Covariance function diagnostics for spatial linear models     

Ronald Christensen  Wesley Johnson  Larry M. Pearson 《Mathematical Geology》1993,25(2):145-160

Case deletion diagnostics are developed for detecting observations that are influential in estimating the covariance function of a spatial random field. Diagnostics are developed within the context of universal kriging. Computational formulae are given that make the procedures feasible and the diagnostics are illustrated in an example.  相似文献   

An Apollo 15 mare basalt fragment and lunar mare provinces     

Graham Ryder  Trina Cox Burling 《Meteoritics & planetary science》1996,31(1):50-59

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Cyclic characteristics of sediments in the Moon Island Beach Subgroup, Newcastle Coal Measures, New South Wales     

K. R. Johnson  A. C. Cook 《Mathematical Geology》1973,5(1):91-110

Cyclic characteristics of a sequence of Permian coal-measure sediments have been studied using Markov chain analysis on borehole data. Fining-upwards and oscillating sequences can be distinguished, and depositional regimes are proposed to explain the observed sequences. However, there is no clearly defined relationship of sequence type to tectonosedimentary environment. The relationship of the number of coal-defined and fining-upwards cycles to total thickness and mean cycle thickness is examined using linear regression. The relationships for coal-defined and fining-upwards cycles are essentially the same. Significant positive correlations are present between the number of cycles and total thickness and significant inverse relationships are present for the number of cycles and the mean cycle thickness.  相似文献   

METAL AND SCHREIBERSITE IN MAYO BELWA,AN ENSTATITE ACHONDRITE     

A.L. Graham 《Meteoritics & planetary science》1978,13(2):235-244

The Mayo Belwa meteorite (an aubrite) contains discrete metal grains ranging in size from less than 1 μm to 300 μm across, and schreibersites up to 25 μm across. Intergrowths of metal and schreibersite also occur. These phases are distributed heterogeneously throughout the meteorite and are present both in the fine-grained matrix and within silicate crystals. The concentrations of the elements Ni, Fe, Si, Co, P, were determined in grains larger than 4 μm across. Most metal grains have 1–8% Ni, the total range being 0.8–23.5% Ni. The 1–8% Ni metal may be sub-divided into two compositional groups, one relatively compact, having 1–3.8% Ni, 0.1-0.3% Si; the second having a much greater range in both Ni and Si (～ 4–12%, 0.1-1.2% respectively). There is no zonation in the Si contents of individual grains. Neither the size of the grains nor their environment correlates with their Ni or Si contents, though there is a tendency for low Ni, low Si metal to be within enstatite crystals. Schreibersite (8–14.4% Ni) occurs as isolated grains or associated with low-Ni metal; it generally contains less than 500 ppm Si. The wide range in the Ni contents of the metal distinguishes it from the metal of the E-chondrites, and argues against an E-chondrite source for this metal.  相似文献   

Dust in Jupiter''s magnetosphere: Time variations     

G.E. Morfill  E. Grün  T.V. Johnson 《Planetary and Space Science》1980,28(12):1111-1114

The stability to temporal variations of the Jovian dust ring is a property which may soon be measured, and can in principle give a clue as to the origin of the ring. In this analysis fluctuations in the ring topology and intensity are determined over various relevant time scales, assuming the origin model proposed by Johnson etal. (1980) and Morfill etal. (1980a, b) to apply. It is concluded that the ring is a quasi-permanent and quasi-stable feature of the Jovian system.  相似文献   

Thermal protons in the morning magnetosphere: Filling and heating near the equatorial plasmapause     

G.L. Wrenn  J.J. Sojka  J.F.E. Johnson 《Planetary and Space Science》1984,32(3):351-363

