고분자 매트릭스 내 분산염료의 확산이 초임계이산화탄소를 이용한 PET의 염색속도론에 미치는 영향

학위논문 (석사) -- 서울대학교 대학원 : 공과대학 화학생물공학부, 2021. 2. 이윤우.Supercritical dying (SCD) of PET using carbon dioxide with three disperse dyes (Disperse Yellow 54, Disperse Yellow 211, and Disperse Blue 359) was studied under 393 K, 250 bar. To find the governing factor that is consistent with the dyeing kinetics, dissolution rate, solubility of dyes, solubility parameter, and dye uptake were measured and compared. Dye uptake showed proportionality to √(D_AB t) which implied SCD process not only occurred in a similar manner as the unsteady-state diffusion in semi-infinite medium but was also limited by the diffusion step. From the hypothesis that diffusion was the rate determining step for the SCD process, governing equation for the dye uptake was achieved and the expected outcomes from the equation were compared with the experimental results. It was observed from the comparison that the governing equation overestimated the dye uptake and thus, the dyeing rate for all three dyes of use. Deviation of the experimental values from the theoretical ones could have been the result of low concentration of the dyes in the scCO2 when the SCD process begun. The governing equation was obtained using the assumption that the scCO2 is saturated with dyes at t=0 or to have dye concentration of C_0. From the dissolution rate measurement, however, the concentration of the dyes in the scCO2 did not reach the maximum value until around 20 minutes into dissolution which suggested that for all of the SCD processes, dye concentration was not at the maximum in the beginning but rather increased to the value after some time span. Lower concentration of the dyes at the fabric surface at t=0, which was caused by slow dissolution rate, may have caused the deviations of the data. To test the hypothesis, the governing equation was plotted with the initial values C_0 or the saturation concentration, 0.75C_0, and 0.50C_0 and the resulting curves were compared with the experimental results. It was shown that for short dyeing time, the experimental results match well with the curves obtained from either 0.75C_0 or 0.50C_0 whereas the experimental results for long dyeing time fitted better with the curve from C_0. The observation, therefore, matched the assumption that the deviation was caused by the lower C_0 which resulted from slow dissolution rate of dyes into scCO2. Apart from the deviation, the governing equation seemed to predict the dye uptake or the dyeing rate for the overall SCD process well and the equation can be used to predict the dyeing kinetics of the untested dyes.현대 사회에서 천의 사용은 섬유 산업뿐만 아니라 다양한 사업 부문에서 큰 비중을 차지하고 있다. 따라서 천에 대한 다양한 분야에서의 연구가 선행되었고 그중에서 PET의 염색은 PET의 많은 사용량 때문에 많은 관심이 집중되고 있다. PET의 염색은 기존의 수계 염색뿐만 아니라 초임계이산화탄소를 이용한 초임계 염색으로도 염색할 수 있다. 초임계염색은 크게 염료의 초임계이산화탄소로의 용해, 용해된 염료가 섬유의 표면으로 이동하는 물질전달 그리고 섬유 내에서 분산염료의 확산으로 나뉠 수 있다. 본 연구는 온도와 압력에 따른 변화를 최소화하기 위해 기존 선행연구들에서 많이 쓰이는 393K, 250bar에서 진행되었고 총 3가지 분산염료를 (Disperse Yellow 54, Disperse Yellow 211, Disperse Blue 359) 사용했습니다. 초임계염색공정을 총괄할 수 있는 변수를 찾기 위해 염료의 용해속도, 용해도, 용해도 계수, 염색량을 비교하였고 이를 통하여 염색량이 √(D_AB t) 에 비례하는 결과를 얻을 수 있었다. 이를 통하여 전체 염색공정 중 섬유 내에서 염료의 확산이 속도 결정 단계라는 것을 확인할 수 있었고 이 가정을 통하여 속도식을 세울 수 있었다. 이후 세 가지 염료에 대한 염색량과 속도식을 비교를 통하여 속도식이 모든 염료에 대해서 염색량을 과대평가하는 것을 확인할 수 있었다. 반응을 시작할 때 이산화탄소는 염료에 포화된 상태라는 가정을 속도식을 구하기 위해 사용했지만 실제로는 이산화탄소가 포화농도에 도달하지 못한 것을 용해속도 실험을 통해서 알 수 있었다. 따라서 반응을 시작할 때 이산화탄소 내의 염료 농도가 속도식에 미치는 영향을 보기 위해 50%와 75%의 포화농도를 가정하여 속도식을 다시 구하였다. 염료의 농도가 50%와 75%이고 염색 시간이 짧을 때 실험값과 속도식이 작은 편차를 보였고 염색 시간이 길어질수록 실험값이 포화농도를 이용한 속도식과 비슷해지는 것을 확인할 수 있었다. 이를 통하여 용해속도를 증가시키면 실험값과 속도식으로 예측된 값이 작은 편차를 보일 것이라 예상할 수 있다. 따라서 위 방법으로 얻게되는 속도식으로부터 새로운 염료에 대한 속도식을 예측할 수 있을 것이라 생각한다.Contents................................................................................. iv Chapter 1. Introduction 8 1.1 Research background 8 1.1.1 Supercritical fluid 10 1.1.2 Supercritical dyeing process 14 1.2 Selection of fabric 16 1.3 Disperse dyes 18 1.4 Aim of the study 20 Chapter 2. Experimental 21 2.1 Materials 21 2.2 Apparatus for dissolution of dyes into scCO2 22 2.3 Apparatus for supercritical dyeing 25 2.4 Apparatus for extraction of impregnated dye 26 2.5 Analytical methods 28 2.5.1 Measurement of the dissolution rate and solubility 28 2.5.2 Measurement of the dye uptake 29 Chapter 3. Results and discussion 30 3.1 Dye uptake 30 3.1.1 Solvent selection for soxhlet extraction 32 3.2 Calculation of the solubility parameter, δ 33 3.2.1 Dissolution of dyes into CO2 35 3.2.2 Mass transfer to polymer surface 38 3.3 Diffusion of dyes inside the polymer matrix 40 Chapter 4. Conclusion 49 Bibliography 52 국 문 초 록 55Maste

