Rotational History Research Articles

Constraints on the early luminosity history of the Sun: applications to the Faint Young Sun problem

ABSTRACT Stellar evolution theory predicts that the Sun was fainter in the past, which can pose difficulties for understanding Earth’s climate history. One proposed solution to this Faint Young Sun (FYS) problem is a more luminous Sun in the past. In this paper, we address the robustness of the solar luminosity history using the yrec code to compute solar models including rotation, magnetized winds, and the associated mass-loss. We present detailed solar models, including their evolutionary history, which are in excellent agreement with solar observables. Consistent with prior standard models, we infer a high solar metal content. We provide predicted X-ray luminosities and rotation histories for usage in climate reconstructions and activity studies. We find that the Sun’s luminosity deviates from the standard solar model trajectory by at most 0.5 per cent during the Archean (corresponding to a radiative forcing of 0.849 W m$^{-2}$). The total mass-loss experienced by solar models is modest because of strong feedback between mass and angular momentum loss. We find a maximum mass-loss of $1.35 \times 10^{-3} \,{\rm M}_\odot$ since birth, at or below the level predicted by empirical estimates. The associated maximum luminosity increase falls well short of the level necessary to solve the FYS problem. We present compilations of paleotemperature and CO$_2$ reconstructions. One-dimensional ‘inverse’ climate models demonstrate a mismatch between the solar constant needed to reach high temperatures (e.g. 60–80 $^{\circ }$C) and the narrow range of plausible solar luminosities determined in this study. Maintaining a temperate Earth, however, is plausible given these conditions.

Geological evidence reveals a staircase pattern in Earth’s rotational deceleration evolution

The Earth’s rotation has been decelerating throughout its history due to tidal dissipation, but the variation of the rate of this deceleration through time has not been established. We present a detailed analysis of eight geological datasets to constrain the Earth’s rotational history from 650 to 240 Mya. The results allow us to test physical tidal models and point to a staircase pattern in the Earth’s deceleration from 650 to 280 Mya. During this time interval, the Earth–Moon distance increased by approximately 20,000 km and the length of day increased by approximately 2.2 h. Specifically, there are two intervals with high Earth rotation deceleration, 650 to 500 Mya and 350 to 280 Mya, separated by an interval of stalled deceleration from 500 to 350 Mya. The interval with stalled deceleration is attributed mainly to reduced tidal dissipation due to the continent-ocean configuration at the time, not to changes in Earth’s dynamical ellipticity from continental assembly or glaciation. Modeling indicates that, except for the very recent time, tidal dissipation is the main driver for decelerating Earth rotation. One potential implication of our findings is that the Earth’s tidal dissipation, along with Earth’s rotation deceleration, may play a role in the evolving Earth.

The viscosity of Venus’ mantle inferred from its rotational state

Venus’ retrograde rotation is the slowest of all planetary objects in the solar system. It is commonly admitted that such a rotation state results from the balance between the torques created by solid and atmospheric tides (Dobrovolskis and Ingersol, 1980; Correia and Laskar, 2001; Correia and Laskar, 2003a; Revol et al. 2023). The internal viscous friction associated with gravitational tides drives the planet into synchronization (i.e. deceleration to a tidally locked rotation) while the bulge due to atmospheric thermal tides tends to accelerate the planet out of this synchronization (Correia and Laskar, 2001; Leconte et al., 2015). The purpose of this work is first to provide an estimate of the viscosity of Venus’ mantle explaining the current balance with atmospheric forcing. A second goal is to quantify the impact of the internal structure and its past evolution on the rotation history of Venus.Using atmospheric pressure simulations, we first provide an estimate of the atmospheric thermal torque value contrasting with previous estimates (Leconte et al., 2015). Computing the viscoelastic response of the interior to gravitational tides and to atmospheric loading (Dumoulin et al., 2017; Kervazo et al., 2021), we show that the current viscosity of Venus’ lower mantle must range between 2 × 1020 Pa s and 6 × 1021 Pa s to explain a rotation in equilibrium. We then investigate the possible past evolution of Venus’ rotation by considering simple viscosity and thermal evolution paths. We show that in absence of additional dissipation processes, viscous friction cannot slow down Venus’ rotation to its current state from an initial rotation period shorter than 1 day.

