In this study, the ion composition of flux transfer events (FTEs) observed within the magnetosheath proper is examined. These FTEs were observed just upstream of the Earth's postnoon magnetopause by ...the National Aeronautics and Space Administration (NASA) Magnetospheric Multiscale (MMS) spacecraft constellation. The minor ion characteristics are described using energy spectrograms, flux distributions, and ion moments as the constellation encountered each FTE. In conjunction with electron data and magnetic field observations, such observations provide important contextual information on the formation, topologies, and evolution of FTEs. In particular, minor ions, when combined with the field‐aligned streaming of electrons, are reliable indicators of FTE topology. The observations are also placed (i) in context of the solar wind magnetic field configuration, (ii) the connection of the sampled flux tube to the ionosphere, and (iii) the location relative to the modeled reconnection line at the magnetopause. While protons and alpha particles were often depleted within the FTEs relative to the surrounding magnetosheath plasma, the He+ and O+ populations showed clear enhancements either near the center or near the edges of the FTE, and the bulk plasma flow directions are consistent with magnetic reconnection northward of the spacecraft and convection from the dayside toward the flank magnetopause.
Key Points
Long‐duration magnetosheath FTEs observed under at postnoon local times and under similar solar wind conditions are compared and contrasted
Minor ions from the magnetosphere are observed at higher energies at the edges than at the center of the FTEs
The cores of the magnetosheath FTEs are on closed field lines
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The controls on the spatial distribution of soil moisture include static and dynamic variables. The superposition of static and dynamic controls can lead to different soil moisture patterns for a ...given catchment during wetting, draining, and drying periods. These relationships can be further complicated in snow-dominated mountain regions where soil water input by precipitation is largely dictated by the spatial variability of snow accumulation and melt. In this study, we assess controls on spatial and temporal soil moisture variability in a small (0.02 km2), snow-dominated, semi-arid catchment by evaluating spatial correlations between soil moisture and site characteristics through different hydrologic seasons. We assess the relative importance of snow with respect to other catchment properties on the spatial variability of soil moisture and track the temporal persistence of those controls. Spatial distribution of snow, distance from divide, soil texture, and soil depth exerted significant control on the spatial variability of moisture content throughout most of the hydrologic year. These relationships were strongest during the wettest period and degraded during the dry period. As the catchment cycled through wet and dry periods, the relative spatial variability of soil moisture tended to remain unchanged. We suggest that the static properties in complex terrain (slope, aspect, soils) impose first order controls on the spatial variability of snow and resulting soil moisture patterns, and that the interaction of dynamic (timing of water input) and static influences propagate that relative constant spatial variability through most of the hydrologic year. The results demonstrate that snow exerts significant influence on how water is retained within mid-elevation semi-arid catchments and suggest that reductions in annual snowpacks associated with changing climate regimes may strongly influence spatial and temporal soil moisture patterns and catchment physical and biological processes.
Context.
Observations at millimeter wavelengths of bright protoplanetary disks have shown the ubiquitous presence of structures such as rings and spirals in the continuum emission. The derivation of ...the underlying properties of the emitting material is nontrivial because of the complex radiative processes involved.
Aims.
In this paper we analyze new observations from the Atacama Large Millimeter/submillimeter Array (ALMA) and the
Karl G. Jansky
Very Large Array (VLA) at high angular resolution corresponding to 5 – 8 au to determine the dust spatial distribution and grain properties in the ringed disk of HD 163296.
Methods.
We fit the spectral energy distribution as a function of the radius at five wavelengths from 0.9 to 9 mm, using a simple power law and a physical model based on an analytic description of radiative transfer that includes isothermal scattering. We considered eight dust populations and compared the models' performance using Bayesian evidence.
Results.
Our analysis shows that the moderately high optical depth (
τ
>1) at
λ ≤
1.3 mm in the dust rings artificially lower the millimeter spectral index, which should therefore not be considered as a reliable direct proxy of the dust properties and especially the grain size. We find that the outer disk is composed of small grains on the order of 200 µm with no significant difference between rings at 66 and 100 au and the adjacent gaps, while in the innermost ~30 au, larger grains (≥mm) could be present. We show that the assumptions on the dust composition have a strong impact on the derived surface densities and grain size. In particular, increasing the porosity of the grains to 80% results in a total dust mass about five times higher with respect to grains with 25% porosity. Finally, we find that the derived opacities as a function of frequency deviate from a simple power law and that grains with a lower porosity seem to better reproduce the observations of HD 163296.
Conclusions.
While we do not find evidence of differential trapping in the rings of HD 163296, our overall results are consistent with the postulated presence of giant planets affecting the dust temperature structure and surface density, and possibly originating a second-generation dust population of small grains.
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States of peripheral autonomic arousal accompany emotional behaviour, physical exercise and cognitive effort, and their central
representation may influence decision making and the regulation of ...social and emotional behaviours. However, the cerebral
functional neuroanatomy representing and mediating peripheral autonomic responses in humans is poorly understood.
Six healthy volunteer subjects underwent H 2 15 O positron emission tomography (PET) scanning while performing isometric exercise and mental arithmetic stressor tasks, and
during corresponding control tasks. Mean arterial blood pressure (MAP) and heart rate (HR) were monitored during scanning.
