Excitation of extremely low-frequency chorus emissions: The role of background plasma density

Low-frequency chorus emissions have recently attracted much attention due to the suggestion that they may play important roles in the dynamics of the Van Allen Belts.However, the mechanism(s) generating these low-frequency chorus emissions have not been well understood..In this letter, we report an interesting case in which background plasma density lowered the lower cutoff frequency of chorus emissions from above 0.1 f_(ce)(typical ordinary chorus) to 0.02 f_(ce)(extremely low-frequency chorus).Those extremely low-frequency chorus waves were observed in a rather dense plasma, where the number density N_e was found to be several times larger than has been associated with observations of ordinary chorus waves.For suprathermal electrons whose free energy is supplied by anisotropic temperatures, linear growth rates(calculated using in-situ plasma parameters measured by the Van Allen Probes) show that whistler mode instability can occur at frequencies below 0.1 f_(ce) when the background plasma density N_e increases.Especially when N_e reaches 90 cm–3 or more, the lowest unstable frequency can extend to 0.02 f_(ce) or even less, which is consistent with satellite observations.Therefore, our results demonstrate that a dense background plasma could play an essential role in the excitation of extremely lowfrequency chorus waves by controlling the wave growth rates.

Hemispheric Distribution of Lower-band Chorus Waves Observed by Van Allen Probes

Whistler mode chorus waves are important electromagnetic emissions due to their dual roles in acceleration and loss processes of Earth's radiation belt electrons.A detailed global survey of lower-band chorus is performed using EMFISIS data from Van Allen Probes in near-equatorial orbits.In addition to the confirmation of the positive correlation of chorus wave intensities to geomagnetic activity and dayside-nightside distribution asymmetry of wave amplitude and occurrence probability,the analysis results find that in statistics lower-band chorus emissions exhibit higher wave occurrence rates and larger normalized peak wave frequencies in the magnetically northern hemisphere but somehow stronger peak wave intensities in the magnetically southern hemisphere.While overall the differences between the two magnetically hemispheric distributions tend to be not significant,it is important to establish the magnetically hemispheric distribution profiles of lowerband chorus with respect to L-shell,magnetic local time,and geomagnetic latitude for improved understanding of chorus-induced dynamics of radiation belt electrons.

Numerical simulation of chorus-driving acceleration of relativistic electrons at extremely low L-shell during geomagnetic storms

During 2018 major geomagnetic storm,relativistic electron enhancements in extremely low L-shell regions(reaching L∼3)have been reported based on observations of ZH-1 and Van Allen probes satellites,and the storm is highly likely to be accelerated by strong whistler-mode waves occurring near very low L-shell regions where the plasmapause was suppressed.It is very interesting to observe the intense chorus-accelerated electrons locating in such low L-shells and filling into the slot region.In this paper,we further perform numerical simulation by solving the two-dimensional Fokker-Planck equation based on the bounce-averaged diffusion rates.Numerical results demonstrate the evolution processes of the chorus-driven electron flux and confirm the flux enhancement in low pitch angle ranges(20◦-50◦)after the wave-particle interaction for tens of hours.The simulation result is consistent with the observation of potential butterfly pitch angle distributions of relativistic electrons from both ZH-1 and Van Allen probes.

50%CHORUS WG防治辣椒灰霉病药效试验初报

对新型苯氨基嘧啶类杀菌剂50%CHORUSWG防治辣椒灰霉病的田间效果进行了试验。结果表明:50%CHO-RUSWG防治辣椒灰霉病的防治效果较好。用量为120g/100L水,喷药液50～70L/667m2,药后7d、10d对叶部病害的防效分别为71.63%、72.83%,对果实病害的防效分别为74.49%、75.337%。50%CHORUSWG是二甲酰亚胺类杀菌剂的良好替代药剂。

Radiation belt electron scattering by whistler-mode chorus in the Jovian magnetosphere: Importance of ambient and wave parameters

Whistler-mode chorus waves are regarded as an important acceleration mechanism contributing to the formation of relativistic and ultra-relativistic electrons in the Jovian radiation belts. Quantitative determination of the chorus wave driven electron scattering effect in the Jovian magnetosphere requires detailed information of both ambient magnetic field and plasma density and wave spectral property, which however cannot be always readily acquired from observations of existed missions to Jupiter. We therefore perform a comprehensive analysis of the sensitivity of chorus induced electron scattering rates to ambient magnetospheric and wave parameters in the Jovian radiation belts to elaborate to which extent the diffusion coefficients depend on a number of key input parameters. It is found that quasi-linear electron scattering rates by chorus can be strongly affected by the ambient magnetic field intensity, the wave latitudinal coverage, and the peak frequency and bandwidth of the wave spectral distribution in the Jovian magnetosphere, while they only rely slightly on the background plasma density profile and the peak wave normal angle, especially when the wave emissions are confined at lower latitudes. Given the chorus wave amplitude, chorus induced electron scattering rates strongly depend on Jovian L-shell to exhibit a tendency approximately proportional to L_J^3. Our comprehensive analysis explicitly demonstrates the importance of reliable information of both the ambient magnetospheric state and wave distribution property to understanding the dynamic electron evolution in the Jovian radiation belts and therefore has implications for future mission planning to explore the extreme particle radiation environment of Jupiter and its satellites.

