Twist Distortion Research Articles

Theoretical and experimental studies on the effect of the 1,2-diketone group on geometry distortion for phenacene-type polycyclic aromatic compounds

Abstract This paper addresses the geometry distortion of orthoquinone-containing phenacene-type compounds by comparing the structures of phenanthrene-9,10-dione, chrysene-5,6-dione, and picene-13,14-dione. Interestingly, the calculated geometry of chrysene-5,6-dione under the isolated state was drastically different from the experimental one observed by single-crystal X-ray analysis. Theoretical calculations suggested that the molecular geometry of the o-quinone derivatives was sensitive not only to the sterically intramolecular proximity between the carbonyl oxygen and the hydrogen atoms of the benzene rings but also to intermolecular interactions. The twist distortion affects properties such as oscillator strength and 1-electron transitions, for low-lying excited states.

Inversion ring in chromonic twisted hedgehogs: theory and experiment

ABSTRACT Twisted hedgehogs are defects in spherical cavities with homeotropic anchoring for the nematic director that arise when twist distortions are sufficiently less energetic than splay (and bend) distortions. They bear a characteristic inversion ring, where the director texture changes the sense it spirals about the centre of the cavity. This paper applies a quartic twist theory recently proposed to describe the elasticity of chromonics to explain a series of inversion rings observed in spherical microcavities containing aqueous solutions of SSY at two different concentrations. The theory features a phenomenological length a, whose measure is extracted from the data and shown to be fairly independent of the cavity radius, as expected for a material constant.

Magnetic field-induced Freedericksz transition in a chiral liquid crystal

A wedge cell made of homeotropically treated glass plates is filled with a chirally doped nematic liquid crystal. When a sufficiently large magnetic field is applied in the cell plane, a bend-like distortion occurs above a Fréedericksz threshold field Hth. Hth is reduced from the achiral case because of a field-induced bend distortion that facilitates a chiral twist distortion. Measurements of Hth vs sample thickness are reported and compared favorably with a theoretical model presented herein. A further theoretical comparison is made between Hth and the electric-field-induced transition in a geometry, exhibiting a 2π azimuthal degeneracy. The results may have technological implications in, for example, in-plane switching devices.

Magnetic Anisotropy and Relaxation of Pseudotetrahedral [N2 O2 ] Bis-Chelate Cobalt(II) Single-Ion Magnets Controlled by Dihedral Twist Through Solvomorphism.

The methanol solvomorph 1 ⋅ 2MeOH of the cobalt(II) complex [Co(LSal,2-Ph )2 ] (1) with the sterically demanding Schiff-base ligand 2-(([1,1'-biphenyl]-2-ylimino)methyl)phenol (HLSal,2-Ph ) shows the thus far largest dihedral twist distortion between the two chelate planes compared to an ideal pseudotetrahedral arrangement. The cobalt(II) ion in 1 ⋅ 2MeOH exhibits an easy-axis anisotropy leading to a spin-reversal barrier of 55.3 cm-1 , which corresponds to an increase of about 17 % induced by the larger dihedral twist compared to the solvent-free complex 1. The magnetic relaxation for 1 ⋅ 2MeOH is significantly slower compared to 1. An in-depth frequency-domain Fourier-transform (FD-FT) THz-EPR study not only allowed the direct measurement of the magnetic transition between the two lowest Kramers doublets for the cobalt(II) complexes, but also revealed the presence of spin-phonon coupling. Interestingly, a similar dihedral twist correlation is also observed for a second pair of cobalt(II)-based solvomorphs, which could be benchmarked by FD-FT THz-EPR.

Similar Signatures of Coplanar Gas Inflow and Disk Warps in Galactic Gas Kinematic Maps

Hydrodynamic simulations suggest that galactic gas disks form when coplanar gas spirals into the inner regions of the disk. We recently presented a simple modified accretion disk model of viscous galactic disks in which star formation is fed by a radial flow of gas. However, little observational evidence has been presented for such inflows, which are expected to be only a few kilometers per second in the central regions of the disk, i.e., within four disk scale lengths, but could reach of order 50–100 km s−1 in the very outer disk. The effects of systematic inflow on the 2D velocity field are examined and it is shown that these are quite similar to those produced by geometric warps of the disks, with twist distortions of both the kinematic major and minor axes. This makes it potentially difficult to distinguish between these in practice. By comparing the handedness of the observed twisting of the kinematic axes and of the spiral arms for a sample of nearby galaxies, we find (assuming that the spiral arms are generally trailing) that the effects of warps are in fact likely to dominate over the effects of radial inflows. However, the common practice of treating these twist distortions of the kinematic major and minor axes as being due only to warps can lead, for galaxies of low-to-intermediate inclinations, to substantial underestimates of any systematic inflow.

