• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.10
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• pp.2617-2629
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• 1995

The flow through a centrifugal compressor rotor was calculated using the quasi-3-dimensional and fully 3-dimensional Navier-Stokes solution methods. The calculated results, obtained during the development of the computer codes for both methods are discussed. In the inviscid quasi 3-dimensional analysis, stream function formulation was used for the blade to blade (B-B) plane calculations, and the streamline curvature method was used for the meridional (H-S) plane calculations. In the viscous 3-dimensional flow analysis, a control volume method based on a general rotating curvilinear coordinate system was used to solve the time-averaged Navier-Stokes equations, and a standard k-.epsilon. model was used to obtain eddy viscosity. The quasi-3-dimensional analysis reasonably predicts the pressure distributions and requires much less computation time in the region where viscous effects are not strong; however, it fails to predict velocity field and loss mechanism through the impeller passage. The viscous 3-dimensional flow analysis shows reasonable pressure distributions and typical jet-wake flow field through the impeller passage. Secondary flow and total pressure distributions on cross-sectional planes explain the loss mechanisms through the impeller.

• Korean Journal of Materials Research
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• v.20 no.12
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• pp.645-648
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• 2010

The structure and morphology of epitaxial layer defects in epitaxial Si wafers produced by the Czochralski method were studied using focused ion beam (FIB) milling, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Epitaxial growth was carried out in a horizontal reactor at atmospheric pressure. The p-type Si wafers were loaded into the reactor at about $800^{\circ}C$ and heated to about $1150^{\circ}C$ in $H_2$. An epitaxial layer with a thickness of $4{\mu}m$ was grown at a temperature of 1080-$1100^{\circ}C$. Octahedral void defects, the inner walls of which were covered with a 2-4 nm-thick oxide, were surrounded mainly by $\{111\}$ planes. The formation of octahedral void defects was closely related to the agglomeration of vacancies during the growth process. Cross-sectional TEM observation suggests that the carbon impurities might possibly be related to the formation of oxide defects, considering that some kinds of carbon impurities remain on the Si surface during oxidation. In addition, carbon and oxygen impurities might play a crucial role in the formation of void defects during growth of the epitaxial layer.

• Steel and Composite Structures
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• v.5 no.6
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• pp.443-458
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• 2005

Steel angles are widely used in roof trusses as web and chord members and in lattice towers. Very often angle members are connected eccentrically. As a result, not only an angle member is under an axial force, but it is also subject to a pair of end eccentric moments. Moreover, the connection at each end provides some fixity so neither pinned nor the fixed end represents the reality. Many national design codes allow for the effects due to eccentricities by modifying the slenderness ratio and reducing the compressive strength of the member. However, in practice, it is difficult to determine accurately the effective length. The concept behind this method is inconsistent with strength design of members of other cross-sectional types such as I or box sections of which the buckling strength is controlled by the Perry constant or the initial imperfection parameters. This paper proposes a method for design of angle frames and trusses by the second-order analysis. The equivalent initial imperfection-to-length ratios for equal and unequal angles to compensate the negligence of initial curvatures, load eccentricities and residual stresses are determined in this paper. From the obtained results, the values of imperfection-to-length ratios are suggested for design and analysis of angle steel trusses allowing for member buckling strength based on the Perry-Robertson formula.

• Journal of the Korean Society for Marine Environment & Energy
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• v.8 no.2
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• pp.67-73
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• 2005

The characteristics of the floating breakwater is briefly reviewed and their performance is numerically investigated. The numerical scheme is a boundary integral method for inviscid potential flows, and various two-dimensional floating breakwater modules are studied focusing on the transmission coefficient. The general characteristics of pontoons is studied as function of mooring line stiffness, mass moment inertia and draft. Trapezoidal-, hat- and table-shape cross-sections are also studied with varying shape-parameters. The efficiency varies with changes in each shape-parameter and for some cases satisfying tranquility can be expected with even longer waves.

• The Journal of Asian Finance, Economics and Business
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• v.7 no.8
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• pp.407-417
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• 2020

Entrepreneurship has become an important topic for governments to shape and influence the quantity and quality of entrepreneurship and improve policy toward the entrepreneurial economy. This study investigates the factors affecting the entrepreneurial decision of nascent entrepreneurs belonging to Generation Y in Vietnam. A mixed-method including both qualitative and quantitative methodologies was utilized. A focus group was carried out with 11 participants for exploring, reviewing, and testing content validity of constructs and measurement items. The conceptual model and hypotheses were developed using data collected by a questionnaire survey. The cross-sectional survey method was applied. A sample of 221 respondents was constituted, by both electronic and paper surveys with non-probability and convenience sampling techniques. SmartPLS 3 software was employed to analyze the data collected. The results show that nine factors were affecting the entrepreneurial decision of nascent entrepreneurs belonging to Generation Y in Vietnam, including entrepreneurial education, family background, entrepreneurial ecosystem, perceived behavioral control, social valuation, perceived opportunity, attitude, entrepreneurial self-efficacy, and entrepreneurial intention. The findings show the importance of entrepreneurial education, social value, and ecosystems. Therefore, in order to promote successful entrepreneurship, it is necessary to strengthen entrepreneurship education and have a strategy for the improvement of the entrepreneurship ecosystem.

