• The Korean Journal of Pesticide Science
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• v.17 no.1
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• pp.65-71
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• 2013

The modified QuEChERS method was evaluated for rapid determination of pesticide residues in spinach by gas chromatography-nitrogen phosphorous detector (NPD) and electron capture detector (ECD). Fifty GC-amenable pesticides which were most frequently detected in monitoring were selected in the current study. Matrix-matched calibration was performed. The detector response for all pesticides was linear with determination coefficients higher than 0.995. LODs for most compounds ranged between 0.001 and 0.1 ug/g, and about 90% of the compounds had LODs of less than 0.05 ug/g. LOQs ranged from 0.001 to 0.32 ug/g, which were well below the MRLs permitted for most of pesticides. In the majority of cases, the recoveries (80-120%) and relative standard deviations (RSDs) (less than 20%) were within acceptable levels except for dichlorvos, propamocarb, chlorothalonil, dichlofluanid, cyhalothrin and fenvalerate. Also, this method which is applied to routine samples showed good results when comparing with traditional multi-residue method.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.42 no.1
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• pp.65-73
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• 2016

Korea Food and Drug Administration (KFDA) has officially announced 2,4-dinitrophenylhydrazine (DNPH) derivatization - high performance liquid chromatography (HPLC) methods for analysis of formaldehyde. This study was conducted to develop a convenient derivatization method for cosmetics by improving complex pre-treatment procedures included in KFDA method. To simplify pre-treatment procedures of KFDA method, reaction conditions including pH, time and temperature were optimized. This pre-treatment method does not require complicate pre-treatment steps of KFDA method such as pH adjustment of test solution with acetate buffer (pH 5.0), solvent-solvent partitioning with dichloromethane and concentrating procedure with vacuum evaporator. Formaldehyde-dinitrophenylhydrazone (formaldehyde-DNP) product produced by derivatization reaction was separated and quantified with a reversed-phase HPLC, which was slightly modified with KFDA method. The linearity test showed good results with 0.9999 of correlation coefficient ($r^2$) in the range of 2 ~ 40 ppm of standard solutions. In this method, limit of detection (LOD) and limit of quantitation (LOQ) values for formaldehyde were 0.2 ppm and 0.5 ppm, respectively. In addition, recovery test demonstrated that the method was also accurate and reproducible. Therefore, the proposed method can be applicable to rapid analysis of formaldehyde in cosmetics.

• Journal of the Korean Chemical Society
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• v.50 no.1
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• pp.23-31
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• 2006

carbon modified methods were used for the preconcentration and determination of copper in some real samples using the flame atomic absorption spectrometry. The copper ions was adsorbed quantitatively on the activated carbon due to their complexation with 4- amino-2, 3-dimethyl-1-phenyl-3-pyrazoline (ADMPP) or 4-(4- methoxybenzylidenimin) thiophenole (MBITP). The adsorbed copper on solid phase was eluted quantitatively using small amount of nitric acid. The influence of important parameters including pH, amount of carrier, flow rate, amount of activated carbon and type and concentration of eluting agent for obtaining maximum recovery were investigated. The methods based on ADMPP and MBITP at optimum conditions is linear over concentration range of 0.05-1.5 g mL-1 and 0.05-1.2 g mL-1 of copper with correlation coefficient of 0.9997 and 0.9994 and both detection limit of 1.4 ng mL-1, respectively. The preconcentration leads to enrichment factor of 310 and break through volume of 1550 mL for both ligands. The method has a good tolerance limit of interfering ion and a selectivity that has been successfully applied for the determination of copper content in real sample such as tap, spring, river and waste water.

