• Journal of the Korean Geotechnical Society
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• v.37 no.3
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• pp.19-30
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• 2021

The presence of the hydrate-bearing sediments in Ulleung Basin of South Korea has been confirmed from previous studies. Researches on gas production methods from the hydrate-bearing sediments have been conducted worldwide. As production mechanism is a complex phenomenon in which thermal, hydraulic, and mechanical phenomena occur simultaneously, it is difficult to accurately conduct the productivity and stability analysis of hydrate bearing sediments through lab-scale experiments. Thus, the importance of numerical analysis in evaluating gas productivity and stability of hydrate-bearing sediments has been emphasized. In this study, the numerical parametric analysis was conducted to investigate the effects of the bottom hole pressure and the depressurization rate on the gas productivity and stability of hydrate-bearing sediments during the depressurization method. The numerical analysis results confirmed that as the bottom hole pressure decreases, the productivity increases and the stability of sediments deteriorates. Meanwhile, it was shown that the depressurization rate did not largely affect the productivity and stability of the hydrate-bearing sediments. In addition, sensitivity analysis for gas productivity and stability of the sediments were conducted according to the depressurization rate in order to establish a production strategy that prevents sand production during gas production. As a result of the analysis, it was confirmed that controlling the depressurization rate from a low value to a high value is effective in securing the stability. Moreover, during gas production, the subsidence of sediments occurred near the production well, and ground heave occurred at the bottom of the production well due to the pressure gradient. From these results, it was concluded that both the productivity and stability analyses should be conducted in order to determine the bottom hole pressure when producing gas using the depressurization method. Additionally, the stress analysis of the production well, which is induced by the vertical displacements of sediments, should be evaluated.

• Korean Journal of Environmental Biology
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• v.40 no.4
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• pp.413-422
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• 2022

Barnea manilensis is a bivalve which bores soft rocks, such as, limestone or mudstone in the low intertidal zone. They make burrows which have narrow entrances and wide interiors and live in these burrows for a lifetime. In this study, the morphology and the microstructure of the valve of rock-boring clam B. manilensis were observed using a stereoscopic microscope and FE-SEM, respectively. The chemical composition of specific part of the valve was assessed by energy dispersive X-ray spectroscopy (EDS) analysis. 3D modeling and structural dynamic analysis were used to simulate the boring behavior of B. manilensis. Microscopy results showed that the valve was asymmetric with plow-like spikes which were located on the anterior surface of the valve and were distributed in a specific direction. The anterior parts of the valve were thicker than the posterior parts. EDS results indicated that the valve mainly consisted of calcium carbonate, while metal elements, such as, Al, Si, Mn, Fe, and Mg were detected on the outer surface of the anterior spikes. It was assumed that the metal elements increased the strength of the valve, thus helping the B. manilensis to bore sediment. The simulation showed that spikes located on the anterior part of the valve received a load at all angles. It was suggested that the anterior part of the shell received the load while drilling rocks. The boring mechanism using the amorphous valve of B. manilensis is expected to be used as basic data to devise an efficient drilling mechanism.

• Childhood Kidney Diseases
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• v.14 no.2
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• pp.143-153
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• 2010

Purpose: Recently, massive proteinuria has been observed in some transplant patients after switching cyclosporine A (CsA) to sirolimus. To evaluate the pathogenesis of sirolimus-associated proteinuria, we investigated the early changes in slit diaphragm molecules by various administrative conditions of sirolimus and CsA. Methods: In vitro-Mouse podocytes were incubated with buffer (C), sirolimus ($10\;{\mu}g/mL$) after CsA ($10\;{\mu}g/mL$) (C-S), sirolimus only (S) and CsA and sirolimus simultaneously (C+S) for 12, 24, and 48 hours. In vivo- twenty four SPF female Wistar rats were divided into 4 groups buffer (C), sirolimus after 2 weeks of CsA (C-S), sirolimus only (S) and CsA and sirolimus simultaneously (C+S). All groups were treated by intraperitoneal injection every other day for 4 weeks (CsA: 25 mg/kg, sirolimus: 0.5 mg/kg). The changes in mRNA of slit diaphragm molecules were examined by RT-PCR. Results: The mRNA of nephrin was significantly decreased in group C-S and C+S in vitro. In vivo, the mRNA of nephrin in all groups using sirolimus and the mRNA of podocin in group C-S and C+S were decreased. Microscopically, group C-S and C+S showed small vacuolization and calcification in proximal tubular epithelial cells. Immunohistochemistry using nephrin and podocin antibodies did not show remarkable decrease of staining along the glomerular capillaries. Electron-microscopically, focal fusion of foot processes was seen in group C-S and C+S. Conclusion: This study suggests the decrease of slit diaphragm molecules (nephrin and podocin) in podocyte may be one of the causes of sirolimus associated proteinuria, and podocyte injury by sirolimus may need a primary hit by CsA to develop the proteinuria.