Equilibrium analysis of cellular neural networks

Cellular neural networks are dynamical systems, described by a large set of coupled nonlinear differential equations. The equilibrium point analysis is an important step for understanding the global dynamics and for providing design rules. We yield a set of sufficient conditions (and a simple algorithm for checking them) ensuring the existence of at least one stable equilibrium point. Such conditions give rise to simple constraints, that extend the class of CNN, for which the existence of a stable equilibrium point is rigorously proved. In addition, they are suitable for design and easy to check, because they are directly expressed in term of the template elements

The evolution of obscured accretion

Our current understanding of the evolution of obscured accretion onto supermassive black holes is reviewed. We consider the literature results on the relation between the fraction of moderately obscured, Compton-thin AGN and redshift, and discuss the biases which possibly affect the various measurements. Then, we discuss a number of methods - from ultradeep X-ray observations to the detection of high-ionization optical emission lines - to select the population of the most heavily obscured, Compton-thick AGN, whose cosmological evolution is basically unknown. The space density of heavily obscured AGN measured through different techniques is discussed and compared with the predictions by current synthesis models of the X-ray background. Preliminary results from the first half of the 3 Ms XMM observation of the Chandra Deep Field South (CDFS) are also presented. The prospects for population studies of heavily obscured AGN with future planned or proposed X-ray missions are finally discussed.Comment: 6 pages, 2 figures. Invited talk at the conference "X-ray Astronomy 2009: Present status, multiwavelength approach and future perspectives", September 2009, Bologna. To appear in AIP Conf. Proc. (editors: A. Comastri, M. Cappi, L. Angelini)

The high-redshift Universe with the International X-ray Observatory

We discuss some of the main open issues related to the light-up and evolution of the first accreting sources powering high redshift luminous quasars. We discuss the perspectives of future deep X-ray surveys with the International X-ray Observatory and possible synergies with the Wide Field X-ray Telescope.Comment: 6 pages, 6 figures. Proceedings of "The Wide Field X-ray Telescope Workshop", held in Bologna, Italy, Nov. 25-26 2009. To appear in Memorie della Societ\`a Astronomica Italiana 2010 (arXiv:1010.5889

The Diversity of Extrasolar Terrestrial Planets

Extrasolar planetary host stars are enriched in key planet-building elements. These enrichments have the potential to drastically alter the building blocks available for terrestrial planet formation. Here we report on the combination of dynamical models of late-stage terrestrial planet formation within known extrasolar planetary systems with chemical equilibrium models of the composition of solid material within the disk. This allows us to constrain the bulk elemental composition of extrasolar terrestrial planets. A wide variety of resulting planetary compositions exist, ranging from those that are essentially "Earth-like", containing metallic Fe and Mg-silicates, to those that are dominated by graphite and SiC. This implies that a diverse range of terrestrial planets are likely to exist within extrasolar planetary systems.Comment: 4 pages, 1 figure. Submitted to the proceedings of IAU symposium 265 Chemical Abundances in the Universe: Connecting First Stars to Planet

The XMM deep survey in the CDF-S. X. X-ray variability of bright sources

We aim to study the variability properties of bright hard X-ray selected Active Galactic Nuclei (AGN) with redshift between 0.3 and 1.6 detected in the Chandra Deep Field South (XMM-CDFS) by a long XMM observation. Taking advantage of the good count statistics in the XMM CDFS we search for flux and spectral variability using the hardness ratio techniques. We also investigated spectral variability of different spectral components. The spectra were merged in six epochs (defined as adjacent observations) and in high and low flux states to understand whether the flux transitions are accompanied by spectral changes. The flux variability is significant in all the sources investigated. The hardness ratios in general are not as variable as the fluxes. Only one source displays a variable HR, anti-correlated with the flux (source 337). The spectral analysis in the available epochs confirms the steeper when brighter trend consistent with Comptonisation models only in this source. Finding this trend in one out of seven unabsorbed sources is consistent, within the statistical limits, with the 15 % of unabsorbed AGN in previous deep surveys. No significant variability in the column densities, nor in the Compton reflection component, has been detected across the epochs considered. The high and low states display in general different normalisations but consistent spectral properties. X-ray flux fluctuations are ubiquitous in AGN. In general, the significant flux variations are not associated with a spectral variability: photon index and column densities are not significantly variable in nine out of the ten AGN over long timescales (from 3 to 6.5 years). The photon index variability is found only in one source (which is steeper when brighter) out of seven unabsorbed AGN. These results are consistent with previous deep samples.Comment: 14 pages, 11 figures. Accepted in A&

