• Journal of the Korean Institute of Telematics and Electronics
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• v.21 no.2
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• pp.24-28
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• 1984

A new type of digital echo canceler for two-wire digital transmission is presented. The new principle estimates an echo signal by use of the arithmetic means estimate for each transmitted data pattern, which leads to relatively simple hardware. The principle is compared with adaptive digital filter methods through theoretical analysis and computer simulation. The results show that the proposed method has fast convergence property with respect to its hardware simplicity and that the convergence time is independent of echo level. Quantization effects are also analyzed.

• Journal of radiological science and technology
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• v.26 no.1
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• pp.51-62
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• 2003

We carried out studies on develop of the ultrasound tissue mimicking materials(TMM) by synthesis of polymer urethane(C, CCR, $TiO_2$, tungsten, graphite, silver type). The major finding were as follows; (1) C type TMM was shown good homogeneity, penetration, gray scale like as liver tissue and propagated speed 1,540 m/s, attenuation $0.5{\sim}0.7\;dB/cm/MHz$. (2) $TiO_2$ type TMM was shown heterogeneous dot echo pattern. (3) Silver type TMM was appear good homogeneous echo pattern like as echo texture of thyroid gland. Therefor, C type TMM will be useful for ultrasound Q/A phantom materials and previous phantom materials.

• The Journal of the Convergence on Culture Technology
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• v.5 no.3
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• pp.9-23
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• 2019

The artificial intelligence speaker market is in a new age of mounting displays. This study aimed to analyze the difference of experience using artificial intelligent speakers in terms of usage context, according to the presence or absence of displays. This was achieved by using semantic network analysis to determine how the online review texts of Amazon Echo Show and Echo Plus consisted of different UX issues with structural differences. Based on the physical context and the social context of the user experience, the ego network was constructed to draw out major issues. Results of the analysis show that users' expectation gap is generated according to the display presence, which can lead to negative experiences. Also, it was confirmed that the Multimodal interface is more utilized in the kitchen than in the bedroom, and can contribute to the activation of communication among family members. Based on these findings, we propose a user experience strategy to be considered in display type speakers to be launched in Korea in the future.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.27 no.1
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• pp.43-50
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• 2017

Acoustic tiles are typically installed on the surface of pressure vessels in submarines to minimize echoes based on the ship's own noise and active sonar. In this study, we studied low frequency active echo reduction techniques to reduce underwater target echo signals. Active control algorithms using tile type projectors and FxLMS logic have been developed and the projectors have been installed in the assumed hull structure. The effectiveness of projectors and control algorithms has been evaluated in time and frequency domain analysis through experiments in the tank.

• The Journal of Korean Society of Virology
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• v.26 no.2
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• pp.215-225
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• 1996

Aseptic meningits, an acute inflammation of the meninges, is a common illness during childhood. Virus is the most important cause of aseptic meningitis. Especially enterovirus causes approximately above 85% of all cases of aseptic meningitis. In 1993, there was a big epidemic of aseptic meningitis by ECHO 9 and ECHO 30 viruses. And ECHO 3 virus was isolated as a causative agent of aseptic meningitis in 1994. This study was aimed to detect the causative agent of aseptic meningitis in 1995 and to analyze the 5'-noncoding region which was used to detect virus. Virus was isolated from 87 stools and cerebrospinal fluid specimens of the patients by cultured RD and HEp-2 cell. Neutralizing antibody tests using enterovirus serum pool were performed on the specimens with cytopathic effect. 3 of ECHO 7 viruses and 5 of Coxsackie B3 viruses were isolated from stool specimens and 1 of ECHO 7 and Coxsackie B3 mixed type was confirmed from cerebrospinal fluid specimens. RNA was isolated from the culture supernatants of infected cells and general primers were selected in highly conserved part of the 5'-noncoding region of the enteroviral genome for RT-PCR. PCR product from this virus showed a 152bp band on gel electrophoresis. Sequence of obtained DNA was compared with prototype sequences by accessing to the Genebank database. 5'-noncoding region of isolated Coxsackie B3 virus, which has point mutations in nucleotide sequence positions 493, 497, 502, 523, was closely related to that of polio virus type 1, Mahoney strain. In case of isolated ECHO 7 virus, nucleotide has been changed from cytosine to thymine at position 581 and from thymine to cytosine at position 583. We concluded the causative agents of the outbreak of aseptic meningitis during June to July in 1995 were both ECHO 7 and Coxsackie B3 virus, and the primer used in this study could allow a rapid diagnosis of enteroviruses by PCR.

