Stardust interstellar dust calibration: Hydrocode modeling of impacts on Al‐1100 foil at velocities up to 300 km s−1 and validation with experimental data     

Mark C. PRICE  Anton T. KEARSLEY  Mark J. BURCHELL  Lauren E. HOWARD  Jon K. HILLIER  Natalie A. STARKEY  Penny J. WOZNIAKIEWICZ  Mike J. COLE 《Meteoritics & planetary science》2012,47(4):684-695

Abstract– We present initial results from hydrocode modeling of impacts on Al‐1100 foils, undertaken to aid the interstellar preliminary examination (ISPE) phase for the NASA Stardust mission interstellar dust collector tray. We used Ansys’ AUTODYN to model impacts of micrometer‐scale, and smaller projectiles onto Stardust foil (100 μm thick Al‐1100) at velocities up to 300 km s^?1. It is thought that impacts onto the interstellar dust collector foils may have been made by a combination of interstellar dust particles (ISP), interplanetary dust particles (IDP) on comet, and asteroid derived orbits, β micrometeoroids, nanometer dust in the solar wind, and spacecraft derived secondary ejecta. The characteristic velocity of the potential impactors thus ranges from <<1 to a few km s^?1 (secondary ejecta), approximately 4–25 km s^?1 for ISP and IDP, up to hundreds of km s^?1 for the nanoscale dust reported by Meyer‐Vernet et al. (2009) . There are currently no extensive experimental calibrations for the higher velocity conditions, and the main focus of this work was therefore to use hydrocode models to investigate the morphometry of impact craters, as a means to determine an approximate impactor speed, and thus origin. The model was validated against existing experimental data for impact speeds up to approximately 30 km s^?1 for particles ranging in density from 2.4 kg m^?3 (glass) to 7.8 kg m^?3 (iron). Interpolation equations are given to predict the crater depth and diameter for a solid impactor with any diameter between 100 nm and 4 μm and density between 2.4 and 7.8 kg m^?3.  相似文献   

A model for assessing iceberg hazard     

Bigg  Grant R.  Cropper  T. E.  O’Neill  Clare K.  Arnold  Alex K.  Fleming  A. H.  Marsh  R.  Ivchenko  V.  Fournier  Nicolas  Osborne  Mike  Stephens  Robin 《Natural Hazards》2018,92(2):1113-1136

Natural Hazards - With the polar regions opening up to more marine activities but iceberg numbers more likely to increase than decline as a result of global warming, the risk from icebergs to...  相似文献   

Anorthositic lunar regolith breccia Dhofar 1769—Clear indications for repeated mixing of impact melt lithologies     

Addi Bischoff  Mike Komnik  Jakob Storz  Jasper Berndt 《Meteoritics & planetary science》2023,58(9):1260-1273

The lunar regolith breccia Dhofar 1769, which was found in 2012 as a single 125 g piece in the Zufar desert area of Oman, contains a relatively large, dark-colored impact melt breccia embedded in a fine-grained clastic matrix. The internal texture of the fragment indicates the repeated melt breccia formation on the lunar surface, their repeated brecciation, and mixing in second, third, and fourth generations of brecciated rock types. The chemical and mineralogical data reveal the incorporation of a feldspar-rich subophitic crystalline melt within a feldspar-rich microporphyritic crystalline melt breccia. This lithic paragenesis itself is embedded within a mafic, crystalline melt breccia. The entire breccia with the three different impact melts has been finally incorporated into the whole rock breccia. The three impact melts are mixtures of different source rocks and impact projectiles, based on the obtained minor and trace element compositions (in particular of Ni and the rare earth elements [REE]) of the impact melt lithologies. For all processes of impact melt formation, additional steps of their brecciation and re-lithification require a minimum number of seven impact processes.  相似文献   

Employability and flexible retirement: Variations in academia in an age of austerity     

