32 research outputs found
An observation on the experimental measurement of dislocation density
The common practice of ignoring the elastic strain gradient in measurements
of geometrically necessary dislocation (GND) density is critically examined. It
is concluded that the practice may result in substantial errors. Our analysis
points to the importance of spatial variations of the elastic strain field in
relation to its magnitude in inferring estimates of dislocation density from
measurements
Spatial behaviour in thermoelastostatic cylinders of indefinitely increasing cross-section
The final publication is available at Springer via http://dx.doi.org/10.1007/s10659-015-9523-8Alternative growth and decay estimates, reminiscent of the classical Phragmén-Lindelöf principle, are derived for a linearised thermoelastic body whose plane crosssections increase unboundedly with respect to a given direction. The proof uses a modified Poincaré inequality to construct a differential inequality for a weighted linear combination
of the cross-sectional mechanical and thermal energy fluxes. Decay estimates are deduced also for the cross-sectional mean square measures of the displacement and temperature. An explicit upper bound in terms of base data is established for the amplitude occurring in the decay estimates.Peer ReviewedPostprint (authorâs final draft
Spatial decay in transient heat conduction for general elongated regions
Zanaboni's procedure for establishing Saint-Venant's principle is ex-
tended to anisotropic homogeneous transient heat conduction on regions
that are successively embedded in each other to become indefinitely elon-
gated. No further geometrical restrictions are imposed. The boundary
of each region is maintained at zero temperature apart from the common
surface of intersection which is heated to the same temperature assumed
to be of bounded time variation. Heat sources are absent. Subject to
these conditions, the thermal energy, supposed bounded in each region,
becomes vanishingly small in those parts of the regions suficiently remote
from the heated common surface. As with the original treatment, the
proof involves certain monotone bounded sequences, and does not depend
upon differential inequalities or the maximum principle. A definition is
presented of an elongated region.Peer ReviewedPostprint (author's final draft
On quasi-static approximations in linear thermoelastodynamics
The validity of the coupled and uncoupled quasi-static approximations is considered for the initial boundary value problem of linear thermoelasticity subject to homoge-neous Dirichlet boundary conditions, and for solutions and their derivatives that are mean-square integrable. Essential components in the proof, of independent interest, are conservation laws and associated estimates for the exact and approximate systemsPeer ReviewedPostprint (author's final draft
Non-Uniqueness in Plane Fluid Flows
Examples of dynamical systems proposed by Artstein and Dafermos admit
non-unique solutions that track a one parameter family of closed circular
orbits contiguous at a single point. Switching between orbits at this single
point produces an infinite number of solutions with the same initial data.
Dafermos appeals to a maximal entropy rate criterion to recover uniqueness.
These results are here interpreted as non-unique Lagrange trajectories on a
particular spatial region. The corresponding velocity is proved consistent with
plane steady compressible fluid flows that for specified pressure and mass
density satisfy not only the Euler equations but also the Navier-Stokes
equations for specially chosen volume and (positive) shear viscosities. The
maximal entropy rate criterion recovers uniqueness.Comment: 25 pages, 10 figure
The importance of post-translocation monitoring of habitat use and population growth: insights from a Seychelles Warbler (Acrocephalus sechellensis) translocation
Translocations are a valuable tool within conservation, and when performed successfully can rescue species from extinction. However, to label a translocation a success, extensive post-translocation monitoring is required, ensuring the population is growing at the expected rate. In 2011, a habitat assessment identified FrĂ©gate Island as a suitable island to host a Seychelles Warbler (Acrocephalus sechellensis) population. Later that year, 59 birds were translocated from Cousin Island to FrĂ©gate Island. Here, we determine Seychelles Warbler habitat use and population growth on FrĂ©gate Island, assessing the status of the translocation and identifying any interventions that may be required. We found that territory quality, an important predictor of fledgling production on Cousin Island, was a poor predictor of bird presence on FrĂ©gate Island. Instead, tree diversity, middle-storey vegetation density, and broad-leafed vegetation density all predicted bird presence positively. A habitat suitability map based on these results suggests most of FrĂ©gate Island contains either a suitable or a moderately suitable habitat, with patches of unsuitable overgrown coconut plantation. To achieve the maximum potential Seychelles Warbler population size on FrĂ©gate Island, we recommend habitat regeneration, such that the highly diverse subset of broad-leafed trees and a dense middle storey should be protected and replace the unsuitable coconut. FrĂ©gate Islandâs Seychelles Warbler population has grown to 141 birds since the release, the slowest growth rate of all Seychelles Warbler translocations; the cause of this is unclear. This study highlights the value of post-translocation monitoring, identifying habitat use and areas requiring restoration, and ultimately ensuring that the population is growing
