Evolution of Supermassive Black Holes from Cosmological Simulations

The correlations between the mass of supermassive black holes and properties of their host galaxies are investigated through cosmological simulations. Black holes grow from seeds of 100 solar masses inserted into density peaks present in the redshift range 12-15. Seeds grow essentially by accreting matter from a nuclear disk and also by coalescences resulting from merger episodes. At z=0, our simulations reproduce the black hole mass function and the correlations of the black hole mass both with stellar velocity dispersion and host dark halo mass. Moreover, the evolution of the black hole mass density derived from the present simulations agrees with that derived from the bolometric luminosity function of quasars, indicating that the average accretion history of seeds is adequately reproduced . However, our simulations are unable to form black holes with masses above $10^9 M_{\odot}$ at $z\sim 6$, whose existence is inferred from the bright quasars detected by the Sloan survey in this redshift range.Comment: Talk given at the International Workshop on Astronomy and Relativistic Astrophysics (IWARA 2009), Maresias, Brazil. to be published in the International Journal of Modern Physics

Dynamics of Rumor Spreading in Complex Networks

We derive the mean-field equations characterizing the dynamics of a rumor process that takes place on top of complex heterogeneous networks. These equations are solved numerically by means of a stochastic approach. First, we present analytical and Monte Carlo calculations for homogeneous networks and compare the results with those obtained by the numerical method. Then, we study the spreading process in detail for random scale-free networks. The time profiles for several quantities are numerically computed, which allow us to distinguish among different variants of rumor spreading algorithms. Our conclusions are directed to possible applications in replicated database maintenance, peer to peer communication networks and social spreading phenomena.Comment: Final version to appear in PR

Equilibrium configurations for quark-diquark stars and the problem of Her X-1 mass

We report new calculations of the physical properties of a quark-diquark plasma. A vacuum contribution is taken into account and is responsible for the appearance of a stable state at zero pressure and at a baryon density of about 2.2 times the nuclear matter density in this model. The resulting equation of state was used to integrate numerically the Tolman-Oppenheimer-Volkoff equations. The mass-radius relationship has been derived from a series of equilibrium configurations constituted by a mixture of quarks and diquarks. These stellar models, which are representative of a whole class, may be helpful to understand the possible compactness of the X-ray source Her X-1 and related objects.Comment: 15 pp., PlainTex file + 3 figures available upon request at [email protected]. Submitted to Int. Jour. Mod. Phys.

Double fermiophobic Higgs boson production at the LHC and LC

We consider the phenomenology of a fermiophobic Higgs boson (h_f) at the Large Hadron Collider (LHC) and a e+e- Linear Collider (LC). At both machines the standard production mechanisms which rely on the coupling h_fVV (V=W,Z) can be very suppressed at large tan beta. In such cases the complementary channels pp to H^\pm h_f, A^0 h_f and e+e- to A^0 h_f offer promising cross-sections. Together with the potentially large branching ratios for H^\pm to h_fW* and A^0 to h_fZ*, these mechanisms would give rise to double h_f production, leading to signatures of gamma gamma gamma gamma, gamma gamma VV and VVVV.Comment: 19 pages, 9 figures, expanded discussion, fig.1 changed slightly, version to appear in Phys.Rev.

Instability of scale-free networks under node-breaking avalanches

The instability introduced in a large scale-free network by the triggering of node-breaking avalanches is analyzed using the fiber-bundle model as conceptual framework. We found, by measuring the size of the giant component, the avalanche size distribution and other quantities, the existence of an abrupt transition. This test of strength for complex networks like Internet is more stringent than others recently considered like the random removal of nodes, analyzed within the framework of percolation theory. Finally, we discuss the possible implications of our results and their relevance in forecasting cascading failures in scale-free networks.Comment: 4 pages, 4 figures, final version to be published in Europhys. Let

S wave velocity structure below central Mexico using high-resolution surface wave tomography

