Variations in Δ14C of humic substances in the Lake Biwa waters

Carbon isotopes (13C and 14C) were used to study the characteristics and origin of humic substances in water samples from Lake Biwa in Japan. Humic substances were isolated from surface lake waters in each season by the XAD extraction method and their carbon isotopic ratios were measured by accelerator mass spectrometry. The Δ14C values of Biwa humic and fulvic acids indicate that these substances consist mainly of pre-bomb 14C. There is a negative correlation between Δ14C and δ13C values for the Biwa fulvic acids. The fulvic acid consists of younger organic materials with lower δ13C value in January, but older organics with higher δ13C in April and October. The major part of fulvic acid may be supplied from soil solution and/or groundwater in the watershed and their contribution varies with season

Gene transfer by electroporation into protoplasts isolated from mulberry calli

For callus induction, explants were excised from the roots of mulberry seedlings grown in a medium containing 10-5 M 6-benzylaminopurine and subject to culture in a solid medium supplemented with 10-6 M 2, 4-dichlorophenoxyacetic acid and 10-6 M thidiazuron. The isolated calli were repeatedly subcultured in the liquid medium, resulting in a faster-growing callus line. In this callus line, clumps of 20-30 cells, which were highly meristematic, were released into the medium. Protoplasts were enzymatically isolated from these clumped cells, and transfer of the B-glucuronidase (GUS) gene by electroporation was carried out at various pulse voltages. Histochemical observation showed that successful transient expression of the GUS gene was accomplished in 20-30% of protoplasts at the specified pulse voltages

Pore-scale imaging of asphaltene-induced pore clogging in carbonate rocks

We propose an experimental methodology to visualize asphaltene precipitation in the pore space of rocks and assess the reduction in permeability. We perform core flooding experiments integrated with X-ray microtomography (micro-CT). The simultaneous injection of pure heptane and crude oil containing asphaltene induces the precipitation of asphaltene in the pore space. The degree of precipitation is controlled by the measurement of differential pressure across the sample. After precipitation, doped heptane is injected to replace the fluid to enhance the contrast between precipitated asphaltene and doped heptane. The micro-CT images are segmented into three phases: void, precipitated asphaltene, and rock. In the experiment, we observed that the precipitated asphaltene which occupied 39.1% of the pore volume caused a 29-fold reduction in permeability. Furthermore, we analyze the spatial distribution of precipitated asphaltene which showed that the asphaltene tended to clog the larger pores. We also computed the flow field numerically on the images and obtained good agreement between simulated and measured permeability. The distribution of local velocity showed that after precipitation the flow was confined to narrow channels in the pore space. This method can be applied to any type of porous system with precipitation