• Wind and Structures
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• v.20 no.6
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• pp.763-791
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• 2015

"Wind and Ports" is a European project that has been carried out since 2009 to handle wind forecast in port areas through an integrated system made up of an extensive in-situ wind monitoring network, the numerical simulation of wind fields, the statistical analysis of wind climate, and algorithms for medium-term (1-3 days) and short term (0.5-2 hours) wind forecasting. The in-situ wind monitoring network, currently made up of 22 ultrasonic anemometers, provides a unique opportunity for detecting high resolution thunderstorm records and studying their dominant characteristics relevant to wind engineering with special concern for wind actions on structures. In such a framework, the wind velocity of thunderstorms is firstly decomposed into the sum of a slowly-varying mean part plus a residual fluctuation dealt with as a non-stationary random process. The fluctuation, in turn, is expressed as the product of its slowly-varying standard deviation by a reduced turbulence component dealt with as a rapidly-varying stationary Gaussian random process with zero mean and unit standard deviation. The extraction of the mean part of the wind velocity is carried out through a moving average filter, and the effect of the moving average period on the statistical properties of the decomposed signals is evaluated. Among other aspects, special attention is given to the thunderstorm duration, the turbulence intensity, the power spectral density and the integral length scale. Some noteworthy wind velocity ratios that play a crucial role in the thunderstorm loading and response of structures are also analyzed.

• The Journal of Engineering Geology
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• v.10 no.2
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• pp.79-97
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• 2000

Trend of earthquake occurrence of Korea represents that the term from 1978 to 1982 may be called as "active period", the term from 1983 to 1991 is rather tranquil, and from 1992, the occurrence number is increasing greatly. Instrumental earthquake observation of Korea started in 1905 by Japan. It continued until 1943 and ceased then through social disorders such as the independence from Japan Empire and the civil war. After that the observation restarted in 1963 by the establishment the World Wide Standard Seismograph Network. And the fundamental earthquake observation period started in 1978 with the Hongsung earthquake event. KMA(Korea Meteorological Administration) has constructed and operated the 24-hour earthquake and tsunami monitoring system and it propels new construction project of the national seismographic network system. In the result of this project, KMA operates 27 seismic networks, 42 accelerator networks, seismic analyzing system, and sea level monitoring system now. It has the plan to enlarge these systems that 31 seismic networks and 75 accelerator networks until 2001.

• Health Policy and Management
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• v.29 no.2
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• pp.228-236
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• 2019

Background: This study investigates the impact of weekend admission with a patient safety indicator (PSI) on 30-day mortality among long-term insurance beneficiaries. Methods: Data were obtained from the National Health Insurance Service-Senior claim database from 2002 to 2013. To obtain unbiased estimates of odds ratio, we used a nested case-control study design. The cases were individuals who had a 30-day mortality event after their last medical utilization, while controls were selected by incidence density sampling based on age and sex. We examined the interaction between the main independent variables of weekend admission and PSI by categorizing cases into four groups: weekend admission/PSI, weekend admission/non-PSI, weekday admission/PSI, and weekday admission/non-PSI. Results: Of the 83,400 individuals in the database, there were 20,854 cases (25.0%) and 62,546 controls (75.0%). After adjusting for socioeconomic, health status, seasonality, and hospital-level factors, the odds ratios (ORs) of 30-day mortality for weekend admission/PSI (OR, 1.484; 95% confidence interval [CI], 1.371-1.606) and weekday admission/PSI (OR, 1.357; 95% CI, 1.298-1.419) were greater than for patients with weekday admission/non-PSI. Conclusion: This study indicated that there is an increased risk of mortality after weekend admission among patients with PSI as compared with patients admitted during the weekday without a PSI. Therefore, our findings suggest that recognizing these different patterns is important to identify at-risk diagnosis to minimize the excess mortality associated with weekend admission in those with PSI.

• Journal of Climate Change Research
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• v.8 no.2
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• pp.109-123
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• 2017

The effects of recent climate change on hydrological systems could affect the Winter Olympic Games (WOG) because the event is dependent on suitable snow and ice conditions to support elite-level competitions. We investigate the long-term variability and change in winter total precipitation (P), snowfall water equivalent (SFE), and ratios of SFE to P during the period 1973/74~2015/16 in Gangwon province. The climatological percentages of SFE relative to winter total precipitation were 71%, 28%, and 44% in Daegwallyeong, Chuncheon, and Gangneung, respectively. The winter total P, SFE, and SFE/P has decreased (but not significantly), although significant increases of winter maximum and minimum temperature were detected at a 95% confidence level. Notably, a significant negative trend of SFE/P at Daegwallyeong in February, the month of the WOG, was attributable to a larger decrease in SFE related to the increases in maximum and minimum temperature. Winter wet-day minimum temperatures were warmer than climatological minimum temperatures averaged over the study period. The 20-year return values of daily maximum P and SFE decreased in Yongdong area. Since the SFE/P decrease with increasing temperature, the probability of rainfall rather than snowfall can increase if global warming continues.

