1,938 research outputs found
The development of a spatial decision support system to optimise agricultural resource use in the Western Cape
This paper describes the development of a decision support model for regional agricultural resource utilisation. The analysis was generated in a spatial context and the optimisation technique was interactive with a geographical information system (GIS). Economic and operational research methodologies were linked to the GIS in the process of determining the appropriate resource uses for the region. The optimisation technique was applied for the Western Cape Province for eight crops. The results of this research are discussed in this paper, with specific reference to its application value for the public sector and agri-business.Farm Management, Resource /Energy Economics and Policy,
Radioactive silicon as a marker in thin-film silicide formation
A new technique using radioactive 31Si (half-life =2.62 h), formed in a nuclear reactor, as a marker for studying silicide formation is described. A few hundred angstroms of radioactive silicon is first deposited onto the silicon substrate, followed immediately by the deposition of a few thousand angstroms of the metal. When the sample is heated, a silicide is first formed with the radioactive silicon. Upon further silicide formation, this band of radioactive silicide can move to the surface of the sample if silicide formation takes place by diffusion of the metal or by silicon substitutional and/or vacancy diffusion. However, if the band of radioactive silicide stays at the silicon substrate interface it can be concluded that silicon diffuses by interstitial and/or grain-boundary diffusion. This technique was tested by studying the formation of Ni2Si on silicon at 330 °C. From a combination of ion-beam sputtering, radioactivity measurement, and Rutherford backscattering it is found that the band of radioactive silicide moves to the surface of the sample during silicide formation. From these results, implanted noble-gas marker studies and the rate dependence of Ni2Si growth on grain size, it is concluded that nickel is the dominant diffusing species during Ni2Si formation, and that it moves by grain-boundary diffusion
Comparisons of binary black hole merger waveforms
This a particularly exciting time for gravitational wave physics.
Ground-based gravitational wave detectors are now operating at a sensitivity
such that gravitational radiation may soon be directly detected, and recently
several groups have independently made significant breakthroughs that have
finally enabled numerical relativists to solve the Einstein field equations for
coalescing black-hole binaries, a key source of gravitational radiation. The
numerical relativity community is now in the position to begin providing
simulated merger waveforms for use by the data analysis community, and it is
therefore very important that we provide ways to validate the results produced
by various numerical approaches. Here, we present a simple comparison of the
waveforms produced by two very different, but equally successful
approaches--the generalized harmonic gauge and the moving puncture methods. We
compare waveforms of equal-mass black hole mergers with minimal or vanishing
spins. The results show exceptional agreement for the final burst of radiation,
with some differences attributable to small spins on the black holes in one
case.Comment: Revtex 4, 5 pages. Published versio
Universality and properties of neutron star type I critical collapses
We study the neutron star axisymmetric critical solution previously found in
the numerical studies of neutron star mergers. Using neutron star-like initial
data and performing similar merger simulations, we demonstrate that the
solution is indeed a semi-attractor on the threshold plane separating the basin
of a neutron star and the basin of a black hole in the solution space of the
Einstein equations. In order to explore the extent of the attraction basin of
the neutron star semiattractor, we construct initial data phase spaces for
these neutron star-like initial data. From these phase spaces, we also observe
several interesting dynamical scenarios where the merged object is supported
from prompt collapse. The properties of the critical index of the solution, in
particular, its dependence on conserved quantities, are then studied. From the
study, it is found that a family of neutron star semi-attractors exist that can
be classified by both their rest masses and ADM masses.Comment: 13 pages, 12 figures, 1 new reference adde
Black Hole Mergers and Unstable Circular Orbits
We describe recent numerical simulations of the merger of a class of equal
mass, non-spinning, eccentric binary black hole systems in general relativity.
