Commentary by Gregory B. McKenna and John D. Barnes

McKenna, Gregory B.; Barnes, John

doi:10.1002/pen.11789

Cited by 27 publications

(40 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Cephaloleia was monophyletic only with the inclusion of eight a priori designated Cephaloleia-like taxa from other genera, in agreement with ref. 22. Interspecific ingroup p distances were high (mean: 16.07%), consistent with deep divergences between taxa.…”

Section: Resultsmentioning

confidence: 62%

See 1 more Smart Citation

Tropical forests are both evolutionary cradles and museums of leaf beetle diversity

McKenna

Farrell

2006

Proc. Natl. Acad. Sci. U.S.A.

202

210

View full text Add to dashboard Cite

The high extant species diversity of tropical lineages of organisms is usually portrayed as a relatively recent and rapid development or as a consequence of the gradual accumulation or preservation of species over time. These explanations have led to alternative views of tropical forests as evolutionary ''cradles'' or ''museums'' of diversity, depending on the organisms under study. However, biogeographic and fossil evidence implies that the evolutionary histories of diversification among tropical organisms may be expected to exhibit characteristics of both cradle and museum models. This possibility has not been explored in detail for any group of terrestrial tropical organisms. Cephaloleia ͉ diversification ͉ evolutionary radiation ͉ phylogeny T he extraordinarily high species diversity of tropical forest floras and faunas is often attributed to the recent and rapid accumulation of species via high speciation rates (1-4) or the gradual accumulation and͞or preservation of species over time via low extinction rates (5-8). These observations have led to the widespread belief that tropical forests are evolutionary ''cradles'' of diversity for some lineages and ''museums'' of diversity for others (6, 7).Evidence in support of cradle models comes largely from geographic patterns of distribution, species richness, and endemism of extant tropical organisms. These patterns are often ascribed to evolutionary radiation in response to relatively recent climatic, tectonic, or biotic events; e.g., Pleistocene [Ϸ1.8-0.01 mega-annum (Ma) ago] glaciation or Pliocene (Ϸ5.3-1.8 Ma ago) bridging of the Isthmus of Panama (1-4). However, paleontological evidence implies that many of the evolutionary radiations that account for the present diversity (''crown diversification'') of taxonomically disparate groups of tropical organisms may have occurred comparatively early, during the late Paleocene and early to middle Eocene (Thanetian, Ypresian, and Lutetian Ages, Ϸ58.7-40.4 Ma ago) (9-17), associated with global warming, Cenozoic maximum global temperatures (18), and the latitudinal expansion (16, 19) and taxonomic diversification (9,11,14,16,17) of characteristically tropical lineages of plants, consistent with museum models of diversification. Although cradle and museum models are often presented as temporal alternatives (4, 7), their predictions are not mutually exclusive, and, as the aforementioned observations suggest, the evolutionary histories of tropical lineages of organisms may be expected to exhibit features of both kinds of models. However, this possibility has not been explored in detail for any group of terrestrial tropical organisms.Using molecular genetic, paleontologic, and biogeographic evidence, we investigated timing and tempo in the diversification of Cephaloleia, a species-rich genus of herbivorous Neotropical leaf beetles (Chrysomelidae: Cassidinae). Our goals were to determine (i) whether the evolutionary history of Cephaloleia diversification (speciation-extinction) departs significantly from a constant rate m...

show abstract

Section: Resultsmentioning

confidence: 62%

“…21). All life stages feed on monocots, mostly in the order Zingiberales (22). A subset of species feed only in the juvenile rolled leaves of Zingiberales (Fig.…”

mentioning

confidence: 99%

Tropical forests are both evolutionary cradles and museums of leaf beetle diversity

McKenna

Farrell

2006

Proc. Natl. Acad. Sci. U.S.A.

