(A) Study of a Numerical Analysis on Three-Dimensional Solidification and Bulging of Continuous Casting Slabs

In the continuous casting process, the internal cracks should be prevented to achieve the improvement of productivity by high speed casting. The internal cracks can occur when tensile strains at the solidification front exceed a certain threshold level. The bulging of the strand is presumed to play a major role in occurrence of tensile strains that cause internal cracks. In particular, when the casting speed is high, strains caused by the bulging become large because of the decrease of the solidified shell thickness and the increase of the surface temperature of the strand. In this paper, solidification analysis of strand-casting under air-mist spray condition, which uses air-mist mixture, is carried out by the two-dimensional finite difference method. In the solidification analysis, the boundary conditions of width face of slab are defined by considering zones directly cooled by sprays and indirectly by rolls and radiation, and the boundary conditions of narrow face of slab are only defined by considering zones by radiation. In order to deal with complicated deformation of the slab, the three-dimensional elastic-plastic and creep models are used for analyzing bulging in the strand casting. The bulging deflections and strains are obtained by using the well-known finite element code ANSYS and are compared with those from the experiments under the same condition. For efficient bulging analysis, the output data of the finite difference method are automatically transformed to input data for ANSYS. The effects of important parameters in casting process of the slabs, such as casting speed, roll pitch and slab shape, are analyzed by implementation of the presented method. When comparing with different casting speeds, the bulging strain obtained in the high speed casting appears to be larger than that at the low speed casting. Also, creep has great influence on the casting directional strain, which increases up to three times of the resulted value by the elasto-plastic model. Therefore, the effect of creep cannot be neglected in the computation of the bulging. When the ratio of width to thickness is smaller than 3.0, the values of casting directional strain and bulging deflection drastically decrease with decreasing of the slab width. It is shown that the secondary cooling condition, roll pitch of the continuous caster and slab width are important process parameters to restrain the bulging and prevent the crack in high speed casting.Abstract = ⅰ 사용기호 = ⅲ List of Tables = ⅵ List of Figures = ⅶ 제 1 장 서론 = 1 1.1 연구 배경 = 1 1.2 연구 동향 = 2 1.3 연구목적 및 범위 = 4 제 2 장 응고해석 = 7 2.1 열전달 방정식 적용조건 = 8 2.2 유한차분법 = 9 2.3 지배방정식 및 경계조건 = 10 2.4 재료의 물성치 = 12 2.5 각 냉각구간에서의 열전달 경계조건 = 15 2.5.1 1차 냉각(몰드 냉각) = 15 2.5.2 2차 냉각 = 15 2.5.3 복사냉각 = 16 2.5.4 롤 접촉 냉각 = 17 2.6 응고해석결과 = 18 2.6.1 주조속도의 영향 = 18 2.6.2 슬래브폭의 영향 = 19 제 3 장 벌징해석 = 27 3.1 벌징해석 모델 = 27 3.2 해석 이론 = 28 3.2.1 유한요소 해석이론 = 29 3.2.2 탄소성 해석 = 29 3.2.3 크리프 해석 = 31 3.3 해석결과 = 33 3.3.1 롤피치의 영향 = 33 3.3.2 벌징에 있어 크리프의 영향 = 33 3.3.3 주조속도의 영향 = 34 3.3.4 슬래브폭의 영향 = 34 제 4 장 내부크랙 = 45 4.1 크랙의 유형에 따른 발생원인 = 45 4.2 내부크랙과 응고면에 발생하는 변형률 사이의 관계 = 45 4.2.1 굽힘롤러구간 = 45 4.2.2 교정롤러구간 = 46 제 5 장 결론 = 47 참고문헌 = 5

Pathophysiologic and Therapeutic Perspectives Based on Thrombus Histology in Stroke

Recent advances in endovascular thrombectomy have enabled the histopathologic analysis of fresh thrombi in patients with acute stroke. Histologic analysis has shown that the thrombus composition is very heterogeneous between patients. However, the distribution pattern of each thrombus component often differs between patients with cardiac thrombi and those with arterial thrombi, and the efficacy of endovascular thrombectomy is different according to the thrombus composition. Furthermore, the thrombus age is related to the efficacy of reperfusion therapy. Recent studies have shown that neutrophils and neutrophil extracellular traps contribute to thrombus formation and resistance to reperfusion therapy. Histologic features of thrombi in patients with stroke may provide some clues to stroke etiology, which is helpful for determining the strategy of stroke prevention. Research on thrombus may also be helpful for improving reperfusion therapy, including the development of new thrombolytic agents.ope

