Torsional Motion Research Articles

Charge-State Dependent Vibrational Relaxation in a Single-Molecule Junction.

The outcome of an electron-transfer process is determined by the quantum-mechanical interplay between electronic and vibrational degrees of freedom. Nonequilibrium vibrational dynamics are known to direct electron-transfer mechanisms in molecular systems; however, the structural features of a molecule that lead to certain modes being pushed out of equilibrium are not well understood. Herein, we report on electron transport through a porphyrin dimer molecule, weakly coupled to graphene electrodes, that displays sequential tunneling within the Coulomb-blockade regime. The sequential transport is initiated by current-induced phonon absorption and proceeds by rapid sequential transport via a nonequilibrium vibrational distribution of low-energy modes, likely related to torsional molecular motions. We demonstrate that this is an experimental signature of slow vibrational dissipation, and obtain a lower bound for the vibrational relaxation time of 8ns, a value dependent on the molecular charge state.

Development of nuclear fuel assembly 3D reduced model and modal analysis

Due to the geometric complexity of fuel assembly (FA), virtually all reactor dynamic analysis models incorporated drastically simplied FA by lumped mass and beam. Considering the rapid advances of computer technology and analysis software, improving reactor dynamic analysis by 3D model is now possible. As a first step toward this goal, this research investigates and attempts to develop a reduced 3D FA dynamic analysis model to assess more accurate and detailed dynamic response of FA. A modal analysis of a 3D FA model was developed and showed the responses of the FA. The model was tuned to the test results up to 4th modes which were the upper value of test results. The model showed 3D response of FA and revealed additional modes of dynamic behaviors such as torsional motion and composite of bending and torsional motion.

Flexural-torsional-coupled vibration analysis of Euler-Bernoulli beam by using the differential transform method

This study introduces an analytical solution method which is called the differential transform method (DTM) to analyze the free vibration response of a beam which features material coupling between flapwise bending and torsional vibrations. The governing differential equations of motion are solved by applying DTM. The mode shapes and the natural frequencies are obtained and plotted for bending and torsional behavior, separately. Application of the model solved by DTM is investigated for a typical cantilever aircraft wing when flexural and torsional motions are coupled and the bending-torsion coupling effect is ignored, separately, using a numeric computing environment, MATLAB.

Origami-Inspired Soft Twisting Actuator.

Soft actuators have shown great advantages in compliance and morphology matched for manipulation of delicate objects and inspection in a confined space. There is an unmet need for a soft actuator that can provide torsional motion to, for example, enlarge working space and increase degrees of freedom. Toward this goal, we present origami-inspired soft pneumatic actuators (OSPAs) made from silicone. The prototype can output a rotation of more than one revolution (up to 435°), more significant than its counterparts. Its rotation ratio ( = rotation angle/aspect ratio) is more than 136°, about twice the largest one in other literature. We describe the design and fabrication method, build the analytical model and simulation model, and analyze and optimize the parameters. Finally, we demonstrate the potentially extensive utility of the OSPAs through their integration into a gripper capable of simultaneously grasping and lifting fragile or flat objects, a versatile robot arm capable of picking and placing items at the right angle with the twisting actuators, and a soft snake robot capable of changing attitude and directions by torsion of the twisting actuators.

Benzothiazole-based Schiff bases as novel AIE(E)gens: Mechanistic insights into distinction between dimethylphenylamine and triphenylamine fragments in double bond-bridged D-A system

Excited-state torsional motions around single or double bond are crucial to the photophysical properties of double bond-bridged diaryl systems. However, the correlations between specific electronic and geometric setup and different types of photo-induced torsional motions remain elusive. In this article, five D-π-A type benzothiazole-based Schiff bases (BAMI-1−5) were synthesized and identified as AIE(E)gens with solid-state fluorescence quantum yields up to 76.5%. Detailed electronic structure/hole-electron analysis and potential energy curve scanning illustrate that electron-donating aniline fragments with different types of N-substituents such as dimethyl (BAMI-1) and diphenyl (BAMI-2) exert distinctive effects on their excitation and decay processes. In addition, crystallographic and computational results imply that the major factors for the redshifted AIE of BAMI Schiff bases may also be different and depend on their specific structures and excitation characters.

