• Restorative Dentistry and Endodontics
• /
• v.35 no.6
• /
• pp.445-452
• /
• 2010

Objectives: The aim of this study was to compare apical sealing ability and physical properties of MTA, MTA - AH-plus mixture (AMTA) and experimental Portland cement - Epoxy resin mixture (EPPC) for a development of a novel retro-filling material. Materials and Methods: Forty-nine extracted roots were instrumented and filled with gutta-percha. Apical root was resected at 3 mm and the retro-filling cavity was prepared for 3 mm depth. Roots were randomly divided into 3 groups of 15 roots each. The retro-filling was done using MTA, AMTA, and EPPC as the groups divided. Four roots were used as control groups. After setting in humid condition for 24 hours, the roots were immersed in 1% methylene blue dye solution for 72 hours to test the apical leakage. After immersion, the roots were vertically sectioned and photos were taken to evaluate microleakage. Setting times were measured with Vicat apparatus and digital radiographs were taken to evaluate aluminum equivalent thickness using aluminum step wedge. The results of microleakage and setting time were compared between groups using one-way ANOVA and Scheffe's post-hoc comparison at the significance level of 95%. Results: AMTA and EPPC showed less microleakage than MTA group (p < 0.05). AMTA showed the highest radio-opacity than other groups and the novel EPPC showed 5 mm aluminum thickness radio-opacity. EPPC showed the shortest initial and final setting times than other groups while the MTA showed the longest (p < 0.05). Conclusions: Under the condition of this study, the novel composite using Portland cement-Epoxy resin mixture may useful for retro-filling with the properties of favorable leakage resistance, radio-opacity and short setting time.

• Journal of the Korean Institute of Intelligent Systems
• /
• v.27 no.1
• /
• pp.1-6
• /
• 2017

Recent researches on radio frequency energy harvesting networks(RF-EHNs) with limited energy resource like battery have been focusing on the development of a new scheme that can effectively extend the whole lifetime of a network to semipermanent. In order for considerable increase both in the amount of energy obtained from radio frequency energy harvesting and its charging effectiveness, it is very important to design a network that supports energy harvesting and data transfer simultaneously with the full consideration of various characteristics affecting the performance of a RF-EHN. In this paper, we proposes an interference-based charging aware routing protocol(ICARP) that utilizes interference information and charging time to maximize the amount of energy harvesting and to minimize the end-to-end delay from a source to the given destination node. To accomplish the research objectives, this paper gives a design of ICARP adopting new network metrics such as interference information and charging time to minimize end-to-end delay in energy harvesting wireless networks. The proposed method enables a RF-EHN to reduce the number of packet losses and retransmissions significantly for better energy consumption. Finally, simulation results show that the network performance in the aspects of packet transmission rate and end-to-end delay has enhanced with the comparison of existing routing protocols.

• Korean Chemical Engineering Research
• /
• v.54 no.4
• /
• pp.568-573
• /
• 2016

We investigated the charging characteristics of a conducting solid sphere (glassy carbon sphere) comparing with that of a water droplet and check the applicability of the perfect conductor theory. For the systematic research, sphere size, applied voltages, viscosity of the medium were changed and the results were compared with that of corresponding water droplets and the perfect conductor theory. Basically, a glassy carbon sphere follows the perfect conductor theory but the charging amount was lower as much as 70~80% of theoretical prediction value due to oil film formed between electrode and a carbon sphere. We hope this result provides basic understandings on the solid sphere contact charging phenomenon and related applications.

• Restorative Dentistry and Endodontics
• /
• v.31 no.4
• /
• pp.323-329
• /
• 2006