Cardiac function and outcome in patients with cardio-embolic stroke

BACKGROUND: The relationship between whole spectrum of Ejection fraction (EF) and cardioembolic stroke (CES) outcome has not been fully described yet. Notably, it remains unclear whether borderline EF (41∼49%) is related with poor outcome after CES. We sought to evaluate whether lower ejection fraction and borderline EF could predict the outcome in patients with CES. METHOD AND RESULTS: We evaluated the relationship between EF and functional outcome in 437 consecutive patients with CES. EF was introduced as continuous and categorical (EF≤40%, EF 41∼49%, EF≥50%) variable. Patients with CES and the subgroup with AF were evaluated separately. Poor short-term outcome (modified Rankin Score≥3at discharge or death within 90 days after stroke onset) and long-term mortality were evaluated. A total of 165 patients (37.8%) had poor short-term outcomes. EF tends to be lower in patients with poor short-term outcome (56.8±11.0 vs. 54.8±12.0, p-value 0.086). Overall cumulative death was136 (31.1%) in all CES patients and 106 (31.7%) in the AF subgroup. In a multivariable model adjusted for possible covariates, the hazard ratio for mortality significantly decreased by 3% for every 1% increase in ejection fraction in CES patients and 2% for every 1% increase in the AF subgroup. Reduced EF (EF≤40%) showed higher mortality (HR 2.61), and those with borderline EF (41∼49%) had a tendency of higher mortality (HR 1.65, p-value 0.067)compared with those with normal EF. CONCLUSION: We found a strong association between lower EF and CES outcome. Echocardiographic evaluation helps to better determine the prognosis in CES patients, even in subgroup of patients with AF.ope

Clopidogrel preventive effect based on cytochrome P450 2C19 genotype in ischaemic stroke: protocol for multicentre observational study

Introduction: Clopidogrel is an antiplatelet agent that is widely used for the secondary prevention of cardiovascular and cerebrovascular events. The genotype of cytochrome P450 2C19 (CYP2C19) differentially affects the liver's metabolism of clopidogrel, which may influence the drug's response and efficacy for cardiovascular event prevention. In contrast to prior studies of patients with coronary artery diseases, little is known about whether the CYP2C19 genotype influences the preventive efficacy of clopidogrel in patients who had a stroke. We hypothesise that, among patients who had an acute ischaemic stroke who are prescribed clopidogrel, the patients with a loss-of-function CYP2C19 genotype (poor and intermediate metabolisers) may be at a higher risk of composite cardiovascular events than those who are non-carriers (extensive metabolisers). Methods and analysis: This prospective observational multicentre study was designed to determine whether composite cardiovascular events would differ among patients who had an ischaemic stroke prescribed clopidogrel according to CYP2C19 genotype (poor or intermediate vs extensive metabolisers). Inclusion criteria were patients who had an acute ischaemic stroke who underwent CYP2C19 genotype evaluation and received clopidogrel within 72 hours of stroke onset. The primary outcome is composite cardiovascular events (stroke, myocardial infarction, or cardiovascular death) within 6 months after acute ischaemic stroke between patients categorised as poor or intermediate metabolisers and those categorised as extensive metabolisers according to their CYP2C19 genotype. Ethics and dissemination: The Institutional Review Board of Severance Hospital, Yonsei University College of Medicine approved this study (3-2019-0195). We received study approval from the institutional review board of each participating hospital. We plan to disseminate our findings at relevant conferences and meetings and through peer-reviewed journals. Trial registration number: NCT04072705.ope

Recurrent stroke risk and cerebral microbleed burden in ischemic stroke and TIA: A meta-analysis

