Changes of microbial characteristics of retained sludge during low-temperature operation of an EGSB reactor for low-strength wastewater treatment.

In this study, a lab scale EGSB reactor was operated for 400 days to investigate the influence of temperature-decrease on the microbial characteristic of retained sludge. The EGSB reactor was started-up at 15 degrees C seeding with 20 degrees C-grown granular sludge. The influent COD of synthetic wastewater was set at 0.6-0.8 gCOD/L. The process-temperature was stepwise reduced from 15 degrees C to 5 degrees C during 400 days operation. Decrease of temperature of the reactor from 15 degrees C to 10 degrees C caused the decline of COD removal efficiency. However, continuous operation of the EGSB reactor led the efficient treatment of wastewater (70% of COD removal, 50% of methane recovery) at 10 degrees C. We confirmed that the both acetate-fed and hydrogen-fed methanogenic activities of retained sludge clearly increased under 15 to 20 degrees C. Changes of microbial profiles of methanogenic bacteria were analyzed by 16S rDNA-targeted DGGE analysis and cloning. It shows that genus Methanospirillum as hydrogen-utilizing methanogen proliferated due to low temperature operation of the reactor. On the other hand, genus Methanosaeta presented in abundance as acetoclastic-methanogen throughout the experiment.     

Effects of temperature and substrate concentration on biological hydrogen production from starch

This study investigates the effects of temperature and substrate concentration on biological hydrogen production from starch using mixed cultures. In this work, although hydrogen was successfully produced under the thermophilic condition, stable hydrogen production was not observed under the mesophilic condition. In the thermophilic reactor, the maximum hydrogen yield was 2.8 mol H₂/mol glucose at 20 g/l-starch; however, hydrogen yield decreased drastically with the change of by-product distribution when substrate concentration was over 30 g/l-starch. A negative correlation was observed between the hydrogen yield and the total concentration of undissociated acids.     

Switching mechanism of sensor-motor coordination through an oscillator network model.

Insects have small brains, but their behavior is highly adaptive; this leads us to conclude that their brains possess a simple adaptation mechanism. This paper focuses on the pheromone processing of crickets, varying their aggression depending on their global neural connection, and proposes a behavior selection mechanism that can be controlled by network transformation. The controller is composed of an oscillator network, and its behavior is decided by the synchrony of organic oscillations. Furthermore, every network component corresponds to a certain brain module. A model is realized by using an analog circuit, and it is applied to a simple robot that displays the behavior of a real insect.     

Hydrolytic activity of alpha-amylase in anaerobic digested sludge.

Hydrolysis is usually considered to be a rate-limiting step in anaerobic digestion. For improving anaerobic solid waste treatments, it is essential to elucidate the mechanism of hydrolysis. In this study, alpha-amylase, one of the hydrolytic enzymes, was investigated for the elucidation of more precise mechanism of hydrolysis. Alpha-amylase activity of solid starch-degrading bacteria (SDB) was estimated through batch experiments with several different substrates and with distinction between cell-bound and cell-free alpha-amylase. Monitoring of newly isolated strains of SDB was done by fluorescence in situ hybridization. Results indicated that cell-bound alpha-amylase is chiefly responsible for the hydrolysis in the digested sludge, providing very useful information that the contact between microbial cells and solids is significantly important. The activity of alpha-amylase of the digested sludge remained quite low when not required, but increased as they recognized appropriate substrates. Several-fold higher activity was obtained for starch or maltose as compared to glucose only.     

Effects of boron-doping and heat-treatment on the electrical resistivity of carbon nanohorn-aggregates

Boron-doping of carbon nanohorn-aggregates was carried out by using arc-vaporization of a boron-containing composite carbon rod in a balanced gas of Ar with 5% of O₂. Transmission and scanning electron microscopy revealed that the obtained sample powder consisted of high purity nanohorn-aggregates. The temperature dependence of the electrical resistivity of a pellet formed from the sample indicated a feature based on the three-dimensional variable-range hopping (3D-VRH) conduction. From the analyses of 3D-VRH, it was found that the electronic density of states near the Fermi-level, N(0), was enhanced due to the boron-doping, reaching an enhancement factor of ∼1.7 × 10³ compared with the N(0) of the un-doped nanohorns. Moreover, the magnitude of the electrical resistivity decreased as the boron concentration increased. The electrical resistivity of the un-doped nanohorns also decreased with heat-treatment, but the N(0) value did not change significantly. These facts suggest that the change in N(0) should be associated with the boron atoms that are substitutionally doped in the sp²-bonded carbon network.     

k-Coteries for tolerating network 2-partition

A network partition, which makes it impossible for some pairs of processes to communicate with each other, is one of the most serious network failures. Although the notion of k-coterie is introduced to design a k-mutual exclusion algorithm that is robust against network failures, the number of processes allowed to simultaneously access the critical section may fatally decrease once network partition occurs. We discuss how to construct a k-coterie such that the k-mutual exclusion algorithm adopting it is robust against a network 2-partition. To this end, we introduce the notion of complemental k-coterie, and show that complemental k-coteries meet our requirements. We then give methods for constructing complemental k-coteries, and show a necessary and sufficient condition for a k-coterie to be complemental.     

Optimal Formally Self-Dual Codes over ?5 and ?7

In this paper, we study optimal formally self-dual codes over ?₅ and ?₇. We determine the highest possible minimum weight for such codes up to length 24. We also construct formally self-dual codes with highest minimum weight, some of which have the highest minimum weight among all known linear codes of corresponding length and dimension. In particular, the first known [14, 7, 7] code over ?₇ is presented. We show that there exist formally self-dual codes which have higher minimum weights than any comparable self-dual codes. Received: May 18, 1998; revised version: September 4, 1999