Anisotropy In Space Research Articles

New insight into pore characteristics for cake layers formed on nanocomposite membranes: Effect of membrane surface fractality

Over the past two decades, there has been extensive research that attempts to relate membrane's performance to its surface roughness. However, applicability of this approach to nanocomposite membranes is questionable, given the highly diverse membrane structures. In this study, three types of carbon nanotube composite membranes (CNT_S, CNT_M, and CNT_L) were prepared and used to filter fluorescent polystyrene particles under favorable surface interaction conditions. The resulting cake structures were imaged using laser confocal microscopy and analyzed for pore characteristics. It was found that cake layers with lower porosity and smaller average pore size also had more tortuous and complex pore channels, leading to lower water permeability. Moreover, simulations of the cake layers with a pore network model reveal that pore radius and throat length are key factors affecting water permeability. Further application of the machine learning (ML) model accurately predicts cake permeability based on the 3D fractal dimension (2.44–2.81), anisotropy (0.64–0.81) and porosity (0.3–0.71) of the pore space and R2 of the test set reaches 0.96. Finally, the Weierstrass-Mandelbrot equation is applied to describe the self-similar fractal surfaces possessed by the CNT membranes. The respective fractal dimensions of three membrane surfaces (Df) are 2.31, 2.11 and 2.57. At a Df value of 2.31, the cake layer exhibits greater pore homogeneity and connectivity, and thus higher water permeability. Overall, this study revealed the fractal nature of CNT membrane surface and its relevance to pore structure and water permeability of the cake layers.

Space–time topology optimization for anisotropic materials in wire and arc additive manufacturing

Wire and Arc Additive Manufacturing (WAAM) has great potential for efficiently producing large metallic components. However, like other additive manufacturing techniques, materials processed by WAAM exhibit anisotropic properties. Assuming isotropic material properties in design optimization thus leads to less efficient material utilization. Instead of viewing WAAM-induced material anisotropy as a limitation, we consider it an opportunity to improve structural performance. This requires the integration of process planning into structural design. In this paper, we propose a novel method to utilize material anisotropy to enhance the performance of structures both during fabrication and in their use. Our approach is based on space–time topology optimization, which simultaneously optimizes the structural layout and the fabrication sequence. To model material anisotropy in space–time topology optimization, we derive the material deposition direction from the gradient of the pseudo-time field, which encodes the fabrication sequence. Numerical results demonstrate that leveraging material anisotropy effectively improves the performance of intermediate structures during fabrication as well as the overall structure.

Age-related brain-region-specific changes in diffusion anisotropy in subarachnoid space of young adults

The glymphatic system theory postulates that brain waste is removed through the cerebrospinal fluid (CSF) flow. According to this theory, CSF in the subarachnoid space (SAS) moves to the perivascular space around the penetrating arteries, flows into parenchyma to mix with interstitial fluid and brain waste, and then moves to the perivenous space to be flushed out of the brain. Despite the controversies about the glymphatic theory, it is clear that SAS plays a key role in waste clearance. For instance, the SAS around the middle cerebral artery is known to be highly involved in glymphatic influx. While diffusion tensor imaging has been used for studying the glymphatic system, there has been limited exploration of age-related changes in diffusion anisotropy within SAS and their regional variations. Given the narrow and heterogeneous morphology of SAS, the fractional anisotropy (FA) in diverse brain regions may be more relevant to glymphatic transport than mean diffusivity (MD). The goal of this study was to investigate FA in SAS to observe age-related changes across different brain regions and to interpret the results based on the glymphatic transport. We segmented SAS in the whole brain of 83 young adults and divided SAS into four cortical lobes. We demonstrated regional variations in FA and MD within SAS and an age-related decline in FA among young adults, indicating that diffusion within SAS becomes more isotropic with aging. These findings raise new questions about the factors influencing diffusion anisotropy within SAS, which are relevant to glymphatic transport.

Brain Image Segmentation for Ultrascale Neuron Reconstruction via an Adaptive Dual-Task Learning Network.

