Study on Characteristics of a High-Precision Cold Gas Micro Thruster

In order to improve the reliability of the spacecraft micro cold gas propulsion system and realize the precise control of the spacecraft attitude and orbit, a micro-thrust, high-precision cold gas thruster is carried out, at the same time due to the design requirements of the spacecraft, this micro-thrust should be continuous working more than 60 minutes, the traditional solenoid valve used for the thrusts can’t complete the mission, so a long-life micro latching valve is developed as the control valve for this micro thruster, because the micro latching valve can keep its position when it cuts off the outage. Firstly, the authors introduced the design scheme and idea of the thruster. Secondly, the performance of the latching valve and the flow characteristics of the nozzle were simulated. Finally, from the experimental results and compared with the numerical study, it shows that the long-life micro cold gas thruster developed in this paper meets the mission requirements.

Amino-functionalized UiO-66-doped mixed matrix membranes with high permeation performance and fouling resistance

For the reduction of bovine serum proteins from wastewater,a novel mixed matrix membrane was prepared by functionalizing the substrate material polyaryletherketone(PAEK),followed by carboxyl groups(C-SPAEKS),and then adding amino-functionalized UiO-66-NH_(2)(Am-UiO-66-NH_(2)).Aminofunctionalization of UiO-66 was accomplished by melamine,followed by an amidation reaction to immobilize Am-UiO-66-NH_(2),which was immobilized on the surface of the membrane as well as in the pore channels,which enhanced the hydrophilicity of the membrane surface while increasing the negative potential of the membrane surface.This nanoparticle-loaded ultrafiltration membrane has good permeation performance,with a pure water flux of up to 482.3 L·m^(-2)·h^(-1) for C-SPAEKS/AmUiO-66-NH_(2) and a retention rate of up to 98.7%for bovine serum albumin(BSA)-contaminated solutions.Meanwhile,after several hydrophilic modifications,the flux recovery of BSA contaminants by this series of membranes increased from 56.2%to 80.55%of pure membranes.The results of ultra-filtration flux time tests performed at room temperature showed that the series of ultrafiltration membranes remained relatively stable over a test time of 300 min.Thus,the newly developed mixed matrix membrane showed potential for high efficiency and stability in wastewater treatment containing bovine serum proteins.

Amine-functionalized metal organic framework@graphene oxide as filler in PAEK-containing carboxyl group membrane for ultrafiltration with ultra-high permeability and strong fouling resistance

Achieving high fouling resistance and permeability using membrane separation technology in water treatment processes remains a challenge.In this work,a novel mixed-matrix membrane(MMM)(poly(arylene ether ketone)[PAEK]-containing carboxyl groups[PAEK-COOH]/UiO-66-NH_(2)@graphene oxide[GO])with superb fouling resistance and high permeability was prepared by the nonsolvent-induced phase separation method,by in-situ growth of UiO-66-NH_(2) on the GO layer,and by preparing hydrophilic PAEK-COOH.On the basis of the structure and performance analysis of the MMM,the maximum water flux reached 591.25 L·m^(-2)·h^(-1) for PAEK-COOH/UiO-66-NH_(2)@GO,whereas the retention rate for bovine serum albumin increased from 85.40%to 94.87%.As the loading gradually increased,the hydrophilicity of the MMMs increased,significantly enhancing their fouling resistance.The strongest anti-fouling ability observed was 94.74%,which was 2.02 times greater than that of the pure membrane.At the same time,the MMMs contained internal amide and hydrogen bonds during the preparation process,forming a cross-linked structure,which further enhanced the mechanical strength and chemical stability.In summary,the MMMs with high retention rate,strong permeability,and anti-fouling ability were successfully prepared.

Hydrologic Response of the Climatic Change Based on SWAT Model in Beijiang River Basin

[ Objective] The research aimed to establish SWAT distributed hydrologic model and analyze influence of the climatic change on runoff in Beijiang River basin. [ Method] Beijiang River basin as research object, SWAT model was used to simulate runoff in basin. Monthly water flow in Shijiao station from 1961 to 1980 was used to determine model parameter, while monthly water flow from 1981 to 1990 was used to verify. Setting 15 kinds of climate change scenarios, SWAT model was used to simulate influence of the future climatic change on runoff in Beijiang River basin. [Result] Simulated accuracy of the SWAT model was high, and it could be used to simulate runoff in Beijiang River basin. Under the situation of in- variable rainfall, temperature rise made that evaporation capacity increased, and runoff depth decreased. When temperature unchanged, rainfall increase made that evaporation capacity and runoff depth increased somewhat. [ Conclusion] The research could provide reference basis for water re- source management in Beijiang River basin.

Heavy Metal Emission Characteristics of Urban Road Runoff

Pavement runoff sampling points were set up on the main roads of Chengdu city.Six rainfall-runoff events from July to September in 2017 were sampled by synchronous observation of rainfall,runoff and pollution.The concentration changes of copper,lead,zinc,chromium and cadmium in the runoff process were monitored,and the pollution emission regularity and initial scouring effect were studied.The results show that the emission regularity of pavement runoff pollution is closely related to rainfall characteristics and pollutant occurrence,and the concentration of dissolved heavy metals reaches its peak at the initial stage of runoff.The peak time of particulate heavy metal concentration lagged slightly behind that of rainfall intensity.There is a big difference between the strength of initial scouring degree and dissolved heavy metals the stronger the initial scouring degree of total heavy metals,the weaker the dissolved heavy metals.Reducing pavement runoff in the early stage of rainfall is an effective means to control heavy metal pollution.

