• ETRI Journal
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• v.16 no.4
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• pp.1-11
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• 1995

A GaAs power metal semiconductor field effect transistor (MESFET) operating at a voltage as low as 3.3V has been developed with the best performance for digital handheld phone. The device has been fabricated on an epitaxial layer with a low-high doped structure grown by molecular beam epitaxy. The MESFET, fabricated using $0.8{\mu}m$ design rule, showed a maximum drain current density of 330 mA/mm at $V_{gs}$ =0.5V and a gate-to-drain breakdown volt-age of 28 V. The MESFET tested at a 3.3 V drain bias and a 900 MHz operation frequency displayed an output power of 32.5-dBm and a power added efficiency of 68%. The associate power gain at 20 dBm input power and the linear gain were 12.5dB and 16.5dB, respectively. Two tone testing measured at 900.00MHz and 900.03MHz showed that a third-order intercept point is 49.5 dBm. The power MESFET developed in this work is expected to be useful as a power amplifying device for digital hand-held phone because the high linear gain can deliver a high power added efficiency in the linear operation region of output power and the high third-order intercept point can reduce the third-order intermodulation.

• Journal of Electrical Engineering and Technology
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• v.4 no.3
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• pp.382-388
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• 2009

Recently, hydrogen energy has been anticipated to change the paradigm of conventional power systems because it can expand sustainable energy utilization and conceptually provide remarkable flexibility to power system operation. Since hydrogen energy can be converted to electric energy through fuel cells, fuel cells are expected to play an important role in the future hydrogen economy. In this paper, a Proton Exchange Membrane Fuel Cell (PEMFC) is modeled as an equivalent circuit and its steady-state characteristics investigated using the model. PEMFCs can be connected to power systems through power conditioning systems, which consist of power electronic circuits, and which are operated as distributed generators. This paper analyzes the effects of the characteristics of the PEMFC internal voltages and investigated the dynamic responses of the PEMFC under fault conditions. The results show that the fault current contribution of the PEMFC is different from those of conventional generators and is closely related to its operating point.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.1
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• pp.77-86
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• 1992

This paper discusses the thermodynamic study on the suction cooling-steam injected gas turbine cycle. The aim of this study is to improve the thermal efficiency and the specific output by steam injection produced by the waste heat from the waste heat recovery boiler and by cooling compressor inlet air by an ammonia absorption-type suction cooling system. The operating region of this newly devised cycle depends upon the pinch point limit and the outlet temperature of refrigerator. The higher steam injection ratio and the lower the evaporating temperature of refrigerant allow the higher thermal efficiency and the specific output. The optimum pressure ratios and the steam injection ratios for the maximum thermal efficiency and the specific output can be found. It is evident that this cycle considered as one of the most effective methods which can obtain the higher thermal efficiency and the specific output comparing with the conventional simple cycle and steam injected gas turbine cycle.

• Journal of Nutrition and Health
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• v.37 no.4
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• pp.310-315
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• 2004

The purposes of this study were to: a) develop the quality assessment tool of Web-based Instruction (WBI) for nutrition education, b) evaluate the operated WBI (NutriZone) by this tool, and c) do the feasibility study about quality assessment tool for WBI by establishing the instruction and operating strategies. The developed quality assessment tool of WBI for nutrition education was divided into three categories of instruction design, contents and support ＆ operation. And a total of forty items were measured by Likert 5 point scale, computed as one point per item, and amounted to forty points in all. As a result of evaluation, NutriZone got 21.79 out of 40 points and fulfillment rate of 54.5%. The IPA (Importance-Performance Analysis) was applied to establish the instruction and operating strategies, and nine items characterized as attractiveness, multimedia, and learner-initiative were in 'Doing Great, Keep It Up', and so it was regar-ded as program designed with concern in WBI's characteristics unlike the conventional face-to-face education. But twelve items such as 'Errors on switch to other screens are few.', 'Ready correction leads to be out of systemic error.', 'Highlight marks and moving pictures were used in sign of importance.' and etc. that got high importance and low performance needed to be focused in instructional strategy.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.3
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• pp.45-53
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• 2015

A I-V and P-V characteristic of solar cell is changed to nonlinear by radiation and temperature. Therefore, to use efficiently PV system, operating point of PV system is must operate at maximum power point always. A performance of conventional the PO and the IC method is depend on the step size. So it has weakness which is must select optimal step size. Also, MPPT control applying PI and fuzzy control is not expected satisfactory performance, because of PI controller has fixed gain and fuzzy control has cumulative error by an integral calculus. Therefore, this paper proposes the VS-PO(Variable Stepsize - Perturbation & Observation) MPPT control that is automatically adjusted the step size according to the operating conditions. The VS-PO MPPT method proposed in this paper analyzes control characteristic about condition of radiation and compares with conventional methods. The validity of this paper proves using this results.

