551 research outputs found
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Tohoku Universityæž
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Quantum point contact conductance in NINS junctions
The effect of an insulating barrier located at a distance 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 , 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 . 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 m-sized porous amorphous olivine (; ) with crystalline pyroxene. The optical
depth is , while the total IR luminosity and stellar
mass are estimated to be and
, respectively. In such low
and ranges, there are few galaxies which show that
large . 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 szĂnĂ©nek vĂĄltozĂĄsa szĂĄraz hĆkezelĂ©s hatĂĄsĂĄra 90°C Ă©s 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.
SzĂĄraz körĂŒlmĂ©nyek között vĂ©grehajtott termikus kezelĂ©s szĂnvĂĄltoztatĂł hatĂĄsĂĄt vizsgĂĄltuk akĂĄc (Robinia pseudoacacia L.), nyĂĄr (Populus x euramericana cv. Pannonia), erdei fenyĆ (Pinus sylvestris L.), lucfenyĆ (Picea abies Mill) Ă©s vörösfenyĆ (Larix decidua L.) faanyag esetĂ©ben 90 â 200 °C hĆmĂ©rsĂ©klet tartomĂĄnyban. A szĂn adatokat a CIE L*a*b* koordinĂĄta rendszerben adtuk meg Ă©s Ă©rtĂ©keltĂŒk. Az alkalmazott hĆkezelĂ©sek a faanyag szĂnĂ©t, fĂŒggetlenĂŒl az alkalmazott hĆmĂ©rsĂ©klettĆl, a prĂłbatestek teljes keresztmetszetĂ©ben megvĂĄltoztattĂĄk. Alacsony hĆmĂ©rsĂ©kleten az extrakt anyagtartalom volt meghatĂĄrozĂł a szĂnvĂĄltozĂĄsban. A hemicellulĂłzok degradĂĄciĂłs termĂ©kei hatĂĄroztĂĄk meg döntĆ mĂ©rtĂ©kben a vilĂĄgossĂĄg vĂĄltozĂĄsĂĄt 200 °C-on. A szĂĄzalĂ©kosan megadott vörös szĂnezetvĂĄltozĂĄs sokkal nagyobb mĂ©rtĂ©kƱ volt, mint a sĂĄrga szĂnezet Ă©s a vilĂĄgossĂĄg vĂĄltozĂĄsa. A luc faanyaga mutatta a legnagyobb szĂnezeti koordinĂĄta-vĂĄltozĂĄst (a*Ă©s b*) a vizsgĂĄlt faanyagok közĂŒl. A vörös Ă©s a sĂĄrga
szĂnezet vĂĄltozĂĄsa követte az Arrhenius törvĂ©nyt a szĂĄraz termikus kezelĂ©sek sorĂĄn mutatva, hogy ezeknek a paramĂ©tereknek a hĆmĂ©rsĂ©klet fĂŒggĂ©se exponenciĂĄlis faanyag esetĂ©ben
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