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21.
E. Farmer S.D. Jones R.E. Deakin 《International journal of geographical information science》2013,27(9):1545-1558
This paper reviews the utility of polygon centroid algorithms for natural resource management applications. Following a review of ‘standard’ centroid derivation algorithms, and their limitations, alternative approaches are proposed. Building upon current polygon-reduction algorithms an iterative edge-erosion model is presented. Resilient centroids derived via this model are shown to: (1) maximise the distance to all internal and external edges; (2) be located within the polygon boundary; and (3) be insensitive to patch vertex outliers. The resilient centroid is demonstrated to have utility in a range of natural resource management applications including the matching of disparate data sources. Exemplar studies conclude that resilient centroids support an appropriate allocation of vegetation condition point samples both within and between native vegetation patches. Further, the utilisation of resilient centroids enables the (1) sub-division of vegetation patches into homogenous regions (core areas) and (2) interrogation of the relationship between vegetation condition and core area proximity. 相似文献
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通过引入带有二阶正则算子的正则化项,建立了一种双参数混合正则化方法.为确定最佳正则化参数,这里主要应用L-曲线法、偏差原理和广义交叉校验准则的优化组合来确定.首先对理论模型进行了数值模拟,通过与截断奇异值分解法、共轭梯度法及标准Tikhonov正则化法的结果比较,表明该方法不仅精度高,而且对于数据的随机扰动具有稳定性.... 相似文献
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Results of the Viking mission are reviewed and possibilities for ancient life on Mars are explored. Goals of the Global Surveyor Program are outlined. 相似文献
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G. Lang Farmer David E. Broxton Richard G. Warren William Pickthorn 《Contributions to Mineralogy and Petrology》1991,109(1):53-68
Nd, Sr and O isotopic data were obtained from silicic ash-flow tuffs and lavas at the Tertiary age (16–9 Ma) Timber (Mountain/Oasis Valley volcanic center (TMOV) in southern Nevada, to assess models for the origin and evolution of the large-volume silicic magma bodies generated in this region. The large-volume (>900 km3), chemically-zoned, Topopah Spring (TS) and Tiva Canyon (TC) members of the Paintbrush Tuff, and the Rainier Mesa (RM) and Ammonia Tanks (AT) members of the younger Timber Mountain Tuff all have internal Nd and Sr isotopic zonations. In each tuff, high-silica rhyolites have lower initial
Nd values (1
Nd unit), higher87Sr/86Sr, and lower Nd and Sr contents, than cocrupted trachytes. The TS, TC, and RM members have similar
Nd values for high-silica rhyolites (-11.7 to -11.2) and trachytes (-10.5 to -10.7), but the younger AT member has a higher
Nd for both compositional types (-10.3 and -9.4). Oxygen isotope data confirm that the TC and AT members were derived from low
Nd magmas. The internal Sr and Nd isotopic variations in each tuff are interpreted to be the result of the incorporation of 20–40% (by mass) wall-rock into magmas that were injected into the upper crust. The low
Nd magmas most likely formed via the incorporation of low
18O, hydrothermally-altered, wall-rock. Small-volume rhyolite lavas and ash-flow tuffs have similar isotopic characteristics to the large-volume ash-flow tuffs, but lavas erupted from extracaldera vents may have interacted with higher
18O crustal rocks peripheral to the main magma chamber(s). Andesitic lavas from the 13–14 Ma Wahmonie/Salyer volcanic center southeast of the TMOV have low
Nd (-13.2 to -13.8) and are considered on the basis of textural evidence to be mixtures of basaltic composition magmas and large proportions (70–80%) of anatectic crustal melts. A similar process may have occurred early in the magmatic history of the TMOV. The large-volume rhyolites may represent a mature stage of magmatism after repeated injection of basaltic magmas, crustal melting, and volcanism cleared sufficient space in the upper crust for large magma bodies to accumulate and differentiate. The TMOV rhyolites and 0–10 Ma old basalts that erupted in southern Nevada all have similar Nd and Sr isotopic compositions, which suggests that silicic and mafic magmatism at the TMOV were genetically related. The distinctive isotopic compositions of the AT member may reflect temporal changes in the isotopic compositions of basaltic magmas entering the upper crust, possibly as a result of increasing basification of a lower crustal magma source by repeated injection of mantle-derived mafic magmas. 相似文献
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Alison J. Farmer 《Icarus》2009,202(1):280-286
The detection of outgassing water vapor from Enceladus is one of the great breakthroughs of the Cassini mission. The fate of this water once ionized has been widely studied; here we investigate the effects of purely neutral-neutral interactions within the Enceladus torus. We find that, thanks in part to the polar nature of the water molecule, a cold (∼180 K) neutral torus would undergo rapid viscous heating and spread to the extent of the observed hydroxyl cloud, before plasma effects become important. We investigate the physics behind the spreading of the torus, paying particular attention to the competition between heating and rotational line cooling. A steady-state torus model is constructed, and it is demonstrated that the torus will be observable in the millimeter band with the upcoming Herschel satellite. The relative strength of rotational lines could be used to distinguish between physical models for the neutral cloud. 相似文献
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