• 한국지능시스템학회논문지
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• 제19권5호
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• pp.689-694
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• 2009

본 논문은 일별 및 주별로 시계열 주가를 예측할 수 있는 퍼지 모델을 구성하는 방법을 제안한다. 전통적인 시계열 분석으로 주가를 예측하는 것은 어렵지만 퍼지 모델은 비선형적인 주가 데이터의 특성을 잘 기술할 수 있는 장점을 갖고 있다. 주가 예측 모델에 사용될 입력 정보를 결정하는 데는 상당한 수고가 필요한데, 본 논문에서는 전통적인 캔들 스틱 차트의 정보를 입력변수로 고려한다. 주가 예측 퍼지 모델은 사다리꼴 멤버쉽함수를 갖는 전건부와 비선형식인 후건부로 된 퍼지 규칙으로 구성된다. 차분 진화를 통해 퍼지 모델은 최적화된다. 일별 및 주별로 코스피 지수의 시가, 고가, 저가 및 종가를 예측하는 모델을 만들고 그 성능을 평가한다.

• 한국농공학회논문집
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• 제61권6호
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• pp.123-132
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• 2019

This study is to estimate the spatial soil moisture using Terra MODIS (Moderate Resolution Imaging Spectroradiometer) satellite data and machine learning technique. Using the 3 years (2015~2017) data of MODIS 16 days composite NDVI (Normalized Difference Vegetation Index) and daily Land Surface Temperature (LST), ground measured precipitation and sunshine hour of KMA (Korea Meteorological Administration), the RDA (Rural Development Administration) 10 cm~30 cm average TDR (Time Domain Reflectometry) measured soil moisture at 78 locations was tested. For daily analysis, the missing values of MODIS LST by clouds were interpolated by conditional merging method using KMA surface temperature observation data, and the 16 days NDVI was linearly interpolated to 1 day interval. By applying the RNN-LSTM (Recurrent Neural Network-Long Short Term Memory) artificial neural network model, 70% of the total period was trained and the rest 30% period was verified. The results showed that the coefficient of determination ($R^2$), Root Mean Square Error (RMSE), and Nash-Sutcliffe Efficiency were 0.78, 2.76%, and 0.75 respectively. In average, the clay soil moisture was estimated well comparing with the other soil types of silt, loam, and sand. This is because the clay has the intrinsic physical property for having narrow range of soil moisture variation between field capacity and wilting point.

• Steel and Composite Structures
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• 제25권2호
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• pp.157-175
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• 2017

The novelty of this work is the use of a new displacement field that includes undetermined integral terms for analyzing thermal buckling response of functionally graded (FG) sandwich plates. The proposed kinematic uses only four variables, which is even less than the first shear deformation theory (FSDT) and the conventional higher shear deformation theories (HSDTs). The theory considers a trigonometric variation of transverse shear stress and verifies the traction free boundary conditions without employing the shear correction factors. Material properties of the sandwich plate faces are considered to be graded in the thickness direction according to a simple power-law variation in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic material. The thermal loads are assumed as uniform, linear and non-linear temperature rises within the thickness direction. An energy based variational principle is employed to derive the governing equations as an eigenvalue problem. The validation of the present work is checked by comparing the obtained results the available ones in the literature. The influences of aspect and thickness ratios, material index, loading type, and sandwich plate type on the critical buckling are all discussed.

• Smart Structures and Systems
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• 제19권1호
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• pp.21-31
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• 2017

