The effects of vehicular and pedestrian traffic on dune vegetation in South Africa     

C.A. Rickard  A. McLachlan  G.I.H. Kerley 《Ocean & Coastal Management》1994,23(3)

The effects of varying intensities of off-road vehicle and pedestrian traffic on vegetation height and percent-cover were investigated at two sites representing pioneer and climax dune shrubland communities in South African dune systems. In all cases, a decreasing trend in vegetation height and percentage cover subsequent to application of the treatments was evident, although this was more clear in the shrub than in the pioneer community. The impact on vegetation variables increased with increasing intensity of vehicle and pedestrian treatments. Vehicles driven along a curved path resulted in greater vegetation destruction than those driven along a straight path. High intensity (single application) treatments resulted in an initial decrease in vegetation height and cover immediately after the impact, which was followed by a further decline over the next 3 months. This two-step response was attributed to the subsequent gradual death of the vegetation which was not evident immediately following the impact. Due to their faster growth rate, pioneer dune communities appear to have the capacity to recover following impacts, while dune shrub communities tend to be more vulnerable, exhibiting signs of damage for longer periods. The results of this study have value for managers of coastal dune systems, particularly those impacted by human recreational activities.  相似文献   

Discussion—Timing of regional deformation of the hill end trough     

M. J. Rickard 《Australian Journal of Earth Sciences》2013,60(1-2)

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Defining the Potential of Nanoscale Re‐Os Isotope Systematics Using Atom Probe Microscopy          下载免费PDF全文

Luke Daly  Phil A. Bland  Svetlana Tessalina  David W. Saxey  Steven M. Reddy  Denis Fougerouse  William D.A. Rickard  Lucy V. Forman  Alexandre La Fontaine  Julie M. Cairney  Simon P. Ringer  Bruce F. Schaefer  Daniel Schwander 《Geostandards and Geoanalytical Research》2018,42(3):279-299

Atom probe microscopy (APM) is a relatively new in situ tool for measuring isotope fractions from nanoscale volumes (< 0.01 μm³). We calculate the theoretical detectable difference of an isotope ratio measurement result from APM using counting statistics of a hypothetical data set to be ± 4δ or 0.4% (2s). However, challenges associated with APM measurements (e.g., peak ranging, hydride formation and isobaric interferences), result in larger uncertainties if not properly accounted for. We evaluate these factors for Re‐Os isotope ratio measurements by comparing APM and negative thermal ionisation mass spectrometry (N‐TIMS) measurement results of pure Os, pure Re, and two synthetic Re‐Os‐bearing alloys from Schwander et al. (2015, Meteoritics and Planetary Science, 50, 893) [the original metal alloy (HSE) and alloys produced by heating HSE within silicate liquid (SYN)]. From this, we propose a current best practice for APM Re‐Os isotope ratio measurements. Using this refined approach, mean APM and N‐TIMS ¹⁸⁷Os/¹⁸⁹Os measurement results agree within 0.05% and 2s (pure Os), 0.6–2% and 2s (SYN) and 5–10% (HSE). The good agreement of N‐TIMS and APM ¹⁸⁷Os/¹⁸⁹Os measurements confirms that APM can extract robust isotope ratios. Therefore, this approach permits nanoscale isotope measurements of Os‐bearing alloys using the Re‐Os geochronometer that could not be measured by conventional measurement principles.  相似文献   

Temperature dependence of calcite dissolution kinetics between 1 and 62°C at pH 2.7 to 8.4 in aqueous solutions   总被引：1，自引：0，他引：1  

E.Lennart Sjöberg  David T. Rickard 《Geochimica et cosmochimica acta》1984,48(3):485-493

The kinetics of calcite dissolution in aqueous KCl-solutions far from equilibrium, between 1 and 62°C in the pH-range 2.7 to 8.4 have been investigated using a rotating disc apparatus. At neutral and alkaline pH in the mixed kinetic regime the empirical apparent activation energy (EAAE) for the surface chemical reaction rate constant is 54 ± 4 kJ mole^?1 for Carrara marble and 46 ± 4 kJ mole^?1 for Iceland spar. Under similar conditions the EAAE of the transport rate constant increases with decreasing temperature, but has a mean value of 27 ± 2 kJ mole^?1. The corresponding diffusion coefficient has a mean EAAE of 37 ± 3 kJ mole^?1 and this high EAAE is consistent with transport dependence on product diffusion in this H⁺-independent regime.In contrast, in acid solutions, where the rate approaches end-member transport control, the EAAE of the diffusion coefficient is 16 kJ mole^?1, also decreasing with increasing temperature. This is compatible with H⁺-diffusion to the surface being rate-controlling.In inhibitor-free natural systems, calcite dissolution kinetics far from equilibrium can be described in terms of three regimes: an H⁺-dependent regime (pH < 4 at 25°C), a transition regime (4 < pH < 5.5 at 25°C) and an H⁺-independent regime (pH > 5.5 at 25°C). At lower temperatures these boundaries move to higher pH values. The presence of inhibitors in natural systems may enhance surface controlled kinetics.  相似文献   