Prediction of a Novel Electromechanical Response in Polar Polymers with Rigid Backbones: Contrasting Furan-Derived Nanothreads to Poly(Vinylidene Fluoride).

Syn furan nanothreads have all oxygen atoms arranged on one side of the thread backbone; these polar threads present intriguing opportunities in electromechanical response owing to their rigid ladder-like backbone. We retrained a C/H/O reactive force field to simulate their response to external electric field for both end-anchored individual threads and bulk nanothread crystals, contrasting the results to those for poly(vinylidene fluoride) (PVDF) polymer. Whereas the field induces a length-independent torque in PVDF through backbone rotation about σ bonds, furan-derived nanothreads generate a length-dependent torque by progressively twisting their rigid backbone. This mode of response couples the rotational history of the electric field to axial tension in the anchored thread. In simulations of densely packed syn furan nanothread crystals without anchors, the crystals pole in a field (∼3 GV/m at 300 K) similar to that seen in simulations of PVDF, suggesting that crystals of polar nanothreads can be ferroelectric.

Inoculum sources and management of bean scab caused by Elsinoë phaseoli

AbstractBean scab caused by Elsinoë phaseoli is a major challenge to common bean cultivation in Kenya. However, knowledge about its epidemiology and management is limited. This study conducted three experiments in Kakamega, Kenya, evaluating scab inoculum sources and control options. The first experiment evaluated three different inoculum sources over two seasons; bean crop residue caused the highest scab incidence in both the 2021 (62.1%) and 2022 (81.1%) seasons. The second experiment assessed the effect of rotation history on scab over three seasons. Scab incidence consistently surpassed 90% within the first 30 days after planting in half‐yearly rotated fields across all seasons, while the disease was absent after planting in fields with no recent history of legumes. Fields rotated out of legumes consistently had the highest grain yield, averaging 1.5 t ha−1 over the seasons. Additionally, the rotation land treatment displayed significantly more pods per plant during the 2021 (9.7), 2022a (9.8), and 2022b (12.5) seasons. In the third experiment, the impact of five fungicides and four cropping systems on bean scab was investigated over two seasons. Neither fungicide treatments nor cropping systems had an effect on bean scab incidence even when only severe symptoms were considered. Carbendazim had the highest yield (1.9 t ha−1) outperforming the unsprayed control only in the 2022 season while none of the other fungicides outperformed the control treatment in yield parameters in either season. This study emphasizes the challenge of managing bean scab without proper crop rotation and underscores the role of crop residue as a critical inoculum source.

Ductility demand estimation of high-rise steel special moment frames due to structure-pile-soil interaction

ABSTRACT This study is concerned with variation of ductility demands in a range of tall buildings comprising 15, 20, 25, and 30-story steel special moment frames resting on pile groups in a flexible soil medium. Nonlinear soil–structure interaction analysis is performed using the direct method by considering an adequate extent of soil around the structures terminating at appropriate boundaries. Eleven consistent ground motions are used for nonlinear dynamic analysis of the systems and the ductility demands are evaluated by tracing the rotation history of the plastic hinges. It is concluded that simultaneous contribution of soil–structure interaction and p-∆ effect results in more than 40% increase of the ductility demand and 20% increase of the story drifts in the worst case that includes the lower stories of the tallest building.

Shortening and asthenospheric flow drove Miocene vertical-axis rotations in the northern Tibetan Plateau: A palaeomagnetic study of the northeast Qaidam Basin of China

The timing and magnitude of upper crustal deformation in the northern Tibetan Plateau are important for testing models of plateau uplift and for understanding Cenozoic environmental variations and monsoon evolution in central and eastern Asia. Most published studies focus on the upward and outward growth of the northern Tibetan Plateau, whereas its tectonic, vertical-axis rotation history has received less attention. Here we evaluate paleomagnetic data from six stratigraphic sections in the northeastern Qaidam Basin of China, revealing a phase of clockwise rotation from ca. 20–11 Ma followed by counterclockwise rotation from ca. 11–5 Ma. We propose that differential crustal shortening and right-lateral shear drove early to middle Miocene clockwise rotation, whereas eastward flow of the Tibetan asthenosphere induced the post-middle Miocene counterclockwise rotation. These processes coincide with increased activity of first-order strike-slip faults in the northeastern plateau, emphasizing the important role of strike-slip faults in accommodating crustal deformation in northern Tibetan Plateau during the late Cenozoic.

