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Background Cosmic radiation exposures have been found to elicit cognitive impairments involving a wide-range of underlying neuropathology including elevated oxidative stress, neural stem cell loss, and compromised neuronal architecture. Cognitive impairments have also been associated with sustained microglia activation following low dose exposure to helium ions. Space-relevant charged particles elicit neuroinflammation that persists long-term post-irradiation. Here, we investigated the potential neurocognitive benefits of microglia depletion following low dose whole body exposure to helium ions. Methods Adult mice were administered a dietary inhibitor (PLX5622) of colony stimulating factor-1 receptor (CSF1R) to deplete microglia 2 weeks after whole body helium irradiation ( 4 He, 30 cGy, 400 MeV/n). Cohorts of mice maintained on a normal and PLX5622 diet were tested for cognitive function using seven independent behavioral tasks, microglial activation, hippocampal neuronal morphology, spine density, and electrophysiology properties 4–6 weeks later. Results PLX5622 treatment caused a rapid and near complete elimination of microglia in the brain within 3 days of treatment. Irradiated animals on normal diet exhibited a range of behavioral deficits involving the medial pre-frontal cortex and hippocampus and increased microglial activation. Animals on PLX5622 diet exhibited no radiation-induced cognitive deficits, and expression of resting and activated microglia were almost completely abolished, without any effects on the oligodendrocyte progenitors, throughout the brain. While PLX5622 treatment was found to attenuate radiation-induced increases in post-synaptic density protein 95 (PSD-95) puncta and to preserve mushroom type spine densities, other morphologic features of neurons and electrophysiologic measures of intrinsic excitability were relatively unaffected. Conclusions Our data suggest that microglia play a critical role in cosmic radiation-induced cognitive deficits in mice and, that approaches targeting microglial function are poised to provide considerable benefit to the brain exposed to charged particles.

Despite continuous improvements in machine elements over the past few decades, lubrication issues have impeded human exploration of the universe because single solid or liquid lubrication systems have been unable to satisfy the ever-increasing performance requirements of space tribology. In this study, we present an overview of the development of carbon-based films as protective coatings, with reference to their high hardness, low friction, and chemical inertness, and with a particular focus on diamond-like carbon (DLC) films. We also discuss the design of carbon-based solid-liquid synergy lubricating coatings with regards to their physicochemical properties and tribological performance. Solid-liquid composite coatings are fabricated via spinning liquid lubricants on solid lubricating films. Such duplex lubricating coatings are considered the most ideal lubrication choice for moving mechanical systems in space as they can overcome the drawback of adhesion and cold-welding associated with solid films under harsh space conditions and can minimize the crosslinking or chain scission of liquid lubricants under space irradiation. State of the art carbon-based solid-liquid synergy lubricating systems therefore holds great promise for space applications due to solid/liquid synergies resulting in superior qualities including excellent friction reduction and anti-wear properties as well as strong anti-irradiation capacities, thereby meeting the requirements of high reliability, high precision, high efficiency, and long lifetime for space drive mechanisms.

The electric transmission failure induced by the electrostatic migration and deposition of the friction-pair-produced abrasive dusts in the Solar Array Drive Assembly (SADA) is studied for the first time by integrating experiments and Finite Element Method (FEM) simulation. Particle morphology and composition are characterized by SEM and X-ray EDS, respectively. The size, distribution and average charge of the abrasive dusts are characterized by PSDA as well as the home-made particle charge measurement device. The results show that the dusts’ sizes are in the range of 10–40 μm, and the dusts are primarily composed of Ag and a small amount of Cu and S. Sliced abrasive dusts with an average diameter of 30 μm and a charge of 85 e are used for the FEM prediction of particle trajectory, which is consistent with the theoretical calculation results. The electromagnetic field distribution in the SADA and the electrostatic migration and deposition of abrasive dusts are predicted and analyzed by adopting the FEM method. The experimentally observed dusts’ trajectories in a vacuum chamber with 0.02 Pa vacuum degree are consistent with the simulation results, which qualitatively verifies the accuracy of the FEM model. The predicted results show that the irradiation-induced conductivity increase in polyimide material has little influence on the electric field distribution and the migration and deposition of the abrasive dusts but has great influence on the local current density. Both the potential differences between the two adjacent conducting rings and the loose contact between the electric brush and the conducting rings have significant influence on the migration and deposition of the abrasive dusts, which may greatly increase the surface discharge risk and the electrical transmission instability in the SADA. This study is conducive to the safe and stable operation of the on-orbit spacecrafts.

