Large-scale Morphology Research Articles

Impact of accretor size on the morphology of supersonic, non-relativistic, axisymmetric Bondi-Hoyle-Lyttleton accretion flows

Fast-moving accretors are a ubiquitous phenomenon in astrophysics. Their interaction with the surrounding gas can leave characteristic imprints on the form of morphological structures like bow shocks, Mach cones, and trails with different densities. We study how various physical processes affect the flow structure around an accretor with a one-way surface, its accretion rate, and accretion anisotropy. These processes correspond to distinct length scales: the Bondi radius, the stand-off distance of the bow shock, and the Hoyle-Lyttleton radius. We conducted adiabatic hydrodynamic simulations using a spherical coordinate grid centred on the accretor's location. By varying the accretor's (numerical) size across various scales — from much smaller than the stand-off distance to much larger than the Bondi radius — we analyse how the processes on these spatial scales affect the physics of the steady-state flow. All simulations achieve a steady state. When the accretor is smaller than the stand-off distance, a bow shock forms ahead of the object, and a nearly spherically symmetric atmosphere develops within this distance. Accretors smaller than the Hoyle-Lyttleton radius produce a Mach cone, while larger accretors exhibit a supersonic-to-subsonic flow transition on larger scales. Fully resolved simulations align with the Hoyle-Lyttleton theory, showing slightly anisotropic accretion with enhanced inflow from behind the object. In contrast, larger accretors approach the geometrical limit, with accretion primarily from the flow direction and a low-density `shadow' forming behind the object. The accretor's size greatly influences the small-scale and large-scale morphologies. Resolving the Hoyle-Lyttleton radius is essential for representing large-scale flow characteristics. Resolving the smaller stand-off distance is required only for studying the bow shock in front of the moving object: since the stand-off distance determines the bow shock's position, its non-resolution does not affect the larger-scale flow morphology.

Magnetic field morphology and evolution in the Central Molecular Zone and its effect on gas dynamics

The interstellar medium in the Milky Way's Central Molecular Zone (CMZ) is known to be strongly magnetised, but its large-scale morphology and impact on the gas dynamics are not well understood. We explore the impact and properties of magnetic fields in the CMZ using three-dimensional non-self gravitating magnetohydrodynamical simulations of gas flow in an external Milky Way barred potential. We find that: (1) The magnetic field is conveniently decomposed into a regular time-averaged component and an irregular turbulent component. The regular component aligns well with the velocity vectors of the gas everywhere, including within the bar lanes. (2) The field geometry transitions from parallel to the Galactic plane near $z=0$ to poloidal away from the plane. (3) The magneto-rotational instability (MRI) causes an in-plane inflow of matter from the CMZ gas ring towards the central few parsecs of $0.01 that is absent in the unmagnetised simulations. However, the magnetic fields have no significant effect on the larger-scale bar-driven inflow that brings the gas from the Galactic disc into the CMZ. (4) A combination of bar inflow and MRI-driven turbulence can sustain a turbulent vertical velocity dispersion of $ on scales of $20 in the CMZ ring. The MRI alone sustains a velocity dispersion of $ Both these numbers are lower than the observed velocity dispersion of gas in the CMZ, suggesting that other processes such as stellar feedback are necessary to explain the observations. (5) Dynamo action driven by differential rotation and the MRI amplifies the magnetic fields in the CMZ ring until they saturate at a value that scales with the average local density as $B 102 \, (n/10^3 \ G $. Finally, we discuss the implications of our results within the observational context in the CMZ.

