• Journal of The Korean Association For Science Education
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• v.38 no.2
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• pp.249-257
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• 2018

The purpose of this study was to analyze the knowledge and ability levels of middle school students in four areas: conceptual understanding, argument construction, justification schemes, and use of scientific knowledge in a causal explanation for a genetic phenomenon. A group of 162 middle school students who have taken a class titled Genetics and Evolution participated in the study. Each student answered-and justified the answer to-one question pertaining to genetics. Ability levels were rated from level 0 to level 4, with 4 being the top rating. Students were required to choose one of two competing arguments to explain whether green seed pimps and red seed pimps of the same size and shape were the same species or not. Analyzing conceptual understanding: 47% of the respondents provided the correct answer. Analyzing their abilities for constructing an argument: 75% of the students with the correct answer and 42% of the students with the incorrect answer were evaluated to be at ability level 3 or 4 for argument construction. Analyzing the students' justification schemes: "Scientific idea" and "Analogy" were the most frequently used schemes. Analyzing their use of scientific knowledge: of the students who selected the scientific idea justification scheme, 36% used the correct scientific knowledge, but the remainder used inaccurate or nonspecific scientific knowledge. These findings provide implication for encouraging argumentative writing explaining scientific phenomena regarding epistemic practice.

• Journal of The Korean Astronomical Society
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• v.29 no.spc1
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• pp.63-64
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• 1996

The nature of distant faint blue field galaxies remains a mystery, despite the fact that much attention has been devoted to this subject in the last decade. Galaxy counts, particularly those in the optical and near ultraviolet bandpasses, have been demonstrated to be well in excess of those expected in the 'no-evolution' scenario. This has usually been taken to imply that galaxies were brighter in the past, presumably due to a higher rate of star formation. More recently, redshift surveys of galaxies as faint as B$\~$24 have shown that the mean redshift of faint blue galaxies is lower than that predicted by standard evolutionary models (de-signed to fit the galaxy counts). The galaxy number count data and redshift data suggest that evolutionary effects are most prominent at the faint end of the galaxy luminosity function. While these data constrain the form of evolution of the overall luminosity function, they do not constrain evolution in individual galaxies. We are carrying out a series of observations as part of a long-term program aimed at a better understanding of the nature and amount of luminosity evolution in individual galaxies. Our study uses the luminosity-linewidth relation (Tully-Fisher relation) for disk galaxies as a tool to study luminosity evolution. Several studies of a related nature are being carried out by other groups. A specific experiment to test a 'no-evolution' hypothesis is presented here. We have used the AUTOFIB multifibre spectro-graph on the 4-metre Anglo-Australian Telescope (AAT) and the Rutgers Fabry-Perot imager on the Cerro Tolalo lnteramerican Observatory (CTIO) 4-metre tele-scope to measure the internal kinematics of a representative sample of faint blue field galaxies in the red-shift range z = 0.15-0.4. The emission line profiles of [OII] and [OIII] in a typical sample galaxy are significantly broader than the instrumental resolution (100-120 km $s^{-l}$), and it is possible to make a reliable de-termination of the linewidth. Detailed and realistic simulations based on the properties of nearby, low-luminosity spirals are used to convert the measured linewidth into an estimate of the characteristic rotation speed, making statistical corrections for the effects of inclination, non-uniform distribution of ionized gas, rotation curve shape, finite fibre aperture, etc.. The (corrected) mean characteristic rotation speed for our distant galaxy sample is compared to the mean rotation speed of local galaxies of comparable blue luminosity and colour. The typical galaxy in our distant sample has a B-band luminosity of about 0.25 L$\ast$ and a colour that corresponds to the Sb-Sd/Im range of Hub-ble types. Details of the AUTOFIB fibre spectroscopic study are described by Rix et al. (1996). Follow-up deep near infrared imaging with the 10-metre Keck tele-scope+ NIRC combination and high angular resolution imaging with the Hubble Space Telescope's WFPC2 are being used to determine the structural and orientation parameters of galaxies on an individual basis. This information is being combined with the spatially resolved CTIO Fabry-Perot data to study the internal kinematics of distant galaxies (Ing et al. 1996). The two main questions addressed by these (preliminary studies) are: 1. Do galaxies of a given luminosity and colour have the same characteristic rotation speed in the distant and local Universe? The distant galaxies in our AUTOFIB sample have a mean characteristic rotation speed of $\~$70 km $s^{-l}$ after correction for measurement bias (Fig. 1); this is inconsistent with the characteristic rotation speed of local galaxies of comparable photometric proper-ties (105 km $s^{-l}$) at the > $99\%$ significance level (Fig. 2). A straightforward explanation for this discrepancy is that faint blue galaxies were about 1-1.5 mag brighter (in the B band) at z $\~$ 0.25 than their present-day counterparts. 2. What is the nature of the internal kinematics of faint field galaxies? The linewidths of these faint galaxies appear to be dominated by the global disk rotation. The larger galaxies in our sample are about 2"-.5" in diameter so one can get direct insight into the nature of their internal velocity field from the $\~$ I" seeing CTIO Fabry-Perot data. A montage of Fabry-Perot data is shown in Fig. 3. The linewidths are too large (by. $5\sigma$) to be caused by turbulence in giant HII regions.

