arXiv subjects

Luiza Angheluta

Publications and source records attributed to Luiza Angheluta.

At least 19 recordsLinked to original sources

arXiv2026

A phase-field modeling approach to sea-ice fracturing

The thin ice that covers the polar oceans is a complex geomaterial that is constantly stressed and fractured by winds and ocean currents. In the central Arctic, this forcing produces deformations in the form of shear bands, within which individual ice plates detach, locally generating a granular medium. Capturing this transition from a continuous to a granular sea-ice cover has implications for the adequate representation of the mechanical and dynamical behavior of sea-ice in regional and large-scale models used for operational and climate prediction purposes. Our work investigates the feasibility of a phase-field approach to capture this granularization processes and focuses on fracture propagation in the material. The model combines a double-well free-energy formulation with an overdamped displacement response. The governing equations are solved using a spectral method in Fourier space. The implementation accounts for body forces, representative of the main forcings on sea-ice, and remains computationally tractable despite the highly nonlinear character of the double-well energy formulation. We first validate the framework against a benchmark problem: the opening of an inclusion embedded into an elastic matrix under tensile loading. Then, additional simple shear configurations are investigated: an inclusion solicited under plane shear and a cylindrical Couette experiment, for which the analytical solution of the displacement field is known. The resulting fracture patterns and displacement fields demonstrate that our phase-field framework captures key features of tensile and shear fracture propagation, including the linear scaling between crack speed and applied load predicted by the Griffith's theory.

physics.class-ph↗

arXiv2026

Memory-driven topological ordering during the transition from dormant to migrating epithelia

Transitions from quiescence to collective migration in epithelia underlie wound healing and cancer invasion, yet their physical origin remains poorly understood. Here we show that quiescent epithelial monolayers store spatially contractile stresses that function as a form of mechanical memory. Upon serum-induced reactivation, these pre-stressed regions nucleate extensile asters that emit propagating polarity domain walls. Along these interfaces, topological defects are created, advected and annihilated, leading to defect coarsening with faster kinetics than by elastic interactions. An active elastic model quantitatively reproduces the observed dynamics and identifies stored stress as the origin of rapid topological reorganization. Our results establish a mechanism in which mechanical memory in quiescent epithelia triggers active stress release, driving collective migration via rapid topological ordering, distinct from conventional unjamming and flocking transitions.

cond-mat.soft↗

arXiv2026

Unified Hydrodynamic Analogue of Aharonov-Bohm and Lense-Thirring Effects

We show that surface waves in a draining-bathtub vortex provide a hydrodynamic realization of both Aharonov-Bohm phase shifts and Lense-Thirring frame dragging within a single system. A static time transformation maps the flat (2+1)-dimensional wave equation onto the convected shallow-water equation, yielding an effective vector potential set by the background flow. In this geometry, the circulation defines a global phase holonomy that controls wave structure. Traveling waves exhibit wavefront dislocations characteristic of Aharonov-Bohm scattering, while standing-wave superpositions produce nodal patterns that rotate at an angular velocity fixed by the circulation, providing a direct analogue of frame dragging. For noninteger circulation, the problem is naturally defined on the universal cover, ensuring single-valued partial-wave solutions. Experiments on a controlled vortex confirm these predictions and establish a laboratory platform in which topological phase and inertial effects, central to gauge and gravitational physics, emerge from a measurable velocity field.

physics.flu-dyn↗

arXiv2026

Dislocation dynamics on deformable surfaces

We develop a fully coupled theoretical description of dislocation dynamics on deformable crystalline surfaces, using continuum modeling and the amplitude-phase-field crystal (APFC) framework extended to curved geometries. We derive a general kinematic expression for dislocation velocity directly from the complex-amplitude evolution equations, which is also applicable to deformed surfaces through curvature-modified differential operators. From numerical simulations, we show that even small out-of-plane deformations reshape the phenomenology of defect motion through curvature-induced self-propulsion, modified glide directions, and non-classical defect-defect interactions. Our results show how surface geometry profoundly influences defect dynamics and establish the surface-APFC model as a powerful framework for predicting and interpreting curvature-defect coupling across a wide range of systems, from stiff but deformable layers to soft matter surfaces and membranes that retain crystalline order.

cond-mat.soft↗

arXiv2025

Topological interactions in vortex-wave collisions in Bose-Einstein condensates

We study vortex-vortex and vortex-wave collisions in two-dimensional weakly interacting Bose-Einstein condensates, processes that play a central role in decaying quantum turbulence. Using numerical simulations of the Gross-Pitaevskii equation, we show that during collisions of vortex-antivortex dipoles, the kinetic energy is transferred from incompressible to compressible modes by two distinct mechanisms. Below the critical vortex separation for annihilation, the transfer is mediated by quantum energy released during annihilation events, while above the threshold it arises from vortex acceleration. In wave-vortex collisions, an incoming solitary wave splits into transient phase slips that interact with the vortex, one of the phase slips contributes to vortex annihilation, and the other phase slip acquires a stable core and forms a new vortex. By analyzing vortex trajectories and energy spectra, we provide new insights into energy transfer mechanisms in quantum turbulence and offer broader implications for topological interactions mediated by vortices.

