Study on Microstructure and Mechanical Properties of the Al–25Cr–5Si (at%) Alloy Powder Using Gas-Atomization and SPS Process

Yong‑Ho Kim,Hyo‑Sang Yoo,Jeong‑Han Lee,Ik‑Hyun Oh,Hyun‑Kuk Park,Hyeon‑Taek Son 대한금속·재료학회 2021 METALS AND MATERIALS International Vol.27 No.7

In order to investigate the microstructure and mechanical properties on Al–25Cr–5Si (at%) alloy, a mixed powder with pureelements and an alloy powder using a gas atomization process were used. Fine and high purity Al–25Cr–5Si (at%) alloypowder was successfully prepared by gas atomization and densified using a spark plasma sintering (SPS) process. The overallpowder size distribution of the mixed Al, Cr, and Si elemental powders was in the range of 10–15 μm. The atomized Al–Cr–Sialloy powder was fine and spherical in morphology and difficult to be formed by intermetallic formation. Densification wasclearly confirmed at 1000 °C, with almost isolated pores formed, by clear removal of pores between particles, deformationof particles, an increase in the number of contacts, and a change in size between particles. As a result of XRD analysis ofthe sintered compacts, single phase was observed using the mixed powder, but the compact using gas atomization remainedthe alloy phase even at the process temperature. The Vickers hardness of the compacts by mixed powder was observed at59.70 Hv and the compact using gas atomized powders on the temperature 1000 °C of the Vickers hardness increased to702.6 Hv. The compressive yield strength of the compact with mixed powder was 195.24 MPa and the compressive strengthof the compact with gas atomized powder increased to 802.07 MPa. It is considered not to be decomposed by the AlCrSi,Al13Cr4Si4and Al8Cr5phases sintering process, resulting from the improvement of mechanical properties.

그람양성구균에 대한 Teicoplanin과 Vancomycin의 시험관내 항균력

최태열,김경숙,전용관,서일혜,김정욱,이웅수,안정열,김홍석,정재용,최효선,김덕언,유진우 대한감염학회 1994 감염 Vol.26 No.1

An increasing frequency of methicillin resistant S. aureus(MRSA), methicillin resistant coagulase negative staphylococci(MRCNS) and Enterococcal infection have been observed in recent years. Teicoplanin is a new glycopeptide antibiotic obstained from the Actinoplanes teicomycetius. The molecular structure and spectrum of antimicrobial activity of teicoplanin is simillar to those of vancomycin, and has been reported to have an excellent in vitro and in vivo effect against various gram-positive infections. Therefore, we evaluated the in vitor susceptibility of gram positive cocci, such as, S. aureus, coagulase negative Staphylococci(CNS), and Enterococci to teicoplanin and vancomycin. The total 253 strains consisted of MSSA(40), MRSA(53), MSCNS(47), MRCNS(48), and Enterococci(65). They were assayed by disc diffusion and agar dilution. During the study, 57% of S. aureus and 49% of CNS showed resistance to methicillin. The inhibitory diameter of teicoplanin was 15-20mm in MSSA, 12-19mm in MRSA, 13-24mm in MSCNS, 11-23mm in MRCNS, and 15-22mm in Enterococci respectively, and showed sensitivity in all but 8 strains(3.2%). The range of the minimum inhibitory concentration (MIC) of teicoplanin to MSSA, MRSA, MSCNS, MRCNS and Enterococci were 9.12-2.0㎍/ml, 0.25-2.0㎍/ml, & 0.25-32㎍/ml, 0.12-1.0㎍/ml respectively. One case of S. haemolyticus was resistant to teicoplanin (32㎍/ml) by the agar dilution method. Eight minor (3.2%) and one major(0.4%) error was observed when the MIC and disk diffusion data were correlated with teicoplanin. As for vancomycin the inhibitory diameter was 17-21mm in MSSA, 15-21mm in MRSA, 18-26mm in MSCNS, 18-25mm in MRCNS, and 16-22mm in Enterococci respectively. The range of the MIC of vancomycin to MSSA, MRSA, MSCNS, MRCNS, and Enterococci were 0.25-1.0㎍/ml, 0.25-4.0㎍/ml, 0.5-2.0㎍/ml and 0.5-2.0㎍/ml respectively. One minor error (0.4%) was seen with the vancomycin disk. The MIC90 of MSSA and MRSA exhibited the same results in teicoplanin (1.0㎍/ml, 1.0㎍/ml), and vancomycin(2.0㎍/ml, 2.0㎍/ml). MSCNS and MRCNS exhibited greater MIC90 with teicoplanin(4.0㎍/ml, 8.0㎍/ml) than vancomycin(2.0㎍/ml, 2.0㎍/ml). Incontrase Enterococci were more susceptible to teicoplanin(0.5㎍/ml) than to vancomucin (2.0㎍/ml). Results from this analysis indicated that both teicoplanin and vancomycin were very excellent for gram positive infections, especially those resistant to methicillin.

