In order to make a robot precisely track desired periodic trajectories, this work proposes a sliding mode based repetitive learning control method, which incorporates characteristics of sliding mode control into repetitive learning control. The learning algorithm not only utilizes shape functions to approximate influence functions in integral transforms, but also estimates inverse dynamics functions based on integral transforms. It learns at each sampling instant the desired input joint torques without prior knowledge of the robot dynamics. To carry out sliding mode control, a reaching law method is employed, which is robust against model uncertainties and external disturbances. Experiments are performed to validate the proposed method. [S0022-0434(00)02001-3]

Modulated photoinduced absorption and photoluminescence are used to study triplet-to-triplet Dexter energy transfer in Ir-complexes/polyfluorene blend systems. There is no Dexter energy transfer for red iridium ͑III͒bis͓2-͑9,9-dibutylfluorenyl͒-1-isoquinoline͑acetylacetonate͔͒ ͑DFIr͒ and red iridium ͑III͒ bis͓͑2-͑2-benzo-thienyl͒pyridinatoN,C3͔ acetyl-acetonate͒ ͑BtpIr͒ dopants. Although green iridium͑III͒tris͓2-͑4-tolyl͒pyridinato-N,C2͔ ͓Ir͑mppy͒ 3 ͔ has no triplet confinement in polyfluorene host, it has clear evidence for Dexter energy transfer. Aggregation and dopant lifetime are shown to significantly affect the energy transfer. The presence of Dexter transfer implies the possibility to harvest triplet excitons of polyfluorene in polymer light-emitting diodes even without carrier trapping and triplet exciton confinement.