Accurate morphological reconstruction of neurons in whole brain images is critical for brain science research. However, due to the wide range of whole brain imaging, uneven staining, and optical system fluctuations, there are significant differences in image properties between different regions of the ultrascale brain image, such as dramatically varying voxel intensities and inhomogeneous distribution of background noise, posing an enormous challenge to neuron reconstruction from whole brain images. In this paper, we propose an adaptive dual-task learning network (ADTL-Net) to quickly and accurately extract neuronal structures from ultrascale brain images. Specifically, this framework includes an External Features Classifier (EFC) and a Parameter Adaptive Segmentation Decoder (PASD), which share the same Multi-Scale Feature Encoder (MSFE). MSFE introduces an attention module named Channel Space Fusion Module (CSFM) to extract structure and intensity distribution features of neurons at different scales for addressing the problem of anisotropy in 3D space. Then, EFC is designed to classify these feature maps based on external features, such as foreground intensity distributions and image smoothness, and select specific PASD parameters to decode them of different classes to obtain accurate segmentation results. PASD contains multiple sets of parameters trained by different representative complex signal-to-noise distribution image blocks to handle various images more robustly. Experimental results prove that compared with other advanced segmentation methods for neuron reconstruction, the proposed method achieves state-of-the-art results in the task of neuron reconstruction from ultrascale brain images, with an improvement of about 49% in speed and 12% in F1 score.

Pore-space characterisation of Tamusu mudstone based on FIB-SEM

This study focuses on characterising the pore space in Tamusu mudstone, a preferred nuclear waste disposal host medium in China, using focused ion beam/scanning electron microscopy (FIB-SEM). The investigation is conducted at the mesoscale, with a sample volume of 7·96 × 9·16 × 10·00 μm3 and voxel sizes of 5 × 5 × 10 nm3. The findings reveal that the pores in Tamusu mudstone primarily exist at the nanoscale, typically within its mineral matrix or at interfaces with non-porous minerals. At the FIB/SEM-imaged scale, the pore space in the Tamusu mudstone is mainly unconnected, with an analysed porosity of approximately 3·5%. Pore characteristics within the specimen exhibit relative consistency within a box size of 6–8 μm. Furthermore, the pore paths in Tamusu mudstone exhibit a preferred orientation within the bedding plane, suggesting anisotropy in pore space, possibly attributed to changes in pore path orientation and tortuosity.

Spatial distribution of vertical density and microstructure profiles in near-surface firn around Dome Fuji, Antarctica

Abstract. To better understand the near-surface evolution of polar firn in low-accumulation areas (<30 mm w.e. yr−1), we investigated the physical properties – density, microstructural anisotropy of ice matrix and pore space, and specific surface area (SSA) – of six firn cores collected within 60 km of Dome Fuji, East Antarctica. The physical properties were measured at intervals of ≤0.02 m over the top 10 m of the cores. The main findings are (i) a lack of significant density increase in the top ∼4 m, (ii) lower mean density near the dome summit (∼330 kg m−3) than in the surrounding slope area (∼355 kg m−3) in the top 1 m, (iii) developments of a vertically elongated microstructure and its contrast between layers within the top ∼3 m, (iv) more pronounced vertical elongation at sites and periods with lower accumulation rates than those with higher accumulation rates, (v) a rapid decrease in SSA in the top ∼3 m, and (vi) lower SSA at lower-accumulation sites, but this latter trend is less pronounced than that of microstructural anisotropy. These observations can be explained by a combination of the initial physical properties on the surface set by wind conditions and the metamorphism driven by water vapor transport through the firn column under a strong vertical temperature gradient (temperature gradient metamorphism, TGM). The magnitude of TGM depends on the duration of firn layers under the temperature gradient, determined by the accumulation rate; longer exposure causes a more vertically elongated microstructure and lower SSA. Overall, we highlight the significant spatial variability in the near-surface physical properties over the scale of ∼100 km around Dome Fuji. These findings will help us better understand the densification over the whole firn column and the gas-trapping process in deep firn and possible difference in them between existing deep ice cores and the upcoming “Oldest-Ice” cores collected tens of kilometers apart.

