• Proceedings of the Korean Society of Surveying, Geodesy, Photogrammetry, and Cartography Conference
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• 2006.04a
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• pp.83-88
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• 2006

We intend to increase in efficiency of the topographic monitoring of seabed or riverbed by combined with DGPS, RTK GPS and echo sounder. For this study, we defined the error correction of the echo sounder with the experiment of water tank, which is considered the characteristic of estuary riverbed and then we developed the s/w for 3-dimensional monitoring of estuary riverbed and applied the s/w to field test and improved the various problems. On analyzing topography of estuary riverbed by combined GPS with echo sounder, the draught error which is yielded to change of length from the water surface by the movement of survey vessel to the end of the transducer was eliminated by geometrical rearrangement and we defined the correction formula, z = BM+ SAH- $DBR_{(i)}$ - DRT - ED. The sounding error about the echo sounder and characteristic of estuary riverbed was found by understanding the relation of average diameter and residual error and we defined correction formula, Y= -0.00474*In(X) -0.0045 by the regression analysis. and then we verified applicability of correction formula.

• The Journal of the Acoustical Society of Korea
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• v.18 no.5
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• pp.3-11
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• 1999

The conventional stereophonic acoustic echo cancellers need two adaptive filters to estimate one channel echo signal. Since the two channel signals are strongly correlated, the ESR of the input signals is considerably increased whatever the input signals may be. This causes the slow convergence of the adaptive filter for echo cancellation. To speed up the convergence, the AP algorithm is frequently used for the stereophonic acoustic echo canceller although there isn't a fast version for 2-channel case. The AP algorithm can be approximated with the Gram-Schmidt orthogonalization and a TDL structure. We propose a two channel algorithm for stereophonic acoustic echo canceller with the approximated AP algorithm.

• The Journal of the Acoustical Society of Korea
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• v.19 no.7
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• pp.15-22
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• 2000

This paper proposes a distributed highlight algorithm to generate efficiently echo signal for underwater target. In this algorithm, echo signal is synthesized by discontinuity highlights that are varied to incident angle, by equivalent and specified position highlights according to the spatial target structure. Completed UTAHID(Underwater TArget by Highlight Distribution) model is confrimed that PTS, ETS, echo elongation effect, target time spreading loss and envelope fluctuation are satisfied to expected values by various simulations. Thus it can be efficiently used in all sorts of real systems related to underwater target echo signal synthesis in active sonar.

• Journal of Astronomy and Space Sciences
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• v.35 no.2
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• pp.83-92
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• 2018

The summer polar lower thermosphere (90-100 km) has an interesting connection to meteors, adjacent to the mesopause region attaining the lowest temperature in summer. Meteors supply condensation nuclei for charged ice particles causing polar mesospheric summer echoes (PMSE). We report the observation of meteor trail with nearly horizontal transit at high speed (20-50 km/s), and at last with re-enhanced echo power followed by diffusive echoes. Changes in phase difference between radar receivers aligned in meridional and zonal directions are used to determine variations in horizontal displacements and speeds with respect to time by taking advantage of radar interferometric analysis. The actual transit of echo target is observed along the straight pathway vertically and horizontally extended as much as a distance of at least 24 km and at most 29 km. The meteor trail initially has a signature similar to 'head echoes', with travel speeds from 20 - 50 km/s. It subsequently transforms into a different type of echo target including specular echo and then finally the power reenhanced. The reenhancement of echo power is followed by fume-like diffusive echoes, indicating sudden release of plasma as like explosive process probably involved. We discuss a possible role of meteor-triggered secondary plasma trail, such as fireball embedded with electrical discharge that continuously varies the power and transit speed.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.64 no.9
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• pp.1337-1346
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• 2015

In this paper, pattern classifier is designed to classify precipitation and non-precipitation events from weather radar data. The proposed classifier is based on Fuzzy Neural Network(FNN) and consists of three FNNs which operate in parallel. In the proposed network, the connection weights of the consequent part of fuzzy rules are expressed as two polynomial types such as constant or linear polynomial function, and their coefficients are learned by using Least Square Estimation(LSE). In addition, parametric as well as structural factors of the proposed classifier are optimized through Differential Evolution(DE) algorithm. After event classification between precipitation and non-precipitation echo, non-precipitation event is to get rid of all echo, while precipitation event including non-precipitation echo is to get rid of non-precipitation echo by classifier that is also based on Fuzzy Neural Network. Weather radar data obtained from meteorological office is to analysis and discuss performance of the proposed event and echo patter classifier, result of echo pattern classifier compare to QC(Quality Control) data obtained from meteorological office.

