Improving the performance of a two-sided vibro-impact energy harvester with asymmetric restitution coefficients

We study the influence of asymmetric restitution coefficients in a model of a two-sided vibro-impact energy harvester (VI-EH), considering the dynamical behavior and the implications for energy output. In the VI-EH, a ball moves freely within a forced cylinder and collides with a compliant dielectric polymer on either end, thus converting the motion into output voltage. We develop (semi-)analytical results for 1:1 periodic solutions, with alternating impacts on either end, focusing on the case of asymmetric restitution coefficients on the top and bottom of the cylinder. New types of 1:1 periodic solutions are found, with energy output clearly different from the symmetric setting. The analysis covers non-intuitive results, including the non-monotonic dependencies of the energy output on the asymmetric restitution coefficients. We find unexpected parameter ranges with improved levels of energy output, as well as stability results indicating that this output is robust to parameter fluctuations or external perturbations. Furthermore, by identifying parameter combinations that limit performance through asymmetries, we show how asymmetric restitution coefficients can counteract these detrimental effects. The analysis is based on maps for the dynamics between impacts, leading to a series of conditions for stable 1:1 periodic solutions in terms of the system parameters. We compare stability and bifurcation structure obtained analytically and numerically. The analysis shows possible regions of bi-stability between different behaviors that may not be captured by numerical approaches.</p

Effects of once-weekly exenatide on cardiovascular outcomes in type 2 diabetes

BACKGROUND: The cardiovascular effects of adding once-weekly treatment with exenatide to usual care in patients with type 2 diabetes are unknown. METHODS: We randomly assigned patients with type 2 diabetes, with or without previous cardiovascular disease, to receive subcutaneous injections of extended-release exenatide at a dose of 2 mg or matching placebo once weekly. The primary composite outcome was the first occurrence of death from cardiovascular causes, nonfatal myocardial infarction, or nonfatal stroke. The coprimary hypotheses were that exenatide, administered once weekly, would be noninferior to placebo with respect to safety and superior to placebo with respect to efficacy. RESULTS: In all, 14,752 patients (of whom 10,782 [73.1%] had previous cardiovascular disease) were followed for a median of 3.2 years (interquartile range, 2.2 to 4.4). A primary composite outcome event occurred in 839 of 7356 patients (11.4%; 3.7 events per 100 person-years) in the exenatide group and in 905 of 7396 patients (12.2%; 4.0 events per 100 person-years) in the placebo group (hazard ratio, 0.91; 95% confidence interval [CI], 0.83 to 1.00), with the intention-to-treat analysis indicating that exenatide, administered once weekly, was noninferior to placebo with respect to safety (P<0.001 for noninferiority) but was not superior to placebo with respect to efficacy (P=0.06 for superiority). The rates of death from cardiovascular causes, fatal or nonfatal myocardial infarction, fatal or nonfatal stroke, hospitalization for heart failure, and hospitalization for acute coronary syndrome, and the incidence of acute pancreatitis, pancreatic cancer, medullary thyroid carcinoma, and serious adverse events did not differ significantly between the two groups. CONCLUSIONS: Among patients with type 2 diabetes with or without previous cardiovascular disease, the incidence of major adverse cardiovascular events did not differ significantly between patients who received exenatide and those who received placebo