SlimFTL: a Small and Fast Page-level FTL using Hash Functions

학위논문 (석사) -- 서울대학교 대학원 : 공과대학 컴퓨터공학부, 2020. 8. 김지홍.As the capacity of an SSD increases, the amount of DRAM for managing the SSD increases proportionally. Since the DRAM cost directly affects the overall SSD price, it is important to minimize the DRAM size without degrading the SSD performance. In this paper, we propose a novel hash-based FTL mapping technique, SlimFTL, that meets this goal. SlimFTL overcomes the GC inefficiency problem of an existing hash-based FTL in two directions. By employing an efficient indirection layer between the logical page and its hashed physical block, SlimFTL reduces the block copy overhead during GC. SlimFTL exploits the spatial sequentiality among successive writes so that sequential writes can be mapped to the same physical block, which significantly reduces the number of valid copies during GC. Experimental results show that SlimFTL can achieve the same performance level of a page-level mapping scheme with only 44% of the DRAM capacity.Chpater 1. Introduction 1 1.1 Motivation 1 1.2 Contribution 3 1.3 Thesis Structure 6 Chapter 2. Background 7 2.1 Overview of Hash-based FTL 7 2.2 Existing Hash-based FTL 10 2.3 Evaluation Result of HPFTL 13 Chapter 3 SlimFTL 16 3.1 Overview of SlimFTL 16 3.2 Hash-based Mapping Table 18 3.3 Sequentiality-Aware Hasher 21 3.4 Hash Collision Handler 24 3.5 Garbage Collection 26 Chapter 4 Experiments 27 4.1 Experimental Setup 27 4.2 Experimental Results 29 Chapter 5 Related Works 34 5.1 Related Works 34 Chapter 6 Conclusions 36 6.1 Summary 36 6.2 Future Work 37 Bibliography 38 초록 41Maste

Feasibility of Coronary Artery Calcium Scoring on Dual-Energy Chest Computed Tomography: A Prospective Comparison with Electrocardiogram-Gated Calcium Score Computed Tomography

Rationale and Objectives: This study aimed to evaluate the feasibility of assessment using the coronary artery calcium score (CACS) in dual-energy chest computed tomography (CT). Materials and Methods: We prospectively enrolled 30 patients (19 male, 11 female; mean age, 63.73 ± 9.40 years) who clinically required contrast-enhanced chest CT. The patients underwent electrocardiogram-gated cardiac calcium-scoring CT with a slice thickness of 2.5 mm followed by a sequentially non-gated contrast-enhanced dual-energy chest CT using 140/80 fast kVp switching technology with slice thicknesses of 1.25 mm and 2.5 mm. Virtual unenhanced (VUE) images were then reconstructed from the dual-energy CT using the material suppressed iodine (MSI) technique. Results: The mean heart rates were 63.33 ± 12.01 beats per minute. The mean CACS on the coronary calcium-scoring CT was 361.1 ± 435.5, and CACSs of the VUE images were 76.8 ± 128.6 (2.5 mm slice) and 108.7 ± 165.1 (1.25 mm slice). The correlation coefficients of CACS between the coronary calcium-scoring CT with the VUE 2.5 mm and 1.25 mm images were 0.888 and 0.904, respectively. The inter-observer agreements for the calcium score measurement between the calcium-scoring CT, VUE 2.5 mm, and VUE 1.25 mm were 1.000, 0.999, and 1.000, respectively. Conclusions: In conclusion, assessment of CACS using dual-energy chest CT might be feasible when using MSI virtual unenhanced dual-energy chest CT images with a slice thickness of 1.25 mm.ope

