5,043 research outputs found
An STL-based Formulation of Resilience in Cyber-Physical Systems
Resiliency is the ability to quickly recover from a violation and avoid
future violations for as long as possible. Such a property is of fundamental
importance for Cyber-Physical Systems (CPS), and yet, to date, there is no
widely agreed-upon formal treatment of CPS resiliency. We present an STL-based
framework for reasoning about resiliency in CPS in which resiliency has a
syntactic characterization in the form of an STL-based Resiliency Specification
(SRS). Given an arbitrary STL formula , time bounds and
, the SRS of , , is the STL formula
, specifying
that recovery from a violation of occur within time
(recoverability), and subsequently that be maintained for duration
(durability). These -expressions, which are atoms in our SRS logic,
can be combined using STL operators, allowing one to express composite
resiliency specifications, e.g., multiple SRSs must hold simultaneously, or the
system must eventually be resilient. We define a quantitative semantics for
SRSs in the form of a Resilience Satisfaction Value (ReSV) function and
prove its soundness and completeness w.r.t. STL's Boolean semantics. The
-value for atoms is a singleton set containing a
pair quantifying recoverability and durability. The -value for a composite
SRS formula results in a set of non-dominated recoverability-durability pairs,
given that the ReSVs of subformulas might not be directly comparable (e.g., one
subformula has superior durability but worse recoverability than another). To
the best of our knowledge, this is the first multi-dimensional quantitative
semantics for an STL-based logic. Two case studies demonstrate the practical
utility of our approach.Comment: 16 pages excluding references and appendix (23 pages in total), 6
figure
An STL-based Approach to Resilient Control for Cyber-Physical Systems
We present ResilienC, a framework for resilient control of Cyber-Physical
Systems subject to STL-based requirements. ResilienC utilizes a recently
developed formalism for specifying CPS resiliency in terms of sets of
real-valued pairs, where
represents the system's capability to rapidly recover from a property violation
(recoverability), and is reflective of its ability to avoid
violations post-recovery (durability). We define the resilient STL control
problem as one of multi-objective optimization, where the recoverability and
durability of the desired STL specification are maximized. When neither
objective is prioritized over the other, the solution to the problem is a set
of Pareto-optimal system trajectories. We present a precise solution method to
the resilient STL control problem using a mixed-integer linear programming
encoding and an a posteriori -constraint approach for efficiently
retrieving the complete set of optimally resilient solutions. In ResilienC, at
each time-step, the optimal control action selected from the set of
Pareto-optimal solutions by a Decision Maker strategy realizes a form of Model
Predictive Control. We demonstrate the practical utility of the ResilienC
framework on two significant case studies: autonomous vehicle lane keeping and
deadline-driven, multi-region package delivery.Comment: 11 pages, 6 figure
Model driven testing based on test history
We consider software systems consisting of a set of components running as a sequential process. We model such software systems as a special class of transition systems. The difference with existing approaches is that we propose a test procedure based on the structure of the model and the prior test history that can be used for exhaustive testing in an efficient way. On top of that we provide a statistical stopping rule, that is independent of the underlying way of walking through the system, which allows us to stop earlier with a certain statistical reliability.</p
Cardiometabolic risk factors and mental health status among truck drivers : a systematic review
The first author (AG) has received funding for their PhD Studentship from the Colt Foundation. The Colt Foundation had no role in study design; election, synthesis and interpretation of data; writing of the report; or the decision to submit the manuscript for publication. SC and JAK are in receipt of funding from the NIHR Public Health Research Programme (reference: NIHR PHR 15/190/42) for the evaluation of a multi-component health behaviour intervention in truck drivers. They are also supported by the NIHR Leicester Biomedical Research Centre – Lifestyle theme. The views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health and Social Care.Peer reviewedPublisher PD
Multidimensional Quasi-Monte Carlo Malliavin Greeks
We investigate the use of Malliavin calculus in order to calculate the Greeks
of multidimensional complex path-dependent options by simulation. For this
purpose, we extend the formulas employed by Montero and Kohatsu-Higa to the
multidimensional case. The multidimensional setting shows the convenience of
the Malliavin Calculus approach over different techniques that have been
previously proposed. Indeed, these techniques may be computationally expensive
and do not provide flexibility for variance reduction. In contrast, the
Malliavin approach exhibits a higher flexibility by providing a class of
functions that return the same expected value (the Greek) with different
accuracies. This versatility for variance reduction is not possible without the
use of the generalized integral by part formula of Malliavin Calculus. In the
multidimensional context, we find convenient formulas that permit to improve
the localization technique, introduced in Fourni\'e et al and reduce both the
computational cost and the variance. Moreover, we show that the parameters
employed for variance reduction can be obtained \textit{on the flight} in the
simulation. We illustrate the efficiency of the proposed procedures, coupled
with the enhanced version of Quasi-Monte Carlo simulations as discussed in
Sabino, for the numerical estimation of the Deltas of call, digital Asian-style
and Exotic basket options with a fixed and a floating strike price in a
multidimensional Black-Scholes market.Comment: 22 pages, 6 figure
Symbolic dynamics for the -centre problem at negative energies
We consider the planar -centre problem, with homogeneous potentials of
degree -\a<0, \a \in [1,2). We prove the existence of infinitely many
collisions-free periodic solutions with negative and small energy, for any
distribution of the centres inside a compact set. The proof is based upon
topological, variational and geometric arguments. The existence result allows
to characterize the associated dynamical system with a symbolic dynamics, where
the symbols are the partitions of the centres in two non-empty sets
Comment on ``Spin Polarization and Magnetic Circular Dichroism in Photoemission from the 2p Core Level of Ferromagnetic Ni''
Although the Ni_4 cluster includes more information regarding the Ni band
structure with respect to the Anderson impurity model, it also favors very
peculiar ground states which are incompatible with a coherent picture of all
dichroism experiments.Comment: 1 page, RevTeX, 1 epsf figur
Large non-Gaussianities in the Effective Field Theory Approach to Single-Field Inflation: the Bispectrum
The methods of effective field theory are used to study generic theories of
inflation with a single inflaton field and to perform a general analysis of the
associated non-Gaussianities. We investigate the amplitudes and shapes of the
various generic three-point correlators, the bispectra, which may be generated
by different classes of single-field inflationary models. Besides the
well-known results for the DBI-like models and the ghost inflationary theories,
we point out that curvature-related interactions may give rise to large
non-Gaussianities in the form of bispectra characterized by a flat shape which,
quite interestingly, is independently produced by several interaction terms. In
a subsequent work, we will perform a similar general analysis for the
non-Gaussianities generated by the generic four-point correlator, the
trispectrum.Comment: Version matching the one published in JCAP, 2 typos fixed, references
added. 30 pages, 20 figure
- …