Chandra and XMM–Newton observations of NGC 4214: the hot interstellar medium and the luminosity function of dwarf starbursts     

Joanna M. Hartwell  Ian R. Stevens  David K. Strickland †  Timothy M. Heckman  Lesley K. Summers 《Monthly notices of the Royal Astronomical Society》2004,348(2):406-420

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Origin of low energy cosmic ray positrons at energies ≳2 MeV     

J. J. Burger  S. A. Stephens  B. N. Swanenburg 《Astrophysics and Space Science》1970,8(1):20-28

It is shown that an appreciable flux of positrons below a few MeV in the cosmic radiation could arise from the decay of cobalt nuclei in the decay chain⁵⁶Ni⁵⁶Co⁵⁶Fe, which occurs in the silicon burning shells of supernovae just after their ejection at relativistic velocities. The equilibrium spectrum of positrons in the interstellar space has been calculated on the assumption that the observed abundance of iron nuclei in the cosmic radiation is the result of the above process. It is found that the observation below about 10 MeV can be well explained with a moderate acceleration of the positrons in the expanding envelope of supernovae prior to their propagation in the interstellar space. The total⁵⁶Ni content in the shells of supernova necessary to account for the observed positrons is in agreement with that required to explain the peak luminosity during the supernova outburst. Since this model deals with positrons created at the time of injection of cosmic rays into the interstellar space, it becomes possible to study the shape of the injection spectrum of cosmic rays.On leave from Tata Institute of Fundamental Research, Bombay, India.  相似文献   

Valley-marginal sand dunes in the south-west Kalahari: their nature, classification and possible origins   总被引：3，自引：0，他引：3  

Joanna E. Bullard  David J. Nash 《Journal of Arid Environments》2000,45(4):369

This paper considers the nature, classification and possible origin of a variety of desert sand dunes which occur in association with ephemeral drainage features in the south-west Kalahari. The dune forms, which we term valley-marginal dunes, are found at the top of valley flanks, and are narrow, elongate forms with arcuate and straight planform elements which mirror the course of extant and ancient channels. Following a discussion of the major schemes used to classify different dune types, we describe the morphology and situation of these valley-marginal dunes. We suggest that whilst the basic morphometry of these dunes is similar to many other dune types, the topographic setting in which they occur is relatively unusual. We conclude that valley-marginal dunes are a previously unrecognized landform which cannot be fitted into current classificatory schemes. It is suggested that one reason for this may be the lack of an explicit temporal dimension in most dune classifications.  相似文献   

Lithospheric structure north of Scotland—II. Poisson's ratios and waveform modelling     

Claire Price  Joanna Morgan 《Geophysical Journal International》2000,142(3):737-754

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The application of terrestrial laser scanning to aeolian saltation cloud measurement and its response to changing surface moisture     

Joanna M. Nield  Giles F.S. Wiggs 《地球表面变化过程与地形》2011,36(2):273-278

Saltation is the dominant form of aeolian transport of sand sized grains, yet its heterogeneous spatial and temporal distribution, and inherent feedback and interaction with the surface over which sand is transported, hinders large scale quantification. In this letter we present preliminary data on saltation cloud characteristics quantified using terrestrial laser scanning (TLS). These data, together with surface moisture and surface roughness patterns, elucidate the importance of saltation in the development of protodunes on a drying beach, and indicate the potential usefulness of TLS in examining aeolian processes in both beach and desert environments. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Lake District pioneers – the earliest footprints on land     

Eric W. Johnson  Derek E.G. Briggs  Joanna L. Wright 《Geology Today》1996,12(4):147-151

New evidence reveals that the first arthropods colonized dry land over 450 million years ago, more than 20 million years before the appearance of vascular plants. Traditionally, it was thought that animals only emerged on to land after plants had become established, thus providing a plentiful new food source. The earliest known terrestrial trace fossils occur in volcanogenic sediments from the English Lake District. The trace fossils are thought to have been made on land by a small millipede-like creature. These rocks contain no other fossils.  相似文献   

Dynamical evolution of triple systems     

Joanna P. Anosova  Victor V. Orlov 《Astrophysics and Space Science》1991,177(1-2):359-363

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The topology and polarization of sub-beams associated with the 'drifting' subpulse emission of pulsar B0943 + 10 – III. Analysis of Pushchino 103/40-MHz observations     

Joanna M. Rankin  †  Svetlana A. Suleymanova  Avinash A. Deshpande ‡ 《Monthly notices of the Royal Astronomical Society》2003,340(4):1076-1086

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Jamaica Bay studies III: Abiotic determinants of distribution and abundance of gulls (Larus)     

Joanna Burger 《Estuarine, Coastal and Shelf Science》1983,16(2):191-216

The distribution and abundance of gulls were examined at Jamaica Bay Wildlife Refuge (New York) from 31 May 1978 to 31 May 1979. Gulls were found to be affected by tidal, temporal and weather-related factors. The distribution of gulls was affected primarily by tidal factors on the bay, and by temporal (seasonal, circadian) and weather-related factors on the freshwater ponds. The most important weather-related factors were temperature, wind velocity and wind direction. Herring (L. argentatus), great black-backed (L. fuscus) and ring-billed gulls (L. delawarensis) fed on the bay at low tides, and used the ponds at high tide. Laughing gulls (L. atricilla) fed on the bay at low tide and on rising tides. Herring and great black-backed gulls were present all year, but were most abundant in the winter, ring-billed gulls were abundant in spring and early fall, and laughing gulls were present in the summer following the breeding season but were absent in winter. Gulls used the ponds during high velocity, north winds, when they usually rested or preened. Multiple regression models were used to determine the factors explaining the variability in the numbers of gulls. Temporal variables were important contributors to accounting for the variability in the numbers of great black-backed and herring gulls only; tidal variables were significant for great black-backed and herring gulls on the bay, and for ring-billed and laughing gulls on all areas; and weather variables were significant for all species.  相似文献   

Occurrence of selected domestic and hospital emerging micropollutants on a rural surface water basin linked to a groundwater karst catchment     

Joanna Doummar  Michel Aoun 《Environmental Earth Sciences》2018,77(9):351

The occurrence of specific micropollutants (MPs), indicators of domestic and hospital wastewater, was investigated in a river connected to a karst spring based on two sampling campaigns under varying flow conditions. The MPs characterized by a high frequency of occurrence (acesulfame-K, ibuprofen, gemfibrozil, nonylphenol, and iohexol) were highly reflective of wastewater discharged in ephemeral streams and tributaries, as well as specific point sources such as farms and hospital effluents. A mixing model based on chloride mass fluxes allows the quantification of the percentage of untreated wastewater effluents in inflowing water from river tributaries, which varied between 0.7–99% and 5.0–10% in low flow and high flow, respectively. The frequency of occurrence of MPs is related to the volume of wastewater input, extent of river dilution, persistence of the MPs, and type of point source contamination on the river. Relationships were established between MPs such as ibuprofen and acesulfame-K (ACE-K), indicating their co-existence in highly consumed generic medicine and their suitability as wastewater co-tracers. Additionally, the number of consumers of gemfibrozil (GEM) and acesulfame-K were estimated based on mass loads in the river tributaries for management purposes. Groundwater contamination is mostly due to diffuse and point sources infiltration occurring on the spring catchment, including the sinking stream that could contribute up to 17% to the mass loads of some micropollutants (e.g., ACE-K and GEM) at the spring. Nevertheless, the increase of MPs use with growing urbanization is expected to have a much significant impact on the groundwater quality in the future.  相似文献