Intracranial Stenting; the Current Landscape

ope

A Preliminary Cut-off Indoor Positioning Scheme Using Relative Ranks between Peaks of RSSI

Recently, the indoor positioning schemes have been actively studied. The indoor positioning scheme can be roughly classified into four schemes using triangulation, fingerprint map, proximity or visualization, respectively. This paper introduces the preliminary cut-off indoor positioning scheme using the fingerprint map. The preliminary cut-off scheme improves the accuracy of the K-Nearest-Neighbor (KNN) algorithm, which is a typical scheme of using the fingerprint map. This scheme consists of two phases: off-line and on-line phases. The off-line phase constitutes a fingerprint map necessary for real-time positioning. APs that periodically generate a signal are arranged and reference points predefined in indoor environment are selected. Then, the RSSIs received from nearby beacons at each reference point are stored in the fingerprint map. The on-line phase actually estimates indoor position. The user’s device receives the signal of the nearby APs. User’s position is estimated by comparing the RSSI received in real-time and RSSI stored in the fingerprint map. The KNN algorithm uses the Euclidean distance to compare the RSSI received in real-time and the RSSI stored in the fingerprint map. The K reference points with the shortest distance are selected and the position of user is estimated as the center of these reference points. However, since there are many obstacles in the indoor environment, the strength of signal is not constant even at the same position. To mitigate the instability and variability of the radio signal, the preliminary cut-off scheme utilizes the relative rank of the peak of signal strength, not the signal strength. Then, the user’s position is estimated as the center of K reference points with the greatest similarity after calculating the similarity between the real-time ranking and the ranking of the fingerprint map. This paper describes a continually improved study to improve the accuracy of the preliminary cut-off scheme. As a result, not only similarity to the relative rank of the peak of the signal strength but also the similarity to the peak is calculated and a weight based on this similarity is assigned. The user’s position is estimated to be the calculated position by weighting each reference position, not the center of the K reference positions.List of Tables iv List of Figures vi Abstract viii 제 1 장 서 론 1 제 2 장 관련 연구 4 2.1 삼각측량법을 이용한 실내 위치 추정 방식 4 2.2 핑거프린트 지도를 이용한 실내 위치 추정 방식 5 2.3 보행자의 걸음과 스마트폰을 이용한 실내 위치 추정 방식 8 제 3 장 비콘과 참조위치의 배치 관계 10 3.1 비콘과 참조위치의 배치에 대한 중요성 10 3.2 비콘과 참조위치 배치 간격에 대한 실험 10 3.2.1 실험 환경 10 3.2.2 실험 결과 12 3.3 최적의 비콘과 참조위치 배치 간격 14 제 4 장 핑거프린트 지도 구성방식 15 4.1 기존 핑거프린트 지도 구성 방식의 문제점 15 4.2 컷-오프 핑거프린트 지도 구성 방식 16 4.2.1 개요 16 4.2.2 실험 환경 및 구성 18 4.2.3 실험 결과 19 4.3 여러 컷-오프 지도를 조합하는 핑거프린트 지도 구성방식 26 4.3.1 개요 26 4.3.2 실험 및 성능 평가 28 제 5 장 핑거프린트 지도를 이용한 사전 컷-오프 방식 32 5.1 사전 컷-오프 실내 위치 추정 방식 32 5.2 이웃 참조 위치가 없는 경우를 개선한 사전 컷-오프 방식 36 5.3 신호유사도가 일치하는 참조 위치를 고려한 사전 컷-오프 방식 40 5.4 최대 RSSI 간의 유사도를 기반으로 한 가중치를 부여한 사전 컷-오프 방식 43 제 6 장 실험 및 성능 평가 46 6.1 사전 컷-오프 실내 위치 추정 방식 46 6.1.1 실험 환경 및 구성 46 6.1.2 실험 결과 47 6.2 이웃 참조 위치가 없는 경우를 개선한 사전 컷-오프 방식 51 6.2.1 실험 환경 및 구성 51 6.2.2 실험 결과 52 6.3 신호유사도가 일치하는 참조 위치를 고려한 사전 컷-오프 방식 57 6.3.1 실험 환경 및 구성 57 6.3.2 실험 결과 58 6.4 최대 RSSI간의 유사도를 기반으로 한 가중치를 부여한 사전 컷-오프 방식 62 6.4.1 실험 환경 및 구성 62 6.4.2 실험 결과 62 제 7 장 결 론 66 참고문헌 68Maste

