The Dependence of Dynamo α\alpha-Effect on Reynolds Numbers, Magnetic Prandtl Number, and the Statistics of MHD Turbulence

We generalize the derivation of dynamo coefficient $\alpha$ of Field et al (1999) to include the following two aspects: first, the de-correlation times of velocity field and magnetic field are different; second, the magnetic Prandtl number can be arbitrary. We find that the contributions of velocity field and magnetic field to the $\alpha$ effect are not equal, but affected by their different statistical properties. In the limit of large kinetic Reynolds number and large magnetic Reynolds number, $\alpha$-coefficient may not be small if the de-correlation times of velocity field and magnetic field are shorter than the eddy turn-over time of the MHD turbulence. We also show that under certain circumstances, for example if the kinetic helicity and current helicity are comparable, $\alpha$ depends insensitively on magnetic Prandtl number, while if either the kinetic helicity or the current helicity is dominated by the other one, a different magnetic Prandtl number will significantly change the dynamo $\alpha$ effect.Comment: 44 pages, 4 figures, to appear in ApJ (vol. 552

Jupiter's magnetosphere

Magnetosphere, ionosphere, and thermal radiation of planet Jupite

Electrodynamic effects of Jupiter's satellite Io

Electrodynamic effects of Jupiters satellite I

Preparing for “Peak Oil”: towards a preliminary agenda

“In summary, the problem of the peaking of conventional world oil production is unlike any yet faced by modern industrial society. The challenges and uncertainties need to be much better understood. Technologies exist to mitigate the problem. Timely, aggressive risk management will be essential.” This quotation is from the executive summary of a major report issued in February 2005 on the peaking of world oil production. That in itself is unremarkable, but the document – which has come to be known as “The Hirsch Report” – was sponsored by the United States Department of Energy (DOE). There are all the usual disclaimers about the policy of the United States Government. Nevertheless, as early as 2003, DOE clearly decided that a sound technical analysis of the issues raised by the approach of “Peak Oil” was a job which would be worth the investment of time and money

Eulerian on Lagrangian Cloth Simulation

This thesis introduces a novel Eulerian-on-Lagrangian (EoL) approach for simulating cloth. This approach allows for the simulation of traditionally difficult cloth scenarios, such as draping and sliding cloth over sharp features like the edge of a table. A traditional Lagrangian approach models a cloth as a series of connected nodes. These nodes are free to move in 3d space, but have difficulty with sliding over hard edges. The cloth cannot always bend smoothly around these edges, as motion can only occur at existing nodes. An EoL approach adds additional flexibility to a Lagrangian approach by constructing special Eulerian on Lagrangian nodes (EoL Nodes), where cloth material can pass through a fixed point. On contact with the edge of a box, EoL nodes are introduced directly on the edge. These nodes allow the cloth to bend exactly at the edge, and pass smoothly over the area while sliding. Using this ‘Eulerian-on-Lagrangian’ discretization, a set of rules for introducing and constraining EoL Nodes, and an adaptive remesher, This simulator allows cloth to move in a sliding motion over sharp edges. The current implementation is limited to cloth collision with static boxes, but the method presented can be expanded to include contact with more complicated meshes and dynamic rigid bodies

Environmental Taxation in New Zealand: What Place Does it Have?

The 2001 Tax Review (McLeod et al, 2001) includes a timely discussion about the place of environmental taxation in New Zealand. The review’s discussion paper released on 20 June 2001 and the final report in October 2001 both devote a whole chapter to environmental taxation. This is not surprising given the current influence of the Greens in Parliament, the Kyoto Protocol and the enthusiasm of some analysts for using economic instruments to achieve environmental outcomes. In reviewing the academic case for environment taxation, it is appropriate to go back to the Pigouvian tradition, and its more recent interpretation by Coase, Tietenberg and others. At its simplest, an efficient Pigouvian tax and an effect regulation achieve the same outcome. The policy analyst is indifferent. However, given the range of real world circumstances, comparisons can be made between doing nothing, imposing a regulation, imposing a tax, implementing a tradeable permits system or some other policy instrument. Analysts are left to choose between instruments by comparing each instrument against a set of criteria. The Tax Review discussion paper took a cautious approach suggesting that eco-taxes are only appropriate when “damage of each unit of emissions is the same across the geographic area to which the tax applies; the volume of emission is measurable; and the marginal net damage of emissions is measurable”. At a regional level they are more optimistic, suggesting “eco-charges may be appropriate at a local level”. The review does see a real possibility for carbon taxes and notes there is no research available about the potential impact of methane taxes. The Tax Review discussion paper conclusions are driven by some critical assumptions. The authors place a tough standard as a requirement for any environmental tax. This requirement is not always or often met with regulations and other policy instruments. The authors are also concerned about taxes attenuating property rights at all levels of production. This is certainly an impact but it is an efficient impact. The authors suggest that double dividends result from the transfer of rents to the Crown and not productive efficiency. This assumption needs to be tested theoretically and empirically. The authors assume New Zealand should be slow to implement taxes as part of its response to the Kyoto protocol. This ignores the possibility that there may be gains from early adoption. Environmental taxation will continue to be an important political issue in this part of the world as evidenced by the current fuel tax enquiry in Australia. Despite its importance, the consideration of environmental taxation by the Tax Review Committee is unsatisfactory. Further analysis is required which considers the performance of environmental taxation against other instruments used to achieve government goals. This paper provides some history of the concept of environmental taxation as a framework for further research to address the issues raised by the Taxation Review 2001. This paper should form a basis for further work in New Zealand examining specific opportunities for environmental and resource-use taxation

The magnetospheric radiation belt and tail plasma sheet

Magnetospheric radiation belt and tail plasma shee

Early Australian Optical and Radio Observations of Centaurus A

The discoveries of the radio source Centaurus A and its optical counterpart NGC 5128 were important landmarks in the history of Australian astronomy. NGC 5128 was first observed in August 1826 by James Dunlop during a survey of southern objects at the Parramatta Observatory, west of the settlement at Sydney Cove. The observatory had been founded a few years earlier by Thomas Brisbane, the new governor of the British colony of New South Wales. Just over 120 years later, John Bolton, Gordon Stanley and Bruce Slee discovered the radio source Centaurus A at the Dover Heights field station in Sydney, operated by CSIRO's Radiophysics Laboratory (the forerunner of the Australia Telescope National Facility). This paper will describe this early historical work and summarise further studies of Centaurus A by other Radiophysics groups up to 1960.Comment: 45 pages, 43 figure