The nonlinear dynamics of cantilevered piezoelectric beams is investigated under simultaneous parametric and external excitations. The beam is composed of a substrate and two piezoelectric layers and assumed as an Eul...The nonlinear dynamics of cantilevered piezoelectric beams is investigated under simultaneous parametric and external excitations. The beam is composed of a substrate and two piezoelectric layers and assumed as an Euler-Bernoulli model with inextensible deformation. A nonlinear distributed parameter model of cantilevered piezoelectric energy harvesters is proposed using the generalized Hamilton＇s principle. The proposed model includes geometric and inertia nonlinearity, but neglects the material nonlinearity. Using the Galerkin decomposition method and harmonic balance method, analytical expressions of the frequency-response curves are presented when the first bending mode of the beam plays a dominant role. Using these expressions, we investigate the effects of the damping, load resistance, electromechanical coupling, and excitation amplitude on the frequency-response curves. We also study the difference between the nonlinear lumped-parameter and distributed- parameter model for predicting the performance of the energy harvesting system. Only in the case of parametric excitation, we demonstrate that the energy harvesting system has an initiation excitation threshold below which no energy can be harvested. We also illustrate that the damping and load resistance affect the initiation excitation threshold.展开更多
Hydrogen energy is considered to be an ideal new energy carrier in the 21st century due to its clean,environmentally friendly,renewable characteristics and high energy density.The generation of hydrogen by hydrolysis ...Hydrogen energy is considered to be an ideal new energy carrier in the 21st century due to its clean,environmentally friendly,renewable characteristics and high energy density.The generation of hydrogen by hydrolysis of Mg-based alloys/hydrides has attracted extensive attention attributed to the high hydrogen yield,environmentally-benign by-products,high crust abundance,and well-developed industrial production of Mg.However,in the hydrolysis process of Mg or MgH_(2)to generate hydrogen,the formed Mg(OH)_(2)passivation layer attaches to the surface of the active materials to prevent the reaction from continuing.To improve the hydrolysis performance,a series of methods have been put forward.In this paper,focusing on the mechanisms of hydrogen generation by hydrolysis of Mg-based alloys/hydrides,we summarize the recent research progress from four different perspectives:electrochemical corrosion promotion by constructing galvanic cells,active sites increment by refining the particles,mass transfer enhancement by breaking Mg(OH)_(2)and corresponding kinetic improvement.展开更多
What is known about this topic?Dengue fever is an acute febrile illness caused by four types of dengue virus(DENV 1–4),and is a mosquitoborne infectious disease.The incidence of dengue has increased dramatically arou...What is known about this topic?Dengue fever is an acute febrile illness caused by four types of dengue virus(DENV 1–4),and is a mosquitoborne infectious disease.The incidence of dengue has increased dramatically around the world in recent decades.An estimated of 3.9 billion people in 128 countries are at risk of infection with dengue viruses,70%of whom are in Asia.In 2017,the first local infections of dengue virus(DENV-2)in Jiangxi Province was reported in Zhanggong District,Ganzhou City.What is added by this report?From August to September 2019,the first dengue outbreak happened in Xin’gan County,where 81 local dengue fever cases were reported,35 were laboratoryconfirmed cases,and 46 were clinically-diagnosed cases;all cases were dengue virus type 1.The DENV-virus strains isolated from the cases of Xin’gan County were close to the strains isolated in Singapore(MF033254|25657|Singapore|2016)and Henan(MK905537|He nan201903|China:Henan Province|2019).What are the implications for public health practice?The outbreak might have been caused by imported cases or covert infections.The outbreak in Xin’gan County indicated that more proactive countermeasures should be taken during the dengue epidemic period such as intensifying surveillance for dengue cases,virus serotype,and Aedes vector density and strengthening cooperation with customs and tourism departments.Moreover,the outbreak should prompt training in medical institutions and improved ability for doctor’s to diagnose dengue fever,which is very important for early detection of dengue cases and taking preventive measures.展开更多
基金supported by the National Natural Science Foundation of China (Grant 11172087)
文摘The nonlinear dynamics of cantilevered piezoelectric beams is investigated under simultaneous parametric and external excitations. The beam is composed of a substrate and two piezoelectric layers and assumed as an Euler-Bernoulli model with inextensible deformation. A nonlinear distributed parameter model of cantilevered piezoelectric energy harvesters is proposed using the generalized Hamilton＇s principle. The proposed model includes geometric and inertia nonlinearity, but neglects the material nonlinearity. Using the Galerkin decomposition method and harmonic balance method, analytical expressions of the frequency-response curves are presented when the first bending mode of the beam plays a dominant role. Using these expressions, we investigate the effects of the damping, load resistance, electromechanical coupling, and excitation amplitude on the frequency-response curves. We also study the difference between the nonlinear lumped-parameter and distributed- parameter model for predicting the performance of the energy harvesting system. Only in the case of parametric excitation, we demonstrate that the energy harvesting system has an initiation excitation threshold below which no energy can be harvested. We also illustrate that the damping and load resistance affect the initiation excitation threshold.
基金the National Key R&D Program(No.2022YFB3803700)Key R&D Program of Sichuan Province(No.2022YFG0116)the Fundamental Research Funds for Central Universities,China.
文摘Hydrogen energy is considered to be an ideal new energy carrier in the 21st century due to its clean,environmentally friendly,renewable characteristics and high energy density.The generation of hydrogen by hydrolysis of Mg-based alloys/hydrides has attracted extensive attention attributed to the high hydrogen yield,environmentally-benign by-products,high crust abundance,and well-developed industrial production of Mg.However,in the hydrolysis process of Mg or MgH_(2)to generate hydrogen,the formed Mg(OH)_(2)passivation layer attaches to the surface of the active materials to prevent the reaction from continuing.To improve the hydrolysis performance,a series of methods have been put forward.In this paper,focusing on the mechanisms of hydrogen generation by hydrolysis of Mg-based alloys/hydrides,we summarize the recent research progress from four different perspectives:electrochemical corrosion promotion by constructing galvanic cells,active sites increment by refining the particles,mass transfer enhancement by breaking Mg(OH)_(2)and corresponding kinetic improvement.
文摘What is known about this topic?Dengue fever is an acute febrile illness caused by four types of dengue virus(DENV 1–4),and is a mosquitoborne infectious disease.The incidence of dengue has increased dramatically around the world in recent decades.An estimated of 3.9 billion people in 128 countries are at risk of infection with dengue viruses,70%of whom are in Asia.In 2017,the first local infections of dengue virus(DENV-2)in Jiangxi Province was reported in Zhanggong District,Ganzhou City.What is added by this report?From August to September 2019,the first dengue outbreak happened in Xin’gan County,where 81 local dengue fever cases were reported,35 were laboratoryconfirmed cases,and 46 were clinically-diagnosed cases;all cases were dengue virus type 1.The DENV-virus strains isolated from the cases of Xin’gan County were close to the strains isolated in Singapore(MF033254|25657|Singapore|2016)and Henan(MK905537|He nan201903|China:Henan Province|2019).What are the implications for public health practice?The outbreak might have been caused by imported cases or covert infections.The outbreak in Xin’gan County indicated that more proactive countermeasures should be taken during the dengue epidemic period such as intensifying surveillance for dengue cases,virus serotype,and Aedes vector density and strengthening cooperation with customs and tourism departments.Moreover,the outbreak should prompt training in medical institutions and improved ability for doctor’s to diagnose dengue fever,which is very important for early detection of dengue cases and taking preventive measures.
