• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2003년도 추계 학술발표회논문집
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• pp.326-333
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• 2003

Most long-span bridges such as a cable-stayed bridges have a number of long-period modes due to the flexibility, thus the design concept extending the natural period of structures using base isolation system may be difficult to use directly to these structures. But, the effectiveness of LRB for cable-stayed bridges is indicated in several papers. In this study, the guidelines of designing LRB for a seismically excited cable-stayed bridge using benchmark cable-stayed bridge are presented. The design properties of LRB are chosen that the design index(DI) is minimized or little changed for variation of properties. And the seismic performance of designed LRB is also investigated. The consequences show that the perforamnce of designed LRB is better than that of simply designed LRB for several history earthquakes. Moreover, the design properties of LRB are researched to several diffrent dominant frequency of earthquake. The results present that the plastic and elastic stiffness of LRB are affected by the dominant frequency of earthquake.

• Steel and Composite Structures
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• 제33권3호
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• pp.403-432
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• 2019

Axially functionally graded (AFG) beams are a new class of composite structures that have continuous variations in material and/or geometrical parameters along the axial direction. In this study, the exact analytical solutions for the free vibration of AFG and uniform beams with general elastic supports are obtained by using Euler-Bernoulli beam theory. The elastic supports are modeled with linear rotational and lateral translational springs. Moreover, the material and/or geometrical properties of the AFG beams are assumed to vary continuously and together along the length of the beam according to the power-law forms. Accordingly, the accuracy, efficiency and capability of the proposed formulations are demonstrated by comparing the responses of the numerical examples with the available solutions. In the following, the effects of the elastic end restraints and AFG parameters, namely, gradient index and gradient coefficient, on the values of the first three natural frequencies of the AFG and uniform beams are investigated comprehensively. The analytical solutions are presented in tabular and graphical forms and can be used as the benchmark solutions. Furthermore, the results presented herein can be utilized for design of inhomogeneous beams with various supporting conditions.

• 한국산업융합학회 논문집
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• 제25권4_2호
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• pp.645-653
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• 2022

Recently, deep reinforcement learning has been applied to a variety of industries, such as games, robotics, autonomous vehicles, and data cooling systems. An algorithm called reinforcement learning allows for automated asset allocation without the requirement for ongoing monitoring. It is free to choose its own policies. The purpose of this paper is to carry out an empirical analysis of the performance of asset allocation strategies. Among the strategies considered were the conventional Mean- Variance Optimization (MVO) and the Proximal Policy Optimization (PPO). According to the findings, the PPO outperformed both its benchmark index and the MVO. This paper demonstrates how dynamic asset allocation can benefit from the development of a reinforcement learning algorithm.

• Archives of Plastic Surgery
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• 제41권2호
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• pp.116-121
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• 2014

Background Understanding risk factors that increase readmission rates may help enhance patient education and set system-wide expectations. We aimed to provide benchmark data on causes and predictors of readmission following inpatient plastic surgery. Methods The 2011 National Surgical Quality Improvement Program dataset was reviewed for patients with both "Plastics" as their recorded surgical specialty and inpatient status. Readmission was tracked through the "Unplanned Readmission" variable. Patient characteristics and outcomes were compared using chi-squared analysis and Student's t-tests for categorical and continuous variables, respectively. Multivariate regression analysis was used for identifying predictors of readmission. Results A total of 3,671 inpatient plastic surgery patients were included. The unplanned readmission rate was 7.11%. Multivariate regression analysis revealed a history of chronic obstructive pulmonary disease (COPD) (odds ratio [OR], 2.01; confidence interval [CI], 1.12- 3.60; P=0.020), previous percutaneous coronary intervention (PCI) (OR, 2.69; CI, 1.21-5.97; P=0.015), hypertension requiring medication (OR, 1.65; CI, 1.22-2.24; P<0.001), bleeding disorders (OR, 1.70; CI, 1.01-2.87; P=0.046), American Society of Anesthesiologists (ASA) class 3 or 4 (OR, 1.57; CI, 1.15-2.15; P=0.004), and obesity (body mass index ${\geq}30$) (OR, 1.43; CI, 1.09-1.88, P=0.011) to be significant predictors of readmission. Conclusions Inpatient plastic surgery has an associated 7.11% unplanned readmission rate. History of COPD, previous PCI, hypertension, ASA class 3 or 4, bleeding disorders, and obesity all proved to be significant risk factors for readmission. These findings will help to benchmark inpatient readmission rates and manage patient and hospital system expectations.

