• Restorative Dentistry and Endodontics
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• 제18권1호
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• pp.1-26
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• 1993

The purpose of this study was to investigate the effect of acid etching on the surface appearance and fracture toughness of five glass ionomer cements. Five kinds of commercially available glass ionomer cements including chemical curing filling type, chemical curing lining type, chemical curing metal reinforced type, light curing tilling type and light curing lining type were used for this study. The specimens for SEM study were fabricated by treating each glass ionomer cement with either visible light curing or self curing after being inserted into a rubber mold (diameter 4mm, depth 1mm). Some of the specimens were etched with 37% phosphoric acid for 0, 15, 30, 60, go seconds, at 5 minutes, 1 hour and 1 day after mixing of powder and liquid. Unetched ones comprised the control group and the others were the experimental groups. The surface texture was examined by using scanning electron microscope at 20 kV. (S-2300, Hitachi Co., Japan). The specimens for fracture toughness were fabricated by curing of each glass ionomer cement previously inserted into a metal mold for the single edge notch specimen according to the ASTME399. They were subjected to a three-point bend test after etching for 0, 30, 60, and 90 seconds at 5 minutes-, 1 hour-and 1 day-lapse after the fabrication of the specimens. The plane strain fracture toughness ($K_{IC}$) was determined by three-point bend test which was conducted with cross-head speed of 0.5 mm/min using Instron universal testing machine (Model No. 1122) following seven days storage of the etched specimens under $37^{\circ}C$, 100% humidity condition. Following conclusions were drawn. 1. In unetched control group, crack was present, but the surface was generally smooth. 2. Deterioration of the surface appearance such as serious dissolving of gel matrix and loss of glass particles occured as the etching time was increased beyond 15 s following Immediate etching of chemical curing type of glass ionomer cements. 3. Etching after 1 h, and 1 d reduced surface damage, 15 s, and 30s etch gave rough surface appearance without loss of glass particle of chemical curing type of glass ionomer cements. 4. Light curing type glass ionomer cement was etched by acid, but there was no difference in surface appearances according to various waiting periods. 5. It was found that the value of plane stram fracture toughness of glass ionomer cements was highest in the light curing filling type as $1.79\;MNm^{-1.5}$ followed by the light curing lining type, chemical curing metal reinforced type, chemical curing filling type and chemical curing lining type. 6. The value of plane stram fracture toughness of the chemical curing lining type glass ionomer cement etched after 5 minutes was lower than those of the cement etched after 1 hour or day or unetched (P < 0.05). 7. Light curing glass ionomer cement showed Irregular fractured surface and chemical curing cement showed smooth fractured surface.

• 한국정보과학회논문지:정보통신
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• 제30권4호
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• pp.559-571
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• 2003

PSTN(Public Switched Telephone Network)과 IP Network의 연동을 제공하는 새로운 프로토콜 ENUM(tElephone Numbering Mapping)은 전 세계적으로 유일성을 가지는 전화번호를 DNS 기반의 구조에서 사용되는 F.Q.D.N.(Fully Qualified Domain Name)으로 변환함으로써 E.164 번호를 사용하여 PSTN에서 제공하는 서비스와 IP 네트워크에서 제공하는 서비스를 동시에 사용 가능케 하는 새로운 인터넷 주소체계이다. 본 논문에서는 미국과 유럽에서 활발히 진행중인 ENUM 모델 표준화 연구 및 개발에 발맞추어 ENUM 기반의 서비스를 사용할 때 ENUM resolution 성능 향상을 위한 Tier 2 네임서버 관리기법을 제시한다. ENUM 위임구조에서 Tier 2 네임서버 제공업자가 지역번호 별로 ENUM 등록 대행업 및 NAPTR RR(Naming Authority PoinTeR 리소스 레코드)을 제공함으로써 ENUM resolution의 성능이 향상됨을 증명하기 위해 ENUM 기반의 네트워크 모델링을 사용하였다. ENUM 프로토콜이 IP 네트워크 사용자와 PST리 사용자에게 유연성 및 편의성을 제공하는 반면 사용자가 ENUM을 사용할 때 지불해야할 인내력을 측정할 척도가 없는 현재 이 논문에서 제안하는 방법은 사용자의 ENUM 서비스 선택 결정에 긍정적인 영향을 미치고, ENUM Tier 2 네임서버 관리를 위한 정책에 도움이 될 것으로 기대된다.

