Dynamics of the 2D two-component plasma near the Kosterlitz-Thouless transition

We study the dynamics of a classical, two-component plasma in two dimensions, in the vicinity of the Kosterlitz-Thouless (KT) transition where the system passes from a dielectric low-temperature phase (consisting of bound pairs) to a conducting phase. We use two ``complementary'' analytical approaches and compare to simulations. The conventional, ``intuitive'' approach is built on the KT picture of independently relaxing, bound pairs. A more formal approach, working with Mori projected dynamic correlation functions, avoids to assume the pair picture from the start. We discuss successes and failures of both approaches, and suggest a way to combine the advantages of both.Comment: 4 pages, LaTeX, 4 eps figures included; to appear in the proceedings of the ``1999 International Conference on Strongly Coupled Coulomb Systems'', 4-11 Sept 1999 in Saint-Malo (France); some typos correcte

Charge Transport in the Dense Two-Dimensional Coulomb Gas

The dynamics of a globally neutral system of diffusing Coulomb charges in two dimensions, driven by an applied electric field, is studied in a wide temperature range around the Berezinskii-Kosterlitz-Thouless transition. I argue that the commonly accepted ``free particle drift'' mechanism of charge transport in this system is limited to relatively low particle densities. For higher densities, I propose a modified picture involving collective ``partner transfer'' between bound pairs. The new picture provides a natural explanation for recent experimental and numerical findings which deviate from standard theory. It also clarifies the origin of dynamical scaling in this context.Comment: 4 pages, RevTeX, 2 eps figures included; some typos corrected, final version to be published in Phys. Rev. Let

Possible first order transition in the two-dimensional Ginzburg-Landau model induced by thermally fluctuating vortex cores

We study the two-dimensional Ginzburg-Landau model of a neutral superfluid in the vicinity of the vortex unbinding transition. The model is mapped onto an effective interacting vortex gas by a systematic perturbative elimination of all fluctuating degrees of freedom (amplitude {\em and} phase of the order parameter field) except the vortex positions. In the Coulomb gas descriptions derived previously in the literature, thermal amplitude fluctuations were neglected altogether. We argue that, if one includes the latter, the vortices still form a two- dimensional Coulomb gas, but the vortex fugacity can be substantially raised. Under the assumption that Minnhagen's generic phase diagram of the two- dimensional Coulomb gas is correct, our results then point to a first order transition rather than a Kosterlitz-Thouless transition, provided the Ginzburg-Landau correlation length is large enough in units of a microscopic cutoff length for fluctuations. The experimental relevance of these results is briefly discussed. [Submitted to J. Stat. Phys.]Comment: 36 pages, LaTeX, 6 figures upon request, UATP2-DB1-9

High Frequency Oscillation Modes in a Transformer winding Disc

The high frequency resonant behavior of a winding disc is studied by measurements on a test setup, and by computer simulation of lumped-element circuit models. It is shown that in order to achieve satisfactory agreement between both, every turn must be described by several segments in the model. The reason is that the high frequency end of the spectrum is dominated by “azimuthal” resonance modes which are not present in models with lower resolution. The intermediate frequency range is characterized by “radial” resonances, present even in lower resolution models. The different physical character and properties of these modes are discussed. Our findings provide new insight into the interpretation of frequency response measurements on power transformers.QC 2011103

High Frequency Oscillation Modes in a Transformer winding Disc

The high frequency resonant behavior of a winding disc is studied by measurements on a test setup, and by computer simulation of lumped-element circuit models. It is shown that in order to achieve satisfactory agreement between both, every turn must be described by several segments in the model. The reason is that the high frequency end of the spectrum is dominated by “azimuthal” resonance modes which are not present in models with lower resolution. The intermediate frequency range is characterized by “radial” resonances, present even in lower resolution models. The different physical character and properties of these modes are discussed. Our findings provide new insight into the interpretation of frequency response measurements on power transformers.QC 2011103

Dynamics of the 2D two-component plasma near the Kosterlitz-Thouless transition

We study the dynamics of a classical, two-component plasma in two dimensions, in the vicinity of the Kosterlitz-Thouless (KT) transition where the system passes from a dielectric low-temperature phase (consisting of bound pairs) to a conducting phase. We use two "complementary" analytical approaches and compare to simulations. The conventional, "intuitive" approach is built on the KT picture of independently relaxing, bound pairs. A more forma1 approach, working with Mori projected dynamic correlation functions, avoids to assume the pair picture from the start. We discuss successes and failures of both approaches, and suggest a way to combine the advantages of both

Comparison of a simple and a detailed model of magnetic hysteresis with measurements on electrical steel

Purpose - For efficient magnetic field calculations in electrical machines, the hysteresis and losses in laminated electrical steel must be modeled in a simple and reliable way. The purpose of this paper is to investigate and discuss the potential of a simple complex-permeability model. Design/methodology/approach - A frequency dependent complex-permeability model as well as a more detailed model (describing hysteresis, classical eddy current effects, and excess losses separately) are compared to single-sheet measurements on laminated electrical steel. It is discussed under which circumstances the simple complex-mu model is an adequate substitute for the more detailed model. Findings - A satisfactory agreement of the simple complex-mu model was found with both detailed model and measurements, improving with increasing frequencies. This is true not only for the effective permeability function, but holds also for the detailed H-B characteristics (hysteresis). Originality/value - It is demonstrated that the complex-A model is a reliable and convenient starting point for the estimation of flux distribution and losses in complicated magnetic core geometries.QC 2011031