Periodical propagation of torsion in polymer gels

Gel actuators have potential in soft robotics. Although gel actuators can realize various motions like contraction, expansion, and bending, most require external inputs such as batteries and circuits. Herein we propose a periodical torsional motion hydrogel driven by chemical energy from the Belousov-Zhabotinsky (BZ) reaction. Our BZ gel system exhibits autonomous motion without a battery. The elastic moduli of the redox states of the BZ gel are investigated using stress–strain analysis. An experimental system, which integrates the BZ gel and two PDMS (dimethylpolysiloxane) rotators, is designed to evaluate torsion angles. The experimental pre-twist angle dependence of the rotary motion is compared with a theoretical rotation model. The results agree qualitatively. This study should contribute to the development of soft actuators without external components.

Detecting chiral asymmetry in the interstellar medium using propylene oxide

Context.Life is distinctly homochiral. The origins of this homochirality are under active debate. Recently, propylene oxide has been detected in the gas-phase interstellar medium (ISM). The enantiomeric composition of ISM propylene oxide may be probed through circular polarization measurements, but accurate estimates of the circular dichroism properties of the microwave transitions of propylene oxide are not available.Aims.Our aim is to develop a model of the circular dichroic activity in torsion–rotation transitions of closed-shell chiral molecules such as propylene oxide. With this model we can estimate the viability, and optimize the observation strategies, of enantiomeric excess detection in ISM propylene oxide.Methods.Circular dichroism in spectral lines manifests through the simultaneous interaction of an electromagnetic radiation field with the molecular electric dipole moment and magnetic dipole moment. We developed techniques to quantify electric dipole and magnetic dipole moments of torsion–rotation transitions by expanding on earlier modeling of the electric and magnetic dipole properties of single torsion–rotation levels. To model the circular dichroism properties of propylene oxide, we used these techniques in combination with ab initio quantum chemical calculations.Results.The expressions for the dichroic activity of the microwave transitions of torsionally active molecules are derived. We find that the torsional motion of molecules exhibiting internal rotation contributes significantly to the total magnetic moment. We present estimates for the dichroic activity of the torsion–rotation transitions of propylene oxide. We predict that the circular polarization fractions of emission lines of enantiopure propylene oxide relevant to astronomical detections are on the order of 10−6.Conclusions.Due to the low predicted circular polarization fractions, we conclude that enantiomeric characterization of propylene oxide in the gas phase of the ISM is impossible with the current astronomical observation techniques. We suggest that only chiral radical species may be viably employed for purposes of enantiomeric excess detection. We estimate that laboratory experiments may be successful in detecting the enantiomeric composition of a mixture of propylene oxide through microwave dichroism spectroscopy.

Analysis of vibration characteristics of stators of electrical machines under actual boundary

This paper presents a general method for the studies of the vibration characteristics of an electrical machine stator with encased construction under practical boundary conditions. In this paper, artificial springs are introduced at both ends of the stator, and arbitrary boundary conditions can be simulated by adjusting the spring stiffness, including the support conditions in practical applications of the stator. In order to cooperate with the solution of the vibration characteristics of the stator with arbitrary edges, the Gram-Schmidt method is employed to construct characteristic orthogonal polynomial series to simulate the mode shape functions under arbitrary boundary conditions. The analysis is based on the Novozhilov shell theory, which is more applicable to the construction and actual operating environment of stators of electric vehicle drive motors, and takes into account moment of inertia neglected in the past. Further, the effects of teeth, windings, frame and cooling ribs are incorporated in the analysis, and the teeth with complicated shapes are considered as longitudinal ribs of unlimited cross-section, with bending and torsional coupling motion and warping deformation considered. The Rayleigh-Ritz method is used to build a unified dynamic analysis model of the stator of an electric machine, which can provide information on the radial, circumferential and axial vibrations of the stator with higher time efficiency, and a series of comparison studies and experiments are performed to demonstrate the general validity and accuracy of the model. On this basis, the possibility of construction optimization of the stator is discussed to improve the vibration and noise performance while reducing the cost.

