High-level cognition is often accomplished not byindividuals working in isolation, but by distributed, complexcognitive systems. Examples include teams of scientists orcollaboratively improvising musicians. These distributedsystems can undergo critical transitions, suddenly movingfrom one stable pattern of activity to another. For instance,in ‘free jazz,’ where musicians improvise without apredetermined plan or a central leader, the performance willoften settle into a particular texture or style beforetransitioning to something entirely new, often quitesuddenly. When do these transitions occur? Are theyforeseeable? Inspired by suggestions that cognitive systemsare, in some sense, a kind of ‘ecosystem,’ we draw on recentwork in quantitative ecology that has begun to describegeneric early warning signals of impending criticaltransitions in ecosystems. We apply these techniques to acorpus of audio recordings of professional jazz quartetsplaying improvised music. We find that the same genericmeasures that have been used successfully to predict criticaltransitions in natural ecosystems describe the complexdynamics of improvised musical performance in the lead-upto transitions. By taking seriously the metaphor thatcognition occurs in ‘ecosystems,’ we gain new insights intohow stable patterns of thought can emerge suddenly incomplex cognitive systems.

Collective improvisation is remarkable. When people improvise—whether dancing, making music, or conversing— they coordinate their behavior while exploring abstract spaces of movements, sounds, and ideas. How do improvisers navigate these abstract spaces? One possibility is that improvisation builds on foraging strategies used to search the physical world. Here, we investigate the dynamics of an especially complex and abstract form of collective improvisation: free jazz. We quantify how professional jazz ensembles navigate a space of sounds and show that it resembles a foraging strategy known as Area Restricted Search. In particular, ensembles change their playing dynamics in response to encounters with novel ‘soundworlds.' Before encountering a new soundworld, ensembles engage in widespread exploration; immediately after, they shift to focused exploitation of the new sound. While collective improvisation pushes at our cognitive limits and is a paradigm of human creativity, it may build on evolutionarilyancient strategies for searching space.

Serious climate changes and energy-related environmental problems are currently critical issues in the world. In order to reduce carbon emissions and save our environment, renewable energy harvesting technologies will serve as a key solution in the near future. Among them, triboelectric nanogenerators (TENGs), which is one of the most promising mechanical energy harvesters by means of contact electrification phenomenon, are explosively developing due to abundant wasting mechanical energy sources and a number of superior advantages in a wide availability and selection of materials, relatively simple device configurations, and low-cost processing. Significant experimental and theoretical efforts have been achieved toward understanding fundamental behaviors and a wide range of demonstrations since its report in 2012. As a result, considerable technological advancement has been exhibited and it advances the timeline of achievement in the proposed roadmap. Now, the technology has reached the stage of prototype development with verification of performance beyond the lab scale environment toward its commercialization. In this review, distinguished authors in the world worked together to summarize the state of the art in theory, materials, devices, systems, circuits, and applications in TENG fields. The great research achievements of researchers in this field around the world over the past decade are expected to play a major role in coming to fruition of unexpectedly accelerated technological advances over the next decade.