미세 채널에서의 항복력 유체 흐름 분석

학위논문 (석사) -- 서울대학교 대학원 : 공과대학 화학생물공학부, 2020. 8. 남재욱.In this paper, the flow of a polymer microgel, e.g. Carbopol, in microchannel was analyzed in consideration of the effect of microgel size and slip on the wall of microchannel. From the previous flow visualization experiment, we proposed a new system that channels can move in the opposite direction of flow. This not only shows the velocity of particles but also the overall pathlines at microchannel after fully-developed flow. With a new system and particle tracking velocimetry code, We conduct the study for two direction. First, we compare the velocity profiles obtained from flow visualizations and simulations in the mid-plane of the microchannel. Simulation with constitutive equation obtained from the rheological property did not coincide with velocity profile from visualizations. For example, the experimental results was slower than computation results near the wall. The reason for this phenomenon was explained by drawing pathlines of particles. Additionally, we suggest the method to find parameters for constitutive equations from the small-gap rheometry. When we compared with the results of flow visualization, it was reasonable. velocity profile from flow visualization. Second, we observe the effect of slip at wall on the velocity profiles. Unlike previous computation, which ruled out the effects of slip, the calculations proceeded with no slip condition. In our study, we consider both no slip condition and slip condition. For the fair comparison between experiment and computation results, we show that simulation with slip condition is close to the experimental results comparing with simulation with no slip condition. When we consider flow in the microchannel, we have to be careful on obtaining rheological property and considering slip condition.이 연구에서는 벽에서의 슬립 현상과 미세 영역에서의 마이크로젤의 크기 비율로 인한 효과를 고려하여 마이크로 채널에서의 카보풀과 같은 고분자 용액의 흐름을 분석하고자 한다. 이전의 흐름 시각화 연구들에서 더 나아가, 마이크로 채널을 흐름의 반대 방향으로 움직일 수 있도록 새로운 시스템을 구축하였다. 이 시스템은 입자의 흐름뿐만 아니라 마이크로 채널의 전반적인 내부 입자 이동경로 또한 관찰할 수 있다. 새로운 시스템과 입자 추적 속도 측정 코드를 가지고 두 가지 방향으로 연구를 진행했다. 첫 번째로, 기존 실험들과 같이 채널 중앙에서 흐름 시각화를 통해 구한 속도 프로파일과 시뮬레이션 결과를 비교하였다. 이 두 결과는 일치하지 않았고, 벽 근처에서의 실제 흐름 속도가 이론적으로 계산된 결과보다 느렸다. 이 현상의 이유를 채널 내부 흐름 속 형광입자의 이동경로를 통해 설명하였다. 추가적으로, 시뮬레이션을 통해 흐름 시각화의 속도 프로파일에 맞도록 피팅할 때, 적합한 파라미터를 레오미터 데이터로부터 찾아낼 수 있는 가능성을 제시하였다. 두 번째로, 벽면에서의 슬립으로 인해 속도 프로파일의 분포에 주는 영향을 보았다. 기존 연구에서는 슬립으로 인해 더 흘러간 유량만큼을 제하고 no slip condition으로 계산하였다. 각 높이에서의 속도를 구한 후, 시뮬레이션 결과와 흐름 시각화 속도 프로파일을 높이별로 비교해보았다. 이를 통해 슬립을 반영한 시뮬레이션 계산결과가 실제의 속도 프로파일을 비교적 알맞게 예측할 수 있다는 것을 파악했다. 작은 마이크로채널에서의 흐름을 예측하기 위해서는 작은 갭에서 구한 레오미터 파라미터를 활용하고 슬립을 고려해야한다.1. Introduction 9 2. Experiment 13 2.1 Fabrication of microchannel 13 2.2 Fluid preparation 14 2.3 Rheology properties 15 2.4 Micro particle tracking velocimetry 16 2.5 Computation 19 3. Results 22 3.1 Rheometer data 22 3.2 Slip velocity function at wall 23 3.3 Mid-plane velocity profile in microchannel 25 3.4 Computation with slip condition 29 4. Final Remarks 30 5. Reference 34Maste

