• Journal of the Korean School Mathematics Society
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• v.9 no.3
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• pp.317-345
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• 2006

The purpose of this paper is to provide readers related to mathematics education with information and guidelines on 'Teaching and Learning Materials for Differentiated Instruction in Mathematics'. This paper is generally comprised of two parts. The one part is basically focused on understanding the meaning of differentiated education. The focus of the other part is on developing differentiated instructional materials for mathematics, according to the following procedures: 1. Analyzing the current differentiated mathematics curriculum and textbooks 2. Drawing a framework for developing the differentiated teaching and learning materials, and planning the procedure of developing the materials in detail. 3. Developing, checking, and revising the materials 4. Proposing how to utilize the materials effciently and effectively in class

• Journal of The Korean Association For Science Education
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• v.5 no.2
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• pp.81-88
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• 1985

The purpose of the study was to establish a new view of textbook which may contribute to the abolishment of the instruction mainly based on the only textbook and to the promotion of creativities of students. We first reviewed science textbooks and related teaching-learning materials of foreign countries with emphasis on the relationship among textbook and teaching-learning materials and practical use of them. In western countries the roles of traditional textbook has been changed. That is, various kinds of materials such as reading book, work-book, worksheet, experimental guidebook, filmstrips are used to raise effect of instruction besides of traditional type of textbook. Secondary, we identified the problems related to the science textbook-view of textbook, textbook contents, practical use of textbook-through opinion survey administered to principals akd teachers of elementary schools. The results of the survey are as follows; Concerning the view of textbook, most teachers did not recognize textbook as an absolute materials. They thought that textbook contents could be taught reorganized according to their judgements. On the contrary, teachers responded to the question of whether or not they follow contents of textbook as they are presented in it were approximately 30%. Further, more than 75% of them have seldom used instructional materials except textbooks. In order to revise the problems of our present textbook as stated above, a new view of textbook should be established. We, above all, established 4 basic premises for searching a new view of textbook. 1) Textbook should not be considered as the only material but as being at the center of various teaching -learning materials. 2) The importance of textbook should be illustrated Among Curriculum, textbook and related teaching-learning materials, instruction and evaluation. 3. Textbook contents should not be regarded as definitely fixed or absolute ones. 4. Human being can understand environment more fully by commanding his swnsory organ multilaterally. Under these premises we disscussed about curriculum and textbook, textbook, and instruction, akd evaluation method.

• Journal of Powder Materials
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• v.22 no.4
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• pp.240-246
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• 2015

Anodic aluminum oxide (AAO) has been widely used for the development and fabrication of nano-powder with various morphologies such as particle, wire, rod, and tube. So far, many researchers have reported about shape control and fabrication of AAO films. However, they have reported on the shape control with different diameter and length of anodic aluminum oxide mainly. We present a combined mild-hard (or hard-mild) anodization to prepare shape-controlled AAO films. Two main parameters which are combination mild-hard (or hard-mild) anodization and run-time of voltage control are applied in this work. The voltages of mild and hard anodization are respectively 40 and 80 V. Anodization was conducted on the aluminum sheet in 0.3 mole oxalic acid at $4^{\circ}C$. AAO films with morphologies of varying interpore distance, branch-shaped pore, diameter-modulated pore and long funnel-shaped pore were fabricated. Those shapes will be able to apply to fabricate novel nano-materials with potential application which is especially a support to prevent volume expansion of inserted active materials, such as metal silicon or tin powder, in lithium ion battery. The silicon powder electrode using an AAO as a support shows outstanding cycle performance as 1003 mAh/g up to 200 cycles.

• Korean Journal of Materials Research
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• v.28 no.9
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• pp.489-494
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• 2018

