919 results for Journal article, 1990

  • Talking About 'My Place'/My Place: Feminism, Criticism and the Other's Autobiography

    Cooper, Annabel (1995)

    Journal article
    University of Otago

    A few years ago I edited an autobiography written in 1936 by a working- class New Zealand woman, Mary Lee's The Not So Poor. Setting out on a project of "restoring a voice," allowing the as yet unpublished speech of a member of a largely silenced group to be heard, I nevertheless found that my research and commentary, with its access to research tools and specialised knowledges, undermined the authority of that voice even as it attempted to assert it, delivering not a formerly silenced truth but a problematic and strategic text which negotiated uneasily with more powerful texts of its historical moment. To borrow the formulation Gayatri Spivak uses, "representation" in the politico-legal sense of "speaking for" could rapidly slide into something more like "substitution" (Spivak 275-6). In what follows, therefore, I contest parts of the critical pieces I discuss, but write from a position of complicity rather than out of a claim to purity. Indeed, it is central to the argument of this article that in these matters there is no position of purity, no clean place.

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  • Community family tenure - An Examination of Scotland's Crofting and Zimbabwe's Communal Area Tenure.

    Goodwin, David (1998)

    Journal article
    University of Otago

    This paper summarizes legislation in Scotland (some in place for over a century) and Zimbabwe (some in place for fifteen years) relating to Crofting and Communal Areas - both of which are forms of what in this paper has been termed Communal Family Tenure. The effectiveness of legislation and funding for Crofting is examined, including grants, public and private capital supporting new industries, recreation facilities, LIS, etc. This legislation has often resulted in thriving rural communities, and may provide a yardstick against which proposed Zimbabwean legislation with the same aim can be gauged.

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  • Crucifixion, State Terror, and Sexual Abuse

    Tombs, David (1999)

    Journal article
    University of Otago

    A version of this paper was first presented under the title 'Biblical Interpretation in Latin America' at the Society of Biblical Literature International Conference, Cracow, Poland, 20 July 1998.

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  • Linear transport of solar wind fluctuations

    Oughton, Sean; Matthaeus, William H. (1995)

    Journal article
    University of Waikato

    Numerical solutions for the linear transport of solar wind fluctuations are presented. The model used takes into account the effects of advection, expansion, and wave propagation, as well as the recently illuminated effects of (non-WKB) “mixing” terms. The radial evolution of the fluctuating kinetic and magnetic energies and of the cross helicity is computed, and it is demonstrated that in appropriate limits the solutions converge to the WKB forms. In more general cases, however, where the fluctuations consist of a superposition of various types of turbulence, mixing leads to solutions which differ substantially from those predicted by WKB theory. The degree of mixing shows considerable dependence on the nature of the turbulence, giving rise to varying levels, at 1 ∼ AU, of the ratio of “inward” and “outward” fluctuation energies and the ratio of kinetic and magnetic fluctuation energies. The transport properties described here may provide a partial explanation for the observed decrease of cross helicity with increasing heliocentric distance in the solar wind.

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  • Anisotropic three-dimensional MHD turbulence

    Matthaeus, William H.; Ghosh, Sanjoy; Oughton, Sean; Roberts, D. Aaron (1996)

    Journal article
    University of Waikato

    Direct spectral method simulation of the three-dimensional magnetohydrodynamics (MHD) equations is used to explore anisotropy that develops from initially isotropic fluctuations as a consequence of a uniform applied magnetic field. Spectral and variance anisotropies are investigated in both compressible and incompressible MHD. The nature of the spectral anisotropy is consistent with the model of Shebalin et al. [1983] in which the spectrum broadens in the perpendicular wavenumber direction, the anisotropy being greater for smaller wavenumbers. Here this effect is seen for both incompressible and polytropic compressible MHD. In contrast, the longitudinal (compressive) velocity fluctuations remain isotropic. Variance anisotropy is observed for low plasma beta compressible MHD but not for incompressible MHD. Solar wind observations are qualitatively consistent with both variance and spectral anisotropies of the type discussed here.

