• 한국시스템다이내믹스연구
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• 제4권2호
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• pp.95-130
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• 2003

The purpose of this study is to find what causes make public projects hold off, going beyond the planned deadline and budget. Using System Dynamics(SD) and their derivative Urban Dynamics(UD) models, it intends to analyze major feedback loops based on VENSIM and to simulate them with STELLA software, all of which are interrelated with various causes of project delay. To prevent or ameliorate project delay, first of all it advises to focus on endogenous delaying factors not exogenous ones. These factors either reinforce or balance certain loops in complex causal structure, In the case example on the Cremation Building Project in Cheongju, Residents’ participation demand make negotiation put off and delayed negotiation reinforces administrative-expediency planning in order to observe a time limit, on the other hand, once building consensus, it increase both the level of planning performance and public trust. In the meantime, the real planning process used to neglect residents opinions and manage public grievance only through compensation, he a result of simulation, visible fruit of negotiation in the initial phase seems to be not satisfactory owing to funds and time consumed, but after reaching an mutual agreement among stakeholders, planning performance is effective and strategic than administrative-expediency planning viewed in both financial and time angle. It proposes to devise specific tools schematizing project implementation. In order to upgrade the quality of project management, it recommends for planners to adopt key concepts based on SD/UD diagrams and causal loops, which would contribute to enriching Planning abbots.

• Food Science and Biotechnology
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• 제18권4호
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• pp.959-964
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• 2009

Production of the antioxidant substances by Bacillus polyfermenticus SCD was investigated using shake-flask fermentation. The one-factor-at-a-time method was first employed to determine the key ingredients for optimal medium composition, then further investigation of the medium composition was performed using response surface methodology (RSM). The antioxidant activity was measured using 2,2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) assays. After screening various elements, fructose, tryptone, and $MgSO_4\;7H_2O$ were chosen as the main factors for study in the statistical experimental design. Central composite design (CCD) was then used to determine the optimal concentrations of these 3 components. Under the proposed optimized medium containing 2.8% fructose, 1.34% tryptone, 0.015% $MgSO_4\;7H_2O$), 0.5% NaCl, and 0.25% $K_2HPO_4$, the model predicted an antioxidant activity of 80.5% ($R^2=0.9421$. The actual experimental results were in agreement with the prediction.

• 무역상무연구
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• 제30권
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• pp.27-58
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• 2006

The purpose of this study is to identify key obstacles to the adoption of electronic bill of lading and to suggest an effective way to promote the utilization of electronic bill of lading in international trade field. This study finds that all the respondants have not used 'true' electronic bill of lading that is issued and distributed electronically, and most of them agreed the needs of e-B/L adoption, but their intentions to adopt e-B/L remain very low in the present situation. Five obstacles to the adoption of e-B/L were derived from an explanatory factor analysis: 'integration' factor, 'law institution' factor, 'usability' factor, 'economic efficiency' factor, and 'security' factor. Solutions to promote the utilization of e-B/L in international trade field are as follows; Firstly, to endow e-B/L with the legal force through amending relevant laws including the commercial law. Secondly, to conclude the relevant international agreement, and to carry out joint projects between nations are needed. Thirdly, to conduct publicity campaigns is required to increase the understanding of the concepts and benefits of e-B/L to all concerned parties. Fourthly, stable and reliable system must be constructed with high level security. Fifthly, to readjust the service fee of e-B/L system to a realistic level is to be needed in order for user companies to use e-B/L service.

• Structural Engineering and Mechanics
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• 제35권2호
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• pp.241-256
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• 2010

The interaction between steel tube and concrete core is the key issue for understanding the behavior of concrete-filled steel tube columns (CFTs). This study investigates the force transfer by natural bond or by mechanical shear connectors and the interaction between the steel tube and the concrete core under three types of loading. Two and three-dimensional nonlinear finite element models are developed to study the force transfer between steel tube and concrete core. The nonlinear finite element program ABAQUS is used. Material and geometric nonlinearities of concrete and steel are considered in the analysis. The damage plasticity model provided by ABAQUS is used to simulate the concrete material behavior. Comparisons between the finite element analyses and own experimental results are made to verify the finite element models. A good agreement is observed between the numerical and experimental results. Parametric studies using the numerical models are performed to investigate the effects of diameterto-thickness ratio, uniaxial compressive strength of concrete, length of shear connectors, and the tensile strength of shear connectors.

• Structural Engineering and Mechanics
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• 제46권1호
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• pp.39-51
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• 2013

An extremum method is presented to predict the wrinkling characteristics of the inflated cone in bending. The wrinkling factor is firstly defined so as to obtain the wrinkling condition. The initial wrinkling location is then determined by searching the maximum of the wrinkling factor. The critical wrinkling load is finally obtained by determining the ratio of the wrinkling moment versus the initial wrinkling location. The extremum method is proposed based on the assumption of membrane material of beam wall, and it is extended to consider beam wall with thin-shell material in the end. The nondimensional analyses show that the initial wrinkling location is closely related to the taper ratio. When the taper ratio is higher than the critical value, the initial wrinkles will be initiated at a different location. The nondimensional critical wrinkling load nonlinearly increases as the taper ratio increases firstly, and then linearly increases after the critical taper ratio. The critical taper ratio reflects the highest load-carrying efficiency of the inflated cone in bending, and it can be regarded as a measure to optimize the geometry of the inflated cone. The comparative analysis shows fairly good agreement between analytical and numerical results. Over the whole range of the comparison, the mean differences are lower than 3%. This gives confidence to use extremum method for bending-wrinkling analysis of inflated conical cantilever beam.

