纳米塑料和二氧化钛食相暴露对凡纳滨对虾血细胞功能及抗氧化系统的影响

纳米塑料和纳米金属氧化物粒子在不同领域的使用量日益增多,这些纳米材料进入水生系统可能带来的相关环境风险引起了人们的关注.本文通过食相暴露,分析了100 nm纳米聚苯乙烯(PS)和纳米二氧化钛(TiO2)暴露对凡纳滨对虾(Litopenaeus vannamei)的血细胞功能和氧化还原平衡的干扰.实验组对虾分别投喂混有2...     

Response of a porous seabed around breakwater heads

The evaluation of wave-induced pore pressures and effective stresses in a porous seabed near a breakwater head is important for coastal engineers involved in the design of marine structures. Most previous studies have been limited to two-dimensional (2D) or three-dimensional (3D) cases in front of a breakwater. In this study, we focus on the problem near breakwater heads that consists of incident, reflected and diffracted waves. Both wave-induced oscillatory and residual liquefactions will be considered in our new models. The mistake in the previous work [Jeng, D.-S., 1996. Wave-induced liquefaction potential at the tip of a breakwater. Applied Ocean Research 18(5), 229–241] for oscillatory mechanism is corrected, while a new 3D boundary value problem describing residual mechanism is established. A parametric study is conducted to investigate the influences of several wave and soil parameters on wave-induced oscillatory and residual liquefactions around breakwater heads.     

The penetration experiment to predict liquefaction resistance of reclaimed soils

The liquefaction resistance of the soils used to be estimated through the in situ tests, such as standard penetration test and cone penetration test; or by means of cyclic triaxial test in laboratory. However, both in situ tests and cyclic triaxial test are time-consuming and costly; this study introduces a quick and cost-effective method to evaluate the liquefaction resistance of soils under certain confining pressure in laboratory. A particular device modified from the conventional triaxial compression test apparatus, namely “Triaxial Cone Penetration Test”, was developed to obtain the peak values of cone resistance in soils so as to correlate the liquefaction resistance of the reclaimed soils evaluated by cyclic triaxial tests. The test result indicates a good correlation between the peak value of cone resistance and the corresponding cyclic stress ratio (CSR) at the state of initial liquefaction, in which the correlation for loose samples is better than that for dense samples. Besides, both peak values of cone resistance and corresponding CSR increase with fine content of soils reaches 10% and decreased with fine content varying between 10% and 50%. By examining the compositions of the soils with scanning electron microscopy and X-ray diffraction, it is found that the proportion and characteristics of the fines plays an important role on the liquefaction resistance of the reclaimed soils.     

Climate change and coral reef bleaching: An ecological assessment of long-term impacts,recovery trends and future outlook

Since the early 1980s, episodes of coral reef bleaching and mortality, due primarily to climate-induced ocean warming, have occurred almost annually in one or more of the world's tropical or subtropical seas. Bleaching is episodic, with the most severe events typically accompanying coupled ocean–atmosphere phenomena, such as the El Niño-Southern Oscillation (ENSO), which result in sustained regional elevations of ocean temperature. Using this extended dataset (25+ years), we review the short- and long-term ecological impacts of coral bleaching on reef ecosystems, and quantitatively synthesize recovery data worldwide. Bleaching episodes have resulted in catastrophic loss of coral cover in some locations, and have changed coral community structure in many others, with a potentially critical influence on the maintenance of biodiversity in the marine tropics. Bleaching has also set the stage for other declines in reef health, such as increases in coral diseases, the breakdown of reef framework by bioeroders, and the loss of critical habitat for associated reef fishes and other biota. Secondary ecological effects, such as the concentration of predators on remnant surviving coral populations, have also accelerated the pace of decline in some areas. Although bleaching severity and recovery have been variable across all spatial scales, some reefs have experienced relatively rapid recovery from severe bleaching impacts. There has been a significant overall recovery of coral cover in the Indian Ocean, where many reefs were devastated by a single large bleaching event in 1998. In contrast, coral cover on western Atlantic reefs has generally continued to decline in response to multiple smaller bleaching events and a diverse set of chronic secondary stressors. No clear trends are apparent in the eastern Pacific, the central-southern-western Pacific or the Arabian Gulf, where some reefs are recovering and others are not. The majority of survivors and new recruits on regenerating and recovering coral reefs have originated from broadcast spawning taxa with a potential for asexual growth, relatively long distance dispersal, successful settlement, rapid growth and a capacity for framework construction. Whether or not affected reefs can continue to function as before will depend on: (1) how much coral cover is lost, and which species are locally extirpated; (2) the ability of remnant and recovering coral communities to adapt or acclimatize to higher temperatures and other climatic factors such as reductions in aragonite saturation state; (3) the changing balance between reef accumulation and bioerosion; and (4) our ability to maintain ecosystem resilience by restoring healthy levels of herbivory, macroalgal cover, and coral recruitment. Bleaching disturbances are likely to become a chronic stress in many reef areas in the coming decades, and coral communities, if they cannot recover quickly enough, are likely to be reduced to their most hardy or adaptable constituents. Some degraded reefs may already be approaching this ecological asymptote, although to date there have not been any global extinctions of individual coral species as a result of bleaching events. Since human populations inhabiting tropical coastal areas derive great value from coral reefs, the degradation of these ecosystems as a result of coral bleaching and its associated impacts is of considerable societal, as well as biological concern. Coral reef conservation strategies now recognize climate change as a principal threat, and are engaged in efforts to allocate conservation activity according to geographic-, taxonomic-, and habitat-specific priorities to maximize coral reef survival. Efforts to forecast and monitor bleaching, involving both remote sensed observations and coupled ocean–atmosphere climate models, are also underway. In addition to these efforts, attempts to minimize and mitigate bleaching impacts on reefs are immediately required. If significant reductions in greenhouse gas emissions can be achieved within the next two to three decades, maximizing coral survivorship during this time may be critical to ensuring healthy reefs can recover in the long term.     

