Strong Rotation Research Articles

Time-integrated polarizations in the prompt phase of gamma-ray bursts via the multi-window interpretation

We used multi-window observations, including the light curve and evolutions of the spectral peak energy (E_p), the polarization degree (PD), and the polarization angle (PA), to infer the model parameters for predicting the time-integrated PD in the prompt phase of gamma-ray bursts (GRBs). We selected 23 GRBs that were codetected by Fermi/GBM and polarization detectors (i.e., GAP, POLAR, and AstroSat). In our multi-window fitting, the light curve, E_p curve, PD curve, and PA curve were interpreted simultaneously under the synchrotron radiation model in ordered magnetic fields (i.e., the aligned-field case and the toroidal-field case). For bursts with strong (∼90^∘) PA rotations, the predicted time-integrated PD of the aligned-field case roughly matches the corresponding observed best-fit value, while it is higher for the toroidal-field case. For bursts without strong (∼90^∘) PA rotation(s), the predicted PDs of the aligned-field case and the toroidal-field case are comparable and can interpret the observational data equally well. The observed time-resolved and time-integrated PDs for GRB 170206A are comparable and are both lower than our predicted upper limits in ordered magnetic fields. This means that mixed magnetic fields, that is, magnetic fields with both ordered and random components, probably reside in the radiation regions of this burst. Except for one out of the total 23 bursts, the predicted time-integrated PDs, which are ∼44% for the aligned-field case and around $49%$ for the toroidal-field case, are consistent with the corresponding observed values. Consistent with previous study, the models with synchrotron radiation in ordered magnetic fields can therefore interpret most of the current polarization data within an error bar of $1σ$.

Boosting Covalent Organic Framework Luminescence by Suppressing Nonradiative Pathways†

Comprehensive SummaryThe construction of luminescent two‐dimensional (2D) imine‐linked covalent organic frameworks (COFs) is a formidable challenge due to the strong interlayer stacking and bond rotations that typically suppress intramolecular charge transfer (ICT), leading to nonradiative energy dissipation. Herein, three COFs with tailored interlayer distances and bond rotations are designed to modulate the ICT behaviours. The targeted COF (TPAZ‐TPE‐COF) achieved a significantly enhanced photoluminescence quantum yield (PLQY) of 21.22% in the solid state by restricting bond rotation and enlarging the layer distance. This represents a 3.5‐fold and 530.5‐fold improvement over TPAZ‐PYTA‐COF (6.15%), which has a shortened interlayer space, and TPAZ‐PATA‐COF (0.04%), which exhibits strong bond rotations, respectively. Importantly, TPAZ‐TPE‐COF also exhibits exceptional sensing performance for iron ions, with a detection limit at the ppb level. Both experimental and theoretical analyses reveal that the prominent luminescent performance of TPAZ‐TPE‐COF is assigned to the effective suppression of nonradiative pathways, especially those arising from interlayer stacking and bond vibrations. These findings pave the way for deliberate construction of imine‐linked 2D COFs with high PL intensity, thereby expanding the portfolio of luminescent COFs with potential applications in sensing and optoelectronics.

Scoliosis instrumentation alters primary and coupled motions of the spine: An in vitro study using entire thoracolumbar spine and rib cage specimens.

