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One major challenge in the study of late-Quaternary extinctions (LQEs) is providing better estimates of past megafauna abundance. To show how megaherbivore population size varied before and after the last extinctions in interior Alaska, we use both a database of radiocarbon-dated bone remains (spanning 25–0 ka) and spores of the obligate dung fungus, Sporormiella, recovered from radiocarbon-dated lake-sediment cores (spanning 17–0 ka). Bone fossils show that the last stage of LQEs in the region occurred at about 13 ka ago, but the number of megaherbivore bones remains high into the Holocene. Sporormiella abundance also remains high into the Holocene and does not decrease with major vegetation changes recorded by arboreal pollen percentages. At two sites, the interpretation of Sporormiella was enhanced by additional dung fungal spore types (e.g., Sordaria). In contrast to many sites where the last stage of LQEs is marked by a sharp decline in Sporormiella abundance, in interior Alaska our results indicate the continuance of megaherbivore abundance, albeit with a major taxonomic turnover (including Mammuthus and Equus extinction) from predominantly grazing to browsing dietary guilds. This new and robust evidence implies that regional LQEs were not systematically associated with crashes of overall megaherbivore abundance.
Geophysical granular flows, such as avalanches, debris flows, lahars and pyroclastic flows, are always strongly influenced by the basal topography that they flow over. In particular, localised bumps or obstacles can generate rapid changes in the flow thickness and velocity, or shock waves, which dissipate significant amounts of energy. Understanding how a granular material is affected by the underlying topography is therefore crucial for hazard mitigation purposes, for example to improve the design of deflecting or catching dams for snow avalanches. Moreover, the interactions with solid boundaries can also have important applications in industrial processes. In this paper, small-scale experiments are performed to investigate the flow of a granular avalanche over a two-dimensional smooth symmetrical bump. The experiments show that, depending on the initial conditions, two different steady-state regimes can be observed: either the formation of a detached jet downstream of the bump, or a shock upstream of it. The transition between the two cases can be controlled by adding varying amounts of erodible particles in front of the obstacle. A depth-averaged terrain-following avalanche theory that is formulated in curvilinear coordinates is used to model the system. The results show good agreement with the experiments for both regimes. For the case of a shock, time-dependent numerical simulations of the full system show the evolution to the equilibrium state, as well as the deposition of particles upstream of the bump when the inflow ceases. The terrain-following theory is compared to a standard depth-averaged avalanche model in an aligned Cartesian coordinate system. For this very sensitive problem, it is shown that the steady-shock regime is captured significantly better by the terrain-following avalanche model, and that the standard theory is unable to predict the take-off point of the jet. To retain the practical simplicity of using Cartesian coordinates, but have the improved predictive power of the terrain-following model, a coordinate mapping is used to transform the terrain-following equations from curvilinear to Cartesian coordinates. The terrain-following model, in Cartesian coordinates, makes identical predictions to the original curvilinear formulation, but is much simpler to implement.
EURO-GANEX aims to recycle both major and minor actinides. As the final waste
composition is free from actinides, adapted immobilization matrices should be
developed. Synroc is a potential wasteform that has proven itself to be
efficient in immobilizing high-level wastes (HLW). In this study, a new
composition of Synroc, Synroc-Z, is designed and characterized. The key
modification is in decreasing the amount of zirconolite phase, which is the main
host phase for actinides and increasing the amount of other phases (hollandite
and perovskite). As designed the obtained amount of zirconolite is lower than in
Synroc-C compositions. Synroc-Z samples were synthesized with a waste loading of
20 wt.% at various temperatures and pressures via hot-pressing to determine the
optimum process parameters, which were determined to be 1150-1200°C and
20 MPa, respectively.
Ferromagnetic (FM) electrodes chemically anchored with thiol functionalized
molecules can yield novel molecular spintronics devices (MSDs). However,
significant challenges lie in developing commercially viable MSD fabrication
approach utilizing FM electrodes. A practical MSD fabrication approach should
consider FM electrodes’ susceptibility to oxidation, chemical
etching, and stress induced deformations during fabrication and usage. This
paper will discuss NiFe, an alloy used in the present day memory devices and
high-temperature engineering applications, as a candidate for FM electrode and
for the fabrication of MSDs. Our spectroscopic reflectance studies show that
NiFe starts oxidizing aggressively beyond ∼90 ⁰C. The NiFe
surfaces, aged for several months or heated for several minutes below
∼90 ⁰C, were suitable for chemical bonding with the
thiol-functionalized molecules. NiFe also demonstrated excellent etching
resistance in widely used dichloromethane solvent for dissolving molecular
device elements. NiFe also reduced the mechanical stress induced deformities in
other FM metals like cobalt. This paper also discusses the successful
utilization of NiFe electrodes in the magnetic tunnel junction based molecular
device fabrication approach. This research is expected to address the knowledge
gap blocking the experimental development of FM based MSDs.
Annual rings are not commonly produced in tropical trees because they grow in a relatively aseasonal environment. However, in the subalpine zones of Hawaiʻi's highest volcanoes, there is often strong seasonal variability in temperature and rainfall. Using classical dendrochronological methods, annual growth rings were shown to occur in Sophora chrysophylla, a native tree species on Maunakea, Hawaiʻi. Chronologies were established from nearby non-native, live conifer trees and these were used to verify the dates from a total of 52 series from 22 S. chrysophylla trees, establishing an 86-y chronology (1926–2011). Ring-width patterns were significantly correlated with monthly rainfall from August of the previous year. This study is the first in the eastern tropical Pacific region to demonstrate annual growth rings in trees.
On the death of Edward Gibbon (1737–94), his unpublished papers were left to his friend John Baker Holroyd, first earl of Sheffield, who published them in two volumes in 1796. Gibbon had written six manuscript accounts of his own life, and, according to Sheffield, had always intended to publish his autobiography in his lifetime. The memoir as edited by Sheffield begins with Gibbon's family history, and taking in his education, travels, and career as a historian, finishes with his anxiety over the future of Europe in 1788. Sheffield then continues the story until Gibbon's death through his correspondence, providing a linking narrative, and this, together with 210 other letters to and from Gibbon, takes up Volume 1. His great work, The History of the Decline and Fall of the Roman Empire, is also reissued (in the 1896–1900 edition by J. B. Bury) in the Cambridge Library Collection.