scholarly journals Oblique light incidence method to study topological defects in nematic layers with conical boundary conditions

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Mikhail N. Krakhalev
Keyword(s):  
Boundary Conditions ◽  
Phase Difference ◽  
Tilt Angle ◽  
Twist Angle ◽  
Azimuthal Angle ◽  
Topological Defects ◽  
Polarization Microscopy ◽  
Chiral Nematic ◽  
Microscopy Method

AbstractA polarization microscopy method to investigate the orientational structures and boojums formed in the chiral and achiral nematic layers under conical (tilted) boundary conditions has been developed. Oblique light incidence on nematic layer is used, due to which the phase difference between the ordinary and extraordinary waves depends on the director’s azimuthal angle. The phase difference gets maximal when the director azimuthal angle of achiral nematic $$\varphi (x,y) = 0$$ φ ( x , y ) = 0 and an azimuthal angle at the center of the chiral nematic layer $$\varphi _0(x,y) = 0$$ φ 0 ( x , y ) = 0 independently of the total twist angle $$\varphi _{TOTAL}$$ φ TOTAL . It has been found that the $$m=+1$$ m = + 1 boojums with the phase $$\xi = \pm 90^\circ$$ ξ = ± 90 ∘ and $$\xi = (-90^\circ + \varphi _{TOTAL}/2)$$ ξ = ( - 90 ∘ + φ TOTAL / 2 ) are formed in achiral and chiral nematics, respectively, at the director tilt angle $$\theta _{d/2} \cong 40^\circ$$ θ d / 2 ≅ 40 ∘ at the interface. In addition, the defectless structure of chiral nematic with the periodically variable azimuthal director angle on the substrates has been studied.

scholarly journals Twisting Techniques Used in Freestyle Aerial Skiing

1989 ◽  
Vol 5 (2) ◽  
pp. 275-281 ◽  
Author(s):  
Maurice R. Yeadon
Keyword(s):  
Computer Simulation ◽  
Simulation Model ◽  
Tilt Angle ◽  
Twist Angle ◽  
Computer Simulation Model ◽  
Winter Olympics

At the 1988 Calgary Winter Olympics, six triple somersaults with three twists or four twists were filmed using two cameras. Angles describing body configuration and orientation were determined and were used as input into a computer simulation model of aerial movement. It was found that the twist angle of each simulation deviated from the corresponding angle obtained from film by less than 0.08 revolutions during the first somersault of each movement. Contributions to the tilt angle after one somersault were determined using simulations based on modifications of the film data. It was found that of the six competitors, two initiated the twist during the takeoff phase, two initiated the twist during the aerial phase, and two used a combination of both methods.

Topological defects in nematic films between planar degenerate surfaces. A Monte Carlo study

2021 ◽  
pp. 2250016
Author(s):  
Cesare Chiccoli ◽  
Paolo Pasini ◽  
Luiz Roberto Evangelista ◽  
Rodolfo Teixeira de Souza ◽  
Claudio Zannoni
Keyword(s):  
Monte Carlo ◽  
Boundary Conditions ◽  
Monte Carlo Simulations ◽  
Defect Structure ◽  
Topological Defects ◽  
Monte Carlo Study ◽  
Geometric Parameters ◽  
Molecular Organization ◽  
The One

The molecular organization of a nematic film sandwiched between two planar randomly aligned surfaces is studied by means of detailed Monte Carlo simulations. The formation as well as the evolution of topological defects induced by these particular boundary conditions are investigated. The resulting defect structure is compared with the one induced by hybrid aligned surfaces. The observation of such defects and some features of their structures can be associated with geometric parameters of the film and with properties of the confining surfaces.

scholarly journals Modification of the twist angle in chiral nematic polymer films by photoisomerization of the chiral dopant

1999 ◽  
Vol 85 (11) ◽  
pp. 7517-7521 ◽  
Author(s):  
Peter van de Witte ◽  
Edda E. Neuteboom ◽  
Martin Brehmer ◽  
Johan Lub
Keyword(s):  
Polymer Films ◽  
Twist Angle ◽  
Chiral Nematic ◽  
Nematic Polymer

scholarly journals Characterization of Orientation Correlation Kinetics: Chiral-mesophase Domains in Suspensions Charged DNA-rods

