인산칼슘 시멘트를 이용한 자가 경화형 경조직 재생 마이크로 전달체의 개발

박정휘 단국대학교 일반대학원 2011 국내석사

현대사회에서는 인구의 증가와 고령화로 인한 사고나 질병 등이 증가 하여 치과와 정형외과 영역에서 우리 몸을 구성하는 206개의 손실된 뼈를 수복하기 위한 여러 분야의 연구가 진행되고 있다. 현재 다양한 종류의 뼈 대체제를 생체 재료로서 사용하고 있다. 각각의 특징이 있는 금속, 세라믹, 고분자 등 쓰이는 물질이 광범한데, 그 중 세라믹 분야인 인산칼슘(CaP)을 이용하여 뼈 재생 연구에 접근하였다. 인산칼슘의 종류에서 α-tricalcium phosphate(α-TCP)와 수산화인회석(HA: Hydroxy apatite), 교원섬유(collagen)을 사용하였다. 이 세가지 물질들은 뼈의 재생을 도와주는 탁월한 효과를 주는 것으로 알려져 있다. 그리고 비슷한 실험으로 콜라겐 대신 알긴산을 사용하였다. 본 연구의 목적은 자가 경화를 목적으로 water in oil(w/o)의 방법으로 마이크로 입자를 제조하여 뼈세포와의 세포반응성을 측정하여 뼈 조직 재생용 입자로서 가능성이 있는지 실험하였다. 탄산칼슘(CC: calcium carbonate)과 인산이칼슘(DCP: dicalcium phosphate)를 일정한 양을 섞어 1400℃에 5시간을 열처리하여 HA를 혼합하여 collagen과 섞어서 oil bath에 떨어뜨려 마이크로 입자를 만든다. 다음으로 생체모방용액(SBF: Simulated Body Fluid solution)에 반응시켜 표면에 미네랄인 HA를 생성되는 것을 관찰하였다. 세포실험에서는 MC3T3E-1 세포와 반응시켜서 증식과 분화를 비교하여 생체적합성인지 실험하였다. alginate 실험은 MSC 세포를 사용하였다. 증식 실험에서는 3, 7, 14일 배양하여 MTS법으로 관찰하였고, 분화 실험에서는 7, 14일 배양하여 일반 dish에 비하여 높은 결과를 나타났다. 본 실험의 결과 인산칼슘과 collagen의 혼합하여 만든 마이크로 입자는 뼈세포를 부착, 증식, 분화하여 손상된 뼈조직에 대한 치유가 직접적으로 재생시킬 수 있는 뼈 조직용 마이크로 입자의 가능성이 있다는 것을 확인하였다.

대형 크랭크샤프트 열간단조 공정의 삼차원 비등온 시뮬레이션

박정휘 경상대학교 대학원 2009 국내석사

In this paper, non-isothermal analysis of a closed die forging process for a large crankshaft is conducted. A simple and computationally efficient approach to non-isothermal three-dimensional hot forging simulation, theoretically based on a rigid-thermoviscoplastic finite element method, is employed. In the approach, the temperatures of dies are considered to be constant. Hot compression test of the material is made to acquire the material property of flow stress. The fitted flow stress information is verified by comparing the compression loads of experiments and predictions which are obtained by simulating the compression test under the same conditions as the actual hot compression test. Hot forging of large crankshaft is simulated using AFDEX 3D and the simulated result is compared with the actually forged one in detail. It has been verified that the predictions are in good agreement with the experiments. The successful simulation and development of a large crankshaft by the closed die forging technology will contribute to opening a new area of closed-die forging application and to enhancing competitiveness of national machinery industries especially including ship part and power generation industries.

