Proton Trapping Research Articles

The Impact of the 8–10 March 2012 Geomagnetic Storm on Inner Zone Protons as Measured by Van Allen Probes

AbstractThe Relativistic Electron Proton Telescope (REPT) instrument on the Van Allen Probes observed a double‐peaked inner zone proton population throughout the 7 year lifetime of the mission. M. Hudson et al. (2023) showed that a strong SEP event accompanied by a CME‐shock in early March 2012 provided the Solar Energetic Proton (SEP) source for the higher L trapped proton population, which then diffused radially inward to be observed by REPT at . The study followed trajectories of SEP protons launched isotropically from a sphere at 7 Re for 2.5 hr in fields calculated by the LFM‐RCM global MHD model, which includes electric fields needed to model the transport and trapping of the protons by the shock, and then a radial diffusion simulation was run for 2 years using the result from the test‐particle simulation as the initial condition. The simulation result was compared with REPT measurement in November 2013 and showed reasonable agreement. However, the simulation overestimated the Phase Space Density by a factor of four due to lack of field line curvature scattering during the storm in the model. In this study, a test‐particle simulation is performed for 2 days following the injection and trapping of protons in March 2012 using TS05 fields to simulate the field line curvature scattering of the trapped SEP due to the buildup of the ring current during the geomagnetic storm. The resulting sample distribution was then weighted using the flux at the end of the two‐hour MHD‐test particle simulation. A radial diffusion simulation is then run using the initial profile that included the loss effect, with improved comparison with REPT measurements after 2 years.

High-Temperature Mechanical–Conductive Behaviors of Proton-Conducting Ceramic Electrolytes in Solid Oxide Fuel Cells

Proton-conducting solid oxide fuel cells (P-SOFCs) are widely studied for their lower working temperatures than oxygen-ion-conducting SOFCs (O-SOFCs). Due to the elevated preparation and operation temperatures varying from 500 °C to 1500 °C, high mechanical stresses can be developed in the electrolytes of SOFCs. The stresses will in turn impact the electrical conductivities, which is often omitted in current studies. In this work, the mechanical–conductive behaviors of Y-doped BaZrO3 (BZY) electrolytes for P-SOFCs under high temperatures are studied through molecular dynamics modeling. The Young’s moduli of BZY in fully hydrated and non-hydrated states are calculated with different Y-doping concentrations and at different temperatures. It is shown that Y doping, oxygen vacancies, and protonic point defects all lead to a decrease in the Young’s moduli of BZY at 773 K. The variations in the conductivities of BZY are then investigated by calculating the diffusion rates of protons in BZY at different triaxial, biaxial, and uniaxial strains from 673 K to 873 K. In all cases, the diffusion rate present a trend of first increasing and then decreasing from compression state to tension state. The variations in elementary affecting factors of proton diffusion, including hydroxide rotation, proton transfer, proton trapping, and proton distribution, are then analyzed in detail under different strains. It is concluded that the influences of strains on these factors collectively determine the changes in proton conductivity.

Improved thermal stability and electrical conductivity of dysprosium doped barium zirconium cerate electrolyte

Acceptor-doped perovskites based on the BaCeO3 have been extensively investigated as promising candidates for proton-conducting electrolyte at intermediate temperatures. This operational regime is characterized by proton conduction facilitated via hydroxyl protons that effectively occupy vacancies of oxide ions within the perovskite crystal lattice structure. While the trade-off parameters (proton conductivity and chemical stability) concern the utility of cerium-based electrolytes, acceptor doped compounds hinder the mobility of protons due to dopant-charge and dopant-host interactions. However, Dy-doped compounds reveal a promising behavior relative to most acceptor substituents with marginal constraints at higher doping concentration. As a result, a threshold doping range is essential to combat material inconsistencies such as cationic disorder to proton trapping effect. Therefore in the present study we synthesize the single-phase dysprosium and zirconium co-doped barium cerate at different doping concentrations (BaCe0.8-xZr0.2DyxO3-δ (x = 0.0–0.20)) to showcase the chemical inertness of the compound against oxidizing and reducing atmospheres preserving high ionic conductivity. According to our experimental outcomes, higher ionic conductivity among wet atmospheric conditions suggests the role of moisture to contribute additional charge carriers among the Dy-doped samples via explicitly generated oxygen vacancies. As a result, BaCe0.65Zr0.2Dy0.15O3-δ demonstrates a highest total conductivity, reaching 2.44 x 10-2 S cm−1 at 575 °C, with an associated activation energy of 0.61 eV within the temperature range of 300–600 °C. The study also reveals the optimal operating temperature of the proton conducting electrolyte to avoid mixed ionic (H+ and O2–) conduction.

