Ion dynamics associated with substorm dipolarization fronts     

Song Fu  Maha Ashour-Abdalla  XiaoHua Deng  Mostafa El-Alaoui  Meng Zhou  Robert L. Richard  Raymond J. Walker  ZhiGang Yuan 《中国科学:地球科学(英文版)》2014,57(10):2543-2551

We report where and how ions are accelerated in the proximity of earthward propagating dipolarization fronts(DFs) in the magnetotail during a magnetospheric substorm on February 15, 2008. Two DFs were observed by multiple THEMIS spacecraft in the near-Earth magnetotail(~?10 Re). We studied the ion dynamics associated with these DFs by comparing observed results with large scale kinetic(LSK) simulation results. The LSK simulation reproduced the sudden ion energy flux enhancement concurrent with the arrival of the DF at the satellite locations. We found that ions can be accelerated to more than 100 keV energy at the DF. These ions were initially non-adiabatically accelerated near magnetic reconnection site and then still non-adiabatically accelerated at the DF structure.  相似文献   

Aeromagnetic surveying using a simulated unmanned aircraft system     

Raymond M. Caron  Claire Samson  Paul Straznicky  Stephen Ferguson  Luise Sander 《Geophysical Prospecting》2014,62(2):352-363

Carleton University and Sander Geophysics are developing an unmanned aircraft system (UAS) for aeromagnetic surveying. As an early indication of the expected performance of the unmanned aircraft system, a simulated unmanned aircraft system (sUAS) was built. The simulated unmanned aircraft system is a T‐shaped structure configured as a horizontal gradiometer with two cesium magnetometers spaced 4.67 m apart, which is the same sensor geometry as planned for the unmanned aircraft system. The simulated unmanned aircraft system is flown suspended beneath a helicopter. An 8.5 km² area in the Central Metasedimentary Belt of the Grenville Province, near Plevna, Ontario, Canada, was surveyed with the simulated unmanned aircraft system suspended 50 m above ground. The survey site was chosen on the basis of its complex geological structure. The total magnetic intensity (TMI) data recorded were compared to that obtained during a conventional fixed‐wing survey and a ground survey. Transverse magneto‐gradiometric data were also recorded by the simulated unmanned aircraft system. The simulated unmanned aircraft system total magnetic intensity data have a higher resolution than the conventional fixed‐wing data and were found to have a similar resolution to that of the ground survey data. The advantages of surveying with the simulated unmanned aircraft system were: (1) the acquisition of a detailed data set free of gaps in coverage at a low altitude above the terrain and (2) substantial saving of time and effort. In the survey site, the 4.67 m simulated unmanned aircraft system gradiometer measured the transverse magnetic gradient reliably up to an altitude of 150 m above ground.  相似文献   

Limnological and sedimentary processes at Sawtooth Lake,Canadian High Arctic,and their influence on varve formation   总被引：1，自引：0，他引：1  

Pierre Francus  Raymond S. Bradley  Ted Lewis  Mark Abbott  Mike Retelle  Joseph S. Stoner 《Journal of Paleolimnology》2008,40(3):963-985

This paper synthesizes data collected to document the modern limnological and sedimentary processes in South Sawtooth Lake located on northern Ellesmere Island, Nunavut, Canada. Field observations show that the finely laminated sediments deposited in the distal basin are formed by the settling of overflows and interflows, and in rare occasions, by non-erosive hyperconcentrated density flows. Thin-sections of these sediments allowed for the classification of the sedimentary fabrics into six facies, each representing different limnological processes. The sediments in this distal basin are considered to be continuous and annually laminated (varved) based on radioisotope analyses, and both limnological and sedimentological evidence.  相似文献   

Volcanology and lava flow morpho-types from the Koyna-Warna region,western Deccan Traps,India     

Raymond A. Duraiswami  Purva Gadpallu  Babaji Maskare  Aishwarya Purwant  Pooja Meena  P. Krishnamurthy  B. Mahabaleshwar 《Journal of the Geological Society of India》2017,90(6):742-747

Flow mapping and physical volcanology of 15 basaltic lavas exposed in three critical road pass sections (ghats) in the Koyna-Warna region of the western Deccan Traps is presented in this paper. Transitional lavas like rubbly pahoehoe are most common morpho-type exposed in these ghat sections. Sinking of rubbly breccia into flow interiors and formation of breccia-cored rosette are common in some lava flows. Few rubbly lavas exhibit slabby tendencies. The amount and nature of the associated rubble is variable and result from the mechanical fracturing and auto-brecciation of the upper vesicular crust in response to distinctive stages in the cooling, crystallization and emplacement history of individual lava flows. Occurrence of aa and pahoehoe morpho-types in the lava flow sequence is subordinate. Three prominent pahoehoe flows separated by red bole horizons are seen in the upper parts of the Kumbharli ghat. These are thick, P-type sheet pahoehoe. The pahoehoe lavas represent compound flow fields that grew by budding, endogenous lava transfer and inflation. Presence of pahoehoe lavas in the Koyna-Warna region hints at possible hitherto unrecorded southern extension of Bushe-like flow fields. This study reconfirms the existence of pahoehoe-slabby-rubbly-aa flow fields and transitions even in the upper echelons of the Deccan Trap stratigraphy. The study of morphology and internal structure of lava flows exposed at the ghat sections in the Koyna-Warna region could guide subsurface core-logging that is critical in deciphering the physical volcanology and emplacement dynamics of basaltic lava flows penetrated by drill holes sunk under the scientific deep drilling programme.  相似文献   

