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유기 금속 화학 증착법(MOCVD)의 희석된 SiH4을 활용한 Si-Doped β-Ga2O3 에피 성장
김형윤,김선재,천현우,이재형,전대우,박지현 한국재료학회 2023 한국재료학회지 Vol.33 No.12
β-Ga2O3 has become the focus of considerable attention as an ultra-wide bandgap semiconductor following the successful development of bulk single crystals using the melt growth method. Accordingly, homoepitaxy studies, where the interface between the substrate and the epilayer is not problematic, have become mainstream and many results have been published. However, because the cost of homo-substrates is high, research is still mainly at the laboratory level and has not yet been scaled up to commercialization. To overcome this problem, many researchers are trying to grow high quality Ga2O3 epilayers on hetero-substrates. We used diluted SiH4 gas to control the doping concentration during the heteroepitaxial growth of β-Ga2O3 on c-plane sapphire using metal organic chemical vapor deposition (MOCVD). Despite the high level of defect density inside the grown β-Ga2O3 epilayer due to the aggregation of random rotated domains, the carrier concentration could be controlled from 1 × 1019 to 1 × 1016 cm-3 by diluting the SiH4 gas concentration. This study indicates that β-Ga2O3 hetero-epitaxy has similar potential to homo-epitaxy and is expected to accelerate the commercialization of β-Ga2O3 applications with the advantage of low substrate cost.
Determinants of sensitization to allergen in infants and young children
김형윤,신윤호,한만용 대한소아청소년과학회 2014 Clinical and Experimental Pediatrics (CEP) Vol.57 No.5
Atopic sensitization is a complex phenomenon that changes dynamically with age throughout childhood;its prevalence increases with age in young children. Additionally, with increasing age, the prevalenceof sensitization to inhalant allergens and the prevalence of polysensitization to allergens increase. It isalso well established that the development of atopic sensitization is the result of a complex interplayof genetic and environmental factors. However, there is considerable heterogeneity in the literature interms of the effect of different environmental exposures in young children on the subsequent risk ofatopic sensitization and allergic diseases. Previous studies on the relationship, in early life, between petownership, sex, exposure to secondhand smoke, exposure to traffic-related air pollution components,and atopic sensitization have yielded different results. Recent studies have highlighted the importanceof gene-environment interactions, especially during early childhood, on the risk of subsequent atopicsensitization and allergic diseases. Therefore, pediatricians should consider the genetic and environmentaldeterminants of atopic sensitization in infants and young children when diagnosing and treatingpatients with allergic diseases. Determining ways in which early exposure to these risk factors in youngchildren may be reduced could be beneficial in preventing the likelihood of developing atopic sensitization.
김형윤,이상철,박성지,최진오,장성아,김성목,최연현,오재건,박승우 한국심초음파학회 2015 Journal of Cardiovascular Imaging (J Cardiovasc Im Vol.23 No.3
Transesophageal echocardiography (TEE) is considered relatively safe but semi-invasive. The hypopharyngeal and esophagealinjury is infrequent complication of TEE but could be serious, even life-threatening. We present a case of a 74-year-old manwho experienced a deep neck infection secondary to hypopharyngeal injury following TEE. The diagnosis was made becauseof the subcutaneous emphysema developed 3 hours after TEE. In spite of antibiotics therapy with prolonged fasting, a rightparapharyngeal and retropharyngeal abscess was developed 5 days later. With ultrasound-guided drainage of abscess andcontinuous antibiotic treatment, infection was controlled. The patent underwent mitral valve repair after 14 days of antibiotictherapy. The patient recovered uneventfully. For cardiologists performing TEE, it is required to know complications and theirrisk factors to minimize hypopharyngeal and esophageal injury.
Natural Course of Adult Ebstein Anomaly When Treated according to Current Recommendation
김형윤,장신이,문주령,김은경,장성아,송진영,허준,강이석,양지혁,전태국,박승우 대한의학회 2016 Journal of Korean medical science Vol.31 No.11
The objectives of this study were to assess the clinical outcomes of adults with Ebstein Anomaly (EA) according to their treatment modalities. All adult EA patients diagnosed between October 1994 and October 2014 were retrospectively evaluated by medical record review. Total 60 patients were categorized into 3 groups according to their treatment strategy, i.e. non-operative treatment (Group I, n = 23), immediate operative treatment (Group II, n = 27), and delayed operative treatment (Group III, n = 10). A composite of major adverse cardiac and cerebrovascular events (MACCE) and factors associated with MACCE were assessed in each treatment group. MACCE occurred in 13.0% patients in Group I, 55.6% patients in Group II and 50% in Group III (P = 0.006). Event free survivals at 5 years were 90% in Group I, 52.7% in Group II, 50.0% in Group III (P = 0.036). Post-operatively, most patients showed improvement on clinical symptoms. However, event free survival rate was lower in patients with operation compared to those with non-operative treatment (58.7% vs. 90.9%; P = 0.007). Major arrhythmic event occurred more frequently even after surgical ablation (50.0% vs. 20.0%; P = 0.034). Re-operation was more frequent in patients underwent delayed surgery compared to those with immediate surgery (50.0% vs. 18.5%; P = 0.001). Current guideline to decide patient’s treatment strategy appeared to be appropriate in adult patients with EA. However, surgical ablation for arrhythmia was not enough so that concomitant medical treatment should be considered. Therefore, attentive risk stratification and cautious decision of treatment strategy by experienced cardiac surgeon are believed to improve clinical outcome.
How to Utilize Coronary Computed Tomography Angiography in the Treatment of Coronary Artery Disease
김형윤,최진호 한국심초음파학회 2015 Journal of Cardiovascular Imaging (J Cardiovasc Im Vol.23 No.4
Coronary computed tomography angiography (CCTA) has high negative predictive power for detecting coronary artery disease. However CCTA is limited by moderate positive predictive power in the detection of myocardial ischemia. This is not unexpectedbecause the diameter of a stenosis is a poor indicator of myocardial ischemia and discrepancy between the severity of stenosis andnoninvasive tests is not uncommon. The value of stenosis for predicting future development of acute coronary syndrome representedby plaque rupture has been questioned. CCTA identifies the characteristics of high-risk plaque including positive remodeling,low density plaque and spotty or micro-calcification. Also, additional evaluation of myocardial ischemia using computationalflow dynamics, and luminal attenuation gradient are expected to increase both diagnostic performance for hemodynamicallysignificant stenosis and the predictive power for future cardiovascular risk. Technical advances in CCTA would enable evaluationof both coronary artery stenosis and myocardial ischemia simultaneously with high predictive performance, and would improvevastly the clinical value of CCTA.
A Rare Case of Aortic Valve Myxoma: Easy to Confuse With Papillary Fibroelastoma
김형윤,권성욱,장우익,김한성,김진석,이한상,박민영,김태완,이성윤,도준형,남궁준,이원로 대한심장학회 2012 Korean Circulation Journal Vol.42 No.4
Myxoma of the aortic valve is an exceedingly uncommon condition. In this article, we report the case of a 72-year-old man with myxoma arising from the aortic valve. We extirpated the mass and repaired the aortic valve with the patient under cardiopulmonary bypass. The postoperative course was uneventful. Histological examination confirmed that the mass was a myxoma.