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地球与行星物理

ISSN  2096-3955

CN  10-1502/P

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PLANETARY SCIENCES
Large-scale episodic enhancements of relativistic electron intensities in Jupiter's radiation belt
ChongJing Yuan, YiQiao Zuo, Elias Roussos, Yong Wei, YiXin Hao, YiXin Sun, Norbert Krupp
Recently Published , doi: 10.26464/epp2021037
[Abstract](48) [FullText HTML](7) [PDF 0KB](0)
Abstract:
Previous studies indicate that, in the Jovian magnetosphere, the long-term trend of the radial profile of relativistic electron intensities is primarily shaped by slow radial diffusion. However, measurements by the Galileo spacecraft reveal the existence of transient increases in MeV electron intensities well above the ambient distribution. It is unclear how common such transient enhancements are, and to which dynamic processes in Jupiter's magnetosphere their occurrence is linked. We investigate the radial distributions of \begin{document}$>$\end{document}11 MeV and \begin{document}$>$\end{document}1 MeV electron intensities from \begin{document}$9R_{J}$\end{document} to \begin{document}$40R_{J}$\end{document} (\begin{document}$R_{J}=71492\;{\rm{km}}$\end{document} denotes the Jovian radius), measured by the Galileo spacecraft from 1996 to 2002. We find transient enhancements of MeV electrons during seven Galileo crossings, mostly occurring around ~20RJ. An apparent dawn-dusk asymmetry of their occurrence is resolved, with a majority of events discovered at dawn. This dawn-dusk asymmetry, as well as the average recurrence time scale of a few days, implies a potential relationship between the MeV electron transients and the storm-like dynamics in the middle and outer magnetosphere detected using a variety of Galileo, Juno and remote sensing aurora observations. We suggest that the observations of some of these transients in the inner magnetosphere may result from a synergy between the convective transport by a large-scale dawn-dusk electric field and the sources provided by injections in the middle magnetosphere.
SPACE PHYSICS: MAGNETOSPHERIC PHYSICS
Preservation and variation of ion-to-electron temperature ratio in the plasma sheet in geo-magnetotail
ChuXin Chen
Recently Published , doi: 10.26464/epp2021035
[Abstract](92) [FullText HTML](14) [PDF 437KB](8)
Abstract:
The ion-to-electron temperature ratio is a good indicator of the processes involved in solar wind plasma entering and being transported inside Earth’s plasma sheet. In this study, we have demonstrated that patchy magnetic reconnection has the potential to preserve the ion-to-electron temperature ratio under certain conditions. If the charged particles are non-adiabatically accelerated no more than once in a single reconnection, the temperature ratio would be preserved; on the other hand, this ratio would not be preserved if they are accelerated multiple times. Consequently, under a northward interplanetary magnetic field (IMF) condition, the reconnection in the nonlinear phase of the Kelvin–Helmholtz instability is the dominant process for solar-originated plasma entering the Earth’s magnetosphere, and the ion-to-electron temperature ratio is preserved inside the plasma sheet. When the direction of the IMF is southward, the reflection of electrons from the magnetic mirror point, and subsequent multiple non-adiabatic accelerations at the reconnection site, are the primary reasons for the observed low ion-to-electron temperature ratio close to the Earth at midnight. While reconnections that occur in the night-side far tail might preserve the ratio, turbulence on the boundaries of the bursty bulk flows (BBFs) could change the ratio in the far tail through the violation of the frozen-in condition of the ions. The plateau in the contour of the calculated ion-to-electron temperature ratio in the down tail distance between 40 and 60 Earth radii may explain the strong correlation between the ion and electron temperatures in the outer central plasma sheet, which has not been clearly understood till date.
