scholarly journals Annihilation of Highly-Charged Topological Defects

Crystals ◽  
2020 ◽  
Vol 10 (8) ◽  
pp. 673
Author(s):  
Eva Klemenčič ◽  
Pavlo Kurioz ◽  
Milan Ambrožič ◽  
Charles Rosenblatt ◽  
Samo Kralj
Keyword(s):  
Topological Defects ◽  
Phenomenological Approach ◽  
Experimental Sample ◽  
Surface Anchoring ◽  
Nematic Order ◽  
Atomic Force ◽  
Sharp Edges ◽  
Additional Defect ◽  
Cartesian Coordinate ◽  
External Stimuli

We studied numerically external stimuli enforced annihilation of a pair of daughter nematic topological defect (TD) assemblies bearing a relatively strong topological charge |m|=3/2. A Landau- de Gennes phenomenological approach in terms of tensor nematic order parameter was used in an effectively two-dimensional Cartesian coordinate system, where spatial variations along the z-axis were neglected. A pair of {m=3/2,m=−3/2} was enforced by an appropriate surface anchoring field, mimicking an experimental sample realization using the atomic force microscope (AFM) scribing method. Furthermore, defects were confined within a rectangular boundary that imposes strong tangential anchoring. This setup enabled complex and counter-intuitive annihilation processes on varying relevant parameters. We present two qualitatively different annihilation paths, where we either gradually reduced the relative surface anchoring field importance or increased an external in-plane spatially homogeneous electric field E. The creation and depinning of additional defect pairs {12,−12} mediated the annihilation in such a geometry. Furthermore, we illustrate the absorption of TDs by sharp edges of the confining boundary, accompanied by m=±1/4↔∓1/4 winding reversal of edge singularities, and also E-driven zero-dimensional to one-dimensional defect core transformation.

scholarly journals Impact of Nanoparticles on Nematic Ordering in Square Wells

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
Author(s):  
M. Slavinec ◽  
E. Klemenčič ◽  
M. Ambrožič ◽  
M. Krašna
Keyword(s):  
Order Parameter ◽  
Liquid Crystalline ◽  
Topological Defects ◽  
Nematic Order ◽  
Parameter Correlation ◽  
Nematic Ordering ◽  
Order Reconstruction ◽  
Square Well ◽  
Cartesian Coordinate ◽  
Cell Thickness

Nematic liquid crystalline structures within square wells are studied numerically using both Lebwohl-Lasher lattice semimicroscopic and the Landau-de Gennes mesoscopic approach. At lateral boundary wall strong planar anchoring is enforced. The cell thicknesshalong thezCartesian coordinate is assumed to be smaller than the characteristic square well sizeR. Using semimicroscopic modelling we restrict to effectively two-dimensional systems which we study in terms of the tensor nematic order parameter. We consider impact of appropriate nanoparticles (NPs) on nematic configuration for cases whereRbecomes comparable to the biaxial order parameter correlation length. In this case a star-like order reconstruction biaxial profile could be formed in absence of NPs. We demonstrate existence of a rich variety of different nematic structures, including topological defects, which are enabled by presence of appropriate NPs.

Topological liquid crystal superstructures as structured light lasers

2021 ◽  
Vol 118 (49) ◽  
pp. e2110839118
Author(s):  
Miha Papič ◽  
Urban Mur ◽  
Kottoli Poyil Zuhail ◽  
Miha Ravnik ◽  
Igor Muševič ◽  
...  
Keyword(s):  
Self Assembly ◽  
Soft Matter ◽  
Structured Light ◽  
Topological Defects ◽  
Photonic Devices ◽  
Light Polarization ◽  
Self Healing ◽  
Fabry Perot ◽  
Self Assembled ◽  
External Stimuli

Liquid crystals (LCs) form an extremely rich range of self-assembled topological structures with artificially or naturally created topological defects. Some of the main applications of LCs are various optical and photonic devices, where compared to their solid-state counterparts, soft photonic systems are fundamentally different in terms of unique properties such as self-assembly, self-healing, large tunability, sensitivity to external stimuli, and biocompatibility. Here we show that complex tunable microlasers emitting structured light can be generated from self-assembled topological LC superstructures containing topological defects inserted into a thin Fabry–Pérot microcavity. The topology and geometry of the LC superstructure determine the structuring of the emitted light by providing complex three-dimensionally varying optical axis and order parameter singularities, also affecting the topology of the light polarization. The microlaser can be switched between modes by an electric field, and its wavelength can be tuned with temperature. The proposed soft matter microlaser approach opens directions in soft matter photonics research, where structured light with specifically tailored intensity and polarization fields could be designed and implemented.