비 조영증강 흉부 CT에서 관상동맥 칼슘스코어 측정을 위한 16 cm 축상 촬영 기법의 유용성: 전향적 탐색적 연구

Purpose This study aimed to evaluate the utility of the 16-cm axial volume scan technique for calculating the coronary artery calcium score (CACS) using non-enhanced chest CT. Materials and Methods This study prospectively enrolled 20 participants who underwent both, non-enhanced chest CT (16-cm-coverage axial volume scan technique) and calcium-score CT, with the same parameters, differing only in slice thickness (in non-enhanced chest CT = 0.625, 1.25, 2.5 mm; in calcium score CT = 2.5 mm). The CACS was calculated using the conventional Agatston method. The difference between the CACS obtained from the two CT scans was compared, and the degree of agreement for the clinical significance of the CACS was confirmed through sectional analysis. Each calcified lesion was classified by location and size, and a one-to-one comparison of non-contrast-enhanced chest CT and calcium score CT was performed. Results The correlation coefficients of the CACS obtained from the two CT scans for slice thickness of 2.5, 1.25, and 0.625 mm were 0.9850, 0.9688, and 0.9834, respectively. The mean differences between the CACS were −21.4% at 0.625 mm, −39.4% at 1.25 mm, and −76.2% at 2.5 mm slice thicknesses. Sectional analysis revealed that 16 (80%), 16 (80%), and 13 (65%) patients showed agreement for the degree of coronary artery disease at each slice interval, respectively. Inter-reader agreement was high for each slice interval. The 0.625 mm CT showed the highest sensitivity for detecting calcified lesions. Conclusion The values in the non-contrast-enhanced chest CT, using the 16-cm axial volume scan technique, were similar to those obtained using the CACS in the calcium score CT, at 0.625 mm slice thickness without electrocardiogram gating. This can ultimately help predict cardiovascular risk without additional radiation exposure.ope

Optimization of a chest computed tomography protocol for detecting pure ground glass opacity nodules: A feasibility study with a computer-assisted detection system and a lung cancer screening phantom

Objective: This study aimed to optimize computed tomography (CT) parameters for detecting ground glass opacity nodules (GGNs) using a computer-assisted detection (CAD) system and a lung cancer screening phantom. Methods: A lung cancer screening phantom containing 15 artificial GGNs (-630 Hounsfield unit [HU], 2-10 mm) in the left lung was examined with a CT scanner. Three tube voltages of 80, 100, and 120 kVp were used in combination with five tube currents of 25, 50, 100, 200, and 400 mA; additionally, three slice thicknesses of 0.625, 1.25, and 2.5 mm and four reconstruction algorithms of adaptive statistical iterative reconstruction (ASIR-V) of 30, 60, and 90% were used. For each protocol, accuracy of the CAD system was evaluated for nine target GGNs of 6, 8, or 10 mm in size. The cut-off size was set to 5 mm to minimize false positives. Results: Among the 180 combinations of tube voltage, tube current, slice thickness, and reconstruction algorithms, combination of 80 kVp, 200 mA, and 1.25-mm slice thickness with an ASIR-V of 90% had the best performance in the detection of GGNs with six true positives and no false positives. Other combinations had fewer than five true positives. In particular, any combinations with a 0.625-mm slice thickness had 0 true positive and at least one false positive result. Conclusion: Low-voltage chest CT with a thin slice thickness and a high iterative reconstruction algorithm improve the detection rate of GGNs with a CAD system in a phantom model, and may have potential in lung cancer screening.ope

Differential Diagnosis of Thick Myocardium according to Histologic Features Revealed by Multiparametric Cardiac Magnetic Resonance Imaging

Left ventricular (LV) wall thickening, or LV hypertrophy (LVH), is common and occurs in diverse conditions including hypertrophic cardiomyopathy (HCM), hypertensive heart disease, aortic valve stenosis, lysosomal storage disorders, cardiac amyloidosis, mitochondrial cardiomyopathy, sarcoidosis and athlete's heart. Cardiac magnetic resonance (CMR) imaging provides various tissue contrasts and characteristics that reflect histological changes in the myocardium, such as cellular hypertrophy, cardiomyocyte disarray, interstitial fibrosis, extracellular accumulation of insoluble proteins, intracellular accumulation of fat, and intracellular vacuolar changes. Therefore, CMR imaging may be beneficial in establishing a differential diagnosis of LVH. Although various diseases share LV wall thickening as a common feature, the histologic changes that underscore each disease are distinct. This review focuses on CMR multiparametric myocardial analysis, which may provide clues for the differentiation of thickened myocardium based on the histologic features of HCM and its phenocopies.ope

