2,954 research outputs found
The influence of a mean magnetic field on three-dimensional magnetohydrodynamic turbulence
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 (Bâ) is imposed on viscous and resistive MHD systems, excitations are preferentially transferred to modes with wavevectors perpendicular to Bâ). The anisotropy increases with increasing mechanical and magnetic Reynolds numbers, and also with increasing wavenumber. The tendency of Bâ to inhibit development of turbulence is also examined
Flow reversals in turbulent convection via vortex reconnections
We employ detailed numerical simulations to probe the mechanism of flow
reversals in two-dimensional turbulent convection. We show that the reversals
occur via vortex reconnection of two attracting corner rolls having same sign
of vorticity, thus leading to major restructuring of the flow. Large
fluctuations in heat transport are observed during the reversal due to this
flow reconfiguration. The flow configurations during the reversals have been
analyzed quantitatively using large-scale modes. Using these tools, we also
show why flow reversals occur for a restricted range of Rayleigh and Prandt
numbers
A framework for evaluating flood risk governance
Calls to strengthen flood risk governance are echoed across Europe amidst a growing consensus that floods will increase in the future. Accompanying the pursuit of societal resilience, other normative agendas relating legitimacy (e.g. accountability and public participation), and resource efficiency, have become attached to discussions concerning flood risk governance. Whilst these represent goals against which âsuccessâ is socially and politically judged, lacking from the literature is a coherent framework to operationalise these concepts and evaluate the degree to which these are achieved. Drawing from cross-disciplinary and cross-country research conducted within the EU project STAR-FLOOD, this paper presents a framework for evaluating the extent to which flood risk governance arrangements support societal resilience, and demonstrate efficiency and legitimacy. Through empirical research in England, this paper critically reflects on the value of this approach in terms of identifying entry points to strengthen governance in the pursuit of these goals
Free to Write: a case study in the impact of cultural history research and creative writing practice.
An account of LJMU's Free to Write project, exploring the impact of creative writing practice, informed by cultural-historical research, on prisoners and probationers
Translating the complexities of flood risk science using KEEPER - a knowledge exchange exploratory tool for professionals in emergency response
Within flood risk management (FRM) decision making, there is a growing interest in participatory approaches to engage and integrate stakeholder expertise. Decision support tools are becoming common features in the FRM âtoolkitâ, yet there is a limited application of participatory methodologies in the construction of such tools. This paper reports on completed FRMRC research (Flood Risk Management Research Consortium, UK http://www.floodrisk.org.uk/) and the construction of a geographic information system-based flood risk assessment tool, KEEPER â a Knowledge Exchange Exploratory tool for Professionals in Emergency Response. An iterative methodology was used to engage emergency professionals throughout the research process, allowing a mixing of scientific and professional expertise in the co-production of KEEPER. KEEPER was both instrumental in facilitating participation and knowledge exchange, and informing recommendations for future tools in practice. This paper argues that participation is both essential for supporting pragmatic flood research and as a means of enhancing communication across traditionally divided communities
Flux and field line conservation in 3--D nonideal MHD flows: Remarks about criteria for 3--D reconnection without magnetic neutral points
We make some remarks on reconnection in plasmas and want to present some
calculations related to the problem of finding velocity fields which conserve
magnetic flux or at least magnetic field lines. Hereby we start from views and
definitions of ideal and non-ideal flows on one hand, and of reconnective and
non-reconnective plasma dynamics on the other hand. Our considerations give
additional insights into the discussion on violations of the frozen--in field
concept which started recently with the papers by Baranov & Fahr (2003a;
2003b). We find a correlation between the nonidealness which is given by a
generalized form of the Ohm's law and a general transporting velocity, which is
field line conserving.Comment: 9 pages, 2 figures, submitted to Solar Physic
A multiwavelength radial velocity search for planets around the brown dwarf LP 944-20
The nearby brown dwarf LP 944-20 has been monitored for radial velocity
variability at optical and near-infrared wavelengths using the VLT/UVES and the
Keck/NIRSPEC spectrographs, respectively. The UVES radial velocity data
obtained over 14 nights spanning a baseline of 841 days shows significant
variability with an amplitude of 3.5 km s. The periodogram analysis of
the UVES data indicates a possible period between 2.5 hours and 3.7 hours,
which is likely due to the rotation of the brown dwarf. However, the NIRSPEC
data obtained over 6 nights shows an rms dispersion of only 0.36 km s
and do not follow the periodic trend. These results indicate that the
variability seen with UVES is likely to be due to rotationally modulated
inhomogeneous surface features. We suggest that future planet searches around
very low-mass stars and brown dwarfs using radial velocities will be better
conducted in the near-infrared than in the optical.Comment: accepted by ApJ Letter
The rationales of resilience in English and Dutch flood risk policies
We compared the governance of flood risk in England and the Netherlands, focusing on the general policies, instruments used and underlying principles. Both physical and political environments are important in explaining how countries evolved towards very different rationales of resilience. Answering questions as âwho decidesâ, âwho should actâ and âwho is responsible and liable for flood damageâ systematically, results in a quite fundamental difference in what resilience means, and how this affects the governance regime. In the Netherlands, there is nationwide collective regime with a technocracy based on the merit of water expertise, legitimated by a social contract of government being responsible and the general public accepting and supporting this. In England there also is a technocracy, but this is part of a general-political and economic-rational decision-making process, with responsibilities spread over state, insurance companies, individuals and communities. The rationales are connected to specific conceptions of the public interest, leading to specific governance principles. In both countries, flood risk strategies are discussed in the light of climate change effects, but resilience strategies show more persistence, although combined with gradual adaptation of practices on lower scales, than great transformations
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