Copper sulphide formation chemistry at low temperatures   总被引：1，自引：0，他引：1  

Dr. D. T. Rickard 《Mineralogy and Petrology》1973,19(1):60-76

Summary Covellite, blaubleibender covellite, djurleite and chalcocite have been synthesized by the reaction between Cu₂O with aqueous Na₂S solutions at low temperatures. Digenite was produced by heating the dried products of the aqueous experimentation at 105°C for 50 days, but not directly from aqueous solution. Anilite was formed through air oxidation of chalcocite at room temperature. The pH and Eh conditions of formation of these phases have been studied and it has been shown that the synthetic results broadly reflect the theoretical stability fields for these compounds, inasmuch as more reduced copper sulphides are formed under higher pH and lower Eh conditions. Studies of the changes in these parameters during the course of the experiments have been used to outline the mechanisms involved in the reactions. It has been demonstrated that the form of the copper sulphide produced around neutral pH values is almost independent of the oxidation state of the copper reactant, but highly sensitive to the presence and concentration of elemental sulphur. A detailed discussion of the formation chemistry of copper sulphides in low temperature aqueous solutions is presented.

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Chemie der Kupfersulfidbildung bei niedrigen Temperaturen

Zusammenfassung Covellin, blaubleibender Covellin, Djurleit und Chalkosin wurden durch Reaktion zwischen Cu₂O und wäßrigen Na₂S-Lösungen bei niedrigen Temperaturen synthetisiert. Digenit entstand, wenn die getrockneten Produkte aus wäßrigen Lösungen 50 Tage bei 105°C getempert wurden, aber nicht direkt aus wäßriger Lösung. Anilit bildete sich aus Chalkosin bei Zimmertemperatur durch Oxidation an der Luft. Die pH- und Eh-Bedingungen für die Bildung dieser Phasen wurden untersucht und es wurde gezeigt, daß die Syntheseergebnisse im wesentlichen den theoretischen Stabilitätsfeldern dieser Verbindungen entsprechen, indem sich die stärker reduzierten Kupfersulfide unter höherem pH und kleinerem Eh bilden. Untersuchungen über die Änderung dieser Parameter im Verlauf der Experimente wurden zur Umreißung der Reaktionsmechanismen benützt. Es wurde gezeigt, daß die Art des Kupfersulfides, welches sich um neutrale pH-Werte bildet, fast nicht vom Oxidationszustand des reagierenden Kupfers, aber stark von der Anwesenheit und der Konzentration von elementarem Schwefel abhängt. Die Chemie der Bildung von Kupfersulfiden in wäßrigen Lösungen niedriger Temperatur wird ausführlich diskutiert.

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With 2 Figures  相似文献   

Zur Bildung des Roten Tones     

H. Pettersson 《Meteorology and Atmospheric Physics》1954,7(1):477-481

Zusammenfassung Der Verfasser, der seit mehr als 30 Jahren die Tiefseesedimente und insbesondere den Roten Ton untersucht, ist namentlich auf Grund der Ergebnisse der Schwedischen Tiefsee-Expedition mit der Albatross zur Überzeugung gelangt, daß die landläufige Erklärung für das Verschwinden des Kalks, dank dessen es zur Bildung des Roten Tones kommt, nicht genügt. Die Bildung desselben während des Tertiärs darf nicht der Wirkung kalter antarktischer und arktischer Grundströmungen zugeschrieben werden; diese werden im Gegenteil sehr schwach gewesen sein oder gar nicht existiert haben, da es damals keine polaren Eiskappen gab und die Bodentemperatur der Ozeane um 8 bis 10° C höher war als heute. Viel eher kommen für die Bildung des Roten, Tones magmatische Gase wie CO₂, HCl usw. als wichtigste Kalklöser in Betracht, die zu der Zeit ausgeworfen wurden, als submarine Vulkanausbrüche oder Extrusionen von Tiefenmaterial zur Bildung des mittelatlantischen Rückens und anderer submariner Gebirgszüge geführt haben.