Inversion for Inferring Solar Meridional Circulation: The Case with Constraints on Angular Momentum Transport inside the Sun

We have carried out inversions of travel times as measured by Gizon et al. to infer the internal profile of the solar meridional circulation (MC). A linear inverse problem has been solved by the regularized least-squares method with a constraint that the angular momentum (AM) transport by MC should be equatorward (HK21-type constraint). Our motivation for using this constraint is based on the result by Hotta & Kusano (hereafter HK21), where the solar equator-fast rotation was reproduced successfully without any manipulation. The inversion result indicates that the MC profile is a double-cell structure if the so-called HK21 regime, in which AM transported by MC sustains the equator-fast rotation, correctly describes the physics inside the solar convective zone. The sum of the squared residuals computed with the inferred double-cell MC profile is comparable to that computed with the single-cell MC profile obtained when we exclude the HK21-type constraint, showing that both profiles can explain the data more or less at the same level. However, we also find that adding the HK21-type constraint degrades the resolution of the averaging kernels. Although it is difficult for us to determine the large-scale morphology of the solar MC at the moment, our attempt highlights the relevance of investigating the solar MC profile from both theoretical and observational perspectives.

Dune Morphology Classification and Dataset Construction Method Based on Unmanned Aerial Vehicle Orthoimagery.

Dunes are the primary geomorphological type in deserts, and the distribution of dune morphologies is of significant importance for studying regional characteristics, formation mechanisms, and evolutionary processes. Traditional dune morphology classification methods rely on visual interpretation by humans, which is not only time-consuming and inefficient but also subjective in classification judgment. These issues have impeded the intelligent development of dune morphology classification. However, convolutional neural network (CNN) models exhibit robust feature representation capabilities for images and have achieved excellent results in image classification, providing a new method for studying dune morphology classification. Therefore, this paper summarizes five typical dune morphologies in the deserts of western Inner Mongolia, which can be used to define and describe most of the dune types in Chinese deserts. Subsequently, field surveys and the experimental collection of unmanned aerial vehicle (UAV) orthoimages for different dune types were conducted. Five different types of dune morphology datasets were constructed through manual segmentation, automatic rule segmentation, random screening, and data augmentation. Finally, the classification of dune morphologies and the exploration of dataset construction methods were conducted using the VGG16 and VGG19 CNN models. The classification results of dune morphologies were comprehensively analyzed using different evaluation metrics. The experimental results indicate that when the regular segmentation scale of UAV orthoimages is 1024 × 1024 pixels with an overlap of 100 pixels, the classification accuracy, precision, recall, and F1-Score of the VGG16 model reached 97.05%, 96.91%, 96.76%, and 96.82%, respectively. The method for constructing a dune morphology dataset from automatically segmented UAV orthoimages provides a reference value for the study of large-scale dune morphology classification.

Quality assessment of the wide-angle detection option planned at the high-intensity/extended Q-range SANS diffractometer KWS-2 combining experiments and McStas simulations.

For a reliable characterization of materials and systems featuring multiple structural levels, a broad length scale from a few ångström to hundreds of nanometres must be analyzed and an extended Q range must be covered in X-ray and neutron scattering experiments. For certain samples or effects, it is advantageous to perform such characterization with a single instrument. Neutrons offer the unique advantage of contrast variation and matching by D-labeling, which is of great value in the characterization of natural or synthetic polymers. Some time-of-flight small-angle neutron scattering (TOF-SANS) instruments at neutron spallation sources can cover an extended Q range by using a broad wavelength band and a multitude of detectors. The detectors are arranged to cover a wide range of scattering angles with a resolution that allows both large-scale morphology and crystalline structure to be resolved simultaneously. However, for such analyses, the SANS instruments at steady-state sources operating in conventional monochromatic pinhole mode rely on additional wide-angle neutron scattering (WANS) detectors. The resolution must be tuned via a system of choppers and a TOF data acquisition option to reliably measure the atomic to mesoscale structures. The KWS-2 SANS diffractometer at Jülich Centre for Neutron Science allows the exploration of a wide Q range using conventional pinhole and lens focusing modes and an adjustable resolution Δλ/λ between 2 and 20%. This is achieved through the use of a versatile mechanical velocity selector combined with a variable slit opening and rotation frequency chopper. The installation of WANS detectors planned on the instrument required a detailed analysis of the quality of the data measured over a wide angular range with variable resolution. This article presents an assessment of the WANS performance by comparison with a McStas [Willendrup, Farhi & Lefmann (2004). Physica B, 350, E735-E737] simulation of ideal experimental conditions at the instrument.

