Localization properties of a tight-binding electronic model on the Apollonian network

An investigation on the properties of electronic states of a tight-binding Hamiltonian on the Apollonian network is presented. This structure, which is defined based on the Apollonian packing problem, has been explored both as a complex network, and as a substrate, on the top of which physical models can defined. The Schrodinger equation of the model, which includes only nearest neighbor interactions, is written in a matrix formulation. In the uniform case, the resulting Hamiltonian is proportional to the adjacency matrix of the Apollonian network. The characterization of the electronic eigenstates is based on the properties of the spectrum, which is characterized by a very large degeneracy. The $2\pi /3$ rotation symmetry of the network and large number of equivalent sites are reflected in all eigenstates, which are classified according to their parity. Extended and localized states are identified by evaluating the participation rate. Results for other two non-uniform models on the Apollonian network are also presented. In one case, interaction is considered to be dependent of the node degree, while in the other one, random on-site energies are considered.Comment: 7pages, 7 figure

Least Dependent Component Analysis Based on Mutual Information

We propose to use precise estimators of mutual information (MI) to find least dependent components in a linearly mixed signal. On the one hand this seems to lead to better blind source separation than with any other presently available algorithm. On the other hand it has the advantage, compared to other implementations of `independent' component analysis (ICA) some of which are based on crude approximations for MI, that the numerical values of the MI can be used for: (i) estimating residual dependencies between the output components; (ii) estimating the reliability of the output, by comparing the pairwise MIs with those of re-mixed components; (iii) clustering the output according to the residual interdependencies. For the MI estimator we use a recently proposed k-nearest neighbor based algorithm. For time sequences we combine this with delay embedding, in order to take into account non-trivial time correlations. After several tests with artificial data, we apply the resulting MILCA (Mutual Information based Least dependent Component Analysis) algorithm to a real-world dataset, the ECG of a pregnant woman. The software implementation of the MILCA algorithm is freely available at http://www.fz-juelich.de/nic/cs/softwareComment: 18 pages, 20 figures, Phys. Rev. E (in press

Instability of hyper-compact Kerr-like objects

Viable alternatives to astrophysical black holes include hyper-compact objects without horizon, such as gravastars, boson stars, wormholes and superspinars. The authors have recently shown that typical rapidly-spinning gravastars and boson stars develop a strong instability. That analysis is extended in this paper to a wide class of horizonless objects with approximate Kerr-like geometry. A detailed investigation of wormholes and superspinars is presented, using plausible models and mirror boundary conditions at the surface. Like gravastars and boson stars, these objects are unstable with very short instability timescales. This result strengthens previous conclusions that observed hyper-compact astrophysical objects with large rotation are likely to be black holes.Comment: 15 pages, 3 figures. To be published in CQ

pH influence on oxygen mass transfer coefficient in a bubble column. Individual characterization of kL and a

Experiments were performed in a laboratory scale bubble column (10 L), to investigate the pH influence on oxygen mass transfer coefficient, in order to achieve a better control of biological processes. The liquid-side mass transfer coefficient, kL, and the specific interfacial area, a, were studied individually. The specific interfacial area was obtained using the new automatic image analysis technique developed by Ferreira et al. (2012). The pH was changed by the addition to the system of the most common acids and base used in biological process: hydrochloric acid (HCl), phosphoric acid (H3PO4) and potassium hydroxide (KOH). The results show that aqueous systems containing HCl, H3PO4 or KOH present lower volumetric liquid side mass transfer coefficient, kLa, in relation to pure systems (distilled water), this decrease being not linear. It was found that the specific interfacial area presents higher values in KOH and HCl solutions in comparison with distilled water. However, an opposite behavior was observed in the liquid-side mass transfer coefficient values. The kL behavior on the impure systems was explained based on bubble surface contamination. Higbie's and Fröessling's equations were adapted in the present work in order to be used in bubble dispersion systems

Partition functions and elliptic genera from supergravity

We develop the spacetime aspects of the computation of partition functions for string/M-theory on AdS(3) xM. Subleading corrections to the semi-classical result are included systematically, laying the groundwork for comparison with CFT partition functions via the AdS(3)/CFT(2) correspondence. This leads to a better understanding of the "Farey tail" expansion of Dijkgraaf et. al. from the point of view of bulk physics. Besides clarifying various issues, we also extend the analysis to the N=2 setting with higher derivative effects included.Comment: 34 page

Elastic turbulence in shear banding wormlike micelles

We study the dynamics of the Taylor-Couette flow of shear banding wormlike micelles. We focus on the high shear rate branch of the flow curve and show that for sufficiently high Weissenberg numbers, this branch becomes unstable. This instability is strongly sub-critical and is associated with a shear stress jump. We find that this increase of the flow resistance is related to the nucleation of turbulence. The flow pattern shows similarities with the elastic turbulence, so far only observed for polymer solutions. The unstable character of this branch led us to propose a scenario that could account for the recent observations of Taylor-like vortices during the shear banding flow of wormlike micelles

Desempenho produtivo de cultivares de feijão-caupi no Agreste Paraibano.

O objetivo desta pesquisa foi avaliar o comportamento de cultivares de feijão-caupi nas condições do Agreste paraibano. O delineamento experimental foi de blocos casualizados com dez tratamentos (Cultivares: Miranda IPA-207, BRS Marataoã, BRS Guariba, BRS Xique-Xique, BRS Paraguaçu, BRS Cauamé, BRS Tumucumaque, Epace 10, BR 17 Gurguéia e Canapu - local) com quatro repetições. As cultivares apresentaram respostas diferenciadas quanto aos componentes de rendimentos: comprimento de vagem, número de grãos por vagem, peso médio de vagem, massa de 100 grãos e produtividade de grãos. As cultivares de feijão-caupi: BRS Marataoã, BRS Guariba, BRS Xique-Xique, BRS Potengi e Miranda IPA-207 se destacaram com produtividades de grãos acima de 1.000 kg ha-1.CONAC 2012. Disponível em: http://www.conac2012.org/resumos/pdf/139d.pdf. Acesso em: 24 jul. 2013

Efeito de densidades de planta sobre a produtividade de grãos do feijão-caupi.

O objetivo do projeto foi avaliar os efeitos da densidade de plantas sobre o rendimento de grãos e componentes de rendimento da cultivar de feijão-caupi BRS Marataoã. O experimento foi conduzido, sob condições de sequeiro, no período de 01.05.2011 a 23.07.2011 na Estação Experimental de Lagoa Seca - PB . O delineamento experimental foi o de blocos ao acaso com seis tratamentos: densidades: 20, 60,100, 140, 180 e 220 mil plantas ha-1 com cinco repetições. Foram avaliadas o número de vagens por planta, produção de grãos por planta, massa de 100 grãos e produtividade de grãos. Houve efeito linear decrescente do número de vagens por planta e da produção de grãos por planta com o aumento da densidade de plantas e quadrático para massa de 100 grãos e produtividade de grãos. A maior produtividade de grãos (1.233 kg ha-1) foi alcançada com 120 mil plantas ha-1.CONAC 2012. Disponível em: http://www.conac2012.org/resumos/pdf/139c.pdf. Acesso em: 24 jul. 2013