Twisted Surface Research Articles

A Theoretical Study on Charge Transfer of Twisted T-Graphene Nanoribbon Surface

Non-equilibrium Green’s functions (NEGF) combined with tight-binding (TB) model, are utilized to study the charge transport properties of the twisted armchair tetragonal-graphene nanoribbons (ATGNRs). The present work has considered twisted deformation of ATGNR for the different angles. The results revealed that the action of twisting leads to an outstanding effect on the charge transport features of a T-graphene device. It will be stated that bandstructure is reduced by increasing the width of ATGNR. Moreover, I-V characteristics are carefully illustrated and it is proved that the electronic conduction becomes gradually stronger with the twisted angle increasing from 0° to 360° angles. Bandstructure of electrodes, Density of states (DOS), transmission spectrum, the molecular projected self-consistent Hamiltonian (MPSH) and I-V characteristics are discussed thus making the charge transport properties of ATGNR devices elucidated. The obtained results can provide a valuable guideline for designing of T-graphene nanoribbons in developing nano-scale devices.

Structure and Ligand-Binding Properties of the O Antigen ABC Transporter Carbohydrate-Binding Domain

A hallmark of Gram-negative bacteria is an asymmetric outer membrane containing lipopolysaccharides (LPSs) in the extracellular leaflet. LPS molecules consist of lipid A, which is connected to the inner and outer core oligosaccharides. This LPS core structure is extended in the periplasm by the O antigen, a variable and serotype-defining polysaccharide. In the ABC transporter-dependent LPS biosynthesis pathway, the WzmWzt transporter secretes the complete O antigen across the inner membrane for ligation to the LPS core. In some O antigen transporters, the nucleotide-binding domain of Wzt is fused C-terminally to a carbohydrate-binding domain (CBD) that interacts with the O antigen chain. Here, we present the crystal structure of the Aquifex aeolicus CBD that reveals a conserved flat and a variable twisted jelly-roll surface. The CBD dimer is stabilized by mutual β strand exchange. Microbial glycan array binding studies with the isolated CBD provide insights into its interaction with complex carbohydrates.

Chirality Induces the Self-Assembly To Generate a 3D Porous Spiral-like Polyhedron as Metal-Free Electrocatalysts for the Oxygen Reduction Reaction.

The sluggish kinetics and large overpotential of the oxygen reduction reaction (ORR) severely limit the widespread production and application of metal-air batteries. Herein, a conductive three-dimensional (3D) porous spiral-like polyhedron structure composed of nitrogen-doped carbon nanosheets (L/D-SPNC) was utilized as catalysts with combination of 3D hierarchical porous properties and distinguishing intrinsic properties of two-dimensional (2D) nanosheets for ORR. The chiral template, l/d-tartaric acid, induces the self-assembly of the supramolecule and the formation of an orderly array of carbon with spiral-like surface feature on a molecular scale. The resulting L/D-SPNC exhibits a small wall thickness (2.5 nm), large specific surface area (2034.2 m2/g), and high conductivity (155.76 S/m), which indicates that the properties of 2D nanosheets building blocks are kept in 3D mode. As catalysts for ORR, the optimized L-SPNC-950-1 exhibits a more positive onset potential of 1.03 V compared with those of Pt/C (1.00 V) and a half-wave potential of 0.87 V is also comparable to those of Pt/C (0.87 V). Al-air battery discharge data demonstrate that the spiral-like structure facilitates the diffusion of the electrolyte and oxygen on a three-phase interface, causing weak polarization. Density functional theory (DFT) calculations prove that the twisted surface aggravates the differential charge distribution between C-C/C-N bonds.

Twisted Surface Plasmons with Spin‐Controlled Gold Surfaces

AbstractTwisted photon, associated with orbital angular momentum (OAM), is a physical notion that has long captivated the intriguing imagination and wide applications. Owing to the native orthogonality between different topological charges of the vortices, it will be of significant value to generate, access, and discriminate the vortex on integrated chips. Archimedean spirals or multiple split gratings are commonly employed to generate OAMs on plasmonic films. However, the single‐crystalline plasmonic surface sets a very stringent condition of probing the on‐chip OAM dynamics at sub‐femtosecond scale. In previous reports, spins of the incident light and actual topological charge of the on‐chip OAM generator are also hybridized due to the intrinsic spin‐to‐orbital angular momentum conversion, making the direct discrimination of plasmonic vortex impossible. Here, a paradigm of generating twisted surface plasmons is presented in a fully spin‐controlled fashion. With the two‐photon photoemission electron microscopy, the dynamics of OAM formation is demonstrated at subwavelength spatial resolution and sub‐femtosecond temporal resolution simultaneously, revealing its OAM‐dependent angular velocity. In addition, this scheme of twisting on‐chip plasmons shows that the challenging crystalline requirement of the thin film can be significantly alleviated. The results open up a distinct way to multiplex, record, and read the information with plasmons.