A Rattle Noise Severity Index for Multi-Mesh Gear Trains Subjected to Torque Fluctuations

AbstractExternal fluctuation torques acting on gear trains having clearances often cause vibro-impact motions with resultant rattle noise issues. In this study, an impact velocity-based rattle severity parameter that correlates with the resultant rattling noise is proposed for multimesh gear trains. An experimental setup is employed to measure torsional vibro-impact motions and the corresponding sound pressure levels of a three-axis gear train under various torque fluctuation conditions. A discrete torsional model of the experimental setup is developed and validated through comparisons to the vibration measurements. An impact velocity-based rattle severity index defined from the predicted response is proposed and shown to correlate well with the measured rattle noise sound pressure levels within a wide range of operating conditions. The demonstrated ability of the proposed rattle severity index in tracking rattle noise allows for the assessment of rattle consequences of a multimesh drivetrain solely from its predicted torsional response.

Self-Sensing WS2 Nanotube Torsional Resonators.

We demonstrate self-sensing tungsten disulfide nanotube (WS2 NT) torsional resonators. These resonators exhibit all-electrical self-sensing operation with electrostatic excitation and piezoresistive motion detection. We show that the torsional motion of the WS2 NT resonators results in a change of the nanotube electrical resistance, with the most significant change around their mechanical resonance, where the amplitude of torsional vibrations is maximal. Atomic force microscopy analysis revealed the torsional and bending stiffness of the WS2 NTs, which we used for modeling the behavior of the WS2 NT devices. In addition, the solution of the electrostatic boundary value problem shows how the spatial potential and electrostatic field lines around the device impact its capacitance. The results uncover the coupling between the electrical and mechanical behaviors of WS2 and emphasize their potential to operate as key components in functional devices, such as nanosensors and radio frequency devices.

Torsion in symmetric buildings due to soil‐structure interaction: A discussion on code values of accidental eccentricity factor in seismic design

AbstractSoil‐structure interaction (SSI) is often neglected in seismic design because of its inherent complexity. Therefore, SSI‐related research is crucial for ensuring that more significant issues reach engineering practice. This study focused on torsional motion to investigate the accidental eccentricity caused by SSI effect by comparing the proportional relationship between the torsional motion of an SSI system and the translational motion of a fixed‐base oscillator. The SSI model was created using a three‐dimensional rectangular foundation embedded in a layered half‐space with an oscillator mounted on the top. We employed an indirect boundary element method (IBEM) combined with non‐singular Green's functions of distributed loads to calculate the system responses of the SSI. Parametric analysis‐based results in the frequency domain revealed that the accidental eccentricity factor owing to SSI was typically in the range of 0.03–0.15. Additionally, a case study of four buildings subjected to 42 earthquakes revealed that the accidental eccentricity factor exceeded 0.05 in several cases, and 0.2 in some cases. Furthermore, it depended on the excitation spectral shape and dynamic characteristics of the SSI system. Therefore, the coded accidental eccentricity factor value of 0.05 is insufficient for ensuring the safety of buildings from the torsional effect of SSI, and a value of 0.1 is more reasonable.

Assessment of binocular fixational eye movements including cyclotorsion with split-field binocular scanning laser ophthalmoscopy

Fixational eye movements are a hallmark of human gaze behavior, yet little is known about how they interact between fellow eyes. Here, we designed, built and validated a split-field binocular scanning laser ophthalmoscope to record high-resolution eye motion traces from both eyes of six observers during fixation in different binocular vergence conditions. In addition to microsaccades and drift, torsional eye motion could be extracted, with a spatial measurement error of less than 1 arcmin. Microsaccades were strongly coupled between fellow eyes under all conditions. No monocular microsaccade occurred and no significant delay between microsaccade onsets across fellow eyes could be detected. Cyclotorsion was also firmly coupled between both eyes, occurring typically in conjugacy, with gradual changes during drift and abrupt changes during saccades.

Extension of the SMP, AFMP, and NADP procedures to one-way asymmetric-plan tall buildings

