一种新型掺气设施的试验研究

设置在泄洪洞竖井内的环形掺气设施是不同于传统掺气技术的新创意。为了更好地认识这种新型的掺气技术,基于公伯峡水平旋流泄洪洞原型和模型试验,对环形掺气坎的通风和掺气特性进行了研究。结果表明环形通气孔的通风是由通气孔进出口的压差引起的,通风量与相对空腔长度的关系服从线性分布;环形掺气坎掺气减蚀的作用明显,其掺气是由于射流冲击竖井水体形成大尺度旋涡并挟带气泡所致,且掺气浓度沿高程呈乘幂分布;模型通风和掺气特性的缩尺效应明显。在结构设计满足要求的前提下,有必要在旋流泄洪洞的竖井段设置掺气设施,可改善水流流态,并增加消能效果。     

基于麻雀搜索算法优化的BP神经网络卫星钟差预报

使用麻雀搜索算法(sparrow search algorithm,SSA)对BP神经网络的初始权值和阈值进行优化和调整,以提高神经网络模型短期预报的精度和稳定性.采用IGS产品中的卫星钟差数据,对SSA-BP神经网络模型、PSO-BP神经网络模型、传统BP神经网络模型及传统二次多项式模型(QP模型)进行实验对比,结果...     

Discriminating the long distance dispersal of fine ash from sustained columns or near ground ash clouds: The example of the Pomici di Avellino eruption (Somma-Vesuvius,Italy)

Ash samples from tephra layers correlated with the Pomici di Avellino (Avellino Pumice) eruption of Somma-Vesuvius were collected in distal archives and their composition and particle morphology investigated in order to infer their behaviour of transportation and deposition. Differences in composition and particle morphologies were recognised for ash particles belonging to the magmatic Plinian and final phreatomagmatic phases of the eruption. The ash particles were dispersed in opposite directions during the two different phases of the eruption, and these directions are also different from that of coarse-grained fallout deposits. In particular, ash generated during magmatic phase and injected in the atmosphere to form a sustained column shows a prevailing SE dispersion, while ash particles generated during the final phreatomagmatic phase and carried by pyroclastic density currents show a general NW dispersion. These opposite dispersions indicate an ash dispersal influenced by both high and low atmosphere dynamics. In particular, the magmatic ash dispersal was first driven by stratospheric wind towards NE and then the falling particles encountered a variable wind field during their settling, which produced the observed preferential SE dispersal. The wind field encountered by the rising ash clouds that accompanied the pyroclastic density currents of the final phreatomagmatic phase was different with respect to that encountered by the magmatic ash, and produced a NW dispersal. These data demonstrate how ash transportation and deposition are greatly influenced by both high and low atmosphere dynamics. In particular, fine-grained particles transported in ash clouds of small-scale pyroclastic density currents may be dispersed over distances and cover areas comparable with those injected into the stratosphere by Plinian, sustained columns. This is a point not completely addressed by present day mitigation plans in case of renewal of activity at Somma-Vesuvius, and can yield important information also for other volcanoes potentially characterised by explosive activity.     

Heat budget for a shallow,sinuous salt marsh estuary

An experimental study of temperature cycles and the heat budget in the Duplin River, a tidal creek bordered by extensive intertidal salt marshes, was carried out in late summer of 2003 and spring of 2004 near Sapelo Island on the central Georgia coast in the southeastern US. Three water masses are identified with differing temperature and salinity regimes, the characteristics of which are dictated by channel morphology, tidal communication with the neighboring sound, ground water hydrology, the extent of local intertidal salt marshes and side channels and the spring–neap tidal cycle (which controls both energetic mixing and, presumably, ground water input). For the first experiment, heat budgets are constructed for the upper (warmer) and lower (cooler) areas of the Duplin River showing the diminishing importance of tidal advection away from the mouth of the creek along with the concomitant increase in the importance of both direct atmospheric fluxes and of interactions with the marsh and side creeks. The second experiment, in the spring of 2004, reexamines the heat budget on seasonal and daily averaged scales revealing the decreased importance of advective fluxes relative to direct atmospheric fluxes on this scale but the constant importance of marsh/creek interactions regardless of time scale or season. Short period temperature fluctuations which affect larval development are examined and analogies are drawn to use heat to understand the marsh as a source of sediment, carbon and other nutrients.     