Thermal tides in neutrally stratified atmospheres: Revisiting the Earth’s Precambrian rotational equilibrium

Rotational dynamics of the Earth, over geological timescales, have profoundly affected local and global climatic evolution, probably contributing to the evolution of life. To better retrieve the Earth’s rotational history, and motivated by the published hypothesis of a stabilized length of day during the Precambrian, we examined the effect of thermal tides on the evolution of planetary rotational motion. The hypothesized scenario is contingent upon encountering a resonance in atmospheric Lamb waves, whereby an amplified thermotidal torque cancels out the opposing torque generated by the oceans and solid interior, driving the Earth into rotational equilibrium. With this scenario in mind, we constructed an ab initio model of thermal tides on rocky planets describing a neutrally stratified atmosphere. The model takes into account dissipative processes with Newtonian cooling and diffusive processes in the planetary boundary layer. We retrieved, from this model, a closed-form solution for the frequency-dependent tidal torque, which captures the main spectral features previously computed using 3D general circulation models. In particular, under longwave heating, diffusive processes near the surface and the delayed thermal response of the ground prove to be responsible for attenuating, and possibly annihilating, the accelerating effect of the thermotidal torque at the resonance. When applied to the Earth, our model prediction suggests the occurrence of the Lamb resonance in the Phanerozoic, but with an amplitude that is insufficient for the rotational equilibrium. Interestingly, though our study was motivated by the Earth’s history, the generic tidal solution can be straightforwardly and efficiently applied in exoplanetary settings.

Asteroseismology and Spectropolarimetry of the Exoplanet Host Star λ Serpentis

The bright star λ Ser hosts a hot Neptune with a minimum mass of 13.6 M ⊕ and a 15.5 day orbit. It also appears to be a solar analog, with a mean rotation period of 25.8 days and surface differential rotation very similar to the Sun. We aim to characterize the fundamental properties of this system and constrain the evolutionary pathway that led to its present configuration. We detect solar-like oscillations in time series photometry from the Transiting Exoplanet Survey Satellite, and we derive precise asteroseismic properties from detailed modeling. We obtain new spectropolarimetric data, and we use them to reconstruct the large-scale magnetic field morphology. We reanalyze the complete time series of chromospheric activity measurements from the Mount Wilson Observatory, and we present new X-ray and ultraviolet observations from the Chandra and Hubble space telescopes. Finally, we use the updated observational constraints to assess the rotational history of the star and estimate the wind braking torque. We conclude that the remaining uncertainty on the stellar age currently prevents an unambiguous interpretation of the properties of λ Ser, and that the rate of angular momentum loss appears to be higher than for other stars with a similar Rossby number. Future asteroseismic observations may help to improve the precision of the stellar age.

Survey of glyphosate- and dicamba-resistant kochia (Bassia scoparia) in Saskatchewan

Kochia ( Bassia scoparia (L.) A.J. Scott) is a problematic tumbleweed, which infests row crops and ruderal areas within western Canada. Herbicide resistance makes kochia management challenging for producers. Widespread resistance to acetolactate synthase-inhibitors, evolution and spread of glyphosate resistance, and the occurrence of dicamba resistance has been previously noted in Saskatchewan. This study's objective was to evaluate the occurrence and distribution of glyphosate- and dicamba-resistant kochia in central and southern Saskatchewan. A randomized, stratified survey was conducted in the fall of 2019 at 303 sites. Rotational history was obtained using the Agriculture and Agri-Food Canada Annual Crop Inventory. Kochia samples were collected from cropped fields (78%), ditches (17%), oil well sites (2%), and railway grades (3%). Glyphosate resistance was detected in 87% of samples ( n = 275) within 137 Rural Municipalities (RMs). Dicamba resistance was detected in 45% of kochia samples ( n = 255) in 87 RMs. Crops infested with herbicide-resistant kochia included wheat ( Triticum aestivum L. and T. durum Desf.), canola ( Brassica napus L.), lentils ( Lens culinaris Medik.), barley ( Hordeum vulgare L.), flax ( Linum usitatissimum L.), and peas ( Pisum sativum L.). Reducing the soil seedbank and preventing dispersal will be critical to mitigating resistance. Good herbicide stewardship including mixing multiple modes of action is paramount. Cultural strategies to increase canopy closure and crop competitiveness to limit biomass and seed production are recommended. Kochia occupies many environments outside of cropped fields, and a community-wide management approach may be necessary to reduce dispersal potential of tumbling plants that disperse seed.