Plant Species\u27 Origin Predicts Dominance and Response to Nutrient Enrichment and Herbivores in Global Grasslands
Exotic species dominate many communities; however the functional significance of species\u27 biogeographic origin remains highly contentious. This debate is fuelled in part by the lack of globally replicated, systematic data assessing the relationship between species provenance, function and response to perturbations. We examined the abundance of native and exotic plant species at 64 grasslands in 13 countries, and at a subset of the sites we experimentally tested native and exotic species responses to two fundamental drivers of invasion, mineral nutrient supplies and vertebrate herbivory. Exotic species are six times more likely to dominate communities than native species. Furthermore, while experimental nutrient addition increases the cover and richness of exotic species, nutrients decrease native diversity and cover. Native and exotic species also differ in their response to vertebrate consumer exclusion. These results suggest that species origin has functional significance, and that eutrophication will lead to increased exotic dominance in grasslands
TRY plant trait database â enhanced coverage and open access
Plant traits - the morphological, anatomical, physiological, biochemical and phenological characteristics of plants - determine how plants respond to environmental factors, affect other trophic levels, and influence ecosystem properties and their benefits and detriments to people. Plant trait data thus represent the basis for a vast area of research spanning from evolutionary biology, community and functional ecology, to biodiversity conservation, ecosystem and landscape management, restoration, biogeography and earth system modelling. Since its foundation in 2007, the TRY database of plant traits has grown continuously. It now provides unprecedented data coverage under an open access data policy and is the main plant trait database used by the research community worldwide. Increasingly, the TRY database also supports new frontiers of traitâbased plant research, including the identification of data gaps and the subsequent mobilization or measurement of new data. To support this development, in this article we evaluate the extent of the trait data compiled in TRY and analyse emerging patterns of data coverage and representativeness. Best species coverage is achieved for categorical traits - almost complete coverage for âplant growth formâ. However, most traits relevant for ecology and vegetation modelling are characterized by continuous intraspecific variation and traitâenvironmental relationships. These traits have to be measured on individual plants in their respective environment. Despite unprecedented data coverage, we observe a humbling lack of completeness and representativeness of these continuous traits in many aspects. We, therefore, conclude that reducing data gaps and biases in the TRY database remains a key challenge and requires a coordinated approach to data mobilization and trait measurements. This can only be achieved in collaboration with other initiatives
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Plant species' origin predicts dominance and response to nutrient enrichment and herbivores in global grasslands
Exotic species dominate many communities; however the functional significance of speciesâ biogeographic origin remains highly contentious. This debate is fuelled in part by the lack of globally replicated, systematic data assessing the relationship between species provenance, function and response to perturbations. We examined the abundance of native and exotic plant species at 64 grasslands in 13 countries, and at a subset of the sites we experimentally tested native and exotic species responses to two fundamental drivers of invasion, mineral nutrient supplies and vertebrate herbivory. Exotic species are six times more likely to dominate communities than native species. Furthermore, while experimental nutrient addition increases the cover and richness of exotic species, nutrients decrease native diversity and cover. Native and exotic species also differ in their response to vertebrate consumer exclusion. These results suggest that species origin has functional significance, and that eutrophication will lead to increased exotic dominance in grasslands