Varifocal liquid lens driven by a conical dielectric elastomer actuator.

A varifocal lens is an important part of optical systems with applications in biomedicine, photography, smartphones, and virtual reality. In this paper, we propose and demonstrate a varifocal liquid lens driven by a conical dielectric elastomer actuator. When the conical dielectric elastomer is subjected to an actuation voltage, the conical dielectric elastomer works as an out-plane actuator and makes the surface curvature of the liquid droplet increase; then the focal length of the proposed varifocal liquid lens changes. The overall dimensions of the proposed varifocal liquid lens are 9.4 mm in diameter and 12.5 mm in height. The focal length tuning range is 15.07mm∼9.50mm when the actuation voltage increases from 0 kV to 5.0 kV. The focal power variation of the proposed varifocal liquid lens is 35.5 D. The rise and fall times of the proposed varifocal liquid lens are 215 ms and 293 ms, respectively. The ability of the proposed liquid lens to focus on objects at different distances without any moving parts is demonstrated. The compact varifocal liquid lens driven by the conical dielectric elastomer actuator in the current study has the potential to be used in various compact imaging systems in the future.

Phylogenetic conservatism and climate factors shape flowering phenology in alpine meadows.

The study of phylogenetic conservatism in alpine plant phenology is critical for predicting climate change impacts; currently we have a poor understanding of how phylogeny and climate factors interactively influence plant phenology. Therefore, we explored the influence of phylogeny and climate factors on flowering phenology in alpine meadows. For two different types of alpine plant communities, we recorded phenological data, including flowering peak, first flower budding, first flowering, first fruiting and the flowering end for 62 species over the course of 5 years (2008-2012). From sequences in two plastid regions, we constructed phylogenetic trees. We used Blomberg's K and Pagel's lambda to assess the phylogenetic signal in phenological traits and species' phenological responses to climate factors. We found a significant phylogenetic signal in the date of all reproductive phenological events and in species' phenological responses to weekly day length and temperature. The number of species in flower was strongly associated with the weekly day lengths and followed by the weekly temperature prior to phenological activity. Based on phylogenetic eigenvector regression (PVR) analysis, we found a highly shared influence of phylogeny and climate factors on alpine species flowering phenology. Our results suggest the phylogenetic conservatism in both flowering and fruiting phenology may depend on the similarity of responses to external environmental cues among close relatives.