Search

We report on a set of experiments directed to a problem of microparticles interaction with a disclination in a nematic liquid crystal matrix. The idea of the study consists in the visualization of the disclination by filling it with particles efficiently scattering light. A θ-cell possessing a topological defect of undetermined twist which can capture micro-sized objects was exploited. The results obtained for samples of different shape can be used as for the understanding of the nature of self-assembling clusters, as for the practical goal of increasing the visibility of a disclination being a dynamic object sensitive to temperature and other external factors and able to move the trapped particles. [ABSTRACT FROM AUTHOR]

In solids, external stress induces the Peach-Koehler force, which drives dislocations to move. Similarly, in liquid crystals, an external angular stress creates an analogous force, which drives disclinations to move. In this work, we develop a method to calculate the relevant angular stress either analytically or numerically, and hence to determine the force on a disclination. We demonstrate this method by applying the Peach-Koehler force theory to four problems: (a) Single disclination in a liquid crystal cell between two uniform in-plane alignments perpendicular to each other. (b) Array of disclinations in a liquid crystal cell with patterned substrates. (c) Pair of disclinations in a long capillary tube with homeotropic anchoring. (d) Radial hedgehog or disclination loop inside a sphere with homeotropic anchoring, and its response to an applied magnetic field. In all of these problems, the Peach-Koehler force theory predicts the equilibrium defect structure, and the predictions are consistent with the results of minimising the total free energy. [ABSTRACT FROM AUTHOR]

In this paper, our principal objective is to investigate the impact of disclination and throat radius of a three-dimensional traversable wormhole on quantum oscillator fields. Specifically, we focus on Perry–Mann-type wormhole with disclination while also considering the influence of rainbow gravity's. We derive the radial equation of the relativistic Klein–Gordon oscillator within this wormhole background under the effects of gravity's rainbow and the analytical eigenvalue solution is obtained using the confluent Heun function. In fact, we show that the behavior of the oscillator fields is significantly influenced not only by the presence of disclination and the throat radius but also by the parameter of rainbow gravity's. We choose various such rainbow functions to present and analyze the eigenvalue solutions of the quantum oscillator fields. [ABSTRACT FROM AUTHOR]

The classical description of the elastic field of an edge dislocation is modified by the addition of a line force to the Burgers vector. Also, partitioning of displacements is imposed, consistent with the topological theory of defects at interfaces, agreeing with symmetry requirements as are inherent in nonlinear or atomistic calculations. Much of the classical theory is unchanged. However, displacement fields and image effects differ. [ABSTRACT FROM AUTHOR]

Disclinations in nematic liquid crystals are of great interest both theoretically and practically. The ability to create and reconfigure disclinations connecting predetermined points on substrates could enable novel applications such as directed self-assembly of micro/nanoparticles and molecules. In this study, we present a novel approach to design and create disclination interconnects that connect predetermined positions on substrates. We demonstrate that these interconnects can be switched between different states by re-writing photoalignment materials with linearly polarised light and can be switched between metastable states using electric fields. [ABSTRACT FROM AUTHOR]

Experimental observations reveal that disclinated non-equilibrium grain boundaries (GBs) exist extensively in polycrystalline metals; however, the interaction between these GBs and irradiation-induced point defects is rarely reported. In the present work, Molecular statics simulation was used to evaluate the capacity of disclinated non-equilibrium GBs to accommodate point defects in tungsten. Simulation results showed that disclinated non-equilibrium GBs are more efficient sinks for point defects than their equilibrium counterparts because of long-range stress field around them. Continuous segregation of point defects will change the structure of the disclinated non-equilibrium GBs and leads to the GBs tending to relax to equilibrium state. According to theoretical calculation, the disclinated non-equilibrium GBs can absorb a large number of point defects before transforming into equilibrium state; therefore, disclinated non-equilibrium GBs have very strong capacity to accommodate point defects and can be used as strong defect sinks for developing radiation resistance materials. [ABSTRACT FROM AUTHOR]

Twisting is a simple and effective method for assembling individual carbon nanotubes (CNTs) into high-strength, tough, and continuous CNT yarns. However, the unexpectedly low stretching performance of the resulting carbon nanotube bundle (CNTB) structures is a problem that must be resolved. In this study, we investigated the impact of twisting on the structure and stretching performance of CNTBs through molecular dynamics (MD) simulations while considering the presence of disclinations within the CNTB structure. We found that disclinations nucleate in twisted CNTBs, and the longer the disclination line in CNTBs, the lower the Young's modulus. The presence of disclination lines in the twisted CNTBs may be an important reason for the decrease in the tensile properties of the CNT yarns. Although the theoretical equations in textile field can be applied to describe the mechanical properties of CNT yarns, there are significant relative errors between the equations and the MD simulation results presented herein. Therefore, we revised the equations based on the simulation results to reduce the relative error for seven-layer CNTBs to less than 10 %. This paper provides new insights into the low tensile performance of CNT yarns and offers potential guidance for the production of high-performance CNT yarns through twisting. [Display omitted] • Twisting loads induces the nucleation of disclination in carbon nanotube bundles. • The more layers in the bundle, the smaller the twist angle when disclination occurs. • Disclination partially counteracts torque accumulation in carbon nanotube bundles. • Disclination manifests as curved lines in carbon nanotube bundles. • Longer disclination lines correlate with lower Young's modulus of bundles. [ABSTRACT FROM AUTHOR]