• Journal of Climate Change Research
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• v.9 no.3
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• pp.209-221
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• 2018

The characteristics of heat wave events in Seoul are analyzed using weather station data from Korea Meteorological Administration (KMA) and European Centre for Medium-Range Weather Forecast (ECMWF) ERA-Interim reanalysis data from 1979 to 2016. Heat waves are defined as events in the upper 10th percentile of the daily maximum temperatures. The associated synoptic weather patterns are then classified into six clusters through Self-Organizing Map (SOM) analysis for sea-level pressure anomalies in East Asia. Cluster 1 shows an anti-cyclonic circulation and weak troughs in southeast and west of Korea, respectively. This synoptic pattern leads to southeasterly winds that advect warm and moist air to the Korean Peninsula. Both clusters 2 and 3 are associated with southerly winds formed by an anti-cyclonic circulation over the east of Korea and cyclonic circulation over the west of Korea. Cluster 4 shows a stagnant weather pattern with weak winds and strong insolation. Clusters 5 and 6 are associated with F?hn wind resulting from an anti-cyclonic circulation in the north of the Korean Peninsula. In terms of long-term variations, event frequencies of clusters 4 and 5 show increasing and decreasing trends, respectively. However, other clusters do not show any long-term trends, indicating that the mechanisms that drive heat wave events in Seoul have remained constant over the last four decades.

• Journal of Chest Surgery
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• v.52 no.2
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• pp.61-69
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• 2019

Background: Scarce data have been reported on the efficacy of concomitant atrial fibrillation (AF) ablation in patients undergoing bioprosthetic valve replacement. Methods: From 2001 and 2014, 146 consecutive patients ($69.3{\pm}9.4years$, 84 females) who underwent bioprosthetic heart valve replacement concomitant with AF ablation were assessed. We evaluated long-term rhythm and valve-related outcomes. Results: During 49.1 months of follow-up (interquartile range, 22.5-96.8 months), 7 in-hospital and 49 (6.7% per person-year) post-discharge deaths occurred. The thromboembolic event-free survival rate at 5 years was $79.2%{\pm}3.5%$. The freedom from AF recurrence rate at 5 years was $59.8%{\pm}4.9%$. Multivariate analysis showed that old age (hazard ratio [HR], 1.06; 95% confidence interval [CI], 1.02-1.11; p=0.002), previous cardiac operation (HR, 3.01; 95% CI, 1.22-7.43; p=0.02), and a large left atrial (LA) dimension (HR, 1.02; 95% CI, 1.00-1.05; p=0.045) were significantly associated with AF recurrence. Conclusion: The overall long-term clinical outcomes in these predominantly elderly patients undergoing AF ablation concomitantly with bioprosthetic valve replacement were satisfactory; however, AF recurrence was frequent. Older age, a history of prior cardiac surgery, and large LA size were associated with an increased risk of AF recurrence.

• Journal of Korean Society on Water Environment
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• v.35 no.1
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• pp.35-42
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• 2019

Urbanization has led to extreme changes in land use on urban watersheds. Most cities are becoming residential, commercial and industrial areas, making infiltration and storage of rainfall less favorable. The demand for LID (Low Impact Development) technology is increasing in order to mitigate this water cycle distortion and return to existing hydrological conditions. The LID technique is effective in reducing runoff by permeating the urban impervious area. However, considering the limit of the installation area and the financial requirement of the installation, there is not much research on the linkage of each LID component technology for optimum efficiency according to the appropriate scale. In this study, the effects of the LID facilities applied to the target site were simulated using the SWMM model, suggesting the optimal linkage method considering interconnectivity, and applying the effects as an existing installation of individual facilities. The water balance at the time of application of the LID technology, short-term and long-term rainfall event were compared. Also, the individual application and the linkage application were compared with each other. If each component technology has sufficient processing size, then linkage application is more effective than individual application.

