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In order to alleviate oxygen limitation and improve the yield of poly-gamma-glutamic acid (gamma-PGA) during fermentation, the Vitreoscilla hemoglobin gene (vgb) was integrated into the chromosome of Bacillus subtilis and expressed during gamma-PGA production. The activity of the expressed Vitreoscilla hemoglobin (VHb) was confirmed by CO-difference(More)
Response surface methodology (RSM) was employed to optimize medium composition for the production of a thermostable xylanase from T. lanuginosus SDYKY-1 using economical carbon and nitrogen sources (soybean meal and corncobs, respectively). Plackett-Burman (P-B) design was applied to evaluate the effects of nine variables (powdered corncobs, soybean meal,(More)
After comparing the spatial reuse efficiency between RF based networks and acoustic based networks in terms of our newly defined metric, spatial reuse index, we found that the spatial reuse efficiency in acoustic based networks is significantly lower due to the relatively low spreading loss of acoustic signals, which further degrades the network throughput.(More)
In this paper, we propose a new metric to measure the spatial reuse efficiency in networks: the spatial reuse index. We observed that the spatial reuse index in Underwater Sensor Networks (UWSNs) is significantly lower than in RF networks due to the relatively low spreading loss of acoustic signals. As a result, UWSNs generally have much lower network(More)
In this paper, we propose a multi-channel medium access control (MAC) protocol, named underwater multi-channel MAC protocol (UMMAC), for underwater acoustic networks (UANs). UMMAC is a split phase and reservation based multi-channel MAC protocol which enables hosts to utilize multiple channels via a channel allocation and power control algorithm (CAPC). In(More)
Underwater sensor networks (UWSNs) have become a hot research topic because of their various aquatic applications. As the underwater sensor nodes are powered by built-in batteries which are difficult to replace, extending the network lifetime is a most urgent need. Due to the low and variable transmission speed of sound, the design of reliable routing(More)
Physical layer security is an attractive security mechanism, which exploits the randomness characteristics of wireless transmission channel to achieve security. However, it is hampered by the limitation of the channel condition that the main channel must be better than the eavesdropper channel. To alleviate the limitation, cooperative communication is(More)