An empirical expression is proposed to describe the K-shell ionization cross sections by electron impact over a wide range of atomic numbers (i.e. 6 Z 79) and overvoltages U (i.e. 1 U 10 4 ) defined as being the ratio between the incident electron energy and the ionization energy of the electrons in the K shell. The study is based on the analysis of existing experimental databases for atoms. Agreement is obtained with an accuracy of 10% over the entire atomic number and overvoltage ranges including the near-threshold region. Results are compared with those obtained with other analytical expressions.

Abstract-We present a description of opaque minerals, opaque mineral compositions, magnetic properties, and paleomagnetic record of the Tissint heavily shocked olivine-phyric shergottite that fell to Earth in 2011. The magnetic mineralogy of Tissint consists of about 0.6 wt% of pyrrhotite and 0.1 wt% of low-Ti titanomagnetite (in the range ulv€ ospinel 3-15 magnetite 85-97). The titanomagnetite formed on Mars by oxidation-exsolution of ulv€ ospinel grains during deuteric alteration. Pyrrhotite is unusual, with respect to other shergottites, for its higher Ni content and lower Fe content. Iron deficiency is attributed by an input of regolith-derived sulfur. This pyrrhotite has probably preserved a metastable hexagonal monosulfide solution structure blocked at temperature above 300°C. The paleomagnetic data indicate that Tissint was magnetized following the major impact suffered by this rock while cooling at the surface of Mars from a post-impact equilibrium temperature of approximately 310°C in a stable magnetic field of about 2 µT of crustal origin. Tissint is too weakly magnetic to account for the observed magnetic anomalies at the Martian surface.

Doping material with nanoparticles is increasingly used as an effective method for improving their mechanical, optical, and sturdiness properties in many fields. More specifically, effective material development will depend on our ability to control nanoparticles’ shape, composition, and size. While crystalline nanophase can be examined easily, characterization of amorphous nanoparticles remains a challenge. Here, we investigate the chemical composition of sub-20-nm oxide nanoparticles grown in rare-earth doped silicate glass through the phase separation mechanism occurring under heat treatment. Using a combination of analytical techniques, we demonstrate that nanoparticle composition and, therefore, the chemical environment of encapsulated rare-earth ions, is nanoparticle size dependent. This new experimental evidence of composition change contributes unique insights on the phase separation mechanism that will lead to better comprehension and will guide development of future materials.