A Study on the Power Converter for Superconducting Magnetic Energy Storage System

에너지 저장 기술은 전력의 품질 및 공급에 있어서 안정성을 높이기 위한 중요한 기술이다. 그 중 초전도 자기에너지 저장 기술은 특정 조건에서 전기 저항이 Zero의 특징을 가지는 초전도 물질을 이용하여 코일의 형태로 저장 장치를 만들어 전류를 흐르게 하여 자기에너지를 저장하는 기술로, 시스템 응답시간이 빨라 충/방전에 용이하고 효율이 좋다. 이러한 초전도 자기에너지 저장 장치의 전력변환기를 고전압 대전류에 용이한 사이리스터 브리지를 이용하여 AC-DC 정류기로써의 충전모드, DC-AC 인버터로써의 방전모드, 충전된 에너지를 저장하고 있는 영구전류모드의 세 가지 작동 모드에서 Psim 시뮬레이션을 진행하였다. 출력전압을 피드백 받아 사용자가 원하는 기준전압에 대하여 사이리스터 점호각이 자동으로 변하는 폐루프 제어 시스템을 구현하였다. 또한, 입력전류 및 출력전압의 고조파 왜율을 감소하기 위하여 6-pulse, 12-pulse에 대해 각각 시뮬레이션 하였다. 무효전력을 감소하기 위한 비대칭 제어의 두 가지 방식에 대해 비교 분석하고 용도에 따라 어떤 제어방법을 사용해야 적합한지 판단하였다.|Energy storage technology is one the most important technology to improve stability and quality in the electric power distribution system. Superconducting Magnetic Energy Storage (SMES) technology is using superconducting material, which has zero electric resistance under a certain condition. SMES stores electric energy in the form of magnetic flux using superconducting coil. This system has fast response time and easy to charge or discharge electric energy and also has high conversion efficiency. Using thyristor bridge as power converter which has high voltage and current capacity, power converter for superconducting magnetic energy storage system has three operating mode, those are charging energy mode of 'AC-DC rectifier', discharging energy mode of 'DC-AC inverter' and permanent current mode. With Psim simulation of these three operation mode. thyristor bridge power converter is proved to be a suitable SMES converter option. And also, simulation for SMES closed loop operation is carried out and obtained good result. For the purpose of reducing reactive power in charging and discharging the coil, asymmetric control analysis is carried out both inside one bridge and two bridge with different control angle. From these simulation result, asymmetric control method in two different bridges would be the best option for the SMES power converter operation rather than inside asymmetric control in one bridge.목 차 목 차 ⅰ 그림 목차 ⅱ Abstract ⅳ 제 1 장 서 론 01 제 2 장 관련이론 03 2.1 에너지 저장 장치 03 2.1.1 에너지 저장 장치의 필요성 03 2.1.2 각종 에너지 저장 장치 03 2.2 초전도체 (Superconductor) 05 2.2.1 특징 05 2.2.2 초전도 자기에너지 저장장치 07 2.3 초전도 자기에너지 저장장치용 전력변환기 10 2.3.1 다이오드 정류기와 PWM 인버터 10 2.3.2 6-pulse thyristor bridge 12 2.3.3 12-pulse thyristor bridge 22 2.3.4 비대칭 제어 24 제 3 장 본론 27 3.1 3상 6-pulse thyristor bridge 시뮬레이션 27 3.2 3상 12-pulse thyristor bridge 시뮬레이션 34 3.3 thyristor bridge feedback 제어 41 3.4 비대칭 제어 45 제 4 장 결론 50 참 고 문 헌 52Maste

Two Cases of Seasonal Influenza Virus (H3N2) and Acute Respiratory Distress Syndrome

Compared with the 2009 pandemic influenza A (H1N1), the seasonal influenza A (H3N2) in 2011?2012 was self-limited and mild. However, some cases proceeded to acute respiratory distress syndrome (ARDS) due to underlying medical history. Here we report two cases with influenza A (H3N2) progressing to fatal ARDS. One case with several underlying medical conditions eventually died from multi-organ failure despite the application of extracorporeal membrane oxygenation. When patients are suspected to have influenza, it is imperative to investigate their medical histories and risk factors. If they have many co-morbidities or risk factors, clinicians should initiate aggressive management immediately regardless of the type of influenza infection.ope