Angiographic characteristics and treatment of cervical spinal dural arteriovenous shunts

Spinal DAVSs of the cervical level are rare lesions. The purpose of this study is to describe the clinical and angiographic characteristics of cervical spinal DAVSs. From a prospectively collected database including 449 cases of brain and spinal DAVSs, lesions located at the cervical level were selected. The clinical presentation, angiographic characteristics, and treatment outcome were assessed. Twelve cases of spinal DAVSs were identified at the level of the cervical spinal canal (male to female ratio = 8:4; mean age = 56.5 years). Five patients (41.7%) presented with hemorrhage including SAH (n = 4) and cerebellar hemorrhage (n = 1). Coincidental spinal DAVSs with cranial DAVSs or brain AVMs were noted in 5 cases (41.7%). The spinal DAVS was the symptomatic lesion in 10 cases and was incidentally discovered during evaluation for SAH from a coincidental lesion in 2 cases. Combined endovascular and surgical resection resulted in symptomatic improvement in 10 patients. In conclusion, DAVSs of the cervical spine are rare lesions which often present with hemorrhage and are frequently associated with complex coincidental vascular lesions. Combined endovascular and surgical treatment will result in good outcome.ope

금융주의 새로운 규모요인에 관한 연구

학위논문 (석사)-- 서울대학교 대학원 : 경영학과, 2015. 2. 채준.2008년 글로벌 금융위기 이후 주요 20개국을 중심으로 금융시스템의 위험이 실물경제로 파급되는 것을 막기 위해 시스템적으로 중요한 은행(Systemically Important Financial Institution)을 지정하는 등 다양한 노력을 기울이고 있다. 본 연구에서는 Gandhi and Lustig(2013)의 방법론에 따라 한국거래소에 상장된 금융업종 주식을 2000년부터 2013년까지 분석하여 Fama and French(1993)의 위험요인 외에 금융업종 주식수익률의 변동을 설명하는 새로운 위험요인이 존재하는지에 대하여 분석하였다. 본 연구에서는 규모가 큰 금융기업에 대하여 정부가 암묵적인 보증을 한다는 선행연구에 기반을 두었다. Fama-French의 3요인에 더하여 금융업 주식의 수익률을 설명할 수 있는 새로운 위험요인을 구성하고자 잔차항에 주성분 분석 기법을 적용하였다. 새로운 규모요인이 규모에 따라 분류한 금융기관의 포트폴리오의 주식 수익률의 변동에 대한 설명할 근거는 발견되지 않았으나 4대 금융지주와 비 4대 금융지주를 구분하여 분석한 결과 4대 금융지주의 주식 수익률을 통계적으로 유의미하게 설명하는 것으로 나타났다. 또한 새로운 규모요인의 경기 순응성에 대해서도 분석하였으나 이 요인이 경기에 순응한다는(procyclical) 근거를 찾을 수 없었다.제 1 장 서론 ‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧1 제 2 장 국내외 선행연구 ‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧4 제 3 장 표본자료와 연구방법론 ‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧7 제 4 장 새로운 규모효과에 관한 실증 모형 ‧‧‧‧‧10 제 5 장 금융지주회사 및 업종 간 비교 ‧‧‧‧‧‧‧‧‧21 제 6 장 결론 ‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧23 참고문헌 ‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧35 Abstract ‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧‧38Maste