SOLID EARTH: SEISMOLOGY
A preliminary report of the Yangbi, Yunnan, MS6.4 earthquake of May 21, 2021
ZhiGao Yang, Jie Liu, Xue-Mei Zhang, WenZe Deng, GuangBao Du, XiYan Wu
Recently Published , doi: 10.26464/epp2021036
[Abstract](143) [FullText HTML](22) [PDF 473KB](6)
Abstract:
SPACE PHYSICS: IONOSPHERIC PHYSICS
Review of ionospheric irregularities and ionospheric electrodynamic coupling in the middle latitude region
Yi Liu, Chen Zhou, Tong Xu, Qiong Tang, ZhongXin Deng, GuanYi Chen, ZhuangKai Wang
Recently Published , doi: 10.26464/epp2021025
[Abstract](160) [FullText HTML](26) [PDF 14023KB](1)
Abstract:
This paper briefly reviews ionospheric irregularities that occur in the E and F regions at mid-latitudes. Sporadic E (ES) is a common ionospheric irregularity phenomenon that is first noticed in the E layer. ES mainly appears during daytime in summer hemispheres, and is formed primarily from neutral wind shear in the mesosphere and lower thermosphere (MLT) region. Field-aligned irregularity (FAI) in the E region is also observed by Very High Frequency (VHF) radar in mid-latitude regions. FAI frequently occurs after sunset in summer hemispheres, and spectrum features of E region FAI echoes suggest that type-2 irregularity is dominant in the nighttime ionosphere. A close relationship between ES and E region FAI implies that ES may be a possible source of E region FAI in the nighttime ionosphere. Strong neutral wind shear, steep ES plasma density gradient, and a polarized electric field are the significant factors affecting the formation of E region FAI. At mid-latitudes, joint observational experiments including ionosonde, VHF radar, Global Positioning System (GPS) stations, and all-sky optical images have revealed strong connections across different scales of ionospheric irregularities in the nighttime F region, such as spread F (SF), medium-scale traveling ionospheric disturbances (MSTID), and F region FAI. Observations suggest that different scales of ionospheric irregularities are generally attributed to the Perkins instability and subsequently excited gradient drift instability. Nighttime MSTID can further evolve into small-scale structures through a nonlinear cascade process when a steep plasma density gradient exists at the bottom of the F region. In addition, the effect of ionospheric electrodynamic coupling processes, including ionospheric E-F coupling and inter-hemispheric coupling on the generation of ionospheric irregularities, becomes more prominent due to the significant dip angle and equipotentiality of magnetic field lines in the mid-latitude ionosphere. Polarized electric fields can map to different ionospheric regions and excite plasma instabilities which form ionospheric irregularities. Nevertheless, the mapping efficiency of a polarized electric field depends on the ionospheric background and spatial scale of the field.
SOLID EARTH: SEISMOLOGY
Teleseismic waves reveal anisotropic poroelastic response of wastewater disposal reservoir
Andrew J Barbour, Nicholas M Beeler
Recently Published , doi: 10.26464/epp2021034
[Abstract](184) [FullText HTML](49) [PDF 1789KB](14)
Abstract:
Connecting earthquake nucleation in basement rock to fluid injection in basal, sedimentary reservoirs, depends heavily on choices related to the poroelastic properties of the fluid-rock system, thermo-chemical effects notwithstanding. Direct constraints on these parameters outside of laboratory settings are rare, and it is commonly assumed that the rock layers are isotropic. With the Arbuckle wastewater disposal reservoir in Osage County, Oklahoma, high-frequency formation pressure changes and collocated broadband ground velocities measured during the passing of large teleseismic waves show a poroelastic response of the reservoir that is both azimuthally variable and anisotropic; this includes evidence of static shifts in pressure that presumably relate to changes in local permeability. The azimuthal dependence in both the static response and shear coupling appears related to tectonic stress and strain indicators such as the orientations of the maximum horizontal stress and faults and fractures. Using dynamic strains from a nearby borehole strainmeter, we show that the ratio of shear to volumetric strain coupling is \begin{document}$ \sim 0.41 $\end{document} which implies a mean Skempton's coefficient of \begin{document}$ A = 0.24 $\end{document} over the plausible range of the undrained Poisson's ratio. Since these observations are made at relatively low confining pressure and differential stress, we suggest that the hydraulically conductive fracture network is a primary control on the coupling between pore pressure diffusion and elastic stresses in response to natural or anthropogenic sources.
