Improvement of adhesion properties of glass prepared using SiC‑deposited graphite mold via low‑temperature chemical vapor deposition

Kyoung‑Ho Kim,Kuk‑Jin Hwang,Heesoo Lee,Seong‑Min Jeong,이명현,배시영 한국세라믹학회 2020 한국세라믹학회지 Vol.57 No.1

Compression glass molding is a promising technique for mass production of near net-shaped, high-precision, and low-cost optical glass elements. However, the glass molding process causes the damage of glass and the mold during demolding because of the chemical or physical adhesion of the glass to the mold. To overcome this limitation, graphite molds are used owing to their good lubrication and easy machining. However, graphite materials show rapid oxidation at high temperatures in the presence of oxygen. Therefore, in this study, a thin SiC coating layer was deposited on the graphite mold using the chemical vapor deposition (CVD) method to utilize the lubrication properties of graphite and the anti-oxidation properties of SiC. The specimen obtained using the low-temperature CVD method showed high carbon content and good lubrication properties than that obtained using the high-temperature CVD method.

Sulforaphane protects against acetaminophen-induced hepatotoxicity

Noh, Jung-Ran,Kim, Yong-Hoon,Hwang, Jung Hwan,Choi, Dong-Hee,Kim, Kyoung-Shim,Oh, Won-Keun,Lee, Chul-Ho Elsevier 2015 Food and chemical toxicology Vol.80 No.-

<P><B>Abstract</B></P> <P>Oxidative stress is closely associated with acetaminophen (APAP)-induced toxicity. Heme oxygenase-1 (HO-1), an antioxidant defense enzyme, has been shown to protect against oxidant-induced tissue injury. This study investigated whether sulforaphane (SFN), as a HO-1 inducer, plays a protective role against APAP hepatotoxicity <I>in vitro</I> and <I>in vivo</I>. Pretreatment of primary hepatocyte with SFN induced nuclear factor E2-factor related factor (Nrf2) target gene expression, especially HO-1 mRNA and protein expression, and suppressed APAP-induced glutathione (GSH) depletion and lipid peroxidation, which eventually leads to hepatocyte cell death. A comparable effect was observed in mice treated with APAP. Mice were treated with 300 mg/kg APAP 30 min after SFN (5 mg/kg) administration and were then sacrificed after 6 h. APAP alone caused severe liver injuries as characterized by increased plasma AST and ALT levels, GSH depletion, apoptosis, and 4-hydroxynonenal (4-HNE) formations. This APAP-induced liver damage was significantly attenuated by pretreatment with SFN. Furthermore, while hepatic reactive oxygen species (ROS) levels were increased by APAP exposure, pretreatment with SFN completely blocked ROS formation. These results suggest that SFN plays a protective role against APAP-mediated hepatotoxicity through antioxidant effects mediated by HO-1 induction. SFN has preventive action in oxidative stress-mediated liver injury.</P> <P><B>Highlights</B></P> <P> <UL> <LI> SFN pretreatment increases the cell viability against APAP-induced toxicity. </LI> <LI> SFN pretreatment protects depletion of cellular GSH after APAP treatment. </LI> <LI> SFN pretreatment enhances Nrf2 target gene expression, especially HO-1 after APAP treatment. </LI> <LI> SFN has protective effect against APAP overdose-induced liver injury <I>in vivo</I> model as well. </LI> </UL> </P>

국가정보보호수준 측정 및 활용에 관한 연구

황철중,주용완,민경식,정경호 한국정보사회진흥원 2006 정보화정책 Vol.13 No.3

정보보호 수준을 측정하는 것은 매우 어려운 일로써 정보보호의 영역이 계속 확장됨에 따라 개념자체를 정의하기가 어렵고 아울러 다차원적인 요인을 포함하는 정보보호 지표 선정의 어려움, 시계열적인 통계 데이터 부족, 상이한 정보보호 지표를 하나의 지수로 통합하는 문제가 있기 때문이다. 그럼에도 불구하고 정보보호수준을 계량적으로 측정하기 위한 방법론으로 가장 적합한 것은 지수화하는 것이다. 이는 정책입안자나 정보보호 이해관련자들이 종합적인 측면에서 정보보호수준 목표를 결정하고 실행결과를 평가하는데 용이하기 때문이다. 본 연구의 목적은 정보보호정책 수립 및 평가의 기초 자료로 활용할 수 있는 지수를 산출하기 위한 종합적인 정보보호수준 평가지수 모델을 제시하고 지수를 산출하는데 있다. 지수산출결과, 정보보호수준은 2002년부터 2005년까지를 시계열적으로 보면 매년 평균 5.8%의 증가추세를 보이고 있다. 반면 역기능수준은 2003년 1.25 인터넷 대란으로 증가한 것을 제외하고 꾸준한 감소추세를 나타내고 있다. 특히 정보보호수준과 역기능수준이 발산하고 있어 정보보호정책이 유효하게 작용하고 있다고 판단되어진다.

