• Journal of Aquaculture
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• v.15 no.2
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• pp.87-93
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• 2002

To improve the efficiency of biological filters used for treating recycled wastewater of aquaculture, the conventional and advanced DynaSand Filters were tested. Applying the fluid mechanics and physical chemistry theories to wastewater treatment plant, the advanced filter focuses on detection of wastewater characteristics and automatic operation of DynaSand Filter to improve backwashing, oxygen transport, turbidity removal and continuous head loss. The Filter removes COD, ammonia, and suspended solids (SS), the major pollutants in aquaculture wastewater. The total volume of the DynaSand Filter is 70 L, while the working volume is 35 L per cycle. The removal efficiency of the advanced DynaSand Filter is 71 % for SS (as against 55 % for the conventional filter), 84 % for ammonia, 85 % for T-P, and 88 % for SRP.

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.22 no.2
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• pp.134-139
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• 2012

Objectives: This study was conducted to study the analytical variability of A & B counting rules in counting using a phase contrast microscope airborne fibers collected on filters in man-made mineral or vitreous fibers (MMMFs) industries. Methods: Fibers in filters were counted using A & B rules of NIOSH Method 7400. Intra-counter and inter-counter variations by fiber type and density were obtained. The types of MMMFs analyzed were glass wool fiber, rock wool fiber, slag wool fiber, and refractory ceramic fibers. The densities of fibers classified were <20 $fibers/mm^2,$ 20 - <50 $fibers/mm^2$, 50 - <100 $fibers/mm^2,$ and ${\geq}100$ $fibers/mm^2,$ respectively. Results: Intra-counter relative standard deviations by rule A were 0.084, 0.102, 0.071 for glass wool fibers, rock wool fibers and refractory ceramic fibers, and those by rule B were 0.139, 0.120 and 0.142, respectively. Inter-counter relative standard deviations by rule A were 0.281, 0.296, 0.180 for glass wool fibers, rock wool fibers and refractory ceramic fibers, and those by rule B were 0.396, 0.337 and 0.238, respectively. Conclusions: Intra-counter variation was not different significantly among fiber types (p>0.05), but B rule variation for ceramic fibers approximately 2 times greater than corresponding A rule estimates, and intra-counter and inter-counter variations were higher in the low fiber density.

• Analytical Science and Technology
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• v.14 no.5
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• pp.451-457
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• 2001

Because liquids with high molecular weight such as mineral oil have low vapor pressure at room temperature, it is generally thought to be difficult to lose them to evaporation. However, when they are dispersed into air in small droplets during application in machining processes, their surface area becomes considerably higher. To determine the potential for metalworking fluids (MWF) filter losses, MWF mist was generated and collected on polyvinyl chloride (PVC) filters in test chamber. After collected MWF was exposed to clean air during designated period (range 10~240 minutes) and the filters were desiccated, losses were evaluated. As duration of clean air passing through PVC filter increased, loss of MWF gradually increased. MWF lost after 10 minutes ranged form 12.4 % to 21.8 % of the original loading mass, on average 53.3 % of the total loss. These results indicate that significant mass of MWF collected on PVC filters can be lost at the beginning of air sampling. Loss of MWF collected on PVC filter also occurred during desiccation without active airflow. In multiple regression to identify which factors influence the loss of MWF collected on PVC filter, both duration of air passing through PVC filter and MWF age (fresh vs. used) were significant predictor (p=0.0001). Therefore, workers' exposure to MWF measured method 0500, may underestimate true concentration. Further study is needed to develop a new method to quantify the workers' exposure to airborne MWF mist accurately.

• Environmental Analysis Health and Toxicology
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• v.21 no.1 s.52
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• pp.45-56
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• 2006

