Isotropic Domain Research Articles

Evaluating a Stochastic Singularity Level in a V-Notch Isotropic Domain Due to Randomness in Material Properties

Abstract The singular level of a v-notched isotropic domain is crucial as it relates to the domain’s stress intensity factor (SIF), which is essential for failure prediction. Typically, the singular level is calculated using deterministic material properties (like mean values), but this can misrepresent the severity of the singularity. The singular level’s accuracy is influenced by the stochastic nature of material properties, particularly Poisson’s ratio. This paper presents a stochastic approximation of eigenvalues for an isotropic v-notched domain with stochastic material properties. While both Young’s modulus and Poisson’s ratio are independent stochastic variables, only the stochasticity of Poisson’s ratio affects the eigenvalues. The generalized polynomial chaos method is applied to these stochastic eigenvalues, resulting in a polynomial approximation based on the domain’s stochastic Poisson ratio. The polynomial’s deterministic constants are derived from eigenvalues computed using chosen deterministic material properties according to the stochastic properties of Young’s modulus and Poisson’s ratio. A numerical example illustrates the stochastic approximation of the first two eigenvalues, showing fast convergence as the number of polynomials increases. Results are validated against the Monte Carlo method, highlighting the importance of stochastic approximation in accurately predicting the singular level, which may be more severe than expected when using deterministic approximations. These findings have significant practical implications, as they underscore the need to consider stochastic material properties in structural design and failure prediction.

Meshless method for wave propagation in poroelastic transversely isotropic half‐space with the use of perfectly matched layer

AbstractNumerical investigation of wave propagation in transversely isotropic poroelastic half‐space with the use of a new stretched coordinate system through the Meshless Local Petrov–Galerkin (MLPG) formulation is presented in this paper. To this end, the u−p formulation of Biot is adopted as the framework of the porous media. One approach to numerically solve the infinite domain problems is the use of an absorber layer in which the whole half‐space is divided into two parts, that is (i) a finite part, in which the responses are interested, and (ii) the remaining semi‐infinite part, which is replaced by a Perfectly Matched Layer (PML). The stretched coordinates in the PML are introduced in such a way that the wave propagating in it does not generate spurious reflection to the finite part. Comparing the numerical results with some existing exact solutions and evaluating the norm of error demonstrate that the response functions in the finite part are achievable as precise as desired. Some new results are also presented which show the validity of the numerical approach in poroelastic transversely isotropic domain.

Microstructural investigation and performance of carbon matrix composites developed through facile pitch modification route

Increasing demand of high-performance materials lead to development of composites with affordable cost and processing route. Present work involves facile chemical modification (nitric acid and melamine) route to produce carbon matrix composites exhibiting progressive performance. Modified pitches and resultant carbon matrix composites were characterized by FTIR, optical microscopy, SEM, XRD, TGA, TMA, tribological study and compression strength. Chemical treatment given to pitch imparts active functional groups which help to improve affinity between pitch particles. Additionally, to evaluate influence of high temperature treatment, composites were also heated to 1400 °C. Optical images show that microstructure of carbonized (1000 °C) and further heat-treated (1400 °C) composites contain fine isotropic grains and flow domains, attributed to the effective influence of chemical modification. SEM images and Raman spectroscopy also confirmed the similar results of arrangement of carbon layers. TGA analysis revealed that heat-treated composites with acid modified pitch have better thermal stability at 800 °C in zero air. Coefficient of thermal expansion of all composites was measured and found very low i.e. 5 to 10 ppm/°C. Chemical treatment applied to the pitch yielded improved results for tribological performance, coupled with enhanced compressive strength. Notably, up until the present, it was difficult to find reports on fabrication of carbon matrix composites from chemically modified pitch.

Structure Engineered High Piezo-Photoelectronic Performance for Boosted Sono-Photodynamic Therapy.