Shear wave velocity of the crust below central Mexico is estimated using surface wave dispersion measurements from regional earthquakes recorded on a dense, 500 km long linear seismic network. Vertical components of regional records from 90 well-located earthquakes were used to compute Rayleigh-wave group-velocity dispersion curves. A tomographic inversion, with high resolution in a zone close to the array, obtained for periods between 5 and 50 s reveals significant differences relative to a reference model, especially at larger periods (>30 s). A 2-D S wave velocity model is obtained from the inversion of local dispersion curves that were reconstructed from the tomographic solutions. The results show large differences, especially in the lower crust, among back-arc, volcanic arc, and fore-arc regions; they also show a well-resolved low-velocity zone just below the active part of the Trans Mexican Volcanic Belt (TMVB) suggesting the presence of a mantle wedge. Low densities in the back arc, inferred from the low shear wave velocities, can provide isostatic support for the TMVB

Synchronization of Kuramoto Oscillators in Scale-Free Networks

In this work, we study the synchronization of coupled phase oscillators on the underlying topology of scale-free networks. In particular, we assume that each network's component is an oscillator and that each interacts with the others following the Kuramoto model. We then study the onset of global phase synchronization and fully characterize the system's dynamics. We also found that the resynchronization time of a perturbed node decays as a power law of its connectivity, providing a simple analytical explanation to this interesting behavior.Comment: 7 pages and 4 eps figures, the text has been slightly modified and new references have been included. Final version to appear in Europhysics Letter

Número mínimo de famílias de meios-irmãos para representar uma população de milho-pipoca.

O numero minimo de familias de meios-irmaos, no melhoramento genetico, e aquele que representa uma populacao, permitindo obter estimativas consistentes e estaveis dos parametros geneticos. A media e a variancia genetica foram escolhidas para caracterizar a populacao de 166 familias de meios-irmaos de milho-pipoca CMS 43, avaliada em Sete Lagoas e em Coimbra, MG, no deliamento em blocos casualizados, com duas repeticoes, 1997/1998. A tecnica de simulacao bootstrap foi utilizada para se obterem as informacoes necessarias. A determinacao do numero minimo e feita para analise visual dos graficos da estabilizacao da media e da variancia de subamostras. Na caracteristica prolificidade foram necessarias 20 familias na caracteristica producao de graos/ha, 161; e na capacidade de expansao, 141. Este e o numero minimo de familias considerado adequado para representar esta populacao. O metodo de simulacao de subamostras proposto contribui para reduzir os trabalhos e os custos da pesquisa agronomica, mantendo a precisao e a exatidao desejada

Utilização da estatística Pi na predição de ganhos por seleção em famílias de meios-irmãos de milho-pipoca.

Neste trabalho utiliza-se da estatistica Pi, medida de estabilidade, adaptabilidade e adaptacao, como criterio alternativo a selecao com base nas medias da analise de variancia conjunta. Foram utilizadas as avaliacoes de 166 familias de meios-irmaos de milho-pipoca CMS 43, em Sete Lagoas, MG, e Coimbra, MG, no delineamento em blocos casualizados, com duas repeticoes. Utilizou-se o estimador baseado no diferencial de selecao para estimar os ganhos preditos. Nos dois locais esses ganhos, com base na estatistica Pi, foram semelhantes aos ganhos preditos com base nos dados da analise de variancia conjunta. Considera-se que a selecao com base na estatistica Pi e um novo procedimento valido e de interesse na fase de predicao de ganhos de um programa de melhoramento

Predição de ganhos em famílias de meios irmãos do milho-pipoca CMS 43.

Foram avaliadas 166 famílias de meios irmãos de milho-pipoca (Zea mays L), da população CMS 43, em Sete Lagoas, Minas Gerais, em 1997-1998. O objetivo foi predizer ganhos simultâneos nas características capacidade de expansão e produtividade e identificar características positivamente correlacionadas com esses dois caracteres. Usou-se o delineamento em blocos casualizados, com duas repetições e com testemunhas. Os ganhos diretos preditos foram superiores aos ganhos correlacionados. Os descritores produtividade e capacidade de expansão foram negativamente correlacionados, inferindo-se que a seleção para um deles implicará em perdas prováveis na expressão do outro. O descritor altura de planta poderá ser usado na seleção indireta para aumento simultâneo de produtividade e capacidade de expansão