Dense snow flowing past a deflecting obstacle: An experimental investigation

International audienceDense snow flowing down a rough inclined chute and interacting with a deflecting obstacle is experimentally investigated. These experiments are of considerable practical interest for the design of deflecting dams that are built to defend against large-scale snow avalanches. Our study focused on the maximum run-up reached by the dense flowing snow on a deflector. It was found that the maximum run-up was strongly correlated to the upstream Froude number and the deflecting angle of the obstacle. The data was compared with the predictions from a simple conversion of kinetic energy to potential energy on one hand and with oblique shock calculations on the other hand. The predicted values from the first approach were in better agreement with the measured values in comparison with the second approach. During a short transient phase at the end of the flow, it was shown that the flow features from our snow experiments were identical to the flow features from the previous granular and water experiments. In these conditions, the shallow-layer theory was also found to be relevant for snow flows

Dense snow flowing past a deflecting obstacle: An experimental investigation

International audienceDense snow flowing down a rough inclined chute and interacting with a deflecting obstacle is experimentally investigated. These experiments are of considerable practical interest for the design of deflecting dams that are built to defend against large-scale snow avalanches. Our study focused on the maximum run-up reached by the dense flowing snow on a deflector. It was found that the maximum run-up was strongly correlated to the upstream Froude number and the deflecting angle of the obstacle. The data was compared with the predictions from a simple conversion of kinetic energy to potential energy on one hand and with oblique shock calculations on the other hand. The predicted values from the first approach were in better agreement with the measured values in comparison with the second approach. During a short transient phase at the end of the flow, it was shown that the flow features from our snow experiments were identical to the flow features from the previous granular and water experiments. In these conditions, the shallow-layer theory was also found to be relevant for snow flows

Organelle mapping in dendrites of human iPSC-derived neurons reveals dynamic functional dendritic Golgi structures

Secretory pathways within dendrites of neurons have been proposed for local transport of newly synthesized proteins. However, little is known about the dynamics of the local secretory system and whether the organelles are transient or stable structures. Here, we quantify the spatial and dynamic behavior of dendritic Golgi and endosomes during differentiation of human neurons generated from induced pluripotent stem cells (iPSCs). In early neuronal development, before and during migration, the entire Golgi apparatus transiently translocates from the soma into dendrites. In mature neurons, dynamic Golgi elements, containing cis and trans cisternae, are transported from the soma along dendrites, in an actin-dependent process. Dendritic Golgi outposts are dynamic and display bidirectional movement. Similar structures were observed in cerebral organoids. Using the retention using selective hooks (RUSH) system, Golgi resident proteins are transported efficiently into Golgi outposts from the endoplasmic reticulum. This study reveals dynamic, functional Golgi structures in dendrites and a spatial map for investigating dendrite trafficking in human neurons

Distinct anterograde trafficking pathways of BACE1 and amyloid precursor protein from the TGN and the regulation of amyloid-beta production

Processing of amyloid precursor protein (APP) by the beta-secretase BACE1 is the initial step of the amyloidogenic pathway to generate amyloid-beta (A beta). Although newly synthesized BACE1 and APP are transported along the secretory pathway, it is not known whether BACE1 and APP share the same post-Golgi trafficking pathways or are partitioned into different transport routes. Here we demonstrate that BACE1 exits the Golgi in HeLa cells and primary neurons by a pathway distinct from the trafficking pathway for APP. By using the Retention Using Selective Hooks system, we show that BACE1 is transported from the trans-Golgi network to the plasma membrane in an AP-1- and Arf1/4-dependent manner. Subsequently, BACE1 is endocytosed to early and recycling endosomes. Perturbation of BACE1 post-Golgi trafficking results in an increase in BACE1 cleavage of APP and increased production of both A beta 40 and A beta 42. These findings reveal that Golgi exit of BACE1 and APP in primary neurons is tightly regulated, resulting in their segregation along different transport routes, which limits APP processing

Chimera states in mechanical oscillator networks

The synchronization of coupled oscillators is a fascinating manifestation of self-organization that nature employs to orchestrate essential processes of life, such as the beating of the heart. Although it was long thought that synchrony or disorder were mutually exclusive steady states for a network of identical oscillators, numerous theoretical studies in recent years have revealed the intriguing possibility of `chimera states', in which the symmetry of the oscillator population is broken into a synchronous and an asynchronous part. However, a striking lack of empirical evidence raises the question of whether chimeras are indeed characteristic to natural systems. This calls for a palpable realization of chimera states without any fine-tuning, from which physical mechanisms underlying their emergence can be uncovered. Here, we devise a simple experiment with mechanical oscillators coupled in a hierarchical network to show that chimeras emerge naturally from a competition between two antagonistic synchronization patterns. We identify a wide spectrum of complex states, encompassing and extending the set of previously described chimeras. Our mathematical model shows that the self-organization observed in our experiments is controlled by elementary dynamical equations from mechanics that are ubiquitous in many natural and technological systems. The symmetry breaking mechanism revealed by our experiments may thus be prevalent in systems exhibiting collective behaviour, such as power grids, opto-mechanical crystals or cells communicating via quorum sensing in microbial populations.Comment: Main text, supplementary info and 3 ancillary movie