• Tunnel and Underground Space
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• v.4 no.2
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• pp.132-143
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• 1994

Many methods and techniques to reduce ground vibrations are well known. Some of them are to adopt electric millisecond detonators with a sequential blasting machine or an initiating system with an adequate number of delay intervals. The types of electric detonators manufactured in korea include instantaneous, decisecond and millisecond delays but numbers of delay intervals are only limited from No.1 to No.20 respectively. It is not sufficient to control accurately millisecond time with these detonators in tunnel excavation. Sequential fire time refers to adding an external time delay to a detonators norminal firing time to obtain sequential initiation and it is determined by sequential timer setting. To reduce the vibration level, sequential blasting machine(S.B.M) with decisecond detonators was adopted. A total of 134 blasts was recorede at various sites. Blast-to-structure distances ranged from 20.3 to 42.0 meter, where charge weight varied from 0.24 to 0.75 kg per delay. The results can be summarized as follow: 1. The effects of sequential blasting machine on the vibration level are discussed. The vibration level by S.B.M are decreased approximately 14.38~18.05% compare to level of conventional blasting and cycle time per round can be saved. 2. The empirical equations of particle velocity were obtained in S.B.M and conventional blasting. V=K(D/W1/3)-n, where the values for n and k are estimated to be 1.665 to 1.710 and 93.59 to 137 respectively. 3. The growth of cracks due to vibrations are found but the level fall to within allowable value.

• Korean Journal of Materials Research
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• v.21 no.11
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• pp.604-610
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• 2011

The effect of $BaF_2$ flux in $Y_3Al_5O_{12}:Ce^{3+}$(YAG:Ce) formation was investigated. Phase transformation of $Y_3Al_5O_{12}$(YAG) was characterized by using XRD, SEM, and TEM-EDS, and it was revealed that the sequential formation of the $Y_4Al_2O_9$(YAM), $YAlO_3$(YAP) and $Y_3Al_5O_{12}$(YAG) in the temperature range of 1000-1500$^{\circ}C$. Single phase of YAG was revealed from 1300$^{\circ}C$. In order to find out the effect of $BaF_2$ flux, three modeling experiments between starting materials (1.5$Al_2O_3$-2.5$Y_2O_3$, $Y_2O_3$-$BaF_2$, and $Al_2O_3$-$BaF_2$) were done. These modeling experiments showed that the nucleation process occurs via the dissolution-precipitation mechanism, whereas the grain growth process is controlled via the liquid-phase diffusion route. YAG:Ce phosphor particles prepared using a proposed technique exhibit a spherical shape, high crystallinity, and an emission intensity. According to the experimental results conducted in this investigation, 5% of $BaF_2$ was the best concentration for physical, chemical and optical properties of $Y_3Al_5O_{12}:Ce^{3+}$(YAG:Ce) that is approximately 10-15% greater than that of commercial phosphor powder.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.9
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• pp.641-646
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• 2016

Soot particles generated by fossil fuel combustion normally have fractal morphology with aggregates consisting of small spherical particles. Thus, Rayleigh or Mie elastic light scattering theory is not feasible for determining the fractal properties of soot aggregates. This paper describes a detailed process for applying Rayleigh-Debye Gans (RDG) scattering theory to effectively extract the morphological properties of any nano-scale particles. The fractal geometry of soot aggregates produced from an isooctane diffusion flame was observed using ex situ transmission electron microscopy (TEM) after thermophoretic sampling. RDG scattering theory was then used to analyze their fractal morphology, and various properties were calculated, such as the diameter of individual soot particles, number density, and volume fraction. The results show indiscernible changes during the soot growth process, but a distinct decreasing trend was observed in the soot oxidation process. The fractal dimension of the soot aggregates was determined to be around 1.82, which is in good agreement with that produced for other types of fuel. Thus, it can be concluded that the value of the fractal dimension is independent of the fuel type.

• Korean Journal of Metals and Materials
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• v.50 no.3
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• pp.201-205
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• 2012

The effects of various manganese precursors for the low-temperature selective catalytic reduction (SCR) of $NO_x$ were investigated in terms of structural, morphological, and physico-chemical analyses. $MnO_x/TiO_2$ catalysts were prepared from three different precursors, manganese nitrate, manganese acetate(II), and manganese acetate(III), by the sol-gel method. The manganese acetate(III)-$MnO_x/TiO_2$ catalyst tended to suppress the phase transition from the anatase structure to the rutile or the brookite after calcination at $500^{\circ}C$ for 2 h. It also had a high specific surface area, which was caused by a smaller particle size and more uniform distribution than the others. The change of catalytic acid sites was confirmed by Raman and FT-IR spectroscopy and the manganese acetate(III)-$MnO_x/TiO_2$ had the strongest Lewis acid sites among them. The highest de-NOx efficiency and structural stability were achieved by using the manganese cetate(III) as a precursor, because of its high specific surface area, a large amount of anatase $TiO_2$, and the strong catalytic acidity.

