The Elastic Compliance of Imperfect Interfaces: Review and Relationship to Ultrasonic Scattering

When a tensile load is applied to an elastic solid with an imperfect interface containing cracks or voids, the farfield displacement that would occur in the absence of the interface will be increased by localized deformations [1]. This extra extension can be modeled as the response of two half-spaces connected by a distributed spring. The spring stiffness per unit area, K, is a function of the topography of the partially contacting surfaces

The interaction of ultrasound with a partially contacting solid-solid interface in the low frequency regime

When real engineering surfaces touch, contact occurs between the asperities of the surface roughness. For this reason the true area of contact between components can be significantly less than the apparent contact area and the stresses at the asperities are considerably higher than the average (nominal) contact pressure. Measurement of the degree of contact between solids is important in a number of applications such as the design of contacting elements (e.g. gears and bearings) [1] and the detection of ‘kissing’ bonds [2]

Moonstruck Primates: Owl Monkeys (Aotus) Need Moonlight for Nocturnal Activity in Their Natural Environment

Primates show activity patterns ranging from nocturnality to diurnality, with a few species showing activity both during day and night. Among anthropoids (monkeys, apes and humans), nocturnality is only present in the Central and South American owl monkey genus Aotus. Unlike other tropical Aotus species, the Azara's owl monkeys (A. azarai) of the subtropics have switched their activity pattern from strict nocturnality to one that also includes regular diurnal activity. Harsher climate, food availability, and the lack of predators or diurnal competitors, have all been proposed as factors favoring evolutionary switches in primate activity patterns. However, the observational nature of most field studies has limited an understanding of the mechanisms responsible for this switch in activity patterns. The goal of our study was to evaluate the hypothesis that masking, namely the stimulatory and/or inhibitory/disinhibitory effects of environmental factors on synchronized circadian locomotor activity, is a key determinant of the unusual activity pattern of Azara's owl monkeys. We use continuous long-term (6–18 months) 5-min-binned activity records obtained with actimeter collars fitted to wild owl monkeys (n = 10 individuals) to show that this different pattern results from strong masking of activity by the inhibiting and enhancing effects of ambient luminance and temperature. Conclusive evidence for the direct masking effect of light is provided by data showing that locomotor activity was almost completely inhibited when moonlight was shadowed during three lunar eclipses. Temperature also negatively masked locomotor activity, and this masking was manifested even under optimal light conditions. Our results highlight the importance of the masking of circadian rhythmicity as a determinant of nocturnality in wild owl monkeys and suggest that the stimulatory effects of dim light in nocturnal primates may have been selected as an adaptive response to moonlight. Furthermore, our data indicate that changes in sensitivity to specific environmental stimuli may have been an essential key for evolutionary switches between diurnal and nocturnal habits in primates

Ultrasonic Investigation of the Stiffness of Graphite- Graphite Interfaces

Many nuclear reactors incorporate large assemblies of enclosing graphite blocks. The load-deflection relationship and seismic response of these blocks are of great importance, and are believed to be partially determined by the surface roughness effects at the interface between blocks. Payne [1] has attempted to calculate the ‘effective’ modulus of a graphite core structure to include the effect of contact between the individual bricks. He noted that if the brick faces become curved through irradiation, the inter-brick load will be unevenly distributed across the interface.</p

80-Gbps to 10-Gbps OTDM De-multiplexer based on wavelength exchange in highly-nonlinear fibre

All-optical 1:8 de-multiplexer for 80Gbps optical time-division multiplexing signals is demonstrated using fibrebased wavelength exchange. Error-free operation is achieved over all de-multiplexed channels with ≤2.1dB power penalty at 10 -9 bit-error rate. © 2008 IEEE.link_to_subscribed_fulltex