• Magazine of the Korea Concrete Institute
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• v.11 no.1
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• pp.279-288
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• 1999

The creep of concrete structures caused by variable stresses is generally calculated by step-by-step method based on the superposition of creep function. Although most practical application is carried out by this linear assumption. significant deviations between predictions and experiments have been observed when unloading takes place, that is. stress is reduced. This shows that the superposition of creep function does not describe accurately the effect of sustained compressive preload. The main purpose of this study is to propose a creep analysis model which is expressed with both creep function and creep recovery function where increase or decrease of stress is repeated. In these two function method, the creep behavior is modelled by using linear creep law for loading and creep recovery law for unloading. To apply two function method to time analysis of concrete structures, the calculation method of creep strain increment under varying stress is proposed. The calculation results based on the present method correlates very well with test data, but the conventional superposition method exhibits large deviation from test results. This paper provides a more accurate method for the time dependent analysis of concrete structures subjected to varying stress, i.e. increasing or decreasing stress. The present method may be efficiently employed in the revision of future concrete codes.

• Analytical Science and Technology
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• v.16 no.5
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• pp.1041-1051
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• 2003

Neutron induced prompt gamma activation analysis (PGAA) offers a nondestructive, sensitive and relatively rapid method for the determination of trace and major elements and is proven to be convenient for online analysis of minerals, metals, coal, cement, petrochemical, coating, paper as well as many other materials and products. The technique has found many uses in medicine, industry, research, security and the detection of contraband items. This report reviews the present status and future trends of the PGAA techniques. Requirements for the system are neutron source, high resolution HPGe detectors with a high-voltage power supply, an amplifier, analog-to-digital converter, and a multichannel analyzer for the detection and measurement of prompt ${\gamma}$-ray emit form the neutron capture elements. Introducing a ${\gamma}$-${\gamma}$ coincidence system also improves the quality of the ${\gamma}$-ray spectrum by suppressing the background created from the Compton scattering of high energy prompt ${\gamma}$-rays. A PGAA system using a $^{252}Cf$ neutron source is currently under construction for the on-line measurement of several elements in aqueous samples at KAERI. The system can be applied for the detection of chemical weapons and explosives as well as various narcotics.

• Journal of Science Education
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• v.34 no.1
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• pp.33-46
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• 2010

The purpose of this study was to find out the image as science teachers recognized by pre-service science teachers. The data was collected from 312 pre-service science teachers from Kyungpook National University in Daegu and participants were asked to write about the image of science teachers they liked most and least in their secondary school years freely. The result of this research was as follows. The image as science teachers categorized 2 factors: science instructional situation, image of science teacher. Each factor was subdivided into more detailed ones. First of all, 'science instructional situation' category subdivided into lesson style, teaching-learning materials, teaching methods, and class atmosphere. In lesson style, 'experiment' and 'observation' gained the most favorable comments, and questioning-answering gained the least. In teaching-learning materials, print materials such as handouts, worksheets, reports were the most liked, and 'writing on the blackboard' was the least liked. In teaching methods, the 'detailed and systematic explanation of the theory and concepts' was preferred to rote learning and memorization lacking explanation. In class atmosphere, friendly and free atmosphere was the most preferred, and uncomfortable, boring one was the least preferred. Secondly, in 'image of the science teachers' category and 'quality as the teachers' sub-category, thoughtful and considerate teachers who respect students' personality was the most preferred. On the contrary, they didn't prefer teachers who were indifferent and humiliated students. Finally in 'characteristics of the teachers' sub-category, the participants liked clear, energetic voice, and mild expression, and they didn't like formal style, overly fancy clothes, etc. Based on the result of this study, more empirical study on the teachers' image is needed, and the thoughts of educational administrators, students, parents, and teachers should be reflected because an undesirable teacher can be advised and get opportunity to be a better teacher.

• Korean Journal of Construction Engineering and Management
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• v.6 no.1 s.23
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• pp.99-108
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• 2005

Interactive electronic technical manual(IETM) for construction projects means an electronic tool that regulations and specifications related to construction method or maintenance process ale described by electronic book type. It has a meaning of integrated information system that includes virtual reality(VR), 3D animation and image contents for representing real construction information so that user can easily understand the construction situation and maintenance process. The basic information and technical manuals of construction facilities are being written as paper documents in our construction industry. As the result, the information management in the maintenance phase of construction projects is inefficient, and maintenance cost is being increased. This study attempts to improve the lack of understanding about construction IETM through the analysis of necessity and unique function of construction IETM comparing with the IETMS in other industry, Finally, this study shows a scenario of construction IErM for mitigating natural disaster of construction facilities to verify applicability of IETM.

• Journal of the Korean Chemical Society
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• v.55 no.1
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• pp.57-62
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• 2011

Sometimes inhabitants in remote areas have inadequate or no access to modern medicines or medical services. They can get benefit in term of the treatment against malaria by cultivating selected breeding of A. annua and making teas or decoctions from the plant materials following the proper way of tea preparation. In order to have the maximum extraction efficiency for artemisinin, different ways of tea preparations of A. annua were investigated by applying the developed DPP method and described in this article. Tea was prepared by three different ways (cooking, without cooking with/without shaking and microwave oven) with different times. From the results, it has been found that higher concentration of artemisinin (84.7%) can be attained by following the approach for tea preparation without cooking with shaking for 15 minutes (R.S.D. 2.34%). The concentration of artemisinin decreases with cooking more than 1.5 min in microwave oven. The utmost extraction (88.9% of artemisinin) is possible to extract by shaking with boiled 5% ethanol in distilled water (R.S.D. 2.28%).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.18 no.8
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• pp.106-114
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• 2017

