Orientations of laser induced periodic surface structures(LIPSS)are usually considered to be governed by the laser polarization state.In this work,we unveil that fluid dynamics induced by femtosecond(fs)laser ablation...Orientations of laser induced periodic surface structures(LIPSS)are usually considered to be governed by the laser polarization state.In this work,we unveil that fluid dynamics induced by femtosecond(fs)laser ablation in liquid(fs-LAL)can easily break this polarization restriction to produce irregular circular-LIPSS(CLIPPS)and crisscross-LIPSS(CCLIPSS).Fs laser ablation of silicon in water shows formation of diverse LIPSS depending on ablation conditions.At a high power of 700 mW(repetition rate of 100 kHz,pulse duration of 457 fs and wavelength of 1045 nm),single/twin CLIPSS are produced at the bottom of macropores of several microns in diameter due to the formation of strong liquid vortexes and occurrence of the vortex shedding effect.Theoretical simulations validate our speculation about the formation of liquid vortex with an ultrahigh static pressure,which can induce the microstructure trenches and cracks at the sidewalls for fs-LAL of Si and tungsten(W)in water,respectively.At a low power of 50 mW,weak liquid vortexes are produced,which only give birth to curved LIPSS in the valleys of grooves.Consequently,it is deduced that liquid vortex plays a crucial role in the formation of macropores.Mountain-like microstructures induce complex fluid dynamics which can cause the formation of CCLIPSS on them.It is believed that liquid vortexes and fluid dynamics presented in this work open up new possibilities to diversify the morphologies of LIPSS formed by fs-LAL.展开更多
This paper selected the typical wind-water erosion crisscross region Xiliugou watershed for research to reveal the impact of the landscape pattern change of the underlying surface in wind-water erosion crisscross regi...This paper selected the typical wind-water erosion crisscross region Xiliugou watershed for research to reveal the impact of the landscape pattern change of the underlying surface in wind-water erosion crisscross region where soil erosion is most serious on rainfall and runoff as well as erosion and sediment.Based on the Landsat TM image data and measured data of runoff-sediment in that watershed,the paper analyzed the characteristics of watershed landscape pattern change and runoff-sediment and explored the relationship between landscape index and runoff-sediment yield by means of GIS and Fragstats.The results were included as follows.(1)Grassland was the dominant landscape.In terms of the number of patches and area change rate,from 1985 to 2010,cultivated land,forest land and construction land were most stable,followed by unused land.Unused land,grassland and cultivated land experienced the most dramatic conversion and maximally affected by human activities.(2)The inter-annual difference between annual runoff and annual sediment load was significant.Compared with the annual sediment load,the trend of decreasing runoff was more obvious.The correlation coefficient of runoff-sediment was 0.67,representing a significant correlation.(3)There was a significant correlation between the landscape index and runoff-sediment.The runoff was negatively correlated with the largest patch index,patch cohesion index,aggregation index and contagion index,but positively correlated with landscape morphology index and landscape division index.And the sediment was negatively correlated with the contagion index,aggregation index and plaque cohesion index,but positively correlated with other landscape indexes.The results indicate that with the increase of the largest patch index,patch cohesion index and aggregation index,the rainfall infiltration capacity increase obviously and the soil erosion reduce significantly.Therefore,increasing the largest patch index,patch cohesion and aggregation index of the watershed landscape can enhance the function of water storage and soil conservation as well as ecological optimization in the windwater erosion crisscross region.The results can provide theoretical support for the ecological environment construction and comprehensive utilization of water and soil resources.展开更多
Shielding effect and emission criterion of a screw dislocation near an interracial crisscross crack are dealt within this paper. Utilizing the conformal mapping technique, the closed-form solutions are derived for com...Shielding effect and emission criterion of a screw dislocation near an interracial crisscross crack are dealt within this paper. Utilizing the conformal mapping technique, the closed-form solutions are derived for complex potentialsand stress fields due to a screw dislocation located near the interracial crisscross crack. The stress intensity factor onthe crack tips and the critical stress intensity factor for dislocation emission are also calculated. The influence of theorientation of the dislocation and the morphology of the crisscross crack as well as the material elastic dissimilarity onthe shielding effect and the emission criterion is discussed in detail. The results show that positive screw dislocations canreduce the stress intensity factor of the interracial crisscross crack tip (shielding effect). The shielding effect increases withthe increase of the shear modulus of the lower half-plane, but it decreases with the increase of the dislocation azimuthangle and the distance between the dislocation and the crack tip. The critical loads at infinity for dislocation emissionincreases with the increase of emission angle and the vertical length of the crisscross crack, and the most probable anglefor screw dislocation emission is zero. The present solutions contain previous results as special cases.展开更多
