Highly enhanced and stable activity of defect-induced titania nanoparticles for solar light-driven CO2 reduction into CH4

Photocatalytic reduction of CO₂ to fuel offers an exciting opportunity for helping to solve current energy and global warming problems. Although a number of solar active catalysts have been reported, most of them suffer from low product yield, instability, and low quantum efficiency. Therefore, the design and fabrication of highly active photocatalysts remains an unmet challenge. In the current work we utilize hydrogen-doped, blue-colored reduced titania for photocatalytic conversion of CO₂ into methane (CH₄). The photocatalyst is obtained by exposure of TiO₂ to NaBH₄ at 350 °C for 0.5 h. Sensitized with Pt nanoparticles, the material promotes solar spectrum photoconversion of CO₂ to CH₄ with an apparent quantum yield of 12.40% and a time normalized CH₄ generation rate of 80.35 μmol g^?1 h^?1, which to the best of our knowledge is a record for photocatalytic-based CO₂ reduction. The material appears intrinsically stable, with no loss in sample performance over five 6 h cycles, with the sample heated in vacuum after each cycle.     

Pulsed electric field (PEF) technology for microbial inactivation in low-alcohol red wine

The decontamination of spoilage-related microbes in low-alcohol red wine was performed using a serial multiple electrode pulsed electric field (PEF) treatment system. The system consisted of seven electrodes connected in series, and it has been designed to produce square-wave high-voltage pulses of 1 μs duration at various electric field strengths and frequencies for decontamination. The initial counts of aerobic bacteria, yeast and lactic acid bacteria (spoilage-associated microbes) in the wine were 5.56, 5.61 and 5.22 log CFU/mL, respectively. The pattern of decontamination of the spoilage microorganisms followed first-order kinetics and the decontamination effect increased as the field strength and frequency increases. D_Hz and D_PEF values were inversely related to the electric field strength of the PEF treatment. The yeast exhibited relatively low D_PEF-value than the aerobic and lactic acid bacteria. The lowest Z_PEF-value was observed for the lactic acid bacteria (24.6 kV/cm) among the spoilage microbes.     

Very high cycle fatigue characteristics of a chrome‐molybdenum steel treated by ultrasonic nanocrystal surface modification technique

Characterization of very high cycle fatigue (VHCF) performance is of significant issue for ensuring long‐term durability and reliability of machinery and structural components due to the growing industrial demands and significant requirements of the advanced systems. In this study, VHCF characteristics of nanocrystallized skins (nanoskin) on JIS SCM435 (AISI 4137) steels were investigated as three different nanoskins on the surface, which was fabricated by altering the static load of ultrasonic nanocrystal surface modification (UNSM) treatment. The fatigue characterization, which shows linearly proportional correlation in the range of 80–120 µm depth of subsurface, was subjected to severe plastic deformation by altering the static loads of UNSM treatment to 40, 70 and 100 N, respectively. The fatigue strength increased up to 30% in the regime of VHCF. The improved strength mainly resulted from the generation of nanocrystalline structure, the enhanced surface uniformity, hardness and residual stress.     

Shock tube measurements of species time-histories in monomethyl hydrazine pyrolysis

The first measurements of NH₂ and NH₃ time-histories in monomethyl hydrazine (MMH) pyrolysis were performed behind reflected shock waves in a shock tube using laser absorption techniques. An improved measurement of MMH using IR laser absorption is also presented. MMH concentrations of ∼1% in Ar were employed, over the temperature range 941–1252 K, at pressures near 2 atm. NH₂ was measured at the peak of the overlapping doublet lines at 16739.90 cm⁻¹ (597.4 nm). NH₃ and MMH were measured using direct absorption of CO₂ laser lines at 9.22 and 10.22 μm, respectively. These measurements were then compared to a current comprehensive MMH pyrolysis mechanism based on the work of Sun et al. (2009) and Zhang et al. (2010). Based on the measurements of NH₂ and NH₃, it was possible to measure rate coefficients for two key reactions in the MMH pyrolysis system:(1)CH₃NHNH₂→CH₃NH+NH₂(2)CH₃NHNH₂+NH₂→CH₃NNH₂+NH₃These rates combined with the measured overall MMH decomposition rate strongly imply that Reaction (1) is the dominant MMH decomposition channel. The following rate coefficients (2 atm, 900–1300 K) were uniquely determined:Based on the MMH measurement, the value of the CH₃ decomposition channel is 0–20% of the NH₂ channel, and a value of 1.64 × 10⁵⁸ * T^−12.84 exp(−39580/T) s⁻¹ is recommended for the overall unimolecular decomposition of MMH. Further analysis of the NH₂ measurements indicate that the rate of the following reaction used in the Princeton mechanism should also be significantly increased:(4)CH₃NNH+NH₂→CH₃NN+NH₃The changes to the MMH pyrolysis mechanism recommended in this work result in greatly improved agreement between measured and modeled NH₂, NH₃, and MMH time-histories over the entire range of the study.     

