中性子標的による閾値近傍K0Λ光生成

Tohoku University清水肇課

Quantum point contact conductance in NINS junctions

The effect of an insulating barrier located at a distance $a$ from a NS quantum point contact is analyzed in this work. The Bogoliubov de Gennes equations are solved for NINS junctions (S: anysotropic superconductor, I: insulator and N: normal metal), where the NIN region is a quantum wire. For $a\neq0$, bound states and resonances in the differential conductance are predicted. These resonances depend on the symmetry of the pair potential, the strength of the insulating barrier and $a$. Our results show that in a NINS quantum point contact the number of resonances vary with the symmetry of the order parameter. This is to be contrasted with the results for the NINS junction, in which only the position of the resonances changes with the symmetry.Comment: 5 pages, 5 Figures, RevTex

Near- to mid-infrared spectroscopy of the heavily obscured AGN LEDA 1712304 with AKARI/IRC

Context. Although heavily obscured active galactic nuclei (AGNs) have been found by many observational studies, the properties of the surrounding dust are poorly understood. Using AKARI/IRC spectroscopy, we discover a new sample of a heavily obscured AGN in LEDA 1712304 which shows a deep spectral absorption feature due to silicate dust. Aims. We study the infrared (IR) spectral properties of circumnuclear silicate dust in LEDA 1712304. Methods. We perform IR spectral fitting, considering silicate dust properties such as composition, porosity, size and crystallinity. Spectral energy distribution (SED) fitting is also performed to the flux densities in the UV to sub-millimeter range to investigate the global spectral properties. Results. The best-fit model indicates 0.1 $\mu$m-sized porous amorphous olivine (${\rm Mg_{2x}Fe_{2-2x}SiO_4}$; $x=0.4$) with $4\%$ crystalline pyroxene. The optical depth is $\tau_{\rm sil}{\sim}2.3$, while the total IR luminosity and stellar mass are estimated to be $L_{\rm IR}=(5\pm1){\times}10^{10}\,L_{\odot}$ and $M_{\rm star}=(2.7\pm0.8){\times}10^{9}\,M_{\odot}$, respectively. In such low $L_{\rm IR}$ and $M_{\rm star}$ ranges, there are few galaxies which show that large ${\tau}_{\rm sil}$. Conclusions. The silicate dust in the AGN torus of LEDA 1712304 has properties notably similar to those in other AGNs as a whole, but slightly different in the wing shape of the absorption profile. The porosity of the silicate dust suggests dust coagulation or processing in the circumnuclear environments, while the crystallinity suggests that the silicate dust is relatively fresh.Comment: 9 pages, 6 figures, accepted for publication in A&

Electronic transport properties of carbon nanotubes: the impact of atomic charged impurities

Even changing one atom in nanoscale materials is expected to alter their properties due to their small physical sizes. Such sensitivity can be utilized to modify materials\u27 properties from bottom up and is essential for the utility of nanoscale materials. As such, the impact of extrinsic atomic adsorbates was measured on pristine graphene and a network of carbon nanotubes using atomic hydrogen, cesium atoms, and dye molecules. In order to further quantify such an atomic influence, the resistance induced by a single potassium atom on metallic and semiconducting carbon nanotubes was measured for the first time. Carbon nanotubes are sensitive to adsorbates due to their high surface-to-volume ratio. The resistance arising from the presence of extrinsic impurity atoms depends on the types of nanotubes. Metallic carbon nanotubes are resilient to a long-ranged, Coulomb-like potential, whereas semiconducting carbon nanotubes are susceptible to these impurities. The difference in the scattering strength originates from the chirality of carbon nanotubes, which defines their unique electronic properties. This difference had not directly measured experimentally because of the issue of contact resistance, the difficulty of chirality identification, and the uncertainty in the number of impurity atoms introduced on carbon nanotubes. We synthesized atomically clean, long ( \u3e 100 ?m) carbon nanotubes, and their chirality was identified by Rayleigh scattering spectroscopy. We introduced potassium atoms on the nanotubes to impose a long-range, Coulomb potential and measured the change in resistivity, excluding the contact resistance, by plotting the resistance as a function of the carbon nanotube length. The flux of potassium atoms coming onto the nanotubes was monitored by quartz crystal microbalance, and the scattering strength of a single potassium atom was deduced from the change in resistivity and the density of potassium atoms on the nanotubes. We found that the scattering strength of potassium atoms on semiconducting nanotubes depends on the charge carrier type (holes or electrons). Metallic nanotubes were found to be less affected by the presence of potassium atoms than semiconducting nanotubes, but the scattering strength showed a large dependence on Fermi energy. These experimental results were compared to theoretical simulations, and we found a good agreement with the experiments. Our findings provide crucial information for the application of carbon nanotubes for electronic devices, such as transistors and sensors

