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Abstract The magnetospheres of the Earth and other magnetized planets are replete with high‐frequency fluctuations, which are sometimes accompanied by multiple‐harmonic electron cyclotron waves, and lower frequency waves of the whistler‐mode type. Such waves are presumed to be excited by energetic electrons trapped in the dipolar magnetic field, the so‐called loss‐cone electrons, the electron ring distribution being a highly idealized example. The present paper investigates the stability of electron ring distribution with respect to the excitation of quasi‐electrostatic upper‐hybrid wave instability as well as the quasi‐electromagnetic whistler mode instability that operates near electron cyclotron frequency. By employing a two‐dimensional particle‐in‐cell numerical simulation, it is demonstrated that the relatively early dynamics is dominated by the upper‐hybrid wave instability, but over a longer time period it is the whistler mode instability that ultimately determines the final relaxed state. The simulation results are interpreted with the quasilinear theoretical framework. 

Cellulose, the most abundant polysaccharide on earth composing plant cell walls, is synthesized by coordinated action of multiple enzymes in cellulose synthase complexes embedded within the plasma membrane. Multiple chains of cellulose fibrils form intertwined extracellular matrix networks. It remains largely unknown how newly synthesized cellulose is assembled into an intricate fibril network on cell surfaces. Here, we have established an in vivo time-resolved imaging platform to continuously visualize cellulose biosynthesis and fibril network assembly onArabidopsis thalianaprotoplast surfaces as the primary cell wall regenerates. Our observations provide the basis for a model of cellulose fibril network development in protoplasts driven by an interplay of multiscale dynamics that includes rapid diffusion and coalescence of nascent cellulose fibrils, processive elongation of single fibrils, and cellulose fibrillar network rearrangement during maturation. This study provides fresh insights into the dynamic and mechanistic aspects of cell wall synthesis at the single-cell level. 

Understanding the depolarization of ferroelectric materials caused by external stimuli is critical for maintaining the aligned polarization states. Although thermal depolarization in poled materials is well established, the mechanisms of electric field-induced depolarization remain largely unexplored. In this study, we investigate the electrical depoling behavior of [001]-oriented rhombohedral Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) single crystals poled using direct current poling (DCP) and alternating current poling (ACP). We reveal that the ACP sample exhibits a lower reverse coercive field than the DCP specimen. We compare the effects of bipolar and unipolar electric fields applied in the reverse poling direction, analyzing the changes in permittivity and piezoelectric resonance. Piezoresponse force microscopy is employed to characterize domain configurations in poled and electrically depoled samples. Our findings suggest that property degradation may arise from the nucleation and growth of domains oriented opposite to the initial arrangement. 

Solute transport and biogeochemical reactions in porous and fractured media flows are controlled by mixing, as are subsurface engineering operations such as contaminant remediation, geothermal energy production, and carbon sequestration. Porous media flows are generally regarded as slow, so the effects of fluid inertia on mixing and reaction are typically ignored. Here, we demonstrate through microfluidic experiments and numerical simulations of mixing-induced reaction that inertial recirculating flows readily emerge in laminar porous media flows and dramatically alter mixing and reaction dynamics. An optimal Reynolds number that maximizes the reaction rate is observed for individual pore throats of different sizes. This reaction maximization is attributed to the effects of recirculation flows on reactant availability, mixing, and reaction completion, which depend on the topology of recirculation relative to the boundary of the reactants or mixing interface. Recirculation enhances mixing and reactant availability, but a further increase in flow velocity reduces the residence time in recirculation, leading to a decrease in reaction rate. The reaction maximization is also confirmed in a flow channel with grain inclusions and randomized porous media. Interestingly, the domain-wide reaction rate shows a dramatic increase with increasing Re in the randomized porous media case. This is because fluid inertia induces complex three-dimensional flows in randomized porous media, which significantly increases transverse spreading and mixing. This study shows how inertial flows control reaction dynamics at the pore scale and beyond, thus having major implications for a wide range of environmental systems. 

Abstract The current state-of-the-art climate models when combined together suggest that the anthropogenic weakening of the Atlantic Meridional Overturning Circulation (AMOC) has already begun since the mid-1980s. However, continuous direct observational records during the past two decades have shown remarkable resilience of the AMOC. To shed light on this apparent contradiction, here we attempt to attribute the interdecadal variation of the historical AMOC to the anthropogenic and natural signals, by analyzing multiple climate and surface-forced ocean model simulations together with direct observational data. Our analysis suggests that an extensive weakening of the AMOC occurred in the 2000s, as evident from the surface-forced ocean model simulations, and was primarily driven by anthropogenic forcing and possibly augmented by natural variability. However, since the early 2010s, the natural component of the AMOC has greatly strengthened due to the development of a strong positive North Atlantic Oscillation. The enhanced natural AMOC signal in turn acted to oppose the anthropogenic weakening signal, leading to a near stalling of the AMOC weakening. Further analysis suggests that the tug-of-war between the natural and anthropogenic signals will likely continue in the next several years.