黄土丘陵沟壑区山坡道路防蚀措施初步研究

山坡道路连接农田、果园 ,对山区经济发展有重要作用。黄土高原山坡道路存在严重的水土流失 ,侵蚀方式主要有沟蚀、泻溜、崩塌、陷穴、悬沟侵蚀与滑坡等。山坡道路网应按照小流域综合治理规划合理布置 ,其主要防护措施 :①修筑梯田 ,防止坡面径流冲刷道路 ;②将路面整修成拱形以分散径流 ;③在道路内侧修蓄水窑窖 ,拦蓄径流 ;④路面及边坡栽植草灌 ,防止雨水冲刷

Corrosion behaviour of steel in beach soil along Bohai Bay

Research on corrosion of steel structures in various marine environments is essential to assure the safety of structures and can effectively prolong their service life. In order to provide data for anticorrosion design of oil exploitation structures in the Bohai Bay, the corrosion behaviour and properties of steel in beach soil, using typical steel samples (Q235A carbon steel and API 5Lx52 pipeline steel) buried 0.5, 1.0 and 1.5 m deep under typical beach soils in Tanggu, Yangjiaogou, Xingcheng, Yingkou and Chengdao for 1-2 years were studied. The carbon steel and pipeline steel were both corroded severely in the beach soil, with the form of corrosion being mainly uniform with some localised attack (pitting corrosion). The corrosion rate of the carbon steel was up to 0.16 mm/year with a maximum penetration depth of 0.76 mm and that of the pipeline steel was up to 0.14 mm/year, with a maximum penetration depth of 0.53 mm. Compared with carbon steel, the pipeline steel generally had better corrosion resistance in most test beach soils. The corrosion rates and the maximum corrosion depths of carbon steel and pipeline steel were in the order: Tanggu>Xingcheng>Chengdao>Yingkou>Yangjiaogou with corrosion altering with depth of burial. The corrosion of steel in the beach soil involves a mixed mechanism with different degrees of soil aeration and microbial activity present. It is concluded that long term in situ plate laying experiments must be carried out to obtain data on steel corrosion in this beach soil environment so that the effective protection measures can be implemented.

Research Progress On Thermal Protection Materials And Structures Of Hypersonic Vehicles

Hypersonic vehicles represent future trends of military equipments and play an important role in future war. Thermal protection materials and structures, which relate to the safety of hypersonic vehicles, are one of the most key techniques in design and manufacture of hypersonic vehicles. Among these materials and structures, such as metallic temperature protection structure, the temperature ceramics and carbon/carbon composites are usually adopted in design. The recent progresses of research and application of ultra-high temperature materials in preparation, oxidation resistance, mechanical and physical characterization are summarized.

Experimental Demonstration Of A New Concept Of Drag Reduction And Thermal Protection For Hypersonic Vehicles

A new idea of drag reduction and thermal protection for hypersonic vehicles is proposed based on the combination of a physical spike and lateral jets for shock-reconstruction. The spike recasts the bow shock in front of a blunt body into a conical shock, and the lateral jets work to protect the spike tip from overheating and to push the conical shock away from the blunt body when a pitching angle exists during flight. Experiments are conducted in a hypersonic wind tunnel at a nominal Mach number of 6. It is demonstrated that the shock/shock interaction on the blunt body is avoided due to injection and the peak pressure at the reattachment point is reduced by 70% under a 4A degrees attack angle.

A small arc-heated plasma testing facility for thermal protection materials

Experimental research on a 150 kW arc-heated plasma testing facility was conducted. Stable plasma jets with different gas compositions, temperatures and velocities were obtained at chamber pressure between 400 Pa – 100 kPa. Stagnation ablation experiments were conducted on samples of typical super alloys used for thermal protection systems. The microstructure and hardness of alloys before and after ablation were compared.

Foraging habitats and utilization distributions of Black-necked Cranes wintering at the Napahai Wetland, China

One of the most endangered populations of Black-necked Cranes (Grus nigricollis), the central population, is declining due to habitat loss and degradation, but little is known about their space use patterns and habitat preferences. We examined the space use and habitat preferences of Black-necked Cranes during the winter of 2007-2008 at the Napahai wetland in northwest Yunnan, China, where approximately 300 Black-necked Cranes (>90% of the total central population) spent the winter. Euclidean distance analysis was employed to determine the habitat preferences of Black-necked Cranes, and a local nearest-neighbor, convex-hull construction method was used to examine space use. Our results indicate that Black-necked Cranes preferred shallow marsh and wet meadow habitats and avoided farmland and dry grassland. Core-use areas (50% isopleths) and total-use areas (100% isopleths) accounted for only 1.2% and 28.2% of the study area, respectively. We recommend that habitat protection efforts focus on shallow marsh and wet meadow habitats to maintain preferred foraging sites. Core-use areas, such as the primary foraging areas of Black-necked Cranes, should be designated as part of the core zone of the nature reserve. Monthly shifts in the core-use areas of the cranes also indicate that the reserve should be large enough to permit changes in space use. In addition to preserving habitat, government officials should also take measures to decrease human activity in areas used by foraging Black-necked Cranes.