• Journal of the Korea Concrete Institute
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• v.15 no.6
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• pp.924-929
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• 2003

A majority of infrastructures has been deteriorated over time. Therefore, it is very important to verify the quality of construction, and the level of structural deterioration in existing structures, to ensure their safety and functionality. Many researchers have studied non-destructive testing (NDT) methods to identify structural problems in existing structures. The impact echo technique is one of the widely used NDT techniques. The impact echo technique has several inherent problems, including the difficulties in P-wave velocity evaluation due to inhomogeneous concrete properties, deterioration of evaluation accuracy where multiple reflection boundaries exist, and the influence of the receiver location in evaluating the thickness of the tested structures. Therefore, the objective of this paper is to propose an enhanced impact echo technique that can reduce the aforementioned problems and develop a Virtual Instrument for the application via a thickness evaluation technique which has same technical background to find deterioration in concrete structures. In the proposed impact echo technique, transfer function from dual channel system analysis is used, and coherence is improved to achieve reliable data. Also an averaged signal -ensemble- is used to achieve more reliable results. From the analysis of transfer function, the thickness is effectively identified.

• Health Policy and Management
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• v.23 no.4
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• pp.369-375
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• 2013

Background: This study aimed to investigate the association between employment transitions and suicide ideation among the echo generation. Methods: This study used survey data from the 2008 and 2010 Seoul Welfare Panel Study (Wave I, II). The sample population was restricted to the echo generation aged between18 and 31, and the total of 882 samples were included in the final dataset. Employment transitions were categorized into four groups. The groups were defined as 'employed-employed', 'unemployed-employed', 'employed-unemployed', and 'unemployed-unemployed'. We used logistic regression to find out the association between employment transitions and suicide ideation among the echo generation. Results: 'Employed-unemployed' and 'unemployed-unemployed' groups were likely to have an association with depression (odds ratio [OR], 1.49; 95% confidence interval [CI], 1.46 to 1.51; OR, 1.57; 95% CI, 1.56 to 1.59) accordingly. 'Unemployed-unemployed' group also was related to suicide ideation (OR, 1.39; 95% CI, 1.36 to 1.42). Interestingly, 'unemployed-employed' group showed a strong association with suicide ideation among the echo generation (OR, 3.85; 95% CI, 3.75 to 3.95). Conclusion: Experience in unemployment increases the risk of depression and suicide ideation. Moreover, the precarious job also increases the risk of suicide ideation.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.23 no.7
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• pp.1650-1658
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• 1998

This paper describes how to remove echoes effectively using speech parameter information provided form speech coder. More specially, the proposed adaptive echo canceller utilizes the excitation signal or linearly predicted error signal instead of output speech signal of vocoder as the input signal for adaptation algorithm. The normalized least mean ssquare(NLMS) algorithm is used for the adaptive echo canceller. The proposed algorithm showed a fast convergece charactersitcis in the sinulatio compared to the conventional method. Specially, the proposed echo canceller utilizing the excitation signal of speech coder showed about four times fast convergence speed over the echo canceller utilizing the output speech signal of the speech coder for the adaptation input.

• Journal of Home Health Care Nursing
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• v.23 no.1
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• pp.34-44
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• 2016

Purpose: This study investigated the factors associated with suicidal ideation in the Korean Echo Generation using 2012 Korea Health Panel Data. Methods: The 2012 Korea Health Panel Data were collected from February 2012 to July 2012 and included 2,303 people who responded to a question asking whether they had experienced suicidal ideation. The data were analyzed by chi-square and multiple logistic regression test using SPSS 22.0. Results: The rate of suicidal ideation was 4.2% in the Echo Generation. Factors associated with suicidal ideation in the Echo Generation revealed that the following variables increased the rate of suicidal ideation: sex(odd ratio: 2.39, CI: 1.39-4.09), education(odd ratio: 1.95, CI: 1.08-3.52), depression(odd ratio: 12.06, CI: 6.92-21.03), frustrating experience(odd ratio: 2.52, CI: 1.22-5.20), anxiety about the future(odd ratio: 14.58, CI: 3.20-66.41), self-rated health status(odd ratio: 2.39, CI: 1.39-4.09 and odd ratio: 6.41, CI 2.87-14.33). Conclusion: This study provides a preliminary examination of the factors associated with suicidal ideation in the Echo Generation. A more careful examination may be warranted.

• Geophysics and Geophysical Exploration
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• v.3 no.3
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• pp.94-100
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• 2000

Many nondestructive test methods used for metallic materials have some limit in application to concrete materials due to their heterogeneity. Impact echo method utilizes the resonance frequency of reflected seismic waves from defects or the boundary between two materials and can be applied to investigate the interior of concrete structures. In this study, a field data acquisition system for the impact echo method was assembled and field tests under various conditions were performed. The impact echo method was applied for investigating thickness/defects/backfilling of concrete structures/tunnel lining/airport pavement. The applicability of the impact echo method to the civil engineering field was substantiated by providing results within $10\%$ errors.