We collect recent results on deriving useful response relations also for nonequilibrium systems. The approach is based on dynamical ensembles, determined by an action on trajectory space. (Anti)Symmetry under time-reversal separates two complementary contributions in the response, one entropic the other frenetic. Under time-reversal invariance of the unperturbed reference process, only the entropic term is present in the response, giving the standard fluctuation-dissipation relations in equilibrium. For nonequilibrium reference ensembles, the frenetic term contributes essentially and is responsible for new phenomena. We discuss modifications in the Sutherland-Einstein relation, the occurence of negative differential mobilities and the saturation of response. We also indicate how the Einstein relation between noise and friction gets violated for probes coupled to a nonequilibrium environment. We end with some discussion on the situation for quantum phenomena, but the bulk of the text concerns classical mesoscopic (open) systems. The choice of many simple examples is trying to make the notes pedagogical, to introduce an important area of research in nonequilibrium statistical mechanics.
Non-Equilibrium Thermodynamic Description of the Coupling between Structural and Entropic Modes in Supercooled Liquids
在结构重排（α弛豫）和热扩散发生在同一时间尺度的温度范围内（T=200-340 K），研究了过冷甘油对脉冲受激热光栅（q=0.63 μ m ^-1）的密度响应。两种模式之间发生强相互作用，从而引起表观热导率的T依赖性下降和冷却时表观α弛豫时间的平坦化。建立了弛豫流体长时间响应的非平衡热力学模型。该模型能够再现实验数据，并解释所观察到的现象。
