Electromagnetic wave absorbing materials are urgently required in the fields of medicine,communication,and military.However,the thickness,weight,narrow effective bandwidth,and weak absorbing ability of the materials r...Electromagnetic wave absorbing materials are urgently required in the fields of medicine,communication,and military.However,the thickness,weight,narrow effective bandwidth,and weak absorbing ability of the materials restrict their further application.In this work,a double-layer hollow nanocube with a dielectric titanium dioxide(TiO_(2))shell and a magnetic CoFe oxide inner shell is prepared.Prussian blue(PB)is prepared by the hydrothermal method,and used as the template to prepare PB@CoFe PB analogue(PBA).After selective etching and further calcination,hollow CoFe oxide particles are obtained.The obtained particles are then coated with SiO_(2)and TiO_(2),respectively,and the intermediate layer is dislodged to obtain the final CoFe oxide@TiO_(2)with the hollow double shell structure.The obtained double-layer hollow structure can effectively capture the incident electromagnetic waves,and increase the propagation path.Moreover,the obvious enhancement of interface polarization and the improvement of impedance matching enhance the wave absorbing ability of the material.The analysis results show that,the structure is stable and the dispersion is good.The maximum reflection loss(RL)at 10 GHz is as high as-46.1 dB with the sample thickness of 1.6 mm.The light-weight and high-efficiency CoFe oxide@TiO_(2)absorber is promised to be used in commercial and military aerospace fields.展开更多
The paper is concerned with the fluid flow in the impeller side clearances of a centrifugal pump with volute cas-ing.The flow conditions in these small axial gaps are of significant importance for a number of effects ...The paper is concerned with the fluid flow in the impeller side clearances of a centrifugal pump with volute cas-ing.The flow conditions in these small axial gaps are of significant importance for a number of effects such as disk friction,leakage losses or hydraulic axial thrust to name but a few.In the investigated single stage pump,the flow pattern in the volute turns out to be asymmetric even at design flow rate.To gain a detailed insight into the flow structure,numerical simulations of the complete pump including the impeller side clearances are accom-plished.Additionally,the hydraulic head and the radial pressure distributions in the impeller side clearances are measured and compared with the numerical results.Two configurations of the impeller,either with or without balancing holes,are examined.Moreover,three different operating points,i.e.:design point,part load or overload conditions are considered.In addition,analytical calculations are accomplished to determine the pressure distri-butions in the impeller side clearances.If accurate boundary conditions are available,the 1D flow models used in this paper can provide reasonable results for the radial static pressure distribution in the impeller side clearances.Furthermore,a counter rotating wake region develops in the rear impeller side clearances in absence of balancing holes which severely affects the inflow and outflow conditions of the cavity in circumferential direction.展开更多
In this paper,an analytic method is developed to address steady SH-wave scattering and perform dynamic analysis of multiple circular cavities in half space.The scattered wave function used for scattering of SH-waves b...In this paper,an analytic method is developed to address steady SH-wave scattering and perform dynamic analysis of multiple circular cavities in half space.The scattered wave function used for scattering of SH-waves by multiple circular cavities,which automatically satisfies the stress-free condition at the horizontal surface,is constructed by applying the symmetry of the SH-wave scattering and the method of multi-polar coordinates system.Applying this scattered wave function and method of moving coordinates,the original problem can be transformed to the problem of SH-wave scattering by multiple circular cavities in the full space.Finally,the solution of the problem can be reduced to a series of algebraic equations and solved numerically by truncating the infinite algebraic equations to the finite ones.Numerical examples are provided for case with two cavities to show the effect of wave number,and the distances between the centers of the cavities and from the centers to the ground surface on the dynamic stress concentration around the cavity impacted by incident steady SH-wave.展开更多
The autonomous and controllable Dual Synthetic Jet Actuator(DSJA)is firstly integrated into the Unmanned Aerial Vehicle(UAV),and flight tests without the deflection of rudders are carried out to verify the viability o...The autonomous and controllable Dual Synthetic Jet Actuator(DSJA)is firstly integrated into the Unmanned Aerial Vehicle(UAV),and flight tests without the deflection of rudders are carried out to verify the viability of DSJA to control the attitudes of UAV during cruising.DSJA is improved into an actuator with two diaphragms and three cavities,which has higher energy levels.Actuators,differentially distributed on both sides of the wings,are installed on the trailing edge close to the wing tips.Flight tests,containing Differential Circulation Control(DCC)using double-side actuators,Positive Circulation Control(PCC)using left-side actuators and Negative Circulation Control(NCC)using right-side actuators,are implemented at cruising speed of 25 m/s.Results show that roll attitude control without rudders could be realized by DSJAs.DCC and NCC can generate the rightward roll and yaw angular velocity,prompting UAV to turn right.The stronger controlling ability can be achieved by DCC,with the maximum roll angular velocity of 15.62(°)/s.PCC can generate a rightward roll moment,but a leftward yaw moment will be produced at the same time.Leftward yaw induces the leftward rolling moment,which weakens the roll control effect,making UAV keep to yaw to the left with a small slope.展开更多