• 구강회복응용과학지
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• 제34권4호
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• pp.262-269
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• 2018

목적: 치은 형성 후 인공치아의 이동에 대하여 평가를 시행하였다. 연구 재료 및 방법: 10벌의 동일한 치아배열과 치은의 외형을 가진 납의치를 이용하여 실험하였다. 이 납의치 상에서 치은 형성을 시행하였고, 10분 간격으로 120분 간 모델 스캔을 시행하여 치아 간 거리를 측정하였다. SPSS Ver. 22. 0를 이용하여 통계학적 분석을 시행하였다. 결과: 치은 형성 후 평균적으로 치아 사이의 거리가 0.0999 mm에서 0.1787 mm로 나타났다. 인공치아 이동의 변화율에 대해서는 40 - 50분과 50 - 60분 사이와 50 - 60분과 60 - 70분 사이에서 통계학적으로 유의한 차이가 관찰되었고, 그 이후에는 변화율의 유의한 차이가 없었다. 결론: 120분 간 측정한 결과 인공치아의 이동이 관찰되었고, 60 - 70분 이후에는 시간에 따른 평균 이동량의 변화가 관찰되지 않았다. 이를 종합하면, 치은 형성 후 60분 이상 경과된 시점에서 교합에 대한 재평가를 시행한 후에 최종 의치를 제작하는 것이 필요하다.

• Animal Bioscience
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• 제34권10호
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• pp.1643-1652
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• 2021

Objective: Two experiments were conducted to provide a new approach for evaluating feed nutritional value by metabolizable glucose (MG) in piglet diets with different levels of starch and crude fiber. In Exp 1, a regression equation for MG was generated. In Exp 2, the equation was verified, and the optimal growth performance of piglets under appropriate MG levels was tested. Methods: In Exp 1, 20 weaned piglets (7.74±0.81 kg body weight [BW]) were randomly assigned to 1 of 4 treatments, including the basal diet containing different levels of MG (starch, 25.80%, 31.67%, 45.71%, 49.36%; crude fiber, 1.23%, 1.35%, 1.80%, 1.51%). The piglets were implanted with an ileal fistula, cannulation of the carotid artery, portal vein, and mesenteric artery. The chyme from the ileum fistula and blood samples were collected. In Exp 2, 30 weaned piglets (8.96±0.50 kg BW) were randomly assigned to 1 of 5 treatments, including the experimental diets with different levels of MG (37.6, 132.5, 300.0, 354.3, and 412.5 g/kg). The piglets' BW, and feed consumption were recorded to calculate growth performance during the 28-d experiment. Results: In Exp 1, the MG levels in 4 diets were 239.62, 280.68, 400.79, and 454.35 g/kg. The regression equation for the MG levels and dietary nutrients was: Y (MG) = 12.13×X₁ (starch)+23.18×X₂ (crude fiber)-196.44 (R² = 0.9989, p = 0.033). In Exp 2, treatments with 132.5 and 300.0 g/kg MG significantly (p<0.05) increased average daily gain and feed conversion efficiency of weaned piglets, increased digestibility of crude fat, and had no effect on digestibility of crude protein compared to 300.0 to 412.5 g/kg MG. Conclusion: The pig model combining the ileum fistula and cannulation of blood vessels was successfully used to determine the dietary MG levels. The recommended MG level in weaned pig diets is 132.5 to 300.0 g/kg.