Lead free $(1-x)(0.675BiFeO_3-0.325BaTiO_3)-xLiTaO_3$ (BFBTLT, x = 0, 0.01, 0.02, and 0.03, with 0.6 mol% $MnO_2$ and 0.4 mol% CuO) were prepared by a solid state reaction method, followed by air quenching and their crystalline phase, morphology, dielectric, ferroelectric and piezoelectric properties were explored. An X-ray diffraction study indicates that lithium (Li) and tantalum (Ta) were fully incorporated in the BFBT materials with the absence of any secondary phases. Dense ceramic samples (> 92 %) with a wide range of grain sizes from $3.70{\mu}m$ to $1.82{\mu}m$ were obtained in the selected compositions ($0{\leq}x{\leq}0.03$) of BFBTLT system. The maximum temperatures ($T_{max}$) were mostly higher than $420^{\circ}C$ in the studied composition range. The maximum values of maximum polarization ($P_{max}{\approx}31.01{\mu}C/cm^2$), remnant polarization ($P_{rem}{\approx}22.82{\mu}C/cm^2$) and static piezoelectric constant ($d_{33}{\approx}145pC/N$) were obtained at BFBT-0.01LT composition with 0.6 mol% $MnO_2$ and 0.4 mol% CuO. This study demonstrates that the high $T_{max}$ and $d_{33}$ for BFBTLT ceramics are favorable for industrial applications.

• Journal of Environmental Science International
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• v.27 no.2
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• pp.75-81
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• 2018

At present research on mining backfill materials is being carried out to prevent ground subsidence and breaking by underground cavern of exhausted mines. However, backfill materials can cause secondary environmental issues such as ground pollution. To solve these issues, liner and cover materials are constructed before backfill materials constructed, to inhibit toxic substances form moving to the surroundings. Liner and cover materials, however, should have an accelerating performance after construction and when the accelerating performance is degraded, the work efficiency can be lowered, and the construction cost can be increased, by many rebound content. Therefore, this study develops mining liner and cover materials, and evaluates their accelerating performance and physical properties of liner and cover materials by types and content of accelerating agent. In case of aluminate accelerating agent, it is mixed with more than 5% of liner and cover materials(binder/ratio); thus an accelerating performance satisfying Korean Industrial Standards(KS) occurs, and in case of alkali-free accelerating agent, when it is mixed with more than 7%(binder/ratio), accelerating performance satisfying KS occurs. The more the accelerating agent capacity increases, the more compressive strength decreases. In addition, it is confirmed that compressive strength of aluminate accelerating agent is more degraded than compressive strength of the alkali-free accelerating agent. It is also confirmed that drying shrinkage stability of the alkali-free accelerating agent is better than the drying shrinkage stability of the aluminate accelerating agent.

• Korean Journal of Materials Research
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• v.21 no.11
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• pp.596-603
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• 2011

The very high temperature gas reactor (VHTR) is one of the next generation nuclear reactors for its safety, long-term stability, and proliferation-resistance. The high operating temperature of over 800$^{\circ}C$ enables various applications with high energy efficiency. Heat is transferred from the primary helium loop to the secondary helium loop through the intermediate heat exchanger (IHX). The IHX material requires creep resistance, oxidation resistance, and corrosion resistance in a helium environment at high operating temperatures. A Ni-based superalloy such as Alloy 617 is considered as a primary candidate material for the intermediate heat exchanger. In this study, the microstructures of Alloy 617 crept in pure helium and air environments at 950$^{\circ}C$ were observed. The rupture time in helium was shorter than that in air under small applied stresses. As the exposure time increased, the thickness of outer oxide layer of the specimens clearly increased but delaminated after a long creep time. The depth of the carbide-depleted zone was rather high in the specimens under high applied stress. The reason was elucidated by the comparison between the ruptured region and grip region of the samples. It is considered that decarburization caused by minor gas impurities in a helium environment caused the reduction in creep rupture time.

• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.4
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• pp.342-348
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• 2018

The present study examined the various strength and deformation performances of molding materials recycled using film packaging wastes to ascertain the their applicability to secondary products in construction industries. The stress-strain relationships of molding materials were measured under compression, tension, and flexure in accordance with the ASTM procedure. The measured mechanical properties of recycled molding materials were comparable to typical ranges observed in low-density polyethylene and/or high-density polyethylene. However, to stabilize the properties of the molding materials, further management systems are required as follows: 1) evaluation of mechanical properties of materials with respect to various mixing proportions of waste ingredients; 2) estimation of the effect of foreign substance and moisture contents on the mechanical properties; and 3) establishment of comprehensive database including various sources such as manufacture process including applied pressure to produce the molding materials, and collection region and time of wastes.

