On the role of topology in autonomously coping with failures in content dissemination systems

2014 Fall.Includes bibliographical references.Content dissemination systems provide a substrate that allows large numbers of entities to communicate with each other. These entities could be processes, sensors, and networked instruments that produce and consume data streams. To ensure scaling, the content dissemination substrate comprises a large number of distributed nodes. As the number of participating nodes increases, the likelihood of failures also increases. These failures can occur for any number of reasons, including: faulty hardware, programmer or user error, power failure, and network outages. Node failures can result in partitions with the original set of connected nodes disintegrating into smaller, disjoint subsets. Brewer's CAP theorem limits the choices for a partitioned system: availability or consistency but not both. It is therefore desirable to ensure that partitions are less likely. This thesis explores how nodes comprising the content dissemination system can be organized into topologies with the objective of improved partition tolerance. The topologies we consider are based on random, regular, power law, and Watts-Strogatz small world graphs. Connections within these topologies can account for network proximity and are suitable for real-time communications. We explore specific attributes of a topology that contribute to its partition resiliency, such as clustering coefficients, distribution of random links, and preferential attachment. Metrics we use to profile suitability of different topologies include: communication path lengths, migration of workloads, and the impact on system throughput. This research will allow designers to choose topologies or configure metrics to achieve performance objectives and the degree of partition tolerance

Scalable visual analytics over voluminous spatiotemporal data

2018 Fall.Includes bibliographical references.Visualization is a critical part of modern data analytics. This is especially true of interactive and exploratory visual analytics, which encourages speedy discovery of trends, patterns, and connections in data by allowing analysts to rapidly change what data is displayed and how it is displayed. Unfortunately, the explosion of data production in recent years has led to problems of scale as storage, processing, querying, and visualization have struggled to keep pace with data volumes. Visualization of spatiotemporal data pose unique challenges, thanks in part to high-dimensionality in the input feature space, interactions between features, and the production of voluminous, high-resolution outputs. In this dissertation, we address challenges associated with supporting interactive, exploratory visualization of voluminous spatiotemporal datasets and underlying phenomena. This requires the visualization of millions of entities and changes to these entities as the spatiotemporal phenomena unfolds. The rendering and propagation of spatiotemporal phenomena must be both accurate and timely. Key contributions of this dissertation include: 1) the temporal and spatial coupling of spatially localized models to enable the visualization of phenomena at far greater geospatial scales; 2) the ability to directly compare and contrast diverging spatiotemporal outcomes that arise from multiple exploratory "what-if" queries; and 3) the computational framework required to support an interactive user experience in a heavily resource-constrained environment. We additionally provide support for collaborative and competitive exploration with multiple synchronized clients

Building the Kingdom: A Supervision Training Program in Pastoral Care and Homiletics

We believe deeply in the importance of supervision for all ministers and would call supervision an essential ministry of and for the ecclesia. With this in mind, we created a certificate program in supervision that would foster lifelong learning and best practices in ministry. In writing this article, we hope to share our work with the larger community and invite conversation regarding the training and practice of supervision for pastoral ministry and preaching

A UV to Mid-IR Study of AGN Selection

We classify the spectral energy distributions (SEDs) of 431,038 sources in the 9 sq. deg Bootes field of the NOAO Deep Wide-Field Survey (NDWFS). There are up to 17 bands of data available per source, including ultraviolet (GALEX), optical (NDWFS), near-IR (NEWFIRM), and mid-infrared (IRAC/MIPS) data, as well as spectroscopic redshifts for ~20,000 objects, primarily from the AGN and Galaxy Evolution Survey (AGES). We fit galaxy, AGN, stellar, and brown dwarf templates to the observed SEDs, which yield spectral classes for the Galactic sources and photometric redshifts and galaxy/AGN luminosities for the extragalactic sources. The photometric redshift precision of the galaxy and AGN samples are sigma/(1+z)=0.040 and sigma/(1+z)=0.169, respectively, with the worst 5% outliers excluded. Based on the reduced chi-squared of the SED fit for each SED model, we are able to distinguish between Galactic and extragalactic sources for sources brighter than I=23.5. We compare the SED fits for a galaxy-only model and a galaxy+AGN model. Using known X-ray and spectroscopic AGN samples, we confirm that SED fitting can be successfully used as a method to identify large populations of AGN, including spatially resolved AGN with significant contributions from the host galaxy and objects with the emission line ratios of "composite" spectra. We also use our results to compare to the X-ray, mid-IR, optical color and emission line ratio selection techniques. For an F-ratio threshold of F>10 we find 16,266 AGN candidates brighter than I=23.5 and a surface density of ~1900 AGN per deg^2.Comment: Submitted to ApJ, 35 pages, 17 figures, 2 table

The NuSTAR Extragalactic Surveys: unveiling rare, buried AGNs and detecting the contributors to the peak of the Cosmic X-ray Background

