Symmetric Torsion Research Articles

Massless Dirac perturbations of black holes in f(Q) gravity: quasinormal modes and a weak deflection angle

This article considers a static and spherical black hole (BH) in f(Q) gravity. f(Q) gravity is the extension of symmetric teleparallel general relativity, where both curvature and torsion are vanishing and gravity is described by nonmetricity. In this study, we investigate the possible implications of quasinormal mode (QNM) modified Hawking spectra and deflection angles generated by the model. The Wentzel–Kramers–Brillouin method is used to solve the equations of motion for massless Dirac perturbation fields and explore the impact of the nonmetricity parameter (Q 0). Based on the QNM computation, we can ensure that the BH is stable against massless Dirac perturbations and as Q 0 increases the oscillatory frequency of the mode decreases. We then discuss the weak deflection angle in the weak field limit approximation. We compute the deflection angle up to the fourth order of approximation and show how the nonmetricity parameter affects it. We find that the Q 0 parameter reduces the deflection angle.

Gauge-invariant cosmological perturbations in general teleparallel gravity

We study linear cosmological perturbations in the most general teleparallel gravity setting, where gravity is mediated by the torsion and nonmetricity of a flat connection alongside the metric. For a general linear perturbation of this geometry around a homogeneous and isotropic background geometry, we derive the irreducible decomposition of the perturbation variables, as well as their behavior under gauge transformations, i.e., infinitesimal diffeomorphisms generated by a vector field. In addition, we also study these properties for the most general set of matter variables and gravitational field equations. We then make use of these result to construct gauge-invariant perturbation variables, using a general approach based on gauge conditions. We further calculate these quantities also in the metric and symmetric teleparallel geometries, where nonmetricity or torsion is imposed to vanish. To illustrate our results, we derive the energy-momentum–hypermomentum conservation equations for both the cosmological background and the linear perturbations. As another example, we study the propagation of tensor perturbations in the f(G), f(T) and f(Q) class of theories.

Fatigue fracture surface of bronze RG7 under proportional cyclic torsion and bending

The paper presents the results of fatigue cyclic tests performed on MZGS stand of RG7 bronze under symmetric bending, symmetric torsion, and the combination of proportional symmetric bending and torsion, where τa = σa and τa = 0.5σa. Causes of damage were determined by scanning electron microscopic observation. The fracture images were observed using a Tescan Vega 4 Scanning Electron Microscope operating at 20 kV. Secondary electron detection (SE) was used to obtain SEM images. For topographic analysis, an optical profilometer by Sensofar 3D S neox was used, which includes modern software for surface analysis by Digital Surf Mountains Map. Fatigue crack analysis was performed by observing samples for each combination under the following scheme: one with a low load level with a lifetime of 1,000,000 cycles and the other with a high load level and a lifetime of 30,000 cycles.

On the Cooperative Origin of Solvent-Enhanced Symmetry-Breaking Charge Transfer in a Covalently Bound Tetracene Dimer Leading to Singlet Fission.

Singlet fission in covalently bound acene dimers in solution is driven by the interplay of excitonic and singlet correlated triplet 1(TT) states with intermediate charge-transfer states, a process which depends sensitively on the solvent environment. We use high-level electronic structure methods to explore this singlet fission process in a linked tetracene dimer, with emphasis on the symmetry-breaking mechanism for the charge-transfer (CT) states induced by low-frequency antisymmetric vibrations and polar/polarizable solvents. A combination of the second-order algebraic diagrammatic construction (ADC(2)) and density functional theory/multireference configuration interaction (DFT/MRCI) methods are employed, along with a state-specific conductor-like screening model (COSMO) solvation model in the former case. This work quantifies, for the first time, an earlier mechanistic proposal [Alvertis et al., J. Am. Chem. Soc. 2019, 141, 17558] according to which solvent-induced symmetry breaking leads to a high-energy CT state which interacts with the correlated triplet state, resulting in singlet fission. An approximate assessment of the nonadiabatic interactions between the different electronic states underscores that the CT states are essential in facilitating the transition from the bright excitonic state to the 1(TT) state leading to singlet fission. We show that several types of symmetry-breaking inter- and intra-fragment vibrations play a crucial role in a concerted mechanism with the solvent environment and with the symmetric inter-fragment torsion, which tunes the admixture of excitonic and CT states. This offers a new perspective on how solvent-induced symmetry-breaking CT can be understood and how it cooperates with intramolecular mechanisms in singlet fission.

