Discrete Dynamical Systems: A Brief Survey

Dynamical system is a mathematical formalization for any fixed rule that is described in time dependent fashion. The time can be measured by either of the number systems - integers, real numbers, complex numbers. A discrete dynamical system is a dynamical system whose state evolves over a state space in discrete time steps according to a fixed rule. This brief survey paper is concerned with the part of the work done by José Sousa Ramos [2] and some of his research students. We present the general theory of discrete dynamical systems and present results from applications to geometry, graph theory and synchronization

Superlens made of a metamaterial with extreme effective parameters

We propose a superlens formed by an ultra-dense array of crossed metallic wires. It is demonstrated that due to the anomalous interaction between crossed wires, the structured substrate is characterized by an anomalously high index of refraction and supports strongly confined guided modes with very short propagation wavelengths. It is theoretically proven that a planar slab of such structured material makes a superlens that may compensate for the attenuation introduced by free-space propagation and restore the subwavelength details of the source. The bandwidth of the proposed device can be quite significant since the response of the structured substrate is non-resonant. The theoretical results are fully supported by numerical simulations.Comment: Accepted for publication in Phys. Rev. B (in press

Modeling the input history of programs for improved instruction-memory performance

When a program is loaded into memory for execution, the relative position of its basic blocks is crucial, since loading basic blocks that are unlikely to be executed first places them high in the instruction-memory hierarchy only to be dislodged as the execution goes on. In this paper we study the use of Bayesian networks as models of the input history of a program. The main point is the creation of a probabilistic model that persists as the program is run on different inputs and at each new input refines its own parameters in order to reflect the program's input history more accurately. As the model is thus tuned, it causes basic blocks to be reordered so that, upon arrival of the next input for execution, loading the basic blocks into memory automatically takes into account the input history of the program. We report on extensive experiments, whose results demonstrate the efficacy of the overall approach in progressively lowering the execution times of a program on identical inputs placed randomly in a sequence of varied inputs. We provide results on selected SPEC CINT2000 programs and also evaluate our approach as compared to the gcc level-3 optimization and to Pettis-Hansen reordering

Assessing consistency of fish survey data : uncertainties in the estimation of mackerel icefish (Champsocephalus gunnari) abundance at South Georgia

Acknowledgments The authors wish to thank the crews, fishermen and scientists who conducted the various surveys from which data were obtained, and Mark Belchier and Simeon Hill for their contributions. This work was supported by the Government of South Georgia and South Sandwich Islands. Additional logistical support provided by The South Atlantic Environmental Research Institute with thanks to Paul Brickle. Thanks to Stephen Smith of Fisheries and Oceans Canada (DFO) for help in constructing bootstrap confidence limits. Paul Fernandes receives funding from the MASTS pooling initiative (The Marine Alliance for Science and Technology for Scotland), and their support is gratefully acknowledged. MASTS is funded by the Scottish Funding Council (grant reference HR09011) and contributing institutions. We also wish to thank two anonymous referees for their helpful suggestions on earlier versions of this manuscript.Peer reviewedPostprin

BOND: Bayesian Oxygen and Nitrogen abundance Determinations in giant H II regions using strong and semi-strong lines

We present BOND, a Bayesian code to simultaneously derive oxygen and nitrogen abundances in giant H II regions. It compares observed emission lines to a grid of photoionization models without assuming any relation between O/H and N/O. Our grid spans a wide range in O/H, N/O and ionization parameter U, and covers different starburst ages and nebular geometries. Varying starburst ages accounts for variations in the ionizing radiation field hardness, which arise due to the ageing of H II regions or the stochastic sampling of the initial mass function. All previous approaches assume a strict relation between the ionizing field and metallicity. The other novelty is extracting information on the nebular physics from semi-strong emission lines. While strong lines ratios alone ([O III]/Hbeta, [O II]/Hbeta and [N II]/Hbeta) lead to multiple O/H solutions, the simultaneous use of [Ar III]/[Ne III] allows one to decide whether an H II region is of high or low metallicity. Adding He I/Hbeta pins down the hardness of the radiation field. We apply our method to H II regions and blue compact dwarf galaxies, and find that the resulting N/O vs O/H relation is as scattered as the one obtained from the temperature-based method. As in previous strong-line methods calibrated on photoionization models, the BOND O/H values are generally higher than temperature-based ones, which might indicate the presence of temperature fluctuations or kappa distributions in real nebulae, or a too soft ionizing radiation field in the models.Comment: MNRAS in press; 21 pages, 22 figures, 2 tables; code, data and results available at http://bond.ufsc.b

A Caldeira do Fogo : génese e evolução das formas do relevo

Projecto de investigação apresentado à Universidade dos Açores para obtenção do grau de doutor em Geografia.Prova complementar de doutoramento.Olhado no passado como peça fundamental na contextura da expansão europeia e, no presente, como fonte inesgotável de recursos, o mar foi, e ainda é, um obstáculo de declarada importância no desenvolvimento económico dos Açores, porque quebra a continuidade do espaço territorial do arquipélago, porque o torna longe dos dois continentes mais próximos e porque condiciona a ocupação humana à escassez do chão insular. Para uma sociedade de tradições agro-pastoris como a açoriana que do amanho da terra retira a sua maior riqueza, o último aspecto referido reveste-se de particular acuidade. Não só as águas confinam as suas terras como, do eterno antagonismo entre o oceano e a terra firme, aquele sai sempre vitorioso. Outrossim, o mar é, por excelência, a bacia receptora dos solos que, no interior das ilhas, a erosão pouco a pouco vai roubando. O lento, mas persistente recuo da costa, é um processo natural que resulta da continuada agressividade das ondas: contra a poderosa força destas, pouca ou nenhuma oposição pode o habitante ilhéu oferecer. A erosão, tomada aqui como desgaste, é um processo de denudaçao dos continentes, natural também e tão antigo como estes o são. Neste campo porém, a interferência do homem pode revestir-se de aspectos significativos que visem retardar ou minimizar o mecanismo erosivo ou de outros que, pelo contrário criem condições ao disparar do processo ou a sua aceleração. No arquipélago dos Açores, e apesar do prejuízo irreparável que actualmente representa o transporte de camadas de solo pelas escorrência superficial, os efeitos da erosão têm sido descorados pelo homem ou olhados com alguma negligência. [...