Effects of damming on population sustainability of Chinese sturgeon, Acipenser sinensis: evaluation of optimal conservation measures

The numbers of spawning sites for Chinese sturgeon have been drastically reduced since the construction of the Gezhouba Dam across the Yangtze River. This dam has blocked migration of Chinese sturgeon to their historic spawning ground causing a significant decline of the Chinese sturgeon population. We conducted a VORTEX population viability analysis to estimate the sustainability of the population and to quantify the efficiency of current and alternative conservation procedures. The model predicted the observed decline of Chinese sturgeon, resulting from the effect of the Gezhouba Dam. These simulations demonstrated the potential interest of two conservation measures: increasing spawning area and reducing predation on sturgeon eggs. The simulations also demonstrated that the actual restocking program is not sufficient to sustain sturgeon population as the artificial reproduction program induce the loss of more wild mature adults that the recruitment expected by the artificial reproduction.

Population status, threats and conservation of the Yangtze finless porpoise

The Yangtze finless porpoise (Neophocaena phocaenoides asiaeorientalis) is currently limited to the middle and lower reaches of the Yangtze River from Yichang to Shanghai, China, and the adjoining Poyang and Dongting Lakes. Its population size has decreased remarkably during the last several decades due to the heavy impact of human activities, including overfishing of prey species, water development projects that cause attendant habitat loss and degradation, water pollution, and accidental deaths caused by harmful fishing gear and collisions with motorized vessels. It was estimated that the number of remaining individuals was down to approximately 1800 in 2006, a number that is decreasing at a rate as high as 5% per year. Three conservation measures - in situ and ex situ conservation and captive breeding have been applied to the protection of this unique porpoise since the early 1990s. Seven natural and two "semi-natural" reserves have so far been established. Since 1996, a small group of finless porpoises has been successfully reared in a facility at the Institute of Hydrobiology of the Chinese Academy of Sciences; three babies were born in captivity on July 5, 2005, June 2, 2007 and July 5, 2008. These are the first freshwater cetaceans ever born in captivity in the world. Several groups of these porpoises caught in the main stream of the Yangtze River, or rescued, have been introduced into the Tian'e-Zhou Semi-natural Reserve since 1990. These efforts have proven that, not only can these animals survive in the area, they are also to reproduce naturally and successfully. More than 30 calves had been born in the reserve since then, with one to three born each year. Taking deaths and transfers into account, there were approximately 30 individuals living in the reserve as of the end of 2007. Among eight mature females captured in April 2008, five were confirmed pregnant. This effort represents the first successful attempt at off-site protection of a cetacean species in the world, and establishes a solid base for conservation of the Yangtze finless porpoise. A lesson must be drawn from the tragedy of Chinese River Dolphin (Lipotes vexillifer), which has already been declared likely extinct. Strong, effective and appropriate protective measures must be carried out quickly to prevent the Yangtze finless porpoise from becoming a second Chinese River Dolphin, and save the biodiversity of the Yangtze River as a whole.

Enhanced protection against oxidative stress in an astaxanthin-overproduction Haematococcus mutant (Chlorophyceae)

Many unicellular green algae can become yellow or red in various natural habitats due to mass accumulation of a secondary carotenoid, such as lutein, or astaxanthin. The accumulation of secondary carotenoids is generally thought to be a survival strategy of the algae under photo-oxidative stress or other adverse environmental conditions. The physiological role of the carotenoids in stress response is less well understood at the subcellular or molecular level. In this study, a stable astaxanthin overproduction mutant (MT 2877) was isolated by chemical mutagenesis of a wild type (WT) of the green microalga Haematococcus pluvialis Flotow NIES-144. MT 2877 was identical to the WT with respect to morphology, pigment composition, and growth kinetics during the early vegetative stage of the life cycle. However, it had the ability to synthesize and accumulate about twice the astaxanthin content of the WT under high light, or under high light in the presence of excess amounts of ferrous sulphate and sodium acetate. Under stress, the mutant exhibited higher photosynthetic activities than the WT, based on considerably higher chlorophyll fluorescence induction, chlorophyll autofluorescence intensities, and oxygen evolution rates. Cell mortality caused by stress was reduced by half in the mutant culture compared with the WT. Enhanced protection of the mutant against stress is attributed to its accelerated carotenogenesis and accumulation of astaxanthin. Our results suggest that MT 2877, or other astaxanthin overproduction Haematococcus mutants, may offer dual benefits, as compared with the wild type, by increasing cellular astaxanthin content while reducing cell mortality during stress-induced carotenogenesis.

The involvement of the antioxidant system in protection of desert cyanobacterium Nostoc sp against UV-B radiation and the effects of exogenous antioxidants

In this study, we found that UV-B radiation decreased photosynthetic activity and boosted lipid peroxidation of desert Nostoc sp., and exogenous chemicals (ascorbate acid (ASC), N-acetylcysteine (NAC), and sodium nitroprusside (SNP)) had obvious protective effects on photosynthesis and membranes under UV-B radiation. High-concentration SNP boosted the activities of antioxidant enzymes, but low-concentration SNP reduced the activities of antioxidant enzymes. Both NAC and ASC treatments of cells decreased activities of antioxidant enzymes. The results suggested that those chemicals possibly had different mechanisms of protection of algae cells against UV-B radiation. SNP might play double roles as a signal molecule in the formation of algae cell protection of Photosystem 11 under UV-B radiation and as a (reactive oxygen species) scavenger, while NAC and ASC might function as antioxidant reagents or precursors of other antioxidant molecules, which could protect cells directly against ROS initiated by UV-B radiation. (c) 2006 Elsevier Inc. All rights reserved.