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Purification and Characterization of Cyclodextrin Glucanotransferase from Paenibacillus sp. JK - 12
Yong Kang,Sung-Koo Kim,Hong-Ki Jun 한국식품영양과학회 2002 Preventive Nutrition and Food Science Vol.7 No.3
Extracellular cyclodextrin glucanotransferase (CGTase) from Paenibacillus sp. JK-12 was purified through several purification steps consisting of ammonium sulfate precipitation and chromatographies on DEAE-sephadex A-50 and Mono QIM HR5/5. The purified CGTase exhibited a single band on SDS-PAGE and was estimated to be approximately 82 kDa. The isoelectric point of the enzyme was 7.2 as determined by isoelectric focusing. The CGTase from Paenibacillus sp. JK-12 had a transglucosylation activity at the C-2 position of L-ascorbic acid. The optimum pH and temperature for the CGTase activity were 8.0 and 50oC, respectively. The enzyme activity was stable from pH 6.0 to 9.0 and at temperatures up to 55℃ at pH 8.0, having 80% residual activity. The activity of the CGTase was strongly resistant to metals such as Ag^+ and Ba^(2+) but slightly inhibited by Hg^+, Ni^(2+) and Mg^(2+). The enzymeproducedα-cyclodextrin (α-CD) and β-CD as the main products from starch, but not γ-CD.
Influence of cerium and cesium promoters on vanadium catalyst for sulfur dioxide oxidation
Yong Kang,Xin Wang,Jie Li,Dan Li 한국화학공학회 2019 Korean Journal of Chemical Engineering Vol.36 No.5
We studied the catalytic performance of vanadium catalyst promoted with cerium and cesium for sulfur dioxide oxidation. The catalyst samples were characterized by FT-IR, Raman, XRD, SEM, BET and XPS. The results showed that the properties of the catalyst promoted with 4 wt% CeO2 and 7 wt% Cs2SO4 were superior to the commercial V2O5-K2SO4/SiO2 and V2O5-K2SO4-Cs2SO4/SiO2 catalysts, in terms of low temperature activity, thermal stability, SO2 oxidation efficiency and ignition temperature. The FT-IR, Raman, XRD and XPS results evidenced the formation of V2O5-Cs2S2O7 pyrosulfate, CeVO4 and CeO2 crystalline phase in V2O5-K2SO4-Cs2SO4-CeO2/SiO2 catalyst. These crystalline phases play an important role in redox reaction at low temperature and can increase the available oxygen for the redox reaction. The characterization results also showed that cerium can promote the formation of pyrosulfate, increase the proportion of large macropores, and improve stability of VV at high temperature. Due to its excellent lowtemperature and high-temperature activity, the V2O5-K2SO4-Cs2SO4-CeO2 /SiO2 catalyst appears to be more efficient for the conversion of SO2 in a larger concentration range.
Temperature Dependence of Exchange Coupling on Magnetic Tunnel Junctions
Yongkang Hu,CheolGi Kim,Tomasz Stobiecki,Chong-Oh Kim,Kimin Hong 한국자기학회 2003 Journal of Magnetics Vol.8 No.1
Magnetic Tunnel Junctions (MTJs) were fabricated on thermally oxidized Si (100) wafers using DC magnetron sputtering. The film structures were Ta(50 Å)/Cu(100 Å)/Ta(50 Å)/Ni_(80)Fe_(20)(20 Å)/Cu(50 Å)/Mn_(75)Ir_(25)(100 Å)/Co_(70)Fe_(30)(25 Å)/Al-O(15 Å)/Co_(70)Fe_(30)(25 Å)/Ni_(80)Fe_(20)(t)/Ta(50 Å), with t = 0 Å, 100 and 1000 Å, respectively. X-ray diffraction has shown improvement of (111) texture of IrMn₃ and Cu by annealing. The exchange-biased energy is almost inversely proportional to temperature. The difference between the coercivity Hc and the exchange biased field H_E for t = 0 Å sample is smaller than that for t = 1000 Å. For the pinned layer, the decreasing rate of the coercivity with the temperature is higher compared to that of the exchange field, but variation of Hc is similar to that of the exchange field for free layer.
