Preparation and characterization of PbFe12−xGaxO19 single crystals

The single crystals of the magnetoplumbite type of the general formula Pb_12?xGa_xO₁₉ were prepared by the growing from lead oxide flux. The deviations from the ideal compositions are explained by the substitution of S and/or T blocks into the … SRS1R1SR … chains. The structural and magnetic study show on the change of the substitution mechanism of small metallic ions at x = 3. The last member of the serie was found the composition of x = 10.38. The limited mutual substitution of iron and gallium ions is probably caused by an unwillingness of gallium ions to enter into five-fold sites.     

Follicular tumidus retro-auricular lichen planus (author''s transl)

Referring to three comparable cases, a new form of lichen planus is described. This form is characterized by a prominent lesion, violaceus in color or pigmented, with white yellowish specks mimicking milia. The histologic picture of lichen follicularis, the presence of typical papules of lichen distant from the retro-auricular lesion make it possible to consider this clinical aspect as a variety of lichen planus.     

Elastodynamic fields near running cracks by finite elements

A finite element method is developed for the computation of elastodynamic stress intensity factors at a rapidly moving crack tip. The method is restricted to bodies whose surfaces and two-material interfaces are either parallel to the direction of propagation or are sufficiently remote. The crack tip starts to move at the instant that it is struck by an incident wave. The finite element grid moves undeformed with the crack tip. The main result consists in the fact that the method of non-singular calibrated crack tip elements, in which the stress-intensity factor is determined from its statically calibrated ratio to the crack opening displacement in an adjacent node, is extended to dynamic problems with moving cracks, for both in-plane and anti-plane motions. The dependence of the calibration ratio on the crack tip velocity is established from previously developed analytical solutions for the near-tip displacement fields. Numerical results compare favorably with known analytical solutions for cracks moving in an infinite solid. The grid motion causes an apparent asymmetric additional damping matrix.     

Use of patent information at a Czechoslovak research institute

This article describes the patent information services in Czechoslovakia and the use made of patent information in applied research and in patent practice. The various possibilities which exist centrally, regionally and in industry are discussed.     

Effect of CO2 on porous concrete

Through the action of CO₂ and moisture, 11 Å-tobermorite of porous concrete is decomposed into vaterite, calcite and SiO₂-gel. Due to pseudo-morphosis, the morphology of the crystals of the cementing phase undergoes no substantial change. The lowest compressive strengths were obtained after 30 days storage in 30 and 10% CO₂. The compressive strengths drop after 1 year of storage was less than 10%. As regards shrinkage of porous concrete, the main influence is exerted by CO₂, and only in the second place by the humidity of the environment. Porous concrete exposed to air (0.03% CO₂) at r.h. of 50, 75 and 100% expanded slightly in one year.     

Comparison of recent rubber-elasticity theories with biaxial stress-strain data: the slip-link theory of Edwards and Vilgis

The Edwards-Vilgis (EV) slip-link theory (1986) derives the elastic free energy of a rubber-like network model containing stable and sliding network junctions (crosslinks and slip-links) and predicts both low-strain softening and high-strain hardening. The four-parameter stress-strain relations calculated by the theory for geometrically different deformation modes up to high strains were tested experimentally using published biaxial stress-strain data on simple covalently crosslinked networks. For networks with low degrees of strain softening and low extensibilities, the experimental dependencies could be described rather well but, generally, a simultaneous satisfactory fit to uniaxial, pure shear and equibiaxial data was not obtained. Systematic experiment-theory deviations exceeding 10% were observed and some of the parameters had a tendency to assume values lying outside the reasonably expected range. The prediction of a pronounced maximum in the strain dependence of stress supported by slip-links seems to be a reason for the discrepancy. Also, modeling of the high-strain singularity in entropy is done in the EV theory using a rather simple approximation. As a result, the finite extensibility contribution to the stress of a slip-link-free network model becomes improbably high and significantly exceeds that following, at a given modulus and locking stretch, from the rigorously derived Langevin-statistics-based eight-chain-network elasticity theory of Arruda and Boyce.     

Mitteilungen der Schweizer Informatik Gesellschaft · 5/2004

Ohne Zusammenfassung     

A new family of telechelic copolymers

Summary A new initiation system is described, allowing bulk polymerizations of isobutylene to be carried out at about-78°C, in the absence of a polar chlorinated solvent. The initiation system consists of two components, the first of which is boron trichloride (BCl₃) used as co-initiator, and the other component is a polymer insoluble in the monomer and containing chloroallyl structures or structures with a chlorine atom bound at the tertiary carbon atom in their chains. Bulk polymerizations of isobutylene proceed at the boundary between the solid and the liquid phase for many hours, and the polymeric initiator used is grafted by isobutylene. Dichloromethane raises reactivity of the initiation system.