• The korean journal of orthodontics
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• v.20 no.2
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• pp.283-291
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• 1990

The purpose of this study was to measure and compare tensile and shear strength for 4 types of new direct-bonding brackets and same brackets after recycling and to evaluate the change of bracket slot width after recycling. Four types of new direct-bond brackets were bonded to recently extracted human premolar teeth and the tensile and shear strength was measured by Universal Testing Machine. The brackets were recycled by chemical process and the tensile and shear test was repeated. To evaluate the change of the bracket slot width, slot width was measured by the Topcon Universal Measuring Microscope before and after recycling. Following results were obtained: 1. There was no satistically significant difference between the tensile and shear strength of recycled brackets and those of new brackets. 2. In both new and recycled brackets, the tensile and shear strength of perforated base bracket was lower than those of photoetched, foilmesh and contou-lok mesh base brackets. (P<0.01) 3. There was no statistically significant difference in bonding strengths of control group bonded only once and two times. 4. There was no statistically significant difference in the change of the bracket slow width after recycling process. 5. Of the failure, the combination type (58%) in the tensile strength and the tooth adhesive interface (65%) in the shear strength was the most common type.

• Journal of Korean Academy of Oral and Maxillofacial Radiology
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• v.25 no.1
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• pp.89-97
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• 1995

The radiographic findings of soft tissue calcification in the oral and maxillofacial area was analysed using panoramic, skull P-A and intraoral radiographs in 250 patients. The obtained results were as follows ; 1. Salivary stone had the highest rate of occurrence at 46％(116 cases), followed by lymph node calcification(97 cases), phleholith(21 cases), multiple miliary osteoma(15 cases), antrolith(l case), vessel calcification(l case) and cysticercosis(1 case). 2. The prevalence of salivary stone was slightly higher in females, on the right side and in the middle-aged group and was especially higher in the submandibular gland(83％). The majority of them were round-shaped, homogeneously radiopaque and associated with sialodochitis. 3. The prevalence of lymph node calcification was higher in the female and old-aged group. Irregular shape and radiopaque bodies were seen in the cervical area, bilaterally. 4. The prevalence of phlebolith was slightly higher in the male, and the third decade group. The radiopaque bodies were 4-8 mm in diameter and had laminated appearance. 5. The prevalence of multiple miliary osteoma was higher in old-aged females. The numerous doughnut-shaped radiopaque bodies, sized 2-4 mm in diameter, were seen bilaterally in the cheek and were usually associated with the edentulous ridge.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.7
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• pp.674-679
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• 2008

In this paper, we introduce a new design approach for self-sustained resonant accelerometer, that takes advantage of the automatic gain control (AGC) loop to achieve a stabilized oscillation dynamics. Fundamental idea of this accelerometer is to maintain uniform amplitude of oscillation under input accelerations. Through system modeling and loop transformation considering the envelope of oscillation, the controller is designed to maintain uniform amplitude in oscillation under dynamic input acceleration. The simulation results demonstrate the feasibility of the proposed accelerometer design, which is applicable to control grade inertial measurement system in industrial and civil application fields.

• Proceedings of the Korean Society for Bio-Environment Control Conference
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• 1998.05a
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• pp.45-53
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• 1998

농산물 수입개방으로 외국산 농산물의 대량 유입은 우리 농업의 기반을 흔들고 있는 실정이다. 가격 면에서 여러 가지 어려운 점을 감안한다면 국민의 감정에 국내산 농산물 애용을 호소하기에는 시대적으로 쉬운 일은 아니다. 따라서 농산물의 고품질화 및 생산비 절감으로 대외 경쟁력을 높일 수밖에 없는 실정이다. 이를 위해서 농산물의 적기 수확은 재배기술 못지 않게 중요하다. (중략)

• Transactions of the Korean Society of Mechanical Engineers A
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• v.25 no.5
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• pp.850-856
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• 2001

Even though the hydraulic servo system has been widely used in industrial and military equipments since it has a lot of advantages, it is not easy to design controller due to the high nonlinearities and the parametric uncertainties. The dynamic behavior of the real process in the hydraulic servo system differs from that described by its model because the model is linearized. Another reason of the difference is caused by the variety of parameters, since the system parameters of the dynamic equation are affected by the operating conditions such as temperature and pressure. In this study, the designing process of the MRNC with a PID compensator is introduced and applied to the load sensing hydraulic servo system. The results show that the designed controller guarantees the robust control performance despite of both the nonlinearities and the parametric uncertainties.

