Evaluation of elastic properties of DLC layers using resonant ultrasound spectroscopy and AFM nanoindentation

Elastic properties of diamond-like carbon (DLC) layers with gradient carbon–silicon interlayer were studied by resonant ultrasound spectroscopy (RUS) and standard nano-indentation technique. The DLC layers were prepared by pulsed laser deposition on SiC/Si substrates. The RUS method is based on modal analysis of the specimen vibration. The resonant frequency shifts caused by the layer are for the evaluation of the dynamic in-plane elastic properties of the deposited DLC. The results were compared with the quasi-statical quantities — Young's modulus and hardness, obtained by nanoindentation using the AFM tip.     

Atomic-volume variations of α-Pu alloyed with Al, Ga, and Am from first-principles theory

First-principles methods are employed to calculate the ground-state atomic densities (or volumes) of α-Pu alloyed with Al, Ga, and Am. Three configurations for the alloying atom are considered. (i) It is located at the most open and energetically most favorably site. (ii) It is located at the least open site. (iii) It is randomly distributed within the α-Pu matrix. When alloyed with Al or Ga, α-Pu behaves similarly, it expands considerably for configurations (ii) and (iii), while for (i) only small changes of the density occur. Interestingly, for Am, the alloying effects are quite different from that of Al and Ga. Small expansion is noted for the ordered configurations (i) and (ii), whereas for the disordered (iii), only insignificant changes of the density take place. The bonding character is thus differently influenced in Pu by the addition of Al and Ga on one hand and Am on the other. This is consistent with the view that Al and Ga stabilize the δ over the α phase in Pu by a different mechanism than Am, as has been discussed in recent publications. The U.S. Government’s right to retain a non-exclusive, royalty-free license in and to any copyright is acknowledged.     

Solving timetabling problems using a cultural algorithm

This paper addresses the solution of timetabling problems using cultural algorithms. The core idea is to extract problem domain information during the evolutionary search, and then combine it with some previously proposed operators, in order to improve performance. The proposed approach is validated using a benchmark of 20 instances, and its results are compared with respect to three other approaches: two evolutionary algorithms and simulated annealing, all of which have been previously adopted to solve timetabling problems.     

Advances in Linear Modeling of Microwave Transistors

Heterojunction field effect transistors (HFET) based on gallium nitride (AlGaN/GaN) and metal semiconductor field effect transistors (MESFETs) based on silicon carbide (SiC) are the preferred transistors for high-power amplifier circuit designs rather than MESFETs, high electron mobility transistors (HEMTs) and pseudomorphic HEMTs based on gallium arsenide (GaAs) or indium phosphide (InP) semiconductor technology. While AlGaN/GaN and SiC are good candidates for high-power applications, GaAs and InP semiconductor technologies are the preferred transistors in low-power, low-voltage, and low-noise applications [1].