We give a brief review of the developments in terahertz time-domain spectroscopy(THz-TDS) systems and microcavity components for probing samples in the University of Shanghai for Science and Technology. The broadband ...We give a brief review of the developments in terahertz time-domain spectroscopy(THz-TDS) systems and microcavity components for probing samples in the University of Shanghai for Science and Technology. The broadband terahertz(THz) radiation sources based on GaAs m-i-n diodes have been investigated by applying high electric fields. Then, the free space THz-TDS and fiber-coupled THz-TDS systems produced in our lab and their applications in drug/cancer detection are introduced in detail. To further improve the signal-to-noise ratio(SNR) and enhance sensitivity, we introduce three general micro-cavity approaches to achieve tiny-volume sample detection, summarizing our previous results about their characteristics, performance, and potential applications.展开更多
We propose and experimentally demonstrate a 2×2 thermo-optic(TO) crossbar switch implemented by dual photonic crystal nanobeam(PCN)cavities within a silicon-on-insulator(SOI)platform.By thermally tuning the refra...We propose and experimentally demonstrate a 2×2 thermo-optic(TO) crossbar switch implemented by dual photonic crystal nanobeam(PCN)cavities within a silicon-on-insulator(SOI)platform.By thermally tuning the refractive index of silicon,the resonance wavelength of the PCN cavities can be red-shifted.With the help of the ultrasmall mode volumes of the PCN cavities,only～0.16 mW power is needed to change the switching state.With a spectral passband of 0.09 nm at the 1583.75 nm operation wavelength,the insertion loss(IL)and crosstalk(CT)performances were measured as IL(bar)=-0.2 dB,CT(bar)=-15 dB,IL(cross)=-1.5 dB,and CT(cross)=-15 dB.Furthermore,the thermal tuning efficiency of the fabricated device is as high as1.23 nm/mW.展开更多
基金the National Natural Science Foundation of China(Nos.51773060,5207309151573045)the Shanghai Key Laboratory of Advanced Polymer Materials。
文摘Electromagnetic wave absorbing materials are urgently required in the fields of medicine,communication,and military.However,the thickness,weight,narrow effective bandwidth,and weak absorbing ability of the materials restrict their further application.In this work,a double-layer hollow nanocube with a dielectric titanium dioxide(TiO_(2))shell and a magnetic CoFe oxide inner shell is prepared.Prussian blue(PB)is prepared by the hydrothermal method,and used as the template to prepare PB@CoFe PB analogue(PBA).After selective etching and further calcination,hollow CoFe oxide particles are obtained.The obtained particles are then coated with SiO_(2)and TiO_(2),respectively,and the intermediate layer is dislodged to obtain the final CoFe oxide@TiO_(2)with the hollow double shell structure.The obtained double-layer hollow structure can effectively capture the incident electromagnetic waves,and increase the propagation path.Moreover,the obvious enhancement of interface polarization and the improvement of impedance matching enhance the wave absorbing ability of the material.The analysis results show that,the structure is stable and the dispersion is good.The maximum reflection loss(RL)at 10 GHz is as high as-46.1 dB with the sample thickness of 1.6 mm.The light-weight and high-efficiency CoFe oxide@TiO_(2)absorber is promised to be used in commercial and military aerospace fields.
文摘The paper is concerned with the fluid flow in the impeller side clearances of a centrifugal pump with volute cas-ing.The flow conditions in these small axial gaps are of significant importance for a number of effects such as disk friction,leakage losses or hydraulic axial thrust to name but a few.In the investigated single stage pump,the flow pattern in the volute turns out to be asymmetric even at design flow rate.To gain a detailed insight into the flow structure,numerical simulations of the complete pump including the impeller side clearances are accom-plished.Additionally,the hydraulic head and the radial pressure distributions in the impeller side clearances are measured and compared with the numerical results.Two configurations of the impeller,either with or without balancing holes,are examined.Moreover,three different operating points,i.e.:design point,part load or overload conditions are considered.In addition,analytical calculations are accomplished to determine the pressure distri-butions in the impeller side clearances.If accurate boundary conditions are available,the 1D flow models used in this paper can provide reasonable results for the radial static pressure distribution in the impeller side clearances.Furthermore,a counter rotating wake region develops in the rear impeller side clearances in absence of balancing holes which severely affects the inflow and outflow conditions of the cavity in circumferential direction.
