• Earthquakes and Structures
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• 제7권3호
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• pp.333-347
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• 2014

Multi-scale model can take both computational efficiency and accuracy into consideration when it is used to conduct elasto-plastic seismic response analysis for complex steel bridges. This paper proposed a method based on pushover analysis of member sharing the same section pattern to verify the accuracy of multi-scale model. A deck-through type steel arch bridge with a span length of 200m was employed for seismic response analysis using multi-scale model and fiber model respectively, the validity and necessity of elasto-plastic seismic analysis for steel bridge by multi-scale model was then verified. The results show that the convergence of load-displacement curves obtained from pushover analysis for members having the same section pattern can be used as a proof of the accuracy of multi-scale model. It is noted that the computational precision of multi-scale model can be guaranteed when length of shell element segment is 1.40 times longer than the width of section where was in compression status. Fiber model can only be used for the predictions of the global deformations and the approximate positions of plastic areas on steel structures. However, it cannot give exact prediction on the distribution of plastic areas and the degree of the plasticity.

• 대한치과보철학회지
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• 제30권1호
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• pp.1-14
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• 1992

The purpose of this study was to evaluate the accuracy of reproduction of stone casts made from complete-arch impressions using different trays. The trays used were : 1) nonperforated custom tray, 2) perforated custom tray, 3) nonperforated Rim-Lock tray, 4) perforated stock tray. Impressions were made from an dentulous acrylic resin model with metal inserts in first premolars and second molars. Transverse distance, sagittal distance and diagonal distance were measured using 4 landmarks. Measurements were made by using 3 dimensional measuring machine. The impression material used was an addition silicone. Impressions were poured at once with a Type IV dental stone. Data were analyzed using ANOVA and student t-test with a sample size of five. The results were as follows : 1. There were statistical differences in amount of dimensional change in according to the tray types. In amount of mean dimensional change, perforated custom tray was the first smallest, nonperforated custom tray was the second, nonperforated Rim-Lock tray and perforated stock tray were the largest. 2. There were statistical differences in amount of dimensional change between nonperforated custom tray and nonperforated Rim-Lock tray, and between perforated custom tray perforated stock tray. 3. There were satistical differences in amount of dimensional change between nonperforated custom tray and perforated custom tray, but there was not a statistical difference between nonperforated Rim-Lock tray and perforated stock tray. 4. There was not a statistical difference in amount of dimensional change between upper and lower arch in all tray types.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2757-2762
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• 2007

A cyclone design concept named Convex cyclone was developed to reduce pressure losses. Contrary to conventional cylinder-on-con type cyclone, inner wall of Convex cyclone are defined with a continuous curve and it has convex shape body. The discontinuity of inner diameter variation rate of cylinder-on-con type cyclone cause additional pressure loss. Continuous wall of Convex cyclone prevent additional pressure loss. In order to verify Convex cyclone design concept, we make a comparative experiments between Stairmand HE and Convex cyclone. Experimental Convex cyclone designed based on Stairmand HE model, and inner wall are defined with circular arch. The experimental result clearly shows that Convex cyclone can achieve maximum 50% pressure loss reduction with a few percent of collection efficiency drop. In addition, the experimental results indicated the existence of optimum convexity, minimum pressure loss, of cyclone wall.

• 대한영상의학회지
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• 제84권1호
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• pp.197-211
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• 2023

목적 기능장애 혈액투석 접근로에서 나이티놀 비피복형 스텐트 설치 후 접근로 유형과 스텐트의 위치에 따른 개통성을 평가하고자 한다. 대상과 방법 2017년 1월과 2019년 12월 사이에 159명의 환자(평균 연령, 64.1 ± 13.2세)가 혈액투석 접근로 기능장애를 치료를 위해 나이티놀 스텐트를 설치하였다. 스텐트의 위치는 다음과 같다; 18개 팔머리 정맥, 51개 노쪽피부정맥궁, 40개 위팔 정맥, 10개 문합부위 인접 정맥, 7개 동정맥 문합부 및 33개 인조혈관-정맥 문합부. 12개월 개통률은 카플란-마이어 방법과 콕스 회귀 모델로 평가하였다. 결과 총 159개의 스텐트가 103개의 자가동정맥루와 56개의 인조혈관접근로에 성공적으로 설치되었다. 인조혈관접근로는 자가동정맥루에 비해 12개월 일차 및 이차 개통률이 더 낮았다(일차 개통률; 25.0%대 44.7%; p = 0.005, 이차 개통률; 76.8%대 92.2%; p = 0.014). 스텐트 설치 후 노쪽피부정맥궁 및 인조혈관-정맥 문합부에서 다른 부위에 비해 12개월 일차 개통성이 불량하였다. 결론 나이티놀 비피복형 스텐트 설치 후 자가동정맥루는 인조혈관접근로와 비교하여 더 좋은 12개월 일차 및 이차 개통률을 보인다. 노쪽피부정맥궁 및 인조혈관-정맥 문합부의 스텐트는 다른 위치의 스텐트에 비해 더 낮은 12개월 일차 개통률을 보인다.