SandSnap: Measuring and mapping beach grain size using crowd-sourced smartphone images

Sediment grain size is a critical parameter for sediment mobilization and transport, but often has the highest uncertainty of any coastal sediment transport model input parameter. SandSnap is an initiative to engage the public to amass a beach grain size database by taking photos of the beach sand with a coin in the image for scale and uploading the image to a web application. Images are analyzed with two deep learning convolutional neural networks one to detect the coin and the second to measure the grain size, which is trained on sediment samples within the sand regime. The results for nine gradation metrics are returned to the user within 2 min of image upload. Results from 263 test images have a mean percent error of −6.5% and median absolute error of 22.4% for the median grain size (d50) with a small fine bias of −0.042 mm. The use of the database is highlighted by applying SandSnap output as an input to the AeoLiS aeolian sediment transport model to predict coastal dune growth at a nearly national scale using the full eight grain size classes (d10 – d90) from the SandSnap database. These outputs are used to inform the potential value of having spatially comprehensive grain size distribution information as part of coastal engineering design and planning. Education and outreach techniques for the SandSnap initiative are described in the manuscript. Though some challenges remain, the spatially and temporally robust beach grain size database being developed by SandSnap will help to improve numerous coastal engineering analyses including coastal resilience and vulnerability quantification, beach nourishment life cycle and uncertainty analysis, beach compatibility for the beneficial use of dredged sediment, and large-scale coastal morphology modeling.

Molecular line polarisation from the circumstellar envelopes of asymptotic giant branch stars

Context. Polarisation observations of masers in the circumstellar envelopes (CSEs) around asymptotic giant branch (AGB) stars have revealed strong magnetic fields. However, masers probe only specific lines of sight through the CSE. Non-masing molecular line polarisation observations can more directly reveal the large-scale magnetic field morphology and hence probe the effect of the magnetic field on AGB mass loss and the shaping of the AGB wind. Aims. Observations and models of CSE molecular line polarisation can now be used to describe the magnetic field morphology and estimate its strength throughout the entire CSE. Methods. We used observations taken with the Atacama Large Millimeter/submillimeter Array (ALMA) of molecular line polarisation in the envelope of two AGB stars: CW Leo and R Leo. We modelled the observations using the multi-dimensional polarised radiative transfer tool PORTAL. Results. We found linearly polarised emission, with maximum fractional polarisation on the order of a few percent, in several molecular lines towards both stars. Towards R Leo, we also found a high level of linear polarisation (up to ∼35%) for one of the SiO v = 1 maser transitions. We can explain the observed differences in polarisation structure between the different molecular lines by alignment of the molecules through a combination of the Goldreich-Kylafis effect and radiative alignment effects. We specifically show that the polarisation of CO traces the morphology of the magnetic field. Competition between the alignment mechanisms allowed us to describe the behaviour of the magnetic field strength as a function of the radius throughout the circumstellar envelope of CW Leo. The magnetic field strength derived using this method is inconsistent with the magnetic field strength derived using a structure-function analysis of the CO polarisation and the strength previously derived using CN Zeeman observations. In contrast with CW Leo, the magnetic field in the outer envelope of R Leo appears to be advected outwards by the stellar wind. Conclusions. The ALMA observations and our polarised radiative transfer models show the power of using multiple molecular species to trace the magnetic field behaviour throughout the circumstellar envelope. While the observations appear to confirm the existence of a large-scale magnetic field, further observations and modelling are needed to understand the apparent inconsistency of the magnetic field strength derived with different methods in the envelope of CW Leo.

Electronic Couplings and Conversion Dynamics between Localized and Charge Transfer Excitations from Many-Body Green's Functions Theory.

We investigate the determination of electronic coupling between localized excitations (LEs) and charge-transfer (CT) excitations based on many-body Green's functions theory in the GW approximation with the Bethe-Salpeter equation (GW-BSE). Using a small molecule dimer system, we first study the influence of different diabatization methods, as well as different model choices within GW-BSE, such as the self-energy models or different levels of self-consistency, and find that these choices affect the LE-CT couplings only minimally. We then consider a large-scale low-donor morphology formed from rubrene and fullerene and evaluate the LE-CT couplings based on coupled GW-BSE-molecular mechanics calculations. For these disordered systems of bulky molecules, we observe differences in the couplings based on the Edmiston-Ruedenberg diabatization compared to the more approximate Generalize Mulliken-Hush and fragment charge difference diabatization formalisms. In a kinetic model for the conversion between LE and CT states, these differences affect the details of state populations in an intermediate time scale but not the final populations.

