12,092 research outputs found
Grassland Landscape Design: Working with Land-Managers
We are entering an era of landscape design in order to simultaneously tackle largescale issues such as salinity and rising water tables, whole-farm profitability and the maintenance or enhancement of rural communities. In Australia, an important element of landscape design will be the reintroduction or broadening of the base of perennial grasses within farm systems. The goal of this project was to accelerate awareness and adoption of perennial grasses in a large but ecologically-specific area, namely the already-cleared steep uplands in the high rainfall recharge areas of the Murray-Darling Basin. We used a participatory model, in which land-managers made monthly observations of grassland composition and condition, and of livestock. This paper describes the project, some of the outcomes eg that stocking rate varied more within grassland types than between types, and could be relatively high, eg 10 adult sheep equivalents per hectare on indigenous grasslands. Land-managers\u27 data eg height, were coupled to correlations with other variates such as dry matter and leaf area, to derive seasonal estimates of digestible dry matter-on-offer, and environmentally-important variates such as seasonal evaporation. Collection of these data by land-managers creates opportunities for local awareness and the development of regional data sets which are not possible through traditional small-plot research. In our view, land-manager participation, leading to awareness and in some cases enthusiasm, will be a prerequisite for regional landscape design
On the Persistent Shape and Coherence of Pulsating Auroral Patches
The pulsating aurora covers a broad range of fluctuating shapes that are
poorly characterized. The purpose of this paper is therefore to provide
objective and quantitative measures of the extent to which pulsating auroral
patches maintain their shape, drift and fluctuate in a coherent fashion. We
present results from a careful analysis of pulsating auroral patches using
all-sky cameras. We have identified four well-defined individual patches that
we follow in the patch frame of reference. In this way we avoid the space-time
ambiguity which complicates rocket and satellite measurements. We find that the
shape of the patches is remarkably persistent with 85-100% of the patch being
repeated for 4.5-8.5 min. Each of the three largest patches has a temporal
correlation with a negative dependence on distance, and thus does not fluctuate
in a coherent fashion. A time-delayed response within the patches indicates
that the so-called streaming mode might explain the incoherency. The patches
appear to drift differently from the SuperDARN-determined
X convection velocity.
However, in a nonrotating reference frame the patches drift with 230-287 m/s in
a north eastward direction, which is what typically could be expected for the
convection return flow
Development of an Autonomous Visual Perception System for Robots Using Object-Based Visual Attention
Chaos in an Exact Relativistic 3-body Self-Gravitating System
We consider the problem of three body motion for a relativistic
one-dimensional self-gravitating system. After describing the canonical
decomposition of the action, we find an exact expression for the 3-body
Hamiltonian, implicitly determined in terms of the four coordinate and momentum
degrees of freedom in the system. Non-relativistically these degrees of freedom
can be rewritten in terms of a single particle moving in a two-dimensional
hexagonal well. We find the exact relativistic generalization of this
potential, along with its post-Newtonian approximation. We then specialize to
the equal mass case and numerically solve the equations of motion that follow
from the Hamiltonian. Working in hexagonal-well coordinates, we obtaining
orbits in both the hexagonal and 3-body representations of the system, and plot
the Poincare sections as a function of the relativistic energy parameter . We find two broad categories of periodic and quasi-periodic motions that we
refer to as the annulus and pretzel patterns, as well as a set of chaotic
motions that appear in the region of phase-space between these two types.
Despite the high degree of non-linearity in the relativistic system, we find
that the the global structure of its phase space remains qualitatively the same
as its non-relativisitic counterpart for all values of that we could
study. However the relativistic system has a weaker symmetry and so its
Poincare section develops an asymmetric distortion that increases with
increasing . For the post-Newtonian system we find that it experiences a
KAM breakdown for : above which the near integrable regions
degenerate into chaos.Comment: latex, 65 pages, 36 figures, high-resolution figures available upon
reques
Exact Black Hole and Cosmological Solutions in a Two-Dimensional Dilaton-Spectator Theory of Gravity
Exact black hole and cosmological solutions are obtained for a special
two-dimensional dilaton-spectator () theory of gravity. We show how
in this context any desired spacetime behaviour can be determined by an
appropriate choice of a dilaton potential function and a ``coupling
function'' in the action. We illustrate several black hole solutions
as examples. In particular, asymptotically flat double- and multiple- horizon
black hole solutions are obtained. One solution bears an interesting
resemblance to the string-theoretic black hole and contains the same
thermodynamic properties; another resembles the Reissner-Nordstrom
solution. We find two characteristic features of all the black hole solutions.
