• 대한소아치과학회지
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• 제25권2호
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• pp.277-284
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• 1998

For the purpose of comparing the shear bond strengths of pit and fissure sealants, and finding out the more efficient method of tooth surface treatment when the etched surface is contaminaed by saliva or moisture, an experiment was performed on 3 types of pit and fissure sealants. 120 extracted human molars were divided into 3 groups, each of which was composed of 40 specimens sealed with Helioseal, Teethmate-F and Fuji III respectively. And each groups was again divided into 4 subgroups according to tooth surface treatment. The shear bond strengths of each groups and subgroup was measured and statistically analyzed. The results obtained were as follows : 1. Shear bond strengths of nonfluoridated resin sealant, Helioseal were shown to be higher than those of fluoridated resin sealant, Teethmate-F, but, not significantly different. 2. Shear bond strengths of GI sealant, Fuji III were to be markedly lower than those of two resin sealants. 3. When there is moisture contamination, applying primer under sealant(Group IV) results in a significantly stronger bond strength of sealant to enamel than when using sealant alone(Group II) in case of all sealants. 4. When there is no moisture contamination, using primer under sealant (Group III) results in bond strength equivalent to bond strength on using sealant alone (Group I). 5. Based on the results above, it was demonstrated that the bond of sealant to tooth surface is greatly affected by saliva contamination and that the complete tooth isolation method should be fully emphasized. The application of primer is recommended when performing sealant under the environment very susceptible to saliva contamination.

• 한국재료학회지
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• 제16권12호
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• pp.777-781
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• 2006

Recently, there are a lot of study to alternate polycarbonate which is being used as storage material in CD, DVD. In this study, we alternated polycarbonate with glass. We observed the change of shape in a surface of the glass which was focused by Nd:YAG Laser. The change of shape and property was studied by thermal mechanical analysis (TMA), UV-Vis spectrometer, AFM and SEM. According to Laser power and quantity of additives, the Bump's size and shape are showed differently. In high energy, the Bump will be transformed into Pit. And also according to CTE, $T_d$ and absorption ratio of glass, difference between Bump and Pit is confirmed. From these investigation, we could control that the minimum size of bump which is more useful shape than pit's is about 1.3 $\mu$m, H 70 nm, and it is near same the spot size.

• Animal cells and systems
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• 제6권3호
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• pp.247-252
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• 2002

The effect of paraquat (PQ, 1,1＇-dimethyl-4,4＇-bipyridium) on the histogene-sis and glycoconjugates (GCs) properties of the pyloric region of the stomach in a perinatal rat was examined by histological and histochemical methods. Oral administration of PQ (9 mg/kg per day in 0.2 mL of D.W.) on 7 to 14 days of gestation revealed growth retardation with significant reductions in the length of pyloric gland and their pit. As for histochemical properties of GCs in the pyloric region of the stomach, the PQ-treated rats showed some differences, such as delayed initial appearance of the sulfated GCs and lectin affinities compared with the vehicle group. These different GCs properties in the surface and gastric pit were usually detected in the fetal rats and more prominent and evident differences were revealed in the gland epithelium of the early postnatal rat. These results suggest that maternal PQ administration causes intrauterine growth retardation asso-ciated with delayed histogenesis and GCs immaturation of pyloric mucosa in developing rat.

• Geomechanics and Engineering
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• 제9권4호
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• pp.513-530
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• 2015

Commonly, the base stability of sheeted excavation pits against seepage failure by heave is evaluated by using two-dimensional groundwater flow models and Terzaghi's failure criterion. The objective of the present study is to investigate the effect of three-dimensional groundwater flow on the heave for sheeted excavation pits with various dimensions. For this purpose, the steady-state groundwater flow analyses are performed by using the finite element program ABAQUS 6.12. It has been shown that, in homogeneous soils depending on the ratio of half of excavation width to embedment depth b/D, the ratio of safety factor obtained from 3D analyses to that obtained from 2D analyses $FS_{(3D)}/FS_{(2D)}$ can reach up to 1.56 and 1.34 for square and circular shaped excavations, respectively. As failure body, both an infinitesimal soil column adjacent to the wall (Baumgart & Davidenkoff's criterion) and a three-dimensional failure body with the width suggested by Terzaghi for two-dimensional cases are used. It has been shown that the ratio of $FS_{(Terzaghi)}/FS_{(Davidenkoff)}$ varies between 0.75 and 0.94 depending on the ratio of b/D. Additionally, the effects of model size, the shape of excavation pit and anisotropic permeability on the heave are studied. Finally, the problem is investigated for excavation pits in stratified soils, and important points are emphasized.

• Progress in Superconductivity
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• 제9권1호
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• pp.1-4
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• 2007

The most common technique to fabricate $MgB_2$ superconducting wire is by powder-in-tube (PIT) technique. Therefore, the starting powder for the processing of $MgB_2$ superconductors is an important factor influencing the superconducting properties and performance of the conductors. In this study, the influence of magnesium precursor powders and annealing temperatures on the transition temperatures ($T_c$) and critical current densities ($J_c$) of $MgB_2/Fe$ wires was investigated. All the $MgB_2/Fe$ wires were fabricated by in situ PIT process. It was found that higher $J_c$ was obtained for $MgB_2$ wires with smaller particle size of magnesium precursor powders. The $J_c$ also increases with decreasing annealing temperatures.

