DXL: a sounding rocket mission for the study of solar wind charge exchange and local hot bubble X-ray emission     

Massimiliano Galeazzi  Meng Chiao  Michael R. Collier  Thomas Cravens  Dimitra Koutroumpa  Kip D. Kuntz  Susan Lepri  Dan McCammon  Frederick S. Porter  Krishna Prasai  Ina Robertson  Steve Snowden  Youaraj Uprety 《Experimental Astronomy》2011,32(2):83-99

The Diffuse X-rays from the Local galaxy (DXL) mission is an approved sounding rocket project with a first launch scheduled around December 2012. Its goal is to identify and separate the X-ray emission generated by solar wind charge exchange from that of the local hot bubble to improve our understanding of both. With 1,000 cm² proportional counters and grasp of about 10 cm² sr both in the 1/4 and 3/4 keV bands, DXL will achieve in a 5-min flight what cannot be achieved by current and future X-ray satellites.  相似文献   

Image analysis algorithms for estimating porous media multiphase flow variables from computed microtomography data: a validation study     

Mark L. Porter  Dorthe Wildenschild 《Computational Geosciences》2010,14(1):15-30

Image analysis of three-dimensional microtomographic image data has become an integral component of pore scale investigations of multiphase flow through porous media. This study focuses on the validation of image analysis algorithms for identifying phases and estimating porosity, saturation, solid surface area, and interfacial area between fluid phases from gray-scale X-ray microtomographic image data. The data used in this study consisted of (1) a two-phase high precision bead pack from which porosity and solid surface area estimates were obtained and (2) three-phase cylindrical capillary tubes of three different radii, each containing an air–water interface, from which interfacial area was estimated. The image analysis algorithm employed here combines an anisotropic diffusion filter to remove noise from the original gray-scale image data, a k-means cluster analysis to obtain segmented data, and the construction of isosurfaces to estimate solid surface area and interfacial area. Our method was compared with laboratory measurements, as well as estimates obtained from a number of other image analysis algorithms presented in the literature. Porosity estimates for the two-phase bead pack were within 1.5% error of laboratory measurements and agreed well with estimates obtained using an indicator kriging segmentation algorithm. Additionally, our method estimated the solid surface area of the high precision beads within 10% of the laboratory measurements, whereas solid surface area estimates obtained from voxel counting and two-point correlation functions overestimated the surface area by 20–40%. Interfacial area estimates for the air–water menisci contained within the capillary tubes were obtained using our image analysis algorithm, and using other image analysis algorithms, including voxel counting, two-point correlation functions, and the porous media marching cubes. Our image analysis algorithm, and other algorithms based on marching cubes, resulted in errors ranging from 1% to 20% of the analytical interfacial area estimates, whereas voxel counting and two-point correlation functions overestimated the analytical interfacial area by 20–40%. In addition, the sensitivity of the image analysis algorithms on the resolution of the microtomographic image data was investigated, and the results indicated that there was little or no improvement in the comparison with laboratory estimates for the resolutions and conditions tested.  相似文献   

An occurrence of cadmiferous phosphorite soil concretions in Jamaica     

Robert G. Garrett  Anthony R.D. Porter  Patricia A. Hunt 《Applied Geochemistry》2010

Bauxite exploration drilling revealed the presence of phosphate minerals through the chemical and XRD analysis of recovered drill hole samples at Spitzbergen, in Manchester Parish, Jamaica. A subsequent pit led to the discovery of phosphorite concretions composed of hard competent masses of finely crystalline fluorapatite, with some minor crandallite. The phosphorite contains anomalously high levels of Zn (>5000 mg kg⁻¹), Cd (>1.1%), Ag (>20 mg kg⁻¹), Be (>80 mg kg⁻¹) and, to a lesser extent, U. Textural and geochemical evidence indicates that the phosphorite concretions were most likely formed by the replacement of limestone by secondary deposition proximal to fossil guano deposits, postulated to be Late Miocene or Pliocene sea-bird colonies. Mechanical dispersion of the phosphorite concretions through karst weathering processes has led to their wider spatial distribution than the original guano deposits. Subsequent weathering of the concretions and the admixture of their decomposition products into the bauxitic and Terra Rossa soils is postulated to be the cause of the widespread anomalous levels of Zn, Cd and Be in these soils in central Jamaica, and the elevated levels of P in the bauxite.  相似文献   

Impacts and Timing of the First Human Settlement on Vegetation of the Faroe Islands     

Gina E. Hannon  Richard H. W. Bradshaw 《Quaternary Research》2000,54(3):404

Stratigraphically precise AMS-radiocarbon-dated plant remains, pollen, charcoal, and microtephra analyses from the Faroe Islands were used to establish the timing and effects of the first human settlement. The first occurrence of cultivated crops from three locations dated from as early as the sixth century A.D. and was older than implied from previous archaeological and historical studies, but consistent with earlier palaeoecological investigations. The effects of settlement on the vegetation were rapid and widespread. The transformation of the flora of this fragile ecosystem was best expressed by the large assemblage of ruderal, postsettlement plants recorded as macrofossils. The earliest known introduction of domestic animals (sheep/goat) was ca. A.D. 700. Their arrival on these relatively small islands probably contributed to the widespread change in vegetation and the loss of restricted native woody cover. Settlement was the critical disturbance that transformed an ecosystem that was already stressed by climatic change, as sensed by regional marine sediments. The settlement dates conform to a pattern of older dates developing from throughout the north Atlantic region.  相似文献   

Creating a thinking space for the rising stars of Australian urban geography     

Dallas Rogers  Libby Porter  Wendy Steele  Donna Houston 《The Australian geographer》2019,50(2):141-143

The Institute of Australian Geographers Urban Study Group and Australian Geographer present the first essay in our Leading Insights/Thinking Space partnership. We discuss Dr Natalie Osborne's 2018 essay, flag Dr Marilu Melo's 2019 essay and talk about creating a thinking space for the rising stars of Australian urban geography.  相似文献   

Deep-sea mining of seafloor massive sulfides     

Porter Hoagland  Stace Beaulieu  Maurice A. Tivey  Roderick G. Eggert  Christopher German  Lyle Glowka  Jian Lin 《Marine Policy》2010

The potential emergence of an ocean mining industry to exploit seafloor massive sulfides could present opportunities for oceanographic science to facilitate seafloor mineral development in ways that lessen environmental harms.  相似文献   

Fisheries observers as enforcement assets: Lessons from the North Pacific     

Read D. Porter 《Marine Policy》2010

Fisheries observers can both collect scientific data and report on compliance with fisheries regulations. Observers are used only for scientific purposes in most US fisheries. However, North Pacific groundfish fisheries observers are required to report violations of fisheries regulations that they witness. Based on evaluation of historical enforcement incidents and survey data, this paper considers the effects of mandatory reporting in the North Pacific. The goal of this analysis is to determine whether and how observer enforcement in the North Pacific differs from observer enforcement in other US fisheries and to determine what benefits observer enforcement might yield if adopted in other fisheries.  相似文献