General covariant geometric momentum, gauge potential and a Dirac fermion on a two-dimensional sphere

For a particle that is constrained on an ($N-1$)-dimensional ($N\geq2$) curved surface, the Cartesian components of its momentum in $N$-dimensional flat space is believed to offer a proper form of momentum for the particle on the surface, which is called the geometric momentum as it depends on the mean curvature. Once the momentum is made general covariance, the spin connection part can be interpreted as a gauge potential. The present study consists in two parts, the first is a discussion of the general framework for the general covariant geometric momentum. The second is devoted to a study of a Dirac fermion on a two-dimensional sphere and we show that there is the generalized total angular momentum whose three cartesian components form the $su(2)$ algebra, obtained before by consideration of dynamics of the particle, and we demonstrate that there is no curvature-induced geometric potential for the fermion.Comment: 8 pages, no figure. Presentation improve

Microscopy of glazed layers formed during high temperature sliding wear at 750C

The evolution of microstructures in the glazed layer formed during high temperature sliding wear of Nimonic 80A against Stellite 6 at 750 ◦C using a speed of 0.314ms−1 under a load of 7N has been investigated using scanning electron microscopy (SEM), energy dispersive analysis by X-ray (EDX), X-ray diffraction (XRD) analysis, scanning tunnelling microscopy (STM) and transmission electron microscopy (TEM). The results indicate the formation of a wear resistant nano-structured glazed layer. The mechanisms responsible for the formation of the nano-polycrystalline glazed layer are discussed

Effects of kink and flexible hinge defects on mechanical responses of short double stranded DNA molecules

We predict various detectable mechanical responses to the presence of local DNA defects which are defined as short DNA segments exhibiting mechanical properties obviously different from the 50 nm persistence length based semiflexible polymer model. The defects discussed are kinks and flexible hinges either permanently fixed on DNA or thermally excited. Their effects on extension shift, the effective persistence length, the end-to-end distance distribution, and the cyclization probability are computed using a transfer-matrix method. Our predictions will be useful in future experimental designs to study DNA nicks or mismatch base pairs, mechanics of specific DNA sequences, and specific DNA-protein interaction using magnetic tweezer, fluorescence resonance energy transfer or plasmon resonance technique, and the traditional biochemistry cyclization probability measurements.Comment: 9 pages with 9 figures. Theoretical calculation based on transfer matrix. Minor updates, a new figure and more discussions are adde

Susceptibility of Chinese grapes to grape phylloxera

Research Note

The role of early childhood development and education (ECDE) in supporting learning and well-being in rural early childhood and primary schools in South Africa

This paper examines how early childhood and primary schools can be constructed as enabling spaces to improve the learning and well-being of children aged six to nine who live in multidimensionally poor, low-resourced rural communities in South Africa. Quality early childhood development and education (ECDE) can be the catalyst to break the cycle of poverty for many young children in rural areas. A systematic review was conducted based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses flowchart. A comprehensive search strategy using electronic databases and hand searches systematically whittled down an initial database of 30,080 articles to 16 articles for this study. A thematic analysis identified enablers and constraints for supporting children’s learning and well-being across three themes: (1) infrastructure, educational resources and child agency (2) initial teacher education (ITE) and (3) socioeconomic status. The findings and discussion highlight child agency as an enabler to learning and well-being and the structural and pedagogical challenges of implementing ITE curricula specific to rural educational contexts

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