Risk factors for unfavorable clinical outcomes in patients with brain abscess in South Korea

Background: Brain abscess can be life-threatening and manifest various neurological findings, although the mortality rate has decreased recently. We investigated the risk factors for unfavorable outcomes of patients with brain abscess. Methods: A retrospective cohort study examined patients with brain abscess seen from May 2005 to December 2018 in a tertiary care hospital in Seoul, South Korea. We reviewed the medical records for clinical findings, therapeutic modalities, and prognostic factors of brain abscess. Unfavorable clinical outcomes were defined as death, moderate to severe disability with neurological deficits, or vegetative state at 1 year or at the time of discharge from outpatient follow-up. Results: The study enrolled 135 patients: 65.2% were males; the mean age was 56 years. 35.6% had unfavorable outcomes. In multivariate analysis, higher Sequential Organ Failure Assessment (SOFA) (p < 0.001), pre-existing hemiplegia (p = 0.049), and higher Charlson comorbidity index (CCI) (p = 0.028) were independently associated with unfavorable outcomes. Conclusions: Higher SOFA, pre-existing hemiplegia and higher Charlson comorbidity index were significant risk factors for unfavorable clinical outcomes in patients with brain abscess.ope

Risk factors for mortality in patients with Stenotrophomonas maltophilia bacteremia

Stenotrophomonas maltophilia is a nosocomial pathogen associated with high morbidity and mortality, particularly in immunocompromised or critically ill patients. In this study, we investigated the risk factors for mortality in patients with S. maltophilia bacteremia.Retrospectively, medical records from all patients with S. maltophilia bacteremia between December 2005 and 2014 at Severance Hospital, a 2000-bed tertiary care hospital in Seoul, Korea, were reviewed. Analysis was performed to identify factors associated with 28-day mortality.In total, 142 bacteremia patients were enrolled in this study. The overall 28-day mortality rate was 36.6%. Based on the univariate analysis, hematologic malignancy (P?=?0.015), Sepsis-related Organ Failure Assessment (SOFA) score (P?<?0.001) and the removal of a central venous catheter (CVC) (P?=?0.040) were significantly related to mortality. In the intensive care unit patients, the Acute Physiology and Chronic Health Evaluation II score (P?=?0.001) also had significance. Based on the multivariate analysis, the SOFA score (odds ratio [OR]?=?1.323; 95% confidence interval [CI]: 1.159, 1.509; P?<?0.001) and removal of the CVC (OR?=?0.330; 95% CI: 0.109, 0.996; P?=?0.049) were independent factors associated with mortality.Our results suggest that removing a CVC may considerably reduce mortality in patients with S. maltophilia bacteremia.ope

Tacrolimus-induced, Transplant-associated Thrombotic Microangiopathies after Lung Transplantation

We report a case of tacrolimus-induced transplant-associated thrombotic microangiopathies (TA-TMA) after lung transplantation. A 71-year-old man underwent lung transplantation secondary to idiopathic pulmonary fibrosis. After 4 months, he presented with abdominal discomfort and dyspnea, and was diagnosed with hemolytic anemia and thrombocytopenia. Tacrolimus was considered the cause of the TMA. Tacrolimus was stopped and several sessions of plasma exchange were performed immediately after diagnosis of TA-TMA. However, his platelet count did not normalize, gastrointestinal bleeding was recurrent, and severe pneumonia developed, following which he died. TA-TMA are rare but severe, life-threatening complications in lung transplant recipients. Therefore, the possibility of TA-TMA should be considered in posttransplant recipients.ope

Characteristics of Resting-State Functional Connectivity in HIV-Associated Neurocognitive Disorder.