Sono-photodynamic therapy is hindered by the limited tissue penetration depth of the external light source and the quick recombination of electron-hole owing to the random movement of charge carriers. In this study, orthorhombic ZnSnO3 quantum dots (QDs) with piezo-photoelectronic effects are successfully encapsulated in hexagonal upconversion nanoparticles (UCNPs) using a one-pot thermal decomposition method to form an all-in-one watermelon-like structured sono-photosensitizer (ZnSnO3 @UCNPs). The excited near-infrared light has high penetration depth, and the watermelon-like structure allows for full contact between the UCNPs and ZnSnO3 QDs, achieving ultrahigh Förster resonance energy transfer efficiency of up to 80.30%. Upon ultrasonic and near-infrared laser co-activation, the high temperature and pressure generated lead to the deformation of the UCNPs, thereby driving the deformation of all ZnSnO3 QDs inside the UCNPs, forming many small internal electric fields similar to isotropic electric domains. This piezoelectric effect not only increases the internal electric field intensity of the entire material but also prevents random movement and rapid recombination of charge carriers, thereby achieving satisfactory piezocatalytic performance. By combining the photodynamic effect arising from the energy transfer from UCNPs to ZnSnO3 , synergistic efficacy is realized. This study proposes a novel strategy for designing highly efficient sono-photosensitizers through structural design.

Physics-informed UNets for discovering hidden elasticity in heterogeneous materials

Soft biological tissues often have complex mechanical properties due to variation in structural components. In this paper, we develop a novel UNet-based neural network model for inversion in elasticity (El-UNet) to infer the spatial distributions of mechanical parameters from strain maps as input images, normal stress boundary conditions, and domain physics information. We show superior performance – both in terms of accuracy and computational cost – by El-UNet compared to fully-connected physics-informed neural networks in estimating unknown parameters and stress distributions for isotropic linear elasticity. We characterize different variations of El-UNet and propose a self-adaptive spatial loss weighting approach. To validate our inversion models, we performed various finite-element simulations of isotropic domains with heterogenous distributions of material parameters to generate synthetic data. El-UNet is faster and more accurate than the fully-connected physics-informed implementation in resolving the distribution of unknown fields. Among the tested models, the self-adaptive spatially weighted models had the most accurate reconstructions in equal computation times. The learned spatial weighting distribution visibly corresponded to regions that the unweighted models were resolving inaccurately. Our work demonstrates a computationally efficient inversion algorithm for elasticity imaging using convolutional neural networks and presents a potential fast framework for three-dimensional inverse elasticity problems that have proven unachievable through previously proposed methods.

A Study of Free-Form Shape Rationalization Using Biomimicry as Inspiration.

Bridging the gap between the material and geometrical aspects of a structure is critical in lightweight construction. Throughout the history of structural development, shape rationalization has been of prime focus for designers and architects, with biological forms being a major source of inspiration. In this work, an attempt is made to integrate different phases of design, construction, and fabrication under a single framework of parametric modeling with the help of visual programming. The idea is to offer a novel free-form shape rationalization process that can be realized with unidirectional materials. Taking inspiration from the growth of a plant, we established a relationship between form and force, which can be translated into different shapes using mathematical operators. Different prototypes of generated shapes were constructed using a combination of existing manufacturing processes to test the validity of the concept in both isotropic and anisotropic material domains. Moreover, for each material/manufacturing combination, generated geometrical shapes were compared with other equivalent and more conventional geometrical constructions, with compressive load-test results being the qualitative measure for each use case. Eventually, a 6-axis robot emulator was integrated with the setup, and corresponding adjustments were made such that a true free-form geometry could be visualized in a 3D space, thus closing the loop of digital fabrication.

Dynamic anti-plane response of circular inclusion in bi-material structure with interfacial periodic cracks due to the SH wave

This paper investigates the dynamic anti-plane response of the circular inclusion in the bi-material structure with interfacial periodic cracks due to the SH wave. In our analysis, we use the ‘conjunction’ technology and Green’s function method. The bi-material structure consists of two isotropic elastic right-angle domains consisting of a circular elastic inclusion and a series of periodic cracks at the bi-material interface. The periodic cracks are created to satisfy the free conditions of the stresses by using the interface ‘conjunction’ technology. The Green’s functions are also solved to obtain the displacement solutions of the out-place point source loaded on the vertical boundaries of the right-angle plane. The first Fredholm integral equations with unknown force systems are then established based on the continuity conditions at the bi-material interface. As an example, the distributions of the dynamic stress concentration factor (DSCF) around the circular inclusion are obtained and shown graphically. The numerical results indicate that compared with a single crack having periodic cracks strengthens the situation of the dynamic stress concentration around the inclusion.

