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151.
Herkenhoff KE Squyres SW Arvidson R Bass DS Bell JF Bertelsen P Cabrol NA Gaddis L Hayes AG Hviid SF Johnson JR Kinch KM Madsen MB Maki JN McLennan SM McSween HY Rice JW Sims M Smith PH Soderblom LA Spanovich N Sullivan R Wang A 《Science (New York, N.Y.)》2004,305(5685):824-826
The Microscopic Imager on the Spirit rover analyzed the textures of the soil and rocks at Gusev crater on Mars at a resolution of 100 micrometers. Weakly bound agglomerates of dust are present in the soil near the Columbia Memorial Station. Some of the brushed or abraded rock surfaces show igneous textures and evidence for alteration rinds, coatings, and veins consistent with secondary mineralization. The rock textures are consistent with a volcanic origin and subsequent alteration and/or weathering by impact events, wind, and possibly water. 相似文献
152.
Bell JF Squyres SW Arvidson RE Arneson HM Bass D Blaney D Cabrol N Calvin W Farmer J Farrand WH Goetz W Golombek M Grant JA Greeley R Guinness E Hayes AG Hubbard MY Herkenhoff KE Johnson MJ Johnson JR Joseph J Kinch KM Lemmon MT Li R Madsen MB Maki JN Malin M McCartney E McLennan S McSween HY Ming DW Moersch JE Morris RV Dobrea EZ Parker TJ Proton J Rice JW Seelos F Soderblom J Soderblom LA Sohl-Dickstein JN Sullivan RJ Wolff MJ Wang A 《Science (New York, N.Y.)》2004,305(5685):800-806
Panoramic Camera images at Gusev crater reveal a rock-strewn surface interspersed with high- to moderate-albedo fine-grained deposits occurring in part as drifts or in small circular swales or hollows. Optically thick coatings of fine-grained ferric iron-rich dust dominate most bright soil and rock surfaces. Spectra of some darker rock surfaces and rock regions exposed by brushing or grinding show near-infrared spectral signatures consistent with the presence of mafic silicates such as pyroxene or olivine. Atmospheric observations show a steady decline in dust opacity during the mission, and astronomical observations captured solar transits by the martian moons, Phobos and Deimos, as well as a view of Earth from the martian surface. 相似文献
153.
Squyres SW Arvidson RE Bell JF Brückner J Cabrol NA Calvin W Carr MH Christensen PR Clark BC Crumpler L Marais DJ d'Uston C Economou T Farmer J Farrand W Folkner W Golombek M Gorevan S Grant JA Greeley R Grotzinger J Haskin L Herkenhoff KE Hviid S Johnson J Klingelhöfer G Knoll AH Landis G Lemmon M Li R Madsen MB Malin MC McLennan SM McSween HY Ming DW Moersch J Morris RV Parker T Rice JW Richter L Rieder R Sims M Smith M Smith P Soderblom LA Sullivan R Wänke H Wdowiak T Wolff M Yen A 《Science (New York, N.Y.)》2004,306(5702):1698-1703
The Mars Exploration Rover Opportunity has investigated the landing site in Eagle crater and the nearby plains within Meridiani Planum. The soils consist of fine-grained basaltic sand and a surface lag of hematite-rich spherules, spherule fragments, and other granules. Wind ripples are common. Underlying the thin soil layer, and exposed within small impact craters and troughs, are flat-lying sedimentary rocks. These rocks are finely laminated, are rich in sulfur, and contain abundant sulfate salts. Small-scale cross-lamination in some locations provides evidence for deposition in flowing liquid water. We interpret the rocks to be a mixture of chemical and siliciclastic sediments formed by episodic inundation by shallow surface water, followed by evaporation, exposure, and desiccation. Hematite-rich spherules are embedded in the rock and eroding from them. We interpret these spherules to be concretions formed by postdepositional diagenesis, again involving liquid water. 相似文献
154.
Greeley R Squyres SW Arvidson RE Bartlett P Bell JF Blaney D Cabrol NA Farmer J Farrand B Golombek MP Gorevan SP Grant JA Haldemann AF Herkenhoff KE Johnson J Landis G Madsen MB McLennan SM Moersch J Rice JW Richter L Ruff S Sullivan RJ Thompson SD Wang A Weitz CM Whelley P 《Science (New York, N.Y.)》2004,305(5685):810-813
Wind-abraded rocks, ripples, drifts, and other deposits of windblown sediments are seen at the Columbia Memorial Station where the Spirit rover landed. Orientations of these features suggest formative winds from the north-northwest, consistent with predictions from atmospheric models of afternoon winds in Gusev Crater. Cuttings from the rover Rock Abrasion Tool are asymmetrically distributed toward the south-southeast, suggesting active winds from the north-northwest at the time (midday) of the abrasion operations. Characteristics of some rocks, such as a two-toned appearance, suggest that they were possibly buried and exhumed on the order of 5 to 60 centimeters by wind deflation, depending on location. 相似文献
155.
