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Atlas of karst area based on Web GIS technology 总被引：1，自引：0，他引：1
Leszek Litwin 《Environmental Geology》2008,54(5):1029-1036
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C. Litwin R. Rosner D. Q. Lamb 《Monthly notices of the Royal Astronomical Society》1999,310(2):324-330
We address the problem of plasma penetration of astrophysical magnetospheres, an important issue in a wide variety of contexts, ranging from accretion in cataclysmic variables to flows in protostellar systems. We point out that under well-defined conditions, penetration can occur without any turbulent mixing (driven, for example, by Rayleigh–Taylor or Kelvin–Helmholtz instabilities) caused by charge polarization effects, if the inflowing plasma is bounded in the direction transverse to both the flow velocity and the magnetic field. Depolarization effects limit the penetration depth, which nevertheless can, under specific circumstances, be comparable to the size of the magnetosphere. We discuss the effect of ambient medium on plasma propagation across the stellar magnetic field and determine the criteria for deep magnetosphere penetration. We show that, under conditions appropriate to magnetized white dwarfs in AM Her type cataclysmic variables, charge polarization effects can lead to deep penetration of the magnetosphere. 相似文献
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Lenz Dawn D. DeLuca Edward E. Golub Leon Rosner Robert Bookbinder Jay A. Litwin Christof Reale Fabio Peres Giovanni 《Solar physics》1999,190(1-2):131-138
An initial study of long-lived loops observed with TRACE (Lenz et al., 1999) shows that they have no significant temperature stratification and that they are denser than the classic loop model
predicts. Models that agree better with the observations include a loop consisting of a bundle of filaments at different temperatures
and a loop with momentum input by MHD waves. Some implications for coronal heating models and mechanisms are discussed. 相似文献
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Helaine W. Markewich Ronald J. Litwin Milan J. Pavich George A. Brook 《Quaternary Research》2009,71(3):409-425
Inactive parabolic dunes are present in southeastern Maryland, USA, along the east bank of the Potomac River. More elongate and finer-grained eolian deposits and paha-like ridges characterize the Potomac River–Patuxent River upland and the west side of Chesapeake Bay. These ridges are streamlined erosional features, veneered with eolian sediment and interspersed with dunes in the low-relief headwaters of Potomac- and Patuxent-river tributaries. Axis data for the dunes and ridges indicate formation by WNW–NW winds. Optically stimulated luminescence and radiocarbon age data suggest dune formation from 33–15 ka, agreeing with the 30–13 ka ages Denny, C.S., Owens, J.P., Sirkin, L., Rubin, M., 1979. The Parsonburg Sand in the central Delmarva Peninsula, Maryland and Delaware. U.S. Geol. Surv. Prof. Pap. 1067-B, 16 pp. suggested for eolian deposits east of Chesapeake Bay. Age range and paleowind direction(s) for eolian features in the Bay region approximate those for late Wisconsin loess in the North American midcontinent. Formation of midcontinent loess and Bay-region eolian features was coeval with rapid growth of the Laurentide Ice Sheet and strong cooling episodes (δ18O minima) evident in Greenland ice cores. Age and paleowind-direction coincidence, for eolian features in the midcontinent and Bay region, indicates strong mid-latitude WNW–NW winds for several hundred kilometers south of the Laurentide glacial terminus that were oblique to previously simulated anticyclonic winds for the last glacial maximum. 相似文献
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Spatial data were used to develop complex characteristics of a high-mountain karst. The numeric elaboration was conducted
using the analytical capabilities of GIS software. Analysis was based on spatial data gained by elaborating aerial photography.
The results were presented in map sets, as well as Geographic Information System format. The set of matched numerical methods
used and the proposed algorithm for data analysis may be applied at other karst sites. 相似文献
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Ronald J. Litwin Joseph P. Smoot Milan J. Pavich Helaine W. Markewich George Brook Nancy J. Durika 《Quaternary Research》2013
We document frequent, rapid, strong, millennial-scale paleovegetation shifts throughout the late Pleistocene, within a 100,000+ yr interval (~ 115–15 ka) of terrestrial sediments from the mid-Atlantic Region (MAR) of North America. High-resolution analyses of fossil pollen from one core locality revealed a continuously shifting sequence of thermally dependent forest assemblages, ranging between two endmembers: subtropical oak-tupelo-bald cypress-gum forest and high boreal spruce-pine forest. Sedimentary textural evidence indicates fluvial, paludal, and loess deposition, and paleosol formation, representing sequential freshwater to subaerial environments in which this record was deposited. Its total age–depth model, based on radiocarbon and optically stimulated luminescence ages, ranges from terrestrial oxygen isotope stages (OIS) 6 to 1. The particular core sub-interval presented here is correlative in trend and timing to that portion of the oxygen isotope sequence common among several Greenland ice cores: interstades GI2 to GI24 (≈ OIS2–5 d). This site thus provides the first evidence for an essentially complete series of ‘Dansgaard–Oeschger’ climate events in the MAR. These data reveal that the ~ 100,000 yr preceding the Late Glacial and Holocene in the MAR of North America were characterized by frequently and dynamically changing climate states, and by vegetation shifts that closely tracked the Greenland paleoclimate sequence. 相似文献
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