• 대한기계학회논문집A
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• 제26권6호
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• pp.1107-1113
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• 2002

This study presents the hydrogen emblittlement in the metal, which decreases the ductility and then induces the brittle fracture. The contribution deals with the effect of strain rate and notch geometry on hydrogen emblittlement of 1.25Cr-0.5Mo and 2.25Cr-1Mo steels, which are in use at high pressure vessel. Smooth and notched specimens were examined to obtain the elongation and tensile strength. For charging the hydrogen in the metal, the cathodic electrolytic method was used. In this process, current density is maintained constant. The amount of hydrogen penetrated in the specimen was detected by the hydrogen determenator(LECO RH404) with the various charging time. The distribution of hydrogen concentration penetrated in the specimen was obtained by finite element analysis. The amount of hydrogen is high in smooth specimen and tends to concentrate in the vicinity of surface. The elongation and tensile strength decreased with the passage of charging time in 1.25Cr-0.5Mo and 2.25Cr-1Mo steels. The elongation increased and tensile strength decreased as strain rate increased. As a result of this study, it is supposed that 1.25Cr-0.5Mo steel is more sensitive than 2.25Cr-lMo steel in hydrogen embrittlement. Hydrogen embrittlement susceptibility of notched specimen after hydrogen charging is more remarkable than that of smooth specimen.

• International Journal of Industrial Entomology and Biomaterials
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• 제31권1호
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• pp.14-19
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• 2015

In a previous report, we identified several candidate antimicrobial peptides through de novo RNA sequencing of the centipede Scolopendra subspinipes mutilans. Here, we identify and characterize one of these peptides, Scolopendrasin I. We identified the centipede antimicrobial peptide Cecropin from the centipede transcriptome using an SVM algorithm, and subsequently analyzed the amino acid sequence for predicted secondary structure using a GOR algorithm. We identified an alpha helical region of Cecropin and named it Scolopendrasin I. We then assessed antimicrobial and hemolytic activity of Scolopendrasin I. Scolopendrasin I showed antimicrobial activity against various microbes, including antibiotic-resistant Gram-negative bacteria, in a radial diffusion assay. Scolopendrasin I had potent antibacterial activity against acne-associated microbes in a colony count assay and showed no hemolytic activity in a hemolysis assay. In addition, we confirmed that Scolopendrasin I bound to the surface of bacteria via a specific interaction with lipoteichoic acid and lipopolysaccharide, two components of bacterial cell membranes. In conclusion, the results presented here provide evidence that this is an efficient strategy for antimicrobial peptide candidate identification and that Scolopendrasin I has potential for successful antibiotic development.

• 한국진공학회지
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• 제10권1호
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• pp.112-118
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• 2001

본 논문에서는 축 방향으로 자화된 용량결합형 13.65 MHz/40 KHz RF 방전에서 Langmuir Probe, Emissive Probe를 통해 이온 전류 밀도, 전자 온도, 플라즈마 전위의 자장 의존성 및 자기 바이어스 전위를 조사하였다. 자장을 인가함으로서 실험변수 범위 내에서 최대 3배의 이온 전류밀도증가를 얻었고 점화가능한 기체 압력의 최저값을 줄일 수 있었다. 플라즈마가 자화된 경우 공간 전위는 평균적으로 감소하였고 RF 전압의 한주기 동안 시 변동폭이 크게 증가하였다. 플라즈마 전위의 자장 의존성은 Particle-in-Cell Simulation을 수행하여 실험 결과와 비교하였다. 대표적 실험 조건에서 전자 온도는 자장에 따라 약 4 eV에서 5 eV로 약간 증가하는 경향을 보였으나 방전 주파수를 40 KHz로 줄인 경우 1.8 eV에서 0.8 eV로 감소하였다. 실험 장치의 응용 예로서 플루오로 카본 가스에 의한 식각실험이 수행되었다. 자화 플라즈마의 산화막 식각속도 증가를 확인함으로서 축방향 자장이 실제 공정에 긍정정인 영향을 미침을 확인 할 수 있었다.

