• Journal of Astronomy and Space Sciences
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• v.27 no.3
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• pp.239-244
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• 2010

A simulation for the design of a $90^{\circ}$ differential phase shifter aimed toward Korean VLBI Network (KVN) 129 GHz band polarizer is described in this paper. A dual-circular polarizer for KVN 129 GHz band consists of a $90^{\circ}$ differential phase shifter and an orthomode transducer. The differential phase shifter is made up of a square waveguide with two opposite walls loaded with corrugations. Three-dimensional electromagnetic simulation has been performed to predict the $90^{\circ}$ differential phase shifter's characteristics. The simulation for the differential phase shifter shows that the phase shift is $90^{\circ}{\pm}3.3^{\circ}$ across 108-160 GHz and the return losses of two orthogonal modes are better than -30 dB within the design frequency band. According to the simulation results the calculated performance is quite encouraging for KVN 129 GHz band application.

• Journal of Astronomy and Space Sciences
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• v.27 no.2
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• pp.145-152
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• 2010

In this paper, we developed a local oscillator (LO) system of millimeter wave band receiver for radio astronomy observation. We measured the phase and amplitude drift stability of this LO system. The voltage control oscillator (VCO) of this LO system use the 3 mm band Gunn oscillator. We developed the digital phase locked loop (DPLL) module for the LO PLL function that can be computer-controlled. To verify the performance, we measured the output frequency/power and the phase/amplitude drift stability of the developed module and the commercial PLL module, respectively. We show the good performance of the LO system based on the developed PLL module from the measured data analysis. The test results and discussion will be useful tutorial reference to design the LO system for very long baseline interferometry (VLBI) receiver and single dish radio astronomy receiver at the 3 mm frequency band.

• Journal of Fisheries and Marine Sciences Education
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• v.26 no.3
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• pp.639-646
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• 2014

A heat exchanger using two-phase loop thermosyphons was developed as a waste heat recovery system. An experimental study was carried out on the heat transfer characteristics of two-phase loop thermosyphons heat exchanger and the results from the experiments were used to see the possibility which the two-phase loop thermosyphons could be an alternate solution for waste heat recovery system. In the present work, R134a has been used as the working fluid and the filling rate do working fluid and heat flux have been used as the experimental parameters. The results show that the filling rate of working fluid and heat flux are very important factors for the operation of two-phase loop thermosyphons. The experimental results showed the provisional results as a waste heat recovery system.

• Korean Journal of Remote Sensing
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• v.28 no.3
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• pp.329-336
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• 2012

This paper give further assessment on the original DoP-CPD classification scheme. This paper provides some additional comparative study on the DoP-CPD with H/A/alpha classifier in terms of multi look effects and classification performances. The statistics and multi looking effects of the DoP and CPD were analyzed with measured polarimetric SAR data. DoP-CPD is less sensitive to the number of averaging pixels than the entropy-alpha technique. A DoP-CPD diagram with appropriate boundaries between six different classes was then developed based on the data analysis. A polarimetric SAR image DoP-CPD classification technique is verified with C-band polarimetric RADARSAT-2 images.

• Proceedings of the KIEE Conference
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• 1998.07f
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• pp.1960-1962
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• 1998

Reference/modulating waveform continuity is not a necessary condition for the implementation of switching patterns for three-phase pulse-width modulated(PWM) converters. This is based on the fact that the converter phase-voltages do not need to be sinusoidal and switching pattern discontinuities do not degrade the quality of output/input voltage/current waveforms by introducing low-order harmonics if certain parameters are optimized. This paper introduces the selected harmonic elimination to reduce the switching frequency and low-order harmonics compared with continuous PWM techniques and some discontinues switching patterns for PWM converter.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.55 no.1
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• pp.47-53
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• 2006

In this paper, a simple scheme compensating for the effect of dc-link ripple voltages on output voltage of two-leg and three-phase PWM inverters is proposed, where single-phase half-bridge PWM convertor and two-leg inverter are used. The voltage at neutral point of the dc-link is controlled so that the upper-half of do-link voltage is equal to the lower-half voltage in average concept. However, the effect of the do-link ripple voltage results in the inverter output voltage and current distortion. This effect can be eliminated by introducing a compensation voltage in switching time calculation. Also, the inverter dead time should be compensated for sinusoidal output waveform. The proposed scheme has been verified by experimental results which were obtained from the V/F constant operation of the induction motor fed by two-leg inverter.

• Journal of the Korean Society for Heat Treatment
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• v.3 no.2
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• pp.1-9
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• 1990

Since the reverse shape memory effect(RSME) was reported in a CuZnAl alloy, further study has been done on the mechanism of this phenomenon and reported that it occurs by the bainitic transformation. But the present authors revealed in the previous work that the RSME in a B2 CuZnAl alloy is not caused by the shear process involved in the bainitic transformation and also that the RSME takes place as the remaining ${\alpha}^{\prime}{_2}$ phase, which is two-step transformed strain induced martensite, is newly transformed into ${\alpha}$ phase. In order to provide further evidence in supporting the facts, thus, more detailed investigations have been carried out in a $DO_3$ CuZnAl alloy.

• Korean Journal of Computational Design and Engineering
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• v.18 no.5
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• pp.338-347
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• 2013

Since it is common that design BIM data created by designers and engineers do not afford to consider constructability for the site, it is usually necessary to optimize the design BIM data to construction BIM data. While this optimization process requires various design updates depending on the construction methods and requirements, most designers in the projects do not participate the construction phase, which can arise another obstacle factor in utilizing construction BIM. In order to prevent this issue, we need cooperation system, where all the parties work together from the initial stage of project to create quality assured BIM model. However this kind of system is not realistic in Korea with most of the working processes being conventional yet. Therefore, at this point of time, it is realistic for us to secure basic construction qualities in the design phase and keep those qualities by the construction phase. This study suggested a relevant quality management plan for BIM usage in construction phase.

• Applied Chemistry for Engineering
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• v.8 no.4
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• pp.617-623
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• 1997

In this study, the mechanism on the phase behavior of polysorbate nonionic surfactants was investigated. In the ternary system containing water, hexanol as a polar oil and surfactant, the phase behaviors ranging from micellar region to occurrence of liquid crystal phase were observed by crossed microscope. As results, fine mosaic texture of liquid crystal phase and other phases were examined in the range of 20~70 wt%. This range if thought to give information about the basic data for the formulation of more stable emulsifying systems or dispersed systems. According to the alkyl chain length, three phase region diminished, whereas two phase range increased without an observation of the anisotropic liquid crystalline phase.

• Proceedings of the KSR Conference
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• 1999.05a
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• pp.328-335
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• 1999

Three phase full bridge rectifier has been used to obtain dc voltage from three phase ac voltage source. The rectifier system has drawbacks that power factor is low and power flow is unidirectional. Therefore, when dc voltage increases due to regeneration of power the dynamic resister for dissipation of regeneration power must be installed. But three phase PWM converter can be controlled to operate with unity power factor and bidirectional power flow. Therefore when the PWM converter is used as do supply system, the dissipating resistor is not necessary. On this thesis, in order to design a controller having good performance, the hee phase PWM converter is completely modeled by using circuit DQ-transformation and thus a general and simple instructive equivalent circuit is obtained; the inductor set becomes a second order gyrator-coupled system and three phase inverter becomes a transformer as well. Under given phase angle(${\alpha}$) and modulation index(MI) of the three phase inverter, the dc and ac characteristics are obtained by analysis of the transformed equivalent circuit The validity of the equivalent circuit is confirmed through PSPICE simulation. And based on the dc and ac characteristics a controller with unity power factor is proposed.