arXiv subjects

L. M. Pismen

Publications and source records attributed to L. M. Pismen.

At least 19 recordsLinked to original sources

arXiv2026

Vector Nematodynamics with Symmetry-driven Energy Exchange

We review inadequacy of existing nematodynamic theories and suggest a novel way of establishing relations between nematic orientation and flow based on the \emph{local} symmetry between simultaneous rotation of nematic alignment and flow, which establishes energy exchange between the the two without reducing the problem to near-equilibrium conditions and invoking Onsager's relations. This approach, applied in the framework of the vector-based theory with a variable modulus, involves antisymmetric interactions between nematic alignment and flow and avoids spurious instabilities in the absence of an active inputs.

cond-mat.soft↗

arXiv2024

Strong Interactions in Crystalline Vacuum

A multiscale expansion procedure reveals a crystalline vacuum state arising as a result of resonant interactions among weak Planck-scale waves on spinor and cospinor manifolds. Quarks are presented as elastic modulations of the vacuum crystal. The complementing modes are identified with colors, and distinctions between flavors are attributed to asymmetries of the vacuum lattice. Repercussion of the theory include insights into the nature of quantum uncertainty and dark matter and energy.

physics.gen-ph↗

arXiv2022

Vector Formalism for Active Nematics in Two Dimensions

Specific features of two-dimensional nematodynamics give rise to shortfalls of the tensor representation of the nematic order parameter commonly used in computations, especially in theory of active matter. The alternative representation in terms of the vector order parameter follows with small adjustments the classical director-based theory, but is applicable to 2D problems where both nematic alignment and deviation from the isotropic state are variable. Stability analysis of nematic alignment and flow is used as a testing ground. A director-based analysis demonstrates a shortfall of the standard theory, which does not ensure relaxation to equilibrium in a passive system. It also demonstrates the inadequacy of the director-based description, which misses a stabilizing effect of perturbations of the modulus ensuring stability of a passive system on scales far exceeding the healing length.

cond-mat.soft↗

arXiv2019

Programmable Filaments and Textiles

We analyze the various morphing structures obtained by actuating Janus filaments comprising driven and passive sectors and textiles incorporating driven and passive filaments. Transitions between alternative shapes and coexistence of absolutely stable and metastable states within a certain range of relative extension upon actuation are detected both in Janus rings and textiles. Both single filaments and textiles can be reverse designed to bend into desired shapes by controlling both the size and orientation of driven sectors.

cond-mat.soft↗

arXiv2018

The biological frontier of pattern formation

Morphogenetic patterns are highly sophisticated dissipative structures. Are they governed by the same general mechanisms as chemical and hydrodynamic patterns? Turing's symmetry breaking and Wolpert's signalling provide alternative mechanisms. The current evidence points out that the latter is more relevant but reality is still far more complicated.

nlin.PS↗

arXiv2018

Multiplicity of actuated shapes in woven fabrics with twisted Janus fibres

We investigate actuation of woven fabrics including active Janus fibres with an imposed twist, which bend in variable directions upon phase transition between isotropic and nematic state. The essential feature of textiles incorporating a pair of Janus fibres with a mismatched pitch or handedness of coiling is the existence of multiple stable shapes with different energies within a certain range of the extension coefficient. If the active fibres are closed into a ring, torsion develops to accommodate adjustment of the direction of bending. The structure is generally stabilised by adding more passive filaments, and multistability is observed also in this case.

cond-mat.soft↗

arXiv2018

Reshaping of a Janus ring

We consider reshaping of closed Janus filaments acquiring intrinsic curvature upon actuation of an active component -- a nematic elastomer elongating upon phase transition. Linear stability analysis establishes instability thresholds of circles with no imposed twist, dependent on the ratio $q$ of the intrinsic curvature to the inverse radius of the original circle. Twisted circles are proven to be absolutely unstable but the linear analysis well predicts the dependence of the looping number of the emerging configurations on the imposed twist. Modeling stable configurations by relaxing numerically the overall elastic energy detects multiple stable and metastable states with different looping numbers. The bifurcation of untwisted circles turns out to be subcritical, so that nonplanar shapes with a lower energy exist at $q$ below the critical value. The looping number of stable shapes generally increases with $q$.

cond-mat.soft↗

arXiv2017

Active textiles with Janus fibres

We describe reshaping of active textiles actuated by bending of Janus fibres comprising both active and passive components. A great variety of shapes, determined by minimising the overall energy of the fabric, can be produced by varying bending directions determined by the orientation of Janus fibres. Under certain conditions, alternative equilibrium states, one absolutely stable and the other metastable coexist, and their relative energy may flip its sign as system parameters, such as the extension upon actuation, change. A snap-through reshaping in a specially structured textile reproduces the Venus flytrap effect.

cond-mat.soft↗

arXiv2017

Textures and shapes in nematic elastomers under the action of dopant concentration gradients

We explore a novel strategy of patterning nematic elastomers that does not require inscribing the texture directly. It is based on varying the dopant concentration that, beside shifting the phase transition point, affects the nematic director field via coupling between the gradients of concentration and nematic order parameter. Rotation of the director around a point dopant source causes topological modification manifesting itself in a change of the number of defects. A variety of shapes, dependent on the dopant distribution, are obtained by anisotropic deformation following the nematic--isotropic transition.

