Recursos de colección

Hokkaido University Collection of Scholarly and Academic Papers (135.711 recursos)

HUSCAP (Hokkaido University Collection of Scholarly and Academic Papers) contains peer-reviewed journal articles, proceedings, educational resources and any kind of scholarly works of Hokkaido University.

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Mostrando recursos 1 - 20 de 2.121

  1. Spectroscopic gamma camera for use in high dose environments

    Ueno, Yuichiro; Takahashi, Isao; Ishitsu, Takafumi; Tadokoro, Takahiro; Okada, Koichi; Nagumo, Yasushi; Fujishima, Yasutake; Kometani, Yutaka; Suzuki, Yasuhiko; Umegaki, Kikuo
    We developed a pinhole gamma camera to measure distributions of radioactive material contaminants and to identify radionuclides in extraordinarily high dose regions (1000 mSv/h). The developed gamma camera is characterized by: (1) tolerance for high dose rate environments; (2) high spatial and spectral resolution for identifying unknown contaminating sources; and (3) good usability for being carried on a robot and remotely controlled. These are achieved by using a compact pixelated detector module with CdTe semiconductors, efficient shielding, and a fine resolution pinhole collimator. The gamma camera weighs less than 100 kg, and its field of view is an 8 m...

  2. Symmetry conditions of a nodal superconductor for generating robust flat-band Andreev bound states at its dirty surface

    Ikegaya, Satoshi; Kobayashi, Shingo; Asano, Yasuhiro
    We discuss the symmetry property of a nodal superconductor that hosts robust flat-band zero-energy states at its surface under potential disorder. Such robust zero-energy states are known to induce the anomalous proximity effect in a dirty normal metal attached to a superconductor. A recent study has shown that a topological index N-ZES describes the number of zero-energy states at the dirty surface of a p-wave superconductor. We generalize the theory to clarify the conditions required for a superconductor that enables N-ZES not equal 0. Our results show that N-ZES not equal 0 is realized in a topological material that belongs...

  3. Multifold paths of neutrons in the three-beam interferometer detected by a tiny energy kick

    Geppert-Kleinrath, Hermann; Denkmayr, Tobias; Sponar, Stephan; Lemmel, Hartmut; Jenke, Tobias; Hasegawa, Yuji
    A neutron optical experiment is presented to investigate the paths taken by neutrons in a three-beam interferometer. In various beam paths of the interferometer, the energy of the neutrons is partially shifted so that the faint traces are left along the beam path. By ascertaining an operational meaning to "the particle's path," which-path information is extracted from these faint traces with minimal perturbations. Theory is derived by simply following the time evolution of the wave function of the neutrons, which clarifies the observation in the framework of standard quantum mechanics. Which-way information is derived from the intensity, sinusoidally oscillating in...

  4. Generation of Cation Radicals from 2-Tributylstannyl-1,3-dithianes and Their Reaction with Olefins

    Narasaka, Koichi; Okauchi, Tatsuo; Arai, Noriyoshi
    Oxidation of 2-tributylstannyl-1,3-dithianes with metallic oxidants generates reactive species such as 1,3-dithian-2-yl radical and/or cation by eliminating the stannyl group. Those intermediates react with olefins to give the intermolecular addition products.

  5. Generation of α-Nitroalkyl Radicals by Oxidation of Nitronate Anions with Cerium(IV) Ammonium Nitrate and Their Addition Reaction to Electron-Rich Olefins

    Arai, Noriyoshi; Narasaka, Koichi
    α-Nitroalkyl radicals are generated by oxidation of nitronate anions with cerium(IV) ammonium nitrate. When the reactions are carried out in the presence of electron-rich olefins, such as silyl enol ethers, intermolecular addition of the radicals proceeds to afford β-nitroketones, which are further converted to α,β-unsaturated ketones in good yield.

  6. Generation of α-Alkylthio Radicals by Photoinduced One-Electron Oxidation of α-Stannyl Sulfides and Their Use for Carbon-Carbon Bond Formation

    Ikeno, Taketo; Harada, Manabu; Arai, Noriyoshi; Narasaka, Koichi
    Cation radicals, generated from α-stannyl sulfides by the photoinduced single electron transfer, cleave into α-alkylthio radical intermediates with the elimination of the stannyl group. The α-alkylthio radicals thus formed are utilized for carbon-carbon bond forming reactions.

  7. Oxidative Generation of 1-Nitroalkyl Radicals and Their Addition Reaction to Olefins

    Arai, Noriyoshi; Narasaka, Koichi
    1-Nitroalkyl radicals are generated by oxidation of potassium salt of 1-aci-nitroalkanes with ammonium hexanitratocerate(IV). When the oxidation is carried out in the presence of electron-rich olefins, such as silyl enol ethers, intermolecular addition of the radicals onto the olefins proceeds to afford β-nitro ketones, which are further converted to α,β-unsaturated ketones in high yield. Stereoselective construction of fused ring systems is achieved by intramolecular addition of 1-nitroalkyl radicals.

