Calorimetric and Rheological Measurements of Three Commercial Thermosetting Prepreg Epoxies

The cure kinetics of three different thermosetting resins are investigated using differential scanning calorimetry and oscillatory shear rheometry. For the latter, two different types of plates are used, smooth plates and grooved plates; the latter are used to improve sample–plate contact. In addition, oscillatory compression rheology is used; however, machine compliance prevents accurate measurements at high conversions. A fractional conversion is defined based on the maximum storage modulus achieved at a given temperature, and is compared to the fractional conversion calculated from enthalpy measurements. As expected, the rates of reaction derived from these fractional conversions are very different for calorimetry and rheometry. However, the rates of reaction using the two types of plates are identical, although the grooved plates give much more reproducible storage moduli. A number of previously used mathematical expressions are employed to fit the calorimetric and rheological data, and the activation energies calculated from these fits are compared.Yeshttps://us.sagepub.com/en-us/nam/manuscript-submission-guideline

Palaeoenvironmental control on distribution of crinoids in the Bathonian (Middle Jurassic) of England and France

Bulk sampling of a number of different marine and marginal marine lithofacies in the British Bathonian has allowed us to assess the palaeoenvironmental distribution of crinoids for the first time. Although remains are largely fragmentary, many species have been identified by comparison with articulated specimens from elsewhere, whilst the large and unbiased sample sizes allowed assessment of relative proportions of different taxa. Results indicate that distribution of crinoids well corresponds to particular facies. Ossicles of Chariocrinus and Balanocrinus dominate in deeper-water and lower-energy facies,with the former extending further into shallower-water facies than the latter. Isocrinus dominates in shallower water carbonate facies, accompanied by rarer comatulids, and was also present in the more marine parts of lagoons. Pentacrinites remains are abundant in very high-energy oolite shoal lithofacies. The presence of millericrinids within one, partly allochthonous lithofacies suggests the presence of an otherwise unknown hard substrate from which they have been transported. These results are compared to crinoid assemblages from other Mesozoic localities, and it is evident that the same morphological ad-aptations are present within crinoids from similar lithofacies throughout the Jurassic and Early Cretaceous

Long-range volcanic ash transport and fallout during the 2008 eruption of Chaitén volcano, Chile

The May 2008 eruption of Chaitén volcano, Chile, provided a rare opportunity to measure the long-range transport of volcanic emissions and characteristics of a widely-dispersed terrestrial ash deposit. Airborne ash mass, quantified using thermal infrared satellite remote sensing, ranged between 0.2 and 0.4 Tg during the period 3–7 May 2008. A high level of spatiotemporal correspondence was observed between cloud trajectories and changes in surface reflectivity, which was inferred to indicate ash deposition. The evolution of the deposit was mapped for the first time using satellite-based observations of surface reflectivity.The distal (>80 km) ash deposit was poorly sorted and fine grained, and mean particle size varied very little beyond a distance >300 km. There were three particle size subpopulations in fallout at distances >300 km which mirror those identified in fallout from the 18 May 1980 eruption of Mount St. Helens, known to have a high propensity for aggregation. Discrete temporal sampling and characterisation of fallout demonstrated contributions from specific eruptive phases. Samples collected at the time of deposition were compared to bulk samples collected months after deposition and provided some evidence for winnowing.Experimentally-derived ash leachates had near-neutral pH values and charge balance which indicates minimal quantities of adsorbed acids. X-ray Photoelectron Spectroscopy (XPS) analyses revealed surface enrichments in Ca, Na and Fe and the presence of coatings of mixed Ca-, Na- and Fe-rich salts on ash particles prior to deposition. Low S:Cl ratios in leachates indicate that the eruption had a low S content, and high Cl:F ratios imply gas–ash interaction within a Cl-rich environment. We estimate that ash fallout had potential to scavenge ~42% of total S released into the atmosphere prior to deposition. XPS analyses also revealed ash particle surfaces were strongly enriched in Fe (in contrast to the results from bulk leachate analyses), which suggests that Chaitén ash fallout over oceans had potential to influence productivity in high-nutrient, low-chlorophyl regions of the oceans. Therefore ash particle surface geochemical analysis should be applied to quantify Fe-modulated biologically-forced CO2 draw-down potential of volcanic ash fallout over oceans