Correction of hypermutability, N-methyl-N'-nitro-N-nitrosoguanidine resistance, and defective DNA mismatch repair by introducing chromosome 2 into human tumor cells with mutations in MSH2 and MSH6

The human DNA mismatch repair genes hMSH2 and hMSH6 encode the proteins that, together, bind to mismatches to initiate repair of replication errors. Human tumor cells containing mutations in these genes have strongly elevated mutation rates in selectable genes and at microsatellite loci, although mutations in these genes cause somewhat different mutator phenotypes. These cells are also resistant to killing by certain drugs and are defective in mismatch repair. Because the elevated mutation rates in these cells may lead to mutations in additional genes that are causally related to the other defects, here we attempt to establish a cause-effect relationship between the hMSH2 and hMSH6 gene mutations and the observed phenotypes. The endometrial tumor cell line HEC59 contains mutations in both alleles of hMSH2. The colon tumor cell line HCT15 contains mutations in hMSH6 and also has a sequence change in a conserved region of the coding sequence for DNA polymerase delta, a replicative DNA polymerase. We introduced human chromosome 2 containing the wild-type hMSH2 and hMSH6 genes into HEC59 and HCT15 cells. Introduction of chromosome 2 to HEC59 cells restored microsatellite stability, sensitivity to N-methyl-N'-nitro-N-nitrosoguanidine treatment, and mismatch repair activity. Transfer of chromosome 2 to HCT15 cells also reduced the mutation rate at the HPRT locus and restored sensitivity to N-methyl-N'-nitro-N-nitrosoguanidine treatment and mismatch repair activity. The results demonstrate that the observed defects are causally related to mutations in genes on chromosome 2, probably hMSH2 or hMSH6, but are not related to sequence changes in other genes, including the gene encoding DNA polymerase delta.     

Ion conducting properties of hydrogen-containing Ta2O5 thin films prepared by reactive sputtering

Hydrogen-containing Ta₂O₅ (Ta₂O₅:H) thin films are considered to be a candidate for a proton-conducting solid-oxide electrolyte. In this study, Ta₂O₅:H thin films were prepared by reactively sputtering a Ta metal target in an O₂ + H₂O mixed gas. The effects of sputtering power and post-deposition heat treatment on the ion conducting properties of the Ta₂O₅:H thin films were studied. The ionic conductivity of the films was improved by decreasing the RF power and a maximum conductivity of 2 × 10⁻⁹ S/cm was obtained at an RF power of 20 W. The ionic conductivity decreased by heat-treatment in air, and no ion-conduction was observed after treatment at 300 °C due to the decrease in hydrogen content in the films.     

Molecular orbital calculations of hydrogen storage in carbon and boron nitride clusters

Hydrogen gas storage ability in carbon and boron nitride (BN) clusters was investigated by molecular orbital calculations. From single point energy calculations, H₂ molecules would enter from hexagonal rings of C₆₀ and B₃₆N₃₆ clusters and octagonal rings of B₂₄N₂₄ cluster because of lower energy barrier. Chemisorption calculation of hydrogen for BN clusters showed that hydrogen bonding with nitrogen atoms was more stable than that with boron atoms. Stability of H₂ molecules in BN clusters seems to be higher than that of carbon clusters.     

Specific heat of the Hf2Fe,Hf2Co,and Hf2Rh intermetallic compounds

The specific heat under constant pressure, C _p, of intermetallic compounds Hf₂Fe, Hf₂Co and Hf₂Rh with the Ti₂Ni structure was obtained by means of differential thermal analysis in the temperature range 275–740 K. The results differ significantly from the Debye theory, even when a correction for optical phonons in Einstein approximation is considered, which indicates existence of a defect contribution to the specific heat. Relative entropy has been determined and the obtained results were fitted and analysed. The anomalous temperature behaviour of C _p is discussed, having in mind results of previous investigations of these and similar systems, obtained by other methods.     

Structures and purification of boron nitride nanotubes synthesized from boron-based powders with iron particles

Boron nitride (BN) nanotubes, nanohorns and nanocoils were synthesized by annealing Fe₄N/B, FeB and Fe/B powders at 1000 °C for 1–24 h in nitrogen gas atmosphere, and large amounts of BN nanotubes were obtained by annealing Fe₄N/B. The growth mechanism and atomic structures were investigated on cup-stacked BN nanotubes synthesized from Fe₄N/B by X-ray diffraction, high-resolution electron microscopy, electron diffraction and energy dispersive X-ray spectroscopy. As-produced BN soot was purified by removing non-BN nanomaterials such as metal catalyst particles and unreacted boron, and high purity BN nanotubes were obtained.     

Ammonothermal synthesis of thick gallium nitride film employing acidic mineralizers

Fabrication of wurtzite-type gallium nitride (GaN) thick films on HPVE-grown {0001} GaN substrates under moderate ammonothermal conditions is reported. Supercritical ammonia (NH₃) as solvent and the mineralizer ammonium chloride (NH₄Cl) is employed for temperature and pressure conditions of 400–550 °C and ≤135 MPa, respectively. Growth rates of 30 μm per day over long-term growth runs were obtained. The effect of surface morphology of the substrate on homoepitaxial nucleation of GaN films prepared from ammonoacid solutions is investigated. Two-dimensional nucleation is obtained for substrates etched by hot concentrated KOH prior film growth. In this case the interface between film and the ( ) substrate does not show any signs of voids or island nucleation. Cracking pattern reveals similar mechanical-elastical properties for film and substrate.     

Vibration analysis and cutting simulation of structural nonlinearity for machine tool

The dynamic behavior of a machine tool is affected by the forces applied to the structure. However, cutting processes have been analyzed considering the linear systems in most of the studies so far. In this study, a machine tool structure was excited by using an electromagnetic shaker and the force-dependant frequency response characteristics were measured. Based on the measured result, the nonlinear characteristics of the machine tool structure was identified, and a machine tool with the nonlinear characteristics was mathematically reproduced, which enabled to analyse the nonlinear frequency response characteristics and simulate cutting processes.     

Development of Adiabatic Demagnetization Refrigerator for X-ray Microcalorimeter Operation

We are developing of adiabatic demagnetization refrigerator for X-ray microcalorimeter operation. By improving thermal environment in the cryostat, it achieved the lowest temperature of 80 mK, temperature stability of 9?μK rms at 100?mK, and a hold time of 7 hours at 100?mK. The excess heat load to the saltpill decreased from 10?μW to 3?μW. Using this system, we demonstrated a measurement of R–T curve of a TES microcalorimeter and ?–V curve of a SQUID.     

A high efficiency thin film silicon solar cell and module

A photoelectric conversion efficiency of over 10% has been achieved in thin-film microcrystalline silicon solar cells which consist of a 2 μm thick layer of polycrystalline silicon. It was found that an adequate current can be extracted even from a thin film due to the very effective light trapping effect of silicon with a low absorption coefficient. As a result, this technology may eventually lead to the development of low-cost solar cells. Also, an initial aperture efficiency as high as 13.5% has been achieved with a large area (91 cm × 45 cm) tandem solar cell module of microcrystalline silicon and amorphous silicon (thin film Si hybrid solar cell). An even greater initial efficiency of 14.7% has been achieved in devices with a small size (area of 1 cm²), and further increases of efficiency can be expected.