Effect of pulsed DC current on atomic diffusion of Nb–C diffusion couple

The effect of pulsed DC current on the atomic diffusion of an Nb–C system using Spark Plasma Sintering (SPS) was investigated. In all experiments, a current density of approximately 723 A/cm² was applied to the specimen and used in a temperature range of 1,673–1,973 K. From the results of X-ray diffraction analysis, the product phases formed between Nb and C were found to be Nb₂C and NbC. The growth of product layers significantly increased in the presence of current. However, the thickness of the product layer did not change in the current direction in the SPS. The activation energies for the formation of the Nb₂C and NbC layers were calculated to be 298 ± 4 kJ/mol and 282 ± 3 kJ/mol in the presence of current, which were similar values compared to the activation energies of 300 ± 5 kJ/mol and 285 ± 2 kJ/mol in the absence of current, respectively.     

A thin-film solar cell of high-quality -FeSi2/Si heterojunction prepared by sputtering

High-quality (1 1 0)/(1 0 1)-oriented epitaxial β-FeSi₂ films were fabricated on Si (1 1 1) substrate by the sputtering method. The critical feature was the formation of a high-quality thin β-FeSi₂ template buffer layer on Si (1 1 1) substrate at low temperature. It was demonstrated that the template is very important for the epitaxial growth of thick β-FeSi₂ films and for the blocking of Fe diffusion into the Si at the β-FeSi₂/Si interface. Hall effect measurements for β-FeSi₂ films showed n-type conductivity, with residual electron concentration around 2.0 × 10¹⁷ cm⁻³ and mobility of 50–400 cm²/V s. A prototype thin-film solar cell was fabricated by depositing n-β-FeSi₂ on p-Si (1 1 1). Under 100 mW/cm² sunlight, an energy conversion efficiency of 3.7%, with an open-circuit voltage of 0.45 V, a short-circuit current density of 14.8 mA/cm² and a fill factor of 0.55, was obtained.     

Scission of the poly(methyl methacrylate‐co‐methacrylic acid) chain by excited‐state acridine

A photochemical reaction between acridine and poly(methyl methacrylate‐co‐methacrylic acid) (PMCA) was studied in benzene to build a recyclable polymer photodegradation system. The illumination of acridine in the presence of PMCA with 365‐nm light induced the bleaching of acridine and the degradation of PMCA. The average molecular weight of the degraded polymer decreased rapidly for the first 30 min of the photolysis. A nonvolatile product of this reaction was found to have a 2‐methyl‐2‐propenyl end group. The efficiency of the PMCA scission by this method was 30 times as large as that of poly(methyl methacrylate). These results suggest that an efficient photochemical polymer decomposition system can be built by adding the mixing process of a little methacrylic acid into the synthetic processes of general vinyl polymers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1209–1212, 2005     

Formation of TiO2 hollow microparticles by spraying water droplets into an organic solution of titanium tetraisopropoxide (TTIP) — Effects of TTIP concentration and TTIP-protecting additives

Hollow, spherical TiO₂ microparticles of several tens of micrometers in diameter can be prepared by spraying water into an organic phase containing titanium tetraisopropoxide (TTIP) as a titanium source. The concentration of TTIP did not affect the shell thickness. On the contrary, the shell thickness was increased with the concentration of the additives such as acetic acid and acetylacetone, having effects to protect TTIP from hydrolysis and condensation. The formation of a hollow particle was described by a simple model involving the hydrolysis of TTIP at the water–oil interface, the inward diffusion of hydrolyzed titanium hydroxide through the passage in the shell and its incorporation into the TiO₂ shell by condensation. The reduction of porosity of shell inhibits the diffusion, resulting in the formation of hollow structure. The simulation based on this model predicted that the shell thickness increased as the diffusion rate increased or the reaction rate decreased, and was independent of the outer TTIP concentration. These predictions were in qualitative agreement with the experimental results.     

