Effect of polyethyleneimine-fatty acid complex type dispersant structure on the overall processing chain of Si3N4 ceramics using multicomponent non-aqueous slurries

The effect of fatty acid structure of polyethyleneimine (PEI)-fatty acid complex, which was designed as a polymer dispersant for multi-component non-aqueous slurries, on the overall processing chain of Si₃N₄ ceramics involving slurry stabilization, spray drying, compaction, and liquid sintering was investigated using PEI-oleic acid (PEI-OA) and PEI-isostearic (PEI-ISA) complexes. Si₃N₄-Y₂O₃-Al₂O₃-AlN-TiO₂/toluene slurries were selected as a real model for Si₃N₄-based multicomponent slurries. It was observed that both PEI-OA and PEI-ISA can stabilize Si₃N₄-Y₂O₃-Al₂O₃-AlN-TiO₂/toluene slurries; however, the PEI-ISA system tended to have slightly higher slurry viscosity, which was suspected to be due to the interactions between protruded PEI segments among short ISA chains. The spray-dried granules from PEI-ISA-stabilized slurry were observed to have filled structures with higher surface roughness whereas those prepared from PEI-OA-stabilized slurry were observed to have hollow-structured granules. The granules prepared from PEI-OA slurry had improved flow and compaction properties with higher relative density of green compacts compared with those prepared from PEI-ISA-stabilized slurry, whereas the relative density and microstructural homogeneity of S₃N₄ ceramics sintered at 1600?°C for 2?h were observed to be higher for the PEI-ISA system. It is suspected that PEI-OA effectively improved the dispersion stability of multicomponent slurries and flow/compaction properties of granules; however, the inhomogeneous microstructures of green compacts induced by the hollow-structured granules had an adverse effect on the sintering of Si₃N₄ ceramics.     

Characteristics of plasma produced by MHD technology and its application to propulsion systems

This paper analyzes plasma characteristics for the newly proposed concept of a closed-loop MHD power generation combined cycle system, which is used as a pulse-driven MHD accelerator to accelerate plasma to high velocity, with a nuclear plant. In this paper, since the final goal is for the space propulsion system applications, the performance of a MHD acceleration system is also analyzed by the Q1D analysis program. Results reveal that the radial velocity with the MHD effect is accelerated rapidly at the channel exit, with a calculated maximum velocity of about 4700 m/s. Consequently, specific impulse approximately 480 s and thrust of about 6550 N are estimated. The static gas temperature is evaluated at less than 600 K, while the value of about 1800 K is calculated for the stagnation gas temperature in the MHD channel.     

“Disturbance observers in D‐module” for sensorless drive of synchronous motors—new phase estimation with zero phase lag

This paper proposes two new “disturbance observers in the D‐module” for sensorless drive of synchronous motors including permanent‐magnet synchronous motors and synchronous reluctance motors. The disturbance filter for the observers can estimate speed‐varying rotor phase (in other words, rotor position) with zero phase lag. It is constructed by means of “the filter in the D‐module,” which has the following desired characteristics for variable sensorless drive: (1) it makes distinction between positive and negative frequencies of two‐phase signals; (2) it can allow processing of the signals based on frequency polarities; (3) it can also change dynamically its center frequency of bandpass filtering according to rotor speed estimates; (4) its passband and transition can be designed independently; and (5) it can be easily realized. The new disturbance observers also have a generality such that they contain the recently proposed disturbance observer as a special case. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(3): 63–70, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20602     

Investigation of electron trapping behavior in n-channel organic thin-film transistors with ultrathin polymer passivation on SiO2 gate insulator

Electron trapping behavior at the interface between N,N′-ditridecyl-3,4,9,10-perylene tetracarboxylic diimide (PTCDI-C13) film and thermal SiO₂ was investigated by utilizing ultrathin poly(methyl methacrylate) (PMMA) gate passivation layers. From the capacitance–voltage analysis for the PTCDI-C13/PMMA/SiO₂ interface, it is found that the electron tunneling appeared with PMMA thinner than 0.8 nm, and that the thickness of the gate passivation layer should be at least 1 nm for preventing injection-type hysteresis in the capacitance–voltage curve. The effective electron mobility of organic thin-film transistors (OTFTs) based on PTCDI-C13 with SiO₂ gate insulator was increased by suppressing shallow-level interface traps on SiO₂ with the PMMA layer, which can be partially accounted for by the multiple trap and release model. In this work, the thickness and the density of the PMMA layers were precisely controlled with a simple spin-coating process. Even 1.3-nm thick PMMA layer caused the improvements of the electron mobility and the air stability of the n-channel conduction.     

Molecular dynamics simulation of 〈<Emphasis Type="Bold">c</Emphasis>+<Emphasis Type="Bold">a</Emphasis>〉 dislocation core structure in hexagonal-close-packed metals

