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Search Results: 1 - 10 of 1430 matches for " Yuya Sakai "
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Surface Properties of Cement Paste Evaluated by Scanning Probe Microscopy  [PDF]
Yuya Sakai
Open Journal of Civil Engineering (OJCE) , 2016, DOI: 10.4236/ojce.2016.64052
Abstract: The microscopic physical properties of Hardened Cement Paste (HCP) surfaces were evaluated by using Scanning Probe Microscopy (SPM). The cement pastes were cured under a hydrostatic pressure of 400 MPa and the contacting surfaces with a slide glass during the curing were studied. Scanning Electron Microscope (SEM) observation at a magnification of 7000 revealed smooth surfaces with no holes. The surface roughness calculated from the SPM measurement was 4 nm. The surface potential and the frictional force measured by SPM were uniform throughout the measured area 24 h after the curing. However, spots of low surface potential and stains of low frictional force and low viscoelasticity were observed one month after curing. This change was attributed to the carbonation of hydrates.
Non-Destructive Imaging of Water Permeation through Cementitious Materials Using MRI  [PDF]
Yuya Sakai, Yuki Yokoyama, Toshiharu Kishi
Open Journal of Civil Engineering (OJCE) , 2017, DOI: 10.4236/ojce.2017.73026
Abstract: In this study, water permeation through cementitious materials was observed using magnetic resonance imaging (MRI). The influence of cement type on the magnetic resonance signal was studied subsequent to determining the parameters required for imaging. Consequently, adequate imaging of water permeating through hardened cement paste (HCP) made with white Portland cement was achieved, while water permeation through ordinary Portland cement-based HCP yielded poor signal. HCPs maintained at various levels of relative humidity (RH) were observed, and the signal was detected only from those maintained at an RH of higher than 85%. The water permeation depths in HCP were observed by using MRI, and the measured depths were compared to those measured via a spraying water detector on the split surface of the specimens. As a result, good agreement was confirmed between the two methods. Additionally, MRI was applied to concrete specimens; although it was found that water was not detected when a lightweight aggregate was used, water permeation through concrete with limestone aggregate was detectable via MRI. MRI will help in understanding how water permeation causes and accelerates concrete deteriorations such as rebar corrosion and freezing and thawing.
Superconducting gap structure of CeIrIn5 from field-angle-resolved measurements of its specific heat
Shunichiro Kittaka,Yuya Aoki,Toshiro Sakakibara,Akito Sakai,Satoru Nakatsuji,Yasumasa Tsutsumi,Masanori Ichioka,Kazushige Machida
Physics , 2011, DOI: 10.1103/PhysRevB.85.060505
Abstract: In order to identify the gap structure of CeIrIn5, we measured field-angle-resolved specific heat C(phi) by conically rotating the magnetic field H around the c axis at low temperatures down to 80 mK. We revealed that C(phi) exhibits a fourfold angular oscillation, whose amplitude decreases monotonically by tilting H out of the ab plane. Detailed microscopic calculations based on the quasiclassical Eilenberger equation confirm that the observed features are uniquely explained by assuming the dx2-y2-wave gap. These results strongly indicate that CeIrIn5 is a dx2-y2-wave superconductor and suggest the universal pairing mechanism in CeMIn5 (M = Co, Rh, and Ir).
Recyclable Cyclohexanediamine Derivatives as Organocatalysts: Organocatalytic Reduction with Trichlorosilane and Aldol Reaction  [PDF]
Yuya Tanimura, Kaori Ishimaru
International Journal of Organic Chemistry (IJOC) , 2013, DOI: 10.4236/ijoc.2013.34034

Reduction of ketimine with trichlorosilane was carried out using bisformamide catalyst 1a derived from cyclohexanediamine to give the corresponding product in 81% yield with 39% ee. Deprotection of the formyl groups of the catalysts 1 gave the corresponding diamines 2 which were utilized in aldol reaction of acetone with 4-nitrobenzaldehyde. The reaction using 2b in brine afforded the aldol adduct in 81% yield with 29% ee.


