Isotropic Field Research Articles

Heat transport in a non-homothermal turbulent particle-laden flow in the collisional regime

In this investigation, we explore the impact of particle collisions on turbulent heat flux within a temporally developing thermal mixing layer arising from the interaction of two homothermal regions driven by a statistically homogeneous and isotropic velocity field. Employing two-way thermally coupled Eulerian-Lagrangian Direct Numerical Simulations (DNSs) at a Taylor microscale Reynolds number up to 124, we examine the influence of particle collisions for a Stokes number from 0.2 to 3, maintaining a fixed thermal to kinetic relaxation times ratio of 4.43. Our study quantifies the reduction in average heat transport induced by particle-to-particle collisions, which disrupt the temperature-velocity correlation created by the initial temperature difference. Notably, while collisions diminish this correlation, our analysis reveals their overall impact remains minor, even at the highest simulated Stokes number. Additionally, we present statistics of the temperature difference among colliding particles across various flow conditions.

Geometry and evolution of polygonal fault systems under a regionally anisotropic stress field: Insights from 3D seismic analysis of the Qiongdongnan Basin, NW South China Sea

AbstractPolygonal fault systems (PFS) are developed in many sedimentary basins, and their formation, growth, and ultimate geometry have been widely studied. The geometry and growth of PFS forming under the influence of regionally anisotropic stresses, however, are poorly understood, despite the fact these structures may serve as key paleo‐stress indicators that can help reconstruct the tectonic and stress history of their host basins. We here use high‐quality 3D seismic reflection data and quantitative fault analysis to determine the geometry and evolution of a PFS in the Qiongdongnan Basin (NW South China Sea), and its possible relationship with the geological and stress history of the basin. The PFS is dominated by two intersecting NNW‐to‐N‐ and E‐striking fault sets, which initiated in the Early Miocene. The dominant fault strike at the structural level at which the faults nucleated and where strain is greatest (i.e., Lower Miocene) is close to NW–SE. However, at the top and bottom of the PFS tier faults strike NNW–SSE, thereby defining a very slight vertical, clockwise rotation of strike. Based on the observation that the host rock is flat‐lying, it is unlikely that basin‐tilting perturbed (i.e., δ2 ≠ δ3) the otherwise radially isotropic stress field that typically characterize PFS. Likewise, diapirs that punctuate the host rock and that are spatially related to the PFS appear not to control fault geometry. We instead infer that the PFS geometry reflects a combination of local isotropic and regional, extension‐related tectonics stress affecting the Qiongdongnan Basin during the Early Oligocene to Middle Miocene. Regional studies suggest that during this time, extensional stresses in eastern Qiongdongnan Basin rotated clockwise from roughly NNW to N; we noticed the rotation of strike of the PFS, within which the vertical change in fault strike being relatively minor. Our study determines the timing of polygonal fault growth within the Qiongdongnan Basin and the associated geometry, highlighting the key role played by regional and local stresses.

First-principles NMR of oxide glasses boosted by machine learning.

Solid-state NMR has established itself as a cutting-edge spectroscopy for elucidating the structure of oxide glasses thanks to several decades of methodological and instrumental progress. First-principles calculations of NMR properties combined with molecular-dynamics (MD) simulations provides a powerful complementary approach for the interpretation of NMR data, although they still suffer from limitations in terms of size, time and high consumption of computational resources. We address this challenge by developing a machine-learning framework to boost predictive modelling of NMR spectra. We use kernel ridge regression techniques (least-squares support vector regression and linear ridge regression) combined with smooth overlap of atomic position (SOAP) atom-centered descriptors to efficiently predict NMR interactions: the isotropic magnetic shielding and the electric field gradient (EFG) tensor. As illustrated in this work, this approach enables the simulation of magic-angle spinning (MAS) and multiple-quantum magic-angle spinning (MQMAS) NMR spectra of very large models (more than 10 000 atoms) and an efficient averaging of NMR properties over MD trajectories of nanoseconds for incorporating finite-temperature effects, at the computational cost of classical MD simulations. We illustrate these advances for sodium silicate glasses (SiO2-Na2O). NMR parameters (isotropic chemical shift and electric field gradient) could be predicted with an accuracy of 1 to 2% in terms of the total span of the NMR parameter values. To include vibrational effects, an approach is proposed of scaling the EFG tensor in NMR simulations with a factor obtained from the time auto-correlation functions computed on MD trajectories.

