• Journal of Food Hygiene and Safety
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• v.15 no.1
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• pp.46-50
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• 2000

Totally, twenty seven specimens of tiger puffer, Fugu rubripes rubripes were collected at Jagalchi fish market in Pusan, Korea during January, April and September in 1995. Anatomical distribution of pufferfish toxin in tiger puffer was examined by mouse bioassay. The frequency rate of toxic specimens containing $\geq$ 10 MU/g was 14.8％ in liver; 16.7％ in gonad; and 14.8％ in skin, and no toxin was detected in muscle. The highest toxin level found was 160 MU/g in liver, 600 MU/g in gonad and 26 MU/g in skin, and each average toxin level (mean$\pm$ standard error) was 7$\pm$6, 50$\pm$35 and 5$\pm$1 MU/g, respectively. Some specimens collected in January and April were toxic, while none of the specimens collected in September showed its toxicity. Although toxicity of tiger puffer showed the seasonal variation, tested tiger puffer was evaluated as a safe seafood fur consumption, in that an acceptable level of toxin was found in the edible muscle and skin.

• Imaging Science in Dentistry
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• v.42 no.2
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• pp.65-70
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• 2012

Purpose : The aim of this study was to compare the effective dose for imaging of mandible between multi-detector computed tomography (MDCT) and cone-beam computed tomography (CBCT). An MDCT with low dose technique was also compared with them. Materials and Methods : Thermoluminescent dosimeter (TLD) chips were placed at 25 organ sites of an anthropomorphic phantom. The mandible of the phantom was exposed using 2 different types of MDCT units (Somatom Sensation 10 for standard-dose MDCT, Somatom Emotion 6 for low-dose MDCT) and 3 different CBCT units (AZ3000CT, Implagraphy, and Kavo 3D eXaM). The radiation absorbed dose was measured and the effective dose was calculated according to the ICRP 2007 report. Results : The effective dose was the highest for Somatom Sensation 10 (425.84 ${\mu}Sv$), followed by AZ3000CT (332.4 ${\mu}Sv$), Somatom Emotion 6 (199.38 ${\mu}Sv$), and 3D eXaM (111.6 ${\mu}Sv$); it was the lowest for Implagraphy (83.09 ${\mu}Sv$). The CBCT showed significant variation in dose level with different device. Conclusion : The effective doses of MDCTs were not significantly different from those of CBCTs for imaging of mandible. The effective dose of MDCT could be markedly decreased by using the low-dose technique.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.15 no.2
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• pp.190-197
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• 2002

In this thesis, ZnO varistors with various formulation, such as A∼E, were fabricated according to ceramic fabrication method. The microstructure, electrical properties, and surge characteristics of ZnO varistors were investigated according to ZnO varistors with various formulation. In the microstructure, A∼E\`s ZnO varistor ceramics sintered at 1130$\^{C}$ was consisted of ZnO grain(ZnO), spinel phase (Zn$\_$2.33/Sb$\_$0.67/O$\_$4/), Bi-rich phase(Bi$_2$O$_3$) and intergranuler phase, wholly. Lightning impulse residual voltage of A, B, C and E\`s ZnO varistors suited standard characteristics, below 12kV at current of 5kA. On the contrary, D\`s ZnO varistor exhibited high residual voltage as high reference voltage. In the accelerated aging test, leakage current and watt loss of B, C and D\`s ZnO varistors increases abruptly with stress time under the first a.c. stress(115$\^{C}$/3.213kV/300h). Consequently, C varistor exhibited a thermal run away. On the contrary, leakage current and watt loss of A and C\`s ZnO varistors which show low initial leakage current exhibited constant characteristics. After high current impulse test, A\`s ZnO varistor has broken the side of varistor but impulse current flowed. On the contrary, E\`s ZnO Varistor exhibited good discharge characteristics which the appearance of varistor was not wrong such as puncture, flashover, creaking and other significant damage. After long duration impulse current test, E\`s ZnO varistor exhibited good discharge characteristics which the appearance of varistor was not wrong such as puncture, flashover, creaking and other significant damage. After high current impulse test and long duration impulse current test, E\`s ZnO varistor exhibited very good characteristics which variation rate of residual voltage is 1.4% before and after test.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2002.11a
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• pp.552-556
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• 2002

