Methanogenic pathway and community structure in a thermophilic anaerobic digestion process of organic solid waste

The methanogenic pathway and microbial community in a thermophilic anaerobic digestion process of organic solid waste were investigated in a continuous-flow stirred-tank reactor using artificial garbage slurry as a feedstock. The decomposition pathway of acetate, a significant precursor of CH₄ and a key intermediate metabolite in the anaerobic digestion process, was analyzed by using stable isotopes. A tracer experiment using ¹³C-labeled acetate revealed that approximately 80% of the acetate was decomposed via a non-aceticlastic oxidative pathway, whereas the remainder was converted to methane via an aceticlastic pathway. Archaeal 16S rRNA analyses demonstrated that the hydrogenotrophic methanogens Methanoculleus spp. accounted for > 90% of detected methanogens, and the aceticlastic methanogens Methanosarcina spp. were the minor constituents. The clone library targeting bacterial 16S rRNA indicated the predominance of the novel Thermotogales bacterium (relative abundance: ~ 53%), which is related to anaerobic acetate oxidizer Thermotoga lettingae TMO, although the sequence similarity was low. Uncultured bacteria that phylogenetically belong to municipal solid waste cluster I were also predominant in the microflora (~ 30%). These results imply that the microbial community in the thermophilic degrading process of organic solid waste consists exclusively of unidentified bacteria, which efficiently remove acetate through a non-aceticlastic oxidative pathway.     

Fluctuation analysis of partial discharge pulse occurrence with an integral equation

This paper proposes an integral equation to describe the stochastic fluctuation of partial discharge (PD) occurrence under sinusoidal voltage stress based on a simple PD model. In the model, the stochastic behavior of PD fluctuation is assumed to arise from the fluctuation of the PD delay time after the inception voltage is built up across a discharge gap. For simplicity of calculation, the delay time is assumed to have an exponential distribution. Based on these assumptions, it is found that the proposed integral equation provides the basic characteristics such as the PD pulse distribution in the applied voltage phase angle domain. The authors have solved the equation numerically and demonstrate several ?–n distribution patterns with average delay times of 0.05 to 5 ms at low applied voltage. The solution is compared with PD characteristics obtained by Monte Carlo simulation based on the same PD model, and good agreement is found. © 2001 Scripta Technica, Electr Eng Jpn, 136(1): 16–28, 2001     

3D imaging of lightning channel and leader progression velocity

Three‐dimensional imaging of lightning channels by means of UHF interferometers is performed. To realize this, a field campaign was conducted with two observation sites in Darwin, Australia. The distance between the two sites is about 14 km, and the triangulation scheme is applied to estimate locations of UHF radiation sources. Since the UHF radiation is more likely during the leader progression than in the return stroke phase, imaging of lightning channels is obtained mainly for downward leaders. Velocities of downward leaders are estimated and statistics are presented for first and subsequent strokes. The result is consistent with those of former investigations obtained by optical observations. The statistics for the velocity of leader propagation inside thunderclouds are presented herein. Using optical measurement, velocity estimation of leader progressions inside thunderclouds is impossible, and the presented results are concluded to be the first results of their kind. © 2001 Scripta Technica, Electr Eng Jpn, 137(3): 22–28, 2001     

The accuracy and parametric sensitivity of algebraic models for turbulent flow and convection

Predictions of turbulent flow and convection in round tubes, channels and concentric circular annuli based on a correlating equation for the fraction of the shear stress due to turbulence have previously been shown to be within the scatter of the best experimental data. However, the sufficiency of this agreement has been questioned because of the scatter and limitations in scope of that data. As a supplementary test, the sensitivity of the predictions to each of the numerical empiricisms and arbitrary functions of the model has been investigated. On the whole, the uncertainties in these values and functions are not found to influence the predictions significantly.     

Morphological study by TEM on uniaxially oriented thin films of PBT

We prepared uniaxially oriented thin films of poly(butylene terephthalate) (PBT) by applying shear strain to the melt and studied their resulting morphology by transmission electron microscopy (TEM), and could show visually that stacked-lamellar structures are formed in aromatic polyesters. On the basis of crystallographic consideration, we assigned each of the recognized stacked-lamellar structures to a shish-kebab structure or a part of it. In addition, we successfully demonstrated that in one shish-kebab structure all or almost all kebabs (namely, lamellae) have a same crystallographic orientation.     

Origins of Improved Hole‐Injection Efficiency by the Deposition of MoO3 on the Polymeric Semiconductor Poly(dioctylfluorene‐alt‐benzothiadiazole)

The electronic structure of the interfaces formed after deposition of MoO₃ hole‐injection layers on top of a polymer light‐emitting material, poly(dioctylfluorene‐alt‐benzothiadiazole) (F8BT), is studied by ultraviolet photoelectron spectroscopy (UPS), X‐ray photoelectron spectroscopy and metastable atom electron spectroscopy. Significant band bending is induced in the F8BT film by MoO₃ “acceptors” that spontaneously diffuse into the F8BT “host” probably driven by kinetic energy of the deposited hot MoO₃. Further deposition leads to the saturation of the band bending accompanied by the formation of MoO₃ overlayers. Simultaneously, a new electronic state in the vicinity of the Fermi level appears on the UPS spectra. Since this peak does not appear in the bulk MoO₃ film, it can be assigned as an interface state between the MoO₃ overlayer and underlying F8BT film. Both band bending and the interface state should result from charge transfer from F8BT to MoO₃, and they appear to be the origin of the hole‐injection enhancement by the insertion of MoO₃ layers between the F8BT light‐emitting diodes and top anodes.     

Highly thermal conductive metal/carbon composites by pulsed electric current sintering

Various composites with metals such as aluminum and copper, and carbons such as pitch based carbon fiber and carbon nanotube, and scale-like graphite have been prepared to realize high thermal conductive materials utilizing pulsed electric current sintering method. The composites have high thermal conductivity and one- or two-dimensional low thermal expansion coefficient.