Pulsed counterclockwise rotation of the southwestern Sichuan Basin in response to the India-Asia convergence during 128-42 Ma

Deciphering the building history of the eastern Tibetan Plateau since the India-Asia convergence is crucial to understand geodynamic models of plateau formation. The Sichuan Basin adjacent to the eastern Tibetan Plateau margin potentially provides valuable records of when and how the Tibetan Plateau expanded eastward. In this study, we reconstruct ∼128–42 Ma rotation history of the southwestern Sichuan Basin using detailed paleomagnetic declination data from the Early Cretaceous to Eocene sedimentary sequence of ∼2400 m thick. A total of 78 sampling sites (774 samples) yield primary remanent magnetization confirmed by positive paleomagnetic tests. Our results show that the southwestern Sichuan Basin experienced a long-term clockwise rotation during 128–42 Ma which was interrupted by three transient and rapid counterclockwise rotation pulses. The earlier two pulses (86–82 Ma and 66–60 Ma) coincide with two India Plate acceleration episodes which are probably induced by the Marion and/or Réunion mantle plume upwelling, whereas the later pulse (53–46 Ma) temporally corresponds to the sudden slowdown of the India Plate caused by the India-Asia collision. Our findings indicate that the eastern Tibetan Plateau experienced prolonged and episodic building processes since the Late Cretaceous, long predating the traditional view of the late Miocene. The Tibetan Plateau was built synchronously from the Himalayas to its eastern margin. Lateral extrusion, block rotation, and strike-slip deformation collectively contribute to the mountain building in the eastern Tibetan Plateau region.

BCTC-KSM: A blockchain-assisted threshold cryptography for key security management in power IoT data sharing

With the rapid advancement of the manufacturing industry from digital stage to network stage, the massive data generated by the production, consumption and other links in power IoT (PIoT) needs to be analyzed and processed urgently. However, due to the limited storage and computing capacity of PIoT devices, the collected industrial data are usually encrypted and stored in the cloud. Data security will be highly dependent on key security, and it is crucial for data privacy protection in PIoT to securely manage keys. Therefore, this paper proposes a Blockchain-Assisted Threshold Cryptography for Key Security Management in Power IoT Data Sharing (BCTC-KSM). We use the Pedersen threshold secret sharing algorithm off-chain to split the symmetric keys used to encrypt cloud-outsourcing data in PIoT into multiple key fragments and publish them on-chain, and use the ledger technology of blockchain to record the rotation history of each key fragment and its access subjects, and then restrict the user access to the key fragments through attribute access control policies on-chain. Security analysis and experimental results show that the BCTC-KSM can significantly improve the security and availability in PIoT data sharing at a slightly higher time cost than the state-of-the-art cryptography scheme.

Hybrid Learning of Time-Series Inverse Dynamics Models for Locally Isotropic Robot Motion

Applications of force control and motion planning often rely on an inverse dynamics model to represent the high-dimensional dynamic behavior of robots during motion. The widespread occurrence of low-velocity, small-scale, locally isotropic motion (LIMO) typically complicates the identification of appropriate models due to the exaggeration of dynamic effects and sensory perturbation caused by complex friction and phenomena of hysteresis, e.g., pertaining to joint elasticity. We propose a hybrid model learning base architecture combining a rigid body dynamics model identified by parametric regression and time-series neural network architectures based on multilayer-perceptron, LSTM, and Transformer topologies. Further, we introduce novel joint-wise rotational history encoding, reinforcing temporal information to effectively model dynamic hysteresis. The models are evaluated on a KUKA iiwa 14 during algorithmically generated locally isotropic movements. Together with the rotational encoding, the proposed architectures outperform state-of-the-art baselines by a magnitude of 10$^3$ yielding an RMSE of 0.14 Nm. Leveraging the hybrid structure and time-series encoding capabilities, our approach allows for accurate torque estimation, indicating its applicability in critically force-sensitive applications during motion sequences exceeding the capacity of conventional inverse dynamics models while retaining trainability in face of scarce data and explainability due to the employed physics model prior.