Spatio-Temporal Gradient Enhanced Surrogate Modeling Strategies

This research compares the performance of space-time surrogate models (STSMs) and network surrogate models (NSMs). Specifically, when the system response varies over time (or pseudo-time), the surrogates must predict the system response. A surrogate model is used to approximate the response of computationally expensive spatial and temporal fields resulting from some computational mechanics simulations. Within a design context, a surrogate takes a vector of design variables that describe a current design and returns an approximation of the design’s response through a pseudo-time variable. To compare various radial basis function (RBF) surrogate modeling approaches, the prediction of a load displacement path of a snap-through structure is used as an example numerical problem. This work specifically considers the scenario where analytical sensitivities are available directly from the computational mechanics’ solver and therefore gradient enhanced surrogates are constructed. In addition, the gradients are used to perform a domain transformation preprocessing step to construct surrogate models in a more isotropic domain, which is conducive to RBFs. This work demonstrates that although the gradient-based domain transformation scheme offers a significant improvement to the performance of the space-time surrogate models (STSMs), the network surrogate model (NSM) is far more robust. This research offers explanations for the improved performance of NSMs over STSMs and recommends future research to improve the performance of STSMs.

Extracting edge stress intensity function for isotropic 3D cracked domains having stochastic material properties

The Stress Intensity Factors (SIFs) are fundamental and valuable parameters in fracture mechanics since many failure criteria involve them. In the case of a 3D crack, the SIFs extraction, based on a post-processing solution using the Finite-Element Method (FEM), is performed repeatably at several points along the singular edge (as a point-wise method) to evaluate the functional representation of the SIF along the crack edge. The Quasi Dual Function Method (QDFM) provides a polynomial approximation of the SIFs along the edge and eliminates the need for point-wise repeated calculations along the edge. Herein, we extend the QDFM to provide a broader 3D extraction method that includes stochasticity in the material properties in the case of an isotropic cracked domain having a straight edge, using the generalized Polynomial chaos (gPC). We apply the 2D gPC SIF extraction method over the QDFM to provide a stochastic Edge Stress Intensity Function (ESIF) polynomial approximation for 3D cracked domains with stochastic material properties (stochastic variables). The obtained ESIF is expressed using three families of orthogonal polynomials: Jacobi polynomials which approximate the deterministic solution of the ESIF (as part of the QDFM) and two families of orthogonal polynomials, selected by the probability distribution function of the material properties. The proposed method provides a functional polynomial presentation of the stochastic ESIF along the crack edge. Numerical example problems are provided where the stochastic approximation of the ESIF is computed. The stochastic properties of the ESIF: Mean, Variance, Skewness and Kurtosis are calculated, and the convergence of these properties is examined. The stochastic approximation of the ESIF is compared with results obtained using the 2D point-wise gPC SIFs extraction method. The proposed method is very efficient compared with the known point-wise methods since it provides a continuous function along the singular edge, unlike the point methods that require a new calculation for each point separately. The numerical examples demonstrate the robustness and high accuracy of the proposed method.

Stacking domain morphology in epitaxial graphene on silicon carbide

Terrace-sized, single-orientation graphene can be grown on top of a carbon buffer layer on silicon carbide by thermal decomposition. Despite its homogeneous appearance, a surprisingly large variation in electron transport properties is observed. Here, we employ Aberration-Corrected Low-Energy Electron Microscopy (AC-LEEM) to study a possible cause of this variability. We characterize the morphology of stacking domains between the graphene and the buffer layer of high-quality samples. Similar to the case of twisted bilayer graphene, the lattice mismatch between the graphene layer and the buffer layer at the growth temperature causes a moir\'e pattern with domain boundaries between AB and BA stackings. We analyze this moir\'e pattern to characterize the relative strain and to count the number of edge dislocations. Furthermore, we show that epitaxial graphene on silicon carbide is close to a phase transition, causing intrinsic disorder in the form of co-existence of anisotropic stripe domains and isotropic trigonal domains. Using adaptive geometric phase analysis, we determine the precise relative strain variation caused by these domains. We observe that the step edges of the SiC substrate influence the orientation of the domains and we discuss which aspects of the growth process influence these effects by comparing samples from different sources.

