Compositional mapping of Saturn's satellite Dione with Cassini VIMS and implications of dark material in the Saturn system

Cassini VIMS has obtained spatially resolved imaging spectroscopy data on numerous satellites of Saturn. A very close fly-by of Dione provided key information for solving the riddle of the origin of the dark material in the Saturn system. The Dione VIMS data show a pattern of bombardment of fine, sub-0.5-μm diameter particles impacting the satellite from the trailing side direction. Multiple lines of evidence point to an external origin for the dark material on Dione, including the global spatial pattern of dark material, local patterns including crater and cliff walls shielding implantation on slopes facing away from the trailing side, exposing clean ice, and slopes facing the trailing direction which show higher abundances of dark material. Multiple spectral features of the dark material match those seen on Phoebe, Iapetus, Hyperion, Epimetheus and the F-ring, implying the material has a common composition throughout the Saturn system. However, the exact composition of the dark material remains a mystery, except that bound water and, tentatively, ammonia are detected, and there is evidence both for and against cyanide compounds. Exact identification of composition requires additional laboratory work. A blue scattering peak with a strong UV-visible absorption is observed in spectra of all satellites which contain dark material, and the cause is Rayleigh scattering, again pointing to a common origin. The Rayleigh scattering effect is confirmed with laboratory experiments using ice and 0.2-μm diameter carbon grains when the carbon abundance is less than about 2% by weight. Rayleigh scattering in solids is also confirmed in naturally occurring terrestrial rocks, and in previously published reflectance studies. The spatial pattern, Rayleigh scattering effect, and spectral properties argue that the dark material is only a thin coating on Dione's surface, and by extension is only a thin coating on Phoebe, Hyperion, and Iapetus, although the dark material abundance appears higher on Iapetus, and may be locally thick. As previously concluded for Phoebe, the dark material appears to be external to the Saturn system and may be cometary in origin. We also report a possible detection of material around Dione which may indicate Dione is active and contributes material to the E-ring, but this observation must be confirmed.     

Hard and Soft Skills in Preparing GIS Professionals: Comparing Perceptions of Employers and Educators

Organizations that hire GIS professionals look for entry‐level employees with specialized technical skills but also other competencies such as effective communication and a capacity to think critically and creatively. Indeed, the success of GIS projects and initiatives often depends on individuals who possess a combination of specialized GIS skills and more general competencies that influence their ability to collaborate and manage resources. This article presents findings from a survey of GIS employers and educators concerning the importance of hard and soft skills among entry‐level GIS professionals. A key finding is the high level of consistency in ratings assigned by employers and educators concerning hard skills such as data editing and GIS analysis and soft skills including problem solving and adaptability. However, the groups were less similar in ratings assigned to data capture skills, project management, and written/verbal skills. GIS qualifications were also compared, revealing a greater emphasis on internships among educators and higher ratings assigned to academic GIS certificates among employers.     

The Instructor Element of GIS Instruction at US Colleges and Universities

Over the last two decades, higher education has made substantial investments in GIS education through equipment and software purchases, upgrades to teaching facilities, and the creation of innovative academic programs such as certificates and degrees. However, comparatively less attention and fewer resources have been directed towards what might be called the “instructor element” of GIS instruction. In this article we look at the preparation and ongoing professional development of GIS educators through a survey of 270 individuals teaching GIS at US colleges and universities. Along with assessing the education and professional background of GIS instructors, we evaluate their perceptions concerning the importance of various GIS subject areas. Our findings demonstrate considerable breadth in the range of education and experience held by faculty members who are presently teaching GIS courses. In evaluating the importance placed on GIS teaching elements, we found little variation among individuals according to their institution type or educational attainment. However, significant differences in the perceived importance of GIS teaching areas were found across disciplinary areas.     

Chronic light reduction reduces overall resilience to additional shading stress in the seagrass Halophila ovalis

Seagrasses have substantial capacity to survive long periods of light reduction, but how acclimation to chronic low light environments may influence their ability to cope with additional stress is poorly understood. This study examines the effect of temporal light reduction by adding two levels of shading to Halophila ovalis plants in two meadows with different light histories, one characterized by a low light (turbid) environment and the other by a relatively high light (clear) environment. Additional shading resulted in complete mortality for both shading treatments at the turbid site while the clear site showed a pattern of decreased shoot density and increased photochemical efficiency (F_v/F_m) with increased shading. These contrasting results for the same species in two different locations indicate that acclimation to chronic low light regimes can affect seagrass resilience and highlights the importance of light history in determining the outcome of exposure to further (short-term) stress.     

