C IV BAL disappearance in a large SDSS QSO sample

Broad absorption lines (BALs) in the spectra of quasi-stellar objects (QSOs) originate from outflowing winds along our line of sight; winds are thought to originate from the inner regions of the QSO accretion disk, close to the central supermassive black hole (SMBH). Winds likely play a role in galaxy evolution and aid the accretion mechanism onto the SMBH. BAL equivalent widths can change on typical timescales from months to years; such variability is generally attributed to changes in the covering factor and/or in the ionization level of the gas. We investigate BAL variability, focusing on BAL disappearance. We analyze multi-epoch spectra of more than 1500 QSOs -the largest sample ever used for such a study- observed by different programs from the Sloan Digital Sky Survey-I/II/III (SDSS), and search for disappearing C IV BALs. The spectra rest-frame time baseline ranges from 0.28 to 4.9 yr; the source redshifts range from 1.68 to 4.27. We detect 73 disappearing BALs in the spectra of 67 sources. This corresponds to 3.9% of disappearing BALs, and 5.1% of our BAL QSOs exhibit at least one disappearing BAL. We estimate the average lifetime of a BAL along our line of sight (~ 80-100 yr), which appears consistent with the accretion disk orbital time at distances where winds are thought to originate. We inspect properties of the disappearing BALs and compare them to the properties of our main sample. We also investigate the existence of a correlation in the variability of multiple troughs in the same spectrum, and find it persistent at large velocity offsets between BAL pairs, suggesting that a mechanism extending on a global scale is necessary to explain the phenomenon. We select a more reliable sample of disappearing BALs following Filiz Ak et al. (2012), where a subset of our sample was analyzed, and compare the findings from the two works, obtaining generally consistent results.Comment: 22 pages, 9 figures. Accepted for publication in A&

Optically variable active galactic nuclei in the 3 yr VST survey of the COSMOS field

The analysis of the variability of active galactic nuclei (AGNs) at different wavelengths and the study of possible correlations among different spectral windows are nowadays a major field of inquiry. Optical variability has been largely used to identify AGNs in multivisit surveys. The strength of a selection based on optical variability lies in the chance to analyze data from surveys of large sky areas by ground-based telescopes. However the effectiveness of optical variability selection, with respect to other multiwavelength techniques, has been poorly studied down to the depth expected from next generation surveys. Here we present the results of our r-band analysis of a sample of 299 optically variable AGN candidates in the VST survey of the COSMOS field, counting 54 visits spread over three observing seasons spanning > 3 yr. This dataset is > 3 times larger in size than the one presented in our previous analysis (De Cicco et al. 2015), and the observing baseline is ~8 times longer. We push towards deeper magnitudes (r(AB) ~23.5 mag) compared to past studies; we make wide use of ancillary multiwavelength catalogs in order to confirm the nature of our AGN candidates, and constrain the accuracy of the method based on spectroscopic and photometric diagnostics. We also perform tests aimed at assessing the relevance of dense sampling in view of future wide-field surveys. We demonstrate that the method allows the selection of high-purity (> 86%) samples. We take advantage of the longer observing baseline to achieve great improvement in the completeness of our sample with respect to X-ray and spectroscopically confirmed samples of AGNs (59%, vs. ~15% in our previous work), as well as in the completeness of unobscured and obscured AGNs. The effectiveness of the method confirms the importance to develop future, more refined techniques for the automated analysis of larger datasets.Comment: 21 pages, 10 figures; accepted for publication in A&

SUDARE-VOICE variability-selection of Active Galaxies in the Chandra Deep Field South and the SERVS/SWIRE region

One of the most peculiar characteristics of Active Galactic Nuclei (AGN) is their variability over all wavelengths. This property has been used in the past to select AGN samples and is foreseen to be one of the detection techniques applied in future multi-epoch surveys, complementing photometric and spectroscopic methods. In this paper, we aim to construct and characterise an AGN sample using a multi-epoch dataset in the r band from the SUDARE-VOICE survey. Our work makes use of the VST monitoring program of an area surrounding the Chandra Deep Field South to select variable sources. We use data spanning a six month period over an area of 2 square degrees, to identify AGN based on their photometric variability. The selected sample includes 175 AGN candidates with magnitude r < 23 mag. We distinguish different classes of variable sources through their lightcurves, as well as X-ray, spectroscopic, SED, optical and IR information overlapping with our survey. We find that 12% of the sample (21/175) is represented by SN. Of the remaining sources, 4% (6/154) are stars, while 66% (102/154) are likely AGNs based on the available diagnostics. We estimate an upper limit to the contamination of the variability selected AGN sample of about 34%, but we point out that restricting the analysis to the sources with available multi-wavelength ancillary information, the purity of our sample is close to 80% (102 AGN out of 128 non-SN sources with multi-wavelength diagnostics). Our work thus confirms the efficiency of the variability selection method in agreement with our previous work on the COSMOS field; in addition we show that the variability approach is roughly consistent with the infrared selection.Comment: Published in A & A, 15 pages, 6 figure

