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We have demonstrated the high yield (∼900 μm) and highly single-wall selective (>95%) growth of carbon nanotube (CNT) forest using aluminium nitride (AlN) as a catalyst underlayer. Such high efficiency and single-wall selectivity have not been previously reported using this underlayer system. Evaluation with transmission electron microscopy showed that the average diameter of the grown carbon nanotubes was ∼3.0 nm, which is similar to those grown on alumina underlayers. In addition, characterization of the catalyst/underlayer system using atomic force microscopy and X-ray photoelectron spectroscopy suggests that neither Ostwald ripening along the surface nor catalyst subsurface diffusion into the AlN underlayer are severely occurring at the growth temperature, leading to the creation of the stable and dense small nanoparticle array to achieve an efficient growth of single-wall CNTs.
Recently, the millimetre-scale, highly efficient growth of single-wall carbon nanotube (SWCNT) forests from iron (Fe) catalysts has been reported through the annealing of the magnesia (MgO) underlayer. Here, we report the modulation of the CNT yield (height) and average number of CNT walls for a Fe/MgO catalyst system through the collective effects of initial Fe amount and MgO annealing temperature. Our results revealed the existence of a well-defined region for high yield SWCNT forest growth in the domain of deposited Fe thickness and MgO annealing temperature. Through topographic examinations of the catalyst surface using atomic force microscopy, we confirmed that our results stem from the collective effects of increased amounts of surface-bound Fe through the amount of deposition and suppression of Fe subsurface diffusion, together govern the amount of surface-bound catalyst. The combination of these mechanisms determined the final nanoparticle size, density, and stability and could explain the three distinctly defined regions: low yield SWCNT growth, high yield SWCNT growth, and high yield multiwall CNT growth. Furthermore, we explained the observed borders between these three regions.
We have demonstrated the high yield and highly single wall selective synthesis of carbon nanotube forest grown using a MgO single crystal as a catalyst underlayer without any surface treatment. Such efficiency has not been previously reported using this underlayer system. Our investigation revealed that the growth ambient which contained no hydrogen but small amounts of water is essential for such efficiency. Evaluation of the growth kinetics by in-situ height monitoring revealed that the 350 μm tall forest with 65% single wall selectivity possessed a catalyst lifetime of about 5 minutes. Investigation by AFM, and XPS depth profiling revealed that this longer lifetime compared with as-deposited MgO can be attributed to the stability of the catalyst particle array with small size and high number density on MgO single crystal substrate. Shorter growth lifetime, when compared to the alumina underlayer system, resulted from an instability in the catalyst nanoparticle size and composition.
A confocal micro-X-ray fluorescence (XRF) method with a vacuum chamber was used for investigation of underfilm corrosion that occurs on a painted steel sheet used for automotive applications. A painted steel sheet was prepared by applying electrodeposition coating onto an electro-galvanized steel sheet with a zinc phosphate conversion coating. The spatial resolution of the confocal micro-XRF was about 10.9 ?m at an energy of 17.4 keV. The phosphorus signal from the zinc phosphate layer was able to be observed nondestructively by measuring under the vacuum condition. Each layer of the painted steel sheet was observed from the depth profile analysis of the characteristic elements of each layer. The painted steel sheet was scratched to expose the substrate surface, and then the sheet was then immersed in a NaCl solution for 10 days. The in-depth elemental map of Ti of the corroded steel sheet revealed blister-type corrosion around the scratch. The in-depth elemental maps of Zn and P suggested that the zinc phosphate layer dissolved from the scratched part into the NaCl solution.
Micro-X-ray fluorescence (XRF) analysis provides us with elemental maps that are very useful for understanding the samples under test. Usually, scanning-type elemental mapping is performed. That means a sample stage is scanned to a fixed X-ray microbeam. XRF analysis is performed at the scanned points, leading to 2D elemental mapping. One of the drawbacks of this technique is the long acquisition time depending on the area being mapped and the lateral resolution required. Thus, projection-type elemental mapping has been studied. We have studied the projection type XRF imaging by using a straight polycapillary optic combined with an X-ray CCD camera. To obtain the elemental map, we applied a wavelength dispersive spectrometer (WDS). In this paper, we report a newly developed 2D dispersive device. The construction and analytical performance of this X-ray optic will be explained.
