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排序方式： 共有79条查询结果，搜索用时 15 毫秒
1.
全数字化PDH复接系统的设计 总被引：1，自引：0，他引：1
为了便于ＰＤＨ复接系统的集成和设备的小型化，以及改善系统的性能，本文介绍了复接系统的几个主要部分（定时提取，码速调整，收端支路时钟恢复等）的数字化实现方法，还介绍了采用这些数字化方法的多功能复接专用集成电路－ＭＸＺＷ６８２３１。 相似文献
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朝鲜问题一直是甲午战争前夕东北亚地区国际斗争的焦点之一,在中日双方就中朝宗藩关系体制的存废争执不休的同时,英国和俄国也为争夺对远东的控制而进行了明争暗斗。中国清廷在英俄两国之间展开外交斡旋,中国清廷本着维护中国对朝鲜的宗主权为出发点利用英俄两国的矛盾,使两国的争端得以缓和,最终以俄国允诺不侵占朝鲜领土和英国撤出巨文岛为结束。巨文岛事件的解决是晚清中国政府利用外交斡旋手段处理大国矛盾的比较成功的特例,但也使得清廷滋长了对未来朝鲜问题再度尖锐化的麻痹,盲目自信的态度也为日后甲午战争的外交失败埋下了伏笔。 相似文献
3.
A preliminary modeling analysis of water quality in Lake Okeechobee, Florida: Calibration results 总被引：9，自引：0，他引：9
To gain understanding of nutrient and phytoplankton dynamics in Lake Okeechobee, Florida, we developed and applied a deterministic, mass balance, water quality model at the whole-lake spatial scale. The model was calibrated to a comprehensive set of field data for 1985–1986, and then used to simulate the period 1973–1992. The model represented the mean behavior of in-lake total phosphorus, dissolved available phosphorus, total nitrogen and chlorophyll a concentrations reasonably well during the calibration period. The model did not represent dissolved available nitrogen concentrations very well, nor did it capture much of the observed temporal variability during the calibration period. The model results identified important information needs to improve our understanding of the nitrogen cycle including, sediment-water nitrogen fluxes, denitrification and nitrogen fixation. Results from the 1973–1992 simulation indicated that model assumptions and/or calibration parameters were not uniformly applicable over this period. Total phosphorus concentration results from this model were compared with results from two site-specific, empirical loading models for the lake. None of these models represented annual average concentrations uniformly well over the entire 20-year period, and none captured much of the observed inter-annual variability. External total phosphorus loadings and lake hydrology are not sufficient to fully describe total phosphorus dynamics in Lake Okeechobee. Other important factors are diffusive sediment-water fluxes, wind-induced sediment resuspension, and the spatial heterogeneity in the lake. 相似文献
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介绍了北京电信网155Mbit/s信号时隙编号统一问题产生的原因，探讨了北京电信网155Mbit/s信号时隙编号统一原则，并论述了北京电信传输网、交换网155Mbit/s信号时隙编号统一策略。 相似文献
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Rachel E. Bowes Eva Bergman Serena Donadi Larry Greenberg Leonard Sandin Lovisa Lind 《河流研究与利用》2023,39(6):1025-1036
Rivers networks represent hierarchical dendritic habitats within terrestrial landscapes and differences in connectivity and land use influence dispersal, and consequently biodiversity patterns. We, therefore, measured variation in water chemistry and fish abundance and related these to a number of landscape characteristics (e.g., wetland, urban, wooded, and agricultural) in the River Klarälven and its 30 permanently flowing tributaries. We hypothesized that these environmental attributes would differ between tributary and main stem habitat and that these differences would be driven by landscape attributes including land use. We found considerable intertributary variation in temperature and nutrient levels, and between the tributaries and the main stem. Generally, water temperature was lower in the tributaries, whereas nutrient levels were higher in the tributaries. The lower water temperature has implications for coldwater fishes, and we found two fishes, burbot and lamprey, associated with coldwater tributaries. We also found an inverse relationship between water quality and anthropogenic land use. Protecting tributaries with low anthropogenic impact will likely become increasingly important with ongoing global warming as they can function as thermal refugia for coldwater fishes. Hence, this study underscores the need to evaluate water courses at regional scales to identify spatial refuges and ensure connectivity. 相似文献
7.
Flushing time is an integrative parameter that can represent water exchange capacity and sensitivity to pollution threats. As bays formed where tributaries enter the Three Gorges Reservoir of China have experienced frequent algal blooms over the past decade, we examine the spatially variable flushing time of a typical tributary bay (Xiangxi Bay) by numerical tracer experiments. First, the tracer concentration reduction could be approximated well by a double exponential decay curve, and the local flushing time of Xiangxi Bay is determined using key flushing coefficients. Second, a sensitivity analysis is performed to examine the influence of upstream inflow, temperature difference, wind, water level of the reservoir, and daily water level fluctuation on the spatial variation in local flushing time. Finally, according to local flushing time values and the sensitivity analysis results, the bay can be generally characterized by three zones: riverine, transitional, and mainstream‐influenced zones. In particular, the local flushing times in the riverine zone are mainly affected by the upstream inflow. The difference in temperature between the reservoir mainstream and Xiangxi Bay is the main forcing in the transitional and mainstream‐influenced zones. This study is the first to investigate different driving factors for flushing time in a typical reservoir tributary bay. The findings provide insights on the transport processes in such water bodies, suggesting the possibility of using the longitudinal zonation of flushing time for reservoir management. 相似文献
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B. J. Goodman C. S. Guy S. L. Camp W. M. Gardner K. M. Kappenman M. A. H. Webb 《河流研究与利用》2013,29(8):1004-1015
Many lotic fish species use natural patterns of variation in discharge and temperature as spawning cues, and these natural patterns are often altered by river regulation. The effects of spring discharge and water temperature variation on the spawning of shovelnose sturgeon Scaphirhynchus platorynchus have not been well documented. From 2006 through 2009, we had the opportunity to study the effects of experimental discharge levels on shovelnose sturgeon spawning in the lower Marias River, a regulated tributary to the Missouri River in Montana. In 2006, shovelnose sturgeon spawned in the Marias River in conjunction with the ascending, peak (134 m3/s) and descending portions of the spring hydrograph and water temperatures from 16 °C to 19 °C. In 2008, shovelnose sturgeon spawned in conjunction with the peak (118 m3/s) and descending portions of the spring hydrograph and during a prolonged period of increased discharge (28–39 m3/s), coupled with water temperatures from 11 °C to 23 °C in the lower Marias River. No evidence of shovelnose sturgeon spawning was documented in the lower Marias River in 2007 or 2009 when discharge remained low (14 and 20 m3/s) despite water temperatures suitable and optimal (12 °C?24 °C) for shovelnose sturgeon embryo development. A similar relationship between shovelnose sturgeon spawning and discharge was observed in the Teton River. These data suggest that discharge must reach a threshold level (28 m3/s) and should be coupled with water temperatures suitable (12 °C?24 °C) or optimal (16 °C?20 °C) for shovelnose sturgeon embryo development to provide a spawning cue for shovelnose sturgeon in the lower Marias River. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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