Contributions to the theory of a two-scale homogeneous dynamo experiment

The principle of the Karlsruhe dynamo experiment is closely related to that of the Roberts dynamo working with a simple fluid flow which is, with respect to proper Cartesian co-ordinates x, y and z, periodic in x and y and independent of z. A modified Roberts dynamo problem is considered with a flow more similar to that in the experimental device. Solutions are calculated numerically, and on this basis an estimate of the excitation condition of the experimental dynamo is given. The modified Roberts dynamo problem is also considered in the framework of the mean-field dynamo theory, in which the crucial induction effect of the fluid motion is an anisotropic alpha-effect. Numerical results are given for the dependence of the mean-field coefficients on the fluid flow rates. The excitation condition of the dynamo is also discussed within this framework. The behavior of the dynamo in the nonlinear regime, i.e. with backreaction of the magnetic field on the fluid flow, depends on the effect of the Lorentz force on the flow rates. The quantities determining this effect are calculated numerically. The results for the mean-field coefficients and the quantities describing the backreaction provide corrections to earlier results, which were obtained under simplifying assumptions.Comment: 12 pages, 9 figures, accepted for publication in Phys. Rev.

What party competition in England will look like after European Parliament elections end

European Parliament elections may not have been popular, but they used proportional representation – something which England’s national elections lack. Heinz Brandenburg looks at what this means for smaller parties, which have a hard time making headway under the first-past-the-post system

What do British newspaper readers think about Brexit?

The various Brexit allegiances of Britain’s newspapers are clear. But what do their readers think? Heinz Brandenburg analyses data from the British Election Study Internet Panel to find out how intransigent – or open to compromise – their readers are, and how readerships have shifted since Brexit

General election 2019: what difference are the Unite to Remain and Brexit party pacts likely to make?

The Unite to Remain alliance means the Lib Dems, Plaid Cymru and the Greens are trying to pool their votes to ensure a Remain-backing candidate is elected. But the Brexit Party’s decision to stand down their candidates in Tory-held seats makes this tougher. Heinz Brandenburg concludes that the overall effect of these pacts will be minimal

While there are differences, there are also important similarities between the profiles of UKIP and BNP’s respective support bases

While UKIP has seen a rise in support, another party on the right, the BNP, have witnessed a dramatic decline. Heinz Brandenburg and Anders Widfeldt studied the similarities and differences between the UKIP and BNP support bases, finding that BNP fits the electoral profile of a radical right party better than UKIP in some ways; for instance, support for BNP is associated with little regard for the British democracy while UKIP supporter exhibit a high regard. But in other ways both parties fit the typical profile of radical right support; their supporters are predominantly male, young, lower class and less educate

Are citizens good judges of government performance? Evaluations of promise keeping by governing parties

Only a minority of UK citizens think that politicians generally keep their election promises. However, research by Robert Thomson and Heinz Brandenburg indicates that the public are good at evaluating whether politicians have kept specific policy pledges, but this is affected by their pre-existing levels of distrust in politicians and in particular parties

Nonlinear magnetic diffusivity and alpha tensors in helical turbulence

The effect of a dynamo-generated mean magnetic field of Beltrami type on the mean electromotive force is studied. In the absence of the mean magnetic field the turbulence is assumed to be homogeneous and isotropic, but it becomes inhomogeneous and anisotropic with this field. Using the testfield method the dependence of the alpha and turbulent diffusivity tensors on the magnetic Reynolds number Rm is determined for magnetic fields that have reached approximate equipartition with the velocity field. The tensor components are characterized by a pseudoscalar alpha and a scalar turbulent magnetic diffusivity etat. Increasing Rm from 2 to 600 reduces etat by a factor ~5, suggesting that the quenching of etat is, in contrast to the 2-dimensional case, only weakly dependent on Rm. Over the same range of Rm, however, alpha is reduced by a factor ~14, which can qualitatively be explained by a corresponding increase of a magnetic contribution to the alpha effect with opposite sign. The level of fluctuations of alpha and etat is only 10% and 20% of the respective kinematic reference values.Comment: 4 pages, 3 figs, ApJL (accepted version

EU cohesion policy helps build a European identity

EU cohesion policy aims to bring Europe closer to citizens and promote solidarity, but how successful is it at achieving these goals? Drawing on a new study, Gabriela Borz, Heinz Brandenburg and Carlos Mendez find that citizens who are aware of cohesion policy funding are more likely to develop a form of European identity. The evidence suggests that identification with Europe is linked to the benefits citizens perceive from cohesion policy in their personal life and for their region

How important are the parties' Brexit pledges to voters?

Is this really the 'Brexit election', or do voters care as much (if not more) about other issues? Heinz Brandenburg (University of Strathclyde), Fraser McMillan (University of Glasgow) and Marcel Hanegraaff (Universiteit van Amsterdam) tested the relative importance of Brexit vis-a-vis health, education and the environment. They found that Labour supporters are less attached to ensuring the party fulfills its pledges on Brexit than Conservative and Lib Dem voters

Mean-field effects in the Galloway-Proctor flow

The coefficients defining the mean electromotive force in a Galloway-Proctor flow are determined. This flow shows a two-dimensional pattern and is helical. The pattern wobbles in its plane. Apart from one exception a circular motion of the flow pattern is assumed. This corresponds to one of the cases considered recently by Courvoisier, Hughes and Tobias (2006, Phys. Rev. Lett., 96, 034503). An analytic theory of the alpha effect and related effects in this flow is developed within the second-order correlation approximation and a corresponding fourth-order approximation. In the validity range of these approximations there is an alpha effect but no gamma effect, or pumping effect. Numerical results obtained with the test-field method, which are independent of these approximations, confirm the results for alpha and show that gamma is in general nonzero. Both alpha and gamma show a complex dependency on the magnetic Reynolds number and other parameters that define the flow, that is, amplitude and frequency of the wobbling motion. Some results for the magnetic diffusivity eta_t and a related quantity are given, too. Finally a result for alpha in the case of a randomly varying flow without the aforementioned circular motion is presented. This flow may be a more appropriate model for studying the alpha effect and related effects in flows that are statistical isotropic in a plane.Comment: 12 pages, 14 figures, submitted to MNRA