cond-mat.quant-gas↗

arXiv2025

Spontaneous elongation of 3D gastruloids from local cell polarity alignment

Gastruloids are 3D stem cell aggregate models for early embryogenesis that provide a unique platform to study how collective cell dynamics drive tissue symmetry breaking and axial elongation. Using 3D light sheet imaging, we show that a pulse of Chiron, a Wnt activator, induces coherent alignment of cell polarity during elongation. While nuclear elongation occurs with or without treatment, only Chiron-treated gastruloids exhibit quasi-long-range alignment of nuclear axes, linking cell polarity coherence to tissue-scale remodeling. A minimal physical model of polarized cells, incorporating alignment-dependent torques and polarity-mediated adhesion, reproduces symmetry breaking and elongation, demonstrating that local cell polarity alignment alone can drive tissue-scale convergence-extension flows.

physics.bio-ph↗

arXiv2025

Modeling dislocations in quasicrystals through amplitude equations

Quasicrystals (QCs) are a class of aperiodic ordered structures that emerge in various systems, from metallic alloys to soft matter and driven non-equilibrium systems. Within a mesoscale theory based on slowly-varying complex amplitudes for QCs, we track dislocations as topological defects harbored by the amplitudes and characterize their Burgers vectors and induced deformations. We study the formation of dislocations at semicoherent interfaces, particularly those emerging from rotated inclusions, and find a hierarchy of dislocations forming at such interfaces. We further analyze interfaces in strained systems, revealing conditions for the emergence of periodic dislocation arrays and discussing the energetics of dislocations associated with different phonon and phason deformations. The stability, interaction, and motion of dislocation dipoles and quadrupoles are also discussed. These findings provide new insights into the mesoscale modeling of dislocations in QCs and their distinct behavior compared to conventional crystals, while demonstrating a versatile framework for studying dislocations in systems exhibiting quasicrystalline order.

cond-mat.mtrl-sci↗

arXiv2025

Biomechanics of orientationally ordered epithelial tissue

Organogenesis involves large deformations and complex shape changes that require elaborate mechanical regulation. Models of tissue biomechanics have been introduced to account for the coupling between mechanical response and biochemical processes. Recent experimental evidence indicates that the mechanical response of epithelial tissue is strongly anisotropic, with the degree of anisotropy being correlated with the existence of long range orientational order of cytoskeletal organization across the tissue. A theoretical framework is introduced that captures the dynamic feedback between tissue elastic response and cytoskeletal reorganization under stress. Within the linear regime for small and uniform applied strains, the shear modulus is effectively reduced by the nematic order in cytoskeletal alignment induced by the applied strain. This prediction agrees with experimental observations of epithelial response in lithographically patterned micro tissues.

cond-mat.soft↗

arXiv2025

Topological defects in polar active matter

Polar active matter - including animal herds, aggregates of motile cells and active colloids - often forms coordinated migration patterns, such as flocking. This orderly motion can be disrupted by full-integer topological defects representing localized disturbances where polar alignment is lost. Such polar defects can serve as key organizing centers across scales, sustaining collective behavior, such as swirling motion and other large-scale coherent states. While significant progress in understanding active matter principles have been made in recent years, a quantitative understanding of how topological defects influence active polar matter is needed. We present a brief overview of recent experimental observations in synthetic active colloids and various biological systems. We describe how polar defects mediate dynamical transitions and contribute to the spontaneous emergence of large-scale coherent states. We also discuss theoretical advancements in physical modeling of coupled processes involving polar defects and collective behavior in active polar matter.

cond-mat.soft↗

arXiv2025

A computational study of nematic core structure and disclination interactions in elastically anisotropic nematics

A singular potential method in the Q tensor order parameter representation of a nematic liquid crystal is used to study the equilibrium configuration of a disclination dipole. Unlike the well studied isotropic limit (the so called one constant approximation), we focus on the case of anisotropic Frank elasticity (bend/splay elastic constant contrast). Prior research has established that the singular potential method provides an accurate description of the tensor order parameter profile in the vicinity of a disclination core of a highly anisotropic lyotropic chromonic liquid crystal. This research is extended here to two interacting disclinations forming a dipole configuration. The director angle is shown to decay in the far field inversely with distance to the dipole as is the case in the isotropic limit, but with a different angular dependence. Therefore elastic constant anisotropy modifies the elastic screening between disclinations, with implications for the study of ensembles of defects as seen, for example, in active matter in the extended system limit.

cond-mat.soft↗

arXiv2025

Emergent cell migration from cell shape deformations and T1 transitions

T1 transitions, which are localised cell rearrangements, play an important role in the fluidization of epithelial monolayers. Using a multi-phase field model and an active elastic solid model, we show that although each cell undergoes T1 transitions in time as uncorrelated, random events, the spatial distribution of these events is highly correlated and is dependent on cell shape. T1 transitions have a dual effect. Cells losing neighbours tend to relax their shape, while those gaining neighbours tend to elongate. By analysing the statistics of successive T1 transitions undergone by a deformable cell, we find asymmetric spatial distributions related to how cells lose or gain neighbours. These asymmetric spatial patterns of T1 transitions promote directed cell migration, and form the backbone for coherent flow patterns at tissue scales.

