Radar observations of 8P/Tuttle: A contact-binary comet     

John K. Harmon  Michael C. Nolan  Ellen S. Howell 《Icarus》2010,207(1):499-502

Arecibo radar imagery of Comet 8P/Tuttle reveals a 10-km-long nucleus with a highly bifurcated shape consistent with a contact binary. A separate echo component was also detected from large (>cm-size), slow-moving grains of the type expected to contribute to the Ursid meteor stream.  相似文献   

Magnetic Flux Transport in the ISM Through Turbulent Ambipolar Diffusion     

Fabian Heitsch  Ellen G. Zweibel  Adrianne D. Slyz  Julien E.G. Devriendt 《Astrophysics and Space Science》2004,292(1-4):45-51

Under ideal MHD conditions the magnetic field strength should be correlated with density in the interstellar medium (ISM). However, observations indicate that this correlation is weaker than expected. Ambipolar diffusion can decrease the flux-to-mass ratio in weakly ionized media; however, it is generally thought to be too slow to play a significant role in the ISM except in the densest molecular clouds. Turbulence is often invoked in other astrophysical problems to increase transport rates above the (very slow) diffusive values. Building on analytical studies, we test with numerical models whether turbulence can enhance the ambipolar diffusion rate sufficiently to explain the observed weak correlations. The numerical method is based on a gas-kinetic scheme with very low numerical diffusivity, thus allowing us to separate numerical and physical diffusion effects.  相似文献   

A methodology for constraining lava flow rheologies with MOLA     

Lori S. Glaze  Stephen M. Baloga  Ellen R. Stofan 《Icarus》2003,165(1):26-33

Topography as measured by the Mars Orbiter Laser Altimeter (MOLA), when supplemented with imaging data, can be used to infer physical emplacement processes in lava flows on Mars with a level of detail analogous to what can be done with unobserved lava flow eruptions on Earth. MOLA, Viking Orbiter and Mars Orbiter Camera (MOC) data are used to develop new inferences regarding the rheology of a typical lava flow near Elysium Mons on Mars. We present a technique that uses MOLA Precision Experiment Data Records (PEDRs) to directly determine the longitudinal thickness profile of lava flows. This technique is preferable to using gridded topography derived from MOLA, particularly for features such as lava flows, with thickness variations at the same scale as their surroundings. Thickness profiles and underlying slope estimates can then be compared with results from rheologic models. The longitudinal thickness profile of the Elysium example discussed here exhibits a concave-up flow surface that is consistent with an exponential viscosity increase. The viscosity shows a relative increase of about 50 times over the length of flow examined when the density of the lava increases as a result of lava degassing.  相似文献   

The Lofar Central Processing Facility Architecture     

Kjeld Van Der Schaaf  Chris Broekema  Ger Van Diepen  Ellen Van Meijeren 《Experimental Astronomy》2004,17(1-3):43-58

Reconfiguration is a key feature characteristic of the LOFAR telescope. Software platforms are utilised to program out the required data transformations in the generation of scientific end-products. Reconfigurable resources nowadays often replace the hard-wired processing systems from the past. This paper describes how this paradigm is implemented in a purely general-purpose telescope back-end. Experiences from high performance computing, stream processing and software engineering have been combined, leading to a state-of-the-art processing platform. The processing platform offers a total processing power of 35 TFlops, which is used to process a sustained input data- stream of 320 Gbps. The architecture of this platform is optimised for streaming data processing and offers appropriate processing resources for each step in the data processing chains. Typical data processing chains include Fourier transformations and correlation tasks along with controlling tasks such as fringe rotation correction. These tasks are defined in a high level programming language and mapped onto the available resources at run time. A scheduling system is used to control a collection of concurrently executing observations, providing each associated application with the appropriate resources to meet its timing constraint and give the integrated system the correct on-line and off-line look and feel.  相似文献   

