• 설비공학논문집
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• 제17권12호
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• pp.1095-1105
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• 2005

Numerical analysis has been carried out to investigate transient turbulent convective heat transfer in a vertical tube for supercritical water near the thermodynamic critical point. Heat transfer and fluid flow in the tube we strongly coupled due to the large variations of thermodynamic and transport properties such as density, specific heat, and turbulent viscosity. As pressure in the tube approaches to the critical pressure, the properties variation with time becomes larger. Heat transfer coefficient rapidly decreases along the tube near the pseudocritical temperature at the tube wall for $P_R<1.2$. Stanton number variation with time is largely reduced in the region of gas-like phase in comparison with Nusselt number. Turbulent viscosity ratio close to the wall increases near the pseudocritical temperature and it gradually decreases with time.

• 한국건축시공학회지
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• 제19권5호
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• pp.467-475
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• 2019

Delay is one of the most critical issues for construction projects and leads to huge losses in both developing and industrialized countries. The construction sector in Rwanda, a rapidly-developing nation, is no exception. Delays can be mitigated only once we have identify their primary causes, and these may not be the same in each region. This study aims to ascertain the main critical factors responsible for delays in building construction in Rwanda through an intensive literature review and questionnaire survey. A total of 40 delay causative factors were obtained from a literature review and were further classified into nine major categories. The questionnaire survey was distributed to about 80 respondents from clients, contractors, and consultants. From the list of 40 different factors, the top twelve most critical causes were identified as stoppage of work due to cash flow constraints, delay in approving design documents, confidentiality of physical plan, price fluctuations and delay in approving significant change, change orders, delay in performing inspections, Ineffective project planning, inadequate drawing details, unqualified labor, lack of materials on the market and dishonesty.

• Bulletin of the Korean Chemical Society
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• 제7권3호
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• pp.224-228
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• 1986

A nonlinear theory is presented for the fluctuations of intermediates in the Brusselator near the critical point caused by diffusion. The method used is the two time scaling method different from the conventional method in the sense that a slight nonlinear effect is included in the initial time region where the linear approximation is conventionally valid. The result obtained by the nonlinear theory shows that fluctuations close to the critical point approach the value of a stable steady state or deviate infinitely from an unstable steady state, as time goes to infinity, while the linear theory gives approximately time-independent fluctuations. A brief discussion is given for the correlation at a time between fluctuating intermediates when the system approaches a stable steady state.

• 한국치위생학회지
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• 제19권6호
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• pp.1037-1046
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• 2019

Objectives: This study was conducted to test the critical thinking tendency, clinical practice satisfaction, and clinical performance, and analyze the factors impacting clinical practice satisfaction and clinical performance of dental hygiene students. Methods: The study conducted a written survey during the period between 30 July ~20 August 2019, among 3rd and 4th year dental hygiene students from Seoul, Gyung-gi region, who had taken clinical practice courses. Using SPSS 22.0 program (IBM SPSS statistics, New York, USA), the study analyzed the final 174 cases. Results: Dental hygiene students scored 3.33±0.43, 3.48±0.83, and 3.30±0.58 for critical thinking, clinical practice satisfaction, and clinical performance, respectively. The clinical thinking score was higher when their study performance was good (p<0.001), clinical practice satisfaction was higher when their major satisfaction was satisfactory (p<0.001), higher when their relationship with their clinical practice partner was good, and the clinical performance was better when the students' major satisfaction was good (p<0.001). The study performance yielded better results when their study achievement was better (p<0.05). Clinical practice satisfaction (r=0.156) and clinical performance (r=0.393) showed a positive correlation with critical thinking, and clinical performance had a positive correlation with clinical practice satisfaction. The impact factor for clinical practice satisfaction appeared to be clinical performance (p<0.05) and major satisfaction (p<0.001), and the factors impacting the clinical performance were among the sub-causes of critical thinking (p<0.05), intellectual fairness (p<0.05), watchfulness (p<0.05), clinical practice satisfaction (p<0.05), and major satisfaction (p<0.01). Conclusions: Results of the study showed that for dental hygiene students, critical thinking, clinical practice satisfaction, clinical performance, and major satisfaction were the impact factors affecting the students' clinical performance. Therefore, the study recommends that development of educational programs and operation of a field-based curriculum is necessary to improve critical thinking, clinical practice satisfaction, and major satisfaction.

• 한국도로학회논문집
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• 제17권6호
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• pp.27-32
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• 2015

PURPOSES : It is difficult to estimate tunnel stability because of lack of timely information during tunnel excavation. Tunnel deformability refers to the capacity of rock to strain under applied loads or unloads during tunnel excavation. This study was conducted to analyze a methods of pre-evaluation of stability during tunnel construction using the critical strain concept, which is applied to the results of tunnel settlement data and unconfined compression strength of intact rock or rock mass at the tunnel construction site. METHODS : Based on the critical strain concept, the pre-evaluation of stability of a tunnel was performed in the Daegu region, at a tunnel through andesite and granite rock. The critical strain concept is a method of predicting tunnel behavior from tunnel crown settlement data using the critical strain chart that is obtained from the relationship between strain and the unconfined compression strength of intact rock in a laboratory. RESULTS : In a pre-evaluation of stability of a tunnel, only actually measured crown settlement data is plotted on the lower position of the critical strain chart, to be compared with the total displacement of crown settlement, including precedent settlement and displacement data from before the settlement measurement. However, both cases show almost the same tunnel behavior. In an evaluation using rock mass instead of intact rock, the data for the rock mass strength is plotted on the lower portion of the critical strain chart, as a way to compare to the data for intact rock strength. CONCLUSIONS : From the results of the pre-evaluation of stability of the tunnel using the critical strain chart, we reaffirmed that it is possible to promptly evaluate the stability of a tunnel under construction. Moreover, this research shows that a safety evaluation using the actual instrumented crown settlement data with the unconfined compression strength of intact rock, rather than with the unconfined compression strength of a rock mass in the tunnel working face, is more conservative.