Light-Controlled Lyotropic Liquid Crystallinity of Polyaspartates Exploited as Photo-Switchable Alignment Medium

Two polyaspartates bearing ortho-fluorinated azobenzenes (pFAB) as photo-responsive groups in the side chain were synthesized: PpFABLA (1) and co-polyaspartate PpFABLA-co-PBLA [11, 75%(n/n) PpFABLA content]. As a consequence of the E/Z-isomerization of the side chain, PpFABLA (1) undergoes a visible-light-induced reversible coil-helix transition in solution: Green light (525 nm) affords the coil, and violet light (400 nm) affords the helix. pFAB significantly increases the thermal stability of the Z-isomer at 20 °C (t1/2 = 66 d for the Z-isomer) and effectively counters the favored back formation of the helix. At 20%(w/w) polymer concentration, the helical polymer forms a lyotropic liquid crystal (LLC) that further orients unidirectionally inside a magnetic field, while the coil polymer results in an isotropic solution. The high viscosity of the polymer solution stabilizes the coexistence of liquid crystalline and isotropic domains, which were obtained with spatial control by partial light irradiation. When used as an alignment medium, PpFABLA (1) enables (i) the measurement of dipolar couplings without the need for a separate isotropic reference and (ii) the differentiation of enantiomers. PpFABLA-co-PBLA (11) preserves the helical structure, by intention, independently of the E/Z-isomerization of the side chain: Both photo-isomers of PpFABLA-co-PBLA (11) form a helix that─at a concentration of 16%(w/w)─form an LLC. Despite the absence of a change in the secondary structure, the E/Z-isomerization of the side chain changes the morphology of the liquid crystal and leads to different sets of dipolar coupling for the same probe molecule.

Charged anisotropic solutions through decoupling in f(G,T) gravity

This paper formulates two charged interior anisotropic spherical solutions through extended gravitational decoupling scheme in the context of [Formula: see text] theory, where [Formula: see text] and [Formula: see text] symbolize the Gauss–Bonnet term and trace of the stress–energy tensor, respectively. The inclusion of an extra sector in the isotropic domain results in the production of anisotropy in the inner geometry. This technique splits the field equations into two independent arrays by deforming the temporal and radial metric coefficients, giving rise to the seed and extra fluid distributions, respectively. The Krori–Barua metric potentials are used to calculate solution of the first set, while some constraints are used to solve the unknowns present in the second array. The resulting anisotropic solution is a combination of both the obtained solutions. We inspect the influence of charge as well as decoupling parameter on the physical variables and anisotropic factor. Finally, the viability and stability of the developed solutions are checked by energy conditions and stability criteria, respectively. We conclude that the first solution is viable as well as stable for the particular range of the decoupling parameter, whereas the second solution is viable but not stable.

K původu analcimu v mezozoických a kenozoických vulkanitech České republiky a jeho úloze v názvosloví hornin

Magmatic origin of analcime has been discussed for decades (e. g., Karlsson and Clayton 1991, 1993; Pearce 1993). Despite the fact that analcime has been re-classified as zeolite and its secondary (post-magmatic) origin is globally accepted (e. g., Roux and Hamilton 1976, Giannetti and Masi 1989, Wilkinson and Hensel 1994), it is still commonly used in classification of alkaline rocks in the Czech Republic. In these rocks, analcime can be mostly found in the pseudomorphs after leucite (Fig. 1a; see Rapprich 2003), or as a homogeneous anhedral filling in the groundmass (Fig. 1b). In the second case, the boundaries of individual analcime crystals cannot be identified due to the isotropic optical properties of analcime. Therefore, origin and growth of analcime is difficult to reconstruct. For this contribution, we have studied samples of Mesozoic and Cenozoic alkaline rocks from three localities across the Czech Republic, where partly analcimized glass in the groundmass was preserved, with an aim to better understand the origin of analcime in alkaline rocks. Mesozoic augitite from the southwestern slope of the Petřkovice Mt. near Nový Jičín (sample TG05) displays small isometric colourless, optically isotropic domains (analcime) enclosed in originally glassy groundmass (Fig. 1c–f ). This texture suggests the analcime is replacing original glass in the groundmass, enclosing also microcrysts of the stable minerals in groundmass. Very similar texture was observed also in Oligocene augitite from Mětikalov in Doupovské hory Mts. (sample DR338, Fig. 2). In this rock, the analcime domains either mantle larger phenocrysts, or are distributed within the groundmass. The growth of the analcime domains on the edges of larger phenocrysts resembles growth of spherulites, which represent products of silica-rich glass recrystallization (e. g., Breitkreuz 2013). To further investigate this possibility, additional samples were collected from Kamenický vrch near Zákupy (Fig. 3). In individual samples, number and size of analcime domains vary, which suggests, that these domains represent various stages of a continuous growth. The X-ray elemental mapping of Al and Na (Fig. 4) then shows, that the analcime domains are represented by single grains of cubic analcime. As a result, we may conclude that analcime in groundmass of Mesozoic and Cenozoic alkaline rocks originates from devitrification of original glass. These rocks hence should not be classified as “analcimites” or “analcimic …” but rather as “analcimized …” according to Le Maitre et al. (2005).

