Preparation of poly(amide-imide)s derived from biphenyltetracarboxylic dianhydrides

Four new diimide-dicarboxylic acids (I–IV) were prepared by condensation of s- or a-BPDA with para- or meta-aminobenzoic acid. A series of aromatic poly(amide-imide)s containing these diimide-dicarboxylic units was prepared by three methods: (1) acid chloride method, (2) triphenylphosphite method, and (3) one-pot method. A typical polymer of the series is readily soluble in polar aprotic solvents such as N-methyl-2-pyrrolidone (NMP), dimethylsulfoxide (DMSO), and pyridine (py) and could be cast into tough and flexible films. These were characterized by inherent viscosity, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA) measurements. The glass transition temperatures of these polymers were in the range of 220–290°C, and the 5% weight loss temperatures were 450–500°C. Films prepared by casting from polymer solutions exhibited good tensile properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 865–873, 1997     

Preparation of phosphoric acid resins with large cation exchange capacities from macroreticular poly(glycidyl methacrylate-co-divinylbenzene) beads and their behavior in uptake of metal ions

In order to prepare phosphoric acid resins (RGPs) with large cation exchange capacities, effects of porosity and cross-linking of the precursory poly(glycidyl methacrylate-co-divinylbenzene) beads on their functionalization with phosphoric acid were studied. Two series of precursory copolymers were prepared: one was prepared by changing the amount of divinylbenzene (1–25 mol %) but by fixing that of isobutyl acetate (porogen) at 140 vol % per monomer mixture; the other by changing the amount of the porogen (40–160 vol %) but by fixing that of the cross-linker at 10 mol %. It was clarified that porosity of the precursors plays an important role in the functionalization. Highly porous precursors were functionalized with high efficiency; for example, even the precursors containing 10 mol % of divinylbenzene resulted in RGPs having cation exchange capacities as large as 6–7 meq/g, so long as BET specific surface areas of the precursors were greater than ca. 30 m²/g. The selectivity study has revealed that RGP exhibits the characteristic metal ion selectivity. Lithium ion was adsorbed in preference to sodium and potassium ions; and so-called hard Lewis acid cations, such as uranyl, ferric, and aluminum ions, are adsorbed even from strongly acidic media (1 < pH < 2). Among common divalent metal ions, in addition, the resin exhibits the highest selectivity toward lead ion. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1327–1334, 1997     

Accumulation of Misfolded Protein Aggregates Leads to the Formation of Russell Body-like Dilated Endoplasmic Reticulum in Yeast

RNAP-I, an aspartic proteinase from a filamentous fungus Rhizopus niveus, is secreted very efficiently in Saccharomyces cerevisiae. It is synthesized first as a precursor form with signal sequence and prosequence in its amino-terminus. Our previous study indicated that the prosequence of RNAP-I had important roles in its correct folding and secretion in yeast, and that a prosequence-deleted derivative of RNAP-I, Δpro, was not secreted but was retained and degraded in the yeast endoplasmic reticulum (ER). In the present study, we show that the accumulation of Δpro in the yeast ER caused elevated synthesis of ER resident chaperones, indicating that Δpro is recognized as an unfolded protein species in the ER. Our biochemical data demonstrated that Δpro formed aggregates which contained BiP, but not protein disulfide isomerase (PDI), in the ER. Immunoelectron microscopical analysis revealed that the Δpro aggregates were indeed visible as electron-dense regions in the ER and nuclear envelope. Such ‘chaperone-associated misfolded protein bodies’ were observed for the first time in yeast. Morphologies of the ER and nucleus were drastically altered by the accumulation of the Δpro aggregates. The ER lost its flat cisternal shape; the ER lumen extended aberrantly and the ER membrane irregularly proliferated. The misfolded Δpro proteins are probably sorted from the ordinary ER lumen to form the aggregates so that the ER function would not be grossly impaired, and the dilated ER may represent an ER subcompartment where the Δpro aggregates are degraded. © 1997 by John Wiley & Sons, Ltd.     

A digital application of chaotic oscillation modes in Josephson circuit

Novel digital circuits utilizing the chaotic oscillation and its associated oscillations produced in a Josephson junction (JJ) circuit are proposed, as an application of chaotic oscillations in JJ circuit. To begin with, what oscillation modes can be produced in a JJ circuit are described in detail. Next, a novel idea showing the possibility of digital circuits by use of chaotic oscillations is proposed. As an example, the fundamental digital circuits performing AND, NAND, Exclusive-OR, and so on are shown. The simulation results of these novel digital circuits show that reliable and high performance circuits can be realized by utilizing chaotic behavior. © 1997 John Wiley & Sons, Inc.     

