Temporal variations of reference evapotranspiration and controlling factors:Implications for climatic drought in karst areas

Variations in reference evapotranspiration(ET_(0)) and drought characteristics play a key role in the effect of climate change on water cycle and associated ecohydrological patterns.The accurate estimation of ET_(0) is still a challenge due to the lack of meteorological data and the heterogeneity of hydrological system.Although there is an increasing trend in extreme drought events with global climate change,the relationship between ET_(0) and aridity index in karst areas has been poorly studied.In this study,we used the Penman-Monteith method based on a long time series of meteorological data from 1951 to 2015 to calculate ET_(0)in a typical karst area,Guilin,Southwest China.The temporal variations in climate variables,ET_(0)and aridity index(AI)were analyzed with the Mann-Kendall trend test and linear regression to determine the climatic characteristics,associated controlling factors of ET_(0) variations,and further to estimate the relationship between ET_(0) and AI.We found that the mean,maximum and minimum temperatures had increased significantly during the 65-year study period,while sunshine duration,wind speed and relative humidity exhibited significant decreasing trends.The annual ET_(0) showed a significant decreasing trend at the rate of−8.02 mm/10a.However,significant increase in air temperature should have contributed to the enhancement of ET_(0),indicating an“evaporation paradox”.In comparison,AI showed a slightly declining trend of−0.0005/a during 1951-2015.The change in sunshine duration was the major factor causing the decrease in ET_(0),followed by wind speed.AI had a higher correlation with precipitation amount,indicating that the variations of AI was more dependent on precipitation,but not substantially dependent on the ET_(0).Although AI was not directly related to ET_(0),ET_(0)had a major contribution to seasonal AI changes.The seasonal variations of ET_(0)played a critical role in dryness/wetness changes to regulate water and energy supply,which can lead to seasonal droughts or water shortages in karst areas.Overall,these findings provide an important reference for the management of agricultural production and water resources,and have an important implication for drought in karst regions of China.

A new interacting capillary bundle model on the multiphase flow in micropores of tight rocks

Surfactants are widely used in the fracturing fluid to enhance the imbibition and thus the oil recovery rate. However, current numerical models cannot capture the physics behind capillary imbibition during the wettability alteration by surfactants. Although the interacting capillary bundle(ICB) model shows potential in characterizing imbibition rates in different pores during wettability alteration, the existing ICB models neglect the influence of wettability and viscosity ratio on the imbibition behavior, making it difficult to accurately describe the oil-water imbibition behavior within the porous media. In this work,a new ICB mathematical model is established by introducing pressure balance without assuming the position of the leading front to comprehensively describe the imbibition behavior in a porous medium under different conditions, including gas-liquid spontaneous imbibition and oil-water imbibition.When the pore size distribution of a tight rock is known, this new model can predict the changes of water saturation during the displacement process in the tight rock, and also determine the imbibition rate in pores of different sizes. The water saturation profiles obtained from the new model are validated against the waterflooding simulation results from the CMG, while the imbibition rates calculated by the model are validated against the experimental observations of gas-liquid spontaneous imbibition. The good match above indicates the newly proposed model can show the water saturation profile at a macroscopic scale while capture the underlying physics of the multiphase flow in a porous medium at a microscopic scale. Simulation results obtained from this model indicate that both wettability and viscosity ratio can affect the sequence of fluid imbibition into pores of different sizes during the multiphase flow, where less-viscous wetting fluid is preferentially imbibed into larger pores while more-viscous wetting fluid tends to be imbibed into smaller pores. Furthermore, this model provides an avenue to calculate the imbibition rate in pores of different sizes during wettability alteration and capture the non-Darcy effect in micro-and nano-scale pores.

Macroscopic Regulation of Hierarchical Nanostructures in Liquid-crystalline Block Copolymers towards Functional Materials

The great potential of liquid-crystalline block copolymers(LCBCs)containing photoresponsive mesogens toward novel applications in photonics and nanotechnology has been attracting increasing attention,due to the combination of the inherent property of microphase separation of block copolymers and the hierarchically-assembled structures of liquid-crystalline polymers(LCPs).The periodically ordered nanostructures in bulk film of LCBCs can be acquired by supramolecular cooperative motion,derived from the interaction between liquid-crystalline elastic deformation and microphase separation,which are able to improve physical properties of polymer film toward advanced functional applications.Moreover,various micro/nano-patterned structures have been fabricated via light manipulation of photoresponsive LCBCs with good reproducibility and mass production.Thanks to recent developments in synthesis and polymerization techniques,diverse azobenzene-containing LCBCs have been designed,resulting in the creation of a wide variety of novel functions.This review illustrates recent progresses in macroscopic regulation of hierarchical nanostructures in LCBCs towards functional materials.The existing challenges are also discussed,showing perspectives for future studies.

Strong shape-dependence of Morin transition in α-Fe2O3 single-crystalline nanostructures

单人赛水晶的赤铁矿(-Fe2O3) nanorings (短 nanotubes ) 和 nanotubes 被一个热水的方法综合。高分辨率的传播电子显微镜学和精选区域的电子衍射证实 nanorings 和 nanotubes 的轴的方向与水晶的 c 轴平行。有趣地， Morin 转变与大约 115 nm 和大约 169 nm 的一条吝啬的外部直径的吝啬的试管长度在短 nanotubes 发生在大约 210 K。然而，它不与大约 317 nm 和大约 148 nm 的一条吝啬的外部直径的吝啬的试管长度发生在 nanotubes。磁化数据， X 光检查衍射模式，和房间温度 M 的详细分析 ? ssbauer 系列证明 Morin 转变的这很强壮的形状依赖对赤铁矿内在。我们向这吸引人的形状依赖份量上解释，以表面的相反的符号与 c 轴平行、垂直的表面飞机的磁性的 anisotropy 常数。