The aim of this study was to evaluate the retrievability of Resilon as a root canal filling material Twenty-seven human single-rooted extracted teeth were instrumented utilizing a crown down technique with Gates-Glidden burs and ProFile system. In group1 (n = 12) canals were obturated with gutta percha and AH-26 plus sealer using a continuous wave technique and backfilled. In group 2 (n = 15) Resilon was used as a filling material. Then teeth were sealed and kept in $37^{\circ}C$ and 100% humidity for 7 days. For retreatment, the samples were re-accessed and filling material was removed using Gates-Glidden burs and ProFiles. Teeth were sectioned longitudinally to compare the general cleanliness and amount of debris $({\times}\;75)$ using SEM. Chi-square test was used $({\alpha}\;=\;0.05)$ to analyze the data. The total time required for removal of filling materials was expressed as mean ${\pm}SD$ (min) and analyzed by the Student t-test $({\alpha}\;=\;0.05)$, Required time for retreatment was $3.25\;{\pm}\;0.32$ minutes for gutta percha/ AH 26 plus sealer and $3.05\;{\pm}\;0.34$ minutes for Resilon. There was no statistically significant difference between the two experimental groups. There was no significant difference between the groups in the cleanliness of the root canal wall. This study showed that Resilon was effectively removed by Gates-Glidden burs and ProFiles.

• Clean Technology
• /
• v.13 no.1 s.36
• /
• pp.16-21
• /
• 2007

This study estimated the effect of hydraulic residence time(HRT), influent total ammonia nitrogen(TAN) concentration, temperature and pH in the packed-bed bioreactor using immobilized nitrifiers. Removal rate of ammonia nitrogen was increased with decreasing HRT and the optimum HRT was 0.2 hour when influent TAN was $2g/m^3$. At this point, removal rate was $226.1\;g/m^3{\cdot}day$ and removal efficiency was 88.8%. Removal rate of ammonia nitrogen was Increased with increasing TAN concentration. Removal rate and efficiency of ammonia nitrogen were kept constant at $20{\sim}35^{\circ}C$ and pH $8{\sim}9$ value.

• Restorative Dentistry and Endodontics
• /
• v.34 no.3
• /
• pp.208-214
• /
• 2009

The purpose of this study was to compare the dye leakage of MTA (mineral trioxide aggregate) apical plug produced by two orthograde placement techniques (hand condensation technique and ultrasonically assisted hand condensation technique). To simulate straight canal, 60 transparent acrylic blocks with straight canal were fabricated. These transparent acrylic blocks were divided into 2 groups (Group C; hand condensation technique (HC) and Group U; ultrasonically assisted hand condensation technique (UAHC)) of 30 blocks with each MTA application method. Each group was divided into 2 subgroups (n=15) with different canal size of #70 (subgroup C70 and subgroup U70) and #120 (subgroup C120 and subgroup U120). After apical plug was created, a wet paper point was placed over the MTA plug and specimen was kept in a humid condition at room temperature to allow MTA to set. After 24 hours, remaining canal space was backfilled using Obtura II. All specimens were transferred to floral form socked by 0.2% rhodamine B solution and stored in 100% humidity at room temperature. After 48 hours, resin block specimens were washed and scanned using a scanner. The maximum length of micro leakage was measured from the scanned images of four surfaces of each resin block using Photoshop 6.0. Statistical analysis was performed with Mann-Whitney U test. Group U of UAHC had significantly lower leakage than Group C of HC in #70-size canal (subgroup U70) (p<0.05).

• Proceedings of the Korean Geotechical Society Conference
• /
• 2006.10a
• /
• pp.278-284
• /
• 2006

암반내 존재하는 불연속면은 암반거동에 중대한 영향을 미치게 되며, 특히 불연속면내에 충전물이 협재되어 있는 경우에는 암반구조물의 안정성에 보다 심각한 문제를 가져오는 경우가 많다. 이는 불연속면의 거동과 충전물의 거동이 복합적으로 작용하게 되며, 장기적인 시간을 두고 나타나기 때문이다. 본 검토에서는 충전된 불연속면의 특성을 분석하고, 점토나 흑연이 협재되어 문제가 되었던 현장 사례분석을 통하여 충전된 불연속면이 암반사면이나 터널과 같은 암반구조물에 미치는 영향을 검토하였다. 이를 통하여 충전물의 열화에 의한 장기적이고 잠재적인 거동을 수반할 수 있는 충전된 불연속면의 공학적 문제점을 고찰하였다.