Late and middle Pleistocene ungulates dietary diversity in Western Europe indicate variations of Neanderthal paleoenvironments through time and space     

Florent Rivals  Ellen Schulz  Thomas M. Kaiser 《Quaternary Science Reviews》2009,28(27-28):3388-3400

Mesowear and microwear on enamel from 763 teeth of middle and late Pleistocene ungulates were analysed to infer the potential of dental wear analysis of faunal remains as a paleoenvironmental and paleoclimatic proxy in relation to climatic changes and diversity of vegetation available in the environment. Fossil localities including levels belonging to two glacial and two interglacial stages were selected in Germany, France, and Spain. At a temporal scale, results indicate that the dietary diversity in ungulates is higher during interglacial phases (MIS 5 and 3) than during pleniglacial phases (MIS 8 and 4). Dietary diversity is concluded to be related to climate-driven vegetation changes which during interglacials lead to increased variety of potential food items available to ungulates. At the geographical scale, during interglacials, changes in diet composition are evident along geographical gradients. The corresponding dietary gradients are proposed to be related to climate and vegetation gradients reflecting more arid climates in the Mediterranean area compared to North-Western Europe. Species consistently represented at all localities investigated are Cervus elaphus (Cervidae, Artiodactyla) and Equus ferus (Equidae, Perissodactyla). C. elaphus populations are found to consistently have less abrasive diets than E. ferus populations but dietary traits of both species varied largely, revealing a significant plasticity in the feeding adaptation of both species. Those traits are concluded to be related to differences in vegetation structure at each locality and complement the evidence that ungulates have broader dietary habits than what is usually assumed.  相似文献   

CAREGIVING ENVIRONMENTS AND ELDERLY RESIDENTIAL MOBILITY*     

Judith W. Meyer  Ellen K. Cromley 《The Professional geographer》1989,41(4):440-450

Formal and informal caregiving, an aspect of the environment of older elderly people, helps differentiate their residential mobility decisions from those of younger people. A recently proposed developmental model of elderly mobility that focuses on caregiving and health is evaluated through the literature and by a survey of recently hospitalized individuals over 75 years old. The model is expanded to include an anticipatory stage of mobility during which older Americans consciously try to organize their environments.  相似文献   

Climate policy at the local level: Insights from California     

Louise W. Bedsworth  Ellen Hanak 《Global Environmental Change》2013,23(3):664-677

Local governments in the United States have been hotbeds of climate change activity. Recently, states have sought to incorporate these primarily voluntary actions into broader climate change mitigation programs. Using the example of California, a national leader in U.S. climate policy, this article examines the scope for effectiveness of local climate action and assesses factors related to adoption of local climate policies. The analysis draws on two original surveys of city and county governments, designed to learn about adoption of comprehensive policy tools (emission inventories and climate action plans) and programs in specific areas (energy, water, land use, transportation). Adoption rates are fairly high and growing; by mid 2010 roughly 70% of all jurisdictions were already engaged or planning to engage in comprehensive climate actions, up from roughly 50% in 2008. The adoption of specific programs varies with the degree of local government authority in different sectors, and is generally higher for programs targeting municipal facilities and operations than those targeting residents and businesses. Population size, household income, and strong support from local leaders and the public are all associated with higher rates of adoption, particularly for comprehensive actions. Partisan attitudes are more important for comprehensive actions than for programs in specific areas such as energy efficiency and renewable energy, mirroring the findings of state and national public opinion surveys, which find broader support for actions like clean energy than for explicit climate change-oriented actions. Qualitative analysis reveals additional keys to success, including partnering with other local governments and private organizations and leveraging cost savings and other potential co-benefits of action. As states move to incorporate local actions into broader plans, mandates will also play an increasing role in setting a floor for local efforts.  相似文献   

It is a moral issue: The relationship between environmental self-identity,obligation-based intrinsic motivation and pro-environmental behaviour     

Ellen van der Werff  Linda Steg  Kees Keizer 《Global Environmental Change》2013,23(5):1258-1265