The core structures of 〈c+a〉 dislocations in hexagonal-close-packed (hcp) metals have been investigated by molecular dynamics (MD) simulation using a Lennard-Jones-type pair potential. The 〈c + a〉 edge dislocation has two types of core at 0 K; one is a perfect dislocation (type A), and the other has two 1/2 〈c+a〉 partials (type B). Type A transforms to type B by abruptly increasing temperature from 0 K to 293 K, while type B is stable in temperature range from 0 K to 293 K. In contrast, type A extends parallel to (0001) at 30 K, and this extended core is still stable at 293 K. These results suggest that the 〈c+a〉 edge dislocation glides on the {11 2} as two 1/2 〈c+a〉 partial dislocations and becomes sessile due to changes of the core structure. The 〈c+a〉 screw dislocation spreads over two {10 1} planes at 0 K. The core transforms into a unsymmetrical structure at 293 K, which is spread over {11 2} and {10 1}, and core spreading occurs parallel to {11 2} at 1000 K. A critical strain to move screw dislocations depends on the sense of shear strain. The dependence of the yield stress on the shear direction can be explained in terms of these core structures. This article is based on a presentation made in the symposium entitled “Defect Properties and Mechanical Behavior of HCP Metals and Alloys” at the TMS Annual Meeting, February 11–15, 2001, in New Orleans, Louisiana, under the auspices of the following ASM committees: Materials Science Critical Technology Sector, Structural Materials Division, Electronic, Magnetic & Photonic Materials Division, Chemistry & Physics of Materials Committee, Joint Nuclear Materials Committee, and Titanium Committee.     

Catalytic C-h/olefin coupling

The cleavage and addition of ortho C-H bonds in various aromatic compounds such as ketones, esters, imines, imidates, nitrile, and aldehydes to olefins and acetlylenes can be achieved catalytically with the aid of ruthenium catalysts. The reaction is generally highly efficient and useful in synthetic methods. The coordination to the metal center by a heteroatom in directing groups such as carbonyl and imino groups is the key. The reductive elimination to form a C-C bond is the rate-determining step.     

Ammonia assimilation in Klebsiella pneumoniae F-5-2 that can utilize ammonium and nitrate ions simultaneously: purification and characterization of glutamate dehydrogenase and glutamine synthetase

The two ammonia-assimilating enzymes glutamate dehydrogenase (GDH; EC 1.4.1.4) and glutamine synthetase (GS; EC 6.3.1.2) were synthesized steadily during the cell growth of Klebsiella pneumoniae F-5-2 that can utilize NH4+ and NO3- simultaneously under aerobic conditions. The enzymes were purified to homogeneity from cell extracts and characterized. The molecular mass of the purified GDH was 300 kDa with six identical 52-kDa subunits. GDH showed its maximal activity (aminating) at pH 8.0 and was stable between pHs 5.5 and 11.5. The enzyme was NADP-specific and strongly inhibited by Ag+. It catalyzed the amination of 2-ketovalerate, 2-ketoadipate, and 2-ketobutyrate, in addition to 2-ketoglutarate. The purified GS has a molecular mass of 470 kDa with eight identical 60-kDa subunits. GS showed its maximal activity at pH 8.0 and was stable between pHs 6.0 and 7.0. The enzyme was strongly inhibited by Fe3+, Hg2+, and Cu2+.     

Stability tests and stabilization for piecewise linear systems based on poles and zeros of subsystems

This paper provides several stability tests for piecewise linear systems and proposes a method of stabilization for bimodal systems. In particular, we derive an explicit and exact stability test for planar systems, which is given in terms of coefficients of transfer functions of subsystems. Restricting attention to the bimodal and planar case, we show simple stability tests. In addition, we drive a necessary stability condition and a sufficient stability condition for higher-order and bimodal systems. They are given in terms of the eigenvalue loci and the observability of subsystems. All the stability tests provided in this paper are computationally tractable, and our results are applied to the stabilizability problem. We confirm the exactness and effectiveness of our approach by illustrative examples.     

Molecular cloning and characterization of a novel bacteriophage-associated sialidase

Bacteriophage 63D, previously isolated from sewage, is associated with alpha-2,8-linked polysialic acid degrading activity. We cloned a DNA fragment containing the sialidase gene from a 63D phage genomic library and the enzyme was functionally expressed in Escherichia coli. Determination of the nucleotide sequence of the fragment revealed that it contained one open reading frame (ORF) coding for a 108-kDa polypeptide consisting of 984 amino acid residues. The fragment had promoter sequences similar to the E. coli consensus promoters for sigma70. The deduced amino acid sequence of the central region of the ORF showed homology to those of phages K1F (51.6% identity) and PK1E (51.7% identity) endosialidases. Two Asp-box motifs that are widely found in sialidases were conserved. Purification of the soluble enzyme from lysed culture broth of infected E. coli yielded a 90-kDa protein upon SDS polyacrylamide gel electrophoresis, suggesting that the primary translational product is processed to the mature 90-kDa protein. The molecular mass of the enzyme was determined as 360 kDa by gel filtration, indicating that the native enzyme was probably a tetramer of identical 90-kDa subunits.     

Growth induction of rat primary hepatocytes using antisense oligonucleotides

We examined growth control of adult and fetal hepatocytes by regulating the expression of cell-cycle-related proteins using antisense S-oligonucleotides to tumor suppressors retinoblastoma (RB) protein and p53, and cyclin-dependent kinase (CDK) inhibitors p21 and p27. The protein expression in both adult and fetal hepatocytes was significantly suppressed with the addition of corresponding antisense oligonucleotides at a concentration of 2.5 microM. For the evaluation of growth, 3H-thymidine incorporation and DNA content were measured and the results demonstrated that all the antisense oligonucleotides had growth-promoting effects and the promoting potential was equivalent or slightly greater than that with the addition of hepatocyte growth factor (HGF) (10 ng/ml). The growth-promoting effect of the antisense oligonucleotides was enhanced by HGF in both adult and fetal hepatocyte cultures, and the effects on hepatocyte growth were also observed in a suspension culture.