• Animal Systematics, Evolution and Diversity
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• v.35 no.2
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• pp.84-90
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• 2019

The brittle star, Amphistigma minuta H.L. Clark, 1938, was collected from Munseom Island, Jeju-do, Korea, by SCUBA diving. This species has distinct morphological features, as follows: a small disk with large papillae on the disk margin; slender arms and four arm spines at proximal; and oral parts the same as those of the genus Amphipholis. Additionally, we obtained partial sequences of the cytochrome c oxidase subunit I gene (COI) (513 bp) and compared them with sequences from Australian A. minuta and 13 other species of Amphiuridae. As a result, intraspecific pairwise distance was 0.4% between two Korean individuals and intraspecific distance between the Australian and the Korean populations was 2.6-2.8%, which indicates they should be considered as the same species. Ultimately, 15 species of the family Amphiuridae have currently been recorded in Korea, including A. minuta.

• Animal Systematics, Evolution and Diversity
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• v.38 no.4
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• pp.157-161
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• 2022

Parartotrogus minutus n. sp. is described as a parasite of the brittle star Ophiuroglypha kinbergi (Ljungman) from the intertidal zone on the Yellow Sea coast of Korea. The new species is characterized by a combination of morphological features that the body is small, less than 0.5 mm long, the caudal ramus is 1.73 times longer than wide, leg 3 bears three-segmented rami, and the exopod of leg 5 is armed with two setae. The new species is the third known species in the genus, following P. richardi Scott T. and Scott, A., 1893 known from European waters and P. arcticus Scott T., 1901 known from both North Atlantic and North Pacific.

• Korean Journal of Environmental Biology
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• v.41 no.3
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• pp.291-297
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• 2023

This study introduces a newly discovered brittle star, Amphiophiura megapoma, from the mesophotic zone in the East Sea, Korea. It is the second species belonging to the genus Amphiophiura (which includes 57 species) to be recorded in Korean waters after A. sculpta. The specimen was discovered during a September 2022 survey, by SCUBA diving in the upper mesophotic zone of the East Sea, Korea. This study presents the morphological characteristics of A. megapoma, highlighting its differences from the related species within a comprehensive taxonomic description. It provides high-resolution images of A. megapoma and a taxonomic key for Amphiophiura species in Korea.

• Proceedings of the KWS Conference
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• 1998.10a
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• pp.292-294
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• 1998

• Proceedings of the KWS Conference
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• 1998.05a
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• pp.133-137
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• 1998

• Proceedings of the Korean Society for Rock Mechanics Conference
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• 2004.10a
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• pp.119-134
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• 2004

• Proceedings of the Korean Nuclear Society Conference
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• 2005.10a
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• pp.358-359
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• 2005

• Corrosion Science and Technology
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• v.6 no.4
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• pp.159-163
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• 2007

Micron size Co-alloy 800 (T800) powder is coated on the high temperature, oxidation and corrosion resistant super alloy Inconel 718 substrate by the optimal high velocity oxy-fuel (HVOF) thermal spray coating process developed by this laboratory. For the study of durability improvement of high speed spindle operating without lubricants, friction and sliding wear behaviors of the coatings are investigated both at room and at an elevated temperature of $1000^{\circ}F(538^{\circ}C)$. Friction coefficients, wear traces and wear debris of coatings are drastically reduced compared to those of non-coated surface of Inconel 718 substrate both at room temperature and at $538^{\circ}C$. Friction coefficients and wear traces of both coated and non-coated surfaces are drastically reduced at higher temperature of $538^{\circ}C$ compared with those at room temperature. At high temperature, the brittle oxides such as CoO, $Co_{3}O_{4}$, $MoO_2$ and $MoO_3$ are formed rapidly on the sliding surfaces, and the brittle oxide phases are easily attrited by reciprocating slides at high temperature through oxidation and abrasive wear mechanisms. The brittle solid oxide particles, softens, melts and partial-melts play roles as solid and liquid lubricants reducing friction coefficient and wear. These show that the coating is highly recommendable for the durability improvement coating on the machine component surfaces vulnerable to frictional heat and wear.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.5
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• pp.932-938
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• 2002

In structural applications, brittle materials such as soda-lime glasses and ceramics are usually subjected to multiaxial stress state. Brittle materials with cracks or damage by foreign object impacts are apt to fracture abruptly from cracks, because of their properities of very high strength and low fracture toughness. But in most cases, the residual strength of structural members with damage has been tested under uniaxial stress condition such as the 4-point bend test. Depending upon the crack pattern developed, the strength under multiaxial stress state might be different from the one under uniaxial. A comparative study was carried out to investigate the influence of stress state on the residual strength evaluation. In comparable tests, the residual strength under biaxial stress state by the ball-on-ring test was greater than that under the uniaxial one by the 4-point bend test, when a small size indendation crack was introduced. In the case that crack having an angle of 90deg. to the applied stress direction, the ratio of biaxial to uniaxial flexure strength was about 1.12. The residual strength was different from crack angles to loading direction when it was evaluated by the 4-point bend test. The ratio of residual strength of 45deg. crack to 90deg. one was about 1.20. In the case of specimen cracked by a spherical impact, it was shown that an overall decrease in flexure strength with increasing impact velocity, and the critical impact velocity for formation of a radial and/or cone crack was about 30m/s. In those cases that relatively large cracks were developed as compared with the case of indented cracks, the ratio of residual strength under biaxial stress state to one uniaxial became small.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.37 no.2
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• pp.213-218
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• 2013

Ultrasonic machining (USM) is a new method used in metal cutting. This process does not involve heating or any electrochemical effects, causes low surface damage, has small residual stress, and does not rely on the conductivity of the workpiece. These characteristics are suitable for the machining of brittle materials such as glass or ceramics. However, the use of USM for brittle materials generates cracks on the workpiece. Therefore, in this study, Taguchi's method was used to optimize the processing conditions of micro holes drilled in glass and ceramics. This method was used to successfully reduce the number of cracks at the entrance and the exit of the micro holes.