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Recent observations and particle‐tracing models have revealed a counterintuitive difference between the behaviors of magnetospheric protons and oxygen ions when they encounter the magnetopause. The oxygen ions usually meander around the magnetopause without a full escape to the magnetosheath, whereas the protons can more easily stream across the magnetopause despite their smaller gyroradii. Here, we analytically identify the mechanisms that cause this species dependence. As magnetospheric ions drift toward the magnetopause, the grazing angle of their magnetopause encounter is constrained within a narrow range near 0°, with its maximum being proportional to the square root of the ion gyroradius. It is the grazing angle that largely determines the follow‐up ion motion. The ions with larger grazing angles would meander around the magnetopause, whereas the meandering motion for ions with smaller grazing angles could be easily disrupted to enable their escape even if the normal magnetic field is very weak. Plain Language Summary: The Earth's magnetic field is constrained by the interplanetary field within a finite region named the magnetosphere. The boundary of this region, the magnetopause, separates the magnetospheric plasma from the cooler and denser population in the shocked solar wind. Some of the magnetospheric particles, however, can still penetrate the magnetopause and escape into the interplanetary space. One may expect that heavy ions, like singly charged oxygen ions, are more likely to escape than protons due to their larger gyroradii; however, the opposite trend has been identified in spacecraft observations. This counterintuitive feature, although reproduced in a particle‐tracing model, has not yet been fully understood. Here, we analyze the particle trajectories to identify the mechanism underlying the species dependence of the ion escape. When magnetospheric ions encounter the magnetopause, their grazing angles are constrained within a narrow range near 0°, with the maximum angle depending positively on ion gyroradius. We find that the ions with larger grazing angles would meander around the magnetopause without a full escape, whereas the meandering motion for those with smaller angles could be more easily disrupted by a weak normal magnetic field to enable their field‐aligned escape. Key Points: Despite their smaller gyroradii, protons are found more likely to escape from the magnetosphere than oxygen ionsA mechanism leading to the counterintuitive species dependence is analytically identified based on a simple modelThe model also explains the bifurcated gyrophase bunching of the oxygen ions observed in the magnetosheath [ABSTRACT FROM AUTHOR]

The present study reports a gas‐phase photoelectrochemical (GPEC) system in which photoanode and photocathode materials are coated on each side with a pellet of the oxygen‐ion conductor yttria‐stabilized zirconia (YSZ), where light irradiation is feasible on both sides. As a model gas‐phase reaction, we chose dry reforming of methane (DRM), which converts greenhouse gases into valuable syngas. Consequently, the stoichiometric DRM reaction proceeded in our GPEC system, indicating that the oxygen ions in a YSZ pellet act as mediators to link the redox reactions. It was also noted that UV light irradiation on the anodic side was more effective than that on the cathodic side, suggesting that the photogenerated holes in the anodic YSZ side activate methane molecules, while photogenerated electrons are injected into Rh nanoparticles to cause carbon dioxide reduction in the cathodic side. Our GPEC system converts greenhouse gases into valuable syngas by light irradiation. [ABSTRACT FROM AUTHOR]

The D‐shaped ion velocity distribution generated by the time‐of‐flight (ToF) effect can be considered as an important characteristic of reconnection exhausts in the magnetopause and magnetotail reconnection processes. In this study, we reported the D‐shaped velocity distribution of O+ ions produced by the ToF effect in the magnetotail reconnection exhaust based on the observations from the Cluster spacecraft. The observed cutoff velocity of O+ ions is smaller than that of H+ ions at the same time, which is different from the previous theoretical prediction. We suggested that the difference between the two cutoff velocities is probably due to O+ ions having a larger reconnection diffusion region than H+ ions. We also demonstrated a remote‐sensing method to estimate the spatial scale ratio between the O+ and H+ diffusion regions and the distance from the observation site to the center of the magnetotail reconnection region. Plain Language Summary: The reconnection processes at the Earth's magnetopause and magnetotail can convert the magnetic energy into the kinetic energy of the plasma, thus producing high‐speed reconnection exhausts. The exhausting ions usually show a D‐shaped velocity distribution caused by the time‐of‐flight effect. Previous works usually focused only on exhausting protons from the reconnection site, while O+ ions could also be abundant during geomagnetic active times. In this study, we analyzed a reconnection event to investigate the behaviors of O+ and H+ ions in the magnetotail reconnection exhaust region using the observations from the Cluster spacecraft. It is suggested that different behaviors of H+ and O+ ions are probably due to O+ ions having a larger reconnection diffusion region than H+ ions. In addition, we proposed a remote‐sensing method to estimate the spatial scale ratio between the O+ and H+ diffusion regions and the distance from the observation site to the center of the magnetotail reconnection region. Key Points: The time‐of‐flight effect of O+ ions in magnetotail reconnection exhaust was observed by the Cluster spacecraftThe observed cutoff velocity of O+ is smaller than that of H+, indicating that O+ may have a larger diffusion region than H+A remote‐sensing method to estimate the spatial scale ratio between O+ and H+ diffusion regions is introduced [ABSTRACT FROM AUTHOR]

