• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.10
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• pp.1542-1547
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• 2012

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. When 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.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.6
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• pp.837-843
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• 2012

Asynchronous motors are widely used in many fields. The various starting methods have been developed for the asynchronous motors which have large power compared to source power. The most popular ways to start the motors are to reduce the voltage of motor's stator or change the resistance fed rotor. It is needed to the specific time to reduce the voltage and change the resistance at a specific step. We call it the switching time. It is very difficult to know the switching time exactly. It varies with different types of motors as well as load characteristics. Thus, this paper focuses on the design and development for the mathematical models of motor and load. And then it is implemented in SIMULINK in order to calculate this time. The simulation results are both compared and discussed in detail so that it can be applied for new system with various motors and loads.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.15 no.4
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• pp.1-7
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• 2015

Until now, face to face coaching has been applied almost for completing the goal in various field. Face to face coaching is difficult always to reach each other anywhere, anytime due to the availability of internet and mobile devices. Recently, e-coaching is attempted to expend. But current e-coaching is supporting the secondary role for face to face coaching. E-coaching system has many benefits to use advancement technologies in internet. Therefore, the development of e-coaching system based on horizontal relationships between coach and coachee needs to communication anytime and anywhere in Internet. Usually previous online coaching systems have four types of interactions i.e. electronic mail, video chat, text chat, phone call. Most of the e-coaching approaches are easy to access and provide communication synchronous; video chat is an excellent visibility, whereas e-mail is asynchronous and document-centric. In this paper, we design and implement the integration e-coaching system based on synchronous and asynchronous. This system provides the asynchronous coaching offered by way of e-mail, and the synchronous coaching used P2P (Peer to Peer) video chat and text group chat. This system allows simultaneously asynchronous and synchronous coaching, and supports individual and group communication for periodical or informal coaching.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.15 no.3
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• pp.660-672
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• 2011

The Web is widely used to share information, utilizing the client-server model. In the client-server model, since the server only responds according to explicit requests from the client, the model seems hard to support sharing of massive information rapidly changing in today's Internet. The technology known as Server Push enables the server to actively provide information to clients without explicit requests from the clients using Web pages. Although various studies have been done to realize the Server Push technologies, there are many problems in the development of push application without push engines which support infrastructures for the effective development of push application. In this paper, we develop JPE(Java Push Engine) which presents the effective support for push services over the Internet. JPE is composed of two main components: the JPE Core supporting Epoll and the JPE Library supporting asynchronous communication. In addition, JPE defines various push functions and provides programming interfaces supporting the functions. Push applications developed using JPE effectively manages client connections with Epoll mechanism, providing push services through AJAX-based asynchronous communication.

• Journal of Korea Multimedia Society
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• v.9 no.5
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• pp.681-690
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• 2006

With the rapid development of network and multimedia technologies, computer mediated communication has been realized and there has been a great potential to use and research on asynchronous voice communication systems. This paper reports a case study where 6 groups(3 for documentation work, 3 for software development) of 24 people who used voice mail when carrying out their projects. The purpose of this study is to obtain an overall understanding of usability of voice mail which is a typical example of asynchronous voice communication systems, under a particular situation where project works are performed. Through the study, we came to understand general purposes of usage of voice mail, patterns of using it revealed during the project process, different ways of using it according to different types of projects, and reasons why people are currently not likely to use voice mail. The results hopefully provide systems developers with a guideline to understand the nature of voice mail from users' perspectives.

• Journal of the Korean Institute of Telematics and Electronics
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• v.23 no.1
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• pp.10-19
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• 1986

This is the last part of the four-part describing the development of a packet-switched computer communication network named the KORNET. In this paper we describe the design and implementation of the packet assembler/dissassembler (PAD) protocol for the asynchronous channel service, and of the network management softwares. The line processing module-B(LPMB) system supporting the asynchronous line includes a PAD protocol, a packet mode DTE/DCE protocol converting to the X.25 protocol, and the asynchronous receiver/transmitter(ART) software. The network management software is operated in master central processing module(MCPM) which includes virtual circuit management (VCM) managing the user channel, the routing management and the high level protocol for communication between the network management center (NMC) and the network node processor(NNP). In this paper, the design, implementation and operation of the softwares for the above service functions will be described in detail.

