• Journal of Korean Society on Water Environment
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• v.35 no.2
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• pp.131-144
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• 2019

Climate Change affects the hydrological cycle in agricultural watersheds through rising air temperature and changing rainfall patterns. Agricultural watersheds in Korea are characterized by extensive paddy fields and intensive water use, a resource that is under stress from the changing climate. This study analyzed the effects of climate change on river flows for Geum Cheon and Eun-San Choen watershed using STREAM, a semi-distributed watershed model. In order to evaluate the performance and improve the reliability of the model, calibration and validation of the model was done for one flow observation point and three reservoir water storage ratio points. Climate change scenarios were based on RCP data provided by the Korea Meteorological Administration (KMA) and bias corrections were done using the Quantile Mapping method to minimize the uncertainties in the results produced by the climate model to the local scale. Because of water mass-balance, evapotranspiration tended to increase steadily with an increase in air temperature, while the increase in RCP 8.5 scenario resulted in higher RCP 4.5 scenario. The increase in evapotranspiration led to a decrease in the river flow, particularly the decrease in the surface runoff. In the paddy agricultural watershed, irrigation water demand is expected to increase despite an increase in rainfall owing to the high evapotranspiration rates occasioned by climate change.

• Korean Journal of Agricultural and Forest Meteorology
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• v.11 no.1
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• pp.27-38
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• 2009

The multi-level profile system is designed to measure the vertical profile of $H_2O$ and $CO_2$ concentrations in the surface layer to estimate the storage effects within the plant canopy. It is suitable for long-term experiments and can be used also in advection studies for estimating the spatial variability and vertical gradients in concentration. It enables the user to calculate vertical fluxes of water vapor, $CO_2$ and other trace gases using the surface layer similarity theory and to infer their sources or sinks. The profile system described in this report includes the following components: sampling system, calibration and flow control system, closed path infrared gas analyzer(IRGA), vacuum pump and a datalogger. The sampling system draws air from 8 inlets into the IRGA in a sequence, so that for 80 seconds air from all levels is measured. The calibration system, controlled by the datalogger, compensates for any deviations in the calibration of the IRGA by using gas sources with known concentrations. The datalogger switches the corresponding valves, measures the linearized voltages from the IRGA, calculates the concentrations for each monitoring level, performs statistical analysis and stores the final data. All critical components are mounted in an environmental enclosure and can operate with little maintenance over long periods of time. This report, as a practical manual, is designed to provide helpful information for those who are interested in using profile system to measure evapotranspiration and net ecosystem exchanges in complex terrain.

• Applied Science and Convergence Technology
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• v.23 no.2
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• pp.97-102
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• 2014

A vacuum chamber for a commercial atomic force microscope (AFM) is designed and fabricated. Only minimal modifications were made to an existing microscope in an effort to work in a vacuum environment, while most of the available AFM functionalities were kept intact. The optical alignment needed for proper AFM operations including a SLD (superluminescent diode) and a photodiode can be made externally without breaking the vacuum. A vacuum level of $5{\times}10^{-3}$ torr was achieved with a mechanical pump. An enhancement of the quality factor was observed along with a shift in the resonance frequency of a non-contact-mode cantilever in a vacuum. Topographical data of a calibration sample were also obtained in air and in a low vacuum using the non-contact mode and the results were compared.

• Journal of Radiation Protection and Research
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• v.12 no.1
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• pp.1-11
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• 1987

Central axis percentage depth-doses, P(%), were measured at the points from the 2.5cm depth of reference point to 20 cm depth with 2.5 cm interval. Distance from the X-ray target to the water phantom($30{\times}30{\times}30cm^3$) surface was 1 m, and at this point three different beam sizes of $5cm{\phi},\;10cm{\phi},\;and\;15cm{\phi}$ were used. While the X-ray tube voltage varied from 150 to 250 kV, the tube current remained constant at 5 mA. Absorbed dose rate in water, $\dot{D}_w$, was determined using the air kerma calibration factor, $N_k$, which was derived from the exposure calibration factor, $N_x$, of the NE 2571 ion chamber. The reference exposure rate, $\dot{X}_c$, was measured using the Exradin A-2 ion chamber calibrated at ETL, Japan. The half value layers of the X-rays determined to meet ETL calibration qualities. The absorbed dose rates determined at the calibration point were compared to the values obtained from Burlin's general cavity theory, and the percentage depth-dose values determined from $N_k$ showed a good agreement with the values of the published depth dose data(BJR Suppl. 17).

• Journal of Korean Society of Occupational and Environmental Hygiene
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• v.22 no.3
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• pp.200-208
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• 2012

Objectives: This study investigated the performance of three separate units of a portable photoionization detector (PID, ppb-RAE 3000) for measuring volatile organic compounds (VOCs) in a laboratory. Methods: A laboratory evaluation of the accuracy, precision, and inter-instrumental variance of three separate units of a portable PID (ppb-RAE 3000) was performed. The evaluation was based on the preparation of a test air sample of known toluene or ethylacetate concentration in a Tedlar$^{(R)}$ bag. The test air sample was monitored and data were logged consecutively by the three PIDs. A certified gas of 50 ppm toluene was also monitored during the test to ensure the reliability of the generated test air sample. Four different concentrations ranging from 0.1 to 2 TLV were used and a series of five measurements for each concentration level was performed. The accuracy was evaluated using National Institute for Occupational Safety and Health (NIOSH) criteria. Results: The results from the oldest ppb-RAE3000 unit among the three test units generally fell outside the NIOSH recommended accuracy criteria of ${\pm}25%$, whereas the other two units produced results which were acceptable at, or greater than, 25 ppm of toluene, or 0.5 TLV. These units also met the NIOSH criteria for some ethylacetate measurements but the results were not consistent. Conclusions: Considering the inconsistent performance of these ppb-RAE 3000 units, this device may not be appropriate for use as an alternative to the standard measurement methods. However, it can serve good survey instruments to identify exposure sources or concentration profiles. For all applications, the ppb-RAE 3000 should be used with frequent calibration checks, additional validation using a reference material, and careful maintenance.

