• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2008.03a
• /
• pp.700-710
• /
• 2008

A Bubble size distribution model has been developed for the numerical simulation of cryogenic high-speed cavitating flow of the turbo-pumps in the liquid fuel rocket engine. The new model is based on the previous one proposed by the authors, in which the bubble number density was solved as a function of bubble size at each grid point of the calculation domain by means of Eulerian framework with respect to the bubble size coordinate. In the previous model, the growth/decay of bubbles due to pressure difference between bubble and liquid was solved exactly based on Rayleigh-Plesset equation. However, the unsteady heat transfer between liquid and bubble, which controls the evaporation/condensation rate, was approximated by a theoretical solution of unsteady heat conduction under a constant temperature difference. In the present study, the unsteady temperature field in the liquid around a bubble is also solved exactly in order to establish an accurate and efficient numerical simulation code for cavitating flows. The growth/decay of a single bubble and growth of bubbles with nucleation were successfully simulated by the proposed model.

• The Journal of Asian Finance, Economics and Business
• /
• v.7 no.8
• /
• pp.653-660
• /
• 2020

The paper examines the impact of proctoring environments on student performance in two different exam proctoring environments: online versus offline proctored exams. This study employs a set of aggregated data from 1,762 students over the eight-year period from 2009 to 2016 in a university. Although there were nine courses offered, they could have been counted more than once as students may appear several times to take exams for different courses. This study employs independent samples t-test and regression analysis to compare the means of two independent groups and to test the hypothesis. The results of the independent samples t-test and the regression analysis indicate that there is no difference in the mean scores of exams and, therefore, the findings suggest that the exam proctoring environment is unlikely related to student performance even when students take their exams either in online proctoring or offline proctoring environments. This study concludes that the proctoring environment unlikely results in a statistically significant difference of exam scores and, thus, the exam proctoring environment does not appear to cause any change in student performance. The findings suggest that the exam proctoring environments does not appear to impact on student academic achievements and assessments.

• Journal of the Architectural Institute of Korea Planning & Design
• /
• v.36 no.4
• /
• pp.41-49
• /
• 2020

The purpose of this study was to investigate the use of the Deep Neural Networks(DNN) model to classify user's emotions, in particular Electroencephalography(EEG) toward Virtual-Reality(VR) based 3D design alternatives. Four different types of VR Space were constructed to measure a user's emotion and EEG was measured for each stimulus. In addition to the quantitative evaluation based on EEG data, a questionnaire was conducted to qualitatively check whether there is a difference between VR stimuli. As a result, there is a significant difference between plan types according to the normalized ranking method. Therefore, the value of the subjective questionnaire was used as labeling data and collected EEG data was used for a feature value in the DNN model. Google TensorFlow was used to build and train the model. The accuracy of the developed model was 98.9%, which is higher than in previous studies. This indicates that there is a possibility of VR and Fast Fourier Transform(FFT) processing would affect the accuracy of the model, which means that it is possible to classify a user's emotions toward VR based 3D design alternatives by measuring the EEG with this model.

• Journal of Ecology and Environment
• /
• v.46 no.1
• /
• pp.8-17
• /
• 2022

Background: Parthenium hysterophorus L. (Asteraceae; hereafter Parthenium) is an invasive alien species of global significance because of its' negative ecological and socioeconomic impacts. This species is spreading rapidly from lowland Tarai to Middle Mountain regions in Nepal. In the present study, we analyzed the impacts of Parthenium on plant community composition including their soil seedbank in subtropical grasslands located in central Nepal. Data was collected in a 10 m long transects passing through areas of high (> 90% cover), medium (40%-60%) and low (< 10%) levels of Parthenium cover using a plot of 1 m². Altogether, we sampled 90 plots in 30 transects. Seedling emergence method was used to estimate soil seedbank density in the soil samples (0-10 cm depth) collected from the plots with high Parthenium cover. Results: There was no significant difference in the plant species richness at different levels of Parthenium invasion whereas there was a significant change in the species composition of above ground flora due to Parthenium invasion. There was also a significant difference in species composition between soil seedbank and aboveground flora in the highly invaded plots. Parthenium was the most dominant in soil seedbank, contributing 65% to the total soil seedbank. Conclusions: Our study suggests that Parthenium has considerable negative impact on the native grassland flora, and the dominance of Parthenium in the soil seedbank means there is a challenge for its management. It also suggests the need of monitoring the soil seedbank dynamics while managing Parthenium weed.

