2,363 research outputs found
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 ,
the coordinates reduce to Doran coordinates for the Kerr solution with the
replacement , where and are the mass and charge of
the black hole, respectively. Such coordinates are valid only for , however, which corresponds to the region that a neutral particle
released from rest at infinity can penetrate. By contrast, for and
of opposite sign to , the new coordinates have a progressively extended
range of validity as increases and tend to advanced Eddington-Finkelstein
(EF) null coordinates as , hence becoming global in this limit.
The Kerr solution (i.e.\ with ) may also be written in terms of the new
coordinates by setting , where is a real parameter
unrelated to charge; in this case the coordinate system is global for all
non-negative values of and the limits and 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
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