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Average Walk Length in One-Dimensional Lattice Systems
Lee Eok Kyun Korean Chemical Society 1992 Bulletin of the Korean Chemical Society Vol.13 No.6
We consider the problem of a random walker on a one-dimensional lattice (N sites) confronting a centrally-located deep trap (trapping probability, T=1) and N-1 adjacent sites at each of which there is a nonzero probability s(0 < s < 1) of the walker being trapped. Exact analytic expressions for < n > and the average number of steps required for trapping for arbitrary s are obtained for two types of finite boundary conditions (confining and reflecting) and for the infinite periodic chain. For the latter case of boundary condition, Montroll's exact result is recovered when s is set to zero.
Catalytically-etched hexagonal boron nitride flakes and their surface activity
Kim, Do-Hyun,Lee, Minwoo,Ye, Bora,Jang, Ho-Kyun,Kim, Gyu Tae,Lee, Dong-Jin,Kim, Eok-Soo,Kim, Hong Dae Elsevier 2017 APPLIED SURFACE SCIENCE - Vol.402 No.-
<P><B>Abstract</B></P> <P>Hexagonal boron nitride (h-BN) is a ceramic compound which is thermally stable up to 1000°C in air. Due to this, it is a very challenging task to etch h-BN under air atmosphere at low temperature. In this study, we report that h-BN flakes can be easily etched by oxidation at 350°C under air atmosphere in the presence of transition metal (TM) oxide. After selecting Co, Cu, and Zn elements as TM precursors, we simply oxidized h-BN sheets impregnated with the TM precursors at 350°C in air. As a result, microscopic analysis revealed that an etched structure was created on the surface of h-BN flakes regardless of catalyst type. And, X-ray diffraction patterns indicated that the air oxidation led to the formation of Co<SUB>3</SUB>O<SUB>4</SUB>, CuO, and ZnO from each precursor. Thermogravimetric analysis showed a gradual weight loss in the temperature range where the weight of h-BN flakes increased by air oxidation. As a result of etching, pore volume and pore area of h-BN flakes were increased after catalytic oxidation in all cases. In addition, the surface of h-BN flakes became highly active when the h-BN samples were etched by Co<SUB>3</SUB>O<SUB>4</SUB> and CuO catalysts. Based on these results, we report that h-BN flakes can be easily oxidized in the presence of a catalyst, resulting in an etched structure in the layered structure.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Hexagonal boron nitride flakes are etched at low temperature in air by catalysts. </LI> <LI> The presence of transition metal oxides produces an etched structure in the flakes. </LI> <LI> Etched surfaces become highly active due to vacancy defects formed in the flakes. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Cha, Jae-Eun,Lee, Tae-Ho,Eoh, Jae-Hyuk,Seong, Sung-Hwan,Kim, Seong-O,Kim, Dong-Eok,Kim, Moo-Hwan,Kim, Tae-Woo,Suh, Kyun-Yul Korean Nuclear Society 2009 Nuclear Engineering and Technology Vol.41 No.8
Systematic research has been conducted by KAERI to develop a supercritical carbon dioxide Brayton cycle energy conversion system coupled with a sodium cooled fast reactor. For the development of the supercritical $CO_2$ Brayton cycle ECS, KAERI researched four major fields, separately. For the system development, computer codes were developed to design and analyze the supercritical $CO_2$ Brayton cycle ECS coupled with the KALIMER-600. Computer codes were developed to design and analyze the performance of the major components such as the turbomachinery and the high compactness PCHE heat exchanger. Three dimensional flow analysis was conducted to evaluate their performance. A new configuration for a PCHE heat exchanger was developed by using flow analysis, which showed a very small pressure loss compared with a previous PCHE while maintaining its heat transfer rate. Transient characteristics for the supercritical $CO_2$ Brayton cycle coupled with KALIMER-600 were also analyzed using the developed computer codes. A Na-$CO_2$ pressure boundary failure accident was analyzed with a computer code that included a developed model for the Na-$CO_2$ chemical reaction phenomena. The MMS-LMR code was developed to analyze the system transient and control logic. On the basis of the code, the system behavior was analyzed when a turbine load was changed. This paper contains the current research overview of the supercritical $CO_2$ Brayton cycle coupled to the KALIMER-600 as an alternative energy conversion system.