• Structural Engineering and Mechanics
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• 제68권2호
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• pp.159-170
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• 2018

This paper aims to develop response modification factors for stiffness degrading structures by incorporating soil-structure interaction effects. A comprehensive parametric study is conducted to investigate the effects of key SSI parameters, natural period of vibration, ductility demand and hysteretic behavior on the response modification factor of soil-structure systems. The nonlinear dynamic response of 6300 soil-structure systems are studied under two ensembles of accelograms including 20 recorded and 7 synthetic ground motions. It is concluded that neglecting the stiffness degradation of structures can results in up to 22% underestimation of inelastic strength demands in soil-structure systems, leading to an unexpected high level of ductility demand in the structures located on soft soil. Nonlinear regression analyses are then performed to derive a simplified expression for estimating ductility-dependent response modification factors for stiffness degrading soil-structure systems. The adequacy of the proposed expression is investigated through sensitivity analyses on nonlinear soil-structure systems under seven synthetic spectrum compatible earthquake ground motions. A good agreement is observed between the results of the predicted and the target ductility demands, demonstrating the adequacy of the expression proposed in this study to estimate the inelastic demands of SSI systems with stiffness degrading structures. It is observed that the maximum differences between the target and average target ductility demands was 15%, which is considered acceptable for practical design purposes.

• Earthquakes and Structures
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• 제8권5호
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• pp.1091-1111
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• 2015

Base isolation is an effective method for protecting structures against earthquake hazard. It elongates the period of vibration and introduces supplemental damping to the structural system. The stiffness, damping and displacement are coupled forcing the code seismic design procedure to be unnecessarily complicated. In addition, the force reduction factor -a key parameter in the design procedurehas not been well addressed by seismic design codes at the high levels of damping due to the pronounced difference between pseudo and actual accelerations. In this study, a comparison has been conducted to evaluate eight different methods, in the literature, for calculating the force reduction factor due to damping. Accordingly, a simplified seismic analysis procedure has been proposed based on the well documented N2 method. Comprehensive analysis has been performed for base-isolated structure models for direct application and verification of the proposed procedure. The results have been compared with those of the European code EC8, the nonlinear time history analysis and investigations in the literature, where good agreement has been reported. In addition, a discussion has been elaborated for the resulted response of the base-isolated structure models with respect to the dynamic characteristics of the base isolation system.

• Steel and Composite Structures
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• 제13권4호
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• pp.397-408
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• 2012

This paper describes the refined 3-D finite element (FE) modeling of composite frames composed of concrete-filled steel tubular (CFST) columns and steel-concrete composite beams based on the test to get a better understanding of the seismic behavior of the steel-concrete composite frames. A number of material nonlinearities and contact nonlinearities, as well as geometry nonlinearities, were taken into account. The elastoplastic behavior, as well as fracture and post-fracture behavior, of the FE models were in good agreement with those of the specimens. Besides, the beam and panel zone deformation of the analysis models fitted well with the corresponding deformation of the specimens. Parametric studies were conducted based on the refined finite elememt (FE) model. The analyzed parameters include slab width, slab thickness, shear connection degree and axial force ratio. The influences of these parameters, together with the presence of transverse beam, on the seismic behavior of the composite frame were studied. And some advices for the corresponding seismic design provisions of composite structures were proposed.

• 산경연구논집
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• 제8권6호
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• pp.33-40
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• 2017

Purpose - This study attempted to discover the impact of the Korea-China FTA(Free Trade Agreement) on electronic products distribution industry. Strategies will be provided to expand both countries' trade after the Korea-China FTA. Research design, data, and methodology - This study analyzed the differences before and after the Korea-China FTA, using an RCA(Revealed Comparative Advantage) index, TC(Technology Sophistication Index) index and TSI(Trade Specialization Index) that considered the FTA tariff situation. Data was collected from the International Trade Statistics Database and Korea, China Customs Service. Results - The results indicate that following the Korea-China FTA, China and Korea's bilateral trade of electronic products is expected to expand, and both countries will experience net welfare gains from the markets' expansion. Korea is competitive in several key products, although it faces competition from China. China's electronic products' competitiveness have indicated an increasing trend. Conclusions - The two countries should closely cooperate and communicate with each other. Ultimately, Korea should focus on high-tech, sophisticated techniques to gain market advantage. On the other hand, with the tariff decrease as well as the labor cost and labor force base, China will greatly be able to benefit from the manufacturing of medium- to low-end products in the future.

• 영어어문교육
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• 제5호
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• pp.27-48
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• 1999

College students frequently feel their grammar knowledge from primary and middle school is not useful when they are asked to speak in college conversation classes. Because of their frustration at their lack of communicational ability as well as inappropriate teaching methods and class textbooks that have little to do with the student's major course of study, the student often has a low motivation to study. It is not uncommon for students to seek English education outside of their college classrooms by going to language institutes or studying abroad. College teachers need to find a way to use the student's background in grammar from primary and secondary schools. Despite the student's sentiment about his/her grammar education, grammar is an essential key to successful English conversation. Some ways that teachers can close the gap between primary and secondary school grammar education and college conversation classes are: to use a theme-based methodology, cue cards, and modeling. Activities such as Grammar Clinic, Grammar Police, and Show and Tell can be effective ways to bridge this gap. Teachers can use these activities and methods to correct such student errors as: incorrect word order, missing or unnecessary be verbs, confusion between be and do verbs, subject-verb agreement. and incorrect tense.