Ultraviolet photometry from the orbiting astronomical observatory XXII. Ultraviolet light variation ofβ Lyrae     

Yoji Kondo  George E. McCluskey  Joel A. Eaton 《Astrophysics and Space Science》1976,41(1):121-137

Six-color ultraviolet light curves of the complex eclipsing binary system Lyr were obtained with the OAO-2 Wisconsin Experiment Package. The filters had a typical width at half maximum of 150 to 200 Å and centered at 1430, 1550, 1910, 2460, 2980 and 3320 Å. The most striking characteristics of the ultraviolet light curves are that the secondary minimum deepens at shorter wavelengths. This indicates that we arenot observing the eclipse effect of two stars having roughly a Planckian distribution of energy. In combination with the high resolution far ultraviolet spectra of Lyr recently obtained withCopernicus (OAO-3) Princeton Telescope Spectrometer, it is concluded that the far ultraviolet light curves are dominated by emission from the high temperature gas surrounding the binary system. The ultraviolet observations with OAO-2 andCopernicus are consistent with a model in which the enigmatic secondary component involves a gravitationally collapsed object, i.e., a black hole; however, alternative models are also admissible.  相似文献   

A conceptual model for meander initiation in bedload‐dominated streams     

Brett C. Eaton  Michael Church  Tim R. H. Davies 《地球表面变化过程与地形》2006,31(7):875-891

A simple analytic model is presented relating local sediment transport capacity to variance in the transverse shear stress distribution in a stream channel. The model is used to develop a physically based conceptual model for the initiation of meandering in straight, bedload‐dominated streams as a result of a feedback mechanism. The feedback maximizes the cross‐sectional shear stress variance and – in order to achieve stability – ultimately minimizes the energy slope at repeated locations along the channel, subject to steady‐state mass flux and the stability of the channel boundary. These locations develop into pools in a fully developed meandering channel; they represent attractor states wherein sediment continuity is satisfied using the least possible energy expenditure per unit length of channel. However, since the cross‐sectional geometry of a pool (and the adjacent bar) is asymmetric, these attractor states are only conditionally stable, requiring strong, curvature‐induced secondary circulation to maintain their asymmetry. Between two successive pools, a stream occupies a metastable, higher energy state (corresponding to a riffle) that requires greater energy expenditure per unit length of channel to transport the same volume of sediment. The model we present links processes at the scale of a channel width to adjustments of the channel sinuosity and slope at the scale of a channel reach. We argue that the reach‐scale extremal hypotheses employed by rational regime models are mathematical formalisms that permit a one‐dimensional theory to describe the three‐dimensional dynamics producing stream morphology. Our model is consistent with the results from stream table experiments, with respect to both the rate of development of meandering and the characteristics of the equilibrium channel morphology. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Rational regime model of alluvial channel morphology and response     

Brett C. Eaton  Michael Church  Robert G. Millar 《地球表面变化过程与地形》2004,29(4):511-529

A theoretical model is developed for predicting equilibrium alluvial channel form. The concept of greatest relative stability, achieved by maximizing resistance to ?ow in the ?uvial system, is presented as the basis for an optimization condition for alluvial systems. Discharge, sediment supply (quantity and calibre) and valley gradient are accepted as independent governing variates. The model is used to de?ne a dimensionless alluvial state space characterized by aspect ratio (W/d), relative roughness (D/d), and dimensionless shear stress (τ*) or, equivalently, channel slope (S). Each alluvial state exhibits unique values of Froude number and sediment concentration. The range of alluvial states for constant values of relative bank strength (parameterized by an apparent friction angle, ?′) forms a single plane in the state space (W/d, D/d, τ* or S). The scaling relations produced by the model are consistent with laboratory channels exhibiting a range of bank strengths, and with the behaviour of natural channels. Copyright © 2004 John Wiley & Sons, Ltd.  相似文献   

Quartzite terrains, geologic controls, and basin denudation by debris flows: their role in long-term landscape evolution in the central Appalachians     

Robert J. Sas Jr.  L. Scott Eaton 《Landslides》2008,5(1):97-106

A large storm in 1995 that impacted the central Blue Ridge Mountains of Virginia triggered over a thousand debris flows, which deeply incised stream channels in zero-, first-, and second-order basins underlain primarily by granite, metabasalt, and quartzite. This event provided an opportunity to gain insight into geologic controls on debris-flow initiation and rates of basin denudation. Intensive investigations in quartzite terrain indicated that well-developed joints provide for rapid infiltration of rainwater and thus affected debris-flow initiation. Possible mechanisms of slope failure include (1) elevated rates of fracture recharge in steep valleys and/or (2) bedrock bedding planes. Fracture recharge may serve to substantially increase rock pore pressure during high intensity rainfall, especially when coupled with antecedent moisture. The quartzite bedrock tends to break into orthogonal blocks due to jointing. Statistical analysis shows the presence of a minimum of two joint populations that serve as bedrock controls on lateral erosion. Resistant bedding planes, parallel to slope, control vertical erosion below a finer-grained layer of saprolite. The combination of increased recharge and joint orientations in quartzite basins are likely the main factors resulting in the highest measured values of basin denudation from debris flows, relative to other lithologies, in the central Appalachians. Additionally, these joint and bedding planes produce a topographic signature at all scales and, therefore, are an important factor controlling long-term landscape evolution.  相似文献   

