Abstract
Controlling magnetism at nanometer length scales is essential for realizing high-performance spintronic, magneto-electric and topological devices and creating on-demand spin Hamiltonians ...probing fundamental concepts in physics. Van der Waals (vdW)-bonded layered magnets offer exceptional opportunities for such spin texture engineering. Here, we demonstrate nanoscale structural control in the layered magnet CrSBr with the potential to create spin patterns without the environmental sensitivity that has hindered such manipulations in other vdW magnets. We drive a local phase transformation using an electron beam that moves atoms and exchanges bond directions, effectively creating regions that have vertical vdW layers embedded within the initial horizontally vdW bonded exfoliated flakes. We calculate that the newly formed two-dimensional structure is ferromagnetically ordered in-plane with an energy gap in the visible spectrum, and weak antiferromagnetism between the planes, suggesting possibilities for creating spin textures and quantum magnetic phases.
A survey of the bulk plasma ion properties observed by the Cassini Plasma Spectrometer instrument over roughly the first 4.5 years of its mission in orbit around Saturn is presented. The moments ...(density, temperature, and flow velocity) of the plasma distributions below 50 keV have been computed by numerical integration of the observed counts in the “Singles” (non‐mass‐resolved) data, partitioned into species on the basis of concurrent determinations of the composition from the time‐of‐flight data. Moments are presented for three main species: H+, W+ (water group ions), and ions with m/q = 2, which are presumed to be H2+. While the survey extends to radial distances of 30 RS and thus includes some solar wind or magnetosheath values, our principal interest is the large‐scale spatial variation of the magnetospheric plasma properties, so we focus attention on radial distances inside of 17 RS. Principal findings include the following: (1) the densities of all three components are highly variable but are generally well organized by dipole L and magnetic latitude; (2) the density of ions with m/q = 2 varies from a few percentage of the H+ density in the inner magnetosphere to a maximum of several tens of percentage near the orbit of Titan, suggesting that Titan is an important source for H2+ in the outer magnetosphere; (3) water group ions are the dominant population in the inner magnetosphere, but only within ∼3 RS of the equatorial plane because of their strong centrifugal confinement; (4) derived latitudinal scale heights are largest for the light ions and generally increase with radial distance; (5) the L dependence of the calculated temperatures is not consistent with adiabatic transport but is in fair agreement with the expectations for plasma originating from ion pickup; (6) in agreement with the findings of Sergis et al. (2010), inside of L ∼ 11, the particle pressure is dominated by ions with energies below a few keV; (7) the derived flow velocities reveal the global circulation pattern of relatively dense populations in the magnetosphere, with no evidence for return circulation from the nightside to the dayside beyond ∼20 RS; and (8) the azimuthal flow speeds are typically less than full corotation over the entire L range examined, varying from ∼50% to 70% of full corotation.
Saturn's magnetospheric dynamics Thomsen, M. F.
Geophysical research letters,
28 October 2013, Letnik:
40, Številka:
20
Journal Article
Recenzirano
Odprti dostop
The dynamics of Saturn's magnetosphere are driven by two major features of the system: First, the dominant source of magnetospheric plasma is the icy moon Enceladus, located deep within the ...magnetosphere; and second, like Jupiter, Saturn is a very fast rotator, with a rotational period of only 10.7 h. The dynamical imperative is to rid the magnetosphere of the continuously supplied plasma, and the fast rotation provides the mechanisms to do so. Thus, magnetospheric dynamics are intimately related to mass transport processes, including radial diffusion, flux tube interchange, magnetic reconnection, and plasmoid formation. We review recent progress and new questions relating to these processes at Saturn.
Key Points
Centrifugal interchange and tail reconnection move plasma toward the solar wind
Cassini observations and numerical simulations illuminate these processes
Ultimate loss processes for Saturnian plasma are not yet quantitatively known
Relativistic electron flux in the outer radiation belt tends to increase during the high‐speed solar wind stream (HSS) events. However, HSS events do not always cause large flux enhancement. To ...determine the HSS events that cause such enhancement and the mechanisms that are responsible for accelerating the electrons, we analyzed long‐term plasma data sets, for periods longer than one solar cycle. We demonstrate that during HSS events with the southward interplanetary magnetic field (IMF)‐dominant HSS (SBz‐HSS), relativistic electrons are accelerated by whistler mode waves; however, during HSS events with the northward IMF‐dominant HSS, this acceleration mechanism is not effective. The differences in the responses of the outer radiation belt flux variations are caused by the differences in the whistler mode wave–electron interactions associated with a series of substorms. During SBz‐HSS events, hot electron injections occur and the thermal plasma density decreases due to the shrinkage of the plasmapause, causing large flux enhancement of relativistic electrons through whistler mode wave excitation. These results explain why large flux enhancement of relativistic electrons tends to occur during SBz‐HSS events.
