• Journal of the Korea Academia-Industrial cooperation Society
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• v.13 no.11
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• pp.5326-5336
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• 2012

Most middle and high school students in Korea use internet for gaming and recreation. This study aimed to classify middle and high school students according to amount of time they spend playing games and analyze relationship domestic factors. Weekday game times and environmental factors of the adolescents in Korea. The group with average game time of 30 min, 0:30-1:30 hours, 1:30-3:00 hours, over 4:00 hours. Subjects in this study were 6,487 middle and high school students. For the category "thoughts about game characters", the group with average game time of 1:30~3:00 hours replied "not at all" but the group with average game time of over 4:00 hours replied "sometimes", which was significantly different from the previous group. Similarly, for the category "lack of time for homework", the group with average game time of 1:30~3:00 hours replied "not at all", which significantly differed from the "sometimes" response from the group with average game time. For satisfaction with interest, "average" was the most frequent response from all the groups. Analyzing correlation of factors influencing game addiction in subjects with game time showed that factors related to game addiction diagnosis and academic performance were especially different in the group with average game time of over 4:00 hours compared to other groups. Nowadays internet has taken a large and significant part of our life such that a life without internet is hard to imagine, and our dependency on internet has risen at the same time. Accordingly, education on appropriate utilization and correct usage of internet to youths who lack self-control and judgment is very needed.

• The KIPS Transactions:PartB
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• v.9B no.5
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• pp.587-598
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• 2002

In multicast environment, the main objective of group key management is to provide security services to group communications by sharing a single group key among all the members of the group and subsequently encrypting and decrypting all the communication messages exchanged among the members of the group. Up to now, there has been no effort to develop group key management mechanism that considers the rate of users' join/leave operations. Hence, in this research, we propose group key management mechanisms that consider the rate of user's join/leave operations. We also define a new tree structure called variable tree which is much more flexible than full regular trees and show that variable trees are more efficient than full regular trees for group key management. Especially, we propose an algorithm that minimizes the necessary number of rekey messages according to the rate of join and leave operations. We also shows that if the rate of leave operation is greater than 50%, then the tree structure with degrees 2 or 3 are the optimal structures.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.11 no.6
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• pp.41-51
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• 2001

Group signature schemes allow a group member to sign messages anonymously on behalf of the group. In case of dispute, only a designated group manager can reveal the identity of the member. During last decade, group signature schemes have been intensively investigated in the literature and applied to various applications. However, there has been no scheme properly handling the situation that a group member wants to leave a group or is excluded by a group manager. As noted in[3], the complexity of member deletion stands in the way of real world applications of group signatures and the member deletion problem has been a pressing open problem. In this paper we propose an efficient group signature scheme that allows member deletion. The length of the group public key and the size of signatures all independent of the size of the group and the security of the scheme relies on the RSA assumption. In addition, the method of tracing all signatures of a specific member is introduced.

• Journal of Korean Society for Geospatial Information Science
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• v.21 no.3
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• pp.37-46
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• 2013

Similarity measure of catchments is essential for regionalization studies, which provide in depth analysis in hydrological response and flood estimations at ungauged catchments. However, this similarity measure is often biased to the selected catchments and is not clearly explained in hydrological sense. This study applied a type of hydrological similarity distance measure-Flood Estimation Handbook to 25 Geum River catchments, Korea. Three Catchment Characteristics, Area(A)-Annual precipitation(SAAR)-SCS Curve Number(CN), are used in Euclidian distance measures. Furthermore, six index of Flow Duration Curve are applied to clustering analysis of SPSS. The catchments' grouping of hydrological similarity measures suggests three groups (H1, H2 and H3) and the four catchments are not grouped in this study. The clustering analysis of FDC provides four Groups; F1, F2, F3 and F4. The six catchments (out of seven) of H1 are grouped in F1, while Sangyeogyo is grouped in F2. The four catchments (out of six) of H2 are also grouped in F2, while Cheongju and Guryong are grouped in F1. The catchments of H3 are categorized in F1. The authors examine the results (H1, H2 and H3) of similarity measure based on catchment physical descriptors with results (F1 and F2) of clustering based on catchment hydrological response. The results of hydrological similarity measures are supported by clustering analysis of FDC. This study shows a potential of hydrological catchment similarity measures in Korea.