BACKGROUND: HIV-associated neurocognitive disorder (HAND) can occur in patients without prior AIDS defining illness and can be debilitating. This study aimed to evaluate the difference in the patterns of intrinsic brain activity between patients with or without HAND for deepening our understanding of HAND. METHODS: We evaluated 24 HIV-infected individuals, 12 with previously diagnosed HAND and 12 previously diagnosed without HAND, and 11 seronegative individuals. These individuals then underwent repeat NP testing and a functional brain MRI scan. For functional MRI analysis, seed-based analysis with bilateral precuneus cortex seed was applied. RESULTS: Among the 12 individuals with previously diagnosed HAND, 3 showed improvement of their neurocognitive function and 1 was excluded for worsening liver disease. Among the 12 patients who previously had normal neurocognitive function, 2 showed neurocognitive impairment. Overall, the HAND group, who had impaired cognitive function at the time of MRI scan, showed significant decrease of resting status functional connectivity between bilateral precuneus and prefrontal cortex (PFC) compared with nonHAND group, those who had normal neurocognitive function (Corrected P<0.05). The functional connectivity with the right inferior frontal operculum and right superior frontal gyrus was positively correlated with memory and learning ability. CONCLUSIONS: This cross-sectional study found a significant difference in fMRI patterns between patients with and without HAND. Decreased functional connectivity between precuneus and PFC could be possible functional substrate for cognitive dysfunction in HIV patients, which should be characterized in a longitudinal study.ope

A mathematical model of COVID-19 transmission in a tertiary hospital and assessment of the effects of different intervention strategies

Novel coronavirus (named SARS-CoV-2) can spread widely in confined settings including hospitals, cruise ships, prisons, and places of worship. In particular, a healthcare-associated outbreak could become the epicenter of coronavirus disease (COVID-19). This study aimed to evaluate the effects of different intervention strategies on the hospital outbreak within a tertiary hospital. A mathematical model was developed for the COVID-19 transmission within a 2500-bed tertiary hospital of South Korea. The SEIR (susceptible-exposed-infectious-recovered) model with a compartment of doctor, nurse, patient, and caregiver was constructed. The effects of different intervention strategies such as front door screening, quarantine unit for newly admitted patients, early testing of suspected infected people, and personal protective equipment for both medical staff and visitors were evaluated. The model suggested that the early testing (within eight hours) of infected cases and monitoring the quarantine ward for newly hospitalized patients are effective measures for decreasing the incidence of COVID-19 within a hospital (81.3% and 70% decrease of number of incident cases, respectively, during 60 days). Front door screening for detecting suspected cases had only 42% effectiveness. Screening for prohibiting the admission of COVID-19 patients was more effective than the measures for patients before emergency room or outpatient clinic. This model suggests that under the assumed conditions, some effective measures have a great influence on the incidence of COVID-19 within a hospital. The implementation of the preventive measures could reduce the size of a hospital outbreak.ope

Effectiveness of Convalescent Plasma Therapy in Severe or Critically Ill COVID-19 Patients: A Retrospective Cohort Study

Purpose: Coronavirus disease-2019 (COVID-19) is a novel respiratory infectious disease caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2); there are few specific treatments. Convalescent plasma (CP), donated by people who have recovered from COVID-19, is an investigational therapy for severe or critically ill patients with COVID-19. Materials and methods: This retrospective cohort study evaluated the effectiveness of CP therapy in patients with severe or life-threatening cases of COVID-19 at two hospitals in Seoul, Korea, between May and September 2020. Clinical outcomes were evaluated in 20 patients with CP therapy in a descriptive manner. Additionally, the changes in cycle threshold (Ct) values of 10 patients with CP therapy were compared to those of 10 controls who had the same (±0.8) initial Ct values but did not receive CP. Results: Of the 20 patients (mean age 66.6 years), 18 received high-dose oxygen therapy using mechanical ventilators or high-flow nasal cannulas. Systemic steroids were administered to 19 patients who received CP. The neutralizing antibody titers of the administered CP were between 1:80 and 1:10240. There were two ABO-mismatched transfusions. The World Health Organization ordinal scale score and National Institutes of Health severity score improved in half of the patients within 14 days. Those who received CP showed a higher increase in Ct values at 24 h and 72 h after CP therapy compared to controls with similar initial Ct values (p=0.002). No transfusion-related side effects were observed. Conclusion: CP therapy may be a potential therapeutic option in severe or critically ill patients with COVID-19.ope