Energy-dispersive XAFS study on the decarbonylation process of Mo(CO)6 in NaY zeolite

The temperature-programmed decarbonylation process of Mo(CO)₆ in NaY zeolite was studied by means of a time-resolved energy-dispersive XAFS method. The XANES analysis demonstrated that the decarbonylation proceeded by two successive steps via a stable intermediate which existed between 440 and 490 K. The curve fitting analysis of the EXAFS data revealed that the intermediate was a molybdenum monomer subcarbonyl species Mo(CO)₃(O_L)₃ coordinated by three CO ligands and three oxygen atoms of zeolite framework (O_L). Molybdenum dimer subcarbonyl species were not observed. This study demonstrated that the DXAFS technique is a powerful method to study the dynamic behavior of the Mo carbonyl species during decarbonylation process.     

Isolation and characterization of a novel hydrogen-producing strain Clostridium sp. suitable for immobilization

A hydrogen-producing strain of bacteria suitable for immobilization was isolated from anaerobic sludge obtained from a methane fermentation plant. The isolated strain, CFPA-20 was identified as a novel species of the genus Clostridium by phylogenetic analysis of the 16S rRNA sequence. The changes in free energy of interaction of adhesion to polymer resin and self-aggregation were both negative. This indicated that CFPA-20 was thermodynamically favored for immobilization. CFPA-20 grew at a temperature range of 25–37 °C and at a pH range of 4.5–9.0. Immobilization of CFPA-20 on block copolymer polyethylene glycol-b-polypropylene glycol gave a radically improved hydrogen production yield (2.91 mol/mol-glucose) and a maximum hydrogen production rate (568 mL/L-culture/h) compared to the non-immobilized isolate. In addition, the biofilm of CFPA-20 acquired tolerance for volatile fatty acids. Further investigation into this mechanism may ultimately improve the hydrogen production capacity of CFPA-20.     

Identification and analysis of specific chromosomal region adjacent to exogenous Dhfr-amplified region in Chinese hamster ovary cell genome

Chinese hamster ovary (CHO) cells are widely used for the stable production of recombinant proteins. Gene amplification techniques are frequently used to improve of protein production, and the dihydrofolate reductase (DHFR) gene amplification system is most widely used in the CHO cell line. We previously constructed a CHO genomic bacterial artificial chromosome (BAC) library from a mouse Dhfr-amplified CHO DR1000L-4N cell line and one BAC clone (Cg0031N14) containing the CHO genomic DNA sequence adjacent to Dhfr was selected. To identify the specific chromosomal region adjacent to the exogenous Dhfr-amplified region in the CHO cell genome, we performed further screening of BAC clones to obtain other Dhfr-amplified regions in the CHO genome. From the screening by high-density replica filter hybridization using a digoxigenin-labeled pSV2-dhfr/hGM-CSF probe, we obtained 8 new BAC clones containing a Dhfr-amplified region. To define the structures of the 8 BAC clones, Southern blot analysis, BAC end sequencing and fluorescence in situ hybridization (FISH) were performed. These results revealed that all the selected BAC clones contained a large palindrome structure with a small inverted repeat in the junction region. This suggests that the obtained amplicon structure in the Dhfr-amplified region in the CHO genome plays an important role in exogenous gene amplification.     

Experiments and evaluation of a mobile high-density snow storage system

This paper aims to contribute to the introduction and promotion of the snow and ice energy in cold and heavy snowfall regions in the future. To achieve this goal, we have developed a new concept for improvement of the performance of a snow and ice energy system. We propose the high-density snow storage (HSS) system and the urban cold spring (UCS) for the purpose of efficient energy use and cost saving. The snow density of conventional snow storage systems is 450-550 kg/m³. The high construction cost of these systems has been caused by a large space for the snow storage. The snow density is heightened to 750-800 kg/m³ for the HSS system. UCS is the large HSS system for cities and communities. In 2002, HSS was applied to an actual office building in Oshu, Japan. The mass of stored snow was approximately 450 tonnes. The thermal insulation of snow storage room is 100-200 mm in thickness. Melt water is gathered in the cool water tank and is pumped to the heat exchanger. In 2003, space cooling was operated by using this HSS system. We evaluated the efficiency of storing snow and space cooling.