• 대한산업공학회지
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• 제26권2호
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• pp.117-127
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• 2000

In this paper, we propose a new convex combination weight rule for the cross decomposition method which is known to be one of the most reliable and promising strategies for the large scale optimization problems. It is called generalized cross decomposition, a modification of linear mean value cross decomposition for specially structured linear programming problems. This scheme puts more weights on the recent subproblem solutions other than the average. With this strategy, we are having more room for selecting convex combination weights depending on the problem structure and the convergence behavior, and then, we may choose a rule for either faster convergence for getting quick bounds or more accurate solution. Also, we can improve the slow end-tail behavior by using some combined rules. Also, we provide some computational test results that show the superiority of this strategy to the mean value cross decomposition in computational time and the quality of bounds.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제16권1호
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• pp.319-333
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• 2022

In order to enhance system energy efficiency, bidirectional link resource allocation strategy in GFDM-based multiuser SWIPT systems is proposed. In the downlink channel, each SWIPT user applies power splitting (PS) receiver structure in information decoding (ID) and non-linear energy harvesting (EH). In the uplink channel, information transmission power is originated from the harvested energy. An optimization problem is constructed to maximize weighted sum ID achievable rates in the downlink and uplink channels via bidirectional link power allocation as well as subcarriers and subsymbols scheduling. To solve this non-convex optimization problem, Lagrange duality method, sub-gradient-based method and greedy algorithm are adopted respectively. Simulation results show that the proposed strategy is superior to the fixed subcarrier scheme regardless of the weighting coefficients. It is superior to the heuristic algorithm in larger weighting coefficients scenario.

• 한국전기전자재료학회논문지
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• 제29권1호
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• pp.30-34
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• 2016

In this paper, we report that selective etching on N-polar face by EC (electro-chemical)-etching effect on the reduction of bowing and strain of FS (free-standing)-GaN substrates. We applied the EC-etching to concave and convex type of FS-GaN substrates. After the EC-etching for FS-GaN, nano porous structure was formed on N-polar face of concave and convex type of FS-GaN. Consequently, the bowing in the convex type of FS-GaN substrate was decreased but the bowing in the concave type of FS-GaN substrate was increased. Furthermore, the FWHM (full width at half maximum) of (1 0 2) reflection for the convex type of FS-GaN was significantly decreased from 601 to 259 arcsec. In the case, we confirmed that the EC-etching method was very effective to reduce the bowing in the convex type of FS-GaN and the compressive stress in N-polar face of convex type of FS-GaN was fully released by Raman measurement.

• 한국실내디자인학회논문집
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• 제21권1호
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• pp.203-210
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• 2012

Since a private museums started in Europe 17C, many private museums established for high-class people like aristocrats to collect and to keep art works and to appreciate for limited members. After the French Revolution in 18C, the publicity became an important social issue through all European regions, and the museum gradually changed into public ones. Like that, as the concept of museum changed, its social role as well as its function was also changed. The concept of collection and display or preservation changed into the concept of exhibition and appreciation featuring the publicity. With the year-round exhibition, a classical concept, the planned-exhibition, a new active concept set as an important factor for a museum's projects. The latter concept embraces new social issues. Therefore as the space for planned-exhibitions reflecting social issues every season was needed, a museum sets its planned-exhibition space with the changeability, and gradually expands this kind of space in size. It is expected that planned-exhibition spaces characterized as the changeability may give some changes on the flow of a museum's overall space, and may have substantial influences on the flow. To recognize the changes in a planned-exhibition space's influence on the museum, this study selected some national, public museums having the planned-exhibition space, and investigated their influences on each museum's overall space structure through the analysis on space syntax. This study assumed the change of planned-exhibition space as the changes in the number of convex spaces, and measured it. And to understand the planned-exhibition's changes on a museum's overall spaces, such changed assumed as the numeric changes in convex spaces and measured them. In addition, the numeric changes's influence on the overall space structure was analyzed by measuring the overall space's average integration level. Through the above two factors, the 3 research methodologies and analyzed results were drawn out.

