Rotation Pole Research Articles

Insights on the Rotational State and Shape of Asteroid (203) Pompeja from TESS Photometry

The Main Belt asteroid (203) Pompeja shows evidence of extreme variability in visible and near-infrared spectral slope with time. The observed spectral variability has been hypothesized to be attributed to spatial variations across Pompeja’s surface. In this scenario, the observed spectrum of Pompeja is dependent on the geometry of the Sun and the observer relative to the asteroid’s spin-pole and surface features. Knowledge of the rotational spin pole and shape can be gleaned from light curves and photometric measurements. However, dense light curves of Pompeja are only available from two apparitions. Further, previous estimates of Pompeja’s sidereal period are close to being Earth commensurate, making ground-based light curves difficult to obtain. To overcome these difficulties, we implement a pipeline to extract a dense light curve of Pompeja from cutouts of Transiting Exoplanet Survey Satellite (TESS) full-frame images. We succeeded in obtaining a dense light curve of Pompeja covering ∼22 complete rotations. We measure a synodic period of P syn = 24.092 ± 0.005 hr and amplitude of 0.073 ± 0.002 mag during Pompeja’s 2021 apparition in the TESS field of view. We use this light curve to refine models of Pompeja’s shape and spin-pole orientation, yielding two spin-pole solutions with sidereal periods and spin-pole ecliptic coordinates of P sid,1 = 24.0485 ± 0.0001 hr, λ 1 = 132°, and β 1 = +41° and P sid,2 = 24.0484 ± 0.0001 hr, λ 2 = 307°, and β 2 = +34°. Finally, we discuss the implications of the derived shape and spin models for spectral variability on Pompeja.

Nested active regions anchor the heliospheric current sheet and stall the reversal of the coronal magnetic field

During the solar cycle, the Sun's magnetic field polarity reverses due to the emergence, cancellation, and advection of magnetic flux towards the rotational poles. Flux emergence events occasionally cluster together, although it is unclear if this is due to the underlying solar dynamo or simply by chance. Regardless of the cause, we aim to characterise how the reversal of the Sun's magnetic field and the structure of the solar corona are influenced by nested flux emergence. From the spherical harmonic decomposition of the Sun's photospheric magnetic field, we identified times when the reversal of the dipole component stalls for several solar rotations. Using observations from sunspot cycle 23 to present, we located the nested active regions responsible for each stalling and explored their impact on the coronal magnetic field using potential field source surface extrapolations. Nested flux emergence has a more significant impact on the topology of the coronal magnetic field than isolated emergences as it produces a coherent (low spherical harmonic order) contribution to the photospheric magnetic field. The heliospheric current sheet, which separates oppositely directed coronal magnetic fields, can become anchored above nested active regions due to the formation of strong opposing magnetic fluxes. Further flux emergence, cancellation, differential rotation, and diffusion, then effectively advects the heliospheric current sheet and shifts the dipole axis. Nested flux emergence can restrict the evolution of the heliospheric current sheet and impede the reversal of the coronal magnetic field. The sources of the solar wind can be more consistently identified around nested active regions because the magnetic field topology remains self-similar for multiple solar rotations. This highlights the importance of identifying and tracking nested active regions to guide the remote-sensing observations of modern heliophysics missions.

A NICER View of PSR J1231−1411: A Complex Case

Recent constraints on neutron star mass and radius have advanced our understanding of the equation of state (EOS) of cold dense matter. Some of them have been obtained by modeling the pulses of three millisecond X-ray pulsars observed by the Neutron Star Interior Composition Explorer (NICER). Here, we present a Bayesian parameter inference for a fourth pulsar, PSR J1231−1411, using the same technique with NICER and XMM-Newton data. When applying a broad mass-inclination prior from radio timing measurements and the emission region geometry model that can best explain the data, we find likely converged results only when using a limited radius prior. If limiting the radius to be consistent with the previous observational constraints and EOS analyses, we infer the radius to be 12.6 ± 0.3 km and the mass to be 1.04−0.03+0.05 M ⊙, each reported as the posterior credible interval bounded by the 16% and 84% quantiles. If using an uninformative prior but limited between 10 and 14 km, we find otherwise similar results, but Req=13.5−0.5+0.3 km for the radius. In both cases, we find a nonantipodal hot region geometry where one emitting spot is at the equator or slightly above, surrounded by a large colder region, and where a noncircular hot region lies close to southern rotational pole. If using a wider radius prior, we only find solutions that fit the data significantly worse. We discuss the challenges in finding the better fitting solutions, possibly related to the weak interpulse feature in the pulse profile.