• 한국수자원학회논문집
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• 제33권2호
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• pp.181-193
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• 2000

본 논문에서는 파랑이 존재할 때 모래결위에서의 흐름과 부유사의 거동에 관하여 기술한다. 새로운 수치모형시스템을 구축하였으며 이를 규칙파랑을 이용한 기존 실험실 실험조건과 가상적불규칙파랑조건에 적용하였다. 흐름장 계산은 SMAC 방법에 근거한 프로그램 SOLA를 Kim 등(1994)이 일부 수정하여 제시한 프로그램을 사용하였다. 흐름계산 부모형은 x-z 면에서의 연속방정식과 Reynolds의 운동방정식을 기본방정식으로 한다. 흐름부모형으로 파랑궤적도, 전단응력, 압력의 분포를 계산하였다. 모형실험결과 중 수직방향궤적도는 관측자료와 잘 일치하였다. 퇴적물이동 부모형은 부유사의 이류확산을 나타내는 식을 기본방정식으로 한다. 수치기법은 분리기법을 이용하며, 모래결 표면으로부터 퇴적물이 연행되어 유체내로 투입된다. 규칙파랑 실험조건에 수치모형을 적용한 결과, 부유사농도의 연직분포가 Deltaflume의 실험자료와 유사하게 재현되었다. 가상적인 불규칙 파랑조건에 모형을 적용한 결과 부유사농도의 높게, 부유사확산 범위가 더 넓게 예측되었다.

• 한국재료학회지
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• 제2권1호
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• pp.35-42
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• 1992

실릴콘 산화막을 $CHF_3/C_2F_6$ 혼합가스를 사용하여 반응성이온 건식식각을 행할 때 실리콘 표면에 형성되는 잔류막과 손상충의 열적 거동을 X-선 광전자 분광기(XPS)와 이차이온 질량 분석기 (SIMS)를 사용, 연구하였다. 저항가열을 통한 in-situ 분석에 의해 폴리머 잔류막은 $200^{\circ}C$부터 분해가 시작되고 $400^{\circ}C$ 이상의 가열에서는 graphite 형태의 탄소 결합체를 형성하며 분해됨을 알았다. 질소 분위기하의 급속 열처리를 통해 잔류막의 열분해는 $800^{\circ}C$ 이상에서 완료되고 손상층을 형성하는 침투 불순원소의 기판 외부로의 확산이 관찰되었다.

• 한국재료학회지
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• 제20권4호
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• pp.187-193
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• 2010

Chromium nitride (CrN) samples with two different layer structures (multilayer and single layer) were coated on bipolar plates of polymer electrolyte membrane fuel cells (PEMFC) using the reactive sputtering method. The effects with respect to layer structure on corrosion resistance and overall cell performance were investigated. A continuous and thin chromium nitride layer ($Cr_{0.48}\;N_{0.52}$) was formed on the surface of the SUS 316L when the nitrogen flow rate was 10 sccm. The electrochemical stability of the coated layers was examined using the potentiodynamic and potentiostatic methods in the simulated corrosive circumstances of the PEMFC under $80^{\circ}C$. Interfacial contact resistance (ICR) between the CrN coated sample and the gas diffusion layer was measured by using Wang's method. A single cell performance test was also conducted. The test results showed that CrN coated SUS316L with multilayer structure had excellent corrosion resistance compared to single layer structures and single cell performance results with $25\;cm^2$ in effective area also showed the same tendency. The difference of the electrochemical properties between the single and multilayer samples was attributed to the Cr interlayer layer, which improved the corrosion resistance. Because the coating layer was damaged by pinholes, the Cr layer prevented the penetration of corrosive media into the substrate. Therefore, the CrN with a multilayer structure is an effective coating method to increase the corrosion resistance and to decrease the ICR for metallic bipolar plates in PEMFC.

• 한국재료학회지
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• 제18권11호
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• pp.597-603
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• 2008

Oxide effects experiments on massive hydriding reactions of Zr alloy with hydrogen gas were carried out at $400^{\circ}C$ under 1 atm in a $H_2$ environment with a thermo-gravimetric apparatus (TGA). Experimental results for oxide effects on massive hydriding kinetics show that incubation time is not proportional to oxide thickness. The results also show that the massive hydriding kinetics of pre-filmed Zr alloys follows linear kinetic law and that the hydriding rates are similar to that of oxide-free Zr alloys once massive hydriding is initiated. Unlikely microstructure of the oxide during incubation time, physical defects such as micro-cracks and pores were observed in the oxide after incubation time. Therefore, it seems that the massive hydriding of Zr alloys can be ascribed to short circuit paths and mechanical or physical defects, such as micro-cracks and pores in the oxide, rather than to hydrogen diffusion through the oxide resulting from the increase of oxygen vacancies in the hypo-stoichiometric oxide.

