Percolation Analyses on Transport Properties of YBa2Cu3O7−δ-Ag System

The transport properties of YBa ₂ Cu ₃ O _7– -Ag composite ceramic system have been studied from the viewpoint of the percolation theory. The percolation threshold volume fraction f _c of Ag determined from the electrical resistivity and from the thermal conductivity is f _c =0.125±0.005. This markedly smaller value than the theoretical value ( f _c =0.16) suggests the segregative distribution of Ag. The critical exponent t depends on the component conductivity ratio h = _YBCO / _Ag , which can be explained on the basis of the scaling hypothesis.     

Fractal dimension of the grain boundary fracture in creep-fracture of cobalt-based heat resistant alloys

The effects of grain boundary configuration and creep conditions on the fractal dimension of the grain boundary fracture (D _f) were investigated using commercial cobalt-based heat resistant alloys, namely, HS-21 and L-605 alloys. Creep-rupture experiments were carried out under the initial creep stresses of 19.6–176 MPa in the temperature range from 1089–1422 K in air. The value of D _f was larger in specimens with serrated grain boundaries than in those with straight grain boundaries in the HS-21 alloy under the same creep condition, and the difference in the value of D _f between these specimens was large in the scale range of the analysis which was less than about one grain boundary length. However, there was almost no difference in the value of D _f between the specimens with serrated grain boundaries and those with straight grain boundaries in the L-605 alloy, because there was no obvious difference in the microstructure between these specimens. The value of D _f increased with decreasing creep stress in the scale range of the fractal analysis larger than about one grain boundary length in both HS-21 and L-605 alloys, while the stress dependence of D _f was larger in the HS-21 alloy. The stress dependence of D _f was explained by the stress dependence on the number of grain boundary microcracks linked to the fracture surface. The value of D _f estimated in the scale range smaller than about one grain boundary length showed essentially no stress dependence in both L-605 and HS-21 alloys.     

Thermal conductivity and phonon scattering mechanisms in La#x2212;x#x2212;x#x2212;xMxCuO4

The thermal conductivity of high density La_2–xM_xCuO₄ (M=Ba, Sr) sintered materials was measured between 15K and 150K for the various concentrations of Ba and the phonon thermal conductivity was analyzed comparing with that of Nd_2–xCe_xCuO₄. The pretty large value for pure La₂CuO₄ was drastically diminished by substituting La by a small amount of Ba atoms especially at low temperatures. It was found that a new type of the phonon scattering center such as a two-level tunneling must be taken account of in order to explain the observed reduction.     

Fiber template approach toward preparing one-dimensional silica nanostructure with rough surface

Silica nanofibers were grown on the surface of chitosan nanofibers used as templates by coating the surface with silica derived from the hydrolysis and condensation of tetraethoxysilane using ammonium hydroxide as a catalyst. This was followed by the decomposition of the chitosan template. The relationship between different processing factors (type of templates as well as amounts of catalyst and template) and the formation of silica nanofibers was examined. Varying the processing factors was found to be effective in controlling the morphology of the silica nanofibers. The use of chitosan nanofibers effectively led to the formation of one-dimensional silica nanofibers as the positively charged chitosan nanofibers promoted the deposition of the negatively charged silica nanoparticles through electrostatic attractive forces. Therefore, the chitosan nanofibers acted as good deposition sites for interacting with silica nanoparticles. Although a large amount of catalyst promoted the sol-gel reaction, the silica nanoparticles grew excessively in the solvent. Therefore, the surface structure of the prepared silica nanofibers could be controlled by varying the amount of chitosan template as this also varied the formation mechanism of the silica nanofibers. The resultant samples had a rough silica wall composed of densely assembled silica nanoparticles, with a high specific surface area (338 m²/g).     

Improvement of production efficiency of spray-synthesized HKUST-1

Spray synthesis of metal–organic frameworks (MOFs) is desirable for scaled production. In this study, we designed a new apparatus for spray-synthesizing MOFs, wherein an upward spraying and swirling air flow was applied to prevent loss of the precursor solution. We evaluated the effects of the flow rate and temperature of swirling air, temperature of the reactor tube, initial feed rate of the precursor solution, and precursor concentration on the yield, purity, space–time yield (STY), BET surface area, and average particle size. The swirling air flow along with re-spraying of the solution accumulated on the upward spray nozzle improved yield significantly. The highest STY was 45.7 kg/m³/day obtained at a precursor feed rate of 5 mL/min; the highest surface area was 1,872 m²/g obtained at a precursor concentration of 1.38 mol/L. The sample with the highest surface area exhibited 2.60 wt% of hydrogen adsorption capacity at 77 K and 1 bar, with 7.6–6.1 kJ/mol of heat of hydrogen adsorption.     