We show that with appropriate fine-tuning of the initial conditions to a region
of parameter space we denote the threshold of immediate merger, the binary
enters a phase of close interaction in a near-circular orbit, stays there for
an amount of time proportional to logarithmic distance from the threshold in
parameter space, then either separates or merges to form a single Kerr black
hole. To gain a better understanding of this phenomena we study an analogous
problem in the evolution of equatorial geodesics about a central Kerr black
hole. A similar threshold of capture exists for appropriate classes of initial
conditions, and tuning to threshold the geodesics approach one of the unstable
circular geodesics of the Kerr spacetime. Remarkably, with a natural mapping of
the parameters of the geodesic to that of the equal mass system, the scaling
exponent describing the whirl phase of each system turns out to be quite
similar. Armed with this lone piece of evidence that an approximate
correspondence might exist between near-threshold evolution of geodesics and
generic binary mergers, we illustrate how this information can be used to
estimate the cross section and energy emitted in the ultra relativistic black
hole scattering problem. This could eventually be of use in providing estimates
for the related problem of parton collisions at the Large Hadron Collider in
extra dimension scenarios where black holes are produced.Comment: 16 pages, 12 figures; updated to coincide with journal versio
Constraining the evolutionary history of Newton's constant with gravitational wave observations
Space-borne gravitational wave detectors, such as the proposed Laser
Interferometer Space Antenna, are expected to observe black hole coalescences
to high redshift and with large signal-to-noise ratios, rendering their
gravitational waves ideal probes of fundamental physics. The promotion of
Newton's constant to a time-function introduces modifications to the binary's
binding energy and the gravitational wave luminosity, leading to corrections in
the chirping frequency. Such corrections propagate into the response function
and, given a gravitational wave observation, they allow for constraints on the
first time-derivative of Newton's constant at the time of merger. We find that
space-borne detectors could indeed place interesting constraints on this
quantity as a function of sky position and redshift, providing a
{\emph{constraint map}} over the entire range of redshifts where binary black
hole mergers are expected to occur. A LISA observation of an equal-mass
inspiral event with total redshifted mass of 10^5 solar masses for three years
should be able to measure at the time of merger to better than
10^(-11)/yr.Comment: 11 pages, 2 figures, replaced with version accepted for publication
in Phys. Rev. D
Universities as Living Labs for sustainable development : a global perspective
Walter Leal Filho, Baltazar Andrade Guerra, Mark Mifsud
and Rudi Pretorius use case studies from Brazil, Malta and
South Africa to reflect on how the Living Labs approach can
contribute towards a more sustainable futurepeer-reviewe
Critical Collapse of a Complex Scalar Field with Angular Momentum
We report a new critical solution found at the threshold of axisymmetric
gravitational collapse of a complex scalar field with angular momentum. To
carry angular momentum the scalar field cannot be axisymmetric; however, its
azimuthal dependence is defined so that the resulting stress energy tensor and
spacetime metric are axisymmetric. The critical solution found is
non-spherical, discretely self-similar with an echoing exponent of 0.42 (+-
4%), and exhibits a scaling exponent of 0.11 (+- 10%) in near critical
collapse. Our simulations suggest that the solution is universal (within the
imposed symmetry class), modulo a family-dependent constant phase in the
complex plane.Comment: 4 pages, 4 figure
Ecorestore: Decision Support System to Restore the Productivity of Degraded Rangelands in Southern Africa
Land degradation is a multifaceted problem that affects the agricultural productivity of land due to a loss of vegetation cover and can often be ascribed to bush encroachment in savanna and grassland rangelands. Bush encroachment entails the increase in abundance and density of indigenous and alien woody vegetation (i.e. shrub thickening), which has a negative impact on the tree-grass ratio, biodiversity, as well as on a range of ecosystem services that affect the well-being of land users, often causing an increase in poverty and the introduction of non-sustainable land management practices, especially in arid- and semi-arid regions mostly affected by climate change. In response, the North-West University, in collaboration with the Natural Resource Management (NRM) programme of the South African Department of Environment, Forestry and Fisheries (DEFF) and consultants, developed the Bush Expert Information Management System (BEIMS) that will help land users to make scientifically sound decisions regarding the restoration/rehabilitation and sustainable management of degraded land. The core components of the BEIMS are the EcoRestore Decision Support System (DSS) that contains guidelines for restoration after bush control and the Bushmon database that contains information (including spatial location) of bush encroachment restoration research projects. The BEIMS (abbreviated as Bush Expert) is a cloud-based, easily accessible online system which can also be linked to a standalone Global Information System via a spatial database link. Stemming from the BEIMS, the EcoRestore DSS can provide scientifically assessed information on projects where restoration technologies have been applied – including aerial photography that track the before and after successes of restoration/rehabilitation processes. To follow is a discussion of the results of a number of restoration applications derived with the aid of BEIMS, with due consideration for the current functionality and accessibility of the system
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