• 대한기계학회논문집A
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• 제32권2호
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• pp.143-147
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• 2008

Super-hydrophobic surfaces showed that contact angle of water was higher than 140 degrees. That surface could be made several methods such as Carbon nano tubes grown vertically, PDMS asperities arrays, hydrophobic fractal surfaces, and self assembled monolayers coated by CVD and so on. However, we fabricated super-hydrophobic surfaces with plasma treatments which were very cost efficient processes. Their surfaces were characterized by static contact angles, advancing, receding, and stability against UV irradiation. Optimal surfaces showed static contact angles were higher than 150 degrees. Super-hydrophobic property was remained after UV irradiation for one week.

• 대한수학회보
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• 제35권1호
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• pp.149-156
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• 1998

We relate the existence of rational curves with the existence of rigid bundles of any even rank on Enriques surfaces and compare with the case of K3 surfaces.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2000년도 제32회 추계학술대회 정기총회
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• pp.3-8
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• 2000

Chemical nature of nascent metal surfaces which is one of the important active sources for tribochemical reactions was investigated using a newly developed method. Some enhanced activities were observed. For example, organic compounds chemisorbed on nascent gold surfaces and aromatic compounds decomposed on nascent nickel surfaces resulting in hydrogen evolution. Non-polar compounds such as organic sulfides had a higher chemisorption activity on nascent steel surfaces than polar compounds such as fatty acids and phosphates. Organic sulfides reacted directly with nascent steel surfaces and the surface was covered with metal sulfides. The activity for the chemisorption of organic compounds was closely dependent on the electronic structure of metals. Although benzene chemisorbed very easily on nascent surfaces of transition metals, it did not chemisorb ell nascent surfaces of simple metals. Boundary lubricating behaviors of extreme pressure additives were explained on the bases of the chemical activities of nascent surfaces obtained in this investigation. Under mild conditions, polar compounds such as fatty acids and phosphates were effective for boundary lubrication, because surfaces are covered with oxide layers. On the other hand, sulfides were more effective under severe conditions where the oxide layers were removed and the nascent surfaces were formed.

• 대한수학회보
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• 제39권3호
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• pp.431-440
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• 2002

Recently P. Ozsv$\'{a}$th Z. Szab$\'{o}$ proved higher type adjunction inequalities for embedded surfaces in 4-manifolds of non-simple type. The aim of this short paper is to give a simple and direct proof of such higher type adjunction inequalities for smoothly embedded surfaces with negative self-intersection number in smooth 4-manifolds of non-simple type. This will be achieved through a relation between the Seiberg-Witten invariants used to get adjunction inequalities of 4-manifolds of simple type and a blow-up formula.

• 한국환경과학회지
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• 제24권6호
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• pp.819-826
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• 2015

This study measured temperatures and albedos of urban surfaces for different colors and materials during summer, and calculated the energy budget over different urban surfaces to find out the thermal performance affecting the heat built-up. The study selected six surface colors and 13 materials common in urban landscape. Their surface temperatures (Ts) and albedos were measured at a given time interval in the daytime from June to August. Average Ts over summer season for asphalt-colored brick was $4.0^{\circ}C$ higher than that for light red-colored one and $9.7^{\circ}C$ higher than that for white-colored one. The Ts for artificial surface materials of asphalt paving, brown brick wall, and green concrete wall was $6.0^{\circ}C$ higher than that for natural and semi-natural ones of grass, grassy block, and planted concrete wall. There was the greatest difference of $16.3^{\circ}C$ at midafternoon in the Ts between asphalt paving and planted concrete wall. Average albedo over summer season of surface materials ranged from 0.08 for asphalt paving to 0.67 for white concrete wall. This difference in the albedo was associated with a maximum of $15.7^{\circ}C$ difference at midafternoon in the Ts. Increasing the albedo by 0.1 (from 0.22 to 0.32) reduced the Ts by about $1.3^{\circ}C$. Average storage heat at midday by natural and semi-natural surfaces of grass and grassy block was about 10% lower than that by artificial ones of asphalt, light-red brick, and concrete. Reflected radiation, which ultimately contributes to heating the urban atmosphere, was 3.7 times greater for light-red brick and concrete surfaces than for asphalt surface. Thus, surfaces with in-between tone and color are more effective than dark- or white-colored ones, and natural or semi-natural surfaces are much greater than artificial ones in improving the urban thermal environment. This study provides new information on correlation between Ts and air temperature, relationship between albedo and Ts, and the energy budget.