3종 구강스캐너의 정확도 비교 평가를 위한 비임상 연구

학위논문(석사) -- 서울대학교대학원 : 치과대학 치의과학과, 2023. 2. 임범순.As a result of the technological advances, digitalization is being applied in various areas of dentistry. As intraoral scanners are widely used for digital impression with the advantage of being easy to use and comfortable for patients, many studies are being conducted. However, new intraoral scanners with various mechanisms and characteristics are constantly pouring out, and comparative evaluation for clinical application is continuously needed. The purpose of this study is to evaluate and verify the performance of the intraoral scanner through trueness and precision comparison. In this study, trueness and precision are evaluated for the accuracy comparison of intraoral scanners (ISO 5725). The object was designed with the CAD software (SolidworksTM 2016, 3D Systems SolidWorks Corp., Waltham, MA, USA) and the model was fabricated from the NextDent C&B MFH (3D Systems, Rockhill, USA) using the 3D printer (NextDent 5100, 3D Systems, Rockhill, SC, USA). Inlay, Onlay and three-unit Bridge were produced by representing deep and narrow forms frequently used in clinical practice, and the same resin model was used in all experimental groups. Three types of intraoral scanners were evaluated: TRIOS 4® (3 Shape, Copenhagen, Denmark), I500 (Medit Co, Seoul, South Korea), COMFORT+ (DDS, Seoul, South Korea), and five scan data were obtained by the same trained researcher for consistency. The acquired data was superimposed with the reference data by the 'best-fit alignment' of the Geomagic Control XTM (3D Systems, Rock Hill, SC, USA) software, and the tolerance range was set to ±30μm for 3D comparison to calculate RMS (Root Mean Square). For comparison, the one-way ANOVA and Bonferroni t-test were performed with a significance level of 0.05. For trueness, the RMS values in the Inlay (36.32μm~37.22μm) model increased in the order of TRIOS4, COMFORT+, and I500, but the trueness tended to decrease. In Onlay (35.98μm~37.22μm) and three-unit Bridge (52.24μm~ 56.64μm) models, RMS values increased in order of I500, TRIOS4, and COMFORT+, but the trueness tended to decrease. But no significance was found between each scanner group on the All pairwise multi-analysis Bonferroni t-test (p>0.05). For precision, there was a significant difference between TRIOS4 and I500, I500 and COMFORT+ in the Inlay model (respectively p=0.027, p<0.001). In the Onlay and three-unit Bridge models, a significant difference was found between COMFORT+ and the remaining two intraoral scanners (TRIOS4, I500). Trueness and precision are lowered if the optimal distance between the scanner and the model is not maintained due to the narrow and deep part such as a three-unit bridge or the insufficient space between the units. Thus, errors tend to accumulate when the scan range increases. This study provides accuracy information on intraoral scanners, contributing to decision making it offer a view on which intraoral scanners is appropriate for use.본 연구에서는 최근 소개된 구강스캐너의 진실도 (trueness) 및 정밀도 (precision) 비교를 통해 스캐너 자체 정확도 (accuracy) 등의 성능에 대하여 평가하고 검증하고자 하였다. ISO 5725를 참고하여 구강스캐너의 정확도 비교를 위해 진실도 및 정밀도를 평가하였다. 진실도는 모델스캐너로 측정한 참조 데이터에 대하여 구강스캐너로 측정한 비교 데이터 간의 차이를 나타내는 값이며, 정밀도는 3 종류의 구강스캐너를 이용해 반복하여 얻은 데이터를 서로 중첩하여 얻은 오차 값이다. CAD 소프트웨어인 Solidworks 2016TM (Dassault Systèmes SolidWorks Corp., Waltham, MA, USA) 으로 모델을 설계하였고, NextDent C&B MFH (3D Systems, RockHill, SC, USA) 3D 프린팅 레진으로 NextDent 5100 (3D Systems, RockHill, SC, USA) 3D 프린터를 이용하여 모델로 제작하였다. 임상에서 자주 쓰이는 깊고 좁은 형태 등을 재현하여 인레이, 온레이 및 3본-브릿지 모델을 제작하였으며, 모든 실험군에서 동일한 레진 모델을 사용하여 제품 비교 평가에 용이하였다. 또한, 본 논문에서는 TRIOS4 (3 Shape, Copenhagen, Denmark), I500 (Medit Co, Seoul, South Korea), COMFORT+ (DDS, Seoul, South Korea) 3가지 종류의 구강스캐너를 평가하였는데, 일관성을 위해 숙련된 동일한 연구자에 의해 각각 5개의 스캔 데이터를 채득하였다. 채득된 데이터는 Geomagic Control XTM (3D Systems, RockHill, SC, USA) 소프트웨어의 최적 적합 중첩법(베스트-핏 정렬)을 통해 참조 데이터와 중첩하였고, 3D 비교 시 허용범위는 ±30μm으로 설정하여 RMS (Root Mean Square) 를 산출하였다. 진실도와 정밀도 비교를 위해 유의수준 0.05를 기준으로 일원분산분석, Bonferroni test로 통계 분석하였다. 진실도의 경우, 인레이 모델에서 RMS 값은 36.32μm~37.22μm에 걸쳐 TRIOS4, COMFORT+, I500 순으로 커지며 진실도가 낮아지는 경향을 보였다. 온레이와 3본-브릿지 모델에서 RMS 값은 각각 35.98μm~37.22μm와 52.24μm~56.64μm를 보였으나, 일원분산분석 후 다중비교분석 Bonferroni t-test에서 모든 모델에 있어 구강스캐너 종류에 따른 진실도 값의 유의한 차이는 발견되지 않았다. 정밀도의 경우, 인레이 모델에서 TRIOS4와 I500, I500과 COMFORT+간 유의한 차이가 있었으며 (각각 p=0.027, p<0.001), 온레이와 3본-브릿지 모델에서는 COMFORT+와 나머지 두 종류의 구강스캐너 (TRIOS4, I500) 사이에서 유의한 차이를 발견하였다. 결론적으로, 3본-브릿지와 같이 폭이 좁고 깊은 부분을 포함하고, 구성 단위(unit) 사이 간격이 좁아 스캐너와 모델 간의 최적의 거리가 확보되지 않을 경우 진실도와 정밀도는 낮아진다. 더하여, 스캔의 범위가 넓어질수록 오차는 축적되어 정확도는 감소하게 된다. 본 연구를 통해 구축된 실험 데이터를 기반으로 임상에서 적절한 구강스캐너의 선택 및 스캔 전략에 도움되고자 하였다.Ⅰ. INTRODUCTION 1 Ⅱ. MATERIALS AND METHODS 10 Ⅲ. RESULTS 16 Ⅳ. DISCUSSION 22 Ⅴ. CONCLUSIONS 30석

