• Restorative Dentistry and Endodontics
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• 제39권3호
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• pp.201-209
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• 2014

Objectives: This study evaluated the solubility, dimensional alteration, pH, electrical conductivity, and radiopacity of root perforation sealer materials. Materials and Methods: For the pH test, the samples were immersed in distilled water for different periods of time. Then, the samples were retained in plastic recipients, and the electrical conductivity of the solution was measured. The solubility, dimensional alteration, and radiopacity properties were evaluated according to Specification No. 57 of the American National Standards Institute/American Dental Association (ANSI/ADA). Statistical analyses were carried out using analysis of variance (ANOVA) and Tukey's test at a significance level of 5%. When the sample distribution was not normal, a nonparametric ANOVA was performed with a Kruskal-Wallis test (${\alpha}$ = 0.05). Results: The results showed that white structural Portland cement (PC) had the highest solubility, while mineral trioxide aggregate (MTA)-based cements, ProRoot MTA (Dentsply-Tulsa Dental) and MTA BIO ($\hat{A}$ngelus Ind. Prod.), had the lowest values. MTA BIO showed the lowest dimensional alteration values and white PC presented the highest values. No differences among the tested materials were observed in the the pH and electrical conductivity analyses. Only the MTA-based cements met the ANSI/ADA recommendations regarding radiopacity, overcoming the three steps of the aluminum step wedge. Conclusions: On the basis of these results, we concluded that the values of solubility and dimensional alteration of the materials were in accordance with the ANSI/ADA specifications. PCs did not fulfill the ANSI/ADA requirements regarding radiopacity. No differences were observed among the materials with respect to the pH and electrical conductivity analyses.

• Journal of Periodontal and Implant Science
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• 제45권1호
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• pp.23-29
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• 2015

Purpose: This study was conducted to compare the cumulative survival rates (CSRs) and the incidence of postloading complications (PLCs) between a bone-level internal connection system (ICS-BL) and an external connection system (ECS). Methods: The medical records of patients treated with either a ICS-BL or ECS between 2007 and 2010 at Asan Medical Center were reviewed. PLCs were divided into two categories: biological and technical. Biological complications included >4 mm of probing pocket depth, thread exposure in radiographs, and soft tissue complications, whereas technical complications included chipping of the veneering material, fracture of the implant, fracture of the crown, loosening or fracture of the abutment or screw, loss of retention, and loss of access hole filling material. CSRs were determined by a life-table analysis and compared using the log-rank chi-square test. The incidence of PLC was compared with the Pearson chi-squared test. Results: A total of 2,651 implants in 1,074 patients (1,167 ICS-BLs in 551 patients and 1,484 ECSs in 523 patients) were analyzed. The average observation periods were 3.4 years for the ICS-BLs and 3.1 years for the ECSs. The six-year CSR of all implants was 96.1% (94.9% for the ICS-BLs and 97.1% for the ECSs, P=0.619). Soft tissue complications were more frequent with the ECSs (P=0.005) and loosening or fracture of the abutment or screw occurred more frequently with the ICS-BLs (P<0.001). Conclusions: Within the limitations of this study, the ICS-BL was more prone to technical complications while the ECS was more vulnerable to biological complications.

• 한국가스학회지
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• 제8권3호
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• pp.8-15
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• 2004

본 논문은 내부탱크 바닥판의 중심부에서 바닥판의 가장자리인 코너부로 연결되는 반경 방향의 거리를 따라서 바닥판에 걸리는 von Mises 응력, 변위량, 회전 뒤틀림 모멘트를 나타내고 있다. 계산결과에 의하면 내부탱크를 냉각하는 초기과정에서 LNG의 충진율, 즉 LNG와 직접 접촉하는 반경방향 거리는 내부탱크의 바닥판에 대하여 중요한 영향을 미치게 된다. 내부탱크에 공급된 $-162^{\circ}C$의 액상 LNG와 내부에서 증발된 $-80^{\circ}C$의 LNG 가스가 내부탱크의 바닥판과 환상판, 측벽면 등에 접촉하면서 온도차 하중에 의한 열적거동 특성을 위치에 따라 서로 다르게 보여주고 있다. 유한요소해석 결과로부터, LNG의 증발가스와 초저온 액체($-162^{\circ}C$)에 의한 온도차는 바닥판의 열적 불안정성을 일으키는 원인으로 작용하며, 이러한 열적 뒤틀림 현상은 내부탱크 시스템의 안전성을 위협할 수도 있다.

