The effect of non-storm time substorms on the ring current dynamics

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 supersubstorms,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.

Evolutions of equatorial ring current ions during a magnetic storm

In this paper, we present evolutions of the phase space density(PSD) spectra of ring current(RC) ions based on observations made by Van Allen Probe B during a geomagnetic storm on 23–24 August 2016. By analyzing PSD spectra ratios from the initial phase to the main phase of the storm, we find that during the main phase, RC ions with low magnetic moment μ values can penetrate deeper into the magnetosphere than can those with high μ values, and that the μ range of PSD enhancement meets the relationship: S(O^+) >S(He^+)>S(H^+). Based on simultaneously observed ULF waves, theoretical calculation suggests that the radial transport of RC ions into the deep inner magnetosphere is caused by drift-bounce resonance interactions, and the efficiency of these resonance interactions satisfies the relationship: η(O^+) > η(He^+) > η(H^+), leading to the differences in μ range of PSD enhancement for different RC ions. In the recovery phase,the observed decay rates for different RC ions meet the relationship: R(O^+) > R(He^+) > R(H^+), in accordance with previous theoretical calculations, i.e., the charge exchange lifetime of O^+ is shorter than those of H^+ and He^+.

Effects of polarization-reversed electromagnetic ion cyclotron waves on the ring current dynamics

Electromagnetic ion cyclotron(EMIC)waves are widely believed to play an important role in influencing the radiation belt and ring current dynamics.Most studies have investigated the effects or characteristics of EMIC waves by assuming their left-handed polarization.However,recent studies have found that the reversal of polarization,which occurs at higher latitudes along the wave propagation path,can change the wave-induced pitch angle diffusion coefficients.Whether such a polarization reversal can influence the global ring current dynamics remains unknown.In this study,we investigate the ring current dynamics and proton precipitation loss in association with polarization-reversed EMIC waves by using the ring current-atmosphere interactions model(RAM).The results indicate that the polarization reversal of H-band EMIC waves can truly decrease the scattering rates of protons of 10 to 50 keV or>100 keV in comparison with the scenario in which the EMIC waves are considered purely left-handed polarized.Additionally,the global ring current intensity and proton precipitation may be slightly affected by the polarization reversal,especially during prestorm time and the recovery phase,but the effects are not large during the main phase.This is probably because the H-band EMIC waves contribute to the proton scattering loss primarily at E<10 keV,an energy range that is not strongly affected by the polarization reversal.

Prediction of Partial Ring Current Index Using LSTM Neural Network

The local time dependence of the geomagnetic disturbances during magnetic storms indicates the necessity of forecasting the localized magnetic storm indices.For the first time,we construct prediction models for the SuperMAG partial ring current indices(SMR-LT),with the advance time increasing from 1 h to 12 h by Long Short-Term Memory(LSTM)neural network.Generally,the prediction performance decreases with the advance time and is better for the SMR-06 index than for the SMR-00,SMR-12,and SMR-18 index.For the predictions with 12 h ahead,the correlation coefficient is 0.738,0.608,0.665,and 0.613,respectively.To avoid the over-represented effect of massive data during geomagnetic quiet periods,only the data during magnetic storms are used to train and test our models,and the improvement in prediction metrics increases with the advance time.For example,for predicting the storm-time SMR-06 index with 12 h ahead,the correlation coefficient and the prediction efficiency increases from 0.674 to 0.691,and from 0.349 to 0.455,respectively.The evaluation of the model performance for forecasting the storm intensity shows that the relative error for intense storms is usually less than the relative error for moderate storms.

Ring current proton scattering by low-frequency magnetosonic waves

Magnetosonic (MS) waves are believed to have the ability to affect the dynamics of ring current protons both inside and outside the plasmasphere. However, previous studies have focused primarily on the effect of high-frequency MS waves (f > 20 Hz) on ring current protons. In this study, we investigate interactions between ring current protons and low-frequency MS waves (< 20 Hz) inside the plasmasphere. We find that low-frequency MS waves can effectively accelerate < 20 keV ring current protons on time scales from several hours to a day, and their scattering efficiency is comparable to that due to high-frequency MS waves (>20 Hz), from which we infer that omitting the effect of low-frequency MS waves will considerably underestimate proton depletion at middle pitch angles and proton enhancement at large pitch angles. Therefore, ring current proton modeling should take into account the effects of both low- and highfrequency MS waves.

