• Imaging Science in Dentistry
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• 제52권3호
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• pp.245-258
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• 2022

Purpose: This study compared the root canal anatomy between cone-beam computed tomography (CBCT) and micro-computed tomography (micro-CT) images before and after biomechanical preparation and root canal filling. Materials and Methods: Isthmus-containing mesial roots of mandibular molars(n=14) were scanned by micro-CT and 3 CBCT devices: 3D Accuitomo 170 (ACC), NewTom 5G (N5G) and NewTom VGi evo (NEVO). Two calibrated observers evaluated the images for 2-dimensional quantitative parameters, the presence of debris or root perforation, and filling quality in the root canal and isthmus. The kappa coefficient, analysis of variance, and the Tukey test were used for statistical analyses(α=5%). Results: Substantial intra-observer agreement (κ=0.63) was found between micro-CT and ACC, N5G, and NEVO. Debris detection was difficult using ACC (42.9%), N5G (40.0%), and NEVO (40%), with no agreement between micro-CT and ACC, N5G, and NEVO (0.05<κ<0.12). After biomechanical preparation, 2.4%-4.8% of CBCT images showed root perforation that was absent on micro-CT. The 2D parameters showed satisfactory reproducibility between micro-CT and ACC, N5G, and NEVO (intraclass correlation coefficient: 0.60-0.73). Partially filled isthmuses were observed in 2.9% of the ACC images, 8.8% of the N5G and NEVO images, and 26.5% of the micro-CT images, with no agreement between micro-CT and ACC, and poor agreement between micro-CT and N5G and NEVO. Excellent agreement was found for area, perimeter, and the major and minor diameters, while the roundness measures were satisfactory. Conclusion: CBCT images aided in isthmus detection and classification, but did not allow their classification after biomechanical preparation and root canal filling.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 춘계학술발표회논문집(2)
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• pp.467-472
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• 1996

This study discusses special aspects of severe accident related recriticality modeling and analysis in the Advanced Neutron Source (ANS) reactor.$^{1, 2)}$ The analytical comparison of three elements core to former two elements case is conducted including evaluation of suitable nuclear cross-section sets to account for the effects of system configulation, fuel and moderator mixture temperature, material dispersion and the other thermal-hydraulics. Three elements core ANS reactor is the alternative core design which was proposed as a modified core design, with three fuel elements instead of two, that would allow operation with only 50% enriched uranium (former uranium fuel is the baseline design value of 93%) A comprehensive test matrix of calculations to evaluate the threat of a criticality event in the ANS is described. Strong dependencies still on geometry, material constituents, and thermal-hydraulic conditions are verified. Therefore, the concepts of mitigative design features are qualified.d.

• KSTLE International Journal
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• 제4권2호
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• pp.47-51
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• 2003

Sliding wear tests have been carried out in room temperature air and water in order to compare the wear resistance of Zr-xNb-xSn alloys of various alloying elements (Nb and Sn). The main focus was to quantitatively compare the wear properties of the recently developed Zr-xNb-xSn alloys with the commercial ones using the evaluation parameters of the wear resistance with the consideration of the worn area. As a result, the recently developed alloys had a similar wear resistance compared with the commercial ones. The dominant factor governing the wear resistance was the protruded volume of the wear debris that was formed on the worn area in the air condition, but the accommodation of the plastic deformation on the contact area in water. In addition, the worn area size appeared to be very different depending on the tested alloys. To evaluate the wear resistance of each test specimen, the ratio of the wear volume or the protruded volume to the worn area ($D_e$ or $D_p$) is investigated and proposed as the evaluation parameters of the wear resistance.

• 한국안전학회지
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• 제37권6호
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• pp.148-157
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• 2022

Every year, particularly during the monsoon rainy season, landslides at the Chuncheon province of South Korea cause tremendous damage to lives, properties, and infrastructures. More so, the high rainfall intensity and long rainfall days that occurred in 2020 have increased the water content in the soil, thereby increasing the chances of landslide occurrences. Besides this, the rainfall thresholds and characteristics responsible for the initiation of landslides in this region have not been properly identified. Therefore, this paper addresses the rainfall thresholds responsible for the initiation of landslides at Chuncheon from a regional perspective. Using data obtained from rainfall measurements taken from 2002 to 2011, we identify a threshold relationship between rainfall intensity and rainfall duration for the initiation of landslides. In addition, we identify the relationship between the rainfall intensity using a 3-day, 7-day, and 10-day antecedent rainfall observation. Specifically, we estimate the rainfall data at 8 sites where debris flow occurred in 2011 by kriging. Following this, the estimated data are used to construct the relationship between the intensity (I), duration (D), and frequency (F) of rainfall. The results of the intensity-duration-frequency (IDF) analysis show that landslides will occur under a rainfall frequency below a 2-year return period at two areas in Chuncheon. These results will be effectively used to design structures that can prevent the occurrence of landslides in the future.