Dispersion and Polar Component of Specific Surface Free Energy of NaCl(100), KCl(100), and KBr(100) Single Crystal Surfaces  [PDF]
Takaomi Suzuk, Yuya Yamada
Journal of Crystallization Process and Technology (JCPT) , 2015, DOI: 10.4236/jcpt.2015.53006
Abstract: Contact angle of ethylene glycol and formamide on (100) faces of NaCl, KCl, and KBr single crystal was measured, and the specific surface free energy (SSFE) was calculated. Dispersion component of the SSFE was 90.57, 93.78, and 99.52 mN·m-1 for NaCl, KCl, and KBr, respectively. Polar component of the SSFE was 1.05, 0.65, and 0.45 mN·m-1 for NaCl, KCl, and KBr. Such a large ratio of dispersion component of SSFE results from the neutrality of the crystal surface of alkali halide. Lattice component of alkali halide is 780, 717 and 689 kJ·mol-1 for NaCl, KCl, and KBr. The larger lattice enthalpy decreases dispersion component, and increases polar component of the SSFE. The larger lattice enthalpy is considered to enhance the rumpling of the crystal surface more strongly, and such rumpling is considered to decrease the neutrality of the crystal surface.
Asymmetric Electrostatic Force  [PDF]
Katsuo Sakai
Journal of Electromagnetic Analysis and Applications (JEMAA) , 2014, DOI: 10.4236/jemaa.2014.610026
Abstract: Asymmetric electrostatic forces are a very interesting and new phenomenon. The magnitude of an electrostatic force that acts on a point charge does not change when the direction of the electric field is reversed. On the contrary, the magnitude of the electrostatic force that acts on a charged asymmetric shaped conductor does change when the direction of the electric field is reversed. 5 years ago, this phenomenon was reported by a simple experiment and a simulation and named as an Asymmetric electrostatic force unofficially by the author. After that, several simulations confirmed this phenomenon. However, several experiments did not yet confirm it clearly. The difference between the simulations and the experiments depends upon differences of their conditions. The simulations had been done under ideal (perfect) conditions; the experiments, on the contrary, had been done under actual (not perfect) conditions. In the new experiment, its conditions were improved to near ideal (perfect) conditions. As a result the existence of the Asymmetric electrostatic force was more clearly confirmed.
A Study of Weighted Polynomial Approximations with Several Variables (II)  [PDF]
Ryozi Sakai
Applied Mathematics (AM) , 2017, DOI: 10.4236/am.2017.89093
Abstract: In this paper we investigate weighted polynomial approximations with several variables. Our study relates to the approximation for \"\" by weighted polynomial. Then we will give some results relating to the Lagrange interpolation, the best approximation, the Markov-Bernstein inequality and the Nikolskii- type inequality.
A Study of Weighted Polynomial Approximations with Several Variables (I)  [PDF]
Ryozi Sakai
Applied Mathematics (AM) , 2017, DOI: 10.4236/am.2017.89095
Abstract: In this paper, we investigate the weighted polynomial approximations with several variables. Our study relates to the approximation for \"\" by weighted polynomials. Then we will estimate the degree of approximation.
Thermal leptogenesis scenarios in the predictive left-right symmetric model
Wakabayashi, Yuya
High Energy Physics - Phenomenology , 2007, DOI: 10.1143/PTP.117.1099
Abstract: We investigated thermal leptogenesis scenarios in the left-right symmetric extension of the standard model. In the SO(10) GUT framework, we impose the D-parity realization below GUT scale. These two conditions makes our model more restrictive and predictive. In such a case, a D-parity odd singlet in the 4-index antisymmetric tensor representation of SO(10) have a critical role. This singlet have prospects of causing a very large mass hierarchy between SU(2)L and SU(2)R triplet scalars. We test our model by computing baryogenesis via leptogenesis. The heavy right-handed neutrinos N's and the SU(2)L triplet scalar can generate the lepton number asymmetry. Leptogenesis scenarios can be categorized by these mass scales. If the light neutrinos are Majorana and have a hierarchical mass spectrum, we can obtain a successful result in leptogenesis through lightest N-decay. But we found that the normal mass hierarchy of the light neutrinos conflicts with leptogenesis through triplet-decay.
Flow equation of functional renormalization group for three-body scattering problems
Tanizaki, Yuya
High Energy Physics - Phenomenology , 2013,
Abstract: Functional renormalization group (FRG) is applied to the three-body scattering problem in the two-component fermionic system with an attractive contact interaction. We establish a new and correct flow equation on the basis of FRG and show that our flow equation is consistent with integral equations obtained from the Dyson-Schwinger equation. In particular, the relation of our flow equation and the Skornyakov and Ter-Martirosyan equation for the atom-dimer scattering is made clear.
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