• Journal of the Korean Operations Research and Management Science Society
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• v.1 no.1
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• pp.111-125
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• 1976

This study investigates the one-year performance of the Seoul Metropolitan Rail Transit(SMRT) operation. It intends to provide a basic understanding for railway operation in Seoul Metropolitan Area and thereby for making rational transport policy. The paper is conceptually comprised of four sections; analysis of passenger travel characteristics; SMRT costing and traffic cost function: its operating characteristics in terms of finance and utilization; primary social benefits of SMRT and suggestions. In the first year of operation (1974), the average daily traffic was about 335,000, After the drastic increases of fare in both Subway and KNR rail-lines, the travel volume has been cut by almost 10 percent, though most pronounced on intra-Subway line. The spatial distribution of passengers indicates that travelers use the SMRT line mainly for uninterrupted direct travel toward the CBD. In the prospective costing, the opereting expenses are divided into three groups; those which vary directly with volume; those partially variable with volume; and those entirely unrelated to volume change, With this information, cost function was derived for varying schedules of operation. Primary social benefits of the SMRT are assessed, though preliminary. Account should be taken of the nature of common costs of the SMRT in fare-rate making, especially when much of the operating expenses are accounted for by the fixed costs such that the revenue may not readily turn into break-even. The accounting results of the one-year operation coincide reasonably well with the prospective costing estimates. According to the findings of this annd another travelers' behavior studies, managerial effort would bring more revenue gain to the SMRT than fare increase does, not to speak of greater social benefits by so doing.

• Journal of Preventive Medicine and Public Health
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• v.24 no.3 s.35
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• pp.400-413
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• 1991

The purpose of this paper is to identify factors affecting the optimum mix of required inputs and other relevant factors which account for the variation in physician's productivity in general hospitals, and to find out their implications for the efficient health planning and management. An extended version of Cobb-Douglas production function and cross sectional data of one day patient census from all general hospitals in Korea in 1988 were used in the analysis. Main results of the analysis and their implications could be summarized as follows : (1) The production function for physician's inpatient service shows the evidence of economies of scale, but the production function for physician's outpatient and adjusted-patient service, which combines both out- and in-patient service, shows that of dis-economies of scale. (2) The physician's role for production for all service is smaller than auxiliary personnel's, which imply that more intensive utilization of nurses, nursing aides and other auxiliary personnel is desirable for improving general hospital productivity (3) In case of physician's inpatient and adjusted-patient service, nurses' role is greater than nursing aides'. Therefore, more extensive utilization of nurses is recommended for the efficient operation of general hospitals. (4) The factor of hospital beds plays the leading role among required inputs in the production for physician's in- and adjusted-patient service. (5) The physician's productivity of general hospitals in rural area is lower than that in urban area. And the productivity of teaching hospitals is lower than that of the other hospitals. Further analysis was made in physician production function based upon the size of hospitals, namely those hospitals below 250 beds and those above. Explained variances by the factor of hospital beds was significantly increased in the case of those hospitals above 250. A more detailed and thorough investigation is needed for verifying factors influencing physician's productivity in general hospitals in Korea.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.10 no.1
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• pp.58-73
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• 2000

Objectives : This study was performed to evaluate BTEX exposure to gas station service attendants and the critical affect of benzene and MtBE airborne concentration. Methods : the degree of exposure to airborne BTEX and MtBE was examined in the service attendants at seven gas stations across the country during a summer season. The TWAs(time-weighted averages) of atmospheric concentration of substances in personal and area samples, were calculated. The component ratio of BTEX and MtBE in the samples of bulk gasoline from each station studied was also measured. Results : The airborne concentrations of BTEX and MtBE showed a lognormal distribution and The TWA concentrations of benzene in personal samples from each station were 0.089 ppm - 0.18 ppm, and those of toluene were 0.097 ppm - 0.2 ppm. The average TWA concentrations of xylene and ethyl benzene was 0.03 ppm and 0.001 ppm, respectively. The TWA concentrations of MtBE were 0.4 ppm - 1.3 ppm. The volume concentrations of MtBE, toluene, ethyl benzene and xylene in the bulk gasoline samples were 3 - 7.4 %, 3 - 12 %, 0.64 % and 1.5 - 10 %, respectively. Conclusions : The benzene concentration was detected to exceed the ACGIH threshold benzene level of 0.5 ppm, in one of 74 personal and area samples. MtBE, a substitute for aromatic compounds such as benzene in gasoline, was found to bring about a greater chance of exposure to carcinogen, due to its high vapor pressure and carcinogenicity.