Effects of rigid posterior instrumentation on the three-dimensional post-operative spinal flexibility are widely unknown. Purpose of this in vitro study was to quantify these effects for characteristic adolescent idiopathic scoliosis instrumentations. Six fresh frozen human thoracic and lumbar spine specimens (C7-S) with entire rib cage from young adult donors (26-45 years) without clinically relevant deformity were loaded quasi-statically with pure moments of 5 Nm in flexion/extension, lateral bending, and axial rotation. Primary and coupled motions of all segments were measured using optical motion tracking. Specimens were tested without instrumentation and with posterior rod instrumentations ranging from T2 to L1 (for Lenke Type 2) and from T8 to L3 (for Lenke Type 5) based on survey results among spinal deformity surgeons. Statistical differences were evaluated using the pairwise Friedman test. Primary ranges of motion were significantly (p < 0.05) reduced in all six motion directions in the entire thoracic spine (T1-L1) for both instrumentations, but solely in extension and axial rotation in the entire lumbar spine (L1-S) for T8-L3 instrumentation. Without instrumentation, strong ipsilateral axial rotation during primary lateral bending and strong contralateral lateral bending during primary axial rotation were detected in the thoracic spine (T1-L1) and slight inverse coupled motions in the lumbar spine (L1-S). While coupled axial rotation was significantly (p < 0.05) reduced, especially in the upper thoracic spine (T1-T5) for T2-L1 instrumentation and in the lumbar spine (L1-S) for T8-L3 instrumentation, coupled lateral bending was solely significantly (p < 0.05) reduced in the upper thoracic spine (T1-T5) for T2-L1 instrumentation. Coupled motions in primary flexion and extension were non-existent and not affected by any fixation (p > 0.05). Instrumentation reduces the primary flexibility and diminishes the natural coupling behavior between lateral bending and axial rotation, primarily in the upper thoracic spine, potentially causing correction loss and junctional deformity in the long-term.

Effect of rotation on wake vortices in stratified flow

Stratified wakes past an isolated conical seamount are simulated at a Froude number of $Fr = 0.15$ and Rossby numbers of $Ro = 0.15$ , 0.75 and $\infty$ . The wakes exhibit a Kármán vortex street, unlike their unstratified, non-rotating counterpart. Vortex structures are studied in terms of large-scale global modes, as well as spatially localised vortex evolution, with a focus on rotation effects. The global modes are extracted by spectral proper orthogonal decomposition (SPOD). For all three studied $Ro$ ranging from mesoscale, submesoscale and non-rotating cases, the frequency of the SPOD modes at different heights remains coupled as a global constant. However, the shape of the SPOD modes changes from slanted ‘tongues’ at zero rotation ( $Ro=\infty$ ) to tall hill-height columns at strong rotation ( $Ro=0.15$ ). A novel method for vortex centre tracking shows that, in all three cases, the vortices at different heights advect uniformly at approximately $0.9U_{\infty }$ beyond the near wake, consistent with the lack of variability of the global modes. Under system rotation, cyclonic vortices and anticyclonic vortices (AVs) present considerable asymmetry, especially at $Ro = 0.75$ . The vorticity distribution as well as the stability of AVs are tracked downstream using statistics conditioned to the identified vortex centres. At $Ro=0.75$ , intense AVs with relative vorticity up to $\omega _z/f_{c}=-2.4$ (where $\omega_z$ is the vertical vorticity and $f_c$ is the Coriolis frequency) are seen with small regions of instability and they maintain large $\omega _z/f_{c}$ magnitude in the far wake. Recent stability analysis that accounts for stratification and viscosity is found to improve on earlier criteria and show that these intense AVs are stable.

Autodetachment of Diatomic Carbon Anions from Long-Lived High-Rotation Quartet States.

We show that strong molecular rotation drastically modifies the autodetachment of C_{2}^{-} ions in the lowest quartet electronic state a^{4}Σ_{u}^{+}. In the strong-rotation regime, levels of this state only decay by a process termed "rotationally assisted" autodetachment, whose theoretical description is worked out based on the nonlocal resonance model. For autodetachment linked with the exchange of six rotational quanta, the results reproduce a prominent, hitherto unexplained electron emission signal with a mean decay time near 3ms, observed on stored C_{2}^{-} ions from a hot ion source.

Two-point statistics in non-homogeneous rotating turbulence

Time-resolved two-dimensional two-component particle image velocimetry measurements with high spatial resolution are carried out in a water tank agitated by four blades rotating at constant speed. Different blade geometries and rotation speeds are tested for the purpose of modifying turbulent flow conditions. In all cases where no baffles are used to break the rotation, the Zeman length is an order of magnitude smaller than the Taylor length. Compared with the cases with baffles which break the rotation, in the unbaffled cases turbulence production and/or mean advection are significant and the turbulence nonlinearity is dramatically reduced for the horizontal (i.e. normal to the axis of rotation) two-point turbulence fluctuating velocities. This nonlinearity reduction is manifest not only in the interscale turbulent energy transfer but also in the interspace turbulent energy transfer, which nearly vanishes. However, the nonlinearity is not reduced for the vertical two-point turbulence fluctuating velocities: the corresponding interscale turbulent transfer rate is in fact intensified, and its dependence on the two-point separation distance, as well as that of the corresponding interspace turbulent transfer rate, which does not vanish, is significantly modified. Even though non-homogeneities are very different for different blades and rotation speeds in the unbaffled cases, the horizontal fluctuating velocity's second-order structure function collapses with scalings which resemble predictions for homogeneous turbulence subject to strong rotation. The vertical fluctuating velocity's second-order structure function does not collapse for different blade geometries by neither these nor the Kolmogorov predictions.

