The Inner Rings of Beta Pictoris

We present Keck images of the dust disk around Beta Pictoris at 17.9 microns that reveal new structure in its morphology. Within 1" (19 AU) of the star, the long axis of the dust emission is rotated by more than 10 degrees with respect to that of the overall disk. This angular offset is more pronounced than the warp detected at 3.5" by HST, and in the opposite direction. By contrast, the long axis of the emission contours at ~ 1.5" from the star is aligned with the HST warp. Emission peaks between 1.5" and 4" from the star hint at the presence of rings similar to those observed in the outer disk at ~ 25" with HST/STIS. A deconvolved image strongly suggests that the newly detected features arise from a system of four non-coplanar rings. Bayesian estimates based on the primary image lead to ring radii of 14+/-1 AU, 28+/-3 AU, 52+/-2 AU and 82+/-2 AU, with orbital inclinations that alternate in orientation relative to the overall disk and decrease in magnitude with increasing radius. We believe these new results make a strong case for the existence of a nascent planetary system around Beta Pic.Comment: 5 pages, 2 figures, PDF format. Published in ApJL, December 20,200

PAH Emission from Ultraluminous Infrared Galaxies

We explore the relationships between the Polycyclic Aromatic Hydrocarbon (PAH) feature strengths, mid-infrared continuum luminosities, far-infrared spectral slopes, optical spectroscopic classifications, and silicate optical depths within a sample of 107 ULIRGs observed with the Infrared Spectrograph on the Spitzer Space Telescope. The detected 6.2 micron PAH equivalent widths (EQWs) in the sample span more than two orders of magnitude (0.006-0.8 micron), and ULIRGs with HII-like optical spectra or steep far-infrared spectral slopes (S_{25} / S_{60} < 0.2) typically have 6.2 micron PAH EQWs that are half that of lower-luminosity starbursts. A significant fraction (~40-60%) of HII-like, LINER-like, and cold ULIRGs have very weak PAH EQWs. Many of these ULIRGs also have large (tau_{9.7} > 2.3) silicate optical depths. The far-infrared spectral slope is strongly correlated with PAH EQW, but not with silicate optical depth. In addition, the PAH EQW decreases with increasing rest-frame 24 micron luminosity. We argue that this trend results primarily from dilution of the PAH EQW by continuum emission from dust heated by a compact central source, probably an AGN. High luminosity, high-redshift sources studied with Spitzer appear to have a much larger range in PAH EQW than seen in local ULIRGs, which is consistent with extremely luminous starburst systems being absent at low redshift, but present at early epochs.Comment: 15 pages, 9 Figures; Accepted for publication in Ap

Decentralization's impact on the health workforce: Perspectives of managers, workers and national leaders

Designers and implementers of decentralization and other reform measures have focused much attention on financial and structural reform measures, but ignored their human resource implications. Concern is mounting about the impact that the reallocation of roles and responsibilities has had on the health workforce and its management, but the experiences and lessons of different countries have not been widely shared. This paper examines evidence from published literature on decentralization's impact on the demand side of the human resource equation, as well as the factors that have contributed to the impact. The elements that make such an impact analysis exceptionally complex are identified. They include the mode of decentralization that a country is implementing, the level of responsibility for the salary budget and pay determination, and the civil service status of transferred health workers. The main body of the paper is devoted to examining decentralization's impact on human resource issues from three different perspectives: that of local health managers, health workers themselves, and national health leaders. These three groups have different concerns in the human resource realm, and consequently, have been differently affected by decentralization processes. The paper concludes with recommendations regarding three key concerns that national authorities and international agencies should give prompt attention to. They are (1) defining the essential human resource policy, planning and management skills for national human resource managers who work in decentralized countries, and developing training programs to equip them with such skills; (2) supporting research that focuses on improving the knowledge base of how different modes of decentralization impact on staffing equity; and (3) identifying factors that most critically influence health worker motivation and performance under decentralization, and documenting the most cost-effective best practices to improve them. Notable experiences from South Africa, Ghana, Indonesia and Mexico are shared in an annex

Measurement of corrosion content of archaeological lead artifacts by their Meissner response in the superconducting state; a new dating method

Meissner fraction in the superconducting state of lead archaeological artifacts is used to evaluate the mass of the uncorroded metal in the sample. Knowing the total mass of the sample the mass of all corrosion products is established. It is shown that this mass correlates with the archaeological age of the lead artifacts over a time span of ~2500 years. Well-dated untreated lead samples from Tel-Dor, the Persian period, Caesarea, the Byzantine and the Crusader periods as well as contemporary data were used to establish the dating correlation. This new chemical dating method is apparently applicable to lead artifacts buried in soils with the pH>6.5. In such soils the corrosion process is very slow and the corrosion products, mainly PbO and PbCO3, accumulate over hundreds of years. The method presented is in principle non-destructive. (corresponding author: )Comment: File ARCH_4.pdf 14 pages including 1 table and 5 figure

