6,725 research outputs found
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
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