• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.6
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• pp.451-459
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• 2010

This paper describes the performance comparison results for a hybrid back-to-back converter, which is composed of a 3-level 24-pulse converter and a 3-level PWM converter, in order to interconnect a large scale wind farm with the power grid. Also it describes the performance comparison results when the 24-pulse converter operates in only firing-angle control, and both firing-angle and the zero-voltage control. For the purpose of systematic performance comparison, computer simulations with PSCAD/EMTDC software were carried out, and based on simulation results a scaled hardware model with 2 kVA rating was built and tested.

• Korean Journal of Food Science and Technology
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• v.32 no.2
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• pp.356-362
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• 2000

Yakju(rice wine) was sterilized with high-voltage square-wave pulses of $1\;{\mu}s$ duration at various electric field strengths and frequencies on a serial multiple electrode pulsed electric field(PEF) treatment system consisted of 7 electrodes connected in series. The initial microbial counts of Yakju were $1.88{\times}10^3{\sim}2.13{\times}10^4$ CFU/mL for total aerobes, $1.55{\times}10^3{\sim}2.85{\times}10^4$ CFU/mL for lactic acid bacteria and $1.72{\times}10^3{\sim}2.39{\times}10^4$ CFU/mL for yeasts. The sterilization of microorganisms in Yakju was a first order reaction and the sterilization effect increased as the field strength and the frequency increased. The $D_{Hz}-value$ and the $D_{PEF}-value$ decreased with the electric field strength. Yeast showed lower $D_{PEF}-value$ than bacteria. Lactic acid bacteria showed lower $D_{PEF}-value$ than general aerobic bacteria under the electric field strength below 30 kV/cm, but higher ones under that above 40 kV/cm. The $Z_{PEF}-value$ of general aerobic bacteria, lactic acid bacteria and yeast in Yakju were 39.4, 49.3 and 47.6 kV/cm, respectively. The PEF sterilization resulted in less changes in color and sensory properties than heat sterilization, and the PEF treated Yakju showed superior quality to the heat treated one. The commercial sterilization of Yakju was accomplished with 2-cycle treatment on the tested serial PEF treatment system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.1A
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• pp.8-18
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• 2011

Visible light communication (VLC) using optical sources which can be simultaneously utilized for illumination and communication is currently an attractive option for wireless personal area network. Improving the data rate in optical wireless communication system is challenging due to the limited bandwidth of the optical sources. In this paper, we design the singular value decomposition (SVD)-based multiplexing multi-input multi-output (MIMO) system to support two data streams in optical wireless channels. In order to improve the spectral efficiency, the rate adaptation using multi-level pulse amplitude modulation (PAM) is applied according to the channel condition and we propose the method to allocate the optical power, the offset and the size of modulation scheme theoretically under the constraints of the nonnegativity of the modulated signals, the aggregate optical power and the bit error rate (BER) requirement. The simulation results show that the proposed allocation method gives the better performance than the method to allocate the optical power equally for each data stream.

• Journal of the Institute of Electronics Engineers of Korea TC
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• v.43 no.2 s.344
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• pp.7-15
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• 2006

Recently, Ultra-wideband (UWB) Communication systems have become a popular research topic. UWB system is characterized by the fact that the digital information represented by a subnanosecond pulses is transmitted through the air. In this paper, we consider the PPSM scheme that combine PPM and PSM. We provide the performance in AWGN and SV multipath channel which consists of $CM1\~CM4$. The optimal symbol set for M-ary system in multipath channel which shows good performance is also presented. The simulation results show that the performance in CM4 is worse than that in CMI due to long delay spread, many multipath components, 4-ary system outperforms binary system in Low$E_b/N_0$ but not in high $E_b/N_0$. We find system have the optimal symbol set in multipath channel.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.9C
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• pp.778-785
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• 2010

This paper proposes a high-precision ranging scheme based on channel estimation technique and multipath delay analysis in IR-UWB systems. When the IR-UWB signal is transmitted and received, the high-precision ranging is estimated with the time-of-arrival information of the signal. In the proposed scheme, the channel estimation process with the minimum mean square error technique or zero forcing technique is performed and the overlapped multipath within the pulse is analyzed with matrix pencil (MP) algorithm to achieve the ranging accuracy of centimeters. The performance of proposed scheme is evaluated with various IEEE 802.15.4a channel models and the relationship between the ranging performance and the computational complexity is analyzed in terms of the MP parameter values.