SOLID EARTH: SEISMOLOGY
Determination of the local magnitudes of small earthquakes using a dense seismic array in the Changning−Zhaotong Shale Gas Field, Southern Sichuan Basin
Wen Yang, GuoYi Chen, LingYuan Meng, Yang Zang, HaiJiang Zhang, JunLun Li
Recently Published , doi: 10.26464/epp2021026
[Abstract](534) [FullText HTML](128) [PDF 4574KB](22)
Abstract:
With the development of unconventional shale gas in the southern Sichuan Basin, seismicity in the region has increased significantly in recent years. Though the existing sparse regional seismic stations can capture most earthquakes with \begin{document}$ {M}_{\mathrm{L}}\ge 2.5 $\end{document}, a great number of smaller earthquakes are often omitted due to limited detection capacity. With the advent of portable seismic nodes, many dense arrays for monitoring seismicity in the unconventional oil and gas fields have been deployed, and the magnitudes of those earthquakes are key to understand the local fault reactivation and seismic potentials. However, the current national standard for determining the local magnitudes was not specifically designed for monitoring stations in close proximity, utilizing a calibration function with a minimal resolution of 5 km in the epicentral distance. That is, the current national standard tends to overestimate the local magnitudes for stations within short epicentral distances, and can result in discrepancies for dense arrays. In this study, we propose a new local magnitude formula which corrects the overestimated magnitudes for shorter distances, yielding accurate event magnitudes for small earthquakes in the Changning−Zhaotong shale gas field in the southern Sichuan Basin, monitored by dense seismic arrays in close proximity. The formula is used to determine the local magnitudes of 7,500 events monitored by a two-phased dense array with several hundred 5 Hz 3C nodes deployed from the end of February 2019 to early May 2019 in the Changning−Zhaotong shale gas field. The magnitude of completeness (\begin{document}$ {M}_{\mathrm{C}} $\end{document}) using the dense array is −0.1, compared to \begin{document}$ {M}_{\mathrm{C}} $\end{document} 1.1 by the sparser Chinese Seismic Network (CSN). In addition, using a machine learning detection and picking procedure, we successfully identify and process some 14,000 earthquakes from the continuous waveforms, a ten-fold increase over the catalog recorded by CSN for the same period, and the \begin{document}$ {M}_{\mathrm{C}} $\end{document} is further reduced to −0.3 from −0.1 compared to the catalog obtained via manual processing using the same dense array. The proposed local magnitude formula can be adopted for calculating accurate local magnitudes of future earthquakes using dense arrays in the shale gas fields of the Sichuan Basin. This will help to better characterize the local seismic risks and potentials.

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RESEARCH ARTICLE
SPACE PHYSICS: INTERPLANETARY PHYSICS
Propagation of large-scale solar wind events in the outer heliosphere from a numerical MHD simulation
XiaoCheng Guo, YuCheng Zhou, Chi Wang, Ying D. Liu
2021, 5(3): 223 -231   doi: 10.26464/epp2021024
Abstract:
Voyager 1 occasionally detected sudden jumps of the local interstellar magnetic field strength since its heliopause crossing in August 2012. These events were believed to be associated with outward propagating solar wind shocks originating in the inner heliosphere. Here we investigate the correlation between interstellar shocks and large-scale solar wind events by means of numerical MHD simulation. The solar wind is simplified as a symmetric flow near the equatorial plane, and the interstellar neutrals are treated as a constant flow with a fixed density distribution along the upwind direction of the local interstellar medium. The charge exchanges between the solar wind plasma and the interstellar neutrals are taken into account. At a heliocentric distance of 1 AU, the solar wind data from OMNI, STEREO A and B during the period between 2010 and 2017 are used as the inner boundary conditions to drive the simulation. The simulation results showed that the solar wind gradually merges into large-scale structures as the radial distance increases, consistent with observations by New Horizons. After propagating into the inner heliosheath, the shocks are fully developed and the corresponding pressure pulses roughly agree with the observations by Voyager 2 in the inner heliosheath. The arrival of the shocks beyond the heliopause is estimated and found to be consistent with the observed signatures of interstellar shocks by Voyager 1. The possible origins of interstellar shocks in the inner heliosheath are discussed based on the simulation.