Results on using X-ray optics with a monocapillary attached to a microfocus Mo X-ray tube for a high-intensity XRF analysis are reported. Au-coated glass monocapillaries with 400 and 700 μm inner diameters were used to obtain focused and intensive incident Mo X-rays for the measurements of XRF intensities from pure metal samples. Intensity enhancements obtained by using the Au-coated monocapillaries were found to be up to 1.5 times higher than those obtained by using similar inner diameter uncoated glass capillaries. The XRF intensity profiles were measured by the wire scanning method to investigate the reasons. The traces of the incident X-rays were calculated by taking into account of X-ray total reflection of the incident X-rays from the inner wall of the capillaries. The calculated XRF intensity profiles agree with those of the measured XRF intensity profiles. The observed enhancements in XRF intensity were the results of the incident X-rays emitted from the Mo X-ray tube being totally reflected on the inner wall of the Au-coated monocapillaries.
To investigate the association between eating behaviour and metabolic risk in the broader population.
The association between metabolic risk factors (overweight, hypertension, hyperglycaemia, hypertriacylglycerolaemia, low HDL cholesterol, hyperuricaemia and fatty liver) and various eating behaviours were compared for four groups defined by subjective reporting: not eating until feeling full and not eating rapidly (G1); eating until feeling full only (G2); eating rapidly only (G3); and eating both rapidly and until feeling full (G4).
A medical centre for health examinations in Tokyo, Japan.
Men (n 8240) and women (n 2955) who underwent health examinations.
The distribution of participants in G1 to G4 was 49·8 %, 11·5 %, 26·3 % and 12·4 % among men and 55·3 %, 15·0 %, 19·0 % and 10·7 % among women, respectively. Compared with G1, the age-adjusted OR (95 % CI) for overweight were significantly higher in G2 to G4, being respectively 1·85 (1·58, 2·17), 1·98 (1·76, 2·23) and 3·46 (2·99, 4·01) for men and 2·20 (1·62, 2·97), 2·59 (1·97, 3·39) and 3·12 (2·27, 4·26) for women. The age-adjusted OR were also significantly higher for hypertriacylglycerolaemia, hyperuricaemia and fatty liver in G2 and for all risks in G3 and G4 among men; and for hyperuricaemia in G2, for hyperglycaemia, hypertriacylglycerolaemia and fatty liver in G3 and for hypertriacylglycerolaemia and fatty liver in G4 among women.
Both eating until feeling full and eating rapidly increase metabolic risk factors. Although the mechanism between rapid eating and metabolic risk requires further exploration, eating slowly and ending meals shortly before feeling full are important public health messages for reducing metabolic risk factors.
Brown dwarfs (hereafter BDs) are of particular interest because of their extremely low-temperature atmospheres for comparison with atmospheres of giant planets. Aiming to obtain clues to understand the formation and disappearance of dust clouds and molecular abundances in BD photospheres, we conducted an observation programme of space-borne near-infrared spectroscopy of bright BDs with the Infrared Camera (IRC) on-board AKARI.
We fabricated a laser diode (LD) exhibiting a lasing from strained GaInAs quantum wells (QWs) embedded in Er,O-codoped GaAs (GaAs:Er,O) by organometallic vapor phase epitaxy (OMVPE). The lasing wavelength was designed to tune to the energy separation between the second excited states 4I11/2 and the ground state 4I15/2 of Er3+ ions. The threshold current for the lasing at room temperature was six times larger than that of a GaInAs QW-LD without Er doping, reflecting ultrafast carrier capture by an Er-related trap in GaAs:Er,O. The Er intensity revealed initially steep increase with injected current density in the region for spontaneous emission from the GaInAs QWs. In the stimulated QW emission region, the intensity continued to increase with the current density.
v sin i has been measured from high-resolution (λ/Δλ~50000) infrared spectra of ~30 M and L dwarfs. The spectral region observed covers approximately 0.01 μm centered at 2.312 μm in the CO 2-0 band. v sin i, measured from the CO lines, increases dramatically from the M to L dwarfs. In extreme cases the rotational periods are a few hours.
Based on a simple thermodynamical argument, we proposed a cloudy model with a warm dust cloud deep in the photosphere. We showed, for the first time, that a single grid of model photospheres (800 ≲ Teff ≳ 2600 K) offers a natural explanation not only for the division of dwarfs cooler than M into the two distinct types L and T but also for the changes of the spectra and colors along the L – T spectral sequence.
We have obtained near-infrared spectra of three L dwarfs discovered by 2MASS, 1146+22 (L3), 1507-16 (L5), and 0920+35 (L6.5). From the comparison of the H and K band spectra of these L dwarfs, we have found the presence of methane absorption in 0920+35. This implies that detectable methane absorption in the H and K bands, usually considered the signature of a T dwarf, can be present in objects classified optically as late L. Methane detection in L dwarfs is consistent with the presence of a dust layer deep in the atmosphere as the unified model of Tsuji suggests. (This work has been published in Nakajima, Tsuji & Yanagisawa (2001).)
