• Korean Journal of Mathematics
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• 제23권3호
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• pp.379-391
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• 2015

We investigate the existence of solutions of the nonlinear biharmonic equation with variable coefficient polynomial growth nonlinear term and Dirichlet boundary condition. We get a theorem which shows that there exists a bounded solution and a large norm solution depending on the variable coefficient. We obtain this result by variational method, generalized mountain pass geometry and critical point theory.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2002년도 추계학술대회 논문집(II)
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• pp.892-897
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• 2002

The research was requested by Meridian Rail Corporation in United States. The Swing Motion Bogie can application by Korea style if synthesize study result of bogie strength evaluation, bogie dynamic characteristics analysis, actual test(maximum speed, derailment coefficient, lateral force, vertical force, vibration acceleration, steady state lateral acceleration) etc..

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2004년도 추계학술대회 논문집 Vol.17
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• pp.628-631
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• 2004

A tetrafluoromethane$(CF_4)$ is most useful gas in plasma dry etching, because it has a electron attachment cross-section. therefor it is important to calculate transport coefficients like electron drift velocity, ionization coefficient, attachment coefficient, effective ionization coefficient. and critical E/N. The aim of this study is to get these transport coefficients for information of the insulation strength and efficiency of etching process. Electron transport coefficients in $CF_4+Ar$ gas mixture are simulated in range of E/N values from 1 to 250 [Td] at 300[K} and 1 [Torr] by using Boltzmann equation method. The results of this method can be important data to present characteristic of gas for plasma etching and insulation, specially critical E/N is a data to evaluate insulation strength of a gas. and is presented in this paper for various mixture ratios of $CF_4+Ar$ gas mixture.

• 대한기계학회논문집
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• 제13권3호
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• pp.424-432
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• 1989

본 연구에서는 정적절삭실험으로 결정될수 있는 절삭변수로 표현되는 동적 절삭력을 해석적으로 구한다. 이 모델은 3차원 절삭형태에도 적용될 수 있는 특성을 갖는다. 새로이 제안된 절삭 과정의 모델은 동적절삭상태에서 절삭력 합력의 변화를 고려한 절삭기구를 통해 이루어지며, 해석적으로 한계절삭폭을 구한다. 실험적 규명 은 채터진동이 발생하지 않는 한계절삭 공작물에 비해 공구의 강성이 상대적으로 적은 보링(boring)작업에서 발생하는 것을 대상으로 하였다.

• Tuberculosis and Respiratory Diseases
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• 제84권4호
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• pp.274-281
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• 2021

Background: The Korea National Health and Nutrition Examination Survey (KNHANES) is a well-designed survey to collect national data, which many researchers have used for their studies. In KNHANES, although portable spirometry was used, its reliability has not been verified. Methods: We prospectively enrolled 58 participants from four Korean institutions. The participants were classified into normal pattern, obstructive pattern, and restrictive pattern groups according to their previous spirometry results. Lung function was estimated by conventional spirometry and portable spirometry, and the results were compared. Results: The intraclass correlation coefficients of forced vital capacity (FVC) (coefficient, 9.993; 95% confidence interval [CI], 0.988-0.996), forced expiratory volume in 1 second (FEV₁) (coefficient, 0.997; 95% CI, 0.995-0.998), FEV₁/FVC ratio (coefficient, 0.995; 95% CI, 0.992-0.997), and forced expiratory flow at 25-75% (FEF25-75%; coefficient, 0.991; 95% CI, 0.984-0.994) were excellent (all p<0.001). In the subgroup analysis, the results of the three parameters were similar in all groups. In the overall and subgroup analyses, Pearson's correlation of all the parameters was also excellent in the total (coefficient, 0.986-0.994; p<0.001) and subgroup analyses (coefficient, 0.915-0.995; p<0.001). In the paired t-test, FVC, FEV₁/FVC, and FEF25-75% estimated by the two instruments were statistically different. However, FEV₁ was not significantly different. Conclusion: Lung function estimated by portable spirometry was well-correlated with that estimated by conventional spirometry. Although the values had minimal differences between them, we suggest that the spirometry results from the KNHANES are reliable.

