8,338 research outputs found
Efficient Monitoring of Parametric Context Free Patterns
Recent developments in runtime verification and monitoring show that parametric regular and temporal logic specifications can be efficiently monitored against large programs. However, these logics reduce to ordinary finite automata, limiting their expressivity. For example, neither can specify structured properties that refer to the call stack of the program. While context-free grammars (CFGs) are expressive and well-understood, existing techniques of monitoring CFGs generate massive runtime overhead in real-life applications. This paper shows for the first time that monitoring parametric CFGs is practical (on the order of 10% or lower for average cases, several times faster than the state-of-the-art). We present a monitor synthesis algorithm for CFGs based on an LR(1) parsing algorithm, modified with stack cloning to account for good prefix matching. In addition, a logic-independent mechanism is introduced to support partial matching, allowing patterns to be checked against fragments of execution traces
Multi-Output Gaussian Processes for Crowdsourced Traffic Data Imputation
Traffic speed data imputation is a fundamental challenge for data-driven
transport analysis. In recent years, with the ubiquity of GPS-enabled devices
and the widespread use of crowdsourcing alternatives for the collection of
traffic data, transportation professionals increasingly look to such
user-generated data for many analysis, planning, and decision support
applications. However, due to the mechanics of the data collection process,
crowdsourced traffic data such as probe-vehicle data is highly prone to missing
observations, making accurate imputation crucial for the success of any
application that makes use of that type of data. In this article, we propose
the use of multi-output Gaussian processes (GPs) to model the complex spatial
and temporal patterns in crowdsourced traffic data. While the Bayesian
nonparametric formalism of GPs allows us to model observation uncertainty, the
multi-output extension based on convolution processes effectively enables us to
capture complex spatial dependencies between nearby road segments. Using 6
months of crowdsourced traffic speed data or "probe vehicle data" for several
locations in Copenhagen, the proposed approach is empirically shown to
significantly outperform popular state-of-the-art imputation methods.Comment: 10 pages, IEEE Transactions on Intelligent Transportation Systems,
201
Cram\'er-Rao bound for time-continuous measurements in linear Gaussian quantum systems
We describe a compact and reliable method to calculate the Fisher information
for the estimation of a dynamical parameter in a continuously measured linear
Gaussian quantum system. Unlike previous methods in the literature, which
involve the numerical integration of a stochastic master equation for the
corresponding density operator in a Hilbert space of infinite dimension, the
formulas here derived depends only on the evolution of first and second moments
of the quantum states, and thus can be easily evaluated without the need of any
approximation. We also present some basic but physically meaningful examples
where this result is exploited, calculating analytical and numerical bounds on
the estimation of the squeezing parameter for a quantum parametric amplifier,
and of a constant force acting on a mechanical oscillator in a standard
optomechanical scenario.Comment: 9 pages, 2 figure
Spatial properties of entangled photon pairs generated in nonlinear layered structures
A spatial quantum model of spontaneous parametric down-conversion in
nonlinear layered structures is developed expanding the interacting vectorial
fields into monochromatic plane waves. A two-photon spectral amplitude
depending on the signal- and idler-field frequencies and propagation directions
is used to derive transverse profiles of the emitted fields as well as their
spatial correlations. Intensity spatial profiles and their spatial correlations
are mainly determined by the positions of transmission peaks formed in these
structures with photonic bands. A method for geometry optimization of the
structures with respect to efficiency of the nonlinear process is suggested.
Several structures composed of GaN/AlN layers are analyzed as typical examples.
They allow the generation of photon pairs correlated in several emission
directions. Photon-pair generation rates increasing better than the second
power of the number of layers can be reached. Also structures efficiently
generated photon pairs showing anti-bunching and anti-coalescence can be
obtained. Three reasons for splitting the correlated area in photonic-band-gap
structures are revealed: zig-zag movement of photons inside the structure,
spatial symmetry and polarization-dependent properties. Also spectral splitting
can be observed in these structures.Comment: 13 pages, 17 figure
Nonlinear Quantum Behavior of Ultrashort-Pulse Optical Parametric Oscillators
The quantum features of ultrashort-pulse optical parametric oscillators (OPOs) are theoretically investigated in the nonlinear regime near and above threshold. Starting from basic premises of input-output theory, we derive a general quantum model for pulsed OPOs subject to χ(2) interactions between a multimode signal cavity and a non-resonant broadband pump field, elucidating time scale conditions required for such pulsed OPOs to admit an input-output description. By employing a supermode decomposition of the nonlinear Lindblad operators governing pump-signal interactions, we perform multimode quantum simulations in the regime of strong nonlinearity and study effects such as pump depletion and corrections to the squeezing spectrum of the linearized model. We observe non-Gaussian states with Wigner function negativity and show that multimode interactions with the pump can act as decoherence channels
- …