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Simultaneous Assimilation Model of Drifting Buoy and Altimetric Data for Ocean Surface Circulations
Awaji, Toshiyuki,Ishikawa, Yoichi,Akitomo, Kazunori 대한원격탐사학회 1996 International Symposium on Remote Sensing Vol.12 No.1
A simultaneous assimilation model of drifting buoy and altimetric data is proposed to determine the mean sea surface height(SSH) as well as the temporal evolution of the surface circulation on synoptic scales. The result shows that realistic buoy deployment (32 in a 40° square) ca.n effectively constrain the model variables; that is, both the absolute (mean plus time varying) velocity and SSH (interface depth) fields are significantly improved. Successive correction of the mean SSH is made with the simultaneous assimilation of drifting buoy and altimetric data. Consequently, a better correction of the mean SSH is obtained: The initial error of the mean SSH is reduced by approximately 40% after the 1-year experiment. These results clearly show that simultaneous assimilation of drifting buoy and altimetric data into the dynamical model is a very useful tool for improving the model's realism.
Air-Sea Heat Flux Estimation by Ocean Data Assimilation Using Satellite and TOGA/TAO Buoy Data
Awaji, Toshiyuki,Ishikawa, Yoichi,Iida, Masatora,In, Teiji 대한원격탐사학회 1999 International Symposium on Remote Sensing Vol.15 No.1
A data assimilation system for a 1-dimensional mixed layer model has been constructed using the adjoint method. The classical adjoint method does not work well for the mixed layer variabilities due to the occurrence of spikes in the gradient of the cost function. To solve this problem, the two techniques of scaling the cost function and optimization in the frequency space are used. As a result, the heat flux can be reliably estimated with an accuracy of 8Wm^(-2) rms error in the identical twin experiments. We then applied this system to the tropical Pacific TOGA-TAO buoy data. The air-sea heat flux as well as the mixed layer variability were estimated in close approximation to the buoy data, particularly on time scales longer than the seasonal one.
GLOBAL OCEAN STATE EATIMATION BY 4D-VAR DATA ASSIMILATION USING SATELLITE DATA
Awaji, Toshiyuki,Sugiura, Nozomi,Baba, Kinji,Masuda, Shuhei,Horiuchi, Kazutoshi,Jiang, Qin.,Ishikawa, Yoichi,Toyoda, Takahiro,Komori, Nobumasa 대한원격탐사학회 2001 International Symposium on Remote Sensing Vol.17 No.1
By using a free-surface ocean general circulation model and the variational adjoint method, our joint group has constructed a global ocean data assimilation system capable of providing a comprehensive 4-dimensional dataset from many of the available observational data such as satellite data and thereby estimating ocean circulation processes with high accuracy and good dynamical consistency. The system was applied to an experiment to define the climatological seasonal state of a global ocean. The result showed the efficiency of our assimilation system in reproducing the detailed features similar to those of ocean circulations reported so far. For example, a low salinity distribution associated with the North Pacific Intermediate Water is reproduced much better than in other simulations. The accuracy of estimated heat and freshwater fluxes is also better than that by the flux correction method currently used in most of ocean-atmosphere coupled models. These results suggest that our data assimilation system is a very powerful tool for ocean climate researches.
Thermal Shock Tests and Thermal Shock Parameters for Ceramics
Awaji, Hideo,Choi, Seong-Min The Korean Ceramic Society 2012 한국세라믹학회지 Vol.49 No.4
Thermal shock test methods and thermal shock parameters for ceramics were reviewed from the following viewpoints: (1) The test methods should be based on the precise estimation of both temperature and thermal stress distributions in a specimen taking into account the temperature-dependent thermo-mechanical properties; (2) The thermal shock parameters must be defined as a physical property of the materials and described as a function of temperature at the fracture point of the specimen; (3) The relation between the strength and fracture toughness of brittle ceramics under a thermal shock load must be the same as the relation under a mechanical load. In addition, appropriate thermal shock parameters should be defined by the thermal shock strength and thermal shock fracture toughness based on stress and energy criteria, respectively. A constant heat flux method is introduced as a testing technique suitable for estimating these thermal shock parameters directly from the electric power charged.
Thermal Shock Tests and Thermal Shock Parameters for Ceramics
Hideo Awaji,최성민 한국세라믹학회 2012 한국세라믹학회지 Vol.49 No.4
Thermal shock test methods and thermal shock parameters for ceramics were reviewed from the following viewpoints: (1) The test methods should be based on the precise estimation of both temperature and thermal stress distributions in a specimen taking into account the temperature-dependent thermo-mechanical properties; (2) The thermal shock parameters must be defined as a physical property of the materials and described as a function of temperature at the fracture point of the specimen; (3) The relation between the strength and fracture toughness of brittle ceramics under a thermal shock load must be the same as the relation under a mechanical load. In addition, appropriate thermal shock parameters should be defined by the thermal shock strength and thermal shock fracture toughness based on stress and energy criteria, respectively. A constant heat flux method is introduced as a testing technique suitable for estimating these thermal shock parameters directly from the electric power charged.
Magnetic field effects on synthesis process of high-Tc superconductors
S.Awaji,Y.Ma,W.P.Chen,H.Maeda,K.Watanabe,M.Motokawa 한국물리학회 2003 Current Applied Physics Vol.3 No.5
Materials synthesis processes in high magnetic fields are investigated for high-Tc superconductors at the High Field Laboratoryfor Superconducting Materials, Institute for Materials Research, Tohoku University. On a melt growth process of YBa2Cu3O7 bulkalso the decrease of the crystal growth rate by the magnetic field, which is suggested from a dierential temperature analysismeasurement in magnetic fields. On a chemical vapor deposition process of YBa2Cu3O7 lms deposited on the polycrystalline Agsubstrates in high magnetic elds, the microstructure changes drastically from the rectangular large grains with 10l m in size to thesmall complex shaped grains. The spiral growth mode is observed for the samples prepared at 0 T but it changes into the island2Sr2CaCu2O8 tapes in magneticelds, the homogeneous texture is obtained and it results in the increase of the critical current density.. 2003 Elsevier B.V.
淡路英夫(Hideo Awaji),千承昊(Sung-Ho Cheon),崔成珉(Seong-Min Choi) 한국세라믹학회 2006 세라미스트 Vol.9 No.6
Intra-type alumina-based nanocomposites, in which second-phase nanoparticles are embedded within alumina grains, use dislocation activities to enhance strength and fracture toughness. The dislocations are generated around the nanoparticles by residual stresses during cooling process. In this paper, first, we explain strengthening and toughening mechanisms of alumina-based nanocomposites based on dislocation activities. Second, we propose a soaking method to construct the intra-type nanostructure and fabricate alumina/nickel and alumina/silver nanocomposites. The nanocomposites are then annealed in order to enhance the fracture toughness of the materials. Finally, we discuss the relation between the strength, fracture toughness, and critical frontal process zone size of the materials.
Seasonal Transport Variations in the Japan Sea
Yoshikawa, Yutakawa,Awaji, Toshiyuki,Akitomo, Kazunori 대한원격탐사학회 1995 International Symposium on Remote Sensing Vol.11 No.1
The Japan(East) Sea circulation has been examined with an $quot;incomplete$quot; robust diagnostic model. The simulated Japan Sea circulation shows strong seasonal variations, the major features being in good agreement with observational findings. To identify the sources and pathways of water masses in such a complicated current system, the Lagrangian water-mass movement is examined, providing useful informations about water-mass formation processes. The renewal time of the water masses is estimated to be at least tens years.