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  • Magnetic helicity in magnetohydrodynamic turbulence with a mean magnetic field

    Stribling, Troy; Matthaeus, William H.; Oughton, Sean (1995)

    Journal article
    University of Waikato

    A computational investigation of magnetic helicity of the fluctuatingmagnetic fieldHm in ideal and freely decaying three‐dimensional (3‐D) magnetohydrodynamics (MHD) in the presence of a uniform mean magnetic field is performed. It is shown that for ideal 3‐D MHDHm, which is a rugged invariant in the absence of a mean magnetic field [Frisch et al., J. Fluid Mech. 77, 796 (1975)], decays from its initial value and proceeds to oscillate about zero. The decay of Hm is shown to result from the presence of a new ‘‘generalized’’ helicity invariant, which includes contributions from the uniform magnetic field. The loss of invariance of Hm will diminish the effects of inverse transfer of Hm on freely decaying turbulence. This is demonstrated in a discussion of the selective decay relaxation process.

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  • Evolution of energy-containing turbulent eddies in the solar wind

    Matthaeus, William H.; Oughton, Sean; Pontius, Duane H.; Zhou, Ye (1994)

    Journal article
    University of Waikato

    Previous theoretical treatments of fluid-scale turbulence in the solar wind have concentrated on describing the state and dynamical evolution of fluctuations in the inertial range, which are characterized by power law energy spectra. In the present paper a model for the evolution of somewhat larger, more energetic magnetohydrodynamic (MHD) fluctuations is developed by analogy with classical hydrodynamic turbulence in the quasi-equilibrium range. The model is constructed by assembling and extending existing phenomenologies of homogeneous MHD turbulence, as well as simple two-length-scale models for transport of MHD turbulence in a weakly inhomogeneous medium. A set of equations is presented for the evolution of the turbulence, including the transport and nonlinear evolution of magnetic and kinetic energy, cross helicity, and their correlation scales. Two versions of the model are derived, depending on whether the fluctuations are distributed isotropically in three dimensions or restricted to the two-dimensional plane perpendicular to the mean magnetic field. This model includes a number of potentially important physical effects that have been neglected in previous discussions of transport of solar wind turbulence. Numerical solutions are shown for several cases of interest that demonstrate the advantages of this approach. We suggest that this model may prove useful in studies of solar wind heating and acceleration, as well as in describing the response of interplanetary turbulence to wave energy injected by pickup ions and planetary upstream waves.

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  • The influence of a mean magnetic field on three-dimensional magnetohydrodynamic turbulence

    Oughton, Sean; Priest, Eric R.; Matthaeus, William H. (1994)

    Journal article
    University of Waikato

    Building on results from two-dimensional magnetohydrodynamic (MHD) turbulence (Shebalin, Matthaeus & Montgomery 1983), the development of anisotropic states from initially isotropic ones is investigated numerically for fully three-dimensional incompressible MHD turbulence. It is found that when an external d.c. magnetic field (B₀) is imposed on viscous and resistive MHD systems, excitations are preferentially transferred to modes with wavevectors perpendicular to B₀). The anisotropy increases with increasing mechanical and magnetic Reynolds numbers, and also with increasing wavenumber. The tendency of B₀ to inhibit development of turbulence is also examined.

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  • Transport theory and the WKB approximation for interplanetary MHD fluctuations

    Matthaeus, William H.; Zhou, Ye; Zank, Gary P.; Oughton, Sean (1994)

    Journal article
    University of Waikato

    An alternative approach, based on a multiple scale analysis, is presented in order to reconcile the traditional WKB approach to the modeling of interplanetary fluctuations in a mildly inhomogeneous large-scale flow with a more recently developed transport theory. This enables us to compare directly, at a formal level, the inherent structure of the two models. In the case of noninteracting, incompressible (Alfvén) waves, the principle difference between the two models is the presence of leading-order couplings (called “mixing effects”) in the non-WKB turbulence model which are absent in a WKB development. Within the context of linearized MHD, two cases have been identified for which the leading order non-WKB “mixing term” does not vanish at zero wavelength. For these cases the WKB expansion is divergent, whereas the multiple-scale theory is well behaved. We have thus established that the WKB results are contained within the multiple-scale theory, but leading order mixing effects, which are likely to have important observational consequences, can never be recovered in the WKB style expansion. Properties of the higher-order terms in each expansion are also discussed, leading to the conclusion that the non-WKB hierarchy may be applicable even when the scale separation parameter is not small.