• Proceedings of the Korea Water Resources Association Conference
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• 2011.05a
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• pp.284-288
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• 2011

비점오염원 원단위는 적용이 간편하기 때문에 많은 국가에서 비점오염원 유출량을 산정하기 위하여 사용하고 있다. 그러나 비점오염원의 유출은 지역, 지형, 기후, 토지이용 등과 같은 여러 가지 조건들에 따라 배출양상이 다양하게 나타나므로 신뢰성 있는 원단위를 산정하기 위해서는 장기간에 걸친 실측자료가 뒷받침되어야 한다. 우리나라에서는 지난 1980년대 초부터 비점오염 원단위에 대한 연구가 시작되었으며 수많은 문헌과 연구에서 비점오염원 유출특성을 제시하고 있다. 따라서 본 연구에서는 지난 3년간 낙동강 수계에서 모니터링된 비점오염원 자료를 통하여 유출모형인 SWMM(Storm Water Management Model) 구축하고 또한 구축된 모형을 이용하여 실측한 자료를 통한 EMC값과 기존 문헌에서 제시하고 있는 EMC값을 서로 비교함으로서 본 연구에서 제시하고 있는 EMC값의 적정성 및 선행 자료에서 제시하고 있는 값들의 범위를 분석하고자 하였다. 따라서, 본 연구는 모델링을 통하여 비점오염원 유출특성을 파악함과 동시에 실측값 및 기존 문헌에서 제시 하고 있는 EMC를 비교 분석함으로서 적정한 비점오염원의 EMC 값 범위를 파악하여 지목별 비점오염원 원단위 산정에 큰 도움이 되리라 판단된다.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.357.1-357.1
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• 2014

Superhydrophobic WOx nanowire (NW) arrays were fabricated using a thermal evaporation and surface chemistry modification methods by self-assembled monolayer (SAM). As-prepared non-wetting WOx NWs surface shows water contact angle of $163.2^{\circ}$ and has reliable stability in underwater conditions. Hence the superhydrophobic WOx NWs surface exhibits silvery surface by total reflection of water layer and air interlayer. The stability analysus of underwater superhydrophobicity of WOx NWs arrays was conducted by changing hydrostatic pressure and surface energy of WOx NWs arrays. The stability of superhydrophobicity in underwater conditions decreased exponentially as hydrostatic pressure applied to the substrates increased3. In addition, as surface energy decreased, the underwater stability of superhydrophobic surface increased sharply. Specifically, sueprhydrophobic stability increased exponentially as surface energy of WOx NWs arrays was decreased. Based on these results, the models for explaining tendencies of superhydrophobic stability underwater resulting from hydrostatic pressure and surface energy were designed. The combination of fugacity and Laplace pressure explained this exponential decay of stability according to hydrostatic pressure and surface energy. This study on fabrication and modeling of underwater stability of superhydrophobic W18O49 NW arrays will help in designing highly stable superhydrophobic surfaces and broadening fields of superhydrophobic applications even submerged underwater.

• Korean Journal of Materials Research
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• v.9 no.7
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• pp.670-674
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• 1999

Accurate measurements of elastic constants are important from the view points of both science and engineering. The measurement can be viewed from scientific principle as a service tools for analyzing and improving the understanding of the nature of bondings between atoms and between ions. Also, from engineering perspective it would became an important factor to be definitely considered for the design of machinery equipments. In this investigation, two dynamic experimental methods of vibrations (acoustic method and Impulse technique method) are utilized and the results from the both methods are compared to obtain elastic constants data with a high degree of accuracy. The resonance frequencies obtained from the two methods are applied to both Euler and Timoshenko beam equations respectively, to determine the sources for possible differences.

• Journal of the Korean Institute of Rural Architecture
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• v.5 no.3
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• pp.1-7
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• 2003

This study is to find out the betterment way of cost down in the architectural temporary work. To do so, it is more important to check every case above all and find and choice optimum way fitting a scene of a construction field. In addition, in case that the way to apply in proportion to a given condition is complicated, the way to find out cost down way is to adopt the individual peculiarity instead of the generality. Hereupon this study is rather to find out the better way to reduce such as material and manpower cost than to leave matters not to be settled to get the best way in the existing temporary work. So this study is composed with finding the existing problems, fixing the focus about the developmental way to reduce cost in the exterior and interior temporary work, presenting the new construction way and describing the merits and attentions of an improved exterior and interior temporary work.

• Proceedings of the KIEE Conference
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• 2008.10c
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• pp.142-144
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• 2008

This paper is studied on the characteristic analyses of a high performance buck-boost converter added electric isolation by using a soft switching method. To be achieved of a high performance system, the proposed buck-boost converter is constructed by using a partial resonant circuit. The control switches using in the converter are operated with soft switching for a Partial resonant method. The controlling switches are operated without increasing their voltage and current stresses by the soft switching technology. The result is that the switching loss is very low and the converter efficiency is high. And the proposed converter is added in a electric isolation. When the power conversion system is required to electric isolation, the proposed converter is adopted with the system development of high efficiency. The soft switching operation and system efficiency of the proposed converter is verified by digital simulation and experimental results.