Bertelsen P Goetz W Madsen MB Kinch KM Hviid SF Knudsen JM Gunnlaugsson HP Merrison J Nørnberg P Squyres SW Bell JF Herkenhoff KE Gorevan S Yen AS Myrick T Klingelhöfer G Rieder R Gellert R 《Science (New York, N.Y.)》2004,305(5685):827-829
The magnetic properties experiments are designed to help identify the magnetic minerals in the dust and rocks on Mars-and to determine whether liquid water was involved in the formation and alteration of these magnetic minerals. Almost all of the dust particles suspended in the martian atmosphere must contain ferrimagnetic minerals (such as maghemite or magnetite) in an amount of approximately 2% by weight. The most magnetic fraction of the dust appears darker than the average dust. Magnetite was detected in the first two rocks ground by Spirit. 相似文献
156.
157.
Viktor Milkevych Per Madsen Hongding Gao Just Jensen 《Zeitschrift für Tierzüchtung und Züchtungsbiologie》2021,138(1):14-22
This work focuses on the effects of variable amount of genomic information in the Bayesian estimation of unknown variance components associated with single‐step genomic prediction. We propose a quantitative criterion for the amount of genomic information included in the model and use it to study the relative effect of genomic data on efficiency of sampling from the posterior distribution of parameters of the single‐step model when conducting a Bayesian analysis with estimating unknown variances. The rate of change of estimated variances was dependent on the amount of genomic information involved in the analysis, but did not depend on the Gibbs updating schemes applied for sampling realizations of the posterior distribution. Simulation revealed a gradual deterioration of convergence rates for the locations parameters when new genomic data were gradually added into the analysis. In contrast, the convergence of variance components showed continuous improvement under the same conditions. The sampling efficiency increased proportionally to the amount of genomic information. In addition, an optimal amount of genomic information in variance–covariance matrix that guaranty the most (computationally) efficient analysis was found to correspond a proportion of animals genotyped ***0.8. The proposed criterion yield a characterization of expected performance of the Gibbs sampler if the analysis is subject to adjustment of the amount of genomic data and can be used to guide researchers on how large a proportion of animals should be genotyped in order to attain an efficient analysis. 相似文献
158.
L. E. Christiansen J. S. Andersen H. C. Wegener H. Madsen 《Journal of Agricultural, Biological & Environmental Statistics》2006,11(4):411-424
The spatial scan statistic is widely used to search for clusters. This article shows that the usually applied elimination
of secondary clusters as implemented in Sat Scan is sensitive to smooth changes in the shape of the clusters. We present an
algorithm for generation of a set of confocal elliptic windows and propose a new way to present the information when a spatial
point process is considered. This method gives smooth changes for smooth expansions of the set of clusters. A simulation study
is used to show how the elliptic windows outperforms the usual circular windows. The proposed method for graphical representation
of the information in a set of clusters contain more information than just presenting nonoverlapping clusters. We suggest
that more than one graphical representation of a set of clusters should be used to easily extract more information and to
avoid pitfalls of the selected method. 相似文献
159.
Abstract – Downstream movement of a wild population of brown trout was examined in a small Danish stream in relation to morphological and physiological smolt status from March to May. Downstream movement was monitored in a Wolf-type trap covering all possible passage routes in the stream. Trout caught in the trap were classified as parr, pre-smolt or smolt based on morphological criteria and compared with trout randomly caught by electrofishing upstream of the trap. Representative gill samples from trap-caught and electrofished trout were analysed for gill Na+ , K+ -ATPase activity and used as a measure of physiological smolt status. Only a few parr occurred in the trap. Few pre-smolts occurred in the trap evenly in March and early April. In late April, pre-smolt movement peaked. By comparison, the main downstream movement of smolts occurred in distinct peaks through late March and April. The majority of fish caught in the trap were judged as pre-smolts or smolts based on morphological criteria's and they were characterised by relatively high gill Na+ , K+ -ATPase activity compared with trout judged as parr. Trout caught by electrofishing upstream the trap, were classified as parr, pre-smolts and smolts early in the season (March). During and after the main smolt-run in April the distribution of the remaining trout in the brook became skewed in favour of pre-smolt and parr. The study suggests that smolting trout initiate downstream movement once having reached a certain physiological smolt condition (judged by increased gill Na+ , K+ -ATPase activity). 相似文献
160.
Conventional approaches for proving in situ biodegradation of organic pollutants in aquifers have severe limitations. In the approach described here, patterns in a comprehensive set of microbiological activity and distribution data were analyzed. Measurements were performed on sediment samples gathered at consistent depths in aquifer boreholes spanning a gradient of contaminant concentrations at a buried coal tar site. Microbial adaptation to polyaromatic hydrocarbons (PAHs) was demonstrated by mineralization of naphthalene and phenanthrene in samples from PAH-contaminated, but not adjacent pristine, zones. Furthermore, contaminant-stimulated in situ bacterial growth was indicated because enhanced numbers of protozoa and their bacterial prey were found exclusively in contaminated subsurface samples. The data suggest that many convergent lines of logically linked indirect evidence can effectively document in situ biodegradation of aquifer contaminants. 相似文献