197 research outputs found
Abstract Interpretation with Unfoldings
We present and evaluate a technique for computing path-sensitive interference
conditions during abstract interpretation of concurrent programs. In lieu of
fixed point computation, we use prime event structures to compactly represent
causal dependence and interference between sequences of transformers. Our main
contribution is an unfolding algorithm that uses a new notion of independence
to avoid redundant transformer application, thread-local fixed points to reduce
the size of the unfolding, and a novel cutoff criterion based on subsumption to
guarantee termination of the analysis. Our experiments show that the abstract
unfolding produces an order of magnitude fewer false alarms than a mature
abstract interpreter, while being several orders of magnitude faster than
solver-based tools that have the same precision.Comment: Extended version of the paper (with the same title and authors) to
appear at CAV 201
Strain, size and composition of InAs Quantum Sticks, embedded in InP, by means of Grazing Incidence X-ray Anomalous Diffraction
We have used x-ray anomalous diffraction to extract the x-ray structure
factor of InAs quantum stick-like islands, embedded in InP. The average height
of the quantum sticks (QSs), as deduced from the width of the structure factor
profile is 2.54nm. The InAs out of plane deformation, relative to InP, is equal
to 6.1%. Diffraction Anomalous Fine Structure provides a clear evidence of pure
InAs QSs. Finite Difference Method calculations reproduce well the diffraction
data, and give the strain along the growth direction. Chemical mixing at
interfaces is at most of 1MLComment: 9 pages, 7 figures, submitte
Field test of quantum key distribution in the Tokyo QKD Network
A novel secure communication network with quantum key distribution in a
metropolitan area is reported. Different QKD schemes are integrated to
demonstrate secure TV conferencing over a distance of 45km, stable long-term
operation, and application to secure mobile phones.Comment: 21 pages, 19 figure
Dynamics on Multiple Potential Energy Surfaces: Quantitative Studies of Elementary Processes Relevant to Hypersonics
The determination of thermal and vibrational relaxation rates of triatomic
systems suitable for application in hypersonic model calculations is discussed.
For this, potential energy surfaces for ground and electronically excited state
species need to be computed and represented with high accuracy and
quasiclassical or quantum nuclear dynamics simulations provide the basis for
determining the relevant rates. These include thermal reaction rates,
state-to-state cross-sections, or vibrational relaxation rates. For exemplary
systems - [NNO], [NOO], and [CNO] - all individual steps are described and a
literature overview for them is provided. Finally, as some of these quantities
involve considerable computational expense, for the example of state-to-state
cross sections the construction of an efficient model based on neural networks
is discussed. All such data is required and being used in more coarse-grained
computational fluid dynamics simulations.Comment: Review article, 46 pages, 8 figure
Liquid-infiltrated photonic crystals - enhanced light-matter interactions for lab-on-a-chip applications
Optical techniques are finding widespread use in analytical chemistry for
chemical and bio-chemical analysis. During the past decade, there has been an
increasing emphasis on miniaturization of chemical analysis systems and
naturally this has stimulated a large effort in integrating microfluidics and
optics in lab-on-a-chip microsystems. This development is partly defining the
emerging field of optofluidics. Scaling analysis and experiments have
demonstrated the advantage of micro-scale devices over their macroscopic
counterparts for a number of chemical applications. However, from an optical
point of view, miniaturized devices suffer dramatically from the reduced
optical path compared to macroscale experiments, e.g. in a cuvette. Obviously,
the reduced optical path complicates the application of optical techniques in
lab-on-a-chip systems. In this paper we theoretically discuss how a strongly
dispersive photonic crystal environment may be used to enhance the light-matter
interactions, thus potentially compensating for the reduced optical path in
lab-on-a-chip systems. Combining electromagnetic perturbation theory with
full-wave electromagnetic simulations we address the prospects for achieving
slow-light enhancement of Beer-Lambert-Bouguer absorption, photonic band-gap
based refractometry, and high-Q cavity sensing.Comment: Invited paper accepted for the "Optofluidics" special issue to appear
in Microfluidics and Nanofluidics (ed. Prof. David Erickson). 11 pages
including 8 figure
Near-field mapping of quantum dot emission from single-photonic crystal cavity modes
We directly investigate, by means of near-field spectroscopy, the spatial distribution of the optical cavity modes of 2D photonic crystal microcavities. Numerical simulations confirm that the photoluminescence maps of quantum dots embedded in the photonic structure qualitatively match the spatial modulation of the electric field intensity. (C) 2007 Elsevier B.V. All rights reserved
Moving liquids with light: Photoelectrowetting on semiconductors
Liquid transport in microchip-based systems is important in many areas such
as Laboratory-on-a-chip, Microfluidics and Optofluidics. Actuation of liquids
in such systems is usually achieved using either mechanical displacement11 or
via energy conversion e.g. electrowetting which modifies wetting. However, at
the moment there is no clear way of actuating a liquid using light. Here, by
linking semiconductor physics and wetting phenomenon a brand new effect
"photoelectrowetting" is demonstrated for a droplet of conducting liquid
resting on an insulator-semiconductor stack. Optical generation of carriers in
the space-charge region of the underlying semiconductor alters the capacitance
of the insulator-semiconductor stack; the result of this is a modification of
the wetting contact angle of the droplet upon illumination. The effect is
demonstrated using commercial silicon wafers, both n- and p-type having a
doping range spanning four orders of magnitude (6\times1014-8\times1018 cm-3),
coated with a commercial fluoropolymer insulating film (Teflon\textregistered).
Impedance measurements confirm that the observations are semiconductor
space-charge related effects. The impact of the work could lead to new
silicon-based technologies in the above mentioned areas
Observation of soliton pulse compression in photonic crystal waveguides
We demonstrate soliton-effect pulse compression in mm-long photonic crystal
waveguides resulting from strong anomalous dispersion and self-phase
modulation. Compression from 3ps to 580fs, at low pulse energies(~10pJ), is
measured via autocorrelation
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