Nontrivial topological defects of micro-rods immersed in nematics and their phototuning

2022 ◽  
Author(s):  
Satoshi Aya ◽  
Junichi Kogo ◽  
Fumito Araoka ◽  
Osamu Haba ◽  
Koichiro Yonetake
Keyword(s):  
Topological Defects ◽  
Single System ◽  
Surface Anchoring ◽  
Topological Structures ◽  
Colloid Systems

Combinations of different geometry and the surface anchoring conditions give rise to the diversity of topological structures in nematic colloid systems. Tuning these parameters in a single system offers possibilities...

scholarly journals Topology control of human fibroblast cells monolayer by liquid crystal elastomer

2020 ◽  
Vol 6 (20) ◽  
pp. eaaz6485 ◽  
Author(s):  
Taras Turiv ◽  
Jess Krieger ◽  
Greta Babakhanova ◽  
Hao Yu ◽  
Sergij V. Shiyanovskii ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Orientational Order ◽  
Topological Defects ◽  
Density Fluctuations ◽  
Dermal Fibroblasts ◽  
Produce Cell ◽  
Surface Anchoring ◽  
Liquid Crystal Elastomer ◽  
Anisotropic Surface ◽  
Living Tissues

Eukaryotic cells in living tissues form dynamic patterns with spatially varying orientational order that affects important physiological processes such as apoptosis and cell migration. The challenge is how to impart a predesigned map of orientational order onto a growing tissue. Here, we demonstrate an approach to produce cell monolayers of human dermal fibroblasts with predesigned orientational patterns and topological defects using a photoaligned liquid crystal elastomer (LCE) that swells anisotropically in an aqueous medium. The patterns inscribed into the LCE are replicated by the tissue monolayer and cause a strong spatial variation of cells phenotype, their surface density, and number density fluctuations. Unbinding dynamics of defect pairs intrinsic to active matter is suppressed by anisotropic surface anchoring allowing the estimation of the elastic characteristics of the tissues. The demonstrated patterned LCE approach has potential to control the collective behavior of cells in living tissues, cell differentiation, and tissue morphogenesis.

Influence of Tunable External Stimuli on the Self-Assembly of Guanosine Supramolecular Nanostructures Studied By Atomic Force Microscope

Langmuir ◽  
2009 ◽  
Vol 25 (23) ◽  
pp. 13432-13437 ◽  
Author(s):  
Yinli Li ◽  
Mingdong Dong ◽  
Daniel E Otzen ◽  
Yuheng Yao ◽  
Bo Liu ◽  
...  
Keyword(s):  
Atomic Force Microscope ◽  
Self Assembly ◽  
The Self ◽  
Atomic Force ◽  
External Stimuli

scholarly journals Machine Learning-Based Multidomain Processing for Texture-Based Image Segmentation and Analysis

2020 ◽  
Author(s):  
Nikolay Borodinov ◽  
Wan-Yu Tsai ◽  
Vladimir V. Korolkov ◽  
Nina Balke ◽  
Sergei Kalinin ◽  
...  
Keyword(s):  
Machine Learning ◽  
Topological Defects ◽  
Physical Parameters ◽  
General Strategy ◽  
Nanoscale Systems ◽  
Force Microscopy ◽  
Atomic Force ◽  
Periodical Structure ◽  
Physical And Chemical ◽  
Selection Of

<a>Atomic and molecular resolved atomic force microscopy (AFM) images </a>offer unique insights into materials properties such as local ordering, molecular orientation and topological defects, which can be used to pinpoint physical and chemical interactions occurring at the surface. Utilizing machine learning for extracting underlying physical parameters increases the throughput of AFM data processing and eliminates inconsistencies intrinsic to manual image analysis thus enabling the creation of reliable frameworks for qualitative and quantitative evaluation of experimental data. Here, we present a robust and scalable approach to the segmentation of AFM images based on flexible pre-selected classification criteria. Usage of supervised learning and feature extraction allows to retain the consideration of specific problem-dependent features (such as types of periodical structure observed in the images and the associated numerical parameters: spacing, orientation, etc.). We highlight the applicability of this approach for segmentation of molecular resolved AFM images based on crystal orientation of observed domains, automated selection of boundaries and collection of relevant statistics. Overall, we outline a general strategy for machine learning-enabled analysis of nanoscale systems exhibiting periodic order that could be applied to any analytical imaging technique.

scholarly journals A Bidimensional Gay-Berne Calamitic Fluid: Structure and Phase Behavior in Bulk and Strongly Confined Systems

2021 ◽  
Vol 8 ◽  
Author(s):  
A. Calderón-Alcaraz ◽  
J. Munguía-Valadez ◽  
S. I. Hernández ◽  
A. Ramírez-Hernández ◽  
E. J. Sambriski ◽  
...  
Keyword(s):  
Order Parameter ◽  
Nematic Phase ◽  
Orientational Order ◽  
Topological Defects ◽  
Md Simulations ◽  
Structural Behavior ◽  
Nematic Order ◽  
Lower Temperature ◽  
Geometry Characteristic ◽  
Strong Confinement

