• Journal of the Korean Society for Precision Engineering
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• v.21 no.5
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• pp.38-45
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• 2004

As optical communication is being substituted for telecommunication, the demand of a large variety of fiber optic components is increasing. V-groove substrates, one of the module components, are used to connect optical fibers to optical planar circuits and to arrange fibers. Their applications are multi-channel optical connectors and optical waveguide fiber coupling, etc. Because these substrates are a critical part of the splitter in a multiplexer and a multi fiber connector, precise and reliable fabrication process is required. For precisely aligning core pitch between fibers, machined core pitch tolerance should be within sub-microns. Therefore, these are generally produced by state-of-the-art micro-fabrication like MEMS. However, most of the process equipment is very expensive. It is also difficult to change the process line for custom designs to meet specific requirements using various materials. For various design specifications such as different values of the V angle and low-priced process, the fabrication method should be flexible and low cost. To achieve this goal, we have suggested a miniaturized machine tool with high accuracy positioning system. Through this study, it is shown that this cutting process can be applied to produce V-groove subtracts. We also show the possibility of using a miniaturized machining system for producing small parts.

• The Journal of Asian Finance, Economics and Business
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• v.6 no.2
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• pp.33-44
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• 2019

The Indonesian government launched a new people's business credit program as part of a package of economic policy and deregulation. The interest rate is set lower than the average of the current loan interest rates, especially when compared with rural bank interest rates. To capture the social spatial aspects, quota sampling is applied to ten areas that divided based on the social culture. Further, the method utilized in this research is logit models, which designed to analyse the determinants of asymmetric information particularly on the rural bank and small micro enterprises. The study was conducted in East Java as the province with the largest number of rural banks in Indonesia. Based on the estimation of asymmetric information model to the respondent of rural banks and small businesses, the result shows that adverse selection can be avoided by strengthening the information about prospective borrowers. Regarding moral hazard, rural banks and small businessmen argued that the imposition of the collateral to the debtor has an important role to avoid moral hazard. Rural bank respondents stated that the KUR program with low-interest rates has affected their business development. The results implied the need of broadening the collaboration schemes between this people's business credit program and rural banks.

• Journal of Welding and Joining
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• v.28 no.5
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• pp.80-85
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• 2010

This study focused on laser assisted machining (LAM) of silicon nitride ceramic that efficiently removes the material through machining of the softened zone by local heating. The effects of laser-assisted machining parameters were studied for cost reduction, and active application in processing of silicon nitride ceramics in this study. Laser assisted machining of silicon nitride allows effective cutting using CBN tool by local heating of the cutting part to the softening temperature of YSiAlON using by the laser beam. When silicon nitride is sufficiently preheated, the surface is oxidized and decomposed and then forms bloating, micro crack and silicate layer, thereby making the cutting process more advantageous. HIPSN and SSN specimens were used to study the machining characteristics. Higher laser power makes severer oxidation and decomposition of both materials. Therefore, HIPSN and SSN specimens were machined more effectively at higher power.

• Steel and Composite Structures
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• v.13 no.6
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• pp.587-606
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• 2012

Concrete-filled-steel-tubular (CFST) columns have been well proven to improve effectively the strength, stiffness and ductility of concrete members. However, the central part of concrete in CFST columns is not fully utilised under uni-axial compression, bending and torsion. It has small contribution to both flexural and torsion strength, while it can be replaced effectively by steel with smaller area to give similar load-carrying capacity. Also, the confining pressure in CFST columns builds up slowly because the initial elastic dilation of concrete is small before micro-crackings of concrete are developed. From these observations, it is convinced that the central concrete can be effectively replaced by another hollow steel tube with smaller area to form double-skinned concrete-filled-steel-tubular (CFDST) columns. In this study, a series of uni-axial compression tests were carried out on CFDST and CFST columns with and without external steel rings. From the test results, it was observed that on average that the stiffness and elastic strength of CFDST columns are about 25.8% and 33.4% respectively larger than CFST columns with similar equivalent area. The averaged axial load-carrying capacity of CFDST columns is 7.8% higher than CFST columns. Lastly, a theoretical model that takes into account the confining effects of steel tube and external rings for predicting the uni-axial load-carrying capacity of CFDST columns is developed.

• Korean Journal of Plant Taxonomy
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• v.49 no.3
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• pp.215-223
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• 2019

Recently, it has become known that Gotjawal terrain is an important area, therefore the study on this area has conducted in the geological, ecological, and cultural aspects. The studies on bryophytes of Gotjawal, however, have not been sufficiently performed. This study presents a survey on the bryophytes of the evergreen broad-leaved forest of Cheongsu-ri at Hangyeong Gotjawal in the southwestern part of Jejudo Island, Korea. A total of 72 taxa belonging to the Bryophyta (18 families 43 genera 55 species) and Marchantiophyta (11 families 13 genera 17 species) were determined and the liverwort index was 23.6%. Predominant life-form was weft. The rates of the bryophytes dominating in mesic to hygric sites were higher than the bryophytes mainly observed in xeric habitats. These values indicate that the forests are widespread and dense in this study area. Upon an investigation of the substrates, the bryophytes on rocks were most diverse. The results appear to stem from the fact that volcanic rock masses of various sizes lay scattered over the study area, offering numerous micro-habitats for bryophyte due to one of the characteristics of Gotjawal. We suggest that more detailed studies should be conducted at the regional scale to establish the bryophyte flora of Gotjawal and the evergreen broad-leaved forests on Jejudo Island.

