• Journal of the Korean Magnetics Society
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• v.5 no.5
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• pp.478-482
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• 1995

The iron-based Metglas 2605S3A amorphous alloy ribbons are annealed at $435^{\circ}C$ for various periods from 5 to 210 min, and the effect of annealing is investigated on the dc magnetic properties of the ribbon. Typical square-type hysteresis loops are observed for the ribbons annealed fo 5 min, indicative of the nearly complete removal of residual stresses which are produced during melt-quenching. As the annealing time increases, the coercivity increases and the shape of hysteresis loops transforms to round type and finally to sheared one at the longest annealing time of 210 min. These results may be explained by the formation of clusters with chemical shortorder and very fine crystallites (at the annealing time of 210 min), and the diffusion-induced stresses during the formation of the clusters. For the samples annealed for 5 min, very good dc properties of the squareness ratio, coercivity and maximum permeability are observed, but, rather unexpectedly, the initial permeability is found to be very low. These results are considered to be due to a simple domain structure consisting of very small number of $^{\circ}$ domains.

• Journal of the Korean Society of Clothing and Textiles
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• v.45 no.5
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• pp.840-851
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• 2021

In this study, we used a chemiluminescence reaction to investigate the removal effect of pet soil, such as dog blood, urine and feces. The soiled fabrics were washed with a standard laundry course of 30℃ and a washing time of 30 min and a pet care laundry course of 40-60℃ and a washing time of 100 min. The detergency was evaluated by the surface reflectance and chemiluminescence reaction (bloodstain detection by luminol test and urine-stain and feces-stain detection by UV blacklight test) before and after washing. The surface reflectance results did not show any difference in detergency for both courses, whereas the chemiluminescence reaction did. The detergency of the pet care course compared to the standard course was 101% according to the surface reflectance and 120% according to the chemiluminescence reaction. Therefore, residual stains not detected by surface reflectance can be evaluated through chemiluminescence reaction, and it was confirmed that pet stains can be managed more hygienically by washing for a long time at a high temperature.

• Korean Journal of Remote Sensing
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• v.40 no.2
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• pp.141-150
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• 2024

Ground subsidence in urban areas is mainly caused by anthropogenic factors such as excessive groundwater extraction and underground infrastructure development in the subsurface composed of soft materials. Global Navigation Satellite System data with high temporal resolution have been widely used to measure surface displacements accurately. However, these point-based terrestrial measurements with the low spatial resolution are somewhat limited in observing two-dimensional continuous surface displacements over large areas. The synthetic aperture radar interferometry (InSAR) technique can construct relatively high spatial resolution surface displacement information with accuracy ranging from millimeters to centimeters. Although constellation operations of SAR satellites have improved the revisit cycle, the temporal resolution of space-based observations is still low compared to in-situ observations. In this study, we evaluate the extraction of a time-series of surface displacement in Incheon Metropolitan City, South Korea, using the small baseline subset technique implemented using the commercial software, Gamma. For this purpose, 24 COSMO-SkyMed X-band SAR observations were collected from July 12, 2011, to August 27, 2012. The time-series surface displacement results were improved by reducing random phase noise, correcting residual phase due to satellite orbit errors, and mitigating nonlinear atmospheric phase artifacts. The perpendicular baseline of the collected COSMO-SkyMed SAR images was set to approximately 2-300 m. The surface displacement related to the ground subsidence was detected approximately 1 cm annually around a few Incheon Subway Line 2 route stations. The sufficient coherence indicates that the satellite orbit has been precisely managed for the interferometric processing.

• Journal of Positioning, Navigation, and Timing
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• v.13 no.1
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• pp.103-110
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• 2024

In this paper, a test bed for real-time network Real-Time Kinematic (RTK) research was constructed using reference stations of the NGII. A group of candidate station networks was derived, including three stations in Seoul. The group consisted of four stations with a distance of less than 100 km between them. Among several candidates, a network composed of stations with short distances between them and demonstrating good data quality for all reference stations was selected as the test bed. After collecting real-time data in Radio Technical Committee for Maritime services (RTCM) format from the selected stations and conducting a noise analysis on measurements, mm-level carrier phase measurement noise was confirmed. Afterwards, the user set the reference station inside the test bed and analyzed the network RTK positioning performance of the MAC method using the GPS L1 frequency as post-processing. From the result of the analysis it was confirmed that the residual error for all users was within 10 cm after applying the correction. Additionally, after determining integer ambiguities through Least-squares AMBiguity Decorrelation Adjustment (LAMBDA), it was confirmed that the fix rate was 100%, and all ambiguities were resolved as true values.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.17 no.4
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• pp.183-189
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• 2024

In order to effectively predict time series data, this study proposed a hybrid prediction model that decomposes the data into trend, seasonality, and residual components using Seasonal-Trend Decomposition on Loess, and then applies ARIMA to the trend component, Fourier Series Regression to the seasonality component, and XGBoost to the remaining components. In addition, performance comparison experiments including ARIMA, XGBoost, LSTM, EMD-ARIMA, and CEEMDAN-LSTM models were conducted to evaluate the prediction performance of each model. The experimental results show that the proposed hybrid model outperforms the existing single models with the best performance indicator values in MAPE(3.8%), MAAPE(3.5%), and RMSE(0.35) metrics.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.9
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• pp.34-40
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• 2005

In present study, a two dimensional unsteady Navier-Stokes solver has been developed using the Diagonalized ADI (DADI) method and implicit dual time stepping method. The jacobian matrices in steady state Navier-Stokes equations are introduced from inviscid flux terms. The implicit treatment of artificial dissipation terms results in a block penta-diagonal matrix system and it becomes a scalar penta-diagonal matrix by diagonalization. In steady state equations about fictitious time, a new residual including a real time derivative term is introduced. From a converged solution about fictitious time, a real time unsteady solution can be obtained, which is called 'implicit dual time stepping method'. For code validation, an oscillating flat plate, a regular Karman vortices past a circular cylinder and shock buffeting around a bicircular airfoil problems are numerically solved. And they are compared with a theoretical solution, experiments and other researcher's computations.

