3,820 research outputs found
Marginalised herders: social dynamics and natural resource use in the fragile environment of the Richtersveld National Park, South Africa
This research article published by Elsevier B.V., 2018In the contractual Richtersveld National Park (RNP), park officials and neighbouring communities jointly manage resources, with the aim to harmonize biodiversity conservation and human land use. Our socio-ecological approach compared herding practices and livelihoods of 36 livestock owners and 35 hired herders inside and outside RNP, and further assessed soil quality and vegetation characteristics under different livestock grazing patterns and access to natural resources. Hired herders were mainly in charge of animal movement patterns but were not included in formal agreements, which negatively impacted on natural resource management, livelihoods, animal well-being and communication amongst stakeholders. Soil properties and vegetation were generally negatively affected through grazing and herding practices in this fragile semi-arid biodiversity hotspot that encompasses many endangered and endemic species. Our research highlights the complex social relationships and dynamics between diverse stakeholders engaged in the contractual park and accentuates the need to improve herders’ social and economic status
Grid-based Hybrid 3DMA GNSS and Terrestrial Positioning
The paper discusses the increasing use of hybridized sensor information for
GNSS-based localization and navigation, including the use of 3D map-aided GNSS
positioning and terrestrial systems based on different geometric measurement
principles. However, both GNSS and terrestrial systems are subject to negative
impacts from the propagation environment, which can violate the assumptions of
conventionally applied parametric state estimators. Furthermore, dynamic
parametric state estimation does not account for multi-modalities within the
state space leading to an information loss within the prediction step. In
addition, the synchronization of non-deterministic multi-rate measurement
systems needs to be accounted.
In order to address these challenges, the paper proposes the use of a
non-parametric filtering method, specifically a 3DMA multi-epoch Grid Filter,
for the tight integration of GNSS and terrestrial signals. Specifically, the
fusion of GNSS, Ultra-wide Band (UWB) and vehicle motion data is introduced
based on a discrete state representation. Algorithmic challenges, including the
use of different measurement models and time synchronization, are addressed. In
order to evaluate the proposed method, real-world tests were conducted on an
urban automotive testbed in both static and dynamic scenarios.
We empirically show that we achieve sub-meter accuracy in the static scenario
by averaging a positioning error of m, whereas in the dynamic scenario
the average positioning error amounts to m.
The paper provides a proof-of-concept of the introduced method and shows the
feasibility of the inclusion of terrestrial signals in a 3DMA positioning
framework in order to further enhance localization in GNSS-degraded
environments
Multiband effective bond-orbital model for nitride semiconductors with wurtzite structure
A multiband empirical tight-binding model for group-III-nitride
semiconductors with a wurtzite structure has been developed and applied to both
bulk systems and embedded quantum dots. As a minimal basis set we assume one
s-orbital and three p-orbitals, localized in the unit cell of the hexagonal
Bravais lattice, from which one conduction band and three valence bands are
formed. Non-vanishing matrix elements up to second nearest neighbors are taken
into account. These matrix elements are determined so that the resulting
tight-binding band structure reproduces the known Gamma-point parameters, which
are also used in recent kp-treatments. Furthermore, the tight-binding band
structure can also be fitted to the band energies at other special symmetry
points of the Brillouin zone boundary, known from experiment or from
first-principle calculations. In this paper, we describe details of the
parametrization and present the resulting tight-binding band structures of bulk
GaN, AlN, and InN with a wurtzite structure. As a first application to
nanostructures, we present results for the single-particle electronic
properties of lens-shaped InN quantum dots embedded in a GaN matrix.Comment: 10 pages, 5 figures, two supplementary file
Relationship between Nanostructure and Deformation Behavior of Microphase-Separated Styrene/Butadiene Systems
The relationship between the morphology
and the mechanical properties of nanostructured blends,comprising an asymmetric styrene/butadiene star block copolymer,exhibiting cocontinuous-like morphology and low molar mass homopolymers, was studied by electron microscopy,
microindentation hardness, and tensile testing methods. Results show that the deformation behavior of these systems is significantly modified by the presence of unentangled homopolymer chains, leading partly to a decrease in mechanical properties. In contrast to common polymer
blends, in which usually, the hardness values do not markedly deviate from the additivity law, the H-values in the
system investigated show large deviations from the linear additivity behavior. The observed anomalous behavior is discussed in terms of the enhanced local flow processes
induced by the phase-separated morphology at a nanometer scale.Peer reviewe
Hierarchical Fractal Weyl Laws for Chaotic Resonance States in Open Mixed Systems
In open chaotic systems the number of long-lived resonance states obeys a
fractal Weyl law, which depends on the fractal dimension of the chaotic saddle.
We study the generic case of a mixed phase space with regular and chaotic
dynamics. We find a hierarchy of fractal Weyl laws, one for each region of the
hierarchical decomposition of the chaotic phase-space component. This is based
on our observation of hierarchical resonance states localizing on these
regions. Numerically this is verified for the standard map and a hierarchical
model system.Comment: 5 pages, 3 figure
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