文摘In this paper,an analytic method is developed to address steady SH-wave scattering and perform dynamic analysis of multiple circular cavities in half space.The scattered wave function used for scattering of SH-waves by multiple circular cavities,which automatically satisfies the stress-free condition at the horizontal surface,is constructed by applying the symmetry of the SH-wave scattering and the method of multi-polar coordinates system.Applying this scattered wave function and method of moving coordinates,the original problem can be transformed to the problem of SH-wave scattering by multiple circular cavities in the full space.Finally,the solution of the problem can be reduced to a series of algebraic equations and solved numerically by truncating the infinite algebraic equations to the finite ones.Numerical examples are provided for case with two cavities to show the effect of wave number,and the distances between the centers of the cavities and from the centers to the ground surface on the dynamic stress concentration around the cavity impacted by incident steady SH-wave.
基金co-supported by the National Natural Science Foundation of China(Nos.11972369,11872374)the Youth Science and Technology Innovation Award Funded Project of National University of Defense Technology,China(No.434517314)。
文摘The autonomous and controllable Dual Synthetic Jet Actuator(DSJA)is firstly integrated into the Unmanned Aerial Vehicle(UAV),and flight tests without the deflection of rudders are carried out to verify the viability of DSJA to control the attitudes of UAV during cruising.DSJA is improved into an actuator with two diaphragms and three cavities,which has higher energy levels.Actuators,differentially distributed on both sides of the wings,are installed on the trailing edge close to the wing tips.Flight tests,containing Differential Circulation Control(DCC)using double-side actuators,Positive Circulation Control(PCC)using left-side actuators and Negative Circulation Control(NCC)using right-side actuators,are implemented at cruising speed of 25 m/s.Results show that roll attitude control without rudders could be realized by DSJAs.DCC and NCC can generate the rightward roll and yaw angular velocity,prompting UAV to turn right.The stronger controlling ability can be achieved by DCC,with the maximum roll angular velocity of 15.62(°)/s.PCC can generate a rightward roll moment,but a leftward yaw moment will be produced at the same time.Leftward yaw induces the leftward rolling moment,which weakens the roll control effect,making UAV keep to yaw to the left with a small slope.
基金the National Key R&D Program of China (No. 2018YFF01013003)the Program of Shanghai Pujiang Program, China (No. 17PJD028)+4 种基金the National Natural Science Foundation of China (Nos. 61671302, 61601291, and 61722111)the Shuguang Program supported by the Shanghai Education Development Foundation and Shanghai Municipal Education Commission, China (No. 18SG44)the Key Scientific and Technological Project of Science and Technology Commission of Shanghai Municipality, China (No. 15DZ0500102)the Shanghai Leading Talent, China (No. 2016-019)the Young Yangtse Rive Scholar, China (No. Q2016212).
文摘We give a brief review of the developments in terahertz time-domain spectroscopy(THz-TDS) systems and microcavity components for probing samples in the University of Shanghai for Science and Technology. The broadband terahertz(THz) radiation sources based on GaAs m-i-n diodes have been investigated by applying high electric fields. Then, the free space THz-TDS and fiber-coupled THz-TDS systems produced in our lab and their applications in drug/cancer detection are introduced in detail. To further improve the signal-to-noise ratio(SNR) and enhance sensitivity, we introduce three general micro-cavity approaches to achieve tiny-volume sample detection, summarizing our previous results about their characteristics, performance, and potential applications.
基金National Natural Science Foundation of China(NSFC)(61235007,61505104,61605112)Science and Technology Commission of Shanghai Municipality(15ZR1422800,16XD1401400)National Key R&D Program of China(2016YFB0402501)
文摘We propose and experimentally demonstrate a 2×2 thermo-optic(TO) crossbar switch implemented by dual photonic crystal nanobeam(PCN)cavities within a silicon-on-insulator(SOI)platform.By thermally tuning the refractive index of silicon,the resonance wavelength of the PCN cavities can be red-shifted.With the help of the ultrasmall mode volumes of the PCN cavities,only～0.16 mW power is needed to change the switching state.With a spectral passband of 0.09 nm at the 1583.75 nm operation wavelength,the insertion loss(IL)and crosstalk(CT)performances were measured as IL(bar)=-0.2 dB,CT(bar)=-15 dB,IL(cross)=-1.5 dB,and CT(cross)=-15 dB.Furthermore,the thermal tuning efficiency of the fabricated device is as high as1.23 nm/mW.
