Petculescu Andi G, Lueptow Richard M
Northwestern University, 2145 Sheridan Road, Evanston, Illinois 60208, USA.
Phys Rev Lett. 2005 Jun 17;94(23):238301. doi: 10.1103/PhysRevLett.94.238301. Epub 2005 Jun 14.
Identifying molecular relaxation processes in excitable gases remains challenging. An algorithm that reconstructs the primary relaxation processes is presented. Based on measurements of acoustic attenuation and sound speed at two frequencies, it synthesizes the entire frequency dependence of the complex effective specific heat of the gas, which is the macroscopic "footprint" of relaxation effects. The algorithm is based on the fact that for a simple relaxation process, such as occurs in many polyatomic gases at temperatures around 300 K, the effective specific heat traces a semicircle in the complex plane as a function of frequency. Knowing the high-frequency or instantaneous value of the specific heat provides the capability to not only sense the presence, but also infer the nature and, for mixtures of unlike-symmetry molecules, the concentration of foreign molecules leaking in a host gas.
识别可激发气体中的分子弛豫过程仍然具有挑战性。本文提出了一种重建主要弛豫过程的算法。该算法基于对两个频率下的声衰减和声速的测量，合成气体复有效比热容的全频率依赖性，这是弛豫效应的宏观“印记”。该算法基于这样一个事实：对于简单的弛豫过程，比如许多多原子气体在300K左右温度下发生的过程，有效比热容在复平面中随频率变化呈半圆形轨迹。知道比热容的高频或瞬时值不仅能够检测其存在，还能推断其性质，对于不对称分子的混合物，还能推断主体气体中泄漏的外来分子的浓度。
