Mineralogy and origin of rhizoliths on the margins of saline,alkaline Lake Bogoria,Kenya Rift Valley     

Richard Alastair Owen  Richard Bernhart Owen  Robin W. Renaut  Jennifer J. Scott  Brian Jones  Gail M. Ashley 《Sedimentary Geology》2008,203(1-2):143-163

A wide range of rhizoliths occurs around the margins of Lake Bogoria, Kenya. These include root casts, moulds, tubules, rhizocretions, and permineralised root systems. These rhizoliths are variably composed of opaline silica, calcite, zeolites (mainly analcime), fluorite, and possibly fluorapatite, either alone or in combinations. Some rhizoliths are infilled moulds with detrital silicate grains. Most rhizoliths are in situ, showing both vertical and horizontal orientations. Reworked rhizoliths have been concentrated locally to form dense rhizolites.Hot-spring fluids, concentrated by evapotranspiration and capillary evaporation, have provided most of the silica for the permineralisation of the plant tissues. Precipitation involved the growth of silica nanospheres and microspheres that coalesced into homogeneous masses. Calcite rhizoliths formed following evaporative concentration, evapotranspiration, and (or) CO₂ degassing of Ca-bearing runoff water that infiltrated the sediment, or by mixing of runoff with saline, alkaline groundwater. Fluorite precipitated in areas where mixing of hot-spring and meteoric waters occurred, or possibly where hot-spring fluids came into contact with pre-existing calcite. Zeolitic rhizoliths formed during a prolonged period of aridity, when capillary rise and evaporative pumping brought saline, alkaline waters into contact with detrital silicate minerals around roots.  相似文献   

A simple and inexpensive chromium-reducible sulfur method for acid-sulfate soils   总被引：2，自引：0，他引：2  

Edward D. Burton  Leigh A. SullivanRichard T. Bush  Scott G. JohnstonAnnabelle F. Keene 《Applied Geochemistry》2008

A new chromium-reducible sulfur (CRS) method suitable for the quantification of reduced inorganic S (RIS) in acid-sulfate soils is presented. The new method utilises the reduction of RIS by an acidic Cr(II) solution within a sealed reaction chamber and diffusion of the produced H₂S_(g) into an alkaline Zn solution. It offers rapid sample processing times, without the need for large volumes of high-purity N_2(g) or for specialized, expensive glassware. Examination of pyrite-talc mixtures containing up to 11.8% pyrite, revealed that the method achieves 95–98% recovery of RIS. A comparison between CRS measured by the new diffusion-based method and that measured by a standard purge-and-trap method for 25 pyritic soil samples shows a very strong (r² = 0.996) linear relationship with a slope of 0.995. The ability of the new diffusion-based CRS method to achieve accurate and precise quantification of RIS in acid-sulfate soils is demonstrated.  相似文献   

Suburban gentrification? Examining the geographies of New Urbanism in Atlanta’s inner suburbs     

Scott Markley 《Urban geography》2018,39(4):606-630

Since the 1990s, Atlanta’s inner suburbs have experienced rising rates of poverty alongside growing racial/ethnic diversity. ? Meanwhile, on the built landscape, high-end (re)development projects incorporating New Urbanist features such as pedestrian accessibility, compact densities, and mixed land uses have become increasingly common. Although practitioners suggest that these developments promote social inclusivity and enhanced “livability,” individual cases suggest that some New Urbanist projects may be gentrifying underserved communities of color. This paper tests the extent of this concern by examining Atlanta's inner-suburban geographies of New Urbanism using a logit model. Results indicate that neighborhoods with older housing stock, more renters, lower incomes, lower rents relative to home prices, and higher Latino populations in close proximity to inner-suburban downtowns are most likely to be targeted for New Urbanist (re)development. Thus, despite the optimistic language, New Urbanism in this region appears to be serving as the inner-suburban face of gentrification.?  相似文献   

On the declining relationship between tree growth and climate in the Midwest United States: the fading drought signal     

Justin T. Maxwell  Grant L. Harley  Scott M. Robeson 《Climatic change》2016,138(1-2):127-142

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Antarctic sea ice increase consistent with intrinsic variability of the Amundsen Sea Low     

John Turner  J. Scott Hosking  Gareth J. Marshall  Tony Phillips  Thomas J. Bracegirdle 《Climate Dynamics》2016,46(7-8):2391-2402

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Experimental subsolidus phase relations in the system CaCO3–CaMg(CO3)2 up to 6.5 GPa and implications for subducted marbles     

Jörg Hermann  Ulrike Troitzsch  Dean Scott 《Contributions to Mineralogy and Petrology》2016,171(10):84

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Biot consolidation analysis with automatic time stepping and error control Part 1: theory and implementation     

Scott W. Sloan  Andrew J. Abbo 《国际地质力学数值与分析法杂志》1999,23(6):467-492

A new finite element algorithm for solving elastic and elastoplastic coupled consolidation problems is described. The procedure treats the governing consolidation relations as a system of first-order differential equations and is based on the backward Euler and Thomas and Gladwell schemes with automatic subincrementation of a prescribed series of time increments. The prescribed time increments, which are called coarse time steps, serve to start the procedure and are chosen by the user. The automatic consolidation algorithm attempts to select the time subincrements such that, for a given mesh, the time-stepping (or temporal discretisation) error in the displacements lies close to a specified tolerance. Unlike existing solution techniques, the new algorithm computes not only the displacements and pore pressures, but also their derivatives with respect to time. These extra variables permit a family of unconditionally stable integration algorithms to be constructed which automatically provide an estimate of the local truncation error for each time step. This error estimate is inexpensive to compute and may be used to develop a simple and efficient automatic time stepping mechanism. For the elastic case, the displacements and pore pressures at the end of each subincrement may be solved directly without the need for iteration. For elastoplastic behaviour, however, the governing relationships are non-linear and a system of non-linear equations must be solved to compute the updates. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

The legal context of intellectual property rights and marine biotechnology     

Geoffrey R. Scott 《Ocean & Coastal Management》1998,38(3):229-277

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Shakedown analysis of ballasted track structure using three-dimensional finite element techniques     

Wang  Kangyu  Zhuang  Yan  Kouretzis  George  Sloan  Scott William 《Acta Geotechnica》2020,15(5):1231-1241

Acta Geotechnica - Shakedown analysis is an attractive method for determining the capacity of geostructures to sustain repeated loads involving a large number of cycles, e.g. rolling and sliding...  相似文献   

Near-infrared adaptive optics imaging of nuclear spiral structure in the Seyfert galaxy NGC 3227     

Scott C. Chapman  †‡  Simon L. Morris ‡  Gordon A. H. Walker 《Monthly notices of the Royal Astronomical Society》2000,319(3):666-676

We present high spatial resolution, near-infrared images in J , H and K of the nucleus of NGC 3227, obtained with the Adaptive Optics Bonnette on the Canada–France–Hawaii Telescope. The ∼0.15 arcsec (17 pc) resolution allows structures to be probed in the core region. Dust obscuration becomes significantly less pronounced at longer wavelengths, revealing the true geometry of the core region. We are able to identify two main features in our maps: (i) a spiralling association of knots with a counterpart in a Hubble Space Telescope F606W image; and (ii) a smaller-scale annulus, orthogonal to the spiral of knots. These features may provide a means to transport material inwards to fuel the active nucleus.  相似文献