Phase structure of an Abelian two-Higgs model and high temperature superconductors

We study the phase structure of a three dimensional Abelian Higgs model with singly- and doubly-charged scalar fields coupled to a compact Abelian gauge field. The model is pretending to describe systems of strongly correlated electrons such as high-Tc superconductivity in overdoped regime and exotic phases supporting excitations with fractionalized quantum numbers. We identify the Fermi liquid, the spin gap, the superconductor and the strange metallic phases in which densities and properties of holon and spinon vortices and monopoles are explored. The phase diagram in the 3D coupling space is predicted. We show that at sufficiently strong gauge coupling the spinon-pair and holon condensation transitions merge together and become, unexpectedly, first order.Comment: 5 pages, 9 figures, RevTeX

The temperature dependent bandstructure of a ferromagnetic semiconductor film

The electronic quasiparticle spectrum of a ferromagnetic film is investigated within the framework of the s-f model. Starting from the exact solvable case of a single electron in an otherwise empty conduction band being exchange coupled to a ferromagnetically saturated localized spin system we extend the theory to finite temperatures. Our approach is a moment-conserving decoupling procedure for suitable defined Green functions. The theory for finite temperatures evolves continuously from the exact limiting case. The restriction to zero conduction band occupation may be regarded as a proper model description for ferromagnetic semiconductors like EuO and EuS. Evaluating the theory for a simple cubic film cut parallel to the (100) crystal plane, we find some marked correlation effects which depend on the spin of the test electron, on the exchange coupling, and on the temperature of the local-moment system.Comment: 11 pages, 9 figure

Toward a systematic 1/d expansion: Two particle properties

We present a procedure to calculate 1/d corrections to the two-particle properties around the infinite dimensional dynamical mean field limit. Our method is based on a modified version of the scheme of Ref. onlinecite{SchillerIngersent}}. To test our method we study the Hubbard model at half filling within the fluctuation exchange approximation (FLEX), a selfconsistent generalization of iterative perturbation theory. Apart from the inherent unstabilities of FLEX, our method is stable and results in causal solutions. We find that 1/d corrections to the local approximation are relatively small in the Hubbard model.Comment: 4 pages, 4 eps figures, REVTe

Interacting Electrons and Localized Spins: Exact Results from Conformal Field Theory

We give a brief review of the Kondo effect in a one-dimensional interacting electron system, and present exact results for the impurity thermodynamic response based on conformal field theory.Comment: 6 pages LaTeX. To appear in the Proceedings of the 1995 Schladming Winter School on Low-Dimensional Models in Statistical Physics and Quantum Field Theor

Fabrication, Characterisation and Tribological Investigation of Artificial Skin Surface Lipid Films

This article deals with the tribology of lipid coatings that resemble those found on human skin. In order to simulate the lipidic surface chemistry of human skin, an artificial sebum formulation that closely resembles human sebum was spray-coated onto mechanical skin models in physiologically relevant concentrations (5-100μg/cm2). Water contact angles and surface free energies (SFEs) showed that model surfaces with ≤25μg/cm2 lipids appropriately mimic the physico-chemical properties of dry, sebum-poor skin regions. In friction experiments with a steel ball, lipid-coated model surfaces demonstrated lubrication effects over a wide range of sliding velocities and normal loads. In friction measurements on model surfaces as a function of lipid-film thickness, a clear minimum in the friction coefficient (COF) was observed in the case of hydrophilic, high-SFE materials (steel, glass), with the lowest COF (≈0.5) against skin model surfaces being found at 25μg/cm2 lipids. For hydrophobic, low-SFE polymers, the COF was considerably lower (0.4 for PP, 0.16 for PTFE) and relatively independent of the lipid amount, indicating that both the mechanical and surface-chemical properties of the sliders strongly influence the friction behaviour of the skin-model surfaces. Lipid-coated skin models might be a valuable tool not only for tribologists but also for cosmetic chemists, in that they allow the objective study of friction, adhesion and wetting behaviour of liquids and emulsions on simulated skin-surface condition

