• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.23 no.3
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• pp.196-204
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• 2013

Objectives: The purpose of this study is to analyze the number and influence factors of asbestos fibers in the air of farmhouses with asbestos cement slate roofing, as well as in rainwater per unit area of the asbestos cement slate roofing. Methods: At a distance of 1 m from the end of asbestos cement slate roofing in 20 farmhouses, the asbestos fiber in the air was collected three times on a clear day downwind from the prevailing wind. Rainwater falling from the slate roofing was collected four times with a 1.05-m rainwater pipe on a rainy day at the 20 farmhouses, filtered with a MCE filter, and analyzed with a phase contrast microscope. Results: The geometric mean of the number of asbestos fibers in the air of farmhouses with slate roofing was 0.11 fiber/L, and no samples exceeded the recommended standard of 10 fiber/L. As a result of multiple regression analysis, a factor which gave a significant influence to the asbestos fiber content in the air was the gross area of slate roofing at the target farmhouses. The number of asbestos fibers included in rainwater collected per 1 m2 of slate roofing was 1,753 fiber/$L{\cdot}m2$. As a result of multiple regression analysis, the number of asbestos fibers contained in rainwater per 1 m2 of slate showed a significantly higher tendency as the year of slate roofing installation at the target farmhouses receded. Conclusions: It was confirmed for the first time in Korea that asbestos from asbestos cement slate roofing scatters into the air.

• Korean Journal of Optics and Photonics
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• v.17 no.4
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• pp.312-316
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• 2006

In this study, a miniature fiber-optic radiation sensor has been developed using a water-equivalent organic scintillator for electron beam therapy dosimetry. The intensity of Cerenkov light is measured and characterized as a function of the incident angle of the electron beam from a LINAC. Also, a subtraction method using a background optical fiber without a scintillator and an optical discrimination method using optical filters are investigated to remove Cerenkov light, which could cause problems or limit the accuracy for detecting a fluorescent light signal in a fiber-optic radiation sensor.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.7
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• pp.43-50
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• 2004

For the simultaneous measurement of strain and damage signal a fiber Bragg grating sensor system with a dual demodulator was proposed. The dual demodulator is composed of a demodulator using a tunable Fabry-Perot filter measuring the low-frequency signal with large magnitude such as strain and the other using a passive Mach-Zehnder interferometer detecting the high-frequency signal with small amplitude such as impact or damage signal. Using the proposed fiber Bragg grating sensor system, both the strain and damage signals of a cross-ply laminated composite beam under tensile loading were simultaneously measured. The strain and damage signals detected by single fiber Bragg grating sensor showed that sudden strain shifts were accompanied with vibration at a maximum frequency of several hundreds of kilohertz at the instant of matrix crack propagation in the 90 degree layer in composite beam.

• Applied Biological Chemistry
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• v.34 no.4
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• pp.373-378
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• 1991

The skin and fleshy substance on the net fiber of sponge-gourd fruit pressed mechanically was removed with 0.2% NaOH solution in $3{\sim}5$ hours. The treatment of 0.2% NaOH with 0.02% Monopol(non-ionogenic polyoxethylen derivative) as surfactnat and with 0.1% $Ca(OCl)_2$ as bleaching agent enhanced the effect to remove the fleshy substance and improve the quality of net fiber. Also, the wet hardness and tensile strength of net fiber were controlled by the crosslinkage of the fiber with glu tardialdehyde, glyoxal, and formalin, respectively. The net fiber was stable on the acid and alkaline solutions. Also the range of temperature to degradate the fiber was $338{\sim}385^{\circ}C$. These values indicated a fair stability. The improved net fiber can be used for raw material of bath, dish washing, oil and gas filter, and many kinds of decorations.

• Journal of Wetlands Research
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• v.19 no.3
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• pp.259-270
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• 2017

In this study, field-scale half-saturated bio-filter wetland equipped with recirculation system was operated with stormwater from the paved road, and its operational performance and functions of LID-BMP were analyzed and compared with other facilities. The reduction of TSS, COD, TN, and TP were 92%, 63%, 36%, and 75%, respectively. Comparison of the reduction efficiency were carried out with respect to ratio between surface and catchment areas(SA/CA). In addition, this LID-BMP facility can reduce about 70% of pollutant by treating only 18% of total rainfall runoff. The results show that LID used for this study gave similar efficiency although its ratio was smaller. In addition, comparison study was made between synthetic fiber as a filter media and organic media, which shows that there was not any significant difference between, TSS and TP reduction, but there were large difference in COD and TN removal due to the presence and absence of release of organic carbon. Meanwhile, wetland system in this study equipped with a first-flush capture gave a higher stability in terms of treatment performance.

