• 제어로봇시스템학회:학술대회논문집
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• 2003.10a
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• pp.1794-1797
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• 2003

We developed a web-based virtual laboratory system for electronic circuit experiments on the client/ server distributed environment. Through our virtual laboratory, the learners will be capable of learning the concepts and theories related to electronic circuit experiments and how to operate the experimental equipments such as multimeters, function generators, digital oscilloscopes and DC power suppliers. The proposed virtual laboratory system is composed of four important components: Principle Classroom to explain the concepts and theories of electronic circuit operations, Virtual Experiment Classroom to provide interactive multimedia contents about the syllabus of off-line laboratory class, Assessment Classroom, and Management System. With the aid of the Management System every classroom is organically tied together collaborating to achieve maximum learning efficiency. We have obtained several affirmative effects such as high learning standard, reducing the total experimental hours and the damage rate for experimental equipments.

• Journal of Mechanical Science and Technology
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• v.17 no.11
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• pp.1616-1627
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• 2003

This paper describes a mini linear optical pickup actuator. To reduce the size, inner yokes are designed to guide the mover and outer yokes of permanent magnets are removed. Magnetic circuit method is used to determine the thrust force. Virtual path method is proposed to analyze the open magnetic circuit analysis. The magnetic circuit of the proposed actuator can be a closed circuit due to the virtual path model of the outer magnetic flux. The validity of virtual path method is evaluated by comparing to the FEM analysis. Structural vibration is investigated using FEM and the design of the mover is modified to improve the vibration characteristic. Dynamic characteristic experiments shows that the performance of the proposed actuator is enough to be used as a coarse and fine seeking actuator simultaneously and the thrust force margin for loading a focusing actuator is guaranteed.

• 제어로봇시스템학회:학술대회논문집
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• 2004.08a
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• pp.1178-1182
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• 2004

This paper presents web-based virtual laboratory system for electronic and digital circuit experiments. Through our virtual laboratory, the learners will be capable of learning the concepts and theories related to circuit experiments and how to operate virtual experimental equipments such as multimeters, function generators, digital oscilloscopes, DC power suppliers and bread board etc. The proposed virtual laboratory system is composed of important components: Principle Classroom to explain the concepts and theories of electronic and digital circuit operations, Simulation Classroom to provide a web-based simulator to the learners, Virtual Experiment Classroom to provide interactive multimedia contents about the syllabus of off-line laboratory class, Assessment Classroom, and Management System. With the aid of the management System every classroom is organically tied together collaboration to achieve maximum learning efficiency. We have obtained several affirmative effects such as high learning standard, reducing the total experimental hours and the damage rate for experimental equipments.

• Proceedings of the IEEK Conference
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• 1998.10a
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• pp.15-18
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• 1998

Most existing FRADs support only permanent virtual circuit-based frame relay services. But several applications such as intranets, desktop video conferencing, remote access and voice applications typically do not require the dedicated bandwidth capabilities of PVCs because connections are only occasionally needed. So it drives the need of switched virtual circuit-based FRADs which offer potentail cost savings associated with dynamic bandwidth on demand connectivity. In this paper, we describe Frame Relay Network Access System(FNAS) that provides switched virtual circuit-based frame relay access for dial-up Internet services. The hardware configuration, software architecture and call processing flow of FNAS is explained.

• Journal of Institute of Control, Robotics and Systems
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• v.11 no.6
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• pp.558-563
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• 2005

In this paper, we implemented a web-based virtual laboratory system(VLab system) with creative and interactive multimedia contents, which can be used to enhance the quality of education in the area of digital logic circuits. Since the proposed VLab system is implemented to describe the on-campus laboratory, the learners can obtain similar experimental data through it. Also, the VLab system is designed to increase the learning and teaching efficiencies of both the learners and the educators, respectively. The learners will be able to achieve high teaming standard and the educators save their time and labor. The virtual experiments on our VLab system are performed according to the following procedure: (1) Circuit composition on the virtual bread board (2). Applying input voltage (3) Output measurements (4) Checkout of experiment results. Furthermore, the circuit composition on the virtual bread board and its corresponding online schematic diagram are displayed together on the VLab system for the learner's convenience. Finally, we have obtained several affirmative effects such as reducing the total experimental hours and the damage rate for experimental equipments and increasing learning efficiencies as well as faculty productivity.

