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Ryu, K.,Chae, J.-S.,Lee, E.,Parrot, M. Elsevier Science Ltd ; Pergamon 2014 Journal of Atmospheric and Solar-Terrestrial Physi Vol.121 No.1
While investigating possible precursory signatures of large earthquakes in the ionospheric data measured by the DEMETER and CHAMP satellites, we found ionospheric disturbances related to large earthquakes (M=7.2 and 7.4) that occurred on September 2004 near the south coast of Honshu, Japan. The satellite data were statistically compared with an empirical model and local averages of the large set of data in the study period. A fluctuation in the electron density above the epicenter was observed roughly 2weeks before the main earthquakes. Surveys of the space weather and geomagnetic activities suggest that these fluctuations were not caused by changes in space conditions or by a geomagnetic storm. The features were also distinct from well-known natural ionospheric anomalies. In addition, a peak-like profile in the ion temperature and lowered O<SUP>+</SUP> density around the region of the epicenter was observed a week before the main earthquakes along the satellite passes whose longitudes are close to the epicenter. The features are more apparent when they are compared with the data more distant from the epicenter, suggesting that the disturbances occur along the geomagnetic field lines. The concurrent measurements of the ion drift velocity suggest the fluctuations were triggered by the vertical plasma drift. The observed anomalies disappeared ~2 weeks after the quakes. According to the current theories on the seismo-ionospheric coupling, the horizontal electric field at the lower boundary of the ionosphere should have been strengthened by the seismic activity in order for the ionospheric plasma movements above the epicenter and its geomagnetic conjugate regions to trigger the observed ionospheric anomalies.
Dynamic restructuring process for self-reconfiguration in the fractal manufacturing system
Ryu, K.,Yü,cesan, E.,Jung, M. Taylor Francis 2006 INTERNATIONAL JOURNAL OF PRODUCTION RESEARCH - Vol.44 No.15
<P>To meet the rapidly changing customer needs in the manufacturing environment, future manufacturing systems must be dynamically and flexibly reconfigured. The fractal manufacturing system (FrMS) is one of the new manufacturing paradigms that can meet such requirements. The basic component of the FrMS is referred to as a fractal. Consisting of self-similar agents, each fractal autonomously cooperates and negotiates with others to coordinate its tasks. Dynamic restructuring process (DRP) supports reorganization of the system configurations so that the FrMS can be adapted to dynamically changing environments. Although traditional approaches have endeavoured to demonstrate reconfigurability of a manufacturing system, they are not accurate enough to meet the requirements of circumstances such as high-level autonomy in reconfiguring the system architecture. In this paper, therefore, the DRP, which embodies self-reconfigurability of a system, is proposed focusing on the FrMS. To check the effectiveness of the DRP, we have developed the FrMS test bed and conducted the experimentation on the DRP. A simulation study has been conducted to show the effectiveness of the DRP under an illustrative situation.</P>
Ryu, K.,Hwang, S.Y.,Kim, K.H.,Kang, J.H.,Lee, E.K. Elsevier Science Publishers 2008 Journal of biotechnology Vol.133 No.1
One of the major problems of wild-type lignin peroxidase (LiP) is its inactivity at the presence of excess H<SUB>2</SUB>O<SUB>2</SUB> and high concentration of aromatic compounds. Little is known about the substrate-binding site of LiP, and functionality improvement of LiP was not actively tried by genetic engineering and directed evolution. In order to improve LiPs functionality, we performed directed evolution with a colorimetric screening method. Finally, three types of LiP mutants were screened. The catalytic efficiency of the variants toward 2,4-dichlorophenol (DCP) degradation activity and the stability against H<SUB>2</SUB>O<SUB>2</SUB> was increased over the wild type. The K<SUB>m</SUB> value of the variants toward H<SUB>2</SUB>O<SUB>2</SUB> was increased, but K<SUB>m</SUB> value toward 2,4-DCP degradation was reduced. Overall, The K<SUB>cat</SUB>/K<SUB>m</SUB> values of the mutants toward 2,4-DCP was increased ca. 4-fold, and that toward H<SUB>2</SUB>O<SUB>2</SUB> was increased ca. 89-fold. Amino acid sequence analysis indicated that the most of the mutations were located on the enzyme surface. We expect that these results coupled with recombining mutation can be successfully applied to the molecular evolution cycles for screening of LiPs and other oxidative enzymes with improved functionality and stability.
Electrical Property and Surface Morphology of Silver Nanoparticles After Thermal Sintering
Ryu, K.,Moon, Y. J.,Park, K.,Hwang, J. Y.,Moon, S. J. Springer Science + Business Media 2016 Journal of electronic materials Vol.45 No.1
<P>In this study, the sintering behavior of silver (Ag) nanoparticle inks was investigated when different particle sizes and sintering methods were employed. Ag nanoparticle inks with two different particle sizes were investigated with average particle diameters of 12 nm and 50 nm. The two kinds of Ag nanoparticle inks were inkjet-printed onto glass substrates. The printed inks were sintered by a furnace and a continuous wave (CW) laser at a wavelength of 532 nm. The specific resistance and surface morphology of the Ag nanoparticle (Ag NP) inks were investigated under various furnace temperatures, laser intensities, and time durations. The ex situ specific resistance of each Ag NP ink was measured by a multimeter to determine the effects of various sintering conditions such as the furnace temperature, laser intensity, and sintering duration. To investigate the correlation between the specific resistance and surface morphology of the Ag NP inks, field emission scanning electron microscopy images were obtained. In addition, the effect of the particle size on the specific resistances of the inks annealed by the furnace and CW laser was evaluated.</P>
Study of degradation in bulk lifetime of n-type silicon wafer due to oxidation of boron-rich layer
Ryu, K.,Choi, C.J.,Rohatgi, A.,Ok, Y.W. Elsevier 2016 CURRENT APPLIED PHYSICS Vol.16 No.5
<P>Various boron (B) diffusion techniques are being investigated to fabricate n-type Si solar cells. Thermal oxidation is often used to remove boron-rich layer (BRL) formed as a byproduct of B diffusion because BRL interferes with surface passivation of boron emitter. However, oxidizing the BRL can cause significant degradation in bulk lifetime. In this paper, high resolution electron microscopy (HREM) was performed to detect the presence of BRL after B diffusion and its removal after subsequent oxidation. In addition, bulk lifetime of n-type Si with BRL was measured after various oxidation conditions to systematically investigate the mechanism of oxidation-induced lifetime degradation in n-type Si. Detailed analysis of the oxidized samples revealed that iron (Fe) is primary metal impurity responsible for the bulk lifetime degradation after oxidation. This happens because Fe is gettered in BRL after B diffusion and during the oxidation, when the BRL is consumed, Fe is released into the bulk to degrade lifetime. (C) 2016 Elsevier B.V. All rights reserved.</P>