Typical AGN at intermediate redshifts

We study the host galaxies and black holes of typical X-ray selected AGN at intermediate redshifts (z~0.5-1.4). The AGN are selected such that their spectral energy distributions are dominated by stellar emission, i.e., they show a prominent 1.6micron bump thus minimizing the AGN emission contamination. This AGN population comprises approximately 50% of the X-ray selected AGN at these redshifts. AGN reside in the most massive galaxies at the redshifts probed here, with characteristic stellar masses that are intermediate between those of local type 2 AGN and high redshift (z~2) AGN. The inferred black hole masses of typical AGN are similar to those of optically identified quasars at similar redshifts. Since the AGN in our sample are much less luminous than quasars, typical AGN have low Eddington ratios. This suggests that, at least at intermediate redshifts, the cosmic AGN 'downsizing' is due to both a decrease in the characteristic stellar mass of the host galaxies, and less efficient accretion. Finally there is no strong evidence in AGN host galaxies for either highly suppressed star formation, expected if AGN played a role in quenching star formation, or elevated star formation when compared to mass selected galaxies of similar stellar masses and redshifts.Comment: Conference proceedings of the meeting "Observational Evidence for Black Holes" held in Calcutta, Feb 2008. Paper will be published by AI

Using Hubble Space Telescope Imaging of Nuclear Dust Morphology to Rule Out Bars Fueling Seyfert Nuclei

If AGN are powered by the accretion of matter onto massive black holes, how does the gas in the host galaxy lose the required angular momentum to approach the black hole? Gas easily transfers angular momentum to stars in strong bars, making them likely candidates. Although ground-based searches for bars in active galaxies using both optical and near infrared surface brightness have not found any excess of bars relative to quiescent galaxies, the searches have not been able to rule out small-scale nuclear bars. To look for these nuclear bars we use HST WFPC2-NICMOS color maps to search for the straight dust lane signature of strong bars. Of the twelve Seyfert galaxies in our sample, only three have dust lanes consistent with a strong nuclear bar. Therefore, strong nuclear bars cannot be the primary fueling mechanism for Seyfert nuclei. We do find that a majority of the galaxies show an spiral morphology in their dust lanes. These spiral arms may be a possible fueling mechanism.Comment: To be published in the Astronomical Journal, June 1999. 25 pages and 14 figures. Full resolution figures are available at ftp://www.ciw.edu/pub/mregan/fullfigs.tar.g

Complex dynamics of elementary cellular automata emerging from chaotic rules

We show techniques of analyzing complex dynamics of cellular automata (CA) with chaotic behaviour. CA are well known computational substrates for studying emergent collective behaviour, complexity, randomness and interaction between order and chaotic systems. A number of attempts have been made to classify CA functions on their space-time dynamics and to predict behaviour of any given function. Examples include mechanical computation, \lambda{} and Z-parameters, mean field theory, differential equations and number conserving features. We aim to classify CA based on their behaviour when they act in a historical mode, i.e. as CA with memory. We demonstrate that cell-state transition rules enriched with memory quickly transform a chaotic system converging to a complex global behaviour from almost any initial condition. Thus just in few steps we can select chaotic rules without exhaustive computational experiments or recurring to additional parameters. We provide analysis of well-known chaotic functions in one-dimensional CA, and decompose dynamics of the automata using majority memory exploring glider dynamics and reactions

Cooler and bigger than thought? Planetary host stellar parameters from the InfraRed Flux Method

Effective temperatures and radii for 92 planet-hosting stars as determined from the InfraRed Flux Method (IRFM) are presented and compared with those given by other authors using different approaches. The IRFM temperatures we have derived are systematically lower than those determined from the spectroscopic condition of excitation equilibrium, the mean difference being as large as 110 K. They are, however, consistent with previous IRFM studies and with the colors derived from Kurucz and MARCS model atmospheres. Comparison with direct measurements of stellar diameters for 7 dwarf stars, which approximately cover the range of temperatures of the planet-hosting stars, suggest that the IRFM radii and temperatures are reliable in an absolute scale. A better understanding of the fundamental properties of the stars with planets will be achieved once this discrepancy between the IRFM and the spectroscopic temperature scales is resolved.Comment: 15 pages, 4 figures. Accepted for publication in Ap