• Journal of Fisheries and Marine Sciences Education
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• v.9 no.2
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• pp.236-245
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• 1997

On the basis of the seven species of fish caught by fishing boats with two crewmen belonging to the Iwawada Fisheries Cooperative of Chiba Prefecture, the fishing boats were classified by species withhigh market values, and the results obtainedwere reclassified by discriminant function. As a result, the fishing boats were classified into four groups. These four groups are : G1 featuring themain catchesof yellowtailsand skipjack/tunas ; G2 yellowtails and squids ; G3 squids and skipjack/tunas, and G4 octopus and other miscellaneous specles. Furthermore, principal component analysis were carried out on fish catches of the seven species in terms of the value obtained from a catch from the scores of the first, second and third principal components. The results of analysis show that Groups G1, G2 and G3 assume identical fishing form, while only Group G4 asumes a different fishing form.

• Journal of the Korea Institute of Information Security & Cryptology
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• v.21 no.3
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• pp.75-88
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• 2011

Messages need to transmit to the neighbors securely in wireless sensor network, because a sensor node is deployed in hostile area. Thus it is necessary to support secure communication. One of the most important communication part is secure multicast. Especially, group rekeying is a big problem for multicast key management. So, group rekeying must be proceed securely when secrete information is exposed by attacker. Many group rekeying schemes have been studied for ad hoc networks. However, these schemes are Ill1desirable in WSNs. In this paper, we proposed a novel group rekeying scheme in WSNs that it has very powerful security.

• Journal of the Mineralogical Society of Korea
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• v.18 no.3 s.45
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• pp.165-181
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• 2005

The granitic rocks distributed in the southern part of the Yangsan Fault are classified into five distinct rock facies based on the field relation, petrography and geochemical characteristics. These five different rock facies can be grouped into two considering their origins. Group I, which reveals various evidences of magma mixing, includes three rock facies of granodiorite, enclave-rich porphyritic granite, and enclave-poor porphyritic granite. Group H intruding Croup I includes equigranular granite and micrographic granite with no evidence of magma mixing. It is suggested that the distinctively different trace element and isotopic chemistries between group I and II, support evolution from the different parental magma. It is suggested that the three rock facies in group I were generated by different degrees of magma mixing in addition to fractionation of plagioclase. MMEs experienced fractionation of biotite. The two facies in group H seem to have been generated from different parent magma from group I and evolved by fractionation of K-feldspar. The Rb-Sr whole-rock ages of the group I rocks yield $59.2\~58.9Ma$, and those of the group II rocks give 53. $3\~51.7Ma$, regardless of their distribution whether they occur in the eastern or western parts of the Yangsan Fault. Based on Sm-Nd isotope compositions, depleted mantle model ages $(T_2DM)$ of the group I range $0.8\~0.9Ga$, while those of the group II$0.6\~0.7Ga$.

• Journal of Scientific & Technological Knowledge Infrastructure
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• s.8
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• pp.85-91
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• 2002

서울그리드센터는 서울시립대학교에 사무국을 두고 있다. 현재, KISTI에서 주관한 GRID Forum Korea(GFK)에 참여하여 국가 그리드 사업을 서울지역을 중심으로 전개하고 있다. 서울그리드센터워킹그룹(의장: 이용우교수), 전산물리 워킹그룹(의장: 민현수교수), 그리드 서비스워킹그룹(의장 : 김진석교수)의 3개 Working Group과, 고려대학교의 정창성교수가 의장으로 있는 객체지형 미들웨어 워킹그룹이 현재 참여하고 있다. 또한. 한국기초과학연구원이 의장으로 있는 원격연구그리드워킹그룹과 동반관계에 있다. 서울그리드센터는 다른 기관과 워킹그룹들과 협력하기 위하여 문호를 활짝 개방하고 있다.

• The Journal of Korean Academy of Prosthodontics
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• v.47 no.4
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• pp.406-415
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• 2009

