31,130 research outputs found
Can type II Semi-local cosmic strings form?
We present the simplest possible model for a semi-local string defect in
which a U(1) gauged subgroup of an otherwise global SU(2) is broken to produce
local cosmic strings endowed with current-carrying properties. Restricting
attention to type II vortices for which the non current-carrying state is
unstable, we show that a condensate must form microscopically and
macroscopically evolve towards a chiral configuration. It has been suggested
that such configurations could potentially exist in a stable state, thereby
inducing large cosmological consequences based on equilibrium angular momentum
supported loop configurations (vortons). Here we show that the current itself
induces a macroscopic (longitudinal) instability: we conclude that type II
semi-local cosmic strings cannot form in a cosmological context.Comment: 11 pages, 5 figure
Prussian Blue-coated interdigitated array electrodes for possible analytical application
Thin films of iron(III) hexacyanoferrate(II) (Prussian Blue) were electrochemically deposited on interdigitated array (IDA) electrodes, yielding systems which can be considered as chemiresistors in sensing alkali metal ion concentrations in an adjacent electrolyte. This is due to the fact that the conductivity of the film being measured by a steady-state current on application of a voltage to the two-fingered electrodes of the IDA depends on both the redox stare of the film and the cation concentration in the electrolyte. From the dependence of the steady-state current on the electrode (bias) potential at variable cation concentrations for different alkali metal ions and for mixtures of alkali metal ions, the possibilities of analytical application were elucidated. In addition, by using the methods of staircase coulometry and scanning conductivity, the electron diffusion coefficient De was determined as a function of the redox state of Prussian Blue. It is concluded that Prussian Blue-coated IDA electrodes are, in principle, suitable as chemiresistors for the determination of alkali metal ion concentrations with increasing selectivity in the series Li < Na < K < Rb < Cs
THE ECONOMIC IMPLICATIONS OF CHEMICAL USE RESTRICTIONS IN AGRICULTURE
Agricultural and Food Policy, Crop Production/Industries,
The influence of long-range hopping on ferromagnetism in the Hubbard model
The phase diagram of the Hubbard model in an external magnetic field is
examined by extrapolation of small-cluster exact-diagonalization calculations.
Using a general expression for the hopping matrix elements () the influence of long-range hopping (band asymmetry) on
ferromagnetism in this model is studied. It is found that the long-range
hopping (nonzero ) stabilizes ferromagnetism in an external magnetic field
for . In the opposite limit the fully polarized ferromagnetic
state is generally suppressed with increasing . The critical value of
magnetic field below which the ferromagnetic state becomes unstable is
calculated numerically.Comment: 8 pages, 3 Postscript figures, Late
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