• 대한조선학회논문집
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• 제58권2호
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• pp.90-96
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• 2021

In this study, the method of determining the state of grid points in the adaptable surface particle method based on grid system developed as a free-surface tracing method was improved. The adaptable surface particle method is a method of determining the state of the grid point according to the shape of the free-surface and obtaining the intersection of the given free-surface and grid line where the state of the grid point changes. It is difficult to determine the state of grid points in the event of rapid flow, such as collision or separation of free-surfaces, and this study suggests a method for determining the state of current grid points using the state of surrounding grid points where the state of grid point are known. A grid layer value was assigned sequentially to a grid away from the free-surface, centering on the boundary cell where the free-surface exists, to identify the connection information that the grid was separated from the free-surface, and to determine the state of the grid point sequentially from a grid away from the free-surface to a grid close to the free-surface. To verify the improved method, a numerical analysis was made on the problem of dam break in which a sudden collision of free-surface occurred and the results were compared, and the results were relatively reasonable.

• 한국과학교육학회지
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• 제26권1호
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• pp.1-8
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• 2006

본 연구에서는 고등학교 학생들의 성취 목적(과제지향/수행 지향/수행 회피), 유능감 등의 동기 변인과 학습 전략(심층적/피상적), 자기 조절 능력 등의 인지 변인 및 화학 선다형 수리 문제 해결력 사이의 인과관계를 경로 분석을 통해 조사하였다. 연구 결과, 유능감과 과제 지향 목적은 자기 조절 능력을 통하여 화학 수리 문제 해결력에 긍정적 영향을 미쳤으며, 특히 유능감은 인지 변인을 경유하지 않고도 직접적으로 화학 수리 문제 해결력에 긍정적 영향을 주는 것으로 조사되었다. 인지 변인 중 심층적 학습 전략은 유능감과 과제 지향 목적의 영향을 받았고 피상적 학습 전략은 수행 회피 목적의 영향을 받았으나, 이러한 학습 전략과 화학 수리 문제 해결력 사이에는 인과관계가 존재하지 않았다.

• 한국과학교육학회지
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• 제26권1호
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• pp.16-24
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• 2006

본 연구에서는 실생활 소재를 사용한 문제해결형과 과제해결형 탐구 활동을 적용했을 때, 학생 간 상호작용의 양상을 조사하였다. 연구를 위해, 충북 청원군 소재 중학교 3학년 학생 5명의 실험 수업을 관찰하고, 녹음 및 녹화 후 기록 원고를 작성 분석하였다. 학생들의 대화를 질문, 설명, 사고, 메타인지의 4가지 상호작용 유형으로 분류하고, 각 유형별 학습 접근 수준은 심층적-피상적 접근으로 분류하였다. 실험 형태별 언어적 상호작용의 수와 학습 접근 수준 비교 결과, 문제해결형 탐구실험은 문제점 발견에서 해결까지 상호작용의 수가 문제 발생 이전에 비해 2배 가량 증가하는 것을 볼 수 있었으며, 심층적 접근 수준의 상호작용의 수도 4배 정도 증가하는 것으로 나타났다. 한편, 과제해결형 탐구실험에서는 실험과정 중 상호작용의 수가 고루 분포하였다. 또한 학생들은 문제해결형 탐구실험에서 보다 많은 심층적 접근의 상호작용을 보이는 것으로 나타났다.

• 대한치과보철학회지
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• 제42권3호
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• pp.261-266
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• 2004

Statement of problem. The effects of surface roughness have not or insufficiently been analyzed on earlier events such as cell adhesion though cell behavior most germane to implant performance is cell adhesion. Purpose. The purpose of this study was to evaluate cell adhesion of osteoblast-like cells (MG63) onto three types of titanium disks with varying roughness using the Elisa assay. Materials and methods. Representative disks from each group (SLA, HA, machined) were subjected to surface analysis and surface roughness was measured by the optical interferometer (Accura 2000, Intekplus Co., Seoul, Korea). Following this, MG63 cells were cultured on the titanium disks and released. Cell adhesion measurements using the Elisa assay were performed specifically at three points: after 24, 48, and 72 hours of culture. Results. Among the 3 types of surface analyzed, the SLA surface was the roughest with a Ra value of $1.114{\mu}m$ followed by HA coated surface and machined surface, consecutively. The optical density values for the SLA surface group was significantly higher than that of the machined and HA coated surface groups following 24 and 48 hours of culture. The cell culture on HA coated surface showed significantly higher values compared to the machined surface following 24, 48 and 72 hours of culture. Conclusion. The results suggest that surface treatment of titanium surfaces enhanced cell adhesion of human osteoblast-like cells (MG63).