Photometry and Models of Seven Main-Belt Asteroids

The China Near-Earth Object Survey Telescope (CNEOST) conducted four photometric surveys from 2015 to 2018 using image processing and aperture photometry techniques to obtain extensive light curve data on asteroids. The second-order Fourier series method was selected for its efficiency in determining the rotation periods of the observed asteroids. Our study successfully derived rotation periods for 892 asteroids, with 648 of those matching values recorded in the LCDB (for asteroids with U > 2). To enhance the reliability of the derived spin parameters and shape models, we also amassed a comprehensive collection of published light curve data supplemented by additional photometric observations on a targeted subset of asteroids conducted using multiple telescopes between 2021 and 2022. Through the application of convex inversion techniques, we successfully derived spin parameters and shape models for seven main-belt asteroids (MBAs): (2233) Kuznetsov, (2294) Andronikov, (2253) Espinette, (4796) Lewis, (1563) Noel, (2912) Lapalma, and (5150) Fellini. Our thorough analysis identified two credible orientations for the rotational poles of these MBAs, shedding light on the prevalent issue of “ambiguity in pole direction” that often accompanies photometric inversion processes. CNEOST continues its observational endeavors, and future collected data combined with other independent photometric measurements will facilitate further inversion to better constrain the spin parameters and yield more refined shape models.

Polar cap region and plasma drift in pulsars

ABSTRACT Pulsars often display systematic variations in the position and/or intensity of the subpulses, the components that comprise each single pulse. Although the drift of these subpulses was observed in the early years of pulsar research, and their potential for understanding the elusive emission mechanism was quickly recognized, there is still no consensus on the cause of the drift. We explore the electrodynamics of two recently proposed or refined drift models: one where plasma lags behind corotation, connecting the drift with the rotational pole; and another where plasma drifts around the electric potential extremum of the polar cap. Generally, these are different locations, resulting in different drift behaviours, that can be tested with observations. In this study, however, we specifically examine these models in the axisymmetric case, where the physics is well understood. This approach seems counter-intuitive as both models then predict similar large-scale plasma drift. However, it allows us to show, by studying conditions within the sparks for both models, that the lagging behind corotation model is inconsistent with Faraday’s law. The modified carousel (MC) model, where plasma drifts around the electric potential extremum, not only aligns with Faraday’s law, but also provides a future direction for developing a comprehensive model of plasma generation in the polar cap region. Unlike previous models, which considered the drift only inside the discharging regions, the MC model reveals that the electric field between the discharges is not completely screened, and plasma drifts there – a paradigm shift for the drifting subpulse phenomenon.

Moxibustion improves motor function by down-regulating SNX5 and inhibiting ferroptosis in neurons of corpus striatum in mice with Parkinson's disease.