K2-370 b: a strongly irradiated sub-Neptune transiting a very active solar-type star

ABSTRACT We report on the detailed characterization of K2-370 b, a transiting sub-Neptune on a 2.14-d orbit around the chromospherically active G-type dwarf HD 284521 ($T_\mathrm{eff} = 5662\pm 44$ K, $\lt \log R^\prime _{\rm HK}\gt =-4.49$). The system parameters are derived based on a global fit to K2, TESS and CHEOPS photometry, and HARPS-N and HARPS radial velocities (RVs). A Gaussian process regression analysis is performed simultaneously to the orbital fit of the RVs of K2-370 to effectively model the strong stellar rotation signal with a period of $13.5\pm 0.05$ d and measure the planetary RV signal with semi-amplitude $K_{\rm b}=5.6\pm 0.7$ m s$^{-1}$. We find that K2-370 b has a radius of $2.67\pm 0.05$ ${\rm R}_{\rm{\oplus }}$ and a mass of $11.1\pm 1.4$ ${\rm M}_{\rm{\oplus }}$. With an estimated equilibrium temperature $T_\mathrm{eq}\sim 1480$ K, K2-370 b is the second-hottest sub-Neptune with a highly precise mass determination around primaries with $T_\mathrm{eff}\gt 5500$ K. The resulting density of $3.2\pm 0.4$ g cm$^{-3}$ implies that K2-370 b either retains a significant ($\sim 2~{{\ \rm per\ cent}}$ by mass) H-rich atmosphere or its interior contains a high ($\sim 40~{{\ \rm per\ cent}}$) water–mass fraction.

Magnetic Fields in Massive Star-forming Regions (MagMaR): Unveiling an Hourglass Magnetic Field in G333.46–0.16 Using ALMA

The contribution of the magnetic field to the formation of high-mass stars is poorly understood. We report the high angular resolution (∼0.″3, 870 au) map of the magnetic field projected on the plane of the sky (B POS) toward the high-mass star-forming region G333.46−0.16 (G333), obtained with the Atacama Large Millimeter/submillimeter Array at 1.2 mm as part of the Magnetic fields in Massive star-forming Regions survey. The B POS morphology found in this region is consistent with a canonical “hourglass” with an embedded flattened envelope in a perpendicular direction, which suggests a dynamically important field. This region is fragmented into two protostars that appear to be gravitationally bound in a stable binary system with a separation of ∼1740 au. Interestingly, by analyzing H13CO+ (J = 3–2) line emission, we find no velocity gradient over the extent of the continuum, which is consistent with a strong field. We model the B POS, obtaining a marginally supercritical mass-to-flux ratio of 1.43, suggesting an initially strongly magnetized environment. Based on the Davis–Chandrasekhar–Fermi method, the magnetic field strength toward G333 is estimated to be 5.7 mG. The absence of strong rotation and outflows toward the central region of G333 suggests strong magnetic braking, consistent with a highly magnetized environment. Our study shows that despite being a strong regulator, the magnetic energy fails to prevent the process of fragmentation, as revealed by the formation of the two protostars in the central region.

