• Journal of Korean Society of Water and Wastewater
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• v.13 no.1
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• pp.95-112
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• 1999

In this research, it is proposed that optimization method is introduced and applied to the design of pipeline system in multi-regional water supply project, which has been constructed to settle the regional unbalance problems of available water resources. For the purpose, interface programs are developed to integrate linear programming model and KYPIPE model which is used for optimization and hydraulic analysis, respectively. The developed program is applied to the pipeline system design of multi-regional water supply project. The optimal diameters from the application of linear programming technique are compared with those from conventional method that is time-consuming and tedious trail and error process. Since the conventional design largely depends upon the experience of designers and the results of general hydraulic analysis, it can not be reasonable and consistent. The application of linear programming technique can make it possible to design pipeline system optimally by using same design factors of general hydraulic models. The model can select commercial discrete pipe diameter as optimal size by using pipe length as decision variables. The developed model is applied to Pohang multi-regional water supply system design with two different objective functions, which are initial construction cost and annual cost including electric cost. As results, it is calculated that the initial construction cost of 1,449,740 thousand won is saved and annual cost of 128,951 thousand won is saved for a year within study year. Also, the optimal site of pump station is selected on 5th pipe, which is located between the diverging junction to Kangdong(2) province and the diverging junction to Cheonbuk province. It is explained that pump cost is less than pipe cost in this application case study due to little pump station scale. In the case of water supply with large pump capacity, it is reasonal that the increase of pipe size is more efficient instead the increase of pump station capacity to save annual cost.

• Journal of agriculture & life science
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• v.44 no.3
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• pp.89-97
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• 2010

In the contingent valuation method (CVM) survey, we employed double-bounded discrete choice (DBDC) question to investigate the willingness to pay (WTP). The estimation results for the bivariate logit model show that respondents are willing to pay 329,256 won per year. The model with covariate variables suggests that the covariate effects help describe behavioral or preference tendencies. Double-bounded models increase efficiency over single dichotomous choice models, because the answers yes-no or no-yes yield clear bounds on WTP.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.36 no.5
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• pp.177-185
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• 2020

The building energy performance indicator, called Energy Performance Index (EPI), has been used for the past decades in South Korea. It has a list of design variables assigned with weighting factors (a, b). Unfortunately, the current EPI method is not performance-based but very close to a prescriptive rating. With this in mind, this study aims to propose a new performance-based EPI method. For this purpose, a global sensitivity analysis method, Sobol, is employed. The Sobol method is suitable for complex nonlinear models and can decompose all the output variance due to every input. The Sobol sensitivity index of each variable is defined as 0 to 1 (0 to 100%), and the sum of all sensitivity indices is equal to 1 (100%). In this study, an office building was modeled using EnergyPlus and then the Latin Hypercube Sampling (LHS) was conducted to generate a surrogate model to EnergyPlus. The sensitivity index was suggested to replace weight (a) in the existing EPI. In addition, the discrete weight (b) in the existing EPI was replaced by a set of continuous regression functions. Due to the introduction of the sensitivity index and the continuous regression functions, the new proposed approach can provide far more accurate outcome than the existing EPI (R²: 0.83 vs. R²: 0.01 for cooling, R²: 0.66 vs. R²: 0.01 for total energy). The new proposed approach proves to be more rational, objective and performance-based than the existing EPI method.

• Journal of the Architectural Institute of Korea Structure & Construction
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• v.33 no.12
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• pp.45-52
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• 2017

The precast concrete (PC) method has many advantages in fast construction, quality control, etc. In domestic construction market, however, its application has been quite limited because of the concerns about structural integrity and seismic performances due to the discrete connections between precast concrete members. By applying the post-tensioning method, the precast beam-column connection can be well tightened, allowing improved structural integrity, and proper seismic performances can be also achieved. In this study, reversed cyclic tests have been conducted on the beam-column connection specimens, where the test variables included the compressive strength of grouting mortar and the tensile strengths of prestressing strands, based on which their seismic performances have been examined in detail. The post-tensioned PC beam-column connections showed good seismic performances comparable to that of the monolithic reinforced concrete connection specimen. When 2400 MPa prestressing strands are applied to the beam-column connection, it is preferable to adjust the prestress level similar to that applied for the 1860 MPa prestressing strands to avoid premature local crushing failures at the beam-column connections.

