Special features of manufacturing highly porous materials from silicon nitride,silicon oxynitride,and sialons

Results obtained in a study of factors that affect shaping and sintering of highly porous materials are presented. A technology providing highly porous silicon nitride materials that is based on shaping preliminarily fabricated pieces of thermoplastic slip makes it possible to use initial silicon powders of different dispersities. Highly porous materials can also be produced on the basis of sialons and exhibit a diminished thermal conductivity and a heat resistance at the level of similar silicon nitride materials.Translated from Ogneupory i Tekhnicheskaya Keramika, No. 11, pp. 8 – 13, November, 1996.     

Autonomic paroxysms: their pathogenesis, diagnosis and treatment

In the article the rules about etiology and pathogenesis of vegetative paroxysms are stated based on careful analysis of the publications of researches as Russian, so foreign authors, and also own experimental and clinical supervision. During experimental and clinical researches the modern methods were used, enabling to estimate from positions of the system analysis different parts of pathogenesis of vegetative paroxysms, and also to offer ways of differential diagnostics of the various forms of disease. The application of some new preparations and direction of therapy of vegetative paroxysms are substantiated, and also the various circuits of treatment of the patients with distinguishing forms of given pathology are motivated.     

The influence of phosphate on the properties of clay bricks

The fabrication, properties and composition of heated phosphate-bonded clay bricks are reported. The strength of phosphate-bonded clay bodies is shown to be related to the equilibrium pH of the clay mix. The highest strengths were obtained for mixes with equilibrium pH 7 fired at 500°C which gave a modulus of rupture 60% higher than the unmodified clay heated under similar conditions but at 800°C firing temperature. The phosphate-bonded products were also of low porosity and improved dimensional stability. An insight into the probable mechanism of strength development of the heated product has been obtained from XRD, SEM and DSC studies. The results show that the properties of the phosphate-bonded clay bodies are critically affected by new mineral phases resulting from the reactions of phosphates with clay which subsequently undergo physico-chemical changes above 550°C.     

Novel diterpenoid diacylglycerols from marine molluscs: potent morphogens and protein kinase C activators

Five novel 1,2-sn-diacylglycerols with diterpenoid acyl moieties in the sn-1 position were isolated and characterized, together with the corresponding 1,3-sn-diacylglycerols, from three species of dorid nudibranchs molluscs. Their potent activity as morphogens in vivo in the Hydra tentacle regeneration assay and their parallel activity as activators of rat brain protein kinase C (PKC) in vitro are reported here. Our findings promote the use of these compounds as useful molecular probes for both in vivo and in vitro studies on the participation of PKC in cell development.     

Performance model of interactive video-on-demand systems

An interactive video-on-demand (VoD) system allows users to access video services, such as movies, electronic encyclopedia, interactive games, and educational videos from video servers on a broadband network. This paper develops a performance evaluation tool for the system design. In particular, a user activity model is developed to describe the usage of system resources, i.e., network bandwidth and video server usage, by a user as it interacts with the service. In addition, we allow batching of user requests, and the effect of such batching is captured in a batching model. Our proposed queueing model integrates both the user activity and the batching model. This model can be used to determine the requirements of network bandwidth and video server and, hence, the trade-off in communication and storage costs for different system resource configurations     

Estimation of the through porosity of cloth made of chemical fibres in a blend with natural fibres and its correlation with air permeability

The accuracy and reliability of experimental data are determined by the choice of the method of determining the structural characteristics of materials to a significant degree. The data on the level of correlation and the type of functional dependence of the properties on the structure of materials obtained by correlation and regression analysis are a function of the reliability of the experimental data to a significant degree. Of the three methods of estimating the through porosity of materials examined here, the simplest and most widely used method of calculation provides the least reliable results. The most reliable data on through porosity can be obtained by the projection method of indirect estimation of the through porosity and it is recommended for practical research, especially when processing of materials with defined properties is the final goal.St. Petersburg State University of Design and Technology. Translated from Khimicheskie Volokna, No. 3, pp. 31–33, May–June, 1995.     

Solution structure of the superactive monomeric des-[Phe(B25)] human insulin mutant: elucidation of the structural basis for the monomerization of des-[Phe(B25)] insulin and the dimerization of native insulin

The three-dimensional solution structure of des-[Phe(B25)] human insulin has been determined by nuclear magnetic resonance spectroscopy and restrained molecular dynamics calculations. Thirty-five structures were calculated by distance geometry from 581 nuclear Overhauser enhancement-derived distance constraints, ten phi torsional angle restraints, the restraints from 16 helical hydrogen bonds, and three disulfide bridges. The distance geometry structures were optimized using simulated annealing and restrained energy minimization. The average root-mean-square (r.m.s.) deviation for the best 20 refined structures is 1.07 angstroms for the backbone and 1.92 angstroms for all atoms if the less well-defined N and C-terminal residues are excluded. The helical regions are more well defined, with r.m.s. deviations of 0.64 angstroms for the backbone and 1.51 angstroms for all atoms. It is found that the des-[Phe(B25)] insulin is a monomer under the applied conditions (4.6 to 4.7 mM, pH 3.0, 310 K), that the overall secondary and tertiary structures of the monomers in the 2Zn crystal hexamer of native insulin are preserved, and that the conformation-averaged NMR solution structure is close to the structure of molecule 1 in the hexamer. The structure reveals that the lost ability of des-[Phe(B25)] insulin to self-associate is caused by a conformational change of the C-terminal region of the B-chain, which results in an intra-molecular hydrophobic interaction between Pro(B28) and the hydrophobic region Leu(B11)-Leu(B15) of the B-chain alpha-helix. This interaction interferes with the inter-molecular hydrophobic interactions responsible for the dimerization of native insulin, depriving the mutant of the ability to dimerize. Further, the structure displays a series of features that may explain the high potency of the mutant on the basis of the current model for the insulin-receptor interaction. These features are: a change in conformation of the C-terminal region of the B-chain, the absence of strong hydrogen bonds between this region and the rest of the molecule, and a relatively easy accessibility to the Val(A3) residue.