• 대한치과교정학회지
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• 제25권1호
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• pp.73-85
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• 1995

교정치료시 치축의 개선을 위한 많은 연구와 노력이 이루어져 왔다. 본 교실에서는 치축개선을 위해 MEAW를 응용한 Multi-Vertical Loop Arch Wire(MVLAW : 엠빌로)를 수년 전부터 다수치아의 치축을 동시에 개선코자 사용해 왔다. MVLAW는 일종의 근심경사된 치아를 세우는 장치로써 open vertical loop를 3가지 종류로 변형시켜 적용시켜 왔으며 이를 각각 A, B, C형으로 명명하였다. 각 MVLAW는 .017"x.025" TMAwire로 제작되며, A형 MVLAW의 경우 각 open vertical loop의 apex를 10도 정도 벌려주어 활성화시키며(electric welding stop을 각 loop의 근심측에 위치시킨다), B형과 C형 MVLAW의 경우 open vertical loop의 원심측에 10도의 tip back bend를 형성함으로써 활성화시킨다(B형의 경우 electric welding stop이 각 loop의 원심측에 형성되는 반면 C형의 경우 electric welding stop을 형성하지 않는다). 본 연구는 구치부의 치축을 동시에 개선코자할 때 MVLAW를 3가지 종류로 분류한 후 각 MVLAW의 효과를 알아보고자 상하악 1/2악을 광탄성 모형에 재현하여 그 응력분포를 관찰하여 다음과 같은 결론을 얻었기에 보고하는 바이다. 1. A형 MVLAW의 경우 3급 견인고무를 걸지 않았을 경우 하악 제1대구치와 제2대구치 치근의 원심면에서 강한 응력분포를 나타내나 전치부에 발생한 미약한 응력분포는 3급 견인고무의 장착으로 상쇄되었다. 따라서 A형 MVLAW는 초기에 치관의 직립효과가 있는 것으로 보인다. 2. B형 MVLAW의 경우 3급 견인고무를 걸지 않았을 경우 각 치아의 근심측에 응력분포를 보이며 견인고무를 걸었을 때와 비교시 전치부에 증가된 응력분포를 보였다. 따라서 B형의 경우 초기에 치근의 직립효과가 있는 것으로 보인다. 3. C형 MVLAW의 경우 3급 견인고무를 걸지 않았을 경우 하악전치부를 제외하고는 응력분포를 나타내지 않았으나 견인고무를 걸었을 경우 주로 견치와 소구치 근심면에서 응력분포를 보였다. 따라서 C형의 경우 견인고무 사용시 초기에 견치와 소구치에서 치근의 직립효과가 있는 것으로 보인다.

• 대한치과교정학회지
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• 제51권2호
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• pp.95-104
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• 2021

Objective: To evaluate the trueness and precision of full-arch scans acquired using five intraoral scanners and investigate the factors associated with the dimensional accuracy of the intraoral scan data. Methods: Nine adult participants (mean age, 34.3 ± 8.3 years) were recruited. Four zirconium spheres (Ø 6 mm) were bonded to the canines and the molars. Following acquisition of reference scans using an industrial-grade scanner, five intraoral scanners, namely i500, CS3600, Trios 3, iTero, and CEREC Omnicam, were used to scan the arches. Linear distances between the four reference spheres were automatically calculated, and linear mixed model analysis was performed to compare the trueness and precision of the intraoral scan data among the different scanners. Results: The absolute mean trueness and precision values for all intraoral scanners were 76.6 ± 79.3 and 56.6 ± 52.4 ㎛, respectively. The type of scanner and the measured linear distances had significant effects on the accuracy of the intraoral scan data. With regard to trueness, errors in the intermolar dimension and the distance from the canine to the contralateral molar were greater with Omnicam than with the other scanners. With regard to precision, the error in the linear distance from the canine to the molar in the same quadrant was greater with Omnicam and CS3600 than with the other scanners. Conclusions: The dimensional accuracy of intraoral scan data may differ significantly according to the type of scanner, with the amount of error in terms of trueness being clinically significant.