Mike Danson  Karen Gilmore 《Geoforum》2012,43(6):1323-1332

With both declining and ageing populations, countries are addressing the threats to their competitiveness by attracting more highly educated workers and by investing in human capital, especially through policies to increase the rates of participation by young people in tertiary education. As the population is still ageing, there are concerns over the affordability of state support for the elderly, their roles in society and the economy. Active and flexible lifestyles extend healthy life expectancy, so extending the length of the working life is increasingly seen as a way to ease the transition to an economy where an ageing population is affordable.Senior academic staff, exemplars of such post-industrial flexibility, have long been accommodated beyond the statutory retirement age. Their benign conditions of work; high private and social returns to experience and knowledge; and their high levels of those skills, labour power and other capacities which do not degenerate with age, combine to prolong the length of their effective working lives. Against this, as in other sectors, redundancies, voluntary severance and other schemes to reduce staffing have encouraged early retirement. Increased demand for higher education has driven changes in the lecturing labour mix, with increasing use of a peripheral workforce of both early career and retiring staff. This has seen semi-retirement within higher education evolving to stretch the period over which withdrawal takes place.In this context, the exploratory work reported here considers the initial responses by employers and trades unions in Scottish Higher Education to the abolition of the default retirement age and the introduction of ‘The Employment Equality (Repeal of Retirement Age Provisions) Regulations 2011’.  相似文献   

Wetland Accretion Rate Model of Ecosystem Resilience (WARMER) and Its Application to Habitat Sustainability for Endangered Species in the San Francisco Estuary     

Kathleen M. Swanson  Judith Z. Drexler  David H. Schoellhamer  Karen M. Thorne  Mike L. Casazza  Cory T. Overton  John C. Callaway  John Y. Takekawa 《Estuaries and Coasts》2014,37(2):476-492

Salt marsh faunas are constrained by specific habitat requirements for marsh elevation relative to sea level and tidal range. As sea level rises, changes in relative elevation of the marsh plain will have differing impacts on the availability of habitat for marsh obligate species. The Wetland Accretion Rate Model for Ecosystem Resilience (WARMER) is a 1-D model of elevation that incorporates both biological and physical processes of vertical marsh accretion. Here, we use WARMER to evaluate changes in marsh surface elevation and the impact of these elevation changes on marsh habitat for specific species of concern. Model results were compared to elevation-based habitat criteria developed for marsh vegetation, the endangered California clapper rail (Rallus longirostris obsoletus), and the endangered salt marsh harvest mouse (Reithrodontomys raviventris) to determine the response of marsh habitat for each species to predicted >1-m sea-level rise by 2100. Feedback between vertical accretion mechanisms and elevation reduced the effect of initial elevation in the modeled scenarios. Elevation decreased nonlinearly with larger changes in elevation during the latter half of the century when the rate of sea-level rise increased. Model scenarios indicated that changes in elevation will degrade habitat quality within salt marshes in the San Francisco Estuary, and degradation will accelerate in the latter half of the century as the rate of sea-level rise accelerates. A sensitivity analysis of the model results showed that inorganic sediment accumulation and the rate of sea-level rise had the greatest influence over salt marsh sustainability.  相似文献   

Calcrete formation and implications for buried archaeological deposits in the Mariana Islands,western Pacific     

Mike T. Carson  John A. Peterson 《Geoarchaeology》2011,26(4):501-513

Calcrete zones of cemented sands are found repeatedly at beach sites in the Mariana Islands, western Pacific region, with mid‐ to late‐Holocene artifacts and midden sealed within and beneath these layers. Three site‐specific cases demonstrate that the cementation process of the calcareous sand material post‐dated the deposition of artifacts and midden. Archaeological efforts must be prepared for deep excavation through zones of cemented sand. Also, recovery of preserved ancient materials can proceed by excavating large hardened blocks and soaking in light (5%) acid. This knowledge about formation process and recovery technique may prove useful not only in the Mariana Islands but also more broadly in other regions with similar settings. © 2011 Wiley Periodicals, Inc.  相似文献   

A standardised sampling protocol for robust assessment of reach-scale fish community diversity in wadeable New Zealand streams     

Bruno O David  Mark P Hamer  Kevin J Collier  Mike D Lake  Graham M Surrey  Kate McArthur 《新西兰海洋与淡水研究杂志》2013,47(3):177-187

