• Journal of Astronomy and Space Sciences
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• v.33 no.1
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• pp.29-36
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• 2016

The East African ionosphere (3°S-18°N, 32°E-50°E) was mapped using Total Electron Content (TEC) measurements from ground-based GPS receivers situated at Asmara, Mekelle, Bahir Dar, Robe, Arbaminch, and Nairobi. Assuming a thin shell ionosphere at 350 km altitude, we project the Ionospheric Pierce Point (IPP) of a slant TEC measurement with an elevation angle of >10° to its corresponding location on the map. We then infer the estimated values at any point of interest from the vertical TEC values at the projected locations by means of interpolation. The total number of projected IPPs is in the range of 24-66 at any one time. Since the distribution of the projected IPPs is irregularly spaced, we have used an inverse distance weighted interpolation method to obtain a spatial grid resolution of 1°×1° latitude and longitude, respectively. The TEC maps were generated for the year 2008, with a 2 hr temporal resolution. We note that TEC varies diurnally, with a peak in the late afternoon (at 1700 LT), due to the equatorial ionospheric anomaly. We have observed higher TEC values at low latitudes in both hemispheres compared to the magnetic equatorial region, capturing the ionospheric distribution of the equatorial anomaly. We have also confirmed the equatorial seasonal variation in the ionosphere, characterized by minimum TEC values during the solstices and maximum values during the equinoxes. We evaluate the reliability of the map, demonstrating a mean error (difference between the measured and interpolated values) range of 0.04-0.2 TECU (Total Electron Content Unit). As more measured TEC values become available in this region, the TEC map will be more reliable, thereby allowing us to study in detail the equatorial ionosphere of the African sector, where ionospheric measurements are currently very few.

• The Korean Journal of Food And Nutrition
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• v.33 no.5
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• pp.561-569
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• 2020

In this study, the antioxidative activity of Jeolpyun containing S. glauca (Bunge) Bunge powder (2%, 4%, 6%, and 8%) and extract (2%, 4%, 6%, and 8%) was evaluated based on the total polyphenol contents, electron-donating ability, scavenging of superoxide anion radical, and decomposition of hydrogen peroxide. Total polyphenol contents of Jeolpyun containing 8% S. glauca (Bunge) Bunge powder were the highest with a value of 2,280±0.00 ㎍ GAE/mL. It was observed that total polyphenol content exhibited a significant relation with concentrations at p<0.05. The electron-donating ability of Jeolpyun containing 8% S. glauca (Bunge) Bunge extract was the highest with a value of 83.93±0.69%. The electron-donating abilities revealed significant differences between concentrations (p<0.05). The superoxide radical scavenging ability of the blank was 0.01523±0.00068 and Jeolpyun containing 6% S. glauca (Bunge) Bunge powder was the highest with a value of 0.00977±0.00842. The hydrogen peroxide decomposing ability of Jeolpyun containing 0% S. glauca (Bunge) Bunge powder was -0.00377±0.0049; 8% S. glauca (Bunge) Bunge powder revealed the highest decomposing ability of -0.0476±0.0234. Hydrogen peroxide decomposing abilities revealed significant differences between concentrations (p<0.05). Jeolpyun containing S. glauca (Bunge) Bunge powder and extract demonstrated improved antioxidative activities.

• Proceedings of the KSRS Conference
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• 2003.11a
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• pp.537-539
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• 2003

We present a GPS-derived regional ionosphere model, which estimates Total Electron Content (TEC) in rectangular grids on the spherical shell over Korea. The GPS data from nine GPS stations were used. The pseudorange data were phase-leveled by a linear combination of pseudoranges and carrier phases. During a quiet day of solar activity, the regional ionosphere map indicated 30-45 Total Electron Content Unit (TECU) at the peak of the diurnal variation. In comparison with the Global Ionosphere Map of the Center for Orbit Determination in Europe, RMS differences were at the level of 4-5 TECU for five days.

• Journal of Astronomy and Space Sciences
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• v.28 no.1
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• pp.71-77
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• 2011

Ionospheric error modeling is necessary to create reliable global navigation satellite system (GNSS) signals using a GNSS simulator. In this paper we developed algorithms to generate Klobuchar coefficients ${\alpha}_n$, ${\beta}_n$ (n = 1, 2, 3, 4) for a GNSS simulator and verified accuracy of the algorithm. The eight Klobuchar coefficients were extracted from three years of global positioning system broadcast (BRDC) messages provided by International GNSS service from 2006 through 2008 and were fitted with Fourier series. The generated coefficients from our developed algorithms are referred to as Fourier Klobuchar model (FOKM) coefficients, while those coefficients from BRDC massages are named as BRDC coefficients. The correlation coefficient values between FOKM and BRDC were higher than 0.97. We estimated total electron content using the Klobuchar model with FOKM coefficients and compared the result with that from the BRDC model. As a result, the maximum root mean square was 1.6 total electron content unit.

• Journal of Astronomy and Space Sciences
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• v.27 no.2
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• pp.123-128
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• 2010

This paper analyzes that the global positioning system (GPS) receiver differential code bias (DCB) has effect on the estimation the ionosphere total electron content (TEC). The data from nine permanent GPS sites of the Korea Astronomy and Space Science Institute (KASI) were used for the estimation of the receiver DCB before (Trimble 4000 SSi) and after (Trimble NetRS) the receiver replacement, using the singular value decomposition method. The results showed that the estimated mean value of the receiver DCB varied from 0.11 ns (nanosecond) to 7.54 ns before the receiver replacement, but the receiver DCBs shoed large values than 20 ns except some stations after the replacement. The receiver DCB showed a relatively large difference by types of the receivers, and, as a result, it had a great effect on the estimation the ionosphere TEC using GPS.

