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김교한,허만수,김형일,황운석,高田 雄京,奧野 攻 대한치과기재학회 1999 대한치과재료학회지 Vol.26 No.4
One of the fields in which titanium(Ti) is becoming increasingly valuable is the field of biomaterials. Ti had shown its good corrosion resistance, high strength to weight ratio, and compatibility with human tissues. Such applications of Ti in this area involve replacing stainless steel and cobalt-chromium alloy implant which are used in skull, shoulder joint, spine, and dental implant. In dental field, titanium has been used as dental implant, so it becomes necessary to examine and estimate the anti-corrosion ability of Ti and its alloys at the severe conditions such as crevice corrosion and galvanic corrosion. The purposes of this study was to examine the corrosion mechanisms of the pure Ti showing good corrosion resistance under an oral corrosion environment when it is coupled with dental casting Type Ⅱ and Type Ⅳ gold alloys. These coupling corrosion mechanisms were studied in three conditions. First was by measuring the resting potential of pure Ti, when it was uncoupled and coupled with Type Ⅱ and Type Ⅳ alloys. Second was by measuring anode polarization behavior of pure Ti, Type Ⅱ and Type Ⅳ alloys, and third was by detecting dissolved ions from the pure Ti, uncoupled and coupled with Type Ⅱ and Type Ⅳ gold alloys which were immersed in 0.9% NaCl solution for 7 days. The resting potential showed a low potential value at the initial stage but increasing into a high value (to 0.18 V) with time elapse and reached a stable value. On the contrary, the potentials of Type Ⅱ and Type Ⅳ gold alloys were in their values at the initial stage of immersion, then decreased with the time and reached stable values, being higher than the value of pure Ti. When pure Ti coupled with Type Ⅱ and Type Ⅳ gold alloys, the resting potential of coupled one was between the values of each one. When Type Ⅱ and Type Ⅳ gold alloys were coupled with pure Ti, there was an increase in Ag, Cu, and Zn. Also, Zn ions released the high potential precious metal alloys, compared to the uncoupled case. Ti ion was not detected at any cases of pure Ti or coupled with gold alloys. It was thought that one of the causes of the increase in Ag, Zn, and Cu ions when Ti was coupled with dental gold alloys was that Ag, Zn, and Cu ions were selectively dissoluted from the Ag rich regions around grain boundary and the casting defects. In conclusions, the results of this study suggest that the pure Ti was very stable when coupled with the gold alloys in oral cavity.
Galvanic Coupling Effect on Corrosion Behavior of Al Alloy-Matrix Composites
Hwang, Woon Suk,Kim, Hyoun Woo 대한금속재료학회 2002 METALS AND MATERIALS International Vol.8 No.6
Galvanic coupling effect on the corrosion of SiC-reinforced aluminum alloy-matrix composites was investigated in a sodium chloride solution. The potentiodynamic polarization measurement indicated that pitting potentials of metal matrix composites (MMCs) and AA2124 matrix alloy were similar, and pitting potential of MMCs was almost same as corrosion potential, while pitting susceptibility of MMCs was higher than that of AA2124 alloy. Galvanic current by formation of galvanic couple between SiCw and matrix reveals very low value because of large cathodic polarization of SiC. However, by increasing potential of matrix to pitting potential by this galvanic couple and thus, forming pits easily at the weak passive film near SiC reinforcing phase preferentially, it is concluded that pitting susceptibility of MMCs increases highly than AA2124 alloy of matrix composition.