Short-period domain patterning by ion beam irradiation in lithium niobate waveguides produced by soft proton exchange

The lithium-niobate-based waveguides have emerged as one of the key platforms for enabling integrated optical technologies. The most common method for creating waveguides in lithium niobate is soft proton exchange (SPE) method. The range of the waveguides applications can be expanded further by creation of near-surface periodical structure of stripe ferroelectric domains within a waveguide (periodical poling) to realize various types of nonlinear optical interactions for creation of frequency conversion devices. However, the joint use of these two procedures (SPE and periodical poling) remains a challenging task. In this paper, we propose a focused ion beam (i-beam) periodical poling technique realized after SPE process for creation of an integrated optical frequency conversion device. The choice of i-beam poling parameters is based on the study of the features of domain structure evolution in lithium niobate after SPE process. We have found that SPE process leads to formation of shallow structure of isolated nanodomains. The revealed isotropic domain growth was caused by the sideways domain wall motion by step generation as a result of merging with these nanodomains. This type of domain kinetics is preferable for periodical poling as it decreases the probability of fast merging of stripe domains due to formation of fast domain walls. Eventually, we have created the 1-mm-long 2-μm-period domain structure in a channel waveguide. The obtained second harmonic generation efficiency for pulse pumping at 756 nm was up to 6·107% W−1 cm−2 for average power and 300 % W−1 cm−2 for peak power indicating the high quality of periodical poling.

Stability of non-isothermal Poiseuille flow in a fluid overlying an anisotropic and inhomogeneous porous domain

A two-domain approach is used to investigate the thermal convection of Poiseuille flow in an anisotropic and inhomogeneous porous domain underlying a fluid domain. The flow of the Newtonian fluid is regulated by Darcy's law in the porous domain with the implementation of the Beavers–Joseph condition at the interface. The impact of medium anisotropy and inhomogeneity is inspected by virtue of linear stability analysis along with other governing parameters such as depth ratio (ratio of depth of fluid domain to porous domain), Darcy number, Reynolds number and Prandtl number concerning the stability of the fluid–porous system. The neutral curves are found to be bimodal and unimodal in nature with the anisotropy and inhomogeneity leaving its imprint on parametric variation. An increase in anisotropy or decrease in the inhomogeneity parameter follows the modal change from unimodal (porous) to bimodal (both porous and fluid). Also, it has been identified that, irrespective of the considered variations in anisotropy and inhomogeneity, the least stable mode for the depth ratio ${<}0.05$ is porous and for the depth ratio ${>}0.16$ is fluid. Furthermore, energy budget analysis is carried out to classify the type of instability and validate the type of mode. The instability is found to be thermal–buoyant in nature with omission of low Reynolds numbers along with very low values of the ratio of permeability in the horizontal to vertical direction, where thermal–shear instability is witnessed. Likewise, secondary flow patterns in the context of the streamfunction and temperature contour are analysed to validate the least stable mode and the type of prevailing instability in the fluid–porous system. The presented numerical results find good experimental support from the results of Chen & Chen (J. Fluid Mech., vol. 207, 1989, pp. 311–321) in the limit of natural convection with an isotropic and homogeneous porous domain.

Two-Stage Evolution of Gamma-Phase Spherulites of Poly (Vinylidene Fluoride) Induced by Alkylammonium Salt.

We investigated the evolution of the γ-phase spherulites of poly(vinylidene fluoride) (PVDF) added to 1 wt% of tetrabutylammonium hydrogen sulfate during the isothermal crystallization at 165 °C through polarized optical microscopy and light scattering measurements. Optically isotropic domains grew, and then optical anisotropy started to increase in the domain to yield spherulite. Double peaks were seen in the time variation of the Vv light scattering intensity caused by the density fluctuation and optical anisotropy, and the Hv light scattering intensity caused by the optical anisotropy started to increase during the second increase in the Vv light scattering intensity. These results suggest the two-stage evolution of the γ-phase spherulites, i.e., the disordered domain grows in the first stage and ordering in the spherulite increases due to the increase in the fraction of the lamellar stacks in the spherulite without a change in the spherulite size in the second stage. Owing to the characteristic crystallization behavior, the birefringence in the γ-phase spherulites of the PVDF/TBAHS was much smaller than that in the α-phase spherulites of the neat PVDF.

Cellulose Nanocrystal Aqueous Colloidal Suspensions: Evidence of Density Inversion at the Isotropic-Liquid Crystal Phase Transition.

