排序方式： 共有7条查询结果，搜索用时 15 毫秒
1
1.
Headward and downward erosion near glacier sources, at rates exceeding fluvial erosion, is important in recent discussions of orogen development and the limits to relief. This relates to a long history of debate on how the form of glacial cirques develops, which can be advanced by relating shape to size in large data sets. For 260 cirques in Wales, this confirms different rates of enlargement in the three dimensions: faster in length than in width, and slower in vertical dimension whether expressed as overall height range, axial height range or wall height. Maximum gradient, plan closure and number of cols increase with overall size. This allometric development applies over different cirque types, regions and rock types. Headwall retreat, often by collapse following glacial erosion at the base, is faster than downward erosion. Welsh cirques form a scale-specific population and, as in other regions, size variables follow Gaussian distributions on a logarithmic scale. As in England, width commonly exceeds length. Vertical dimensions correlate with length more than with width. Cirque form varies with geology, but also with relief as both vary between mountain groups. The main contrast is between larger, better-developed cirques and higher relief on volcanic rocks in the north-west, and smaller, less-developed cirques and lower relief on sedimentary rocks in the south. 相似文献
2.
Abelisauroid dinosaurs normally reached an average body length (BL) of 5–9 m, but there are controversies due to the incomplete or fragmentary nature of most specimens. For Ekrixinatosaurus, for example, BL was estimated as 10–11 m or 7–8 m; for Pycnonemosaurus it was proposed 7–8 m, however its preserved bones are larger than any other described abelisauroid. The lack of a consistent methodology complicates comparisons of estimated BL, so we reevaluated the estimative for the seven most complete specimens of abelisauroids and compared the values against 40 measurements from the skull, vertebrae and appendicular elements using bivariate equations. It allowed estimating the BL of other 30, less complete, specimens of abelisauroids and to evaluate the allometric scaling of the skeletal parts. Strong correlations (R2 > 0.96) were obtained for all vertebrae and hindlimb measurements, as well as skull height, and length of skull roof, lacrimal–squamosal, scapulocoracoid and humerus; other skull and forelimb measurements present weak correlation due to extreme morphological transformations observed in Abelisauridae and were not adequate for BL estimation. Abelisauroids gradually increased in size during evolution: the mean BL was 3.3 ± 2.5 m for basal abelisauroids and Noasauridae, 5.4 ± 1.8 m for basal Brachyrostra and Majungasauridae, and 7.1 ± 2.1 m for Furileusaura. Despite this variation, diversity of BL on each geographic region and stratigraphic epoch was relatively constant (BL usually varied from 4 to 8 m). The smallest noasaurid and abelisaurid are, respectively, Velocisaurus (1.5 ± 0.1 m) and Genusaurus (3.6 ± 0.0 m). The largest abelisaurids is Pycnonemosaurus nevesi (8.9 ± 0.3 m) followed by Carnotaurus (7.8 ± 0.3 m), Abelisaurus (7.4 ± 0.7 m) and Ekrixinatosaurus (7.4 ± 0.8 m). Skull measurement scale negatively at a similar rate but the height scales almost isometrically and the skull roof length scales more negatively; this probably caused a bending on the skull that may explain the upward orientation of the snout in large taxa. 相似文献
3.
Sensitivity of the backscatter intensity of ALOS/PALSAR to the above-ground biomass and other biophysical parameters of boreal forest in Alaska 总被引：1，自引：1，他引：0
We investigated the potential of ALOS/PALSAR for estimating the above-ground biomass (AGB) and other biophysical parameters (tree height, diameter at breast height (DBH), and tree stand density) in the boreal forest of Alaska. In July 2007, forest surveys were conducted along a south–north transect (150°W) to profile the ecotone from boreal forest to tundra in Alaska. In situ parameters were measured in 29 forests by a combination of the Bitterlich angle-count sampling method and the sampled-tree measuring method. These in situ values were compared with the backscatter intensity of ALOS/PALSAR. A strong positive logarithmic correlation was found between the backscatter intensity and the forest AGB, with the correlation being stronger in the HV than in the HH polarization mode. No obvious saturation was found in the sensitivity of the HV mode backscatter intensity to the forest AGB up to 120.7 Mg ha?1. Similarly, a robust sensitivity was found in the HV backscatter intensity to both tree height and DBH, but weak sensitivity was observed for tree density. The regression curve of HV backscatter intensity to the forest AGB appeared to be intensified by the uneven forest floor, particularly for forests with small AGB. The geographical distribution of the forest AGB was mapped, demonstrating a generally south-rich and north-poor forest AGB gradient. 相似文献
4.
5.
6.
Jeffrey G. Baguley Paul A. Montagna Larry J. Hyde Gilbert T. Rowe 《Deep Sea Research Part II: Topical Studies in Oceanography》2008,55(24-26):2607
Metazoan meiofauna are ubiquitous in marine soft sediments and play a pivotal role in diagenesis of particulate organic matter. However, the relative importance of meiofauna to the function of deep-sea benthic boundary layer communities has not been resolved. Here, meiofauna biomass, respiration, and grazing on aerobic heterotrophic bacteria were estimated and compared to standing stocks and fluxes of other benthic components (e.g., bacteria and macrofauna). Biomass and respiration declined with depth. Highest biomass and respiration occurred in the proximity of the Mississippi River on the upper continental slope of the central Gulf of Mexico. Meiofauna required 7% of their biomass per day to meet their metabolic energy budget, compared to approximately 24% day−1 in shallow water. Respiration accounted for 8–22% of whole sediment community respiration (SCOC), reflecting the importance of meiofauna in diagenesis, deep-sea carbon budgets, and global biogeochemical cycles. 相似文献
7.
采用实验生态学方法,进行了鮸鱼仔稚鱼发育生长方式及其生态学意义研究。结果表明,鮸鱼的形态学变化和器官分化主要发生在仔鱼期。仔鱼期头部和尾部快于躯干部的生长。仔鱼头部(拐点:9.80mm体长)、眼径(8.87mm)和口径(23.40mm)的正异速生长为仔鱼的呼吸和摄食提供了有利条件;尾长(16.40mm)正异速生长为减少仔鱼运动能耗和成功逃避捕食者准备了条件;虽然躯干部生长比较缓慢,但是体高呈现正异速生长(11.20mm),这可能与仔鱼消化系统为满足其迅速发育的营养需要而快速生长及鳔的发育有关。结果表明,鮸鱼在早期发育阶段优先发育对生长生存起关键作用的器官,即运动、视觉和摄食器官。但在稚鱼阶段,其主要长度量度相对于体长指标均呈现负异速成长。 相似文献
1