Torsional Dependence Research Articles

Searching for dark torsion signatures at LIGO in Nieh–Yan teleparallel chiral gravitational waves and Chern–Simons invariants

Romano has recently found that frequency modulation of gravitational waves (GWs) could be used as a dark matter probe. Many candidates for dark matter (DM) of various sources have been proposed in the literature. In this work, we use a teleparallel modified GW model to obtain DM dark torsion from LIGO data, where frequency modulation and frequency bands from various sources of GWs are investigated with regard to their suitability for DM dark torsion detection. In particular, nonhomogeneous and nonuniform chiral chemical potential generates GWs and dark torsion from primordial magnetic fields. It is shown that pulsar sources for GWs bathing the surface of the Earth on a contortion background of 10-15s-1 possess amplitudes well within the parameters of LIGO capabilities of amplitudes on the order of 10-22. GWs are also investigated in the context of having been produced by a primordial magnetic field and inhomogeneity on the chiral chemical potential. The torsion signatures at LIGO correspond to the amplitude dependence of massive torsion by GWs.

Length and torsion dependence of thermal conductivity in twisted graphene nanoribbons

Length and torsion dependence of thermal conductivity in twisted graphene nanoribbons

Chromatinization modulates topoisomerase II processivity

Type IIA topoisomerases are essential DNA processing enzymes that must robustly and reliably relax DNA torsional stress. While cellular processes constantly create varying torsional stress, how this variation impacts type IIA topoisomerase function remains obscure. Using multiple single-molecule approaches, we examined the torsional dependence of eukaryotic topoisomerase II (topo II) activity on naked DNA and chromatin. We observed that topo II is ~50-fold more processive on buckled DNA than previously estimated. We further discovered that topo II relaxes supercoiled DNA prior to plectoneme formation, but with processivity reduced by ~100-fold. This relaxation decreases with diminishing torsion, consistent with topo II capturing transient DNA loops. Topo II retains high processivity on buckled chromatin (~10,000 turns) and becomes highly processive even on chromatin under low torsional stress (~1000 turns), consistent with chromatin’s predisposition to readily form DNA crossings. This work establishes that chromatin is a major stimulant of topo II function.

A generalization of analytic torsion via differential forms on spaces of metrics

We introduce multi-torsion, a spectral invariant generalizing Ray–Singer analytic torsion. We define multi-torsion for compact manifolds with a certain local geometric product structure that gives a bigrading on differential forms. We prove that multi-torsion is metric-independent in a suitable sense. Our definition of multi-torsion is inspired by an interpretation of each of analytic torsion and the eta invariant as a regularized integral of a closed differential form on a space of metrics on a vector bundle or on a space of elliptic operators. We generalize the Stokes’ theorem argument explaining the dependence of torsion and eta on the geometric data used to define them to the local product setting to prove our metric-independence theorem for multi-torsion.

GAWBS noise correlation between cores in multi-core fibers

We describe experimental and analytical results regarding the guided acoustic-wave Brillouin scattering (GAWBS) noise correlation between cores in a multi-core fiber. First, we evaluated the GAWBS phase noise correlation between cores in an uncoupled four-core fiber (4CF) spaced at equal intervals of 90 degrees. We clarified that there are strong correlations in the TR2,m and TR4,m modes because the profile of the TR n ,m mode has a torsional dependence given by cos(nθ) and sin(nθ). In contrast, the TR3,m modes showed a strong correlation in an uncoupled 19-core fiber (19CF) with a hexagonal close-packed structure since a strong interaction occurs where the cores are arranged at 60 degrees from each other. We also clarified that the correlation strength of the TR3,m mode depends on the distance of the core from the fiber center because the amplitude of the TR3,m mode changes in a radial direction.

Matteucci Effect and Single Domain Wall Propagation in Bistable Microwire under Applied Torsion

Systematic experimental results on the Matteucci effect in torsioned magnetostrictive FeSiB microwire are introduced, observed during the propagation of a single domain wall (DW) under the action of axial driving magnetic field, Hdr. These data are discussed, reviewing current bibliography models and proposing new perspectives. The unidirectional DW velocity is quantified by voltage induced in tiny pickup coils along the microwire. The Matteucci electromotive force (emf) induced between the microwire's ends is associated with depinning and annihilation of the DW, introducing a new method to measure DW velocity. The emf amplitude is proportional to the DW velocity and the time derivative of the azimuthal magnetization, tailored by applied torsion. The data confirm the existence of net values of azimuthal magnetization and spontaneous torsion induced during fabrication. The clockwise/counterclockwise applied torsion dependence of Matteucci emf and DW velocity are experimentally determined for parallel and antiparallel Hdr. Asymmetric behaviors are observed for both, the sense of applied torsion and the direction of Hdr. The experimental data are discussed in terms of the magnetoelastic anisotropy introduced by torsion. Through analysis of the DW dynamics, such asymmetric behaviors are interpreted as a magnetochiral effect derived from the change of chirality of the propagating wall.

