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A unified formation mechanism of nuclear starbursts is presented; all the nuclear starbursts are triggered by binary supermassive black holes made in the final phase of galaxy mergers. Minor mergers cause both nuclear starbursts and hot-spot nuclei while major mergers cause (ultra) luminous infrared galaxies. We discuss the case of Arp 220 in detail.
NGC 7318B in Stephan's Quintet has two optical arms (toward N and S) emanating from the eastern part of the main body. Since these arms are similar morphologically to the tidal tails of merging galaxies such as NGC 4038/9, it is considered that NGC 7318B itself is a major merger with a retrograde orbit. In order to study the emission-line activity in the tidal arms of NGC 7318B, we took CCD narrow-band (Hα ON and OFF) images and then found a large-scale arc in Hα emission which traces closely the arms. This Hα arc resembles both the radio and the soft X-ray arcs morphologically (van der Hulst & Rots 1981; Pietsch et al. 1997), suggesting that a single physical mechanism is responsible for all of these kinds of emission. Our optical spectroscopic observations of the shell-like feature at the southern tip of the arc reveal both broad Hα emission and stronger-than-normal [NII] and [SII] emission lines, which are typical of supernova remnants (SNRs). The required number of SNRs is estimated to be as much as ~ 106.
In order to study environmental effects on the nuclear activity in galaxies, we have been conducting a spectroscopic study of Hickson Compact Groups of galaxies (HCGs, Hickson 1982) which are the densest agglomeration of galaxies. We obtained nuclear spectra of 62 galaxies in 29 HCGs in the spectral range 6200–7000Å with the 188cm telescope at Okayama Astrophysical Observatory. These spectra were classified into the three types by using the emission line ratio [NII]λ6583/Hα; (1) AGN: [NII]λ6583/Hα >0.6, (2) HII nuclei: [NII]λ6583/Hα <0.6, and (3) Absorption: no emission line. We compared the nuclear activity of galaxies in HCGs with that of nearby galaxies (Ho 1996; Ho, Filippenko & Sargent 1997) which provides a representative sample of field galaxies. In early-type spirals (Sa-Sbc), the fraction of HII nuclei in HCGs is smaller than that in the field galaxies, while the fraction of absorption in HCGs is larger than that in field galaxies. On the other hand, in early-type galaxies (E-S0a) and late-type spirals (Sc-P), we found little difference in the nuclear activity between HCGs and field galaxies.
Optical properties of hydrogenated silicon clusters are investigated by density functional pseudopotential calculation. Transitions between the band-edge orbitals are allowed, in contrast to the indirect gap in bulk silicon. The energy gaps of hydrogenated silicon particles of 15 to 30 Å in diameter are estimated to be 2.0 to 1.5 eV. When the cluster is dehydrogenated, localized states related to dangling bonds appear in the mid-gap, which decrease the photoluminescence intensity. These results agree with much experimental evidence and suggest that the photoluminescence of porous silicon is attributable to hydrogenated silicon particles.
Two types of amorphous silicon (a-Si:H)/silicon nitride (a-Si3 N4 :H) multilayers have been prepared either by turning-off the plasma at each step of individual layer growth (step by step deposition) or by quick gas switching without interrupting the plasma (continuous deposition). It is found that the continuous deposition causes a significant mixing of nitrogen into the a-Si:H well layers and deteriorates the compositional abruptness in the a-Si:H/a-Si3N4 :H interface. Also, undesirable incorporation of nitrogen into the a-Si:H well layers tends to induce nonradiative recombination centers near the interface.
By means of a Langevin dynamic simulation we studied the current-voltage characteristics of a two-dimensional (2D) Josephson-coupled lattice as a model high-Tc superconducting film. The result illustrates qualitative features of non-Ohmic power-law scaling behaviors observed in transport measurements, including striking effects of applied magnetic fields. We thereby suggest that the Kosterlitz-Thouless transition associated with 2D vortex-antivortex pairs may dominate over the resistive transition in weak magnetic fields H/Hc2 ≪C 1. Through a simple theoretical estimate, we also show that the KT model illustrates the thickness-dependence of resistive transition temperature and electric field effect in ultra-thin YBa2Cu3O7−x films.
Porphyrin thin films were deposited by ionized cluster beam from a source material of tetraphenylporphyrin iron(III) chloride. It was found that the chlorine atoms are mostly removed from the original molecules during the film formation process, resulting in a film of tetraphenylporphyrin iron(II) complex. The film is chemically active and showed reversible reaction with O2 and CO gases at an elevated temperature. The formation of μ-oxo dimera, which hinders the chemical activity, was not observed. Electrical conductivity of the film was also measured under various atmosphere.
Organic/MoO3 nanohybrid thin films have been successfully prepared by an ex-situ intercalation process. The host MoO3 films were first deposited on LaAlO3 (LAO) single crystal substrates by using a CVD method followed by the intercalation of butylammonium ions, (BuNH3)+, into the MoO3 films to give (BuNH3)xMoO3 thin films. The preparation of highly b-axis oriented MoO3 films is crucial to prepare the (BuNH3)xMoO3 films. The (BuNH3)xMoO3 thin films exhibit a resistance-increasing response to aldehyde gases as in the case of bulk samples, whereas no response was observed for methanol, ethanol, chloroform, acetone, toluene, and xylene. The thin film process developed for intercalative organic-inorganic hybrid makes it possible to apply this material in VOC sensor devices.