Interferometry of red supergiants before 2000: The M2 supergiant Betelgeuse (α Ori) is the first star whose angular diameter was measured by the Michelson stellar interferometer (Michelson & Pease 1921). Since then, however, we had to wait half a century before we witnessed the renaissance of interferometric observations in optical astronomy with novel methods such as speckle interferometry (Laberie 1970). Michelson's classical method was also extended to the infrared regime (e.g. McCarthy et al. 1977). The initial results served not only to compare stellar temperature scale with the measured angular diameters but also to probe scattering and thermal emission in the dust envelope around red supergiant stars (e.g. Tsuji 1978,1979). Interferometry has been more active in the radio domain: In connection with our subject, VLBI observations revealed many masering water clouds around red supergiants such as VY CMa (Imai et al. 1997) and S Per (Richards et al. 1999), but their origin in unknown. Also, radio observation of Betelgeuse with the VLA (Lim et al. 1998) revealed the presence of a new component of modest temperatures (Tex ≲ 3500 K) over the same height range as the classical chromosphere (Tex ≳ 5000 K), but again the nature of the new component remains obscure.
We examine whether dust forms in the photospheres of carbon-rich stars by referring to the case of red and brown dwarfs for which some observational clues on dust formation are now known. Dust may form in the photospheres of dwarf carbon stars and produce significant effects on both their structure and spectra. In carbon-rich asymptotic giant branch stars, dust probably forms in the photosphere, if not in the circumstellar envelope, and radiation pressure on dust is sufficient to expel the matter directly from the photosphere. This fact may play some role in mass-loss from cool luminous stars in general, including non-pulsating stars for which no successful mechanism of mass-loss was known.
Fabrication and evaluation of high voltage n-type 4H-SiC Schottky barrier diodes (SBDs) using 27μm thick epitaxial layers were presented. To achieve the ideal value of the breakdown voltage, various parameters of junction termination extension (JTE) were investigated. We concluded that the termination of triple rings with the concentrations of 6×1017, 3×1017, 1.5×1017cm−1 outwardly was best with the simulations. The SBDs with this termination showed the blocking voltage up to 3.4kV, which is almost the ideal value. We also investigated the distribution of leakage currents at -600V in SBDs with various diameters up to 4mm. High yield was obtained in the SBDs with the diameters below 2mm. The SBDs with high leakage currents showed the excess currents in the low forward voltage region and lots of bright spots could be observed by optical beam induced current analysis.
The molecules involved in determining meiotic competence were determined in porcine oocytes isolated from preantral and antral follicles of different sizes. Oocytes isolated from preantral follicles had a mean diameter of 78 μm, contained diffuse filamentous chromatin in the germinal vesicle and were incapable of progressing from the G2 to the M phase of the cycle even after 72 h in culture. Oocytes from early antral follicles had a mean diameter of 105 μm, showed a filamentous chromatin configuration and about half resumed meiosis but arrested at metaphase I (MI) when cultured. Oocytes from mid-antral (3–4 mm) and large antral follicles (5–6 mm) had mean oocyte diameters of 115 and 119 μm respectively, contained condensed chromatin around the nucleolus and progressed to metaphase II (MII) in 48% and 93% of instances respectively. Analysis of p34cdc2, the catalytic subunit of maturation promoting factor (MPF), by immunoblotting indicates that the inability of small (78 μm) oocytes to resume meiosis is due, at least in part, to inadequate levels of the catalytic subunit of MPF. On the other hand, the inability of intermediate-sized (105 μm) oocytes from antral follicles to complete the first meiotic division by progressing beyond MI appears not to be limited by levels of p34cdc2, which are maximal by this stage. We postulate that an inadequacy of molecules other than p34cdc2 limits progression of MI to MII; the acquisition of these molecules during the final stages of growth may be correlated with the formation of the perinucleolar chromatin rim in the germinal vesicle.
For studies of radiative processes in stellar environment, knowledges on opacities are essential, and molecular line opacities play a dominant role in many cases where temperatures are roughly below 4,000K. Accurate treatments of molecular line opacities require high precision line data for millions (and up to billions?) of lines. Recent progress in theoretical as well as in experimantal molecular physics made it possible to realize such an approach, and dedicated efforts are being done to developing extensive databases for polyatomic (Jørgensen in this volume) as well as for diatomic (Kurucz in this volume) molecules. These accurate databases should be of fundamental importance in our understanding of astronomical observations that are progressing rapidly both in scope and in accuracy.