1,742 research outputs found
Pressure forces on sediment particles in turbulent open-channel flow : a laboratory study
Acknowledgements This research was sponsored by EPSRC grant EP/G056404/1 and their financial support is greatly appreciated. We also acknowledge Dr S. Cameron, who developed the PIV system and its algorithms. The design and construction of pressure sensors was carried out at the workshop and the experiments were conducted in the fluids laboratory at the University of Aberdeen. We therefore express our gratitude to the workshop and laboratory technicians and also to Mr M. Witz and Mr S. Gretland for their assistance in carrying out these experiments. The authors would also like to thank Professor J. Frohlich, Professor M. Uhlmann, Dr C.-B. Clemens and Mr B. Vowinckel for their useful suggestions and discussions throughout the course of this project. The Associate Editor Professor I. Marusic and four anonymous reviewers provided many useful and insightful comments and suggestions that have been gratefully incorporated into the final version.Peer reviewedPublisher PD
A complex speciation-richness relationship in a simple neutral model
Speciation is the "elephant in the room" of community ecology. As the
ultimate source of biodiversity, its integration in ecology's theoretical
corpus is necessary to understand community assembly. Yet, speciation is often
completely ignored or stripped of its spatial dimension. Recent approaches
based on network theory have allowed ecologists to effectively model complex
landscapes. In this study, we use this framework to model allopatric and
parapatric speciation in networks of communities and focus on the relationship
between speciation, richness, and the spatial structure of communities. We find
a strong opposition between speciation and local richness, with speciation
being more common in isolated communities and local richness being higher in
more connected communities. Unlike previous models, we also find a transition
to a positive relationship between speciation and local richness when dispersal
is low and the number of communities is small. Also, we use several measures of
centrality to characterize the effect of network structure on diversity. The
degree, the simplest measure of centrality, is found to be the best predictor
of local richness and speciation, although it loses some of its predictive
power as connectivity grows. Our framework shows how a simple neutral model can
be combined with network theory to reveal complex relationships between
speciation, richness, and the spatial organization of populations.Comment: 9 pages, 5 figures, 1 table, 50 reference
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Beagle 2: Seeking the signatures of life on Mars
ESA's Beagle 2 lander will land on Mars to search for signatures of present and past life. A Gas Analysis Package (GAP) with a mass spectrometer, XRF, Mossbauer, stereo cameras, microscope, environmental sensors, rock corer/grinder, and a Mole attachment are on the lander
Hydraulic resistance in open-channel flows over self-affine rough beds
Acknowledgements The authors wish to express their gratitude to Stephan Spiller for advice regarding the silicone moulds, to Cameron Scott for assisting with manufacturing of the roughness elements and Davide Collautti for help with conducting experiments.Peer reviewedPublisher PD
Flow development in rough-bed open channels : mean velocities, turbulence statistics, velocity spectra, and secondary currents
Acknowledgements: The authors wish to express their gratitude to Roy Gillanders for the help provided in the laboratory and to the School of Engineering of the University of Aberdeen for the support. The comments and suggestions of the Associate Editor and two anonymous reviewers helped to improve the final version of the paper and are much appreciated. Funding The study has been supported by three Engineering and Physical Sciences Research Council/UK grants: âHigh-resolution numerical and experimental studies of turbulence-induced sediment erosion and near-bed transportâ (EP/G056404/1), âBed friction in rough-bed free-surface flows: a theoretical framework, roughness regimes, and quantificationâ (EP/K041088/1) and âSecondary currents in turbulent flows over rough wallsâ (EP/V002414/1). Publisher Copyright: © 2022 The Author(s). Published by Informa UK Limited, trading as Taylor & Francis Group.Peer reviewedPublisher PD
Using fNIRS to Verify Trust in Highly Automated Driving
Trust in automation is crucial for the safe and appropriate adoption of automated driving technology. Current research methods to measure trust mainly rely on subjective scales, with several intrinsic limitations. This empirical experiment proposes a novel method to measure trust objectively, using functional near-infrared spectroscopy (fNIRS). Through manipulating participantsâ expectations regarding driving automation credibility, we have induced and successfully measured opposing levels of trust in automation. Most notably, our results evidence two separate yet interrelated cortical mechanisms for trust and distrust. Trust is demonstrably linked to decreased monitoring and working memory, whereas distrust is event-related and strongly tied to affective (or emotional) mechanisms. This paper evidence that trust in automation and situation awareness are strongly interrelated during driving automation usage. Our findings are crucial for developing future driver state monitoring technology that mitigates the impact of inappropriate reliance, or over trust, in automated driving systems
Geologic and Structural Evolution of the NE Lau Basin, Tonga: Morphotectonic Analysis and Classification of Structures Using Shallow Seismicity
The transition from subduction to transform motion along horizontal terminations of trenches is associated with tearing of the subducting slab and strike-slip tectonics in the overriding plate. One prominent example is the northern Tonga subduction zone, where abundant strike-slip faulting in the NE Lau back-arc basin is associated with transform motion along the northern plate boundary and asymmetric slab rollback. Here, we address the fundamental question: how does this subduction-transform motion influence the structural and magmatic evolution of the back-arc region? To answer this, we undertake the first comprehensive study of the geology and geodynamics of this region through analyses of morphotectonics (remote-predictive geologic mapping) and fault kinematics interpreted from ship-based multibeam bathymetry and Centroid-Moment Tensor data. Our results highlight two unique features of the NE Lau Basin: (1) the occurrence of widely distributed off-axis volcanism, in contrast to typical ridge-centered back-arc volcanism, and (2) fault kinematics dominated by shallow-crustal strike slip-faulting (rather than normal faulting) extending over ~120 km from the transform boundary. The orientations of these strike-slip faults are consistent with reactivation of earlier-formed normal faults in a sinistral megashear zone. Notably, two distinct sets of Riedel megashears are identified, indicating a recent counter-clockwise rotation of part of the stress field in the back-arc region closest to the arc. Importantly, these structures directly control the development of complex volcanic-compositional provinces, which are characterized by variably-oriented spreading centers, off-axis volcanic ridges, extensive lava flows, and point-source rear-arc volcanoes that sample a heterogenous mantle wedge, with sharp gradients and contrasts in composition and magmatic affinity. This study adds to our understanding of the geologic and structural evolution of modern backarc systems, including the association between subduction-transform motions and the siting and style of seafloor volcanism
Testing outer boundary treatments for the Einstein equations
Various methods of treating outer boundaries in numerical relativity are
compared using a simple test problem: a Schwarzschild black hole with an
outgoing gravitational wave perturbation. Numerical solutions computed using
different boundary treatments are compared to a `reference' numerical solution
obtained by placing the outer boundary at a very large radius. For each
boundary treatment, the full solutions including constraint violations and
extracted gravitational waves are compared to those of the reference solution,
thereby assessing the reflections caused by the artificial boundary. These
tests use a first-order generalized harmonic formulation of the Einstein
equations. Constraint-preserving boundary conditions for this system are
reviewed, and an improved boundary condition on the gauge degrees of freedom is
presented. Alternate boundary conditions evaluated here include freezing the
incoming characteristic fields, Sommerfeld boundary conditions, and the
constraint-preserving boundary conditions of Kreiss and Winicour. Rather
different approaches to boundary treatments, such as sponge layers and spatial
compactification, are also tested. Overall the best treatment found here
combines boundary conditions that preserve the constraints, freeze the
Newman-Penrose scalar Psi_0, and control gauge reflections.Comment: Modified to agree with version accepted for publication in Class.
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