신경망 모형을 이용한 무심천 수위 예측

황현경, 김경호 충북대학교 건설기술연구소 2008 충북대학교 건설기술연구소 논문집 Vol.27 No.1

Casualties and loss of property are experienced year after year in Korea because of localized heavy rain in summer. Therefore, appropriate administration of water resources is required and it is needed to predict the water level using the rainfall and runoff effectively in th river. In this study, neural network model is used to overcome the uncertain model parameters in rainfall-runoff model. The first step is to calculate the accumulative rainfall, effective rainfall, discharge and so forth, on the basis of rainfall data in the basin. In order to test and the verify the water level, eleven rainfall events observed in the river basin are used, of which nine events are used for the test data and two events are used for the verification. Using the Levenverg-Maquart method, the water levels in Mushim stream are estimated. The predicted values of the water level is calibrated by the HEC-RAS model. The results show that the water levels obtained by hourly rainfall are more effective than those obtained by accumulative rainfall or effective rainfall. And the results show that water levels obtained by rainfall and the former time's water level as input layer are more accurate than those obtained by the former time's discharge as input layer.

항공기 노즈 랜딩기어의 쉬미 해석

황재혁,김두만,남창호,임경호 한국항공대학교 1993 論文集 Vol.31 No.-

본 연구를 통하여 항공기 노즈 랜딩기어의 동안정성을 지배하는 운동방정식을 유도하고, 이를 수치적으로 해석하는 프로그램을 개발하였다. 개발된 프로그램은 어떠한 초기조건 및 파라메타의 변화가 착륙장치의 동안정성에 미치는 영향을 해석하는데 매우 유용한다. 노즈 랜딩기어의 운동 방정식을 해석한 결과, 동적 불안정을 유발시키는 중요한 파라메타를 결정하였고, 이 파라메타들을 적적히 조절하면 지배장정식은 안정된 해를 갖게 된다. 그 중 대표적인 파라메타는 K?,K₃,C이다. 해의 두번째 특징으로 발산하지 않는 해 가운데서 쉬미(shimmy)현상을 나타내는 해가 있다. 쉬미현상은 비선형 시스템에서 나타나는 리미트사이클로서 고정된 진폭과 주파수를 갖고 진동하는 해를 뜻한다. 이러한 쉬미현상을 해석한 결과, 조향계통의 프리플레이(free play)가 쉬미 발생에 결정적인 원인이 됨을 확인 하였다. In this study, the equations of motion of an nose landing gear system for shimmy analysis has been derived and then the equations have been solved by numerical method. The developed program in this study is useful to evaluate the effect of the initial conditions and parameters of the nose landing gear on the its dynamic stability. It has been found that the parameters such as K?K₃,C? play the most prominent role on the dynamic stability of the nose landing gear. Shimmy is a kind of limit cycle which can be occurred in the nonlinear dynamic systems. Shimmy has been analyzed numerically in this paper. It turns out that the free play in the steering system is the most important factor to generate shimmy.

마이크로 컴퓨터에 의한 심전도 데이타 압축 알고리즘의 개선

이명호,이경중,황선철,정혁구 연세대학교 대학원 1988 延世論叢 Vol.24 No.-

This paper represents an improved ECG data reduction algorithm which is very useful for real time ECG analysis based-on microcomputer. In order to increase data reduction rate of Turning Point(TP), existing real time data reduction algorithm. The results obtained from the improved Modified Turning point(MTP) data reduction algorithm applied to three different pattern ECG signals. (1) The average data reduction rate of MTP algorithm is 67%, which is increased by 17% than that of TP algorithm. (2) The average percent rms difference(APRD) which is a normalized value that indicates the error between two signals is 9.4% for TP algorithm, while the APRD of MTP algorithm is 6.2% for MTP algorithm. It means that the PRD can be improved by 3.19. Therefore, it gives more excellent resolution than that of TP algorithm.

STI571 (Glivec^(�))에 의하여 빠른 치료 반응을 보인 불응성 Gastrointestinal stromal tumor

윤경원,이제중,김여경,황호인,이병환,조상희,정익주,김형준 全南大醫大 2001 전남의대학술지 Vol.37 No.4

Gas Chromatography를 이용한 Methoxime tert.-butyldimethylsilyl 유도체로서 α-Keto Acids의 분석에 관한 연구

金京禮,金正浩,金正漢,吳昌桓,黃恩卿 성균관대학교 약학연구소 1991 成均藥硏論文集 Vol.3 No.1

Abstract-Thirteen α-keto acids which are biochemically important were converted to methoxime(MO) derivatives with MOX and then to tert.-butyldimethylsilyl(TBDMS) derivatives using MTBS-TFA in isooctance prior to dual capillary column GC analysis. Single symmetric peaks were obtained for each MO TBDMS α-keto acids on the dual chromatograms. Optimum methoximation required heating at 60℃ for 2 hours and TBDMS derivatization required heating for 30 minutes. MO α-keto acids were stable during the tert.-butyldimethylsilylation and the methoximation of carbonyl group prevented silylation of enols. Mass spectrometric analysis of MO TBDMS derivatives was performed for structure identification. Base peaks at [M-57], intense ions at m/z=89, and weak ions at [M-15] were present in all spectra. The ions at m/z=89 were characteristic for α-keto acids.

