• Journal of Powder Materials
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• v.25 no.2
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• pp.137-143
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• 2018

In this study, two types of SKD61 tool-steel samples are built by a selective laser melting (SLM) process using the different laser scan speeds. The characteristics of two kinds of SKD61 tool-steel powders used in the SLM process are evaluated. Commercial SKD61 tool-steel power has a flowability of 16.68 sec/50 g and its Hausner ratio is calculated to be 1.25 by apparent and tapped density. Also, the fabricated SKD61 tool steel powder fabricated by a gas atomization process has a flowability of 21.3 sec/50 g and its Hausner ratio is calculated to be 1.18. Therefore, we confirmed that the two powders used in this study have excellent flowability. Samples are fabricated to measure mechanical properties. The highest densities of the SKD61 tool-steel samples, fabricated under the same conditions, are $7.734g/cm^3$ (using commercial SKD61 powder) and $7.652g/cm^3$ (using fabricated SKD61 powder), measured with Archimedes method. Hardness is measured by Rockwell hardness testing equipment 5 times and the highest hardnesses of the samples are 54.56 HRC (commercial powder) and 52.62 HRC (fabricated powder). Also, the measured tensile strengths are approximately 1,721 MPa (commercial SKD61 powder) and 1,552 MPa (fabricated SKD61 powder), respectively.

• Journal of Digital Convergence
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• v.10 no.11
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• pp.29-38
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• 2012

This study conducted a survey 185 adolescents in multi-cultural family to measure the level of their social capital and their acculturation stress and examined how it affects them to adapt to school. Followings are the main results of this study. First, after measuring the social capital level of those surveyed, their average was lower than the normal level, showing 2.24(SD=.32), and their acculturation stress showed 2.54(SD=.58), a bit higher than the normal level. Second, their level of adapting to school showed 2.26(SD=.39), which was lower than the normal level, and there was statistically a meaningful difference between the groups depending on their grade, academic level, economic level, parents' marital status, mother's Korean ability. Third, the factors that affected in adapting to school were in the order of their network of social capital(${\beta}$=.225), mother's Korean ability(${\beta}$=.195), acculturation stress(${\beta}$=-.175), interpersonal trust of social capital(${\beta}$=.171), norm of social capital(${\beta}$=.161), parents' marital status(${\beta}$=.156), academic level(${\beta}$=.151), economic level(${\beta}$=.145). Based on these results, this study suggest ways to promote trust building among people and network formation through active use of information communication, and to improve multi-cultural acceptability by developing and using various contents.

• Journal of Digital Convergence
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• v.10 no.11
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• pp.541-550
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• 2012

The purpose of this study was to investigate the effect of aerobic exercise training and half bath on blood component, cardiorespiratory function, and vascular compliance of middle-aged obese men. The subjects were 3 groups; aerobic exercise(n=10), half bath(n=10), and controlled group(n=10). They were tested on their blood component, cardiorespiratory function, and vascular compliance at the beginning and at the end of the 12-week study(pre-post test). For data analysis, mean and standard deviation scores were calculated, and repeated measure two-way ANOVA and Scheffe were used. The results of this study are as follows. First, aerobic exercise group was significantly improved on all blood component after the 12-weeks, and showed significant difference among groups. Half bath group was better than control groups on Triglyceride, LDL-C, and HDL-C levels. Second, aerobic exercise group was significantly improved on maximum oxygen uptake, maximum heart rate, and maximum ventilation after the 12-weeks. Third, in vascular compliance measured in both hands and both feet, the half bath group and aerobic exercise training group were significantly increases the control group. Therefore, these results imply that aerobic exercise and half bath can be helpful for better blood component, cardiorespiratory function, and vascular compliance in middle-aged obese men.

• Journal of Digital Convergence
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• v.12 no.5
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• pp.13-24
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• 2014

This study is the first model to apply the concept of media engagement to a political campaign by which the voters' mind toward the supporting political candidates, are read. Thus it provides the theoretical and practical implications to the political campaign, and eventually contributes to the development of democracy. For these objectives, the total of 729 people who have the right to vote were telephone surveyed using the peoplemeter, CATI program in the 18th Presidential Election (12 areas including Seoul) of Dec. 19th 2012, and Re and By-election of April 24th 2013. Research question is to examine how the 5 attributes of the media engagement (interest, immersion, relevance, satisfaction and participation), play a role as the moderating variables in cross-correlation, socio-economic status and media properties. The result shows that of the five properties of media engagement, the relevant factor is the important parameter of mediating variable to the causal relationship. The media usage (TV, SNS, print media), socio-economic status (gender, age, income, marriage and area), involvement and the Presidential Election, and Re and By-election are also effective in the five attributes of media engagement. These results suggest that the a study model can measure the campaign effectiveness. This study will contribute significantly to the development of politics, election, media, advertising, and public relations area as well as to promote interdisciplinary research.

• Journal of Digital Convergence
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• v.11 no.1
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• pp.315-320
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• 2013

We have investigated the variation of spherical aberration of the anterior and posterior surface in a Korean sample population with various age between 20 to 71 years old. We used Pentacam (Oculus Inc., Germany) to measure the corneal radius, asphericity, and spherical aberration of 290 patients with normal cornea. There were negative correlation between corneal anterior radius and spherical aberration(r = -0.22, p<0.0001), and, there were negative correlation between corneal posterior radius and spherical aberration(r=-0.27, p < 0.0001). There were positive correlation between anterior asphericity and spherical aberration(r = 0.24, p < 0.0001), however there were negative correlation between posterior asphericity and spherical aberration(r = -0.17, p=0.00288).The average of anterior spherical aberration and posterior spherical aberration was $0.482{\pm}0.099{\mu}m$ and $-0.098{\pm}0.029{\mu}m$. The average of spherical aberration was $0.385{\pm}0.097{\mu}m$. There were significant positive correlations between anterior spherical aberration and age(r = 0.227, p<0.0001), and there were positive correlations between posterior aberration and age(r = 0.349, p<0.0001). It is considered that this data can be used as basic information for furture studies for improving the quality of vision of modern human and, through the analysis of the spherical aberration of cornea was to provide a better understanding of the optical part of the Korean's eye.