상대적 안전비행영역과 상대적 번스타인 다항식을 이용한 다수 쿼드로터의 경로 계획

학위논문 (석사) -- 서울대학교 대학원 : 공과대학 기계항공공학부, 2020. 8. 김현진.Multi-agent systems consisting of unmanned aerial vehicles (UAVs) are receiving attention from many industrial domains due to their mobility, and applicability. To safely operate these multiagent systems, path planning algorithm that can generate safe, dynamically feasible trajectory is required. However, existing multi-agent trajectory planning methods may fail to generate multiagent trajectory in obstacle-dense environment due to deadlock or optimization failure caused by infeasible collision constraints. In this paper, we presents a new e client algorithm which guarantees a solution for a class of multi-agent trajectory planning problems in obstacle-dense environments. Our algorithm combines the advantages of both grid-based and optimization-based approaches, and generates safe, dynamically feasible trajectories without su ering from an erroneous optimization setup such as imposing infeasible collision constraints. We adopt a sequential optimization method with dummy agents to improve the scalability of the algorithm, and utilize the convex hull property of Bernstein polynomial to replace non-convex collision avoidance constraints to convex ones. We validate the proposed algorithm through the comparison with our previous work and SCP-based method. The proposed method reduces more than 50% of the objective cost compared to our previous work, and reduces more than 75% of the computation time compared to SCP-based method. Furthermore, the proposed method can compute the trajectory for 64 agents on average 6.36 seconds with Intel Core i7-7700 @ 3.60GHz CPU and 16G RAM.무인비행체(UAV)로 구성된 다중 에이전트 시스템은 높은 기동성 및 응용 가능성으로 많은 산업 분야에서 관심을 받고 있다. 이러한 다중 에이전트 시스템을 안전하게 운용하려면 안전하고 동적으로 실현 가능 경로를 생성할 수 있는 경로 계획 알고리즘이 필요하다. 그러나 기존의 다중 에이전트 경로 계획 방법은 장애물 환경에서 교착 상태나 부적절한 충돌 회피 조건으로 인한 최적화 실패가 일어날 수 있다는 한계가 있다. 본 논문에서는 장애물 환경에서 해의 존재를 보장하도록 다중 에이전트 경로 계획 문제를 변환한 뒤 이를 효율적으로 풀어낼 수 있는 새로운 경로 계획 알고리즘을 제시한다. 이 알고리즘은 그리드 기반 접근법과 최적화 기반 접근법의 장점을 모두 가지도록 설계되었으며, 불가능한 충돌 구속조건을 부과하지 않고 안전하고 동적으로 실현 가능한 궤적을 생성할 수 있다. 이 알고리즘은 더미 에이전트(dummy agents)을 이용한 순차 최적화 방법을 사용하여 알고리즘의 확장성(scalability)을 높였으며, 번스타인(Bernstein) 다항식의 볼록 껍질(convex hull) 성질을 활용하여 볼록하지 않은 충돌 회피 제약 조건을 볼록화하였다. 제안된 알고리즘의 성능은 선행 연구와 SCP 기반 방법과의 비교를 통해 검증되었다. 제안된 방법은 선행 연구에 비해 목표 비용의 50% 이상 절감하였으며, SCP 기반 방법에 비해 계산 시간의 75% 이상 감소하였다. 또한 제안된 방법은 인텔 코어 i7-7700 @ 3.60GHz CPU 및 16G RAM 환경에서 64개 에이전트의 궤적을 계산하는데 평균 6.36초가 소요된다.1 Introduction 1 1.1 Literature review 2 1.2 Thesis contribution 3 1.3 Thesis outline 3 2 Bernstein polynomial 4 2.1 Definition 4 2.2 Properties 5 2.2.1 Convex hull property 5 2.2.2 Endpoint interpolation property 5 2.2.3 Arithmetic operations and derivatives 6 3 Multi-agent trajectory optimization 7 3.1 Problem formulation 7 3.1.1 Assumption 7 3.1.2 Trajectory Representation 8 3.1.3 Objective function 9 3.1.4 Convex constraints 9 3.1.5 Non-convex collision avoidance constraints 10 3.2 Collision constraints construction 11 3.2.1 Initial trajectory planning 12 3.2.2 Safe flight corridor 14 3.2.3 Relative safe flight corridor 16 3.3 Trajectory optimization 18 4 Sequential optimization with dummy agents 20 5 Experimental results 24 5.1 Comparison with the previous work 24 5.1.1 Success rate 25 5.1.2 Solution quality 26 5.1.3 Scalability analysis 26 5.2 Comparison with SCP-based method 27 5.3 Flight test 29 6 Conclusion 31Maste

