica gels, aluminas, carbon Sibunit and aerogels as host matrices and CaCl₂, LiBr, MgCl₂ as impregnated salts. E-values up to 8.4 kJ/g and 4.0 kJ/g are found for forced and naturally saturated sorbents, which are much higher than for common sorbents, like zeolites and unimpregnated silica gels. The temperature dependence of E gives an estimation of sensible and latent heat contributions as well as the average heat of water desorption and average specific heat of dry sorbents. A comparison between the SWSs and others materials proposed in literature is done.