The origin and dynamics of the Van Allen radiation belts is one of the longest-standing questions of the space age, and one that is increasingly important for space applications as satellite systems become more sophisticated, smaller and more susceptible to radiation effects. The precise mechanism by which the Earth's magnetosphere is able to accelerate electrons from thermal to ultrarelativistic energies (E 0.5 MeV) has been particularly difficult to definitively resolve. The traditional explanation is that large-scale, fluctuating electric and magnetic fields energize particles through radial diffusion 1 . More recent theories 2,3and observations 4,5 have suggested that gyro-resonant waveparticle interactions may be comparable to or more important than radial diffusion. Using data collected simultaneously by multiple satellites passing through the magnetosphere at different distances from the Earth, we demonstrate that the latter of these is the dominant mechanism responsible for relativistic electron acceleration. Specifically, we identify frequent and persistent peaks in equatorial electron phase space density near or inside geosynchronous orbit that provide unambiguous evidence for local wave-particle acceleration. These observations represent an important step towards a more complete physical understanding of radiation belt dynamics and to the development of space-weather models.

Electromagnetic ion cyclotron (EMIC) waves were observed at multiple observatory locations for several hours on 17 January 2013. During the wave activity period, a duskside relativistic electron precipitation (REP) event was observed by one of the Balloon Array for Radiation belt Relativistic Electron Losses (BARREL) balloons and was magnetically mapped close to Geostationary Operational Environmental Satellite (GOES) 13. We simulate the relativistic electron pitch angle diffusion caused by gyroresonant interactions with EMIC waves using wave and particle data measured by multiple instruments on board GOES 13 and the Van Allen Probes. We show that the count rate, the energy distribution, and the time variation of the simulated precipitation all agree very well with the balloon observations, suggesting that EMIC wave scattering was likely the cause for the precipitation event. The event reported here is the first balloon REP event with closely conjugate EMIC wave observations, and our study employs the most detailed quantitative analysis on the link of EMIC waves with observed REP to date.

[1] In this study we perform a reanalysis of the sparse MEA CRRES relativistic electron data using a relatively simple one-dimensional radial diffusion model and a Kalman filtering approach. By combining observations with the model in an optimal way we produce a high time and space resolution reanalysis of the radiation belt electron fluxes over a 50-d period starting on 18 August 1990. The results of the reanalysis clearly show pronounced peaks in the electron phase space density (PSD), which can not be explained by the variations in the outer boundary, and can only be produced by a local acceleration processes. The location of the innovation vector shows that local acceleration is most efficient at L* = 5.5 for electrons at K = 0.11 G 0.5 R E and m = 700 MeV/G. Sensitivity numerical experiments for various values of m and K indicate that peaks in PSD become stronger with increasing K and m. To verify that our results are not affected by the limitations of the satellite orbit and coverage, we performed an ''identical twin'' experiments with synthetic data specified only at the locations for which CRRES observations are available. Our results indicate that the model with data assimilation can accurately reproduce the underlying structure of the PSD even when data is sparse. The identical twin experiments also indicate that PSD at a particular L-shell is determined by the local processes and cannot be accurately estimated unless local measurements are available.Citation: Shprits, Y., D. Kondrashov, Y. Chen, R. Thorne, M. Ghil, R. Friedel, and G. Reeves (2007), Reanalysis of relativistic radiation belt electron fluxes using CRRES satellite data, a radial diffusion model, and a Kalman filter,

We have recently conducted a statistical survey on pitch angle distributions of energetic electrons trapped in the Earth's outer radiation belt, and a new empirical model was developed based upon survey results. This model-relativistic electron pitch angle distribution (REPAD)-aims to present statistical pictures of electron equatorial pitch angle distributions, instead of the absolute flux levels, as a function of energy, L shell, magnetic local time, and magnetic activity. To quantify and facilitate this statistical survey, we use Legendre polynomials to fit long-term in situ directional fluxes observed near the magnetic equator from three missions: CRRES, Polar, and LANL-97A. As the first of this kind of model, REPAD covers the whole outer belt region, providing not only the mean and median pitch angle distributions in the area but also error estimates of the average distributions. Preliminary verification and validation results demonstrate the reliable performance of this model. Usage of REPAD is mainly to predict the full pitch angle distribution of fluxes along a given magnetic field line, or even on a given drift shell, based upon one single unidirectional or omnidirectional flux measurement anywhere on that field line. This can be particularly useful for data assimilation, which usually has large tolerance on data errors. In addition, relatively small variations in pitch angle distributions measured at L shell between~4 and 5 justify the assumption of fixed pitch angle distributions at GPS equatorial crossings (L~4.2) used in our previous studies.