• 건축역사연구
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• 제5권2호
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• pp.9-24
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• 1996

Owing to the energitic studies of the leading shcolars, some paradigmatic theories on the history of Korean dwellings have been suggested. They constructed periodization of their own and defined characteristics of each period with very limited historical materials. However the new historical materials have been discovered in the neighboring academic fields, which require to review the existing theories. This study aims at restructuring periodization in the history of Korean dwellings during the age of The prehistory and The ancient Kingdomes. Through the study, the existing theories on the same period are revived and evaluated based on the new materials. I suggest a new theory on the periodization and the characteristics of each period: a. the paleolithic period(6,000,000 B.P.-10,000 B.P.) : natural shelter, the emergence of man-made dwellings b. the neolithic period(10,000 B.P.-1,000 B.C.) : construction of pit house c. the bronze period(1,000 B.C.- 300 B.C.) : construction of semi-pit house d. the early metalic period(300 B.C. - 300 AD.) : construction of house on the ground level development of the Ondol system e. the ancient kingdomes period(300 AD - 700 AD): classification of housing type

• 동굴
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• 제66호
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• pp.95-109
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• 2005

동강 유역에는 이미 알려진 석회암 동굴이 30여기 발달되어 있다. 이들중 학술적 가치와 아울러 관광자원으로서의 개발의 가치가 높은 동굴로는 백용동굴, 화암굴, 절골굴 등이 있으나 이들 중 으뜸은 백용동굴이다. 따라서 필자는 수몰 위기에 놓인 천연기념물 제260호로 지정된 백용동굴의 2차생성물(speieothem)과 동굴 계통을 과학적으로 분석하고 체계화 함으로써 사라질지도 모를 백용동굴의 모습을 후세에 영구히 남기고자 여기에 동굴 퇴적물 및 그 경관을 중심으로 한 동굴현상을 상론하기로 한다. 백용동굴의 휘귀경관으로서는 (1) 위석순(pseudo stalagmite) (2) 석화(anthodites) (3) 기형석순(erratic stalagmites) (4) 동굴방폐(cave shield) (5) 암하(lost river) (6) 규석 (cave flint) (7) 함정 (Pit fall) 등 일곱 가지가 있으나 기타로도 일반적이며 부수적인 관련 사항들도 종합하였다.

• 화약ㆍ발파
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• 제24권1호
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• pp.1-8
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• 2006

최근 대부분의 석회석 광산은 환경문제 등으로 인하여 노천채광에서 지하채굴로 전환되었다. 그 결과 노천채광과 같은 생산성을 유지하기 위해 갱도가 대형화되고 있다. 이에 따라 갱도 및 광주의 규모 그리고 굴착방법 등에서 많은 문제가 발생하고 있다. 본 연구는 두 갱도의 동시 발파 혹은 단일갱도 내에서 좌운반갱도와 사갱을 동시 발파, 두 갱도를 다단 발파 그리고 각각의 갱도를 단독 발파하여 굴착했을 때의 발파진동을 계측하여 각각의 굴착방법에 따라 발파진동식을 산출하여 노모그램 분석과 암반손상권 분석을 실시하였다.

• Restorative Dentistry and Endodontics
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• 제22권2호
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• pp.575-595
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• 1997

Replacement resorption is followed by the delayed replantation of an avulsed tooth. Currently no effective treatment is substantiated for replacement resorption. The purpose of this study was to investigate the effect of stannous fluoride, bisphosphonate (etidronate disodium) and gallium nitrate, which have been shown to reduce dentin resorption, on human dentin. Osteoclasts were collected from tibeas of chick embryo. The cells were well agitated to prevent adhesion and seeded onto the sliced human dentin wafers which had been soaked in either culture media (control), or several different concentrations of stannous fluoride, etidronate disodium (l-hydroxyethylidene -1,1-bisphosphonate disodium), and gallium nitrate. Resorption was measured by counting the number of resorptive pit produced by the cells. Results are as follows. Stannous fluoride and etidronate disodium showed statistically significant reduction of dentin resorption(p<0.05) but the effect of stannous fluoride seemed to be its high cytotoxicity. Etidronate disodium did not show cytotoxicities in all experimented concentrations. Gallium nitrate did not show differences in resorption either between different concentrations or from the control group.

• Geomechanics and Engineering
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• 제27권5호
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• pp.481-495
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• 2021

This article assesses and estimates the progressive failure mechanism of complex pit-rest secondary toppling of slopes that are located within the vicinity of the Gas Flare Site of Refinery No. 4 in South Pars Special Zone (SPSZ), southwest Iran. The finite element numerical procedure based on the Shear Strength Reduction (SSR) technique has been employed for the stability analysis. In this regard, several step modelling stages that were conducted to evaluate the slope stability status revealed that the main instability was situated on the left-hand side (western) slope in the Flare Site. The toppling was related to the rock column-overburden system in relation to the overburden pressure on the rock columns which led to the progressive instability of the slope. This load transfer from the overburden has most probably led to the separation of the rock column and to its rotation downstream of the slope in the form of a complex pit-rest secondary toppling. According to the numerical modelling, it was determined that the Strength Reduction Factor (SRF) decreased substantially from 5.68 to less than 0.320 upon progressive failure. The estimated shear and normal stresses in the block columns ranged from 1.74 MPa to 8.46 MPa, and from 1.47 MPa to 16.8 MPa, respectively. In addition, the normal and shear displacements in the block columns ranged from 0.00609 m to 0.173 m and from 0.0109 m to 0.793 m, respectively.