In this paper, the enhanced pushover procedures including the single-run multi-mode pushover (SMP), adaptive force-based multi-mode pushover (AFMP), and non-adaptive displacement-based pushover (NADP) procedures are extended to one-way asymmetric-plan tall building structures to consider both higher modes and torsional effects in predicting the seismic responses. For this purpose, the principles of modal response analysis for one-way asymmetric-plan buildings are employed. The SMP and NADP procedures are comprised of multiple single-run force-based and displacement-based pushover analyses, respectively, while, the AFMP procedure consists of some adaptive pushover analyses. Lateral loads as well as torsional moments calculated by modal analysis are employed in the single-run and adaptive pushover analyses. The seismic responses of the structure are finally computed by enveloping the seismic demands derived from the single-run pushover analyses in the SMP and NADP procedures, and from the adaptive ones in the AFMP procedure. In order to evaluate the accuracy of the extended procedures, two one-way asymmetric-plan buildings are studied. These buildings have various coupling degrees between translational and torsional motions. The seismic responses derived from the extended procedures are compared with those from the nonlinear response history analyses (NLRHA) as a benchmark method, and with those from the modal pushover analysis (MPA), consecutive modal pushover (CMP) procedure, and the conventional pushover analysis based on the first-mode. It is demonstrated that the SMP method predicts the seismic responses more accurately than the AFMP and NADP procedures for one-way asymmetric-plan tall buildings.

Molecular Zeeman interactions in NMR spectra of methyl groups.

Methyl groups in organic solids generally behave as uniaxial quantum rotors. The existing nuclear magnetic resonance (NMR) theory appears to be complete, capable of describing even the finest details of the temperature-dependent spectra of such objects. However, the once reported temperature effects in the carbon spectra of the C13-labeled methyl group in a single crystal of acetylsalicylic acid have still not been explained. As the temperature decreases, in the quartet corresponding to the rapid motional averaging regime, the inner lines first begin to broaden, but then, they narrow again, so that at 6K, a pattern similar to that at room temperature was observed. In the present work, these puzzling effects are explained quantitatively by invoking the molecular Zeeman (MZ) interaction. Like the spin-rotation (SR) interaction long known to occur in methyl groups, it engages the magnetic moments generated by their torsional motions. However, it has not been considered in NMR spectroscopy until now. This is a surprising situation because in the magnetic fields currently used in NMR spectroscopy, the MZ interaction is orders of magnitude stronger than the (magnetic field independent) SR effects.

Flutter control of truss-type suspension bridges with a tuned mass damper based on the mass polar moment of inertia's optimum configuration

In suspension bridges, flutter is the primary source of instability, commonly controlled by a tuned mass damper (TMD). In torsional motions, such as flutter, the shape of the mass block, indicating its distribution around the torsion axis, is critical; indeed, an optimal distribution results in a more effective and lighter device. The flutter analysis of the Vincent Thomas suspension bridge was performed using the multi-mode method in this article. Then, a new optimal configuration was used to avoid it; in addition to common parameters such as mass ratio, damping ratio, and frequency ratio, a set of parameters called shape variables was also considered. These parameters take into account the manner in which mass is distributed around the torsion axis. The performance of the aforementioned configuration was compared to that of the other recommended TMD configurations. Additionally, a general formulation of TMD was represented, which included the other configurations. Finally, the effectiveness of TMD was evaluated in comparison to other control systems. The results indicated that the optimal configuration was reliable and that it reduced the mass ratio by up to 0.2 percent by optimizing its distribution around the torsion axis compared to other existing configurations.

Quantum Calculations on a New CCSD(T) Machine-Learned Potential Energy Surface Reveal the Leaky Nature of Gas-Phase Trans and Gauche Ethanol Conformers.

Ethanol is a molecule of fundamental interest in combustion, astrochemistry, and condensed phase as a solvent. It is characterized by two methyl rotors and trans (anti) and gauche conformers, which are known to be very close in energy. Here we show that based on rigorous quantum calculations of the vibrational zero-point state, using a new ab initio potential energy surface (PES), the ground state resembles the trans conformer, but substantial delocalization to the gauche conformer is present. This explains experimental issues about identification and isolation of the two conformers. This “leak” effect is partially quenched when deuterating the OH group, which further demonstrates the need for a quantum mechanical approach. Diffusion Monte Carlo and full-dimensional semiclassical dynamics calculations are employed. The new PES is obtained by means of a Δ-machine learning approach starting from a pre-existing low level density functional theory surface. This surface is brought to the CCSD(T) level of theory using a relatively small number of ab initio CCSD(T) energies. Agreement between the corrected PES and direct ab initio results for standard tests is excellent. One- and two-dimensional discrete variable representation calculations focusing on the trans–gauche torsional motion are also reported, in reasonable agreement with experiment.

