No abstract

No abstract

Synchronization of oscillators, a phenomenon found in a wide variety of natural and engineered systems, is typically understood through a reduction to a first-order phase model with simplified dynamics. Here, by exploiting the precision and flexibility of nanoelectromechanical systems, we examined the dynamics of a ring of quasi-sinusoidal oscillators at and beyond first order. Beyond first order, we found exotic states of synchronization with highly complex dynamics, including weak chimeras, decoupled states, traveling waves, and inhomogeneous synchronized states. Through theory and experiment, we show that these exotic states rely on complex interactions emerging out of networks with simple linear nearest-neighbor coupling. This work provides insight into the dynamical richness of complex systems with weak nonlinearities and local interactions.

This paper introduces an approach to assess and improve the time-dependent resilience of urban infrastructure systems, where resilience is defined as the systems' ability to resist various possible hazards, absorb the initial damage from hazards, and recover to normal operation one or multiple times during a time period T. For different values of T and its position relative to current time, there are three forms of resilience: previous resilience, current potential resilience, and future potential resilience. This paper mainly discusses the third form that takes into account the systems' future evolving processes. Taking the power transmission grid in Harris County, Texas, USA as an example, the time-dependent features of resilience and the effectiveness of some resilience-inspired strategies, including enhancement of situational awareness, management of consumer demand, and integration of distributed generators, are all simulated and discussed. Results show a nonlinear nature of resilience as a function of T, which may exhibit a transition from an increasing function to a decreasing function at either a threshold of post-blackout improvement rate, a threshold of load profile with consumer demand management, or a threshold number of integrated distributed generators. These results are further confirmed by studying a typical benchmark system such as the IEEE RTS-96. Such common trends indicate that some resilience strategies may enhance infrastructure system resilience in the short term, but if not managed well, they may compromise practical utility system resilience in the long run. Urban infrastructure systems are vital to the operation of modern society and its economy, yet they are unavoidably subject to different types of hazards and are vulnerable to cascading failures within and across systems. Hence, different from traditional system safety analyses using scenarios or hypothetical accidents in an attempt to understand their effects and the reasons for their occurrence, the concept of resilience has been proposed in acknowledgment of the unavoidability of hazards or accidents. A number of articles have recently assessed the resilience of systems under single and multiple hazards. However, these studies neither address the evolving features of infrastructure systems due to the steady increase of service demand and post-event improvement efforts, nor address inter-hazards interactions, as the occurrences and effects of future hazards may be affected by previous ones. Capturing these unexplored features leads to the proposal of a time-dependent resilience metric for urban infrastructure systems. This paper uses power transmission systems as examples to show the time-dependent and nonlinear features of resilience, and discusses the effectiveness of some resilienceinspired strategies, including situational awareness (SA) enhancement, consumer demand management, and distributed generators (DGs) integration, in order to emphasize the need to carefully manage emerging smart infrastructure techniques.

No abstract