• Smart Media Journal
• /
• v.11 no.7
• /
• pp.70-75
• /
• 2022

In 2019, the government improved the system to reduce the maximum weight of economic feasibility items in the comprehensive evaluation from 50% to 45% in order to improve the problem that economic feasibility is a decisive factor in passing the preliminary feasibility study. This study is to analyze the effect of system improvement in 2019 and verified the difference between before and after system improvement. As a result of regression analysis and correlation analysis, both periods showed high correlation, and the difference through Z-test was analyzed as not statistically significant. This result means that institutional improvement to reduce the impact of economics was not effective. Therefore, it is judged that it is necessary to discuss the design of a more effective comprehensive evaluation study through research such as reevaluating the weights of each item in the comprehensive evaluation in various ways in existing projects.

• Current Optics and Photonics
• /
• v.7 no.5
• /
• pp.518-528
• /
• 2023

As an effective means of remotely detecting the spectral information of the object, the spectral calibration for the Savart polarization interference imaging spectrometer (SPIIS) is a basis and prerequisite of information quantification, and its experimental calibration scheme is firstly proposed in this paper. In order to evaluate the accuracy of the spectral information acquisition, the linear interpolation, cubic spline interpolation, and piecewise cubic interpolation algorithms are adopted, and the precision of the quadratic polynomial fitting is the highest, whose fitting error is better than 5.8642 nm in the wavelength range of [500 nm, 820 nm]. Besides, the inversed value of the spectral resolution for the monochromatic light is greater than the theoretical value, and the deviation between them becomes larger with the wavelength increasing, which is mainly caused by the structural design of the SPIIS, together with the rationality of the spectral restoration algorithm and the selection of the maximum optical path difference (OPD). This work demonstrates that the SPIIS has achieved high performance assuring the feasibility of its practical use in various fields.

• Journal of Korean Academy of Fundamentals of Nursing
• /
• v.4 no.1
• /
• pp.133-146
• /
• 1997