• 대한심미치과학회지
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• 제27권2호
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• pp.82-96
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• 2018

3D 프린팅은 삼차원 이미지 정보를 이용하여 레이어로 분할한 후 선택한 소재를 적층하여 가공하는 방법을 말한다. 소재를 적층하는 방법에 따라 다양한 종류의 3D 프린팅이 존재하는데 최근 치과분야에서는 SLA방식과 DLP방식으로 광원을 이용한 경화를 통해 적층 가공하는 3D 프린팅이 널리 보급되어 사용되고 있다. 전악 범위의 3D프린팅 치과용 모델은 전통적인 인상 채득으로 제작된 스톤모델보다는 다소 정확성이 부족한 것으로 보고되었으나, 같은 STL파일을 이용하여 4분악 범위를 3D 프린팅한 모델은 밀링 방법으로 가공한 모델보다 정확하였다. 디자인 소프트웨어의 활용도에 따라 보철치료의 진단, 임시 보철물의 제작, 의치의 제작이 가능하였다. 교정에서는 투명 교정 모델과 브라켓 간접 부착을 위한 트레이 제작이 가능하였다. 임플란트 수술에 있어서 CT를 기반으로 한 정확한 위치에 임플란트를 식립하는 가이드 제작에 활용하고 있다. 출력 방식의 발전으로 인하여 3D 프린터의 출력시간이 계속적으로 단축되고 있으며, 이로 인해 치과 진료실 내에서 3D 프린터가 기존의 전통적인 가공 방법을 대체할 수 있을 것으로 기대한다.

• 한국공간구조학회논문집
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• 제3권4호
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• pp.77-84
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• 2003

Tensegrity systems are stable structures which are reticulated spatial structures composed of compressive straight members, struts and cables. But there are some difficulties concerning surface stability, surface formation and construction method. One of the ways to solve this problem reasonably is combination of tesile members and rigid members. This structure is a type of flexible strutural system which is unstable initially because the cable material has little initial rigidity. Therefore tensegrity structure need to be introduced to the Initial stress for the self-equilibrated system having stable state. The rigidification of tensegrity systems is related to selfstress states which can be achieved only when geometrical and mechanical requirements are simultaneously satisfied. In this paper, for the stabilization of tesnsegrity structure it is proposed the modified self-equilibrated equation and the range of the various geometrical parameter about unit system. And we generate the model of double layed single curvature arch using the new squew quadruplex unit system.

• Steel and Composite Structures
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• 제42권2호
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• pp.265-275
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• 2022

A new type of precast steel reinforced concrete (PSRC) column was put forward in this paper. In order to study the static performance of PSRC column and hollow precast steel reinforced concrete (HPSRC) column subjected to combined compression and shear loading, a parametric test was carried out and effects of axial compression ratio, concrete strength and shear ratio on the mechanical behavior of composite PSRC column and HPSRC column were explored. In addition, the cracks development, load-span displacement relationship, strain distribution and shear bearing strength of column specimens were emphatically focused. Test results implied that shear failure of all specimens occurred during the test, and higher strength of cast-in-place concrete, smaller shear ratio and larger axial compression ratio could lead to greater shear resistance, but when the axial compression ratio was larger than 0.36, the shear capacity began to decrease gradually. Furthermore, truss-arch model for determining the shear strength of PSRC column and HPSRC column was proposed and the calculated results obtained from proposed method were verified to be valid.

• 대한치과보철학회지
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• 제35권3호
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• pp.577-608
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• 1997

The purpose of this study is to evaluate the stress distribution in the bone around dental implants supporting mandibular overdenture according to the number of implant and the type of attachment. Two or four implants were placed in an edentulous mandibular model and three dimensional photoelastic stress analysis was carried out to measure the fringe order around the implant supporting structure and also to calculate principal stress components at cervical area of each implant. The attachments tested were rigid and resilient type of Dolder bar, Round bar, Hader bar and Dal-Ro attchment. The results were as follows ; 1. In 2-implant supported overdenture using Round bar, Hader bar, and Dal-Ro attachment, compressive stress pattern was observed on the supporting structure of implant on loaded side, while tensile stress pattern in unloaded side. 2. In 2-implant supported overdenture using Dolder bar, the rigid Dolder bar shared the occlusal loads between 2 implants in a more favorable manner than was exhibited by the resilient type, while the resilient type placed a more stress on the distocervical area of the implant on the loaded side. But compressive stress pattern was observed in both the loaded and unloaded sides in either case. 3. In 2-implant supported overdenture, rigid and resilient type of Dolder bar exhibited more cross arch involvement than the Round bar, Hader bar, or Dal-Ro attachment. 4. In 4-implant supported overdenture using resilient Dolder bar and Hader bar, stress turned out to be distributed evenly among the implants between loaded and unloaded side, but thor was no reduction in the magnitude of the stress in the surrounding structure of implant contratry to 2-implant supported overdenture. 5. The stress pattern at cervical area of implant was different with the number of implant or the type of attachment but the overload, harmful to surrounding structure of implant, was not observed.