Second-order properties of locally stationary processes

Abstract.  In this article, we investigate an optimal property of the maximum likelihood estimator of Gaussian locally stationary processes by the second-order approximation. In the case where the model is correctly specified, it is shown that appropriate modifications of the maximum likelihood estimator for Gaussian locally stationary processes is second-order asymptotically efficient. We also discuss second-order robustness properties.     

Re-assessment of woodfuel supply and demand relationships in Kampong Thom Province,Cambodia

This study re-examined a previously published relationship between supply and demand for woodfuel at different spatial scales within Kampong Thom Province, Cambodia. We considered three different scales: The first was the whole area of the province. The second scale calculated village-scale data in zones of 1, 3, and 5 km from each village and then aggregated for all villages of the province. The third scale also calculated data for the three zones at the village-scale, but the data were then aggregated according to three regional groupings based on population density and forest availability. When evaluating woodfuel supply, we excluded biomass increment of trees with diameter larger than 30 cm because it was found that local people rarely collect trees larger than 30 cm for fuel. On the demand side, dead wood, which was included in the previous assessment, and woodfuel obtained from non-forest sources were excluded to enable comparison of supply and demand that related only to living trees originating from forests. The re-assessment revealed large decreases in both supply and demand at each scale as compared with our previous assessment; supply reduced by 46% and demand by 36% at the whole province scale. However, the ratios of supply to demand at each scale examined were very similar for both assessments. This re-assessment therefore supports our previous findings: there is a deficiency in woodfuel resources in areas of high population density along the main road due to high woodfuel demand and a predominance of agricultural land and regrowth forest in close proximity to villages. This study underscores the usefulness of taking detailed woodfuel consumption patterns into account when assessing the impact of woodfuel demand on forests. For a more accurate assessment on the sustainability of woodfuel resources and utilization, further research is needed to project future woodfuel demand, not only for green wood from forested sources, but also for dead wood and woodfuel from non-forested sources.     

Effect of solution composition on the optimum redox potential for chalcopyrite leaching in sulfuric acid solutions

The leaching rate of chalcopyrite (CuFeS₂) by Fe³⁺ in H₂SO₄ solutions depends on the redox potential determined by the Fe³⁺/Fe²⁺ concentration ratio, and there is a maximum leaching rate at an optimum redox potential. The present study investigated the effects of solution composition on the optimum redox potential by electrochemical measurements using a CuFeS₂ electrode and electrolyte solutions containing 0.01–1 kmol m^− 3 of H₂SO₄, Fe²⁺, and Cu²⁺ at 298 K in nitrogen.Anodic-polarization curves of the CuFeS₂ electrode showed that there was a current peak on the curves in the presence of Cu²⁺ and Fe²⁺, corresponding to the maximum leaching rate. The redox potential of the peak increased markedly with increasing Cu²⁺ concentration, while it was little affected by the H₂SO₄ and Fe²⁺ concentrations. These results agree with the results of leaching experiments reported previously, and indicate that the optimum redox potential for chalcopyrite leaching is a function of the Cu²⁺ concentration. An empirical equation for the optimum redox potential for CuFeS₂ leaching is proposed.     

Direct deposition of nanostructured Pt particles onto a Ni foam from lyotropic liquid crystalline phase by displacement plating

Nanostructured Pt particles are directly deposited onto a Ni foam by utilizing displacement plating after a lyotropic liquid crystalline phase including Pt species was prepared within macropores of the Ni foam. The EDS mapping of Pt after deposition corresponds to the macroscopic framework of the Ni foam, indicating the uniform displacement plating of Pt on the surface of the Ni foam. The Pt particles of 150-250 nm in size are formed over the entire area of the surface of the Ni foam. The TEM images prove that the nanoscale rods (width: about 3 nm) are aggregated with each other to form nanoscale porosity. The active area of Pt can be estimated to be ca. 12 m²/g by using the cyclic voltammogram in sulfuric acid. Our method realizes one-step production of hierarchical macro-meso type porous electrodes.     

Temperature dependence of anelastic behavior in 3Y-TZP ceramics

The unique anelastic behavior in 3Y-TZP has been observed under several temperatures in the range 77–353 K. By employing an elastic strain subtractor and in-situ XRD technique, we found that the anelastic deformation of 3Y-TZP occurred more easily at an elevated temperature, whereas this anelastic behavior disappears dramatically at 77 K, and that the anelastic strain was not induced by the t → m phase transformation.

In the cyclic loadings, the stress versus anelastic strain hysteresis loops were also measured at each temperature. From the shape change of these loops, the possible mechanisms of anelastic deformation of 3Y-TZP were explored. Furthermore, the cyclic softening was observed at every temperature although it was not strong at the lower temperature.

The rupture strengths of this material at different temperatures were investigated as well. It was found that the rupture strength of 3Y-TZP non-crack sample was obviously higher in the lower temperature range than in the higher temperature range. However, in pre-cracked samples, the strength reduction observed in the non-crack sample at higher temperatures could be remedied to some extent due to the mechanism related to anelastic behavior.     

Automatic control strategy for biological nitrogen removal of low C/N wastewater in a sequencing batch reactor.

To establish an automatic control system of external carbon addition in biological nitrogen removal, a bench-scale sequencing batch reactor with real-time control strategy was designed in this study. An oxidation-reduction potential (ORP) profile was used for automatic control of external carbon addition. The mean removal efficiency of total organic carbon was over 98%. Complete denitrification in an anoxic phase and complete denitrification and nitrification in anoxic and oxic phases were accomplished, respectively, because the oxic and anoxic periods were also appropriately controlled with ORP and pH profiles, respectively. Mean removal efficiency of total nitrogen was over 95%. When concentration of influent wastewater was changed, volume of additional carbon was automatically changed with the influent fluctuation, and flexible hydraulic retention time was achieved in this system.     

Mixing characteristics of a submerged jet measured using an isokinetic sampling probe

The flow properties and mixing characteristics of a submerged gas jet near the injection point were measured using an isokinetic sampling probe in a water model. The radial and axial profiles of gas velocity, water velocity, and void fraction were measured. Since the gas velocity was always larger than that of the water, the existence of a slip velocity between gas and water was confirmed. A one-dimensional mathematical model was developed using the dimensionless slip velocity as a parameter. The dimensionless slip velocity (S) was estimated to be 0.3 to 0.6 for the nitrogen-water system. TheS of the He-water system was slightly larger than that of the nitrogen-water system. When the model was applied to calculate the gas fraction in the jet for the nitrogen-mercury system,S was estimated to be 0.95 to 0.97. A large slip velocity between gas and liquid is expected for gas-metal systems. Formerly Research Associate, the Research Institute of Mineral Dressing and Metallurgy, Tohoku University     

Two levels of the Schottky barrier in CVD diamond/silicon heterojunctions at low temperature

The I–V characteristics of some CVD diamond/silicon heterojunctions measured in the temperature range of 129–295 K showed an abnormal increase in current at low voltage and temperature. The devices show a bend in reverse and forward currents due to extra current, suggesting that there are two independent contributions to the thermionic current, corresponding to two levels of the Schottky barrier. When the temperature increases, the influence of the Schottky barrier height at small voltages decreases and normal current behaviour is observed at high temperatures. Conductance curves measured at a test frequency of 200 Hz also present a bend for low voltage and temperature. To explain the atypical current behaviour, an electrical equivalent circuit model composed of two diodes in parallel with different barrier heights was proposed. The results show that lowering of the barrier height in specific areas explains the excess current at low voltage and the origin of this effect is possibly related to non-uniformity in specific regions of the material.