CONTENTS
December 2007
| Vol 35 No 3 |
CONTENTS |
December 2007 |
What do vibrations have to do with termites' food choice?
R. Inta, T.A. Evans, J.C.S. Lai and M. Lenz
Statistical measures to describe the vibrational characteristics of structures with uncertainty
Geoff Lucas and Nicole Kessissoglou
Gravitational oscillators: bouncing balls, rocking beams, and spinning disc
Neville H. Fletcher
The combination of workplace and recreational noise exposure
Warwick Williams and Marion Burgess
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Vol. 35, No. 3 pp 73 - 77 (2007)
ABSTRACT: It has been shown previously that termites are sensiive to vibrations, using them as a communication channel. However, their ability to use vibrations in assessment of food structures is little understood. Here we present timber of differing quantities to two drywood termite species, Ciyptotermes domesticus and Cr secundus. We also expose the termites to vibration signals produced as a byproduct of their feeding, and to food sources with altered effective material properties. We show here that both species have a food size preference, which is determined by vibrations. We also show that Cr. secundus is able to discriminate material properties. Although the exact characteristics in the vibration signals they utilise are yet to be fully identified, these observations reveal previously unexplored aspects of termite foraging decision-making, which might help to minimise their economic impact.
Vol. 35, No. 3 pp 79 - 86 (2007)
ABSTRACT: Predicting the vibro-acoustic responses of structures with uncertainty can be difficult. For example, the dynamic response of body panels in a vehicle can differ greatly across an ensemble of vehicles due to small variations in spot welds from the assembly process. In this paper, several statistical measures including the statistical overlap factor, distribution of modal spacings and an ergodic hypothesis are used to examine the natural frequencies and responses for a range of dynamic systems. Uncertainty across an ensemble of nominally identical structures has been generated by adding small masses and/or springs at random locations. A measure of the uncertainty is obtained by observing the variation in the natural frequencies of an ensemble member from their mean value across the ensemble. Using an ergodic hypothesis, a comparison between the mean vibrational response of an ensemble of nominally identical structures at each frequency is made with the frequency averaged response of a single ensemble member.
Vol. 35, No. 3 pp 87 - 90 (2007)
ABSTRACT: When an object is constrained to lie in a half-space bound by a rigid horizontal wall, it will fall against this wall under the influence of gravity and then rebound in some way so as to execute oscillations which will gradually decay as energy is lost in the collisions. Common cases are bouncing balls, rocking beams, and discs allowed to spin obliquely onto the surface. In this last case, exemplified by coins and saucepan lids, the resulting radiated sound has interesting properties.
Vol. 35, No. 3 pp 91 - 95 (2007)
ABSTRACT: There are many noisy recreational activities undertaken by individuals during their leisure activities. How significant is noise exposure during recreational activities compared to noise exposure in the workplace? This paper reviews noise levels from common recreation activities. Comparisons are then made between possible noise exposures arising from work situations in combination with noise exposure from recreation activities. The findings indicate that the care taken to reduce noise exposure in the workplace can be swiftly negated with recreation noise dominating the overall exposure then recreation noise levels continue unchecked. If individuals are to maintain their hearing health they need to be more aware of the problems from exposure to excessive noise and to take preventative action similar to that used in the workplace.