The colloidal suspensions of aqueous cellulose nanocrystals (CNCs) are known to form liquid crystalline (LC) systems above certain critical concentrations. From an isotropic phase, tactoid formation, growth, and sedimentation have been determined as the genesis of a high-density cholesteric phase, which, after drying, originates solid iridescent films. Herein, the coexistence of a liquid crystal upper phase and an isotropic bottom phase in CNC aqueous suspensions at the isotropic-nematic phase separation is reported. Furthermore, isotropic spindle-like domains are observed in the low-density LC phase and high-density LC phases are also prepared. The CNCs isolated from the low- and high-density LC phases are found to have similar average lengths, diameters, and surface charges. The existence of an LC low-density phase is explained by the presence of air dissolved in the water present within the CNCs. The air dissolves out when the water solidifies into ice and remains within the CNCs. The self-adjustment of the cellulose chain conformation enables the entrapment of air within the CNCs and CNC buoyancy in aqueous suspensions.

Investigating the Magnetotelluric Responses in Electrical Anisotropic Media

When interpreting magnetotelluric (MT) data, because of the inherent anisotropy of the earth, considering electrical anisotropy is crucial. Accordingly, using the edge-based finite element method, we calculated the responses of MT data for electrical isotropic and anisotropic models, and subsequently used the anisotropy index and polar plot to depict MT responses. High values of the anisotropy index were mainly yielded at the boundary domains of anomalous bodies for isotropy cases because the conductive differences among isotropic anomalous bodies or among anomalous bodies and background earth can be regarded as macro-anisotropy. However, they only appeared across anomalous bodies in the anisotropy cases. The anisotropy index can directly differentiate isotropy from anisotropy but exhibits difficulty in reflecting the azimuth of the principal conductivities. For the isotropy cases, polar plots are approximately circular and become curves with a big ratio of the major axis to minor axis, such as an 8-shaped curve for the anisotropic earth. Furthermore, the polar plot can reveal the directions of principal conductivities. However, distorted by anomalous bodies, polar plots with a large ratio of the major axis to minor axis occur in isotropic domains around the anomalous bodies, which may lead to the misinterpretation of these domains as anisotropic earth. Therefore, combining the anisotropy index with a polar plot facilitates the identification of the electrical anisotropy.

Zigzag domains caused by strain-induced anisotropy of the Dzyaloshinskii-Moriya interaction

The influence of the anisotropic interfacial Dzyaloshinskii-Moriya interaction (iDMI) on the structure of magnetic domains in thin Co/Pt films is investigated using magnetic force microscopy. The iDMI anisotropy is induced via application of strong (0.08%) in-plane uniaxial mechanical strain. We observe transformation of an isotropic labyrinth domain structure to oriented stripe domains and zigzag domain structures. According to theoretical considerations, such a transformation appears due to strain-induced strong iDMI anisotropy and change of iDMI sign along the direction perpendicular to the deformation axis.

Domains of Magnetic Pressure Balance in Parker Solar Probe Observations of the Solar Wind

Abstract The Parker Solar Probe (PSP) spacecraft is performing the first in situ exploration of the solar wind within 0.2 au of the Sun. Initial observations confirmed the Alfvénic nature of aligned fluctuations of the magnetic field B and velocity V in solar wind plasma close to the Sun, in domains of nearly constant magnetic field magnitude ∣ B ∣, i.e., approximate magnetic pressure balance. Such domains are interrupted by particularly strong fluctuations, including but not limited to radial field (polarity) reversals, known as switchbacks. It has been proposed that nonlinear Kelvin–Helmholtz instabilities form near magnetic boundaries in the nascent solar wind leading to extensive shear-driven dynamics, strong turbulent fluctuations including switchbacks, and mixing layers that involve domains of approximate magnetic pressure balance. In this work we identify and analyze various aspects of such domains using data from the first five PSP solar encounters. The filling fraction of domains, a measure of Alfvénicity, varies from median values of 90% within 0.2 au to 38% outside 0.9 au, with strong fluctuations. We find an inverse association between the mean domain duration and plasma β. We examine whether the mean domain duration is also related to the crossing time of spatial structures frozen into the solar wind flow for extreme cases of the aspect ratio. Our results are inconsistent with long, thin domains aligned along the radial or Parker spiral direction, and compatible with isotropic domains, which is consistent with prior observations of isotropic density fluctuations or flocculae in the solar wind.