Correction: Neuropsychopharmacology Volume 50 Issue 2
Related Articles
Mechanochemical bistability of intestinal organoids enables robust morphogenesis
Reproducible pattern and form generation during embryogenesis is poorly understood. Intestinal organoid morphogenesis involves a number of mechanochemical regulators such as cell-type-specific cytoskeletal forces and osmotically driven lumen volume changes. It is unclear how these forces are coordinated in time and space to ensure robust morphogenesis. Here we show how mechanosensitive feedback on cytoskeletal tension gives rise to morphological bistability in a minimal model of organoid morphogenesis. In the model, lumen volume changes can impact the epithelial shape via both direct mechanical and indirect mechanosensitive mechanisms. We find that both bulged and budded crypt states are possible and dependent on the history of volume changes. We test key modelling assumptions via biophysical and pharmacological experiments to demonstrate how bistability can explain experimental observations, such as the importance of the timing of lumen shrinkage and robustness of the final morphogenetic state to mechanical perturbations. This suggests that bistability arising from feedback between cellular tensions and fluid pressure could be a general mechanism that coordinates multicellular shape changes in developing systems.
The dynamics of the Reddit collective action leading to the GameStop short squeeze
In early 2021, the stock prices of GameStop, AMC, Nokia, and BlackBerry experienced dramatic increases, triggered by short-squeeze operations that have been largely attributed to Reddit’s retail investors. Here we shed light on the extent and timing of Reddit users’ influence on the GameStop short squeeze. Using statistical analysis tools with high temporal resolution, we find that increasing Reddit discussions anticipated high trading volumes. This effect emerged abruptly a few weeks before the event but waned once the community gained widespread visibility through Twitter. Meanwhile, the collective investment of the community, quantified through posts of individual positions, closely mirrored the market capitalization of the stock. This evidence suggests a coordinated action of users in developing a shared financial strategy through social media—targeting GameStop first and other stocks afterward. Overall, our results provide novel insights into the role of Reddit users in the dynamics of the GameStop short squeeze.
Super-resolved microstructure of pyrolyzing superlight ablators
The microstructural evolution of superlight ablators during pyrolysis was investigated using in situ X-ray micro-computed tomography and generative adversarial networks. Superlight ablators, a type of syntactic foam thermal protection materials, are commonly employed in the backshells of planetary entry probes. Synchrotron X-rays were used to resolve the material constituents during thermal degradation, including resin, silica microballoons, cork filler, refractory fibers, and voids. A super-resolution methodology was implemented, where high-resolution tomography scans were applied to denoise, segment and analyze lower-resolution in situ datasets that captured a large field of view. This multi-scale approach enabled the quantification of morphological and effective properties as a function of temperature during degradation, while also relating these changes to relevant decomposition chemistry. This study demonstrates a strategy for time-resolving rapid, multiphase decomposition events occurring under high-temperature test environments that mimic atmospheric entry.
Exploring effects of platelet contractility on the kinetics, thermodynamics, and mechanisms of fibrin clot contraction
Mechanisms of blood clot contraction – platelet-driven fibrin network remodeling, are not fully understood. We developed a detailed computational ClotDynaMo model of fibrin network with activated platelets, whose clot contraction rate for normal 450,000/µl human platelets depends on serum viscosity η, platelet filopodia length l, and weakly depends on filopodia traction force f and filopodia extension-retraction speed v. Final clot volume is independent of η, but depends on v, f and l. Analysis of ClotDynaMo output revealed a 2.24 TJ/mol clot contraction free energy change, with ~67% entropy and ~33% internal energy changes. The results illuminate the “optimal contraction principle” that maximizes volume change while minimizing energy cost. An 8-chain continuum model of polymer elasticity containing platelet forces, captures clot contractility as a function of platelet count, η and l. The ClotDynaMo and continuum models can be extended to include red blood cells, variable platelet properties, and mechanics of fibrin network.
Frequency shift caused by nonuniform field and boundary relaxation in magnetic resonance and comagnetometers
In magnetic resonance experiments, it is widely recognized that a nonuniform magnetic field can lead to an increase in the resonance line width, as well as a reduction in sensitivity and spectral resolution. However, a nonuniform magnetic field can also cause shifts in resonance frequency, which has received far less attention. In this work, we investigate the frequency shift caused by boundary relaxation and nonuniform magnetic field with arbitrary spatial distribution. We find that this frequency shift is spin-species dependent, implying a systematic error in NMR gyroscopes and comagnetometers. The first order correction to this systematic error is proportional to the difference of boundary relaxation rate, and dominates for small cells. In contrast, the third and higher order corrections arise from the difference of gyromagnetic ratios of spin species, and dominates for large cells. This insight helps understanding the unexplained isotope shifts in recent NMR gyroscopes and new physics searching experiments that utilize comagnetometers. Finally, we propose a tool for wall interaction research based on the frequency shift’s dependency on boundary relaxation.
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