Understanding the tsunami with a simple model

In this paper, we use the approximation of shallow water waves (Margaritondo G 2005 Eur. J. Phys. 26 401) to understand the behaviour of a tsunami in a variable depth. We deduce the shallow water wave equation and the continuity equation that must be satisfied when a wave encounters a discontinuity in the sea depth. A short explanation about how the tsunami hit the west coast of India is given based on the refraction phenomenon. Our procedure also includes a simple numerical calculation suitable for undergraduate students in physics and engineering

Distributional and classical solutions to the Cauchy Boltzmann problem for soft potentials with integrable angular cross section

This paper focuses on the study of existence and uniqueness of distributional and classical solutions to the Cauchy Boltzmann problem for the soft potential case assuming $S^{n-1}$ integrability of the angular part of the collision kernel (Grad cut-off assumption). For this purpose we revisit the Kaniel--Shinbrot iteration technique to present an elementary proof of existence and uniqueness results that includes large data near a local Maxwellian regime with possibly infinite initial mass. We study the propagation of regularity using a recent estimate for the positive collision operator given in [3], by E. Carneiro and the authors, that permits to study such propagation without additional conditions on the collision kernel. Finally, an $L^{p}$-stability result (with $1\leq p\leq\infty$) is presented assuming the aforementioned condition.Comment: 19 page

On the Substitution of Identicals in Counterfactual Reasoning

It is widely held that counterfactuals, unlike attitude ascriptions, preserve the referential transparency of their constituents, i.e., that counterfactuals validate the substitution of identicals when their constituents do. The only putative counterexamples in the literature come from counterpossibles, i.e., counterfactuals with impossible antecedents. Advocates of counterpossibilism, i.e., the view that counterpossibles are not all vacuous, argue that counterpossibles can generate referential opacity. But in order to explain why most substitution inferences into counterfactuals seem valid, counterpossibilists also often maintain that counterfactuals with possible antecedents are transparency‐preserving. I argue that if counterpossibles can generate opacity, then so can ordinary counterfactuals with possible antecedents. Utilizing an analogy between counterfactuals and attitude ascriptions, I provide a counterpossibilist‐friendly explanation for the apparent validity of substitution inferences into counterfactuals. I conclude by suggesting that the debate over counterpossibles is closely tied to questions concerning the extent to which counterfactuals are more like attitude ascriptions and epistemic operators than previously recognized

Spin canted magnetism, decoupling of charge and spin ordering in NdNiO3_3

We report detailed magnetization measurements on the perovskite oxide NdNiO$_3$. This system has a first order metal-insulator (M-I) transition at about 200 K which is associated with charge ordering. There is also a concurrent paramagnetic to antiferromagnetic spin ordering transition in the system. We show that the antiferromagnetic state of the nickel sublattice is spin canted. We also show that the concurrency of the charge ordering and spin ordering transitions is seen only while warming up the system from low temperature. The transitions are not concurrent while cooling the system through the M-I transition temperature. This is explained based on the fact that the charge ordering transition is first order while the spin ordering transition is continuous. In the magnetically ordered state the system exhibits ZFC-FC irreversibilities, as well as history-dependent magnetization and aging. Our analysis rules out the possibility of spin-glass or superparamagnetism and suggests that the irreversibilities originate from magnetocrystalline anisotropy and domain wall pinning.Comment: 8 pages, 7 figure

A Nexafs Study of Nitric Oxide Layers Adsorbed from a nitrite Solution onto a Pt(111) Surface

NO molecules adsorbed on a Pt(111) surface from dipping in an acidic nitrite solution are studied by near edge X-ray absorption fine structure spectroscopy (NEXAFS), X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED) and scanning tunnelling microscopy (STM) techniques. LEED patterns and STM images show that no long range ordered structures are formed after NO adsorption on a Pt(111) surface. Although the total NO coverage is very low, spectroscopic features in N K-edge and O K-edge absorption spectra have been singled out and related to the different species induced by this preparation method. From these measurements it is concluded that the NO molecule is adsorbed trough the N atom in an upright conformation. The maximum saturation coverage is about 0.3 monolayers, and although nitric oxide is the major component, nitrite and nitrogen species are slightly co-adsorbed on the surface. The results obtained from this study are compared with those previously reported in the literature for NO adsorbed on Pt(111) under UHV conditions