The decelerator tester twisting distortion caused angular measurement error calibration, based on the IBSCF-SGDPSO-RBF method

Recently, robot decelerators have beenwidely applied in the automation industry. Thus, the robot decelerator feature measurement, especially rigidity measurement, is essential to estimating the decelerator. However, the angular measurement results of the instrument cannot be used as the decelerator's actual twisting distortion due to the influence of the distortion in the measurement chain. The instrument's twisted distortion characteristics are analyzed in this paper. Based on the analysis, a new method of calibrating the twisted-distortion-caused angular measurement error based on the improved B-spline curve fitting-stochastic gradient descent and particle swarm optimization-radial basis function neural network (IBSCF-SGDPSO-RBF) method is proposed. The steps of the calibration method are presented in this paper, and the measurement experiment from low load to high load is carried out on the full scale. The experiment results show that the instrument distortion caused angular measurement error after compensation is within ± two angular seconds. We can conclude that the problem that the change of instrument distortion affects the angular measurement accuracy of the instrument is solved. The calibration method can eliminate the influence of the instrument's twisting distortion. The authors' main contribution is that a CSF-iPSO-RBF-based angular measurement error calibration method is proposed. It provides a reference for measuring and evaluating the actual twisting rigidity of the Rotary Vector (RV) decelerator under any load.

Empirical formulae assessment of ultimate strength for perforated stiffened panels under longitudinal compression

The present paper studies the influence of cut-outs of local plates on the ultimate strength of stiffened panels based on the tests and numerical simulations. Four intact and perforated stiffened panels subjected to uniaxial compression loads were tested firstly. The initial imperfections of the specimens have been measured before testing, which were used in the FE (finite element) analysis. The tensile tests are used to determine the properties of material. The experimental results are used to verify the modelling technology of FE models. Based on the numerical simulations, the parametric studies with various configurations including the initial twisting distortion, boundary condition and the dimensions of opening are performed to investigate their influences on the collapse behaviours of the stiffened panels. It is found that the residual ultimate strength of perforated stiffened panel mainly depends on the transverse length of opening. Using numerical database, the empirical formulae of ultimate strength of perforated stiffened are developed.

Instances of mixed buckling and post-buckling of steel RHS beams

Simply supported steel beams with rectangular hollow section (RHS) are investigated, taking into account large twist and cross-sections distortions. A closed-form expression for the critical value of the external couple inducing lateral torsional buckling is found; homotopy perturbation method (HPM) is used to investigate the post-buckling non-linear path. The linear and non-linear paths given by HPM are compared to those of: i) a Newton–Raphson algorithm with arc length; and ii) the commercial FEM code Abaqus. Some numerical examples are presented.

Distortional effect on global buckling and post-buckling behaviour of steel box beams

The homotopy perturbation method (HPM) to predict the pre- and post-buckling behaviour of simply supported steel beams with rectangular hollow section (RHS) is presented in this paper. The non-linear differential equations solved by HPM derive from a kinematics where large twist and cross-sections distortions are considered. The results (linear and non-linear paths) given by the present HPM are compared to those provided by the Newton–Raphson algorithm with arc length and by the commercial FEM code Abaqus. To investigate the effect of cross-sectional distortion of beams, some numerical examples are presented.

An experimental study on piezoelectric energy harvesting from wind and ambient structural vibrations for wireless structural health monitoring

Energy harvesting is an emerging technology holding promise of sustainability amid the alarming rate at which the human community is depleting the natural resources to cater its needs. There are several ways of harvesting energy in a renewable fashion such as through solar, wind, hydro-electric, geothermal, and artificial photosynthesis. This study focuses on energy harvesting from wind vibrations and ambient structural vibrations (such as from rail and road bridges) through piezo transducers using the direct piezoelectric effect. First, the potential of the piezoelectric energy harvesting from ambient wind vibrations has been investigated and presented here. Lead zirconate titanate patches have been attached at the fixed end of aluminum rectangular and trapezoidal cantilevers, which have been exposed to varying wind velocity in a lab-size wind tunnel. The effect of perforations and twisting (distortion) on the power generated by the patches under varying wind velocity has also been studied. It has been observed that the power is comparatively higher in rectangular-shaped cantilever than the trapezoidal one. Perforations and shape distortion showed promising result in terms of higher yield. The laboratory experiments have also been extended to the real-life field condition to measure the actual power generated by the lead zirconate titanate patches under the ambient wind vibrations. Next, energy harvesting from the ambient structural vibrations has been done both experimentally and numerically. Four different prototypes have been considered. The power has been measured across the lead zirconate titanate patches individually and in parallel combination. A maximum power output for Prototype 1 to Prototype 4 has been found to be 4.3428, 11.844, 25.97, and 43.12 µW, respectively. Numerical study has also been carried out in ANSYS 14.5 to perform the parametric study to examine the effect of addition of mass at the free end of cantilever. In a nutshell, this article provides a comprehensive study on the effect of various factors on the amount of energy generated by piezoelectric patches under wind and structural vibrations. The energy generated is sufficient for driving low-power-consuming electronics that can further be used for other applications like wireless structural health monitoring, and so on.