• Journal of Korean Society of Environmental Engineers
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• v.35 no.10
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• pp.717-723
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• 2013

The Korea Ministry of Environment prepares some paticulate matter eliminate measures for national health protection, as the Paticulate Matter ($PM_{2.5}$) exceeds the standard at more than half of the monitoring posts installed in the nation's big cities. At the center of JeonJu, when measuring the ultrafine particles of inner car at the different driving conditions, at the condition of the Actuator of inner recirculation mode and the Blower of 2-speed, the reduction speed of the ultrafine particles is most fast and the concentration stays low. When the windows are opened during driving, outer pollutants enter the car and also inner paticulate matter flies in all direction, and the increase of passengers causes the scattering of the ultrafine paticles. As the filter for air cleaning, the using of polypropylene non-woven fabric (used commonly now) is most excellent, but for the removal of volatile organic substance as well as the paticulate matter, it is thought that the using of activated carbon fiber filter, carbon adsorbent, is even more excellent.

• Journal of the Institute of Electronics and Information Engineers
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• v.52 no.11
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• pp.156-163
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• 2015

In the using of FBG(Fiber Bragg Grating) developed in home land, we designed and manufactured united FBG acoustic transducers the first in Korea. they are being applied to multi-point signal detection of FBG Hydrophone used Hopper WDM(national patent NO 10-1502954) in the underwater. On united FBG transducers manufactured, we made an demonstrated on respective frequency response peculiarities in the underwater and analyzed the special characters. As the experimental result on frequency response peculiarities, we made it possible underwater acoustic detection on united FBG acoustic transducers type to maximum 30Hz~2.5KHz. it's the optimum conditions of 1.2KHz frequency in detection. And for the purpose of realization on multi-point signal detection on wide scope in the underwater, in the using of WDM(Wavelength Division Multiplexing) method and passive band-pass filter system, established arrays system and succeeded in multi-point underwater acoustic signal detection to the frequency 200Hz~1.3KHz out of the two united type FBG transducers. Additionally, it would be possible directivity detection for the object of its source as the intensity of detection signal varies with the sound source's direction and angle. From now on we prepared a new moment on the practical use study on FBG hydrophone in the future.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.4
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• pp.122-128
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• 2016

This paper, proposes a new analysis method for the event detection of an OTDR signal. An OTDR signal was passed through the Hamming filter to remove the high frequency noise included in the signal. The signal was then passed consecutively through a differential filter to detect the events of interest. The terminal position was determined using the fact that there is a large gap between the signal and the trailing noise power beyond the terminal. This study examined the local maxima of the signal up to the terminal position and determined the peak regions. The real events were determined from the peak regions using noise information and peak threshold. Finally, the user events were found by inspecting the user peaks beyond the terminal position. The events of the OTDR signal without users are located at less than 17m compared to the optical fiber link setup. The events of the JDSU device are located less than 25m and their users are less than 5m. For the RadianTech device, the events are detected at less than 19m and the users are found in 5m. The results suggest that the proposed method is sufficiently applicable to an optical fiber link monitoring system.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.5
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• pp.418-424
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• 2014

We propose and experimentally demonstrate a photonic microwave notch filter with a negative coefficient. The negative coefficient is obtained by using cross gain modulation (XGM) in a reflective semiconductor optical amplifier (RSOA). When the RSOA is operated in saturated region, the signal carried on the pump wavelength is inversely copied to the probe wavelength by the XGM effect, showing a negative coefficient. Time delay between pump signal and probe signal is provided by single mode fiber (SMF) with wavelength dependent time delay. The proposed microwave notch filter shows notch dips of more than 35.1 dB and free spectral range (FSR) of about 380.6 MHz.

• Composites Research
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• v.12 no.1
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• pp.68-75
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• 1999

This study has observed that the dynamic behavior of Metal Matrix Composites (MMCs) in low velocity impact varies with impact velocity. MMCs with 15 fiber volume percent were fabricated by using the squeeze casting method. The AC8A was used as the matrix, and the alumina and the carbon were used as reinforcements. The tensile and vibration tests conducted yielded the yielded the tensile stress and elastic modulus of MMCs The low pass filter and instrumented impact test machine was adopted to study dynamic behaviors of MMCs corresponding to impact velocity. Stable impact signals were obtained by using the low pass filter. Impact corresponding to impact velocity. Stable impact signals were obtained by using the low pass filter. Impact energy of unreinforced alloy and MM s increased as the impact velocity increased. The increase of crack propagation energy was especially prominent, but the dynamic toughness of each material did not change much. To show the relation between crack initiation energy and dynamic fracture toughness, a simple model was proposed by using the strain energy and stress distribution at notch. The model revealed that crack initiation energy is proportional to the square of dynamic fracture toughness and inversely proportional to elastic modulus.