SPACE PHYSICS: INTERPLANETARY PHYSICS
Dynamics of the charged particles released from a Sun-grazing comet in the solar corona
ChuanPeng Hou, JianSen He, Lei Zhang, Ying Wang, Die Duan
2021, 5(3): 232 -238   doi: 10.26464/epp2021023
Abstract:
The sun-grazing comet C/2011 W3 (Lovejoy) showed a distorted, unconventional tail morphology near its perihelion (1.2Rs). Based on the “Solar Corona and Inner Heliosphere” modeling result of the magnetic field and plasma dynamics in the solar corona, we use the Runge-Kutta method to simulate the moving trajectory of charged dust and ion particles released at different positions from the C/2011 W3 orbit. We find that the dust particles near the sun, which are subject to a strong magnetic Lorentz force, travel differently from their counterparts distant from the sun, where the latter are mainly affected by the solar gravitational force and radiation pressure. According to the simulation results, we propose that the magnetic mirror effect can rebound the charged dust particles back away from the sun and be regarded as one crucial cause of the dust-free zone formation. We find that ions mainly move along magnetic field lines at an acute angle to the comet's direction of motion. The cometary ions' movement direction was determined by the comet's velocity and the coronal magnetic field, which are responsible for the C/2011 W3’s unique comet tail shape near perihelion. Additionally, the ion particles also experience perpendicular drift motion, mainly dominated by the electric field drift, which is similar to and can be used to approximate the solar wind's transverse velocity at its source region.
Characteristics of magnetic dipolarizations in the vicinity of the substorm onset region observed by THEMIS
SuPing Duan, Chi Wang, Weining William Liu, ZhaoHai He
2021, 5(3): 239 -250   doi: 10.26464/epp2021031
Abstract:
With conjunction observations of electromagnetic fields and plasma from Time History of Events and Macroscale Interactions during Substorm (THEMIS) in the near-Earth magnetotail, we investigate the spatial and temporal properties of substorm dipolarizations in the near-Earth plasma sheet (NEPS) during a substorm at 03:23 UT on 12 February 2008. Substorm dipolarizations with different features are detected by three near-Earth THEMIS probes (THA (P5), THD (P3) and THE (P4)) in the magnetotail. In the current sheet with a large plasma beta value (β > 2, where β is the ratio of the plasma thermal pressure to the magnetic pressure), the dipolarization within the substorm onset region, (−10.4, 2.8, −2.6)RE_gsm, has a large initial magnetic field elevation angle, θ > 60°, θ = arctan (Bz/(Bx2+By2)1/2), and is accompanied by energetic ion (tens to hundred keV) dispersionless injection detected by THD (P3). This substorm onset dipolarization is characterized by Bx and By components around 0 nT with significant fluctuations. The Bz component increases sharply and its subsequent magnitude approaches the total magnetic field, Bt. The maximum value of the elevation angle approaches 85° during the later substorm expansion phase. In the NEPS with β ~ 1, the dipolarization outside the substorm onset region is characterized by a magnetic elevation angle with a small beginning value of θ < 45° and following multi-step enhancements during the substorm expansion phase. The maximum value of the elevation angle approaches to 70° during the later substorm expansion phase. Our observation results indicate that characteristics of dipolarization with a large beginning elevation angle within the substorm onset region provide a new indicator to identify substorm onset location.
SPACE PHYSICS: MAGNETOSPHERIC PHYSICS
The effect of non-storm time substorms on the ring current dynamics
EunJin Jang, Chao Yue, QiuGang Zong, SuiYan Fu, HaoBo Fu
2021, 5(3): 251 -258   doi: 10.26464/epp2021032
Abstract:
During geomagnetically active times such as geomagnetic storms, large amounts of energy can be released into the Earth’s magnetosphere and change the ring current intensity. Previous studies showed that significant enhancement of the ring current was related to geomagnetic storms, while few studies have examined substorm effects on ring current dynamics. In this study, we examine the ring current variation during non-storm time (SYM-H > −50 nT) substorms, especially during super-substorms (AE > 1000 nT). We perform a statistical analysis of ring current plasma pressure and number flux of various ion species under different substorm conditions, based on Van Allen Probe observations. The plasma pressure and ion fluxes of the ring current increased dramatically during super-substorms, while little change was observed for substorms with AE < 1000 nT. The results shown in this study indicate that a non-storm time super-substorm may also have a significant contribution to the ring current.
