The axial buckling capacity of a thin cylindrical shell depends on the shape and the size of the imperfections that are present in it. Therefore, the prediction of the shells buckling capacity is difficult, expensive, and time consuming, if not impossible, because the prediction requires a priori knowledge about the imperfections. As a result, thin cylindrical shells are designed conservatively using the knockdown factor approach that accommodates the uncertainties associated with the imperfections that are present in the shells; almost all the design codes follow this approach explicitly or implicitly. A novel procedure is proposed for the accurate prediction of the axial buckling capacity of thin cylindrical shells without measuring the imperfections and is based on the probing of the axially loaded shells. Computational and experimental implementation of the procedure yields accurate results when the probing is done in location of highest imperfection amplitude. However, the procedure overpredicts the capacity when the probing is done away from that point. This study demonstrates the crucial role played by the probing location and shows that the prediction of imperfect cylinders is possible if the probing is done at the proper location.

Optical  fluorescencemicroscopy  is  shown  to  enable  both  highspatial  and  temporal  resolution  of  redox-dependent  fluorescencein  flowing  electrolytes.  We  report  the  use  of  fluorescence  micro-scopy coupled with electrochemistry to directly observe the reac-tion and transport of redox-active quinones within porous carbonelectrodesin  operando.  We  observe  surprising  electrolyte  chan-neling features within several porous electrodes, leading to spatiallydistinguishable  advection-dominated  and  diffusion-dominated  re-gions. These results challenge the common assumption that trans-port in porous electrodes can be approximated by a homogeneousDarcy-like permeability, particularly at the length scales relevant tomany  electrochemical  systems  such  as  redox  flow  batteries.  Thiswork  presents  a  new  platform  to  provide  highly  resolved  spatialand   temporal   insight   into   electrolyte   reactions   and   transportbehavior within porous electrodes.

As a confined thin sheet crumples, it spontaneously segments into flat facets delimited by a network of ridges. Despite the apparent disorder of this process, statistical properties of crumpled sheets exhibit striking reproducibility. Experiments have shown that the total crease length accrues logarithmically when repeatedly compacting and unfolding a sheet of paper. Here, we offer insight to this unexpected result by exploring the correspondence between crumpling and fragmentation processes. We identify a physical model for the evolution of facet area and ridge length distributions of crumpled sheets, and propose a mechanism for re-fragmentation driven by geometric frustration. This mechanism establishes a feedback loop in which the facet size distribution informs the subsequent rate of fragmentation under repeated confinement, thereby producing a new size distribution. We then demonstrate the capacity of this model to reproduce the characteristic logarithmic scaling of total crease length, thereby supplying a missing physical basis for the observed phenomenon.

The reconnection of two interacting vortex tubes is a fundamental process in fluid mechanics, which, at very high Reynolds numbers, is associated with the formation of intense velocity gradients. Reconnection is usually studied using two antiparallel tubes which are destabilized via the long-wavelength Crow instability, leading to a very symmetric configuration and to a strong flattening of the cores into thin sheets. Here, we consider the interaction of two initially straight tubes at an angle of β and show that by relaxing some symmetries of the problem, a rich phenomenology appears. When the angle between the two tubes is close to β=90∘, their interaction leads to pairing of small portions of antiparallel tubes, followed by the formation of thin and localized vortex sheets as a precursor of reconnection. The subsequent breakdown of these sheets involves a twisting of the paired sheets, followed by the appearance of a localized cloud of small-scale vortex structures. By decreasing β, we show that reconnection involves increasingly larger portions of tubes, whose cores are subsequently destabilizing, leaving behind more small-scale vortices. At the smallest values of the angle β studied, the two vortices break down through a mechanism, which leads to a cascadelike process of energy conveyance across length scales similar to what was found for previous studies of antiparallel vortex tubes (β=0) which imposed no symmetries. While, in all cases, the interaction of two vortices depends on the initial condition, the rapid formation of fine-scale vortex structures appears to be a robust feature, possibly universal at very high Reynolds numbers.