• Journal of Communications and Networks
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• v.18 no.3
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• pp.387-396
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• 2016

Multiuser communication has been an important research area of underwater acoustic communications and networking. This paper studies the use of adaptive orthogonal frequency-division multiple access (OFDMA) in a downlink scenario, where a central node sends data to multiple distributed nodes simultaneously. In practical implementations, the instantaneous channel state information (CSI) cannot be perfectly known by the central node in time-varying underwater acoustic (UWA) channels, due to the long propagation delays resulting from the low sound speed. In this paper, we explore the CSI feedback for resource allocation. An adaptive power-bit loading algorithm is presented, which assigns subcarriers to different users and allocates power and bits to each subcarrier, aiming to minimize the bit error rate (BER) under power and throughput constraints. Simulation results show considerable performance gains due to adaptive subcarrier allocation and further improvement through power and bit loading, as compared to the non-adaptive interleave subcarrier allocation scheme. In a lake experiment, channel feedback reduction is implemented through subcarrier clustering and uniform quantization. Although the performance gains are not as large as expected, experiment results confirm that adaptive subcarrier allocation schemes based on delayed channel feedback or long term statistics outperform the interleave subcarrier allocation scheme.

• Journal of the Korean Society of Safety
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• v.26 no.1
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• pp.1-7
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• 2011

When the pumps stopped in the operation by the power failure, the hydraulic transients take place in the sudden change of a velocity of pipe line. Each and every water hammer problem shows the critical stage to be greatly affected the facts of safety and reliability in case of power failure. The field tests of the water hammer executed at Cheong-Yang booster pump station having an air chamber. The effects were studied by both the practical experiments and the CFD(Computational Fluid Dynamics : Surge 2008). The result states that the system with water hammering protection equipment was much safer when power failure happens. The following data by a computational fluid dynamic analysis are to be shown below, securing the system stability and integrity. (1) With water hammering protection equipment. (1) Change of pressure : Up to $15.5\;kg/cm^2$ in contrary to estimating $16.88\;kg/cm^2$. (2) Change rate of water level : 52~33% in contrary to estimating 55~27%. (3) Note that the operational pressure of pump runs approx. 145 m, lowering 155 m of the regularity head of pump. (4) Note that the cycle of water hammering delays from 80 second to 100 second, together with easing the function of air value at the pneumatic lines. (2) Change of pressure without water hammering protection equipment : Approximate $22.86\;kg/cm^2$. The comprehensive result says that the computational fluid dynamics analysis would match well with the practical field-test. It was able to predict Max. or Min. water hammering time in a piping system. This study aims effectively to alleviate water hammering in a pipe line to be installed with air chamber at the pumping station and results in making the stability of pump system in the end.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.8
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• pp.1854-1863
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• 2003

In the recent digital communication systems, the performance of Turbo Code using the mr correction coding depends on the interleaver influencing the free distance determination and the recursive decoding algorithms that is executed in the huh decoder. However, performance depends on the interleaver depth that needs many delays over the reception process. Moreover, turbo code has been blown as the robust coding methods with the confidence over the fading channel. International Telecommunication Union(ITU) has recently adopted it as the standardization of the channel coding over the third generation mobile communications(IMT­2000). Therefore, in this paper, we preposed the interleaver that has the better performance than existing block interleaver, and modified turbo decoder that has the parallel concatenated structure using MAP algorithm. In the real­time voice and video service over third generation mobile communications, the performance of the proposed two methods was analyzed and compared with the existing methods by computer simulation in terms of reduced decoding delay using the variable decoding method over AWGN and fading channels for CDMA environments.

• The KIPS Transactions:PartD
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• v.14D no.7
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• pp.719-726
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• 2007

Recently, NAND flash memory has been used for a storage device in various mobile computing devices such as MP3 players, mobile phones and laptops because of its shock-resistant, low-power consumption, and none-volatile properties. However, due to the very distinct characteristics of flash memory, disk based systems and applications may result in severe performance degradation when directly adopting them on flash memory storage systems. Especially, when a B-tree is constructed, intensive overwrite operations may be caused by record inserting, deleting, and its reorganizing, This could result in severe performance degradation on NAND flash memory. In this paper, we propose an efficient buffer management scheme, called IBSF, which eliminates redundant index units in the index buffer and then delays the time that the index buffer is filled up. Consequently, IBSF significantly reduces the number of write operations to a flash memory when constructing a B-tree. We also show that IBSF yields a better performance on a flash memory by comparing it to the related technique called BFTL through various experiments.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.29 no.8
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• pp.18-22
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• 2015

Digitalization of the substation in Korea has been in progress so far with focusing on Station Bus. However, its application to Process Bus has been delayed due to some technical issues. IEDs based on Process Bus use the data values of SV and GOOSE. As the size of communication data on Process Bus is comparatively bigger than that of Station Bus, it is very important for the evaluating the performance of Process Bus to analyze the transferring speed and quality of data from the first equipment, which is located on process level, to station level. According to the results of related studies, it is said that the most important factor for the design and operation of Process Bus network is the communication delay with consideration of the volume of packets. In the paper, the results of performance test for the network with and without application of VLAN on Process Bus system that uses integrated IEDs are presented. Additionally, the paper proposes the optimal method to analyze the communication delays of network systems through evaluating the maximum delay time, link process ratio and the amount of lost packets by using a simulation tool.

