Characterization of kerogens and study of their evolution by infrared spectroscopy: carbonyl and carboxyl groups     

Pierre L. Robin  Paul G. Rouxhet 《Geochimica et cosmochimica acta》1978,42(9):1341-1349

Measurements of the absorption coefficient of the band around 1710cm^?1, combined with adequate chemical treatments, allow an evaluation of the importance of carbonyl, carboxylic acid and ester groups in various series of kerogens. The concentration of carbonyl and acid groups, the concentration of oxygenated functions other than carbonyl or carboxyl, and the total oxygen content are higher in shallow kerogens originating from higher plants than in those containing an important algal contribution; however the concentration of ester groups varies in the opposite direction.The carboxylic acid groups are the most sensitive to catagenetic evolution or pyrolysis. The carbonyl groups are removed progressively as evolution proceeds but a fraction of them is retained up to advanced degrees of evolution.Study of the band at 1630cm^?1 has shown that, besides the bending vibration of molecular water, there is some contribution of bridged quinones and unsaturated hydrocarbons. However at least 50% of the absorption coefficient is due to polyaromatic structures. This band is generally much more intense for kerogens originating from higher plants.  相似文献   

Fluid compositions in equilibrium with silica-undersaturated magmas in the system Na<Subscript>2</Subscript>O–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiO<Subscript>2</Subscript>–H<Subscript>2</Subscript>O: clues to the composition of fenitizing fluids     

Robin F. Preston  Gary Stevens  Terence S. McCarthy 《Contributions to Mineralogy and Petrology》2003,144(5):559-569

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Environmental Histories of New Zealand     

Libby Robin 《New Zealand geographer》2003,59(1):67-68

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Sediment budget controls on foredune height: Comparing simulation model results with field data          下载免费PDF全文

Robin Davidson‐Arnott  Patrick Hesp  Jeff Ollerhead  Ian Walker  Bernard Bauer  Irene Delgado‐Fernandez  Thomas Smyth 《地球表面变化过程与地形》2018,43(9):1798-1810

The form, height and volume of coastal foredunes reflects the long‐term interaction of a suite of nearshore and aeolian processes that control the amount of sand delivered to the foredune from the beach versus the amount removed or carried inland. In this paper, the morphological evolution of more than six decades is used to inform the development of a simple computer model that simulates foredune growth. The suggestion by others that increased steepness of the seaward slope will retard sediment supply from the beach to the foredune due to development of a flow stagnation zone in front of the foredune, hence limiting foredune growth, was examined. Our long‐term data demonstrate that sediment can be transferred from the beach to the foredune, even with a steep foredune stoss slope, primarily because much of the sediment transfer takes place under oblique rather than onshore winds. During such conditions, the apparent aspect ratio of the dune to the oncoming flow is less steep and conditions are not as favourable for the formation of a stagnation zone. The model shows that the rate of growth in foredune height varies as a function of sediment input from the beach and erosion due to storm events, as expected, but it also demonstrates that the rate of growth in foredune height per unit volume increase will decrease over time, which gives the perception of an equilibrium height having been reached asymptotically. As the foredune grows in size, an increasing volume of sediment is needed to yield a unit increase in height, therefore the apparent growth rate appears to slow. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

Large grains matter: contrasting bed stability and morphodynamics during two nearly identical experiments          下载免费PDF全文

Lucy G. MacKenzie  Brett C. Eaton 《地球表面变化过程与地形》2017,42(8):1287-1295

While the stabilizing function of large grains in step‐pool streams has long been recognized, the role they play in gravel‐bed streams is less clear. Most researchers have ignored the role of large grains in gravel‐bed streams, and have assumed that the median bed surface size controls the erodibility of alluvial boundaries. The experiments presented herein challenge this convention. Two experiments were conducted that demonstrate the significant morphodynamic implications of a slight change to the coarse tail of the bed material. The two distributions had the same range of particle sizes, and nearly identical bulk d₅₀ values (1.6 mm); however the d₉₀ of experiment GSD1 was slightly finer (3.7 mm) than that for experiment GSD2 (3.9 mm). Transport rates during GSD1 were nearly four times greater than during GSD2 (even though the dimensionless shear stress was slightly lower), and the channel developed a sinuous pattern with well‐developed riffles, pools and bars. During GSD2 the initial rectangular channel remained virtually unchanged for the duration of the experiment. The relative stability of GSD2 seems to be associated with a slightly larger proportion of stable (large) grains on the bed surface: at the beginning of GSD1, 3.5% of the bed was immobile, while almost twice as much of it (6.1%) was immobile at the beginning of GSD2. The results demonstrate that the largest grains (not the median size) exert first‐order control on channel stability. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