• Journal of Korea Water Resources Association
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• v.54 no.3
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• pp.157-166
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• 2021

Forecasting dam inflow based on high reliability is required for efficient dam operation. In this study, deep learning technique, which is one of the data-driven methods and has been used in many fields of research, was manipulated to predict the dam inflow. The Long Short-Term Memory deep learning with Sequence-to-Sequence model (LSTM-s2s), which provides high performance in predicting time-series data, was applied for forecasting inflow of Soyang River dam. Various statistical metrics or evaluation indicators, including correlation coefficient (CC), Nash-Sutcliffe efficiency coefficient (NSE), percent bias (PBIAS), and error in peak value (PE), were used to evaluate the predictive performance of the model. The result of this study presented that the LSTM-s2s model showed high accuracy in the prediction of dam inflow and also provided good performance for runoff event based runoff prediction. It was found that the deep learning based approach could be used for efficient dam operation for water resource management during wet and dry seasons.

• Journal of Chest Surgery
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• v.43 no.3
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• pp.246-253
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• 2010

Background: Our objective was to review the long-term prognosis of patients with preoperative mild to moderate ischemic mitral regurgitation who underwent off-pump coronary artery bypass grafting. Material and Method: We prospectively followed 1,000 consecutive and systematic off-pump coronary artery bypass grafting patients who were operated on between September 1996 and March 2004; follow-up was achieved for 97%. Sixty-seven patients (6.7%) had mild to moderate ischemic mitral regurgitation at the time of surgery. Operative mortality, actuarial survival and major adverse cardiac event free survival were compared to assess the effect of ischemic mitral regurgitation. Result: Average follow-up was $66{\pm}22$ months. Patients with ischemic mitral regurgitation were older (p<0.001), had lower ejection fractions (p<0.001) and more comorbidities. Significantly more female patients presented with ischemic mitral regurgitation (p=0.002). There was no significant difference in operative mortality and perioperative myocardial infarction in ischemic mitral regurgitation patients (p=0.25). Eight-year survival was decreased in ischemic mitral regurgitation patients ($39.6{\pm}11.8%$ vs $76.7{\pm}2.2$, p<0.001). However, after correcting for risk factors, mild to moderate ischemic mitral regurgitation was not found to be a significant independent risk factor for long-term mortality (p=0.42). Major adverse cardiac event free survival at 8 years was significantly lower in ischemic mitral regurgitation patients ($53.12{\pm}12%$ vs $77{\pm}2%$, p<0.001). After correction for risk factors, ischemic mitral regurgitation remained a significant independent cause of major adverse cardiac events (HR: 2.31), especially congestive heart failure and recurrent myocardial infarction. Conclusion: In our series, patients with preoperative mild to moderate ischemic mitral regurgitation had a higher prevalence of preoperative risk factors than patients without ischemic mitral regurgitation. They had comparable perioperative mortality and morbidity, but, in the long term, were found to be at elevated risk for recurrent cardiac events.

• Asia-Pacific Journal of Business Venturing and Entrepreneurship
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• v.4 no.4
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• pp.45-70
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• 2009

This article investigates which types of the strategies announced by the listed firms contribute to enhancing the long-term performance of the companies. Since 2002, Korean Exchange adopted the "faire disclosure policy" which mandates that all publicly traded companies must disclose material information to all investors at the same time. Thanks to the policy, Korean investors can, now, easily access the board's decision on management strategies on the same day the decision is made. If the companies trustfully carry out their announced strategies, we can decide which types of strategies actually enhance or deteriorate the long-term performance, simply by comparing the announced strategies and the firm's performance. The sample companies are confined to 60 firms that became listed in the KOSDAQ market through back-door listing from 2003 to 2005. Using only the newly listed companies, we can avoid the interference on the long-term performance of the strategies pursued before the event date. This often holds true, for many companies radically modify their strategies after the listing. Furthermore, the back-door listing companies serve our purpose better than IPO companies do, because the former tend to have a variety of announcement within a given period of time beginning the listing date. Using these sample companies, this article analyzes the effect on one year buy-and-hold returns and abnormal buy-and-hold returns after the listing of the various types of strategies announced during the same period of time. The results show that those evidences of restructuring such as 'reduction of capital' and 'resignation of incumbent board members', actually contribute to the increase in adjusted long-term stock returns. Those strategies which can be view as evidence of new investment such as 'increase in tangible assets', 'acquisition of other companies', do also helps the stockholders better off. On the contrary, 'increase in bank loans', 'changes of CEO' and 'merger' deteriorate the equity value. The last findings let us to presume that the back-door listing companies appear to use the bank loans for value-reducing activities; the change in CEO is not a sign of restructuring, but rather a sign of failure of the restructuring; another merger carried out after back-door listing itself is also value-reducing activity. This article's findings on reduction of capital, merger and bank loans oppose the results of the former empirical studies which analyze only the short-term effect on stock price. Therefore, more long-term performance studies on public disclosures are in order.