2021 ◽  
Author(s):  
Kyongok Kang
Keyword(s):  
Twist Angle ◽  
Equilibrium Phase ◽  
Time Correlation ◽  
Real Space ◽  
Correlation Technique ◽  
Chiral Nematic ◽  
Kinetics Of ◽  
Microscopy Images ◽  
Kinetic Features

Abstract Bacteriophage DNA fd-rods are long and stiff rod-like particles which are known to exhibit a rich equilibrium phase behavior. Due to their helical molecular structure, they form the stable chiral nematic (N*) mesophases. Very little is known about the kinetics of forming various phases with orientations. The present study addresses the kinetics of chiral-mesophases and N*-phase, by using a novel image-time correlation technique. Instead of correlating time-lapsed real-space microscopy images, the corresponding Fourier images are shown for time-correlated averaged orientations. This allows to unambiguously distinguish to detect the temporal evolution of orientations on different length scales, such as domain sizes (depending on their relative orientations), and the chiral pitch within the domains. Kinetic features are qualitatively interpreted in terms of replica symmetry breaking of elastic deformations in the orthogonal directional axes of chiral-mesophase domains, as well by the average twist angle and the order parameter. This work can be interesting for characterizing other types of charged rods, mimicking super-cooled liquids and orientation glasses.

scholarly journals Inference of molecular orientation/ordering change nearby topological defects by the neural network function from the microscopic color information

2021 ◽  
Author(s):  
Haruka Sakanoue ◽  
Yuki Hayashi ◽  
Kenji Katayama
Keyword(s):  
Neural Network ◽  
Order Parameter ◽  
Orientation Angle ◽  
Topological Defects ◽  
Molecular Alignment ◽  
Polarization Microscopy ◽  
Color Information ◽  
Time Resolved ◽  
Network Function ◽  
The Neural Network

Abstract Topological defects in liquid crystals (LCs) dominate molecular alignment/motion in many cases. Here, the neural network (NN) function has been introduced to predict the LC orientation condition (orientation angle and order parameter) at local positions around topological defects from the phase/polarization microscopic color images. The NN function was trained in advance by using the color information of an LC in a planar alignment cell for different orientation angles and temperatures. The photo-induced changes of LC molecules around topological defects observed by the time-resolved measurement was converted into the image sequences of the orientation angle and the order parameter change. We found that each pair of brushes with different colors around topological defects showed different orientation angle and ordering changes. The photo-induced change was triggered by the photoisomerization reaction of molecules, and one pair of brushes increased in its order parameter just after light irradiation, causing gradual rotation in the brush. The molecules in the other pair of brushes were disordered and rotated by the effect of the initially affected region. This combination approach of the time-resolved phase/polarization microscopy and the NN function can provide detailed information on the molecular alignment dynamics around the topological defects.

Aerodynamic Characterization of a High Speed Propeller

2014 ◽  
Author(s):  
Adel Ghenaiet ◽  
Akila Halimi
Keyword(s):  
Mach Number ◽  
Boundary Conditions ◽  
High Speed ◽  
Numerical Study ◽  
Twist Angle ◽  
Computational Domain ◽  
Propulsive Efficiency ◽  
High Rotational Speed ◽  
Open Rotor ◽  
Advance Ratio

This paper presents a numerical study aimed at characterizing the aerodynamics of an advanced propeller distinguished by its high rotational speed, blade sweep and airfoil sections. Many of the difficulties encountered when applying CFD to an open rotor (a propeller) arise due to removal of the casing existing in a conventional aero-engine turbomachinery. For this purpose the propeller computational domain needed to be well parameterized to keep sufficient outer domains distances where the appropriate boundary conditions are imposed. The mesh of a certain resolution was extended radially, five times the tip radii, to fully capture the stream-tube and minimize the effect of free-stream boundary conditions. Comparisons of obtained flow field results with some available experimental data shows in general similar quantitative results and trends. The estimated propulsive efficiency is shown to be strongly dependent upon the cruise flight Mach number, advance ratio and pitch angle. The maximum propulsive efficiency reached a value of 76.2 % around flight Mach number of 0.8, twist angle of 66 deg and advance ratio of 4.1. The effect of blades number has revealed a higher propulsive efficiency for the six and eight-bladed propellers but at the expense of lower power and thrust coefficients.