To explore the effect of moxibustion on the expression of sorting nexin 5 (SNX5), glutathione peroxidase (GPX4) and ferritin heavy chain (FTH1) in the corpus striatum in mice with Parkinson's disease (PD), so as to explore its mechanisms underlying improvement of PD by ameliorating ferroptosis in the substantia nigra striatum. C57BL/6J mice were randomly divided into normal, sham operation, model, and moxibustion groups, with 10 mice in each group. The PD model was established by unilateral injection of 6-hydroxydopamine (3.5 μL) into the right medial forebrain bundle (AP=-1.2 mm, ML=-1.3 mm, DV=-4.75 mm). The mice in the moxibustion group received moxibustion at "Baihui"(GV20) and "Sishencong"(EX-HN1) for 20 min each time, once a day, 6 times a week for 4 weeks. After the intervention, mice received apomorphine rotation behavior detection and pole climbing test. The expression of tyrosine hydroxylase (TH) in the substantia nigra was detected by immunofluorescence, the contents of Fe2+, malondialdehyde (MDA), the ratio of glutathione/oxidized glutathione (GSH/GSSG) in the corpus striatum were detected by using photocolorimetric method, and the expression levels of SNX5 (endocytosomal protein), GPX4 (one of the key targets for inhibiting ferroptosis) and FTH1 proteins and mRNAs in the corpus striatum were detected by Western blot and qPCR, respectively. Behavior tests showed that the pole climbing time and number of body rotation were significantly increased in the model group relevant to the sham operation group (P<0.01), and strikingly decreased in the moxibustion group relevant to the model group (P<0.01). The immunofluorescence intensity of TH in the substantia nigra, the ratio of GSH/GSSG, and the expression levels of GPX4 and FTH1 mRNAs and proteins in the corpus striatum were markedly decreased (P<0.01, P<0.05), while the contents of Fe2+ and MDA and the expression levels of SNX5 mRNA and protein in the corpus striatum significantly increased in the model group relevant to the sham operation group (P<0.01, P<0.05). Compared with the model group, the decreased immunofluorescence intensity of TH, GSH/GSSH, and the expression levels of GPX4 and FTH1 mRNAs and proteins, and the increased contents of Fe2+ and MDA and the expression levels of SNX5 mRNA and protein were reversed in the moxibustion group relevant to the model group (P<0.01, P<0.05). Moxibustion may improve motor dysfunction in PD mice, which may be related to its effects in down-regulating the expression of SNX5, promoting the synthesis of GSH, decreasing the contents of Fe2+ and MDA, up-regulating the ratio of GSH/GSSG and the expression of GPX4 and FTH1 mRNAs and proteins in the corpus striatum, and inhibiting the occurrence of ferroptosis.

Predictions for Sparse Photometry of Jupiter-family Comet Nuclei in the LSST Era

The Legacy Survey of Space and Time (LSST) at Vera C. Rubin Observatory will deliver high-quality, temporally sparse observations of millions of solar system objects on an unprecedented scale. Such data sets will likely enable the precise estimation of small-body properties on a population-wide basis. In this work, we consider the possible applications of photometric data points from LSST to the characterization of Jupiter-family comet (JFC) nuclei. We simulate sparse-in-time lightcurve points with an LSST-like cadence for the orbit of a JFC between 2024 and 2033. Convex lightcurve inversion is used to assess whether the simulation input parameters can be accurately reproduced for a sample of nucleus rotation periods, pole orientations, activity onsets, shapes, and sizes. We find that the rotation period and pole direction can be reliably constrained across all nucleus variants tested, and that the convex shape models, while limited in their ability to describe complex or bilobed nuclei, are effective for correcting sparse photometry for rotational modulation to improve estimates of nucleus phase functions. Based on this analysis, we anticipate that LSST photometry will significantly enhance our present understanding of the spin state and phase function distributions of JFC nuclei.

A Detailed Reconstruction of the Woodlark Basin

AbstractAn animated 100,000‐year‐interval tectonic reconstruction of the Woodlark Basin in the southwest Pacific illustrates how, at intermediate initial spreading rates, orogenic continents break up (dyke model), spreading segments nucleate, transform faults initiate and ocean basins evolve. We refine the location/timing of initial seafloor spreading and Euler poles of rotation back to 6.2 Ma. In the easternmost basin, where spreading younger than 2.6 Ma is not co‐polar with that to the west, we recognize the formation of a Ghizo microplate and Ranongga Transform Fault at ∼2.6 Ma and a 3‐degree rotational opening of the Itina Trough from 2.6 to 1.0 Ma. Allowing for that motion, we show that the 5.2–2.6 Ma seafloor in the easternmost basin formed co‐polar with that to the west. We also identify a ridge jump reorientation at ∼1.0 Ma that formed the NE‐trending Simbo Spreading Segment, whose neovolcanic zone includes Simbo Island and a submarine edifice to its south. Proposed deterministic models of ridge propagation (due to topographic gradients, mantle flow away from hotspots and/or changing plate motion) are not consistent with those observed; mantle chemical heterogeneities and melting anomalies are a potential cause that remains to be tested. We reconstruct the northern conjugate of the oldest extant oceanic crust and estimate the initiation of its subduction at ∼2.6 Ma, concomitant with observed changes in plate motion and segmentation. Where subducted, the young oceanic lithosphere between the conjugate rifted margins appears to be resorbed into the mantle, leaving a slab window where the Pacific subducted slab remains attached.