• 한국건축시공학회지
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• 제20권5호
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• pp.441-448
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• 2020

CLSM은 다량의 산업부산물 및 폐기물을 안전하게 유효 활용할 수 있는 슬러리계의 되메움 재료이다. 본 연구에서는 FA 및 모래의 대체 재료로써 GBFS 및 FNS, GF의 적용가능성을 평가함은 물론 나아가 도로 및 노면 하부, 싱크홀 및 포토홀 등의 되메움 및 공동충전재로서의 현장적용을 위한 품질기준을 제안하고자 하였다. 이를 통해 선진외국 대비 재생자원의 유효 재활용을 향상시킴은 물론 국내에서의 CLSM 확대적용 및 보급을 위한 기초적인 자료로 제안하고자 하였다.

• Journal of Preventive Medicine and Public Health
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• 제45권6호
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• pp.344-352
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• 2012

Mercury is a toxic and non-essential metal in the human body. Mercury is ubiquitously distributed in the environment, present in natural products, and exists extensively in items encountered in daily life. There are three forms of mercury, i.e., elemental (or metallic) mercury, inorganic mercury compounds, and organic mercury compounds. This review examines the toxicity of elemental mercury and inorganic mercury compounds. Inorganic mercury compounds are water soluble with a bioavailability of 7% to 15% after ingestion; they are also irritants and cause gastrointestinal symptoms. Upon entering the body, inorganic mercury compounds are accumulated mainly in the kidneys and produce kidney damage. In contrast, human exposure to elemental mercury is mainly by inhalation, followed by rapid absorption and distribution in all major organs. Elemental mercury from ingestion is poorly absorbed with a bioavailability of less than 0.01%. The primary target organs of elemental mercury are the brain and kidney. Elemental mercury is lipid soluble and can cross the blood-brain barrier, while inorganic mercury compounds are not lipid soluble, rendering them unable to cross the blood-brain barrier. Elemental mercury may also enter the brain from the nasal cavity through the olfactory pathway. The blood mercury is a useful biomarker after short-term and high-level exposure, whereas the urine mercury is the ideal biomarker for long-term exposure to both elemental and inorganic mercury, and also as a good indicator of body burden. This review discusses the common sources of mercury exposure, skin lightening products containing mercury and mercury release from dental amalgam filling, two issues that happen in daily life, bear significant public health importance, and yet undergo extensive debate on their safety.

• Journal of Communications and Networks
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• 제18권3호
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• pp.375-386
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• 2016

Most existing studies on broadcast services in orthogonal frequency division multiplexing (OFDM) systems have focused on how to allocate the transmission power to the subcarriers. However, because a broadcasting system must guarantee quality of service to all users, the performance of the broadcast service dominantly depends on the channel state of the user who has the lowest received signal-to-noise ratio among users. To reduce the effect of the worst user on the system performance, we propose a joint delivery scheme of unicast and broadcast transmissions in OFDM systems with broadcast and unicast best-effort users. In the proposed joint delivery scheme, the BS delivers the broadcast information using both the broadcast and unicast subcarriers at the same time in order to improve the performance of the broadcast service. The object of the proposed scheme is to minimize the outage probability of the broadcast service while maximizing the sum-rate of best-effort users. For the proposed joint delivery scheme, we develop an adaptive power and subcarrier allocation algorithm under the constraint of total transmission power. This paper shows that the optimal power allocation over each subcarrier in the proposed scheme has a multi-level water filling form. Because the power allocation and the subcarrier assignment problems should be jointly solved, we develop an iterative algorithm to find the optimal solution. Numerical results show that the proposed joint delivery scheme with adaptive power and subcarrier allocation outperforms the conventional scheme in terms of the outage probability of the broadcast service and the sum-rate of best-effort users.

• 한국항해항만학회:학술대회논문집
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• 한국항해항만학회 2006년도 International Symposium on GPS/GNSS Vol.1
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• pp.459-464
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• 2006

It has been well proved that shiphandling simulators are efficient and useful facilities for training and education of cadets and seafarers. Most of the maritime universities and many maritime training institutes all over the world have installed shiphandling simulators, which play important roles in maritime education and training. However, most of the Shiphandling simulators are standalone facilities with diversities on system architectures, layouts and functions. STCW78/95 requires simulators used for simulator-based training shall be suitable for the selected objectives and training tasks. To ensure the shiphandling simulator facilities meet the requirements of STCW convention and other expanded applications, collaborated research and coordination are needed in development and application of shiphandling simulators. Performance standard should be established for shiphandling simulator systems considering the advanced research needs as well as the needs in education, training, and assessment of competence. Standardizing and exchanging shiphandling mathematical models will improve critical performance of the system. Cooperated research on model course and training assessment approaches will enhance the training standard. In addition, the rapid spread of the internet technology has shown a promising future of application of shiphandling simulators through internet. Research has been carried out on internet based integration of multiple shiphandling simulators. A multi-agent based system, including necessary hardware, has been developed. Collaborated operation of the system can be of benefit in filling the gaps of the technical and operational level and methodology between maritime universities, enhancing mutual understanding of the navigation customs and culture background among cadets and seafarers from different countries, facilitating communication and maritime English training, and extending the functions of shiphandling simulators.

