• 한국입자에어로졸학회지
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• 제17권1호
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• pp.1-8
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• 2021

The purpose of this study is to assess respirable crystalline silica (RCS) exposure levels in workers who collect and dispose used coal briquette ash (CBA) in sanitation companies that are subcontracted by one medium-sized local government on the collection of municipal household waste (MHW), and to analyze the quartz content in CBA. When the CBA powder that undergone specialized pretreatment in several steps were subjected to mineral identification and quantitative analysis using X-ray diffraction (XRD), it was found that quartz represented 18%, and in addition, mullite, and plagioclase were included. For two CBA collectors, samples were collected by the personal sampling evaluation method. After respirable dust was collected in accordance with the National Institute for Occupational Safety and Health 7500 method, the concentration of quartz was analyzed using XRD. Meanwhile, a portable real-time dust monitor (Sidepak AM520, TSI Inc., USA) was also used to observe the dust exposure level for each time zone and job task. The RCS exposure level of one worker was as high as 0.024 mg/㎥, which was the American Conference of Governmental Industrial Hygienists (ACGIH) Threshold Limit Values (TLV) level. The other worker also exhibited a concentration of 0.013 mg/㎥, which was more than half of TLV. The Sidepak results revealed that the work of collecting CBA and loading it onto a vehicle was hardly exposed to the dust of a significant level. It was found, however, that the work of transferring the collected CBA to a container through a conveyor belt was exposed to a very high average respirable dust concentration of 2.238 mg/㎥. The results of this study confirmed that quartz, which is crystalline silica and a carcinogen, is contained in CBA, one of municipal household waste (MHW), in high concentration. It was also confirmed that workers are exposed to high RCS concentrations while transferring collected CBA into a container. Although each local government in South Korea handles CBA in different ways, it is imperative to investigate the CBA exposure level of sanitation workers and improve their working conditions.

• 전자공학회논문지
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• 제53권6호
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• pp.167-173
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• 2016

압축 센싱은 기존의 섀넌/나이키스트 이론보다 낮은 샘플링률로 신호를 샘플링 하여도 원신호로 복원할 수 있다는 이론이다. 본 논문에서는 압축 센싱을 이용하여 반향 신호의 정량적 주파수 특성을 직접 추출하여 이를 이용한 초음파 감쇠 지수 예측 방법을 제안한다. 일반적인 초음파 감쇠 지수 예측 방법들은 시간 영역에서 수집된 반향 신호를 Fourier 변환 등을 통해 주파수 영역으로 변환하는데, 제안하는 예측 방법은 압축 센싱으로 수집된 데이터를 복원하는 과정에서 적용하는 basis 행렬을 이용하여 시간 영역으로의 완전한 신호 복원 없이 반향 신호의 주파수 특성을 직접 추출하여 감쇠 지수를 예측한다. 3가지의 basis 행렬을 통해 주파수 영역에서 복원된 반향 신호에 대하여 다중 참조 신호를 이용한 Centroid Downshift 방법으로 감쇠 지수를 예측하여 각각의 예측 정확도와 실행 시간을 비교 분석하였다. 컴퓨터 모의 실험 결과 이산 코사인 변환(DCT) 행렬을 적용하는 경우, 50%의 압축률에서는 압축 센싱을 적용하지 않은 경우와 0.35% 이내의 예측 정확도를 보였으며, 압축률을 70%까지 높이는 경우에도 약 6% 이내의 평균 예측 오차를 보였다. 제안한 압축 센싱을 적용한 반향 신호의 주파수 특성 추출 방법은 향후 주파수 영역의 다른 정량적 초음파 분석 방법에 적용할 수 있다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2008년도 추계학술대회 논문집 Vol.21
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• pp.11-11
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• 2008

