Development of the HEFT and NuSTAR focusing telescopes

Hard X-ray/soft gamma-ray astrophysics is on the verge of a major advance with the practical realization of technologies capable of efficiently focusing X-rays above 10 keV. Hard X-ray focusing telescopes can achieve orders of magnitude improvements in sensitivity compared to the instruments based on coded apertures and collimated detectors that have traditionally been employed in this energy band. Compact focal planes enable high-performance detectors with good spectral resolution to be employed in efficient, low-background configurations. We have developed multilayer coated grazing incidence optics and solid state Cadmium Zinc Telluride focal plane systems for the High Energy Focusing Telescope (HEFT) balloon-borne experiment, and for the Nuclear Spectroscopic Telescope Array (NuSTAR) Small Explorer satellite. In this paper we describe the technologies, telescope designs, and performance of both experiments.     

CHARACTERISTICS OF THE AAG MEMBERSHIP IN 1982

A survey of members of the Association of American Geographers (AAG) in 1982 indicated that most were males, from middle class backgrounds, had attended public universities, held academic jobs, and had been born and educated in states bordering the Great Lakes plus California and Massachusetts. Information on characteristics and trends outlined in the study should be of value to the leadership of the AAG in making decisions relative to the future of the organization and the discipline.     

Rheological constraints on martian landslides

We use a dynamic finite-difference model to simulate martian landslides in the Valles Marineris canyon system and Olympus Mons aureole using three different modal rheologies: frictional, Bingham, and power law. The frictional and Bingham modes are applied individually. Fluidized rheology is treated as a combination of frictional and power-law modes; general fluidization can include pore pressure contributions, whereas acoustic fluidization does not. We find that general fluidization most often produces slides that best match landslide geometry in the Valles Marineris. This implies that some amount of supporting liquid or gas was present in the material during failure. The profile of the Olympus Mons aureole is not well matched by any landslide model, suggesting an alternative genesis. In contrast, acoustic fluidization produces the best match for a lunar slide, a result anticipated for dry crust with no overlying atmosphere. The presence of pressurized fluid during Valles Marineris landsliding may be due to liquid water beneath a thin cryosphere (<1-2 km) or flash sublimation of CO₂.     

Polar Plume Anatomy: Results of a Coordinated Observation

On 7 and 8 March 1996, the SOHO spacecraft and several other space- and ground-based observatories cooperated in the most comprehensive observation to date of solar polar plumes. Based on simultaneous data from five instruments, we describe the morphology of the plumes observed over the south pole of the Sun during the SOHO observing campaign. Individual plumes have been characterized from the photosphere to approximately 15 R⊙ yielding a coherent portrait of the features for more quantitative future studies. The observed plumes arise from small (∼ 2-5 arc sec diameter) quiescent, unipolar magnetic flux concentrations, on chromospheric network cell boundaries. They are denser and cooler than the surrounding coronal hole through which they extend, and are seen clearly in both Feix and Fexii emission lines, indicating an ionization temperature between 1.0–1.5 x 10⁶ K. The plumes initially expand rapidly with altitude, to a diameter of 20–30 Mm about 30 Mm off the surface. Above 1.2 R⊙ plumes are observed in white light (as ‘coronal rays’) and extend to above 12 R⊙. They grow superradially throughout their observed height, increasing their subtended solid angle (relative to disk center) by a factor of ∼10 between 1.05 R⊙ and 4–5 R⊙ and by a total factor of 20–40 between 1.05 R⊙ and 12 R⊙. On spatial scales larger than 10 arc sec, plume structure in the lower corona (R < 1.3 R⊙) is observed to be steady-state for periods of at least 24 hours; however, on spatial scales smaller than 10 arc sec, plume XUV intensities vary by 10–20% (after background subtraction) on a time scale of a few minutes. (Dr. Hassler is now employed by Southwest Research Institute, Boulder, CO)     

Effect of an acid mine drainage effluent on phytoplankton biomass and primary production at Britannia Beach, Howe Sound, British Columbia

We investigated the effect of acid mine drainage (AMD) from an abandoned copper mine at Britannia Beach (Howe Sound, BC, Canada) on primary productivity and chlorophyll a levels in the receiving waters of Howe Sound before, during, and after freshet from the Squamish River. Elevated concentrations of copper (integrated average through the water column >0.050 mg l⁻¹) in nearshore waters indicated that under some conditions a small gyre near the mouth of Britannia Creek may have retained the AMD from Britannia Creek and from a 30-m deep water outfall close to shore. Regression and correlation analyses indicated that copper negatively affected primary productivity during April (pre-freshet) and November (post-freshet). Negative effects of copper on primary productivity were not supported statistically for July (freshet), possibly because of additional effects such as turbidity from the Squamish River. Depth-integrated average and surface chlorophyll a were correlated to copper concentrations in April. During this short study we demonstrated that copper concentrations from the AMD discharge can negatively affect both primary productivity and the standing stock of primary producers in Howe Sound.