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Search Results: 1 - 10 of 1484 matches for " Takayuki Sumiyoshi "
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Phase Diagram of an S = 1/2 J1-J2 Anisotropic Heisenberg Antiferromagnet on a Triangular Lattice  [PDF]
Nobuo Suzuki, Fumitaka Matsubara, Sumiyoshi Fujiki, Takayuki Shirakura
Journal of Modern Physics (JMP) , 2019, DOI: 10.4236/jmp.2019.101002
Abstract: We study the ground state of an S=1/2 anisotropic a (Jz/Jxy) Heisenberg antiferromagnet with nearest (J1) and next-nearest (J2) neighbor exchange interactions on a triangular lattice using the exact diagonalization method. We obtain the energy, squared sublattice magnetizations, and their Binder ratios on finite lattices with N36 sites. We estimate the threshold J(t) 2 (a)?between the three-sublattice Néel state and the spin liquid (SL) state, and J(s) 2 (a) between the stripe state and the SL state. The SL state exists over a wide range in the α-J2 plane. For α>1 , the xy component of the magnetization is destroyed by quantum fluctuations, and the classical distorted 120° structure is replaced by the collinear state.
Test of Various Photocathodes
Ryoji Enomoto,Takayuki Sumiyoshi,Yoshio Fujita
Physics , 1994, DOI: 10.1016/0168-9002(94)90540-1
Abstract: A test of various photocathodes was carried out. The tested materials were CsI, CsTe, their multi-layers and so on. The quantum efficiencies of the various materials were measured under a vacuum and/or after exposure to several kinds of gases.
Absence of a classical long-range order in $S=1/2$ Heisenberg antiferromagnet on triangular lattice
Nobuo Suzuki,Fumitaka Matsubara,Sumiyoshi Fujiki,Takayuki Shirakura
Physics , 2014, DOI: 10.1103/PhysRevB.90.184414
Abstract: We study the quantum phase transition of an $S=1/2$ anisotropic $\alpha$ $(\equiv J_z/J_{xy})$ Heisenberg antiferromagnet on a triangular lattice. We calculate the sublattice magnetization and the long-range helical order-parameter and their Binder ratios on finite systems with $N \leq 36$ sites. The $N$ dependence of the Binder ratios reveals that the classical 120$^{\circ}$ N\'{e}el state occurs for $\alpha \lesssim 0.55$, whereas a critical collinear state occurs for $1/\alpha \lesssim 0.6$. This result is at odds with a widely-held belief that the ground state of a Heisenberg antiferromagnet is the 120$^{\circ}$ N\'{e}el state, but it also provides a possible mechanism explaining experimentally observed spin liquids.
Recent progress in the development of large area silica aerogel for use as RICH radiator in the Belle II experiment
Makoto Tabata,Ichiro Adachi,Hideyuki Kawai,Shohei Nishida,Takayuki Sumiyoshi
Physics , 2014,
Abstract: We report recent progress in the development of large-area hydrophobic silica aerogels for use as radiators in the aerogel-based ring-imaging Cherenkov (A-RICH) counter to be installed in the forward end cap of the Belle II detector, which is currently being upgraded at the High Energy Accelerator Research Organization (KEK), Japan. The production of approximately 450 aerogel tiles with refractive indices of either 1.045 or 1.055 was completed in May, 2014, and the tiles are now undergoing optical characterization. Installation of the aerogels was tested by installing them into a partial mock-up of the support structure.
Hydrophobic silica aerogel production at KEK
Makoto Tabata,Ichiro Adachi,Hideyuki Kawai,Takayuki Sumiyoshi,Hiroshi Yokogawa
Physics , 2011, DOI: 10.1016/j.nima.2011.12.017
Abstract: We present herein a characterization of a standard method used at the High Energy Accelerator Research Organization (KEK) to produce hydrophobic silica aerogels and expand this method to obtain a wide range of refractive index (n = 1.006-1.14). We describe in detail the entire production process and explain the methods used to measure the characteristic parameters of aerogels, namely the refractive index, transmittance, and density. We use a small-angle X-ray scattering (SAXS) technique to relate the transparency to the fine structure of aerogels.
Development of transparent silica aerogel over a wide range of densities
Makoto Tabata,Ichiro Adachi,Yoshikazu Ishii,Hideyuki Kawai,Takayuki Sumiyoshi,Hiroshi Yokogawa
Physics , 2011, DOI: 10.1016/j.nima.2010.02.241
Abstract: We have succeeded in developing hydrophobic silica aerogels over a wide range of densities (i.e. refractive indices). A pinhole drying method was invented to make possible producing highly transparent aerogels with entirely new region of refractive indices of 1.06-1.26. Obtained aerogels are more transparent than conventional ones, and the refractive index is well controlled in the pinhole drying process. A test beam experiment was carried out in order to evaluate the performance of the pinhole-dried aerogels as a Cherenkov radiator. A clear Cherenkov ring was successfully observed by a ring imaging Cherenkov counter. We also developed monolithic and hydrophobic aerogels with a density of 0.01 g/cm^3 (a low refractive index of 1.0026) as a cosmic dust capturer for the first time. Consequently, aerogels with any refractive indices between 1.0026 and 1.26 can be produced freely.
A cost-optimal scenario of CO2 sequestration in a carbon-constrained world through to 2050  [PDF]
Takayuki Takeshita
Natural Science (NS) , 2013, DOI: 10.4236/ns.2013.52A043
Abstract:

