• Transactions of Materials Processing
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• v.17 no.7
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• pp.473-480
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• 2008

Sheet metal forming of Mg alloy is usually performed at elevated temperature because of the low formability at room temperature. Therefore, strain rates affected with the forming temperature and speed must be considered as important factor about formability. Effects of process parameters such as various temperatures and forming speeds were investigated in circular cup deep drawing. From the experimental results, it is known that LDR (Limit Drawing Ratio) increase as the strain rate increase. On the contrary, the FLD (Forming Limit Diagram) shows lower value as faster strain rate. Therefore, anisotropy values are investigated according to the temperature and strain rates at each forming temperature. R-values also represent higher value as faster strain rate. It is known that the formability can be different with the deformation mode on warm forming of AZ31 alloy sheet.

• Journal of the Korean earth science society
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• v.26 no.4
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• pp.329-335
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• 2005

The purpose of this study is to suggest the modification of activities to introduce the nature of science in earth science classrooms. A small modification can turn ordinary textbook activities into the nature of science activities. Since earth science could provide a good basis for the tentative, creative, and socially and culturally embedded nature of science, as well as appropriate understanding about scientific methods, careful modification of earth science activities could be effective for students to understand the nature of science. Considering which aspects of the nature of science are appropriate, along with the possible change in the activity, teachers will be able to modify textbook activities effectively. An example modification of H-R diagram activity was also suggested.

• Journal of The Korean Astronomical Society
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• v.16 no.1
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• pp.23-30
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• 1983

About two hundred stars within 50 pc from the sun, whose tangential velocity larger than 100 km/sec, have been selected on the basis of their proper motions and trigonometric parallaxes. A list of them along with their photoelectric UBV data and spectral types is given. The criterion on the tangential velocity, $v_t$ > 132 km/sec, was adopted for selection of high-velocity stars. The H-R diagram of these nearby high-velocity stars resembles that of a globular cluster, with the turnoff around $B-V{\approx}0.35$ and $M_v{\approx}4.0$, and the subdwarfs among these high-velocity stars are fainter than the main-sequence stars of Hyades by the amount of $1^m.25{\pm}0^m.30$ in the region with B-V < 1.40 on the average.

• Journal of the Korean earth science society
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• v.40 no.5
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• pp.538-547
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• 2019

This study analyzes the conceptual understanding of in-service and pre-service earth science teachers about the H-R diagrams and evolution of stars using conceptual status analysis categories. The results show that (a) many teachers use unscientific language in the Intelligibility range, (b) teachers are categorized in Low scientific inquiry ability related to graph creation and unscientific analogy for scientific concept which is hightly corelated to the possibility of misunderstanding in the teaching process, and (c) pre-service teachers lack the understanding of the secondary science curriculum. It is necessary to develop pre-service curriculum that can be applied to the school site. In the category of Plausibility range, (d) both groups understood the cosmological meaning of stellar evolution. However, pre-service teachers do not specifically explain the mechanism of a star. In the category of Fruitfulness range, in-service teachers come up with educational problems reflecting the academic characteristics of earth science and apply their knowledge to actual problem solving. On the other hand, pre-service teachers show high nonresponse ratio, they do not see the H-R diagram and the evolution of stars as a practical concept. In the analysis process, both groups are found to have many unscientific conceptions about the H-R diagram and evolution of stars. Therefore, it is suggested that caution be used in developing a professional development program of earth science teachers.

• Journal of Astronomy and Space Sciences
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• v.22 no.3
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• pp.233-242
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• 2005

The absolute dimensions and orbital elements of 66 near contact binaries, collected from literatures, have been analyzed to investigate the physical characteristics of the near contact binaries as well as co-relations among physical parameters. The relationship between the mass ratio and luminosity ratio of the near contact binary systems have been obtained as a $L_2/L_1{\approx}(M_2/M_1)^{1.45}$, which is similar to that of the early type contact binary system. The physical parameters of the new contact binaries show that the difference in mass, radius, luminosity and temperature between the primary and the secondary components for the F type NCBs are smaller than those for the A type NCBs. In H-R diagram, the components of the A types are located closer to the terminal age main sequence than those of the F types.

