• 대한치과기공학회지
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• 제42권4호
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• pp.321-325
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• 2020

Purpose: This study is to evaluate the accuracy of gypsum replica models made from various gypsum products. Methods: One main model was made of stainless steel by CNC milling process. Molds were formed from the main model, and the gypsum replica models were made using 8 types of type IV gypsum, 10 pieces each. The main model was digitized by a contact scanner (Incise; Renishaw) and the gypsum replicas were digitized by an optical scanner (E4; 3Shape A/S). The difference between the main model and the gypsum replicas were measured by inspection software (3D Systems). One-way ANOVA was performed to evaluate the statistical significance of differences between groups. In addition, the independent sample T test was performed to determine the difference between the conventional and scannable stone group (n=10, α=0.05). Results: The root mean square of the stone models were 7.24 ㎛ to 10.78 ㎛, and statistical significance was found between the two groups (SR, FR) and the other 6 groups (IS, SG, CA, CS, ER, EBG) (p<0.05). The accuracy of the gypsum replicas was 9.04 ㎛ and 7.62 ㎛ in the conventional and scannable stone group, respectively. There was statistical significance between the two groups (p<0.01). Conclusion: In the limited results of this study, the product with low setting expansion and the scannable showed high accuracy. Therefore, in order to obtain a stable and accurate scan model, it is more effective in terms of accuracy to use a scannable stone with a low setting expansion.

• 한국지진공학회논문집
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• 제19권3호
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• pp.103-108
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• 2015

This work introduces a modal testing and analysis results of the mock-up for a layered stone pagoda. The pagoda has been horizontally excited by an impact hammer. As to the measured acceleration time responses, the first five lower mode shapes and natural frequency are extracted by the TDD technique. It is observed that the time delay of a shear wave occurs through friction surfaces. Such phenomena cannot be described by using the traditional analytical models such as a continuum cantilever beam model or a discrete shear building model. However, the time delay typically affects only the phases of the pagoda system. The frequencies of the pagoda system are not affected by such time delay. It is found in the first time that the layered stone pagoda system has a set of closely placed modes in near of natural frequency. It is believed that such modes are due to the friction characteristics in friction surfaces. Based on the stick-slip friction model, it seems that the one of the closely placed mode can be a self-excited one.

• 대한치과기공학회지
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• 제36권2호
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• pp.91-96
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• 2014

Purpose: The purpose of this study was evaluate the validity of polyurethane model fabricated by intra oral scanning method. Methods: Ten sam cases of stone models were manufactured from master model, and polyurethane models were made with the intra oral scanning and CNC milling method. One examiner individually measured 6 distances(intercanine distance, intermolar distance, two dental arch lengths(right, left) and two diagonal of dental arch lengths(right, left) on the stone models and the polyurethane models. The Mann-Whitney U test(${\alpha}$=0.05) were used for statistical analysis. Results: The mean difference between measurements made directly on the stone models and those made on the polyurethane models was 0.31-0.38mm. No statistically differences between the two groups were founded 4 distances(p>0.05), but 2 distances were statistically significant(p<0.05). Conclusion: Stone models showed larger than polyurethane models fabricated by intra oral scanning method.

• 대한치과보철학회지
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• 제42권1호
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• pp.21-29
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• 2004

Statement of problem : Because dental impression can be a cross-infection source, disinfection, such as immersion disinfection is nessecary. However, the disinfection process may change the volume of the impression cast. Purpose : The purpose of this study is to find out the effects on dimensional change of different storage times and methods, of agar-alginate impression when immersed in a 5% idophor disinfectant. Material and Methods : An agar-alginate impression was made from a mandible model and then was disinfected and stored according the experimental conditions and a stone model was produced. Measurements were taken between reference points on the original mandible model and they were compared to measurements taken between reference points on the stone model. The study was divided into 4 groups. In group 1, the impression was stored in a 100% humidor for 30 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 6 hours, 12 hours and 24 hours and stone models were made at each time. In group 2, the impression was immersed in 5% idophor disinfectant and then stored in a 100% humidor for the same length of times as group 1, and stone models were made at each time. In group 3, the impression was stored in extend-A-pourR, a special storage solution for 30 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 6 hours, 12 hours, 24 hours 3 days, and 7 days and stone models were made at each time. In group 4, the impression was immersed in 5% idophor disinfectant and then stored in stored in extend-A-pourR, a special storage solution for the same length of times as group 3, and stone models were made at each time. 5 impressions and stone models were made at each time to make a total of 180. The Student-t test (P < .05) was used to do a statistical analysis of the measurements of the mandible model and stone models. The repeated-measure 2-way analysis of variance (P < .05) was used to do a statistical analysis of the difference in the 4 groups. Results : The percent liner dimensional change was from $0.25{\pm}0.03%$ (group 1, 30 minutes) to $0.34{\pm}0.06%$ (group 4, 7 days). No significant change was noticed between the 4 groups. Conclusion : According to the above study, in both methods, least dimensional change was recorded when the storage times were short and in both methods, immersion in 5% idophor disinfectant did not effect dimensional change in the agar-alginate impression.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2006년도 추계학술대회 논문집
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• pp.1376-1379
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• 2006

Vibro crushed-stone compacted pile (VCCP) method is one of a ground improvement technique by a vibro compaction in vertical direction with crushed stone to build up stone pile foundation in other to ensure stability of soft ground. In spite of its long applied history in geotechnical engineering division, most of studies have not been based on the reliable In-situ condition but on the laboratory tests including model tests. These model tests can express standard and ideal behavior but exceptional status that can be occur in the ground cannot be considered efficiently. This study performed the the series of trial construction to investigate the effect of VCCP method on the improvement of soft ground expecially in railroad construction site.