알루미늄 합금 Al6082의 열간 단조 중 유동 및 윤활 특성과 관련된 거시적 현상의 실험적 및 수치적 연구

박정휘 경상국립대학교 대학원 2024 국내박사

In this paper, the plastic flow behaviors of aluminum alloys at elevated temperatures were studied to conduct an accurate finite element analysis of the hot forging process. Various material models characterizing the flow behaviors for metal forming applications are introduced and evaluated by comparing the experimental flow curves with the fitted low curves from related literature. These models include the Arrhenius model, the improved Johnson-Cook model, the Hensel-Spittel model and its variant, as well as the flow curves of the piecewise bilinear C-m model (power law model), the Ebrahimi et al. model, and the improved Ebrahimi et al. model (referred to as the PLF model). The flow behaviors of metal materials are sensitive to state variables such as strain, strain rate, and temperature, with temperature effects being particularly important. Experimental flow curves are typically obtained at specific strain rates and tempera tures through the hot cylinder compression test. However, this test is inevitably exposed to undesirable effects of friction and temperature on flow characterization. This study revealed the impact of friction and temperature on the flow curves of an Al6082 alloy. By employing a systematic method to correct for the effects of friction and temperature, the flow curves were calculated with high accuracy in terms of the compression loadstroke curve obtained from the test. The enhanced flow information was employed to accurately simulate the hot forging process of an Al6082 alloy automotive part. The predictions were then compared with experimental results, revealing a strong agreement between them. Additionally, an investigation into the impact of friction on the flow pattern in the aluminum forging process was conducted to practically determine acceptable frictional conditions.

