• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.11
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• pp.2000-2006
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• 2011

Asynchronous phenomenon occurs on the synchronous generators under power system when a generator's amplitude of electromagnetic force, phase angle, frequency and waveform etc become different from those of other synchronous generators which can follow instantly varying speed of turbine. Because the amplitude of electromagnetic force, phase frequency and waveform differ from those of other generators with which are to be put into parallel operation due to the change of excitation condition for load sharing and the sharing load change, if reactive current in the internal circuit circulates among generators, the efficiency varies and the stator winding of generators are overheated by resistance loss. Where calculation method of protection settings and Logic for Protection of Generator Asynchronization will be recommended, A distance relay scheme is commonly used for backup protection. This scheme, called a step distance protection, is comprised of 3 steps for graded zones having different operating time. As for the conventional step distance protection scheme, Zone 2 can exceed the ordinary coverage excessively in case of a transformer protection relay especially. In this case, there can be overlapped protection area from a backup protection relay and, therefore, malfunctions can occur when any fault occurs in the overlapped protection area. Distance relays and overcurrent relays are used for backup protection generally, and both relays have normally this problem, the maloperation, caused by a fault in the overlapped protection area. Corresponding to an IEEE standard, this problem can be solved with the modification of the operating time. On the other hand, in Korea, zones are modified to cope with this problem in some specific conditions. These two methods may not be obvious to handle this problem correctly because these methods, modifying the common rules, can cause another coordination problem. To overcome asynchronizing protection this paper describes an improved backup protection coordination scheme using a new Logic that will be suggested.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2006.05a
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• pp.461-465
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• 2006

Recently, the operator modules to control external devices are concerned about automatic management system to process continuously changed signals. They need a efficient data management with high reliability and real time processing. The characteristics of these data are a large volume, a short report interval and asynchronous report time. The typical queries of these systems consist of the current query to search the latest signal value, the snapshot query to search the signal value of a past time, the historical query to search the signal value of a past tine to current. In this paper, we propose the efficient method to manage the above signals by using a file structured database in QNX operating systems. The data communications among the devices are done by Profibus-FMS protocol and the file databases are used for adjusting monitoring frequency and storing signals. The file database adopts a delta version and a periodical back up in due consideration of the resource limit of a small storage and a low computing power in QNX COM(Cabinet Operator Module).

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.7
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• pp.2638-2647
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• 2010

X-MAC reduces transmission delay and energy consumption by using a short preamble instead of the existing long preamble. To solve the problem of X-MAC, this paper proposes a new MAC protocol called Express-MAC. The wireless sensor network is mainly used for the purpose of gathering event data or situation information. Especially, the transmission pattern of the sensor network with the purpose of event detection such as intrusion detection is very intermittent as well as successively occurring when a single event takes place in most cases. By reflecting sensor network's key transmission patterns as above, EX-MAC has used multi-hub path's path reservation system and awake section's transmission time reservation method in data transmission when the first event takes place. The awake time reservation in transmission path has improved successive data transmission's end-to-end delay, and it has also increased efficiency in terms of energy consumption by reducing the preamble length of data transmission and reception node.

• Journal of the Korea Society of Computer and Information
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• v.7 no.3
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• pp.80-91
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• 2002

A general goal of the AT%(Asynchronous Transfer Mode) network is to support connect across various network. On ATM networks, ABR services are provided using the remained ban after allocation CBR and VBR traffic. Realtime services such as transmitting audio or video data may be provided using CBR ado VBR which have a constrained transmission delay, but in these cases, the communications bandwidth may be wasted. In this paper a simulation has been performed to compare and evaluate the performance between the ERICA(Explicit Rate Indicate Avoidance) and EPRCA(Enhanced Proportional Rate Control Algorithm) switches which use Explicit Rate switch algorithm for ABR switch. The variation of the ACR at the source end system, the queue length, the utilization rate of the link bandwidth and the share fairness at the transient and steady states are used as the evaluation criteria for the simulation. As a result of simulation, ERICA algorithm switch was ten times long compared to ERPCA switch to achieve assigned fair share. so EPRCA switch is superior to ERICA about load response. For Fair share and stability, ERICA switch is excellent to EPRCA switch.

• The Journal of the Korea Contents Association
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• v.21 no.4
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• pp.14-25
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• 2021

The purpose of this study is to explore what are the interactive factors of synchronous online education in university and identify the level of interaction. This study used mixed research method. As a result of the interaction level, it was recognized that face-to-face education could be more interactive than synchronous online education. Synchronous online education could have better interactive between instructor and learner, and among learners than asynchronous online education. Factors which influencing the interaction were as follows: small group activities and scaffolding, diversification of communication channels and integration of learner's question in learning content. Detrimental elements were distance felt between instructor and learners, low intimacy among learners, content-focused lecture, restrictions on non-verbal communication, unstable systems and misusing microphones. The necessary factors to promote interaction are planning interactive class activities, etc. Based on the results, it was to suggest what kinds of efforts are needed to make interaction more effective in terms of teaching and learning method & activity, tool & system, and environment.

