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Nearby disc stars in Gaia DR1 (TGAS) and RAVE DR5 show a bimodal velocity distribution in the metal-rich region (characterized by the Hercules stream) and mono-modal velocity distribution in the metal-poor region. We investigate the origin of this [Fe/H] dependence of the local velocity distribution by using 2D test particle simulations. We found that this [Fe/H] dependence can be well reproduced if we assume fast rotating bar models with Ωbar ≃ 52 km s−1 kpc−1. A possible explanation for this result is that the metal-rich, relatively young stars are more likely to be affected by bar's outer Lindblad resonance due to their relatively cold kinematics. We also found that slowly rotating bar models with Ωbar ≃ 39 km s−1 kpc−1 can not reproduce the observed data. Interestingly, when we additionally consider spiral arms, some models can reproduce the observed velocity distribution even when the bar is slowly rotating.
Dengue fever (DF) and leptospirosis are serious public problems in tropical regions, especially in Manila, the Philippines. In attempting to understand the causes of DF and leptospirosis seasonality, meteorological factors have been suspected, but quantitative correlation between seasonality and meteorological factors has not been fully investigated. In this study, we investigated correlation of temporal patterns of reported numbers of laboratory-confirmed cases of both DF and leptospirosis with meteorological conditions (temperature, relative humidity, rainfall) in Manila. We used time-series analysis combined with spectral analysis and the least squares method. A 1-year cycle explained underlying variations of DF, leptospirosis and meteorological data. There was a peak of the 1-year cycle in temperature during May, followed by maxima in rainfall, relative humidity and number of laboratory-confirmed DF and leptospirosis cases. This result suggests that DF and leptospirosis epidemics are correlated not only with rainfall but also relative humidity and temperature in the Philippines. Quantifying the correlation of DF and leptospirosis infections with meteorological conditions may prove useful in predicting DF and leptospirosis epidemics, and health services should plan accordingly.
Seyfert galaxies often have extended emission line regions around their nucleus. We started an observation program of optical tridimensional spectroscopy for circumnuclear regions of nearby Seyfert galaxies to investigate the ionization source of the gas of just vicinity(typically several hundred pc) of nucleus.
A narrow-band imaging observation of the Seyfert galaxy NGC1068 was made in the Fabry-Perot mode of the Kyoto 3D Spectrograph attached to the 188cm telescope of the Okayama Astrophysical Observatory. We observed at wavelengths of Hα, [S ii]λ6716, [S ii]λ6731 and adjacent continua of the respective lines with a “tunable filter”, i.e. a gap-scanning etalon with a spectral resolution of 20 Å.
Infrared Imaging Surveyor (IRIS, officially Astro-F) is a satellite which will be launched in the winter of 2003. The main purpose of the IRIS mission is an all sky survey in the mid- and far-IR with a flux limit much deeper than that of IRAS. In order to examine the performance of the survey and to find a suitable set of bandpasses for tracing galaxy evolution and picking up protogalaxy candidates as effective as possible using IRIS, we estimated the FIR galaxy counts based on a simple model with various sets of cosmological parameters and evolution types.
The Kyoto 3-D Spectrograph was commissioned successfully at the 188-cm telescope of the Okayama Astrophysical Observatory in the spring of 1996. This instrument has four distinct modes (Ohtani et al. 1994): (1) narrow-band imager, which is an ordinary focal-reducer camera; (2) Spectro-NebulaGraph (long-slit spectrograph; Kosugi et al. 1995); (3) imaging Fabry-Perot interferometer, using either of two Fabry-Perot etalons from Queensgate Instruments (a tunable filter with R = 300 and another with R = 7000 for velocity-field observations. Broad-band (400–700 nm) coatings are deposited on both etalons. During observations, the etalon temperature is stabilized within 0.5°C); and (4) integral-field spectrograph of the TIGER-type (Bacon et al. 1995). In this mode, the spectra of 7 × 11 objects can be recorded simultaneously, along with 7 × 2 spectra of the sky 4′ away. The spatial resolution is 1″.3 and the field of view is 9″ × 14″.
Variability of the light curves of the short-period eclipsing binary system GR Tau (, almost-contact binary) is studied. It is found that GR Tau experienced both the state which is characterized by asymmetric light curves and the state characterized by symmetrical light curves.
A super-Chandrasekhar (SC) supernova (SN) has an extremely high luminosity and a slow decline rate of the light curve in the early-phase. We present late-phase observations of the SC SN 2009dc. We find that the optical luminosity a year after maximum is much fainter than that expected from its early luminosity. We attempt to fit the analytic light curve model to the observations using Arnett's rule. The model successfully explains the light curves until 120 days. This suggests that the extremely high luminosity originates from the 56Ni decay. We suggest that the late-phase decline would be caused by dust formation. The existence of strong carbon features in early-phase spectra would support this scenario. We also find a blend of [Ca ii] and [Ni ii] in its late-phase spectrum. This indicates that the calcium is distributed in the inner layer along with nickel and iron. We conclude that the mixing may occur in the inner parts of the ejecta.