치과 재료용 NiTi 합금의 특성에 대한 Ag 첨가의 영향

오근택,박기호,심형민,황충주,김경남 大韓齒科器材學會 2001 대한치과재료학회지 Vol.28 No.4

Equiatomic and near-equiatomic nickel-titanium alloys have shape memory effect and superelasticity. However nickel-titanium alloys are extremely sensitive to the precise nickel-titanium ratio and alloying additions. There are many reports on the alloying additions such as Fe, Al, Cr, Co, V, Pt, Pd, Zr, Hf, Nb and Cu. The purpose of this study was to investigate the effect of silver addition to nickel-titanium alloy for dental and medical application.Arc melting process was used to fabricate nickel-titanium alloys. The casts were heat-treated in a vacuum furnace at 950℃ for 72 hours to homogenize their composition. Subsequently, they were hot-rolled at 950℃ to obtain the plate samples and annealed in a vacuum furnace at 950℃. To investigate the properties of nickel-titanium alloys, phases, transformation temperature, compositions, corrosion resistance and hardness were evaluated using X-ray diffractometer, differential scanning calorimeter, energy dispersive spectroscopy or atomic absorption spectroscopy, potentiostat and micro-vickers hardness tester, respectively. NiTiAg alloys showed the low silver recovery rate for the cast due to its low evaporation temperature, and showed low silver solubility to NiTi alloy. Silver addition to NiTi alloy increased transition temperature range (TTR) above 100℃ and stabilized martensitic phase(monoclinic structure) at room temperature because Ms temperature was above room temperature. Martensitic and austenitic phase existed in x-ray diffraction pattern of solution annealed NiTiAg alloys. The Silver addition is considered to improve corrosion resistance and change largely the mechanical properties depending upon the amount of alloying addition and types of addition elements.

항공기 착륙장치의 충격흡수특성해석

김두만,임경호,황재혁,이환규 한국항공대학교 1992 論文集 Vol.30 No.-

본 연구를 통하여 항공기 착륙장치의 거동(동특성 및 완충기 효율)을 해석하고 평가하는 Software를 개발하엿다. 이 프로그램을 개발하기 위해 착륙장치를 2개의 자유도를 가지는 동역학시스템으로 모델링하고 운동방정식을 유도하였다. 또한 완충기에 작용하는 내력(즉 공기력, orifice force, friction force)을 표현하는 관계식을 정립하였으며, 타이어의 힘을 표현하는 관계식을 유도하였다. 그리고 운동방정식에는 타이어의 Spin Up운동도 고려되었다. 선정된 항공기의 착륙장치의 Parameter의 값을 프로그램의 입력 Data로 사용했을 때 매우 신뢰할 만한 동특성의 결과를 얻었으며, 특히 Drop Test 결과와 본 연구에서 개발된 Software에서 얻어진 결과를 비교했을 때 매우 흡사한 결과를 얻었다. 따라서 본 연구에서 개발된 Software는 앞으로 국산화되는 착륙장치의 개발 및 설계에 매우 유용하게 사용될 것으로 판단된다. 또한 본 연구에서 사용된 입력 Data중 중요한 10개의 Parameter를 선정하여, 각 Parsmeter를 변화시키면서 착륙장치의 동특성 및 효율의 변화를 고찰해 보았다. 완충기 설계시 가장 중요한 Parameter들은 K-factor, Orifice 단면적 등과 같은 완충기의 변수로 사료되며, 타이어의 변수 T??이나 b는 중요한 변수가 아님을 확인하였다. 또한 항공기의 무게 W, Wheel/Tire의 무게, 완충기의 초기 공기압 P??, 항공역학계수 A도 착륙장치의 효율에는 크게 영향을 미치지 않고 있음을 고찰하였다. 그러나 공기실의 Politropic 지수 n, 항공기의 수직착륙속도 V는 착륙장치의 효융에 Non-Monotonic하게 영향을 미치는 것을 고찰하였다. The software which analysis and evaluate the dynamic characteristics of an landing gear has been developed in this study. The landing gear system has been modelled to be 2 DOF dynamic system to drive the equation of motion. The three internal forces, which are air pressure force, orifice force, and friction force, has been formulated and also the tire force has been formulated and also the tire force has been derived. When the typical values of the design parameters is applied to the developed software, the reliable results of the dynamic characteristics are obtained. Furthermore there is a good agreement between the simulation results and experimental drop test extracted from relevant literatures. It can be concluded that the developed software will be useful for the design and development of a landing gear system inside Korea.