• Journal of Korea Society of Industrial Information Systems
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• v.14 no.5
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• pp.11-18
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• 2009

Ajax based on Java Script receives attention as an alternative to ActiveX technology. Most portal sites in korea show a tendency to reopen existing services by combining the technology, because it supports most web browsers, and has the advantages of such a brilliant interface, excellent speed, and traffic reduction through asynchronous interaction. This paper modeled and implemented a multilingual meta-search service using the Ajax and open APIs provided by international famous sites. First, a Korean query is translated into one of the language of 54 countries around the world by Google translation API, and then the translated result is used to search the information of the social web sites such as Flickr, Youtube, Daum, and Naver. Searched results are displayed fast by dynamic loading of portion of the screen using Ajax. Our system can reduce server traffic and per-packet communications charges by preventing redundant transmission of unnecessary information.

• Journal of the Korea Society of Computer and Information
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• v.14 no.2
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• pp.79-89
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• 2009

As an IETF standard protocol, WebDAV provides infrastructure for managing and authoring resources and supports asynchronous collaborative authoring on the Web. The CoSlide server is an extension of the Jakarta Slide WebDAV server, providing various workspaces and collaborative services through the WebDAV protocol. The CoSlide server supports workspaces for storing and sharing information of various users, and provides environment for effective collaborative authoring. Actual collaboration activities are performed through a collaboration client software which provides collaboration services along with the CoSlide server. In this paper, we describe the development of the CoSpace client which operates in association with the CoSlide server, presenting effective collaborative environment. The CoSpace client provides user interfaces for accessing and controlling the resources of each workspace on the CoSlide server. In particular, CoSpace provides the facility to launch an authoring application from its workspace view, automatic locking, and downloading the content to be edited, and resource movement using mouse drag & drop.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.6
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• pp.1369-1380
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• 2011

Most existing mobile distance learning systems are asynchronous ones that allow students to download lecture video and presentation material. However, there are a few synchronous real-time mobile distance learning systems that support slide, annotation, feedback from student, and lecture video and audio at the same time. These live mobile distance learning systems have an advantage of supporting real-time interaction between students and a lecturer thereby making students understand the lecture better. But, they also have a disadvantage in the sense that they don't allow students to experience the past lecture. This problem can be solved by recording and replaying lecture session. So far, there are few mobile distance learning systems that support session recording and replay. This paper presents a synchronous mobile distance learning system that supports video and audio, slide with annotation, and real-time feedback from students, as well as session recording and replay, which is not supported by the existing mobile distance learning systems. The evaluation of the system among students shows that 61.3% of them were satisfied while 3.2% weren't.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.4
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• pp.409-417
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• 2013

Mu-communication board supported by multi-communication is designed with Atxmega 128A1 which is a low power energy consuming of 8-bit microcontroller. ATxmega128A1 microcontroller consists of 8 UART(Universal asynchronous receiver/transmitter) ports which can be setting appropriate user interface having command line interpreter(CLI) program with each port, 2 kbytes EEPROM, 128 kbytes flash memory, 8 kbytes SRAM. 8 URAT ports are used for the multi communication modem, GPS module, etc. and EEPROM is used for saving a configuration for program running, and flash memory of 128 kbytes is used for storing a Firm Ware, and 8 kbytes SRAM is used for stack, storing memory of global variables while program running. If we uses the hybrid communication of path optimization of VHF, TRS and CDMA to remote control AtoN(aid to navigation), it is able to remove the communication shadow area. Even though there is a shadow area for individual communication method, we can select an optimum communication method. The compatibility of data has been enhanced as using of same data frame per communication devices. For the test, 8640 of data has been collected from the each buoy during 30 days in every 5 minutes and the receiving rate of the data has shown more than 99.4 %.

• Journal of KIISE:Information Networking
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• v.28 no.4
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• pp.527-539
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• 2001

The wireless asynchronous transfer mode (ATM) system has the advantage of providing the broadband services with various quality-of-service requirements to the mobile terminal efficiently by utilizing the ATM technology developed for the wired ATM system. The available bit rate (ABR) service among various ATM services utilizes the available bandwidth remaining in the ATM link, which allows the efficient bandwidth usage. During the handoff of the mobile terminal, however, the queue length in the access point (AP) which resides in the boundary of the wired ATM network and the wireless ATM network may increase abruptly. In this paper, we propose a scheme which prevents the buffer-overflow and buffer-underflow in the AP during the handoff of the wireless ABR connection in the wireless ATM system using binary feedback rate-based ABR traffic control. This scheme controls the source's cell generation rate during both handoff period and some time interval after the completion of the handoff procedure. The simulation results show that the proposed scheme prevents the buffer-overflow and buffer-underflow. The proposed scheme can contribute to increasing the throughput of the wireless ABR service during handoff by preventing the buffer overflow and underflow during handoff period.