In 1995, the Galileo spacecraft traversed the wake of Io at ∼900 km altitude. The instruments onboard detected intense bi‐directional field‐aligned electron beams (∼140 eV–150 keV), embedded in a ...dense, cold and slow plasma wake (Nel ∼ 35,000 cm−3, Ti < 10 eV, V < 3 km/s). Similar electron beams were also detected along subsequent Galileo flybys. Using numerical simulations, we show that these electron beams are responsible for the formation of Io's dense plasma wake. We prescribe the composition of Io's atmosphere in S, O, SO and SO2, compute the atmospheric ionization by the beams with a parameterization adapted from study of auroral electrons at Earth, the plasma flow into Io's atmosphere with a Magneto‐Hydro‐Dynamic code, and the ion composition and temperature with a multi‐species physical chemistry code. Results reveal contrasting chemistries between the upstream and wake regions, leading to different ion compositions. The upstream chemistry is driven by the torus thermal electrons at 5 eV with SO2+ becoming the dominant ion because of electron‐impact ionization of the SO2 atmosphere. The wake chemistry is driven by the high‐energy electrons in the beams with S+ and SO+ becoming the dominant ions produced by dissociative‐ionization of SO2. We show that the wake ion composition is highly sensitive to the atmospheric composition. Juno, in its extended mission, will traverse Io's wake and determine its ion composition, which, compared with our numerical simulations will enable us to infer the detailed composition of the atmosphere.
Plain Language Summary
Io, the inner‐most Galilean moon of Jupiter, is the most active volcanic body of the solar system. It has a tenuous atmosphere ultimately supplied by volcanic activity. The atmosphere is mainly composed of sulfur dioxide, oxygen, sulfur and sulfur monoxide, but its detailed composition, density and spatial distribution are still surprisingly poorly known. Between 1995 and 2001, the Galileo spacecraft made five close flybys of Io. The onboard instruments detected intense high‐energy electrons moving along Jupiter's magnetic field lines embedded in a remarkably dense ion wake (∼10 times denser than the surrounding plasma). Identifying the processes that generate this dense wake remains an outstanding issue. We utilize numerical simulations to demonstrate that the production of the dense ion wake is attributed to efficient ionization of Io's atmosphere by the electron beams. Our simulations reveal that the ion composition of the wake is highly sensitive to the atmospheric composition. The Juno spacecraft, currently in orbit around Jupiter, will conduct several flybys in Io's wake in 2023 and 2024 and determine its ion composition. Similar electron beams are likely present near other moons of Jupiter. Such beams have already been detected during a single flyby of Europa by the Juno probe. The Jupiter Icy Moon Explorer spacecraft is presently en route to Ganymede and Callisto, while the future Europa Clipper mission is scheduled to be launched to Europa in 2024. These missions will have the capacity to detect the presence of electron beams and plasma wakes similar to those observed at Io. Our numerical model serves as an effective tool for inferring the atmospheric composition and density of these moons as it predicts the ion composition and density of the wake based on the energy of the electron beams.
Key Points
The Galileo spacecraft detected a dense and cold plasma wake downstream of Io and intense field‐aligned high‐energy electron beams
Using numerical simulations, we show that this dense plasma wake is produced by the electron beams ionization of Io's atmosphere
The ion composition and density in the wake strongly depend on Io's atmospheric density and its neutral composition
Familial Alzheimer's disease (fAD) mutations alter amyloid precursor protein (APP) cleavage by γ-secretase, increasing the proportion of longer amyloidogenic amyloid-β (Aβ) peptides. Using five ...control induced pluripotent stem cell (iPSC) lines and seven iPSC lines generated from fAD patients, we investigated the effects of mutations on the Aβ secretome in human neurons generated in 2D and 3D. We also analysed matched CSF, post-mortem brain tissue, and iPSCs from the same participant with the APP V717I mutation. All fAD mutation lines demonstrated an increased Aβ42:40 ratio relative to controls, yet displayed varied signatures for Aβ43, Aβ38, and short Aβ fragments. We propose four qualitatively distinct mechanisms behind raised Aβ42:40. (1) APP V717I mutations alter γ-secretase cleavage site preference. Whereas, distinct presenilin 1 (PSEN1) mutations lead to either (2) reduced γ-secretase activity, (3) altered protein stability or (4) reduced PSEN1 maturation, all culminating in reduced γ-secretase carboxypeptidase-like activity. These data support Aβ mechanistic tenets in a human physiological model and substantiate iPSC-neurons for modelling fAD.