To control the stochastic vibration of a vibration-sensitive instrument supported on a beam, the beam is designed as a sandwich structure with magneto-rheological visco-elastomer (MRVE) core. The MRVE has dynamic properties such as stiffness and damping adjustable by applied magnetic fields. To achieve better vibration control effectiveness, the optimal bounded parametric control for the MRVE sandwich beam with supported mass under stochastic and deterministic support motion excitations is proposed, and the stochastic and shock vibration suppression capability of the optimally controlled beam with multi-mode coupling is studied. The dynamic behavior of MRVE core is described by the visco-elastic Kelvin-Voigt model with a controllable parameter dependent on applied magnetic fields, and the parameter is considered as an active bounded control. The partial differential equations for horizontal and vertical coupling motions of the sandwich beam are obtained and converted into the multi-mode coupling vibration equations with the bounded nonlinear parametric control according to the Galerkin method. The vibration equations and corresponding performance index construct the optimal bounded parametric control problem. Then the dynamical programming equation for the control problem is derived based on the dynamical programming principle. The optimal bounded parametric control law is obtained by solving the programming equation with the bounded control constraint. The controlled vibration responses of the MRVE sandwich beam under stochastic and shock excitations are obtained by substituting the optimal bounded control into the vibration equations and solving them. The further remarkable vibration suppression capability of the optimal bounded control compared with the passive control and the influence of the control parameters on the stochastic vibration suppression effectiveness are illustrated with numerical results. The proposed optimal bounded parametric control strategy is applicable to smart visco-elastic composite structures under deterministic and stochastic excitations for improving vibration control effectiveness.

• 국제지역연구
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• 제15권3호
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• pp.393-405
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• 2011

미국의 장단기 국채 수익률 스프레드와 한국 거래소시장의 종합주가지수 변화를 통해 한국경제와 미국경제에 동조화가 존재하는지, 또 동조화가 존재한다면 어느 정도의 시차로 동조화가 진행되고 있는지, 그리고 미국의 금융위기로 동조화의 내용에 사실상 어떤 변화가 발생했는지를 분석하였다. 본 연구는 먼저 한국의 대표적 자산시장인 거래소시장이 미국의 장단기 국채금리 스프레드와 동조화를 보이고 있는 사실을 발견하였다. 또 동조화의 방향도 미국 국채의 장단기 금리차가 벌어지면, 즉 세계경제의 견인차 역할을 하고 있는 미국경제의 전망이 밝아지는 경우 자산시장에서 안전자산보다는 위험자산을 선호하는 분위기가 조성되어 국제적으로 자금이 고수익을 기대할 수 있는 한국과 같은 신흥시장으로 흘러들어오면서 신흥시장의 주가를 끌어올리게 될 것이라는 일반적인 예상과 일치하였다. 본 연구에서는 또 다양한 시차를 대상으로 하여 동조화가 극대화되는 시점을 조사했는데 양국 시장의 동조화가 불과 1주일 만에 극대화되는 사실도 발견하였다. 또 가변수를 이용하여 미국에서 시작된 금융위기가 동조화에 어떤 변화를 주었는지에 대한 분석에서는 금융위기 후 동조화의 강도가 현저하게 낮아진 사실도 발견하였다.

• 한국치위생학회지
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• 제19권5호
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• pp.765-776
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• 2019

Objectives: The purpose of this study was to compare the oral health statuses pre- and post-insurance using the $5^{th}$ and $6^{th}$ National Health and Nutrition Examination Survey data to confirm the effect of scaling insurance after a year. Methods: Data were analyzed using IBM SPSS ver. 21.0 (IBM Co., Armonk, NY, USA). The four years were integrated, and a composite sample analysis was performed. A total of 26,990 people were included in the study before applying for scaling insurance (14,343 persons) or after receiving scaling insurance (12,647 persons). A chi-squared test was performed to compare the demographic characteristics and oral health status of the subjects. The significance level of the statistical test was 0.05. Results: The proportion of patients without implants was high before the provision of scaling insurance once a year, however, the proportion of patients with one or more implants was high (p<0.05) after the provision of scaling insurance once a year. Hemorrhagic periodontal tissues and tartar formation in periodontal tissues were highly prevalent before the provision of scaling insurance once a year, however, healthy periodontal tissues and formation of periodontal pockets were highly prevalent (p<0.05) after the provision of scaling insurance once a year. The decay, missing, and filled teeth index scores were higher before the provision of scaling insurance once a year (p<0.05). Conclusions: The aforementioned results showed that scaling once a year helps prevent or treat periodontal disease. In addition, we confirmed the effect of prevention on periodontal disease and dental caries, therefore, we expect it to develop into a stable policy.

