• Transactions of the Korean Society of Mechanical Engineers B
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• v.40 no.3
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• pp.127-138
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• 2016

Diesel vehicles should be equipped with urea-selective catalytic reduction(SCR) system as a high-performance catalyst, in order to reduce harmful nitrogen oxide emissions. In this study, a three-dimensional Eulerian-Lagrangian CFD analysis was used to numerically predict the multiphase flow characteristics of the urea-SCR system, coupled with the chemical reactions of the system's transport phenomena. Then, the numerical spray structure was modified by comparing the results with the measured values from spray visualization, such as the injection velocity, penentration length, spray radius, and sauter mean diameter. In addition, the analysis results were verified by comparison with the removal efficiency of the nitrogen oxide emissions during engine and chassis tests, resulting in accuracy of the relative error of less than 5%. Finally, a verified CFD analysis was used to calculate the interanl flow of the urea-SCR system, thereby analyzing the characteristics of pressure drop and velocity increase, and predicting the uniformity index and overdistribution positions of ammonia.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.8
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• pp.1507-1514
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• 2015

Non-orthogonal multiple access (NOMA) is a promising candidate for 5G networks. NOMA achieves superior spectral efficiency than conventional orthogonal multiple access (OMA), as in NOMA multiple users uses the same time and frequency resources. Multiple-input-multiple-output (MIMO) is one another promising technique that can enhance system performance. In this paper we present a spectral and energy efficient multiple antenna based NOMA scheme, known as spatially modulated NOMA. In the proposed scheme the cell edge users are multiplexed in spatial domain, which means the information to cell edge users is conveyed using the transmit antenna indices. In NOMA the performance of cell edge users are deeply effected as it treats signals of others as noise. The proposed scheme achieves superior spectral efficiency than the conventional NOMA. The number of decoding steps involved in decoding NOMA signal reduces by one as cell edge user is multiplexed in spatial domain. The proposed scheme is more energy efficient as compare to conventional NOMA. All of the three gains high spectral, energy efficiency and one step reduction in decoding comes at cost of multiple transmit antennas at base station.

• Journal of the Institute of Convergence Signal Processing
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• v.12 no.4
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• pp.333-340
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• 2011

KJJVC(Korea-Japan Joint VLBI Correlator) was installed at the KJCC(Korea-Japan Correlation Center) and has been operated by KASI(Korea Astronomy and Space Science Institute) from 2009. KJNC is able to correlate the VLBI observed data through KVN(Korean VLBI Network), VERA(VLBI Exploration of Radio Astrometry), and JVN(Japanese VLBI Network) and its joint network array. And it is used exclusively as computer in order to process the observed data for the scientific purpose KJJVC used the VSI(VLBI Standard Interface) as the VLBI international standard at the data input-output specification between each component. Especially, for correlating the observed data, the data is transmitted with 1024Mbps speed between Mark5B high-speed playback and RVDB(Raw VLBI Data Buffer). The EMI(Electromagnetic lnterference), which is occurred by data transmission with high-speed, cause the data loss and the loss occurrence is frequently often for long transmission cable. Finally it will be caused the data recognition error by decreasing the voltage level of digital data signal. In this paper, in order to minimize the data loss by measuring the EMI noise level in transmission of the VSI specification, the 3 methods such as 1) RC filtering method, 2) lmpedance matching using Microstrip line, and 3) Signal buffering method using Differential line driver, were proposed. To verify the effectiveness of each proposed method, the performance evaluation was conducted by implementing and simulations for each method. Each proposed method was effectively confirmed as the high-speed data transmission of the VSI specification.

• Journal of KIISE:Software and Applications
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• v.29 no.4
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• pp.270-277
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• 2002