The VOICE Survey : VST Optical Imaging of the CDFS and ES1 Fields

Indexación: Scopus.We present the VST Optical Imaging of the CDFS and ES1 Fields (VOICE) Survey, a VST INAF Guaranteed Time program designed to provide optical coverage of two 4 deg2 cosmic windows in the Southern hemisphere. VOICE provides the first, multi-band deep optical imaging of these sky regions, thus complementing and enhancing the rich legacy of longer-wavelength surveys with VISTA, Spitzer, Herschel and ATCA available in these areas and paving the way for upcoming observations with facilities such as the LSST, MeerKAT and the SKA. VOICE exploits VST's OmegaCAM optical imaging capabilities and completes the reduction of WFI data available within the ES1 fields as part of the ESO-Spitzer Imaging Extragalactic Survey (ESIS) program providing ugri and uBVR coverage of 4 and 4 deg2 areas within the CDFS and ES1 field respectively. We present the survey's science rationale and observing strategy, the data reduction and multi-wavelength data fusion pipeline. Survey data products and their future updates will be released at http://www.mattiavaccari.net/voice/ and on CDS/VizieR.https://pos.sissa.it/275/026/pd

Phonons and related properties of extended systems from density-functional perturbation theory

This article reviews the current status of lattice-dynamical calculations in crystals, using density-functional perturbation theory, with emphasis on the plane-wave pseudo-potential method. Several specialized topics are treated, including the implementation for metals, the calculation of the response to macroscopic electric fields and their relevance to long wave-length vibrations in polar materials, the response to strain deformations, and higher-order responses. The success of this methodology is demonstrated with a number of applications existing in the literature.Comment: 52 pages, 14 figures, submitted to Review of Modern Physic

African Americans respond to stigmatization: the meanings and salience of confronting, deflecting conflict, educating the ignorant and ‘managing the self’

Drawing on interviews with 150 randomly sampled African Americans, we analyse how members of a stigmatized group understand their experience of stigmatization and assess appropriate responses when asked about the best approach to deal with stigmatization and about responses to specific incidents. Combining in-depth interviews with a systematic coding of the data, we make original contributions to the previous literature by identifying the relative salience of modalities and tools for responding. We also examine closely through qualitative data the two most salient modalities of response, ‘confronting’ and ‘deflating’ conflict, the most salient tools, teaching out-group members about African Americans, and ‘the management of the self’, a rationale for deflating conflict that is largely overlooked in previous studies. We find that ‘confronting’ is the more popular modality for responding to stigmatization among African Americans.African and African American StudiesSociolog

Optimization over time of reliable 5G-RAN with network function migrations

Resource optimization in 5G Radio Access Networks (5G-RAN) has to face the dynamics over time in networks with increasing numbers of nodes and virtual network functions. In this context, multiple objectives need to be jointly optimized, and key application requirements such as latency must be enforced. In addition, virtual network functions realizing baseband processing are subject to failures of the cloud infrastructure, requiring an additional level of reliability. Overall, this is a complex problem to solve, requiring fast algorithms to cope with dynamic networks while avoiding resource overprovisioning. This paper considers the problem of optimal virtual function placement in 5G-RAN with reliability against a single DU Hotel failure and proposes a solution that takes service dynamics into account. Firstly, the joint optimization of the total number of DU Hotels, of the RU–DU latency and of the backup DU sharing in a static traffic scenario is considered, and the DUOpt algorithm, based on Lexicographic Optimization, is proposed for solving efficiently this multi- objective problem. DUOpt splits the multi-objective problem into smaller Integer Linear Programming (ILP) subproblems that are sequentially solved, adopting for each one the most effective methodology to reduce the total execution time. The proposed DUOpt algorithm is extensively benchmarked to show its effectiveness in optimization of medium to large size networks: in particular, it is shown to greatly outperform an aggregate multi-objective approach, being able to compute optimal or close to optimal solutions for networks of several tens of nodes in computing times of a few seconds. Then, the problem is extended to a dynamic traffic scenario in which optimization is performed over time. In this context, in addition to the aforementioned objectives, the total number of network function migrations induced by multiple reoptimizations must be kept to the minimum. For solving efficiently this problem the DUMig algorithm is proposed, which extends and improves DUOpt. Reoptimization over a time horizon of one day in an illustrative dynamic traffic scenario is performed to evaluate the proposed DUMig algorithm against DUOpt, the latter being oblivious of the traffic dynamics. DUMig shows remarkable savings in the total number of migrations (above 86.1% for primary virtual functions and 83% for backup virtual functions) compared to DUOpt, while preserving near-optimal resource assignment

Uncertainty-Aware QoT Forecasting in Optical Networks with Bayesian Recurrent Neural Networks

We consider the problem of forecasting the Quality-of-Transmission (QoT) of deployed lightpaths in a Wavelength Division Multiplexing (WDM) optical network. QoT forecasting plays a determinant role in network management and planning, as it allows network operators to proactively plan maintenance or detect anomalies in a lightpath. To this end, we leverage Bayesian Recurrent Neural Networks for learning uncertainty-aware probabilistic QoT forecasts, i.e., for modelling a probability distribution of the QoT over a time horizon. We evaluate our proposed approach on the open-source Microsoft Wide Area Network (WAN) optical backbone dataset. Our illustrative numerical results show that our approach not only outperforms state-of-the-art models from literature, but also predicts intervals providing near-optimal empirical coverage. As such, we demonstrate that uncertainty-aware probabilistic modelling enables the application of QoT forecasting in risk-sensitive application scenarios

Hollow-Core-Fiber Placement in Latency-Constrained Metro Networks with edgeDCs

We investigate the optimal placement of Hollow-Core Fibers (HCF) in latency-constrained metro networks with edgeDCs, performing physical-layer validation. Upgrading 24% of links to HCF reduces edgeDCs number by 29% compared to a network without HCFs