• Geomechanics and Engineering
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• 제18권3호
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• pp.329-337
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• 2019

This paper presents an experimental investigation about visualization of bulging development of geosynthetic-encased stone column (GESC) based on the digital image correlation (DIC) technique and transparent soil. Visual model tests on GESC and ordinary stone column (OSC) were carried out. In order to delete the warping effect resulting from transparent soil and experiment setup, a modification for experiment results was performed. The bulging development process of the GESC and the displacement field of the surrounding soil were measured. By comparing with the existing experimental and theoretical results, it demonstrates that the model test system developed for studying the continuous bulging development of GESC is suitable. The current test results show that the bulging depth of GESC ranges from 1.05 to 1.40 times the diameter of GESC. The influence depth of GESC bulging on surrounding soil displacement is 0~3 the times diameter of GESC.

• 한국지반신소재학회논문집
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• 제7권4호
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• pp.25-36
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• 2008

본 논문에서는 수치해석적 접근을 통해 연약지반에 시공되는 지오그리드 감쌈 스톤컬럼의 하중지지 특성을 고찰한 내용을 다루었다. 지오그리드로 감싼 스톤컬럼의 보강효과에 대해 검증된 유한요소모델을 이용하여 축대칭 및 3차원 응력-간극수압연계해석을 토대로 매개변수 연구를 수행하였다. 해석결과를 종합한 결과 지오그리드로 감싼 스톤컬럼의 하중지지 특성이 향상되는 경향을 나타내었다. 아울러 보강재의 감쌈길이와 축강성이 지오그리드 감쌈 스톤컬럼의 주된 설계변수가 되며, 지오그리드 보강효과를 극대화 할 수 있는 지오그리드의 임계감쌈길이 및 임계강성이 존재하는 것으로 나타났다.

• 자원ㆍ환경경제연구
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• 제16권4호
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• pp.781-802
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• 2007

본 연구는 스톤-게리(Stone-Geary) 모형을 이용하여 서울시 가정용 생활용수의 수요를 추정하고 이에 근거하여 물 수요의 가격탄력성과 소득탄력성을 추정한다. 분석결과, 서울시 전체 가정용 물 소비량 중 기초소비가 차지하는 비중이 평균 84%로 나타났다. 가정에서 사용하는 월평균 물 소비량이 최근에는 $16{\sim}20m^3$ 이하인 점을 감안하면, 가격을 통한 실질적인 물 수요관리 효과를 도모하기 위해서는 구간요금체계의 최저 수준을 현재의 월 $30m^3$에서 월 $15m^3$ 정도로 축소 조정할 필요가 있다는 점을 발견하였다.

• 한국지반공학회:학술대회논문집
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• 한국지반공학회 2001년도 봄 학술발표회 논문집
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• pp.299-306
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• 2001

Crushed Stone Pile(CSP) is one of the ground improvement methods available to loose sand and clayey ground by forming compacted CSP in the weak soil layer. The effects of this method are enhancement of ground bearing capacity, reduction of settlement and prevention of lateral ground movement in cohesive layer, reduction of liquefaction potential in sandy ground. This study performs model tests in 1.0m${\times}$1.0m${\times}$1.0m and 1.5m${\times}$1.5m${\times}$l.2m model tank to observe bearing capacity of CSP treated ground. The area replacement ratio of CSP composite ground varies 20%, 30% and 40% with square grid pattern. After the composite ground was consolidated under pressure of 0.5kg/$\textrm{cm}^2$ and 1.0kg/$\textrm{cm}^2$, load tests were carried out. The results show that ultimate bearing capacity increases with area replacement ratio and the preconsolidation pressure of ground.

• 한국지반환경공학회 논문집
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• 제1권1호
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• pp.27-33
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• 2000

쇄석말뚝 공법은 다져진 자갈, 폐석, 쇄석 등을 이용하여 느슨한 사질지반이나 연약점성토 지반을 개량하는 공법으로 일반적으로 말뚝은 70%이상의 치환율로 실트질 점토에 시공되어 지지력을 증진시키는 공법이나 말뚝을 배수층으로 압밀에 의한 점성토의 지반의 강도 증가를 전제로 치환율을 30% 이하로 억제하는 저치환 공법의 효율에 관한 연구가 진행되고 있다. 본 연구에서는 쇄석말뚝의 치환율에 따른 단일 등가원주 모형 실험을 실시하여 쇄석말뚝이 연약지반의 압밀거동에 미치는 영향을 분석하였다. 실험결과 치환율의 증가에 따른 침하감소효과와 침하저감계수를 산정하였으며 복합지반의 압밀시간 단축을 확인하였다. 또한, 복합지반에 대한 이론식을 이용한 장기침하량 예측을 통해 보강지반의 침하억제 경향을 평가하고 베인전단시험을 통해 복합지반의 강도증가특성을 확인하였다.