A new passive control technique for the suppression of vortex-induced motion in deep-draft semisubmersibles

The control of vortex-induced motion (VIM) of deep-draft semisubmersibles has recently emerged as a serious concern in offshore semisubmersible platforms subjected to high ocean currents. With the increased draft of semisubmersibles, the coherent wake vortex fields behind the multi-column platforms become quite significant, which increase the impact of the coupled fluid-structure dynamics on the platform motion. In particular, the effective mitigation of the synchronization of wake vortices in a deep-draft semisubmersible is important for the reliable station-keeping and to extend the fatigue life of risers and mooring systems. The present study aims at the development of a passive control technique for the vortex synchronization of deep-draft semisubmersibles (DDS) via continuous cross-sectional twisting of the rounded square column along the spanwise direction. The computations are performed using a hybrid URAN-LES turbulence model based on the finite volume method. A validation study of the numerical results is performed with the available experimental data for the stationary and vibrating configurations of deep-draft semisubmersible. To begin, we first examine the VIM performance of a single column of the semisubmersible with a twisted angle of 45 °. We next examine the design of twisted column to understand its effect on the vorticity dynamics and the VIM response characteristics. In comparison to the untwisted square-column configuration, the twisted column produces the reduction in the transverse (sway) VIM amplitude up to 90% at the peak lock-in condition. The streamwise (surge) amplitude for the twisted-column semisubmersible is also found to be reduced by approximately 1/3 of the amplitude of the square-column counterpart. The twisted surface on the column results in a continuous spanwise (column-wise) variation of the shear-layer separation points. The three-dimensional (3D) variation of separation lines and the pressure distribution along the twisted and the square columns are analyzed to understand the underlying mechanism of the VIM suppression. We find that the modification of vortex shedding due to the variation in the separation line along the twisted column significantly influences the mean and fluctuating hydrodynamic forces. We extend the twisted column concept to the deep-draft semisubmersibles and demonstrate its effectiveness to produce a remarkable degree of VIM suppression. We explore the effects of the orientation of twisted columns and the incidence angle of the oncoming flow and present the 3D wake vortex structures and the motion histories of the DDS configuration.

Cobalt–Nitrogen‐Doped Helical Carbonaceous Nanotubes as a Class of Efficient Electrocatalysts for the Oxygen Reduction Reaction

AbstractThe oxygen reduction reaction (ORR) is of significant importance in the development of fuel cells. Now, cobalt–nitrogen‐doped chiral carbonaceous nanotubes (l/d‐CCNTs‐Co) are presented as efficient electrocatalysts for ORR. The chiral template, N‐stearyl‐l/d‐glutamic acid, induces the self‐assembly of well‐arranged polypyrrole and the formation of ordered graphene carbon with helical structures at the molecular level after the pyrolysis process. Co was subsequently introduced through the post‐synthesis method. The obtained l/d‐CCNTs‐Co exhibits superior ORR performance, including long‐term stability and better methanol tolerance compared to achiral Co‐doped carbon materials and commercial Pt/C. DFT calculations demonstrate that the charges on the twisted surface of l/d‐CCNTs are widely separated; as a result the Co atoms are more exposed on the chiral CCNTs. This work gives us a new understanding of the effects of helical structures in electrocatalysis.

Cobalt–Nitrogen‐Doped Helical Carbonaceous Nanotubes as a Class of Efficient Electrocatalysts for the Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is of significant importance in the development of fuel cells. Now, cobalt-nitrogen-doped chiral carbonaceous nanotubes (l/d-CCNTs-Co) are presented as efficient electrocatalysts for ORR. The chiral template, N-stearyl-l/d-glutamic acid, induces the self-assembly of well-arranged polypyrrole and the formation of ordered graphene carbon with helical structures at the molecular level after the pyrolysis process. Co was subsequently introduced through the post-synthesis method. The obtained l/d-CCNTs-Co exhibits superior ORR performance, including long-term stability and better methanol tolerance compared to achiral Co-doped carbon materials and commercial Pt/C. DFT calculations demonstrate that the charges on the twisted surface of l/d-CCNTs are widely separated; as a result the Co atoms are more exposed on the chiral CCNTs. This work gives us a new understanding of the effects of helical structures in electrocatalysis.