• Journal of Digital Convergence
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• v.11 no.1
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• pp.255-265
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• 2013

This study deals with the policy proposals focusing on the addiction for the rapidly growing social media service (SNS) and its diagnosis. Researcher intends to define the SNS addiction and develops a diagnostic measure, which is a valuable subject. The reason is why the SNS becomes more convenient with prevalence of smart phones and the SNS addiction becomes enough severe to suggest internet addiction policy. Researcher presents the subjects into three parts. Firstly, the SNS addiction variables are derived and validated. Secondly, the path model between the SNS addiction variables is verified and discussed. Thirdly, researcher proposes the diagnostic results and the group comparison. Therefore, the result of this study is that the SNS addiction can be measured by the four elements, which are the failure in stopping the use of the SNS, time tolerance, living disability, withdrawal and anxiety. Researcher verifies the sequential impact of each variable and figures out the SNS addict through the presentation of a realistic measurement for the addiction index and the determination of the level of the addiction. By the above result, the researcher proposes the public relations of the government policy for the sound usage of the SNS and the self management of user. Finally, various proposed in this study will help to prevent juvenile crime, social problems in the future.

• Journal of Digital Convergence
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• v.17 no.12
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• pp.319-327
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• 2019

The muscle activity and balance ability of the acute stroke patient has been checked by the functional electrical stimulation using biofeedback fusion postural control training in this study. Functional electrical stimulation using biofeedback fusion postural control training have been implemented on 15 trainees and general biofeedback fusion postural control training have been implemented on another 15 trainees for 30 minutes at 5 times per week during 8 weeks, and vastus lateralis, vastus medialis, rectus femoris and biceps femoris have been measured using the biceps femoris to evaluate the muscle activity of the lower extremity. The moving surface area, whole path length and limited of stability have been measured using biorecue to measure the balance ability. There was statistically meaningful difference on the vastus lateralis, vastus medialis, rectus femoris and biceps femoris in the muscle activity of the lower extremity and there was statistically meaningful difference on surface area, whole path length and limited of stability in the balancing ability. Based on above, it is realized that the functional electrical stimulation using biofeedback fusion postural control training is more effective than the general biofeedback fusion postural control training on the improvement of the muscle activity of the lower extremity and the balance ability.

• Journal of Digital Convergence
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• v.17 no.12
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• pp.181-190
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• 2019

The purpose of this study is to evaluate the operational efficiency of Chinese e-commerce companies and to present measures to improve efficiency. This paper selected 16 enterprises as the research objects, from the e-commerce demonstration enterprises of the Ministry of Commerce of China in 2017-2018, to conduct an empirical study on the operating efficiency of e-commerce enterprises. By using DEA method, we selected 3 input and 2 output indicators to measure the input-output efficiency of enterprises from input-oriented. Using different model in DEA, we calculated the technical efficiency, pure technical efficiency and scale efficiency, also efficiency based on the sample of 2018 and horizontal analysis from 2016 to 2018. The analysis showed that the overall efficiency of Chinese e-commerce companies was continuously improving, and that their business capabilities and business scale were also gradually improving. Through the calculation of efficiency, we evaluated the competitiveness of the e-commerce demonstration enterprises, and explored measures to improve their management efficiency. At the same time, it put forward some reasonable suggestions to adjust the scale, and enhance the competitive advantage.

• Journal of Digital Convergence
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• v.16 no.12
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• pp.283-292
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• 2018

UHD (Ultra High Definition) broadcasting technology, and UWV (Ultra Wide Vision) which is the high quality panoramic video of wide view angle based on UHD, were commercialized in Korea for the first time in the world, and those are representative realistic video technologies that maximize the user's sense of presence. By comparing the user's subjective reaction of UHD and UWV, the purpose of this study is to systematically establish the user's subjective video quality evaluation. For this purpose, a large screen projection experiment is designed by setting the screen size (4k x 2k, 8k x 2k) and content types (sports, landscape, concert) as variables to measure the user's subjective video quality evaluation and satisfaction. As a result of the study, the users' evaluation of UWV was higher than UHD in all items of subjective video quality, and satisfaction. Moreover, the results showed the significant differences depending on the video contents. Based on the results of the research, the study proposed the points necessary for the development and commercialization of UWV panoramic technology, and suggestions for the future research.

• Journal of Digital Convergence
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• v.18 no.12
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• pp.267-278
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• 2020

ESS is an essential requirement for resolving power shortages and power demand management and promoting renewable energy at a time when the energy paradigm changes. In this paper, we propose a cost-effective ESS Peak-Shaving operation plan through load and solar power generation forecast. For the ESS operation plan, electric load and solar power generation were predicted through RMS, which is a statistical measure, and a target load reduction guideline for one hour was set through the predicted electric load and solar power generation amount. The load and solar power generation amount from May 6th to 10th, 2019 was predicted by simulation of load and photovoltaic power generation using real data of the target customer for one year, and an hourly guideline was set. The average error rate for predicting load was 7.12%, and the average error rate for predicting solar power generation amount was 10.57%. Through the ESS operation plan, it was confirmed that the hourly guide-line suggested in this paper contributed to the peak-shaving maximization of customers.Through the results of this paper, it is expected that future energy problems can be reduced by minimizing environmental problems caused by fossil energy in connection with solar power and utilizing new and renewable energy to the maximum.