• The Journal of the Korean dental association
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• v.55 no.1
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• pp.63-70
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• 2017

Materials and methods: Sixty extracted premolars were assigned to three groups according to the root canal system (Weine's classification; type I, II and III) of 20 teeth each using radiographic examination. The root tip was cut horizontally 1 mm from the anatomical apex and the apical cross-section was visualized using microscope at x50 magnification and photographed. Minimum and maximum apical root canal diameter of each tooth was measured and classified into three types by canal morphology (round, oval and flattened shape). Statistical analysis was performed to compare the apical root canal diameter and morphology according to the root canal system. Results: In apical root canal morphology at cross-sectional view, the most common shape was round in type I, flat in type II, and oval in type III. In apical root canal diameters at cross-sectional view, there was a significant difference between the minimum and maximum diameter in all types (p<0.05). The maximum diameter was 0.331 mm in type I, 0.519 mm in type II, and 0.310 mm in type III. There was a significant difference among type I, III and type II (p<0.05). Conclusion: The morphology and diameter of apical root canal was different according to the root canal system. Therefore, clinicians should consider the apical file size in view of the apical root canal shape according to the root canal system.

• Journal of Korean Elementary Science Education
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• v.38 no.1
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• pp.116-129
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• 2019

This study investigated elementary students' spatial thinking and visualization when they learned the shape of volcanoes. For this purpose we used GeoMapApp to design instruction program and assessment items. In the instruction, students were asked to connect the floor plan view of Jeju island with the cross-sectional view of the same figure producted by GeoMapApp. Then they were asked to classify four sets of pictures of volcanoes based on the similarities of figures, that is, dome-shaped and shield volcanoes. In the assessment students solved three questions which examined how they connected the plan view and cross-sectional profile of Kilauea, draw cross-sectional profile of Mt. Fuji, and distinguished a shield volcano and dome-shaped one. Students' discourse data during the class were analyzed according to the amount to showing their spatial thinking and visualization. The instruction program using GeoMapApp assisted students to facilitate their spatial thinking for understanding of volcanoes. The outcomes of assessment showed even elementary students had good spatial thinking and visualization. Therefore, we argued spatial thinking and visualization for geoscientific understanding need to be included in the national science curriculum for elementary students.

• Journal of the Korean Society of Industry Convergence
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• v.24 no.6_1
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• pp.683-691
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• 2021

Bipolar plates with channel width of 0.5 mm, 0.4 mm, and 0.3 mm respectively were printed using a 3D printer. The shape of three b ipolar plates was rectangular, the channel depth was 0.5 mm, and the thickness of base was 0.5 mm. The bipolar plate with channel width of 0.5 mm had 45 channels, and their active area was 44.5 mm × 50 mm. The bipolar plate with channel width of 0.4 mm had 57 channels and its active area was 45.2 mm × 50 mm, and the bipolar plate with channel width of 0.3 mm had 75 channels and its active area was 44.7 mm × 50 mm. The bipolar plates were printed using PLA filament. The cross-sectional lengths of the bipolar plates with channel widths of 0.5 mm and 0.4 mm were identical by 96% of the designed cross-sectional length. Whereas the bipolar plate with a channel length of 0.3 mm had a large difference of 25% from the designed cross-sectional length.

• Korea-Australia Rheology Journal
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• v.13 no.2
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• pp.97-106
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• 2001

Three-dimensional flow analysis was performed by using the control volume finite-element method for design of a profile extrusion die. Because polymer melt behavior is complicated and cross-sectional shape of the profile extrusion die is changing continuously, the fluid flow within the die must be analyzed three-dimensionally. A commercially available polypropylene is used for theoretical and experimental investigations. Material properties are assumed to be constant except for the viscosity. The 5-constant modified Cross model is used for the numerical analysis. A test problem is examined in order to verify the accuracy of the numerical method. Simulations are performed for conditions of three different screw speeds and three different die temperatures. Predicted pressure distribution is compared with the experimental measurements and the results of the previous two-dimensional study. The computational results obtained by using three dimensional CVFEM agree with the experimental measurements and are more accurate than those obtained by using the two-dimensional cross-sectional method. The velocity profiles and the temperature distributions within several cross-sections of the die are given as contour plots.

