亚恒星云中非球形尘埃的静电不稳定性
Electrostatic instability of non-spherical dust in sub-stellar clouds
AI总结：
本文研究亚恒星云中带电非球形尘埃的静电稳定性，推导了偏心率临界判据，并量化其对放电、表面积、颗粒分布及偏振的影响。
摘要：
带电尘埃云通过闪电事件或颗粒间放电等放电现象，在亚恒星大气演化中发挥重要作用。由此产生的等离子体活化提供了非平衡化学的另一种来源，可能引发一系列在能量上原本无法发生的化学反应。本文旨在解决亚恒星云中带电椭球形尘埃颗粒的静电稳定性问题，及其对颗粒间静电放电、大气气-固表面化学可用面积、颗粒偏心率分布函数和观测到的偏振信号的影响。本文推导了作为颗粒尺寸 $a\in[0.2,1.8]~\mu$m、浮动电势 $\phi_{f}\in[1,10]$~V 和拉伸强度 $\Sigma_{s}=10^{3}$~Pa 函数的、静电稳定尘埃偏心率允许值的判据。作为静电不稳定性的结果，我们还计算了椭球极点处预期的电场增强、尘埃颗粒表面积的增加、颗粒偏心率分布函数的截断以及由此产生的偏振度。偏心率低于临界值的尘埃颗粒将是静电稳定的；而偏心率高于临界值的颗粒则不稳定。本文给出的结果不仅适用于椭球形尘埃颗粒，也适用于任何非球形尘埃颗粒，只要其非均匀表面电场或非均匀拉伸强度可能易受静电不稳定性影响。在此背景下，静电侵蚀提供了一种可能产生凹凸不平、形状不规则或多孔颗粒的机制。
英文摘要：
Charged dust clouds play an important role in the evolution of sub-stellar atmospheres through electrical discharges such as lightning events or inter-grain discharges. The consequent plasma activation presents an alternative source of disequilibrium chemistry, potentially triggering a set of chemical reactions otherwise energetically unavailable. The aim of this paper is to address the problem of the electrostatic stability of charged spheroidal dust grains in sub-stellar clouds and its impact on inter-grain electrostatic discharges, the available area for atmospheric gas-phase surface chemistry, the particle eccentricity distribution function and observed polarization signatures. This paper has derived the criterion for the allowed values of dust eccentricity that are electrostatically stable as a function of grain size $a\in[0.2,1.8]~μ$m, floating potential $ϕ_{f}\in[1, 10]$~V and tensile strength $Σ_{s}=10^{3}$~Pa. As a consequence of electrostatic instability we also calculate the expected electric field enhancement at the spheroidal poles, the increased surface area of a dust grain, the truncation of the particle eccentricity distribution function and the resultant degree of polarization. Dust grains with an eccentricity below a critical value will be electrostatically stable; whereas, grains with an eccentricity above a critical value will be unstable. The results presented here are applicable not only to spheroidal dust grains but any non-spherical dust grains where non-uniform surface electric fields or inhomogeneous tensile strengths could be susceptible to electrostatic instability. In this context electrostatic erosion presents a mechanism that may produce bumpy, irregularly shaped or porous grains.
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