A new diffusion matrix for whistler mode chorus waves

Global models of the Van Allen radiation belts usually include resonant wave-particle interactions as a diffusion process, but there is a large uncertainty over the diffusion rates. Here we present a new diffusion matrix for whistler mode chorus waves that can be used in such models. Data from seven satellites are used to construct 3,536 power spectra for upper and lower band chorus for 1.5 ≤ L∗ ≤ 10, MLT, magnetic latitude 0o ≤ |λm| ≤ 60o and five levels of Kp. Five density models are also constructed from the data. Gaussian functions are fitted to the spectra and capture typically 90% of the wave power. The frequency maxima of the power spectra vary with L∗ and are typically lower than that used previously. Lower band chorus diffusion increases with geomagnetic activity and is largest between 21:00 and 09:00 MLT. Energy diffusion extends to a few MeV at large pitch angles > 60o and at high energies exceeds pitch angle diffusion at the loss cone. Most electron diffusion occurs close to the geomagnetic equator (< 12o). Pitch angle diffusion rates for lower band chorus increase with L∗ and are significant at L∗ = 8 even for low levels of geomagnetic activitywhile upper band chorus is restricted to mainly L∗ < 6. The combined drift and bounce averaged diffusion rates for upper and lower band chorus extend from a few keV near the loss cone up to several MeV at large pitch angles indicating loss at low energies and net acceleration at high energies

OMEP-EOR: A MeV proton flux specification model for electric orbit raising missions

Electric Orbit Raising (EOR) for telecommunication satellites significantly reduced on-board fuel mass at the price of extended transfer durations. These relatively long transfers, which usually span a few months, cross large spans of the radiation belts, resulting in significant exposure of the spacecraft to space radiations. Since they are not very populated, the radiation environment of intermediate regions of the radiation belts is less constrained than on popular orbits such as low Earth orbit or geostationary orbit in standard environment models. In particular, there is a need for more specific models for the MeV energy range proton fluxes, responsible for solar arrays degradations, and hence critical for EOR missions. ONERA has developed a specification model of proton fluxes dedicated for EOR missions as part of the ESA ARTES program. This model can estimate the average proton fluxes between 60 keV and 20 MeV on arbitrary trajectories on the typical duration of EOR transfers. A global statistical model of the radiation belts was extracted from the Van Allen Probes RBSPICE data. For regions with no or low sampling, simulation results from the Salammbo radiation belt model were used. Special care was taken to model the temporal dynamics of the belts on the considered mission durations. A Gaussian Process model was developed, allowing to compute the distribution of the average fluxes on arbitrary mission durations analytically. Satellites trajectories can be flown in the resulting global distribution, yielding the proton flux spectrum distribution as seen by the spacecraft. We show the results of the model on a typical EOR trajectory. The obtained fluxes are compared to the standard AP8 model, the AP9 model and validated using the THEMIS satellites data. We illustrate the expected effect on solar cell degradation, where our model shows an increase of up to 20% degradation prediction compared to AP8

Characterization of Jason-3 Spacecraft Surface Charging in LEO Polar Regions From AMBER Observations

International audienceWe have characterized spacecraft charging events in low Earth orbit (LEO) polar regions with the Active Monitor Box of Electrostatic Risk (AMBER) instrument onboard the Joint Altimetry Satellite Oceanography Network-3 (Jason-3) ocean topography mission for the first time for this spacecraft. AMBER data, taken at an altitude of 1336 km, over the period January 2017-March 2020, with measurements recorded close to the current solar minimum have been analyzed, using systematic filtering of ions spectrograms with selected threshold energies and time windows to detect negative spacecraft charging events; 109 spacecraft charging events were found. The events are examined visually and characterized by their spatial and temporal location, duration, and intensity (e.g., spacecraft potential). At the Jason-3 altitude (1336 km), the ion signature predominately lasts under 30 s in conjunction with auroral inverted V crossings, while intense fluxes of electrons corresponding to the encounter of the discrete auroral region last between 30 s and 1 min. Most of the detected spacecraft charging events show charging levels between −30 and −1000 V. The spacecraft charging events are located in the magnetic local time (MLT) sector 17h-05h, predominately before midnight. The distribution is equal between the northern and southern hemispheres. We found a high correlation between the charging time profile and that of the auroral electron average energy and energy flux along the satellite path. Overall statistics over three years as well as different event morphologies, electron spectra, and comparisons to worst case electron flux spectral distributions are presented and discussed

