• The Transactions of the Korean Institute of Power Electronics
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• v.8 no.6
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• pp.488-495
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• 2003

In recent years, the multilevel inverter synthesizing the output voltage with step pulse has been widely used rather than PWM method as a solution for high power and high voltage applications. This method takes advantage of lower switching losses due to one switching for one period. This paper proposes a simple method to obtain the conducting angle. This method is implemented by using voltage-second areas of the divided reference voltage according to the output voltage levels. It Is possible to reduce an amount of calculation because it is not required to solve the simultaneous equations by an iterative method. Also, the proposed method can get the conducting angle by means of on-line.

• Journal of Power Electronics
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• v.10 no.2
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• pp.155-164
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• 2010

This paper presents a voltage control algorithm for a hybrid multilevel inverter based on a staged-perception of the inverter voltage vector diagram. The algorithm is applied to control a three-stage eighteen-level hybrid inverter, which has been designed with a maximum number of symmetrical levels. The inverter has a two-level main stage built using a conventional six-switch inverter and medium- and low- voltage three-level stages constructed using cascaded H-bridge cells. The distinctive feature of the proposed algorithm is its ability to avoid the undesirable high switching frequency for high- and medium- voltage stages despite the fact that the inverter's dc sources voltages are selected to maximize the number of levels by state redundancy elimination. The high- and medium- voltage stages switching algorithms have been developed to assure fundamental switching frequency operation of the high voltage stage and not more than few times this frequency for the medium voltage stage. The low voltage stage is controlled using a SVPWM to achieve the reference voltage vector exactly and to set the order of the dominant harmonics. The inverter has been constructed and the control algorithm has been implemented. Test results show that the proposed algorithm achieves the desired features and all of the major hypotheses have been verified.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.18 no.6
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• pp.31-36
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• 2004

Optical coherence tomography system has been extensively studied because it has some advantages such as imaging of high resolution, low cost, and compact size configuration. In order to obtain high resolution of OCT system we configured OCT system using a femto-second laser. We measure the pulse width using autocorrelator function because a femto-second laser is ultra short pulse. And we measured the practical resolution using theoretical equation and the measurement of reference sample. It is confirmed that the proposed OCT system has 1.5 times higher resolution and un distinctive cross-sectional image than OCT system with SLD as a light source.

• Computers and Concrete
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• v.24 no.1
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• pp.19-35
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• 2019

In this paper, the effect of the type and amount of fibers on the physicomechanical properties of concrete containing fine recycled refractory brick (RRB) and natural aggregate subjected to elevated temperatures was investigated. For this purpose, forta-ferro (FF), polypropylene (PP), and polyvinyl alcohol (PVA) fibers with the volume fractions of 0, 0.25, and 0.5%, as well as steel fibers with the volume fractions of 0, 0.75, and 1.5% were used in the concrete containing RRB fine aggregate replacing natural sand by 0 and 100%. In total, 162 concrete specimens from 18 different mix designs were prepared and tested in the temperature groups of 23, 400, and $800^{\circ}C$. After experiencing heat, the concrete properties including the compressive strength, ultrasonic pulse velocity (UPV), weight loss, and surface appearance were evaluated and compared with the corresponding results of the reference (unheated) specimens. The results show that using RRB fine aggregate replacing natural fine aggregate by 100% led to an increase in the concrete compressive strength in almost all the mixes, and only in the PVA-containing mixes a decrease in strength was observed. Furthermore, UPV values at $800^{\circ}C$ for all the concrete mixes containing RRB fine aggregate were above those of the natural aggregate concrete specimens. Finally, regarding the compressive strength and UPV results, steel fibers demonstrated a better performance relative to other fiber types.

• Bulletin of the Korean Chemical Society
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• v.11 no.3
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• pp.200-205
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• 1990

Chemically modified electrodes(CMEs), based on 2-imino-1-cyclopentane-dithiocarboxylic acid (icdc) containing carbon paste, have been characterized using cyclic voltammetric techniques. Ag(I) was chemically deposited on the CMEs, and voltammograms were obtained with the electrode in a separate buffer solution. The CME surface can be regenerated with exposure to acid and reused for deposition. In 10 deposition/measurement/regenerate cycles, the linear response have been reproduced up to $1{\times}10^{-6}$ M in linear sweep voltammetry and 1${\times}$10-8 M in differential pulse voltammetry with relative standard deviation of 5.2% and 12.4%, respectiveiy. The sensitivity increased with deposition time and scanning rate, and detection limit was $1{\times}10^{-7}M\;and\;1{\times}10^{-9}M$ at 20 minutes deposition in the linear sweep voltammetry and differential pulse voltammetry, respectively. The presence of some metal ions does not influence the silver ion response. Satisfactory results were obtained for the analysis of the silver ion for a variety of reference materials without interference of Hg ion at the condition of pH = 5-6.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.3
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• pp.244-250
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• 2018

Multilateration acquires the transponder signal of target from receivers installed on the ground and calculates the position of the target using the difference of the signal acquisition time of each receiver. One of the factors that influence the positioning accuracy of Multilateration using the TDOA calculation method is the error due to the precision measurement of signal input time. When measuring the signal input time at the receiver, the input signal is sampled using the reference clock of the receiver and a reference sample having the same sampling rate is applied to the cross correlation technique. Therefore, the accuracy of the signal input time is proportional to the reference clock. In this paper, the algorithm for precisely measuring the signal input time by performing cross correlation between the input signal of the receiver and DRS(Delayed Reference Sample) is proposed. In order to verify this, we implemented the pulse signal of the transponder that is transmitted from the target using Matlab. Through the simulation, cross correlation between the proposed DRS and the input signal was performed. From this result, the performance of the precise measurement of signal input time was analyzed.

