Leptonic Generation Mixing, Noncommutative Geometry and Solar Neutrino Fluxes

Triangular mass matrices for neutrinos and their charged partners contain full information on neutrino mixing in a most concise form. Although the scheme is general and model independent, triangular matrices are typical for reducible but indecomposable representations of graded Lie algebras which, in turn, are characteristic for the standard model in noncommutative geometry. The mixing matrix responsible for neutrino oscillations is worked out analytically for two and three lepton families. The example of two families fixes the mixing angle to just about what is required by the Mikheyev-Smirnov-Wolfenstein resonance oscillation of solar neutrinos. In the case of three families we classify all physically plausible choices for the neutrino mass matrix and derive interesting bounds on some of the moduli of the mixing matrix.Comment: LaTeX, 12 page

Ex post facto authorisation in South African environmental assessment legislation: a critical review

One of the fundamental tenets underlying environmental assessment both internationally and in South Africa is that it is anticipatory in nature in that it is essentially an evaluation of the effects likely to arise from a major project or other action significantly affecting the natural or artificial environment. Environmental impact assessment (EIA) is therefore a systematic and integrative process for considering possible impacts prior to a decision being taken on whether or not a proposal should be given approval to proceed. This article argues that the current legislative basis for environmental assessment in South Africa, namely Part V of the Environment Conservation Act 73 of 1998 (ECA) and regulations made under it, reflects this philosophy. It argues that the phenomenon of ex post facto or retrospective environmental authorisation is ultra vires and thus not permissible under the current legislative regime. Finally the article outlines and assesses the environmental assessment regime under the National Environmental Management Act 107 of 1998 (NEMA) and recent amendments to it under the NEMA Amendment Act 8 of 2004, which will in future govern the environmental assessment process. The amending Act introduces a new section 24G into the anticipated environmental assessment regime which will permit ex post facto or retrospective environmental authorisation. The authors argue that this is an unwelcome development which will militate against the purposes underlying environmental assessment

Quantum Gravity coupled to Matter via Noncommutative Geometry

We show that the principal part of the Dirac Hamiltonian in 3+1 dimensions emerges in a semi-classical approximation from a construction which encodes the kinematics of quantum gravity. The construction is a spectral triple over a configuration space of connections. It involves an algebra of holonomy loops represented as bounded operators on a separable Hilbert space and a Dirac type operator. Semi-classical states, which involve an averaging over points at which the product between loops is defined, are constructed and it is shown that the Dirac Hamiltonian emerges as the expectation value of the Dirac type operator on these states in a semi-classical approximation.Comment: 15 pages, 1 figur

Ex post facto authorisation in south african environmental assessment legislation: A critical review

One of the fundamental tenets underlying environmental assessment both internationally and in South Africa is that it is anticipatory in nature in that it is essentially an evaluation of the effects likely to arise from a major project or other action significantly affecting the natural or artificial environment. Environmental impact assessment (EIA) is therefore a systematic and integrative process for considering possible impacts prior to a decision being taken on whether or not a proposal should be given approval to proceed. This article argues that the current legislative basis for environmental assessment in South Africa, namely Part V of the Environment Conservation Act 73 of 1998 (ECA) and regulations made under it, reflects this philosophy. It argues that the phenomenon of ex post facto or retrospective environmental authorisation is ultra vires and thus not permissible under the current legislative regime. Finally the article outlines and assesses the environmental assessment regime under the National Environmental Management Act 107 of 1998 (NEMA) and recent amendments to it under the NEMA Amendment Act 8 of 2004, which will in future govern the environmental assessment process. The amending Act introduces a new section 24G into the anticipated environmental assessment regime which will permit ex post facto or retrospective environmental  authorisation. The authors argue that this is an unwelcome development which will militate against the purposes underlying environmental assessment