• Imaging Science in Dentistry
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• v.52 no.2
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• pp.155-164
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• 2022

Purpose: The aim of this study was to systematically screen the literature for studies reporting cosmetic material in the oral and maxillofacial complex to shed light on the types of cosmetic materials, their radiographic appearance, and possible complications. Materials and Methods: Five electronic databases were reviewed for eligible studies. The general search terms were "cosmetic," "filler," "face," and "radiograph." Demographics, material types, clinical and radiographic presentation, and complications were recorded. Results: Thirty-one studies with 53 cases met the inclusion criteria. The mean age was 52.6±15.4 years with a 4 : 3 female-to-male ratio. The most common material was calcium hydroxyapatite (CaHa) (n=14, 26.4%), found incidentally. The materials were generally located within the upper cheek and zygoma (n=35, 66.0%), radiographically well-defined (n=44, 83%), and had no effects on the surrounding structures (n=27, 50.9%). The internal structure was radiopaque (calcification, hyperdensity) for gold wires, CaHa, bone implants, and secondary calcification or ossification. Outdated cosmetic materials or non-conservative techniques were infiltrative, had effects on the surrounding structures, and presented with clinical signs, symptoms, or complications. Conclusion: Conventional radiography, cone-beam computed tomography, and multi-detector computed tomography are useful to differentiate several cosmetic materials. Their magnetic resonance imaging appearance was highly variable. The infrequent inclusion of cosmetic materials in the differential diagnosis implies that medical and dental specialists may be unfamiliar with the radiographic appearance of these materials in the face.

• Progress in Superconductivity
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• v.4 no.1
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• pp.94-98
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• 2002

Two kinds of multifilament Bi-2223／Ag tapes, which are different in the precursor calcination temperatures, were heat treated for different time (12, 20, 30, 50, 70, or 100 h) firstly to obtain varied B2223 contents, and then followed by the same pressing and sintering cycles. The relation of the 2223 phase contents after the first sintering and the transport property of the fully processed tapes was studied. The results show that 75-80% 2223 phase formed in tapes before the first cold pressing is beneficial to get a high $I_{c}$ in the final tapes. Compensating the total heat treatment time of the tapes first sintered for 20 h to the same length as that first sintered for 50 h in the subsequent sintering stages, different $I_{c}$ enhancements were observed in these two tapes. No improvement on $I_{c}$ was found in the tape made from the powder calcined at higher temperature, whereas for the tape prepared with the lower temperature calcined powder, the $I_{c}$ was increased to the same level as that first sintered for 50 h. The 2223 contents before the intermediate mechanical work is related to the residual reactants, especially to the liquid phase, which is of vital importance to the phase conversion and healing microcracks, meanwhile, to the size and distribution of the non-superconducting secondary phases. The lower temperature calcined powder resulted in slow formation of 2223 phase, but also provided more reactants and liquid phase for the further phase conversion, as a consequence, for the Improvement of $I_{c}$. c/.

• Transactions of Materials Processing
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• v.33 no.3
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• pp.178-184
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• 2024

In this study, we investigated the effects of extrusion ratio and extrusion temperature on the microstructure and tensile properties of extruded Mg-6Al-0.3Mn-0.3Ca-0.2Y (SEN6) alloy. As the extrusion ratio and temperature increase, dynamic recrystallization during extrusion is promoted, leading to the formation of a fully recrystallized microstructure with increased grain size. Additionally, the increases in extrusion ratio and temperature lead to texture strengthening, exhibiting a higher maximum texture intensity. The extruded materials contain three types of secondary phases, i.e., Al₈Mn₄Y, Al₂Y, and Al₂Ca, with irregular or polygonal shapes. The quantity, size, distribution, and area fraction of the second-phase particles are nearly identical between the two materials. Despite its larger grain size, the tensile yield strength of the material extruded at 450 ℃ and an extrusion ratio of 25 (450-25) is higher than that of the material extruded at 325 ℃ and an extrusion ratio of 10 (325-10), which is mainly attributed to the stronger texture hardening effect of the former. The ultimate tensile strength is similar in the two materials, owing to the higher work hardening rate in the 325-10 extrudate. Despite differences in grain size and recrystallization fraction, numerous twins are formed throughout the specimen during tensile deformation in both materials; consequently, the two materials exhibit nearly the same tensile elongation.