Phase curve wavelength dependency as revealed by shape- and geometry- corrected asteroid phase curves

ABSTRACT We investigate the photometric properties of 35 well-observed asteroids using dense ground-based and sparse ATLAS survey data. Focusing on two-colour photometric phase functions, derived using inverse methods, we explore the wavelength dependence. Our study reveals distinct (G1, G2) domains for cyan and orange filters, especially among some S-complex asteroids. For other asteroids, substantial uncertainties prevail, or their distributions of phase curve parameters overlap, precluding definitive conclusions on wavelength dependence. Notably, for S-complex objects, the effect appears systematic, characterized by lower G2 values in the cyan filter. The effect can be explained by considering the known geometric albedo correlation: higher albedo corresponds to flatter, whereas lower albedo corresponds to steeper phase curves. In the case of equal albedo, asteroids with red spectral slopes have a more pronounced opposition effect in red and asteroids with blue spectral slopes in blue filters. We explore the variation of slope differences of orange and cyan phase curves with phase angle. For most asteroids, the largest nominal variation is observed at phase angles &amp;lt; 10°. This suggests that the phase colouring for the orange–cyan colour slope is more pronounced at small phase angles. Through meticulous analysis of the opposition effect amplitudes, we also pinpoint preferred rotational pole solutions. We identify inconsistencies between phase curve parameters and spectral types in specific cases. The shape- and geometry-corrected phase curves signify an important advancement in studying asteroid photometric behaviour and may offer a deeper understanding of surface and regolith properties previously obscured by these effects, such as surface roughness.

Unfolding rotational tectonics and topographic evolution from localized verses diffuse plate boundary counterparts

We present a kinematic model developed from geodetic observations, topography analysis and analogue tectonic modelling results, which reveals a striking similarity between the rotational tectonic settings of the Gakkel Ridge-Chersky Range system in the Arctic, and the Central Indian Tectonic Zone within the Indian subcontinent. A crucial aspect of large-scale extensional rift systems is the gradual variation of extension along the rift axis, due to plate rotation about a Euler pole, which may lead to contraction on the opposite side of the Euler pole to form a rotational tectonic system. Our geodetic and topographic analysis, combined with the reanalysis of analogue tectonic modelling results demonstrates such rotational tectonic plate motion in both the Arctic and Indian case. However, the plate boundary between the North American and Eurasian Plates as represented by the Arctic Gakkel Ridge-Chersky Range system is strongly localized, whereas the Central Indian Tectonic Zone that separates the North and South India Plates involves diffuse deformation instead. Furthermore, in both the Arctic and Central Indian we find that the relative Euler rotation pole is located near an indenter-like feature, which possibly controls the present-day rotational tectonics and contrasting topography on opposite sides of the Euler pole.

Formation and structure of circumplanetary disks and envelopes during the late stages of giant planet formation

Giant planets are expected to form within circumstellar disks, which shape their formation history and the local environment. Here, we consider the formation and structure of circumplanetary disks that arise during the late stages of giant planet formation. During this phase, when most of the final mass is accumulated, incoming material enters the Hill sphere and falls toward the planet. In the absence of torques, the falling parcels of gas conserve their specific angular momentum and collect into a circumplanetary disk. Generalizing previous work, we consider a range of possible geometries for the flow entering the sphere of influence of the planet. Specifically, we consider five geometric patterns for the inward flow, ranging from concentration toward the rotational poles of the system to isotropic flow to concentration along the equatorial plane. For each case, we derive analytic descriptions for the density field of the infall region, the disk surface density in the absence of viscosity, and steady-state solutions for viscous disks. These results, in turn, specify the luminosity contributions of the planet, the circumplanetary disk, and the envelope. These power sources, in conjunction with the surrounding material, collectively determine the observational appearance of the forming planet. We conclude with an approximate determination of these radiative signatures.