Correlation between network structure and brittleness of triallyl isocyanurate resins as compared with diallyl phthalate resins

It is not possible to improve the toughness of triallyl isocyanurate (TAIC) resins by applying the procedures useful for diallyl phthalate (DAP) resins as typical allyl resins. The results obtained are discussed in connection with the network structure of TAIC resin. Thus, the polymerization of TAIC would provide a homogeneous network accompanied by the incomplete occurrence of intermolecular crosslinking reactions caused by the rigidity of polymer chains, although DAP resins would consist of the microheterogeneous networks as the agglomerate of colloidal particles.     

A new multi-scale simulation model of the circulation: from cells to system

We developed a comprehensive cell model that simulates the sequential cellular events from membrane excitation to contraction in the human ventricle. By combining this ventricular cell model with a lumped circulation model, we examined how blood pressure dynamics in the ventricle and aorta are related to the cellular processes. To convert cell contraction into ventricular pressure using Laplace's law, we introduced a simple geometric model of a ventricle: one shaped like a thin-walled hemisphere. The force of contraction of a single cell induces tension in the hemispheric ventricular wall, which generates the ventricular and aortic pressures in the lumped circulation model. The time courses of the hemodynamic properties, as well as the volume-pressure trajectory of the left ventricle, were well reproduced. Our multi-scale cardiovascular model, which covers from cardiac cells to the circulatory system, simulates the typical characteristics of heart mechanics, such as the pressure-volume relationship, stroke volume and the effect of the increased maximum free calcium concentration on cardiovascular hemodynamics. To test the cell-circulation coupling characteristics of the model, we simulated the effects of a decrease in L-type calcium channel conductance (cell level) on left ventricular pressure (system level). The variation due to different pacing frequencies for myocyte excitation was also investigated to assess the effects of heart rate on cardiac cells and the circulatory system.     

Formation of 1D and 2D gold nanoparticle arrays by divalent DNA-gold nanoparticle conjugates

Divalent DNA-AuNP (gold nanoparticle) conjugates comprising two DNA strands at diametrically opposed positions are prepared. Highly linear 1D and tetragonal lattice-like 2D AuNP arrays are constructed using the conjugates and DNA assemblies based on T- and double-crossover motifs and the Holliday junction.     

Charge-discharge rate of spinel lithium manganese oxide and olivine lithium iron phosphate in ionic liquid-based electrolytes

Rate capability of Li/spinel LiMn₂O₄ or olivine LiFePO₄ positive electrode cells containing mixed imidazolium ionic liquids electrolytes has been investigated under comparison with conventional organic solvent electrolyte and piperidinium ionic liquid. The LiMn₂O₄ electrode provides variation of rate capabilities among the ionic liquid electrolytes, while ionic liquid electrolytes provide similar extent of capacity degradation under high rate compared with organic solvent electrolyte for LiFePO₄ electrode. Such differences in electrolyte dependences of the rate capabilities can be explained in relation to parameters in the high frequency resistances on AC impedance, assumed as interfacial resistances. The rate capability of LiMn₂O₄ is somewhat related to the activation energy of the high frequency resistance, while for LiFePO₄ the resistance value appears to contribute to the rate capability.     

Experimental characterization of high-speed impact damage behavior in a three-dimensionally woven SiC/SiC composite

This paper discusses high-speed impact damage in a three-dimensionally woven SiC/SiC composite (3D-CMC). The impact damage was introduced by a steel ball projectile in 3D-CMC plates with and without thermal exposure. The surface and internal damages were observed by optical microscopy and X-ray CT. A crater was observed on the collision surface. The X-ray CT measurement revealed that multiple pyramid-shaped cone cracks were generated beneath the crater when the impact speed was relatively low. At an impact speed exceeding the critical speed, a spall fragment was ejected from the back surface, while no internal damage was observed in the fragment. The spall fracture mode differed between the virgin and the thermally-exposed specimens. This difference is the result of embrittlement of the fiber/matrix interface due to oxidation of the carbon coating layer in the thermally-exposed specimen. In addition, it is found that z-yarns improve impact resistance by constraining delamination.     

Growth of ZnO crystal on sapphire and nitridated sapphire substrates at 1000 °C by halide vapor phase epitaxy

Using a halide vapor phase epitaxy (HVPE) technique in which the starting materials are ZnCl₂ generated by the reaction between high purity Zn metal (7 N grade) and Cl₂ gas, and H₂O, ZnO crystals have been grown at a high temperature of 1000 °C on sapphire substrates with and without surface nitridation treatment. It was found that the nitridation treatment resulted in a change of the (112?0) sapphire surface to a (0001) AlN structure, leading to two possible sets of orientations for (0001) ZnO crystals. In addition, the nitridation treatment leads to a smaller average ZnO grain size and a higher density of nuclei.