• Journal of Korean Neurosurgical Society
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• 제65권2호
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• pp.204-214
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• 2022

Objective : Osteoporosis result from age-related decline in the number of osteoblast progenitors in the bone marrow. Probiotics have beneficial effects on the host, when administered in appropriate amounts. This study investigated the effects of probiotics expressing specific genes, especially the effects of genetically modified bone morphogenetic protein (BMP)-2-expressing Lactobacillus plantarum CJNU 3003 (LP) on ovariectomized rats. Methods : Twenty-eight female Wistar rats (250-300 g, 12 weeks old) were divided into four groups : the sham (control), the ovariectomy (OVX)-induced osteoporosis group (OVX), the OVX and LP (OVX/LP), OVX and genetically modified BMP-2-expressing LP (OVX/LP with BMP) groups. The three groups underwent bilateral OVX and two of these groups were administered two different types of LP via oral gavage daily. At 16 weeks post-OVX, blood was collected from the heart and the bilateral tibiae were extracted and were scanned by ex-vivo micro-computed tomography and stained with hematoxylin-and-eosin (H&E) and Masson's trichrome stain for pathological assessment. The serum levels of osteocalcin (OC), rat C-telopeptide of type I collagen (CTX-I), BMP-2, and receptor activator of nuclear factor-ĸB ligand (RANKL) were measured. Results : The 3D-micro-computed tomography images showed that the trabecular structure in the OVX/LP with BMP group was maintained compared with OVX and OVX/LP groups. No significant differences were detected in trabecular thickness (Tb.Th) between control and OVX/LP with BMP groups (p>0.05). Furthermore, a tendency toward increased BMD, trabecular bone volume, Tb.Th, and trabecular number and decreased trabecular separation was found in rats in the OVX/LP with BMP groups when compared with the OVX and OVX/LP groups (p>0.05). The H&E and Masson's trichrome stained sections showed a thicker trabecular bone in the OVX/LP with BMP group compared with the OVX and OVX/LP groups. There was no difference in serum levels of OC, CTX and RANKL control and OVX/LP with BMP groups (p>0.05). In contrast, significant differences were found in OC and CTX-1 levels between the OVX and OVX/LP with BMP groups (p<0.05). Conclusion : Our results showed that the expression of genetically modified BMP-2 showed inhibition effect for bone loss in a rat model of osteoporosis.

• 문화기술의 융합
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• 제9권1호
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• pp.1-9
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• 2023

본 연구에서는 PBL 수업으로 전문대학교 학생들의 현장실습수업 참여능력, 문제해결능력 강화와 동시에 현장실습 참여 역량과 문제해결력을 향상시킬 수 있는 PBL 수업 기초연구자료모델을 구축하는데 목적을 두었다. 대상자는 경북 소재의 D대학교 현장실습 교과수업을 하고 있는 5개 학과의 71명을 최종 분석 대상으로 하여 2021년 10월10일~12월 05일까지 7주간 사전검사, PBL수업 운영, 사후검사의 3단계로 실시하였다. 전·사후 검사를 통해 수집된 자료는 SPSS 20을 활용하으며 사전, 사후 효과를 알아보기 위해 대응표본 t검증을 실시하였다. 연구 내용: PBL 수업을 활용한 수업이 전문 대학생의 현장실습 수업 참여에 미치는 효과를 확인한 결과 전문 대학생의 현장실습 수업참여와 문제해결 능력에 통계적으로 유의미한 효과를 확인하였다. 결론 및 제언: 본 연구에서는 PBL 수업은 전문대학생의 현장실습 수업에서 학생들이 주도적으로 학습을 참여하고 이끌어 가는데 유의미한 도움을 주는 것으로 확인된다. 이는 결국 빠르게 변화해 가고 있는 직업 환경을 준비하는데 있어 직접 문제해결방법을 찾고 그 능력을 높이는데 도움이 되는 것으로 확인된다.

