Regularisation of Chiral Gauge Theories

This article gives a review of the topic of regularising chiral gauge theories and is aimed at a general audience. It begins by clarifying the meaning of chirality and goes on to discussing chiral projections in field theory, parity violation and the distinction between vector and chiral field theories. It then discusses the standard model of electroweak interactions from the perspective of chirality. It also reviews at length the phenomenon of anomalies in quantum field theories including the intuitive understanding of anomalies based on the Dirac sea picture as given by Nielsen and Ninomiya. It then raises the issue of a non-perturbative and constructive definition of the standard model as well as the importance of such formulations. The second Nielsen-Ninomiya theorem about the impossibility of regularising chiral gauge theories under some general assumptions is also discussed. After a brief review of lattice regularisation of field theories, it discusses the issue of fermions on the lattice with special emphasis on the problem of species doubling. The implications of these problems to introducing chiral fermions on the lattice as well as the interpretations of anomalies within the lattice formulations and the lattice Dirac sea picture are then discussed. Finally the difficulties of formulating the standard model on the lattice are illustrated through detailed discussions of the Wilson-Yukawa method, the domain wall fermions method and the recently popular Ginsparg-Wilson method.Comment: LATEX, 26 pages, 7 fig

Relationship between Tree Density and Grass Dry Matter Yield in a Southern African Savanna

The investigation was carried out on a densely wooded area in the Mopani savanna of South Africa. Seven plots were subjected to different intensities of tree thinning, ranging from a totally cleared plot (0 %) to plots thinned to the equivalent of 10 %, 20 %, 35 %, 50 % and 75 % of the leaf biomass of a control plot (100 %). The grasses responded positively to the tree thinning in terms of total dry matter yield. The yields between tree canopies were generally of the same order or higher than under tree canopies, with the yields where trees have been removed initially the highest. At high tree densities, yields differed little between seasons of varying rainfall. No quantitative advantages of C. mopane trees on the grass layer could be established, and the highest grass DM yields were recorded in plots where all trees were removed. The relationship between grass DM yield and tree density (expressed as Evapotranspiration Tree Equivalents ha-1) was curvilinear, best described by the exponential regression equation

The Influence of Tree Thinning and Tree Species on the Dry Matter Yield of Grasses of a Bush Encroached Semi-Arid Savanna in South Africa

The Acacia erubescens-Combetum apiculatum dominated savanna of South Africa is water-limited and an increase in woody plant abundance suppresses the grasses. This is the major reason why thinning or total clearing of all woody plants is often considered by landowners. The objectives of this study were to investigate the influence of intensity of tree thinning and tree species on grass yields in a semi-arid South African savanna

Quadrotor Tour Guide

This poster describes an quadrotor built with projecting capabilities at the Robotics, Intelligent Sensing & Control (RISC) laboratory. A smart and autonomous quadrotor that can fly in a specified path. It has the ability to identify the QR code, scan it and pass the information to the android application. The android application will try to lookup the information related to the QR Code. And the projector mounted on the top of the drone will help in projecting the information

Tree thinning as an option to increase herbaceous yield of an encroached semi-arid savanna in South Africa

BACKGROUND: The investigation was conducted in a savanna area covered by what was considered an undesirably dense stand of Colophospermum mopane trees, mainly because such a dense stand of trees often results in the suppression of herbaceous plants. The objectives of this study were to determine the influence of intensity of tree thinning on the dry matter yield of herbaceous plants (notably grasses) and to investigate differences in herbaceous species composition between defined subhabitats (under tree canopies, between tree canopies and where trees have been removed). Seven plots (65 × 180 m) were subjected to different intensities of tree thinning, ranging from a totally cleared plot (0 %) to plots thinned to the equivalent of 10 %, 20%, 35 %, 50% and 75 % of the leaf biomass of a control plot (100 %) with a tree density of 2711 plants ha(-1). The establishment of herbaceous plants (grasses and forbs) in response to reduced competition from the woody plants was measured during three full growing seasons following the thinning treatments. RESULTS: The grass component reacted positively to the tree thinning in terms of total dry matter (DM) yield, but forbs were negatively influenced. Rainfall interacted with tree density and the differences between grass DM yields in thinned plots during years of below average rainfall were substantially higher than those of the control. At high tree densities, yields differed little between seasons of varying rainfall. The relation between grass DM yield and tree biomass was curvilinear, best described by the exponential regression equation. Subhabitat differentiation by C. mopane trees did provide some qualitative benefits, with certain desirable grass species showing a preference for the subhabitat under tree canopies. CONCLUSION: While it can be concluded from this study that high tree densities suppress herbaceous production, the decision to clear/thin the C. mopane trees should include additional considerations. Thinning of C. mopane with the exclusive objective of increasing productivity of the grass layer would thus invariably involve a compromise situation where some trees should be left for the sake of the qualitative benefits on the herbaceous layer, soil enrichment, provision of browse and stability of the ecosystem