Search

Purpose: Studies are required to determine whether exposures to radiation encountered during manned missions in deep space may have adverse effects on the cardiovascular system. Most of the prior studies on effects of simulated space radiation on the heart and vasculature have been performed in mouse models. To provide data from a second animal species, two studies were performed to assess effects of high-energy charged particle radiation on the heart and abdominal aorta in a rat model., Materials and Methods: In study A, male Long Evans rats were exposed to whole-body protons (250 MeV, 0.5 Gy) or oxygen ions ( 16 O, 600 MeV/n, 0.5 Gy), and ultrasonography was used to measure in vivo cardiac function and blood flow parameters at 3, 5, 9 and 12 months after radiation, followed by tissue collection at 12 months. In study B, male Long Evans rats were exposed to 16 O (1 GeV/n, 0.01-0.25 Gy), and hearts collected at 6 to 7 and 12 months for histology and western-blots., Results: Both protons (250 MeV) and 16 O (600 MeV/n) caused a decrease in left ventricular posterior wall thickness at 3-5 months, but did not change echocardiographic measures of cardiac function. In Pulsed-wave Doppler assessment of the abdominal aorta, an increase was seen in mean velocity, peak velocity, and velocity time integral at 12 months after 16 O (600 MeV/n), suggesting a change in vascular function. There were no significant changes in histopathology or histological quantification of total collagens in heart or aorta. On the other hand, an increase was seen in a 75 kDa peptide of collagen type III in the left ventricle of rats exposed to protons (250 MeV) and 16 O (600 MeV/n and 1 GeV/n), suggesting that radiation caused remodeling of existing collagens in the heart. 16 O (600 MeV/n and 1 GeV/n) caused increases in left ventricular protein levels of immune cell markers CD2, CD4, CD8, and CD68., Conclusion: A single low dose of whole body protons or 16 O in male Long Evans rats did not change cardiac function or induce gross pathological changes in the heart or aorta, but induced mild changes in vascular function and remodeling of existing collagens in the heart. Altogether, studies in prior mouse models and the current work in rats indicate minor changes in cardiac function and structure after a low dose of single-ion radiation., Competing Interests: Declaration of Competing Interests. The authors report no conflicts of interest., (Copyright © 2020 The Committee on Space Research (COSPAR). Published by Elsevier Ltd. All rights reserved.)

Using data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission, we explore the plasma properties of Martian magnetotail current sheets (CS), to further understand the solar wind interaction with Mars and ion escape. There are some CS exhibit energetic oxygen ions that show narrow beam structures in the energy spectrum, which primarily occurs in the hemisphere where the solar wind electric field (Esw) is directed away from the planet. On average, these CS have a higher escaping flux than that of the CS without energetic oxygen ion beams, suggesting different roles in ion escape. The CS with energetic oxygen ion beams exhibits different proton and electron properties to the CS without energetic oxygen ion beams, indicating their different origins. Our analysis suggests that the CS with energetic oxygen ion beams may result from the interaction between the penetrated solar wind and localized oxygen ion plumes. Plain Language Summary: Ion escape into space, driven by solar wind interactions with Mars, plays a pivotal role in the evolution of the Martian atmosphere. An important escape channel of planetary oxygen ions is the current sheet in the nightside magnetotail. Yet, our existing understanding of plasma characteristics within this magnetic structure remains quite limited. Based on the MAVEN observations, we find the current sheets can be categorized into two distinct types according to the energy distribution patterns of oxygen ions: one is with the appearance of energetic oxygen ions with narrow beam structure, the other one is not. On average, the current sheets with energetic oxygen ion beams have a higher escaping flux than those without, suggesting different roles in ion escape. Furthermore, the two types of current sheets exhibit markedly distinct plasma properties, indicating that they have different origins. Here we suggest that the current sheet with energetic oxygen ion beams arise from the interaction between the penetrated solar wind and localized oxygen ion plumes. Key Points: Martian magnetotail current sheets occasionally exhibit energetic oxygen ions that show beam structures in the energy spectrumThe current sheets with energetic oxygen ion beam usually have a higher escaping flux than those withoutPlasma properties in current sheets differ significantly differences between those with and without energetic oxygen ion beams [ABSTRACT FROM AUTHOR]

Atmospheric oxygen is produced and consumed by life on Earth, and the ozone layer protects life on Earth from harmful solar UV radiation. The research on oxygen in the Earth system is of interest to many different geoscientific communities, from paleoclimatology to aeronomy. I provide a brief overview of the research activities and their motivations. In situ measurements and remote sensing of atmospheric oxygen are described. The global evolution, distribution, and trends of atmospheric oxygen are discussed.