• PNF and Movement
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• 제16권1호
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• pp.125-132
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• 2018

Purpose: The aim of this study was to investigate the isolated activation ratio of the quadriceps femoris muscle on different support surfaces during squat exercise. Methods: Twenty participants (10 males and 10 females) voluntarily agreed to participate in the research after receiving an explanation about the purpose and process of the study. Each participant performed squat exercises on three different support surfaces (a flat surface, a form roller, and an unstable surface). Muscle activities of the rectus femoris (RF), vastus medialis (VM), and vastus lateralis (VL) were measured by electromyography. The isolated activation ratio of the quadriceps femoris muscle was calculated using the %isolation formula. Results: For the squat exercise, the %isolation value of the VM was significantly higher on the unstable surface than on the flat surface and form roller. In contrast, the %isolation values for the RF for the squat exercise were significantly higher on the flat surface and form roller than on the unstable surface. There was no significant differences in the %isolation values of the VL on the three different surfaces. Conclusion: The findings indicate that squat exercise on different surfaces results in differential activation of the quadriceps femoris muscle, which suggests that squat exercise on a multi-directional unstable surface could increase the isolated activation ratio of the VM.

• Tribology and Lubricants
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• 제16권4호
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• pp.253-258
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• 2000

Frictional behavior of wire electric discharge machined surfaces of spheroidized annealed STDll steel was investigated. The surfaces were produced with a various series of finish cuts where pulse energy was reduced with increase in the number of finish cuts. Roughness and micro-hardness of the surfaces were also measured. It is observed that the increase in the number of finish cuts produces the surface exhibiting lower frictional resistance followed by higher resistance after considerable wear. Effects of finish cuts on the friction characteristics are discussed with the aid of roughness and micro-hardness of the surfaces.

• 대한지리학회지
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• 제38권2호
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• pp.156-172
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• 2003

정동진, 대진 지역에는 규모가 큰 해안단구 고위면이 형성되어 있을 뿐 아니라. 우리나라 중부 동해안에서 처음으로 구정선고도의 해발고도가 고위면보다 높은 고고위면이 확인되었다. 해안단구의 구정선고도는 고고위 I면(HH I) 해발고도 140m. 고고위 II교면(HH II) 110m, 고위 I면 90m, 고위 II면 70m, 중위면 40m, 저위 I면 25m, 저위 II면dl 10m이다. 그리고 홀로세에 형성된 것으로 추정되는 해발고도 5~6m의 가장 낮은 해안단구가 연구지역 전체에서 나타난다. 고고위면은 인근의 삼척 오십천 해면변동단구와 남동해안 감포지역에서 확인되는 고고위 면과 같은 시기에 형성된 것으로 볼 수 있다. 이것은 연구 지역의 해안단구 형성체계가 이들 지역의 그것과 거의 같은 데서 추론할 수 있다. 해안단구 형성시기는 최종간빙기인 MIS 5시기로 확인된 저위 I면을 단서로 중위면은 MIS 7. 고위 II면은 MIS 9, 고위 I면은 MIS 11로 판단된다. 고고위 II면은 산소동위체 MIS 13, 고고위 I면은 산소 동위체 MIS 15에 형성되었을 것이다. 고위면이 한반도 남동부 지역과 유사하게 큰 규모로 남아있는 것은 이것을 형성한 Holsteinian Interglacial의 기간이 매우 길고, 이 시기의 해면 위치에 기반암의 완사면이 넓게 형성되어 있었으므로 파식대가 비교적 용이하게 만들어진데 기인하는 것으로 생각된다.

• Tribology and Lubricants
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• 제16권3호
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• pp.182-187
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• 2000

In this paper the residual stresses on lubricated sliding surfaces were measured during break-in procedure and up to scuffing by the X-ray diffraction method. The cylinder-on-disk type tribometer was used with the line-contact geometry. Scuffing tests were done using a constant load. In the break-in procedure the loads were increased from very low values in several steps. It was found that the sliding surfaces with break-in represented relatively higher values of residual compressive stresser than those without break-in. The residual stresses below the surfaces showed the small amount of stress increases. The results of scuffing tests with and without break-in showed the same trends as break-in tests did. However, in case of tests with break-in procedure the stresses below the surfaces showed very large increases in the residual compressive stresses. From the tests of break-in and scuffing, it was found that the increases in scuffing lives were related with the increases of residual stresses on the lubricated sliding surfaces with break-in.

• Tribology and Lubricants
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• 제10권3호
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• pp.29-38
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• 1994

The friction and wear of mild steel at dry sliding surfaces under different vacuum conditions have been investigated to understand the wear mechanisms. For the test, a ball-ondisk typed wear-rig has been built and implemented, allowing control of sliding speed, load and vacuum. Results show that, at a high sliding velocity, friction of low carbon steel (SS41) under a high vacuum is much higher than that of ambient condition and wear is much severer. It is due to lack of effective oxidation film formation on which steel surfaces could protect themselves against the severe wear. It has been shown, however, that there is a critical regime with contact conditions (at a low sliding velocity, a low load, and under a medium vacuum) at which effective, protective films of low carbon steel have been built on the surfaces in a friction process with a self-regulating way, resulting in both very low coefficients of friction (about 0.3) and mild wear. In order to investigate the protective films on steel surfaces, the worn surfaces and the wear debris have been experimentally analyzed with SEM, AES/SAM and XRD. A theoretical analysis of frictional heating at sliding surfaces, and an experimental analysis of the influence of oxidation wear under various vacuum conditions are described. The important variables on which self-formations of protective films at dry sliding surfaces depend, and the wear mechanisms are also investigated.