Upflow anaerobic sludge blanket (UASB) treatment of supernatant of cow manure by thermal pre-treatment.

Upflow anaerobic sludge blanket (UASB) methane fermentation treatment of cow manure that was subjected to screw pressing, thermal treatment and subsequent solid-liquid separation was studied. Conducting batch scale tests at temperatures between 140 and 180 degrees C, the optimal temperature for sludge settling and the color suppression was found to be between 160-170 degrees C. UASB treatment was carried out with a supernatant obtained from the thermal treatment at the optimal conditions (170 degrees C for 30 minutes) and polymer-dosed solid-liquid separation. In the UASB treatment with a COD(Cr) loading of 11.7 kg/m3/d and water temperature of 32.2 degrees C, the COD(Cr) level dropped from 16,360 mg/L in raw water to 3,940 mg/L in treated water (COD(Cr), removal rate of 75.9%), and the methane production rate per COD(Cr) was 0.187 Nm3/kg. Using wastewater thermal-treated at the optimal conditions, also a methane fermentation treatment with a continuously stirred tank reactor (CSTR) was conducted (COD(Cr) in raw water: 38,000 mg/L, hydraulic retention time (HRT): 20 days, 35 degrees C). At the COD(Cr) loading of 1.9 kg/m3/d, the methane production rate per COD(Cr), was 0.153 Nm3/kg. This result shows that UASB treatment using thermal pre-treatment provides a COD(Cr), loading of four times or more and a methane production rate of 1.3 times higher than the CSTR treatment.     

DETERMINATION OF PALAEOSTRESSES FROM MESOSCALE SHEAR FRACTURES IN CORE SAMPLES USING THE MULTI-INVERSE METHOD

Palaeostress reconstruction is the key to quantitative characterization of fractured hydrocarbon reservoirs. In order to calculate the palaeostresses responsible for fault activity, faults in oriented core samples can be analysed and the optimal stresses can then be determined from fault-slip data in a least-squares sense. Many fractured reservoir rocks, however, include faults generated during a number of different tectonic phases. In these cases, the optimal stresses can be determined for subgroups of faults which are considered to be of approximately the same age. The difficulty with this is that criteria for accurate age-dating are often absent, especially from core samples.
Recently, the so-called "multi-inverse" method has been proposed to address this problem. This is a numerical technique for separating palaeostresses within a heterogeneous fault assemblage in the absence of a priori information on the faults'relative ages. In this paper, we apply the method to eighteen faults in two short (9m) cores from an exploration well in Hokkaido, northern Japan. The cores came from a fractured hydrocarbon reservoir and were oriented by correlation with borehole images. Core lithologies included massive Cretaceous basalts in which there was no layering which would show fault offsets; for these samples, we determined the sense of shear by studying asymmetric microstructures on the fault surfaces. The results show that the rocks have experienced six different stress regimes. In general, these are compatible with the tectonic history of the study area as inferred from the regional stratigraphy and from macroscale geological structures.
These results show that the multi-inverse method can be used to extract palaeostress data from cores, thereby providing information which will assist with the exploration of (and production from) fractured hydrocarbon reservoirs.     

New fault locating system for air-insulated substations usingoptical current detector

The authors present the basic philosophy, construction, design features, and test results of a new fault locating system. This fault locating system helps to shorten the time required for restoration of service after the occurrence of a busbar fault in an air-insulated distribution substation. Recent optical and electronic technologies allow the design of a highly accurate and compact fault locating system which consists of optical current detectors using the Faraday effect and a fault locating processor using a digital data processing technique. The fault location is carried out by discriminating between the directions of zero-sequence currents. Through various tests and field operations, it has been confirmed that the system has sufficient performance for practical applications     

Diffuse pollution in Japan: issues and perspectives.

Many parts of Japan have experienced rapid urbanization and industrialization over the past 50 years. This trend resulted in severe water pollution in many urban areas. To address the pollution problems, several measures such as construction of sewerage systems and enactment of laws and regulations have been undertaken. Because of these measures, the water quality has been improved to some extent. However, many water quality concerns still remain and are attributed in part to diffuse pollution. In this paper, historical progress, present situation and future aspects of diffuse pollution problems in Japan are reviewed. It is noted that solving diffuse pollution problems will require a combination of several measures including application of conventional treatment technologies and natural purification systems, implementation of appropriate policy measures, and promotion of citizen participation.     

