• 대한산업공학회지
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• 제28권3호
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• pp.283-290
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• 2002

Two-level fractional factorial designs are widely used when many factors are considered. When two-level fractional factorial designs are used, some effects are confounded with each other. To break the confounding between effects, we can use fractional factorial designs, called fold-over designs, in which certain signs in the design generators are switched. In this paper, optimal fold-over designs with four-level quantitative and two-level factors are presented for (1) the initial designs without curvature effect and (2) those with curvature effect. Optimal fold-over design tables are provided for 8-run, 16-run, and 32-run experiments.

• 전기학회논문지
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• 제59권3호
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• pp.604-608
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• 2010

An electric fan for cooling high density electronic devices is limited and operated in very low efficiency. The corona discharge is utilized as the driving mechanism for an ionic gas pump, which allows for air flow control and generation with low noise and no moving parts. These ideal characteristics of ionic pump give rise to variety applications. However, all of these applications would benefit from maximizing the flow velocities and yields of the ionic pump. In this study, a needle-mesh type ionic pump has been investigated by focusing on the radius of curvature of corona needle points elevating the ionic wind velocity and efficiency. It is found that the radius of curvature of the corona discharge needle point influences significantly to produce the ionic wind and efficiency. As a result, an elevated ionic wind velocity and increased ionic wind generation yield can be obtained by optimized the radius of curvature of the corona needle electrode.

• Bulletin of the Korean Chemical Society
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• 제12권5호
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• pp.529-536
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• 1991

In this paper, the question whether the curvature of the minimum energy path can affect the dynamic threshold was tested using the boundary trajectory method developed by Chesnavich and coworkers. For nonreactive system, the MO EXP model potential surface was used with modified equilibrium distance to control the curvature. The results showed that there is no relation between the curvature and the dynamic threshold. In order to study the reactive system, a generalization of the boundary trajectory method was achieved to apply on the nonsymmetric system. We have found no correspondence between the curvature and the dynamic threshold of the system. It was also shown that the fate of the trajectories strongly depends on the shape of potential surface around the turning points along the symmetric stretch line.

• 대한물리치료과학회지
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• 제29권2호
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• pp.38-47
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• 2022

Background: The purpose of this study was to investigate the effect of the combined application of manipulation and stabilization exercises on pain and spinal curvature in patients with chronic back pain. Design: Randomized controlled trial Methods: The research subjects included 24 women in their 40s and 50s who have chronic back pain. The sample was evenly divided into an experimental group, which received the combined application of manipulation and stabilization exercises, and a control group, which received stabilization exercises only. The 30-minute intervention was applied five times a week for eight weeks. A bivariate repeated measures analysis of variances was conducted to identify the differences between the two groups before the experiment, after the fourth week, and at the end of the eight-week experiment. The level of statistical significance was set at.05. This analysis examined the within-group changes and the between-group changes using a paired t-test and an independent t-test, respectively. Results: Changes in pain differed significantly depending on the time of the measurement, the interaction between the time of the measurement and each group, and between the two groups (p<.05). Changes in the curvature of the bones of the neck, the bones of the back, and the lumbar vertebrae differed significantly depending on the time of the measurement and the interaction between the time of the measurement and each group (p<.05). Conclusion: The combined application of manipulation and stabilization exercises demonstrated a positive effect on changes in pain and spinal curvature, and the method is expected to be a useful intervention for reducing pain and improving spinal curvature in patients with back pain.

• 대한토목학회논문집
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• 제29권5B호
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• pp.463-472
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• 2009

본 연구에서는 잠제가 설치된 연안역에서 해안의 곡률반경이 잠제 주변 파동장에 미치는 영향을 파악하기 위하여 파 구조물 해빈/해저지반의 상호작용을 해석할 수 있는 3차원 수치모델 LES-WASS-3D를 이용하여 시뮬레이션을 실시하였다. 먼저 기존의 수리모형실험결과와 비교 검토를 통하여 타당성과 유효성을 확인하였으며, 수치실험을 통해 얻어진 수치해석결과로부터 잠제 주변의 파고분포, 평균수위분포, 상층흐름분포, 평균류분포 그리고 연안에서의 처오름 높이분포를 비롯한 잠제 주변의 3차원적 수리특성에 미치는 해안곡률의 영향에 관하여 고찰하였다.

