141 research outputs found
Overview of the EU FP7-project HISTORIC
HISTORIC aims to develop and test complex photonic integrated circuits containing a relatively large number of digital photonic elements for use in e.g. all-optical packet switching. These photonic digital units are all-optical flip-flops based on ultra compact laser diodes, such as microdisk lasers and photonic crystal lasers. These lasers are fabricated making use of the heterogeneous integration of InP membranes on top of silicon on insulator (SOI) passive optical circuits. The very small dimensions of the lasers are, at least for some approaches, possible because of the high index contrast of the InP membranes and by making use of the extreme accuracy of CMOS processing.
All-optical flip-flops based on heterogeneously integrated microdisk lasers with diameter of 7.5 mu m have already been demonstrated. They operate with a CW power consumption of a few mW and can switch in 60ps with switching energies as low as 1.8 fJ. Their operation as all-optical gate has also been demonstrated. Work is also on-going to fabricate heterogeneously integrated photonic crystal lasers and all-optical flip-flops based on such lasers. A lot of attention is given to the electrical pumping of the membrane InP-based photonic crystal lasers and to the coupling to SOI wire waveguides. Optically pumped photonic crystal lasers coupled to SOI wires have been demonstrated already.
The all-optical flip-flops and gates will be combined into more complex photonic integrated circuits, implementing all-optical shift registers, D flip-flops, and other all-optical switching building blocks. The possibility to integrate a large number of photonic digital units together, but also to integrate them with compact passive optical routers such as AWGs, opens new perspectives for the design of integrated optical processors or optical buffers. The project therefore also focuses on designing new architectures for such optical processing or buffer chips
Phase behavior and critical properties of size-asymmetric, primitive-model electrolytes
The theory of J. Jiang et al. [J. Chem. Phys. 116, 7977 (2002)] for size-symmetric electrolytes is extended to size-asymmetric electrolytes. When compared to molecular-simulation results, this extension gives the correct trend of critical properties with size asymmetry
Field theory for size- and charge asymmetric primitive model of electrolytes. Mean-field stability analysis and pretransitional effects
The primitive model of ionic systems is investigated within a field-theoretic
description for the whole range of size-, \lambda, and charge, Z, ratios of the
two ionic species. Two order parameters (OP) are identified, and their
relations to physically relevant quantities are described for various values of
\lambda and Z. Instabilities of the disordered phase associated with the two
OP's are determined in the mean-field approximation.
A gas-liquid separation occurs for any Z and \lambda different from 1. In
addition, an instability with respect to various types of periodic ordering of
the two kinds of ions is found
Ion pairing in model electrolytes: A study via three particle correlation functions
A novel integral equations approach is applied for studying ion pairing in
the restricted primitive model (RPM) electrolyte, i. e., the three point
extension (TPE) to the Ornstein-Zernike integral equations. In the TPE
approach, the three-particle correlation functions are obtained. The TPE results are compared to molecular
dynamics (MD) simulations and other theories. Good agreement between TPE and MD
is observed for a wide range of parameters, particularly where standard
integral equations theories fail, i. e., low salt concentration and high ionic
valence. Our results support the formation of ion pairs and aligned ion
complexes.Comment: 43 pages (including 18 EPS figs) - RevTeX 4 - J. Chem. Phys. (in
press
Revised and extended analysis in four times ionized xenon Xe V
The atomic-emission spectrum of four times ionized xenon (Xe V) has been observed in the region 500–6700 Å; 233 lines were classified as transition between 5s5p3, 5s25p5d, 5s25p6s with 5s25p2, 5s25p6p and 5s25p4f configurations. Ninty-seven of these lines are reported for the first time. Two new energy level values corresponding to the 5s25p4f configuration have been determined, and we proposed two new values for the previously reported 3D1 and 3G5 energy levels of this configuration. The value of the 5s25p6p 1S0 energy level has also been determined, and we propose a new value for the previously reported 5s25p5d 3F4 energy level. New adjusted values for the previously known levels of the studied configurations are included. Least-squares fitted parametric calculations involving configuration interactions have been carried out to interpret the observed spectrum.Facultad de Ciencias ExactasCentro de Investigaciones Óptica
Revised and extended analysis in four times ionized xenon Xe V
The atomic-emission spectrum of four times ionized xenon (Xe V) has been observed in the region 500–6700 Å; 233 lines were classified as transition between 5s5p3, 5s25p5d, 5s25p6s with 5s25p2, 5s25p6p and 5s25p4f configurations. Ninty-seven of these lines are reported for the first time. Two new energy level values corresponding to the 5s25p4f configuration have been determined, and we proposed two new values for the previously reported 3D1 and 3G5 energy levels of this configuration. The value of the 5s25p6p 1S0 energy level has also been determined, and we propose a new value for the previously reported 5s25p5d 3F4 energy level. New adjusted values for the previously known levels of the studied configurations are included. Least-squares fitted parametric calculations involving configuration interactions have been carried out to interpret the observed spectrum.Facultad de Ciencias ExactasCentro de Investigaciones Óptica
Equilibrium solvation in quadrupolar solvents
We present a microscopic theory of equilibrium solvation in solvents with
zero dipole moment and non-zero quadrupole moment (quadrupolar solvents). The
theory is formulated in terms of autocorrelation functions of the quadrupolar
polarization (structure factors). It can be therefore applied to an arbitrary
dense quadrupolar solvent for which the structure factors are defined. We
formulate a simple analytical perturbation treatment for the structure factors.