Whole-brain perfusion CT patterns of brain arteriovenous malformations: a pilot study in 18 patients.

BACKGROUND AND PURPOSE: Little is known about the pathological mechanism or the anatomic and functional imaging features related to the clinical manifestations in patients with brain AVM. The purpose of this pilot study was to describe the pattern of whole-brain PCT abnormalities in brain AVMs and their potential to differentiate underlying pathomechanisms. MATERIALS AND METHODS: Whole-brain PCT performed on a 320-detector row CT scanner was analyzed in 18 patients with untreated brain AVMs. The patterns of perfusion abnormalities on CBV, CBF, and MTT maps were analyzed and were related to clinical presentation and cerebral angiography. RESULTS: The presenting symptoms were seizures (n = 5), focal neurologic deficit (n = 5), hemorrhage (n = 4), chemosis (n = 1), and none (n = 3). Three types of extranidal brain parenchymal perfusion abnormalities were noted. Decreased CBF, CBV, and MTT (pattern 1, "functional" arterial steal) were identified in 8 patients. Seizure was the most common presenting symptom in these patients (n = 5). Decreased CBF and CBV, and increased MTT (pattern 2, "ischemic" arterial steal) were noted in 4 patients. Focal neurologic deficit was the most common presenting symptom for these patients (n = 3). Increased CBV and MTT (pattern 3, venous congestion) were seen in 5 patients with presenting symptoms of neurologic deficit (n = 2), seizure (n = 1), hemorrhage (n = 1), and chemosis (n = 1). In 2 patients, pre- and posttreatment PCT was performed, which showed improvement of perfusion abnormalities. CONCLUSIONS: Whole-brain PCT shows different patterns of perfusion abnormalities in patients with brain AVM. These perfusion patterns may discriminate the different pathologic mechanisms involved in these malformations.ope

Spontaneous angiographic conversion of intracranial dural arteriovenous shunt: long-term follow-up in nontreated patients

BACKGROUND AND PURPOSE: Dural arteriovenous shunt (DAVS) is a disease in which abnormal arteriovenous communications develop within the dura. Some case series have suggested DAVS may evolve over time, but the natural history is poorly understood. In this study, we aimed to define the incidence and clinical characteristics of patients with DAVS showing spontaneous angiographic pattern conversion. METHODS: We assessed clinical and angiographic features of patients with angiographic conversion without any treatment from a single center database consisting of 335 DAVS cases. Spontaneous angiographic conversion was defined as complete occlusion of a pre-existing DAVS or conversion of a benign into an aggressive lesion on follow-up diagnostic subtraction angiography. RESULTS: One hundred twelve patients were followed without treatment after the initial diagnosis of DAVS. Overall, we saw pattern conversion on angiography in 18 of the 112 cases (16.1%). Fourteen patients showed spontaneous occlusion of the shunt (12.5%); the most common locations of spontaneous obliteration were the transverse and cavernous sinuses. Four patients showed conversion to an aggressive lesion from benign DAVS (4.0%); all of these cases were associated with occlusion of the ipsilateral draining vein. CONCLUSIONS: DAVS is a dynamic disorder, which will show chronological progression. Spontaneous angiographic obliteration or conversion into an aggressive type may occur on follow-up of untreated DAVSs.ope

Monitoring Radiation Doses during Diagnostic and Therapeutic Neurointerventional Procedures: Multicenter Study for Establishment of Reference Levels

