1,389 research outputs found
A pressure-robust embedded discontinuous Galerkin method for the Stokes problem by reconstruction operators
The embedded discontinuous Galerkin (EDG) finite element method for the
Stokes problem results in a point-wise divergence-free approximate velocity on
cells. However, the approximate velocity is not H(div)-conforming and it can be
shown that this is the reason that the EDG method is not pressure-robust, i.e.,
the error in the velocity depends on the continuous pressure. In this paper we
present a local reconstruction operator that maps discretely divergence-free
test functions to exactly divergence-free test functions. This local
reconstruction operator restores pressure-robustness by only changing the right
hand side of the discretization, similar to the reconstruction operator
recently introduced for the Taylor--Hood and mini elements by Lederer et al.
(SIAM J. Numer. Anal., 55 (2017), pp. 1291--1314). We present an a priori error
analysis of the discretization showing optimal convergence rates and
pressure-robustness of the velocity error. These results are verified by
numerical examples. The motivation for this research is that the resulting EDG
method combines the versatility of discontinuous Galerkin methods with the
computational efficiency of continuous Galerkin methods and accuracy of
pressure-robust finite element methods
Modelling Livestock Component in FSSIM
Agricultural and Food Policy, Environmental Economics and Policy, Land Economics/Use, Livestock Production/Industries,
Feeling the future: prospects for a theory of implicit prospection
Mental time travel refers to the ability of an organism to project herself backward and forward in time, using episodic memory and imagination to simulate past and future experiences. The evolution of mental time travel gives humans a unique capacity for prospection: the ability to pre-experience the future. Discussions of mental time travel treat it as an instance of explicit prospection. We argue that implicit simulations of past and future experience can also be used as a way of gaining information about the future to shape preferences and guide behaviour
Localized energy for wave equations with degenerate trapping
Localized energy estimates have become a fundamental tool when studying wave
equations in the presence of asymptotically at background geometry. Trapped
rays necessitate a loss when compared to the estimate on Minkowski space. A
loss of regularity is a common way to incorporate such. When trapping is
sufficiently weak, a logarithmic loss of regularity suffices. Here, by studying
a warped product manifold introduced by Christianson and Wunsch, we encounter
the first explicit example of a situation where an estimate with an algebraic
loss of regularity exists and this loss is sharp. Due to the global-in-time
nature of the estimate for the wave equation, the situation is more complicated
than for the Schr\"{o}dinger equation. An initial estimate with sub-optimal
loss is first obtained, where extra care is required due to the low frequency
contributions. An improved estimate is then established using energy
functionals that are inspired by WKB analysis. Finally, it is shown that the
loss cannot be improved by any power by saturating the estimate with a
quasimode.Comment: 18 page
A large-scale real-life crowd steering experiment via arrow-like stimuli
We introduce "Moving Light": an unprecedented real-life crowd steering
experiment that involved about 140.000 participants among the visitors of the
Glow 2017 Light Festival (Eindhoven, NL). Moving Light targets one outstanding
question of paramount societal and technological importance: "can we seamlessly
and systematically influence routing decisions in pedestrian crowds?"