Directional torsion and strain discrimination based on Mach-Zehnder interferometer with off-axis twisted deformations

An all-fiber sensor based on a Mach-Zehnder interferometer (MZI) is proposed and experimentally demonstrated to measure directional torsion and strain simultaneously. The MZI employing a pair of off-axis twisted deformations (OATDs) on single mode fiber (SMF) is fabricated by continuous arc discharge method. It performs OATDs causing permanent twisted distortion to form light beam splitter and combiner of the MZI. The transmission spectrum of the OATDs-MZI has multiple resonance wavelength dips, which correspond to different cladding modes. The torsion and strain measurement can be simultaneously achieved by monitoring changes in the dips of wavelength. Due to the OATDs, the proposed sensor has the ability to distinguish torsional direction, and a strain sensitivity as high as −0.0285 nm/με was obtained. The proposed sensor exhibits excellent torsion and strain resolution of ±0.0611 rad/m and ±0.8232 με. The device has the advantages of low cost, small size, simple preparation steps, short preparation cycle, etc. Due to its excellent performance, it has the potential to become an excellent universal directional torsion and strain sensor.

Experimental study on composite mechanical properties of a double-deck prestressed concrete box girder

A series of tests were carried out on a scaled (1:8) double-deck prestressed concrete box girder in this study, aiming to study the structural response and failure mechanism of the box girder under prestressed axial compression, transverse bending, and torsion. The test results, such as the twist angle, crack development, and distortion of the box girder, were analyzed in detail. The results show that (1) the box girder eventually suffered lateral bending damage, and the cross-section of the support distorted severely; (2) torsional cracking occurred in the pure torsion region at the mid-span, but the longitudinal and transverse rebars did not yield, indicating that the pure torsion section of the box girder was still in the early stage of torsion failure; and (3) after the cracking of the box girder, stress redistribution phenomenon occurred, resulting in obvious nonlinear strain variations. Comparison of the longitudinal and transverse steel strains showed that transverse steel withstood the most shear stress during the early stage of torsion.

Colloids in confined liquid crystals: a plot twist in the lock-and-key mechanism.

By confining soft materials within tailored boundaries it is possible to design energy landscapes to address and control colloidal dynamics. This provides unique opportunities to create reconfigurable, hierarchically organized structures, a leading challenge in materials science. Example soft matter systems include liquid crystals. For instance, when nematic liquid crystals (NLCs) are confined in a vessel with undulated boundaries, bend and splay distortions can be used to position particles. Here we confine this system in a twist cell. We also study cholesteric liquid crystals, which have an "intrinsic" twist distortion which adds to the ones imposed by the solid boundaries. The cholesteric pitch competes with the other length scales in the system (colloid radius, vessel thickness, wavelength of boundary undulations), enriching the possible configurations. Depending on the pitch-to-radius and pitch-to-thickness ratios the interaction can be attractive or repulsive. By tuning the pitch (i.e. changing the concentration of the chiral dopant), it is possible to selectively promote or inhibit particle trapping at the docking sites.

Curvature-Induced Twist in Homeotropic Nematic Tori.

We confine a nematic liquid crystal with homeotropic anchoring to stable toroidal droplets and study how geometry affects the equilibrium director configuration. In contrast to the case of cylindrical confinement, we find that the equilibrium state is chiral-a twisted and escaped radial director configuration. Furthermore, we find that the magnitude of the twist distortion increases as the ratio of the ring radius to the tube radius decreases; we confirm this with computer simulations of optically polarized microscopy textures. In addition, numerical calculations also indicate that the local geometry indeed affects the magnitude of the twist distortion. We further confirm this curvature-induced twisting using bent cylindrical capillaries.