Text filtering is a task of deciding whether a document has relevance to a specified topic. As Internet and Web becomes wide-spread and the number of documents delivered by e-mail explosively grows the importance of text filtering increases as well. The aim of this paper is to improve the accuracy of text filtering systems by using machine learning techniques. We apply AdaBoost algorithms to the filtering task. An AdaBoost algorithm generates and combines a series of simple hypotheses. Each of the hypotheses decides the relevance of a document to a topic on the basis of whether or not the document includes a certain word. We begin with an existing AdaBoost algorithm which uses weak hypotheses with their output of 1 or -1. Then we extend the algorithm to use weak hypotheses with real-valued outputs which was proposed recently to improve error reduction rates and final filtering performance. Next, we attempt to achieve further improvement in the AdaBoost's performance by first setting weights randomly according to the continuous Poisson distribution, executing AdaBoost, repeating these steps several times, and then combining all the hypotheses learned. This has the effect of mitigating the ovefitting problem which may occur when learning from a small number of data. Experiments have been performed on the real document collections used in TREC-8, a well-established text retrieval contest. This dataset includes Financial Times articles from 1992 to 1994. The experimental results show that AdaBoost with real-valued hypotheses outperforms AdaBoost with binary-valued hypotheses, and that AdaBoost iterated with random weights further improves filtering accuracy. Comparison results of all the participants of the TREC-8 filtering task are also provided.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.4
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• pp.723-730
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• 2015

In this paper, a location tracking compensation algorithm based on the Least-Squares Method ($LCA_{LSM}$) was proposed to improve the autonomous tracking efficiency for the docent robot in exhibition hall, and the performance of the $LCA_{LSM}$ is analyzed by several practical experiments. The proposed $LCA_{LSM}$ compensates the collected location coordinates for the robot using the Least-Squares Method (LSM) in order to reduce the cumulated errors that occur in the Encoder/Giro sensor (E/G) and to enhance the measured tracking accuracy rates in the autonomous tracking of the robot in exhibition hall. By experiments, it was confirmed that the average error reduction rates of the $LCA_{LSM}$ are higher as 4.85% than that of the $LCA_{KF}$ in Scenario 1 (S1) and Scenario 2 (S2), respectively on the location tracking. In addition, it was also confirmed that the standard deviation in the measured errors of the $LCA_{LSM}$ are much more low and constant compared to that of the E/G sensor and the $LCA_{KF}$ in S1 and S2 respectively. Finally, we see that the suggested $LCA_{LSM}$ can execute more the stabilized location tracking than the E/G sensors and the $LCA_{KF}$ on the straight lines of S1 and S2 for the docent robot.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.12B
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• pp.1183-1191
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• 2010

In this paper, I propose an adaptive OFDM CP length algorithm for in PLC systems for smart grid. The proposed scheme calculates the channel delay information at the CP controller of the receiver by taking correlation between a received data frame and the following delayed one. The CP controller, immediately, feeds back the channel delay information to the transmitter. Then, the transmitter adapts CP length for next data frame. As an impulsive noise model, Middleton Class A interference model was employed. The performance is evaluated in terms of packet data rate, cumulative packet data rate, and bit error rate (BER). The simulation results showed data gain (which is the amount of the reduced bits) gets larger as the number of packets increase, but the amount of data gain reduced as the number of branches ($N_{br}$) increase. In respects of BER for the cases $N_{br}$ is 3, 4, and 5, performance of the adaptive CP length algorithm and the fixed CP scheme are similar. Therefore, it is confirmed the proposed scheme achieved data rate increment without BER performance reduction compared to the conventional fixed CP length scheme.

• Korea journal of population studies
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• v.20 no.1
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• pp.27-46
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• 1997

It is generally known that the quality of Korean population census results is very high. The completeness of the census has been over 97% since 1960. The age errors are very low and they belong to the lowest group in the world. However, Korean census has several problems to be solved, which are suggested as the followings: 1) Since most Koreans are basically educated, we will be able to adopt the self-reporting survey method for the next census instead of the interview method. Then, we can save a lot of time and cost in a census. 2) We have to simplify, the items of age since the effects of the four age items (Korean ago, zodiac year at birth, birth date in solar or lunar calendar) are not large enough to compare to the investments of manpower and costs. 3) It should be helpful to improve the quality of census data if the post enumeration survey is conducted more successfully and the results evaluated for more items not only age are published. 4) For the reduction of the error rates for the age groups of infants, young children and the young labours who are moving frequently, we need some special items for the compliteness of the population census by age group. 5) We have to prepare and release the 1995 2% sample data file to the public users for the improvement of the usefuleness in time. Furtheremore, it is also very important for the research in the field of social sciences that the back series of 2% sample files from 1985 census data are reconstructed.

