To understand the discharge characteristics under a gap of micrometers,the breakdown voltage and current–voltage curve are measured experimentally in a needle-to-plate electrode at a microscale gap of 3–50 μm in ai...To understand the discharge characteristics under a gap of micrometers,the breakdown voltage and current–voltage curve are measured experimentally in a needle-to-plate electrode at a microscale gap of 3–50 μm in air.The effect of the needle radius and the gas pressure on the discharge characteristics are tested.The results show that when the gap is larger than 10 μm,the relation between the breakdown voltage and the gap looks like the Paschen curve;while below 10 μm,the breakdown voltage is nearly constant in the range of the tested gap.However,at the same gap distance,the breakdown voltage is still affected by the pressure and shows a trend similar to Paschen＇s law.The current–voltage characteristic in all the gaps is similar and follows the trend of a typical Townsend-to-glow discharge.A simple model is used to explain the non-normality of breakdown in the micro-gaps.The Townsend mechanism is suggested to control the breakdown process in this configuration before the gap reduces much smaller in air.展开更多
The deep structure of the eastward-subducting Indian plate can provide new information on the dynamics of the India-Eurasia collision.We collected and processed waveform data from temporary seismic arrays(networks)on ...The deep structure of the eastward-subducting Indian plate can provide new information on the dynamics of the India-Eurasia collision.We collected and processed waveform data from temporary seismic arrays(networks)on the eastern Tibetan Plateau,seismic arrays in Northeast India and Myanmar,and permanent stations of the China Digital Seismic Network in Tibet,Gansu,Qinghai,Yunnan,and Sichuan.We combined these data with phase reports from observation stations of the International Seismological Center on the Indian plate and selected 124,808 high-quality P-wave relative travel-time residuals.Next,we used these data to invert the 3-D P-wave velocity structure of the upper mantle to a depth of 800 km beneath the eastern segment of the arcuate Himalayan orogen,at the southeastern margin of the Tibetan Plateau.The results reveal a high-angle,easterly dipping subducting plate extending more than 200 km beneath the Indo-Myanmese arc.The plate breaks off at roughly 96°E;its fragments have passed through the 410-km discontinuity(D410)into the mantle transition zone(MTZ).The MTZ beneath the Tengchong volcanic area contains a high-velocity anomaly,which does not exceed the Red River fault to the east.No other large-scale continuous subducted plates were observed in the MTZ.However,a horizontally spreading high-velocity anomaly was identified on the D410 in some regions.The anomaly may represent the negatively buoyant 90°E Ridge plate or a thickened and delaminated lithospheric block experiencing collision and compression at the southeastern margin of the Tibetan Plateau.The Tengchong volcano may originate from the mantle upwelling through the slab window formed by the break-off of the subducting Indian continental plate and oceanic plate in the upper mantle.Low-velocity upper mantle materials on the west side of the Indo-Myanmese arc may have supplemented materials to the Tengchong volcano.展开更多
With the idea of the phononic crystals, a thin rectangular plate with two-dimensional periodic structure is designed. Flexural wave band structures of such a plate with infinite structure are calculated with the plane...With the idea of the phononic crystals, a thin rectangular plate with two-dimensional periodic structure is designed. Flexural wave band structures of such a plate with infinite structure are calculated with the plane-wave expansion （PWE） method, and directional band gaps are found in the ΓX direction. The acceleration frequency response in the ΓX direction of such a plate with finite structure is simulated with the finite element method and verified with a vibration experiment. The frequency ranges of sharp drops in the calculated and measured acceleration frequency response curves are in basic agreement with those in the band structures. Thin plate is a widely used component in the engineering structures. The existence of band gaps in such periodic structures gives a new idea in vibration control of thin plates.展开更多
基金supported by National Natural Science Foundation of China(11475019)the Electrostatic Research Foundation of Liu Shanghe Academicians and Experts Workstation,Beijing Orient Institute of Measurement and Test(BOIMTLSHJD20161002)
文摘To understand the discharge characteristics under a gap of micrometers,the breakdown voltage and current–voltage curve are measured experimentally in a needle-to-plate electrode at a microscale gap of 3–50 μm in air.The effect of the needle radius and the gas pressure on the discharge characteristics are tested.The results show that when the gap is larger than 10 μm,the relation between the breakdown voltage and the gap looks like the Paschen curve;while below 10 μm,the breakdown voltage is nearly constant in the range of the tested gap.However,at the same gap distance,the breakdown voltage is still affected by the pressure and shows a trend similar to Paschen＇s law.The current–voltage characteristic in all the gaps is similar and follows the trend of a typical Townsend-to-glow discharge.A simple model is used to explain the non-normality of breakdown in the micro-gaps.The Townsend mechanism is suggested to control the breakdown process in this configuration before the gap reduces much smaller in air.
基金This work is jointly supported by the Youth Program of National Natural Science Foundation of China(Nos.41874075 and 41904057)
文摘The deep structure of the eastward-subducting Indian plate can provide new information on the dynamics of the India-Eurasia collision.We collected and processed waveform data from temporary seismic arrays(networks)on the eastern Tibetan Plateau,seismic arrays in Northeast India and Myanmar,and permanent stations of the China Digital Seismic Network in Tibet,Gansu,Qinghai,Yunnan,and Sichuan.We combined these data with phase reports from observation stations of the International Seismological Center on the Indian plate and selected 124,808 high-quality P-wave relative travel-time residuals.Next,we used these data to invert the 3-D P-wave velocity structure of the upper mantle to a depth of 800 km beneath the eastern segment of the arcuate Himalayan orogen,at the southeastern margin of the Tibetan Plateau.The results reveal a high-angle,easterly dipping subducting plate extending more than 200 km beneath the Indo-Myanmese arc.The plate breaks off at roughly 96°E;its fragments have passed through the 410-km discontinuity(D410)into the mantle transition zone(MTZ).The MTZ beneath the Tengchong volcanic area contains a high-velocity anomaly,which does not exceed the Red River fault to the east.No other large-scale continuous subducted plates were observed in the MTZ.However,a horizontally spreading high-velocity anomaly was identified on the D410 in some regions.The anomaly may represent the negatively buoyant 90°E Ridge plate or a thickened and delaminated lithospheric block experiencing collision and compression at the southeastern margin of the Tibetan Plateau.The Tengchong volcano may originate from the mantle upwelling through the slab window formed by the break-off of the subducting Indian continental plate and oceanic plate in the upper mantle.Low-velocity upper mantle materials on the west side of the Indo-Myanmese arc may have supplemented materials to the Tengchong volcano.
基金This project is supported by National Basic Research Program of China (973Program, No.51307).
文摘With the idea of the phononic crystals, a thin rectangular plate with two-dimensional periodic structure is designed. Flexural wave band structures of such a plate with infinite structure are calculated with the plane-wave expansion （PWE） method, and directional band gaps are found in the ΓX direction. The acceleration frequency response in the ΓX direction of such a plate with finite structure is simulated with the finite element method and verified with a vibration experiment. The frequency ranges of sharp drops in the calculated and measured acceleration frequency response curves are in basic agreement with those in the band structures. Thin plate is a widely used component in the engineering structures. The existence of band gaps in such periodic structures gives a new idea in vibration control of thin plates.
