Chaos in one-dimensional lattices under intense laser fields

A model is investigated where a monochromatic, spatially homogeneous laser field interacts with an electron in a one-dimensional periodic lattice. The classical Hamiltonian is presented and the technique of stroboscopic maps is used to study the dynamical behavior of the model. The electron motion is found to be completely regular only for small field amplitudes, developing a larger chaotic region as the amplitude increases. The quantum counterpart of the classical Hamiltonian is derived. Exact numerical diagonalizations show the existence of universal, random-matrix fluctuations in the electronic energy bands dressed by the laser field. A detailed analysis of the classical phase space is compatible with the statistical spectral analysis of the quantum model. The application of this model to describe transport and optical absorption in semiconductor superlattices submitted to intense infrared laser radiation is proposed.Comment: 9 pages, RevTex 3.0, EPSF (6 figures), to appear in Europhys. J.

Dos nuevas especies del género Typhlocharis Dieck, 1869 de Portugal y notas sobre especies relacionadas (Coleoptera, Carabidae)

The present study describes two endogean carabid species of Typhlocharis Dieck, Typhlocharis rochapitei n. sp. and Typhlocharis crespoi n. sp., belonging to the T. diecki species group and to the T. outereloi species group, respectively. The work provides diagnostic characters and in particular, the structure of male genitalia. Affinities to putative relatives and keys for the identification of the diecki (all species) and outereloi (Portugal) species groups are also given.Se describen dos nuevas especies de carábidos Anillini endogeos (Coleoptera: Carabidae) de Portugal, Typhlocharis rochapitei n. sp. y Typhlocharis crespoi n. sp., pertencientes a los grupos diecki y outereloi, respectivamente. Se destacan los caracteres que las definen y, en particular, la estructura de la genitalia masculina. Se discute la afinidad con las especies más relacionadas y además se aportan datos ecológicos. Por último, se incluyen claves de todas las especies conocidas del grupo diecki y de las especies del grupo outereloi conocidas en Portugal

Tres nuevas especies del género Geocharis Ehlers, 1883 de Portugal (Coleoptera, Carabidae)

Three endogean carabid species (Coleoptera: Carabidae, Anillini) from Portugal, Geocharis fermini n. sp., Geocharis bivari n. sp. and Geocharis quartaui n. sp. are described. The work provides diagnostic characters of these species, and in particular, the structure of male genitalia. Affinities with closely related species are discussed and ecological data are also included. Faunistic notes on Geocharis olisipensis (Schatzmayr, 1937) and a key for the identification of the species occurring in Portugal north of the Tajo River are also given.Se describen tres nuevas especies de carábidos Anillini endogeos (Coleoptera: Carabidae) de Portugal: Geocharis fermini n. sp., Geocharis bivari n. sp. y Geocharis quartaui n. sp. Se destacan los caracteres que las definen y, en particular, la estructura de la genitalia masculina. Se discute la afinidad con las especies más relacionadas y además se aportan datos ecológicos. También se aportan datos faunísticos sobre Geocharis olisipensis (Schatzmayr, 1937). Por último se incluye una clave de las especies conocidas en Portugal al norte del Río Tajo

Geometric combinatorial algebras: cyclohedron and simplex

In this paper we report on results of our investigation into the algebraic structure supported by the combinatorial geometry of the cyclohedron. Our new graded algebra structures lie between two well known Hopf algebras: the Malvenuto-Reutenauer algebra of permutations and the Loday-Ronco algebra of binary trees. Connecting algebra maps arise from a new generalization of the Tonks projection from the permutohedron to the associahedron, which we discover via the viewpoint of the graph associahedra of Carr and Devadoss. At the same time that viewpoint allows exciting geometrical insights into the multiplicative structure of the algebras involved. Extending the Tonks projection also reveals a new graded algebra structure on the simplices. Finally this latter is extended to a new graded Hopf algebra (one-sided) with basis all the faces of the simplices.Comment: 23 figures, new expanded section about Hopf algebra of simplices, with journal correction

Catastrophic Phase Transitions and Early Warnings in a Spatial Ecological Model

Gradual changes in exploitation, nutrient loading, etc. produce shifts between alternative stable states (ASS) in ecosystems which, quite often, are not smooth but abrupt or catastrophic. Early warnings of such catastrophic regime shifts are fundamental for designing management protocols for ecosystems. Here we study the spatial version of a popular ecological model, involving a logistically growing single species subject to exploitation, which is known to exhibit ASS. Spatial heterogeneity is introduced by a carrying capacity parameter varying from cell to cell in a regular lattice. Transport of biomass among cells is included in the form of diffusion. We investigate whether different quantities from statistical mechanics -like the variance, the two-point correlation function and the patchiness- may serve as early warnings of catastrophic phase transitions between the ASS. In particular, we find that the patch-size distribution follows a power law when the system is close to the catastrophic transition. We also provide links between spatial and temporal indicators and analyze how the interplay between diffusion and spatial heterogeneity may affect the earliness of each of the observables. We find that possible remedial procedures, which can be followed after these early signals, are more effective as the diffusion becomes lower. Finally, we comment on similarities and differences between these catastrophic shifts and paradigmatic thermodynamic phase transitions like the liquid-vapour change of state for a fluid like water

Using the Sound Card as a Timer

Experiments in mechanics can often be timed by the sounds they produce. In such cases, digital audio recordings provide a simple way of measuring time intervals with an accuracy comparable to that of photogate timers. We illustrate this with an experiment in the physics of sports: to measure the speed of a hard-kicked soccer ball.Comment: 3 pages, 4 figures, Late

Variação da contração volumétrica da madeira de Hymenaea sp em função da temperatura de secagem.

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