• Proceedings of the KSME Conference
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• 2008.11a
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• pp.603-608
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• 2008

It is well known that the topology optimization for plastic problem is not easy since the iterative analyses to evaluate the objective and cost function with respect to the design variation are very time-consuming. The finite element limit analysis is an efficient tool which is possible to predict collapse modes and sequential collapse loads of a structure considering not only large deformation but also plastic material behavior with moderate computing cost. In this paper, the optimum topology of a structure considering large and plastic deformation is obtained using the finite element limit analysis. To verify the constructed optimization code, topology optimizations of some typical problems are performed and the optimal topologies by elastic design and plastic design are compared.

• 한국정보디스플레이학회:학술대회논문집
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• 2002.08a
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• pp.163-166
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• 2002

We studied the growth of large-grain pentacene film by organic vapour phase deposition. The optimizations of the growth of pentacene are carried out by varying the gas pressure in the reactor and substrate temperature. We found that the grain size depends strongly on the gas pressure in the reactor. The grain size of $20{\mu}m$ has been obtained at the gas pressure of 200 Torr. The film was found to be strongly (001) oriented and its grain size decreases with decreasing the gas pressure.

• Journal of Computing Science and Engineering
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• v.6 no.1
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• pp.26-38
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• 2012

Java has been increasingly used in programming for real-time systems. However, some of Java's features such as automatic memory management and dynamic compilation are harmful to time predictability. If these problems are not solved properly then it can fundamentally limit the usage of Java for real-time systems, especially for hard real-time systems that require very high time predictability. In this paper, we propose to exploit multicore computing in order to reduce the timing unpredictability that is caused by dynamic compilation and adaptive optimization. Our goal is to retain high performance comparable to that of traditional dynamic compilation, while at the same time, obtain better time predictability for Java virtual machine (JVM). We have studied pre-compilation techniques to utilize another core more efficiently, preoptimization on another core (PoAC) scheme to replace the adaptive optimization system (AOS) in Jikes JVM and the counter based optimization (CBO). Our evaluation reveals that the proposed approaches are able to attain high performance while greatly reducing the variation of the execution time for Java applications.

• Proceedings of the Korean Information Science Society Conference
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• 2005.11b
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• pp.58-60
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• 2005

대표적인 데이터마이닝 문제중의 하나인 연관규칙 탐사에는 지금까지 Apriori 기반의 많은 알고리즘들이 개발되어 왔다. 본 논문에서는 비트맵을 이용한 Apriori 알고리즘 구현방안을 제시한다. 우선, 핵심연산인 비트맵 논리곱(Bitmap AND)과 비트 카운팅(bit-counting)을 컴퓨터 CPU의 고급 기술을 이용해서 효과적으로 구현할 수 있음을 보인다. 또한, 트랜잭션 데이터를 비트맵으로 표현함으로써, 기존 Apriori와는 달리, 비트맵 논리곱 연산을 획기적으로 줄일 수 있는 방법을 제시한다. BAR의 이러한 구현기법을 통해, Apriori 기반의 최신 구현 방법에 비해, 성능이 최대 30배 정도 향상됨을 보인다.

• Journal of Communications and Networks
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• v.13 no.6
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• pp.612-620
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• 2011

Recently, one of the problems with the Internet is the issue of scalability. To this end, locator/identifier separation protocol (LISP), which separates end-system identifiers and routing locators, has been proposed as a solution. In the LISP deployed network, the ingress and egress nodes of inter-AS traffic is determined by edge router selection (ERS) and endpoint identifier-routing locator mapping assignment (ERMA). In this paper, joint optimizations of ERS and ERMA for stub networks with and without predetermined link weights are studied and the mixed integer linear programming (MILP) formulations for the problems are given. To make the problem with optimizable link weights tractable, a revised local search algorithm is also proposed. Simulation results show that joint optimization of ERS and ERMA enables better network performance.

• Proceedings of the KIEE Conference
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• 1997.07b
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• pp.383-385
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• 1997

Back-propagation is one of the efficient algorithms used to nonlinear optimizations or controls. In spite of its structual simplicity and learning ability, learning time is very long or bad case converge local minimum on complicate input patterns. In order to improve these matters varing learning rate and momentums were proposed. In this paper, to improve its performance fuzzy is adjusted in parameters, learning rate and momentums. Parameters are adjusted by errors and change of errors adaptively. In order to evaluate proposed method simulated with MATLAB on inverted pendulum.

