Features of network formation in the chain crosslinking (co)polymerization

Summary Analysis of experimental results on the chain (co) polymerization of bisunsaturated monomers suggests that cyclization plays a decisive role already at the onset of the reaction. At medium and elevated concentrations of the bisunsaturated compound, compact microgel-like particles are formed, which give rise to a gel mainly by participating in the polymerization reaction only with pendant double bonds in their surface layer, and not with double bonds in the interior. This mechanism is reflected in an apparent decrease in reactivity of the pendant double bonds.     

Minimization of norms and logarithmic norms by diagonal similarities

It is a commonly occurring problem to find good norms · or logarithmic norms (·) for a given matrix in the sense that they should be close to respectively the spectral radius (A) and the spectral abscissa (A). Examples may be the certification thatA is convergent, i.e. (A)A<1 or stable, i.e. (A)(A)<0. Often the ordinary norms do not suffice and one would like to try simple modifications of them such as using an ordinary norm for a diagonally transformed matrix. This paper treats this problem for some of the ordinary norms.

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Minimisierung von Normen und Logarithmischen Normen durch Diagonale Transformationen

Zusammenfassung Ein oft vorkommendes praktisches Problem ist die Konstruktion von guten Normen · und logarithmischen Normen (·) für eine gegebene MatrixA. Mit gut wird dann verstanden, daß A den Spektralradius (A)=max |₁| und (A) die Spektralabszisse (A)=max Re _i gut approximieren. Beispiele findet man für konvergente Matrizen wo (A)A<1 gewünscht ist, und für stabile Matrizen wo (A)(A)<0 zu zeigen ist. Wir untersuchen hier, wie weit man mit Diagonaltransformationen und dengewöhnlichsten Normen kommen kann.

     

Quantitative Analyse der Heterogenität des Bruchvorganges von kohlenstoffarmem Stahl bei Kerbschlagbiegeversuchen

Aufnahme von Kerbschlagzähigkeit-Temperatur-Kurven eines unberuhigten Stahles mit 0,04% C für drei Zustände mit unterschiedlicher Korngröße. Elektronenfraktographische Analyse der Bruchflächen. Abhängigkeit der kennzeichnenden Bruchgefügearten von der Temperatur. Möglichkeiten der fraktographischen Analyse für die Beschreibung des Bruchverhaltens.     

Biological properties of copolymer of 2-Hydroxyethyl methacrylate with sulfopropyl methacrylate

Interaction of organism with non-toxic implanted polymers depends on the physicochemical properties of the implant surface, which influence the adsorption of bioactive proteins and subsequently adhesion and growth of cells. The synthetic hydrogels are known as poorly adhesive surfaces. In this study we demonstrated the adsorption of albumin, fibrinogen, fibronectin, basic fibroblast growth factor, heparin-binding epidermal growth factor-like growth factor and epidermal growth factor to poly(2-hydroxyethyl methacrylate) (pHEMA) and copolymer of 2-hydroxyethyl methacrylate (HEMA) and potassium salt of 3-sulfopropyl methacrylate (SPMAK). The adhesion and growth of 3T3 cells and human keratinocytes on surface of these polymers was tested without and with pretreatment of polymers with heparin-binding epidermal growth factor-like growth factor. The adhesion of mixture of human granulocytes and monocytes to these surfaces was also tested. The strips of both polymers were subcutaneously and intracerebrally implanted into the rat and the extent of foreign body reaction and brain biocompatibility was evaluated. The results showed the extensive adsorption of basic fibroblast growth factor and heparin-binding epidermal growth factor-like growth factor to copolymer containing SPMAK. However the adhesion (and growth) of cells to this type of copolymers was very low. Preadsorption of human plasma to pHEMA clearly stimulated the leukocyte adhesion in contrary to copolymer containing SPMAK. The extent of foreign-body reaction was significantly higher against the pHEMA compared to tested copolymer p(HEMA-co-SPMAK). In conclusion, the tested copolymer was a poorly adhesive substrate that is only poorly recognized by the non-specific immunity, although the adsorption of basic growth factors to this substrate is highly significant. Both polymers were well tolerated by the brain tissue. The phenotype of surrounding neurons was more close to the control neurons in the brain tissue surrounding the p(HEMA-co-SPMAK) implants. © 2001 Kluwer Academic Publishers     

Measuring perceived sociability of computer-supported collaborative learning environments

Most asynchronous computer-supported collaborative learning (CSCL) environments can be characterized as functional environments because they focus on functional, task-specific support, often disregarding explicit support for the social (emotional) aspects of learning in groups which are acknowledged by many educational researchers to be essential for effective collaborative learning. In contrast, sociable CSCL environments emphasize the social (emotional) aspects of group learning. We define sociability as the extent to which a CSCL environment is perceived to be able to facilitate the emergence of a sound social space with attributes as trust and belonging, a strong sense of community, and good working relationships. Specific environmental characteristics, which we have designated social affordances, determine sociability.     