Formation of the bow shock indentation: MHD simulation results
BaoHang Qu, JianYong Lu, Ming Wang, HuanZhi Yuan, Yue Zhou, HanXiao Zhang
2021, 5(3): 259 -269   doi: 10.26464/epp2021033
Abstract:
Simulation results from a global magnetohydrodynamic (MHD) model are used to examine whether the bow shock has an indentation and characterize its formation conditions, as well as its physical mechanism. The bow shock is identified by an increase in plasma density of the solar wind, and the indentation of the bow shock is determined by the shock flaring angle. It is shown that when the interplanetary magnetic field (IMF) is southward and the Alfvén Mach number (Mα) of solar wind is high (> 5), the bow shock indentation can be clearly determined. The reason is that the outflow region of magnetic reconnection (MR) that occurs in the low latitude area under southward IMF blocks the original flow in the magnetosheath around the magnetopause, forming a high-speed zone and a low-speed zone that are upstream and downstream of each other. This structure hinders the surrounding flow in the magnetosheath, and the bow shock behind the structure widens and forms an indentation. When Mα is low, the magnetosheath is thicker and the disturbing effect of the MR outflow region is less obvious. Under northward IMF, MR occurs at high latitudes, and the outflow region formed by reconnection does not block the flow inside the magnetosheath, thus the indentation is harder to form. The study of the conditions and formation process of the bow shock indentation will help to improve the accuracy of bow shock models.
SPACE PHYSICS
Analysis of the correlation between horizontal wind and 11-year solar activity over Langfang, China
Bing Cai, QingChen Xu, Xiong Hu, Xuan Cheng, JunFeng Yang, Wen Li
2021, 5(3): 270 -279   doi: 10.26464/epp2021029
Abstract:
In this study, long term observations of medium frequency (MF) radar at Langfang site (39.4°N, 116.7°E) from 2009 to 2020 have been used to analyze the dependence of the 11-year solar cycle on horizontal winds in the local mesosphere and lower thermosphere (MLT). The results show that the zonal wind is positively correlated with solar activity during spring at 80–84 km, and during summer at 80–82 km; the meridional wind is positively correlated with solar activity during spring at 84–88 km and during summer at 84–90 km. In contrast, the results show no correlation between the horizontal wind and solar activity in autumn and winter. We attempt to explain the correlations in terms of the changes in stratospheric temperature and the net flux of gravity waves during solar activities. In addition, annual and semiannual oscillations of the zonal/meridional wind were found by using the least squares fitting method on daily horizontal winds, which show negative correlations with solar activity at heights of 80–90 km.
ATMOSPHERIC PHYSICS
Anomalous changes of temperature and ozone QBOs in 2015−2017 from radiosonde observation and MERRA-2 reanalysis
XiaoYan Bai, KaiMing Huang, ShaoDong Zhang, ChunMing Huang, Yun Gong
2021, 5(3): 280 -289   doi: 10.26464/epp2021028
Abstract:
Anomalous changes of zonal wind quasi-biennial oscillation (QBO) in winter 2015−2016 have received close attention. Combining radiosonde and satellite observations and reanalysis data, we investigate anomalous changes in temperature and ozone QBOs from the lower to middle stratosphere. As wind shear direction is reversed due to unexpected changes of zonal wind QBO at about 24−30 km, the shortest cold phase at 21−27 km appears in temperature QBO. This is different from the completely interrupted westward phase in zonal wind QBO, while the longest cold phase above almost 27 km lasts for 2−3 years from 2015 to 2017, owing to the absence of corresponding warm phase. Meridional scale reduction of temperature QBO causes a small temperature anomaly, thus the thermal wind relationship looks seemingly different from that in the other regular QBO cycles. QBO in the ozone mixing ratio anomaly shows a double-peak with inverse phase, and its phase below (above) 30 km is in agreement with (opposite to) the phase of temperature QBO because of different control mechanisms of ozone. Following temperature QBO variation, QBO in the ozone mixing ratio anomaly exhibits a less positive phase at 20−30 km in 2016−2017, and a very long positive phase above 30 km from 2015 to 2017. QBO in total column ozone shows a small peak in winter 2016−2017 since ozone is mainly concentrated at 20 to 30 km. Anomalous changes of temperature and ozone QBOs due to unexpected QBO zonal wind variation can be well-explained according to thermal wind balance and thermodynamic balance.
