• Progress in Medical Physics
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• v.20 no.2
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• pp.80-87
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• 2009

Phase transformation, superelastic characteristics and variation of surface residual stress were studied for Nitinol shape memory alloy through application of UNSM technology, and life extension methods of stent were also studied by using elastic resilience and corrosion resistance. Nitinol wire of ${\phi}1.778$ mm showed similar surface roughness before and after UNSM treatment, but drawing traces and micro defects were all removed by UNSM treatment. It also changed the surface residual stress from tensile to compressive values, and XRD result showed less intensive austenite peak and clear martensite and additional R-phase peaks after UNSM treatment. Fatigue resistance could be greatly improved through removal of surface defects and rearrangement of surface residual stress from tensile to compressive state, and development of surface modification system to improve not only bio-compatability but also resistance to corrosion and wear will make it possible to develop vascular stent which can be used for circulating system diseases which run first cause of death of recent Koreans.

• Clinical and Experimental Pediatrics
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• v.49 no.6
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• pp.623-629
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• 2006

Purpose : The mortality rate of neonatal sepsis has been decreased, however, the incidence has not significantly decreased because of increased invasive procedures. This study was designed to make guidelines for choosing antibiotics by analyzing the causative microorganisms and their antibiotics sensitivity test according to the onset of neonatal sepsis. Methods : One hundred seven cases of culture proven sepsis in 89 patients admitted to the NICU of Chonnam University Hospital from Jan. 2000 to Dec. 2004, were enrolled. By reviewing the medical records, clinical data, laboratory findings, causative organisms and their antibiotics sensitivity, and mortality were analyzed. Results : The incidence of neonatal sepsis was 1.7 percent and more prevalent in premature and low birth weight infants. 85.4 percent of neonatal sepsis was late onset. Almost all microorganisms(92.9 percent) were gram-positive in early onset, however, two thirds were gram-positive and one third were gram-negative and Candida in late onset. Gram-negative organisms and Candida were more prevalent in patients who had central line. Gram-positive organisms were sensitive to vancomycin, teicoplanin, and gram-negative were sensitive to imipenem, and cefotaxime. Conclusion : Neonatal sepsis was more prevalent in premature and low birth weight infants. More than 90 percent were gram-positive in early onset, however, one third was gram-negative and Candida in late onset. The first choice of antibiotics were a combination of third generation cephalosporin and clindamycin in early onset, and third generation cephalosporin and glycopeptide in late onset. If there is no response to antibiotics treatment, the use of antifungal agents should be considered.

• Journal of Chest Surgery
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• v.40 no.12
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• pp.811-816
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• 2007

Background: We analyzed our experience of arrhythmia surgery in patients with congenital heart disease. Material and Method: A retrospective review was performed on 43 consecutive patients with congenital heart disease, who underwent arrhythmia surgery between June 1998 and June 2006. Result: The median age at surgery was 52 years ($4{\sim}75$ years). The most frequent cardiac anomaly was an atrial septal defect (23/43, 53.5%). The types of arrhythmias were atrial flutter-fibrillation, intermittent non-sustainable ventricular tachycardia and others in 37, 2 and 4, respectively. Arrhythmia surgery consisted of a bi-atrial maze operation in 18 patients (modified cox maze III procedure in 5 patients, and a right side maze plus pulmonary vein cryo-isolation in 13), right side maze operation in 18 patients, cavo-tricuspid isthmus cryoablation for benign atrial flutter in 4 patients, right ventricular endocardial cryoablation in 2 patients and extranodal cryoablation for atrioventricular node re-entry tachycardia in 1 patient. The median follow-up was 23.8 months ($1{\sim}95.2$ months). There was no early mortality, and one late non-cardiac related death. The overall rates of restored sinus rhythm before discharge and $3{\sim}6$ months after surgery were 79% and 81%, respectively (bi-atrial maze group: 72% and 83%, right-side maze group: 77%, 77%). Conclusion: Arrhythmias associated with congenital heart disease can be safely treated surgically with an excellent intermediate-term outcome.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.517-528
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• 2007

Domestic or international existing researches regarding rail damage factors are focused on laying, vehicle conditions, driving speed and driving habits and overlook characteristics of track structure (elasticity, maintenance etc). Also in ballast track, as there is no special lateral spring stiffness of track also called as ballast lateral resistance in concrete track, generally, existing study shows concrete track has 2 time shorter life cycle for rail replacement than ballast track due to abrasion. As a result of domestic concrete track design and operation performance review, concrete track elasticity is lower than track elasticity of ballast track resulting higher damage on rail and tracks. Generally, concrete track has advantage in track elasticity adjustment than ballast track and in case of Europe, in concrete track design, it is recommended to have same or higher performance range of vertical elastic stiffness of ballast track but domestically or internationally review on lateral spring stiffness of track is very minimal. Therefore, through analysis of service line track on site measurement and analysis on performance of maintenance, in this research, dynamic characteristic behaviors of commonly used ballast and concrete track are studied to infer elasticity of service line track and experimentally prove effects of track lateral spring stiffness that influence curved rail damage as well as correlation between track elasticity by track system and rail damage to propose importance of appropriate elastic stiffness level for concrete and ballast track.