First the coupling constants in must be set equal to constants of
integration (typically the mass). Second, the spectator field and its
derivative both diverge at any event horizon. A test particle with
``spectator charge" ({\it i.e.} one coupled either to or ),
will therefore encounter an infinite tidal force at the horizon or an
``infinite potential barrier'' located outside the horizon respectively. We
also compute the Hawking temperature and entropy for our solutions. In
cosmology, two non-singular solutions which resemble two exact solutions
in string-motivated cosmology are obtained. In addition, we construct a
singular model which describes the standard non-inflationary big bang
cosmology (). Motivated by the
similaritiesbetween and gravitational field equations in
cosmology, we briefly discuss a special dilaton-spectator action
constructed from the bosonic part of the low energy heterotic string action andComment: 34 pgs. Plain Tex, revised version contains some clarifying comments
concerning the relationship between the constants of integration and the
coupling constants
On the Relative Strength of Electric and Magnetic ULF Wave Radial Diffusion During the March 2015 Geomagnetic Storm
In this paper, we study electron radial diffusion coefficients derived from Pc4âPc5 ultralow frequency (ULF) wave power during the intense geomagnetic storm on 17â18 March 2015. During this storm the population of highly relativistic electrons was depleted within 2 hr of the storm commencement. This radial diffusion, depending upon the availability of source populations, can cause outward radial diffusion of particles and their loss to the magnetosheath, or inward transport and acceleration. Analysis of electromagnetic field measurements from Geostationary Operational Environment Satellite (GOES), Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellite, and groundâbased magnetometers shows that the main phase stormâspecific radial diffusion coefficients do not correspond to statistical estimates. Specifically, during the main phase, the electric diffusion ( urn:x-wiley:jgra:media:jgra54863:jgra54863-math-0001) is reduced, and the magnetic diffusion ( urn:x-wiley:jgra:media:jgra54863:jgra54863-math-0002) is increased, compared to empirical models based on Kp. Contrary to prior results, the main phase magnetic radial diffusion cannot be neglected. The largest discrepancies, and periods of dominance of urn:x-wiley:jgra:media:jgra54863:jgra54863-math-0003 over urn:x-wiley:jgra:media:jgra54863:jgra54863-math-0004, occur during intervals of strongly southward IMF. However, during storm recovery, both magnetic and electric diffusion rates are consistent with empirical estimates. We further verify observationally, for the first time, an energy coherence for both urn:x-wiley:jgra:media:jgra54863:jgra54863-math-0005 and urn:x-wiley:jgra:media:jgra54863:jgra54863-math-0006 where diffusion coefficients do not depend on energy. We show that, at least for this storm, properly characterizing main phase radial diffusion, potentially associated with enhanced ULF wave magnetopause shadowing losses, cannot be done with standard empirical models. Modifications, associated especially with southward IMF, which enhance the effects of urn:x-wiley:jgra:media:jgra54863:jgra54863-math-0007 and introduce larger main phase outward transport losses, are needed
Gravitational theory without the cosmological constant problem, symmetries of space-filling branes and higher dimensions
We showed that the principle of nongravitating vacuum energy, when formulated
in the first order formalism, solves the cosmological constant problem. The
most appealing formulation of the theory displays a local symmetry associated
with the arbitrariness of the measure of integration. This can be motivated by
thinking of this theory as a direct coupling of physical degrees of freedom
with a "space - filling brane" and in this case such local symmetry is related
to space-filling brane gauge invariance. The model is formulated in the first
order formalism using the metric and the connection as independent dynamical
variables. An additional symmetry (Einstein - Kaufman symmetry) allows to
eliminate the torsion which appears due to the introduction of the new measure
of integration. The most successful model that implements these ideas is
realized in a six or higher dimensional space-time. The compactification of
extra dimensions into a sphere gives the possibility of generating scalar
masses and potentials, gauge fields and fermionic masses. It turns out that
remaining four dimensional space-time must have effective zero cosmological
constant.Comment: 26 page
First-principles dynamical CPA to finite-temperature magnetism of transition metals
We present here the first-principles dynamical CPA (coherent potential
approximation) combined with the tight-binding LMTO LDA+U method towards
quantitative calculations of the electronic structure and magnetism at finite
temperatures in transition metals and compounds. The theory takes into account
the single-site dynamical charge and spin fluctuations using the functional
integral technique as well as an effective medium. Numerical results for Fe,
Co, and Ni show that the theory explains quantitatively the high-temperature
properties such as the effective Bohr magneton numbers and the excitation
spectra in the paramagnetic state, and describes the Curie temperatures
semiquantitatively.Comment: ICM'09 Proceeding
Resonances, and mechanisms of Theta-production
After explaining necessity of exotic hadrons, we discuss mechanisms which
could determine production of the exotic Theta-baryon. A possible important
role of resonances (producing the Theta in real or virtual decays) is
emphasized for various processes. Several experimental directions for studies
of such resonances, and the Theta itself, are suggested. We briefly discuss
also recent negative results on the Theta-baryon.Comment: 6 page
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