Exploration of the mechanism of cavitation vortex rope and vortex development in the draft tube of tubular turbine units

Draft tube vortex rope is considered a special cavitation flow phenomenon in tubular turbine units.Cavitation vortex rope is one of the most detrimental factors affecting the safety of hydraulic turbines.In this study,ANSYS CFX software was utilized to numerically simulate the internal cavitation flow of a hydraulic turbine draft tube.The evolution of the cavitation vortex core was characterized by vortex line distribution and vorticity transport equation.The shape and number of blades influenced the revolving direction and distribution characteristics of the vortex close to the runner cone,which formed a counterclockwise-clockwise-counterclockwise distribution pattern.Simultaneously,there were many secondary flows in the draft tube.Mutual cancellation and dissipation between the flows was one of the reasons for reduction in vorticity.When the cross-sectional shape of the draft tube was changed,the vorticity was distributed from the center of the vortex rope to all parts of the cross-sectional draft tube,with extreme values at the center and at the walls.The vortex stretching and dilatation terms played a major role in the change in vorticity,with the baroclinic torque having an effect at the center of the vortex rope,this study is helpful to understand the flow of water in the draft tube and guide the design and optimization of the draft tube in engineering application.

China’s Drought Disaster Risk Management: Perspective of Severe Droughts in 2009–2010

China has been frequently and heavily affected by drought disasters. During 2009–2010, three large-scale severe droughts struck China, caused considerable social, economic, and ecological losses. These droughts showed significant regional differences. This study employs a two-stage transition framework comprising “entry” and “exit” transitions to discuss disaster risk management of drought in China, by taking the three droughts as comparative case studies. Chinese society’s response in the exit transition is examined and the underlying factors that enable the entry trigger are diagnosed. The policy responses that lead to the exit transition from these drought disasters were appropriate, but there is substantial room for improvement in management strategy regarding both entry and exit transitions. This article suggests that government policies should emphasize entry-prevention measures that reduce adverse impacts early in a drought episode rather than focus solely on improving performance in achieving a rapid exit transition from drought.

Microenvironment-responsive chemotherapeutic nanogels for enhancing tumor therapy via DNA damage and glutathione consumption

Although targeted therapy and immunotherapy are now shining in the treatment of some cancers,chemotherapy is still the cornerstone of drug treatment for many cancer patients.The emergence of chemotherapy prodrugs can improve the drug activity and reduce the side effects of chemotherapy.When used,the tumor microenvironment has characteristics different from normal tissues,and the existence of the microenvironment provided a more convenient way to design responsive nanodrugs.Herein,we designed a glutathione(GSH)-responsive prodrug nanogels for enhancing tumor chemotherapy.In the nanogels of HHNP,10-hydroxycamptothecin(HCPT)played an essential role in killing cancer cells.HCPT was jointed with a cross-linker agent with disulfide bond and was further coated with polyethylene glycol,which not only prolonged the half-life of the drug,but also made HCPT accurate transport to the tumor fractions and achieved precise and controllable release.The proposal of HHNP effectively retained the biological activity of the drug,and introduced functions such as targeting,selective release and biodegradation,which greatly improved the medical efficiency of the drug and effectively reduced the toxic and side effects.This chemotherapeutic prodrug nanogel offers a new window for constructing efficient drug delivery platform.