An acoustic signature of extreme failure on model granular materials.

Unexpectedly, granular materials can fail, the structure even destroyed, spontaneously in simple isotropic compression with stick-slip-like frictional behaviour. This extreme behaviour is conceptually impossible for saturated two-phase assembly in classical granular physics. Furthermore, the triggering mechanisms of these laboratory events remain mysterious, as in natural earthquakes. Here, we report a new interpretation of these failures in under-explored isotropic compression using the time-frequency analysis of Cauchy continuous wavelet transform of acoustic emissions and multiphysics numerical simulations. Wavelet transformation techniques can give insights into the temporal evolution of the state of granular materials en route to failure and offer a plausible explanation of the distinctive hearing sound of the stick-slip phenomenon. We also extend the traditional statistical seismic Gutenberg-Richter power-law behaviour for hypothetical biggest earthquakes based on the mechanisms of stick-slip frictional instability, using very large artificial isotropic labquakes and the ultimate unpredictable liquefaction failure.

High-temporal-resolution quasideterministic dynamics of granular stick-slip.

We report high-temporal-resolution observations of the spontaneous instability of model granular materials under isotropic and triaxial compression in fully drained conditions during laboratory tests representative of earthquakes. Unlike in natural granular materials, in the model granular materials, during the first stage of the tests, i.e., isotropic compression, a series of local collapses of various amplitudes occurs under random triggering cell pressures. During the second stage, i.e., shearing under triaxial compression, the model granular samples exhibit very large quasiperiodic stick-slip motions at random deviatoric triggering stresses. These motions are responsible for very large stress drops that are described by power laws and are accurate over more than 3 decades in logarithmic space. Then, we identify the quasideterministic nature of these stick-slip events, assuming that they are fully controlled by the cell pressure and solid fraction. Finally, we discuss the potential mechanisms that could explain these intriguing behaviors and the possible links with natural earthquakes.

Caudal anesthesia in a patient with severe pulmonary hypertension.

Delivery of anesthesia to patients with severe pulmonary hypertension can be extremely challenging. The profound hemodynamic alterations of the disease can often be exacerbated by alterations in circulatory function brought about by anesthetic and surgical interventions. High perioperative morbidity and mortality rates have been reported. Minimizing adverse outcomes in these patients requires careful perioperative evaluation and planning. Selection of an anesthetic technique suitable for the surgery without causing major hemodynamic alterations, which can lead to cardiac failure and death, is a unique consideration of the anesthesia provider. As shown in this case report, caudal anesthesia, when appropriate, can offer a safe anesthetic for these patients.