• 한국환경보건학회지
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• 제50권1호
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• pp.6-15
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• 2024

Background: People's activities have been restricted due to the COVID-19 pandemic. These changes in activity patterns may lead to a decrease in fine particulate matter (PM_2.5) concentrations. Additionally, the level of population exposure to PM_2.5 may be changed. Objectives: This study aimed to analyze the impact of population movement and meteorological factors on the distribution of PM_2.5 concentrations before and after the outbreak of COVID-19. Methods: The study area was Guro-gu in Seoul. The research period was selected as January to March 2020, a period of significant population movement changes caused by COVID-19. The evaluation of the dynamic population was conducted by calculating the absolute difference in population numbers between consecutive hours and comparing them to determine the daily average. Ambient PM_2.5 concentrations were estimated for each grid using ordinary kriging in Python. For the population exposure assessment, the population-weighted average concentration was calculated by determining the indoor to outdoor population for each grid and applying the indoor to outdoor ratio to the ambient PM_2.5 concentration. To assess the factors influencing changes in the ambient PM_2.5 concentration, a statistical analysis was conducted, incorporating population mobility and meteorological factors. Results: Through statistical analysis, the correlation between ambient PM_2.5 concentration and population movement was positive on both weekends and weekdays (r=0.71, r=0.266). The results confirmed that most of the relationships were positive, suggesting that a decrease in human activity can lead to a decrease in PM_2.5 concentrations. In addition, when population-weighted concentration averages were calculated and the exposure level of the population group was compared before and after the COVID-19 outbreak, the proportion of people exceeding the air quality standard decreased by approximately 15.5%. Conclusions: Human activities can impact ambient concentrations of PM_2.5, potentially altering the levels of PM_2.5 exposure in the population.

• 한국산학기술학회논문지
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• 제20권6호
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• pp.134-141
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• 2019

본 논문은 회전익 항공기의 수평 안정판의 설계 개선에 관한 연구이다. 회전익 항공기의 수평 안정판은 항공기의 피치, 요 등의 거동을 안정화시키는 역할을 수행한다. 이러한 역할로 인해 수평 안정판은 회전익 항공기의 비행 안전에 영향을 미치는 주요 구성 요소(비행안전품목)로 관리되고 있다. 그러나 국내 회전익 항공기 운용 중, 수평 안정판의 내부 구조에 균열이 발견되어 설계 개선의 필요성이 제기되었다. 본 논문에서는 파면 분석과 구조 해석을 통해 수평 안정판 내부 구조 균열의 근본 원인을 2가지로 분석하였다. 첫 번째는 볼트 체결 시 부가되는 체결 토크이며, 두 번째는 항공기 기동에 따른 Lead-lag 거동이다. 이 2가지 원인을 개선하기 위하여 본 연구가 수행되었으며 그 결과 볼트 체결 방법, 볼트 체결 플랜지 구조 및 두께를 변경하고 복합재 링을 추가로 적용하였다. 설계 개선의 검증을 위해 구조 해석이 수행되었으며 구조강도가 향상된 것을 확인할 수 있다. 또한 내부 구조물 (Rib 1)의 피로해석을 수행하여 요구 사항이 충족되었음을 확인하였다.

• 한국산업보건학회지
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• 제7권2호
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• pp.181-195
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• 1997

The purpose of this study was to investigate factors affecting the composition and concentrations of fumes generated from various types of welding processes. The results are as follows. 1. Iron(Fe), zinc(Zn) and manganese(Mn) were predominant in Welding fumes. The Fe content in total fumes was 25.5% in coated electrode and 28.2% in $CO_2$ are welding, and the Zn content was 4.5% and 9.1%, respectively, and the Mn was 3.6% and 7.8%, respectively. 2. It was found that the important factors determining composition and concentration of fumes were type of industries, type of welding processes, type and composition of electrodes, composition of base metals, confinement of workplaces or condition of ventilation, work intensity, coated metals such as lead and Zn in paint. 3. The Mn content in airborne fumes was highly correlated with that of electrode(r=0.77, p<0.01) and was about 4 times higher than that in electrodes or base metals. The results lindicate that Mn is well evaporated into air during welding. The higher vapor pressure of Mn may explain this phenomenon. 4. the airborne total fume concentrations were significantly different among types of industries(p<0.001). The airborne total fume concentration was higher in order of sleel-structure manufacturing($GM=15.1mg/m^3$), shipbuilding($GM=13.2mg/m^3$), automobile-component manufacturing ($GM=7.8mg/m^3$) and automobile assembling industry($GM=3.0mg/m^3$) 5. The airbone total fume concentration was 6 times higher in $CO_2$ welding than in coated electrode welding, and approximately 3 times higher in confined area than in open area, in steel-structure manufacturing industry. 6. The concentration of welding fume outside welding helmet was about 2 times higher than that inside it. It is recommened that air sampling be done inside helmet to evaulate worker's exposure accurately, for it has an outstanding effect on reducing worker exposure to fumes and other contaminants.

