• Journal of Mechanical Science and Technology
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• v.15 no.5
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• pp.646-655
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• 2001

This paper reports the effects of nozzle exit boundary layer swirl on the instability modes of underexpanded supersonic jets emerging from plane rectangular nozzles. The effects of boundary layer swirl at the nozzle exit on thrust and mixing of supersonic rectangular jets are also considered. The previous study was performed with a 30°boundary layer swirl (S=0.41) in a plane rectangular nozzle exit. At this study, a 45°boundary layer swirl (S=1.0) is applied in a plane rectangular nozzle exit. A three-dimensional unsteady compressible Reynolds-Averaged Navier-Stokes code with Baldwin-Lomax and Chiens $\kappa$-$\xi$ two-equation turbulence models was used for numerical simulation. A shock adaptive grid system was applied to enhance shock resolution. The nozzle aspect ratio used in this study was 5.0, and the fully-expanded jet Mach number was 1.526. The \"flapping\" and \"pumping\" oscillations were observed in the jets small dimension at frequencies of about 3,900Hz and 7,800Hz, respectively. In the jets large dimension, \"spanwise\" oscillations at the same frequency as the small dimensions \"flapping\" oscillations were captured. As reported before with a 30°nozzle exit boundary layer swirl, the induction of 45°swirl to the nozzle exit boundary layer also strongly enhances jet mixing with the reduction of thrust by 10%.

• Journal of The Korean Association For Science Education
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• v.14 no.3
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• pp.304-311
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• 1994

Four science concepts were selected from high school science textbook to investigate the differences in priorities of students knowledge activated during solving earth science problems in laboratory and earth science environmental contexts. Two items, one for laboratory context and the other for earth environmental context, were developed for earth selected concept The subjects were constituted of 192 students in 11th grade and 196 in 12th grade in one senior high school. Students' responses were categorized using graph models and analyzed in terms of 'Common Activated Knowledge'(CAK). and 'Specific Activated Knowledge'(SAK) across students' cognitive frames, grades, and sex. As contextual differences of the problems increased, context effects in priorities of CAK were reported in favor of laboratory context, on the contrary those of SAK in favor of earth environmental context. Context effects were reported across cognitive frames, especially students with laboratory cognitive frames showed more significant context effects than others. Lower graders and girls showed relatively large context effects. The results of this study showed that science concepts learned in a laboratory context are not easily transferred to earth environmental context. Therefore, special instructional strategies should be developed to overcome the context effect s according to activated knowledges with high priorities in laboratory and earth environmental context.

• Journal of Family Resource Management and Policy Review
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• v.14 no.4
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• pp.101-126
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• 2010

This Qualitative case study focused on the National Pilot Project to make family-friendly communities. We examined the basic model of the family-friendly community proposed by the Ministry of Gender Equality and Family. One of the three local communities selected as family friendly models was chosen for observation and in-depth interview for its residents. The official performance report shows this project's process, results and future tasks. From the in-depth interview data, we defined the project's characteristics as the government and private sectors collaboration, model transformation from the original family friendly model to the production model, and we found some conflicts among residents upon financial issues and business items. The most important task is the vitalization of the community corporate body to realize this project's performance through these three years. And this study implicates to elaborate the rural family-friendly community model focused on income creating community redesign, different from the urban model focused on caring.

• 한국IT서비스학회:학술대회논문집
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• 2008.11a
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• pp.157-160
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• 2008

The recent successes of systems like Google, Wikipedia and InnoCentive suggest that the time is now ripe for more such systems. Thus, we want to explore these systems and exploit them from a viewpoint of social psychology prior to technological progress. First of all, we examine the difference between 'wisdom of crowds' and 'crowd psychology'. There are two classes, which are for senior management major students. Conditions of two are same, except a class time. Forty five students in one class are tested for this experiment. They form a group with five people and are divided into 9 groups. In a case of a morning class, peer-to-peer evaluations are given to individuals in a class when a group presentation for a final project is given. On the other hand, in a case of afternoon class, peer-to-peer evaluations are given to each group in a class. The result is quite fruitful. The first is that an expert's evaluation for a project agrees with students, who are beginners in this field in the degree of more than 95%. However, in the case of afternoon class, students' group evaluation turns out to agree with an expert's one less than 53%. Morning class experiment result proves the truth of collective intelligence again. It tunrs out independent and confidential opinions are more cost effective and give right answers to questions than group opinions.