This study was conducted to investigate seasonal distributions of fine particles ($PM_{2.5}$) and associated polycyclic aromatic hydrocarbons (PAHs) at three cities. $PM_{2.5}$ samples were collected on glass fiber filters at urban (Chuncheon), metropolitan (Seoul), and industrial complex sites (Ulsan) from September, 2002 to February, 2004 using the Andersen FH 95 Particulate Sampler. About five 24-hour samples were collected from each site per season. The filters were analyzed for mass and six selected PAHs concentrations. $PM_{2.5}$ concentrations were the highest either in winter or spring, which could be attributed to the increase of fossil fuel combustion in winter or the transport of yellow sand to the Korean peninsula from China in spring, respectively. Regional $PM_{2.5}$ concentrations were higher in the order of Seoul>Chuncheon>Ulsan without statistical difference among cities. The filters were extracted using dichloromethane in an ultrasonicator and analyzed for six PAHs (anthracene, fluoranthene, pyrene, benzo[a]anthracene, chrysene, and benzo[a]pyrene) with HPLC. Total PAHs concentrations were statistically different among seasons in each site, and the highest concentrations were observed in winter at each sampling site. For total samples collected, the median total PAHs concentrations in Chuncheon ($4.6ng/m^3$) and Seoul ($4.4ng/m^3$) were approximately two times higher than that in Ulsan ($2.1ng/m^3$). Chrysene was a component found in the highest proportion among total PAHs at each site. Carcinogenic risks calculated based on the BaP toxic equivalency factors (TEFs) over the whole sampling period were higher in the order of Chuncheon>Seoul>Ulsan. This study suggests that the atmosphere of Chuncheon is contaminated with particulate matter and PAHs at the levels equivalent to those of Seoul and that an appropriate measure needs to be taken to mitigate human health risks from inhalation exposure to airborne fine particles.

• BMB Reports
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• v.35 no.5
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• pp.482-487
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• 2002

Early activation of human peripheral blood polymorphonuclear neutrophils is characterized by their morphological changes from spherical to polarized shapes. The endotoxins from enteric pathogens (S. dysenteriae type 1, V. cholerae Inaba 569B, S. typhimurium, and K. pneumoniae) were assessed by their ability to induce morphological polarization of the neutrophils as measures of early activation. Phagocytic activity, adhesion, chemokinetic locomotion, and nitroblue tetrazolium (NBT) dye-reduction ability measured the later activation of the cells. Neutrophils showed distinct morphological polarization in suspension over a wide range of concentrations of these endotoxins when were compared with those that were induced by the standard chemotactic factor, N-formyl-L-methionyl-L-leucyl-L-phenylalanine (FMLP). It was discovered that all of the endotoxins induced locomotor responses in neutrophils in suspension that were dose- and time-dependent. The optimum concentration for the endotoxins of S. dysenteriae, V. cholerae, and K. pneumoniae was 1 mg/ml in which 71, 69, and 66% of the neutrophils were polarized. However, the S. typhimurium dose was 2 mg/ml in which 50% of the cells responded. Neutrophils that were stimulated with endotoxins also showed increased random locomotion (p<0.005) through cellulose nitrate filters, but an enhanced adhesion of the cells to glass surfaces (p<0.03). These are important functions of these cells to reach and phagocytose damaged cells, as well as invading microorganisms. Interestingly, the endotoxins had a highly-significant inhibitory effect upon the proportions of neutrophils phagocytosing opsonized yeast (p<0.01) with a small number of yeast that were engulfed by the cells (p<0.02). Further, endotoxin-treated cells showed an enhanced ability to reduce NBT dye (p<0.03). Therefore, we concluded that endotoxins of enteric pathogens are neutrophil chemotactic factors.

• International Journal of Highway Engineering
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• v.14 no.1
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• pp.55-61
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• 2012

The ability of clay mineral to remove non-point sources such as SS, COD, T-N. T-P in the urban runoff has been tested to develop the porous filter material. The diameter of 3mm ball type filters were made of clay minerals for the tests. The experiments were carried out to measure the concentration of non-point sources of contaminants with flow rate of effluents. The test results show that clay filter has good response to remove SS, COD comparing to those of activated carbon filter. Also the performance of the clay filter to remove T-N and T-P is almost the same when using the activated carbon filter.

