• Korean Journal of Materials Research
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• v.29 no.10
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• pp.579-585
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• 2019

In this study, we investigate the effect of Al/N source ratios and growth rates on the growth and structural properties of AlN films on c-plane sapphires by plasma-assisted molecular beam epitaxy. Both growth rates and Al/N ratios affect crystal qualities of AlN films. The full width at half maximum (FWHM) values of ($10{\bar{1}}5$) X-ray rocking curves (XRCs) change from 0.22 to $0.31^{\circ}$ with changing of the Al/N ratios, but the curves of (0002) XRCs change from 0.04 to $0.45^{\circ}$ with changing of the Al/N ratios. This means that structural deformation due to dislocations is slightly affected by the Al/N ratio in the ($10{\bar{1}}5$) XRCs but affected strongly for the (0002) XRCs. From the viewpoint of growth rate, the AlN films with high growth rate (HGR) show better crystal quality than the low growth rate (LGR) films overall, as shown by the FWHM values of the (0002) and ($10{\bar{1}}5$) XRCs. Based on cross-sectional transmission electron microscope observation, the HGR sample with an Al/N ratio of 3.1 shows more edge dislocations than there are screw and mixed dislocations in the LGR sample with Al/N ratio of 3.5.

• Journal of Ginseng Research
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• v.37 no.4
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• pp.483-490
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• 2013

Gamma-irradiation (0-7 kGy) of ginseng is permitted in Korea for the purpose of microbial decontamination; with strict labeling, traceability and monitoring requirements. An identification study was conducted to determine the photostimulated-luminescence (PSL) and thermoluminescence (TL) properties of gamma-irradiated fresh and white ginsengs cultivated in different areas. Dose- dependent PSL-based screening was possible for white ginseng samples; however, inappropriate results from non-irradiated fresh ginseng samples were obtained, showing intermediate (700 to 5,000) or positive ($T_2$ >5,000, irradiated) PSL counts due to the abundance of minerals on the surfaces of the samples. TL analysis of separated minerals from all non-irradiated samples gave TL glow curves of low intensity with a maximum peak after $300^{\circ}C$. However, well-defined irradiation-specific (high intensity with a maximum peak at about $200^{\circ}C$) glow curves were observed for all the irradiated samples, regardless of their type and origins. TL ratios (first glow curve /second glow curve) were also determined to confirm the irradiated (>0.1) and non-irradiated (<0.1) results. SEM-EDX (scanning electron microscope-energy dispersive X-ray) and XRD (X-ray diffraction) spectroscopic analyses showed that feldspar and quartz minerals were the main source for the typical radiation-specific luminescence properties.

• Proceedings of the Plant Resources Society of Korea Conference
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• 2019.04a
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• pp.110-110
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• 2019

Beet (Beta vulgaris) is a crop similar to sugar beet, chard and leaf beets, and its origin is the Mediterranean coast of southern Europe and Central Asia. Among the components contained in beet, betalain, the main component of the root, has been reported to prevent lipid peroxidation induced by active oxygen and free radicals due to its high radical scavenging ability. Among these, the betalain, betanin (Betanidin 5-O-${\beta}$-glucoside) contains both phenolic and cyclic amine groups, all of which are highly electron-donating and act as antioxidants and has tyrosinase inhibitory activity. Betanin accounts for about 75-95% of the total pigment found in the beet. EM stands for effective microorganisms and is a collection of beneficial microorganisms. EM includes yeast, lactic acid bacteria, mycelia, photosynthetic bacteria, actinomycetes, etc. Human patch test according to CTFA guidelines was observed to be a safe source of no stimulation when 5% (v/v) of the EM fermentation liquid was applied to the human body. In addition, beneficial microorganisms are synergistic in the process of co-existence and cultivation and it has the effect of increasing antioxidant capacity and inhibiting corruption. This study confirms the difference in tyrosinase inhibitory activity and betanin content of beetroot extracts and EM fermented beetroot extracts. Hence, these results confirm that EM fermented beetroot extracts are highly beneficial for the human body.