• 대한지리학회지
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• 제51권1호
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• pp.23-40
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• 2016

본 연구에서는 조선시대 측우기(1777~1907년)와 현대적 기상장비(1908~2015년)로 측정한 강우량 자료를 종합 분석하여 서울의 장마철 강수량과 극한강수현상에 나타난 장기간 변화 양상을 밝히고자 하였다. 또한 이와 관련된 동아시아 영역의 종관 기후장에 나타난 변화 특징을 밝히고자 하였다. 약 239년 동안의 서울의 강수자료 시계열을 분석한 결과, 20세기 후반으로 올수록 장마철(6월 하순~9월 초순) 강수량이 증가하고, 경년변동성도 더 커짐을 알 수 있다. 특히 1990년대 초반부터는 장마철 중에서도 여름장마기(6월 하순~7월 중순)와 장마 휴지기(7월 하순~8월 초순)에 극한강수현상 중심의 강수량이 뚜렷하게 증가하면서 장마기의 구분이 모호해지고 있음을 알 수 있다. 이와 관련하여 변화가 뚜렷한 1990년 전후의 상층 종관기후장을 비교해 보면, 최근에는 북서태평양 주변의 해수면 온도가 상승하고 북태평양 아열대 고기압 강도가 강화되어 해양성 기단이 한반도 방향으로 더 확장하고, 유라시아 대륙 내부 몽골 지역을 중심으로 강한 고기압 편차핵이 형성되면서 고위도로부터 기류가 더 활발하게 유입되고 있음을 알 수 있다. 즉, 서로 다른 성질의 기류들이 강해지면서 이들 기류들이 만나는 북서태평양 연안 지역에 상승 기류 흐름이 활발해지면서 최근에는 서울의 장마철 강수평균 및 극한강수현상이 증가하였다고 할 수 있다.

• 한국환경보건학회지
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• 제36권2호
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• pp.82-94
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• 2010

This study was undertaken in an attempt to provide scientific grounds in explaining the causes of environmental and respiratory diseases resulting from air pollutants in Gyeongju and its neighboring areas. In relation to heavy metals, lead (Pb) was $0.0135{\sim}0.1744\;{\mu}g/m^3$ and high in order of Pohang, Ulsan, and Gyeongju while nickel (Ni) was $0.0023{\sim}0.0115\;{\mu}g/m^3$. The concentrations of heavy metals in the investigated areas did not exceed the environmental standards or Guideline Value of Korea or other countries. However, it is considered necessary to apply intensive control to some heavy metals including cadmium (Cd) that show a relatively high level of hazard. Based on the responses to the survey, measured personal interest in environmental pollution and the basic knowledge of the causes of the respiratory diseases was higher in those with a family history of allergic reactions to metals and bronchial asthma. The incidence of allergic disease was higher in those who are currently in poor health state. In addition, the general knowledge of environmental pollutants was higher in those with higher educational level and those with a higher interest in environmental pollution. Personal interest in environmental pollution was higher in those with higher basic knowledge of environmental pollutants. Therefore, it is necessary to increase the awareness through better education and campaigns on environmental pollution.

• Advances in aircraft and spacecraft science
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• 제3권3호
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• pp.243-257
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• 2016

The increase of air traffic volume has brought an increasing amount of issues related to carbon and NOx emissions and noise pollution. Aircraft manufacturers are concentrating their efforts to develop technologies to increase aircraft efficiency and consequently to reduce pollutant discharge and noise emission. Ultra High By-Pass Ratio engine concepts provide reduction of fuel consumption and noise emission thanks to a decrease of the jet velocity exhausting from the engine nozzles. In order to keep same thrust, mass flow and therefore section of fan/nacelle diameter should be increased to compensate velocity reduction. Such feature will lead to close-coupled architectures for engine installation under the wing. A strong jet-wing interaction resulting in a change of turbulent mixing in the aeroacoustic field as well as noise enhancement due to reflection phenomena are therefore expected. On the other hand, pressure fluctuations on the wing as well as on the fuselage represent the forcing loads, which stress panels causing vibrations. Some of these vibrations are re-emitted in the aeroacoustic field as vibration noise, some of them are transmitted in the cockpit as interior noise. In the present work, the interaction between a jet and wing or fuselage is reproduced by a flat surface tangential to an incompressible jet at different radial distances from the nozzle axis. The change in the aerodynamic field due to the presence of the rigid plate was studied by hot wire anemometric measurements, which provided a characterization of mean and fluctuating velocity fields in the jet plume. Pressure fluctuations acting on the flat plate were studied by cavity-mounted microphones which provided point-wise measurements in stream-wise and spanwise directions. Statistical description of velocity and wall pressure fields are determined in terms of Fourier-domain quantities. Scaling laws for pressure auto-spectra and coherence functions are also presented.

