草原与荒漠交界地区流沙的固定——以沙坡头铁路防护体系旱路固沙为例

在年降水量200~ 300mm左右的草原与荒漠交界地区,无灌溉条件下的流沙固定不仅是可能的,亦是非常成功的。以包兰铁路沙坡头铁路人工植被的建立为例,年平均降水量仅186.2mm,在扎设草方格辅助措施下,栽植固沙植物,成功地从根本上解决了流沙固定问题。油蒿是特别优良的固沙植物,天然更新能力强,并能形成群落,又能稳定相当长时期。理应成为该地区流沙固定的首选。     

西藏日喀则流沙固定的几个问题

1995年首次在西藏日喀则进行固沙植物的引种试验,大多数中国内地固沙植物不适应该地的流动沙丘,沙面高温和生长季短是主要制约因素。沙木蓼和籽蒿表现最好;油蒿种子不能成熟,因此不能做后续植物;乡土植物砂生槐在播种当年出苗率低、生长缓慢,只能用做后期植物。在西藏日喀则,有效的植物固沙程序是:在保护措施(草方格沙障、砾石层)下,在流动沙丘上播种外来种沙木蓼、籽蒿和油蒿或移栽籽蒿,同时播种乡土植物砂生槐。在沙木蓼和籽蒿种群衰退、油蒿种群未衰退但不能靠天然下种自行更新时,砂生槐开始发挥固沙作用,并最终凭其适沙特性和长寿命接替先锋固沙植物有效地固定沙丘。选择乡土固沙植物应将重点放在蒿属和锦鸡儿属上。     

EU 20-20-20 energy policy as a model for global climate mitigation

The EU has established an aggressive portfolio with explicit near-term targets for 2020 – to reduce GHG emissions by 20%, rising to 30% if the conditions are right, to increase the share of renewable energy to 20%, and to make a 20% improvement in energy efficiency – intended to be the first step in a long-term strategy to limit climate forcing. The effectiveness and cost of extending these measures in time are considered along with the ambition and propagation to the rest of the world. Numerical results are reported and analysed for the contribution of the portfolio's various elements through a set of sensitivity experiments. It is found that the hypothetical programme leads to very substantial reductions in GHG emissions, dramatic increases in use of electricity, and substantial changes in land-use including reduced deforestation, but at the expense of higher food prices. The GHG emissions reductions are driven primarily by the direct limits. Although the carbon price is lower under the hypothetical protocol than it would be under the emissions cap alone, the economic cost of the portfolio is higher, between 13% and 22%.     

Increasing rainfall,decreasing winds,and historical changes in Santa Catarina dunefields,southern Brazil

Morphological and vegetation changes on the Moçambique barrier dunefield system are examined for the period 1938–2002 from aerial photography, and a variety of factors are investigated as possible driving factors. Human factors include a decrease in grazing pressure and tree felling from the early 1960s onwards after 200 years of these activities, and fires. In the 1960s tree planting also took place. During the period 1963 to 1970 there was a marked decline in drift potential (DP – potential sand transport), and then a period of very low DPs (1970–1974). This period falls within the time interval when vegetation cover significantly increased by ~70% along the Moçambique barrier (from 1956 to 1978). During the 1960s to present, the rainfall increased. Analyses of other transgressive dunefields in Santa Catarina and Rio Grande do Sul states show similar trends so it is likely that climatic factors such as increasing rainfall and decreasing DPs are responsible for driving dunefield changes and vegetation colonization of the barriers. Copyright © 2013 John Wiley & Sons, Ltd.     

高钙粉煤灰固化重金属污染土的工程性质试验研究

高钙粉煤灰是燃煤电厂排出的固体废物,其堆放不仅需占用大量土地,而且对周围环境存在严重威胁。通过系统的室内试验,着重研究了高钙粉煤灰固化铅与锌污染土的工程性质,揭示了其作用机制,探讨了利用高钙粉煤灰固化重金属污染土的可行性。试验结果表明,土体受到重金属离子污染后其无侧限抗压强度降低,掺入高钙粉煤灰可提高土体强度,并能抑制重金属离子的滤出;污染物浓度较低时,固化污染土中的Pb2+和Zn2+均能得到有效固化,污染物浓度较高时,Zn2+的固化效果优于Pb2+。干湿循环试验结果表明,高钙粉煤灰固化污染土的强度随干湿循环次数的增加,先增大后减小;固化土体中重金属离子浓度较低时,滤出液中金属离子浓度随干湿循环次数增加而增大;重金属离子浓度较高时,滤出液中金属离子浓度基本保持不变。     

Channel and island change in the lower Platte River, Eastern Nebraska, USA: 1855–2005