202

210

View full text Add to dashboard Cite

show abstract

“…29 The glass transition temperature of epoxy/POSS nanocomposites is determined by several competing factors: (1) the POSS cages hinder the motion of the polymer chains giving rise to an increased T g , (2) the bulky POSS cages increase the free volume of the system resulting in a lowered T g , 38 (3) the rigidity of interlayer between the POSS and the polymer matrix can cause T g to increase or decrease, the latter of which was referred to as an internal plasticization effect, 32 and (4) the multifunctionality of the POSS has the effect of increasing the effective crosslink density (increasing functionality of the junctions) and this would be expected to increase the T g . 90 As a result, an increase, no change, or decrease in the glass transition temperature of polymer/POSS nanocomposites are all possible outcomes. The glass transition temperatures measured from DSC and dynamic mechanical measurements along with the b-relaxation peak temperature of the epoxy/POSS nanocomposites are tabulated in Table 1.…”

Section: Viscoelastic Properties Of Epoxy/poss Nanocomposites As a Fumentioning

confidence: 99%

Viscoelastic properties and residual stresses in polyhedral oligomeric silsesquioxane‐reinforced epoxy matrices

Hutcheson

McKenna

et al. 2008

J Polym Sci B Polym Phys

Self Cite

View full text Add to dashboard Cite

Fiber-filled thermosetting polymer composites are extensively used in aerospace industries. One disadvantage of these materials is cure induced or thermally induced residual stresses in the matrix, which may result in deteriorated performance and premature failure. This article explores the use of epoxy/multifunctional polyhedral oligomeric silsesquioxane (POSS) nanocomposites as resins with reduced thermal stress coefficients that result in mitigated residual stresses. The effect of POSS loading on the thermal stress coefficient of the epoxy/POSS nanocomposite resins was investigated from below the b-relaxation to the a-relaxation, or glass transition temperature, (i.e., from À100 to 180 C) by measuring the shear modulus and linear thermal expansion coefficient. The thermal stress coefficient of the epoxy/POSS nanocomposites is found to be a strong function of temperature, decreasing rapidly with decreasing temperature through the a-relaxation region, increasing in the vicinity of the b-relaxation, and then decreasing below the temperature associated with the peak in the b-relaxation. With increasing POSS content, the thermal stress coefficient is reduced compared with the neat resin in the vicinity of the a-relaxation; however, the thermal stress coefficient increases with increasing POSS content below the temperature of the b-relaxation peak.

show abstract

“…Glasses are out of thermodynamic equilibrium [22–24] due to restricted mobility associated with constituent molecules of the same. It is well known that for temperatures less than glass transition temperature, isothermal annealing of amorphous polymeric materials accompany structural evolution so as to enhance their density slowly as a function of time elapsed since thermal quench [25–28].…”

Section: Introductionmentioning

confidence: 99%

Thixotropy and physical aging in acrylic emulsion paint

Baldewa

Joshi

2011

Polymer Engineering & Sci

View full text Add to dashboard Cite

In this article we study thixotropic and time‐dependent rheological behavior of commercial acrylic emulsion paint using a framework of soft glassy rheology. We observe that acrylic emulsion paint, which shows thixotropic rheological behavior, demonstrates various characteristic features of a soft glassy materials such as weak but certain increase in elastic modulus as a function of aging time, maximum in viscous modulus as a function of strain at the onset of yielding, and slow increase in elastic modulus as a function of frequency. Stress relaxation measurements, subsequent to step strain, carried out at different aging times demonstrate slowing down of the relaxation dynamics. This behavior is similar to that observed in polymeric glasses and other soft glassy materials undergoing aging dynamics. Relaxation modulus when plotted against appropriately rescaled time yields a superposition irrespective of the aging time. The rescaled time also known as effective time, which adjusts the material clock by accounting for increasing relaxation time, enables estimation of the rate of change of relaxation time with the aging time. We conclude by relating thixotropy in an emulsion paint sample to an interplay between physical aging and shear melting in the same. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers

show abstract

Commentary by Gregory B. McKenna and John D. Barnes

Cited by 27 publications

References 0 publications

Tropical forests are both evolutionary cradles and museums of leaf beetle diversity

Tropical forests are both evolutionary cradles and museums of leaf beetle diversity

Viscoelastic properties and residual stresses in polyhedral oligomeric silsesquioxane‐reinforced epoxy matrices

Thixotropy and physical aging in acrylic emulsion paint

Contact Info

Product

Resources

About