See no isotropy, hear no isotropy: Perceived distance anisotropy in auditory space

The aim of the present study was to investigate whether the tendency to perceive vertical distances as larger than horizontal ones, called the anisotropy of perceived distance, exists in the auditory modality, too. We performed two experiments in which participants (16+20) had a task to match distances of two sound sources, positioned on horizontal and vertical axes, on three egocentric distances. Besides that, in the second experiment, we varied the head moving towards a sound source (with and without) and sound dispersion around the head (with or without a box-like frame around the head). Results showed that participants managed to differentiate sound source distances, but the effects of head moving (proprioceptive information) and sound dispersion around the head were not obtained. Finally, results showed differences in matched distances between two directions. Distances of the vertical sound source were systematically perceived as larger than physically equal horizontal ones, which coincide with findings from previous studies, related to visual or proprioceptive distance estimates.

АНАЛИЗ ОТРАСЛЕВОЙ АНИЗОТРОПИИ В МЕЖДУНАРОДНОМ МАШИНОСТРОЕНИИ

Industry anisotropy, including in international mechanical engineering, is a poorly studied property of the industry system. At the same time, it is anisotropy that determines the nature of intra-industry competition. The aim of the study is to propose an approach for the analysis of industry anisotropy in the coordinate space “ resilience – efficiency” where a two–petalled R-lens will be formed, which is then clustered, with the allocation of seven reference clusters. The inclusion of such enterprise image points in one of the six selected clusters allows companies from the industry to assess their location, nearest competitors, risks, and methods of repositioning (if applicable). The study is original, it uses methods of fuzzy set theory and soft computing. A new technology for analyzing industry anisotropy based on clustering of R-lenses is proposed.

Nonlinear inverse bremsstrahlung absorption in magnetized laser-fusion plasma

The nonlinear inverse bremsstrahlung absorption (NLIBA) in magnetized plasma has been investigated within the framework of relativistic kinetic theory. Collisions are described by an improved Krook collision term that accounts for relativistic effects and the Landau microscopic collision form. The non-linearity considered in this paper arises from the anisotropy in electron momentum space in the plasma that is heated by an intense laser pulse. The absorption is explicitly expressed, under reasonable approximations, as a function of the plasma, laser pulse, and magnetic field parameters. Numerical treatment of the model equations shows that absorption increases with laser intensity but decreases with plasma temperature and laser wavelength. It has been shown that the polarization of the laser wave has a significant influence on absorption for high-intense magnetic fields used in magneto-inertial fusion (MIF) experiments. Nonlinear effects clearly reduce absorption for laser intensities comparable to the characteristic intensity, I0=me2c3ε0ωL2/e2, where me is the electron mass, c is the speed of light in vacuum, ɛ0 is the electric permittivity of free space, ωL is the laser wave frequency, and e is the elementary electric charge. Within the intensity I ≪ I0 and laser wavelength in the micro-meter range (λ ∼ μm), relativistic effects appear in the third order of absorption. These findings allow for the optimization of laser pulse parameters to achieve efficient absorption in MIF experiments.

Assessment of fabric characteristics with the development of sand liquefaction in cyclic triaxial tests: A DEM study

This paper studies fabric properties with the evolution of sand liquefaction by performing a series of 3D constant-volume cyclic triaxial DEM tests. With calibrated parameters for HN31 sand, the consistency between the obtained DEM results and the counterpart experiments is presented. The evolution of fabric characteristics is then assessed with the coordination number and mechanical coordination number, respectively. For liquefaction issues, the conventional coordination number outperforms the mechanical one since the floating particles with the number of contacts less than or equal to 1 can be fully considered. To analyse the complex inter-particle contacts in a granular assembly, the second-order contact normal fabric tensor is briefly introduced with its important mathematical properties. The second invariant of its deviatoric part can prove to be a proper index describing the degree of anisotropy in the principal fabric space spanned by the three eigenvectors belonging to this tensor. Following the direction of the applied loading, the fabric anisotropy accumulates in a gradual manner and finally reaches a threshold value corresponding to liquefaction triggering on the macro scale. This value is fabric-dependent and thus independent of loading intensity. For gaining a complete insight of sand liquefaction on both the micro and macro scales, the shear strain can act as a bridge to describe the evolution of coordination number and the anisotropy degree, respectively.