• 한국소성가공학회:학술대회논문집
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• 한국소성가공학회 2008년도 추계학술대회 논문집
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• pp.292-296
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• 2008

A new method of evaluating critical damage values of commercial materials is presented in this paper. The method is based on the previous study of the methodology [1] of acquisition of true stress-strain curves or flow stress curves over large strain from the tensile test in which the flow stress is described by the Hollomon law-like form, that is, by the strain dependent strength coefficient and the strain hardening exponent. The strain hardening exponent is calculated from the true strain at the necking point to meet the Considere condition. The strength coefficient is assumed to be constant before necking and represented by a piecewise linear function of strain after necking. With the predicted flow stress, a tensile test is simulated by a rigid-plastic finite element method with higher accuracy of less than 0.5% error between experiments and predictions. The instant when the fracture begins and thus the critical damage is obtained is determined by observing the stress variation at the necked region. It is assumed that the fracture due to damage begins when the pattern of stress around the necked region changes radically. The method is applied to evaluate the critical damage of a low carbon steel.

• Journal of Mechanical Science and Technology
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• 제14권8호
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• pp.816-822
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• 2000

In the core of the nuclear power plant of PWR, several cases of fuel failure by unknown causes have been experienced for various fuel types. From the common features of the failure pattern, failure lead time, flow conditions, and flow induced vibration characteristics in nuclear fuel bundles, it is deduced that the fretting wear failure of the fuel rod at the spacer grid position is due to the fluidelastic vibration. In the past, fluidelastic vibration was simulated by quasi -static semi-analytical model, so called the static model, which could not account for the interaction between the rods within a bundle. To overcome this defect and to provide for more flexibilities applicable to the fuel bundle, Tanaka's unsteady model was modified to accomodate the geometrical differences and governing parameter changes during the operations such as the number of rods, pitch to diameter ratio (P/D), spring force, damping coefficient, etc. The critical velocity was calculated by solving the governing equations with the MATLAB code. A comparison between the estimated critical velocity and the test result shows a good agreement. Finally, the level of decrease of the critical velocity due to the reduction in the spring force and reduced damping coefficient due to the radiation exposure is also estimated.

• 대한간호학회지
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• 제44권2호
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• pp.129-138
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• 2014

Purpose: To develop a Critical Thinking Skill Test for Nursing Students. Methods: The construct concepts were drawn from a literature review and in-depth interviews with hospital nurses and surveys were conducted among students (n=607) from nursing colleges. The data were collected from September 13 to November 23, 2012 and analyzed using the SAS program, 9.2 version. The KR 20 coefficient for reliability, difficulty index, discrimination index, item-total correlation and known group technique for validity were performed. Results: Four domains and 27 skills were identified and 35 multiple choice items were developed. Thirty multiple choice items which had scores higher than .80 on the content validity index were selected for the pre test. From the analysis of the pre test data, a modified 30 items were selected for the main test. In the main test, the KR 20 coefficient was .70 and Corrected Item-Total Correlations range was .11-.38. There was a statistically significant difference between two academic systems (p=.001). Conclusion: The developed instrument is the first critical thinking skill test reflecting nursing perspectives in hospital settings and is expected to be utilized as a tool which contributes to improvement of the critical thinking ability of nursing students.

• The Korean Journal of Ceramics
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• 제3권3호
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• pp.182-186
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• 1997

Diamond-like carbon(DLC) films were deposited on silicon substreates by using an RF plasmaassisted CVD apparatus; the effects of deposition conditions such as CH4 gas pressure and substrate bias voltage on DLC film friction and wear were examined in both friction and scratch tests. In friction tests critical loads at which the friction coefficient increases abruptly depend on substrate bias voltages: critical loads deposited at a bias voltage of -100 V exceed those deposited at other bias voltages. Critical loads are correlated with DLC film hydrogen content. Critical DLC film loads in scratch tests depended considerably less than in friction tests. The friction coefficient of DLC films depends on neither substrate bias voltage nor CH4 gas pressure.

• 설비공학논문집
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• 제28권9호
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• pp.373-380
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• 2016

Spray cooling is a technology of increasing interest for electronic cooling and other high heat flux applications. In this study, heat transfer coefficients (HTCs) and critical heat fluxes (CHFs) are measured on a smooth square flat copper heater of $9.53{\times}9.53mm$ at $36^{\circ}C$ in a pool, a smooth flat surface and Thermoexcel-E surfaces are used to see the change in HTCs and CHFs according to the surface characteristics and FC-72 is used as the working fluid. FC-72 fluid has a significant influence on heat transfer characteristics of the spray over the cooling surface. HTCs are taken from $10kW/m^2$ to critical heat flux for all surfaces. Test results with Thermoexcel-E showed that CHFs of all enhanced surface is greatly improved. It can be said that surface form affects heat transfer coefficient and critical heat flux.