• Applied Chemistry for Engineering
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• v.29 no.2
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• pp.209-214
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• 2018

In this paper, the techno-economic analysis of glycerol steam reforming for $H_2$ production capacity of $300m^3\;h^{-1}$ was carried out. The process of glycerol steam reforming was constructed by using Aspen $HYSYS^{(R)}$, a commercial process simulator, and parametric studies for the effect of the operating temperature on $H_2$ production was performed. Moreover, the economic analysis was conducted through an itemized cost estimation, sensitivity analysis (SA) and cash flow diagram (CFD), and the unit $H_2$ production cost was 5.10 $ ${kgH_2}^{-1}$ through the itemized cost estimation of glycerol steam reforming for $H_2$ production capacity of $300m^3\;h^{-1}$. SA was employed to identify key economic factors and various economic indicators such as net present value (NPV), discounted payback period (DPBP), and present value ratio (PVR) were found according to $H_2$ selling price using CFD.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.06a
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• pp.479-480
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• 2009

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2008.06a
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• pp.671-672
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• 2008

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2009.10a
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• pp.449-450
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• 2009

• The Journal of the Petrological Society of Korea
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• v.25 no.4
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• pp.311-324
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• 2016

The characteristics of the rock cleavage in Jurassic granite from Geochang were analysed. The evaluation for three quarrying planes and three rock cleavages was performed using the parameters such as (1) reduction ratio between the value of spacing and the value of length, (2) microcrack spacing frequency(N), (3) total spacing($1mm{\geq}$), (4) exponential constant(a), (5) magnitude of exponent(${\lambda}$), (6) mean spacing($S_{mean}$), (7) difference value($S_{mean}-S_{median}$) between mean spacing and median spacing($S_{median}$) and (8) density of spacing. Especially the close dependence between the above spacing parameters and the parameters from the spacing-cumulative frequency diagrams was derived. The discrimination factors representing three quarrying planes and three rock cleavages were acquired through these mutual contrast. The analysis results of the research are summarized as follows. First, the reduction ratios of frequency(N), mean value, median value, the above difference value($S_{mean}-S_{median}$) and density for three rock cleavages are in orders of G(grain, (G1 + G2)/2) < H(hardway, (H1 + H2)/2) < R(rift, (R1 + R2)/2), H < G $\ll$ R, H < G $\ll$ R, H < G < R and H < G $\ll$ R. The values of the above five parameters for three planes show the various orders of R'(rift plane) $\ll$ H'(hardway plane) < G'(grain plane), R' $\ll$ G' < H', R' < H' < G', R' < G' < H' and R' $\ll$ H' < G', respectively. Second, the values of (I) parameters(2, 3, 4 and 5) and (II) parameters(6, 7 and 8) are in orders of (I) H < G < R and (II) R < G < H. On the contrary, the values of the above two groups(I~II) of parameters for three planes show reverse orders. Third, to review the overall characteristics of the arrangement among the six diagrams, these diagrams show an order of R2 < R1 < G2 < G1 < H2 < H1 from the related chart. In other words, above six diagrams can be summarized in order of rift(R1 + R2) < grain(G1 + G2) < hardway(H1 + H2). These results indicate a relative magnitude of rock cleavage related to microcrack spacing. Especially, two parameters for each diagram, the above difference value($S_{mean}-S_{median}$) and mean spacing, could provide advanced information for prediction the order of arrangement among the diagrams. Finally, the general chart for three planes and three rock cleavages were made. From the related chart, three exponential straight lines for three rock cleavages show an order of R(R1 + R2) < G(G1 + G2) < H(H1 + H2). On the contrary, three lines for three planes show an order of H'(R2 + G2) < G'(R1 + H2) < R'(G1 + H1). Consequently, correlation of the mutually reverse order between three planes and three rock cleavages can be drawn from the related chart.