Characterization of pore space in Permo-Triassic sandstone from SW-Germany using the anisotropy of magnetic susceptibility

Pore space in siliciclastic rocks is one of the most important petrophysical properties in geothermal and hydrocarbon reservoir rock characterization. We used the anisotropy of magnetic susceptibility (AMS) of ferrofluid-impregnated Permo-Triassic sandstones of different Buntsandstein and Rotliegend facies as a proxy for pore space anisotropy and preferred flow direction as a case study for reservoir characterization. We compared the calculated ferrofluid porosity (2–21%) with He porosity (2–26%) and permeability (0.002–214 mD) and described the sediment microstructure using petrographic point-counting analysis. For water- and oil-based ferrofluid impregnation, we observed a positive correlation with He porosity and mass and susceptibility impregnation efficiency were used to control the quality of the impregnation process. Triaxial to oblate magnetic rock fabrics were mostly mimicked by the magnetic pore fabrics, except for some of the water-based ferrofluid impregnated samples, where magnetic ellipsoid shapes changed from oblate to prolate. AMS of the unimpregnated sandstones reflects well defined primary sedimentary to diagenetic fabrics with grain imbrication and cross bedding along with more laminated sedimentary structures. Deviation in ferrofluid-impregnated AMS axes orientation can be related either to the low anisotropy < 1.07 in sandstones from the Lower and Upper Buntsandstein, or the low impregnation efficiency. The mimicry is mostly better when the magnetic susceptibility of the sandstone is higher due to a higher concentration of phyllosilicates while micro-porosity is controlled by the clay fabric. A comparison of sediment petrography with magnetic pore fabrics suggests that the pore space is controlled by the bedding of the sandstones with mostly no preferred flow direction within the bedding plane.Graphical

Dimensional Transformation of Percolation Structure in Mixed-Matrix Membranes (MMMs).

A large number of studies of mixed-matrix membranes (MMMs) have confirmed the possibility of obtaining new materials with unique transport properties, including for solving specific problems in the separation of mixtures of liquids and gases. The choice of particles with a given affinity for the matrix and separable components allows researchers to adjust the selective properties of MMMs in a wide range, which changes the properties of MMMs in a wide range. However, even within the framework of the most complex percolation mechanism of the formation of the MMM structure, it is possible to explain only some of the observed effects. In particular, questions about the required particle concentration and fluctuation of properties in various MMM samples are still the subject of research. The results of the numerical modeling of such structures presented in this paper determined the possible causes of the observed deviations of the experimental results, for example, particle size dispersion, agglomeration, and interaction with the matrix. According to our research, the key factor that qualitatively changes the parameters of percolation structures is the ratio of the geometric dimensions of the system. We have confirmed in a wide range a significant change in the conditions of cluster formation and its power at different particle diameters and lengths (traditional parameters in percolation studies). But in our work, we additionally studied the effect on the cluster parameters of the interfacial layer and the anisotropy of the matrix (the transition from the cube to the film). The results obtained show that changing the parameters of the matrix-particle interaction affects agglomeration, and the degradation of the percolation structure is possible. That is, with an increase in concentration, the parameters of the percolation cluster, its power, and the probability of formation, may decrease. But even more negative changes in percolation structures are observed during the transition from a volumetric matrix to films. The anisotropy of space leads to the formation of percolation through the film in certain areas at low concentrations of particles. At the same time, in a significant part of the matrix, percolation between the film surfaces will be absent, and the effect of changing the properties of MMMs in the matrix as a whole decreases. Our study explains the observed instability of MMM properties at fixed concentrations and parameters of embedded particles, including the effect of reducing the influence of particles with increasing concentration.