In order to effectively mitigate climate change, people need to adopt environmentally-friendly actions. We argue that some people act in an environmentally-friendly manner without external incentives to do so, but rather because they are intrinsically motivated to do so. There is some initial evidence to suggest that this is particularly likely for people with a strong environmental self-identity. However, not much is known about how environmental self-identity influences pro-environmental actions. In this research, we aimed to test whether, and if so, via which process environmental self-identity is related to environmentally-friendly behaviour. We conducted three studies to test our hypotheses. In the first study, our hypotheses were confirmed in a sample of the general population using a correlational design. In the second study, we replicated our findings with a different indicator of moral obligation and with a different dependent variable. In the third study, we tested our model in an experimental design. Again, we found support for our hypotheses that environmental self-identity is related to one's obligation-based intrinsic motivation (that is, feelings of moral obligation) to act pro-environmentally, which in turn affects pro-environmental actions. As expected, the obligation-based intrinsic motivation mediates the relationship between environmental self-identity and environmentally-friendly behaviour. Our findings suggest that strengthening environmental self-identity may be a cost-effective way to promote pro-environmental actions, as people with a strong environmental self-identity are likely to act in an environmentally-friendly manner without an external incentive to do so.  相似文献   

Comparison of flowpaths to a well and spring in a karst aquifer   总被引：3，自引：0，他引：3  

Toran L  Herman EK  White WB 《Ground water》2007,45(3):281-287

The permeability of some karst aquifers consists of networks of poorly integrated conduits and dissolution-widened fractures. The flow includes conduit flow, especially during storm recharge, but lacks the focused recharge into single master conduits that occurs in more highly developed karst systems. The proportions of conduit and dispersed flow are difficult to quantify in such systems. This study examines the flowpaths in a small karst watershed, based on comparing the physical and chemical response to storm flow at both a spring and a well. By conducting continuous monitoring at both locations, a better understanding of the flowpaths in a poorly integrated network was obtained. A more permeable flowpath to the spring leads to faster storm response and lower ion concentrations. The flowpath to and from the well is more complicated. The higher ion content and slower storm response suggest slower, more dispersed flowpaths. However, the well has greater variation in ion chemistry. Periodic recharge may dilute well concentrations due to faster (conduit or fracture) flowpaths. Although karst systems such as this are difficult to characterize, applying a variety of geochemical and physical monitoring techniques at multiple locations illustrates that the flowpaths can vary in both space and time.  相似文献   

Deep saltwater in Chalk of North-West Europe: origin, interface characteristics and development over geological time     

Ellen P. Bonnesen  Flemming Larsen  Torben O. Sonnenborg  Kurt Klitten  Lars Stemmerik 《Hydrogeology Journal》2009,17(7):1643-1663

High-concentration saltwaters occur in many places in the regional Chalk aquifers of North-West Europe; to investigate deep occurrences, profiles of interstitial porewater chemistry have been studied from three 250–450m deep cores drilled in the eastern parts of Zealand, Denmark. At the studied location, saline water in the Chalk resides at depths from 40 to 80m and salinity increases with depth. Concentrations of chloride up to ca. 30,000ppm have been observed at depths of 400m. Measured vertical hydraulic heads in open boreholes suggest that advective groundwater flow is now restricted in deeper parts of the Chalk formation and diffusive transport is thus the predominant transport mechanism. Laboratory-measured porosity and effective diffusion coefficients were used as input to a numerical 1D diffusion model of the interface between freshwater in an upper, fractured aquifer and modified connate formation water below. The model satisfactorily simulated the observed chloride and δ¹⁸O profiles. The diffusive refreshening of the Chalk formation has been going on for about 0.9 million years. The connate water in the Chalk of parts of the sedimentary basin seems to have been modified by transport of saltwater from underlying Mesozoic and Paleozoic sediments during compaction, which presumably ceased around 4 million years ago.  相似文献