Hydrogen-induced tunable remanent polarization in a perovskite nickelate

Materials with field-tunable polarization are of broad interest to condensed matter sciences and solid-state device technologies. Here, using hydrogen (H) donor doping, we modify the room temperature metallic phase of a perovskite nickelate NdNiO3 into an insulating phase with both metastable dipolar polarization and space-charge polarization. We then demonstrate transient negative differential capacitance in thin film capacitors. The space-charge polarization caused by long-range movement and trapping of protons dominates when the electric field exceeds the threshold value. First-principles calculations suggest the polarization originates from the polar structure created by H doping. We find that polarization decays within ~1 second which is an interesting temporal regime for neuromorphic computing hardware design, and we implement the transient characteristics in a neural network to demonstrate unsupervised learning. These discoveries open new avenues for designing ferroelectric materials and electrets using light-ion doping.

Membrane-less MoO3−x@TiO2-bromine battery with excellent rate capability and cyclic stability

Bromine has attracted significant attention as a cathode material for aqueous batteries due to its high reduction potential of 1.05 V (Br3− + 2e− ↔ 3Br−), impressive theoretical specific capacity of 223 mA h g−1, and rapid reaction kinetics in the electrolyte. However, searching for compatible anode materials to match with bromine has posed a challenge due to its highly corrosive nature. In this study, we developed oxygen-deficient MoO3 with TiO2 coating (referred to as MoO3−x@TiO2) as an anode material to pair with a bromine cathode in static full batteries. The oxygen deficiency contributes to enhanced electronic and protonic diffusion within the MoO3−x lattice, while the TiO2 coating mitigates structural dissolution and proton trapping during cycling. The MoO3−x@TiO2 demonstrates fast charge storage kinetics and excellent resistance to bromine corrosion. The impressive compatibility between MoO3−x@TiO2 and bromine enables the construction of membrane-less full batteries with exceptional rate capability and cyclic stability. The MoO3−x@TiO2-bromine battery achieves an energy density of 70.8 W h kg−1 at a power density of 328.1 W kg−1, showcasing an impressive long-term cyclic life of 20,000 cycles. Our study provides valuable insights for the development of high-performance aqueous secondary batteries.

High proton conduction by full hydration in highly oxygen deficient perovskite

We report high proton conductivity (10 mS cm−1 at 235 °C) of stable BaSc0.8W0.2O2.8, which is attributed to (1) high proton concentration due to full hydration and large amount of oxygen vacancies and (2) high proton mobility due to reduced proton trapping.

Benchmarking trapped proton specification models along an EOR orbit

Benchmarking trapped proton specification models along an EOR orbit

Efficient activation of peroxymonosulfate by molybdenum disulfide cocatalysis of Co and N co-doped porous carbon for degrading perfluorooctanoic acid: Synergistic effect of Co and N by molybdenum and its mechanism

In this study, precursor ultrathin molybdenum disulfide nanosheets and ZIF-67 was selected to prepare Co and N co-doped porous carbon by the support of Mo (MoS2/Co@NPC) to activate peroxymonosulfate (PMS) for perfluorooctanoic acid (PFOA) degradation. The morphology, crystal form and composition of MoS2/Co@NPC are studied by scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and other methods. In MoS2/Co@NPC/PMS process, PFOA was completely degraded in 180 min at pH 7, 0.3 g/L catalyst, 0.1 mM PMS and reaction temperature of 25 °C. The degradation efficiency was much higher than that in other systems. The oxidative species for PFOA degradation was studied using free radical quenching experiments and electron paramagnetic resonance (ESR) tests. SO−4 plays a major role in the degradation of PFOA, OH plays an auxiliary role, and 1O2 contributes the least. The effect of different types and positions of cobalt‑nitrogen and molybdenum atoms on the electrocatalytic activity was investigated by density functional theory (DFT) calculations. The co-doping of Co and N into carbon-based materials can synergistically enhance by Mo for the activation of PMS. The unsaturated S atoms on the surface of metal sulfides can trap protons to form H2S while exposing the reducing metal active site, which also accelerates the rate-limiting step of the Co3+/Co2+ conversion. The core-shell structure of Co@NPC doped with Mo has the characteristics of improving the electron transfer ability of carbon, promoting the mass transfer of reactants, and preventing cobalt metal agglomeration and metal dissolution. The degradation pathways of PFOA were investigated and three possible pathways were proposed. In addition to PFOA, MoS2/Co@NPC-800/PMS system can also remove contaminant in pharmaceutical wastewater, indicating that the process has potential application value in practical wastewater treatment.