Establishing effective crowd steering methods is extremely relevant in the
context of crowd management, e.g. when it comes to keeping floor usage within
safety limits (e.g. during public events with high attendance) or at designated
comfort levels (e.g. in leisure areas). In the Moving Light setup, visitors
walking in a corridor face a choice between two symmetric exits defined by a
large central obstacle. Stimuli, such as arrows, alternate at random and
perturb the symmetry of the environment to bias choices. While visitors move in
the experiment, they are tracked with high space and time resolution, such that
the efficiency of each stimulus at steering individual routing decisions can be
accurately evaluated a posteriori. In this contribution, we first describe the
measurement concept in the Moving Light experiment and then we investigate
quantitatively the steering capability of arrow indications.Comment: 8 page
Optimality and evolution of transcriptionally regulated gene expression
<p>Abstract</p> <p>Background</p> <p>How transcriptionally regulated gene expression evolves under natural selection is an open question. The cost and benefit of gene expression are the driving factors. While the former can be determined by gratuitous induction, the latter is difficult to measure directly.</p> <p>Results</p> <p>We addressed this problem by decoupling the regulatory and metabolic function of the <it>Escherichia coli lac </it>system, using an inducer that cannot be metabolized and a carbon source that does not induce. Growth rate measurements directly identified the induced expression level that maximizes the metabolism benefits minus the protein production costs, without relying on models. Using these results, we established a controlled mismatch between sensing and metabolism, resulting in sub-optimal transcriptional regulation with the potential to improve by evolution. Next, we tested the evolutionary response by serial transfer. Constant environments showed cells evolving to the predicted expression optimum. Phenotypes with decreased expression emerged several hundred generations later than phenotypes with increased expression, indicating a higher genetic accessibility of the latter. Environments alternating between low and high expression demands resulted in overall rather than differential changes in expression, which is explained by the concave shape of the cross-environmental tradeoff curve that limits the selective advantage of altering the regulatory response.</p> <p>Conclusions</p> <p>This work indicates that the decoupling of regulatory and metabolic functions allows one to directly measure the costs and benefits that underlie the natural selection of gene regulation. Regulated gene expression is shown to evolve within several hundreds of generations to optima that are predicted by these costs and benefits. The results provide a step towards a quantitative understanding of the adaptive origins of regulatory systems.</p
Modelling frequency and attestations for OntoLex-Lemon
The OntoLex vocabulary enjoys increasing popularity as a means of publishing lexical resources with RDF and as Linked Data. The
recent publication of a new OntoLex module for lexicography, lexicog, reflects its increasing importance for digital lexicography.
However, not all aspects of digital lexicography have been covered to the same extent. In particular, supplementary information drawn
from corpora such as frequency information, links to attestations, and collocation data were considered to be beyond the scope of
lexicog. Therefore, the OntoLex community has put forward the proposal for a novel module for frequency, attestation and corpus
information (FrAC), that not only covers the requirements of digital lexicography, but also accommodates essential data structures for
lexical information in natural language processing. This paper introduces the current state of the OntoLex-FrAC vocabulary, describes
its structure, some selected use cases, elementary concepts and fundamental definitions, with a focus on frequency and attestations
When at rest: "Event-free” active inference may give rise to implicit self-models of coping potential
Kalisch and colleagues highlight coping potential (CP) as a principle resilience mechanism during event engagement. We complement this discussion by exploring generative implicit CP self-models, arguably emerging during "resting-state,” subsequent and prior to events. Resting-state affords a propitious environment for Bayesian learning, wherein appraisals/reappraisals may update active inferential CP self-models, which then mediate appraisal style organization and resilience factor valuatio
Burning velocity measurement of lean methane-air flames in a new nanosecond DBD microplasma burner platform
This paper presents the initial characterization of a new burner design to study the effect of non-thermal plasma
discharge on combustion characteristics at atmospheric pressure. The burner allows stabilizing an inverted cone
flame in a mixture flowing through a perforated plate designed as a microplasma reactor. The design principle of
the microplasma reactor is based on the dielectric barrier discharge scheme which helps to generate a stable nonthermal
plasma discharge driven by nanosecond high-voltage pulses in the burner holes. The consumed power
and pulse energy have been calculated from simultaneously measurements of current and voltage of the electrical
pulses. Time-resolved measurements of direct emission spectra for nitrogen second positive system N2(C-B)
have been done to determine the rotational and vibrational temperatures of the plasma discharge. By fitting the
spectra with SPECAIR simulation data, it was found that the rotational and vibrational temperatures are 480 K
and 3700 K, respectively, for the discharge in methane-air mixture with an equivalence ratio of 0.5 at atmospheric
pressure. The influence of a high-voltage (5 kV) pulsed nanosecond discharge on the laminar burning
velocity of methane-air flame has been investigated over a range of equivalence ratios (0.55–0.75). The laminar
burning velocity was calculated by the conical flame area method which has been validated by other published
data. CH* chemiluminescence image analysis has been applied to accurately determine the flame area. The
results show an increase of the burning velocity of about 100% in very lean (Φ= 0.55) flames as a result of the
plasma discharge effect
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