Direct Observation of Twisted Surface skyrmions in Bulk Crystals.

Magnetic skyrmions in noncentrosymmetric helimagnets with D_{n} symmetry are Bloch-type magnetization swirls with a helicity angle of ±90°. At the surface of helimagnetic thin films below a critical thickness, a twisted skyrmion state with an arbitrary helicity angle has been proposed; however, its direct experimental observation has remained elusive. Here, we show that circularly polarized resonant elastic x-ray scattering is able to unambiguously measure the helicity angle of surface skyrmions, providing direct experimental evidence that a twisted skyrmion surface state also exists in bulk systems. The exact surface helicity angles of twisted skyrmions for both left- and right-handed chiral bulk Cu_{2}OSeO_{3}, in the single as well as in the multidomain skyrmion lattice state, are determined, revealing their detailed internal structure. Our findings suggest that a skyrmion surface reconstruction is a universal phenomenon, stemming from the breaking of translational symmetry at the interface.

Suppression of vortex-induced vibration of a square cylinder via continuous twisting at moderate Reynolds numbers

Vortex-induced vibration (VIV) of elastic structures with a square-shaped prismatic column exposed to flow has a significant impact on many aspects of structural design and stability. The main aim of the present numerical study is to investigate an alternative design of square column for minimizing the impact of VIV on the elastic structures. The numerical study is carried out at moderate Reynolds numbers (1000 ≤ Re ≤ 22000). For both stationary and freely vibrating square cylinders, a systematic validation of the numerical results is performed with the available experimental data. In particular, various turbulence models are explored to assess their effectiveness to capture the separated wake flow dynamics behind the square cylinder. The simulation results via k−ω SST-SAS (Scale Adaptive Simulation) model are found closer to the reported measurements for both stationary and vibrating cases. After establishing the validity of our numerical methodology, the VIV simulations of twisted square cylinders with different twisted angles are performed at the moderate Reynolds numbers. In comparison to the square cylinder counterpart, the results of the twisted square cylinder demonstrate good controlling effect on the VIV response at two oncoming flow directions (0° and 45°). The twisted surface of the cylinder causes the variation of separation or vortex shedding points as well as the frequency of vortex shedding, which in turn affect the distributions of hydrodynamic forces along the cylinder. The power spectral analysis of hydrodynamic forces of twisted square cylinder indicates that the twisted surface has a significant influence on the frequencies of both drag and lift forces. Finally, comparisons of the detailed flow patterns, the 3D vortex structures and the vortex-shedding modes between square and twisted cylinders are presented in detail.

Cluster-based reduced-order modelling of the wake stabilization mechanism behind a twisted cylinder

The flow around a twisted elliptic cylinder is numerically calculated using large eddy simulation (LES) at the Reynolds number of 2 × 104, along with a circular cylinder for comparison. The mean drag coefficient and the fluctuating lift coefficient of the twisted cylinder are 27.99% and 94.01% lower, respectively, than that of the circular cylinder. The twisted surface leads to more stable wake, longer vortex formation length, higher base pressure and three-dimensional separation. In addition, cluster-based reduced-order modelling (CROM) is performed to analyze phase-dependent variations of the wake flow and evaluate the relationship between derived characteristic flow structures and their impact on forces. It captures the oscillatory behavior of Kármán vortex shedding in the wake of the circular cylinder. Meanwhile, two flow regimes, anti-phased and in-phase-dominated vortex shedding, generated by the twisted cylinder are extracted and distinguished. The two regimes prevail alternately with changing probability of occurrence along the spanwise of the twisted cylinder, which can be attributed to the different separation angles. The in-phase-dominated vortex shedding inhibits the effect of Kármán vortex shedding and is subjected to a lower force compared with the anti-phased vortex shedding.

Toroidal–Poloidal Magnetic Field Generation in Neutron Stars by Spacetime Frame-dragging

Abstract Neutron star magnetic fields, particularly in magnetars, have strong poloidal and toroidal components, reaching magnitudes up to and extending into the magnetosphere, where they cause twisted magnetic fields and surface currents. Here, we show that to a large extent neutron star toroidal and poloidal magnetic fields are due to frame-dragging of spacetime in the stellar exterior. In the explicit case of linearized Kerr metric we show that general relativistic Maxwell equations admit a mixed poloidal and toroidal magnetic field configuration in which the toroidal field strength is comparable with the poloidal magnetic field. Calculations are performed to show that the frame-dragging-induced magnetic field has the observed order of magnitude at the stellar surface, and exhibits the flare-like phenomenon observed in magnetars.