This work designs a new model called PreMevE to predict storm time distributions of relativistic electrons within Earth's outer radiation belt. This model takes advantage of the cross-energy, cross-L-shell, and cross-pitch angle coherence associated with wave-electron resonant interactions, ingests observations from belt boundaries-mainly by a National Oceanic and Atmospheric Administration Polar Operational Environmental Satellite in low-Earth orbit, and provides high-fidelity nowcast (multiple-hour prediction) and forecast (>~1 day) of MeV electron fluxes over L-shells between 2.8 and 7 through linear prediction filters. PreMevE can not only reliably anticipate incoming enhancements of MeV electrons during storms with at least 1-day forewarning time but also accurately specify the evolving event-specific electron spatial distributions afterward. The performance of PreMevE is assessed against long-term in situ data from one Van Allen Probe and a Los Alamos National Laboratory geosynchronous satellite. This new model enhances our preparedness for severe MeV electron events in the future and further adds new science utility to existing and next-generation low-Earth orbit space infrastructure.Plain Language Summary Relativistic electrons in Earth's outer radiation belt present a hazardous radiation environment for spaceborne electronics. These electrons, with energies up to multiple megaelectron-volt (MeV), manifest a highly dynamic and event-specific nature due to the interplay of competing processes. Thus, developing a forecasting model for these electrons has long been a critical but challenging task for space community. Recent studies have demonstrated the vital roles of electron resonance with various wave modes; however, it remains difficult for diffusion radiation belt models to reproduce MeV electron behaviors during geomagnetic storms due to reasons such as large uncertainties in input parameters. This work designs a new model called PreMevE to reliably predict storm time changes of MeV electrons within the whole outer belt. Taking advantage of newly identified coherence caused by wave-electron resonance, this model ingests observations mainly from satellites in low-Earth orbits to provide high-fidelity forecasts. As a first-of-its-kind, PreMevE can not only accurately predict incoming enhancements of MeV electrons with 1-day forewarning time but also reliably specify evolving electron spatial distributions afterward. PreMevE's high performance is assessed against long-term in situ observations. This model enhances our preparedness for future severe MeV electron events and further the science usage of existing and future space infrastructure in low-Earth orbits.

Objective: To assess the risk of neonatal mortality and morbidity in vertex-vertex second twins according to mode of delivery and birth weight.Study design: Data from a historical cohort study based on a twin registry in the US (1995)(1996)(1997) were used. Multivariate logistic regression was used to control for maternal age, race, marital status, cigarette smoking during pregnancy, parity, medical complications, gestational age, and other confounders.Results: A total of 86 041 vertex-vertex second twins were classified into two groups: second twins delivered by cesarean section after cesarean delivery of first twin (C-C) (43.0%), second twins whose co-twins delivered vaginally (V-X) (57.0%). In infants of birth weight X2500 g group, the risks of noncongenital anomaly-related death (adjusted odds ratio (aOR): 4.64, 95% confidence interval (95% CI): 1.90, 13.92), low Apgar score (aOR: 2.39, 95% CI: 1.43, 4.14), and ventilation use (aOR: 1.31, 95% CI: 1.18, 1.47) were higher in the V-X group compared with the C-C group. No asphyxia-related neonatal deaths occurred in C-C group, whereas the incidence of this death was 0.04% in the V-X group. Conclusion:The risks of neonatal mortality and morbidity are increased in vertex-vertex second twins with birth weight X2500 g whose co-twins delivered vaginally compared with second twins delivered by cesarean section after cesarean delivery of first twin.

We report on the transient photoconductivity of hot carriers in undoped bulklike In 0.53 Ga 0.47 As observed via time-resolved terahertz far-infrared spectroscopy. For very dilute photoexcitation densities of Ͻ1ϫ10 15 cm Ϫ3 and an initial excess carrier energy of 630 meV, we find that electrons have an effective intervalley L→⌫ return time of 3.1 ps as measured via the increased electrical conductivity associated with ⌫ electrons. In contrast, a total conductivity risetime of ϳ0.5 ps is observed for electrons with initial excess energy insufficient to cause intervalley scattering. The observed frequency dependent conductivity is analyzed via the Drude theory, allowing the determination of the temporal dynamics of the mobility at dilute excitation densities of ϳ1ϫ10 14 cm Ϫ3 .

The thermoelectric figure-of-merit (ZT) for GeTe powder is able to be raised from ∼0.8 to 1.37 at high temperature near ∼500 °C by tuning the Ge vacancy level through a reversible in situ route.