Growth of superconducting MgB2 thin films via postannealing techniques

We report the effect of annealing on the superconductivity of MgB2 thin films as functions of the postannealing temperature in the range from 700 C to 950 C and of the postannealing time in the range from 30 min to 120 min. On annealing at 900 C for 30 min, we obtained the best-quality MgB2 films with a transition temperature of 39 K and a critical current density of ~ 10^7 A/cm^2. Using the scanning electron microscopy, we also investigated the film growth mechanism. The samples annealed at higher temperatures showed the larger grain sizes, well-aligned crystal structures with preferential orientations along the c-axis, and smooth surface morphologies. However, a longer annealing time prevented the alignment of grains and reduced the superconductivity, indicating a strong interfacial reaction between the substrate and the MgB2 film.Comment: 7 pages, 4 figures include

A new command shaping guidance law using Lagrange multiplier

This article presents a new command shaping guidance law by change of Lagrange multiplier (LM), called CSGL-LM. The Schwarz inequality approach is used to solve the optimal guidance problems considering both terminal constraints on interception and impact angle control. LM is introduced to combine two terminal constraints into a single equation. The main idea of this paper is to use LM as a design parameter for shaping the guidance command as well as controlling the terminal constraints. The guidance command of CSGL-LM is given a unified functional form of the time-to-go, the state variables, and LM. Therefore, through an appropriate choice of LM, we can achieve various shapes of the guidance commands for the interception case, as well as the impact angle control case. As illustrative examples, this paper also shows that a class of previous guidance laws is just one of particular solutions of CSGL-LM. Numerical simulations are performed to validate the properties of CSGL-LM, compared with the conventional guidance law