OBJECTIVE: To determine associations between cerebral microbleed (CMB) burden with recurrent ischemic stroke (IS) and intracerebral hemorrhage (ICH) risk after IS or TIA. METHODS: We identified prospective studies of patients with IS or TIA that investigated CMBs and stroke (ICH and IS) risk during ≥3 months follow-up. Authors provided aggregate summary-level data on stroke outcomes, with CMBs categorized according to burden (single, 2-4, and ≥5 CMBs) and distribution. We calculated absolute event rates and pooled risk ratios (RR) using random-effects meta-analysis. RESULTS: We included 5,068 patients from 15 studies. There were 115/1,284 (9.6%) recurrent IS events in patients with CMBs vs 212/3,781 (5.6%) in patients without CMBs (pooled RR 1.8 for CMBs vs no CMBs; 95% confidence interval [CI] 1.4-2.5). There were 49/1,142 (4.3%) ICH events in those with CMBs vs 17/2,912 (0.58%) in those without CMBs (pooled RR 6.3 for CMBs vs no CMBs; 95% CI 3.5-11.4). Increasing CMB burden increased the risk of IS (pooled RR [95% CI] 1.8 [1.0-3.1], 2.4 [1.3-4.4], and 2.7 [1.5-4.9] for 1 CMB, 2-4 CMBs, and ≥5 CMBs, respectively) and ICH (pooled RR [95% CI] 4.6 [1.9-10.7], 5.6 [2.4-13.3], and 14.1 [6.9-29.0] for 1 CMB, 2-4 CMBs, and ≥5 CMBs, respectively). CONCLUSIONS: CMBs are associated with increased stroke risk after IS or TIA. With increasing CMB burden (compared to no CMBs), the risk of ICH increases more steeply than that of IS. However, IS absolute event rates remain higher than ICH absolute event rates in all CMB burden categories.ope

Range of glucose as a glycemic variability and 3-month outcome in diabetic patients with acute ischemic stroke

Glycemic variability (GV) is reportedly a predictor for poor outcome in various clinical conditions. We aimed to assess whether GV during hospital admission is associated with poor outcomes in patients with acute ischemic stroke (AIS) and diabetes. We prospectively enrolled consecutive patients with AIS from the registry of 6 tertiary hospitals between January 2013 and December 2014. For the GV index, we used a glucose level range that was divided into 4 quartiles. Multivariable binary and ordinal logistic regression analyses were performed to determine the association between GV and the modified Rankin Scale score (3-6) at 3 months. We enrolled 1,504 patients with AIS and diabetes (mean age, 68.1 years; male, 57.2%), of which 35.1% had poor outcomes at 3 months. An increasing glucose range quartile was positively associated with initial neurologic severity and development of hypoglycemia during hospital admission. Multivariable analysis showed that the glucose level range quartile was associated with poor outcomes, even after adjusting for the number of glucose measurement and hypoglycemia (odds ratio [OR] Q2 vs. Q1: 1.50, 95% confidence interval [CI]: 1.02-2.18; OR Q3 vs. Q1: 2.01, 95% CI: 1.34-3.01; OR Q4 vs. Q1: 1.98, 95% CI: 1.22-3.23). These associations remained significant after dichotomization according to glycated hemoglobin levels at admission. An increasing glucose level range as a GV index during hospital admission was associated with poor functional outcomes at 3 months in patients with AIS and diabetes.ope

Traditional Risk Factors for Stroke in East Asia

Stroke is one of the leading causes of death and morbidity worldwide. The occurrence of stroke is strongly dependent on well-known vascular risk factors. After rapid modernization, urbanization, and mechanization, East Asian countries have experienced growth in their aged populations, as well as changes in lifestyle and diet. This phenomenon has increased the prevalence of vascular risk factors among Asian populations, which are susceptible to developing cardiovascular risk factors. However, differing patterns of stroke risk factor profiles have been noted in East Asian countries over the past decades. Even though the prevalence of vascular risk factors has changed, hypertension is still prevalent and the burden of diabetes and hypercholesterolemia will continue to increase. Asia remains a high tobacco-consuming area. Although indicators of awareness and management of vascular risk factors have increased in many East Asian countries, their rates still remain low. Here we review the burdens of traditional risk factors, such as hypertension, diabetes, hypercholesterolemia, and smoking in East Asia. We will also discuss the different associations between these vascular risk factors and stroke in Asian and non-Asian populationsope

Causes, Risk Factors, and Clinical Outcomes of Stroke in Korean Young Adults: Systemic Lupus Erythematosus is Associated with Unfavorable Outcomes

Background and purpose: The incidence of ischemic stroke (IS) in young adults is increasing, and the associated large socioeconomic impact makes understanding IS in young adults important. We investigated the causes of and risk factors for IS in young adults, and their impact on outcomes. Methods: The Stroke in Korean Young Adults (SKY) study is a standardized multicenter prospective study involving eight medical centers of the Republic of Korea. First-ever IS patients aged 18 years to 44 years were prospectively included in this study within 7 days of stroke onset. Their outcomes at 3 months were analyzed. Results: This study enrolled 270 patients from April 2014 to December 2018, most (67.8%) of whom were male. About 41.5% of the patients had one or more vascular risk factors from among hypertension, diabetes mellitus, and dyslipidemia. However, only half of them had received regular treatment. Arterial dissection was more common in males, and systemic lupus erythematosus (SLE) and Moyamoya disease were more common in females. The outcome was favorable (modified Rankin Scale score of 0 or 1) in 81.9% of the patients at 3 months after stroke onset. More severe initial symptoms, higher initial glucose level, and SLE as a comorbidity were associated with unfavorable outcomes. Conclusions: Young adult IS patients in Korea exhibit low awareness and poor management of their risk factors. Although the short-term outcome was relatively favorable in those patients, having SLE was associated with unfavorable outcomes. More attention needs to be paid for improving awareness and controlling risk factors in this population.ope