The lower Platte River has undergone considerable change in channel and bar characteristics since the mid-1850s in four 20–25 km-long study stretches. The same net effect of historical channel shrinkage that was detected upstream from Grand Island, Nebraska, can also be detected in the lower river but differences in the behaviors of study stretches upstream and downstream from major tributaries are striking. The least relative decrease occurred downstream from the Loup River confluence, and the stretch downstream from the Elkhorn River confluence actually showed an increase in channel area during the 1940s. Bank erosion was also greater downstream of the tributaries between ca. 1860 and 1938/1941, particularly in stretch RG, which showed more lateral migration. The cumulative island area and the ratio of island area to channel area relative to the 1938/1941 baseline data showed comparatively great fluctuations in median island size in both downstream stretches. The erratic behavior of island size distributions over time indicates that large islands were accreted to the banks at different times, and that some small, newly-stabilized islands were episodically “flushed” out of the system. In the upstream stretches the stabilization of mobile bars to create new, small islands had a more consistent impact over time. Channel decrease by the abandonment of large, long-lived anabranches and by the in-place narrowing resulting from island accretion were more prominent in these upstream stretches. Across all of the study area, channel area appears to be stabilizing gradually as the rate of decrease lessens. This trend began earliest in stretch RG in the late 1950s and was accompanied by shifts in the size distributions of stabilized islands in that stretch into the 1960s. Elsewhere, even in the easternmost study stretch, stabilizing was occurring by the late 1960s, the same time frame documented by investigations of the Platte system upstream of the study area. Comprehensive management plans for the lower Platte River should account, at least in theory, for the observed differences in stream behavior upstream and downstream of the major eastern tributaries.     

温室气体稳定浓度情景下中国地区温度和降水变化

 利用参与IPCC第四次评估报告（AR4）的多个全球气候系统模式的输出结果,着重分析了2101-2198年温室气体浓度稳定在720 mL/m3和550 mL/m3水平时（S 720和S 550情景）,中国地区地表温度与降水的时空变化特征。结果表明：1) 当温室气体浓度稳定不变时,22世纪中国地表温度仍将呈上升趋势,增温幅度为0.4℃/100a,但升温趋势平缓,幅度明显小于SRES A1B（中等排放）和B1（低排放）情景,冬、春季增温显著且高纬地区增温明显大于低纬地区,夏、秋季次之,因此季节间的温差将会变小;2) S 720（S 550）情景下年平均降水增加幅度基本稳定在11%（8%）左右,冬季降水增加显著,且增幅从南向北逐渐增大,春季次之,夏、秋季大部分地区降水将减少10%～30%。     

Unscented Kalman Filter trained neural networks based rudder roll stabilization system for ship in waves

The large roll motion of ships sailing in the seaway is undesirable because it may lead to the seasickness of crew and unsafety of vessels and cargoes, thus it needs to be reduced. The aim of this study is to design a rudder roll stabilization system based on Radial Basis Function Neural Network (RBFNN) control algorithm for ship advancing in the seaway only through rudder actions. In the proposed stabilization system, the course keeping controller and the roll damping controller were accomplished by utilizing modified Unscented Kalman Filter (UKF) training algorithm, and implemented in parallel to maintain the orientation and reduce roll motion simultaneously. The nonlinear mathematical model, which includes manoeuvring characteristics and wave disturbances, was adopted to analyse ship’s responses. Various sailing states and the external wave disturbances were considered to validate the performance and robustness of the proposed roll stabilizer. The results indicate that the designed control system performs better than the Back Propagation (BP) neural networks based control system and conventional Proportional-Derivative (PD) based control system in terms of reducing roll motion for ship in waves.     

Dredged marine sediments used as novel supply of filling materials for road construction

The dredged marine sediments are classified as waste and how to deal with such kind of abandoned materials is a great challenge. The main objective of this experimental work is to provide a novel way to reuse dredged sediment as filling materials in road section. The laboratory dewatering test is performed to model the in situ evaporation and dewatering process of untreated and treated sediment with chemical binder. The impact of binder amount and time is discussed on the change of water content influenced by evaporation. To valorize dredged sediments as roadbed materials, a hydraulic binder is incorporated to investigate its effect on the bearing capacity and strength performance. The suitability of stabilized sediment is assessed based on the obtained mechanical results followed by a detailed discussion on the in situ test roads.     

Experimental Investigation of Unconfined Compression Strength and Stiffness of Cement Treated Salt-Rich Clay

Soft clay with high sodium chloride salt concentration is a problem encountered by geotechnical and highway engineers. Chemical stabilization using cement is an attractive method to improve the engineering properties of soft soil. However, very limited studies have been conducted to reveal the effect of salt concentration on the engineering properties of cement-stabilized soil and the reported results in literature are not consistent. The impact of sodium chloride salt on the strength and stiffness properties of cement-stabilized Lianyungang marine clay is studied in this study. The clay with various sodium chloride salt concentrations was prepared artificially and stabilized by various contents of Ordinary Portland cement. A series of unconfined compressive strength (UCS) tests of cement stabilized clay specimen after 7, 14, and 28 days curing periods were carried out. The results indicate that a high sodium chloride salt concentration has a detrimental effect on the UCS and stiffness of cement-stabilized clay. The detrimental effect of salt concentration on the strength and stiffness of cement-stabilized clay directly relates to cement content. Soils mixed with high cement content are more resistant to the negative effect of salts than soils mixed with low cement content. The ratio of modulus of elasticity to UCS of cement treated soil does not have an obvious relationship with salt concentration. The findings of this study present a rational basis for the understanding of the impact of salt on the engineering properties of cement-treated soil.