This paper presents an oven controlled N++ [1 0 0] length-extensional mode silicon resonator, with a lookup-table based control algorithm. The temperature coefficient of resonant frequency (TCF) of the N++ doped resonator is nonlinear, and there is a turnover temperature point at which the TCF is equal to zero. The resonator is maintained at the turnover point by Joule heating; this temperature is a little higher than the upper limit of the industrial temperature range. It is demonstrated that the control algorithm based on the thermoresistor on the substrate and the lookup table for heating voltage versus chip temperature is sufficiently accurate to achieve a frequency stability of  ±0.5 ppm over the industrial temperature range. Because only two leads are required for electrical heating and piezoresistive sensing, the power required for heating of this resonator can be potentially lower than that of the oscillators with closed-loop oven control algorithm. It is also shown that the phase noise can be suppressed at the turnover temperature because of the very low value of the TCF, which justifies the usage of the heating voltage as the excitation voltage of the Wheatstone half-bridge.

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This work investigates the anti-saturation attitude tracking control for the tailless aircraft with guaranteed output constraints, in presence of uncertain inertia parameters, bounded external disturbance, and actuator faults/failures. A predefined-time adaptive backstepping attitude control scheme has been proposed, the main features of this scheme lie in (a) designing a predefined-time filter to deal with the 'explosion of complexity' and singularity problem; (b) introducing a nonlinear state-dependent function to handle the asymmetric time-varying output constraints; (c) compensating for the impact of the actuator faults/failures and input saturation by a nonlinear function and bounded estimation simultaneously. Moreover, the proposed control scheme can ensure all signals in the closed-loop system converge to a residual set around the origin within a predefined time, and this time constant can be set freely by the designer, independently of initial conditions. Article Finally, numerical simulations have been conducted to verify the performance of the proposed predefined-time fault-tolerant control scheme.

NbSi 2 coatings were deposited on pure niobium by halide-activated pack cementation method. The effect of copper addition in pack mixture on the siliconizing process was investigated. After siliconizing on niobium at 1050 C for 2 h using a pack mixture composed of Si, NaF and SiC, a single phase of hexagonal NbSi 2 coating was formed. The addition of copper in pack mixture not only increased the growth rate of the coatings, but also led to form a very thin interlayer between the NbSi 2 coating and the niobium substrate.