Uncatalyzed reactions of α-(trihaloethylidene)nitroalkanes with push-pull enamines: a new type of ring-ring tautomerism in cyclobutane derivatives and the dramatic effect of the trihalomethyl group on the reaction pathway

A new type of ring-ring isomerism, which consists of the reversible transformation of cyclobutane derivatives into substituted 1,2-oxazine N-oxides was found and studied by NMR spectroscopy and X-ray diffraction analysis. The starting materials were prepared by the stereoselective reaction of α-(trifluoroethylidene)nitroalkanes, which react with ethyl β-morpholino- and β-piperidinocrotonates at the more nucleophilic α-position, whereas the reaction of α-(trichloroethylidene)nitroalkanes proceeds at the β-methyl group to give the corresponding linear products.     

Crystal structure of a new small-pore zirconosilicate Na2ZrSi2O7·H2O and its relation to stoichiometrically and topologically similar compounds

The small-pore zirconosilicate Na₂ZrSi₂O₇·H₂O crystallizes in monoclinic system with space group C2/c, a = 5.4715(4); b = 9.4111(6); c = 13.0969(8) Å, β = 92.851(7)°. Its framework consists of layers built of ZrO₆ octahedra and SiO₄ tetrahedra and forming condensed [Si₂O₇] pyrogroups by connection. The sodium ions and water molecules are placed in channels set up between the layers. The stoichiometric and structural similarities of the studied phase with anhydrous compounds having general chemical formula A₂₍₃₎MT₂O₇ (A = Na,K; M = Zr,Lu,Sc; T = Si,Ge) are discussed. The topological relationship of their structures is interpreted in the light of spatial combination of silicon and zirconium polyhedra as basic building units into larger composite building units and their three-dimensional arrangement.     

Non-local damage modelling of quasi-brittle composites

Applications of Mathematics - Most building materials can be characterized as quasi-brittle composites with a cementitious matrix, reinforced by some stiffening particles or elements. Their massive...     

A model of dynamics of group structures of human institutions

Given is a review of the substantial theories of cognitivist's trend and also of static and dynamic models of group structures that are based on them. A model of human institutiosn is constructed that explains the origin of balanced structures. This model is realized by a system of locally interacting automatons which are connected by a system of relations and endowed with the ability to react.     

On the Structure of Submanifolds with Degenerate Gauss Maps

An n-dimensional submanifold X of a projective space P ^N (C) is called tangentially degenerate if the rank of its Gauss mapping gamma;; X G(n, N) satisfies 0 < rank < n. The authors systematically study the geometry of tangentially degenerate submanifolds of a projective space P ^N (C). By means of the focal images, three basic types of submanifolds are discovered: cones, tangentially degenerate hypersurfaces, and torsal submanifolds. Moreover, for tangentially degenerate submanifolds, a structural theorem is proven. By this theorem, tangentially degenerate submanifolds that do not belong to one of the basic types are foliated into submanifolds of basic types. In the proof the authors introduce irreducible, reducible, and completely reducible tangentially degenerate submanifolds. It is found that cones and tangentially degenerate hypersurfaces are irreducible, and torsal submanifolds are completely reducible while all other tangentially degenerate submanifolds not belonging to basic types are reducible.     

Oxygen ionic transport in Bi2O3-based oxides: The solid solutions Bi2O3–Nb2O5

The minimum concentration of niobium to stabilize the fluorite-type f.c.c. phase in the Bi₂O₃–Nb₂O₅ oxide system at temperatures below 996 K was ascertained to be about 10 mol%. Thermal expansion, electrical conductivity and crystal lattice parameters of the Bi(Nb)O_1.5+δ solid solutions decrease with increasing niobium content. Thermal expansion coefficients were calculated from the dilatometric data to be (10.314.5)×10⁻⁶ K⁻¹ at temperatures in the range 300–700 K and (17.526.0)×10⁻⁶ K⁻¹ at 700–1100 K. The conductivity of the Bi_{1− x} Nb _x O_1.5+δ ceramics is predominantly ionic. The p-type electronic transference numbers of the Bi(Nb)O_1.5+δ solid solutions in air were determined to be less than 0.1. Annealing at temperatures below 900 K results in a sharp decrease in conductivity of the Bi_{1− x} Nb _x O_1.5+δ ceramics. Received: 18 August 1997 / Accepted: 20 October 1997     

Quantum chemical PM-3 study of the thermal stability of heterocyclic fragments of heteropolymers, 1. Five-membered heterocycles: Azoles and imides

Semiempirical PM-3 calculations of the mechanisms of the decomposition of oxazole and maleimide have been carried out. It has been shown that thermal decomposition of the considered heterocycles proceeds via a consecutive breaking of two ring bonds, the breaking of the second bond being the rate-determining step. Both an activation barrier of heterocycle decomposition and its dissociation energy (E_D) can be used as a measure of heterocycle thermal stability. The correlation between E_D values of azole and imide containing model compounds and the initial degradation temperatures of corresponding heteropolymers makes it possible to clarify some essential features of the thermal degradation of polyazoles, polybenzazoles and polyimides.     

Radical polymerization in micelles of surface-active monomers

Photo- and thermoinitiated radical polymerization was investigated in solution and micelles of cationic surface-active monomers in water. Kinetics of this process depend on the structure of micelles. Polymerization proceeds in aqueous solution of monomers, in their lamellae and spheric micelles, but doesn't occur in anisotropic ones. The polymerization rate in spheric micelles increases with the decrease of counterion size in the “head” and/or the length of the “tail” in monomer molecule. This results from the decrease of the rate of bimolecular termination reaction due to the increase of the density of micelles.     

A Novel Type of Crown Ether‐Containing Metal Ions Optical Sensors Based on Polymer‐Stabilized Cholesteric Liquid Crystalline Films

For the first time, the films based on polymer‐stabilized cholesteric composites containing crown ether fragments with the optical properties sensitive to the complexation with potassium and barium ions were obtained. The complexation with these ions leads to blue spectral shift of the selective light reflection of planar cholesteric texture of composite films. Peculiarities of spectral changes and kinetics of selective light reflection shift were studied. The proposed approach can be used for the creation of the effective and selective sensor materials for different ions or groups of ions.     

Photodynamic Therapy Minimally Affects HEMA-DMAEMA Hydrogel Viscoelasticity

Soft matter implants are a rapidly growing field in medicine for reconstructive surgery, aesthetic treatments, and regenerative medicine. Though these procedures are efficacious, all implants carry risks associated with microbial infection which are often aggressive. Preventative and responsive measures exist but are limited in applicability to soft materials. Photodynamic therapy (PDT) presents a means to perform safe and effective antimicrobial treatments in proximity to soft implants. HEMA-DMAEMA hydrogels are prepared with the photosensitizer methylene blue included at 10 and 100 µM in solution used for swelling over 2 or 4 days. Thirty minutes or 5 h of LED illumination at $9.20\frac{mW}{c{m}^2}$ is then used for PDT-induced generation of reactive oxygen species in direct contact with hydrogels to test viable limits of treatment. Frequency sweep rheological measurements reveal minimal overall changes in terms of loss modulus and loss factor but a statistically significant drop in storage modulus for some PDT doses, though within the range of controls and biological variation. These mild impacts suggest the feasibility of PDT application for infection clearing in proximity to soft implants. Future investigation with additional hydrogel varieties and current implant models will further detail the safety of PDT in implant applications.