크레아틴 화학적 교환 포화 천이 기법을 이용한 심혈관 자기공명 영상 기법을 통한 당뇨병성 심근 병증 쥐모델에서의 이미징 바이오마커 구축

실험 목적 당뇨병성 심근 병증 (diabetic cardiomyopathy, DCM) 쥐 모델을 사용하여 심장 기능 및 구조의 변화 전에 일어나는 DCM 초기의 물질대사 변화를 감지하는 데 있어 크레아틴 화학적 교환 포화 천이 (creatine-chemical exchange saturation transfer, CrCEST) 심혈관 자기 공명 (cardiovascular magnetic resonance, CMR) 영상의 효율성을 평가한다. 실험 배경 당뇨병의 유병률은 전 세계적으로 증가하고 있으며 이는 심부전의 주요 원인 중 하나이다. 현재 DCM의 임상 진단은 심초음파 또는 기존의 CMR 기법을 사용하여 구조적 또는 기능적 심근 이상을 감지하는 것에 기반한다. 그러나 구조적 또는 기능적 심근 변화는 DCM이 매우 진행된 단계에서나 관찰된다. DCM의 조기 진단과 심부전 예방을 위한 치료를 위해서는 DCM 초기의 심근 물질대사 변화를 감지할 수 있어야 한다. 실험 방법 9주령 수컷 Sprague-Dawley 쥐를 무작위로 배정하여 당뇨병 유발 전 (n = 12)과 당뇨병 유발 후 4, 8, 12, 16주차 (각각 n = 8, n = 7, n = 7, n = 6) 에 CMR을 촬영했다. 쥐에게 당뇨병을 유도하기 위해 스트렙토조토신 (Streptozotocin, STZ)이라는 약물을 복강 내로 65mg/kg 용량으로 주사했다. 쥐의 체중과 혈당 수치는 매주 측정했다. Cine, T1 지도화 영상 및 CrCEST 영상을 9.4 T 자기공명영상 스캐너를 사용하여 촬영했다. 심장 기능 및 심근 strain은 cine 이미지에서 상업적으로 이용 가능한 소프트웨어를 사용하여 반자동으로 측정했다. 심근 T1값, 세포외 부피 분율 (extracellular volume fraction, ECV) 및 CrCEST 신호 분석을 시행할 영역은 심실 중격으로, 손으로 영역을 그려주면 역시 소트프웨어가 값을 측정했다. 모든 데이터는 선형 혼합 모델을 사용하여 통계 분석했다. CrCEST 신호에 대한 관찰자 내 및 관찰자 간 일치도는 Intraclass correlation coefficient (ICC)로 평가했다. 심근의 조직학적 평가는 각 그룹에서 최소 3 마리의 쥐에 대해 수행했다. 심장 기능 및 심근 strain, T1 지도화 영상, CrCEST 영상 및 조직학적 검사를 5개 그룹에서 비교했다. 실험 결과 STZ 주사 후 모든 쥐에서 1주일 내에 혈당 수치가 급격히 상승 및 유지되어 당뇨병은 성공적으로 유도되었다. CrCEST 신호 (magnetization transfer ratio asymmetry, MTRasym)는 당뇨 4주, 8주, 12주, 16주차 군에서 (각각 평균 6.04 %, 3.76 %, 2.80 %, 3.34 %)에서 당뇨 유발 전 그룹 (10.86 %)보다 유의미하게 낮았다 (p<0.001). 군간 대응 비교 분석에서는 당뇨 유발 전 그룹과 당뇨 그룹 각각 사이에 유의미한 차이를 보였다 (p<0.001). MTRasym에 대한 관찰자 내 및 관찰자 간 일치도 평가에서 ICC는 각각 0.953 및 0.927이었다. 좌심실 박출율은 군간 유의미한 차이가 있었고 (p<0.001), 군간 대응 비교 분석에서 당뇨 유발 전 그룹과 당뇨 16주차 그룹간에 유의미한 차이를 보였다 (p<0.001). 일회 박출량, 심박출량 및 좌심실 심근량은 5개 그룹간에 유의미한 차이가 없었다. Global radial, longitudinal peak strain은 당뇨 유발 전 그룹과 비교했을 때 당뇨 12주차 (각각 p=0.049, p=0.004) 및 16주차 (각각 p=0.003, p<0.001) 그룹에서 유의미하게 감소했고, Global circumferential peak strain은 당뇨 16주차 그룹 (p=0.005) 그룹에서 유의미하게 감소했다. 심근의 native T1 값과 ECV는 당뇨 유발 전 그룹에 비해 당뇨 12주차 및 16주차 그룹에서 증가했다 (p<0.001). 조직학적 소견상 당뇨 12주차 및 16주차 쥐에서 subendocardial fibrosis, inflammation이 관찰되었다. 투과전자현미경에서 미토콘드리아 내 paracrystalline inclusion body는 당뇨 4주차 쥐에서부터 발견되었고, 미토콘드리아의 평균 면적은 다른 쥐들에 비해서 당뇨 16주차 쥐에서 증가되는 것을 확인했다 (p<0.001). 결론 우리의 연구는 CrCEST CMR이 심장 기능 및 구조의 변화 전에 초기 DCM에서의 물질대사 변화를 감지하여 DCM의 조기 진단에 유용하다는 것을 보여주었다. Purpose: To evaluate the potential effectiveness of creatine (Cr) chemical exchange saturation transfer (CrCEST) cardiovascular magnetic resonance (CMR) imaging in detecting early metabolic changes before cardiac function and structural changes occur in a diabetic cardiomyopathy (DCM) rat model. Background: The clinical diagnosis of DCM is based on detecting structural or functional myocardial abnormalities with echocardiography or conventional CMR at the advanced stage of DCM. Detecting metabolic