Delay-optimal service curve allocation scheme

A service allocation scheme has been proposed in this letter, so that as many real-time sessions with deterministic delay bounds as possible can be admitted in service curve algorithms. The proposed scheme is superior to the previous scheme especially when a session passes through multiple routers.     

Degradation mechanism of GaAs MESFETs

The reliability of the Au/Pt/Ti Schottky gate of low-high doped GaAs MESFETs has been investigated by thermal step stress and accelerated life tests and their degradation mechanisms were analyzed by means of Auger electron spectroscopy, X-ray diffractometry, cross-sectional transmission electron microscopy, current-voltage, and capacitance-voltage measurements. Electrical measurements showed that the failure of the GaAs MESFETs was mainly due to the degradation of the Au/Pt/Ti/GaAs Schottky contact. An activation energy of 1.3 eV and a lifetime of 2 × 10⁸ h at 125°C for Schottky contact were evaluated. At a temperature lower than 350°C, the degradation of the Schottky contact is attributed to the decrease of net electron concentration caused by outdiffusion of host Ga atoms of GaAs. The activation energy for the decrease of net electron concentration is determined to be 1.4 eV using the capacitance-voltage measurement, which is consistent with 1.3 eV obtained by the accelerated life tests. This suggests that the major thermal degradation mechanism at a temperature lower than 350°C is the outdiffusion of Ga atoms from the channel. Meanwhile, the effective channel thickness at a temperature higher than 350°C is reduced by the formation of TiAs at the Schottky interface, the activation energy of which is determined to be 1.74 eV.     

Mechanism of lithium transport through an MCMB heat-treated at 800-1200 °C

Mechanism of lithium transport through a mesocarbon-microbeads (MCMB) heat-treated at 800-1200 °C was elucidated in 1 M LiPF₆-ethylene carbonate-diethyl carbonate (50:50 vol.%) solution by the quantitative analysis of potentiostatic current transient considering the difference in the relative amount of lithium deintercalation sites having different activation energies for lithium deintercalation. From the coincidence between the current transients experimentally measured and theoretically calculated based upon the modified McNabb-Foster equation along with ‘cell-impedance-controlled’ constraint as the governing equation with the boundary condition, respectively, it is suggested that lithium transport through the MCMB electrode is limited by the ‘cell-impedance’, and at the same time the difference in the kinetics of lithium transport between through the four different lithium deintercalation sites is due to the difference in activation energy for lithium deintercalation between from the four different lithium deintercalation sites present within the MCMB. Moreover, it is realised that since the degree of microcrystallinity of the MCMB is increased with rising heat-treatment temperature, the relative charge amount of lithium deintercalated from the lattice-site is increased, but that amount from the extra-sites is decreased. Thus, the inflexion point, i.e. ‘quasi-current plateau’ in the current transient is less clearly observed with rising heat-treatment temperature.     

Effect of particle size on the electrocatalytic activity of platinum dispersions in carbon matrix electrodes for phosphoric acid fuel cells

The loss in electrocatalytic activity of Pt particles in carbon matrix electrodes has been experimentally and theoretically investigated as a function of Pt particle size. The measurement of the cathodic potentiostatic current transient showed that a decrease in oxygen reduction current due to carboxyl group formation, relative to the oxygen reduction current in the absence of carboxyl group, increased with a decreasing Pt particle size. This relative value is a measure of the loss in specific activity. A model describing the electrocatalytic activity loss has been proposed by introducing a new parameter, characterising the effective dead active area produced by the carboxyl group formation, relative to the total active area free of the carboxyl group. The agreement of the experimentally determined relative current decrease with the calculated relative value of the effective dead active area confirms the model.