• Imaging Science in Dentistry
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• 제53권1호
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• pp.53-60
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• 2023

Purpose: This study evaluated maxillary sinus volume changes in military jet aircraft pilot candidates before and after the training program, in comparison with a control group, considering the effects of pressurization, altitude, and total flight hours, through multislice computed tomography. Materials and Methods: Fifteen fighter pilots were evaluated before initiating the training program and after the final approval. The control group consisted of 41 young adults who had not flown during their military career. The volumes of each maxillary sinus were measured individually before and at the end of the training program. Results: When comparing the initial and final volumes in the pilots, a statistically significant increase was observed both in the left and right maxillary sinuses. When evaluating the average total volume of the maxillary sinuses(i.e., the average volume of the right and left maxillary sinuses together), a significant increase in the volume of the maxillary sinuses was observed in the pilot group when compared to the control group. Conclusion: The maxillary sinus volumes in aircraft pilot candidates increased after the 8-month training program. This may be explained by changes in the gravitational force, the expansion of gas, and positive pressure from oxygen masks. This unprecedented investigation among pilots might lead to other investigations considering paranasal sinus alterations in this singular population.

• 한국농림기상학회지
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• 제24권4호
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• pp.275-284
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• 2022

기후변화에 따른 대기 온도 및 이산화탄소 농도의 상승은 농업 생산성에 큰 영향을 미칠 것으로 예상된다. RCP 8.5 시나리오에 따른 21세기말(2071~2100) 기후조건에서는 전 생육기간에 걸쳐 군락광합성이 크게 증가하였으나 이러한 효과가 종실 수량 증가로는 이어지지 않았다. 특히 높은 광합성능으로 인한 바이오매스의 증가는 분지 수 확보에 긍정적으로 작용하여 협수와 립수는 큰 변동이 없었던 반면 립중은 단독 고온 조건과 유사하게 현저히 감소하였다. 이는 등숙기간 중 고온에 의한 동화산물의 축적 및 전류 불량이 주요 요인으로 판단된다. 이러한 결과는 미래 기후 환경에서 종실 수량 감소가 협수와 립수 보다는 립중의 감소에 의한 것임을 의미한다. 이와 같은 결과들은 우리나라 남부지역에서 기후변화에 따른 콩 생육의 불확실성을 해소하고 피해 대책을 마련하기 위한 기초자료로써 유용하게 활용될 것으로 기대된다.

• Asian Journal of Atmospheric Environment
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• 제9권2호
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• pp.173-186
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• 2015

In Bangladesh, increases in the tropospheric ozone ($O_3$) concentration and in soil salinization may lead to crop damage. To clarify the effects of $O_3$ and/or soil salinity on Bangladeshi wheat cultivars, BAW1059 (salt-tolerant) and Shatabdi (salt-sensitive) were exposed to 70-day treatments with $O_3$ (charcoal-filtered air (CF), $1.0{\times}O_3$, and $1.5{\times}O_3$) and different levels of soil salinity (0, 4, and $8dS\;m^{-1}$). In both cultivars, the whole-plant dry mass and grain yield were significantly reduced by exposure to $O_3$. Increased soil salinity caused significant reductions in whole-plant growth and yield in Shatabdi, but the reductions were negligible in BAW1059. No significant interactions between $O_3$ and salinity were detected for growth, yield, and leaf gas exchange parameters in both cultivars. We concluded that the effects of $O_3$ are not ameliorated by soil salinity in two Bangladeshi wheat cultivars, regardless of their salinity tolerance.

• 한국전산구조공학회논문집
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• 제15권1호
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• pp.165-172
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• 2002

일반적으로 모멘트 지지 강구조물은 유한요소법에 의해 이상화되고 해석되어 왔으며 기둥과 기둥의 연결부, 기둥과 보의 접합부의 정확한 비선형 해석 결과를 위해 많은 노력을 해온 반면에 기둥의 지지부에 대한 해석은 고정단 또는 힌지로 간단하게 이루어져 왔다 그러나 실제로 기둥의 지지부는 고정단도 힌지도 아닌 그 중간인 반강성으로 거동한다. 본 논문에서는 이러한 기둥 지지부를 반강성모델을 이용해서 해석하고 그 결과를 고찰하여 기둥 지지부의 강성 및 강도의 변화가 미치는 영향을 평가하였다. 미국 시방서에 의해 설계된 전형적인 두개의 3층 모멘트지지 강구조물을 이미 개발된 강성도법 및 유연도법에 기초한 7iber 유한 요소를 사용하여 해석하였다. 기등의 지지부는 고정단과 힌지사이에 있는 반강성 지지부를 모델하기 위해 다양한 강성도를 갖는 회전 스프링을 사용하였다. 실제의 기둥 지지부와 가깝게 모델된 반강성 지지부를 갖는 구조물의 해석 결과는 고정지지부를 갖는 구조물과 어느 정도 비슷한 결과를 보여주었다. 또한 pushover 해석과 비선형 시간 이력 해석을 통해 기둥 지지부의 강성도가 감소함에 따라 1층 보의 소요 처짐각(rotational demand)이 증가하는 현상이 관찰되었다 시공상의 문제 및 노화로 인한 기동 지지부의 강성도 감소는1층의 접합부에 대한 소요 터짐각의 증가를 유발하고 그것은 곧 soft-story mechanism을 유발하게 된다.