The Study of the Properties of Uranium Dioxide Pellets Depending on the Parameters of Pressing and Sintering

The paper presents dilatometric research of uranium dioxide pellets, fabricated by compaction at different pressure values. Temperature observed at sintering start is determined and it is pointed out that this temperature doesn’t depend on compaction pressure. Keywords: uranium dioxide, compaction, sintering, dilatometry, shrink curves, geometric density, pycnometric density

A possible mechanism for the formation of magnetic field dropouts in the coma of 67P/Churyumov–Gerasimenko

The Rosetta Plasma Consortium MAGnetometer (RPC-MAG) has detected signatures of diamagnetic regions associated with comet 67P/Churyumov–Gerasimenko at distances from 30 to 400 km at different heliocentric distances, which is larger than what has been predicted by numerical simulations of the cometary plasam environment. The physical mechanism behind these diamagnetic regions is still unknown. In this work, we use our newly developed multifluid plasma-neutral model to explore a possible physical mechanism that might create such regions. The model solves the governing multifluid magnetohydrodynamic equations for cometary and solar wind ions and electrons, and the Euler equations for the neutral gas fluid. We find that a local increase of electron thermal pressure is capable of generating many of the observed features of the diamagnetic regions observed by RPC-MAG. The simulation results show that a magnetic field-free region is formed and the recovery phase of the magnetic field magnitude is faster than the declining phase

Ultraviolet observations of the hydrogen coma of comet C/2013 A1 (Siding Spring) by MAVEN/IUVS

We used the Imaging Ultraviolet Spectrograph (IUVS) aboard the Mars Atmosphere and Volatile EvolutioN (MAVEN) orbiting spacecraft to construct images of the hydrogen coma of comet C/2013 A1 (Siding Spring) days before its close encounter with Mars. We obtain a water production rate of 1.1 ± 0.5 × 1028 molecules/s and determine the total impacting fluence of atoms and molecules corresponding to the photodissociation of water and its daughter species to be 2.4 ± 1.2 × 104 kg. We use these observations to confirm predictions that the mass of delivered hydrogen is comparable to the existing reservoir above 150 km. Furthermore, we reconcile disparity between observations and predictions about the detectability of the hydrogen perturbation and thermospheric response. © 2015. American Geophysical Union. All Rights Reserved