The substorm current wedge and midnight sector partial ring current near substorm onset: A synthesis based on a magnetotail magnetic field geometry model

The Substorm Current Wedge （SCW） occurrence in the late growth and onset phases of substorms was proposed as the current system which disrupts cross-tail current by diverting it to the ionosphere. The closure current for the SCW originally was suggested to be the strong westward auroral electrojet （WEJ）. However, the SCW-WEJ system has no viable generator current. Similarly, the asymmetric or Partial Ring Current （PRC） increases in strength during the growth phase, and is sometimes associated with an enhanced Region 2 field-aligned current （FAC） closing to the ionosphere, but specifics of that closure have been lacking. Here we present a tmifying picture which includes the SCW post- and pre-midnight （AM and PM, respectively） currents and a generator current in the midnight portion of the PRC system, with these currents based upon a model of the nightside magnetotail magnetic geometry. That geometry consists of open north and south lobe regions surrounding a plasmasheet with two types of closed field line regions-stretched lines in the central part of the plasmasheet （SPS） and dipolar lines （DPS） between the low lati- tude boundary layer （LLBL） regions and the SPS. There is also an important plasmasheet transition region （TPS） in which the dipolar field near the plasmapause gradually transforms to stretched lines near the earthward edge of the SPS, and in which the midnight part of the PRC flows. We propose that our proposed near-onset current system consists of a central current which be- comes part of the midnight sector PRC and which is the generator, to which are linked two three-part current systems, one on the dawnside and one on the duskside. The three-part systems consist of up and down FACs closing as Pedersen currents in the iono- sphere. These 3-part systems are not activated until near-onset is reached, because of a lack of ionospheric conductivity in the appropriate locations where the Pedersen current closure occurs. The initial downward FAC of the 3-part dawnside system and the final upward FAC of the 3-part duskside system correspond to the AM and PM current segments, respectively, of the originally proposed SCW.

Persistent current in a magnetized Rashba ring

We theoretically study the persistent currents flowing in a Rashba quantum ring subjected to the Rashba spinorbit interaction. By introducing uniform or nonuniform magnetization into the ring, we find that a nonzero persistent charge current circulates in the ring, which stems from the original equilibrium spin current due to the Rashba spinorbit interaction. Because of broken time reversal symmetry, the two oppositely flowing spin-up and spin-down charge currents of the equilibrium spin current are no longer equal, and so a net persistent charge current can flow in the system. It is also found that the persistent current can be modulated by the Fermi energy, the Rashba spin-orbit interaction strength and the magnetization in the ring. Moreover, the magnetization perpendicular to the ring plane can optimize the current. The persistent current flowing in the ring is a manifestation of the nonzero equilibrium spin current existing in the ring.

Oscillation of the spin-currents of cold atoms on a ring due to light-induced spin–orbit coupling

The evolution of two-component cold atoms on a ring with spin-orbit coupling has been studied analytically for the case with N noninteracting particles. Then, the effect of interaction is evaluated numerically via a two-body system. Two cases are considered： （i） Starting from a ground state the evolution is induced by a sudden change of the laser field, and （ii） the evolution starting from a superposition state. Oscillating persistent spin-currents have been found. A set of formulae have been derived to describe the period and amplitude of the oscillation. Based on these formulae the oscillation can be well controlled via adjusting the parameters of the laser beams. In particular, it is predicted that movable stripes might emerge on the ring.

PERSISTENT CURRENT IN A ONE-DIMENSIONAL MESOSCOPIC RING WITH ELECTRON-PHONON INTERACTION IN THE LATTICE MODEL

A new non-perturbative method is used to discuss the persistent current in a one-dimensional mesoscopic ring threaded by a flux φ with electron-phonon interaction in the lattice model. The current is periodic in φ with a flux quantum φ 0 and the electron-phonon interaction suppresses the persistent current. By considering the contributions of many-phonon correlations, we could obtain more accurate results.