• Microbiology and Biotechnology Letters
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• v.49 no.3
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• pp.346-355
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• 2021

Ngoc Linh ginseng is one of the most valuable endemic medicinal herbs in Vietnam. In this study, Ngoc Linh ginseng callus was fermented by Lactobacillus plantarum ATCC 8014 (at 6, 7, and 8 log CFU/ml) to evaluate the extraction efficiency of bioactive compounds. The post-fermentation solution was spray-dried using maltodextrin with or without Stevia rebaudiana (3% and 6% v/v) as the wall material. Bioactive compounds such as polyphenols, polysaccharides, and total saponins, and L. plantarum viability during fermentation and after spray-drying, as well as under simulated gastric digestion, were evaluated in this study. The results showed that probiotic density had a significant effect on bioactive compounds, and L. plantarum at 8 log CFU/ml showed the best results with a short fermentation time compared to other tests. The total content of polyphenols, polysaccharides, and saponins reached 5.16 ± 0.18 mg GAE/g sample, 277.2 ± 6.12 mg Glu/g sample, and 4.17 ± 0.15 mg/g sample, respectively after 20 h of fermentation at the initial density of L. plantarum (8 log CFU/ml). Although there was no difference in the particle structure of the preparation, the microencapsulation efficiency of the bioactive compound in the samples containing S. rebaudiana was higher than that with only maltodextrin. The study also indicated that adding S. rebaudiana improved the viability of L. plantarum in gastric digestion. These results showed that S. rebaudiana, a component stimulating probiotic growth, combined with maltodextrin as a co-prebiotic, improved the survival rate of L. plantarum in simulated gastric digestion.

• Journal of Korea Foundry Society
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• v.39 no.1
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• pp.7-13
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• 2019

Few studies of large blooms over 700 mm thick among those used for the forging of raw materials have been reported. The cooling rate difference between the surface and the center of a large bloom is large, and the degradation of the mechanical properties is likely in cases involving excessively coarse precipitates resulted from the slow cooling rate of a large bloom after casting. Therefore, a schematic investigation of the growth behaviors of precipitates while varying their locations in blooms is necessary. The dissolution behaviors of precipitates were investigated by simulating a reheating process during which the bloom is heated to a high temperature. The segregation behavior of the as-cast large bloom was also investigated. Reheating specimens were obtained after an isothermal heat treatment at $1150^{\circ}C$ with various holding times to simulate the reheating process, with the samples undergoing a subsequent water quenching step. The precipitates were extracted using an electrolytic extractor and a particle size analysis was conducted with the aid of SEM, EDS, and TEM. In the present work, Al oxide, MnS and Nb carbide were mainly observed.

• Progress in Superconductivity and Cryogenics
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• v.20 no.4
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• pp.46-49
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• 2018

To improve in-field critical current densities ($J_c$) of $GdBa_2Cu_3O_{7-{\delta}}$ (GdBCO) coated conductors(CCs) fabricated by the reactive co-evaporation by deposition and reaction (RCE-DR) process, employing the nominal composition of Gd:Ba:Cu=1:1:2.5, we tried to refine the $Gd_2O_3$ particles trapped in the GdBCO superconducting matrix. For this purpose, we carefully selected the processing conditions on the stability phase diagram of GdBCO for this composition. By lowering the growth temperature of $Gd_2O_3$ in the liquid, we could refine the average particle size of $Gd_2O_3$ particles trapped in the GdBCO matrix and also achieve the zero-resistive transition temperatures ($T_{c,zero}$) of 92.3~94.2 K. Unfortunately, however, it was unsuccessful to achieve enhanced in-field $J_c$ values from these samples because of an air-contamination of the amorphous precursor film before its conversion into crystalline GdBCO film, suggesting that any exposure of the amorphous precursor film to air is fatal in obtaining high performance GdBCO CCs via the RCE-DR process.

