The new HiVIS spectropolarimeter and spectropolarimetric calibration of the AEOS telescope

We designed, built, and calibrated a new spectropolarimeter for the HiVIS spectrograph (R 12000-49000) on the AEOS telescope. We also did a polarization calibration of the telescope and instrument. We will introduce the design and use of the spectropolarimeter as well as a new data reduction package we have developed, then discuss the polarization calibration of the spectropolarimeter and the AEOS telescope. We used observations of unpolarized standard stars at many pointings to measure the telescope induced polarization and compare it with a Zemax model. The telescope induces polarization of 1-6% with a strong variation with wavelength and pointing, consistent with the altitude and azimuth variation expected. We then used scattered sunlight as a linearly polarized source to measure the telescopes spectropolarimetric response to linearly polarized light. We then made an all-sky map of the telescope's polarization response to calibrate future spectropolarimetry.Comment: PASP 118, June 200

Initial Results from a Stacked Ring Apparatus for Simulation of a Soil Profile

A stack of 48 rings, lined with a latex membrane, is used to confine a column of soil 12 inches high by 12 inches in diameter (300 mm x 300 mm). Both dry and saturated columns of fine sand are shaken at their base, at a centrifugal acceleration of 35.5 g. Measurements of the settlement of the surface, horizontal displacement and pore pressures show that the columns of soil are behaving essentially (although not exactly) as one-dimensional shear beams

Mars and the early Sun

Global mean temperatures near 273 K on early Mars are difficult to explain in the context of standards solar evolution models. Even assuming maximum CO2 greenhouse warming, the required flux is approximately 15 percent too low. Here we consider two astrophysical models that could increase the flux by this amount. The first model is a nonstandard solar model in which the early Sun had a mass somewhat greater than today's mass (1.02-1.06 solar mass). The second model is based on a standard evolutionary solar model, but the ecliptic flux is increased due to focusing by an (expected) heavily spotted early Sun

Factors That Influence Linkages to HIV Continuum of Care Services: Implications for Multi-Level Interventions

Worldwide, the human immunodeficiency virus (HIV) continuum of care involves health promotion providers (e.g., social workers and health educators) linking patients to medical personnel who provide HIV testing, primary care, and antiretroviral treatments. Regrettably, these life-saving linkages are not always made consistently and many patients are not retained in care. To design, test and implement effective interventions, we need to first identify key factors that may improve linkage-making. To help close this gap, we used in-depth interviews with 20 providers selected from a sample of 250 participants in a mixed-method longitudinal study conducted in New York City (2012–2017) in order to examine the implementation of HIV services for at-risk populations. Following a sociomedical framework, we identified provider-, interpersonal- and environmental-level factors that influence how providers engage patients in the care continuum by linking them to HIV testing, HIV care, and other support services. These factors occurred in four domains of reference: Providers’ Professional Knowledge Base; Providers’ Interprofessional Collaboration; Providers’ Work-Related Changes; and Best Practices in a Competitive Environment. Of particular importance, our findings show that a competitive environment and a fear of losing patients to other agencies may inhibit providers from engaging in linkage-making. Our results suggest relationships between factors within and across all four domains; we recommend interventions to modify factors in all domains for maximum effect toward improving care continuum linkage-making. Our findings may be applicable in different areas of the globe with high HIV prevalence

Atomic Scale Memory at a Silicon Surface

The limits of pushing storage density to the atomic scale are explored with a memory that stores a bit by the presence or absence of one silicon atom. These atoms are positioned at lattice sites along self-assembled tracks with a pitch of 5 atom rows. The writing process involves removal of Si atoms with the tip of a scanning tunneling microscope. The memory can be reformatted by controlled deposition of silicon. The constraints on speed and reliability are compared with data storage in magnetic hard disks and DNA.Comment: 13 pages, 5 figures, accepted by Nanotechnolog

