• Transactions of the Korean hydrogen and new energy society
• /
• v.29 no.2
• /
• pp.163-169
• /
• 2018

The present article discusses about the measurement techniques of acoustic impedance that becomes one of the important acoustic characteristics of various boundaries found inside of propulsion systems. Acoustic characteristics including acoustic impedance and reflection coefficient can be often assessed and estimated by use of the two-microphone method. Theoretical expressions of acoustic impedance and reflection coefficient measured in an impedance tube are presented for both cases with mean flow and without flow, and the practical application of the method through calibration is also provided. The acoustic impedance and the reflection coefficient are related with axial locations of microphones, thermodynamic characteristics of gas inside, and the transfer function between the pressure wave measurements at multiple locations.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.32 no.5
• /
• pp.374-381
• /
• 2008

The correlation coefficient method, which was proposed by our research group, is applied to digital particle holography to locate the focal plane of particles. It uses the fact that the correlation coefficient is maximum at the focal plane. The factors influencing this method are discussed with a numerical simulation of holograms. For real holograms, the Wiener filter was proposed to process both recorded holograms and reconstructed images. The application results using the dot array target showed that the Wiener filter is a very effective tool for processing holography-related images. The effects of the dot size and the object distance on the errors in the determination of the focal plane by the correlation coefficient method were investigated by using the calibration target.

• Journal of the Korean Society of Radiology
• /
• v.13 no.4
• /
• pp.517-522
• /
• 2019

The purpose of this study is to determine the effective energy of CT X-ray beams by using the CT slice images of a CT number calibration insert part in the AAPM CT performance phantom. The CT number calibration insert part in the AAPM CT performance phantom was scanned five times by using a CT canner for 80, 100 and 120 kVp X-ray beams. The average value of CT numbers of each pin were measured for each CT slice image. The correlation coefficients were obtained by linear fit between the average value of CT numbers measured and liner attenuation coefficient under different energy at each pin calculated from data of NIST. A photon energy corresponding to the maximum value of the obtained correlation coefficient was determined as an effective energy. As a result, the effective energy was 56, 62 and 66~67 keV, respectively, for 80, 100 and 120 kVp X-ray beams.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.61 no.5
• /
• pp.69-77
• /
• 2019

The objective of this study was to calibrate and validate the HSPF (Hydrological Simulation Program-Fortran) model for estimating the runoff of the Hapcheon dam watershed. Spatial data, such as watershed, stream, land use, and a digital elevation map, were used as input data for the HSPF model. Observed runoff data from 2000 to 2016 in study watershed were used for calibration and validation. Hydrologic parameters for runoff calibration were selected based on the user's manual and references, and trial and error method was used for parameter calibration. The $R^2$, RMSE (root-mean-square error), RMAE (relative mean absolute error), and NSE (Nash-Sutcliffe efficiency coefficient) were used to evaluate the model's performance. Calibration and validation results showed that annual mean runoff was within ${\pm}4%$ error. The model performance criteria for calibration and validation showed that $R^2$ was in the rang of 0.78 to 0.83, RMSE was 2.55 to 2.76 mm/day, RMAE was 0.46 to 0.48 mm/day, and NSE was 0.81 to 0.82 for daily runoff. The amount of inflow to Hapcheon Dam was calculated from the calibrated HSPF model and the result was compared with observed inflow, which was -0.9% error. As a result of analyzing the relation between inflow and storage capacity, it was found that as the inflow increases, the storage increases, and when the inflow decreases, the storage also decreases. As a result of correlation between inflow and storage, $R^2$ of the measured inflow and storage was 0.67, and the simulated inflow and storage was 0.61.