Refueling of field-reversed configuration core via axial plasmoids injection

This study successfully developed a refueling technique for a field-reversed configuration (FRC) via axial plasmoid injection and demonstrated it on the FAT-CM device at Nihon University. The target FRC is generated using the collisional-merging formation technique combined with conical theta-pinch formation. Plasmoids with an FRC-like configuration are coaxially injected from both ends of the FAT-CM device toward the preexisting target FRC. Postinjection, the system achieves equilibrium, resulting in increases by factors of 1.8 and 2.4 in the total inventory and plasma energy, respectively, compared to cases without injection. This method effectively accomplishes FRC refueling while preserving the intrinsic characteristics of a simply connected, axisymmetric configuration and a high beta value approaching unity. Therefore, this approach offers potential for repetitive refueling in the reactor stage having a FRC plasma core. Experimental outcomes are compared with magnetohydrodynamic simulation results. In the collisional merging process, the characteristics of the pre-collision plasmoids, such as the strong toroidal rotation and coherent FRC-like magnetic field structures of the FRC, are not preserved. Experimental environments have been constructed to investigate such unique properties of the resulting FRCs.

Experimental study on dynamics of a free-falling finite-size sphere associated with its collision with a wall in a boundary layer

To reveal the physical mechanisms of particle transport in the pneumatic and hydraulic transports, this study experimentally investigated the dynamics of a free-falling finite-size sphere associated with its collision with a wall and the surrounding flow field in a boundary layer flow. The simultaneous motion of finite-size sphere and its inducing flow field near the wall were measured by using a time-resolved particle image velocimetry. The results revealed that the free-falling velocity of sphere increases with Reynolds number before the first impaction, and then is almost unrelated to Reynolds number. The effect of gravity on sphere motion becomes weak with increasing Reynolds number. As the sphere approaches to the wall, the vortex appeared at the front of sphere moves to left side near the wall and reduces the sphere falling speed. After the sphere collided on the wall, the upward motion of sphere induces another vortex pair, which generates strong rotation of sphere.

A MeerKAT Polarization Survey of Southern Calibration Sources

We report on full-Stokes L-band observations of 98 MeerKAT calibration sources. Linear polarization is detected in 71 objects above a fractional level of 0.2%. We identify ten sources with strong fractional linear polarization and low Faraday rotation measure that could be suitable for wide-band absolute polarization calibration. We detect significant circular polarization from 24% of the sample down to a detection level of 0.07%. Circularly polarized emission is seen only for flat spectrum sources α > −0.5. We compare our polarized intensities and Faraday synthesis results to data from the NVSS at 1400 MHz and the ATCA SPASS survey at 2300 MHz. NVSS data exist for 54 of our sources and SPASS data for 20 sources. The percent polarization and rotation measures from both surveys agree well with our results. The residual instrumental linear polarization for these observations is measured at 0.16%, and the residual instrumental circular polarization is measured at 0.05%. These levels may reflect either instabilities in the relative bandpass between the two polarization channels with either time or antenna orientation, or atmospheric/ionospheric variations with pointing direction. Tracking of the hourly gain solutions on J0408-6545 after transfer of the primary gain solutions suggests a deterioration of the gain stability by a factor of several starting about 2 hr after sunrise. This suggests that observing during the nighttime could dramatically improve the precision of polarization calibration.

Discovery of a strong rotation of the X-ray polarization angle in the galactic burster GX 13+1

Weakly magnetized neutron stars in X-ray binaries show a complex phenomenology with several spectral components that can be associated with the accretion disk, the boundary, and/or a spreading layer, a corona, and a wind. Spectroscopic information alone, however, is not enough to distinguish these components. The analysis of the timing data revealed that most of the variability, and in particular, kilohertz quasi-period oscillations, are associated with the high-energy component that corresponds to the boundary and/or spreading layer. Additional information about the nature of the spectral components, and in particular, about the geometry of the emission region, can be provided by X-ray polarimetry. One of the objects of the class, a bright, persistent, and rather peculiar galactic Type I X-ray burster was observed with the Imaging X-ray Polarimetry Explorer (IXPE) and the X-ray Multi-Mirror Mission Newton ( Using the data, we obtained the best-fit values for the continuum spectral parameters and detected strong absorption lines associated with the accretion disk wind. IXPE data showed the source to be significantly polarized in the 2--8 keV energy band, with an overall polarization degree (PD) of $1.4&lt;!PCT!&gt; at a polarization angle (PA) of $-2 (errors at the 68&lt;!PCT!&gt; confidence level). During the two-day long observation, we detected rotation of the PA by about 70 with the corresponding changes in the PD from 2&lt;!PCT!&gt; to nondetectable and then up to 5&lt;!PCT!&gt;. These variations in polarization properties are not accompanied by visible spectral state changes of the source. The energy-resolved polarimetric analysis showed a significant change in polarization, from being strongly dependent on energy at the beginning of the observation to being almost constant with energy in the later parts of the observation. As a possible interpretation, we suggest a constant polarization component, strong wind scattering, or a different polarization of the two main spectral components with an individually peculiar behavior. The rotation of the PA suggests a misalignment of the neutron star spin from the orbital axis.