Grain boundary junction (GBJ) disclinations are ubiquitous at the nanoscale in icosahedra and decahedra. These structural motifs consist of several tetrahedra sharing a twin grain boundary. According to the coincident site lattice (CSL) theory this twin grain boundary is referred to as Σ 3 < 110 > {111} grain boundary. In the present work, GBJ disclinations involving a low energy grain boundary Σ 11 < 110 > {113} are reported. Σ 3 − Σ 3 − Σ 11 triple junction disclination is energetically preferred at the nanoscale as opposed to the ideal (without any misorientation mismatch) Σ 3 − Σ 3 − Σ 9 triple junction. Molecular dynamics simulations are employed to study the disclinations in three dynamical processes key for nanoparticle synthesis − growth, coalescence, and solidification; across three metal systems Ag, Cu, and Pt which cover a range of stacking fault energies. Results indicate that Pt has a higher preference for disclinations while they are almost non-existent in Cu and to a lesser degree in Ag. Several types of disclinations have been identified and catalogued. Gaussian images (used as a proxy for simulating scanning transmission electron microscopy high angle annular dark field images) reveal that some of the disclinations induce artifacts which makes it non-trivial to identify them even when they are present in experimental particles. A key characteristic of the GBJ disclinations is the rapid change in misorientation angle around Σ 11 grain boundary with distance away from the disclination. In this scenario, there is a need to reassess the methodology currently in use for identification of grain boundary type at the nanoscale. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • A geometric model for bent kinks is developed based on Inamura's kink model. • Gibbs free energies of systems containing different bent kinks are investigated. • Bending morphology is related to the relaxation of the elastic energy of disclinations. • Theoretical geometry of a smoothly bent kink is confirmed by experiments. In this study, we have developed a geometric model for bent kinks by introducing sequences of ortho-connected kink bands into ridge-kinks to provide insights into the possible reasons why kinks are bent and the resulting geometry when they are bent. We first formulated the Frank angles and coordinates of the disclinations formed in the bent kinks, which enable our discussion on the influence of the introduction of ortho-kinks on the Gibbs energy by utilizing Romanov's disclination model. It turns out that the introduction of ortho-kinks can relax the elastic strain energy and thus reduce the Gibbs energy of the system under compression states with lower external stresses. On the other hand, the introduction of ortho-kinks increases the Gibbs energy at higher compression stresses, implying sharp ridge-kinks are preferred under such conditions. This trend resembles the experimental observations reported by previous studies that the shapes of newly formed kinks tend to transition from pre-kinks with bent shapes to ridge-kinks with sharp shapes as the compression test progresses. The smoothly bent kink with smoothly distributed misorientation, formed by increasing the number of introduced ortho-kinks, can further reduce the Gibbs energy at lower applied stresses. Subsequently, based on the Rank-1 condition for the connection of kink bands, we further analyzed the geometry of such smoothly bent kinks and derived the analytical equations for the constraints on the orientation distribution. Finally, we conducted EBSD measurements on bent kinks observed in directionally solidified (DS) LPSO-Mg alloys and confirmed that the derived equations for the orientation distribution are in good agreement with the experimental results. [ABSTRACT FROM AUTHOR]

In this paper, we discuss the effects of the topology of a disclination on quantum revivals when a quantum particle is subject to an infinite cylindrical well and a logarithmic potential. By using the WKB (Wentzel, Kramers and Brillouin) approximation, we obtain the eigenvalues of energy and show that the influence of the topology of the disclination on them gives rise to an Aharonov–Bohm-type effect. Further, we discuss how the topology of a disclination influences the classical periods and the revival times. [ABSTRACT FROM AUTHOR]

The standard model is applied for partial disclination pairs in hard materials. These defects comprise two partial disclinations and an intervening fault that can be a twin boundary, grain boundary or interphase boundary. In three dimensions there are six types. Two of them can be considered Somigliana disclinations. The standard model includes geometrically nonlinear embedded coordinates. It entails partitioning of displacements that result in configurations and strain fields not considered classically for partial disclinations. These concepts are applied to boundary junctions, disconnections, and multiple twins. Recovered stress-free structures are considered. [ABSTRACT FROM AUTHOR]