• 한국자동차공학회논문집
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• 제23권3호
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• pp.292-298
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• 2015

A wiper is a safety device removing rain and debris from windshield and ensuring visibility of drivers. If contact pressure distribution between rubber of the blade and the windshield is unbalanced, unwanted noise, vibration, and abrasion of the blade can occur and sometimes fatal accidents could occur. To improve the safety of the wiper, there have been many researches on the contact pressure analysis of the wiper, but the analysis results were not converged or require much computational time due to material nonlinearity of the rubber and contact conditions between the blade rubber and the windshield. In this research, a simple model with 1D beam and 2D shell elements was used for the contact pressure analysis instead of the 3D blade model. The simplified model saved computational time of the analysis and resolved convergence problems. The accuracy of the analysis results was verified by comparing them with experimental results for different rail spring curvatures.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.652-655
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• 2001

In this paper, I have studied minimization of the kerf-width and surface burning which are occurred after the singulation process of multi layer $\mu$-BGA( thickness 1.1 mm, 0.9 mm) with a pulsed Nd:YAG( = 532 nm, repetition rate = 10 Hz) laser. The thermal energy of a pulsed Nd:YAG laser is used to cut the copper layer. I have studied are minimization of the surface burning and kerf-width using a photo resist, $N_2$blowing and polyester double sided tape as a cutting parameter. The $N_2$blowing reduces a laser energy loss by debris and suppresses a surface carbonization. Also, I have studied characters of cutting with a choice of side of laser beam incidence. The SEM(Scanning Electron Microscope), non-contact 3D inspector and high-resolution microscope are used to measure kerf width and surface state. The optimum value of 1.1 mm $\mu$-BGA singulation is 524 $\mu$m that is reduced kerf width of 60 % with $N_2$blowing. And I obtained reduction of carbonization of 68 % with a polyester double side tape in 0.9 mm $\mu$-BGA. I used laser intensity of 1.91$\times$10$^{6}$ / $\textrm{cm}^2$ in this study.

• KIEE International Transactions on Electrophysics and Applications
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• 제2C권6호
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• pp.309-313
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• 2002

In this paper, we have studied minimization of the kerf-width and surface burning, which occurred after the conventional singulation process of the multi-layer BGA board with copper, polyethylene and epoxy glass fiber. The high thermal energy of a pulsed Nd:YAG laser is used to cut the multi-layer board. The most considerable matter in the laser cutting of the multi-layer BGA boards is their different absorption coefficient to the laser beam and their different heat conductivity. The cut mechanism of a multi-layer BGA board using a 2$^{nd}$ harmonic Nd:YAG laser is the thermal vaporization by high temperature rise based on the Gaussian profile and copper melting point. In this experiment, we found that the sacrifice layer and Na blowing are effective in minimizing the surface burning by the reaction between oxygen in the air and the laser beam. In addition, N2 blowing reduces laser energy loss by debris and suppresses surface oxidation. Also, the beam incidence on the epoxy layer compared to polyimide was much more suitable to reduce damage to polyimide with copper wire for the multi layer BGA singulation. When the polyester double-sided tape is used as a sacrifice layer, surface carbonization becomes less. The SEM, non-contact 3D inspector and high-resolution microscope are used to measure cut line-width and surface morphology.

• Restorative Dentistry and Endodontics
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• 제27권4호
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• pp.421-431
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• 2002