Weakened Magnetic Braking in the Exoplanet Host Star 51 Peg

The consistently low activity level of the old solar analog 51 Peg not only facilitated the discovery of the first hot Jupiter, but also led to the suggestion that the star could be experiencing a magnetic grand minimum. However, the 50 yr time series showing minimal chromospheric variability could also be associated with the onset of weakened magnetic braking (WMB), where sufficiently slow rotation disrupts cycling activity and the production of large-scale magnetic fields by the stellar dynamo, thereby shrinking the Alfvén radius and inhibiting the efficient loss of angular momentum to magnetized stellar winds. In this Letter, we evaluate the magnetic evolutionary state of 51 Peg by estimating its wind braking torque. We use new spectropolarimetric measurements from the Large Binocular Telescope to reconstruct the large-scale magnetic morphology, we reanalyze archival X-ray measurements to estimate the mass-loss rate, and we detect solar-like oscillations in photometry from the Transiting Exoplanet Survey Satellite, yielding precise stellar properties from asteroseismology. Our estimate of the wind braking torque for 51 Peg clearly places it in the WMB regime, driven by changes in the mass-loss rate and the magnetic field strength and morphology that substantially exceed theoretical expectations. Although our revised stellar properties have minimal consequences for the characterization of the exoplanet, they have interesting implications for the current space weather environment of the system.

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.

Oligomeric donor with appropriate crystallinity for organic solar cells

Improving the performance of all-small-molecule organic solar cells (ASM-OSCs) largely depends on the design and application of novel donors with appropriate crystallinity. Extending molecular conjugation is an effective method for regulating molecular stacking and crystallinity. In this work, we successfully designed and synthesized two novel acceptor-donor-donor-donor-acceptor (A-D-D-D-A) type oligomeric donors with three dithieno[2,3-d:2′,3′-d′]benzo[1,2-b:4,5-b']dithiophene (DTBDT) as the central unit, named as 3DTBDT-Cl and 3DTBDT, depending on with and without chlorine substitution on the thiophene side chains. We found that the introduction of chlorine atoms makes the blend films display stronger crystallinity but with large-scale phase separation morphology and more defects, which eventually leads to a power conversion efficiency (PCE) of only 10.83%, whereas the blend films based 3DTBDT with appropriate crystallinity achieved 13.74% PCE. Compared with 3DTBDT-Cl/L8-BO, the 3DTBDT/L8-BO films exhibited a nanoscale bi-continuous interpenetrating network morphology with a smaller domain size and more suitable crystallinity, which guarantees the corresponding devices obtained more efficient exciton dissociation, efficient charge transport, reduced bimolecular recombination, and performed more balanced carrier mobility. These results demonstrated that regulating the crystallinity of oligomeric donors to obtain the desired phase separation morphology in the blend films could facilitate further improving the performance of ASM-OSCs.

Fully convolutional neural networks applied to large-scale marine morphology mapping