• Journal of Biosystems Engineering
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• v.33 no.6
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• pp.430-437
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• 2008

Optical diffuse reflectance sensing in visible and near-infrared wavelength ranges is one approach to rapidly quantify soil properties for site-specific management. The objectives of this study were to investigate effects of preprocessing of reflectance data and determine the accuracy of the reflectance approach for estimating physical and chemical properties of selected Missouri and Illinois, USA surface soils encompassing a wide range of soil types and textures. Diffuse reflectance spectra of air-dried, sieved samples were obtained in the laboratory. Calibrations relating spectra to soil properties determined by standard methods were developed using partial least squares (PLS) regression. The best data preprocessing, consisting of absorbance transformation and mean centering, reduced estimation errors by up to 20% compared to raw reflectance data. Good estimates ($R^2=0.83$ to 0.92) were obtained using spectral data for soil texture fractions, organic matter, and CEC. Estimates of pH, P, and K were not good ($R^2$ < 0.7), and other approaches to estimating these soil chemical properties should be investigated. Overall, the ability of diffuse reflectance spectroscopy to accurately estimate multiple soil properties across a wide range of soils makes it a good candidate technology for providing at least a portion of the data needed in site-specific management of agriculture.

• Journal of the Korean Society of Radiology
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• v.9 no.7
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• pp.425-431
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• 2015

Measurement accuracy was evaluated for the respiratory air flow transducer developed for applications under emergent situations. Pressure-Flow calibration equation was obtained by acquisition of air flow signals from the transducer in response to 6 flow waveforms, similar to those of artificial ventilation, generated by the standard flow generator system. Tidal volume and maximal flow rate were calculated on the flow signal then compared with the error-free data obtained by the linear displacement transducer of the flow generator system. Mean relative error of the tidal volume was within 3% and that of the maximal flow rate, approximately 5%, demonstrating accurate enough measurements. Therefore, the transducer could be applied to emergent situations to monitor the respiratory air flow signal as well as diagnostic parameters in real time.

• Water for future
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• v.25 no.3
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• pp.65-77
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• 1992

The purpose of this study is to analyse existing hysteresis models and to propose a new type of model. The existing hysteresis models are classified by three types: interpolation model, scaling model and domain model, of which the domain model is based on the theoretical approach. Models which need one branch of hysteresis loop for calibration are developed based on the independent domain concept, however, they are not successful to accurately simulate the real data and Rubicon Sandy Loam and Dune Sand. There is a possibility that a new model is based on the dependent domain model considering the pore blockage effect against air entry for homogeneous porous media(modelIII-1, Mualem, 1984). Concludingly, a new type of hysteresis model is proposed by simplifying ModelIII-1 using a proper assumption.

• Ocean Systems Engineering
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• v.7 no.2
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• pp.157-177
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• 2017

This research is based on the concept of safety airbag to design a self-rescue system for the autonomous underwater vehicle (AUV) using micro inertial sensing module. To reduce the possibility of losing the underwater vehicle and the difficulty of searching and rescuing, when the AUV self-rescue system (ASRS) detects that the AUV is crashing or encountering a serious collision, it can pump carbon dioxide into the airbag immediately to make the vehicle surface. ASRS consists of 10-DOF sensing module, sensing attitude algorithm and air-pumping mechanism. The attitude sensing modules are a nine-axis micro-inertial sensor and a barometer. The sensing attitude algorithm is designed to estimate failure attitude of AUV properly using sensor calibration and extended Kalman filter (SCEKF), feature extraction and backpropagation network (BPN) classify. SCEKF is proposed to be used subsequently to calibrate and fuse the data from the micro-inertial sensors. Feature extraction and BPN training algorithms for classification are used to determine the activity malfunction of AUV. When the accident of AUV occurred, the ASRS will immediately be initiated; the airbag is soon filled, and the AUV will surface due to the buoyancy. In the future, ASRS will be developed successfully to solve the problems such as the high losing rate and the high difficulty of the rescuing mission of AUV.

• Journal of the Korean Solar Energy Society
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• v.33 no.3
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• pp.17-26
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• 2013

The aim of this study is to analyze the performance of a parabolic trough solar collector (PTC) for water heating and to validate the model performance. The simulated model was compared, calibrated and verified with the experimental results. RMSE (Root mean square error) was used to calibrate the convective heat transfer coefficient between the absorber pipe and the ambient air which was the main factor affecting the heat transfer associated with the PTC. The calibrated model was better fitted with the experimental model. The maximum, minimum and mean deviation between the measured and predicted water temperatures differed only $0.81^{\circ}C$, $0.09^{\circ}C$ and $0.31^{\circ}C$ respectively in the calibrated model. RMSE values were decreased from 0.5389 to 0.4910, 0.0134 to 0.0125 and R-squared was increased from 0.9955 to 0.9956 after calibration. The temperature of water was increased from $33.7^{\circ}C$ to $48^{\circ}C$ in 12hour test. The thermal efficiency of the collector was calculated to be 55%. The calibrated model showed good agreement with the experimental data for model validation.