• Smart Structures and Systems
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• v.24 no.2
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• pp.223-231
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• 2019

The properties of Electroactive Polymer (EAP) materials are attracting the attention of engineers and scientists from many different disciplines. From the point-of-view of robotics, Ionic Polymer Metal Composites (IPMC) belong to the most developed group of the EAP class. To allow effective design of IPMC-actuated mechanisms with large induced strains, it is necessary to have adequate analytical tools for predicting the behavior of IPMC actuators as well as simulating their response as part of prototyping methodologies. This paper presents a novel IPMC motor construction. To simulate the bending behavior that is the dominant phenomenon of motor movement process, a nonlinear model is used. To accomplish the motor design, the IPMC model was identified via a series of experiments. In the proposed model, the curvature output and current transient fields accurately track the measured responses, which is verified by measurements. In this research, a three-dimensional Finite Element Method (FEM) model of the IPMC motor, composed of IPMC actuators, simultaneously determines the mechanical and electrical characteristics of the device and achieves reliable analysis results. The principle of the proposed drive and the output signals are illustrated in this paper. The proposed modelling approach can be used to design a variety of controllers and motors for effective micro-robotic applications, where soft and complex motion are required.

• Korean Journal of Heritage: History & Science
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• v.35
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• pp.4-27
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• 2002

During the last 10 more years, more than one hundred of Paleolithic sites were found in the most part of the Korena peninsula by very active third generation of Paleolithic archaeologists. It became quite sure that most parts of the peninsula was populated during the late Pleistocene. High concentratin of Paleolithic sites in the Chollanamdo Province will be one of the most important field of paleolithic archaeology along with the sites in the Hantan -Imjin river basin. The begining of Upper Paleolithic is quite likley sometime earlier than 30,000 BP and possibly upto 40,000 BP. Micorlithic technology was probably introduced into the peninsula sometime around 20,000 BP. It is quite striking that the Acheulean-typed stone industry from the Chongokni site could be older than 350,000 BP that was estimated by sedimentation rate on the basis of the interval between two different types of Japanese tephras found at the site. More Acheulean-typed bifaces were found in some sites in the Hantan-Imjin river basin. Tanged point which originally found at the Suyanggae site were found at many Upper Paleolithic sites and was made until quite late period of Upper Paleolithic along with micro-blade.

• Journal of the Semiconductor & Display Technology
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• v.20 no.2
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• pp.98-102
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• 2021

GaOOH is obtained via hydrothermal synthesis procedure. The formed GaOOH is turned into α-Ga₂O₃ at 500℃ annealing. As the annealing temperatures increase the α-Ga₂O₃ is in part turned into β-Ga₂O₃ and fully turned into β-Ga₂O₃ after 1100℃. XPS and PL results reveal that heterojunction interface between α-Ga₂O₃ and β-Ga₂O₃ become maxim at 500℃ annealing condition, which result in the highest photocatalytic activity. The presence of heterojunction interface slows down the recombination process by separating photogenerated electron-hole pairs and thereby enhance the overall photocatalytic activity.

• Tribology and Lubricants
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• v.38 no.5
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• pp.222-226
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• 2022

Between diaphragms made of stainless steel (SUS), which is the main component of a hydrogen gas compressor, micro-slip occurs owing to repeated bending, resulting in scratches on the surface. The surface scratch of the compressor part is a problem with airtightness, which reduces the efficiency of the compressor; in severe cases, damage is a possibility. In this study, the changes in friction and wear characteristics due to the surface polishing of SUS and carbon-based solid lubricant films (graphene and CNT) were analyzed. Bare SUS, polished SUS, graphene film, and CNT film specimens were prepared. The surface roughness of the SUS was significantly reduced by surface polishing but increased by carbon-based solid lubricating films. In contrast, the friction coefficient maintained a similar value after surface polishing but was significantly reduced by the carbon-based solid lubricant films. In particular, the graphene film exhibited the lowest initial friction coefficient, while the CNT film exhibited the lowest overall average friction coefficient. Regarding the wear rate, polished SUS exhibited the lowest value, but the surface condition of the wear track showed that the carbon-based solid lubricating films were relatively less damaged. Although the wear rate measured was largely attributed to the solid lubricating film peeling off, the SUS surface under the film was considered protected.

• Composites Research
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• v.21 no.6
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• pp.15-22
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• 2008

Reversed plane bending fatigue tests were conducted on SiC particle aluminum composite. The initiation and growth behaviors of small surface fatigue cracks were continuously monitored by the replica technique and investigated in detail. The fatigue life of MMC is shorter than that of matrix because there exists interface debonding of SiC particles and matrix on the whole face of the notch part in the casting metal matrix composite(MMC). The coalescence of micro-cracks was observed in the tests conducted at high stress levels. Due to the coalescence, a higher crack growth rate of small cracks rather than those of long cracks was recognized in da/dn-$K_{max}$ relationship.