Comment on ``Theorem for nonrotating singularity-free universes''

We show that Raychaudhuri's recently proposed theorem on nonrotating universes cannot be used to rule out realistic singularity-free descriptions of the universe, as suggested by him in PRL 80, 654 (1998).Comment: 1 page, to appear in Phys.Rev.Let

Phase space solutions in scalar-tensor cosmological models

An analysis of the solutions for the field equations of generalized scalar-tensor theories of gravitation is performed through the study of the geometry of the phase space and the stability of the solutions, with special interest in the Brans-Dicke model. Particularly, we believe to be possible to find suitable forms of the Brans-Dicke parameter omega and potential V of the scalar field, using the dynamical systems approach, in such a way that they can be fitted in the present observed scenario of the Universe.Comment: revtex, 2 pages, 4 eps figures, to appear in Brazilian Journal of Physics (proceedings of the Conference 100 Years of Relativity, Sao Paulo, Brazil, August 2005

Near-horizon modes and self-adjoint extensions of the Schroedinger operator

We investigate the dynamics of scalar fields in the near-horizon exterior region of a Schwarzschild black hole. We show that low-energy modes are typically long-living and might be considered as being confined near the black hole horizon. Such dynamics are effectively governed by a Schroedinger operator with infinitely many self-adjoint extensions parameterized by $U(1)$, a situation closely resembling the case of an ordinary free particle moving on a semiaxis. Even though these different self-adjoint extensions lead to equivalent scattering and thermal processes, a comparison with a simplified model suggests a physical prescription to chose the pertinent self-adjoint extensions. However, since all extensions are in principle physically equivalent, they might be considered in equal footing for statistical analyses of near-horizon modes around black holes. Analogous results hold for any non-extremal, spherically symmetric, asymptotically flat black hole.Comment: 10 pages, 1 fig, contribution submitted to the volume "Classical and Quantum Physics: Geometry, Dynamics and Control. (60 Years Alberto Ibort Fest)" Springer (2018

Agriculture for Food and Nutrition Security: A Must For Achieving the Millennium Development Goals in Africa

The Millennium Development Goals (MDGs) underscore an overriding importance of human development for sustained economic, social, political and other development, and nutrition is the beginning of human development. Nutrition has, however, not been viewed as a development imperative in many African countries. Agricultural and health policies, projects and programmes and the conduct of agricultural and health research in most African countries do not consider nutrition to any significant degree. The paper argues that food production, poverty, malnutrition and health are very intricately linked and the result of that linkage is probably the most important determinant of development and, thus, the realization of the MDGs in Africa. It also argues that it is a misconception that food security implies or is synonymous with food and nutrition security. The paper proposes that food policies, projects, programmes and research should focus on food and nutrition security and not just food security. In that regard, the paper proposes that the following interlinked processes must be taken into consideration in agricultural policies, projects, programmes and research: (1) Effective marriage of indigenous and “scientific” knowledge in food production, processing, preservation, preparation and consumption. (2) Promotion of agrobiodiversity, including the domestication of known nutritionally-rich semi-wild plants. (3) Development of sustainable farming systems, including effective crop-livestock integration systems. (4) Development of food production-marketing-consumption-nutrition linkage processes at community levels. National and local level nutrition policy research and advocacyAgricultural and Food Policy, Community/Rural/Urban Development, Environmental Economics and Policy, Farm Management, Food Consumption/Nutrition/Food Safety, Food Security and Poverty, International Relations/Trade, Marketing, Production Economics, Research and Development/Tech Change/Emerging Technologies,

Pseudoclassical Model of Spinning Particle with Anomalous Magnetic Momentum

A generalization of the pseudoclassical action of a spinning particle in the presence of an anomalous magnetic momentum is given. The action is written in reparametrization and supergauge invariant form. The Dirac quantization, based on the Hamiltonian analyses of the model, leads to the Dirac-Pauli equation for a particle with an anomalous magnetic momentum in an external electromagnetic field. Due to the structure of first-class constraints in that case, the Dirac quantization demands for consistency to take into account an operators ordering problem.Comment: 9 pages, IFUSP/P-100