• Korean Journal of Materials Research
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• v.29 no.7
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• pp.456-462
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• 2019

ZnO thin-films are grown on a p-Si(111) substrate by RF sputtering. The effects of growth temperature and $O_2$ mixture ratio on the ZnO films are investigated by scanning electron microscopy (SEM), X-ray diffraction (XRD), and room-temperature photoluminescence (PL) measurements. All the grown ZnO thin films show a strong preferred orientation along the c-axis, with an intense ultraviolet emission centered at 377 nm. However, when $O_2$ is mixed with the sputtering gas, the half width at half maximum (FWHM) of the XRD peak increases and the deep-level defect-related emission PL band becomes pronounced. In addition, an n-ZnO/p-Si heterojunction diode is fabricated by photolithographic processes and characterized using its current-voltage (I-V) characteristic curve and photoresponsivity. The fabricated n-ZnO/p-Si heterojunction diode exhibits typical rectifying I-V characteristics, with turn-on voltage of about 1.1 V and ideality factor of 1.7. The ratio of current density at ${\pm}3V$ of the reverse and forward bias voltage is about $5.8{\times}10^3$, which demonstrates the switching performance of the fabricated diode. The photoresponse of the diode under illumination of chopped with 40 Hz white light source shows fast response time and recovery time of 0.5 msec and 0.4 msec, respectively.

• Nuclear Engineering and Technology
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• v.51 no.1
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• pp.176-189
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• 2019

This paper presents a feasibility study for producing the medical isotope $^{99m}Tc$ using the hazardous and currently wasted radioisotope $^{99}Tc$. This can be achieved with the nuclear resonance fluorescence (NRF) phenomenon, which has recently been made applicable due to high-intensity laser Compton scattering (LCS) photons. In this work, 21 NRF energy states of $^{99}Tc$ have been identified as potential contributors to the photo-production of $^{99m}Tc$ and their NRF cross-sections are evaluated by using the single particle estimate model and the ENSDF data library. The evaluated cross sections are scaled using known measurement data for improved accuracy. The maximum LCS photon energy is adjusted in a way to cover all the significant excited states that may contribute to $^{99m}Tc$ generation. An energy recovery LINAC system is considered as the LCS photon source and the LCS gamma spectrum is optimized by adjusting the electron energy to maximize $^{99m}Tc$ photo-production. The NRF reaction rate for $^{99m}Tc$ is first optimized without considering the photon attenuations such as photo-atomic interactions and self-shielding due to the NRF resonance itself. The change in energy spectrum and intensity due to the photo-atomic reactions has been quantified using the MCNP6 code and then the NRF self-shielding effect was considered to obtain the spectrums that include all the attenuation factors. Simulations show that when a $^{99}Tc$ target is irradiated at an intensity of the order $10^{17}{\gamma}/s$ for 30 h, 2.01 Ci of $^{99m}Tc$ can be produced.

• Parasites, Hosts and Diseases
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• v.59 no.1
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• pp.47-53
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• 2021

Echinostoma mekongi was reported as a new species in 2020 based on specimens collected from humans in Kratie and Takeo Province, Cambodia. In the present study, its metacercarial stage has been discovered in Filopaludina martensi cambodjensis snails purchased from a local market nearby the Tonle Sap Lake, Pursat Province, Cambodia. The metacercariae were fed orally to an experimental hamster, and adult flukes were recovered at day 20 post-infection. They were morphologically examined using light and scanning electron microscopes and molecularly analyzed by sequencing of their mitochondrial cox1 and nad1 genes. A total of 115 metacercariae (1-8 per snail) were detected in 60 (60.0%) out of 100 Filopaludina snails examined. The metacercariae were round, 174 ㎛ in average diameter (163-190 ㎛ in range), having a thin cyst wall, a head collar armed with 37 collar spines, and characteristic excretory granules. The adult flukes were elongated, ventrally curved, 7.3 (6.4-8.2)×1.4 (1.1-1.7) mm in size, and equipped with 37 collar spines on the head collar (dorsal spines in 2 alternating rows), being consistent with E. mekongi. In phylogenetic analyses, the adult flukes showed 99.0-100% homology based on cox1 sequences and 98.9-99.7% homology based on nad1 sequences with E. mekongi. The results evidenced that F. martensi cambodjensis snails act as the second intermediate host of E. mekongi, and hamsters can be used as a suitable experimental definitive host. As local people favor to eat undercooked snails, these snails seem to be an important source of human infection with E. mekongi in Cambodia.

• Nuclear Engineering and Technology
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• v.54 no.10
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• pp.3641-3649
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• 2022

