• Resources Recycling
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• v.11 no.5
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• pp.16-20
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• 2002

This experiment was carried out to examine the effects of La-Co substitution on Sr-ferrite. The magnetic properties of calcined and sintered materials varied with the substitutional amount of La and Co elements in Sr-ferrite. Anisotropy field and coercivity for Sr ferrite were increased with raising La-Co substitution amounts. The microstructure observation for Sr ferrite substituted by La-Co revealed that La-Co inhabited grain growth during calcination and promoted lateral grain growth during sintering. The relationship between $B_{r}$ and $_{i}$ /$H_{c}$ for La-Co substituted Sr-ferrite was found to be $B_{r}$$≒0.097_{i}$ /$H_{c}$/+4500. In case of $SrFe_{12}$ $O_{19}$, $B_{r} was 4090 G and $_{ i}$$H_{c}$ was 3560 Oe, but $B_{r}$ was 4080 G and and $_{i}$ $H_{c}$ was 4800 Oe for $Sr_{0.7}$ $La_{0.3}$ $Fe_{11.7}$ /$Co_{0.3}$ $O_{19}$.

• Proceedings of the Korean Vacuum Society Conference
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• 2014.02a
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• pp.372-372
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• 2014

반도체 검출기는 입사되는 X선 에너지에 의하여 이온화되어 발생하는 전자 전공쌍을 수집함으로 방사선 정보를 확인하는 선량계로써 많은 연구와 활용이 이루어지고 있다. 하지만, X선 에너지에 의하여 반도체 검출기에서 발생하는 전기적 신호량이 높지 않기 때문에 누설 전류의 저감이 필수적이다. 누설 전류를 저감시키기 위한 방안으로 반도체 층과 전극 층의 Schottky Contact 구조의 설계, Insulating Layer의 사용, 높은 비저항의 반도체 물질 연구 등이 이루어지고 있다. 하지만, 기존에 누설 전류 저감을 위하여 Insulating Layer를 전극층과 반도체 층 사이에 형성하는 연구에 있어서 Insulating Layer와 반도체 층의 계면 사이에서 발생하는 Charge Trapping으로 인하여 생성되는 신호의 Reproducibility 저하, 동영상 적용의 제한 등의 문제점을 겪어왔다. 이에 본 논문에서는 누설 전류를 저감시킴과 동시에 Charge Trapping의 최소화를 이루기 위하여 Insulating Layer의 두께 최적화 연구를 수행하였다. 본 연구에서 사용한 Insulating Layer는 검출기 표면에 입사하는 X선 정보 손실을 최소화 시키는 동시에 누설 전류와 Charge Trapping을 최소화 시키는 방법으로써 CVD방법으로 검출기 표면에 균일하게 Insulating Layer를 코팅하였다. Insulating 물질은 Parylene을 사용하였으며, 그 중 온도, 습도 등 외부환경에 영향을 적게 받는 type C를 사용하였다. 증착에 사용한 장비의 진공도는 Torr로 설정하여 증착되는 Parylene의 두께가 약 $0.3{\mu}m$가 되게 하였으며, 실험에는 반도체 물질 PbO를 사용하였다. Parylene의 절연 특성은 Dark Current와 Sensitivity를 측정한 SNR을 이용하여 Parylene코팅이 되지 않은 동일 반도체 검출기와의 신호를 비교하였으며 또한 Parylene를 다층 제작한 검출기의 수집 신호량을 비교하였다. 제작한 검출기의 X선 조사 시의 수집 전하량 측정 결과, 100 kVp, 100mA, 0.03s의 X선 조건에서 $1V/{\mu}m$의 기준 시, Parylene를 코팅하지 않은 PbO 검출기의 Dark current는 0.0501 nA/cm2, Sensitivity는 0.6422 nC/mR-cm2, SNR은 12.184이었으며, Parylene단층의 두께인 $0.3{\mu}m$로 증착된 시편의 Dark current는 0.04097 nA/cm2, Sensitivity는 0.53732 nC/mR-cm2으로 Dark current가 감소되고 sensitivity도 감소하였지만 SNR은 13.1150으로 높아진 것을 확인할 수 있었다. Perylene이 $0.6{\mu}m$로 증착된 시편의 경우, Dark Current는 0.04064 nA/cm2, Sensitivity는 0.31473 nC/mR-cm2, SNR은 7.7443으로써 Insulating Layer가 없는 시편보다 SNR이 약 40% 낮아진 것을 확인할 수 있었다. Parylene이 $0.9{\mu}m$로 증착된 시편의 경우 Dark current는 0.0378 nA/cm2, Sensitivity 0.0461 nC/mR-cm2로 Insulating Layer가 없는 시편에 비해 SNR은 약 1/12배 감소한 1.2196이었고, Parylene이 $1.2{\mu}m$로 증착된 시편의 SNR은 1.1252로서 더 감소하였다. 따라서 Parylene을 다층 코팅한 검출기일수록 절연 효과의 영향이 커짐으로써 SNR 비교 시 수집되는 신호량이 줄어드는 것을 확인하였다. 반도체 검출기의 누설 전류를 저감시킴과 동시에 신호 수집율에 영향을 최소화시키기 위하여 Insulating Layer의 두께를 적절하게 설정하여 적용하면 Insulating Layer가 없는 검출기에 비해 누설전류를 최소한으로 줄일 수 있고 신호 검출효율이 감소하는 것을 방지할 수 있을 것이라 사료된다.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.7
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• pp.1777-1783
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• 2014