Current–phase relations of a ring-trapped Bose–Einstein condensate with a weak link

The current–phase relations of a ring-trapped Bose–Einstein condensate interrupted by a rotating rectangular barrier are extensively investigated with an analytical solution. A current–phase diagram, single and multi-valued relation, is presented with a rescaled barrier height and width. Our results show that the finite size makes the current–phase relation deviate a little bit from the cosine form for the soliton solution in the limit of a vanishing barrier, and the periodic boundary condition selects only the plane wave solution in the case of high barrier. The reason for multi-valued current–phase relation is given by investigating the behavior of soliton solution.

2000年10月5日磁暴主相两个不同时段太阳风参数特征告诉我们什么?

本文研究了2000年10月5日磁暴主相两个不同时段期间环电流的变化速度与相应太阳风参数的关系.研究发现,磁暴主相期间环电流的变化速度并不取决于行星际磁场南向分量的平均值和最大值,也不取决于太阳风电场的平均值和最大值.本文的研究证明,磁暴环电流增强期间环电流的变化速度,不仅取决于行星际磁场南向分量和太阳风的速度,还取决于太阳风的动压,而且太阳风的动压起着非常重要的作用.研究还发现,采用Burton et al.(1975)方程和O′Brien,McPherron (2000a)方程估算得到的2000年10月5日的两次地磁活动的强度远低于实际的观测值.

基于驱动导体环的板件电磁成形电磁力分布与成形效果研究

为实现电磁成形中电磁力的可控加载,提升板件成形效果,该文提出一种基于驱动导体环的板件电磁成形技术。该技术在板件与驱动线圈之间引入一驱动环,通过改变驱动环的材料参数与几何参数实现电磁力的调控。基于特定的AA1060铝板(铝板半径70 mm,铝板成形区域半径50 mm)进行了仿真研究。仿真数据表明,驱动导体环的材质和几何结构的变化可以改变感应涡流从而实现电磁力的调控。与传统板件电磁成形相比,基于驱动导体环的板件电磁成形均匀成形范围Dr提高了1.61倍。在仿真基础上,通过驱动导体环板件电磁成形实验验证了仿真模型的可靠性。综上所述,基于驱动导体环的电磁成形技术能有效提高板件成形的均匀度。

接入新能源大基地汇集系统的柔直换流站低电压穿越方法

当新能源大基地经柔直送出系统的汇集线路发生故障时,柔性直流换流站可能由于过电流闭锁导致连接的新能源全部脱网。为解决上述问题,该文在考虑新能源并网换流器控制特性的基础上,对柔性直流换流站低电压穿越控制期间保留电压外环的必要性进行分析,提出基于分序限流与等效阻抗法的汇集系统低电压穿越方法,通过正负序分离处理外环输出的参考电流,进而转换到三相坐标系下,以实现对每相的输出电流的独立处理,解决了不对称故障暂态期间故障相电流越限的问题;同时利用等效阻抗法自适应修正外环电压的参考值,避免了内环限流环节生效后,外环控制因饱和而退出的弊端,从而防止故障稳态期间柔直换流站过电流闭锁。在PSCAD中搭建了新能源基地接入柔性直流换流站的交流汇集系统的精细化模型,通过仿真实验验证了所提控制方法的有效性。

Tunable Kondo Effect of a Three-Terminal Transport Quantum Dot Embedded in an Aharonov-Bohm Ring

We theoretically investigate the Kondo effect of a three-terminal transport quantum dot （QD） embedded in an Aharonov-Bohm ring in the Kondo regime by means of the one-impurity Anderson Hamiltonian. The Hamiltonian is solved by means of the slave-boson mean-field theory. We find that in this system, the Kondo effect depends sensitively oil the parity and size of the ring; the Kondo screening cloud can be tuned by tuning the coupling strength of the reservoir-dot. Thus this model might be a candidate for future device applications.