Imprints from a Riemann–Cartan space-time on the energy levels of Dirac spinors

In this work, we investigate the effects of the torsion–fermionic interaction on the energy levels of fermions within a Riemann–Cartan geometry using a model-independent approach. We consider the case of fermions minimally coupled to the background torsion as well as non-minimal extensions via additional couplings with the vector and axial fermionic currents which include parity-breaking interactions. In the limit of zero-curvature, and for the cases of constant and spherically symmetric torsion, we find a Zeeman-like effect on the energy levels of fermions and anti-fermions depending on whether they are aligned/anti-aligned with respect to the axial vector part of the torsion (or to specific combination of torsion quantities), and determine the corresponding fine-structure energy transitions. We also discuss non-minimal couplings between fermionic fields and torsion within the Einstein–Cartan theory and its extension to include the (parity-breaking) Holst term. Finally we elaborate on the detection of torsion effects related to the splitting of energy levels in astrophysics, cosmology and solid state physics using current capabilities.

Research on flutter-mode transition of a triple-tower suspension bridge based on structural nonlinearity

As the typical span of suspension bridge increases and multi-tower suspension bridges are developed, the linear flutter theory cannot meet the design requirements of modern flexible bridges, and the study of nonlinear flutter of bridges becomes necessary. The author discovered the flutter-mode transition phenomenon in a full-bridge aeroelastic model wind tunnel test of the Maanshan Bridge; that is, the bridge vibration was transformed from first-order anti-symmetric torsion mode (A-T-1) to first-order symmetric torsion mode (S-T-1) and diverged when the flutter critical wind speed was approached. A vertical bending mode acted as a medium for energy transfer between A-T-1 and S-T-1. This phenomenon greatly increased the critical wind speed of flutter, and therefore it is interesting to study its mechanism. Starting from the nonlinear nature of the bridge structure itself, this paper discusses the mechanism of the flutter-mode transition phenomenon, and analyzes the typical characteristics of flutter-mode transition of Maanshan Bridge in depth. A nonlinear discrete mathematical model of the Maanshan Bridge is built, and the transition between the vertical bending mode and torsional mode of the bridge is realized. Adopting the Mathieu function theory and based on the single-degree-of-freedom vibration equation of the Maanshan Bridge corresponding to each mode, the evolution between A-T-1 and S-T-1 is realized, the mechanism of which is also explained.

Slowly rotating neutron stars in scalar torsion theory

In this present paper, a slowly rotating stat is investigated in shift symmetric scalar torsion theory framework using a nondiagonal tetrad that gives an axially symmetric spacetime. We present the general equations for a general Lagrangian in a spherical symmetric space time and then in an axially symmetric spacetime. The obtained equations will allow us to study the behaviour of a specific model at the center of the star and at large distance. We find that this particular model affects the behaviour at the center but it is not case for large value of the radial coordinate r. The integration of the equations of motion, for different realistic equations of state (EoS), confirms that the mass, the radius as well as the moment of inertia are effected by varying the parameters of the model. Finally, we examine the universal relation of normalized moment of inertia and the stellar compactness of neutron star in slow rotation approximation. We showed that for all values of parameters present in the model leads to a deviation from GR for all EoS with a relative deviation below 10%.

