Hydrological Characteristics of the Heihe River Basin in the Arid Inland Area of Northwest China

The hydrological characteristics of the Heihe River Basin in the arid inland area of northwest China were investigated.The spatial distribution of annual precipitation in the basin indicates that it decreases from east to west and from south to north,and increases with elevation by a gradient of 24.4 mm per hundred meters below 2,810 m a.s.l.,but decreases with elevation by that of 37.0 mm per hundred meters above 2,810 m a.s.l.For the last 50 years,the mountain runoff of the ba-sin has a tendency of increase.Except in the mountain area,the aridity is very high in the basin,and the aridity index ranges from 1.6 to 7.0 at the piedmont,to 9.0～20.0 in the midstream area and up to 40.0 in the downstream Ejin region.It is estimated for the last 50 years that a 1oC increment of annual temperature causes a 21.5 mm increase of evaporation in the mountain area,and the equivalent reduction of mountain runoff is 0.215×109 m3/yr at the Yingluoxia Hydrometric Sta-tion.The estimation shows also that a 1oC increment of annual temperature causes 1,842 mm increase of farmland evapotranspiration in the midstream area,an equivalent of 0.298×109 m3/yr more water consumption.The anthropogenic influence on the hydrological processes and water resources is then discussed.

Electron-Beam Irradiation Induced Regulation of Surface Defects in Lead Halide Perovskite Thin Films

Organic-inorganic hybrid perovskites(OIHPs)have been intensively studied due to their fascinating optoelectronic performance.Electron microscopy and related characterization techniques are powerful to figure out their structure-property relationships at the nanoscale.However,electron beam irradiation usually causes damage to these beam-sensitive materials and thus deteriorates the associated devices.Taking a widely used CH_(3)NH_(3)PbI_(3)film as an example,here,we carry out a comprehensive study on how electron beam irradiation affects its properties.Interestingly,our results reveal that photoluminescence(PL)intensity of the film can be significantly improved along with blue-shift of emission peak at a specific electron beam dose interval.This improvement stems from the reduction of trap density at the CH_(3)NH_(3)PbI_(3)surface.The knock-on effect helps expose a fresh surface assisted by the surface defect-induced lowering of displacement threshold energy.Meanwhile,the radiolysis process consistently degrades the crystal structure and weaken the PL emission with the increase of electron beam dose.Consequently,the final PL emission comes from a balance between knock-on and radiolysis effects.Taking advantage of the defect regulation,we successfully demonstrate a patterned CH_(3)NH_(3)PbI_(3)film with controllable PL emission and a photodetector with enhanced photocurrent.This work will trigger the application of electron beam irradiation as a powerful tool for perovskite materials processing in micro-LEDs and other optoelectronic applications.