• International Journal of Aeronautical and Space Sciences
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• 제10권1호
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• pp.67-74
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• 2009

In general, the lunar landing stage can be divided into two distinct phases: de-orbit and descent, and the descent phase usually comprises two sub-phases: braking and approach. And many optimization problems of minimal energy are usually focused on descent phases. In these approaches, the energy of de-orbit burning is not considered. Therefore, a possible low perilune altitude can be chosen to save fuel for the descent phase. Perilune altitude is typically specified between 10 and 15km because of the mountainous lunar terrain and possible guidance errors. However, it requires more de-orbit burning energy for the lower perilune altitude. Therefore, in this paper, the perilune altitude of the intermediate orbit is also considered with optimal thrust programming for minimal energy. Furthermore, the perilune altitude and optimal thrust programming can be expressed by a function of the radius of a parking orbit by using continuation method and co-state estimator.

• 한국항공운항학회지
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• 제23권1호
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• pp.49-55
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• 2015

This paper deals with dynamic modeling and controller design of a future Korean lunar module planned to be launched 2020's in Korea. For dynamic modeling of the lunar module, we first assume the lunar module as a rigid body. And we derive equations of motion for the lunar module by considering allocation of main thrusters and reaction thrusters. With the equation of motion, we design the controller based on the quaternion. A Pulse Width Pulse Frequency modulator(PWPFM) is selected for generating on/off signal. Finally, we construct a 2-phase descent mode including initial guidance mode, terminal guidance mode. The MATLAB simulation is performed for evaluating the descent ability and final landing velocity. The dynamic modeling and descent simulation of the lunar module in this paper could be applied for developing the future work of the Korean lunar exploration program.

• 한국전문물리치료학회지
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• 제22권3호
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• pp.12-22
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• 2015

The purpose of this study was to investigate the effect of taping on knee joint for patellofemoral compressive force (PCF) during stair descent for elderly women. Ten healthy elderly women voluntarily participated in this study. A three-dimensional motion analysis system and force plates were used to analyze the movements of the joints for the lower extremities. The results were as follows: There were no significant differences for the maximum PCF, maximum quadriceps contraction force and maximum knee extension moment (p>.05) but, there was a pattern decreasing all values with the taping during stair descent. There were significant differences for the knee and ankle angle on the event of maximum PCF (p<.05) and there was a pattern decreasing all values with the taping during stair descent. Therefore, taping on the knee would be effective to relieve the pain like patellofemoral pain syndrome in the knee joint.

• 복식
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• 제63권2호
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• pp.125-143
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• 2013

This study aims to clarify the identity of contemporary Chinese fashion design by examining how the characteristics of Chinese tradition are accepted and presented in fashion under the influences of western cultures. This study performed a literature survey on related works. Also this study performed demonstrative analysis of Chinese daily newspapers (People's Daily and Xinmin Evening News, 2007-2010) and fashion collections by Chinese and Chinese descent designers(2007-2011). The results are as follows: First, China is trying to express Chinese traditional ideas and factors in the design areas, and also trying to achieve an universal generalization. Second, the Chinese designers emphasized traditional ideas and culture in their designs. The Chinese descent designers were affected more by western culture. The common aesthetic consciousness were the beauties of sophisticated and splendorous decoration, vastness and elegance. Also the compromised images, neutral images and antique images were common in both groups. Third, the Chinese designers presented fashion designs on formalized and imitation stage. Also they tried to make a metaphorical stage. The Chinese descent designers showed designs on a metaphorical stage. In conclusion, the contemporary Chinese fashion design should find the way to globalize and identity of the traditional culture code simultaneously.

• Genomics & Informatics
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• 제5권3호
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• pp.95-101
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• 2007

In this paper, we consider the variable selection methods in the Cox model when a large number of gene expression levels are involved with survival time. Deciding which genes are associated with survival time has been a challenging problem because of the large number of genes and relatively small sample size (n<

• 전자공학회논문지CI
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• 제38권1호
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• pp.1-6
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• 2001

본 논문에서는 Hebb 학습법에 기초한 Kohonen의 LVQ 학습법을 퍼셉트론 학습에 사용되는 경도 강하 (Gradient descent) 학습법에 의해 재해석한다. Kohonen의 LVQ는 학습법에 따라 두 가지로 나뉠 수 있는데 하나는 자율학습 LVQ(ULVQ)이며 다른 하나는 타율학습 LVQ(SLVQ)이다. 두 경우 모두 출력뉴런의 목표 값을 적당히 생성할 경우 타율학습 경도 강하학습법으로 표현될 수 있다. 결과적으로 LVQ학습법은 타율학습 경도 강하 학습법의 특수한 형태임을 알 수 있으며 또한 LVQ는 보다 일반화된 '퍼셉트론 형태의 LVQ(PLVQ)'알고리즘으로 표현될 수 있음을 알 수 있다. 본 논문에서는 이를 증명하고 결론을 맺는다.