scholarly journals Characterization of large tilt-angle flexoelectro-optic switching in chiral nematic liquid crystal devices

2018 ◽  
Vol 46 (3) ◽  
pp. 408-414 ◽  
Author(s):  
Xiuze Wang ◽  
Julian A. J. Fells ◽  
Chris Welch ◽  
Maria-Gabriela Tamba ◽  
Georg H. Mehl ◽  
...  
Keyword(s):  
Liquid Crystal ◽  
Nematic Liquid Crystal ◽  
Tilt Angle ◽  
Liquid Crystal Devices ◽  
Chiral Nematic

scholarly journals Tension-dependent transverse buckles and wrinkles in twisted elastic sheets

2018 ◽  
Vol 474 (2214) ◽  
pp. 20180062 ◽  
Author(s):  
A. Kudrolli ◽  
J. Chopin
Keyword(s):  
Boundary Conditions ◽  
Large Range ◽  
Twist Angle ◽  
Mode Number ◽  
Covariant Form ◽  
Elastic Sheet ◽  
Von Karman ◽  
Critical Tension ◽  
Von Kármán Equations ◽  
Elastic Sheets

We investigate with experiments the twist-induced transverse buckling instabilities of an elastic sheet of length L , width W and thickness t , that is clamped at two opposite ends while held under a tension T . Above a critical tension T λ and critical twist angle η tr , we find that the sheet buckles with a mode number n ≥1 transverse to the axis of twist. Three distinct buckling regimes characterized as clamp-dominated, bendable and stiff are identified, by introducing a bendability length L B and a clamp length L C (< L B ). In the stiff regime ( L > L B ), we find that mode n =1 develops above η tr ≡ η S ∼( t / W ) T −1/2 , independent of L . In the bendable regime L C < L < L B , n =1 as well as n >1 occur above η tr ≡ η B ∼ t / L T − 1 / 4 . Here, we find the wavelength λ B ∼ L t T − 1 / 4 , when n >1. These scalings agree with those derived from a covariant form of the Föppl-von Kármán equations, however, we find that the n =1 mode also occurs over a surprisingly large range of L in the bendable regime. Finally, in the clamp-dominated regime ( L < L C ), we find that η tr is higher compared to η B due to additional stiffening induced by the clamped boundary conditions.

scholarly journals Inference of molecular orientation/ordering change nearby topological defects by the neural network function from the microscopic color information

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Haruka Sakanoue ◽  
Yuki Hayashi ◽  
Kenji Katayama
Keyword(s):  
Neural Network ◽  
Order Parameter ◽  
Orientation Angle ◽  
Topological Defects ◽  
Molecular Alignment ◽  
Polarization Microscopy ◽  
Color Information ◽  
Time Resolved ◽  
Network Function ◽  
The Neural Network

AbstractTopological defects in liquid crystals (LCs) dominate molecular alignment/motion in many cases. Here, the neural network (NN) function has been introduced to predict the LC orientation condition (orientation angle and order parameter) at local positions around topological defects from the phase/polarization microscopic color images. The NN function was trained in advance by using the color information of an LC in a planar alignment cell for different orientation angles and temperatures. The photo-induced changes of LC molecules around topological defects observed by the time-resolved measurement was converted into the image sequences of the orientation angle and the order parameter change. We found that each pair of brushes with different colors around topological defects showed different orientation angle and ordering changes. The photo-induced change was triggered by the photoisomerization reaction of molecules, and one pair of brushes increased in its order parameter just after light irradiation, causing gradual rotation in the brush. The molecules in the other pair of brushes were disordered and rotated by the effect of the initially affected region. This combination approach of the time-resolved phase/polarization microscopy and the NN function can provide detailed information on the molecular alignment dynamics around the topological defects.

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