Deep geological disposal is generally accepted to be the most practical approach to handling radioactive wastes. Bentonite has been considered as a buffer material in deep geological disposal repositories (DGR) for high-level radioactive wastes. Evaluating the effect of short-term bentonite alteration on EBS performance has limitations in safety assessment over thousands of years. Information on bentonite characteristics under various conditions obtained from natural systems can be used to evaluate long-term safety of bentonite buffer. The purpose of this study was to investigate mineralogical and physicochemical characteristics of bentonite in the Naah mine located in Yangnam-myeon, Gyeongju-si for a natural analogue of the bentonite barrier in DGR. A total of 15 samples were collected at regular intervals from the bentonite layer and andesitic lapilli tuff (i.e., parent rock) at the boundary with the bentonite layer. The bentonite layer is located at a depth of about 1 m below the ground surface. Each sample was separated into particles < < 75 μm and particles < 2 μm through grinding and sedimentation processes. The separated subsamples were characterized mineralogically and physiochemically using various analytic techniques. Bentonite samples have a similar SiO2/Al2O3 ratio to the parent rock and a lower (Na+K)/Si ratio than the parent rock, indicating depletion of alkali components during bentonitization. The parent rock and bentonite samples have similar mineral composition (i.e., quartz, feldspars, opal-cristobalite-tridymite and montmorillonite). Results of XRD analysis on the randomly distributed particles < 2 μm indicate that bentonite is mostly composed of Ca-montmorillonite, which is a typical dioctahedral smectite. Results of FTIR and VNIR analysis indicate that montmorillonite contained in bentonite is Al-dioctahedral montmorillonite, and Al is substituted with Mg in some octahedron units. The mineralogical and physicochemical characteristics are similar regardless of sampling location. These results suggest that bentonite potentially exposed to weathering, located near the ground surface, has hardly altered.

Mitotic spindle formation is regulated by centrosomes, composed of a centriole pair surrounded by pericentriolar materials(PCM) proteins. However, mammalian oocytes rely on acentriolar MTOCs for the function of meiotic spindle. The composition of acentriolar MTOCs and the molecular precesses that regulate the localization and accumulation in mammalian oocyte are not well understood. In this study, we analyzed the mechanisms of spindle microtubule nucleation and stability from MTOCs in mouse oocyte, and indentified Centrosomal protein192(CEP192) as a key regulator for acentriolar MTOC formation. CEP192 specifically colocalized with pericentrin (PCNT) during the oocyte maturaion. CEP192 proteins are localized throughout cytoplasm and around nucleus at GV stage, and then after BD stage, CEP192 proteins were further fragmented into smaller MTOCs around chromosomes. At metaphase, CEP192 proteins were concentrated in spindle pole. Knockdown of CEP192 using siRNAs resulted in metaphase I arrest. The arrested oocytes were characterized by reduced microtubule intensity and misalignment chromosome. Also at BD and ProMI stage, the oocytes reduced microtubule density and PCNT intensity. To confirm the mechanism of CEP192 regulation, we confirmed that PLK1 and AuroraA kinase were involved in CEP192 activation. The investigations for detailed molecular mechanisms of CEP192 and RanGTP for microtubule nucleation in oocytes are underway using various techniques including siRNA, mRNA, and positive or negative dominant injection and inhibitors.

The sintering mechanisms of nanoscale copper powders have been investigated. A molecular dynamics (MD) simulation with the embedded-atom method (EAM) was employed for these simulations. The dimensional changes for initial-stage sintering such as characteristic lengths, neck growth, and neck angle were calculated to understand the densification behavior of copper nano-powders. Factors affecting sintering such as the temperature, powder size, and crystalline misalignment between adjacent powders have also been studied. These results could provide information of setting the processing cycles and material designs applicable to nano-powders. In addition, it is expected that MD simulation will be a foundation for the multi-scale modeling in sintering process.