考虑组合效应的钢框架梁柱节点恢复力模型研究

为了研究考虑节点区组合效应后高层钢框架节点的抗震性能,根据钢框架节点在低周反复荷载作用下足尺模型试验研究成果,总结了各试验节点试件的滞回性能,包括节点的延性、耗能能力等指标.在试验滞回曲线的基础上,考虑试件强度、刚度退化等影响,建立了考虑组合效应的梁柱节点的恢复力模型,所建立的模型可以用于结构弹塑性时程反应分析和钢框架节点抗震设计.     

Stretching characteristics and its dynamic significance of the northern continental margin of South China Sea

To investigate the thinning of the whole crust, and the contribution of the upper versus lower crust to the stretching since Cenozoic, we calculated the stretching factor of the northern margin of South China Sea with data such as whole crustal thickness, depth of Cenozoic sedimentary basement and the horizontal displacement of faults. An isometric line drawing on whole crustal stretching factor is then obtained. Along the seismic Line 1530 in Baiyun sag, we also calculated the stretching factors of the upper and lower crust. The results suggest that the whole crustal thickness decreases seaward while the whole crustal stretching factor increases from shelf to slope. The Moho upwells highest beneath where the crust is thinned most. The value of the whole crustal stretching factor ranges from 1.5 to 6. Two areas were thinned intensely: the center of Yinggehai Basin, and the Baiyun sag in the Pearl River Mouth Basin. The calculation of the upper and lower crustal stretching factors from DSP1530 in Baiyun sag shows that the original crust of Baiyun sag should be thinned before deformation. Its pre-Cenozoic evolution as well as tectonic position during Cenozoic might be responsible for that.     

Mesozoic paleogeography and tectonic evolution of South China Sea and adjacent areas in the context of Tethyan and Paleo-Pacific interconnections

Abstract   During the Mesozoic era, the South China Sea and its environs were located at the south-eastern margin of the Eurasian continent. There has been hot debate on the influences of Tethyan and Paleo-Pacific tectonics to the Mesozoic evolution of the area. This paper compiles lithofacies maps of six time slices and discusses the paleogeographic and tectonic evolution of the area based on this compilation and other data on structural deformation and magmatism. In the Early Triassic, the Paleotethys Ocean extended eastward to the study area through the Song Da passage. Then a significant east–west differential evolution began. In the Late Triassic, the western area uplifted as a result of the collision between the Indosinian and South China blocks during the Indosinian orogeny, and the Song Da passage has closed since then. Meanwhile, a transgression of Paleo-Pacific waters occurred in the eastern and south-eastern portions of the area, forming the 'East Guangdong–North-west Borneo Sea'. In the Early Jurassic, seawater transgression was even more pronounced, resulting into the connection of this sea with the Mesotethys Ocean to the west. Large quantities of Tethyan water carrying Tethyan organisms entered the area. In the Middle Jurassic, a short-lived transgression occurred in the eastern Mesotethys and resulted in the formation of the 'Yunnan–Burma Sea'. The Late Jurassic to Early Cretaceous was the climax of the subduction of both the Mesotethys and Paleo-Pacific towards the Eurasian continent. This led to the formation of the great 'Circum South-east Asia Subduction–Accretion Zone' in the Middle or Late Cretaceous. This paper also presents various lines of evidence for a newly recognized segment of this Mesozoic subduction–accretion zone buried under Cenozoic sediments in the north-eastern South China Sea.     

贵州龙里典型喀斯特地区绿水资源耗用研究

以贵州龙里典型喀斯特地区为例,通过集成RS /GIS技术,利用生态水文评估工具中模块化生态水文综合管理系统( EcoHAT)对研究区绿水资源进行定量模拟,模拟出该区2005年10月- 2006年10月像元尺度上绿水资源量,并分析了其绿水资源消耗效用。结果表明: 研究区林地、草地、灌丛和农用地单位面积土壤蓄变量月均值分别为5. 6mm、6. 3 mm、6. 9 mm、7. 7 mm;林地、草地、灌丛和农用地绿水资源单位面积年有效消耗量分别为: 423. 0mm、344. 2 mm、386. 7 mm、407. 5 m m,其中低消耗量分别为相应植被类型条件下总有效消耗量的47. 0%、48. 3%、52. 7%、61. 3%。在有效消耗量中,农用地低消耗量占较大比重,林地和草地的高效和低效消耗量相近,但草地的低消耗量大于林地。据此,认为贵州龙里典型喀斯特地区绿水资源具有较大的利用潜力。但是在今后的绿水资源利用中,必须加强调控绿水资源消耗效用,增加植被盖度,减少裸地面积,以减少绿水资源的无效消耗量;与此同时,还应调整植被结构,以减少植被棵间土壤的低效消耗量。