Title: The Spheroidal Analog Method for Modeling Irregular Porous Aggregates Show Chinese title

Title: 球面模拟方法用于建模不规则多孔聚集体

Abstract: It is shown that the optical properties of an irregular porous grain with effective radius $a_{\rm eff}\lesssim 3\lambda$ (where $\lambda$ is the wavelength) can be well approximated by a ``spheroidal analog'': a spheroid with appropriate axial ratio and size, with a dielectric function obtained from an effective medium theory. Prescriptions for specifying the axial ratio and porosity of the spheroidal analog, based on simple geometric properties, are given. The accuracy of the spheroidal analogue method is studied for irregular grains with a range of structures and porosities. Different effective medium theories are compared; Bruggeman's theory is found to give the best results. The accuracy of the spheroidal analog method justifies the use of spheroids for modeling absorption, scattering and polarization by interstellar, circumstellar, or interplanetary dust. Show Chinese abstract

Abstract: 研究表明，有效半径为$a_{\rm eff}\lesssim 3\lambda$的不规则多孔颗粒（其中$\lambda$是波长）的光学性质可以很好地用一个“椭球类比”来近似：一个具有适当轴比和尺寸的椭球，其介电函数通过有效介质理论获得。 给出了基于简单几何特性的指定椭球类比的轴比和孔隙率的方案。 研究了不同结构和孔隙率的不规则颗粒的椭球类比方法的准确性。 比较了不同的有效介质理论；发现布里格曼理论给出的结果最好。 椭球类比方法的准确性证明了使用椭球来模拟星际、星周或行星际尘埃的吸收、散射和偏振是合理的。