Coupled Vibrations of Viscoelastic Three-Layer Composite Plates. 2. Numerical Experiments

The results of the numerical studies of the influence of the reinforcement orientation of rigid layers and relative thickness of a soft isotropic viscoelastic polymer layer on the values of natural frequencies and loss factors of the coupled vibrations of symmetric and asymmetric unsupported three-layer rectangular composite plates are discussed. It is shown that in a symmetric three-layer plate, a flexural and torsion interaction arises generating mutual transformations of the natural forms of the coupled vibration modes if at least one of its natural forms in the plate directions is characterized by an even number of quarter-wavelengths, and another natural form is characterized by an odd number of quarter-wavelengths. A flexural–flexural interaction arises in an asymmetric unsupported three-layer plate and generates mutual transformations of the natural forms of coupled vibration modes in two mutually orthogonal planes if both natural forms are characterized by either an even or an odd number of quarter-wavelengths in the main directions of the plate. It has been found that each mode of the natural vibrations of the three-layer plates corresponds to the effective relative thickness of the soft isotropic viscoelastic polymer layer.

CC-stretched formic acid: isomerisation, dimerisation, and carboxylic acid complexation.

The cis-trans-isomerism of the propiolic acid monomer (HC[triple bond, length as m-dash]C-COOH) is examined with linear Raman jet spectroscopy, yielding the first environment-free vibrational band centres of a higher-energy cis-rotamer beyond formic acid (HCOOH) in addition to all fundamentals and a large number of hot and combination/overtone bands of the trans-conformer. Two near-isoenergetic trans-fundamentals of different symmetry (CC[double bond, length as m-dash]O bend and OH torsion) prove to be a sensitive benchmarking target, as their energetic order is susceptible to the choice of electronic structure method, basis set size, and inclusion of vibrational anharmonicity. For the infrared- and Raman-active C[double bond, length as m-dash]O stretching fundamentals of the cyclic (C2h) trans-propiolic acid dimer, resonance couplings are found that in part extend to the Cs-symmetric heterodimer of trans-propiolic and trans-formic acid. Exploratory vibrational perturbation theory (VPT2) calculations show that all perturbing states involve displacements of the OH moieties located on the doubly hydrogen bonded ring. The comparison of the infrared spectra of the propiolic acid dimer and its heterodimer with formic acid to that of several other carboxylic acid dimers from the literature reveals a notable similarity regarding a non-fundamental dimer band around 1800 cm-1, which in most cases is so far unassigned. VPT2 calculations and a simple harmonic model suggest an assignment to a combination vibration of the symmetric and antisymmetric OH torsion.

Study of central buckle effects on flutter of long-span suspension bridges

To investigate the effects of central buckles on the dynamic behavior and flutter stability of long-span suspension bridges, four different connection options between the main cable and the girder near the mid-span position of the Aizhai Bridge were studied. Based on the flutter derivatives obtained from wind tunnel tests, formulations of self-excited forces in the time domain were obtained using a nonlinear least square fitting method and a time-domain flutter analysis was realized. Subsequently, the influences of the central buckles on the critical flutter velocity, flutter frequency, and three-dimensional flutter states of the bridge were investigated. The results show that the central buckles can significantly increase the frequency of the longitudinal floating mode of the bridge and have greater influence on the frequencies of the asymmetric lateral bending mode and asymmetric torsion mode than on that of the symmetric ones. As such, the central buckles have small impact on the critical flutter velocity due to that the flutter mode of the Aizhai Bridge was essentially the symmetric torsion mode coupled with the symmetric vertical mode. However, the central buckles have certain impact on the flutter mode and the three-dimensional flutter states of the bridge. In addition, it is found that the phenomenon of complex beat vibrations (called intermittent flutter phenomenon) appeared in the flutter state of the bridge when the structural damping is 0 or very low.

