Abstract
One of the most important early results from the Parker Solar Probe (PSP) is the ubiquitous presence of magnetic switchbacks, whose origin is under debate. Using a three-dimensional direct ...numerical simulation of the equations of compressible magnetohydrodynamics from the corona to 40 solar radii, we investigate whether magnetic switchbacks emerge from granulation-driven Alfvén waves and turbulence in the solar wind. The simulated solar wind is an Alfvénic slow-solar-wind stream with a radial profile consistent with various observations, including observations from PSP. As a natural consequence of Alfvén-wave turbulence, the simulation reproduced magnetic switchbacks with many of the same properties as observed switchbacks, including Alfvénic
v
–
b
correlation, spherical polarization (low magnetic compressibility), and a volume filling fraction that increases with radial distance. The analysis of propagation speed and scale length shows that the magnetic switchbacks are large-amplitude (nonlinear) Alfvén waves with discontinuities in the magnetic-field direction. We directly compare our simulation with observations using a virtual flyby of PSP in our simulation domain. We conclude that at least some of the switchbacks observed by PSP are a natural consequence of the growth in amplitude of spherically polarized Alfvén waves as they propagate away from the Sun.
Atmospheric gravity waves play an important role in driving the dynamics of the Mesosphere and Lower Thermosphere and the basic structure of this region is determined by momentum deposition of these ...waves. Mesospheric bores are a type of non‐linear response that cause the amplification of gravity wave, due to trapping, that is characterized by a propagating step‐like jump followed by undulating waves. They require a stable layer or duct to travel horizontally with little attenuation thereby capable of transporting wave energy and momentum over larger distances. We present a prominent bright undular bore event observed in the mesospheric O(1S), O2, and OH emission layers on 16 March 2021 over Germany. A striking feature of this observation is the capture of bore's rapid dissipation around the center of the imager's field of view. The vertical temperature profile obtained from the satellite data indicates the presence of temperature inversion layer which acted as a thermal duct for the bore propagation. In addition, we have performed idealized two dimensional direct numerical simulations (DNS) of Navier‐Stokes equations under Boussinesq approximation. The DNS results reproduce many important characteristics of the observed airglow event like the nonlinear wave‐steepening, number of trailing waves, and its dissipation by implementing a thermal duct and a wave‐like perturbation. Furthermore, the DNS results also indicate that the duct width and amplitude of the initial perturbation have a considerable effect on the bore morphology.
Key Points
Observation of a mesospheric bright bore event that dissipated within the field of view
The duct that enabled the bore propagation was near the O(1S) emission layer based on the observational data
The majority of the observed features are reproduced with idealized 2D direct numerical simulations using Boussinesq approximation
A set of 3D physics‐based numerical simulations (PBS) of possible earthquakes scenarios in Istanbul along the North Anatolian Fault (Turkey) is considered in this article to provide a comprehensive ...example of application of PBS to probabilistic seismic hazard (PSHA) and loss assessment in a large urban area. To cope with the high‐frequency (HF) limitations of PBS, numerical results are first postprocessed by a recently introduced technique based on Artificial Neural Networks (ANN), providing broadband waveforms with a proper correlation of HF and low‐frequency (LF) portions of ground motion as well as a proper spatial correlation of peak values also at HF, that is a key feature for the seismic risk application at urban scale. Second, before application to PSHA, a statistical analysis of residuals is carried out to ensure that simulated results provide a set of realizations with a realistic within‐ and between‐event variability of ground motion. PBS results are then applied in a PSHA framework, adopting both the “generalized attenuation function” (GAF) approach, and a novel “footprint” (FP)‐based approach aiming at a convenient and direct application of PBS into PSHA. PSHA results from both approaches are then compared with those obtained from a more standard application of PSHA with empirical ground motion models. Finally, the probabilistic loss assessment of an extended simplified portfolio of buildings is investigated, comparing the results obtained adopting the different approaches: (i) GMPE, (ii) GAF, and (iii) FP. Only FP turned out to have the capability to account for the specific features of source and propagation path, while preserving the proper physically based spatial correlation characteristics, as required for a reliable loss estimate on a building portfolio spatially distributed over a large urban area.
