Societal collapse

Summary

Societal collapse (also known as civilizational collapse) is the fall of a complex human society characterized by the loss of cultural identity and of social complexity as an adaptive system, the downfall of government, and the rise of violence. Possible causes of a societal collapse include natural catastrophe, war, pestilence, famine, economic collapse, population decline or overshoot, mass migration, and sabotage by rival civilizations. A collapsed society may revert to a more primitive state, be absorbed into a stronger society, or completely disappear. Virtually all civilizations have suffered such a fate, regardless of their size or complexity, but some of them later revived and transformed, such as China, India, and Egypt. However, others never recovered, such as the Western and Eastern Roman Empires, the Maya civilization, and the Easter Island civilization. Societal collapse is generally quick but rarely abrupt.

Official source

https://en.wikipedia.org/wiki/Societal_collapse

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Avalanches can occur when a porous snow layer lies beneath a dense cohesive snow slab. Field experiments and simulations now reveal different crack-propagation regimes in slab avalanches, similar to rupture propagation following an earthquake. Snow slab avalanches, characterized by a distinct, broad fracture line, are released following anticrack propagation in highly porous weak snow layers buried below cohesive slabs. The anticrack mechanism is driven by the volumetric collapse of the weak layer, which leads to the closure of crack faces and to the onset of frictional contact. Here, on the basis of snow fracture experiments, full-scale avalanche measurements and numerical simulations, we report the existence of a transition from sub-Rayleigh anticrack to supershear crack propagation. This transition follows the Burridge-Andrews mechanism, in which a supershear daughter crack nucleates ahead of the main fracture front and eventually propagates faster than the shear wave speed. Furthermore, we show that the supershear propagation regime can exist even if the shear-to-normal stress ratio is lower than the static friction coefficient as a result of the loss of frictional resistance during collapse. This finding shows that snow slab avalanches have fundamental similarities with strike-slip earthquakes.

NATURE PORTFOLIO2022

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The convergence of sensor-based vehicle automation and Inter-Vehicle Communication (IVC) will be a key to achieve the full automation of vehicles. In this paper we present a new method for the design and performance evaluation of Cooperative Automated Driving (CAD) systems, based on a bidirectional coupling of vehicle and network simulators (Webots and ns-3). The coupling exploits the comprehensive capabilities of the simulators at a reasonable computational complexity and allows simulating CAD systems with high accuracy. We demonstrate the capabilities of the simulation tool by a case study of convoy driving with automated vehicles using a fully distributed control algorithm and IVC. The study compares CAD-specific metrics (safety distance, headway, speed) for an ideal and a realistic communication channel. The simulation results underline the need of accurate modeling and give valuable insights for the design of CAD systems.

2017

Conformal Passivation of Multi-Channel GaN Power Transistors for Reduced Current Collapse

Kai Cheng, Catherine Erine, Elison de Nazareth Matioli, Luca Nela, Remco Franciscus Peter van Erp, Halil Kerim Yildirim

Multi-channel power devices, in which several AlGaN/GaN layers are stacked to achieve multiple two-dimensional electron gases (2DEGs), have recently led to a significant increase in the device conductivity while maintaining high breakdown voltage, resulting in excellent DC performances. However, their dynamic performance is yet to be demonstrated, especially due to the absence of an effective passivation technique for their 3D structure. Here, we present a surface passivation technology for multi-channel devices based on a conformal deposition of a thin SiO2 interlayer followed by a low-pressure chemical vapor deposition (LPCVD) Si3 N4 layer around the multi-channel fins, which enables to effectively reduce the electron traps both at the AlGaN top surface and at the fin sidewalls. Such an approach led to a significant reduction of the dynamic on-resistance ( RON ) in multi-channel devices under large off-state voltages of 350 V and comparable dynamic performance with passivated single-channel reference devices. This work proves that, in addition to the excellent DC performance, the multi-channel technology can offer reduced current collapse, unveiling the potential of this platform for future power electronic applications.

2020