The microstructure and electrical characteristics of A~C's ZnO varistors fabricated according to variable sintering condition, which sintering temperature is $1130^{\circ}C$ and speeds of pusher are A: 2mm/min, B: 4mm/min, C: 6mm/min, respectively, were investigated. In the microstructure, A~C's ZnO varist-ors fabricated variable sintering condition was consisted of ZnO grain(ZnO), spinel phase$(Zn_{2.33}Sb_{0.67}O_4)$ Bi-rich $phase(Bi_{2}O_{3})$, wholly. Varistor voltage of A~C's ZnO varistors sintered at $1130^{\circ}C$ increased in order A < B < C's ZnO varistors. C's ZnO varistor exhibited good characteristics that nonlinear exponent is 31.70. Leakage current of A~C's ZnO varistors exhibited below 2mA at rated voltage. Lightning impulse residual voltage of A's ZnO varistor suited standard characteristics, which is 3.85kV at 2.5kA, 4.4kV at 5kA and 5.16kV at 10kA. After multi lightning impulse residual voltage test of A's ZnO varistor exhibited good discharge characteristics which ZnO varistor reveals no evidence of puncture, flashover, cracking in visual examination. After high current impulse test of A's ZnO varistor exhibited good discharge characteristics, which variation rate of residual voltage is 0.4% before and after test, and revealed no evidence.

• Proceedings of the KIEE Conference
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• 2006.07b
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• pp.1159-1160
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• 2006

As the grid-connected photovoltaic power conditioning systems (PVPCS) are installed in many residential areas, this has raised potential problems of network protection on electrical power system. One of the numerous problems is an Island phenomenon. There has been an argument that because the probability of islanding is extremely low it may be a non-issue in practice. However, there are three counter-arguments: First, the low probability of islanding is based on the assumption of 100% power matching between the PVPCS and the islanded local loads. In fact, an island can be easily formed even without 100% power matching (the power mismatch could be up to 30% if only traditional protections are used, e.g. under/over voltage/frequency). The 30% power-mismatch condition will drastically increase the islanding probability. Second, even with a larger power mismatch, the time for voltage or frequency to deviate sufficient to cause a trip, plus the time required to execute the trip (particularly if conventional switchgear is required to operate), can easily be greater than the typical re-close time on the distribution circuit. And, third, the low-probability argument is based on the study of PVPCS. Especially, if the output power of PVPCS equals to power consumption of local loads, it is very difficult for the PVPCS to sustain the voltage and frequency in an island. Unintentional islanding of PVPCS may result in power-quality issues, interference to grid-protection devices, equipment damage, and even personnel safety hazards. So the verification of anti-islanding performance is strongly needed. In this paper, the authors propose the improved RPV method through considering power quality and anti-islanding capacity of grid-connected three-phase PVPCS in IEEE Std 1547 ("Standard for Interconnecting Distributed Resources to Electric Power Systems"). And the simulation and experimental results are verified.

• Publications of The Korean Astronomical Society
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• v.35 no.2
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• pp.19-27
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• 2020

We have investigated the North Korean astronomical articles published in five media such as the Rodong Sinmun (노동신문), Minju Choson (민주조선), Tongil Sinbo (통일신보), Munhak Sinmun (문학신 문), and Choson Sinbo (조선신보) for 15 years from 2005 to 2019. The astronomical articles were classified by subject to study the astronomical activity in North Korea. We have examined the perceptions of astronomy in North Korean society through the temporal variation of astronomical articles according to four subjects. As a result, we have found that there are many articles in the subject of Historical Astronomy and Astronomical News in the media. In the era of Kim Jong-un, the articles on the Historical Astronomy decreased while the Astronomy news tended to increase. We have also summarized the specific issues and topics including the change of the standard meridian, launch of satellites, astronomical news, and so forth. The North Korean astronomical article is a valuable resource to examine the current status of North Korea's astronomy and astronomical education. We expect the results of this study to be a useful resource in preparing for inter-Korean astronomical cooperation.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.9
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• pp.89-96
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• 2005

This paper discusses the daytime atmospheric conditions and the possibility of daytime star detection with the purpose of practical use of the star sensor for daylight navigation. In order to estimate the daytime atmospheric data, we use the standard atmospheric model (LOWTRAN 7), from which atmospheric transmittance and radiance from background sky are calculated. Assuming the star sensor with an optical filter to reduce background radiation, different separation angles between the star sensor and the sun are set up to express the effect of the solar radiation. As considerations of field of view (FOV) of the star sensor, the variation of the sky background radiation and the star density of the detectable star are analyzed. In addition, the integration time to achieve a required signal-to-noise ratio and the number of the radiation-caused electrons of the charge coupled detector(CCD) working as the limit to daylight application of the star sensor are calculated.