• 무역학회지
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• 제43권4호
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• pp.155-175
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• 2018

세계경제의 G1을 추구하는 중국은 이를 위한 경제적 성장유지를 위해 중국에서 시작하여 중앙아시아를 관통하여 유럽에 이르는 옛 실크로드를 개척하는 경제벨트를 추진 중이다. 본 연구는 이러한 중국의 경제확장정책에 효율적으로 동참하기 위한 방안으로 글로벌 대중국투자와 한국의 대중국 투자에 영향을 미치는 거시적 결정변수들의 영향력 정도를 비교분석한 연구이다. 이를 위해 한국의 대중국 FDI 결정변수와 글로벌 대중국 직접투자 결정변수를 벡터오차수정모형(VECM)을 통해 각각의 결정변수가 투자결정에 미치는 영향력을 분석하였다. 분석을 위한 자료로 중국지역균형발전 의 상징지역이라 할 수 있는 베이징, 상하이, 충칭, 시안 및 썬양 등 5개의 주요도시를 횡단면으로 하고 2003~2013년간 이들 도시에 대한 한국의 대중국투자, 글로벌 대중국투자, GDP, 실업률, 임금 추이를 시계열로 하는 패널을 구성하였다. 본 연구가 기존의 연구와 차별되는 점은 첫째, 기존의 대 중국 외국인투자와 관련 연구가 대부분 외국기업의 초기 대중국 투자지역인 연해지역도시에 집중된 것과는 달리 본 연구는 해안, 내륙, 동북의 주요도시들을 동시에 비교 분석하였다. 둘째, 이들 지역전체에 대해 공통적으로 외국인투자에 영향을 미치는 투자결정변수요인간의 인과관계뿐만 아니라 각 도시 별로 외국인투자결정요인 변수간의 비중과 인과관계를 비교하였다. 셋째, 최근 중국의 서부내륙개발과 연계되어 동북3성개발등의 균형정책에 발맞추어 우리의 대중국투자의 가이드라인을 제시하였다. 마지막으로 패널데이타가 가지는 지역적, 시간적 특이성분석을 통해 외국인투자의 결정요인을 분석하는 방법론과 투자의 효율성을 위해 모형의 추정력을 높일 수 있는 누락된 변수의 의미가 무엇인지에 대한 인식과 이에 대한 연구의 필요성을 제시한 의미가 있다고 하겠다.

• Steel and Composite Structures
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• 제46권1호
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• pp.53-73
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• 2023

Man-made structure materials like concrete usually contain inclusions. These inclusions affect the mechanical properties of concrete. In this investigation, the influence of inclusion length and inclination angle on three-dimensional failure mechanism of concrete under uniaxial compression were performed using experimental test and numerical simulation. Approach of acoustic emission were jointly used to analyze the damage and fracture process. Besides, by combining the stress-strain behavior, quantitative determination of the thresholds of crack stress were done. concrete specimens with dimensions of 120 mm × 150 mm × 100 mm were provided. One and two holes filled by gypsum are incorporated in concrete samples. To build the inclusion, firstly cylinder steel tube was pre-inserting into the concrete and removing them after the initial hardening of the specimen. Secondly, the gypsum was poured into the holes. Tensile strengths of concrete and gypsum were 2.45 MPa and 1.5 MPa, respectively. The angle bertween inclusions and axial loadind ary from 0 to 90 with increases of 30. The length of inclusion vary from 25 mm to 100 mm with increases of 25 mm. Diameter of the hole was 20 mm. Entirely 20 various models were examined under uniaxial test. Simultaneous with experimental tests, numerical simulation (Particle flow code in two dimension) were carried out on the numerical models containing the inclusions. The numerical model were calibrated firstly by experimental outputs and then failure behavior of models containing inclusions have been investigated. The angle bertween inclusions and axial loadind vary from 0 to 90 with increases of 15. The length of inclusion vary from 25 mm to 100 mm with increases of 25 mm. Entirely 32 various models were examined under uniaxial test. Loading rate was 0.05 mm/sec. The results indicated that when inclusion has occupied 100% of sample thickness, two tensile cracks originated from boundaries of sample and spread parallel to the loading direction until being integrated together. When inclusion has occupied 75% of sample thickness, four tensile cracks originated from boundaries of sample and spread parallel to the loading direction until being integrated together. When inclusions have occupied 50% and 25% of sample thickness, four tensile cracks originated from boundaries of sample and spread parallel to the loading direction until being integrated together. Also the inclusion was failed by one tensile crack. The compressive strength of samples decease with the decreases of the inclusions length, and inclusion angle had some effects on that. Failure of concrete is mostly due to the tensile crack. The behavior of crack, was affected by the inclusion length and inclusion number.