There is an increasing role for biological markers (biomarkers) in the understanding and diagnosis of neurodegenerative disorders. The application of imaging biomarkers specifically for the in vivo ...investigation of neurodegenerative disorders has increased substantially over the past decades and continues to provide further benefits both to the diagnosis and understanding of these diseases. This review forms part of a series of articles which stem from the University College London/University of Gothenburg course "Biomarkers in neurodegenerative diseases". In this review, we focus on neuroimaging, specifically positron emission tomography (PET) and magnetic resonance imaging (MRI), giving an overview of the current established practices clinically and in research as well as new techniques being developed. We will also discuss the use of machine learning (ML) techniques within these fields to provide additional insights to early diagnosis and multimodal analysis.
In the magnetosheath, intense whistler mode waves, called “Lion roars,” are often detected in troughs of magnetic field intensity in mirror mode structures. Using data obtained by the four ...Magnetospheric Multiscale (MMS) spacecraft, we show that reversals of gradient of magnetic field intensity along the magnetic field correspond to reversals of the field‐aligned component of Poynting flux of whistler mode waves in the troughs. Such a characteristic is consistent with the idea that the whistler mode waves are effectively generated near the local minima of magnetic field intensity because of the smallest cyclotron resonance velocity and propagate toward regions of larger magnetic field intensity along the magnetic field lines on both sides. We use the reversal of the Poynting flux as an indicator of wave source regions. In these regions, we find that pancake or an outer edge of butterfly electron distributions above ~100 eV are good candidates for wave generation. Unclear correlations of phase difference and amplitude variations of whistler mode waves in cases of ~40 km spacecraft separation indicate that a simple plane wave approximation with a constant amplitude is not valid at this spatial scale that is much smaller than the ion gyroradius. The whistler mode waves consist of small coherent wave packets from multiple sources with spatial scales smaller than tens of electron gyroradii transverse to the background magnetic field in a mirror mode structure.
Key Points
Whistler mode waves are generated near local minima of magnetic field intensity and propagate along field lines on both sides
Pancake or an outer edge of butterfly electron distributions above ~100 eV are good candidates for wave generation
The waves consist of many small coherent wave packets of tens of electron gyroradii perpendicular to magnetic fields
Objectives
In response to a commissioned research update on dementia during the COVID‐19 pandemic, a UK‐based working group, comprising dementia researchers from a range of fields and disciplines, ...aimed to describe the impact of the pandemic on dementia wellbeing and identify priorities for future research.
Methods
We supplemented a rapid literature search (including unpublished, non‐peer reviewed and ongoing studies/reports) on dementia wellbeing in the context of COVID‐19 with expert group members' consensus about future research needs. From this we generated potential research questions the group judged to be relevant that were not covered by the existing literature.
Results
Themes emerged from 141 studies within the six domains of the NHS England COVID‐19 Dementia Wellbeing Pathway: Preventing Well, Diagnosing Well, Treating Well, Supporting Well, Living Well and Dying Well. We describe current research findings and knowledge gaps relating to the impact on people affected by dementia (individuals with a diagnosis, their carers and social contacts, health and social care practitioners and volunteers), services, research activities and organisations. Broad themes included the potential benefits and risks of new models of working including remote healthcare, the need for population‐representative longitudinal studies to monitor longer‐term impacts, and the importance of reporting dementia‐related findings within broader health and care studies.
