Storage of a lithium-ion secondary battery under micro-gravity conditions

‘HAYABUSA’ is a Japanese inter-planetary spacecraft built for the exploration of an asteroid named ‘ITOKAWA.’ The spacecraft is powered by a 13.2 Ah lithium-ion secondary battery. To realize maximum performance of the battery for long flight operation, the state-of-charge (SOC) of the battery was maintained at ca. 65% during storage, in case it is required for a loss of attitude control. The capacity of the battery was measured during flight operations. Along with the operation in orbit, a ground-test battery was discharged, and both results showed a good agreement. This result confirmed that the performance of the lithium-ion secondary battery stored under micro-gravity conditions is predictable using a ground-test battery.     

Synthesis of polystyrenes having 2-pyridylthio group and their use as phase transfer catalysts for the reduction of carbonyl compounds by sodium borohydride

p-(2-Pyridylthiomethyl)styrene (PTMS) and p-(2-pyridylthioethyl)styrene (PTES) were prepared from the reactions of 2-pyridinethiol with p-chloromethylstyrene and with p-bromoethylstyrene, respectively. These monomers are readily polymerized in the presence of AIBN. From the copolymerization of PTMS with styrene, Q_PTMS = 1.19 and e_PTMS = 0.24 were obtained. The resulting polymers can extract alkali metal ions such as sodium and potassium cations. The extraction ability increases with increasing the density of active sites in polymers. Further these polymers serve as phase transfer catalysts for the reduction of carbonyl compounds by sodium borohydride.     

Reinforcement of rubber using radial single-walled carbon nanotube soot and its shock dampening properties

A soot composed of radial single-walled carbon nanotubes (r-SWCNTs), in which 70 nm length nanotubes are grown radially around the core metal particles, and nanohorn-like carbons (NHCs) was used as reinforcement for a styrene-butadiene rubber (SBR). The fracture stress of r-SWCNT soot (38 phr)/SBR was 6.3 MPa at 60% strain. Furthermore, the hardness value of r-SWCNT soot (38 phr)/SBR was 94, which is 1.38 times larger, and larger than carbon black/SBR. Additionally, the resilience of r-SWCNT soot/SBR with 38 phr filler content was markedly lower than 20% in comparison with standard carbon black filler. These results indicate that r-SWCNT soot/SBR possesses excellent kinetic energy absorbing properties.     

Synthesis of carbon nanotubes by microwave plasma-enhanced hot filament chemical vapor deposition

A combined system of microwave plasma-enhanced chemical vapor deposition (MPECVD) and hot filament CVD (HFCVD) has been developed for the growth of various carbon nanotubes, where the source gas (methane) can be decomposed independently through microwave plasma and hot tungsten filament. It is found that microwave plasma provides more efficiently carbon sources for the growth of carbon nanotubes (CNTs). By the help of microwave plasma, long CNTs array with length of 0.3 mm and high-density single-walled carbon nanotubes (SWNTs) have been grown by thermal CVD and hot filament CVD, respectively. Raman spectra of the SWNTs reveal high crystalline as well as narrow diameter distribution.     

Formation of GdAlO3–Al2O3 composite having fine pseudo-eutectic microstructure

GdAlO₃ and Al₂O₃ powders were mixed and pulverized using ball mills. The prepared powder was sintered by SPS at 1450 °C without holding time. SEM observation of the sintered specimen showed a eutectic-like microstructure. This is called ‘pseudo-eutectic’ in this research. The microstructure formed from a powder pulverized by a tumbling ball mill for one week was much finer than that by a planetary ball mill for 5 and 10 h. The fine homogeneous eutectic-like (pseudo-eutectic) microstructures could be formed at both eutectic and off-eutectic compositions. In case of crystallization from a melt of eutectic components, homogeneous eutectic microstructures can be formed only at restricted compositions very close to the eutectic one. Coarse primary crystals generally exist in the eutectic microstructure at off-eutectic compositions. The pseudo-eutectic microstructures can be formed at any compositions because a mixing ratio of the starting powders can be varied.     

Toward data representation with spiking neurons

Notable advances in the understanding of neural processing were made when sensory systems were investigated from the viewpoint of adaptation to the statistical structure of their input space. For this purpose, mathematical methods for data representation were used. Here, we point out that emphasis on the input structure has been at the cost of the biological plausibility of the corresponding neuron models which process the natural stimuli. The signal transformation of the data representation methods does not correspond well to the signal transformations happening at the single-cell level in neural systems. Hence, we now propose data representation by means of spiking neuron models. We formulate the data representation problem as an optimization problem and derive the fundamental quantities for an iterative learning scheme. This work was presented in part at the 12th International Symposium on Artificial Life and Robotics, Oita, Japan, January 25–27, 2007