We use the Chern–Simons action for a 𝕊 𝕆 (3) -connection for the description of point disclinations in the geometric theory of defects. The most general spherically symmetric 𝕊 𝕆 (3) -connection with zero curvature is found. The corresponding orthogonal spherically symmetric 𝕊 𝕆 (3) matrix and n -field are computed. Two examples of point disclinations are described. [ABSTRACT FROM AUTHOR]

We analyze the interaction of the induced electric dipole moment of a neutral particle with an electric field in elastic medium with a charged disclination from a semiclassical point of view. We show that the interaction of the induced electric dipole moment of a neutral particle with an electric field can yield an attractive inverse-square potential, where it is influenced by the topology of the disclination. Then, by using the Wentzel, Kramers and Brillouin approximation based on the Langer transformation, we show that the centrifugal term of the radial equation must be modified due to the influence of the topology of the disclination. Besides, we obtain the bound states solutions to the Schrödinger equation. [ABSTRACT FROM AUTHOR]

The 't Hooft–Polyakov monopole solution in Yang–Mills theory is given new physical interpretation in the geometric theory of defects. It describes solids with continuous distribution of dislocations and disclinations. The corresponding densities of Burgers and Frank vectors are computed. It means that the 't Hooft–Polyakov monopole can be seen, probably, in solids. [ABSTRACT FROM AUTHOR]

We demonstrate that a first order isotropic-to-nematic phase transition in liquid crystals can be succesfully modeled within the generalized Landau-de Gennes theory by selecting an appropriate combination of elastic constants. The numerical simulations of the model established in this paper qualitatively reproduce the experimentally observed configurations that include interfaces and topological defects in the nematic phase. [ABSTRACT FROM AUTHOR]

A different type of defect, the coherency disclination, is added to disclination types. Disconnections that include disclination content are considered. A criterion is suggested to distinguish disconnections with dislocation content from those with disclination content. Electron microscopy reveals unit disconnections in a low albite grain boundary, defects important in grain boundary sliding. Disconnections of varying step heights are displayed and shown to define both deformed and recovered structures. [ABSTRACT FROM AUTHOR]

We investigate geometry and mechanics of the buckled orthotropic von Kármán elastic plate, with free boundary condition, in the presence of an isolated positive, or negative, disclination. The buckled shape of an isotropic elastic plate is cone-like for a positive disclination and saddle-like for a negative disclination. In either case, with increasing orthotropy, the shape of the buckled plate becomes more tent-like. The Gaussian curvature accordingly spreads along the ridge of the tent. The stress fields too remain focused in the neighbourhood of the defect point and the ridge, indicating that most of the stretching energy is accommodated in these singular regions. • Geometry and mechanics of a disclination in an orthotropic elastic plate are investigated. • A strongly orthotropic elastic sheet buckles into a tent-like shape in the presence of a disclination. • Novel insights into the micromechanics of thin elastic sheets with topological defects. [ABSTRACT FROM AUTHOR]

We consider an elastic medium with a disclination and investigate the topological effects on the interaction of a spinless electron with radial electric fields through the WKB (Wentzel, Kramers, Brillouin) approximation. We show how the centrifugal term of the radial equation must be modified due to the influence of the topological defect in order that the WKB approximation can be valid. Then, we search for bound states solutions from the interaction of a spinless electron with the electric field produced by this linear distribution of electric charges. In addition, we search for bound states solutions from the interaction of a spinless electron with radial electric field produced by uniform electric charge distribution inside a long non-conductor cylinder. [ABSTRACT FROM AUTHOR]

We present singularity-free solution for cracks within polar media in which material points possess both position and orientation. The plane strain problem is addressed in this study for which the generalized continua including micropolar, nonlocal micropolar, and gradient micropolar elasticity theories are employed. For the first time, the variationally consistent boundary conditions are derived for gradient micropolar elasticity. Moreover, having reviewed the solution to line defects including glide edge dislocation and wedge disclination from the literature, the fields of a climb edge dislocation within micropolar, nonlocal micropolar and gradient micropolar elasticity are derived. This completes the collection of line defects needed for an inplane strain analysis. Afterward, as the main contribution, using both types of line defects (i.e., dislocation being displacement discontinuity and disclination being rotational discontinuity), the well-established dislocation-based fracture mechanics is systematically generalized to the dislocation- and disclination-based fracture mechanics of polar media for which we have three translations together with three rotations as degrees of freedom. Due to the application of the line defects, incompatible elasticity is employed throughout the paper. Cracks under three possible loadings including stress and couple stress components are analyzed, and the corresponding line defect densities and stress and couple stress fields are reported. The singular fields are obtained once using the micropolar elasticity, while nonlocal micropolar, and gradient micropolar elasticity theories give rise to singularity-free fracture mechanics. [ABSTRACT FROM AUTHOR]

