Interaction of the cubic boron nitride with the gas phase of chrome iodides

Translated from Poroshkovaya Metallurgiya, No. 3(327), pp. 90–92, March, 1990.     

Surface functionalization of mesoporous antimony doped tin oxide by metalorganic reaction

Electrically conducting mesoporous antimony doped tin oxide was functionalized by the metalorganic reaction with several Grignard reagents. This fast and efficient grafting approach enables a direct connection of the metal atoms with the organic functionalities avoiding the formation of insulating Si–O linkers, which is of special interest for the interfacial charge transfer processes. Using this approach we introduced vinyl, allyl and phenyl groups into the pores of mesoporous ATO, which was confirmed by IR spectroscopy, TGA and nitrogen sorption measurements. We obtained a high loading of organic groups corresponding to about 50–60% of the monolayer surface coverage. The obtained mesoporous inorganic–organic hybrids can serve as a platform for incorporation of electrochemically active species.     

Functionalized oligopolysiloxanes by heterogeneously catalyzed equilibration polymerization reactions

Summary A new general procedure for preparation of functionalized oligopolysiloxanes of predetermined molecular weight is described. It utilizes heterogeneously catalyzed siloxane equilibration polymerization reactions which do not require troublesome and sometimes difficult post-preparative work-up procedures usually encountered with the well known homogeneously catalyzed corresponding reactions. The method is described using as example the preparation of , -telechelic vinyldimethylsiloxy-oligopolydimethylsiloxanes from octamethylcyclotetrasiloxane and 1,3-divinyltetramethyldisiloxane, but reference to the preparations of trimethylsiloxy-, dimethylsiloxy-and carboxypropyldimethylsiloxyoligopolydimethylsiloxanes, oligopolymethylhydridosiloxanes or their copolymers is also made.     

Dual approach to multiple authorship in the study of collaboration/scientific output relationship

This paper presents an empirical study of the relations between scientific output and collaboration performed on two scales: (1) an individual scale, for members of a study model, and (2) a group scale, for three samples varying in the level of productivity. The rank approach was applied in the preparation of the study model resulting in the selection of a set of the most prolific authors. In the course of that process, multiple authorship problem was solved by a dual approach, consisting of normal count and modified straight count procedures. As shown by the analysis of collaborative patterns, either on individual or on group scales, scientific output is highly dependent on the frequency of collaboration among the same authors. Expressed as the collaboration measure, it might serve as an indicator in comparative analyses of scientific productivity in a given field of science.     

Novel alginate based nanocomposite hydrogels with incorporated silver nanoparticles

Alginate colloid solution containing electrochemically synthesized silver nanoparticles (AgNPs) was investigated regarding the nanoparticle stabilization and possibilities for production of alginate based nanocomposite hydrogels in different forms. AgNPs were shown to continue to grow in alginate solutions for additional 3 days after the synthesis by aggregative mechanism and Ostwald ripening. Thereafter, the colloid solution remains stable for 30 days and could be used alone or in mixtures with aqueous solutions of poly(vinyl alcohol) (PVA) and poly(N-vinyl-2-pyrrolidone) (PVP) while preserving AgNPs as verified by UV–Vis spectroscopy studies. We have optimized techniques for production of Ag/alginate microbeads and Ag/alginate/PVA beads, which were shown to efficiently release AgNPs decreasing the Escherichia coli concentration in suspensions for 99.9% over 24 h. Furthermore, Ag/hydrogel discs based on alginate, PVA and PVP were produced by freezing-thawing technique allowing adjustments of hydrogel composition and mechanical properties as demonstrated in compression studies performed in a biomimetic bioreactor.     

NONLINEAR OPTIMAL CONTROL: A CONTROL LYAPUNOV FUNCTION AND RECEDING HORIZON PERSPECTIVE

Two well known approaches to nonlinear control involve the use of control Lyapunov functions (CLFs) and receding horizon control (RHC), also known as model predictive control (MPC). The on-line Euler-Lagrange computation of receding horizon control is naturally viewed in terms of optimal control, whereas researchers in CLF methods have emphasized such notions as inverse optimality. We focus on a CLF variation of Sontag's formula, which also results from a special choice of parameters in the so-called pointwise minnorm formulation. Viewed this way, CLF methods have direct connections with the Hamilton-Jacobi-Bellman formulation of optimal control. A single example is used to illustrate the various limitations of each approach. Finally, we contrast the CLF and receding horizon points of view, arguing that their strengths are complementary and suggestive of new ideas and opportunities for control design. The presentation is tutorial, emphasizing concepts and connections over details and technicalities.     

Comparison of two techniques for reliable characterization of thin metal-dielectric films

In the present study we determine the optical parameters of thin metal-dielectric films using two different characterization techniques based on nonparametric and multiple oscillator models. We consider four series of thin metal-dielectric films produced under various deposition conditions with different optical properties. We compare characterization results obtained by nonparametric and multiple oscillator techniques and demonstrate that the results are consistent. The consistency of the results proves their reliability.     

Ellipsometric study of thermally induced redistribution and crystallization of Ge in Ge:SiO2 mixture layers

Mixture layers of Ge:SiO₂ of 40:60 mol% respectively, have been prepared by co-sputtering. The thermally induced change of optical properties of the layers was studied by variable angle spectroscopic ellipsometry. The mixture was modelled as an unknown material with optical constants described by multiple oscillators. The optical parameters determined from ellipsometric measurements can be well correlated with structural changes in the mixture. The results indicate that Ge in the mixture deposited or annealed up to 600 °C is in an amorphous state and it redistributes with increase of temperature, changing refractive index through the layer. The crystallization starts between 600 and 650 °C, at first next to the substrate. Crystallites size grows with temperature. Results were compared with findings of grazing incidence wide angle X-ray scattering measurements and a good agreement was found. Ellipsometry has been shown to be an appropriate non-invasive technique for characterization of this kind of layers.     

The effect of the mass ratio of hard and soft segments on some properties of thermoplastic poly(ester‐siloxane)s

A series of thermoplastic elastomers based on soft polydimethylsiloxane (PDMS) and hard poly(butylene terephthalate) (PBT) segments was synthesized using a two‐step transesterification reaction in the melt. The molar mass of the soft PDMS component was constant (M?_nPDMS = 1056 g mol^?1) while the starting reaction mixture compositions were varied to obtained copolymers with a mass ratio of hard to soft segments in the range from 70/30 to 40/60. The structure and composition of the copolymers was verified by ¹H NMR spectroscopy. It appeared that there was a pronounced molar mass maximum when the PBT content of the copolymers was approximately 60 mass%, whereas all samples were considerably inhomogeneous with respect to the distribution of the lengths of the hard segments. Differential scanning calorimetry (DSC) thermograms showed that the melting and crystallization temperature increased with increasing PBT content, as did the total degree of crystallinity, which was confirmed by wide‐angle X‐ray scattering (WAXS) analysis. Thermogravimetric analysis (TGA) performed in nitrogen gave subtle differences for samples of different composition, including that of the PBT homopolymer, whereas in oxygen these differences were more pronounced in the way the thermo‐oxidative stability of the obtained copolymers decreased with decreasing PBT content. Finally, it was shown that the hardness depended directly on the PBT content, ie the higher the PBT content, the greater the hardness of the corresponding copolymer. Copyright © 2004 Society of Chemical Industry