Investigating the Structure of the Windy Torus in Quasars

Thermal mid-infrared emission of quasars requires an obscuring structure that can be modeled as a magneto-hydrodynamic wind in which radiation pressure on dust shapes the outflow. We have taken the dusty wind models presented by Keating and collaborators that generated quasar mid-infrared spectral energy distributions (SEDs), and explored their properties (such as geometry, opening angle, and ionic column densities) as a function of Eddington ratio and X-ray weakness. In addition, we present new models with a range of magnetic field strengths and column densities of the dust-free shielding gas interior to the dusty wind. We find this family of models -- with input parameters tuned to accurately match the observed mid-IR power in quasar SEDs -- provides reasonable values of the Type 1 fraction of quasars and the column densities of warm absorber gas, though it does not explain a purely luminosity-dependent covering fraction for either. Furthermore, we provide predictions of the cumulative distribution of E(B-V) values of quasars from extinction by the wind and the shape of the wind as imaged in the mid-infrared. Within the framework of this model, we predict that the strength of the near-infrared bump from hot dust emission will be correlated primarily with L/L_Edd rather than luminosity alone, with scatter induced by the distribution of magnetic field strengths. The empirical successes and shortcomings of these models warrant further investigations into the composition and behaviour of dust and the nature of magnetic fields in the vicinity of actively accreting supermassive black holes.Comment: 11 pages, 6 figures, accepted for publication in MNRA

EXTENSION PROGRAMS ON THE SOIL BANK

Teaching/Communication/Extension/Profession,

Size and phase control of cobalt-carbide nanoparticles using OH- and Cl- anions in a polyol process

Exchange coupled cobalt–carbide nanocomposites and single-phase Co2C nanoparticles were synthesized using the polyol process. Hydroxide and chloride anions were used to controlcarbide phase and particle shape. Synthesized Co x C nanocomposites exhibited average diameters around 300 nm. Co x C nanocomposites synthesized at 0.25 M [OH−] and [Cl−] formed clusters of capped nanorods, whereas synthesis at 0.37 M [OH−] and [Cl−] produced clusters of long blade-like particles. For single-phase Co2C, an [OH−] and [Cl−] of 0.71 M was used and produced clusters of ellipsoidal grains. The Co x C nanocomposites comprised of capped nanorods possessed a BH max of 1.65 MGOe with a magnetic saturation and coercivity values of 38 emu/g and 2.4 kOe, respectively. Co2C possessed a saturation magnetization of 16 emu/g and coercivity of 1.3 kOe

Physical aspects of oracles for randomness, and Hadamard's conjecture

We analyze the physical aspects and origins of currently proposed oracles for (absolute) randomness.Comment: 10 pages, 3 figures. arXiv admin note: substantial text overlap with arXiv:1405.140

On the Dynamics of Suddenly Heated Accretion Disks around Neutron Stars

Type I X-ray bursts and superbursts on neutron stars release sudden and intense radiation fields into their surroundings. Here, we consider the possible effects of these powerful explosions on the structure of the accretion disk. The goal is to account for the apparent evolution of the innermost regions of the accretion disk around 4U 1820-30 during a superburst. Three different processes are considered in detail: radiatively or thermally driven outflows, inflow due to Poynting-Robertson drag, and a structural change to the disk by X-ray heating. Radiatively driven winds with large column densities can be launched from the inner disk, but only for L/L_{Edd} >~ 1, which is expected to be obtained only at the onset of the burst. Furthermore, the predicted mass outflow rate is less than the accretion rate in 4U 1820-30. Estimates of the Poynting-Robertson or radiative drag timescale shows that it is a very efficient means of removing angular momentum from the gas. However, the analytical results are likely only applicable at the innermost edge of the disk. X-ray heating gives a change in the disk scale height that is correlated with the blackbody temperature, as seen in the evolution during the 4U 1820-30 superburst. If this change in the scale height can alter the surface density, then the viscous time (with \alpha ~ 0.03-0.2) is the closest match to the 4U 1820-30 results. We expect, however, that all three processes are likely ongoing when an accretion disk is subject to a sudden heating event. Ultimately, a numerical simulation of a disk around a bursting neutron star is required to determine the exact response of the disk. Magnetic truncation of the accretion flow is also considered and applied to the 4U 1820-30 X-ray reflection results.Comment: 14 pages, 6 figures, accepted by Ap

PARAMETER DEPENDENCE OF ACOUSTOELECTRIC AMPLIFICATION IN InSb

On the basis of a hydrodynamical theory of the acoustoelectric interaction (Fleming-Rowe) reported earlier which included electron inertial terms it is found that for sufficiently large electron drift velocities sharp high-gain peaks occur. Furthermore the peak values of gain achieved greatly exceed the maximum gain of the corresponding theory of Steele. Excellent agreement with recently reported experimental measurements of microwave acoustic gain in InSb is obtained. It is also noted that for large applied fields, empirical field factors are required to give agreement with experiment.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70684/2/APPLAB-18-3-96-1.pd