• Effect of nanoscale amorphization on dislocation emission from a blunt crack is studied. • Nanoscale amorphization occurs through splitting transformation of GB disclinations. • The criterion for the first dislocation emission form the elliptical blunt crack is derived. • Nanoscale amorphization can either enhance or weaken the critical applied SIFs. • There is a critical crack-junction distance making the dislocation emission most difficult. A theoretical model is established to describe the effect of nanoscale amorphization on the lattice dislocation emission from an elliptical blunt crack tip in deformed nanocrystalline and ultrafine-grained materials. Within the description, the nanoscale amorphization occurs through the splitting transformation of grain boundary disclinations which are produced by grain boundary sliding. The criterion for the first dislocation emission form the elliptical blunt crack is derived. The influence of the nanoscale amorphization and the features of the elliptical blunt crack on the critical stress intensity factors for the dislocation emission are discussed in detail. The obtained results show that the nanoscale amorphization can either enhance or weaken the critical applied SIFs for dislocation emission, depending on the emission angle, the radius of curvature of the elliptical blunt crack and the distance between the nanoscale amorphization and the crack tip. There is a critical crack-junction distance making the dislocation emission most difficult and at this critical crack-junction distance, the stress-release effect of the nanoscale amorphization is strongest. [ABSTRACT FROM AUTHOR]

The kinematical relationships among the geometric quantities that characterise kink bands, ridge kinks, and ortho kinks and the existence of disclinations in connecting kink bands were revealed based on the rank-1 connection, which is a condition of the continuity of deformation. Owing to the simple geometry of the kinks, the kink plane and the crystallographic rotation of the kink band were obtained in analytic forms as functions of the magnitude of the shears inside kinks. The geometry of the kink band predicted by the rank-1 connection agreed well with literature experimental data. Ridge kinks and ortho kinks were treated as the rank-1 connection of two kink bands. Positive and negative partial wedge disclinations were inevitably formed in any kink band connections when the junction plane of the kink bands did not reach the surface of the body. The Frank vector of the disclinations was also obtained as a function of the shear magnitudes in the kink bands. There exist compatible kink microstructures in which the disclinations are cancelled. Modes of complete relaxation and annihilation of disclinations by combinations of kinks or slip deformations were revealed. The nature of the kink microstructure and kink strengthening was discussed based on the formation and annihilation of disclinations. Image 1 [ABSTRACT FROM AUTHOR]

In this paper, linear and nonlinear optical properties of a GaAs quantum dot (QD) confined by a parabolic plus inverse square (PIS) potential with a disclination are theoretically studied under the influence of a magnetic field and the Aharonov-Bohm (AB) flux field. To achieve this, the Schrödinger equation for this system is derived, and its solutions of the wave function and the energy levels are obtained using the confluent hypergeometric equation. The effect of the disclination defect on the optical absorption coefficients (OACs) and refractive index changes (RICs) of the PIS quantum dot is examined in detail. The results obtained indicate that the peak positions and amplitudes of the OACs and RICs are significantly affected by changes in the magnitude of the disclination parameter. Furthermore, the effect of the disclination on the peak positions of the OACs and the RICs can be eliminated by adjusting the magnetic field strength. • We study the optical properties of a GaAs quantum dot with a disclination in the presence of external fields. • A disclination which is a topological defect has a great influence on the optical properties of the system. • The observed shift in the peak positions of the optical coefficients due to disclination can be controlled by the application of an external field. [ABSTRACT FROM AUTHOR]

We consider graphene disclination networks (DNs) — periodic distributions of disclination defects. Disclinations manifest themselves as 4-, 5-, 7- or 8-member carbon rings in otherwise 6-member ring ideal 2D graphene crystal lattice. Limiting cases of graphene-like 2D carbon lattices without 6-member motives, i.e., pseudographenes, are also studied. The geometry and energy of disclinated 2D carbon configurations are analyzed with the help of molecular dynamics (MD) simulation technique. A comparison of the obtained MD results with analytical calculations within the framework of the theory of defects of elastic continuum is presented. [ABSTRACT FROM AUTHOR]

The stress-strain state in a hollow decahedral small particle is modeled as that caused by a positive wedge disclination in an elastic hollow sphere. The stress and dilatation distribution in the particle is analyzed in relation to crack nucleation and the particle's catastrophic fracture during chemical etching. A two-stage process of the fracture is suggested, which includes nucleation of initial cracks along twin boundaries around their quintuple junction and subsequent pattern formation in a fivefold star-shaped crack at the junction. The critical sizes of the initial crack and the decahedral small particle at which this two-stage fracture process occurs, are estimated. [ABSTRACT FROM AUTHOR]

