Two-dimensional crossover and strong coupling of plasmon excitations in arrays of one-dimensional atomic wires

The collective electronic excitations of arrays of Au chains on regularly stepped Si(553) and Si(775) surfaces were studied using electron loss spectroscopy with simultaneous high energy and momentum resolution (ELS-LEED) in combination with low energy electron diffraction (SPA-LEED) and tunneling microscopy. Both surfaces contain a double chain of gold atoms per terrace. Although one-dimensional metallicity and plasmon dispersion is observed only along the wires, two-dimensional effects are important, since plasmon dispersion explicitly depends both on the structural motif of the wires and the terrace width. The electron density on each terrace turns out to be modulated, as seen by tunneling spectroscopy (STS). The effective wire width of 7.5\,\AA\ for Si(553)-Au -- 10.2\,\AA\ for Si(775)-Au -- , determined from plasmon dispersion is in good agreement with STS data. Clear evidence for coupling between wires is seen beyond nearest neighbor coupling.Comment: 5 pages, 4 figure

Conceitos e ferramentas para apoiar o ensino de xadrez através de computadores

Orientador: Alexandre Ibrahim DireneDissertação (mestrado) - Universidade Federal do Paraná, Setor de Ciências ExatasResumo: Este trabalho apresenta conceitos e ferramentas para gerar sistemas tutores inteligentes (ITS) desenvolvidos especificamente para o ensino de conceitos visuais para o Jogo de Xadrez. Faz-se uma revisão literária sobre o ensino de conceitos visuais através de sistemas computacionais, atingindo o escopo de ambientes de autoria. Nesta revisão, constata-se a inexistência de tutores automáticos que levem em consideração o forte processamento visual primário exigido na formação de perícia para o Jogo de Xadrez. Este texto apresenta um shell de ITS para o ensino destes conceitos visuais e discute a aplicabilidade limitada de idéias básicas de algoritmos de busca heurística da IA Clássica. O protótipo de ITS deste trabalho, denominado SAEX, combina ferramentas de autoria com ITS, oferecendo um arcabouço integrado, apropriado para o desenvolvimento dos referidos sistemas de ensino. Ao final, são indicadas possibilidades reais de utilização deste ITS e de trabalhos futuros.Abstract: This work presents concepts and software tools for generating intelligent tutoring systems (ITS) specifically developed for the teaching of visual concepts aimed at Chess learners. A literature review is presented on computer based teaching of visual concepts as well as on authoring systems and tutoring shells. It is shown that existing systems for teaching Chess do not cover the issues of primary visual interpretation, an important capacity in acquiring expertise according to previous research work. The text presents an ITS shell for the teaching of visual concepts as an alternative to basic ideas of classical AI heuristic search methods. The prototype system SAEX, implemented as part of the work, combines authoring and intelligent systems techniques in an integrated framework to benefit learning. At the end, the text indicates real possibilities of use of this ITS and future research

Genomic, genetic and structural analysis of pyoverdine-mediated iron acquisition in the plant growth-promoting bacterium Pseudomonas fluorescens SBW25

<p>Abstract</p> <p>Background</p> <p>Pyoverdines (PVDs) are high affinity siderophores, for which the molecular mechanisms of biosynthesis, uptake and regulation have been extensively studied in <it>Pseudomonas aeruginosa </it>PAO1. However, the extent to which this regulatory model applies to other pseudomonads is unknown. Here, we describe the results of a genomic, genetic and structural analysis of pyoverdine-mediated iron uptake by the plant growth-promoting bacterium <it>P. fluorescens </it>SBW25.</p> <p>Results</p> <p><it>In silico </it>analysis of the complete, but un-annotated, SBW25 genome sequence identified 31 genes putatively involved in PVD biosynthesis, transport or regulation, which are distributed across seven different regions of the genome. PVD gene iron-responsiveness was tested using '<it>lacZ </it>fusions to five PVD loci, representative of structural and regulatory genes. Transcription of all fusions increased in response to iron starvation. <it>In silico </it>analyses suggested that regulation of <it>fpvR </it>(which is predicted to encode a cytoplasmic membrane-spanning anti-sigma factor) may be unique. Transcriptional assays using gene expression constructs showed that <it>fpvR </it>is positively regulated by FpvI (an extracytoplasmic family (ECF) sigma factor), and not directly by the ferric uptake regulator (Fur) as for PAO1. Deletion of <it>pvdL</it>, encoding a predicted non-ribosomal peptide synthetase (NRPS) involved in PVD chromophore biosynthesis confirmed the necessity of PvdL for PVD production and for normal growth in iron-limited media. Structural analysis of the SBW25 PVD shows a partly cyclic seven residue peptide backbone, identical to that of <it>P. fluorescens </it>ATCC13525. At least 24 putative siderophore receptor genes are present in the SBW25 genome enabling the bacterium to utilize 19 structurally distinct PVDs from 25 different <it>Pseudomonas </it>isolates.</p> <p>Conclusion</p> <p>The genome of <it>P. fluorescens </it>SBW25 contains an extensively dispersed set of PVD genes in comparison to other sequenced <it>Pseudomonas </it>strains. The PAO1 PVD regulatory model, which involves a branched Fpv signaling pathway, is generally conserved in SBW25, however there is a significant difference in <it>fpvR </it>regulation. SBW25 produces PVD with a partly cyclic seven amino acid residue backbone, and is able to utilize a wide variety of exogenous PVDs.</p

