• 한국산학기술학회논문지
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• 제13권11호
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• pp.5487-5495
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• 2012

무선 센서 네트워크 환경에서 클러스터키 등의 보안키를 적용하기 위한 중요한 고려 사항은 보안키 갱신이 안전하게 이루어져야 하고, 보안키 갱신 시 요구되는 시간과 비용이 적어야 한다는 점이다. 각 센서 노드는 제한된 에너지를 보유하기 때문에 보안키 갱신에 소모되는 에너지가 클 경우 전체 네트워크 수명에 많은 영향을 준다. 따라서 안전하고 에너지 효율적인 보안키 관리 방법이 요구된다. 본 논문에서는 그룹을 기반으로 한 에너지 효율적인 클러스터키 관리 방안을 제안한다. 제안하는 방법에서 대규모 센서 네트워크에서 안전하고 효율적인 키 관리를 위해 5개의 보안키를 사용하고, 섹터, 클러스터 및 그룹 수준의 보안 적합도를 관리하여 보안키 갱신 주기 및 보안에 사용되는 다항식의 차수를 차별화시킨다. 실험을 통해 이전의 보안키 관리 기법보다 네트워크 에너지 효율성이 향상됨을 입증한다.

• 한국정보과학회논문지:시스템및이론
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• 제35권8호
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• pp.361-371
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• 2008

본 논문에서, 정이진트리와 노드수가 증가함에 따라 분지수가 증가하는 하이퍼큐브, 하이퍼피터슨 연결망을 분지수가 고정된 피터슨-토러스(PT) 연결망에 일대일 임베딩 하였다. 일대일 임베딩은 일대다 임베딩이나 다대일 임베딩과 비교하여 프로세서의 낭비나 프로세서의 과부하의 위험이 적다. 하이퍼큐브나 하이퍼 피터슨에서 개발된 알고리즘들이 피터슨-토러스에서 사용될 때 유휴 프로세세가 많지 않도록 확장율 ${\doteqdot}1$, 연장율 1.5n+2 그리고 밀집율 O(n)에 일대일 임베딩 하였고, 메시지 전송길이에 영향을 받지 않는 웜홀 라우팅 방식의 시스템에서 메시지의 병목현상을 피할 수 있도록 정이진트리를 PT 네트워크에 밀집율 1, 확장율 ${\doteqdot}5$ 그리고 연장율 O(n)에 일대일 임베딩 하였다.

• 정보과학회 논문지
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• 제44권1호
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• pp.78-83
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• 2017

최대 밀도 부분 그래프는 소셜 네트워크에서 사용자들이 속한 특정 커뮤니티나 사용자들의 공통 관심사를 나타내기에, 최대 밀도 부분 그래프를 찾는 연구가 다수 있었다. 그러나 기존의 연구들은 단일한 최고 밀도 부분 그래프를 찾는다는 문제점이 있었다. 이 연구에서는 주어진 노드에서 시작하여, 인접하는 노드 중에 연결수(degree)가 가장 높은 노드를 추가하는 방식을 사용한 최고 밀도 부분 그래프를 찾는 상향식 휴리스틱 알고리즘을 제안한다. 이에 따라, 병렬 처리에 용이하게 하였고, 이를 맵리듀스 프레임 워크 상에서 병렬 알고리즘으로 구현하였다. 다양한 그래프 데이터로 실험결과 이전 연구와 비교하여 조기에 최고 밀도 부분 그래프를 찾아냄을 보였다. 또한 다양한 다수의 노드가 주어졌을 때에도 효과적으로 동작함을 보였다.