• Nuclear Engineering and Technology
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• v.54 no.1
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• pp.49-60
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• 2022

Motivated by the high-resolution properties of high-order Weighted Essentially Non-Oscillatory (WENO) and flux limiter (FL) for steep-gradient problems and the robust convergence of Jacobian-free Newton-Krylov (JFNK) methods for nonlinear systems, the preconditioned JFNK fully implicit high-order WENO and FL schemes are proposed to solve the transient two-phase two-fluid models. Specially, the second-order fully-implicit BDF2 is used for the temporal operator and then the third-order WENO schemes and various flux limiters can be adopted to discrete the spatial operator. For the sake of the generalization of the finite-difference-based preconditioning acceleration methods and the excellent convergence to solve the complicated and various operational conditions, the random vector instead of the initial condition is skillfully chosen as the solving variables to obtain better sparsity pattern or more positions of non-zero elements in this paper. Finally, the WENO_JFNK and FL_JFNK codes are developed and then the two-phase steep-gradient problem, phase appearance/disappearance problem, U-tube problem and linear advection problem are tested to analyze the convergence, computational cost and efficiency in detailed. Numerical results show that WENO_JFNK and FL_JFNK can significantly reduce numerical diffusion and obtain better solutions than traditional methods. WENO_JFNK gives more stable and accurate solutions than FL_JFNK for the test problems and the proposed finite-difference-based preconditioning acceleration methods based on the random vector can significantly improve the convergence speed and efficiency.

• Nuclear Engineering and Technology
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• v.25 no.1
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• pp.154-165
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• 1993

A stochastic method using continuous time Markov process is presented to model the one-dimensional convective nuclide transport in geologic media, which have usually heterogeneous feature in physical/geochemical parameters such as velocity, dispersion coefficient, and retardation factor resulting poor description by conventional deterministic advection-dispersion model. The primary desired quantities from a stochastic model are the mean values and variance of the state variables as a function of time. The time-dependent probability distributions of nuclides are presented for each discretized compartment given the volumetric groundwater flux and the intensity of transition. Since this model is discrete in medium space, physical/geochemical parameters which affect nuclide transport can be easily incorporated for the heterogeneous media as well as remarkably layered media having spatially varied parameters. Even though the Markov process model developed in this study was shown to be sensitive to the number of discretized compartments showing numerical dispersion as the number of compartments are increased, this could be easily calibrated by comparing with the analytical deterministic model.

• Asian Pacific Journal of Cancer Prevention
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• v.17 no.3
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• pp.1187-1191
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• 2016

Background: The prevalence of prostate cancer (PCa) has been increasing in recent years. Treatment strategies are largely based on the results of bone scan screening. Therefore, our aim was to investigate predictors of positive bone metastasis in newly diagnosed PCa patients. Materials and Methods: After extensive review, 336 consecutive patients newly diagnosed with PCa between April 2010 and November 2013 at our institution were enlisted in the study. Patients were divided into two groups according to bone scan results. Univariate analyses (Chi-square test for discrete variables and independent t-test for continuous variables) were applied to determine the potentially significant risk factors associated with distant bone metastasis. Binary logistic regression analyses were used to further investigate the influence of these factors on bone metastasis. Results: The patient mean age was $71.9{\pm}8.6years$ (range: 48 to 94 years). The mean prostate specific antigen (PSA) level and biopsy Gleason score were $260.2{\pm}1107.8ng/mL$ and $7.4{\pm}1.5$, respectively. The body mass index (BMI) for the series was $24.5{\pm}3.4kg/m^2$. Sixty-four patients (19.0%) had a positive bone scan result. Patients with positive bone scan results had a significantly lower BMI ($23.3{\pm}3.5$ vs. $24.8{\pm}3.3$; p=0.003), a higher Gleason score ($8.5{\pm}1.1$ vs. $7.1{\pm}1.5$; p < 0.001), and a higher PSA level ($1071.3{\pm}2337.1$ vs. $69.4{\pm}235.5$; p < 0.001) than those without bone metastasis. Multivariate logistic regression analysis employing the above independent predictors demonstrated that a Gleason score of ${\geq}7$, clinical stage ${\geq}T3$, $BMI{\leq}22kg/m^2$, and an initial PSA level of ${\geq}20ng/mL$ were all independent predictors of bone metastasis. Conclusions: A bone scan might be necessary in newly diagnosed PCa patients with any of the following criteria: clinical stage T3 or higher, a Gleason score of 7 or higher, BMI equal to or less than 22, and a PSA level of 20 or higher.

