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531.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2023,71(3):1397-1417
An evaluation of the hydromorphological condition of the Mahananda-Balason River system of the sub-Himalayan foothills, West Bengal, India was attempted using a multiparameter-based Hydromorphological Quality Index (HQI). After segmenting these rivers based on continuity, bed material and channel planform, a total of 18 indicators, divided into 3 subgroups Continuity (C), Planform (P), and Floodplain Morphology (FM), were quantified reach-wise and scaled upon the level of alteration (1 for highly altered and 5 for no alteration). The derived overall HQI (3.6) exhibited a moderate hydromorphological quality of the system, however, significant differences between the HQIs of confined and unconfined reaches were witnessed. Students ‘t-test and Multiple Correspondence Analysis both portrayed vast dissimilarities among the confined and unconfined reaches and the clustering was depending on their confinement. The deviations measured from the system’s mean and least altered conditions portrayed that the confined reaches with lesser human interventions were in comparatively more pristine hydromorphological conditions. Conversely, unconfined reaches showed moderate to very poor hydromorphological conditions chiefly due to intense human-induced alterations regarding urbanization, embanking and sediment extraction. Restorations on these aspects should initiate with immediate effect to avoid a shortage of riverine resources such as fluvial sediment, fish and groundwater. Overall, this methodology was found suitable for continuous monitoring of the river systems along with the precise identification of areas and aspects to be restored for upgrading the hydromorphological quality. More testing of this methodology would eventually help in validating the hydromorphological quality assessment protocol for Indian rivers. 相似文献
532.
为深入了解真实航空发动机燃烧室极端条件下点火性能,在自有CFD平台上对不同高空来流条件下典型航空发动机双旋流燃烧室点火过程进行了数值模拟。为保证模拟精度,对模型包括全部气膜冷却小孔在内的所有精细结构均进行了完全仿真,并完整再现了燃烧室内从燃油雾化到点火燃烧全过程。结果表明3种高空来流条件下单次点火均失败。点火过程显示高温燃气越过旋流杯中心向上回流区扩张是点火的关键时空区域,在此时补充点火可推动火焰顺利传播到整个主燃区。对8km和6km两种状态分别增加点火次数到3次和5次后最终点火成功,结果表明前者着火极限油气比约为0.057,后者为0.038~0.042。 相似文献
533.
534.
《Advances in Space Research (includes Cospar's Information Bulletin, Space Research Today)》2023,71(3):1486-1509
Sea-surface solar radiation (abbreviated as photosynthetically available radiation, PAR) in the visible wavelength (400–700 nm) is an essential parameter to estimate marine primary productivity and understanding phytoplankton dynamics, upper ocean physics and biogeochemical processes. Although many remote-sensing models were developed to estimate daily PAR (DPAR) from ocean colour data, these models often produce biases in the DPAR products under cloudy-sky and complex atmospheric conditions due to the lack of parameterization to deal with the cloud cover conditions and insufficient in-situ DPAR data. This study presents an Extended Sea-surface Solar Irradiance Model (ESSIM) for estimating DPAR over the global ocean. The ESSIM uses the direct and diffuse components from the Simple sea-surface Solar Irradiance Model (SSIM) along with a new parameter to handle cloudy conditions. The ESSIM produced DPAR products with greater accuracy under both clear and cloudy conditions. Its performance was tested on the time-series MODIS-Aqua images and compared with the concurrent in-situ data and the results from two global models. Results showed that the DPAR values produced by ESSIM agree with in-situ data better than the global models for all-sky conditions (with a mean relative error of 11.267 %; a root mean square error of 5.563 Em?2day?1; and a mean net bias of 2.917 Em?2day?1). The ESSIM performed slightly better than the SSIM for clear conditions and the Frouin's Operational Algorithm (FOA) for all-sky conditions. As the new parameterization accounts for cloudy conditions, the ESSIM produced more accurate results for cloud cover conditions across latitudes (up to 60°). The time-series Level-3 binned MODIS-Aqua data (global gridded) also demonstrated that the ESSIM improved the accuracy of DPAR products and produced spatially and temporally consistent DPAR products over the global ocean regardless of the seasons and sky conditions. 相似文献
535.