• Journal of Environmental Health Sciences
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• v.50 no.1
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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.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.20 no.6
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• pp.134-141
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• 2019

This paper is a study on design improvement of rotorcraft horizontal stabilizer. The rotorcraft horizontal stabilizer stabilizes the behavior of the pitch, yaw, etc. from the aircraft. Because of this role, horizontal stabilizers are a major component (Flight Safety Part) that affects flight safety on rotorcraft. However, when the rotorcraft was operated in domestic, cracks were found in the inner structure of the horizontal stabilizer and design improvement was needed. In this paper, we identified the two causes of the horizontal stabilizer crack defects through fracture analysis and structural analysis. The first is the tightening torque when the bolt is tightened, and the second is the lead-lag behavior of aircraft. In order to improve these two causes, bolt fastening method, flange structure and thickness were changed and composite ring was applied. In order to verify the design improvement, the structural analysis was performed and the structural strength was improved. Also Fatigue analysis of the internal structure (Rib 1) was performed and it was confirmed that the requirements were satisfied.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.7 no.2
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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.

• Journal of the Korean Geographical Society
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• v.51 no.1
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• pp.23-40
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• 2016

In this study, long-term changes in means and extreme events of precipitation during summer rainy period called Changma (late June~early September) are examined based on rainfall data observed by Chukwooki during Joseon Dynasty (1777~1907) and by modern rain-gauge onward (1908~2015) in Seoul, Korea. Also, characterizations of the relevant changes in synoptic climate fields in East Asia are made by the examination of the NCEP-NCAR reanalysis I data. Analyses of 239-year time series of precipitation data demonstrate that the total precipitation as well as their inter-annual variability during the entire Changma period (late June~early September) has increased in the late 20th century and onward. Notably, since the early 1990s the means and extreme events during the summer Changma period (late June~mid-July) and Changma break period (late July~early August) has significantly increased, resulting in less clear demarcations of sub-Changma periods. In this regard, comparisons of synoptic climate fields before and after the early 1990s reveal that in recent decades the subtropical high pressure has expanded in the warmer Pacific as the advection of high-latitude air masses toward East Asia was enhanced due to more active northerly wind vector around the high pressure departure core over Mongolia. Consequently, it is suggested that the enhancement of rising motions due to more active confluence of the two different air masses along the northwestern borders of the Pacific might lead to the increases of the means and extreme events of Changma precipitation in Seoul in recent decades.

• Journal of Environmental Health Sciences
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• v.36 no.2
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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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• v.3 no.3
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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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• v.53 no.1
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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.

• Korean Journal of Agricultural and Forest Meteorology
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• v.24 no.4
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• pp.275-284
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• 2022

Changes in air temperature, CO₂ concentration and precipitation due to climate change are expected to have a significant impact on soybean productivity. This study was conducted to evaluate the climate change impact on growth and development of determinate soybean cultivar in the southern parts of Korea. The high temperature during vegetative period, which does not accompany the increase of CO₂ concentration, increased the canopy photosynthetic rate in soybean, but after flowering, the high temperature above the optimal ranges interrupts the photosynthetic metabolism. In yield and yield components, high temperature reduced both the pod and seed number and single seed weight, resulting in a reduction of total seed yield. On the other hand, the increase in CO₂ concentration dramatically increased the canopy photosynthetic rate over the whole growth period. In addition, high CO₂ concentration increased the number of pods and seeds, which had a positive effect on total seed yield. Under concurrent elevation of air temperature and CO₂ concentration, canopy photosynthesis increased significantly, but enhanced canopy photosynthesis did not lead to an increase in soybean seed yield. The increase in biomass and branch by enhanced canopy photosynthesis seems to be attributed to an increase in the total number of pods and seeds per plant, which compensates for the negative effects of high temperature on pod development. However, Single seed weight tended to decrease rapidly by high temperature, regardless of CO₂ concentration level. Elevated CO₂ concentration did not compensate for the poor distribution of assimilations from source to sink caused by high temperature. These results show that the damage of future soybean yield and quality is closely related to high temperature stress during seed filling period.

• Asian Journal of Atmospheric Environment
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• v.9 no.2
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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.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.1
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• pp.165-172
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• 2002

Generally, the steel rigid frame has been analyzed using finite element analysis tools. While many efforts have been poured into the understanding and accurate prediction for the nonlinear behavior of the columns and beam-columns connections, the base of the columns are modeled as simply hinged or fixed. However, the base of the steel columns practically is neither fixed not hinged. It behaves as semi-rigid. In this paper, the supports of the columns we modeled as semi-rigid and the importance of such approach in moment-resisting columns is evaluated. Two typical buildings designed by the US specification are modeled and analyzed by the finite element based on stiffness method and flexibility method. The column bases of three-story buildings are modeled as rotational springs with a varying degree of stiffness and strength that simulates the semi-rigidity of the base. Depending on the degree of stiffness and strength, the semi-rigidity varies from the hinged to the fixed. Buildings with semi-rigid column bases behaves similarly to the building with fixed bases. It has been numerically observed through the pushover and nonlinear time history analyses that the decrease of the stiffness of the column base induces the rotational demand on the int air beams. an increase of rotation demands on the first store connections and lead to a soft-story mechanists Due often to the construction and environmental effects, undesired reduction of column base stiffness may cause an increase of rotation demands on the first store connections and lead to a soft-story mechanism.