Showing papers by "Defence Science and Technology Organisation published in 1990"

Destriping multiple sensor imagery by improved histogram matching

Abstract: Sensor stripes evident in multisensor imagery can cause subsequent image classification to fail, if not removed properly. Of the destriping algorithms investigated, the one published by Horn and Wo...

Atmospheric constituent inversion problems: Implications for baseline monitoring

Abstract: The importance of ill-posed inverse problems in atmospheric chemistry is reviewed. Most models for the determination of sources and sinks of atmospheric constitutents lead to such ill-posed inverse problems. Consequently, source determinations may be subject to severe amplification of observational error, particularly in the most rapidly varying components. Therefore, mathematical analysis of the various inverse problems needs to be undertaken in order to determine the extent to which a given set of data contains usable information about source/sink processes.

Isomer distribution of nitro derivatives of diphenylamine in gun propellants : nitrosamine chemistry

Abstract: The derivatisation of diphenylamine (DPA) in single base gun propellants was studied as a function of aging at 80°C. The relative proportions of 2-nitro DPA and 4-nitro DPA varied from 32 : 68 to 63 : 37 according to propellant type. Preferences for para substitution were seen in experimental lots “stabilized” with 2-nitroDPA, 4-nitroDPA and N-nitrosoDPA. Increasing water content resulted in higher preferences for ortho substitution. 4-NitroDPA is a better stabilizer than 2-nitroDPA. Model studies performed using nitro substituted N-nitrosamines show that para substitution is preferred in boiling acetic acid. Mechanisms for the conversion of N-nitrosamines into isomeric nitro derivatives are discussed with relation to the model studies and the behaviour in propellants. Detailed experimental procedures are given for the preparation of N-nitrosamines.

Elevation angle dependence in tropical regions

Abstract: The variation of path attenuation with elevation angle has been generally considered to approximate a cosecant law, certainly between elevation angles of about 10° and 50°. Such a theory relies on the assumption that the attenuation layer is statiform for most of the time, and is therefore probably reasonable for temperate regions. In tropical areas however the incidence of convective rain is much higher than in temperate regions, so that during rainy periods, particularly at times of high rain rate, the assumption that the attenuating layer is stratiform is no longer valid. The cosecant law does not therefore hold in such conditions. An experiment has been carried out in the tropical rain belt of northern Australia over several years to investigate the elevation-angle dependency. Four radiometers were co-sited, with the same azimuth. Three of these, with a half power beamwidth of 2.2°. were elevated to 15°, 45° and 85°. The fourth. with a beamwidth of 0·6° was elevated to 45° so as to allow an investigation into aperture effects. The antennae were all orientated for horizontal polarization. Rain-gauges were co-sited with the radiometers and placed along the look path. The results obtained clearly indicate that, in tropical regions. the cosecant law is inappropriate for predicting the elevation angle effects of path attenuation. particularly at high rain rates. The presence of rain cells with rates exceeding 300 mm/h ensures that the assumption of a stratiform attenuating layer is invalid.

Region adjacency analysis of remotely-sensed imagery

Abstract: The analysis of image data by region adjacency methods is a long-established, though not currently widely-used, method of region analysis. This lack of use is probably because the technique has usually been applied only to images which have been subjected to many stages of processing and which, as a result, contain only a small number of regions whose analysis could easily be achieved manually. The present paper proposes that there are significant benefits from applying region adjacency analysis to comparatively raw (‘low-level’) imagery, such as is produced by many remote sensing systems, rather than to highly processed images. In fact many high-level processing requirements can be better performed by region analysis of the low-level data. Examples include blob extraction, specific region neighbour searching and region merging. The latter operation is extremely important in reducing complex image-derived data to a less complex form suitable for entry into a geographical information system (GIS)....

Compton‐scattering X‐ray artefacts observed in an STEM with high take‐off angle EDS detector

Abstract: SUMMARY A new spectral artefact has been identified in a high take-off angle energy-dispersive X-ray detector used in a JEOL 2000FX STEM. This artefact has been verified to be due to Compton scattering of Mo K X-rays which are produced in the standard JEOL condenser lens Mo apertures. These Mo X-rays are Compton scattered by a thick carbon insert in the upper objective lens pole-piece of the microscope and are detected as two broad X-ray peaks centred on 16.44 and 18.3 keV. The presence of this artefact severely limited attempts to quantify small concentrations of Nb in a nickel alloy. Possible ways to avoid or minimize the artefact include the use of large apertures, apertures constructed from different materials or thick apertures.

High strain rate properties of three liquid phase sintered tungsten alloys

Abstract: Analyse de la contrainte d'ecoulement dans les alliages de tungstene frittes en phase liquide 90WNiCu, 95WNiFe et 97WNiFeCu pour des vitesses de deformation allant jusqu'a 1,4×10 4 sec −1

Matrix product machine and the Fourier transform

Abstract: The functional architecture of a matrix product machine is described. The machine consists of a set of three custom VLSI chips and a RAM array. Machine performance is 140 Mflops for matrix products. A transformation of the DFT is presented that maps well onto this machine. Performance comparisons with both new architectures and commercial products demonstrate that the matrix product machine is faster over a wide range of transform lengths.

