Terrestrial analogs to lunar dimple (drainage) craters     

Ronald Greeley 《Earth, Moon, and Planets》1970,1(2):237-252

In addition to modes of formation offered by previous investigators, terrestrial drainage craters formed over lava tubes in Oregon are presented as analogs to lunar drainage craters. Craters associated with lava tubes result from: (1) drainage of surface material through roof fractures; (2) plastic collapse of the partially cooled lava tube roof; and (3) drainage of surface material into roof collapses. The former two categories result in shallow, often elongate craters; the latter category forms classic dimple shaped craters. Elongate dimple craters formed over volcanic fissures in southern Idaho are also discussed and presented in support of one mode of formation proposed by previous investigators for lunar drainage craters.Movement of surface material toward the orifice is initiated on Earth largely by wind and water; in lunar conditions, initial movement is attributed to micro- and macro-meteoritic bombardment, seismic disturbances generated by internal and external processes, and by thermal creep.Nat. Res. Council Postdoctoral Resident Research Associate.  相似文献   

Quadratic covariance estimation and equivalence of predictions     

Ronald Christensen 《Mathematical Geology》1993,25(5):541-558

This article illustrates the use of linear and nonlinear regression models to obtain quadratic estimates of covariance parameters. These models lead to new insights into the motivation behind estimation methods, the relationships between different methods, and the relationship of covariance estimation to prediction. In particular, we derive the standard estimating equations for minimum norm quadratic unbiased translation invariant estimates (MINQUEs) from an appropriate linear model. Connections between the linear model, minimum variance quadratic unbiased translation invariant estimates (MIVQUEs), and MINQUEs are examined and we provide a minimum norm justification for the use of one-step normal theory maximum likelihood estimates. A nonlinear regression model is used to define MINQUEs for nonlinear covariance structures and obtain REML estimates. Finally, the equivalence of predictions under various models is examined when covariance parameters are estimated. In particular, we establish that when using MINQUE, iterative MINQUE, or restricted maximum likelihood (REML) estimates, the choice between a stationary covariance function and an intrinsically stationary semivariogram is irrelevant to predictions and estimated prediction variances.  相似文献   

Warfare In Suburbia: A Rebuttal     

Ronald W. Jenkins 《The Professional geographer》1981,33(3):366-371

All opinions and statements appearing in the following communications are those of their writers and do not necessarily reflect the views of the editors or the Association of American Geographers, who assume no responsibility for their contents.  相似文献   

Chemical and biological weathering of oil,from the Amoco Cadiz spillage,within the littoral zone     

Ronald M. Atlas  Paul D. Boehm  John A. Calder 《Estuarine, Coastal and Shelf Science》1981,12(5):589-608

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Non-adiabatic discrete Alfvén waves in coronal loops and prominences     

Rony Keppens  Ronald A. M. Van Der Linden  Marcel Goossens 《Solar physics》1993,144(2):267-281

Discrete Alfvén waves in coronal loops and prominences are investigated in non-ideal magnetohydrodynamics. The non-ideal effects included are anisotropic, thermal conduction, and optically thin radiation. The classic ideal Alfvén continuum is not altered by these non-ideal effects, but the discrete Alfvén modes, which exist under certain conditions above or below the Alfvén continuum in ideal MHD, are shown to be influenced by non-adiabatic effects.The existence of discrete, non-adiabatic Alfvén waves, and their damping and overstability are examined for 1D cylindrical equilibrium states with twisted magnetic fields. First, analytic results are obtained for modes of high radial order by means of a WKB-analysis. The subspectrum of discrete Alfvén modes is computed with a numerical code, with particular emphasis on the modes of low radial order. The results show that discrete Alfvén waves are of potential importance for solar applications and also that the information obtained with the WKB-analysis is of limited use in this context.Research Assistant of the Belgian National for Scientific Research.  相似文献   

Characterization of colloidal and particulate matter transported by the magela creek system,Northern Australia     

Barry T. Hart  Grant B. Douglas  Ronald Beckett  Annick Van Put  Rene E. Van Grieken 《水文研究》1993,7(1):105-118

The composition and amount of colloidal and suspended participate matter transported during a small flood event in Magela Creek in tropical northern Australia was investigated. The flood studied constituted approximately 3 % of the total annual flow, most (90%) of which occurred between mid-January and mid-February of the study year. Three fractions were separated from water samples using a sequential method involving a continuous flow centrifuge to separate suspended particulate matter (SPM; nominally > 1 μm) followed by hollow fibre filtration, first using a 0.1 μm filter to separate course colloidal matter (CCM; nominal size 1–0.1 μm) and then a 0–015 μm filter to separate fine colloidal matter (FCM; nominal size 0.1–0.015 μm). The SPM was predominantly inorganic (organic matter 21 %), whereas the colloidal fractions were dominantly organic matter (CCM 60%; FCM 83%). Analysis of individual particles using electron microprobe and automated image analysis indicated that the mineral fractions in both the SPM and CCM were dominated by iron-enriched aluminosilicates (including kaolinite) (72–82%) and quartz (9–10%), indicative of a highly weathered and extensively laterized catchment. Surprisingly there was very little difference in the composition of the SPM or CCM fractions during the flood event studied, which may indicate either that sediment availability was restricted following the major run-off events in January and February, or that all the sediment sources within the catchment are geochemically similar. Approximately the same amounts of particulate (20 tonne), colloidal (21 tonne) and dissolved material (17 tonne) were transported during the 25 hour period of the main flood peak; over 90% of the colloidal matter was 0.1–1.0 μm in size. These data suggest that previous estimates of the amounts of particulate (and colloidal) matter transported by Magela Creek, which were based on suspended solids measurements, may have underestimated the particulate matter load by as much as 50%. It is possible that the relatively high proportion of colloidal matter is unique to Magela Creek because coagulation and aggregation of colloidal matter to particulate matter is slow due to the very low concentations of calcium and magnesium in these waters. However, if the result is more widespread, there are important implications for the global estimates of fluvially transported particulate and dissolved materials as many of the previous studies may have underestimated the particulate load and overestimated the dissolved load.  相似文献   