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Summary The author who for over 30 years has studied deep-sea sediments and especially the Red clay has, especially on basis of results from the Swedish Deep-Sea Expedition with the Albatross, arrived at the conviction that the current explanation for the disappearance of the lime leading to the formation of Red clay is not sufficient. The formation of Red clay during Tertiary time cannot be ascribed to the action of cold Antarctic and Arctic bottom currents, which must have been very feeble or missing, when there were no polar ice-caps and the bottom temperature of the oceans was about 8° to 10° higher than at present. A principal lime-dissolving agency, responsible for the formation of Red clay are magmatic volatiles, i.e. carbon dioxide, hydrochloric acid etc., released at submarine volcanic eruptions or at the extrusion of subcrustal matter, leading to the formation of the Madatlantic Ridge and other submarine ridges.

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Résumé L'auteur qui, depuis plus de 30 années, étudie les sédiments abyssaux et, en particulier, les argiles rouges, est convaincu, et cela notamment depuis l'expédition océanographique suédoise de «Albatross», que l'explication courante de la disparition du calcaire qui conduit à la formation de cette argile n'est pas suffisante. Pendant la période tertiaire, on ne peut pas en attribuer la formation à l'action, de courants très froids arctiques et antarctiques parcourant le fonds des océans, car ceux-ci durent être très faibles, voire inexistants si l'on admet que les calottes glaciaires des pôles n'existaient pas et que la température abyssale était supérieure de 8° à 10° C à celle d'aujourd'hui. Le principal agent solvant du calcaire à l'origine des argiles rouges doit être reconnu dans certaines volatilisations du magma, tels le dioxyde de carbone et l'acide chlorhydrique par exemple. Celles-ci doivent avoir été provoquées par des éruptions volcaniques sous-marines ou par des extrusions de matériaux volcaniques qui ont conduit à la formation de nombreuses chaînes de montagnes sous-marines comme par exemple celle du centre de l'Atlantique.

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Book reviews     

W. Manshard  W. B. Morgan  Philip Tilley  Atsushi Otomo  G. Kunkel  W. Lauer  K. Kunkel  David Rickard  Joan M. Kenworthy  A. Grotewold  C. Chr Liebmann 《GeoJournal》1981,5(3):291-296

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Timing of megakinks and related structures: Constraints from the Devonian Bunga‐Wapengo Basin,Mimosa Rocks National Park,New South Wales     

M. J. Rickard  S. Love 《Australian Journal of Earth Sciences》2013,60(6):1009-1013

The Bunga beds are bounded by faults adjacent to which are fanglomerates that form part of an early Late Devonian volcanic rift basin. Some cross‐faults acted as precursors for later regional deformation that kinked the Ordovician basement and gently folded the basin sediments in a northwest‐southeast direction. Details of the faulted junction at Picnic Point and orientation of cleavage microstructures in the fanglomerates support the dating of the north‐south regional F₂ deformation as Middle Devonian or older and the northwest‐southeast F₃ kinking as post‐early Late Devonian.  相似文献   

Survey of estrogenic and androgenic disruption in Swedish coastal waters by the analysis of bile fluid from perch and biomarkers in the three-spined stickleback   总被引：1，自引：0，他引：1  

Pettersson M  Hahlbeck E  Katsiadaki I  Asplund L  Bengtsson BE 《Marine pollution bulletin》2007,54(12):1868-1880

The potential for endocrine disruption close to sewage treatment plant and pulp mill effluent discharge points along the Swedish Baltic Sea coast was explored using a dual survey strategy employing two stationary fish species. The levels of vitellogenin and spiggin as biomarkers of endocrine disruption were determined in juvenile three-spined sticklebacks (Gasterosteus aculeatus L.) together with the sex ratios and the presence of intersex. As an indication of exposure, estrogenic and androgenic substances were analysed by GC–MS in bile from perch (Perca fluviatilis L.). Spiggin and vitellogenin levels in juvenile three-spined sticklebacks were generally low, and, for most sampling sites no deviation in gonad type ratios were observed. No remarkable levels of natural or synthetic estrogens or androgens were observed in bile fluid from perch, while bisphenol A and 4-nonylphenol were detected in perch from both reference sites and exposed sites. Taken together, the results did not indicate estrogenic or androgenic disruption in the investigated waters.  相似文献   

Free oscillations of a rotating fluid contained between two spheroidal surfaces     

J. A. Rickard 《地球物理与天体物理流体动力学》2013,107(1):369-383

Abstract

A theoretical study is made of the free periods of oscillation of an incompressible inviscid fluid, bounded by two rigid concentric spheroids. It is shown that the topography of the bounding surfaces can have a significant effect on the distribution of the eigenvalues. The significance of this result is discussed with reference to the observed westward drift of the geomagnetic secular variation.  相似文献