• 응용통계연구
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• 제27권6호
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• pp.975-989
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• 2014

연속적인 변수 선택과 계수 추정을 동시에 활용할 수 있다는 특성 때문에 LASSO (Tibshirani, 1996)와 Elastic Net (Zou와 Hastie, 2005)은 다양한 분야에서 활발하게 사용되고 있다. 조건부 라플라스와 이중 파레토 사전분포를 적용한 공액계층모형을 표현하였고, 각각의 사전분포에 대한 완전 조건 사후분포를 도출하였다. 제안된 사전분포를 적용한 벌점회귀모형을 비교하기 위한 모의 실험을 진행하였고, 예측정확도를 판단하기 위해 아시아 국가 실패(the collapse of governments in Asia)의 실제 데이터에 제안한 모형을 적용하였다.

• 대한의용생체공학회:의공학회지
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• 제42권6호
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• pp.268-276
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• 2021

Functional near-infrared spectroscopy-based brain-computer interface (fNIRS-based BCI) has been receiving much attention. However, we are practically constrained to obtain a lot of fNIRS data by inherent hemodynamic delay. For this reason, when employing machine learning techniques, a problem due to the high-dimensional feature vector may be encountered, such as deteriorated classification accuracy. In this study, we employ an elastic net-based feature selection which is one of the embedded methods and demonstrate the utility of which by analyzing the results. Using the fNIRS dataset obtained from 18 participants for classifying brain activation induced by mental arithmetic and idle state, we calculated classification accuracies after performing feature selection while changing the parameter α (weight of lasso vs. ridge regularization). Grand averages of classification accuracy are 80.0 ± 9.4%, 79.3 ± 9.6%, 79.0 ± 9.2%, 79.7 ± 10.1%, 77.6 ± 10.3%, 79.2 ± 8.9%, and 80.0 ± 7.8% for the various values of α = 0.001, 0.005, 0.01, 0.05, 0.1, 0.2, and 0.5, respectively, and are not statistically different from the grand average of classification accuracy estimated with all features (80.1 ± 9.5%). As a result, no difference in classification accuracy is revealed for all considered parameter α values. Especially for α = 0.5, we are able to achieve the statistically same level of classification accuracy with even 16.4% features of the total features. Since elastic net-based feature selection can be easily applied to other cases without complicated initialization and parameter fine-tuning, we can be looking forward to seeing that the elastic-based feature selection can be actively applied to fNIRS data.

• 대한수학회보
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• 제49권5호
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• pp.961-987
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• 2012

A compartment model of the flow driven by pumping without valves (valveless pumping) in an open tank system is proposed. By the open tank system, we mean that two rigid cylindrical tanks are connected with an elastic tube. An incompressible fluid fills this system up to a certain level in tanks under the gravity. The compartment model for analyzing such open system is derived from the energy principle which will be called the energy conserving compartment model or shortly the ECCM. Based on this ECCM of valveless pumping, we explore the occurrence of directional net flow or directional net power by a specific excitation at an asymmetric part of the elastic tube. The interaction between deformable elastic tube and the fluid inside is considered in the ECCM. The reliability of the ECCMis investigated through some physical examples. The ECCM shows the existence of directional net power of the valveless pump system with open tanks and confirms that the direction and magnitude of the net power depend on the pumping frequency as well. Furthermore, the phase synchronization in time between the fluid pressure difference and the external pinching force over the pumping region is highly related to the direction of energy storing or net power.

• 응용통계연구
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• 제23권1호
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• pp.207-218
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• 2010

일반화가법모형은 기존 선형회귀모형의 문제점을 대부분 해결한 통계모형이지만 의미있는 독립변수의 수를 줄이는 방법이 적용되지 않을 경우 과대적합 문제가 발생할 수 있다. 그러므로 일반화가법모형에서 변수 축소방법을 적용하는 연구가 필요하다. 회귀분석에서 변수 축소방법으로 최근에는 Lasso 계열의 접근법이 연구되고 있다. 본 연구에서는 활용성이 높은 통계모형인 일반화가법모형에 Lasso 계열의 모형 중에서 Group Lasso와 Elastic net 모형을 적용하는 방법을 제시하고 이들의 해를 구하는 절차를 제안하였다. 그리고 제안된 방법을 모의실험과 실제자료인 회계년도 2005년 자동차보혐 자료에 적용을 통해 비교하여 보았다. 그 결과 본 논문에서 제안한 Group Lasso와 Elastic net을 이용하여 변수 축소를 통한 일반화가법모형이 기존의 방법보다 더 나은 결과를 제공하는 것으로 분석 되었다.

• 한국음향학회지
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• 제42권4호
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• pp.364-369
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• 2023

두 개 수신기에 들어오는 신호 간의 시간 지연 추정 기술은 수중 음향 뿐만 아니라 실내 음향 및 로보틱스에 이르기까지 다양한 분야에서 응용되고 있는 기술이다. 시간 지연 추정 기술에는 수신기 사이 상호 상관으로부터 시간 지연량을 추정하는 방법이 한 기술 부류이고, 수신기 사이의 시간 지연을 파라메트릭 모델링을 하여 그 파라미터를 시스템 인식의 방법으로 추정하는 기술 부류가 있다. 두 부류 중 후자의 경우 시스템의 파라미터 중에서 지연과 직접 관련 있는 파라미터는 전체 중 극히 일부라는 특성이 있다. 이 특성을 이용하여 Lasso 정규화 같은 방법으로 추정 정확도를 높이기도 한다. 그러나 Lasso 정규화의 경우 필요한 정보가 소실되는 경우가 발생한다. 본 논문에서는 이를 보완하기 위해서 Lasso 정규화에 Ridge 정규화를 덧붙인 Elastic Net을 사용한 방법을 제안한다. 제안한 방법을 기존의 일반 상호 상관(Generalized Cross Correlation, GCC) 방법 및 Lasso 정규화를 사용한 방법과 비교하여, 백색 가우시안 신호원 및 유색 신호원에서도 추정 오차가 매우 적음을 보인다.

