Turbulence model reduction by deep learning

A central problem of turbulence theory is to produce a predictive model for turbulent fluxes. These have profound implications for virtually all aspects of the turbulence dynamics. In magnetic confinement devices, drift-wave turbulence produces anomalous fluxes via cross-correlations between fluctuations. In this work, we introduce a new, data-driven method for parameterizing these fluxes. The method uses deep supervised learning to infer a reduced mean-field model from a set of numerical simulations. We apply the method to a simple drift-wave turbulence system and find a significant new effect which couples the particle flux to the local \emph{gradient} of vorticity. Notably, here, this effect is much stronger than the oft-invoked shear suppression effect. We also recover the result via a simple calculation. The vorticity gradient effect tends to modulate the density profile. In addition, our method recovers a model for spontaneous zonal flow generation by negative viscosity, stabilized by nonlinear and hyperviscous terms. We highlight the important role of symmetry to implementation of the new method.Comment: To be published in Phys. Rev. E Rap. Comm. 6 pages, 7 figure

Modelling Hen Harrier Dynamics to Inform Human-Wildlife Conflict Resolution : A Spatially-Realistic, Individual-Based Approach

Peer reviewedPublisher PD

Composite fermion state of spin-orbit coupled bosons

We consider spinor Bose gas with the isotropic Rashba spin-orbit coupling in 2D. We argue that at low density its groundstate is a composite fermion state with a Chern-Simons gauge field and filling factor one. The chemical potential of such a state scales with the density as \mu \propto n^{3/2}. This is a lower energy per particle than \mu \propto n for the earlier suggested groundstate candidates: a condensate with broken time-reversal symmetry and a spin density wave state.Comment: 15 pages, 7 figures, Revte

Re-evaluation of Rapakivi Petrogenesis: Source Constraints from the Hf Isotope Composition of Zircon in the Rapakivi Granites and Associated Mafic Rocks of Southern Finland

VertaisarvioitupeerReviewe

The norm-1-property of a quantum observable

A normalized positive operator measure $X\mapsto E(X)$ has the norm-1-property if \no{E(X)}=1 whenever $E(X)\ne O$. This property reflects the fact that the measurement outcome probabilities for the values of such observables can be made arbitrary close to one with suitable state preparations. Some general implications of the norm-1-property are investigated. As case studies, localization observables, phase observables, and phase space observables are considered.Comment: 14 page

Bias dependence of perpendicular spin torque and of free and fixed layer eigenmodes in MgO-based nanopillars

We have measured the bias voltage and field dependence of eigenmode frequencies in a magnetic tunnel junction with MgO barrier. We show that both free layer (FL) and reference layer (RL) modes are excited, and that a cross-over between these modes is observed by varying external field and bias voltage. The bias voltage dependence of the FL and RL modes are shown to be dramatically different. The bias dependence of the FL modes is linear in bias voltage, whereas that of the RL mode is strongly quadratic. Using modeling and micromagnetic simulations, we show that the linear bias dependence of FL frequencies is primarily due to a linear dependence of the perpendicular spin torque on bias voltage, whereas the quadratic dependence of the RL on bias voltage is dominated by the reduction of exchange bias due to Joule heating, and is not attributable to a quadratic dependence of the perpendicular spin torque on bias voltage