• Journal of KIISE:Computing Practices and Letters
• /
• v.15 no.11
• /
• pp.846-850
• /
• 2009

Recently, wireless sensor networks have found their way into a wide variety of applications and systems with vastly varying requirements and characteristics such as environmental monitoring, smart spaces, medical applications, and precision agriculture. The sensor nodes are battery powered. Therefore, the energy is the most precious resource of a wireless sensor network since periodically replacing the battery of the nodes in large scale deployments is infeasible. Energy efficient mechanisms for gathering sensor readings are indispensable to prolong the lifetime of a sensor network as long as possible. There are two energy-efficient approaches to prolong the network lifetime in sensor networks. One is the compression scheme to reduce the size of sensor readings. When the communication conflict is occurred between two sensor nodes, the sender must try to retransmit its reading. The other is the MAC protocol to prevent the communication conflict. In this paper, we propose a novel approaches to reduce the size of the sensor readings in the MAC layer. The proposed scheme compresses sensor readings by allocating the time slots of the TDMA schedule to them dynamically. We also present a mathematical model to predict latency from collecting the sensor readings as the compression ratio is changed. In the simulation result, our proposed scheme reduces the communication cost by about 52% over the existing scheme.

• Journal of Distribution Science
• /
• v.4 no.2
• /
• pp.21-40
• /
• 2006

Small and middle sized Franchise system channels experience conflicts because of constant interaction between franchiser and franchisee. However, it is rarely that attempt has been made to identify causes of conflicts in distribution of franchise industry. The purpose of this study was to explore cause of conflicts from the franchisee. For the study, data were collected from the owner or the shop-manager with a contractor in franchise systems. By means of in-depth interviews with multiple informants, their statement was analyzed qualitatively. From analysis of the resulting data, the causes of conflicts were associated with two broad sets, attitudinal and structural differences between franchisers and franchisees. First, attitudinal sources of conflict were identified as perception of subordinated relationships between channel members, delayed announcement on order changes, difficulties in communication by doing irresponsible behavior, different expectations between channel members in market territory and lack of consistent-supporting. Second, structural sources of conflict involved unilateral decision on interior, payment method, unreasonable delivery issue, treat franchisee with discrimination by the sales, in controlling against free management. There are limitations on generalization due to the results based on interview, but this study will be a useful exploratory step before designing a large scale survey.

• Korean Journal of Heritage: History & Science
• /
• v.48 no.2
• /
• pp.4-29
• /
• 2015

This article considered generally gradational change aspect, character of community for the tombs of the Three kingdoms prepared by some certain homogenous groups. It was completed by tracing the transfering process to grasp character of social structure and organizing System in the community. For this reason, it's analyzed that Wooden chamber tomb was formed in some certain Time-Space of the Yaksadong Buk-dong archaeological site in the Three Kingdom Period. Constructed group was distinguished by the five classes. So perhaps scale of Wooden chamber and sort, material of burial relics, the top layer and the upper layer were established two status those are active the ruling class led the Wooden chamber tomb's society, the general public hold a large majority from the middle class to the lowest class. And it depends on age(nonage-adult) that differed in relation of arrangement, character. It's changed with function or roles, property, purpose etc. of social community in accordance with these individual position, age. Received signification, value of social status were considered with social worth, faith. Members in a community had been conducted under premeditated, organised system for common target, relatedness. Also it seems to attempt organization's own maintenance, persistiveness in norms that given at common law. To do that, relation for combination between members who consisted systems had to be organic. The relation for combination was considered to form relation for the much larger community in based on blood relationship that most vital part. One social structure had established family(house, household) community in based on individual blood relationship, family communities gather up to develop into relative(blood relative, same race) community gradually. Furthermore, relative(blood relative, same race) communities, that focus on the public good gather up to develop into social community in based on regionalism. It's considered to go through the Development Process of family(house, household) community - relative(blood relative, same race) community - social community.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.19 no.3
• /
• pp.179-184
• /
• 2019