• Steel and Composite Structures
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• v.46 no.3
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• pp.385-401
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• 2023

Steel is becoming increasingly popular due to its high strength, excellent ductility, great assembly performance, and recyclability. In reality, steel structures serving for a long time in atmospheric, industrial, and marine environments inevitably suffer from corrosion, which significantly decreases the durability and the service life with the exposure time. For the mechanical properties of corroded steel, experimental studies are mainly conducted. The existing numerical analyses only evaluate the mechanical properties based on corroded morphology at the isolated time-in-point, ignoring that this morphology varies continuously with corrosion time. To solve this problem, the relationships between pit depth expectation, standard deviation, and corrosion time are initially constructed based on a large amount of wet-dry cyclic accelerated test data. Successively, based on that, an in-situ pitting evolution method for evaluating the residual tensile strength of corroded steel is proposed. To verify the method, 20 repeated simulations of mass loss rates and mechanical properties are adopted against the test results. Then, numerical analyses are conducted on 135 models of corrosion pits with different aspect ratios and uneven corrosion degree on two corroded surfaces. Results show that the power function with exponents of 1.483 and 1.091 can well describe the increase in pit depth expectation and standard deviation with corrosion time, respectively. The effect of the commonly used pit aspect ratios of 0.10-0.25 on yield strength and ultimate strength is negligible. Besides, pit number ratio α equating to 0.6 is the critical value for the strength degradation. When α is less than 0.6, the pit number increases with α, accelerating the degradation of strength. Otherwise, the strength degradation is weakened. In addition, a power function model is adopted to characterize the degradation of yield strength and ultimate strength with corrosion time, which is revised by initial steel plate thickness.

• Journal of Korean Society of Environmental Engineers
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• v.28 no.1
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• pp.42-47
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• 2006

The biological nutrient treatment is formed with repetition and rearrangement of anaerobic, anoxic and oxic tank. In this case, VFAs is generated in the anaerobic tank and the anoxic tank. The VFAs is an important factor for removal of nitrogen and phosphate and SVI. So, in this study I investigated to find a relationship among the generation rate of the VFAs according to the change of F/M ratio and the characteristic which can eliminate organic matter and nitrogen according to the change of residual concentration of the VFAs and the efficiency of the process and also SVI in wastewater treatment. $A^2/O$ process was used for wastewater treatment. F/M ratio was under the control of the change of MLSS concentration. When the F/M ratio was changed from 0.16 to 0.08 kg-BOD/kg-MLSS/day, the VFAs's production volume increased based on the reduction of F/M ratio in batch reaction. And the residual concentration of the VFAs decreased at first and then increased later. SVI and SS were high when F/M ratio was $0.16kg/kg{\cdot}d$ and showed stable status when F/M ratio decreased $0.11{\sim}0.13kg/kg{\cdot}d$. However, SVI and SS continuously increased with decrease of F/M ratio and were high at $0.08kg/kg{\cdot}d$. In the result of comparison between residual concentration of the VFAs and denitrification rate in anoxic tank, the less residual volume of the VFAs was in anoxic tank, the higher denitrification ratio became. The optimal residual-concentration of the VFAs considering SVI and removal efficiency of nitrogenwas $1.4{\sim}2.2mg/L$. At that time F/M ratio was $0.11{\sim}0.13$ kg-BOD/kg-MLSS/day.

• Korean Journal of Food Science and Technology
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• v.25 no.6
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• pp.632-636
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• 1993

Gel strength of fish protein at various processing conditions such as heating temperature, heating time and salt content was determined by using compressive stress and residual delay time of ultrasonic wave. The compressive stress, interpreted as indicating the relative gel strength, was increased with increasing the heating temperature and heating time, and with decreasing the salt content, while the delay time of ultrasonic wave reduced, indicating that the gel strength and the delay time are inverse proportion. The result of the multiple regression analysis with factorial design showed that the model equation consisted with delay time and processing condition variables gave the good prediction of the gel compressive stress which was coincided with compressive stress measured.

• Journal of the Korean Geophysical Society
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• v.5 no.2
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• pp.87-97
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• 2002

P wave travel-time delays have been analyzed and average travel-time anomalies due to lateral variation of the crustal structure have been calculated at the broad-band earthquake observatories of Korea Meteorology Administration (KMA) using the teleseismic deata collected during the period from 2000 to 2001. Maximum variation in the relative travel-time residuals is almost 1.5 seconds Azimuthal variation in the travel-time residuals is observed to indicate the existence of lateral P velocity heterogeneity beneath the stations with velocity contrasts of -4~4%. The estimated average travel-time delays are ranging from 0.05 to 0.3 seconds at the stations including Seoul, Chuncheon, Kanneung, Uljin, and Ulleung Island showing slow velocity contrasts of 0~4% P through the crust. Faster velocity contrasts of 0~4% have been observed at the stations including Seosan, Taejeon, Daegu, Seoguipo, and Busan showing average travel-time delays ranging from -0.05 to -0.3 seconds.