188,394 research outputs found
Some Recent Results on Pair Correlation Functions and Susceptibilities in Exactly Solvable Models
Using detailed exact results on pair-correlation functions of Z-invariant
Ising models, we can write and run algorithms of polynomial complexity to
obtain wavevector-dependent susceptibilities for a variety of Ising systems.
Reviewing recent work we compare various periodic and quasiperiodic models,
where the couplings and/or the lattice may be aperiodic, and where the Ising
couplings may be either ferromagnetic, or antiferromagnetic, or of mixed sign.
We present some of our results on the square-lattice fully-frustrated Ising
model. Finally, we make a few remarks on our recent works on the pentagrid
Ising model and on overlapping unit cells in three dimensions and how these
works can be utilized once more detailed results for pair correlations in,
e.g., the eight-vertex model or the chiral Potts model or even
three-dimensional Yang-Baxter integrable models become available.Comment: LaTeX2e using iopart.cls, 10 pages, 5 figures (5 eps files), Dunk
Island conference in honor of 60th birthday of A.J. Guttman
Micro-electroforming metallic bipolar electrodes for mini-DMFC stacks
This paper describes the development of metallic bipolar plate fabrication
using micro-electroforming process for mini-DMFC (direct methanol fuel cell)
stacks. Ultraviolet (UV) lithography was used to define micro-fluidic channels
using a photomask and exposure process. Micro-fluidic channels mold with 300
micrometers thick and 500 micrometers wide were firstly fabricated in a
negative photoresist onto a stainless steel plate. Copper micro-electroforming
was used to replicate the micro-fluidic channels mold. Following by sputtering
silver (Ag) with 1.2 micrometers thick, the metallic bipolar plates were
completed. The silver layer is used for corrosive resistance. The completed
mini-DMFC stack is a 2x2 cm2 fuel cell stack including a 1.5x1.5 cm2 MEA
(membrane electrode assembly). Several MEAs were assembly into mini-DMFC stacks
using the completed metallic bipolar plates. All test results showed the
metallic bipolar plates suitable for mini-DMFC stacks. The maximum output power
density is 9.3mW/cm2 and current density is 100 mA/cm2 when using 8 vol. %
methanol as fuel and operated at temperature 30 degrees C. The output power
result is similar to other reports by using conventional graphite bipolar
plates. However, conventional graphite bipolar plates have certain difficulty
to be machined to such micro-fluidic channels. The proposed
micro-electroforming metallic bipolar plates are feasible to miniaturize DMFC
stacks for further portable 3C applications.Comment: Submitted on behalf of EDA Publishing Association
(http://irevues.inist.fr/handle/2042/16838
Emergent Geometry and Quantum Gravity
We explain how quantum gravity can be defined by quantizing spacetime itself.
A pinpoint is that the gravitational constant G = L_P^2 whose physical
dimension is of (length)^2 in natural unit introduces a symplectic structure of
spacetime which causes a noncommutative spacetime at the Planck scale L_P. The
symplectic structure of spacetime M leads to an isomorphism between symplectic
geometry (M, \omega) and Riemannian geometry (M, g) where the deformations of
symplectic structure \omega in terms of electromagnetic fields F=dA are
transformed into those of Riemannian metric g. This approach for quantum
gravity allows a background independent formulation where spacetime as well as
matter fields is equally emergent from a universal vacuum of quantum gravity
which is thus dubbed as the quantum equivalence principle.Comment: Invited Review for Mod. Phys. Lett. A, 17 page
Phonons in a Nanoparticle Mechanically Coupled to a Substrate
The discrete nature of the vibrational modes of an isolated nanometer-scale
solid dramatically modifies its low-energy electron and phonon dynamics from
that of a bulk crystal. However, nanocrystals are usually coupled--even if only
weakly--to an environment consisting of other nanocrystals, a support matrix,
or a solid substrate, and this environmental interaction will modify the
vibrational properties at low frequencies. In this paper we investigate the
modification of the vibrational modes of an insulating spherical nanoparticle
caused by a weak {\it mechanical} coupling to a semi-infinite substrate. The
phonons of the bulk substrate act as a bath of harmonic oscillators, and the
coupling to this reservoir shifts and broadens the nanoparticle's modes. The
vibrational density of states in the nanoparticle is obtained by solving the
Dyson equation for the phonon propagator, and we show that environmental
interaction is especially important at low frequencies. As a probe of the
modified phonon spectrum, we consider nonradiative energy relaxation of a
localized electronic impurity state in the nanoparticle, for which good
agreement with experiment is found.Comment: 10 pages, Revte
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