Diffusion of point defects during irradiation is simulated via a two-way coupling between mechanical stress and defect diffusion in iron. This diffusion is based on a modified chemical potential that includes not only the local concentration of radiation-induced defects, but also the influence of the residual stress field from both the microstructure (i.e. dislocations or grain boundaries) and the eigenstrain caused by the defects themselves. Defect flux and concentration rates are derived from this chemical potential using Fick’s first and second laws. Mean field rate theory is incorporated to model the annihilation of Frenkel pairs, and increased annihilation near grain boundaries is included based on the elastic energy of each grain boundary. Mechanical equilibrium is coupled with diffusion by computing eigenstrain from point defects and adding this to the total strain. Intrinsic stresses associated with the dislocations and grain boundaries are calculated using dislocation and disclination mechanics. Through this two-way-coupled model, regions of low concentration are seen near grain boundaries, and sink efficiency is calculated for different types of microstructure. The results show that the two-way mechanical coupling has a strong influence on sink efficiency for dislocation loops. The results also suggest that misorientation is a poor metric for determining sink efficiency, with sink density and elastic energy being much more informative. [ABSTRACT FROM AUTHOR]

New lactic acid derivatives have been prepared and studied and found that they form cholesteric phase with the helix pitch length in interval 120-200 nm within a broad temperature range. Due to the positive dielectric anisotropy and the short pitch, the applied electric field causes reversible optical changes in planar cell, in which the applied electric field reorients the long molecular axis. Presence of short pitch and possibility to effectively affect electro-optical properties are promising from the point of view of specific applications. [ABSTRACT FROM AUTHOR]

In this work, we investigate the combined influence of the nontrivial topology introduced by a disclination and non inertial effects due to rotation, in the energy levels and the wave functions of a noninteracting electron gas confined to a two-dimensional pseudoharmonic quantum dot, under the influence of an external uniform magnetic field. The exact solutions for energy eigenvalues and wave functions are computed as functions of the applied magnetic field strength, the disclination topological charge, magnetic quantum number and the rotation speed of the sample. We investigate the modifications on the light interband absorption coefficient and absorption threshold frequency. We observe novel features in the system, including a range of magnetic field without corresponding absorption phenomena, which is due to a tripartite term of the Hamiltonian, involving magnetic field, the topological charge of the defect and the rotation frequency. [ABSTRACT FROM AUTHOR]

The paper focuses on studying the kinetics of radiation-induced point defects formed in TiN/SiN multilayer nanocomposites with account of their generation, diffusion recombination, and the influence of sinks functioning as interfaces. In order to describe the kinetics in nanocrystalline TiN and amorphous SiN phases, a finite-difference method is used to solve the system of balance kinetic equations for absolute defect concentrations depending on the spatiotemporal variables. A model of the disclination-dislocation interface structure is used to study the absorption of radiation-induced point defects on the boundaries in created stress fields. It is shown that the interface effectively absorbs point defects in these phases of TiN/SiN multilayer nanocomposite, thereby reducing their amount within the space between phases. This behavior of point defects partially explains a mechanism of the radiation resistance in this type of nanocomposites. [ABSTRACT FROM AUTHOR]

We investigate the defect structures forming around two nanoparticles in a Gay-Berne nematic liquid crystal using molecular simulations. For small separations, disclinations entangle both particles forming the figure of eight, the figure of omega and the figure of theta. These defect structures are similar in shape and occur with a comparable frequency to micron-sized particles studied in experiments. The simulations reveal fast transitions from one defect structure to another suggesting that particles of nanometre size cannot be bound together effectively. We identify the 'three-ring' structure observed in previous molecular simulations as a superposition of the different entangled and non-entangled states over time and conclude that it is not itself a stable defect structure. [ABSTRACT FROM AUTHOR]

Elastic fields of twist disclinations in an anisotropic elastic plate are derived in the context of Kirchhoff’s plate theory. The solution is utilized to develop a new numerical method for general anisotropic cracked plates containing an arbitrary array of cracks under bending or twisting. Integral equations are constructed by simulating cracks as continuous distributions of disclinations. Using Gauss–Chebyshev integration formulas, the integral equations can be transformed into the form of algebraic equations, with which the disclination densities and the stress intensity factors associated with each crack tip can be computed. Numerical examples are provided for isotropic or orthotropic plates with one to three cracks. [ABSTRACT FROM AUTHOR]

In this paper we consider modification of electronic properties of graphene-based topological insulator in the presence of wedge disclination and magnetic field by adopting the Kane–Mele model with intrinsic spin–orbit coupling. Using the properly defined Dirac–Weyl equation for this system, an exact solution for the Landau levels is obtained. The influence of the topological defect on the evolution of Landau levels is discussed. [ABSTRACT FROM AUTHOR]