• The Journal of the Acoustical Society of Korea
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• v.18 no.6
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• pp.49-56
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• 1999

In many continuous speech recognition systems based on HMMs, decision tree-based state tying has been used for not only improving the robustness and accuracy of context dependent acoustic modeling but also synthesizing unseen models. To construct the phonetic decision tree, standard method performs one-level pruning using just single Gaussian triphone models. In this paper, two novel approaches, two-level decision tree and multi-mixture decision tree, are proposed to get better performance through more accurate acoustic modeling. Two-level decision tree performs two level pruning for the state tying and the mixture weight tying. Using the second level, the tied states can have different mixture weights based on the similarities in their phonetic contexts. In the second approach, phonetic decision tree continues to be updated with training sequence, mixture splitting and re-estimation. Multi-mixture Gaussian as well as single Gaussian models are used to construct the multi-mixture decision tree. Continuous speech recognition experiment using these approaches on BN-96 and WSJ5k data showed a reduction in word error rate comparing to the standard decision tree based system given similar number of tied states.

• Korean Journal of Acupuncture
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• v.22 no.4
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• pp.43-56
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• 2005

Objectives : The acupuncture has been used as treatment of disease in the oriental medicine. In this study, it was investigated at had an effects of Heart JEONGGYEOK(心正格) of SAAM five evolutive phase acupuncture techniques(舍岩五行鑛法) for appling deficiency in the heart induced by experimental focal ischemia. Materials and methods : The focal ischemia was induced by middle cerebral artery occlusion for 2hours. The groups divided into 6 groups, normal(intactness group), control(no therapy group after ischemia-induced), AT1(reinforcing acupoint of Heart JEONGGYEOK : acupuncture therapy group at LR1, HT9 after ischemia-induced), AT2(reinforcing acupoint of Kidney JEONGGYEOK : acupuncture therapy group at LU8, KI7 after ischemia-induced) AT3(combination of reinforcing acupoint of Heart JEONGGYEOK and Kidney JEONGGYEOK : acupuncture therapy group at LR1, HT9, LU8, KI7 after ischemia-induced) AT4(reinforcing and reducing acupoint of Heart JEONGGYEOK : acupuncture therapy group at LR1, HT9, HT3, KI10 after ischemia-induced), AT4(reinforcing and reducing acupoint of Heart JEONGGYEOK : acupuncture therapy group at LRI, HT9, HT3, KI10 after ischemia-induced). Acupuncture therapy was carried out during 3 weeks after focal ischemia-induced. Eight-arm radial maze was used for the behavioral task and neuropretective effect of acupuncture therapy was observed by Cresyl violet, AchE, ChAT-stain. Results : The error rate in the eight-arm radial maze task was significantly decreased in AT3 group on 3days, in AT1 and AT4 groups on 4days, in AT3 and AT4 groups on 5days compared to the control group. The rate of correct choice was significantly increased AT4 group compared to the control group. The density of neurons in the hippocampal CA1 were significantly increased in all experiment groups, AT1, AT2, AT3 and AT4 groups compared to the control group. The density of AchE in the hippocampal CA1 was significantly increased in AT4 group compared to the control group. The density of ChAT in the hippocampal CA1 were significantly increased in AT1 and AT3 group compared to the control group. Conclusions : These results suggest that reinforcing and reducing acupoint of Heart JEONGGYEOK could be used as a medication for controlling the stroke by deficiency in the heart.

• Journal of Korea Water Resources Association
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• v.48 no.5
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• pp.409-423
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• 2015

In this study the very short-term rainfall forecasting and storm water forecasting using the weather radar data were implemented in an urban stream basin. As forecasting time increasing, the very short-term rainfall forecasting results show that the correlation coefficient was decreased and the root mean square error was increased and then the forecasting model accuracy was decreased. However, as a result of the correlation coefficient up to 60-minute forecasting time is maintained 0.5 or higher was obtained. As a result of storm water forecasting in an urban area, the reduction in peak flow and outflow volume with increasing forecasting time occurs, the peak time was analyzed that relatively matched. In the application of storm water forecasting by radar rainfall forecast, the errors has occurred that we determined some of the external factors. In the future, we believed to be necessary to perform that the continuous algorithm improvement such as simulation of rapid generation and disappearance phenomenon by precipitation echo, the improvement of extreme rainfall forecasting in urban areas, and the rainfall-runoff model parameter optimizations. The results of this study, not only urban stream basin, but also we obtained the observed data, and expand the real-time flood alarm system over the ungaged basins. In addition, it is possible to take advantage of development of as multi-sensor based very short-term rainfall forecasting technology.