Poly(ether-imide) and poly(ether-imide)-polydimethyl-siloxane containing isopropylidene groups

Summary A poly(ether-imide) was prepared by thermal imidization of poly(amic-acid) intermediate resulting from the solution polycondensation reaction of a bis(ether-anhydride), namely 2,2′-bis-[(3,4-dicarboxyphenoxy)phenyl]-1,4-phenylene-diisopropylidene dianhydride, with an aromatic diamine containing two isopropylidene groups, namely 4,4′-(1,4-phenylenediisopropylidene)bisaniline. A poly(ether-imide)-polydimethylsiloxane copolymer was prepared by polycondensation reaction of the same bis(ether-anhydride) with an equimolar quantity of the aromatic diamine having isopropylidene groups and a bis(aminopropyl)polydimethylsiloxane oligomer of controlled molecular weight. A solution imidization procedure was used to convert quantitatively the poly(amic-acid) intermediates to the corresponding polyimides. The polymers were easily soluble in polar organic solvents and showed good thermal stability with decomposition temperature being above 400 °C. Electrical insulating properties of poly(ether-imide)-polydimethylsiloxane copolymer film were evaluated on the basis of dielectric constant and dielectric loss and their variation with frequency and temperature.     

Heparin Modulates the Mitogenic Activity of Fibroblast Growth Factor by Inducing Dimerization of its Receptor. A 3D View by Using NMR

In vitro mitogenesis assays have shown that sulfated glycosaminoglycans (GAGs; heparin and heparan sulfate) cause an enhancement of the mitogenic activity of fibroblast growth factors (FGFs). Herein, we report that the simultaneous presence of FGF and the GAG is not an essential requisite for this event to take place. Indeed, preincubation with heparin (just before FGF addition) of cells lacking heparan sulfate produced an enhancing effect equivalent to that observed when the GAG and the protein are simultaneously added. A first structural characterization of this effect by analytical ultracentrifugation of a soluble preparation of the heparin‐binding domain of fibroblast growth factor receptor 2 (FGFR2) and a low molecular weight (3 kDa) heparin showed that the GAG induces dimerization of FGFR2. To derive a high resolution structural picture of this molecular recognition process, the interactions of a soluble heparin‐binding domain of FGFR2 with two different homogeneous, synthetic, and mitogenically active sulfated GAGs were analyzed by NMR spectroscopy. These studies, assisted by docking protocols and molecular dynamics simulations, have demonstrated that the interactions of these GAGs with the soluble heparin‐binding domain of FGFR induces formation of an FGFR dimer; its architecture is equivalent to that in one of the two distinct crystallographic structures of FGFR in complex with both heparin and FGF1. This preformation of the FGFR dimer (with similar topology to that of the signaling complex) should favor incorporation of the FGF component to form the final assemblage of the signaling complex, without major entropy penalty. This cascade of events is probably at the heart of the observed activating effect of heparin in FGF‐driven mitogenesis.     

Performance evaluation of the UVAPS: influence of physiological age of airborne bacteria and bacterial stress

This study evaluated the effect of bacterial physiology, such as physiological age and stress, on the performance of the ultraviolet aerodynamic particle sizer (UV-APS, model 3312, TSI Inc., St. Paul, MN). Intensity of the fluorescent signals was measured for three bacteria having various sensitivities to environmental stresses, Bacillus subtilus (spores and vegetative cells), Pseudomonas fluorescens, and Micrococcus luteus. The performance of the UVAPS was found to depend on the type of airborne bacteria. In addition, the fluorescence signals for stationary-phase bacteria were generally stronger than for their log-phase counterparts. These results indicated that bacterial injury due to environmental stresses has a strong influence on the measured fluorescence signals. This hypothesis was confirmed by obtaining a linear relationship between the percentage of fluorescent particles and the proportion of injured bacteria in the total population of cultivable bacteria in samples simultaneously collected with the AGI-30 impingers. This indicates that the amount of fluorophors (specifically NADH) within injured bacteria is below the UVAPS sensitivity level. The practical implications of these findings are discussed in the paper. The reported results contribute to broadening our understanding of the method and may assist in developing sampling strategies for the application of the UVAPS to various bioaerosol studies.     