In this study we applied for the first time Fully Convolutional Neural Networks (FCNNs) to a marine bathymetric dataset to derive morphological classes over the entire Irish continental shelf. FCNNs are a set of algorithms within Deep Learning that produce pixel-wise classifications in order to create semantically segmented maps. While they have been extensively utilised on imagery for ecological mapping, their application on elevation data is still limited, especially in the marine geomorphology realm. We employed a high-resolution bathymetric dataset to create a set of normalised derivatives commonly utilised in seabed morphology and habitat mapping that include three bathymetric position indexes (BPIs), the vector ruggedness measurement (VRM), the aspect functions and three types of hillshades. The class domains cover ten or twelve semantically distinct surface textures and submarine landforms present on the shelf, with our definitions aiming for simplicity, prevalence and distinctiveness. Sets of 50 or 100 labelled samples for each class were used to train several U-Net architectures with ResNet-50 and VGG-13 encoders. Our results show a maximum model precision of 0.84 and recall of 0.85, with some classes reaching as high as 0.99 in both. A simple majority (modal) voting combining the ten best models produced an excellent map with overall F1 score of 0.96 and class precisions and recalls superior to 0.87. For target classes exhibiting high recall (proportion of positives identified), models also show high precision (proportion of correct identifications) in predictions which confirms that the underlying class boundary has been learnt. Derivative choice plays an important part in the performance of the networks, with hillshades combined with bathymetry providing the best results and aspect functions and VRM leading to an overall deterioration of prediction accuracies. The results show that FCNNs can be successfully applied to the seabed for a morphological exploration of the dataset and as a baseline for more in-depth habitat mapping studies. For example, prediction of semantically distinct classes as “submarine dune” and “bedrock outcrop” can be precise and reliable. Nonetheless, at present state FCNNs are not suitable for tasks that require more refined geomorphological classifications, as for the recognition of detailed morphogenetic processes.

The magnetic fields around the cometary globules L328, L323, and L331

ABSTRACT This work presents the magnetic field geometry in a complex of three cometary (with head–tail morphology) globules, namely LDN 323, LDN 328, and LDN 331, using R-band polarization measurements of background stars. These observations were combined with a Planck sky survey to study the large-scale morphology of the magnetic fields in the region. The distances of the target stars were adopted from the Gaia catalogue. The variation of the degree of polarization and polarization position angle with distances of stars is analysed. The field geometry is mostly found to follow the cometary shape of the cloud, with some randomness at certain locations. For studying the correlation between cloud morphology and magnetic field orientations, a modified version of the histogram of relative orientation (HRO) analysis was employed.

Bridging Electrochemistry and Ultrahigh Vacuum: "Unburying" the Electrode-Electrolyte Interface.

ConspectusElectrochemistry has a central role in addressing the societal issues of our time, including the United Nations' Sustainable Development Goals (SDGs) and beyond. At a more basic level, however, elucidating the nature of electrode-electrolyte interfaces is an ongoing challenge due to many reasons, but one obvious reason is the fact that the electrode-electrolyte interface is buried by a thick liquid electrolyte layer. This fact would seem to preclude, by default, the use of many traditional characterization techniques in ultrahigh vacuum surface science due to their incompatibility with liquids. However, combined UHV-EC (ultrahigh vacuum-electrochemistry) approaches are an active area of research and provide a means of bridging the liquid environment of electrochemistry to UHV-based techniques. In short, UHV-EC approaches are able to remove the bulk electrolyte layer by performing electrochemistry in the liquid environment of electrochemistry followed by sample removal (referred to as emersion), evacuation, and then transfer into vacuum for analysis.Through this Account, we highlight our group's activities using UHV-EC to bridge electrochemistry with UHV-based X-ray and ultraviolet photoelectron spectroscopy (XPS/UPS) and scanning tunneling microscopy (STM). We provide a background and overview of the UHV-EC setup, and through illustrative examples, we convey what sorts of insights and information can be obtained. One notable advance is the use of ferrocene-terminated self-assembled monolayers as a spectroscopic molecular probe, allowing the electrochemical response to be correlated with the potential-dependent electronic and chemical state of the electrode-monolayer-electrolyte interfacial region. With XPS/UPS, we have been able to probe changes in the oxidation state, valence structure, and also the so-called potential drop across the interfacial region. In related work, we have also spectroscopically probed changes in the surface composition and screening of the surface charge of oxygen-terminated boron-doped diamond electrodes emersed from high-pH solutions. Finally, we will give readers a glimpse into our recent progress regarding real-space visualizations of electrodes following electrochemistry and emersion using UHV-based STM. We begin by demonstrating the ability to visualize large-scale morphology changes, including electrochemically induced graphite exfoliation and the surface reconstruction of Au surfaces. Taking this further, we show that in certain instances atomically resolved specifically adsorbed anions on metal electrodes can be imaged. In all, we anticipate that this Account will stimulate readers to advance UHV-EC approaches further, as there is a need to improve our understanding concerning the guidelines that determine applicable electrochemical systems and how to exploit promising extensions to other UHV methods.