• Journal of Powder Materials
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• v.31 no.2
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• pp.137-145
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• 2024

In order to predict the process window of laser powder bed fusion (LPBF) for printing metallic components, the calculation of volumetric energy density (VED) has been widely calculated for controlling process parameters. However, because it is assumed that the process parameters contribute equally to heat input, the VED still has limitation for predicting the process window of LPBF-processed materials. In this study, an explainable machine learning (xML) approach was adopted to predict and understand the contribution of each process parameter to defect evolution in Ti alloys in the LPBF process. Various ML models were trained, and the Shapley additive explanation method was adopted to quantify the importance of each process parameter. This study can offer effective guidelines for fine-tuning process parameters to fabricate high-quality products using LPBF.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.27.1-27.1
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• 2010

Globular cluster (GC) systems in most galaxies, particularly in ellipticals, show bimodal color distributions. Because broadband colors trace metallicity at old ages, this phenomenon has been commonly interpreted as bimodal metallicity distributions, implying the presence of two sub-populations in the globular cluster system within a galaxy. However, a new explanation has recently been proposed, in which the non-linear nature of color-metallicity relations induced by horizontal-branch stars can produce bimodal color distributions even from unimodal metallicity distributions. In this study, we put these two explanations to the test on the origin of color bimodality, using multi-band (U,B,V and I) photometry of globular clusters in NGC 1399, the central giant elliptical galaxy in Fornax galaxy cluster. We find significant changes in the morphology of color distributions when using different colors. The observation is also well reproduced by the Monte Carlo realization of GC color when a unimodal metallicity distribution and the theoretical non-linear color-metallicity relations are assumed. We discuss the implications regarding theories on galaxy formation and evolution.

• Korean Journal of Ecology and Environment
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• v.42 no.2
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• pp.192-199
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• 2009

Freshwater green algae are one of the important sources of bioenergy in the future. Spirogyra is a conjugating filamentous zygnematacean green algal genus that is widely distributed worldwide with more than 400 species. Despite its widespread occurrence throughout the world, cytological studies of the genus have been limited. We investigated karyological features and chromosome numbers for seven Korean Spirogyra species. Most of the species examined in the present study showed significant karyological features, inner organization of nucleolus, heavily stainable nucleolar substance and the diffuse-centric nature of chromosomes, typical of the Conjugales. Chromosome number ranged from n=12 in S. varians to n=38 in S. africana. Aberrant cytokinesis resulted in binucleate and tetranucleate cells, which sometimes provide cytological explanation for different morphology and ploidal changes in clonal culture of Spirogyra or even different cells within the same filament. The present chromosome data also substantiates the earlier held assumption that aneuploidy must have been the chief driving force for speciation and evolution of the genus Spirogyra.