Third‐order elasticity of transversely isotropic field shales

AbstractThe formations above a producing reservoir can exhibit large mechanical changes, creating a risk of significant subsidence and loss of rock integrity. These changes can be monitored by time‐lapse seismic acquisition, which measures the corresponding velocity changes via time‐shifts. Third‐order elastic theory can be used to connect subsurface strains and stress changes to these seismic attribute changes. Existing models assume isotropic strain dependence of the dynamic stiffness in shales. It is important to re‐evaluate this isotropic assumption considering the inherent anisotropy of shales and their abundance in the overburden. Thus, we instead propose a third‐order elastic model with a transversely isotropic strain dependence of the dynamic stiffness. When calibrated, this new model satisfactorily predicted P‐wave velocity changes determined in undrained laboratory experiments conducted on overburden field shales, covering a wide range of propagation directions and stress variations. The shales exhibit anisotropic dynamic strain sensitivity, resulting in a significantly higher strain sensitivity predicted for Thomsen's anisotropy parameters epsilon and delta subjected to a uniaxial strain parallel to the horizontal bedding plane compared to the vertical direction. Geomechanical modelling, considering a depleting disk‐shaped reservoir surrounded by shales, was employed to predict the dynamic stiffness changes of the overburden using the laboratory‐calibrated third‐order elastic model. The overburden time‐shifts increased with offset angle, peaking at about 45°, suggesting a strong influence of shear strains on the time‐shifts. In contrast, a corresponding model with an isotropic third‐order elastic tensor, calibrated to the same data, exhibited a significantly lower sensitivity to the shear strains. These results underscore the importance of considering the anisotropic strain dependence of the dynamic stiffness when studying shales. Interpreting offset‐dependent trends in pre‐stack time‐lapse seismic data, along with geomechanical modelling and an appropriate strain‐dependent rock physics model, can assist in quantifying subsurface strains and stress changes.

A coherence-improved and mass-balanced inflow turbulence generation method for large eddy simulation

Realistic inflow turbulence is crucial in large eddy simulations for obtaining accurate results. In this paper, an improved inflow turbulence generation method is proposed, called the coherence-improved and mass-balanced random flow generation (CMRFG) method. First, a study of the effect of the inlet mass-balanced condition is presented. Subsequently, the proposed method is explicitly deduced to satisfy arbitrary spatial coherence functions and the mass-balanced condition, so the generated turbulent fields effectively preserve the original turbulence characteristics, eliminating the need for additional inlet mass flux corrections. Meanwhile, the novel method retains the advantages of the previous method, satisfying arbitrary turbulence intensities, temporal spectra, temporal correlations, and spatial correlation coefficients. Additionally, the proposed method also ensures compliance with the divergence-free condition and Taylor's frozen hypothesis, which are essential for accurate flow field development. Finally, large eddy simulations of both homogeneous isotropic and anisotropic turbulent fields demonstrate that the turbulent fields generated by CMRFG closely align with experimental results and exhibit no artificial pressure fluctuations within the computational domain.

Isotropic exchange-bias in twinned epitaxial Co/Co3O4 bilayer

Exchange bias (EB) is a unidirectional anisotropy caused by interface coupling between a ferromagnet and an antiferromagnet. It causes a preferential direction of magnetization in the ferromagnet, which manifests as a shift of the hysteresis loop along the magnetic field axis. Here, we demonstrate a large EB of over 1000 Oe at 20 K in a twinned Co(111)/Co3O4(111) thin film epitaxially grown on sapphire(0001) with sixfold rotational lattice symmetry, which is among the highest values reported for Co/Co1−yO systems. In such systems, the effect intensity is largest along the magnetic easy axes, which usually results in an anisotropy of the EB in epitaxial interfaces. However, we observed identical EB values for 0°, 15°, and 30° angles between the magnetic field and the nearest Co[002] magnetic easy axes. The measurements imply a relaxation of the magnetization to the nearest easy axis, suggesting increasingly isotropic EB fields with higher orders of rotational lattice symmetry.