Purpose: The purpose of this study was to compare the marginal fitness and fracture load of the zirconia copings according to the design with different thickness and coloration. Material and methods: The evaluation was based on 80 zirconia copings. Zirconia copings were fabricated in design with different thicknesses using CAD/CAM system (Everset, KAVO dental GmbH, Biberach, Germany). The designs of copings were divided into four groups. The first group consisted of copings with uniform thickness of 0.3 mm. The thickness in the second group was 0.3 mm on the buccal surface and 0.6 mm on the lingual surface. The third group consisted of coping with uniform thickness of 0.6 mm. The thickness in the fourth group was 0.6 mm on the buccal surface and 1mm on the lingual surface. Each group consisted of 10 colored and 10 uncolored copings. Half of the copings (40) processed with a milling system according to the specific design were sent to be given a color (A3) through saturation in special dye by a manufacturing company. Just after sintering, the marginal discrepancies of copings were measured on the buccal, lingual, mesial and distal surfaces of metal die, under a Video Microscope System (sv-35, Sometech, Seoul, Korea) at a magnification of $\times$ 100. It was remeasured after the adjusting of the inner surface. Next, all copings were luted to the metal dies using reinforced cement {GC FujiCEM (GC Corp. Tokyo, Japan)} and mounted on the testing jig in a Universal Testing Machine (Instron 4467, Norwood, MA, USA). The results were analyzed statistically using the one-way ANOVA test. Results: The obtained results were as follow: 1. The measured value of marginal discrepancy right after sintering was the greatest in the contraction of the buccal area in all groups, except for group I2. 2. There was no significant difference of marginal fitness among the groups in the colored zirconia group (P<.05). 3. When the marginal fitness among the groups in the uncolored zirconia group was considered, group II2 had the smallest marginal discrepancy. 4. When the colored and uncolored groups with the same design were compared, there was a significant difference between I1 and II1 groups. In group 2, 3, and 4, the uncolored zirconia had the greatest marginal fitness (P<.05). 5. After adjustment of inner surface, there was no significant difference in the marginal fitness in all groups when color and design of the zirconia coping were compared. 6. The fracture load of CAD/CAM zirconia copings showed significant difference in group 1, 2, 3, and 4. I4 and II4 had the strongest fracture load. 7. When groups with different color and same design were compared, all colored groups showed greater fracture load (P>.05), with no significance. Conclusion: There was difference in the marginal fitness according to the design and coloration of zirconia copings right after sintering, but it was decided that the copings may well be used clinically if the inner surface are adjusted. The copings should be thick enough for the reinforcement of fracture strength. But considering the esthetics of the visible surfaces (labial and buccal surface), the thickness of copings may be a little thin, without giving any significant effect on the fracture strength. This type of design may be considered when giving priority to preservation of tooth or esthetics.

• Journal of Life Science
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• v.20 no.2
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• pp.304-313
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• 2010

Out of the tenth graders of K girl's high school in J city, 24 students whose %fat was over 30% were divided into 3 groups through Purposing Sampling. Groups A and B were exercise groups and C was the control group. Using Borg's RPE (rating of perceived exertion), RPE 15-17 (hard-very hard) $\times$ 3 sets were set up for group A, RPE 11-13 (fairly light-somewhat hard) $\times$ 3 sets were set up for group B, and both groups performed step aerobics (step box: 68cm in length, 28cm in width, 15cm in hight, 450g in weight) for 50-60 minutes a day, 3 days a week for 8 weeks in total. This research was conducted to find out the effects of various RPE in step aerobics on the immunologic function (neutrophil, lymphocyte, monocyte, eosinophil, basophil, IgG, IgA, and IgM levels) of overweight female high school students. By using SPSS Ver. 14.0, a repeated two-way ANOVA was conducted to find out the effects of interaction between the groups and time period, paired t-test to evaluate data within each group, and pre- and post experiment difference rates (%diff) to perform one-way ANOVA for group comparisons. The following results were found. As for WBC, within group A, neutrophil, monocyte, basophil, and eosinophil levels increased, while lymphocyte levels remained the same. Within group B, eosinophil levels decreased while neutrophil, lymphocyte, monocyte, and basophil levels showed no differences. Within the control group, neutrophil, basophil, and eosinophil levels decreased while lymphocyte and monocyte levels showed no differences. As for the group comparisons, neutrophil levels increased more in group A than group B and the control group. There were no differences in lymphocyte levels among the three groups. Monocyte levels increased more in group A and B than the control group. Basophil and Eosinophil increased more in group A than group B and the control group. As for immunoglobin, within group A, the IgG level increased but the levels of IgA and IgM did not change. Within group B, the IgA level increased but the level of IgG decreased, and the level of IgM did not change. Within the control group, the IgG level decreased but the levels of IgA and IgM did not change. As for the group comparisons, the level of IgA increased more in group A than the control group, and the level of IgG increased more in group A than group B and the control group, but levels of IgM among the three groups did not show any difference. In summary, WBC and Ig levels showed that the three groups remained at the reference interval even after the exercise program. However, group A, which performed RPE 15-17 in step aerobics, showed increase in more measured items than the other groups, and this implies that the immunologic function has improved in the range of the reference intervals. Therefore, it will be effective to conduct step aerobics with the RPE 15-17 (hard-very hard) in order to increase the immunologic function.