• Restorative Dentistry and Endodontics
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• 제43권2호
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• pp.16.1-16.9
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• 2018

Objectives: Understanding the reason for an unsuccessful non-surgical endodontic treatment outcome, as well as the complex anatomy of the root canal system, is very important. This study examined the cross-sectional root canal structure of mandibular first molars confirmed to have failed non-surgical root canal treatment using digital images obtained during intentional replantation surgery, as well as the causative factors of the failed conventional endodontic treatments. Materials and Methods: This study evaluated 115 mandibular first molars. Digital photographic images of the resected surface were taken at the apical 3 mm level and examined. The discolored dentin area around the root canal was investigated by measuring the total surface area, the treated areas as determined by the endodontic filling material, and the discolored dentin area. Results: Forty 2-rooted teeth showed discolored root dentin in both the mesial and distal roots. Compared to the original filled area, significant expansion of root dentin discoloration was observed. Moreover, the mesial roots were significantly more discolored than the distal roots. Of the 115 molars, 92 had 2 roots. Among the mesial roots of the 2-rooted teeth, 95.7% of the roots had 2 canals and 79.4% had partial/complete isthmuses and/or accessory canals. Conclusions: Dentin discoloration that was not visible on periapical radiographs and cone-beam computed tomography was frequently found in mandibular first molars that failed endodontic treatment. The complex anatomy of the mesial roots of the mandibular first molars is another reason for the failure of conventional endodontic treatment.

• The Korean Journal of Pain
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• 제20권1호
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• pp.54-59
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• 2007

Background: Selective transforaminal epidural block (STEB) has showen effectiveness as a diagnostic and therapeutic option for the management of patients with low back pain or sciatica. This study was carried out in order to determine the short-term effects and prognostic factors associated with STEB in patients with low back pain or sciatica. Methods: Ninety-seven patients were selectedfor participation in this study. Their diagnosis were based werewason the clinical symptoms and MRI findings. We performed STEB under fluoroscopic guidance and injected 3 ml of radio opaque dye in order to confirm the technical success of the procedure. We then injected 20 mg of triamcinolone mixed into 3 ml of 0.5% mepivacaine. One month later, we classified the patient outcomes as excellent, good, moderate or poor, according to the degree of reduction in VAS score from baseline. The independent variables assessed included symptom duration, block level, number of blocks, primary diagnosis, prior caudal block, anterior epidural space filling of dye, medication history, demographic data, radiating pain, back surgery and spondylolisthesis. Results: At a mean follow-up period of 1 month after STEB, excellent results were noted in the patients diagnosed with herniated lumbar disc (70%), non-specific spondylosis (54%), spinal stenosis (44%), and failed back syndrome (28%). The patients with epidural adhesion and combined spondylolisthesis were associated with poorer outcomes. Combined caudal block, symptom duration and the extent of epidural spread of the drug were not related to the effectiveness of the treatment. Conclusions: Selective transforaminal epidural block is effective in treating patients with radiculopathy, such as herniated lumbar disc, but it isrelatively ineffective in treating patients with structural deformities, such as failed back syndrome and spondylolisthesis.

• 한국구조물진단유지관리공학회 논문집
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• 제24권3호
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• pp.26-38
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• 2020

자기 충전형 콘크리트의 배합물 설계는 전형적인 다기준의사결정의 과정이다. 본 연구에서는 실험설계법과 반응표면법을 이용하여 SCC 배합물 전산 설계가 가능하도록 재료성능 및 비용모델을 생성하고, 요구조건을 반영한 여러 성능 사이의 상대적 중요도를 산정하여 가중 다목적 설계문제로 정식화하여 수치최적해를 계산함으로써 비용효율을 고려한 SCC최적설계를 수행하였다. 실험비용과 시간을 고려하여 SCC의 수많은 요구성능 중 압축강도, 철근충전성, 재료분리저항성, 비용정보 등을 다목적 최적화의 목적함수로 설정하였다. 재료경제성을 최적재료설계프로세스에 합리적으로 반영함으로써 경제적 콘크리트배합설계를 수행할 수 있었으며, 본 연구 결과 실험점 계획에서부터 최적해 산출에 이르는 과정을 객관적인 프로세스로 구성함으로써 콘크리트 범용 최적재료설계기술 및 전산화를 기대할 수 있다.