In many countries, such as developing countries where electricity is scarce, small wind turbines in the form of Off Grid are an effective solution to solve power supply problems. In some countries, the expansion of power systems and the decline of electricity-intensive areas have led to the use of small wind power in urban road lighting, mobile communications base stations, aquaculture and seawater desalination. With this change, the size of the small wind power industry is expected to have greater potential than large-scale wind power. In the case of small wind power generators, the generator is controlled at a variable speed, and the voltage and current generated by the generator have many harmonic components. To solve this problem, the AC to DC converter to be studied in this paper is a three-phase step-up type converter with a single switch. The inductor current is controlled in discontinuous mode, and has a characteristic of having a unit power factor by eliminating the harmonic of the input current. The proposed converter is composed of LCL filter and three phase rectification boost converter at the input stage and a single phase full bridge for grid connection. It is a control system with energy storage system(ESS) that the system stabilization can be pursued against the electric power.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.9
• /
• pp.7-13
• /
• 2019

Unlike a typical video wall system, video wall systems used for integrated monitoring in smart city environments should be able to display various videos, images, and texts simultaneously. In this paper, we propose an Internet Protocol (IP)-based video wall system that has no limit on the number of videos that can be monitored simultaneously, and that can arrange the monitor screen layout without restrictions. The proposed system is composed of multiple display servers, a wall controller, and video source providers, and they communicate with each other through an IP network. Since the display server receives and decodes the video stream directly from the video source devices, and displays it on the attached monitor screens, more videos can be simultaneously displayed on the entire video wall. When one video is displayed over several screens attached to multiple display servers, only one display server receives the video stream and transmits it to the other display servers by using IP multicast communications, thereby reducing the network load and synchronizing the video frames. Experiments show that as the number of videos increases, a system consisting of more display servers shows better decoding and rendering performance, and there is no performance degradation, even if the display server continues to be expanded.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.20 no.9
• /
• pp.412-419
• /
• 2019

Negative space in the discipline of art defines the space around and between the subject of an image. The use of negative space is an element of artistic composition, since it is occasionally used to artistic effect as the "real" subject of an image. In painting, it is a technique that negatively touches the background of an object to be expressed, so that it gives a feeling of unique texture and silhouette by touching unnecessary parts while leaving necessary parts. As in art, negative space in a design can also be useful to identify an image of infeasible design ranges with a straightforward view. Similarity between two disciplines leads to the introduction of the negative space concept for design space exploration. A rough design space exploration using statistics and visual analytics may support more efficient decision-making, and can provide meaningful insights into the direction of early-phase system design. For this, the approach guarantees dynamic interactions between visualized information and human cognitive systems. Visual analytics is useful to summarize complex and large-scale data. It is useful for identifying feasible design spaces, as well as for avoiding infeasible spaces or highly risky spaces. This paper investigates the possible use of the negative space concept by using an application example.

• Journal of Korea Water Resources Association
• /
• v.52 no.5
• /
• pp.313-323
• /
• 2019

Deep Tunnel system is a large-scale urban flood control facility installed underground in order to reinforce the lack of drainage systems in developed cities. In a structure like a deep tunnel system, the undular bore generated in the downstream causes a problem in the hydraulic stability of the tunnel. In this study, to investigate the influence of the undular bore on the hydraulic stability at the "Shinwol rainwater storage and drainage system", under construction for the first time in the country, a hydraulic model experiment was conducted on various flooding inflow scenarios. As a result of the hydraulic model experiment carried out in this study, the undular bore generated downstream is trapped in the pipe while moving to upstream, pushes the compressed air. It is judged that overflow occurred by choking the vertical drop shaft in the process when this compressed air is being exhaust through the upstream vertical drop shaft and blocking flood inflow. In addition, the analysis of velocity of undular bore shows that the undular bore transfers energy, and at this time, the pressure rose in the pipe and the velocity increment occurred of the undular bore. Further studies are needed to predict the size and velocity of undular bore, which plays an important role in the hydraulic stability of the tunnel in the deep tunnel system.