  8. Generation of Radical Species from Cyclohexane-1,2-dione and the Reaction with Olefins : Preparation of 4,5-Dihydro-7(6H)-benzofuranone Derivatives

    Miura, Masanori; Arai, Noriyoshi; Narasaka, Koichi
    Oxidation of cyclohexane-1,2-dione with ammonium hexanitratocerate(IV) (CAN) generates 2,3-dioxocyclohexyl radical, which reacts with electron-rich olefins to afford the corresponding addition products. The adducts thus generated are converted to 4,5-dihydro-7(6H)-benzofuranone by acid treatment. In addition to cyclohexane-1,2-dione, radical species are also generated from cyclopentane-1,2-dione and cycloheptane-1,2-dione.

  9. Synthesis ofN,N′-Disubstituted Urea from Ethylene Carbonate and Amine Using CaO

    Fujita, Shin-ichiro; Bhanage, Bhalchandra M.; Arai, Masahiko
    Calcium oxide has been proved to be an excellent solid catalyst for the synthesis of N,N′-disubstituted ureas from ethylene carbonate and primary amines under mild conditions.

  10. Asymmetric hydrogenation of ketones : Tactics to achieve high reactivity, enantioselectivity, and wide scope

    OHKUMA, Takeshi
    Ru complexes with chiral diphosphines and amine-based ligands achieve high catalytic activity and enantioselectivity for the hydrogenation of ketones under neutral to slightly basic conditions. The chiral environment is controllable by changing the combination of these two ligands. A concerted six-membered transition state is proposed to be the origin of the high reactivity. The η6-arene/TsDPEN–Ru and MsDPEN–Cp*Ir catalysts effect the asymmetric reaction under slightly acidic conditions. A variety of chiral secondary alcohols are obtained in high enantiomeric excess.

  11. Chemical Fixation of Carbon Dioxide : Synthesis of Cyclic Carbonate, Dimethyl Carbonate, Cyclic Urea and Cyclic Urethane

    Fujita, Shin-ichiro; Arai, Masahiko
    Chemical fixation of carbon dioxide (CO2) may be very important in the future as a solution for the problem of increased atmospheric CO2 levels. Recent developments for chemical fixation of CO2 to cyclic carbonate, dimethyl carbonate (DMC), cyclic urea and cyclic urethane are reviewed. Synthesis of cyclic carbonate via CO2 addition to epoxide has been already applied on the industrial scale, but catalyst development continues. Direct oxidative carboxylation of olefin is preferable for the synthesis of cyclic carbonate, but requires the development of catalysis for the epoxidation step in the presence of CO2. Direct synthesis of DMC is not in...

  12. Selective Hydrogenation of Phenylacetylene with Graphite Intercalated Platinum Nanosheets

    Shirai, Masayuki; Bhanage, Bhalchandra M.; Senboku, Hisanori; Fujita, Shin-ichiro; Arai, Masahiko
    Platinum nanosheets between graphite layers were active for hydrogenation of ethynyl group of phenylacetylene but less active for that of aromatic rings of phenylacetylene and benzene due to its structural characteristics.

  13. Triboluminescence of Lanthanide Coordination Polymers with Face-to-Face Arranged Substituents

    Hirai, Yuichi; Nakanishi, Takayuki; Kitagawa, Yuichi; Fushimi, Koji; Seki, Tomohiro; Ito, Hajime; Hasegawa, Yasuchika
    Luminescence upon the grinding of solid materials (triboluminescence, TL) has long been a puzzling phenomenon in natural science and has also attracted attention because of its broad application in optics. It has been generally considered that the TL spectra exhibit similar profiles as those of photoluminescence (PL), although they occur from distinct stimuli. Herein, we describe for the first time a large spectral difference between these two physical phenomena using lanthanide(III) coordination polymers with efficient TL and PL properties. They are composed of emission centers (Tb-III and Eu-III ions), antenna (hexafluoroacetylacetonate=hfa), and bridging ligands (2,5-bis(diphenylphosphoryl)furan=dpf). The emission color upon grinding...

