Their Perceptions: African American Males in African American Male Initiatives at Two Predominantly White Institutions

A capstone submitted in partial fulfillment of the requirements for the degree of Doctor of Education in the College of Education at Morehead State University by Robert De\u27Andre Sparks on April 9, 2019

Computer-assisted planning for minimally invasive anterior two-thirds laser corpus callosotomy: A feasibility study with probabilistic tractography validation.

BACKGROUND: Anterior two-thirds corpus callosotomy is an effective palliative neurosurgical procedure for drug-refractory epilepsy that is most commonly used to treat drop-attacks. Laser interstitial thermal therapy is a novel stereotactic ablative technique that has been utilised as a minimally invasive alternative to resective and disconnective open neurosurgery. Case series have reported success in performing laser anterior two-thirds corpus callosotomy. Computer-assisted planning algorithms may help to automate and optimise multi-trajectory planning for this procedure. OBJECTIVE: To undertake a simulation-based feasibility study of computer-assisted corpus callostomy planning in comparison with expert manual plans in the same patients. METHODS: Ten patients were selected from a prospectively maintained database. Patients had previously undergone diffusion-weighted imaging and digital subtraction angiography as part of routine SEEG care. Computer-assisted planning was performed using the EpiNav™ platform and compared to manually planned trajectories from two independent blinded experts. Estimated ablation cavities were used in conjunction with probabilistic tractography to simulate the expected extent of interhemispheric disconnection. RESULTS: Computer-assisted planning resulted in significantly improved trajectory safety metrics (risk score and minimum distance to vasculature) compared to blinded external expert manual plans. Probabilistic tractography revealed residual interhemispheric connectivity in 1/10 cases following computer-assisted planning compared to 4/10 and 2/10 cases with manual planning. CONCLUSION: Computer-assisted planning successfully generates multi-trajectory plans capable of LITT anterior two-thirds corpus callosotomy. Computer-assisted planning may provide a means of standardising trajectory planning and serves as a potential new tool for optimising trajectories. A prospective validation study is now required to determine if this translates into improved patient outcomes

Spatially-resolved X-ray spectroscopy of the core of the Centaurus cluster

We present Chandra data from a 31.7 ks observation of the Centaurus cluster, using the ACIS-S detector. Images of the X-ray emission show a plume-like feature at the centre of the cluster, of extent 60 arcsec (20 kpc in projection). The feature has the same metallicity as gas at a similar radius, but is cooler. Using adaptive binning, we generate temperature, abundance and absorption maps of the cluster core. The radial abundance profile shows that the previously known, steep abundance gradient peaks with a metallicity of 1.3-1.8 Zsolar at a radius of about 45 arcsec (15 kpc), before falling back to 0.4 Zsolar at the centre of the cluster. A radial temperature profile shows that the temperature decreases inwards. We determine the spatial distributions of each of two temperature components, where applicable. The radiative cooling time of the cooler component within the inner 10 arcsec (3 kpc) is less than 2x10^7 yr. X-ray holes in the image coincident with the radio lobes are seen, as well as two outer sharp temperature drops, or cold fronts. The origin of the plume is unclear. The existence of the strong abundance gradient is a strong constraint on extensive convection or gas motion driven by a central radio source.Comment: 11 pages, 14 figures (3 colour), accepted by MNRAS, high res. version at http://www-xray.ast.cam.ac.uk/papers/cen1_accptd.pdf . Updated version includes a section considering a non-thermal componen

Cold fronts and multi-temperature structures in the core of Abell 2052

The physics of the coolest phases in the hot Intra-Cluster Medium (ICM) of clusters of galaxies is yet to be fully unveiled. X-ray cavities blown by the central Active Galactic Nucleus (AGN) contain enough energy to heat the surrounding gas and stop cooling, but locally blobs or filaments of gas appear to be able to cool to low temperatures of 10^4 K. In X-rays, however, gas with temperatures lower than 0.5 keV is not observed. Using a deep XMM-Newton observation of the cluster of galaxies Abell 2052, we derive 2D maps of the temperature, entropy, and iron abundance in the core region. About 130 kpc South-West of the central galaxy, we discover a discontinuity in the surface brightness of the hot gas which is consistent with a cold front. Interestingly, the iron abundance jumps from ~0.75 to ~0.5 across the front. In a smaller region to the North-West of the central galaxy we find a relatively high contribution of cool 0.5 keV gas, but no X-ray emitting gas is detected below that temperature. However, the region appears to be associated with much cooler H-alpha filaments in the optical waveband. The elliptical shape of the cold front in the SW of the cluster suggests that the front is caused by sloshing of the hot gas in the clusters gravitational potential. This effect is probably an important mechanism to transport metals from the core region to the outer parts of the cluster. The smooth temperature profile across the sharp jump in the metalicity indicates the presence of heat conduction and the lack of mixing across the discontinuity. The cool blob of gas NW of the central galaxy was probably pushed away from the core and squeezed by the adjacent bubble, where it can cool efficiently and relatively undisturbed by the AGN. Shock induced mixing between the two phases may cause the 0.5 keV gas to cool non-radiatively and explain our non-detection of gas below 0.5 keV.Comment: 11 pages, 9 figures, A&A, in pres