Farming system effects on root rot pathogen complex and yield of faba bean (vicia faba) in Germany.

A survey across Germany was undertaken from 2016-2019 to evaluate effects of management system (organic vs conventional), pedo-climatic conditions and crop rotation history on faba bean root health status, diversity of major root rot pathogens and yield. Root rot incidence was generally low and there was no effect of the management system on the spectrum of pathogens isolated. Among the most common fungal species identified, frequencies of Fusarium redolens and Didymella pinodella were significantly higher in roots from organic fields compared with conventional and lower was observed for F. avenaceum, F. tricinctum and F. culmorum. Faba bean roots were colonized at similar rates by F. equiseti and the members of the F. oxysporum (FOSC) and F. solani (FSSC) species complexes in both management systems. Almost no legumes had been grown in the 5-11 years preceding the conventional faba beans surveyed while legumes had almost always been present during this period in the organic fields. This difference in rotational histories between the farming systems led to apparent cropping systems effects on the isolation frequencies of several species. For example, D. pinodella was ubiquitous in organic fields with a high frequency of legumes in the rotations but much rarer and often absent in conventional fields. Pedo-climatic conditions, particularly cool conditions at sowing and plant emergence and/or during the vegetative season favored most of the most prevalent Fusarium species identified in this study. In organic systems, yields correlated negatively with D. pinodella and F. redolens frequencies whereas higher levels of F. tricintum in faba bean roots had a positive correlation with yield. In conventional systems, faba bean yields depended more on the total precipitation before sowing and during the main growing season but were also negatively correlated with the frequencies of FOSC and F. culmorum. Phylogenetic analysis based on the TEF1 alpha locus indicated that the FSSC isolates mainly belonged to the F. pisi lineage. In contrast, the FOSC isolates were placed in 9 different lineages, with a conspicuous dominance of F. libertatis that has until now not been associated with any leguminous host.

Paleomagnetic constraints on Paleogene-Neogene rotation and paleo-stress in the northern Qaidam Basin

Knowing the rotation and paleo-stress history in Qaidam Basin is a fundamental parameter to quantify the mechanism of intracontinental deformation in Tibetan Plateau. However, few studies have been conducted on tectonic rotation and stress evolution over long timescales in the Qaidam Basin. Here, we report new magnetic declination and the anisotropy of magnetic susceptibility (AMS) from a ∼52–7 Ma sequence of fluvial and lacustrine sediments in the Dahonggou (DHG) section in the northern Qaidam Basin. The magnetic declination revealed that the northern Qaidam Basin underwent a clockwise rotation 25.1° ±8.6° during ∼33–17 Ma, followed by a counterclockwise rotation 16.9°±6.8° during ∼17–13.5 Ma. The AMS results showed that the “earliest deformation” fabrics were interrupted by the “pencil structure” fabrics in the intervals of ∼52–45 and ∼21–15 Ma. The interruption, synchronous with the marked deceleration of the India-Asia convergence rate, indicates pulse of strong tectonic compressive stress. In addition, the AMS results documented a transition in stress direction from S-N to SW-NE at ∼15 Ma, suggesting a kinematic shift in the northeastern TP. Our constraints on the rotation and stress from the northern Qaidam Basin support the two-stage evolution of the Altyn Tagh Fault (ATF). The fast-rate slip motion on the ATF during the early Oligocene caused the clockwise rotation in the northern Qaidam Basin; the second stage with enhanced thrusting since the middle Miocene caused extensive crustal shortening and dispersive NW-trending folds and faults in the Qaidam Basin and the northeastern TP.