Key Points
A causal link between the solar wind and radiation belt flux enhancements
Southward IMF causes the enhanced condition of whistler chorus
Whistler chorus is a fundamental driver to cause the electron acceleration
This study presents a survey of ion flow speed, density, temperature, and composition observed by the Jovian Auroral Distributions Experiment Ion (JADE‐I) sensor on Juno from 10–40 RJ in the dawn to ...midnight sector of Jupiter's magnetosphere. The survey covers Juno orbits 5–22, and the observations are separated by equatorial (|zmagRJ| ≤ 1.5) and off‐equator (|zmagRJ|>1.5) regions. Plasma parameters for H+, O+, O2+, O3+, Na+, S+, S2+, and S3+ are derived by forward modeling JADE‐I's energy‐per‐charge versus time‐of‐flight spectra using omnidirectional averaged convected kappa distributions and modeled instrument responses. O+ and S2+ are resolved via a ray‐tracing simulation based on carbon‐foil‐effects. The ion flow speed increases with radial distance and is comparable to rigid corotation speed out to ∼20 RJ. Ion number densities decrease with radial distance, the primary species being H+, O+, and S2+. The relative contribution of H+ and S2+ increases and decreases, respectively, in the off‐equator regions, supporting the interpretation that the latitudinal distribution of ions is mass dependent. The O+ to S2+ and ΣOn+ to ΣSn+ number density ratios are variable, the 5 RJ bin averages for O+ to S2+ ranging from ∼0.75–1.5 (equator) and ∼1.1–1.8 (off‐equator) and ΣOn+ to ΣSn+ from ∼0.6–0.9 (equator) and ∼0.8–1.1 (off‐equator). Both proton and heavy ion temperatures show order of magnitude increases between 10 and 20 RJ and range from ∼100 eV to 10 keV and 1 keV to a few tens of keV, respectively.
Plain Language Summary
The Jovian Auroral Distributions Experiment (JADE) on Juno has continuously investigated the plasma environment in Jupiter's magnetosphere since its arrival in August 2016. The polar‐orbiting spacecraft enables JADE to explore both equatorial and off‐equator regions of Jupiter's plasma sheet. In this study, we present plasma sheet ion characteristics such as ion composition, flow speed, and temperatures for H+, O+, O2+, O3+, Na+, S+, S2+, and S3+ that are originating from the innermost Galilean satellite Io. A spatial dependence of ion characteristics is discussed and compared to previous observations. While the density profiles agree well with the Voyager‐based studies, temperatures found in this study show at least an order of magnitude higher values. A new addition to this paper is that the latitudinal distribution of ions shows trend in the mass. Relative composition of protons increases compared to the heavier ions in the off‐equator regions. These observations provide insights on how the ions are distributed throughout Jupiter's magnetosphere and improve our current understanding on ion dynamics in the plasma sheet.
Key Points
Ion flow speed, number density, temperature, and composition in Jupiter's plasma sheet show radial and/or latitudinal trends
H+, O+, and S2+ are the primary ions, the contribution of H+ and S2+ increasing and decreasing, respectively, in the off‐equator region
The O+ to S2+ density ratio is variable, the 5 RJ bin averages ranging from 0.7–1.5 (equator) and 1.1–1.8 (off‐equator)
We explore the paradigm that Saturn's plasmapause marks the boundary between the magnetic flux tubes that have been circulating around the planet for some time, accumulating a dense load of ...Enceladus‐sourced material, and those that have recently undergone tail reconnection, shedding the bulk of the cold plasma and retaining a more tenuous, heated population. A centrifugally driven interchange instability should develop at this boundary, producing fingers of outward propagating dense plasma and of inward propagating hot, tenuous plasma. The plasmapause should thus be identifiable as a transition from mostly‐dense‐with‐some‐tenuous to mostly‐tenuous‐with‐some‐dense plasma populations. Electron densities from the Cassini Plasma Spectrometer/Electron Spectrometer (CAPS/ELS) instrument are used to identify the location of this transition for all of the low‐latitude (<5° from the magnetic equator) passes through Saturn's inner/middle magnetosphere. The boundary is typically found near and somewhat beyond L=10 (i.e., at ~10 Rs from the planet), with a local time asymmetry such that it is closer to the planet on the night side than on the day side.
