• International Journal of Naval Architecture and Ocean Engineering
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• 제9권4호
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• pp.390-403
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• 2017

Smoothed Particle Hydrodynamics (SPH) method has a good adaptability for the simulation of free surface flow problems. There are two forms of SPH. One is weak compressible SPH and the other one is incompressible SPH (ISPH). Compared with the former one, ISPH method performs better in many cases. ISPH based on Rankine source solution can perform better than traditional ISPH, as it can use larger stepping length by avoiding the second order derivative in pressure Poisson equation. However, ISPH_R method needs to solve the sparse linear matrix for pressure Poisson equation, which is one of the most expensive parts during one time stepping calculation. Iterative methods are normally used for solving Poisson equation with large particle numbers. However, there are many iterative methods available and the question for using which one is still open. In this paper, three iterative methods, CGS, Bi-CGstab and GMRES are compared, which are suitable and typical for large unsymmetrical sparse matrix solutions. According to the numerical tests on different cases, still water test, dam breaking, violent tank sloshing, solitary wave slamming, the GMRES method is more efficient than CGS and Bi-CGstab for ISPH method.

• 자원ㆍ환경경제연구
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• 제14권1호
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• pp.201-220
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• 2005

최근 들어, 우리는 유례 없는 국제 유가의 급등현상을 목격하고 있다. 이러한 시점에서, 의문점은 유가에 대한 예측 가능성과 이의 정확도에 관한 것이다. 본 연구에서는 전문가 예측시스템과 비교하여 선물가격의 상대적인 예측력에 관하여 통계적으로 분석하고자 한다. 이를 위해, 미국 텍사스 중질유(WTI)의 현물가격과 선물가격을 활용하여, 예측 정확도에 관한 단순한 형태의 통계적 분석과 함께 분석수단별 예측오차 차이의 유의성에 관한 체계적 분석을 시도하였다. 통계적 검정결과에 따르면, WTI 선물시장을 활용한 예측은 미국 에너지정보기구(EIA)의 예측과 비교하여 뒤지지 않는 것으로 판명되었다. 결과적으로, 석유 생산자와 소비자 모두가 WTI 선물시장을 유가 예측의 유용한 수단으로 활용할 수 있고, 이로써 효율적인 자원배분 측면에서도 유익할 것으로 판단된다.

• 재활간호학회지
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• 제9권1호
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• pp.72-80
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• 2006

Purpose: This study was conducted to examine the effect of multidimensional program on cognition, physical function and depression among institutionalized elderly and the relationship between study variables and resident's characteristics and health related variables. Method: This study involved a one group pre and post test, comparison of variables over a 12 month period. To investigate this research question, data of 114 residents of a nursing home were analyzed. Results: There was statistically significant difference in MMSE-K (t=-2.63, p=.010), ADL (t=-2.85, p=.005), and depression (t=4.66, p=.000) before and after program participation. Conclusion: These results indicate that, for a year their regular involvement in a broad spectrum of multidimensional program activities can improve in cognitive, physical and emotional perspectives, but the level of IADL decreased significantly (t=-6.72, p=.000). Further testing is required with the control group, to compare with community resident elders in order to explore the effects on social skill of elderly.

• 한국양봉학회지
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• 제34권4호
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• pp.305-313
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• 2019

Honey bees (Apis mellifera) forage in agricultural areas, and are exposed to diverse pesticide poisoning. Toxic effects on Apis mellifera of different groups of pesticides were tested in the laboratory; fungicide (Metconazole), herbicide (Glyphosate), acaricide (Amitraz), organophosphate insecticide(Fenitrothion) and neonicotinoid insecticides(Thiacloprid, Thiamethoxam, Imidacloprid, Acetamiprid, Dinotefuran and Clothianidin). Commercial formulations were serially diluted from the recommended concentration (RC) to 10-6 times to carry out feeding and contact tests. Toxicity was transformed into lethal dose (LD50) and hazard question (HQ). The acute toxicity of pesticides showed similar patterns between feeding and contact tests. But feeding tests showed greater toxic to honey bee than contact test. The organophosphate and nitro-neonicotinoid insecticides were highly toxic with HQ values ranging greater than 1. However, cyano-neonicotinoids of Thiacloprid and Acetamiprid showed low toxicity. Even at the RC, 24 hr mortalities were 18 and 30%. The acaricide (Amitraz) showed intermediate level of toxicity at RC but negligible at the concentration lower than 10-1 times. A fungicide(Metconazole) and herbicide(Glyphosate) showed minimal impacts. The results imply that the selective use of pesticides could help conservation of pollinators in agricultural production systems.