Coupling of torsion and OH-stretching in tert-butyl hydroperoxide. II. The OH-stretching fundamental and overtone spectra.

The vibrational spectra of gas phase tert-butyl hydroperoxide have been recorded in the OH-stretching fundamental and overtone regions (ΔvOH = 1-5) at room temperature using conventional Fourier transform infrared (ΔvOH = 1-3) and cavity ring-down (ΔvOH = 4-5) spectroscopy. In hydroperoxides, the OH-stretching and COOH torsion vibrations are strongly coupled. The double-well nature of the COOH torsion potential leads to tunneling splitting of the energy levels and, combined with the low frequency of the torsional vibration, results in spectra in the OH-stretching regions with multiple vibrational transitions. In each of the OH-stretching regions, both an OH-stretching and a stretch-torsion combination feature are observed, and we show direct evidence for the tunneling splitting in the OH-stretching fundamental region. We have developed two complementary vibrational models to describe the spectra of the OH-stretching regions, a reaction path model and a reduced dimensional local mode model, both of which describe the features of the vibrational spectra well. We also explore the torsional dependence of the OH-stretching transition dipole moment and show that a Franck-Condon treatment fails to capture the intensity in the region of the stretch-torsion combination features. The accuracy of the Franck-Condon treatment of these features improves with increasing ΔvOH.

Spectroscopic Signatures of Resonance Inhibition Reveal Differences in Donor-Bridge and Bridge-Acceptor Couplings.

The torsional dependence of the ground state magnetic exchange coupling (J) and the corresponding electronic coupling matrix element (HDA) for eight transition metal complexes possessing donor-acceptor (D-A) biradical ligands is presented. These biradical ligands are composed of an S = 1/2 metal semiquinone (SQ) donor and an S = 1/2 nitronylnitroxide (NN) acceptor, which are coupled to each other via para-phenylene, methyl-substituted para-phenylenes, or a bicyclo[2.2.2]octane ring. The observed trends in electronic absorption and resonance Raman spectral features are in accord with a reduction in electronic and magnetic coupling between D and A units within the framework of our valence bond configuration interaction model. Moreover, our spectroscopic results highlight different orbital mechanisms that modulate coupling in these complexes, which is not manifest in the ferromagnetic JSQ-B-NN values. The work provides new detailed insight into the effects of torsional rotations which contribute to inhomogeneities in experimentally determined exchange couplings, electron transfer rates, and electron transport conductance measurements.

Noether current, black hole entropy and spacetime torsion

We show that the presence of spacetime torsion, unlike any other non-trivial modifications of the Einstein gravity, does not affect black hole entropy. The theory being diffeomorphism invariant leads to a Noether current and hence to a Noether charge, which can be associated to the heat content of the spacetime. Furthermore, the evolution of the spacetime inheriting torsion can be encoded in the difference between suitably defined surface and bulk degrees of freedom. For static spacetimes the surface and bulk degrees of freedom coincides, leading to holographic equipartition. In doing so one can see that the surface degrees of freedom originate from horizon area and it is clear that spacetime torsion never contributes to the surface degrees of freedom and hence neither to the black hole entropy. We further show that the gravitational Hamiltonian in presence of torsion does not inherit any torsion dependence in the boundary term and hence the first law originating from the variation of the Hamiltonian, relates entropy to area. This reconfirms our claim that torsion does not modify the black hole entropy.

Quantitative Theoretical Predictions and Qualitative Bonding Analysis of the Divinylborinium System and Its Al, Ga, In, and Tl Congeners.

A substituted divinylborinium cation was synthesized recently and characterized crystallographically as a gauche structure with a 153° C1-C2-C3-C4 dihedral angle. A full theoretical geometrical optimization of the bis(2-mesityl-1,2-diphenylvinyl)-borane cation shows excellent agreement with the crystal structure. However, for the parent unsubstituted divinylborinium cation, we predict a nearly 90° C1-C2-C3-C4 dihedral angle using the CCSD(T)/cc-pVTZ coupled cluster method. The cis and trans planar geometries (0° and 180° for the C1-C2-C3-C4 dihedral angle) proved to be transition states with energy barriers of 2.8 and 2.3 kcal/mol, respectively, with respect to unimolecular conversion to the gauche equilibrium. The structures of the heavier boron group cations (Al, Ga, In, and Tl) have also been investigated here, finding even lower energy barriers (0.3-0.7 kcal/mol). After the ZPVE corrections, the barriers are further decreased. The torsional angles for the unknown Al, Ga, In, and Tl dimesityl substituted compounds should be somewhat less than 153°. Many of these findings may be understood in terms of qualitative electronic structure theory. The torsional folding of borane complex, including cationic divinylborinium and elementary vinylborane (C2H3BH2) or chlorovinylborane (C2H3BHCl) precursors, are investigated with natural bond orbital (NBO) analysis to unveil the electronic origins of the torsional properties. The NBO-based descriptors are employed to systematically deconstruct complex torsional dependence into a balanced portrayal of hyperconjugative and steric effects.