Measurement of the intrinsic damping constant in individual nanodisks of YIG and YIG{\textbar}Pt

We report on an experimental study on the spin-waves relaxation rate in two series of nanodisks of diameter $\phi=$300, 500 and 700~nm, patterned out of two systems: a 20~nm thick yttrium iron garnet (YIG) film grown by pulsed laser deposition either bare or covered by 13~nm of Pt. Using a magnetic resonance force microscope, we measure precisely the ferromagnetic resonance linewidth of each individual YIG and YIG{\textbar}Pt nanodisks. We find that the linewidth in the nanostructure is sensibly smaller than the one measured in the extended film. Analysis of the frequency dependence of the spectral linewidth indicates that the improvement is principally due to the suppression of the inhomogeneous part of the broadening due to geometrical confinement, suggesting that only the homogeneous broadening contributes to the linewidth of the nanostructure. For the bare YIG nano-disks, the broadening is associated to a damping constant $\alpha = 4 \cdot 10^{-4}$. A 3 fold increase of the linewidth is observed for the series with Pt cap layer, attributed to the spin pumping effect. The measured enhancement allows to extract the spin mixing conductance found to be $G_{\uparrow \downarrow}= 1.55 \cdot 10^{14}~ \Omega^{-1}\text{m}^{-2}$ for our YIG(20nm){\textbar}Pt interface, thus opening large opportunities for the design of YIG based nanostructures with optimized magnetic losses.Comment: 4 pages, 3 figure

Optical IFU Observations of the Brightest Cluster Galaxy NGC 4696: The Case for a Minor Merger and Shock-excited Filaments

We present deep optical integral-field spectroscopic observations of the nearby (z ~ 0.01) brightest cluster galaxy NGC 4696 in the core of the Centaurus Cluster, made with the Wide Field Spectrograph (WiFeS) on the ANU 2.3m telescope at Siding Spring Observatory. We investigate the morphology, kinematics, and excitation of the emission-line filaments and discuss these in the context of a model of a minor merger. We suggest that the emission-line filaments in this object have their origin in the accretion of a gas-rich galaxy and that they are excited by v ~100-200 km/s shocks driven into the cool filament gas by the ram pressure of the transonic passage of the merging system through the hot halo gas of NGC 4696.Comment: 19 pages, 15 figures, accepted for publication in The Astrophysical Journa

Static displacements and chemical correlations in alloys

Recent experiments in metallic solid solutions have revealed interesting correlations between static pair-displacements and the ordering behavior of these alloys. This paper discusses a simple theoretical model which successfully explains these observations and which provides a natural framework for analyzing experimental measurements of pair-displacements and chemical correlations in solid solutions. The utility and scope of this model is demonstrated by analyzing results of experiments on $Ni-Fe$ and $Cr-Fe$ alloys and results of simulations of $Cu-Au$ and $Cu-Ag$ alloys.Comment: 12 page

HST/ACS Emission Line Imaging of Low Redshift 3CR Radio Galaxies I: The Data

We present 19 nearby (z<0.3) 3CR radio galaxies imaged at low- and high-excitation as part of a Cycle 15 Hubble Space Telescope snapshot survey with the Advanced Camera for Surveys. These images consist of exposures of the H-alpha (6563 \AA, plus [NII] contamination) and [OIII] 5007 \AA emission lines using narrow-band linear ramp filters adjusted according to the redshift of the target. To facilitate continuum subtraction, a single-pointing 60 s line-free exposure was taken with a medium-band filter appropriate for the target's redshift. We discuss the steps taken to reduce these images independently of the automated recalibration pipeline so as to use more recent ACS flat-field data as well as to better reject cosmic rays. We describe the method used to produce continuum-free (pure line-emission) images, and present these images along with qualitative descriptions of the narrow-line region morphologies we observe. We present H-alpha+[NII] and [OIII] line fluxes from aperture photometry, finding the values to fall expectedly on the redshift-luminosity trend from a past HST/WFPC2 emission line study of a larger, generally higher redshift subset of the 3CR. We also find expected trends between emission line luminosity and total radio power, as well as a positive correlation between the size of the emission line region and redshift. We discuss the associated interpretation of these results, and conclude with a summary of future work enabled by this dataset.Comment: 18 pages, 12 figures, accepted for publication in ApJ

The HST survey of the B2 sample of radio galaxies: detection of two optical jets

We present HST observations of previously undetected optical jets in the low-luminosity radio galaxies B2 0755+37 and B2 1553+24. We show that there is accurate spatial coincidence between optical and radio emission, implying that the former is likely to be synchrotron radiation. The physical properties of the jets are similar to those known previously: their radio-optical spectral indices are ~0.7 and in B2 0755+37, the spectrum steepens between optical and X-ray wavelengths. Our results support the hypothesis that optical emission is detectable from jets orientated within ~20 degrees of the line of sight for the B2 sample.Comment: Accepted for publication in A&A, 6 pages, 4 figure