Geomorphology and Age Constraints of Seamounts in the Cabo Verde Archipelago, and Their Relationship to Island Ages and Geodynamic Evolution

AbstractThe Cabo Verde Archipelago is related to a mantle plume located close to the rotational pole of the African Plate. It consists of islands and seamounts arranged in a horseshoe‐shaped pattern open to the west, thus forming two volcanic chains, each with a weak east‐west age progression. High‐resolution swath bathymetry of 12 Cabo Verde seamounts is used here to assign each seamount to its pre‐shield, shield or post‐shield evolutionary stage, respectively. The eastern seamounts exhibit degraded and partially eroded morphologies, and are mainly in their post‐shield stage. A new 40Ar‐39Ar date for Senghor Seamount at 14.872 ± 0.027 Ma supports old ages for the eastern seamounts. The western seamounts generally exhibit younger volcanic‐edifice‐construction morphologies, showing fresh effusive and explosive volcanics, including rarely observed deep‐water explosive volcanism in the Charles Darwin Volcanic Field. Furthermore, the two previously unknown seamounts Sodade and Tavares in the westernmost termini of both volcanic chains exhibit pristine volcanic morphologies, in agreement with present‐day volcanism and seismic activity recorded from the western seamounts. The islands and seamounts rest on three submarine platforms to the east, northwest and southwest, respectively. Taken together, the seamount and island data suggest a shift in igneous activity from the eastern to the other platforms at about 8–6 Ma. However, the complex evolution pattern for both volcanic chains includes the simultaneous occurrence of pre‐shield or shield edifices at any time, followed by erosional and rejuvenation stages. The new seamount data still demonstrate ongoing westward submarine‐growth in both volcanic chains.

Rotation of the Microplates Within the Plate Boundary in Southwestern United States

AbstractI investigate the long‐term, rigid motions of the 20 microplates identified by McCaffrey (2005, https://doi.org/10.1029/2004jb003307) within the Pacific‐North America plate boundary in southwestern United States. Those motions are described by the Euler vectors ( for the ith microplate) given by McCaffrey for each microplate. McCaffrey noticed that the Euler poles for those microplates were aligned along the great circle that connects the geometric center of the microplate distribution with the PACI pole, the pole of rotation of the Pacific Plate (PA) about the North American Plate (NA). To explain that alignment, Thatcher et al. (2016, https://doi.org/10.1002/2015jb0126678.0) proposed replacing each by two, vertical‐axis rotations of the microplate, one describing the trajectory (orbit) of its center of mass (CM) and the other its rotation (spin) about that CM, where . Moreover, they suggested that the orbital motion was being driven by drag from the rotating PA, which suggests that the poles coincide with the PACI pole. Then rotation vectors consistent with the given can be found for 17 of the microplates; the other 3 microplates are apparently affected by Basin‐and‐Range extension as well as PA relative motion. The long‐term motion of each of the 17 microplates then can be described as an orbital rotation about the PACI pole plus spin about the CM of the microplate. The closer the microplate CM is to the PA, the more nearly its orbital rotation rate approaches the rotation rate of the PA about the PACI pole.

ITRF2020 Plate Motion Model

AbstractA tectonic Plate Motion Model (PMM) is essential for geodetic applications, while contributing to the understanding of geodynamic processes affecting the Earth's surface. We introduce a PMM derived from the horizontal velocities of 518 sites extracted from the ITRF2020 solution. These sites were chosen away from plate boundaries, Glacial Isostatic Adjustment regions, and other deforming zones. Unlike the ITRF2014‐PMM, which showed no significant Origin Rate Bias (ORB), velocities used to determine the ITRF2020‐PMM exhibit a statistically significant ORB (0.74 ± 0.09 mm/yr along the Z‐component). Users are advised to add the estimated ORB to the horizontal velocities predicted by the ITRF2020‐PMM rotation poles for full consistency with the ITRF2020. However, the predicted vertical velocities resulting from the addition of the ORB should be discarded. The overall precision with which the ITRF2020 velocity field is represented by the rigid ITRF2020‐PMM is at the level of 0.25 mm/yr WRMS.

Surface distribution of small-scale magnetic field on the active cool star LQ Hydrae

It is well known that small-scale magnetism dominates the surface magnetic field topologies of active late-type stars. However, little information is available on the spatial distribution of this key magnetic field component. Here, we take advantage of the recently developed magnetic field diagnostic procedure relying on the magnetic intensification of iron atomic lines in the optical. We extend this methodology from measuring a single average field strength value to simultaneous Doppler imaging reconstruction of the two-dimensional maps of temperature and magnetic field strength. We applied this novel surface mapping approach to two spectroscopic data sets of the young active Sun-like star LQ Hya. For both epochs, we found a fairly uniform field strength distribution, apart from a latitudinal trend of the field strength increasing from 1.5–2.0 kG at low latitudes to 3.0–3.5 kG, close to the rotational poles. This distribution of the small-scale field does not display a clear correlation with the locations of temperature spots or the global magnetic field structure reconstructed for the same epochs.