Hydroliquefaction of low-sulfur coals using iron carbonyl complexes—Sulfur as catalysts

Hydroliquefaction of low-sulfur Australian coals (Wandoan and Yallourn) was studied using iron carbonyl complexes as catalyst. The addition of Fe(CO)₅ (2.8 wt% Fe of coal) increased coal conversion from 48.6 to 85.2% for Wandoan coal, and from 36.7 to 69.7% for Yallourn coal in 1-methylnaphthalene at 425°C under an initial hydrogen pressure of 50 kg cm^?2. When molecular sulfur was added to iron carbonyls (Fe(CO)₅, Fe₂(CO)₉ and Fe₃(CO)₁₂), higher coal converions ( > 92%) and higher oil yields (>46%) were obtained, along with an increase in the amount of hydrogen transferred to coal from the gas phase (0.2 to 2.8%, d.a.f. coal basis). In the liquefaction studies using a hydrogen donor solvent, tetralin, Fe(CO)₅S catalyst increased the amount of hydrogen absorbed from the gaseous phase and decreased the amount of naphthalene dehydrogenated from tetralin. The direct hydrogen transfer reaction from molecular hydrogen to coal fragment radicals seems to be a major reaction pathway. Organic sulfur compounds, dimethyldisulfide and benzothiophene, and inorganic FeS₂ and NiS were found to be good sulfur sources to Fe(CO)₅. From X-ray diffraction analyses of liquefaction residues, it is concluded that Fe(CO)₅ was converted into pyrrhotite (Fe_1?xS) when sulfur was present, but into Fe₃O₄ in the absence of sulfur.     

High-reliability GaAs-AlGaAs HBTs by MBE with Be base doping andInGaAs emitter contacts

The authors have developed a modified MBE growth process to produce high-gain n-p-n GaAs-AlGaAs heterojunction bipolar transistors (HBTs) with a mean time to failure (MTTF) of 1.5×10⁸ h at 125°C. Beryllium incorporation and diffusion are controlled through a combination of reduced substrate temperature and increased As/Ga flux ratio during MBE growth, resulting in extremely stable HBT profiles. The authors also demonstrate graded InGaAs surface layers with nonalloyed refractory metal contacts that significantly improve ohmic reliability compared to alloyed AuGe contacts. The ability to produce robust HBTs by MBE is critically important to this technology     

A novel method of suppressing the inrush current of transformers by using a series‐connected voltage‐source PWM converter

This paper proposes a novel method of suppressing the inrush current of transformers. A small‐rated voltage‐source PWM converter is connected in series to the transformers through a matching transformer. As the connected PWM converter serves as a resistor for the source current, no inrush phenomena occurs. The required rating of the PWM converter, which serves as the damping resistor for the inrush phenomena, is 1/400 that of the main transformers in single‐phase circuits. In three‐phase circuits, it is 1/900. The basic principle of the proposed method is discussed. Digital computer simulation is implemented to confirm the validity and excellent practicability of the proposed method using the PSCAD/EMTDC. A prototype experimental model is constructed and tested. The experimental results demonstrate that the proposed method can perfectly suppress the inrush phenomena. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 157(4): 56–65, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20174     

Simulation with an improved plasma model utilized to design a new structure of microwave plasma discharge for chemical vapor deposition of diamond crystals

A new structure of microwave plasma for chemical vapor deposition of diamond crystal is proposed. The structure is designed numerically, for which an improved model given in our previous work [H. Yamada et al., J. Appl. Phys. 101 (2007), art. no. 063302.] is utilized. The experimental observations and numerical predictions agree well with each other. It is demonstrated experimentally that the proposed structure can achieve a growth rate larger than 50 μm/h over an area 1 in. in diameter.     

Bonding silicon wafer to silicon nitride with spin-on glass as adhesive

Using spin-on glass (SOG) as an adhesive, an Si wafer with thermal oxide was successfully bonded to one with an RF-sputtered Si3N4 film. This ensures that SOG films are effective in bonding Si wafers to less reactive surfaces than Si or SiO2 such as silicon nitride. It was also found that the previously reported bonding procedure can be simplified by suppressing the spin-induced radial striations of the SOG films.     

Efficient photodiode-waveguide coupling for hybrid integrated optical circuits

A GalnAsP edge-detecting photodiode was coupled with an SiO2-TiO2 single-mode waveguide in a simple hybrid integration scheme. The newly developed edge-detecting photodiode with a window region was used to improve photodiode durability.