Closed-loop Control from Data-Driven Open-Loop Optimal Control Trajectories

We show how the recent works on data driven open-loop minimum-energy control for linear systems can be exploited to obtain closed-loop piecewise-affine control laws, by employing a state-space partitioning technique which is at the basis of the static relatively optimal control. In addition, we propose a way for employing portions of the experimental input and state trajectories to recover information about the natural movement of the state and dealing with non-zero initial conditions. The same idea can be used for formulating several open-loop control problems entirely based on data, possibly including input and state constraints

Integrating Superconductive and Optical Circuits

We have integrated on oxidized silicon wafers superconductive films and Josephson junctions along with sol-gel optical channel waveguides. The fabrication process is carried out in two steps that result to be solid and non-invasive. It is demonstrated that 660 nm light, coupled from an optical fibre into the channel sol-gel waveguide, can be directed toward superconducting tunnel junctions whose current-voltage characteristics are affected by the presence of the radiation. The dependence of the change in the superconducting energy gap under optical pumping is discussed in terms of a non-equilibrium superconductivity model.Comment: Document composed of 7 pages of text and 3 figure

Occupation of X-ray selected galaxy groups by X-ray AGN

We present the first direct measurement of the mean Halo Occupation Distribution (HOD) of X-ray selected AGN in the COSMOS field at z < 1, based on the association of 41 XMM and 17 C-COSMOS AGN with member galaxies of 189 X-ray detected galaxy groups from XMM and Chandra data. We model the mean AGN occupation in the halo mass range logM_200[Msun] = 13-14.5 with a rolling-off power-law with the best fit index alpha = 0.06(-0.22;0.36) and normalization parameter f_a = 0.05(0.04;0.06). We find the mean HOD of AGN among central galaxies to be modelled by a softened step function at logMh > logMmin = 12.75 (12.10,12.95) Msun while for the satellite AGN HOD we find a preference for an increasing AGN fraction with Mh suggesting that the average number of AGN in satellite galaxies grows slower (alpha_s < 0.6) than the linear proportion (alpha_s = 1) observed for the satellite HOD of samples of galaxies. We present an estimate of the projected auto correlation function (ACF) of galaxy groups over the range of r_p = 0.1-40 Mpc/h at = 0.5. We use the large-scale clustering signal to verify the agreement between the group bias estimated by using the observed galaxy groups ACF and the value derived from the group mass estimates. We perform a measurement of the projected AGN-galaxy group cross-correlation function, excluding from the analysis AGN that are within galaxy groups and we model the 2-halo term of the clustering signal with the mean AGN HOD based on our results.Comment: Accepted for publication in The Astrophysical Journa

The Obscured Fraction of AGN in the XMM-COSMOS Survey: A Spectral Energy Distribution Perspective

The fraction of AGN luminosity obscured by dust and re-emitted in the mid-IR is critical for understanding AGN evolution, unification, and parsec-scale AGN physics. For unobscured (Type-1) AGN, where we have a direct view of the accretion disk, the dust covering factor can be measured by computing the ratio of re-processed mid-IR emission to intrinsic nuclear bolometric luminosity. We use this technique to estimate the obscured AGN fraction as a function of luminosity and redshift for 513 Type-1 AGN from the XMM-COSMOS survey. The re-processed and intrinsic luminosities are computed by fitting the 18-band COSMOS photometry with a custom SED-fitting code, which jointly models emission from: hot-dust in the AGN torus, the accretion disk, and the host-galaxy. We find a relatively shallow decrease of the luminosity ratio as a function of Lbol, which we interpret as a corresponding decrease in the obscured fraction. In the context of the receding torus model, where dust sublimation reduces the covering factor of more luminous AGN, our measurements require a torus height which increases with luminosity as h ~ Lbol^{0.3-0.4}. Our obscured fraction-luminosity relation agrees with determinations from SDSS censuses of Type-1 and Type-2 quasars, and favors a torus optically thin to mid-IR radiation. We find a much weaker dependence of obscured fraction on 2-10 keV luminosity than previous determinations from X-ray surveys, and argue that X-ray surveys miss a significant population of highly obscured Compton-thick AGN. Our analysis shows no clear evidence for evolution of obscured fraction with redshift.Comment: 33 pages, 24 figures, ApJ accepte

The Chandra-COSMOS survey IV: X-ray spectra of the bright sample

We present the X-ray spectral analysis of the 390 brightest extragalactic sources in the Chandra-COSMOS catalog, showing at least 70 net counts in the 0.5-7 keV band. This sample has a 100% completeness in optical-IR identification, with 75% of the sample having a spectroscopic redshift and 25% a photometric redshift. Our analysis allows us to accurately determine the intrinsic absorption, the broad band continuum shape ({\Gamma}) and intrinsic L(2-10) distributions, with an accuracy better than 30% on the spectral parameters for 95% of the sample. The sample is equally divided in type-1 (49.7%) and type-2 AGN (48.7%) plus few passive galaxies at low z. We found a significant difference in the distribution of {\Gamma} of type-1 and type-2, with small intrinsic dispersion, a weak correlation of {\Gamma} with L(2-10) and a large population (15% of the sample) of high luminosity, highly obscured (QSO2) sources. The distribution of the X ray/Optical flux ratio (Log(FX /Fi)) for type-1 is narrow (0 < X/O < 1), while type-2 are spread up to X/O = 2. The X/O correlates well with the amount of X-ray obscuration. Finally, a small sample of Compton thick candidates and peculiar sources is presented. In the appendix we discuss the comparison between Chandra and XMM-Newton spectra for 280 sources in common. We found a small systematic difference, with XMM-Newton spectra that tend to have softer power-laws and lower obscuration.Comment: 20 pages, 16 figures. Accepted for Pubblication in MNRAS, 2013 February

Type 2 Quasars at the heart of dust-obscured galaxies (DOGs) at high z

Dust‐obscured galaxies (DOGs) represent a recently‐discovered, intriguing class of mid‐IR luminous sources at high redshifts. Evidence is mounting that DOGs (selected on the basis of extreme optical/mid‐IR color cut and high mid‐IR flux level) may represent systems caught in the process of host galaxy formation and intense SMBH growth. Here we report the results of an X‐ray spectroscopic survey aimed at studying the X‐ray properties of these sources and establishing the fraction of Type 2 quasars among them

High-z X-ray Obscured Quasars in Galaxies with Extreme Mid-IR/Optical Colors

Extreme Optical/Mid‐IR color cuts have been used to uncover a population of dust‐enshrouded, mid‐IR luminous galaxies at high redshifts. Several lines of evidence point towards the presence of an heavily absorbed, possibly Compton‐thick quasar at the heart of these systems. Nonetheless, the X‐ray spectral properties of these intriguing sources still remain largely unexplored. Here we present an X‐ray spectroscopic study of a large sample of 44 extreme dust‐obscured galaxies (EDOGs) with F_(24μm)/F_R > 2000 and F_(24μm) > 1.3 mJy selected from a 6 deg^2 region in the SWIRE fields. The application of our selection criteria to a wide area survey has been capable of unveiling a population of X‐ray luminous, absorbed z > 1 quasars which is mostly missed in the traditional optical/X‐ray surveys performed so far. Advances in the understanding of the X‐ray properties of these recently‐discovered sources by Simbol‐X observations will be also discussed