• 한국정보통신설비학회:학술대회논문집
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• 2002.08a
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• pp.199-207
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• 2002

A virtual laboratory for measurement and instrumentation must aim to realize an integrated environment. To achieve this goal, we designed and implemented a client/server distributed environment and developed a web-based virtual laboratory system for electronic circuits. Since our virtual laboratory system is implemented to describe the on-campus laboratory, the learners can obtain similar experimental data through it. The proposed virtual laboratory system is composed of four important components Principle Classroom, Virtual Experiment Classroom, Evaluation Classroom and Overall Management System. Through our virtual laboratory, the learners will be capable of teaming the concepts and theories related to electronic circuit experiments and how to operate the experimental equipments such as multimeters, function generators, digital oscilloscopes and DC power supplies. Also, every activity occurred in our virtual laboratory is recorded on database and Printed out on the preliminary report form. All of these can be achieved by the aid of the Management System. The database connectivity is made by PHP and the virtual laboratory environment is set up slightly differently for each learner. Finally, we have obtained several affirmative effects such as reducing the total experimental hours and the damage rate for experimental equipments and increasing Loaming efficiencies as well as faculty productivity.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.67 no.9
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• pp.1159-1164
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• 2018

Vacuum circuit breakers(VCB) are widely used for current interruption of high-voltage inductive loads such as induction motors. This VCB can be chopped off before the current zero due to its high arc-extinguishing capability. One of the outstanding features of VCB is that it can cut off high frequency re-ignition current more than other circuit breakers. If the transient recovery voltage generated in the arc extinguishing is higher than the dielectric strength of the circuit breaker, a re-ignition phenomenon occurs. The surge voltage of the re-ignition is very high in magnitude and the steepness of the waveform is so severe that it can act as a high electrical stress on the winding. If the high frequency current of one phase affects the other two phases when the re-ignition occurs, it may cause a high surge voltage due to the virtual current chopping. If the magnitude of the voltage allowed in the motor winding is high or the waveform level is too severe, it may lead to insulation breakdown. Therefore, it is necessary to reduce the voltage to within a certain range. In this study, we briefly explain the various phenomena at the time of interruption, analyzed the magnitude of the dielectric strength and the transient recovery voltage at the simultaneous three-phase interruption that can give the greatest influence to the inductive load, proposed a method to reduce the impact.

• Journal of the Korean Society for Railway
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• v.15 no.2
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• pp.122-128
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• 2012

Considering structure of depot, it is impossible to install the track circuit systems due to iron-beam. Because rails and earth are connected by the iron-beam, there is much leakage current. So, it is hard to apply the track circuit systems. Thus, when trains go to the depot, sign which indicates existence of trains is used manually. In case of wrong sign, accidents occur such as train crash, derailment etc. Currently, location of trains has been found by using optical sensor in the depot to prevent the accidents. However, it costs a great deal to install and maintain the optical sensor. Therefore, this method is hardly used in train operation institutes. In this paper, virtual track circuit systems are introduced by using software program in the depot. Also, algorithm of the virtual track circuit systems is proposed. In case that signal is handled to the depot which is occupied by the train, safety is ensured by indicating sign which means existence of trains and stop signal. Also, proper fault tolerance techniques are proposed to the software by analyzing reliability and availability.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.12 no.1
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• pp.59-64
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• 2008

In this paper, we developed an virtual lecture to study digital logic circuits. The contents is intended fer the students without or with little knowledge about electrics or electronics. For the beginners, the lecture contains the basic electronics and basic circuit theory as well as the degital logic circuits to be more practical lecture. And we developed the virtual circuit lab which uses real-like devices, circuits and interactive objects for the students to experience practical digital circuits. With the features described above, this contents would be useful for the beginners who want to studying digital logic circuits.

• ETRI Journal
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• v.37 no.2
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• pp.369-379
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• 2015

Fault management of virtualized network environments using user-driven network provisioning systems (NPSs) is crucial for guaranteeing seamless virtual network services irrespective of physical infrastructure impairment. The network service interface (NSI) of the Open Grid Forum reflects the need for a common standard management API for the reservation and provisioning of user-driven virtual circuits (VCs) across global networks. NSI-based NPSs (that is, network service agents) can be used to compose user-driven VCs for mission-critical applications in a dynamic multi-domain. In this article, we first attempt to outline the design issues and challenges faced when attempting to provide mission-critical applications using dynamic VCs with a protection that is both user-driven and trustworthy in a dynamic multi-domain environment, to motivate work in this area of research. We also survey representative works that address inter-domain VC protection and qualitatively evaluate them and current NSI against the issues and challenges.