Interplay of Reggeon and photon in pA collisions

We discuss the effects of the electromagnetic interaction in high-energy proton collisions with nuclei of large Z at strong coupling $\lambda=g^2N_c$. Using the holographic dual limit of large $N_c>\lambda\gg 1$, we describe the Reggeon exchange as a twisted surface and show that it gets essentially modified by the electromagnetic interaction.

Large Eddy Simulation and investigation on the flow structure of the cascading cavitation shedding regime around 3D twisted hydrofoil

Cavitating flows are full of complex interactions between cavity evolution and vortical structures difficult to be measured in experiments. In the present work, the flow structure and dynamics of a kind of cascading cavitation shedding regime around a 3D twisted hydrofoil in full-scale water tunnel were numerically investigated using Large Eddy Simulation (LES). A homogeneous cavitation model of vapor fraction transport and a random perturbation generator based on spectral method are adopted. The mesh feasibility was carefully checked to provide an adequate capturing of the intrinsic vortical structure and the turbulence energy spectrum. The predicted cavitation behavior agrees with the experiment in primary aspects such as the cavity topology in periodic evolution, the frequency characteristics and the interlaced spanwise and streamwise vortices. Special emphasis was put on the analysis of flow details including the vortex-cavitation interaction and the pressure wave propagation. The observed convex cascading shedding is found to be caused by the particular re-entrant and side-entrant jet dynamics formed on the twisted surface. The jets reflected on the cavity closure are found to first concentrate then diverge along the minimal local slope of the foil. Another significant phenomenon is that the lift or drag has two peaks of similar magnitude in each cycle, which is analyzed to be a result of the cascading break-up and the ultimate collapse of the cavitation. An approximately linear relationship is predicted between the second-order time derivative of cavity volume and its induced pressure disturbance. The physical mechanism is clarified using a simplified analytical model.

Surface lattice solitons in diffusive nonlinear media with spatially modulated nonlinearity.

Two families of gap and twisted surface lattice solitons in diffusive nonlinear periodic media with spatially modulated nonlinearity are reported. It is shown that the existence and stability of such solitons are extremely spatially modulated nonlinearity sensitive. For self-focusing nonlinearity, gap surface solitons belonging to the semi-infinite gap are stable in whole existence domain, twisted surface solitons are also linearly stable in low modulated strength region and a very narrow unstable region near the upper cutoff appears in high modulated strength region. In the self-defocusing case, surface gap solitons belonging to the first gap can propagate stably in whole existence domain except for an extremely narrow region close to the Bloch band, twisted solitons belonging to this gap are unstable in the entire existence domain.

Twisted Surfaces with Null Rotation Axis in Minkowski 3-Space

We examine curvature properties of twisted surfaces with null rotation axis in Minkowski 3-space. That is, we study surfaces that arise when a planar curve is subject to two synchronized rotations, possibly at different speeds, one in its supporting plane and one of this supporting plane about an axis in the plane. Moreover, at least one of the two rotation axes is a null axis. As is clear from its construction, a twisted surface generalizes the concept of a surface of revolution. We classify flat, constant Gaussian curvature, minimal and constant mean curvature twisted surfaces with a null rotation axis. Aside from pseudospheres, pseudohyperbolic spaces and cones, we encounter B-scrolls in these classifications. The appearance of B-scrolls in these classifications is of course the result of the rotation about a null axis. As for the cones in the classification of flat twisted surfaces, introducing proper coordinates, we prove that they are determined by so-called Clelia curves. With a Clelia curve we mean a curve that has linear dependent spherical coordinates.

레이놀즈 수가 와류 감쇠 및 저항 저감형 나선형 해양 구조물 주위 유동에 미치는 영향

 . To analyze the effect of the twisted surface treatment, a large eddy simulation (LES) with a dynamic subgrid model was employe d. A simulation of the cylindrical structure was also carried out to compare the results with those of the twisted offshore structure. As Re increased, the mean drag and lift coefficient of the twisted offshore structure increased with the same tendency as those of the cylindrical structure. However, the increases in the mean drag and lift coefficient of the twisted offshore structure were much smaller than those of the cylindrical structure. Furthermore, elongated shear layer and suppressed vortex shedding from the twisted offshore structure occurred compared to those of the cylindrical cylinder, resulting in a drag reduction and suppression of the vortex-induced vibration (VIV). In particular, the twisted offshore structure achieved a significant reduction of over 96% in VIV compared with that of the cylindrical structure, regardless of increasing Re. As a result, we concluded that the twisted offshore structure effectively controlled the flow structures with reductions in the drag and VIV compared wi th the cylindrical structure, irrespective of increasing .