physics.bio-ph↗

arXiv2024

Mesoscale Field Theory for Quasicrystals

We present a mesoscale field theory unifying the modeling of growth, elasticity, and dislocations in quasicrystals. The theory is based on the amplitudes entering their density-wave representation. We introduce a free energy functional for complex amplitudes and assume non-conserved dissipative dynamics to describe their evolution. Elasticity, including phononic and phasonic deformations, along with defect nucleation and motion, emerges self-consistently by prescribing only the symmetry of quasicrystals. Predictions on the formation of semi-coherent interfaces and dislocation kinematics are given.

cond-mat.mes-hall↗

arXiv2024

From cell intercalation to flow, the importance of T1 transitions

Within the context of epithelial monolayers, T1 transitions, also known as cell-intercalations, are topological rearrangements of cells that contribute to fluidity of the epithelial monolayers. We use a multi-phase field model to show that the ensemble-averaged flow profile of a T1 transition exhibits a saddle point structure, where large velocities are localised near cells undergoing T1 transitions, contributing to vortical flow. This tissue fluidisation corresponds to the dispersion of cells relative to each other. While the temporal evolution of the mean pair-separation distance between initially neighbouring cells depends on specific model details, the mean pair-separation distance increases linearly with the number of T1 transitions, in a way that is robust to model parameters.

cond-mat.soft↗

arXiv2024

Role of tissue fluidization and topological defects in epithelial tubulogenesis

Cellular rearrangements, as primary sources of tissue fluidization, facilitate topological transitions during tissue morphogenesis. We study the role of intrinsic cell properties such as cell polarity and cell-cell adhesion in shaping epithelial tissues using a minimal model of interacting polarized cells. The presence of a vortex in the cell polarization poses the topological constraint that induces an inwards migration with the formation of a conical shape. Local rearrangements at the tip of the cone lead to the onset of tube formation. Switching between collective migration and structural rearrangements is key for balancing the contrasting tendencies, such as the tissue rigidity needed to preserve shape and the tissue fluidity allowing for topological transitions during tissue morphogenesis.

physics.bio-ph↗

arXiv2023

A unified field theory of topological defects and non-linear local excitations

Topological defects and smooth excitations determine the properties of systems showing collective order. We introduce a generic non-singular field theory that comprehensively describes defects and excitations in systems with $O(n)$ broken rotational symmetry. Within this formalism, we explore fast events, such as defect nucleation/annihilation and dynamical phase transitions where the interplay between topological defects and non-linear excitations is particularly important. To highlight its versatility, we apply this formalism in the context of Bose-Einstein condensates, active nematics, and crystal lattices.

cond-mat.soft↗

arXiv2023

Symmetry-restoring crossover from defect-free to defect-laden turbulence in polar active matter

Coherent flows of self-propelled particles are characterized by vortices and jets that sustain chaotic flows, referred to as active turbulence. Here, we reveal a crossover between defect-free active turbulence and active turbulence laden with topological defects. Interestingly, we show that concurrent to the crossover from defect-free to defect-laden active turbulence is the restoration of the previously broken $\SO(2)$-symmetry signaled by the fast decay of the two-point correlations. By stability analyses of the topological charge density field, we provide theoretical insights on the criterion for the crossover to the defect-laden active turbulent state. Despite the distinct symmetry features between these two active turbulence regimes, the flow fluctuations exhibit universal statistical scaling behaviors at large scales, while the spectrum of polarity fluctuations decays exponentially at small length scales compared to the active energy injection length. These findings reveal a new dynamical crossover between distinct spatiotemporal organization patterns in polar active mater.

cond-mat.soft↗

arXiv2023

Robust statistical properties of T1 transitions in confluent cell tissues

Large-scale tissue deformation which is fundamental to tissue development hinges on local cellular rearrangements, such as T1 transitions. In the realm of the multi-phase field model, we analyse the statistical and dynamical properties of T1 transitions in a confluent tissue. We identify an energy profile that is robust to changes in several model parameters. It is characterized by an asymmetric profile with a fast increase in energy before the T1 transition and a sudden drop after the T1 transition, followed by a slow relaxation. The latter being a signature of the fluidity of the cell tissue. We show that T1 transitions are sources of localised large deformation of the cells undergoing the neighbour exchange and induce other T1 transitions in the nearby cells through a chaining of events that propagate local cell deformation to large scale tissue flows.

physics.bio-ph↗

arXiv2022

Active nematic defects in compressible and incompressible flows

We study the dynamics of active nematic films on a substrate driven by active flows with or without the incompressible constraint.Through simulations and theoretical analysis, we show that arch patterns are stable in the compressible case, whilst they become unstable under the incompressibility constraint. For compressible flows at high enough activity, stable arches organize themselves into a smectic-like pattern, which induce an associated global polar ordering of $+1/2$ nematic defects. By contrast, divergence-free flows give rise to a local nematic order of the $+1/2$ defects, consisting of anti-aligned pairs of neighboring defects, as established in previous studies.

cond-mat.soft↗