2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/29544We present a general introduction to the non-zero temperature dynamic and transport properties of low-dimensional systems near a quantum phase transition. Basic results are reviewed in the context of experiments on the spin-ladder compounds, insulating two-dimensional antiferromagnets, and double-layer quantum Hall systems. Recent large N computations on an extended t-J model (cond-mat/9906104) motivate a global scenario of the quantum phases and transitions in the high temperature superconductors, and connections are made to numerous experiments.11 pages; half-plenary talk at LT22, HelsinkiStrongly Correlated ElectronsSuperconductivitytext