Drug loading and release of Tobramycin from hydroxyapatite coated fixation pins

This paper evaluates the loading and release properties of Tobramycin incorporated by adsorptive loading from a solution into plasma sprayed and biomimetically coated Hydroxyapatite (HA) fixation pins. The aim of this study is to contribute towards designing a functional implant surface offering local release of the antibiotic agent to prevent post-surgical infections. Cathodic arc deposition is used to coat stainless steel fixation pins with a bioactive, anatase phase dominated, TiO₂ coating onto which a HA layer is grown biomimetically. The loading and release properties are evaluated by studying the subsequent release of Tobramycin using high performance liquid chromatography and correlated to the differences in HA coating microstructure and the physical conditions under loading. The results from these studies show that a dual loading strategy consisting of a solution temperature of 90 °C and a pressure of 6 bar during a loading time of 5 min release a sufficient amount of Tobramycin to guarantee the inhibition of Staphylococcus aureus up to 2 days for plasma sprayed HA coatings and for 8 days for biomimetic coatings. The present study emphasizes the advantages of the nanoporous structure of biomimetically deposited HA over the more dense structure of plasma sprayed HA coatings in terms of antibiotic incorporation and subsequent sustained release and provides a valuable outline for the design of implant surfaces aiming for a fast-loading and controlled, local drug administration.     

Fullerene Derivatives, Preparation, Identification and Use

This article is focused on oxidation and halogenation of fullerene, identification of the prepared products and their potential application. The Fourier transform infrared （FTIR） spectrometry was used for analysis of oxidized fullerene derivative and material balance and elemental analysis were used to identify the summary composition of the prepared fullerene halogen derivatives We has conformed yet the radioprotective ability of oxidized fullerene in our recently published work radioprotective properties and toxicity test of C60 fullerene derivative in vivo ＆ in vitro. Since radioprotective properties are associated with the ability to recapture free radicals in the system （formed due to radiolysis of water in the physiological environment）, this property is closely connected also with fire-retarder properties, when the fire is also a radical mechanism. We tested thermal properties of polyvinyl alcohol （hereinafter PVA） nanofibers prepared with C60 and its derivatives as nanocomposites. The TG-DTA and TG-DSC analysis were used for this purpose. We have demonstrated experimentally that a retarder on C600xi basis and C60 halogenderivative has good results in increasing of thermal resistance of PVA-based nanofibers.     

Potential carbon impacts of smart grid development in six European countries

This paper examines reports on work carried out for the European Commission to devise a methodology for estimating the potential impact of smart grids on carbon emissions. It first identifies functionalities that enable carbon benefits to be realised. Each functionality on the demand side is assumed to be mirrored on the supply side, as when dynamic peak shifting ‘replaces’ flexible peak generation. Metrics are developed to describe the state of markets and to estimate customer response to demand response initiatives. Quantitative analysis identifies where the greatest scope for emissions reduction lies, while qualitative assessment indicates where to expect more or less impact from smart grid deployment. The impact of smart grid functionalities by 2020 is then modelled for six representative EU markets (Austria, France, Germany, Great Britain, Portugal and Spain), using a detailed pan-European market model and also a high-level ancillary services model. Three scenarios are developed: baseline, in which no smart grid rollout is assumed; feasible, based on what could be achievable in the light of technology developments and with supportive legislation; and an intermediate expected scenario, in which new technologies are introduced but nothing else changes. The findings indicate the potential for emissions reductions by 2020. They also show that the potential is very unlikely to be reached without regulatory support for user engagement in demand response and demand reduction, along with enabling technology and programmes. Development of regulatory frameworks that allow full advantage to be taken of the new technologies emerges as a challenge for smart grid development.     

Aperture averaging effects on the probability density of irradiance fluctuations in moderate-to-strong turbulence

The lognormal (LN) and gamma-gamma (GG) distributions are compared to simulated and experimental data of the irradiance fluctuations of a Gaussian beam wave propagating through the atmosphere along a horizontal path, near the ground, in the moderate-to-strong turbulence regime. Irradiance data were collected simultaneously at three receiving apertures of different sizes. Atmospheric parameters were inferred from the measurements and scintillation theory and were used to develop the parameters for the theoretical probability density functions. Numerical simulations were produced with the same C(n)(2) value as the experimental data. Aperture-averaging effects were investigated by comparing the irradiance distributions for the three apertures at two different values of the structure parameter C(n)(2), and, hence, different values of the coherence radius rho(0). For the moderate-to-strong fluctuation regime, the GG distribution provides a good fit to the irradiance fluctuations collected by finite-sized apertures that are significantly smaller than rho(0). For apertures larger than or equal to rho(0), the irradiance fluctuations appear to be LN distributed.