Anisotropic Flux Research Articles

Local vorticity computation approach in double distribution functions based lattice Boltzmann methods for flow and scalar transport

Computation of vorticity, or the skew-symmetric velocity gradient tensor, in conjunction with the strain rate tensor, plays an important role in the flow classification, in vortical structure identification and in the modeling of various complex fluids and flows. For the simulation of flows accompanied by the advection-diffusion transport of a scalar field (e.g., temperature), double distribution functions (DDF) based lattice Boltzmann (LB) methods, involving a pair of LB schemes are commonly used. We present a new local vorticity computation approach by introducing an intensional anisotropy of the scalar flux in the third order, off-diagonal moment equilibria of the LB scheme for the scalar field, and then combining the second order non-equilibrium components of both the LB methods. As such, any pair of lattice sets in the DDF formulation that can independently support the third order off-diagonal moments would enable local determination of the complete flow kinematics, with the LB methods for the fluid motion and the transport of the passive scalar respectively providing the necessary moment relationships to determine the symmetric and skew-symmetric components of the velocity gradient tensor. Since the resulting formulation is completely local and do not rely on any finite difference approximations for velocity derivatives, it is by design naturally suitable for parallel computation. As an illustration of our approach, we formulate a DDF-LB scheme for local vorticity computation using a pair of multiple relaxation times (MRT) based collision approaches on two-dimensional, nine velocity (D2Q9) lattices, where the necessary moment relationships to determine the velocity gradient tensor and the vorticity are established via a Chapman-Enskog analysis. Simulations of various benchmark flows demonstrate good accuracy of the predicted vorticity fields using our approach against available solutions, including numerical results, with a second order convergence. Furthermore, extensions of our formulation for a variety of collision models, including those based on cascaded and non-cascaded central moments, to enable local vorticity computation are presented.

Experimental Data of Muon Hodoscope URAGAN for Investigations of Geoffective Processes in the Heliosphere

Muon hodoscope URAGAN continuously detects the angular distribution of muons in a wide range of zenith angles and allows one to obtain information about variations, both in the intensity and in angular characteristics of the muon flux, caused by active processes in the heliosphere, the magnetosphere and atmosphere of the Earth. Various parameters of the muon flux anisotropy and methods of calculation of these parameters are discussed. Real-time processing of a continuous flow of multidimensional data from the muon hodoscope URAGAN is quite a challenge. In the article, methods of formation and primary analysis of the data, their processing in real time and obtaining time series of various parameters of integral counting rate and angular anisotropy of the muon flux, which are important for the physical analysis of modulation processes of cosmic rays in the heliosphere, are presented.

Intrinsic anisotropy and pinning anisotropy in nanostructured YBa2Cu3O7−δ from microwave measurements

Anisotropy is an intrinsic factor that dictates the magnetic properties of YBa2Cu3O7−δ and therefore has a great impact on many applications. Artificial pinning centres are often introduced in an attempt to mitigate its effect, resulting in less anisotropic electrical and magnetic properties. However, the nanoengineering of superconductors makes the quantification of the anisotropy itself uncertain: the intrinsic anisotropy due to the layered structure, quantified by the anisotropy factor γ, mixes with the additional anisotropy due to pinning. As a consequence, there is no consensus on the experimental anisotropy factor γ that can result in YBa2Cu3O7−δ when directional (twin planes, nanorods) or isotropic defects are present. We present measurements of the magnetic field and angular dependent surface impedance in very different nanostructured YBa2Cu3O7−δ films, grown by a chemical route and by pulsed laser deposition with different kind of defects (nanorods, twin planes, nanoparticles). We show that the surface impedance measurements are able to disentangle the intrinsic anisotropy from the directional pinning anisotropy, thanks to the possibility of extracting the true anisotropic flux–flow resistivity and by correctly exploiting the angular scaling. We find in all films that the intrinsic anisotropy γ = 5.3 ± 0.7. By contrast, the pinning anisotropy determines a much more complex, feature–rich and nonuniversal, sample–dependent angular landscape.