The core facility of the Wakasa Wan Energy Research Center (WERC) consists of three ion accelerators: a synchrotron, a tandem accelerator and an ion-implanter. Research on the irradiation effects using these accelerators has been performed on space electronics such as solar cells, radiation detectors, image sensors and LSI circuits. In this report, the accelerator facility and ion-irradiation apparatuses at WERC are introduced, focusing on the research on irradiation effects on space electronics. Then, some recent results are summarized.

Previous epidemiologic data demonstrate that cardiovascular (CV) morbidity and mortality may occur decades after ionizing radiation exposure. With increased use of proton and carbon ion radiotherapy and concerns about space radiation exposures to astronauts on future long-duration exploration-type missions, the long-term effects and risks of low-dose charged particle irradiation on the CV system must be better appreciated. Here we report on the long-term effects of whole-body proton ((1)H; 0.5 Gy, 1 GeV) and iron ion ((56)Fe; 0.15 Gy, 1GeV/nucleon) irradiation with and without an acute myocardial ischemia (AMI) event in mice. We show that cardiac function of proton-irradiated mice initially improves at 1 month but declines by 10 months post-irradiation. In AMI-induced mice, prior proton irradiation improved cardiac function restoration and enhanced cardiac remodeling. This was associated with increased pro-survival gene expression in cardiac tissues. In contrast, cardiac function was significantly declined in (56)Fe ion-irradiated mice at 1 and 3 months but recovered at 10 months. In addition, (56)Fe ion-irradiation led to poorer cardiac function and more adverse remodeling in AMI-induced mice, and was associated with decreased angiogenesis and pro-survival factors in cardiac tissues at any time point examined up to 10 months. This is the first study reporting CV effects following low dose proton and iron ion irradiation during normal aging and post-AMI. Understanding the biological effects of charged particle radiation qualities on the CV system is necessary both for the mitigation of space exploration CV risks and for understanding of long-term CV effects following charged particle radiotherapy.

In the quest of new materials that can withstand severe irradiation and mechanical extremes for advanced applications ( e.g . fission & fusion reactors, space applications, etc.), design, prediction and control of advanced materials beyond current material designs become paramount. Here, through a combined experimental and simulation methodology, we design a nanocrystalline refractory high entropy alloy (RHEA) system. Compositions assessed under extreme environments and in situ electron-microscopy reveal both high thermal stability and radiation resistance. We observe grain refinement under heavy ion irradiation and resistance to dual-beam irradiation and helium implantation in the form of low defect generation and evolution, as well as no detectable grain growth. The experimental and modeling results—showing a good agreement—can be applied to design and rapidly assess other alloys subjected to extreme environmental conditions. Refractory high entropy alloys (RHEAs) have recently been developed in the context of high-temperature and severe environmental applications. Here the authors, by combining simulation and experiments, develop an irradiation resistant, thermally stable, and strong RHEA for nuclear application.

In the quest for renewable fuel production, the selective conversion of CO 2 to CH 4 under visible light in water is a leading-edge challenge considering the involvement of kinetically sluggish multiple elementary steps. Herein, 1-pyrenebutyric acid is post-synthetically grafted in a defect-engineered Zr-based metal organic framework by replacing exchangeable formate. Then, methyl viologen is incorporated in the confined space of post-modified MOF to achieve donor-acceptor complex, which acts as an antenna to harvest visible light, and regulates electron transfer to the catalytic center (Zr-oxo cluster) to enable visible-light-driven CO 2 reduction reaction. The proximal presence of the charge transfer complex enhances charge transfer kinetics as realized from transient absorption spectroscopy, and the facile electron transfer helps to produce CH 4 from CO 2 . The reported material produces 7.3 mmol g −1 of CH 4 under light irradiation in aqueous medium using sacrificial agents. Mechanistic information gleans from electron paramagnetic resonance, in situ diffuse reflectance FT-IR and density functional theory calculation. Maji and coworkers report the selective conversion of CO 2 to CH 4 under visible light by utilizing a charge transfer complex within Zr-MOF-808 pores. The complex ultimately facilitates efficient multielectron reduction at the Zr-catalytic center.

