• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2013년도 춘계학술대회 논문집
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• pp.1327-1328
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• 2013

• 한국산학기술학회논문지
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• 제18권5호
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• pp.278-284
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• 2017

본 연구에서는 일정한 회전 속도에서 용접 속도를 제어하여 AZ61 마그네슘 합금에 적합한 입열량 조건을 도출하였다. 또한 산업적 측면에서는 더 빠른 용접 속도가 요구되기 때문에 용접 속도에 따른 효과를 연구하였다. 회전 속도 변수는 800rpm으로 일정하게 적용하였고, 용접 속도는 100 - 500mm/min 으로 변화시켜 용접부의 거동을 관찰 및 평가하였다. 기계적 물성 평가를 위하여 인장 및 경도 시험을 수행하였으며, 미세구조 관찰과 용접부의 건정성을 판단하기 위하여 광학현미경을 사용하였다. 용접 속도가 400mm/min 이상 적용되었을 때 용접부 내부에서 결함이 관찰되었다. 용접 속도가 증가할수록 교반부의 결정립 크기는 작아졌으며, 경도 또한 비례 증가하는 경향을 보였다. 회전속도 800rpm, 용접 속도 200mm/min과 300mm/min 일 때, 용접부 내 외부 적으로 결함이 없었으며, 우수한 기계적 물성이 기록되었다. 이때, 접합 효율은 각각 100.5%, 101.2%이었고, 최대인장강도가 모재의 강도와 유사하였다. 인장 시편의 파괴는 시편의 전진측과 교반부 사이에서 발생하였으며, 이는 횡단면부 경도 분포에서 경도가 일시적으로 감소하는 위치와 일치하였다.

• 한국식품영양학회지
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• 제15권1호
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• pp.23-28
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• 2002

감잎의 메탄을 추출물과 이를 극성이 다른 용매로 더욱 불리한 용매별 획분들의 돌연변이 유발 억제효과를 spore rec assay를 이용하여 검토하고 사람의 결장암 세포인 HT-29와 사람의 위암 세포인 AZ-521의 증식에 대한 저해효과를 실험하였다. 감잎의 메탄을 추출물은 spore rec assay에서 N-methyl- N'-nitro-N-nitrosoguanidine(MNNG) 의 돌연변이성을 61% 정도 억제하였으며, 감잎의 메탄을 추출물에서 효과가 있었던 활성물질을 정제하기 위하여 다시 극성이 다른 용매들로 각각 추출하여 얻은 획분 중에서는 헥산, 클로로포름 및 에틸아세테이트 획분이 강한 돌연변이 유발억제효과를 나타내었다. 그리고 감잎의 메탄을 추출물은 암세포의 증식을 억제시키는 항발암 효과가 관찰되었는데 사람의 결장암 세포인 UT-29와 사람의 위암 세포인 AZ-521에 감잎의 메탄을 추출물을 50$\mu\textrm{g}$/ml와 100$\mu\textrm{g}$/ml 첨가시 이들 암세포의 증식이 각각 90%와 99%가지 크게 억제되었다. 감잎의 메탄을 추출물을 다시 극성이 다른 용매들로 분리한 획분들 중에서는 사람의 결장암 세포인 HT-29와 사람의 위암세포인 AZ-521에 감잎의 클로로포름 획분을 각각 50$\mu\textrm{g}$/ml와 100$\mu\textrm{g}$/ml 첨가시 이들 암세포의 증식 억제율이 100%에 달하였고 감잎의 에틸아세테이트 획분도 사람의 결장암 세포(HT-29)와 사람의 위암세포(AZ-521)에 대해 클로로포름 획분 다음으로 강한 항발암 효과가 관찰되었으며, 헥산 획분도 이들 두 획분(클로로포름 및 에틸아세테이트)보다는 낮았으나 암세포 증식을 억제하는 효과가 관찰되어 항돌연변이 실험에서와 일치하는 결과를 얻었다.

• 소성∙가공
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• 제24권6호
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• pp.405-410
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• 2015

Sheet-forming of Mg alloys is conducted at elevated temperatures (250℃) due to the low formability at room temperature. The high-temperature process often gives rise to surface damage on the alloy (i.e. galling.) In the current study, the frictional characteristics of DLC coating slid against an AZ31 Mg alloy at various temperatures were investigated. The coating has been used widely for low-friction processes. Dry-sliding friction and galling characteristics of an AZ31 Mg alloy (disk), which slid against uncoated and a DLC-coated STD-61 steel (pin), were investigated using a reciprocating-sliding tribometer at room temperature and 250℃. To represent the real sliding phenomena during a sheet metal forming process, single-stroke tests were used (10mm stroke length) rather than a reciprocating long sliding-distance test. The DLC coating suppressed adhesion between the alloy and the tool steel at room temperature, and exhibited a low friction coefficient. However, during sliding at 250℃, severe adhesion occurred between the two surfaces, which resulted in a high friction coefficient and galling.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.448-451
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• 2008

Magnesium alloys still have a lot of technical challenges to be solved for more applications. There have been many research activities to enhance formability of magnesium alloys. One is to design new alloy composition having better formability. Also, low formability of wrought alloys can be improved by optimizing the processing variables. In the present study, effect of process variables such as forging temperature and forging speed were investigated to forgeability of three different magnesium alloys such as AZ31, AZ61 and ZK60. To understand the effect of process variables more specifically, both numerical and experimental works have been carried out on the model which contains both upsetting and extrusion geometries. Forgeability of magnesium alloys was found to depend more on the forging speed rather than temperature. Forged sample showed a significant activity of twinning, which was found to be closely related with flow uniformity.