Thermal and tribo-mechanical properties of high-performance poly(etheretherketone)/reduced graphene oxide nanocomposite coatings prepared by electrophoretic deposition

The thermal stability and degradation, near-to-surface mechanical properties, and scratch resistance and damage mechanism of poly(etheretherketone) (PEEK)/reduced graphene oxide (RGO) nanocomposite coatings are analyzed and discussed in terms of their nanosheet content and microstructure. Although RGO modified the thermal stability and degradation of the polymeric matrix, for instance, by slightly reducing the onset degradation temperature, its addition was not a limiting factor in the PEEK processing. Respecting the microstructural features induced by the nanosheets, the nanocomposite coatings were found to exhibit (i) a partially exfoliated and large-scale co-continuous morphology related to RGO nanosheets whose basal planes were mainly aligned with the coating surface, (ii) a dendritic morphology of PEEK domains related to transcrystallinity, (iii) and irregular domains associated with the deposition of PEEK particles wrapped by the nanosheets. The changes provoked by RGO in the morphology and PEEK crystalline phase influenced the near-to-surface mechanical properties, scratch resistance, and scratch damage mechanism of the nanocomposite coatings. Within this context, the interlayer strength between the nanosheets in the large-scale co-continuous morphology and PEEK transcrystallinity had an important effect. Furthermore, the random-bumpy surface texture formed by the irregular PEEK domains together with the conformal cracking damage mechanism was decisive in the scratch response of the PEEK/RGO nanocomposite coatings. The comprehensive characterization carried out in this work concludes that PEEK/RGO electrophoretic coatings are suitable for a variety of applications requiring tribo-mechanical resistance.Graphical

On the large scale morphology of Hercules A: destabilized hot jets?

ABSTRACT Extragalactic jets are generated as bipolar outflows at the nuclei of active galaxies. Depending on their morphology, they are classified as Fanaroff–Riley type I (FRI) (centre-brightened) and Fanaroff–Riley type II (FRII) (edge-brightened) radio jets. However, this division is not sharp, and observations of these sources at large scales often show intermediate jet morphologies or even hybrid jet morphologies with a FRI type jet on one side and a FRII type jet on the other. A good example of a radio galaxy that is difficult to classify as FRI or FRII is Hercules A. This source shows jets with bright radio lobes (a common feature of FRII type jets) albeit without the hotspots indicative of the violent interaction between the jet and the ambient medium at the impact region, because the jets seem to be disrupted inside the lobes at a distance from the bow shocks surrounding the lobes. In this paper, we explore the jet physics that could trigger this peculiar morphology by means of three-dimensional relativisitic hydrodynamical simulations. Our results show that the large-scale morphological features of Hercules A jets and lobes can be reproduced by the propagation of a relativistically hot plasma outflow that is disrupted by helical instability modes, and generates a hot lobe that expands isotropically against the pressure-decreasing intergalactic medium. We also discuss the implications that this result may have for the host active nucleus in terms of a possible transition from high-excitation to low-excitation galaxy modes.

Constraints on Magnetic Braking from the G8 Dwarf Stars 61 UMa and τ Cet

During the first half of their main-sequence lifetimes, stars rapidly lose angular momentum to their magnetized winds, a process known as magnetic braking. Recent observations suggest a substantial decrease in the magnetic braking efficiency when stars reach a critical value of the Rossby number, the stellar rotation period normalized by the convective overturn timescale. Cooler stars have deeper convection zones with longer overturn times, reaching this critical Rossby number at slower rotation rates. The nature and timing of the transition to weakened magnetic braking have previously been constrained by several solar analogs and two slightly hotter stars. In this Letter, we derive the first direct constraints from stars cooler than the Sun. We present new spectropolarimetry of the old G8 dwarf τ Cet from the Large Binocular Telescope, and we reanalyze a published Zeeman Doppler image of the younger G8 star 61 UMa, yielding the large-scale magnetic field strengths and morphologies. We estimate mass-loss rates using archival X-ray observations and inferences from Lyα measurements, and we adopt other stellar properties from asteroseismology and spectral energy distribution fitting. The resulting calculations of the wind braking torque demonstrate that the rate of angular momentum loss drops by a factor of 300 between the ages of these two stars (1.4–9 Gyr), well above theoretical expectations. We summarize the available data to help constrain the value of the critical Rossby number, and we identify a new signature of the long-period detection edge in recent measurements from the Kepler mission.