A simple solvothermal reaction was used to prepare a 3-aminopropyl-functionalized silica-gel-based adsorbent for adsorbing Pd(II) from the nitric acid solution. Scanning electron microscopy, fourier transform infrared spectroscopy, and thermogravimetry analysis were performed on the as-synthesized adsorbent to demonstrate the successful introduction of Schiff base groups. Batch experiments were used to investigate the effects of contact time, nitric acid concentration, solution temperature, and adsorption capacity. It is worth noting that the prepared adsorbent exhibited a higher affinity toward Pd(II) with the uptake approximately 100% even in a 2 M HNO₃ solution. At an equilibrium time of 5 h, the maximum adsorption capacity of Pd(II) was estimated to be 0.452 mmol/g. The adsorbed Pd(II) could be completely eluted by dissolving 0.2 M thiourea solution in 0.1 M HNO₃. Using a combination of particle-induced X-ray emission analysis and an X-ray photoelectron spectrometer, the adsorbed Pd was found to be uniformly distributed on the surface of the prepared adsorbent and the existing species were Pd(II) and zero-valent Pd(0). Due to the desirable performances, facile preparation method, and abundant raw material source, the prepared adsorbent demonstrated a high application potential in the recovery of Pd(II) from simulated high-level liquid waste treatment.

• Composites Research
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• v.34 no.6
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• pp.406-411
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• 2021

PEM (proton exchange membrane) fuel cells generate only water as a by-product, and thus are in the spotlight as an eco-friendly energy source. Among the various components composing the stack of the fuel cell, research on the bipolar plate that determines the efficiency of the fuel cell is being actively conducted. The composite bipolar plate has high strength, rigidity and corrosion resistance, but has the disadvantage of having a relatively low electrical conductivity. In this study, to overcome these shortcomings, a gas diffusion layer (GDL)-composite bipolar plate assembly was developed and its performance was experimentally verified. The graphite foil coating method developed in the previous study was applied to reduce the contact resistance between the bipolar plate and the GDL. In addition, in order to improve electron path in the stack and minimize the contact resistance between the GDL and the bipolar plate, a GDL-bipolar plate assembly was fabricated using a thin metal foil. As a result of the experiment, it was confirmed that the developed GDL-bipolar plate assembly had 98% lower electrical resistance compared to the conventional composite bipolar plate.

• Journal of Electrochemical Science and Technology
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• v.13 no.3
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• pp.390-397
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• 2022

The use of microwaves as the energy source for synthesis and sintering of ceramics offers substantial advantages compared to conventional gas-fired and electric resistance furnaces. Benefits include much shorter processing times and reaching the sintering temperature more quickly, resulting in superior final product quality. Most oxide ceramics poorly interact with microwave irradiation at low temperatures; thus, a more complex setup including a susceptor is needed, which makes the whole process very complicated. This investigation pursued a new approach, which enabled us to use microwave irradiation directly in poorly coupled oxides. In many solid-state electrochemical devices, the support is either metal or can be reduced to metal. Metal powders in the support can act as an internal susceptor and heat the entire cell. Then sufficient interaction of microwave irradiation and ceramic material can occur as the sample temperature increases. This microwave heating and exothermic reaction of oxidation of the support can sinter the ceramic very efficiently without any external susceptor. In this study, yttria stabilized zirconia (YSZ) and a Ni-YSZ cermet support were used as an example. The cermet was used as the support, and a YSZ electrolyte was coated and sintered directly using microwave irradiation without the use of any susceptor. The results were compared to a similar cell prepared using a conventional electric furnace. The leakage test and full cell power measurement results revealed a fully leak-free electrolyte. Scanning electron microscopy and density measurements show that microwave sintered samples have lower open porosity in the electrode support than conventional heat treatment. This technique offers an efficient way to directly use microwave irradiation to sinter thin film ceramics without a susceptor.

• Structural Engineering and Mechanics
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• v.87 no.5
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• pp.499-516
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• 2023

To defend against harmful gamma radiation, new types of materials for use in the construction of heavyweight concrete (HWC) are still needed to be developed. This research introduces new materials to be employed as a partial replacement for fine aggregate (FA) to manufacture high-performance heavyweight concrete (HPHWC). These materials include hematite, black sand, ilmenite, and magnetite, with substitution ratios of 50% and 100% of FA. In this research, the hardening and fresh characteristics of HPHWC were obtained. Concrete samples' Gamma-ray linear attenuation coefficient was evaluated utilizing a gamma source of Co-60 through the thicknesses of 2.5, 5, 7.5, 10, 12.5, and 15 cm. High temperatures were studied for HPHWC samples, which were exposed to up to 700℃ for two hours. Energy-dispersive x-rays and a scanning electron microscope carried out microstructure analyses. Magnetite as an FA attained the lowest compressive strength of 87.1 MPa, but the best radiation protection characteristics and the highest density of 3100 kg/m³ were achieved. After 28 days, the attenuation efficiency of concrete mixtures was increased by 6.5% when fine sand was replaced with black sand at a ratio of 50%. HPHWC, which contains hematite, black sand, ilmenite, and magnetite, is designed to reduce environmental and health dangers and be used in medicinal, military, and civil applications.