On the Evolution of the Anisotropic Scaling of Magnetohydrodynamic Turbulence in the Inner Heliosphere

We analyze a merged Parker Solar Probe (PSP) and Solar Orbiter (SO) data set covering heliocentric distances 13 R ⊙ ≲ R ≲ 220 R ⊙ to investigate the radial evolution of power and spectral index anisotropy in the wavevector space of solar wind turbulence. Our results show that anisotropic signatures of turbulence display a distinct radial evolution when fast, V sw ≥ 400 km s−1, and slow, V sw ≤ 400 km s−1, wind streams are considered. The anisotropic properties of slow wind in Earth orbit are consistent with a “critically balanced” cascade, but both spectral index anisotropy and power anisotropy diminish with decreasing heliographic distance. Fast streams are observed to roughly retain their near-Sun anisotropic properties, with the observed spectral index and power anisotropies being more consistent with a “dynamically aligned” type of cascade, though the lack of extended fast wind intervals makes it difficult to accurately measure the anisotropic scaling. A high-resolution analysis during the first perihelion of PSP confirms the presence of two subranges within the inertial range, which may be associated with the transition from weak to strong turbulence. The transition occurs at κ d i ≈ 6 × 10−2 and signifies a shift from −5/3 to −2 and from −3/2 to −1.57 scaling in parallel and perpendicular spectra, respectively. Our results provide strong observational constraints for anisotropic theories of MHD turbulence in the solar wind.

Cosmology in Minkowski space

Theoretical and observational challenges to standard cosmology such as the cosmological constant problem and tensions between cosmological model parameters inferred from different observations motivate the development and search of new physics. A less radical approach to venturing beyond the standard model is the simple mathematical reformulation of our theoretical frameworks underlying it. While leaving physical measurements unaffected, this can offer a reinterpretation and even solutions of these problems. In this spirit, metric transformations are performed here that cast our Universe into different geometries. Of particular interest thereby is the formulation of cosmology in Minkowski space. Rather than an expansion of space, spatial curvature, and small-scale inhomogeneities and anisotropies, this frame exhibits a variation of mass, length and time scales across spacetime. Alternatively, this may be interpreted as an evolution of fundamental constants. As applications of this reframed cosmological picture, the naturalness of the cosmological constant is reinspected and promising candidates of geometric origin are explored for dark matter, dark energy, inflation and baryogenesis. An immediate observation thereby is the apparent absence of the cosmological constant problem in the Minkowski frame. The formalism is also applied to identify new observable signatures of conformal inhomogeneities, which have been proposed as simultaneous solution of the observational tensions in the Hubble constant, the amplitude of matter fluctuations, and the gravitational lensing amplitude of cosmic microwave background anisotropies. These are found to enhance redshifts to distant galaxy clusters and introduce a mass bias with cluster masses inferred from gravitational lensing exceeding those inferred kinematically or dynamically.

Contrastive Learning Models for Sentence Representations

Sentence representation learning is a crucial task in natural language processing, as the quality of learned representations directly influences downstream tasks, such as sentence classification and sentiment analysis. Transformer-based pretrained language models such as bidirectional encoder representations from transformers (BERT) have been extensively applied to various natural language processing tasks, and have exhibited moderately good performance. However, the anisotropy of the learned embedding space prevents BERT sentence embeddings from achieving good results in the semantic textual similarity tasks. It has been shown that contrastive learning can alleviate the anisotropy problem and significantly improve sentence representation performance. Therefore, there has been a surge in the development of models that utilize contrastive learning to fine-tune BERT-like pretrained language models to learn sentence representations. But no systematic review of contrastive learning models for sentence representations has been conducted. To fill this gap, this article summarizes and categorizes the contrastive learning based sentence representation models, common evaluation tasks for assessing the quality of learned representations, and future research directions. Furthermore, we select several representative models for exhaustive experiments to illustrate the quantitative improvement of various strategies on sentence representations.