• Physical Therapy Rehabilitation Science
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• v.10 no.4
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• pp.438-443
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• 2021

Objective: The purpose of this study was to determine the effect of the difference in mask filters on the respiration rate of healthy people. Design: A randomized cross-over design. Methods: A total of 15 subjects were selected for this study (n=15). After filling out the Physical Activity Readiness Questionnaire, the selected participants abstained from caffeinated beverages and meals 30 minutes before and sat in a chair 10 minutes before stabilizing their breathing. Afterwards, the lung function test was performed 3 times for each mask, and the maximum value was used. The provided masks were Mask Free, Dental Mask, KF80, and KF94. Exhalation was measured for 6 seconds for each mask, and breathing was stabilized by repeating inhalation and exhalation until the next time. Results: In this study, the difference in respiratory function according to the mask type was statistically significant except for FEV1 and FVC (p<0.05). As a result of post-hoc analysis, FVC, FEV1, PEF, and FEF values were significantly lower than those of the control group not wearing a mask (p<0.05). When wearing KF94, FVC, FEV1, PEF25-25%, and FEF were significantly lower than when wearing a dental mask (p<0.05). When wearing a KF80 mask, it was significantly lower in FVC and FEV1 than when wearing a dental mask (p<0.05). In FEV1/FVC, the difference by mask type was not statistically significant (p<0.05), but it was lower than the spirometry standard of COPD patients (FEV1/FVC<0.7). Conclusions: As Now that wearing a mask is essential, it has been confirmed that the mask affects the respiratory rate.Therefore, in the case of healthy adults, it is recommended to rest after wearing a mask if attention deficit or headache occurs. People with low breathing capacity are recommended to have low-intensity activities and frequent rest periods after wearing a mask.

• Journal of Korean Society for Atmospheric Environment
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• v.2 no.3
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• pp.57-63
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• 1986

Atmospheric particulate matter (A.P.M.) was collected on quartz fiber filters from March 1985 to May 1986 according to particle size using Andersen high-volume air sampler, and 6 heavy metals (Fe, Mn, Cu, Ni, Zn, Pb) in these particulates were analyzed by atomic absorption spectrophotometry. The arithmetic mean concentration of A.P.M. was 195.57$\mug/m^3$. The arithmetic mean concentrations of 6 metals (Fe, Mn, Cu, Ni, Zn and Pb) were 3385.04, 1451.67, 897.94, 159.68, 127.14 and 59.49 $ng/m^3$ respectively. The order of heavy metals contributing to A.P.M. was as follows: Fe > Zn > Pb > Cu > Mn > Ni. These heavy metals were devided into 3 groups according to their particle size distribution. The contents of heavy metals belonging to the 1st group (Fe, Mn) were increased with the particle size. On the contrary, the content of Pb belonging to the 2nd group (Pb) was increased with the decrease in the particle size. The heavy metal contents in the 3rd group (Ni, Cu, Zn) were lowest in the particle size range of 2.0-3.3 $\mum$ compared with particles larger or smaller tha this range. The seasonal variation of heavy metal concentration were as follows: Fe and Mn contents were highest in spring, but Ni and Pb contents were highest in winter. Statistical analysis showed that there was a significant correlation between A.P.M. and Fe in coarse particles, meanwhile between A.P.M. and Pb in the case of fine particles.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.61 no.3
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• pp.111-115
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• 2012

Generally, brushless DC motor(BLDCM) driving system uses hall sensors or encoders as the mechanical position or speed sensor. It is necessary to achieve the informations of rotor position for driving trapezoidal type brushless DC motor without any position sensor. In this paper, the commutation signals are obtained without the motor neutral voltage, multistage analog filters, A/D converters, or the complex digital phase shift circuits which are indispensable in the conventional sensorless control algorithms. In the proposed method, in stead of detecting the zero crossing point of the nonexcited motor back electromagnetic force for the average motor terminal to neutral voltage, the commutation signal are extracted directly from the specific average line to line voltage with low-pass filter, adder and comparators circuit. In contrast to conventional methods, the neutral voltage is not need; therefore, the commutation signals are insensitive to the common mode noise. Moreover, the complex phase shift circuit can be eliminated. The effectiveness of the proposed method is verified through simulation results.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.333-334
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• 2004

The central aspect of the research into virtual acoustic imaging for multiple listeners involves a detailed study of the relative orientation of both sources and listeners. It is vital in any multiple listener system to first establish the conditioning of the potential geometrical arrangements of transducers and listeners. In this paper, this made clear the important link between the conditioning of the electro-acoustic transfer function matrix between transducers and ears and the design of inverse filters for crosstalk cancellation. This work has been undertaken by using simple free field models of the electro-acoustic transfer functions. Therefore, optimal transducer arrangements have been identified and these have been proved by time domain solutions.