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  • Phenomenology for the decay of energy-containing eddies in homogeneous MHD turbulence

    Hossain, Murshed; Gray, Perry C.; Pontius, Duane H.; Matthaeus, William H.; Oughton, Sean (1995)

    Journal article
    University of Waikato

    We evaluate a number of simple, one‐point phenomenological models for the decay of energy‐containing eddies in magnetohydrodynamic(MHD) and hydrodynamicturbulence. The MHDmodels include effects of cross helicity and Alfvénic couplings associated with a constant mean magnetic field, based on physical effects well‐described in the literature. The analytic structure of three separate MHDmodels is discussed. The single hydrodynamic model and several MHDmodels are compared against results from spectral‐method simulations. The hydrodynamic model phenomenology has been previously verified against experiments in wind tunnels, and certain experimentally determined parameters in the model are satisfactorily reproduced by the present simulation. This agreement supports the suitability of our numerical calculations for examining MHDturbulence, where practical difficulties make it more difficult to study physical examples. When the triple‐decorrelation time and effects of spectral anisotropy are properly taken into account, particular MHDmodels give decay rates that remain correct to within a factor of 2 for several energy‐halving times. A simple model of this type is likely to be useful in a number of applications in space physics, astrophysics, and laboratory plasma physics where the approximate effects of turbulence need to be included.

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  • Properties of mass-loading shocks: 1. Hydrodynamic considerations

    Zank, Gary P.; Oughton, Sean (1991)

    Journal article
    University of Waikato

    The one-dimensional hydrodynamics of flows subjected to mass loading are considered anew, with particular emphasis placed on determining the properties of mass-loading shocks. This work has been motivated by recent observations of the outbound Halley bow shock (Neubauer et al., 1990), which cannot be understood in terms of simple hydrodynamical or magnetohydrodynamical descriptions. By including mass injection at the shock, we have investigated the properties of the Rankine-Hugoniot conditions on the basis of a geometric formulation of the entropy condition. Such a condition, which is more powerful than the usual thermodynamical formulation, serves to determine those solutions to the Rankine-Hugoniot conditions which correspond to a physically realizable downstream state. On this basis a concise theoretical description of hydrodynamic mass-loading shocks is obtained. We show that mass-loading shocks have more in common with combustion shocks than with ordinary nonreacting gas dynamical shocks. It is shown that for decelerated solutions to the Rankine-Hugoniot conditions to exist, the upstream flow speed u0 must satisfy u0 > ucrit > cs, where cs is the sound speed. Besides the usual supersonic-subsonic transition, mass-loading fronts can also admit a decelerating supersonic-supersonic transition, the structure of which consists of a sharp decrease in the flow velocity preceding a recovery and an increase in the final downstream flow speed. We suggest the possibility that such structures may describe the inbound Halley bow shock (Coates et al., 1987a). Both parallel and oblique shocks are considered, the primary difference being that oblique shocks are subjected to a shearing stress due to mass loading. It is conjectured that such a shearing may destabilize the shock.

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  • Selective decay and coherent vortices in two-dimensional incompressible turbulence

    Matthaeus, William H.; Stribling, W.; Martinez, Daniel; Oughton, Sean; Montgomery, David (1991)

    Journal article
    University of Waikato

    Numerical solution of two-dimensional incompressible hydrodynamics shows that states of a near-minimal ratio of enstrophy to energy can be attained in times short compared with the flow decay time, confirming the simplest turbulent selective decay conjecture, and suggesting that coherent vortex structures do not terminate nonlinear processes. After all possible vortex mergers occur, the vorticity attains a particlelike character, suggested by the late-time similarity of the streamlines to Ewald potential contours.

