Improved method to simulate gradient in alumina packing fraction in alumina/epoxy composite fabricated by a centrifugal method

A centrifugal method was used to fabricate large‐scale functionally graded materials (FGMs) from solid‐particles/viscous‐matrix mixtures at room temperature. The conventional simulation procedure of the centrifugal process was improved by considering the dependency of the viscosity η of the mixture on the packing fraction ν_p of particle, the effects of arbitrary shape of the actual fillers on η, the statistical dispersion of the diameters of the actual fillers, and the formation and growth of the fully packed layer (FPL) near the FGM bottom. The new simulation method was applied to three centrifugal processes employed for experimental FGM fabrications from alumina/epoxy mixtures. The numerical profiles of ν_p are in good agreement with the experimental ones regardless of the shapes of fillers and 'ponding viscosity of the solutions without fillers, the total amount of fillers loaded, and the centrifugal conditions. The saturating nature of ν_p near the far end of the FGM column is also simulated with reasonable precision. Finally, the manner in which the particles exert varying influences on the gradient of ν_p is demonstrated: the particles exhibit different movements depending on their size. On the basis of these results, the effectiveness of the new simulation method proposed is confirmed for the modeling of similar processes involved in the fabrication of FGMs from solid‐particles/viscous‐matrix mixtures by the centrifugal method. © 2006 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Small-angle X-ray scattering studies on melting and recrystallization behaviors of poly(oxyethylene) crystallites in poly(d,l-lactide)/poly(oxyethylene) blends

Direct determination of the discrete distribution for crystalline lamellar thickness has been performed for poly(d,l-lactic acid)/poly(oxyethylene) (PDLLA/PEG) blends by conducting small-angle X-ray scattering (SAXS) measurements using synchrotron radiation. The PDLLA used was an random (racemic) copolymer of bio-based poly(l-lactic acid) (PLLA) and poly(d-lactic acid) (PDLA) with the lactide monomer ratio of l:d = 50:50. It is known that PLA is miscible with PEG in the amorphous state. In the current paper, we report comprehensive results on structural analyses of PDLLA/PEG blends in the course of heating and cooling process using SAXS to elucidate the change in the thickness distribution of the lamellae. As a consequence, it was found that the distribution of the lamellar thickness moves toward the larger value (in other words, lamellar thickening) as temperature approaches the melting point. Typically, the thickness distribution was dispersed in the range of 10–20 nm at room temperature and it changed toward 40 nm in the vicinity of the melting temperature. To the best of our knowledge, this is the first report of direct determination of the discrete distribution for the crystalline lamellar thickness and their in-situ changes in the course of the lamellar thickening process. As a result, the lamellar thickening was found to occur at much lower temperature for the blend samples with 10% and 20% of PDLLA contents as compared to the PEG 100% sample. This phenomenon can be ascribed to the melting point depression owing to the miscibility between PEG and PDLLA. Thereby, thinner lamellae were melted and thicker ones appeared at much lower temperature for the blends than for the PEG 100% sample. As for the average repeating distance (long period) of the lamellar stacks, an abrupt increase similar to the critical divergence was observed (from 25 nm to 50 nm) in the heating process. Not only for the melting behavior but also in the course of recrystallization, change in the lamellar-thickness distribution was uncovered, which shows strong hysteresis depending on what temperature the sample was cooled down from.     

TWO-CRACK PROPAGATION PATHS IN A FUNCTIONALLY GRADED MATERIAL PLATE SUBJECTED TO THERMAL LOADINGS

Two-crack propagation paths in a ceramic/metal functionally graded material plate (FGP) under one-cycle temperature change of heating and cooling are considered. When the FGP is subjected to thermal shock, a single crack or multiple cracks often initiate on the ceramic surface during the cooling process and propagate in the FGP. Crack paths are influenced by the heating temperature conditions, a compositional profile of the FGP, the fracture toughness, interaction among multiple cracks, and so on. Transient thermal stresses are treated as a linear quasi-static thermoelastic problem for a plane-strain state. The crack paths are treated under fracture mechanics using the finite-element method. The effects of heating temperature conditions, a compositional profile of the FGP, the fracture toughness, and a crack space on the crack propagation pattern are discussed and are shown in figures.     

DRYING AND DEWATERING R&D IN JAPAN

Presently, it has become an urgent and important concern worldwide to reduce the volume of waste and rationally use the waste for electric power generation. Sludge is a dominant part in the family of wastes. Drying of sludge, not only for volume reduction but also for further utilization, is becoming an essential and integral process. On the other hand, as the requirement of new materials production, for example, fine particles of micron or sub-micron scale for advanced materials, some new drying technologies and techniques have emerged. The market-pull may be the direct and active impetus to drying research and development (R&D). In this paper, drying technologies for sludges, fine particles, coatings as well as advanced dewatering are discussed to reflect the “hot” points of drying and dewatering R&D in Japan. And some novel dryers are also presented.     