Anisotropic Behavior of S-Wave and P-Wave States of Heavy Quarkonia at Finite Magnetic Field

We studied the effect of momentum space anisotropy on heavy quarkonium states using an extended magnetized effective fugacity quasiparticle model (EQPM). Both the real and imaginary part of the potential has been modified through the dielectric function by including the anisotropic parameter ξ. The real part of the medium-modified potential becomes more attractive in the presence of the anisotropy and constant magnetic field. The binding energy of the 1S, 2S, and 1P quarkonium states including anisotropy effects for both the oblate and the isotropic case were studied. We find that the binding energy of QQ¯ states becomes stronger in the presence of anisotropy. However, the magnetic field is found to reduce the binding energy. The thermal width of the charmonium and bottomonium 1S states has been studied at constant magnetic field eB=0.3 GeV2 for isotropic and prolate cases. The effect of magnetic field on the mass spectra of the 1P state for the oblate case was also examined. The dissociation temperature for the 1S, 2S, and 1P states of charmonium and bottomonium has been determined to be higher for the oblate case with respect to the isotropic case.

Scalar Casimir effects in a Lorentz violation scenario induced by the presence of constant vectors

In this work, we consider a theoretical model that presents a violation of Lorentz symmetry in the approach of quantum field theory. The theoretical model adopted consists of a real massive scalar quantum field confined in the region between two large parallel plates. The violation of Lorentz symmetry is introduced by a CPT-even, aether-like approach, considering a direct coupling between the derivative of the scalar field with two orthogonal constant vectors. The main objective of this paper is to analyze the modification of the Casimir energy and pressure caused by the anisotropy of space–time as a consequence of these couplings. The confinement of the scalar quantum field between the plates is implemented by imposing boundary conditions on them.

Magnetic excitations in the helical Rashba superconductor

We investigate the magnetic excitation spectrum in the helical state of a noncentrosymmetric superconductor with inversion symmetry breaking and strong Rashba spin–orbit coupling. For this purpose we derive the general expressions of the dynamical spin response functions under the presence of strong Rashba splitting of conduction bands, superconducting gap and external field which lead to stabilization of Cooper pairs with finite overall momentum in a helical state. The latter is characterized by momentum space regions of paired and unpaired states with different quasiparticle dispersions. The magnetic response is determined by i) excitations within and between both paired and unpaired regions ii) anomalous coherence factors and iii) additional spin matrix elements due to helical Rashba spin texture of bands. We show that as a consequence typical correlated real space and spin space anisotropies appear in the dynamical susceptibility which would be observable as a characteristic fingerprint for a helical superconducting state in inelastic neutron scattering investigations.

Stress-stress correlations reveal force chains in gels.

We investigate the spatial correlations of microscopic stresses in soft particulate gels using 2D and 3D numerical simulations. We use a recently developed theoretical framework predicting the analytical form of stress-stress correlations in amorphous assemblies of athermal grains that acquire rigidity under an external load. These correlations exhibit a pinch-point singularity in Fourier space. This leads to long-range correlations and strong anisotropy in real space, which are at the origin of force-chains in granular solids. Our analysis of the model particulate gels at low particle volume fractions demonstrates that stress-stress correlations in these soft materials have characteristics very similar to those in granular solids and can be used to identify force chains. We show that the stress-stress correlations can distinguish floppy from rigid gel networks and that the intensity patterns reflect changes in shear moduli and network topology, due to the emergence of rigid structures during solidification.

About a Lorentz invariant aether and an alternative view to Minkowski´s diagram

With no criticism to special relativity theory it is demonstrated with the help of a lattice with certain features, that it is feasible to reintroduce the ‘aether’ as a Lorentz invariant media. Such features lie on strings made of fibers at rest in a preferred reference system and analyzes its role as a transmission medium for the propagation both a fermion and a boson. For the approach it is used a sub algebra of Poincare that recovers the Lorentz transformation. Such sub algebra leads to a special type of graphs in which we place at ultra microscopic scale a fermion over one Euclidian space-speed graph coordinates instead of the Minkowski space-time. Finally we locate macroscopic objects and light rays in this graph and show that everything is always in a particular place at a corresponding time and discuss the anisotropy of space and the reversion of the time arrow.