Geochemical reconstruction of late Holocene drainage and mixing in Kluane Lake,Yukon Territory

The level of Kluane Lake in southwest Yukon Territory, Canada, has fluctuated tens of metres during the late Holocene. Contributions of sediment from different watersheds in the basin over the past 5,000 years were inferred from the elemental geochemistry of Kluane Lake sediment cores. Elements associated with organic material and oxyhydroxides were used to reconstruct redox fluctuations in the hypolimnion of the lake. The data reveal complex relationships between climate and river discharge during the late Holocene. A period of influx of Duke River sediment coincides with a relatively warm climate around 1,300 years BP. Discharge of Slims River into Kluane Lake occurred when Kaskawulsh Glacier advanced to the present drainage divide separating flow to the Pacific Ocean via Kaskawulsh and Alsek rivers from flow to Bering Sea via tributaries of Yukon River. During periods when neither Duke nor Slims river discharged into Kluane Lake, the level of the lake was low and stable thermal stratification developed, with anoxic and eventually euxinic conditions in the hypolimnion.     

CATASTROPHIC ECO-ENVIRONMENTAL CHANGE IN THE SONGNEN PLAIN, NORTHEASTERN CHINA SINCE 1900S

Although the Songnen Plain in the northeastern China was developed relatively late in the temperate zone of the world, its eco-environment has changed greatly. This paper analyzes the changes of land cover and the rates and trends ofdesertification during the past 100 years in the Songnen Plain. According to the macroscopic analysis, we find that the eco-environment in the plain has reached to the threshold of catastrophic change since the 1950s. The Thorn Needle Catastrophic Model was used to determine and validate this conclusion. Human activities, including large-scale construction projects, such as huge dams and dikes, and excessive grazing were the primary factors contributing to regional eco-environmental catastrophe. And irrational reclamation of the wilderness also affected the eco-environmental change. The results reveal the complex human-land interactions.     

Logarithmic spiral trajectories generated by Solar sails

Analytic solutions to continuous thrust-propelled trajectories are available in a few cases only. An interesting case is offered by the logarithmic spiral, that is, a trajectory characterized by a constant flight path angle and a fixed thrust vector direction in an orbital reference frame. The logarithmic spiral is important from a practical point of view, because it may be passively maintained by a Solar sail-based spacecraft. The aim of this paper is to provide a systematic study concerning the possibility of inserting a Solar sail-based spacecraft into a heliocentric logarithmic spiral trajectory without using any impulsive maneuver. The required conditions to be met by the sail in terms of attitude angle, propulsive performance, parking orbit characteristics, and initial position are thoroughly investigated. The closed-form variations of the osculating orbital parameters are analyzed, and the obtained analytical results are used for investigating the phasing maneuver of a Solar sail along an elliptic heliocentric orbit. In this mission scenario, the phasing orbit is composed of two symmetric logarithmic spiral trajectories connected with a coasting arc.     

Sedimentary evolution of the Holocene subaqueous clinoform off the southern Shandong Peninsula in the Western South Yellow Sea

Based on the stratigraphic sequence formed since the last glaciation and revealed by 3000 km long high-resolution shallow seismic profiles and the core QDZ03 acquired recently off the southern Shandong Peninsula, we addressed the sedimentary characteristics of a Holocene subaqueous clinoform in this paper. Integrated analyses were made on the core QDZ03, including sedimentary facies, sediment grain sizes, clay minerals, geochemistry, micro paleontology, and AMS 14 C dating. The result indicates that there exists a Holocene subaqueous clinoform, whose bottom boundary generally lies at 15–40 m below the present sea level with its depth contours roughly parallel to the coast and getting deeper seawards. The maximum thickness of the clinoform is up to 22.5 m on the coast side, and the thickness contours generally spread in a banded way along the coastline and becomes thinner towards the sea. At the mouths of some bays along the coast, the clinoform stretches in the shape of a fan and its thickness is evidently larger than that of the surrounding sediments. This clinoform came into being in the early Holocene(about 11.2 cal kyr BP) and can be divided into the lower and upper depositional units(DU 2 and DU 1, respectively). The unit DU 2, being usually less than 3 m in thickness and formed under a low sedimentation rate, is located between the bottom boundary and the Holocene maximum flooding surface(MFS), and represents the sediment of a post-glacial transgressive systems tract; whereas the unit DU 1, the main body of the clinoform, sits on the MFS, belonging to the sediment of a highstand systems tract from middle Holocene(about 7–6 cal kyr BP) to the present. The provenance of the clinoform differs from that of the typical sediments of the Yellow River and can be considered as the results of the joint contribution from both the Yellow River and the proximal coastal sediments of the Shandong Peninsula, as evidenced by the sediment geochemistry of the core. As is controlled mainly by coactions of multiple factors such as the Holocene sea-level changes, sediment supplies and coastal dynamic conditions, the development of the clinoform is genetically related with the synchronous clinoform or subaqueous deltas around the northeastern Shandong Peninsula and in the northern South Yellow Sea in the spatial distribution and sediment provenance, as previously reported, with all of them being formed from the initial stage of the Holocene up to the present.     

