• The Mathematical Education
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• v.63 no.3
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• pp.451-466
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• 2024

This study investigated elementary preservice teachers' conceptions of a generating line, an ambiguous concept in school mathematics. The preservice teachers' conceptions of a generating line can be classified into four types: (a) only cones have generating lines, (b) only cones and cylinders have generating lines, (c) solids of revolution have generating lines, (d) straight lines on the lateral surface are generating lines. 22.1% of all preservice teachers believed that only cones have generating lines, and most of them followed the definition of a generating line presented in elementary mathematics textbooks. The conception that only cones and cylinders have generating lines was the least investigated. However, since there were instances where generating lines were defined with the use of a director curve, it became important to explore topics more thoroughly, such as generating lines of a truncated cone. 27.9% of all preservice teachers believed that solids of revolution have generating lines. This conception was marked by differing opinions on whether spheres also have generating lines. The conception that straight lines on the lateral surface are generating lines was the most frequently investigated. This conception differs from the traditional view in school mathematics because it suggests using a director curve to define generating lines. Based on these analysis results, the researcher developed specific teaching methods that considered both subject matter knowledge and pedagogical content knowledge for preservice teachers. In addition, the researcher proposed a consensus definition of a generating line in mathematics education.

• Structural Engineering and Mechanics
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• v.32 no.2
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• pp.321-335
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• 2009

When a roof frame is subjected to the airblast loading, the conventional way to analyze the damage of the frame or design the frame is to use single degree of freedom (SDOF) model. Although a roof frame consists of beams and girders, a typical SDOF analysis can be conducted only separately for each component. Thus, the rigid body motion of beams by deflections of supporting girders can not be easily considered. Neglecting the beam-girder interaction in the SDOF analysis may cause serious inaccuracies in the response values in both Pressure-Impulse curve (P-I) and Charge Weight-Standoff Diagrams (CWSD). In this paper, an inelastic two degrees of freedom (TDOF) model is developed, based on force equilibrium equations, to consider beam-girder interaction, and to assess if the modified SDOF analysis can be a reasonable design approach.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2006.06a
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• pp.461-462
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• 2006

A single-gap and single-gamma transflective liquid-crystal (LC) display using patterned vertical alignment (PVA) mode was designed. In the device, a vertical electric field drives a vertically aligned LC to tilt down to optimize polarization efficiency. Electrodes of transmissive and reflective area were patterned $22.5^{\circ}$ and $45^{\circ}$ with respect to the polarizer so that a tilt-down direction of the LC director was $22.5^{\circ}$ and $45^{\circ}$ in the reflective and transmissive regions, respectively. In the device, the cell gap was the same for both regions, and the gamma curve matched each other in both regions because tilt angle of LC director was the same according to the applied voltage. Moreover, the dark state was irrespective of the cell retardation value at normal direction, which was highly important in massive fabrications. The switching principle and electro-optic characteristics of the device are reported herein.

• Journal of Mechanical Science and Technology
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• v.18 no.10
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• pp.1700-1711
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• 2004

Piston friction is one of the important but complicated sources of energy loss of a hydraulic axial piston machine. In this paper, two formulas are derived for estimating instantaneous piston friction force and average piston friction moment loss. The derived formula can be applicable for piston guides with or without bushing as well as for axial piston machines of motoring and pumping operations. Through the formula derivation, a typical curve shape of friction force found from several experimental measurements during one revolution of a machine is clearly explained in this paper that it is mainly due to the equivalent friction coefficient dependent on its angular position. Stribeck curve effect can easily be incorporated into the formula by replacing outer and inner friction coefficients at both edges of a piston with the coefficient given by Manring (1999) considering mixed/boundary lubrication effects. Novel feature of the derived formula is that it is represented only by physical dimensions of a machine, hence it allows to estimate the piston friction force and loss moment of a machine without hardworking experimental test.

• Journal of Power System Engineering
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• v.18 no.6
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• pp.45-50
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• 2014

In the previous paper, we have reported on the development of foaming sponge seat with the auxiliary spring member and suggested new possibility of the special seat with the auxiliary plastic member for movie theater chair. In this study, we have examined the major design parameters needed in the development of a foaming sponge seat in which the mesh type plastic member are inserted to improve the vibration transfer effect of a chair seat. Through analyzing several prototypes by applying experimentation as well as the experimental modal analysis method, it was confirmed that the effect of vibration transfer can be improved through the use of a mesh type plastic member and applied to the design of practical chair seat.

• Journal of Mechanical Science and Technology
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• v.18 no.1
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• pp.92-105
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• 2004

A new algorithm for planning a collision-free path based on algebraic curve is developed and the concept of collision-free Path Space (PS) is introduced. This paper presents a Geometry Mapping (GM) based on two straight curves in which the intermediate connection point is organized in elliptic locus ($\delta$, $\theta$). The GM produces two-dimensional PS that is used to create the shortest collision-free path. The elliptic locus of intermediate connection point has a special property in that the total distance between the focus points through a point on ellipse is the same regardless of the location of the intermediate connection point on the ellipse. Since the radial distance, a, represents the total length of the path, the collision-free path can be found as the GM proceeds from $\delta$=0 (the direct path) to $\delta$=$\delta$$\_$max/(the longest path) resulting in the minimum time search. The GM of elliptic workspace (EWS) requires calculation of interference in circumferential direction only. The procedure for GM includes categorization of obstacles to .educe necessary calculation. A GM based on rectangular workspace (RWS) using Cartesian coordinate is also considered to show yet another possible GM. The transformations of PS among Circular Workspace Geometry Mapping (CWS GM) , Elliptic Workspace Geometry Mapping (EWS GM) , and Rectangular Workspace Geometry Mapping (RWS GM), are also considered. The simulations for the EWS GM on various computer systems are carried out to measure performance of algorithm and the results are presented.

• Journal of Soil and Groundwater Environment
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• v.19 no.3
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• pp.134-141
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• 2014

A testing inspection is one of the important in the industry, owing to determine the reliability and directivity of testing inspection results. Therefore, the quality assurance and quality control (QA/QC) work which performed by personnel not directly in the inventory compilation development, in testing inspection must be thoroughly considered. Some agencies for environmental test inspection, they sometimes misunderstood that the QA/QC was ended with proficiency testing performance and on-site assessment by a director. Thus, results were often calculated without QA/QC work by self manual when conducting test. The objective of this study was to improve reliability of testing and inspection agency through the QA/QC case study which basically performed to raising reliability of testing and inspection agency. In this study, it increased reliability of result by verifying calibration curve (IC, ICV, CCV), blank, accuracy (LCS, MS) and precision as QA/QC performance, while performing investigation of soil contamination in mining areas. This study suggests that reliability establishing method of test result and management method of analysis process, through the QA/QC instance of testing agency.

• Analytical Science and Technology
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• v.24 no.1
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• pp.10-14
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• 2011

This study was performed to compare international analytical methods of bromide and applied to determine bromide in bottled mineral water and raw ground water in Korea. Bromide in water was eluted by 10~50 mM potassium hydroxide (KOH) and determined by ion chromatography-suppressed conductivity detector (IC-CD). Sample was purified with Ba- and H-on-guard cartridge and $0.2\;{\mu}m$ membrane filter. The method detection limit (MDL) and the limit of quantitation (LOQ) of bromide were 0.2 and $0.5\;{\mu}g/L$, respectively. The calibration curve showed good lineality above 0.9993 in the ranges of the $0.5\sim80\;{\mu}g/L$. A correlation coefficient of bromide in ground water and sum of bromide and bromate in bottled mineral water is 0.808.