• 한국산업보건학회지
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• 제24권1호
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• pp.65-73
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• 2014

Objectives: The purposes of this study are to investigate workers' exposures to respirable particles generated in taconite mines and to compare two metric methods for mass concentrations using direct-reading instruments. Methods: Air monitorings were conducted at six mines where subjects have been exposed primarily to particulate matters in crushing, concentrating, and pelletizing processes. Air samples were collected during 4 hours of the entire work shift for similarly exposure groups(SEGs) of nine jobs(N=37). Following instruments were employed to evaluate the workplace: a nanoparticle aerosol monitor(particle size range; 10-1000 nm, unit: ${\mu}m^2/cc$, Model 9000, TSI Inc.); DustTrak air monitors($PM_{10}$, $PM_{2.5}$, unit: $mg/m^3$, Model 8520, TSI Inc.); a condensation particle counter(size range; 20-1000 nm, unit: #/cc, P-Trak 8525, TSI Inc.); and an optical particle counter(particle number by size range $0.3-25{\mu}m$, unit: #/cc, Aerotrak 9306, TSI Inc.). Results: The highest airborne concentration among SEGs was for furnace operator followed by pelletizing maintenance workers in number of particle and surface area, but not in mass concentrations. The geometric means of $PM_{2.5}$ by the DustTrak and the Ptrak/Aerotrak were $0.04{\mu}m$(GSD 2.52) and $0.07{\mu}m$(GSD 2.60), respectively. Also, the geometric means of RPM by the DustTrak and the Ptrak/Aerotrak were $0.16{\mu}m$(GSD 2.24) and $0.32{\mu}m$(GSD 3.24), respectively. The Pearson correlation coefficient for DustTrak $PM_{2.5}$ and Ptrak/Aerotrak $PM_{2.5}$ was 0.56, and that of DustTrak RPM and Ptrak/Aerotrak RPM was 0.65, indicating a moderate positive association between the two sampling methods. Surface area and number concentration were highly correlated($R^2$ = 0.80), while $PM_{2.5}$ and RPM were also statistically correlated each other($R^2$ = 0.79). Conclusions: The results suggest that it is possible to measure airborne particulates by mass concentrations or particle number concentrations using real-time instruments instead of using the DustTrak Aerosol monitor that monitor mass concentrations only.

• 한국산업보건학회지
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• 제33권2호
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• pp.93-102
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• 2023

Objectives: With the evolution of direct reading sensors, it is possible to monitor several substances through telecommunication. However, there are some limitations on the use of direct reading technologies in the Occupational Safety and Health Act in South Korea, which only applies to detector tubes, noise, heat, and carbon monoxides. The number of chemicals and their amount of use have been continuously increasing in South Korea. The Ministry of Employment and Labor (MoEL) has concerns about worker's health because exposure is only covered for about 1.2% of all distributed chemicals. Using a direct reading monitor with photoionization detectors (PID-DRMs), gases and vapors chemicals can be measured. Based on the data, business owners are able to create corrective strategies, provide better working routines, and select correct respiratory equipment. PID-DRMs are less expensive and easier to handle for an owner voluntarily controlling chemicals emitted in the workplace. However, there are several limitations on using these PID-DRMs to the degree that the MoEL has not been able to select a legal monitor. The aim of this study was to review previous studies related to PID-DRMs and identify the characterization and limitation on PID-DRMs. Methods: To search for related studies on PID-DRMs, key words were used including direct reading monitors/instruments and/or photoionization detectors. Through that, four domestic and 15 international studies were reviewed. Results: Studies on PID-DRMs were conducted by chamber (enclosed, dynamic, walk-in) and in the field (experimental environment, actual environment). The concentration of PID-DRMs and charcoal tubes were compared for a single substance or mixture, or within the PID-DRMs. There was a high correlation between the two concentrations, but it did not meet the accuracy criteria (95% confidence interval, within 25%) of the NIOSH technical report (2012). In addition, differences in measured values occurred according to environmental factors (temperature, humidity) and high concentration, and concentration values tended to be underestimated due to contamination of the sensor. As a way to improve the accuracy of PID concentration, it was proposed to use correction factors, charcoal tube-based correction factors, or to calibrate the PID-DRMs in the same environment as the workplace. Conclusions: PID-DRMs can likely be used by business owners for the purpose of voluntarily managing the workplace environment, and it is expected that it will be possible to use them as legal equipment if a PID sensor can be upgraded and the limitations of the sensor (temperature, humidity, high concentration evaluation, sensor pollution) can be overcome in the near future.

