On Clifford Subalgebras, Spacetime Splittings and Applications

Z2-gradings of Clifford algebras are reviewed and we shall be concerned with an alpha-grading based on the structure of inner automorphisms, which is closely related to the spacetime splitting, if we consider the standard conjugation map automorphism by an arbitrary, but fixed, splitting vector. After briefly sketching the orthogonal and parallel components of products of differential forms, where we introduce the parallel [orthogonal] part as the space [time] component, we provide a detailed exposition of the Dirac operator splitting and we show how the differential operator parallel and orthogonal components are related to the Lie derivative along the splitting vector and the angular momentum splitting bivector. We also introduce multivectorial-induced alpha-gradings and present the Dirac equation in terms of the spacetime splitting, where the Dirac spinor field is shown to be a direct sum of two quaternions. We point out some possible physical applications of the formalism developed.Comment: 22 pages, accepted for publication in International Journal of Geometric Methods in Modern Physics 3 (8) (2006

Chemical Evolution of the Galaxy Based on the Oscillatory Star Formation History

We model the star formation history (SFH) and the chemical evolution of the Galactic disk by combining an infall model and a limit-cycle model of the interstellar medium (ISM). Recent observations have shown that the SFH of the Galactic disk violently variates or oscillates. We model the oscillatory SFH based on the limit-cycle behavior of the fractional masses of three components of the ISM. The observed period of the oscillation ($\sim 1$ Gyr) is reproduced within the natural parameter range. This means that we can interpret the oscillatory SFH as the limit-cycle behavior of the ISM. We then test the chemical evolution of stars and gas in the framework of the limit-cycle model, since the oscillatory behavior of the SFH may cause an oscillatory evolution of the metallicity. We find however that the oscillatory behavior of metallicity is not prominent because the metallicity reflects the past integrated SFH. This indicates that the metallicity cannot be used to distinguish an oscillatory SFH from one without oscillations.Comment: 21 pages LaTeX, to appear in Ap

Pathway Weathering in Granitoid Rocks from Central Region of Angola: Geochemical and Mineralogical Data

The Central Region of Angola is characterized by the abundance of granitoid rocks, whose weathering “in situ” originated the so-called residual soils. The textural, geochemical and mineralogical properties of these soils depend not only on the chemical composition of parent rock, but mainly on the local climatic and geomorphological characteristics. In the study area, sampling sites were selected, which extend from the region of Kwanza- Norte (Kassenda, Dondo) through Kwanza-Sul (Cangulo, Quibala and Waco Kungo) until the plateau of Huambo, where samples of fresh rock, weathered rock and its residual soil were collected along each weathering profile. Chemical analytical data were determined using X-ray fluorescence (XRF) analysis of the major and minor elements, whereas mineralogical data were determined using X-ray diffraction (XRD), on the samples of rock and on the respective residual soil. The results obtained and their comparative analysis between the sampling sites, as well as along each weathering profile is presented. This paper allows contributing to the knowledge of the geochemical weathering in tropical areas, as is the case of Angola

Reconstructing Deconstruction: High-Velocity Cloud Distance Through Disruption Morphology

We present Arecibo L-band Feed Array 21-cm observations of a sub-complex of HVCs at the tip of the Anti-Center Complex. These observations show morphological details that point to interaction with the ambient halo medium and differential drag within the cloud sub-complex. We develop a new technique for measuring cloud distances, which relies upon these observed morphological and kinematic characteristics, and show that it is consistent with H-alpha distances. These results are consistent with distances to HVCs and halo densities derived from models in which HVCs are formed from cooling halo gas.Comment: 8 pages, 2 figures, 1 tabe, Accepted to Ap

A backwards approach to the formation of disk galaxies I. Stellar and gas content