• 한국연소학회지
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• 제7권4호
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• pp.36-44
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• 2002

Carbon molecules with closed-cage structures are called fullerenes $(C_{60},\;C_{70})$, whose applications include super-conductors, sensors, catalysts, optical and electronic device, polymer composites, and biological and medical materials. The synthesis of fullerenes has been recently studied with low-pressure benzene/argon/oxygen flames. The formation of fullerene is known as molecular weight growth processes of PAHs (polycyclic aromatic hydrocarbon). This study presents results of PAHs and fullerene measurements performed in a low-pressure benzene/argon/oxygen normal co-flow laminar diffusion flame. Through the central tube of the burner, benzene vapors carried by argon are injected. The benzene vapors are made in a temperature-controlled bubbler. The burner is located in a chamber, equipped with a sampling system for direct collection of condensable species from the flame, and exhausted to a vacuum pump. Samples of the condensable are analyzed by HPLC (High Performance Liquid Chromatography) to determine the yields of PAHs and fullerene. Also, we computed mole fraction of fullerene and PAHs in a nearly sooting low pressure premixed, one-dimensional benzene/argon/oxygen flame (equivalence ratio ${\Phi}=2.4$, pressure=5.33kPa). The object of computation was to investigate the formation mechanism of fullerenes and PAHs. The computations were performed with CHEMKIN/PREMIX. As a result of this study, fullerenes were synthesized in a low pressure (20torr) $C_6H_6/Ar/O_2$ flames and the highest concentration of fullerene was detected just above the visible surface of a flame.

• 한국재료학회:학술대회논문집
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• 한국재료학회 2003년도 춘계학술발표강연 및 논문개요집
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• pp.131-131
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• 2003

Surface micromachined uncooled IR detector with the optimized VOx bolometric layer was fabricated based on sandwich structure of the V$_2$O$_{5}$V/V$_2$O$_{5}$. In order to improve the detectivity of the IR detector, we optimized a few factors in the viewpoint of bolometric material. Vanadium oxide thin film is a promising material for uncooled microbolometers due to its high temperature coefficient of resistance at room temperature. It is, however, very difficult to deposit vanadium oxide thin films having high temperature coefficient of resistance and low resistance because of process limits in microbolometer fabrication. In order to increase the responsivity and decrease noise, we increase TCR of bolometric material and decrease room temperature resistance based on the sandwich structure of the V$_2$O$_{5}$V/V$_2$O$_{5}$ by conventional sputter. By oxygen diffusion through low temperature annealing of V$_2$O$_{5}$V/V$_2$O$_{5}$ in oxygen ambient, various mixed phase vanadium oxide was formed and we obtained TCR in range of-1.2 ~-2.6%/$^{\circ}C$ at room temperature resistance of 5~100k$\Omega$.mega$.

• 한국환경과학회지
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• 제9권5호
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• pp.375-384
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• 2000

It is very important to interprete and simulate the variation of phytoplankton maximum region for the prediction and control of red tide. This study was composed of two parts first the hydrodynamic simulation such as residual current and salinity diffusion and second the ecological simulation such as phytoplankton distribution according to freshwater discharge and pollutant loads. Without the Nakdong river discharge residual current was stagnated in inner side of this estuary and surface distribution of salinity was over 25psu. On the contrary with summer mean discharge freshwater stretched very far outward and some waters flowed into Chinhae Bay through the Kadok channel and low salinity extended over coastal sea and salinity front occurred. From the result of contributed physical process to phytioplankton biomass the accumulation was occurred at the west part of this estuary and the Kadok channel with the Nakdong river discharge. When more increased input discharge the accumulation band was transported to outer side of this estuary. The frequently outbreak of red tide in this area is caused by accumulation of physical processes. The phytoplankton maximum region located inner side of this estuary without the Nakdong river discharge and with mean discharge of winter but it was moved to outer side when mean discharge of the Nakdong river was increased. The variation of input concentration from the land loads was not largely influenced on phytoplankton biomass and location of maximum region. When discharge was increased phytoplankton maximum region was transferred to inner side of the Kadok channel. ON the other hand when discharge was decreased phytoplankton maximum region was transferred to inner side of this estuary and chlorophyll a contents increased to over 20$\mu\textrm{g}$/L Therefore if any other conditions are favorable for growth of phytoplankton. decreas of discharge causes to increase of possibility of red tide outbreak.