α-enhanced astrochemistry: the carbon cycle in extreme galactic conditions

ABSTRACT Astrochemistry has been widely developed as a power tool to probe the physical properties of the interstellar medium (ISM) in various conditions of the Milky Way (MW) Galaxy, and in near and distant galaxies. Most current studies conventionally apply linear scaling to all elemental abundances based on the gas-phase metallicity. However, these elements, including carbon and oxygen, are enriched differentially by stellar nucleosynthesis and the overall galactic chemical evolution, evident from α-enhancement in multiple galactic observations such as starbursts, high-redshift star-forming galaxies, and low-metallicity dwarfs. We perform astrochemical modelling to simulate the impact of an α-enhanced ISM gas cloud on the abundances of the three phases of carbon (C+, C, CO) dubbed as ‘the carbon cycle’. The ISM environmental parameters considered include two cosmic-ray ionization rates (ζCR = 10−17 and $10^{-15}\, {\rm s}^{-1}$), two isotropic FUV radiation field strengths (χ/χ0 = 1 and 102), and (sub-)linear dust-to-gas relations against metallicity, mimicking the ISM conditions of different galaxy types. In galaxies with [C/O] < 0, CO, C, and C+, all decrease in both abundances and emission, though with differential biases. The low-J CO emission is found to be the most stable tracer for the molecular gas, while C and C+ trace H2 gas only under limited conditions, in line with recent discoveries of [C i]-dark galaxies. We call for caution when using [C ii] $158\, \mu$m and [C i](1–0) as alternative H2-gas tracers for both diffuse and dense gas with non-zero [C/O] ratios.

Isotropic ΙoT-Based Magnetic Flux Density Meter Implementation for ELF Field Measurements

This article presents the basic principles for an Extremely Low Frequency (ELF) IoT-based isotropic meter implementation, which can measure magnetic flux density from 100 nT up to 10 μT. The identical sensor probes are used for isotropic field measurements in the X, Y, and Z planes. The prototype has a flat response across the frequency range from 40 Hz to 10 kHz, detecting and measuring several magnetic field sources. The proposed low-cost meter can measure fields from the power supply network and its harmonic frequencies in the operating frequency band. The proposed magnetic flux density meter circuit is simple to implement and the measured field can be displayed on any mobile device with Wi-Fi connectivity. An Arduino board with the embedded Wi-Fi Nina module is responsible for data transferring from the sensor to the cloud as a complete IoT solution, supported by the Blynk application via Android and iOS operating systems or web interface. In addition, an ELF energy harvesting (EH) circuit was also proposed in our study for the utilization of the alternating magnetic fields (50 Hz) derived from the operation of several consumer devices such as transformers, power supplies, hair dryers, etc. using low-consumption applications. Experimental measurements showed that the (DC) harvesting voltage can reach up to 4.2 volts from the magnetic field of 33 μΤ, caused by the operation of an electric hair dryer and can fully charge the 100 μF storage capacitor (Cs) of the proposed EH system in about 3 min.

Application of displacement damage dose approach to low-energy proton irradiated GaInP/GaAs/Ge solar cells

In this paper, a displacement damage simulation model for proton-irradiated GaInP/GaAs/Ge triple junction (TJ) solar cells is constructed in Geant4, and the problem of the displacement damage dose curve deviation for low-energy protons is analyzed. The modeling results show that energy loss effects and local displacement damage are important factors for the deviation of the displacement damage dose curve. The non-ionizing energy loss (NIEL) values of GaAs sub-cells calculated by Geant4 can effectively improve the deviation of the curve caused by energy loss effects. The NIEL should be constrained by the structure and size of the device rather than just the proton energy and material type. In addition, the isotropic radiation field numerical method proposed in this paper allows the displacement damage simulation model constructed in Geant4 to be expediently applied to the radiation environment in space.