We successfully obtained the first optical spectra of the faint light echoes around Cassiopeia A and Tycho Brahe's supernova remnants (SNRs) with FOCAS and the Subaru Telescope. We conclude that Cas A and Tycho's SN 1572 belong to the Type IIb and normal Type Ia supernovae, respectively. Light echo spectra are important in order to obtain further insight into the supernova explosion mechanism of Tycho's SN 1572: how the Type Ia explosion actually proceeds, and whether accretion occurs from a companion or by the merging of two white dwarfs. The proximity of the SN 1572 remnant has allowed detailed studies, such as the possible identification of the binary companion, and provides a unique opportunity to test theories of the explosion mechanism and the nature of the progenitor. Future light-echo spectra, obtained in different spatial directions of SN 1572, will enable to construct a three-dimensional spectroscopic view of the explosion.
Iodine release from silver iodide (AgI) to water was evaluated under reducing conditions in the presence of iron-bearing minerals, goethite (FeOOH), magnetite (Fe3O4) and Wüstite (FeO). The release tests were performed in a glove box purged with gas mixture (Ar+5%H2), and the concentrations of dissolved iodine, silver and iron were measured. The apparent equilibrium concentration of dissolved iodine was 4.0 ×10−8, 4.3×10−8 mol/l for the tests with FeOOH and Fe3O4, respectively. The values were almost the same as in the test without minerals. For the test with FeO, the concentration of dissolved iodine was 5.4×10−3 mol/l, which is five orders of magnitude higher than for the other tests. Solid phase analyses by using XRD and SEM/EDS indicated that metallic silver precipitated on the surface of the original AgI for the test with FeO and on the surface of Fe3O4 for the test with Fe3O4, but not for that with FeOOH. These results showed that only FeO could reduce AgI effectively to increase iodine release. The amount of dissolved Fe(II) was a key factor affecting AgI reduction instead of redox potential of solution. Kinetic processes may also play an important role in AgI reduction and associated iodine release under reducing condition.
Interlayers of montmorillonite were pillared with TiO2, SiO2 -TiO2 and SiO2-Fe2O3 sols. The pillared structures were thermally stable at least up to 500°C and retained unusually large basal spacings in the range of 24–45Å and surface areas as high as 300–500 m2 /g. The TiO2 pillared clay showed Type IV adsorption isotherm for nitrogen. Although SiO2 -TiO2 and SiO2-Fe2O3 pillared clays had basal spacings much larger than that of TiO2 pillared clay, these mixed oxide pillared clays had small pores and exhibited Type I isotherm. The acidic strength distributions were determined by a titration method using n-butylamine and Hammett indicators. All of the pillared clays had large acidities, but the acidic strength decreased in the following order: TiO2 - SiO 2 » SiO2-Fe2O3 pillared clays. Temperature-programmed desorption (TPD) spectra of ammonia were measured and interpreted in relation to the acidity distribution. Infrared spectra of pyridine adsorbed on TiO2 pillared clay indicated that the acidity predominantly arises from Lewis acid sites.
The activation of phosphorus implanted into n-type silicon (100) substrate by followed hydrogen ion(H +) implantation was studied by means of spreading resistance technique(SR), secondary ion mass spectroscopy(SIMS) and transmission electron microscopy(TEM).
“The activation ratio” defined by carrier concentration divided by phosphorus concentration was used as a measure of activation of phosphorus. The H + energy, dose and dose rate dependence of activation ratio of phosphorus was investigated.
In the case of thermal annealing at 400 °C for 200 minutes the phosphorus atoms were not activated, on the other hand in the case of H + implantation at 400 °C the phosphorus atoms were activated and the activation ratio was increased almost proportionally with the dose. The SIMS data suggested that the depth profile of phosphorus atoms was not changed after activation by H + implantation. The activation ratio was increased with decreasing the dose rate. The TEM data suggested that the density of residual defects was reduced in the case of lower dose rate. The depth profile of activation ratio was similar to that of hydrogen atoms implanted at 20 °C. From these results the activation and recrystalization mechanism is discussed in the view of contribution of elastic collision process between H + ions and substrate atoms.
