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Modified coincidence Doppler broadening spectroscopy (MCDBS) was used in this study to investigate the electron band structure of zinc aluminate (ZnAl2O4/ZAO). The effect of single and co-doping metal elements on the band structure of valence and core electrons was investigated. At the low momenta range, the annihilation of the maximum number of positrons has been done by the electrons of the pure sample, which indicates more annihilation by valence electrons; in contrast, with the addition of metals, the annihilation of positrons is also done by core electrons. The sample containing silver shows the highest participation of core electrons in the process of positron annihilation. If silver and erbium are simultaneously doped in the sample, the highest participation of electrons in the annihilation of positron occurs in values of momentum of about 15 × 10–3 mOc. Using a new arrangement in electronic panels in the MCDBS allows the detection and study of more energetic momentum of core electrons. [ABSTRACT FROM AUTHOR]

Recent studies show that there is no guarantee for conventional Min-Max structure containing linear compensators to keep engine limitations in transient state, while limit violation can make dangerous events. Careful analysis indicates that despite the design of limitation loops overshoot-free to reduce the possibility of limit violation, exceeding the limits can occur for some variables affected by engine acceleration or deceleration, when other loop controllers are active. In this study, the limit values of these variables are taken into account in controller design of other loops using state feedback techniques and convex optimization problems, and their dynamic compensators are removed from the Min-Max structure. Thus, in addition to improvement of Min-Max limit protection, computational burden also decreases owing to loop reduction. The condition for limit protection in steady state and thrust tracking assurance is also specified. Simulations carried out with linear and nonlinear turbofan engine model show efficient performance of the proposed methodology in comparison with traditional Min-Max and Min-Max/sliding mode control (SMC) approaches. [ABSTRACT FROM AUTHOR]

The problem of relative motion control of spacecraft rendezvous process on elliptical orbit is considered in this paper. Due to the presence of nonlinear dynamics and external disturbances, two robust controllers are developed based on sliding mode control theory. The first one is an optimal sliding mode controller; in which optimal control theory is used to reduce the tracking error and fuel cost, and then integral sliding mode control technique is applied to robustify optimal controller. The other controller is a backstepping sliding mode one that is developed based on nonlinear dynamics of spacecraft rendezvous; having applied the backstepping method to synthesis the tracking errors and Lyapunov functions, a sliding mode controller is developed to guarantee the Lyapunov stability, handling of all nonlinearities, robustness against uncertainties as well as tracking the desired position. It is assumed that the chaser and target spacecraft are in a low Earth orbit and subject to the perturbing effects of J2 and atmospheric drag. In addition, two fault tolerant scenarios, i.e. thruster degradation and short thruster failure are also considered to verify the robustness and efficacy of the control approaches. Simulation results confirm the effectiveness of the proposed controllers in reaching to the desired position in case of actuator fault-free and fault tolerant situations. [ABSTRACT FROM AUTHOR]