• Nuclear Engineering and Technology
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• 제54권7호
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• pp.2714-2719
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• 2022

The present paper proposes some new computational methods and results in the framework of flow computation through congested domains seen as porous media, as it can be found in the core of a Pressurized Water Reactor (PWR). The flow is thus mostly governed by the distribution of pressure losses, both through the porous structures, such as fuel assemblies, and in the thin fluid layers between them. The purpose of the present paper is to consider the question of the interaction of a flow and a rod bundle from an analytical point of view gathering all the contributions through a set of equations as simple and representative as possible. It aims at demonstrating a sound understanding of the relevant phenomena governing the flow establishment in the geometry of interest instead of relying mainly on a posteriori observations obtained both experimentally and numerically. Comparison with two set of experimental results showed good agreement. The model proposed being analytical it appears easily implementable for studies needing an expression of fluid forces in a rod array as for fuel assembly bowing issue. It would be interesting to test the reliability of the model on other geometry with different P/R ratios.

• Educational Technology International
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• 제13권1호
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• pp.207-231
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• 2012

The purpose of this study is to analyze the effects of Critical Thinking Strategy supporting argumentation activities between learners. The research question is whether the form of Critical Thinking Strategy offered to support meaningful interaction of collaborative argumentation between learners influences the knowledge acquisition, learning outcome, and student satisfaction. For this, the collaboration outcome of the group, the level of individual knowledge acquisition, the level of students satisfaction were measured as outcome of argumentation activity and their differences analyzed. This study concludes the following: A comparison of the group that was provided with Critical Thinking Strategy (test group) and the group provided with general argumentation scaffolds (compared group) showed there wasn't statistically significant differences in the quality of the learning outcome of collaboration between the groups and in students satisfaction. But there was significant difference in the degree of individual acquisition depending on the offering of scaffolding for Critical Thinking. Therefore, as premised in this study, supporting meaningful mutual interaction between learners during collaborative argumentation using Critical Thinking Strategy has a positive influence on the individual acquisition of domain knowledge. The group provided with scaffolding for Critical Thinking gained higher effect in the degree of knowledge sharing and individual acquisition of domain knowledge compared to the group provided with general argumentation scaffolding.

• Geomechanics and Engineering
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• 제37권4호
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• pp.371-382
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• 2024

Measurement or prediction of compression index (C_c) of soils is essential for assessment of total and differential settlement of structures. It is a well-known fact that this parameter is controlled by several index identifiers of soil including initial void ratio, Atterberg limits, overconsolidation ratio, specific gravity, etc. Many studies in the past proposed relationships for prediction of C_c based on different index properties. Therefore, this study aims to present a comparison of previously proposed equations for estimation of C_c. Data from literature was compiled, and a total of 90 and 623 test results on remolded and undisturbed specimens were used to question the validity of previously proposed equations. Nevertheless, the modeling ability of 7 and 12 equations for estimation of C_c of remolded and undisturbed soils were questioned by use of compiled data. Moreover, new empirical relationships based on initial void ratio and toughness limit for prediction of C_c was proposed by use of nonlinear multivariable regression and evolutionary based regression analyses. The results are promising-the performances of models established are quite acceptable, which are verified by statistical analyses.

