83,772 research outputs found
Management of Phytophthora cinnamomi for biodiversity conservation in Australia: Part 2. National best practice guidelines
Disease in natural ecosystems of Australia, caused by the introduced plant pathogen Phytophthora cinnamomi, is listed as a key threatening process under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act). The Act requires the Australian Government to prepare and implement a threat abatement plan for nationally coordinated action to mitigate the harm caused by P. cinnamomi to Australian species, particularly threatened flora, fauna and ecological communities. The .National Threat Abatement Plan for Dieback Caused by the Root-Rot Fungus Phytophthora cinnamomi. (NTAP) was released in 2001 (Environment Australia, 2001). The NTAP is designed to promote a common understanding of the national threat P. cinnamomi poses to biodiversity in Australia.
This project, funded by the Australian Government Department of the Environment and Heritage (DEH), is one of the most significant actions to be implemented from the NTAP to date. The project has two major components:
* to review current management approaches and identify benchmarks for best practice
* the development of risk assessment criteria and a system for prioritising management of assets that are or could be threatened by P. cinnamomi.
The project outputs are presented in a four-part document entitled Management of Phytophthora cinnamomi for Biodiversity Conservation in Australia:
Part 1 - A Review of Current Management
Part 2 - National Best Practice Guidelines
Part 3 - Risk Assessment for Threats to Ecosystems, Species and Communities: A Review
Part 4 - Risk Assessment Models for Species, Ecological Communities and Areas.
A model of best practice was developed which encompasses all the components necessary for an informed and integrated approach to P. cinnamomi management, from strategic through to on-ground management. The current document (Part 1 . A Review of Current Management) thoroughly reviews the approaches to P. cinnamomi management in Australia within the context of the best practice model
Geometry Optimization of Crystals by the Quasi-Independent Curvilinear Coordinate Approximation
The quasi-independent curvilinear coordinate approximation (QUICCA) method
[K. N\'emeth and M. Challacombe, J. Chem. Phys. {\bf 121}, 2877, (2004)] is
extended to the optimization of crystal structures. We demonstrate that QUICCA
is valid under periodic boundary conditions, enabling simultaneous relaxation
of the lattice and atomic coordinates, as illustrated by tight optimization of
polyethylene, hexagonal boron-nitride, a (10,0) carbon-nanotube, hexagonal ice,
quartz and sulfur at the -point RPBE/STO-3G level of theory.Comment: Submitted to Journal of Chemical Physics on 7/7/0
Deterministic creation, pinning, and manipulation of quantized vortices in a Bose-Einstein condensate
We experimentally and numerically demonstrate deterministic creation and
manipulation of a pair of oppositely charged singly quantized vortices in a
highly oblate Bose-Einstein condensate (BEC). Two identical blue-detuned,
focused Gaussian laser beams that pierce the BEC serve as repulsive obstacles
for the superfluid atomic gas; by controlling the positions of the beams within
the plane of the BEC, superfluid flow is deterministically established around
each beam such that two vortices of opposite circulation are generated by the
motion of the beams, with each vortex pinned to the \emph{in situ} position of
a laser beam. We study the vortex creation process, and show that the vortices
can be moved about within the BEC by translating the positions of the laser
beams. This technique can serve as a building block in future experimental
techniques to create, on-demand, deterministic arrangements of few or many
vortices within a BEC for precise studies of vortex dynamics and vortex
interactions.Comment: 9 pages, 7 figure
Wide-angle flat field telescope
Described is an unobscured three mirror wide angle telescopic imaging system comprised of an input baffle which provides a 20 deg (Y axis) x 30 deg (X axis) field of view, a primary mirror having a convex spherical surface, a secondary mirror having a concave ellipsoidal reflecting surface, a tertiary mirror having a concave spherical reflecting surface. The mirrors comprise mirror elements which are offset segments of parent mirrors whose axes and vertices commonly lie on the system's optical axis. An iris diaphragm forming an aperture stop is located between the secondary and tertiary mirror with its center also being coincident with the optical axis and being further located at the beam waist of input light beams reflected from the primary and secondary mirror surfaces. At the system focus following the tertiary mirror is located a flat detector which may be, for example, a TV imaging tube or a photographic film. When desirable, a spectral transmission filter is placed in front of the detector in close proximity thereto