Identification of Fungal Species and Detection of Azole-Resistance Mutations in the Aspergillus fumigatus cyp51A Gene at a South Korean Hospital

Purpose: With changing fungal epidemiology and azole resistance in Aspergillus species, identifying fungal species and susceptibility patterns is crucial to the management of aspergillosis and mucormycosis. The objectives of this study were to evaluate performance of panfungal polymerase chain reaction (PCR) assays on formalin-fixed paraffin embedded (FFPE) samples in the identification of fungal species and in the detection of azole-resistance mutations in the Aspergillus fumigatus cyp51A gene at a South Korean hospital. Materials and methods: A total of 75 FFPE specimens with a histopathological diagnosis of aspergillosis or mucormycosis were identified during the 10-year study period (2006-2015). After deparaffinization and DNA extraction, panfungal PCR assays were conducted on FFPE samples for fungal species identification. The identified fungal species were compared with histopathological diagnosis. On samples identified as A. fumigatus, sequencing to identify frequent mutations in the cyp51A gene [tandem repeat 46 (TR46), L98H, and M220 alterations] that confer azole resistance was performed. Results: Specific fungal DNA was identified in 31 (41.3%) FFPE samples, and of these, 16 samples of specific fungal DNA were in accord with a histopathological diagnosis of aspergillosis or mucormycosis; 15 samples had discordant histopathology and PCR results. No azole-mediating cyp51A gene mutation was noted among nine cases of aspergillosis. Moreover, no cyp51A mutations were identified among three cases with history of prior azole use. Conclusion: Panfungal PCR assay with FFPE samples may provide additional information of use to fungal species identification. No azole-resistance mediating mutations in the A. fumigatus cyp51A gene were identified among FFPE samples during study period.ope

Predictive factors for unfavorable outcomes of tuberculous pericarditis in human immunodeficiency virus-uninfected patients in an intermediate tuberculosis burden country

BACKGROUND: In areas where Mycobacterium tuberculosis is endemic, tuberculosis is known to be the most common cause of pericarditis. However, the difficulty in diagnosis may lead to late complications such as constrictive pericarditis and increased mortality. Therefore, identification of patients at a high risk for poor prognosis, and prompt initiation of treatment are important in the outcome of TB pericarditis. The aim of this study is to identify the predictive factors for unfavorable outcomes of TB pericarditis in HIV-uninfected persons in an intermediate tuberculosis burden country. METHODS: A retrospective review of 87 cases of TB pericarditis diagnosed at a tertiary referral hospital in South Korea was performed. Clinical characteristics, treatment outcomes, complications during treatment, duration of treatment, and medication history were reviewed. Unfavorable outcome was defined as constrictive pericarditis identified on echocardiography performed 3 to 6 months after initial diagnosis of TB pericarditis, cardiac tamponade requiring emergency pericardiocentesis, or death. Predictive factors for unfavorable outcomes were identified. RESULTS: Of the 87 patients, 44 (50.6%) had unfavorable outcomes; cardiac tamponade (n?=?36), constrictive pericarditis (n?=?18), and mortality (n?=?4). 14 patients experienced both cardiac tamponade and constrictive pericarditis. During a 1 year out-patient clinic follow up, 4 patients required repeat pericardiocentesis and pericardiectomy was performed in 0 patients. In the multivariate analysis, patients with large amounts of pericardial effusion (P?=?.003), those with hypoalbuminemia (P?=?.011), and those without cardiovascular disease (P?=?.011) were found to have a higher risk of unfavorable outcomes. CONCLUSION: HIV-uninfected patients with TB pericarditis are at a higher risk for unfavorable outcomes when presenting with low serum albumin, with large pericardial effusions, and without cardiovascular disease.ope