In this paper, we designed and fabricated a high-speed semiconductor sensor for use in power control devices and analyzed the characteristics with pulsed radiation tests. At first, radiation sensitive circular Si PIN diodes with various diameters(0.1 mm ~5.0 mm) were designed and fabricated using Si epitaxial wafer, which has a $42{\mu}m$ thick intrinsic layer. The reverse leakage current of the diode with a radius of 2 mm at a reverse bias of 30 V was about 20.4 nA. To investigate the characteristic responses of the developed diodes, the pulsed gamma-radiation tests were performed with the intensity of 4.88E8 rad(Si)/sec. From the test results showing that the output currents and the rising speeds have a linear relationship with the area of the sensors, we decided that the optimal condition took place at a 2 mm diameter. Next, for the selected 2 mm diodes, dose rate tests with a range of 2.47E8 rad(Si)/sec to 6.21E8 rad(Si)/sec were performed. From the results, which showed linear characteristics with the radiation intensity, a large amount of photocurrent over 60mA, and a high speed response under 350ns without saturation, we can conclude that the our developed PIN diode can be a good candidate for the sensor of power control devices.

• Journal of the Korean Chemical Society
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• v.50 no.2
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• pp.163-177
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• 2006

Alpha Nickel hydroxide samples have been synthesized by electrodeposition on platinum and nickel substrates at current densities of 1, 5, 6, 7 and 10 mAcm？2 at a controlled temperature of 30.00 oC from Ni(NO3)2 bath. Platinum substrate shows a tendency to incorporate less nitrate ions with increase in current density thus producing less hydroxy-deficient nickel hydroxide layers. On the whole the interlayer distance (d003) is found to be inversely proportional to the amount of nitrate ions incorporated in-between the lattice. For the first time we have observed a decrease in lattice spacing with increase in concentration of intercalant (anions) and the reason for lattice contraction is attributed to the columbic attractive forces exerted by the oppositely charged nitrate ion and positively charged slabs. The Infrared spectra of the samples with expanded interlayers show two types of OH vibrations corresponding to hydrogen bonded and non-hydrogen bonded OH groups whereas the contracted interlayers show only hydrogen-boded OH groups. Although the faradaic efficiency is found to increase with increase in applied current there is a local minimum at 6.0 mAcm？2 current density on both platinum and nickel substrates. In this manuscript, GC-MS data is provided which clearly demonstrates the electrodeposited nickel hydroxide sample to consist of huge amount of carbonate ions although the electrolyte solution in nickel nitrate.