Dust properties in the cold and hot gas phases of the ATLAS3D early-type galaxies as revealed by AKARI

The properties of the dust in the cold and hot gas phases of early-type galaxies (ETGs) are key to understand ETG evolution. We thus conducted a systematic study of the dust in a large sample of local ETGs, focusing on relations between the dust and the molecular, atomic, and X-ray gas of the galaxies, as well as their environment. We estimated the dust temperatures and masses of the 260 ETGs from the ATLAS3D survey, using fits to their spectral energy distributions primarily constructed from AKARI measurements. We also used literature measurements of the cold (CO and HI) and X-ray gas phases. Our ETGs show no correlation between their dust and stellar masses, suggesting inefficient dust production by stars and/or dust destruction in X-ray gas. The global dust-to-gas mass ratios of ETGs are generally lower than those of late-type galaxies, likely due to dust-poor HI envelopes in ETGs. They are also higher in Virgo Cluster ETGs than in group and field ETGs, but the same ratios measured in the central parts of the galaxies only are independent of galaxy environment. Slow-rotating ETGs have systematically lower dust masses than fast-rotating ETGs. The dust masses and X-ray luminosities are correlated in fast-rotating ETGs, whose star formation rates are also correlated with the X-ray luminosities. The correlation between dust and X-rays in fast-rotating ETGs appears to be caused by residual star formation, while slow-rotating ETGs are likely well evolved, and thus exhausting their dust. These results appear consistent with the postulated evolution of ETGs, whereby fast-rotating ETGs form by mergers of late-type galaxies and associated bulge growth, while slow-rotating ETGs form by (dry) mergers of fast-rotating ETGs. Central cold dense gas appears to be resilient against ram pressure stripping, suggesting that Virgo Cluster ETGs may not suffer strong related star formation suppression.Comment: 18 pages, 7 figures, accepted for publication in A&

Colour Modification of Wood by Dry Thermal Treatment Between 90°C and 200°C = A faanyag színének változása száraz hőkezelés hatására 90°C és 200°C között

The colour modification effect of dry thermal treatment was studied in black locust (Robinia pseudoacacia L.), poplar (Populus x euramericana cv. Pannonia), Scots pine (Pinus sylvestris L.), spruce (Picea abies Mill.) and larch (Larix decidua L.) species in the temperature range 90-200 °C. Colour data were presented and evaluated in the CIE L*a*b* coordinate system. All thermal treatments applied altered the wood colour throughout the entire cross section regardless of the treatment temperature. At lower temperatures, wood extractives played a decisive role in colour change. The degradation products of hemicelluloses were the major determinant of the change in lightness at 200°C. Redness change in percentage showed much greater alteration than the yellowness and the lightness change. Spruce presented the greatest chromaticity coordinate (a* and b*) alteration among the investigated species. Changes in redness and yellowness followed the Arrhenius law during the investigated dry thermal treatments confirming that the temperature dependence of these colour parameters is exponential for wood material. Száraz körülmények között végrehajtott termikus kezelés színváltoztató hatását vizsgáltuk akác (Robinia pseudoacacia L.), nyár (Populus x euramericana cv. Pannonia), erdei fenyő (Pinus sylvestris L.), lucfenyő (Picea abies Mill) és vörösfenyő (Larix decidua L.) faanyag esetében 90 – 200 °C hőmérséklet tartományban. A szín adatokat a CIE L*a*b* koordináta rendszerben adtuk meg és értékeltük. Az alkalmazott hőkezelések a faanyag színét, függetlenül az alkalmazott hőmérséklettől, a próbatestek teljes keresztmetszetében megváltoztatták. Alacsony hőmérsékleten az extrakt anyagtartalom volt meghatározó a színváltozásban. A hemicellulózok degradációs termékei határozták meg döntő mértékben a világosság változását 200 °C-on. A százalékosan megadott vörös színezetváltozás sokkal nagyobb mértékű volt, mint a sárga színezet és a világosság változása. A luc faanyaga mutatta a legnagyobb színezeti koordináta-változást (a*és b*) a vizsgált faanyagok közül. A vörös és a sárga színezet változása követte az Arrhenius törvényt a száraz termikus kezelések során mutatva, hogy ezeknek a paramétereknek a hőmérséklet függése exponenciális faanyag esetében