The objective of this study was to clarify whether there are any differences between normal and over-weight adults in their perceived weight, health status, health conception and health promoting behavior. The sample consisted of 238 normal weight and 106 over-weight(11% above on the Body Index Scale) adults, more than 20 years-old, who live in Seoul metropolitan. One participant per household was selected for conveneience. The findings from this study are summarized below. 1) Among 106 overweight adults, 30 were above 20% on the Body Index Scale and 11 were above 30%. Twenty-one(19.8%) of the overweight group and 34(14.4%) of the normal weight group had one disease, and there were 30(28.3%) in the overweight group and 46(19.6%) in the normal weight group where one of the family members had a disease, but these differences were not statistically significant. The average monthly family income for the overweight group was \2,220,000 compared to \2,070,000 for the normal weight group, and this difference was statistically significant. The age range for the whole group was between 20 and 74(mean=35.6 for total, 39.4 for overweight and 34.0 for normal weight group). Again significant difference was found. Occupations were salaryman(57.6%), teacher(7.4%), student(5.4%) and others(27.3%). Fifty-six salaryman(70.0%) from the overweight group and 92(52.0%) from the normal group did not consitute a statistically significant different. For the educational status, 90(87.5%) of the overweight adults and 222(93.7%) of the normal weight group finished high school or more educational courses, and there was significant statistical difference. Ninety-two(86.8%) of the overweights and 156(65.5%) of the normal weight group were married, and again significant statistical difference was found. 2) A test for difference in health characteristics between the two weight groups indicated that two groups did not show statistical differences in their perceived health status, health conception or health promoting behavior. That is, the overweight group also perceive their health status as good as the normal group, and regard 'Health' as a state that enables them to carry out social roles and functions rather than as the traditional concept of health as no disease or no symptoms. Both group showed slightly high level of health promoting behavior. To determine if no statistical difference might be related to the overweight group's failure of perceive themselves as overweight, the perceived and objective overweight status were compared by the Pearson Correlation Analysis, and a strong corelationship was found(r=.76, p=.000). That is, if participants perceived themselves as overweighted, they thought and replied to be got more weight comparing to the other person who are in same age and sex. However, 43(18.1%) of the normal group perceived themselves as being overweight and 28(26.4%) of the overweight group thought they were of normal weight. Even though the overweight group employed in this study perceived themselves as being overweight, they regarded themselves as healthy as those in the normal weight group. It was shown that there was no statistical difference between the two groups in health conception, health status and health promoting behavior. 3) Perceived health conception was shown to be significantly related to health promoting behavior(r=.20, p=.004 for whole group ; r=.27, p=.009 for overweight group ; and r=.21, p=.001 for normal group). It means that in both group the higher perceived health conception level, the more frequent health promoting behavior. And, perceived health status was also shown to be significantly related to health promoting behavior(r=.16, p=.000) as a whole and especially for overweight group(r=.24, p=.018), but no significant relationship for normal group(r=.08, p=.620). 4) By means of multiple regression analysis, health conception, perceived health status, age, sex and marital status provided predicted 15.18% on health promoting behavior.

• The korean journal of orthodontics
• /
• v.35 no.3 s.110
• /
• pp.163-173
• /
• 2005

The purpose of this study was to compare the asymmetric degree between maxillofacial hard and soft tissues in individuals with facial asymmetry. Computerized tomographies (CT) of 34 adults (17 male, 17 female) who had facial asymmetry were taken. The CT images were transmitted to personal computers and then reconstructed into three-dimensional (3D) images through the use of computer software. In order to evaluate the degree of facial asymmetry, 6 measurements were constructed as the hard tissue measurements while 6 counterpart measurements were taken as the soft tissue measurements. The means and standard deviations were obtained for each measurement using 3D measure, then t-test was used to investigate the differences between each hard tissue measurement and the corresponding soft tissue measurement All measurements used in the present study showed statistically significant differences between the hard and soft tissues. The degree of soft tissue asymmetry was smaller than that of corresponding hard tissue asymmetry in case of chin deviation, frontal ramal inclination difference, and frontal corpus inclination difference. On the other hand, the degree of soft tissue asymmetry was greater than that of underlying hard tissue asymmetry in the measurement of lip canting and lip cheilion height difference The present study suggests that asymmetric differences of hard and soft tissue is observed nu facial asymmetric subjects and thus soft tissue analysis is needed in addition to hard tissue analysis when making an evaluation of facial asymmetry.

• The Journal of Korean Academy of Prosthodontics
• /
• v.46 no.6
• /
• pp.561-568
• /
• 2008