Importance of electron distribution profiles to chorus wave driven evolution of Jovian radiation belt electrons

Wave-particle interactions triggered by whistler-mode chorus waves are an important contributor to the Jovian radiation belt electron dynamics. While the sensitivity of chorus-driven electron scattering to the ambient magnetospheric and wave parameters has been investigated, there is rather limited understanding regarding the extent to which the dynamic evolution of Jovian radiation belt electrons, under the impact of chorus wave scattering, depends on the electron distribution profiles. We adopt a group of reasonable initial conditions based upon the available observations and models for quantitative analyses. We find that inclusion of pitch angle variation in initial conditions can result in increased electron losses at lower pitch angles and substantially modify the pitch angle evolution profiles of > ~500 keV electrons, while variations of electron energy spectrum tend to modify the evolution primarily of 1 MeV and 5 MeV electrons. Our results explicitly demonstrate the importance to the radiation belt electron dynamics in the Jovian magnetosphere of the initial shape of the electron phase space density, and indicate the extent to which variations in electron energy spectrum and pitch angle distribution can contribute to the evolution of Jovian radiation belt electrons caused by chorus wave scattering.

Modeling the Evolution of Chorus Waves into Hiss Waves in the Magnetosphere

In this study, we analyze Cluster observations of whistler-mode chorus and hiss waves during the event of August 19-21, 2006. Chorus is present outside the plasmasphere and hiss occurs inside the plasmasphere. Using a recently constructed plasma boundary layer model, we perform a ray-tracing study on the propagation of chorus. Numerical results show that chorus can penetrate into the plasmasphere through the plasma boundary layer, evolving into hiss. The current data analysis and modeling provide a further observational support for the previous findings that chorus is the origin of plasmaspheric hiss.

A Three-Dimensional Ray Tracing Study on Whistler-Mode Chorus During Geomagnetic Activities

A three-dimensional ray tracing study of a whistler-mode chorus is conducted for different geomagnetic activities by using a global core plasma density model. For the upperband chorus, the initial azimuthal wave angle affects slightly the projection of ray trajectories onto the plane （Z, √（x^2 ＋ y^2））, but controls the longitudinal propagation. The trajectory of the upper-band chorus is strongly associated with the plasmapause and the magnetic local time （MLT） of chorus source region. For the high geomagnetic activity, the chorus trajectory moves inward together with the plasmapause. In the bulge region, the plasmapause extends outward, while the chorus trajectory moves outward together with the plasmapause. For moderately or high geomagnetic activity, the lower-band chorus suffers low hybrid resonance （LHR） reflection before it reaches the plasmapause, leading to a weak correlation with the geomagnetic activity and magnetic local time of the chorus source region. For low geomagnetic activity, the lower-band chorus may be reflected firstly at the plasmapause instead of suffering LHR reflection, exhibiting a propagation characteristic similar to that of the upper-band chorus. The results provide a new insight into the propagation characteristics of the chorus for different geomagnetic activities and contribute to further understanding of the acceleration of energetic electron by a chorus wave.

The Importance and Significance of Chorus Art to College Students’ Quality Education

Guality education emphasizes the all-round development of students’morality,intelligence,physique and beauty,and cultivates compound talents of comprehensive quality education.Music education is an important part of quality education.Chorus art is the key to music education.It is an important and healthy way of aesthetic education in campus culture.It is an important way to improve the quality education of college students.It has an important role and positive significance for the quality education of college students.

Look Forward to 15^th China International Chorus Festival

The 15^th China International Choral Festival will be launched online to present the"2.0 version"of the Festival to the audience.Co-sponsored by the Bureau of International Exchanges and Cooperation,Ministry of Culture and Tourism of the People's Republic of China,China Arts and Entertainment Group Ltd,Beijing Municipal Education Commission,Beiing Xicheng District People's Government.China Chorus Association and International Fed-eration for Choral Music(IFCM),the 15^th China International Chorus Festival(CICF)and IFCM World Choral Education Confer-ence is scheduled to take place from September to October,2020 in Beijing.

