Band-structure and electronic transport calculations in cylindrical wires:the issue of bound states in transfer-matrix calculations

The transfer-matrix methodology is used to solve linear systems of differential equations, such as those that arise when solving Schr\"odinger's equation, in situations where the solutions of interest are in the continuous part of the energy spectrum. The technique is actually a generalization in three dimensions of methods used to obtain scattering solutions in one dimension. Using the layer-addition algorithm allows one to control the stability of the computation and to describe efficiently periodic repetitions of a basic unit. This paper, which is an update of an article originally published in Physical and Chemical News 16, 46-53 (2004), provides a pedagogical presentation of this technique. It describes in details how the band structure associated with an infinite periodic medium can be extracted from the transfer matrices that characterize a single basic unit. The method is applied to the calculation of the transmission and band structure of electrons subject to cosine potentials in a cylindrical wire. The simulations show that bound states must be considered because of their impact as sharp resonances in the transmission probabilities and to remove unphysical discontinuities in the band structure. Additional states only improve the completeness of the representation.Comment: This paper is an update of an article originally published in Physical and Chemical News 16, 46-53 (2004

Genetic Algorithms ::an Evolutionary Approach to Optical Engineering

We present a Genetic Algorithm that we developed to address optimization problems in optical engineering. Our objective is to determine the global optimum of a problem ideally by a single run of the genetic algorithm. We want also to achieve this objective with a reasonable use of computational resources. In order to accelerate the convergence of the algorithm, we establish generation after generation a quadratic approximation of the fitness in the close neighborhood of the best-so-far individual. We then inject in the population an individual that corresponds to the optimum of this approximation. We also use randomly-shifted Gray codes when applying mutations in order to achieve a better exploration of the parameter space. We provide automatic settings for the technical parameters of our algorithm and apply it to typical benchmark problems in 5, 10 and 20 dimensions. We show that the global optimum of these problems can be determined with a probability of success in one run of the order of 95-97 % and an average number of fitness evaluations of the order of 400-750×n, where n refers to the number of parameters to determine. We finally comment some applications of this algorithm to real-world engineering problems

Cutting propagation of ‘Cambona 4’ yerba mate clones

The ‘Cambona 4’ yerba mate (Ilex paraguariensis A. St. Hil. - Aquifoliaceae) stands out for the high productivity and soft taste of the raw material obtained. The seedlings come from the controlled crosses of a female and a male plant. In order to guarantee the planting of even more uniform and productive herbs, the cutting is an alternative of propagation. The objective of this research was to evaluate the rooting capacity of apical and subapical cuttings of six ‘Cambona 4’ clones (C7, C8, C9, C10, C11 and C13) in two seasons, in january (summer/autumn) and april (autumn/winter) treated with 2.000 mg/kg of IBA in the form of talc. The cuttings were standardized with 10 cm, keeping a pair of leaves cut in half. The cutting was done in an agricultural greenhouse, with irrigation by intermittent nebulization, the cuttings were placed to rooting in plastic tubes containing carbonized rice husk. After 120 days, it was verified that the cutting season influenced the response of each clone, but for most clones rooting was higher when performed in summer/autumn, with better rates varying between 78.2% to 90.6% (C8, C9, C11 and C13), while in autumn/winter it was from 59.4% to 75.0% (C7, C10, C11 and C13). In the summer/autumn cutting period, subapical cuttings showed greater survival and rooting than the apical ones, but they didn’t differ when performed in autumn/winter. Leaf retention positively influenced the survival.The ‘Cambona 4’ yerba mate (Ilex paraguariensis A. St. Hil. - Aquifoliaceae) stands out for the high productivity and soft taste of the raw material obtained. The seedlings come from the controlled crosses of a female and a male plant. In order to guarantee the planting of even more uniform and productive herbs, the cutting is an alternative of propagation. The objective of this research was to evaluate the rooting capacity of apical and subapical cuttings of six ‘Cambona 4’ clones (C7, C8, C9, C10, C11 and C13) in two seasons, in january (summer/autumn) and april (autumn/winter) treated with 2.000 mg/kg of IBA in the form of talc. The cuttings were standardized with 10 cm, keeping a pair of leaves cut in half. The cutting was done in an agricultural greenhouse, with irrigation by intermittent nebulization, the cuttings were placed to rooting in plastic tubes containing carbonized rice husk. After 120 days, it was verified that the cutting season influenced the response of each clone, but for most clones rooting was higher when performed in summer/autumn, with better rates varying between 78.2% to 90.6% (C8, C9, C11 and C13), while in autumn/winter it was from 59.4% to 75.0% (C7, C10, C11 and C13). In the summer/autumn cutting period, subapical cuttings showed greater survival and rooting than the apical ones, but they didn’t differ when performed in autumn/winter. Leaf retention positively influenced the survival

La progression électorale du FN et ses limites

La progression du FN se heurte à des obstacles quasi insurmontable

Small and large wetland fragments are equally suited breeding sites for a ground-nesting passerine

Large habitat fragments are generally thought to host more species and to offer more diverse and/or better quality habitats than small fragments. However, the importance of small fragments for population dynamics in general and for reproductive performance in particular is highly controversial. Using an information-theoretic approach, we examined reproductive performance and probability of local recruitment of color-banded reed buntings Emberiza schoeniclus in relation to the size of 18 wetland fragments in northeastern Switzerland over 4years. We also investigated if reproductive performance and recruitment probability were density-dependent. None of the four measures of reproductive performance (laying date, nest failure probability, fledgling production per territory, fledgling condition) nor recruitment probability were found to be related to wetland fragment size. In terms of fledgling production, however, fragment size interacted with year, indicating that small fragments were better reproductive grounds in some years than large fragments. Reproductive performance and recruitment probability were not density-dependent. Our results suggest that small fragments are equally suited as breeding grounds for the reed bunting as large fragments and should therefore be managed to provide a habitat for this and other specialists occurring in the same habitat. Moreover, large fragments may represent sinks in specific years because a substantial percentage of all breeding pairs in our study area breed in large fragments, and reproductive failure in these fragments due to the regularly occurring floods may have a much stronger impact on regional population dynamics than comparable events in small fragment