• 재무관리연구
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• 제26권1호
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• pp.189-220
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• 2009

본 연구는 약형 EMH에 대한 반론으로 제기되어 왔던 모멘텀전략과 반대전략의 우월성에 대하여 검정하였다. 모멘텀전략과 반대전략이 우월한 전략이라면 이는 약형 EMH에 대한 중대한 비판이 된다. 하지만 몬테카를로 시뮬레이션 결과에 따르면 기존의 검정방법은 유의수준왜곡이라는 오류를 갖고 있는 것으로 나타났다. 이에 본 연구는 데이터 스누핑 편의를 해결하는 것으로 알려진 White (2000)의 사실성 체크검정을 이용하여 모멘텀전략과 반대전략의 우월성을 검정하였다. 검정결과는 다음과 같다. 종합주가지수에 대한 정액정기매입전략을 벤치마크 포트폴리오로 정하였을 때 평균수익률을 이용하면 모멘텀전략 중 최선의 전략은 벤치마크 포트폴리오보다 우월한 것으로 나타났다. 하지만 위험을 고려한 성과측정치인 샤프비율을 이용할 경우 모멘텀전략과 반대전략 중 최선의 전략은 우월한 전략이라고 볼 수 없었다. 따라서 위험을 고려한다면 모멘텀전략과 반대전략의 우월성을 근거로 약형 EMH를 기각할 수는 없다.

• Smart Structures and Systems
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• 제23권1호
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• pp.1-14
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• 2019

Control algorithms are the most important aspects in successful control of structures against earthquakes. In recent years, intelligent control methods rather than classical control methods have been more considered by researchers, due to some specific capabilities such as handling nonlinear and complex systems, adaptability, and robustness to errors and uncertainties. However, due to lack of learning ability of fuzzy controller, it is used in combination with a genetic algorithm, which in turn suffers from some problems like premature convergence around an incorrect target. Therefore in this research, the introduction and design of the Fuzzy Cooperative Coevolution (Fuzzy CoCo) controller and Adaptive Neural-Fuzzy Inference System (ANFIS) have been innovatively presented for semi-active seismic control. In this research, in order to improve the seismic behavior of structures, a semi-active control of building using Magneto Rheological (MR) damper is proposed to determine input voltage of Magneto Rheological (MR) dampers using ANFIS and Fuzzy CoCo. Genetic Algorithm (GA) is used to optimize the performance of controllers. In this paper, the design of controllers is based on the reduction of the Park-Ang damage index. In order to assess the effectiveness of the designed control system, its function is numerically studied on a 9-story benchmark building, and is compared to those of a Wavelet Neural Network (WNN), fuzzy logic controller optimized by genetic algorithm (GAFLC), Linear Quadratic Gaussian (LQG) and Clipped Optimal Control (COC) systems in terms of seismic performance. The results showed desirable performance of the ANFIS and Fuzzy CoCo controllers in considerably reducing the structure responses under different earthquakes; for instance ANFIS and Fuzzy CoCo controllers showed respectively 38 and 46% reductions in peak inter-story drift ($J_1$) compared to the LQG controller; 30 and 39% reductions in $J_1$ compared to the COC controller and 3 and 16% reductions in $J_1$ compared to the GAFLC controller. When compared to other controllers, one can conclude that Fuzzy CoCo controller performs better.

• 한국음향학회지
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• 제30권6호
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• pp.303-307
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• 2011

본 논문에서는 주파수 영역에서의 주요 피크를 선정하고, 주파수 크기 응답에 따라 각기 다른 스텝 사이즈를 사용하는 QIM 오디오 워터마킹을 제안한다. 오디오 신호에 대해 사각 윈도우로 오버랩 없이 L샘플을 취하고 영교차율을 통해 해당 프레임에 워터마크 삽입 가능 여부를 판단 후 푸리에 변환을 통해 주파수 영역에서의 크기 응답을 구한다. 프레임 별 주파수 크기 응답의 최대값에 따라 스텝 사이즈를 결정하고 스펙트럼에서 주요 피크 n개를 검출하여 주변 샘플 w개를 포함한 $n{\times}(w+1)$개 샘플에 대해 QIM을 이용하여 워터마크를 삽입한다. 워터마크 검출은 유클리디안 거리 (Euclidean distance)를 이용한 블라인드 검출 방식으로 수행된다. 오디오 워터마크 벤치마킹을 통한 강인성 검증에서 대부분 강인한 특성을 보였다.