The Esthetic Connection between Chorus Voice and “Form”

Music is the art of sound,while chorus is the art of group vocal music.Choral art takes human voice as the carrier to express thoughts,emotions,and artistic images through sound.Harmonious,unified,balanced sound gives people the enjoyment of beauty and brings people-related pictorial association.As a unique form of vocal music art,chorus is also a comprehensive stage art belonging to the category of performance,which is a sister art belonging to the same and different families,such as dance and drama.In the visual arts such as dance and drama,the melody,timbre,and harmony of music match the figures appearing on the stage or screen.So that when we hear some kind of music there will belyrical beautiful,strong magnificent,or lively jumping,dark melancholy and so on feelings and associations.From ancient to modern times,in daily life,people sang and danced scenes were also their immediate reflection of music aesthetic feelings.Some of these aesthetic experiences are vague and some are specific.For example:We may think some music is humorous or sad,but when people hear the music,such as"the devil into the village",we will think of the scene in that movie.Which associated the Anti-Japanese War.In chorus,the influence of“form”on the aesthetic feeling of sound,or from the perspective of reverse thinking,canbe said to be the aesthetic expression of“form”by sound,which can relate to the breath of singing,the resonance position and the effect and change of the expression state.The audience can feel the chorus’s expression of aesthetic emotion directly from their hearing and then has a significant influence on the music sound and singing effect.In this paper,through the association of“form”to sound and aesthetic influence,with the help of some in the dance to tighten the intuitive posture,to chorus vertical sound insporation.Starting from the identity of visual perception and sound perception,this paper tries to understand our requirements for chorus singing from a reverse perspective.To maintain the breath of the chorus sound,to control the state,to establish the sound of harmony,unity and balance,as well as the performance of the overall sound effect,etc,to make a different angle of interpretation.

劲浪JMIab CHORUS725音箱

CHORUS(合唱)系列音箱,是法国著名音箱品牌JMlab(劲浪)旗下目前价格最为低廉的一个产品系列。不过呢。

Frequency Bands and Gaps of Magnetospheric Chorus Waves Generated by Resonant Beam/Plateau Electrons

In this paper, the modifications of the whistler dispersion characteristics are investigated which arise if resonant electrons are taken into account. The following chain of processes is emphasized: Generation of whistler waves propagating at different angles to the magnetic field and their nonlinear interaction with resonant electrons result in the appearance of modulated electron beams in the background plasma. As a result, the dispersion characteristics of waves in this new plasma might be significantly changed. By analysing the modified dispersion characteristics these changes are discussed. Supported by particle simulations and space observations, it is assumed that in the electron distribution function at the resonance velocity a plateau-like beam is formed. Because of the weakness of the beam, the term “beam/plateau population (b/p)” is used. By solving the kinetic dispersion relation of whistler waves in electron plasmas with b/p populations, the associated modifications of the whistler dispersion characteristics are presented in diagrams showing, in particular, the frequency versus propagation angle dependence of the excited waves. It is important to point out the two functions of the b/p populations. Because of the bi-directional excitation of whistler waves by temperature anisotropy, one has to distinguish between up- and downstream populations and accordingly between two b/p modes. The interaction of the beam-shifted cyclotron mode ω= Ωe + k⋅Vb (V bVb is the b/p velocity, Ωe: electron cyclotron frequency) with the whistler mode leads to enhanced damping at the ω-k point where they intersect. This is the origin of the frequency gap at half the electron cyclotron frequency (ω~Ωe/2) for quasi-parallel waves which are driven by temperature anisotropy. Furthermore, it is shown that the upstream b/p electrons alone (in the absence of temperature anisotropy) can excite (very) oblique whistler waves near the resonance cone. The governing instability results from the interaction of the beam/plateau mode ω= k⋅Vb (Vb > 0) with the whistler mode. As a further remarkable effect, another frequency gap at ω~Ωe/2 in the range of large propagation angles may arise. It happens at the triple point where both b/p modes and the whistler mode intersect. Our investigation shows that the consideration of resonant electrons in form of beam/plateau populations leads to significant modifications of the spectrum of magnetospheric whistler waves which are originally driven by temperature anisotropy. Relations to recent and former space observations are discussed.

劲浪JM lab CHORUS 715音箱

当有一天你想感受一下由浪漫的法兰西民族制造的音箱时,几乎可以完全肯定,你头脑中首先出现的品牌便是JM lab,它有一个为国内发烧友所熟知、充满力量的中文名字--劲浪.

热情奔放 表现全面的劲浪Chorus707

这款音箱给人的最大感受就是各频段都有充沛的量感,速度快而且有非常优秀的瞬态响应,表现任何类型的音乐都充满动感与活力。既可以听流行音乐,也适合欣赏古典音乐。

Focal Chorus 826W特别版音箱

要说法国Focal音箱的代表作，无疑是新乌托邦系列。新乌托邦系列中的型号，无论是旗舰的Grande Utopia EM，还是稍小一号的Stella Utopia EM，都是同价位音箱中的佼佼者，

Focal Chorus 836V落地式音箱

在目前的主流品牌中，Focal是一个在单元、箱体技术方面非常成熟的品牌-特别是在近年来，其新一代的多个系列的产品不仅屡获殊荣，而且还得到市场及资深音响爱好者的高度评价。