Demonstration of a Transportable 1 Hz-Linewidth Laser

We present the setup and test of a transportable clock laser at 698 nm for a strontium lattice clock. A master-slave diode laser system is stabilized to a rigidly mounted optical reference cavity. The setup was transported by truck over 400 km from Braunschweig to D\"usseldorf, where the cavity-stabilized laser was compared to a stationary clock laser for the interrogation of ytterbium (578 nm). Only minor realignments were necessary after the transport. The lasers were compared by a Ti:Sapphire frequency comb used as a transfer oscillator. The thus generated virtual beat showed a combined linewidth below 1 Hz (at 1156 nm). The transport back to Braunschweig did not degrade the laser performance, as was shown by interrogating the strontium clock transition.Comment: 3 pages, 4 figure

Morphology of the tropopause layer and lower stratosphere above a tropical cyclone : a case study on cyclone Davina (1999)

During the APE-THESEO mission in the Indian Ocean the Myasishchev Design Bureau stratospheric research aircraft M55 Geophysica performed a flight over and within the inner core region of tropical cyclone Davina. Measurements of total water, water vapour, temperature, aerosol backscattering, ozone and tracers were made and are discussed here in comparison with the averages of those quantities acquired during the campaign time frame. Temperature anomalies in the tropical tropopause layer (TTL), warmer than average in the lower part and colder than average in the upper TTL were observed. Ozone was strongly reduced compared to its average value, and thick cirrus decks were present up to the cold point, sometimes topped by a layer of very dry air. Evidence for meridional transport of trace gases in the stratosphere above the cyclone was observed and perturbed water distribution in the TTL was documented. The paper discuss possible processes of dehydration induced by the cirrus forming above the cyclone, and change in the chemical tracer and water distribution in the lower stratosphere 400–430 K due to meridional transport from the mid-latitudes and link with Davina. Moreover it compares the data prior and after the cyclone passage to discuss its actual impact on the atmospheric chemistry and thermodynamics

The operator product expansion on the lattice

We investigate the Operator Product Expansion (OPE) on the lattice by directly measuring the product (where J is the vector current) and comparing it with the expectation values of bilinear operators. This will determine the Wilson coefficients in the OPE from lattice data, and so give an alternative to the conventional methods of renormalising lattice structure function calculations. It could also give us access to higher twist quantities such as the longitudinal structure function F_L = F_2 - 2 x F_1. We use overlap fermions because of their improved chiral properties, which reduces the number of possible operator mixing coefficients.Comment: 7 pages, 4 postscript figures. Contribution to Lattice 2007, Regensbur

Statistical Mechanics of the Fluctuating Lattice Boltzmann Equation

We propose a new formulation of the fluctuating lattice Boltzmann equation that is consistent with both equilibrium statististical mechanics and fluctuating hydrodynamics. The formalism is based on a generalized lattice-gas model, with each velocity direction occupied by many particles. We show that the most probable state of this model corresponds to the usual equilibrium distribution of the lattice Boltzmann equation. Thermal fluctuations about this equilibrium are controlled by the mean number of particles at a lattice site. Stochastic collision rules are described by a Monte Carlo process satisfying detailed balance. This allows for a straightforward derivation of discrete Langevin equations for the fluctuating modes. It is shown that all non-conserved modes should be thermalized, as first pointed out by Adhikari et al.; any other choice violates the condition of detailed balance. A Chapman-Enskog analysis is used to derive the equations of fluctuating hydrodynamics on large length and time scales; the level of fluctuations is shown to be thermodynamically consistent with the equation of state of an isothermal, ideal gas. We believe this formalism will be useful in developing new algorithms for thermal and multiphase flows.Comment: Submitted to Physical Review E-11 pages Corrected Author(s) field on submittal for