Defence Science and Technology Organisation, Australia

Melbourne, Australia

Defence Science and Technology Organisation, Australia

Melbourne, Australia
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McAnally K.I.,Defence Science and Technology Organisation, Australia | Martin R.L.,Defence Science and Technology Organisation, Australia
Frontiers in Neuroscience | Year: 2014

Previous studies have shown that the accuracy of sound localization is improved if listeners are allowed to move their heads during signal presentation. This study describes the function relating localization accuracy to the extent of head movement in azimuth. Sounds that are difficult to localize were presented in the free field from sources at a wide range of azimuths and elevations. Sounds remained active until the participants' heads had rotated through windows ranging in width of 2°, 4°, 8°, 16°, 32°, or 64° of azimuth. Error in determining sound-source elevation and the rate of front/back confusion were found to decrease with increases in azimuth window width. Error in determining sound-source lateral angle was not found to vary with azimuth window width. Implications for 3-d audio displays: The utility of a 3-d audio display for imparting spatial information is likely to be improved if operators are able to move their heads during signal presentation. Head movement may compensate in part for a paucity of spectral cues to sound-source location resulting from limitations in either the audio signals presented or the directional filters (i.e., head-related transfer functions) used to generate a display. However, head movements of a moderate size (i.e., through around 32° of azimuth) may be required to ensure that spatial information is conveyed with high accuracy. © 2014 Mcanally and Martin.

Rosenberg L.,Defence Science and Technology Organisation, Australia
IEEE Transactions on Geoscience and Remote Sensing | Year: 2013

Knowledge of sea-clutter phenomenology allows accurate models to be developed for assessing target detection performance. The majority of work in this area has been at low grazing angles from clifftops or wave tanks and does not consider scattering in the high grazing angle region beyond 10°. To improve our understanding at high grazing angles of 15°-45°, the Defence Science and Technology Organisation's Ingara airborne X-band fully polarimetric radar has been used to collect 12 days' worth of sea-clutter data. This paper focuses on understanding the characteristics of sea-spikes as they are often the cause of false detections in a radar processor. Using the Ingara data, a threshold is used to isolate these scatterers in the range/time domain with results verified against the KK probability distribution function. Detections due to discrete and persistent scattering are then isolated to provide more information regarding the underlying cause of sea-spikes and answer the question of whether Walker's three-component mean Doppler spectrummodel is suitable at high grazing angles. © 1980-2012 IEEE.

Lynch S.,Defence Science and Technology Organisation, Australia
Corrosion Reviews | Year: 2012

Mechanisms of hydrogen embrittlement in steels and other materials are described, and the evidence supporting various hypotheses, such as those based on hydride formation, hydrogen-enhanced decohesion, hydrogen-enhanced localized plasticity, adsorption-induced dislocation emission, and hydrogen-vacancy interactions, are summarised. The relative importance of these mechanisms for different fracture modes and materials are discussed based on detailed fractographic observations and critical experiments. © 2012 by Walter de Gruyter.

Foster S.,Defence Science and Technology Organisation, Australia
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2012

Thermodynamic phase fluctuations in optical fiber cavities are analyzed in detail, with an emphasis on asymptotic behavior in the low-frequency regime. Both exact series solutions and closed-form approximations are derived for thermal noise under a range of different boundary conditions. These results clarify theoretical limits to strain resolution in optical fiber sensors at low frequency, enabling correct interpretation of recent experiments. © 2012 the American Physical Society.

Molent L.,Defence Science and Technology Organisation, Australia
Fatigue and Fracture of Engineering Materials and Structures | Year: 2014

This paper reviews some analyses of quantitative fractography measurements of the fatigue fracture surfaces of 7050 aluminium alloy specimens along with relevant fatigue crack information including crack initiating discontinuity size and type. These data were used to assess whether surface finish or applied stress level has any effect on the estimated effective crack initiating discontinuity size, namely the equivalent pre-crack size (EPS). The statistical distributions for the EPSs of the following initiating discontinuity types were examined: chemically etched pits, glass bead peening damage, mechanical damage, inclusions and porosity. The EPSs at various percentile levels for these types were determined on the basis of the samples considered. Finally, the correlation between measured initiating discontinuity depth and EPS was investigated, and good correlation was found in the case of mechanical damage. The purpose of conducting these analyses was to gain a better understanding of the parameters governing the fatigue crack-like effect of discontinuities to facilitate the better prediction of fatigue lives. © 2014 Wiley Publishing Ltd.

