Vortex Studies Relating to Boundary Layer Turbulence and Noise

The present study considers the two-dimensional case of an array of N rectilinear, like-sign vortices above an infinite flat boundary. The method of images can be employed with this configuration to reduce the problem to that of 2N vortices in free space, constrained by 2N symmetry relations. This system is Hamiltonian and therefore certain invariants of the motion are known. Further, from the Hamiltonian constant, the equations of motion are readily derived and may be integrated numerically to determine the vortex trajectories. This knowledge of the time-dependent vortex motion then allows the resulting noise radiation to be computed by standard aeroacoustic techniques

Structural sensitivity analysis: Methods, applications, and needs

Some innovative techniques applicable to sensitivity analysis of discretized structural systems are reviewed. These techniques include a finite-difference step-size selection algorithm, a method for derivatives of iterative solutions, a Green's function technique for derivatives of transient response, a simultaneous calculation of temperatures and their derivatives, derivatives with respect to shape, and derivatives of optimum designs with respect to problem parameters. Computerized implementations of sensitivity analysis and applications of sensitivity derivatives are also discussed. Finally, some of the critical needs in the structural sensitivity area are indicated along with Langley plans for dealing with some of these needs

Xenon in Mercury-Manganese Stars

Previous studies of elemental abundances in Mercury-Manganese (HgMn) stars have occasionally reported the presence of lines of the ionized rare noble gas Xe II, especially in a few of the hottest stars with Teff ~ 13000--15000 K. A new study of this element has been undertaken using observations from Lick Observatory's Hamilton Echelle Spectrograph. In this work, the spectrum synthesis program UCLSYN has been used to undertake abundance analysis assuming LTE. We find that in the Smith & Dworetsky sample of HgMn stars, Xe is vastly over-abundant in 21 of 22 HgMn stars studied, by factors of 3.1--4.8 dex. There does not appear to be a significant correlation of Xe abundance with Teff. A comparison sample of normal late B stars shows no sign of Xe II lines that could be detected, consistent with the expected weakness of lines at normal abundance. The main reason for the previous lack of widespread detection in HgMn stars is probably due to the strongest lines being at longer wavelengths than the photographic blue. The lines used in this work were 4603.03A, 4844.33A and 5292.22A.Comment: 8 pages, 4 figures. Accepted by Monthly Notices of the Royal Astronomical Society, 8 January 200

A finite element for thermal stress analysis of shells of revolution

A new finite element is described for performing detailed thermal stress analysis of thin orthotropic shells of revolution. The element provides for temperature loadings which may vary over the surface of the shell as well as through the thickness. In a number of sample calculations, results from the present method are compared with analytical solutions as well as with independent numerical analyses. Such calculations are carried out for two cylinders, a conical frustum, a truncated hemisphere, and an annular plate. Generally, the agreement between the present solution and the other solutions is excellent

Academic Law Library Director Status Since the Great Recession: Strengthened, Maintained, or Degraded?

The status of the academic law library director is central to the educational mission of the law library. We collected data from 2006 to 2016 showing a 25 percent decrease in tenure-track directorships. We also found one in four changes in directorships since 2013 resulted in the new director having a degraded status compared to her predecessor

Extremely metal-poor stars from the SDSS

We give a progress report about the activities within the CIFIST Team related to the search for extremely metal-poor stars in the Sloan Digital Sky Survey's spectroscopic catalog. So far the search has provided 25 candidates with metallicities around or smaller -3. For 15 candidates high resolution spectroscopy with UVES at the VLT has confirmed their extremely metal-poor status. Work is under way to extend the search to the SDSS's photometric catalog by augmenting the SDSS photometry, and by gauging the capabilities of X-shooter when going to significantly fainter targets.Comment: 6 pages, 6 figures, Proceedings paper of the conference "A stellar journey: A symposium in celebration of Bengt Gustafsson's 65th birthday

Transversely Driven Charge Density Waves and Striped Phases of High-Tc_c Superconductors: The Current Effect Transistor

We show that a normal (single particle) current density $J_x$ {\em transverse} to the ordering wavevector $2k_F{\bf\hat{z}}$ of a charge density wave (CDW) has dramatic effects both above and {\em below} the CDW depinning transition. It exponentially (in $J_x$) enhances CDW correlations, and exponentially suppresses the longitudinal depinning field. The intermediate longitudinal I-V relation also changes, acquiring a {\em linear} regime. We propose a novel ``current effect transistor'' whose CDW channel is turned on by a transverse current. Our results also have important implications for the recently proposed ``striped phase'' of the high-T$_c$ superconductors.Comment: change of title and minor corrections, 4 RevTeX pgs, to appear in Phys. Rev. Lett., 81, 3711 (1998

Astrometric-spectroscopic determination of the absolute masses of the HgMn binary star Phi Herculis

The Mercury-Manganese star Phi Her is a well known spectroscopic binary that has been the subject of a recent study by Zavala et al. (2006), in which they resolved the companion using long-baseline interferometry. The total mass of the binary is now fairly well established, but the combination of the spectroscopy with the astrometry has not resulted in individual masses consistent with the spectral types of the components. The motion of the center of light of Phi Her was clearly detected by the Hipparcos satellite. Here we make use of the Hipparcos intermediate data (`abscissa residuals') and show that by combining them in an optimal fashion with the interferometry the individual masses can be obtained reliably using only astrometry. We re-examine and then incorporate existing radial-velocity measurements into the orbital solution, obtaining improved masses of 3.05 +/- 0.24 M_Sun and 1.614 +/- 0.066 M_Sun that are consistent with the theoretical mass-luminosity relation from recent stellar evolution models. These mass determinations provide important information for the understanding of the nature of this peculiar class of stars.Comment: Total of 18 pages including figures and tables, in emulateapj format. To appear in The Astronomical Journal, June 2007 issu

The nuclear radio structure of X-ray bright AGN

The physical nature of the X-ray/radio correlation of AGN is still an unsolved question. High angular resolution observations are necessary to disentangle the associated energy dynamics into nuclear and stellar components. We present MERLIN/EVN 18cm observations of 13 X-raying AGN. The sample consists of Seyfert 1, Narrow Line Seyfert 1, and LINER-like galaxies. We find that for all objects the radio emission is unresolved and that the radio luminosities and brightness temperatures are too high for star formation to play an important role. This indicates that the radio emission in these sources is closely connected to processes that occur in the vicinity of the central massive black hole, also where the X-ray emission is believed to originate in.Comment: 5 pages, 3 figures, submitted to "The Universe under the Microscope - Astrophysics at High Angular Resolution", Bad Honnef, German