• Advances in aircraft and spacecraft science
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• 제11권1호
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• pp.83-103
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• 2024

Adhesive bonding is currently widely used in many industrial fields, particularly in the aeronautics sector. Despite its advantages over mechanical joints such as riveting and welding, adhesive bonding is mostly used for secondary structures due to its low peel strength; especially if it is simultaneously exposed to temperature and humidity; and often presence of bonding defects. In fact, during joint preparation, several types of defects can be introduced into the adhesive layer such as air bubbles, cavities, or cracks, which induce stress concentrations potentially leading to premature failure. Indeed, the presence of defects in the adhesive joint has a significant effect on adhesive stresses, which emphasizes the need for a good surface treatment. The research in this field is aimed at minimizing the stresses in the adhesive joint at its free edges by geometric modifications of the ovelapping part and/or by changing the nature of the substrates. In this study, the finite element method is used to describe the mechanical behavior of bonded joints. Thus, a three-dimensional model is made to analyze the effect of defects in the adhesive joint at areas of high stress concentrations. The analysis consists of estimating the different stresses in an adhesive joint between two 2024-T3 aluminum plates. Two types of single lap joints(SLJ) were analyzed: a standard SLJ and another modified by removing 0.2 mm of material from the thickness of one plate along the overlap length, taking into account several factors such as the applied load, shape, size and position of the defect. The obtained results clearly show that the presence of a bonding defect significantly affects stresses in the adhesive joint, which become important if the joint is subjected to a higher applied load. On the other hand, the geometric modification made to the plate considerably reduces the various stresses in the adhesive joint even in the presence of a bonding defect.

• Journal of Radiation Protection and Research
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• 제40권3호
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• pp.124-131
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• 2015

원료물질 또는 공정부산물을 가공하거나 이를 원료로 하여 제조된 제품인 가공제품은 함유된 천연방사성핵종(우라늄, 토륨, 포타슘 등)으로부터 감마선 방출로 외부피폭을 유발할 수 있다. 따라서 본 연구에서는 방사성핵종 농도 우라늄 토륨 $1Bq{\cdot}g^{-1}$, 포타슘 $10Bq{\cdot}g^{-1}$을 가정하고 평형상태의 감마선방출을 가정하여 최종사용자의 사용환경을 반영하여 몬테칼로 전산모사로 복셀팬텀인 ICRP 기준팬텀과 ICRP 권고 103을 적용하여 가공제품의 연간피폭선량을 계산하고 체계를 개발하였다. 가공제품은 사용환경에 따라 피부비밀착형(석고보드, 음이온 벽지, 음이온 페인트)과 피부밀착형(팔찌, 목걸이, 벨트, 뜸질기)으로 구분하였고 기하학적 모델링은 일반가구가 거주하는 주택의 유형 분포추이와 설계지침을 반영하여 룸모델링($3m{\times}4m{\times}2.8m$ 보수적으로 밀폐된 방)과 복셀팬텀 분할면에 직접 가공제품을 모사하였다. 사용시간은 한국형 노출지수 개발 및 운영체계 구축 보고서를 참고하였으며 알 수 없는 제품은 보수적으로 24시간을 가정하였다. 본 연구에서 가공제품의 연간 유효선량은 0.00003 ~ 0.47636 mSv로 평가되었으며 벨트류 장기등가선량률을 확인하여 복셀팬텀에 가공제품을 직접 모사하는 것의 의미를 확인하였다.