On the mechanisms of radiation-induced structural transformations in deposited gold clusters

Physical mechanisms of structural transformations in deposited metallic clusters exposed to an electron beam of a scanning transmission electron microscope are analyzed theoretically and computationally. Recent experiments with size-selected Au$_{923}$ clusters softly deposited on a carbon substrate showed that the clusters undergo structural transformations from icosahedron to decahedron and face-center cubic (fcc) structures upon exposure to a 200-keV electron beam. However, a detailed theoretical description of the underlying physical mechanisms of the observed phenomena is still lacking. We demonstrate that the relaxation of plasmon excitations formed in deposited metal clusters is a plausible mechanism for the experimentally observed structural transformations. Plasmon excitations in the clusters are formed mainly due to the interaction with low-energy secondary electrons emitted from a substrate. The characteristic occurrence times for plasmon-induced energy relaxation events are several orders of magnitude shorter than those for the momentum transfer events by energetic primary electrons to atoms of the cluster. The theoretical analysis is supported by the results of molecular dynamics simulations. The simulations show that an icosahedral Au$_{923}$ cluster softly deposited on graphite undergoes a structural transformation to an fcc structure due to the vibrational excitation of the cluster.Comment: 12 pages, 10 figure

Application of Composite Materials in an Upgraded Engine Low-Pressure Compressor for a Regional Passenger Aircraft

Computational and experimental studies have been carried out to evaluate the robustness and durability of components produced of polymer composite materials (PCM), as a part of the modernization of the low-pressure compressor (LPC) of the engine for the regional aircraft. For a preliminary assessment of the static and dynamic strength of the parts, a series of three-dimensional finite element calculations and tests of laboratory specimens, structural elements cut from finished parts, have been performed. Testing the laboratory samples made it possible to compare the obtained mechanical properties with the properties declared by PCM suppliers and to conduct a mor e correct assessment of the safety margins of the parts. To decide whether to install parts on the engine, fatigue and erosion tests of the structural elements cut from the finished parts were carried out. The final decision on the performance of the PCM parts was made after testing them as part of the upgraded LPC on the engine. The criterion for evaluating the erosion resistance of PCM parts has been introduced, which makes it possible to assess their performance during operation

Current Status of the Novel 3D SuperFGD Detector for the T2K Experiment

This paper is devoted to the current status of the novel fully active 3D (three-dimensional) fine-grained scintillator detector SuperFGD as a main part of the near off-axis detector upgrade program for the T2K experiment. The following important components related to the SuperFGD such as SuperFGD electronics and mechanics, wavelength shifting (WLS) fibers, and light emitting diode (LED) calibration system are also discussed here as well as the detector’s near future