Synthesis of gold nanofluids using a Solution Plasma
YongKang Heo,SangYul Lee,JongHo Oh 한국표면공학회 2010 한국표면공학회 학술발표회 초록집 Vol.2010 No.5
In this study, gold nanofluids were synthesized with various experimental using Solution Plasma Processing (SPP). The size distribution and the shape of gold nanoparticles in the nanofluids were investigated using transmission electron microscopy (TEM). The dispersion stability of gold nanofluids was characterized using zeta-potential, as well. The results demonstrated that the various experimental have a strong effect on the formation of gold nanoparticles in nanofluids. Possible mechanisms for the formation of nanoparticles in SPP are suggested. The electrons provided from the solution plasma are believed to play a vital role in producing the Au nanoparticles. Also, increased electrical energy from the plasma is responsible not only for increasing the surface areas of the nanoparticles in the solution by making the nanoparticles even smaller in size, but also for facilitating good dispersion stability by charging up the nanoparticles negatively. Preliminary resultsshowed that uniform and very fine nanoparticles in solution could be synthesized successfully using SPP.
Defending and Detecting Audio Adversarial Example using Frame Offsets
( Yongkang Gong ),( Diqun Yan ),( Terui Mao ),( Donghua Wang ),( Rangding Wang ) 한국인터넷정보학회 2021 KSII Transactions on Internet and Information Syst Vol.15 No.4
Machine learning models are vulnerable to adversarial examples generated by adding a deliberately designed perturbation to a benign sample. Particularly, for automatic speech recognition (ASR) system, a benign audio which sounds normal could be decoded as a harmful command due to potential adversarial attacks. In this paper, we focus on the countermeasures against audio adversarial examples. By analyzing the characteristics of ASR systems, we find that frame offsets with silence clip appended at the beginning of an audio can degenerate adversarial perturbations to normal noise. For various scenarios, we exploit frame offsets by different strategies such as defending, detecting and hybrid strategy. Compared with the previous methods, our proposed method can defense audio adversarial example in a simpler, more generic and efficient way. Evaluated on three state-of-the-arts adversarial attacks against different ASR systems respectively, the experimental results demonstrate that the proposed method can effectively improve the robustness of ASR systems.
YongKang Heo,SangYul Lee 한국표면공학회 2010 한국표면공학회 학술발표회 초록집 Vol.2010 No.11
The gold nanoparticles were synthesized with various discharge duration using solution plasma processing (SPP). The effects of the discharge duration between 0 sec. and 900 sec. Analysis of solution plasma were using optical emmision spectrocopy(OES), oscilloscope. on the size and shape of the gold nanoparticles in SPP were investigated using UV-vis nir spectrophotometer and transmission electron microscopy (TEM). Results showed that discharge duration had a strong effect on the formation of the gold nanoparticles. In the UV-vis nir spectrocopy, an absorbance peak at the wavelength approximately 520㎚ was observed, which indicates the formation of gold nanoparticles. As the discharge duration became longer, the average particle size and the size distribution became smaller. Especially for discharge durationof approximately 900 second, the average size of the gold nanoparticles were measured to be the smallest, an average of 23.2±9.0 ㎚ in diameter and most uniform in size. The particle shape became more spherical with an increase in duration time.
Thermal balance performance simulation and optimization of full-ground crane cabins
Yongkang Shi,Zhenlei Chen,Haitao He,Fan Shi,Penyong Liu,Yong Wang 대한기계학회 2021 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.35 No.2
To solve the excessive thermal load problem of the crane engine and engine compartment, a combined 1-D and 3-D thermal simulation method is developed to numerically simulate the heat flow field inside and outside the engine compartment, the engine thermal system and the cooling system. Simultaneously, to ensure the accuracy of the numerical calculation boundary and the feasibility of the combined thermal simulation method, the trailer heat balance test is conducted under the rated conditions and the maximum torque conditions. By reasonably sealing the heat dissipation assembly at the front of the nacelle, bottom guards under the engine are added and other improvement measures are taken. It is found that the engine outlet’s coolant temperature is decreased by 15.9 °C under rated conditions when the improved crane is in the 36 °C environment. While the outlet’s coolant temperature is decreased by 20 °C under maximum torque conditions.