• 영어어문교육
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• 제5호
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• pp.1-25
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• 1999

The objective of the present study was to model the relationships between language learning strategy use and language proficiency among the Asian (Korean, Japanese, and Taiwanese) students studying English in the United States. The instruments were a language learning strategy Questionnaire and the Institutional Testing Program Test of English as a Foreign Language (ITP TOEFL). Structural equation modeling was utilized to model the relationships between language learning strategies and language proficiency. The present study found only weak relationships between language learning strategies and language proficiency. Only 13% and 15% of variance of the listening and grammar/reading factor were explained by the language learning strategies. The metacognitive strategies appeared not to have direct relationships to the language skill factors, as was found in other studies (Purpura, 1996, 1997). The effects of the social and affective strategies were very small. They in combination could account about 1% and 4% of the variance of the listening and grammar/reading factors.

• Restorative Dentistry and Endodontics
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• 제45권2호
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• pp.25.1-25.12
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• 2020

Objectives: This systematic review evaluated the influence of autoclave sterilization procedures on the cyclic fatigue resistance of heat-treated nickel-titanium (NiTi) instruments. Materials and Methods: A systematic search without restrictions was conducted in the following electronic databases: PubMed, Scopus, Web of Science, ScienceDirect, Cochrane, and Open Grey. The hand search was also performed in the main endodontic journals. The eligible studies were submitted to the methodological assessment and data extraction. Results: From 203 abstracts, a total of 10 articles matched the eligible criteria. After reading the full articles, 2 were excluded because of the absence of the heat-treated instruments in the experimental design and 3 due to the lack of a control group using heat-treated instruments without autoclave sterilization. From the 5 included studies, 1 presented a low risk of bias, 3 presented moderate and 1 high risk. It was observed heterogeneous findings in the included studies, with autoclave sterilization cycles increasing, decreasing or not affecting the cyclic fatigue life of heat-treated NiTi instruments. However, the retrieved studies evaluating the cyclic fatigue resistance of endodontic instruments presented different protocols and assessing outcomes, this variability makes the findings less comparable within and also between groups and preclude the establishment of an unbiased scientific evidence base. Conclusions: Considering the little scientific evidence and considerable risk of bias, it is still possible to conclude that autoclave sterilization procedures appear to influence the cyclic fatigue resistance of heat-treated NiTi instruments.

• 한국산업보건학회지
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• 제34권1호
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• pp.67-76
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• 2024

Objectives: Direct reading instruments (DRIs) are widely used by industrial hygienists and other experts for preliminary survey and identifying source locations in many industrial fields. Photoionization detectors (PIDs), which are a form of hand-held portable DRIs, have been used for a variety of airborne vaporized chemicals, especially evaporated hydrocarbon solvents. The benefits of PIDs are high sensitivity between each chemical, competitive price, and portability. With the goal of increasing the accuracy of logged PID concentrations, previous studies have performed tests for the assessment of single chemical compounds, not mixtures. The purpose of this preliminary study was to measure mixtures with a PID and charcoal tube at the same time and compare the accuracy between them. Methods: A chamber test was implemented with different mixtures of hydrocarbon chemicals (acetone, isopropyl alcohol, toluene, m-xylene) and levels in the range of 14 to 864 ppm. Three PIDs and charcoal tubes were connected to the chamber and measured the chemical mixtures simultaneously. A comparison of accuracy and the PID group of concentrations with manufacture correction factor (M_CF) and field correction factor (F_CF) applied was performed. Results: The accuracy of the PID concentrations data-logged from the PID did not meet the accuracy criteria except for the mixture level B and C logged from PID No. 2, which was 18% of all tests for meeting accuracy criteria. The mean and standard deviation (SD) of concentration (ppm) of the charcoal tube followed by each mixtures' level were 10.37±0.26, 155.33±5.28, 300.80±11.65, and 774.93±22.65, respectively. When applying F_CF into the PID concentrations, the accuracy increased by nearly 82%. However, in the case of M_CF, none met the accuracy criterion. Between the PID there were differences of logged concentrations. Conclusions: In this preliminary study, the concentration of a logged PID with F_CF applied was a better way to increase accuracy compared to applying M_CF. We suggest that additional research is necessary to consider environmental factors such as temperature and humidity.

• 한국산업보건학회지
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• 제29권2호
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• pp.159-166
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• 2019

Objectives: The purpose of this study was to evaluate the personal exposure to $PM_{10}$ by body parts for the development of dust monitoring wearable device for swine farmers. Methods: Tasks were classified by using motion pictures taken by action cameras attached to swine farmers. Concentrations of $PM_{10}$ were measured by attaching direct-reading instruments at the head, neck and waist of worker. Differences of $PM_{10}$ exposure between body parts were analyzed with linear regression. Results: We identified three tasks(vaccination, moving pigs, and manure treatment). $PM_{10}$ concentration during vaccination was the highest among the tasks, and the body part showing the highest concentration of $PM_{10}$ was the waist regardless of task. In all tasks, the closer distance between the body parts, the higher were the R-squared values(vaccination 0.4221, moving pigs 0.6990, and manure treatment 0.2164). Conclusions: We presumed that $PM_{10}$ concentrations were affected by the parts of the body in which they were measured. In order to develop swine farmer's wearable device for monitoring dust concentration in air, the determination of the positions of monitoring sensor to ensure accurate measurement is essential. Considering the results of this study, wearable sensor should be positioned at the waist.