Twisted and Bent Out of Shape: Symmetry and Chirality Analysis of Substituted Ferrocenes

Ferrocene symmetry is commonly described as either eclipsed (D5h) or staggered (D5d), but this symmetry does not hold when substitution is involved. Here we examine and quantify the effect of substitution on the geometry of the core structure of ferrocene, and provide means to distinguish between its various distortion paths. Continuous symmetry analysis of the core structure of 7418 substituted ferrocenes extracted from the Cambridge Crystallographic Database was used to explore its twisting and bending distortion paths, as well as asymmetric bond stretch that deforms the symmetry of its cyclopentadienyl rings. Gas-phase density functional theory calculations provided a theoretical background to describe these distortion paths and define symmetry profiles for conformer interconversion processes and the interplay between them. Our results show that the distortion of ferrocene can often be substantial. Furthermore, its geometry is highly flexible, and almost always chiral to some degree. Handedness in term...

Mechanistic Study of Suzuki–Miyaura Cross‐Coupling Reactions of Amides Mediated by [Pd(NHC)(allyl)Cl] Precatalysts

AbstractWe report a combined experimental and computational investigation of the Suzuki–Miyaura cross‐coupling of amides enabled by [Pd(NHC)(allyl)Cl] precatalysts. Most crucially, mechanistic details pertaining to the Pd0/NHC catalytic cycle were elucidated by computational methods. Mechanistic insights shed light on the role of each ligand about the metal. Sterics play a key role in the initial activation of the catalyst. As a key insight, we have shown that water participates in the activation of the Pd‐NHC catalytic system. Easier activation has led to effect room temperature cross‐coupling of a broad range of amides through selective N−C bond scission under the mildest conditions reported to date. The use of sterically hindered [Pd(IPr*)(cin)Cl] reported herein for the first time in the amide cross‐coupling indicates that increasing flexible steric bulk of the isopropyl wingtip groups of the NHC ligand provides a modular scaffold for promoting amide cross‐coupling in high yields. The precatalytic pathway involving both NHC ligands as well as the catalytic cycle beginning from the Pd0 species are discussed. The mechanistic details provide insight into the amide bond twist (distortion) that leads to N−C cross‐coupling reactions and is required for the efficient N−C bond activation.

Fine structures of defect cores induced by elastic anisotropy and biaxiality in hybrid alignment nematics**Project supported by the National Natural Science Foundation of China (Grant Nos. 11374087 and 11447179) and the Key Subject Construction Project of Hebei Province University, China.

Based on Landau–de Gennes theory and two-dimensional finite-difference iterative method, the spontaneous distortion in hybrid alignment nematic cells with M = ±1/2 disclination lines is investigated by establishing two models. The fine structures of defect cores are described in the order space S2/Z2. The joint action of elastic anisotropy (L2/L1) and biaxiality of defects induces the spontaneous twist distortion, accompanied by the movement of the defect center to the upper or lower plate. For each model, four mixed defect structures appear with the same energy, which are defined as energetically degenerated quadruple states.

Twist transitions and force generation in cholesteric liquid crystal films

The response of a cholesteric liquid crystal film to mechanical confinement is theoretically investigated considering planar anchoring conditions on the limiting surfaces and pure twist distortion of the liquid crystal director. We evaluate the total twist angle and normal force acting on the surfaces as a function of the film thickness. Assuming the Rapini-Papoular functional form for the surface anchoring energy, we show that the surface twist angle undergoes discontinuous jumps or continuous transitions as a function of the film thickness and anchoring strength. The transitions take place at well-defined film thicknesses, related to the intrinsic periodicity of the cholesteric liquid crystal, and produce oscillations in the normal force and position of the optical band-gap as the film thickness is varied.

Twisted Amides: From Obscurity to Broadly Useful Transition-Metal-Catalyzed Reactions by N-C Amide Bond Activation.

The concept of using amide bond distortion to modulate amidic resonance has been known for more than 75 years. Two classic twisted amides (bridged lactams) ingeniously designed and synthesized by Kirby and Stoltz to feature fully perpendicular amide bonds, and as a consequence emanate amino-ketone-like reactivity, are now routinely recognized in all organic chemistry textbooks. However, only recently the use of amide bond twist (distortion) has advanced to the general organic chemistry mainstream enabling a host of highly attractive N-C amide bond cross-coupling reactions of broad synthetic relevance. In this Minireview, we discuss recent progress in this area and present a detailed overview of the prominent role of amide bond destabilization as a driving force in the development of transition-metal-catalyzed cross-coupling reactions by N-C bond activation.

PB54 膨潤SmC*相のツイスト弾性定数に対する溶媒効果(ソフトマター,ポスター発表,2015年日本液晶学会討論会)

PB54 膨潤SmC*相のツイスト弾性定数に対する溶媒効果(ソフトマター,ポスター発表,2015年日本液晶学会討論会)