• Korean Journal of Mathematics
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• 제18권4호
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• pp.369-380
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• 2010

We give a criterion for vertex extremal length parabolicity of locally finite planar graphs, and use it to show that a disk triangulation graph is circle packing parabolic if and only if its immediate finer graphs are circle packing parabolic.

• 한국세라믹학회지
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• 제31권9호
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• pp.989-994
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• 1994

This study aims at finding the closest packings of regular shape particles such as sphere, circle rod and hexagonal rod type. As the ratio of particle size to container lowered to less than 1/10, the wall effect decreased gradually. The tap density of spherical particles with almost orthorhombic arrangement was 59.5%, while those of circle rod and hexagonal rod type particles were 63.5% and 63.0% respectively. And it was decreased with increasing the aspect ratio of regular particles. The tap density of binary mixtures was larger than that corresponding to the monosized particles packing by about 15%. The tap density of ternary mixtures was larger than that of corresponding to the packing of binary mixtures by about 9%. This work employed the binary mixture of 60% coarse particles and 40% fine particles with size ratio of 1.0 to 1/10 and the ternary mixture of 60% coarse particles, 20% medium and 20% fine particles with size ratio of 1:1/10:1/400 respectively.

• 대한화학회지
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• 제34권1호
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• pp.29-36
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• 1990

Cholesteryl pentyl carbonate $(C_{33}H_{56}O_3)$의 분자 및 결정구조를 X-선 회절법으로 연구하였다. 이 결정은 단사정계에 속하며 공간군은$P2_1$이며, 단위세포 상수는 a = 12.484(3), b = 9.043(3), c = 14.053(3)$\AA$, ${\beta} = 94.12(2)^{\circ}$이다. Four-circle automatic diffractometer로 회절 강도들을 얻었으며, 구조는 cholesteryl octanoate의 원자좌표를 시행구조로 이용 결정하였고 최소자승법으로 정밀화하였다. 최종 신뢰도 R 값은 1164개의 반점들에 대하여 0.12이었다. Cholesteryl부분의 결합길이와 결합각은 정상적이나 pentyl기는 이 영역에서의 열적 진동 때문에 결합길이가 짧았다. b-축을 따르는 $2_1$ screw symmetry에 의해 관련된 인접한 분자들은 서로 반대로 나란히 놓여 있으며 monolayer를 형성하고 있다. Monolayer 내에서 cholesteryl군들이 서로 촘촘히 쌓인 구조를 만들어 Monolayer Type II packing mode에 해당하며, cholesteryl hexanoate, octanoate, hexyl carbonate, oleate 등의 결정구조들과 비슷한 구조로 되어 있다.

• 대한기계학회논문집A
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• 제25권6호
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• pp.1004-1014
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• 2001

The fully automatic algorithm from initial finite element mesh generation to remeshing in two dimensional geometry is introduced using bubble packing method (BPM) for finite element analysis. BPM determines the node placement by force-balancing configuration of bubbles and the triangular meshes are made by Delaunay triangulation with advancing front concept. In BPM, we suggest two node-search algorithms and the adaptive/recursive bubble controls to search the optimal nodal position. To use the automatically generated mesh information in FEA, the new enhanced bandwidth minimization scheme with high efficiency in CPU time is developed. In the remeshing stage, the mesh refinement is incorporated by the control of bubble size using two parameters. And Superconvergent Patch Recovery (SPR) technique is used for error estimation. To verify the capability of this algorithm, we consider two elasticity problems, one is the bending problem of short cantilever beam and the tension problem of infinite plate with hole. The numerical results indicate that the algorithm by BPM is able to refine the mesh based on a posteriori error and control the mesh size easily by two parameters.

• 대한수학회보
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• 제54권4호
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• pp.1361-1371
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• 2017

In this paper, we introduce a framework of (${\alpha},{\beta}$)-flows on triangulated manifolds with two and three dimensions, which unifies several discrete curvature flows previously defined in the literature.

