608 research outputs found
Andreev tunneling into a one-dimensional Josephson junction array
In this letter we consider Andreev tunneling between a normal metal and a one
dimensional Josephson junction array with finite-range Coulomb energy. The
characteristics strongly deviate from the classical linear Andreev
current. We show that the non linear conductance possesses interesting scaling
behavior when the chain undergoes a T=0 superconductor-insulator transition of
Kosterlitz-Thouless-Berezinskii type. When the chain has quasi-long range
order, the low lying excitation are gapless and the curves are power-law
(the linear relation is recovered when charging energy can be disregarded).
When the chain is in the insulating phase the Andreev current is blocked at a
threshold which is proportional to the inverse correlation length in the chain
(much lower than the Coulomb gap) and which vanishes at the transition point.Comment: 8 pages LATEX, 3 figures available upon reques
Gauge invariance and effective sources in classical electrodynamics—A methodological note
It is shown by direct integration how transverse currents can be looked at as a strict consequence of gauge invariants in the restricted Coulomb gauge. Some consequences as about “clothed charges” even at the classical level are also briefly exploited, jointly to a brief touch on the role played by gauge symmetry vs. Lorentz invariance into the electromagnetic properties of the physical vacuum
Thermodynamic stability of fluid-fluid phase separation in binary athermal mixtures: The role of nonadditivity
We study the thermodynamic stability of fluid-fluid phase separation in
binary nonadditive mixtures of hard-spheres for moderate size ratios. We are
interested in elucidating the role played by small amounts of nonadditivity in
determining the stability of fluid-fluid phase separation with respect to the
fluid-solid phase transition. The demixing curves are built in the framework of
the modified-hypernetted chain and of the Rogers-Young integral equation
theories through the calculation of the Gibbs free energy. We also evaluate
fluid-fluid phase equilibria within a first-order thermodynamic perturbation
theory applied to an effective one-component potential obtained by integrating
out the degrees of freedom of the small spheres. A qualitative agreement
emerges between the two different approaches. We also address the determination
of the freezing line by applying the first-order thermodynamic perturbation
theory to the effective interaction between large spheres. Our results suggest
that for intermediate size ratios a modest amount of nonadditivity, smaller
than earlier thought, can be sufficient to drive the fluid-fluid critical point
into the thermodinamically stable region of the phase diagram. These findings
could be significant for rare-gas mixtures in extreme pressure and temperature
conditions, where nonadditivity is expected to be rather small.Comment: 17 pages, 7 figures, to appear in J. Phys. Chem.
Geometric approach to nonvariational singular elliptic equations
In this work we develop a systematic geometric approach to study fully
nonlinear elliptic equations with singular absorption terms as well as their
related free boundary problems. The magnitude of the singularity is measured by
a negative parameter , for , which reflects on
lack of smoothness for an existing solution along the singular interface
between its positive and zero phases. We establish existence as well sharp
regularity properties of solutions. We further prove that minimal solutions are
non-degenerate and obtain fine geometric-measure properties of the free
boundary . In particular we show sharp
Hausdorff estimates which imply local finiteness of the perimeter of the region
and a.e. weak differentiability property of
.Comment: Paper from D. Araujo's Ph.D. thesis, distinguished at the 2013 Carlos
Gutierrez prize for best thesis, Archive for Rational Mechanics and Analysis
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