Phase-Space Noncommutativity and the Dirac Equation

We consider full phase-space noncommutativity in the Dirac equation, and find that in order to preserve gauge invariance, configuration space noncommutativity must be dropped. The resulting space structure gives rise to a constant magnetic field background and this effect is explicitly seen on the spectrum of the hydrogen atom. Computing this spectrum we find a bound on the momentum noncommutative parameter $\eta$, \sqrt{\eta}\lsim2.26\mu eV/c.Comment: 11 pages. To match version to appear in Physics Letters

New occurrences of Pleurocarpous mosses for the state of Bahia, Brazil

Four new records of pleurocarpous mosses are reported for the first time for the State of Bahia: Phyllodon truncatulus (Hypnaceae), Trichosteleum brachydictyon, Sematophyllum tequendamense and Potamium lonchophyllum (Sematophyllaceae). These species were found in the Tropical Atlantic Rainforest situated in the South of Bahia

Occurrence of some Lejeuneaceae (Jungermanniophyta) in Bahia, Brazil

Five species of Lejeuneaceae, tribe Lejeuneae from state of Bahia, Brazil are described and illustrated. Data on geographic distributions, distribution in Brazil and habitat in Bahia are also given

Some new additions to the hepatic flora (Jungermanniophyta) for the State of Bahia, Brazil

In this paper are recorded 18 taxa of hepatics (Jungermanniophyta) for the first time for the state of Bahia, Brazil. Of these, Harpalejeunea ovata (Hook.) Schiffn. is new for Brazil. Morphological characters, notes on habitat and substrate are given for each species. Illustrations for Harpalejeunea ovata, Pycnolejeunea callosa (Lindenb.) Steph., Pycnolejeunea macroloba (Nees & Mont.) Schiffn., Rectolejeunea berteroana (Gott. ex Steph.) Evans and Trachylejeunea crenata (Mont. & Nees) Schust. are given

Child poverty - a discussion on conceptualization and measurement. A Portuguese case study

This work deals with child poverty. Although it is a very topical issue, it is scarcely studied by the social scientists. The analysis of this problem normally appears as a sub-product of poverty. In fact the living conditions of children cannot be divorced from the family context. Nevertheless poverty at the level of children displays its own specific features, along with a number of consequences that justify the study of childhood poverty per se. In this work the child is assumed to be a statistical unit. Therefore, from the economic point of view, the analysis of its living conditions is undertaken by considering those elements felt to be more important to its well being. In this context, a direct methodology has been adopted to directly evaluate child poverty. The paper begins by presenting the objectives of the study, as well the methodology used. The second and third points address questions related to conceptualization of the phenomenon and its quantification. This analysis allows one to make an initial distinction between the overall poverty problem and that of child poverty. The conclusions prove that, although they are interconnected, the two phenomena could be studied autonomously. The fourth point synthesizes the results of an empirical analysis of the phenomenon reviewed. To perform this analysis, a survey on the well-being of children living in an urban area was conducted through a sampling process, and its results were subsequently modeled. An econometric methodology was used to accurately verify the conclusions arising from the survey. The techniques employed are not that common in poverty studies.