• International Journal of Fluid Machinery and Systems
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• v.2 no.2
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• pp.179-188
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• 2009

Recent development of high speed computers and use of optimization techniques have given a big momentum of turbomachinery design replacing expensive experimental cost as well as trial and error approaches. The surrogate based optimization techniques being used for aerodynamic turbomachinery designs coupled with Reynolds-averaged Navier-Stokes equations analysis involve single- and multi-objective optimization methods. The objectives commonly tried to improve were adiabatic efficiency, pressure ratio, weight etc. Presently coupling the fluid flow and structural analysis is being tried to find better design in terms of weight, flutter and vibration, and turbine life. The present article reviews the surrogate based optimization techniques used recently in turbomachinery shape optimizations.

• Journal of the Optical Society of Korea
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• v.15 no.2
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• pp.187-195
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• 2011

We have designed two photonic crystal waveguide (PCW) structures with output focused beams in order to achieve more coupling between photonic devices and decrease the mismatch losses in photonic integrated circuits. PCW with coupled resonator optical waveguide (CROW) termination has been optimized by both one dimensional (1D) and seven dimensional (7D) particle swarm optimization (PSO) algorithms by evaluating the fitness function by the finite difference time domain (FDTD) method. The 1D and 7D-optimizations caused the factors of 2.79 and 3.875 improvements in intensity of the main lobe compared to the non-optimized structure, whereas the FWHM in 7D-optimized structure was increased, unlike the 1D case. It has also been shown that the increment of focusing causes decrement of the bandwidth.

• The Journal of the Acoustical Society of Korea
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• v.17 no.4
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• pp.23-29
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• 1998

본 논문은 foraming층이 음파의 전달 특성에 미치는 영향 및 멘드릴형 광섬유 하이 드로폰의 광음향 감도 특성에 미치는 영향을 분석한 것이다. 유한 요소법을 이용하여 foaming층의 내부 구조에 따른 음파의 전달 특성을 분석하였고, AL(Aluminium)/foaming 및 Nylon/foaming 멘드릴(mandrel) 각각에 대하여 foaming층의 재질 및 두께 변화에 따른 광음향감도 변화를 분석하였다. 그 결과, foaming층 내의 구조변화의 영향을 무시할 수 있 었다. 또한 AL al cNylon층상 복합체인 멘드릴에서 foaming층의 탄성율이 낮을수록, 두께 가 증가할수록 공음향 감도는 증가하였다. 그러므로 1GPa 이하의 탄성율을 지닌 두꺼운 Foaming층을 사용하여 층상 복합체 멘드릴을 구성하는 것이 광음향 감도의 향상을 위하여 효율적이다.

• The Journal of the Acoustical Society of Korea
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• v.17 no.4
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• pp.30-37
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• 1998

본 논문은 중공형 층상 복합체 멘드릴(mandrel)을 이용하여 기본 공진주파수가 15kHz이상이고, 우수한 감도 특성을 지닌 광섬유 하이드로폰의 최적 구조를 설계하는 것에 관한 것이다. 유한요소법을 이용하여 Al/foraming 및 Nylon/foaming층상 복합체의 공지주 파수를 분석하여 설계 변수의 범위를 결정하였고, 멘드릴 형상에 따른 광음향 감도 특성을 분석하여 최적구조를 결정하였다. 그 결과로 멘드릴의 외경이 감소할수록, 길이가 증가할수 록 감도가 향상되었다. AL 멘드릴의 경우, 내경/외경 비가 낮을수록, Nylon멘드릴의 경우 내경/외경 비가 높을수록 감도 증가를 위하여 효율적이다. 그리고 결정된 최적구조의 Al/foaming 및 Nylon/foaming멘드릴을 사용한 광섬유 하이드로폰의 감도는 각각 1rad./Pa 대비 약 82dB 및 85.7dB 정도 이었고, Al층상 복합체 보다는 Nylon층상 복합체를 이용하는 것이 고 감도의 광섬유 하이드로폰을 제조하는데 유리함을 알 수 있었다.