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  • Reply to “Comment on ‘Evolution of energy-containing turbulent eddies in the solar wind’ by W. H. Matthaeus, S. Oughton, D. H. Pontius Jr., and Y. Zhou”

    Matthaeus, William H.; Oughton, Sean; Pontius, Duane H.; Zhou, Ye (1995)

    Journal article
    University of Waikato

    In their preceding comment on our paper [Matthaeus et al., 1994] (hereinafter reffered to as paper 1), Tu and Marsh [this issue] object vehemently to what they perceive as undeserved criticism of the class of solar wind turbulence models developed by Tu and coworkers[Tu et al., 1984, Tu, 1987, 1988]. Our intent was not to slight the valuable contributions made in those groundbreaking theories for incorporating turbulence into models for spatial transport. Rather, we wished to point out certain shortcomings in existing theories and suggest how they might be improved.

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  • Mass-loading and parallel magnetized shocks

    Zank, Gary P.; Oughton, Sean; Neubauer, F. M.; Webb, G. M. (1991)

    Journal article
    University of Waikato

    Recent observations at comets Giacobini-Zinner and Halley suggest that simple non-reacting gas dynamics or MHD is an inappropriate description for the bow shock. The thickness of the observed (sub)shock implies that mass-loading is an important dynamical process within the shock itself, thereby requiring that the Rankine-Hugoniot conditions possess source terms. This leads to shocks with properties similar to those of combustion shocks. We consider parallel magnetized shocks subjected to mass-loading, describe some properties which distinguish them from classical MHD parallel shocks, and establish the existence of a new kind of MHD compound shock. These results will be of importance both to observations and numerical simulations of the comet-solar wind interaction.

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  • Ion parallel viscosity and anisotropy in MHD turbulence

    Oughton, Sean (1996)

    Journal article
    University of Waikato

    We report on results from direct numerical simulation of the incompressible three- dimensional magnetohydrodynamic (MHD) equations, modified to incorporate viscous dissipation via the strongly anisotropic ion-parallel viscosity term. Both linear and nonlinear cases are considered, all with a strong background magnetic field. It is found that spectral anisotropy develops in almost all cases, but that the contribution from effects associated with the ion-parallel viscosity is relatively weak compared with the previously reported nonlinear process. Furthermore, and in contrast to this earlier work, it is suggested that when B₀ is large, the anisotropy will develop and persist for many large-scale turnover times even for non-dissipative runs. Resistive dissipation is found to dominate over viscous even when the resistivity is several orders of magnitude smaller than the ion parallel viscosity. A variance anisotropy effect and anisotropy dependence on the polarization of the fluctuations are also observed.

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  • Phenomenology of hydromagnetic turbulence in a uniformly expanding medium

    Matthaeus, William H.; Zank, Gary P.; Oughton, Sean (1996)

    Journal article
    University of Waikato

    A simple phenomenology is developed for the decay and transport of turbulence in a constant-speed, uniformly expanding medium. The fluctuations are assumed to be locally incompressible, and either of the hydrodynamic or non-Alfvénic magnetohydrodynamic (MHD) type. In order to represent local effects of nonlinearities, a simple model of the Kaármá-Dryden type for locally homogeneous turbulent decay is adopted. A detailed discussion of the parameters of this familiar one-point hydrodynamic closure is given, which has been shown recently to be applicable to non-Alfvénic MHD as well. The effects of the large-scale flow and expansion are incorporated using a two-scale approach, in which assumptions of particular turbulence symmetries provide simplifications. The derived model is tractable and provides a basis for understanding turbulence in the outer heliosphere, as well as in other astrophysical applications.

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  • Properties of mass-loading shocks, 2. Magnetohydrodynamics

    Zank, Gary P.; Oughton, Sean; Neubauer, F. M.; Webb, G. M. (1992)