• Korean Chemical Engineering Research
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• v.46 no.6
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• pp.1087-1094
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• 2008

This article presents a multi-scale simulation approach starting from the molecular level for the adsorption process development, specifically, in n-hexane adsorption on activated carbon. A grand canonical Monte-Carlo(GCMC) method is used for the prediction of adsorption isotherms of n-hexane on activated carbon at the molecular level. Geometric effects and hydrodynamic properties of the adsorption column are examined by means of the two dimensional CFD(computational fluid dynamics) simulation. The adsorption isotherms from the molecular simulation and the axial diffusivity from the CFD simulation are exploited for the process simulation where the elution curve of n-hexane is obtained. For the first moment(mean residence time) of the pulse-response with respect to temperature and flowrate, the process simulation results obtained from this three-steps multiscale simulation approach show a good agreement with experimental data within 20% of maximum difference. The multi-scale simulation approach addressed in this study will be useful to accelerate the adsorption process development, while reducing the number of experiments required.

• Journal of Advanced Navigation Technology
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• v.7 no.1
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• pp.14-21
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• 2003

We investigated the optimum pump light power compensating distorted WDM signal due to both chromatic dispersion and self phase modulation (SPM). The considered system is $3{\times}40$ Gbps intensity modulation direct detection (IM/DD) WDM transmission system with path-averaged intensity approximation (PAIA) mid-span spectral inversion (MSSI) as compensation method. This system have highly nonlinear dispersion shifted fiber (HNL-DSF) as nonlinear medium of optical phase conjugator (OPC) in the mid-way of total transmission line. We confirmed that HNL-DSF is an useful nonlinear medium in OPC for wideband WDM transmission, and the excellent compensation is obtained when the pump light power of HNL-DSF OPC was selected to equalize the conjugated light power into the second half fiber section with the input WDM signal light power depending on total transmission length. By this approach, it is verified the possibility to realize a long-haul high capacities WDM system by using PAIA MSSI compensation method, which have HNL-DSF OPC with optimal pump light power depending on transmission length.

• Journal of Biomedical Engineering Research
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• v.23 no.1
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• pp.49-60
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• 2002

Receive dynamic focusing with an array transducer can provide near optimum resolution only in the vicinity of transmit focal depth. A customary method to increase the depth of field is to combine several beams with different focal depths, with an accompanying decrease in the frame rate. In this Paper. we Present a simultaneous multiple transmit focusing method in which chirp signals focused at different depths are transmitted at the same time. These chirp signals are mutually orthogonal in a sense that the autocorrelation function of each signal has a narrow mainlobe width and low sidelobe levels. and the crossorelation function of any Pair of the signals has values smaller than the sidelobe levels of each autocorrelation function. This means that each chirp signal can be separated from the combined received signals and compressed into a short pulse. which is then individually focused on a separate receive beamformer. Next. the individually focused beams are combined to form a frame of image. Theoretically, any two chirp signals defined over two nonoverlapped frequency bands are mutually orthogonal In the present work. however, a tractional overlap of adjacent frequency bands is permitted to design more chirp signals within a given transducer bandwidth. The elevation of the rosscorrelation values due to the frequency overlap could be reduced by alternating the direction of frequency sweep of the adjacent chirp signals We also observe that the Proposed method provides better images when the low frequency chirp is focused at a near Point and the high frequency chirp at a far point along the depth. better lateral resolution is obtained at the far field with reasonable SNR due to the SNR gain in Pulse compression Imaging .

• Journal of the Institute of Electronics Engineers of Korea SD
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• v.37 no.1
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• pp.53-59
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• 2000

We propose a modified nonlinear fiber optic interferometer which can serve to generate binary optical pulse sequences for CDMA networks, and to decode them. In one arm cross-phase modulation between a CW signal and a counter- or copropagating high-power pulse takes place in sequences of segment connected via VDM couplers. Preliminary experimental results on code generation as well as autocorrelation and crosscorrelation are presented, using Sagnac interferometer. As we expected, the experimental results show that the outputs of the interferometer device are not summed simply on the basis of power, but the sin-squared version of it. Arbitrary codes can in principle be implemented.

• Proceedings of the Korea Contents Association Conference
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• 2008.05a
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• pp.69-73
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• 2008

In this paper, analytical methods for calculating the average probability of bit error of time hopping pulse position modulation ultra wideband (TH-PPM UWB) system are given. For the multi-user DS-PAM UWB system, the bipolar pulse amplitude modulation is used in order to achieve better performance. As we know, more attention is paid to the TH-PPM UWB systems recently. In this paper, we first introduce the accurate BER calculation methods of the multi-user TH-PPM UWB systems and then give the performance analysis over the ideal AWGN channel and a correlation receiver. Furthermore, we also introduce their applications in image transmission and data transmission and give the simulation results. The analytical method yields simple and exact formulas relating the performance to the system parameters.