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1. Simulating Long‐Term Dynamics of Radiation Belt Electrons Using DREAM3D Model

   https://doi.org/10.1029/2023JA032286  

   Lee, Sang‐Yun; Tu, Weichao; Cunningham, Gregory S; Cowee, Misa M; Wang, Dedong; Shprits, Yuri Y; Henderson, Michael G; Reeves, Geoffrey D (February 2024, Journal of Geophysical Research: Space Physics)

   Abstract We compared the performance of DREAM3D simulations in reproducing the long‐term radiation belt dynamics observed by Van Allen Probes over the entire year of 2017 with various boundary conditions (BCs) and model inputs. Specifically, we investigated the effects of three different outer boundary conditions, two different low‐energy boundary conditions for seed electrons, four different radial diffusion (RD) coefficients (D_LL), four hiss wave models, and two chorus wave models from the literature. Using the outer boundary condition driven by GOES data, our benchmark simulation generally well reproduces the observed radiation belt dynamics insideL* = 6, with a better model performance at lowerμthan higherμ, whereμis the first adiabatic invariant. By varying the boundary conditions and inputs, we find that: (a) The data‐driven outer boundary condition is critical to the model performance, while adding in the data‐driven seed population doesn't further improve the performance. (b) The model shows comparable performance withD_LLfrom Brautigam and Albert (2000,https://doi.org/10.1029/1999ja900344), Ozeke et al. (2014,https://doi.org/10.1002/2013ja019204), and Liu et al. (2016,https://doi.org/10.1002/2015gl067398), while withD_LLfrom Ali et al. (2016,https://doi.org/10.1002/2016ja023002) the model shows less RD compared to data. (c) The model performance is similar with data‐based hiss models, but the results show faster loss is still needed inside the plasmasphere. (d) The model performs similarly with the two different chorus models, but better capturing the electron enhancement at higherμusing the Wang et al. (2019,https://doi.org/10.1029/2018ja026183) model due to its stronger wave power, since local heating for higher energy electrons is under‐reproduced in the current model. 

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2. Complete Charge Regulation by a Redox Enzyme Upon Single Electron Transfer

   https://doi.org/10.1002/anie.202001452  

   Zhang, Ao Yun; Koone, Jordan C.; Dashnaw, Chad M.; Zahler, Collin T.; Shaw, Bryan F. (April 2020, Angewandte Chemie International Edition)

   Abstract The degree by which metalloproteins partially regulate net charge (Z) upon electron transfer (ET) was recently measured for the first time using “protein charge ladders” of azurin, cytochrome c, and myoglobin [Angew. Chem. Int. Ed.2018,57(19), 5364–5368;Angew. Chem.2018,130, 5462–5466]. Here, we show that Cu, Zn superoxide dismutase (SOD1) is unique among proteins in its ability to resist changes in net charge upon single ET (e.g., ΔZ_ET(SOD1)=0.05±0.08 per electron, compared to ΔZ_ET(Cyt‐c)=1.19±0.02). This total regulation of net charge by SOD1 is attributed to the protonation of the bridging histidine upon copper reduction, yielding redox centers that are isoelectric at both copper oxidation states. Charge regulation by SOD1 would prevent long range coulombic perturbations to residue pK_a’s upon ET at copper, allowing SOD1’s “electrostatic loop” to attract superoxide with equal affinity (at both redox states of copper) during diffusion‐limited reduction and oxidation of superoxide. 

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3. On the Annual Asymmetry of High‐Latitude Sporadic F

   https://doi.org/10.1029/2019SW002305  

   Chartier, Alex T.; Huba, J. D.; Mitchell, Cathryn N. (November 2019, Space Weather)

   Abstract The polarFregion ionosphere frequently exhibits sporadic variability (e.g., Meek, 1949,https://doi.org/10.1029/JZ054i004p00339; Hill, 1963,https://doi.org/10.1175/1520‐0469(1963)020<0492:SEOLII>2.0.CO;2). Recent satellite data analysis (Noja et al., 2013,https://doi.org/10.1002/rds.20033; Chartier et al., 2018,https://doi.org/10.1002/2017JA024811) showed that the high‐latitudeFregion ionosphere exhibits sporadic enhancements more frequently in January than in July in both the northern and southern hemispheres. The same pattern has been seen in statistics of the degradation and total loss of GPS service onboard low‐Earth orbit satellites (Xiong et al. 2018,https://doi.org/10.5194/angeo‐36‐679‐2018). Here, we confirm the existence of this annual pattern using ground GPS‐based images of TEC from the MIDAS algorithm. Images covering January and July 2014 confirm that the high‐latitude (>70 MLAT)Fregion exhibits a substantially larger range of values in January than in July in both the northern and southern hemispheres. The range of TEC values observed in the polar caps is 38–57 TECU (north‐south) in January versus 25–37 TECU in July. First‐principle modeling using SAMI3 reproduces this pattern, and indicates that it is caused by an asymmetry in plasma levels (30% higher in January than in July across both polar caps), as well as 17% longer O⁺plasma lifetimes in northern hemisphere winter, compared to southern hemisphere winter. 

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4. Rotation‐Inversion Isomerization of Tertiary Carbamates: Potential Energy Surface Analysis of Multi‐Paths Isomerization Using Boltzmann Statistics

   https://doi.org/10.1002/cphc.202200893  

   Jameson, Brian; Glaser, Rainer (January 2023, ChemPhysChem)

   Abstract The front cover artwork is provided by Prof. Rainer Glaser's group at the Missouri University of Science and Technology. The image shows one of four potential energy surfaces generated from our rotation‐inversion study of tertiary carbamates and highlights two of the eight possible transition state pathways between two ensembles of E‐ and Z‐minima. In the context of synthetic studies of fluorinated carbamates R₁O−CO−N(R₂)CH₂CF₃, we unexpectedly observed two sets of ¹³C NMR quartets for the CF₃ group and we needed to understand their origin. Read the full text of the Research Article at 10.1002/cphc.2022005442. 

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5. Formation of Plasma Around a Small Meteoroid: Electrostatic Simulations

   https://doi.org/10.1029/2018JA026434  

   Sugar, G.; Oppenheim, M. M.; Dimant, Y. S.; Close, S. (May 2019, Journal of Geophysical Research: Space Physics)

   Abstract Obtaining meteoroid mass from head echo radar cross section depends on the assumed plasma density distribution around the meteoroid. An analytical model presented in Dimant and Oppenheim (2017a,https://doi.org/10.1002/2017JA023960; 2017b,https://doi.org/10.1002/2017JA023963) and simulation results presented in Sugar et al. (2018,https://doi.org/10.1002/2018JA025265) suggest the plasma density distribution is significantly different than the spherically symmetric Gaussian distribution used to calculate meteoroid masses in many previous studies. However, these analytical and simulation results ignored the effects of electric and magnetic fields and assumed quasi‐neutrality. This paper presents results from the first particle‐in‐cell simulations of head echo plasma that include electric and magnetic fields. The simulations show that the fields change the ion density distribution by less than ∼2% in the meteor head echo region, but the electron density distribution changes by up to tens of percent depending on the location, electron energies, and magnetic field orientation with respect to the meteoroid path. 

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