428 research outputs found
Examples of scalar-flat hypersurfaces in
Given a hypersurface of null scalar curvature in the unit sphere
, , such that its second fundamental form has rank
greater than 2, we construct a singular scalar-flat hypersurface in \Rr^{n+1}
as a normal graph over a truncated cone generated by . Furthermore, this
graph is 1-stable if the cone is strictly 1-stable.Comment: Paper accepted to publication in Manuscripta Mathematic
Huge Seebeck coefficients in non-aqueous electrolytes
The Seeebeck coefficients of the non-aqueous electrolytes tetrabutylammonium
nitrate, tetraoctylphosphonium bromide and tetradodecylammonium nitrate in
1-octanol, 1-dodecanol and ethylene-glycol are measured in a temperature range
from T=30 to T=45 C. The Seebeck coefficient is generally of the order of a few
hundreds of microvolts per Kelvin for aqueous solution of inorganic ions. Here
we report huge values of 7 mV/K at 0.1M concentration for tetrabutylammonium
nitrate in 1-dodecanol. These striking results open the question of
unexpectedly large kosmotrope or "structure making" effects of
tetraalkylammonium ions on the structure of alcohols.Comment: Submitted to J. Chem. Phy
Thermal diffusion by Brownian motion induced fluid stress
The Ludwig-Soret effect, the migration of a species due to a temperature
gradient, has been extensively studied without a complete picture of its cause
emerging. Here we investigate the dynamics of DNA and spherical particles sub
jected to a thermal gradient using a combination of Brownian dynamics and the
lattice Boltzmann method. We observe that the DNA molecules will migrate to
colder regions of the channel, an observation also made in the experiments of
Duhr, et al[1]. In fact, the thermal diffusion coefficient found agrees
quantitatively with the experimental value. We also observe that the thermal
diffusion coefficient decreases as the radius of the studied spherical
particles increases. Furthermore, we observe that the thermal
fluctuations-fluid momentum flux coupling induces a gradient in the stress
which leads to thermal migration in both systems.Comment: 6 pages, 5 figue
Majorana Spin Liquids, Topology and Superconductivity in Ladders
We theoretically address spin chain analogs of the Kitaev quantum spin model
on the honeycomb lattice. The emergent quantum spin liquid phases or Anderson
resonating valence bond (RVB) states can be understood, as an effective model,
in terms of p-wave superconductivity and Majorana fermions. We derive a
generalized phase diagram for the two-leg ladder system with tunable
interaction strengths between chains allowing us to vary the shape of the
lattice (from square to honeycomb ribbon or brickwall ladder). We evaluate the
winding number associated with possible emergent (topological) gapless modes at
the edges. In the Az phase, as a result of the emergent Z2 gauge fields and
pi-flux ground state, one may build spin-1/2 (loop) qubit operators by analogy
to the toric code. In addition, we show how the intermediate gapless B phase
evolves in the generalized ladder model. For the brickwall ladder, the
phase is reduced to one line, which is analyzed through perturbation theory in
a rung tensor product states representation and bosonization. Finally, we show
that doping with a few holes can result in the formation of hole pairs and
leads to a mapping with the Su-Schrieffer-Heeger model in polyacetylene; a
superconducting-insulating quantum phase transition for these hole pairs is
accessible, as well as related topological properties.Comment: 25 pages, 10 figures, final version - to be published in PR
Multiple time-scale approach for a system of Brownian particles in a non-uniform temperature field
The Smoluchowsky equation for a system of interacting Brownian particles in a
temperature gradient is derived from the Kramers equation by means of a
multiple time-scale method. The interparticle interactions are assumed to be
represented by a mean-field description. We present numerical results that
compare well with the theoretical prediction together with an extensive
discussion on the prescription of the Langevin equation in overdamped systems.Comment: 8 pages, 2 figure
Vortex dynamics in layered superconductors with correlated defects: influence of interlayer coupling
We report a detailed study of the vortex dynamics and vortex phase diagrams
of two amorphous Ta_0.3Ge_0.7/Ge multilayered films with intrinsic coplanar
defects, but different interlayer coupling. A pinned Bose-glass phase in the
more weakly coupled sample exists only below a cross-over field H* in striking
contrast to the strongly coupled film. Above H* the flux lines are thought to
break up into pancake vortices and the cross-over field is significantly
increased when the field is aligned along the extended defects. The two films
show different vortex creep excitations in the Bose-glass phase.Comment: zip file: 1 RevTex, 5 figures (png
Observing Far-Ultraviolet Oxygen Aurorae in the Martian Night-Side Atmosphere with MAVEN-IUVS
Vortex dynamics and states of artificially layered superconducting films with correlated defects
Linear resistances and -characteristics have been measured over a wide
range in the parameter space of the mixed phase of multilayered a-TaGe/Ge
films. Three films with varying interlayer coupling and correlated defects
oriented at an angle from the film normal were investigated.
Experimental data were analyzed within vortex glass models and a second order
phase transition from a resistive vortex liquid to a pinned glass phase.
Various vortex phases including changes from three to two dimensional behavior
depending on anisotropy have been identified. Careful analysis of
-characteristics in the glass phases revealed a distinctive and
-dependence of the glass exponent . The vortex dynamics in the
Bose-glass phase does not follow the predicted behavior for excitations of
vortex kinks or loops.Comment: 16 pages, 10 figures, 3 table
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