• Journal of Agricultural Extension & Community Development
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• v.19 no.4
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• pp.961-987
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• 2012

The present study is to investigate the characteristics and determinants of spatial distribution of strong small farm by defining the term, strong small farm (SSF) extracting the SSF households data dealing with apples, from 2010 Census of Agriculture, Forestry and Fisheries, Korea. Spatial distribution and concentration of SSF are analyzed based on spatial clustering techniques. We construct discrete dependent variables on strong and non-strong small farms and then analyze the determinants of the SSFs using probit model, with independent variables including population and economic characteristics and management characteristics. As of 2010, the apple SSFs, 1,529 households in total, are geographically concentrated in Gyeonsangbuk-do according to the analysis results. The determinants of SSF are similar to those of farms' earnings. When located in the apple producing area, and participating in producers organization while selling products directly, the farm is highly likely an SSF. The findings and results of the present study are expected to provide fundamental information helpful for preparing and implementing policies for SSFs in that the present study investigates the characteristics of SSF, which is a prerequisite step for SSF-related policies.

• Environmental and Resource Economics Review
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• v.19 no.3
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• pp.597-632
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• 2010

There is general agreement that global warming is occurring and that the main contributor to this probably is the buildup of green house gasses, GHG, in the atmosphere. Two main contributors are the utilization of fossil fuels and the deforestation of many regions of the world. The burning of fossil fuels increases atmospheric carbon while the burning of fuel-wood reducing fossil fuel consumption along with its forest source maintain an atmospheric carbon level. The standing timber in the forests is a carbon sink, as are wood buildings and structures, and fossil fuel in the ground. This paper is designed to examine a number of current issues related to mitigating the global warming problem through forestry. For this purpose, we develop a modeling approach by integrating timber market, fossil fuel market and carbon cycling model. We use discrete time optimal control theory to identify optimal time paths, the laws of motion, and stationary stats solutions of endogenous variables in the model. On the basis of these results, we identify the optimal amounts of subsidies to be provided or taxes to be imposed by the regulatory agency to mitigate atmospheric carbon accumulation. We also present a numerical example to help illustrate the characteristics of variables in the model when the social cost for atmospheric carbon incrementally shifts upward. A surprising result is that the social cost function for atmospheric carbon has a very smaller impact on the optimal rotation period than previous literature suggested.

• Korean Journal of Clinical Laboratory Science
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• v.55 no.4
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• pp.269-275
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• 2023

Echocardiography is a non-invasive method that is useful for diagnosing pulmonary arterial hypertension. It is known that echocardiography depends on the experience, education, and knowledge level of the cardiac sonographer. This study aimed to compare the agreement values between cardiac sonographer with different practical experiences in the diagnosis of pulmonary arterial hypertension using echocardiography. Three readers re-evaluated the echocardiography images of 148 patients who were diagnosed with pulmonary arterial hypertension at the S Medical Center from January 1, 2020, to December 31, 2020. The echocardiography values measured by each reader were compared and analyzed. The results of the analysis of discrete variables revealed that the agreement values of the cardiac sonographers showed excellent consistency for both reader 3 and the cardiologist group, indicating that more experience leads to better predictive accuracy for diagnosis of the condition. Furthermore, in terms of continuous variables, all the cardiac sonographer demonstrated good agreement in the measured values of the right atrium, which was easier to assess and clearer than the structurally complex measurements of the right ventricle. This study represents the first analysis in Korea of the agreement values measured by medical technologists who are cardiac sonographers.