Flow behaviour of molten 2,4,6-trinitrotoluene (TNT) between concentric cylinders

Abstract: The flow behaviour of pure and commercial molten TNT when subjected to very high rates of shear in a rotational viscometer over the temperature range 82.0 to 95.4°C is presented. All data obtained suggest that the behaviour of molten TNT is Newtonian, contrary to the conclusions of some published work, and the temperature dependence of the viscosity of pure TNT is adequately described by an Arrhenius-type relationship of the formη = A eB/T whereA = 0.000 541,B = 3 570 andT is the Kelvin temperature. A similar relationship is obtained for commercial TNT. Under some instrumental conditions discontinuities are seen in the shear stress—shear rate flow curves. An analysis of these discontinuities shows them to be caused by the transition from laminar to turbulent flow. Possible implications for processibility and initiation of explosives are discussed.

Effects of Notch Geometry and Moisture on Fracture Strength of Carbon/Epoxy and Carbon/Bismaleimide Laminates

Abstract: : Cross-ply panels of various ply orientations and 1 to 2-mm thickness were tested in tension with a center notch to determine the translaminar fracture toughness and in bending with no notch to determine the bulk flexural strength and modulus Carbon/epoxy panels with a variety of notch lengths and widths were subjected to laboratory air conditions before testing Carbon/ bismaleimide panels with one basic notch configuration were tested in three pretest exposure conditions: laboratory air; a 4000-hour exposure in a controlled moisture chamber; and a 4000-hour exposure in a natural tropical environment

A software simulator for a knowledge-based ESM system

Abstract: A computer simulation of a receiver intercepting radar emissions in a tactical maritime environment has been developed as a means of stimulating a knowledge-based system for signal interpretation. The development of the model from concept, through a prototype in Prolog, to the current version in C is described in this paper. The model is designed to run in a multi processing environment providing real-time simulation of the signal environment to allow the performance of the knowledge- based system to be evaluated. The model provides a language for specifying scenarios in an object-oriented style, and uses inter process communication facilities provided by the UNIX operating system to connect to the application system. Interactive tools to control the runtime characteristics of the simulation are also provided.

Modulation transfer function of photographic emulsion: the small-angle approximation in radiative transfer theory.

Abstract: The modulation transfer function (MTF) of photographic emulsion can be conveniently represented by an expression derived from the theory of radiative transfer. Small-angle scattering is assumed to simplify the transfer equation and a Gaussian model is used to represent the forward lobe of the scattering phase function. The MTF depends on such variables as emulsion thickness, crystal size and concentration, relative refractive index, and the wavelength of incident light. The experimental results show that the Gaussian model adequately represents the phase function and also that useful MTF predictions are possible in the spatial frequency bandwidth 0–40 cycles/mm for AgBr crystals in a gelatin matrix.

Time-frequency filtering and synthesis from convex projections

Abstract: This paper describes the application of the theory of projections onto convex sets to time-frequency filtering and synthesis problems. We show that the class of Wigner-Ville Distributions (WVD) of L2 signals form the boundary of a closed convex subset of L2(R2). This result is obtained by considering the convex set of states on the Heisenberg group of which the ambiguity functions form the extreme points. The form of the projection onto the set of WVDs is deduced. Various linear and non-linear filtering operations are incorporated by formulation as convex projections. An example algorithm for simultaneous time-frequency filtering and synthesis is suggested.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Verification of heuristic diagnostic knowledge by comparison with a causal/qualitative model

Abstract: An approach to verify the knowledge base of a diagnostic expert system is described. An heuristic knowledge base collected from domain experts by interviews was analysed and the reasons for changes between versions were noted. The knowledge base was then compared with a small causal qualitative model of the device covered by the heuristic knowledge. Conclusions are drawn regarding the quality of the heuristic knowledge and indicate how it is planned to use the comparison of heuristic and causal knowledge in further development of the knowledge base.

Radar signal synthesis with constraints: a group theoretic approach

Abstract: This paper addresses the problem of designing signals for general group representations subject to constraints which are formulated as convex sets in the Hilbert space of the group states. In particular, the paper considers irreducible representations in an infinite dimensional Hilbert space and derives an iterative producedure for proceeding from an arbitrary element of the Hilbert space to a state of the group subject to a priori imposed constraints with closed convex range. As examples, the paper focuses on narrowband and wideband radar ambiguity synthesis.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The flow stress of a 0.21% C mild steel over strain rates from 10−3 to 2×104 sec−1

Abstract: This article presents data for a 0.21 % C mild steel target material used in projectile impact studies, and the subject of current studies in computation. The strain rate range covered is 10 −3 sec −1 to 2×10 4 sec −1

General procedures to determine the composition of commercial, two‐part polysulfide aircraft sealants

Abstract: Interpretation of the chemical processes which polysulfide sealants undergo either on storage or when the cured material is subjected to environmental influences requires detailed knowledge of formulations. Procedures have been developed to isolate and identify a range of additives in two-part commercial aircraft sealants of both the dichromate and manganese dioxide cure types. Solvents, curing agent dispersants, and cure rate modifiers were separated chemically and thermal analysis was demonstrated to provide a ready means to estimate carbon in fillers. The phenolic resin adhesion enhancers were conveniently determined using 13C-NMR spectroscopy and could also be identified using size exclusion chromatography. It was shown that virtually no interaction occurred between polysulfide liquid polymers and phenolic resins following aging at 70°C for 7 days. The most appropriate methods for determining curative levels were established and new means of assessing thiol content of the polysulfides by both 13C-NMR and PMR spectroscopy are described. The significance of aspects of the sealant formulations is discussed.