All characteristics of vegetation,runoff and sediment from 1960 to 2010 in the Xiliu Gully Watershed,which is a representative watershed in wind-water erosion crisscross region in the upper reaches of the Yellow River...All characteristics of vegetation,runoff and sediment from 1960 to 2010 in the Xiliu Gully Watershed,which is a representative watershed in wind-water erosion crisscross region in the upper reaches of the Yellow River of China,have been analyzed in this study.Based on the remote sensing image data,and used multi-spectral interpretation method,the characteristics of vegetation variation in the Xiliu Gully Watershed have been analyzed.And the rules of precipitation,runoff and sediment's changes have been illuminated by using mathematical statistics method.What′s more,the influence mechanism of vegetation on runoff and sediment has been discussed by using the data obtained from artificial rainfall simulation test.The results showed that the main vegetation type was given priority to low coverage,and the area of the low vegetation coverage type was reducing year by year.On the country,the area of the high vegetation coverage type was gradually increasing.In a word,vegetation conditions had got better improved since 2000 when the watershed management project started.The average annual precipitation of the river basin also got slightly increase in 2000–2010.The average annual runoff reduced by 37.5%,and the average annual sediment reduced by 73.9% in the same period.The results of artificial rainfall simulation tests showed that the improvement of vegetation coverage could increase not only soil infiltration but also vegetation evapotranspiration,and then made the rainfall-induced runoff production decrease.Vegetation root system could increases the resistance ability of soil to erosion,and vegetation aboveground part could reduce raindrop kinetic energy and splash soil erosion.Therefore,with the increase of vegetation coverage,the rainfall-induced sediment could decrease.展开更多
To solve the problem of slow convergence and easy to get into the local optimum of the spider monkey optimization algorithm,this paper presents a new algorithm based on multi-strategy(ISMO).First,the initial populatio...To solve the problem of slow convergence and easy to get into the local optimum of the spider monkey optimization algorithm,this paper presents a new algorithm based on multi-strategy(ISMO).First,the initial population is generated by a refracted opposition-based learning strategy to enhance diversity and ergodicity.Second,this paper introduces a non-linear adaptive dynamic weight factor to improve convergence efficiency.Then,using the crisscross strategy,using the horizontal crossover to enhance the global search and vertical crossover to keep the diversity of the population to avoid being trapped in the local optimum.At last,we adopt a Gauss-Cauchy mutation strategy to improve the stability of the algorithm by mutation of the optimal individuals.Therefore,the application of ISMO is validated by ten benchmark functions and feature selection.It is proved that the proposed method can resolve the problem of feature selection.展开更多
基金This work was supported by the national key R&D program for internation-al collaboration under grant No.2018YFE9103900in part by the Nat-ural Science Foundation of China(NSFC)grant No.11972384 and the Guangdong MEPP Fund,grant No.GDOE[2019]A01.
文摘Orientations of laser induced periodic surface structures(LIPSS)are usually considered to be governed by the laser polarization state.In this work,we unveil that fluid dynamics induced by femtosecond(fs)laser ablation in liquid(fs-LAL)can easily break this polarization restriction to produce irregular circular-LIPSS(CLIPPS)and crisscross-LIPSS(CCLIPSS).Fs laser ablation of silicon in water shows formation of diverse LIPSS depending on ablation conditions.At a high power of 700 mW(repetition rate of 100 kHz,pulse duration of 457 fs and wavelength of 1045 nm),single/twin CLIPSS are produced at the bottom of macropores of several microns in diameter due to the formation of strong liquid vortexes and occurrence of the vortex shedding effect.Theoretical simulations validate our speculation about the formation of liquid vortex with an ultrahigh static pressure,which can induce the microstructure trenches and cracks at the sidewalls for fs-LAL of Si and tungsten(W)in water,respectively.At a low power of 50 mW,weak liquid vortexes are produced,which only give birth to curved LIPSS in the valleys of grooves.Consequently,it is deduced that liquid vortex plays a crucial role in the formation of macropores.Mountain-like microstructures induce complex fluid dynamics which can cause the formation of CCLIPSS on them.It is believed that liquid vortexes and fluid dynamics presented in this work open up new possibilities to diversify the morphologies of LIPSS formed by fs-LAL.