Triple antibiotics와 관련한 치아 변색의 예방

Regenerative endodontics has a potential to heal a partially necrotic pulp, which can be beneficial for the continued root development and strengthening of immature teeth. For this purpose, triple antibiotic mixture of ciprofloxacin, metronidazole, and minocycline was recommended as intracanal medicament in an attempt to disinfect the root canal system for revascularization of a tooth with a necrotic pulp. However, discoloration of the tooth was reported after applying this. This case shows the idea for preventing the tooth discoloration using a delivery syringe (SW-O-01, Shinwoo dental) to avoid the contact between the clinical crown and the antibiotics.ope

The First Case Series of Cryopyrin-Associated Periodic Syndrome in Korea

Cryopyrin-associated periodic syndrome (CAPS) is a hereditary autoinflammatory syndrome caused by mutations in NLRP3 (encoding cryopyrin), which presents with fever, fatigue and arthralgia. Thus far, however there have been no reports of CAPS in Korea. Herein, we report 3 cases of CAPS for the first time in Korea. The first case, a 28-year-old man with recurrent urticaria, arthralgia and fever induced by cold, all of which were observed in his father, showed elevated erythrocyte sedimentation rate and C-reactive protein. He exhibited a p.Gly303Asp variant of the NLPR3 gene. The second case, a 2-year-old girl who had recurrent urticaria, arthritis and oral and genital ulcers, was positive for HLA B51 and a p.Glu569Lys mutation in exon 3 of the NLRP3 gene. Administration of anakinra greatly improved her symptoms. The third case, a 4-year-old boy who presented with recurrent urticaria, arthralgia, and fever, exhibited a p.Val72Met mutation in exon 1 of the NLRP3 gene. Administration of tocilizumab improved all of his symptoms. This small case series suggests that clinicians consider CAPS and conduct genetic studies when arthralgia and fever are accompanied by urticaria in Korea.ope

Comparison of bond strengths of ceramic brackets bonded to zirconia surfaces using different zirconia primers and a universal adhesive