Data were analysed using statistical parametric mapping (SPM99). Conjunction analyses were used to determine significant changes
in regional cerebral blood flow (rCBF) during states of cardiovascular arousal common to both exercise and mental stressor
tasks.
Exercise and mental stressor tasks, relative to their control tasks, were associated with significantly ( P < 0.001) increased MAP and HR. Significant common activations (increased rCBF) were observed in cerebellar vermis, brainstem
and right anterior cingulate. In both exercise and mental stress tasks, increased rCBF in cerebellar vermis, right anterior
cingulate and right insula covaried with MAP; rCBF in pons, cerebellum and right insula covaried with HR. Cardiovascular arousal
in both categorical and covariance analyses was associated with decreased rCBF in prefrontal and medial temporal regions.
Neural responses in discrete brain regions accompany peripheral cardiovascular arousal. We provide evidence for the involvement
of areas previously implicated in cognitive and emotional behaviours in the representation of peripheral autonomic states,
consistent with a functional organization that produces integrated cardiovascular response patterns in the service of volitional
and emotional behaviours.
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We report Magnetospheric Multiscale observations of high‐frequency electrostatic waves in the vicinity of the reconnection ion diffusion region on the dayside magnetopause. The ion diffusion region ...is identified during two magnetopause crossings by the Hall electromagnetic fields, the slippage of ions with respect to the magnetic field, and magnetic energy dissipation. In addition to electron beam modes that have been previously detected at the separatrix on the magnetospheric side of the magnetopause, we report, for the first time, the existence of electron cyclotron harmonic waves at the magnetosheath separatrix. Broadband waves between the electron cyclotron and electron plasma frequencies, which were probably generated by electron beams, were found within the magnetopause current sheet. Contributions by these high‐frequency waves to the magnetic energy dissipation were negligible in the diffusion regions as compared to those of lower‐frequency waves.
Key Points
Ion diffusion region was identified by MMS spacecraft in the Earth's dayside magnetopause
High‐frequency electrostatic waves were observed in the vicinity of the ion diffusion region
Energy dissipated by these high‐frequency waves is negligible compared to that by the lower‐frequency process
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We present multi-epoch Very Long Baseline Array imaging of the 28SiO v = 1 and v = 2, J = 1-0 maser emission toward the massive young stellar object (YSO) Orion Source I. Both SiO transitions were ...observed simultaneously with an angular resolution of ~0.5 mas (~0.2 AU for d = 414 pc) and a spectral resolution of ~0.2 km s-1. Here we explore the global properties and kinematics of the emission through two 19-epoch animated movies spanning 21 months (from 2001 March 19 to 2002 December 10). These movies provide the most detailed view to date of the dynamics and temporal evolution of molecular material within ~20-100 AU of a massive (8 M ) YSO. As in previous studies, we find that the bulk of the SiO masers surrounding Source I lie in an -shaped locus; the emission in the south and east arms is predominantly blueshifted, and emission in the north and west is predominantly redshifted. In addition, bridges of intermediate-velocity emission are observed connecting the red and blue sides of the emission distribution. We have measured proper motions of over 1000 individual maser features and found that these motions are characterized by a combination of radially outward migrations along the four main maser-emitting arms and motions tangent to the intermediate-velocity bridges. We interpret the SiO masers as arising from a wide-angle bipolar wind emanating from a rotating, edge-on disk. The detection of maser features along extended, curved filaments suggests that magnetic fields may play a role in launching and/or shaping the wind. Our observations appear to support a picture in which stars with masses as high as at least 8 M form via disk-mediated accretion. However, we cannot yet rule out that the Source I disk may have been formed or altered following a recent close encounter.
The study of hot corinos in solar-like protostars has been so far mostly limited to the Class 0 phase, hampering our understanding of their origin and evolution. In addition, recent evidence suggests ...that planet formation starts already during Class I phase, which therefore represents a crucial step in the future planetary system chemical composition. Hence, the study of hot corinos in Class I protostars has become of paramount importance. Here, we report the discovery of a hot corino towards the prototypical Class I protostar L1551 IRS5, obtained within the ALMA (Atacama Large Millimeter/submillimeter Array) Large Program FAUST (Fifty AU STudy of the chemistry in the disc/envelope system of solar-like protostars). We detected several lines from methanol and its isotopologues (13CH3OH and CH2DOH), methyl formate, and ethanol. Lines are bright towards the north component of the IRS5 binary system, and a possible second hot corino may be associated with the south component. The methanol lines' non-LTE analysis constrains the gas temperature (∼100 K), density (≥1.5 × 10^8 per cu.cm), and emitting size (∼10 au in radius). All CH3OH and 13CH3OH lines are optically thick, preventing a reliable measure of the deuteration. The methyl formate and ethanol relative abundances are compatible with those measured in Class 0 hot corinos. Thus, based on this work, little chemical evolution from Class 0 to I hot corinos occurs.