Blue phases (BPs) obtained by doping a commercially available liquid crystalline compound (4-butyl-N-(4-ethoxybenzylidene)aniline (EBBA)) with (2R,3R)-2,3-bis(4-octyloxyphenylbenzoyloxy)-N-(hydroxydecyl)succinimide (1) were highly stabilised by the addition of a small amount of alkane diols. Especially, addition of only 0.5 mol% of octane-1,8-diol increased theBP–Isotransition temperature by 10 K and widened theBPtemperature range up to 35 K. A model stabilisation mechanism based on the construction of a hydrogen bond network in each disclination zone in BPs was proposed. [ABSTRACT FROM PUBLISHER]

We have developed a new device called the dynamic cell, whereby the twist angle and cell thickness of a liquid crystal cell can be dynamically varied. For a twist angle larger than 90°, there occurs a breaking of anchoring at a certain threshold cell thickness. This structural transition converts the super-twisted state to a normal twisted state by flipping the surface director by 180°. A disclination loop separates the normal twisted region from the super-twisted region. By controlling the twist and thickness, we can stabilize this loop and calculate its line tension. [ABSTRACT FROM AUTHOR]

Mg–Zn–Y alloys that contain an Mg-based long-period stacking ordered (LPSO) phase exhibit excellent mechanical properties because of the kink bands formed by plastic deformation. Such "kink-band strengthening" has attracted significant attention. Herein, we conducted deformation tests on directionally solidified single-phase LPSO Mg 85 Zn 6 Y 9 alloys to investigate the kink-band strengthening mechanism. High-angular resolution electron backscatter diffraction was performed to detect misorientation between the matrices on either side of the kink bands. The misorientations corresponded to the magnitudes of the Frank vectors of the disclinations around the kink, and closely matched the estimations from geometric analysis, which supported the existence of disclinations. Moreover, the Frank vector of the kink bands increased after shear deformation, which indicates that shear deformation introduced new disclinations around the kinks. Scanning electron microscopy demonstrated that the kinks clearly obstructed basal ⟨ a ⟩ slip. Furthermore, scanning transmission electron microscopy of a sheared kink band revealed dislocation pile-ups on both sides of the kink/matrix interface, as well as the formation of secondary kinks that stabilized the structure against shear deformation (i.e., self-accommodation) and bend contours caused by elastic stress fields. The results suggest that disclinations behave as long-range obstacles to dislocation motion (e.g., by reducing the increase in kink-band self-energy or by the elastic stress field of disclinations). We believe that this study will play a key role in identifying the factors responsible for kink-band strengthening in LPSO-phase Mg alloys and in understanding the phenomena underlying the strengthening mechanism. [Display omitted] [ABSTRACT FROM AUTHOR]

The interaction between nanoscale amorphization and crack in deformed nanocrystalline materials is investigated. Effects of nanoscale amorphization characterized by three disclination dipoles on the emission of lattice dislocations from the crack tip are theoretically investigated. The critical stress intensity factors (SIFs) for dislocation emission from the crack tip are calculated. The influences of nanoscale amorphization as well as crack length on the critical SIFs are discussed in detail. The results show that nanoscale amorphization can suppress lattice dislocation emission. The most probable angle of dislocation emission decreases with increment of disclination strength and the shorter length crack drivers easier the dislocation emission from the crack tip. [ABSTRACT FROM AUTHOR]

We present the results of large-scale molecular dynamics simulations of grain growth in polycrystalline nickel with nanoscale grains. The simulations show that grain growth is accompanied by coherent twin boundary (CTB) generation. As the grains grow, twins collide; such collisions result in twin junctions. We catalog all possible twin junctions and show examples of each from the simulations. These include junctions of 2–4 CTBs with grain boundaries and five-fold twin junctions (penta-twins). We elucidate the mechanisms by which all of these junctions form and their relative frequencies. Penta-twins, which are rare in coarse microstructures, occur frequently in nanocrystalline metals. Their absence in macro-scale samples can be traced to the wedge-disclination character (and, consequently, an elastic energy that diverges with sample size). In the nanocrystalline case, the presence of penta-twins can be traced to this twin collision formation mechanism, which is responsible for their wedge-disclination dipole character (relatively small elastic energy). We demonstrate how all CTB junctions, especially penta-twins, retard grain growth. [ABSTRACT FROM AUTHOR]

We present continuous modelling at inter-atomic scale of a high-angle symmetric tilt boundary in forsterite. The model is grounded in periodic arrays of dislocation and disclination dipoles built on information gathered from discrete atomistic configurations generated by molecular dynamics simulations. The displacement, distortion (strain and rotation), curvature, dislocation and disclination density fields are determined in the boundary area using finite difference and interpolation techniques between atomic sites. The distortion fields of the O, Si and Mg sub-lattices are detailed to compare their roles in the accommodation of lattice incompatibility along the boundary. It is shown that the strain and curvature fields associated with the dislocation and disclination fields in the ‘skeleton’ O and Si sub-lattices accommodate the tilt incompatibility, whereas the elastic strain and rotation fields of the Mg sub-lattice are essentially compatible and induce stresses balancing the incompatibility stresses in the overall equilibrium. [ABSTRACT FROM PUBLISHER]