A Framework on Fast Mapping of Urban Flood Based on a Multi-Objective Random Forest Model

Fast and accurate prediction of urban flood is of considerable practical importance to mitigate the effects of frequent flood disasters in advance.To improve urban flood prediction efficiency and accuracy,we proposed a framework for fast mapping of urban flood:a coupled model based on physical mechanisms was first constructed,a rainfall-inundation database was generated,and a hybrid flood mapping model was finally proposed using the multi-objective random forest(MORF)method.The results show that the coupled model had good reliability in modelling urban flood,and 48 rainfall-inundation scenarios were then specified.The proposed hybrid MORF model in the framework also demonstrated good performance in predicting inundated depth under the observed and scenario rainfall events.The spatial inundated depths predicted by the MORF model were close to those of the coupled model,with differences typically less than 0.1 m and an average correlation coefficient reaching 0.951.The MORF model,however,achieved a computational speed of 200 times faster than the coupled model.The overall prediction performance of the MORF model was also better than that of the k-nearest neighbor model.Our research provides a novel approach to rapid urban flood mapping and flood early warning.

Selective photo-reduction of nitrate to nitrogen with a two-step process by a KBH_(4)/Cu(II)modified CuFe_(2)O_(4)photocatalyst

Nitrate(NO_(3)^(-))removal by photochemical-reduction has received extensive attention.However,the low selectivity of NO_(3)^(-)reduction to N_(2)hinders the application of this technology.In this study,a novel Cu@Fe-Cu-CuFe_(2)O_(4)-x photocatalyst was prepared by modifying CuFe_(2)O_(4)with KBH4 and Cu(II),and used to selectively reduce NO_(3)^(-)to N_(2)with a two-step reduction process.In step(1),with Cu@Fe-Cu-CuFe_(2)O_(4)-x/ultraviolet(UV)system,91.0%NO_(3)^(-)was reduced to 52.3%NO_(2)-and 39.4%N_(2)within 60 min.The rapid removal of NO_(3)^(-)was due to the synergistic effect of oxygen vacancies,Fe-Cu corrosion cell,and CuFe_(2)O_(4)photocatalysis.In step(2),H_(2)C_(2)O_(4)and H_(2)O_(2)were introduced into the effluent of step(1)to promote CO_(2)·-formation via Fe(II)and Fe(III)catalysis and UV radiation,which boosted the selective reduction of NO_(2)-to N_(2).When H_(2)C_(2)O_(4)and H_(2)O_(2)dosages were both 4.0 mmol·L^(-1)and the reaction time was 30 min,the removal efficiency of NO_(2)-achieved 100%and the selectivity of N_(2)was 83.0%.Overall,the two-step reduction process achieved 95.0%NO_(3)^(-)removal efficiency and 90.1%N_(2)selectivity with initial NO_(3)^(-)concentration of 30 mg·N·L^(-1).In addition,the denitrification mechanism of the two-step reduction process was tentatively proposed.

Simulation Performance Evaluation and Uncertainty Analysis on a Coupled Inundation Model Combining SWMM and WCA2D

Urban floods are becoming increasingly more frequent,which has led to tremendous economic losses.The application of inundation modeling to predict and simulate urban flooding is an effective approach for disaster prevention and risk reduction,while also addressing the uncertainty problem in the model is always a challenging task.In this study,a cellular automaton(CA)-based model combining a storm water management model(SWMM)and a weighted cellular automata 2D inundation model was applied and a physical-based model(LISFLOOD-FP)was also coupled with SWMM for comparison.The simulation performance and the uncertainty factors of the coupled model were systematically discussed.The results show that the CA-based model can achieve sufficient accuracy and higher computational efficiency than can a physical-based model.The resolution of terrain and rainstorm data had a strong influence on the performance of the CA-based model,and the simulations would be less creditable when using the input data with a terrain resolution lower than 15 m and a recorded interval of rainfall greater than 30 min.The roughness value and model type showed limited impacts on the change of inundation depth and occurrence of the peak inundation area.Generally,the CA-based coupled model demonstrated laudable applicability and can be recommended for fast simulation of urban flood episodes.This study also can provide references and implications for reducing uncertainty when constructing a CA-based coupled model.

Nitrogen-doped carbon nanotubes by multistep pyrolysis process as a promising anode material for lithium ion hybrid capacitors

Lithium-ion hybrid capacitors(LIHCs) is a promising electrochemical energy storage devices which combines the advantages of lithium-ion batteries and capacitors.Herein,we developed a facile multistep pyrolysis method,prepared an amorphous structure and a high-level N-doping carbon nanotubes(NCNTs),and by removing the Co catalyst,opening the port of NCNTs,and using NCNTs as anode material.It is shows good performance due to the electrolyte ions enter into the electrode materials and facilitate the charge transfer.Furthermore,we employ the porous carbon material(APDC) as the cathode to couple with anodes of NCNTs,building a LIHCs,it shows a high energy density of 173 Wh/kg at 200 W/kg and still retains 53 Wh/kg at a high power density of 10 kW/kg within the voltage window of 0-4.0 V,as well as outstanding cyclic life keep 80% capacity after 5000 cycles.This work provides an opportunity for the preparation of NCNTs,that is as a promising high-performance anode for LIHCs.