• Journal of the Korean Electrochemical Society
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• v.8 no.2
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• pp.88-93
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• 2005

Anode-supported solid oxide fuel cell (SOFC) was investigated to increase the cell power density at intermediate temperature through control of the cathode structure. The anode-supported SOFC cell were fabricated by wet process, in which the electrolyte of $8mol\%\;Y_2O_3-stabilized\;ZrO_2 (YSZ)$ was coated on the surface of anode support of Ni/YSA and then the cathode was coated. The cathode has two- or three- layered structure composed of $(La_{0.85}Sr_{0.15})_{0.9}MnO_{3-x}(LSM),\;LSM/YS$ composite (LY), and $La_{0.6}Sr_{0.4}Co_{0.2}Fe_{0.8}O_3{LSCF)$ with different thickness. Their single cells with different cathode structures were characterized by measuring the cell performance and ac impedance in the temperature range of 600 to $800^{\circ}C$ in humidified hydrogen with $3\%$ water and air. The cell with $LY\;9{\mu}m/LSM\;9{\mu}m/LSCF\;17{\mu}m$ showed best performance of $590mW/cm^2$, which was attributed to low polarization resistance due to LY and to low interfacial resistance due to LSCF.

• Korean Journal of Food Science and Technology
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• v.48 no.1
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• pp.66-71
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• 2016

Delphinidin is a blue-red pigment and one of the major anthocyanins in plants. It plays an important role in anti-oxidant, anti-inflammatory, anti-mutagenic and anti-cancer properties. In this study, we investigated the inhibitory effects of delphinidin on vascular endothelial growth factor (VEGF) gene expression, an important factor involved in angiogenesis and tumor progression in human prostate cancer. Delphinidin decreased levels of epidermal growth factor (EGF)-induced VEGF mRNA expression in PC-3M cells. The expression of the EGF-induced hypoxia inducible factor-$1{\alpha}$ (HIF-$1{\alpha}$) and signaling transducer and activator of transcription 3 (STAT3) proteins, which are the major transcription factors for VEGF, were inhibited by delphinidin. In addition, delphinidin decreases HRE-promoter reporter gene activity, suggesting that delphinidin can suppress the transcription of HIF-$1{\alpha}$ under EGF induction, leading to a decrease in the expression of VEGF. Delphinidin specifically suppressed the phosphorylation of Akt, p70S6K, and 4EBP1, but not the phosphorylation of EGFR. Therefore, our results suggest that delphinidin may inhibit human prostate cancer progression and angiogenesis by inhibiting HIF-$1{\alpha}$, STAT3 and VEGF gene expression.

• Applied Chemistry for Engineering
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• v.32 no.5
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• pp.509-515
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• 2021

In this study, poly lactic-co-glycolic acid (PLGA) nanoparticles (PNP) were prepared through double (w/o/w) emlusion and emulsifying solvent-evaporation technique using PLGA, which has biocompatibility and biodegradability. To maximize stability and bioavailability of the particles, chitosan-coated PLGA nanoparticles (CPNP) were prepared by charge interaction between PNP and chitosan. We demonstrated that CPNP can be utilized as a drug carrier of oral administration. The chemical structure of CPNP was analyzed by ¹H-NMR and FT-IR, and all characteristic peaks appeared, confirming that it was successfully prepared. In addition, particle size and zeta potential of CPNP were analyzed using dynamic light scattering (DLS) while morphological images were obtained using transmission electron microscope (TEM). Thermal decomposition behavior of CPNP was observed through thermogravimetric analysis (TGA). In addition, the cytotoxicity of CPNP was confirmed by MTT assay at HEK293 and L929 cell lines, and it was proved that there is no toxicity confirmed by the cell viability of above 70% at all concentrations. These results suggest that the CPNP developed in this study may be used as an oral drug delivery carrier.

• Journal of the Microelectronics and Packaging Society
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• v.29 no.4
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• pp.63-69
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• 2022

Vanadium dioxide shows a unique and interesting property of metal-insulator transition, which has attracted great attention from the viewpoints of fundamental materials science and industrial applications. In this study, the effect of Mg and W addition on the metal-insulator transition of VO₂ were investigated for the bulk materials that are prepared by spark plasma sintering. The X-ray diffraction analysis of the sintered specimens revealed that the lattice parameters barely change, and the secondary phases are present. The transition temperature of MIT appears in the range of 64.2-64.6℃, regardless of the impurity element and content. On the other hand, the addition of Mg and W alters the electrical conductivity, i.e., the electrical conductivity increases by a factor of up to 2.4 or decrease by a factor of up to 57.4 depending on the impurity type and its content. The thermal conductivity showed the values of 1.8~2.5 W/m·K below the transition temperature, and the values of 1.9~2.8 W/m·K above the transition temperature. These changes in electrical and thermal conductivities can be attributed to the combination of the change in charge carrier density, the impurities as scattering centers, and the change in microstructures.