Jurassic-Paleogene spreading history of the northern Indian Ocean as a constraint on the evolution of the north Australia continental margin

The spreading history of the northern Indian Ocean is re-examined with the aim of interpreting the late Mesozoic-Paleogene evolution of the northern Australian continental margin in eastern Indonesia and Timor-Leste. The earliest seafloor spreading (‘Argo phase’) developed between approximately 155-131Ma (Kimmeridgian, Late Jurassic to Valanginian, Early Cretaceous). A clockwise pole of rotation relative to Australia (‘Argo pole’) is interpreted at 7°09’S, 133°07’E, a present-day location near the Tanimbar islands in eastern Indonesia. A second ‘Gascoyne’ phase of spreading, between 131-100Ma (late Early Cretaceous), had an interpreted clockwise rotation pole at 3°40’N, 125°00’E, a present-day location between the islands of Mindanao (southern Philippines) and Sulawesi (eastern Indonesia). A third ‘Wharton’ phase of spreading, commencing at the beginning of the Late Cretaceous (~100Ma) had a more distant pole (clockwise pole at 5°S, 171°E: Jacob et al., 2014), although more local rotations are interpreted for the Greater Sula Spur continental terrane, about a pole estimated at 9°24’S, 134°40’E, close to the earlier Argo pole.The motions of two continental terranes are inferred from the spreading history. The Argoland Terrane, which is identified in this study as eastern Sundaland (Borneo and Java), would not have entirely detached from Australia before the mid Cretaceous due to the relatively proximal locations of the Argo and Gascoyne rotation poles. In this scenario Argoland could not have collided with Eurasia in the Cretaceous, as suggested by several previous studies. The Greater Sula Spur Terrane (several continental fragments in present-day eastern Indonesia), is repositioned in the initial reconstructions immediately north of Timor, and did not move northward to its late Paleogene (pre-Neogene collision) location until the Wharton phase of rifting that commenced in the Late Cretaceous. This northward motion of the Greater Sula Spur was accommodated by the development of a narrow oceanic basin (the Banda Embayment).The reconstructions suggest that the Argoland and Greater Sula Spur continental terranes formed a continuous crustal connection between SE Asia and northern Australia throughout the late Mesozoic and early Paleogene, and that the Indian Ocean developed entirely within the body of the disrupting Gondwanaland supercontinent, rather than linking eastwards into the Pacific Ocean.

Shape models and spin states of Jupiter Trojans

The leading theory for the origin of Jupiter Trojans (JTs) assumes that JTs were captured to their orbits near the Lagrangian points of Jupiter during the early reconfiguration of the giant planets. The natural source region for the majority of JTs would then be the population of planetesimals born in a massive trans-Neptunian disk. If true, JTs represent the most accessible stable population of small Solar System bodies that formed in the outer regions of the Solar System. For this work, we compiled photometric datasets for about 1000 JTs and applied the convex inversion technique in order to assess their shapes and spin states. We obtained full solutions for 79 JTs, and partial solutions for an additional 31 JTs. We found that the observed distribution of the pole obliquities of JTs is broadly consistent with expectations from the streaming instability, which is the leading mechanism for the formation of planetesimals in the trans-Neptunian disk. The observed JTs’ pole distribution has a slightly smaller prograde vs. retrograde asymmetry (excess of obliquities &gt;130°) than what is expected from the existing streaming instability simulations. However, this discrepancy can be plausibly reconciled by the effects of the post-formation collisional activity. Our numerical simulations of the post-capture spin evolution indicate that the JTs’ pole distribution is not significantly affected by dynamical processes such as the eccentricity excitation in resonances, close encounters with planets, or the effects of nongravitational forces. However, a few JTs exhibit large latitude variations of the rotation pole and may even temporarily transition between prograde- and retrograde-rotating categories.