Cluster observed two intermittent oxygen ion (O+) flux enhancements with energy dispersions in a dipolarizing flux bundle, which is known as a region of enhanced northward magnetic field (Bz) embedded in the earthward high‐speed flow. The flux enhancements of O+ show clear pitch angle dependences, which are termed as butterfly distributions. Two corresponding flux enhancements of field‐aligned protons (H+) are also shown in its spectrum, but they are weaker and emerge later (~10 s) than those of O+. Simulation shows that both enhanced ion species are the counterstreaming populations. They originated from the lobe region and were driven into the center plasma sheet by the dawn‐dusk electric field (Ey). Backward tracing test‐particle simulations reproduce the butterfly O+ and the counterstreaming H+ distribution. The differences between O+ and H+ are because of their different gyroradii. The lobe O+ can arrive at the magnetic equatorial plane in less than one gyromotion due to its large gyroradius, and O+ with a larger field‐aligned velocity can arrive at the equatorial plane earlier, leading to the energy and pitch angle dependence. While H+ with similar energy can drift into dipolarizing flux bundle through electric field drift (E × B motion) and arrive at the equatorial plane through adiabatic motion, which consequently forms the field‐aligned flux enhancements in dipolarizing flux bundle, that is, the Bz‐dominant region. The simulation further confirms that intermittent increases of Ey component can produce the two intermittent flux enhancements, as indicated in the in situ observation. Key Points: Two intermittent butterfly O+ and counterstreaming H+ flux enhancements are observed in a dipolarizing flux bundleO+ enhancements are more intense and emerge earlier than those of H+Convection electric field plays a key role in the formation of butterfly O+ and counterstreaming H+ [ABSTRACT FROM AUTHOR]

Oxygen (O+) enhancements in the inner magnetosphere are often observed during geomagnetically active times, such as geomagnetic storms. In this study, we quantitatively examine the difference in ring current dynamics with and without a substantial O+ ion population based on almost 6 years of Van Allen Probes observations. Our results have not only confirmed previous finding of the role of O+ ions to the ring current but also found that abundant O+ ions are always present during large storms when sym‐H < −60 nT without exception, while having the pressure ratio (ℛ) between O+ and proton (H+) larger than 0.8 and occasionally even larger than 1 when L < 3. Simultaneously, the pressure anisotropy decreases with decreasing sym‐H and increasing L shell. The pressure anisotropy decrease during the storm main phase is likely related to the pitch angle isotropization processes. In addition, we find that ℛ increases during the storm main phase and then decreases during the storm recovery phase, suggesting faster buildup and decay of O+ pressure compared to H+ ions, which are probably associated with some species dependent source and/or energization as well as loss processes in the inner magnetosphere. Plain Language Summary: The behavior of the ionospheric O+ ions in the Earth's ring current should be carefully examined in order to advance our understanding of the role of ion composition in ring current dynamics. This problem has been extensively studied using past spacecraft missions. In this study, we revisit this problem based on almost 6 years of high‐quality data from the Van Allen Probes and have confirmed previous finding about the role of O+ ions to the ring current. For example, more O+ ions contribute to the ring current as sym‐H decreases, and O+ and total plasma pressures dramatically build up during storm time. Besides, our statistical results also provide evidence that without exception, ionospheric O+ ions make a significant contribution to the ring current during active time and their relative contribution to the ring current increases during the storm main phase and then decreases during the storm recovery phase compared to those of H+ ions, suggesting a faster buildup and decay of O+ pressure. In addition, the decrease of pressure anisotropy during the storm main phase is related to the pitch angle isotropization, which is probably caused by current sheet scattering or wave‐particle interaction. Key Points: We quantitatively examine how the total plasma pressure and pressure anisotropy changes with and without a substantial O+ ion populationO+ ions always make a nonnegligible contribution to the ring current when sym‐H < ‐60 nT with ℛ > 0.8The decrease of pressure anisotropy during storm main phase is related to pitch angle isotropization [ABSTRACT FROM AUTHOR]

Enlargement of memory window through forming compliance current was demonstrated in Gd:SiO2 resistive random access memory (RRAM) with a gadolinium (Gd) electrode. Lower forming compliance current for Gd:SiO2 RRAM with a Gd electrode results in larger memory window as compared with the RRAM with a Pt electrode. Through analyses on the current conduction mechanism, we demonstrate that a lower forming compliance current leads to a thinner conductive filament forming and less oxygen ions penetrating into Gd electrode, which caused higher on current and lower off current. Furthermore, a possible resistive switching model was proposed to explain the effect of Gd electrode on RRAM device. [ABSTRACT FROM AUTHOR]