UQ staff Publications - UQ eSpace
http://espace.library.uq.edu.au/
The University of QueenslandenFez http://blogs.law.harvard.edu/tech/rssComment on: 'Peculiarities in the energy transfer by waves on strained strings' (Phys. Scr. 88 065402)
http://espace.library.uq.edu.au/view/UQ:366993
2015-08-11T00:24:44Z
Rowland, David R. On claims that general relativity differs from Newtonian physics for self-gravitating dusts in the low velocity, weak field limit
http://espace.library.uq.edu.au/view/UQ:366891
Galaxy rotation curves are generally analyzed theoretically using Newtonian physics; however, two groups of authors have claimed that for self-gravitating dusts, general relativity (GR) makes significantly different predictions to Newtonian physics, even in the weak field, low velocity limit. One group has even gone so far as to claim that nonlinear general relativistic effects can explain flat galactic rotation curves without the need for cold dark matter. These claims seem to contradict the well-known fact that the weak field, low velocity, low pressure correspondence limit of GR is Newtonian gravity, as evidenced by solar system tests. Both groups of authors claim that their conclusions do not contradict this fact, with Cooperstock and Tieu arguing that the reason is that for the solar system, we have test particles orbiting a central gravitating body, whereas for a galaxy, each star is both an orbiting body and a contributor to the net gravitational field, and this supposedly makes a difference due to nonlinear general relativistic effects. Given the significance of these claims for analyses of the flat galactic rotation curve problem, this article compares the predictions of GR and Newtonian gravity for three cases of self-gravitating dusts for which the exact general relativistic solutions are known. These investigations reveal that GR and Newtonian gravity are in excellent agreement in the appropriate limits, thus supporting the conventional use of Newtonian physics to analyze galactic rotation curves. These analyses also reveal some sources of error in the referred to works.2015-08-09T00:46:06Z
Rowland, David R. On the value of geometric algebra for spacetime analyses using an investigation of the form of the self-force on an accelerating charged particle as a case study
http://espace.library.uq.edu.au/view/UQ:194347
The ability to treat vectors in classical mechanics and classical electromagnetism as single geometric objects rather than as a set of components facilitates physical understanding and theoretical analysis. To do the same in four-dimensional spacetime calculations requires a generalization of the vector cross product. Geometric algebra provides such a generalization and is much less abstract than exterior forms. It is shown that many results from geometric algebra are useful for spacetime calculations and can be presented as simple extensions of conventional vector algebra. As an example, it is shown that geometric algebra tightly constrains the possible forms of the self-force that an accelerating charged particle experiences and predicts the Lorentz–Abraham–Dirac equation of motion up to a constant of proportionality. Geometric algebra also makes the important physical content of the Lorentz–Abraham–Dirac equation more transparent than does the standard tensor form of this equation, thus allowing a proposed modification to this equation free from the problems of preacceleration and runaway motion to be easily predicted.2010-01-31T00:07:28Z
Rowland, David R. Small amplitude transverse waves on taut strings: exploring the significant effects of longitudinal motion on wave energy location and propagation
http://espace.library.uq.edu.au/view/UQ:294624
Introductory discussions of energy transport due to transverse waves on taut strings universally assume that the effects of longitudinal motion can be neglected, but this assumption is not even approximately valid unless the string is idealized to have a zero relaxed length, a requirement approximately met by the slinky spring. While making this additional idealization is probably the best approach to take when discussing waves on strings at the introductory level, for intermediate to advanced undergraduate classes in continuum mechanics and general wave phenomena where somewhat more realistic models of strings can be investigated, this paper makes the following contributions. First, various approaches to deriving the general energy continuity equation are critiqued and it is argued that the standard continuum mechanics approach to deriving such equations is the best because it leads to a conceptually clear, relatively simple derivation which provides a unique answer of greatest generality. In addition, a straightforward algorithm for calculating the transverse and longitudinal waves generated when a string is driven at one end is presented and used to investigate a cos2 transverse pulse. This example illustrates much important physics regarding energy transport in strings and allows the ‘attack waves’ observed when strings in musical instruments are struck or plucked to be approximately modelled and analysed algebraically. Regarding the ongoing debate as to whether the potential energy density in a string can be uniquely defined, it is shown by coupling an external energy source to a string that a suggested alternative formula for potential energy density requires an unphysical potential energy to be ascribed to the source for overall energy to be conserved and so cannot be considered to be physically valid.2013-03-24T00:09:25Z
Rowland, David R. The potential energy density in transverse string waves depends critically on longitudinal motion
http://espace.library.uq.edu.au/view/UQ:262319
2011-11-27T06:48:18Z
Rowland, David R. The surprising influence of longitudinal motion in vibrating strings: Comment on "Video-based spatial portraits of a nonlinear vibrating string" [Am. J. Phys. 80(10), 862-869 (2012)]
http://espace.library.uq.edu.au/view/UQ:376270
An error in the quoted nonlinear coefficient that is commonly found in the literature is identified. The subtle origin of this error is identified as the neglect of longitudinal displacements of points in the string, which leads to a nonlinear coefficient that is a factor of 3/2 too large. A correct derivation is outlined and numerical simulations verify the correction.2015-12-29T00:33:39Z
Rowland, David R. Understanding nonlinear effects on wave shapes: comment on "an experimental analysis of a vibrating guitar string using high-speed photography" [Am. J. Phys. 82(2), 102-109 (2014)]
http://espace.library.uq.edu.au/view/UQ:373489
In a recent paper, Whitfield and Flesh found unusual bowing behavior in the waveform of a guitar string for large amplitude plucks. This Comment discusses the theory needed to understand this nonlinear effect, and it is shown that this theory provides reasonably good qualitative agreement with the observed wave form. This theory is interesting because: (i) it allows one to quantify the boundary between linear and nonlinear behavior in terms of key physical parameters; (ii) it reveals the importance of taking into account longitudinal displacements even when they are much smaller than the associated transverse displacements; and (iii) it reveals that dispersion due to tension changes and dispersion due to flexural rigidity have very similar functional forms, which leads to the question of when one effect can be neglected in comparison to the other.2015-11-17T00:24:28Z
Rowland, David R. Visualising publication data: UQ Library Author Statistics App
http://espace.library.uq.edu.au/view/UQ:373606
2015-11-17T17:25:29Z
Morgan, Helen; Bignell, Elisha Working effectively within a changing organisational environment
http://espace.library.uq.edu.au/view/UQ:64312
2007-08-14T19:04:45Z
Burke, M.; MacKenzie, M.