• Korean Journal of Construction Engineering and Management
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• v.18 no.2
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• pp.58-70
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• 2017

The planning for material lifting operations is one of the key processes in high-rise building construction. Several previous studies have used rough calculations by referring to existing practices or establishing a target value for lifting cycle time or operating rate. Therefore, the purpose of this study is to propose a material lifting process optimization method for reducing the lifting cycle time and increasing the operating rate. In this study, we improve the cyclic operation network (CYCLONE) modeling method that considers the duration and zone information of each work task. This method can be used to hand over work tasks to another crew group in the work process. According to this methodology, this study optimizes the material lifting process, performs a sensitivity analysis, and evaluates the field applicability of the proposed material lifting process optimization method. Therefore, the optimized process was then applied to a high-rise building construction site. The lifting work process time and operating rate for the simulated as - is lifting process data, optimized process data, and field application result data were compared for each lifting height. From this comparison, the effectiveness of the optimization methodology was confirmed.

• Analytical Science and Technology
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• v.18 no.4
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• pp.320-328
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• 2005

The most common five chlorophenols (4-chloro-3-methylphenol, 2,4,5-trichlorophenol, 2,4,6-trichlorophenol, 2,3,4,6-tetrachlorophenol, pentachlorophenol) were determined from the industrial wastewater by GC/MS. The samples were collected from the petrochemical company, textile company and leather making company. The developed analytical method was modified by USEPA Method 3510. The samples were extracted with dichloromethane under pH 2 and pH 5-6, and determined by the GC/MS with SIM mode. There were good linearities (above $R^2=0.9943$) on e ranges of the 0.1 ng/mL~10 ng/mL and 0.5 ng/mL~10 ng/mL, and the limit of detection were between 0.1 ng/mL and 0.5 ng/mL. The absolute recoveries were measured at the concentration of 1, 5, and 10 ng/mL, and the recovery was 71.6~98.9% except for PCP. The relative standard deviation (RSD) was 1.2~14.3% and it gave a good reproducibility for the assay. The bias, which shows the accuracy, was a good although it was a little high values (11.3~22.1%) at the low concentration (1 ng/mL).

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.6
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• pp.517-534
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• 2021

Hydrogen fuel is emerging as an new energy source to replace fossil fuels in that it can solve environmental pollution problems and reduce energy imbalance and cost. Since hydrogen is eco-friendly but highly explosive, there is a high concern about fire and explosion accidents of hydrogen fueled vehicles. In particular, in semi-enclosed spaces such as tunnels, the risk is predicted to increase. Therefore, this study was conducted on the applicability of the equivalent TNT model and the numerical analysis method to evaluate the hydrogen explosion pressure in the tunnel. In comparison and review of the explosion pressure of 6 equivalent TNT models and Weyandt's experimental results, the Henrych equation was found to be the closest with a deviation of 13.6%. As a result of examining the effect of hydrogen tank capacity (52, 72, 156 L) and tunnel cross-section (40.5, 54, 72, 95 m²) on the explosion pressure using numerical analysis, the explosion pressure wave in the tunnel initially it propagates in a hemispherical shape as in open space. Furthermore, when it passes the certain distance it is transformed a plane wave and propagates at a very gradual decay rate. The Henrych equation agrees well with the numerical analysis results in the section where the explosion pressure is rapidly decreasing, but it is significantly underestimated after the explosion pressure wave is transformed into a plane wave. In case of same hydrogen tank capacity, an explosion pressure decreases as the tunnel cross-sectional area increases, and in case of the same cross-sectional area, the explosion pressure increases by about 2.5 times if the hydrogen tank capacity increases from 52 L to 156 L. As a result of the evaluation of the limiting distance affecting the human body, when a 52 L hydrogen tank explodes, the limiting distance to death was estimated to be about 3 m, and the limiting distance to serious injury was estimated to be 28.5~35.8 m.