Torsional Dependence of the Critical Current in 2G Tapes

Since the second-generation (2G) superconducting wires started to be produced in a large scale almost a decade ago, the quality of the materials manufactured has been continually improved. Every year, the manufacturers present new materials with better electrical properties, increasing the critical current density, critical magnetic field, and the total length produced with continuous homogeneity. The mechanical properties of the coated conductor should be taken into account since electro-dynamical forces appear in working conditions as stress in the cooling and heating processes. In applications such as fault-current limiters, superconducting magnetic energy storage, transformers, electromagnets, motors, cables, etc., the consideration of them is mandatory to the project of those devices. In this context, this paper studies the electrical and mechanical properties of 12-mm 2G wires samples under torsion without axial tension. Critical current is measured as a function on the torsion angle. Details of the experiment and their results are here presented.

Rotation/Torsion Coupling in H5(+), D5(+), H4D(+), and HD4(+) Using Diffusion Monte Carlo.

Two methods for studying the rotation/torsion coupling in H5(+) are described. The first involves a fixed-node treatment in which the nodal surfaces are obtained from a reduced dimensional calculation in which only the rotations of the outer H2 groups are considered. In the second, the torsion and rotation dependence of the wave function is described in state space, and the other internal coordinates are described in configuration space. Such treatments are necessary for molecules, like H5(+), where there is a very low-energy barrier to internal rotation. The results of the two approaches are found to be in good agreement with previously reported energies for J = 0. The diffusion Monte Carlo treatment allows us to extend the calculations to low J, and results are reported for the three lowest energy torsion excited states with J ≤ 3. For the level of rotational and vibrational excitation investigated, only modest changes in the vibrational wave functions are found. The effects of deuteration are also investigated, focusing on D5(+) and the symmetric variants of H4D(+) and HD4(+).

Determining the Conformational Landscape of σ and π Coupling Using para-Phenylene and "Aviram-Ratner" Bridges.

The torsional dependence of donor-bridge-acceptor (D-B-A) electronic coupling matrix elements (H(DA), determined from the magnetic exchange coupling, J) involving a spin SD = 1/2 metal semiquinone (Zn-SQ) donor and a spin S(A) = 1/2 nitronylnitroxide (NN) acceptor mediated by the σ/π-systems of para-phenylene and methyl-substituted para-phenylene bridges and by the σ-system of a bicyclo[2.2.2]octane (BCO) bridge are presented and discussed. The positions of methyl group(s) on the phenylene bridge allow for an experimentally determined evaluation of conformationally dependent (π) and conformationally independent (σ) contributions to the electronic and magnetic exchange couplings in these D-B-A biradicals at parity of D and A. The trend in the experimental magnetic exchange couplings are well described by CASSCF calculations. The torsional dependence of the pairwise exchange interactions are further illuminated in three-dimensional, "Ramachandran-type" plots that relate D-B and B-A torsions to both electronic and exchange couplings. Analysis of the magnetic data shows large variations in magnetic exchange (J ≈ 1-175 cm(-1)) and electronic coupling (H(DA) ≈ 450-6000 cm(-1)) as a function of bridge conformation relative to the donor and acceptor. This has allowed for an experimental determination of both the σ- and π-orbital contributions to the exchange and electronic couplings.

Velocity and forced excitation effects on atomic friction force with deformable substrate

We have investigated the effect of scan velocity on atomic friction force in a Prandtl–Tomlinson model at finite temperature. We use a nonsinusoidal substrate potential with variable shape to capture surface features. The velocity dependence of atomic friction force is classified into two regimes: thermal and athermal regimes. We numerically find turning velocity between these two regimes, and its shape parameter dependence is determined. Furthermore, we have studied the torsional oscillation effect on a cantilever. We show that friction force can be reduced by controlling the frequency and the amplitude of the superimposed torsional oscillation at low scan velocity. The numerical calculations have shown that the substrate shape strongly affects the occurrence of resonances, so the torsional resonance frequency dependence of the shape parameter is established.

