A model for Hopfions on the space-time S^3 x R

We construct static and time dependent exact soliton solutions for a theory of scalar fields taking values on a wide class of two dimensional target spaces, and defined on the four dimensional space-time S^3 x R. The construction is based on an ansatz built out of special coordinates on S^3. The requirement for finite energy introduces boundary conditions that determine an infinite discrete spectrum of frequencies for the oscillating solutions. For the case where the target space is the sphere S^2, we obtain static soliton solutions with non-trivial Hopf topological charges. In addition, such hopfions can oscillate in time, preserving their topological Hopf charge, with any of the frequencies belonging to that infinite discrete spectrum.Comment: Enlarged version with the time-dependent solutions explicitly given. One reference and two eps figures added. 14 pages, late

Hole-LO phonon interaction in InAs/GaAs quantum dots

We investigate the valence intraband transitions in p-doped self-assembled InAs quantum dots using far-infrared magneto-optical technique with polarized radiation. We show that a purely electronic model is unable to account for the experimental data. We calculate the coupling between the mixed hole LO-phonon states using the Fr\"ohlich Hamiltonian, from which we determine the polaron states as well as the energies and oscillator strengths of the valence intraband transitions. The good agreement between the experiments and calculations provides strong evidence for the existence of hole-polarons and demonstrates that the intraband magneto-optical transitions occur between polaron states

Potencial produtivo e implicações para o manejo de capoeiras em áreas de agricultura tradicional no nordeste paraense.

bitstream/item/40139/1/ComTec56.pd

Generating derivative structures: Algorithm and applications

We present an algorithm for generating all derivative superstructures--for arbitrary parent structures and for any number of atom types. This algorithm enumerates superlattices and atomic configurations in a geometry-independent way. The key concept is to use the quotient group associated with each superlattice to determine all unique atomic configurations. The run time of the algorithm scales linearly with the number of unique structures found. We show several applications demonstrating how the algorithm can be used in materials design problems. We predict an altogether new crystal structure in Cd-Pt and Pd-Pt, and several new ground states in Pd-rich and Pt-rich binary systems

A reaction-diffusion model for the growth of avascular tumor

A nutrient-limited model for avascular cancer growth including cell proliferation, motility and death is presented. The model qualitatively reproduces commonly observed morphologies for primary tumors, and the simulated patterns are characterized by its gyration radius, total number of cancer cells, and number of cells on tumor periphery. These very distinct morphological patterns follow Gompertz growth curves, but exhibit different scaling laws for their surfaces. Also, the simulated tumors incorporate a spatial structure composed of a central necrotic core, an inner rim of quiescent cells and a narrow outer shell of proliferating cells in agreement with biological data. Finally, our results indicate that the competition for nutrients among normal and cancer cells may be a determinant factor in generating papillary tumor morphology.Comment: 9 pages, 6 figures, to appear in PR

Argamassas multifuncionais para armazenamento de calor, despoluição do ar e auto-limpeza, processo para a sua preparação e utilização

Patente Portuguesa n.º PT 106935A presente invenção diz respeito a argamassas, para aplicação no revestimento interior e exterior de sistemas construtivos, que compreende misturas, em diferentes proporções, de microcápsulas de materiais de mudança de fase (PCM) e nanopartículas de dióxido de titânio, juntamente com um ou mais ligantes, à base de cal, cimento ou gesso, agregados, água e outros materiais auxiliares. A invenção diz também respeito a um processo para a elaboração das referidas argamassas por mistura prévia e homogeneização, em seco, dos componentes sólidos, com posterior mistura com água e homogeneização numa máquina misturadora. A argamassa de acordo com a invenção é utilizada no revestimento interior e exterior de sistemas construtivos, com o objectivo de poupar energia, melhorar a qualidade do ar e assegurar auto-limpeza.Fundação para a Ciência e a Tecnologia (FCT