Rainer Hollerbach

Bio: Rainer Hollerbach is an academic researcher from University of Leeds. The author has contributed to research in topics: Spherical shell & Magnetic field. The author has an hindex of 38, co-authored 203 publications receiving 5062 citations. Previous affiliations of Rainer Hollerbach include Monash University & University of Cambridge.

Influence of the Earth's inner core on geomagnetic fluctuations and reversals

Abstract: IN view of its relatively small size (one-third the radius of the outer core), many geodynamo models neglect the inner core entirely1, or otherwise treat it as a non-conducting insulator2,3. In a previous steady-state model4, we considered some effects of a finitely conducting inner core, in particular the resulting electromagnetic coupling between inner and outer core. Here we include a prescribed buoyancy force, which is geophysically more realistic, and also yields time-dependent rather than time-independent solutions. The field in the finitely conducting inner core does not then adjust instantaneously to the field in the outer core, but has a diffusive timescale of its own of a few thousand years. Rather large, rapid fluctuations in the outer core are then effectively averaged out by the inner core, producing a relatively stable external dipole field. We speculate that a geomagnetic reversal could only occur as a result of a particularly large fluctuation, large enough and lasting long enough to reverse the field throughout the inner core as well.

A spectral solution of the magneto-convection equations in spherical geometry

Abstract: A fully three-dimensional solution of the magneto-convection equations-the nonlinearly coupled momentum, induction and temperature equations-is presented in spherical geometry. Two very different methods for solving the momentum equation are presented, corresponding to the limits of slow and rapid rotation, and their relative advantages and disadvantages are discussed. The possibility of including a freely rotating, finitely conducting inner core in the solution of the momentum and induction equations is also discussed.

Experimental evidence for magnetorotational instability in a Taylor-Couette flow under the influence of a helical magnetic field.

Abstract: A recent Letter [R. Hollerbach and G. R\"udiger, Phys. Rev. Lett. 95, 124501 (2005)] has shown that the threshold for the onset of the magnetorotational instability in a Taylor-Couette flow is dramatically reduced if both axial and azimuthal magnetic fields are imposed. In agreement with this prediction, we present results of a Taylor-Couette experiment with the liquid metal alloy GaInSn, showing evidence for the existence of the magnetorotational instability at Reynolds numbers of order 1000 and Hartmann numbers of order 10.

New type of magnetorotational instability in cylindrical taylor-couette flow.

Abstract: We study the stability of cylindrical Taylor-Couette flow in the presence of combined axial and azimuthal magnetic fields, and show that adding an azimuthal field profoundly alters the previous results for purely axial fields. For small magnetic Prandtl numbers Pm, the critical Reynolds number ${\mathrm{Re}}_{c}$ for the onset of the magnetorotational instability becomes independent of Pm, whereas for purely axial fields it scales as ${\mathrm{Pm}}^{\ensuremath{-}1}$. For typical liquid metals, ${\mathrm{Re}}_{c}$ is then reduced by several orders of magnitude, enough that this new design should succeed in realizing this instability in the laboratory.

Oscillatory internal shear layers in rotating and precessing flows

Abstract: We present a direct numerical solution of a particular inertial oscillation, the so-called ' spin-over' mode, in spherical geometry. This mode is particularly relevant to the fluid flow within a precessing oblate spheroid. We demonstrate that the oscillatory Ekman layer breaks down at k30" latitude, and that this breakdown spawns internal shear layers. We show that the structure of these shear layers is different for a full sphere and a spherical shell, as noted in the preceding paper (Kerswell 1995). Despite the existence of these shear layers, however, the numerical decay rates agree to within 1 % with the asymptotic decay rates, which neglect any possible shear layers. Finally, we consider the nonlinear mean flow profiles driven by this mode, and demonstrate that our numerical results agree reasonably well with experimental results.

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Parameter estimation in astronomy through application of the likelihood ratio. [satellite data analysis techniques

Abstract: Many problems in the experimental estimation of parameters for models can be solved through use of the likelihood ratio test. Applications of the likelihood ratio, with particular attention to photon counting experiments, are discussed. The procedures presented solve a greater range of problems than those currently in use, yet are no more difficult to apply. The procedures are proved analytically, and examples from current problems in astronomy are discussed.

A three-dimensional self-consistent computer simulation of a geomagnetic field reversal

Abstract: A three-dimensional, self-consistent numerical model of the geodynamo is described, that maintains a magnetic field for over 40,000 years. The model, which incorporates a finitely conducting inner core, undergoes several polarity excursions and then, near the end of the simulation, a successful reversal of the dipole moment. This simulated magnetic field reversal shares some features with real reversals of the geomagnetic field, and may provide insight into the geomagnetic reversal mechanism.

Dynamo Models of the Solar Cycle

Abstract: This chapter details a series of dynamo models applicable to the sun and solar-type stars. After introducing the theoretical framework known as mean-field electrodynamics, a series of increasingly complex dynamo models are constructed, with the primary aim of reproducing the various basic observed characteristics of the solar magnetic activity cycle. Global and local magnetohydrodynamcial simulations of solar convection, and dynamo action therein, are also considered, and the resulting magnetic cycles compared and contrasted to those obtained in the simpler dynamo models. The focus throughout the chapter is on the sun, simply because the amount of available observational material on the solar magnetic field and its cycle dwarfs anything else in the astrophysical realm, in terms of spatial and temporal resolution, sensitivity, and time span.