• Journal of the Korean association of regional geographers
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• v.16 no.2
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• pp.123-136
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• 2010

To grasp the migration characteristics in the Busan Metropolitan Area (BMA), this study analyzed household characteristics and migration selectivity. The major findings of the study are as follows: first, young (especially 25 to 34 years of age) and single person households have greater propensity to migrate out from BMA, and their home ownership rate is low. These trends are much stronger in households that migrate out towards the Seoul Metropolitan Area from Busan. Second, age and educational selectivity of migration is evident. The characteristics of movers are quite different from those of stayers at Busan. Young people are more likely to migrate out of Busan, and higher levels of education are deeply associated with higher mobility. Through analyzing four high schools in Busan, it is acknowledged that most honor students entered 4-year universities in Seoul. The outflow of highly educated young people may induce the brain drain. Busan is undergoing both population decline and the problems caused by the brain drain.

• Journal of Energy Engineering
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• v.24 no.4
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• pp.71-80
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• 2015

Steel stiffener is required for reinforcing the structure of the window frame made of versatile but weak PVC material. Steel stiffener however becomes a source of greater heat loss and frequently plays a role of thermal bridge due to its high thermal conductivity. To maintain thermal resistance similar to PVC frame, steel stiffener is perforated to reduce the effective heat transfer area. To compensate the structural strength of the steel stiffener which is weakened by the perforation, the thickness is increased. Increase in thickness will also increase the thermal heat resistance. Five samples which are PVC frame, PVC frame + original steel stiffener, PVC frame + 30% perforated steel stiffener, PVC frame + 50% perforated steel stiffener, PVC frame + 65% perforated steel stiffener are modeled and simulated for 2nd moment of area and thermal resistance. Therm/window version 6.3 is used for thermal analysis. The results show that among the five samples analyzed, PVC frame + 65% perforated steel stiffener best satisfies both structural strength and thermal resistance.

• Journal of Chest Surgery
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• v.53 no.6
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• pp.325-331
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• 2020

Background: We evaluated the association between tricuspid annular dilatation and the development of moderate or severe tricuspid regurgitation (TR). Additionally, we determined the optimal tricuspid annular dilatation threshold to use as an indicator for tricuspid annuloplasty in patients with less-than-moderate functional TR (FTR). Methods: Between August 2007 and December 2014, 227 patients with less-than-moderate TR underwent mitral valve surgery without a tricuspid valve (TV) procedure. The TV annular diameter was measured via transthoracic echocardiography. The TV annular index (TVAI) was calculated as the TV annular diameter divided by the body surface area. The mean duration of echocardiographic follow-up was 42.0 months (interquartile range, 9.3-66.6 months). Results: Eight patients (3.5%) developed moderate or severe TR. The rate of freedom from development of moderate or severe TR at 5 years was 96.2%. TV annular diameter, left atrial diameter, preoperative atrial fibrillation, and TVAI were found to be associated with the development of moderate or severe TR in the univariate analysis. A cut-off TVAI value of 19.8 mm/㎡ was found to predict the development of moderate or severe TR, and a significant difference was observed in the development of TR of this severity based on this cut-off (p<0.001). Conclusion: The progression of TR was not infrequent in patients with untreated lessthan-moderate FTR. An aggressive treatment approach can be helpful to prevent the progression of FTR for patients with risk factors, especially TVAI greater than 19.8 mm/㎡.

• The Korean Journal of Ecology
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• v.19 no.4
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• pp.253-261
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• 1996

This study was conducted to clarify the relationship between bird community and forest structure from early May to mid June, 1988 in two sites which had different forest structures due to silvicultural practice, located in the Tomakomai Experimental Forest of Hokkaido University, Hokkaido, Japan. Quantitative ahbitat analysis was applied to elucidate difference between the two study sites, and territory mapping method and guild analysis were used for assessment of the bird community. Dominant tree species were Quercus mongolica, Magnolia obovata, Prunus sargentii, Acer mono and Tilia japonica. Unithinned site had more foliage coverage in upper and middle layers, but in lower layer had less coverage than thinned site. Thirty four species of birds were recorded and of them only 21 species occupied territories within the study area. Dominant species were Ficedula narcissina, Phylloscopus occipitalis, Parus major, Passer rutilans, Sitta europaea and Parus palustris in the study area. The unmber of breeding species of the two sites were equal, but the species composition of breeding bird communities was different between the sites. The number of species and pairs on hole-nesting guild were greater in the unthinned site, but those on ground-nesting guild were greater in the thinned site. Canopy-nesting guild showed no significant difference between the two sites. Silvicultural practice such as proper thinning appeared to be not inadequate to all of the forest birds, probably good to bush and ground nesting guild, and to tree & bush and ground foraging guild. The silvicultural practice also did not considerably affect the hole and canopy-nesting guild.