Added Value of 3D Proton-Density Weighted Images in Diagnosis of Intracranial Arterial Dissection

Background: An early and reliable diagnosis of intracranial arterial dissection is important to reduce the risk of neurological complication. The purpose of this study was to assess the clinical usefulness of three-dimensional high-resolution MRI (3D-HR-MRI) including pre- and post-contrast T1-weighted volumetric isotropic turbo spin echo acquisition with improved motion-sensitized driven equilibrium preparation (3D-iMSDE-T1) and proton-density weighted image (3D-PD) in detecting dissection and to evaluate the added value of 3D-PD in diagnosing intracranial arterial dissection. Methods: We retrospectively recruited patients who underwent 3D-HR-MRI with clinical suspicion of arterial dissection. Among them, we selected patients who were diagnosed with definite dissection according to the Spontaneous Cervicocephalic Arterial Dissections Study criteria. For each patient, the presence of intimal flap, intramural hematoma, and vessel dilatation were evaluated independently by two neuroradiologists on each sequence. Interobserver agreement was assessed. Results: Seventeen patients (mean age: 41 ± 10 [SD] years; 13 men) were diagnosed with definite dissection. The intimal flaps were more frequently detected on 3D-PD (88.2%, 15/17) than on 3D-iMSDE-T1 (29.4%, 5/17), and post-contrast 3D-iMSDE-T1 (35.3%, 6/17; P = 0.006 and P = 0.004, respectively). No significant difference was found in the detection rate of intramural hematomas (59-71%) and vascular dilatations (47%) on each sequence. Interobserver agreement for detection of dissection findings showed almost perfect agreement (k = 0.84-1.00), except for detection of intimal flaps on pre-contrast 3D-iMSDE-T1 (k = 0.62). After addition of 3D-PD to pre- and post-contrast 3D-iMSDE-T1, more patients were diagnosed with definite dissection with the initial MRI (88.2% vs. 47.1%; P = 0.039). Conclusions: The intimal flap might be better visualized on the 3D-PD sequence than the 3D-iMSDE-T1 sequences, allowing diagnosis of definite dissection without follow-up imaging.ope

Atrial fibrillation in patients with first-ever stroke: Incidence trends and antithrombotic therapy before the event

BACKGROUND: Atrial fibrillation (AF) is the most common cardiac arrhythmia among adults. Despite the proven advantages in primary and secondary stroke prevention in patients with AF, oral anticoagulation (OAC) therapy is still underused in many countries. In this study, we investigated the incidence of AF-related ischemic stroke over the past decade in South Korea and trends of preventive antithrombotic therapy use before stroke in a nationwide cohort. METHODS AND FINDINGS: The data source for this study was a nationwide sample cohort comprising 1,025,340 individuals that was established by the nationwide health insurance system in 2002. A total of 10,215 patients with acute ischemic stroke (AIS) were selected from the cohort between 2004 and 2013. AF was identified in 1,662 patients, and 979 patients had preexisting AF before AIS. The annual proportion of patients with AIS with AF gradually increased from 13.4% to 22.6% over the study period (p for trends <0.001). Only 14.0% of patients with high risk AF were receiving OAC before the stroke, and this proportion remained relatively constant during the study period. However, the proportion of patients treated with antiplatelet agents had increased from 18.8% in 2004 to 45.3% in 2013, while that of patients receiving no antithrombotic agent decreased from 64.6% in 2004 to 43.9% in 2013. As a limitation, no information was available about non-vitamin K antagonist oral anticoagulants, because they were widely used since late 2014 in Korea. CONCLUSIONS: The number of patients with AIS and AF has steadily increased over the last 10 years in Korea. However, a small portion of patients with AF were receiving OAC therapy before the stroke and about half of the patients did not receive any antithrombotic medication. Our study demonstrates that there is huge gap between clinical practice and treatment guidelines for patients with AF in Korea.ope