• Journal of ILASS-Korea
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• v.14 no.2
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• pp.59-64
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• 2009

These experiments are close examination of spray characteristics that are continuous liquid jet and modulated liquid jet. The experiments were conducted using water, over a range of crossflow velocities from $42{\sim}l36\;m/s$, with modulation frequencies of $35.7{\sim}166.2\;Hz$. Between continuous crossflow jet and modulated cross-flow jet of penetration, breakup point, spray angle and macro spray shape are experimentally investigated with image analysis. In cross-flow field, main parameter of liquid jet for breakup was cross-flow stream rather than modulation effect. As oscillation of the periodic pressure that could make liquid jet moved up and down, the mixing efficiency was increased. Also, a bulk of liquid jet puff was detected at upper field of liquid surface. So, this phenomenon has a good advantage of mixing spray from concentration of center area to outer area. Because of modulation frequency, SMD inclination of the structured layer was evanescent. Cross-sectional characteristics of SMD at downstream area were non-structured distributions. Then cross-sectional characteristics of SMD size were about same tendency over a range that is effect of spray mixing. The tendency of volume flux value for various modulation frequency was same distribution. And volume flux was decreased when the modulation frequency increase.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2012.05a
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• pp.709-710
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• 2012

• 한국도로학회:학술대회논문집
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• 2010.09a
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• pp.265-270
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• 2010

• Steel and Composite Structures
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• v.18 no.4
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• pp.985-1000
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• 2015

The method of cross-section analysis for different sections in a structural frame has been widely investigated since the 1960s for determination of sectional capacities of beam-columns. Many hand-calculated equations and design graphs were proposed for the specific shape and type of sections in pre-computer age decades ago. In design of many practical sections, these equations may be uneconomical and inapplicable for sections with irregular shapes, leading to the high construction cost or inadequate safety. This paper not only proposes a versatile numerical procedure for sectional analysis of beam-columns, but also suggests a method to account for residual stress and geometric imperfections separately and the approach is applied to design of high strength steels requiring axial force-moment interaction for advanced analysis or direct analysis. A cross-section analysis technique that provides interaction curves of arbitrary welded sections with consideration of the effects of residual stress by meshing the entire section into small triangular fibers is formulated. In this study, two doubly symmetric sections (box-section and H-section) fabricated by high-strength steel is utilized to validate the accuracy and efficiency of the proposed method against a hand-calculation procedure. The effects of residual stress are mostly not considered explicitly in previous works and they are considered in an explicit manner in this paper which further discusses the basis of the yield surface theory for design of structures made of high strength steels.

• Transactions of Materials Processing
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• v.24 no.3
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• pp.187-193
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• 2015

The objective of the current study is to determine cross-sectional profile of intermediate dies in order to improve the plastic strain homogeneity which directly affects not only the dimensional accuracy but also the mechanical properties of final product by redesigning the intermediate dies using the conventional electric field analysis (EFA) method. Initially, the multi-pass shape wire drawing was designed by using the equivalent potential lines from EFA. The area reduction ratio was calculated from the number of passes in multi-pass shape wire drawing but constrained by the capacity of the drawing machine and the drawing force. In order to compensate for a concentration of strain in a region of the cross section of the wire, the process for multi pass wire drawing from initial round material to an intermediate die was redesigned again using the electric field analysis. Both drawing process designs were simulated by the finite element method in which the strain distribution and standard deviation plastic strain of the cross section of drawn wires were examined.

• Transactions of the Korean Society of Automotive Engineers
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• v.25 no.3
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• pp.350-359
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• 2017

This paper presents a new holistic development approach for the carbon continuous-fiber composite frame of an automotive sunroof assembly. The original steel frame has been designed to get higher bending stiffness with its corrugated cross-sectional shape. The new approach uses the prepregs of a fast cure epoxy and PCM manufacturing processing. For higher productivity, the new frames feature a very simple plat cross sectional shape but achieve high bending stiffness through the laminate design. The sandwich structure with a PET foam core was presented. The frames were made of carbon UD laminae covered single carbon fabric on the outer surfaces. The fabrics provide torsional stiffness and also hold the carbon UD fibers floating in the low viscous epoxy resin of prepregs at the curing temperature during processing. The final product yields approximately 18 % savings in weight compared with the original.