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Natural vegetation on erodible land surfaces, such as the loose sandy soils found in the southwestern United States and in Soviet Central Asia, absorbs part of the wind momentum flux (stress) and thus protects the erodible soil to a degree that depends on the geometry of plant distribution and profile. The sheltering effect of natural plants may be expressed as the ratio, R, of threshold friction velocity for the bare soil (determined in the laboratory or in specially prepared areas of bare soil in the field) to that for the naturally vegetated surface. We used new automated instrumentation to detect erosion thresholds in locations where erosion events are widely separated in time. Measured values of R were low for our most vegetated sites and nearer unity for the sparsely vegetated site. 相似文献
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An experiment that investigated the establishment of seven grass and legume seed mixes on opencast coal mining spoil in South Wales is described. After three years, mixtures containing Poa pratensis and Festuca rubra var. rubra were the most successful in covering the spoil; the ‘Johnson JR33’ seed mix proved the best of those commercially available that was tested. Tree growth was not detrimentally affected by the establishment of a grass ground cover. Erosion was not an important process at the experimental site, though slumping occurred locally from plough ridge to plough furrow. 相似文献
44.
自然保护地原则上按核心区和一般管控区实行分区管控.各类保护地巡护道路设计体系目前没有相关设计规范.文章对保护地内巡护道路的等级、平纵设计指标、横断面指标的确定需考虑的因素进行分析,提出了相应的设计指标和参数,以期对后续巡护道路设计提供参考. 相似文献
45.
Nanelle R. Barash Erin Lashnits Zachary T. Kern Mary Katherine Tolbert Katharine F. Lunn 《Journal of veterinary internal medicine / American College of Veterinary Internal Medicine》2022,36(2):500
BackgroundBone foreign bodies are commonly encountered in small animal practice. Esophageal bone foreign bodies (E‐bFBs) warrant removal, whereas gastric bone foreign bodies might not.ObjectivesDescribe management and outcomes for dogs with esophageal or gastric bone foreign bodies.AnimalsOne hundred twenty‐nine dogs with esophageal (n = 45) or gastric (n = 84) bone foreign bodies.MethodsRetrospective review of medical records.ResultsDogs with E‐bFBs were younger than dogs with gastric bone foreign bodies (median age esophageal, 4 years [IQR 2‐8]; median age gastric, 6 years [IQR 3‐10]; P = .03), and had a higher bone cross‐sectional area relative to body weight (median esophageal, 98.21 mm2/kg [IQR 48.25‐142.6]; median gastric, 28.6 mm2/kg [IQR 17.25‐64.28]; P < .001). Forty‐two of 45 esophageal foreign bodies were resolved non‐surgically and 3 by esophagotomy. Esophageal erosions were more likely with distal entrapment (OR 12.88, [95% CI 31.95‐129.29], P = .01) and longer duration (OR 18.82 [95% CI 2.22‐273.97], P = .01). Sixty‐two of 84 bone gastric foreign bodies were left in situ. Endoscopic removal was successful in 20 of 22 (91%; 95% CI 70‐99) attempts.Conclusions and Clinical ImportanceWhile all E‐bFBs were dislodged either by advancement into the stomach, endoscopic removal, or esophagotomy, the majority of gastric bone foreign bodies were left in situ for dissolution, with no reported complications. Gastric advancement of E‐bFBs should be considered when oral removal is not feasible, and dissolution can be considered even with large bones. 相似文献
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基于磁流变半主动悬架的振动压路机动力学与控制 总被引:1,自引:0,他引:1
在对振动压路机和磁流变减振器研究的基础上,应用磁流变减振器对振动压路机进行半主动控制,并对其进行动力学仿真研究.仿真结果表明,采用磁流变减振器进行半主动控制的振动压路机,其减振性能明显改善. 相似文献
48.
孙祖明 《农业装备与车辆工程》2009,(8):15-17
讨论了汽车转向路感的形成及定义,对电动助力转向系统的路感特性进行了分析,研究了电动助力转向系统路感的影响因素,提出了改善电动助力转向系统路感的方法,并对电动助力转向系统进行仿真分析,结果表明所提出的方法是正确有效的. 相似文献
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中亚包括哈萨克斯坦、吉尔吉斯斯坦、塔吉克斯坦、土库曼斯坦、乌兹别克斯坦五国,是"丝绸之路经济带"的核心区域,内陆渔业资源禀赋雄厚,世界第一大湖里海以及第四大湖咸海均分布在域内。在前苏联时期中亚各国捕捞渔业和水产养殖发展态势良好,随着东欧巨变及前苏联政局陷入动荡直至解体,渔业生产急剧萎缩,至今虽有复苏但尚未能恢复到苏联时期的发展水平。本文主要基于我们前期研究基础以及FAO和世界银行等统计数据,提出对苏联解体后中亚各国渔业崩溃的原因解读,并探讨在"一带一路"框架下,中国和中亚各国可行的渔业合作方式以及重振中亚渔业的策略方法。 相似文献