A General Approach to the Design of the Fractional-Order Superdirective Beamformer

The superdirective beamformer (SD) with a linear array exhibits the maximum directivity factor (DF) in the isotropic noise field. Previously, a fractional-order SD (FO-SD) has been designed to achieve a compromise between the robustness and the DF. However, this method may suffer from two limitations. First, it only considers the Jacobi-Anger expansion-based beampattern synthesis. Second, it cannot control the DF in spherically isotropic noise field. To address these problems, we propose a general approach to the design of the FO-SD, which is a linear combination of two SDs with the integer order that can be designed with any beampattern synthesis method. Moreover, the proposed approach is able to control the WNG and the DF in both spherically and cylindrically isotropic noise field. Computer simulations substantiate the effectiveness of the proposed FO-SD over the existing SDs.

The Impact of Angle-dependent Partial Frequency Redistribution on the Scattering Polarization of the Solar Na i D Lines

The long-standing paradox of the linear polarization signal of the Na i D1 line was recently resolved by accounting for the atom’s hyperfine structure and the detailed spectral structure of the incident radiation field. That modeling relied on the simplifying angle-averaged (AA) approximation for partial frequency redistribution (PRD) in scattering, which potentially neglects important angle–frequency couplings. This work aims at evaluating the suitability of a PRD-AA modeling for the D1 and D2 lines through comparisons with general angle-dependent (AD) PRD calculations in both the absence and presence of magnetic fields. We solved the radiative transfer problem for polarized radiation in a 1D semiempirical atmospheric model with microturbulent and isotropic magnetic fields, accounting for PRD effects and comparing PRD-AA and PRD-AD modelings. The D1 and D2 lines are modeled separately as a two-level atomic system with hyperfine structure. The numerical results confirm that a spectrally structured radiation field induces linear polarization in the D1 line. However, the PRD-AA approximation greatly impacts the Q/I shape, producing an antisymmetric pattern instead of the more symmetric PRD-AD one while presenting a similar sensitivity to magnetic fields between 10 and 200 G. Under the PRD-AA approximation, the Q/I profile of the D2 line presents an artificial dip in its core, which is not found for the PRD-AD case. We conclude that accounting for PRD-AD effects is essential to suitably model the scattering polarization of the Na i D lines. These results bring us closer to exploiting the full diagnostic potential of these lines for the elusive chromospheric magnetic fields.

Further results on maximal ratio combining under correlated noise for multi-carrier underwater acoustic communication using vector sensors

In the isotropic marine ambient noise field, the pressure and particle velocity signal processing based on the maximal ratio combining (MRC) algorithm can effectively improve the signal-to-noise ratio (SNR) for the underwater acoustic (UWA) communication using acoustic vector sensors (VS). However, the assumption of isotropic ambient noise is not always valid, especially when combined with VS manufacturing errors, which increase the correlation between pressure and velocity branches for the noise and reduce MRC performance. Therefore, a correlation coefficient weighted MRC (CCW-MRC) method is proposed to achieve the optimal combination under correlated noise. And we derive the optimal weighting factors and apply the CCW-MRC method to the multi-carrier M-ary Frequency Shift Keying (MFSK) based UWA communication system with the single acoustic VS. Simulation and the field trial results demonstrate that the proposed CCW-MRC method can improve the received SNR by 2-3 dB compared with the traditional MRC in the multicarrier MFSK based UWA communication system using the single acoustic VS.

MRI-detected intraosseous bone marrow edema recedes after effective therapy of periodontitis

ObjectivesT2 STIR MRI sequences can detect preclinical changes associated with periodontal inflammation, i.e. intraosseous edema in the tooth-supporting bone. In this study, we assessed whether MRI can be used for monitoring periodontal disease.Material and methodsIn a prospective cohort study, we examined 35 patients with periodontitis between 10/2018 and 04/2019 by using 3D isotropic T2-weighted short tau inversion recovery (STIR) and Fast Field Echo T1-weighted Black bone sequences. All patients received standardized clinical exams before and three months after non-surgical periodontal therapy. Bone marrow edema extent was quantified in the STIR sequence at 922 sites before and after treatment. Results were compared with standard clinical findings. Non-parametric statistical analysis was performed.ResultsNon-surgical periodontal treatment caused significant improvement in mean probing depth (p < 0.001) and frequency of bleeding on probing (p < 0.001). The mean depth of osseous edema per site was reduced from a median [IQR] of 2 [1, 3] mm at baseline to 1 [0, 3] mm, (p < 0.001). Periodontal treatment reduced the frequency of sites with edema from 35 to 24% (p < 0.01).ConclusionThe decrease of periodontal bone marrow edema, as observed with T2 STIR MR imaging, is indicative of successful periodontal healing.Clinical relevance statementT2 STIR hyperintense bone marrow edema in the periodontal bone decreases after treatment and can therefore be used to evaluate treatment success. Furthermore, MRI reveals new options to depict hidden aspects of periodontitis.Key Points• T2 STIR hyperintense periodontal intraosseous edema was prospectively investigated in 35 patients with periodontitis before and after treatment and compared to clinical outcomes.• The frequency of affected sites was reduced from 35 to 24% (p < 0.001), and mean edema depth was reduced from a median [IQR] of 2 [1, 3] mm at baseline to 1 [0, 3] mm 3 months after treatment. (p < 0.001).• T2 STIR sequences can be used to monitor the posttreatment course of periodontitis.