• Proceedings of the KSR Conference
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• 1998.05a
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• pp.604-611
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• 1998

High-speed railway trains entering and leaving tunnels generate finite amplitude pressure wave which propagate back and forth along the tunnels, reflecting at the open ends of the tunnels and at other discontinuities such as ventilation shafts and the train themselves. In present day railways, the magnitudes of the pressure waves are much too small to cause structual damage, but they are a serious potential source of aural discomport for passengers on unsealed trains. Almost always do the pressure waves propagating along the tunnels lead to a hazardous impulse noise near the exit portal of the tunnel. In order to alleviate such undesirable phenomena, some control strategies have been applied to the compression wave propagating inside the tunnel. The objective of the current work is to investigate the effect of tunnel entrance hoods on the entry compression wave at the vicinity of the tunnel entrance. Three types of entrance hoods were tested by the numerical method using the characteristics of method for a wide range of train speeds. The results show that the maximum pressure gradient of compression wave can be considerably reduced by the tunnel entrance hood. Desirable hood shape for reduction of the pressure transients and impulse noise was found to be of abrupt type hood with its cross-sectional area 2.5times the tunnel area.

• The Journal of Korean Academic Society of Nursing Education
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• v.26 no.3
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• pp.238-247
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• 2020

Purpose: The purpose of this study was to identify the relationship between intrinsic motivation and learning outcomes of nursing college students who took the Fundamentals of nursing as a problem-based learning method. Methods: In this cross-sectional study, we identified the intrinsic motivations of 114 nursing students who completed problem-based learning using the Intrinsic Motivation Inventory. The t-test was conducted to identify differences according to intrinsic motivation, and correlation analysis was performed to confirm the relationship between intrinsic motivation and learning outcomes. Results: The group with higher intrinsic motivation showed higher scores in all domains of self-assessed learning outcomes than the lower group. It was the 'Relatedness with an instructor' that showed the highest correlation with the learning outcomes in the domains of intrinsic motivation. Conclusion: Problem-based learning is an effective learning method for cultivating the competencies needed for nurses. The intrinsic motivation of students is an important factor in the performance of problem-based learning. For the efficiency of problem-based learning, efforts should be made to develop and apply autonomy-supportive interventions that can enhance intrinsic motivation.

• Korean Journal of Health Education and Promotion
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• v.26 no.2
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• pp.35-47
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• 2009

Purpose: The purpose of this study was to investigate the chronic disease, health status and lifestyle, and to test the chronic disease and health status and lifestyle of rural elderly by gender. Method: The interview survey was performed in September 2004 with structured questionnaires(Scale of Long-Term Health and Welfare Need Survey) to 770 of the elderly who lived in Muan-Gun of Chunnam Province. The percentage, Chi-squire test and regression method were used for some of the cross-sectional data. Results: The 770 elderly respondents were composed of 51.3% male and 48.7% female. 59.1% of the elderly had chronic disease. About the subjective health status that 54.3% of the respondents have been answered not good health status, 87.9% of the respondents have been health examination. The related variables of chronic disease and general characteristics were education and religious level in male, age, marital status, type of social security, education and religious level in female, and health status variables were subjective health status, cognitive function, ADL, IADL, and lifestyle factors was exercise in male, examination in female. Conclusion: These results suggested that special health promotion and education programs of the health habits such as physical exercise and health examination were necessities for the elderly of rural area.

• Journal of Korean Critical Care Nursing
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• v.11 no.3
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• pp.1-11
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• 2018

Purpose : This study compares experiences of ethical dilemma between nurses working in intensive care units and those in general units under specific situations of treatment decisions and confidentiality. Method : This cross-sectional descriptive study utilizes the self-report survey method. The survey questionnaires were completed by 50 and 52 nurses working in intensive care units and general units, respectively. The instrument, which consisted of 16 items of ethical dilemma situations about treatment decision and confidentiality, was used. The mean scores for each item were compared between the two groups. Results : The study found no differences in terms of age, gender, education level, clinical experience in years, and being educated on healthcare ethics. For 9 out of 16 items, the mean scores of nurses in intensive care units were significantly higher than those of nurses in general units. Conclusions : Nurses in intensive care units experienced ethical dilemmas regarding treatment decisions and confidentiality more often than those in general units. This study emphasizes the need to establish strategies for improving the ethical competence of critical care nurses.

• Advances in Computational Design
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• v.3 no.2
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• pp.165-190
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• 2018

In this article, the static behavior of non-prismatic sandwich beams composed of functionally graded (FG) materials is investigated for the first time. Two types of beams in which the variation of elastic modulus follows a power-law form are studied. The principle of minimum total potential energy is applied along with the Ritz method to derive and solve the governing equations. Considering conventional boundary conditions, Chebyshev polynomials of the first kind are used as auxiliary shape functions. The formulation is developed within the framework of well-known Timoshenko and Reddy beam theories (TBT, RBT). Since the beams are simultaneously tapered and functionally graded, bending and shear stress pushover curves are presented to get a profound insight into the variation of stresses along the beam. The proposed formulations and solution scheme are verified through benchmark problems. In this context, excellent agreement is observed. Numerical results are included considering beams with various cross sectional types to inspect the effects of taper ratio and gradient index on deflections and stresses. It is observed that the boundary conditions, taper ratio, gradient index value and core to the thickness ratio significantly influence the stress and deflection responses.