Purpose: To assess patient radiation doses during diagnostic and therapeutic neurointerventional procedures from multiple centers and propose dose reference level (RL). Materials and methods: Consecutive neurointerventional procedures, performed in 22 hospitals from December 2020 to June 2021, were retrospectively studied. We collected data from a sample of 429 diagnostic and 731 therapeutic procedures. Parameters including dose-area product (DAP), cumulative air kerma (CAK), fluoroscopic time (FT), and total number of image frames (NI) were obtained. RL were calculated as the 3rd quartiles of the distribution. Results: Analysis of 1160 procedures from 22 hospitals confirmed the large variability in patient dose for similar procedures. RLs in terms of DAP, CAK, FT, and NI were 101.6 Gy·cm2, 711.3 mGy, 13.3 minutes, and 637 frames for cerebral angiography, 199.9 Gy·cm2, 3,458.7 mGy, 57.3 minutes, and 1,000 frames for aneurysm coiling, 225.1 Gy·cm2, 1,590 mGy, 44.7 minutes, and 800 frames for stroke thrombolysis, 412.3 Gy·cm2, 4,447.8 mGy, 99.3 minutes, and 1,621.3 frames for arteriovenous malformation (AVM) embolization, respectively. For all procedures, the results were comparable to most of those already published. Statistical analysis showed male and presence of procedural complications were significant factors in aneurysmal coiling. Male, number of passages, and procedural combined technique were significant factors in stroke thrombolysis. In AVM embolization, a significantly higher radiation dose was found in the definitive endovascular cure group. Conclusion: Various RLs introduced in this study promote the optimization of patient doses in diagnostic and therapeutic interventional neuroradiology procedures. Proposed 3rd quartile DAP (Gy·cm2) values were 101.6 for diagnostic cerebral angiography, 199.9 for aneurysm coiling, 225.1 for stroke thrombolysis, and 412.3 for AVM embolization. Continual evolution of practices and technologies requires regular updates of RLs.ope

Image contrast enhancement using K-means algorithm

Contrast enhancement has an important role in image processing applications. Conventional contrast enhancement techniques either often fail to produce satisfactory results for a broad variety of low-contrast images, cannot be automatically applied to different images. Because their parameters must be specified manually to produce a satisfactory result for a given image. So, this paper proposes a new contrast enhancement method based on the K-means algorithm. This method is to cluster the histogram components of a low-contrast image using K-means algorithm. And then these clustering histogram components are stretching and equalizing. From the experimental results, the proposed method was more effective than conventional contrast enhancement techniques.1. 서 론 1 2. 명암도 대비 향상법 4 2.1 히스토그램 스트레칭법 4 2.2 히스토그램 균등화법 8 2.3 히스토그램 명세화법 11 3. K-means 알고리즘을 적용한 히스토그램의 군집화 13 4. K-means 알고리즘을 이용한 영상의 명암도 대비 향상 15 5. 실험 및 고찰 21 6. 결 론 3

MR-DWI–Positive Lesions and Symptomatic Ischemic Complications After Coiling of Unruptured Intracranial Aneurysms

BACKGROUND AND PURPOSE: The aims of this study are to evaluate the risk factors for symptomatic ischemic complication (symptomatic ischemic complication [SIC], transient ischemic attack, or stroke) and microembolisms detected as MR diffusion-weighted imaging (MR-DWI)-positive (DWI(+)) lesions, and the relationship between DWI(+) and SIC after coiling of unruptured intracranial aneurysm. METHODS: Between March 2009 and November 2011, 382 unruptured intracranial aneurysms in 343 patients underwent both coiling and posttreatment MR-DWI. The incidence of and risk factors for SIC and DWI(+), and the relationship between DWI(+) and SIC were retrospectively analyzed. RESULTS: The incidence of SIC was 4.1%. The incidence of DWI(+) was 54.5%. The number of DWI(+) lesions was significantly larger in the SIC group, than in the asymptomatic one (12.1±10.4 versus 5.0±8.7, P<0.00). The cutoff value of DWI(+) for predicting SIC was ≥6 (sensitivity 85.7%, specificity 70.7%). The patients with DWI(+) ≥6 was 28.6%. Of the patients with SIC, the patients with DWI(+) ≥6 was 78.6%. Patients aged≥65 years had a trend for SIC, and it was the only independent risk factor for DWI(+) ≥cutoff (n=6; 95%CI, 1.167-3.083). CONCLUSIONS: The number of DWI(+) lesions was significantly larger in the SIC group than in the asymptomatic one after coiling of unruptured intracranial aneurysm. Patients aged≥65 had a trend for SIC, and it was the only independent risk factor for the number of DWI(+) ≥cutoff value (n=6) for predicting SIC.ope