Zonal jets and eddy tilts in barotropic geostrophic turbulence

The spontaneous formation of zonal jets is a distinctive feature of geostrophic turbulence with the phenomenon witnessed in numerous numerical studies. In such systems, strong rotation anisotropises the spectral evolution of the energy density such that zonal modes are favoured. In physical space, this manifests as eddies zonally elongating and forming into zonal jets. In the presence of large scale dissipation, the flow may reach statistical stationarity such that the zonal structure persists in the zonal and time mean, and is supported by a flux of eddy momentum. What is unclear is how the excitation of Rossby waves arranges the underlying eddy momentum stresses to support the mean flow structures. To study this, we examine a steady-state flow in the so-called ‘zonostrophic’ regime, in which characteristic scales of geostrophic turbulence are well separated and there are several alternating zonal jets that have formed spontaneously. We apply a geometric eddy ellipse formulation, in which momentum fluxes are cast as ellipses that encode information about the magnitude and direction of flux; the latter is described using the tilt angle. With the aid of a zonal filter, it is revealed that the scales responsible for providing the momentum fluxes associated with the jet structure are much smaller than the characteristic scales identified, and occupy a region of the energy spectrum that has been typically associated with isotropic dynamics.

A closed-form Timoshenko beam element with multiple localized singularities for nonlinear material behavior using the strong discontinuity approach

The development of a novel closed-form beam element for nonlinear material behavior in structures is described, which is formulated according to Timoshenko beam theory and the embedded strong discontinuity approach. Multiple strong transverse and rotation discontinuities are considered to model several dissipative mechanisms due to localized singularities in the shear strain and curvature fields. Issues of dependence on numerical techniques, as occurs in displacement- and forced-based beam elements with the finite element method, are overcome since the formulated element is derived from a pure mathematical treatment. Theoretical principles are stemming from a Lagrangian variational model, from which singularities are naturally derived. The proposed formulation is solved by the conventional methods of calculus of variations, resulting in the boundary value problem. Then, closed-form expressions for any boundary conditions are obtained. By particularizing closed-form expressions for a basic system, a symmetric closed-form flexibility matrix is obtained. This matrix naturally leads to a symmetric closed-form stiffness matrix for any type of loading and unloading process, in which the nodeless degrees of freedom of the multiple embedded strong discontinuities are naturally condensed. Since Gauss integration methods are not used, the multiple localized singularities are not influenced by predefined positions of the integration points. However, the accuracy depends on the chosen number of singularities and their positions. Then, the proposed element is mesh independent when sufficient discontinuities are considered, which does not imply an increase in the degrees of freedom. Softening discontinuities are modeled at arbitrary positions in a single element, which overcomes the drawbacks of other embedded beam theories where more than one element is necessary to identify failure since strong discontinuities are generally located at the midpoint of the beam element. The obtained closed-form stiffness matrix is not always positive definite for strain-softening problems. Nevertheless, there are no major convergence issues as it is a symmetric matrix that does not require a constraint equation, so even the complex snap-back behavior in structures is adequately modeled. The capability of the formulated beam element for nonlinear material behavior in structures is validated with representative examples.

