When is a Network a Network? Multi-Order Graphical Model Selection in Pathways and Temporal Networks

We introduce a framework for the modeling of sequential data capturing pathways of varying lengths observed in a network. Such data are important, e.g., when studying click streams in information networks, travel patterns in transportation systems, information cascades in social networks, biological pathways or time-stamped social interactions. While it is common to apply graph analytics and network analysis to such data, recent works have shown that temporal correlations can invalidate the results of such methods. This raises a fundamental question: when is a network abstraction of sequential data justified? Addressing this open question, we propose a framework which combines Markov chains of multiple, higher orders into a multi-layer graphical model that captures temporal correlations in pathways at multiple length scales simultaneously. We develop a model selection technique to infer the optimal number of layers of such a model and show that it outperforms previously used Markov order detection techniques. An application to eight real-world data sets on pathways and temporal networks shows that it allows to infer graphical models which capture both topological and temporal characteristics of such data. Our work highlights fallacies of network abstractions and provides a principled answer to the open question when they are justified. Generalizing network representations to multi-order graphical models, it opens perspectives for new data mining and knowledge discovery algorithms.Comment: 10 pages, 4 figures, 1 table, companion python package pathpy available on gitHu

Dynamics of Enceladus and Dione inside the 2:1 Mean-Motion Resonance under Tidal Dissipation

In a previous work (Callegari and Yokoyama 2007, Celest. Mech. Dyn. Astr. vol. 98), the main features of the motion of the pair Enceladus-Dione were analyzed in the frozen regime, i.e., without considering the tidal evolution. Here, the results of a great deal of numerical simulations of a pair of satellites similar to Enceladus and Dione crossing the 2:1 mean-motion resonance are shown. The resonance crossing is modeled with a linear tidal theory, considering a two-degrees-of-freedom model written in the framework of the general three-body planar problem. The main regimes of motion of the system during the passage through resonance are studied in detail. We discuss our results comparing them with classical scenarios of tidal evolution of the system. We show new scenarios of evolution of the Enceladus-Dione system through resonance not shown in previous approaches of the problem.Comment: 36 pages, 12 figures. Accepted in Celestial Mechanics and Dynamical Astronom

Symplectic integration of space debris motion considering several Earth's shadowing models

In this work, we present a symplectic integration scheme to numerically compute space debris motion. Such an integrator is particularly suitable to obtain reliable trajectories of objects lying on high orbits, especially geostationary ones. Indeed, it has already been demonstrated that such objects could stay there for hundreds of years. Our model takes into account the Earth's gravitational potential, luni-solar and planetary gravitational perturbations and direct solar radiation pressure. Based on the analysis of the energy conservation and on a comparison with a high order non-symplectic integrator, we show that our algorithm allows us to use large time steps and keep accurate results. We also propose an innovative method to model Earth's shadow crossings by means of a smooth shadow function. In the particular framework of symplectic integration, such a function needs to be included analytically in the equations of motion in order to prevent numerical drifts of the energy. For the sake of completeness, both cylindrical shadows and penumbra transitions models are considered. We show that both models are not equivalent and that big discrepancies actually appear between associated orbits, especially for high area-to-mass ratios

Doped carrier formulation of the t-J model: the projection constraint and the effective Kondo-Heisenberg lattice representation

We show that the recently proposed doped carrier Hamiltonian formulation of the t-J model should be complemented with the constraint that projects out the unphysical states. With this new important ingredient, the previously used and seemingly different spin-fermion representations of the t-J model are shown to be gauge related to each other. This new constraint can be treated in a controlled way close to half-filling suggesting that the doped carrier representation provides an appropriate theoretical framework to address the t-J model in this region. This constraint also suggests that the t-J model can be mapped onto a Kondo-Heisenberg lattice model. Such a mapping highlights important physical similarities between the quasi two-dimensional heavy fermions and the high-T$_c$ superconductors. Finally we discuss the physical implications of our model representation relating in particular the small versus large Fermi surface crossover to the closure of the lattice spin gap.Comment: corrected and enlarged versio

Desenvolvimento de linhagens de feijão-caupi de porte ereto e crescimento determinado e de tipo Canapu na Embrapa Semi-Árido.

