• Journal of the Korean Geotechnical Society
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• v.29 no.1
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• pp.49-59
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• 2013

Heavy rainfall intensity may cause shallow slope failures and debris flow by rill erosion and scour on land surface. The paper represents the difference between native soil (weathered soil) and reinforced soil, which is mixed by hardening agent with flyash as main material, for investigating experimental findings of rill erosion and erosion. Results obtained from artificial rainfall simulator show that erosion rate of reinforced soil mixed with hardening agent is reduced by 20% because an amount of eroded soil on slope surface is inversely proportional to the increase of soil strength. For example, rainfall of 45mm (at the elapsed time of 25mins in rainfall intensity of 110mm/hr) triggers rill erosion on native soil surface, but the rill erosion on reinforced soil surface does not even occur at 330mm rainfall (at the elapsed time of 3hrs in rainfall intensity of 110mm/hr). As a result of slope stability analysis, it was found that the construction method for reinforced soil surface would be more economical, easy and fast construction technology than conventional reinforcement method.

• The korean journal of orthodontics
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• v.28 no.6 s.71
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• pp.947-954
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• 1998

The purpose of this study was to compare shear bonding strengths and debonding patterns of the ceramic brackets attached on the crystal which were grown on the enamel surface of a tooth with different concentrations of lithium sulphate-contained polyacrylic acid in different application times. Four kinds of concentrations of mixed solutions were made and applied to the enamel surface on extracted human premolars. The solutions were made by adding 0.3M or 0.6M of lithium sulfate to $50\%\;or\;65\%$ of polyacrylic acid with 0.3M sulfuric acid. The solutions were applied for 30 or 60 seconds. After bonding, a universal testing machine was used to measure the shear bond strength, and then observations were made of debonding patterns through the stereoscope. And the enamel surface was observed through the scanning electron microscope to examine the pattern of crystal growth and debonding. The results were as follows: 1. Shear bond strength in the enamel surface treated with $50\%$ polyacrylic acid was higher than that with $65\%$ polyacrylic acid. 2. There were no statistical differences in shear bond strength according to concentration of lithium sulfate and application time of solutions . 3. Enamel surface was almost free of resin debris after debonding. 4. Enamel surface treated with $50\%$ polyacrylic acid showed higher density of crystal growth than that with $65\%$ polyacrylic acid under scanning electron microscope.

• Pediatric Gastroenterology, Hepatology & Nutrition
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• v.1 no.1
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• pp.138-143
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• 1998

Chronic diarrhea in children is a common problem with numerous causes. Although most of these causes are benign, critical illness may present as chronic diarrhea. In a patient of chronic diarrhea, gastrointestinal infections are the most common causes in children of all ages and antibiotics may cause chronic diarrhea by altering intestinal microflora, which can result in the emergence of bacterial overgrowth. Overgrowth of Clostridium difficile may cause pseudomembranous colitis. We experienced 25-month-old boy who suffered from chronic diarrhea and partially treated with antibiotics irregularly. Colonoscopic findings of this child showed multiple plaques with white to yellowish exudate which adhere to the mucosal surface of a variable length of rectum. Histollogically, each plaque comprised a pseudomembrane of mucous debris, inflammatory cells, and exudate overlying groups of partially disrupted glands. A latex agglutination test on patient's stool was positive to toxin A of Clostridium difficile. He was recovered after stopping the antibiotics he has been prescribed, and being given vancomycin for 2 weeks. We report this case with brief review of literature.

• Journal of Environmental Science International
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• v.6 no.5
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• pp.497-503
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• 1997

This study was performed to Investigate the utilization of waste concretes for neutralization and removal of heavy metals In plating wastewater, because waste concretes have been known to be very porous, to have high species surface area and to have alkaline minerals such as calcium. The results obtained from this research showed that waste concretes had a buffer capacity to neutralize an acidic alali system in plating wastewater. Generally, neutralization and removal rate of heavy metals were excellent in the increase of waste concrete amounts and a small size. Because a coefficient of correlation was high, it seemed that removal of heavy metals could be explained by Freundlich and Langmuir isotherms. If we reflected the adsorption capacity(k) and adsorption intensity(1/n) of Freundlich isotherm, we couldn't consider waste concretes as a good adsorbent. But, we could know that waste concretes were capable of removing a part of heavy metals. In point of building waste debris, if waste concretes substituted for a valuable adsorbent such as actuated carbon, they could look forward to an expected economical effect.

• Tribology and Lubricants
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• v.28 no.3
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• pp.117-123
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• 2012

Tribological properties of hybrid type friction materials were studied. Hybrid friction materials were produced by combining non-steel(NS) and low-steel(LS) type friction materials. The emphasis of the investigation was given to possible synergistic effects from the two different friction materials, in terms of friction stability at high temperatures and the amplitude of friction oscillation, also known as stick-slip at low sliding speeds. The high temperature friction test results showed that the friction effectiveness of the hybrid friction material was well sustained compared to LS and NS friction materials. Wear resistance of the hybrid type was similar to LS friction materials. Examination of the rubbing surfaces after tests revealed that the friction characteristics of the hybrid friction material were attributed to the wear debris produced from low-steel friction materials, which were migrated to the surface of the non-steel friction material, forming new contact plateaus. The stick-slip amplitude and its frequency were pronounced when non-steel friction material was tested, while hybrid and low-steel types showed relatively small stick-slip amplitudes. These results suggest possible improvement of tribological properties by designing a hybrid composite of low-steel and non-steel friction materials.