• Journal of Korean Society of Transportation
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• v.28 no.2
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• pp.45-52
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• 2010

The objective of this paper is to develop and apply a method that estimates the amount of traffic congestion (vehicle hours of delay) caused by traffic accidents that occur on freeways in Korea. A key feature of this research is the development of a method to separate the non- recurrent delay from any recurrent delay that is present on the road at the time and place of a reported accident. The main idea to separate these two delays is to use the speed difference between speed under accident condition and speed under normal flow condition. For the case study application, two datasets were combined to accomplish the objective of the study: (1) accident data and (2) traffic flow data. Eventually, the results can be useful for the performance evaluation of accident reduction program, for strategic plans to cope with congestion caused by traffic accidents, and for rectification of the estimation method for traffic congestion costs.

• Journal of Biomedical Engineering Research
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• v.19 no.2
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• pp.143-152
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• 1998

In this paper, we present the performances of a Doppler system using single channel RF(Radio Frequency) sampling. This technique consists of undersampling the ultrasonic blood backscattered RF signal on a single channel. Conventional undersampling method in Doppler imaging system have to use a minimum of two identical parallel demodulation channels to reconstruct the multigate analytic Doppler signal. However, this system suffers from hardware complexity and problem of unbalance(gain and phase) between the channels. In order to reduce these problems, we have realized a multigate pulsed Doppler system using undersampling on a single channel, It requires sampling frequency at $4f_o$(where $f_o$ is the center frequency of the transducer) and 12bits A/D converter. The proposed " single-Channel RF Sampling" method aims to decrease the required sampling frequency proportionally to $4f_o$/(2k+1). To show the influence of the factor k on the measurements, we have compared the velocity profiles obtained in vitro and in vivo for different intersequence delays time (k=0 to 10). We have used a 4MHz center frequency transducer and a Phantom Doppler system with a laminar stationary flow. The axial and volumetric velocity profiles in the vessel have been computed according to factor k and have been compared. The influence of the angle between the ultrasonic beam and the flow axis direction, and the fluid viscosity on the velocity profiles obtained for different values of k factor is presented. For experiment in vivo on the carotid, we have used a data acquisition system with a sampling frequency of 20MHz and a dynamic range of 12bits. We have compared the axial velocity profiles in systole and diastole phase obtained for single channel RF sampling factor.ng factor.

• Journal of the Korea Society of Computer and Information
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• v.18 no.11
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• pp.87-97
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• 2013

In the RFID system, multiple tags respond in the process of identifying multiple tags in the reader's interrogation zone, resulting in collisions. Tag collision occurs when two or more tags respond to one reader, so that the reader cannot identify any tags. These collisions make it hard for the reader to identify all tags within the interrogation zone and delays the identifying time. In some cases, the reader cannot identify any tags. The reader needs the anti-collision algorithm which can quickly identify all the tags in the interrogation zone. The proposed algorithm efficiently divides tag groups through an efficient separation to respond, preventing collisions. Moreover, the proposed algorithm identifies tags without checking all the bits in the tags. The prediction with efficient separation reduces the number of the requests from the reader.

• Journal of the Korean Geophysical Society
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• v.4 no.1
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• pp.21-33
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• 2001

Simultaneous inversion of first-arrivals of local earthquakes recorded by the Korea Meteorological Administration(KMA) seismograph network from 1991 to 1998 is made to derive 1D crustal velocity structure of the Korean peninsula. Twenty-nine events with 178 observations are used in the inversion. Average crustal P-wave velocity turns out to be about 6.3 km/sec, and crustal thickness and upper mantle P-wave velocity are estimated as 33 km and 7.9 km/sec, respectively. Results of inversion indicate the possibility of the low velocity layer in the lower crust. Joint inversion is applied to estimate hypocenters, station delays, and velocities simultaneously. Relative station corrections for 11 stations range from zero to about 1.2 sec. Analysis of the synthetic data shows that estimates of hypocenter locations and station corrections as well as averaged crustal structure are reliable for the given data set..

• BMB Reports
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• v.52 no.11
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• pp.653-658
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• 2019

MYB-type transcription factors (TFs) play important roles in plant growth and development, and in the rapid responses to unfavorable environmental conditions. We recently reported the isolation and characterization of a rice (Oryza sativa) MYB TF, OsMYB102, which is involved in the regulation of leaf senescence by downregulating abscisic acid (ABA) biosynthesis and the downstream signaling response. Based on the similarities of their sequences and expression patterns, OsMYB102 appears to be a homolog of the Arabidopsis thaliana AtMYB44 TF. Since AtMYB44 is a key regulator of leaf senescence and abiotic stress responses, it is important to examine whether AtMYB44 homologs in other plants also act similarly. Here, we generated transgenic Arabidopsis plants expressing OsMYB102 (OsMYB102-OX). The OsMYB102-OX plants showed a delayed senescence phenotype during dark incubation and were more susceptible to salt and drought stresses, considerably similar to Arabidopsis plants overexpressing AtMYB44. Real-time quantitative PCR (RT-qPCR) revealed that, in addition to known senescence-associated genes, genes encoding the ABA catabolic enzymes AtCYP707A3 and AtCYP707A4 were also significantly upregulated in OsMYB102-OX, leading to a significant decrease in ABA accumulation. Furthermore, protoplast transient expression and chromatin immunoprecipitation assays revealed that OsMYB102 directly activated AtCYP707A3 expression. Based on our findings, it is probable that the regulatory functions of AtMYB44 homologs in plants are highly conserved and they have vital roles in leaf senescence and the abiotic stress responses.