• 기술혁신연구
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• 제21권3호
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• pp.41-72
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• 2013

정보화 사회의 도래에 따른 정보통신기술의 발전과 활용이 국가 경제구조 및 성장에 급격한 영향을 미치고 있는 추세에 맞춰 본 연구는 자료포락분석과 맘퀴스트지수를 활용하여 국가별 정보통신기술의 활용성과를 상대적 효율성 및 생산성의 관점에서 접근하고자 하였다. 투입요소로 ICT환경과 ICT이용준비도 그리고 산출물로 ICT활용도를 이용하여 총 28개 국가를 대상으로 2008년부터 2011년 동안 정보통신기술 활용성과를 진단한 결과, 자료포락분석에서는 전체적인 ICT 효율성이 감소한 것으로 나타나 외형적 성장에 비해 실질적인 ICT 활용 부문은 부진한 것으로 판단되었고, 맘퀴스트지수 분석결과에서도 전체적인 ICT 생산성은 지난 3개년 구간동안 개선되지 않은 것으로 분석되었다. 이러한 분석결과를 종합적으로 고려해 볼 때, ICT 활용성과를 제고하기 위해서는 지금까지 추진해온 물리적 요소의 양적 투입에 의존하는 외형적 개발정책보다는 투입요소와 산출물을 합목적적으로 연계시키고 ICT 활용 효율성을 증진시킬 수 있는 다각적인 운영 합리화 방안이 필요하다고 본다.

• Steel and Composite Structures
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• 제50권3호
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• pp.299-318
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• 2024

The main objective of this paper is to compute the far-field acoustic radiation (sound radiation) of functionally graded plates (FGM) loaded by sinusoidally varying point load subjected to the arbitrary boundary condition is carried out. The governing differential equations for thin functionally graded plates (FGM) are derived using classical plate theory (CPT) and Rayleigh integral using the elemental radiator approach. Four cases, segregated on power-law index k=0,1,5,10, are studied. A novel approach is illustrated to compute sound fields of vibrating FGM plates using the physical neutral surface with an elemental radiator approach. The material properties of the FGM plate for all cases are calculated considering the power law indexes. An in-house MATLAB code is written to compute the natural frequencies, normal surface velocities, and sound radiation fields are analytically calculated using semi-analytical formulation. Ansys is used to validate the computed sound power level. The parametric effects of the power law index, modulus ratios, different constituent of FGM plates, boundary conditions, damping loss factor on the sound power level, and radiation efficiency is illustrated. This work is the benchmark approach that clearly explains how to calculate acoustic fields using a solid layered FGM model in ANSYS ACT. It shows that it is possible to asymptotically stabilize the structure by controlling the intermittent layers' stiffness. It is found that sound fields radiated by the elemental radiators approach in MATLAB, ANSYS and literatures are in good agreement. The main novelty of this research is that the FGM plate is analyzed in the low-frequency range, where the stiffness-controlled region governs the whole analysis. It is concluded that a clamped mono-ceramic FGM plate radiates a lesser sound power level and higher radiation efficiency than a mono-metallic or metal-rich FGM plate due to higher stiffness. It is found that change in damping loss factor does not affect the same constituents of FGM plates but has significant effects on the different constituents of FGM plates.

• 지능정보연구
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• 제22권4호
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• pp.177-192
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• 2016

기계학습(Machine Learning)은 인공 지능의 한 분야로, 데이터를 이용하여 기계를 학습시켜 기계 스스로가 데이터 분석 및 예측을 하게 만드는 것과 관련한 컴퓨터 과학의 한 영역을 일컫는다. 그중에서 SVM(Support Vector Machines)은 주로 분류와 회귀 분석을 목적으로 사용되는 모델이다. 어느 두 집단에 속한 데이터들에 대한 정보를 얻었을 때, SVM 모델은 주어진 데이터 집합을 바탕으로 하여 새로운 데이터가 어느 집단에 속할지를 판단해준다. 최근 들어서 많은 금융전문가는 기계학습과 막대한 데이터가 존재하는 금융 분야와의 접목 가능성을 보며 기계학습에 집중하고 있다. 그러면서 각 금융사는 고도화된 알고리즘과 빅데이터를 통해 여러 금융업무 수행이 가능한 로봇(Robot)과 투자전문가(Advisor)의 합성어인 로보어드바이저(Robo-Advisor) 서비스를 발 빠르게 제공하기 시작했다. 따라서 현재의 금융 동향을 고려하여 본 연구에서는 기계학습 방법의 하나인 SVM을 활용하여 매매성과를 올리는 방법에 대해 제안하고자 한다. SVM을 통한 예측대상은 한국형 변동성지수인 VKOSPI이다. VKOSPI는 금융파생상품의 한 종류인 옵션의 가격에 영향을 미친다. VKOSPI는 흔히 말하는 변동성과 같고 VKOSPI 값은 옵션의 종류와 관계없이 옵션 가격과 정비례하는 특성이 있다. 그러므로 VKOSPI의 정확한 예측은 옵션 매매에서의 수익을 낼 수 있는 중요한 요소 중 하나이다. 지금까지 기계학습을 기반으로 한 VKOSPI의 예측을 다룬 연구는 없었다. 본 연구에서는 SVM을 통해 일 중의 VKOSPI를 예측하였고, 예측 내용을 바탕으로 옵션 매매에 대한 적용 가능 여부를 실험하였으며 실제로 향상된 매매 성과가 나타남을 증명하였다.