STATEMENT OF PROBLEM: Currently, many implant systems are developed and divided into two types according to their joint connection: external or internal connection. Regardless of the connection type, screw loosening is the biggest problem in implant-supported restoration. PURPOSE: The purpose of this study is to assess the difference in stability of abutment screws between the external and internal hexagonal connection types under cyclic loading. MATERIAL AND METHODS: Each of the 15 samples of external implants and internal abutments were tightened to 30 N/cm with a digital torque gauge, and cemented with a hemispherical metal cap. Each unit was then mounted in a $30^{\circ}$ inclined jig. Then each group was divided into 2 sub-groups based on different periods of cyclic loading with the loading machine (30 N/ cm - 300 N/cm,14 Hz: first group $1{\times}10^6$, $5{\times}10^6$ cyclic loading; second group $3{\times}10^6$, $3{\times}10^6$ for a total cyclic loading of $6{\times}10^6$) The removal torque value of the screw before and after cyclic loading was checked. SPSS statistical software for Windows was used for statistical analysis. Group means were calculated and compared by ANOVA, independent t-test, and paired t-test with ${\alpha}$=0.05. RESULTS: In the external hexagonal connection, the difference between the removal torque value of the abutment screw before loading, the value after $1{\tims}10^6$ cyclic loading, and the value after $1{\times}10^6$, and additional $5{\times}10^6$ cyclic loading was not significant. The difference between the removal torque value after $3{\times}10^6$ cyclic loading and after $3{\times}10^6$, and additional $3{\times}10^6$ cyclic loading was not significant. In the internal hexagonal connection, the difference between the removal torque value before loading and the value after $1{\times}10^6$ cyclic loading was not significant, but the value after $1{\times}10^6$, and additional $5{\times}10^6$ cyclic loading was reduced and the difference was significant (P < .05). In addition, in the internal hexagonal connection, the difference between the removal torque value after $3{\times}10^6$ cyclic loading and the value after $3{\times}10^6$, and additional $3{\times}10^6$ cyclic loading was not significant. CONCLUSION: The external hexagonal connection was more stable than the internal hexagonal connection after $1{\times}10^6$, and additional $5{\times}10^6$ cyclic loading (t = 10.834, P < .001). There was no significant difference between the two systems after $3{\times}10^6$, and additional $3{\times}10^6$ cycles.

• The Journal of Korean Society for School & Community Health Education
• /
• v.4
• /
• pp.79-95
• /
• 2003

This dissertation aims to analyze various safety accidents taking place during physical education class according to physical education teacher's value orientation, to identify teacher's value orientation that can minimize safety accidents, and to provide basic materials for safe and smooth class management. For this purpose, data have been collected from 261 physical education teachers at some middle and high schools in G City in Kyung-Ki Province and Busan Metropolitan City. The materials were treated as follows: The variables on demographic characteristics of physical education teachers are determined by t-test ; The analysis of one-way ANOVA and relationship between value orientation and safety accident prevention activities was conducted through Pearson's linear correlation analysis and multiple regression; The analysis of the relationship between value orientation and actual conditions of safety accidents was conducted through logistic regression. First, there is almost no awareness difference of physical education teachers' value orientation according to demographical variables. The value orientation physical education teachers consider to be the most important is, however, mainly 'mastery of disciplinary lesson.' There is a statistically significant difference in safety accident prevention activities according to demographical variables. Teachers' focuses in class contents showed a significant difference according to teaching experience and working area, while the dependency on facility has a significant difference according to teaching experience and school type. Second, there is no correlation between physical education teacher's value orientation and safety accident prevention activities because there is virtually no statistically significant difference between them. It means that safety accident prevention activities are not related with on which teachers place emphasis among mastery of disciplinary lesson, social reconstruction, self-realization, ecological integration and value orientation on learning process. Third, the analysis of safety accident prevention activities according to physical education teachers' value orientation revealed that the lower value orientation in social reconstruction is, the more safety accidents teachers experience. It is also found that crashes among students, ball games and leg injuries are inter-related with social reconstruction in value orientation, over-motivation and unskilled motor function ; athletic sports with value orientation on learning process and safety prevention training ; unskilled motor functions with value orientation in ecological integration and disobedience to teacher's directions ; winter accidents with mastery of disciplinary lesson in value orientation. In conclusion, the research indicates that physical education teacher's value orientation according to demographical variables didn't show any significant difference, while one according to safety accident prevention activities showed significant difference. Besides, physical education teachers' value orientation is not related to safety accident prevention activities, but the relationship between value orientation and actual conditions of safety accidents showed correlations according to each variable. Especially, teachers with lower value orientation in social reconstruction experienced more safety accidents. Therefore, physical education teachers can manage physical education class more safely with more emphasis on value orientation in social reconstruction.