Anisotropy of cosmic ray fluxes measured with AMS-02 on the ISS

A measurement of the cosmic ray anisotropy on the arrival directions of elementary particles (electrons, positrons and protons) and light nuclei (helium, carbon and oxygen) has been performed in galactic coordinates by the Alpha Magnetic Spectrometer onboard the International Space Station. The analysis is based on the sample of events collected in the first 6.5 years (electrons and positrons), and 7.5 (protons, helium, carbon and oxygen) of data taking. The results are consistent with isotropy for all cosmic ray species and upper limits on the dipole amplitude have been computed. In particular, 95% credible interval upper limits of δ < 1.9% and δ < 0.5% are obtained for positrons and electrons, respectively, above 16 GeV. On the other hand, the upper limits of protons, helium, carbon and oxygen above 200 GV are found to be δ < 0.38%, δ < 0.36%, δ < 1.9% and δ < 1.7%, respectively.

Combined Whistler Heat Flux and Anisotropy Instabilities in Solar Wind

AbstractWhistler heat flux and electron temperature anisotropy instabilities are spontaneously generated in the expanding solar wind. The present study investigates the interplay between the two unstable modes and how each contributes to the dynamical evolution of macroscopic quantities. Whistler heat flux instability is excited in the forward direction along the heat flow, whereas anisotropy instability propagates in both backward and forward directions. Velocity moment‐based quasi‐linear theory is employed in order to investigate the saturation behavior of these instabilities, and it is shown that under certain conditions, the forward propagating whistler heat flux instability dominates, while for other conditions, especially when the temperature anisotropies are sufficiently high, it is shown that the backward mode may also contribute to the dynamical process, and even dominate. These saturation behaviors cannot be predicted by linear growth rate alone and that they imply that in the global‐kinetic models of the solar wind, bidirectional nature of these instabilities must be carefully taken into account.

Layer-by-Layer Growth of Complex-Shaped Three-Dimensional Nanostructures with Focused Electron Beams.

The fabrication of three-dimensional (3D) nanostructures is of great interest to many areas of nanotechnology currently challenged by fundamental limitations of conventional lithography. One of the most promising direct-write methods for 3D nanofabrication is focused electron beam-induced deposition (FEBID), owing to its high spatial resolution and versatility. Here we extend FEBID to the growth of complex-shaped 3D nanostructures by combining the layer-by-layer approach of conventional macroscopic 3D printers and the proximity effect correction of electron beam lithography. This framework is based on the continuum FEBID model and is capable of adjusting for a wide range of effects present during deposition, including beam-induced heating, defocusing, and gas flux anisotropies. We demonstrate the capabilities of our platform by fabricating free-standing nanowires, surfaces with varying curvatures and topologies, and general 3D objects, directly from standard stereolithography (STL) files and using different precursors. Real 3D nanoprinting as demonstrated here opens up exciting avenues for the study and exploitation of 3D nanoscale phenomena.

Accelerated Electron Propagation Model for the Flare Arcade of the September 23, 2014, Event from RHESSI, SDO, and Nobeyama Radioheliograph Observations

A multi-wavelength study and simulation is conducted for the solar flare SOL2014-09-23T23:11. GOES-class M2.5. Radio (Nobeyama Radioheliograph) and X-ray (Reuven Ramaty High Energy Solar Spectroscopic Imager) maps and energy spectra are studied, including their temporal and spatial evolution, with the superposition of radiation sources on the magnetic field structure. For the first time, a simulation of accelerated electrons transport in several characteristic magnetic structures of a flare arcade simultaneously is conducted. Accelerated electron injection functions, which depend on the space along the magnetic loop, pitch angle, and energy, are fitted to reconcile observations with the simulation results such that the calculated radiation parameters are consistent with the observed brightness distributions of hard X‑rays in the range of 28–135 keV and gyrosynchrotron radiation of 17 and 35 GHz. The energy spectrum of the electron beam corresponds in this case to one- and two-power law functions with spectral indices in the ranges δ1 ≈ 4–5 and δ2 ≈ 2.0–2.4 and spectrum break energy Ebr ≈ 240–320 keV, depending on the specific magnetic structure. The pitch-angle distribution of accelerated electrons is essentially an anisotropic electron flux with an divergence angle of ~80° from the magnetic looptops towards the footpoint with a dominant hard X-ray source.