Fracture evaluation of square transversal section specimens subjected by torsional cyclic loads

ABSTRACTIn this work, the evaluation of the growth of cracks in specimens of square cross section requested by symmetrical cyclic torsion moments was performed. The specimens were manufactured from AISI 1015. A pre-crack was machined on one side to induce the crack growth. The crack length with the increase in the number of cycles was measured by means of penetrating liquids method. By means of the Finite Element Method, the stress – strain state of the specimens was simulated. The displacements in the crack tip were determined to apply the technique of the Crack Tip Opening Displacements to calculate the Stress Intensity Factor. The calculated Stress Intensity Factor was related to the dimensions of the specimen and the size of the crack to propose an equation for the shape function.

Identification of Aeroelastic Models for the X-56A Longitudinal Dynamics Using Multisine Inputs and Output Error in the Frequency Domain

System identification from measured flight test data was conducted using the X-56A aeroelastic demonstrator to identify a longitudinal flight dynamics model that included the short period, first symmetric wing bending, and first symmetric wing torsion modes. Orthogonal phase-optimized multisines were used to simultaneously excite multiple control effectors while a flight control system was active. Non-dimensional stability and control derivatives parameterizing an aeroelastic model were estimated using the output-error approach to match Fourier transforms of measured output response data. The predictive capability of the identified model was demonstrated using other flight test data with different inputs and at a different flight conditions. Modal characteristics of the identified model were explored and compared with other predictions. Practical aspects of the experiment design and system identification analysis, specific to flexible aircraft, are also discussed. Overall, the approach used was successful for identifying aeroelastic flight dynamics models from flight test data.

Torsional fatigue with axial constant stress of oligo‐crystalline 316L stainless steel thin wire

AbstractA series of symmetric torsional fatigue with axial constant stress tests, a kind of multiaxial fatigue test, was conducted on oligo‐crystalline 316L stainless steel thin wire, which was less than 3.5 grains across diameter of 200 μm. The material presents significant cyclic hardening under symmetric torsion cycling, and hardening is more obvious with the increasing shear strain amplitude. However, symmetric torsional cycle with constant axial stresses tests characterize rapid initial hardening and then gradually softening until fatigue failure. The axial stress has a great effect on torsional fatigue life. Fractography observation shows a mixed failure mode combined torsional fatigue with tensile strain because of axial tensile stress. A newly proposed model with axial stress damage parameter is used to predict the torsional fatigue life with constant axial stress of small scale thin wire.

Prediction of the Limit State and Life of Structural Materials Under the Action of Symmetric Cyclic Bending and Static Torsion

The paper considers a limit state and fatigue life calculation problem of prismatic bars under the joint action of symmetric cyclic bending and static torsion. The solution is constructed using the equivalent stress method. A cyclic stress under symmetric cycle conditions was chosen as an equivalent stress. The results of the calculation have been evaluated experimentally for alloyed steels and an aluminum alloy as an example.

Original Surgical Repair for an Adult Pectus Excavatum Patient: A Case Report

Backgroud: Pectus excavatum, the most common congenital thoracic deformity, is particularly difficult to correct in adults with reduced chest wall flexibility. For the repair of pectus excavatum, we have conducted sterno-costal elevation, which consists of resecting the redundant costal cartilages and the lower part of the sternum and resuturing the remaining costal cartilages to the sternum, and does not use any exogenous materials or require a second operation. Methods: We treated a 27-year-old female patient with an asymmetrical chest concavity who was referred to us because of consistent precordial pain with sterno-costal elevation. In this case, we added an oblique osteotomy across the anterior sternal table to reform the torsion of the sternum with a pneumatic powered drill. Results: The procedure corrected the deformity well, and the patient was very satisfied with the result one year after the operation. Conclusions: Sterno-costal elevation for pectus excavatum, which does not require any exogenous materials or additional operations, is effective in the treatment of pectus excavatum in a female adult patient with a symmetrical chest deformity and moderate sternal torsion.