数字化地形测量、地籍测量成果验收方案的设计     

饶国和 《测绘通报》2008,(4):66-68

地形测量、地籍测量是市县基础测量的主体工程,但目前国家有关测绘法规尚未规定对测绘工程进行独立的监理。如何保证资金的合理使用及评定测绘产品的质量是亟待研究和解决的问题。根据多年的工作经验,设计测量成果验收方案,能较好地评定测绘产品的质量。  相似文献   

Ecosystems and environmental earth science     

G. P. Eaton 《Environmental Geology》1994,24(4):309-311

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Hurricane-induced landslide activity on an alluvial fan along Meadow Run, Shenandoah Valley, Virginia (eastern USA)     

Gerald F. Wieczorek  L. Scott Eaton  Thomas M. Yanosky  Eric J. Turner 《Landslides》2006,3(2):95-106

Although intense rainfall and localized flooding occurred as Hurricane Isabel tracked inland northwestardly across the Blue Ridge Mountains of central Virginia on September 18–19, 2003, few landslides occurred. However, the hurricane reactivated a dormant landslide along a bluff of an incised alluvial fan along Meadow Run on the western flanks of the Blue Ridge Mountains. Subsequent monitoring showed retrogressive movement involving several landslide blocks for the next several months. Using dendrochronology, aerial photography, and stream discharge records revealed periods of landslide activity. The annual variation of growth rings on trees within the landslide suggested previous slope instability in 1937, 1972, 1993, 1997, and 1999, which correlated with periods of local flood events. The avulsive and migrating nature of Meadow Run, combined with strong erosional force potential during flood stages, indicates that landslides are common along the bluff-channel bank interface, locally posing landslide hazards to relatively few structures within this farming region.  相似文献   

Introduction     

D.B. Snyder  D.W. Eaton  C.A. Hurich   《Tectonophysics》2006,420(1-2):1

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Toxicity of chromated copper arsenate (CCA)-treated wood to non-target marine fouling communities in Langstone Harbour, Portsmouth, UK     

Brown CJ  Eaton RA 《Marine pollution bulletin》2001,42(4):310-318

The effect of the anti-marine-borer timber preservative chromated copper arsenate (CCA) (a pressure impregnated solution of copper, chromium and arsenic compounds) on non-target marine fouling animals was investigated during a subtidal exposure trial. Panels of Scots pine treated to target retentions of 12, 24 and 48 kg CCA per m-3 of wood, plus untreated controls were submerged at a coastal site on the south coast of the UK for 6, 12 and 18 months. After each exposure period the fouling communities that formed on the surface of panels were assessed both qualitatively and quantitatively. Community structure was similar on panels treated to the three CCA loadings, but was significantly different from community structure on untreated panels. The total number of species (species richness) was similar on all panels, although the number of individual organisms attached to the surface of panels was significantly higher on CCA-treated panels than on untreated panels. k-dominance curves revealed that the difference in numbers of individuals between CCA-treated and untreated panels was caused by higher numbers of the dominant species (Elminius modestus, Hydroides ezoensis, and Electra pilosa) on CCA-treated panels. Other species were present in similar numbers on panels of all treatments. Results indicate that there are no detrimental toxic effects to epibiota caused by the presence of CCA preservative within the matrix of the wood at any of the treatment levels. Differences in community structure between CCA-treated and untreated panels may be due to enhanced larval settlement on CCA-treated timber by some species as a result of modifications to the surface properties of the timber by the CCA preservative.  相似文献   

Aquifer-yield continuum as a guide and typology for science-based groundwater management     

Suzanne A. Pierce  John M. Sharp Jr.  Joseph H. A. Guillaume  Robert E. Mace  David J. Eaton 《Hydrogeology Journal》2013,21(2):331-340

Groundwater availability is at the core of hydrogeology as a discipline and, simultaneously, the concept is the source of ambiguity for management and policy. Aquifer yield has undergone multiple definitions resulting in a range of scientific methods to calculate and model availability reflecting the complexity of combined scientific, management, policy, and stakeholder processes. The concept of an aquifer-yield continuum provides an approach to classify groundwater yields along a spectrum, from non-use through permissive sustained, sustainable, maximum sustained, safe, permissive mining to maximum mining yields, that builds on existing literature. Additionally, the aquifer-yield continuum provides a systems view of groundwater availability to integrate physical and social aspects in assessing management options across aquifer settings. Operational yield describes the candidate solutions for operational or technical implementation of policy, often relating to a consensus yield that incorporates human dimensions through participatory or adaptive governance processes. The concepts of operational and consensus yield address both the social and the technical nature of science-based groundwater management and governance.  相似文献