The conditional Lyapunov exponents and synchronisation of rotating turbulent flows

The synchronisation between rotating turbulent flows in periodic boxes is investigated numerically. The flows are coupled via a master–slave coupling, taking the Fourier modes with wavenumber below a given value $k_m$ as the master modes. It is found that synchronisation happens when $k_m$ exceeds a threshold value $k_c$ , and $k_c$ depends strongly on the forcing scheme. In rotating Kolmogorov flows, $k_c\eta$ does not change with rotation in the range of rotation rates considered, $\eta$ being the Kolmogorov length scale. Even though the energy spectrum has a steeper slope, the value of $k_c\eta$ is the same as that found in isotropic turbulence. In flows driven by a forcing term maintaining constant energy injection rate, synchronisation becomes easier when rotation is stronger. Here, $k_c\eta$ decreases with rotation, and it is reduced significantly for strong rotations when the slope of the energy spectrum approaches $-3$ . It is shown that the conditional Lyapunov exponent for a given $k_m$ is reduced by rotation in the flows driven by the second type of forcing, but it increases mildly with rotation for the Kolmogorov flows. The local conditional Lyapunov exponents fluctuate more strongly as rotation is increased, although synchronisation occurs as long as the average conditional Lyapunov exponents are negative. We also look for the relationship between $k_c$ and the energy spectra of the Lyapunov vectors. We find that the spectra always seem to peak at approximately $k_c$ , and synchronisation fails when the energy spectra of the conditional Lyapunov vectors have a local maximum in the slaved modes.

Direct-write 3D printing of plasmonic nanohelicoids by circularly polarized light

Chiral plasmonic surfaces with 3D "forests" from nanohelicoids should provide strong optical rotation due to alignment of helical axis with propagation vector of photons. However, such three-dimensional nanostructures also demand multi-step nanofabrication, which is incompatible with many substrates. Large-scale photonic patterns on polymeric and flexible substrates remain unattainable. Here, we demonstrate the substrate-tolerant direct-write printing and patterning of silver nanohelicoids with out-of-plane 3D orientation using circularly polarized light. Centimeter-scale chiral plasmonic surfaces can be produced within minutes using inexpensive medium-power lasers. The growth of nanohelicoids is driven by the symmetry-broken site-selective deposition and self-assembly of the silver nanoparticles (NPs). The ellipticity and wavelength of the incident photons control the local handedness and size of the printed nanohelicoids, which enables on-the-fly modulation of nanohelicoid chirality during direct writing and simple pathways to complex multifunctional metasurfaces. Processing simplicity, high polarization rotation, and fine spatial resolution of the light-driven printing of stand-up helicoids provide a rapid pathway to chiral plasmonic surfaces, accelerating the development of chiral photonics for health and information technologies.

Solar Tachocline Confinement by the Nonaxisymmetric Modes of a Dynamo Magnetic Field

We recently presented the first 3D numerical simulation of the solar interior for which tachocline confinement was achieved by a dynamo-generated magnetic field. In this follow-up study, we analyze the degree of confinement as the magnetic field strength changes (controlled by varying the magnetic Prandtl number) in a coupled radiative zone (RZ) and convection zone (CZ) system. We broadly find three solution regimes, corresponding to weak, medium, and strong dynamo magnetic field strengths. In the weak-field regime, the large-scale magnetic field is mostly axisymmetric with regular, periodic polarity reversals (reminiscent of the observed solar cycle) but fails to create a confined tachocline. In the strong-field regime, the large-scale field is mostly nonaxisymmetric with irregular, quasi-periodic polarity reversals and creates a confined tachocline. In the medium-field regime, the large-scale field resembles a strong-field dynamo for extended intervals but intermittently weakens to allow temporary epochs of strong differential rotation. In all regimes, the amplitude of poloidal field strength in the RZ is very well explained by skin-depth arguments, wherein the oscillating field that gives rise to the skin depth (in the medium- and strong-field cases) is a nonaxisymmetric field structure at the base of the CZ that rotates with respect to the RZ. These simulations suggest a new picture of solar tachocline confinement by the dynamo, in which nonaxisymmetric, very long-lived (effectively permanent) field structures rotating with respect to the RZ play the primary role, instead of the regularly reversing axisymmetric field associated with the 22 yr cycle.