• Journal of Broadcast Engineering
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• v.11 no.2 s.31
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• pp.229-241
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• 2006

In this paper we propose and analyze a novel modulation and pre-equalization method to minimize signal processing time delay for the Equalization Digital On-Channel Repeater (EDOCR) in ATSC (Advanced Television Systems Committee) terrestrial digital TV system. The proposed modulation method uses Equi-Ripple (ER) filter coefficients instead of conventional Square Root Raised Cosine (SRRC) after coefficients for VSB (Vestigial Side Bands) pulse shaping. And the proposed pre-equalization method calculates pre-equalizer filter coefficients by using baseband signal as reference signal and demodulated repeater output signal, then generates a new VSB pulse shaping filter coefficients by convolutioning ER filter coefficients and pre-equalizer filter coefficients. The newly generated pulse shaping filter does not have minimized time delay by adjusting the number of pre-taps of the filter, but also compensates linear distortions caused by ER filter and mask filter.

• Journal of the Korean Society of Radiology
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• v.14 no.6
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• pp.791-800
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• 2020

Ultrasonography is widely used to evaluate the function of fetal heart, but due to the subjective nature of the test, there are differences in measurement methods for each examiner, and especially the myocardial performance index has no reference index to date. Therefore, in this study, we wanted to analyze pulse Doppler waveforms of normal fetuses and develop an automatic measurement program to make objective measurements. One hundred and thirty-three pregnant women who visited the hospital for prenatal examinations were studied, myocardial performance index was measured after acquiring a pulse doppler image of the left ventricle. As a result, the early, mid and late pregnancy myocardial performance index, measured by the automatic measurement program conducted in this study, was found to increase as pregnancy continued.

• Journal of Radiation Protection and Research
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• v.44 no.2
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• pp.53-63
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• 2019

Background: As neutron fields are always accompanied by gamma rays, it is essential to distinguish neutrons from gamma rays in the detection of neutrons. Neutrons and gamma rays can be separated by pulse shape discrimination (PSD) methods. Recently, we performed characterization of a stilbene scintillator detector and an EJ-301 liquid scintillator detector with a high-speed digitizer DT5730 and investigated optimized PSD variables for both detectors. This study is for providing a basis for developing fast neutron/gamma-ray dual-particle imager. Materials and Methods: We conducted PSD experiments using stilbene scintillator and EJ-301 liquid scintillator and evaluated neutron and gamma ray discriminability of each PSD method with a $^{137}Cs$ gamma source and a $^{252}Cf$ neutron source. We implemented digital signal processing techniques to apply two PSD methods - the charge comparison (CC) method and the constant time discrimination (CTD) method - to distinguish neutrons from gamma rays. We tried to find optimized PSD variables giving the best discriminability in a given experimental condition. Results and Discussion: For the stilbene scintillator detector, the charge comparison method and the constant time discrimination method both delivered the PSD FOM values of 1.7. For the EJ-301 liquid scintillator detector, both PSD methods delivered the PSD FOM values of 1.79. With the same PSD variables, PSD performance was excellent in $300{\pm}100keVee$, $500{\pm}100keVee$, and $700{\pm}100keVee$ energy regions. This result shows that we can achieve an effective discrimination of neutrons from gamma rays using these scintillator detector systems. Conclusion: We applied both PSD methods to a stilbene and a liquid scintillator and optimized the PSD performance represented by FOM values. We observed a good separation performance of both scintillators combined with a high-speed digitizer and digital PSD. These results will provide reference values for the dual-particle imager we are developing, which can image both fast neutrons and gamma rays simultaneously.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.38A no.12
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• pp.991-997
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• 2013

A new frequency tuning scheme and a transconductor with a wide tuning range and low harmonic distortion is presented. This frequency tuning technique is based on the relationship between the time-constant and the elapsed times in charging a capacitor up to a certain level. Its structure is as simple as that of a conventional tuning scheme using a VCF(Voltage-Controlled Filter) and it does not need a pure sine wave but uses a CLK(Clock) pulse as a reference signal, which is easily obtained from on-chip system clocks or external X-tal oscillators. When a certain reference CLK is given, without complex capacitor arrays the pole frequency of the filter can be controlled continuously in the frequency domain. Simulation results are presented to confirm the operation of the proposed approach.