• Journal of Astronomy and Space Sciences
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• v.37 no.1
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• pp.61-68
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• 2020

Recent studies have suggested that detectable ionospheric disturbances precede earthquakes. In the present study, variations in the vertical total electron content (TEC) for eight earthquakes with magnitudes of M ≥ 5.5 in the western United States were investigated during the solar maximum of 2013-2015 using United States total electron content (US-TEC) data provided by the National Oceanic and Atmospheric Administration. Analyses of 12 earthquakes with magnitudes of 5.0 ≤ M < 5.5 in the same region were also performed. The TEC variations were examined for 40 days, including the times when the earthquakes occurred. The results indicated a correlation between earthquakes with magnitudes of M ≥ 5.0 and ionospheric TEC anomalies. TEC anomalies occurred before 60% of the earthquakes. Additionally, they were more frequently observed for large earthquakes (75%, M ≥ 5.5) than for small earthquakes (50%, 5.5 > M ≥ 5.0). Anomalous increases in the TEC occurred 2-18 days before the earthquakes as an ionospheric precursor, whereas solar and geomagnetic activities were low or moderate.

• Journal of Astronomy and Space Sciences
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• v.23 no.3
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• pp.237-244
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• 2006

We produced the electron density distribution in the ionosphere over South Korea using the data from nine permanent GPS (Global Positioning System) stations which have been operated by KASI (Korea Astronomy and Space Science Institute). The dual-frequency GPS receiver data was used to precisely estimate the electron density in the ionosphere and we obtained the precise electron density profile based on two-dimensional TEC (Total Electron Contents). We applied ART (Algebraic Reconstruction Technique), which is one of the most commonly used algorithms to develop the tomography model. This paper presented the electron density distribution over South Korea with time. We compared with the electron density profiles derived from the GPS tomography reconstruction, Ionosonde measurement data obtained by observations, and the IRI-2001 values. As a result, the electron density profile by GPS reconstruction was in excellent agreement with the electron density profile obtained by Ionosonde measurement data.

• Korean Journal of Medicinal Crop Science
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• v.21 no.4
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• pp.255-261
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• 2013

The purpose of this study was to examined the antioxidant activities by water and 70% ethanol extract from durian (Durio zibethinus.) seed, sarcocarp and peel. Durian extract were studied for reducing sugar content, polyphenol content, superoxide dismutase (SOD) like activity, electron donating ability, nitrite scavenging ability, flavonoid content, hydroxy radical scavenging activity. Reducing sugar content were increased peel > sarcocarp > seed. Total polyphenol, flavonoid content, DPPH radical scavenging ability and SOD like activity were increased seed > peel > sarcocarp. Total polyphenol content was relatively high as $21.90{\pm}0.50mg/g$ in the ethanol extract of the seed. DPPH radical scavenging ability was relatively high as $62.08{\pm}2.63%$ in the water extract of the seed. Nitrite scavenging ability was no significant difference. Hydroxy radical scavenging activity was increased seed > peel > sarcocarp, was relatively high as $58.27{\pm}1.13%$ in the water extract of the seed.

• The Korean Journal of Food And Nutrition
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• v.35 no.2
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• pp.96-105
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• 2022

This study compared and analyzed the antioxidant effect of Doenjang prepared from vegetable water, and explored the optimal addition ratio of vegetables of 5 kinds and the possibility of application to Doenjang. The sample is three kinds of vegetable water (VW1, VW2, VW3) prepared by adding different ratios of radish, carrot, green onion, onion and shiitake mushroom and Denjang prepared using it. Doenjang was aged and fermented at about 40℃ for 40 days, and then separated and used only solids. The content of their antioxidant compounds was measured the content of total phenolic acid contents and total flavonoid contents. In addition, the antioxidant effect was measured by electron donating activity, SOD-like activity, ABTs radical scavenging activity and reducing power. The total phenolic acid contents and total flavonoid contents were high at VW3 and that Doenjang made with VW3. Electron donating activity and SOD-liked activity were high at VW2 and Doenjang made with VW2. ABTs radical scavenging activity was high in Doenjang made of VW3, and Reducing power was high in VW3. Therefore, if Doenjang is prepared with vegetable water prepared by properly mixing 5 types of vegetables, the possibility of developing Doenjang with high antioxidant effect was suggested.

• Korean Journal of Food Science and Technology
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• v.34 no.6
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• pp.1013-1017
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• 2002

Functional activities of Flammulina velutipes extract including electron donating ability, nitrite-scavenging effect, and tyrosinase inhibition activity was examined. Extraction were carried out by microwave-assisted extraction (MAE) under different conditions including solvent and microwave power. Tyrosinase inhibition activity and nitrite-scavenging effect increased as microwave power increased during extraction. Total phenol content and electron-donating ability reached maximum at the microwave power of 90 W. Total polyphenol content and electron-donating ability increased as extraction time extended up to 15 min, with the highest tyrosinase inhibition obtained after 5 min extraction. Significantly higher tyrosinase inhibition activity was found in 99% ethanol extract, whereas greater nitrite-scavenging effect was observed in the water extract. The maximum nitrite-scavenging effect was found at pH 1.2 and decreased as pH increased.