11,116 research outputs found
Analytical and numerical studies of disordered spin-1 Heisenberg chains with aperiodic couplings
We investigate the low-temperature properties of the one-dimensional spin-1
Heisenberg model with geometric fluctuations induced by aperiodic but
deterministic coupling distributions, involving two parameters. We focus on two
aperiodic sequences, the Fibonacci sequence and the 6-3 sequence. Our goal is
to understand how these geometric fluctuations modify the physics of the
(gapped) Haldane phase, which corresponds to the ground state of the uniform
spin-1 chain. We make use of different adaptations of the strong-disorder
renormalization-group (SDRG) scheme of Ma, Dasgupta and Hu, widely employed in
the study of random spin chains, supplemented by quantum Monte Carlo and
density-matrix renormalization-group numerical calculations, to study the
nature of the ground state as the coupling modulation is increased. We find no
phase transition for the Fibonacci chain, while we show that the 6-3 chain
exhibits a phase transition to a gapless, aperiodicity-dominated phase similar
to the one found for the aperiodic spin-1/2 XXZ chain. Contrary to what is
verified for random spin-1 chains, we show that different adaptations of the
SDRG scheme may lead to different qualitative conclusions about the nature of
the ground state in the presence of aperiodic coupling modulations.Comment: Accepted for publication in Physical Review
Topological superconductivity in lead nanowires
Superconductors with an odd number of bands crossing the Fermi energy have
topologically protected Andreev states at interfaces, including Majorana states
in one dimensional geometries. Superconductivity, a low number of 1D channels,
large spin orbit coupling, and a sizeable Zeeman energy, are present in lead
nanowires produced by nanoindentation of a Pb tip on a Pb substrate, in
magnetic fields higher than the Pb bulk critical field. A number of such
devices have been analyzed. In some of them, the dependence of the critical
current on magnetic field, and the Multiple Andreev Reflections observed at
finite voltages, are compatible with the existence of topological
superconductivity
Efeito residual da aplicação do lodo de esgoto em milho (Zea mays L).
Este trabalho teve como objetivo avaliar o efeito residual da aplicação de lodo de esgoto na produtividade do milho (Zea mays L). O experimento iniciou-se em 1999 e a partir de então foram feitas várias aplicações ao solo de lodos oriundos da Estação de Tratamento de Barueri e de Franca. O delineamento foi de blocos ao acaso, com três repetições, e os seguintes tratamentos: controle, sem adição de lodo ou de fertilizantes, fertilização mineral completa, dose 1 do lodo de Franca, dose 2 do lodo de Franca, dose 1 do lodo de Barueri e dose 2 do lodo de Barueri. A dose 1 de lodo foi calculada baseando-se na recomendação de N pela cultura. A dose 2 foi o dobro da dose 1. As avaliações deste trabalho foram feitas no ano agrícola 2007/2008, quando somente o lodo de Franca foi aplicado. Apesar da não aplicação do lodo de Barueri os rendimentos do milho neste tratamento foram similares ao do tratamento com fertilização mineral. A aplicação do lodo de Franca produziu os maiores rendimentos e retornou mais N ao solo por meio dos restos vegetais. Os resultados demonstraram que aplicações anuais de lodo podem levar a perdas de N para o ambiente e que os efeitos residuais do lodo deveriam ser considerados no cálculo de recomendação daquele composto, quando se utiliza os requerimentos da planta em nitrogênio
Differential elastic electron scattering cross sections for CCl₄ by 1.5–100 eV energy electron impact
We report absolute elastic differential, integral and momentum transfer cross sections for electron interactions with CCl₄. The incident electron energy range is 1.5-100 eV, and the scattered electron angular range for the differential measurements varies from 15°-130°. The absolute scale of the differential cross section was set using the relative flow technique with helium as the reference species. Comparison with previous total cross sections shows good agreement. Atomic-like behaviour in this scattering system is shown here for the first time, and is further investigated by comparing the CCl₄ elastic cross sections to recent results on the halomethanes and atomic chlorine at higher impact energies [H. Kato, T. Asahina, H. Masui, M. Hoshino, H. Tanaka, H. Cho, O. Ingólfsson, F. Blanco, G. Garcia, S. J. Buckman, and M. J. Brunger, J. Chem. Phys. 132, 074309 (2010)].This work was conducted under the support of the
Japanese Ministry of Education, Sport, Culture and Technology.
H.K. acknowledges the Japan Society for the Promotion
of Science (JSPS) for his fellowships as grants-in-aid for scientific
research. S.J.B also acknowledges the JSPS Invitation
Fellowship for Research in Japan
Utilizando o Rsync para atualizar os bancos de dados do Sting Millennium Suite.
Entendendo o Rsync. Usando o Rsync em modo servidor. Usando o Rsync com protocolo Shell de conexão remota.bitstream/CNPTIA/11566/1/ct82.pdfAcesso em: 28 maio 2008
Biosorption: a solution to pollution?
To solve the water pollution problem by toxic heavy metal contamination resulting from humans technological activities has for long presented a challenge. Biosorption can be a part of the solution. Some types of biosorbents such as seaweeds, molds, yeasts, bacteria or crab shells are examples of biomass tested for metal biosorption with very encouraging results. The uptake of heavy metals by biomass can in some cases reach up to 50% of the biomass dry weight. New biosorbents can be manipulated for better efficiency and multiple re-use to increase their economic attractiveness
Self-Similarity of Friction Laws
The change of the friction law from a mesoscopic level to a macroscopic level
is studied in the spring-block models introduced by Burridge-Knopoff. We find
that the Coulomb law is always scale invariant. Other proposed scaling laws are
only invariant under certain conditions.}Comment: Plain TEX. Figures not include
Quantification and distribution of vibrio species in water from an estuary in Ceará-Brazil impacted by shrimp farming
Vibrios were quantified and their distribution determined for the estuary of the Coreaú river, in Northeastern Brazil, based on 24 water samples collected between June and October 2005. The most probable number of vibrios per 100 mL ranged from 230 x 10³ to 240 x 10(11). The pH value was the environmental factor most strongly associated with the abundance of vibrios. Sixty-two vibrio strains were isolated belonging to 15 species (6 of which observed in June-September and 8 in October). The most frequently isolated species were V. parahaemolyticus and V. cholerae.Foram realizadas análises concernentes à quantificação e distribuição de Vibrio em 24 amostras de água do estuário do Rio Coreaú (CE) no período de junho a novembro de 2005. O Número Mais Provável (NMP/100 mL) de Vibrio oscilou de 230 x 10³ a 240 x 10(11). O pH foi o fator ambiental que mais favoreceu ao aumento da microbiota de Vibrio. Foram isoladas 62 cepas de Vibrio, sendo observada uma distribuição de sete espécies nos meses de junho a setembro, e oito espécies no mês de outubro. As espécies mais freqüentes nos isolamentos foram V. parahaemolyticus e V. cholerae
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