• Safety and Health at Work
• /
• v.10 no.4
• /
• pp.452-460
• /
• 2019

Background: Monitoring and control of PM_2.5 are being recognized as key to address health issues attributed to PM_2.5. Availability of low-cost PM_2.5 sensors made it possible to introduce a number of portable PM_2.5 monitors based on light scattering to the consumer market at an affordable price. Accuracy of light scatteringe-based PM_2.5 monitors significantly depends on the method of calibration. Static calibration curve is used as the most popular calibration method for low-cost PM_2.5 sensors particularly because of ease of application. Drawback in this approach is, however, the lack of accuracy. Methods: This study discussed the calibration of a low-cost PM_2.5-monitoring device (PMD) to improve the accuracy and reliability for practical use. The proposed method is based on construction of the PM_2.5 sensor network using Message Queuing Telemetry Transport (MQTT) protocol and web query of reference measurement data available at government-authorized PM monitoring station (GAMS) in the republic of Korea. Four machine learning (ML) algorithms such as support vector machine, k-nearest neighbors, random forest, and extreme gradient boosting were used as regression models to calibrate the PMD measurements of PM_2.5. Performance of each ML algorithm was evaluated using stratified K-fold cross-validation, and a linear regression model was used as a reference. Results: Based on the performance of ML algorithms used, regression of the output of the PMD to PM_2.5 concentrations data available from the GAMS through web query was effective. The extreme gradient boosting algorithm showed the best performance with a mean coefficient of determination (R²) of 0.78 and standard error of 5.0 ㎍/㎥, corresponding to 8% increase in R² and 12% decrease in root mean square error in comparison with the linear regression model. Minimum 100 hours of calibration period was found required to calibrate the PMD to its full capacity. Calibration method proposed poses a limitation on the location of the PMD being in the vicinity of the GAMS. As the number of the PMD participating in the sensor network increases, however, calibrated PMDs can be used as reference devices to nearby PMDs that require calibration, forming a calibration chain through MQTT protocol. Conclusions: Calibration of a low-cost PMD, which is based on construction of PM_2.5 sensor network using MQTT protocol and web query of reference measurement data available at a GAMS, significantly improves the accuracy and reliability of a PMD, thereby making practical use of the low-cost PMD possible.

• Journal of Korean Society of Occupational and Environmental Hygiene
• /
• v.9 no.1
• /
• pp.23-40
• /
• 1999

The analysis of thiodiglycolic acid in urine has been used as an index of biological exposure to vinyl chloride. Unfortunately thiodiglycolic acid has a strong hydrophilic character, because it has two carboxylic groups, so that it can only be extracted with organic solvent with a great difficulty. Underivatized thiodiglycolic acid tends to tail because of non-specific interaction with the inert support. Therefore, esterification is the obvious first choice for derivatization of thiodiglycolic acid, particularly for gas chromatography. In this study, the focus of interest is to compare two method of esterifications (methylation and silylation). Methylation is to make the methyl ester of thiodiglycolic acid by reaction with diazomethane. Silylation is to make the trimethylsilyl ester of thiodiglycolic acid by reaction with N-trimethylsily-ldiethylamine. The results and conclusions are as the following: 1. The detection limit (sensitivity) of methylated thiodiglycolic acid was $5.00{\mu}g/m{\ell}$ and silylated thiodiglycolic acid was $3.07{\mu}g/m{\ell}$ by gas chromatography with flame ionization detector. 2. The optimal liquid-liquid extraction of thiodiglycolic acid was as following: To each of the tubes, $15m{\ell}$ of urine, concentrated sulfuric acid (pH 1 - 2) and 5 gsodium sulfate were added. The samples was extracted three times with $5m{\ell}$ ethylacetate each time. 3. The methylated thiodiglycolic acid was more stable than silylated thiodiglycolic acid in extractional solvent which contained humidity. 4. The precision (pooled coefficient of variation for 4 days) of the analysis was 0.07324 in methylated thiodiglycolic acid with external standard calibration, and 0.07033 in methylated thiodiglycolic acid with internal standard calibration. 5. The precision (pooled coefficient of variation for 4 days) of the analysis was 0.10914 in silylated thiodiglycolic acid with external standard calibration, and 0.13602 in silylated thiodiglycolic acid with internal standard calibration. From the above results, the analysis of methylated thiodiglycolic acid was more sensitive (limit of detection) than silylated thiodiglycolic acid by gas chromatography. However, the methylated thiodiglycolic acid was stable in the humidity and was separated sharply on chromatogram. Also, analysis of methylated thiodiglycolic acid was more precise (pooled coefficient of variation for 4 days) than silylated thiodiglycolic acid. In conclusion, it is established that the analysis of methylated thiodiglycolic acid is appropriate for biological monitoring of exposure to vinyl chloride.

