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Cross-flow filtration of culture broth from Aureobasidium pullulans, which elaborates pullulan, was done with a thin channel-type module and microfiltration membranes made of different materials and with different pore sizes. Various factors affecting the results of the filtration were studied. The specific resistance of the microbial cake was found to be higher than that of bakers' yeast, the cells of which are about the same size as an A. pullulans cell, and resistance increased with cultivation time. The flux and transmission of pullulan through the membrane decreased with cultivation time as the specific resistance increased. The flux and transmission of pullulan depended on the structure and pore size of the membrane and also on the pH of the broth. With a polysulphone membrane with a nominal pore size of 2.0 microns, transmission was nearly 100% with negligible leakage of cells and the flux was high when the pH of the broth was adjusted to 2.0.

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In low-power wireless networks, maintaining multihop connectivity is considered effective in constructing communication routes between individual nodes to a gateway. Since sensor networks are typically used for data collection, multihop routing protocols are designed to find routes optimal in upward directions. As sensor networks become widely applied to diverse applications, efficient downward traffic delivery also becomes important. To achieve this, we consider an asymmetric transmission power-based network (APN), where a power-supplied gateway uses high-power radios to cover the entire network via single-hop transmission, whereas common nodes use low-power transmissions. For effective APN operations, we propose a single-hop downlink protocol (SHDP) that consists of direct downlink transmission, local acknowledgment, neighbor forwarding, and contention resolution among the destination’s neighbors. We evaluate SHDP through mathematical analysis, simulations, and testbed experiments. Our proposal outperforms other competitive multihop routing protocols. Specifically, SHDP shows high packet delivery performance and lowers the duty cycle greatly while reducing the packet transmission overhead by >50%.

To improve the performance of cross-flow membrane filtration of pullulan broth from Aureobasidium pullulans, the effect of the cultivation conditions was examined. In particular, the sucrose concentration in the medium was changed over a wide range. By decreasing the sucrose concentration the distribution of morphology of the microbial cells in the broth changed; the yeast-like form became predominant and, as a result, the specific resistance of the microbial cake was lowered. When the broth was fermented with a sucrose concentration of 2.5% or lower, the filtration characteristics were greatly improved by periodic closure of permeation during cross-flow filtration.

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