• 한국콘텐츠학회논문지
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• 제9권8호
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• pp.49-56
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• 2009

본 논문에서는 무선 ad-hoc 네트워크에서 보다 효율적인 라우팅을 위해 기존의 에너지, 연결강도와 이력 정보를 추가하는 CDS 구성 방법을 제안한다. 무선 ad-hoc 네트워크에서는 CDS(connected dominating set)를 구성할 때 보다 빠르고 간단하며 효율적인 전력 소모 관리가 가능한 알고리즘이 필요하다. CDS로 결정된 노드는 그렇지 않은 노드에 비해 통신량이 많기 때문에 CDS는 최소화 되어야 하며 지속적인 위치 이동이 이루어지지 않는 무선 ad-hoc 네트워크에서는 가장 효율적연 CDS를 결정하고 망 구성이 이루어진 후 가급적 재구성 되지 않아야 한다. 이 문제점들을 개선하고자 기존에 제안된 EL + ND 기반 CDS 구성법보다 효율적인 EL + ND + Sel 기반 CDS 구성법을 제안하고 실험을 통하여 성능을 비교 검증하였다.

• 대한건축학회논문집:계획계
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• 제35권12호
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• pp.105-114
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• 2019

The goal of this study is to quantitatively evaluate the effects of the additional construction of urban railroads. To this end, 1) establish accessibility as a measure of quantitative evaluation of construction effects; 2) select the 'Integration' of Space Syntax as a quantifiable indicator of accessibility; 3) represent the Seoul railroads as a network; 4) calculate the 'Integration' form the network before and after the additional construction of the urban railroads. By calculating the change of the 'Integration' of the individual nodes and the change of the sum of the 'Integration' of given zones, the change in accessibility of a particular node and the change in accessibility of a particular region were calculated. After analyzing the change in accessibility in nodes and areas as well, it was confirmed that the additional construction of urban railroads was improving accessibility as a whole of Seoul. It was also identified that there was a degree of difference in the extent of the accessibility change for the different areas. It is particularly noteworthy that changes occur in the accessibility ranking. While certain regions were improving relative rankings, others fell in rank. With this finding, it could be argued that active consideration of the areas in which the relative decline occurs is needed when the planned urban railroad is being built.

• Structural Engineering and Mechanics
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• 제66권3호
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• pp.329-341
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• 2018

This paper considers the smooth receding contact problem between a homogeneous half-plane and a composite laminate composed of an inhomogeneously coated elastic layer. The inhomogeneity of the elastic modulus of the coating is approximated by an exponential function along the thickness dimension. The three-component structure is pressed together by either a concentrated force or uniform pressures applied at the top surface of the composite laminate. Both semianalytical and finite element analysis are performed to solve for the extent of contact and the contact pressure. In the semianalytical formulation, Fourier integral transformation of governing equations and boundary conditions leads to a singular integral equation of Cauchy-type, which can be numerically integrated by Gauss-Chebyshev quadrature to a desired degree of accuracy. In the finite element modeling, the functionally graded coating is divided into homogeneous sublayers and the shear modulus of each sublayer is assigned at its lower boundary following the predefined exponential variation. In postprocessing, the stresses of any node belonging to sublayer interfaces are averaged over its surrounding elements. The results obtained from the semianalytical analysis are successfully validated against literature results and those of the finite element modeling. Extensive parametric studies suggest the practicability of optimizing the receding contact peak stress and the extent of contact in multilayered structures by the introduction of functionally graded coatings.

• Journal of Gastric Cancer
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• 제1권4호
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• pp.197-201
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• 2001

