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1. Cage Match: Comparing the Anion Binding Ability of Isostructural Versus Isofunctional Pairs of Metal‐Organic Nanocages

   https://doi.org/10.1002/chem.202303013  

   Dutton, Kaitlyn G; Jones, Taro J; Emge, Thomas J; Lipke, Mark C (January 2024, Chemistry – A European Journal)

   Abstract Affinities of six anions (mesylate, acetate, trifluoroacetate,p‐toluenecarboxylate,p‐toluenesulfonate, and perfluorooctanoate) for three related Pt²⁺‐linked porphyrin nanocages were measured to probe the influence of different noncovalent recognition motifs (e. g., hydrogen bonding, electrostatics, π bonding) on anion binding. Two new hosts of M₆L₃¹²⁺(1b) and M₄L₂⁸⁺(2) composition (M=(en)Pt²⁺, L=(3‐py)₄porphyrin) were prepared in a one‐pot synthesis and allowed comparison of hosts that differ in structure while maintaining similar N−H hydrogen‐bond donor ability. Comparisons of isostructural hosts that differ in hydrogen‐bonding ability were made between1band a related M₆L₃¹²⁺nanoprism (1a, M=(tmeda)Pt²⁺) that lacks N−H groups. Considerable variation in association constants (K₁=1.6×10³ M⁻¹to 1.3×10⁸ M⁻¹) and binding mode (exovs.endo) were found for different host–guest combinations. Strongest binding was seen betweenp‐toluenecarboxylate and1b, but surprisingly, association of this guest with1awas only slightly weaker despite the absence of NH⋅⋅⋅O interactions. The high affinity betweenp‐toluenecarboxylate and1acould be turned off by protonation, and this behavior was used to toggle between the binding of this guest and the environmental pollutant perfluorooctanoate, which otherwise has a lower affinity for the host. 

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2. Determination of Outer Radiation Belt MeV Electron Energization Rates and Delayed Response Times to Solar Wind Driving During Geomagnetic Storms

   https://doi.org/10.1029/2023JA032115  

   Srinivas, P; Spencer, E (July 2024, Journal of Geophysical Research: Space Physics)

   Abstract Radiation Belt Storm Probes (RBSP) data show that seed electrons generated by sub‐storm injections play a role in amplifying chorus waves in the magnetosphere. The wave‐particle interaction leads to rapid heating and acceleration of electrons from 10's of keV to 10's of MeV energies. In this work, we examined the changes in the radiation belt during geomagnetic storm events by studying the RBSP REPT, solar wind, AL, SML, and Dst data in conjunction with the WINDMI model of the magnetosphere. The field‐aligned current output from the model is integrated to generate a proxy E index for various energy bands. These E indices track electron energization from 40 KeV to 20 MeV in the radiation belts. The indices are compared to RBSP data and GOES data. Our proxy indices correspond well to the energization data for electron energy bands between 1.8 and 7.7 MeV. Each E index has a unique empirical loss rate term (τ_L), an empirical time delay term (τ_D), and a gain value, that are fit to the observations. These empirical parameters were adjusted to examine the delay and charging rates associated with different energy bands. We observed that theτ_Landτ_Dvalues are clustered for each energy band.τ_Landτ_Dconsistently increase going from 1.8 to 7.7 MeV in electron energy fluxE_eand the dropout interval increases with increasing energy level. The average trend of Δτ_D/ΔE_ewas 4.1 hr/MeV and the average trend of Δτ_L/ΔE_ewas 2.82 hr/MeV. 

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3. Feynman path description of the effects of dephasing of spatial coherences on the transmission and reflection probabilities through a one-dimensional potential

   https://doi.org/10.1088/1402-4896/acad39  

   Nagalla, Karna; Walls, Jamie D (January 2023, Physica Scripta)

   Abstract In this work, we examine the effects of spatial dephasing of coherences on the transmission and reflection probabilities for electrons with energyEincident to a one-dimensional rectangular barrier of heightV₀. Statistical models are presented where the coherence between different scattering pathways or ‘Feynman paths’ undergo dephasing over a length scale,L_ϕ. For incident waves withE>V₀, three different dephasing models that attenuate the contributions of spatial coherence to the transmission and reflection probabilities while preserving unitarity (i.e., conserving charge) were investigated. In the tunneling regime (incident waves withE<V₀), however, preserving unitarity requiresL_ϕ→ ∞ , suggesting that elastic tunneling through a rectangular barrier is 100% spatially coherent for these dephasing models. However, wave absorption models are shown to preserve unitarity in the tunneling regime, which is not the case for scattering above the barrier. 

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4. Constraining Vector Dark Matter with neutrino experiments

   https://doi.org/10.1007/JHEP08(2023)181  

   Brzeminski, Dawid; Das, Saurav; Hook, Anson; Ristow, Clayton (August 2023, Journal of High Energy Physics)

   A<sc>bstract</sc> Vector Dark Matter (VDM) that couples to lepton flavor (L_e,L_μ,L_τ) acts similarly to a chemical potential for the neutrino flavor eigenstates and modifies neutrino oscillations. VDM imparts unique signatures such as time and directional dependence with longer baselines giving better sensitivity. We use the non-observation of such a signal at Super-Kamiokande to rule out the existence of VDM in a region of parameter space several orders of magnitude beyond other constraints and show the projected reach of future experiments such as DUNE. 

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5. In Situ and 2D and 3D in Silico Redox Cycling Studies for Design Optimization of Coplanar Arrays of Microband Electrodes in a 70 μm × 100 μm Electroactive Footprint

   https://doi.org/10.1149/1945-7111/ad5409  

   Abrego_Tello, Miguel A; Lotfi_Marchoubeh, Mahsa; Fritsch, Ingrid (June 2024, Journal of The Electrochemical Society)

   Optimization of redox-cycling currents was performed by adjusting the height (sidewalls,h), width (w), and length (l) of band electrodes and their spacing (w_gap) in coplanar arrays restricted to a small-electroactive window of 70 × 100μm. These arrays can function inμL-volumes for chemical analysis (e.g., in-vivo dopamine detection using probes). Experiments were conducted with an array of five electrodes (N_E= 5),w= 4.3μm,w_gap= 3.7μm,h= 0.150μm, andl= 99.2μm. Reasons for disparities between currents from experiments and approximate equations were determined by high-density mesh simulations and were found to arise from sluggish heterogeneous electron transfer kinetics and diffusion at electrode ends, edges, and heights. Ferricyanide, with its moderately slow kinetics, exhibits redox-cycling currents that fall below predictions by the equations asw_gapdecreases and diffusional flux outpaces reaction rates. Simulations aid investigations of various array designs, achievable through conventional photolithography, by decreasingwandw_gapand increasingN_Eto fit within the electroactive window. A coplanar array,N_E= 58,w=w_gap= 0.6μm,h= 0.150μm andl= 100μm, yielded ferricyanide sensitivities of 0.266, 0.259 nA·μM⁻¹, enhancements of 8 × and 9 × overw=w_gap= 4μm, and projected dopamine lower limits of quantitation of 139 nM, 171 nM at generator and collector electrodes, respectively. 

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