• Journal of Ginseng Research
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• v.46 no.5
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• pp.621-627
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• 2022

Background: Panax ginseng (ginseng) is a traditional medicine that is reported to have cardioprotective effects; ginsenosides are the major bioactive compounds in the ginseng root. Methods: Magnetic molecularly imprinted polymer (MMIP) nanoparticles might be useful for both the extraction of the targeted (imprinted) molecules, and for the delivery of those molecules to cells. In this work, plant growth regulators were used to enhance the adventitious rooting of ginseng root callus; imprinted polymeric particles were synthesized for the extraction of ginsenoside Rb₁ from root extracts, and then employed for subsequent particle-mediated delivery to cardiomyocytes to mitigate hypoxia/reoxygenation injury. Results: These synthesized composite nanoparticles were first characterized by their specific surface area, adsorption capacity, and magnetization, and then used for the extraction of ginsenoside Rb₁ from a crude extract of ginseng roots. The ginsenoside-loaded MMIPs were then shown to have protective effects on mitochondrial membrane potential and cellular viability for H9c2 cells treated with CoCl₂ to mimic hypoxia injury. The protective effect of the ginsenosides was assessed by staining with JC-1 dye to monitor the mitochondrial membrane potential. Conclusion: MMIPs can play a dual role in both the extraction and cellular delivery of therapeutic ginsenosides.

• Nuclear Engineering and Technology
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• v.56 no.5
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• pp.1747-1753
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• 2024

The accurate determination of formation density and the physical properties of rocks is the most critical logging tasks which can be obtained using gamma-ray transport and detection tools. Though the simulation works published so far have considerably improved the knowledge of the parameters that govern the responses of the detectors in these tools, recent studies have found considerable differences between the results of using a conventional model of a homogeneous mixture of formation and fluid and an inhomogeneous fractured medium. It has increased concerns about the importance of the complexity of the model used for the medium in simulation works. In the present study, we have suggested two various models for the flow of the fluid in porous media and fractured rock to be used for logging purposes. For a typical gamma-gamma logging tool containing a ¹³⁷Cs source and two NaI detectors, simulated by using the MCNPX code, a simplified porous (SP) model in which the formation is filled with elongated rectangular cubes loaded with either mineral material or oil was investigated. In this model, the oil directly reaches the top of the medium and the connection between the pores is not guaranteed. In the other model, the medium is a large 3-D matrix of 1 cm³ randomly filled cubes. The designed algorithm to fill the matrix sites is so that this realistic random (RR) model provides the continuum growth of oil flow in various disordered directions and, therefore, fulfills the concerns about modeling the rock textures consist of extremely complex pore structures. For an arbitrary set of oil concentrations and various formation materials, the response of the detectors in the logging tool has been considered as a criterion to assess the effect of modeling for the distribution of pores in the formation on simulation studies. The results show that defining a RR model for describing heterogeneities of a porous medium does not effectively improve the prediction of the responses of logging tools. Taking into account the computational cost of the particle transport in the complex geometries in the Monte Carlo method, the SP model can be satisfactory for gamma-gamma logging purposes.

• Journal of Sensor Science and Technology
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• v.33 no.5
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• pp.288-297
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• 2024

Currently, numerous studies are being conducted on metal oxide semiconductor (MOS) gas sensors for hydrogen detection, using Palladium (Pd) and Pd-based alloy nanoparticles (NPs) owing to their hydrogen absorption ability. Furthermore, several studies have reported that Pd-Iridium (Ir) alloys possess high hydrogen absorption capabilities in their bulk state. However, Ir growth is limited to above 2 nm and it does not mix extensively with other metals. Furthermore, as the hydrogen absorption capacity decreases with the reduction in particle size, it is necessary to synthesize nanoparticles of an appropriate size. Therefore, the synthesis of Pd-Ir alloy NPs larger than 10 nm is challenging. In this study, we report the synthesis of Pd-Ir NPs with an average diameter of 19 nm using a hydrothermal technique for the first time and fabricated Pd-Ir alloy NPs through calcination at 500℃ in Ar and air. To confirm alloy formation and oxidation behavior, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were performed. In addition, we synthesized Pd-Ir@CeO₂ core-shell nanoparticles (CSNPs) as hydrogen gas-sensing materials. The Pd-Ir core was partially oxidized during heat treatment at 500℃ in air, and Pd-Ir@CeO₂ CSNPs were finally changed into Pd-Ir(alloy)/PdO-IrO₂@CeO₂ CSNPs, which exhibited higher sensitivity and selectivity toward H₂ gas compared to totally oxidized PdO-IrO₂@CeO₂ CSNPs and pure CeO₂ NPs. The enhanced gas-sensing performance was attributed to the hydrogen absorption effect of the Pd-Ir(alloy) NPs.