• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.2
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• pp.85-91
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• 2022

This study proposes a high efficiency bridgeless Power Factor Correction (PFC) converter with improved common mode noise characteristics. Conventional PFC has limitations due to low efficiency and enlarged heat sink from considerable conduction loss of bridge diode. By applying a Common Mode (CM) coupled inductor, the proposed bridgeless PFC converter generates less conduction loss as only a small magnetizing current of the CM coupled inductor flows through the input diode, thereby reducing or removing heat sink. The input diode is alternately conducted every half cycle of 60 Hz AC input voltage while a negative node of AC input voltage is always connected to the ground, thus improving common mode noise characteristics. With the aim to improve switching loss and reverse recovery of output diode, the proposed circuit employs Critical Conduction Mode (CrM) operation and it features a simple Zero Current Detection (ZCD) circuit for the CrM. In addition, the input current sensing is possible with the shunt resistor instead of the expensive current sensor. Experimental results through 480 W prototype are presented to verify the validity of the proposed circuit.

• Journal of the Korean Society for Nondestructive Testing
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• v.22 no.5
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• pp.465-473
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• 2002

Images are easily corrupted by noise during the data transmission, data capture and data processing. A technical method of noise analyzing and adaptive filtering for reducing of quantum noise in radiography is presented. By adjusting the characteristics of the filter according to local statistics around each pixel of the image as moving windowing, it is possible to suppress noise sufficiently while preserve edge and other significant information required in reading. We have proposed adaptive weighted median(AWM) filters based on local statistics. We show two ways of realizing the AWM filters. One is a simple type of AWM filter, whose weights are given by a simple non-linear function of three local characteristics. The other is the AWM filter which is constructed by homogeneous factor(HF). Homogeneous factor(HF) from the quantum noise models that enables the filter to recognize the local structures of the image is introduced, and an algorithm for determining the HF fitted to the detection systems with various inner statistical properties is proposed. We show by the experimented that the performances of proposed method is superior to these of other filters and models in preserving small details and suppressing the noise at homogeneous region. The proposed algorithms were implemented by visual C++ language on a IBM-PC Pentium 550 for testing purposes, the effects and results of the noise filtering were proposed by comparing with images of the other existing filtering methods.

• Proceedings of the KSPS conference
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• 2004.05a
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• pp.231-234
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• 2004

This paper describes an efficient method for improving the noise-robustness in speech recognition in a running car by considering wind noise. In driving car, mainly three kind of noises engine noise, tire noise and wind noise, are severely affect recognition performance. Especially wind noise is an important factor in driving car with window opened. We analyzed wind noise in various driving conditions that are 60, 80, 100 km/h with window fully opened, window half opened. We clarified that the recognition rate is significantly degenerated when the wind noise components in the frequency range above 200 Hz are large. We developed a preprocessing method to improve the noise robustness despite of wind noise. We adaptively changed the cutoff frequency of the front-end high-pass filter from 100 through 200 Hz according to the level of the wind noise components. By this method, the recognition rate is considerably improved for all kind of driving conditions

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.11
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• pp.1056-1063
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• 2007

Recently, there has been a growing consumer interest in the amount of noise produced by household electrical appliances. The designer of the product must identify the source of the noise, in order to reduce the noise. In the case of a household electric appliance such as the washing machine, there is consumer's complaint about the noise that is generated during the dehydrating condition. Because of several noise sources combined each other. It is difficult to identify the noise sources that contribute to the noise output. Multi-Dimensional Spectral Analysis (MDSA) is a method that can remove the correlation between different noise sources, and it expresses the key contributing factor as a unique output. This study utilized MDSA to analyze the contribution of each input in the noise output during the dehydrating condition.

• Safety and Health at Work
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• v.12 no.2
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• pp.230-237
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• 2021

Background: Noise-induced hearing loss is a well-known occupational disease that affects many fish harvesters from many fisheries worldwide, whose risk factor is prolonged exposure to hazardous noise levels. To date, academic research activities and regulatory bodies have not provided any comparative analysis among the existing methods to assess noise exposure levels of fish harvesters. This paper provides a comparison of four relevant assessment methods of noise exposure, examining the results of a measurement campaign performed onboard small fishing vessels from Newfoundland and Labrador. Methods: We traveled onboard 11 vessels engaged in multiple fisheries from Newfoundland and Labrador and performed extensive noise exposure surveys using the simplified International Maritime Organization method, the full-day measurement method, and the two methods provided by ISO 9612:2009, the task-based method and job-based method (JBM). Results: The results showed that the four methods yield similar values when the noise components are dominated by the engine and auxiliaries (steady-state sources); when noise components are dominated by the fishing gear, task-based method and the simplified International Maritime Organization method estimates are less accurate than JBM, using full-day measurements as baseline. Conclusion: The JBM better assesses noise exposure in small-scale fisheries, where noise exposure has significant variance and uncertainties on the exposure levels are higher.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.9 no.1
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• pp.41-55
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• 1999

In order to evaluate the effects of knowledge, attitude and practice on noise-induced hearing loss or hearing threshold level, questionnaire survey was performed and hearing thresholds of 1 kHz and 4 kHz were measured on 1,040 subjects with workers exposed to noise, safety and health officers. industrial hygienists, analysts rind office workers. The results were as follows ; 1. The following 6 factors were obtained by factor analysis and factor rotation of 30 questionnaire of knowledge, attitude and practice about noise; knowledge of noise (F1), concern of hearing protective devices (F2), concern of noise induced hearing loss (F3), concern of noise level and hearing impairment (F4), concern of noise in workplace (F5) and recognition of noised-induced hearing loss (F6). 56.1% of variance was explained by 6 factors. 2. Significant variables influencing knowledge, attitude and practice about noise were education level and age in F1, personal protective devices (PPE) and education level in F2, age and education level in F3, education level, age and sex in F4, PPE, education level, age and work duration in F5, and work duration and PPE in F6. 3. Hearing thresholds of 4 kHz were significantly higher in workers exposed to noise than that of in the other subjects and tended to be higher in industrial hygienists, safety and health officers and analysts than that of the office workers. 4. Significant variables influencing hearing thresholds of 1 kHz were age, education level, F5 and F6 in workers exposed to noise, and F1 in industrial hygienists. 5. Significant variables influencing hearing thresholds of 4 kHz were age, F6, sex, work duration, F1, F5, F2 and F3 in workers exposed to noise, F1 and age in safety and health officers, and F6, sex and F4 in industrial hygienists. With the above results, it suggested that workers exposed to noise be needed the education of knowledge, attitude and practice about noise in hearing conservation program for the prevention of noise induced hearing loss. Also, it suggested that health managers in workplace be needed countermeasures to prevent hearing loss although they are intermittently exposed to noise.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.433-434
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• 2014

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.550-551
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• 2014

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.04a
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• pp.73-74
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• 2014

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2010.05a
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• pp.685-686
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• 2010