A 2D-3V implicit immersed-finite-element particle-in-cell(IFE-PIC)model is introduced to investigate the radio-frequency(RF)self-bias accelerating system applied in the RF ion thruster.A set of holes in a two-grid sys...A 2D-3V implicit immersed-finite-element particle-in-cell(IFE-PIC)model is introduced to investigate the radio-frequency(RF)self-bias accelerating system applied in the RF ion thruster.A set of holes in a two-grid system with slit apertures is simulated in Cartesian coordinates.The characteristics of the plasma plume,such as the ion density,the neutralization rate and the ion and electron current density were investigated for different RF voltage amplitudes(600-1200V)and frequencies(6-30 MHz).Furthermore,the performance of the thruster was also carefully studied.The simulation results show that a well-focused plasma beam can be formed when the voltage amplitude is larger than 900 V and the frequency exceeds the reciprocal of ion transit time(≥12 MHz)in our simulation cases.The performance of the system can be evidently improved by increasing the voltage amplitude and the frequency,and the losses of the particle and thrust are reduced correspondingly.The bulk region of the plasma beam downstream shows good quasi-neutrality,and the ions are dominant in the peripheral region when a well-focused state is achieved.The high ion density beamlet in the periphery of the ion beam is closer to the axis when the voltage amplitude is increasing,while it is expanded radially when increasing the frequency.Backstream electrons have been observed upstream,and this mainly occurs in the phase in which the electron cannot escape.展开更多
Awards are important markers of success in any career, and in academia they can play an important role in hiring, promotion and tenure decisions. This study compares awards data for disciplinary societies in STEM （sc...Awards are important markers of success in any career, and in academia they can play an important role in hiring, promotion and tenure decisions. This study compares awards data for disciplinary societies in STEM （science, technology, engineering and mathematics） to the proportion of women in each respective field. By establishing availability pool estimates of women who should be eligible for senior scholarly awards, a comparison can be made between the proportion of female award winners and the percentage of women active in the discipline. The CBMS （conference board of mathematical sciences） survey in 2005 reported that women were 9% of all full-time tenured professors in doctoral-level mathematics departments; yet during the last decade, women received only 4.8% of scholarly awards from the AMS （American mathematical society）. Similar disparities exist for scholarly achievement awards from the MAA （mathematical association of America）, the SIAM （society for industrial and applied mathematics） and the ASA （American statistical association）. The under-recognition of women for scholarly contributions cannot be attributed solely to low numbers of women, so further explanation must be sought elsewhere. Curiously, women received more than their expected proportion of awards for service and teaching. Decades of research in the social sciences points to ＂implicit associations＂ or subconscious social stereotypes as the mechanism by which both men and women de-value women＇s intellectual accomplishments and praise their communal contributions, which may explain the gender disparity between scholarly and service awards. Gender disparities in scholarly recognition can hinder the advancement of women and limit their numbers as leaders in STEM fields. AWIS （association for women in science） is working with seven disciplinary societies （including AMS, ASA, MAA and SIAM） to identify patterns of behavior that perpetuate unconscious bias in the awards selection process and to pinpoint ways to mitigate its deleterious effects.展开更多
基金supported by the China Postdoctoral Science Foundation(No.2022M710977)National Natural Science Foundation of China(No.51907039)+1 种基金the Natural Science Foundation of Guangdong Province(Nos.2022A1515110215 and 2023A1515010137)Shenzhen Technology Projects(Nos.JCYJ20190806142603534 and ZDSYS201707280904031)。
文摘A 2D-3V implicit immersed-finite-element particle-in-cell(IFE-PIC)model is introduced to investigate the radio-frequency(RF)self-bias accelerating system applied in the RF ion thruster.A set of holes in a two-grid system with slit apertures is simulated in Cartesian coordinates.The characteristics of the plasma plume,such as the ion density,the neutralization rate and the ion and electron current density were investigated for different RF voltage amplitudes(600-1200V)and frequencies(6-30 MHz).Furthermore,the performance of the thruster was also carefully studied.The simulation results show that a well-focused plasma beam can be formed when the voltage amplitude is larger than 900 V and the frequency exceeds the reciprocal of ion transit time(≥12 MHz)in our simulation cases.The performance of the system can be evidently improved by increasing the voltage amplitude and the frequency,and the losses of the particle and thrust are reduced correspondingly.The bulk region of the plasma beam downstream shows good quasi-neutrality,and the ions are dominant in the peripheral region when a well-focused state is achieved.The high ion density beamlet in the periphery of the ion beam is closer to the axis when the voltage amplitude is increasing,while it is expanded radially when increasing the frequency.Backstream electrons have been observed upstream,and this mainly occurs in the phase in which the electron cannot escape.
文摘Awards are important markers of success in any career, and in academia they can play an important role in hiring, promotion and tenure decisions. This study compares awards data for disciplinary societies in STEM （science, technology, engineering and mathematics） to the proportion of women in each respective field. By establishing availability pool estimates of women who should be eligible for senior scholarly awards, a comparison can be made between the proportion of female award winners and the percentage of women active in the discipline. The CBMS （conference board of mathematical sciences） survey in 2005 reported that women were 9% of all full-time tenured professors in doctoral-level mathematics departments; yet during the last decade, women received only 4.8% of scholarly awards from the AMS （American mathematical society）. Similar disparities exist for scholarly achievement awards from the MAA （mathematical association of America）, the SIAM （society for industrial and applied mathematics） and the ASA （American statistical association）. The under-recognition of women for scholarly contributions cannot be attributed solely to low numbers of women, so further explanation must be sought elsewhere. Curiously, women received more than their expected proportion of awards for service and teaching. Decades of research in the social sciences points to ＂implicit associations＂ or subconscious social stereotypes as the mechanism by which both men and women de-value women＇s intellectual accomplishments and praise their communal contributions, which may explain the gender disparity between scholarly and service awards. Gender disparities in scholarly recognition can hinder the advancement of women and limit their numbers as leaders in STEM fields. AWIS （association for women in science） is working with seven disciplinary societies （including AMS, ASA, MAA and SIAM） to identify patterns of behavior that perpetuate unconscious bias in the awards selection process and to pinpoint ways to mitigate its deleterious effects.