• Structural Engineering and Mechanics
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• 제89권6호
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• pp.579-588
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• 2024

The present paper investigates the curvature ductility of confined reinforced concrete (RC) beams with normal (NSC) and high strength concrete (HSC). For the purpose of predicting the curvature ductility factor, an analytical model was developed based on the equilibrium of internal forces of confined concrete and reinforcement. In this context, the curvatures were calculated at first yielding of tension reinforcement and at ultimate when the confined concrete strain reaches the ultimate value. To best simulate the situation of confined RC beams in flexure, a modified version of an ancient confined concrete model was adopted for this study. In order to show the accuracy of the proposed model, an experimental database was collected from the literature. The statistical comparison between experimental and predicted results showed that the proposed model has a good performance. Then, the data generated from the validated theoretical model were used to train the artificial neural network (ANN) prediction model. The R² values for theoretical and experimental results are equal to 0.98 and 0.95, respectively which proves the high performance of the ANN model. Finally, a parametric study was implemented to analyze the effect of different parameters on the curvature ductility factor using theoretical and ANN models. The results are similar to those extracted from experiments, where the concrete strength, the compression reinforcement ratio, the yield strength, and the volumetric ratio of transverse reinforcement have a positive effect. In contrast, the ratio and the yield strength of tension reinforcement have a negative effect.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2005년도 창립60주년 기념 추계 학술대회
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• pp.66.1-66.1
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• 2005

• 한국해양공학회지
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• 제24권6호
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• pp.61-70
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• 2010

This study presents free vibration analyses of perforates steel plates with various cutouts. Four different parameters (shape, size, curvature radius ratio, and rotation of cutouts) were considered to investigate the effects of those parameters on the free vibration characteristics, such as natural frequencies of the perforated steel plates. Three different shapes of cutouts are circle, square, and triangle, and the considered sizes are 5, 10, 15, 20, and 25 mm. For the triangular and square cutouts, the characteristic radii of the inscribed circles of those cutouts were defined. In addition, the curvature radius ratio was defined as the ratio of curvature radius of bluntness and the characteristic radius. Then, total seven different curvature radius ratios (0, 0.1, 0.3, 0.5, 0.7, 0.9, and 1) were considered. To investigate the rotation effect of the cutouts, it was considered four rotations ($0^{\circ}$, $15^{\circ}$, $30^{\circ}$, and $45^{\circ}$) for the square cutouts and three rotations (0, 15, and 30) for the triangular cutouts. All the free vibration analyses were conducted using a general purpose finite element program. From the analyses we found that the most influential parameter for the free vibration response of the perforated plates is the size of cutout. The other factors such as the shape, curvature radius ratio, and rotation are minors; they mainly change the natural frequency as long as the size effect is accompanied.

• Geomechanics and Engineering
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• 제18권2호
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• pp.141-151
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• 2019

In this paper, it is aimed to present a detail investigation about the comparison of static and dynamic behavior of historical masonry arch bridges considering different arch curvature. $G{\ddot{o}}derni$ historical masonry two-span arch bridge which is located in Kulp town, Diyarbakir, Turkey is selected as a numerical application. The bridge takes part in bowless bridge group and built in large measures than the others. The restoration projects were approved and rehabilitation studies have still continued. Finite element model of the bridge is constituted with special software to determine the static and dynamic behavior. To demonstrate the arch curvature effect, the finite element model are reconstructed considering different arch curvature between 2.86 m-3.76 m for first arch and 2.64 m-3.54 m for second arch with the increment of 0.10 m, respectively. Dead and live vehicle loads are taken into account during static analyses. 1999 Kocaeli earthquake ground motion record is considered for time history analyses. The maximum displacements, principal stresses and elastic strains are compared with each other using contour diagrams. It is seen that the arch curvature has more influence on the structural response of historical masonry arch bridges. At the end of the study, it is seen that with the increasing of the arch heights, the maximum displacements, minimum principal stresses and minimum elastic strains have a decreasing trend in all analyses, in addition maximum principal stresses and maximum elastic strains have unchanging trend up to optimum geometry.

• 콘크리트학회논문집
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• 제15권5호
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• pp.747-758
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• 2003

The moment-curvature envelope describes the changes in the flexural capacity with deformation during a nonlinear analysis. Therefore, the moment-curvature analysis for reinforced concrete columns, indicating the available flexural strength and ductility, can be conducted providing the stress-strain relation for the concrete and steel are known. The moments and curvatures associated with increasing flexural deformations of the column may be computed for various column axial loads by incrementing the curvature and satisfying the requirements of strain compatibility and equilibrium of forces. Clearly it is important to have accurate information concerning the complete stress-strain curve of confined high-strength concrete in order to conduct reliable moment-curvature analysis that assesses the ductility available from high-strength concrete columns. However, it is not easy to explicitly characterize the mechanical behavior of confined high-strength concrete because of various parameter values, such as the confinement type of rectilinear ties, the compressive strength of concrete, the volumetric ratic and strength of rectangular ties. So a stress-strain model is developed which can simulate complete inelastic moment-curvature relations of high-strength concrete columns.