3D hydrodynamics simulations of core convection in supermassive main-sequence stars

ABSTRACT Supermassive stars are Population III stars with masses exceeding $10^4\, {\rm M}_{\odot }$ that could be the progenitors of the first supermassive black holes. Their interiors are in a regime where radiation pressure dominates the equation of state. In this work, we use the explicit gas dynamics code ppmstar to simulate the hydrogen-burning core of a $10^4\, {\rm M}_{\odot }$ supermassive main-sequence star. These are the first three-dimensional hydrodynamics simulations of core convection in supermassive stars. We perform a series of 10 simulations at different heating rates and on Cartesian grids with resolutions of 7683, 11523, and 17283. We examine different properties of the convective flow, including its large-scale morphology, its velocity spectrum, and its mixing properties. We conclude that the radiation pressure-dominated nature of the interior does not noticeably affect the behaviour of convection compared to the case of core convection in a massive main-sequence star where gas pressure dominates. Our simulations also offer support for the use of mixing-length theory in one-dimensional models of supermassive stars.

Recent advances of Au@Ag core-shell SERS-based biosensors.

The methodological advancements in surface-enhanced Raman scattering (SERS) technique with nanoscale materials based on noble metals, Au, Ag, and their bimetallic alloy Au-Ag, has enabled the highly efficient sensing of chemical and biological molecules at very low concentration values. By employing the innovative various type of Au, Ag nanoparticles and especially, high efficiency Au@Ag alloy nanomaterials as substrate in SERS based biosensors have revolutionized the detection of biological components including; proteins, antigens antibodies complex, circulating tumor cells, DNA, and RNA (miRNA), etc. This review is about SERS-based Au/Ag bimetallic biosensors and their Raman enhanced activity by focusing on different factors related to them. The emphasis of this research is to describe the recent developments in this field and conceptual advancements behind them. Furthermore, in this article we apex the understanding of impact by variation in basic features like effects of size, shape varying lengths, thickness of core-shell and their influence of large-scale magnitude and morphology. Moreover, the detailed information about recent biological applications based on these core-shell noble metals, importantly detection of receptor binding domain (RBD) protein of COVID-19 is provided.

LOFAR Observations of Substructure Within a Traveling Ionospheric Disturbance at Mid‐Latitude

AbstractThe large scale morphology and finer sub‐structure within a slowly propagating traveling ionospheric disturbance (TID) are studied using wide band trans‐ionospheric radio observations with the LOw Frequency ARray (LOFAR; van Haarlem et al., 2013, https://doi.org/10.1051/0004-6361/201220873). The observations were made under geomagnetically quiet conditions, between 0400 and 0800 on 7 January 2019, over the UK. In combination with ionograms and Global Navigation Satellite System Total Electron Content anomaly data we estimate the TID velocity to ∼60 ms−1, in a North‐westerly direction. Clearly defined substructures with oscillation periods of ∼300 s were identified within the TID, corresponding to scale sizes of 20 km. At the geometries and observing wavelengths involved, the Fresnel scale is between 3 and 4 km, hence these substructures contribute significant refractive scattering to the received LOFAR signal. The refractive scattering is strongly coherent across the LOFAR bandwidth used here (25–64 MHz). The size of these structures distinguishes them from previously identified ionospheric scintillation with LOFAR in Fallows et al. (2020), https://doi.org/10.1051/swsc/2020010, where the scale sizes of the plasma structure varied from ∼500 m to 5 km.