To estimate carbon sequestration potential in the karst area,soil respiration in a natural recovering karst abandoned farmland in Shawan,Puding,Guizhou,southwest China was continuously and automatically monitored for ...To estimate carbon sequestration potential in the karst area,soil respiration in a natural recovering karst abandoned farmland in Shawan,Puding,Guizhou,southwest China was continuously and automatically monitored for more than two years.The results show that the CO2flux of soil respiration(2.63±1.89 lmol m^-2s-^1)is higher in the karst area than in non-karst areas under similar conditions but that regional value(1.32 lmol m-2s-1)is lower because of larger rock fragment coverage(~50%).A the same time,the temperature sensitivity of soil respiration(Q10)in this study area is significantly higher than that of non-karst areas under similar conditions.Soil respiration has an obvious temporal variation,which is reflected in a significant exponential relationship between soil respiration and soil temperature,but the relationship between soil respiration and soil moisture is very complex.Especially soil respiration has an obvious spatial variation,which is likely affected by different diffusion or water-rock reaction processes.展开更多
The design approach and performance of a 22.5°/45°digital phase shifter based on a switched filter network for X-band phased arrays are described.Both the MMIC phase shifters are fabricated employing a 0.25 ...The design approach and performance of a 22.5°/45°digital phase shifter based on a switched filter network for X-band phased arrays are described.Both the MMIC phase shifters are fabricated employing a 0.25 m gate GaAs pHEMT process and share in the same chip size of 0.82 1.06 mm^2.The measurement results of the proposed phase shifters over the whole operating frequency range show that the phase shift error is less than 22.5°˙2.5°,45°˙3.5°,which shows an excellent agreement with the simulated performance,the insertion loss is within the range of 0.9–1.2 dB for the 22.5° phase shifter and 0.9–1.4 dB for the 45°phase shifter,and the input/output return loss is better than –12.5 and –11 dB respectively.They also achieve the similar P（1dB）continuous wave power handing capability of 24.8 dBm at 10 GHz.The phase shifters show a good phase shift error,insertion loss and return loss in the X-band（40%）,which can be employed into the wide bandwidth multi-bit digital phase shifter.展开更多
This is our first report on the high performance 1 mm AlGaN/GaN high electron mobility transistor(HEMT)which was developed using home-made AlGaN/GaN epitaxy structures based on SiC substrate.Metal-organic chemical vap...This is our first report on the high performance 1 mm AlGaN/GaN high electron mobility transistor(HEMT)which was developed using home-made AlGaN/GaN epitaxy structures based on SiC substrate.Metal-organic chemical vapor deposition(MOCVD)was used to generate the epitaxy layers.Corresponding experiments show that the device has a gate length of 0.8 mm exhibiting drain current density of 1.16 A/mm,transconductance of 241 ms/mm,a gate-drain break-down voltage larger than 80 V,maximum current gain frequency of 20 GHz and maximum power gain frequency of 28 GHz.In addition,the power gain under the continues wave condition is 14.2 dB with a power density of 4.1 W/mm,while under the pulsed wave condition,power gain reaches 14.4 dB with power density at 5.2 W/mm.Furthermore,the two-port network impedance characteristics display great potential in microwave application.展开更多
基金supported jointly by the National Key Research and Development Program of China(2016YFC0502300 and 2016YFC0502102)the United Fund of the Karst Science Research Center(No.U1612441)the National Natural Science Foundation of China(41571130042,41673121,and 41571130074)。
文摘To estimate carbon sequestration potential in the karst area,soil respiration in a natural recovering karst abandoned farmland in Shawan,Puding,Guizhou,southwest China was continuously and automatically monitored for more than two years.The results show that the CO2flux of soil respiration(2.63±1.89 lmol m^-2s-^1)is higher in the karst area than in non-karst areas under similar conditions but that regional value(1.32 lmol m-2s-1)is lower because of larger rock fragment coverage(~50%).A the same time,the temperature sensitivity of soil respiration(Q10)in this study area is significantly higher than that of non-karst areas under similar conditions.Soil respiration has an obvious temporal variation,which is reflected in a significant exponential relationship between soil respiration and soil temperature,but the relationship between soil respiration and soil moisture is very complex.Especially soil respiration has an obvious spatial variation,which is likely affected by different diffusion or water-rock reaction processes.
文摘The design approach and performance of a 22.5°/45°digital phase shifter based on a switched filter network for X-band phased arrays are described.Both the MMIC phase shifters are fabricated employing a 0.25 m gate GaAs pHEMT process and share in the same chip size of 0.82 1.06 mm^2.The measurement results of the proposed phase shifters over the whole operating frequency range show that the phase shift error is less than 22.5°˙2.5°,45°˙3.5°,which shows an excellent agreement with the simulated performance,the insertion loss is within the range of 0.9–1.2 dB for the 22.5° phase shifter and 0.9–1.4 dB for the 45°phase shifter,and the input/output return loss is better than –12.5 and –11 dB respectively.They also achieve the similar P（1dB）continuous wave power handing capability of 24.8 dBm at 10 GHz.The phase shifters show a good phase shift error,insertion loss and return loss in the X-band（40%）,which can be employed into the wide bandwidth multi-bit digital phase shifter.
基金This work was supported by the National Basic Research Program of China(No.2002CB311903 and G20000683)the funds of the Chinese Academy of Sciences for Key Topics in Innovation Engineering(No.KGCX2-SW-107).
文摘This is our first report on the high performance 1 mm AlGaN/GaN high electron mobility transistor(HEMT)which was developed using home-made AlGaN/GaN epitaxy structures based on SiC substrate.Metal-organic chemical vapor deposition(MOCVD)was used to generate the epitaxy layers.Corresponding experiments show that the device has a gate length of 0.8 mm exhibiting drain current density of 1.16 A/mm,transconductance of 241 ms/mm,a gate-drain break-down voltage larger than 80 V,maximum current gain frequency of 20 GHz and maximum power gain frequency of 28 GHz.In addition,the power gain under the continues wave condition is 14.2 dB with a power density of 4.1 W/mm,while under the pulsed wave condition,power gain reaches 14.4 dB with power density at 5.2 W/mm.Furthermore,the two-port network impedance characteristics display great potential in microwave application.