ZnO has a very large exciton binding energy (60 meV) as well as thermal and chemical stability, which are expected to allow efficient excitonic emission, even at room temperature. ZnO based electronic devices have attracted increasing interest as the backplanes for applications in the next-generation displays, such as active-matrix liquid crystal displays (AMLCDs) and active-matrix organic light emitting diodes (AMOLEDs), and in solid state lighting systems as a substitution for GaN based light emitting diodes (LEDs). Most of these electronic devices employ the electrical behavior of n-type semiconducting active oxides due to the difficulty in obtaining a p-type film with long-term stability and high performance. p-type ZnO films can be produced by substituting group V elements (N, P, and As) for the O sites or group I elements (Li, Na, and K) for Zn sites. However, the achievement of p-type ZnO is a difficult task due to self-compensation induced from intrinsic donor defects, such as O vacancies (Vo) and Zn interstitials ($Zn_i$), or an unintentional extrinsic donor such as H. Phosphorus (P) doped ZnO thin films were grown on c-sapphire substrates by radio frequency magnetron sputtering with various Ar/ $O_2$ gas ratios. Control of the electrical types in the P-doped ZnO films was achieved by varying the gas ratio with out post-annealing. The P-doped ZnO films grown at a Ar/ $O_2$ ratio of 3/1 showed p-type conductivity with a hole concentration and hole mobility of $10^{-17}cm^{-3}$ and $2.5cm^2/V{\cdot}s$, respectively. X-ray diffraction showed that the ZnO (0002) peak shifted to lower angle due to the positioning of $p^{3-}$ ions with a smaller ionic radius in the $O^{2-}$ sites. This indicates that a p-type mechanism was due to the substitutional Po. The low-temperature photoluminescence of the p-type ZnO films showed p-type related neutral acceptor-bound exciton emission. The p-ZnO/n-Si heterojunction LEO showed typical rectification behavior, which confirmed the p-type characteristics of the ZnO films in the as-deposited status, despite the deep-level related electroluminescence emission.

• 한국자기학회지
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• 제18권2호
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• pp.67-70
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• 2008

$Tb_2Bi_1Ga_xFe_{5-x}O_{12}$(x=0, 1)의 조성을 가지는 분말 시료를 sol-gel 법과 진공봉합 열처리를 이용하여 합성하였다. x선 회절기, $M\ddot{o}ssbauer$ 분광기를 이용하여 시료의 결정구조 및 Ga 이온의 점유도에 관하여 연구하였다. XRD측정결과 $Tb_2Bi_1Ga_xFe_{5-x}O_{12}$ (x=0, 1)의 결정구조는 Ia3d의 공간그룹을 갖는 cubic 구조이며, $Tb_2Bi_1Fe_5O_{12}$와 $Tb_2Bi_1Ga_1Fe_4O_{12}$의 격자상수 $a_0$는 각각 $12.497\AA$, $12.465\AA$으로 분석되었다. Rietveld 분석법을 이용하여 각 이온들이 점유하는 각각의 부격자 위치를 연구하였다. $Tb_2Bi_1Ga_1Fe_4O_{12}$ 시료의 분석결과, Tb, Bi 이온은 24c 자리에, Fe 이온은 24d, 16a 자리를 점유하였으며, 비자성 이온인 Ga 이온은 모두 16a 자리를 점유하는 것으로 분석되었다. $Tb_2Bi_1Ga_xFe_{5-x}O_{12}$(x=0, 1)의 미시적인 자기구조를 분석하기 위해 시료들의 $M\ddot{o}ssbauer$스펙트럼을 측정하였다. 상온에서의 $M\ddot{o}ssbauer$스펙트럼 측정결과 철 이온들의 흡수 면적비는 $Tb_2Bi_1Fe_5O_{12}$의 경우 24d와 16a자리에서 각각 60.8%, 39.2%로, $Tb_2Bi_1Ga_1Fe_4O_{12}$의 경우 24d와 16a자리에서 각각 74.7%, 25.3%로 분석되었다. 철 이온들의 흡수 면적비 분석을 통해 비자성이온인 Ga은 모두 16a 자리를 점유하는 것을 알 수 있었다.