We report on the results of active galactic nuclei (AGNs) detection by NuSTAR performed in three extragalactic survey fields (COSMOS, UDS, ECDFS) in three hard bands, namely H1 (8-16 keV), H2 (16-24 keV) and VH (35-55 keV). The aggregated area of the surveys is $\sim 2.7$ deg$^2$. While a large number of sources is detected in the H1 band (72 at the $97\%$ level of reliability), the H2 band directly probing close to the peak of the Cosmic X-ray Background (CXB) returns four significant detections, and two tentative, although not significant, detections are found in the VH band. All the sources detected above 16 keV are also detected at lower energies. We compute the integral number counts for sources in such bands, which show broad consistency with population synthesis models of the CXB. We furthermore identify two Compton-thick AGNs, one in the COSMOS field, associated with a hard and faint Chandra source, and one in the UDS field, never detected in the X-ray band before. Both sources are at the same redshift $z \sim 1.25$, which shifts their Compton-hump into the H1 band, and were previously missed in the usually employed NuSTAR bands, confirming the potential of using the H1 band to discover obscured AGNs at $z > 1$ in deep surveys.Comment: 12 pages, 5 figures, accepted for publication in The Astrophysical Journa

The X-Ray and Mid-infrared Luminosities in Luminous Type 1 Quasars

Several recent studies have reported different intrinsic correlations between the AGN mid-IR luminosity (LMIR) and the rest-frame 2-10 keV luminosity (LX) for luminous quasars. To understand the origin of the difference in the observed LX−LMIR relations, we study a sample of 3,247 spectroscopically confirmed type 1 AGNs collected from Bo\ {o}tes, XMM-COSMOS, XMM-XXL-North, and the SDSS quasars in the Swift/XRT footprint spanning over four orders of magnitude in luminosity. We carefully examine how different observational constraints impact the observed LX−LMIR relations, including the inclusion of X-ray non-detected objects, possible X-ray absorption in type 1 AGNs, X-ray flux limits, and star formation contamination. We find that the primary factor driving the different LX−LMIR relations reported in the literature is the X-ray flux limits for different studies. When taking these effects into account, we find that the X-ray luminosity and mid-IR luminosity (measured at rest-frame 6μm, or L6μm) of our sample of type 1 AGNs follow a bilinear relation in the log-log plane: logLX=(0.84±0.03)×logL6μm/1045ergs−1+(44.60±0.01) for L6μm\u3c1044.79ergs−1, and logLX=(0.40±0.03)×logL6μm/1045ergs−1+(44.51±0.01) for L6μm≥1044.79ergs−1. This suggests that the luminous type 1 quasars have a shallower LX−LMIR correlation than the approximately linear relations found in local Seyfert galaxies. This result is consistent with previous studies reporting a luminosity-dependent LX−LMIR relation, and implies that assuming a linear LX−LMIR relation to infer the neutral gas column density for X-ray absorption might overestimate the column densities in luminous quasar

The X-Ray and Mid-infrared Luminosities in Luminous Type 1 Quasars

Several recent studies have reported different intrinsic correlations between the AGN mid-IR luminosity (LMIR) and the rest-frame 2-10 keV luminosity (LX) for luminous quasars. To understand the origin of the difference in the observed LX−LMIR relations, we study a sample of 3,247 spectroscopically confirmed type 1 AGNs collected from Bo\ {o}tes, XMM-COSMOS, XMM-XXL-North, and the SDSS quasars in the Swift/XRT footprint spanning over four orders of magnitude in luminosity. We carefully examine how different observational constraints impact the observed LX−LMIR relations, including the inclusion of X-ray non-detected objects, possible X-ray absorption in type 1 AGNs, X-ray flux limits, and star formation contamination. We find that the primary factor driving the different LX−LMIR relations reported in the literature is the X-ray flux limits for different studies. When taking these effects into account, we find that the X-ray luminosity and mid-IR luminosity (measured at rest-frame 6μm, or L6μm) of our sample of type 1 AGNs follow a bilinear relation in the log-log plane: logLX=(0.84±0.03)×logL6μm/1045ergs−1+(44.60±0.01) for L6μm\u3c1044.79ergs−1, and logLX=(0.40±0.03)×logL6μm/1045ergs−1+(44.51±0.01) for L6μm≥1044.79ergs−1. This suggests that the luminous type 1 quasars have a shallower LX−LMIR correlation than the approximately linear relations found in local Seyfert galaxies. This result is consistent with previous studies reporting a luminosity-dependent LX−LMIR relation, and implies that assuming a linear LX−LMIR relation to infer the neutral gas column density for X-ray absorption might overestimate the column densities in luminous quasar

STRS SpaceWire FPGA Module

An FPGA module leverages the previous work from Goddard Space Flight Center (GSFC) relating to NASA s Space Telecommunications Radio System (STRS) project. The STRS SpaceWire FPGA Module is written in the Verilog Register Transfer Level (RTL) language, and it encapsulates an unmodified GSFC core (which is written in VHDL). The module has the necessary inputs/outputs (I/Os) and parameters to integrate seamlessly with the SPARC I/O FPGA Interface module (also developed for the STRS operating environment, OE). Software running on the SPARC processor can access the configuration and status registers within the SpaceWire module. This allows software to control and monitor the SpaceWire functions, but it is also used to give software direct access to what is transmitted and received through the link. SpaceWire data characters can be sent/received through the software interface, as well as through the dedicated interface on the GSFC core. Similarly, SpaceWire time codes can be sent/received through the software interface or through a dedicated interface on the core. This innovation is designed for plug-and-play integration in the STRS OE. The SpaceWire module simplifies the interfaces to the GSFC core, and synchronizes all I/O to a single clock. An interrupt output (with optional masking) identifies time-sensitive events within the module. Test modes were added to allow internal loopback of the SpaceWire link and internal loopback of the client-side data interface