• Journal of Magnetics
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• v.16 no.4
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• pp.457-460
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• 2011

In this paper, magnetic property and magnetocaloric effect (MCE) in perovskite manganites of the type $La_{(0.75-X)}Ce_XCa_{0.25}MnO_3$ (x = 0.0, 0.2, 0.3 and 0.5) synthesized by using the standard solid state reaction method have been reported. From the magnetic measurements as a function of temperature and applied magnetic field, we have observed that the Curie temperature ($T_C$) of the prepared samples strongly dependent on Ce content and was found to be 255, 213 and 150 K for x = 0.0, 0.2 and 0.3, respectively. A large magnetocaloric effect in vicinity of $T_C$ has been observed with a maximum magnetic entropy change (${\mid}{\Delta}S_M{\mid}_{max}$) of 3.31 and 6.40 J/kgK at 1.5 and 4 T, respectively, for $La_{0.55}Ce_{0.2}Ca_{0.25}MnO_3$. In addition, relative cooling power (RCP) of the sample under the magnetic field variation of 1.5 T reaches 59 J/kg. These results suggest that $La_{0.55}Ce_{0.2}Ca_{0.25}MnO_3$ compound could be a suitable candidate as working substance in magnetic refrigeration at 213 K.

• Archives of Pharmacal Research
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• v.28 no.5
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• pp.518-528
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• 2005

In the present study, the antioxidative and inhibitory activity of Zingiber officinale Rosc. Rhizomes-derived materials (on mushroom tyrosinase) were evaluated. The bioactive co mponents of Z. officinale rhizomes were characterized by spectroscopic analysis as zingerone and dehydrozingerone, which exhibited potent antioxidant and tyrosinase inhibition activities. A series of substituted dehydrozingerones [(E)-4-phenyl-3-buten-2-ones] were prepared in admirable yields by the reaction of appropriate benzaldehydes with acetone and the products were evaluated in terms of variation in the dehydrozingerone structure. The synthetic analogues were examined for their antioxidant and antityrosinase activities to probe the most potent analogue. Compound 26 inhibited Fe$^{2+}$-induced lipid peroxidation in rat brain homogenate with an IC$_{50}$ = 6.3${\pm}$0.4 ${\mu}$M. In the 1,1-diphenyl- 2-picrylhydrazyl (DPPH) radical quencher assay, compounds 2, 7, 17, 26, 28, and 29 showed radical scavenging activity equal to or higher than those of the standard antioxidants, like ${\alpha}$-tocopherol and ascorbic acid. Compound 27 displayed superior inhibition of tyrosinase activity relative to other examined analogues. Compounds 2, 17, and 26 exhibited non-competitive inhibition against oxidation of 3,4- dihydroxyphenylalanine (L-DOPA). From the present study, it was observed that both number and position of hydroxyl groups on aromatic ring and a double bond between C-3 and C-4 played a critical role in exerting the antioxidant and antityrosinase activity.

• Journal of the Korean Chemical Society
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• v.13 no.4
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• pp.401-407
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• 1969

The results of water analysis for 10 stations in the main Naktong and 11 stations in the tributaries from March to December 1968 are as follows: The water quality of the Naktong River Basin is generally the frist class of water, especially the tributaries, Hwang river, Nam river, Milyang river, Naesongchun, Hoechun, Wichun and Panbyunchun were dissolved in less than 100 mg/l as the amount of the total ion of the main component. In comparison with river discharge, the amount of the total ion of the main component is decreased in June and July, because of the river discharge is increased in those periods. According to the measurement of the conductivity and the hardness, the better water quality is distinguished by the following order: lower part of river (Namji), middle part of river (Waegwan), upper part of river (Yean). The conductivity of Kumho river, Tongchon is higher than the middle part of the main river and Nam river, Chongam is smaller than lower part of the main rivller. The variation of the amount of the total ion of main component in the basin is mainly effected by $HCO_3^-, SO_4^{-2}, Cl^-, Ca^{+2}$. The relationship between $[K^+]\;and\;[C^l-]\;and\;[Na^+]\;and\;[Cl^-]\;are\;[K^+]=0.04\;[Cl^-]+1.7\;mg/l,\;[Na^+]=0.06\;[Cl^-]$ mg/l .The main river was much contaminated by Kumho river and C.O.D. at Gang-chung, Kumho river in June was recorder over the standard about 7 times.