1,232 research outputs found
General fourth order Chapman-Enskog expansion of lattice Boltzmann schemes
In order to derive the equivalent partial differential equations of a lattice
Boltzmann scheme,the Chapman Enskog expansion is very popular in the lattive
Boltzmann community. A maindrawback of this approach is the fact that
multiscale expansions are used without any clearmathematical signification of
the various variables and operators. Independently of thisframework, the Taylor
expansion method allows to obtain formally the equivalent partialdifferential
equations. In this contribution, we prove that both approaches give
identicalresults with acoustic scaling for a very general family of lattice
Boltzmann schemes and upto fourth order accuracy. Examples with a single scalar
conservation illustrate our purpose
Machine Learning Can Predict the Timing and Size of Analog Earthquakes
Despite the growing spatiotemporal density of geophysical observations at subduction zones, predicting the timing and size of future earthquakes remains a challenge. Here we simulate multiple seismic cycles in a laboratory‐scale subduction zone. The model creates both partial and full margin ruptures, simulating magnitude M_w 6.2–8.3 earthquakes with a coefficient of variation in recurrence intervals of 0.5, similar to real subduction zones. We show that the common procedure of estimating the next earthquake size from slip‐deficit is unreliable. On the contrary, machine learning predicts well the timing and size of laboratory earthquakes by reconstructing and properly interpreting the spatiotemporally complex loading history of the system. These results promise substantial progress in real earthquake forecasting, as they suggest that the complex motion recorded by geodesists at subduction zones might be diagnostic of earthquake imminence
A lattice Boltzmann study of non-hydrodynamic effects in shell models of turbulence
A lattice Boltzmann scheme simulating the dynamics of shell models of
turbulence is developed. The influence of high order kinetic modes (ghosts) on
the dissipative properties of turbulence dynamics is studied. It is
analytically found that when ghost fields relax on the same time scale as the
hydrodynamic ones, their major effect is a net enhancement of the fluid
viscosity. The bare fluid viscosity is recovered by letting ghost fields evolve
on a much longer time scale. Analytical results are borne out by
high-resolution numerical simulations. These simulations indicate that the
hydrodynamic manifold is very robust towards large fluctuations of non
hydrodynamic fields.Comment: 17 pages, 3 figures, submitted to Physica
Towards higher order lattice Boltzmann schemes
In this contribution we extend the Taylor expansion method proposed
previously by one of us and establish equivalent partial differential equations
of DDH lattice Boltzmann scheme at an arbitrary order of accuracy. We derive
formally the associated dynamical equations for classical thermal and linear
fluid models in one to three space dimensions. We use this approach to adjust
relaxation parameters in order to enforce fourth order accuracy for thermal
model and diffusive relaxation modes of the Stokes problem. We apply the
resulting scheme for numerical computation of associated eigenmodes and compare
our results with analytical references
Dissection of the transcriptional regulation of grape ASR and response to glucose and abscisic acid
Despite the fact that the precise physiological function of ASRs [abscisic acid (ABA), stress, ripening] remains unknown, they have been suggested to play a dual role in the plant response to environmental cues, as highly hydrophilic proteins for direct protection, as well as transcription factors involved in the regulation of gene expression. To investigate further the biological positioning of grape ASR in the hormonal and metabolic signal network, three promoters corresponding to its cDNA were isolated and submited to a detailed in silico and functional analysis. The results obtained provided evidence for the allelic polymorphism of the grape ASR gene, the organ-preferential expression conferred on the GUS reporter gene, and the specific phloem tissue localization revealed by in situ hybridization. The study of glucose and ABA signalling in its transcriptional control, by transfection of grape protoplasts using the dual luciferase system, revealed the complexity of ASR gene expression regulation. A model was proposed allowing a discussion of the place of ASR in the fine tuning of hormonal and metabolic signalling involved in the integration of environmental cues by the plant organism
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