K-cut quartz SAW resonators for stable frequency sources

A new type of quartz SAW resonator for use as a stable frequency source has been developed. It was studied from the point of view of frequency instability caused by transient thermal behavior, and a new angle of cut named the K-cut for quartz SAW resonators was found. The static and dynamic frequency temperature coefficients are both zero at a room temperature. Taking into consideration the influence of the electrode-film thickness, the width modes of the waves, and power-flow angles, optimized resonators and oscillators were designed. These devices had frequency stability of 2x10(-10) for the mean time of 0.01 s.     

Stochastic models of the meridional overturning circulation: time scales and patterns of variability

The global meridional overturning circulation (MOC) varies over a wide range of space and time scales in response to fluctuating 'weather' perturbations that may be modelled as stochastic forcing. This study reviews model studies of the effects of climate noise on decadal to centennial MOC variability, on transitions between the MOC regimes and on the dynamics of Dansgaard-Oeschger events characteristic of glacial periods.     

Stochastic models for degradation-based reliability

This paper presents a degradation-based procedure for estimating the full and residual lifetime distribution of a single-unit system subject to Markovian deterioration. The hybrid approach unites real degradation measures with analytical, stochastic failure models to numerically compute the distributions and their moments. Two distinct models are shown to perform well when compared with simulated data. Moreover, results obtained from the second model are compared with empirically generated lifetimes of 2024-T3 aluminum alloy specimens. The numerical experiments indicate that the proposed techniques are useful for remaining lifetime prognosis in both cases.     

Simple, fast, bright, and stable light sources

In this work we show that solution-processed light-emitting electrochemical cells (LECs) based on only an ionic iridium complex and a small amount of ionic liquid exhibit exceptionally good performances when applying a pulsed current: sub-second turn-on times and almost constant high luminances (>600 cd m(-2) ) and power efficiencies over the first 600 h. This demonstrates the potential of LECs for applications in solid-state signage and lighting.     

Characterization of the frequency stability of frequency-hopping sources

A method that applies time-domain stability measures, hitherto used only in the context of fixed-frequency sources, to the characterization of frequency-hopped sources is introduced. This method has been successfully applied to the testing of a novel practical frequency-hopping synthesizer. It is shown that despite the fact that hopping sources exhibit an orders-of-magnitude larger amount of short term noise than stable free-running frequency sources, some of the techniques used to estimate the noise of stable sources are also applicable to hopping voltage-controlled oscillator systems.     

Stochastic process models for earthquake ground motion

In this paper we present a review of stochastic process models proposed for the simulation of seismic ground motion. The models reviewed include those based on filtered white noise processes, filtered Poisson processes, spectral representation of stochastic processes, and finally those based on stochastic wave theory. Mathematical expressions are provided for all models along with comments on their usefulness, advantages and disadvantages.Together with the review of auto-regressive moving-average models by F. Kozin in this PEM review series on earthquake engineering (June issue), this paper represents an overview of stochastic models of earthquake ground motion, which is hopefully of some use to researchers as well as practitioners.     

Stochastic models of cumulative damage in composite materials

Stochastic models of fracture for composite materials based on the concept of damage accumulation are proposed. An assumption is used that the density of defects leading to the fracture (or to the failure in a more general sense) is sufficiently small. Asymptotic formulas for probability distributions of the damage rate, failure stress, life time and other reliability and longevity parameters are obtained. A possibility of application of the proposed stochastic models to the reliability and size effect prediction in composite materials is shown.