排序方式: 共有13条查询结果,搜索用时 15 毫秒
11.
N = 406), highlight some important issues concerning the design and management of wildland recreation environments that are
primarily used for mountain biking. For example, bikers were found to significantly prefer water bars above all other tested
soil erosion management techniques; trail erosion factors, including the presence of rocks, roots, and gullies, all added
to biking experiences on average; trail design factors, such as the presence of turns, bumps, jumps, and obstacles, all added
to biking experiences in general. These findings were used to address questions that resource managers should consider when
striving to effectively manage wildland recreation areas primarily used for mountain biking. 相似文献
12.
C.?N.?WhittakerEmail authorView authors OrcID profile R.?I.?Nokes H.-Y.?Lo P.?L.-F.?Liu M.?J.?Davidson 《Environmental Fluid Mechanics》2017,17(5):929-958
This paper presents a study of the waves generated by a solid block landslide moving along a horizontal boundary. The landslide was controlled using a mechanical system in a series of physical experiments, and laser-induced fluorescence measurements resolved both spatial and temporal variations in the free surface elevation. During its constant-velocity motion, the landslide transferred energy into ‘trapped’ offshore-propagating waves within a narrow frequency band. The wave trapping is demonstrated by investigating the wave dispersion characteristics using a two-dimensional Fourier Transform. The first of the trailing waves broke at Froude numbers greater than or equal to 0.625. The parametric dependence of the largest-amplitude waves and the potential energy within the wave field are discussed. The experimental results were compared to the predictions of an incompressible Navier–Stokes solver with and without turbulence models. The numerical model under-predicted the measured wave amplitudes, although it accurately predicted the measured wave phasing. The turbulent model more accurately predicted the shapes of the trailing waves. Both experimental and numerical results confirmed that investigations into wave generation by submerged objects moving at constant velocity should also consider the initial acceleration of the object, as this affects the overall evolution of the wave field. The applicability of the horizontal-boundary results to more realistic field scenarios is discussed. 相似文献
13.
I.D. Pulford R.L. Allan G.T. Cook A.B. MacKenzie 《Environmental geochemistry and health》1998,20(2):95-101
This paper describes a study of the geochemical associations of Sellafield waste radionuclides in saltmarsh sediments from south-west s]Scotland. The contaminant radionuclides are transported to this environment in association with particulate material and 137Cs was found to be predominantly (80-98%) non-extractable. In the case of 239+240Pu there was a redistribution from the oxalate extractable oxide fraction to the pyrophosphate extractable organic fraction as a consequence of on-shore transfer of contaminated sediment. The relatively aggressive nature of the chemical extractants required to remove the radionuclides from the sediments suggests that they were in a form which was unlikely to result in their being released into the aquatic environment or taken up by plants. Plutonium had a greater potential mobility or bioavailability than Cs. Values of KD for the desorption of 137Cs from the sediment by freshwater, groundwater and seawater were all approximately 105 L kg-1, confirming its immobility in this environment. The desorption KD values for stable 133Cs were all approximately 106 L kg-1, so the stable Cs did not have a significant influence on the radiocaesium in this sediment. 相似文献