Oxidation-induced three-dimensional morphological changes in Ni nanoparticles observed by coherent X-ray diffraction imaging

Three-dimensional structures of Ni nanoparticles undergoing significant morphological changes on oxidation were observed non-destructively using coherent X-ray diffraction imaging. The Ni particles were oxidized into Ni1O1 while forming pores of various sizes internally. For each Ni nanoparticle, one large void was identified at a lower corner near the interface with the substrate. The porosity of the internal region of the agglomerated Ni oxide was about 38.4%. Regions of high NiO density were mostly observed at the outer crust of the oxide or at the boundary with the large voids. This research expands our understanding of general catalytic reactions with direct observation of oxidation-induced nanoscale morphological changes.

Model of heat diffusion in the outer crust of bursting neutron stars

ABSTRACT We study heat diffusion after an energy release in a deep spherical layer of the outer neutron star crust (107 ≲ ρ ≲ 4 × 1011 g cm−3). We demonstrate that this layer possesses specific heat-accumulating properties, absorbing heat and directing it mostly inside the star. It can absorb up to ∼1043–1044 erg due to its high heat capacity, until its temperature exceeds T ∼ 3 × 109 K and triggers a rapid neutrino cooling. A warm layer (T ∼ 108–3 × 109 K) can serve as a good heat reservoir, which is thermally decoupled from the inner crust and the stellar core for a few months. We present a toy model to explore the heat diffusion within the heat-accumulating layer, and we test this model using numerical simulations. We formulate some generic features of the heat propagation that can be useful, for instance, for the interpretation of superbursts in accreting neutron stars. We present a self-similar analysis of late afterglow after such superbursts, which can be helpful to estimate properties of bursting stars.

Contribution of Gravity to Lunar Science, Exploration and Resource Assessment

<p>The recent development of high-resolution models of the lunar gravity field based on data from the NASA GRAIL mission have been instrumental in gaining knowledge about the structure of the Moon, and particularly, of the upper crust. Beneath the outer layer GRAIL data reveal evidence of massive ancient dikes and past processes that no longer have any surficial expression due to heavy bombardment during the Moon’s post-accretional epoch that pulverized the shallow crust. The gravity field of this outer crust, with lower density and higher porosity than expected, also reveals anomalies that indicate the presence of regions of even lower density possibly indicating the existence of lava tubes, as well as regions of higher density where mass anomalies could conceivably indicate locations of resources. Lava tubes, long suspected of existing beneath the maria, are places protected from particle and EM radiation and therefore potential locations for safe location of humans.  Gravity anomaly regions are thus prime locations for exploration studies that could help sustain a human presence. The use of high-resolution  gravity in lunar exploration, as well as science, is a tool for survivability for human expeditions.</p>

Crystallization of the inner crust of a neutron star and the influence of shell effects

Context. In the cooling process of a non-accreting neutron star, the composition and properties of the crust are thought to be fixed at the finite temperature where nuclear reactions fall out of equilibrium. A lower estimate for this temperature is given by the crystallization temperature, which can be as high as ≈7 × 109 K in the inner crust, potentially leading to sizeable differences with respect to the simplifying cold-catalyzed matter hypothesis. Aims. We extend a recent work on the outer crust to the study of the crystallization of the inner crust and the associated composition in the one-component plasma approximation. Methods. The finite temperature variational equations for non-uniform matter in both the liquid and the solid phases are solved using a compressible liquid-drop approach with parameters optimized on four different microscopic models that cover current uncertainties in nuclear modeling. Results. We consider the effect of the different nuclear ingredients with their associated uncertainties separately: the nuclear equation of state, the surface properties in the presence of a uniform gas of dripped neutrons, and the proton shell effects arising from the ion single-particle structure. Our results suggest that the highest source of model dependence comes from the smooth part of the nuclear functional. Conclusions. We show that shell effects play an important role at the lowest densities close to the outer crust, but the most important physical ingredient to be settled for a quantitative prediction of the inner crust properties is the surface tension at extreme isospin values.

Evolution of mobile phases in cometary interiors

Beginning with loose aggregations of dust particles coated with heterogeneous ices under vacuum at Kuiper Belt temperatures, moving to Jupiter/Saturn distances and eventually to low-perihelion orbit, we consider the likely development of the gaseous phase within a cometary nucleus over the course of its lifetime. From the perspective of physical chemistry, we consider limits on the spatial and temporal distribution and composition of this gaseous phase. The implications of the gaseous phase for heat transfer and for the possible spatial and temporal development of liquid phases are calculated. We conclude that the likely temperatures, pressures, and compositions beneath the outer crust of typical cometary nuclei are such that fluidised phases can exist at significant depths and that these reservoirs give a coherent explanation for the high-intensity outbursts observed from cometary nuclei at large distances from perihelion.