This study was a one-group pre-post test design experimental investigation conducted to evaluate the effects of problem-based learning by type of learning in nursing students. The subjects of the study were 125 senior students in the Department of Nursing Science at a single university located in A. City, and the study was conducted for eight weeks from April 18 through June 10, 2016. Data analysis consisted of descriptive statistics, ANOVA, ${\chi}^2$-tests and t-tests. Most nursing students underwent converger type of learning, and after problem-based learning, their learning flow, problem-solving ability and critical thinking disposition increased significantly. In problem-based learning by type of learning, the problem-solving ability was significantly higher in the converger type than in the accommodator type, and there were no significant differences in learning flow and critical thinking disposition; however,in all types of learning, learning flow and critical thinking disposition increased. Since these results suggest that teaching and learning strategies should be set up for each type of learning, it is necessary to seek plans for teaching and learning strategies to make up for the weak points and strengthen the strong points by each type of learning when applying the problem-based learning method.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.10 no.11
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• pp.2075-2082
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• 2006

This paper presents modeling and optimization techniques for hish efficiency solar cell process on single-crystalline float zone (FZ) wafers. Among a sequence of multiple steps of fabrication, the followings are the most sensitive steps for the contact formation: 1) Emitter formation by diffusion; 2) Anti-reflection-coating (ARC) with silicon nitride using plasma-enhanced chemical vapor deposition (PECVD); 3) Screen-printing for front and back metalization; and 4) Contact formation by firing. In order to increase the performance of solar cells in terms of efficiency, the contact formation process is modeled and optimized using neural networks and genetic algorithms, respectively. This paper utilizes the design of experiments (DOE) in contact formation to reduce process time and fabrication costs. The experiments were designed by using central composite design which consists of 24 factorial design augmented by 8 axial points with three center points. After contact formation process, the efficiency of the fabricated solar cell is modeled using neural networks. Established efficiency model is then used for the analysis of the process characteristics and process optimization for more efficient solar cell fabrication.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.14 no.1
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• pp.85-93
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• 2013

While relatively many researches have been performed on the legal issues of leverage buyout(LBO) in the Korean capital market, the on-going 'interdisciplinary studies' between the legal and the financial aspects of LBO financing structure seems to be relatively few so far. In this particular study, the concept and major financing structures on LBO have been discussed, by which domestic investors including institutional investors, may acquire in-depth knowledge on the issue given the dynamically changing circumstances surrounding the Korean domestic capital market. Moreover, legal analyses related to the conventional case studies on two types of LBO structures such as 'asset-backed LBO' and 'merger-related LBO', have been illustrated, coupled with the review of the previous literature on mergers & acquisitions(M&A) related to the financial aspects of LBO financing structure. From the director's perspective, who is employed by an acquired firm, legal issues in terms of 'fiduciary duty' and 'duty of loyalty' have been discussed, along with the logical scope of 'business judgement principle' in terms of modern finance theory.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.610-618
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• 2016

This study was conducted to investigate the level of moral sensitivity, critical thinking disposition and perceived ethical confidence, as well as to identify the factors influencing the perceived ethical confidence in nursing students. The study evaluated 170 nursing students in D Province from May 16-20, 2016. Data were analyzed using a t-test, one-way ANOVA, Pearson's correlation and multiple regression. The mean score of the perceived ethical confidence was $3.54({\pm}0.51)$, the moral sensitivity was $4.92({\pm}0.59)$ and the critical thinking disposition was $3.45({\pm}0.39)$. There were positive correlations between the perceived ethical confidence and moral sensitivity (r=0.410, p<0.001) and critical thinking disposition (r=0.523, p<0.001). The significant factors influencing the perceived ethical confidence were moral sensitivity and critical thinking disposition, which explained 33.2% of the variance in perceived ethical confidence. Based on these findings, programs and teaching methods that develop moral sensitivity and critical thinking disposition are necessary for college nursing students to promote perceived ethical confidence.

• Geophysics and Geophysical Exploration
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• v.1 no.1
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• pp.31-42
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• 1998

Recently crosshole seismic tomography has come to be widely used especially for the civil engineering, because it can provide more detail information than any other surface method, although the resolution of tomogram will be inevitably deteriorated to some extent due to the limited wavefield aperture on the nonuniqueness of traveltime inversion. In addition, our field sites often consist of a high-velocity bed rock overlain by low-velocity rock, sometimes with a contrast of more than 45 percent, and furthermore the bed rock is folded. The first arriving waves can be then the refracted ones that travel along the bed rock surface for some source/receiver distances. Thus, the desirable first arrivals can be easily misread that cause severe distortion of the resulting tomogram, if it is concerned with (straight ray) traveltime inversion procedure. In this case, comparision with synthetic data (forward modeling) is a valuable tool in the interpretation process. Besides, abundant information is contained in the crosshole data. For instance, examination of tube waves can be devoted to detecting discontinuities within the borehole such as breakouts, faults, fractures or shear zones as well as the end of the borehole. Specific frequency characteristics of marine silty mud will help discriminate from other soft rocks. The aim of this paper is to present several strategies to analyze and interpret the crosshole data in order to improve the ability at first to determine the spatial dimensions of interwell anomalies and furthermore to understand the underground structures. To this end, our field data are demonstrated. Possibility of misreading the first arrivals was illustrated. Tube waves were investigated in conjunction with the televiewer images. Use of shot- and receiver gathers was examined to benefit the detectabilities of discontinuities within the borehole.