기업가정신이 조직몰입 및 직무불안정성에 미치는 영향 : 에너지 분야 관련 종사자를 중심으로

박정휘 중앙대학교 산업·창업경영대학원 2020 국내석사

에너지전환정책에 따른 불확실성의 증대는 에너지 관련 기업 구성원들의 안정된 고용관계를 위협하고 직무 불안정성을 인식하게 하고 있으며, 조직에 대한 충성심 저하, 성과 저하 등을 심화시키고 있다. 따라서 급변하는 환경에서 에너지 관련 기업이 지속 성장하고 발전하기 위해서는 기업가정신에 대한 이해 제고와 재정립이 필요한 상황이다. 본 연구에서는 선행연구를 바탕으로 기업가정신이 에너지 기업 구성원의 조직몰입에 미치는 영향을 검증하고, 나아가 공공기관 종사자들의 기업가정신이 직무불안정성에 미치는 영향을 규명하고자 한다. 또한, 기업가정신의 인구 통계적 특성을 분석하여 각각의 차이를 검증하고, 질적연구를 통해 인구 통계적 특성에 따른 기업가정신의 차이에 대한 원인을 분석하고자 한다. 실증분석을 위해 에너지관련 기업 내 구성원을 대상으로 설문지를 배포하여 311명을 대상으로 자료를 수집하였으며 기업가정신과 조직몰입, 직무불안정성의 인과관계 분석을 위해 다중회귀분석, 분산분석 등의 양적연구를 실시하였다. 또한 심층면접을 통한 질적연구를 실시하여 변수의 수준에 대한 차이를 검증하였다. 본 연구의 주요 결과는 첫째, 기업가정신의 구성요소인 진취성, 위험감수성은 구성원의 조직몰입에 정(+)의 영향을 미치는 반면, 혁신성은 유의한 결과를 보여주지 않았다. 둘째, 기업가정신의 구성요소인 위험감수성은 구성원의 직무불안정성에 부(-)의 영향을 미치는 반면, 혁신성, 진취성은 유의한 결과를 보여주지 않았다. 셋째, 기업가정신의 하위요인에 대한 인구 통계적 특성의 차이를 분석한 결과 기업가정신은 연령이 많을수록, 직급이 높을수록, 근무경력이 많을수록, 남자의 경우에 더 높은 수준의 기업가정신을 가지는 것으로 규명되었다. 본 연구의 시사점은 첫째, 정부의 에너지 정책변경에 따라 불확실성이 증가하더라도 에너지 관련 기업의 기업가정신은 조직몰입에 중요한 역할을 하고 있는 것으로 분석되었다. 안정적인 환경 속에서 사업을 추진하는 특성에 따라 기업이 혁신적인 의사결정 보다는 진취적이고 위험을 감수하는 정책이 기업활동 및 구성원의 조직몰입에 긍정적인 영향을 줄 수 있다는 것을 유추할 수 있다. 둘째, 기업가정신의 하위요인이 직무불안정성에 미치는 영향을 확인함으로써 기존 연구에서 확인하지 못한 결과를 확인하였다는 점이며, 기업가정신의 특성이 직무불안정성을 감소시킨다는 것을 알 수 있었다. 셋째, 에너지 관련 기업 구성원의 인구 통계적 분석 결과를 통해 간접적으로 현재 우리 사회의 연령별, 경력별, 급여에 대한 기업가정신의 수준차이를 확인할 수 있었다. 특히 구성원의 기업가정신을 육성하기 위해서는 교육 체계구축과 지속적인 교육 시행, 프로젝트 등 실무 중심의 경험을 가지는 것이 유효하다는 것을 알 수 있었다. 넷째, 질적연구를 통해 기업가정신 수준의 차이가 발생하는 원인에 대해 확인할 수 있었으며 우리 경제의 역동성과 청년세대의 기업가정신 육성이 필수적인 과제임을 인식하게 하였다. Growing uncertainty which accompanies energy transition policies threatens the stable employment relationship of those in energy-related corporations as they feel a sense of job insecurity, and exacerbates the decline in the loyalty and performance these people demonstrate in their organization. Thus, it is necessary to enhance and reestablish one’s understanding of entrepreneurship for businesses which are engaged in the energy industry to keep growing and developing. Based on preceding studies, this research seeks to verify the effect entrepreneurship has on the organizational commitment of workers in the energy industry, and also identify how job insecurity is affected by the entrepreneurship of people employed in public institutions. In addition, the differences of each are verified by analyzing the demographic statistics of entrepreneurship, while qualitative research tools were used to analyze the reasons behind the differences. For an empirical analysis, a survey was conducted on 311 people who were employed in energy businesses, and quantitative research methods, including Multiple Regression Analysis and the Analysis of Variance were utilized to examine the causal relationship between entrepreneurship, organizational commitment, and job insecurity. Furthermore, differences in the level of the variables were examined through in-depth interviews. The key findings of this study are as follows. First, proactiveness and risk-taking, both of which are elements of entrepreneurship, had a positive impact on the organizational commitment of the individual, while innovativeness turned out to have little in relation. Second, job insecurity was negatively affected by risk-taking, but it had no visible correlation with innovativeness and proactiveness. Thirdly, analyzing the differing demographic features in the sub-factors of entrepreneurship revealed that entrepreneurship was stronger among those who were older, of a higher rank, and had more work experience. Furthermore, males tended to display higher levels of entrepreneurship than females. A number of implications can be deduced from this study. For one, even if a shift in the government’s energy policy may lead to growing uncertainty, the entrepreneurship of energy corporations plays an important role in organizational commitment. From this, it can be inferred that, taking into account the stable environment in which energy companies operate in, a proactive and risk-taking policy, instead of innovative decision-making, will have a positive effect on business activity and the organizational commitment of employed individuals. Secondly, this study confirmed for the first time that job insecurity was influenced by sub-factors of entrepreneurship, with the characteristics of the latter playing a role in reducing job insecurity. Third, through a demographical analysis on workers in the energy industry, this study indirectly revealed how the level of entrepreneurship varied within Korean society depending on age, experience, and wage. In particular, it was found that establishing an educational system, continuously providing education, and gaining actual experience through work such as projects was essential in cultivating entrepreneurship. Lastly, a qualitative research shed light into the causes behind the differing levels of entrepreneurship, which culminated in the lesson that promoting the dynamics of our economy and the entrepreneurship of our youth were the key tasks facing our society.

작품<The coming-out party>에 나타난 즉흥적 움직임 분석

박정휘 세종대학교 공연예술대학원 2013 국내석사

이 연구는 사람의 마음속의 잠재적인 공간에 있는 기억과 기분에 대한 개개인의 상황을 끌어내서 본능적인 기억에 입각하여 창작한 작품 <The coming-out party> 에 관한 연구이다. 이 작품은 사람이 경험한 일 중 숨 쉬는 것처럼 너무 당연해서 인지하지 못하고 지나가는 상황을 배경으로 생각하여 창작되었으며 그 상황의 기억, 기분을 회상하고 그 당시를 한 번 더 느낄 수 있길 희망하였다.

