• The Journal of the Acoustical Society of Korea
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• v.17 no.1E
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• pp.54-65
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• 1998

This study attempts to test the classifying performance of a neural network and thereby examine its applicability to the signals distorted in a shallow water environment. Linear frequency modulated(LFM) signals are simulated by using an acoustic model and also measured through sea experiment. The network is constructed to have three layers and trained on both data sets. To get normalized power spectra as feature vectors, the study considers the three transforms : shot-time Fourier transform (STFT), wavelet transform (WT) and pseudo Wigner-Ville distribution (PWVD). After trained on the simulated signals over water depth, the network gives over 95% performance with the signal to noise ratio (SNR) being up to-10 dB. Among the transforms, the PWVD presents the best performance particularly in a highly noisy condition. The network performs worse with the summer sound speed profile than with the winter profile. It is also expected to present much different performance by the variation of bottom property. When the network is trained on the measured signals, it gives a little better results than that trained on the simulated data. In conclusion, the simulated signals are successfully applied to training a network, and the trained network performs well in classifying the signals distorted by a surrounding environment and corrupted by noise.

• Korean Journal of Optics and Photonics
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• v.13 no.5
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• pp.435-441
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• 2002

In this paper, we propose an optimal 2-dimensional construction algorithm of a code family for a high-speed optical code division multiple access network. The optimal 2-D code family generated by search algorithm has better spectrum efficiency than previous codes, having relatively many code sets with short code length and the same or lower BER. Using the optimal 2-D code, OCDMA systems make it possible to utilize the spectrum more efficiently than WDM systems. The probability of bit error for high-speed OCDMA transmissions is calculated as a function of the number of users in the presence of receiver and shot noise(additive white Gaussian noise).

• The Journal of Korean Society for School & Community Health Education
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• v.14 no.2
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• pp.93-112
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• 2013

Objectives: This study was conducted to investigate the incidence rate of noise-induced hearing loss (NIHL) in Korean youths using the National Health Insurance Data Methods: We obtained the case of NIHL with the National Health Insurance Data and calculated the incidence rate of NIHL after classifying them by year (from 2005 through 2008), age, gender, birth cohort. Results: The age-adjusted incidence rate by year of NIHL per 100,000 population increased by 40.6% from 13.8 persons in 2005 to 19.4 persons in 2008, which showed a increasing trend every year. In particular, the incidence rate per 100,000 population among the adolescents (15-19 years of age) shot up by 78.2% from 8.7 persons in 2005 to 15.5 persons in 2008. According to the incidence rate by birth cohort of NIHL, the birth cohorts showed the gradually increase in incidence rate as time passed by. Adolescents in early 20s (20-24 years of age) had a higher incidence rate than teenage and men had a higher incidence rate than women. Conclusions: The results suggest that incidence rate of NIHL in Korean youths has rapidly increased among adolescents. Therefore, it is required to educate adolescents about the risk of hearing loss due to noise, establish program to prevent NIHL among adolescents and provide them with health education on hearing loss prevention.

• Investigative Magnetic Resonance Imaging
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• v.7 no.2
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• pp.108-115
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• 2003

Purpose : To evaluate the effect of the gradient switching noise on the ECD source localization with the EEG data recorded during the MRI scan. Materials and Methods : We have fabricated a spherical EEG phantom that emulates a human head on which multiple electrodes are attached. Inside the phantom, electric current dipole(ECD) sources are located to evaluate the source localization error. The EEG phantom was placed in the center of the whole-body 3.0 Tesla MRI magnet, and a sinusoidal current was fed to the ECD sources. With an MRI-compatible EEG measurement system, we recorded the multi channel electric potential signals during gradient echo single-shot EPI scans. To evaluate the effect of the gradient switching noise on the ECD source localization, we controlled the gradient noise level by changing the FOV of the EPI scan. With the measured potential signals, we have performed the ECD source localization. Results : The source localization error depends on the gradient switching noise level and the ECD source position. The gradient switching noise has much bigger negative effects on the source localization than the Gaussian noise. We have found that the ECD source localization works reasonably when the gradient switching noise power is smaller than $10\%$ of the EEG signal power. Conclusion : We think that the results of the present study can be used as a guideline to determine the degree of gradient switching noise suppression in EEG when the EEG data are to be used to enhance the performance of fMRI.