Twisted ferroelectric liquid crystals dynamic behaviour modification under electric field: A Mueller matrix polarimetry approach using birefringence

A low frequency and high amplitude rectangular voltage V has been applied during different increased duration to Twisted Surface Stabilized Ferroelectric Liquid crystal (TwFLC) samples in which the alignment layers of the two substrates were rubbed along two different directions between 0° and 90°. The optical bistability properties have been evaluated using the specific Mueller Matrix formalism that allows a simultaneous access, through a single-shot measurement, to different polarimetric coefficients. In this new approach, the ellipticity ϵR and the azimuthal αR polarimetric parameters, extracted from the birefringence Mueller Matrix MR will be considered in priority. Several significant parameters, such as the horizontal offset ΔV, the degree of asymmetry DA, the characteristic area S of the hysteresis loop, are used to characterize the degradation observed into the hysteretic behaviour of the samples, for different values of ψ, at different duration T of exposure to V, before reaching the so-called stripes regime, giving a new experimental point of view concerning the evolution of the dynamic properties of the samples studied. The αR(V) and the ϵR(V) hysteresis loops are specifically examined. Static mapping related to ϵR(T) is given too. Among the different possible physical origins of the observed degradation, the in-plane anchoring energy contribution will be particularly examined, and a theoretical model is proposed that also gives access to different physical parameters, through a new approach.

Error prediction and compensation based on interference-free tool paths in blade milling

We propose a method which uses interference-free tool paths to predict and compensate for deformation error during the spiral milling of blades. Firstly, a finite element simulation of the blisk blade milling process was conducted using an interference-free spiral milling NC machining tool path based on the curvature attribute of the blade twisted surface, observing the variation in blade milling error under different processing parameters and yielding a surface quality variation law. Next, the model was corrected by combining this error prediction data with precision design requirements, and a blade deformation error compensation scheme was suggested. Finally, an interference-free processing program containing the error compensation information was applied to carry out another blade milling simulation and a blisk milling experiment. The results showed that both the blade deformation error and the surface quality satisfied design requirements, while the accuracy of the simulation was verified.

Use of a twisted 3D Cauchy condition surface to reconstruct the last closed magnetic surface in a non-axisymmetric fusion plasma

The three-dimensional (3D) Cauchy condition surface (CCS) method code, ‘CCS3D’, is now under development to reconstruct the 3D magnetic field profile outside a non-axisymmetric fusion plasma using only magnetic sensor signals. A new ‘twisted CCS’ is introduced, whose elliptic cross-section rotates with the variation in plasma geometry in the toroidal direction of a helical-type device. Independent of the toroidal angle, this CCS can be placed at a certain distance from the last closed magnetic surface (LCMS). With this new CCS, it is found through test calculations for the Large Helical Device that the numerical accuracy in the reconstructed field is improved. Furthermore, the magnetic field line tracing indicates the LCMS more precisely than with the use of the axisymmetric CCS. A new idea to determine the LCMS numerically is also proposed.

Three-dimensional kinematics of saccadic and pursuit eye movements in humans: Relationship between Donders’ and Listing’s laws

For Listing’s law to be obeyed during eye movements, the “half-angle rule” must be satisfied: the eye velocity axis must tilt away from Listing’s plane by half the angle of eye position eccentricity from primary position. We aimed to determine if this rule is satisfied during horizontal and vertical pursuit compared with saccades. Three-dimensional (3-d) eye rotation data were acquired from five normal head-fixed humans using the search coil technique. Saccades were recorded in response to 40° horizontal or vertical steps in target position, at different elevations and azimuths. Pursuit was recorded while tracking a target moving horizontally or vertically at 20°/s, with peak-to-peak amplitude of 40°, at the same elevations and azimuths. First- and second-order surfaces were fitted to 3-d eye position data from periods of fixation. In all subjects, eye positions did not lie on a planar surface, but on a twisted surface in 3-d space. The tilt-angle coefficient (TAC) during saccades and pursuit was calculated as the ratio of the angle of eye velocity axis tilt to the angle of eye position eccentricity. During horizontal saccades and pursuit, mean TACs were 0.58 and 0.64, respectively. During vertical saccades and pursuit, mean TACs were 0.35 and 0.43, respectively, and lower than their horizontal counterparts (p<0.05). These findings suggest that Listing’s law is not perfectly satisfied during saccades or pursuit. On the basis of model simulations, we propose that the discrepancy in horizontal and vertical TACs causes eye positions to lie on a twisted rather than a planar surface.