Activation of a Au/TiO2 Catalyst by Loading a Large Amount of Fe–Oxide: Oxidation of CO Enhanced by H2 and H2O

Catalytic activity of a 1 wt% Au/TiO₂ catalyst is markedly improved by loading a large amount of FeO_x, on which the oxidation of CO in excess H₂ is selectively promoted at temperature lower than 60 °C. Oxidation of CO with O₂ on the FeO_x/Au/TiO₂ catalyst is markedly enhanced by H₂, and H₂O moisture also enhances the oxidation of CO but its effect is not so large as the promotion by H₂. We deduced that activation of Au/TiO₂ catalyst by loading FeO_x is not caused by the size effect of Au particles but a new reaction path via hydroxyl carbonyl intermediate is responsible for the superior activity of the FeO_x/Au/TiO₂ catalyst.     

Development of reel-to-reel microchip mounting system for fabrication of meter-long LED lighting tapes

We have developed a reel-to-reel microchip mounting system that continuously mounts LED chips and other microchips on meter-long flexible printed circuit board (PCB) tape for 1.2-m-long standard LED light tubes. Mounting microchips on meter-long PCBs is difficult because a large chip mounter is expensive and the chip positioning stage is difficult to move in a meter-wide area with an accuracy of hundreds of micrometers. Hence, we developed a new microchip mounting system that utilizes a small chip mounter and reel winding machines. The system repeatedly moves the long PCB tape by a certain length with the reel winding machines and mounts the chips on it. The PCB tape (which is 5 mm wide) is made by fabricating long PCB tapes which are 25 cm × 26.6 m through a roll-to-roll PCB process and slitting them into meter-long tapes. The reel-to-reel system repeatedly mounts chips by adjusting their positions through image processing of the copper wiring pattern on the PCBs. Our constructed system mounted 24 LED chips with a pitch of 5 cm with an accuracy of 0.082 mm to form a 1.2-m-long LED tape. The luminance of the tape is 12.4 lx at a distance of 1 m, which is the luminance of outdoor corridor lighting. Therefore, this system can be used for meter-long tape lighting.     

Thermal strain of high strength polyethylene fiber in low temperature

High strength polyethylene fiber (Toyobo, Dyneema® fiber: hereinafter abbreviated to DF) has a negative thermal expansion coefficient. Relation between fiber structure and thermal strain of DF used as reinforcement of DF reinforced plastic (DFRP) for cryogenic use was investigated. The crystallinities and orientation angles of several kinds of polyethylene fibers having different modulus from 15 to 134Gpa (herein after abbreviated to DFs) were measured by NMR and X‐ray. We obtained the parameters of the mechanical series‐parallel model composed of crystal and amorphous by crystallinity and modulus. Thermal expansion coefficients of DFs were estimated by mechanical series‐parallel model. All DFs having different modulus showed negative thermal expansion coefficients in the temperature range from 180 to 300K, and absolute values of those markedly increased by increasing tensile modulus of DF. The estimated thermal expansion coefficients showed negative values, and thermal strains showed a similar curve to observed ones mostly. Average thermal expansion coefficients in the temperature range from 180 to 300K estimated by mechanical model agreed with the observed ones. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2918–2925, 2004     

Flexural and tensile moduli of polypropylene nanocomposites and comparison of experimental data to Halpin‐Tsai and Tandon‐Weng models

This research focuses on the reinforcing efficiency of nanomateterials and the role of the reinforcement's dispersion and orientation on the nanocomposite's flexural and tensile moduli. Polypropylene‐based composites reinforced with (i) exfoliated graphite nanoplatelets, xGnP?, (ii) vapor grown carbon fibers, (iii) PAN‐based carbon fibers, (iv) highly structured carbon black and (v) montmorillonite clay were fabricated by extrusion and injection molding. It was found that graphite platelets are the best reinforcement in terms of flexural modulus whereas PAN‐based carbon fibers cause the largest improvement in the tensile modulus. The difference in the reinforcing efficiency during the flexural and tensile testing is attributed to (i) the degree of fiber alignment along the flow direction during injection molding, which is higher in the thinner tensile specimens than in the flex specimens; and (ii) the different deformation modes of the two tests. The importance of good dispersion of the reinforcements within the polymer matrix and of perfect contact between the two phases is emphasized comparing the experimental modulus data to theoretical predictions made using the Halpin‐Tsai and the Tandon‐Weng models. POLYM. ENG. SCI., 47:1796–1803, 2007. © 2007 Society of Plastics Engineers     

WATER MIST FLOW IN A SUPERCONDUCTING MAGNET INCLINED AT VARIOUS ANGLES

Water mist (diamagnetic) flow in a superconducting magnet of 10 T at various angles is studied experimentally and numerically. Water mist is produced by ultrasonic atomizers and fed into a cylindrical Plexiglas pipe (inner diameter, 90 mm) placed in a bore space of an inclined superconducting magnet. The water mist is found to stop at some locations in the magnet at inclined angles ψ ≤ π/6. At ψ ≥ π/4, the amount of mist flowing out of the other opening of the pipe increases with an increase in inclined angle. In the computation of this phenomenon, water mist is simulated with 1000 water droplets of 3 μm diameter. Brownian motion is considered and the Langevin equation is solved. The numerical results show that at ψ ≤ π/6, most of the water droplets accumulate above the magnetic coil. However, at ψ ≥ π/4, with an increase in inclined angle, the number of water droplets passing through the magnetic coil increases.     