Torsional angle dependence and switching of inner sphere reorganisation energies for electron and hole transfer processes involving phenyl substituted diketopyrrolopyrroles; a density functional study

Determination of inner sphere reorganisation energies is important in the development of organic charge mediating materials and electron transfer reactions. In this study, hole and electron inner sphere reorganisation energies, λh and λe respectively, have been computed for the first time for a series of structurally related diketopyrrolopyrrole (DPP) molecular motifs. Inner sphere reorganisation energies for self-exchange electron transfer reactions are calculated as being lower than those associated hole transfer processes in model planar phenyl and thiophenyl substituted DPP systems. It is found that λe < λh for all planar ring/DPP core structures examined. The effect on λh/e of non-planarity between phenyl substituents and DPP core is explored in detail. The relative ordering of λh and λe is dependent upon the torsional angle of phenyl rings and reverses at twist angles of greater than 60° such that λe > λh.

Natural bond orbital/natural J-coupling study of vicinal couplings.

NBO-NJC decomposition of vicinal (3)J HH spin-spin coupling constants into Lewis, delocalization, and repolarization contributions are presented. A deep study allows to assign the main contributions to specific orbitals or electron delocalizations between two orbitals. (3)J HH torsional dependence and the substituent effect are analyzed according to the main orbital contributions for ethane and fluoroethane molecules using different basis sets. The torsional dependence for the energies corresponding to electron delocalization is also studied.

Chain length and torsional dependence of exciton binding energies in P3HT and PTB7 conjugated polymers: A first-principles study

Exciton binding energies (Eb) in promising organic photovoltaic (OPV) materials, specifically in poly(3-hexylthiophene) (P3HT) and thieno[3,4-b]thiophene-alt-benzodithiophene copolymer (PTB7) are investigated using density functional theory (DFT) and time-dependent DFT methods at the molecular level. A systematic investigation of the dependence of Eb on backbone torsion and chain length in P3HT and PTB7 is carried out by calculating the fundamental gap (Egfund), HOMO–LUMO gap (Eghl) and optical gap (Egopt) of these systems. We found that PTB7 has lower Egfund,Eghl,Egopt and Eb that are less-dependent on torsional angle compared to P3HT. These findings indicate that excitons are easily dissociated to produce charge carriers in PTB7 than in P3HT and hence supports recent experimental findings that PTB7-based OPV devices with improved active layer morphology have much higher power conversion efficiency than the most investigated P3HT-based OPV devices.

Breakup and then makeup: a predictive model of how cilia self-regulate hardness for posture control

Functioning as sensors and propulsors, cilia are evolutionarily conserved organelles having a highly organized internal structure. How a paramecium's cilium produces off-propulsion-plane curvature during its return stroke for symmetry breaking and drag reduction is not known. We explain these cilium deformations by developing a torsional pendulum model of beat frequency dependence on viscosity and an olivo-cerebellar model of self-regulation of posture control. The phase dependence of cilia torsion is determined, and a bio-physical model of hardness control with predictive features is offered. Crossbridge links between the central microtubule pair harden the cilium during the power stroke; this stroke's end is a critical phase during which ATP molecules soften the crossbridge-microtubule attachment at the cilium inflection point where torsion is at its maximum. A precipitous reduction in hardness ensues, signaling the start of ATP hydrolysis that re-hardens the cilium. The cilium attractor basin could be used as reference for perturbation sensing.

Torsion sensor based on the coil-less fluxgate effect

The torsion dependence of the coil-less fluxgate properties of amorphous (Co0.94Fe0.06)72.5Si12.5B15 wire was investigated. The results show that the second harmonic of the output voltage from the wire ends, Uwire, varied linearly at the ±30π rad/m torsion range for as-cast wire and ±5π rad/m torsion range for annealed wire. It was also found that if the sample was annealed at higher torsion, the curve shifted negatively or positively depending on the direction of torsion applied during the annealing. Most importantly, the output signal changed its sign as the direction of external torsion reversed, and therefore the proposed torsion sensor could detect whether torsion was in the negative or positive (clockwise or anti-clockwise) direction.

Torsional instability of chiral carbon nanotubes

In this work we investigate the presence of a torsional instability in single-wall carbon nanotubes which causes small diameter chiral carbon nanotubes to show natural torsion. To obtain insight into the nature of this instability, the natural torsion is calculated using an extended tight-binding model and is found to decrease as the inverse cube of the diameter. The dependence of the natural torsion on chiral angle is found to be different for metallic and semiconducting nanotubes, specially for near-armchair nanotubes, for which the behavior of semiconducting nanotubes deviates from the simple $\text{sin}(6\ensuremath{\theta})$ behavior observed for metallic nanotubes. The presence of this natural torsion implies a revision of the calculation of the chiral angle of the nanotubes.