The influence of high-linear energy transfer (LET) particle radiation on the functionalities of mesenchymal stromal cells (MSCs) is largely unknown. Here, we analyzed the effects of proton (1H), helium (4He), carbon (12C) and oxygen (16O) ions on human bone marrow-MSCs. Cell cycle distribution and apoptosis induction were examined by flow cytometry, and DNA damage was quantified using γH2AX immunofluorescence and Western blots. Relative biological effectiveness values of MSCs amounted to 1.0-1.1 for 1H, 1.7-2.3 for 4He, 2.9-3.4 for 12C and 2.6-3.3 for 16O. Particle radiation did not alter the MSCs' characteristic surface marker pattern, and MSCs maintained their multi-lineage differentiation capabilities. Apoptosis rates ranged low for all radiation modalities. At 24 h after irradiation, particle radiation-induced ATM and CHK2 phosphorylation as well as γH2AX foci numbers returned to baseline levels. The resistance of human MSCs to high-LET irradiation suggests that MSCs remain functional after exposure to moderate doses of particle radiation as seen in normal tissues after particle radiotherapy or during manned space flights. In the future, in vivo models focusing on long-term consequences of particle irradiation on the bone marrow niche and MSCs are needed. [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]

We present a statistical study of magnetotail flows that change direction from earthward to tailward using Cluster spacecraft. More precisely, we study 318 events of particle flux enhancements in the O+ data for which the pitch angle continuously changes with time, either from 0° to 180° or from 180° to 0°. These structures are called "Pitch Angle Slope Structures" (PASSes). PASSes for which the pitch angle changes from 0° to 180° are observed in the Northern Hemisphere while those for which the pitch angle changes from 180° to 0° are observed in the Southern Hemisphere. These flux enhancements result in a reversal of the flow direction from earthward to tailward regardless of the hemisphere where they are observed. Sometimes, several PASSes can be observed consecutively which can therefore result in oscillatory velocity signatures in the earth‐tail direction. The PASS occurrence rate increases from 1.8% to 3.7% as the AE index increases from ∼0 to ∼600 nT. Also, simultaneously to PASSes, there is typically a decrease in the magnetic field magnitude due to a decrease (increase) of the sunward component of the magnetic field in the Northern (Southern) Hemisphere. Finally, based on the 115 (out of 318) PASSes that show energy‐dispersed structures, the distance to the source from the spacecraft is estimated to be typically <25RE along the magnetic field line. This study is important as it sheds light on one of the causes of tailward velocities in Earth's magnetotail. Key Points: Flow reversals from earthward to tailward can be due to an enhanced flux of earthward moving particles which move tailward after mirroringFlow reversals can be flux enhancements for which the pitch angle changes from 0° (180°) to 180° (0°) in the Northern (Southern) HemisphereThe particles forming the flow reversals have typically traveled <25RE from the apparent source to the spacecraft [ABSTRACT FROM AUTHOR]

Purpose: The main advantages of charged particle radiotherapy compared to conventional X-ray external beam radiotherapy are a better tumor conformality coupled with the capability of treating deep-seated radio-resistant tumors. This work investigates the possibility to use oxygen beams for hadron therapy, as an alternative to carbon ions. Materials and Methods: Oxygen ions have the advantage of a higher relative biological effectiveness (RBE) and better conformality to the tumor target. This work describes the mixed radiation field produced by an oxygen beam in water and compares it to the one produced by a therapeutic carbon ion beam. The study has been performed using Geant4 simulations. The dose is calculated for incident carbon ions with energies of 162 MeV/u and 290 MeV/u, and oxygen ions with energies of 192 MeV/u and 245 MeV/u, and hence that the range of the primary oxygen ions projectiles in water was located at the same depth as the carbon ions. Results: The results show that the benefits of oxygen ions are more pronounced when using lower energies because of a slightly higher peak-to-entrance ratio, which allows either providing higher dose in tumor target or reducing it in the surrounding healthy tissues. It is observed that, per incident particle, oxygen ions deliver higher doses than carbon ions. Conclusions: This result coupled with the higher RBE shows that it may be possible to use a lower fluence of oxygen ions to achieve the same therapeutic dose in the patient as that obtained with carbon ion therapy. [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]

Ion transport from the plasma sheet to the ring current is the main cause of the development of the ring current. Energetic (>150 keV) ring current ions are known to be transported diffusively in several days. A recent study suggested that energetic oxygen ions are transported closer to the Earth than protons due to the diffusive transport caused by a combination of the drift and drift‐bounce resonances with Pc 3–5 ultralow frequency waves during the 24 April 2013 magnetic storm. To understand the occurrence conditions of such selective oxygen increase (SOI), we investigate the phase space densities (PSDs) between protons and oxygen ions with the first adiabatic invariants (μ) of 0.1–2.0 keV/nT measured by the Radiation Belt Storm Probes Ion Composition Experiment instrument on the Van Allen Probes at L ~ 3–6 during 90 magnetic storms in 2013–2017. We identified the SOI events in which oxygen PSDs increase while proton PSDs do not increase during a period of ~9 hr (one orbital period). Among the 90 magnetic storms, 33% were accompanied by the SOI events. Global enhancements of Pc 4 and Pc 5 waves observed by ground magnetometers during the SOI events suggest that radial transport due to combination of the drift‐bounce resonance with Pc 4 oscillations and the drift resonance with Pc 5 oscillations can be the cause of SOIs. The contribution of the SOI events to the magnetic storm intensity is roughly estimated to be ~9% on average. Key Points: Increases of >150‐keV oxygen ions without proton increases are observed in the inner magnetosphere during 30 magnetic storms out of 90The selective oxygen increases occur simultaneously with global enhancements of Pc 4 and Pc 5 ULF waves at L > 4 and L > 3, respectivelyStatistical results suggest that the selective oxygen increases are caused by the combination of drift and drift‐bounce resonances [ABSTRACT FROM AUTHOR]