SOLID EARTH: GEODYNAMICS
Thermal structure of continental subduction zone: high temperature caused by the removal of the preceding oceanic slab
Ting Luo, Wei Leng
2021, 5(3): 290 -295   doi: 10.26464/epp2021027
Abstract:
The thermal structure of the continental subduction zone can be deduced from high-pressure and ultra-high-pressure rock samples or numerical simulation. However, petrological data indicate that the temperature of subducted continental plates is generally higher than that derived from numerical simulation. In this paper, a two-dimensional kinematic model is used to study the thermal structure of continental subduction zones, with or without a preceding oceanic slab. The results show that the removal of the preceding oceanic slab can effectively increase the slab surface temperature of the continental subduction zone in the early stage of subduction. This can sufficiently explain the difference between the cold thermal structure obtained from previous modeling results and the hot thermal structure obtained from rock sample data.
SOLID EARTH: SEISMOLOGY
Depth variation of the Conrad discontinuity in the Qaidam Basin, northwestern China, and its crustal dynamic implications
Biao Yang, YanBin Wang, Li Zhao, LiMing Yang, ChengNing Sha
2021, 5(3): 296 -304   doi: 10.26464/epp2021030
Abstract:
We use broadband records from a dense seismic network deployed in and around the Qaidam Basin in northwestern China to analyze the crustal phases and investigate the depth of the Conrad and Moho discontinuities as well as the P-wave velocity. Waveform cross-correlation is used to assist in the identification of the crustal phases and in determining their arrival times. Depth of the Conrad discontinuity is determined by fitting the travel times of Conrad-diffracted P-waves using a two-layer model. The depth of the Conrad discontinuity under the eastern part of the basin is shallower than the western part, which can be attributed to different crustal shortening mechanisms. The upper crust shortening in the western part of the basin leads to thickening of the upper crust, while multiple thrust faults result in the rise of the Conrad discontinuity in the east. These two different mechanisms determine the depth change of the Conrad discontinuity in the basin from the west to the east, which is supported by the results in this study.
show more results
Corotating drift-bounce resonance of plasmaspheric electron with poloidal ULF waves
Qiu-Gang Zong, YongFu Wang, Jie Ren, XuZhi Zhou, SuiYan Fu, Robert Rankin, Hui Zhang
2017, 1(1): 2-12   doi: 10.26464/epp2017002
Ambient noise surface wave tomography of marginal seas in east Asia
Qing Wang, XiaoDong Song, JianYe Ren
2017, 1(1): 13-25   doi: 10.26464/epp2017003
A brief review of equatorial ionization anomaly and ionospheric irregularities
Nanan Balan, LiBo Liu, HuiJun Le
2018, 2(4): 257-275   doi: 10.26464/epp2018025
A seismic model for crustal structure in North China Craton
TianYu Zheng, YongHong Duan, WeiWei Xu, YinShuang Ai
2017, 1(1): 26-34   doi: 10.26464/epp2017004
Thermal structures of the Pacific lithosphere from magnetic anomaly inversion
Chun-Feng Li, Jian Wang
2018, 2(1): 52-66   doi: 10.26464/epp2018005
The first joint experimental results between SURA and CSES
XueMin Zhang, Vladimir Frolov, ShuFan Zhao, Chen Zhou, YaLu Wang, Alexander Ryabov, DuLin Zhai
2018, 2(6): 527-537   doi: 10.26464/epp2018051
Different earthquake patterns for two neighboring fault segments within the Haiyuan Fault zone
ZhiKun Ren, ZhuQi Zhang, PeiZhen Zhang
2018, 2(1): 67-73   doi: 10.26464/epp2018006
Monitoring the geospace response to the Great American Solar Eclipse on 21 August 2017
Shun-Rong Zhang, Philip J. Erickson, Larisa P. Goncharenko, Anthea J. Coster, Nathaniel A. Frissell
2017, 1(1): 72-76   doi: 10.26464/epp2017011
Radiation belt electron scattering by whistler-mode chorus in the Jovian magnetosphere: Importance of ambient and wave parameters
BinBin Ni, Jing Huang, YaSong Ge, Jun Cui, Yong Wei, XuDong Gu, Song Fu, Zheng Xiang, ZhengYu Zhao
2018, 2(1): 1-14   doi: 10.26464/epp2018001
A simulation study of 630 nm and 557.7 nm airglow variations due to dissociative recombination and thermal electrons by high-power HF heating
Tong Dang, JiuHou Lei, XianKang Dou, WeiXing Wan
2017, 1(1): 44-52   doi: 10.26464/epp2017006

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