• 한국세라믹학회지
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• 제56권1호
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• pp.98-103
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• 2019

Optical filters to control light wavelength of displays or cameras are fabricated by multi-layer stacking process of low and high index thin films. The process of multi-layer stacking of thin films has received much attention as an optimal process for effective manufacturing in the optical filter industry. However, multi-layer processing has disadvantages of complicated thin film process, and difficulty of precise control of film morphology and material selection, all of which are critical for transmittance and coloring effect on filters. In this study, the composite $TiO_2$, which can be used to control of UV absorption, coated on nano hollow silica sol, was synthesized as a coating material for optical filters. Furthermore, systematic analysis of the process parameters during the chemical reaction, and of the structural properties of the coating solutions was performed using SEM, TEM, XRD and photo spectrometry. From the structural analysis, we found that the 85 nm nano hollow silica with 2.5 nm $TiO_2$ shell formation was successfully synthesized at proper pH control and titanium butoxide content. Photo luminescence characteristics, excited by UV irradiation, show that stable absorption of 350 nm-light, correlated with a 3.54 eV band gap, existed for the $TiO_2$ shell-nano hollow silica reacted with 8.8 mole titanium butoxide solution. Transmittance observed on substrate of the $TiO_2$ shell-nano hollow silica showed effective absorption of 200-300 nm UV light without deterioration of visible light transparency.

• 한국추진공학회지
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• 제24권3호
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• pp.12-17
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• 2020

황색 산화철을 적용한 추진제의 기계적 특성은 적색산화철을 적용한 추진제와 비교하여 기계적물성이 다소 증가하였다. 또한 황색산화철을 적용한 추진제는 두 종류의 AP 입자를 사용하였으며 총량을 유지하고 작은 입자의 AP 비율 증가 시 연소속도가 증가하였다. 황색산화철을 첨가한 추진제는 압력 지수 값이 0.5인 17.5 mm/sec 이하의 운용조건에서 추진기관에 적용 가능하다. 혼합 믹서 Scale-up 시연소속도 감소, 최대인장강도 감소, 최대인장강도에서의 연신율은 증가하였다. 황색산화철은 내열재/라이너/추진제 사이의 접착력에는 큰 영향을 끼치지 않는다.

• Steel and Composite Structures
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• 제39권5호
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• pp.631-643
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• 2021

The aim of this work is to study the hygro-thermo-mechanical bending responses of simply supported FG plate resting on a Winkler-Pasternak elastic foundation. The effect transverse shear strains is taken into account in which the zero transverse shear stress condition on the top and bottom surfaces of the plate is ensured without using any shear correction factors. The developed model contains only four unknowns variable which is reduced compared to other HSDTs models. The material properties of FG-plate are supposed to vary across the thickness of the plate according to power-law mixture. The differential governing equations are derived based on the virtual working principle. Numerical outcomes of bending analysis of FG plates under hygro-thermo-mechanical loads are performed and compared with those available in the literature. The effects of the temperature, moisture concentration, elastic foundation parameters, shear deformation, geometrical parameters, and power-law-index on the dimensionless deflections, axial and transverse shear stresses of the FG-plate are presented and discussed.

• Steel and Composite Structures
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• 제39권1호
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• pp.95-107
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• 2021

In this work, the dynamic response of functionally graded beams on variable elastic foundations is studied using a novel higher-order shear deformation theory (HSDT). Unlike the conventional HSDT, the present one has a new displacement field which introduces undetermined integral variables. The FG beams were assumed to be supported on Winkler-Pasternak type foundations in which the Winkler modulus is supposed to be variable in the length of the beam. The variable rigidity of the elastic foundation is assumed to be linear, parabolic and sinusoidal along the length of the beam. The material properties of the FG porous beam vary according to a power law distribution in terms of the volume fraction of the constituents. The equations of motion are determined using the virtual working principle. For the analytical solution, Navier method is used to solve the governing equations for simply supported porous FG beams. Numerical results of the present theory for the free vibration of FG beams resting on elastic foundations are presented and compared to existing solutions in the literature. A parametric study will be detailed to investigate the effects of several parameters such as gradient index, thickness ratio, porosity factor and foundation parameters on the frequency response of porous FG beams.