교량진동의 사용성평가를 위한 현장시험및 분석

김상호,이용선 연세대학교 산업기술연구소 2000 논문집 Vol.32 No.2

The main purpose of this research is to evaluate the vibration serviceability of highway bridges and investigate various influential parameters of the vibration characteristics through field experiments as well as analytical works. The evaluation criterion of vibration serviceability are generally based on the natural frequency and amplitude of vibration in terms of either displacement or acceleration of a structure. In this study, the serviceability criterion proposed by Meister are employed. Dynamic loading tests are performed with 4 bridges. Some of them are reported as bridges with vibration problem. Others are selected randomly. The parametric studies by field tests and analytical evaluation are performed with various factors such as bridge types, vehicle weights, traveling speeds, road roughness, etc. Finally a systematic and rational evaluation process for vibration serviceability of highway bridges are suggested.

Vanadate가 집토끼의 심근수축력과 활동전압에 미치는 효과

김충수,방효원,엄대용,이상돈 중앙대학교 의과대학 의과학연구소 1985 中央醫大誌 Vol.10 No.1

Rabbit papillary muscle preparations were used to investigate the effects of vanadate on isometric contractility and variabilities of action potential. To record the myocardial contractility and action potential of rabbit papillary muscles, 3M KCI-filled glass microelectrodes were directly introduced into the muscle cells. The following results were obtained: 1. By increase of concentration of vanadate, myocardial isometric contractility increased but action potential did not change. 2. In case of preparation with the calcium antagonist(Diltiazem) myocardial contractility decreased and the overshoot potential and APD50 also decreased. 3. In case of preparations simultaneously with vanadate and Diltianzem, the effect in case of initial treatment with vanadate was completely reversed ay later treatment with Diltiazem. Above results could be interpreted as that the inflow of calcium ion was increased at the myocardial cell membrane level and then the myocardial contractility was increased by vanadate.