• 한국전자파학회논문지
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• 제29권1호
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• pp.68-76
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• 2018

표적 우선순위 할당은 다수의 표적이 존재하는 전술 환경에서 다기능 레이다(Multifunction Radar: MFR)가 중요한 표적을 추적하고 레이다 자원을 효율적으로 관리하기 위해 필요한 기능이다. 본 논문에서는 레이다에서 수집한 정보로부터 표적에 대한 우선순위를 산출하는 인공 신경망(Artificial Neural Network: ANN) 모델을 구현한다. 더 나아가, 기존의 경사 하강법(gradient descent) 기반 역전파(backpropagation) 알고리즘을 발전시켜 표적 우선순위 할당에 더욱 적합한 최급 강하법(steepest descent) 기반 신경망 학습 알고리즘을 제안한다. 시뮬레이션에서는 훈련 데이터와 신경망의 결과값 사이의 오차와 특정 테스트 시나리오에서 할당된 우선순위의 합리성을 분석하여 제안된 방법의 성능을 확인한다.

• 한국운동역학회지
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• 제25권3호
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• pp.249-256
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• 2015

Objective : The purposes of this study was to perform a kinematical analysis on age and walkway types in elderly women subjects. Method : Forty subjects participated in the experiment (A1 group - age: $67.30{\pm}1.49yrs$, height: $153.81{\pm}4.47cm$, weight: $61.80{\pm}5.24kg$, A2 group - age: $71.70{\pm}1.10yrs$, height: $152.01{\pm}2.84cm$, weight: $59.69{\pm}7.34kg$, A3 group - age: $76.80{\pm}0.98yrs$, height: $150.16{\pm}6.08cm$, weight: $57.27{\pm}6.42kg$, A4 group - age: $81.80{\pm}0.60yrs$, height: $152.18{\pm}4.77cm$, weight: $55.80{\pm}7.78kg$). The study method adopted was the 3D analysis with six cameras. Ground type were classifed as gait pattern on flat, ascent and descent ramp. For the statistical analysis, the SPSS 21.0 was used to perform Repeated measured Two-way ANOVA. Results : In velocity of CM, there was faster movement on flat ground. When it came to the velocity of right toe, there was no significance in early mid-swing of right foot, but A4 was the slowest in late mid-swing of right foot on flat ground. In joint angle in left foot strike, the left hip joint and knee joint were more flexed in descent ramp, In addition left and right ankle joints were more plantarflexed in descent ramp, and left ankle joint was more plantarflexed in the over 75 yrs age groups. Conclusion : The higher age group were more flexed in lower body joints during descent ramp.

• 한국항공우주학회지
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• 제46권5호
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• pp.402-409
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• 2018

이 논문에서는 무인 달착륙 임무를 위해 고려하고 있는 달착륙 시나리오를 제안하고 제안된 시나리오를 기반으로 동력하강단계에서의 최적화 착륙궤적을 구현한다. 동력하강단계에서 달착륙선의 자세 변화는 사용 연료량뿐만 아니라 영상기반 항법의 센서 운용에도 영향을 주므로 자세 변화가 급격하게 이루어지지 않도록 자세각속도를 최적제어 가격함수에 포함하고 이때 자세각속도의 영향을 조절하는 가중치가 최적화 착륙궤적에 미치는 영향을 분석한다. 분석된 결과를 바탕으로 연료 사용을 최소화하고 안정된 자세 변화를 갖도록 최적화 착륙궤적을 설계할 수 있는 적절한 가중치를 제시한다.

• Journal of the Korean Data and Information Science Society
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• 제27권4호
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• pp.911-923
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• 2016

빅데이터 시대에 머신러닝의 중요성은 더욱 부각되고 있고 로지스틱 회귀는 머신러닝에서 분류를 위한 방법으로 의료, 경제학, 마케팅 및 사회과학 전반에 걸쳐 널리 사용되고 있다. 지금까지 R과 Hadoop의 통합환경인 RHIPE 플랫폼은 설치 및 MapReduce 구현의 어려움으로 인해 거의 연구가 이루지 지지 않았다. 본 논문에서는 대용량 데이터에 대해 로지스틱 회귀 추정을 위한 두가지 알고리즘 즉, Gradient Descent 알고리즘과 Newton-Raphson 알고리즘에 대해 MapReduce로 구현하고, 실제 데이터와 모의실험 데이터를 가지고 이들 알고리즘 간의 성능을 비교하고자 한다. 알고리즘 성능 실험에서 Gradient Descent 알고리즘은 학습률에 크게 의존하고 또한 데이터에 따라 수렴하지 않는 문제를 갖고 있다. Newton-Raphson 알고리즘은 학습률이 불필요 할 뿐만 아니라 모든 실험 데이터에 대해 좋은 성능을 보였다.