High proton conductivity within the ‘Norby gap’ by stabilizing a perovskite with disordered intrinsic oxygen vacancies

Proton conductors are attractive materials with a wide range of potential applications such as proton-conducting fuel cells (PCFCs). The conventional strategy to enhance the proton conductivity is acceptor doping into oxides without oxygen vacancies. However, the acceptor doping results in proton trapping near dopants, leading to the high apparent activation energy and low proton conductivity at intermediate and low temperatures. The hypothetical cubic perovskite BaScO2.5 may have intrinsic oxygen vacancies without the acceptor doping. Herein, we report that the cubic perovskite-type BaSc0.8Mo0.2O2.8 stabilized by Mo donor-doing into BaScO2.5 exhibits high proton conductivity within the ‘Norby gap’ (e.g., 0.01 S cm−1 at 320 °C) and high chemical stability under oxidizing, reducing and CO2 atmospheres. The high proton conductivity of BaSc0.8Mo0.2O2.8 at intermediate and low temperatures is attributable to high proton concentration, high proton mobility due to reduced proton trapping, and three-dimensional proton diffusion in the cubic perovskite stabilized by the Mo-doping into BaScO2.5. The donor doping into the perovskite with disordered intrinsic oxygen vacancies would be a viable strategy towards high proton conductivity at intermediate and low temperatures.

Hydrated doped-BaZrO3 proton conductors studied by positron annihilation lifetime spectroscopy

The study of defect chemistry for doped BaZrO3 proton conductors is of particular interest because of defect interactions that can affect the proton conductivity of the material. Protons incorporated due to the material's hydration can be trapped by negatively charged immobile dopants, reducing proton mobility. The reduction of the proton conduction impedes the use of BaZrO3 materials in energy conversion applications at intermediate temperatures (300 °C – 600 °C). The probing of proton trapping in doped BaZrO3 is hindered by the limited availability of techniques sensitive to defect chemistries. In this work, we used positron annihilation lifetime spectroscopy (PALS) to study the defect chemistry of Y-doped and Sc-doped BaZrO3. Using a two-state positron trapping model we showed that PALS can be applied to study the defect chemistry of hydrated dense proton conductors. Positron trapping rates and lifetimes were correlated with doping levels of the materials. Probability significance t-tests were carried out for PALS parameters to verify whether there are differences/similarities for various populations: non-doped/doped, level and type of doping, high temperature, and surface effects. The results revealed that the initial doping generates a significant number of traps available for positrons. Doping with yttrium increased the positron trapping rate, while this effect was not observed with scandium. Low-temperature hydration affects specimens significantly inhibiting positron trapping at undoped BaZrO3 material and highly doped specimens. Positronium formation in rough surface layers, and highly doped specimens was detected but does not exceed 1%.

Benchmarking the yttrium content in the low temperature/low humidity electrical properties of yttrium-doped barium cerate

