38,110 research outputs found
Temporal introduction patterns of invasive alien plant species to Australia
We examined temporal introduction patterns of 132 invasive alien plant species (IAPS) to Australia since European colonisation in 1770. Introductions of IAPS were high during 1810–1820 (10 species), 1840– 1880 (51 species, 38 of these between 1840 and 1860) and 1930–1940 (9 species). Conspicuously few introductions occurred during 10-year periods directly preceding each introduction peak. Peaks during early European settlement (1810–1820) and human range expansion across the continent (1840-1860) both coincided with considerable growth in Australia’s human population. We suggest that population growth during these times increased the likelihood of introduced plant species becoming invasive as a result of increased colonization and propagule pressure. Deliberate introductions of IAPS (104 species) far outnumbered accidental introductions (28 species) and were particularly prominent during early settlement. Cosmopolitan IAPS (25 species) and those native solely to South America (53 species), Africa (27 species) and Asia (19 species) have been introduced deliberately and accidentally to Australia across a broad period of time. A small number of IAPS, native solely to Europe (5 species) and North America (2 species), were all introduced to Australia prior to 1880. These contrasting findings for native range suggest some role for habitat matching, with similar environmental conditions in Australia potentially driving the proliferation of IAPS native to southern-hemisphere regions. Shrub, tree and vine species dominated IAPS introduced prior to 1840, with no grasses or forbs introduced during early colonisation. Since 1840, all five growth forms have been introduced deliberately and accidentally in relatively large numbers across a broad period of time. In particular, a large number of grass and forb IAPS were deliberately introduced between 1840 and 1860, most likely a direct result of the introduction of legislation promoting intensive agriculture across large areas of the continent. Since the 1980s, only three IAPS have been introduced (all deliberately introduced forbs). The decline in IAPS introductions is most likely a reflection of both increased surveillance and biosecurity efforts and the likelihood that many potential IAPS are still within a pre-expansion lag period
Diapause in the Boll Weevil, Anthonontus grandis Boheman, As Related to Fruiting Activity in the Cotton Plant
Studies in Arkansas show that boll weevil diapause is related to changes in fruiting activity of the cotton plant. Generally, when larval development took place while fruiting levels were increasing or being held at a high level, diapause in resulting adults was low (0-20%). Diapause was approximately 20-50% when larval development coincided with decreasing fruiting levels, and was 50-100% as true cut-out approached. Regrowth cotton generally lowered diapause incidence and as fruiting levels decreased, diapause increased. Therefore, the boll weevil not only responds to short photoperiods that are characteristic during the fall in the temperate zone, but also may respond throughout the season to changes in fruiting activity of the cotton plant
Concept for a research project in early crustal genesis
Planetary volatiles, physical and chemical planetary evolution, surface processes, planetary formation, metallogenesis, crustal features and their development, tectonics, and paleobiology are discussed
Pion-mass dependence of three-nucleon observables
We use an effective field theory (EFT) which contains only short-range
interactions to study the dependence of a variety of three-nucleon observables
on the pion mass. The pion-mass dependence of input quantities in our
``pionless'' EFT is obtained from a recent chiral EFT calculation. To the order
we work at, these quantities are the 1S0 scattering length and effective range,
the deuteron binding energy, the 3S1 effective range, and the binding energy of
one three-nucleon bound state. The chiral EFT input we use has the inverse 3S1
and 1S0 scattering lengths vanishing at mpi_c=197.8577 MeV. At this
``critical'' pion mass, the triton has infinitely many excited states with an
accumulation point at the three-nucleon threshold. We compute the binding
energies of these states up to next-to-next-to-leading order in the pionless
EFT and study the convergence pattern of the EFT in the vicinity of the
critical pion mass. Furthermore, we use the pionless EFT to predict how doublet
and quartet nd scattering lengths depend on mpi in the region between the
physical pion mass and mpi=mpi_c.Comment: 24 pages, 9 figure
Finite-Temperature Quasicontinuum: Molecular Dynamics without All the Atoms
Using a combination of statistical mechanics and finite-element interpolation, we develop a coarse-grained (CG) alternative to molecular dynamics (MD) for crystalline solids at constant temperature. The new approach is significantly more efficient than MD and generalizes earlier work on the quasicontinuum method. The method is validated by recovering equilibrium properties of single crystal Ni as a function of temperature. CG dynamical simulations of nanoindentation reveal a strong dependence on temperature of the critical stress to nucleate dislocations under the indenter
Water bath calorimetric study of excess heat generation in 'resonant transfer' plasmas
Water bath calorimetry was used to demonstrate one more peculiar phenomenon
associated with a certain class of mixed gas plasmas termed resonant transfer,
or RT plasmas. Specifically, He/H2 (10%) (500 mTorr), Ar/H2 (10%) (500 mTorr),
and H2O(g) (500 and 200 mTorr) plasmas generated with an Evenson microwave
cavity consistently yielded on the order of 50% more heat than non RT plasma
(controls) such as He, Kr, Kr/H2 (10%), under identical conditions of gas flow,
pressure, and microwave operating conditions. The excess power density of RT
plasmas was of the order 10 W / cm-3. In earlier studies with these same RT
plasmas it was demonstrated that other unusual features were present including
dramatic broadening of the hydrogen Balmer series lines, unique vacuum
ultraviolet (VUV) lines, and in the case of water plasmas, population inversion
of the hydrogen excited states. Both the current results and the earlier
results are completely consistent with the existence of a hitherto unknown
exothermic chemical reaction, such as that predicted by Mills, occurring in RT
plasmas.Comment: 30 pages, 2 tables, 5 figure
Dislocation plasticity in thin metal films
This article describes the current level of understanding of dislocation plasticity in thin
films and small structures in which the film or structure dimension plays an important
role. Experimental observations of the deformation behavior of thin films, including
mechanical testing as well as electron microscopy studies, will be discussed in light of
theoretical models and dislocation simulations. In particular, the potential of applying
strain-gradient plasticity theory to thin-film deformation is discussed. Although the
results of all studies presented follow a “smaller is stronger” trend, a clear functional
dependence has not yet been established
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