• Structural Engineering and Mechanics
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• 제75권3호
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• pp.401-414
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• 2020

Unlike the existing truss models for shear and torsion analysis, in this study, the torsional capacities of reinforced concrete (RC) members were estimated by introducing multi-potential capacity criteria that considered the aggregate interlock, concrete crushing, and spalling of concrete cover. The smeared truss model based on the fixed-angle theory was utilized to obtain the torsional behavior of reinforced concrete member, and the multi-potential capacity criteria were then applied to draw the capacity of the member. In addition, to avoid any iterative calculation in the existing torsional behavior model, a simple strength model was suggested that considers key variables, such as the effective thickness of torsional member, principal stress angle, and strain effect that reduces the resistance of concrete due to large longitudinal tensile strain. The proposed multi-potential capacity concept and the simple strength model were verified by comparing with test results collected from the literature. The study found that the multi-potential capacity could estimate in a rational manner not only the torsional strength but also the failure mode of RC members subjected to torsional moment, by reflecting the reinforcing index in both transverse and longitudinal directions, as well as the sectional and material properties of RC members.

• 디지털융복합연구
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• 제15권11호
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• pp.221-229
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• 2017

본 연구의 목적은 기존의 기업소득환류세제와 새롭게 도입되는 투자 상생협력촉진세제에서 공통적으로 고려하고 있는 기업의 미환류소득을 보다 효율적으로 사용하여 기업가치를 증진시키기 위한 방안을 모색하는 것이다. 구체적으로, 두 개 세제에서 공통적으로 고려하고 있는 임금과 고정자산 투자 부분에 대한 소득환류활동과 과세소득 재원이 상황에 따라 기업가치에 미치는 영향을 실증분석하였다. 분석결과, 단기사내유보이익과 소득환류활동은 기업가치에 부의 영향을 미치고, 장기사내유보금과 소득환류활동은 기업가치에 정의 영향을 미치는 것을 확인할 수 있었다. 이는 기업의 장기사내유보금을 재원으로 투자 임금 증가의 활성화를 유도해야함을 권고한다. 또한, 세제 내용에 소득환류활동의 비율과 같은 일률적인 기준만 제정할 것이 아니라 기업의 내부 사내유보 상황과 과세소득 재원을 면밀히 고려해 세재를 적용할 것을 권고한다.

• Advances in aircraft and spacecraft science
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• 제4권1호
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• pp.37-52
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• 2017

Gas turbines operating in dusty or sandy environment polluted with micron-sized solid particles are highly prone to blade surface erosion damage in compressor stages and molten sand attack in the hot-sections of turbine stages. Commercial/Military fixed-wing aircraft engines and helicopter engines often have to operate over sandy terrains in the middle eastern countries or in volcanic zones; on the other hand gas turbines in marine applications are subjected to salt spray, while the coal-burning industrial power generation turbines are subjected to fly-ash. The presence of solid particles in the working fluid medium has an adverse effect on the durability of these engines as well as performance. Typical turbine blade damages include blade coating wear, sand glazing, Calcia-Magnesia-Alumina-Silicate (CMAS) attack, oxidation, plugged cooling holes, all of which can cause rapid performance deterioration including loss of aircraft. The focus of this research work is to simulate particle-surface kinetic interaction on typical turbomachinery material targets using non-linear dynamic impact analysis. The objective of this research is to understand the interfacial kinetic behaviors that can provide insights into the physics of particle interactions and to enable leap ahead technologies in material choices and to develop sand-phobic thermal barrier coatings for turbine blades. This paper outlines the research efforts at the U.S Army Research Laboratory to come up with novel turbine blade multifunctional protective coatings that are sand-phobic, sand impact wear resistant, as well as have very low thermal conductivity for improved performance of future gas turbine engines. The research scope includes development of protective coatings for both nickel-based super alloys and ceramic matrix composites.