Yttrium-doped barium cerate (BCY) is one of the best proton-conducting ceramics to be used in fuel cells/electrolyzers at intermediate temperatures, due to its high hydration enthalpy and high conductivity. Nonetheless, it has commonly been discarded for these applications due to its instability in the presence of carbonaceous and humidified atmospheres. A recent work has addressed this issue, by suggesting the use of this material in very low water vapor partial pressures (pH2O ∼ 10−4 atm) [Electrochimica Acta 334 (2020) 135625] and at low temperatures (T ≤ 400 °C). Under these conditions, BCY can still offer pure protonic conductivity while also offering suitable stability. In the current work, we provide a comprehensive analysis of the effects of the acceptor dopant concentration (Y2O3) in the structural, microstructural, and electrical properties in a wide compositional series of BaCe1-xYxO3-δ (x = 0.05, 0.10, 0.20 and 0.30) at low levels of humidity in the low temperature range (100–400 °C). The results show that BaCe0.9Y0.1O3-δ (BCY10) offers the highest bulk conductivity in these conditions, while further increase in dopant concentration leads to impairment due to “proton trapping” effects. In contrast, the specific grain boundary conductivity increases with increasing dopant concentration due to a reduction of Schottky barrier height at the space-charge layer. We demonstrate that, by operating at very low temperatures (e.g., below 400 °C), the peak performing, BCY10 material can still operate at very low levels of water vapor partial pressure (pH2O ∼ 10−4 atm), where its stability can be maintained. This work paves the way for the optimization of this material, with a focus on utilizing low humidity levels and low temperatures, where it can offer a competitive advantage over that of the majority of other proton-conducting perovskites for potential applications operating under these conditions.

A review of proton migration and interaction energies in doped barium zirconate

Barium zirconate is a promising material for application as solid electrolyte in ceramic fuel cells due to its high protonic conductivity when doped with trivalent oxides such as yttria. On the atomic level, the transport behaviour can be elucidated using density functional theory and energy parameters controlling the mobility have been calculated by several researchers in the last years. In this work, we give a summarizing overview of the available literature data. We consider the interaction energies between protons and dopant ions and the migration barriers of proton motion for individual jumps in bulk BaZrO3 with the focus on Y-doping. Generally, there is a large spread of energy values, which is related to the variations in the calculation parameters and variable distortions in the ionic lattice introduced by defects. Especially the cell size has a paramount influence on the results. In comparison to other dopants, yttrium exhibits a similar trapping of protons in both nearest and second nearest neighbour positions. This seems to be beneficial for conductivity as it leads to overlapping trapping zones and probably moderate barriers for the detrapping jump to the third nearest neighbour position.Based on the collected data, we estimated the protonic conductivity using kinetic Monte Carlo simulations. We applied energy models with different radii of interactions and further varied the energy parameters within the range of literature values. The results show that the interaction radius has only a limited effect while the impact due to the variable energy range is more pronounced. Nevertheless, similar trends are found for all models, especially a minimum in the mobility at low dopant fractions.

Enhanced grain boundary conductivity of Gd and Sc co-doping BaZrO3 proton conductor for proton ceramic fuel cell

Applicability of BaZrO3 proton conductor as electrolytes in fuel cells and electrolysis cells is limited due to lower grain boundary conductivity and serious sintering activity. Herein, we report the enhancement of grain boundary conductivity and sintering performance of BaZrO3 proton conductor by Sc and Gd co-doping at B site. Combining experimental characterization and theoretical calculations, we found that the incorporation of Sc can effectively promote the generation of proton defects and lower the proton migration energy barrier. Meanwhile, the clustering of positively charged oxygen vacancy to acceptors can suppress proton trapping, thus positively affecting the long-range proton transport and effectively improving bulk conductivity. In addition, the space charge quantification by Mott-Schottky approximation confirms that Sc and Gd co-doping is significantly reduce the Schottky barrier height and the width of space charge layer, resulting in lower proton depletion and higher grain boundary conductivity. Benefiting from these two positive effects, these electrolytes show the highest proton conductivity of 2.99 × 10-3 ∼ 3.63 × 10-2 S cm−1 in the temperature range of 250 ∼ 750 ℃. This indicates that co-doping of Gd and Sc is one of the effective and feasible strategy to improve the sinterability and conductivity of BaZrO3-based proton conductors.

Study on the cationic polymerization of isobutyl vinyl ether initiated by dual active species based on [Ph3C][B(C6F5)4] and its mechanism

AbstractThe cationic polymerization of isobutene vinyl ether(IBVE) contains waters system was achieved by using triphenylmethylium tetrakis‐(pentafluorophenyl)borate [Ph3C][B(C6F5)4], which overcame the harsh experimental requirements of traditional cationic polymerization. The influences of water content, solvent polarity, and reaction temperature on polymerization were studied. The end structure of the polymer was analyzed by 1H‐NMR. Combined with the effect of the proton trapping agent and triethylamine salt which can trap [H+], it was found that there was a reversible equilibrium between [Ph3C+] and [H+] active species during the polymerization process. The cationic polymerizations of isobutyl vinyl ether were initiated by these two active species simultaneously. The controllable cationic polymerization of isobutyl vinyl ether was achieved by the addition of ethyl methyl carbonate and ethyl benzoate. Gaussian 09 W simulation confirms the polymerization mechanism.