• Journal of the Korean Magnetics Society
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• v.4 no.3
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• pp.249-255
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• 1994

Magneto-optical disks with dielectric layers for optical tunning are useful for maximizing the SNR. We have developed a computer program based on characteristic matrix to investigate the best combination of the film thicknesses. We have optimized the thicknesses of the multilayers which were composed of TbFeCo, dielectric, and AI layers at the wavelengh of 830nm. The criterion for the optimization of the film thickness was to maximize the figure of merit with maintaining the low ellipticity and rmre than 10% reflectivity.

• Journal of Institute of Control, Robotics and Systems
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• v.14 no.5
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• pp.483-488
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• 2008

An active omni-directional raging system using an omni-directional vision with structured light has many advantages compared to the conventional ranging systems: robustness against external illumination noise because of the laser structured light and computational efficiency because of one shot image containing $360^{\circ}$ environment information from the omni-directional vision. The omni-directional range data represents a local distance map at a certain position in the workspace. In this paper, we propose a matching algorithm for the local distance map with the given global map database, thereby to localize a mobile robot in the global workspace. Since the global map database consists of line segments representing edges of environment object in general, the matching algorithm is based on relative position and orientation of line segments in the local map and the global map. The effectiveness of the proposed omni-directional ranging system and the matching are verified through experiments.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.328-328
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• 2020

본 연구에서는 강우앙상블 멤버를 입력자료로 한 강우기반 유출앙상블 멤버와 관측 강우자료를 입력자료로 한 모형기반 유출앙상블 멤버를 생성하고 각 유출앙상블 멤버의 정확도를 비교·평가하였다. 본 연구에서는 강우앙상블 멤버 생성을 위해 서울 지역을 대상으로 강우장 이동 모의에 필요한 모의 격자망을 구축하였다. 다음으로 최근 10년 동안 발생한 37개 호우사상의 관측자료를 토대로 격자별 특성방향을 결정하고 특성방향의 통계치로부터 유도된 베타분포를 기반으로 강우앙상블 멤버를 생성하였다. 유출앙상블 멤버는 대한민국 서울에 위치한 구로1 빗물펌프장 배수유역을 대상으로 shot noise process 기반 강우-유출모형을 이용하여 생성하였다. 강우-유출모형 매개변수의 난수 생성을 위해서 감마분포를 이용하였다. 2017년과 2018년 발생한 호우사상을 대상으로 강우기반 및 모형기반 유출앙상블을 생성한 결과, 강우의 방향성을 조정하여 생성한 강우기반 유출앙상블의 정확도가 더 높은 것으로 나타났다.

• Investigative Magnetic Resonance Imaging
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• v.10 no.2
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• pp.108-116
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• 2006