Abstract Turbulent states are ubiquitous in plasmas, and the understanding of turbulence is fundamental in modern astrophysics. Numerical simulations, which are the state-of-the-art approach to the ...study of turbulence, require substantial computing resources. Recently, attention shifted to methods for generating synthetic turbulent magnetic fields, affordably creating fields with parameter-controlled characteristic features of turbulence. In this context, the B x C toolkit was developed and validated against direct numerical simulations (DNSs) of isotropic turbulent magnetic fields. Here, we demonstrate novel extensions of B x C to generate realistic turbulent magnetic fields in a fast, controlled, geometric approach. First, we perform a parameter study to determine quantitative relations between the B x C input parameters and the desired characteristic features of the turbulent power spectrum, such as the extent of the inertial range, its spectral slope, and the injection and dissipation scale. Second, we introduce in the model a set of structured background magnetic fields, B 0 , as a natural and more realistic extension to the purely isotropic turbulent fields. Third, we extend the model to include anisotropic turbulence properties in the generated fields. With all these extensions combined, our tool can quickly generate any desired structured magnetic field with controlled, anisotropic turbulent fluctuations, faster by orders of magnitude with respect to DNSs. These can be used, e.g., to provide initial conditions for DNSs or easily generate synthetic data for many astrophysical settings, all at otherwise unaffordable resolutions.
Polyelectrolyte multilayer nanofiltration membranes (PEMMs) achieve tailor-made rejection and selectivity of ions for water treatment applications through a layer-by-layer coating procedure, in which ...a charged support membrane surface is sequentially contacted with positively and negatively charged polyelectrolytes. This results in the adsorption and formation of such selective multilayer membrane skins with defined molecular compositions. The selective properties of the PEMM depend on the intrinsic properties of the respective layers. Today’s research efforts aim to correlate the membrane’s selective characteristics, its structural parameters, and the operating conditions to a model representation of the membrane’s properties. We use our previously published pEnPEn model, which solves the pressure (p) driven transport of ions through n electrolyte layers (En) and n polyelectrolyte layers (PEn). Here, we expand the model to predict the multi-ionic pressure-induced transport through PEMMs solving one-dimensional Nernst–Planck–Poisson equations. The simulations quantify the influence of asymmetric charge distributions and individual PE layers on the ion selectivity for multi-ion solutions. These asymmetric layer properties represent the nanometer-scale membrane properties emerging from the ionic crosslinking, fixed charge compensation, and overcompensation. The model gives insight into each ion’s concentration profile for n layers of electrolyte and n layers of polyelectrolytes. Now, multi-ion compositions inside and outside of the membrane are simulated, and it is shown that the membrane charge distribution even influences the onset of scaling at the fluid membrane interface. As pEnPEn provides a detailed understanding of the rejection and selectivity characteristics as a function of membrane flux and feed concentration including feed side concentration polarization, it can now predict flux-scaling boundaries for the different membrane charge distributions, making it a powerful tool for choosing process parameters and even for designing tailored PEMMs for specific separation tasks.
Display omitted
•Modeling multi-ionic transport through polyelectrolyte multilayers using pEnPEn.•Evaluating the impact of intermixed realistic charge distributions on selectivity.•Intermixed multilayers consider charge compensation and overcompensation.•Extension of pEnPEn for calculation of saturation at the fluid membrane interface.•Extended model gives insights into the onset of scaling at the membrane interface.
Mutual impedance (MI) experiments are a kind of plasma diagnostic techniques for the identification of the in situ plasma density and electron temperature. These plasma parameters are retrieved from ...MI spectra, obtained by perturbing the plasma using a set of electric emitting antennas and, simultaneously, retrieving using a set of electric receiving antennas the electric fluctuations generated in the plasma. Typical MI experiments suppose a linear plasma response to the electric excitation of the instrument. In the case of practical space applications, this assumption is often broken: low temperature plasmas, which are usually encountered in ionized planetary environments (e.g., RPC‐MIP instrument onboard the Rosetta mission, RPWI/MIME experiment onboard the JUICE mission), force toward significant perturbations of the plasma dielectric. In this context, we investigate MI experiments relaxing, for the first time, the assumption of linear plasma perturbations: we quantify the impact of large antenna emission amplitudes on the (a) plasma density and (b) electron temperature diagnostic performance of MI instruments. We use electrostatic 1D‐1 V full kinetic Vlasov‐Poisson numerical simulations. First, we simulate the electric oscillations generated in the plasma by MI experiments. Second, we use typical MI data analysis techniques to compute the MI diagnostic performance in function of the emission amplitude and of the emitting‐receiving antennas distance. We find the plasma density and electron temperature identification processes robust (i.e., relative errors below 5% and 20%, respectively) to large amplitude emissions for antenna emission amplitudes corresponding to electric‐to‐thermal energy ratios up to ϵ0E2/n0kBTe=0.1 $\left({{\epsilon}}_{0}{E}^{2}\right)/\left({n}_{0}{k}_{B}{T}_{e}\right)=0.1$.
