Level-resolved quantum statistical theory of electron capture into many-electron compound resonances in highly charged ions

The strong mixing of many-electron basis states in excited atoms and ions with open f shells results in very large numbers of complex, chaotic eigenstates that cannot be computed to any degree of accuracy. Describing the processes which involve such states requires the use of a statistical theory. Electron capture into these “compound resonances” leads to electron-ion recombination rates that are orders of magnitude greater than those of direct, radiative recombination and cannot be described by standard theories of dielectronic recombination. Previous statistical theories considered this as a two-electron capture process which populates a pair of single-particle orbitals, followed by “spreading” of the two-electron states into chaotically mixed eigenstates. This method is similar to a configuration-average approach because it neglects potentially important effects of spectator electrons and conservation of total angular momentum. In this work we develop a statistical theory which considers electron capture into “doorway” states with definite angular momentum obtained by the configuration interaction method. We apply this approach to electron recombination with W²⁰⁺, considering 2×10⁶ doorway states. Despite strong effects from the spectator electrons, we find that the results of the earlier theories largely hold. Finally, we extract the fluorescence yield (the probability of photoemission and hence recombination) by comparison with experiment.

Laser-Driven Ion Accelerators: State of the Art and Applications

Laser-plasma based accelerators of protons and heavier ions are a source of potential interest for several applications, including in the biomedical area. While the potential future use in cancer hadrontherapy acts as a strong aspirational motivation for this research field, radiobiology employing laser-driven ion bursts is alreadyan active field of research. Here we give a summary of the state of the art in laser driven ion acceleration, of the main challenges currently faced by the research inthis field and of some of the current and future strategies for overcoming them.

Simulation of Oil Shale Semi-Coke Particle Cold Transportation in a Spouted Bed Using CPFD Method

The spouted bed was widely used due to its good mixing of particles and effective phase transferability between the gas and solid phase. In this paper, the transportation process of particles in a 3D spouted bed was studied using the Computational Particle Fluid Dynamics (CPFD) numerical method. Experiments were conducted to verify the validity of the simulation results. Distributions of the pressure, velocities and particle concentration of transportation devices were investigated. The motion state and characteristics of multiphase flows in the transportation device were demonstrated under various operating conditions. The results showed that a good consistency was obtained between the simulated results and the experimental results. The motion characteristics of the gas-solid two-phase flow in the device was effectively predicted, which could assist the optimal operating condition estimation for the spouted transportation process.

At the Moscow State Circus

A single poem in a special W B Yeats edition of the journal.

Direct observation of a long-lived single-atom catalyst chiseling atomic structures in graphene

Fabricating stable functional devices at the atomic scale is an ultimate goal of nanotechnology. In biological processes, such high-precision operations are accomplished by enzymes. A counterpart molecular catalyst that binds to a solid-state substrate would be highly desirable. Here, we report the direct observation of single Si adatoms catalyzing the dissociation of carbon atoms from graphene in an aberration-corrected high-resolution transmission electron microscope (HRTEM). The single Si atom provides a catalytic wedge for energetic electrons to chisel off the graphene lattice, atom by atom, while the Si atom itself is not consumed. The products of the chiseling process are atomic-scale features including graphene pores and clean edges. Our experimental observations and first-principles calculations demonstrated the dynamics, stability, and selectivity of such a single-atom chisel, which opens up the possibility of fabricating certain stable molecular devices by precise modification of materials at the atomic scale.