Objectives: The aim of this study is to compare the shear bond strengths of ceramic brackets bonded to zirconia surfaces using different zirconia primers and universal adhesive. Materials and Methods: Fifty zirconia blocks (15 x 15 x 10 mm, Zpex, Tosoh Corporation) were polished with 1,000 grit sand paper and air-abraded with 50 microm Al2O3 for 10 seconds (40 psi). They were divided into 5 groups: control (CO), Metal/Zirconia primer (MZ, Ivoclar Vivadent), Z-PRIME Plus (ZP, Bisco), Zirconia Liner (ZL, Sun Medical), and Scotchbond Universal adhesive (SU, 3M ESPE). Transbond XT Primer (used for CO, MZ, ZP, and ZL) and Transbond XT Paste was used for bracket bonding (Gemini clear ceramic brackets, 3M Unitek). After 24 hours at 37 degrees C storage, specimens underwent 2,000 thermocycles, and then, shear bond strengths were measured (1 mm/min). An adhesive remnant index (ARI) score was calculated. The data were analyzed using one-way analysis of variance and the Bonferroni test (p = 0.05). Results: Surface treatment with primers resulted in increased shear bond strength. The SU group showed the highest shear bond strength followed by the ZP, ZL, MZ, and CO groups, in that order. The median ARI scores were as follows: CO = 0, MZ = 0, ZP = 0, ZL = 0, and SU = 3 (p < 0.05). Conclusions: Within this experiment, zirconia primer can increase the shear bond strength of bracket bonding. The highest shear bond strength is observed in SU group, even when no primer is used.ope

Probe-based confocal laser endomicroscopy in the differential diagnosis of inflammatory bowel diseases:

ope

Effect of moisture and drying time on the bond strength of the one-step self-etching adhesive system

OBJECTIVES: To investigate the effect of dentin moisture degree and air-drying time on dentin-bond strength of two different one-step self-etching adhesive systems. MATERIALS AND METHODS: Twenty-four human third molars were used for microtensile bond strength testing of G-Bond and Clearfil S(3) Bond. The dentin surface was either blot-dried or air-dried before applying these adhesive agents. After application of the adhesive agent, three different air drying times were evaluated: 1, 5, and 10 sec. Composite resin was build up to 4 mm thickness and light cured for 40 sec with 2 separate layers. Then the tooth was sectioned and trimmed to measure the microtensile bond strength using a universal testing machine. The measured bond strengths were analyzed with three-way ANOVA and regression analysis was done (p = 0.05). RESULTS: All three factors, materials, dentin wetness and air drying time, showed significant effect on the microtensile bond strength. Clearfil S(3) Bond, dry dentin surface and 10 sec air drying time showed higher bond strength. CONCLUSIONS: Within the limitation of this experiment, air drying time after the application of the one-step self-etching adhesive agent was the most significant factor affecting the bond strength, followed by the material difference and dentin moisture before applying the adhesive agent.ope

Influence of additional etching on shear bond strength of self-etching adhesive system to enamel

Recently, self-etching adhesive system has been introduced to simplify the clinical bonding procedures. It is less acidic compared to the phosphoric acid, thus there is doubt whether this system has enough bond strength to enamel. The purpose of this study was to investigate the influence of additional etching on the adhesion of resin composite to enamel. Ninety extracted bovine permanent anterior teeth were used. The labial surfaces of the crown were ground with 600-grit abrasive paper under wet condition. The teeth were randomly divided into six groups of 15 teeth each. Clearfil SE Bond®, Adper™ Prompt L-Pop and Tyrian SPE™ were used as self-etching primers. Each self-etching primers were applied in both enamel specimens with and without additional etching. For additional etching groups, enamel surface was pretreated with 32% phosphoric acid (UNI-ETCH, Bisco, Inc., Schaumburg, IL, USA). Hybrid resin composite Clearfil AP-X, (Kuraray Co., Ltd., Osaka, Japan) was packed into the mold and light-cured for 40 seconds. Twenty-four hours after storage, the specimens were tested in shear bond strength. The data for each group were subjected to independent t - test at p < 0.01 to make comparisons among the groups. In Clearfil SE Bond®, shear bond strength of additional etching group was higher than no additional etching group (p 0.01). In conclusion, self-etching adhesive system with weak acid seems to have higher bond strength to enamel with additional etching, while self-etching adhesive system with strong acid seems not.ope

Enrique Dussel. 1492. El encubrimiento del Otro. Hacia el mito

이 책은 해방 신학자로 우리에게 더 잘 알려진 엔리케 두셀이 아메리카 대륙 발견 오백주년이 되기 얼마 전인 1992년 독일 프 랑크푸르트에서 행한 강연문을 책으로 엮어 낸 것이다. 포스트모더니즘이라는 용어도 이제 학문적 유행의 뒤안으로 사라져가는 즈음, 다시 근대를 논하는 이 책에 대해서, 특히 라틴아메리카 맥락을 탐구한 그의 저 작을 지금 한국에서 읽는 이유는 무엇일까?.