• Korean Journal of Hydrosciences
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• v.7
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• pp.21-35
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• 1996

This Study is to develop the suitable hydrologic models for determination of the size and location of detention storage facilities to restrain stormwater runoff in urban areas. Hypothetical areas of two levels are considered to seize the hydrologic response characteristics. A one-square-kilometer ares is selected for the catchment level, and a 10-square-kilometer area consisting of 10 catchments is adapted at the watershed level as representative of urban drainage area. In this analysis, different rainfall freqyencies, land uses, drainage patte군, basin shates and detention storage policies are considered. Folw reduction effect of detention storage facilities is deduced from storage ratio and detention basin factor. A substantial saving in detention storage volumes is achieved 노두 the detention storage is planned at the watershed level rather than the catchment level. For the application of real watersheds, two watersheds in Seoul metropolitan area-Jamshil 2 and Seongnae 1-are selected on the basis of hydrologic response charactaristics. Through the regression analysis between dimensionless deterntion storage volume, dimensionless upstream area ratio and reduction rate of storage ratio, the regression equations to determine the size and location of detention storage faclities are presented.

• Geomechanics and Engineering
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• v.37 no.1
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• pp.31-48
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• 2024

To stabilize the excavations in urban area, soil anchorage is among the very common methods in geotechnical engineering. A more efficient deformation analysis can potentially lead to cost-effective and safer designs. To this end, a total of 116 three-dimensional (3D) finite element (FE) models of a deep excavation supported by tie-back wall system were analyzed in this study. An initial validation was conducted through examination of the results against the Texas A&M excavation cases. After the validation step, an extensive parametric study was carried out to cover significant design parameters of tie-back wall system in deep excavations. The numerical results indicated that the maximum horizontal displacement values of the wall (δ_hm) and maximum surface settlement (δ_vm) increase by an increase in the value of ground anchors inclination relative to the horizon. Additionally, a change in the wall embedment depth was found to be contributing more to δ_vm than to δ_hm. Based on the 3D FE analysis results, two simple equations are proposed to estimate excavation deformations for different scenarios in which the geometric configuration parameters are taken into account. The model proposed in this study can help the engineers to have a better understanding of the behavior of such systems.

• KIPS Transactions on Computer and Communication Systems
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• v.10 no.9
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• pp.251-260
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• 2021

Gait analysis is one of the research fields for obtaining various information related to gait by analyzing human ambulation. It has been studied for a long time not only in the medical field but also in various academic areas such as mechanical engineering, electronic engineering, and computer engineering. Efforts have been made to determine whether there is a problem with gait through gait analysis. In this paper, as a pre-step to find out gait abnormalities, it is investigated whether it is possible to differentiate whether experiment participants wear elderly simulation suit or not by applying gait data to machine learning models for the same person. For a total of 45 participants, each gait data was collected before and after wearing the simulation suit, and a total of six machine learning models were used to learn the collected data. As a result of using an artificial neural network model to distinguish whether or not the participants wear the suit, it showed 99% accuracy. What this study suggests is that we explored the possibility of judging the presence or absence of abnormality in gait by using machine learning.

• Asia pacific journal of information systems
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• v.19 no.2
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• pp.73-94
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• 2009