• 한국항행학회논문지
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• 제25권3호
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• pp.211-216
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• 2021

다수 무인기를 이용한 시스템은 정찰, 네트워킹, 항공 촬영 등 다양한 목적으로 활용되고 있다. 이러한 시스템에서 다수 무인기로 구성된 대형을 형성하고 유지하는 것은 필수적이다. 본 논문에서는 다수 무인기의 대형을 형성하기 위한 자율화된 분산형 제어를 수행하는 알고리즘을 제안하였다. 제어명령은 근접 무인기 또는 임무 영역으로부터 서로 밀어내는 방향으로 작용하는 2차 시스템 형태의 힘을 고려하였다. 제어명령은 외부의 개입 없이 계측과 통신으로부터 획득되는 상대위치/속도를 통해 계산된다. 이는 개별 무인기들이 기준거리를 추종하도록 하며 임무영역 안에 겹치지 않고 최대한 조밀하게 배치되도록 한다. 기준거리 결정에는 채우기 문제를 풀기 위한 최적화 기법과 유사한 방식을 적용하였다. 임무영역은 형성하고자 하는 대형의 외곽선으로 정의되며 임무에 따라 유동적으로 설정될 수 있다. 제안한 알고리즘의 성능을 확인하기 위하여 수치 시뮬레이션을 수행하였다. 복잡성과 확장성을 고려한 영역에서 약 26.94초에 대형이 형성되며 약 71.91%의 채우기 밀도를 가지는 것을 확인하였다.

• Bulletin of the Korean Chemical Society
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• 제10권2호
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• pp.177-184
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• 1989

The structure of cholesteryl isobutyrate, $(CH_3)_2CHCOOC_{27}H_{45}$, was determined by single crystal X-ray diffraction methods. Cholesteryl isobutyrate crystallized monoclinic space group $P2_1$, with a = 15.115 (8)${\AA}$, b = 9.636 (5)${\AA}$, c = 20.224 (9)${\AA}$, ${\beta}$ = 93.15 (5)$^{\circ}$, z = 4, $D_c = 1.03 g/cm^3 $and Dm= 1.04 g/$cm^3$. The intensity data were measured for the 3417 reflections, within $sin{\theta}/{\lambda} = 0.59{\AA}^{-1}$, using an automatic four-circle diffractometer and graphite monochromated Mo-$K_{\alpha}$ radiation. The structure was solved by fragment search Patterson methods and direct methods and refined by full-matrix least-squares methods. The final R factor was 0.129 for 2984 observed reflections. The two symmetry-independent molecules (A) and (B) are almost fully extended. The molecules are in antiparallel array forming monolayers with thickness $d_{100}$ = 15.2${\AA}$, and molecular long axes are nearly parallel to the [$\bar{1}$01] directions. The two distinct molecules form separate stacks with almost the same orientations, but with differing degrees of steroid overlap. Thers is a close packing of cholesteryl groups within the monolayers. The packing type is similar to those of cholesteryl hexanoate and cholesteryl oleate.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2008년도 추계 학술논문 발표대회
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• pp.117-120
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• 2008

The Purpose of this is properties of CFT filled with expansion concrete. CFT(concrete filled steel tube) is the structure that circle shape steel column filled with concrete. 3 kinds of expansive additives and variation of replacement rate. we changed expansive additive from 0%, 10%, 20%, 30% of ratio of addition rate are selected for this experiment. Merits of CFT are concrete internal force rising influenced by steel shape restriction, reinforcing the local buckling, excellent resistance to transformation. Generally, High rise building using CFT utilize the high strength and fluidity concrete for packing the tube inside. As the result a steel tube charged expensive concrete has stiffness 1.5times more than a steel tube not charged concrete. Increase of resisting power about compressive stress by binding expansion of expansive concrete affects strength increase and softness.

• Computers and Concrete
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• 제27권3호
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• pp.283-295
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• 2021

Existing meso-scale models of concrete need to refine the mesh grids of aggregate and cement mortar, which may greatly reduce the computational efficiency. To overcome this problem, a novel meso-scale modeling strategy, which is based on rigid body spring method and Voronoi diagram, is proposed in this study to establish the meso-scale model of concrete. Firstly, establish numerical aggregate models according to user-defined programs. Circle aggregates are adopted due to their high efficiency in generation and packing process, and the grading of aggregate are determined according to the distribution curve proposed by Full and Thompson; Secondly, extract the centroids of aggregates, and then develop the Voronoi diagram in which aggregate centroids are defined as initial scatters; Finally, establish the rigid body spring model for concrete based on the Voronoi diagram. Aggregates are represented by rigid blocks, and assumed to be unbreakable. Cement mortar is concentrated into the interface between adjacent blocks and represented by two uniform springs. The number of grids is consistent with that of aggregates in specimens, and no mesh-refinement of aggregates and cement mortar is required. The accuracy and efficiency of the proposed modeling strategy are firstly identified by comparing the numerical results with the experimental ones, and then the applicability of the proposed strategy with different volume percentage occupied by aggregates is investigated.