Spatiotemporal studies of black spruce forest soils and implications for the fate of C

Post-fire storage of carbon (C) in organic-soil horizons was measured in one Canadian and three Alaskan chronosequences in black spruce forests, together spanning stand ages of nearly 200 yrs. We used a simple mass balance model to derive estimates of inputs, losses, and accumulation rates of C on timescales of years to centuries. The model performed well for the surface and total organic soil layers and presented questions for resolving the dynamics of deeper organic soils. C accumulation in all study areas is on the order of 20–40 gC/m2/yr for stand ages up to ∼200 yrs. Much larger fluxes, both positive and negative, are detected using incremental changes in soil C stocks and by other studies using eddy covariance methods for CO2. This difference suggests that over the course of stand replacement, about 80% of all net primary production (NPP) is returned to the atmosphere within a fire cycle, while about 20% of NPP enters the organic soil layers and becomes available for stabilization or loss via decomposition, leaching, or combustion. Shifts toward more frequent and more severe burning and degradation of deep organic horizons would likely result in an acceleration of the carbon cycle, with greater CO2 emissions from these systems overall

Positive solutions for the fractional Schrödinger equations with logarithmic and critical non-linearities

In this paper, we study a class of fractional Schrödinger equations involving logarithmic and critical non-linearities on an unbounded domain, and show that such an equation with positive or sign-changing weight potentials admits at least one positive ground state solution and the associated energy is positive (or negative). By applying the Nehari manifold method and Ljusternik–Schnirelmann category, we investigate how the weight potential affects the multiplicity of positive solutions, and obtain the relationship between the number of positive solutions and the category of some sets related to the weight potential

Tandem photoelectrochemical cells for solar water splitting

Photoelectrochemical (PEC) water splitting without an external bias is a potential solution to the growing energy crisis because this method can directly convert solar energy into chemical energy. A tandem cell is a frequently used configuration for unassisted overall water splitting because of the advantages that each component are tied together to form a highly efficient integration. A tandem PEC water splitting device is based on different photoelectrode absorbers, and there are two main models including photoanode/photocathode (PEC/PEC) and photoelectrode/photovoltaic (PEC/PV) tandem cells. In this review, we will focus on the concepts, configurations and recent progress of PEC/PEC and PEC/PV cells. Light absorption and energy band matching are the key points to enhance the solar-to-hydrogen (STH) efficiency. Promoting the performance of a standalone semiconductor material and finding new materials, coupled with an optimized configuration, are future steps for the practical application of tandem PEC cells

PREDICTION OF MULTIAXIAL LOAD FATIGUE LIFE FOR RUBBER BUSHING

The calculation methods of the maximum principal engineering strain,maximum principal logarithmic strain,maximum principal Green-Lagrange strain,and maximum principal Euler strain and octahedron shear strain peak under uniaxial and multiaxial loading stress condition are studied. It is found that the five damage parameters can be calculated only by outputting the deformation gradient tensor of the dangerous area in the finite element analysis. Based on the fatigue crack initiation theory and the fatigue test data of dumbbell rubber test piece,the life prediction models are established by the above five damage parameters,and the accuracy of the five life prediction models is measured by the goodness of fit value. Among them,the life prediction model with octahedron shear strain peak as damage parameter has the best fitting value. The fatigue life prediction model is established based on the fatigue crack growth theory and the crack growth test data of one-sided notch,pure shear specimen. The life prediction model with octahedral shear strain peak as damage parameter and the life prediction model based on crack growth theory were used to predict the life of the same bushing product respectively. It is found that the life prediction model with octahedral shear strain peak as damage parameter has better prediction effect,and the predicted life is near the triple scatter line of the measured life

Promotion effect of metal phosphides towards electrocatalytic and photocatalytic water splitting

Abstract Hydrogen evolution from water splitting over semiconductors has been considered one of the most promising ways to address energy shortages and environmental pollution. Searching for low‐cost, highly efficient, and durable catalysts is the key to improve the hydrogen production rate. Expensive noble metals, such as Pt and Au, are generally loaded onto semiconductors to promote photocatalytic activity. Metal phosphides are promising candidates to replace noble metals in hydrogen generation via electrocatalytic or photocatalytic water splitting due to their low hydrogen‐producing overpotential, tunable electronic structure, high electrical conductivity, and low price. In this review article, the characteristics and synthetic methods of metal phosphides are briefly introduced, and the development of metal phosphides for electrocatalytic or photocatalytic water splitting is presented. Finally, the challenges and future directions of metal phosphides are discussed

Photocatalytic H2 or O2 Evolution over A-Site Deficient Perovskite-Type Compounds La1/3MO3 (M = Nb, Ta) from Aqueous Solutions

Two compounds La1/3MO3 (M = Nb, Ta) with A-site deficient perovskite-type structure were synthesized by the solid state reaction method. The photocatalytic properties of these compounds were characterized by H2 evolution with Pt cocatalyst from CH3OH/H2O solution and by O2 evolution from AgNO3 aqueous solution under UV light irradiation. The results showed that the average rate of H2 evolution was about 61.07 μmol h-1 for La1/3NbO3 and 95.79 μmol h-1 for La1/3TaO3 after 24 hours of reaction time, while the initial rate of O2 evolution was 26.31 μmol h-1 for La1/3NbO3 and 16.21 μmol h-1 for La1/3TaO3, respectively. H2 evolution was also observed over La1/3MO3 (M = Nb, Ta) with NiO cocatalyst from pure water under UV light irradiation