Biochar enhances soil hydraulic function but not soil aggregation in a sandy loam

© 2018 British Society of Soil Science Biochar has the potential to modify soil structure and soil hydraulic properties because of its small particle density, highly porous structure, grain size distribution and surface chemistry. However, knowledge of the long-term effects of biochar on soil physical properties under field conditions is limited. Using an 8-year field trial, we investigated the effects of successive additions of high-dose maize-cob-derived biochar (9.0 t ha −1 year −1 , HB), low-dose maize-cob-derived biochar (4.5 t ha −1 year −1 , LB), straw return (SR) and control (no biochar or straw, CK) on soil aggregate distribution, three-dimensional (3-D) pore structure, hydraulic conductivity and water retention in the upper 10 cm of a sandy loam soil from the North China Plain. Results showed that LB and HB treatments increased soil organic C content by 61.0–116.3% relative to CK. Interestingly, biochar amendment did not enhance the proportion of macroaggregates (> 2 and 0.25–2 mm) or aggregate stability, indicating limited positive effects on soil aggregation. The HB treatment decreased soil bulk density, and increased total porosity and macroporosity (> 30 μm). The retention of soil water, including gravitational water (0–33 kPa), capillary water (33–3100 kPa) and hygroscopic water (> 3100 kPa), was improved under HB soil. The HB and LB treatments increased plant-available water content by 17.8 and 10.1%, respectively, compared with CK. In contrast, SR showed no significant increase in soil porosity and water retention capacity but improved the water stability of macroaggregates. We concluded that biochar used in the coarse-textured soil enhanced saturated hydraulic conductivity and water-holding capacity, but did not improve soil aggregation. Highlights: Pore structure and hydraulic properties were studied in an 8-year biochar-amended sandy loam. HB (high-dose biochar) increased total soil porosity and CT-identified macroporosity (> 30 μm). Water retention improved under HB soil. Biochar addition had no effect on the formation of macroaggregates

New measurement of θ13\theta_{13} via neutron capture on hydrogen at Daya Bay

This article reports an improved independent measurement of neutrino mixing angle $\theta_{13}$ at the Daya Bay Reactor Neutrino Experiment. Electron antineutrinos were identified by inverse $\beta$-decays with the emitted neutron captured by hydrogen, yielding a data-set with principally distinct uncertainties from that with neutrons captured by gadolinium. With the final two of eight antineutrino detectors installed, this study used 621 days of data including the previously reported 217-day data set with six detectors. The dominant statistical uncertainty was reduced by 49%. Intensive studies of the cosmogenic muon-induced $^9$Li and fast neutron backgrounds and the neutron-capture energy selection efficiency, resulted in a reduction of the systematic uncertainty by 26%. The deficit in the detected number of antineutrinos at the far detectors relative to the expected number based on the near detectors yielded $\sin^22\theta_{13} = 0.071 \pm 0.011$ in the three-neutrino-oscillation framework. The combination of this result with the gadolinium-capture result is also reported.Comment: 26 pages, 23 figure

Improved Measurement of the Reactor Antineutrino Flux and Spectrum at Daya Bay

A new measurement of the reactor antineutrino flux and energy spectrum by the Daya Bay reactor neutrino experiment is reported. The antineutrinos were generated by six 2.9~GW$_{\mathrm{th}}$ nuclear reactors and detected by eight antineutrino detectors deployed in two near (560~m and 600~m flux-weighted baselines) and one far (1640~m flux-weighted baseline) underground experimental halls. With 621 days of data, more than 1.2 million inverse beta decay (IBD) candidates were detected. The IBD yield in the eight detectors was measured, and the ratio of measured to predicted flux was found to be $0.946\pm0.020$ ($0.992\pm0.021$) for the Huber+Mueller (ILL+Vogel) model. A 2.9~$\sigma$ deviation was found in the measured IBD positron energy spectrum compared to the predictions. In particular, an excess of events in the region of 4-6~MeV was found in the measured spectrum, with a local significance of 4.4~$\sigma$. A reactor antineutrino spectrum weighted by the IBD cross section is extracted for model-independent predictions.Comment: version published in Chinese Physics

Rubber Impact on 3D Textile Composites

A low velocity impact study of aircraft tire rubber on 3D textile-reinforced composite plates was performed experimentally and numerically. In contrast to regular unidirectional composite laminates, no delaminations occur in such a 3D textile composite. Yarn decohesions, matrix cracks and yarn ruptures have been identified as the major damage mechanisms under impact load. An increase in the number of 3D warp yarns is proposed to improve the impact damage resistance. The characteristic of a rubber impact is the high amount of elastic energy stored in the impactor during impact, which was more than 90% of the initial kinetic energy. This large geometrical deformation of the rubber during impact leads to a less localised loading of the target structure and poses great challenges for the numerical modelling. A hyperelastic Mooney-Rivlin constitutive law was used in Abaqus/Explicit based on a step-by-step validation with static rubber compression tests and low velocity impact tests on aluminium plates. Simulation models of the textile weave were developed on the meso- and macro-scale. The final correlation between impact simulation results on 3D textile-reinforced composite plates and impact test data was promising, highlighting the potential of such numerical simulation tools