changes in the myocardium is necessary for the early diagnosis and management of DCM. Materials and methods: Nine-week-old male Sprague-Dawley rats were randomly assigned to undergo CMR scans before and at 4, 8, 12, and 16 weeks after being intraperitoneally injected with streptozotocin to induce diabetes. Cine, T1 mapping, and CrCEST MR images were obtained. Cardiac function and myocardial strain were semiautomatically assessed on the cine MR images. The regions of interest for myocardial T1 values, extracellular volume fraction, and CrCEST signals were located in the interventricular septum. Data were analyzed using the linear mixed model. The intra- and interobserver agreements on the CrCEST signal were assessed with the intraclass correlation coefficient (ICC). Shortly after the CMR scan, the myocardium of sacrificed rats in each group was histologically evaluated. Cardiac function, T1 mapping images, CrCEST images, and histological examination of myocardium of the five groups were compared. Results: The blood glucose levels of the rats increased rapidly 1 week after the streptozotocin injections. The CrCEST signals (magnetization transfer ratio asymmetry) were significantly lower in the diabetic groups than in the prediabetic group (P<0.001). The pairwise comparisons showed significant differences between the prediabetic group and each of the four diabetic groups (P<0.001). The ICCs for intra- and interobserver agreements on the CrCEST signal were 0.953 and 0.927, respectively. The left ventricular ejection fraction was significantly different between the groups (P<0.001). The pairwise comparison showed a significant difference between the prediabetic and 16-week diabetic groups (P<0.001). Stroke volumes, cardiac output, and left ventricular myocardial mass were not significantly different between the five groups. The global radial peak strain and longitudinal peak strain were decreased significantly in the 12-week (P=0.049 and P=0.004, respectively) and 16-week diabetic groups (P=0.003 and P<0.001, respectively). The global circumferential peak strain was lower in the 16-week diabetic group (P=0.005) than in the prediabetic group. The myocardial native T1 values and extracellular volume fractions were higher in the 12- and 16-week diabetic groups than in the prediabetic group (P<0.001). Myocardial histology revealed subendocardial fibrosis in the 12- and 16-week diabetic rats. Transmission electron microscopy revealed mitochondrial paracrystalline inclusion bodies since 4 weeks after the onset of diabetes. The mean area of the mitochondria was significantly increased in the 16-week diabetic rats, compared to that of the other rat groups (P<0.001). Conclusions: CrCEST CMR revealed metabolic changes in early diabetic cardiomyopathy before cardiac function and structural changes occurred.open박