• 대한기계학회논문집
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• 제10권3호
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• pp.357-366
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• 1986

본 연구에서는 3공피토우관 및 열선유속계를 사용하여 벽에 평행한 2차원 난류제트의 난류량들을 측정하였고, 스캐니 밸브를 이용하여 벽면아력분포를 측정함 으로써 재순환 영역을 포함한 전체유동장에서의 유동특성을 고찰하였다. 또한 잘 알려진 표준 k-.epsilon. 난류모형 및 유선곡률을 고려한 수정된 k-.epsilon. 난류모형을 이용하여 측정 수치해석을 수행하였다.

• 한국세라믹학회지
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• 제41권6호
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• pp.430-434
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• 2004

The values of fracture energy and mechanical flexural strength of Fiber Reinforced Cement (FRC) with polypropylene (PP) fiber modified by Ion Assisted Reaction (JAR), by which functional groups were grafted on the surface of PP fiber, was improved about 2 times as those of fracture energy and flexural strength of cement reinforced by untreated PP fiber. PP fiber was irradiated in O$_2$ environment by Ar$\^$+/ ion. The contact angle of PP treated by IAR decreased largely when compared with untreated PP. From this result, we expected that surface energy and interfacial adhesion force of treated PP fiber increased. The strain hardening occurred in the strain-stress curve of FRC including PP treated by IAR when compared with that of FRC with untreated PP. These enhanced mechanical properties might be due to strong interaction between hydrophilic group on modified PP fiber and hydroxyl group in cement matrix. This hydrophilic group on surface modified PP fiber was confirmed by XPS analysis. We clearly observed hydration products that were fixed at modified PP fiber due to the strong adhesion force of interface in cement reinforced modified PP by SEM (Scanning Electron Microscopy) study.

• Biotechnology and Bioprocess Engineering:BBE
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• 제10권3호
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• pp.218-224
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• 2005

Surface modification of glutaraldehyde fixed bovine pericardium (GFBP) was success­fully carried out with hyaluronic acid (HA) derivatives. At first, HA was chemically modified with adipic dihydrazide (ADH) to introduce hydrazide functional group into the carboxyl group of HA backbone. Then, GFBP was surface modified by grafting HA-ADH to the free aldehyde groups on the tissue and the subsequent HA-ADH hydrogel coating. HA-ADH hydrogels could be prepared through selective crosslinking at low pH between hydrazide groups of HA-ADH and crosslinkers containing succinimmidyl moieties with minimized protein denaturation. When HA­ADH hydrogels were prepared at low pH of 4.8 in the presence of erythropoietin (EPO) as a model protein, EPO release was continued up to $85\%$ of total amount of loaded EPO for 4 days. To the contrary, only $30\%$ of EPO was released from HA-ADH hydrogels prepared at pH=7.4, which might be due to the denaturation of EPO during the crosslinking reaction. Because the carboxyl groups on the glucuronic acid residues are recognition sites for HA degradation by hyaluronidase, the HA-ADH hydrogels degraded more slowly than HA hydrogels prepared by the crosslinking reaction of divinyl sulfone with hydroxyl groups of HA. Following a two-week subcutaneous implantation in osteopontin-null mice, clinically significant levels of calcification were observed for the positive controls without any surface modification. However, the calcification of surface modified GFBP with HA-ADH and HA-ADH hydrogels was drastically reduced by more than $85\%$ of the positive controls. The anti-calcification effect of HA surface modification was also confirmed by microscopic analysis of explanted tissue after staining with Alizarin Red S for calcium, which followed the trend as observed with calcium quantification.

• 한국기계가공학회지
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• 제15권1호
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• pp.42-49
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• 2016

This study was analyed V-bending in order to analyze the spring-back phenomenon in the roll forming process. The material of forming sheet used in the roll forming process is high tension steel and the product name of sheet material is POSTEN 60. The most important variable is the number of roll passes (3-Pass, 4-Pass, 5-Pass, 6-Pass and 10-Pass) and other roll forming process variables were fixed. To determine the characteristics of the tension and compression, the forming sheet was analyzed by dividing the layer (Upper and Bottom) in the thickness direction from the center line. The results of FEM simulation analysis was derived to von-mises stress equivalent strain, and the spring-back value was calculated according to the final forming shape. The more number of the roll pass, von-mises stress and equivalent strain value of forming sheet were lowed. Also, spring-back values tended to decrease. The results of this study can be utilized for prediction and trend of spring-back value in the roll forming process applied to high tension steel sheet. So, development time and cost of the roll forming process is expected to be reduced.