• Journal of Astronomy and Space Sciences
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• 제11권1호
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• pp.31-40
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• 1994

The IUE low dispersion spectra of AZ Cas have been analyzed for line identifications and energy distribution in ultraviolet region. Highly ionized atoms, SiIV and CIV are identified. We could infer a temperature range of the B star between 15,000K and 20,000K. The energy density distribution shows a hump between IUE short wavelength and long wavelength regions. Photometric and spectroscopic elements were revised based on the Florkowisk photeelectric observations and collected radial velocities. The temperature of both stars were reduced as 16,000K and 3,800K. The radii of both stars are $10 R_{\odot}\;and\;320R_{\odot}$. The eccentricity and longitude of periastron are 0.61 and $10.5^{\circ}$, respectively.

• 동력기계공학회지
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• 제18권4호
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• pp.66-71
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• 2014

In this study, effect of heat treatment on the microstructure and damping capacity of hot rolled magnesium alloys was investigated. The microstructure of hot rolled magnesium consisted of dendrite structure and $Mg_{17}Al_{12}$ compounds precipitated along the grain boundry. The dendrite structure was dissipated and $Mg_{17}Al_{12}$ compounds was decomposed by annealing treatment, and then they dissolved in ${\alpha}-Mg$. With an increasing the annealing temperature and time, damping capacity was slowly increased by the growth of grain size and decreasing of defects induced by hot rolling. Two kinds of magnesium alloys AZ 31 and AZ 61 after annealing showed no difference in damping capacity.

• Hip & pelvis
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• 제35권1호
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• pp.54-61
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• 2023

Purpose: The purpose was to examine the clinical and radiological outcomes after surgical treatment of acetabular fractures with total hip arthroplasty with a dual mobility cup cemented into a porous multihole cup in the population of frail elderly patients. Materials and Methods: A retrospective review of 16 patients who underwent surgery (mean age, 76.7 years) with a mean follow-up period of 36.9 months was conducted. Following surgery, patients underwent postoperative follow-up at six weeks, three, six, and 12 months and clinical and radiological examinations were performed. Results: Classification of fractures was based on the Letournel classification. Following surgery, all patients were allowed weight-bearing as tolerated immediately postoperative. Fourteen patients showed maintenance of preoperative mobility status at one year. The mean Harris hip score was 64.8 (range, 34.7-82.8) and 80.0 (range, 60.8-93.8) at three months and one year, respectively. The mortality rate was 12.5% at one year (2/16). Complications included heterotopic ossification (2/16), deep venous thrombosis (1/16), heamatoma (1/16), and femoral revision due to a Vancouver B2 fracture (1/16). No case of deep infection, dislocation, or implant loosening was reported. Conclusion: Total hip arthroplasty using a dual mobility cup cemented into a porous multihole cup with locking screws resulted in a stable construct with a capacity for immediate weight-bearing as tolerated with rapid relief of pain. The findings of this study suggest that this procedure can be regarded as a safe method that has shown promising clinical and radiological outcomes for treatment of patients with medical frailty.

• Journal of Welding and Joining
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• 제34권3호
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• pp.23-30
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• 2016

This paper discusses the optimization of friction stir spot welding (FSSW) process parameters for joining Aluminum alloy (AA6061-T6) with Magnesium alloy (AZ31B) sheets. Prior to optimization an empirical relationship was developed to predict the Tensile Shear Fracture Load (TSFL) incorporating the four most important FSSW parameters, i.e., tool rotational speed, plunge rate, dwell time and tool diameter ratio, using response surface methodology (RSM). The experiments were conducted based on four factor, five levels central composite rotatable design (CCD) matrix. The maximum TSFL obtained was 3.61kN, with the tool rotation of 1000 rpm, plunge rate of 16 mm/min, dwell time of 5 sec and tool diameter ratio of 2.5.

• 한국수학사학회지
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• 제17권2호
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• pp.61-72
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• 2004

본 연구에서는 문헌 연구를 통해, 수학사적 발전 과정 및 교수학적 변환을 통해 얻어진 체바 정리의 변환에 대한 구체적인 자료를 제시하였으며, 이를 통해 체바 정리가 변환되고 확장되는 패턴을 고찰하였다. 특히, 본 연구에서는 체바 정리의역, 유향선분, 삼각함수, 벡터 등의 개념과 관련된 체바 정리의 변형 및 발전을 분석하였으며, n각형에 대한 체바 정리, 사면체에 대한 체바 정리를 제시하면서 일반화 및 유추에 관련된 체바 정리의 변환과 확장을 고찰하였다.