  14. Prevention of Catastrophic Volcanic Eruptions, Large Earthquakes underneath Big Cities, and Giant Earthquakes at Subduction Zones

    Fujii, Yoshiaki; Sheshpari, Morteza; Kodama, Jun-ichi; Fukuda, Daisuke; Dassanayake, Anjula BN
    Catastrophic volcanic eruptions, large earthquakes beneath big cities, or giant earthquakes at subduction zones are apparently the biggest problems facing the sustainability of human society. However, imminent prediction methods for these events have never been established, except that volcanic eruptions can only be predicted by exceptional efforts by dedicated researchers. Even if a prediction method has been established, the method cannot significantly reduce infrastructure damage, although it could slightly reduce the number of fatalities. On the other hand, prevention of eruptions or earthquakes could significantly reduce, not only the number of fatalities, but also infrastructure damage. Therefore, the authors propose...

  15. Synoptic climatology of winter daily temperature extremes in Sapporo, northern Japan

    Farukh, M. A.; Yamada, Tomohito J.
    Extreme winter daily temperature is an important parameter for determining winter precipitation. This study used a principal component analysis and k-means clustering to characterize the circulation patterns of extreme daily temperatures for 19 winter seasons in Sapporo, Hokkaido, Japan. Climatological anomaly maps were constructed for sea level pressure (SLP) and the 500-hPa geopotential height for the identified minimum (Tmin(10); 239days) and maximum (Tmax(90); 236days) daily temperature extremes. The Tmax(90) SLP anomaly pattern was the opposite (west-east orientation) of the Tmin(10) pattern. The circulation patterns that predominantly contributed to winter rainfall were derived from cyclones over the Sea of Japan via...

  16. Controlling Rashba spin-orbit interaction in quantum wells by adding symmetric potential

    Egami, Yoshiyuki; Akera, Hiroshi
    The incorporation of a symmetric electrostatic potential into quantum wells (QWs) is proposed as a method for modifying the coefficient a of the Rashba spin-orbit interaction. In a symmetric QW for which a = a(so)E(z), where E-z is the perpendicular electric field, the constant a(so) can be controlled by the symmetric potential. The sign reversal of a(so) with the increasing strength of the symmetric potential is demonstrated in (001)-oriented GaAs/AlGaAs QWs via a tight-binding model. The present findings can be used to realize structures with vanishing a in nonzero E-z.

  17. Genetic Analysis of Norovirus Strains that Caused Gastroenteritis Outbreaks Among River Rafters in the Grand Canyon, Arizona

    Kitajima, Masaaki; Iker, Brandon C.; Magill-Collins, Anne; Gaither, Marlene; Stoehr, James D.; Gerba, Charles P.
    Toilet solid waste samples collected from five outbreaks among rafters in the Grand Canyon were subjected to sequencing analysis of norovirus partial capsid gene. The results revealed that a GI.3 strain was associated with one outbreak, whereas the other outbreaks were caused by GII.5 whose sequences shared > 98.9% homology.

  18. Excitation of cavitation bubbles in low-temperature liquid nitrogen

    Sasaki, Koichi; Harada, Shingo
    We excited a cavitation bubble by irradiating a Nd: YAG laser pulse onto a titanium target that was installed in liquid nitrogen at a temperature below the boiling point. To our knowledge, this is the first experiment in which a cavitation bubble has been successfully excited in liquid nitrogen. We compared the cavitation bubble in liquid nitrogen with that in water on the basis of an equation reported by Florschuetz and Chao [J. Heat Transfer 87, 209 (1965)].

  19. Mechanisms of photo-induced degradation of polythiophene derivatives: re-examination of the role of singlet oxygen

    Ohta, Hiroki; Koizumi, Hitoshi
    Roles of singlet oxygen (1O2) in photo-induced degradation of poly(3-hexylthiophene) (P3HT) and poly(3-hexyloxythiophene) (P3HOT) were examined. The results indicate that 1O2 has a considerable role in the degradation of P3HT and P3HOT. Photo-irradiation of P3HT in air resulted in the reduction of the pi-conjugation. The photo-induced reduction also occurred for P3HOT, and it was much faster than that of P3HT. Manceau et al. have reported that 1O2 was generated by photo-irradiation of P3HT in the presence of oxygen and, nevertheless, 1O2 is not the principal photo-oxidative degradation intermediate of P3HT (Manceau et al., Macromol Rapid Commun 29:1823-1827, 2008). However, exposures...

  20. Reaction kinetics for the production of methylene urea from synthetic human urine

    Kabore, Steve; Ito, Ryusei; Funamizu, Naoyuki
    The production of methylene urea from human urine is an important contribution to the world demand of nitrogen fertilizer. In this study, a simplified reaction model was proposed. The kinetics parameters at room temperature were assessed and the reaction constants k(1), k(2), k(3), k(4) were evaluated and determined for the different parts of the proposed reaction model. The relationship between the Formaldehyde/Urea (F/U ratio) and the recovery of nitrogen was also evaluated based on the contribution of the by-products from the reaction. The optimum F/U condition to maximize the recovery of nitrogen was determined.

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