• Journal of Korean Society of Transportation
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• v.26 no.1
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• pp.25-35
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• 2008

The ridership and transit systems are influenced by the expansion of metro-rail in Seoul metropolitan area. However, it has been difficult to measure its precise quantitative influences. Also effective policy implementations have been limited due to the lack of practical evidences. Thus an empirical analysis for an operating metro-rail is essentially required. In this regard, this study examines the impact of the Jungang line on transportation system, whose metro-rail block has been recently started new service. The main interest of this study is to find out the changes of ridership and to forecast the ridership changes by the metro-rail service. The results indicate that the effect on auto users is less than that of bus users. The auto demand is decreased by 33.3% and the bus demand by 66.6%. Additionally, its influence on Gyeonggi-do bus was greater compared with that on the Seoul bus. From questionnaire survey, this results could be confirmed. To sum up, the metro-rail gives less influences on auto users, while it gives greater influences on bus users.

• Korean Journal of Radiology
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• v.24 no.12
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• pp.1190-1199
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• 2023

Objective: This study aimed to investigate the feasibility of ultrafast magnetic resonance imaging (MRI) and radiomic features derived from breast MRI for predicting the upstaging of ductal carcinoma in situ (DCIS) diagnosed using percutaneous needle biopsy. Materials and Methods: Between August 2018 and June 2020, 95 patients with 98 DCIS lesions who underwent preoperative breast MRI, including an ultrafast sequence, and subsequent surgery were included. Four ultrafast MRI parameters were analyzed: time-to-enhancement, maximum slope (MS), area under the curve for 60 s after enhancement, and time-to-peak enhancement. One hundred and seven radiomic features were extracted for the whole tumor on the first post-contrast T1WI and T2WI using PyRadiomics. Clinicopathological characteristics, ultrafast MRI findings, and radiomic features were compared between the pure DCIS and DCIS with invasion groups. Prediction models, incorporating clinicopathological, ultrafast MRI, and radiomic features, were developed. Receiver operating characteristic curve analysis and area under the curve (AUC) were used to evaluate model performance in distinguishing between the two groups using leave-one-out cross-validation. Results: Thirty-six of the 98 lesions (36.7%) were confirmed to have invasive components after surgery. Compared to the pure DCIS group, the DCIS with invasion group had a higher nuclear grade (P < 0.001), larger mean lesion size (P = 0.038), larger mean MS (P = 0.002), and different radiomic-related characteristics, including a more extensive tumor volume; higher maximum gray-level intensity; coarser, more complex, and heterogeneous texture; and a greater concentration of high gray-level intensity. No significant differences in AUCs were found between the model incorporating nuclear grade and lesion size (0.687) and the models integrating additional ultrafast MRI and radiomic features (0.680-0.732). Conclusion: High nuclear grade, larger lesion size, larger MS, and multiple radiomic features were associated with DCIS upstaging. However, the addition of MS and radiomic features to the prediction model did not significantly improve the prediction performance.

• Journal of Korean Society of Rural Planning
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• v.19 no.1
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• pp.109-122
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• 2013

The rapid rural urban migration and aging has generated an over-depopulation problems in rural areas since the 1980s. The purpose of this study constructs the marginal size of rural over-depopulated village through the analysis of the residential disparities such as farmer's ratio, basic life service accessibility, and levels of social and economic factors for each village community. This marginal scale could support evaluating diverse rural policies, which have been planned to apply to the rural development programs at the village level. The major challenges for over-depopulated villages are the lack of basic facilities, production infrastructures and inactive communities in the village. Therefore, the quantitative analysis of rural residential disparities according to rural village scale can provide the criteria for rural over-depopulated villages. We utilized Korea Agricultural Survey Data(2010) including specific residential condition of village level. The present study adopt multinomial-logit model for quantitative analysis of different village scales and decomposition techniques to separate the direct effect by the village scale factor from the endowment effects by regional or area characteristics, and residual effect by unknown factors. The present study found that the minimum scale of a rural over-depopulated village was 40 and 60 houses for the respective conditions of farmer's ratios less than 50% and greater than 75%. It was concluded based on the study findings that threshold scale could support evaluating the diverse rural policies, which have been planned to apply to the rural development programs at the village level.