Dynamics of wrinkling in ultrathin elastic sheets

The wrinkling of thin elastic objects provides a means of generating regular patterning at small scales in applications ranging from photovoltaics to microfluidic devices. Static wrinkle patterns are known to be governed by an energetic balance between the object’s bending stiffness and an effective substrate stiffness, which may originate from a true substrate stiffness or from tension and curvature along the wrinkles. Here, we investigate dynamic wrinkling induced by the impact of a solid sphere onto an ultrathin polymer sheet floating on water. The vertical deflection of the sheet’s center induced by impact draws material radially inward, resulting in an azimuthal compression that is relieved by the wrinkling of the entire sheet. We show that this wrinkling is truly dynamic, exhibiting features that are qualitatively different to those seen in quasistatic wrinkling experiments. Moreover, we show that the wrinkles coarsen dynamically because of the inhibiting effect of the fluid inertia. This dynamic coarsening can be understood heuristically as the result of a dynamic stiffness, which dominates the static stiffnesses reported thus far, and allows control of wrinkle wavelength.

Investigating “self-conscious” speech: The performance register in Ocracoke English

ABSTRACTThis article examines PERFORMANCE SPEECH in the historically isolated island community of Ocracoke, North Carolina. Over the past several decades islanders have come into increasingly frequent contact with tourists and new residents, who often comment on the island's “quaint” relic dialect. In response, some Ocracokers have developed performance phrases that highlight island features, particularly the pronunciation of/ay/ with a raised/backed nucleus, i.e. [Λ-1]. The analysis of/ay/ in the performance and non-performance speech of a representative Ocracoke speaker yields several important insights for the study of language in its social context. First, performance speech may display more regular patterning than has traditionally been assumed. Second, it lends insight into speaker perception of language features. Finally, the incorporation of performance speech into the variationist-based study of style-shifting offers support for the growing belief that style-shifting may be primarily proactive rather than reactive. (Keywords: Ocracoke, performance speech, style-shifting, stylistic variation, register, self-conscious speech.)