Gas sensors based on organically hybridized SnO2 films are demonstrated. Upon exposure to CO gas, the electrical resistance of the hybrid sensor with amino groups in the organic components increases (R-increasing response), whereas other reducing gases such as H2 and CH4 gases cause the decreasing in the sensor resistance. For the n-type semiconductors like SnO2, the R-increasing response cannot be explained by the ordinary combustion mechanism. The appearance of the anomalous R-increasing response to CO gas can be controlled by the functional groups of the organic component. The hybrid sensor with hydroxy groups also exhibits the R-increasing response to CO gas, whereas it is not observed for the sensor with alkyl groups. The hybridization can improve gas selectivity of the SnO2 semiconducting gas sensors.
High temperature Pd-SiC Schottky diode gas sensors are known to thermally degrade due to interdiffusion and reaction at the metal-semiconductor interface. To understand and possibly eliminate this problem, detailed surface studies of thermally induced Pd-SiC surface interactions have been performed. These experiments compare standard 6H-SiC (0001) surfaces typical of those used in device fabrication with periodically stepped surfaces prepared by high temperature hydrogen etching. The Pd films range in thickness from the monolayer level (∼0.4 nm) to actual device dimensions (∼46.5 nm) and are deposited under ultrahigh vacuum conditions at ∼50 °C. These films are characterized in-situ using Auger electron spectroscopy both before and after annealing at 670 °C. The Auger lineshapes provide quantitative information on the chemistry of the reaction products. Ex-situ atomic force microscopy is used to characterize changes in surface morphology.
An MIS Hydrogen sensor with a Pd0.96Cr0.04/AlN/Si structure was fabricated, exhibiting the dynamic range considerably wider than that of analogous devices with pure Pd gates. A useful response could be obtained for Hydrogen concentrations as large as 50, 000 ppm. Although the response amplitude was much reduced at the lower concentrations, satisfactory signal to noise down to 50 ppm could be obtained. The saturating magnitude of the electrical response is in the range of 0.1 to 0.5 V, which is the same as that for the pure Pd gated devices, inspite of the 3 orders of magnitude difference in the saturation hydrogen concentration. This result will be discussed in terms of the response mechanism of these devices.
We have prepared polypyrrole (PPy) / MoO3 nanohybrid thin films and evaluated their volatile organic compound (VOC) gas sensing properties. The (PPy)xMoO3 thin films have been prepared by intercalation reactions of highly oriented MoO3 thin films. Intercalation of hydrated sodium ions successfully proceeded without loosing the crystallographic orientation. The (PPy)xMoO3 thin films was obtained by replacing the hydrated sodium ions with PPy. The (PPy)xMoO3 thin films can detect formaldehyde gas by increasing in their electrical resistance, whereas they showed no response to toluene.
Resistive type sensors using 10 mol% Hf-doped ceria and 10 mol% Zr-doped ceria, which had a single cubic phase obtained by solid state reaction, were fabricated and their sensing properties were investigated. The resistance and resistivity of the 10 mol% Hf-doped ceria or 10 mol% Zr-doped ceria were smaller than those of non-doped ceria. In the case of the same temperature of solid state reaction, the resistance and resistivity of the 10 mol% Hf-doped ceria were much smaller than those of the 10 mol% Zr-doped ceria. Furthermore, in the case of the same dopant, the resistance and resistivity of the sensor prepared from the solid state reaction at 1773 K were much smaller than those at 1673 K. The sensor using the 10 mol% Hf-doped ceria could be used as an oxygen gas sensor in wide oxygen partial pressure range and could be applicable to a λ sensor and a universal A/F sensor.
An experimental study is carried out to clarify the mechanism of the ozone zero phenomenon. Temporal variations of both the discharge characteristics and the metallic electrode surface in the ozone generator are investigated by the Lissajous figure method and Auger electron spectroscopy (AES), respectively. The AES results suggest that a number of oxygen atoms penetrate into the stainless-steel electrode owing to the exposure to ozone. Such a surface change would result in the temporal variation of the discharge characteristics of the generator.
The number of patients with severe invasive group-G streptococcal (Streptococcus dysgalactiae subsp. equisimilis) infections has been increasing in Japan. The emm genotypes and SmaI-digested pulsed-field gel electrophoresis DNA profiles were variable among the strains isolated, suggesting there has not been clonal expansion of a specific subpopulation of strains. However, all strains carried scpA, ska, slo and sag genes, some of which may be involved in the pathogenesis of the disease.
We surveyed T serotypes and emm genotypes of Streptococcus pyogenes isolates from streptococcal toxic shock-like syndrome (TSLS) patients. T1 (emm1) remained dominant through 1992 to 2000, but the dominant T3 (emm3.1) strains from 1992 to 1995 disappeared during 1996–2000. Strains of several emm genotypes emerged during 1996–2000, indicating alterations in the prevalent strains causing TSLS.
To clarify the relationship between the epidemics of severe
invasive group A streptococcal
infections (streptococcal Toxic Shock-Like Syndrome; TSLS) and common group
streptococcal infections in Japan, we examined the T serotypes of
S. pyogenes strains (group A
streptococci) isolated from clinical specimens of the streptococcal
infections (17999 cases) in
the period 1990–5, including the severe infections (TSLS)
(29 cases) in the period 1992–5.
Characteristic points of the analyses were: (1) dominant serotypes
of the infections in these
periods were T12, T4, T1, T28 and TB3264, which were consistently isolated;
(2) isolates of T3
rapidly increased through 1990 to 1994 while T6 decreased in the
period 1990–3; (3) when
Japanese area was divided into three parts, T3 serotype tended to spread
out from the north-eastern to the south-western area; (4) strains of T3
and T1 serotypes were dominant in the
TSLS. Dominant-serotype strains of streptococcal infections did not
always induce severe
infections and dominance of T3 serotype in the TSLS seemed to be
correlated with the increase
of T3 in streptococcal infections. These results may indicate that
certain clones of S. pyogenes are involved in the
pathogenesis of the TSLS.