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Cho, J.,Lee, J.,Park, J.,Kim, M.J. Pergamon 2015 Tetrahedron, asymmetry Vol.26 No.15
The kinetic and dynamic kinetic resolution of alkyl aryl carbinols carrying a trimethylsilyl group with a highly active lipase preparation containing lipoprotein lipase, dextrin, and ionic surfactant 1 has been explored. It was found that all the trimethylsilyl-containing substrates were accepted by lipoprotein lipase-dextrin 1 (LPL-D1) with perfect enantioselectivity (E=>200). As a result, the dynamic kinetic resolution of these substrates with LPL-D1 in the presence of a Ru-based racemization catalyst provided single enantiomeric products (>99% ee) with good yields. Furthermore, the dynamic kinetic resolution products were readily desilylated or halodesilylated to yield enantiopure alkyl aryl carbinols. Thus a useful protocol for the highly enantioselective synthesis of alkyl aryl carbinols, particularly those carrying a long alkyl chain (C<SUB>6</SUB>-C<SUB>10</SUB>) has been established.
Cho, J.,Lee, Y. W.,Yeh, P. J.,Han, K. S.,Kanae, S. Springer Science + Business Media 2014 Environmental Earth Sciences Vol.71 No.9
Arid regions in Asia are commonly characterized by rapidly growing populations with limited land resources and varying rainfall frequencies under climatic change. Despite being one of the most important environmental challenges in Asia, the changing aridity in this region, particularly due to large-scale land cover change, has not been well documented. In this study, we used rainfall data and a new land heterogeneity index to identify recent trend in land cover changes in the Asian arid regions. The result indicates a significant decreasing trend of barren lands and an increasing trend of vegetated lands. Although the potential land cover change is commonly believed to be strongly sensitive to rainfall change, such sensitivity has not been observed during the nine-year period (2001-2009) analyzed. Through the analyses of two separate periods (2001-2005 and 2005-2009), the sensitivity of rainfall to land cover change in arid regions is found to be dependent on the initial spatial heterogeneity of vegetated land cover. The approach used and the findings in this study represent an important step toward better understanding of large-scale land cover change in the Asian arid regions, and have the potential to predict future land cover change under various climate change scenarios.
Cho, J.,Oh, H.,Park, J.,Min, K.,Lee, E.,Jyoung, J.Y. Pergamon Press ; Elsevier Science Ltd 2014 International journal of hydrogen energy Vol.39 No.1
Although characteristics of the gas diffusion layer (GDL) affect the performance of a proton exchange membrane fuel cell (PEMFC), mass transfer mechanisms inside the GDL and the performance of the PEMFC have not been directly correlated. To determine the design parameters of the GDL, the effects of substrate design of the GDL on performance of a PEMFC are investigated. By adding an active carbon fiber (ACF), which has a high surface area, the substrate is designed to have a different pore size structure. The results show that steady-state and transient responses are determined by capillary pressure gradient characteristics of the GDL made by pore size distribution of the substrate. The small macro-pore functions as water-retaining passage and the large macro-pore functions as water-removal passage. It is concluded that both small and large macro-pore must be present on the substrate to facilitate its function in a wide range of operating conditions.
Characterization of particle aggregation in a colloidal suspension of magnetite particles
Cho, J.,Koo, S. Korean Society of Industrial and Engineering Chemi 2015 Journal of industrial and engineering chemistry Vol.27 No.-
We investigate relation between hydrodynamic transport properties of a colloidal suspension of magnetite particles and aggregation of the particles. The magnetite particles are of 0.3μm in diameter and are dispersed in Newtonian ethylene glycol. The volume fraction of the particles in the suspension ranges from 0.003 to 0.04. Shear viscosity and average sedimentation velocity of the suspension are measured as a function of the particle volume fraction. To predict the aggregation of the suspended particles particle-scale analysis of sedimentation and viscosity behavior of the suspension is correlated with scaling theories for fractal aggregates. The sedimentation velocity as a function of particle concentration gives the fractal dimension of 1.91 for the magnetite aggregates in the suspension. Shear dependence of the aggregate size which is expressed by a power law is determined from intrinsic viscosity for the aggregates and yield stress of the suspension, respectively. It is found that the shear dependence from intrinsic viscosity is in good agreement with that from yield stress.
Cho, J.,Shin, Y.H.,Hwang, I.S. North-Holland Pub. Co 2015 Nuclear engineering and design Vol.289 No.-
Although current pressurized water reactors (PWRs) have significantly contributed to global energy supply, PWR technology has not been considered a trustworthy energy solution owing to its problems of spent nuclear fuels (SNFs), nuclear safety, and nuclear economy. In order to overcome these problems, a lead-bismuth eutectic (LBE) fully passive cooling small modular reactor (SMR) system is suggested. This technology can not only provide the solution for the problems of SNFs through the transmutation feature of the LBE coolant, but also strengthen safety and economy through the concept of natural circulation cooling SMRs. It is necessary to maximize the advantages, namely safety and economy, of this type of nuclear power plants for broader applications in the future. Accordingly, the objective of this study is to maximize the reactor core power while satisfying the limitations of shipping size, materials endurance, and criticality of a long-burning core as well as safety under beyond design basis events. To achieve these objectives, the design limitations of natural circulating LBE-cooling SMRs are derived. Then, the power maximization method is developed based on obtaining the design limitations. The results of this study are expected to contribute to the effectiveness of the reactor design stage by providing insights to designers, as well as by formulating methods for the power maximization of other types of SMRs.
Cho, J.,Hong, Y.,Lee, J. H.,Kang, Y. Royal Society of Chemistry 2015 Nanoscale Vol.7 No.18
<P>A novel structure denoted a 'hollow nanosphere aggregate' is synthesized by introducing nanoscale Kirkendall diffusion to the spray pyrolysis process. The hollow Fe2O3 nanosphere aggregates with spherical shape and micron size are synthesized as the first target material. A solid iron oxide-carbon composite powder that is prepared by a one-pot spray pyrolysis process is transformed into the hollow Fe2O3 nanosphere aggregates by sequential post-pyrolysis treatments under reducing and oxidizing atmospheres. The nanoscale Kirkendall diffusion plays a key role in the formation of the hollow Fe2O3 nanosphere aggregates with spherical shape and micron size. The unique structure of the hollow Fe2O3 nanosphere aggregates results in their superior electrochemical properties as an anode material for lithium ion batteries by improving the structural stability during cycling. The hollow metal oxide nanosphere aggregates with various compositions for wide applications including energy storage can be prepared by the simple fabrication method introduced in this study.</P>
Power dissipation and area comparison of 512-bit and 1024-bit key AES
Cho, J.,Soekamtoputra, S.,Choi, K.,Moon, J. Pergamon Press ; Elsevier Science Ltd 2013 COMPUTERS & MATHEMATICS WITH APPLICATIONS - Vol.65 No.9
Advanced Encryption Standard (AES) has replaced its predecessor, Double Encryption Standard (DES), as the most widely used encryption algorithm in many security applications. Up to today, AES standard has key size variants of 128, 192, and 256-bit, where longer bit keys provide more secure ciphered text output. In the hardware perspective, bigger key size also means bigger area and power consumption due to more operations that need to be done. Some companies that employ ultra-high security in their systems may look for a key size bigger than 256-bit AES. In this paper, 128 and 256-bit AES hardware, as well as two variants of an AES encryption algorithm for 512-bit and 1024-bit key size, are implemented and compared in terms of power consumption and area. The experiment is done in 45 nm CMOS technology at 1.1 V using a Synopys DC Compiler and Modelsim and total power consumption and area results are presented and graphically compared.