• 한국도서관정보학회지
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• 제45권2호
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• pp.205-234
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• 2014

이 연구는 우리나라 학교도서관 비정규직 인력 문제에 대해 구조적인 관점으로 살펴보고 정리하였다. 비정규적 인력이 확대된 배경과 계기를 살펴보고 비정규직 인력의 직무상 주요 문제점들을 검토하였다. 그리고 비정규직 인력 문제의 표면과 이면의 내용과 구조를 체계적으로 탐구하여 문제의 성격과 내적 갈등 양상을 확인하였다. 이를 바탕으로 현재 제안되거나 진행되고 있는 비정규직 인력 문제의 해결 방안에 대해 점검하고 문제 해결을 위해 요청되는 기본적인 자세를 제안하였다.

• Structural Engineering and Mechanics
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• 제48권2호
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• pp.241-255
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• 2013

The receding contact problem for two elastic layers whose elastic constants and heights are different supported by two elastic quarter planes is considered. The lower layer is supported by two elastic quarter planes and the upper elastic layer is subjected to symmetrical distributed load whose heights are 2a on its top surface. It is assumed that the contact between all surfaces is frictionless and the effect of gravity force is neglected. The problem is formulated and solved by using Theory of Elasticity and Integral Transform Technique. The problem is reduced to a system of singular integral equations in which contact pressures are the unknown functions by using integral transform technique and boundary conditions of the problem. Stresses and displacements are expressed depending on the contact pressures using Fourier and Mellin formula technique. The singular integral equation is solved numerically by using Gauss-Jacobi integration formulation. Numerical results are obtained for various dimensionless quantities for the contact pressures and the contact areas are presented in graphics and tables.

• 산업경영시스템학회지
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• 제29권1호
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• pp.63-71
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• 2006

In this paper, we consider a planning problem arising from printed circuit board manufacturing industries. Given a set of several types of PCBs, component feeders and surface mounting machines in series in a PCB assembly line, the problem is to define the feeder allocation and job sequence with the objective of minimizing the total operation time of the line. We formulate the problem as a mathematical model. And, the problem is proven to be NP-hard, so a genetic algorithm is developed. Finally, we give test results to evaluate the performance of the genetic algorithm.

• Tribology and Lubricants
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• 제20권6호
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• pp.343-349
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• 2004

The adsorption of soot particles onto a sensor surface of the engine soot detector posses a critical problem in the measurement. In order to prevent the optical rod surface from soot contamination, various functional coatings and flow-induced cleaning were applied to the surface in this work. For surface coatings, various materials of self-assembled monolayers (SAM) such as OTS (octadecyltrichlorosilane), PFDTES (perfluorodecyl-triethoxysilane) and PFDTMS (perfluorodecyltrimethoxysilane) were coated on the optical rod surface ,which have different characteristics in both hydrophobicity and oleophobicity. These coatings were tested with soot content varying from $0\%\;to\;3wt\%$ and oil temperature from 20 to $70^{\circ}C$. Test results showed that surface coatings were not effective for preventing the adsorption of soot panicles on the surface of optical rod. It was thought that these coatings provided the surface with additional attractive surface forces. However, it was found that adsorption of soot particles onto a sensor surface was minimized by flow-induced cleaning. This effect was tested with varying the flow velocity.

• Steel and Composite Structures
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• 제35권4호
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• pp.555-566
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• 2020

This paper aims to present an analytical methodology to investigate influences of nanoscale and surface energy on buckling stability behavior of perforated nanobeam structural element, for the first time. The surface energy effect is exploited to consider the free energy on the surface of nanobeam by using Gurtin-Murdoch surface elasticity theory. Thin and thick beams are considered by using both classical beam of Euler and first order shear deformation of Timoshenko theories, respectively. Equivalent geometrical constant of regularly squared perforated beam are presented in simplified form. Problem formulation of nanostructure beam including surface energies is derived in detail. Explicit analytical solution for nanoscale beams are developed for both beam theories to evaluate the surface stress effects and size-dependent nanoscale on the critical buckling loads. The closed form solution is confirmed and proven by comparing the obtained results with previous works. Parametric studies are achieved to demonstrate impacts of beam filling ratio, the number of hole rows, surface material characteristics, beam slenderness ratio, boundary conditions as well as loading conditions on the non-classical buckling of perforated nanobeams in incidence of surface effects. It is found that, the surface residual stress has more significant effect on the critical buckling loads with the corresponding effect of the surface elasticity. The proposed model can be used as benchmarks in designing, analysis and manufacturing of perforated nanobeams.

• Journal of Ship and Ocean Technology
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• 제11권3호
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• pp.39-50
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• 2007

This study aims the observation of wing-in-ground effect near free surface. Numerical computations are carried out to observe the deformation of free surface and the effects on lift and drag. The detailed flow fields around two- and three-dimensional wings with NACA 0012 section are observed from the results of a commercial CFD program, FLUENT, and the local deformations of free surface are obtained by applying a Rankine panel method. In the present cases, the small deformation of free surface under the wings is observed, but different forces are found between solid wall and free surface when the speed of wings becomes large.