Minkowski functionals of CMB polarization intensity with pynkowski: theory and application to Planck and future data

ABSTRACT The angular power spectrum of the cosmic microwave background (CMB) anisotropies is a key tool to study the Universe. However, it is blind to the presence of non-Gaussianities and deviations from statistical isotropy, which can be detected with other statistics such as Minkowski functionals (MFs). These tools have been applied to CMB temperature and E-mode anisotropies with no detection of deviations from Gaussianity and isotropy. In this work, we extend the MF formalism to the CMB polarization intensity, P2 = Q2 + U2. We use the Gaussian kinematic formula to derive the theoretical predictions of MFs for Gaussian isotropic fields. We develop a software that computes MFs on P2healpix maps and apply it to simulations to verify the robustness of both theory and methodology. We then estimate MFs of P2 maps from Planck, both in pixel space and needlet domain, comparing them with realistic simulations that include CMB and instrumental noise residuals. We find no significant deviations from Gaussianity or isotropy in Planck CMB polarization intensity. However, MFs could play an important role in the analysis of CMB polarization measurements from upcoming experiments with improved sensitivity. Therefore, we forecast the ability of MFs applied to P2 maps to detect much fainter non-Gaussian anisotropic signals than with Planck data for two future complementary experiments: the LiteBIRD satellite and the ground-based Simons Observatory. We publicly release the software to compute MFs in arbitrary scalar healpix maps as a fully documented python package called pynkowski.

A Data-Driven Variance Reduction Technique for Efficiently Modelling Astronaut Radiation Doses in Spacecraft in High-Energy Isotropic Radiation Fields.

The ionizing radiation exposure to crew on current and future space missions can significantly increase their health risks for cancers, degenerative diseases, and other acute and late effects. A common approach for estimating risk to crew is by completing stochastic (e.g., Monte Carlo) or deterministic particle transport simulations. Within the simulated environment, a small fraction of the particle histories tracked will interact with the astronaut or detector, particularly for larger spacecraft such as the International Space Station, Tiangong Space Station or Lunar Gateway. These simulations can be computationally intensive as they require a very large number of particle histories to achieve a low statistical uncertainty. Variance reduction techniques are applied to simulations to reduce the computational time of the simulation while maintaining the same (or less) statistical uncertainty. The variance reduction technique developed herein involves applying a directional source bias to an isotropic radiation field, such as galactic cosmic rays, to reduce the quantity of particles that have a low probability of interacting with the astronaut or detector. A custom application has been developed utilizing the Geant4 Toolkit that computes the trajectories and energies of particles in three dimensions in the International Space Station using the Monte Carlo method. The results demonstrate the impact of our variance reduction technique on effective dose equivalence depending on: primary and secondary particle type (proton, neutron, photon, heavy ion, etc.), geometric volumes and spacecraft materials. Our variance reduction technique can be tuned by the user to optimize the simulation time depending on their objectives and enables rapid testing of different shield configurations and materials. This variance reduction technique is implemented easily using several input parameters for boundary conditions. Recommended values are presented for rapid implementation in simulations.

Local repulsion of planar Gaussian critical points

We study the local repulsion between critical points of a stationary isotropic smooth planar Gaussian field. We show that the critical points can experience a soft repulsion which is maximal in the case of the random planar wave model, or a soft attraction of arbitrary high order. If the type of critical points is specified (extremum, saddle point), the points experience a hard local repulsion, that we quantify with the precise magnitude of the second factorial moment of the number of points in a small ball.