In this paper, a regionally disaggregated global energy system model with a detailed treatment of the whole chain of CO2 capture and storage (CCS) is used to derive the cost-optimal global pattern of CO2 sequestration in regional detail over the period 2010-2050 under the target of halving global energy-related CO2 emissions in 2050 compared to the 2005 level. The major conclusions are the following. First, enhanced coalbed methane recovery will become a key early opportunity for CO2 sequestration, so coalrich regions such as the US, China, and India will play a leading role in global CO2 sequestration. Enhanced oil recovery will also have a participation in global CO2 sequestration from the initial stage of CCS deployment, which may be applied mainly in China, southeastern Asia, and West Africa in 2030 and mainly in the Middle East in 2050. Second, CO2 sequestration will be carried out in an increasing number of world regions over time. In particular, CCS will be deployed extensively in today’s developing countries. Third, an increasing amount of the captured CO2 will be stored in aquifers in many parts of the world due to their abundant and widespread availability and their low cost. It is shown that the share of aquifers in global CO2 sequestration reaches 82.0% in 2050.

Prospects for Renewable and Fossil-Based Electricity Generation in a Carbon-Constrained World  [PDF]
Takayuki Takeshita
International Journal of Clean Coal and Energy (IJCCE) , 2013, DOI: 10.4236/ijcce.2013.22B008
Abstract: In this paper, a regionally disaggregated global energy system model with a detailed treatment of the electricity supply sector is used to derive the cost-optimal choice of electricity generation technologies for each of 70 world regions over the period 2010-2050 under a constraint of halving global energy-related CO2 emissions in 2050 compared to the 2000 level. It is first shown that the long-term global electricity generation mix under the CO2 constraint becomes highly diversified, which includes coal, natural gas, nuclear, biomass, hydro, geothermal, onshore and offshore wind, solar photovoltaics (PV), and concentrated solar power (CSP). In this carbon-constrained world, 89.9% of the electricity generation from coal, natural gas, and biomass is combined with CO2 capture and storage (CCS) in 2050. It is then shown that the long-term electricity generation mix under the CO2 constraint varies significantly by world region. Fossil fuels with CCS enter the long-term electricity generation mix in all world regions. In contrast, there is a sharp regional difference in the renewable generation technology of choice in the long term. For example, the world regions suitable for PV plants include the US, Western Europe, Japan, Korea, and China, while those suitable for CSP plants include the Middle East, Africa, Australia, and western Asia. Offshore wind is deployed on a large scale in the UK, Ireland, Nordic countries, the southern part of Latin America, and Japan.
Prospects for Coalbed Methane and Shale Gas in a Carbon-Constrained World: A Preliminary Analysis  [PDF]
Takayuki Takeshita
International Journal of Clean Coal and Energy (IJCCE) , 2013, DOI: 10.4236/ijcce.2013.22B007
Abstract:

Using a regionally disaggregated global energy system model with a detailed treatment of the natural gas resource base, this paper analyzes the competitiveness of coalbed methane and shale gas in the global primary energy mix and the cost-optimal pattern of their production in regional detail over the period 2010-2050 under a constraint of halving global energy-related CO2 emissions in 2050 compared to the 2000 level. It is first shown that neither coalbed methane nor shale gas could become an important fuel in the global primary energy mix throughout the time horizon, although each of them could become an important source of world natural gas production from around 2030 onwards. It is then shown that unlike findings of previous studies, coalbed methane would be more attractive than shale gas as a primary energy source globally under the CO2 constraint used here. The results indicate that North America continues to be the world’s largest coalbed methane producer until 2030, after which China overtakes North America and retains this position until 2050. Also, India, Russia, South Africa, and Australia contribute noticeably to world coalbed methane production. The results also indicate that North America continues to dominate world shale gas production until 2040, after which a number of world regions, notably India, Europe, and China, begin to participate visibly in world shale gas production.


Application of Fast N-Body Algorithm to Option Pricing under CGMY Model  [PDF]
Takayuki Sakuma
Journal of Mathematical Finance (JMF) , 2017, DOI: 10.4236/jmf.2017.72016
Abstract: The N-body problem is an active research topic in physics for which there are two major algorithms for efficient computation, the fast multipole method and treecode, but these algorithms are not popular in financial engineering. In this article, we apply a fast N-body algorithm called the Cartesian treecode to the computation of the integral operator of integro-partial differential equations to compute option prices under the CGMY model, a generalization of a jump-diffusion model. We present numerical examples to illustrate the accuracy and effectiveness of the method and thereby demonstrate its suitability for application in financial engineering.
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