Teaching earth pressure theory using physical models: an example in civil engineering

The transition from basic Engineering courses in the first year of Civil Engineering curriculum, into the analysis and design of Civil Engineering structures can be challenging for students. Indeed, most students find it difficult in learning some of the theoretical courses in later years of their engineering studies. In this paper, discussions will be directed to the role of physical models in assisting the teachings of advanced Civil Engineering courses. Examples of physical models will be shown by making use of those developed by the authors in the teaching of Geotechnical Engineering at University of Southern Queensland, Australia

Simulations of astronomical imaging phased arrays

We describe a theoretical procedure for analyzing astronomical phased arrays with overlapping beams, and apply the procedure to simulate a simple example. We demonstrate the effect of overlapping beams on the number of degrees of freedom of the array, and on the ability of the array to recover a source. We show that the best images are obtained using overlapping beams, contrary to common practise, and show how the dynamic range of a phased array directly affects the image quality.Comment: 16 pages, 26 figures, submitted to Journal of the Optical Society of America

Optical Physics of Imaging and Interferometric Phased Arrays

Microwave, submillimetre-wave, and far-infrared phased arrays are of considerable importance for astronomy. We consider the behaviour imaging phased arrays and interferometric phased arrays from a functional perspective. It is shown that the average powers, field correlations, power fluctuations, and correlations between power fluctuations at the output ports of an imaging or interferometric phased array can be found once the synthesised reception patterns are known. The reception patterns do not have to be orthogonal or even linearly independent. It is shown that the operation of phased arrays is intimately related to the mathematical theory of frames, and that the theory of frames can be used to determine the degree to which any class of intensity or field distribution can be reconstructed unambiguously from the complex amplitudes of the travelling waves at the output ports. The theory can be used to set up a likelihood function that can, through Fisher information, be used to determine the degree to which a phased array can be used to recover the parameters of a parameterised source. For example, it would be possible to explore the way in which a system, perhaps interferometric, might observe two widely separated regions of the sky simultaneously

How to take the interstellar weather with you in pulsar timing analysis

Here we present a Bayesian method of including discrete measurements of dispersion measure due to the interstellar medium in the direction of a pulsar as prior information in the analysis of that pulsar. We use a simple simulation to show the efficacy of this method, where the inclusion of the additional measurements results in both a significant increase in the precision with which the timing model parameters can be obtained, and an improved upper limit on the amplitude of any red noise in the dataset. We show that this method can be applied where no multi-frequency data exists across much of the dataset, and where there is no simultaneous multi-frequency data for any given observing epoch. Including such information in the analysis of upcoming International Pulsar Timing Array (IPTA) and European Pulsar Timing Array (EPTA) data releases could therefore prove invaluable in obtaining the most constraining limits on gravitational wave signals within those datasets.Comment: 7 pages, 1 Table, 3 Figures. arXiv admin note: substantial text overlap with arXiv:1310.212

New form of the Kerr-Newman solution

A new form of the Kerr-Newman solution is presented. The solution involves a time coordinate which represents the local proper time for a charged massive particle released from rest at spatial infinity. The chosen coordinates ensure that the solution is well-behaved at horizons and enable an intuitive description of many physical phenomena. If the charge of the particle $e = 0$, the coordinates reduce to Doran coordinates for the Kerr solution with the replacement $M \to M - Q^2/(2r)$, where $M$ and $Q$ are the mass and charge of the black hole, respectively. Such coordinates are valid only for $r \ge Q^2/(2M)$, however, which corresponds to the region that a neutral particle released from rest at infinity can penetrate. By contrast, for $e \neq 0$ and of opposite sign to $Q$, the new coordinates have a progressively extended range of validity as $|e|$ increases and tend to advanced Eddington-Finkelstein (EF) null coordinates as $|e| \to \infty$, hence becoming global in this limit. The Kerr solution (i.e.\ with $Q=0$) may also be written in terms of the new coordinates by setting $eQ = -\alpha$, where $\alpha$ is a real parameter unrelated to charge; in this case the coordinate system is global for all non-negative values of $\alpha$ and the limits $\alpha = 0$ and $\alpha \to \infty$ correspond to Doran coordinates and advanced EF null coordinates, respectively, without any need to transform between them.Comment: 4 pages, no figures, accepted as a Letter by PRD. Contains minor updates to match accepted versio