Thermal H⁺ distributions have been measured as the European Space Agency GEOS-1 satellite passed through the late morning equatorial magnetosphere, plasmapause and plasmasphere. The unique capabilities of the on-board Supralhermal Plasma Analysers (SPA) have been used to overcome the retarding floating potential of the satellite and measure the velocity distribution of the cold protons. In the magnetosphere an enhanced source cone of such ions with a temperature of ~ 0.5 eV is a signature of the filling process occurring outside the plasmapause where flux tubes are relatively empty. In the plasmasphere the thermal H⁺ is essentially isotropic with a temperature less than 0.5 eV but the motion of the satellite introduces apparent drift.These measurements of cold proton velocity distribution now permit a reappraisal of the definition of the “plasmapause”. It becomes inappropriate to use an arbitrary empirical density, e.g. the conventional 10 cm ^?3, in order to establish a boundary. It is now possible to identify a plasmapause interaction region where the two cold proton populations co-exist. This region generally lies Earthward of the 10 cm ^?3 density level, has a width which is strongly dependent on magnetic activity and the temperature is typically between 0.5 and 1.5 eV. The change from “filled” to “unfilled” flux tubes relates to the physical processes which are occurring and the controlling electric field configuration; in particular, the last closed equipotential. Throughout this region, in going from the plasmasphere to the magnetosphere, the plasma drift motion is expected to change from corotation to a convection which is controlled by E ×B, and is predominantly Sunward due to the dawn-dusk electric field. Crossing the plasmapause on the morning side, little change in drift direction should occur but subtle variations in the ionic velocity distribution do reflect the change in the degree of flux tube density equilibrium.Our first direct measurement of the magnetospheric E × B drift has been reported previously but here measurements from a selected six day period show how the plasma in the plasmapause region responds to changing magnetospheric activity. The drift velocities cannot he derived with high accuracy but the analysis shows that the technique can provide a valid mapping of the magnelospheric electric field. In addition, since the magnetospheric cold plasma distribution is observed after it has come from the ionosphere, a distance of many Earth radii, the scattering and accelerating mechanisms along the flux tube can be studied. For this particular data-set taken in the late morning, the maximum potential drops along the flux tubes were less than a volt. The ionospheric proton source cone is observed to be broad, pitch angle scattering persists up to 40 or even 70°.Although these results throw new light on the plasmaspheric filling process one must recognise that, however the plasmapause is defined, it is not a simple matter to map this boundary from the equatorial plane down to low altitudes and the mid-latitude trough.  相似文献   

The 1.7- to 4.2-μm spectrum of asteroid 1 Ceres: Evidence for structural water in clay minerals     

Larry A. Lebofsky  Michael A. Feierberg  Alan T. Tokunaga  Harold P. Larson  James R. Johnson 《Icarus》1981,48(3):453-459

A high-resolution Fourier spectrum (1.7–3.5 μm) and medium-resolution spectrophotometry (2.7–4.2 μm) were obtained for Asteroid 1 Ceres. The presence of the 3-μm absorption feature due to water of hydration was confirmed. The 3-μm feature is compared with the 3-μm bands due to water of hydration in clays and salts. It is concluded that the spectrum of Ceres shows a strong absorption at 2.7–2.8 μm due to structural OH groups in clay minerals. The dominant minerals on the surface of Ceres are therefore hydrated clay minerals structurally similar to terrestrial montmorillonites. There is also a narrow absorption feature at 3.1 μm which is attributable to a very small amount of water ice on Ceres. This is the first evidence for ice on the surface of an asteroid.  相似文献   

Geochemistry of Pyramid Lake sediments: influence of anthropogenic activities and climatic variations within the basin     