Schemes over symmetric monoidal categories and torsion theories

Let (C,⊗,1) be an abelian symmetric monoidal category satisfying certain conditions and let X be a scheme over (C,⊗,1) in the sense of Toën and Vaquié. In this paper, we construct torsion theories on the categories OX-Mod and QCoh(X) respectively of OX-modules and quasi-coherent sheaves on X, when X is Noetherian and integral over (C,⊗,1). Thereafter, we study these torsion theories with respect to the quasi-coherator QX:OX-Mod⟶QCoh(X) that is right adjoint to the inclusion iX:QCoh(X)⟶OX-Mod. Finally, we obtain an alternative description of the quasi-coherator QX(F) as a subsheaf of F, when F∈OX-Mod satisfies certain conditions. Along the way, we present further results on the notions of “Noetherian” and “integral” for schemes over (C,⊗,1) that we believe to be of independent interest.

Influence of Phase Shift and Amplitude Ratio on the Principal Stresses and Directions in Multiaxial Fatigue Testing

The maximum values of normal and shear stresses are the basic parameters which influence directly the initiation and propagation of multiaxial fatigue cracks.Based on the above, the first part of the paper presents an analysis of principal stresses (normal and shear) in case of symmetrical tension-compression loadings with superimposed phase-shifted symmetrical torsion cycles. The influence of stress amplitude ratio and phase shift on the maximum (normal and shear) stresses and on the directions of the planes along which these act is analyzed and graphically represented using stress hodographs.The second part of the paper highlights the possibility of using the maximum value of the normal or shear stress as base parameter for durability studies under multiaxial fatigue, based on existing experimental data. The mentioned data is correlated with the results of an original experimental program carried out by the authors on 41Cr4 steel and conclusions are formulated with regard to the role of maximum shear stress in life-time calculation.

Multiaxial ratcheting-fatigue interaction on acrylonitrile-butadiene-styrene terpolymer

A series of multiaxial tests on an industrial acrylonitrile-butadiene-styrene (ABS) tube were conducted at room temperature. The ratcheting strain accumulation was found to be closely related to the shear strain amplitude and axial mean stress. The ratcheting strain and its rate increased with increasing shear strain amplitude as well as axial mean stress. At the same time, the ratcheting strain accumulation was retarded with a negative mean stress, and the ratcheting shakedown appeared when the negative mean stress reached −10 MPa. To understand the influences of loading history on axial ratcheting strain, a series of multistep loading tests under constant symmetrical torsion at different axial mean stresses of 5, 0, and −5 MPa were performed. The results showed that both the compressive viscous strain and strain relaxation of ABS could lead to the decrease of axial ratcheting strain. Furthermore, the compressive viscous strain and strain relaxation are independent of the loading history. Considering the influence of mean stress, a modified fatigue life model based on the Basquin law was presented to predict the pure torsional fatigue and multiaxial fatigue of ABS. The results of the modified fatigue life model show it can give relatively accurate fatigue life predictions. POLYM. ENG. SCI., 55:664–671, 2015. © 2014 Society of Plastics Engineers

The Influence of Fatigue Life for Shoulder Fillet Parameter in Stepped Shaft under Torsion Load

The principle of fatigue life computation was presented on the basis of local stress-strain method. It was set up that the finite element model of stepped shaft with different radii of round corner and radius ratios. The local stress and strain were computed at shaft shoulder fillet under torsion load. The fatigue crack initiation life was determined by means of local stress-strain method under symmetric cyclic torsion load. The result showed that the fatigue life increased with the values of fillet increase and decreased with the values of radius ratio increase, and the smaller of the transition radius was, the shorter of the life would be.

Experimental studies on high-cycle fatigue and damping properties of R2MA rotor steel in torsion

High-cycle fatigue curves in symmetrical torsion were plotted, the endurance limit–mean cycle stress relation was derived, and damping of torsional vibrations was evaluated by the results of R2MA rotor steel specimen testing.