Impact of diversification and intensification of crop rotation (DICR) in soil bacterial microbiota in on-farm study after four and seven years

No-till agricultural diversification and intensification of crop rotations (DICR) effects on soil biological properties were studied in an on-farm study. DICR stands for increasing soil cultivation period and consequent reduction of fallow times by using different winter and summer crops, including cover crops, in two and three-year rotation schemes. Five different levels of DICR were tested -typical local rotation, intermediate rotation, high intensification with grasses, high intensification with legumes, and a continuous multispecies pasture-, and replicated at three different agricultural farms situated in the Argentinean Pampa. The soils were analyzed at four and seven years after DICR started. The on-farm studies were established at each site in a plot of ca. fifty hectares with a typical local rotation history and evaluated after four and seven years of changes. The impact on prokaryotic soil communities was measured by 16S rRNA gene sequencing. Overall, the sustained DICR showed a progressive effect with reduced Bray-Curtis dissimilarities at second sampling. At the phylum level, Actinobacteria, Bacteroidetes, Verrucomicrobia, BCR1, and WS3 increased with the level of DICR while Acidobacteria, Firmicutes, Gemmatimonadetes, OD1, and TM7 showed the opposite trend. Selected taxa based on LEfSe detection were associated with typical historical rotation after the four years and pasture after the seven years, expressing the cumulative effect of DICR. Bacterial communities' structures were associated with plant stubble and crop yield. Understanding how more sustainable practices such as DICR shift the soil microbiota can assist in designing agricultural systems that increase soil health, C sequestration, and crop yield.

Impacts of near‐natural management in eucalyptus plantations on soil bacterial community assembly and function related to nitrogen cycling

Abstract Eucalyptus trees have been widely planted in China as commercial timber, which has caused severe soil erosion and water deficiency. Near‐natural management by mixing eucalyptus with nitrogen‐fixing tree species has been used in plantations to alleviate these problems. In the present study, we investigated the changes in soil microbial community and function in eucalyptus plantations mixed with nitrogen‐fixing trees and with different rotation histories (first and second generation) using Illumina MiSeq. of 16S rRNA gene, coupled with Functional Annotation of Prokaryotic Taxa (FAPROTAX) and Quantitative Microbial Element Cycling (QMEC) analyses. Both management systems (mixed with nitrogen‐fixing trees and with different rotating time) increased the soil bacterial α‐diversity. The plantations with different management histories formed different bacterial communities and potential functional structures. Mixing with nitrogen‐fixing trees increased the abundance of Actinobacteria involved in the nitrogen cycle and the abundance of K‐strategy bacteria (Acidobacteria, Verrucomicrobia, Chloroflexi) in both first‐ and second‐generation plantations. Functionally, the expression of nitrogen‐fixing (nifH) and nitrification genes (amoA1 and hao) increased and that of denitrification genes (nirk2, nirk3, nirS1 and nosZ2) decreased in plantations mixed with nitrogen‐fixing trees. The soil pH, soil water content and bacterial biomass were the key factors driving bacteria community and functional structures. The strategy of mixing eucalyptus with nitrogen‐fixing trees can increase the efficiency of nitrogen cycling by accelerating the nitrogen‐fixing and nitrifying process while inhibiting the denitrifying process. The results highlight the importance of mixing eucalyptus with nitrogen‐fixing trees for soil microbes and provide useful information on the management of eucalyptus plantations in the future. Read the free Plain Language Summary for this article on the Journal blog.

Angular momentum transport in a contracting stellar radiative zone embedded in a large-scale magnetic field