Relocation of urban poor in Chicago: HOPE VI policy outcomes

The HOPE VI program was created in 1992 as a tool for public housing authorities in the US to deconcentrate poverty in project-based public housing neighborhoods. As part of the process, thousands of public housing residents have been required to relocate. They have the option to move to temporary housing in another project unit, to leave the subsidized housing system all together, or to participate in local housing voucher programs. This study focuses on those public housing residents in Chicago who move with a housing voucher certificate. The purpose of the study is to evaluate and reveal the relocation outcomes of these voucher users, both numerically and geographically. Conditions in their origin and relocation tracts are examined using 1990 and 2000 US census data to determine if they relocated to less poor and segregated neighborhoods. Evidence shows that voucher users are moving in an outward direction away from the central city. This movement is reshaping the landscape of advantage and disadvantage in Chicago: suburbs are becoming poorer while the old neighborhoods are gentrifying. Poverty is highly concentrated in the neighborhoods chosen by most voucher recipients, but not as high as the poverty levels which existed in the old neighborhoods. Mapping relocation shows that outcomes vary geographically, demonstrating the importance for future research to address spatial and contextual differences.     

Using a topographic index to distribute variable source area runoff predicted with the SCS curve‐number equation

Because the traditional Soil Conservation Service curve‐number (SCS‐CN) approach continues to be used ubiquitously in water quality models, new application methods are needed that are consistent with variable source area (VSA) hydrological processes in the landscape. We developed and tested a distributed approach for applying the traditional SCS‐CN equation to watersheds where VSA hydrology is a dominant process. Predicting the location of source areas is important for watershed planning because restricting potentially polluting activities from runoff source areas is fundamental to controlling non‐point‐source pollution. The method presented here used the traditional SCS‐CN approach to predict runoff volume and spatial extent of saturated areas and a topographic index, like that used in TOPMODEL, to distribute runoff source areas through watersheds. The resulting distributed CN–VSA method was applied to two subwatersheds of the Delaware basin in the Catskill Mountains region of New York State and one watershed in south‐eastern Australia to produce runoff‐probability maps. Observed saturated area locations in the watersheds agreed with the distributed CN–VSA method. Results showed good agreement with those obtained from the previously validated soil moisture routing (SMR) model. When compared with the traditional SCS‐CN method, the distributed CN–VSA method predicted a similar total volume of runoff, but vastly different locations of runoff generation. Thus, the distributed CN–VSA approach provides a physically based method that is simple enough to be incorporated into water quality models, and other tools that currently use the traditional SCS–CN method, while still adhering to the principles of VSA hydrology. Copyright © 2004 John Wiley & Sons, Ltd.     

Field methods for amending marine sediment with activated carbon and assessing treatment effectiveness

Previous laboratory studies have shown reductions in PCB bioavailability for sediments amended with activated carbon (AC). Here we report results on a preliminary pilot-scale study to assess challenges in scaling-up for field deployment and monitoring. The goals of the preliminary pilot-scale study at Hunters Point Shipyard (San Francisco, USA) were to (1) test the capabilities of a large-scale mixing device for incorporating AC into sediment, (2) develop and evaluate our field assessment techniques, and (3) compare reductions in PCB bioavailability found in the laboratory with well-mixed systems to those observed in the field with one-time-mixed systems. In this study we successfully used a large-scale device to mix 500kg of AC into a 34.4m(2) plot to a depth of 1ft, a depth that includes the majority of the biologically active zone. Our results indicate that after 7 months of AC-sediment contact in the field, the 28-day PCB bioaccumulation for the bent-nosed clam, Macoma nasuta, field-deployed to this AC-amended sediment was approximately half of the bioaccumulation resulting from exposure to untreated sediment. Similar PCB bioaccumulation reductions were found in laboratory bioassays conducted on both the bivalve, M. nasuta and the estuarine amphipod, Leptocheirus plumulosus, using sediment collected from the treated and untreated field plots one year after the AC amendment occurred. To further understand the long-term effectiveness of AC as an in situ treatment strategy for PCB-contaminated sediments under field conditions, a 3-year comprehensive study is currently underway at Hunters Point that will compare the effectiveness of two large-scale mixing devices and include both unmixed and mixed-only control plots.