Conclusions
The COVID‐19 pandemic has had a disproportionately negative impact on people affected by dementia. Researchers and funding organisations have responded rapidly to try to understand the impacts. Future research should highlight and resolve outstanding questions to develop evidence‐based measures to improve the quality of life of people affected by dementia.
Key Points
The COVID‐19 pandemic has had a disproportionately negative impact on people affected by dementia, dementia services and research.
Further research on the impacts of the pandemic is needed, and directions for future work are identified in this study.
It is important to explore the potential benefits and risks of remote health and care, design inclusive and longitudinal studies to monitor longer‐term impacts, and report dementia‐specific findings within broader studies.
The role and properties of lower hybrid waves in the ion diffusion region and magnetospheric inflow region of asymmetric reconnection are investigated using the Magnetospheric Multiscale (MMS) ...mission. Two distinct groups of lower hybrid waves are observed in the ion diffusion region and magnetospheric inflow region, which have distinct properties and propagate in opposite directions along the magnetopause. One group develops near the ion edge in the magnetospheric inflow, where magnetosheath ions enter the magnetosphere through the finite gyroradius effect and are driven by the ion‐ion cross‐field instability due to the interaction between the magnetosheath ions and cold magnetospheric ions. This leads to heating of the cold magnetospheric ions. The second group develops at the sharpest density gradient, where the Hall electric field is observed and is driven by the lower hybrid drift instability. These drift waves produce cross‐field particle diffusion, enabling magnetosheath electrons to enter the magnetospheric inflow region thereby broadening the density gradient in the ion diffusion region.
Key Points
Two groups of lower hybrid waves are observed in the ion diffusion and magnetospheric inflow regions
In the magnetospheric inflow region lower hybrid waves develop when cold magnetospheric ions are present and can heat cold ions
In the diffusion region lower hybrid waves develop at the density gradient and can cause cross‐field particle diffusion
Voltage-gated potassium channel (VGKC)-complex antibodies can be associated with a range of immunotherapy-responsive clinical presentations including limbic encephalitis, Morvan's syndrome and ...acquired neuromyotonia. However, there are patients with positive levels in whom the significance is uncertain.
To evaluate the clinical significance associated with positive (>100 pM) VGKC-complex antibodies.
Over a 4-year period, 1053 samples were sent for testing of which 55 were positive. The clinical presentations, final diagnoses and responses to immunotherapies, when given, were assessed retrospectively and the likelihood of autoimmunity was categorised as definite, possible, unlikely or undetermined (modified from Zuliani et al 2012).
Only 4 of the 32 patients with low-positive (100-400 pM) levels were considered definitely autoimmune, 3 with peripheral nerve hyperexcitability and 1 with a thymoma; 3 were given immunotherapies. Of the remaining 28 with low-positive levels, 13 (3 of whom had tumours) were considered possibly autoimmune, and 15 were unlikely or undetermined; 1 was given immunotherapy unsuccessfully. Of the 23 patients with high-positive (>400 pM) levels, 12 were given immunotherapies, 11 of whom showed a good response. 11 were considered definitely autoimmune, 10 with limbic encephalitis (antibody specificity: 5 LGI1, 1 contactin2, 2 negative, 2 untested) and 1 with a tumour. In the remaining 12, autoimmunity was considered possible (n=9; most had not received immunotherapies), or unlikely (n=3).
As antibody testing becomes more widely available, and many samples are referred from patients with less clear-cut diagnoses, it is important to assess the utility of the results. VGKC-complex antibodies in the range of 100-400 pM (0.1-0.4 nM) were considered clinically relevant in rare conditions with peripheral nerve hyperexcitability and appeared to associate with tumours (12.5%). By contrast high-positive (>400 pM; >0.4 nM) levels were considered definitely (38%) or possibly (49%) clinically relevant, but not all patients had a 'classical' limbic encephalitis and some did not receive immunotherapies.
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