基于水利益共享的跨境流域水资源多目标分配研究——以澜沧江-湄公河为例

以水利益共享代替分水的理念有利于充分发挥水资源效益和减少区域矛盾冲突,但由于缺乏具体可实施的分配模式一直停留在设想阶段。基于水利益共享理念,建立跨境流域水资源多目标分配指标体系,并结合澜沧江-湄公河流域跨境水资源利用现状及需求,提出澜沧江-湄公河流域跨境水资源多目标分配模型。为基于水利益共享的跨境水资源多目标分配提供了具有充分可操作性的指标体系和分配模型,有助于推进跨境流域水利益共享的实施,实现区域双边或多边在水资源利用上的共赢和发展目标。     

Application of saddlepoint approximation in reliability analysis of dynamic systems

The application of the saddlepoint approximation to reliability analysis of dynamic systems is investigated. The failure event in reliability problems is formulated as the exceedance of a single performance variable over a prescribed threshold level. The saddlepoint approximation technique provides a choice to estimate the cumulative distribution function (CDF) of the performance variable. The failure probability is obtained as the value of the complement CDF at a specif ied threshold. The method requires computing the saddlepoint from a simple algebraic equation that depends on the cumulant generating function (CGF) of the performance variable. A method for calculating the saddlepoint using random samples of the performance variable is presented. The applicable region of the saddlepoint approximation is discussed in detail. A 10-story shear building model with white noise excitation illustrates the accuracy and effi ciency of the proposed methodology.     

生物生态防治虾病研究

本文探索虾病防治新途径,采用低值海藻江蓠和对虾混养的生态学方法,江蓠吸收水中二氧化碳进行光合作用,产生大量氧气;同时吸收有机物的分解物 NH_3—N,加速有机物分解。减少 H_2S 积累;从而消除水中紧迫因子威胁,大大减少池水自污及病害,起到抑菌、抑虫、净化水质作用,提高成活率,试验圹对虾成活率达95.1%,对照圹56.6%。试验结果表明,虾病防治效果显著,经济效益明显。     

怒江迪庆州陡坡耕地的改良和持续利用研究

滇西北的怒江、迪庆两州地处云南省高寒高山峡谷区，地形破碎而陡峻，耕地稀缺，陡坡种植业占有很高的比重。由于人口的增长，陡坡耕地仍将作为该地区的主要耕地长期存在。这种传统的耕种方式已对环境产生了深刻的负效应。本文根据其生存条件和利用现状就通过改良以取得持续利用的方向和途径作了初步探讨。     

Lateral continuity of basement seismic reflections in 15 Ma ultrafast-spreading crust at ODP Site 1256

The Ocean Drilling Program (ODP) initiated drilling at Site 1256D in the Guatemala Basin, about 1,000 km off the East Pacific Rise to penetrate plutonic rocks, anticipated to be relatively shallow in this region, formed at an ultra-fast spreading rate. IODP Expedition E312 successfully drilled into gabbros at ~1,150 m in basement. Multi-channel seismic traces show weak laterally coherent sub-basement reflections at borehole depths. Synthetic reflectivity seismograms were computed using a Ricker wavelet and impedance profiles from borehole sonic logs. These seismograms show significant sub-basement amplitude peaks. A zero-offset vertical seismic profile, shot on E312, was processed to investigate the authenticity of these reflections and their relationship to borehole geology. A dual scheme of the median filtering and F–K dip filtering was used. Tests with synthetic seismograms indicate the approach is effective at reasonable SNR levels. Downgoing energy is clearly identified but negligible upgoing energy is visible over random noise. These results indicate that lava flows and igneous contacts in upper ocean crust have significant topography on lateral scales less than the Fresnel Zone (~300 m) due to igneous and tectonic processes.     

四川紫色土退化的分类与分区

四川紫色土耕地面积406.1万公顷,占全省耕地面积的36.5％,属全省农业生产的主体区域。四川紫色土普遍退化。退化分为物理性(含构造性)、化学性、营养性三类。用模糊综合评判方法,评价了四川(主要为盆地丘陵区)紫色土退化的程度和状况。同时又建立了退化紫色土的分区原则,将四川紫色土退化分布区域划分为6个退化亚区,10个退化小区。