Dynamic response of flexible rockfall barriers under different loading geometries   总被引：1，自引：1，他引：0  

Raymond C. H. Koo  Julian S. H. Kwan  Carlos Lam  Charles W. W. Ng  Jack Yiu  Clarence E. Choi  Axel K. L. Ng  Ken K. S. Ho  W. K. Pun 《Landslides》2017,14(3):905-916

Flexible steel barriers are commonly constructed on steep hillsides to mitigate rockfall. The evaluation of the dynamic response of proprietary flexible barriers is conventionally performed using full-scale field tests by dropping a weight onto the barriers in accordance with the European test standard ETAG 27. The weight typically has a spherical or polyhedral shape and cannot reproduce more complex rockfall scenarios encountered in the field. A rigid slab may load a barrier over a larger area and its effect has not been investigated. In this study, a calibrated three-dimensional finite-element model was developed to study the performance of vertically and horizontally orientated rockfall barriers under concentrated areal impact loads. A new bilinear force-displacement model was incorporated into the model to simulate the behavior of the energy-dissipating devices on the barriers. The effect of different weight geometries was studied by considering impacts by a rigid single spherical boulder and a rigid slab. Results reveal that areal loading induced by a rigid slab increases the loading on the barrier foundation by up to 40 % in both horizontally and vertically positioned barriers when compared to a concentrated load scenario with a single boulder. This indicates that barriers tested under the current test standard does not give the worst-case scenario in terms of foundation loads, and barrier designers should take into account the possible effect of increased foundation loads by reinforcing the barrier posts and/or increasing their spacing.  相似文献   

Temporospatial dynamics and public health significance of bacterial flora identified on a major leatherback turtle (Dermochelys coriacea) nesting beach in the Southern Caribbean          下载免费PDF全文

Ayanna Carla N. Phillips  Johanna Coutou  Stacy Rajh  Neville Stewart  Antonio Watson  Adam Jehu  Hamish Asmath  Francis Dziva  Chandrashekhar Unakal  Ridley Holder  Raymond Raoul Carthy 《Marine Ecology》2017,38(2)

Grande Riviere beach, on the island of Trinidad, supports the largest nesting population of leatherback turtles in the Caribbean region. Throughout the nesting season, nests are naturally disturbed by newly nesting females, resulting in egg breakage and loss of some nest viability. This environment is ideal for the growth and proliferation of microorganisms. The range of bacterial flora present in beach sand and egg shells was examined, with emphasis on bacteria that may pose a threat to public and animal health. The extent to which the bacterial load and genera on the beach changed throughout the season was also assessed. Twenty‐five genera were identified, with Pseudomonas spp. found to be the most predominant environmental bacteria. Four genera identified possess zoonotic potential, while five additional genera are known to be of public and animal health significance. Distinct shifts in the density and distribution of bacteria were observed along the beach from early to peak nesting season. Shifts were seen across heavily traversed zones, thus highlighting the potential exposure threats posed to beach visitors and animals alike. Further studies aimed at speciating this population of bacteria, as well as isolating potential fungal pathogens may mitigate this threat. Identification of bacterial agents that are specifically pathogenic to leatherback turtles, turtle eggs, hatchlings and those who may interact with these animals will serve to enhance and guide efforts to better conserve this species and protect the health of all who visit this ecologically significant site.  相似文献   

The equatorial and low-latitude ionosphere within the context of global modeling     

Michael Mendillo  Joei Wroten  Raymond Roble  Henry Rishbeth 《Journal of Atmospheric and Solar》2010,72(4):358-368

The thermosphere–ionosphere–mesosphere-electrodynamics coupled model TIME-GCM, coupled to NCEP lower atmosphere data, is used to simulate the noontime ionospheric peak electron density NmF2 at low latitudes for year 2002. Model output are compared with observations a three ionosonde stations: Jicamarca, Ascension Island and Darwin, stations at geomagnetic latitudes of 3°S, 10°S and 22°S, respectively. The modeled electron density at the peak of the F2-layer (NmF2) matches the general trend of the data fairly well at noon throughout the year. The shapes of the diurnal curves of NmF2 vs. local time are not well produced in the model, and particularly so at the two stations away from the geomagnetic equator. At all sites the day-to-day variability of NmF2, assessed using the percent standard deviation about the monthly mean, is about twice the modeled variability. Possible sources of this shortfall in the model may be due to the under-representation of coupling from below and/or from auroral sources.  相似文献