Modelling the induced magnetic signature of naval vessels

In the construction of naval vessels stealth is an important design feature. With recent advances in electromagnetic sensor technology the war time threat to shipping posed by electromagnetically triggered mines is becoming more significant and consequently the need to understand, predict and reduce the electromagnetic signature of ships is growing. There are a number of components to the electromagnetic field surrounding a ship, with each component originating from different physical processes. The work presented in this study is concerned with the magnetic signature resulting from the magnetisation of the ferromagnetic material of the ship, under the influence of the earth's magnetic field. The detection threat arising from this induced magnetic signature has been known for many years, and consequently, warships are generally fitted with degaussing coils which aim to generate a masking field to counteract this signature. In this work computational models are developed to enable the induced magnetic signature and the effects of degaussing coils to be studied. The models are intended to provide a tool set, to aid the electromagnetic signature analyst in ensuring that pre-production designs of a vessel lie within specified induced magnetic signature targets. Techniques presented where also allow the rapid calculation of currents in degaussing coils. This is necessary because the induced magnetisation of a vessel changes with orientation. Three models are presented within this work. The first model represents a ship as a simple geometric shape, a prolate spheroidal shell, of a given relative permeability. Analytical expressions are derived which characterise the magnetic perturbation to a previously uniform magnetic field, the earth's magnetic field, when the spheroid is placed within its influence. These results provide a quantitative insight into the shielding of large internal magnetic sources by the hull. This model is intended for use in preliminary design studies. A second model is described which is based on the finite element method. This is a numerical model which has the capability of accurately reproducing the relatively complex geometry of a ship and of including the effects of degaussing coils. For these reasons this model is intended for detailed quantitative studies of the induced magnetic signature. A method is described to calculate the optimal set of degaussing coil currents required to minimise the induced magnetic signature. The induced signature without and with degaussing is presented. For the successful application of the finite element method the generation of a mesh is of extreme importance. In this work a mesh generation procedure is described which permits meshes to be generated around a collection of planar surfaces. The relatively complex geometry of a ship can be easily specified as a number of planar surfaces and from this, the finite element mesh can be automatically generated. The automatic mesh generation detailed in this work eliminates an otherwise labour intensive step in the analysis procedure. These techniques are sufficiently powerful to allow meaningful calculations for real ships to be performed on desk-top computers of modest power. An example is presented which highlights the application of this model to a hypothetical ship structure. The third model detailed is specifically designed to study the induced magnetic signature of mine countermeasures vessels. Here the induced magnetic signature is no longer dominated by the gross structure of the ship, which is constructed from non-magnetic materials, but arises from the combined effect of the individual items of machinery onboard the craft

Function extraction

AbstractLow-level imperative programming languages typically have complex operational semantics (e.g. derived from an underlying processor architecture). In this paper, we describe an automatic method for extracting recursive functions from such low-level programs. The functions are derived by formal deduction from the semantics of the programming language. For each function extracted, a proof of correspondence to the original program is automatically constructed. Subsequent program verification can then be done without referring to the details of the low-level programming language semantics at all: it suffices to prove properties of the extracted function. The technique is explained for simple while programs and also for the machine code of a widely used processor. We show how heuristics can enhance the output from the function extractor/decompiler and how the technique aids implementation of a trustworthy compiler. Our tools have been implemented in the HOL4 theorem prover

An Observational Test of Two-field Inflation

We study adiabatic and isocurvature perturbation spectra produced by a period of cosmological inflation driven by two scalar fields. We show that there exists a model-independent consistency condition for all two-field models of slow-roll inflation, despite allowing for model-dependent linear processing of curvature and isocurvature perturbations during and after inflation on super-horizon scales. The scale-dependence of all spectra are determined solely in terms of slow-roll parameters during inflation and the dimensionless cross-correlation between curvature and isocurvature perturbations. We present additional model-dependent consistency relations that may be derived in specific two-field models, such as the curvaton scenario.Comment: 6 pages, latex with revtex, no figures; v2, minor changes, to appear in Physical Review

Rights or containment? The politics of Aboriginal cultural heritage in Victoria

Aboriginal cultural heritage protection, and the legislative regimes that underpin it, constitute important mechanisms for Aboriginal people to assert their rights and responsibilities. This is especially so in Victoria, where legislation vests wide-ranging powers and control of cultural heritage with Aboriginal communities. However, the politics of cultural heritage, including its institutionalisation as a scientific body of knowledge within the state, can also result in a powerful limiting of Aboriginal rights and responsibilities. This paper examines the politics of cultural heritage through a case study of a small forest in north-west Victoria. Here, a dispute about logging has pivoted around differing conceptualisations of Aboriginal cultural heritage values and their management. Cultural heritage, in this case, is both a powerful tool for the assertion of Aboriginal rights and interests, but simultaneously a set of boundaries within which the state operates to limit and manage the challenge those assertions pose. The paper will argue that Aboriginal cultural heritage is a politically contested and shifting domain structured around Aboriginal law and politics, Australian statute and the legacy of colonial history

Single-Inclusive Jet Production in Polarized pp Collisions at O(alpha_s^3)

We present a next-to-leading order QCD calculation for single-inclusive high-p_T jet production in longitudinally polarized pp collisions within the ``small-cone'' approximation. The fully analytical expressions obtained for the underlying partonic hard-scattering cross sections greatly facilitate the analysis of upcoming BNL-RHIC data on the double-spin asymmetry A_{LL}^{jet} for this process in terms of the unknown polarization of gluons in the nucleon. We simultaneously rederive the corresponding QCD corrections to unpolarized scattering and confirm the results existing in the literature. We also numerically compare to results obtained with Monte-Carlo methods and assess the range of validity of the ``small-cone'' approximation for the kinematics relevant at BNL-RHIC.Comment: 23 pages, 8 eps-figure

Towards a global analysis of polarized parton distributions

We present a technique for implementing in a fast way, and without any approximations, higher-order calculations of partonic cross sections into global analyses of parton distribution functions. The approach, which is set up in Mellin-moment space, is particularly suited for analyses of future data from polarized proton-proton collisions, but not limited to this case. The usefulness and practicability of this method is demonstrated for the semi-inclusive production of hadrons in deep-inelastic scattering and the transverse momentum distribution of ``prompt'' photons in pp collisions, and a case study for a future global analysis of polarized parton densities is presented.Comment: 20 pages, LaTeX, 6 eps figures, final version to appear in PRD (minor changes

On the properties of the transition matrix in bouncing cosmologies

We elaborate further on the evolution properties of cosmological fluctuations through a bounce. We show this evolution to be describable either by ``transmission'' and ``reflection'' coefficients or by an effective unitary S-matrix. We also show that they behave in a time reversal invariant way. Therefore, earlier results are now interpreted in a different perspective and put on a firmer basis.Comment: 4 pages, 1 figure, to appear in PR