Effect of cation structure on the electrochemical and thermal properties of ion conductive polymers obtained from polymerizable ionic liquids

Several onium cations having vinyl group formed ionic liquids after coupling with bis(trifluoromethanesulfonyl)imide. These monomers were polymerized, and the relation between onium cation structure and properties of thus polymerized ionic liquids was investigated. The polymerized ionic liquid having ethylimiadzolium cation unit showed the highest ionic conductivity of around 10⁻⁴ S cm⁻¹ at 30 °C among the obtained polymers reflecting the lowest glass transition temperature of −59 °C. These polymers were thermally stable and their decomposition temperatures were about 350 °C. The ionic conductivity of the polymerized ionic liquids decreased by both the addition of lithium bis(trifluoromethanesulfonyl)imide and the polymerization in the presence of cross-linker. However, the polymerized ionic liquid having 1-methylpiperidinium cation structure showed good lithium ion transference number of 0.43 at room temperature.     

Barium Carbonate Phase on the Surfaces of Barium Titanate Particles and in Situ Transmission Electron Microscopy Observation of Its Decomposition

A BaCO₃ phase is found on the surfaces of hydrothermally synthesized BaTiO₃ particles; it occurs as aggregates or small protuberances. A small proportion of the phase decomposes to BaO crystallites when heated by a convergent electron beam in a transmission electron microscope. The BaO and BaCO₃ crystallites disappear when they are irradiated successively by the convergent electron beam. The BaO crystallites and the BaCO₃ phase sublimate and/or react with BaTiO₃ crystals whose surface layers are deficient in Ba²⁺ ions.     

Alteration of substrate specificity of cholesterol oxidase from Streptomyces sp. by site-directed mutagenesis

Despite the structural similarities between cholesterol oxidasefrom Streptomyces and that from Brevibacterium, both enzymesexhibit different characteristics, such as catalytic activity,optimum pH and temperature. In attempts to define the molecularbasis of differences in catalytic activity or stability, substitutionsat six amino acid residues were introduced into cholesteroloxidase using site-directed mutagenesis of its gene. The aminoacid substitutions chosen were based on structural comparisonsof cholesterol oxidases from Streptomyces and Brevibacterium.Seven mutant enzymes were constructed with the following aminoacid substitutions: L117P, L119A, L119F, V145Q, Q286R, P357Nand S379T. All the mutant enzymes exhibited activity with theexception of that with the L117P mutation. The resulting V145Qmutant enzyme has low activities for all substrates examinedand the S379T mutant enzyme showed markedly altered substratespecificity compared with the wild-type enzyme. To evaluatethe role of V145 and S379 residues in the reaction, mutantswith two additional substitutions in V145 and four in S379 wereconstructed. The mutant enzymes created by the replacement ofV145 by Asp and Glu had much lower catalytic efficiency forcholesterol and pregnenolone as substrates than the wild-typeenzyme. From previous studies and this study, the V145 residueseems to be important for the stability and substrate bindingof the cholesterol oxidase. In contrast, the catalytic efficiencies(k_cat/K_m) of the S379T mutant enzyme for cholesterol and pregnenolonewere 1.8- and 6.0-fold higher, respectively, than those of thewild-type enzyme. The enhanced catalytic efficiency of the S379Tmutant enzyme for pregnenolone was due to a slightly high k_catvalue and a low K_m value. These findings will provide severalideas for the design of more powerful enzymes that can be appliedto clinical determination of serum cholesterol levels and assterol probes.     

An absolute requirement of fructose 1,6-bisphosphate for the Lactobacillus caseiL-lactate dehydrogenase activity induced by a single amino acid substitution

Lactobacillus casei allosteric L-lactate dehydrogenase (L-LDH)absolutely requires fructose 1,6-bisphosphate [Fru(1,6)P2] forits catalytic activity under neutral conditions, but exhibitsmarked catalytic activity in the absence of Fru(1,6)P₂ underacidic conditions through the homotropic activation effect ofsubstrate pyruvate. In this enzyme, a single amino acid replacement,i.e. that of His205 conserved in the Fru(1,6)P₂-binding siteof certain allosteric L-LDHs of lactic acid bacteria with Thr,did not induce a marked loss of the activation effect of Fru(1,6)P₂or divalent metal ions, which are potent activators that improvethe activation function of Fru(1,6)P₂ under neutral conditions.However, this replacement induced a great loss of the Fru(1,6)P₂-independentactivation effect of pyruvate or pyruvate analogs under acidicconditions, consequently indicating an absolute Fru(1,6)P₂ requirementfor the enzyme activity. The replacement also induced a significantreduction in the pH-dependent sensitivity of the enzyme to Fru(1,6)P₂,through a slight decrease and increase of the Fru(1,6)P₂ sensitivityunder acidic and neutral conditions, respectively, indicatingthat His205 is also largely involved in the pH-dependent sensitivityof L.casei L-LDH to Fru(1,6)P₂. The role of His205 in the allostericregulation of the enzyme is discussed on the basis of the knowncrystal structures of L-LDHs.