Z. Yang  E. Graham  W. Lyons 《Environmental Geology》2003,43(6):688-697

In 1998, a 59-cm sediment box core (PLB98-2) was taken from the deepest part of Pyramid Lake (water depth =106 m), Nevada. Age control for PLB98-2 was provided using a variety of approaches. Dried sediment samples were leached with 10% ultra-pure nitric acid and analyzed for their elemental concentrations using standard ICP techniques. The variations in elemental concentrations can be divided into two periods: one prior to European settlement and one influenced by anthropogenic activities. The concentrations of K, Al, Na, Zn, and Mn all began to increase after pre-European manipulation of the watershed in ~1860, which indicates the increasing soil erosion in the watershed was due to deforestation and development. The highest concentrations of these elements and lithogenic elements such as P, Mg, Fe, Cu, Ba, and Si occurred during the flood event of the 1990s. The Pb enrichment times are similar to what has been observed in estuaries draining the western Sierra Nevada, but the Pb enrichments in Pyramid Lake are much less. The Ca, TOC, TIC, Sr, and Ba concentrations show a strong association that is closely related to drought-wet variations of climate and the construction of Derby Dam for water diversions in the early 1900s. Se concentrations vary with the '¹⁸O of the carbonate in the sediments. Although the '¹⁸O "leads" the other species and Truckee River discharge by a few years, it is an excellent indicator of the hydrological change of Pyramid Lake, which is related to climate changes and human activities. From ~1920, Mn and Mo vary inversely in the sediments. In general, the Mo concentrations varies directly with the organic carbon content of the sediments from 1910 to ~1980, suggesting enhanced removal of Mo during times of increased productivity in the lake, and anoxic conditions at the sediment/water interface. This coincides with low lake levels. The elemental composition of the sediments in Pyramid Lake clearly reflect the timing of important anthropogenic activities and climatic variations that have taken place within the watershed over the past 240 years.  相似文献   

Geochemical Reactions During Biodegradation/Vapor-Extraction Remediation of Petroleum Contamination in the Vadose Zone     

Regina M. Capuano  Mark A. Johnson 《Ground water》1996,34(1):31-40

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Ion microprobe analysis of O/O in authigenic and detrital quartz in the St. Peter Sandstone, Michigan Basin and Wisconsin Arch, USA: Contrasting diagenetic histories     

Colin M. Graham  John W. Valley  Bryce L. Winter 《Geochimica et cosmochimica acta》1996,60(24):5101-5116

The oxygen isotopic compositions of authigenic quartz cements in sandstones provide a monitor of the temperatures, compositions, and origins of pore-occluding fluids during diagenesis, but quartz overgrowths are too fine-grained to be amenable to conventional isotopic analysis. We have used a Cameca ims-4f ion microprobe to determine oxygen isotopic variations in authigenic and detrital quartz in four samples of the Ordovician St. Peter Sandstone from the Michigan Basin and Wisconsin Arch, midwestern USA. Ion microprobe isotopic analyses have been successfully accomplished with an internal precision of ±1‰ (1 σ) and a spatial resolution of 20–30 μm at low mass resolution using a high voltage offset technique. Repeated analyses of the quartz standard demonstrate a reproducibility of close to ±1‰ (1 sd) in good agreement with that expected from counting statistics. The four ion probe samples were chosen as representative of thirteen samples that were mechanically and chemically disaggregated, sieved, and analysed as a function of sieve size by conventional bulk-mineral techniques. Conventional and ion microprobe analyses are mutually consistent, supporting the accuracy of the ion microprobe analyses. Within-sample isotopic variations of up to 13%. and micro-scale isotopic variations of at least 4‰ over a distance of 100 μm have been measured within quartz overgrowths in a sandstone from the Wisconsin Arch. Overgrowths are uniformly higher in δ¹⁸O than detrital grains, and gradients of up to 25% exist across a few microns.

¹⁸O-enriched quartz overgrowths in sandstones from the Wisconsin Arch show complex CL zonation and reflect one of two possible processes: (1) low-temperature quartz precipitation during mixing of meteoric waters with upwelling basinal fluids; (2) higher temperature quartz precipitation during episodic gravity-driven upwelling of warm basinal fluids (of comparable isotopic composition to Michigan Basin fluids) from the Illinois Basin, related to evolution of Mississippi Valley type Pb---Zn ore-forming fluids. Quartz overgrowths in Michigan Basin sandstones, which derived their silica locally by pressure solution, are thought to have precipitated continuously over a range of temperatures from hot basinal fluids of restricted isotopic composition and circulation. Detrital quartz shows significant intea-grain and intergrain isotopic variation (5–13‰) but no significant inter-sample variation, consistent with a uniform source of granitoid and metamorphic quartz in space and time.  相似文献