Localized Excitons and Breaking of Chemical Bonds at III-V (110) Surfaces

Electron-hole excitations in the surface bands of GaAs(110) are analyzed using constrained density-functional theory calculations. The results show that Frenkel-type autolocalized excitons are formed. The excitons induce a local surface unrelaxation which results in a strong exciton-exciton attraction and makes complexes of two or three electron-hole pairs more favorable than separate excitons. In such microscopic exciton "droplets" the electron density is mainly concentrated in the dangling orbital of a surface Ga atom whereas the holes are distributed over the bonds of this atom to its As neighbors thus weakening the bonding to the substrate. This finding suggests the microscopic mechanism of a laser-induced emission of neutral Ga atoms from GaAs and GaP (110) surfaces.Comment: submitted to PRL, 10 pages, 4 figures available upon request from: [email protected]

Rapid Display of Radiographic Images

The requirements for the rapid display of radiographic images exceed the capabilities of widely available display, computer and communication technologies. Computed radiography captures data with a resolution of about four megapixels. Large format displays are available that can present over four megapixels. One megapixel displays are practical for use in combination with large format displays and in areas where the viewing task does not require primary diagnosis. This paper describes an electronic radiology system that approximates the highest quality systems, but through the use of several interesting techniques allows the possibility of its widespread installation throughout hospitals. The techniques uses can be grouped under three major systems concepts: a local, high-speed Image Server, one of more physician\u27s workstations each with one or more high-performance Auxiliary Displays specialized to the radiology viewing task, and dedicated, high-speed communication links between the server and the displays. This approach is enhanced by the use of a progressive transmission scheme to decrease the latency for viewing four megapixel images. The system includes an Image Server with storage for over 600 4 megapixel images and high-speed link. A subsampled megapixel image is fetched from disk and transmitted to the display in about one second followed by the full resolution 4 megapixel in about 2.5 seconds. Other system components include a megapixel display with a 6 megapixel display memory space and frame-rate update of image roam, zoom and contrast. Plans for clinical use are presented

Structure and Stability of Si(114)-(2x1)

We describe a recently discovered stable planar surface of silicon, Si(114). This high-index surface, oriented 19.5 degrees away from (001) toward (111), undergoes a 2x1 reconstruction. We propose a complete model for the reconstructed surface based on scanning tunneling microscopy images and first-principles total-energy calculations. The structure and stability of Si(114)-(2x1) arises from a balance between surface dangling bond reduction and surface stress relief, and provides a key to understanding the morphology of a family of surfaces oriented between (001) and (114).Comment: REVTeX, 4 pages + 3 figures. A preprint with high-resolution figures is available at http://cst-www.nrl.navy.mil/papers/si114.ps . To be published in Phys. Rev. Let

Speech Communication

Contains research objectives and three research projects.U. S. Air Force (Electronic Systems Division) under Contract AF 19(604)-6102National Science Foundation (Grant G-16526)National Institutes of Health (Grant MH-04737-02

Variation in abundance, diversity and composition of coral reef fishes with increasing depth at a submerged shoal in the northern Great Barrier Reef

Coral reef fishes often exhibit specific or restricted depth distributions, but the factors (biotic or abiotic) that influence patterns of depth use are largely unknown. Given inherent biological gradients with depth (i.e. light, nutrients, habitat, temperature), it is expected that fishes may exploit certain depths within their environment to seek out more favourable conditions. This study used baited remote underwater video (BRUV) systems to document variation in the taxonomic and functional (trophic and size) structure of a fish assemblage along a shallow to upper-mesophotic depth gradient (13–71 m) at a submerged, offshore shoal in the northern Great Barrier Reef. BRUVs were deployed during two separate time periods (February and August 2017), to separately examine patterns of depth use. Both the relative abundance and diversity of reef fishes declined with depth, and there were pronounced differences in the taxonomic and functional structure of the fish assemblage across the depth gradient. In shallow habitats ( 30 m) was dominated by piscivores and mobile invertivores. Depth and habitat type were also strong predictors for important fisheries species such as coral trout (Plectropomus spp.), emperors (Lethrinus spp.) and trevallies (Carangid spp.). We found limited evidence of temporal changes in depth and habitat use by fishes (including fisheries target species), although recorded temperatures were 4 °C higher in February 2017 compared to August 2017