The preparation of materials with a developed surface by changing the morphology of electrolytic icosahedral small copper particles was described. At first, icosahedral small copper particles were electrodeposited from an electrolyte solution to a metal support, and then the support with the deposited metal was thermally treated and chemically etched; as a result, the specific surface area of particles and coatings significantly increased. [ABSTRACT FROM AUTHOR]

Cosserat continuum for particulate materials has characteristic lengths commensurate with small particle sizes leading to small-scale Cosserat continuum – an asymptotics intermediate between the characteristic length and the crack length. We show that the main asymptotic term can be obtained from the classical crack problem by finding rotations from the displacements and, using the Cosserat constitutive equations finding the moment stresses. We obtained that Mode I, II stress singularities are the same in classical continuum; the moment stress has a stronger singularity (power 3/2). Bond bending and breakage caused by relative particle rotations constitutes the dominant mechanism of crack propagation. [ABSTRACT FROM AUTHOR]

The effect of temperature and annealing atmosphere on the structure and morphology of small icosahedral copper particles and filamentary pentagonal crystals has been investigated. Particles and filamentary crystals were obtained by electrodeposition of metal, and their structure and morphology were investigated by electron microscopy and x-ray diffraction. It has been shown that during annealing, whiskers are formed on the surface of the particles together with porous and 'flake' structures, and cavities are formed inside them. [ABSTRACT FROM AUTHOR]

Various dichroic dyes were synthesized and applied to two different host materials for the study of optimized molecular structures of guest–host system for the coatable polarizer using liquid crystalline polymers. The host material containing planar and linear mesogens had an advantage in exhibiting high orientation orders, but easily formed disclinations due to causing the strong intermolecular attraction between the guest and host molecules. The balance of intermolecular attraction and repulsion between the guest and host molecules is important to simultaneously achieve high orientations and uniform alignments without disclinations. The highest dichroic ratio of coatable polarizers was obtained when the π-conjugation lengths of guest and host molecules have an appropriate ratio. Also, the guest molecules with a long π-conjugation length improved the orientation of host molecules. [ABSTRACT FROM AUTHOR]

A coarse-grained extension of a recent nanoscale elasto-plastic model of polar dislocation and disclination density fields is developed to model grain boundary-mediated plasticity in polycrystals. At a small resolution length scale, the polar dislocation/disclination densities render continuously the discontinuities of the elastic displacements/rotations across grain boundaries. When the resolution length scale increases, the net polarities of a crystal defect ensemble decrease, perhaps to the point where no strain/curvature incompatibility is left in the body. The defect densities are then labeled “statistical”. However both polar and statistical dislocation/disclination densities contribute to plastic flow, and a coarse-grained mesoscopic plastic curvature rate needs to be defined. In addition, whereas it is overlooked at nanoscale where grain boundaries are seen as continua, tangential continuity of the elastic/plastic curvature/strain rates across grain boundaries needs to be considered at mesoscale, because the latter are seen as singular discontinuity interfaces. It induces long-range, grain-to-grain, elastic/plastic interactions across interfaces. The mesoscale model allow preserving the essential features of the lower scale approach. In particular, it is shown that it allows accounting for such plastic deformation mechanisms as grain boundary migration and grain boundary misorientation variation by disclination motion and concurrent dislocation nucleation, when plasticity by dislocation glide is unavailable. Accumulation of polar defect densities in the vicinity of the grain boundaries and triple lines, leading to long-range inter-granular activation of slip and grain size effects, are also predicted by the model. [ABSTRACT FROM AUTHOR]

We present the results on the modelling of structural changes in pentagonal small particles (PSPs) during their growth. We prove that after a certain critical size it becomes energetically favourable for a PSP to form a subsurface layer free of twin boundaries (TBs), which are only typical structural elements for smaller size PSPs. In this layer, the low-angle dislocation boundaries (DBs) are formed. Our calculations of the energy stored in the transformed PSP are based on the disclination model of a PSP, in which the TB junctions, as well as TB–DB junctions are treated as wedge disclinations. [ABSTRACT FROM PUBLISHER]

Temperature plays a vital role in the nucleation and growth of nanocrystals in the hydrothermal method, but the heating methods would cause some side reactions during the temperature rising period. Here, we modify the synthesis process of Marks decahedral Pd nanoparticles and do a detailed analysis of the internal structure of a Marks decahedral Pd Nanoparticle using aberration-corrected high resolution transmission electron microscopy (HRTEM) and the geometric phase analysis (GPA). The yield rate of Marks decahedral Pd nanoparticles increases to more than 60%. Our measurements confirm the existence of disclinations, which is consistent with the results given by the inhomogeneous strain model. [ABSTRACT FROM AUTHOR]