cond-mat.soft↗

arXiv2017

Phase separation and folding in swelled nematoelastic films

We explore reshaping of nematoelastic films upon imbibing an isotropic solvent under conditions when isotropic and nematic phases coexist. The structure of the interphase boundary is computed taken into account the optimal nematic orientation governed by interaction of gradients of the nematic order parameter and solvent concentration. This structure determines the effective line tension of the boundary. We further compute equilibrium shapes of deformed thin sheets and cylindrical and spherical shells with the rectilinear or circular shape of the boundary between nematic and isotropic domains. A differential expansion or contraction near this boundary generates a folding pattern spreading out into the bulk of both phases. The hierarchical ordering of this pattern is most pronounced on a cylindrical shell.

cond-mat.soft↗

arXiv2016

Flexible helical yarn swimmers

We investigate the motion of a flexible Stokesean flagellar swimmer realised as a yarn made of two intertwined elastomer fibres, one active, that can reversibly change its length in response to a local excitation causing transition to the nematic state or swelling, and the other one, a passive isotropic elastomer with identical mechanical properties. A propagating chemical wave may provide an excitation mechanism ensuring a constant length of the excited region. Generally, the swimmer moves along a helical trajectory, and the propagation and rotation velocity are very sensitive to the ratio of the excited region to the pitch of the yarn, as well as to the size of a carried load. External excitation by a moving beam is less effective, unless the direction of the beam is adjusted to rotation of the swimmer.

cond-mat.soft↗

arXiv2015

Nemato-elastic crawlers

A propagating "beam" triggering a local phase transition in a nematic elastomer sets it into a crawling motion, which may morph due to buckling. We consider the motion of the various configurations of slender rods and thin stripes with both uniform and splayed nematic order in cross-section, and detect the dependence of the gait and speed on flexural rigidity and substrate friction.

physics.bio-ph↗

arXiv2015

Multiscale modelling of tumour growth induced by circadian rhythm disruption in epithelial tissue

We propose a multiscale chemo-mechanical model of cancer tumour development in an epithelial tissue. The model is based on transformation of normal cells into the cancerous state triggered by a local failure of spatial synchronisation of the circadian rhythm. The model includes mechanical interactions and chemical signal exchange between neighbouring cells, as well as division of cells and intercalation, and allows for modification of the respective parameters following transformation into the cancerous state. The numerical simulations reproduce different dephasing patterns - spiral waves and quasistationary clustering, with the latter being conducive to cancer formation. Modification of mechanical properties reproduces distinct behaviour of invasive and localised carcinoma.

q-bio.CB↗

arXiv2015

Reshaping nemato-elastic sheets

We consider three-dimensional reshaping of thin nemato-elastic sheets containing half-charged defects upon nematic-isotropic transition. Gaussian curvature, that can be evaluated analytically when the nematic texture is known, differs from zero in the entire domain and has a dipole or hexapole singularity, respectively, at defects of positive or negative sign. The latter kind of defects appears in not simply connected domains. Three-dimensional shapes dependent on boundary anchoring are obtained with the help of finite element computations.

cond-mat.soft↗

arXiv2014

Metric theory of nematoelastic shells

We consider three-dimensional reshaping of a thin nematoelastic film upon nematic-isotropic transition in the field of a charge one topological defect, leading to either cone or anticone (d-cone) shells. The analysis is based on the relation between the shell metric and the tensor order parameter under the assumption of no elastic deformation and volume change. The shape of the shell can be modified by doping, creating cones with curved generatrices. Anticones necessarily have an even number of radial creases. The curvature singularity at the apex is resolved due to decay of the nematic order parameter at the defect core.

cond-mat.soft↗

arXiv2014

Step-emulsification in nanofluidic device

In this paper we present a comprehensive study of the step-emulsification process for high-throughput production of (sub-)$μ$m-size monodisperse droplets. The microfluidic device combines a Hele-Shaw nanofluidic cell with a step-like outlet to a deep and wide reservoir. The proposed theory based on Hele-Shaw hydrodynamics provides the quasi-static shape of the free boundary between the disperse liquid phase engulfed by the co-flowing continuous phase prior to transition to oscillatory step-emulsification at low enough capillary number. At the transition the proposed theory anticipates a simple condition for critical capillary number as a function of the Hele-Shaw cell geometry. The transition threshold is in excellent agreement with experimental data. A simple closed-form expression for the size of the droplets generated in step-emulsification regime derived using simple geometric arguments also shows a very good agreement with the experimental results.

physics.flu-dyn↗

arXiv2013

Dynamics of defects in active nematics

Defect dynamics in a thin active nematic layer is studied by asymptotic matching of solutions in the defect core and the far field. The analysis is facilitated by the correspondence between the 2D nematic and complex scalar field models. Self-propulsion and topological interactions are identified as the primary drivers of the defect motion, surpassing the influence of both passive backflow and active flow induced by other defects.

cond-mat.soft↗

arXiv2012

Chemo-mechanical instabilities in polarizable active layers

We formulate and explore a generic continuum model of a polarizable active layer with neo-Hookean elasticity and chemo-mechanical interactions. Homogeneous solutions of the model equations exhibit a stationary long-wave instability when the medium is activated by expansion, and an oscillatory short-wave instability in the case of compressive activation. Both regimes are investigated analytically and numerically. The long-wave instability initiates a coarsening process, which provides a possible mechanism for the establishment of permanent polarization in spherical geometry.

physics.bio-ph↗