• KOREAN JOURNAL OF CROP SCIENCE
• /
• v.51 no.spc1
• /
• pp.304-309
• /
• 2006

Near infrared reflectance spectroscopy (NIRS) was used to develop a rapid and nondestructive method for the determination of fatty acid composition in sesame (Sesamum indicum L.) seed oil. A total of ninety-three samples of intact seeds were scanned in the reflectance mode of a scanning monochromator, and reference values for fatty acid composition were measured by gas-liquid chromatography. Calibration equations were developed using modified partial least square regression with internal cross validation (n=63). The equations obtained had low standard errors of cross-validation and moderate $R^2$ (coefficient of determination in calibration). Prediction of an external validation set (n=30) showed significant correlation between reference values and NIRS estimated values based on the SEP (standard error of prediction), $r^2$ (coefficient of determination in prediction) and the ratio of standard deviation (SD) of reference data to SEP. The models developed in this study had relatively higher values (more than 2.0) of SD/SEP(C) for oleic and linoleic acid, having good correlation between reference and NIRS estimate. The results indicated that NIRS, a nondestructive screening method could be used to rapidly determine fatty acid composition in sesame seeds in the breeding programs for high quality sesame oil.

• The KSFM Journal of Fluid Machinery
• /
• v.14 no.1
• /
• pp.42-47
• /
• 2011

Measurement uncertainty analysis of fuel flow using turbine flowmeter was performed for the case of altitude engine test. SAE ARP4990 was used as the fuel flow calculation procedure, as well as the mathematical model for the measurement uncertainty assessment. The assessment was performed using Sensitivity Coefficient Method. 11 parameters involved in the calculation of the flow rate were considered. For the given equipment setup, the measurement uncertainty of fuel flow was assessed in the range of 1.19~1.86 % for high flow rate case, and 1.47~3.31 % for low flow rate case. Fluctuation in frequency signal from the flowmeter had the largest influence on the fuel flow measurement uncertainty for most cases. Fuel temperature measurement had the largest for the case of low temperature and low flow rate. Calibration of K-factor and the interpolation of the calibration data also had large influence, especially for the case of very low temperature. Reference temperature, at which the reference viscosity of the sample fuel was measured, had relatively small contribution, but it became larger when the operating fuel temperature was far from reference temperature. Measurement of reference density had small contribution on the flow rate uncertainty. Fuel pressure and atmospheric pressure measurement had virtually no contribution on the flow rate uncertainty.

• Journal of The Korean Society of Agricultural Engineers
• /
• v.52 no.5
• /
• pp.77-86
• /
• 2010

Hydrologic Simulation Program-Fortran (HSPF) coupled with PEST which is optimization program was calibrated and validated at Bochung watershed by using monitoring data of water quantities and nutrient loading. Although the calibrated data were limited, model parameters of each land use type were optimized and coefficient of determinations were ranged from 0.94 to 0.99 for runoff, from 0.89 to 1.00 for TN loading, and from 0.92 to 1.00 for TP loading. The optimized hydrological parameters indicated that the forested land could retain rainfall within soil layer with high soil layer depth and infiltration rate compared with other land use type. Hydrological characteristics of paddy rice field are low infiltration rate and coefficient of roughness. The calibrated parameters related to nutrient loading indicated generation of nutrient pollution from agricultural area including upland and paddy rice field higher than other land use type resulting from fertilizer application. Overall PEST program is useful tool to calibrate HSPF automatically without consuming time and efforts.

• Journal of Environmental Science International
• /
• v.21 no.12
• /
• pp.1449-1454
• /
• 2012

The ion selective microelectrodes (ISME) have been applied to observe the continuous profiles of NO3-N and NH4-N in bulk solutions or biofilms. In order to evaluate the performance and applicability of ion concentration measuring system, the characteristics, such as slope of calibration curve, detection limit and potentiometric selectivity coefficient were investigated. The slopes of calibration curve showed high degree of correspondence for each target ion concentrations. And the detection limits of nitrate and ammonia ion selective microelectrode were 10-4.7 M and 10-4.4 M, respectively. These ion selective microelectrodes were proved that their own performance could be maintained for 16 days after making. NO3-N and NH4-N selective microelectrodes were also adapted to detect the continuous ion profiles of cilia media packed MLE (Modified Ludzack-Ettinger) process. And the monitored nitrate and ammonia ion profiles with the ion selective microelectrode were stable and well corresponded to the results with conventional ion chromatograph. However, the electric potential was unstable until 8 hr because of the unknown noise. The tip shape and performance of the ion selective microelectrode was stably kept over 2 days continuous monitoring.