• Applied Chemistry for Engineering
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• v.7 no.5
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• pp.925-937
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• 1996

Three types of mordenites treated by steaming($SM_{6.5}$), HF solution for $SM_{6.5}(FM_a)$ and HF solutlon+steaming for $SM_{6.5}(FM_b)$ were prepared and used as cracking catalysts of vacuum gas oil. These samples were analysed by XRF and XPS for average and surface Si/Al atomic ratio, XRD for unit cell constants, nitrogen adsorption/desorption for porosity, pyridine-IR for acidic properties. In comparison with three type samples, $SM_{6.5}$ had a lot of acid amount and showed micropore volume mostly(>85% to total volume). Dealuminated $FM_a$, compared with $SM_{6.5}$, was decreased a little in acid amount and improved for porosity. Also, $FM_b$ was decreased further in acid amount and developed in mesopore dramatically. The catalytic activity and the yield of gasoline, kerosine+diesel and branched aromatic over the modified mordenites which have developed mesopore were improved. This is due to limited access of diffusion of large molecules within pore of the modified mordenites.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.19 no.4
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• pp.123-131
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• 2018

This study analyzed the collapse course of a mud stone cut slope during the construction of a express and suggested a countermeasure. Experiments were carried out on bedrock mudstone to investigate the engineering characteristics and the slope stability analysis at the time the design was reviewed. In addition, stability analysis, considering the strength softening characteristics of the slope due to the Swelling-Slaking phenomenon, was also performed. As a result of the Swelling-Slaking test, the slake durability was Low-Medium, and the swell potential was Very Low. A review of the stability analysis performed at the time of the design showed different results from the actual results because LEM analysis had been performed without considering the engineering characteristics of mudstone. As a result of additional stability analysis considering the strength softening characteristics, the slope collapse point and the maximum shear strain point of the stability analysis were the same and the standard safety factor was not satisfied. As a countermeasure, a slope mitigation method was found to be most appropriate. The mitigation slope was calculated by Finite element Analysis. A comparison with BIPS to determine the applicability of a mitigation slope revealed most of the unconsolidated mudstone.

• Korean Journal of Agricultural Science
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• v.23 no.1
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• pp.25-38
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• 1996

To investigate the stability problem of irrigation-drainage channel excavation slope on soft ground, analyzed the behavior of the soft ground with excavation slope by the limit equilibrium method and the finite element method, and compared with field tests. The results of this study were summarized as follows; 1. When rapid drawdown the water level, the crack was occurred by the effect of the excess pore water pressure, and the pore water pressure was decreased slowly. 2. As the width of excavation was larger, the crack width was larger. And, excavated depth was deeper, the progressive failure was appeared. 3. When the soft ground excavation was small-scale, the minimum safety factor was more effected by cohesion(1.0, 1.5, 2.0, 2.5, 3.0) than excavated slope inclination(1:l, 1:1.5, 1:2). 4. As excavation was progressed, the settlement occurred on the top-slope due to plastic domain, and heaving was occurred at the bottom of excavation. 5. The maximum shear stress was appeared greatly as the base part of slope went down. Because of the increase of the maximum shear stress, tension area occurred and local failure possibility was increased. 6. As the excavation depth was increased, the maximum shear strain was appeared greatly at the base of slope and distribution pattern was concentrated beneath the middle of slope.

• Journal of the Korea Convergence Society
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• v.8 no.9
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• pp.365-372
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• 2017

Squat exercise is one of the important free weight exercises that can safely and effectively expect the athletic performance by establishing the rationale. Therefore, it is necessary to study the side effects caused by incorrect exercise, scientific countermeasures and to develop a exercise estimation model. It is effective and accurate to use a variety of assistive devices to calibrate athletic posture. The issues of the structural analysis for designing a foot plate for squat exercise is to model the behavior by the dynamic behavior. It should be consider that the center of gravity of each segmented body is different when the maximum load is applied. It is applied to complete system design through simulation method with kinematic dynamic, ground reaction force and load analysis for the free weight exercise equipment, VR device, and safety foot plate. In this paper, the authors propose the design method for the vertical load distribution applied in the design of the foot plate used for the squat exercise mechanism, and based on these results, design make the more safe and reliable free weight exercise equipment system.