Three Earth-sized planets—receiving similar irradiation to Venus and Earth, and ideally suited for atmospheric study—have been found transiting a nearby ultracool dwarf star that has a mass of only eight per cent of that of the Sun. Three planets to watch Theory predicts that terrestrial or rocky planets are likely to be orbiting the lowest-mass stars. This paper reports the detection of a system of three Earth-sized planets transiting a very nearby (12 parsec) ultracool dwarf star of only 8% of the mass of the Sun. The planets are similar in irradiation to Venus and Earth, and particularly well suited for detailed atmospheric characterization. Star-like objects with effective temperatures of less than 2,700 kelvin are referred to as ‘ultracool dwarfs’ 1 . This heterogeneous group includes stars of extremely low mass as well as brown dwarfs (substellar objects not massive enough to sustain hydrogen fusion), and represents about 15 per cent of the population of astronomical objects near the Sun 2 . Core-accretion theory predicts that, given the small masses of these ultracool dwarfs, and the small sizes of their protoplanetary disks 3 , 4 , there should be a large but hitherto undetected population of terrestrial planets orbiting them 5 —ranging from metal-rich Mercury-sized planets 6 to more hospitable volatile-rich Earth-sized planets 7 . Here we report observations of three short-period Earth-sized planets transiting an ultracool dwarf star only 12 parsecs away. The inner two planets receive four times and two times the irradiation of Earth, respectively, placing them close to the inner edge of the habitable zone of the star 8 . Our data suggest that 11 orbits remain possible for the third planet, the most likely resulting in irradiation significantly less than that received by Earth. The infrared brightness of the host star, combined with its Jupiter-like size, offers the possibility of thoroughly characterizing the components of this nearby planetary system.

The radiation environment in Low Earth Orbit (LEO) is dominated by protons captured by Earth’s magnetic field in the Inner Van-Allen belt. Defunct satellites and other space debris objects can be resident in this environment for several decades and even centuries. So far, there is little knowledge about the impact of long-duration proton exposure to the surface morphology and reflectivity in LEO environment. We report on a laboratory test campaign exposing typical spacecraft materials with protons of 100 keV and 2.5 keV kinetic energy and a fluence corresponding to an in-orbit duration of 100 years and 120 years, respectively, in an 800 km sun-synchronous orbit. Although we find microscopic changes in surface morphology, reflectivity changes of all tested materials were smaller than 15%. This result brings positive news for on-going efforts to use optical methods, e.g. lightcurve measurements or active polarimetry, for characterizing space objects, since it suggests that data can - to a good approximation - be analyzed without accounting for proton induced aging effects that might affect the materials’ optical properties over time.

Groundbased and spacecraft telescopic observations, combined with an intensive modeling effort, have greatly enhanced our understanding of hot giant planets and brown dwarfs over the past ten years. Although these objects are all fluid, hydrogen worlds with stratified atmospheres overlying convective interiors, they exhibit an impressive diversity of atmospheric behavior. Hot Jupiters are strongly irradiated, and a wealth of observations constrain the day-night temperature differences, circulation, and cloudiness. The intense stellar irradiation, presumed tidal locking and modest rotation leads to a novel regime of strong day-night radiative forcing. Circulation models predict large day-night temperature differences, global-scale eddies, patchy clouds, and, in most cases, a fast eastward jet at the equator—equatorial superrotation. The warm Jupiters lie farther from their stars and are not generally tidally locked, so they may exhibit a wide range of rotation rates, obliquities, and orbital eccentricities, which, along with the weaker irradiation, leads to circulation patterns and observable signatures predicted to differ substantially from hot Jupiters. Brown dwarfs are typically isolated, rapidly rotating worlds; they radiate enormous energy fluxes into space and convect vigorously in their interiors. Their atmospheres exhibit patchiness in clouds and temperature on regional to global scales—the result of modulation by large-scale atmospheric circulation. Despite the lack of irradiation, such circulations can be driven by interaction of the interior convection with the overlying atmosphere, as well as self-organization of patchiness due to cloud-dynamical-radiative feedbacks. Finally, irradiated brown dwarfs help to bridge the gap between these classes of objects, experiencing intense external irradiation as well as vigorous interior convection. Collectively, these diverse objects span over six orders of magnitude in intrinsic heat flux and incident stellar flux, and two orders of magnitude in rotation rate—thereby placing strong constraints on how the circulation of giant planets (broadly defined) depend on these parameters. A hierarchy of modeling approaches have yielded major new insights into the dynamics governing these phenomena.