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Free, publicly-accessible full text available August 5, 2025
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Cryptic species complexes consist of geographically confluent, closely related species that were once classified as a single species. The diversification mechanisms of cryptic species complexes often are mediated by environmental factors, which in some cases lead to ecological speciation. Niche-based distribution modeling can be an important tool in characterizing the extent of ecological divergence between species that may have resulted from environmentally driven speciation scenarios. We used climatic niche modeling to examine the degree of ecological divergence within the Paragalago zanzibaricus species complex in East Africa. We expected parapatrically distributed P. cocos and P. zanzibaricus to display a significant degree of climatic niche distinction and allopatrically distributed P. zanzibaricus and P. granti to exhibit a degree of niche conservatism. The extent of niche overlap between the three species was assessed by using a Niche Similarity Analysis (NSA) on bioclimatic values. Selected models for all three species exhibited good predictive ability, although the model for P. cocos was most optimal and appeared most consistent with its known range. NSA showed that P. cocos and P. zanzibaricus were statistically more similar than predicted from null distributional values. Results for NSA between the other two species pairings appear to be within the null distribution. The extent of niche overlap between all three species is consistent with the expectations of allopatric speciation processes. Future studies should examine alternative hypotheses for speciation within this group, including the role of sensory drive, interspecific competition, and the impact of Plio-Pleistocene climatic cycles.more » « less
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We consider a model equation for the Navier–Stokes strain equation which has the same identity for enstrophy growth and a number of the same regularity criteria as the full Navier–Stokes strain equation, and is also an evolution equation on the same constraint space. We prove finite-time blowup for this model equation, which shows that the identity for enstrophy growth and the strain constraint space are not sufficient on their own to guarantee global regularity for Navier–Stokes. The mechanism for the finite-time blowup of this model equation is the self-amplification of strain, which is consistent with recent research suggesting that strain self-amplification, not vortex stretching, is the main mechanism behind the turbulent energy cascade. Because the strain self-amplification model equation is obtained by dropping certain terms from the full Navier–Stokes strain equation, we will also prove a conditional blowup result for the full Navier–Stokes equation involving a perturbative condition on the terms neglected in the model equation.more » « less
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Evaluating new, promising organic molecules to make next-generation organic optoelectronic devices necessitates the evaluation of charge carrier transport performance through the semi-conducting medium. In this work, we utilize quantum chemical calculations (QCC) and kinetic Monte Carlo (KMC) simulations to predict the zero-field hole mobilities of ∼100 morphologies of the benchmark polymer poly(3-hexylthiophene), with varying simulation volume, structural order, and chain-length polydispersity. Morphologies with monodisperse chains were generated previously using an optimized molecular dynamics force-field and represent a spectrum of nanostructured order. We discover that a combined consideration of backbone clustering and system-wide disorder arising from side-chain conformations are correlated with hole mobility. Furthermore, we show that strongly interconnected thiophene backbones are required for efficient charge transport. This definitively shows the role “tie-chains” play in enabling mobile charges in P3HT. By marrying QCC and KMC over multiple length- and time-scales, we demonstrate that it is now possible to routinely probe the relationship between molecular nanostructure and device performance.more » « less