Long-term dynamics of the inner Jovian electron radiation belts

International audienceLong-term variations of total Jovian synchrotron emission are well known to vary slowly in time. Several hypotheses have been proposed to explain these variations, they can be solar wind driven and/or induced by the geometrical effect of the declination of the Earth in the jovicentric coordinates, DE. However, until now, not any of them have been definitely proved. We propose here to investigate, this long-term dynamics based on appropriate simulation from a 3D model, Salammbô-3D. This model has been developed to study spatial distribution of electrons in the inner Jovian radiation belts. We will carry out two different approaches, the first one being based on synchrotron simulation from the Salammbô code and the second one being based on GALILEO EPD measurements. Two-dimensional images of Jupiter synchrotron emission can be obtained from our model, for any geometrical configuration ( lambdaIII(CML), DE). Comparisons show a good agreement between modeling results and VLA observations. With Salammbô-3D, we can also study long-term variations of total Jovian synchrotron emission. The role of the two geometrical factors, lambdaIII(CML) and DE, will be analyzed. First, we will present beaming curves (evolution of Jovian synchrotron emission in terms of lambdaIII(CML)), resulting from the simulation to validate the geometry of the system in the code. Then, the evolution of the non-thermal flux density of synchrotron emission, in terms of DE, joviographic declination of the Earth, will be studied. With the help of simulations resulting from Salammbô-3D, we will try to discriminate between geometrical induced variations and natural dynamics. On the other hand we will investigate on GALILEO EPD measurements from 1995 until now, restricted to 5-10 Rj, to find out any similarity with the long-term variations of non-thermal flux density of synchrotron emission

Influence of Filler Pore Structure and Polymer on the Performance of MOF-Based Mixed-Matrix Membranes for CO 2 Capture

International audienceMembrane gas separation units are gaining increasing attention owing to their relatively low energy consumption, ease of operation and environmental aspects. Metal-organic framework (MOF)-mixed matrix membranes (MMMs) are proposed as alternative materials delivering both the promising performance benefits from embedded MOF fillers and the processing features of polymers. In order to gain insight into the influence of MOF filler and polymer on membrane performance, eight different composites are studied by combining four MOFs and two polymers. MOF materials (NH2-MIL-53(Al), MIL-69(Al), MIL-96(Al) and ZIF-94(Zn)) with various chemical functionalities, topologies, and dimensionalities of porosity were employed as fillers, while two typical polymers with different permeability-selectivity properties (6FDA-DAM and Pebax) were deliberately selected as matrices. Separation results are rationalized on the basis of thorough characterization of the main components of the composites. The observed differences in membrane performance in the separation of CO2 from N2 are explained on the basis of gas solubility, diffusivity properties and compatibility between the filler and polymer phases

Forecasting the Earth"s radiation belts and modeling solar energetic particle events: Recent results from SPACECAST

High-energy charged particles in the van Allen radiation belts and in solar energetic particle events can damage satellites on orbit leading to malfunctions and loss of satellite service. Here we describe some recent results from the SPACECAST project on modelling and forecasting the radiation belts, and modelling solar energetic particle events. We describe the SPACECAST forecasting system that uses physical models that include wave-particle interactions to forecast the electron radiation belts up to 3 h ahead. We show that the forecasts were able to reproduce the >2 MeV electron flux at GOES 13 during the moderate storm of 7-8 October 2012, and the period following a fast solar wind stream on 25-26 October 2012 to within a factor of 5 or so. At lower energies of 10- a few 100 keV we show that the electron flux at geostationary orbit depends sensitively on the high-energy tail of the source distribution near 10 RE on the nightside of the Earth, and that the source is best represented by a kappa distribution. We present a new model of whistler mode chorus determined from multiple satellite measurements which shows that the effects of wave-particle interactions beyond geostationary orbit are likely to be very significant. We also present radial diffusion coefficients calculated from satellite data at geostationary orbit which vary with Kp by over four orders of magnitude. We describe a new automated method to determine the position at the shock that is magnetically connected to the Earth for modelling solar energetic particle events and which takes into account entropy, and predict the form of the mean free path in the foreshock, and particle injection efficiency at the shock from analytical theory which can be tested in simulations

Importance of Baseline Prognostic Factors With Increasing Time Since Initiation of Highly Active Antiretroviral Therapy: Collaborative Analysis of Cohorts of HIV-1-Infected Patients

Background: The extent to which the prognosis for AIDS and death of patients initiating highly active antiretroviral therapy (HAART) continues to be affected by their characteristics at the time of initiation (baseline) is unclear. Methods: We analyzed data on 20,379 treatment-naive HIV-1- infected adults who started HAART in 1 of 12 cohort studies in Europe and North America (61,798 person-years of follow-up, 1844 AIDS events, and 1005 deaths). Results: Although baseline CD4 cell count became less prognostic with time, individuals with a baseline CD4 count 350 cells/μL (hazard ratio for AIDS = 2.3, 95% confidence interval [CI]: 1.0 to 2.3; mortality hazard ratio = 2.5, 95% CI: 1.2 to 5.5, 4 to 6 years after starting HAART). Rates of AIDS were persistently higher in individuals who had experienced an AIDS event before starting HAART. Individuals with presumed transmission by means of injection drug use experienced substantially higher rates of AIDS and death than other individuals throughout follow-up (AIDS hazard ratio = 1.6, 95% CI: 0.8 to 3.0; mortality hazard ratio = 3.5, 95% CI: 2.2 to 5.5, 4 to 6 years after starting HAART). Conclusions: Compared with other patient groups, injection drug users and patients with advanced immunodeficiency at baseline experience substantially increased rates of AIDS and death up to 6 years after starting HAART