• 한국소음진동공학회논문집
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• 제25권12호
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• pp.866-873
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• 2015

The transverse vibration of the deploying beam from rigid hub was analyzed by simulation and experiment. The linear governing equation of the deploying beam was obtained using the Euler-Bernoulli beam theory. To discretize the governing equation, the Galerkin method was used. After transforming the governing equation into the weak form, the weak form was discretized. The discretized equation was expressed by the matrix-vector form, and then the Newmark method was applied to simulate. To consider the damping effect of the beam, we conducted the modal test with various beam length. The mass proportional damping was selected by the relation of the first and second damping ratio. The proportional damping coefficient was calculated using the acquired natural frequency and damping ratio through the modal test. The experiment was set up to measure the transverse vibration of the deploying beam. The fixed beam at the carriage of the linear actuator was moved by moving the carriage. The transverse vibration of the deploying beam was observed by the Eulerian description near the hub. The deploying or retraction motion of the beam had the constant velocity and the velocity profile with acceleration and deceleration. We compared the transverse vibration results by the simulation and experiment. The observed response by the Eulerian description were analyzed.

• 지역사회간호학회지
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• 제14권2호
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• pp.351-361
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• 2003

Purpose: The purposes of this study were to understand the types of coping strategies that family caregivers experience during the process of caring demented elderly: to grasp the coping strategies used for resolving this problem: and to develop a substantive theory by analyzing the coping types of the family caregivers of demented elderly. Method: The methodology of data collection and analysis used in this study was grounded theory proposed by Strauss and Corbin (1990). The data was collected through in-depth interviews with participants using open-ended and descriptive questions about their coping experiences. All data were were audio-taped and transcribed. The data were collected from February, 2000 to February, 2001. The participants of this study were 17 women. Results: Caregiver's coping types varied according to 'family's support', 'the condition of caregiver's health', 'the relationship with dementia elderly', 'family perception of dementia', 'fixed idea of traditional female role' and 'economic state'. In this study, five types of coping strategies were emerged: active role allotment tyle, meaning grant tyle, devotion tyle, duty defense type, and pessimism type. Among these, those who belong to the types of active role allotment, meaning grant, and devotion, including caregiver's good health were found to adapt themselves to caregiver roles. Conclusion: The results of this study may be helpful for developing effective and individualized nursing strategies suitable for individual caregivers coping types. It is suggested to practice nursing mediation and to analyze the changes in nursing effect and family members' adaptation based on coping types of the well-adapted caregivers as we as on their affirmative coping strategy.

• 한국초등과학교육학회지:초등과학교육
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• 제34권3호
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• pp.265-275
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• 2015

The purpose of this study was to develop forensic science program for the improvement of scientific creative problem-solving abilities in gifted elementary-school students. A program that consists of six sessions (18 hours) is developed in accordance with the CPS model, which has been already proven effective for the improvement of creative problem-solving abilities. This program was applied to sixth-grade 18 gifted students in an elementary school in Gyeonggi province. Examinations of scientific creative problem-solving abilities were performed before and after applying the program in order to determine its effect on gifted elementary students. A qualitative analysis of students' activity sheets, peer assessment and teacher's class journal was made in order to examine the process of improvement of students' scientific creative problem-solving abilities. The results of this study are as follows: First, forensic science program to enhance the scientific creative problem-solving abilities of gifted students was developed. Second, forensic science program is significantly effective in the improvement of scientific creative problem-solving abilities of gifted children of elementary school (p<.05). Third, in early stage of the class, a student, who showed the highest range of change in pre and post tests, revealed the trend of responding in a short answer type. In the late stage of the class, he revealed the capability of producing various creative ideas promptly. On the other hand, students belonging to the upper group of both pre and post test revealed the improvement of divergent thinking skills such as fluency, flexibility, and originality. Fourth, after class, the students responded that the forensic science program developed in this study intrigued the interests and curiosities, and helped them break away from fixed ideas.