Invesigation of the Local Anisotropy of Cosmic Ray Muon Flux During Coronal Mass Ejections in 2007–2018

Coronal mass ejections are among the most powerful disturbances of the interplanetary space. They can influence the state of the near-Earth space, including magnetosphere of the Earth. In addition, such disturbances modulate the flux of cosmic rays and penetrate both the heliosphere and the Earth’s magnetosphere. In order to find an early alert of such events, it is necessary to investigate the flux of particles arriving to the Earth and providing information about events in the heliosphere. The paper presents the results of investigation of the anisotropy of the cosmic ray muon flux by means of the muon hodoscope URAGAN in the period from 2007 to 2018.

A multidimensional implementation of the Advanced Spectral neutrino Leakage scheme

ABSTRACT We present a new, multidimensional implementation of the Advanced Spectral Leakage (ASL) scheme with the purpose of modelling neutrino–matter interactions in neutron star mergers. A major challenge is the neutrino absorption in the semitransparent regime, which is responsible for driving winds from the merger remnant. The composition of such winds is crucial in the understanding of the electromagnetic emission in the recently observed macronova following GW170817. Compared to the original version, we introduce an optical-depth-dependent flux factor to model the average angle of neutrino propagation, and a modulation that accounts for flux anisotropies in non-spherical geometries. We scrutinize our approach by first comparing the new scheme against the original one for a spherically symmetric core-collapse supernova snapshot, both in 1D and in 3D, and additionally against a two-moment (M1) scheme as implemented in 1D into the code GR1D. The luminosities and mean energies agree to a few per cents in most tests. Finally, for the case of a binary merger remnant snapshot we compare the new ASL scheme with the M1 scheme that is implemented in the Eulerian adaptive mesh refinement code flash. We find that the neutrino absorption distribution in the semitransparent regime is overall well reproduced. Both approaches agree to within $\lesssim 15{{\ \rm per\ cent}}$ for the average energies and to better than $\sim 35 {{\ \rm per\ cent}}$ in the total luminosities.

Photoelectron Sheath on Lunar Sunlit Regolith and Dust Levitation

Abstract Photoelectron sheath formation and subsequent fine dust levitation over the sunlit lunar regolith have been investigated by consistently accounting for the continuous interaction of the solar wind and solar radiation with the Moon. In deriving the photoelectron sheath, the Poisson equation is coupled with the latitude-dependent population density of the Fermionic photoelectrons. The altitude and latitude profiles of the electric potential, electric field, and electron density within the photoelectron sheath have been derived. A larger sheath is predicted near the terminator compared to the subsolar point. Accounting for the sheath features, the charging of levitating particles under the kinetic balance of anisotropic photoelectron flux, solar radiation, and solar wind plasma has been calculated. The dust charge is coupled with a characteristic sheath field to evaluate the altitude profile of the particle size, displaying levitation under its electrostatic equilibrium with the lunar gravity. Our analysis suggests that in equilibrium, the submicron particles may levitate up to a couple of meters above the lunar surface; for instance, at the subsolar point (0° latitude) 200 and 50 nm particles may float up to an altitude of ∼64 and ∼194 cm, respectively, while at 70° latitude near the terminator these particles are estimated to levitate at an altitude of ∼18 and ∼227 cm, respectively. The floating charged submicron dust may electrostatically interact with the functioning of experiments and can significantly affect the instrument operation.

A Way of Detecting Local Muon-Flux Anisotropies with the Matrix-Form Data of the URAGAN Hodoscope

A way of detecting local anisotropies of the muon flux using the matrix-form data of the URAGAN hodoscope (MEPhI) is proposed. Confidence intervals for estimating the matrix-data mathematical expectations in observations with reference and sliding data-sampling periods are selected, indicator functions are constructed, and a procedure for space–time filtering is developed. The results are presented from a search for local anisotropy in the muon flux recorded in the matrix-form data of the URAGAN hodoscope.