• The Korean Journal of Rheology
• /
• v.5 no.1
• /
• pp.34-48
• /
• 1993

최근 CAD/CAM의 발전과 더불어 사출성형공정은 여러분야에 폭넓게 응용되고 있 다. 사출성형공정은 크게 충전과정(filling stage), 냉각과정(cooling stage), 보압과정(packing stage)로 나누어 지는데 이중 충전과정은냉각과정과 보압과정에서 나타날 물리적인 현상과 최종 성형품의 기계적 성질에 중요한 영향을 끼치게 된다. 충전과정의 수치 해석 방법은 대 표적으로 control volume method, branching flow method, transient moving boun-dary method로 구분된다. 본 연구에서는 격자의 형태를 양호하게 형성시키고 유동선단의 형태를 개선하기위한 기법인 Spline 곡선을 이용한 선단격자 재구성(frontal remeshing using spline curve)과 수치해석에 소요되는 시간을 줄이기 위하여 벽면경계조건 처리를 위한 선단 유동 장생성(frontal flow field construction for wall boun-dary condition treatment)기법을 개발 하고 transient moving voundary method에 적용시켜 원형 평판과 인장 및 굽힘시편 그리고 두께가 변하는 사각 형상을 가진 캐비터에서의 충전과정을 수치해석하였다. 그결과 압력 분 포, 온도분포, 속도장, 유동선단의 진전형태 등이 기존에 제출된 해석결과와 비교하여 볼 때 만족스러운 수치해석결과를 보였다.

• Journal of the Korean Ceramic Society
• /
• v.37 no.9
• /
• pp.921-926
• /
• 2000

에틸렌과 프로판가스로부터 Ni 및 Ni-Cu의 합금촉매를 사용하는 화학증착반응에 의해 제조한 나노탄소섬유에 충전재로 하고, 환경 친화적인 폴리비닐알코올을 매트릭스로 이용하여 복합재를 제조하여 전자파 차폐효능을 조사해 보았다. 전자파 차폐용 충전재의 중요한 물성치인 전기전도도는 나노탄소섬유의 반응조건에 따라 매우 민감하게 변했는데, 전체적으로 10000 psi 압력에서 4.2~29 S/cm 사이에 분포하였고 합금촉매보다도 순수한 Ni로 제조된 나노탄소섬유의 전기전도도 값이 높았다. 한편, 나노탄소섬유/폴리비닐알코올 복합재의 전기전도도는 Ni:Cu(7:3) 합금촉매에서 제조된 나노탄소섬유를 충전시켰을 때, 가장 높게 얻어져서 충전재의 전기전도도 외에도 비표면적이 중요한 변수임을 알 수 있었다. PVA 양에 대한 나노탄소섬유의 함량이 증가할수록 나노탄소섬유 복합재의 전기전도도는 기하급수적으로 증가했고, 110$0^{\circ}C$에서 1시간 동안 나노탄소섬유의 열처리를 통하여 복합재의 전기전도도는 5~7배 증가하였으며, 전자파 차폐율은 2~3 dB 정도 향상시킬 수 있었다.

• Proceedings of the Korean Nuclear Society Conference
• /
• 1995.05a
• /
• pp.580-587
• /
• 1995

1979. 3.28 미국 TMI-2의 사고를 계기로 개발된 증상기준 비상운전절차서는 고리 3,4/영광 1,2호기의 경우 '92. 2에 개정된 ERG-18를 근거로 하여 각 발전소 운전담당 자들에 의하여 확인 및 검증 (Verification S Validation) 작업을 통하여 금년부터 본격적으로 적용되기에 이르렀다. 그러나 비상운전절차서의 특성상 리 발전소별 특정 설정치의 계산에서 어려움을 겪었으며 아직도 재확인 작업을 통한 최적화 여지가 상 당부분 잔존하고 있다. 여기어서는 고압발전소인 고리-3,4/영장-1,2호기 비상운전절차서에 있어서 증기발생기에 공급되는 정상 밋 비상급수의 전체 상실사고시 노심 노출 방지 및 노심 열 제거를 위해 적응되는 기능회복절차서의 "2차 열제거원 상실시 조치" 중 방출 및 충전 운전의 성공적 시작점을 계산, 개정된 비상운전절차서와 비교하여 특정 발전소의 방출 및 충전 운전 설정치를 제시하였고, 이러한 결과로부터 현재 보수적으로 설정된 값의 완화를 유도하여 방출 및 충전 운전 시작전, 운전원으로 하여금 급수확보를 시도할 수 있는 시간여유의 연장을 도출할 수 있었다.도출할 수 있었다.