• 영재교육연구
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• 제22권1호
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• pp.117-139
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• 2012

이 연구의 목적은 Peer Instruction 수업을 통해 문항의 난이도에 따른 과학영재의 인지갈등의 특성을 알아보고, 일반 학생들의 인지갈등 정도와 비교 분석하였다. 서울시와 경기도 소재 교육청 부설 영재교육원 과학영재학생 49명, 일반 중학교 학생 71명을 대상으로 빛의 직진 및 합성에 관한 개념 검사에 대해 동료 토론 전 후의 인지갈등 검사를 실시하였다. 과학영재는 인지적 재평가 요인 측면에서는 문항의 난이도와 관계없이 동료와의 토론 후 유의미하게 인지갈등이 감소했다. 과학 영재는 동료에 대한 신뢰가 높은 편이었으며 동료와 토론하는 동안 자신의 개념을 동료에게 설명하면서 머릿속의 개념을 명료화할 수 있고 반성적 사고를 하게 되므로 갈등이 해소되어 인지갈등이 감소한 것으로 나타났다. 문항의 난이도가 높아질수록 과학영재는 일반학생과 같이 동료 토론 전에 불안 정도가 높았지만, 일반학생에 비해 그 불안 정도는 낮았고, 동료 토론 후에 불안 정도는 통계적으로 유의미하게 감소함을 알 수 있었다. 과학영재의 인지갈등변화를 분석한 결과를 바탕으로 과학영재의 학습자 특성을 고려한 다양한 인지갈등 전략의 개발과 적용이 필요하다는 것을 알 수 있다. 또한 과학영재를 위한 개념검사 문항을 개발할 때, 문항의 난이도에 대한 고려 사항에서 본 연구의 결과는 시사하는 바가 크다고 할 수 있다.

• 대한지구과학교육학회지
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• 제9권2호
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• pp.123-138
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• 2016

본 연구의 목적은 자기질문전략 중 QAR(Question-Answer-Relationship) 전략을 적용한 과학수업이 학습유형에 따라 초등학교 5학년 학생들의 과학적 태도에 어떠한 영향을 미치는지를 알아보는 것이다. 따라서 연구대상은 초등학교 5학년 4개 학급 97명을 대상으로 실험집단 49명과 비교집단 48명을 선정하였다. 수업실시 전과 후, 각 집단을 대상으로 검사를 실시하여 자기질문전략이 과학적 태도에 미치는 영향을 알아보았다. 또한 실험집단 학생을 대상으로 Kolb의 자기보고식 학습유형 검사를 실시하여 학습유형에 따른 과학적 태도의 변화를 비교 분석 하였다. 연구결과는 다음과 같다. 이 연구에서 밝혀진 결과는 다음과 같다. 첫째, 과학적 태도에 있어 수업 실시 후 실험집단과 비교집단 사이에 유의미한 차이가 있었다. 둘째, 실험집단의 학습유형을 분류한 결과 적응자(46.9%), 수렴자(24.5%), 분산자(20.4%), 융합자(8.2%) 순이었다. 자기질문전략을 적용한 수업 후 과학적 태도에 있어 학습유형 집단 간에는 통계적인 유의미한 차이를 보이지 않았으나 학습유형 중 융합자 보다는 적응자, 수렴자, 분산자의 과학적 태도에 더 긍정적인 영향을 끼쳤다.

• 한국과학교육학회지
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• 제32권3호
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• pp.428-445
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• 2012

The objective of this study is developing an instrument for investigating views of the respondents on nature of science(NOS) by using experienced scientific knowledge, atomic model. It consists of total six questions and 36 detail items, and each question is reflected the aspects of different NOS which are 'recognition on the model', 'tentativeness of scientific knowledge', 'subjectivity in science', 'use of inference and imagination', 'myths of the scientific method', and 'comparison between science and art'. Particularly, 'comparison between science and art' is addressed almost for the first time in this questionnaire. In the class environment almost not to teach nature of science linking with concrete scientific knowledge, to inquire how the students recognize nature of science, relating to experienced scientific knowledge through this questionnaire will give the data of scientific knowledge based recognition on the nature of science and an important implication for nature of science teaching with concrete scientific knowledge. Developing processes have gone through four steps. In first step, we chose aspects of NOS and developed questions and details. In second step, we tested the draft into fifteen science teachers and, reflecting their opinions, corrected the form and contents of questionnaires. In third step, we tested the questionnaire included writing section for expressing thoughts of the respondents into 55 students in science high school and checked index of coincidence between Likert and open-ended responses which shows 88.2% degree of consensus. Furthermore, to identify the feature of using concrete scientific knowledge we applied this and views on science and education questionnaires together into six university students. We performed final test to 68 university students and measured Cronbach's, and ultimately completed final questionnaire in last step.