A simple chemical enrichment code is described where the two basic mechanisms driving the evolution of the ages and metallicities of the stellar populations are the star formation efficiency and the fraction of gas ejected from the galaxy. Using the observed Tully-Fisher relation in different passbands as a constraint, it is found that a steep correlation between the maximum disk rotational velocity and star formation efficiency must exist either for a linear or a quadratic Schmidt law. Outflows do not play a major role. The redshift evolution of disk galaxies is explored, showing that a significant change in the slope of the Tully-Fisher relation is expected because of the different age distributions of the stellar components in high and low-mass disk galaxies. The slope measured in the rest frame B,K bands is found to change from 3(B); 4(K) at z=0 up to 4.5(B); 5(K) at z~1, with a slight dependence on formation redshift.Comment: Accepted for publication in ApJ. Uses emulateapj.sty. 12 pages with 10 embedded EPS figure

Phase transitions in simplified models with long-range interactions

We study the origin of phase transitions in some simplified models with long range interactions. For the ring model, we show that a possible new phase transition predicted in a recent paper by Nardini and Casetti from an energy landscape analysis does not occur. Instead of such phase transitions we observe a sharp, although without any non-analiticity, change from a core-halo to an only core configuration in the spatial distribution functions for low energies. By introducing a new class of solvable simplified models without any critical points in the potential energy, we show that a similar behaviour to the ring model is obtained, with a first order phase transition from an almost homogeneous high energy phase to a clustered phase, and the same core-halo to core configuration transition at lower energies. We discuss the origin of these features of the simplified models, and show that the first order phase transition comes from the maximization of the entropy of the system as a function of energy an an order parameter, as previously discussed by Kastner, which seems to be the main mechanism causing phase transitions in long-range interacting systems

Estimates of genetic parameters for physic nut traits based in the germplasm two years evaluation.

Apesar do crescente interesse no plantio do pinhão manso, os esforços de melhoramento ainda estão em seu início. Nesse contexto, um importante recurso recentemente estabelecido visando a futuros trabalhos de melhoramento foi a montagem de um banco de germoplasma com cerca de 200 acessos. O objetivo deste estudo foi estimar parâmetros genéticos, coeficientes de repetibilidade e correlações genéticas entre sete características, mensuradas em 110 acessos (famílias de meios-irmãos) desse banco de germoplasma em diferentes estágios de desenvolvimento. Os resultados demonstram que valores elevados de variância genética aditiva foram encontrados apenas para produção e altura e a existência de baixa variação ambiental (tanto de natureza temporária quanto permanente) entre parcelas dentro de blocos. Dado os altos valores de repetibilidade encontrados para todas as características, em média três mensurações são necessárias para se predizer, acurada e eficientemente, o real valor de melhoramento de um indivíduo. Baseado nos resultados de correlações genéticas, esforços de melhoramento devem inicialmente ser usados para se identificar árvores de elevado diâmetro de caule, elevado número de ramos e volume de copa, de modo a aumentar as chances de se encontrar árvores excepcionalmente produtivas

Energy of general 4-dimensional stationary axisymmetric spacetime in the teleparallel geometry

The field equation with the cosmological constant term is derived and the energy of the general 4-dimensional stationary axisymmetric spacetime is studied in the context of the hamiltonian formulation of the teleparallel equivalent of general relativity (TEGR). We find that, by means of the integral form of the constraints equations of the formalism naturally without any restriction on the metric parameters, the energy for the asymptotically flat/de Sitter/Anti-de Sitter stationary spacetimes in the Boyer-Lindquist coordinate can be expressed as $E=\frac{1}{8\pi}\int_S d\theta d\phi(sin\theta \sqrt{g_{\theta\theta}}+\sqrt{g_{\phi\phi}}-(1/\sqrt{g_{rr}})(\partial{\sqrt{g_ {\theta\theta} g_{\phi\phi}}}/\partial r))$. It is surprised to learn that the energy expression is relevant to the metric components $g_{rr}$, $g_{\theta\theta}$ and $g_{\phi\phi}$ only. As examples, by using this formula we calculate the energies of the Kerr-Newman (KN), Kerr-Newman Anti-de Sitter (KN-AdS), Kaluza-Klein, and Cveti\v{c}-Youm spacetimes.Comment: 12 page