• 한국산업보건학회지
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• 제32권4호
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• pp.381-392
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• 2022

Objectives: Objective of this study is to review briefly exposure characteristics, monitoring instruments and threshold limit values for extremely low frequency-magnetic field (ELF-MF) methods. This study was undertaken through brief literature review. We performed a literature search in PubMed to identify ELF-MF studies conducted in workplaces. Initial search keywords such as 'extremely low frequency-magnetic field (ELF-MF)' and 'electromagnetic fields (EMF)' combined or singly. We limited our review to occupational rather than general nonworkplace environmental exposures. Methods: The contents we reviewed: key industry and occupations generating ELF-MF, several direct-reading instruments monitoring ELF-MF and threshold limit values (TLV) preventing health effects may be caused by the exposure to ELF-MF. Results: The industries related to the generation and supply of electricity, electrolytic installations, welding, and induction heating and more were regarded as high ELF-MF exposure industries. All jobs handling or employed performed in power cable lines, electrical wiring, and electrical equipment are found to be exposed to ELF-MF. Threshold or ceiling limit, 1,000 µT, is established to prevent acute effects of exposure to low-frequency EMFs on the nervous system: the direct stimulation of nerve and muscle tissues and the induction of retinal phosphenes. The International Agency for Research on Cancer (IARC) has classified ELF-MF as possibly carcinogenic to humans chiefly based on epidemiological studies on childhood leukemia. However, a causal relationship between magnetic fields and several types of cancer including childhood leukemia has not been established nor has any other long-term effects. Risk management using precautionary measures, has been initiated by the US and EU to prevent chronic health effects related to ELF-MF exposure in workplaces. Conclusion: This study recommends the implementation of various measures such as theestablishment of occupational exposure limit values for ELF-MF and precautionary principle to prevent potential chronic occupational health effects may be caused by ELF-MF in Korea.

• 한국산업보건학회지
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• 제20권4호
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• pp.248-255
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• 2010

Airborne nanoparticle concentrations in three metrics (particle surface area concentration, particle number concentration, and particle mass concentrations) were measured by task in a laboratory making carbon nanotubes (CNTs) films using three direct reading instruments. Because of the conducted other researcher's experiment before the tasks, airborne nanoparticle surface area and number concentrations are the highest at the first time conducted weighing and mixing by sonication task, respectively. Because of the mist generated during mixing by sonication, the highest airborne nanoparticle surface area and PM1 concentrations were measured in the task among the total. Nanoparticle surface area concentrations at the researchers' breathing zones had high correlation (r=0.93, p<0.01) with those measured at an area in the laboratory. This result indicates that nanoparticles generated during the experiment contaminated the whole room air. When the experiment performed all the fume hoods weren't operated and making CNTs films task were conducted in the out of the fume hoods. In conclusion, researchers performing making CNTs film experiments were exposed to airborne nanoparticles generated during the experiment without adequate controls. We recommend that adequate controls should be implemented so that workers' exposures to airborne nanoparticle are limited to minimum levels.

• 한국과학교육학회지
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• 제17권2호
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• pp.127-137
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• 1997

The purpose of this study was to assess elementary student's ability of measuring length, area, and volume and reading metric scales. The findings of this study were as follows. All students were successful in measuring without scale, regardless of grades. But they were less successful in measuring the task using standard and nonstandard scales. Especially, in measuring area, lower grade students were not able to perform the task using nonstandard instruments, but higher grade students were able to perform the task. Measuring area using grade paper was least successful for sixth graders. In measuring volume, students under fifth grade read the upper scale when using graduated cylinder. In measuring by direct comparison, students were more successful in measuring length than in measuring area and volume using given material. The use of given nonstandard material was successful for 4th, 5th, and 6th grade students. In measuring using metric scale, lower grade students did not pay attention to the zero of the scale, but just read the end point. Higher grade students considered both zero and end points.

• Journal of Preventive Medicine and Public Health
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• 제20권2호
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• pp.255-260
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• 1987

The digital dust indicator (Sibata P-5), one of the direct·reading instruments was evaluated for the respirable dust in the underground coal mine environments. As a reference, respirable dust was determined using three cyclones and/or impactors. All the tests were performed on aerosol in twenty underground coal mines. The coefficients of mass-relative concentration were $0.067{\pm}0.054$ (Mean$\pm$Standard deviation) (range: 0.006-0.172). The relationship between relative concentration and temperature was not significant statistically. Also, the relationship of relative concentration and relative humidity was not significant. Mass concentration and relative concentration were $5.31{\pm}5.22mg/m^3$ and $162{\pm}163$ CPM ($Mean{\pm}Standard$ deviation) respectively. The range of mass concentration was $1.22-22.69mg/m^3$; relative concentration 16-628 CPM. The relationship of mass concentration and relative concentration was not significant in these ranges.