Simulated Trapping of Solar Energetic Protons for the 8–10 March 2012 Geomagnetic Storm: Impact on Inner Zone Protons as Measured by Van Allen Probes

AbstractSolar energetic protons (SEPs) have been shown to contribute significantly to the inner zone trapped proton population for energies <100 MeV and L > 1.3 (Selesnick et al., 2007, https://doi.org/10.1029/2006sw000275). The Relativistic Electron Proton Telescope (REPT) on the Van Allen Probes launched 30 August 2012 observed a double‐peaked (in L) inner zone population throughout the 7‐year lifetime of the mission. It has been proposed that a strong SEP event accompanied by a CME‐shock in early March 2012 provided the SEP source for the higher L trapped proton population, which then diffused radially inward to be observed by REPT at L ∼ 2. Here, we follow trajectories of SEP protons launched isotropically from a sphere at 7 Re in 15 s cadence fields from an Lyon‐Fedder‐Mobarry coupled to Rice Convection Model global magnetohydrodynamic (MHD) simulation driven by measured upstream solar wind parameters. The timescale of the interplanetary shock arrival is captured, launching a magnetosonic impulse propagating azimuthally along the dawn and dusk flanks inside the magnetosphere, shown previously to produce SEP trapping. The MHD‐test particle simulation uses Geostationary Operational Environmental Satellite (GOES) proton energy spectra to weight the initial radial profile required for the radial diffusion calculation over the following 2 years. GOES proton measurements also provide a dynamic outer boundary condition for radial diffusion. A direct comparison with REPT measurements 20 months following the trapping event in March 2012 supports this novel combination of short‐term and long‐term evolution of the newly trapped protons.

Contribution of the Collective Excitations to the Coupled Proton and Energy Transport along Mitochondrial Cristae Membrane in Oxidative Phosphorylation System.

The results of many experimental and theoretical works indicate that after transport of protons across the mitochondrial inner membrane (MIM) in the oxidative phosphorylation (OXPHOS) system, they are retained on the membrane-water interface in nonequilibrium state with free energy excess due to low proton surface-to-bulk release. This well-established phenomenon suggests that proton trapping on the membrane interface ensures vectorial lateral transport of protons from proton pumps to ATP synthases (proton acceptors). Despite the key role of the proton transport in bioenergetics, the molecular mechanism of proton transfer in the OXPHOS system is not yet completely established. Here, we developed a dynamics model of long-range transport of energized protons along the MIM accompanied by collective excitation of localized waves propagating on the membrane surface. Our model is based on the new data on the macromolecular organization of the OXPHOS system showing the well-ordered structure of respirasomes and ATP synthases on the cristae membrane folds. We developed a two-component dynamics model of the proton transport considering two coupled subsystems: the ordered hydrogen bond (HB) chain of water molecules and lipid headgroups of MIM. We analytically obtained a two-component soliton solution in this model, which describes the motion of the proton kink, corresponding to successive proton hops in the HB chain, and coherent motion of a compression soliton in the chain of lipid headgroups. The local deformation in a soliton range facilitates proton jumps due to water molecules approaching each other in the HB chain. We suggested that the proton-conducting structures formed along the cristae membrane surface promote direct lateral proton transfer in the OXPHOS system. Collective excitations at the water-membrane interface in a form of two-component soliton ensure the coupled non-dissipative transport of charge carriers and elastic energy of MIM deformation to ATP synthases that may be utilized in ATP synthesis providing maximal efficiency in mitochondrial bioenergetics.