Context. High-mass star formation remains poorly understood due to observational difficulties (e.g. high dust extinction and large distances) hindering the resolution of disk-accretion and ...outflow-launching regions. Aims. Orion Source I is the closest known massive young stellar object (YSO) and exceptionally powers vibrationally-excited SiO masers at radii within 100 AU, providing a unique probe of gas dynamics and energetics. We seek to observe and image these masers with Very Long Baseline Interferometry (VLBI). Methods. We present the first images of the 28SiO v = 1, J = 2−1 maser emission around Orion Source I observed at 86 GHz (λ3 mm) with the Very Long Baseline Array (VLBA). These images have high spatial (~0.3 mas) and spectral (~0.054 km s-1) resolutions. Results. We find that the λ3 mm masers lie in an X-shaped locus consisting of four arms, with blue-shifted emission in the south and east arms and red-shifted emission in the north and west arms. Comparisons with previous images of the 28SiO v = 1,2, J = 1−0 transitions at λ7 mm (observed in 2001–2002) show that the bulk of the J = 2−1 transition emission follows the streamlines of the J = 1−0 emission and exhibits an overall velocity gradient consistent with the gradient at λ7 mm. While there is spatial overlap between the λ3 mm and λ7 mm transitions, the λ3 mm emission, on average, lies at larger projected distances from Source I (~44 AU compared with ~35 AU for λ7 mm). The spatial overlap between the v = 1, J = 1−0 and J = 2−1 transitions is suggestive of a range of temperatures and densities where physical conditions are favorable for both transitions of a same vibrational state. However, the observed spatial offset between the bulk of emission at λ3 mm and λ7 mm possibly indicates different ranges of temperatures and densities for optimal excitation of the masers. We discuss different maser pumping models that may explain the observed offset. Conclusions. We interpret the λ3 mm and λ7 mm masers as being part of a single wide-angle outflow arising from the surface of an edge-on disk rotating about a northeast-southwest axis, with a continuous velocity gradient indicative of differential rotation consistent with a Keplerian profile in a high-mass proto-binary.
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Interest in spatial omics is on the rise, but generation of highly multiplexed images remains challenging, due to cost, expertise, methodical constraints, and access to technology. An alternative ...approach is to register collections of whole slide images (WSI), generating spatially aligned datasets. WSI registration is a two-part problem, the first being the alignment itself and the second the application of transformations to huge multi-gigapixel images. To address both challenges, we developed Virtual Alignment of pathoLogy Image Series (VALIS), software which enables generation of highly multiplexed images by aligning any number of brightfield and/or immunofluorescent WSI, the results of which can be saved in the ome.tiff format. Benchmarking using publicly available datasets indicates VALIS provides state-of-the-art accuracy in WSI registration and 3D reconstruction. Leveraging existing open-source software tools, VALIS is written in Python, providing a free, fast, scalable, robust, and easy-to-use pipeline for registering multi-gigapixel WSI, facilitating downstream spatial analyses.
Flux transfer events (FTEs) are transient phenomena frequently observed at the Earth's magnetopause. Their usual interpretation is a flux rope moving away from the reconnection region. However, the ...Magnetospheric Multiscale Mission revealed that magnetic reconnection sometimes occurs inside these structures, questioning their flux rope configuration. Here we investigate 229 FTE‐type structures and find reconnection signatures inside 19% of them. We analyze their large‐scale magnetic topology using electron heat flux and find that it is significantly different across the FTE reconnecting current sheets, demonstrating that they are constituted of two magnetically disconnected structures. We also find that the interplanetary magnetic field (IMF) associated with reconnecting FTEs presents a strong By component. We discuss several formation mechanisms to explain these observations. In particular, the maximum magnetic shear model predicts that for large IMF By, two spatially distinct X lines coexist at the magnetopause. They can generate separate magnetic flux tubes that may become interlaced.
Plain Language Summary
The solar wind and the Earth's magnetosphere are two gigantic magnetic structures that collide constantly over our heads, in the near‐space environment. At the boundary of their interaction (the magnetopause), the fundamental process of magnetic reconnection can occur. It is there that dynamic magnetic structures called “flux transfer events” are formed. They travel fast along the magnetopause and transport a lot of energy, from the solar wind into the magnetosphere. These structures are yet not well understood, as underlined by the recent observations made by the Magnetospheric Multiscale Mission (MMS), launched in 2015 by National Aeronautics and Space Administration. The four‐spacecraft mission, specifically designed to study the physics happening at the magnetopause, is capable of measuring right into these magnetic structures, collecting data on their particles and magnetic field properties. When analyzing MMS data, we found that 19% of the flux transfer events were not constituted of one, but two structures with very different properties. These dual magnetic structures tend to appear when the solar wind's magnetic field is oriented mainly toward the east or the west. From these observations and based on existing models of the magnetopause, we propose a scenario that allows such dual structures to form as interlaced magnetic tubes.
Key Points
Nineteen percent of FTE‐type structures observed by MMS during Phases 1A and 1B present signatures of magnetic reconnection in their core
They seem to be formed by two magnetically disconnected interlaced flux tubes and are typically observed for large IMF By
Several formation models are discussed, including a bifurcated X line scenario that results from the maximum shear angle model
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