Irreducible actions and compressible modules

Any finite set of linear operators on an algebra $A$ yields an operator algebra $B$ and a module structure on A, whose endomorphism ring is isomorphic to a subring $A^B$ of certain invariant elements of $A$. We show that if $A$ is a critically compressible left $B$-module, then the dimension of its self-injective hull $A$ over the ring of fractions of $A^B$ is bounded by the uniform dimension of $A$ and the number of linear operators generating $B$. This extends a known result on irreducible Hopf actions and applies in particular to weak Hopf action. Furthermore we prove necessary and sufficient conditions for an algebra A to be critically compressible in the case of group actions, group gradings and Lie actions

Caprinocultura e ovinocultura: crescimento promissor x desorganização preocupante.

bitstream/item/52348/1/Midia-Caprinocultura-e-ovinocultura.pd

Natural and anthropogenic variations in a channelized water course in Centre of Portugal

The present study took place in the Mondego River, located in the Centre of Portugal. The lower sector of the river (Lower Mondego) is largely man-made due to regularization and rectification of the channel. The objective was to assess the impacts on the aquatic communities (fishes and benthic invertebrates). Fauna inventories were performed in June and September of 2000 and 2001, together with habitat characterization. Three sampling sites were selected in this segment and compared to a reference site located upstream. It is concluded that the presence of structures such as submerged weirs and riprap, promoted the diversity, due to the physical complexity, which they introduced into the system. The dramatic flood peaks that occurred in the winter of 2000/01 also caused substantial changes in the fluvial dynamics and in the habitats: the large amount of suspended solids transported resulted in a riverbed of unstable fine materials, and in a subsequent biological impoverishment. However, both communities displayed a high resilience to these changes; the inter-annual differences being obscured by the seasonal ones on macroinvertebrate communities.El presente trabajo tuvo lugar en el río Mondego, localizado en el Centro de Portugal. El tramo bajo del río (Bajo Mondego) se encuentra intensamente transformado debido al regularización y rectificación del cauce. El objetivo fue evaluar los impactos en las comunidades acuáticas (peces e invertebrados bentónicos). Se realizaron inventarios de fauna en Junio y Septiembre de 2000 y 2001, junto con la caracterización del hábitat. Se seleccionaron tres localidades en este segmento fluvial y se compararon con una localidad de referencia localizada aguas arriba. Se concluye que la presencia de varias estructuras como los azudes sumergidos y enrocamentos, promovió la diversidad, derivado de la complejidad física que ellos introdujeron en el sistema. Las riadas dramáticas que ocurrieron en el invierno de 2000/01 también causaron cambios sustanciales en la dinámica fluvial y en los hábitats: la gran cantidad de sólidos en suspensión transportada dio lugar a un substrato constituido por materiales finos inestables, y al empobrecimiento biológico consecuente. Sin embargo, ambas comunidades mostraron una elevada resiliencia a estos eventos, quedando las diferencias interanuales ocultadas por las diferencias estaciónales en las comunidades de invertebrados

On the electrical conductivity of composites with a polymeric matrix and a non-uniform concentration of carbon nanotubes

We present a multiscale modelling approach to explore the effects of a non-uniform concentration of carbon nanotubes (CNTs) on the electrical conductivity of CNT-polymer composites. Realistic three-dimensional representative volume elements (RVEs) are generated from a two-dimensional CNT concentration map, obtained via microscopy techniques. The RVEs capture the measured probability density function of the CNT concentration and include a length-scale to represent the details of the spatial distribution of the concentration. The homogenized conductivity of the RVEs is computed via multiscale FE analyses for different values of such length-scale, and it is compared to measurements. The modelling strategy is then used to explore the effects of the microstructural features of these materials on their electrical conductivity

Application of machine learning to predict the multiaxial strain-sensing response of CNT-polymer composites

We present predictive multiscale models of the multiaxial strain-sensing response of conductive CNT-polymer composites. Detailed physically-based finite element (FE) models at the micron scale are used to produce training data for an artificial neural network; the latter is then used, at macroscopic scale, to predict the electro-mechanical response of components of arbitrary shape subject to a non-uniform, multiaxial strain field, allowing savings in computational time of six orders of magnitude. We apply this methodology to explore the application of CNT-polymer composites to the construction of different types of sensors and to damage detection

Working Group Report on the "TeV Particle Astrophysics and Physics Beyond the Standard Model"

This working group focused mainly on the complementarity among particle physics and astrophysics. The analysis of data from both fields will better constrain theoretical models. Much of the discussion focused on detecting dark matter and susy particles, and on the potential of neutrino and gamma-ray astrophysics for seeking or constraining new physics.Comment: Report on Working Group in the TeV Particle Astrophysics Workshop II - Madison - Aug 200

Yang-Lee Zeros of the Two- and Three-State Potts Model Defined on ϕ3\phi^3 Feynman Diagrams

We present both analytic and numerical results on the position of the partition function zeros on the complex magnetic field plane of the $q=2$ (Ising) and $q=3$ states Potts model defined on $\phi^3$ Feynman diagrams (thin random graphs). Our analytic results are based on the ideas of destructive interference of coexisting phases and low temperature expansions. For the case of the Ising model an argument based on a symmetry of the saddle point equations leads us to a nonperturbative proof that the Yang-Lee zeros are located on the unit circle, although no circle theorem is known in this case of random graphs. For the $q=3$ states Potts model our perturbative results indicate that the Yang-Lee zeros lie outside the unit circle. Both analytic results are confirmed by finite lattice numerical calculations.Comment: 16 pages, 2 figures. Third version: the title was slightly changed. To be published in Physical Review

New results for the t-J model in ladders: Changes in the spin liquid state with applied magnetic field. Implications for the cuprates

Exact Diagonalization calculations are presented for the t-J model in the presence of a uniform magnetic field. Results for 2xL ladders (L=8,10,12) and 4x4 square clusters with 1 and 2 holes indicate that the diamagnetic response to a perpendicular magnetic field tends to induce a spin liquid state in the spin background. The zero-field spin liquid state of a two-leg ladder is reinforced by the magnetic field: a considerable increase of rung antiferromagnetic correlations is observed for J/t up to 0.6, for 1 and 2 holes. Pair-breaking is also clearly observed in the ladders and seems to be associated in part with changes promoted by the field in the spin correlations around the zero-field pair. In the 4x4 cluster, the numerical results seem to indicate that the field-induced spin liquid state competes with the zero-field antiferromagnetic short-range-order, the spin liquid state being favored by higher doping and smaller values of J/t. It is interesting to note that the field-effect can also be observed in a 2x2 plaquette with 1 and 2 holes. This opens up the possibility of gaining a qualitative understanding of the effect.Comment: 16 pages, 7 figures, latex New results adde