The solute is described by coordinates, radii, and partial charges of
constituent atoms. The theory is tested on Monte Carlo simulations of solvation
in model quadrupolar solvents. It is also applied to the calculation of the
activation barrier of electron transfer reactions in a cleft-shaped
donor-acceptor complex dissolved in benzene with the structure factors of
quadrupolar polarization obtained from Molecular Dynamics simulations.Comment: Submitted to J. Chem. Phys., 20 pages and 13 figure
Theory of solvation in polar nematics
We develop a linear response theory of solvation of ionic and dipolar solutes
in anisotropic, axially symmetric polar solvents. The theory is applied to
solvation in polar nematic liquid crystals. The formal theory constructs the
solvation response function from projections of the solvent dipolar
susceptibility on rotational invariants. These projections are obtained from
Monte Carlo simulations of a fluid of dipolar spherocylinders which can exist
both in the isotropic and nematic phase. Based on the properties of the solvent
susceptibility from simulations and the formal solution, we have obtained a
formula for the solvation free energy which incorporates experimentally
available properties of nematics and the length of correlation between the
dipoles in the liquid crystal. Illustrative calculations are presented for the
Stokes shift and Stokes shift correlation function of coumarin-153 in
4-n-pentyl-4'-cyanobiphenyl (5CB) and 4,4-n-heptyl-cyanopiphenyl (7CB) solvents
as a function of temperature in both the nematic and isotropic phase.Comment: 19 pages, 9 figure
Asymmetric Primitive-Model Electrolytes: Debye-Huckel Theory, Criticality and Energy Bounds
Debye-Huckel (DH) theory is extended to treat two-component size- and
charge-asymmetric primitive models, focussing primarily on the 1:1 additive
hard-sphere electrolyte with, say, negative ion diameters, a--, larger than the
positive ion diameters, a++. The treatment highlights the crucial importance of
the charge-unbalanced ``border zones'' around each ion into which other ions of
only one species may penetrate. Extensions of the DH approach which describe
the border zones in a physically reasonable way are exact at high and low
density, , and, furthermore, are also in substantial agreement with
recent simulation predictions for \emph{trends} in the critical parameters,
and , with increasing size asymmetry. Conversely, the simplest
linear asymmetric DH description, which fails to account for physically
expected behavior in the border zones at low , can violate a new lower bound
on the energy (which applies generally to models asymmetric in both charge and
size). Other recent theories, including those based on the mean spherical
approximation, have predicted trends in the critical parameters quite opposite
to those established by the simulations.Comment: to appear in Physical Review
Coexistence and Criticality in Size-Asymmetric Hard-Core Electrolytes
Liquid-vapor coexistence curves and critical parameters for hard-core 1:1
electrolyte models with diameter ratios lambda = sigma_{-}/\sigma_{+}=1 to 5.7
have been studied by fine-discretization Monte Carlo methods. Normalizing via
the length scale sigma_{+-}=(sigma_{+} + sigma_{-})/2 relevant for the low
densities in question, both Tc* (=kB Tc sigma_{+-}/q^2 and rhoc* (= rhoc sigma
_{+-}^{3}) decrease rapidly (from ~ 0.05 to 0.03 and 0.08 to 0.04,
respectively) as lambda increases. These trends, which unequivocally contradict
current theories, are closely mirrored by results for tightly tethered dipolar
dimers (with Tc* lower by ~ 0-11% and rhoc* greater by 37-12%).Comment: 4 pages, 5 figure
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