The rogue wave type solutions from multiple solitons interactions in the rotating reduced Maxwell–Bloch equations

Rogue waves are usually considered as the large amplitude waves that come from nowhere and disappear without trace. The formation of rogue waves are generally related to the degradation of breather solutions. In some special cases, a special form of the interactions between two solitons can be explained by the breather solutions. The types of soliton collisions are very rich, such as weak interactions, strong interactions, and solitons decay: rogue waves (the large amplitude waves that come from nowhere and disappear without trace), and partial-rogue waves (the large amplitude waves that come from nowhere but leave with a trace). Different from the rogue waves and partial-rogue waves, we mainly study the rogue wave type solutions (the large amplitude waves that come and leave with a trace) from the degeneracy in soliton solutions caused by the interactions of solitons synchronization and resonance in the Rotating reduced Maxwell–Bloch equations, which originated from circularly polarized light propagation on two isotropic electronic field components from optical system. These results systematically illustrate the formation of rogue wave type solutions in terms of boundary conditions, spectral parameters and the number of soliton interactions.

Dorsal subthalamic deep brain stimulation improves pain in Parkinson's disease.

Inconsistent effects of subthalamic deep brain stimulation (STN DBS) on pain, a common non-motor symptom of Parkinson's disease (PD), may be due to variations in active contact location relative to some pain-reducing locus of stimulation. This study models and compares the loci of maximal effect for pain reduction and motor improvement in STN DBS. We measured Movement Disorder Society Unified PD Rating Scale (MDS-UPDRS) Part I pain score (item-9), and MDS-UPDRS Part III motor score, preoperatively and 6-12 months after STN DBS. An ordinary least-squares regression model was used to examine active contact location as a predictor of follow-up pain score while controlling for baseline pain, age, dopaminergic medication, and motor improvement. An atlas-independent isotropic electric field model was applied to distinguish sites of maximally effective stimulation for pain and motor improvement. In 74 PD patients, mean pain score significantly improved after STN DBS (p = 0.01). In a regression model, more dorsal active contact location was the only significant predictor of pain improvement (R2 = 0.17, p = 0.03). The stimulation locus for maximal pain improvement was lateral, anterior, and dorsal to that for maximal motor improvement. STN stimulation, dorsal to the site of optimal motor improvement, improves pain. This region contains the zona incerta, which is known to modulate pain in humans, and may explain this observation.

Dependence of the acoustic propulsion of nano- and microcones on their orientation and aspect ratio

Recent research revealed the orientation-dependent propulsion of a cone-shaped colloidal particle that is exposed to a planar traveling ultrasound wave. Here, we extend the previous research by considering nano- and microcones with different aspect ratios and studying how the propulsion of a particle depends on its orientation and aspect ratio. We also study how the orientation-averaged propulsion of a cone-shaped particle, which corresponds to an isotropic ultrasound field, depends on its aspect ratio and identify an aspect ratio of 1/2 where the orientation-averaged propulsion is particularly strong. To make our simulation results easier reusable for follow-up research, we provide a corresponding simple analytic representation.

An isotropic viscoelastic phase field fracture model for flexural loading of freshwater columnar ice

This work presents the development and implementation of a coupled isotropic phase field fracture and viscoelastic computational model to simulate the fracture of freshwater columnar ice undergoing flexural stresses. An existing incremental constitutive model is extended to capture ice behavior up to and just after material fracture occurs. Crack initiation and propagation is modeled through a Griffith’s energy-based phase field formulation that includes contributions from viscous energy dissipation. The variational formulation and implementation of the material model in the open-source platform Dolfinx is discussed. We present 3-point flexural bending experimental data of freshwater columnar ice grown in controlled conditions which are used to inform the model’s mechanical properties. We find that the coupled model captures the creep and fracture behavior of ice specimens well for strain rates on the order of 10−5s−1 at −10 °C. Finally we show that although our model includes viscoplastic effects, freshwater ice under these conditions develops little viscous energy and therefore instantaneous mechanisms dominate its fracture behavior.