Amplification of pip3 signalling by macropinocytic cups

In a role distinct from and perhaps more ancient than that in signal transduction, PIP3 and Ras help to spatially organize the actin cytoskeleton into macropinocytic cups. These large endocytic structures are extended by actin polymerization from the cell surface and have at their core an intense patch of active Ras and PIP3, around which actin polymerizes, creating cup-shaped projections. We hypothesize that active Ras and PIP3 self-amplify within macropinocytic cups, in a way that depends on the structural integrity of the cup. Signalling that triggers macropinocytosis may therefore be amplified downstream in a way that depends on macropinocytosis. This argument provides a context for recent findings that signalling to Akt (an effector of PIP3) is sensitive to cytoskeletal and macropinocytic inhibitors.</p

Neurohumoral stimulation in type-2-diabetes as an emerging disease concept

Neurohumoral stimulation comprising both autonomic-nervous-system dysfunction and activation of hormonal systems including the renin-angiotensin-aldosterone system (RAAS) was found to be associated with Type-2-diabetes (T2D). Therapeutic strategies such as RAAS interference proved to be beneficial in both T2D treatment and prevention. In addition to an activated RAAS, hyperleptinemia in obesity, hyperinsulinemia in conditions of peripheral insulin resistance and overall oxidative stress in T2D represent known activators of the sympathetic component of the autonomic nervous system. Here, we hypothesize that sympathetic activation may cause peripheral insulin resistance defined as partial blocking of insulin effects on glucose uptake. Resulting hyperinsulinemia or hyperglycemia-related oxidative stress may further aggravate sympatho-excitation. This notion leads to a secondary hypothesis: sympathetic activation worsens from obesity towards insulin resistance, and further towards T2D. In this review, existing evidence relating to neurohumoral stimulation in T2D and consequences thereof, such as oxidative stress and inflammation, are discussed. The aim of this review is to provide a rationale for therapies, which are able to intercept neuroendocrine pathways in T2D and precursor states such as obesity

Spin Foams and Noncommutative Geometry

We extend the formalism of embedded spin networks and spin foams to include topological data that encode the underlying three-manifold or four-manifold as a branched cover. These data are expressed as monodromies, in a way similar to the encoding of the gravitational field via holonomies. We then describe convolution algebras of spin networks and spin foams, based on the different ways in which the same topology can be realized as a branched covering via covering moves, and on possible composition operations on spin foams. We illustrate the case of the groupoid algebra of the equivalence relation determined by covering moves and a 2-semigroupoid algebra arising from a 2-category of spin foams with composition operations corresponding to a fibered product of the branched coverings and the gluing of cobordisms. The spin foam amplitudes then give rise to dynamical flows on these algebras, and the existence of low temperature equilibrium states of Gibbs form is related to questions on the existence of topological invariants of embedded graphs and embedded two-complexes with given properties. We end by sketching a possible approach to combining the spin network and spin foam formalism with matter within the framework of spectral triples in noncommutative geometry.Comment: 48 pages LaTeX, 30 PDF figure

Akt and SGK protein kinases are required for efficient feeding by macropinocytosis

Macropinocytosis is an actin-driven process of large-scale and non-specific fluid uptake used for feeding by some cancer cells and the macropinocytosis model organism Dictyostelium discoideum. In Dictyostelium, macropinocytic cups are organized by ‘macropinocytic patches’ in the plasma membrane. These contain activated Ras, Rac and phospholipid PIP3, and direct actin polymerization to their periphery. We show that a Dictyostelium Akt (PkbA) and an SGK (PkbR1) protein kinase act downstream of PIP3 and, together, are nearly essential for fluid uptake. This pathway enables the formation of larger macropinocytic patches and macropinosomes, thereby dramatically increasing fluid uptake. Through phosphoproteomics, we identify a RhoGAP, GacG, as a PkbA and PkbR1 target, and show that it is required for efficient macropinocytosis and expansion of macropinocytic patches. The function of Akt and SGK in cell feeding through control of macropinosome size has implications for cancer cell biology.<br/