Surface etching effects of amorphous C:H and CNx:H films formed by supermagnetron plasma for field emission use

Supermagnetron plasma was used to deposit amorphous hydrogenated carbon (a-C:H) and hydrogenated carbon nitride (a-CN_x:H) films for field-emission devices using i-C₄H₁₀/(H₂ or N₂). It was also used to improve the field-emission characteristics by surface etching using N₂/H₂ plasma. The best emission threshold electric field (E_TH) was 13 and 12 V/μm for devices using as-deposited a-C:H and as-deposited a-CN_x:H films, respectively, while they were remarkably improved to 11 and 8 V/μm by surface etching using N₂/H₂ (120/40 sccm) gas, though surface roughness was slightly increased by the surface etching. The hardness of as-deposited films was higher than 22 GPa.     

Stabilization by harmonic intensities for the output signal in heterodyne detection

We experimentally demonstrated that the technique to stabilize the output signal by harmonic intensities is useful in heterodyne detection with an incoherent light source such as a halogen lamp. The relation between the relative standard deviation of an output signal and the fluctuation of the light intensity is analyzed and simulated. Using the fundamental to sixth harmonics increases the stabilities of output signal approximately 3 times, and subtracting the relative standard deviation of the intensity of light source enhances the stabilities 49 times. The fluctuating phase that is due to the fluctuating frequency and temperature and its power spectrum density for an interferometer is also calculated with the Allan variance.     

Detection of six single-nucleotide polymorphisms associated with rheumatoid arthritis by a loop-mediated isothermal amplification method and an electrochemical DNA chip

An electrochemical DNA chip using an electrochemically active intercalator and DNA probe immobilized on a gold electrode has been developed for genetic analysis. In this study, the six polymorphisms associated with rheumatoid arthritis (RA), N-acetyltransferase2 (NAT2) gene polymorphisms T341C, G590A, and G857A, methylenetetrahydrofolate reductase (MTHFR) gene polymorphisms C677T and A1298C, and serum amyloid A1 (SAA1) gene promoter polymorphism C-13T were simultaneously detected by the electrochemical DNA chip and the loop-mediated isothermal amplification (LAMP) method, which is a novel technique for DNA amplification. Human genomic DNAs were extracted from blood, and the targets containing the six polymorphisms were amplified by the LAMP method. A sample containing the six LAMP products was reacted with the electrochemical DNA chip using a DNA detection system that controls hybridization reaction, washing, electrochemical detection, and data analysis automatically. A total of 31 samples were genotyped by this method, and the results were completely consistent with those determined by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis or the PCR direct sequence analysis. The time required for this method was only 2 h, and operations were very simple. Therefore, this method is expected to contribute to personalized medicine based on genotype.     

Nanopillar array chip integrated with on-line stacking for fast DNA separation with high sensitivity and high resolution

Recent developments of nanofabrication techniques have created a trend switching from randomly ordered polymeric matrices, such as gel, to highly ordered sieving nanostructures in the separation of biomolecules. These nanostructures have enormous potential for fast separation of biomolecules, while nanostructure-based separation techniques suffer from critical scaling problems; they are efficient in handling less than nanoliter amounts of sample fluids, but most biomolecule samples are available in a liquid volume that is over several microliter, leading to a reduction in sensitivity and resolution. In this study, we developed a nanopillar array chip integrated with an easy and rapid on-line stacking method and achieved fast DNA separation with high sensitivity and high resolution. The developed on-line stacking method is based on the balance of two forces driven by electric fields: electroosmotic flow (EOF) and electrophoresis. The EOF mobility from the microchannel to the nanopillar-channel is drastically decreased, while, on the other hand, electrophoresis has constant mobilities in the whole length of the channels. The on-line stacking was realized at the well-balanced position of the two forces, and the on-line stacking using the nanopillar array chip can also be achieved within 10 s by just applying electric voltages without any other special reagents and materials. After applying on-line stacking using the nanopillar array chip, the relative fluorescence intensity increased 1,000-fold, and the resolution was twice as good as that without on-line stacking.