The New Zealand fish fauna contains species that are affected not only by river system connectivity, but also by catchment and local-scale changes in landcover, water quality and habitat quality. Consequently, native fish have potential as multi-scale bioindicators of human pressure on stream ecosystems, yet no standardised, repeatable and scientifically defensible methods currently exist for effectively quantifying their abundance or diversity in New Zealand stream reaches. Here we report on the testing of a back-pack electrofishing method, modified from that used by the United States Environmental Protection Agency, on a wide variety of wadeable stream reaches throughout New Zealand. Seventy-three first- to third-order stream reaches were fished with a single pass over 150–345 m length. Time taken to sample a reach using single-pass electrofishing ranged from 1–8 h. Species accumulation curves indicated that, irrespective of location, continuous sampling of 150 stream metres is required to accurately describe reach-scale fish species richness using this approach. Additional species detection beyond 150 m was rare (<10%) with a single additional species detected at only two out of the 17 reaches sampled beyond this distance. A positive relationship was also evident between species detection and area fished, although stream length rather than area appeared to be the better predictor. The method tested provides a standardised and repeatable approach for regional and/or national reporting on the state of New Zealand's freshwater fish communities and trends in richness and abundance over time.  相似文献   

The role of suprathermal particle measurements in CrossScale studies of collisionless plasma processes     

Mike Hapgood  Chris Perry  Mick Denton 《Planetary and Space Science》2011,59(7):618-629

The CrossScale mission will advance our understanding of fundamental plasma processes in collisionless plasmas. It will exploit the excellent natural plasma laboratory provided by the Earth’s magnetosphere and the near-Earth solar wind and, in particular, carry out multi-scale studies that will strongly complement plasma studies in ground-based laboratories. Previous studies of collisionless plasmas in space environments across the solar system have shown the ubiquitous nature of suprathermal particles and that these particles exhibit a power-law energy spectrum. In this paper we discuss the great significance of these suprathermal particles for CrossScale studies. We show that the presence of these particles is a natural consequence of the collisionless regime as they can propagate across the heliosphere with little spectral change and are not thermalised by collisions. They are a key indicator of the non-equilibrium nature of collisionless plasmas and an important source of free energy that can drive plasma processes. We discuss how these suprathermal particles influence the overall properties of the plasma. In particular, the energy distribution of particles follows a Kappa, rather than Maxwellian, distribution and thus the plasma does not have a single thermodynamic temperature. We also discuss the importance of the suprathermal tail as a tool to diagnose the processes responsible for particle energisation in collisionless plasmas. Such energisation is a common feature in collisionless plasmas, especially in terms of the primary science targets for CrossScale: reconnection, shocks and turbulence. Finally we also touch on the value of using CrossScale studies to provide ground truth measurements for a number of astrophysical techniques that exploit the effects of energetic electrons in the distant universe. Throughout the paper, we stress that suprathermal (30 keV-1 MeV) measurements are essential to fully characterise particle distributions. We show that such measurements will benefit greatly from the improved spatial and temporal resolution (compared to Cluster) that is proposed for the HEP instrument on CrossScale.  相似文献   

Establishing boundary classes for the classification of UK marine waters using phytoplankton communities   总被引：2，自引：0，他引：2  

Devlin M  Best M  Coates D  Bresnan E  O'Boyle S  Park R  Silke J  Cusack C  Skeats J 《Marine pollution bulletin》2007,55(1-6):91-103

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Effects of variations in hydrogeological parameters on water-table mounding in sandy loam and loamy sand soils beneath stormwater infiltration basins     

Anita Thompson  Mike Nimmer  Debasmita Misra 《Hydrogeology Journal》2010,18(2):501-508

The two-dimensional variably-saturated numerical model HYDRUS-2D, previously calibrated to recharge events from an infiltration basin, was used to predict water-table mounding under hypothetical basin design scenarios, and the primary factors that affect water-table mounding were evaluated. Infiltration basins are often utilized in urban environments to recharge stormwater to the aquifer. As a result of localized recharge beneath these basins, mound formation may reduce the thickness of the unsaturated zone available to filter pollutants and may reduce the infiltration rate of the basin. Understanding the effects of various physical factors on water-table mound formation is important for infiltration basin siting. For sandy loam and loamy sand subsurface materials, mound heights increased as the thickness of both the unsaturated and saturated zones decreased. Mound heights increased as the initial soil moisture, basin size and ponding depth increased. A thin sedimentation layer on the basin floor delayed mound formation, but only slightly decreased the maximum mound height. This analysis could be used in future selection of infiltration basin locations; however, the analysis is limited to conditions that represent only a select range of basin design conditions and parameters typical of a glacial till environment in Wisconsin, USA.  相似文献