11,791 research outputs found
Highly conductive, ionic liquid-based polymer electrolytes
In this manuscript is reported a thermal and impedance spectroscopy investigation carried out on quaternary polymer electrolytes, to be addressed as separators for lithium solid polymer batteries, containing large amount of the N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)imide ionic liquid. The target is the development of Li+ conducting membranes with enhanced ion transport even below room temperature. Polyethylene oxide and polymethyl methacrylate were selected as the polymeric hosts. A fully dry, solvent-free procedure was followed for the preparation of the polymer electrolytes, which were seen to be self-consistent and handled even upon prolonged storage periods (more than 1 year). Appealing ionic conductivities were observed especially for the PEO electrolytes, i.e., 1.6 × 10-3and 1.5 × 10-4 S cm-1 were reached at 20 and -20°C, respectively, which are ones the best, if not the best ion conduction, never detected for polymer electrolytes
q-State Potts model metastability study using optimized GPU-based Monte Carlo algorithms
We implemented a GPU based parallel code to perform Monte Carlo simulations
of the two dimensional q-state Potts model. The algorithm is based on a
checkerboard update scheme and assigns independent random numbers generators to
each thread. The implementation allows to simulate systems up to ~10^9 spins
with an average time per spin flip of 0.147ns on the fastest GPU card tested,
representing a speedup up to 155x, compared with an optimized serial code
running on a high-end CPU. The possibility of performing high speed simulations
at large enough system sizes allowed us to provide a positive numerical
evidence about the existence of metastability on very large systems based on
Binder's criterion, namely, on the existence or not of specific heat
singularities at spinodal temperatures different of the transition one.Comment: 30 pages, 7 figures. Accepted in Computer Physics Communications.
code available at:
http://www.famaf.unc.edu.ar/grupos/GPGPU/Potts/CUDAPotts.htm
Analysis of second harmonic generation in photonic-crystal-assisted waveguides
We study second harmonic generation in a planar dielectric waveguide having a
low-index, polymer core layer, bounded by two multilayer stacks. This geometry
allows exceptionally strong confinement of the light at the fundamental
wavelength inside the core region with virtually zero net propagation losses
for distances that exceed several centimeters, provided material and scattering
losses are neglected. A phase-matched configuration of the waveguide is
reported in which the pump signal is the lowest-order mode of the waveguide,
and the generated second harmonic signal corresponds to the third propagation
mode of the waveguide. Using a polymer waveguide core, having chi(2)=100 pm/V,
we predict a conversion efficiency of approximately 90% after a propagation
distance of 2 mm, using peak pump intensities inside the core of the waveguide
of 1.35 GW/cm^2. If the waveguide core contains polymer layers with different
glass transition temperatures, the layers can be poled independently to
maximize the overlap integral, and similar pump depletions may be achieved over
a distance of approximately 500 microns.Comment: 20 pages, 7 figures, 330k
From hidden symmetry to extra dimensions: a five dimensional formulation of the Degenerate BESS model
We consider the continuum limit of a moose model corresponding to a
generalization to N sites of the Degenerate BESS model. The five dimensional
formulation emerging in this limit is a realization of a RS1 type model with
SU(2)_L x SU(2)_R in the bulk, broken by boundary conditions and a vacuum
expectation value on the infrared brane. A low energy effective Lagrangian is
derived by means of the holographic technique and corresponding bounds on the
model parameters are obtained.Comment: Latex file, 40 pages and 5 figure
Why haven't loose globular clusters collapsed yet?
We report on the discovery of a surprising observed correlation between the
slope of the low-mass stellar global mass function (GMF) of globular clusters
(GCs) and their central concentration parameter c=log(r_t/r_c), i.e. the
logarithmic ratio of tidal and core radii. This result is based on the analysis
of a sample of twenty Galactic GCs with solid GMF measurements from deep HST or
VLT data. All the high-concentration clusters in the sample have a steep GMF,
most likely reflecting their initial mass function. Conversely,
low-concentration clusters tend to have a flatter GMF implying that they have
lost many stars via evaporation or tidal stripping. No GCs are found with a
flat GMF and high central concentration. This finding appears
counter-intuitive, since the same two-body relaxation mechanism that causes
stars to evaporate and the cluster to eventually dissolve should also lead to
higher central density and possibly core-collapse. Therefore, more concentrated
clusters should have lost proportionately more stars and have a shallower GMF
than low concentration clusters, contrary to what is observed. It is possible
that severely depleted GCs have also undergone core collapse and have already
recovered a normal radial density profile. It is, however, more likely that GCs
with a flat GMF have a much denser and smaller core than suggested by their
surface brightness profile and may well be undergoing collapse at present. In
either case, we may have so far seriously underestimated the number of post
core-collapse clusters and many may be lurking in the Milky Way.Comment: Four pages, one figure, accepted for publication in ApJ Letter
Inhomogeneous loop models with open boundaries
We consider the crossing and non-crossing O(1) dense loop models on a
semi-infinite strip, with inhomogeneities (spectral parameters) that preserve
the integrability. We compute the components of the ground state vector and
obtain a closed expression for their sum, in the form of Pfaffian and
determinantal formulas.Comment: 42 pages, 31 figures, minor corrections, references correcte
Loop model with mixed boundary conditions, qKZ equation and alternating sign matrices
The integrable loop model with mixed boundary conditions based on the
1-boundary extended Temperley--Lieb algebra with loop weight 1 is considered.
The corresponding qKZ equation is introduced and its minimal degree solution
described. As a result, the sum of the properly normalized components of the
ground state in size L is computed and shown to be equal to the number of
Horizontally and Vertically Symmetric Alternating Sign Matrices of size 2L+3. A
refined counting is also considered
Quantum Knizhnik-Zamolodchikov equation: reflecting boundary conditions and combinatorics
We consider the level 1 solution of quantum Knizhnik-Zamolodchikov equation
with reflecting boundary conditions which is relevant to the Temperley--Lieb
model of loops on a strip. By use of integral formulae we prove conjectures
relating it to the weighted enumeration of Cyclically Symmetric Transpose
Complement Plane Partitions and related combinatorial objects
Constraining Modified Gravity with Euclid
Future proposed satellite missions as Euclid can offer the opportunity to
test general relativity on cosmic scales through mapping of the galaxy weak
lensing signal. In this paper we forecast the ability of these experiments to
constrain modified gravity scenarios as those predicted by scalar-tensor and
theories. We found that Euclid will improve constraints expected from
the PLANCK satellite on these modified gravity models by two orders of
magnitude. We discuss parameter degeneracies and the possible biases introduced
by modified gravity
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