Testing isomorphism of graded algebras
We present a new algorithm to decide isomorphism between finite graded
algebras. For a broad class of nilpotent Lie algebras, we demonstrate that it
runs in time polynomial in the order of the input algebras. We introduce
heuristics that often dramatically improve the performance of the algorithm and
report on an implementation in Magma
Hyper-Raman scattering from vitreous boron oxide: coherent enhancement of the boson peak
Hyper-Raman scattering spectra of vitreous BO are reported and
compared to Raman scattering results. The main features are indexed in terms of
vibrations of structural units. Particular attention is given to the low
frequency boson peak which is shown to relate to out-of-plane librations of
BO boroxol rings and BO triangles. Its hyper-Raman strength is
comparable to that of cooperative polar modes. It points to a sizeable coherent
enhancement of the hyper-Raman signal compared to the Raman one. This is
explained by the symmetry of the structural units.Comment: 4 pages, 3 figure
Do Teens Make Rational Choices? The Case of Teen Nonmarital Childbearing
With emphasis on the role of economic incentives, we explore the determinants of a woman’s choice of whether or not to give birth as an unmarried teenager. Our data are taken from the Panel Study of Income Dynamics. Guided by a simple utility-maximization model, we represent the income possibilities available to teenaged women if they do and do not give birth out of wedlock. We estimate these choice-conditioned income possibilities through a two-stage probit procedure, relying on the observed incomes of a secondary sample of somewhat older women. The response of the young women in our primary sample to these income expectations is measured after controlling for the effects of a variety of other factors, including the characteristics of the girl’s family, the social and economic environment in which she lives (including such policy-related factors as expenditures by states on family planning programs and education), and her own prior choices. We use the estimated structural parameters from our model to simulate the effects of a variety of policy interventions on the probability of becoming an unmarried teen mother. Our estimations provide evidence that income expectations have a persistent influence on the childbearing decision. They also provide evidence that the provision of public family planning expenditures and increases in parental education could reduce the prevalence of teen nonmarital births.
Induced scattering of short radio pulses
Effect of the induced Compton and Raman scattering on short, bright radio
pulses is investigated. It is shown that when a single pulse propagates through
the scattering medium, the effective optical depth is determined by the
duration of the pulse but not by the scale of the medium. The induced
scattering could hinder propagation of the radio pulse only if close enough to
the source a dense enough plasma is presented. The induced scattering within
the relativistically moving source places lower limits on the Lorentz factor of
the source. The results are applied to the recently discovered short
extragalactic radio pulse.Comment: submitted to Ap
Correspondence between sound propagation in discrete and continuous random media with application to forest acoustics
Although sound propagation in a forest is important in several applications, there are currently no rigorous yet computationally tractable prediction methods. Due to the complexity of sound scattering in a forest, it is natural to formulate the problem stochastically. In this paper, it is demonstrated that the equations for the statistical moments of the sound field propagating in a forest have the same form as those for sound propagation in a turbulent atmosphere if the scattering properties of the two media are expressed in terms of the differential scattering and total cross sections. Using the existing theories for sound propagation in a turbulent atmosphere, this analogy enables the derivation of several results for predicting forest acoustics. In particular, the second-moment parabolic equation is formulated for the spatial correlation function of the sound field propagating above an impedance ground in a forest with micrometeorology. Effective numerical techniques for solving this equation have been developed in atmospheric acoustics. In another example, formulas are obtained that describe the effect of a forest on the interference between the direct and ground-reflected waves. The formulated correspondence between wave propagation in discrete and continuous random media can also be used in other fields of physics
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