In order to precisely measure the ion parameters in a microwave electron cyclotron resonance plasma using an ion sensitive probe,the dependences of the current-voltage（I-V）characteristics on the shielding height（h...In order to precisely measure the ion parameters in a microwave electron cyclotron resonance plasma using an ion sensitive probe,the dependences of the current-voltage（I-V）characteristics on the shielding height（h）and the potential difference between inner and outer electrodes（V_B）have been investigated at different working pressures of 0.03 Pa and 0.8 Pa.Results show that the I-V curves at higher pressure are more sensitive to the variation of h than those at lower pressure.The influence of V_B on ion temperature（T_i）measurement becomes more prominent when the pressure is increased from 0.03 Pa to 0.8 Pa.Under both pressures,the optimized h is obtained at the condition where the current reaches zero in the positive voltage region with a suitable V_B of-1.5 V because of effective shielding of the electron E×B drift.展开更多
Work zone safety continues to be one of the important focus areas for transportation agencies. Previous studies have identified that vehicle speed and lighting conditions are significant risk factors impacting work zo...Work zone safety continues to be one of the important focus areas for transportation agencies. Previous studies have identified that vehicle speed and lighting conditions are significant risk factors impacting work zone safety. </span><span style="font-family:Verdana;">This study evaluated the impact of the use of presence lighting and digital </span><span style="font-family:Verdana;">speed limit trailers on nighttime motorist speeds using commercially available connected vehicle speed data. Geospatial analysis was conducted on over 500,000 connected vehicle records to linear reference nearly 18,000 records from 195 unique trajectories to study section during the study period of 2 days. Results showed that median speeds reduced by 4 to 13 mph from 11PM to 7AM during the deployment of presence lighting and speed limit trailers </span><span style="font-family:Verdana;">compared to base conditions. A Kolmogorov-Smirnov (KS) statistical test</span><span style="font-family:Verdana;"> com</span><span style="font-family:Verdana;">paring 105 vehicles traveling through the construction zone with presence</span><span style="font-family:Verdana;"> lighting and speed limit trailers with a group of 90 vehicles during base condition indicated the speeds during the deployment of presence lighting and speed limit trailers were lower than the base condition. Also, increased compliance with the 55 mph speed limit was observed when the presence lighting and digital speed limit trailers were deployed. However, there were two hours (3AM to 5AM) where speeds increased by 0</span></span><span style="font-family:""> </span><span style="font-family:Verdana;">-</span><span style="font-family:""> </span><span style="font-family:Verdana;">4 mph, perhaps due to the low volume at that hour. The encouraging results support the further deployment of presence lighting and speed limit trailers in nighttime construction zones for reducing vehicle speeds. Those future deployments should be monitored with connected vehicle speeds to collect additional data to broaden the evaluation of these speed mitigation techniques over a diverse set of construction zone activities.展开更多
A probe-hole field emission microscope system,controlled by the Apple Ⅱ computer,has been developed and operated successfully for measuring the work function of a single crystalplane.The detection screen,the phototub...A probe-hole field emission microscope system,controlled by the Apple Ⅱ computer,has been developed and operated successfully for measuring the work function of a single crystalplane.The detection screen,the phototube and the amplifier are combined for measuring theprobe-hole current.The combination is calibrated and the calibrated data are used in the com-puter program.The high voltage on the viewing screen is adjusted by using a D/A converter.The total current and the probe-hole current are acquired by using an A/D converter.A programin BASIC is used for processing all data and the Fowler-Nordheim plot parameters are given.Work functions of single crystal planes can then be calculated;as examples,the work functionson the clean W(100)and W(111)planes are measured to be 4.67 eV and 4.45 eV,respectively.展开更多
基金supported by National Natural Science Foundation of China(No.10875093)
文摘In order to precisely measure the ion parameters in a microwave electron cyclotron resonance plasma using an ion sensitive probe,the dependences of the current-voltage（I-V）characteristics on the shielding height（h）and the potential difference between inner and outer electrodes（V_B）have been investigated at different working pressures of 0.03 Pa and 0.8 Pa.Results show that the I-V curves at higher pressure are more sensitive to the variation of h than those at lower pressure.The influence of V_B on ion temperature（T_i）measurement becomes more prominent when the pressure is increased from 0.03 Pa to 0.8 Pa.Under both pressures,the optimized h is obtained at the condition where the current reaches zero in the positive voltage region with a suitable V_B of-1.5 V because of effective shielding of the electron E×B drift.
文摘Work zone safety continues to be one of the important focus areas for transportation agencies. Previous studies have identified that vehicle speed and lighting conditions are significant risk factors impacting work zone safety. </span><span style="font-family:Verdana;">This study evaluated the impact of the use of presence lighting and digital </span><span style="font-family:Verdana;">speed limit trailers on nighttime motorist speeds using commercially available connected vehicle speed data. Geospatial analysis was conducted on over 500,000 connected vehicle records to linear reference nearly 18,000 records from 195 unique trajectories to study section during the study period of 2 days. Results showed that median speeds reduced by 4 to 13 mph from 11PM to 7AM during the deployment of presence lighting and speed limit trailers </span><span style="font-family:Verdana;">compared to base conditions. A Kolmogorov-Smirnov (KS) statistical test</span><span style="font-family:Verdana;"> com</span><span style="font-family:Verdana;">paring 105 vehicles traveling through the construction zone with presence</span><span style="font-family:Verdana;"> lighting and speed limit trailers with a group of 90 vehicles during base condition indicated the speeds during the deployment of presence lighting and speed limit trailers were lower than the base condition. Also, increased compliance with the 55 mph speed limit was observed when the presence lighting and digital speed limit trailers were deployed. However, there were two hours (3AM to 5AM) where speeds increased by 0</span></span><span style="font-family:""> </span><span style="font-family:Verdana;">-</span><span style="font-family:""> </span><span style="font-family:Verdana;">4 mph, perhaps due to the low volume at that hour. The encouraging results support the further deployment of presence lighting and speed limit trailers in nighttime construction zones for reducing vehicle speeds. Those future deployments should be monitored with connected vehicle speeds to collect additional data to broaden the evaluation of these speed mitigation techniques over a diverse set of construction zone activities.
基金Subject Supported by the Natural Science Fund of China.
文摘A probe-hole field emission microscope system,controlled by the Apple Ⅱ computer,has been developed and operated successfully for measuring the work function of a single crystalplane.The detection screen,the phototube and the amplifier are combined for measuring theprobe-hole current.The combination is calibrated and the calibrated data are used in the com-puter program.The high voltage on the viewing screen is adjusted by using a D/A converter.The total current and the probe-hole current are acquired by using an A/D converter.A programin BASIC is used for processing all data and the Fowler-Nordheim plot parameters are given.Work functions of single crystal planes can then be calculated;as examples,the work functionson the clean W(100)and W(111)planes are measured to be 4.67 eV and 4.45 eV,respectively.
