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971.
972.
蜜瓜运输共振频率的测定及其对储藏品质的影响 总被引:1,自引:1,他引:1
为避免蜜瓜运输过程中因发生共振现象导致储藏期间品质的下降,试验通过数据采集与信号分析软件中的加窗函数结合传递函数分析测出蜜瓜的共振频率,同时测定了共振频率与硬度的变化趋势以及共振频率和低频振动后储藏期间蜜瓜品质的变化。结果表明:通过加窗函数结合传递函数分析可以将有效信号从杂乱信号中提取,可稳定检测到蜜瓜的共振频率;不同硬度区间的蜜瓜可测得不同范围的共振频率,硬度较高的蜜瓜其共振频率也相对较大,共振频率与硬度呈极显著正相关,决定系数R2=0.9132;不论共振频率还是低频率使振动后的果品硬度、可溶性固形物均呈下降趋势,损伤体积率表现为显著上升,不论低频还是共振频率,对振后可溶性固形物含量的影响无明显区别,共振频率下引起的损伤率增大明显高于低频率的情况,因此共振是引起果品运输损伤的主要原因;振动后储藏期间可溶性固形物含量和损伤率的变化与储藏时间均存在很高的线性拟合关系,拟合决定系数大于0.95,实际运输中可通过设计采用缓冲包装和适当的运输方式避开共振频率、达到最大程度减小果品品质衰变和预测并延长货架期的目的。采用加窗函数结合传递函数的测定和分析方法也为同类型和其他果品寻求共振频率、在运输过程中避开共振频率点而达到减损目的提供了借鉴和参考,为相关运输保护措施的建立奠定理论基础。 相似文献
973.
地下滴灌土壤水运动和溶质运移数学模型的应用 总被引:11,自引:7,他引:11
利用建立的地埋点源土壤水运动和溶质运移数学模型描述地下滴灌条件下土壤水、肥运动的分布规律,将土壤质地结构、滴头出流量、滴头埋深和单次灌水历时等因素对土壤水分布的影响进行模拟分析。结果表明,在确定的土壤质地条件下,滴头出流量和埋深是影响地下滴灌系统性能的两个最重要的灌水设计参数,应尽量采用增加滴头数量而不是选用大流量滴头的方法来满足作物的需水要求。此外,合理的灌溉施肥时机应依据当地的土壤质地条件予以确定 相似文献
974.
975.
黄土高原坡耕地泥沙输移特征分析 总被引:1,自引:0,他引:1
在野外利用人工模拟降雨试验,分析了20,40,60m坡长下的输沙率、含沙量及累积产沙量—径流量的变化特征。结果显示,当雨强小于2.0mm/min时,最大输沙率出现在40m坡长;而当雨强大于2.0mm/min时,最大输沙率出现在60m坡长。在试验雨强范围内,最大含沙量总是出现在20m坡长。累积产沙量—径流量随时间变化趋于平稳。试验结果表明,为遏制黄土高原坡耕地水土流失,实践中应采取垄作等措施增加坡面糙度和改变坡面形态,防止在20m坡长形成高含沙水流和后续坡长的输沙率。 相似文献
976.
We investigated the effect of Z-ligustilide (LIG) on scopolamine-induced memory impairment in ICR mice. LIG (2.5–40 mg/kg) or tacrine (10 mg/kg) was orally administrated for 26 days. Behavior was examined in the Morris water maze and Y-maze after scopolamine administration (2 mg/kg, i.p.). The central acetylcholinesterase (AChE) and choline acetyltransferase (ChAT) activities were assessed spectrophotometrically. LIG significantly improved spatial long-term memory and short-term memory impairment, inhibited AChE activity and increased ChAT activity. Moreover, LIG and tacrine showed the comparable efficacy in both neurobehavioral and cholinergic evaluation. These data suggest that LIG may alleviate memory deficits probably via enhancing cholinergic function. 相似文献
977.
978.
Stewart A.W. Diemont Jessica L. BohnDonald D. Rayome Sarah J. KelsenKaity Cheng 《Forest Ecology and Management》2011,261(10):1696-1705
Numerous communities associated with at least five distinct ethnic Mayan groups in southern Mexico and Central America continue to rely upon forested areas as integral components of their agricultural systems. They carefully manage these areas so that forests provide food, raw materials, and animals. Management practices include removing and planting of woody and herbaceous species, apiculture, and seed harvest. Mayan agroforestry systems in geographically and ecologically distinct areas of Mesoamerica were evaluated to better understand traditional agroforestry system components and how indigenous Mayan agroforestry could be a part of regional forest conservation and restoration. Systems were within Mexican land grant areas (ejidos) or on contested land. Although these systems rely upon different woody species and management techniques, common among them are: (1) the use of multi-stage and successional pathways with forest as a part of the larger system, (2) species that are believed by traditional ecological knowledge (TEK) to accelerate forest regeneration - more than 30 tree species are recognized and managed as potential facilitators of forest regeneration and (3) direct human consumption of forest products at all stages of regeneration. 相似文献
979.
The effects of 4 years of simulated nitrogen (N) and sulfur (S) depositions on gross N transformations in a boreal forest soil in the Athabasca oil sands region (AOSR) in Alberta, Canada, were investigated using the 15N pool dilution method. Gross NH4+ transformation rates in the organic layer tended to decline (P < 0.10, marginal statistical significance, same below) in the order of control (CK, i.e., no N or S addition), +N (30 kg N ha−1 yr−1), +S (30 kg S ha−1 yr−1), and +NS treatments, with an opposite trend in the mineral soil. Gross NH4+ immobilization rates were generally higher than gross N mineralization rates across the treatments, suggesting that the studied soil still had potential for microbial immobilization of NH4+, even after 4 years of elevated levels of simulated N and S depositions. For both soil layers, N addition tended to increase (P < 0.10) the gross nitrification and NO3− immobilization rates. In contrast, S addition reduced (P < 0.001) and increased (P < 0.001) gross nitrification as well as tended (P < 0.10) to reduce and increase gross NO3− immobilization rates in the organic and mineral soils, respectively. Gross nitrification and gross NO3− immobilization rates were tightly coupled in both soil layers. The combination of rapid NH4+ cycling, negligible net nitrification rates and the small NO3− pool size after 4 years of elevated N and S depositions observed here suggest that the risk of NO3− leaching would be low in the studied boreal forest soil, consistent with N leaching measurements in other concurrent studies at the site that are reported elsewhere. 相似文献
980.