Plain Language Summary
In Saturn's inner magnetosphere, cold dense plasma originating from the moon Enceladus is transported outward into the outer magnetosphere, where Saturn's rapid rotation causes the magnetic field to become strongly distended and to pinch off in the nightside tail region, releasing cold plasma downtail, and returning hot, tenuous plasma on shortened, more‐dipolar magnetic field lines back toward the inner magnetosphere. The boundary separating the returning tenuous plasma from the dense cold plasma that has not yet pinched off is the plasmapause. An interchange instability forms at this boundary, producing fingers of outward‐propagating dense plasma and of inward‐propagating hot, tenuous plasma. The plasmapause should thus be identifiable as a transition from mostly‐dense‐with‐some‐tenuous to mostly‐tenuous‐with‐some‐dense plasma populations. Electron densities from the Cassini Plasma Spectrometer/Electron Spectrometer (CAPS/ELS) instrument are used to identify the location of this transition for all of the low‐latitude (<5° from the magnetic equator) passes through Saturn's inner/middle magnetosphere. The boundary is typically found near and somewhat beyond ~10 Rs from the planet, and it is closer to the planet on the night side than on the day side.
Key Points
Plasmapause separates flux tubes of dense cold plasma from those that have undergone tail reconnection, leaving a tenuous, heated population
Plasmapause is identified as transition from mostly‐dense‐with‐some‐tenuous to mostly‐tenuous‐with‐some‐dense plasma electron populations
Boundary is typically found near and slightly beyond 10 Rs from the planet and is closer to the planet on the night side than on the dayside
With knowledge of typical hydrodynamic behavior of waste plastic material, models predicting the dispersal of benthic plastics from land sources within the ocean are possible. Here we investigated ...the hydrodynamic behavior (density, settling velocity and resuspension characteristics) of non-buoyant preproduction plastic pellets in the laboratory. From these results we used the MOHID modelling system to predict what would be the likely transport and deposition pathways of such material in the Nazaré Canyon (Portugal) during the spring/summer months of 2009 and the autumn/winter months of 2011. Model outputs indicated that non-buoyant plastic pellets would likely be transported up and down canyon as a function of tidal forces, with only a minor net down canyon movement resulting from tidal action. The model indicated that transport down canyon was likely greater during the autumn/winter, primarily as a result of occasional mass transport events related to storm activity and internal wave action. Transport rates within the canyon were not predicted to be regular throughout the canyon system, with stretches of the upper canyon acting more as locations of pellet deposition than conduits of pellet transport. Topography and the depths of internal wave action are hypothesized to contribute to this lack of homogeneity in predicted transport.
We report on the first observations of 100 eV to 100 keV electrons over the auroral regions of Jupiter by the Jovian Auroral Distributions Experiment (JADE) on board the Juno mission. The focus is on ...the regions that were magnetically connected to the main auroral oval. Amongst the most remarkable features, JADE observed electron beams, mostly upward going but also some downward going in the south, at latitudes from ~69° to 72° and ~ −66° to −70° corresponding to M shells (“M” for magnetic) from ~18 to 54 and ~28 to 61, respectively. The beams were replaced by upward loss cones at lower latitudes. There was no evidence of strongly accelerated downward electrons analogous to the auroral “inverted Vs” at Earth. Rather, the presence of upward loss cones suggests a diffuse aurora process. The energy spectra resemble tails of distributions or power laws (suggestive of a stochastic acceleration process) but can also have some clear enhancements or even peaks generally between 1 and 10 keV. Electron intensities change on timescales of a second or less at times implying that auroral structures can be of the order of a few tens of kilometers.