• International Journal of Naval Architecture and Ocean Engineering
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• 제6권3호
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• pp.529-561
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• 2014

The two-phase turbulent flow past an interface-piercing circular cylinder is studied using a high-fidelity orthogonal curvilinear grid solver with a Lagrangian dynamic subgrid-scale model for large-eddy simulation and a coupled level set and volume of fluid method for air-water interface tracking. The simulations cover the sub-critical and critical and post critical regimes of the Reynolds and sub and super-critical Froude numbers in order to investigate the effect of both dimensionless parameters on the flow. Significant changes in flow features near the air-water interface were observed as the Reynolds number was increased from the sub-critical to the critical regime. The interface makes the separation point near the interface much delayed for all Reynolds numbers. The separation region at intermediate depths is remarkably reduced for the critical Reynolds number regime. The deep flow resembles the single-phase turbulent flow past a circular cylinder, but includes the effect of the free-surface and the limited span length for sub-critical Reynolds numbers. At different Froude numbers, the air-water interface exhibits significantly changed structures, including breaking bow waves with splashes and bubbles at high Froude numbers. Instantaneous and mean flow features such as interface structures, vortex shedding, Reynolds stresses, and vorticity transport are also analyzed. The results are compared with reference experimental data available in the literature. The deep flow is also compared with the single-phase turbulent flow past a circular cylinder in the similar ranges of Reynolds numbers. Discussion is provided concerning the limitations of the current simulations and available experimental data along with future research.

• 천문학회지
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• 제24권1호
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• pp.1-12
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• 1991

The mathematical properties of gravitational lens equations are examined in the frame work of gravitational micro-lensing effects. The caustics of the gravitational lens may be defined in terms of "cusp" and "folding" in general. In some cases for overfocussing, however, the critical curves (caustics) have no cusp and no folding. If the observer is in the overfocussed region, he may not see any lensed image.

• 한국대기환경학회지
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• 제21권2호
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• pp.169-178
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• 2005

A critical component of air pollution modeling is the representation of atmospheric flow fields within a model domain, since an accurate air quality simulation requires an accurate portrayal of the three-dimensional wind fields. The present study investigated data assimilation using surface observational data in the complex coastal regions to simulate a realistic atmospheric flow fields. Surface observational data were categorized into three groups (Near coastal region, Far coastal region 1, Far costal region 2) by the locations where the sites are. Experiments were designed according to the location of observational stations and MM5/CALPUFF was used. The results of numerical simulation of atmospheric flow fields are used as input data for CALPUFF which predicts dispersion fields of air pollutants. The result of this study indicated that data assimilation using data in the far coastal region 2 provided an attractive method for generating realistic meteorological fields and dispersion fields of air pollutants in Gwangyang area because data in the near coastal region are variable and narrow representation.

• 한국농촌건축학회논문집
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• 제15권1호
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• pp.47-56
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• 2013

As architecture has a role of vessel that contains human life, architecture of museums in a region must be a vessel that contains identity of the region. Jeju Province possesses excellent natural landscape acknowledged by the world. As such, architectural design of museums in Jeju region, differentiated in terms of natural, humanistic and cultural characteristics from other regions, must include identity of Jeju. Jeju has established and is operating so many museums with different themes that it is referred to as the heaven of museums. In addition, museums as cultural facilities must be the measure of cultural level representing regional identity and perform the role of advance guard that leads architectural culture of the region. Also, such excellent architectural asset is an important landscape element that increases value of the region. Based on Landscape Management Guideline established in 2009 by Jeju Special Self-governing Province under such critical mind, this study will support design problems and improvements of museums through case study and analysis on design characteristics of national and private museums in Jeju. Accordingly, the purpose of this study is to provide basic data to be pursued by future museums that contain identity of Jeju, based upon the results of analysis described above.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2003년도 추계학술대회논문집
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• pp.84-91
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• 2003

Flow-Induced Vibration of steam generator tubes may result in fretting wear damage at the tube-to-support locations. KSNP(Korean Standard Nuclear Power plant) steam generators experienced fretting wear in the upper part of U-bend above the central cavity region of steam generators. This region has conditions susceptible to the flow-induced vibration, such as high flow velocity, high void fraction, and longer unsupported span. To improve its performance, APR1400 steam generator is designed with additional supports in this region to reduce unsupported span and to reduce peak velocity in the central cavity region. In this paper, we examined its performance improvement using ATHOS code. The thermal-hydraulic condition in the region of secondary side of APR1400 steam generator is obtained using the ATHOS3 code. The effective mass for modal analysis is calculated using the void fraction, enthalpy, and operating pressure information from ATHOS3 code result. With the effective mass distribution along the tube, natural frequency and mode shape is obtained using ANSYS code. Finally, stability ratios and real mean squared displacements for selected tubes of the APR1400 steam generator are computed. From these results, the current design of the APR1400 steam generator are examined.