The degradation mechanism of the Schottky contact of Al/Ti/n-GaAs and Al/Pt/Ti/n-GaAs under the heat treatment of 300°C has been investigated. Barrier height of the Al/Ti/n-GaAs Schottky contact degrades drastically after the heat treatment, in which Ti-Al alloy and Ga out-diffusion have been observed. On the other hand, the barrier height of Al/Pt/Ti/n-GaAs contacts is stable under the heat treatment and, Al-Ti alloying as well as Ga out-diffusion in the metals could not be noticed. From these results, it is presumably concluded that the degradation of the Schottky contacts under the heat treatment is closely correlated with the Ga atom out-diffusion from GaAs surface into the metal films after Al-Ti alloy reach to the GaAs surface. The barrier height reduction after the heat treatment can be explained by the formation of the donor type level at the interface due to the Ga vacancy pile-up arose from the Ga out-diffusion. Pt layer was proved to be an effective barrier suppressing the intermetallic alloying and preventing out-diffusion of Ga.
A new method for the direct observation of two-dimensional gas flow patterns in a CVD reactor has been developed by combining a laser scanning technique with generating micron-sized TiO2 particles. With this specially developed technology, the size of generated TiO2 particles are quite uniform, and of high density by the use of hydrolysis of Ti-alkoxide in the ceramic honeycomb at the top inlet of the model chamber. In this system, vertical cross sections of the gas flow patterns can be visualized by illuminated TiO2 particles in a He-Ne laser light sheet. Using this technique, detailed gas flow patterns can be clearly identified in the reaction chamber. Changes in the gas flow patterns with the various growth conditions, such as gas flow rate and pressure, have been measured. In this presentation, GaAs thin film growth by the MOCVD method will be reported as an example.
This gas flow visualization method could be a useful tool to identify the mechanism of CVD reactions to give better understanding about carrier gas transport and thin film growth for wide band gap semiconductors such as GaN, a-SiC, SiNx, etc.
We investigated the initial oxidation of MBE-grown Si (100) surfaces with atomic flatness using x-ray photoemission spectroscopy (XPS) and reflection high energy electron diffraction (RHEED). It was found that the MBE-grown surfaces are inert and hardly oxidized even after exposure to molecular oxygen up to 1500 Langmuir (L) at room temperature. At elevated temperatures, the surface oxidation was substantially promoted. On the contrary, the surface oxidation was found to be substantiated on a deliberately corrugated Si surface prepared by low temperature MBE growth, even at room temperature.
A novel configuration for Fourier-transform infrared reflection absorption spectroscopy (FT-IR-RAS) has been devised to study the nature of silicon wafer surfaces in the wide IR irradiation region (especially below 1300 cm−1) with high sensitivity. The configuration is basically similar to a conventional one of FT-IR-RAS except that a optical-flat mirror is placed on a silicon wafer surface and the IR beam is incident on the back side of the wafer with a grazing angle. The sensitivity of the novel technique was estimated by the observation of the stretching vibration absorption of the Si-Hx bond (2070-2150 cm−1) on HF/NH4F-treated Si(111) surfaces and Si-O bond (1000-1250 cm−1) of chemically oxidized layer ( ∼0.7 nm ) on Si(111) surfaces. The dependence of Si-Hx absorption peaks intensities on the composition of HF/NH4.F solutions was clearly observed. Furthermore, Si-O bond peak corresponding to the longitudinal optical phonon was also detected.
The initial stage of oxidation of 40wt-% NH4F treated Si(111) surface at 300 °C in dry oxygen with a pressure of 133 Pa and the subsequent oxidation at 600 and 800°C were studied. It was found from the analysis of Si 2p photoelectron spectra that non-uniform layer by layer oxidation proceeds at 300°C, while the layer by layer oxidation proceeds at 600 and 800°C. Furthermore, at these temperatures the interface becomes atomically flat with the progress of oxidation.
The initial stages of SiO2/Si interface formation on hydrogen-terminated n-type and p-type Si(111) surfaces, which are obtained by the treatment in 40% NH4F solution, were investigated in details at 300°C in dry oxygen with a pressure of 1 Torr up to nearly two molecular layers of silicon oxide. It was found that the oxidation proceeds more uniformly on p-type Si than on n-type Si. However, even on p-type Si the oxidation does not proceed uniformly.
A series of experimental investigations has been made on the a-Si // poly-Si tandem solar cell which is one of the most promised candidate of high cost-performance photovoltaic cell, e.g., high efficiency, low cost with almost no light induced degradation. Employing high conductivity with wide optical band gap p type microcrystalline SiC (μ-SiC) as a window material together with a-SiC as an interface buffer layer and also n type μc-Si as a back ohmic contact layer in the poly-Si based bottom cell, the conversion efficiency of 17.2 % has been obtained. Combining an optically transparent a-Si p-i-n cell as a top cell with an optical coupler between the top and the poly-Si bottom cell, a total efficiency of 20.3 % has been obtained so far on the four-terminal stacked mode structure. A systematic technical data for the optimization of cell structure variation on the developed tandem solar cells are presented and further possibility to improving the performance are discussed.