Effects of exogenous lactase administration on hydrogen breath excretion and intestinal symptoms in patients presenting lactose malabsorption and intolerance

To establish whether supplementation with a standard oral dose of Beta-Galactosidase affects hydrogen breath excretion in patients presenting with lactose malabsorption. METHODS: Ninety-six consecutive patients positive to H2 Lactose Breath Test were enrolled. Mean peak H2 levels, the time to reach the peak H2, the time to reach the cut-off value of 20 ppm, the cumulative breath H2 excretion, the areas under the curve, and a Visual Analogical 10-point Scale for symptoms were calculated. Genotyping of the C/T-13910 variant was carried out. RESULTS: Following the oral administration of Beta-Galactosidase, in 21.88% of the cases, H2 Lactose Breath Test became negative (Group A), while mean peak H2 levels (74.95 ppm versus 7.85), P < 0.0000, in 17.71% (Group B) were still positive, with the H2 level 20 ppm above the baseline, but the peak H2 levels were significantly lower than those observed at the baseline test (186.7 ppm versus 66.64), P < 0.0000, while in 60.41% (Group C) they were still positive with the peak H2 levels similar to those observed at the baseline test (94.43 versus 81.60 ppm). All 96 individuals tested presented the C/C-13910 genotype nonpersistence. CONCLUSIONS: The response to oral administration of Beta-Galactosidase in patients with symptoms of lactose malabsorption presents a significant variability

X-ray observation of ULAS J1120+0641, the most distant quasar at z=7.08

We aim at probing the emission mechanism of the accreting super massive black holes in the high redshift Universe. We study the X-ray spectrum of ULAS1120+0641, the highest redshift quasar detected so far at z=7.085, which has been deeply observed (340 ks) by XMM-Newton. Despite the long integration time the spectral analysis is limited by the poor statistics, with only 150 source counts being detected. We measured the spectrum in the 2-80 keV rest-frame (0.3-10 keV observed) energy band. Assuming a simple power law model we find a photon index of 2.0+/-0.3 and a luminosity of 6.7+/-0.3 10^44 erg/s in the 2-10 keV band, while the intrinsic absorbing column can be only loosely constrained (NH< 1E23 cm^-2). Combining our data with published data we calculate that the X-ray-to-optical spectral index alpha_OX is1.8+/-0.1, in agreement with the alpha_OX-UV luminosity correlation valid for lower redshift quasars. We expanded to high energies the coverage of the spectral energy distribution of ULAS1120+0641. This is the second time that a z >6 quasar has been investigated through a deep X-ray observation. In agreement with previous studies of z~6 AGN samples, we do not find any hint of evolution in the broadband energy distribution. Indeed from our dataset ULAS 1120+0641 is indistinguishable from the population of optically bright quasar at lower redshift.Comment: 5 pages, 4 figures, A&A in press; updated with the accepted versio

Simulating the WFXT sky

We investigate the scientific impact of the Wide Field X-ray Telescope mission. We present simulated images and spectra of X-ray sources as observed from the three surveys planned for the nominal 5-year WFXT lifetime. The goal of these simulations is to provide WFXT images of the extragalactic sky in different energy bands based on accurate description of AGN populations, normal and star forming galaxies, groups and clusters of galaxies. The images are realized using a detailed PSF model, instrumental and physical backgrounds/foregrounds, accurate model of the effective area and the related vignetting effect. Thanks to this comprehensive modelization of the WFXT properties, the simulated images can be used to evaluate the flux limits for detection of point and extended sources, the effect of source confusion at very faint fluxes, and in general the efficiency of detection algorithms. We also simulate the spectra of the detected sources, in order to address specific science topics which are unique to WFXT. Among them, we focus on the characterization of the Intra Cluster Medium (ICM) of high-z clusters, and in particular on the measurement of the redshift from the ICM spectrum in order to build a cosmological sample of galaxy clusters. The end-to-end simulation procedure presented here, is a valuable tool in optimizing the mission design. Therefore, these simulations can be used to reliably characterize the WFXT discovery space and to verify the connection between mission requirements and scientific goals. Thanks to this effort, we can conclude on firm basis that an X-ray mission optimized for surveys like WFXT is necessary to bring X-ray astronomy at the level of the optical, IR, submm and radio wavebands as foreseen in the coming decade.Comment: "Proceedings of "The Wide Field X-ray Telescope Workshop", held in Bologna, Italy, Nov. 25-26 2009. To appear in Memorie della Societa Astronomica Italiana 2010 (arXiv:1010.5889)