A bidimensional (2D) thermotropic liquid crystal (LC) is investigated with Molecular Dynamics (MD) simulations. The Gay-Berne mesogen with parameterization GB(3, 5, 2, 1) is used to model a calamitic system. Spatial orientation of the LC samples is probed with the nematic order parameter: a sharp isotropic-smectic (I-Sm) transition is observed at lower pressures. At higher pressures, the I-Sm transition involves an intermediate nematic phase. Topology of the orthobaric phase diagram for the 2D case differs from the 3D case in two important respects: 1) the nematic region appears at lower temperatures and slightly lower densities, and 2) the critical point occurs at lower temperature and slightly higher density. The 2D calamitic model is used to probe the structural behavior of LC samples under strong confinement when either planar or homeotropic anchoring prevails. Samples subjected to circular, square, and triangular boundaries are gradually cooled to study how orientational order emerges. Depending on anchoring mode and confining geometry, characteristic topological defects emerge. Textures in these systems are similar to those observed in experiments and simulations of lyotropic LCs.

scholarly journals Atomic force microscopy in the assessment of erythrocyte membrane mechanical properties with exposure to various physicochemical agents

2021 ◽  
Vol 49 (6) ◽  
pp. 427-434
Author(s):  
E. A. Sherstyukova ◽  
V. A. Inozemtsev ◽  
A. P. Kozlov ◽  
O. E. Gudkova ◽  
V. A. Sergunova
Keyword(s):  
Mechanical Properties ◽  
Young’S Modulus ◽  
Erythrocyte Membrane ◽  
Uv Radiation ◽  
Structural Organization ◽  
Young's Modulus ◽  
Homogeneous Medium ◽  
Topological Defects ◽  
Erythrocyte Membranes ◽  
Atomic Force

Background: Mechanical properties of cell membranes and their structural organization are considered among the most important biological parameters affecting the functional state of the cell. Under the influence of various pathogenic factors, erythrocyte membranes lose their elasticity. The resulting changes in their biomechanical characteristics is an important, but poorly studied topic. It is of interest to study the deformation of native erythrocytes to a depth compatible with their deformation in the bloodstream.Aim: To investigate the patterns of deep deformation and the particulars of structural organization of native erythrocyte membranes before and after their exposure to physicochemical agents in vitro.Materials and methods: Cell morphology, nanostructure characteristics, and membrane deformation of native erythrocytes in a  solution of hemoconservative CPD/SAGM were studied with atomic force microscope NTEGRA Prima. Hemin, zinc ions (Zn2+), and ultraviolet (UV) radiation were used as modifiers. To characterize the membrane stiffness, we measured the force curves F(h), hHz (the depth to which the probe immersion is described by interaction with a homogeneous medium), and the Young's modulus values of the erythrocyte membrane.Results: Exposure to hemin, Zn2+ and UV radiation led to transformation of the cell shape, appearance of topological defects and changes in mechanical characteristics of erythrocyte membranes. Under exposure to hemin, Young's modulus increased from 10±4  kPa to 27.2±8.6  kPa (p<0.001), exposure to Zn2+, to 21.4±8.7  kPa (p=0.002), and UV, to 18.8±5.6  kPa (p=0.001). The hHz value was 815±210  nm for the control image and decreased under exposure to hemin to 420±80 nm (p<0.001), Zn2+, to 370±90 nm (p<0.001), and UV, to 614±120 nm (p=0.001).Conclusion: The results obtained contribute to a  deeper understanding of interaction between membrane surfaces of native erythrocytes and small vessel walls. They can be useful in clinical medicine as additional characteristics for assessment of the quality of packed red blood cells, as well as serve as a basis for biophysical studies into the mechanisms of action of oxidative processes of various origins.

scholarly journals Topological defects in the nematic order of actin fibers as organization centers of Hydra morphogenesis

2020 ◽  
Author(s):  
Yonit Maroudas-Sacks ◽  
Liora Garion ◽  
Lital Shani-Zerbib ◽  
Anton Livshits ◽  
Erez Braun ◽  
...  
Keyword(s):  
Functional Outcomes ◽  
Topological Defects ◽  
Coarse Grained ◽  
Orientation Field ◽  
Biochemical Processes ◽  
Nematic Order ◽  
Mechanical Signaling ◽  
Defect Sites ◽  
Functional Patterns ◽  
Effective Description

Animal morphogenesis arises from the complex interplay between multiple mechanical and biochemical processes with mutual feedback. Developing an effective, coarse-grained description of morphogenesis is essential for understanding how these processes are coordinated across scales to form robust, functional outcomes. Here we show that the nematic order of the supra-cellular actin fibers in regenerating Hydra defines a slowly-varying field, whose dynamics provide an effective description of the morphogenesis process. We show that topological defects in this field, which are long-lived yet display rich dynamics, act as organization centers with morphological features developing at defect sites. These observations suggest that the nematic orientation field can be considered a “mechanical morphogen” whose dynamics, in conjugation with various biochemical and mechanical signaling processes, result in the robust emergence of functional patterns during morphogenesis.

scholarly journals Topological defects in the nematic order of actin fibres as organization centres of Hydra morphogenesis

2020 ◽  
Author(s):  
Yonit Maroudas-Sacks ◽  
Liora Garion ◽  
Lital Shani-Zerbib ◽  
Anton Livshits ◽  
Erez Braun ◽  
...  
Keyword(s):  
Topological Defects ◽  
Nematic Order
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