• Journal of Astronomy and Space Sciences
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• v.35 no.2
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• pp.93-103
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• 2018

Non-specular, vertically upward transit, fast-moving radar echoes are observed in the summer polar upper mesosphere near 90 km using 52 MHz VHF radar at Esrange, Sweden. By resolving maximum echo power movement, the unusual meteor trails propagate vertically upward with taking horizontal displacements at an initial speed of 10 km/s exponentially decreasing with increasing height from 85-89 km, lasting for 3.5 sec. Another upward transit is observed as following a downward transit echo target in about ~1 sec, lasting over 5 sec. The upward motion cannot be explained with the dynamics of penetrating meteors or by atmospheric dynamics. The observation proposes that secondary produced plasma jets occurring from meteor trail are possibly responsible for upward fast moving echoes. The long-lasting (3-5 sec), ascending meteor trails at speeds of a few $10^4m/s$ are distinctive from any previous occurrences of meteors or upper atmospheric electrical discharges in the aspect of long-lasting upward/downward motions. This result possibly suggests a new type of meteor-trail leader discharge occurring in the summer polar upper mesosphere and lower thermosphere.

• Journal of the Institute of Electronics Engineers of Korea SP
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• v.39 no.2
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• pp.128-136
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• 2002

In this paper, we developed an acoustic echo canceller in real-time using TeakLite DSP Core, which will be placed in the vocoder chip of a mobile handset. Considering the limited computational capacity given to the acoustic echo canceller in a vocoder chip, we employed a FIR-type adaptive filter using a conventional NLMS algorithm. To begin with, we designed and implemented an acoustic echo canceller with floating-point format C-source code, and then converted it into fixed-point format through integer simulation. Then we programmed and optimized it in the assembler level to make it run ill real-time. After optimization procedure, the implemented echo canceller has approximately 624 words of program memory and 811 words of data memory. With 8 KHz sampling rate and 256 filter taps in the echo canceller that corresponds to 32 msec of echo delay, it requires 14.12 MIPS of computational capacity. For coverage of 16 msec echo delay, i.e., 128 filter taps, 9 MIPS is requited.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.48 no.2
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• pp.174-179
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• 2012

A new absorption material, cellulose sponge soaked in cement, was made for anechoic water tank and its acoustical properties were investigated by pulse methods. The sound absorption coefficient a (dB/cm) of the material was obtained in the frequency range of 40~120kHz from the echo reduction ER (dB) and insertion loss IL (dB) data. The result was averagely 1.8dB/cm higher than the sound absorption coefficient a (dB/cm) of cork-filled rubber which is one of the most effective absorption materials. The wedge (1.2~5.0cm long) type absorption tiles were made with this new material. The echo reduction ER (dB) of the absorption tile with 5.0cm wedge measured in water tank was higher than 20dB in the experimental frequency range.

• Proceedings of the Korean Geotechical Society Conference
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• 2005.03a
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• pp.33-40
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• 2005

Impact-echo test, a kind of simple and economical method to evaluate the integrity of drilled piles has some limitations to use because the stress wave can be generated only on the head of a pile and the wave propagation in the pile with surrounding soils are very complicated. Numerical analyses and model tests in the laboratory have shown that both the ratio of length to diameter of a pile and the stiffness ratio of pile to soil have influence on the resolution of testing results. Full scale testing piles which have artificial defects were used to verify the capability of impact-echo technique as a tool for the pile integrity evaluation. Behaviour of the reflected signal of stress wave was investigated according to the type of defects. Elastic modulus of the pile was calculated using the wave velocity in the pile and the unconfined strength of concrete specimen. Influences of the stiffness difference between the pile and the ground on the characteristics of a wave signal were also examined.

• Proceedings of the KIEE Conference
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• 2000.07d
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• pp.3216-3218
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• 2000

Projection-type Fast Spin Echo (PFSE) imaging has robustness against motion artifacts due to patient motion during magnetic resonance imaging data acquisition, or reduce flow artifacts. However, it has difficulty in controlling T2 contrast. In this paper, T2 contrast in the PFSE method is analyzed. The contrasts in FSE and PFSE method are compared by computer simulation and experiments with volunteers.