    Journal article
    University of Waikato

    The one-dimensional magnetohydrodynamics of shocked flows subjected to significant mass loading are considered. Recent observations at comets Giacobini-Zinner and Halley suggest that simple nonreacting MHD is an inappropriate description for active cometary bow shocks. The thickness of the observed cometary shock implies that mass loading represents an important dynamical process within the shock itself, thereby requiring that the Rankine-Hugoniot condition for the mass flux possess a source term. In a formal sense, this renders mass-loading shocks qualitatively similar to combustion shocks, except that mass loading induces the shocked flow to shear. Nevertheless, a large class of stable shocks exist, identified by means of the Lax conditions appropriate to MHD. Thus mass-loading shocks represent a new and interesting class of shocks, which, although found frequently in the solar system, both at the head of comets and, under suitable conditions, upsteam of weakly magnetized and nonmagnetized planets, has not been discussed in any detail. Owing to the shearing of the flow, mass-loading shocks can behave like switch-on shocks regardless of the magnitude of the plasma beta. Thus the behavior of the magnetic field in mass-loading shocks is significantly different from that occurring in nonreacting classical MHD shocks. It is demonstrated that there exist two types of mass-loading fronts for which no classical MHD analogue exists, these being the fast and slow compound mass-loading shocks. These shocks are characterized by an initial deceleration of the fluid flow to either the fast or the slow magnetosonic speed followed by an isentropic expansion to the final decelerated downstream state. Thus these transitions take the flow from a supersonic to a supersonic, although decelerated, downstream state, unlike shocks which occur in classical MHD or gasdynamics. It is possible that such structures have been observed during the Giotto-Halley encounter, and a brief discussion of the appropriate Halley parameters is therefore given, together with a short discussion of the determination of the shock normal from observations. A further interesting new form of mass-loading shock is the “slow-intermediate” shock, a stable shock which possesses many of the properties of intermediate MHD shocks yet which propagates like a slow mode MHD shock. An important property of mass-loading shocks is the large parameter regime (compared with classical MHD) which does not admit simple or stable transitions from a given upstream to a downstream state. This suggests that it is often necessary to construct compound structures consisting of shocks, slip waves, rarefactions, and fast and slow compound waves in order to connect given upstream and downstream states. Thus the Riemann problem is significantly different from that of classical MHD.

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  • 'Green Protectionism' and Organic Food Exporting from New Zealand: Crisis Experiments in the Breakdown of Fordist Trade and Agricultural Policies

    Campbell, Hugh; Coombs, Brad L. (1999)

    Journal article
    University of Otago

    The exporting of organic produce from New Zealand is a response to the ongoing breakdown of Fordist regulatory measures for agriculture in destination markets. The unambiguous neoliberal revolution in New Zealand has survived only through the expansion of food exports, especially by large corporate entities and producer marketing boards. It has also rendered the country's exporters of food products particularly sensitive to the trade and agricultural policies of the United States, Japan, and the European Union. Some commentators consider New Zealand's experiment in agricultural deregulation indicative of a wider coherence in global food trade, a new stability institutionalized in the Uruguay Round of the GATT and regulated under the auspices of the World Trade Organization. The case of organic and low input food exporting from New Zealand shows that no such `new times' exist. Rather, these new types of food exporting are crisis experiments induced by green protectionism the use of health and food safety issues as an impediment to trade. In turn, green protectionism is a direct result of the continuing breakdown of Fordist agricultural regulation in key nations: the global trade in food products remains in crisis.

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  • Dependant Reproduction of Alternative Modes of Agriculture: Organic Farming in New Zealand

    Coombs, Brad; Campbell, Hugh (1998)

    Journal article
    University of Otago

    Recent studies of organic agriculture are characterized by an assumption that it is relatively easy for agribusiness to transform the meaning of organic food and marginalize the position of small-scale organic producers. In this paper, it is argued that such studies pay insufficient attention to the contradictions and limitations of capitalist agriculture as established in recent and classical formulations of the agrarian question. Attempts to liberate international trade and globalize the food system, which are particularly evident in New Zealand, result in disruption of food security and quality, so the agrarian question remains central in contemporary agri-food research. Tempered by biological conditions and associated with alternative social groups, organic production is strongly influenced by those forces which comprise the agrarian question, so attempts by agribusiness to manipulate the organic industry are fraught with contradiction. Research findings from four regional case studies in New Zealand show that small-scale organic producers are persistent, despite the increasing involvement of agribusiness in organic agriculture.

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  • Determinants of shoe retailers' perceptions of promotion tools

    Fam, Kim-Shyan; Merrilees, Bill (1996-07)

    Journal article
    University of Otago

    The full text of this item is available only via the related link.

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