• Journal of Power System Engineering
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• v.4 no.3
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• pp.25-33
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• 2000

This study represents three-dimensional turbulent flow characteristics around an axial fan measured at the operating point ${\varphi}=0.32$, which is equivalent to the maximum flowrate region, by using three-dimensional fiber-optic type LDA system. This LDA system is composed of a 5 W Argon-ion laser, two optics in back-scatter mode, three BSA's, a PC, and a three-dimensional automatic traversing system. A kind of paraffin fog is used for laser particles in this study. Mean velocity profiles around an axial fan along the downstream radial distance show that the streamwise and the tangential components exist as a predominant velocity and have the maximum value at the radial distance ratio 0.8, while the radial component has a small scale distribution and its flow direction is inward except a part of blade tip. The turbulent intensity profiles show that the radial component exists the most greatly. And also the turbulent kinetic energy shows about 60% as a maximum value at the radial distance ratio 0.9. Moreover, the Reynolds shear stresses do not exist at upstream flow, but the streamwise and the radial components of them show about 20% as a maximum value at the radial distance ratio 0.9 at downstream flow.

• Journal of Electrical Engineering and Technology
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• v.10 no.4
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• pp.1518-1526
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• 2015

For now, there are some low frequency oscillations in the power system which feature low frequency oscillation with positive damping and cannot be explained by traditional low frequency oscillation mechanisms. Concerning this issue, the dynamic damping effect is put forward on the basis of the power-angle curve and the study of damping torque in this article. That is, in the process of oscillation, damping will dynamically change and will be less than that of the stable operating point especially when the angle of the stable operating point and the oscillation amplitude are large. In a situation with weak damping, the damping may turn negative when the oscillation amplitude increases to a certain extent, which may result in an amplitude-increasing oscillation. Finally, the simulation of the two-machine two-area system verifies the arguments in this paper which may provide new ideas for the analysis and control of some unclear low frequency phenomena.

• Journal of Advanced Navigation Technology
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• v.17 no.2
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• pp.177-182
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• 2013

In this paper, printed antenna which can be applied to a built-in wireless module of the security controller operating at global positioning system(GPS) L1 frequency band(1.575GHz) is proposed. The proposed antenna is basically composed of a microstrip patch antenna with inserting feed. In particular left and right slots which are respectively asymmetric are used for impedance matching, whereas slot with one open-end and shorting point are used on the bottom plane to set operating frequency and enhance bandwidth. It is observed at the desired GPS L1 frequency band that the radiation efficiency and gain of the proposed antenna are 90% and more than 4.8dBi respectively.

• The KIPS Transactions:PartC
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• v.15C no.3
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• pp.141-148
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• 2008

Windows Vista published by Microsoft provides more powerful security mechanisms than previous Windows operating systems. In the forensics point of view, new security mechanisms make it more difficult to get data related to the criminals in a storage device. In this paper, we analyze BitLocker introduced as an new security mechanism in Windows Vista. Also, compared to the previous Windows operating systems, the changes and security issues of UAC and EFS in Windows Vista are discussed in the forensics point of view. Futhermore, we discuss other characteristics of Windows Vista useful for forensic examinations.

• Journal of the Korean Society of Costume
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• v.44
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• pp.168-179
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• 1999

In order to settle down structural causes of the process of distribution and apparel production in domestic fashion industry, and to raise competitive power with changing market environment, we need to bulid up Quick Response(QR) system based on information technology such as EDI(Electronic Data Interchange), KAN(Korea Article Number), and POS(Point of Sales), POS is the most valuable information tool to promote QR system paractically. The purpose of this study was to investigate motivation of POS adoption, problems in operating the system, and satisfaction on POS effects. Data were collected by sending questionnaire to the managers in apparel firms which were using POS. Statistical devices were t-test, frequency with SAS program. The results fo the study were as follows: 1. The degree of satisfaction to POS effects was rather good. Especially, rapid evaluations on new products gave the greatest satisfaction to the users. 2. Satisfaction degree of POS effects according to introduces time and organization characteristic(number of employees) have no significant difference, but the firms which have higher annual sales volume showed higher satisfaction degree. Merchandise department showed higher satisfaction on POS effects. 3. The motivation of POS adoption was an effective logistics control with consumer information as a marketing strategy. The problems in operating the system were lack of investment, and professionals. They almost didn't have KAN code, instead, have their own code system.