• Proceedings of the IEEK Conference
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• 2001.09a
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• pp.963-966
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• 2001

The wideband DS-CDMA (W-CDMA) system is one of the candidates for the next generation mobile communication system known as IMT-2000. The important concept of W-CDMA is the introduction of intercell asynchronous operation. In this paper, we design and analyze the system level simulator for the International Mobile Tele communication - 2000 (IMT-2000) 3-rd generation partnership project (3GPP) system. We confirm how the simulator works by BER over different Eb/NO. This study will be expected to use as reference data in the development of asynchronous IMT-2000. In this paper, we analyze a physical layer of W-CDMA system and design a transmitter and receiver by using ADS (Advanced Design System). Also, we simulated a link level performance in Rayleigh fading channel environment. This study will be useful in the analysis and design of W-CDMA system.

• Journal of Korean Society of Transportation
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• v.12 no.3
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• pp.49-64
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• 1994

The development of a mathematical modular framework based on Petri Network theory to model a traffic network is the subject of this paper. Traffic intersections are the primitive elements of a transportation network and are characterized as event driven and asynchronous systems. Petri network have been utilized to model these discrete event systems; further analysis of their structure can reveal information relevant to the concurrency, parallelism, synchronization, and deadlock avoidance issuse. The Petri-net based model of a generic traffic junction is presented. These modular networks are effective in synchronizing their components and can be used for modeling purposes of an asynchronous large scale transportation system. The derived model is suitable for simulations on a multiprocessor computer since its program execution safety is secured. The software pseudocode for simulating a transportation network model on a multiprocessor system is presented.

• International Journal of Contents
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• v.12 no.2
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• pp.49-57
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• 2016

This paper aims to explore instructional design of a cyber classroom for secondary students' basic English language competence. A paucity of support for low or under achieving students' English learning exists particularly at the secondary level. In order to bridge the gap, there has been demand for online educational resources considered to be an effective tool in improving students' self-directed learning and motivation. This study employs a comprehensive approach to instructional design for the asynchronous cyber classroom with the underlying premise that different learning theories can be applied in a complementary manner to serve different pedagogical purposes best. Gagné's conditions of learning theory, Bruner's constructivist theory, Carroll's minimalist theory, and Vygotsky's social cognitive development theory serve as the basis for designing instruction and selecting appropriate media. The ADDIE model is used to develop online teaching and learning materials. Twenty-five key grammatical features were selected through the analysis of the national curriculum of English, being grouped into five units. Each feature is covered in one cyber asynchronous class. An Integration Class is given at the end of every five classes for synthesis, where students can practice grammatical features in a communicative context. Related theories, pedagogical practices, and practical web-design strategies for cyber Basic English classes are discussed with suggestions for research, practice and policy to support self-directed learning through a cyber class.

• The Journal of the Acoustical Society of Korea
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• v.39 no.3
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• pp.163-169
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• 2020

The asynchronous bistatic sonar needs to estimate direct blast arrival time at a receiver to localize targets, and therefore the direct blast arrival time estimation error could be added to target localization error in comparison with synchronous system. Direct blast especially appears as several peaks at the matched filter output by multipath, thus we compared the first peak detection technique and the maximum peak detection technique of those peaks for direct blast arrival time estimation through sea trial data. The test was performed in a shallow sea with bistatic sonar made up of spatially separated source and line array sensors. Line array sensors obtained the target signal which is generated from the echo repeater. As a result, the first peak detection technique is superior to maximum peak detection technique in direct blast arrival time estimation error. The result of this analysis will be used for further research of target tracking in the asynchronous bistatic sonar.