Purpose : High-resolution spiral-scan imaging is performed at 3 Tesla MRI system. Since the gradient waveforms for the spiral-scan imaging have lower slopes than those for the Echo Planar Imaging (EPI), they can be implemented with the gradient systems having lower slew rates. The spiral-scan imaging also involves less eddy currents due to the smooth gradient waveforms. The spiral-scan imaging method does not suffer from high specific absorption rate (SAR), which is one of the main obstacles in high field imaging for rf echo-based fast imaging methods such as fast spin echo techniques. Thus, the spiral-scan imaging has a great potential for the high-speed imaging in high magnetic fields. In this paper, we presented various high-resolution images obtained by the spiral-scan methods at 3T MRI system for various applications. Materials and Methods : High-resolution spiral-scan imaging technique is implemented at 3T whole body MRI system. An efficient and fast higher-order shimming technique is developed to reduce the inhomogeneity, and the single-shot and interleaved spiral-scan imaging methods are developed. Spin-echo and gradient-echo based spiral-scan imaging methods are implemented, and image contrast and signal-tonoise ratio are controlled by the echo time, repetition time, and the rf flip angles. Results : Spiral-scan images having various resolutions are obtained at 3T MRI system. Since the absolute magnitude of the inhomogeneity is increasing in higher magnetic fields, higher order shimming to reduce the inhomogeneity becomes more important. A fast shimming technique in which axial, sagittal, and coronal sectional inhomogeneity maps are obtained in one scan is developed, and the shimming method based on the analysis of spherical harmonics of the inhomogeneity map is applied. For phantom and invivo head imaging, image matrix size of about $100{\times}100$ is obtained by a single-shot spiral-scan imaging, and a matrix size of $256{\times}256$ is obtained by the interleaved spiral-scan imaging with the number of interleaves of from 6 to 12. Conclusion : High field imaging becomes increasingly important due to the improved signal-to-noise ratio, larger spectral separation, and the higher BOLD-based contrast. The increasing SAR is, however, a limiting factor in high field imaging. Since the spiral-scan imaging has a very low SAR, and lower hardware requirements for the implementation of the technique compared to EPI, it is suitable for a rapid imaging in high fields. In this paper, the spiral-scan imaging with various resolutions from $100{\times}100$ to $256{\times}256$ by controlling the number of interleaves are developed for the high-speed imaging in high magnetic fields.

• 월간산업보건
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• s.5
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• pp.4-15
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• 1988

In order to proffer the fundamental data for the better working environment and the effective establishment of hearing conservation program on workers exposed to industrial noise, author assessed noise levels on the 42 noisy processes among 84 manufactures of 9 industries and measured noise gearing loss by the type of industries on 3,104 workers at these noisy processes from March, 1986 to Februry, 1987. The results were summarized as follows: 1. The averge of A-weight sound level of 23 processes(54.8%) and the avergae of sound level at each octave band of 14 processes(33.3%) exceeded the permissible exposure limits in 8 hours per day. 2. The noise level was the highest in process of cocking of ship building(109.1dBA), and followed by plating of steel rolling(104.3dBA), rivet of manufacture of motor vehicles(102.5dBA), shot of ship building(98.5dBA), aciding(95.7BA) and steel tubing(95.0dBA) of steel rolling, weaving of textiles(95.0dBA). 3. The permissible exposure time for the average of sound level at each octave band was only 30 minutes in the process of cocking of ship building, plating of steel rolling and rivet of manufacture of motor vehicles. 4. As a result of audiometric examination in 3,104 workers, the rate of hearing loss over 50dB at 4,000Hz was 7.3%(227 workers) and the rate of hearing loss over 41dB at 60average method was 2.9%(89 workers). 5. The prevalence of occupational hearing loss in ship building and manufacture of motor vehicle was 5.2% and it was the highest among prevalence of these 9 industries. 6. As a result of this suvery, the noise control and gearing conservation program were required especially in the industry of ship building and manufacture of motor vehicle.

• Journal of the Korean Society of Radiology
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• v.17 no.7
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• pp.1025-1031
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• 2023

We aimed to evaluate the radiation dose and image quality by changing the Scout view voltage in low-dose chest CT (LDCT) and applying scan parameters such as AEC (auto exposure control) and ASIR (adaptive statistical iterative reconstruction) to find the optimal protocol. Scout view voltage was varied at 80, 100, 120, 140 kV and after measuring the dose 5 times using the existing low-dose chest CT protocol, the appropriate kV was selected for the study using the Dose report provided by the equipment. After taking a basic LDCT shot at 120 kV, 30 mAs, ASIR 50% was applied to this condition. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were assessed by measuring Background noise (B/N). For dose comparison, CTDI_vol and DLP provided by the equipment were compared and analyzed using the formulas. The results indicated that the protocol of scout 140 + LDCT + ASIR 50 + AEC reduced radiation exposure and improved image quality compared to traditional LDCT, providing an optimal protocol. As demonstrated in the experiment, LDCT screenings for asymptomatic normal individuals are crucial, as they involve concerns over excessive radiation exposure per examination. Therefore, applying appropriate parameters is important, and it is expected to contribute positively to the public health in future LDCT based health screenings.