Dynamics analysis of vibration process in Particle Impact Noise Detection

Particle Impact Noise Detection (PIND) test is a reliability screening technique for hermetic device that is prescribed by MIL-PRF-39016E. Some test conditions are specified, although MIL-PRF-39016E did not specify how to obtain these condi- tions. This paper establishes the dynamics model of vibration process based on first order mass-spring system. The corresponding Simulink model is also established to simulate vibration process in optional input excitations. The response equations are derived in sinusoidal excitations and the required electromagnetic force waves are computed in order to obtain a given vibration and shock accelerations. Last, some simulation results are given.

ELEMENTARY BIFURCATIONS FOR A SIMPLE DYNAMICAL SYSTEM UNDER NON-GAUSSIAN LVY NOISES

Nonlinear dynamical systems are sometimes under the influence of random fluctuations. It is desirable to examine possible bifurcations for stochastic dynamical systems when a parameter varies.A computational analysis is conducted to investigate bifurcations of a simple dynamical system under non-Gaussian a-stable Levy motions, by examining the changes in stationary probability density functions for the solution orbits of this stochastic system. The stationary probability density functions are obtained by solving a nonlocal Fokker-Planck equation numerically. This allows numerically investigating phenomenological bifurcation, or P-bifurcation, for stochastic differential equations with non-Gaussian Levy noises.

Research on Feature Extraction of Remnant Particles of Aerospace Relays

The existence of remnant particles, which significantly reduce the reliability of relays, is a serious problem for aerospace relays. The traditional method for detecting remnant particles-particle impact noise detection （PIND）-can be used merely to detect the existence of the particle; it is not able to provide any information about the particles＇ material. However, information on the material of the particles is very helpful for analyzing the causes of remnants. By analyzing the output acoustic signals from a PIND tester, this paper proposes three feature extraction methods： unit energy average pulse durative time, shape parameter of signal power spectral density （PSD）, and pulse linear predictive coding coefficient sequence. These methods allow identified remnants to be classified into four categories based on their material. Furthermore, we prove the validity of this new method by processing P1ND signals from actual tests.

Sound Insulation of Floors： A New Composite with a Resilient Layer of Recycled Polymer

PU （polyurethane） integral skin and PVC （polyvinyl chloride） are polymeric materials which have favorable physical characteristics to reduce the impact noise when applied to floor systems. In civil construction, floating floors systems are composed of two layers above the slab： a resilient layer and, above this, a rigid layer of cement matrix that works as a subfloor. This research aims to evaluate the incorporation of PVC and PU skin waste in the resilient layer of the floating floor, for impact noise insulation. It was conducted physical, mechanical and morphological tests in the composite, as SEM （scanning electron microscopy）, determination of compressive creep, and impact noise test to evaluate the absorption capacity of the floor system over time. Furthermore, experimental results were compared with theoretical studies. These correlations may assist in understanding the behavior of impact noise damping and its relation to the size of the samples.

Potential impacts of shipping noise on Indo-Pacific humpback dolphins and implications for regulation and mitigation:a review

Shipping noise is a widespread and relatively loud sound source among human-induced underwater sounds.The impacts of shipping noise are of special concern for Indo-Pacific humpback dolphins(Sousa chinensis),as they inhabit shallow and nearshore habitats and are highly dependent on sound for survival.This study synthesizes our current understanding of the potential impacts of shipping noise on Indo-Pacific humpback dolphins combined with knowledge on sound production and hearing of these animals and the impacts of noise on other whales and dolphins.For further protection and management of Indo-Pacific humpback dolphins and their habitats,shipping noise should be regulated and mitigated to modify sound from ships,to reduce overall noise levels,and to set more marine protected areas(MPAs)covering most Indo-Pacific humpback dolphin habitats with seasonal and geographical restrictions to avoid ensonification of shipping noise.The emphasis for future research should be on obtaining more baseline information about the population distribution,sound production,hearing capabilities at the population level,behavior,and stress hormones of the humpback dolphins under different noise conditions or under different noise-producing activities,and/or in high-noise areas compared with relatively quiet areas,and the noise characteristics of ships of different types,sizes and speeds.