1,722,334 research outputs found
An empirical model of long-term thermospheric density change
No full textPredicting the positions of satellites in Low Earth Orbit (LEO) requires a comprehensive understanding of the dynamic nature of the atmosphere. For objects in LEO the most significant orbit perturbation is atmospheric drag, which is a function of the local atmospheric density from a layer in the atmosphere called the thermosphere. For long-term predictions of satellite orbits and ephemerides, any density trend in the thermosphere is a necessary consideration, not only for satellite operators, but also for studies of the future LEO environment in terms of space debris. Numerous studies of long-term thermospheric density change have been performed.Predictions by Roble & Ramesh (2002), along with evidence by Keating (2000), Emmert et al.(2004), Marcos et al. (2005), Qian et al. (2006) and Emmert et al. (2008), strongly suggest the existence of such a phenomenon. Therefore, the objective of the research presented in this thesis is to provide a novel method to evaluate quantitatively thermospheric density change. Satellite drag data is an effective medium through which one can investigate local thermospheric density and changes thereof. There are many ways of determining atmospheric density, but inferring thermospheric density from satellite drag data is a relatively cost-effective way of gathering in-situ measurements. To do this, knowledge about a satellite’s physical properties that are intrinsic to atmospheric drag is required. A study by Saunders et al. (2009) highlighted problems with estimating a satellite’s physical properties directly from data given explicitly by Two-Line Element (TLE) sets. This prompted an investigation into ways to estimate ballistic coefficients: a required satellite parameter associated with drag coefficient and area-to-mass ratio. A novel way of estimating satellite ballistic coefficients was derived and is presented in this thesis. Additionally, novel consideration of atmospheric chemical composition was applied on long-term drag coefficient variability. Using a quantitative estimate of a ballistic coefficient one can propagate numerically a satellite’s orbit and predict the effects of atmospheric drag. Given an initial satellite orbit from TLE data, one approach is to use an orbital propagator to predict the satellite’s state at some time ahead and then to compare that state with TLE data at the same epoch. The difference between the semi-major axes of the initial orbit and that after the orbit propagation is then integrated and can be used to estimate the global average density. The method employed in this study utilises this process. To achieve this, a specially developed, computer-based, numerical orbital propagator was written in the programming language C/C++. The underlying theories and implementation tests for this propagator are presented in this thesis
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Chapter 3: Challenges in determining the effectiveness of sustainability assessment
Get PDFConsidering the environment (including the place of human beings in it), and how best it might be managed, is really thinking about environmental governance. As an approach to environmental governance sustainable development is just one of many ‘discourses’ which exist and we have previously made the point that it reflects a view that socio-economic development and environmental conservation are, to an extent, compatible goals and that socio-economic development is necessary (Bond and Morrison-Saunders, 2009). Not everyone shares this view and it is important to bear in mind that whilst this book assumes sustainable development is a good thing, proponents of ‘deep ecology’ (as just one example) would argue that sustainable development inappropriately favours an anthropocentric view of the world in which humans have a right to dominate nature (Grey, 1993; Jacob, 1994; Williams and Millington, 2004).
Sustainability assessment is based on an implicit premise that sustainable development is the appropriate discourse on environmental governance. The fact that there are other discourses on environmental governance has implications for whether sustainability assessment can ever be considered 'effective' as it is promoting a governance view which is not universally held. That said, Sustainable Development “has become the dominant rhetorical device of environmental governance” (Adger et al., 2003, p.1095) and, therefore, could be argued to be the dominant discourse in environmental decision-making in most jurisdictions at present. In this context, sustainability assessment needs to be contributing to the achievement of sustainable development, and it is based on this assumption that this chapter and the overall book is written
Comet march [music] : pianoforte solo /
No full text"Paling edition".; Cover title.; Also available online http://nla.gov.au/nla.mus-an4829259; N, MUS/019
Through shot and shell [music] : march for piano /
No full textCover title.; Also available online http://nla.gov.au/nla.mus-an5734961; MUS: N, MUS/131 ; A, MUS/092; A copy contains hand written ms. parts for cornet in B flat and bass trombone
Italian peasant dance [music] : piano solo /
No full textAlso available online http://nla.gov.au/nla.mus-vn2979726
- …