• Corrosion Science and Technology
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• v.8 no.3
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• pp.126-131
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• 2009

The interaction between wear and corrosion can significantly increase total material losses in water chemistry environment. The corrosive wear tests of a PWR steam generator tube material (Alloy 690) against the anti vibration bar material (409 SS) were performed at room temperature. The tests were performed in alkaline water chemistry conditions. NaOH solution was selected for test condition to investigate the corrosive wear effect of steam generator tube material in alkaline pH condition without other factors. The flow induced vibration can caused tube damage and the corrosion can be occurred by water chemistry. The test results showed that, in the alkaline solution at pH 13.9, the corrosion current density was increased about ten times than that in the distilled water. And wear rate at pH 13.9 was increased about ten times from that at neutral condition. However, the wear rate was decreased with time. The decrease would be attributed to the change in roughness of specimen or sub-layer of the worn surface with time. From microstructure observation, severe abrasive shape and several wear debris were found. From those results, it could infer that the oxide film on Alloy 690 changed to easily breakable one in the alkaline water, and then abrasion with corrosion became the main wear mechanism.

• The Korean Journal of Air & Space Law and Policy
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• v.22 no.1
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• pp.55-74
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• 2007

When the People's Republic of China destroyed one of its own defunct meteorological satellites, the Fengyun-1C, at an altitude of some 865 km above the earth's surface, the PRC was accused of initiating, or at the very least risking an(other) arms race in outer space also. The test also gave rise to a few legal questions as to the permissibility of this test, and the broader permissibility of using space for military and other weapon-touting activities, Whilst the test cannot be considered to constitute a direct threat to international peace and security so as to invoke relevant legal principles and consequences in terms of the UN Charter for example, it highlights the importance of such clauses in international space law as requiring international cooperation and consultation, due regard for the interests of all other countries both on earth and in outer space, and the further development of general regimes of registration and space debris-prevention. From that perspective, the PRC violated international outer space law not so much by the test itself but by the accompanying lack of information, consultation and due regard for other states', and indeed mankind's, interests.

• The Korean Journal of Air & Space Law and Policy
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• no.spc
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• pp.181-199
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• 2007

When the People's Republic of China destroyed one of its own defunct meteorological satellites, the Fengyun-1C, at an altitude of some 865 km above the earth's surface, the PRC was accused of initiating, or at the very least risking an(other) arms race in outer space also. The test also gave rise to a few legal questions as to the permissibility of this test, and the broader permissibility of using space for military and other weapon-touting activities, Whilst the test cannot be considered to constitute a direct threat to international peace and security so as to invoke relevant legal principles and consequences in terms of the UN Charter for example, it highlights the importance of such clauses in international space law as requiring international cooperation and consultation, due regard for the interests of all other countries both on earth and in outer space, and the further development of general regimes of registration and space debris-prevention. From that perspective, the PRC violated international outer space law not so much by the test itself but by the accompanying lack of information, consultation and due regard for other states', and indeed mankind's, interests.

• Journal of the Korean Society for Precision Engineering
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• v.27 no.10
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• pp.40-44
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• 2010

Laser drilling is an enabling technology for Through Silicon Via (TSV) interconnect applications. Recent advances in picoseconds laser drilling of blind, micron sized vias in silicon is presented here highlighting some of the attractive features of this approach such as excellent sidewall quality. In this study, we dealt with comparison of heat affection around drilled hole between a picosecond laser and a nanosecond laser process under the UV wavelength. Points which special attention should be paid are that picosecond laser process lowered experimentally recast layer, surface debris and micro-crack around hole in comparison with nanosecond laser process. These finding suggests that laser TSV process has possibility to drill under $10{\mu}m$ via. Finally, the laser drilling platform was constructed successfully.

• Transactions of Materials Processing
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• v.26 no.6
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• pp.365-371
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• 2017

During sling wear of a ferrous metal, a surface layer is formed. Its microstructure, constituting phases, and mechanical property are different from those of the original wearing material. Since wear occurs at the layer, it is important to characterize the layer and understand how wear rate changes with different layers. Various layers are formed depending on external wear conditions such as load, sliding speed, counterpart material, and environmental conditions. In this research, sliding wear tests of pure iron were carried out against two different counterparts (AISI 52100 bearing steel and $Al_2O_3$) in the air and in an inert Ar gas atmosphere. Pure iron was employed to exclude other effects from secondary phases in steel on the wear. Wear tests were performed at room temperature. Worn surfaces, wear debris, and cross-sections were analyzed after the test. It was found that these two different counterparts and environments produced diverse layers, resulting in significant changes in wear rate. Against the bearing steel, pure iron showed higher wear rate in an Ar atmosphere due to severe adhesion than that in the air. On the contrary, the iron showed much higher wear rate in the air against $Al_2O_3$. Different layers and wear rates were analyzed and discussed by oxidation, severe plastic deformation, and adhesion at wearing surfaces.