Hwang, Geon-Tae,Palneedi, Haribabu,Jung, Byung Mun,Kwon, Suk Jin,Peddigari, Mahesh,Min, Yuho,Kim, Jong-Woo,Ahn, Cheol-Woo,Choi, Jong-Jin,Hahn, Byung-Dong,Choi, Joon-Hwan,Yoon, Woon-Ha,Park, Dong-Soo,L American Chemical Society 2018 ACS APPLIED MATERIALS & INTERFACES Vol.10 No.38
<P>We report the effect of epoxy adhesion layers with different mechanical or physical property on a magnetoelectric (ME) composite laminate composed of FeBSi alloy (Metglas)/single-crystal Pb(Mg<SUB>1/3</SUB>Nb<SUB>2/3</SUB>)O<SUB>3</SUB>-Pb(Zr,Ti)O<SUB>3</SUB>/Metglas to achieve an improved ME conversion performance. Through theoretical simulation, it was revealed that the Young’s modulus and the thickness of interfacial adhesives were major parameters that influence the conversion efficiency in ME composites. In the experimental evaluation, we utilized three epoxy materials with a distinct Young’s modulus and adjusted the average thickness of the adhesion layers to optimize the ME conversion. The experimental results show that a thin epoxy layer with a high Young’s modulus provided the best performance in the inorganic-based ME conversion process. By tailoring the interfacial adhesion property, the ME laminate generated a high conversion coefficient of 328.8 V/(cm Oe), with a mechanical quality factor of 132.0 at the resonance mode. Moreover, we demonstrated a highly sensitive alternating current magnetic field sensor that had a detection resolution below 10 pT. The optimization of the epoxy layers in the ME laminate composite provided significant enhancement of the ME response in a simple manner.</P> [FIG OMISSION]</BR>
Hwang, Jung-Suk,Chung, Hye-Kyung,Bae, Eun-Kyong,Lee, Ah-Young,Ji, Hee-Jung,Park, Dong-Woon,Jung, Hwa-Jin,Cho, Chung-Won,Choi, Hyun-Ju,Lee, Dong-Seok,Lee, Kang-Ro,Youn, Hyun-Joo The Pharmaceutical Society of Korea 2003 Archives of Pharmacal Research Vol.26 No.4
A polysaccharide fraction, AIP1, purified from Artemisia iwayomogi was shown to have immunomodulating and anti-tumor activities in mice. In order to determine how the AIP1 fraction exhibits the immunomodulating activity, the effect of the fraction on the apoptosis of mouse spleen cells was investigated. Treatment of the mouse spleen cells with the AIP1 fraction resulted ,in the suppression of apoptotic death and an extension of cell survival in culture, indicating that the fraction might modulate the death of spleen cells. Treatment of the mice with the AIP1 fraction in vivo also resulted in less apoptosis of the spleen cells, which indicates the physiological relevance of the anti-apoptosis effect of the fraction in vitro. A mouse gene array was used to determine the profile of the gene expression change showing a pattern of up- and down-regulated genes by the AIP1 treatment. This study provides preliminary information regarding the immunomodulatory mechanism of the AIP1 fraction.
Unconstrained Sleep Apnea Monitoring Using Polyvinylidene Fluoride Film-Based Sensor
Hwang, Su Hwan,Lee, Hong Ji,Yoon, Hee Nam,Jung, Da Woon,Lee, Yu-Jin G.,Lee, Yu Jin,Jeong, Do-Un,Park, Kwang Suk IEEE 2014 IEEE Transactions on Biomedical Engineering Vol.61 No.7
<P>We established and tested an unconstrained sleep apnea monitoring method using a polyvinylidene (PVDF) film-based sensor for continuous and accurate monitoring of apneic events occurred during sleep. Twenty-six sleep apnea patients and six normal subjects participated in this study. Subjects' respiratory signals were measured using the PVDF-based sensor during polysomnography. The PVDF sensor comprised a 4 × 1 array, and a thin silicon pad was placed over the sensor to prevent damage. Total thickness of the merged system was approximately 1.1 mm which was thin enough to prevent the subject from being consciously aware of its presence. It was designed to be placed under subjects' backs and installed between a bed cover and mattress. The proposed method was based on the standard deviation of the PVDF signals, and it was applied to a test set for detecting apneic events. The method's performance was assessed by comparing the results with a sleep physician's manual scoring. The correlation coefficient for the apnea-hypopnea index (AHI) values between the methods was 0.94 (p <; 0.001). The areas under the receiver operating curves at three AHI threshold levels (>5, >15, and >20) for sleep apnea diagnosis were 0.98, 0.99, and 0.98, respectively. For min-by-min apnea detection, the method classified sleep apnea with an average sensitivity of 72.9%, specificity of 90.6%, accuracy of 85.5%, and kappa statistic of 0.60. The developed system and method can be applied to sleep apnea detection in home or ambulatory monitoring.</P>
Jeong Suk Kim,Jin Hyo Park,Kyung Kyoon Kim,Duck Kun Hwang,Woon-Yong Choi,안성훈,Myung-Chang Kang 대한기계학회 2007 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.21 No.10
This study is to investigate the nitrogen ion implantation process in PC (Polycarbonate) composite for improving surface electrical conductivity. The suggested process is applied for the thin wall shape polymer which is composed of low carbon black and carbon fiber in order to increase electric conductivity. The acceleration voltage which is relatively low 3~50 keV in ion implantation process is used to obtain the thin conductive surface layer around 2 micrometer. The surface electrical conductivity of PC composite is realized up to below 106 Ω/cm2 by controlling ion dose without degrading mechanical properties. This technology can be adopted to make conductive plastic product which is applicable for static electricity prevention and electromagnetic wave masking. In order to evaluate the effect of surface modification of PC by nitrogen ion implantation, its surface resistance, tensile strength, tensile elongation, and half-life have been measured. The properties of PC/CF and PC/CB increased surface resistance and tensile strength. Also, the properties of PC/CF and PC/CB significantly decreased tensile elongation and half-life.