The intergranular fracture toughness of plastic deformable crystalline materials is strongly controlled by the plastic work ahead of the intergranular crack tip. Therefore, in studies of intergranular fracture toughness, the grain boundaries (GBs) should be regarded as both a cleavage plane and dislocation source. Combining continuum analyses and atomic simulations, this study investigates the atomic-scale mechanism of intergranular crack tip plasticity in aluminum 〈1 1 2〉 tilt GBs as an effective dislocation source. To quantitatively predict the first plastic deformation near the intergranular crack tip, we first model the dislocation emission from the GBs ahead of the intergranular crack tip and analytically derive the critical stress intensity factor. If the predicted first plastic phenomenon is dislocation emission from the GBs, the resulting wedge disclination can shield the stress field near the crack. Dislocation emissions from the crack tip are accompanied by dislocation emissions from the GBs, despite the predicted difficulty of the latter. The lattice defect evolution nucleates a nanograin with a disclination at the triple-junction ahead of the crack tip, which can weaken the mechanical field near the crack tip. Consequently, when improving the intergranular fracture toughness of materials, the role of GBs as dislocation sources cannot be ignored. [ABSTRACT FROM AUTHOR]

We investigate orientational nematic liquid crystal structures that form at the polymer surface due to adsorption, their stability against the schlieren texture and features of point and linear singularities in them. We demonstrate that surface disclination lines, which also occur due to molecular adsorption, can lead to azimuthal anchoring of a bulk layer and make the singularities with the chargem = ±1 stable. We consider the director field distribution in a nematic layer as a result of the combination of two aligning factors, which are the linear disclination that tend to impose uniform planar ordering and point defects that impart the radial configuration to the director. With the use of the calculation, we analyse the energies of elastic distortions of the director field for the radial–planar, radial–homeotropic and radial–radial configurations, depending on the nematic layer thickness. [ABSTRACT FROM AUTHOR]

Abstract: An experimental testing of a disclination structure in a liquid crystal was performed. The origin of a disclination is a conflict between opposite-sign twist in a planar 90° twist-cell or a θ-cell. A theoretical analysis has shown a topological defect with the charge 1/2 (π variation in the azimuth angle of a twist along a close loop around the disclination). In the experiment we have tested a disclination zone by plane-wave linearly polarized light. The presence of the Mauguin lines was revealed in a numerical modeling and direct experiment. To resolve the structure around the disclination we used interferometric technique. The theoretical predictions were confirmed by the detection of the phase π-step occurring between the Mauguin lines. [Copyright &y& Elsevier]

This article establishes a theoretical model to study the effect of grain boundary sliding deformation on the dislocation emission from the crack tip in nanocrystalline solids. Within our description, stress concentration near the crack initiates grain boundary sliding which results in the formation the dipole of disclinations at triple junctions of grain boundaries. The grain size-dependent criterion for the dislocation emission from a semi-infinite crack tip is derived. The influence of the grain size and the features of dipole of disclinations on the critical stress intensity factors for dislocation emission is evaluated. It is shown that grain boundary sliding deformation enhances the critical stress intensity factor for dislocation emission. The critical stress intensity factor will increase with the decrement of the grain size, which indicates that the emission of the dislocation becomes more difficult for smaller size of grain due to the effect of grain boundary sliding deformation. [ABSTRACT FROM PUBLISHER]

Abstract: A grain size-dependent model is theoretically established to describe the effect of a special physical micromechanism of plastic flow on the dislocation emission from an elliptical blunt crack tip in nanocrystalline solids. The micromechanism represents the fast nanoscale rotational deformation (NRD) occurring through collective events of ideal nanoscale shear near crack tips, which as a stress source is approximately equivalent to a quadrupole of wedge disclinations. By the complex variable method, the grain size-dependent criterion for the dislocation emission from an elliptical blunt crack tip is derived. The influence of the grain size and the features of NRD on the critical stress intensity factors for dislocation emission is evaluated. The results indicate that NRD releases the high stresses near the crack tip region and thereby enhances the critical stress intensity factor for dislocation emission. The NRD has great influence on the most probable angle for dislocation emission. The critical stress intensity factor will increase with the increment of the grain size, which means the emission of the dislocation becomes more difficult for larger grain size due to the effect of NRD. [Copyright &y& Elsevier]

We report a new method for the detection and measurement of the chirality of liquid crystal compounds. The method is based on the determination of an azimuth of a disclination line in aθ-cell, with the director aligning unidirectionally at one side and circularly at another one. Experimental observation of disclination rotation was performed with a composition of ZLI-4801-0000 liquid crystal and dopants of opposite-sign chirality (R-2011, S-2011, 7-dehydrocholesterol). Dynamic behavior of the disclinaton line was revealed under the influence of continuous illumination by actinic UV radiation. [ABSTRACT FROM PUBLISHER]