The origin of the Musicians Seamount Province and its inferences for Late Cretaceous Pacific Plate Motion

Linear chains of seamounts, sourced from mantle plume processes, have the potential to refine plate motion models because the hotspot remains fixed relative to the moving lithospheric plate. However, to define plate motion, consistent seamount age progression and geometry are required. Some seamount chains, such as the Musician Seamount Province (MSP), have complex geometries and age distributions, which complicates calibrating plate motion. The MSP resides northwest of the Hawaiian Islands and is composed of seamounts and volcanic elongated ridges (VERs) that cover ∼420,000 km2 of Pacific seafloor. Here we provide new 40Ar/39Ar age determinations for a series of lava flows recovered from the MSP during expedition EX1708 of the National Oceanic and Atmospheric Administration's Ocean Exploration program. The MSP was built by four distinct volcanic processes: (1) age-progressive hotspot volcanism associated with the Euterpe Plume (ca. 98–79 Ma). (2) VER formation from plume-ridge channelization (ca. 97–94 Ma; 86–79 Ma) where the VERs only form when the hotspot is within ∼600 km of the ridge. (3) Eocene volcanism driven by extension during the ca. 50 Ma change in Pacific rotation poles (ca. 54–47 Ma). (4) Some near-ridge shear-driven upwelling or diffuse extensional volcanism that preceded the southern MSP lithosphere overriding the plume (ca. 86–84 Ma). By filtering lava flows with only robust statistically concordant 40Ar/39Ar age determinations as well as geologic setting, we develop a dataset of samples valuable for constraining Pacific plate motion. A local plate velocity of 42 ± 9 km/Ma for the 98–81 Ma time frame is calculated. Furthermore, the seamount track indicates that large shifts in Pacific rotation pole locations are required prior to 98 Ma and at ca. 81 Ma.

Multi-parameter optimization of ferrofluid seal pole teeth based on magnetic-flow coupling and taboo genetic algorithm

Ferrofluid seals are a high-performance seal technology. Rational pole tooth structure and size can enhance the performance of ferrofluid seals. However, most current methods for optimizing pole tooth structure and size ignore the influence of the flow field. Therefore, this paper presents a pole tooth optimization method based on magnetic-flow coupling and considers the shaft rotational speeds. Combining this method with the taboo genetic algorithm establishes the mathematical model and simulation model of magnetic pole tooth size optimization. The optimal pole tooth size at different rotational speeds is obtained through optimization. Additionally, the effects of rotational speed and pole tooth parameters on pressure capacity are studied. The results show that both the rotational speeds and the parameters of the pole teeth significantly affect pressure capacity. The rotational speeds also influence the parameters of the pole teeth.

Volcanism straddling the Miocene–Pliocene boundary on Patmos and Chiliomodi islands (southeastern Aegean Sea): insights from new 40Ar ∕ 39Ar ages

Abstract. The island of Patmos, in the eastern Aegean Sea, consists almost entirely of late Miocene to Pliocene volcanic rocks. The magmatism in the Aegean is governed by subduction of the African plate below the Eurasian plate, back-arc extension, slab rollback, slab edge processes and westward extrusion of central Anatolia to the west along the Northern Anatolian Fault into the Aegean domain. The evolution of the Aegean basin is that of a back-arc setting, with a southerly trend in the locus of both convergent tectonics and back-arc stretching, allowing intermittent upwelling of arc, lithospheric and asthenospheric magmas. Here, we present new 40Ar/39Ar age data for Patmos and the nearby small island of Chiliomodi to place this volcanism in a new high-resolution geochronological framework. High-resolution geochronology provides a key to understanding the mechanisms of both the tectonic and magmatic processes that cause the extrusion of magma locally and sheds light on the tectonic evolution of the larger region of the back-arc basin as a whole. The volcanic series on Patmos is alkalic, consistent with a back-arc extensional setting, and ranges from trachybasalt to phonolites, trachytes and rhyolites, with SiO2 ranging from 51.6 wt % to 80.5 wt %, K2O ranging from 2 wt % to 11.8 wt % and extrusion ages ranging from 6.59 ± 0.04 (0.14) Ma to 5.17 ± 0.02 (0.11) Ma. Volcanism on Patmos and adjacent Chiliomodi can be understood as a combination of mantle and crustal tectonic processes including the influence of transform faults and rotational crustal forces that also caused the widening of the southern Aegean basin due to two opposite rotational poles in the east and west and rollback of the subducting slab south of Crete.