Black Hole Spin Properties of 130 AGN

Supermassive black holes may be described by their mass and spin. When supermassive black holes are active, the activity provides a probe of the state of the black hole system. The spin of a hole can be estimated when the black hole mass and beam power of the source are known for sources with powerful outflows. Seventy-five sources for which both the black hole mass and beam power could be obtained are identified and used to obtain estimates of black hole spins. The 75 supermassive black holes studied include 52 FRII radio galaxies and 23 FRII radio loud quasars with redshifts ranging from about zero to two. The new values are combined with those obtained previously for 19 FRII radio galaxies, 7 FRII radio loud quasars, and 29 radio sources associated with CD galaxies to form samples of 71 FRII radio galaxies, 30 FRII quasars, and a total sample of 130 spin values; all of the sources are associated with massive elliptical galaxies. The new values obtained are similar to those obtained earlier at similar redshift, and range from about 0.1 to 1 for FRII sources. The overall results are consistent with those obtained previously: the spins tend to decrease with decreasing redshift for the FRII sources studied. There is a hint that the range of values of black hole spin at a given redshift is larger for FRII quasars than for FRII radio galaxies. There is no indication of a strong correlation between supermassive black hole mass and spin for the supermassive black holes studied here. The relation between beam power and black hole mass is obtained and used as a diagnostic of the outflows and the dependence of the magnetic field strength on black hole mass.Comment: 12 pages, 12 figures, 5 table

Creep of Sylramic-iBN Fiber Tows at Elevated Temperature in Air and in Silicic Acid-Saturated Steam

Stressed oxidation experiments on Sylramic-iBN fiber tows were performed to evaluate the novel fiber\u27s mechanical performance, creep behavior, and creep mechanisms. This research effort investigated creep response of Sylramic-iBN fiber tows at elevated temperatures in both air and in silicic acid-saturated steam environments. Creep experiments were conducted at creep stresses ranging from 127 to 762 MPa at 400°C and 500°C in order to examine the mechanical behavior of the Sylramic-iBN fiber tows at temperatures below and above the melting point of boria (450°C). Sylramic-iBN fibers are known to have excellent creep resistance, better than most other non-oxide fibers and significantly better than oxide fibers. These fibers have a near-stoichiometric SiC composition, so they are a strong candidate for use in advanced aerospace CMCs. This research effort is a pilot program on the study of the effects of steam on Sylramic-iBN fibers. Previous attempts to study creep of SiC fiber tows in steam at elevated temperatures at the Air Force Institute of Technology\u27s (AFIT) Mechanics of Advanced Aerospace Materials Research Laboratory have yielded inconclusive results. Prior work at AFIT showed that the steam extracted silicon from the fiber tow and became saturated with silicic acid (Si[OH]4) . As the steam traveled along the SiC fiber, it also chemically altered the fiber surface producing inconsistent chemical compositions along the length of the fiber tow specimen. Along the fiber portion exposed to the unsaturated steam, the fiber experienced a chemical change leading to material loss, while the fiber portion exposed to the saturated steam experienced a silica scale growth along the fiber surface. A new test facility had to be designed to accurately evaluate the effects of steam on SiC fibers. The facility design incorporated an apparatus for saturating steam with silicic acid prior to entering the test chamber

The Relationship Between Beam Power and Radio Power for Classical Double Radio Sources

Beam power is a fundamental parameter that describes, in part, the state of a supermassive black hole system. Determining the beam powers of powerful classical double radio sources requires substantial observing time, so it would be useful to determine the relationship between beam power and radio power so that radio power could be used as a proxy for beam power. A sample of 31 powerful classical double radio sources with previously determined beam and radio powers are studied; the sources have redshifts between about 0.056 and 1.8. It is found that the relationship between beam power, Lj, and radio power, P, is well described by Log(Lj) = 0.84 Log(P) + 2.15, where both L_j and P are in units of 10^(44) erg/s. This indicates that beam power is converted to radio power with an efficiency of about 0.7%. The ratio of beam power to radio power is studied as a function of redshift; there is no significant evidence for redshift evolution of this ratio over the redshift range studied. The relationship is consistent with empirical results obtained by Cavagnolo et al. (2010) for radio sources in gas rich environments, which are primarily FRI sources, and with the theoretical predictions of Willott et al. (1999).Comment: 6 pages, 2 figures, 2 tables; accepted for publication in MNRA

Dissipation of stop-and-go waves via control of autonomous vehicles: Field experiments

Traffic waves are phenomena that emerge when the vehicular density exceeds a critical threshold. Considering the presence of increasingly automated vehicles in the traffic stream, a number of research activities have focused on the influence of automated vehicles on the bulk traffic flow. In the present article, we demonstrate experimentally that intelligent control of an autonomous vehicle is able to dampen stop-and-go waves that can arise even in the absence of geometric or lane changing triggers. Precisely, our experiments on a circular track with more than 20 vehicles show that traffic waves emerge consistently, and that they can be dampened by controlling the velocity of a single vehicle in the flow. We compare metrics for velocity, braking events, and fuel economy across experiments. These experimental findings suggest a paradigm shift in traffic management: flow control will be possible via a few mobile actuators (less than 5%) long before a majority of vehicles have autonomous capabilities

Directed self-organization of graphene nanoribbons on SiC

Realization of post-CMOS graphene electronics requires production of semiconducting graphene, which has been a labor-intensive process. We present tailoring of silicon carbide crystals via conventional photolithography and microelectronics processing to enable templated graphene growth on 4H-SiC{1-10n} (n = 8) crystal facets rather than the customary {0001} planes. This allows self-organized growth of graphene nanoribbons with dimensions defined by those of the facet. Preferential growth is confirmed by Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM) measurements, and electrical characterization of prototypic graphene devices is presented. Fabrication of > 10,000 top-gated graphene transistors on a 0.24 cm2 SiC chip demonstrates scalability of this process and represents the highest density of graphene devices reported to date.Comment: 13 pages, 5 figure

So you think you can track?

This work introduces a multi-camera tracking dataset consisting of 234 hours of video data recorded concurrently from 234 overlapping HD cameras covering a 4.2 mile stretch of 8-10 lane interstate highway near Nashville, TN. The video is recorded during a period of high traffic density with 500+ objects typically visible within the scene and typical object longevities of 3-15 minutes. GPS trajectories from 270 vehicle passes through the scene are manually corrected in the video data to provide a set of ground-truth trajectories for recall-oriented tracking metrics, and object detections are provided for each camera in the scene (159 million total before cross-camera fusion). Initial benchmarking of tracking-by-detection algorithms is performed against the GPS trajectories, and a best HOTA of only 9.5% is obtained (best recall 75.9% at IOU 0.1, 47.9 average IDs per ground truth object), indicating the benchmarked trackers do not perform sufficiently well at the long temporal and spatial durations required for traffic scene understanding