In-situ sulfidation to fabricate NiSx modified g-C3N4/NiO composite for efficient photocatalytic hydrogen production under visible-light

Graphitic carbon nitride is a very potential photocatalytic catalyst for H2 production, but its practical application is seriously limited by the fast recombination of photogenerated carriers and insufficient utilization of surface charge. In order to solve these problems, herein, a series of g-C3N4-NiO-NiSx photocatalysts were synthesized by first calcining the precursor to load NiO on g-C3N4 and subsequently partial sulfidation of NiO into NiSx in situ via a hydrothermal process. Under the irradiation of visible light, the photocatalytic H2 production rate of g-C3N4-NiO-0.4T can be up to 1248.1 μmol·g−1·h−1 using triethanolamine as sacrificial agent. In addition, recycling test also confirmed g-C3N4-NiO-0.4T has excellent photostability. It is believed that the formation of p-n junction between NiO and g-C3N4 and the presence of NiSx promote the spatially fast separation of photogenerated carriers, while the abundant interface of NiS2 and NiS also leads to the good proton trapping ability. These two factors jointly determine the efficient H2 production of the composite photocatalysts. Furthermore, the detailed energy band structure and plausible photocatalytic mechanism of g-C3N4-NiO-NiSx are also proposed. This work can offer a new route and useful reference for the design and research of high efficiency composite photocatalysts for H2 production.

Structural and electrophysical perturbations in Y3+ doped BaCeO3 proton conducting electrolyte: A first principles approach

Structural and electrophysical diversity in doped proton conductors (PCs) pacifies the operational efficiency of energy conversion devices. Inflexions in M—O and O–H bond distance within a BO6 octahedra inflects the charge kinetics. Electrochemical characteristics and hybridizations of individual compositional constituents determine the material's electrical attributes (proton conductivity and customized charge transfer pathways). Fluctuations in proton diffusion and hence the proton trapping effect are all a consequence of perturbed chemical bonding and different electrostatic interactions between dopant-host neighbourhood. The current work thus emphasizes the impact of structural phase transition over electrical properties (bandstructure and density of states) and addresses the proton trapping effect. Phase transitions from single phase Pbnm to I12/m1 monoclinic symmetry progresses via multiphase coexistence at intermediate doping concentrations (x = 0.125 and 0.375). On the electronic analogue, the synergy imposes an equivalent impact upon discrete high symmetry pathways in DFT-VASP simulated band structures. The distant overlapping between Y – 4d with O – 2p orbitals establishes a weak binding energy between Y3+ and O2− and favours large oxygen vacancies with non-linear behaviour. A considerable shift of Y – 4f orbitals towards Fermi level at higher doping concentrations (x > 0.25) illustrates the early instance of proton trapping phenomenon.

Simulated Trapping of Solar Energetic Protons for the 8-10 March 2012 Geomagnetic Storm: Impact on Inner Zone Protons as Measured by Van Allen Probes

Simulated Trapping of Solar Energetic Protons for the 8-10 March 2012 Geomagnetic Storm: Impact on Inner Zone Protons as Measured by Van Allen Probes

Newly Formed Dawnside, Duskside, and Nightside Subauroral Flows Developed During Magnetically Active Times

AbstractWe study the newly formed (with an upper limit of ∼101 min) subauroral flows in the topside ionosphere. These include the dawnside subauroral flows observed at ∼5–6 magnetic local time (MLT), the duskside sub‐auroral polarization streams (SAPS) at ∼15 MLT, and the nightside sub‐auroral ion drifts (SAID) at ∼19–20 MLT. We employ the same types of observations for investigating the various underlying magnetospheric processes related to the development of the newly formed subauroral flows. These processes include (a) the stretching of magnetic field lines (leading to plasma density dropouts) due to the unfolding magnetotail reconnection, (b) the dawnside and nightside diversions of the magnetotail‐reconnection—related earthward plasma flows, (c) the ongoing particle injections, and (d) the trapping of ring current protons at subauroral and auroral latitudes. Based on these processes (a–d), we found strong similarities in the development of the newly formed dawnside and duskside/nightside subauroral flows investigated. At the dawnside plasmapause in the inner magnetosphere equatorial plane, the outward and duskward electric (E) field components provide observational evidence that the newly formed dawnside rapid narrow subauroral flows were SAID developing in the dawn sector. Evidence shows that the newly formed dawnside broad subauroral flow channel was associated with upward Region 2 (R2) field‐aligned currents (FACs) and equatorward subauroral polarization E field, and thus, was the dawnside equivalent of the duskside SAPS associated with downward R2 FACs and poleward subauroral polarization E field. Further evidence includes the inner magnetosphere observations of the hot zone both on the dusk/nightside and on the dawnside.