The statistical characteristics and auto-regeneration of backflow in non-Newtonian turbulent pipe flow

The backflow phenomenon in shear-thinning and shear-thickening fluids is investigated in pipe flows at friction Reynolds number Reτ=180 via direct numerical simulations. Conditional average results show that the extreme fluctuation of wall shear stress around the backflow regions is more abrupt under the shear-thinning effect. The statistical characteristics of the backflow at different flow indices from 0.5 to 1.5 show remarkable differences. The probability of the backflow events at the wall increases in both the shear-thinning and the shear-thickening fluids under different mechanisms. The backflow occurs more frequently and exists further away from the wall in the shear-thinning fluids owing to the suppressed near-wall turbulent structures and the laminarization at low flow indices. The increase in the probability of the backflow events in the shear-thickening fluids is caused by increased Q2 and Q4 events in the near-wall region. The variation in the size and the lifespan of the backflow regions with the flow index is very prominent which both increase with the shear-thinning effect and decrease as the flow becomes dilatant. In the weakly turbulent flow of shear-thinning fluid, large backflow regions appear near the leading edge of the turbulent spots where the off-axial turbulent fluctuations are significantly lowered. Observations show the linked evolution between the hairpin vortices and the backflow regions induced underneath the strong spanwise rotations. The backflow follows the auto-regeneration process of the hairpin vortices in a packet which results in coherent streamwise-aligned backflow regions under the hairpin packets confined closer to the wall.

Rotation and Confined Eruption of a Double Flux-rope System

We perform a data-constrained simulation with the zero-β assumption to study the mechanisms of strong rotation and failed eruption of a filament in active region 11474 on 2012 May 5 observed by Solar Dynamics Observatory and Solar Terrestrial Relations Observatory. The initial magnetic field is provided by nonlinear force-free field extrapolation, which is reconstructed by the regularized Biot–Savart laws and magnetofrictional method. Our simulation reproduces most observational features very well, e.g., the filament large-angle rotation of about 130°, the confined eruption, and the flare ribbons, allowing us to analyze the underlying physical processes behind observations. We discover two flux ropes in the sigmoid system, an upper flux rope (MFR1) and a lower flux rope (MFR2), which correspond to the filament and hot channel in observations, respectively. Both flux ropes undergo confined eruptions. MFR2 grows by tether-cutting reconnection during the eruption. The rotation of MFR1 is related to the shear-field component along the axis. The toroidal field tension force and the nonaxisymmetry forces confine the eruption of MFR1. We also suggest that the mutual interaction between MFR1 and MFR2 contributes to the large-angle rotation and the eruption failure. In addition, we calculate the temporal evolution of the twist and writhe of MFR1, which is a hint of probable reversal rotation.

Investigation on the roles of equilibrium toroidal rotation during edge-localized mode mitigated by resonant magnetic perturbations

The effects of equilibrium toroidal rotation during edge-localized mode (ELM) mitigated by resonant magnetic perturbation (RMP) are studied with the experimental equilibria of the EAST tokamak based on the four-field model in the BOUT++ code. As the two main parameters to determine the toroidal rotation profiles, the rotation shear and magnitudes were separately scanned to investigate their roles in the impact of RMPs on peeling–ballooning (P-B) modes. On one hand, the results show that strong toroidal rotation shear is favorable for the enhancement of the self-generated shearing rate with RMPs, leading to significant ELM mitigation with RMP in the stronger toroidal rotation shear region. On the other hand, toroidal rotation magnitudes may affect ELM mitigation by changing the penetration of the RMPs, more precisely the resonant components. RMPs can lead to a reduction in the pedestal energy loss by enhancing the multimode coupling in the turbulence transport phase. The shielding effects on RMPs increase with the toroidal rotation magnitude, leading to the enhancement of the multimode coupling with RMPs to be significantly weakened. Hence, the reduction in pedestal energy loss by RMPs decreased with the rotation magnitude. In brief, the results show that toroidal rotation plays a dual role in ELM mitigation with RMP by changing the shielding effects of plasma by rotation magnitude and affecting by rotation shear. In the high toroidal rotation region, toroidal rotation shear is usually strong and hence plays a dominant role in the influence of RMP on P-B modes, whereas in the low rotation region, toroidal rotation shear is weak and has negligible impact on P-B modes, and the rotation magnitude plays a dominant role in the influence of RMPs on the P-B modes by changing the field penetration. Therefore, the dual role of toroidal rotation leads to stronger ELM mitigation with RMP, which may be achieved both in the low toroidal rotation region and the relatively high rotation region that has strong rotational shear.