Defence Research Agency

About: Defence Research Agency is a based out in . It is known for research contribution in the topics: Synthetic aperture radar & Radar. The organization has 1211 authors who have published 1109 publications receiving 31542 citations.

Cooperation and Leadership in Military Organisations Modelled with Methods of Social Network Analysis

Abstract: Modern military organisations have become more cooperation-oriented rather than abide by traditional, leadership-oriented, hierarchical structures. ‘Teams of teams’ have proven effective as organisational structures in actual battlefield situations. Additionally, future battles rely more and more on utilising civilian technology and expert personnel. We present mathematical methods for modelling modern military organisations that are based on teams and networking between team members when performing military tasks or operations. Social network analysis is a novel approach to study relationships between leadership and sub-ordinate roles. We present interactions between units in an organisation with bidirectional relationships, which enables us to illustrate both outward and inward influence of the units. The method is demonstrated with different model parameter values that describe both modern and traditional military organisations.

Boundary element analysis of crack intersection, initiation and growth at pin loaded holes

Abstract: The dual boundary element method for the analysis of cracks in linear elastic materials has been previously generalised by the authors to allow for automatic remeshing when crack tips intersect other cracks or boundaries, and initiation and growth of small cracks at positions of high stress concentration. The new cracks are assumed to result from sudden events such as an overload or the subsequent stress redistribution when cracks intersect other cracks or holes. In this paper a crack at the edge of one hole in a row of pin-loaded holes is investigated; various values are considered for the stress at which new cracks may initiate. Two rows of aligned or staggered holes are examined also. The spacing between the holes was typical for lines of holes in overlap joints in plates. For the same load transfer between the plates, new cracks are initiated less readily and grow more slowly for a double row of aligned holes than for a single row or for staggered rows.

Why is the retina capable of resolving finer detail than the eye's optical and neural systems?

Abstract: It is established that the resolving power of the eye accords with that predicted by diffraction theory. Campbell and Green (J. Physiol. 181, 576-593, 1965) and Campbell and Gubisch (J. Physiol. 186, 558-578, 1966) demonstrated that the eye exhibits nearly diffraction-limited performance at 2 mm pupil diameter, resolving up to approximately 60 cycdeg-1. However, Williams (Vision Res. 25, 195-205, 1985) has demonstrated that foveal receptors can respond at up to 200 cyc deg-1, in agreement with measured receptor separation (Hirsch and Curcio, Vision Res. 29, 1095-1101, 1989). The obvious question is: why is there such an apparent mismatch between the eye's optics and receptors? It is shown that the change in optical energy distribution corresponding to 1 just noticeable difference of defocus has the form of a difference of Gaussians, for which the contrast sensitivity function peaks at 16 cyc deg-1, with a bandwidth from 0 to approximately 70 cyc deg-1. The reason for the even higher-density packing of receptors, in the fovea, appears to be the need to allow the different colour-response cones to be spatially inhomogeneous without excessive aliasing. Prompted by this analysis, some data of Williams (1985) are re-examined, leading to a mapping of the averaged aperture-sensitivity of foveal cones, and demonstrating the reason for the diffuse cutoff of the postulated defocus channel.

Optimization of intrinsic damping by exploitation of fiber orientation within viscoelastic composites

Abstract: A mathematical model is used to describe the effect of fiber alignment on viscoelastic composite dynamic Young's Moduli and loss factors. The model, supported by experimental validation, requires the dynamic physical properties of the matrix resin for the range of operational temperatures and frequencies of interest. The model predicts that the resulting loss factor of a fiber reinforced viscoelastic resin composite behaves in an anisotropic fashion, however, damping optimization may be achieved in two different ways dependent on the angle of fiber alignment. The model predicts that the loss factors of a viscoelastic composite employing a woven roving with low modulus fibers, aligned in equal proportions at 0 degrees and 90 degrees are highest along a direction where fiber alignment angles are between 30 degrees and 60 degrees. The loss factor is a maximum when matrix resin loss factor is highest. Along a direction of 0 degrees and 90 degrees loss factors are generally lower, they no longer peak as a result of high loss factors in the matrix resin but are highest when the matrix loss modulus is a maximum. Furthermore, it is shown that increase in fiber modulus results in a decrease of composite loss factors at angles around 0 degrees and 90 degrees, but higher loss factors are obtained over a much wider range of angles that are typically between 5 degrees to 85 degrees.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.