Anderson S.J.,Defence Science and Technology Organisation, Australia
IEEE Transactions on Geoscience and Remote Sensing | Year: 2013

The deployment of a network of HF surface wave radar (HFSWR) systems is a complex task with many factors to be considered, particularly when the radars are expected to perform multiple roles. Failure to treat the siting problem with appropriate care could seriously degrade performance in one or more radar missions. In this paper, we describe a practical technique for HFSWR network design, based on a genetic algorithm adapted to multi-objective optimization, and demonstrate its efficacy in the context of a hypothetical two-radar system deployed in the Strait of Malacca, a major waterway along which many critical surveillance requirements have been identified. The results confirm that quite disparate criteria can be taken into account with this approach and support our claim that this methodology can be extended to higher dimensions where exhaustive search is completely out of the question. Copyright © 1980-2012 IEEE.

Molent L.,Defence Science and Technology Organisation, Australia
International Journal of Fatigue | Year: 2010

The 1969 in-flight failure of an F-111 wing due to the presence of a rogue manufacturing flaw precipitated the adoption of the damage tolerance aircraft design philosophy by the United States Air Force. This article compares this flaw to several flaws or initiating discontinuities that led to unexpected failures in combat-type aircraft operated by the RAAF and found these to be in general an order of magnitude smaller. Failure in the RAAF examples considered here were also dependent upon several other design and production factors in-addition to the initial discontinuity size. Crown Copyright © 2009.

Weinberg G.V.,Defence Science and Technology Organisation, Australia
IET Radar, Sonar and Navigation | Year: 2013

Pareto distribution has been introduced into the radar community recently as a suitable model for X-band high resolution maritime sea clutter returns. This intensity clutter model is a simple two parameter power law distribution. It is thus important to consider the development of constant false alarm rate detection processes for targets embedded within such clutter. It is shown that a simple functional transform can produce such detection schemes, whose false alarm probability and threshold are related through simple analytical expressions. These relationships are related intrinsically to Gaussian detection counterparts. Three detectors will be introduced and their performance analysed in both homogeneous and heterogeneous clutter environments. The effect of interfering targets in the training cells will also be examined. © Reproduced with permission of the Australian Commonwealth 2013.

Dong Y.,Defence Science and Technology Organisation, Australia
IET Radar, Sonar and Navigation | Year: 2012

An optimal detector in the sense of generalised likelihood ratio test (GLRT) for coherent radar detection in a compound K-distributed clutter environment is re-studied in detail. A few properties of the detector are derived showing potential of its implementation in radar systems. To the optimal detector, sea spikes (abnormally high radar returns from the sea surface) are unlikely to trigger false alarms, leading to a significant improvement in target detection. Two suboptimal detectors, aiming at saving computational cost, are proposed, and their performance is compared with the GLRT detector. The detector is assessed using true radar sea clutter data, and the problem of sea spikes causing excessive false alarms is identified and discussed. © 2012 Published with permission Commonwealth of Australia.

Brinkworth C.S.,Defence Science and Technology Organisation, Australia
Analytical Chemistry | Year: 2010

Ricin is a toxic protein produced in the seeds of the castor bean plant. The toxicity of the protein and the ease in which it can be extracted from the seeds makes it a potential biological warfare agent. There has been extensive work in the development of analytical techniques that can identify the protein robustly and rapidly. On-target tryptic digestion and MALDI MS was used to distinguish ricin from bovine serum albumin and three other type 2 ribsome-inactivating proteins (RIPs), abrin, agglutinin (RCA120), and viscumin, using the peptide mass fingerprint. The sequence coverage obtained was enhanced using methanol-assisted tryptic digestion and was particularly useful for the detection of these toxins in complex matrixes. When used in conjunction with intact protein MALDI mass measurement, a positive identification of ricin (or any of the other RIPs) was achieved including confirmation of the integrity of the disulfide bond between the A and B chains. This applicability of this methodology was demonstrated by the identification of ricin in a typical "crude white powder" that may be illicitly produced in a clandestine lab. The analysis on the solubilized sample using this method can be undertaken in around an hour with minimal sample preparation. © Published 2010 by the American Chemical Society.

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