• 한국방사선학회논문지
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• 제16권7호
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• pp.975-984
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• 2022

선형 탐촉자는 탐촉자의 길이만큼의 관심 영역을 갖기 때문에 장비에 탑재된 virtual convex 기능을 사용하여 관심 영역을 확장 시킬 수 있다. 하지만 관심 시각 영역의 변화에 따라 초음파 음속 방향의 변화로 인해 화질에 영향을 미칠 것으로 생각되어 이를 객관적으로 확인하고자 하였다. 본 연구를 위해 초음파 정도 관리용 팬텀의 영상 평가와 SNR·CNR을 측정하였다. 그 결과 팬텀 영상 평가에서는 두 영상 모두 기능적 분해능, 회색조 및 동적 범위에서 모두 구조물 식별이 가능했다. 하지만 구조물의 크기와 형태 재현성에는 Standard 영상이 우수한 것을 확인할 수 있었다. SNR·CNR 평가결과, 특정 위치의 구조물을 제외하고는 대부분이 Trapezoidal 영상의 SNR·CNR이 낮았다. 또한, 통계 분석 그래프를 통해 낭성 구조물의 크기가 작아질수록 깊이별 SNR과 CNR이 감소하는 것을 추가로 확인할 수 있었다. 본 연구를 통해 기능사용이 넓은 관심 시각 영역을 제공하는 장점이 있으나 화질에 영향을 준다는 것을 확인할 수 있었으며 Virtual Convex 기능사용 시 검사자는 이를 적절한 상황에 사용하고 질 높은 영상 획득과 장비의 이해도와 숙련도 향상을 위해 다양한 연구를 해야 할 것으로 판단된다.

• Structural Engineering and Mechanics
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• 제5권5호
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• pp.565-576
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• 1997

The material-based homogenization design method generates arbitrary topologies of initial structural design as well as reinforcement structural design by controlling the amount of material available. However, if a small volume constraint is specified in the design of Lightweight structures, thin and slender structures are usually obtained. For these structures stability becomes one of the most important requirements. Thus, to prevent overall buckling (that is, to increase stability), the objective of the design is to maximize the buckling load of a structure. In this paper, the buckling analysis is restricted to the linear buckling behavior of a structure. The global stability requirement is defined as a stiffness constraint, and determined by solving the eigenvalue problem. The optimality conditions to update the design variables are derived based on the sequential convex approximation method and the dual method. Illustrated examples are presented to validate the feasibility of this method in the design of structures.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2007년도 심포지엄 논문집 정보 및 제어부문
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• pp.149-151
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• 2007

For several decades, VSC has gained much attention as one of the useful design tools for handling the practical system with uncertainties or disturbances. Generally, the disturbances in the matching condition can be perfectly rejected via VSC; however, these in the mismatching condition are known to be hardly rejected. There have been some trials on it, in which the resulting controls in fact belong to the class of robust control guaranteeing disturbance ${\gamma}$-attenuation. Therefore, in this paper, we propose a new Variable Structure Control (VSC) for a system with mismatched disturbances. The proposed controller is composed of linear and nonlinear parts; the former plays a role in stabilizing the system and the latter takes care of attenuating the disturbances. The main contribution is to introduce the concept of switching-zone, rather than switching-surface, that is designed through piece-wise Lyapunov functions. The resulting non-convex conditions are formulated with an iterative linear programming algorithm, which provides an excellent performance of almost rejecting the disturbances.

• Nuclear Engineering and Technology
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• 제53권5호
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• pp.1416-1428
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• 2021

Pebble flow characteristics can be significantly affected by the configuration of pebble bed, especially for HTGR pebble beds. How to achieve a desired uniform flow pattern without stagnation is the top priority for reactor design. Pebbles flows inside some specially designed pebble bed with arc-shaped contraction configurations at the bottom, including both concave-inward and convex-outward shapes are explored based on discrete element method. Flow characteristics including pebble retention, residence-time frequency density, flow uniformity as well as axial velocity are investigated. The results show that the traditionally designed pebble bed with cone-shape bottom is not the most preferred structure with respect to flow pattern for reactor design. By improving the contraction configuration, the flow performance can be significantly enhanced. The flow in the convex-shape configuration featured by uniformity, consistency and less stagnation, is much more desirable for pebble bed design. In contrast, when the shape is from convex-forward to concave-inward, the flow shows more nonuniformity and stagnation in the corner although the average cross-section axial velocity is the largest due to the dominant middle pebbles.

• 대한수학회보
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• 제34권2호
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• pp.211-223
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• 1997

Lehmann [13] introduced the concept of positive(negative) dependence together with some other dependence concepts. Since then, a great numerous multivariate inequalities have been obtained. For a references of available results, see Karlin and Rinott [12], Ebrahimi and Ghosh [8] and Sampson [14]. Whereas a number of dependence notions exist for multivariate processes (see Friday [10]), recently, Ebrahimi [7] introduced some new dependence concepts of the hitting times of stochastic processes.

• Journal of applied mathematics & informatics
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• 제6권3호
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• pp.959-968
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• 1999

In this paper we are obtained new results for bivariate pro-cesses which help us to tell the dependent structure among hitting times of the processes. We are proposed both dependence properties and the-oretical results among the processes and certain kinds of dependence properties when we are imposed on processes are reflected as analo-gous properties of corresponding hitting times. Finlly we are given some examples to illustrate these concepts.