USP13에 의한 HMGB1 안정성과 위치이동 조절

Department of Medical ScienceHigh Mobility Group Box 1(HMGB1)은 손상 관련 분자적 패턴으로서 선천면역에 있어서 핵심적인 역할을 담당한다. HMGB1은 염증성 자극에 능동적으로 분비되어 염증반응의 후기 매개자로서 작용한다. 아세틸화, 인산화, 그리고 산화 같은 몇몇 번역 후 변형이 HMGB1 분비를 조절한다고 알려져 있으나, HMGB1이 탈유비퀴틴화에 의해서 어떻게 조절되는지는 밝혀진 바 없다. 이 연구에서는 ubiquitin-specific-protease (USP13)가 HMGB1의 새로운 결합 파트너이며, 탈유비퀴틴화를 통하여 그 안정성을 조절함을 밝혔다. 또한 과발현된 USP13은 HMGB1의 세포질로의 이동과 세포 밖 분비도 유도했는데, 탈유비퀴틴화 효소 활성이 제거된 돌연변이 형의 USP13도 HMGB1 분비를 촉진시킴을 관찰할 수 있었다. 이는 USP13이 HMGB1의 세포 내 위치와 이동을 탈유비퀴틴화 효소 활성과는 무관하게 조절한다는 것을 의미한다. 결론적으로, USP13은 HMGB1의 안정성과 그 분비로 이어지는 위치 이동을 조절하는 두 가지 역할을 한다는 것을 보고하는 바이다.open석

Generating a Process Simulation Model and Optimal Schedule for Steelmaking Process using Process Mining

MasterDigital twin is an advanced simulation environment that can reflect real-world models into the virtual world. By applying digital twins to manufacturing processes, production prediction and process optimization can be achieved to improve process efficiency. Simulation model generation and process optimization technologies are key technologies in digital twin. In this study, three steps were taken to generate process simulation model and optimal schedule for steelmaking process. First, an event log error repair method that reflects the characteristics of the process was presented. After that, a simulation model that reflects the characteristics of the steelmaking process, such as idle patterns, queue rules, and continuous activity patterns, was constructed, and the effectiveness of the model was confirmed by comparing the simulation log with the actual log. Finally, the process optimization problem was defined by simplifying the entire process, and an optimization model was built using the process mining method used to generate simulation model. The performance of the optimization model was verified by comparing the simulation logs based on the optimization schedule and original schedule

Optimization of Hydrogen Refueling Stations Deployment and Supply Chain Networks: Current Status and Research Suggestions

Hydrogen infrastructure consisting of hydrogen refueling stations and supply chain network is critical in the hydrogen mobility economy. This paper overviews the important key concepts of the hydrogen mobility economy and investigates the status of hydrogen vehicles and refueling stations in Korea and other countries. It also reviews the methodologies for hydrogen station and supply chain network optimization and suggests research agenda for the hydrogen mobility economy.22Nkc

모빌리티를 위한 수소 충전소 배치 최적화

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