Key Points
The plasma response to large antenna emission amplitudes triggering non‐linear plasma perturbations is simulated
Ion dynamics contributions to large amplitude propagating electric signals in the plasma are crucial and therefore should not be neglected
Mutual impedance diagnostic performances are acceptable for emission amplitudes corresponding to electric‐to‐kinetic energy ratios up to 0.1
An epidemiological model is proposed for three different types of novel fractional-order derivative operators known as the Caputo, the Caputo–Fabrizio, and the Atangana–Baleanu–Caputo operators. The ...classical model is fractionalized while taking care of the dimensional consistency for each ordinary differential equation of the model. The true field data, obtained through some authentic sources, for the dengue fever outbreak in Cape Verde islands in 2009 is the major motivation behind analysis of the present research study. The proposed model, being nonlinear, possesses the possibility of having no closed form solution. It is, therefore, existence and uniqueness for the solutions of the models are investigated via fixed point theory. The residuals computed via least-squares approach for all types of cases under consideration reveal the better performance of the models under fractional-order derivative operators proving that the dynamics of the disease (dengue virus) can be well understood if non-local effects are taken into consideration within the model. Based upon the results obtained, the efficiency rates of the fractional-order operators under the Caputo, Caputo–Fabrizio and the Atangana–Baleanu–Caputo are higher than that of the existing classical model.
•Three new fractional-order epidemiological models are proposed.•True field data is used to support the analysis.•Existence and Uniqueness for the solutions of the models has been thoroughly investigated.•Sum of squared residuals approach is employed to show the model with better performance.
This study assesses the spatial correlation of broadband earthquake ground motions from 3D physics‐based numerical simulations in near‐source conditions. State‐of‐the‐art models for predicting the ...spatial correlation are derived from wide datasets including densely recorded earthquakes in different areas worldwide and, therefore, they may be poorly representative of specific regions and near‐source effects. A large set of broadband ground motions simulated by the SPEED code, and enriched in the high‐frequency range with an Artificial Neural Network technique, is used to investigate the sensitivity of crucial parameters in geostatistical analysis (number of receivers), as well as of source, path, and site effects on spatial correlation, with a level of detail which could not be possible otherwise due to the paucity of recordings. First of all, the comparison of our results with those derived from earthquake recordings validates successfully the numerical approach in predicting the spatial correlation in a broad frequency range. Furthermore, the study points out that spatial correlation of response spectral accelerations is significantly affected by the magnitude, forward directivity effects, ground‐motion directionality (fault normal versus fault parallel), and relative position from the causative fault. These features may make critical the use of isotropic and stationary models especially in near‐fault conditions.
With mining depth increasing, the mining structure becomes more and more complex. It is easy to cause dynamic disaster during coal mining. To reveal the failure process of gas-bearing coal at complex ...mining environment, the dynamics experiments were conducted through Split Hopkinson Pressure Bar of gas-bearing coal (SHPB-GAS) experimental system. The results showed that the filtered stress waveform presented to be sine-like. With the impact load increasing, the amplitude of incident wave, reflected wave and transmission wave also increased. After calculation of stress wave data, the stress-strain curves were obtained, which included linear elastic stage, step stage, yield and rupture stage. The dynamic mechanical strength increased with the increase of impact load, and the specimen developed from stratiform rupture with macro cracks to crush rupture in fragments. To verify the experimental results, COMSOL Multiphysics software was adopted to conduct numerical simulation. The simulation results indicated that the high stress area was formed at the end faces of specimen firstly and expanded to interior of specimen gradually under different impact load. High stress induced the plastic deformation in coal specimen, which also developed from end faces to specimen inside. These results were consistent with the phenomenon of experiments, which explained the causes of failure process of gas-bearing coal. Based on the experimental and simulation achievements, the formed mechanism of dynamic disaster induced by impact load were discussed.
•Stress waveform, stress-strain and failure process of gas-bearing coal were researched.•Stress distribution and plastic deformation ware discussed in numerical simulation.•Dynamic disaster of gas-bearing coal in coal mine was discussed.
PDF