Mutational analysis of structure--activity relationships in human tumor necrosis factor-alpha

To determine the region of human tumor necrosis factor-alpha(TNF-), essential for cytotoxic activity against mouse L-M cells,single amino-acid-substituted TNF- mutant proteins (muteins)were produced in Escherichia coli by protein engineering techniques.An expression plasmid for TNF- was mutagenized by passage throughan E.coli mutD5 mutator strain and by oligonucleotide-directedmutagenesis. Approximately 100 single amino-acid-substitutedTNF- muteins were produced and assayed for cytotoxic activity.The cytotoxic activities of purified TNF- muteins, e.g. TNF-31T,-32Y, -82D, -85H, -115L, -141Y, -144K and -146E, were < 1%of that of parent TNF-. These results indicate that the integrityof at least four distinct regions of the TNF- molecule is requiredfor full biological activity. These regions are designated asfollows: region I, from position 30 to 32; region II, from position82 to 89; region III, from position 115 to 117; region FV, fromposition 141 to 146. In addition, TNF-141Y could not completelycompete with parent TNF- for binding to the receptor. This demonstratesthat region IV, and at least aspartk acid at position 141, mustbe involved in the TNF receptor binding site.     

A study on hot carrier effects on N-MOSFETs under high substrate impurity concentration

A systematic investigation of the influences of high substrate doping on the hot carrier characteristics of small geometry n-MOSFETs down to 0.1 /spl mu/m has been carried out. Results indicate that the dependence of substrate current and impact ionization rate on substrate impurity concentration is reversed in long channel and short channel devices. In the long channel case, both increase with rising substrate impurity concentration, while they decrease in the case of short channel devices. An explanation for this phenomenon based on the lucky electron model has been developed. The dependence of other characteristics on impurity concentration has also been studied. The dependence of off-leakage current has been found to fall as the gate oxide is reduced in thickness. Regarding the dependence of hot carrier degradations, the degradation of drain currents becomes smaller as the substrate impurity concentration increases in the case of short channel devices. Further, in the extremely high impurity doping region, a new hot carrier degradation mode was found, in which the maximum transconductance values of n-MOSFETs increase after hot carrier stress. This new degradation mode can be explained in terms of effective channel length shortening caused by electron trapping.<>     

Competitive interaction of polyanions and anionic dye with bovine serum albumin

The binding of anionic dye, p-(2-amino-6-sulfonyl-8-naphthylazo)benzene sulfonic acid disodium salt (ASANA) to bovine serum albumin (BSA) at pH 7.5 has been studied by spectrophotometric techniques. The values of the dissociation constants were obtained with the use of the Benesi-Hildebrand equation for ASANA. Competitive binding of polyanions, sodium poly(styrene sulfonate) (PSSNa), potassium poly(vinyl sulfonate) (PVSK), poly(acrylic acid) (PAA), and poly(methacrylic acid) (PMAA) and anionic dye to BSA was evaluated through the variations in the different spectra of BSA-dye-polymer systems.     

Examination of simple analytical method for calculating 60-Hz magnetic field in power substations

In the last decade, increasing attention has been paid to ELF (Extremely Low Frequency) electromagnetic environments in work areas as well as in and near homes, regarding their interaction both with electric apparatus such as CRT's and with biological systems. Experimental and theoretical analyses are presented of 60 Hz magnetic field (B-field) characteristics at and near ground level in both 187/66-kV EHV and 66/6.6-kV HV power substations. Experimental results of B-field profiles along horizontal paths as well as harmonic contents in B-field waveforms at several positions are shown and discussed. Furthermore, analytical B-field profiles calculated by using a B-field approximation method based on Biot-Savart law are shown and compared with the measured ones. The comparisons verify that the assumptions employed are applicable to the substation B-field calculation, and that the B-field calculation method employed can estimate B-field in EHV and HV power substation to significant accuracy, except for areas where localized B-field sources, such as power transformers and underground power cables, exist. The analytical profiles of three orthogonal components of B-field are also described in terms of equiflux contour maps, which show 3-D characteristics of B-field in power substations.     

Mixed mode fracture criterion of interface crack between dissimilar materials

This study presents an application of fracture mechanics to the interface crack between dissimilar materials. In this study, a concept of the stress intensity factors of an interface crack is discussed, and various types of specimens are tested experimentally for investigating the mixed mode fracture toughness criterion of an interface crack. The fracture toughness based on the stress intensity factors of an interface crack is decided by the fracture test and the boundary element analysis using the contour integral method. The mixed mode fracture toughness criterion is successfully characterized by the stress intensity factors of an interface crack.