A decadal-scale numerical model for wandering,cobble-bedded rivers subject to disturbance     

Kathryn De Rego  J. Wesley Lauer  Brett Eaton  Marwan Hassan 《地球表面变化过程与地形》2020,45(4):912-927

Alluvial rivers are composed of self-formed channels which are sensitive to disturbances in their flow and sediment-supply regimes. Regime changes commonly occur over decadal and longer timescales and can be caused by anthropogenic alterations such as dam construction and removal. Advances in numerical modeling have increased our ability to explore geomorphic adjustments over long timescales; however, many models designed to be run for decades or longer assume that banks are immovable or that channel width is constant. Since river channels often respond to disturbance by adjusting their geometry, this is a significant shortcoming. To investigate the impact of long-term sediment supply alterations on channel geometry and stability, we have adapted MAST-1D, a reach-scale bed evolution model, to incorporate functions for bank erosion, vegetation encroachment, and local avulsions. The model is designed for medium-large, coarse multithreaded rivers and can be run over long (decades–centuries) timescales. Bank erosion is a function of the mobility and transport capacity for structurally-important grains which protect the bank toe. Vegetation growth is proportional to point bar width and occurs during conditions of low shear stress. Local avulsions occur when aggradation causes channel depth to drop below a threshold. We apply the model to the Elwha River in Washington, USA with the goal of investigating if and when the river recovers from dam emplacement and removal. The Elwha was dammed for nearly 100 years, and then two dams were removed, releasing a large pulse of sediment. We have modeled the set of reaches between the two dams. Our simulations suggest that channel response to dam emplacement occurs gradually over several decades but that the channel recovers to near pre-dam conditions within about a decade following the removal. The dams leave a lasting legacy on the floodplain, which does not completely recover, even after two centuries. © 2019 John Wiley & Sons, Ltd.  相似文献   

Symplectic integrators for long-term integrations in celestial mechanics     

Brett Gladman  Martin Duncan  Jeff Candy 《Celestial Mechanics and Dynamical Astronomy》1991,52(3):221-240

We discuss the use of symplectic integration algorithms in long-term integrations in the field of celestial mechanics. The methods' advantages and disadvantages (with respect to more common integration methods) are discussed. The numerical performance of the algorithms is evaluated using the 2-body and circular restricted 3-body problems. Symplectic integration methods have the advantages of linear phase error growth in the 2-body problem (unlike most other methods), good conservation of the integrals of the motion, good performance for moderately eccentric orbits, and ease of use. Its disadvantages include a relatively large number of force evaluations and an inability to continuously vary the step size.  相似文献   

ANALYSIS OF COUNT DATA USING POISSON REGRESSION*     

Andrew Lovett  Robin Flowerdew 《The Professional geographer》1989,41(2):190-198

In geographical research the data of interest are often in the form of counts. Standard regression analysis is inappropriate for such data, but if certain assumptions are met, a form of regression based on the Poisson distribution can be used. This paper illustrates the use of Poisson regression in the computer package GLIM with an example from historical geography. Apprentice migration to Edinburgh is regressed on a combination of categorical, count, and continuous explanatory variables.  相似文献   

Impacts of environmental degradation on rivers,with some examples from the Hawkesbury‐Nepean system     

Robin F. Warner 《The Australian geographer》1991,22(1):1-13

Environmental degradation is a widespread contemporary problem. It will be exacerbated by Greenhouse. The alteration of the land surface by humans is examined in terms of on-site impacts as well as off-site effects in other storages, notably rivers. Examples of bank erosion in the Hawkesbury-Nepean system are related to regime shifts, dams and dredging. Examples of environmental pollution by different forms of sewage disposal are given for Wollondilly Shire. It is suggested that much more relevant information is required to effect total catchment management.  相似文献   

Emotional geographies     

Robin Kearns 《New Zealand geographer》2007,63(2):156-157

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