Charging and dynamics of dust particles in lunar photoelectron sheath

Sunlight scattering from electrostatically charged floating particles is considered accountable for the lunar twilight observations of horizon glow and streamers. In this work, the dynamics of the fine charged particles within the photoelectron sheath over the sunlit lunar surface has been investigated. Accounting for the influence of solar radiation, solar wind plasma, and lunar gravity, the present transport model consistently takes account of the coexisting phenomenon of particle charging, and characteristic photoelectron sheath screening in deriving the vertical motion of the particle. As novel features, half Fermi-Dirac statistics of the photoelectron velocity in determining the electron population and the sheath structure through the Poisson equation, and anisotropic photoelectron flux in evaluating the particle charge as it traverses through the sheath, have adequately been included in the analysis. In this framework, the electrostatic sheath features are observed to dominate over the lunar gravity in determining the dynamics of smaller (nanometer) size grains; for instance, ∼10 nm sized particles detached from the lunar regolith with a finite velocity are shown to loft up to the kilometer altitude. Depending on the initial particle velocity and size, a parametric regime defining the particle hopping over the lunar surface has been identified.

A novel method for expressing anisotropy of subgrid-scale components for thermal and scalar fields

Some types of mixed subgrid-scale (SGS) models combining an isotropic eddy-viscosity model and a scale-similarity model can be used to effectively increase the accuracy of large eddy simulation (LES). For example, Abe (2013) recently proposed a stabilized mixed model, which can successfully express the anisotropy of the SGS stress, and remarkably improves the predictive performance for wall turbulence at coarse grid resolutions without sacrificing computational stability. In the present work, this approach is extended for thermal and scalar field modeling to express the anisotropy of SGS heat (scalar) flux. A priori tests using direct numerical simulation data demonstrated that the proposed model can accurately predict the anisotropic SGS heat flux in channel flow and its variation with Prandtl number in the range 0.1–2. Its effectiveness is also confirmed by a posteriori tests under flow conditions corresponding to those in the a priori tests.

Matter Growth in Imperfect Fluid Cosmology

Extensions of Einstein’s General Relativity (GR) can formally be given a GR structure in which additional geometric degrees of freedom are mapped on an effective energy-momentum tensor. The corresponding effective cosmic medium can then be modeled as an imperfect fluid within GR. The imperfect fluid structure allows us to include, on a phenomenological basis, anisotropic stresses and energy fluxes which are considered as potential signatures for deviations from the cosmological standard Λ -cold-dark-matter ( Λ CDM) model. As an example, we consider the dynamics of a scalar-tensor extension of the standard model, the e Φ Λ CDM model. We constrain the magnitudes of anisotropic pressure and energy flux with the help of redshift-space distortion (RSD) data for the matter growth function f σ 8 .

Anisotropy of the high energy cosmic ray flux measured by means of muon bundles in the Experimental complex NEVOD

The work is devoted to the study of the anisotropy of the high energy cosmic ray flux by means of muon bundles registered during 2012-2018 with the coordinate-tracking detector DECOR, which is a part of the Unique Scientific Facility «Experimental complex NEVOD». We have analyzed data for two event samples corresponding to E > 1015 eV and E > 1016 eV energy ranges of primary particles. The method of data processing is described and estimates of the dipole anisotropy parameters (the amplitude and the phase) are presented.

Excitation of Highly Oblique Lower Band and Upper Band Chorus by a Loss Cone Feature and Temperature Anisotropy Distribution

AbstractRecent studies have indicated that highly oblique lower band chorus could be excited by temperature anisotropy with a low‐energy electron plateau. Here we present another excitation mechanism of highly oblique lower and upper band chorus by using the simultaneous observations and numerical modeling. During 23:00–24:00 UT on 3 July 2016, Van Allen probe A observed chorus with the wave normal angle close to the resonance cone both in the lower and upper bands around L = 5.0 and MLT = 3. Enhanced flux and pitch angle anisotropy of energetic electrons were observed in the same spatial region. Calculations of chorus growth rates show that highly oblique chorus waves can be excited by the energetic electrons with a loss cone feature and distinct temperature anisotropy, particularly more efficient in the presence of a low‐energy plateau. The temperature anisotropy for the oblique upper band is higher than that for the lower band.