Cluster-induced crater formation

Using molecular-dynamics simulation, we study the crater volumes induced by energetic impacts ($v= 1- 250$ km/s) of projectiles containing up to N=1000 atoms. We find that for Lennard-Jones bonded material the crater volume depends solely on the total impact energy $E$. Above a threshold \Eth, the volume rises linearly with $E$. Similar results are obtained for metallic materials. By scaling the impact energy $E$ to the target cohesive energy $U$, the crater volumes become independent of the target material. To a first approximation, the crater volume increases in proportion with the available scaled energy, $V=aE/U$. The proportionality factor $a$ is termed the cratering efficiency and assumes values of around 0.5.Comment: 9 page

Métodos alternativos de estimativa da evapotranspiração de referência anual e nas diferentes estações do ano em Curitiba-PR, Brasil

Curitiba-PR é um grande centro consumidor de alimentos, sua região metropolitana produz hortifrutigranjeiros durante o ano inteiro e quase a totalidade dos agricultores utiliza irrigação, sendo esse o principal custo da produção. No entanto, em muitos locais, por serem de difícil acesso, há carência de dados climáticos para obtenção da evapotranspiração de referência (ETo) por modelos consagrados, gerando a necessidade de testar modelos alternativos para essa estimativa que é tão importante para determinar a demanda hídrica vegetal na região, diminuindo os custos de produção e maximizando o uso eficiente da água. Teve-se como objetivo no presente trabalho avaliar cinco métodos alternativos (Thornthwaite, Camargo, Hargreaves e Samani, Budyko e Linacre) de estimativa da ETo em relação ao método de Penman-Monteith em Curitiba-PR, anualmente e nas diferentes estações do ano. Os dados climáticos compreenderam o período de 1998 a 2007. Os dados foram analisados por meio do coeficiente de correlação (R), índices de concordância e desempenho, e estimativas dos erros. O método de Camargo, seguido de Thornthwaite, demonstram melhor desempenho para estimativa anual da ETo em Curitiba-PR, necessitando pequena quantidade de dados de entrada para uma estimativa adequada. Considerando as estações do ano, os melhores métodos para o verão são Linacre, Camargo e Thornthwaite, para o outono é Camargo, para o inverno são Camargo, Linacre e Thornthwaite, e para a primavera são Linacre e Camargo. Os métodos de Hargreaves e Samani, e Budyko são inadequados para estimar a ETo para o tipo climático Cfb na região de Curitiba-PR

Natural Nanoparticles: A Particular Matter Inspired by Nature

During the last couple of decades, the rapidly advancing field of nanotechnology has produced a wide palette of nanomaterials, most of which are considered as “synthetic” and, among the wider public, are often met with a certain suspicion. Despite the technological sophistication behind many of these materials, “nano” does not always equate with “artificial”. Indeed, nature itself is an excellent nanotechnologist. It provides us with a range of fine particles, from inorganic ash, soot, sulfur and mineral particles found in the air or in wells, to sulfur and selenium nanoparticles produced by many bacteria and yeasts. These nanomaterials are entirely natural, and, not surprisingly, there is a growing interest in the development of natural nanoproducts, for instance in the emerging fields of phyto- and phyco-nanotechnology. This review will highlight some of the most recent—and sometimes unexpected—advances in this exciting and diverse field of research and development. Naturally occurring nanomaterials, artificially produced nanomaterials of natural products as well as naturally occurring or produced nanomaterials of natural products all show their own, particular chemical and physical properties, biological activities and promise for applications, especially in the fields of medicine, nutrition, cosmetics and agriculture. In the future, such natural nanoparticles will not only stimulate research and add a greener outlook to a traditionally high-tech field, they will also provide solutions—pardon—suspensions for a range of problems. Here, we may anticipate specific biogenic factories, valuable new materials based on waste, the effective removal of contaminants as part of nano-bioremediation, and the conversion of poorly soluble substances and materials to biologically available forms for practical use