Os objetivos do melhoramento do feijão-caupi na Embrapa Semi-Árido tem sido o desenvolvimento de cultivares de porte ereto, de crescimento determinado e de llinhagens tipo canapu, com tolerância às principais viroses. O genótipo 'PI 293588' foi usado em cruzamentos com 'IPA 206', 'Epace 11' e BR 17 Gurguéia', enquanto o 'Canapu' foi usado nos cruzamentos com 'IPA 206', 'BR 17 Gurguéia' e 'TE 97-309-G3'. Quatro avanços de gerações foram realizados por ano, em regime irrigado, com forte pressão para as variáveis de interesse, na quase ausência de inseticidas e fertilizantes. Foram selecionadas 117 progênies F6 de porte ereto e hábito de crescimento determinado. O cruzamento 'Epace 11' x 'PI 293588' possibilitou a seleção do maior número de grãos de tegumento marrom. Foram selecionadas 267 progênies F5 tipo canapu. O cruzamento 'IPA 206' x 'Canapu' possibilitou a seleção do maior número de progênies sem sintomas de campo para viroses, em duas avaliações independentes. No geral, as linhagens F6 de porte ereto e crescimento determinado e as linhagens F5 tipo Canapu, com tolerância de campo às viroses sugerem a pssibilidade de desenvolvimento de novas cultivares, algumas com grande potencial para a colheita mecânica, outras com potencial para a agricultura de base familiar

Colonização de fragmentos de árvores para produção de inóculo de Armillaria sp.

Organizado por Patricia Póvoa de Mattos, Celso Garcia Auer, Rejane Stumpf Sberze, Katia Regina Pichelli e Paulo César Botosso

Tidal Limits to Planetary Habitability

The habitable zones of main sequence stars have traditionally been defined as the range of orbits that intercept the appropriate amount of stellar flux to permit surface water on a planet. Terrestrial exoplanets discovered to orbit M stars in these zones, which are close-in due to decreased stellar luminosity, may also undergo significant tidal heating. Tidal heating may span a wide range for terrestrial exoplanets and may significantly affect conditions near the surface. For example, if heating rates on an exoplanet are near or greater than that on Io (where tides drive volcanism that resurface the planet at least every 1 Myr) and produce similar surface conditions, then the development of life seems unlikely. On the other hand, if the tidal heating rate is less than the minimum to initiate plate tectonics, then CO_2 may not be recycled through subduction, leading to a runaway greenhouse that sterilizes the planet. These two cases represent potential boundaries to habitability and are presented along with the range of the traditional habitable zone for main sequence, low-mass stars. We propose a revised habitable zone that incorporates both stellar insolation and tidal heating. We apply these criteria to GJ 581 d and find that it is in the traditional habitable zone, but its tidal heating alone may be insufficient for plate tectonics.Comment: 13 pages, 2 figures, accepted to ApJ Letters. A version with full resolution images is available at http://www.astro.washington.edu/users/rory/publications/bjgr09.pd

Themes and criteria selection for an agro-environmental diagnosis of sugar cane production chain.

The purpose of this study was to select themes and criteria to be used in agro-environmental diagnoses of the sugar cane (Sacharum spp.) chain for ethanol production. The selection of the themes and criteria was done after a literature research; interview with specialist, participation in meetings for ethanol production and the final union of all information. As a result the following themes and criteria were selected: 1) Land use (listed as theme) ? soil and climate, land use planning, competition for food production (listed as criteria); 2) Biodiversity - disturbance of flora and fauna, planning and management of biodiversity; 3) Quality of natural resources ? residue emissions for surface and ground waters, residue emissions to the atmosphere, recycling of residues, management and conservation of soil/plant system, yield planning and traceability of the product 4) Waste generation and recycling ? water, vinasse, bagasse, straw or cover residue, oil and filter cakes and toxic waste and 5) Energy ? energetic balance, integrated ethanol and biodiesel production, energetic planning and carbon market insertion

Herdabilidades e estimativas do número mínimo de genes para os caracteres comprimento da haste principal e dias para floração em três cruzamentos de feijão-caupi.

Neste trabalho são apresentadas as estiativas de herdabilidades e do número de genes para os caracteres comprimento da vagem e dias para floração nos cruzamentos IPA 206 x PI 293588, Epace 11 x PI 293588 e BR 17 Gurgueia x PI 293588, avaliados nas condições de Petrolina, PE.Suplemento. Edição dos resumos expandidos do 45 Congresso Brasileiro de Olericultura; 15 Congresso Brasileiro de Floricultura e Planta Ornamentais; 2 Congresso Brasileiro de Cultura de Tecidos de Plantas, Fortaleza, ago. 2005

The role of chaotic resonances in the solar system

Our understanding of the Solar System has been revolutionized over the past decade by the finding that the orbits of the planets are inherently chaotic. In extreme cases, chaotic motions can change the relative positions of the planets around stars, and even eject a planet from a system. Moreover, the spin axis of a planet-Earth's spin axis regulates our seasons-may evolve chaotically, with adverse effects on the climates of otherwise biologically interesting planets. Some of the recently discovered extrasolar planetary systems contain multiple planets, and it is likely that some of these are chaotic as well.Comment: 28 pages, 9 figure