We study the effect of a dimplelike geometric imperfection on the critical buckling load of spherical elastic shells under pressure loading. This investigation combines precision experiments, finite element modeling, and numerical solutions of a reduced shell theory, all of which are found to be in excellent quantitative agreement. In the experiments, the geometry and magnitude of the defect can be designed and precisely fabricated through a customizable rapid prototyping technique. Our primary focus is on predictively describing the imperfection sensitivity of the shell to provide a quantitative relation between its knockdown factor and the amplitude of the defect. In addition, we find that the buckling pressure becomes independent of the amplitude of the defect beyond a critical value. The level and onset of this plateau are quantified systematically and found to be affected by a single geometric parameter that depends on both the radius-to-thickness ratio of the shell and the angular width of the defect. To the best of our knowledge, this is the first time that experimental results on the knockdown factors of imperfect spherical shells have been accurately predicted, through both finite element modeling and shell theory solutions.

In patients with an ICD, the development of MCD is an independent predictor of cardiac and arrhythmic mortality. If this finding is confirmed in larger studies, it may help to identify patients in whom other therapeutic alternatives, ie, heart transplantation, should be considered during follow-up after ICD implantation.

We study the buckling of hemispherical elastic shells subjected to the combined effect of pressure loading and a probing force. We perform an experimental investigation using thin shells of nearly uniform thickness that are fabricated with a well-controlled geometric imperfection. By systematically varying the indentation displacement and the geometry of the probe, we study the effect that the probe-induced deflections have on the buckling strength of our spherical shells. The experimental results are then compared to finite element simulations, as well as to recent theoretical predictions from the literature. Inspired by a nondestructive technique that was recently proposed to evaluate the stability of elastic shells, we characterize the nonlinear load-deflection mechanical response of the probe for different values of the pressure loading. We demonstrate that this nondestructive method is a successful local way to assess the stability of spherical shells.

We investigate the influence of curvature and topology on crystalline dimpled patterns on the surface of generic elastic bilayers. Our numerical analysis predicts that the total number of defects created by adiabatic compression exhibits universal quadratic scaling for spherical, ellipsoidal, and toroidal surfaces over a wide range of system sizes. However, both the localization of individual defects and the orientation of defect chains depend strongly on the local Gaussian curvature and its gradients across a surface. Our results imply that curvature and topology can be utilized to pattern defects in elastic materials, thus promising improved control over hierarchical bending, buckling, or folding processes. Generally, this study suggests that bilayer systems provide an inexpensive yet valuable experimental test bed for exploring the effects of geometrically induced forces on assemblies of topological charges.

Background: Cardiac rehabilitation (CR) is recommended in clinical practice guidelines, but dose prescribed varies highly by country. This study characterized the dose offered in supervised CR programs and alternative models worldwide and their potential correlates. Methods and Results: In this cross-sectional study, an online survey was administered to CR programs globally. Cardiac associations and local champions facilitated program identification. Countries were classified based on region and income categories. Dose was operationalized as program duration×sessions per week. Generalized linear mixed models were performed to assess correlates. Of 203 countries in the world, 111 (54.7%) offered CR; data were collected in 93 (83.8% country response rate; n=1082 surveys, 32.1% program response rate). Globally, supervised CR programs were a median of 24 sessions (n=619, 57.3% programs ≥12 sessions); home-based and community-based programs offered 6 and 20 sessions, respectively. There was significant variation in supervised CR dose by region ( P ≤0.001), with the Americas (median, 36 sessions) offering a significantly greater dose than several other regions; there was also a trend for variation by country income classification. There was no difference in home-based dose by region ( P =0.43) but there was for community-based programs ( P <0.05; Americas offering greater dose). There was a significant dose variation in both home- and community-based programs by income classification ( P =0.002 and P <0.001, respectively), with higher doses offered by upper-middle-income than high-income countries. Correlates of supervised CR dose included more involvement of physicians ( P =0.026), proximity to other programs ( P =0.002), and accepting patients with noncardiac indications ( P =0.037). Conclusions: CR programs in many countries may need to increase their dose, which could be supported through physician champions.