• Computers and Concrete
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• 제19권1호
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• pp.1-6
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• 2017

Prestressed concrete I-girders are subject to different load types at their construction stages. At the time of strand release, i.e., detensioning, prestressed concrete girders are under the effect of dead and prestressing loads. At this stage, the camber, total net upward deflection, of prestressed girder is summation of the upward deflection due to the prestressing force and the downward deflection due to dead loads. For the calculation of the upward deflection, it is generally considered that prestressed concrete I-girder behaves linear-elastic. However, the field measurements on total net upward deflection of prestressed I-girder after detensioning show contradictory results. In this paper, camber calculations with the linear-elastic beam and elastic-stability theories are presented. One of a typical precast I-girder with 120 cm height and 31.5 m effective span length is selected as a case study. 3D finite element model (FEM) of the girder is developed by SAP2000 software, and the deflections of girder are obtained from linear and nonlinear-static analyses. Only geometric nonlinearity is taken into account. The material test and field measurement of this study are performed at prestressing girder plant. The results of the linear-elastic beam and elastic-stability theories are compared with FEM results and field measurements. It is seen that the camber predicted by elastic-stability theory gives acceptable results than the linear-elastic beam theory while strand releasing.

• 대한기계학회논문집B
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• 제37권2호
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• pp.111-117
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• 2013

탄성튜브가 연결된 펌핑 챔버를 이용한 무밸브 펌프를 가상경계방법을 이용하여 수치적으로 연구하였다. 탄성 튜브와 펌핑 챔버 사이의 상호작용으로 인하여 무밸브 펌프 내의 유동이 생성되었으며, 탄성튜브의 스트레칭 계수, 벤딩 계수, 종횡비가 무밸브 펌프의 전체 유량에 미치는 영향을 살펴보았다. 펌프의 메커니즘을 이해하고자, 시간에 따른 탄성 튜브의 움직임과 그에 따른 유동 속도의 변화를 자세히 살펴보았으며, 탄성 튜브의 직경 크기와 펌프의 평균 유량 사이의 관계를 분석하였다.

• 한국전산구조공학회:학술대회논문집
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• 한국전산구조공학회 2000년도 가을 학술발표회논문집
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• pp.331-338
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• 2000

In this paper, a non-linear finite element formulation for the spatial cable-net structures is simulated and using this formulation, the characteristics of structural behaviors for the elastic catenary cable are examined In the simulating procedure for the elastic catenary cable, nodal forces and tangential stiffness matrices are derived using catenary parameters of the exact solutions by a governing differential equation of catenary cable, cable self-weights and unstressed cable length. Dynamic Relaxation Method that considers kinetic damping is used for the structure analysis and Newton Raphson Method is used to verify the accuracy of solutions. In the analysis of two dimensional cable, the results obtain from the elastic catenary elements are shown more accurate than does of truss elements and in the case of spatial cable-net structures, Dynamic Relaxation Method is more stable to be converged than Newton Raphson Method.

• 대한정형도수물리치료학회지
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• 제27권2호
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• pp.27-36
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• 2021

Background : Prone hip extension (PHE) is commonly used for exercises and tests in patients with low back pain. Previous studies have shown that pelvic compression belts (PCB) and non-elastic taping (NET) contribute greatly to improvements in lumbopelvic stability. This study aimed to compare the effect of two lumbopelvic stability methods such as PCB and NET on the trunk and hip extensor muscle activities during PHE tests. Methods: Subjects who experienced low back pain (low back pain group, LBPG; n=20) and those who did not experience low back pain (non-LBPG; n=20) participated in this study. The subjects were instructed to perform PHE with and without a PCB and NET. PHE tests were performed in the condition wherein the two stabilization methods were applied, and the actions of the muscles at that time were measured using surface electromyography (EMG). EMG data were collected from the hamstring, gluteus maximus, erector spine (ES), and multifidus (MF) muscles. The data were collected three times for 5 s with a 1-min rest between each of the three sets. Results: In the LBPG, EMG of the ES muscle was significantly reduced when NET or a PCB was applied (p<.05). There was no difference in the change in the ES muscle activity when NET and a PCB were applied. The ratio of MF/ES muscleactivity showed a significant increase in the LBPG with NET (p<.05). Conclusion: Both NET and PCB applied to subjects who experienced low back pain significantly reduced the ES muscle activity during PHE exercises and helped control the balance of the superficial and deep trunk extensor muscles.

• Communications for Statistical Applications and Methods
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• 제21권4호
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• pp.349-361
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• 2014

This paper compares of lasso type estimators in various high-dimensional data situations with sparse parameters. Lasso, adaptive lasso, fused lasso and elastic net as lasso type estimators and ridge estimator are compared via simulation in linear models with correlated and uncorrelated covariates and binary regression models with correlated covariates and discrete covariates. Each method is shown to have advantages with different penalty conditions according to sparsity patterns of regression parameters. We applied the lasso type methods to Arabidopsis microarray gene expression data to find the strongly significant genes to distinguish two groups.