Thermoluminescence of zircon: a kinetic model

The mineral zircon, ZrSiO4, belongs to a class of promising materials for geochronometry by means of thermoluminescence (TL) dating. The development of a reliable and reproducible method for TL dating with zircon requires detailed knowledge of the processes taking place during exposure to ionizing radiation, long-term storage, annealing at moderate temperatures and heating at a constant rate (TL measurements). To understand these processes one needs a kinetic model of TL. This paper is devoted to the construction of such amodel. The goal is to study the qualitative behaviour of the system and to determine the parameters and processes controlling TL phenomena of zircon. The model considers the following processes: (i) Filling of electron and hole traps at the excitation stage as a function of the dose rate and the dose for both (low dose rate) natural and (high dose rate) laboratory irradiation. (ii) Time dependence of TL fading in samples irradiated under laboratory conditions. (iii) Short time annealing at a given temperature. (iv) Heating of the irradiated sample to simulate TL experiments both after laboratory and natural irradiation. The input parameters of the model, such as the types and concentrations of the TL centres and the energy distributions of the hole and electron traps, were obtained by analysing the experimental data on fading of the TL-emission spectra of samples from different geological locations. Electron paramagnetic resonance (EPR) data were used to establish the nature of the TL centres. Glow curves and 3D TL emission spectra are simulated and compared with the experimental data on time-dependent TL fading. The saturation and annealing behaviour of filled trap concentrations has been considered in the framework of the proposed kinetic model and comparedwith the EPR data associated with the rare-earth ions Tb3+ and Dy3+, which play a crucial role as hole traps and recombination centres. Inaddition, the behaviour of some of the SiOmn− centres has been compared with simulation results.

Stable rate of slip along the Karakax section of the Altyn Tagh Fault from observation of inter-glacial and post-glacial offset morphology and surface dating

Digital elevation maps obtained using TanDEM‐X and Pleiades data combined with newly obtained surface age estimates using Cosmogenic Radionuclide (CRN) and Optically Simulated Luminescence (OSL) methods are used to quantify the slip‐rate along the western section of the Altyn Tagh fault in southern Xinjiang. The reconstruction of the conical shape of massive alluvial fans inferred to be from the Eemian (115±7 ka) from CRN dating shows consistent left‐lateral offsets of 300±20 m, yielding a slip rate of 2.6±0.3 mm/yr. Successive episodes of incision have left cut terraces inset in wide canyons, 10‐25 m below the fans' surface. The incision was followed by the deposition of a broad terrace of early Holocene age, which is re‐incised by modern stream channels. Near the village of Shanxili, a 200 m‐wide valley is partially dammed by a shutter ridge displaced by the fault. A fill terrace deposited upstream from the ridge has an OSL age of.8±0.6 ka. The 23±2 m offset of the riser incising the terrace indicates a minimum post‐depositional movement on the fault, yielding a Holocene rate of 2.6±0.5 mm/yr, consistent with the 115 ka‐average slip rate. Scarp degradation analysis using mass diffusion reveals a non‐linear relationship between fault displacement and degradation coefficient along the progressively exposed fault scarp, a pattern suggesting either seismic clustering or variable diffusion rate since the Eemian. Together with the Gozha Co‐Longmu Co fault to the south, the Karakax section of the Altyn Tagh Fault contributes to the eastward movement of the western corner of Tibet

N-band Imaging of Seyfert Nuclei and the MIR-X-ray correlation

We present new mid-infrared (N-band) images of a sample of eight nearby Seyfert galaxies. In all of our targets, we detect a central unresolved source, which in some cases has been identified for the first time. In particular, we have detected the mid-infrared emission from the active nucleus of NGC 4945, which previously remained undetected at any wavelength but hard X-rays. We also detect circumnuclear extended emission in the Circinus galaxy along its major axis, and find marginal evidence for extended circumnuclear emission in NGC 3281. The high spatial resolution (1.7") of our data allows us to separate the flux of the nuclear point sources from the extended circumnuclear starburst (if present). We complement our sample with literature data for a number of non-active starburst galaxies, and relate the nuclear N-band flux to published hard (2-10 kev) X-ray fluxes. We find tight and well-separated correlations between nuclear N-band flux and X-ray flux for both Seyfert and starburst nuclei which span over 3 orders of magnitude in luminosity. We demonstrate that these correlations can be used as a powerful classification tool for galactic nuclei. For example, we find strong evidence against NGC 1808 currently harbouring an active Seyfert nucleus based on its position in the mid-infrared-X-ray diagram. On the other hand, we confirm that NGC 4945 is in fact a Seyfert 2 galaxy.Comment: 31 pages, incl. 4 figures, uses AASTex. Replaced with accepted version after minor modifications. To appear in Ap

PHASES Differential Astrometry and Iodine Cell Radial Velocities of the kappa Pegasi Triple Star System

kappa Pegasi is a well-known, nearby triple star system. It consists of a ``wide'' pair with semi-major axis 235 milli-arcseconds, one component of which is a single-line spectroscopic binary (semi-major axis 2.5 milli-arcseconds). Using high-precision differential astrometry and radial velocity observations, the masses for all three components are determined and the relative inclinations between the wide and narrow pairs' orbits is found to be 43.8 +/- 3.0 degrees, just over the threshold for the three body Kozai resonance. The system distance is determined to 34.60 +/- 0.21 parsec, and is consistent with trigonometric parallax measurements.Comment: Accepted for publication in ApJ, complete versions of tables 2 and 4 can be found at http://stuff.mit.edu/~matthew1/kapPegTables

Experimental observation of superradiance in millimeter-wave band

The first experimental results of the observation of superradiance from a single subnanosecond electron bunch are presented. Superradiance was associated with different varieties of stimulated emission (bremstruhlung, cyclotron, Cherenkov, etc). Unique megawatt power level microwave pulses of short duration (0.3-0.5 ns) have been obtained