葦莖湯·加味葦莖湯의 A549에 對한 細胞毒性과 S-180에 對한 抗癌效果

박정휘 大田大學校 1995 국내석사

강상자형의 전단지연 변이현상에 관한 연구

박정휘 東國大學校 大學院 1999 국내석사

In the beam theory, it is assumed that the plane sections remain plane after deformations. However, this assumption is not always suitable for steel box girders with wide flanges. Because the action of in-plane shear strain in the flange, the longitudinal displacements in the parts of the flange remote from the webs lag behind those nearer the webs. Here, the longitudinal strain in the web must be equal to that in the flange at the junction of the web with the flange. This phenomenon termed shear lag or positive shear lag. It has been known that shear lag anomaly called negative shear lag occurs when a cantilever box girder is subjected to a uniformly distributed load. Since Foutch and Chang discovered it in 1982, numerous researchers have studied to describe this shear lag anomaly. However, this anomalous phenomenon still needs further investigations on the origin from more primary and physical point of view. In this study, a research was carried out aiming to trace the origin of shear lag anomaly from a new point of view. The results of this study reveal that there are two sources for negative shear lag using the finite element method which appeared to be the most suitable way for this purpose. The first one is the constraint of transverse deformations of the flange prescribed at certain locations such as the clamped edge. It is found that the local effect on negative shear lag is not so serious that it can be neglected. The second is the shear lag-aftereffect. Various case studies indicate that shear lag-aftereffect is the primary source for shear lag anomaly. Finally, at any given locations negative shear lag can take place whenever the portion of shear flow acting along the flange edges which tends to cause negative shear lag by means of the shear lag-aftereffect is predominant over the remaining portion of shear flow.

Development of composite microspheres for bone tissue engineering

박정휘 Graduate School of Dankook University 2017 국내박사

Microspheres are attracting considerable interest in areas of tissue regeneration, such as cell and drug delivery vehicles, bone defect fillers and tissue engineering matrices. Spherical shaped materials with sizes ranging from several to hundreds of micrometers have been shown to be effective in delivering drugs, such as polypeptides, proteins and genes. Microspheres have gained recent interest as a three-dimensional matrix for tissue cells, showing the potential to be injected directly into defective tissues. This suggests that microspherical forms, in comparison to large porous blocks, have merits of being tuned to the size and shape of tissue defects. Some recent in vitro and in vivo studies have reported the potential of microspheres in supporting initial cell adhesion and multiplication as well as further differentiation and matrix formation. A novel nanocomposite microspherical cell-carrier was developed to populate stem cells and to stimulate their osteogenesis for bone tissue engineering. Bioactive glass nanoparticles were incorporated within the poly(caprolactone) PCL / poly(lactic acid) PLA blend biopolymer to improve bone bioactivity, and the surface was mineralized with apatite phase. The emulsified in surfactant water bath while gentle stirring to produce spherical shaped. During the emulsification camphene solidifies accompanied by a solvent evaporation to form a bi-continuous network with the polymer phase. Rat mesenchymal stem cells populated well onto the porous microspheres, exhibiting tight anchorage with the underlying surface and active spreading and proliferation behaviors. In vivo tests in rat calvarial defects confirmed the excellent tissue compatibility of the microspheres. The mineralized surface was specifically effective in loading and releasing of biological proteins. The porous microspheres developed in this study are considered to have great feasibility for the cell delivered bone tissue engineering with simultaneously delivering therapeutic proteins. The microfluidic device could generate homogeneous structured microspheres with excellent mono-dispersity. The relationship between the microsphere size and the sheath flow rate was examined using pure PCL composition. The pure PCL microspheres generated using microfluidic system showed spherical shapes and excellent uniformity in diameter. The size of the pure PCL microsphere decreased with increasing sheath flow rate. After solidifying the microsphere, the size of the microspheres decreased by 45 %, while maintaining the uniformity in diameter. The microstructure of the PCL microspheres was significantly influenced by camphene content in the initial mixture solution. The average size of the solidified microspheres increased with increasing the camphene content. It was notable that the size distribution of PCL microspheres was still monodisperse, regardless of camphene content. Furthermore the micropore channels were formed on the microspheres when the camphene was incorporated and the size of the micropores also increased with increasing camphene content. The initial cell growth study on the microporous spheres showed good cell viability and the possible use as cell carriers.

Wavelet 변환과 벡터양자화기를 이용한 화상 데이타 압축에 관한 연구

박정훈 漢陽大學校 大學院 1993 국내석사