• Communications of Mathematical Education
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• v.37 no.2
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• pp.135-157
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• 2023

Double scale models have been introduced in elementary mathematics textbooks under the 2015 revised mathematics curriculum. However, few studies have examined in detail how students understand or utilize such models. In this study, we analyzed how 154 sixth-grade students who had learned the division of fractions from textbooks containing double scale models understood such models. The results showed that the students tended to identify the components of the model relatively well, but had difficulties exploring the unit or the meaning of the bottom number line of a model. They also had a lot of difficulties using the double scale model to complete the computation process and explain the computation principle. Based on these findings, we discuss the implications of teaching double scale models.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.841-846
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• 2001

The applicability of the concept of IPC(Incrementally Prestressed Concrete) girder which effectively reduces the depth of the conventional prestressed girders by introducing prestress in two different stages is theoretically reviewed in this research. Expressions on top and bottom stresses resulting from different loading stages are presented. Beneficial effects of IPC girder compared with those traditional prestressed girders are evaluated by investigating the girder depth for the same span or girder span for the same girder depth. Parking structures and ware house structures which need relatively longer span and are subject to large live loads are considered in comparison. It was found that the single or double tee slab designed by IPC concept could be built upto 50% longer in its span and upto 45% less in its depth compared to those of traditionally prestressed single or double tee slabs. In addition, the amount of prestressing tendons could be reduced.

• Journal of Multimedia Information System
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• v.5 no.3
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• pp.179-188
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• 2018

In order to overcome the problems of contact palmprint recognition, a non-contact palmprint recognition system is developed on personal computer (PC) platform. Three methods, namely "double-line-single-point" (DLSP), "double-assistant-crosshair" (DAC) and "none-assistant-graphic" (NAG), are implemented for the palmprint localization to solve the severe technical challenges, including the complex background, variant illuminations, uncontrollable locations and gestures of hands. In NAG, hand segmentation and the cropping of region of interest are performed without any assistant graphics. The convex hull contour of hand helps detect the outside contour of little finger as well as the valley bottom between thumb and index finger. The three methods of palmprint localization have good operating efficiency and can meet the performance requirements of real-time system. Furthermore, an attendance system on PC platform is designed and developed based on non-contact palmprint recognition.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.11 no.1
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• pp.71-83
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• 2007

The double diffusive convection of cold water in the vicinity of its density maximum in a rectangular partitioned enclosure of aspect ratio 5 with isothermal side walls and insulated top and bottom is studied numerically. A thin partition is attached to the hot wall. The species diffusivity of the fluid is assumed to vary linearly with concentration. The governing equations are solved by finite difference scheme. The effects of position and height of the partition, variable species diffusivity and enclosure width are analyzed for various hot wall temperatures. It has been found that adding partition on the hot wall reduces the heat transfer. The density inversion of the water has a great influence on the natural convection. When increasing species diffusivity parameter heat and mass transfer rate is decreased.

• 한국금형공학회:학술대회논문집
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• 2008.06a
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• pp.209-213
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• 2008

In this work, we have proposed a method for calculating the residual stress developed during the PCB thermo-compression bonding precess. Residual stress is the most important factor that causes PCB warpage in accordance with the pattern design. In this work, a single-layed double-sided PCB, which is comprised of the dielectric (FR-4) substrate in the middle and copper cladding on the both top and bottom sides, is considered. A reference temperature, where all stress is free, is calculated by comparing the calculated and measured warapge of a PCB of which copper cladding of the top side is removed. Then, the reesidual stress values is calculated for the double-sided PCB.

• Special Issue of the Society of Naval Architects of Korea
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• 2007.09a
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• pp.135-141
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• 2007

CSR(Common Structure Rules) enter into force on $1^{st}$ April 2006. Generally for double hull tankers of less than 150m in length, the Rules of the individual Classification Society are to be applied. Where high tensile stresses act through an intermediate plate, increased fillet welds or penetration welds are to be used longitudinal/transverse bulkhead primary support member end connections to the double bottom. If workers have begun to make used of established procedures between corrugated BHD and lower stool joint, first to welding on groove of face and then it has to gouging to blow on groove of root. So amount of man-hour increased, productivity secreased.

• Journal of the Korean Solar Energy Society
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• v.26 no.1
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• pp.57-64
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• 2006

Cr-CrO cermet solar selective coatings with a double cermets layer film structure were prepared using a special direct current (dc) magnetron sputtering technology. The typical films structures from surface to bottom substrate were measured to be an $Al_2O_3$ anti-reflection layer on a double Cr-CrO cermet layer on an Al metal infrared reflection layer. Optical properties of optimized Cr-CrO cermet solar selective coating were absorptance (${\alpha}$) = 0.95 and emittance (${\varepsilon}$) = 0.10 ($100^{\circ}C$). Atomic force microscopy (AFM) image showed that Cr-CrO cermet film was very smooth and their grain size was also very small The results of thermal stability test showed that the Cr-CrO cermet solar selective coatings were stable for use at temperature of $400^{\circ}C$.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2008.06a
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• pp.264-264
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• 2008

We fabricated a pentacene thin-film transistor with a Polymer/$SiO_2$ Double Gate Dielectrics and obtained a device with better electrical characteristics. This device was found to have a field-effect mobility of $0.04cm^2$/Vs, a threshold voltage of -2V, an subthreshold slope of 1.3 V/decade, and an on/off current ratio of $10^7$.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.29A no.3
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• pp.66-71
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• 1992

We fabricated highly stable a-Si:H solar cell using low band gap intrinsic layer fabricated by RP-CVD. We obtained a-Si:H with optical band gap of less than 1.65 eV with deposition rate of 0.18 $\AA$/sec, and used this material as bottom i-layer of a-Si:H double stacked solar cells. We have succeeded in the fabrication of very stable a-Si:H double stacked solar cell of which the conversion efficiency is about 9% and the degradation is less than 4% after light illumination for 100h under 350mW/cm$^{2}$.

• Solar Energy
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• v.6 no.2
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• pp.15-21
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• 1986

In this study, an experimental double diffusive thermohaline system heated from below was constructed and the phenomena of each layer developed in the system were observed. The experiment was performed with the initial salt concentration gradient of $-436.2kg/m^4$ and the net heat flux of approximately $176w/m^2$. An electroconductivity-temperature probe was made and used for the measurements of salt concentration. As the result of this study, it was found that the salt concentration decreased in the bottom mixed layer and increased in the top mixed layer during the experiment while the salt concentration gradient in the diffusive layer unchanged. It was also found that the interfacial boundary layers were due largely to variations in salt concentration rather than temperature.