Spin-polarization-dependent transport in a quantum dot array coupled with an Aharonov-Bohm ring

In this paper the quantum transport in a dot-array coupled with an Ahaxonov-Bohm （AB） ring is investigated via single-band tight-binding Hamiltonian. It is shown that the output spin current is a periodic function of the magnetic flux in the quantum unit Ф0. The resonance positions of the total transmission probability do not depend on the size of the AB ring but the electronic spectrum. Moreover, the persistent currents in the AB ring is also spin-polarization dependent and different from the isolated AB ring where the persistent current is independent of spin polarization.

基于Mel-CNN和电流频谱的电机轴承外圈故障声纹检测方法

外轴承滚道缺陷是电机轴承的一种高发故障。针对如何高效检测外轴承滚道故障,提出一种基于Mel-CNN和电流频谱的轴承外圈故障声纹检测方法,首先构造外轴承滚道缺陷导致的径向转子运动机制,采集正常与故障状态下的定子电流,并使用小波阈值去噪排除噪声成分。其次,利用鲸鱼算法(WOA)优化变分模态分解(VMD)去除电机噪声中的高频成分,提取Mel谱声纹特征。最后,利用卷积神经网络(CNN)重新提取Mel声纹特征,获取表征轴承外圈故障的高维抽象特征并利用声纹融合电流神经网络模型对轴承进行故障诊断。结果表明,Mel谱结合电流频谱特征能够准确地表征轴承外圈故障。该方法通过对数据集的学习,有效区分了故障状态和健康状态,完善了神经网络在检测异步电动机轴承外圈故障中的缺陷。

大气及真空环境下电流对柔性环滚动载流摩擦性能的影响

使用外滚道、柔性环和内滚道构成滚动载流摩擦副,对比研究了大气及真空(1×10-3Pa)环境下电流对柔性环滚动载流摩擦磨损性能的影响.随着电流从0 A增至20 A,电致黏着导致摩擦力随电流增大而增大.大气环境下氧化作用可促进摩擦表面材料剥落,导致磨痕宽度更大,进而导致大气摩擦力更高,表层塑性变形更严重.真空环境下氧化磨损被抑制,接触表面材料剥落和塑性变形相对较轻.电流从0 A增加至20 A,大气磨损面O与Cu原子比从0.379 7减少至0.144 3,真空磨损面O与Cu原子比从0.093 9减少至0.029 9.硬度测试显示:在塑性硬化和电致软化共同影响下,摩擦表层硬度随电流的增大先增加后降低,硬度最高点对应的电流为5 A,真空下电致软化效果更明显.

双环椭圆传感器阵列串扰误差优化研究

阵列式霍尔电流传感器采用了无磁芯设计,解决了传统电流传感器质量大、体积大的缺点,可以有效检测电流,以达到检测、控制和保护电路的目的。然而在汽车电子、工业仪器等应用场景中,线路排布较为密集,电流传感器在采集电流时易产生串扰误差。首先利用投影法将圆形阵列转化为椭圆形阵列;然后采用双环设计,每对传感器排布在同一径上,方向相反;接着提出了一种运用于椭圆阵列传感器的串扰优化算法,以减小导体偏移阵列中心和干扰导体造成的影响;最后搭建了实验平台,对不同的传感器阵列进行了测量,对串扰优化算法进行了验证。实验结果表明,串扰优化算法可以有效抑制干扰导体产生的串扰误差,将测量误差控制在1%以内,极大地提升了电流检测精度。

一种热释电红外控制芯片设计

热释电红外技术已广泛应用于交通出行和智能家居等领域。用于接收、放大、处理热释电红外传感器输入信号的控制芯片的优劣,是衡量热释电红外产品性能的重要标准。设计出一款用于照明控制、防盗报警等领域的热释电红外控制芯片。该芯片是一款基于5 V 1P3M CMOS工艺的低静态功耗、芯片面积小的热释电红外控制芯片,只有8个引脚,外围器件少,可与传感器合封,具有小型化,能有效抑制手机、Wi-Fi等射频干扰的优势。仿真结果表明,芯片的静态功耗小于20μA,动态功耗小于1 mA,在3.0~5.5 V电压范围内能正常工作,有效面积约为0.309 mm^(2)。