275 research outputs found
Relating statistics to dynamics in axisymmetric homogeneous turbulence
The structure and the dynamics of homogeneous turbulence are modified by the
presence of body forces such that the Coriolis or the buoyancy forces, which
may render a wide range of turbulence scales anisotropic. The corresponding
statistical characterization of such effects is done in physical space using
structure functions, as well as in spectral space with spectra of two-point
correlations, providing two complementary viewpoints. In this framework,
second-order and third-order structure functions are put in parallel with
spectra of two-point second- and third-order velocity correlation functions,
using passage relations. Such relations apply in the isotropic case, or for
isotropically averaged statistics, which, however, do not reflect the actual
more complex structure of anisotropic turbulence submitted to rotation or
stratification. This complexity is demonstrated in this paper by
orientation-dependent energy and energy transfer spectra produced in both cases
by means of a two-point statistical model for axisymmetric turbulence. We show
that, to date, the anisotropic formalism used in the spectral transfer
statistics is especially well-suited to analyze the refined dynamics of
anisotropic homogeneous turbulence, and that it can help in the analysis of
isotropically computed third-order structure function statistics often used to
characterize anisotropic contexts.Comment: Physica
Dimensional transition in rotating turbulence
In this work we investigate, by means of direct numerical simulations, how
rotation affects the bi-dimensionalization of a turbulent flow. We study a thin
layer of fluid, forced by a two-dimensional forcing, within the framework of
the "split cascade" in which the injected energy flows both to small scales
(generating the direct cascade) and to large scale (to form the inverse
cascade). It is shown that rotation reinforces the inverse cascade at the
expense of the direct one, thus promoting bi-dimensionalization of the flow.
This is achieved by a suppression of the enstrophy production at large scales.
Nonetheless, we find that, in the range of rotation rates investigated,
increasing the the vertical scale causes a reduction of the flux of the inverse
cascade. Our results suggest that, even in rotating flows, the inverse cascade
may eventually disappear when the vertical scale is sufficiently large with
respect to the forcing scale
Land Use History and the Build-Up and Decline of Species Richness in Scandinavian Semi-Natural Grasslands
Scandinavian semi-natural grasslands have an exceptionally high small-scale species richness. In the past, these grasslands covered extensive areas but they have declined drastically during the last century. How species richness of semi-natural grasslands was built up during history, and how species respond to land use change, are discussed. The agricultural expansion from the late Iron Age was associated with increasing grassland extent and spatial predictability, resulting in accumulation of species at small spatial scales. Although few species directly depend on management, the specific composition of these grasslands is a product of haymaking and grazing. Grassland fragmentation initially has small effects on species richness, due to slow extinction of many species. Species loss in grasslands is, however, expected in the coming decades. Restoration efforts may fail due to slow colonization. Effects of landscape configuration may be overlooked, if land use history is not considered, since present-day species richness largely reflects landscape history
Electrophysiological evidence for differences between fusion and combination illusions in audiovisual speech perception
Accepted manuscript online: 4 October 2017Incongruent audiovisual speech stimuli can lead to perceptual illusions such as fusions or combinations. Here, we investigated
the underlying audiovisual integration process by measuring ERPs. We observed that visual speech-induced suppression of P2
amplitude (which is generally taken as a measure of audiovisual integration) for fusions was similar to suppression obtained with
fully congruent stimuli, whereas P2 suppression for combinations was larger. We argue that these effects arise because the phonetic
incongruency is solved differently for both types of stimuli.MB was supported by the Spanish Ministry of Economy and Competitiveness
(MINECO grant FPDI-2013-15661) and the Netherlands Organization
for Scientific Research (NWO VENI grant 275-89-027)
Consent and privacy in telemedicine.
The electronic broadcast of a medical interview, or a video tele-consultation (VTC), challenges many of our traditional concepts of privacy and confidentiality. The nature of a doctor-patient relationship changes dramatically when the open airwaves carry the personal histories, images, and concerns of a patient. Discussions of telemedicine often allude to inherent ethical concerns yet there are no established guidelines for the ethical conduct of a VTC
“I Did It My Way”: Moving Away from the Tyranny of Turn-by-Turn Pedestrian Navigation
No abstract available
Comment on "Reinterpreting aircraft measurement in anisotropic scaling turbulence" by Lovejoy et al. (2009)
Recently, Lovejoy et al. (2009) argued that the steep ~k−3 atmospheric kinetic energy spectrum at synoptic scales (≥1000 km) observed by aircraft is a spurious artefact of aircraft following isobars instead of isoheights. Without taking into account the earth's rotation they hypothesise that the horizontal atmospheric energy spectrum should scale as k−5/3 at all scales. We point out that the approximate k−3-spectrum at synoptic scales has been observed by a number of non-aircraft means since the 1960s and that general circulation models and other current models have successfully produced this spectrum. We also argue that the vertical movements of the aircraft are far too small to cause any strong effect on the measured spectrum at synoptic scales
Curve Your Enthusiasm: Concurvity Regularization in Differentiable Generalized Additive Models
Generalized Additive Models (GAMs) have recently experienced a resurgence in
popularity due to their interpretability, which arises from expressing the
target value as a sum of non-linear transformations of the features. Despite
the current enthusiasm for GAMs, their susceptibility to concurvity - i.e.,
(possibly non-linear) dependencies between the features - has hitherto been
largely overlooked. Here, we demonstrate how concurvity can severly impair the
interpretability of GAMs and propose a remedy: a conceptually simple, yet
effective regularizer which penalizes pairwise correlations of the non-linearly
transformed feature variables. This procedure is applicable to any
differentiable additive model, such as Neural Additive Models or NeuralProphet,
and enhances interpretability by eliminating ambiguities due to self-canceling
feature contributions. We validate the effectiveness of our regularizer in
experiments on synthetic as well as real-world datasets for time-series and
tabular data. Our experiments show that concurvity in GAMs can be reduced
without significantly compromising prediction quality, improving
interpretability and reducing variance in the feature importances
Speech-specific audiovisual integration modulates induced theta-band oscillations
Published: July 16, 2019MB was supported by The Netherlands Organization for Scientific Research (NWO: VENI Grant 275-89-027)
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