Purpose: There are variants of gastric cancer assoclated with predominantly peritoneal spread of with haematogenous metastases. Perioperative intraperitoneal chemotherapy as an adjuvant to surgery is considered as a rational therapeutic modality to prevent peritoneal spread. We evaluated the influence of early postoperative intraperitoneal chemotherapy on the prognosis of resectable advanced gastric cancer. Materials and Methods: From 1990 to 1995, 246 patients with biopsy proven advanced gastric cancer were enrolled in the study. Among them 123 patients received early postoperative intraperitoneal mitomycin C and 5-fluorouracil. The survival rate was calculated using by the Kaplan-Meier method and was compared using the log-rank test according to 13 clinico-pathologic factors. Multivariate analysis was performed with the Coxproportional hazards model. Results: Gastric resection plusearly postoperative intraperitoneal chemotherapy showed an improved survival rate as compared to surgery alone ($54.1\%\;versus\;40.3\%;$ P=0.0325). Depth of tumor invasion, degree of regional lymph vode metastasis, distant metastasis, tumor size, tumor location, extent of gastric resection, and curability of surgery significantly influenced survival. When a multivariate analysis was performed, depth of tumor invasion, lymph node metastasis, early postoperative intraperitoneal chemotherapy, curability of surgery, and extent of gastric resection emerged as the statistically significant and independent prognostic factors. Conlusion: Early postoperative intraperitoneal chemotherapy is one of the independent prognostic indicators of resectable advanced gastric cancer.

• 대한기계학회논문집
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• 제19권6호
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• pp.1439-1450
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• 1995

Bellows is a familiar component in piping systems as it provides a relatively simple means of absorbing thermal expansion and providing system flexibility. In routine piping flexibility analysis by finite element methods, bellows is usually considered to be straight pipe runs modified by an appropriate flexibility factor; maximum stresses are evaluated using a corresponding stress concentration factor. The aim of this study is to develop a bellows finite element, which similarly includes more complex shell type deformation patterns. This element also does not require flexibility or stress factors, but evaluates more detailed deformation and stress patterns. The proposed bellows element is a 3-D, 2-noded line element, with three degrees of freedom per node and no bending. It is formulated by including additional 'internal' degrees of freedom to account for the deformation of the bellows corrugation; specifically a quarter toroidal section of the bellows, loaded by axial force, is considered and the shell type deformation of this is include by way of an approximating trigonometric series. The stiffness of each half bellows section may be found by minimising the potential energy of the section for a chosen deformation shape function. An experiment on the flexibility is performed to verify the reliability for bellows finite element.

• 한국농공학회논문집
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• 제57권6호
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• pp.59-68
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• 2015

Traditional structure analysis method is based on numerical matrix analysis to use the geometries consisting of the structure. The characteristics require a lot of computer memories and computational time. To avoid these weaknesses, new approach to analyze truss structure was suggested by adopting topological load redistribution method. The axial forces to be not structurely analyzed yet against outside loads were redistributed by using nodal equation of equilibrium randomly at each node without constructing global matrix. However, this method could not calculate the axial forces if structure is statically indeterminate due to degree of many indeterminacies. Therefore, to apply the method suggested in this research, all redundancies of truss structure were replaced by unit loads. Each unit load could make the deformation of a whole structure, and a superposition method was finally adopted to solve the simultaneous equations. The axial forces and deflections agreed with the result of commercial software within the relative error of 1 %, whereas in the case that the axial forces are relatively very smaller than others, the relative errors were increased to 2 %. However, as the values were small enough not to be considered, it was practically useful as a structural analysis model. This model will be used for structural analysis of truss type of large structure such as agricultural farming facility.

• 대한설비공학회지:설비저널
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• 제15권1호
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• pp.87-96
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• 1986

An experiment on the devices that enchance the stratification of storage tanks in a solar heat ins system has been carried out. The benefits of thermal stratification in sensible heat storage are to increase the system performance such as the collector efficiency or the fraction of the total load supplied by solar energy. Using the diffuser and the distributor as the stratification enchancement device, the expeliments were perfomed in the different condition of diameter and material of the distributor. As a result of experiments, there exists the diameter of distributor in which the stratification is made maximum under certain design and operation condition. Also it was identified that the kind of distributor material influenced the degree of stratification. Comparing the experimental result to the computational results calculated under the same conditions, the node number N(stratification index) was determined. The results of computer simulation that was performed about the actual solar heating system in Seoul for 24 hours show the relative advantage of stratified over well-mixed storage and the significant improvements in system performance.