Elasticity soltion of rupture model of shallow earthquake

Based on the theory of elastic mechanics, and using the typical rupture model of shallow earthquake, the authors considered the shallow earthquake as a plane mechanical problem, which was constructed the corresponding mechanical model. By the stress components' formulas of the semi-infinite model acted by the finite even shearing force, the main stress is deduced. It is clear that the sector on the right of the center section is squeezed zone, where the maximum principal stress points at the "source of stress", and that on the left is tensile zone, where the minimum principal stress points to the "source of stress".     

海底双层管单层连接管道结构受力分析

粘性高的海洋石油通常需要通过海底保温管道加温输送.温度变化会引起管道变形,并在管壁内产生较大的温度应力.同时,管道正常运营期间还受到管道内压、外压、管内流体粘滞力和土体摩擦力等环境荷载的作用.复杂的环境可能导致海底管道轴向应力过大发生破坏.为了提高铺管效率,提出了双层管单层连接管道这一特殊管道形式,并从理论上分析温度变化和环境荷载对该管道的影响,计算正常运行时管道不同位置处横截面内最大Von-Mises应力.最后得到了Von-Mises应力沿管道轴线分布情况,发现内管和单层连接管的应力一般比外管大,变径管和内管的焊缝处是Von-Mises应力最大的地方.     

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秭归龙会观5.1级震区及其邻区新生代以来的地壳应力场特征

为了研究三峡坝库区的地壳稳定性,根据奥陶－侏罗纪地层中构造变形的实际观测资料,计算了秭归龙会观５．１级震区及其邻区新生代以来区域应力场的主应力方向。结果表明：主压应力为北东东向,主张应力为北北西向;现代构造应力场与新生代以来应力场基本一致;晚第三纪以来,该区构造应力场相对稳定和统一。     

Temporal and Spatial Dynamics Analysis of Grassland Ecosystem Pressure in Kazakhstan

Affected by climate change and policy factors, Kazakhstan is the country with the most severe ecological degradation and grassland conflicts in Central Asia. Therefore, studying the state of grassland carrying resources in Kazakhstan is particularly important for understanding the responses of grassland ecosystems to climate change and human activities. Based on Kazakhstan's remote sensing data and animal husbandry statistics, this study analyzes the patterns of changes in grassland ecosystems in Kazakhstan based on the supply and consumption of these ecosystems. The results show that: 1) From 2003 to 2017, the number of livestock raised in Kazakhstan showed a trend of sustained and steady growth. Due to freezing damage, the scale of livestock farming decreased in 2011, but a spatial difference in the livestock farming structure was not obvious. 2) The fluctuation of grassland supply in Kazakhstan has increased, while the consumption due to animal husbandry has also continued to increase, resulting in an increasing pressure on the grassland carrying capacity. 3) Between 2003 and 2017, the overall grassland carrying status of Kazakhstan have been abundant, but the grassland carrying pressure index has shown a steadily increasing trend, the grassland carrying pressure is growing, and it is mainly determined by grassland productivity. The greater pressure in lower Kyzylorda state, the southern Kazakhstan state of the cultivated land and the northern Kazakhstan state has gradually expanded to include the agro-pastoral zone and the semi-desert zone.