The general aspects for the future warfare shows that the concept of firepower and maneuver centric warfare has been replacing with that of information and knowledge centric warfare. Thus, some developed countries are now trying to establish the information systems to perform intelligent warfare and innovate defense operations. The C4I(Command, Control, Communication, Computers and Intelligence for the Warrior) systems make it possible to do modern and systematic war operations. The basic idea of this study is to investigate how TAM(Technology Acceptance Model) can explain the acceptance behavior in military organizations. Because TAM is inadequate in explaining the acceptance processes forcomplex technologies and strict organizations, a revised research model based upon TAM was developed in order to assess the usage of the C4I system. The purpose of this study is to investigate factors affecting the usage of C4I in the Korean Army. The research model, based upon TAM, was extended through a belief construct such as self-efficacy as one of mediating variables. The self-efficacy has been used as a mediating variable for technology acceptance, and the variable was included in the research model. The external variables were selected on the basis of previous research. The external variables can be classified into following: 1) technological, 2) organizational, and 3) environmental factors on the basis of TOE(Technology-Organization-Environment) framework. The technological factor includes the information quality and the task-technology fitness. The organizational factor includes the influence of senior colleagues. The environmental factor includes the education/train data. The external variables are considered very important for explaining the behavior patterns of information technology or systems. A structured questionnaire was developed and administrated to those who were using the C4I system. Total 329 data were used for statistical data analyses. A confirmatory factor analysis and structured equation model were used as main statistical methods. Model fitness Indexes for measurement and structured models were verified before all 18 hypotheses were tested. This study shows that the perceived usefulness and the self-efficacy played their roles more than the perceived ease of use did in TAM. In military organizations, the perceived usefulness showed its mediating effects between external variables and dependent variable, but the perceived ease of use did not. These results imply that the perceived usefulness can explain the acceptance processes better than the perceived ease of use in the army. The self-efficacy was also used as one of the three mediating variables, and showed its mediating effects in explaining the acceptance processes. Such results also show that the self-efficacy can be selected as one possible belief construct in TAM. The perceived usefulness was influenced by such factors as senior colleagues, the information quality, and the task-technology fitness. The self-efficacy was affected by education/train and task-technology fitness. The actual usage of C4I was influenced not by the perceived ease of use but by the perceived usefulness and selfefficacy. This study suggests the followings: (1) An extended TAM can be applied to such strict organizations as the army; (2) Three mediation variables are included in the research model and tested at real situations; and (3) Several other implications are discussed.

• Journal of Technologic Dentistry
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• v.11 no.1
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• pp.71-81
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• 1989

This study was aimed for bettering productivity and technical level of the dental 1 aboratory, and helping the dental technician's benefits and rights, and then endowing them some belonged atmospher and stability on their post by Improving job- satisfaction and maintaining the transferability of one's post at a proper limitation. Therefore, 320 dental technicians extracted randomly from all the technicians working at 494 dental laboratories were subjected for this study. The approach to the study was a way through some postal questionaires executed from March 29, 1988 until May 4, the same year, in which total 254 technicians answered, showing 79% resp"nserate. responserate. The data-analysis was done by a model of the dental technician's transferability from their post, as considering Mobley's(1978)-model of post-transferability, and results through the study are as follows : 1. Satisfaction at a given post showed that the married is better than the unmarried(<0.05), and the experienced is better than the inexperienced(P<0.01). 2. Age, sex, educational experience, and one's service-duration did not affect significantly to the respondent's satisfaction on their post, statistically. 3. Satisfaction at a given post differed in adccordance with given conditions of one's post, i. e.,it stowed high when the monthly payment was good(P<0.05), and when too much duty on their job was given, it was the worst as shown in an example of the next order, too much

• Journal of the Korean earth science society
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• v.39 no.5
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• pp.501-515
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• 2018

In this study, the method of multiple working hypotheses (MMWH) as a method of earth scientific inquiry was applied in a context of abductive reasoning about the formation of a rock with a specific structure, and the characteristics of MMWH revealed in the reasoning process were explored. Participants were 31 senior undergraduate students enrolled in a course in a university of education. As part of the course, the participants performed abductive inquiry with multiple working hypotheses about the formation of a rock. The students were asked to record both the processes and results of their reasoning in sketchbooks. The content of the students' sketchbook reports was analyzed according to the principle of analytic induction. Results demonstrated four assertions. First, the participants' working hypotheses were suggested in the use of resource models, and the adaption of the resource models often occurred in this process. Second, the perceptual properties of evidence influenced the activation of the resource models. Third, the kinds of observed evidence and the different interpretations of evidence resulted into different judgments on working hypotheses. Fourth, sometimes new hypotheses were generated by the combination of alternative hypotheses. Implications of these findings for earth science education and relevant research were discussed.