Context. Some contracting or expanding stars are thought to host a large-scale magnetic field in their radiative interior. By interacting with the contraction-induced flows, such fields may significantly alter the rotational history of the star. They thus constitute a promising way to address the problem of angular momentum transport during the rapid phases of stellar evolution. Aims. In this work, we aim to study the interplay between flows and magnetic fields in a contracting radiative zone. Methods. We performed axisymmetric Boussinesq and anelastic numerical simulations in which a portion of the radiative zone was modelled by a rotating spherical layer, stably stratified and embedded in a large-scale (either dipolar or quadrupolar) magnetic field. This layer is subject to a mass-conserving radial velocity field mimicking contraction. The quasi-steady flows were studied in strongly or weakly stably stratified regimes relevant for pre-main sequence stars and for the cores of subgiant and red giant stars. The parametric study consists in varying the amplitude of the contraction velocity and of the initial magnetic field. The other parameters were fixed with the guidance of a previous study. Results. After an unsteady phase during which the toroidal field grew linearly and then back-reacted on the flow, a quasi-steady configuration was reached, characterised by the presence of two magnetically decoupled regions. In one of them, magnetic tension imposes solid-body rotation. In the other, called the dead zone, the main force balance in the angular momentum equation does not involve the Lorentz force and a differential rotation exists. In the strongly stably stratified regime, when the initial magnetic field is quadrupolar, a magnetorotational instability is found to develop in the dead zones. The large-scale structure is eventually destroyed and the differential rotation is able to build up in the whole radiative zone. In the weakly stably stratified regime, the instability is not observed in our simulations, but we argue that it may be present in stars. Conclusions. We propose a scenario that may account for the post-main sequence evolution of solar-like stars, in which quasi-solid rotation can be maintained by a large-scale magnetic field during a contraction timescale. Then, an axisymmetric instability would destroy this large-scale structure and this enables the differential rotation to set in. Such a contraction-driven instability could also be at the origin of the observed dichotomy between strongly and weakly magnetic intermediate-mass stars.

Lattice rotation effect on the dislocation pattern of Cu deformed in tension

ABSTRACT The dislocation pattern of cold deformed FCC metals follows an orientation-dependent rule. However, only final orientation after deformation has been considered in related studies, i.e. without considering lattice rotation effect, although metals have undergone heavy lattice rotation during plastic deformation. In this work, the lattice rotation effect on the dislocation structures of Cu is investigated by combining electron backscatter diffraction, focused ion beam lift-out and scanning transmission electron microscopy techniques. The dislocation patterns of [110]-[110], [111]-[111] and [110]-[111] type grains deformed in tension under room temperature are compared. The notation [h1k1l1]-[h2k2l2] represents the lattice rotation history of a grain, meaning that the grain rotates from [h1k1l1] corner to [h2k2l2] corner during tension. It is found that for a given strain range, the dislocation cell structure is observed in [111]-[111] grain, while the dislocation cell block structure is dominant in [110]-[111] grain. This demonstrates that for Cu grains with a final orientation near [111] corner, dislocation pattern type is influenced by the lattice rotation feature. Same with [110]-[111] type grain, cell block structure is the main feature found in [110]-[110] grain, indicating that for grain with initial orientation near [110] corner, lattice rotation has a marginal effect on the dislocation structure. The relation between the dislocation structure, lattice rotation, slip system and strain level of Cu is discussed.

Seismic pounding damage to adjacent reinforced concrete frame–shear wall buildings and freestanding contents

AbstractClosely spaced tall buildings are common in modern urban areas due to limited supply of land to accommodate rapid growth of population. These buildings are vulnerable in seismically active regions particularly when earthquake‐induced pounding occurs between adjacent buildings, resulting in high floor acceleration spikes that may lead to excessive demands on building contents (BCs). This paper examines the effect of seismic pounding on damage to adjacent reinforced concrete (RC) frame–shear wall buildings and their freestanding contents using nonlinear response‐history analyses (RHA). A cascading analysis approach is adopted to obtain absolute floor accelerations of pounding tall buildings, which are then applied to determine response of freestanding contents dominated by either sliding or rocking motions. In order to provide a useful tool for practicing engineers and facilitate analyses, the buildings are simplified as story‐based multiple‐degree‐of‐freedom (MDOF) flexural‐shear models, and unanchored contents are idealized as single‐degree‐of‐freedom (SDOF) oscillators, all of which are approximated using OpenSees and verified against solutions to their exact equations of motion solved using Matlab. It is shown that seismic pounding leads to higher building damage and alters story damage distribution patterns. It is concluded that pounding significantly increases sliding potential and maximum sliding displacement demands on stocky contents, especially those on higher floors. The transitions of stick–slip response of the contents coincide well with pounding occurrences. It is also concluded that pounding has detrimental effects on slender rocking contents, but rocking rotation histories of these contents do not show abrupt changes upon impact.