돈지, 들깨유 및 달맞이꽃 종자유의 혼합급이가 흰쥐의 간장, 뇌 및 고환의 지질 성분에 미치는 영향

김성희,김한수,서인숙,정효숙,정승용 慶尙大學校 1992 論文集 Vol.31 No.2

돈지 및 들깨유와 달맞이꽃 종자유등 2종 식물 종자유와의 혼합급이가 흰쥐의 체내 조직의 지질 성분에 미치는 영향을 구명하기 위해 S·D계 숫쥐에게 돈지 2.55및 들깨유와 달맞이꽃 종자유의 혼합비율을 달리하여 4주간 급이 사육한 후 간장,뇌 및 고환의 지질 성분을 분석 검토한 결과는 다음과 같다. 간장의 총콜레스테롤 함량은 D군이 대조군에 비해 유의적으로 낮았으며, 인지질 함량은 각 군간의 유의적인 차이가 없었고, 중성지질 함량은 B및 C군이 대조군에 비해 현저하게 낮았다. 콜레스테롤 급이군의 간장 총콜레스테롤 함량은 대조군에 비해 c,d및 e군이 유의적으로 낮았고, 인지질 및 중성지질의 함량은 b군이 낮게 나타났다. 뇌의 총콜레스테롤 함량은 대조군에 비해 B및 C군이 유의적으로 낮았으며, 인지질 및 중성지질의 함량은 대조군에 비해 전 군이 유의적으로 낮데 나타났다. 콜레스테롤 급이군에 있어 뇌의 총콜레스테롤 함량은 각 군간의 유의적인 차이가 없었고, 인지질 함량은 c군이 중성지질 함량은 e군이 대조군에 비해 낮게 나타났다. 고환의 총콜레스테롤 및 인지질 함량은 각 군간의 유의적인 차이가 없었으나, 중성지질 함량은 대조군에 비해 전 군이 유의적으로 낮았다. 콜레스테롤 급이군은 콜레스테롤 무급이군과 거의 유사한 경향을 나타내었다. In order to observe the effects of the feeds mixed with the lard and two vegetable seed oils, which mixed with 2.5% lard and various level of perilla oil and evening primrose oil were administered to the male rats of Sprague Dawley for 4 weeks on lipid components of liver, brain and testes. In livers , total cholesterol contents were remarkably lower in the D group(2.5% lard+2.5% perilla oil+5.0% evening primrose oil,free cholesterol) than in the control group , and phospholipid contents were not significant difference in each groups. Triglyceride contents were remarkably lower in the B(2.5% lard+7.5% perilla oil+5.0% ,free cholesterol) and C(2.5% lard+5.0% perilla oil+2.5% evening primrose oil,free cholesterol) group than in the control group. In the supplemented cholesterol groups, total cholesterol contents were significantly lower in c(C group+cholesterol diet), d(D group+cholesterol diet) and e(2.5% lard+7.5% evening primrose oil,free cholesterol) group, phhspholipid and triglyceride contents were lower in the b group(B group+cholesterol diet) than in the control groups than in the control group, phospholipid and triglyceride contents in brain were considerably lower in the other groups than in the control group. In the supplemented cholesterol groups, total cholesterol contents were not significant difference in each groups. Phospholipid and triglyceride contents were conspicuously lower in the c and e groups. respectively. In testes, total cholesterol and phospholipid contents were not significant difference in the groups, but triglyceride contents were lower in the all groups except for control group The contents of total cholesterlo, phospholipid and triglyceride were similar between the supplimented cholesterol groups and the nonsupplemented cholesterol groups.

동방결절의 부위별 전기적 특성에 관한 연구

김봉식,조성일,방효원,엄대용,이상돈 중앙대학교 의과대학 의과학연구소 1986 中央醫大誌 Vol.11 No.1

In order to investigate the regional eiectrophysiological characteristics of the rabbit SA node, the node was tied with fine silk threads into small preparations(0.5XO.5mm in size) and electrotonic connection between them was insulated. The preparations were divided into three groups, as peripheral, transitional and central areas. Three glass microelectrodes were inserted into the cells in each area and the data were collected when transmembrane potentials of each area was recorded simultaneously. 1. As the Na^+ concentration of the solution was reduced to 80, 60, and 40% of control, the beating frequency, the maximum diastolic potential(MDP), overshoot and the maximum upstroke velocity(Vmax) were decreased. The decrease of the beating frequency was more marked in the central area, and the spontaneous beating was arrested by the reduction of Na^+ concentration more than 60%. 2. In the peripheral area, MDP was decreased as the 2mM K^+ concentration reduced to 1 mM. At high K^+ concentration(12mM), the spontaneous beating of the central area was stopped in the 50% of preparations. 3. The decrease of the spontaenous beating frequency, due to Ach(Acetylcholine) was more prominent in the central area. The increase of the MDP was marked in the central area, however, the decrease of overshoot was distinct in the peripheral area. 4. The peripheral area was the most sensitive to TTX(Tetrodotoxin). The effects of epinephrine which changed the parameters of the action potential were more marked in the central area, but the effects were more marked in the peripheral area when the preparations were pre-treated with TTX. 5. The amplitude of the Na^+-K^+ pump activity of the peripheral area was larger and decreased in the transitional and the central area in sequence. The electrophysiological characteristics of the SA nodal cells have shown various differences by the locations. Especially, the central area which considered as the leading pacemaker are generally more sensitive to the various interventions.

빌트인 모터를 이용한 2축 제어 미세 가공기 개발

김건희,김효식,양순철,이상용,국명호,이선규,김윤중,홍권희 한국공작기계학회 2007 한국공작기계학회 추계학술대회논문집 Vol.2007 No.-

This paper describes development of low cost precision machine that has combined the Build-in Motor with a vacuum chuck. This study mainly aims to find out a cutting condition for maintaining optimum surface condition and to examine cutting characteristics of the precision machine that is equipped by diamond bites. The cutting materials is Al alloy. Several experiments were carried out to find out the main factors that affect the surface roughness such as principal axis RPM(rotation per minute), feeding speed, and cutting depth. As a result, we obtain The optimum cutting condition of the developed precision machine.