C-shaped canal configuration is very difficult to treat because that clues about preoperative canal anatomy cannot be ascertained from clinical crown morphology and limited information can be derived from radiographic examination. This study was done to get more informations about the root and canal configuration of C-shape root by 3-dimensionally reconstructing for the purpose of enhancing success rate of endodontic treatment. 30 mandibular molars with C-shaped root were selected. Six photo images from occlusal, apical, mesial, distal, buccal, lingual directions and radiographic view were taken as preoperative ones to compare them with 3-D image. After crown reduction to the level of 1-2mm over pulpal floor was performed, teeth were stored in 5.25% sodium hypochlorite solution for the removal of pulp tissue and debris. They were cleaned under running water, allowed to bench dry and embedded in a self-curing resin. This resin block was serially ground with a microtome (Accutom-50, Struers, Denmark) and the image of each level was recorded by digital camera (FinePix S1-pro, Fuji Co., Japan). The thickness of each section was 0.25mm. Photographs of serial sections through all root canal were digitized using Adobe Photoshop 5.0 and then minimum thickness of open and closed sites were measured (open site is the surface containing occluso-apical groove closed site is oppsite). After dizitization using 3-D Doctor (Able software Corp, USA). 3D reconstruction of the outer surface of tooth and the inner surface of pulp space was made. Canal classsification of C-shaped roots was performed from this 3-D reconstructed image. The results were as follows : 1. Most C-shape rooted teeth showed lingual groove (28/30). 2 According to Vertuccis' calssification, type I, II, III, IV, VII were observed. but also new canal types suck as 2-3-2, 1-2-3-2. 2-3-2-1, 2-3-2-3 were shown. 3 There was little difference in minimum thickness on coronal and apical portions, but open site were thinner than closed site on mid portion. Conclusively, 3D reconstruction method could make the exact configurations of C-shape root possible to be visualized and analyzed from multi-directions. Data from minimum thickness recommend cleaning and shaping be more carefully done on dangerous mid portion.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2011년도 학술발표회
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• pp.170-174
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• 2011

홍수시 저수지 상류로부터 유입되는 다량의 오염물, 협잡물은 저수지의 경관 및 수질에 악영향을 미친다. 이러한 오염물질은 홍수시 일시에 유입되어 표층에 부유하므로 수거를 위한 시간 및 비용이 비교적 크게 발생된다. 따라서 이러한 부유쓰레기를 효과적으로 차단할 수 있는 시설물 설치는 필연적이다. 이렇게 부유쓰레기 수거를 위한 방법 중, 저수지 내부에 선 차단 시설을 설치하여 부유쓰레기를 홍수터로 유도하여 수거하는 방법은 일시에 많은 양의 부유쓰레기를 차단하게 되는데 유지관리, 경제적 측면에서 유리하다. 본 연구에서는 부유쓰레기 수거를 위한 선 차단시설 운영 방안을 검토하기 위하여 홍수시 저수지 내로 유입되는 유속흐름을 2차원 수치해석 모형인 RMA-2 모형으로 해석하고, 저수지의 내 외부 지형분석을 통하여 시범 지구의 선 차단시설 설치 위치를 선정하였고, 3차원 수치해석 모형인 FLOW-3D 모형으로 검증하였다. 선 차단시설 설치 시범지역 위치 선정을 위하여 저수지의 규모, 접근성, 시공 장비의 대여 편이성 등을 종합적으로 고려하여 기흥저수지를 시범예정 구역으로 선정하였다. 저수지 내로 유입되는 유속특성을 2차원 수치해석 모형인 RMA-2 모형으로 해석하여 시범 지구의 선 차단시설 설치 위치를 제안하고 홍수터 부지를 결정하였다. 부유쓰레기 유도를 위한 선차단시설은 저수지 급확대로 인한 유속 감소구간과 와류발생 구간이 적절한 것으로 분석되었으며 시범설치 지역인 기흥저수지 상류 급확대부에 선 차단시설을 제안하였다. 홍수터의 규모는 Armitage와 Rooseboom(2000)이 제안한 경험식을 바탕으로 $5,300m^2$을 제안하였으며, 기흥저수지 상류부 우안에 항아리 모양으로 설치하도록 계획하였다. 또한, 3차원 수치모형실험을 통하여 검토한 결과, 차단막 설치로 부유 쓰레기의 하류 이송은 차단되고, 원활하게 홍수터로 유도됨을 확인하였다.

• Advances in Computational Design
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• 제4권2호
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• pp.141-153
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• 2019

This research is comprised of virtually simulating behavior while experiencing low gravity effects in advance of real world testing in low gravity aboard Zero Gravity Corporation's (Zero-G) research aircraft (727-200F). The experiment simulated a drill rig penetrating a regolith simulant. Regolith is a layer of loose, heterogeneous superficial deposits covering solid rock on surfaces of the Earth' moon, asteroids and Mars. The behavior and propagation of space debris when drilled in low gravity was tested through simulations and visualization in a leading dynamic simulation software as well as discrete element modeling software and in preparation for comparing to real world results from flying the experiment aboard Zero-G. The study of outer space regolith could lead to deeper scientific knowledge of extra-terrestrial surfaces, which could lead us to breakthroughs with respect to space mining or in-situ resource utilization (ISRU). These studies aimed to test and evaluate the drilling process in low to zero gravity environments and to determine static stress analysis on the drill when tested in low gravity environments. These tests and simulations were conducted by a team from Texas A&M University's Department of Construction Science, the United States Air Force Academy's Department of Astronautical Engineering, and Crow Industries