基金Sponsored by National Program on Key Basic Research Project(2011CB403303)A Special Fund for Central Public Welfare Research Institutes(HKY-2011-15)
文摘This paper selected the typical wind-water erosion crisscross region Xiliugou watershed for research to reveal the impact of the landscape pattern change of the underlying surface in wind-water erosion crisscross region where soil erosion is most serious on rainfall and runoff as well as erosion and sediment.Based on the Landsat TM image data and measured data of runoff-sediment in that watershed,the paper analyzed the characteristics of watershed landscape pattern change and runoff-sediment and explored the relationship between landscape index and runoff-sediment yield by means of GIS and Fragstats.The results were included as follows.(1)Grassland was the dominant landscape.In terms of the number of patches and area change rate,from 1985 to 2010,cultivated land,forest land and construction land were most stable,followed by unused land.Unused land,grassland and cultivated land experienced the most dramatic conversion and maximally affected by human activities.(2)The inter-annual difference between annual runoff and annual sediment load was significant.Compared with the annual sediment load,the trend of decreasing runoff was more obvious.The correlation coefficient of runoff-sediment was 0.67,representing a significant correlation.(3)There was a significant correlation between the landscape index and runoff-sediment.The runoff was negatively correlated with the largest patch index,patch cohesion index,aggregation index and contagion index,but positively correlated with landscape morphology index and landscape division index.And the sediment was negatively correlated with the contagion index,aggregation index and plaque cohesion index,but positively correlated with other landscape indexes.The results indicate that with the increase of the largest patch index,patch cohesion index and aggregation index,the rainfall infiltration capacity increase obviously and the soil erosion reduce significantly.Therefore,increasing the largest patch index,patch cohesion and aggregation index of the watershed landscape can enhance the function of water storage and soil conservation as well as ecological optimization in the windwater erosion crisscross region.The results can provide theoretical support for the ecological environment construction and comprehensive utilization of water and soil resources.
基金Supported by the National Natural Science Foundation of China under Grant Nos. 10872065, 50801025Hunan Provincial Innovation Foundation for Postgraduate under Grant No. CX2009B067
文摘Shielding effect and emission criterion of a screw dislocation near an interracial crisscross crack are dealt within this paper. Utilizing the conformal mapping technique, the closed-form solutions are derived for complex potentialsand stress fields due to a screw dislocation located near the interracial crisscross crack. The stress intensity factor onthe crack tips and the critical stress intensity factor for dislocation emission are also calculated. The influence of theorientation of the dislocation and the morphology of the crisscross crack as well as the material elastic dissimilarity onthe shielding effect and the emission criterion is discussed in detail. The results show that positive screw dislocations canreduce the stress intensity factor of the interracial crisscross crack tip (shielding effect). The shielding effect increases withthe increase of the shear modulus of the lower half-plane, but it decreases with the increase of the dislocation azimuthangle and the distance between the dislocation and the crack tip. The critical loads at infinity for dislocation emissionincreases with the increase of emission angle and the vertical length of the crisscross crack, and the most probable anglefor screw dislocation emission is zero. The present solutions contain previous results as special cases.
基金Under the auspices of National Basic Research Program of China(No.2011CB403303)Innovation Scientists and Technicians Troop Construction Projects of Henan Province(No.162101510004)Foundation of Yellow River Institute of Hydraulic Research of China(No.HKY-2011-15)
文摘All characteristics of vegetation,runoff and sediment from 1960 to 2010 in the Xiliu Gully Watershed,which is a representative watershed in wind-water erosion crisscross region in the upper reaches of the Yellow River of China,have been analyzed in this study.Based on the remote sensing image data,and used multi-spectral interpretation method,the characteristics of vegetation variation in the Xiliu Gully Watershed have been analyzed.And the rules of precipitation,runoff and sediment's changes have been illuminated by using mathematical statistics method.What′s more,the influence mechanism of vegetation on runoff and sediment has been discussed by using the data obtained from artificial rainfall simulation test.The results showed that the main vegetation type was given priority to low coverage,and the area of the low vegetation coverage type was reducing year by year.On the country,the area of the high vegetation coverage type was gradually increasing.In a word,vegetation conditions had got better improved since 2000 when the watershed management project started.The average annual precipitation of the river basin also got slightly increase in 2000–2010.The average annual runoff reduced by 37.5%,and the average annual sediment reduced by 73.9% in the same period.The results of artificial rainfall simulation tests showed that the improvement of vegetation coverage could increase not only soil infiltration but also vegetation evapotranspiration,and then made the rainfall-induced runoff production decrease.Vegetation root system could increases the resistance ability of soil to erosion,and vegetation aboveground part could reduce raindrop kinetic energy and splash soil erosion.Therefore,with the increase of vegetation coverage,the rainfall-induced sediment could decrease.
文摘To solve the problem of slow convergence and easy to get into the local optimum of the spider monkey optimization algorithm,this paper presents a new algorithm based on multi-strategy(ISMO).First,the initial population is generated by a refracted opposition-based learning strategy to enhance diversity and ergodicity.Second,this paper introduces a non-linear adaptive dynamic weight factor to improve convergence efficiency.Then,using the crisscross strategy,using the horizontal crossover to enhance the global search and vertical crossover to keep the diversity of the population to avoid being trapped in the local optimum.At last,we adopt a Gauss-Cauchy mutation strategy to improve the stability of the algorithm by mutation of the optimal individuals.Therefore,the application of ISMO is validated by ten benchmark functions and feature selection.It is proved that the proposed method can resolve the problem of feature selection.