시차주사열량분석기를 이용한 치과용 접착시멘트의 경화기전 및 반응열에 관한 연구

김철위,이용근,윤태호,김효종,남세진 大韓齒科器材學會 2000 대한치과재료학회지 Vol.27 No.3

The working time of dental cement has a close relation with the setting time, where the setting reaction can be said as the result of the chemical reaction between cement liquid and powder. The purpose of this experiment was to investigate the setting characteristics and setting rate of dental cements by measuring the exothermic heat(Joule/gram) from the setting reaction at specified times using a differential scanning calorimeter (Differential Scanning Calorimeter, DSC 204, TASC 414/3A Controller, Netzche, Germany). Graphs of time-exothermic heat at 37℃ isothermal condition, showing the setting reaction of dental cements were plotted. Three types of luting cements studied were zinc-phosphate cement (ZPC), polycarboxylate cement (PCC), and glass ionomer cement (GIC). The effects of powder-liquid ratio on the setting characteristics of cements were also included. The amount of heat (calory) released per one gram of cement was calculated at each specified time, and was analyzed. ANOVA and Scheff's multiple comparison test (p=0.05) were used for statistical analysis using SPSS/PC+. The setting rate of cement was not constant during the setting reaction, and different setting characteristics were observed depending on the type of cement and powder/liquid ratio. Generally, 70∼90% of the setting reaction, measured by the exothermic heat release, occurred within 5 minutes after mixing. The exothermic heat released by ZPC was very high immediately after mixing, and the duration of the heat release was prolonged compared with other cements. The exothermic heat release of PCC finished most rapidly. It was generally observed that the amount of heat release (rise in temperature) per one gram of cement was highest for ZPC, followed by GIC, and then PCC. However, heat release during the first 2∼5 minutes after mixing was highest for GIC, followed by ZPC and then PCC. According to the Scheff's multiple comparison test, the duration of the total setting reaction did not show any significant difference among the cements(p>0.05), and also among the different power/liquid ratio groups(p>0.05). It was observed that more heat was released with the lower powder/liquid ratio than the higher powder/liquid ratio.

"人類의 共同遺産" 槪念의 法的 意味

김효진,엄응용 경운대학교 산업기술연구소 2001 産業技術硏究論文誌 Vol.3 No.2(B)

After the world war Ⅱ, an international society has been concerned about the outside region of national jurisdiction(Deep seabed, Outer Space, Moon, South Pole etc), and the development and conservation of its resources. As a result, Antarctic Treaty(1959), Outer Space Treaty(1967), the Moon Treaty(1979), and UNCLOS(1982) were concluded. Above all, through the treaties common Heritage of Mankind(CHM) was induced expressly or analogically as a new approach for the development and conservation of International Common Spaces. However, the question at issue is that the concept, character , extent, and regulations of CHM which was induced by the treaties have been interpreted and applied according to each treaty or standpoint of each nation. This lead to denunciation on the status of the CHM in international law. By the way, the core cause of this denunciation could be that there's no right legal definition on the terms of the CHM. It means that a prior question on the status of the CHM from the point of the international law is to analyze and examine closely the terms of this concept and define the legal implication. Therefore, I am willing to describe the appearance and development of the concept of CHM, analyze the legal significance on each term of the concept and evaluate generally the legal position of it through this study.

Nylon6,6/Polyaniline 전도성 복합체의 제조 및 전기적 성질에 관한 연구

김효용,허양일,이완진 全南大學校 觸媒硏究所 1998 觸媒硏究 論文集 Vol.20 No.-

The conducting composite using polyaniline as a conducting polymer and nylon6,6 as a matrix by blending method was prepared. The m-cresol was used as a solvent in blending. The PANI was protonated using camphorsulfonic acid(CSA) or dodecylbenzenesulfonic acid (DBSA) such as alkylbenzenesulfonic acid. In the conducting composite, DBSA was found to be more superior dopant to CSA and the electrical conductivity was increased with the amount of PANI complex. Also, in the temperature range of -196℃ to 160℃, the electrical conductivity was measured. The temperature dependency for conducting composites varied with the content of PANI complex and followed variable range hopping model. The electric conductivity was increased up to 0.19 S/cm with the amount of PANI complex protonated with DBSA having long alkyl chain.