• 호남수학학술지
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• 제31권2호
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• pp.177-183
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• 2009

In this article, we study ruled surfaces in a Lorentzian space-time, which have finite type immersion. We give a condition for bi-finite type surfaces to be of finite type.

• East Asian mathematical journal
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• 제38권3호
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• pp.347-355
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• 2022

For a nondegenerate projective variety, it is a classical problem to study its defining equations with respect to a given embedding. In this paper, we precisely determine minimal sets of generators of the defining ideals of some curves of maximal regularity in ℙ⁵.

• 충청수학회지
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• 제37권2호
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• pp.67-74
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• 2024

Maximal surfaces have a prominent place in the field of differential geometry, captivating researchers with their intriguing properties. Bearing a direct analogy to the minimal surfaces in Euclidean space, investigating both their similarities and differences has long been an important issue. This paper is aimed to give a local characterization of maximal surfaces in 𝕃³ in terms of their geodesic curvatures, which is analogous to the minimal surface case presented in [8]. We present a classification of the maximal surfaces under some simple condition on the geodesic curvatures of the parameter curves in the line of curvature coordinates.

• 공업화학
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• 제17권3호
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• pp.286-290
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• 2006

새로운 4급 염화 암모늄염, {alkyldimethyl-[5-(2-phenylthiazol-4-yl]-1,3,4-oxadiazol-2-ylmethyl]quaternary ammonium chlorides (ADOQACs): 6}을 화합물 5와 몇 가지 N,N-dimethylalkyl amine을 반응시켜 합성하였다. 합성한 화합물들의 구조와 물리적 특성을 조사하였고 계면활성을 측정하였다. 화합물 6의 표면장력($\gamma_{cmc}$)과 최소저해농도(MIC)는 알킬기의 영향을 받은 것으로 나타났으며, 특히 화합물 6c와 6d가 좋은 항균력과 계면활성을 보였다.

• 대한기계학회논문집A
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• 제41권8호
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• pp.737-744
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• 2017

최근 Shellular라는 새로운 극저밀도 재료가 소개되었다. Shellular는 주기적 구조를 가지면서도 한장의 부드러운 곡면의 쉘로 구성되어 있다. 최초의 Shellular는 리쏘그래피를 이용하여 제조되며 3주기최소곡면의 일종인 P-곡면과 유사한 형태를 갖는다. 본 연구에서는 와이어 직조에 기반하여 D-곡면과 유사한 Shellular를 제작하는 새로운 방법을 제시한다. 실험과 유한요소해석을 통하여 압축하중 하의 재료물성을 평가하고 종래의 극저밀도 재료와 비교하였다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1999년도 제14차 학술회의논문집
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• pp.41-44
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• 1999

Nonlinear sliding surface design in variable structure systems for spacecraft attitude control problems is studied. A robustness analysis is performed for regular form of system, and calculation of actuator bandwidth is presented by reviewing sliding surface dynamics. To achieve non-singular attitude description and minimal parameterization, spacecraft attitude control problems are considered based on modified Rodrigues parameters(MRP). It is shown that the derived controller ensures the sliding motion in pre-determined region irrespective of unmodeled effects and disturbances.

• 대한족부족관절학회지
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• 제6권2호
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• pp.201-207
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• 2002

Purpose: To present the clinical analysis of the results obtained in 38 cases of displaced intraarticular calcaneal fractures undergone combined percutaneous axial pin fixation of calcaneal body and minimal internal fixation using extensile lateral approach. Materials and Methods: From March 2000 to February 2002, thirty-eight displaced intraarticular fractures of the calcaneus in 35 patients were fixed with 3.5mm cannulated screws and percutaneous 2.5mm K-wires. The extensile lateral approach was used in all cases. The average follow-up period was 16 months. Clinical evaluation was assessed according to the Ankle-Hind Foot Scale of American Orthopedic Foot and Ankle Society. Results: The clinical results were graded as excellent in 8 cases(21%), good in 22 cases(58%), fair in 6 cases(16%), and poor in 2 cases(5%). Two cases of poor result were type IV of Sanders classification. The postoperative reduction status of the articular surface was analyzed by computed tomography in all cases and was found to be less 2mm of step off in 30 cases and between 2 and 4mm in 8 cases. Unsatisfactory results were correlated with severity of articular comminution and failure to obtain accurate reduction of the articular surface. Using early functional postoperative care, all fractures healed without secondary displacement except 1 case on an average of ten weeks. Two cases had superficial necrosis of the wound margins, however, secondary wound healing was uneventful and skin grafting was not needed. Conclusion: Combined minimal internal fixation and percutaneous pin fixation using extensile lateral approach is useful operative method of intraarticular calcaneal fractures because providing enough stability to permit functional aftercare and allowing excellent anatomical reduction. In addition, this method diminishes the risk of lateral soft tissue problems.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2002년도 proceedings of the second asia international conference on tribology
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• pp.309-310
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• 2002

A minimal quantity lubrication (MQL) machining is able to achieve both functions of cooling and lubrication with an extremely low quantity of a cutting fluid and a large amount of air blow. Using a biodegradable ester oil, turning tests were carried out to evaluate the effectiveness of the MQL system. It was found that the performance of MQL cutting was equivalent to, or better than, that of conventional cutting, because the MQL system tends to prevent the heat damage of the tool tip and, if an effective lubricant such as a particular polyol ester is applied to the system, it can avoid the extensive transfer of workpiece materials on to the tool surface.

• 대한수학회지
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• 제32권4호
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• pp.803-814
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• 1995

Let $\Sigma$ be the class of all complex-valued, harmonic, orientation-preserving, univalent mappings defined on $\Delta = {z : $\mid$z$\mid$ > 1}$ that map $\infty$ to $\infty$.

• 한국재료학회지
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• 제27권10호
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• pp.563-568
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• 2017

In this study, the coating of an Al-Cr layer on the surface of a Zircaloy-4 alloy was carried out through plasma pretreatment coating and a laser surface melting process. Two different conditions for laser treatment, severe or minimal surface melting of the Zr alloy substrate, were applied to form the final coating. When there was significant surface melting of the Zr alloy, the solidification microstructure of the newly formed coating layer was mainly composed of needle-shaped $Al_3Zr$, Al(Cr) and $Al_7Cr$ phases. On the other hand, the solidification microstructure of the coating layer was mainly composed of Al(Cr) and $Al_7Cr$ phases when there was minimal surface melting of Zr base in the laser process. However, when the coating was maintained at $1100^{\circ}C$ for 2 hours, significant inter-diffusion occurred between the phases in the coating. As a result, the upper part of the coating layer was observed to mainly consist of $Al_3Zr$ and $Al_8Cr_5$ phases, regardless of the laser treatment conditions.