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281.
Anthony C. Runkel Robert G. Tipping Jessica R. Meyer Julia R. Steenberg Andrew J. Retzler Beth L. Parker Jeff A. Green John D. Barry Perry M. Jones 《Hydrogeology Journal》2018,26(7):2133-2159
A hydrogeologic conceptual model that improves understanding of variability in aquitard integrity is presented for a fractured sedimentary bedrock unit in the Cambrian-Ordovician aquifer system of midcontinent North America. The model is derived from multiple studies on the siliciclastic St. Lawrence Formation and adjacent strata across a range of scales and geologic conditions. These studies employed multidisciplinary techniques including borehole flowmeter logging, high-resolution depth-discrete multilevel well monitoring, fracture stratigraphy, fluorescent dye tracing, and three-dimensional (3D) distribution of anthropogenic tracers regionally. The paper documents a bulk aquitard that is highly anisotropic because of poor connectivity of vertical fractures across matrix with low permeability, but with ubiquitous bed parallel partings. The partings provide high bulk horizontal hydraulic conductivity, analogous to aquifers in the system, while multiple preferential termination horizons of vertical fractures serve as discrete low vertical hydraulic conductivity intervals inhibiting vertical flow. The aquitard has substantial variability in its ability to protect underlying groundwater from contamination. Across widespread areas where the aquitard is deeply buried by younger bedrock, preferential termination horizons provide for high aquitard integrity (i.e. protection). Protection is diminished close to incised valleys where stress release and weathering has enhanced secondary pore development, including better connection of fractures across these horizons. These conditions, along with higher hydraulic head gradients in the same areas and more complex 3D flow where the aquitard is variably incised, allow for more substantial transport to deeper aquifers. The conceptual model likely applies to other fractured sedimentary bedrock aquitards within and outside of this region. 相似文献
282.
Tangential discontinuities and the optical analogy for stationary fields IV. High speed fluid sheets
E. N. Parker 《地球物理与天体物理流体动力学》2013,107(4):229-247
Abstract It was shown in the previous paper that a sufficiently strong pressure maximum applied to an equilibrium flux surface, by the fields on either side of the surface, produces a gap in the flux surface. The fields on either side make contact through the gap to produce a surface of tangential discontinuity (current sheet). It is shown in the present paper that there is a high speed sheet of fluid and field sliding over the surface of discontinuity when the applied pressure moves slowly across the flux surface. Conditions in the active X-ray corona of the sun suggest that such sheets are generally present, with velocities of the order of 102 km/sec, but with thicknesses too small to be observed. More substantial high speed sheets of fluid may occur in solar flares. 相似文献
283.
284.
285.
Martin Cohen Jessica M. Chapman Rachel M. Deacon † Robert J. Sault Quentin A. Parker Anne J. Green 《Monthly notices of the Royal Astronomical Society》2006,369(1):189-196
We present radio observations of the unique, recently formed, planetary nebula (PN) associated with a very long-period OH/IR variable star V1018 Sco that is unequivocally still in its asymptotic giant branch phase. Two regions within the optical nebula are clearly detected in non-thermal radio continuum emission, with radio spectral indices comparable to those seen in colliding-wind Wolf–Rayet binaries. We suggest that these represent shocked interactions between the hot, fast stellar wind and the cold nebular shell that represents the PN's slow wind moving away from the central star. This same interface produces both synchrotron radio continuum and the optical PN emission. The fast wind is neither spherical in geometry nor aligned with any obvious optical or radio axis. We also report the detection of transient H2 O maser emission in this nebula. 相似文献
286.
Pirin Erdodu Ofer Lahav John P. Huchra † Matthew Colless Roc M. Cutri Emilio Falco † Teddy George Thomas Jarrett D. Heath Jones Lucas M. Macri Jeff Mader Nathalie Martimbeau Michael A. Pahre Quentin A. Parker Anaïs Rassat Will Saunders 《Monthly notices of the Royal Astronomical Society》2006,373(1):45-64
287.
E.N. Parker 《Astrophysics and Space Science》2001,277(1-2):1-11
The Sun and the heliosphere form a single dynamical system, driven by the convection in the Sun and the magnetic fields generated
by that convection. The magnetic fields are the primary channel for producing the high temperatures and high velocities that
extend outward to form the heliosphere. The essential point is that, while the general picture seems to be reasonable, several
important steps in the process are not understood, and several concepts commonly employed in explanation are false physics.
These scientific gaps should not be forgotten in the rush to pursue new and exotic discoveries.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
288.
E. N. Parker 《中国天文和天体物理学报》2001,1(2):99-124
1 INTRODUCTION
The Sun is close enough to observe in some detail, and it shows that a star is more than
the traditional stable self-gravitating thermonuclear body established half a celltury ago. For
the fact is that out of sight beneath the visible surface the outward flow of heat from the
thermonuclear core drives hydrodynamics that generates magnetic fields. It is the complicated
dynamics of those magnetic fields that produces the modern mysteries of the active Sun. The… 相似文献
289.
E. N. Parker 《Astrophysics and Space Science》1974,31(1):261-266
There has been discussion of the possibility of resolving the solar neutrino dilemma with a sufficiently strong magnetic field (5×108 G) in the solar interior to relieve the gas pressure by some ten percent or more. We examine the time in which magnetic buoyancy will bring a strong field to the surface and find it to be less than 108 yr. We see no possibility for retaining a suitably strong magnetic field in the solar interior. 相似文献
290.
Terrestrial vertebrates in the western United States are functionally linked to environmental settings, as revealed by principal components analyses. Species number in five major vertebrate feeding guilds increases as vegetation structure becomes more complex and environmental conditions become more varied, and as evolutionary history has promoted species richness. Two other major vertebrate feeding guilds increase with temperature and evolutionary factors. Results support the view of animals as adapted parts of deterministic environmental systems, although complete explanations of species distributions require consideration of evolutionary history and stochastic processes. 相似文献