A joint experimental and theoretical study of the valence electron momentum distributions of trans-stilbene

This paper reports an experimental and theoretical study on the valence orbital momentum distributions of trans-stilbene. Experimentally, an (e, 2e) electron-impact ionization measurement is performed to obtain momentum profiles of the outer valence orbitals. Theoretically, calculations of the momentum profiles are carried out at the level of density functional theory, including the influences of thermally induced torsional motions of phenyl rings as well as contributions from other vibrational modes. The theoretical analysis shows that despite the structural flexibility of trans-stilbene, molecular vibration does not significantly affect the momentum profiles. The experimental results for the high-lying occupied π orbitals reveal that the position of the maximum in each momentum profile reflects the bonding character of the corresponding orbital. It provides a basis to apply electron momentum spectroscopy to large π-conjugated molecules, such as oligomers of conducting polymers.

A Code-Type Method to Assess the Running Safety of Railway Vehicles on Bridges Shaken by Earthquakes Including Girder’s Torsional Motion

The safety of railway vehicles running on bridges needs to be evaluated in the seismic design of bridges. This study examined the spectral intensity calculated from the lateral vibration of the bridge deck during earthquakes, a Japanese code-based index to measure bridge vibration’s strength. In addition, the effect of the torsion of the bridge deck on vehicle derailment is investigated using a nonlinear vehicle–track–bridge model. The bridge deck torsion increases the derailment risk, especially for bridges with a low natural frequency. The reason lies in that the lateral and torsional deck motions are highly correlated for bridges with lower frequency. Based on this observation, a code-type formula was proposed to evaluate the vehicle running safety including both lateral and torsional motions of the bridge deck. The accuracy of the proposed formula was demonstrated by comparison with vehicle–track–bridge simulation excited by ground motion records. The new procedure overcomes the non-conservative assessment of derailment caused by ignoring bridge torsion.

Dexterity Analysis and Motion Optimization of In-Situ Torsionally-Steerable Flexible Surgical Robots

Flexible robots with <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-situ</i> torsion can be used in laryngeal endoscopic surgery which can maintain the position and approach vector of the end-effector during the operation. However, the inherent errors would be produced by <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-situ</i> torsional motion which are different due to the various configuration of serpentine module in robot. In this letter, the kinematic model is established according to the structure of serpentine module. The dexterity analysis shows that the singular position is reduced and the angular velocity of dexterity is improved comparing with the robot without <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-situ</i> torsion function. The theoretical position errors caused by <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-situ</i> torsion is quantitatively analyzed by simulation. It is found that the maximum error is 5.19 mm at the bending angle of 120 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${^\circ }$</tex-math></inline-formula> . In addition, the existence of joints in the robot arm also leads to the occurrence of rotation errors. The configuration and number of the joints are optimized to improve the accuracy. Finally, the experiments are carried out to verify the effectiveness of the proposed design and the model. The results indicate that the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in-situ</i> torsionally steerable flexible robots have higher motion dexterity, its inherent error during the in-situ torsion motion can be eliminated by structural optimization.

Insight into the addition of multi-walled carbon nanotubes to dynamics of water conveying single surface carbon nanotubes due to torsional motion of cylinder subject to Lorentz force and joule heating

Hybrid nanofluid is deployed to optimize the heat transfer features of an axisymmetric magnetohydrodynamic (MHD) flow exterior to a rotating cylinder. Hybrid nanofluids contain composite nanoparticles, which improve thermal conductivity. Here, two distinct particles single and multi-walled carbon nanotubes (CNTs) are taken and mixed to form hybrid nanoparticles, and water is taken as the working fluid. The energy transport phenomenon is examined by incorporating the Joule heating effect. The axial pressure gradient is generated as a consequence of the torsional motion of the cylinder, which results in the wall jet phenomenon on the axial axis. The governing equations are transformed into an ordinary differential system in view of the similarity group. The numerical approach bvp4c is employed to solve the problem. The graphical results for flow and thermal energy transport with a comparison of nanofluid and hybrid nanofluid are analyzed. The axial component of velocity escalates by augmenting Reynolds number, while the azimuthal components of velocity and thermal profile decline. Moreover, the numerical outcomes of wall stresses and Nusselt number enhance for higher Reynolds number. The temperature field declines by increasing the Prandtl number because of less thermal diffusivity.