• Journal of the Korean Institute of Landscape Architecture
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• v.37 no.2
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• pp.90-103
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• 2009

The poem 'Kyungjusipiyung(慶州十二詠)' written by Seo, Geo-jeong(徐居正) describes sentiments felt for the ruined historical and cultural landscape of Silla's capital city, Kyungju. It differs from the existing 'Eight Sceneries(八景)' as it conveys the strong metaphorical aesthetics of ruins as the episodes and figures are sung, as well as the myths and stories related to the representative holy places of the Silla culture: Gyelim(鷄林), Banwolseong(半月城), Najeong(蘿井), Oneung(五陵), Geumosan(金鰲山), the scenic beauty of deep placeness, Poseokjeong(鮑石亭), Mooncheon(蚊川), Cheomseongdae(瞻星臺), Boonhwangsa(芬皇寺), Youngmyosa(靈妙寺) and Grave of the General Kim Yu-Sin(金庾信墓). Compared with the former "Eight Sceneries" Poems, including Seo Geojeong's 'Kyungjusipiyung', there is a difference in the content of theme recitation, as well as in structure and form, especially with the deep impression of the classical features of the meanings and acts. The sequence of theme recitation seems to be composed of more than two visual corridors visited during trips that last longer than two days. The dominant emotions expresses in this poem, through written in the spring, are regret and sadness such as 'worn', 'broken and ruined', 'old and sad', without touching on the beauty of nature and the taste for life that is found in most of the Eight Sceneries Poems. Thus, the feelings of the reciter himself, Seo, Geo-jeong, about the described sceneries and their symbolism are more greatly emphasized than the beauty of form. The characteristic aspect of his experiences of ruins expressed from 'Kyungjusipiyung' is that the experiences were, first of all, qualitative of the aura conveyed; that is, the quality omnipresent throughout the culture of Silla as reflected in the twelve historical and cultural landscapes. In this poem, the cultural ruins of the invisible dimension such as the myths and legends are described by repetition, parallelism, juxtaposition, reflection and admiration from the antiphrases, as well as the civilized ruins of the visible dimension such as the various sceneries and features of Kyungju. This seems to be characteristic of the methods by which Seo, Geo-jeong appreciates 'Silla' in the poem 'Kyungjusipiyung'. Ruins as an Aesthetic Object imply the noble pride of Seo, Geo-jeong in identifying himself with the great nature of ruins. In 'Kyungjusipiyung', the images of the ruins of Silla and Kyungju are interspersed in spite of his positive recognition of 'the village of Kyungju' based on his records. However, though the concept of ruins has a pessimistic tone connoting the road of extinction and downfall, the aspect here seems to ambivalently contain the desire to recover and revive Kyungju through the Chosun Dynasty as adominant influence on the earlier Chosun's literary tide. The aesthetics of the scenery found in Seo, Geo-jeong's 'Kyungjusipiyung' contain the strongest of metaphor and symbolism by converting the experiences of the paradoxical ruins into the value of reflective experiences.

• Journal of Radiation Protection and Research
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• v.35 no.2
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• pp.69-76
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• 2010

Prototype double-scattering Compton camera, which consists of three gamma-ray detectors, that is, two double-sided silicon strip detectors (DSSDs) as scatterer detectors and a NaI(Tl) scintillation detector as an absorber detector, could provide high imaging resolution with a compact system. In the present study, the energy resolution and the timing resolution of component detectors were measured, and the parameters affecting the energy resolution of the DSSD were examined in terms of equivalent noise charge (ENC). The energy resolutions of the DSSD-1 and DSSD-2 were, in average, $25.2keV{\pm}0.8keV$ FWHM and $31.8keV{\pm}4.6keV$ FWHM at the 59.5 keV peak of $^{241}Am$, respectively. The timing resolutions of the DSSD and NaI(Tl) scintillation detector were 57.25 ns FWHM and 7.98 ns FWHM, respectively. In addition, the Compton image was obtained for a point-like $^{137}Cs$ gamma source with double-scattering Compton camera. From the present experiment, the imaging resolution of 8.4 mm FWHM (angular resolution of $8.1^{\circ}$ FWHM), and the imaging sensitivity of $1.5{\times}10^{-7}$ (intrinsic efficiency of $1.9{\times}10^{-6}$) were obtained.