R -parity violating supersymmetric explanation of the anomalous events at ANITA

The ANITA balloon experiment has observed two EeV-energy, upgoing events originating from well below the horizon. This is puzzling, because (i) no Standard Model (SM) particle is expected to survive passage through Earth at such energies and incident angles, and (ii) no such events were reported by IceCube. In this paper, we address both these issues by invoking a beyond SM interpretation of the EeV events as due to the decay of a long-lived bino in the R-parity violating (RPV) supersymmetry. In particular, a TeV-scale slepton/squark can be resonantly produced through the interaction of the EeV neutrino with electrons/nucleons inside Earth, that decays to a light, long-lived bino, which survives the propagation through Earth matter before decaying back to neutrinos, leptons and/or quarks, thus producing upgoing air showers in the atmosphere near ANITA. We find that the ANITA events can be explained with a GeV-scale bino and ${\cal O}(0.1)$ RPV couplings, which are consistent with all existing high and low-energy constraints. We also find that an isotropic neutrino flux is inadequate for a beyond the SM explanation of this kind, and an anisotropic flux must be invoked. Finally, we also address the apparent tension of these observations with IceCube. Various aspects of our interpretation are testable in the near future at different frontiers, such as by the LHC, Belle II, ANITA-IV and IceCube.

Full-3D relativistic MHD simulations of bow shock pulsar wind nebulae: dynamics

Bow shock pulsar wind nebulae (BSPWNe) are know to show a large variety of shapes and morphologies, both when comparing different objects, and for the same object in different energy bands. It is unclear if such a variety is related to differences in the pulsar wind properties, or to differences in the conditions of the ambient medium. We present here a set of full three-dimensional, relativistic and magneto-hydrodynamic simulations of BSPWNe, with the intention of determining how differences in the injection conditions by the pulsar wind reflect in the nebular dynamics. To achieve a good coverage of the available parameter space we have run several simulations varying those parameters that are most representative of the wind properties: the latitudinal anisotropy of the wind energy flux with respect to the pulsar spin axis, the level of magnetization, the inclination of the pulsar spin axis with respect to the pulsar direction of motion. We have followed the dynamics in these systems, not just in the very head, but also in the tail, trying to assess if and how the system retains memory of the injection at large distances from the pulsar itself. In this paper we focus our attention on the characterization of the fluid structure and magnetic field properties. We have tried to evaluate the level of turbulence in the tail, and its relation to injection, the survival of current sheets, and the degree of mixing between the shocked ambient medium and the relativistic pulsar wind material.

3D dynamics and morphology of bow-shock pulsar wind nebulae

Bow-shock pulsar wind nebulae (PWNe) show a variety of morphological shapes. We attribute this diversity to the geometrical factors: relative orientations of the pulsar rotation axis, proper velocity, and the line of sight (magnetic inclination angle may also have a certain influence on the morphology). We identify three basic types of bow-shock nebulae: (i) a "Rifle Bullet" (pulsar spin axis and proper velocity are aligned); (ii) a "Frisbee" (pulsar spin axis and proper velocity are orthogonal with the spin axis lying in the plane of the sky), and (iii) a Cart Wheel" (like frisbee but the spin axis is perpendicular to the plane of the sky). Using 3D RMHD simulations, as well as analytical calculations, we reproduce the key morphological features of the bow-shock PWNe, as well as variations, are seen across different systems. magnetic stresses within the shocked pulsar wind affect the overall structure strongly, producing "whiskers", "tails", "filled-in" and "mushroom" shapes, as well as non-symmetric morphologies. On the other hand, the interstellar medium inhomogeneities and the anisotropy of the energy flux in the pulsar wind have only a mild impact of the PWN morphology. In a few cases, when we clearly identify specific morphological structures, our results do not favor alignment of the pulsar spin axis and proper velocity. Our calculations of the underlying emission processes explain the low synchrotron X-ray efficiency (in terms of the spin-down luminosity) and imply an energetical subdominant contribution of the inverse Compton process.

Studying the Anisotropy of the Muon Flux during Nongeoeffective Coronal Mass Ejections of 2016

Coronal mass ejections (CMEs) are the brightest manifestations of solar activity. During periods of higher solar activity, dozens of ejections are observed daily and affect cosmic ray fluxes in interplanetary space. Observation of CMEs is usually carried out by means of various satellite apparatuses. In this work, features of the investigation of coronal mass ejections that are detected in the muon flux by the ground-based URAGAN muon hodoscope operating as a part of the Experimental complex NEVOD at the Moscow Engineering Physics Institute are discussed. Results of studying the anisotropy of the cosmic ray muon flux during the CMEs of 2016 are presented.