Effect of temperature on microbial community of a glucose-degrading methanogenic consortium under hyperthermophilic chemostat cultivation

We continuously fed an anaerobic chemostat with synthetic wastewater containing glucose as the sole source of carbon and energy to study the effects of temperature on the microbial community under hyperthermophilic (65-80 degrees C) conditions. Methane was produced normally up to 77.5 degrees C at a dilution rate of 0.025 d(-1). However, the concentration of microorganisms and the rate of gas production decreased with increasing operation temperature. The microbial community in the chemostat at various temperatures was analyzed based on the 16S rRNA gene using molecular biological techniques including clone library analysis and denaturing gradient gel electrophoresis (DGGE). Aceticlastic methanogens related to Methanosarcina thermophila were detected at 65 degrees C and hydrogenotrophilic methanogens related to Methanothermobacter thermautotrophicus were the dominant methanogens between 70 degrees C to 77.5 degrees C. Bacteria related to Clostridium stercorarium and Thermoanaerobacter subterraneus comprised the dominant glucose-fermenting bacteria at temperatures of 65 degrees C and above, respectively. Bacteria related to Thermacetogenium phaeum and to Tepidiphilus margaritifer and Petrobacter succinatimandens were the dominant acetate-oxidizing bacteria at 70 degrees C and at 75-77.5 degrees C, respectively. The results suggested that, at temperatures of 70 degrees C and above, methane production via the aceticlastic pathway was negligible and indirect methanogenesis from acetate was dominant. Since acetate oxidation is a rate limiting step and a higher temperature favors the hydrolysis and acid formation, a two stage fermentation process, acidogenic and methanogenic fermentation stages operated under different temperatures, should be more suitable for the thermophilic anaerobic treatment at temperatures above 65 degrees C.     

Emission factor for antimony in brake abrasion dusts as one of the major atmospheric antimony sources

Abrasion tests were conducted using a brake dynamometer to determine the antimony (Sb) emission factor originating from automobiles. Abrasion dusts from commercially available brake pads (nonasbestos organic type) were emitted into an enclosed chamber under various braking conditions in terms of initial driving speed and deceleration. Suspended dusts inside the chamber were collected on a quartz fiber filter and weighed. From the experimental data, dust emission could be regressed as a function of the initial kinetic energy loading and the braking time. Using the regression function, the emission factors of brake abrasion dusts under the typical braking conditions (initial driving speed; 50 km/h, deceleration; 1.0 m/s2) were calculated as 5.8 mg/braking/car for PM10 and 3.9 mg/braking/car for PM2.5. The elemental composition of the collected dusts indicated that the fraction originating from disk wear contributed to approximately 30% of the suspended dusts. From these analytical results, it was concluded that the Sb emission factors originating from automobiles were approximately 32 microg Sb/braking/car for PM10 and 22 microg Sb/ braking/car for PM2.5. These essential data will contribute to the modeling of atmospheric Sb concentration alongside roadways and also to the better understanding of Sb source apportionment.     

Observation of Remanent Vortices Attached to Rough Boundaries in Superfluid 4He

We report the study on remanent vortices attached to rough boundaries in superfluid ⁴He after the turbulent transition. We used 2.6 µm vibrating wires with smooth surfaces and rough surfaces, a cover box and slow cooling method, in order to investigate the effect of surface roughness on the condition and the number of vortices attached to a wire. The responses of the wire with smooth surfaces show large hysteresis at the turbulent transition. This result indicates that remanent vortices attached between the wire and surrounding boundaries cause turbulence. At first sweep of driving force of the wire with rough surfaces, we also observed hysteresis as large as the case of the smooth wire: at the other sweeps, however, small hysteresis was observed. These results indicate that once turbulence is generated at a wire velocity during first sweep, vortex lines newly attach between rough surfaces of the wire, which easily cause turbulence at a low wire velocity. Therefore, we conclude that a smooth wire can reduce the number of vortices attached to a wire.     

Two parallel penny-shaped or annular cracks in a functionally graded piezoelectric strip under electric loading

In this paper, the mixed-mode fracture problem of a functionally graded piezoelectric material strip with two penny-shaped or annular cracks is considered. It is assumed that the electroelastic properties of the strip vary continuously along the thickness of the strip, and that the strip is under electric loading. The problem is formulated in terms of a system of singular integral equations, which are solved numerically. Numerical calculations are carried out, and the stress and electric displacement intensity factors are presented for various values of dimensionless parameters representing the crack size, the crack location, and the material nonhomogeneity.     

Luminosity monitor for the venus detector at TRISTAN

We constructed a luminosity monitor of the lead-scintillator sandwich type for the VENUS detector at the e⁺e⁻ collider TRISTAN. Photomultiplier tubes with transmissive mesh dynodes could be operated fairly well in a high magnetic field and hence the readout optics system was considerably simplified. We present the performance of the luminosity monitor for e⁺e⁻ collisions at √s = 50 and 52 GeV.     

High-resolution electron microscopy of a SiC/SiC joint brazed by a Ag-Cu-Ti alloy

A high-resolution electron microscope observation (HREM) was performed on the joined portion of a brazed polycrystalline or single crystal SiC to itself with (Ag-28wt% Cu) + 2wt% Ti alloy foil. The brazing was done under vacuum at temperatures of 800° C to 950° C with a holding period of up to 30 min. Reaction products formed at the joined interface were found to be mainly TiC. In the specimen brazed at 800° C with the holding time of 0 min, reaction product TiC formed itself into small crystallites with a diameter of less than 20 nm, and an amorphous like layer was found between SiC and TiC. On the other hand, TiC was formed as a layer along the joined interface for the specimen brazed at 950° C for the holding time of 30 min. Lattice matching of SiC to TiC crystals appeared to be good so the high bonding strength of the joint was attributed to the formation of this epitaxial interface between SiC and TiC.     

In situ HVEM studies on the effects of electron-irradiation on the thermal stability of Ni-based amorphous alloys

In situ high voltage electron microscope (HVEM) studies on the thermal stability of splat-cooled Ni-based amorphous alloys were made and three kinds of accelerated crystallization modes were observed during bombardment by focused 1000 keV electrons. In one case the crystalline grains induced by irradiation were coarser near the edge of the irradiated region (IR) than in other parts. This type of crystallization was observed in Ni₇₅B₁₇Si₈ and Ni₇₅B₁₅Si₈C₂ amorphous alloys subjected to a continuous increase in temperature of irradiation. The second case was one where there was no appreciable difference in size distribution of the crystalline grains throughout the IR. This type was observed in a Ni₈₀P₁₀B₁₀ amorphous alloy which again was subjected to a continuous increase in irradiation temperature and also observed in Ni₇₅B₁₇Si₈ amorphous alloy irradiated during isothermal annealing. In these two cases, the crystalline grains induced during irradiation did not cover the whole of the IR before crystallization started in the unirradiated region. In the third case, however, the amorphous phase completely disappeared from the IR before crystallization in the unirradiated region occurred. This type of crystallization was observed in Ni₈₀P₂₀ amorphous alloy whilst the temperature was being increased continuously during irradiation.