Color display of well logs     

Peter L. Briggs 《Mathematical Geology》1985,17(4):481

Information displayed in image form is conventionally at least two-dimensional. One-dimensional data can also be displayed as imagery by amplitude slicing a function and representing these amplitude slices as grey levels or as intensities of a particular color. An image having length and width can be formed from one-dimensional data by arranging a sequence of such color levels along the length of the image, corresponding to the independent space or time variable, and by extending these color levels arbitrarily along the width of the image. Such an image is of arbitrary width and exhibits changes, or information, only along its length. If three such images are made, one in each of the three primary colors, each image representing a different one-dimensional function over the same range of a common independent space or time variable, standard primary color composition can be used to unite these three images into a single full-color image in either computer graphic or photographic media. When three different well logs from a single borehole are combined in this manner, the resulting full-color image is equivalent to a three-axis cross-plot of the logs involved. Because primary colors appear to the human eye to be orthogonal and miscible, the color image preserves all information present in the three original data sets.Further, because this color representation of data can be arranged conveniently in depth sequence, the color composite image presents both information best visualized in cross-plot presentation (e.g., lithologic clustering and differentiation) and information lacking in cross-plots that is best seen in conventional wiggle-trace displays of well logs (e.g., stratigraphic or depth sequence). Such color presentations of well log data reduce the number of displays competing for an interpreter's attention by uniting three wiggle traces into one display and relieve the burden of mentally combining data from several separate displays. Combined interpretation is particularly essential in well log interpretation where one must analyze individually ambiguous data sets; color log presentation automatically provides combination while leaving interpretation to the scientist. Color log images also present log data to the user in a form that differs from conventional wiggle trace and so appeals to a different and richer set of human perceptions and pattern recognition skills.  相似文献   

Monte Carlo simulation of temperature fluctuations in interstellar iron grains     

Ronald G. Tabak 《Astrophysics and Space Science》1987,134(1):145-152

The Monte Carlo technique is used to simulate the temperature fluctuations in interstellar iron grains exposed to a particular radiation field. It is found that iron grains attain time-averaged temperatures almost an order of magnitude greater than dielectrics and that their temperatures may fluctuate by as much as 100 K. The effect that this will have on the catalytic formation of molecular hydrogen is examined. It is also found that small metallic grains are unlikely candidates for explaining the extended red emission observed in many reflection nebulae.  相似文献   

The use of magnetic field excursions in stratigraphy     

Ronald T. Merrill  Phillip L. McFadden 《Quaternary Research》2005,63(3):232-237

The use of magnetic field excursions in stratigraphy is difficult primarily because the excursion field is complex and not dominantly dipolar. In contrast with a reversal, which is a global event, an excursion can be evidenced at one location but not another. Although this does not by itself rule out the use of excursions in stratigraphy, it does limit the geographic area over which they may be correlated. We recommend, somewhat conservatively, that excursions can be used to correlate between sedimentary cores separated by angular distances of less than 30° on Earth's surface. Correlation between cores separated by more than 45° should not be attempted.  相似文献   

Pleistocene geomorphology and geochronology of eastern Grand Canyon: linkages of landscape components during climate changes     

Matt D. Anders  Joel L. Pederson  Tammy M. Rittenour  Warren D. Sharp  John C. Gosse  Karl E. Karlstrom  Laura J. Crossey  Ronald J. Goble  Lisa Stockli  Guang Yang 《Quaternary Science Reviews》2005,24(23-24):2428-2448

We report new mapping, soils, survey, and geochronologic (luminescence, U-series, and cosmogenic-nuclide) data from Pleistocene deposits in the arid setting of eastern Grand Canyon. The result is a stratigraphic framework of inset fill gravels and associated terraces that provide a record of the responses of hillslopes, tributary streams, and the Colorado River to the last 400 kyr of glacial–interglacial climate change. The best-preserved last 80 kyr of this record indicates a stratigraphic–chronologic disconnect between both deposition and incision along the Colorado River versus along the trunks of local tributaries. For example, the Colorado River finished aggrading and had already begun incising before the main pulse of aggradation in the trunks of local catchments during Marine Isotope Stage 3, and then tributary incision followed during the millennial-scale fluctuations of the last glacial epoch, potentially concurrent with mainstem aggradation. The mainstem record appears to broadly correlate with regional paleoclimate and upstream geomorphic records and thus may be responding to climatic–hydrologic changes in its mountain headwaters, with aggradation beginning during full-glacial times and continuing into subsequent interglacials. The contrasting lag time in responses of the dryland catchments within Grand Canyon may be largely a function of the weathering-limited nature of hillslope sediment supply.  相似文献