• Smart Structures and Systems
• /
• v.24 no.6
• /
• pp.769-781
• /
• 2019

Dynamic displacement response of civil structures is an important index for in-construction and in-service structural condition assessment. However, accurately measuring the displacement of large-scale civil structures such as high-rise buildings still remains as a challenging task. In order to cope with this problem, a vision-based system with the use of industrial digital camera and image processing has been developed for long-distance, remote, and real-time monitoring of dynamic displacement of supertall structures. Instead of acquiring image signals, the proposed system traces only the coordinates of the target points, therefore enabling real-time monitoring and display of displacement responses in a relatively high sampling rate. This study addresses the in-situ experimental verification of the developed vision-based system on the Canton Tower of 600 m high. To facilitate the verification, a GPS system is used to calibrate/verify the structural displacement responses measured by the vision-based system. Meanwhile, an accelerometer deployed in the vicinity of the target point also provides frequency-domain information for comparison. Special attention has been given on understanding the influence of the surrounding light on the monitoring results. For this purpose, the experimental tests are conducted in daytime and nighttime through placing the vision-based system outside the tower (in a brilliant environment) and inside the tower (in a dark environment), respectively. The results indicate that the displacement response time histories monitored by the vision-based system not only match well with those acquired by the GPS receiver, but also have higher fidelity and are less noise-corrupted. In addition, the low-order modal frequencies of the building identified with use of the data obtained from the vision-based system are all in good agreement with those obtained from the accelerometer, the GPS receiver and an elaborate finite element model. Especially, the vision-based system placed at the bottom of the enclosed elevator shaft offers better monitoring data compared with the system placed outside the tower. Based on a wavelet filtering technique, the displacement response time histories obtained by the vision-based system are easily decomposed into two parts: a quasi-static ingredient primarily resulting from temperature variation and a dynamic component mainly caused by fluctuating wind load.

• Journal of the Korean School Mathematics Society
• /
• v.23 no.4
• /
• pp.449-468
• /
• 2020

TIMSS is a representative international comparative study that analyzes changes in mathematics and science achievement, and it collects information on the educational system, curriculum, teaching and learning situation of participating countries as well as research and check, and provides implications for each country's mathematics and science education. Although domestic TIMSS studies focused on the results of achievement related to the evaluation of mathematics, not many have taken a closer look at the content and characteristics of the assessment framework. Therefore, the purpose of this study was to analyze the characteristics of the TIMSS 2019 mathematics assessment framework, and to derive implications for the mathematics curriculum and mathematics learning by examining the students' study time in light of the Korean mathematics curriculum. The implications derived from the results of this study are summarized as follows: First, it is necessary to check the connection between content elements in the mathematics and education process. Second, it is necessary to check the appropriateness and connectivity of the learning timing of the content elements in the mathematics and education courses. Finally, it is necessary to verify that the hierarchy of content areas and the structure of content systems in mathematics and education courses are consistent with the direction of mathematics education at the international level. This study can be used as a basis for mathematics and curriculum revisions, and can be used to set directions for the development of large-scale evaluation frameworks.

• Journal of the Korean earth science society
• /
• v.42 no.1
• /
• pp.76-87
• /
• 2021

In this study, temporal trend of researches in earthquake with groundwater level, water quality, radon, remote sensing, electrical resistivity, gravity, and geomagnetism was searched from 2001 to 2020, using the journals indexed in Web of Science, and the number of articles published in international journals was counted in relation to the occurrences of earthquakes (≥Mw 5.0, ≥Mw 6.0, ≥Mw 7.0, ≥Mw 8.0, and ≥Mw 9.0). The number of articles shows an increasing trend over the studied period. This is explained by that studies on earthquake precursor and seismic monitoring becomes active in various fields with integrated data analysis through the development of remote sensing technology, progress of measurement equipment, and big data. According to Mann-Kendall and Sen's tests, gravity-related articles exhibit an increasing trend of 1.30 articles/yr, radon-related articles (0.60 articles/yr), groundwater-related articles (0.70 articles/yr), electrical resistivity-related articles (0.25 articles/yr), and remote-sensing-related articles (0.67 articles/yr). By cross-correlation analysis of the number of articles in each field with removing trend effect and the number of earthquakes of ≥Mw 5.0, ≥Mw 6.0, ≥Mw 7.0, ≥Mw 8.0, and ≥Mw 9.0, radon and remote sensing fields exhibit a high cross-correlation with a delay time of one year. In addition, large-scale earthquakes such as the 2004 and 2005 Sumatra earthquake, the 2008 Sichuan earthquake, the 2010 Haiti earthquake, and the 2010 Chile earthquake are estimated to be related with the increase in the number of articles in the corresponding periods.