Results 1 - 10 of 1053
Results 1 - 10 of 1053. Search took: 0.023 seconds
|Sort by: date | relevance|
[en] Complete text of publication follows. The self-exciting dynamo mechanism is central to understanding the behaviour of Earth's and other astroplanetary magnetic fields. The first numerically convincing laminar kinematic dynamos in spherical conductors were reported by various authors between 1971 and 1975. All these dynamos were based on multi-cellular flows of some complexity. However, early in this period four models based on simple single or double cell axisymmetric flows were studied without yielding self-exciting dynamos (Fraser 1972). We have reinvestigated these models and found that for appropriate choices of parameters, they do support self-sustaining dynamos. We have also found numerous other similar simple flows that support self-exciting dynamos. For most models a straightforward intuitive search of parameter space yielded growing magnetic modes. Some models were more difficult, requiring systematic wide-ranging searches, allowing for high frequency magnetic oscillations. Other models only yielded growing magnetic modes under asymptotic analysis. The resulting magnetic field parities are dipole, quadrupole, or neither. Some fields are steady; others are rapid rotators that are steady in some rotating reference frame. These many positive results add weight to the occasionally made conjecture that all but special isolated flows (e.g. purely toroidal) can support dynamo action in some region of parameter space. However, we give several examples, only marginally different from our successful flows, where no dynamo action has been found, despite extensive searching of parameter space in both finite and asymptotic domains.
[en] In this communication, we will use three kinds of shell models, namely i) the traditional (static) shell model, which may be either spherical or deformed, ii) the boosted shell model, which differs from the latter by just boost operations, and iii) a completely new shell model, which accounts for intermediate states during transitions
[en] The D→ infinity of the D-vectorial model of a ferromagnetic film with free surfaces is exactly solved. The mathematical mechanism responsible for the onset of a phase transition in the system is a generalized sticking phenomenon. It is shown that the temperature at which the sticking appears, the transition temperature of the model is monotonously increasing with increasing the number of layers of the film, contrary to what happens in the spherical model with overall constraint. Certain correlation inequalities of Griffiths type are shown to hold. (author)
[en] We present a spherical version of the grand-canonical minority game (GCMG) and solve its dynamics in the stationary state. The model displays several types of transitions between multiple ergodic phases and one non-ergodic phase. We derive analytical solutions, including exact expressions for the volatility, throughout all ergodic phases and compute the phase behaviour of the system. In contrast to conventional GCMGs, where the introduction of memory loss precludes analytical approaches, the spherical model can also be solved when exponential discounting is taken into account. For the case of homogeneous incentives to trade ε and memory-loss rates ρ, an efficient phase is found only if ρ = ε = 0. Allowing for heterogeneous memory-loss rates we find that efficiency can be achieved as long as there is any finite fraction of agents which is not subject to memory loss