Key Points
First 100 eV to 100 keV electron measurements in the auroral regions of Jupiter
Upward and downward electron beams observed in the polar regions and on field lines connected to the middle plasma sheet
Upward loss cone on the field lines connected to the inner plasma sheet suggesting a diffuse aurora process
The low‐altitude, high‐velocity trajectory of the Juno spacecraft enables the Jovian Auroral Distributions Experiment to make the first in situ observations of the high‐latitude ionospheric plasma. ...Ions are observed to energies below 1 eV. The high‐latitude ionospheric ions are observed simultaneously with a loss cone in the magnetospheric ions, suggesting precipitating magnetospheric ions contribute to the heating of the upper ionosphere, raising the scale height, and pushing ionospheric ions to altitudes of 0.5 RJ above the planet where they are observed by Jovian Auroral Distributions Experiment. The source of the magnetospheric ions is tied to the Io torus and plasma sheet, indicated by the cutoff seen in both the magnetospheric and ionospheric plasma at the Io M‐shells. Equatorward of the Io M‐shell boundary, the ionospheric ions are not observed, indicating a drop in the scale height of the ionospheric ions at those latitudes.
Plain Language Summary
The Jovian Auroral Distributions Experiment (JADE) ion sensor has made the first in situ observations of the upper, high‐latitude ionosphere of Jupiter. Flown on the Juno spacecraft, JADE observes the ionosphere at altitudes of approximately half a Jovian radii, with the spacecraft traveling at the high speed of ~50 km/s. For comparison, a proton traveling at 50 km/s has an energy of approximately 10 eV. The combination of the low‐altitude and high ram velocity enables JADE to measure ionospheric ions to energies below 1 eV. These observations reveal a cold ionospheric population of protons at high latitudes, seen coincident with precipitating magnetospheric ions. This indicates that the precipitating magnetospheric ions heat the upper ionosphere, raising the height where these protons can be observed. The ionospheric protons are seen in bands in the northern and southern latitudes, bounded on the equator edge by the field lines that connect to Io, and inside the auroral oval to the poleward side.
Key Points
The high‐latitude ionosphere is observed between the magnetic latitudes bounded by the auroral oval and Io's magnetic flux shell
Two populations are observed at high latitudes: (1) magnetospheric ions consisting of H, S, and O ions and (2) cold ionospheric H+ ions
Observation of a loss cone suggests precipitating magnetospheric ions heat the upper ionosphere to heights ~0.5 RJ above the clouds
Children with atopic dermatitis (AD) may have disturbed sleep, affected self-esteem and decreased quality of life, likely interfering with performance in school.
To examine the association between ...hospital-managed paediatric AD, school performance and cognitive function.
In this cross-sectional study we linked data from the Danish national registers and identified three populations between 2001 and 2019. Population 1 comprised children with graduation grades registered from lower secondary school, population 2 comprised adolescents with registration of an upper secondary graduation mean, and population 3 comprised male conscripts with registration of an IQ test score. AD was defined as a hospital diagnostic code (inpatient or outpatient) prior to the exam or conscription date, and was stratified according to severity, activity and atopic comorbidity. Outcomes included graduation mean from lower and upper secondary school, special educational assistance in primary and lower secondary school, and IQ at conscription.
In total, 770 611 (12 137 with AD), 394 193 (6261 with AD) and 366 182 (4539 with AD) children and adolescents were included in populations 1 (lower secondary graduation), 2 (upper secondary graduation) and 3 (conscription), respectively. In lower secondary school, children with severe AD had significantly lower overall, written and oral graduation grade means compared with children with mild AD: respectively, difference -0.29 95% confidence interval (CI) -0.45 to -0.13, P < 0.001, difference -0.26 (95% CI -0.42 to -0.10, P = 0.0016) and difference -0.30 (95% CI -0.49 to -0.11, P = 0.0018). In upper secondary school, adolescents with AD performed similarly to their peers without AD. Young men with AD scored significantly lower IQ test means at conscription examination than male conscripts without AD: difference -0.60 (95% CI -0.87 to -0.32, P < 0.001).
AD, in particular when severe, is associated with lower school performance in childhood and IQ in young men, which can interfere with academic achievements in life. Optimization of treatment of children with AD and specific educational support to children with severe AD could be needed.
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