Copoly(1,3,4-oxadiazole-ether)s containing phthalide groups and thin films made therefrom

A series of aromatic copolyethers containing 1,3,4-oxadiazole rings and phthalide groups was prepared by nucleophilic substitution polymerization technique of phenolphthalein, 1, or of an equimolecular amount of 1 and different bisphenols 2, such as: 4,4′-isopropylidenediphenol, 4,4′-(hexafluoroisopropylidene)diphenol, 4,4′-(1,4-phenylene-diisopropylidene)bisphenol, 4,4′-cyclohexylidene-bisphenol and 2,7-dihydroxynaphthalene, with 2,5-bis(p-fluorophenyl)-1,3,4-oxadiazole, 3. The polymers were easily soluble in polar solvents such as N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide and chloroform and can be cast from solutions into thin flexible films. They showed high thermal stability, with decomposition temperature being above 400 °C. The polymers exhibited a glass transition temperature in the range of 220-271 °C, with reasonable interval between glass transition and decomposition temperature. Electrical insulating properties of some polymer films were evaluated on the basis of dielectric constant and dielectric loss and their variation with frequency and temperature. The values of the dielectric constant at 10 kHz and 20 °C were in the range of 2.98-3.15.     

A multiagent player system composed by expert agents in specific game stages operating in high performance environment

This paper proposes a new approach for the non-supervised learning process of multiagent player systems operating in a high performance environment, being that the cooperative agents are trained so as to be expert in specific stages of a game. This proposal is implemented by means of the Checkers automatic player denominated D-MA-Draughts, which is composed of 26 agents. The first is specialized in initial and intermediary game stages, whereas the remaining are specialists in endgame stages (defined by board-games containing, at most, 12 pieces). Each of these agents consists of a Multilayer Neural Network, trained without human supervision through Temporal Difference Methods. The best move is determined by the distributed search algorithm known as Young Brothers Wait Concept. Each endgame agent is able to choose a move from a determined profile of endgame board. These profiles are defined by a clustering process performed by a Kohonen-SOM network from a database containing endgame boards retrieved from real matches. Once trained, the D-MA-Draughts agents can actuate in a match according to two distinct game dynamics. In fact, the D-MA-Draughts architecture corresponds to an extension of two preliminary versions: MP-Draughts, which is a multiagent system with a serial search algorithm, and D-VisionDraughts, which is a single agent with a distributed search algorithm. The D-MA-Draughts gains are estimated through several tournaments against these preliminary versions. The results show that D-MA-Draughts improves upon its predecessors by significantly reducing training time and the endgame loops, thus beating them in several tournaments.     

Dependability issues in visual–haptic interfaces

Dependability of a system is commonly referred to its reliability, its availability and its maintenability (RAM), but when this concept is applied to user interfaces there is no common agreement on what aspects of user–system interaction are related to a satisfactory RAM level for the whole system. In particular, when dealing with haptic systems, interface dependability may become a crucial issue in medical and in military domains when life-critical systems are to be manipulated or where costly remote control operations are to be performed, like in industrial processes control or in aerospace/automotive engineering and manufacturing. This paper discusses the role of dependability in haptic user interfaces, aiming to the definition of a framework for the assessment of the usability and dependability properties of haptic systems and their possible correlations. The research is based on the analysis of a visual–haptic-based simulator targeted to maintenance activity training for aerospace industry which is taken as a case study. As a result, we propose a novel framework able to collect and then process relevant interaction data during the execution of haptic tasks, enabling to analyze dependability vs. usability correlations.     

Fractional convolution quadrature based on generalized Adams methods

In this paper we present a product quadrature rule for Volterra integral equations with weakly singular kernels based on the generalized Adams methods. The formulas represent numerical solvers for fractional differential equations, which inherit the linear stability properties already known for the integer order case. The numerical experiments confirm the valuable properties of this approach.