• Journal of Science and Technology Studies
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• v.2 no.2 s.4
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• pp.55-89
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• 2002

The purpose of this article is to examine and assess the main issues in social constructivism with reference to the history of technology. Social constructivism, as an alternative explanation to technological change, has developed its points actively responding to various criticisms. Historians of technology have joined in dialogues with social constructivists through controversies about narrative vs theory, reliability vs performance, and evolution of bicycle. Social constructivists tend to use new jargons excessively, don't deal historical materials rigorously, and don't consider content-dependency sufficiently. To apply social constructivism to Korean cases many problems should be identified including the deficiency of historical materials, the importance of technological learning, and the peculiarity of relevant social group.

• Transactions of Materials Processing
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• v.21 no.4
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• pp.240-245
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• 2012

With the increasing demand for light-weight materials to reduce fuel consumption, the automobile industry has extensively studied magnesium alloys which are light weight metals. The intrinsic poor formability and poor ductility at ambient temperature due to the hexagonal close-packed (HCP) crystal structure and the associated insufficient number of independent slip systems restricts the practical usage of these alloys. Hot working of magnesium alloys using a forging or extrusion enables net-shape manufacturing with enhanced formability and ductility since there are several operative non-basal slip systems in addition to basal slip plane, which increases the workability. In this research, the thermomechanical properties of AZ80 Mg alloy were obtained by compression testing at the various temperatures and strain rates. Optical microscopy and EBSD were used to study the microstructural behavior such as misorientation distribution and dynamic recrystallization. The results were correlated to the hardening and the softening of the alloy. The experimental data in conjunction with a physical explanation provide the optimal conditions for net-shape forging under hot or warm temperatures through control of the grain refinement and the working conditions.

• Tunnel and Underground Space
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• v.26 no.4
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• pp.266-273
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• 2016

We have numerically modeled thermal evolution of Ulleung Island after an emplacement of magma chamber. The disk-shape magma chamber is assumed to locate at 2.9 km beneath the island and has a diameter and a thickness of 10 km and 300 (or 600) m, respectively. The geothermal gradients evaluated from the numerical modeling coincide well with the range of the geotherms (${\sim}95^{\circ}C/km$) observed from the well logging. Although there are limitations in the application of the numerical results directly to the interpretation of the observed geotherms, we believe that an existence of a hot magma chamber in molten or in solidified state is the most plausible explanation for the observed geotherms.

• Journal of Korea Society of Industrial Information Systems
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• v.10 no.3
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• pp.15-20
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• 2005

Since the invention of Web, it became part of our daily life replacing the routine information search and effecting many activities which otherwise could have been done off-line without it. It was a natural evolution of the web technology, which had started out as a simple test based pattern matching, to be based on the optimized match process for its multi-media Web environment, like still images, music and movies that we are to face today. In this paper, we proposed and implemented the model which the multimedia resources can be efficiently shared in semantic web. After converting multimedia resource information(metadata) into RDF, for efficient management, the model separate and allotment actual multimedia resource and corresponding metadata changed to RDF to each server. The proposed model could be applied in all multimedia resources. For easy explanation and implementation, however, we applied it to the digital photograph in example.

• Journal of The Korean Association For Science Education
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• v.36 no.4
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• pp.591-606
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• 2016

The purpose of this study is to develop the argumentation program to build scientific concepts on natural selection for science-gifted elementary students and to know how to implement this program. For this study, nine key concepts about natural selection such as the overproduction of offspring, limited resources, population stability, competition, variation, heredity of variation, differential survival, change of the population and speciation were selected through the literature study. The programs were developed by learning cycle instructional model. Argument writings and discourses have been collected, analyzed and compared before and after the program. Two questionnaires to compare pre and post concept change consist of multiple choice questionnaire and open-ended response question were developed and applied to 19 science-gifted elementary students. Sufficiency of the explanation and conceptual quality of the explanation were used to assess the quality of their arguments before and after the program. Discourse and visual models collected from the highest and lowest group about score improvement were compared. The scores of the gifted statistically improved significantly in multiple choice questionnaire. Students' alternative conceptions about natural selection at the beginning of the program decreased and changed scientifically after the program. Visual models drawn by the students supported the results as well. This study asserts that elementary science-gifted students are able to explain evolutionary perspectives about organism change and use the key concepts of natural selection. The study means that evolutionary perspective is possible to be reflected in elementary science curriculum for the gifted.